CHAPTER 3

FCC Catalysts

The introduction of zeolite in commercial FCC catalysts in the early 960s was one of the most significant advances in the history of cat racking. Zeolite catalysts provided a greater profit with little capital vestment. Simply stated, zeolite catalysts were and still are the iggest bargain of all time for the refiner. Improvements in catalyst chnology have continued, enabling refiners to meet the demands of eir market with minimum capital investment.

Compared to amorphous silica-alumina catalysts, the zeolite catalysts re more active and more selective. The higher activity and selectivity anslate to more profitable liquid product yields and additional crack- g capacity. To take full advantage of the zeolite catalyst, refiners ave revamped older units to crack more of the heavier, loweralue feedstocks.

A complete discussion of FCC catalysts would fill another book. his chapter provides enough information to select the proper catalyst nd to troubleshoot the unit's operation. The key topics discussed are:

•Catalyst Components

•Catalyst Manufacturing Techniques

•Fresh Catalyst Properties

•Equilibrium Catalyst Analysis

•Catalyst Management

•Catalyst Evaluation

•Additives

ATALYST COMPONENTS

FCC catalysts are in the form of fine powders with an average article size in the range of 75 microns. A modern cat cracking catalyst as four major components:

•Zeolite

•Matrix

84

FCC Catalysts

85

* Binder

• Filler

eolite

Zeolite, or more properly, faujasite, is the key ingredient of the FCC atalyst. It provides product selectivity and much of the catalytic ctivity. The catalyst's performance largely depends on the nature and uality of the zeolite. Understanding the zeolite structure, types, racking mechanism, and properties is essential in choosing the "right" atalyst to produce the desired yields.

eolite Structure

Zeolite is sometimes called molecular sieve. It has a well defined attice structure. Its basic building blocks are silica and alumina etrahedra (pyramids). Each tetrahedron (Figure 3-1) consists of a ilicon or aluminum atom at the center of the tetrahedron, with oxygen toms at the four corners.

Zeolite lattices have a network of very small pores. The pore diameter f nearly all of today's FCC zeolite is approximately 8.0 angstroms (°A). hese small openings, with an internal surface area of roughly 600 square

Figure 3-1. Silicon/aluminum-oxygen tetrahedron [15].

				FCC Catalysts		8?
			Table 3-1
		Properties of Major Synthetic Zeolites
	Pore Size		Silica-to-
Zeoiite	Dimensions		Alumina
Type	(°A)		Ratio	Applications
eolite A	4.1		2-5	Detergent manufacturing
aujasite	7.4		3-6	Catalytic cracking and	hydrocracking
SM-5	5.2	x 5.8	30-200	Xylene isomerization,	benzene
				alkylation, catalytic cracking,
				catalyst dewaxing, and methanol
				conversion.
ordenite	6.7	x 7.0	10-12	Hydro-isomerization,	dewaxing

tability than the Y zeolite. Some of the earlier FCC zeolite catalysts ontained X zeolite; however, virtually all of today's catalysts contain

zeolite or variations thereof (Figure 3-2).

ZSM-5 is a versatile zeolite that increases olefin yields and octane. ts application is further discussed later in this chapter.

Until the late 1970s, the NaY zeolite was mostly ion exchanged with are earth components. Rare earth components, such as lanthanum and

USY Zeolite (~ 7 Al Atoms/u.c.)	Equilibrium REY (-23 Al Atoms/u.c.)
nit Cell Dimension =24.25 A (SiO2/AI2O3=54)	Unit Cell Dimension= 24.39 A (SiO2/AI2O3 « 15)

Figure 3-2. Geometry of USY and REY zeolites [14].

FCC Catalysts

89

ossess any activity. The UCS is related to the number of aluminum toms per cell (NAf) by [1]:

NA, + 111 x (UCS - 24.215)

he number of silicon atoms (Nsi) is;

Nsi = 192 - NA,

The SAR of the zeolite can be determined either from the above two quations or from a correlation such as the one shown in Figure 3-3. The UCS is also an indicator of zeolite acidity. Because the alumium ion is larger than the silicon ion, as the UCS decreases, the acid ites become farther apart. The strength of the acid sites is determined y the extent of their isolation from the neighboring acid sites. The lose proximity of these acid sites causes destabilization of the zeolite tructure. Acid distribution of the zeolite is a fundamental factor ffecting zeolite activity and selectivity. Additionally, the UCS easurement can be used to indicate octane potential of the zeolite. lower UCS presents fewer active sites per unit cell. The fewer acid ites are farther apart and, therefore, inhibit hydrogen transfer reactions, hich in turn increase gasoline octane as well as the production of 3 and lighter components (Figure 3-4). The octane increase is due o a higher concentration of olefins in the gasoline.

Zeolites with lower UCS are initially less active than the conentional rare earth exchanged zeolites (Figure 3-5). However, the ower UCS zeolites tend to retain a greater fraction of their activity nder severe thermal and hydrothermal treatments, hence the name ltrastable Y.

A freshly manufactured zeolite has a relatively high UCS in the ange of 24,50°A to 24.75°A. The thermal and hydrothermal environent of the regenerator extracts alumina from the zeolite structure and, herefore, reduces its UCS. The final UCS level depends on the rare arth and sodium level of the zeolite. The lower the sodium and rare arth content of the fresh zeolite, the lower UCS of the equilibrium atalyst (E-cat).

Rare Earth Level. Rare earth (RE) elements serve as a "bridge" stabilize aluminum atoms in the zeolite structure. They prevent the

FCC Catalysts

91

24.24

24.28

24.32

24.36

Unit Cell Size, A

6.0

5.5

>

s t

1 5.0

«*>

o

4.5

4.0

24.20

24.24

24.28

24.32

24.36

Unit Cell Size, A

Figure 3-4. Effects of unit cell size on octane and C3-gas make [4].

4 Fluid Catalytic Cracking Handbook

MOTOR OCTANE VS. SODIUM OXIDE

81.5 - , ;

81.0

O 5

80.5

80.0

0.2

0.3

0.4

0.5

0.6

Na2O, wt% on catalyst

RESEARCH OCTANE VS. SODIUM OXIDE

94

93

92

91

0

1

2

3

4

5

Na2O, wt% on zeolite

igure 3-7.	Effects of soda on motor and research octanes: motor octane
. sodium	oxide [11]; research octane vs. sodium oxide [4].

Na^aoHte

Crystallization

00 F, 12-24Hr

Filtrate to waste treatment

Figure 3-8, Typical manufacturing steps to produce FCC catalyst.

Data
	C.F.	G.F.	S.A.	P.V.	ABD	0-20	0-40		0-80	APS	AI2O3
			m2/gm,	cc/gm	gm/cc	wt%	wt%		wt%		ppm
69	1.3	2.2	147	0.30	0.83	0	10		63	70	28.9
69	1.2	1.9	148	0.28	0.83	0	7		61	72	29.1
70	1.2	3.1	147	0.29	0.84	0	8		67	69	29.2
69	1.3	2.6	148	0.29	0.83	2	9		69	68	28.7
68	1.4	3.2	148	0.28	0.83	0	6		65	70	28.7
69	1.3	2.6	150	0,29	0.84	0	9		67	69	28.7
69	1.2	2.3	148	0.28	0.85	2	10		71	67	28.7
67	1.4	2.8	148	0.29	0.85	0	7		64	71	28.8
70	1.2	2.9	148	0.28	0.84	4	10		67	69	28.8
	Fe	C	V	Ni	Cu	Sb	UCS	RE203		Z	M
	ppm	wt%	ppm	ppm	ppm	ppm
00	5600	0.23	4106	1997	25	416	24.27		1.79	130	17
00	5600	0.23	4093	1948	23	446			1,80	130	18
00	5600	0.16	4051	1940	24	440 '	24.27	r	1.79	130	17
00	5600	0.23	4099	1974	24 r™44i				TM	130	18
00	5600	0.22	4017	1942	24	445	24.25		1.79	130	18
00	5600	0.20	3962	1910	23 [_ 420				1.80	132	18
00	5600	0.24	3892	1893	24	458	24.27		179	131	18
00	5600	0.15	3893 L_J885		25	432			1.79	130	18
00	5600	0.24	3875	1873	24	409	24.27		1.76	130]	18
			Figure 3-12.		Typical E-cat analysis.

FCC Catalysts

101

ore Volume (PV), cc/g

Pore volume is an indication of the quantity of voids in the catalyst articles and can be a clue in detecting the type of catalystdeactivation at takes place in a commercial unit. Hydrothermal deactivation has ery little effect on pore volume, whereas thermal deactivation decreases ore volume.

ore Diameter (°A)

The average pore diameter (APD) of a catalyst can be calculated om the E-cat analysis sheet by using the following equation:

APD(°A) = PV x 4 x 10,000

SA

Example 3-1

For an E-cat with a PV = 0.40 cc/g and SA = 120 m2/g, deterine APD,

APD = 133 °A

article Size Distribution (PSD)
PSD	is an important	indicator of	the	fluidization characteristics
f the	catalyst, cyclone	performance,	and	the attrition resistance of

e catalyst. A drop in fines content indicates the loss of cyclone ficiency. This can be confirmed by the particle size of fines collected ownstream of the cyclones. An increase in fines content of the E-cat dicates increased catalyst attrition. This can be due to changes in esh catalyst binder quality, steam leaks, and/or internal mechanical roblems, such as those involving the air distributor or slide valves.

hemical Properties

The key elements that characterize chemical composition of the catalyst e alumina, sodium, metals, and carbon on the regenerated catalyst.

lumina (A12O3)

The alumina content of the E-cat is the total weight percent of umina (active and inactive) in the bulk catalyst. The alumina content

FCC Catalysts

111

100

90

80

70

60

50

40

0.0

0.5

1.0

1.5

CRC(wt%)

igure 3-15. Catalyst activity retention vs. carbon on regenerated catalyst [12].

om the unit to control the catalyst level in the regenerator. Catalyst nes leave the unit with the regenerator flue gas and the reactor vapor. The catalyst ages in the unit, losing its activity and selectivity. The eactivation in a given unit is largely a function of the unit's mechanical onfiguration, its operating condition, the type of fresh catalyst used, nd the feed quality. The primary criterion for adding fresh catalyst to arrive at an optimum E-cat activity level. A too-high E-cat activity ill increase delta coke on the catalyst, resulting in a higher regenrator temperature. The higher regenerator temperature reduces the atalyst circulation rate, which tends to offset the activity increase.

The amount of fresh catalyst added is usually a balance between atalyst cost and desired activity. Most refiners monitor the MAT data om the catalyst vendor's equilibrium data sheet to adjust the fresh atalyst addition rate. It should be noted that MAT numbers are based n a fixed-bed reactor system and, therefore, do not truly reflect the ynamics of an FCC unit. A catalyst with a high MAT number may r may not produce the desired yields. An alternate method of measur- g catalyst performance is dynamic activity. Dynamic activity is alculated as shown below:

12	Fluid Catalytic	Cracking Handbook
r v	. . . .	(Second Order Conversion)

Dynamic Activity =

(Coke Yield, Wt% of Feed)

here;

(MAT Conversion, Vol%)

Second Order Conversion =

(100 - MAT Conversion, Vol%)

or example, a catalyst with a MAT number of 70 vol% and a 3.0 t% coke yield will have a dynamic activity of 0.78. However, another atalyst with a MAT conversion of 68 vol% and 2.5 wt% coke yield ill have a dynamic activity of 0.85. This could indicate that in a ommercial unit the 68 MAT catalyst could outperform the 70 MAT atalyst, due to its higher dynamic activity. Some catalyst vendors have egun reporting dynamic activity data as part of their E-cat inspecon reports. The reported dynamic activity data can vary significantly om one test to another, mainly due to the differences in feedstock uality between MAT and actual commercial application. In addition, e coke yield, as calculated by the MAT procedure, is not very ccurate and small changes in this calculation can affect the dynamic

tivity		appreciably.
The most widely accepted model							to predict E-cat activity is based
n a first-order decay type [7]:
A	-	A	X c~(S+K)t	, A0	X S	v n	_,	-<K+S)fv
A(t)	-	A(0)	xe	c	i i^	^	e	'
				o	4" IV

t steady state, the above equation reduces to:

A	-	A	(0)	xx ce -(S+K)t I A°	X	S	x f'1 -	p-tK+S)')	'
(t)	~~			c	,	v	^
				O	+	IS.

here:

t) = Catalyst microactivity at anytime

0= Catalyst microactivity at starting time

- Time after changing catalyst or makeup rate

=Daily fractional replacement rate = addition rate/inventory

=Deactivation constant = ln(At - A0)/-t

16 Fluid Catalytic Cracking Handbook

3, Obtain vendor responses

a.Obtain catalyst recommendation

b.Obtain alternate recommendation

c.Obtain comparative yield projection 4, Obtain current product price projections

a.For present and future four-quarters

5, Perform economic evaluations on vendor yields

a.Select catalysts for MAT evaluations 6, Conduct MAT of selected list

a.Perform physical and chemical analyses

b.Determine steam deactivation conditions

c.Deactivate incumbent fresh catalyst to match incumbent E-cat

d.Use same deactivation steps for each candidate catalyst

7, Perform economic analysis of alternatives

	a. Estimate commercial yield from MAT evaluations
8,	Request commercial proposals
	a. Consult at least two vendors
	b. Obtain references
	c. Check references
9,	Test the selected catalysts in a pilot plant

a.Calibrate the pilot plant steaming conditions using incumbent E-cat

b.Deactivate the incumbent and other candidate catalysts

c.Collect at least two or three data points on each by varying the catalyst-to-oil ratio

10.Evaluate pilot plant results

a.Translate the pilot plant data

b.Use the kinetic model to heat-balance the data

c.Identify limitations and constraints

11.Make the catalyst selection

a.Perform economic evaluation

b.Consider intangibles-research, quality control, price, steady supply, manufacturing location

c.Make recommendations

12.Post selection

a.Monitoring transition-% changeover

b.Post transition test run

c.Confirm computer model

FCC Catalysts

117

13.Issue the final report

a.Analyze benefits

b.Evaluate selection methodology

There is a redundancy of flexibility in the design of FCC catalysts. ariation in the amount and type of zeolite, as well as the type of ctive matrix, provide a great deal of catalyst options that the refiner an employ to fit its needs. For smaller refiners, it may not be practical employ pilot plant facilities to evaluate different catalysts. In this ase, the above methodology can still be used with emphasis shifted ward using the MAT data to compare the candidate catalysts. It is mportant that MAT data are properly corrected for temperature,

soaking time," and catalyst strippability effects.

For many years, cat cracker operators have used additive compounds r enhancing cat cracker performance. The main benefits of these dditives (catalyst and feed additives) are to alter the FCC yields and duce the amount of pollutants emitted from the regenerator. The dditives discussed in this section are CO promoter, SOX reduction, SM-5, and antimony.

O Promoter

The CO promoter is added to most FCC units to assist in the ombustion of CO to CO2 in the regenerator. The promoter is added accelerate the CO combustion in the dense phase and to minimize e higher temperature excursions that occur as a result of afterburning the dilute phase. The promoter allows uniform burning of coke, articularly if there is uneven distribution between spent catalyst and

ombustion air.

Regenerators operating in full or partial combustion can utilize the enefits of the CO promoter. The addition of the promoter tends to crease the regenerator temperature and NOx emission. The metallurgy the regenerator internals should be checked for tolerance of the

gher temperature.

The active ingredients of the promoter are typically the platinum oup metals. The platinum, in the concentration of 300 ppm to 800

CHAPTER 4

Chemistry of FCC

Reactions

A complex series of reactions (Table 4-1) take place when a large as-oil molecule comes in contact with a 1,200°F to 1,400°F (650°C 760°C) FCC catalyst. The distribution of products depends on many ctors, including the nature and strength of the catalyst acid sites. lthough most cracking in the FCC is catalytic, thermal cracking actions also occur. Thermal cracking is caused by factors such as on-ideal mixing in the riser and poor separation of cracked products the reactor.

The purpose of this chapter is to:

•Provide a general discussion of the chemistry of cracking (both thermal and catalytic).

•Highlight the role of the catalyst, and in particular, the influence of zeolites.

•Explain how cracking reactions affect the unit's heat balance.

Whether thermal or catalytic, cracking of a hydrocarbon means the eaking of a carbon to carbon bond. But catalytic and thermal crack- g proceed via different routes. A clear understanding of the different echanisms involved is beneficial in areas such as:

• Selecting the "right" catalyst for a given operation

•Troubleshooting unit operation

•Developing a new catalyst formulation

Topics discussed in this chapter are:

•Thermal cracking

•Catalytic cracking

•Thermodynamic aspects

125

2 Fluid Catalytic Cracking Handbook

R — CH2 -—CH2 — CH2 — CH3 (removal of H~ @ Lewis site)

_» R _ c+H — CH2 — CH2 — CH3

(4-8}

Both the Bronsted and Lewis acid sites on the catalyst generate rbenium ions. The Bronsted site donates a proton to an olefin olecule and the Lewis site removes electrons from a paraffin molele. In commercial units, olefins come in with the feed or are prouced through thermal cracking reactions.

The stability of carbocations depends on the nature of alkyl groups tached to the positive charge. The relative stability of carbenium ions as follows [2] with tertiary ions being the most stable:

Tertiary		>	Secondary >		Primary		+	>	Ethyl	+	> Methyl
C ~ C	+	P P P+ P R P				P		P P			P*
. '"•"""" V-- "" V.-		V_^ \*s	V~"	V-"'	JLX. V-'	V_--		V--	*—•		V,,'

c

One of the benefits of catalytic cracking is that the primary and condary ions tend to rearrange to form a tertiary ion (a carbon with ree other carbon bonds attached). As will be discussed later, the creased stability of tertiary ions accounts for the high degree of anching associated with cat cracking.

Once formed, carbenium ions can form a number of different actions. The nature and strength of the catalyst acid sites influence e extent to which each of these reactions occur. The three dominant actions of carbenium ions are:

*The cracking of a carbon-carbon bond

*Isomerization

*Hydrogen transfer

racking Reactions

Cracking, or beta-scission, is a key feature of ionic cracking. Betaission is the splitting of the C-C bond two carbons away from the ositive-charge carbon atom. Beta-scission is preferred because the ergy required to break this bond is lower than that needed to break e adjacent C-C bond, the alpha bond. In addition, short-chain hydrorbons are less reactive than long-chain hydrocarbons. The rate of

e Tabl4 4-

Som Thermodynami dDatr fo sIdealize Reactionf o Importancn i Catalytig Crac

			t	Kg Lo	E
			m	(equilibriu)	constant
Clas	c	nSpecifi Reactio	F	850°F 950°F 980°

	n-C10H22> -				n-C7H61 + C3H6						4		2.0		6	2.4		—
transfe	1~C8H61> -				2C4Hg						8		1.6		0	2.1	3	2.2
	4C H»		-		3C H		+ C H				4		12.4	9		11.0		—
	6	21			6	41	6		6
atio	cyclo-C6H32l				+	1-C5H0!> - 3n-C5H21					+ C6H6 2		11.2	5		10.3		—
	1-C4H»8 -				trans-2-C4H8						2		0.3
															5	0.2	9	0.0
	n-C	H»		-	iso-C H						0	-0.2 3			-0.2 6		-0.3
	6	01				4	01
	o-C6H4(CH3>)2 - m-C6H4(CH3)2										3		0.3		0	0.3		—
	cyclo-C H»				-	CH -cyclo-C H					0		1.0		9	1.0	0	1.1
ylatio			6	21			3		5	9
	C6H6 + m-C6H4(CH3>)2 -								2C6H5CH3		5		0.6		5	0.6	5	0.6
o	1-C H»			-	CH -cyclo-C H						1		2.1		4	1.5		—
tio	7	41				3		6	11
	iso-C3H7-C6H>5					-	C6H6	+ C3H6			1		0.4		8	0.8
																	5	1.0
genatio	n-C6H41 ^				1-C6H21H +				2		1	-2.2		2	-1.5			—
zatio	3C H		—> 1-C H										—			— 2 -1.
Alkylatio	2	4			6	21							—
	1-C H		+ iso-C H>				-	iso-C H								—	3 3.
	4	8				4 01			8	81

nuto [2]

n

0

CHAPTER 5

Unit Monitoring

and Control

The only proper way to monitor the performance of a cat cracker by periodic material and heat balance surveys on the unit. By arrying out these tests frequently, one can collect, trend, and evaluate e unit operating data. Additionally, meaningful technical service to

ptimize the unit operation should be based on regular test runs. Understanding the operation of a cat cracker also requires in-depth nowledge of the unit's heat balance. Any changes to feedstock quality, perating conditions, catalyst, or mechanical configuration will impact e heat balance. Heat balance is an important tool in predicting and valuating the changes that will affect the quantity and the quality of CC products.

Finally, before the unit can produce one barrel of product, it must irculate catalyst smoothly. One must be familiar with the dynamics f pressure balance and key process controls.

The main topics discussed in this chapter are:

•Material Balance

•Heat Balance

•Pressure Balance

•Process Control Instrumentation

the material and heat balance sections, the discussions include:

•Two methods for performing test runs

•Some practical steps for carrying out a successful test run

•A step-by-step method for performing a material and heat balance survey

•An actual case study

139

Unit Monitoring and Control

141

External Streams^-"

Figure 5-1. FCC unit input/output streams.

alance, gasoline and light cycle oil (LCO) yields and unit converion are reported based on fixed end points. The common end points re 430°F (221 °C) TBP for gasoline and 700°F TBP for LCO, Other opular cut points are 430°F (221°C) ASTM D-86 for gasoline and 50°F (343°C) or 670°F (354°C) ASTM D-86 for LCO. Using fixed

Sample probe

Gate and ball valves

Slop container

Figure 5-2, Reaction mix sampling [2].

Dry Air versus Relative Humidity & Temperature

50	70	80	100	1tO
	Temperature,Deg F
Figure 5-3,	Dry air versus relative humidity		and temperature.

52 Fluid Catalytic Cracking Handbook

Example 5-2

onversion of Input and Output Streams to the Unit of Weight (Ib/hr)

	„ , „	. 50,000bbl	1day			141.5	350.3 Ib
• Fresh Feed = —-—--			x -	-x -		• -- x - ——
		day	24 hr		(131.5+ 25.2)		bbl
		= 658,964 lb/hr
»	„,	3,000,000 SCF 1day				1mole	27.8 lbs ni«		«,„,,.
	v^UJVCIf^r\lrpir gasCTQG —*"_!_ " !_ ........		A.V	,	•*A. v	. *„._„,„_ _^	V._.....,.._L... ,..,..,........u	_.-_...-...-— Q« 1| JvJ.OSf\ x1U/m/nr111
		day	24 hr		379.5 SCF		1mole
	.™ ..	16,000,000 SCF		Iday		Imole	22.6 Ibs		-
• FCC tail gas = —-- --				x - ^x -				x
		day		24 hr		379.5 SCF		Imole

= 39,701Ib/hr

he amount of inerts in the FCC tail gas is:

KT	16,000,OOOSCF			1day	_ _ _ „	Imole		281bs	3,542lb/hr
• N2	= —-- --			x - i-x 0.072 x -				x -	= 3,542 Ib/hr
		day		24 hr		379.5 SCF		Imole
„	16,000,OOOSCF!			A n -t	1day		1mole	441bs	,,»«,,„
. CO2 = — - --				x 0.021 x - ^-x - -				x -	= 1,623 Ib/hr
		day			24 hr	379.5 SCF Imole
• Inert-free		FCC tail gas = 39,701 - (3,542 + 1,623) = 34,537 Ib/hr
. LpG=H.565bblxldayx					141.5		X35031b =
		day	24 hr (131.5+ 123.5)				bbl
„	r	30,000bbl		day	141.5		350.31b
• Gasoline = —--				x --x -			x	-
		day		24 hr	(131.5 + 58.5)			bbl

= 326, 102Ib/hr

	141.5
day	24hr (131.5 + 21.5)	bbl

f

3,000bbl	1day	141.5	350.31b ., «--,.,,
= —- x -i-x -			x -- = 46,2731b/hr
day	24 hr	(131.5+ 2.4)	bbl

6 Fluid Catalytic Cracking Handbook

djustment of Gasoline and LCO Cut Points

As discussed earlier in this chapter, gasoline and LCO yields are enerally corrected to a constant boiling range basis. The most comonly used bases are 430°F TBP gasoline and 640°F TBP LCO end oints. Since TBP distillations are not routinely performed, they are ten estimated from the D-86 distillation data. The adjustments to the nd points involve the following:

* Adding to the raw LCO all the 430°F+ in the raw gasoline and subtracting the 430°F in the LCO stream.

«Adding to the raw LCO all the 650°F~ in the raw decanted oil and subtracting the 650°F~ in the decant oil stream.

*Adding to the raw gasoline all the 430°F~ in the raw LCO and subtracting the 430°F* in the gasoline stream.

•Adding to the raw decanted oil all the 650°F+ in the raw LCO and subtracting the 650°F~ in the decant oil stream.

Table 5-5 illustrates steps used to convert ASTM D-86 data to TBP. he laboratory usually converts D-1160 and reports the data as D-86, xtrapolation of the TBP data indicates the following:

«	The 430°F+ content of the FCCU gasoline is		3 vol%, or	859 bpd.
«	The	gasoline (430°F~) content of LCO is 8 vol%, or 806 bpd.
«	The	650°F+ content ofLCO is 12 vol%, or	1,209 bpd.

•The LCO (650°F~) content of the decanted oil is 17 vol%, or 514 bpd.

herefore, the adjusted rates are as follows:

Gasoline (C5+ to 430°F TBP end point) = 28,650 - 859 + 806

= 28,597	bpd
LCO (430°F to 650°F TBP end point) = 10,077	+ 514 - 1,209 - 806

+ 859 = 9,435 bpd DO (650°F+) = 3,023 + 1,209 - 514 = 3,718 bpd

able 5-6 shows the normalized FCC weight balance with the adjusted t points.

Unit Monitoring and Control

159

Steam

team

Oil Feed

Figure 5-4. Reactor-regenerator heat balance.

W «M#

I 0J

f E

to	20	30	40	50	60
		Alumina Content, Wt.%
yre	of the FCC	as	a function	of the	content,

1Fluid Catalytic Cracking Handbook

I.Calculation of heat of reaction

Total heat out = total heat in

Total heat out = 878 x 106 + 512.6 x 106 + 15.2 x 106 + 6.1 x 1C)6 +

overall heat of reaction =

Total heat in = 1,499.6 x 106Btu/hr

Overall endothermic heat of reaction = 84.5 x 106 Btu/hr or —» 128.2

Btu/lb of feed.

nalysis of Results

Once the material and heat balances are complete, a report must be ritten. It will first present the data. It will then discuss factors fecting product quality and any abnormal results. It will then discuss e key findings and recommendations to improve unit operation.

In the previous examples, the feed characterizing correlations in hapter 2 are used to determine composition of the feedstock. The sults show that the feedstock is predominantly paraffinic (i.e., 61.6% araffins, 19.9% naphthenes, and 18.5% aromatics). Paraffinic feedocks normally yield the most gasoline with the least octane. This onfirms the relatively high FCC gasoline yield and low octane bserved in the test run. This is the kind of information that should e included in the report. Of course, the effects of other factors, such catalyst and operating parameters, will also affect the yield structure d will be discussed.

The coke calculation showed the hydrogen content to be 9.9 wt%. s discussed in Chapter 1, every effort should be made to minimize e hydrogen content of the coke entering the regenerator. The hydroen content of a well-stripped catalyst is in the range of 5 wt% to wt%. A 9.9 wt% hydrogen in coke indicates either poor stripper peration and/or erroneous flue gas analysis.

RESSURE BALANCE

Pressure balance deals with the hydraulics of catalyst circulation in e reactor/regenerator circuit. The pressure balance starts with the atic pressures and differential pressures that are measured. The arious pressure increases and decreases in the circuit are then callated. The object is to:

920

940

960

980

1000

1020

1040

1060

1080

Deg.F

-*-K«11 -*-K-t2 -*-K»13

Figyre 5-8. Hydrocarbon vapor enthalpies at various Watson K factors.

	Unit Monitoring and Control	169
«	Maximize catalyst circulation
*	Ensure steady circulation
*	Maximize the available pressure drop at the slide valves
*	Minimize the loads on the blower and the wet gas compressor

A clear understanding of the pressure balance is extremely important
n "squeezing" the most out of a unit. Incremental capacity can come
rom increased catalyst circulation or from altering the differential
ressure between	the reactor-regenerator to "free up" the wet gas
ompressor or air	blower loads. One must know how to manipulate

he pressure balance to identify the "true" constraints of the unit. Using the drawing(s) of the reactor-regenerator, the unit engineer

ust be able to go through the pressure balance and determine whether makes sense. He or she needs to calculate and estimate pressures, ensities, pressure buildup in the standpipes, etc. The potential for mprovements can be substantial.

asic Fluidization Principals

A fluidized catalyst behaves like a liquid. Catalyst flow occurs in he direction of a lower pressure. The difference in pressure between ny two points in a bed is equal to the static head of the bed between hese points, multiplied by the fluidized catalyst density, but only if he catalyst is fluidized.

FCC catalyst can be made to flow like a liquid, but only if the ressure force is transmitted through the catalyst particles and not the essel wall. The catalyst must remain in a fluidized state as it makes loop through the circuit.

To illustrate the application of the above principals, the role of each ajor component of the circuit is discussed in the following sections, ollowed by an actual case study. As a reference, Appendix 8 contains luidization terms and definitions commonly used in the FCC.

Major Components of the Reactor-Regenerator Circuit

The major components of the reactor-regenerator circuit that either roduce or consume pressure are as follows:

*Regenerator catalyst hopper

*Regenerated catalyst standpipe

4 Fluid Catalytic Cracking Handbook

Rx Vapor

Reactor

Psi diff.

Oil Feed

Figure 5-9. Preliminary pressure balance survey.

6 Fluid Catalytic Cracking Handbook

Rx Vapor

Reactor

Psi diff.

Oil Feed

igure 5-10. Pressure balance survey with calculated standpipe densities.

80 Fluid Catalytic Cracking Handbook

With a host computer framework, the control package is all in the oftware. Changing the program can still be agonizing, but the program an be tested off-line. There is more flexibility in the computer system, hich can be used for many other purposes, including on-line heat nd weight balances.

isadvantages of Multivariable Modeling and Control

A multivariable model is like a "black box." The constraints go in nd the signals come out. Operators do not trust a system that takes e unit away from them. Successful installations require good training nd continual communication. The operators must know the interconections in the system.

The model may need expensive work if changes are made during a rnaround. If the feed gets outside the range the unit was modeled r, results can be at best unpredictable. An upset can happen for which e system was not programmed.

The DCS-based APC is installed in a modular form, meaning operators an understand what the controlled variable is tied to more easily.

The host computer-based system may have its own problems, includ- g computer-to-computer data links.

In any APC, the operators must be educated and brought into it efore they can use it. The control must be properly designed, meaning e model must be configured and properly "tuned." The operators hould be involved early and all of them should be consulted since l four shifts may be running the unit differently.

UMMARY

The only proper method to evaluate the performance of a cat cracker by conducting a material and heat balance. One balance will tell here the unit is; a series of daily or weekly balances will tell where e unit is going. The heat and weight balance can be used to evaluate revious changes or predict the result of future changes. As discussed

the next chapter, material and heat balances are the foundation for etermining the effects of operating variables.

The material balance test run provides a standard and consistent pproach for daily monitoring. It allows for accurate analysis of yields nd trending of unit performance. The reactor effluent can be deter-

CHAPTER 6

Products and

Economics

The previous chapters explained the operation of a cat cracker. owever, the purpose of the FCC unit is to maximize profitability for e refinery. The cat cracker provides the conversion capacity that very refinery needs to survive. All crudes have heavy gas oils and el oil; unfortunately, the market for these products has disappeared. FCC economics makes the refinery a viable entity. Over the years, fineries without cat crackers have been shut down because they were ot profitable.

Understanding the economics of the unit is as important as underanding the heat and pressure balance. The dynamics of FCC economics hanges daily and seasonally. It is dependent on market conditions and e availability of feedstocks. The 1990 Clean Air Act Amendment CAAA) has imposed greater restrictions on quality standards for asoline and diesel. The FCC is the major contributor to the gasoline nd diesel pool and is significantly affected by these new regulations. This chapter discusses the factors affecting yields and qualities of CC product streams. The section on FCC economics describes several ptions that can be used to maximize FCC performance and the efinery's profit margin.

CC PRODUCTS

The cat cracker converts less valuable gas oils to more valuable roducts. A major objective of most FCC units is to maximize the onversion of gas oil to gasoline and LPG. The products from the cat racker are:

•Dry Gas

•LPG

•Gasoline

182

Products and Economics

0

5

10

15

ZSM-5 wt% in Catalyst Inventory

Figure 6-2. The effect of ZSM-5 on light-ends yield [5].

*Increasing reactor temperature (if the increase does not over-crack the already produced gasoline)

asoline Quality

The Clean Air Act Amendment (CAAA), passed in November 1990, as set new quality standards for U.S. gasoline. A complete discussion f the new gasoline formulation requirements can be found in Chap- r 10.

Products and Economics

189

93

92

U

Z

o

91

90

20

22

24

26

Feed Gravity, "API

82

81

Q

Z

O

s

80

79

20

22

24

26

Feed Gravity, "API

Figure 6-3. Feed gravity comparisons (MON and RON) [7].

Products and Economics

191

RONC vs.SODIUM

COMMERICAL DATA

0.40

0.60

EQUILIBRIUM CAT. SODIUM, WT.%

< 80.5 -

§80.0 -

79.5-

79.0-

78.5_

78.0

0.20

0.40

0.80

EQUILIBRIUM CAT SODIUM, WT. %

Figure 6-4. Effect of sodium on gasoline octane [8J.

92 Fluid Catalytic Cracking Handbook

84

	83	PILOT PLANT DATA
		C5-265T/C5-129"C
	82
		265-430"F/129-221*C

; 81 o

80
79				—8
78
77
0.0	1.0	2.0	3.0	4.0

REO, WT.%

Figure 6-5. Effect of fresh REO on MON [9].

95 82

94

81

93

					UJ
					z 80
					O
					O
91					o: 79
					O
auon					I
89 -					78
88	I I I	I	I I	I I	77		I	I	i i
24.20	24.24	24.28	24.32	24.36	24,20	24.24	24.28	24.32	24.36
	UNIT CELL SIZE, A					UNIT CELL SIZE, A

Figure 6-6. Effects of unit cell size on research and motor octane [10].

Products and Economics

113

0.1			High N VGO
0.03
0.01
o.oos			34% Recycle
0,001
0.05	0.1	0.2	0.5	1

FCCU Feed Sulfur, wt%

Figure 6-7. FCC gasoline sulfur yield [4].

2,000

Non-Hydrotreated

1.000

.

.

Hydrotreated

FCCU FEEDSTOCK SULFUR (wt%)

Figure 6-8. Hydrotreating reduces FCC gasoline sulfur [4].

94 Fluid Catalytic Cracking Handbook

1,000

Guff Coast FCCU Feed. 0.62 w% S I

HT FCCU Feed, 0.68 w%S

350	450
	FCC Gasoline End Point (°F)
Figure 6-9.	FCC gasoline sulfur increases with end point [4],

400

.

"350

Octane Catalyst

3

300

Octane BBL Catalyst

250
475	500	525	550

FCC Reactor Isothermal Temperature (°C)

Figure 6-10. FCC gasoline sulfur increases with temperature [4j.

/O WHSV

EC

RX

Products and Economics

201

=0.65

=cat-to-oil ratio

=weight of hourly space velocity, weight of total feed/hr divided by weight of catalyst inventory in reaction zone, hr-1

=activation energy ~ 2,500 Btu/lb-mole (5828 J/G - mole)

=gas constant, 1.987 Btu/lb-mole-°R (8.314 J/G- mole °K)

=reactor temperature, °R

The coke yield of a given cat cracker is essentially constant. The CC produces enough coke to satisfy the heat balance. However, more important term is delta coke. Delta coke is the difference etween the coke on the spent catalyst and the coke on the regenerated atalyst. At a given reactor temperature and constant CO2/CO ratio, elta coke controls the regenerator temperature.

Reducing delta coke will lower the regenerator temperature. Many enefits are associated with a lower regenerator temperature. The esulting higher cat/oil ratio improves product selectivity and/or rovides the flexibility to process heavier feeds.

Many factors influence delta coke, including quality of the FCC eedstock, design of the feed/catalyst injection system, riser design, perating conditions, and catalyst type. The following is a brief iscussion of these factors:

*Feedstock quality. The quality of the FCC feedstock impacts the concentration of coke on the catalyst entering the regenerator. A "heavier" feed containing a higher concentration of coker gas oil will directionally increase the delta coke as compared with a "lighter," resid-free feedstock.

*	Feed/catalyst injection. A well-designed injection system provides
	a rapid and uniform vaporization of the liquid feed. This will
	lower delta coke by minimizing non-catalytic coke deposition as
	well as reducing the deposits of heavy material on the catalyst.
•	Riser design. A properly designed riser will help reduce delta coke
	by reducing the back-mixing of already "coked-up" catalyst with
	fresh feed. The back-mixing causes unwanted secondary reactions.
•	Cat/oil ratio. An increase in the cat/oil ratio reduces delta coke
	by spreading out some coke-producing feed components over
	more catalyst particles and, thus, lowering the concentration of
	coke on each particle.

02Fluid Catalytic Cracking Handbook

«Reactor temperature. An increase in the reactor temperature will also reduce delta coke by favoring cracking reactions over hydrogen transfer reactions. Hydrogen transfer reactions produce more coke than cracking reactions.

*Catalyst activity. An increase in catalyst activity will increase delta coke. As catalyst activity increases so does the number of adjacent sites, which increases the tendency for hydrogen transfer reactions to occur. Hydrogen transfer reactions are bimolecular and require adjacent active sites.

CC ECONOMICS

The cat cracker's operational philosophy is dictated by refinery conomics. Economics of a refinery are divided into internal and xternal economics.

Internal economics largely depends on the cost of raw crude and e FCC unit's yields. The cost of crude can outweigh the benefit from e cat cracker yields. Refiners who operate their units by a kind of tuition may drive for more throughput, but this may not be the most rofitable approach.

External economics are factors that are generally forced upon the fineries. Refiners prefer not to have their operations dictated by xternal economics. However, they may have to meet particular quirements such as those for reformulated gasoline.

To maximize the FCCU's profit, the unit must be operated against l its mechanical and operating constraints. Generally speaking, the cremental profit of increasing feed is more than the incremental ofit from increasing conversion. The general target is to maximize asoline yield while maintaining the minimum octane that meets lending requirements.

Because of the high cost of new units and the importance of the CC on refinery profitability, improvements should be made to the xisting units to maximize their performance. These performance dices are:

*Improving product selectivity

*Enhancing operating flexibility

*Increasing unit capacity

*Improving unit reliability

CHAPTER 7

Project Management

and Hardware Design

Since 1942, when the first FCC unit came onstream, numerous rocess and mechanical changes have been introduced. These changes mproved the unit's reliability, allowed it to process heavier feedstocks, operate at higher temperatures, and to shift the conversion to more

aluable products.

However, incorporating these changes in an existing unit is a major roject, usually more complicated than building a new unit. The two ritical components of a successful mechanical upgrade (or erection of a ew unit) are effective project management and proper design standards. This chapter addresses project management aspects of a revamp. It lso provides design guidelines that can be used by a refiner in electing the revamp components. The original driving force for a roject is often a particular mechanical problem or a process bottleeck. The ultimate objective of a revamp should be a safe, reliable, nd profitable operation.

ROJECT MANAGEMENT ASPECTS

F AN FCC REVAMP

The modifications/upgrades to the reactor and regenerator circuit are ade for a number of reasons: equipment failure, technology changes, nd/or changes in processing conditions. The primary reasons for upgrad- g the unit are improving the unit's reliability, increasing the quantity nd quality of valuable products, and enhancing operating flexibility.

The revamp (or erection of a new unit) requires successful execution f each phase of the project:

•Pre-project

•Process design

206

14Fluid Catalytic Cracking Handbook

*Standpipe system

*Air and spent catalyst distributors

*Reactor and regenerator cyclones

*Expansionjoints

*Refractory

eed Injection System

Any mechanical revamp to improve the unit yields should always egin with installing an efficient feed and catalyst distribution system. his is the single most-important component of the FCC unit. An fficient feed and catalyst injection system maximizes gasoline yield nd conversion at the expense of lower gas, coke, and decant oil and llows downstream technology to perform at its full potential.

Ideally, a well-designed feed and catalyst injection system will

chieve the following objectives:
»	Distribute the feed and regenerated	catalyst throughout the cross-
	section of the riser to ensure that	all feed components are sub-
	jected to the same cracking severity
»	Atomize the feed uniformly and instantaneously
*	Avoid re-contacting of the "spent	catalyst" with the fresh feed

*Produce proper oil droplet size to penetrate through the catalyst over the 360° cross-sectional area of the riser

*	Avoid erosion of the riser	wall and attrition of the catalyst
*	Perform without plugging	or erosion

rocess Design Considerations for Feed Nozzles

Table 7-1 contains a summary of the process and mechanical design riteria commonly used in specifying high-efficiency feed nozzles. The mechanical design of any feed nozzle should be robust and easy to aintain. Its long-term mechanical reliability is critical in achieving he expected benefits of the upgrade. The following mechanical problems re often encountered: erosion of the nozzle tip(s), erosion of the riser all, and blockage of the nozzles.

atalyst Lift Zone Design Considerations

To maximize the benefits of feed nozzles, the regenerated catalyst ust be distributed evenly throughout the cross-section of the riser.

16 Fluid Catalytic Cracking Handbook

Hydrocarbon

Feed

Dispersion Steam

Figure 7-1. Schematic of a typical feed nozzle.

Table 7-2

Process and Mechanical Design Guidelines for FCC Risers

Hydrocarbon	1 second to 3 seconds based on the riser outlet
residence time	conditions. Depending on the degree of catalyst
	back-mixing in the riser, the catalyst residence
	time is usually 1.5 to 3.5 times longer than the
	hydrocarbons.
Vapor Velocity	20 ft/sec (6 m/s) minimum (without oil feed),
	65 ft/sec to 85 ft/sec (20 to 25 m/s) at the design
	feed rate.
Geometry	Vertical: to simulate plug flow and to minimize
	catalyst	back-mixing
ermination	Riser-cyclone separator attached to another separation
	device to minimize re-cracking of hydrocarbon vapors.
onfiguration	External	or internal.
Material	Carbon	steel, "cold wall" as opposed to "hot wall,"

Project Management and Hardware Design

217

To Reactor or Cyclone

T

3 to 5

Riser

Daimeters

Disf

ISteam

(Typical for Multiple Nozzles)

Superficial velocity

0.3 - 0.4 ft/sec

Steam or fuel gas

Drain

Figure 7-2. Schematic of a typical catalyst lift system.

4 Fluid Catalytic Cracking Handbook

Table 7-6

Process and Mechanical Design guidelines for Slide Valves

perating pressure drop	Minimum 1.5 psi (10 Kp), maximum 10 psi
	(70 KP)
opening @ design	40%–60%
circulation
aterial	Shell: carbon steel with 4-5 in. (10-12 cm)
	thick heavy weight, single-layer, cast-vibrated
	refractory with needles.
	Internals: 304H stainless steel for temperature
	>1,200°F (650°C) and Grade H, \\% chrome
	for <1,200°F.
	Internal components exposed to catalyst should
	be refractory-lined for erosion resistance.
	Sliding surfaces should be hard-faced, mini-
	mum thickness \ in. (3 mm).
onnet design	Sloped bonnet (30° minimum) for self-draining
	of catalyst.
urge	Purgeless design of stuffing box. Guides:
	slotted, hard-surfaced, and supplied with purge
	connections (normally closed). Nitrogen is the
	preferred choice of purge gas.
ctuator type	Electro-hydraulic for fast response and accu-
	rate control.
ctuator response time	A maximum of 3 seconds

e said for spent catalyst distributors. This is particularly true in the se of side-by-side FCC units. Most side-by-side units suffer from neven distribution of the spent catalyst.

A well-designed air distributor system has the following characteristics:

•Distributes the air uniformly to the spent catalyst

•Mechanically withstands a wide range of operating conditions,

including start-up, shutdown, normal operation, and upset conditions

• Provides reliability with minimum maintenance

Project Management and Hardware Design

227

rifice

Figure 7-5. Typical layout of a pipe grid distributor.

28 Fluid Catalytic Cracking Handbook

Outlet

Tube

Catalyst/Vapor

Barrel

Cone

Dustbin

Dipleg

Figure 7-6. Schematic of a typical cyclone.

Project Management and Hardware Design

233

Ratterman, M., "An Approach to the Design and Analysis of Data from the Standpipe System on FCC Units," Gulf Research and Development, Pittsburgh, Pennsylvania, October 1983.

Wrench, R. E., and Glasgow, P. E., The M.W. Kellogg Company, "FCC Hardware Options," Paper No. 125C, presented at the AIChE National Meeting, Los Angeles, California, November 17–22, 1991.

CHAPTER 8

Troubleshooting

The cat cracker plays a key role in the overall profitability of the efinery. It must operate reliably and efficiently. It must also operate afely and comply with federal, state, and local environmental requireents. A typical FCC unit circulates tons of catalyst per minute, rocesses various types of feedstock and uses hundreds of control oops, any of which can make operation difficult. Proper troublehooting will ensure that the unit operates at maximum reliability and fficiency while complying with environmental concerns.

Troubleshooting deals with identifying and solving problems. Problems an be immediate or long term and can be associated with off-spec roducts, poor efficiency, process improvements, capacity increases, r potential shutdown items. Problems can be related to management, peration, hardware and equipment, or process issues. Solutions can nclude improved operating procedures and training, preventative aintenance, or installation of new equipment or controls.

This chapter outlines fundamental steps toward effective troublehooting. It provides a practical and systematic approach to developing solution. General guidelines are provided for identifying problems nd determining a diagnosis. In particular, the following FCC-related roblem areas are addressed in detail:

•CatalystCirculation

•Catalyst Loss

•Coking/Fouling

•Flow Reversal

•High Regenerator Temperature

•Afterburn

•Hydrogen Blistering

•Hot Gas Expander

•Products Quality and Quantity

234

I

o o

.c

CO

I

<

^>

CO

0

S

2

a.

CO

Low Pressure Upstream of the Slide Valve

Insufficient pressure	Low Catalyst density
build-up in the Standpipe	in the Standpipe

	e-fluidization of the	Too much, too little	Improper placement	Restriction
				Orifices are
	talyst in the Standpipe	or no Aeration Gases	of the Aeration taps
				either plugged
				or improperly
				sized

		Check if the		i
			Verify Aeration Gas	Use Rotameters
	ake sure instrument	Catalyst		instead of
			flow to maximize
	adings are correct	properties have		Restriction
			pressure build-up
		changed		Oriffces(RO's)

Figured-IB. Troubleshooting catalyst circulation.

High Pressure Downstream of the Slide Valve

r

High delta P across the Overhead Condensers

) r

• Add Fins to the Trim Coolers -19 flns per inch

* Water Wash the

Condensers

•Reduce No. of tube passes on the water

side

*Check pressure drop between Fin-Fans and Trim Coolers

High delta P across the Main Fractionator

r \^

\

f ^.

•Adjust the Pumparound rates

•Add Top or Side P/A

v

^/

High Delta P across	High Delta P
the Reactor Ovhd.	across the
vapor line	Riser
J \.	J V

\(		\ f
	•	Increase
Refer to		Fluffing Gas or
'Coking/Fouling'		Steam to the
Troubleshooting		base of Riser
Section	«	Replace the
		Curved section
V	J	of the Riser
	V

Figure8-1 C. Troubleshooting catalyst circulation.

8Fluid Catalytic Cracking Handbook

•Confirm that the restriction orifices used for instrument purges are

in proper working condition and that the orifices are not missing.

•Consider switching to a harder catalyst. For a short-term solution, if the losses are from the reactor side, consider recycling slurry to the riser. If the catalyst losses are from the regenerator, consider recycling catalyst fines to the unit.

igure 8–4 is a summary of the above discussions.

Nearly every cat cracker experiences some degree of coking/fouling. oke has been found on the reactor walls, dome, cyclones, overhead apor line, and the slurry bottoms pumparound circuit. Coking and uling always occur, but they become a problem when they impact roughput or efficiency.

vidence of Coking/Fouling

Coking/fouling in the reactor and the main column can be detected by:

*Cavitation and/or loss of the main column bottoms pumps

*Fouling and subsequent loss of heat transfer coefficient in the bottoms pumparound exchange

*High pressure drop across the reactor overhead vapor line

*Excessive catalyst carryover to the main column

auses of Coking/Fouling

Coke forms in the reactor and main column circuit because of:

*Changes in operating parameters

*Changes in catalyst properties

*Changes in feedstock properties

*Changes in mechanical condition of the equipment

hanges in Operating Parameters

The operating conditions of the unit, particularly during startups and ed interruptions, will have a large influence on the formation of coke. oke normally grows wherever there is a cold spot in the reactor stem. When the temperature of the metal surfaces in the reactor

50 Fluid Catalytic Cracking Handbook

alls and/or the vapor line falls below the dew point of the vapors, ondensation occurs. Condensation and subsequent coke buildup are ue to cooling effects at the surface.

A high fractionator bottoms level, a low riser temperature, and a igh residence time in the reactor dome/vapor line are additional perating factors that increase coke buildup. If the main column level ses above the vapor line inlet nozzle, "donut" shaped coke can form t the nozzle entrance.

A low reactor temperature may not fully vaporize the feed; unvaorized feed droplets will aggregate to form coke around the feed ozzles on the reactor walls and/or the transfer line. A long residence me in the reactor and transfer line also accelerate coke buildup.

Insufficient bottoms pumparound to the main column heat-transfer one can also form coke.

hanges in Catalyst Properties

Certain catalyst properties appear to increase coke formation. Catalysts ith high rare earth content tend to promote hydrogen transfer reacons. Hydrogen transfer reactions are bimolecular reactions that can roduce multi-ring aromatics.

hanges in Feedstock Properties

The quality of the FCC feed also impacts coke buildup in the reactor ternals and vapor line and fouling/coking of the main column circuit. he asphaltene or the resid content of the feed, if not converted in e riser, can contribute to this coking.

hanges in Mechanical Condition of the Equipment

Damaged or partially plugged feed nozzles can contribute to coke rmation due to poor feed atomization.

Damaged shed-trays in the bottom section of the main cloumn can ause coke formation due to non-uniform contact between upflowing apors and downflowing liquid.

roubleshooting Steps

The following are some of the steps that can be taken to minimize oking/fouling:

Unscheduled Unit interruptions

loss of profit and higher maintenance costs

:	Cavitation and/or loss	Fouling and loss of
	of Main ColumnBottoms	Heat Transfer in
	Pumps	Bottoms Exchanger

Higher pressure drop across the Reactor Overhead vapor line

in Operating

ns
intheReactor	High Levelof Rare-
heat-up	Earth in the
Column Bottoms	Catalyst
or temperature	Low Catalyst Micro
	Activity Test (MAT)
dence Time in the
d Main Column
ms temperature
msPumparoundRate
nger tube wall

Changes in feedstock Properties

High Moleweight Asphaltene & Resins, precipitate and bind to process equip.

High Levelsof

Cracked Feedstock

Changes in Mechan

Conditions of the

Equipment

Damaged or par plugged Feed N Loss of the Shed Feed leaking thr Bottoms exchan Feed Diversion

re

J

Figure 8-5A. Troubleshooting coking/fouling.

Recommendations:

erly insulate RXOverhead piping Main Column Inlet nozzle

p the tube velocity > 7ft/sec p Main Column Bottoms perature < 700°F

a "dry"Dome SteamSystem

mber:

comesto Coking, g Residence Time is e as increasing

s temp, by 25°F

*Increase Bottomstraffic

*Inject a continuous CycleOilflush into inlet Bottoms PAExchangers

*Install duplex filters upstream of Bottoms Pumps

*Install high efficiency feed nozzles

*Use 1" or larger tube diameter

*Keep C7 insolublesin Slurry System less than 5% wt

*Use U-tube for BottomsExch.

*Draw more Bottoms Product

*Have a spare BottomsExchanger bundle

Figure 8-5B. Troubleshooting coking/fouling.

Table 8-1

A Cause and Effect Shutdown Matrix

Effect:	Regan	Riser				Spent	Regan
	Catalyst	Emergency	Feed to	Slurry	HCO	Catalyst	Emergency
	Slide Valve	Steam	Riser	Recycle	Recycle	Slide Valve	Steam
	Process	Closed	Process	Process	Process	Process	Closed
ue low
sure
ue	Close	Open	Close	Close	Close
ntial
slide
rential
slide						Close	Open
ssure
/low	Close	Open	Close	Close	Close		Open
eed	Open	Close
			Close
r high	Close	Open	Close	Close	Close
wn	Close	Open	Close	Close	Close	Close	Open

Low Catalyst/Oil ratio Poor Yields

Loss of Catalyst Activity Equipment Wear

V

,

'Feedstock

•High Fraction of 1050°F+ Material

V

^	' Catalyst		Operating	Mechanical
	• High Level		Conditions	Conditions
	of Rare		Low StrippingSteam	• Damaged Strippin
	Earth		Low Dispersion	Steam distributor
	• High Level		Steam	• Damaged Feed
)	of MaWx		High Preheat	Nozzles
	Activity	J	Temperature	• Damaged Air or
	v		High Reactor	Catalyst Distributo
			Temperature
			Low Cat/Oil Ratio

endations	Install high efficiency Feed Nozzles
	Lower Preheat Temperature
	Inject Naphtha Quench to Riser
	increase Stripping and Dispersion Steam
	Switch to a Coke Selective Catalyst
	Figure 8-7, Troubleshooting high regenerator temperature.

o

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3 CO

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0)

2

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Hydrogen Blistering, Cyanide Attack

Feed	Catalyst	Operating
Properties	Properties	Conditions
ncrease in	•Increase in	•A lower Main Column
eed Nitrogen	Matrix Activity	top temperature
		•Partial Combustion
		•Higher Reactor
		Temp.

/Mechanical Conditi

•Lack of stress relief •Poor material & workmanship

• Inadequate Reside Time to Separate G Lean OH, & Water

nitor Ammonia & Chloride in the Overhead Water, keep Ammonia Sulfide <5,000 ppm e Steam Condensate as Water Wash at a Rate of 1-2 gpm/1000 bbl of Fresh Feed

e Ammonium Polysulfide Solution (especially if HCN > 25 ppm) to 10–20ppm Residual HCN ke sure the WashWater is injected uniformly into the Gas Stream

e "Feed Forward" Water Wash Scheme instead of "ReverseCascade" tall & monitor Hydrogen probes in the key areas ect a Dehazer Additive into the High Pressure Separator (HPS)

tall Coalescer in the Lean Oil and Sponge Oil Streams ess relieve carbon steel

Figure 8-9. Troubleshooting hydrogen blistering.

64 Fluid Catalytic Cracking Handbook

invisible while everything is running well. Compare the readings month-to-month to spot trends.

3.Continuous monitoring of the third-stage separator performance. If catalyst is showing up downstream, consider using more than the "standard" 3% flue gas underflow. The blowcase needs more attention than it usually gets.

4.On-line cleaning—inject walnut hulls into the inlet of the expander weekly.

5.Thermal shocking—reduce feed in 20% increments while maintaining maximum air rate to the regenerator. Cool the expander inlet temperature to around 1,000°F (540°C) and hold for at least one hour. This is not a procedure that the expander vendor supports, but it is practiced by many refiners.

Figure 8-10 provides an outline of the above discussion.

The performance of the unit is a function of feed quality, catalyst roperties, operating variables, and the mechanical condition of the nit. The indicators used to measure the unit's performance are:

*Conversion

*Dry gas yield

• Gasoline quality * Light olefin yield

Observing a Low Conversion

"True" conversion is affected by feed quality, catalyst, operating ariables, and mechanical conditions (Figure 8–11A).

eedstock Quality

The feed properties that lower conversion are:

• Increase in residue (1,050°F+) (565°C+) content

•Increase in feed impurities such as nickel, vanadium, sodium, or nitrogen

« Increase in naphthene and aromatic fractions of the feed

	Problem:	Loss of Revenue	Reduce Gasoline Olefins
		Off-Spec Products		Figure 8-11E
	wer Conversion	High Dry Gas Yield I.ower GasolineYield			Lower GasolineOcta
		Fig. 8-11 B	Figure 8-1 1C	[	Figure 8-11D

^	f	^ t
		Changes in
Changes in
eed Properties		Catalyst Conditions
	•	•

*

re Residue

re Contaminants sParaffins

re Aromatics

d of run for Feed T

ew Fee^ perties

ck for changes in gen, Nl, V,

0°F

d APIgravity, K tor, Rl & 650°F

\	r•Loss of Micro	>
	*
	Activity

•Loss of Surface Area dueto Thermal and Hydro-thermal Oeact. increase in

J CRC

•Change in Catalyst ^formulation j

i

•Track Catalyst

Activity

•Cheek Fresh Catalyst

availability & source

,•Verify Catalyst

•addition rate

> r

Changes in

Operating Conditionss

•I

•Lower Reactor temp.

•Lower cat/oil Ratio •Lower Dispersion Steam

^

J

^Trend Reactor Temp, ^ cat/oil Ratio and Dispersion SteamRate •Check recent temp, and/or press, excursions

•Verify accuracy of VReactortemo J

^ f

Changes in

Mechanical Conditio

\f

c•Damaged or plugged^ feednozzles

•Damaged Stripper

Steam Distributor

V

	\t
f	»

•Check pressure profil around FeedNozzles •Track H2 in Coke •Survey ttie Stripper

>-

Figure 8-11A. Troubleshooting desired product quantity and quality.

Troubleshooting 267

The decreases in microactivity and surface area are strong functions thermal deactivation in the regenerator and the presence of metals the feed.

perating Variables

The following operating parameters lower conversion:

•Decrease in the reactor temperature

•Decrease in the catalyst-to-oil ratio

•Decrease in the atomizing steam

•Decrease in the fresh catalyst addition rate

echanical Conditions

Damaged or plugged feed nozzle(s) and/or damaged stripping steam stributor(s) are the common causes of mechanical failures that fect "true" conversion. Note that the "apparent" conversion, as scussed in Chapter 5, is affected by the distillation cut point and ain column operations.

roubleshooting Steps

•Trend the feedstock properties; look for changes in the K factor, 1,050°F+ (565°C+), aniline point, refractive index, and °API

gravity. The feed endpoint may have been increased to fill the unit. The conversion penalty may be a small price to pay for the increased capacity, but the penalty can be minimized. Verify that the refinery LP reflects current data on yields and product quality.

•Plot properties of the fresh and equilibrium catalysts; ensure that the catalyst vendor is meeting the agreed quality control specifications. Verify that the catalyst vendor has the latest data on feed properties, unit condition, and target products. Verify the fresh makeup rate. Check for recent temperature excursions in the regenerator or afterburning problems.

•Trend the reactor temperature, cat-to-oil ratio, and atomizing steam rate. Verify the accuracy of the reactor temperature thermocouple and atomizing steam flow meter.

•Perform a single-gauge pressure survey around the feed nozzles. Calculate the hydrogen content of the spent catalyst. Conduct a

68 Fluid Catalytic Cracking Handbook

gamma ray scan test to verify the mechanical condition of the stripping steam distributor.

Observing a High Dry Gas Yield

Dry gas yield is affected by everything that affects conversion Figure 8-11B). Changes to increase conversion can increase the dry as yield.

High gas yield shows up as higher speed on the compressor (if entrifugal). In many cases, lower molecular weight (due to higher ydrogen content) can have the same effect.

eedstock Quality

The feed parameters that increase the dry gas yield are:

*	Increase	in nickel and vanadium content
*	Increase	in naphthene, olefin, and aromatic concentration, which
	is indicated by an increase in the refractive index and decreases
	in aniline point and K factor

atalyst Properties

The E-cat properties that increase dry gas yield are:

* Increase in the level of nickel, vanadium, and sodium

*Decrease in E-cat activity, surface area, fresh catalyst activity, and rare earth content

*Increase in the gas and coke factors of the E-cat

perating Variables

Operating parameters that increase dry gas yield are:

*Increase in the reactor temperature

*Increase in the regenerator temperature

«Decrease in the atomizing steam

*Increase in slurry or HCO recycle

echanical Conditions

Mechanical conditions that can increase dry gas yield are:

»	A failing reactor temperature thermocouple
*	Partially plugged or damaged feed nozzles

0 Fluid Catalytic Cracking Handbook

roubleshooting Steps

The following steps should be carried out:

•Track changes in feed metals content, trend the aniline point, and refractive index.

•Trend changes in catalyst activity, surface area, rare earth, and metals content. Consider adding/increasing metals inhibitor.

•Trend changes in the molecular weight of the gas at the firststage suction. Verify that overhead cooling and wash systems are in order.

•Verify the position of the wet gas compressor spillback. Determine if the compressor turbine needs water washing. Trend the level

of inert gases in the dry gas.

«Calibrate the reactor temperature controller. Conduct a pressure survey around the feed nozzle piping to verify its mechanical

integrity.

•If no significant problems are found other than feedstock changes, verify that the refinery LP team has current data on unit yields and product quality with this feedstock. The result of troubleshooting may be that increasing dry gas may be a necessary price for changes in the feed.

bserving a Lower Gasoline Yield

The FCC "true" gasoline yield largely depends on changes in feed uality, catalyst properties, operating variables, and mechanical contions (Figure 8–11C).

eedstock Quality

Paraffinic feedstocks produce the most gasoline yield (but the west octane). The common indicators of any increase in feed parfinicity are:

•Increase in the K factor

•Increase in the aniline point

•Increase in the nickel-to-vanadium ratio

•Decrease in the fraction of "cracked" material

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74 Fluid Catalytic Cracking Handbook

Higher Feed K Factor

Increase in the Catalyst Rare

Earth content

olutions:

Decrease in the Catalyst Matrix

Activity

Larger Zeolite Unit Cell Size

Add ZSM-5 Additive

Higher Cat/Oil ratio

Higher Mix Zone temperature

Split Feed injection

Riser Quench

Figure 8-11E. Troubleshooting high gasoline olefins.

eedstock Quality

Gasoline octane is increased by:

•Increases in the refractive index

•Decrease in the K factor and aniline point

•Increase in the bromine number

atalyst Properties

The fresh catalyst's chemical properties also influence the FCC asoline octane. Gasoline octane is increased by:

• Decrease in rare earth and unit cell size

•Decrease in sodium content

•Increase in matrix activity

perating Conditions

A number of operating variables can change the octane value. The ctors that increase octane are:

• Increase in the reactor temperature. In general, one research octane number increase per 17°F (10°C) increase in the reactor temperature.

• Decrease in the catalyst-to-oil ratio (by increasing thermal reactions).

Troubleshooting 275

•Increase in coke content of the regenerated catalyst.

•Increase in the regenerator temperature.

•Increase in the naphtha quench or HCO recycle.

•Decrease in the gasoline end point.

•Decrease in the gasoline vapor pressure.

echanical Conditions

The main mechanical conditions that affect octane are the type and ondition of the feed nozzles. Low-efficiency feed nozzles actually crease the gasoline octane due to promotion of thermal reactions in e mix zone. High-efficiency feed nozzles improve feed/catalyst ixing and increase the gasoline yield, but decrease gasoline octane.

roubleshooting Steps

• Plot the feed refractive index, °API gravity, and aniline point. Determine any shift in the amount of cracked gas oil in the feed.

•Track the unit cell size, matrix activity, and rare earth content of the catalyst.

•Determine if coke on the catalyst has changed.

«	Verify accuracy of	the reactor temperature.
•	Check for changes	in the gasoline end point and vapor pressure.

•Check the conditions of the feed nozzles and amount of atomizing steam.

asoline Vapor Pressure/Light Olefln Yield

Reformulated gasoline specifications require lower vapor pressure the blended gasoline. It also requires maximum feed to the alkylaon unit. This puts more pressure on the gas plant, particularly the ebutanizer. Floating the tower pressure is often the best way to meet oth constraints.

This chapter highlights the common problems, symptoms, and obable causes that may be encountered in troubleshooting FCC units. addition, a systematic approach is outlined to provide solutions and rrective action. The suggested solutions are necessarily generic but ply to a wide variety of units.

CHAPTER 9

Debottlertecking

and Optimization

Troubleshooting, optimization, and debottlenecking are three steps a continuous process. There is some overlap and gray area among them. Troubleshooting refers to the solution of short-term problems. The signment is usually initiated by operations or maintenance. The lution usually involves something that can be done online. Troubleooting was discussed in Chapter 8.

Optimization refers to maximizing feed rate and/or conversion with e existing equipment while reaching as many constraints as possible. can be the response to changes in the feed quality, ambient contions, or the market demands. Although it is not discussed separately ere, it is the incentive for most debottlenecking projects.

Debottlenecking often refers to hardware changes, small or large. It is rected at the bottlenecks identified during optimization. It includes rojects that cannot be completed online, such as installing new ternals in a vessel. Debottlenecking is the main focus of this chapter.

NTRODUCTION

Most FCC units are big profit makers. Therefore, they are operated several constraints. Debottlenecking is the effort to locate and vercome these constraints. The profitability of an FCC operation is aximized when the unit is "pushed" simultaneously against multiple nstraints. Debottlenecking means finding the constraint or combinaon of constraints that cost the refinery lost opportunities and arriving

the right fix.

A properly configured advanced process control (APC) system could low for on-line, continuous optimal unit operation and push the FCC perations to multiple constraints simultaneously.

The main purpose of debottlenecking is to increase the refinery's ofit margin. In the FCC, this usually means:

276

	Debottlenecking and Optimization	27?
•	Raising the feed rate
»	Processing lower quality feedstocks

•Reducing dry gas and coke yields, therefore, increasing total liquid products

As with troubleshooting, a proper debottlenecking exercise must onsider the effects of feedstock, catalyst, operating conditions, mechanical ardware, environmental issues, and the ability of the rest of the finery to handle the additional feed/product rates and quality.

PPROACH TO DEBOTTLENECKING

Debottlenecking requires a comprehensive test run to determine the peration's present status. Elements of a test run include:

« Overall and component material balance

•Reactor/regenerator heat balance

•Hydrogen balance

•Sulfur balance

•Reactor/regenerator pressure survey

•Utility balance

•Evaluation of the interaction among feed quality, catalyst properties, and operating conditions

•Main fractionator and gas plant modeling

If the object of debottlenecking is to run heavier feeds, multiple test ns may be needed with heavy feed added in stages.

The next step is to identify the incremental value of:

» Fresh feed rate

•Each FCC product

•Octane and cetane numbers

•Other product quality issues (sulfur, slurry ash level, etc.)

ith this information, the constraints on operation can be identified nd the value of addressing them can be evaluated.

mproving FCC Profitability through Proven Technologies

Once the performance of the FCC unit is optimized through the use f new catalyst and operating practices, the unit's profitability can be rther improved by installing proven hardware technologies. The urpose of these technology upgrades is to enhance product selectivity

			Debottlenecking and	Optimization	281
			Example 9-2
Changing Piping in Furnace from Two-Pass				to Four-Pass
Case I: Two-Pass Furnace
50,000 BPD total charge (25,000 BPD to each pass)
°API gravity of feed			= 25
Furnace outlet temp. = 500°F
Furnace tube diameter (I.D.) = 4.5 in.
AP100= 0.0216 x
here:
Pi(K) = Pressure	drop	(psi) per	100 feet of pipe
f = Friction	factor	= 0.017	lb/ft3
p = Flowing density = 47.4

Q = Actual flow rate = 864 GPM d = Tube inside diameter = 4.5 in.

AP!00 = 7.0 psi

Assuming a total 700 ft of equivalent pipe in the furnace, the total essure drop is 49 psi

Case II: Switching to Four-Pass

AP1(X!= 1.9 psi

Assuming a total 500 ft of equivalent pipe in the furnace, the total essure drop is 9.4 psi

aving in pressure drop = 49.0 - 9.5 = 39.5 psi or an 81% reduction

This section addresses the following:

*	Mechanical limitations
•	Riser	termination	device
«	Feed	and catalyst	injection system

Debottlenecking and Optimization

285

Stripper

Gas

(D

</>

be

P 1 > P 2 > P 3

Figure 9-2. Lummus direct-coupled cyclone design.

surance in case the trickle valves stick open. In this design, the riser clones operate at a positive pressure and sealing the diplegs miniizes carry-under of reactor vapors into the reactor housing.

The catalyst must be fluidized to provide an effective seal for the plegs. Fluidization is critical; without it, the diplegs cannot discharge e catalyst and will plug, with possible massive carry-over to the main actionator. To ensure this uniform fluidization, the system uses an ditional steam distributor.

86 Fluid Catalytic Cracking Handbook

Cyclone Dipleg*

Restraint

Figure 9–3. Typical trickle valve.

Cyclone Dipleg

Pivot

Counterweight

\

Figure 94. Typical flapper valve.

In KBR closed cyclone technology, each set of riser and upper eactor cyclones is connected via the use of a "slip joint" conduit. The tripper steam and hydrocarbons, as well as dome steam, exit e reactor housing by entering through this conduit as shown in igure 9-5.

Debottlenecking and Optimization

287

Cyclone

Dipleg

05

16 o

Braces (as required)

Splash Plate

Figure 9-4A. Typical splash plate.

OP VSS System

UOP's current RTD offering is the vortex separation system (VSS), shown in Figure 9-6. VSS is for FCC units having an internal riser nd a similar design (VDS) is for external risers. The catalyst-vapor ixture travels up the riser through the chamber and exits through veral arms. These arms generate a centrifugal flow pattern that parates the catalyst from the vapor inside the chamber. The catalyst ccumulates in a dense phase at the base of chamber, where it is "pre~ ripped" prior to flowing into the reactor stripper. The stripped ydrocarbon vapors are fully contained in the chamber and exit with e rest of the riser effluent vapors to the secondary cyclones.

The reactor vapors leave the VSS through an outlet pipe. Secondary clones are directly connected to this outlet pipe through an expansion

88 Fluid Catalytic Cracking Handbook

Product

Dome

Riser

Catalst

Level

Splash

Plate

Figure 9-5. KBR closed cyclone system.

int. The VSS outlet pipe contains several vent pipes in which the actor dome steam and a portion of the stripping steam/hydroarbon vapors leave the reactor through these vent pipes.

tone & Webster Engineering Corporation (SWEC)

SWEC offers a reactor quench system rather than a closed cyclone ystem. Their typical RTD is an external, rough-cut cyclone (see Figure -7). The vapors from the rough-cut cyclone enter the reactor vessel.

Debottlenecking and Optimization

289

Expansion

Joint

Flapper

Valve

Spent

Catalyst to Stripper

Figure 9-6. UOP vortex separation system.

0 Fluid Catalytic Cracking Handbook

LCO

Quench

To Catalyst

Pre-Stripping Stripper

Steam

Figure 9-7. SWEC external cyclone with quench.

92 Fluid Catalytic Cracking Handbook

eed Nozzles

Important features of a feed injection system include:

• Fine atomization of feed

• High velocity coverage of riser cross-section

•Intimate mixing of catalyst and oil

•Rapid heat transfer from catalyst to oil

•Instantaneous vaporization of feed

•Minimum catalyst back-mixing

•Maximum catalytic reactions while minimizing thermal reactions

A good feed injection system will produce:

•Small droplet size

•Efficient mixing of oil and catalyst

•Complete riser coverage

The feed injection system has come a long way. The early designs eatured open pipes with no consideration for feed vaporization or atalyst/vapor mixing. Currently, FCC technology licensors offer many ersions of feed injection systems. Figure 9-8 is a typical modern feed ozzle. In general, these nozzles incorporate some of the following esign features:

Oil Inlet

Diverging Dual Slot

Target Bolt

Figure 9-8. SWEC feed nozzle.

Debottlenecking and Optimization

2§3

* Steam is used to disperse and atomize the oil/residue feed

•The spray pattern of the oil/steam leaving the nozzle tips tends to be flat (fan spray)

•The assembly includes multiple nozzles in a radial pattern

*The nozzles are designed for a "medium" oil-side pressure drop, generally in the order of 50 psi

Some of the general criteria for choosing feed injection technology clude:

• Total installed cost

* Dispersion steam and/or lift steam/gas requirements, including flow rate, temperature, and pressure

* Oil pressure requirement

• Proven track-record of operational reliability

he choice of the feed injection system should be based on the endor's experience in similar units with similar feeds and on his yield rojection and/or performance guarantee. However, it may be difficult substantiate the guarantee when other changes are being made in

he unit.

pent Catalyst Stripper

Spent catalyst from the reactor/cyclones discharges into the stripper. tripping steam displaces hydrocarbon vapors entrained with the atalyst and removes volatile hydrocarbons from the catalyst.

As part of optimizing the unit, the stripping steam rate should be djusted up or down by 5%. The regenerator temperature and/or CO2/ O ratio will be the main indicator of insufficient stripping. The test ends hen there is no significant response in the regenerator temperature. In the past several years, more attentions have been given to improv- g mechanical performance of the reactor stripper. Proprietary stripper esigns are being offered by the FCC technology licensers in attempts o improve the catalyst/steam contact.

ebottlenecking Catalyst Circulation

Any attempt to increase the unit feed rate will generally require an crease in catalyst circulation. The unit pressure balance and catalyst irculation were covered in Chapter 8.

94 Fluid Catalytic Cracking Handbook

The following should be considered when debottlenecking:

*Differential pressure alarm/shutdown

*Increasing slide valve size

*Standpipes

*Catalyst selection

ifferential Pressure Alarm/Shutdown

Differential pressure shutdowns are a critical part of the unit's safety ystem. No attempt to lower the setting on the shutdown should be ade without adequate consideration. On the other hand, pressure is ost across the slide valves and costs money.

Multiple, independent differential pressure alarm/shutdown switches an be installed with two out of three voting. This can satisfy the afety requirement, increase the comfort factor, and gain valuable ressure drop.

Radial feed nozzles also minimize the possibility of a reversal. New alve actuators can operate more quickly and reliably, also increasing he safety factor.

The test run may indicate that the slide valve is open too far. Most perators prefer to keep the valve in the 40% to 60% range. They lose major comfort zone if the valves open more than this. A larger valve r larger port can be installed in the existing valve.

tandpipes

If the unit pressure balance	indicates that either the pressure gain
n the Standpipes is inadequate	or the delta P across the slide valves

erratic, standpipe aeration and instrumentation should be examined. edesigning the aeration systems or replacing the Standpipes can gain aluable pressure drop. Proper instrumentation can include independent eration flow to each tap, flow indicators/controllers on each, and ifferential pressure indicators between the taps.

Beyond the Standpipes, the available delta P across the valve is

ffected by the pressure drop in other circuits. For		the regenerated
atalyst slide valve, downstream pressure is affected		by:
*	Feed injection system
»	Riser

96 Fluid Catalytic Cracking Handbook

Other more capital-intensive modifications include installing a edicated air blower for the spent catalyst riser. The spent catalyst riser ften requires a higher back-pressure than the main air blower to eliver the catalyst into the regenerator. Therefore, less total combuson air would be available if one common blower is used to transfer pent catalyst and provide combustion air to the air distributors.

Taking higher-pressure services off the main air blower can allow to run out on the curve and deliver more air. The main air blower an also be upgraded to provide added capacity. This includes reducing eal clearance, increasing the flow passing area, and increasing the heel tip diameter. The original equipment manufacturer (OEM) can e contacted for feasibility of this upgrade.

egeneration

Regenerator designs have changed since most units were built. If he unit test run indicates high CRC or if the catalyst will benefit from lower CRC, the regenerator internals should be reviewed. If the data ndicates wide temperature differences across the bed or afterburning, r if the unit has had some excursions, it should be examined.

The regenerator review will include spent catalyst distribution, air istribution, and cyclones. If the test run with heavy feed indicates a emperature limitation, catalyst coolers, partial combustion, or riser uench should be considered.

LUE GAS SYSTEM

The FCC is usually constrained by environmental permits. If the unit ndergoes significant expansion, it may lose "grandfather" protection. he environmental limits include the amount of coke burned in the egenerator and emission rates of particulates, SOx, NOX, and gasoline ulfur. Increasing the feed rate or running heavier crude can increase ll of these emissions. The technology for control is discussed in hapter 10.

CC CATALYST

The FCC catalyst's physical and chemical properties dictate how uch feed can be processed. Chemical properties, such as rare earth

Debottlenecking and Optimization

2§7

nd unit cell size (UCS), affect the unit heat balance and wet gas ompressor loading. Physical properties, such as particle size distriution and density, can limit catalyst circulation.

Consider reformulating the catalyst—custom formulations are availble. Increasing rare-earth content can reduce the wet gas rate. Catalyst usually selected for properties other than its ability to flow. Howver, if it does not flow, it is not going to work well. Catalyst physical roperties should be compared with those of catalysts that have circuted well. Evaluate the economics of using metal passivation additives nd other catalyst enhancing additives.

ebottlenecking Main Column and Gas Plant

Debotflenecking usually results in more feed. Both the main fractionator nd the gas plant must be able to recover the incremental product. The main fractionator can be limited by several factors including:

• Heat removal limitations » Tray flooding

• Fouling and coking

Heat removal can be limited by several factors including:

• Fixed reboiling duties in the gas plant

•Lack of heat exchanger in the pumparound circuits

•Jet or liquid flooding in one or more sections of the main fractionator

•High bottoms temperature leading to fouling or high LCO endpoint

•Overhead condensing capacity

Moving heat up the tower improves fractionation by increasing the apor-liquid traffic. This is limited by flooding constraints and excesve temperature in the bottom.

One method of maximizing the LCO end point is to control the main actionator bottoms temperature independent of the bottoms pumpound. Bottoms quench ("pool quench") involves taking a slipstream om the slurry pumparound directly back to the bottom of the tower, ereby bypassing the wash section (see Figure 9-9). This controls the ottoms temperature independent of the pumparound system. Slurry kept below coking temperature, usually about 690°F, while increas- g the main column flash zone temperature. This will maximize the CO endpoint and still protect the tower.

Debottlenecking and Optimization

301

•Closing the spillback valves.

•Removing external streams. If gas comes from another unit or vents from a column in the gas concentration unit, consider routing it to the interstage rather than the suction. The refinery needs to evaluate if external streams are worth recovering or whether they can be routed elsewhere.

•Installing an advanced surge control system.

•Verifying that the flow rates of corrosion inhibitor and antifoulant are adequate for the new operating conditions.

mproving Performance of Absorber and Stripper Columns

The objective of the primary absorber/stripping towers is to maxiize recovery of C3 and heavier components while rejecting C2 and ghter to fuel. C3 is first absorbed and then C, and lighter components e stripped. Although maximizing C3-C4 recovery for alkylate feed very profitable, lower recoveries are often accepted to maximize the CC conversion and/or feed rate.

Propane/propylene recovery can be enhanced by:

•Increasing the gas plant pressure. A 10 psi increase in absorber pressure increases C3 recovery by 2% (Figure 9-10). However, this can reduce the wet gas compressor capacity. Fractionation efficiency decreases as the column pressure increases.

•Reducing the operating temperature. Consider adding an intercooler on the absorber. Minimize lean oil temperature. Consider the use of a chiller. Each 10°F reduction in lean oil temperature will increase C3's recovery about 0.8% (Figure 9–11).

•Increasing lean oil rate. This rate is often limited by the debutanizer hydraulic and reboiling/cooling capacity. A 50% increase

in lean oil/off-gas ratio increases C3's recovery about 2%.

• Removing waterfrom the lean oil. Installation of water draws and/ or a coalescer can improve recovery. Water can become trapped in the tower and cause poor tray efficiencies, foaming, and premature flooding.

•Minimizing over-stripping. Over-stripping can start a wheel with

the absorber. A 10% cut in stripping rate can increase C3's recovery by 0.8% (see Figure 9-12).

(text continued on page 304)

3-

1

lg

CHAPTER 10

Emerging Trends in

Fluidized Catalytic

Cracking

Although the demand for transportation motor fuels in North America projected to be limited, economic growth in other parts of the world ill require crude oil-based fuels. The Far East, Latin America, and e former Soviet Union are areas where there will be substantial mand for transportation fuels. The collapse of communism, the ivatization of state-owned oil companies, and the global awareness "environmentally clean fuels" will cause this growth.

In the coming years, the refining industry will be experiencing major allenges. In the United States, refiners are faced with excess refining pacity, projected slow growth, and high capital and operating costs comply with environmental health and safety regulations. The oil dustry in general, and the refining industry in particular, are techlogically sophisticated. They have a long history of innovations and oven track records in responding to challenge.

It is likely that the reliable crude oil supply will not diminish any me soon. Petroleum-derived fuels will remain the primary source of ansportation energy for well into the twenty-first century. Producers d refiners have been, and will be, environmentally responsible. The isting infrastructure of advanced product distribution systems can mpete with alternative fuels readily. Future fuels will be competitive, th economically and environmentally. New global market conditions ill dictate closure of inefficient facilities and investment in new chnology. Larger and more efficient operations will survive and will cus on the "niche market."

In the U.S., the crude processing capacity is expected to increase odestly, at a projected rate of 0.5 percent per year. No new refinery

307

400	410	420	430	440
	Gasoline EndPoint, Deg. F
Figure 10-3,	Gasoline	sulfur versus its end point

ui

O

8 ti

%'|OA '

22 Fluid Catalytic Cracking Handbook

.0 Volume of propylene + 1.3 volume of isobutane -> 1.80 volume alky late.

utyiene Alk\ lation

CH3

CH3 — C = CH2 + CH3 — CH — CH2 -> CH3 — CH — CH, — CH — CH3

CH,

CH3

CH,

CH3

PROPYLENE + ISOBUTANE -» 2,2,4 TRIMETHYLPENTANE

ypical Yield:

.0 volume of butylene +1.2 volume of isobutane —>1.70 volume alkylate.

Example 10-2

Etherification of Isobutviene

CH3 — C — CH3 + CH3 — OH -> CH3 — C — O — CH3

CH? CH3

ISOBUTYLENE + METHANOL -> METHYL TERTIARY BUTYL ETHER (MTBE)

ypical Yield:

0 volume of isobutane + 0.43 volume of methanol —> 1.27 volume MTBE.

There are etherification processes, such as MTBE and TAME, aimed producing ethers from C5, C6, and C7 tertiary olefins.

Both alkylate and ether have excellent properties as gasolineblending omponents. They have a low RVP,a high road octane, no aromatics, nd virtually zero sulfur. The emphasis on alkylation and etherification ill continue in both the U.S. and the rest of the world.

24 Fluid Catalytic Cracking Handbook
	Table 10-6
	U.S. Crude Characteristics
Year	°APi Gravity	Wt% Sulfur
1983	32.92	0.88
1984	32.96	0.94
1985	32.46	0.91
1986	32.33	0.96
1987	32.22	0.99
1988	31.93	1.04
1989	32.14	1.06
1990	31.86	1. 10
1991	31.64	1.13
1992	31.32	1.16
1993	31.30	1.15

Source: Swain [24]

pgrade the atmospheric and/or vacuum bottoms in the residual fluidzed catalytic cracking (RFCC) unit. Although residue upgrading in he United States is mostly delayed coker based, most new FCC units re either residue crackers or have in-place provisions to process esidue at a later date. This is more pronounced in the new units built n the Far East, Europe, and Australia. The residue from their crude ils is more paraffinic and contains less metals than North Sea or Middle Eastern crude oils, which makes them more suitable for RFCC.

An RFCC is distinguished from a conventional vacuum gas oil FCC n the quality of the feedstock. The residue feed has a high coking endency and an elevated concentration of contaminants.

Coking Tendency

Residue feedstocks have a higher coking tendency, which is indiated by higher levels of Conradson carbon and a higher boiling point. he common definition of residue is the fraction of the feed that boils bove 1,050°F and Conradson carbon levels greater than 0.5 wt%. The esidual portion of the feed contains hydrogen-deficient asphaltenes nd polynuclear compounds. Some of these compounds will lay down n active catalyst sites as coke, reducing catalyst activity and selectivity.

28 Fluid Catalytic Cracking Handbook

Table 10-7

EPA's New Source Performance Standards (NSPS) for Gaseous Emissions from the FCC Regenerators

Source		Allowable Limits
arbon monoxide	(CO)*	Less than 500 ppmv in the flue gas
itrogen oxides (NOX)		None (local and regional only)
articipates**		A maximum of 1.0 pound of solids in the
		flue gas per 1,000 pounds of coke burned
ulfur oxides (SO2	+ SO3)*	Exempt if the feed sulfur is less than
		0.30 wt%

If there is no add-on control such as a wet gas scrubber, 9.8 kilograms of (SO2 + SO3) per 1,000 kilograms of coke burned. This is approximately equal to 500 ppmv. Add-on device: reduce (SO2 + SO3) by at least 90% or no more than 500 ppmv, whichever is less stringent.

Effective January 1984

*Effective June 1973

he quality of FCC stocks, operating conditions, catalyst type, and echanical condition of the unit. Processing feeds that contain a high oncentration of residue, sulfur, nitrogen, and metals will release a reater amount of SOX, NOX, and particulates. Various technologies re available to reduce flue gas emissions.

articulates

Electrostatic precipitators (ESP) and wet gas scrubbers (WGS) are idely used to remove particulates from the FCC flue gas. Both can ecover over 80% of filtrable solids. An ESP (Figure 10-6) is typically nstalled downstream of the flue gas heat recovery (prior to atmosheric discharge) to minimize particulate concentration. If both low articulate and low SOX requirements are to be met, a wet gas scrubber uch as Belco's (Figure 10-7) should be considered. If SOX removal

BUS DUCT-

INSULATOR COMPARTMENT,

ROOF

EN

ORMER

FIER

DISCHARGE ELECTRODE

RAPPER

RAPPER INSULATOR

HIGH-VOLTAGE SYSTEM

SUPPORT INSULATOR

COLLECTING SURFACE

RAPPER

•SIDE

DOO

DISCHARGE ELECTRODE

HOPPER-

Figure 10-6. Typical electrostatic precipitator (ESP),

C SODA

CULATING

PUMP

Figure 10-7. Schematic of Belco scrubbing system (courtesy of Belco Corporation).

32 Fluid Catalytic Cracking Handbook

pm. For units operating in partial combustion, the flue gas must e sent to a CO boiler. For units operating in complete combustion, he concentration of CO largely depends on the operating conditions f the regenerator (mainly temperature and excess oxygen), the CO romoter level, and the efficiency of the air/spent catalyst distriution system.

OX

NOX levels in the FCC flue gas typically range from 50-500 ppm. itrogen content of the feed, excess oxygen, regenerator residence me, dense phase temperature, and CO promoter all influence the oncentration of NOX.

In the regenerator, most of the NOX is formed as NO, with little 2O or NO2. About 90% of organic nitrogen in the spent catalyst is onverted to inorganic nitrogen, and a very small amount becomes NO. O can be lowered by reducing excess oxygen and CO promoter. The resent platinum-based promoter oxidizes intermediates such as HCN nd NH3 to NO and decreases the reducing agent such as CO.

To reduce nitrogen oxide, thermal and catalytic processes are availble. The thermal process is licensed by Exxon. NH3 or urea is injected nto the flue gas at an elevated temperature (-1600°F, 870°C); NOX reduced to nitrogen. This process is applicable to FCC units that ave CO boilers. NOX can also be reduced over a catalyst at 500°F

o 750°F (260°C to 400°C).

MERGING DEVELPMENTS IN CATALYSTS, ROCESSES, AND HARDWARE

The FCC process has a long history of innovation and will continue o play a key role in the overall success of the refining industry. The ontinuing developments will primarily be in the areas of catalyst, rocess, and hardware technologies.

atalyst

Since the mid-1960s, formulation of FCC catalysts has improved teadily. The focus of the research is in the following areas:

APPENDIX 2

Correction to Volumetric Average Boiling Point

WABP C 80) F V

==• ""^

WABP O 603F VABP

A8TM Diet, 10% - 90 %Slop*

339

APPENDIX 3

TOTAL Correlations

romatic Carbon Content:

CA = -814.136 + 635.192 x RI(20) - 129.266 x SG + 0.1013 x MW- 0.340 x S - 6.872 x ln(v)

ydrogen Content:

H2 = 52.825 - 14.26 x RI(20) - 21.329 x SG- 0.0024 x MW - 0.052 x S + 0.757 xln(v)

olecular Weight:

MW = 7.8312 x 10-3 x SG-0-0976 x AP°C1238

efractive Index @ 20°C:

RI(20) = 1 + 0.8447 x SG1-2056 x (VABPoc+273.16r)0557 x

efractive Index @ 60°C:

RK60) = 1 + 0.8156 x SG12392 x (VABP0(: + 273.16)-0.0576 x

ource: Dhulesia, H., "New Correlations Predict FCC Feed Characterization Paramers," Oil & Gas Journal, Jan. 13, 1986, pp. 51-54.

340

APPENDIX 4

n-d-M Correlations

v = 2.5 x (RI20OC - 1.4750) - (d2()OC - 0.8510)

05	= (d2()OC - 0.8510) -	1.11 x (RI2fn,	- 1.4750)
If v is positive: %CA		= 430 x v +	3660
If	v is negative: %CA	= 670 x v +
			M

If 03 is positive: %CR = 8 2 0 x G J - 3 x S + 10,000/M

If 03 is negative: %CR = 1440 x 03 - 3S +10,600

M

%CN = %CR — %CA
%C_ = 100— %CR
r	K

verage Number of Aromatic Rings per Molecule (RA):

RA	= 0.44 + 0.055	x M x v If v is positive
R^	= 0.44 + 0.080	x M x v If v is negative
verage Total Number of Rings per Molecule (RT):
RT	= 1.33 + 0.146	x M x (03-	0.005	x S)	If 03is positive
RN	= RT — RA
RT	= 1.33 + 0.180 x M x (03-		0.005	x S)	If 05is negative

verage Number of Napthene Rings per Molecule (RN):

RM = RT—RA

urce: ASTM Standard D-3238-80. Copyright ASTM. Used with permission.

341

APPENDIX 5

Estimation

of Molecular Weight

of Petroleum Ofts

from Viscosity

Measurements

Tabulation of H Function

H

40	334	336	339	341	343	345	347	349	352	354
50	355	357	359	361	363	364	366	368	369	371
60	372	374	375	377	378	380	381	382	384	385
70	386	387	388	390	391	392	393	394	395	397
80	398	399	400	401	402	403	404	405	406	407
90	408	409	410	410	411	412	413	414	415	415
00	416	417	418	419	420	420	421	422	423	423
10	424	425	425	426	427	428	428	429	430	430
20	431	432	432	433	433	434	435	435	436	437
30	437	438	438	439	439	440	441	441	442	442
40	443	443	444	444	445	446	446	447	447	448
50	448	449	449	450	450	450	451	451	452	452
60	453	453	454	454	455	455	456	456	456	457
70	457	458	458	459	459	460	460	460	461	461
80	461	462	462	463	463	463	464	464	465	465
0	465	466	466	466	467	467	468	468	468	469

342

Molecular Weight of Petroleum Oils

343

Viscosity-Molecular Weight Chart

LINES OF CONSTANT 210*F (98,89*C) VISCOSITY, cST

500

5400

300

too	)0 j/	400	500	600

RELATIVE MOLECULAR MASS

ource: ASTM Standard D-2502-92. Copyright ASTM. Used with permission.

APPENDIX 6

Kinematic Viscosity

o Saybolt Universal

Viscosity

	Equivalent Saybolt	Universal
inematic Viscosity, cSt	Viscosity, Sus
	At 100°F	At 210°F
1.81	32.0	32.2
2.71	35.0	35.2
4.26	40.0	40.3
7.37	50.0	50.3
10.33	60.0	60.4
13.08	70.0	70.5
15.66	80.0	80.5
18.12	90.0	90.6
20.54	100.0	100.7
43.0	200.0	202.0
64.6	300.0	302.0
86.2	400.0	402.0
108.0	500.0	504.0
129.5	600.0	604.0
139.8	648.0	652.0
151.0	700.0
172.6	800.0
194.2	900.0
215.8	1000.0

xtracted from ASTM Method D-2161-87. Copyright ASTM. Used with permission.

344

APPENDIX 7

API Correlations

Xr = a + b x (R.) + c x (VG)

Xn = d + e x (R.) + f x (VG)

Xn = g + h x (R.) + i x (VG)

here constants vary with molecular weight range given below:

onstants		Heavy Fractions 200 < MW < 600
a		+2.5737
b		+1.0133
c		-3.573
d		+2.464
e		-3.6701
f		+1.96312
g		-4.0377
h		+2.6568
j		+1.60988
.	= Refractivity Intercept
GC = Viscosity Gravity Constant
K	K
R,	~-Ri(20)

here:

(2()) = Refractive Index @ 20°C

= Density @ 20°C

ource: Riazi, M. R., and Daubert, T. E., "Prediction of the Composition of Petroleum actions," Ind. Eng. Chem. Process Dev., Vol. 19, No. 2, 1982, pp. 289-294.

345

46 Fluid Catalytic Cracking Handbook

VGC = SG ~ °-24 - °-022 x log(V210 ~ 35.5) 0.755

Where:

= Saybolt Universal Viscosity @ 210°F in seconds

efractive Index @ 20°C (68°F):

I = A x exp(B x MeABP + C x SG + D x MeABP x SG)

x MeABPE x SGF

onstants	2.341 * 10~2
A
B	6.464 xIQ"4
C	5.144
D	-3.289 x 10-4
E	-0.407
F	-3.333

MW = a x exp(b x MeABP + c x SG + d x MeABP x SG)

x MeABP6 x SGf

here:
onstants
a	20.486
b	1.165 x10~4
c	-7.787
d	1.1582 x 10-3
e	1.26807
f	4.98308

APPENDIX 8

Definitions of

Fluidization Terms

eration. Any supplemental gas (air, steam, nitrogen, etc.) that increases fluidity of the catalyst.

ngle of Internal Friction—a. Angle of internal friction, or angle of shear, is the angle of solid against solid. It is the angle at which a catalyst will flow on itself in the nonfluidized state. For an FCC catalyst, this is about 80°.

ngle of Repose—p. The angle that the slope of a poured catalyst will make with the horizontal. For an FCC catalyst, this is typically 30°.

SoHdSurfaca

347

Definitions of Fluidization Terms

349

keletal Density—SD. The actual density of the pure solid materials that make up the individual catalyst particles. For an FCC catalyst, the skeletal density can be calculated as follows:

SD =

3.42.1

Where: Al = Alumina content of the catalyst, wt%

Si = Silica content of the catalyst, wt%

ip Factor. The ratio of vapor velocity to catalyst velocity.

ick Slip Flow. The continuous sudden stoppage and resumption of catalyst flow in a standpipe. This is usually caused by underaeration.

uperficial Velocity. The velocity of the gas through the vessel or pipe without any solids present. It is a volumetric flow rate of fluidization gas divided by the cross-sectional area.

APPENDIX 9

Conversion of ASTM

50% Point to TBP

50% Point

Temperature

The following equation can be used to convert an ASTM D-86 50% mperature to a TBP 50% temperature.

TBP (50) = 0.87180 x ASTM D-86 (50)1.0258

here:
BP(50)	= true boiling point distillation temperature at 50 vol%
	distilled,	°F
STM D86(50) = observed		ASTM D-86 distillation temperature at
	50 vol% distilled, °F

xample:

iven ASTM D-86(50) = 547°F, determine TBP 50% temperature:

BP(50) = 0.87180 x (547)1.058

BP(50) = 561°F

ource: Daubert, T. E., "Petroleum Fraction Distillation Interconversions," Hydrocarbon ocessing, September 1994, pp. 75-78.

350

APPENDIX 10

Determination

of TBP Cut Points

from ASTMD-86

The difference between adjacent TBP cut points can be determined y the following equation:

Y.= A XB

!I

here:

. = difference in TBP distillation between two cut points, °F

	i	= observed difference in ASTM D-86 distillation between two cut
		points, °F

,B = constants varying for cut points ranges, shown in the following table:

i	Cut Point Range	A	B
1	100%–90%	0.11798	1 .6606
7	90%-70%	3.0419	0.75497
3	70%–50%	2.5282	0.820072
4	50%–30%	3.0305	0.80076
5	30%– 10%	4.9004	0.71644
6	10%–0%	7.4012	0.60244

ource: Daubed, T. E., "Petroleum Fraction Distillation Interconversions," Hydrocarbon ocessing, September 1994, pp. 75-78.

351

2 Fluid Catalytic Cracking Handbook

BP (0)	= TBP(50) - Y4 - Y5- Y6
BP (10)	= TBP(50) - Y4 - Y~
BP (30)	= TBP(50) - Y4
BP (70)	= TBP(50) + Y3
BP (90)	= TBP(50) + Y3 + Y2
BP (100)	= TBP(50) + Y" + Y, + Y,

APPENDIX 11

Nominal Pipe Sizes

			Identification
ominal		Steel		Stainless	Wall	Inside
Pipe	Outside	Iron		Steel	Thickness	Diameter
Size	Diameter	Pipe	Sched.	Sched.	(t)	(d)
nches	Inches	Size	No.	No.	Inches	Inches
1/4	0.540	STD	40	40S	.088	.364
		xs	80	80S	.119	.302
3/8	0.675	STD	40	40S	.091	.493
		XS	80	SOS	.126	.423
1/2	0.840	STD	40	40S	.109	.622
		XS	80	80S	.147	.546
		—	160	.__	.187	.466
		xxs	—	—	.294	.252
3/4	1 .050	STD	40	40S	.113	.824
		XS	80	80S	.154	.742
		—	160	—	.219	.612
		XXS	—	—	.308	.434
1	1.315	STD	40	40S	.133	1.049
		XS	80	80S	.179	.957
		—	160	—	.250	.815
		XXS	—	—	.358	.599
1-1/4	1.660	STD	40	40S	.140	1.380
		XS	80	80S	.191	1 .278
		—	160	_	.250	1 . 1 60
		XXS	—	—	.382	.896
1-1/2	1.900	STD	40	40S	.145	1.610
		XS	80	80S	.200	1.500
		—	160	—	.281	1.338
		XXS	—	—	.400	1.100

353

4 Fluid Catalytic Cracking Handbook

			Identification
ominal			Siteei	Stainless
Pipe	Outside	Iron		Steel
Size	Diameter	Pipe	Sched.	Sched.
nches	Inches	Size	No.	No.
2	2.375	STD	40	40S
		XS	80	80S
		—	160	—
		xxs	—	—
2-1/2	2.875	STD	40	40S
		XS	80	80S
		—	160	—
		XXS	—	—
3	3.500	STD	40	40S
		XS	80	80S
		—	160	—
		xxs	—	—
3-1/2	4.000	STD	40	40S
		XS	80	80S
4	4.5	STD	40	40S
		XS	80	80S
		—	120	—
		—	160	—
		xxs	—	—
5	5.563	STD	40	40S
		XS	80	80S
		—	120	—
		—	160	—
		xxs	—
				—
6	6.625	STD	40	40S
		XS	80	80S
		—	120	—
		—	160
				—
		XXS	—
				—

Wall inside Thickness Diameter

(t)(d)

Inches	Inches
.154	2.067
.218	1.939
.344	1.687
.436	1.503
.203	2.469
.276	2.323
.375	2.125
.552	1.771
.216	3.068
.300	2.900
.438	2.624
.600	2.300
.226	3.548
.318	3.364
.237	4.0.26
.337	3.826
.438	3.624
.531	3.438
.674	3.152
.258	5.047
.375	4.813
.500	4.563
.625	4.313
.750	4.063
.280	6.065
.432	5.761
.562	5.501
.719	5. 187
.864	4.897