02 BOPs / Woods D.R 2008 rules-of-thumb-in-Engineering-practice (epdf.tips)

10.3 Bins and Hoppers for Bulk Solids 331

x Good Practice

Bins and hoppers: In general, the cohesive strength of powders increases with consolidation pressure.

x Trouble Shooting

If the flow of solids is not as anticipated, a bin vibrator can be installed on the slope of the hopper.

“No flow”: [arching]*/[ratholing]*.

“Erratic flow”: obstructions alternating between arching and ratholing/cohesive material plus [sequential arching then ratholing]*/noncohesive plus bin walls not steep enough to produce flow at the wall/noncohesive plus star feeder draws only from one wall/noncohesive plus constant pitch screw conveyor with diameter I exit hole from hopper.

“Flooding or flushing” when a rathole collapses it entrains air, becomes fluidized and the material floods through the outlet uncontrollably:” fine powders such as pigments, additives and precipitates that tend to rathole/insufficient residence time in hopper for deaeration.

“Flow rate limitation”: fine particles where movement of the interstitial air causes an adverse Dp.

“Limited live capacity”: [ratholing]*. “Product degradation”: [ratholing]*.

“Incomplete or nonuniform processing”: [ratholing]*.

[Arching]*: particle diameter large compared to outlet/cohesive particles probably caused by moisture or compaction/AI too high/AI i conical hopper outlet diameter. [Ratholing]*: cohesive particles probably caused by increased moisture or by compaction (fine powders I 100 mm such as pigments, additives and precipitates)/ outlet diameter from hopper I RI/HII steepest hopper angle (as measured from the vertical).

[Semi-stable ratholing]*: outlet diameter of hopper slightly larger than RI and HI I steepest hopper angle and AI I conical hopper outlet diameter.

[Sequential arching then ratholing]*: cohesive material and bin walls not steep enough/cohesive material and bin walls wrong shape/cohesive material and screw conveyor diameter I exit hole from hopper.

feeders

“Solids initially flow from the hopper but if solids rest, then no flow”: instantaneous

AII outlet diameter but after resting AI i outlet diameter. “Flow initially OK but stops after several minutes:” [ratholing]*.

“No flow at the front of the feeder”: instantaneous AI I conical outlet diameter but instantaneous RI is large/solid is pressure sensitive.

“Sometimes the feeder is full; other times feeder is starved (all particles I 150 mm)”: [semi-stable ratholing]*.

“Feeder overflows when solids level in hopper is low”: FRI is small/small diameter particles do not allow entrapped air to escape.

“Feeder overflows when solids level in hopper is high”: FRI is small and HI is small /source of air at or near hopper outlet causes fluidization.

332 10 Process Vessels and Facilities

“Feeder overflows only when solids are being conveying into the hopper”: FRI is small/ air entrained with particles entering the hopper.

“Feeder overflows independent of level in hopper or solids entering hopper”: FRI is small and HI is small/excess air entering hopper via leaks or with feed/gate partially closed/flexible sock partially closed/obstruction in the hopper exit.

“Solids flowrate from feeder does not increase with increasing speed of feeder”: FRI

I required flowrate/solids diameter small enough to form a limited rate into the feeder caused by the upflow of air a hopper exit/air injection location too low.

“Solids flowrate does not increase when rpm of rotary valve is increased”: moderately low FRI/air introduced by the rotary valve at hopper outlet/venting the returning high-pressure cavity is insufficient.

10.4

Bagging Machines

x Application

Three options are usual: volume fill, simultaneous fill and weigh, SFW, and preweigh, PW.

Usually fill the 40–50 kg bag based on volume of powder, not weight – provided that the particles have consistent bulk density, are not easily aerated and the particles flow easily.

Volume fill: particles must have consistent bulk density.

Use SFW if bulk density varies; SFW with accuracy of e 0.125 to 0.25 %; use PW for more accuracy.

Use valve bag filler for bag size 10–55 kg. Select the feed system based on density and size of the particles:

–for powders, flakes, granules 0.4–1.7 Mg/m3; size 44–12 000 mm (examples cocoa, flour, black peppers, cement, plaster, pigments, organic resins), use auger.

–for free flowing, flaked or powdery, granules 0.13–1.9 Mg/m3; (examples fertilizer, seeds, plastic pellets, concrete, stucco, grout, sand & refractory; bentonite, TiO2, iron oxide, carbon black), use air.

–for fine particles with mid to high density, 1–1.6 Mg/m3; size I 3000 mm; (example portland cement, mortar mix, stucco, grout, lime gypsum, barite), select vertical impeller.

–for fine particles with low to mid density, 0.16–1 Mg/m3; size I 3000 mm; (example lightweight concrete mixes, vermiculite, polystyrene, kaolin, silica, graphite, carbon black, organic pigments, oat and rice hull ash), select horizontal impeller.

–for extremely fine and light powders, 0.016–0.4 Mg/m3; size I 150 mm; select vacuum.

–for free flowing granular, (example fertilizer, corn, soybeans, salt, sugar; sand, refractories, plastic pellets), select gravity.

–for pharmaceuticals, food products use polymer bags or kraft bag with polyethylene liner and thermally seal.

10.4 Bagging Machines 333

Auxiliary equipment includes vibrating packers: machines to vibrate a bag or solid container so that the maximum dry bulk solid is in the minimum container space.

x Guidelines

For 40–50 kg bags, one person can handle up to 5 bags/min. To achieve up to 8 bags/min add another set of scales.

For foodstuffs and pharmaceuticals, 25 bags/min with I 20 kg bags. With 2 mil thick liner, the capacity is twice as fast as with 6 mil polymer liner.

Vibrating packer: about 0.7 kW drive motor.

x Good Practice

Air packer: if feed is not free flowing, set dribble time of 3 s. Do not place a partially filled bag into filler; this will produce subsequently many off spec bags.

x Trouble Shooting

“Erratic weights”: bag too small/pressure chamber not filled/feed density I design/obstruction between lower chamber and bag/bulk/dribble valve sticks/flow through valves different from design/vibration/sleeve of valve is not clear of the opening/vent in spout plugged/bag clamp fault/mechanical bind.

“Fill time excessive”: bag incorrectly put on filling spout/excessive fluidization/density different from design.

“Chamber pressure does not drop to zero during refill”: sticky valve/exhaust time incorrect.

Appendix A:

Units and Conversion of Units

The units are organized by dimension starting with length L and progressing through mass, force, energy, electrical and magnetic units. Under each cluster of units may also be included the reciprocal. Thus the set of units of dimensions M/L2T also has the units of dimensions L2T/M. Order-of-magnitude values are often included. At the end of this appendix are the physical constants and conversion of temperatures.

SI Prefixes:
1024	yotta Y	10–1	deci d
1021	zetta Z	10–2	centi c
1018	exa E	10–3	milli m
1015	peta P	10–6	micro m
1012	tera T	10–9	nano n
109	giga G	10–12	pico p
106	mega M	10–15	femto f
103	kilo k	10–18	atto a
102	hecto h	10–21	zepto z
10	deca da	10–24	yocto y

Rules of Thumb in Engineering Practice. Donald R. Woods

Copyright c 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

ISBN: 978-3-527-31220-7

Appendix A: Units and Conversion of Units 335

Figure A-1 Conversions among systems of units for kinematic viscosity for liquids.

Conversions for distance, length, dimensions: L

meter, m	inch	q 0.0254	= m
	foot	q 0.3048	= m
height of adult: 1.6 to 1.8 m	yard	q 0.914	= m
	mile	q 1.609	= km
height of giraffe: 10 m	minch	q 0.0254	= mm
	mil	q 0.00254	= cm
	cm	q 0.01	= m
	angstrom	q 10–10	= m
	angstrom	q 0.1	= nm
	micron	q 10–6	= m
	nautical mile	q 1.853218	= km

336 Appendix A: Units and Conversion of Units

Conversions for area, permeability, dimensions: L2

square meter, m2	inch2	q 6.45E-4	= m2
	ft2	q 0.0929	= m2
card table: 0.6 m2	yard2	q 0.836	= m2
	mile2	q 2.5899	= km2
square micrometer, mm2	acre	q 4047	= m2
	dm2	q 10–2	= m2
28 mm filter: 10 mm2	cm2	q 10–4	= m2
clay: 0.01 mm2	mm2	q 10–6	= m2
	angstrom2	q 10–2	= nm2
	micron2	q 10–12	= m2
	km2	q 106	= m2
	hectare (ha)	q 104	= m2
	D’Arcy	q 0.9869	= mm2
	ft3lbm/h2lbf	q 222.62	= mm2
	ft3lbm/s2lbf	q 2.885E9	= mm2

Appendix A: Units and Conversion of Units 337

Conversions for volume, dimensions: L3

	Volume. reciprocal: amount of substance/volume
	cubic meter, m3		inch3	q 16.39E-6	= m3
			ft3	q 28.2E-3	= m3
	box car: 100 m3		yard3	q 0.7646	= m3
	refrigerator: 1 m3		Imp. gallon	q 4.55	= L
	large pail: 10 L		US gallon	q 3.785	= L
	brick: 1 L		Imp. quart	q 1.1365	= L
	golf ball: 40 cm3		kL	q 1	= m3
	1 m3 Z 1 tonne water		barrel (oil)	q 0.15899	= m3
			fluid oz	q 28.413E-3	= L
			pint	q 0.568	= L
			std ft3 (STP)	q 28.2E-3	= Nm3 (STP)
			std ft3 (STD)	q 26.7E-3	= Nm3 (STP)
	standard conditions:		std ft3 (STP)	q 29.7E-3	= m3 (STD)
	STP gas = 0 hC, 101.325 kPa dry; metric uses		dm3 = L	q 10–3	= m3
	the prefix “N” to designate this condition.		hectoliter	q 0.10	= m3
	Other “standard” conditions used include:		cm3	q 10–6	= m3
	STD gas = 15.6 hC, 101.325 kPa dry		cm3	q 1	= mL
	NTP(API) = 15 hC, 101.325 kPa		mm3	q 10–9	= m3
		reciprocal	nm3	q 10–27	= m3
	kilomol per cubic meter, kmol/m3		micron3 = mm3	q 10–18	= m3
			(km)3	q 109	= m3
	pure gaseous CO2 at STP: 0.0446 kmol/m3		(hectom)3	q 106	= m3
			(decam)3	q 103	= m3
	1 kmol = 22.4 m3 at STP		bushel	q 3.524 q 10–2	= m3
	DO NOT USE: molarity or “M” for molar		mol/L	q 1	= kmol/m3
			lb mol/ft3	q 16.02	= kmol/m3
	solution.

Another obsolete term is molality: dimensions 1/M. This would have units of measurement of mol/kg

Conversions for volume ratio, dimensions: dimensionless

scfm/100 USgpm	q 7.45	= dm3/100 L
USgal/1000 acf	q 0.134	= L/m3
USgal/bbl.	q 0.0238	= m3/m3
scf/bbl	q 0.1773696	= m3/m3
UK gal/1000 ft3	q 0.161348	= L/m3

338 Appendix A: Units and Conversion of Units

Conversions for surface/volume ratio, dimensions: 1/L

	cm2/cm3	q 100	= m2/m3
	ft2/ft3	q 3.28084	= m2/m3
	ft2/UK gal	q 20.418	= m2/m3
Conversions for volumetric flow, dimensions: L3/T
cubic meters per second, m3/s	ft3/s	q 28.317	= dm3/s
cubic decimeter per second, dm3/s or L/s	ft3/min	q 0.4719	= dm3/s
	scfm	q 1.6699	= m3/h (STP)
fast running tap into a sink: 0.1 L/s	scfm	q 1.5	= Nm3/h
liquid pumped through a 5 cm diam. pipe:	scfm	q 0.4719	= dm3/s(STP)
2.5 L/s	scfh	q 0.028	= m3/h (STP)
	scfh	q 7.756	= cm3/s
gas flowing through 10 cm diam. pipe:	106 scfd	q 1.17E3	= m3/h (STP)
150 dm3/s	US gpm	q 0.0631	= L/s
	Imp. gpm	q 0.07577	= L/s
	Imp gph	q 1.26E-6	= m3/s
	106 Imp. gpd	q 0.0526	= m3/s
	106 US gpd	q 0.0438	= m3/s
	103 bbl/d	q 1.84	= L/s
	103 bbl/d	q 6.62	= m3/h
	bbl/d	q 0.159	= m3/d
	mm3/s	q 10–9	= m3/s
	cm3/s	q 10–6	= m3/s
	dm3/s = L/s	q 10–3	= m3/s
	L/s	q 3.6	= m3/h
	L/min	q 1.667E-5	= m3/s
	m3/h	q 2.778E-4	= m3/s
	Million scfd	q 0.325	= m3/s
	USgph	q 0.0010514	= L/s
	in3/s	q 16.39	= cm3
Conversions for acceleration, dimensions: L/T2
m/s2	cm/s2	q 10–2	= m/s2
	ft/s2	q 0.3048	= m/s2
acceleration of gravity Z 9.8 m/s2
std. 9.80665 m/s2

Appendix A: Units and Conversion of Units 339

Conversions for angular acceleration, dimensions: 1/T2

radians per second, r/s2

Conversions for velocity, dimensions: L/T

Volumetric flowrate per unit area, volume flux, mass transfer coefficient for a concentration driving force, mass

flux per unit concentration driving force
meter per second, m/s		ft/s	q 0.3048	= m/s
		ft/min	q 0.00508	= m/s
		ft/min	q 5.08	= L/m2 s
liquid pumped	1 m/s	cfm/ft2	q 0.00508	= m/s
		ft3/ft2 min	q 5.08	= dm3/m2 s
highway driving	25 m/s	US gal/ft2 day	q 0.04074	= m3/m2 day
		US gal/ft2 day	q 4.715E-4	= L/m2 s
		US gal/ft2 h	q 0.04074	= m3/m2 h
Mass transfer coefficient		US gal/ft2 h	q 0.011316	= L/m2 s
		US gal/ft2 min	q 2.45	= m3/m2 h
for gases	85 mm/s	US gal/ft2 min	q 0.6789	= L/m2 s
for liquids	0.85 mm/s	miles/h	q 1.6093	= km/h
		miles/h	q 0.447	= m/s
		ft3/acre s	q 0.06998	= m3/(ha.s)
		ft3/acre s	q 6.998E-6	= m/s
		mpy (mil per year)	q 0.025	= mm/a
		cm/s	q 10–2	= m/s
		cm/min	q 0.166	= L/m2 s
		cm3/cm2 h	q 0.0028	= L/m2 s
		dm/s	q 10–1	= m/s
		m/min	q 1.6667E-2	= m/s
		m/h	q 2.7778E-4	= m/s
		mm/s	q 1	= L/m2 s
		L/m2 s	q 3.6	= m3/m2 h
		scfm/1000 ft3	q 0.01666	= dm3/m2.s.
		106 US gal/acre-d	q 0.0108247	= L/m2.s.
		knot
		(nautical mile/h)	q 1.853184	= km/h

340 Appendix A: Units and Conversion of Units

Conversions for volumetric flow per unit length, dimensions: L2/T

Kinematic viscosity, thermal or molecular diffusivity; overflow weir rate
Square meter per second, m2/s		US gal/(day ft)	q 0.01242	= m3/day.m
		m3/(day.m)	q 1.157E-5	= m2/s
Diffusivities:		centistokes		= mm2/s
for gases	0.1 to 1 cm2/s	(1 stoke = cm2/s)	q 10–4	= m2/s
		ft2/s	q 0.0929	= m2/s
for liquids	1000 mm2/s	m2/h	q 2.7778E-4	= m2/s
		ft2/h	q 2.5806E-5	= m2/s
for solids	0.1 to 104 nm2/s	in2/s	q 6.451E-4	= m2/s
		dm2/s	q 10–2	= m2/s
Kinematic viscosity:		mm2/s	q 10–6	= m2/s
		cm2/s	q 10–4	= m2/s
for water	106 mm2/s	cm2/s	q 108	= mm2/s
		mm2/s	q 10–12	= m2/s
		nm2/s	q 10–18	= m2/s
		SSU	q 2.165E-3	= cm2/s
		USgpm/in	q 2.484252	= L/s.m
		USgpm/ft	q 0.207021	= L/s.m

Conversions for mass, dimensions: M

kilogram, kg	lbm	q 0.4536	= kg
	grain	q 6.48E-2	= g
metric ton = Mg	ton (2000 lbm)	q 0.9072	= Mg
	long ton (2240 lbm)	q 1.016	= Mg
your mass 50 to 90 kg	metric tonne	q 1.000	= Mg
	g	q 10–3	= kg
	mg	q 10–6	= kg
	oz	q 28.349	= g
	cwt (long)	q 50.8023	= kg
	cwt (short)	q 45.3592	= kg

Conversions for molar mass, dimensions: M

kg/kmol

depends on the substance

g/mol

for water: molar mass is 18 kg/kmol

for air: molar mass is 29 kg/kmol