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

1.24 Rules of Thumb about the Context in Which We Function: Entrepreneurship 41

1.23

Rules of Thumb about the Context in Which We Function: Intrepreneurship

(based on Valikangas, 2003 and Cooper, 1987)

Innovation within the corporation:

1.Create the motivation first: want to bring new products to the market. This is a high risk but vital activity.

2.Ensure management commitment: concrete, consistent and explicit.

3.Set concrete and achievable goals with resources to support.

4.Create the infrastructure: a process (and reward system) to identify winners, develop a plan and market the new product. A major cause of failure of new products is marketing: underestimating the competition, and overestimating the potential.

5.Build into the process elements to manage risk: if the uncertainty is high, keep the stakes low, reduce uncertainty by using an incremental decision process, buy information to reduce the uncertainty, don’t be afraid to stop one project when it now looks unattractive.

6.Cultivate innovation routines and name your innovation ambassadors. Often select a person to lead who has a Kirton KAI inventory (Kirton, 1976) value of about 100 to 110, midway between the adaptors 85–100 and the innovators 110–130.

7.Evaluate progress effectively, purposefully and regularly.

8.Focus on quality first.

1.24

Rules of Thumb about the Context in Which We Function: Entrepreneurship

Creating your own company:

1.Need technology, creativity, courage and business know-how.

2.Kondratieff wave of world-wide prosperity with highs 1860, 1920, 1960.

3.Major innovation cycles 6 years; next major high 2035.

4.Cost of invention, R&D 5–10 %. Conception and product design 10–20 %.

Fabrication & process development 40–60 %. Fine tuning and manufacturing 5–10 %. Market launch 10–25 %.

5.Business plan, business plan, business plan.

6.Use the rules of thumb for intrapreneurship that are pertinent.

421 Rules of Thumb

7.It takes 15 years between a company’s inception and a viable product entering the market.

8.One in ten brilliant start-up ideas is successful financially; nine are not.

9.The startup idea should be patented.

10.The startup company should have an address, a board, a CEO, a business plan and a bank account.

For more see Doyle (1983) and Curran (1991).

1.25

Rules of Thumb about the Context in Which We Function: e-Business

e-Business uses the same business and marketing principles, combined with ideas related to change management and building consumer trust.

1.Start small.

2.Write out your goals and focus on the goals.

3.Develop consumer trust by knowing your product and customers, through careful design of the consumer–vendor interface.

4.Astutely select the informational content: create value, be credible, be transparent, show company values and the real people behind the company by providing names and photographs, describe the company’s achievements, address security concerns up-front, provide reassurance in case of fraud, give a privacy policy and let consumers be in control of their data.

5.Continue to build trust after the purchase by giving different means of contact, by handling customer inquiries efficiently, and by giving feedback about the order. Provide great after sales service.

6.Take your best people on developing e-business and take care of them.

7.Spend at least 10 % of the advertising budget on on-line advertising.

1.26

Rules of Thumb about Mentoring and Self-management

Whether it is managing yourself or giving advice as a mentor to someone else, here are my personal suggestions.

1.Complete jobs as if you were a consultant. Do them well and on time. Indeed, add a few extras.

1.27 Summary 43

2.Learn to say No.

3.Keep a balance in your life among physical, emotional, spiritual and intellectual.

4.Honor yourself; feel good about yourself.

5.Keep a sense of humor.

6.Be positive.

7.Be trustworthy and build trust.

8.Do things right the first time.

9.Keep good records. For example, sign and date all calculations.

10.Keep good personal files. Become an active member in professional organizations, subscribe to professional journals and set time aside to read and keep up to date.

11.Learn the company’s economics.

12.Use the above ideas to learn how to cope well with the current “instant response” expectations. The e-mail and the internet have fostered a new concept of time. Many now seem to leave things to the last minute; expect instant response and incorrectly select some action, even if they know it is not the best choice. We need to re-establish that it takes time to do jobs well; we need lead times for meetings. Be patient with yourself and with others.

13.Apply the main principle of networking: “give to your network five times for any single time you want to draw on your network.” (Woods and Ormerod, 1993)

1.27 Summary

The major focus of this book is on the rules of thumb for selecting, rough sizing, costing, operating and trouble shooting many different types of equipment used in chemical processes. This is what the book is about. The introduction and details of the organization of these rules of thumb were given in Section 1.1. Details for each major type of equipment are given in Chapters 2 to 10.

However, in selecting equipment engineers need information about the properties of materials, corrosion, process control, batch versus continuous and economics. We refer to this as the context for the chemical process and provided rules of thumb for each in Sections 1.2 to 1.7, respectively.

Rules of thumb for the thinking process used, or how engineers design and practice their skills, were given in Sections 1.8 to 1.16. More specifically the emphasis was on problem solving, goal setting, decision making, thermal pinch, systems thinking, process design, process improvement, trouble shooting and health-safety-environment issues, respectively.

44 1 Rules of Thumb

Sections 1.17 to 1.20 summarized the rules of thumb for the people part of engineering (communication, listening, interpersonal skills and team work).

Finally, the context in which engineers function (performance review, leadership, intrepreneurship, entrepreneurship, e-business and self management) were described in Sections 1.21 to 1.26.

References

Cooper, R.G. (1987) “Winning with New Products” Gage Publishing, Agincourt, Ontario.

Covey, S.R. (1989) “The Seven Habits of Highly Effective People”, Simon and Schuster, New York.

Curren, Alex (1991) “Making Ventures Succeed: Earning the Right to Succeed in Business,” Curren Publishing, Oakville, Ontario.

Doyle, D.J. (1983) “Making Technology Happen”, Doyletech, Kanata, Ontario.

Fisher, K. et al. (1995) “Tips for Teams”, McGraw Hill, New York.

Francis, D., Young, D. (1979) “Improving Work Groups: A Practical Manual for

Team Building”, University Associates, San Diego.

Holmes, T.H., Rahe, R. H. (1967) “The Social Readjustment Rating Scale,” J. Psychosomatic Res., Aug., 213–218.

Kirton, M. (1976) “Adaptors and Innovators: a description and measure”, J. Appl. Psychol., 61, no. 5, 622–629.

Valikangas, Liisa (2003) “ Manage Innovation as a Corporate Capability” Chem. Eng. Prog., Jan. pp. 64 –69.

Woods, D.R., Ormerod, S. D. (1993) “Networking: How to Enrich Your Life and Get Things Done” Pfeiffer & Co., San Diego.

2 Transportation

The fundamentals for fluid movement are that fluids move because of (i) a pressure difference; (ii) a density difference; (iii) gravity and (iv) boundary movement. These are expressed, on the macroscopic level, as Bernoulli’s equation. Resisting the momentum transfer (fluid flow) is friction. We express the friction as a friction factor and correlate it with the Reynolds no. Centrifugal pumps are often selected to pump liquids; pumps operate on their head capacity curve showing decreasing head with increasing capacity. In this chapter we consider gas moving (pressure, and vacuum service), liquid moving, gas–liquid, liquid–solid or slurry and solid conveying. Ducts and pipes are discussed in Section 2.7. Storage, including bins and hoppers, is considered in Chapter 10.

2.1

Gas Moving: Pressure Service

x Area of Application (M)

Fans: 0.1–30 kPa; 1–105 dm3/s. Blowers: 10–300 kPa; 1–103 dm3/s.

Rotary screw compressors: 20–2500 kPa; 10–104 dm3/s.

Centrifugal compressors: 20–30 000 kPa; 200–3 q 105 dm3/s.

Reciprocating piston compressors: 30–400 000 kPa; 5–104 dm3/s. Usually economical for i 6 MPa and I 150 dm3/s or any discharge pressure and flows I 100 dm3/s.

Axial compressors: 20–2000 kPa; 4 q 103 –106 dm3/s.

x Guidelines

Fans: Power: up to 7.5 kW/m3/s. For fan air-conditioning package units: 13.5 Ndm3/s per m2 of floor area. For the process area, allow 13.5 Ndm3/s per kW for refrigeration; for office space, q 3; for stores, q 7. Allow 0.5 L/s of cooling water/kW of refrigeration. Related topic Section 3.12, refrigeration.

Blowers, centrifugal: Power: up to 125 kW/m3/s.

Blowers, rotary lobe: maximum pressure ratio 2:1.

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

46	2 Transportation
	Compressors:
	adiabatic	pVk = constant
	isothermal	pV = constant
	polytropic	pVn = constant: for uncooled internally n i k; for internally
		cooled 1 I n I k with n z k.

Heat capacity ratio, k = cp/cv = 1.04 for gases with molar mass i 100. The value of k increases to 1.67 as the molar mass decreases. For air = 1.4 and for such gases as ethylene, carbon dioxide, steam, sulfur dioxide, methane, ammonia = 1.2–1.3.

Temperature rise between feed 1 and exit 2:

T2/T1 = (p2/p1) (n–1)/n

(n – 1)/n = (k – 1)/k hp hp = polytropic efficiency

For each stage keep the exit temperature (T2 –298) I 120–150 hC. For diatomic gases, k = 1.4, this limits compression ratio (p2/p1) to 4; for triatomic gases, 6.

hp i hadiabatic. For uncooled compressors, polytropic, hydraulic and temperature rise efficiencies are the same and range from 0.7–0.8 with the usual value 0.72.

Rotary screw compressors: Power: 100–750 kW/m3/s.

Centrifugal compressors: Centrifugal compressors deliver actual volumetric flows (cubic decimeters per second and performance should not be expressed as mass, mols or standard volumetric flow). Assume compression ratios equal in all stages. Maximum number of stages that can be on one shaft or fit in the “frame” = 8 minus 1 stage for each side nozzle. Compression ratio 2.5–4. The pressure coefficient = 0.5–0.65; assume 0.55. The pressure differential increases with increase in suction gas density (increased molar mass, suction pressure or decrease inlet temperature, decrease in k). Power: up to 7.5 kW/m3/s. Efficiency of large centrifugal compressors: 76–78 %.

Centrifugal compressors operate between low volumetric flowrate “surge” conditions and high volumetric flowrate limited by the sonic velocity at the eye of the impeller. At “surge” conditions, the gas flows back through the compressor causing damage to the thrust bearings. The surge point is usually 0.33–0.5 of the normal operating capacity of the compressor. During startup the machine goes through the surge region. The point of surge is a minimum for a single impeller. The range of stable operation decreases 5 % with the addition of each impeller. High molar mass decreases the range of operation. Surge may be caused by system disturbance (especially changes in the molar mass of the feed gas) and insufficient flow.

Surge is related to power used.

When the molar mass of the inlet gas increases, the motor amps increase.

If the molar mass increases by 20 % and we control the suction drum pressure by recycling exit gas to the inlet (spill back control) the motor amps increase by 20 %; if control is by throttle of the suction line, the motor amps increase by 10 %. For every 10 % decrease in the total number of moles compressed, the amps load on the motor drive decreases by 5 %. For control valves on the suction or discharge side, allow a Dp of 5 % of the absolute suction pressure or 50 % of the dynamic loss, whichever is greater.

2.1 Gas Moving: Pressure Service 47

Reciprocating piston compressors: Compression ratios 1.2–6; select to keep outlet temperature I 150 hC. Efficiencies for reciprocating compressors 65 % for compression ratio 1.5; 75 % compression ratio 2, 80–85 % for compression ratio 3–6. Power: 70–1200 kW/m3/s.

Axial compressors: Compression ratios of 1.2–1.5 per stage and 5–6.5 per machine. Efficiency 70 % except for liquid ring 50 %. Power: 35–950 kW/m3/s.

In general:

Velocity: pump gas 30 to 60 m/s [$]

pump oxygen/chlorine: 20 m/s [S] pump steam 60 m/s [$]

Pressure drop for gas flow through pipes: 1 velocity head per 45 to 50 Length/ pipe diameter [$, J]

through shell & tube exchangers: 5 kPa/pass

through wet sieve tray: 0.3 to 0.65 kPa/theoretical stage through packing tower: 0.2 to 0.75 kPa/m packing moderate to high pressure distillation: 0.3–0.6 kPa/m vacuum distillation: 0.08–0.16 kPa/m

absorbers: 0.15–0.5 kPa/m

through porous bed: 2 to 50 kPa (porous bed diam., mm)3/m depth through cyclone: 0.5 to 1.6 kPa.

through venturi scrubber: 0.5 to 6 kPa.

See other individual pieces of equipment for specifics.

x Good Practice

Usually driven by electric motors except for larger compressors that are driven by steam turbines (see Section 3.1).

Compressor exit gas: cool if temperature i 175 hC; include oil knock out pots and filter if the compressor is oil-lubricated. Don’t let lubricating oil/mist collect or remain for a long time in the hot discharge side of the compressor. Instead of one compressor on load and a second on standby, use two compressors with each handling 60 % of load. Reduce recycle in compressor operations.

For reciprocating compressors, if temperature rise I theoretical temperature rise, suspect problems with compressor valves or piston rings. For reciprocating: consider downstream pulsation dampeners or accumulators to smooth out delivery volume and pressure, use variable speed drive, especially if load varies or unit may be oversized. To minimize vibrations for reciprocating equipment, the base should be 1.5 q mass of the machine.

Compressor inlet gas: consider the use of mist knockout pots.

Fans: Prefer backward bladed because they are self-limiting in power demand. Blowers: For rotary lobe: when used for pressure pneumatic conveying install a check valve in the blower discharge.

Centrifugal. Good practice: allow safety margins of design speed 5 %, design head 10 % and design power 15 %. The sonic velocity decreases with an increase in gas molar mass.

Reciprocating piston: Good practice: design velocity through valves I 40 m/s.

48 2 Transportation

x Trouble Shooting

Fans: “Noise”: vortex, flow separation/loose bearings. “Discharge pressure low”: instrument error/fans in series rotating in the same direction/operating below the stall point/density increase. “Low flowrate”: instrument error/flow separation/ pitch angle of blades too shallow/speed slow/required system discharge high.

Blowers: “Discharge pressure high”: instrument error/restriction in downstream line/check valve jammed in closed position/dirty intake filter. “Discharge pressure low” : instrument error/slippage of the drive belts/relief valve stuck open/increasing air loss at the rotary valve due to larger clearance opening from wear/loss of air caused by larger lobe clearance in the blower due to wear/a leak, such as a ruptured hose, in a vacuum system/a ruptured bag in the downstream bag house. Centrifugal: “Surging”: insufficient flow/increased discharge pressure required by system/deposit buildup in diffuser. “Discharge pressure low”: instrument error/ compressor not up to speed/excessive inlet temperature/leak in discharge system. Provide separate anti-surge system for compressors operating in parallel; careful design of suction piping for double flow compressors.

Reciprocating piston: major faults: valves and piston rings: “Knocking”: frame lubrication inadequate/head clearance too small/crosshead clearance too high; “Vibration”: pipe support inadequate/loose flywheel or pulley/valve LP unloading system defective. “Discharge pressure high”: instrument error/valve LP unloading system defective/required system discharge high. “Discharge pressure low”: instrument error/valve LP unloading system defective/LP valve worn/system leakage. “Discharge temperature high”: instrument error/LP valve worn/valve LP unloading system defective/required system discharge pressure high. “Cooling water temperature high” : instrument error/water flowrate low/fouled area/LP valve worn. “Valve temperature high”: instrument error/required system discharge pressure high/run unloaded too long/LP valve worn. “Cylinder temperature high”: instrument error/ required system discharge pressure high/LP valve worn/wrong speed. “Flow low”: instrument error/LP valve worn/valve LP unloading system defective/dirty suction filter.

2.2

Gas Moving: Vacuum Service

x Area of Application

Liquid-piston vacuum pump: down to 12 kPa absolute; 0.01 to 1000 kg/h air; see also Section 6.37.

Rotary sliding vane vacuum pump: down to 4 kPa abs.; 0.01 to 300 kg/h; Wet reciprocating vacuum pump: down to 3 kPa abs.; 0.01 to 100 kg/h; Dry reciprocating vacuum pump: down to 0.1 kPa abs.; 0.01 to 300 kg/h; Mechanical vacuum pump: down to 0.01 kPa abs.; 0.01 to 40 kg/h;

2.2 Gas Moving: Vacuum Service 49

Steam ejector:

1 stage: down to 5–6.7 kPa abs.; 0.01 to 100 kg/h air exhausted; 2 stage: down to 0.5–1.4 kPa abs.; 0.01 to 100 kg/h;

3 stage: down to 0.1–0.2 kPa abs.; 0.01 to 50 kg/h; 4 stage: down to 0.01–0.25 kPa.; 0.01 to 10 kg/h;

5 stage: down to 0.001–0.0025 kPa abs.; 0.01 to 8 kg/h; 6 stage: 0.0004 kPa abs.

Practical limit is 0.0004 kPa abs; usually 0.05–0.15 kPa abs.

For most steam ejector applications, direct contact condensers between stages were frequently used. For vacuum steam stripping, use shell and tube condensers with refrigerant at –8 to –12 hC upstream of the booster ejector with interstage dry condensers plus a liquid ring vacuum pump.

x Guidelines

Air leakage into unit: 50 kg/h.

Liquid-piston pump: 100 to 200 kW/m3/s exhausted air. Rotary sliding vane: 130 to 250 kW/m3/s air exhausted. Wet reciprocating: 2 to 50 kW/m3/s air exhausted.

Dry reciprocating: 2 to 50 kW/m3/s air exhausted. Mechanical vacuum: 2 to 50 kW/m3/s air exhausted.

Steam ejector:

1 stage: 0.002 to 10 kg steam/kg air exhausted/kPa abs. 2 stage: 100 kg steam/kg air exhausted/kPa abs.

3 stage: 1 Mg steam/kg air exhausted/kPa abs.

4 stage: 2 Mg steam/kg air exhausted/kPa abs.

5 stage: 40 Mg steam/kg air exhausted/kPa abs.

Steam ejector, general:

down to 10 kPa abs., 1 to 200 kg/h air; 1.3 kg steam/kg air exhausted/kPa abs. down to 30 kPa abs., 1 to 20 kg/h air exhausted; 0.1 kg steam/kg air exhausted The compression ratio of the first stage ejector is set primarily by the intercon-

denser cooling water temperature.

Assume the discharge pressure to atmosphere after the last stage = average barometric pressure +7 kPa. Assume motive steam = minimum steam pressure in header less 5–10 %. Pressure drop on shell side of surface condenser usually I 5 % of absolute design operating pressure.

Related topic Section 3.9 for interstage direct contact G–L condensers, although current practice is to use surface shell and tube condensers (H).

x Good Practice

Liquid piston vacuum pump: cool seals with 0.03 L/s of clean cooling water at pressure at least 35 kPa greater than discharge pressure of pump.

Dry vacuum pump: size for usual discharge pressure 20–35 kPa gauge to allow for downstream discharge. Vacuum pumps run hot: 50–70 hC. Allow 30 min warmup period before putting on-line. Allow 60 min purge before shutdown. Try not to have the pump discharge into a common header. Multistage pumps

50 2 Transportation

tend to run cooler than single stage. Install a check valve on the discharge. If the discharge pressure is i 35 kPa, add a positive displacement blower (designed for 6 Ndm3/s at design conditions for the vacuum pump) with a bypass that is open for startup.

Steam ejectors: Operability of steam ejectors is very sensitive to the stability in the motive fluid (steam) pressure. Prefer vacuum pumps to steam ejectors (H). Keep diameter of pipes = diameter of inlet and discharge flanges of ejectors. As the column overhead mass flowrate increases above design, so will the column overhead pressure and vice versa. Compression ratios per ejector: 6:1 to 15:1. If inlet gas temperature I 0 hC or below the triple point of water (0.61 Pa) then add steam jacketing to cope with ice formation. Seal for the hot well: submerge i 30 cm. The volume in the hotwell between the pipe and the overflow weir should be 1.5 times the volume in the down spout sealed. Replace any nozzles or diffusers where the area is i 7 % larger than design.

x Trouble Shooting

Liquid piston vacuum pump: “Noisy”: service liquid level too high/coupling misaligned. “Capacity low”: suction leakage/service liquid temperature too high/speed too low/seal water flowrate I design. “power excessive”: service liquid level too high/coupling misaligned. “service liquid temperature high”: clogged strainer/partially closed valve/fouled heat exchanger.

Dry vacuum pump: “Loss of vacuum”: condensation in the suction line/condensation of species from other units connected to a common exhaust header/increase in discharge pressure from restriction in downstream processing or pressure blowout in other units connected via common discharge header. “Excessive corrosion”: for systems handling acid gas or connected to such systems via common discharge header: warmup period too short/shutdown purge too short. “Overheating”: low cooling water flow/fouled cooling system/inlet gas temperature i 70 hC. “High amps.”: buildup of polymer caused by operating temperature too high/polymerizable species gain access via common discharge header.

Steam ejectors: related topic, barometric condensers, Section 3.9.

Check the last stage first and then move upstream: “ Unstable operation or loss of vacuum”: steam pressure I 95 % or i 120 % of design/steam superheated i 25 hC/wet steam/inlet cooling water temperature hot/cooling water flowrate low/condenser flooded/heat exchange surface fouled/20–30 % higher flow of non-condensibles (light end gases, air leaks or leaks from fired furnaces)/seal lost on barometric condenser/entrained air in condenser water/required discharge pressure requirement high/fluctuating water pressure. “Water coming out of discharge”: upstream condenser flooded.