Compressors and Expanders

This chapter presents brief descriptions and some theoretical background of the most widely used pumps for liquids, and compressors and expanders for gases, all of which are modeled in simulators. Heuristics for the application of these devices during the synthesis of a chemical process are presented in Chapter 5. Further information on their selection and capital cost estimation is covered in Chapter 16. More comprehensive coverage of the many types of pumps, compressors, and expanders available is presented in Sandler and Luckiewicz (1987) and in Perry s Chemical Engineers Handbook (1997). After studying this chapter and the materials on pumps, compressors, and turbines on the multimedia CD-ROM that accompanies this book, the reader should be able to explain how the more common types of pumps, compressors, and expanders work and how a simulator computes their power input or output 

The main purpose of a pump is to provide the energy needed to move a liquid from one location to another. The net result of the pumping action may be to increase the elevation, velocity, and/or pressure of the liquid. However, in most process applications, pumps are designed to increase the pressure of the liquid. In that case, the power required is 

The two most important characteristics of a pumping operation are the capacity and the head. The capacity refers to the flow rate of the fluid being pumped. It may be stated as a mass flow rate, a molar flow rate, or a volumetric flow rate. Most common is the volumetric flow rate, Q, in units of either m /hr or gal/min (gpm). The head, or pump head, H, refers to the increase in total head across the pump from the suction, s, to the discharge, d, where the head is the sum of the velocity head, static head, and pressure head. Thus, 

When a centrifugal pump is installed in a pumping system and operated at a particular rotational rate, N, (usually 1,750 to 3,450 rpm), the flow rate can be varied by changing the opening on a valve located in the pump discharge line. The variation of H with Q defines a unique characteristic curve for the particular pump operating at N with a fluid of a particular viscosity. Each make and model of a centrifugal pump is supplied by the manufacturer with a 

When a characteristic curve for just one rotation rate and/or impeller diameter is available and an approximate characteristic curve is desired for another rotation rate and/or impeller diameter, the affinity laws for a centrifugal pump can be applied  

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Published analyses of cascade cycles by means of energy balances under conditions comparable to those used in analyzing expander cycles are very scarce. Longwell and Kruse tabulated computer-calculated compressor and expander powers for a C3Hg-C2Fl4-CF[4 cascade. For a feed of 1,566 Ib-moles/hr at 515 psia and 60°F, 490 lb-moles of LNG and two gaseous products were produced. 

Figure 4-10. Compressor train for dual-pressure installation consisting of an axial flow air compressor with adjustable stator blades and a radial flow nitrous gas compressor and expander. Mass flow air = 139,000 Nm /h, nitrous gases = 122,500 Nm /h Pressure air = 0.82/4.75 bar, nitrous gases = 4.38/10.8 bar Power input total = 16,840 kW Power recovery by expander = 10,950 kW.

Obviously, large turbotrains require modern coupling anangements. At least one manufacturer, Sulzer-Roteq, makes extensive use of solid couplings between compressors and expanders. The thrust bearing is usually located in the low-pressure compressor. 

Figure 4-29. 360-t/d packaged unit—top foundation plate 13 m long, 3.6 m wide, 0.93 m high. The oil system is situated at the front end, followed by the steam turbine, compressor, and expander. The oil coolers are located separately. 

Compressors and Expanders Selection and Application for the Process Industry, Heinz P. Bloch, Joseph A. Cameron, Frank M. Danowski, Jr., Ralph James, Jr., Judson S. Swearingen, and Marilyn E. Weightman Metering Pumps Selection and Application, James P. Poynton Hydrocarbons from Methanol, Clarence D. Chang Form Flotation Theory and Applications, Ann N. Clarke and David J. Wilson... 

The use of the pinch technology method in the design of heat exchanger networks has been outlined in Sections 3.17.1 to 3.17.6. The method can also be applied to the integration of other process units such as, separation column, reactors, compressors and expanders, boilers and heat pumps. The wider applications of pinch technology are discussed in the Institution of Chemical Engineers Guide, IChemE (1994) and by Linnhoff et al. (1983), and Townsend and Linnhoff (1982), (1983), (1993). 

Compressors and Expanders Selection and Applications for the Process Industries (Dekker). Boland, D. and Linnhoff, B. (1979) Chem. Engr, London No. 343 (April) 222. The preliminary design of networks for heat exchangers by systematic methods. 

Compressors and Expanders Selection and Application for the Process Industry, Heinz R Bloch, Joseph A. Cameron,... 

While the stack, insulation and stack balance in this simple-cycle system is a key component the balance of plant is also an important factor. The stack cost again mainly depends on the achievable power density. Small systems like these will likely not be operated under high pressure. While this simplifies the design and reduces cost for compressors and expanders (which are not readily available at low cost for this size range in any case) it might also negatively affect the power density achievable. 

The performance of a SOFC system with a Brayton-Rankine bottoming cycle for heat and fuel recovery has been calculated. Gas turbine compressor and expander efficiencies of 83% and 89% and a steam turbine efficiency of 90% have been assumed. 

API Standard 617, Axial and Centrijugal Compressors and Expanders— Compressors for Petroleum, Chemical, and Gas Industry Services,... 

Generally, the compressor and expander maps plot referred or corrected mass flow rate, speed and torque. For instance, the mass flow rate and rotational speed are... 

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