Intercooled

Space needs to be provided for the auxiliaries, including the lube oil and seal systems, lube oil cooler, intercoolers, and pulsation dampeners. A control panel or console is usually provided as part of the local console. This panel contains instmments that provide the necessary information for start-up and shutdown, and should also include warning and trouble lights. Access must be provided for motor repair and ultimate replacement needs to be considered. If a steam turbine is used, a surface condenser is probably required with a vacuum system to increase the efficiency. AH these additional systems need to be considered in the layout and spacing. In addition, room for pulsation dampeners required between stages has to be included. Aftercoolers may also be required with knockout dmms. Reference 8 describes the requirements of compressor layouts and provides many useful piping hints. 

If the compression cycle approaches the isothermal condition, pV = constant, as is the case when several stages with intercoolers are used, a simple approximation of the power is obtained from the following formula ... 

Screw-Type This type of rotary compressor, as shown in Fig. 10-80, is capable of hancmng capacities up to about 4.248 X lO" m m (25,000 fF/min) at pressure ratios of 4 1 and higher. Relatively small-diameter rotors allow rotative speeds of several thousand rev/min. Unhke the straight-lobe rotary machine, it has male and female rotors whose rotation causes the axial progression of successive sealed cavities. These machines are staged with intercoolers when such an... 

FIG. 10-86 Two -stage double-acting compressor cylinders with intercooler. 

FIG. 11-78 Typical two-stage system with two evaporating temperatures, flash-gas removal, and intercooling. 

Approximately 0.016 (kg-mol)/s [126 (lb-mol)/li] of vapor is absorbed with an energy liberation of about 198,000 W (670,000 Btii/b), 20 percent of which is removed by the intercooler on stage 7. The temperature profile departs from a smooth curve at stages 4 and 7, where secondary oil enters and heat is removed respectively... 

FIG. 23-3 Temperature and composition profiles, a) Oxidation of SOp with intercooling and two cold shots, (h) Phosgene from GO and Gfi, activated carbon in 2-in tubes, water cooled, (c) Gumene from benzene and propylene, phosphoric acid on < uartz, with four quench zones, 260°G. (d) Mild thermal cracking of a heavy oil in a tubular furnace, hack pressure of 250 psig and sever heat fluxes, Btu/(fr-h), T in °F. (e) Vertical ammonia svi,ithesizer at 300 atm, with five cold shots and an internal exchanger. (/) Vertical methanol svi,ithesizer at 300 atm, Gr O -ZnO catalyst, with six cold shots totaling 10 to 20 percent of the fresh feed. To convert psi to kPa, multiply by 6.895 atm to kPa, multiply by 101.3. 

The Intercooled Regenerative Reheat Cycle The Carnot cycle is the optimum cycle between two temperatures, and all cycles try to approach this optimum. Maximum thermal efficiency is achieved by approaching the isothermal compression and expansion of the Carnot cycle or by intercoohng in compression and reheating in the expansion process. The intercooled regenerative reheat cycle approaches this optimum cycle in a practical fashion. This cycle achieves the maximum efficiency and work output of any of the cycles described to this point. With the insertion of an intercooler in the compressor, the pressure ratio for maximum efficiency moves to a much higher ratio, as indicated in Fig. 29-36. 

Specimen Location Heat exchanger tube from a carbon dioxide compressor intercooler... 

For adiabatic reactors one example was presented by Berty et al (1968) on a six-stage adiabatic reactor system that had intercoolers between the stages. Every adiabatic stage is always sensitive or unstable but the full six-stage... 

Figure 9.7.1 Staged adiabatic reactor with intercoolers. ...

The need to keep a concave temperature profile for a tubular reactor can be derived from the former multi-stage adiabatic reactor example. For this, the total catalyst volume is divided into more and more stages, keeping the flow cross-section and mass flow rate unchanged. It is not too difficult to realize that at multiple small stages and with similar small intercoolers this should become something like a cooled tubular reactor. Mathematically the requirement for a multi-stage reactor can be manipulated to a different form ... 

For small flowrates, the single-casing radial compressor without intercooling is employed for delivery pressures of up to 4-6 bar. Higher pressures of up to 15 bar are attained with intercooled machines of single- and double-casing design. 

Figure 4-13. Sidestream radial machines of four to eight stages with horizontally split casing and one or two pairs of intermediate nozzles, generally for connecting external intercoolers.

The way to enhance the power output of a gas turbine can be achieved by intercooling and reheat. 

Intercooling and Reheat Effects. The net work of a gas turbine cycle is given by... 

Therefore, if a simple gas turbine cycle is modified with the compression accomplished in two or more adiabatic processes with intercooling between them, the net work of the cycle is increased with no change in the turbine work. 

The thermal efficiency of an ideal simple cycle is decreased by the addition of an intercooler. Figure 2-7 shows the schematic of such a cycle. The ideal simple gas turbine cycle is 1-2-3-4-1, and the cycle with the intercooling added is -a-b-c-2- i-A-. Both cycles in their ideal form are reversible and can be simulated by a number of Carnot cycles. Thus, if the simple gas turbine cycle 1-2-3-4-1 is divided into a number of cycles like m-n-o-p-m,... 

All the Carnot cycles making up the simple gas turbine cycle have the same efficiency. Likewise, all of the Carnot cycles into which the cycle a-b-c-2-a might similarly be divided have a common value of efficiency lower than the Carnot cycles which comprise cycle 1-2-3-4-1. Thus, the addition of an intercooler, which adds a-b-c-2-a to the simple cycle, lowers the efficiency of the cycle. 

The addition of an intercooler to a regenerative gas turbine cycle increases the cycle s thermal efficiency and output work because a larger portion of the heat required for the process c-3 in Figure 2-7 can be obtained from the hot turbine exhaust gas passing through the regenerator instead of from burning additional fuel. 

A simple cycle with intercooler can reduce total compressor work and improve net output work. Figure 2-7 shows the simple cycle with intercooling between compressors. The assumptions made in evaluating this... 

This cycle produces an increase of 30% in work output, but the overall efficiency is slightly decreased as seen in Figure 2-15. An intercooling regenerative cycle can increase the power output and the thermal efficiency. This combination provides an increase in efficiency of about 12% and an increase in power output of about 30%, as indicated in Figure 2-16. Maximum efficiency, however, occurs at lower pressure ratios, as compared with the simple or reheat cycles. 

Figure 2-16. Performance map showing the effect of pressure ratio and turbine inlet temperature on an intercooled regenerative cycle.

Figure 2-18. The intercooled regenerative reheat split-shaft gas turbine cycle.

This cycle achieves the maximum efficiency and work output of any of the cycles described to this point. With the insertion of an intercooler in the compressor, the pressure ratio for maximum efficiency moves to a much higher ratio, as indicated in Figure 2-19. 

The compressor train is driven by the motor/generator, which has a pair of clutches that enable it to act as a motor when the compressed air is being generated for storage in the cavern, declutches it from the expander train, and connects it to the compressor train. The compressor train consists of a three-section compressor each section having an intercooler to cool the compressed air before it enters the other section, thus reducing the overall compressor power requirements. 

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