Surface intercoolers

Macchi et al. [9] made an extensive study of water injection cycles in their two classic papers and their results are worth a detailed study. Some of their calculations (for ISTIG, RWI and HAT) are reproduced in Figs. 6.18-6.20, all for surface intercooling (parallel calculations for evaporative intercooling are given in the original papers). 

Macchi et al. provided a similar comprehensive study of the more complex RWI cycles as illustrated in Fig. 6.19, which shows similar carpet plots of thermal efficiency against specific work for maximum temperatures of 1250 and 1500°C, for surface intercoolers. The division of pressure ratio between LP and HP compressors is again optimised within these calculations, leading to an LP pressure ratio less than that in the HP. For the RWI cycle at 1250°C the optimisation appears to lead to a higher optimum overall pressure ratio (about 20) than that obtained by Horlock [5], who assumed LP and HP pressure ratios to be same in his study of the simplest RWI (EGT) cycle. His estimate of optimum pressure ratio... 

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. 

Figure 10-149. Exchanger rating for intercooler, using low-fin tubes. Note specifications here are for illustration purposes. The design as developed represents more conservative surface area than substantiated by current data.

Water Jackets, Intercoolers, Receivers and Aftercoolers.—The cooling surface in an intercooler is generally designed from the formula S = Q/0.25(ta — tw), where S is the cooling surface in square feet, Q is the number of cubic feet of free air per minute, and ta and are the temperatures, in degrees F. of the air leaving and the water entering the intercooler, respectively. 

Exothermic processes, widi cooling through heat transfer surfaces or cold shots. In use are shell-and-tube reactors with small-diameter tubes, or towers with internal recirculation of gases, or multiple stages with intercooling. Chlorination of methane and other hydrocarbons results in a mixture of products whose relative amounts... 

Another NG-fired OTM-based oxy-fuel plant is the zero emission ion transport membrane oxygen power (ZEITMOP) cycle (Fig. 10.11) proposed by Yantovski and co-authors. The cycle is based on a supercritical CO2 cycle, where CO2 is compressed in an intercooled compressor to over 200 bar, heated in a recuperative heat exchanger and expanded in a high pressure turbine to 15 bar. It is then used as sweep gas in an OTM, where it is enriched with O2 separated from a stream of compressed air. The CO2/O2 flow is used as oxidant in a NG combustor which produces high temperature oxidized gas to be expanded to nearly ambient temperature in a low pressure turbine. Efficiencies of 50.4-52.0% with virtually zero CO2 emissions are reported. " A reactive membrane configuration can also be adopted to reduce the required membrane surface area. In this case, cycle efficiency... 

Example A compressor for 300 000 m h of process air with a stage pressure ratio of Pgyj/Pjjj - 1.8 has a power input of about 7 MW per stage. This amount of heat determines the heat transfer surface to be provided in the intercoolers. Therefore, it is not surprising, that the appearance of the compressors is dominated by the large intercoolers and that these can make up almost 30% of the compressor costs. 

Much better catalysts now provide improved operation. Hydrogenation can be controlled by adding traces of carbon monoxide to the hydrogen. Adsorbed carbon monoxide modifies the relative adsorption of acetylene and ethylene on the palladium and minimizes ethylene loss. The catalyst itself can also be made more selective by alloying the palladium with a further metal such as copper or silver. This also affects pallacfium dispersion and the relative adsorption of acetylene and ethylene on the catalyst surface to improve selectivity. To minimize temperature rise catalyst suppliers recommend that one or more catalyst beds with intercoolers be used in each reactor, depending on the acetylene content of the C2 stream ... 

---