Capital cost of compressors for conceptual design

Many process intensification techniques involve the use of gas compressors. Gas recycles is typically used to improve yield and selectivity in reactor/separation processes. Vapor recompression in distillation systems are becoming more widely applied, particularly with complex separations such as divided-wall, reactive, extractive and azeotropic distillation systems. At the conceptual design stage it is vital to have reasonable estimates of the capital cost of compressors involved in these processes. The literature correlations use only the compressor power to estimate capital cost, and there are significant differences in the published methods. However, in addition to power, it appears that suction pressure also must be considered in cost estimation. The proprietary Aspen Economics program gives results that show a strong dependency of cost on the pressure of the gas being compressed. The purpose of this paper is to provide a simple method to estimate compressor capital cost that incorporates both compressor power and compressor suction pressure. A case study illustrates that the conventional heuristic of using equal compression ratios in multistage compression trains does not give the optimum economic design.