Compressor Intercoolers

Compressor IntercoolersCompressors need inter-stage heat recovery to maximize capacity while minimizing head and power requirements in the pumping of gases through process equipment.  Lower compressor inter-cooler pressure drop translates into decreased energy consumption for the compressor when upgrading with improved heat exchanger designs.  Well designed compressor intercoolers can have a useful life of 10-20 years, but occasionally failures result from higher loads caused by gradual plant expansion.  Additional operating problems also develop, such as reduced intercooling from fouling, generally from the cooling water side or mechanical leaks through the tubes or at tube-tubesheet joints, resulting in gas loss into the cooling water.  In certain low gas pressure intercooler applications failures causing leaks may result in cooling water entering the compressor with the gas, resulting in damage to interstage seals and deteriorating compressor efficiency and capacity.  In instances of such leakage, contamination can become a critical problem, since suspended and dissolved solids from cooling water pass into the compressor and build up or result in other problems.

When redesigning exchangers, changing TEMA Shell types can provide cost efficient solutions for achieving reduced intercooler gas pressure losses and energy savings.  For example, TEMA X cross-flow designs can provide extremely low pressure drop performance at lower performance based cost compared with the more commonly used TEMA E, F and J shell types.  In the application of cross-flow intercoolers, careful attention must be given to proper design of seal strips and dummy tubes in partition spaces in multi-tube pass configurations to prevent shell side fluid bundle bypassing, which could otherwise impact on thermal performance.

Compressor Intercoolers Some typical examples of energy savings benefits for improving gas pressure drop in compressor intercoolers in Ammonia plants with modern compressors are given below.                                               % Downstream Compressor                                               Section Power Savings for                                               1 Psi Lower Intercooler LossAir Compressor First Stage Intercooler (Approx 35 Psia)               3.2Second Stage Intercooler (Approx 100 Psia)        1.4Third Stage Intercooler (Approx 220 Psia)            0.65 Refrigeration Compressor First Stage Intercooler (Approx 45 Psia)               2.9Second Stage Intercooler (Approx 105 Psia)        1.3 Synthesis Gas Compressor Stage Intercoolers (Approx 985 Psia)                  0.15 Replacing outdated, damaged or overloaded compressor intercooler equipment can provide additional heat removal, lowering downstream stage power requirements.  Some typical examples of energy savings benefits for improving heat transfer are given below.                                               % Downstream Compressor                                               Section Power Savings for 5 Deg F                                               Lower Intercooler Outlet Temp Air Compressor First Stage Intercooler (Approx 35 Psia)             0.89Second Stage Intercooler (Approx 100 Psia)       1.0Third Stage Intercooler (Approx 220 Psia)          1.0 Refrigeration Compressor First Stage Intercooler (Approx 45 Psia)             0.47Second Stage Intercooler (Approx 105 Psia)       0.68 Energy savings benefits for each inter-stage intercooler depend on individual stage loads.  For refrigeration compressors reducing pressure losses of existing intercoolers or adding low pressure drop intercoolers where none exist (commonly first stage) can provide economic solutions to improve compressor capacity while reducing power usage of the compressor.  In this era of increasing energy cost, replacement of damaged or under-performing intercoolers with updated designs can improve plant efficiency, lower plant operating costs and restore operating reliability.