heat exchanger conversely strictly adiabatic compression requires much greater mechanical energy which the thermal savings in the heat exchanger are not sufficient to offset by combining isothermal and adiabatic compression in that order at least a 5 net energy savings is realized in the overall process relative to using either type of compression alone provided each compressor carries at least 25 of the total compression duty the pressurized purified air is heated in heat exchanger 4 and then reacted with the oxygen acceptor in absorption tower 5 this tower can be any configuration in which multistaged countercurrent contact is obtained between the salt and air for example packed tower bubble cap or sieve tray tower etc the exhaust air substantially depleted in oxygen content then enters a combustion chamber 6 and it is reacted with a fuel such as distillate natural gas or fuel gas this raises its temperature and further depletes its free oxygen content then it is partially expanded in turbo expander 7 the degree of expansion is controlled to regulate the turbine exhaust temperature which in turn controls the temperature of the air entering the absorption tower after the partially expanded exhaust is heat exchanged against the incoming air in heat exchanger 4 the expansion to ambient pressure is completed in turbo expander 8 the above exhaust treatment sequence ensures that heat is added to the process at the hottest possible temperature which improves efficiency also the hottest temperature in heat exchanger 4 is substantially below maximum process temperature oxygen loaded salt from absorption tower 5.