Closed-cycle gas turbines (CCGT) have numerous advantages, among which are the flexibility of utilising waste heat at low and high temperatures, the possibility of using a variety of fuels, the ability to use high pressures and thereby reduce the cost of turbomachines, and controlling the part-load output efficiently by varying the gas pressure and mass, rather than the turbine inlet temperature. In this work the waste energy in the exhaust gas of a 1-MW gas-turbine engine is partly recovered in a heat-exchanger, to heat helium which drives the turbine compressor system in two closed cycles. The hot cycle produces power, whereas the cold cycle provides a refrigerating effect to liquefy nitrogen at a rate of about 1300 t/day. A parametric study by means of a specially designed computer program, to simulate running conditions over a wide range, shows that such a system could produce the cooling effect with an overall efficiency of about 60% at a compressor pressure ratio of 2.5.