Heat exchanger

A heat exchanger fitted around a section of an exhaust duct (2) recovers energy from the hot exhaust gasses, e.g. to produce steam to power a turbine in a closed system. To cover periods when the exhaust gasses are not sufficiently hot, e.g. during start up, an additional external heating system is applied to the heat exchanger. This can be powered by injected fuel, e.g. a small amount of fuel burnt to boost power. The hot exhaust duct can be positioned straight or in a spiral through the heat exchanger.