Working fluid compositions for use in semi-closed brayton cycle gas turbine power systems

Abstract

A semi-closed combined cycle power system is provided which can also convert an open combined cycle gas turbine into a non-polluting zero emissions power system. The prior art open combined cycle gas turbine includes a compressor which compresses air A′ and combusts the air A′ with a fuel, such as natural gas. The products of combustion and the remaining portions of the air form the exhaust E′ which is expanded through the turbine . The turbine drives the compressor band outputs power. The exhaust E′ exits the turbine and then can optionally be routed through a heat recovery steam generator to function as a combined cycle. According to this invention, the exhaust E′ is not emitted into the atmosphere, but rather is routed to a divider . The divider includes two outlets for the exhaust E′ including a return duct and a separation duct which both receive a portion of the exhaust E′. The return duct routes a portion of the exhaust E′ back to the compressor . Before reaching the compressor , an oxygen duct adds additional oxygen to the exhaust E′ to form a gas mixture C which includes CO and steam from the exhaust E′ and oxygen from the oxygen duct 150. This gas mixture C has characteristics which mimic those of air, so that the compressor need not be modified to effectively compress the gas mixture C. The gas mixture C is compressed within the compressor and routed to the combustor where the fuel combusts with the oxygen of the gas mixture C′ and produces exhaust E′ which is substantially entirely CO and steam. This exhaust E′ is routed through the turbine and expanded to drive the compressor and output power. The exhaust E′ exits the turbine and is routed back to the divider , preferably by way of a heat recovery steam generator or other heat removal device, so that the semi-closed cycle operates as a combined cycle power system . The divider directs a portion of the exhaust E′ to a separation duct which leads to a condenser . In the condenser the exhaust E′ is separated by condensation of the steam/water portion of the exhaust and removal of the remaining CO as gas from the condenser . The only exhaust from the semi-closed power system is water and CO from the condenser. The CO exhaust is substantially pure and ready for appropriate further handling and disposal. Hence, no pollutants are emitted from the semi-closed power system . The return duct can include a partial condenser to condense a portion of the steam within the exhaust E′. This condensed steam is then routed back through the heat recovery steam generator , where it is converted to steam. This steam can be injected through a steam injection port directly into the combustor to enhance the power output and efficiency of a steam injection power system variation of this invention.