A gas-turbine-cycle modification has been proposed, optimized primarily for (district) heating purposes, with a side-effect of obtaining gas-turbine exhaust gas at very low temperatures and potentially GHG-emission-free. Since its primary purpose is district heating without power generation, the associated gas-turbine-cycle equipment (compressors, turbines, heat exchangers) is typically arranged so that a maximum possible ratio of heat output and heat input is achieved. Whenever the heat ratio is greater than unity, that is, greater than 100% of the heat input, the exhaust gas temperature at the last gas-turbine exit is lower than atmospheric temperature. In other words, this means that it is possible to achieve greater heat output (or GT-cycle "waste heat") than the heat input, at the "expense" of the cold GT exhaust gas (its internal energy).It is possible to arrange proposed GT-cycle modification in various configurations, such as: simple GT cycle, recuperated, intercooled, intercooled-recuperated, reheat-recuperated and intercooled-reheat-recuperated GT cycle. Maximum achievable ratio of heat output and heat input is estimated to about 1.15 (115%) and corresponding minimum GT exhaust gas temperature can be lower than the CO_2 solidification temperature at atmospheric pressure (-78°C or 195 K or -108.4°F). This also means that the GT exhaust-gas stream could be entirely GHG-emission-free, without GHG-s like H_2O and/or CO2, which could therefore be captured and sequestered in solid state, and in addition at very low refrigerating temperature. Such low-temperature GT exhaust gas could then be used for refrigeration purposes, or ultimately to refrigerate the Earth's atmosphere and thus mitigate global-warming effects.
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