Thermal Performance Models And Optimization Study On Gas-steam Combined Cycle Unit Using Blast Furnace Gas

The application of gas-steam combined cycle technology using blast furnace gas is in the ascendant in China. The study on thermal performances of gas-steam combined cycle unit using blast furnace gas under off-design conditions is momentous theoretical and practical significance for further development of gas turbine technology and improvement operation and management level of combined cycle unit.In this dissertation, the 50MW split shaft gas turbine gas-steam combined cycle generator using blast furnace gas in LY steel is researched. The thermal performances of the combined cycle unit under the off-design conditions were studied. The principal contents of the dissertation are as following:(1)The thermal perfrmances of the gas-steam combined cycle unit in LY steel were tested. The factors influencing the combined cycle's thermal performances were analyzed based on the thermal testing's results.And these factors such as the load of unit, ambient temperature, fuel's low heat value, bypass flow, component characteristics, etc.were very important for the combined cycle's thermal performances.(2) The thermal performance models of the gas-steam combined cycle unit using blast furnace gas were established with the mechanism-based-gray-box modeling method. The models established chiefly through the combined cycle's design parameters and assisted by characteristic curves, correction curves, and the actual operating data. And the models were validated by three thermal testing data. The results showed that:the maximum ralative error of the output and efficiency was recpectively 0.57% and 2.36% for gas turbine; but for combined cycle unit, the error was 1.13% and 5.07%.(3)The thermal performances of the gas turbine and combined cycle based on the mathematical models were calculated after changing the load of unit, ambient temperature, fuel's heat value, bypass flow, etc. According to the calculated results, the optimal operation's measures and recommendations were put forward as following:the combined cycle worked with a basic load and the load was usually more than 80%; the inlet air of gas turbine was cooled by inlet cooling technology; the control system of gas's low heat value was optimized to ensure gas's low heat value less than 3300kJ/Nm3;the bypass valve was turned down or fully closed. Most of the recommendations were adopted and implemented and the operation indicator of the gas-steam combined cycle unit improved significantly.