Research On Retrofitting Natural Gas Combined Cycle To Integrated Gasification Combined Cycle And Power-Methanol Co-Production System

The integrated gasification combined cycle (IGCC) and co-production system is a very important direction for the development of the coal-based energy system. Retrofitting the natural gas combined cycle (NGCC) with the shortage of the natural gas into coal-fueled IGCC power plants is expected to avoid the idleness of expensive equipments. Besides, it proposes a solution to the problem of costly investment during the early stage of commercialization for the IGCC, and has extreme practical importance. In this thesis, a PG9351FA NGCC Power Plant is taken as the retrofitting object, and the integration rule and the techno-economic of retrofitting are investigated.The thesis can be divided into the following four parts:1. Research on retrofitting PG9351FA NGCC to oxygen-blown gasification IGCC.The research shows that, with the integration increasing, the system thermal performance improves, and the oxygen-blown transport gasification retrofitted systems have the highest efficiency, which is up to 44.54% utilizing existing HRSG and steam turbine. In order to meet the level of NOx emission, the passage problem of gas turbine would be serious with non-integration of gas turbine and air separation unit (ASU), gas turbine needs to reduce the turbine inlet temperature T3 appropriately. Compared to taking nitrogen as diluents, steam has less impact on gas turbine. In the two cases of using steam as diluents, humidifying the fuel gas is better than injecting superheated steam into fuel gas directly. Recovering the low-grade heat from the syngas after quenching has great impact on system efficiency. In the retrofitted system that utilizes existing HRSG and steam turbine, the main parameters of the existing HRSG and steam turbine deviate from the design point is within 15%.2. Research on retrofitting PG9351FANGCC to air-blown gasification IGCC.The studies show that, utilization of the existing HRSG and steam turbine, the highest efficiency of retrofitted system can be up to 43.41%. Recovering the high temperature heating in waste heat boiler contributes more than 5 percentage points on the system efficiency. Due to the low heating value of fuel gas and massive flow of syngas, it is suggested to integrate gas turbine and gasifier to improve the efficiency and net power of the retrofitted system, and the optimal integration degree is about 90%.3. Economic analysis when retrofitting NGCC to IGCC system.The study shows that, compared to conventional newly built IGCC, the electricity price at 8% internal rate of return and investment of retrofitted system have a much more significant reduction. The transport gasifier retrofitted IGCC system has certain advantages on investment and electricity price at 8% internal rate of return. When the natural gas price is 1.4 Yuan/Nm3, the retrofitting is feasible on economic as long as the price of coal is less than 600 Yuan/ton.4. Research on off-design performance of IGCC and retrofitting NGCC to power-methanol co-production system. The results show that, if the retrofitted IGCC system adopting air-blown transport gasifier requires to realize 50%-100% load variation range of gas turbine, the load variation range of gasifier should be 60%-100%. If the retrofitted IGCC system adopting oxygen-blown transport gasifier requires to realize 50%-100% load variation range of gas turbine, it can deploy a methanol synthesis unit has a design capacity ranged from 0.94 million tons/year to 1.09 million tons/year.