Research On CO₂ Capture Of IGCC Power Plants

In recent years, CO2 abatement has received worldwide attention. In China, about half of the CO2 emission comes from coal-fired power plants. And this will not change in a long time due to the important role of coal in China's energy structure. Controlling the CO2 emission of coal based power stations is especially important for China. Integrated Gasification Combined Cycle (IGCC) power plants is one of the important clean coal technology in the future. Research on the IGCC with CO2 capture is one of the grand issues in energy field. This thesis focuses on the technic and economic evaluation of IGCC with mature and future CO2 capture technologies. Influences of key technologies and parameters are analyzed and compared. The content includes:1. Key components models of IGCC with CO2 captureKey components models of IGCC with CO2 capture are built and verified, including four kinds of gasifiers, Water Gas Shift (WGS), different kinds of CO2 removal processes, gas turbines and so on. Performance of CO2 removal process with MDEA and NHD solutions with the varying of inlet gas condition and CO2 removal percentage are investigated and compared.2. Unit cost models and economic evaluation software platform of IGCC power plant with CO2 captureBy cost regressing, scaling and modifying with district factors, cost models of different units are built, including different kinds of gasifier, WGS unit, different kinds of CO2 removal process, CO2 compression unit and so on. These models are all based on Chinese condition and take the technical performance parameters as input data. Economic evaluation software platform of IGCC power plants with CO2 capture is built through combining the new built unit cost models with existing IGCC economic evaluation software platform and making some complements and modifications to the equipment contingencies and costs of operation and maintenance.3. Economic evaluation of coal based power plants with CO2 capture under present technology Influences of gasifiers, oxidants (with oxygen or air), syngas cooling methods, CO2 removal methods and CO2 removal percentage are studied under the condition of IGCC with CO2 capture. Several conclusions have been attained. Transport gasifier IGCC power plants have higher efficiencies and lower cost of electricity (COE) than entrained gasifier plants. For transport gasifier IGCC plants, NHD CO2 removal process is preferred than MDEA process. Compared to air blown transport gasifier plant, oxygen blown plant has higher efficiency and COE. As for the gas cooling process choice, slurry feed entrained gasifier and transport gasifier plants should adopt syngas cooler. While, for dry feed entrained gasifier, plant will has lower COE with quench process. For CO2 capture of IGCC, CO2 avoidance cost is lowest when the CO2 removal efficiency is around 87%.Comparisons between IGCC and PC power plants show that, after CO2 capture is adopted, the energy penalty and COE increase percentage of IGCC power plants is lower than that of PC power plant. The cost of CO2 avoidance of IGCC power plants is also lower than that of PC power plants. While, as for the performance of capture power plants, PC power plants with CO2 capture is more economic under present technology condition. To battle with the PC power plants, IGCC power plants with air blown transport gasifier, oxygen blown transport gasifier, slurry feed entrained gasifier and dry feed entrained gasifier should reduce their investments under 7925 RMB/kW,7945 RMB/kW,7346 RMB/kW and 7742 RMB/kW respectively.Scenario analysis is conducted to investigate the influences of different CO2 treatment ways and carbon tax policy. Critical CO2 selling price and carbon tax rate for PC and IGCC power plant respectively have been got, below which power plants with CO2 capture and storage will be preferred. Results show that, the critical CO2 selling price and carbon tax of IGCC power plants are much lower than that of PC power plants.4. Techno-economic analysis of coal power plants with calcium based absorbentThe calcium-based absorbent can be integrated with WGS process to capture CO2 during CO shift process, which is Calcium Looping Process (CLP). It can also be adopted in the gasifier to capture CO2 during gasification process, which is in-situ gasification process. Based on CLP and in-situ gasification process, IGCC-CLP and in-situ gasification systems for power generation and hydrogen production have been built.For power generation systems, the influences of calcinator pressure and oxygen supply methods are studied. Results show that for both the two kinds of system, calcinator should be operated under ambient pressure. Compared to systems with low pressure cryogenic air separation units, systems using oxygen carrier to supply oxygen for calcinators have a little lower efficiencies. Influences of steam/C ratio are also similar for the two kinds of systems. Systems efficiencies increase with the decrease of steam supply. While under lower steam/C ratio, the CO2 emission rate is high. Different kinds of coal power plants are compared under the same CO2 emission restriction. Results show that efficiency of in-situ carbon capture power system is higher than that of oxygen blown transport gasifier IGCC-CLP system and IGCC-NHD system by about 4.7 and 7.7 percent points respectively.Besides power plants systems, hydrogen production systems with in-situ carbon capture process and IGCC-CLP process are studied, and compared with the conventional system with IGCC-NHD process. Results show that the energy efficiencies of the three hydrogen production systems are 70.6%,60.2% and 58.3%. As for IGCC-CLP system, it can output a certain amount of electricity during the production of hydrogen as a cogeneration system, which has a higher efficiency by 7.1 percent points compared to the same output scale IGCC-NHD cogeneration system.As for power generation systems based on CLP and in-situ capture gasification process, the influences of key units investments are investigated by sensitivity analysis. By comparing with the IGCC and PC capture power plants with conventional CO2 capture processes, critical investments of CLP process and in-situ carbon capture processes are obtained, under which the new kinds of calcium-based IGCC power plants will has lower COE. Such as, for an in-situ carbon capture power system with three reactors, is the investment of reactor system is lower than that of three oxygen blown transport gasifiers, the COE of the power system will lower than that of PC power plants without CO2 capture.