Abstract
Over the past few decades, anthropogenic carbon emission has been recognized as an important contributing factor to global warming and climate change. Therefore, carbon dioxide capture, sequestration and utilization have become new focuses of chemical process technology research. Flue gas from coal-fired power plant is the main source of CO2 emission. In order to capture and separate CO2 effectively, several types of technologies have been developed. Among these methods, absorption/stripping CO2 capture system is considered the most feasible method to deal with existing power plants. In this thesis, plantwide control of CO2 capture plant was investigated using dynamic simulation. To stabilize system and maintain capture efficiency, the following control structure was proposed. In this scheme, CO2 removal target is guaranteed using the lean solvent feed rate to the top of the absorber column. In order to operate process with an appropriate lean solvent loading, the temperature at the bottom of stripper is controlled by reboiler duty. This control structure was tested by disturbances involving inlet flue gas flow, CO2 concentrations and H2O concentrations as well as changes in removal targets. Dynamic simulations showed that system can achieve removal targets, stabilize quickly while keeping optimum lean loading constant. To ensure minimum energy consumption, optimizing control can be carried out by adjusting the setpoint of reboiler temperature. For a CO2 capture plant integrated with power plant, about 20% penalty of electricity output is incurred. To meet electricity demand in peak load period, flexible operation decreasing CO2 capture rate can be implemented to increase power plant output. However, large variation of liquid and gas flow during flexible operation may cause fluctuations to packed columns. Operating strategies were proposed and testified through dynamic simulations. In varying lean solvent strategy, by delivering all flue gas to absorber, instability of absorber could be partly reduced. Capture rate is changed by varying lean solvent flow rate. Optimum lean solvent loading is guaranteed by controlling reboiler temperature. In varying lean loading strategy, capture rate is shifted by varying lean solvent loading so that lean solvent rate is unchanged. Stripper’s fluctuation can be avoided by recycling part of CO2 product vapor. Although in this strategy energy requirement for regeneration will slightly increase, operating stability is promised.