| CO2 reduction and environment protection are the key issues to maintain sustainable development for human society, whilst seeking for feasible and effective pathways to solve these problems becomes consensus around the world. As one of promising carbon capture, utilization and sequestration options, oxy-combustion technology is applied to capture enormous CO2 from coal-fired power plants, and now is ready for commercial demonstration. However, the control approach, operating strategy, energy performance and economic cost for oxy-combustion power plants would face significant challenges and opportunities since plant configuration becomes more complex, combustion atmosphere alters from N2/O2 to CO2/O2, flue gas recirculation is added, and operation interacts among each subsystem, etc.. Based on these considerations, thermodynamic evaluation, dynamic modeling and simulation, control system design, operating strategy identification and dynamic exergy analysis were applied to oxy-combustion boiler island, CO2 compression and purification unit (CPU), and air separation unit (ASU) to achieve optimal control, flexible operation, low energy penalty and low cost for these systems, which will then provide theoretical basis and technical guide for their commercial applications. (1) At the beginning, dynamic simulation, control system design and mode switching for oxy-combustion boiler island were conducted to explore its control performance, operating strategy and dynamic behavior, which then uncover oxygen supply demands for ASU and flue gas properties for CPU. It is found that dynamic characteristics from flue gas side and water side were quite related to operating disturbance types during different operating scenarios, in which flue gas composition, furnace exit pressure, oxygen concentration in primary and secondary oxidants, oxygen content at furnace inlet, and steam temperature appeared with robust performance. Flue gas O2 control was chosen as control system for oxy-combustion boiler island since its dynamic behavior leaded to acceptable influences on CPU operation and mode switching process can be implemented when compared to that in oxidant O2 control. Staged switching approach and partial control strategy were proposed to realize stable transition, and found that mode switching process was competed after 17 minutes, flue gas O2 content was maintained around 3.36 mol.%. flue gas component varied in a similar s-shape manner, and oxygen concentration in primary and secondary oxidants changed in the reasonable ranges.(2) To understand energy performance, cost distribution and cost formation for CPU, thermodynamic evaluation, techno-economic assessment and thermoeconomic cost analysis were first implemented on the basis of flue gas conditions from oxy-combustion boiler island and CO2 product requirements from customer. Results showed that exergy destructions and investment costs mainly resulted from compression process, while thermoeconomic cost mainly derived from separation process. Then, multi-variable optimization was implemented through choosing specific power consumption as objective function when objective variables and operating constraints were considered, and the optimized discharge pressure from main CO2 compressor, flue gas temperature after compression, operating temperatures in first and second flash separators were 30 bar, 30.42?,-24.64? and -55?, respectively. Finally, these optimal operating parameters were selected as initial conditions for dynamic simulation to identify dynamic responses during load and flue gas composition change processes after alternative control structures were designed, compared and configured. Double temperature control rather than single temperature control was chosen as control system for CPU because it can satisfy the targets of CO2 product purity (>96 mol.%), CO2 recovery rate (?90%), and stream temperature (>-56.57?) simultaneously.(3) Based on oxygen supplying demands and potential operating modes with oxy-combustion boiler island, steady-state and dynamic simulations for ASU with rational designed process flow diagram were conducted to complete the design and comparison of different logic control strategies, and then identify dynamic characteristics under different operating disturbances and flexible operating strategies. For satisfying oxygen product quality, energy saving and operating flexibility, feedforward-feedback control structure was chosen as control system for ASU. ASU-following strategy was adopted to accomplish peak and off-peak (POP) or energy storage operations, and oversized ASU configured with liquid oxygen storage drum was recommended to be integrated into oxy-combustion power plant, where ASU load was turned down to the minimum load (60%) whilst power consumption from main air compressor was decreased about 32.85%.(4) For characterizing thermodynamic performance dynamically and identifying the influences of process control on system operation from the viewpoint of thermodynamics, a systematic and powerful dynamic exergy method was proposed. Through this method, steady-state modeling and simulation, dynamic modeling and simulation, and exergy calculation were combined effectively to obtain exergy values at different time points during different operating scenarios for forming dynamic exergy plots which can be used to define assessment indicators by mathematical tools for realizing the optimization of control, operation and energy performance. When applied it to oxy-combustion power plant, energy consumption under every operating condition, the sensitivity of operating parameters, the influences of control loops, control layers and control structures on system operation, and determination of control strategy can be quantified. Energy consumptions mainly come from system itself while process control resulted in little influence and its effects were determined by its function played during system operation, which indicates that refining plant configuration and improving equipment characteristics would be the key points to enhance thermodynamic performance for system. |
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