Plantwide control and operating strategy for air separation unit in oxy-combustion power plants

Abstract

To ensure that air separation unit can bear high ramp rate and flexible operations when integrated into oxy-combustion power plant, this paper focuses on the investigations of plantwide control design and operating strategy for double-column air separation unit without or with liquid oxygen storage drum through dynamic simulation. It is found that three air separation unit types (normal, oversize, and downsize) with the proposed control structure configured with logic control loops (strategies 1, 2, and 3) can achieve 5%/min of high ramp rate and flexible operations such as peak and off-peak or/and energy storage. Compared between the latter two logical controls, strategy 2 would be better because its oxygen product qualities can be maintained closer to their targets. Three integrated patterns between air separation unit and oxy-combustion boiler are proposed to improve operating flexibility, among which oversize case would be more suitable for oxy-combustion power plant since its energy saving (20.33MW) is larger and operating strategy is more flexible than those in downsize (10.76MW) and normal cases. Process control for flexible operations would be an opportunity for engineering, and comprehensive dynamic model with specified control system provides possibility to integrate air separation unit with full-train oxy-combustion power plants.