Optimal design and operation of pressurized oxy-coal combustion with a direct contact separation column

Simultaneous multi-variable gradient-based optimization is performed on a 300 MWe wet-recycling pressurized oxy-coal combustion process with carbon capture and sequestration. A direct contact separation column is utilized for practical and reliable low-temperature thermal recovery. The models for the components include realistic behavior like heat losses, steam leaks, pressure drops, and cycle irreversibilities. Moreover, constraints are used for technoeconomical considerations. Optimization involves 17 optimization variables and 10 constraints, with the objective of maximizing the thermal efficiency. The optimization procedure utilizes recent design rules and optimization procedures for optimal Rankine cycle performance speeding up the plant optimization process by eliminating variables and avoiding constraint violations. Moreover, the procedure partially alleviates convergence to suboptimal local optima. The basecase of the study is a comprehensively optimized cycle that utilizes a surface heat exchanger, a more thermodynamically-effective form of thermal recovery which however bears significant materials challenges. Upon optimization, the cycle utilizing the direct column is seen to be very attractive regarding efficiency and performance. Moreover, the optimization results unveil potential for reducing capital costs by eliminating the first carbon sequestration intercooled compressor and by showing possibilities of process intensification between the separation column and the carbon sequestration purification columns.

► Direct contact column is viable technology for acid removal and heat recovery.
► Direct contact column results in higher optimal operating pressure than surface heat exchanger.
► Direct contact column allows for reduction of capital costs.