Exergy-based method for evaluating the dynamic optimization of a supercritical water fluidized bed

Abstract

Dynamic optimization of hydrogen production from coal gasification within an industrial-scale supercritical water fluidized bed is studied. Coal slurry and supercritical water mass flow rates are selected as the manipulated variables to investigate the optimal operation for scenarios involving variations in hydrogen demand. For the temperature-constrained scenario, supercritical water mass flow rate and temperature are manipulated. The results demonstrate that the optimal time-dependent profiles of the manipulated variables enable the supercritical water fluidized bed to meet variable demands of hydrogen and improve availability. Dynamic exergy methods are implemented to assess the thermodynamic behavior of different optimization schemes for efficient operation. The results show that more attention should be paid to the process of adjusting the mass flow rates of coal slurry and supercritical water simultaneously to vary the hydrogen yield because it requires the largest energy consumption. Manipulating the supercritical water mass flow rate causes less exergy destruction at a temperature constraint of 600 °C, but more exergy destruction at a temperature constraint of 700 °C.