Optimal design and thermodynamic analysis on the hydrogen oxidation reactor in a combined hydrogen production and power generation system based on coal gasification in supercritical water

Abstract

The novel power generation system based on coal gasification in supercritical water (SCW) holds great promise to meet the increasing energy demands in China, with less emissions in comparison to the traditional coal-fired power generation. The stable and complete oxidation of hydrogen occurring in the supercritical water oxidation (SCWO) reactor is paramount to the safety and overall energy efficiency of the system. In order to better understand and improve the performance of this reactor, optimal design and thermodynamic analysis were conducted using Aspen Plus. The outlet hydrogen concentration and the internal temperature of the reactor were taken as the two key indicators of the optimal design. The optimized results for the reactor were found to be the reactor diameter of 90 mm, axial length of 10.75 m, oxygen inlet number of 3 with the oxygen ratio of 11.0%/39.9%/49.1%, under the given inlet working fluid components and flow rates. The three-stage reactor design was confirmed to have good robustness when different types of coals are adopted for generating syngas. In addition, by analyzing the enthalpy and exergy flow distributions in the reactor, it was revealed that the total exergy destruction for the whole three-stage reactor is only about 6.29%, and that the exergy destruction is consistent with the oxidation process. These findings could be used as guidelines for the design and implementation of the SCWO reactor towards higher safety margin and energy efficiency for this new coal-boiled power generation technique.