Combined power and hydrogen production from coal. Part B: Comparison between the IGHP and CPH systems

Abstract

Currently, plants for hydrogen production from coal are based on IGCC (Integrated Gasification Combined Cycle) technologies with CO 2 capture and electrical power is also produced by using the purge gas coming from the hydrogen separation unit as fuel in a gas turbine combined cycle. The combined power and hydrogen systems (CPH systems), investigated and analysed in this two-part paper, have been designed to co-generate electrical power already within the gasification island by a steam power section in which the losses due to the steam condensation are reduced because the steam needed for the gasification is bled, at the gasifier operating pressure, from the expansion line. In this Part B, a sensitivity analysis of CPH systems has been carried out, varying two operating parameters: the steam to carbon ratio at the gasifier, S/C, and the gasification pressure. Therefore, the performances of the CPH plants have been evaluated and the plant configurations have been compared by using new parameters, the apparent and marginal efficiencies. Results show that, in the pressurized configurations, even if less hydrogen is produced with respect to the IGHP (Integrated Gasifier for Hydrogen Production) reference plant, defined in the Part A (∼21.6 vs. 23.1 MW HHV), electrical power is generated with efficiencies higher than both the conversion efficiency of hydrogen in a fuel cell system (for CPH,70 the apparent efficiency, referred to the higher heating value, is 92.6%) and the conversion efficiency of coal in an IGCC (for CPH,70 the marginal efficiency, referred to the HHV, is 81.9%). The hydrogen production efficiency is 67.5% (HHV) and the cogeneration ratio reaches a value of 10.2%.