Combined power and hydrogen production from coal. Part A—Analysis of IGHP plants

Abstract

Recent studies have demonstrated the possibility of an efficient and clean employment of fossil fuels by using a new concept of cogeneration of power and hydrogen. This concept is based on the considerations that steam power plants discharge heat by condensing steam, while coal gasification plants require steam to produce hydrogen: an integration of these systems results in a very high conversion efficiency.This two-part paper analyses these plants, the so-called combined power and hydrogen (CPH) systems, and compares their performances with a plant for only hydrogen production, the integrated gasifier for hydrogen production (IGHP) plant, by means of new parameters, the marginal efficiency and the apparent efficiency. The use of these parameters requires the definition of a IGHP reference plant, which must be designed to maximize the hydrogen production with minimum power consumption.Thus, Part A investigates the IGHP plants to define the reference plant, Part B analyses and evaluates different plant configurations of CPH systems by comparison with the IGHP reference plant.In order to identify the thermodynamically favourable operating conditions for the IGHP plant (maximum hydrogen production with minimum power consumption), a sensitivity analysis has been conducted at a gasification temperature of 1350°C, varying the gasification pressure from 1 to 80bar, the steam to carbon ratio at the gasifier, S/C, from 0.1 to 0.9, and the steam to carbon ratio at the water–gas shift reactors, SSHIFT/C, from 0.6 to 1.2.Results show that the hydrogen production depends significantly on the steam to carbon ratio at both the gasifier and the shift reactors, while the influence of gasification pressure is negligible even though it is a very important factor to minimize the power consumption (or to generate electrical power). Better performances are achieved for a gasification pressure of 70bar, a S/C ratio of 0.2, and a SSHIFT/C ratio equal to 1.2. The hydrogen production efficiency, referred to the HHV, is 72%.