Experimental development of sorption enhanced reforming by the use of an advanced gasification test plant

Abstract

Dual fluidized bed steam gasification of solid fuels enables the production of a nitrogen-free medium calorific product gas. Several commercial industrial sized plants are already operating the dual fluidized bed gasification process. The present work illustrates an improvement of the gasification process itself by the use of wood as fuel and calcite as bed material to produce a hydrogen-rich gas. Hereby, in the combustion reactor calcite (CaCO3) is calcined to calcium oxide (CaO) by the release of carbon dioxide (CO2) at high temperatures (∼850 °C). In the gasification reactor, CaO acts as a sorbent for CO2 from the produced calorific gas stream at lower temperatures (∼650 °C). Experimental results from two different test plants are compared by the use of a process simulation software. The results illustrate the observed improvements with respect to process performance by the application of an advanced reactor design operating this so called sorption enhanced reforming process. It is shown that the water conversion rate in the gasification reactor is raised up to 36% and the overall cold gas efficiency was improved from 58 to 71% with the advanced reactor design. Since the sorption enhanced reforming process is highly dependent on temperature, the influence of gasification temperature and further, bed material circulation rate are discussed as well. It is demonstrated, that a hydrogen (H2) to carbon monoxide (CO) ratio between 9 and 2 can be set by operating the gasification reactor with a certain temperature. Further, it is shown that a low bed material circulation rate is favorable to obtain high hydrogen (H2) contents in the product gas.