Membrane air separation for intensification of coal gasification process,

High-ash and other low-quality coals are available in huge quantities in Russia and in other East European countries. Similar solid fuels can also be obtained as by-product of the enrichment process of coal. The aim of this work is the analysis of the possibility to use such low-quality coals as alternative energy sources in fluidised bed gasification process. In order to intensify gasification process in conditions where possible ash melting is avoided, it is proposed to use oxygen-enriched air (OEA) instead of air as a blow and gasification agent. The supply of OEA as fluidisation medium can be beneficial in other respects: it allows to burn at least a part of fly ash before they leave the furnace, thus improving energy efficiency and ecological impacts of the process. In this paper, the first successful example of combination of membrane air separation and coal gasification process is given. This paper summarises the performance of coal gasification in the presence of different oxygen/nitrogen mixtures as a blow for processing of low-quality (high moisture content) coal. The optimal content of O2 in the blow is in the range 27–33% v/v. The heating value of synthesis gas obtained in optimal conditions was in the range 3.5–4.7 MJ/m3 (STP). In second part of the paper, the performance of several membranes available for cheap and efficient air separation is analysed and, after comparing them, recommendations on appropriate selection of membrane type and module needed are given.