TASK 1: Indirect gasification and gas filtration

Filtration is typically one of the first gas cleanup steps in gasification concepts. In air or oxygen-blown biomass gasification concepts the optimal filtration temperature is in the range of 400-550 °C. At higher temperatures the tar-laden gasification gas forms a sticky, coke and soot containing cake on the filter surface which ultimately results in filter blinding.

To avoid filter blinding issues, the gasification gas must be cooled down before filtration and reheated before reforming which reduces the process efficiency (Figure 1). In an improved process concept the filter unit would operate at the same temperature level (at appr. 750 °C) as the gasifier and the reformer when also heat exchanger investments could be avoided.

In this project, the hot gas filtration will be studied and developed for the indirect gasification with emphasis on the research related to filter blinding phenomenon. Experimental work will be carried out with a bench-scale pressurised hot gas filtration unit (ALMA) which was successfully tested in the UCGFunda project in 2010.

The main objective is to study which process conditions favour filter blinding and how it can be prevented at higher temperatures. Test runs will be carried out with a gas composition typical for indirect steam gasification both at atmospheric and elevated pressures. The main variables to be studied are as follows:

• Filtration temperature
• Particulate (fly ash) concentration in the gasification gas
• Tar concentration in the gasification gas
• Introduction of different sorbents and additives.