Clean and "Dirty" Tar Reforming of Biomass Gasification Gas

A prerequisite for the establishment of an efficient biomass-to-chemicals production or CHP applications utilizing engines is a good thermodynamic utilization of the hot synthesis gas exiting a biomass gasifier. A second and important criteria is the extraction or conversion of tars (polyaromatic hydrocarbons), which, if left untreated, leads to fouling of downstream equipment and issues around waste water treatment. Both above criteria are met by steam reforming the tar components at high temperatures in the sulfur-laden exit gas from the biomass gasifier. We discuss the benefits of different approaches depending on pressurized or near atmospheric gasification, leading to the concepts of “clean” and “dirty” tar reforming.

The basic difference between the two approaches is how dust is handled. In the dirty tar reforming processes the residual dust in the gas - after having passed cyclones - is removed downstream the tar reformer. In the clean tar reformer the dust removal takes place upstream the tar reformer and preferentially the dust removal takes place at temperatures in the vicinity of the gasifier exit temperature to minimize loss of exergy. The catalyst and processes are widely different. In the dusty tar reformer monolithic catalysts are a necessity whereas the clean reformer can use pelletized catalysts with a much higher content of active material.

We will discuss the virtues of the different approaches and look into the requirements for producing CHP, SNG or fuels like gasoline or diesel, supplemented by our achievements in clean and dirty tar reforming in industrial and pilot settings.