Pressurized Entrained Flow Gasifiers for Biomass

A new concept for the gasification of dry lignocellulosic biomass has been developed. Special attention was paid to the process compatibility with biomass feedstocks from agriculture, mainly straw, which have a higher ash, potassium, and chlorine content and a lower ash softening point than wood. The first process step is a fast pyrolysis at atmospheric pressure, which produces much condensate and only little char and gas. Pyrolysis condensate and pulverized pyrolysis char are then mixed to a slurry, containing up to 90% of the initial biomass energy. In contrast to the loose-packed original biomass, the dense slurries are easily pumped and stored in tanks. From a number of regional pyrolysis plants, the slurries can be transported by rail to a large central gasification facility. Thus, the economy of scale can make possible an efficient but more complex gasification and syngas utilization technology, to produce the most valuable products. The slurries are pumped into a slagging entrained flow gasifier and are atomized and converted to syngas at high operating temperatures and pressures, above the operating pressure of a downstream synthesis plant. At very high pressures, alternative operation of pressure locks with a low-bulk density biomass will become too expensive. High gasification temperatures and pressures help to produce a tarfree syngas, simplify downstream gas cleaning steps and obviate intermediate compression before synthesis. To achieve a high process efficiency, the utilization of chemical energy in synthesis products like methanol must be complemented by the use of sensible heat for electric power generation. Various chemical and engineering aspects of the new process concept are being investigated in the laboratory. A test campaign at a pressurized entrained flow gasifier with ca. 5 MW(th) slurry throughput is under preparation. A fast pyrolysis facility designed for continuous operation with several kg/h biomass throughput is under construction. Fast pyrolysis of biomass will be achieved by mixing with an excess of hot sand in a special twin-screw reactor.