Wood chips gasification in a fixed-bed multi-stage gasifier for decentralized high-efficiency CHP and biochar production: Long-term commercial operation

Abstract

Gasification of woody biomass coupled with combined heat and power (CHP) production is an effective way to produce renewable energy from woody biomass. The tar content of the producer gas is considered to be the most problematic aspect of a biomass gasification for CHP production. Staged gasification allows the minimization of the tar production by the optimization of individual thermochemical subprocesses. This paper presents the operational results from a newly developed type of fixed-bed multi-stage gasifier GP750, which combines the principles of both twin-fire and two-stage gasification. This unique construction enables the production of a low-tar producer gas even by units with a power output as high as 0.7 MW. Here, we present the data measured during stable operation of the gasifier in a CHP plant operated by BOR Biotechnology company, including the composition of permanent gases measured on-line and the comprehensive gas and tar composition from the long-term operation, measured off-line. The measurements proved that the gasifier can produce a gas with low tar content (5–50 mg/m3), which is well beyond the limits for internal combustion engines. The energetic balance showed that the gross efficiency of the production of electricity of the whole power plant was as high as 32.9%. The gasifier also produced 36 kg of char per tonne of dry fuel on average. This char had a surface area in the range of 350–700 m2/g and very low content of both volatile matter and PAHs. Therefore, the char produced could potentially be sold as biochar.