Downdraft gasifier

Fixed bed gasifiers are generally used for small-scale operation with gas engines, having an electrical output of about 80-500 kWe. They divide into updraft and downdraft gasifiers. 

SVZ (Sekundarrohstoff Verwertungszentrum Schwarze Pumpe) is a centre for the re-nse of secondary raw material. This plant consists of seven downdraft fixed-bed gasifiers and two entrained flow reactors [73]... 

Figure 2.10. Gasifier types (a) updraft (b) downdraft and (c) fluidised bed (from B. Sorensen, Renewable Energy, 2004, used with permission from Elsevier.)...

TABLE 9.10 Effects of Moisture Content of Poplar Wood Chips on Product Yield, Gas Composition, and Thermal Efficiency in a Fixed-Bed, Air-Blown, Downdraft Gasifier"... 

Atmospheric Downdraft Gasifiers (ADG) are attractive for small scale applications (<1.5 MWth) as there is a very big market not only in developed but developing economies too (19). However, the problem of efficient tar removal is still a major problem to be addressed and there is a need for more automated operation especially for small scale industrial applications. Nevertheless, recent progress in catalytic conversion of tar (see below) gives credible options and ADG can therefore be considered of average technical strength. 

No company is presently developing pressurised systems for downdraft, updraft, cyclonic or entrained bed gasifiers for biomass feedstocks and it is difficult to imagine that such a technology could ever be developed into a commercial product due to the inherent problems of scale, tar removal and cost. 

Paul.P.J., et al., (1997) Tar characterisation in new generation agro-residue gasifier-cyclone and downdraft open top twin air entry systems, in Biomass Gasification and Pyrolysis. State of the Art and Future Prospects, (Ed. by M. Klatschmitt and A.V. Bridgwater), Cpl Press Newbury. 

Milligan, J.B., Evans, G.D. Bridgwater, A. V. (1993) Results from a transparent open-core downdraft gasifier. Advances in Thermochemical Biomass Conversion, Proceedings of the International Conference on Advances in Thermochemical Biomass Conversion, 11-15 may 1992, Interlaken, Switzerland. 

Di Blasi, C. (2000) Dynamic behaviour of stratified downdraft gasifiers. Chemical Engineering Science 55, pp 2931-2944. 

The temperature in the sampling line of the product gas of the updraft gasifier is kept at 00 250 C (to be examined) and in downdraft and fluid ised-bed gasification at 250 C. 

For tars sampled from downdraft and fluidised bed gasifiers, it has to be shown whether no solvent" can be as effective as sampling with a solvent. For the first version of the Guideline, the Group of Contractors has chosen to use a solvent. This choice will be evaluated during the running EU project. 

Coirqpared to conventional downdraft gasifiers the economics of the process are improved, provided that ambient air is used as gasifying medium... 

A small-scale stratified downdraft gasifier coupled to a gas engine for combined heat and power production... 

---