Testing of Renewable Fuels in a 80 KWE Downdraft Gasifier

Abstract:

Biomass Engineering Ltd. have demonstrated that their downdraft gasification technology is capable of producing very low tar levels in the producer gas, as independently measured, and have four gasifiers in operation. Developments in the gasifier configuration have led to a very low tar gas, allowing a simplified hot has filtration system to be used. Recent independent analysis of the "tars" from the Mossborough Hall farm gasifier at Rainford, NW England has shown that over 80wt% of the condensable organics in the gas are benzene, toluene, xylene and naphthalene and that problematic tar components in the gas were less than 20 mg/Nm³ under prolonged operation. The gasification technology of Biomass Engineering Ltd. is therefore close to a warrantable commercial reality.

Biomass Engineering Limited has succeeded in developing a downdraft gasifier capable of producing a very low tar, low particulate gas of consistent high calorific value (> 5 MJ/Nm³ for wood feedstocks). However, with the development of a technology capable of handling a well-defined wood, there is a requirement to assess the possibility of using other non-standard fuels, especially as these are more readily available in some locations and where other disposal and transportation options are not economical. To this end this work was concerned with testing a variety of fuels in an existing 80 kg/h (80 kWe) gasification system and measuring a range of process emissions and assess whether they could possibly be used in a downdraft gasifier for gas production for use in a boiler or engine. The fuels used were: dried papermill sludge (briquetted), Dried leather wastes (briquetted), palletwood wastes (and some demolition wood), medium density fibreboard (MDF), panel board (and other chipped pallets), pine/bark mixed waste strippings and renewable biomass fuel (RBF) produced form the organic fraction of MSW.

The Biomass Engineering Ltd. technology is a throated downdraft gasifier and it can be operated using different gas cleaning systems, including cyclones for dust removal, hot gas filter for very high dust capture efficiencies (>99wt%) on low tar gases and a wet scrubbing system for contaminated (volatile metals) and high tar gases. Wastes with high ash contents are more prone to high levels of tar formation. Tests of over 60 hours on each fuel were carried out, except for the RBF, of which there was only a limited quantity and of highly variable quality, which caused various processing difficulties.

Tests on the fuels showed that the high ash feedstocks (>15wt%, RBF and papermill sludge) were problematical in gasifier operation and not unexpectedly gave a producer gas with low heating values in the range of 1-3 MJ/Nm³. The buffings dust, pine/bark mix and the palletwood could be satisfactorily gasified to give a has with a good lower heating value of 4-5 MJ/Nm³. This is the expected value for low ash feedstocks and low tar levels in the gas. Extensive analyses of the feedstocks, the by-products chars and ashes, the producer gas and some of the condensates were made. The RBF fuel was prone to clinker formation on the grate possibly by the formation of low melting eutectic of SiO₂ and CaO (or a derivative). The chars exhibited high carbon conversions of typically over 85wt%.

1. Introduction
2. System Configuration and Operation
3. Operation on Various Feedstocks
4. Product Analysis
5. Conclusions
6. Recommendations
7. Acknowledgements
8. References

Publication Year:

2006

Publisher:

Department of Trade and Industry

DOI:

No DOI minted

Author(s):

Biomass Engineering Ltd