The authors discuss an updraft biomass gasification reactor with a maximum firing rate of 25 kg/h. The novel design features of this reactor are a self-generated steam injection system at the appropriate points, a natural-draft air-control system, and the choice of an appropriate reactor chamber volume. The reactor is useful for producing process heat. The heat is extracted by means of a heat-exchange unit, which is placed directly above the reactor at a maximum efficiency of 49%. The system produces hot water or steam continuously. Another feature is that a variety of biomass fuels, such as wood wastes, sawdust, coconut fiber, and briquettes of cattle manure and dried leaves, can be fired in this reactor. >

Intensive animal feeding operations create large amounts of animal waste that must be safely disposed of in order to avoid environmental degradation. Cattle feedlots and chicken houses are two examples. In feedlots, cattle are confined to small pens and fed a high calorie grain-diet diet in preparation for slaughter. In chicken houses, thousands of chickens are kept in close proximity. In both of these operations, millions of tons of manure are produced every year. The manure could be used as a fuel by mixing it with coal in a 90:10 blend and firing it in an existing coal suspension fired combustion systems. This technique is known as co-firing, and the high temperatures produced by the coal will allow the biomass to be completely combusted. Reburn is a process where a small percentage of fuel called reburn fuel is injected above the NO{sub x} producing, conventional coal fired burners in order to reduce NO{sub x}. The manure could also be used as reburn fuel for reducing NO{sub x} in coal fired plants. An alternate approach of using animal waste is to adopt the gasification process using a fixed bed gasifier and then use the gases for firing in gas turbine combustors. In this report, the cattle manure is referred to as feedlot biomass (FB) and chicken manure as litter biomass (LB). The report generates data on FB and LB fuel characteristics. Co-firing, reburn, and gasification tests of coal, FB, LB, coal: FB blends, and coal: LB blends and modeling on cofiring, reburn systems and economics of use of FB and LB have also been conducted. The biomass fuels are higher in ash, lower in heat content, higher in moisture, and higher in nitrogen and sulfur (which can cause air pollution) compared to coal. Small-scale cofiring experiments revealed that the biomass blends can be successfully fired, and NO{sub x} emissions will be similar to or lower than pollutant emissions when firing coal. Further experiments showed that biomass is twice or more effective than coal when used in a reburning process. Computer simulations for coal: LB blends were performed by modifying an existing computer code to include the drying and phosphorus (P) oxidation models. The gasification studies revealed that there is bed agglomeration in the case of chicken litter biomass due to its higher alkaline oxide content in the ash. Finally, the results of the economic analysis show that considerable fuel cost savings can be achieved with the use of biomass. In the case of higher ash and moisture biomass, the fuel cost savings is reduced.

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Comparative study of biomass fuels in an updraft gasifier

Citations

Co-firing coal: feedlot and litter biomass (cfb and clb) fuels in pulverized fuel and fixed bed burners

Optimal heat extraction from an updraft biomass reactor

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