Char and Tar Production From Dairy Biomass Gasification Using Air-Steam for Partial Oxidation

The increase in air pollution caused by combustion of fossil fuels demands the exploration of renewable energy sources in order to mitigate the dependence on fossil fuels. Research includes the efforts to partially replace fossil fuels with renewable energy-sources in thermal conversion processes in order to reduce the emission of CO₂. The animal wastes can be considered as biomass fuels since their properties are almost similar to ration fed to animals. Concentrated animal feeding operations (CAFOs) such as cattle feedlots and dairies produce a large amount of feedlot manure or feedlot biomass (FB) and dairy manure or dairy biomass (DB), which may lead to land, water, and air pollution if waste handling systems and storage and treatment structures are not properly managed. Both FB and DB are grouped under cattle manure or cattle biomass (CB). The concentrated production of low quality CB at these feeding operations can serve as a good feedstock for locally based gasification for syngas (CO and H₂) production and subsequent use in combined heat and power generation. If thermal gasification technology is developed for DB fuels, the environmental impact from both animal feeding operations and fossil-fuels could be mitigated. The current paper presents experimental results obtained from adiabatic fixed-bed gasification of DB using a 10 KW fixed bed counter-flow gasifier and air-steam for partial oxidation. A mass spectrometer (ProLab Thermo ONIX) was used to analyze the gas composition continuously and at real time. The effect of the operating parameters studied, which includes equivalence ratio (1.6 < Φ < 6.4) and steam to fuel (S:F) ratio (0.4 < S:F < 0.8, on the yields of gases, char, and tar are discussed. Also, results from gasification of dairy biomass–ash blend (DB-Ash) and dairy biomass Wyoming coal blend (DB-WYC) is presented for comparison effects. In general, for the set of experiments performed using DB, the gas yield was 1.54 to 5.30 dry tar-free kg of gases per each kg of DAF DB gasified while the char production ranged from 0 to 0.18 kg of char per DAF kg of DB gasified. The average of tar concentration in gases leaving the gasifier was about 80 g/ SATP m³.