Kinetics and Economics of Catalytic Steam Gasification of Broiler Litter

In the U.S. in 1996, approximately 7.6 billion broiler chickens were produced. This number has risen continuously over the last few years, with more than 75% of the production coming from the southeastern U.S. Because of the significant growth in broiler production, the amount of litter produced is substantial. Unfortunately, much of the litter is not used properly for fertilizer and ends up polluting rivers and surface waters. Because of decreased availability of land and potential federal regulations, appropriate actions must be taken to find a better way to handle this material. Recently, catalytic steam gasification has been considered as an alternative option to manage broiler litter. The process requires an alkali metal or alkaline earth metal salt and steam to convert the feedstock to a fuel gas consisting primarily of carbon monoxide, carbon dioxide, hydrogen, and methane. The gas may be used as a possible energy source or chemical feedstock. Broiler litter provides a good feedstock for catalytic steam gasification. Litter contains potassium and several other alkali metal salts that can be used as catalyst. If the inherent salts are not sufficient, additional sources, such as naturally occurring langbeinite and potassium carbonate, can be used with minimum additional cost. Broiler litter, with low sulfur content, produces low quantities of unwanted hydrogen sulfide. Moisture present in the wet litter can also provide the steam for gasification, and the solid residue left after gasification can be used as a fertilizer or in cement/concrete manufacturing. Previous bench–scale experiments, at the University of Tennessee Space Institute, (UTSI), showed the technical and economic viability of the steam gasification concept. In the present study, this past work was extended by experimentally determining the optimum conditions for steam gasification as well as by estimating the preliminary economics of a stationary steam gasification system to produce low to medium Btu fuel gas. Results are presented in this article.