Exploration of Renewable Energy Usage in a Cement Kiln Using Downdraft Gasification of Poultry Litter

Waste biomass, most notably poultry litter, is a potential source of energy that is widely available and cheap, especially in the southeast. Using poultry litter as an energy source provides a year-round outlet for this waste product. One major energy user that currently utilizes alternative solid fuels is the cement industry. Poultry litter in its raw state, however, is limited in use because of its high chlorine content and relatively large concentration of other unwanted constituents. Downdraft biomass gasification of pelletized poultry litter is a proposed solution to this problem as a means to produce a clean, consistent product gas for injection into the kiln. In this study, this process has been analyzed through experimentation on a pilot-scale 65 Nm3 /hr syngas production downdraft gasifier to determine its effectiveness and consistency in this application. The low ash fusion temperature and high alkali content of poultry litter prove to be difficult obstacles to overcome as ash clinker formation is an issue. Experiments with temperature depression via flue gas recirculation as well as experiments employing an additive (lime) to prevent fusion and aid in chlorine retention in the ash have been carried out. Flue gas recirculation allowed the reduction of the gasifier secondary air oxygen concentration by 40–45%, yielding an approximately 100°C depression in average temperature. Results have shown that the clinkering is temperature independent, at least within the controllable temperature range. Lime also has only a slight effect on the fusion when used to coat the pellets. However, lime addition does display some promise in regards to chlorine capture, as ash analyses show chlorine concentrations of more than four times greater in the lime infused ash as compared to raw poultry litter. Experiments were also conducted to explore the effectiveness of mixing lime with raw poultry litter, the object being to coat more surface area and have a more even mixture. These resulted in more consistent experiments with no ash clinkering.Copyright © 2011 by ASME