(238f) Use of Alternative Fuels to Replace Coal in the Manufacture of Cement

A multiyear DOE-supported study is underway to identify, determine, and understand fundamental burn characteristics and properties of alternative fuel sources to replace coal for energy generation, with emphasis on impacts in cement processing. An operating cement plant (Lafarge North America's Roberta Plant in Calera, Alabama) serves as model to reduce dependence on traditional fuels through the use of bio-based and waste fuels. Portland cement manufacturing involves the combustion of solid fuels along with raw materials to produce clinker. Temperatures exceeding 1,400°C are needed to carry out reactions for cement chemistry. Energy needs for a manufacturing plant are 12,000 MMBTU/day. Potential alternatives to fossil fuels must provide adequate and economical energy but they must also result in products of combustion that have negligible impact on cement quality.

Results will be presented from a comprehensive evaluation of the raw materials, fuels, clinker, cement, and emissions from test burns at Lafarge's Roberta Cement Plant when using scrap tires, waste plastics, woodchips, switch grass, poultry litter, forests trimmings, and scrap railroad ties as fuel alternative to coal. The evaluation includes analyses and long-term testing of the concrete product, impacts on process operations, emissions effects, and materials handling. Sixteen three-day trial burns were conducted in 2007, 2008, and 2009. Each trial burn contained one or more of the alternative fuels. An elaborate sampling and analysis plan was carried out for each trial burn with close cooperation between the Lafarge plant, the Lafarge testing laboratory, Auburn University, and outside laboratories.

All of the alternative solid fuels were deemed technically viable as supplements for coal for direct burn in a manufacturing plant. Replacement ratios (on a BTU basis) were up to 8% for the bio-based fuels and up to 18% for the waste plastics and the synergistic burns where two or more of the alternative materials were used together. No negative impacts were seen on product quality or emissions. Alternative Solid Fuel (ASF) handling and process operations were established for the use of each of these fuels.