08-05-10

“Co-firing Biomass, Sewage Sludge and Municipal Waste” was Hot Topic Hour Aug. 5, 2010

Dr. Dirk T. Van Essendelft, Chemical and Biochemical Engineer, U.S. Department of Energy National Energy Technology Laboratory (NETL), Separations and Fuels Processing Division, described the research programs being conducted in the NETL Office of Research and Development to identify, understand and address the technical and logistical challenges involved in utilizing biomass in conjunction with traditional fossil fuels to produce energy with significantly reduced or negative carbon footprints. The strategic focus lies with gasification technologies, but much of the research has applicability in direct combustion as well. The research at NETL has been broken down into five topics: material preparation and feeding, computational modeling, reaction chemistry, materials, and systems analysis.

Dirk is working on materials preparation. Challenges include the seasonal availability, transportation and storage. Biomass can rot or otherwise degrade. It is important to know the biomass structure and mechanical properties and their impact on flowability and grindability.

Barry Freel, Vice-president for Technology at Ensyn, described a process that converts biomass to combustible oil. UOP, a Honeywell company, and Ensyn have formed a joint venture called Envergent Technologies, to provide a proven, practical thermal conversion process that converts biomass to pyrolysis oil (PyOil) that can be used in heat applications, power projects or converted to transportation fuels. Co-firing of PyOil can readily be accomplished in existing boiler applications offering the advantage of supplementing fossil fuels with renewable, very low sulfur, green liquid fuel.

There was an interesting discussion relative to this option versus gasification and other approaches. Dirk pointed out that the energy required to reduce the particle size to be suitable for use in a liquefaction process is substantial. Barry pointed out that they are using sawdust which is already at the desired particle size.

Marc A. Cremer, Ph.D., Manager of Engineering Analysis at Reaction Engineering International, told participants that practical implementation of biomass combustion can be complex. In addition, the limited base of commercially relevant experience and the unique properties of biomass fuels lead to even greater uncertainty, thereby limiting industry acceptance. There are significant fuel-related impacts on combustion performance and emissions.

The application of computational fluid dynamics (CFD) software provides an understanding and guidance in evaluating various biomass firing strategies and furnace designs. The efficiency of co-firing is greater than when using a dedicated boiler. Concerns include catalyst deactivation, flyash properties and combustion stability.

Murat Dogru of Beltran Technologies, Inc., discussed biomass gasifier systems. There is a successful 2-MW system in Turkey that uses refuse derived fuel. The municipal garbage is sorted to remove metals and then directly gasified when the gasifier and sorting are at the same location. Otherwise it is densified and shipped to the gasifier location. The emissions from the gasifer are cooled to condense tars and then pass through a wet electrostatic precipitator before being directed to the gas engine which provides heat and power. The advantage of the 2-MW module concept is that the power generation can occur where the refuse is located, thus eliminating costly hauling.