(163d) Process Intensification and Cost Reduction for in-Plant Biomass Preprocessing Equipment

Michael Blaise^*, Nicholas, R. Schwartz, Paul E. Yelvington
Mainstream Engineering Corporation, Rockledge, FL
^*Corresponding Author: mblaise@mainstream-engr.com
Abstract

With growing concern about the sustainability and environmental impact of fossil fuels, interest in fuels derived from biomass feedstocks (e.g., agricultural residues, forestry residues, energy crops, and organics in mixed solids wastes) has risen steadily. Designing low-cost feedstock preprocessing systems that can handle a variety of materials is crucial to ensuring efficient and economic plant operation. Conventional preprocessing and solids handling consists of size reduction (i.e., comminution), drying, conveyance, and an inerting system to purge and pressurize the feedstock prior to introduction into a substantially oxygen-free conversion reactor such as a fluidized-bed fast-pyrolysis reactor. In this work, process intensification of preprocessing equipment for thermochemical biomass conversion was designed to take advantage of existing hot flue gas and eliminate the need for separate energy-intensive drying or purging steps. This approach combines drying, knife milling with in-line sharpening, conveyance, and inerting functions. This process-intensified approach is referred to as the integrated DCIMS (drying, conveyance, inerting, milling-sharpening) in-plant feedstock preprocessing. The DCIMS approach eliminated the need for a rotary drum dryer and second conveyor compared to the baseline conventional approach. A better than 5% additional reduction of moisture content was achieved when heating the knife mill with hot flue gas compared to an unheated baseline. Synergy between drying and milling led to reduced heat duty and reduced mill shaft power through combining these processes. The DCIMS approach demonstrated a more uniform (and smaller) milled product without increasing the energy required for milling. Experiments showed that the final moisture content for pine feedstock was 9% (a 15% reduction from a 24% starting moisture), for sugar cane bagasse was 8% (a 20% reduction from a 28% starting moisture), and for mixed waste was 5% (a 25% reduction from a 30% starting moisture). Internal integrated sharpening was also demonstrated successfully. The quality of the blade improved significantly—feedstock product was more uniform, and the power required for milling decreased by 17%. The estimated operating cost savings from the internal sharpening system was 4%. Heated pneumatic conveyance was also shown to effectively perform biomass drying. A custom motive nozzle for an eductor allowed for low-pressure flue gas to be used directly in the pneumatic conveyance of the feedstock. Integrated DCIMS feedstock preprocessing reduced the operating costs by 37% to $27/dry ton at a 1,000 ton/day scale, based on a technoeconomic analysis (TEA) of the process.

Keywords: Fast pyrolysis, process intensification, preprocessing, biomass, bio-oil