Thermal Conversion of Animal Manure to Biofuel Samy Sadaka, Ph.D., P.E., P. Eng. Assistant Professor - Extension Engineer University of Arkansas Division of Agriculture - Cooperative Extension Service Department of Biological & Agricultural Engineering PO Box 391, 2301 S. University Ave. Little Rock, AR 72204 Team members: Mahmoud Sharara, PhD student Rick Fields, Program Associate Andrew Wright, Researcher Associate Outline Manure availability and characteristics Motivation for returning to biorefienries Manure conversion technologies Combustion, gasification and pyrolysis Gasification issues Conclusion Biorefinery approaches A biorefinery is a processing and conversion facility that converts biomass to individual components, then processes these components to marketplace products such as biofuel, biopower and conventional and new bioproducts. The biorefinery concept is similar to petroleum refinery, which produces multiple fuels and products from petroleum. 3
Biorefinery approaches Sugar platform: employs enzymatic hydrolysis to convert cellulose to simple sugars suitable for fermentation to ethanol and other products. Biochemical platform: employs transestrefication to produce biodiesel from vegetable oil or animal fat. Thermochemical platform: employs gasification or fast pyrolysis as the route to convert biomass to fuels and chemicals. Motivation for returning to biorefinery Excess manure production Global climate change Rural development Reduced reliance on foreign Countries Availability of animal waste In the United States, animal operations produce about 60 million ton dry weight of manure annually. According to the U.S. Department of Agriculture, the number of animal farms decreased by 5% from 1997 to 2007, while the average farm size, in acres, increased by 3%. 6
Energy and value-added products recovery from residues and wastes Farm Residues and Wastes Biological/Chemical Thermochemical Anaerobic Digestion Alcoholic Fermentation Combustion Pyrolysis Gasification Methane Ethanol Heat Oil and Char Gas Manure biological conversion Methods Anaerobic digestion Composting Biodrying Manure biodrying Temperature Moisture Content Moisture content (%) 90 Beef 80 Swine 70 Poultry 60 50 40 30 20 10 0 7 14 21 28 35 42 Time (d) 9
Manure thermochemical conversion methods Combustion: manure + excess air to produce heat Pyrolysis: manure + heat bio oil Gasification: manure + limited air + initial heat gas + char + tar Gasification Gasification is a thermochemical process (650-1000 o C) where a ratio of the combustion oxygen (less than 1) is supplied to convert carbonaceous materials in the fuel into gaseous products using different gasifying media Gasification Heat Air Manure Producer gas Tar Char
Reactors Used to Convert Manure to Gas Updraft System Downdraft System BiomassProduct gas Biomass Fixed bed of biomass Oxidant Ash Oxidant Grate Fixed bed of biomass Product gas + ash Biomass Oxidant Throat Feeder Distributor plate Freeboard Fluid bed Airflow Schematic diagram of a fluidized bed gasifier Cyclones Hopper Gas cleaning Gas analyzer Reactor U of A mobile fluidized bed gasifier
4 2 Livestock and Poultry Environmental Learning Center Webcast Series February 28, 2014 Auger gasifier How does this work? Advantages of the auger gasifier Disadvantages of the auger gasifier Auger gasifier Gas flowmeter Tar trap Data recorder Condenser train Tar cracking Air Hopper Feeder Gas analyzer C C CH C CO H4 O O 2 H O H 2 O 2 2 Char collection Heated reactor The externally-heated auger gasification system
Combustible gases from air blown gasifier Gas Compositions and Average Bed Temperature versus Time Air-Blown Gasification Gas Composition (Vol. %) 25 1000 900 20 800 700 15 600 500 10 400 300 5 200 100 0 0 0 4 8 12 16 20 24 Time (min) Temperature ( C) Hydrogen (H2) Carbon Monoxide (CO) Methane (CH4) Average Bed Temperature Combustible gases heating values Challenges facing thermochemical conversion of manure High moisture content Feeding challenges High ash content Low BTU producer gas Agglomeration
Challenges facing thermochemical conversion of manure (continued) Ash Tar Ammonia Sulfur Particulate matter (PM) Low BTU gas Fixed and variable costs Permit: We like manure gasification but not in our backyard. Reported gasification processes Manure into energy and ash - New Gasification Technology (North Carolina) Poultry manure gasification (West Virginia) Turkey farm uses a gasification system to produce Heat (Minnesota) Reported gasification processes Assembly and testing of an onfarm Manure to energy conversion for animal waste pollution Control (Texas A&M) Rice husk/straw gasification to generate 12.0 MW of electricity and up to 100,000 Pound Per Hour of process steam (Riceland, Arkansas).
Biochar Reactor Temperature of 300oC (1 h, 2 h, 3 h) Reactor Temperature of 350oC (1 h, 2 h, 3 h) Reactor Temperature of 400oC (1 h, 2 h, 3 h) Continuous system (400oC, 500oC, 600oC) Carbon sequestration Aside from the production of gaseous fuel, gasification process produces biochar. Biochar soil application could potentially provide an ecological service by sequestering carbon in the soil thus creating a carbon sink. Carbon sequestration from auger gasification could reach about 30% of the raw feedstock carbon which could be returned back to the soil in the form of biochar carbon. Why should we consider gasification as a plan? Any instability in the supply of fossil fuels would profoundly effect the quality, availability and prices of food commodities, especially if it happen during the grains drying season The recent propone supply shortage, during the grain-drying season, in the Mid-West is a clear example of this dependency. Therefore, we need to have a plan B.
Conclusion Although the gasification process have been extensively developed, it still have several limitations. Some of these limitations are related to gasifiers design while others are related to the feedstock characteristics. Gasification of manure and/or agricultural wastes can be the backup plan in cases of fossil fuel supply shortages. Thank You for your attention ssadaka@uaex.edu