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Energy from Wastes

Energy from Wastes. Goals. Obtain additional value from wastes – wastewaters, animal wastes, sludges and solid wastes from agricultural, industrial and municipal sources Reduce amount of waste that must be disposed of by other means. Technologies Available. Direct combustion

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Energy from Wastes

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  1. Energy from Wastes

  2. Goals • Obtain additional value from wastes – wastewaters, animal wastes, sludges and solid wastes from agricultural, industrial and municipal sources • Reduce amount of waste that must be disposed of by other means

  3. Technologies Available • Direct combustion • Biological conversion to ethanol • Anaerobic digestion to produce biogas • Digesters • Covered lagoons

  4. Drawbacks of Biomass Energy • Dispersed feedstock if using crop wastes • Distributed small-scale production for on-site conversion • High transportation costs for centralized conversion • Technical expertise required to implement • High capital and operating expenses

  5. Fermentative bacteria Focus: Biogas Production Acetogenic bacteria Methanogenic bacteria

  6. Focus: Biogas Production Hydrolysis Acidogenesis Acetogenesis Methanogenesis

  7. Types of Digesters • Completely mixed (CSTR)

  8. Types of Digesters • Contact digester (CSTR with recycle)

  9. Types of Digesters • Plug flow

  10. Types of Digesters • Packed bed/fixed film

  11. Types of Digesters • Upflow anaerobic sludge blanket

  12. Two-stage

  13. Types of Digesters • Covered lagoon

  14. Covered Lagoon

  15. Types of Digesters • Landfill

  16. Digester Operation • Solids concentration: ≤ 10% to pump as slurry • Solids separation to remove large particles • Temperature: • Mesophilic • Operates at 95 – 100 °F (35 – 38 °C) • Most common for manure treatment • Hydraulic retention time: 10 – 30 d • Thermophilic • Operates at 125 – 140 °F (50 – 60 °C) • Hydraulic retention time: 6 h – 10 d

  17. Digester Operation • Feedstock composition • C:N ratio should be 8 – 25 • Most manure within acceptable range • If bedding or crop residue mixed with manure, C:N may be too high • pH 6.0-8.0, optimum 7.0

  18. Biogas Production • Composition • CH4 50-70 % typically 60 % • CO2 30-50 % typically 40 % • H2 0-2 % • H2S 100-7000 ppm • Energy content: 20 MJ/m3(540 Btu/SCF) • Biogas yield: 0.3-0.5 m3/kg VS (4.8-8.0 SCF/lb VS) • Production rate: 1-5 m3/m3(digester vol)·d

  19. Biogas Utilization • Heating on-site is most economical usage • may be applied to heat buildings for swine operation in colder climate • usually not enough heating demand in dairies • Generate electricity • may supply electrical energy for operation with some to sell back to grid • difficult to get utility company to accept • capital investment costly • Pipeline quality gas • must be scrubbed to remove CO2, H2S, NH3 and other impurities

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