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Plasma gasification as a viable waste-to-energy treatment of MSW

Plasma gasification as a viable waste-to-energy treatment of MSW. Larry Gray MANE 6960 – Solid and Hazardous Waste Prevention and Control Engineering Rensselaer Hartford Hartford, CT, USA April 24, 2014. Waste-to-Energy Processes. Incineration Oxidizing reaction

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Plasma gasification as a viable waste-to-energy treatment of MSW

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  1. Plasma gasificationas aviable waste-to-energy treatment of MSW Larry Gray MANE 6960 – Solid and Hazardous Waste Prevention and Control Engineering Rensselaer Hartford Hartford, CT, USA April 24, 2014

  2. Waste-to-Energy Processes • Incineration • Oxidizing reaction • Temperatures 850°C - 1200°C • Excess air for complete combustion • CO2, H2O and heat • Gasification [Pyrolysis] • Reducing reaction • Temperatures 400°C - 900°C • Air < stoichiometric air [Pyrolysis - thermal decomposition in absence of air] • CO, CO2, H2 H2O CH4and some heat • Partial combustion provides heat to sustain process • Plasma gasification • Reducing reaction • Temperatures 1500°C - 5000°C • Air < stoichiometric air • CO, CO2, H2 H2O CH4 and heat • Requires electricity input ( 1200 – 1500 MJ / tonne of waste), 15% - 20% of gross output energy

  3. Plasma Gasification Furnace (source: Zhang et al., 2013) (source: Zhang et al., 2012)

  4. Plasma Gasification Process • Plasma • Heating a gas to very high temperatures where molecules and atoms ionize • Thermally and electrically conductive • Plasma torches • Electric arc • Concentric flow of air from torches to form plasma • Secondary air fed into melting chamber to control gasification • Steam can be fed into furnace to enhance syngas yield

  5. Gasification Process Gasification of MSW The Boudouard reaction: The water – gas reaction: The methanation reaction: Water-Gas Shift: Gasification enhanced with steam: Solving for 7 unknowns: (3) mass balance equations (C, H, O) (3) equilibrium constant equations (1) energy balance equation

  6. Plastics and Rubber are Best Feedstock for Plasma Gasification

  7. Plastics / Rubber – highest efficiency η = ṁ syngas* LHVsnygas/ (ṁ waste * LHVwaste + PPlasma) Cold Gas Efficiency = where ṁ = mass flow rate of syngas and solid wastePplasma= electrical power for plasma torch Cold Gas Efficiency

  8. Sensitivities Change in Air Flow Change in Temperature Change in Moisture

  9. Summary • Lower emissions – less amount of air to clean • Reduced volume of waste - 6% to 15% of original volume • Very good means to disposing of hazardous and medical waste • Vitrified slag is inert and could be used as filler material • For best production of syngas and best efficiencies use MSW feedstock of plastics, rubber • Syngas produced can be used to serve a variety of energy needs • Use heat from syngas for district heating • Electrical power generation • Fuel cells • Make liquid fuels

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