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 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 CH4 and some heat Partial combustion provides heat to sustain process Plasma gasification 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

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

Plasma Gasification Process 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

Gasification Process Gasification of MSW 𝐶 𝐻 𝑥 𝑂 𝑦 +𝑤H2O + 𝑚 𝑂 2 +3.76 𝑁 2 → 𝑛 1 𝐻 2 + 𝑛 2 CO + 𝑛 3 𝐶𝑂 2 + 𝑛 4 𝐻 2 O + 𝑛 5 𝐶𝐻 4 + 𝑛 6 𝑁 2 + 𝑛 7 𝐶 The Boudouard reaction: 𝐶 + 𝐶𝑂 2 ↔ 2𝐶𝑂  The water – gas reaction: 𝐶 + 𝐻 2 𝑂 ↔ 𝐶𝑂 + 𝐻 2  The methanation reaction: 𝐶 +2 𝐻 2 ↔ 𝐶𝐻 4 Water-Gas Shift: 𝐶𝑂 + 𝐻 2 𝑂 ↔ 𝐶𝑂 2 + 𝐻 2 Gasification enhanced with steam: 𝐶𝐻 4 + 𝐻 2 𝑂 ↔ 𝐶𝑂 + 3 𝐻 2 Solving for 7 unknowns: (3) mass balance equations (C, H, O) (3) equilibrium constant equations (1) energy balance equation

Plastics and Rubber are Best Feedstock for Plasma Gasification

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

Sensitivities Change in Air Flow Change in Temperature Change in Moisture

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