1. 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

2. Waste-to-Energy Processes
Incineration
Oxidizing reaction
Temperatures °C °C
Excess air for complete combustion
CO2, H2O and heat
Gasification [Pyrolysis]
Reducing reaction
Temperatures °C °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 °C °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
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
𝐶 𝐻 𝑥 𝑂 𝑦 +𝑤H2O + 𝑚 𝑂 𝑁 2 → 𝑛 1 𝐻 𝑛 2 CO + 𝑛 3 𝐶𝑂 𝑛 4 𝐻 2 O + 𝑛 5 𝐶𝐻 𝑛 6 𝑁 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 ↔ 𝐶𝐻 4
Water-Gas Shift:
𝐶𝑂 + 𝐻 2 𝑂 ↔ 𝐶𝑂 𝐻 2
Gasification enhanced with steam:
𝐶𝐻 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

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 waste Pplasma = 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