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

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Waste-to-Energy Processes

Incineration  Oxidizing reaction    Temperatures 850°C - 1200°C Excess air for complete combustion CO 2 , H 2 O and heat  Gasification [Pyrolysis]  Reducing reaction     Temperatures 400°C - 900°C Air < stoichiometric air [Pyrolysis - thermal decomposition in absence of air] CO, CO 2 , H 2 H 2 O CH 4 and some heat Partial combustion provides heat to sustain process  Plasma gasification  Reducing reaction  Temperatures 1500°C - 5000°C    Air < stoichiometric air CO, CO 2 , H 2 H 2 O CH 4 and heat Requires electricity input ( 1200 – 1500 MJ / tonne of waste), 15% - 20% of gross output energy 2

Plasma Gasification Furnace

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(source: Zhang et al., 2012) (source: Zhang et al., 2013)

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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

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Gasification Process

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

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Plastics and Rubber are Best Feedstock for Plasma Gasification

Waste Category

heterogeneous MSW * Paper Wood Food waste Textiles Plastic Rubber Ulitimate Composition - Dry Basis

% C

57.1

43 49.5

45.4

55 76.3

78

% H

7.6

6.0

6.0

6.9

6.6

11.5

10

% O

33.3

43.8

42.7

32.2

31.2

4.4

0

% N

2 0.36

0.2

3.3

4.6

0.26

2

% S

0 0.17

0.1

0.32

0.15

0.2

0

Ash (% weight)

25 6.3

1.5

11 2.5

5.3

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Moisture (% weight)

35% 24% 2% 65% 27% 13% 2%

HHV, as received (KJ/kg)

24,198 13,414 16,715 7,229 16,049 33,264 31,285 * Original values in the GasifEq model representing heterogeneous MSW

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Plastics / Rubber – highest efficiency

Cold Gas Efficiency = η = ṁ syngas * LHV snygas / ( ṁ waste * LHV waste + P Plasma ) where ṁ = mass flow rate of syngas and solid waste P plasma = electrical power for plasma torch Cold Gas Efficiency

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Sensitivities

Change in Air Flow Change in Temperature Change in Moisture

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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