Environment and the Plasma Gasification of Garbage

The Discordant

I wanted to bring to your attention a very interesting article that I read on the New York Times. The link is: Garbage Plasma Gasification.

It was a while ago when I read it, but didn’t have time to write about it! So here it is:

The first thing I saw was the word “Garbage”… I didn’t really give much attention to it because even though it is something really important, and that people should be aware of, I already know what most articles usually say about it. Things like: “Oh, the toxins from incinerating the garbage are bad”, “We have to start disposing of medical/toxic garbage in safe places”, “Soon there will be a shortage of places where to dump garbage and it will have to be thrown into space” or “Everyone should recycle because it will help the world by producing less waste and save money”.  These are all…

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What is Plasma Waste-to-Energy Technology

Plasma Gasification

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Clean Energy Diary

The World Bank development indicators 2008 shows that the wealthiest 20% of the world accounts for 76.6% of total private consumption. The poorest fifth just 1.5%.The report further states,

“Today’s consumption is undermining the environmental resource base. It is exacerbating inequalities. And the dynamics of the consumption-poverty-inequality-environment nexus are accelerating. If the trends continue without change — not redistributing from high-income to low-income consumers, not shifting from polluting to cleaner goods and production technologies, not promoting goods that empower poor producers, not shifting priority from consumption for conspicuous display to meeting basic needs — today’s problems of consumption and human development will worsen. The real issue is not consumption itself but its patterns and effects. Inequalities in consumption are stark. Globally, the 20% of the world’s people in the highest-income countries account for 86% of total private consumption expenditures — the poorest 20% a minuscule 1.3%. More specifically, the richest…

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Analyzing Different Waste-to-Energy Technologies

Major components of Waste-to-Energy Processes

  1. Front end MSW pre-processing is used to prepare MSW for treatment and separate any recyclables
  2. Conversion unit (reactor)
  3. Gas and residue treatment plant (optional)
  4. Energy recovery plant (optional): Energy / chemicals production system includes gas turbine, boiler, internal combustion engines for power production. Alternatively, ethanol or other organic chemicals can be produced
  5. Emissions clean up

Incineration

  • Combustion of raw MSW, moisture less than 50%
  • Sufficient amount of oxygen is required to fully oxidize the fuel
  • Combustion temperatures are in excess of 850oC
  • Waste is converted into CO2 and water concern about toxics (dioxin, furans)
  • Any non-combustible materials (inorganic such as metals, glass) remain as a solid, known as bottom ash (used as feedstock in cement and brick manufacturing)
  • Fly ash APC (air pollution control residue) particulates, etc
  • Needs high calorific value waste to keep combustion process going, otherwise requires high energy for maintaining high temperatures

Anaerobic Digestion

  •  Well-known technology for domestic sewage and organic wastes treatment, but not for unsorted MSW
  • Biological conversion of biodegradable organic materials in the absence of oxygen at temperatures 55 to 75oC (thermophilic digestion – most effective temperature range)
  • Residue is stabilized organic matter that can be used as soil amendment after proper dewatering
  • Digestion is used primarily to reduce quantity of sludge for disposal / reuse
  • Methane gas generated used for electricity / energy generation or flared

Gasification

  • Can be seen as between pyrolysis and combustion (incineration) as it involves partial oxidation.
  • Exothermic process (some heat is required to initialize and sustain the gasification process).
  • Oxygen is added but at low amounts not sufficient for full oxidation and full combustion.
  • Temperatures are above 650oC
  • Main product is syngas, typically has net calorific value of 4 to 10 MJ/Nm3
  • Other product is solid residue of non-combustible materials (ash) which contains low level of carbon

Pyrolysis

  • Thermal degradation of organic materials through use of indirect, external source of heat
  • Temperatures between 300 to 850oC are maintained for several seconds in the absence of oxygen.
  • Product is char, oil and syngas composed primarily of O2, CO, CO2, CH4 and complex hydrocarbons.
  • Syngas can be utilized for energy production or proportions can be condensed to produce oils and waxes
  • Syngas typically has net calorific value (NCV) of 10 to 20 MJ/Nm

Plasma Gasification

  • Use of electricity passed through graphite or carbon electrodes, with steam and/or oxygen / air injection to produce electrically conducting gas (plasma)
  • Temperatures are above 3000oC
  • Organic materials are converted to syngas composed of H2, CO
  • Inorganic materials are converted to solid slag
  • Syngas can be utilized for energy production or proportions can be condensed to produce oils and waxes

 

        Net Energy Generation Potential Per Ton MSW

Waste Management Method

Energy Potential*

(kWh per ton MSW)

Recycling

2,250

Landfilling

   105

WTE Incineration

   585

Gasification

   660

Pyrolysis

   660

Anaerobic Digestion

   250

Cost Economics of WTE Processes

Technology

Plant capacity

(tons/day)

Capital cost

(M US$)

O&M cost

(US$/ton)

Planning to commissioning

(months)

Pyrolysis

70-270

16 – 90

80 – 150

12 – 30

Gasification

900

15 – 170

80 – 150

12 – 30

Incineration

1300

30 – 180

80 – 120

54 – 96

Plasma gasification

900

50 – 80

80 – 150

12 – 30

Anaerobic digestion

300

20 – 80

60 – 100

12 – 24

In vessel composting

500

50 – 80

30 – 60

9 – 15

Sanitary landfill

500

5 – 10

10 – 20

9 – 15

Bioreactor landfill

500

10 – 15

15 – 30

12 – 18

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