Skip to main content

Comparison of Different Waste-to-Energy Processes


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

Enhanced by Zemanta
Labels:

Popular posts from this blog

Woody Biomass and Conversion Efficiency

Every energy conversion system wastes a portion of its input energy. For biomass to electricity conversion systems, 50% or more of the energy input can be lost - even up to 90% for some small-scale and alternative technologies. However, the energy rejected from a conversion system can often be used productively for industrial or residential heating purposes in place of burning fuels separately for that purpose. When this is done the overall efficiency can jump to 75-80%. Most systems must reduce their electricity production somewhat to make cogeneration feasible. Thermal applications are the most efficient conversion technology for turning woody biomass into energy and should be considered in the development of a national Renewable Portfolio Standard (RPS). Thermal applications for woody biomass can be up to 90% efficient, compared to 20% for electricity and 50-70% for bio-fuels. Thermal systems can be applied at multiple scales, and are often more economically viable, particularly in...
Read more

CDM Potential in MENA Countries

The Middle East and North Africa (MENA) region is highly susceptible to climate change, on account of its water scarcity, high dependence on climate-sensitive agriculture, concentration of population and economic activity in urban coastal zones, and the presence of conflict-affected areas. Moreover, the region is one of the biggest contributors to greenhouse gas emissions on account of its thriving oil and gas industry. The world’s dependence on Middle East energy resources has caused the region to have some of the largest carbon footprints per capita worldwide. Not surprisingly, the carbon emissions from UAE are approximately 55 tons per capita, which is more than double the US per capita footprint of 22 tons per year. The MENA region is now gearing up to meet the challenge of global warming, as with the rapid growth of the carbon market. During the last few years, many MENA countries, like UAE, Qatar, Egypt and Saudi Arabia have unveiled multi-billion dollar investment plans i...
Read more