Chapter: Science & Technology

Topic: Deriving Energy From Waste

Q. There are how many ways by which energy is produced from waste?

There are various procedures through which energy from waste can be generated.

• A. Biomethanation: First and foremost is Anaerobic Bigestion or Biomethanation. In this process, the organic waste is segregated and fed into a biogas digester. The waste undergoes biodegradation under anaerobic conditions to produce methane rich biogas. The so produced biogas can be used for cooking, heating, generating electricity etc. The sludge can be used as a manure depending on the composition of the input waste.

• B. Combustion/Incineration: The next procedure is Combustion/Incineration which is direct burning of wastes in the presence of excess air (oxygen) at high temperatures (about 800C). It results in conversion of 65%-80% of heat content of organic matter into hot air, steam and hot water. The steam generated can be used in steam turbines to generate power.

• C. Pyrolysis/Gasification: Pyrolysis/Gasification is another process of chemical decomposition of organic matter through heat. The organic matter is heated in the absence or restricted supply of air till it breaks down into smaller molecules of gas (known collectively as syngas). The gas so produced is k n o wn a s p rodu ce r g a s wh ich co n st it u te s ca rbo n m o n o x ide (25 % ), h y dro g e n a nd hydrocarbons(15%), carbon dioxide and nitrogen(60%). The producer gas is burnt in internal combustion (IC) generator sets or turbines to produce electricity.

• D. Landfill Gas Recovery: Landfill Gas Recovery is another measure of recovering gas from waste dumps wherein the waste slowly decomposes to produce ‘Landfill gas’. This gas consists of high percentage of methane (approx.50%) and has a high calorific value of about 4500kcal/cubic metre and hence can be used for heating cooking and generating power.

• E. Plasma Arc: Plasma Arc is a relatively new technology for disposal of wastes, particularly, hazardous and radioactive wastes. Since it involves nearly complete destruction of waste while producing energy, it is less polluting. It does not produce oxides of nitrogen and sulphur and makes toxic ash left in the process easier to handle. However, the technology is costly and has not been tried in India.

Q. What are the advantages of using waste for Energy?

Ans.

• It reduces in the demand for landfills in land scarce cities.

• The cost of transportation of wastes is also reduced.

• In some cases, it can produce fertilizer as a by- product.

Q. What are the potential, achievements and hurdles in using waste for energy?

Ans. It is estimated that there is a potential of generating 3600MW of power from urban, municipal and industrial wastes in the country and it is likely to be increased to 5200MW by 2017.

At the end of February, 2012 the cumulative achievement of grid interactive power from waste was 36.20 MW in urban sector and 53.46 MW in industrial sector. In off-grid/ captive power cases the cumulative achievement of waste to energy capacities was 3.50 MWeq for urban sector and 90.15 MWeq for industrial sector.

The technologies are at present often expensive and even imported in India. The approximate cost per MW for waste to energy projects based on different technologies is high. While for Biomethanation, it ranges between 6-9 crores, for Gasification and Combustion, it is in the order of 9-10 crores. However, there is a financial support provided in the scheme ranging from 20 lakhs to 3 crores.

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