Waste-to-Energy Plants - Understanding the Conversion Process and Challenges | UPSC Notes

An Introduction to Waste-to-Energy Conversion

Waste-to-Energy, often abbreviated as WtE, is a cutting-edge approach to waste disposal that leverages modern technology.

• One of the main benefits of Waste-to-Energy is its ability to significantly reduce greenhouse gases like methane from landfills, which is a potent climate-warming gas, even more so than CO₂.

The Working of Waste-to-Energy Plants

• In a typical Waste-to-Energy plant, municipal solid waste (MSW) is incinerated to produce steam in a boiler, which is then used to power an electric generator turbine.
• MSW is a combination of energy-rich materials such as paper, plastics, yard waste, and wood products.

An illustration of a mass-burn waste-to-energy plant

The energy generation process in a mass-burn waste-to-energy plant involves the following steps:

1. Collection and dumping of waste into a large pit.
2. Transfer of the dumped waste to a combustion chamber.
3. Incineration of the waste (fuel) to release heat.
4. Conversion of water into steam in a boiler using the heat.
5. Production of electricity by moving the blades of a turbine generator with the high-pressure steam.
6. Elimination of pollutants from the combustion gas before they are released into the atmosphere through a smokestack with the help of an air pollution control system.
7. Collection of ash from the boiler and the air pollution control system.

Various Waste-to-Energy (WTE) Technologies

• BIOMETHANATION: This is a process of anaerobic digestion of organic materials, converting them into biogas. It is a bacterial fermentation process that operates without free oxygen, resulting in biogas composed mostly of methane (~60%), carbon dioxide (~40%), and other gases. Biomethanation offers dual benefits – it produces biogas and manure as end products.
• INCINERATION: This involves the complete combustion of waste (MSW or refuse-derived fuel) with the recovery of heat to produce steam, which in turn generates power through steam turbines.
• GASIFICATION: This is a process that uses high temperatures (500-1800 degrees C) in the presence of limited amounts of oxygen to decompose materials to produce synthetic gas (a mixture of carbon monoxide (CO) and hydrogen (H2)). Biomass, agro-residues, segregated MSW, and RDF pellets are used in the gasifier to produce Syngas. This gas can then be used for thermal or power generation purposes.
• PYROLYSIS: Pyrolysis is a process that uses heat energy to break down combustible materials in the absence of oxygen. It produces a mixture of combustible gases (e.g., methane, complex hydrocarbons, hydrogen, and carbon monoxide), liquids, and solid residues.

Challenges Encountered by Waste-to-Energy Projects

• Low calorific value: Solid wastes in India have a low calorific value, primarily due to improper segregation.
  • The calorific value refers to the heat energy released during the complete combustion of a unit mass of fuel.
  • For instance, the calorific value of coal is around 8,000 kcal/kg.
  • However, the calorific value of mixed waste in India is around 1,500 kcal/kg, rendering it unfit for power generation.
  • Mixed wastes consist of biodegradable waste that has a high moisture content and hence, cannot be used for power generation.
• High costs of energy production: The cost of producing power from waste is about ₹7-8/unit, whereas the cost at which the electricity boards of the States purchase power from coal, hydroelectric, and solar power plants is around ₹3-4/unit.
• Other issues: Other key challenges faced by waste-to-energy plants in India include unrealistic expectations, improper assessment and characterisation studies, and neglect of on-ground realities while establishing such plants.

The Way Forward:

In India, the total estimated energy generation potential from urban and industrial organic waste is approximately 5690 MW. This could significantly boost our energy security efforts. Furthermore, WTE plants can play a pivotal role in battling global warming and climate change. They can also help mitigate various types of pollutants, thereby safeguarding the environment.