LANDFILL GAS TO ENERGY
Convert Waste Solid into Energy or Methane – Natural gas
Hundreds of municipalities across the world have landfills which often produce methane in commercial quantities. By capturing the methane and using it to power electrical generation, or cleaning it and sending it to a pipeline, energy is saved and waste reduced.
This solution is most effective if a thermal load, such as a boiler or incinerator, is close-by. The process involves collection and some level of clean up of the landfill gas. The gas is then piped to the thermal load for use as boiler or burner fuel.
This is the most common Landfill Gas to Energy (LFGE) project using Steam Turbines to convert Boiler waste into free electricity. Electric generation is a proven concept with many facilities that have been in operation for over 20 years.
Each million tons of Municipal Solid Waste is equivalent to:
- Approximately 432,000 cubic feet per day of landfill gas and 800 kilowatts of electricity
- Is composed of about 55% Methane and of about 45% Carbon Dioxide.
In order to get rid of MSW, plants have been designed based on “COMBUSTION”, the so-called “incinerators”.
- These plants burn the waste and the heat generated is converted into electric energy. In incinerators, the combustion reaction is carried out at temperatures (> 800 °C).
- The truck discharges waste in a hole. A spider crane transports the waste on grates, where it burns up. Ash and metals residuals are collected from the bottom. The hot fumes are in contact with a heat exchanger and the steam generated is discharged into a turbine, which moves an alternator. More ash (so-called “flying”) is collected from the exchanger bottom. Air control systems follow the exchanger and purified fumes are released into the atmosphere.
» Emissions from the combustion process are controlled using state-of-the-art spray dryer absorbers, also known as dry scrubbers, to control acid gases, heavy metals, and organic pollutants; fabric filter bag houses to collect particulate matter; selective non-catalytic reduction systems to control ozone-forming nitrogen oxides; and activated carbon to control emissions of mercury and trace organic emissions.
» After the garbage is completely processed, ferrous metals are separated from the residue. As a result of the combus¬tion and metals recovery processes, the volume of incoming garbage is reduced by more than 90%.
There is another way to get rid of MSW called “GASIFICATION”
It is a new process where waste is deposited in a closed container and burnt up at temperatures between 300 and 500 °C in an atmosphere with low oxygen content (approximately 6% in volume).
As a consequence, carbon bonds in complex molecules are broken and simpler chemical compounds are obtained. Thus, a “molecular dissociation” process is carried out, which brings to the formation of the so-called “syngas”, mainly a mixture of carbon monoxide and carbon dioxide, hydrogen and methane.
Purified syngas is a very good fuel, clean and flexible, quite comparable with natural gas. Consequently, it can be converted into electric power and the conversion modes depend only on the end-user’s needs.
- Burn it in a boiler to obtain heat: Boiler
- Use it as a fuel in a gas engine: Gas engine
- Use it in a gas turbine: Gas turbine
- Reform it to hydrogen to be used in a fuel cell