Landfill Gas to Renewable Energy
Landfill gas (LFG) is a natural byproduct of the decomposition of organic waste in landfills. It consists of methane, carbon dioxide, and other organic compounds. Methane (CH4) is a significant component of LFG that is more than 25 times as potent as carbon dioxide (CO2) at trapping heat in the atmosphere. Methane is a potent greenhouse gas (GHG) and a significant contributor to global warming. While LFG can be harmful to the environment, it can also be harnessed as a valuable source of renewable energy. Many landfills collect and treat LFG to generate electricity or heat while reducing environmental impact.
- Gas Generation: When organic materials, such as food waste and yard clippings, are disposed of in landfills, they decompose under anaerobic (low-oxygen) conditions. As a result, they produce methane gas as a byproduct.
- Gas Collection: To mitigate the release of methane into the atmosphere, landfill operators install a network of gas collection systems. These systems consist of pipes and wells that are strategically placed throughout the landfill to capture the methane gas as it is generated.
- Gas Treatment: The collected landfill gas may contain impurities, such as moisture, volatile organic compounds, and siloxanes. Before it can be used, the gas undergoes treatment to remove these impurities and ensure its quality and safety.
- Gas Utilization: Once treated, the methane gas can be utilized in several ways:
- Electricity Generation
- Heat Generation
- Renewable natural gas
According to the EPA, around 68 percent of the energy projects that use landfill gas in the United States make electricity to power homes, businesses, or even sold to the power grid. There are different ways to make electricity from landfill gas, like using engines, turbines, microturbines, or fuel cells. The most common way is to use a reciprocating engine because it's not too expensive, works well, and matches the amount of gas that comes out of landfills. Gas turbines are used for bigger projects, while micro-turbines are used for smaller amounts of landfill gas.
Some projects use landfill gas to make both electricity and heat, which can be steam or hot water. These projects are called cogeneration or combined heat and power (CHP). They can be found in places like factories, businesses, and schools. Using engines or turbines in cogeneration projects is a good idea because it makes the projects more efficient and saves energy.
A small percentage of projects use LFG to replace other fuels like natural gas, coal, or fuel oil. They use it in things like boilers, dryers, kilns, greenhouses, and other heating equipment. Instead of throwing away the gas, they send it through pipes to nearby customers who use it as fuel. They only need to do a little bit of cleaning and filtering, and making some changes to the combustion equipment.
Heat generation is considered medium-Btu gas which is a type of LFG. There are many different industries that use LFG, like car manufacturing, making chemicals, processing food and drinks, making medicine, producing cement and bricks, treating wastewater, creating electronics, making paper, producing steel, and even in places like prisons and hospitals.
Renewable natural gas
LFG can be transformed into RNG by changing the amount of methane in the gas and reducing the levels of CO2, nitrogen, and oxygen. RNG can be used instead of regular natural gas, whether it's for pipelines, compressed gas, or even as a liquefied natural gas (LNG).
To make RNG, landfill gas needs to be captured and upgraded to comply with pipeline specifications. This means getting rid of almost all the moisture, carbon dioxide, nitrogen, hydrogen sulfide, siloxanes, and other chemicals in the gas. There are different technologies (companies) to do this, and each one has its own advantages. The best method depends on things like how much it costs to set up the equipment, how much it costs to run it, and how much methane we can recover.
Once we have RNG, we can use it in different ways.
- Create heat or electricity
- Inject into natural gas transmission or distribution pipelines
- Use it as fuel for vehicles as compressed natural gas (CNG)
- Use the RNG locally at the site as needed
- Send it to another place where it's needed