Article: Overview and benefits of landfill gas-to-energy conversion systems

About the Author

Rabih Hayek is an Electrical Engineer (Lebanese University 2001 graduate) who achieved an interesting large experience in electrical design, quotations & tenders proposals, detailing and execution for various project (Hydroelectric power plant, industrial and commercial projects). He currently holds the position of Senior Electrical Engineer at SPP (Solution Power Partner SAL Offshore / Lebanon) since November 2015, and is a member of the engineering orders of Lebanon and Quebec.

Previously, Rabih accumulated large experience in Canada with SNC-Lavalin, CegertecWorleyParsons and WSP. His theoretical skills and practical approach in solving problems give him the ability to implement functional tactics and ideas, and to achieve his duties at best.

Introduction
There are many forms of renewable energy. Wind and hydroelectric power are the direct result of differential heating of the Earth's surface which leads to air moving (wind) and precipitation (rain) forming as the air is lifted; solar energy is the direct conversion of sunlight using solar thermal collectors; biomass energy is created from landfill gas; geothermal energy ranges from the shallow ground to hot water and hot rock found beneath the Earth's surface, and deeper to the magma; tidal energy is created by the gravitational effect of the sun and the moon on the earth causing cyclical movement of the seas.

In this article, I will be focusing on Biomass landfill gas-to-energy from all the renewable energy sources. Imagine a future where communities are powered by the trash they throw away. Our waste can now be used as a source of renewable and sustainable energy. This happens primarily through two technologies: landfill gas-to-energy and waste-to-energy.

Overview

Landfill gas is a product that is released during the fermentation of organic substances under anaerobic conditions (without oxygen). It is a high-energy fuel that can substitute fossil fuel. Depending upon the landfill design, as well as waste composition, compaction, moisture and several other factors, landfills are available to collect and use this valuable renewable energy source for power generation.

If landfill gas is allowed to escape to atmosphere, methane (CH4) is 21 times more powerful greenhouse gas than carbon dioxide (CO2). Instead of escaping into the atmosphere, the landfill gas can be captured, converted, and used as a source of energy. Using landfill gas can help reduce odors and emissions, and prevent methane from migrating into the atmosphere and contributing to local smog and global climate change. Therefore, its prevention from escaping to the atmosphere and its utilization as a renewable fuel energy source is a win-win situation to the power producers and the communities.

Landfill gas contains roughly 45% to 55% of methane (CH4) and 35% to 45% of carbon dioxide (CO2), 5% to 15% oxygen (O2) and nitrogen (NO2) and minor amounts of other organics and contaminants.

For landfill sites, many factors have to be taken into consideration when selecting the location:

  • The distance from the outer limits of the landfill site to residential area, water surfaces, agriculture and urban areas;
  • The presence of ground water or natural reserves in the area;
  • The geological, hydrological and geo-technical conditions;
  • The risk of flooding, mudflows;
  • The protection of the natural or cultural heritage of the area.

Collection

Landfill gas collection typically begins after a portion of the landfill is closed to additional waste. It can be collected by either a passive or an active collection system. A typical collection system, either passive or active, is composed of a series of gas collection wells placed throughout the landfill. The number and spacing of the wells depend on landfill-specific characteristics, such as volume, density, depth, and area.

Most collection systems are designed with a degree of redundancy to ensure continued operation and protect against system failure. Redundancy in a system may include extra gas collection wells in case one well fails.

Passive gas collection systems use existing variations in landfill pressure and gas concentrations to vent landfill gas into the atmosphere. These systems can be installed during active operation of a landfill or after closure, and use collection wells, also referred to as extraction wells, to collect landfill gas. The collection wells are typically constructed of perforated plastic and are installed vertically throughout the landfill to depths ranging from 50% to 90% of the waste thickness. The efficiency of a passive collection system partly depends on how well the gas is contained within the landfill.

Active gas collection systems include vertical and horizontal gas collection wells similar to passive collection systems. Unlike the gas collection wells in a passive system, however, wells in the active system should have valves to regulate gas flow and to serve as a sampling port. Sampling allows the system operator to measure gas generation, composition, and pressure.
Active gas collection systems include vacuums or pumps to move gas out of the landfill and pipe that gas into the facility.

Treatment

Using landfill gas in an energy recovery system requires some treatment to remove excess moisture and impurities. Once out of the landfill, first the gas is filtered to take out any liquids or small pieces of debris that came up in the vacuum. Next, the gas is compressed until it can be used as a fuel. Then the gas is chilled, using condensation as a way of separating any remaining liquids. Lastly, the gas is filtered a second time and then it’s ready for use. The whole process takes seconds.

Boilers and most internal combustion engines generally require minimal treatment (usually dehumidification, particulate filtration and compression). Some internal combustion engines and many gas turbine and micro-turbine applications also require siloxane and hydrogen sulfide removal after the dehumidification phase.

The cost of gas treatment depends on the gas purity. The cost of a system to filter the gas and remove condensate for electric power production is considerably less than the cost of a system that must also remove siloxane and sulfur that are present at elevated levels in some landfill gases.

Total collection system costs vary widely, based on a number of site-specific factors. For example, if the landfill is deep, collection costs are higher because well depths will need to be increased. Collection costs also increase with the number of wells.

Electricity generation

The three most commonly used technologies for landfill gas-to-energy projects that generate electricity are internal combustion engines, gas turbines and micro-turbines.

Most (>70%) of the landfill gas energy projects that generate electricity use internal combustion engines, which are well-suited for 800 kW to 3 MW projects; multiple internal combustion engine units can be used together for projects larger than 3 MW. Gas turbines are more likely to be used for large projects, usually 5 MW or larger. Micro-turbines are much smaller than gas turbines, with a single unit having between 30 and 250 kW in capacity, and are generally used for projects smaller than 1 MW.

Energy from these generators is sent to a utility grid, which then transfers the power for residential and business use. Think of this whole process as a circle – it starts at your residence and ends at your residence. That’s closing the loop for our environment.

Environment

Converting landfill gas to energy offsets the need for non-renewable resources such as coal and oil, and reduces the emissions of air pollutants that contribute to the local smog and the acid rain. Landfill gas-to-energy projects go hand in hand with community commitments to have a cleaner air and reduce greenhouse effect that causes global warming.

Landfills are in fact the third-largest human-caused source of methane emissions. Methane is a heat-trapping gas and has a short atmospheric life (10 to 14 years). Because methane is both potent and short lived, reducing methane emissions from landfills is one of the best ways to reduce the human impact on global climate change. During its operational lifetime, a landfill gas-to-energy project will capture an estimated 60% to 90% of the methane created by a landfill, depending on system design and effectiveness. The methane captured is converted to water and carbon dioxide when the gas is burned to produce electricity or heat.

By participating in landfill gas-to-energy projects, a country can enhance its image as an environmental leader. Reducing landfill gas emissions by converting them to energy reduces local ozone levels and smog formation, diminishes explosion threats and odors created by the landfill. This makes the area surrounding the landfill a better place to live. A country that uses its landfill gas to generate energy is both a friend to the environment and a leader in ensuring the well-being of its citizens.

Economics benefits

Landfill gas-to-energy projects as mentioned before are win-win opportunities for the power producers and their surrounding communities. Such projects produce profits from the sale and use of electricity, and generate related benefit for communities: involving engineers, construction firms, equipment vendors and end-users.

Much of the project cost is spent locally for drilling, piping, construction, and operational personnel, providing additional economic benefits to the community through increased employment.

Once the Landfill gas-to-energy system is in place, the captured gas can be sold on the energy market as renewable green energy. In so doing, the community can turn a financial liability into an asset.

Conclusion

Solving the problem of biodegradable waste disposal and the treatment of the organic portion of the waste is becoming increasingly urgent in a time of decreasing raw material reserves, increasing energy costs and environmental impact from improper waste disposal.

Even though the electricity created is a product of waste, when compared to fossil fuels like coal and diesel, as well as other renewable sources of energy like wind and solar energy, converting landfill gas into energy has several benefits:

  • A Renewable Source of Energy: generated electricity is often the result of consuming waste materials;
  • A Cheaper Technology: energy production can be carried out through small plants.
  • Large Number of Jobs: work opportunities are created for the community;
  • Little Capital Investment: easy to set up and requires little capital investment;
  • A Constant Energy Output: not dependent on sunlight, wind or other environmental variables;
  • Greenhouse Effect Reduction: this is a major reason why its use has started catching on.

References

  1. Waste – to – Energy in Austria: White book – Figures, Data, Facts – 2nd edition, Vienna, May 2010
  2. http://altenergy.org website. Page: http://www.altenergy.org/renewables/renewables.html
  3. EPA - United States Environmental Protection Agency. http://www3.epa.gov
  4. Energy Justice Network. http://www.energyjustice.net

 

 

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