From Biological Gases
Landfill gas is created during the anaerobic decomposition of organic substances in municipal solid waste (MSW) and commercial and industrial (C&I) wastes. Depending upon the landfill design and its management, as well as waste composition, compaction, moisture and several other factors, thousands of landfills are available worldwide to collect and utilise this valuable renewable energy source for power generation. If landfill gas is allowed to escape to atmosphere, methane contained within it is a powerful greenhouse gas, 21 times more so than carbon dioxide. Therefore, its prevention of escape to atmosphere and its utilisation as a renewable fuel source is a win-win situation.
For a landfill restoration that prevents greenhouse gas from migrating into the atmosphere while avoiding offensive smells and smouldering fires, the gas must be continuously extracted under controlled conditions. Perforated tubes are drilled into the landfill body and interconnected by a pipework system. Using a blower, the gas is sucked from the landfill. A well-designed gas collection system will flexibly capture the gas from various spots and handful high temperatures, leachate, condensates and air content – thus ensuring a cost-efficient collection as well as stable gas quality. Several engineering companies specialise in this field and offer their services on a worldwide basis.
Landfill gas composition and production rates are primarily affected by the waste that has been deposited in the landfill site. MSW contains 150-250 kg of organic carbon per tonne which micro-organisms convert to landfill gas via anaerobic processes. The gas formation is influenced by a number of factors such as waste composition, landfill storage height and density, air temperature, atmospheric pressure and precipitation levels. Landfill gas production starts one to two years after the waste is deposited in the landfill and lasts 15-25 years. The continuously decreasing landfill gas volume can be compensated by the disposal of additional waste during this period. With a calorific value of 3.5 to 5.5 kWh Nm3 (35-55% methane), landfill gas constitutes a high-value fuel for gas engines that can be effectively used for power generation.
Landfill Gas Component: Composition (by volume)
- Methane (CH4): 35-55%
- Carbon dioxide (CO2): 30-44%
- Nitrogen (N2): 5-25%
- Oxygen (O2): 0-6%
- Water vapour: Saturated
Consequently, 1 million tonnes of MSW generate 1.7-2.5 million m3 of collectable methane, enough to fuel a gas engine capacity of 850-1,250 kWe producing 6,500 to 10,000 MWh of electricity per year. That roughly corresponds to the average power demand of 1,500-2,200 EU households.
The broad range of GE's Jenbacher landfill gas engines is specifically designed to run at full load with high efficiency and high availability, despite a low heating value and fluctuating gas quality and pressure. The high quality and specially designed engine parts resist the impurities that usually appear in this type of fuel. Before the landfill gas can be fed into the gas engines, it needs to be dried and compressed. Severe contaminants such as siloxanes should be removed if exceeding a certain level. Not only will these measures considerably increase the availability of the generator, but they will also reduce the costs associated with operation.
Since landfills are usually located near big cities, emission standards are becoming more and more ridged in many countries. To comply with these standards, the whole system must be managed, beginning with the fuel gas conditions up to the installation of an exhaust treatment service, if needed. Clarke Energy is committed to not only supplying the gas engines, but also offering ancillary equipment and giving support for an integrated solution, from the gas flange to the grid connection.
- Smooth operation despite low heating value and fluctuations in gas composition and pressure.
- Electrical efficiency of up to 42%, and up to 90% efficiency in the case of combined heat and power.
- Low weight containerised units that are easy to move and adjust to changing project capacity.
- Basic design and support for gas conditioning, if required.
- TSA: In-house gas cleaning unit in case of high siloxane load in landfill gas.
- CL.AIR: Integrated exhaust after-treatment solution complying with country-specific standards.
- Flexible Contractual Service Agreements.
- Alternative disposal of a problem gas while simultaneously harnessing it as an energy source.
- Revenues for power and heat production when fed into the public grid.
- Carbon credits for reduction of methane releases or special renewable energy tariffs.
Clarke Energy has installed and commissioned over 550MW of landfill gas generation equipment globally and is one of the leading players in its field. Globally Jenbacher units are applied in over 1,400 landfill gas systems with a total output of approximately 1,400MW. The Clarke Energy and Jenbacher product teams offer an unparalleled breadth of expertise, references and solutions. These plants generate about 11 million MWh of electricity annually, enough to supply more than 2.7million EU homes. In addition, by capturing landfill gas instead of emitting it directly into atmosphere and using if for power generation in place of fossil fuels, these engines can reduce greenhouse gas emissions by about 40 million tonnes CO2 equivalent each year. The amount of greenhouse gas emission savings equals the annual emissions related to nearly 22 million EU passenger cars.