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Landfill gas is created during the anaerobic decomposition of organic substances in municipal solid waste (MSW) and commercial and industrial (C&I) wastes. Its production results from chemical reactions and microbes acting upon the waste as the putrescible materials begin to break down in the landfill. Gas production starts one to two years after the waste is deposited in the landfill and lasts 15-25 years. The rate of production is affected by waste composition and landfill geometry, which in turn influence the microbial populations within it, chemical make-up of waste, thermal range of physical conditions, and the biological ecosystems co-existing simultaneously within most sites. This heterogeneity, together with the frequently unclear nature of the contents, makes landfill gas production more difficult to predict and control than standard industrial bioreactors for sewage treatment.

 

Due to the continual production of landfill gas, the increase in pressure within the landfill (together with differential diffusion) causes the gases release into the atmosphere. Such emissions lead to important environmental, hygiene and security problems in the landfill.

 

General options for managing landfill gas are:

  • flaring without any beneficial use,

  • burn into boilers to produce heat,

  • burn into internal combustion engines to generate electricity.

 

Landfill Gas composition

 

MSW contains 150-250 kg of organic carbon per ton which micro-organisms convert to landfill gas via anaerobic processes. Landfill gas is approximately forty to sixty percent methane (CH4), with the remainder being mostly carbon dioxide (CO2). Landfill gas also contains varying amounts of nitrogen and oxygen gas, water vapor, hydrogen sulphide, and other contaminants. Some inorganic contaminants, such as mercury, are also present in the gas of some landfills.

 

Collection of Landfill gas

 

In a landfill facility special care shall be taken to prevent greenhouse gas from migrating into the atmosphere while avoiding offensive smells and smoldering fires. The gas must be continuously extracted under controlled conditions. Perforated tubes are drilled into the landfill body and interconnected by a pipework system. The gas is sucked from the landfill with the assistance of a blower. A well-designed gas collection system will flexibly capture the gas from various spots and handful high temperatures, leachate, condensates and air content, ensuring a cost-efficient collection and a stable gas quality. Several engineering companies specialize in this field and offer their services on a worldwide basis.

Advantages of CHP systems utilizing Landfill gas

 

  • Smooth operation despite low heating value and fluctuations in gas composition and pressure.

  • Electrical efficiency of up to 42%, and combined heat and power efficiency up to 90%.

  • Available containerized units with low weight that are easy to move and adjust to changing project capacity.

  • Basic design and support for gas conditioning, if required.

  • TSA: In case of high siloxane load in landfill gas available in-house gas cleaning unit.

  • CL.AIR: Integrated exhaust after-treatment solution complying with country-specific standards.

  • Flexible Contractual Service Agreements (CSA).

  • Alternative disposal of a problem gas while simultaneously harnessing it as an energy source.

  • Revenues from the offer of produced power and heat into the public grid.

  • Carbon credits for reduction of methane releases or special renewable energy tariffs.