Landfill gas progresses in the Netherlands
by W van Zanten, Novem, the Netherlands

The extraction of gas from landfill sites has been increasing in the Netherlands since the early 1980s. The exploitation of landfill gas as an energy source has also increased. By mid-1997, around 75% of the sites extracting gas were using it profitably, mainly for electricity generation.

Background

Landfill gas is produced from organic waste as it decays in a landfill site. The gas consists of up to 60% methane and 40% carbon dioxide. If no precautionary measures are taken, the gas escapes uncontrolled into the atmosphere and presents a hazard to the environment. In particular, methane is a flammable and explosive gas that can asphyxiate humans and animals in confined spaces, and vegetation when it enters the soil.

In addition, methane is a potent “greenhouse” gas. Together with carbon dioxide, it accumulates in the upper atmosphere and causes global warming and climate change. The effect of methane, in terms of global warming, is around 25 times greater than that of carbon dioxide. At the United Nations Conference on Environment and Development in Rio de Janeiro in 1992, and at the more recent Kyoto Conference, governments worldwide agreed to deliver considerable reductions in atmospheric emissions.

Incentives

In the Netherlands, about 35% of all methane emissions originate from landfill gas. Collecting the gas in a controlled way reduces these emissions, as well as those of carbon dioxide. Moreover, if the collected gas is used as a source of energy, offsetting the need to rely on fossil fuels, emissions of carbon dioxide to the atmosphere can be reduced even further.

Landfill gas exploitation can also be financially attractive. Experience in the Netherlands has shown that exploitation of landfill gas as an energy source is a cost-effective technology. Whereas many environmental protection measures cost money, but have no financial benefit, this technology gives a return on investment, with a payback period of 4 to 12 years. This makes it one of the most economically effective methods of preventing methane emissions and lessening the use of fossil fuels.

Extracting landfill gas

A landfill site can produce large amounts of gas.

It is important to start extracting gas as soon as possible after the site has stopped receiving waste, or even while it is still in operation. In this way, emissions of harmful gases are substantially reduced and financial gains maximised. At a typical site, 1 tonne of degradable waste will produce about 13 m3 of landfill gas in the first year. In 40 years, 1 tonne of waste will generate 150 to 250 m3 of gas, with a heating value of 19 MJ/m3.

For a developer of a landfill gas-to-energy project, it is very important to estimate accurately the quantities of extractable landfill gas in a site, in order to establish optimum plant size and project feasibility. Lots of gas may well have been produced before the extraction system is completed and realistically only 50% of the available gas can be extracted. It should be noted, too, that environmental and economic drivers can work against each other in terms of establishing optimum plant size – for maximum environmental benefit, an extraction plant needs to be designed in line with maximum expected gas yield; from a purely economic point of view, design would be based on the minimum expected yield.

There are three possible options for extracting landfill gas: surface collection, horizontal gas wells drilled through the waste, and vertical gas wells. Surface collection or vertical wells may be more appropriate for existing landfill sites, whereas during site build-up either horizontal or vertical systems, or a combination of both, would be preferable. Sometimes, a combination of all three systems is used.

Surface collection – Due to layered compacting and settling of the waste, the horizontal permeability of a landfill body is many times greater than its vertical permeability. As a result, landfill gas leaves the body mainly via slopes. This must be taken into account when designing a surface extraction system, which is installed after putting a watertight top cover over the landfill body. The gas flows through narrow ducts to a few central collection points through the use of so-called “matting”. Alternatively, perforated pipes are installed beneath the cover; in this case the landfill body must settle before gas extraction can begin. This will take some years, during which lots of gas will escape.

Vertical wells – These extraction systems are built while, or after, a landfill site is operating as a waste disposal facility. Shortly after the shutdown of a landfill section, vertical shafts are drilled down through the waste using specially designed telescopic cranes. By establishing the well shaft during dumping, between a third and a half of the costs of constructing a gas well can be saved.

Horizontal wells – The building of horizontal wells must start relatively early in a landfill site’s life, which is a significant advantage. The collection pipes must be laid so that dumping is not hindered. The wells should also be adequately protected. This option is particularly effective on sites where dumping is carried out in layers.

The extracted gas is transported via a pipeline, either on the surface of the landfill or buried just below it, to where it is to be processed. 

Gas utilisation

Gas extraction from landfill sites has been practised in the Netherlands since the early 1980s, to prevent environmental problems in the immediate neighbourhood of the sites. In the same decade, stimulated by increasing energy prices and recognising the commercial potential of landfill gas as an energy source, energy companies initiated the development of gas extraction techniques. Then, at the end of the 1980s, interest in the productive use of landfill gas increased further, for global environmental reasons. As a result of the benefits it offered (ie emissions reduction and reduced reliance on other energy sources), landfill gas exploitation was integrated into national waste disposal policies and favoured by energy companies.

Since 1992 there has been a significant rise in the number of landfill gas utilisation projects in the Netherlands. By mid-1997 some 44 sites were extracting gas, with 32 of these using it profitably. The total volume of gas extracted from all these sites, by the end of 1996, was 170 million m3. Nearly 46 million m3 of this (27%) was flared off and the remainder, some 124 million m3 (73%), was used for energy production.

In the Netherlands, there are three main forms of landfill gas utilisation:

  • direct use of raw landfill gas (8%);
  • upgrading of landfill gas to natural gas quality (20%); in 1996, six sites upgraded 25 million m3 to 12.4 million m3 of natural gas quality;
  • generation of electricity by landfill gas combustion (72%); in 1996, 28 installations with a total generating capacity of 29.5 MW produced 152 GWh of power; of this, 120 GWh was fed into the grid and 32 GWh was used by the generation plants themselves.

To sum up, landfill gas extraction and utilisation has made important strides in the Netherlands over the last two decades, and will continue to provide an environmentally friendly, cost-effective source of energy in the years ahead. Readers may be interested to know that a guidebook on landfill gas extraction and use, based on Dutch expertise, has been produced for the European Commission’s THERMIE programme. It is avaliable from Grontmij Consulting Engineers, Process and Environmental Engineering Division, PO Box 203, 3730 AE DE BILT, the Netherlands. Tel: +31 302 207 911; Fax: +31 302 210 730; E-mail: gmpi@knoware.nl (price NLG 50).

For more information contact the CADDET Dutch National Team in Sittard.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

Enquiries concerning the Newsletter should be addressed to Pauline Toole, Editor, CADDET Centre for  Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.