Arbejdsrapport fra Miljøstyrelsen, 13/2005 – Optimering af gasindvinding på deponeringsanlæg i Danmark

Optimering af gasindvinding på deponeringsanlæg i Danmark

Summary and conclusions

Summary

In landfills which contain organic material an anaerobic decomposition takes place, and landfill gas (LFG) is produced. The LFG contains approximately 50 % of methane (CH₄), which contributes to the greenhouse effect when emitted from the landfill. Approximately 19 % of the greenhouse gases in the atmosphere are CH₄ and approx. 8 % of these are emissions from landfills, which means that roughly 1.5 % of the global warming are related to emissions from landfills.

For environmental reasons and explosion risks, extraction of LFG was started 30 years ago in the USA. At the same time utilization of LFG for energy purposes was started, as the calorific value is approximately half that of natural gas. Worldwide approximately 1,200 LFG plants are utilizing the LFG for energy purposes today. Of these, roughly 13 billion m³ of LFG are recovered per year, which means that it no longer contributes to the greenhouse effect, but prevents emission of an equivalent of roughly 100 million tonne CO₂ per year.

In Denmark 26 LFG plants have been established since 1985 from which the gas is utilized for energy in gas engine/generator units for CHP production (Combined Heat and Power) or only power production. In some cases the LFG is used in gas burners in connection to boilers for district heating systems. 24 million m³ of LFG was recovered in 2004, which is equivalent to a CO₂ reduction of 160,000 tonnes of CO₂/year.

According to the Danish Climate Strategy, Denmark is to reduce greenhouse gas emissions by 21 % compared to emissions in 1990. Large companies must take care of approximately 50 % of the reduction, and the other 50 % is to be purchased as CO₂ quotas abroad or found from other domestic sources. One of the possibilities is to optimize the extraction of LFG from existing LFG plants or establish new LFG plants on landfills where an extraction system is not required.

The Danish Environmental Protection Agency (Danish EPA) has therefore decided to carry out an investigation of the possibility for optimizing LFG extraction and establishing LFG plants. During the period from September 2004 and until January 2005 LFG Consult has made this investigation, which is presented in the present report.

The report includes the following sections:

Summary and Conclusion:
- An overview of the project and the conclusions and results from the investigation.
Introduction:
- Background for the project, the aims of the project, the Danish Climate Strategy and the target group are described.
ERFA Group for LFG (group of operation managers from the individual LFG plants):
- A description of a group of primarily O&M managers who have until year 2002 exchanged experience and reported monthly operation result from the Danish LFG plants. The intention is to start up these activities again.
Website for LFG plants in Denmark:
- Prepare a new website for monthly reporting data for gas extraction and energy production from the plants. The website will be made by students as their final examination project at the Technical College at Horsens.
International Cooperation:
- A short description of the possibility for cooperation about a website for plant operation data.
Optimizing of existing LFG plants in Denmark:
- All existing Danish LFG plants are described. 14 of these are visited and investigated, and suggestions for optimizing of the gas extraction are described. The resulting extra CO₂ reduction is estimated.
New possibilities for LFG plants in Denmark:
- 6 existing landfills are selected and visited with a view to possible establishment of LFG plants for further CO₂ reduction from Danish landfills.

Conclusion

In 2004 Denmark had a total of 26 LFG plants. From the individual plants between 30 and 700 m³ of LFG are extracted per hour, which results in extraction of approximately 3,700 m³/h or 24 million m³ in total per year. This corresponds to 160,000 tonnes of CO₂ reduction of the contribution to the greenhouse effect, assuming that the total gas amount would be emitted from the landfill if no LFG extraction took place. The total electricity production is 36,000 MWh, and the heat production 38,000 MWh for 2004.

In Annex 1 the details of the production and operation data for year 2002 – 2004 can be found. In Annex 2 gas production and the corresponding CO₂ reduction are shown for all the years where registration for the individual plants has taken place.

For the 14 LFG plants visited and investigated, suggestions for optimizing the extraction are made in collaboration with the operation managers at the plants. Some typical suggestions are mentioned in the following:

When the landfill gets old the gas quality decreases, and in some cases it is so low that it can no longer operate a gas engine. In some cases the LFG plant is stopped for some hours or a day before starting up again, when the quality normally increase after some hours. As a result of this on-off situation, a lot of gas is not extracted, but emitted to the atmosphere. A possible solution is to change the use of the LFG in another system, for example a Dual-Fuel engine, which uses a mix of diesel oil and gas. This mix allows gas of a poor quality, and, yet continuous operation. Some of the existing gas engines can probably also be adjusted to a lower gas quality, even though they cannot operate on the same very low quality as a Dual-Fuel engine.
In some landfills the quality varies a lot in different areas, and therefore it is suggested to connect all the wells with a good quality into one system, and the other with a bad quality into another system. Then each of the systems can be used for different utilization systems or purposes.
Establishment of supplementary gas wells and/or horizontal fascines for gas extraction.
Extraction of gas from the leachate system.
High water level in the well can prevent gas extraction and must be removed with water pumps.
Installation of condensate trap at low points on horizontal gas pipelines, to ensure that condensate does not hamper the gas extraction.
Installation of flow meters or other measurement systems on the gas pipes from the individual wells.
Calibration of gas analyses and gas flow meters.
Daily control of the LFG plant to avoid longer periods with inefficient operation and extraction at the plant.

Most of the suggestions will require new investments, of which many probably will not be done without some means of economic support or other initiatives that can make it interesting for the owners to invest in improvements for optimizing the plants.

The future CO₂ reduction resulting from the suggested improvements for the 14 visited plants is estimated. In Annex 3 the details for the CO₂ reduction from the plants are shown over a five year period from 2005 to 2012. The total yearly reduction from the improvement of the plants is between 24,000 and 44,000 tonnes of CO₂.

The economy for six of the visited plants is estimated, and a cash flow sheet can be seen in Annex 4. All of these have a positive Net Present Value (NPV).

Among other existing Danish landfills without LFG plants, six were visited, and for five of these the possibility for establishing an LFG plant is investigated. The total yearly CO₂ reduction from extraction of LFG is estimated to be between 20,000 and 31,000 tonnes of CO₂.

The economy for two of the new LFG plants is estimated, and a cash flow sheet is presented in Annex 5. One of the plants will have a positive NPV after ten years, but the other plants need economic support to have a positive NPV. If the support is given for the Emission Reduction (ER), it requires approximately 120 DKK/tonne CO₂ to give a positive NPV. In general, it will be difficult to start up new plants without a test pumping to verify the gas prognoses for the LFG extraction. The test pumps probably needs a great deal of economic support to be executed.