Methane Collection Efficiency of Horizontal Landfill Gas Collectors

Pumping test and closed flux chamber technique were used to evaluate the performance of horizontal landfill gas collection system at the Rachathewa sanitary landfill, Samutprakan, Thailand. Two investigated areas consisting of three horizontal extraction wells each with a total length of 150 meters with a well spacing of 15 m were used. The closed flux chambers were used to measure the surface landfill methane emissions before and during pumping tests. Pumping tests were done for a period of two weeks. The gas adjustment was tuned to maintain landfill gas (LFG) quality of greater than 50% CH₄ and less than 2% O₂. Portable landfill gas analyzer and pre-calibrated orifice plates were used to control composition and collection rates of landfill gas from the collection system, respectively.

The average spatial methane emission rate without extraction process was 82 g/m²/d and with extraction process was 8.5 g/m²/d. The results showed that the spatial distribution of methane emissions without extraction process is very high and is reduced when the extraction process is applied. The efficiency of horizontal landfill gas extraction system was markedly above 80%. The collection efficiency from this study can be used for evaluation of landfill gas to energy projects. Furthermore, from the methane emissions data, it is recommended that in order to distribute suction force into the middle area to improve the collection efficiency, the position of wellhead should be offset about 10 to 15 meters from the end of collector. Thus, the collection of LFG by forced extraction would be an effective option in order to utilize LFG as well as reduce the global warming and local air pollution problems.