Biogas Technology Limited

Development of Low noise landfill gas flare

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Courtesy of Biogas Technology Limited

Summary: Increasing requirements of the environmental standards and planning permission conditions create more challenges to the equipment providers. Environment Agency guidance demands low emission levels and local planners put low noise levels in their conditions for landfill sites. Achieving both at the same time with conventional equipment was found problematic. Biogas Technology has developed a new flare based on innovative type of burners. These burners characterise with significantly lower noise levels in comparison to commonly used pre-mix jet burners. Although the burners had some use in other, non-landfill applications, there was no experience of using them on relatively difficult and variable fuel like landfill gas. Theoretical considerations followed by practical tests in situ resulted in satisfactory solution and new type of flare, compliant with the current market demands.

1. Introduction
Matching low emissions and low noise posed significant technical challenge. First requirement points towards improvement of mixing of the fuel and combustion air, i.e. developing standard pre-mix burners that by their nature are noisy. The second demand suggested completely opposite direction, i.e. going back to open flares with quiet diffusion type flame. Initial stage of development work entailed improvements of the existing flare. However it was realised after several experiments that the noise level cannot be reduced to satisfactory values. Most difficult issue was low frequency noise that resulted from both pre-mix burners and resonance of the stack. On the next stage several academic organisations were approached with negative result. Their proposals contained interesting theoretical points nevertheless somehow remote from practical solutions that could have been achieved in relatively short time. Proposed R&D programmes were costly, time consuming and did not give guarantees that the desired end effect can be achieved. The third stage entailed involving specialist combustion companies. Several proposals were evaluated; however it became obvious that the level of understanding of the specific combustion parameters of landfill gas was not sufficient. Eventually, it was decided to select most promising option, based on new, patented burner. The burner initially was scaled down, extensively tested in the field, and then incorporated into full scale plant. Along with the practical experiments, some aspects of combustion were investigated using academic potential and Computational Fluid Dynamics software. This was the only approach that gave an opportunity to achieve tangible results in realistic timescales, resulting in marketable product.

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