Risk-based Evaluation of Landfill Gas Flare Efficiency Using Computational Fluid Dynamics (CFD)

Abbassi, Rouzbeh and Hawboldt, Kelly (2012) Risk-based Evaluation of Landfill Gas Flare Efficiency Using Computational Fluid Dynamics (CFD). Project Report. The Harris Centre, St. John's, Newfoundland.

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Abstract

Methane is produced in landfills through the anaerobic digestion of organic material. Methane is a greenhouse gas with 24.5 times the global warming potential when compared to carbon dioxide (CO2). Landfill gas also contains hydrogen sulfide which may account for up to 1 percent by volume of landfill gas emissions and impacts human health even in low concentrations. As a result, landfill gas is typically collected and either flared (to convert methane and hydrogen sulphide to carbon dioxide and sulfur dioxide respectively) or used for power on site. Flaring is typically an incomplete combustion process, producing many other pollutants that may result in environmental and human health impacts. Quantifying these emissions would result in better flare designs and plume dispersion estimates. However, the efficiency of flare combustion is site and flare design specific, making predictions difficult. In this work a Computational Fluid Dynamics (CFDs) model (using Fluent as a tool) was developed to simulate the flow and combustion mechanisms of the flare. The model can be used as a tool in flare design and as a method to ensure an operating flare is working properly. It can also be used to predict dispersed gases concentrations, allowing operators to optimize environmental monitoring stations and flare operations. The model is a function of the input data and therefore critical parameters such as exit gas velocities, stack height and diameter among other parameters must be specified. The model was validated using lab data from published work. A risk assessment model is proposed as part of this work which integrates the CFD model with a risk model.

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