Research On Coupled Model And Simulation Of Mass And Heat Transfer Of Landfill Gas

With the increase of municipal solid waste, society wide attention has been drawn to the potential hazards and environment problems caused by landfill gas (shorted as LFG) which is the main by-product during the operation of landfill, as well was a significant contaminant. The generation and migration of LFG in landfill and nearby geological area is an complicated dynamic process with non-isothermal condition and fluctuation of temperature two aspects should not be neglected. With consideration of these two aspects and energy transportation during the migration of LFG, a mass and heat generation and transfer coupled model for LFG is developed. Numerical simulation within landfill and around nearby geological area is conducted. The main achievements are as follows:(1) Based on gas seepage theory in porous media and heat transfer theory, a mass and heat coupled model for generation and migration of LFG is established;(2) Numerical scheme of model is given by using Galerkin finite element method, and the reliability of the model is certified under 1-D simulation;(3) 2-D simulation for mass and heat transfer in landfill and nearby geological area is conducted with results show:1) In landfill gas pressure increases gradually into a stable level due to augment of landfill gas at the beginning and the stable production rate of landfill gas in the middle and post period of landfill operation;2) With time moving on, the gas pressure starts to increase at the geological area closing to the landfill.3) Temperature presents a similar variation as gas pressure does in landfill. But in the geological area, there is hardly any augment of temperature.(4) 2-D simulation on gas pressure and temperature in landfill with single vertical extraction well is conducted with results showing that:1) Gas pressure near extraction well is always lower than that of interior part of landfill which forms a distribution of gradual augment of gas pressure from extraction well to the other side of landfill simulation area.2) Temperature near extraction well presents an increase of 20oC to 60 oC since simulation begins which shows that the movement of landfill gas towards the extraction well facilitates the transfer of heat from interior of landfill to extraction side.The above research achievements could be technically supportive to the reduction and control of landfill gas emission and the environmental impact assessment, as well as to the confirmation of the thermal property of all the temperature concerned components of landfill.