Hae-Seung Lee* and Nobutoshi Tanaka*
* Department of Environmental and Sanitary Engineering, Faculty of Engineering, Hokkaido University
+ Correspondence should be addressed to Nobutoshi Tanaka:
(Kita 13 Nishi 8, Kita-ku, Sapporo 060 Japan)
Abstract
This study presents a numerical method for calculating gas flow around a sanitary landfill gas vent, when gas flows by pressure. The method described is a three-dimensional compartmental model and includes methods to determine the dimensions for the model. Using the numerical method, the following results are obtained.
1) In the case of gas generation rate (G[s-1]) Xdepth of refuse layer (Lz[m]) …leakage gas flux through final cover soil, qc obtained from Eq. (9), a landfill-gas vent such as that studied in this paper is ineffective.
2) It is pointed out that the landfill-gas vent should be designed by fitting both the landfill gas collection efficiency (¬) and the maximum pressure under final cover soil (¬¬Pmax) .
3) Non¬-dimensional differential pressure ¬¬Pmax, which is defined as ¬¬Pmax/¬¬P*, and ¬ can be mainly estimated using two parameters (Ks/Kx, Lx/Lz), where Lx = half of distance between two vents, Kx = horizontal permeability of refuse layer, Kz = vertical permeability of refuse layer, and Ks = permeability of final cover soil, ¬¬P*߬G (Lz) 2/Kx, ¬ = viscosity[PaEs].
4) ¬¬ and ¬¬Pmax are not influenced by the intermediate soil layers and horizontal daily cover soil layers.
5) Vertical daily cover soil layers strongly influence ¬ and ¬¬Pmax. Therefore soil with high permeability should be used for daily cover soil.
6) When a gas vent is used for collection of both leachate and gas, both 1-¬ and ¬¬Pmax decrease by 80% compared with the case that the gas vent used only for gas collection.
Key words: Sanitary landfill, Landfill gas, Gas vent, Darcy's law, Landfill-gas collection