垃圾填埋场抽气竖井周边气体运移规律研究

Study on gas migration around vertical extraction wells in municipal solid waste landfills

通过建立填埋场抽气竖井周边气体轴对称稳态运移模型,分析了单层和分层垃圾体中气压力分布,并提出"降压百分比"的概念用于判定抽气影响范围,研究了垃圾产气率、气体渗透率、覆盖层厚度、覆盖层气体渗透率、抽气井深度和抽气负压对抽气影响范围和抽气量的影响,获得了竖井深度和井间距的确定方法.分析结果表明,抽气井的降压作用明显,抽气井深度和抽气负压越大,则抽气影响范围和抽气量越大.覆盖层厚度增加或其渗透率降低有助于扩大抽气影响范围和提高抽气量.抽气影响范围随气体渗透率的增加而增大,但随垃圾产气率的增加而减少;抽气量则随气体渗透率和产气率的增大而增加.抽气井深度是控制抽气影响范围的关键参数,建议竖井深度取垃圾填埋厚度的65%～75%,井间距取1.5～2.5倍竖井深度.

An axisymmetric steady-state model of gas transport around vertical extraction wells in municipal solid waste （MSW） landfills was established. Distribution of gas pressure in monolayer and multi-layer MSW landfills was analyzed. The term ＂pressure drop percentage＂ was proposed to determine the radius of influence for a vertical gas extraction well. The influences of gas generation rate, gas permeability of MSW, cover parameters, well depth and exhaust pressure on influence area and gas flow for a vertical well were investigated. The calculation method for depth and spacing of vertical wells was proposed. The results showed that gas pressure in landfill could be significantly reduced by vertical gas extraction wells. Radius of influence and extraction gas flow increased with the increase of well depth and exhaust pressure. It was favorable to expand the radius of influence and increase the gas flow by increasing cover thickness and decreasing gas permeability of cover. Radius of influence increased with the increase of gas generation rate, but decreased with the increase in gas permeability of MSW. Gas flow increased with the increase of gas generation rate and gas permeability of MSW. The well depth is the key parameter to control the radius of influence. It is recommended that the design depth of wells be 0.65- 0.75 times of landfill depth and the spacing of wells be 1.5 - 2.5 times of the well depth.