Heat Extraction from Municipal Solid Waste Landfills

Abstract

Municipal solid waste in landfills has been shown to reach temperatures of greater than 50C for more than 20 years due to the activity of methanotropic bacteria. Other landfills with industrial or mining wastes may reach even greater temperatures. The internal heat generation in landfills provides an interesting renewable heat source that can be exploited for heating of nearby buildings or infrastructure. This paper will first present the results from a series of thermal response tests using a heat extraction boundary condition on horizontal geothermal heat exchangers installed at three depths within a municipal solid waste landfill in San Diego, CA. These tests were performed primarily to evaluate the thermal properties (thermal conductivity and specific heat capacity) of the waste at different depths using analytical solutions for horizontal geothermal heat exchangers. The thermal properties are a function of depth due to the distributions of density, initial temperature, and degree of saturation within the waste. The results from the tests are also useful to provide validation data for more complex numerical simulations involving coupled heat transfer and water flow in unsaturated geomaterials. Once validated, these simulations can be used to consider the effects of different initial conditions with height from municipal solid waste for the design of geothermal heat extraction systems in this material.