Well-to-Wheels analysis of landfill gas-based pathways and their addition to the GREET model.

Waste-to-wheel analysis of anaerobic-digestion-based renewable natural gas pathways with the GREET model.

“…Unlike the LFG pathways already contained in GREET (see Mintz et al, 2010), AD pathways include the bio-methane production step and soil application of AD residue. Therefore, the amount of bio-methane produced is important and can be estimated for a given livestock type as follows:…”

“…Pre-purification removes impurities including corrosive hydrogen compounds, low concentrations (parts per million) of non-methane organic compounds, and water; purification removes CO 2 and increases CH 4 concentration. We examine four major technologies (membrane separation, adsorption, absorption, and cryogenic distillation) and define the process efficiency of NG production, i.e., the energy in the produced NG divided by the sum of the energy in the biogas feed to the pre-purification step and the process energy for pre-purification and purification (Mintz et al, 2010). The electricity for NG production and subsequent processes is assumed to be generated from ICEs powered by prepurified biogas.…”

“…The electricity for NG production and subsequent processes is assumed to be generated from ICEs powered by prepurified biogas. The efficiency of ICEs is assumed to be 35% (Mintz et al, 2010). CH 4 vented or leaked from equipment during AD, NG production or upgrading is a major source of GHG emissions.…”

“…Thus, results for CNG-and LNG-fueled vehicles are compared to those for petroleum gasoline cars and diesel HDVs, respectively. We also assume that gasoline cars achieve the GREET default fuel economy, which is 23.4 mpgge (miles per gallon gasoline equivalent), and that CNG cars are as efficient as gasoline cars (Mintz et al, 2010). For HDVs, we reviewed several sources.…”

“…Because it is chemically identical to fossil NG yet produces far fewer GHG emissions, the blending of relatively small quantities of RNG with fossil gas can provide significant GHG benefits. For example, our previous analysis of compressed NG (CNG) and liquefied NG (LNG) from LFG showed 77-101% reductions in GHG emissions as compared with petroleum gasoline (Mintz et al, 2010). Even blends of 20% RNG and 80% fossil NG were found to yield reductions of 30% or more (Mintz and Han, 2011).…”