SBIR-STTR Award

Landfill gas (LFG), comprised of methane (CH,) and carbon dioxide (CO2) in roughly equal proportions along with myriad trace contaminants, is now essentially a wasted resource that could provide locally significant supplemental energy. LFG has both explosive and toxic properties that must be mitigated at the landfill site; consequently most installed LFG technology is control oriented and addresses valid safety and environmental concerns. Energy-oriented LFG technology recovers methane as low BTU fuel gas or as high BTU pipeline-quality gas but unrecovered CH,, Copious C02, and various trace contaminants are usually flared or vented. LFG recovery incentives rise or fall in lockstep with the price of pipeline natural gas and have not been attractive in recent years. This project is developing a process that recovers both high pressure CH4 methane and food grade C02 from LFG. The process uses no solvents or separating agents, foreign to the LFG system, that often themselves become environmental problems. High pressure CH, for compressed natural gas (CNG) vehicles is separated by a sequence of compression, cooling, condensation, and flashing steps. LFG methane is effectively scrubbed clean of trace contaminants by condensed liquid CO,. Food grade CO, is produced by one stage of triple-point crystallization, a C02 purification technique previously found to be highly effective in removing a variety of undesirable contaminants typical of coal gasifiers. In Phase I of this project, favorable solubilities are being determined for key LFG trace contaminants in liquid C02 at temperatures near the triple point of C02, and batch freezing experiments should provide evidence for the sharp separation of pure C02 from these LFG contaminants.Anticipated Results/Potential Commercial Applications as described by the awardee:If the project produces favorable results, an economic LFG recovery process becomes feasible which produces high pressure methane for incineration, as pipeline gas, or for transportation. Adoption of these uses have favorable aspects in saving energy, providing saleable byproducts (CH, and C02) and reducing environmental pollution. In addition, the technique can be applied to other waste gas streams, including subquality natural gas, Claus plant tail gas, and contaminated C02 such as flue gas from powerplants.

Landfill gas (LFG), comprised of methane and carbon dioxide in roughly equal proportions along with myriad trace contaminants, is now essentially a wasted resource that could provide locally significant supplemental energy. Research is planned to further develop a process that recovers both high form value methane and food grade carbon dioxide. The process requires no solvents, absorbents, or other physical separating agents that often themselves become environmental problems. Vehicular natural gas (VNG) ties the value of methane recovered from LFG to transportation fuels rather than pipeline gas. The market for VNG is expanding rapidly with the advent of clean air concerns and the push for altemative clean transportation fuel. LFG methane is scrubbed clean of trace contaminants by condensed liquid carbon dioxide. Food grade carbon dioxide is produced in one stage of triple point crystallization. Phase I has established the technical and economic feasibility of the technology. The primary objective of Phase II is demonstration of carbon dioxide purification by triple point crystallization on a scale commensurate with landfill gas recovery applications. Production of approximately 25 tons per day of pure liquid carbon dioxide corresponds to treatment of about 2 million standard cubic feet/day of raw LFG. Secondary objectives are continued expansion of the process data base, examination of final LFG dehydration, and completion of a refined design and economic analysis of the Phase I commercial LFG recovery process.Anticipated Results /Potential Commercial Applications as described by the awardee:The successful separation by triple-point crystallization of foodgrade quality carbon dioxide from waste LFG at 25 tons per day will encourage installation of this technology at local municipal landfills. Local consumers of carbon dioxide benefit by reduced transportation costs, urban environment benefits by capture and utilization of methane, concentration and disposal of LFG contaminants, etc. The process, or portions thereof, would find wide application (benefits) beyond LFG recovery, in the following areas: (1) LFG (energy, commodity gas, environment); (2) subquality natural gas(energy, commodity gases and chemicals,environment); (3) Claus plant tail gas (commodity sulfur, environment); (4) synthesis gas and hydrogen produced via coal gasification, and (5)naturally occurring contaminated carbon dioxide.