LANDFILL GAS RECOVERY FOR COMPRESSED NATURAL GAS VEHICLES AND FOOD GRADE CARBON DIOXIDE

LANDFILL GAS (LFG), COMPRISED OF METHANE (CH4) AND CARBON DIOXIDE (CO2) IN ROUGHLY EQUAL PROPORTIONS ALONG WITH MYRIAD TRACE CONTAMINANTS, IS NOW ESSENTIALLY A WASTED RESOURCE THAT COULD PROVIDE LOCALLY SIGNIFICANT SUPPLEMENTALENERGY. 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 CH4, COPIOUS CO2, 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 CO2 FROM LFG. THE PROCESS USES NO SOLVENTS OR SEPARATING AGENTS, FOREIGN TO THE LFG SYSTEM, THAT OFTEN THEMSELVES BECOME ENVIRONMENTAL PROBLEMS. HIGH PRESSURE CH4FOR COMPRESSED NATURAL GAS (CNG) VEHICLES IS SEPARATED BY A SEQUENCE OF COMPRESSION, COOLING, CONDENSATION, AND FLASHINGSTEPS. LFG METHANE IS EFFECTIVELY SCRUBBED CLEAN OF TRACE CONTAMINANTS BY CONDENSED LIQUID CO2. FOOD GRADE CO2 IS PRODUCED BY ONE STAGE OF TRIPLE-POINT CRYSTALLIZATION, A CO2PURIFICATION 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 CO2 AT TEMPERATURES NEAR THE TRIPLE POINT OF CO2, AND BATCH FREEZING EXPERIMENTS SHOULD PROVIDE EVIDENCE FOR THE SHARP SEPARATION OF PURE CO2 FROM THESE LFG CONTAMINANTS.