TECHNICAL AND ECONOMIC FEASIBILITY OF UPGRADING DAIRY MANURE-DERIVED BIOGAS FOR NATURAL GAS PIPELINE

The objective of this thesis was to evaluate the current technical and economical feasibility of processing dairy manure-derived biogas to natural gas quality for injection into the natural gas pipeline. Dairy farms across the county and around the world are utilizing anaerobic digestion to treat manure, improve nutrient recovery and generate biogas. Biogas, which consists mainly of methane and carbon dioxide, with smaller amounts of hydrogen sulfide, water vapor and other impurities, can be used in heating and power applications. Biogas can also be used directly as a high BTU value fuel, comparable to natural gas, if processed to remove carbon dioxide, hydrogen sulfide, water vapor and other impurities. In order to determine the processing requirements necessary to transform dairy manure-derived biogas to natural gas quality, a compositional analysis of biogas was conducted. Using gas chromatography to analyze biogas samples taken from Dairy Development International, located near Homer, NY, it was determined that the methane and carbon dioxide content of the biogas does not vary significantly over a 24 hour period. The data suggests that DDI?s biogas composition is approximately 60% methane and about 40% carbon dioxide, with a hydrogen sulfide content ranging from approximately 1,500 to 3,000 ppm. In order for biogas to be suitable for the natural gas pipeline, it must go through a two step process. The first step, known as ?cleaning?, removes hydrogen sulfide and other trace impurities. The second step, ?upgrading?, removes carbon dioxide, which lowers the energy value of the biogas. This thesis contains an overview of processes that can be used to clean and upgrade diary biogas. In order to determine the economic feasibility of processing dairy biogas to natural gas quality, a present worth analysis was conducted, using the following variables: number of cows on the dairy farm, selling price of processed biogas, interest rate and proximity of biogas producer to the natural gas pipeline. The results of the economic analysis show that for all farm sizes considered (500, 1,000, 3,000, 5,000 and 10,000 cows), profit is made, as long as the selling price of the processed biogas is high enough. For example, on a relatively small dairy (500 cows), a profit is made if the processed biogas is sold for $12/MBtu or more, given a low interest rate (3%) and no additional pipeline installation. On 1,000 and 3,000 cow dairies, a profit will not be made unless the processed biogas is sold for at least $6.00/MBtu and $4.00/MBtu, respectively, assuming a low interest rate and no pipeline installation. For a 10,000 cow dairy, a profit is made even if 1 mile of pipeline is installed, as long as the selling price of the processed gas is $4.00/MBtu or above and the interest rate is low. The economic analysis presented in this thesis demonstrates the importance of economy of scale in biogas processing projects, but also demonstrates that smaller biogas producers may be able to sell their processed biogas and make a profit if the selling price is high enough. These initial results are encouraging and future work is warranted for examining the site specific technical and economical feasibility of processing dairy biogas to natural gas quality for the natural gas pipeline on individual farms