In 2007, COSTELLO provided engineering services to the Microgy biogas plant in Stephenville, Texas. This plant was the largest plant in the United States to produce pipeline grade biomethane from dairy cow manure.
The Microgy plant converted dairy cow manure and other organic matter into biogas using an anaerobic process. The bacteria were thermophilic. The biogas produced was treated and converted to biomethane that was injected into the natural gas sales pipeline.
Incoming manure from neighboring dairies and other organic matter was treated in eight digesters. One heater will maintain temperatures in the digesters to allow for optimum production of biogas. This biogas was composed of 60% methane (CH4), 40% carbon dioxide (CO2) and trace amounts of other gases including hydrogen sulfide (H2S). These produced gases will exit the digesters through a compressor that provides a draft on the eight digesters. The gas flows to an amine unit and multi stage reciprocating compression system. The amine unit removed almost all of the H2S and CO2. The gas was then dehydrated in a glycol unit before finally entering the natural gas sales pipeline.
Reject gases from the amine unit, H2S and CO2, were directed to a biofilter that converted the H2S to weak sulfuric acid and the CO2 was emitted to the air.
The effluent in the digesters was discharged from the digesters per requirements of the Wastewater Division in Texas. A flare was an integral part of the entire system to burn off gases in emergency situations such as when the downstream upgrading system was inoperative but the digesters were still producing gas.
Later on, COSTELLO designed a system to take waste heat from the modular amine unit and supply this to the digesters to maintain the temperature of the digesters in the winter time.
The digesters were supplemented with waste glycerin from a local biodiesel plant.
The plant was eventually sold to Element Markets, in Houston. As the price of natural gas dropped the biogas plant became uneconomic to operate. It was eventually shut down and the equipment auctioned off.
This was a sad day for renewal energy because the engineering effort and money put into the project was lost. However, thinking minds have changed since a decade ago and COSTELLO retains the knowledge gained on this project that can help you with your Biogas plant.