MSU Builds Combined Heat and Power System using Anaerobic Digestion
Posted on July 11, 2013 3:21pm
CONTACT: Wei Liao, liaow@msu.edu , 517-432-7205
EAST LANSING, Mich. — Michigan State University officials will hold a ribbon-cutting ceremony Aug. 13 to officially commission and start operations of the South Campus Anaerobic Digester (SCAD). That same day, MSU and MSU Extension will host Keeping it Green: Recycling Waste to Resources to highlight this and other campus-based projects focused on reducing and reusing organic waste. Participants will tour the SCAD, the University Farms composting facility, Anaerobic Digestion Research and Education Center (ADREC), MSURecycling, T.B. Simon Power Plant and the Student Organic Farm.
Anaerobic digestion is a biological process that converts organic materials (called feedstocks) in the absence of oxygen (anaerobic conditions) into biogas. Methane (CH4) and carbon dioxide (CO2) are the primary gaseous components of biogas. Biogas can be burned to generate electricity and heat (steam), or purified and compressed for use as natural gas.
The SCAD is a single-tank complete mixed anaerobic digester. Once operational, the digester will utilize roughly 17,000 tons of organic waste from MSU and the greater Lansing area per year as feedstock to produce biogas that will be used to generate over 2.8 million kWh of electricity per year. Feedstocks for the system will include dairy manure from the MSU Dairy Teaching and Research Center, food waste from several campus dining halls, fruit and vegetable waste from the Meijer Distribution Center in Lansing, and fats, oil and grease from local restaurants. Electricity generated by the system—roughly equivalent to the energy used at Holmes Hall—will be used to power several buildings on South Campus.
Feedstock will be received in two reception tanks, one designated for manure and the second for other materials. Depending on the delivery schedule and the target blend of feedstock, feedstocks will be pumped from each reception tank into a central mix tank, where the blend of feedstocks will be homogenized. The blended material is then pumped through a heat exchanger, which brings the material up to the operating temperature of 100 degrees F, before entering the complete mix anaerobic digester. The digester is an aboveground steel tank with a liquid capacity of more than 450,000 gallons. It is designed for a 25-day hydraulic retention time. A flexible membrane is used to keep the tank air-tight and seal in the biogas. Two hydraulically powered submersible mixers are used to keep the digester contents well blended.
Biogas produced by the digester will be used to power a 450 kW combined heat and power (CHP) system. The electricity that it generates will be used to power buildings on the south side of the campus. Hot water produced by the CHP system will be used to maintain the digester temperature at 100 degrees F and to provide heat to the other buildings at the site. Excess biogas will be destroyed using an integrated flare.
The mix of solids and liquid remaining after digestion (digestate) will be pumped to a solid-liquid separator. Separated solids will be composted; the liquid will be transferred to the digestate storage tank, an aboveground steel tank with a 2.4 million-gallon capacity. An airtight membrane will allow the headspace (the space above the digestate) to be used as biogas storage and reduce odors from the systems. The digestate will be land applied seasonally as carbon-rich fertilizer.
The on-campus digester project will provide many benefits, including renewable energy, emissions reduction, landfill and wastewater diversion, and enhanced fertilizer with few weed seeds and first-year-available plant nutrients.
