SBIR-STTR Award

Current anaerobic digester systems are designed for capturing energy from waste from large herds of farm animals. GHD, Inc., a leading manufacturer of anaerobic digesters, has stated that a minimum dairy herd size for economical implementation of a biogas system is 800 cows. These require turbine or diesel generator sets of 100 Kilowatt size and larger, a limiting factor in economically scaling down these systems. The need exists for a smaller waste-to-energy conversion approach for implementation at farms with herds less than 800 animals. The need also exists for a universal energy conversion system for other solid and liquid waste streams utilizing syngas from pyrolytic reactors, or in some cases, heat from directly combusting solid waste. These can be used for providing combined heat and power for rural homes or small farm plots typical of third world countries. Fluidic microControls, Inc. (FmC) has been developing a variety of technologies for micro energy systems, including ultra micro turbines, air bearings, and micromachined heat exchangers. Most recently, FmC has combined these into a 5 Kilowatt Rankine cycle waste heat recovery system for an on-farm electricity-to-nitrogen-fertilizer manufacturing system, the development of which was initiated with partial funding from the U.S. Department of Agriculture (USDA). The heart of this system is the novel FmC gas-bearing turbo-alternator, which may be cost-effectively utilized with a variety of off-the-shelf boiler, pump, heat exchanger, pyrolytic reactor, and digester technologies in a waste-to-energy conversion system sized for small farm biogas systems. The gas bearing turbo-alternator consists of a supersonic impulse turbine riding on air bearings, a permanent magnet alternator, and compressors that provide fluid power to the gas bearings and pump waste combusting products to follow-on treatment or storage sites. The patent-pending, fluidically damped gas bearing system has been successfully demonstrated at more than 300,000 RPM and operates with much larger, contamination-tolerant flow passages and clearances than other air bearing types, while providing critical damping to the rotating mass system. Nozzles, bearings, turbines and heat exchanger channels are manufactured using proprietary micromachining and laminate assembly processes that have been developed to make compact, cost-effective energy recovery components. The primary goal of this program is to apply this technology to provide an effective energy conversion module for small-farm manure digestion systems, with an ultimate goal of providing a universal energy recovery module that can cost-effectively recover energy from a variety of waste streams, regardless of size. Supplemental

Keywords:
anaerobic digester, farm, biogas, combustion, solid waste, animal waste, micro energy system, waste-to-energy conversion,waste heat recovery, small farm biogas system, SBIR

In 2011, there were 60,000 dairy farms in the US. Of there, 56,600 had herds of fewer than 500 animals. Currently, manure digester installations are only considered economical for herds of at least 500 animals. There require turbine or diesel generator sets of 100 Kilowatt size and larger. The need exists for a smaller waste to energy conversion approach for implementation on small farms were methane is typically released, unburned and unutilized, to the environment. This project evaluates the feasibility of an electrical-power-generating system based upon a steam Rankine cycle, sized and designed to burn untreated digester gas from small animal herds. The system uses a residence-sized boiler, modified to produce higher operating temperature and pressures to improve cycle efficiency. The steam from the boiler powers a unique turbo-alternator spinning on fluidically-damped gas bearings, also energized by system steam. The analysis and studies conducted in Phase I showed feasibility of the steam Rankine system and fluidic bearing turbo-alternator approach. Key features which were analyzed and/or demonstrated are a follows: A Rankine Cycle system may be scaled to herd of only 25 cows. A representative turbine rotor is capable of high speed operation when spinning of fluidically-damped gas bearings. Fluidic bearing operation was demonstrated using system steam. A closed system with fluidic bearings is capable of high efficiency, simplicity, reliability and long life. Electrical power generation efficiency of nearly30% is achievable. Combined Heat and Power (CHP) efficiency greater then 90% is achievable. Price of a Rankin CHP system may be as low as $500/kilowatt. We estimate a market for 90,000 10-kilowatt digester gas to electrical power modules for hears of 500 cows or fewer. Our agricultural CHP unit may be applied to provide all the power needs for the farm or an average home, and it may be simply modified to also burn natural gas. 30 to 50 million homes in North America are candidates for CHP. The high volume potential of the residential market can provide a great reduction in manufacturing costs, allowing us to meet our $500/kilowatt price target for CHP modules for small digesters. The first year Phase II effort will be concentrated on turbo-alternator design and development. A mass-producible, high-pressure boiler and development of a CHP manufacturing and distribution partner will be a new emphasis in the second year as part of the commercializat