Grantee Research Project Results
Final Report: Pipeline-Quality Methane from Anaerobic Digestion Streams
EPA Contract Number: EPD12037Title: Pipeline-Quality Methane from Anaerobic Digestion Streams
Investigators: Jayaraman, Ambal
Small Business: TDA Research Inc.
EPA Contact: Richards, April
Phase: II
Project Period: June 1, 2012 through May 31, 2014
Project Amount: $300,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2012) Recipients Lists
Research Category: SBIR - Waste Management and Monitoring , Small Business Innovation Research (SBIR)
Description:
Large farms and feedlot operations produce large quantities of manure in a small area. Installing anaerobic digester units capable of producing pipeline quality methane at each farm or dairy could be instrumental in eliminating the difficulties associated with the transport of manure off site, be a source of heating and electricity, and significantly reduce disposal costs and operating expenses for the animal farms. If consumed properly, use of manure-derived fuels can also protect against environmental problems such as groundwater leaching and the greenhouse gas (methane) emissions associated with land filling of the farm wastes. The use of anaerobic digester gas reduces the amount of methane emitted into the atmosphere and provides a new and untapped resource of energy.
TDA Research, Inc. (TDA) set out to develop a low cost biogas purification system for upgrading the biogas produced from farm wastes to pipeline specifications. TDA’s system consists of a low cost two-stage process that removes a wide variety of contaminants from the gases produced by any anaerobic digester. The contaminants removed include inorganic sulfur, organic sulfur, siloxanes, and bulk gases such as CO2, and moisture, producing a product that is greater than 95% bio-methane. The first stage is based on a low-cost, high-capacity and expendable sorbent called SulfaTrapTM that simultaneously removes sulfur and siloxane down to ppb levels. The second stage is a vacuum swing adsorption system based on a regenerable mesoporous carbon media modified with surface functional groups that reduces the CO2 and H2O concentration in the biogas to pipeline specifications. The vacuum swing adsorption process results in a low methane loss; 90% of the methane entering the separation unit is sent to the pipeline. Further, the unit has very low operating and capital costs.
This technology will enable the animal and dairy farms to solve a major waste “manure” handling problem. This will also provide a cheaper way to upgrade the biogas to a high-value fuel, pipeline methane that can be exported from the farm. It will also find use in waste water treatment or any other facilities that may use anaerobic digestion and want to sell pipeline quality natural gas instead of burning the gas on-site.
Summary/Accomplishments (Outputs/Outcomes):
In this Phase II project, we continued to improve the sorbent properties, optimized the sorbent formulation and scaled up the preparation batch size to larger scale using high throughput production equipment. These included a continuous rotary furnace, roller ball-mill, and screw extruder. As part this Phase II SBIR project, we built a sub-scale prototype 3-bed VSA unit to demonstrate the system performance in real biogas and to optimize the VSA cycle parameters. The system was capable of unattended 24/7 operation and achieve more than 90% methane recovery with methane purity in excess of 96%.
TDA’s VSA based biogas purification system was demonstrated in conjunction with a food waste anaerobic digester run at the U.S. Air Force Academy (USAFA) in Colorado Springs, CO. This demonstration was carried out in collaboration with our field test partner CDM Smith. The field tests were funded by Department of Defense’s environmental technology demonstration and validation program (ESTCP Project Number ER 200933) while the initial operation of the VSA unit in the field to optimize the VSA cycle parameters in real biogas was funded by EPA SBIR project (EP-D-12-037). The two projects complemented each other in demonstrating the waste-to-energy system that converts organic waste to high purity methane that can be used for a variety of uses, including pipeline introduction and vehicle transportation. In this demonstration, TDA’s pilot scale biogas purification system was installed and tested with biogas generated via anaerobic digestion of a variety of food wastes, including pre- and post-consumer food waste, waste cooking oil, and grease trap waste to produce pipeline quality bio-methane. The sulfur in the raw biogas was typically around 1,000 – 1,500 ppm H2S with trace amounts of organic sulfur compounds. The SulfaTrapTM-R7 desulfurization sorbent removed the sulfur compounds to less than 0.25 ppmv.
We initially carried out breakthrough tests with the CO2 sorbent beds in the field. We used desulfurized food waste derived biogas to measure the capacity of the saturated VSA adsorbent beds, which was above 4.4% wt. CO2. We then optimized the VSA cycles in the field, and the optimized VSA cycle scheme was used to produce high purity bio-methane with a methane recovery greater than 90%. VSA cycle schemes with both feed end and product end pressurizations provided sorbent CO2 working capacities of 2.8% wt., and the CO2 concentration in the bio-methane product was reduced to less than 0.5% by vol. The dew point of the biogas was reduced from 10-15°C to less than -40°C, providing essentially a dry bio-methane product. The methane purity of the bio-methane produced was confirmed by a CO2 probe and an IR based methane analyzer. We operated the biogas purification system for a total of 54 hours, purifying more than 3,620 SCF of biogas to produce bio-methane with greater than 90% methane recovery.
Finally, we carried out a design for a VSA unit that is sized to process 1,000 m3/day of biogas with a composition of 65% CH4, 35% CO2 (on dry basis) that is saturated with water at 24°C. We estimated the vacuum power requirement to be 7.3 kWe, the sorbent bed size to be 300 L/bed, the operating power cost was $0.04 per m3 CH4 produced and the total operating cost including the sorbent replacement cost was $0.08 per m3 CH4 produced with a methane purity and recovery of 99.5% and 80.3%, respectively. The methane recovery can be further increased to 90% or above by relaxing the methane purity to 96%+% and increasing operating power cost to $0.05 per m3 CH4 produced, which results in a total operating cost (including sorbent replacement) of $0.09 per m3 CH4 produced.
Conclusions:
TDA’s VSA based CO2 separation unit provides a novel cost effective solution for upgrading the biogas produced from farm wastes to pipeline specifications. TDA’s VSA system has the advantages of high-effectiveness, lower-cost, small size and portability. Specifically, TDA’s vacuum swing adsorption process results in a low methane loss (95+% of the methane entering the separation unit is sent to the pipeline) and the rest of the methane is used to generate power and heat for the ADG and VSA process. TDA’s system also removes moisture from the methane and eliminates the need for a dehydration system. TDA’s VSA system works equally well in the presence of sulfur compounds and moisture unlike commercial adsorption systems. The unit has very low operating and capital costs; on the order of 1/4 the cost of current systems that separate CO2. The size of the VSA unit compared to other gas cleanup systems is also less than 1/2 the size of current technology and the unit can be skid-mounted rather than installed, allowing for portability and low cost (it can be factory built instead of custom or on-site built).
TDA is working with commercial partners to license this technology and is also actively marketing the technology directly to customers through our subsidiary unit SulfaTrap, LLC which provides sulfur removal systems for biogas and other process streams.
Journal Articles:
No journal articles submitted with this report: View all 2 publications for this projectSupplemental Keywords:
Biogas purification, biogas upgrading, bio-methane, pipeline quality, VSA system, CO2 removal system.Relevant Websites:
TDA Research wins EPA award for biogas technology Exit
SBIR Phase I:
Pipeline-Quality Methane from Anaerobic Digestion Systems | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.