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Mass Natural feasibility study funding with MTC grant of $40,000, plus $5,000 match
MTC now Mass Clean Energy (MCE)
Other food waste anaerobic digestion feasibility studies sponsored by MCE at Southbridge and the six dairy farms project
MASS NATURAL PROJECT TEAM
Steve Brunner, P.E., The Brundle Group: anaerobic digestion technology and biogas generation assessment
Richard Gross, P.E.: electrical interconnect assessment
Katherine Gegas: Renewable energy credits
Bruce Fulford: Regulatory assessment
Bob Spencer: Project management, waste stream survey, and tour of AD facilities in Germany
Bill Page: Integration with existing operations at Mass Natural
MASS NATURAL COMPOSTING FACILITY
MASS NATURAL’S OPERATION
Composting pads and a detention basin for runoff control
Composting is accomplished by static pile and turned windrows
Mass Natural recently purchased two in-vessel composting systems that have expanded the range of materials composted
MN also has a vermicomposting operation to produce vermicompost, as well as red wiggler worms which are offered for sale through the MDEP web site
MATERIALS COMPOSTED SINCE 1987: 23 YEARS OF OPERATION
Paper mill sludge, or short paper fiber
Chicken and horse manure
Industrial food waste from processors of cranberries, juices, soy, fish, bakeries, FOG
Animal mortalities from former chicken egg farm at Mass Natural and as emergency disposal site for MDEP
Numerous TRIALS with commercial food waste from restaurants and supermarkets (ALWAYS too much inorganic contaminants!!!)
EXISTING PERMITS AT MASS NATURAL
Solid Waste Facility Site Assignment from the Town of Westminster Board of Health
Solid waste composting permits from the Massachusetts Department of Environmental Protection
Agricultural composting registration from the Massachusetts Department of Agricultural Resources.
MASS NATURAL COMPOST PRODUCTS
“ Top Shelf” organic loam, a blend of compost, sand, loam is distributed by a number of garden centers
Compost is distributed by a number of garden centers
Vermicompost and red worms for MDEP and garden centers
Products have been used by the landscaping industry for new lawns, organic lawn care, and athletic fields
Wetland replication projects
Landfill cap vegetative cover
HIGH PROFILE COMPOST PROJECTS USING MASS NATURAL PRODUCTS
U.S. Army Corps of Engineers wetland reclamation
New England Patriots Foxboro Stadium playing field reconstruction
MIT’s Steinbrenner Stadium in-field soil
Boston Convention & Exposition Center tree plantings
Clay tennis court soil mix at a private resort on Martha’s Vineyard
Bank stabilization project for the Mass DEP in Worcester, MA
Asian Longhorn Beetle control project in Worcester County: loam for tree removal area
Existing permits to compost organics;
Under-utilized, existing buildings within permitted area
Local electrical distribution line is capable of receiving considerable current from an on-site engine generator;
Existing equipment (front-end loaders, rotary drum aerobic compost vessel, agitated bay compost system, deck screens, trucks, etc.) and personnel to handle large volumes of organic material;
Many years of experience with, and understanding of, the local organics market;
Compost the dry fraction of the digested effluent to add value to its current product;
6 former chicken houses with concrete pads 65 feet wide by 450 feet long, which may be suitable as a floor for some portion of a new AD facility
A 9,000 sf former egg processing/packaging/storage facility
Electrical building with 3-phase power
Existing padmount distribution transformer that is rated 1,000 kVA, sufficient to export the entire 848 kW output from the proposed anaerobic digester
Water supply wells
WET VS DRY TECHNOLOGY OR LOW SOLIDS VS HIGH SOLIDS
Project started by looking at both wet and dry fermentation systems
Decision to not pursue wet fermentation due to the fact that there is no sewer connection available at Mass Natural to handle the significant amount of liquid wastewater that would be generated by a wet fermentation system
Although the liquid wastewater can potentially be land applied, that scenario would have required construction of very large holding tanks, and then contracting for land application, something Mass Natural is not prepared to do at this point in time.
FEEDSTOCKS FOR HIGH SOLIDS ANAEROBIC DIGESTION
Approximately 52 tons/day
Solids Content 62%
Volatile Solids 88% of Total Solids
Ammonia/Ammonium Concentration: 3,777Mg/l
Biogas Generation: 480 m3/hour
Methane Content 62%
Electrical Output Potential 1,109kW
Based on engine-genset electrical efficiency of 36.3%
COMPARISON OF BIOGAS OUTPUT FROM TECHNOLOGY PROVIDERS
At full output, the Jenbacher JS3 316 engine genset has a heat rate of approximately 9,400 Btu/kWh, which translates to an electrical efficiency of 36.3%.
Given typical operations and maintenance schedules, one can expect an engine genset to operate at full capacity a maximum of 90% of the hours in a year
A dry digestion system will typically use about 7.5% of the rated electrical output to run the pumps and controls of the plant
Mass Natural can expect to export a maximum of 6,128,496 kWh/yr.
Mass Natural can benefit from the thermal energy released from the waste heat from the engine
The combined heat that can be captured from the engine jacket is about 1.95 MMBtu/hr
The amount of heat that can be captured from the exhaust stack is about 1.9 MMBtu/hr
A potential use of the heat is to dry incoming feedstocks
A rotary drum dryer that would be appropriate at Mass Natural would have a thermal efficacy of about 60%
For each 4 MMBtu/hr of heat available, a dryer can evaporate approximately 2,500 pounds of water or 300 gallons
Therefore, in a typical 8-hour shift, MNF could dry 5 tons of material that has a solids content of 35% into 4 tons of material that has a solids content of 45%
Mass Natural could utilize the 3.85 MMBtu/hr available from the waste heat of the engine
Another option would be to uses the thermal heat for a greenhouse
HIGH SOLIDS BATCH PROCESSING
In a batch process, the digester is completely filled with organic matter and closed with a gas- and liquid-tight seal
The digester remains closed until the end of the desired retention time, typically 14 to 28 days
It is then emptied and filled with new material, often a mixture of partially digested material that was just removed and fresh, undigested material
The partially digested material acts a seed material to re-start the digestion process.
LOADING A DRY-BATCH DIGESTER CELL
GENERATOR AT BEKON FACILITY
ADVANTAGES OF HIGH SOLIDS AD TECHNOLOGY
Because dry material is stackable, the digester can be loaded with a front-end loader, which is already at a compost facility
When the material is finished digesting, it still has a relatively high solids content. Therefore, the effluent can be composted without having to remove much liquid from it
Pumping liquid percolate is much easier than pumping slurries, which is the case in most commercial digestion systems. Pumping slurry requires significant horsepower, and the pipes are prone to clogging
To reduce the impact of reduced biogas production that occurs when the digester is re-filled, multiple digester “cells” can be employed so that several are operating at capacity at any one time
If one digester cell has an upset condition, the percolate from it is diluted by the percolate from the other cells, making it easier to re-start a “stuck” cell. In an extreme case, the percolate can be completely isolated and removed from circulation
Dry-Batch Digester Installations in Europe
BEKON AND BIOFERM
Mass Natural solicited proposals from two German companies, Bekon and Bioferm, that appear to be market leaders
Each has more than a dozen operating digesters in Europe and is constructing more each month
Both technologies share a similar process
Digestible, organic matter is loaded into a long, narrow gas-tight building
Once the building is sealed, it is saturated with percolate that contains anaerobic micro-organisms from an active digester
Percolate is periodically drained and re-sprayed into the digester over a period of approximately 28 days
Biogas is collected and a combusted in an engine-genset to produce electricity
Waste heat from the engine is used to maintain an ideal temperature within the digesters
After the prescribed retention time, the digester is opened, the organic matter is removed, and some of it (a third to half of it) is mixed with fresh organic material and loaded back inside the digester
The digested material is actively composted.
BEKON AD TECHNOLOGY
COMPUTER MONITORING OF EACH DIGESTER BATCH
SUMMARY OF FEASIBILITY STUDY
High solids anaerobic process was best suited for the site.
Mass Natural could digest approximately 52 ton per day of mixed organic matter
Sufficient biogas to power an 848-kW engine genset that would export over 6.1 MWh a year of renewable electricity
The system would cost $5.5M to $8.4M
Annual operating budget of about $277,000
Ancillary benefits would include over 3.8 MMBtu/hr of thermal energy for on-site use
Over 3,250 greenhouse gas emissions credits for sale.
Operating costs for the anaerobic digester system were estimated by the Brendle report to be approx-imately $130,000 per year assuming 1.5 full-time equivalent employees
Operating costs for the CHP operation are estimated at $137,000 per year
Total operating cost of $277,000 per year
MASS NATURAL PROJECT REVENUE AND FINANCING FOR $8.4 MILLION FACILITY
Project revenue is estimated at approximately $1.9 million in the first year of full operation. That revenue is based on an average tipping fee of $45/ton of feedstock, and receipt of $0.10/kwh of electricity generated.
Assumptions for project financing were based on 35.5% of total costs financed with solid waste bonds, 23% by investment tax credit, and the balance by equity investment. With this combination of revenue and financing the estimated return on investment, EBITDA (earnings before interest, taxes, depreciation and amortization), divided by pre-debt capital costs, is 13.4%
This yields a payback period of 7.5 years
• Based on laboratory testing of many of these food wastes, it was determined that 20,000 tons per year of food wastes would generate sufficient quantities of biogas to power a 848 kW generator.
• Two technology vendors with numerous, successfully operating high solids anaerobic digestion technologies currently operating in Germany have technology that is technically feasible for implementation at Mass Natural.
• Sufficient types and quantities of industrial food waste are available within economical hauling distances of Mass Natural’s Westminster, Massachusetts composting facility to supply a 20,000 ton per year high solids anaerobic digestion facility.
• The electrical interconnection from a generator powered by an anaerobic digester is feasible and economical at Mass Natural.
• The Mass Natural site has sufficient space to locate an anaerobic digestion facility
• The current composting operation at Mass Natural would be a complimentary operation for an anaerobic digestion facility
• The regulatory approval process for an anaerobic digestion facility at Mass Natural was determined to be feasible.
• The capital costs for an anaerobic digestion facility at Mass Natural was determined to be between $5.5 and $8.4 million. For a 20,000 ton per year facility this was determined by Mass Natural to be a marginal investment.
• Mass Natural would like to conduct further evaluation to identify less costly high solids dry fermentation technologies.