December 22, 2010 | General

Centralized Digester Feeds The Pipeline

BioCycle December 2010, Vol. 51, No. 12, p. 42
Catalyst Power’s new digester in Abbotsford, British Columbia is processing feedstocks including livestock manure, silage, FOG and slaughterhouse waste. Pipeline quality biomethane is being sold to the local gas utility.
Diane Greer

IN October, Chris Bush started selling upgraded biomethane produced on his Abbotsford, British Columbia dairy farm to Terasen Gas Inc. (Terasen), the province’s largest provider of natural gas. The project is the first on-farm anaerobic digester in British Columbia (BC) and Canada’s first to upgrade biogas for pipeline injection. Phase one of the $5.5 million facility is expected to produce 300-gigajoules a day (over 100,000-gigajoules/95,000-mmbtu per year) of biomethane, enough to supply more than 1,000 homes for a year.
Bush started work on the project over four years ago after reading a Popular Science article about a Vermont farm generating electricity from biogas produced in a digester. “Something that I can’t completely explain lit,” he says. He became obsessed with the idea and started researching technologies and the economics of the process. At the time Bush was working on a real estate development project and did not own a farm. He ultimately formed a company, Catalyst Power Inc, Abbotsford, BC, Canada, to develop the project.
Analysis quickly showed that using biogas to generate electricity in a cogenerating system was not economic in the province. “Seven cents a kilowatt-hour is all we have to work with here while the cost of producing the energy is probably in the 18 cent range,” Bush explains. He started looking into biogas upgrading technologies to produce pipeline quality biomethane.
Terasen, the local gas utility, agreed to a multiyear contract to purchase pipeline quality biomethane produced by Catalyst. The utility sees the project as an opportunity to offer a renewable and carbon-neutral energy source to its customers. “Terasen was excited and eager to support the program from the very beginning,” Bush says. “They have been absolutely fantastic.”
On the other hand, finding a farmer willing to work with Bush on his anaerobic digestion system proved difficult. “We understood what was required to do a project like this, but frankly at the time the consensus was that you can’t do anaerobic digestion in BC,” he says. “So no existing farmers were willing to come along side.”
Realizing he needed to make a bold move to insure that the project happened, Bush sold his house and just about everything else he owned to fund project development and purchase a dairy farm in Abbotsford. The location was ideal because of the proximity and number of dairy and chicken farms in the immediate area, and access to a nearby Terasen pipeline.
A dearth of regulations and guidelines for producing biomethane from organic wastes in British Columbia represented one of the biggest challenges to the project. “Literally when we got started there were no guidelines,” Bush says. “It was an absolute and complete wilderness. That’s why our proposals included established best practices from Europe.” Navigating through the regulatory maze slowed the project. “I was surprised at how long it has taken to get here,” he adds. “We are over two years behind schedule.”
Bush received much needed validation for his idea when the project received a $1.5 million grant from the provincial government’s Innovative Clean Energy fund in July 2008. Remaining funding came from a shareholder group that raised $1 million in private equity and a bank loan.

Bush selected PlanET Biogas Solutions in St. Catharines, Ontario, Canada, to supply the mesophilic anaerobic digestion (AD) system for the project. PlanET is the Canadian partner of PlanET Biogastechnik GmbH in Verden, Germany, which has installed over 200 digesters – 160 plants in Germany and the rest in Europe and Asia. The five-year old Canadian operation recently started work on its sixth digester project in North America.
“We did a lot of research on the different choices and suppliers,” Bush explains. “We selected PlanET since they had a lot of experience with mixed feedstocks, especially poultry manure. In the Frasier Valley where our project is located, poultry manure is a significant issue.”
The AD system is composed of two primary and one secondary complete stirred tank reactors (CSTR) operating in series at 99°F (37°C). A fourth tank stores spent effluent. The reactors and storage tank each measure about 20-feet high and 79-feet in diameter and have a capacity of 2,700-m3 (over 700,000 gallons). When fully operational the system is designed to accept 140 tons/day of feedstocks.
The reactors are constructed with concrete walls embedded with heating pipes and a double roof system supported by wooden beams. The inner flexible polyethylene roof captures the biogas in the headspace of the digester while the outer PVC roof protects the structure from the elements. The wooden roof beams enable thiobacillus bacteria to grow when a small amount of air or compressed oxygen are injected into the headspace of the digester. The bacteria convert hydrogen sulfide (H2S) in the biogas into water and elemental sulfur. The elemental sulfur forms into stalactites that hang from the beams. “Ultimately the sulfur stalactites drop into the digestate and exit the digester,” explains Matt Lensink, application manager with PlanET.
Three input streams are fed to the primary reactors. Liquid manure from dairy cows is pumped directly into the reactors from a holding tank. Dry feedstock, such as corn silage and chicken manure, are input with PlanET’s dry feeder technology, which employs an auger to move materials from the hopper into the reactors. Off-farm wastes, such as FOG (fats, oils and grease) and slaughterhouse waste, are delivered to two reception tanks. Pumps draw the wastes from the tanks into a pasteurization system that heats the material to 70°C for one hour as required by local regulations and discharged into the digesters.
“All inputs meet inside the digester,” Lensink explains. “We do all our agitation in the tank with submerged mixers. There is no external agitation or heating.” Retention times average 40 days with wastes processed in the primary digester for about 20 days and the secondary digester for 20 days. The project is designed to reach full digester capacity in two phases. Phase one, currently underway, is expected to produce 800 m3/hour (470-scfm) of raw biogas, Bush says.
Feedstocks will ultimately come from five area farms once the system is fully up and running, and will include manure from about 1,000 dairy cows, 450,000 broiler chickens and 80,000 layers (chickens). These materials are combined with off-farm wastes consisting of FOG and DAF (wash water from meat processing operations containing fats and proteins). “We have approval for 25 percent off farm materials,” Bush explains.
Commissioning and testing the system, which started to produce biogas in October, is underway. “We are in the ramp up process, running at about 25 percent of ultimate capacity,” Bush explains. At present only one primary and one secondary digester are operational.
PlanET’s in-house microbiologist is working with Bush on an ongoing basis to monitor the health of the digesters’ biology. “He has testing equipment on site and we do some tests through a lab to monitor pH, volatile fatty acids and total inorganic carbon levels,” Lensink says. “The parameters need to fall within a range to insure biogas production and quality. The end goal is to maximize gas output but do so in a way that minimizes the risk. This means insuring that the family of microbes develops at a consistent pace and to the point where Chris avoids system disturbances.”

Biogas produced by the digesters must be upgraded and purified to pipeline quality biomethane before it is injected into Terasen’s natural gas pipeline. Upgrading and purification reduces the level of contaminates, such as H2S, particulates, water vapor and siloxanes, and removes CO2 to increase methane concentrations and the energy content of the gas.
Bush selected Swedish-based Greenlane Biogas’ RIMU biogas upgrading plant, which employs water-scrubbing technology in conjunction with pressure and temperature swing adsorption (PSA/TSA) units to upgrade and purify the biogas. Under pressure, H2S, CO2 and siloxanes are more soluble in water than methane. The water scrubber operates by feeding pressurized biogas into the bottom of a 40-ft tall vessel in counter-flow to water sprayed from the top of the vessel. The H2S, CO2 and siloxanes are dissolved in the water drained from the bottom of the tank.
Biomethane exiting the top of the tank goes through a PSA/TSA unit for drying and to remove impurities that made it through the water scrubbing process, explains Sean Mezei, North American president of Flotech Services, parent company of Greenlane. “Water from the scrubber is sent to a flash tank where it is depressurized so that any small amounts of absorbed methane are removed from the water,” Mezei says. The water is then sent to a stripper that removes the other gases dissolved in the water. This is Greenlane’s 40th installation and its first project in North America.
The biomethane is continuously sampled to insure it meets Terasen’s specifications. Remote monitoring enables Greenlane personnel to log into the system and check biomethane quality and system operation. The gas then flows through Terasen’s gas monitoring equipment, which take samples every 30 seconds to insure gas quality meets its specifications before it is injected into the pipeline.
Gas specifications require 96 percent methane, H2S levels under 3-ppm, siloxanes below 1-ppm and the gas dried to a dew point of -50°C. “We are better than spec already and we are still just getting set up,” Bush says. Within two weeks of receiving biogas from the digesters the Greenlane system was producing biomethane that met the utility’s specifications. “Since start-up, we have been a reliable source of renewable natural gas for the gas company,” adds Mezei.
The upgrading plant, designed to process 500-scfm (830 m3/hr) of raw biogas, was producing around 100 gigajoules per day (95 mcf) in mid-November. “We have roughly about one month of actually running the system,” Bush adds. “I am pleased with the performance of the scrubber and Greenlane is very good in terms of support.”

About half of the digestate produced by the digesters will be returned to the farms supplying the feedstock. “We are only allowed to return what is necessary for their nutrient requirements,” Bush says. “So we have to find other outlets for it.”
He is working with a number of fertilizer companies and exploring opportunities in the horticulture and landscaping sectors. “Wherever there is a need for fertilizer manure the digestate has a market value,” he says. “Adding the poultry manure gets the nitrogen numbers up and you have a much better product.” Bush adds that being the first gives his company the ability to create markets. The flipside, however, is that there are no established markets “so this is another area where we need to be pioneers.”
Catalyst Power is also working on strategies to recycle by-products from the scrubbing operations, such as water and CO2, in an onsite greenhouse. “Our intention is to do a bunch of work with micro and macro algae,” Bush explains. Right now he is investigating growing duckweed. “Duckweed has an incredible appetite for nutrients and CO2 and literally cleans the water,” he says. Since it floats, duckweed can be harvested with a rake, a much easier process then harvesting micro algae. The material can be fed to cows and used in a variety of different applications.
Bush is currently focused on getting everything right in phase one before expanding production in phase two. Once everything is stable with the Abbotsford facility, his ultimate goal is to replicate the model and build multiple biogas upgrading plants. “We are looking forward to getting all this stuff done and getting on to the next one,” he says. “Certainly the next one will be so much easier.”

Diane Greer is a Contributing Editor to BioCycle.

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