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Everything you need to know about - Renewable Natural Gas To The Natural Gas Pipeline

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  • #16
    Katie Fletcher for BioMass Magazine May 05, 2016 - New cogen system triples energy output from biogas at Oregon WWTP

    On 4 May 2016, Clean Water Services, Energy Trust of Oregon and the Oregon Department of Energy formally announced a new cogeneration system that converts wastewater and grease into renewable energy at the Clean Water Services Durham Treatment Facility.

    Since 1993, Durham has operated a 500-kW cogeneration system using biogas from the communities’ wastewater to offset its own energy usage. By replacing this smaller engine with two new Jenbacher 848-kW engines, Durham now has a 1.7 MW cogeneration system fueled by biogas produced from the anaerobic digestion (AD) of municipal wastewater solids as well as FOG from Washington County restaurants, commercial food processors and others. Average gallons of FOG codigested per week will start at 70,000 gallons and is expected to increase to 100,000 gallons within the next six months. The Durham campus hosts two, 1.3 million gallon digesters.

    Prior to being fed to the engine, the biogas will need to be treated with a gas treatment system made by Unison Solutions that will remove hydrogen sulfide particulates, siloxane and moisture from the raw biogas.

    “Clean Water Services Durham took the steps very deliberately and smartly to design a system that works for increasing the production of biogas to help maximize generation at the plant,” said Dave Moldal, senior renewable project manager with the Energy Trust of Oregon.

    “From our perspective, this is another classic example of the evolution of wastewater treatment plants to resource recovery facilities,” Moldal said. According to Moldal, the first generation was really about protecting public health and the second generation of WWTP—in the ‘70s, ‘80s—began producing value-added products like water, soil amendments and also generating power. “Cogeneration is not new, but this is really the third generation, where we’re using this facility’s existing infrastructure to achieve GHG reduction goals.”

    The $16.8 million project was funded by CWS. The agency received $3 million in cash incentives from Energy Trust and tax credits for combined-heat-and-power from the Oregon Department of Energy in the amount of $2.8 million. The project is expected to cut CWS’ operating costs saving ratepayers money. Around $690,000 savings in electrical costs in the first year is expected and $100,000 savings in heating costs. The project will generate $340,000 annually in tipping fees for FOG disposal.

    CWS also operates the Rock Creek WWTP in Hillsboro. Cordon said the company is looking at implementing RNG for transportation use at this facility.


    • #17
      Nora Goldstein for BioCycle July 2016 - Biogas To Fleet Fuel In South San Francisco

      SSFSC/Blue Line Transfer operates a fully enclosed one-quarter-acre facility comprised of an aerated receiving bay, 8 modular digesters, and two in-vessel composting (IVC) tunnels that can process 11,200 tons/year of food scraps and yard trimmings.

      SSFSC collects both commercial and residential organics in a service area that includes South San Francisco, Brisbane, Millbrae, Colma, San Francisco International Airport and San Mateo County.

      Collected organics are sorted for all visible contaminants — primarily plastic bags. Cleaned material stays in the aeration bay for 2 to 3 days prior to being loaded into one of the 8 digesters. The bay is operated under negative pressure; exhaust air is treated in an acid scrubber that uses sulfuric acid to cleanse gases. Gas from the acid scrubber passes through a biofilter made of wood chips and kept in a moist condition. “The digesters and IVC tunnels are less than 100 yards away from a 800,000 sq. ft. complex of Genentech buildings, as well as other neighbors, so odor control is a main priority,” notes Button.

      SSFSC/Blue Line installed the SmartFerm dry fermentation anaerobic digestion and IVC composting system developed by Eggersmann, and supplied by Zero Waste Energy, LLC, the North American licensee. Each digester has capacity for 240 cubic yards of material. Digesters are loaded with an average of 62 tons/batch; design tonnage is 81 tons/batch.

      On average, the mix going into the digesters is 60 to 65 percent food waste, and 35 to 40 percent green waste. The amount of food waste is kept as high as possible in order to produce more biogas. But there is a delta, where if too much food waste is in the mix, it may not all break down and generate the maximum amount of biogas in the 21-day digestion cycle. The green waste provides adequate porosity year-round.

      Once inside the digester, material is aerated using an in-floor air supply system until the material reaches 125° to 130°F. Exhaust air from this stage is sent to the acid scrubber and biofilter to remove ammonia, VOCs and particulates. After the desired temperature is achieved, the system switches over to the anaerobic process, with microbes consuming the available oxygen. Material is sprayed with a fine mist of liquid from the percolate tank, located under the digesters, facilitating decomposition and biogas production.

      Retention time in the digester is 19 to 21 days. Biogas is produced almost immediately after the system is switched to anaerobic digestion mode. It is pulled into the percolate tank, where biogas from all 8 digesters (all loaded at different times) is mixed and homogenized. Each digester is making different amounts of gas which is captured in the percolate tank. Biogas then is pulled into a storage bladder located on top of the digesters. Ever few hours, the bladder is drained by a small compressor. The biogas is cleaned up using a BioCNG conditioning system, and then put into storage.

      Once the methane content drops below one percent, and hydrogen sulfide is not detected, the digester can be opened. Material is moved to one of the IVC tunnels from 12:00 am to 4:00 am to minimize odor impacts. There is a lot of ammonia in the digestate, so the main purpose of the IVC stage is to scrub out the ammonia before the material is transported to the composting facility. It stays in the IVC for 2 to 3 days. Compostable products break down during digestion, and then are fully disintegrated following the curing phase. Plastic is the primary contaminant when material is removed from the IVCs.

      The digestate from the IVC is very wet at this point, so goes through a curing phase at the composting site for about 45 to 60 days before it is screened. Outbound tonnages from SSFSC/Blue Line are on average 48 percent of the weight of inbound tonnages.

      Fleet Fuel

      SSFSC has converted 27 of the 40 trucks in its fleet to run on CNG. It uses Cummins Westport CNG engines. The 27 trucks are fueled every night between 10:00 pm and 5:00 am using a slow fill system. The digesters produce 380 to 500 diesel gallon equivalents (DGE)/day of compressed RNG, depending on the quantity of food waste in the feedstock mix. Each truck utilizes an average of 30 gallons/day. Instead of fueling about a dozen of its trucks on RNG only, SSFSC uses it in all 27 trucks with CNG engines.

      On week nights, each truck is time-filled with a little bit of RNG and then the tank is topped off with line [natural] gas. On weekends, however, when the trucks are parked for several nights, all 27 trucks get 100 percent RNG. The RNG has a methane content of 92 to 94 percent, whereas the line gas is slightly lower - the engines don’t know the difference.

      The tail gases (lean gas) from the biogas conditioning system, such as propane and butane, are combusted in an on-site boiler. Heat generated by the boiler is used to warm the air for the IVC tunnels and heat the percolate tank. No gas is being flared.

      The RNG has a carbon negative value of -23.95, which makes it a valuable commodity in California, which has aggressive greenhouse gas reduction requirements. This is better than any other technology out there for reducing carbon emissions from fuels. In 2015, 828 metric tons of CO2 equivalent were avoided, and about 48,000 gallons of diesel fuel displaced.

      SSFSC received about $3 million in state grants and tax credits for facility construction. Solid waste tipping fees in the Bay area are $90 to $100/ton, which contributes to the facility’s revenue stream. Recently, the company sold its first Low Carbon Fuel Standard (LCFS) credits for the RNG, which are trading at $85-$100/credit. The LCFS program is an initiative of the California Air Resources Board, which administers the state’s GHG emissions reduction programs.So far, SSFSC has not been able to tap the federal RIN market, which is part of the U.S. EPA’s Renewable Fuel Standard (RFS) incentive program for alternative fuels such as biogas (classified as an advanced biofuel).

      Right now, savings from using RNG instead of diesel fuel are not being realized. As a solid waste and organics collection company, taking this plunge made more sense when diesel fuel was $5/gallon versus $2 to $2.50/gallon. But that will go up again.


      • #18
        GlobeNewswire Dec 05, 2019 Xebec Enters California Dairy RNG Market with Maas Energy Works

        MONTREAL, Dec. 05, 2019 (GLOBE NEWSWIRE) -- Xebec Adsorption Inc. signed a letter of intent on December 4th, 2019, with Maas Energy Works for five RNG systems. Xebec will supply dairy farmers with an initial four Biostream™ container systems, each with a 280 SCFM capacity. This renewable natural gas will be injected into the California gas grid. Project delivery dates are throughout 2020.