BIOGAS 3FOEFSJOHBQFSGFDUGJU NORTH STATE RENDERING has been serving Northern California for over 75 years, processing dead stock, slaughterhouse waste, grease trap material, and food waste into tallow, yellow grease, and bone meal. Owners Chris and Pat Ottone were looking for ways to cut costs, secure new waste supply contracts, and improve wastewater treatment. Given the nature of the rendering business, transportation fuel, process energy and wastewater treatment represent significant ope- rational costs. Grease trap waste and food waste from kitchens, restaurants, and food manufacturers is expensive to render, so diverting this material to the digester for biogas production instead allows North State Rendering to free up rendering capacity for higher-value materials while reducing costs. Flexible feedstock With the help of a grant from the state of California, North State Rendering hired Biogas Energy to build and integrate an anaerobic digestion (AD) facility at the rendering plant. – For a rendering plant, biogas is a natural fit. Investing in technology that eliminates electricity bills, slashes diesel costs and reduces natural gas imports all makes sense. The economics seriously stack up – not to mention a massive reduction in carbon footprint, said Brian Gannon of Biogas Energy, the company who built the biogas plant for North State Rendering. The waste reception equipment prepares high-solids feedstock for the digester, whilst a grease trap reception 24 Bioenergy International No 78, 2-2015 system separates out contaminants such as plastic and metals. With this flexible reception facility configuration, the digester can process a wide variety of materials, from food and yard waste to high-liquid grease trap material. Wastewater from the rendering process is also added to the mix. In addition North State Rendering can also add dead stock to the digester during warmer months when rendering can become problematic due to rapid degradation of the material. External mixing system From the reception area, the material is pumped into two heated tanks where the first acid-forming phase of the biogas production process takes place pre-treating the substrate for the main digester tank. Modifying the anaerobic digestion (AD) process of the biogas plant to integrate it with the rendering plant took some fine-tuning. – This included a very positive modification to the digester’s mixing system and we see how we got it right. We had been using submersible propeller mixers inside our main digester, but with our re-design of the tank, we switched to an externally mounted Landia digester mixing system that meets all of our needs, said Gannon. According to Gannon, one of the main issues with submersible digester mixing systems is maintenance. As the equipment is inside the tank the downtime caused by having to open the digester to lift the mixers out for repairs and maintenance causes serious process interruptions and has safety issues. – With the external mounting maintenance is now much easier. Even during commissioning when the digester biology was at a delicate stage, we were able to carry out some tweaks without any interruption whatsoever to the biogas production process. With submersible mixers we would have had to start over again, which would have been very expensive and used up a ton of manpower, Gannon explained. He added that another key benefit of the Landia GasMix system was its ability to agitate the entire digester tank preventing crust formation on the top. The rendering business is not known for its glamour or its cutting edge technology. Yet when North State Rendering in Oroville, California were looking for ways to cut costs, secure new waste supply contracts and improve wastewater treatment, the solution was to build a state-of-the-art biogas plant. The investment, a first-of-a-kind project in North America, is already paying dividends.
Bioenergy no 2 - March 2015
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