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Cheese Factory Biogas Heats Production


©2014 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 56, no. 8, August 2014.

By Gheorghe Mihalache, ing., Member ASHRAE

About the Author
Gheorghe Mihalache, ing., is engineering director at Atis Technologies, Montreal. He is a member of ASHRAE's Montreal chapter

The Fromagerie des Basques family cheese factory in Trois Pistoles, Quebec, Canada, transforms about 800,000 gallons (3 million L) of milk into cheese each year. However, until 2012, the factory’s boiler was in the middle of the production area, and the pasteurizer used so much power that all other power consumers had to be turned off when it was running. In 2011, a project was developed that included building a mechanical room, constructing a treatment plant to turn whey and white water into biogas to produce heat for cheese production, and modifying the high-temperature, short-time pasteurizer to use rejected heat to preheat milk. The projects reduced the amount of heating oil used by 64%, even with the addition of several buildings increasing the total square footage by 8,100 ft2 (753 m2).


Whey and White Water Treatment

The main issue was the whey and white water treatment. The cheese factory sent whey to a pork farm until the farm closed in 2009. The municipality was unable to treat all the whey. So, the cheese factory’s option was to invest in a treatment plant. The classic solution was aerobic treatment. The alternative we offered the client was an anaerobic treatment plant that transforms the effluent into biogas (methane and carbon dioxide) and uses the biogas to produce heat for cheese production. The remaining clear water is sent to an absorption field. The project was economically sustainable due to savings associated with reducing the amount of heating oil (Number 2) used and grants received due to greenhouse gas reductions.



The whey resulting from cheese fabrication and the white water are pumped into storage tanks. A dissolved air flotation system removes the fat and the remaining effluent is injected into the complete mix digester and retained for one to two days, producing biogas (Figure 1). In the digester the biomass is in a fluid bed generated by continuous recirculation up to 7 ft/h (2 m/h). The temperature is kept to 88°F (31°C) and the obtained efficiency is more than 90%. The produced biogas has a measured concentration of ~60% methane and is burned in an adapted atmospheric burner water boiler with a maximum output temperature of 208°F (98°C).

High temperature accumulation is needed because biogas is produced 24 hours per day, and production heating needs are high but for limited periods of time. To eliminate potential explosion danger, complex installations and high capacity boilers, hot water storage was preferred to biogas storage. In the summer (from June to October) biogas is enough to supply all necessary hot water.

In winter, when milk processing is reduced, the original heating oil-powered water boiler is used part of the time. Through the course of the year, 66% of the hot water needed in the plant is produced using the new 11.7 hp (115 kW) biogas boiler and the rest by the original boiler. And, if cheese production increases, still more biogas is produced and less heating oil used.


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