ASHRAE Journal - August 2014 - 81

2014 ASHRAE TEcHnology AwARd cASE STudiES
nology

Above Biogas boiler supplies all of hot water

needed during the summer.

Left Overview of cheese factory.

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.

Biogas
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.

Energy
An ancient warehouse was transformed into a
mechanical room for the heating, refrigeration and
digester infrastructure, and a new building was constructed for the effluent post treatment. All the heating
and refrigeration is now produced only in the mechanical room, and the various pieces of equipment are
supplied by distributed liquid loops.
Refrigeration is delivered by a 23°F to 28°F (-5°C
to -2°C) glycol loop, and heating is delivered by two
different water loops, one ~90°F to 100°F (~32°C to
~38°C) and the other ~149°F to ~194°F (~65°C to ~90°C).
Heating from the ~90°F to ~100°F (~32°C to ~38°C) loop
is delivered by the chiller condenser, and the heating
from the ~149°F to ~194°F (~65°C to ~90°C) by one of
the two boilers. Heat from both boilers is accumulated
in two 1,236 ft3 (35 m3) water tanks.
Ten small refrigeration units with air condensers
were replaced with one central 80 ton (280 kW), 4
stage and two independent R-410A circuit chillers.
Condenser heat rejection is accumulated in a 883
ft3 (25 m3) water tank, up to 100°F (38°C). From this
tank, the ~90°F to 100°F (~32°C to ~38°C) loop preheats the washing potable water needed in production, heats the fresh air ventilation unit, preheats the
39°F (4°C) milk before pasteurization due to the hightemperature, short-time pasteurizer modification (to
use low temperature "free" energy from the chiller
condenser and minimize high temperature energy
use) and heats the digester supply effluent.
Au g ust 2014

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