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Faunsdale, AL | When I started kicking around ideas about building a pasteurizer, one thing I considered was a stainless steel batch pasteurizer that had come out of a dairy plant. Those upright cylindrical heated process vats have a steam/water jacket and an agitator inside. We had had a couple around from a cheese plant but they had been scrapped already, so I worked with heat exchangers and portable "totes" instead. In our situation I think the portable and easily replaceable totes were an advantage.
Our heat source was a 200,000 BTU LP gas tankless water heater and a 3/4 hp circulating pump pushing water through stainless steel heat exchangers. Our heater had 3/4" pipe water connections while the heat exchangers had 2" connections, so we set the recirculating pump loop up to bypass some of the 40-50 gpm flow and only a fraction actually went through the heater. The heater would automatically modulate the burner to maintain 180 degrees F water temp on its outlet, so I just closed the water bypass valve until all the burner stages were on all the time. On the milk side we had a 3/4 hp Delaval milk pump that probably pumped 20-25 gpm through a filter sock, the heat exchangers and then back to the tank. Like I mentioned in the post back in 2012, I had wanted to use a high temperature short time process (HTST = 161 degrees F for 15 seconds), but when I tried to control the milk flow from the milk pump with a butterfly valve, it was just too sensitive to be reliable. Commercial HTST pasteurizers used to use positive displacement pumps so flow rate was adjustable and predictable. My butterfly valve was neither, so I reverted to a batch process where the control variable was simply how long to recirculate the milk in the tote with the heater on!
To calculate what is possible when heating milk take your desired volume and convert to pounds. Specific heat of milk is about 0.92 BTU/pound/degree F. In our setup there was a lot of loss. A good part of that was probably in the heater since it was heating recirculated warm/hot water instead of cool water from the well. Then we had a lot of exposed piping and tank surface are where heat loss occurred.
Rough figures from memory are 80 gallons of milk heated from 70 degrees to 153 degrees in 1/2 hour. 80 gal x 8.6 pounds/gal x 83 degrees x 0.92 BTU/pound =52,535 BTU required. Our efficiency getting the heat from the fuel to the milk was about 50% (52,535รท100,000). Heater is rated 200,000 BTU per hour INPUT from the burner, so the efficiency of the heat exchange inside is important.
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Calf milk pasteurizer, what's the best model? Ever build ur own?
