Dairy Condensers

The Last Effect Sets the Vacuum

In a multi-effect falling-film evaporator, boiling temperature cascades down from the first effect to the last. If the final condenser loses capacity, last-effect pressure rises, every effect boils hotter and the product sees more heat. Burn-on in the first effect increases and the run heads toward an early CIP.

Summer cooling water temperature is the usual hidden limit, so rate the condenser at the warmest water the plant will actually deliver in August.

Air leakage is the other half of vacuum control. Every evaporator draws some air through seals and sight glasses, and the condenser must collect it in a cooled vent section so the vacuum pump removes air rather than saturated vapor. A vent zone sized as an afterthought shows up as a vacuum pump running hot and a condenser that seems short of area.

Carryover and Burn-On

Entrainment separators remove most droplets upstream, but some milk solids reach the condenser, especially when an effect floods or foams. Protein and lactose deposit on condenser surfaces, the condensate picks up COD and the downstream polisher works harder. Watch condensate conductivity and COD; a step change usually points to separator trouble rather than to the condenser itself.

Which Exchanger Goes Where

Fixed Tubesheet shell and tube units take the large-volume vacuum vapor and can be built for CIP on the vapor side with spray devices or full flooding. Gasketed Plate & Frame units fit the liquid duties around the evaporator, such as condensate-to-milk preheating, where the recovered heat justifies the gaskets and the frame can be opened for 3-A inspection.

Washing on the Evaporator Schedule

Dairy evaporator wash cycles typically run hot caustic followed by acid after each production run, often every 12 to 20 hours. The condenser vapor side has to take the same chemistry, drain completely and present no shadowed areas to the spray.

Where condensate is reused, 3-A sanitary standards and 316L product-contact surfaces are the norm, and tube-to-tubesheet joints should be designed without crevices that can hold residue between washes.

Recovering Cow Water

An evaporator removing 20,000 lb/hr of water produces nearly that much condensate. Run through a plate exchanger to preheat raw milk and then polished by reverse osmosis, it can replace a large share of plant fresh water for CIP rinses and boiler makeup. Specify the target condensate temperature as well as vacuum, since it decides how much preheat is available.

Reading Vacuum and Condensate Trends

Trend last-effect pressure, cooling water inlet and outlet temperatures and the noncondensable vent temperature. Rising pressure with a steady water temperature rise means fouling or air; rising pressure with a shrinking water temperature rise means cooling water flow is short. Both appear in powder moisture and concentrate solids before anyone thinks to look at the condenser.