Caloris consultant Jim Munch recently helped a customer achieve a huge efficiency improvement on their evaporator by implementing a basic fix — resolving vacuum leaks.
The customer operates a whey plant in Wisconsin with a circa 1985 4-effect MVR evaporator. They were aware that they had vacuum leaks and enlisted Munch to help resolve them.
Before starting to look for vacuum leaks, Munch did an overall mass balance on the evaporator. He determined that the unit was evaporating 58,000 lbs/hour water.
Munch next used a handheld anemometer to measure the air flow off of the vacuum pumps. This flow rate represents the air leaking into the evaporator. The anemometer indicated there was a very large vacuum leak somewhere in the system.
As a note, newer Caloris units already have an anemometer installed on the evaporator for this purpose.
Meet The Engineer
Jim Munch represents Caloris at customer sites for assessments, training sessions and more.
Munch then used two different types ultrasonic microphones to locate the vacuum leaks. He found several using this method, but couldn’t find what appeared to be a really big leak using the microphones.
Flooding the unit would be another way to look for leaks, but it wasn’t an option in this particular case.
Munch instead used steam to increase the pressure to the evaporator to just above atmospheric pressure. This procedure can be tricky to do without damaging the equipment, but the technique is effective because it can reveal leaks by showing where the steam escapes the unit.
This procedure has to be done very carefully. The entire system pressure has to be monitored during the test. Before beginning, Munch had the plant purchase 8 new, high quality 30”Hg to 0 to 15 PSIG compound gauges and mount these gauges onto critical points of the evaporator. Munch made sure the pressure on the evaporator never exceeded 3 PSIG during this test.
The pressure test revealed numerous small leaks and a large crack on the vapor side of the condenser. The vertical condenser was wedged into one of the corners of the room. The leak was on the back of the condenser, up against the corner area, which is why it hadn’t been found before. A temporary fix to this problem was to apply metal duct tape until the crack could be welded shut.
After the leaks were found and corrected, Munch returned to observe an evaporation test on the unit. The evaporator had started out at 58,000 lbs/hour evaporation and increased to almost 76,000 lbs/hour evaporation after the vacuum leaks were repaired — an efficiency improvement of almost 30%! This illustrates how detrimental vacuum leaks can be to the performance of an evaporator.
“There’s always more than one way to tackle a problem,” Munch said. “We weren’t able to flood the evaporator to look for leaks. We came up with different ways to find the leaks.”
Munch advises processors to record the mass flows on their evaporators periodically, in order to spot problems in a timely manner.
“Take a full set of readings to see the temperature differentials across your effects,” he said. “Do a vacuum test and see how tight it is. You can tell in 15 minutes whether you’ve got a big vacuum leak or not.”
“Your evaporator should not lose more than 2″Hg (1 PSIA)/hour of vacuum,” he said. “This is a good rule of thumb for almost any size evaporator.”
If you are experiencing vacuum leaks, don’t delay repairs! Contact us at 410-822-6900 or firstname.lastname@example.org to arrange a service visit at your facility. We can also look for other ways to achieve an efficiency improvement for your equipment.