Evaporation Process Improvement, Service, and Training. Let me help you
Angola, New York 14006, United States
Fundamentals of CIP
Clean In Place (CIP)
If your evaporator looks like what is pictured at the above right then read on please.
The first rule of trying to solve a dirty evaporator is to stop making it dirty. In other words get the processing conditions addressed and under control so you don't find yourself cleaning up a mess. So, stop making the mess and the normal fouling which occurs during the course of a campaign will easily be removed.
Always refer to the chemical Manuf. Recommendations for safe chemical temp & concentrations which will take precedence over the following suggested values.
Flow Rate & Evaporation:
• Flow rates should be increased as high as practical, without flooding the separators.
• Steam is left on during wash cycles to enhance scouring effect with condensate routed back to the balance tank. To promote a scouring effect vapors must be generated during evaporation. Evaporation occurs by having a delta T between the first and last effects. The greater the delta T the more vapor is produced during evaporation. The more vapor the higher the scouring velocity within the plate. Vacuum should be set for the desired wash temperature. Caustic 185-165F Acid 130-110F to prevent precipitation of the scale back onto the surfaces as shown in the pictorial on the upper right
Chemical Strength
Pre-Caustic Flush (for Dairy)
• ½% solution of liquid caustic compatible with your gasket materials
• Wetting and chelating agents should be added. Do not use any solutions containing chlorides.
Caustic wash
• 1 ½% - 2% solution of liquid caustic compatible with your gasket materials
• Maintain at or above 11.5 PH or what the manufacturer recommends.
• Monitor pH at outlet closely to maintain proper strength.
• Wetting and chelating agents should be added. Do not use any solutions containing chlorides.
Acid wash
• 1 - 2% solution strength compatible with your gasket materials
• Maintain at or below 2 pH leaving the evaporator
• Monitor pH at outlet closely while on acid to maintain proper strength
• Phosphoric or Citric acids preferred
• Nitric, Hydrochloric, and Hydrofluoric acids should not be used. Do not use any solutions containing chlorides.
Temperature
Caustic should be run with at a temperature of up to 180F (82C) at the first effect separator vessel as seen at the 2nd effect steam chest. Use the system absolute pressure control loop or hand vacuum break to lower system vacuum, and raise the last effect boiling temperature to no less than 150oF (65C) or 3.8 PSIA (22” Hg) as measured at the vapor duct to the condenser. It may be necessary to adjust the set point of the steam pressure controller to maintain temperature at the second effect steam chest.
Acid should be run with the vacuum at 1.27 PSIA (27” Hg) 110F and first effect boiling point temperature at 130F. Why so low you may ask? Looking at the pictorial you can see atop the acid temperature was too high and the mineral scale precipitated out leaving a chalky residue on the surfaces. A colder acid was will prevent this and give you the clean shine as seen in the lower picture. Always refer to the chemical manufactures recommended temperatures.
Time
Typical procedure:
• Rinse 15-20 minutes
• Caustic 60-90 minutes Check PH every 10 minutes and add when required if below 11.5 PH.
• Rinse 15-20 minutes Until PH is below 8.0
• Acid 20-30 minutes Check PH every 10 minutes and add when required if below above 2.0 PH.
• Rinse 15-25 minutes Until PH is 5.0
CIP of Tubular Evaporators
Cleaning the lower tube sheet
Pictured above top is a spray ball affectively cleaning the lower tube sheet. This is viewed from a sight glass located in the top side of the separator vessel showing the end of the tube bundle where product and product vapor leave the tubes and enter into the separator vessel.
What is important to note in this picture is that during this cleaning procedure there is no wash water leaving the tubes because the pump feeding the evaporator is momentarily stopped or paused during this step in the spray routine. The reason why is self evident. Imagine if a torrential flow of wash water and vapor was rushing down the tubes and colliding with the spray. The spay would be totally ineffective.
Unfortunately this mistake has been made in nearly all tubular evaporator CIP spray sequences that I have encountered leaving the bottom of the tube sheet unclean. The above bottom picture shows how the corners where the tube sheet is welded to the separator vessel has deposits left behind. The force of the spray is meant to impinge on the surfaces it is supposed to clean. Direct forceful contact is required to clean a vessel or a tank. If the force of the spray is obstructed and diminished by the falling wash water from the tube the spray is rendered useless.
The solution to this is a programmed pause of the pump feeding the tubes long enough to allow the spray to be affectively unobstructed by the falling wash water. If the CIP program is written correctly it will first focus on cleaning the tubes and product pipes. This is done with as much flow as possible to create a turbulent flow of great velocity in the product pipes to clean them without flooding.
The evaporator tubes must also have the same high velocity but high flow rates alone will not be adequate. Therefor, we need to depend on evaporating in the tubes to create vapors. It is this generation of vapor which will provide the velocity and scouring action required to clean the tubes thoroughly.
So the first phase of CIP wash is operated at high flow rates with evaporation applied. The second phase is the spray ball sequence. This phase follows after the tubes and pipes have been cleaned. Flow rates can then be lowered to prevent flooding of the effect separator vessels. The pausing of the pumps will have no detrimental affect on the tubes as they are already clean.
The spray wash phase for multi effect evaporators should be sequenced as follows for a multi effect process. A three effect is our example here.
During the spray wash phase the effects are sprayed from the 3rd effect first, then the second, and then the first with a proper dwell time to allow each effect to pump out to minimize flooding.
The reverse sequence of the wash is used for rinsing as you want to move the rinse water from the first to the second and then the third and to drain.
