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DKL Engineering, Inc.
Maintenance and Inspection - Plate Heat Exchanger
September 12, 2003
Opening the Unit
Closing the Unit
Plate heat exchangers are found in both the gas cleaning and strong acid section of an acid plant. The maintenance and care required for either of the units is identical.
Fouling of the plate exchange can occur on both the cooling water and sulphuric acid sides of the exchanger although fouling on the cooling water side is most common. Cleaning-In-Place (CIP) allows the exchanger to be cleaned without the need to open and dismantle the entire unit which can be very time consuming.
Packaged CIP system may be available from the vendor but can be easily made up if none is available. A typical CIP will consist of a reservoir for holding the cleaning solution or chemical, a circulating pump, valves, piping and flexible hose. The vendors recommendations for cleaning the unit should be followed.
If the deposits and buildup in the exchanger are severe, the unit may need to be dismantled for manual cleaning of each plate. In some cases the plates can be left hanging from the carrying bar while each plates is scrubbed with a soft brush and running water. The plates are then rinsed with a high pressure hose.
If a cleaning solution is required to clean the plates, the plates should be removed from the frame and scrubbed with a soft brush and cleaning solution and then rinsed with water.
Care should be taken not to damage the gaskets.
|Calcium Carbonate||Nitric Acid||4 wt%||60°C|
|Calcium Sulphate||Sulfamic Acid||4 wt%||60°C|
|Silicates – Silt||Citric Acid||4 wt%||60°C|
|Silicates – Alumina||Phosphoric Acid||4 wt%||60°C|
|Silicates – Diatomic Organisms||Complexing Agents (EDTA, NTA)Sodium Polyphophates||4 wt%||80°C|
|Bacteria Growth/Slime||Sodium Hydroxide||4 wt%||80°C|
Hydrochloric acid should never be used on stainless steel plates. As well, water used for the preparation of cleaning solutions should contain no more than 300 ppm chlorides.
The following chemicals are not recommended for use: Ketones, Esters, Halogenated Hydrocarbons and Aromatics.
Dismantling a plate heat exchanger for inspection, cleaning or maintenance should be done according to the manufacturers instructions. Most manufacturers recommend the following:
Measure the width of the plate pack at the bolts prior to opening and record the figures. When the heat exchanger is reassembled, the measurements will be used to ensure that the plate pack has been tightened adequately to prevent leaks.
Mark the outside of the plate pack with a diagonal line. This will ensure that the plates are assembled in their original order. Alternatively, each plate can be numbered.
Reassembling the plate heat exchanger should be done according to the manufacturuer’s instructions. The following are general guidelines common to most manufacturers:
Ensure that all sealing services are clean
Clean and lubricate the threads of the bolts
Ensure that all plate gaskets are secure
Ensure that the plates are reassembled in the same order as they were removed. The diagonal line marked on the edge of the plate pack before disassembly should once again be visible in its original form. Alternatively, the plates can be reassembled according to the numbers marked on the plates during removal.
When the plates are all installed, the side of the plate pack should have a honeycomb pattern
Compression of the plate pack should be done in an even manner ensuring that the fixed and floating (pressure) plate remain parallel. Bolts should be tightened in a cross pattern.
Check the distance from the fixed plate to the floating plate against those measured before the unit was disassembled. The manufacturer’s tolerances for this dimension should be followed.
Never torque the bolts more that the manufacturer’s maximum torque values
Re-gasketing of the plate pack may be required if leaks occur in the unit. Most manufacturers offer re-gasketing service but this requires that the entire plate pack be sent back to the factory. On-site re-gasketing can be done if time or costs are a factor.
By far the easiest type of gasket to replace are the clip-on type gaskets. The old gasket is simply removed, the sealing service cleaned and the new gasket installed.
Glue on gaskets are more difficult to replace. Gluing and replacement procedures will be provided by the manufacturer if this method if required.