Maintenance and Inspection - Plate Heat Exchanger
September 12, 2003

Introduction Cleaning Opening the Unit Closing the Unit Re-Gasketing

Associated Links Strong Acid Coolers Weak Acid Coolers

Introduction

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.

Cleaning

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.

Cleaning Agents

Deposit	Cleaning Agent	Concentration (Maximum)	Temperature (Maximum)
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.

Opening the Unit

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.

• Loosen the bolts evenly so that the fixed and floating (pressure) plate always remain parallel.

Closing the Unit

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

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.