How to Clean and Maintain Your Heat Exchanger
Heat exchangers are designed to optimize heat transfer from one gas or liquid to another during processing and Clean-in-place (CIP). Degraded heat exchanger performance from fouling or aging results in extra operating and energy costs to compensate for gaps in the target temperature. Cleaning and maintenance of heat exchangers is therefore important to keeping systems running efficiently. Regular maintenance ensures equipment is in working condition and helps prevent emergency repairs. The cost of cleaning a heat exchanger is small compared to the cost of lost production should a heat exchanger require an unscheduled shutdown.
Product or chemical deposits on heat-transfer surfaces weaken an exchanger’s heat-transfer capacity and must be cleaned away regularly to maintain high performance and prevent disruption of processing. Heat exchanger fouling, or the unwanted accumulation of deposits on heat-transfer surfaces, can result in several costs:
- Production loss from shutdowns
- Maintenance costs for removal of heavy fouling deposits
- Replacement of plugged equipment
Deposits that affect heat exchanger performance occur as fouling and aging.
- Fouling is the freshly deposited material on contact surfaces
- Aging occurs close to the surface of heat transfer components
Three key factors play into the frequency and degree of fouling:
- Fluid temperature
- Nature of the fluid
- Fluid velocity
1. Fluid temperature
Water can produce scaling from minerals such as calcium carbonate (CaCO3). Salts deposit on the heat exchanger surface with increases in temperature. Similarly with increase in temperature during food processing, biological growth can occur.
2. Nature of the fluid
During milk processing, for example, fouling leads to a rise in pressure drop across the exchanger by reducing flow from the growth of deposits. In dairy industries, proteins, fats, sugars, and minerals from milk and dairy products that can come out of solution and deposit on heat exchanger surfaces and foul channels.
3. Fluid velocity
In most cases, fouling decreases at higher fluid velocities because increasing flow velocity increases the fluid shear stress which causes more removal of deposits. For particulate fouling, increasing the flow velocity may completely eliminate fouling.
But for stronger deposits, increasing the flow velocity beyond a particular point may not decrease fouling significantly, and in the case of very strong deposits, increasing flow velocity may not have any effect.
Important definitions
In this article, we outline cleaning procedures for the most commonly occurring types of fouling and aging in hygienic processing:
- Incrustation: the accumulation of a crust or coating of processed fluids, minerals, or cleaning agents on the surface of heat exchanger parts.
- Scaling: a type of incrustation caused by calcium carbonate, calcium sulphate, and silicates.
- Sediment: comes from corrosion products, metal oxides, silt, alumina, and diatomic organisms (microalgae) and their excrement.
- Biological growth: Sources of biological fouling include bacteria, nematodes, and protozoa.
How do I know when to clean a heat exchanger?
You can tell when it’s time to clean your heat exchanger when the exchanger doesn’t achieve the correct product temperatures for heating or cooling. The incorrect temperatures result from plate surface fouling that reduces temperature transfer.
You might also see pressure drops higher than specified because fouling is constricting the channel passage and increasing fluid velocity.
Cleaning-In-Place (CIP)
Cleaning-In-Place (CIP) equipment can clean plate heat exchangers without disassembly. CIP is a combination of time, temperature and concentration. CIP provides both chemical and mechanical cleaning to the heat exchanger. If system configuration prohibits CIP, operators must perform manual cleaning.
CIP cleaning of heat exchangers typically includes several goals:
- Cleaning lime deposits
- Passivating surfaces to reduce susceptibility to corrosion
- Neutralizing cleaning chemicals before draining.
The importance of flow rate
The proper flow rate ensures effective mechanical action of fluids during cleaning. Some manufacturers recommended approximately 1 ft/sec velocity across heat exchanger plates, but requirements vary by manufacturer.
The flow rate during the cleaning of the product side should always be at least the same as the production’s flow rate. An increased flow rate may be required in some cases--for example, in milk sterilisation and the processing of viscous liquids or liquids containing particles.
Recommended limits for cleaning solutions
• 5% by volume caustic at a maximum of 70°C
• 0.5% by weight acid solution at a maximum of 70°C
Manufacturers can provide more detailed information about cleaning and sterilization for specific equipment.
Basic chemical cleaning process
Chemical cleaning in CIP offers several advantages:
- Quicker cleaning process
- Less labor intensity
- Cleans components that mechanical cleaning can’t do
Operators typically follow four steps in the chemical cleaning process in CIP:
- Alkaline clean: removes build-up of organic materials
- Rinse: generally completed with a high-flow water flusher to remove loose debris and remaining residue from the alkaline step
- Acid cleaning: helps dissolve and soften fouling materials more deeply
- Final rinse
Choosing the right cleaning agents
Selecting the right chemicals for cleaning heat exchangers is important to ensure proper cleaning and to avoid damaging exchanger components. For example, the following solvents and other cleaning agents can damage heat exchanger plates and gaskets:
- Ketones such as Acetone, Methyletylketone, Methylisobutylketone
- Esters such as Ethylacetate, Butylacetate
- Halogenated hydrocarbons such as Chlorothene, Carbon tetrachloride, Freons
- Aromatics such as Benzene, Toluene
Cleaning agents to use, by purpose
Incrustation, scaling
Cleaning incrustation or scaling is a process of removing calcium carbonate, calcium sulphate, or silicates from plate surfaces. Cleaning agents must be compatible with both the plate metal and the composition of gaskets.
In the case of titanium and stainless steel plates, never use hydrochloric acid. Also, never use water of more than 300 ppm of chlorine during the preparation of cleaning solutions. Chlorine, commonly used as growth inhibitor in cooling water systems, reduces the corrosion resistance of stainless steels, including Hastelloy, Incoloy, Inconel and SMO. Chlorine weakens the protection layer of these steels, making them more susceptible to corrosion attacks than they otherwise should be. In every case where chlorination of non-titanium equipment cannot be avoided, you must consult your equipment supplier.
Removing sediment
Sediment most commonly consists of metal Oxides, silt, Alumina, and Diatomic organisms and their excrement. Sediment accumulates because heat releases minerals and other particles from fluids during processing cycles, and those settle and deposit on heat transfer surfaces.
You should never use hydrochloric acid with stainless steel or titanium plates because the acid causes general corrosion, pitting, and stress corrosion cracking.
Removing biological growth
When using heat exchangers to increase the temperature of processed foods, biological growth such as bacteria, nematodes, and protozoa can occur. Removing the growth requires the same attention to plate and gasket composition as for incrustation.
Cleaning a Shell and Tube Heat Exchanger
Shell-and-tube heat exchangers have comparatively low internal fluid velocities so are more susceptible to fouling than plate heat exchangers. To maintain efficient operation, keep the heat transfer surfaces of the heat exchanger clean.
Cleaning chemicals depend on the same variables for a plate-and-frame heat exchanger, and cleaning compounds must be compatible with the metallurgy of the heat exchanger.
In all cleaning processes, operators must use proper protective equipment, such as safety boots, safety gloves and eye protection, to avoid injury.
Maintaining a Plate and Frame Heat Exchanger
To keep the heat exchanger in good condition, regular maintenance is required. In addition to cleaning plates on a regular basis, gaskets must be replaced as needed to prevent leaks.
Regasketing
For clip-on gaskets, the regasketing process is as easy as taking the current gasket off and clipping a new one on.
For glued gaskets
- Remove the old gasket
- Clean the sealing surface until it is free of foreign matter such as fat, grease or other soil.
- Check the new gasket and remove rubber residual before attaching.
- Clip on a new gasket or apply glue as required by gasket type
- Perform heat treatment to set the glued gasket according to manufacturer’s instructions.
The new gasket is wrongly positioned if it rises out of the gasket groove or is positioned outside the groove.
Why does my plate heat exchanger leak?
When closing a heat exchanger after maintenance, the plate pack dimension must be within the manufacturer’s specified tolerance to ensure proper operation. Overtightening can damage the plates, while under tightening can cause the plates to leak.
Illustration: Tightening bolts as needed to maintain the correct dimension A. Tighten the four bolts (1), (2), (3), (4) evenly until dimension A has been reached. Measure dimension A during tightening.
Additional Maintenance
Pressure testing must be performed by a person authorized according to local laws and regulations.
A hydrostatic leakage test confirms the internal and external sealing function of the heat exchanger. The specialist tests one media side at a time with the other side open to the ambient pressure. In a multi-pass set up, all sections of the same side must be tested simultaneously.
Regular maintenance keeps the heat exchanger in good working orders and makes opening and closing more efficient.
- Keep the carrying bar and guiding bar clean with paraffin oil.
- Keep the tightening bolts cleaned for ease of opening, closing, and adjusting the A dimension.
- Lubricate threads of tightening bolts with an EP (extreme pressure) grease. For example, use Gleitmo 800 or its equivalent.
- Grease the suspension wheels on the pressure plate and the connection plates.
If stainless steel surfaces of the frame plate, pressure plate and connection plates are glass blasted, they should be cleaned with a cloth wetted with paraffin oil.
Heat exchanger monitoring
Heat exchange monitoring helps to keep the heat exchange system running effectively
- Inlet and outlet temperature for cold fluid
- Inlet and outlet temperature for hot fluid
- Mass flow rates for both cold and hot fluids
- Pressure change across the heat exchanger for both hot and cold fluids
Guide to Choosing the Right Heat Exchanger
This guide is designed for processors, production managers, and mechanical engineers to help in the heat exchanger selection process.
Next Steps
Whether you need replacement parts to keep your current units operating, a direct replacement for a worn out or inefficient heat exchanger, or a new unit for a new process, CSI can support you.
Our customer service team, engineers, designers, and product specialists provide solutions through a broad range of brands, technologies, and capabilities.
Notes:
1 Boloorchi, A. S., & Jafari Nasr, M. R. (2011). A model for fouling of plate‐and‐frame heat exchangers in food industry. Asia-Pacific Journal of Chemical Engineering 7(3). 427-433. https://doi-org.ezp2.lib.umn.edu/10.1002/apj.585
ABOUT CSI
Central States Industrial Equipment (CSI) is a leader in distribution of hygienic pipe, valves, fittings, pumps, heat exchangers, and MRO supplies for hygienic industrial processors, with four distribution facilities across the U.S. CSI also provides detail design and execution for hygienic process systems in the food, dairy, beverage, pharmaceutical, biotechnology, and personal care industries. Specializing in process piping, system start-ups, and cleaning systems, CSI leverages technology, intellectual property, and industry expertise to deliver solutions to processing problems. More information can be found at www.csidesigns.com.