How to avoid the top 10 heat exchanger ‘mistakes’
By Matt Hale, International Sales & Marketing Director, HRS Heat Exchangers
With 40 years’ experience as a company, our engineers and sales staff have encountered a wide range of issues on sites. Here are ten of the most common mistakes that can occur as a result of poorly-specified or badly-installed heat exchanger systems – and how you can avoid them.
- Excessive fouling
The consequences of excessive fouling within a heat exchanger can range from minor inconvenience (a greater need for regular cleaning) to catastrophic (material failure). Excessive fouling during operation can also reduce operational efficiency and increase energy consumption.
There can be many reasons, but the best solution is to avoid excessive fouling in the first place by choosing the right type of heat exchanger, and scraped surface or corrugated tube designs reduce fouling by increasing turbulence in the tube. Maintaining the correct temperature range will also help to reduce the problem, and where particular problems are anticipated, additional chemical treatment, such as acid dosing, may be required.
- Wrong material choice
Cheaper isn’t necessarily best. For example, although carbon steel is cheaper than stainless steel and easier to work with – making it a popular choice for those on a budget – it is also more vulnerable to corrosion and chemical reaction.
Thicker tube walls are required compared to stainless steel, which increases the weight and may add to associated costs, such as concrete bases and mounting brackets. Furthermore, carbon steel is brittle and while it may have a higher thermal conductivity than other materials, this can rapidly be degraded by the build-up of corrosion or fouling layers, reducing its service life.
Opt for a material which is both hygienic and hard-wearing, but which also provides good thermal characteristics in the design of heat exchanger that you are considering, such as stainless steel.
- Incorrect pressure drop
Pressure problems usually occur when the pressure drop in the heat exchanger is higher than the design parameters; one reason might be a change in raw material specification.
You should always request full details about any new products from your suppliers and, if necessary, ask your heat exchanger supplier to test them before use. This will ensure that any new heat exchangers are correctly specified, and will also help to prevent problems when switching products or ingredients.
- Poor location
We have encountered heat exchangers crammed into corners, obstructed by pipework or other equipment, or fed by excessively long or complex pipework. If it is inconvenient to clean and service the heat exchanger, then such routine tasks may get overlooked or extended beyond the recommended intervals, leading to bigger problems.
If you are tight on space, then ensure you specify a heat exchanger suitable for a small footprint. For example, corrugated tube designs are more efficient and require less space than a smooth-tube unit with the same capacity. This means that they can often be housed in smaller spaces or novel locations, such as a specially constructed mezzanine, while still allowing full access for cleaning and maintenance.
- Insufficient capacity
While it may be tempting to invest in a smaller unit to save money, this can be a false economy. Specifying a heat exchanger which is not large enough to cope with the maximum volume or processing capacity can result in extended running hours or, in a worst-case scenario, having to turn business away.
One option may be to choose a modular solution, so that additional units can be added if and when extra capacity is required. Although allowing for the additional space and infrastructure may incur some cost, this is likely to be less than a much larger over-specified unit, and will save money in the long term when expansion is required.
- Product damage
Inappropriate product handling can affect quality parameters, such as taste, appearance and viscosity. Common examples include rough handling of cream causing curdling; pizza sauce losing its viscosity so that it falls off the pizza; fats and spreads becoming demulsified; and fruit juices losing their fresh taste when pasteurised.
All of these effects can be prevented by using the right heat exchanger. For example, not only are scraped-surface heat exchangers good at preventing fouling with viscous products, they can also handle sauces more gently than a turbulent tubular design, retaining the all-important product characteristics.
- Lack of backup or safety systems
If the production system fails elsewhere, material may remain too long in the heat exchanger, becoming too hot or too cold. This can result in product damage, but may also have additional effects on the equipment.
A well-designed heat exchanger should therefore include failsafes to prevent damage from occurring in the event of a system failure elsewhere in the production line. It is also important to make sure that heat exchanger equipment is included within any monitoring and alarm systems.
- Insufficient cleaning or maintenance
Heat exchangers that are easy to service are more likely receive the prescribed levels of maintenance. Being able to remove and inspect individual components or tubes separately and easily is the key starting point. The way in which tubeplates and covers are attached is just one of many small details that can have a big effect, as can the siting of drain plugs and inspection covers. Any good heat exchanger design should therefore make routine checking and cleaning as quick and hassle-free as possible.
- Poor energy efficiency
The potential for heat regeneration or product-to-product heat transfer should not be overlooked when designing your heat exchanger system, as in most cases, there will be some ‘heat’ (or cooling effect) left over in the service fluid after it has passed through the heat exchanger. Using a design which reuses (or ‘regenerates’) this heat will reduce overall energy and running costs.
- Incorrect design parameters
If the information provided to the designers of the heat exchanger is wrong or incomplete, then the installed unit will not perform optimally for the product and service fluid in question. While intentionally supplying misleading information is extremely rare (not to mention counter-productive), seemingly inconsequential information can sometimes be overlooked.
It may appear as if the heat exchanger designers and engineers require an unnecessary amount of information, but this is only because they have the experience to know what variables will affect the performance and longevity of such an important asset – so trust them, and provide as much information as you can. Any uncertainty should be flagged up immediately; rather than guessing.
This is by no means an exhaustive list, and the severity of almost all of the issues listed above can range from mild inconvenience or extra costs, through to severe and catastrophic equipment failure. Safety must always be the prime concern and any equipment which is potentially unsafe should not be used until it has been checked and certified by a competent authority.
For less serious issues, if you find that processing is taking longer than anticipated, or you are spending longer than expected cleaning your heat exchanger, it may be time to get a second opinion.