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The average life span for a thermal fluid heater is more than 25 years, with some still fully operational after 50 years! The key to long, reliable life is not really down to maintenance, how you use it, or the environment in which it is used. The real key to longevity comes down to the quality of the thermal fluid heater. Etienne Fourie examines what constitutes quality in a thermal fluid heater, to cover:
The key to long, reliable life is not really down to ongoing maintenance, as thermal fluid heaters require very little maintenance (although I am in no ways advocating ditching planned preventative maintenance). It is not really in how you use it. And it is not really about the environment in which it is used. The real key to longevity, and to system efficiency, comes down to the quality of the thermal fluid heater.
The word ‘quality’ gets bandied about all over the place, but just saying it doesn’t make it so. How do you choose between the different thermal fluid heaters on the market and ensure you select a quality one?
Product design
While all thermal fluid heaters work on the same closed-loop principal – featuring a heater connected to carbon steel flow and return pipework which has a thermal fluid running through it as the heat transfer medium – the design of that heater is key.
Thermal fluid heaters based on cone designs, where the combustion chamber used to heat the thermal fluid is located down the centre of the heater, tend to be quite inefficient and the thermal degradation is much higher due to a lower velocity of the fluid traveling across the heat transfer surfaces. For maximum efficiency, a coil-type, multi-pass design is preferential. This effectively places the flu gases in the middle, travelling up and down between the coils. In this type of design, the combustion air is preheated on the final pass, before it goes into the burner and it also enables the outer skin of the heater to be cooled down. This not only makes for improved efficiency but also reduces the requirements for insulation. If you have got less insulation, it’s much easier to maintain. In a coil design, you can also control the velocity of the fluid going through the coil and thereby minimise thermal degradation of the thermal fluids. So, as you can see, there are multiple benefits to a coil-type design.
On the subject of keeping the outer skin of the heater-cooler, look for a heater that has been designed with a barrier between the hot combustion gases and the outer structure, as this will help encourage long heater life as the higher pressure and cooler outer air helps prevent any escape of combustion gases as the plant ages over time. It also makes for a safer heater that won’t burn to the touch. Babcock Wanson’s TPC and EPC range of thermal fluid heaters, for example, come with an integral, air-cooled outer case that provides this barrier, as well as acting as both a combustion air pre-heater/economiser. The standard pre-heated jacket is bolstered with an additional shell and tube-type heat recovery device built into the actual case of the heater. It enables even more heat to be recovered from the flue gases by heating the combustion air, which reduces the amount of energy required to take it from ambient to normal combustion temperature. This can mean a flue gas temperature of circa 200°C, whilst still heating the thermal fluid to 300°C. This novel design allows 5-6% energy recovery with no operator involvement or further heat sink required – it’s an entirely self-contained solution.
When it comes to choosing downward or horizontal-fired heater configurations, this will almost certainly depend on the space you have available and the site layout. However, heaters that will best stand the test of time are mostly designed for a downward-fired configuration which ensures stress-free and unrestricted expansion of the heater coils during normal operation.
Burners are the next big consideration. Wherever possible opt for a thermal fluid heater with integrated burner rather than a third-party packaged burner. Matching the burner to the heater’s combustion chamber and exhaust gas passes is fundamentally important and is very easy to get wrong, resulting in under or over-firing. Babcock Wanson is one of the few thermal fluid heater manufacturers that makes its own burners that have been designed in parallel with the design of the combustion chamber. With high efficiency in operation, this optimal design results in an extended operational life.
With decarbonisation on the top of many organisation’s agendas, we should also note that gas-fired thermal fluid heaters are no longer the only option, with companies introducing electric models such as our own EPC EL range of electric thermal fluid heaters, providing customers with an effective low carbon process heater with no direct emissions.
Product build
Like most things in life, you get what you pay for. You may have the best-designed thermal fluid heater in the world, but if it is been built from low-cost materials and components, its integrity is seriously compromised.
As a customer, it’s near on impossible to assess this from looking at the product or from sales material. My advice here is first to check the heater is CE marked and then to ask the manufacturer where key materials and components come from. Are they manufactured in-house? If not, what countries/suppliers are they sourced from? European steel, for example, is far superior to that made in China and India. The same is true when it comes to valves, although even across Europe there is a big difference in quality, with German valves our preference for their longevity. It pays to do your homework here. It also pays to listen to the silence. A manufacturer who has invested in quality materials and components will shout about this, so if they aren’t, then you can only assume one of two things – they are not very commercially minded, or their choice of materials is dictated by the price tag not the quality.
Good quality components do not just make for heater longevity, they can also impact safety. Ensure the thermal fluid heater’s critical safety loop components and the overall loops are Safety Integrity Level (SIL) rated. SIL is a measure of safety system performance, ranging from SIL 1 to the highest safety level, SIL 4.
Product integration and factory testing
When it comes to thermal fluid heaters, you can either have the complete system delivered to site ready to go, or you can have the separate parts – the casing with the coil in it, a third-party burner, a control system, etc – delivered for you to construct the finished system. Whilst there’s no right or wrong option, I do strongly believe the benefits of the former easily outweigh the latter.
A system that has been integrated by the manufacturer using components and systems that it has either designed and manufactured in-house, or that it knows to be of good quality and fully compatible with that particular thermal fluid systems, is almost certainly going to perform better than one that has been assembled by a third party. It also means less work for you.
Manufacturer support
Thermal fluid heaters are as close to a fit-and-forget process heating system as you are likely to find, but that does not mean you do not need support from the manufacturer. A quality manufacturer will supply you with extensive technical information, from wiring diagrams and installation guidance, through to safety guidance and ensuring your new heater complies with relevant regulations.
For an increasing number of customers, that support needs to stretch Europe wide and be country specific. Whilst your manufacturer of choice may be able to provide you with a thermal fluid heater that meets NOx limits of 100 mg/m3 on gas in the UK, can they meet the more stringent limits set in Switzerland, which is less than 40? Do they have someone local to the countries in which you operate?
With their efficiency and ease of use, thermal fluid heaters have replaced fire tube and coil-type steam generators in a very large number of applications. But select wisely and invest in a quality thermal fluid heater if you want to gain maximum efficiency and see that heater continue to operate well into your own retirement!
Etienne Fourie, Technical Sales Manager, Babcock Wanson. www.babcock-wanson.com
