Thermal fluid heaters: buyer, be aware 

Did you know that the average life span for a Babcock Wanson thermal fluid heater is 25-plus years?  Mind you, we have a number fully operational after 50 years of ongoing service.  And we’re not alone; other manufacturers can also boast product longevity.  But not all.

The key to long, reliable life isn’t really down to ongoing maintenance, as thermal fluid heaters require very little maintenance (although I’m in no ways advocating ditching planned preventative maintenance).  It isn’t really in how you use it.  And it’s not really about the environment in which it’s used.  The real key to longevity, and to system efficiency, comes down to the quality.

Product design

Whilst 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.

Those 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 travelling across the heat transfer surfaces.  For maximum efficiency, a coil type, multi-pass design is preferential.  This effectively places the flue 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've 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.  Ours is one of the few 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 heaters are no longer the only option, with companies introducing electric models, 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 fluid heater in the world, but if it’s 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 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’re not very commercially minded, or their choice of materials is dictated by the price tag not the quality.

Good quality components don’t 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. 

Integration & factory testing

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 using components and systems that the manufacturer has either designed and made in-house, or knows is good quality and compatible, is almost certainly going to perform better than one that has been assembled by a third party.  It also means less work for you.

Thermal fluid heaters are as close to a fit and forget process heating system as you’re likely to find, but that doesn’t mean you don’t need support.  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 NO_x limits of 100 mg/m3 on gas in the UK, can they meet the more stringent limit 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 one for maximum efficiency and see that heater continue to operate well into your own retirement!

Etienne Fourie is technical sales manager at Babcock Wanson