The rise of the electric thermal fluid heater

With their energy efficiency, versatility, ease of use and ability to provide precise temperature control, thermal fluid heaters have never been so popular across a wide range of industries and processes, whether replacing traditional steam systems or for new production lines and sites.

Thermal fluid heating is based on a similar basic principle to a low pressure hot water system. It consists of a heater connected to carbon steel flow and return pipework which can provide heat to one or more users or systems. Instead of water running through the pipework, a thermal fluid - often a mineral or synthetic oil - is used as the heat transfer medium.

This simple and easily automated closed loop design, allowing for high temperatures (up to 350°C in standard form), means thermal fluid heating systems can use 20-50% less energy overall to transfer the same amount of heat when compared to steam heating systems. What’s more, if you opt for a thermal fluid heating system with integral economiser, even less fuel is consumed, even when operating at high fluid temperatures.

However, as energy efficient as they are, the majority of thermal fluid heaters in the UK remain gas or oil fired, courtesy of our reserves of North Sea gas. That must change if we are to meet our legally binding net zero commitment by 2050. With industry accounting for over 13% of GHG emissions in 2023, decarbonisation is a top priority and process heating is moving away from fossil fuels, to more sustainable energy sources which, in most cases, will be electricity.

Electric thermal fluid heaters are readily available to aid that transition and are tried and tested; Babcock Wanson has been building them since the 1970s. Whilst their uptake in the UK has been historically low due to the comparative cost of electricity over gas, the push to decarbonise is seeing a rapid rise in the sales of electric thermal fluid heaters.

If you are considering investing in electric thermal fluid heaters as part of your decarbonisation strategy, there are some important differences between these and their fired counterparts that need to be factored in.

Design and construction

First and foremost, an electric thermal fluid heater has a fundamentally different design from fired models. 

Fired units have a central combustion chamber designed for high efficiency heat transfer in the radiant and convective sections, combustion air pre-heating and combustion controls.  This result is a relatively large unit, incorporating the integration of the safety circuits associated with the burner management system. 

Clearly, electrical units have no need for a combustion chamber or combustion controls.  Instead, electric heating elements deliver the necessary heat.  The design is more focused on the heat flux from these elements and ensuring a controlled high velocity of thermal fluid over the elements to avoid overheating. 

There are essentially two key designs to choose between: those with a single element and those with multiple.  The former are the more costly and require more space to allow for maintenance, whilst the latter simplifies the design, installation and maintenance of the heater.  Babcock Wanson electric thermal fluid heaters are based on multiple 50 or 60kW elements mounted in individual tubes which also enable better control of the flow path, reducing the risk of degradation of the thermal fluid and thermal shock of the system, and improving turndown. 

Whilst electric thermal fluid heaters themselves are often more compact than fired heaters, they have a second, separate unit which houses the controls, power section and safety circuits, which is large.  This latter unit varies significantly depending on the manufacturer.  Step control on the elements is the most frequently used method of control, but this brings the risk of over heating the thermal fluid, and thermal shock.  At Babcock Wanson, we instead use thermistor controls to reduce this risk and to provide a 50:1 turndown on the units.  We also use high integrity safety loops of flow providing and over temperature controls.  Finally, we fit Siemens PLCs with data logging to improve the operator interface and simplify fault finding.  

Installation

Apart from the obvious decarbonisation benefits electric thermal fluid heaters bring, having no direct emissions also means no need for flues and no discharge of flue gasses, which simplifies the positioning and installation of the units.  There is also no need for fuel supply pipework and infrastructure, grid supply or the safety implications of having combustible materials on site.

Operation

Operationally, there is little difference between electric and fired thermal fluid heaters.  In all cases, a pump pushes the thermal fluid through the heater, picking up the heat and transferring it to the users.  Startup is also the same, with a straightforward push of a button. 

Maintenance

An important aspect to consider when looking at electric thermal fluid heaters is maintenance.  With fired heaters, your maintenance team need to be qualified to work on fuel systems and combustion controls, whereas for the electrical units they need qualifications on 3-phase electrical systems.  There are some similarities but essentially the majority of the maintenance work on electric thermal fluid heaters is carried out using an ammeter rather than a flue gas analyser.

Whilst the number of hours maintaining thermal fluid heaters, be they fired or electric, is roughly the same, electric systems overall have less maintenance requirements as there is no fuel pipework, gas boosters, gas metering stations etc to be maintained. 

Safety

Unlike water based heating systems, thermal fluid heating systems do not operate under pressure (other than the very small pressure of the circulating pump), which already make 

them a safer system to operate. With electric versions, combustible fuels and their associated risks are removed altogether, making for an even safer system.

Impediments

Electric thermal fluid heaters put a lot of ticks in a lot of boxes for sure, which does beg the obvious question: why isn’t everyone moving over to them?

Electricity costs remain the main stumbling block, but even if costs became comparable with gas, we don’t have the infrastructure in place for a mass migration to electric. In the Net Zero Emissions by 2050 Scenario (NZE Scenario), the electrification of heating applications will see a 45% rise in electricity consumption in light industry by 2030 and 38% rise in hard to abate industry. Even with the government’s plan to unblock the grid, speed up planning decisions and build more renewables, it seems wholly implausible that the grid will be able to generate this amount of energy by 2030, or have the connectivity in place to transmit it nationwide.

There’s no doubt that electric thermal fluid heater sales will continue their upwards trajectory, but the reality is that in the UK for the immediate future most of these installations will be for small to medium sized units.

Artilce written By Etienne Fourie, Technical Sales Manager, Babcock Wanson

Babcock Wanson offers a complete range of products and services for boiler houses and other process heating needs.

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