Key points
Why aren’t more companies reaping the benefits?
Chris Horsley, Managing Director of Babcock Wanson asks why more companies aren’t reaping the benefits of thermal fluid heating systems with integral economisers.
Economisers for Steam Generators have been around for many years and virtually all boiler makers offer them. Economisers for thermal fluid heating systems, on the other hand, are a different matter; few manufacturers offer them as they are more difficult to integrate into the process and even fewer still are able to provide integral economisers.
With thermal fluid systems becoming an increasingly popular process heating method because of their very high overall process efficiency, ease of use and compact nature, it’s a wonder why more manufacturers don’t provide them and why more customers don’t demand them.
If a customer has opted for a suitably sized thermal fluid heating system because of its energy and cost saving factors, then buying one with an integral economiser would seem to be a no brainer; after all, they provide added savings from recovering and reusing what would otherwise be waste heat.
What are economisers?
In case you are unfamiliar with the concept of economisers, they are essentially heat exchange devices that extract the residual heat from the exhaust gas generated by the combustion process. Often, that recovered heat is fed back in to the process; in the case of Steam Boilers to preheat the feed water, thus lowering overall fuel consumption and ultimately resulting in reduced operating costs and lower total exhaust emissions.
But what about when higher process fluid temperatures are required?
For thermal fluid systems, return fluid economisers are not really practical due to the high fluid temperatures involved. Systems do exist which work to recover heat to an external heat sink, but there is always the challenge of matching the heat load of the slave system to that recovered from the Thermal Fluid Heater.
This is not always an easy task and it often results in having to dump valuable recovered energy when the needs of the two systems do not match up all the time. As a result, a different approach needs to be taken.
One such approach has been to create an integral, double, combustion air pre- heater. The standard pre heated jacket, which is fitted to the majority of thermal fluid heaters, 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. However, extra floor space is needed – up to 50% over thermal fluid heaters without economisers – but as the systems are so compact in the first place, this shouldn’t be an issue for most facilities.
Take a thermal fluid system with a 1000kW load as an example. To reach the heat load absorbed by the process using a standard heater you would need around 1300kW gross heat input, which allows for energy loss from chimneys etc. Having a high surface integral economiser fitted in that heater will reduce the energy input demand by circa 65kW/h.
Over a single year, assuming the heater is working 60-70% of the time, this could equate to anywhere between 340,000 – 400,000 kWh. Translating that to monetary value, if we assume a gas cost of 0.02p per kWh gross, we can easily see a saving of circa £7000 per year and that’s just on the smaller heaters.
In terms of payback period, one to two years is average, although for larger heaters the payback is even quicker; just a single year on a 2000-3000kW heater.
Keep in mind also that with an integral economiser there is no water or other intermediary fluid required, so no water treatment and no risk of corrosion. The inbuilt preheater works on clean combustion air and high velocity flue gas, so is virtually maintenance free and will provide very high performance for the life of the heater.
As you can see, economisers quickly pay for themselves. They have grown in popularity over recent years to reflect changes in the political and social landscape where energy saving has made it on to the agenda. Rather ironically, when fuel was at its peak price economisers were rarely specified in a system!
As mentioned, economisers can work with both steam and thermal fluid heating systems.
In the case of Steam Generators, the economiser is fitted on the flue box and the recovered heat is mainly used to preheat the feed water. The harder the Generator works, the greater amount of heat recovered. It’s very simple to use, with no operator intervention necessary and no heat sink required. It’s also very easy to retro fit to any manufacturer’s boiler.
The only considerations are fuel source, so consider one that permits dual fuel operation with both gas and light oil whilst greatly extending periods between cleaning due to the non-fouling fins of the extended heating surface.
Benefits of thermal fluid heating systems with economisers
To show the benefit of thermal fluid heating systems with integral economisers in real settings, let us look at a client of ours. Formica – a leading provider of branded, designed surfacing solutions – has fitted one of our EPC 1500ES fully automatic coil type, multi-pass Thermal Fluid Heater with an integral exhaust gas to combustion air economiser at its North Shields site to heat a newly installed oven used in the manufacturing process.
During commissioning, with an outlet thermal fluid temperature of 287°C, the flue gas was cooled to 200°C giving a combustion efficiency of 90-91 %. However, in subsequent operating tests under production loads and with a lower outlet thermal fluid temperature of 251°C, flue gas temperature was only 127°C and combustion efficiency increased to 94%.
This high level of efficiency under working conditions really reduces the overall fuel consumption below that normally anticipated when high temperature fluids are required for process heating applications.
Similarly, Total UK Ltd has installed two 2500kW EPC ES Thermal Fluid Heaters at its Preston based Bitumen Division to improve operating costs and cut emissions.
They are being used to heat the bitumen to a constant 180°C to maintain its fluid state, enabling it to be pumped to where it needs to go, and the key benefits already reaped include a reduction in fuel costs from greater efficiency plus a reduction in stack emissions.
With lower energy input demand also comes lower total exhaust emissions, so there are also environmental benefits.
So, with the efficiency improvements and energy savings that are readily achievable by using a thermal fluid heating system with integral economisers, and with a remarkably short payback period, the question remains: why aren’t more companies reaping the benefits of this proven technology?
Let’s hope that’s not a question we’ll be continuing to ask for the foreseeable future.
