Integral high efficiency economisers

Economisers for steam generators have been around for many years but few manufacturers offer economisers for thermal fluid heating systems and fewer still provide integral economisers. The main reason for this is that they are more difficult to integrate into the process and return fluid economisers – as used with steam generators – are not really practical due to the high fluid temperatures involved. Systems 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.  

Babcock Wanson’s approach has been to create an integral, double, combustion air pre-heater as found in the EPC-ES Thermal Fluid Heater. 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 design allows 5 to 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.

Delivering savings 

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 to 400,000kWh.  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 to 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.

So, with the efficiency improvements and energy savings that are readily achievable by using thermal fluid heating systems 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?