Process heating that is kinder to the environment

Paul Boughton

Thermal fluid heating has had a major impact in terms of greater sustainability and reduced energy costs whilst maintaining efficient production. Chris Horsley reports.

Process heating is integral to nearly all manufacturing processes, be it food processing, metal finishing, pharmaceuticals – in fact the list is pretty much endless. In an age where traditional fuel sources are understood to be finite, energy prices are rocketing and environmental considerations are being taken seriously by industry at large, a huge amount of time, expertise and resources has gone into finding alternative ways to raise heat for industry. Significant strides have been made in reducing energy consumption in the process. 

One of the most notable developments has been the widespread adoption of thermal fluid heating systems as an energy efficient, more sustainable alternative to water based steam systems that were the norm 50 years ago.

Thermal fluid heating systems have had a major impact across industry, and have become the heating system of choice for most applications requiring regular, large amounts of heat, including high temperature applications.

The operating principle and physical construction of a thermal fluid heating system has many similarities to that of a standard domestic hot water system, consisting of a heater connected to mild steel flow and return pipework providing heat to one or more users/systems. The key difference is the replacement of water in the pipework with a thermal fluid.

You may initially - and logically - think that water has to be more environmentally friendly than any special thermal fluid as it’s a naturally occurring, plentiful substance and usually has a very low initial cost. All true, but the water used within a steam system needs to be pre-conditioned and chemically treated to remove harmful compounds such as hardness and dissolved Oxygen before it can be used, otherwise the water will cause scaling and corrosion which can very quickly lead to equipment failure.  Advances have been made in developing more environmentally friendly water treatment processes but these are not in widespread use and inevitably cost more.

On the other hand there are a wide range of thermal fluids available which act as excellent heat transfer mediums. The majority are industrial grade mineral oils, some are synthetic, and some are food grade fluids which are approved for incidental contact with food. Most thermal fluids tend to have a very long life - often more than ten years, depending on the temperature of operation, how close it is to maximum bulk range and the number of thermal cycles. Furthermore, the fluids are generally recyclable in the case of oils, whilst most of the specialist fluids can be re processed so end of life requirements are easily managed.

But the most notable environmental contributions a thermal fluid heating system has over its rivals comes from the overall substantial energy savings achieved and the subsequent reduction in overall emissions from the system.

Thermal fluid heating systems are closed circuit, no-loss systems which results in minimal heat loss. When compared with a steam system this means no change of state of the fluid so no condensate and therefore no flash steam losses also no blow down losses or make up water are required. Plus, because it is a closed loop system where pressure is not related to temperature, they are able to economically work at high temperatures (up to 350°C in standard form). It all adds up to substantial savings for the user.

With Babcock Wanson’s TPC1000B thermal fluid heating system, for example, between 20-50 per cent energy savings can be made when compared to the transfer of the same amount of heat using traditional steam boilers. The system precisely matches fuel input to plant energy requirements for high efficiency. 

Of course, the less you have to fire the burner and the lower energy input demand, the lower mass flow of pollutants get discharged to the atmosphere, so there are important environmental benefits to consider. The nature of the exhaust gas is dependent on the fuel, but in the UK it is mainly natural gas, resulting in generally clean exhausts containing small amounts of CO and NOx. This is the same for any natural gas fired appliance. Discharge water from boiler blow down is also no longer an issue. Although considered as non toxic, the water needs to be cooled before being sent to the drain and is usually quite alkaline so avoiding this procedure altogether is a further environmental benefit.

Lastly, if we are to cover all environmental considerations, we should look at the amount of equipment used within the process and length of life. 

With thermal fluid heating systems, there is considerably less associated equipment required than with steam boilers. There is no need for water treatment systems and no equipment to handle condensate, etc. They are highly compact, so take up less space and can often be installed in the immediate processing area thereby cutting down the amount of energy lost in transmission of the heat to the point of use to the absolute minimum.  hey also require much less day-to-day management or maintenance and can often run for many months at a time with only the minimum of monitoring.

Thermal fluid heating systems score high on longevity as well. Babcock Wanson is still servicing heaters that are more than 40 years old. You would be hard pushed to say this for much other processing equipment. In fact, it would be difficult to find any equipment, process or otherwise, that can match this level of service. ake a car, for example. Assuming the car runs at an average 30mph and covers 200,000 miles before being scrapped it will operate for about 6000 hours in its total life. A Babcock Wanson thermal fluid heater, on the other hand, will usually run for 20 years - more than 100,000 hours or the equivalent of 3,000,000 miles. Not bad going! In fact, even when the heaters themselves might be at the end of their life, the pipe work system holding the thermal fluid is often as good as new so upgrades are simple and cost effective to implement at any time.

Process heating by its very nature will always be a large energy consumer and its widespread use across manufacturing only goes to exacerbate this. There’s no magic wand to change this situation – if we want to continue manufacturing, we have to continue to apply heat to many of the processes involved. However, what we can do is manage that energy consumption and manage the waste by-product. By reducing the former through the use of energy efficient thermal fluid heaters we also reduce the latter; it is a sensible way to combine sustainability with efficient production and reduced energy costs.

Chris Horsley is Managing Director of Babcock Wanson UK Ltd, Borehamwood, Hertfordshire, UK.