Heat Transfer Using Thermal Fluid

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Steam has been a valuable servant to the human race, from a means of powering engines to a method of cooking food. However, there’s one area where steam has been outdone in recent years – heat transfer using thermal fluid. Here Clive Jones, CEO of Global Heat Transfer outlines the benefits of using thermal fluids instead of steam in a heat transfer process.

Clive Jones - CEO, Global Heat Transfer — *Clive Jones – CEO, Global Heat Transfer*

Historically, if heat transfer was needed in a chemical process and heating via naked flame wasn’t feasible, steam was the preferred method. This was mainly due to the ease of sourcing water, the minimal cost of the resource and the perceived absence of environmental issues. However, using steam in a heat transfer system comes with numerous drawbacks.

Safety

Steam requires a high operating pressure to achieve temperatures necessary for operating heat transfer systems. For example, to reach 300 degrees Celsius, steam would require a pressure of 85 bars. This is roughly 14 times the pressure inside your average bottle of bubbly. Picture what happens to Champagne when pressure in the bottle builds up and is given a means of release through the weakest point – the cork.

Now times this by 14. Needless to say, the presence of high pressure brings with it the When steam reaches critical pressure and has no way of venting, the system can burst a pipe, seam or valve. This can result in an explosion of extremely hot steam and shrapnel from pipes.

In contrast, most thermal fluid systems are vented and operate at atmospheric pressure, which means the risk to life and infrastructure from pressure is minimal. The widely held view that heat transfer fluids and systems present an operational fire and explosion hazard is a misconception. This can largely be explained by the use of inappropriately designed systems or the use of inappropriate heat transfer products and their mismanagement in a system.

Efficiency

Steam heat transfer systems rely on the generation of steam to drive pressure and ultimately, temperature. Due to this dependence on a delicate pressure balance, accuracy is generally limited to swings of ±6 degrees Celsius. This value is likely to increase as the system ages and corrosion takes its toll. In addition, condensate removal in steam heat transfer systems also affects the uniformity of heating.

In comparison, thermal fluid systems can have an average temperature control of ±0.8 degrees Celsius. That's a whopping precision of 99.8 per cent at a temperature of 550 degrees. This precision is accomplished by efficient metering and mixing of cooler return fluid with warmer fluid from the supply line.

Heat Transfer Using Thermal Fluid

Maintenance

Steam heat transfer systems require constant maintenance. In fact, in some countries – such as the US – it’s a legal requirement that a qualified person must continuously monitor and maintain operations. This creates an additional maintenance and cost burden that isn’t present with thermal fluid systems.

Furthermore, steam system infrastructure is far more intricate compared to thermal fluid applications. Safety valves, condensate return pumps, expansion joints, blow downs, chemical additions and drains all need to be correctly managed for the steam systems to run efficiently. Thermal fluid systems, on the other hand, only require a pump, an expansion and storage tank and heat exchangers.

The maintenance problems don’t stop there. Common issues with water and steam systems include corrosion and freezing.

Despite steam systems depending on the use of demineralised water, the combination of water vapour and hot air alone is enough for corrosion and scaling to take place inside the pipes. To combat this, you could use stainless steel for piping, but this brings with it an added cost.

Water in steam heat transfer systems is also prone to freezing if left unused in cold conditions – for example, if a facility closes for winter or the Christmas period. If the water in the system freezes there’s a significant potential for pipes to burst, causing harm to the system and water damage to surrounding infrastructure.

In comparison, thermal fluids are extensively used in systems designed to work at low temperatures. Specific types of fluid such as Globaltherm EDT or Globaltherm ECO containing anti-freeze are specially formulated to pump at sub-zero temperatures and must be used in these cases.

Although thermal fluids don’t require constant assessment, maintenance should be frequent and comprehensive. Annual sampling of heat transfer fluids is a minimal requirement to demonstrate compliance with the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR).

However, quarterly sampling is necessary to detect any short-term changes in the status of the fluid. This acts as a means of predicting future degradation and allows companies time to take appropriate action to avoid unnecessary downtime and high costs. A strategic maintenance plan is imperative for healthy and efficient heat transfer systems.

Disposal

Engineers must treat water in steam heat transfer systems to minimise corrosion to pipes and protect from freezing. These chemicals mean that the water cannot be disposed of into drains because they are harmful to the environment.

In addition, some countries regulate the temperature of wastewater upon disposal.

Again, this is in order to protect the environment.

The disposal of water and thermal fluids that have been used in heat transfer systems, has to be carried out by qualified professionals in accordance with environmental regulations. This can be extremely expensive if unplanned, hence the need to have a comprehensive maintenance contract in place.

Conclusion

Increased safety and flexibility combined with better efficiency and more manageable maintenance has meant thermal fluid systems have definitely come out on top in recent years. Steam may have once reigned supreme in heat transfer, but thanks to increasingly sophisticated products and maintenance practices, thermal fluids now dominate industries from pharmaceutical to food and beverage manufacturing.