High Temperature Thermal Oil Circulating Pumps

In our latest case study, we’re going to be looking at high temperature thermal oil transfer and circulating pumps.

We were recently contacted by a company which installs industrial boiler rooms. They regularly carry out boiler maintenance and overhaul, and asked if we could supply five bareshaft thermal oil pumps which they could install at short notice. 

A bareshaft pump is a standalone pump that is supplied without any motor or base attached. Therefore, our five pumps would be coupled up to the client’s own existing motors and used to circulate thermal oil. 

What is a thermal oil system?

Also known as a thermal fluid or hot oil system, a thermal oil system uses special thermal oil to transfer heat to machinery, materials and a variety of industrial processes. 

The actual system is surprisingly simple. A heater warms the thermal oil which the thermal oil circulating pump then pumps through a closed-loop system. When passing through, the special thermal oil transfers heat to the processes involved and then returns to the heater to be warmed up again.

What are the benefits of a thermal oil system?

Thermal oils are basically used as a heat transfer medium to indirectly transfer heat within a closed system.

One of the major benefits is that the pumps which transfer them do it without creating hot spots which can damage a product through thermal cracking, thermal decomposition or solidification.

In addition, hot oils provide uniform heating at a high temperature where it’s not possible to use direct flame or high heat. This makes them perfect for applications based around flammable liquids like heavy fuel oils that demand safe handling at high temperatures. 

In short, the benefits of a thermal oil system are:

• High temperature applications - thermal oil pumps are specifically designed to handle very high temperatures, making them suitable for processes that would be impossible with other methods
• Heat transfer – they circulate special oils able to withstand high temperatures. These then transfer heat from a heat source to the required process area without burning or evaporating
• Safe handling of flammable liquids if direct heating of flammable liquids is risky. Thermal oil pumps are a safe way to transfer heat through the circulating oil 
• Preventing hot spots - by continuously moving the thermal oil, the pump helps to prevent localised hot spots which could damage materials or cause safety issues 
• Precise temperature control – the system can operate at precisely the right temperature needed for each process 
• Indirect heat – the heater and the object being heated never come into contact 
• Safer and more efficient - thermal oil systems are safer and more efficient than steam-based processes as they operate at substantially lower pressures making leaking or venting far less likely, and processes less hazardous.

Where are they used?

Thermal oil applications often use high-viscosity pumps and positive displacement pumps, as they provide reliable circulation and consistent heat distribution. 

A good example of this are tank farms. These are facilities that store massive quantities of liquids, gases or vapours in large tanks. They are commonly known as oil terminals, installations or depots. 

As you can imagine, tank farms are hazardous environments handing extremely flammable liquids. Air-cooled thermal oil pumps help heat tanks and reduce stored liquid viscosity for easier, safer handling. 

The perfect solution for tank farms

Thermal oil circulating pumps can operate at high temperatures up to 400°C but without high pressure, which is preferable due to higher equipment cost and safety issues around high-pressure processes. 

In fact, thermal oil transfer pumps work at much lower pressures down to as little as 1 to 2 bar without the risk of leaks. If water was used as a heating medium it would need to be pressurised to high pressures to stop the water evaporating as steam.

What’s more, at 233°C a pressure of 30 bar would be needed to keep the water liquid and stop it evaporating. This also means that piping and equipment would need to be rated right up to 40 bar and would need regular safety checks. 

Furthermore the viscosity of thermal oil is much higher than steam meaning it is less likely to find ways to leak out. Plus, heated water transfer systems require treatments to prevent calcification as well as higher grades of materials. 

Thermal oil systems also play a crucial role in industrial processes requiring precise temperature control such as:

• Chemical processing plants - used for heating up reaction vessels or drying materials
• Power generation - thermal oil systems preheat boiler feedwater
• Food processing facilities - used for heating large tanks or cooking processes

What can be used as thermal oil?

Thermal oils can be synthetic or mineral. Synthetic oils like silicone or terphenyl are less likely to form carbon, while mineral oils are petroleum-based hydrocarbons.

So, some examples of liquids used for high temperature transfer include water glycol and propylene glycol within food. Mobiltherm, Dowtherm and Duratherm are all popular brands of heat transfer fluids used in a range of industries. 

Duratherm S has the industry's highest flash point of 324°C and can be used across applications demanding incredibly high temperature transfer. While Therminol 66 is the world's most popular high temperature heat transfer fluid. It can be pumped at low temperatures too but still provides thermal stability at high temperatures.

When choosing a heat transfer fluid, you need to look at things like safety, chemical composition and compatibility with other fluids. 

Possible issues with thermal oil system pumps

1. Seal failure or leakage

If thermal oil transfer pumps aren’t regularly maintained and inspected, or if the thermal oil degrades and deposits build up in the system, then the seals can fail.

Depending on how long the pumps are operating each day, the mechanical seals and gland packing should be replaced to ensure that the pump works as efficiently as designed.

What’s more, due to the high temperatures involved bearings should be regularly inspected and regreased using the right grease for high temperatures and rigorous operational conditions.

2. Poor performance

Sometimes, high temperature oil pumps struggle to achieve the desired flow and pressure. This can be because the oil is more viscous than was briefed at design stage for the specified duty point of the pump. 

In most cases, centrifugal hot oil pumps are specified which means that the pump’s duty point depends on pre-agreed values of viscosity, pressure and speed. 

If the oil is heated to a different temperature or under-heated, then the pump might not be able to deliver the necessary performance. This would then lead to higher circulation within the pump head, overheating of the seal and much higher wear on the pump. 

To avoid this happening, the NPSH available to the pump and the oil temperature should be checked regularly. The pump speed should also be correct to achieve the required output. 

The NPSH or Net Positive Suction Head is simply a measure of the pressure acting on a fluid on the suction side of a centrifugal pump. It’s monitored to stop the pump running under conditions which might cause cavitation.

What pumps did we specify for this client?

At North Ridge Pumps, we’re not limited in the type of pumps we can specify. As the UK’s largest pump supplier with over 25 years in business, we’re expert at choosing pumps for a vast range of applications.

In fact, we draw on our specialist knowledge and experience to come up with the right specification for every client - not a standard solution picked off the shelf. Just as important, we specify the best pump for every project brief offering the most cost-effective long-term option. 

For applications like this, our thermal oil pumps offer safe, consistent heating where direct heat is impractical. In short, we’re experienced at supporting high-temperature operations across diverse industries such as power generation, chemical manufacturing and food processing.

We can supply air-cooled thermal oil pumps offering variable speed drives to match your required levels of demand, and with double mechanical seals and cooling fins so external cooling isn’t necessary.

The five bareshaft pumps needed by our boiler installation client were for the circulation of hot oil at temperatures up to 300°C.

So all of the five high temperature oil pumps we supplied are self-cooling thanks to the fins at the rear of the casing. In addition, they have a double sealing mechanism as mentioned incorporating both mechanical seals and gland packing.

This double level of protection ensures that should the seals fail, they will continue operating without interruption. The pumps also work at different pressure levels, some delivering 100M³H and others 75M³H.

If you have an application requiring high temperature heat circulation, or are involved in any kind of fluid transfer, and need advice on the right pump for you, speak to North Ridge Pumps to see how we can help.