Chris Horsley explores the longevity of thermal fluid heaters
For a process heating equipment manufacturer, you might just say thermal fluid heaters are bad for business. They just go on and on and on, and maintenance and service requirements are low, in fact a fraction of the cost of maintaining an equivalent heat output steam plant. Where’s the repeat business? Where’s the big service contracts and money to be made replacing worn parts? Of course, for a customer, this is music to your ears!
Thermal fluid heaters frequently run for 20 years and often longer. Even when the heaters themselves might be at the end of their working life, the pipe work system and other plant is often as good as new, so upgrades are simple and cost effective to implement at any time.
What is a thermal fluid heater?
Thermal fluid heating is based on a similar principle to a simple hot water system. It consists of a heater connected to carbon steel flow and return pipework that can provide heat to one or more users or systems. Instead of water running through the pipework, a thermal fluid – typically a specialist mineral oil or synthetic based fluid – is used as the heat transfer medium. Different fluids can be used to meet specific process heating requirements including high temperature operations and processes requiring heating and cooling thereby making it a very flexible system.
Thermal fluid heaters typically operate at up to 350°C at atmospheric pressure and remain pumpable down to minus 20°C and lower with special fluids, which makes it a solution suitable for a multitude of applications.
The rise of thermal fluid heaters
Thermal fluid heaters have rapidly grown in popularity across all industry sectors over the years. This is mainly due to their far-ranging benefits which include their ease of use, compact size, safer operation when compared to steam generators, precise heat control, low exhaust emissions and their energy efficiency. They also operate outside the Pressure Systems Safety Regulations as the fluid is not maintained in the liquid phase by pressure, so statutory inspections are eliminated. This further reduces operating costs and increases plant availability.
When it comes to flexibility in use, thermal fluid heaters often work at high temperatures in a simple closed loop. Compared to a steam system this means no change of state of the fluid, so no condensate and therefore no flash steam losses, no blow down losses or make up water required, no effluent discharge and completely corrosion free operation without the need for expensive chemical treatment. The savings thermal fluid heaters bring are very significant, often up to 50% of the overall cost of running a process heating system.
But one aspect that frequently gets overlooked is the longevity thermal fluid heaters enjoy, which should be a major point when deciding how to heat a process, especially in these uncertain times when many businesses are having to buckle belts that much tighter. With sustainability a key issue, plant longevity is not only about reducing capex, but also reducing wastage and equipment redundancy.
What constitutes long life?
As mentioned, a thermal fluid system should easily serve you 20 or more years without any reduction in productivity as it ages. It would be difficult to find any equipment, process or otherwise, that can match this level of service. Take 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 more than 100,000 hours - or the equivalent of 3,000,000 miles with the minimum of service requirements! And that’s just looking at heaters with a typical lifespan; Babcock Wanson is still servicing heaters that are more than 40 years old and working away every day quite happily!
The secret to long life
There’s no secret elixir for long life when it comes to thermal fluid heaters. Their exceptional longevity is a direct result from their passive nature (there are very few moving parts) and the swapping out of water for a thermal fluid as the heat transfer medium. Unlike water and steam based systems, thermal fluid heaters are unaffected by corrosion caused by water over time, or by ambient temperature where water freezing within pipes leads to costly failures. In fact, most thermal fluids are mineral oil based so are effectively lubricants that help keep the system components protected in use.
However, not all thermal fluid heaters are equal, so it pays to do your homework. Heaters that will best stand the test of time are mostly designed for a downward fired configuration which ensures stress free and unrestricted expansion of the heater coils during normal operation. Also look for a heater that has been designed with a barrier between the hot combustion gases and the outer structure, as this will help provide long heater life as the higher pressure and cooler outer air helps prevent any escape of combustion gases as the plant ages over time. Babcock Wanson’s TPC and EPC range of thermal fluid heaters, for example, come with an integral, air-cooled outer case that provides this barrier, as well as acting as both a combustion air pre-heater/economiser. Lastly, ensure the heater is fully integrated and has a factory tested control system.
Another key factor is overall emissions. With higher process operating efficiency comes lower total emissions which provides savings in operating costs whilst being much better for the environment.
It’s also vital that the thermal fluid heater you decide upon is correctly installed, commissioned and maintained. Thermal Fluid Systems - A Practical Guide for Safe Design, Operation and Maintenance’from the Combustion Engineering Association (CEA) proffers excellent advice for designers, owners, managers and operators of new and existing thermal fluid heating systems to operate safe and efficient installations. It addresses system design considerations such as choice of fluid, heat source, expansion and deaeration, pumps and pipework, to installation and commissioning and operation and maintenance. It’s important to understand how thermal fluid heaters work to ensure you get the most out of your investment, including long life.
With careful system design and careful choice of heater design a thermal fluid system will provide many years of trouble-free ownership, allowing the operator to concentrate on their process needs in the sure knowledge they are getting the best from their process heating investment.
Chris Horsley, is Process Engineering Director at Babcock Wanson