Energy efficient process heating

BOTH FIRE tube and coil type steam generators produce ‘dry’ saturated steam to maximise the delivery of heat to the user. Both types of boiler operate along the same basic principles in that water is confined in a restricted space and is heated by burning a fuel source. The energy of combustion is transferred from the flame to the water by radiation and conduction, heating the water and ultimately raising steam.

Modern steam generators have progressed considerably and now include a very accurately controlled burner which creates a defined heat input to a double coil of steel tube through which a precise quantity of feed water is pumped. Only a small amount of excess water is fed into the coil to provide the correct operating conditions at all times and a steam/water separator is usually incorporated at the coil outlet to ensure dry steam is provided to the process.  

Using this method, steam generators consume less energy as they only fire on demand for steam from the process, and can be very quickly brought up to working pressure when steam is required. This means the bare minimum of standing losses resulting in reduced overall emissions. Steam generators also offer improved safety due to their low water volume content and simplicity of control and operation. Babcock Wanson ESM steam generators, for example, give operating efficiencies of up to 96% with very low overall emissions.  

Developments have also been made by most good fire tube boiler/burner makers to improve overall efficiency and control, which also means reduced fuel demand, better control of the burner and general boiler safety systems and improved emissions.

With all these developments in design and control, both fire tube and coil type steam generators are ideal for use where both direct and indirect heating are required simultaneously and where heat transfer at a constant temperature is required.

The New(er) Contender

In a very large number of applications, fire tube and coil type steam generators have, however, been replaced by thermal fluid heaters.

Thermal fluid heating is based on a similar basic principle to a low pressure hot water system. It consists of a heater connected to carbon steel flow and return pipework which can provide heat to one or more users or systems. Instead of water running through the pipework, a thermal fluid – often a simple mineral oil – is used as the heat transfer medium.  

This simple and easily automated closed loop design, allowing for high temperatures (up to 350°C in standard form), means thermal fluid heating systems can use 20-50% less energy overall to transfer the same amount of heat when compared to the steam heating systems above. What’s more, if you opt for a thermal fluid heating system with integral economiser, even less fuel is consumed, even when operating at high fluid temperatures. The Babcock Wanson EPC ES Thermal Fluid Heater, for example, is an automatic coil type, multi-pass thermal fluid heater which precisely matches fuel input to plant energy requirements and includes its own in-built exhaust gas to combustion air economiser for highest practicable operating efficiency.  

There are a number of other very important benefits – financial, environmental, safety and otherwise – to be had from using thermal fluid heaters.

Massive gains have been made in making process heating systems more energy efficient and, in doing so, have also reduced emissions: a double win. If you are still relying on older steam based technology, rather than commit to a new, more energy efficient system, you might want to think again as the energy savings alone could well save you money over a short period of time. 

Etienne Fourie is technical sales manager at Babcock Wanson

www.babcock-wanson.com