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BOILERS, PUMPS & VALVES FEATURE


ENERGY EFFICIENT PROCESS HEATING


Chris Horsley, process engineering director at Babcock Wanson, explains how massive gains have been made in making process heating systems more energy efficient and, in doing so, have also reduced emissions


Right:


The EPC ES Thermal Fluid Heater 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


A


plant room in the 1980/90s invariable featured fire tube boilers


and steam generators – big fuel guzzling beasts that had relatively limited temperature control and required skilled engineers to be available at all times to operate them. Energy efficiency was not high on the list of priorities when it came to process heating back then – fossil fuel was low in cost and the idea that it might run out at some point wasn’t a consideration. And, as for the wider green agenda, including concerns over pollution and air quality, well that barely made it on to the radar. A lot can change in 30 years – and


now every aspect of manufacturing has come under the energy efficiency spotlight. With heat raising systems being particularly large energy users, manufacturers have invested considerable R&D resources into improving existing systems and developing entirely new energy efficient ones.


Babcock Wanson ESM steam generators give operating efficiencies of up to 96% with very low overall emissions


IMPROVING ON THE PAST 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 the new kid on the block: 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


/ ENERGYMANAGEMENT


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, but that’s for another time. 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.


Babcock Wanson www.babcock-wanson.com


ENERGY MANAGEMENT | WINTER 2020 19


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