There’s no denying that process heating systems that are widely used across industry are large consumers of energy. With sky high energy prices to contend with and Net Zero on the horizon, efforts to reduce energy consumption, improve efficiency and reduce emissions are centre stage. In the case of large organisations, assessment of the energy used within their buildings, industrial processes and transport is mandatory under the Energy Saving Opportunities Scheme (ESOS). But of course, businesses of all sizes can benefit from improved energy management.
When it comes to Firetube boilers, manufacturers of these systems have been working hard to improve overall efficiency and control of boilers and burners. Here we look at the key developments that, combined, could increase your Firetube boiler efficiency by 45% – a substantial figure.
Variable Speed Drive
Electric motors represent around 50% of global electricity consumption. In the EU alone, there around 8 billion electric motors in use. Whilst many motors are very small and use little electricity, those in industry are often large and major consumers of electricity.
Motors used on boiler feed pump and combustion air blowers traditionally operate at a constant speed. In the case of pump applications, the motor is used alongside a modulating control valve to control the pressure or flow of water. With the air blower, the motor is accompanied with variable inlet vanes or a modulating outlet damper to control the pressure or flow of air.
However, boilers are rarely operated continually at full capacity, so maintaining the motor at the same speed at all times is wasteful. Where process load demands are variable, motors can be fitted with a variable speed drive (VSD) which can increase efficiency by up to 30% (based in reduced electrical consumption).
A VSD is an electronic device used to adjust the rotation speed of an electric motor according to the needs of the application. In a Firetube boiler they can be used to vary the pump or fan speed according to demand, ramping up or down the frequency and voltage to the motor, reducing overall energy consumption.
A further benefit to be had from the use of a VSD is equipment longevity. The inherent soft-start function of a VSD, means the motor starting current can be reduced, which decreases thermal and mechanical stresses.
Flue Gas & Condensing Economisers
Economisers are essentially heat exchange devices that extract the residual heat from the exhaust gas generated by the combustion process. That recovered heat is usually fed back into the process, typically to the boiler feed water thereby optimising the overall efficiency of the plant in the most compact and cost-effective manner.
By using economisers, you can expect to increase efficiency of your Firetube boiler by 15-20%. Babcock Wanson offers a broad range of exhaust gas economisers perfectly matched to the boiler to which they will be fitted, incorporating ultra-robust extended surface tubes, which ensure the best practicable heat transfer and allow boiler thermal efficiencies of 98% and greater to be achieved. So efficient are they, that the return on investment can be as little as a single year.
Different types of economisers are available to meet a wide variety of processes and site needs, including economisers that can be mounted in a drawer in the back box of the boiler and those suitable for mounting in casing on the smoke outlet, plus economisers with feed water exchanger, and those that come with fumes / water / combustion air exchanger. One aspect that is important, especially when operating on an interruptible gas supply, is that the economiser is able to work with both natural gas and Class D Fuel Oil.
Micro Modulating Burner
By swapping to one of the latest generation of micro-modulating burners you can improve operational efficiency of a Firetube boiler by 5%.
Traditional burners are often imprecise and not well matched with the boiler. The new style micro-modulating burners, such as our Optimo range, achieve very accurate control of low excess air levels throughout the turndown range resulting in an excellent combustion efficiency no matter what the process load.
Furthermore, the latest burners have been designed with a very high turndown ratio, enabling the burner to adjust its output to meet the needs of the process. This avoids the costly energy losses incurred by continual stop/start cycles.
O2/CO Trim
Variable environment conditions, such as air temperature and humidity, as well as fuel quality fluctuations, have negative effects on the combustion process, efficiency and emissions. Not enough or too much air leads to the risk of CO production. Too much air also reduces efficiency. To protect against climatic variations, burner settings are usually done with air excess at 5-8%.
Efficiency can be increased by 0.9% by incorporating O2 control and CO measurement equipment. A combined probe measures the residual O2 and the CO level in the flue gas and communicates the information to the O2 and CO transmitter which sends a correction 4-20 mA signal to the BMS in order to adjust the combustion air damper position, or combustion air fan inverter speed. This makes for optimal excess air, ensuring complete combustion.
Conclusion
Firetube boilers have been around for nearly two centuries and, as you would expect, have changed considerably since those early days. From the energy crises of the 1970s onwards, the focus of R&D has been on improving efficiency, but only in recent years have we seen a truly concerted effort to reduce energy consumption and emissions. By their very nature, firetube boilers will remain one of the major energy consumers in any plant, but we can – and must! – take steps to reduce that energy.
Babcock Wanson offers a complete range of products and services for boiler houses and other process heating needs.
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info@babcock-wanson.com
