Raising the bar for steam boiler efficiency
Byworth Boilers are yet again raising the bar for steam boiler efficiency with the addition of an air to air heat exchanger to pre-heat the combustion air. This, together with other fuel saving design features gives a predicted net efficiency of 94.3% for these new boilers which are currently being installed in Surrey.
Byworth’s Managing Director Peter Baldwin commented, “We have placed a great deal of importance on R&D in the past few years, the goal being reduced energy costs for our customers. As an independent boiler maker, with all production taking place here in the UK and having our own expert design team, developing new concepts is perhaps relatively easy for us.”
The two Yorkshireman2 boilers are each 3500 kg/hr output and have a working pressure of 17 bar g. The basic design of the Yorkshireman boiler is in itself important for efficient operation. The three pas wetback boiler range is designed with generous shell and furnace dimensions. A plentiful steam space is important for good quality dry steam and to reduce the risk of priming and “carry over”. The furnace length and diameter ratio, which is critical to reduce NOx formation, and the heating surface for optimum efficiency are all important features of the boiler design. As a most efficient and reliable boiler range, the Yorkshireman has featured predominantly in Byworth’s R&D. Peter believes, “If you want to push the boundaries of efficiency it is obvious to start with the best available boiler and add energy saving features to that basic design”.
The inclusion of special X-ID fire tubes in the Yorkshireman2 boiler range gives a significant increase in efficiency. The internal helical ribbing of these special tubes not only increases surface area, but creates a complex boundary layer attachment/reattachment phenomenon. This reattachment vastly increases heat transfer from the tubes, up to 85% greater than for a plain tube. The overall boiler efficiency for these 3500kg/hr boilers is increased by around 2%, and with a modest premium paid for this feature, payback is literally achieved in a few weeks. Maintenance is the same as for plain tubes, and X-ID can be used with great results on fuel, even heavy oil.
Flue gas economisers are a proven concept and can improve boiler efficiency by up to 5%. The heat in flue gases, which would otherwise be lost up the stack, is utilised in an air to water heat exchanger to preheat the feed water to the boiler. The Byworth economiser seen here in the photo is a drawer type for ease of maintenance and located above the rear smoke box.
Even after the flue gases have passed through the economiser there is still usable heat. The air to air heat exchanger shown here above the economiser draws clean air past banks of tubes in which the flue gases pass en route to the stack. The combustion air then travels through specially designed ducting incorporating a bypass section for use should preheating not be required. Air pre-heaters can be used without an economiser providing very cost effective fuel saving on all fuels.