Steam Boiler Efficiency

Improvements in Boiler Efficiency reduces fuel bills by up to 16%

First, I wish to thank all those who took the time to reply after reading “Beating Boiler Failure”. I am encouraged by the response, more anon.

One of the aims of the FORUM is to share knowledge and it has been pointed out by ‘Helen of Keighley’ that the statement in the article regarding ‘Boiler Efficiency’ is out of date.

There has been much improvement over the last 10 to 15 years and boiler efficiency has risen from the commonly stated 80% to 90% and even as high as 92.3%.

Trust a Yorkshireman to correct a Lancastrian.

Boiler Efficiency is very topical as fuel prices continue to rise. Any increase that has an impact on profitability of the company tends to focus the mind on ways of reducing costs.

The possibility of reducing a monthly fuel bill of £30,000 by £4000 or £5000 has to be worthy of investigation.

Boiler efficiency, the ratio of heat output against heat input, where the heat output is equivalent to the heat input minus the sum of the losses.

Improvements in boiler efficiency can therefore only be achieved by reducing the losses.

Those losses are:-

1.      Sensible and Latent heat content of the exit gases…….Flue gas temperature

2.      Incomplete combustion of the fuel……………...Incorrect Air/Fuel mixture

3.      Radiated heat losses from the boiler shell……….Insufficient or poor lagging

Modern burners, with microprocessor based modulating controls and inverter driven fans have all but eliminated incorrect air/fuel mixture and improvements in lagging materials has further reduced heat losses, which between them account for 1% to 2% of the losses at Maximum Continuous Rating (MCR). 17% to 20% of the losses were accredited to the heat content of the flue gases.

It follows therefore that any significant increase in efficiency has to come from improvements in transferring the heat content of the fuel into the boiler water. The more heat you absorb the lower the flue gas temperature will be and the greater the efficiency.

There is a practical limit to the amount of heat that can be transferred, getting that balance right is the Boiler Manufacturer’s art.

To maximise the heat transfer surfaces, the shell and furnace tube has to be generously sized to generate good quality steam and achieve good combustion, whilst optimising the diameter and wall thickness of the boiler tubes. Too thin they become weak when hot too thick and it affects the heat transfer rate.

A recent press release in November issue of Factory Equipment highlights that Byworth Boilers had won the Lord Ezra award 2007 for excellence in the combustion industry. This followed a 4 year R&D project in conjunction with Leeds University culminating with proven increase in boiler efficiency from 90% to 92.3%. They have achieved the optimum configuration of shell, furnace and tube with a double benefit of higher efficiency and lower emissions.

Byworth’s stated claim that the Yorkshireman2 boiler is the most efficient steam boiler available in the UK today is based on the utilisation of the XiD tube in place of the common plain boiler tube, which greatly increases the heat transfer rate by up to, an impressive, 85%.

The boiler efficiency of 80%, which I quoted in the inaugural article ‘Beating Boiler Failure’ was based on the governments ECA scheme estimates that most old boilers run at around 80% efficient. That statement is only relevant if the boilers are well maintained, with all the heat transfer surfaces clean and in good condition.

Oversized or undersized boilers impact on overall efficiency as does incorrect or lack of water treatment.

This conveniently brings me back to my pet subject of the importance of improving boiler water treatment.

‘Beating Boiler Failure’ part2 will appear next month and focus on the effect incorrect treatment has on the heat transfer surfaces. In the meantime why not follow the link to Byworth’s web site www.byworth.co.uk for more information about improving boiler efficiency and opportunities to save money.

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