RETRO-FIT ECONOMISERS: by Taj Heer, M.D, Wellman Robey

Every boiler house is capable of achieving higher fuel efficiency and lower carbon emissions. There are many modifications and small adjustments that can lead to achieving these goals, but none are more significant that the “Economiser”, which deals with flue gas heat recovery.

The majority of new boilers are fitted with economisers; however there are a great number of nationwide installations with many years service left that are capable of significantly reducing fuel costs is Economisers were fitted.

The Economisers enables the boiler to operate at a much higher rate of efficiency with the result of lowering the fuel usage requirements. This is due to the capture and recycling of waste heat. The recovered heat is used to increase the temperature of the boiler feed water, which in turn reduces the amount of additional heat required for steam production. This has a direct impact by reducing the fuel requirement, hence reducing the running cost. An added benefit is the lowered environmental impact linked to reducing the amount of carbon and the volume of flue gases entering the atmosphere via the boiler chimney.

In an economic environment in which capital expenditure is often the first area that fall under the sword it is important for application/technology supply organisations to identify effective economic solutions which enable their customers to see favourable pay-back periods on spend. The Wellman Robey Economiser Retro-Fit range does exactly that by easily enhancing the boiler efficiency by 5%-7% hence giving a payback period that can be very short indeed. In addition, the design of the economisers is such that waste heat recovery is maximised dues to the large heat transfer surface areas (finned tubing) for fuel oil or gas fired boilers.

An example of cost savings once an economiser is fitted is relatively easy to understand, for example, take a customer who is operating a 7500kg/hr boiler which is fired on natural gas with a net heating value of 48,250 kj/kg- the net boiler efficiency would be 88% (according to BS845 pt1) with a flue gas outlet temperature of 238°c. Adding an economiser would reduce the flue gas temperature to 140°c and improve efficiency (again using BS845 pt1) to 94%. In pure saving terms, if you assume a natural gas price of 2.2p/kWh and that the boiler is operated 24hrs a day for 258 days of the year; the fuel consumption without the economiser would be 5,877kWk. With an economiser, the fuel consumption drops to 5,550 kWh; 327 kWk; 327 kWh x 2.2p x 258days equates to savings worth over £44,500 per year.

Wellman Robey retro-fit an average of 20 economisers a year. The single largest order has been from Glaxo Smith Kline who have recently fitted eight retro-fit Economisers at their manufacturing sites around the U.K.

As an added bonus there is a “green spin-off” which results from the fact that every economiser has the potential to save a small forest over its life span.

For more details contact Wellman Robey- 0121 543 0000

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