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How Much Of Your Heat Goes Up The Chimney?

fluHow Much Of Your Heat Goes Up The Chimney?

By Grant Bailey, Global Corporate Account Director, Thermal Energy International Inc.

If your boiler or CHP system, flue gases from your boiler exhausts are taking away significant amounts of energy. Potentially 15-20% of your energy is literally “going up in smoke”. That means that along with other losses from the system, for every pound spent, only 55p of (Read More)

energy is actually being utilised.  For shell type steam boilers, flue losses account for 18% of wasted energy; heat transfer gas and water losses 2%, insulated chamber radiation losses 2% and water outlet blown-down losses 3%.  Therefore it is easy to note that the greatest energy loss is through the flue. Much of this lost heat can be regained by using a flue gas condensing economiser, which can enable the boiler’s efficiency to be

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increased to as high as 93% gross efficiency.  Because of their simple design, flue gas condensing economisers have minimal maintenance, long life and attractive payback periods.
Fuel costs and environmental regulations within the healthcare sector have created a strong need for environmental solutions to enhance boiler performance, decrease fuel costs and lower CO2 emissions.  Recent advances using equipment such as flue gas condensing economisers enable hospitals and businesses to operate boilers more efficiently and in a more sustainable way thereby including heat recovery and sustainability in one package. Flue gas condensing economisers effectively convert an industrial boiler into a condensing boiler, recovering waste heat to make hot water.
Boilers are used to create energy in the form of hot water or steam to provide heat for establishments.  During the process residual excess heat is exhausted and is wasted via the boiler flue.  A flue gas condensing economiser saves energy by recycling this waste heat from the combustion exhaust gas providing an additional energy stream, which can be used instead of the boilers original energy stream.
The economiser works by passing cold water counter flow, and in direct contact with, the entering hot boiler flue gases.   As the two stream pass each other through the stainless steel transfer media of the economiser, the cold water is heated and the hot flue gasses are cooled. Used on its own or with an indirect economiser, water temperatures of up to 120°C can be achieved, while exhaust temperatures are reduced, often to as little as 25°C.
All hydrocarbon fu¬els release significant quantities of water vapour as a combustion by product. When one molecule of methane is burned, the primary constituent of natural gas, it produces two molecules of water.  This water absorbs a portion of the fuel energy (~11%) as it turns to vapour in the burner flame.  Normally this water vapour and its associated combustion losses are exhausted in through the flue.  By cooling the flue gas to below its dew point the water is condensed and this latent heat of vaporization (as well as any sensible heat) is recovered.  By recovering this heat and putting it to beneficial use elsewhere on site, the economizer effectively improves boiler efficiency and reduces fuel consumption
The exact savings from installing a flue gas economiser vary, dependant on a number of factors, the stack temperature, the feed water volume and the hours of operation. Where a flue gas condenser economiser is fitted to the flue of a high-temperature hot water boiler, the water circulated through the economiser can be used for alternative heating purposes local to the boiler house such as space heating, domestic hot water or pre-heating of other process’.
Before deciding on purchasing a flue stack economiser system, you should first find out the features of each boiler. Learn about its combustion efficiency, maximum hours of operation, fuel consumption, stack gas temperature, steam production, and the boiler’s capacity. You should also determine what your in-plant uses for the boiler will be, like domestic water heating, makeup heating, preheating and so on. Once you distinguish all these, the decisions will come easily.
Flue gas heat recovery systems, such as those sold by Thermal Energy International, which utilise direct contact economisers, ensure maximum heat transfer and this results in maximum possible thermal efficiencies providing the highest possible energy savings for each kW of waste energy. Under the Government’s CRC Carbon Reduction Scheme, large energy users have to buy allowances for each tonne of carbon dioxide at a rate of £12 per tonne per annum.  As a consequence, participants successful in reducing energy consumption will not only save money on energy bills, but will also need to purchase fewer allowances.  As a result, for a hospital that constantly operates a boiler, installing a flue gas economizer can be a great business decision. Flue gas heat recovery systems are not just about going green they are also about saving money.
In an economic environment in which capital expenditure is often the first area that falls under the sword it is important for Energy Managers to identify effective economic solutions which enable companies to see favourable pay-back periods on spend. From a financial stand point installing a condensing flue gas economiser recovery system is one of the best choices you could make for your hospital. Quality condensing economisers usually pay for themselves within 24 – 48 months, and go on to provide you with significant energy savings for decades to come.  In addition there are many important environmental reasons why every company that operates natural gas boiler or CHP system should seriously consider investing in flue gas economiser technology. Reducing C02 emissions is good for the planet, good for government compliance, and good for public image.


Thermal Energy International Ltd., 1 John Street, Bristol, BS1 2HR Tel: 0117 917 7010
Fax: 0117 917 7011