SITE, BUILDINGS, ENERGY
WORKS MANAGEMENT
H E AT R E C O V E R Y
How much of your
Heat goes up the
Chimney?
Flue gases exhausting from your boiler or CHP system
are taking away significant amounts of energy. Potentially,
15-20% of your energy is literally ‘going up in smoke’
explains Grant Bailey, global corporate account director
with Thermal Energy International. This means that along
with other losses from the system, for every pound spent,
only 55p of energy is actually being utilised.
F
or 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 increased to as high
as 93% gross efficiency. Because of their simple design,
such economisers have minimal maintenance, long life
and attractive ROI.
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.
The economiser works by passing cold water
counter flow, and in direct contact with, the entering
hot boiler flue gases. As the two streams 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 burnt, 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 products are
exhausted 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 (eg space heating,
domestic hot water or pre-heating of other processes),
the economizer effectively improves boiler efficiency and
reduces fuel consumption
The exact savings from installing an economiser
vary, dependant on a number of factors - the stack
temperature, the feed water volume and the hours of
operation. 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, capacity and what
the boiler is used for on site. Once you establish all these,
the decision will come easily.
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 business 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 business. Quality condensing
economisers usually pay for themselves within 24 – 48
months, and go on to provide significant energy savings
for decades to come. In addition there are many
important environmental reasons why every company
that operates a natural gas boiler or CHP system
should seriously consider investing in the technology.
Reducing C02 emissions is good for the planet, good for
government compliance, and good for public image.
t: +44 (0)117 917 7010
www.thermalenergy.com
ME | Nov/Dec 2012 | 51