Contents:
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Heat Recovery
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Environemntal Benefits of Closed Loop Cooling Systems
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Energy Savings
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Leak detection
Heat Recovery:
Although many traditional heat
exchanger applications can be considered heat recovery, we are seeing a
significant increase in new heat recovery opportunities. Most of the
applications we focus on involve exhaust gas heat recovery and
wastewater heat recovery.
Flue gas heat recovery systems are a simple and
cost-effective way to capture the energy that is lost in flue
gas exhaust and to use that energy elsewhere. Installed in exhaust
stacks for steam boilers, hot water boilers or high temperature ovens
for process work, heat recovery coils can capture this waste heat to
generate low, medium or high temperature fluids (air, thermal
fluid, glycol, or water) for use in process fluid pre-heat, facility
heat, combustion air preheat, etc.
Our flue gas heat exchangers can be built for
either condensing or non-condensing applications to match your
requirements. Combined with Thermal Storage Systems or Heat Pumps, these
systems can reduce flue gas temperatures to nearly room temperature -
increasing combustion efficiency to greater than 95% - and store energy
at a variety of temperatures.
The heat exchangers can be designed for gas,
oil or even chemical vapor and depending on the application may be
coated to suit the exhaust gas conditions. Stainless steel, carbon
steel, and aluminum heat exchangers are available with fin spacing and
fin-tube construction designed to match temperature, fouling potential
and maintenance requirements.
Hot or cold water going to waste is an another
opportunity for heat recovery. Similar to exhaust gas applications, the
exhaust water can be used to heat or cool air, thermal fluid, glycol,
water or other fluids. Even in circumstances where the water may be high
fouling an appropriate heat exchanger can be selected.
I cases of poor water quality, energy recovery
systems can be designed to recover heat or cold from process grey water.
Specifically designed for fibre-contaminated water, these systems can
recovery 90% of the energy in hot or cold water systems:
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Commercial laundry services
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Hospital laundry wash water
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Hotel laundry wash water
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Institutional laundry wash water
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Textile manufacturers
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Vegetable wash water
Environmental Benefits of Closed-Loop, Evaporative Cooling:
Closed-Loop: We are fortunate in Canada
that we have an abundance of cold water naturally available for our
use. A common use of this water has often be to cool industrial
equipment often through an intermediate heat exchanger. This practice
has become less practical with the environmental concerns of leaks and
also the changing water chemistry of river water can require some exotic
and expensive metallurgy in the heat exchangers. Many “once -through”
cooling systems are being replaced by Closed-Loop Systems.
The
alternative to “once-through” type cooling has typically been to
deliver water that has been cooled by a Cooling Tower, however the cold
temperature of the river water often cannot be matched by a Cooling
Tower. Using Closed-Loop, Evaporative Cooling also know at Wet Surface
Air Coolers (or WSAC) can typically gain a few degrees more cooling than
a Cooling Tower/Heat Exchanger system. This can often be achieved with
lower power demand, less water consumptions and a significant reduction
in chemical treatments to the make-up water which is an added
environmental benefit.
Power Consumption: Closed Loop
Evaporative Coolers consume less parasite energy than a traditional
cooling tower for the same heat rejection. Typical fan horsepower is
reduced by 10-25% and a ypical pumping horsepower reduction of 10-40%.
Water Conservation:
Spray Water Source
One of the key advantages to a Wet Surface Air
Cooler over a traditional cooling tower is its capability to use poor
quality water as the spray water. The fact that the spray water is not
being sent through a heat exchanger, fouling is not a concern. Water
that cannot be used for other processes can often be used as spray water
in Wet Surface Air Cooler. Common spray water sources are;
Cycles of Concentration
As discussed previously, the spray water is not
being sent through a heat exchanger and fouling is not a concern,
therfore higher cycles of concentration can be run.
Cycles of concentration represents the
accumulation of dissolved minerals in the recirculating cooling water.
In a cooling tower or Wet Surface Air Cooler, the evaporated water
leaves its dissolved salts behind in the bulk of the water that has not
been evaporated, thus raising the salt concentration in the water. To
prevent the salt concentration of the water from becoming too high, a
portion of the water is drawn off for disposal (called blowdown). Fresh
water makeup is supplied to compensate for the loss of evaporated water,
drift and the blowdown.
The chemistry of the makeup water including the
amount of dissolved minerals can vary widely. Makeup waters low in
dissolved minerals such as those from surface water supplies (lakes,
rivers etc.) tend to be aggressive to metals (corrosive). Makeup waters
from ground water supplies (wells) are usually higher in minerals and
tend to be scaling (deposit minerals).
Increasing the amount of minerals present in the
water by cycling can make water less aggressive to piping however
excessive levels of minerals can cause scaling problems. As the cycles
of concentration increase the water may not be able to hold the minerals
in solution. In a typical cooling tower / heat exchanger system, When
the solubility of these minerals have been exceeded they can precipitate
out as mineral solids and cause fouling and heat exchange problems in
the cooling tower or the heat exchangers.
In a Wet surface Air Cooler the water is sprayed
on the outside of the tubes. The air and water are cocurrent, therfore
the outside of the tube is completely covered by water, creating an even
temperature and reducing the formation of deposits and scaling.
Concentration cycles in the majority of cooling
towers usually range from 3 to 7. Wet Surface Air Coolers can run cycles
of up to 50 in some cases, reducing annual water consumption up to 70%.
Auxilary Load
The fact that a Wet Surface Air Cooler can
operate under higher cycles of concentration that a cooling tower and
the fact that cooling tower blowdown can be used as a spray water
source, the opportunity exists to cool an additional cooling load using
the cooling tower blowdown as a spray water source. This principle can
be applied to an upgrade, new process or just to reduce the demand and
water consumption of an existing cooling tower. The schematic below
shows an example where 57,000,000 gallons of water is saved annually as
well as a 57,000,000 gallon annual reduction of blowdown.
Dry/Wet Cooler combination
An alternative to Wet Surface Air Coolers and
cooling towers are air cooled heat exchangers or dry coolers. They have
the advantage of not requiring water as part of the cooling process,
however they have the limitation that they cannot cooler to the same
temperature as either WSAC's or cooling towers. Typically, at best, a
dry cooler can cool a fluid to a temperature of 10°F above the ambient
dry bulb temperature. Considering that typical ambient temperatures are
86°F (30°c) to 104°F (40°c), the lowest temperature that can be expected
from dry coolers would be between 96°F (36°c) and 114°F (46°c).
A wet surface air cooler can
be used in combination with a dry cooler to cool a process below the
temperature that a dry cooler can achieve on its own and provide
significant water savings over a cooling tower or WSAC handling the
total cooling load. The example to the right shows an application where a
process stream is cooled from 170°F to 90°F in a 95°F ambient dry bulb
temperature.
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Energy Savings:
Industry strives to increase productivity, reduce
costs and become more efficient and at the same time meet environmental
regulations in a world where energy costs are increasing.
Where shell
and tube heat exchangers are the bottleneck, Koch Heat Transfer Group
(KHT) has two solutions that can increase production and reduce energy
costs and can often be the most economical solution to achieve both of
these goals.
Twisted Tube® heat exchangers use a unique
tube and distinctive design and construction that often allows increased
performance in the same size as a conventional bundle at lower pressure
drops on both the shell side and the tube side. Often reduced energy
costs provide the justification for installing Twisted Tube® heat
exchangers.
Click Here for More Information on Twisted Tube Heat Exchangers ...
Leak Protection:
A leak in a heat exchanger, at a
minimum, can cause maintenance headaches but also leaks can cause
operational problems and can be a serious cause for environmental
concern. Heat exchangers commonly contain environmentally sensitive
fluid that, if exposed to air, ground, water, or river water, an
environmental risk can result.
In
the case of the water-cooled transformers, the risk of a leak is
two-fold. If transformer oil leaks into the water side, a significant
environmental problem has occurred. If water leaks into the transformer
oil, serious damage can occur to the transformer.
Unifin International, LP has developed a
design to deal with this risk. Unifin's leak detector design involves
two tubes bonded together with the “leak-off” channels to capture drain
and isolate either fluid in the event of a leak. This transformer oil
cooler can be fitted with an alarm to signal a leak has occurred and the
isolation chamber will hold the leaked fluid until repair or
replacement can occur during the next outage.
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