Types of waste heat
Cement industry
Waste heat recovery of kiln back-end cooling machine [1]
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Exhaust gas temperature is generally about 200 ~ 300°C in the low-temperature part of
cooling machine at the end of cement rotary kiln. This part of waste heat is of low quality,
and its best usage is for producing low-pressure steam for domestic water, warming and
bathroom water heating in winter; and for the heat source of LiBr air-conditioning system in
summer for the cooling of production workshop and living areas, or for boiler water supply of
heat exchanger in other sections’ boiler.
Some factory with a φ3.5 m × 145 m cement rotary kiln and with a 1.37 m × 30.48 m gratevibration cooler, exhaust emissions (standards state) is 51673 m³/h, exhaust temperature is
about 240°C. A water heater is installed in the flue to heat domestic water; specific
parameters are as shown in Table 1.
Waste heat recovery of cement kiln back-end [1]
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Waste gas temperature is around 450 ~ 600°C in rotary kiln firing back-end of many small
cement plant, since the output is small, waste emission is also small. The 0.3 ~ 0.8 MPa lowpressure steam produced by the waste heat recycled will be generally used in the production
processes or life use. Its processes are as shown. Waste gas enters into heat pipe steam
generator through cyclone dusting from the dry and hollow rotary kiln, emission
temperature drops from around 600°C to below 200°C , and enters into the bag collecting
system, and then enters into the chimney through the chimney. Its advantages are:
o Reduce high-temperature exhaust to below 200 ℃,which directly enters into the bag
collector;
o 0.4 to 0.5 tons of low-pressure steam can be recycled per ton of clinkers;
o Compact structure and low pressure, generally less than 500 Pa;
o
No fouling, wall temperature can be adjusted above dew point, self-cleaning
purposes can be achieved.
Waste heat recovery of cement rotary kilns surface [1]
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Whole sect kilns surface temperature can be up to 300-350°C when rotary kilns works, aircooled method is currently used and a lot of heat is directly distributed into the atmosphere,
which not only causes a waste of a lot of heat, but also causes high temperatures pollution
around the kiln. Heat dissipation of kiln surface can be recycled, thus our company
developed the kiln collector surface waste heat recovery systems. According to the needs of
enterprises, waste heat recovery can be used to heat water or air, and hot water can be used
for life and refrigeration, while hot air can be used for drying, which not only reduces the kiln
temperature, but also saves fuel for water or air heating, electricity for fan, and reduces dust
and carbon dioxide emissions. One stone for two birds, with energy conservation and
environmental protection. Investment can be fully obtained within a year, which is of
significant economic efficiency.
Waste heat recovery of ceramic industry
Firing is a major process of ceramic production in the kiln. There are continuous (tunnel kiln) and
gap-structure (down draught) kilns in ceramic production, of which whether in the tunnel kiln or
down draught kiln, the thermal efficiency is relatively low. Besides combustion loss reason, heat loss
reason and other reasons, the most important reason is the exhaust loss reason. Firing tunnel kiln
emissions of heat loss is about 20 percent to 40 percent of the total calories, while down draught kiln
emissions of heat loss accounts for about 30 percent to 50 percent of fuel consumption. Therefore
recovery of the kiln back-end emission of heat is the key to improve the efficiency of the kiln.
Domestic tunnel kiln gas temperature is general 200 ~ 300°C, some are up to 400°C, individually
some down draught kiln exhaust gas temperature can be as high as 560°C.On the one hand, large
waste heat in furnace exhausts away, on the other hand, in order to dry blank pieces, some factories
have constructed furnace or boiler producing hot air and steam to meet the requirements of drying
blank pieces. Using heat pipe heat exchanger to recycle waste heat in the smoke and gas to heat air
as heat source for drying blank pieces can get good energy-saving efficiency.
Waste heat recovery of tunnel kiln flue gas
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Tunnel kiln waste heat recovery is mainly used for heating air as heat source for drying blank
pieces, and also as combustion air to improve the thermal efficiency of the kiln itself, which
can be chosen depending on specific circumstances of factories. The recycle process is as
shown in the picture.
Waste heat recovery of tunnel kiln cooling belt in electric ceramic factory
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Draw the 400°C ~ 450°C exhaust smoke from electric ceramic factory tunnel kiln cooling belt,
and pass it through the heat pipe heat exchanger then the temperature drops to 300 ℃, and
then turn it back to kiln firing belt as the use of atmosphere film wind. The heated fresh air is
sent into drying room to dry blank pieces of electric ceramic. Process of heat pipe heat
exchanger is as shown in the picture.
Waste heat recovery of down draught kiln flue gas
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Down draught kiln exhaust smoke temperature is 564°C in a factory, while the furnace
thermal efficiency is only 23 percent measured. Since blank pieces are required to preheat
before entering into the kiln, it is need to build a drying kiln, with coal as fuel and the smoke
as drying heat. According to calculation, if the 560°C smoke drops to 160°C and is exhausted
to heat the fresh air to 60 ~ 120°C, it will be enough to dry blank pieces. Waste heat recycle
process is as shown in the picture.
Heat pipe hot air preheater parameters
The waste heat recovery of textile industry
A lot of energy-consuming machines are used in the textile industry, such as heat-setting machine,
sizing machine, dryer and so on. These energy-consuming machines can work with electricity, fuel,
gas, steam, etc, as sources of heat. Therefore, how to maximize the use of low-temperature waste
heat and reduce the consumption of high-grade thermal in textile industry energy saving is an
important task.
Waste heat recovery and utilization of heat-setting machine
Heat-setting machine (or Lafu machine) is one of the main energy-consuming machines which are
used in textile industry. Heat-setting machine is a device using hot air to dry and deal with the
textiles (cloth) and make them case-hardened. There are various ways of hot air supply, for example,
gas or light diesel oil, which can be directly combusted within the heat-setting machine. The recycle
of hot oil or steam heating can be used, electric heating can also be used. Generally, air temperature
inside heat-setting machine is about 200 ℃. Air temperature is generally about 170 ℃ when
leaving the heat-setting machine. Therefore a lot of waste heat is discharged into the air. If we add
fuel combustion loss and body heat loss, more than 90 percent calories in heat-setting machine
waste heat are scattered into the atmosphere by exhaust after estimate. Only 2.9 percent of the
input heat is really used in dealing with the fabric. The dissipation of heat not only causes a waste of
energy but also causes environmental pollution. Therefore heat-setting machine waste heat recovery
is inevitable. Waste heat recovery method of heat-setting machine is to use hot air from the exhaust
to heat fresh airs and return them to the heat-setting machine. If the heat-setting machine directly
burns gas or diesel, part of preheating air can also be used as a combustion air or hot water heating.
The use of heat pipe heat exchanger can be the most effective solution of the problem compared in
the integrated indicators of waste heat recovery efficiency, pressure loss blockage prevention and
cleanness.
Sketch map of heat-setting machine waste heat recovery systems processes, as the diagram shows:
Waste heat recovery of sizing machine
Sizing machine is for drying sizing purposes. There is a hot air heating system in the lower part of
sizing machine, when the hot air goes into the sizing machine, it will absorb the sizing moisture,
which will then be discharged. Since the drying process is mainly of the transfer process, the
temperature of hot gases decrease little, with only the increment of the moisture content. Use the
discharged of wet air to heat fresh air and recycle wet air heat, then return it to the sizing machine
and mix with hot air, which will obtain energy-saving purposes.
Sketch map of processes of sizing machine waste heat recovery systems, as the picture
shows:
Heat pipe air preheater parameters of sizing machine
The waste heat recovery of glass Industry
Introduction
Smokes are generally under 500°C from furnace regenerator and heat exchanger room (or heat
exchanger)in the process of glass production. These hot smokes can generate steam through heat
pipe waste heat boiler. The steam can be used for heating, atomization of heavy oil, pipeline
insulation and warming, etc. Large amount of smoke, high temperature smoke can be used to
generate electricity through heat pipe waste heat boiler which generates a high pressure steam (3.5
MPa) for the steam turbine, or directly drives turbine compressor, fan, water pumps and other
machinery. For smoke from working pool and material supplying pipe, etc, the amount of gas is small
while the temperature is high. A small number of high-temperature heat pipes can be used
(temperature> 650 ℃) to preheat the air. When the smoke temperature is 1000 ~ 1200 ℃ from the
furnace, air preheating temperature can be up to 400 ~ 500 ℃, oil saving efficiency can be up to 20%.
Good energy-saving efficiency can be obtained when heat pipe heat exchangers are fixed in the
annealing furnace flue and in the field behind cold relief zone of annealing furnace, which recycles
the waste heat and dissipate heat to preheat the air used as combustion air, dry heat, or heat
source,etc.
[1] [Online]. Available: http://www.xmgpkj.com/en/pro.asp?Pid=8&a=6.