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Guidelines on Thermal Energy Management |
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CHAPTER 4 Heat Transfer and Heat Insulation |
4.1 Benchmark of heat transfer and heat insulation |
4.1 .l Management standards of heat transfer and insulation |
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The management of heating and cooling should be based on the required temperature to choose the heat transfer medium and set up the management standard in advance. |
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The surface of heat exchange or heat conduction of boiler, furnace, and heat exchanger should keep clean, avoid the attach of any dirt or foreign materials. |
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The insulation and construction of heating equipment and heat medium piping should be based on the latest standards. |
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When choosing insulation material for a newly constructed furnace, new insulation material and standard should be chosen.
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Heating equipment should be maintained periodically to avoid steam leaking and extra heat loss. |
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Heat insulation device should be periodically maintained to avoid heat loss due to improper insulation. |
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Steam traps must be maintained periodically to avoid steam loss. |
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The efficiency of furnace should be tested periodically. |
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4.1.2 Detecting and recording heat transfer and insulation property |
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The heating and cooling temperature and heat transfer medium operation condition should be tested and recorded periodically. |
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When make heat balance and analysis of beating equipment the related data should be detected and
recorded. |
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4.1.3 Improvement |
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For heating equipment such as dryer, heat exchanger etc., the operation temperature, pressure and flow rate of the heat transfer medium should be controlled at an adequate range according to the operation condition of each equipment. |
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The heat input to equipment should be adjusted to avoid the heating load fluctuation. |
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When multi-stage heating was chosen, the retention time between each heating stage should be minimized to avoid the heat loss. |
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When batch type heating equipment was used, the feed to each batch should be arranged as close as it can be, or make the runs continuously to avoid the heat loss due to cooling down of the equipment between each batch |
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Components of heating equipment based on conduction heating should be made of material with high heat conductivity |
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When new heating equipment are need, equipment with high heat efficiency should be chosen. |
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In a production line, instead of repeated heating process the integrated or continuous heating should be used. |
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Use radiation heating instead of air convection heating. |
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For equipment need insulation, low conductivity insulation material or multi-layer insulation should be applied. |
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The design of heating medium piping should be reasonable, such as pipe diameter, and union and joint arrangement. The application of insulation material at joint point could decrease heat loss. |
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4.2 Various surface heat loss |
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4.2.1 Heat loss through pipe surfaces |
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Example: |
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Iron pipe diameter = 0.14 m
t1 = 250 ¢J (pipe surface temperature)
t2 = 30 ¢J (ambient temperature)
h = l8 (rate of heat transfer from pipe surface, unit kcal/m2h¢J)
Q =£kdh.(tl -t2) = 3.14¡Ñ0.1 4¡Ñ18¡Ñ(250-30)=1740 kcal/mh
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4.2.2 Heat loss through wall of a furnace |
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(1) Heat loss through furnace wall
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Example: |
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When the temperature of outer wall surface of a furnace is 100¢J, and ambient air temperature is 30¢J under the conditions of breeze, the heat loss through wall surface is 1000 kcal/ m2h. If the area of the wall outer surface is 450 m2, then the total heat through wall will be 450,000 kcal/h.
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(2) Correction factor of heat loss through the wall of furnaces
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(3) Standard temperature of a furnace wall outer surface
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| Furnace temperature(inner wall: ¢J) |
Furnace outer wall surface temperature(¢J) |
| Furnace top |
Side walls |
| 1300 |
140 |
120 |
| 1000 |
125 |
110 |
| 900 |
110 |
85 |
| 700 |
90 |
80 |
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(4) Heat loss through boiler outer surface
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4.3 Heat insulation |
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4.3.1 Heat insulation of pipes |
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(1) Diagram of insulation thickness
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(2) Diagram of insulation thickness
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4.3.2 Economical thickness of insulation material |
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Example: |
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For an insulation matter, the rate of heat transfer is 0.04 kcal/ m2h¢J, the life cycle is 20,000 hours, unit price is 30,000 dollars/cubic meter, the temperature difference between hot and cool side is 300 ¢J ,the unit price of thermal energy is 7 dollars per 10,000 kcal. According to the given data and the chart shown above, the economical thickness of the insulation, 75 mm, was obtained.
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