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Technical Paper T-140
Heating and Storing Asphalt at HMA Plants
Publication No. T-140
 download T-140 in PDF format
Pages: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
13, 14, 15, 16, 17, 18, 19, 20, 21
Heat loss
Heat loss is the difference between the amount of heat energy produced and that used. It is heat produced without getting any benefit from it. Thus, it is wasted energy, which is costly. Because of the need to avoid wasted cost and to conserve our resources every effort should be made to avoid heat loss. This is especially true at a HMA facility because of the large amount of heat energy needed to produce hot mix. Heat losses can be minimized by proper use of insulation, a very cost effective solution (Figure 31).
Figure 31. Insulation on Coil Tank
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The cause of most heat loss in asphalt heating systems is too little insulation on some components and no insulation on others. Figure 32 shows an infrared photo of a well-insulated vertical asphalt storage tank and depicts temperatures on the skin and on the concrete at its base. Compare this photo with Figure 33, which shows temperatures at similar points on a poorly insulated vertical tank. Thus, when components are purchased, proper insulation should be specified. And when the system is installed all asphalt piping and hot oil piping should be properly insulated.
Figure 32. Infrared photo of a well insulated tank
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Figure 32. Infrared photo of a poorly insulated tank
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Heat loss occurs when heat from materials and components in an asphalt system escapes into the atmosphere.
The greater the temperature differences between the ambient air and these materials and components, the greater the rate of heat loss. Thus, in locales with low temperatures the losses are greater than in areas of high temperature. But regardless of the locale, the following components should be insulated to minimize heat loss:
- All asphalt storage tanks
- Hot oil heaters
- All asphalt piping
- All hot oil piping
- Metering pumps
- Unloading pumps
While the need to insulate storage tanks and heaters is obvious to most people, many overlook the need to insulate piping. But it is one of those details that shouldn’t be overlooked. Note the heat loss from various pipe sizes and temperatures as shown in Figure 34.
Figure 34. Piping Heat Losses
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Jacketed Asphalt Piping
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Asphalt Pipe
Nominal Size
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Hot Oil Jacket
Nominal Size
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Loss Per Linear Foot
Btu Per Hour
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Loss Per Flange
Btu Per Hour
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Uninsulated
Jacket
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Insulated
Jacket
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Uninsulated
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Insulated
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3 inches
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4 inches
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1598
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86
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1890
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120
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4 inches
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6 inches
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2349
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122
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2600
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134
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5 inches
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8 inches
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3057
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148
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3240
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178
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Hot Oil Piping
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Pipe Diameter
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Loss Per Linear Foot
Btu Per Hour
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Loss Per Flange
Btu Per Hour
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Uninsulated
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Insulated
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Uninsulated
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Insulated
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1-1/2 inches
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676
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47
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1205
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97
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2 inches
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846
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54
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1660
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115
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2-1/2 inches
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1024
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55
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2155
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125
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3 inches
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1243
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72
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2485
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130
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Asphalt temperature = 300 degrees F. Hot oil temperature = 350 degrees F.
Pipe insulation = 1-1/2 inches (Figure 35).
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The Thermal Insulation Handbook by Turner and Malloy recommends insulation thickness for pipes as shown in Figure 35.
Figure 35. Minimum Recommended Insulation For Pipes
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Insulation Thickness For Various Operating Temperatures
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Pipe
Diameter
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150
Degrees F
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200
Degrees F
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300
Degrees F
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400
Degrees F
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500
Degrees F
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600
Degrees F
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| 1 inch |
1 inch
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1 inch
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1 inch
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1-1/2 inches
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1-1/2 inches
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2 inches
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| 1-1/4 inches |
1 inch
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1 inch
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1 inch
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1-1/2 inches
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1-1/2 inches
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2 inches
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| 1-1/2 inches |
1 inch
|
1 inch
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1 inch
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1-1/2 inches
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2 inches
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2 inches
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| 2 inches |
1 inch
|
1 inch
|
1 inch
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1-1/2 inches
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2 inches
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2-1/2 inches
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| 2-1/2 inches |
1 inch
|
1 inch
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1 inch
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1-1/2 inches
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2 inches
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2-1/2 inches
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| 3 inches |
1 inch
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1 inch
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1 inch
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1-1/2 inches
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2 inches
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2-1/2 inches
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| 3-1/2 inches |
1 inch
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1 inch
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1 inch
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1-1/2 inches
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2 inches
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2-1/2 inches
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| 4 inches |
1 inch
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1 inch
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1 inch
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1-1/2 inches
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2 inches
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2-1/2 inches
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| 5 inches |
1 inch
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1 inch
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1 inch
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1-1/2 inches
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2-1/2 inches
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2-1/2 inches
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| 6 inches |
1-1/2 inches
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1-1/2 inches
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1-1/2 inches
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2 inches
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2-1/2 inches
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3 inches
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| 8 inches |
1-1/2 inches
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1-1/2 inches
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1-1/2 inches
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2 inches
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2-1/2 inches
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3 inches
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| Thickness according to Turner/Malloy (emmisivity 0.05) |
You can see just how important insulation is by comparing the heat required to maintain the temperatures of various sizes of insulated and non-insulated tanks. Figure 36 compares asphalt tanks. Figure 37 compares fuel tanks.
Figure 36. Asphalt Tanks—Maintaining Temperature
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Capacity
(Gallons)
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Btu Per Hour
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Horizontal Tank
No Insulation
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Horizontal Tank
3-inch Insulation*
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Horizontal Tank
6-inch Insulation*
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10,000
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633,850
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21,217
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11,760
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15,000
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791,621
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26,179
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14,347
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20,000
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1,006,753
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33,117
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18,118
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25,000
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1,221,886
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40,054
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21,889
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30,000
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1,437,018
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46,992
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25,660
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35,000
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1,562,050
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50,933
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27,755
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40,000
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1,786,536
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58,411
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31,813
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*Btu values are for new Heatec tanks and do not include heat for valves or connections. Old tanks may require double the heat or more.
Asphalt temperature = 300 degrees F.
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Figure 37. Fuel Tanks—Maintaining Temperature
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Capacity
(Gallons)
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Btu Per Hour
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No Insulation
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3-inch Insulation*
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10,000
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170,952
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5,941
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15,000
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213,504
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7,330
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20,000
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271,526
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9,273
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25,000
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329,548
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11,215
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30,000
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387,570
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13,158
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*Btu values are for new Heatec tanks and do not include heat for valves or connections. Old tanks may require double the heat or more.
Type of fuel = No. 6 fuel oil. Fuel temperature = 150 degrees F |
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