T-140: Proper insulation, HMA plant heating costs

Proper insulation
Not all insulation can be considered as proper insulation. Proper insulation involves using the appropriate type of insulation, the appropriate thickness and using good workmanship when installing it. Generally, the thicker the insulation the better. In cold climates it is very important to use the thickest insulation available for the application. Moreover, the thickest insulation is appropriate even in warm climates, although not as critical. The insulation will usually always pay for itself over a period of time. It may take a little longer in warm climates.

Using good workmanship means installing the insulation carefully. The insulation should cover virtually all hot surfaces exposed to ambient air. It should be installed so that it is not subject to being wetted by rain storms. And it should not be compressed any more than absolutely necessary. Compressing two inches of material to one inch cuts its insulating value to that of one inch of the material. And six inches of material compressed to three inches is no better than three inches uncompressed.

Five types of insulation are commonly used in asphalt heating equipment: 1) ceramic fiber blanket; 2) fiberglass blanket; 3) mineral wool blanket; 4) molded foamglass; and 5) calcium silicate. Refractory could also be regarded as a type of insulation. It is used in combustion chambers to protect metal parts from the burner flame and to shape the flame. However, it has almost no effect on heat loss.

The term most commonly used in asphalt heating to denote the efficiency of insulating materials is thermal conductivity. Thermal conductivity is a measure of the ability of a material to conduct heat flow. It is designated by the letter “k,” and is usually called the k-factor. Thermal conductivity, k, is expressed in Btu per hour per square foot per degree F per inch of thickness of the material.

A measure of the ability of insulation to resist or impede heat flow is denoted by its R-value. This term is very common in the building industry. It is typically marked on the wrapper or container of insulating materials. Increasing R-values denote greater resistance to flow. Thus, the higher the R-value the better the insulation. R-values are very easy to use for comparing the insulating properties of various materials. Doubling the thickness of the material doubles the R-value.

R-value can be expressed either as resistance per inch of thickness, or as the resistance for the thickness stated. Both R-value per inch and R-value per stated thickness are used in actual practice when heat insulating materials are being specified.

R-value per inch is the reciprocal of K-value or 1/k.

HMA plant heating costs
Figure 38 shows the daily costs for heating asphalt, fuel and plant components at a typical stationary HMA plant. Figure 39 shows the daily costs for heating asphalt and plant components at a typical relocatable HMA plant.

Figure 38. Heating Costs For A Typical Stationary Plant
	Hourly Usage			Daily Usage (24 hours)
	Btu	Gallons No. 2 Fuel	CCF Natural Gas	Btu	Gallons No. 2 Fuel	CCF Natural Gas
Two 30,000 gallon horizontal coil tanks for virgin asphalt	93,984	0.8	1.2	2,255,620	20	29.3
One 25,000 gallon vertical asphalt tank for PMAC	40,054	0.4	0.5	961,305	9	12.5
Heavy fuel preheater	336,709	3.0	4.4	8,081,020	72	105.1
Double Barrel drum mixer 9 ft x 46 ft	43,520	0.4	0.6	1,088,000	10	14.1
Drag conveyor, 42 inch x 100 ft	68,250	0.6	0.9	1,706,250	15	22.2
Three 300-ton storage silos	99,649	0.9	1.3	2,391,570	21	31.1
Traverse conveyor, 36 inch x 33 ft	19,500	0.2	0.3	487,500	4	6.3
100 feet of asphalt piping, 4-inch dia jacket	9,940	0.1	0.1	238,560	2	3.1
230 feet of hot oil piping, 2-1/2 inch dia	14,920	0.1	0.2	358,080	3	4.7
Total Quantity	726,526	6.5	9.5	17,567,905	157	228.4
Cost		6.48	6.52		156.58	157.58
Asphalt temperature = 300 degrees F. Thermal oil temperature = 350 degrees F. Fuel temperature = 150 degrees F. Heater efficiency = 85%. Tank insulation = 3 inches. Pipe insulation = 1-1/2 inches. No. 2 fuel cost = $1.00 per gallon. Natural gas cost = $0.69 per CCF. Heavy fuel oil is used only for drum mixer. Usage includes heating for unloading pump and metering. Highlighted cells Include additional heat load for first hour cold start.

Figure 39. Heating Costs For A Typical Relocatable Plant
	Hourly Usage			Daily Usage (24 hours)
	Btu	Gallons No. 2 Fuel	CCF Natural Gas	Btu	Gallons No. 2 Fuel	CCF Natural Gas
Two 30,000 gallon horizontal coil tanks for asphalt	93,984	0.8	1.2	2,255,620	20	29.3
Double Barrel drum mixer 8ft x 39 ft	38,640	0.3	0.5	966,000	8.6	12.6
Drag conveyor, 36 Inch x 95 ft	55,575	0.5	0.7	1,389,375	12.4	18.1
Two 200-ton storage silos	51,439	0.5	0.7	1,234,533	11.0	16.1
Traverse conveyor, 36 Inch x 14 ft	9,750	0.1	0.1	243,750	2.2	3.2
100 feet of asphalt piping, 4-inch dia jacket	9,940	0.1	0.1	238,560	2.1	3.1
230 feet of hot oil piping, 2-1/2 inch dia	14,920	0.1	0.2	358,080	3.2	4.7
Total Quantity	274,248	2.5	3.6	6,685,918	59.6	86.9
Cost		2.45	2.46		59.58	59.97
Asphalt temperature = 300 degrees F. Thermal oil temperature = 350 degrees F. Fuel temperature = 150 degrees F. Heater efficiency = 85%. Tank insulation = 3 inches. Pipe insulation = 1-1/2 inches. No. 2 fuel cost = $1.00 per gallon. Natural gas cost = $0.69 per CCF. Heavy fuel oil is used only for drum mixer. Usage includes heating for unloading pump and metering. Highlighted cells Include additional heat load for first hour cold start.

Figure 40 shows the daily costs for heating asphalt and plant components at a typical portable HMA plant.

Figure 40. Heating Costs For A Typical Portable Plant
	Hourly Usage			Daily Usage (24 hours)
	Btu	Gallons No. 2 Fuel	CCF Natural Gas	Btu	Gallons No. 2 Fuel	CCF Natural Gas
One 30,000 gallon Heli-tank for asphalt	42,260	0.4	0.6	1,014,240	9.0	13.2
Double Barrel drum mixer 7 ft x 35 ft	35,200	0.3	0.5	880,000	7.8	11.4
Drag conveyor on surge bin, 24 inch x 50 ft	19,500	0.2	0.3	487,500	4.3	6.3
70 feet of asphalt piping, 4-inch dia jacket	7,360	0.1	0.1	176,640	1.6	2.3
150 feet of hot oil piping, 2-inch dia	10,600	0.1	0.1	254,400	2.3	3.3
Total Quantity	114,920	1.0	1.5	2,812,780	25.1	36.6
Cost		1.0	1.0		25.06	25.23
Asphalt temperature = 300 degrees F. Thermal oil temperature = 350 degrees F. Fuel temperature = 150 degrees F. Heater efficiency = 85%. Tank insulation = 3 inches. Pipe insulation = 1-1/2 inches. No. 2 fuel cost = $1.00 per gallon. Natural gas cost = $0.69 per CCF. Heavy fuel oil is used only for drum mixer. Usage includes heating for unloading pump and metering. Highlighted cells Include additional heat load for first hour cold start.

Note that daily usage shown in figures 38, 39 and 40 is not equal to 24 times the hourly usage. This is because the heat load on the hot oil system drops while the plant is operating. We assumed that the plant was operating for 8 hours during the 24 hour period.

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