Heatec heaters
Our hot oil heaters are designed around a helical coil, the same as the very first heaters the company built in 1977. The thermal efficiency rating for the current generation of these heaters without pre-heaters (Figure 26) is 85 percent. Actually, the efficiency varies slightly, depending on capacity and fuel used.
Figure 26. Heatec Helical Coil Heater
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Helical coil heaters are widely recognized for long life and low maintenance, in addition to their high efficiency. Moreover, we have continued to refine our helical coil heaters to take advantage of new technologies, especially those in electronics and insulation. Consequently, our heaters have always been among the most efficient heaters available.
Equipping them with an optional heat exchanger boosts efficiency to 88 percent or more. Heatec offers the two types of secondary heat exchangers discussed above. They increase efficiency by recovering some of the exhaust gas heat that would otherwise be lost.
Figure 27 shows the construction of our helical coil heater. It has a steel cylindrical shell that houses a helical coil. Steel pads inside the shell support the coil leaving an annular space between coil and shell. The inner surface of the shell is covered with ceramic blanket insulation that has low thermal conductivity and low heat storage.
Figure 27. Cross section of Heatec Helical Coil Heater
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The burner fires through the center axis of the coil. Its flame produces radiant energy that heats the inner side of the coil without impinging on its surfaces. Radiant energy accounts for about 70 percent of the heat transferred to the coil.
Hot combustion gases turn outwards at the end of the coil. They double back into the annular space between the insulation and the exterior side of the coil, heating its outer surfaces by convection. Convection accounts for about 30 percent of the heat transferred to the coil.
The gases exit through the exhaust stack in the heater shell near the burner after traveling back the full length of the coil. Very little energy is lost through the shell.
Our heaters with an optional combustion air pre-heater have a heat exchanger built into the stack. The hot gases pass through tubes of the heat exchanger and exit the heater. The tubes are sealed so exhaust gases do not enter into the chamber surrounding them.
A blower forces fresh air into the chamber surrounding the hot tubes where it is heated. It then travels through a duct that carries it to the combustion chamber where it augments heat from the burner.
Thermal fluid is pumped through the hot helical coil and is heated by the process of conduction. The hot fluid exits the heater and flows through piping to asphalt tanks and other plant components.
Determining efficiency
The exhaust gas temperature of a heater gives a reasonably good indication of its efficiency. By measuring the temperature of the gases exiting the exhaust stack and looking it up on the chart shown in Figure 28 you can learn the efficiency.
Figure 28. Stack Temperature Vs. Heater Efficeincy. Click here to expand table in a new window.
Heatec checks the efficiencies of heaters as a free service to HMA plant owners. So if you would like for Heatec to do this for you please give us a call. We will be happy to check the efficiency of your heater and tell you if savings are possible with a more efficient heater.
Case histories
We calculated the potential savings a HMA plant in Arizona could expect by replacing their old heater. It had an efficiency of about 52 percent. We estimated that a new Heatec heater would save them an average of $3882 per month. The total cost of the new heater installed was $42,072. The savings paid for the new heater in 11 months. The savings now increase the owner’s profits and will do so for the remainder of the heater’s 20-year life.
On another occasion we replaced an old Hopkins heater (6 million Btu/hr) at an asphalt terminal in Kansas City, MO. Estimated savings are $5852 a month. The new heater paid for itself in only 10 months.
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