Piping
In addition to equipment layout there are several important factors to consider when choosing hot oil and asphalt piping. These factors affect setup and operating costs.
All asphalt lines should have outer heating jackets. Hot oil is pumped through the jackets to maintain the temperature of the liquid asphalt flowing through the lines when making HMA. And when the plant is idle the hot oil keeps the asphalt from solidifying.
Heatec jackets for portable plants incorporate flexible jumpers at the joints (Figure 45). The jumpers provide fast heating on start-up and minimize unheated spots. The diameter of the jumpers is 1-1/2 inches, much larger than those provided by some manufacturers. Some use only 1/2-inch jumpers, which slow down the heating and make it difficult to obtain the desired temperature.
Figure 45. Flexible Jumpers Minimize Unheated Spots.
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All hot oil lines and asphalt lines— including those that are jacketed—should be insulated to minimize heat loss. Heatec offers insulation with 1-1/2 inch pre-formed fiberglass material. The insulation is covered with a protective outer shell made of aluminum.
Ball joints are highly recommended in asphalt piping for portable asphalt plants. They make piping installation faster and easier (Figure 46). Moreover, they are stronger than flexible lines and less likely to rupture when stressed—an important safety precaution for lines carrying hot asphalt. A minimum of three ball joints are required. They allow up to 2 feet of misalignment between tank and mixer. As a result the units don’t have to be positioned with as much accuracy as would be required without them. When traveling to another site, the lines stay attached and are simply rotated into transport position.
Figure 46. Ball Joint Piping Reduces Need For Precise Alignment.
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Small HMA plants with only one asphalt storage tank usually only need one hot oil circuit with one hot oil pump. The single pump circulates the hot oil through heated components and through the heater. Heatec helical coil heaters for single circuits are designated by the prefix HCS. HC stands for helical coil and S stands for single circuit.
Plants with HMA storage silos and two or more asphalt storage tanks can usually benefit from using two or more hot oil circuits, each with its own pump (Figure 47). One pump, known as the circulating or main pump, serves solely to re-circulate the oil through the heater. Each of the other pumps, known as side or loop pumps, only circulates oil through a single circuit.
Figure 47. Using A Hot Oil Heater With A Manifold Facilitates Extra Circuits.
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A manifold is used on the hot oil heater to split off the extra circuits. Using extra circuits reduces the size of each pump, its operating pressure and the size of the motor that drives it. Operation of the system is much more flexible because each circuit can be operated independently. Thus, when some units are not in use, the hot oil to them can be shut off.
There are other important advantages to having a pump used solely for circulating the hot oil. It ensures that there is always an optimum flow of oil through the helical coil of the heater regardless of the heat demand. This ensures that the coil always operates at favorable wall temperatures, which can significantly extend the life of both the coil and the thermal fluid. It also allows adding or removing tanks or other heat users to the hot oil system without affecting the flow of oil through the coil of the heater.
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