Horizontal Vs vertical tanks
Heated asphalt storage tanks are cylindrical and may be either horizontal or vertical. Horizontal tanks are installed so their long axes are horizontal and they occupy a ground area equal to their diameter times their length. They are easily equipped with wheels and suspension for highway travel.
Vertical tanks are installed so that their long axes are upwards and they occupy a ground area only the size of their diameter (Figure 61). Consequently, you can fit four vertical tanks in the space of one horizontal tank (Figure 62).
Figure 61. Vertical Tanks Have Small Footprints.
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Figure 62. Ground Area Of Vertical Tanks Vs. Horizontal Tanks.
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Another advantage is that the surface area of asphalt cement exposed to atmosphere inside a vertical tank is smaller than that inside a horizontal tank for the same amount of liquid. Thus, there is less oxidation of asphalt cement in a vertical tank. Moreover, when mixers are installed to keep polymers in suspension, the liquid in vertical tanks has better flow patterns than in horizontal tanks.
However, there are other considerations when polymers are used and the tanks must also be portable. Horizontal tanks are best-suited for portability. But, as already noted, direct-fired tanks are not recommended for polymer-modified asphalts, even though they can be portable. So, the best-suited tanks for both portability and polymer asphalts are horizontal tanks that have coils heated by hot oil. And where only a single tank is needed, a unit that combines a coil tank with a heater, such as a Heli-Tank, is an excellent choice.
Heli-Tanks and other horizontal tanks heated with hot oil can incorporate either a spray bar re-circulation system (Figure 63) or mixers (Figure 64) to keep the polymer from separating from the asphalt. Although the mixing action in a horizontal tank is not as good as in a vertical tank, current experience indicates that the mixing is quite satisfactory. (Please refer to Heatec Technical Paper T-133.)
Figure 63. Horizontal Tank With Re-circulation System For PMAC.
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Figure 64. Horizontal Tank With Mixers For PMAC.
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