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Shell Length and Diameter

Determine shell dimensions by trying various combinations of diameter, length, and liquid depth. For any trial diameter, the maximum liquid level is known from the vapor cross-section calculation above. The minimum liquid level is at a height of one-eighth diameter from the bottom. (See Figure 300-6.)

The volume in between is hydrocarbon liquid surge. For each trial diameter, compute the required drum length. Include portions of the heads. Several combinations of length and diameter will be found which satisfy the volume requirement. Use a length-to-diameter ratio (L/D) of at least 2.0. The distance from inlet to vapor outlet should be at least 4 feet. It has been found that the cost of a horizontal vessel of given volume does not vary greatly as length-to-diameter ratio (L/D) varies from 2 to 10. However, wave action is a concern in long vessels. Limiting the L/D ratio to a maximum of 6.0 is recommended for horizontal vessels. For large vessels, a tangent-tangent length of 20 feet is a convenient length.