Details to Improve Separation

A horizontal separator is not often used ahead of a compressor because of the possibility of entrained liquid in the vapor. The situation can be improved by use of a demister pad over the vapor outlet. The pad cross-sectional area is found by Equation 300-3. The pad is supported in a housing of either round or rectangular cross section as shown in Figure 300-4.

Difficult hydrocarbon-water separation may be helped by a wire mesh coalescer pad. The pad is located as close as possible to the inlet end of the separator. See Figure 300-4. The pad extends up to the maximum liquid level. Vane-type pads may be used in production separators.

The water rate may be so large, or the upward settling rate of oil droplets so slow, that a water boot of impractical diameter would be required. In this case, water holdup time and hydrocarbon-water interface area are provided by holding water volume within the main compartment of the separator. See Figure 300-4. The hydrocarbon outlet is raised to a point 2 to 6 inches above the highest hydrocarbon-water interface level.

If the primary concern is to provide interface area and water holdup time for separation of oil droplets, then a transverse weir may be used to assure that water volume within the main compartment is maintained. Drain holes are provided in the weir to empty the water at shutdown. The water-hydrocarbon interface is controlled in the boot as before. Since the water behind the weir is not controllable, it does not serve as surge volume.

Improved Separation in Horizontal Vessels

If increased water surge volume must be provided, then one controller maintains the hydrocarbon-water interface within the vessel and another controller handles the hydrocarbon level. A water boot is not required.

Categories: Process Design | Leave a comment