Water Separation from Hydrocarbon

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If water separation is not a requirement, any of the vessel sizes meeting the surge volume and L/D requirements in Section 352 may be chosen. Otherwise, water separation must be checked. Using Equation 300-5 or 300-7 depending on the Reynolds number, compute the settling velocity for a 100-micron water droplet in hydrocarbon. Hydrocarbon residence time […]

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Shell Length and Diameter

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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 […]

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Vapor Cross Section

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The cross-sectional area for longitudinal flow of vapor will be the largest of the following: 1. An area equal to 10% of the vessel cross section. 2. The area which results when the vertical height above the maximum liquid level (Dimension “D” minus Dimension “H” in Figure 300-6) is equal to 12 inches. 3. The […]

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Length of Vessel

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Length of Vessel

The minimum dimensions in Figure 300-5 are based on the experience and laboratory studies mentioned above. Use these dimensions or increase Dimension “C” if required for liquid residence time. If surge volume is unspecified, a minimum of 3 minutes residence time should be provided within the controllable range. For compressor protection, a minimum of 5 […]

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Design Gas and Liquid Rates

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Base design conditions and rates on examination of all likely plant operating cases. Provide flexibility for extreme operating conditions. A separator must not limit plant operation. The design liquid rate should include “slugs” that may occur during startup or upset operation.

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Design of Knockout Drums and Vertical Two Phase Separators

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The following design procedure is based on successful experience, plus some laboratory studies which indicate the desirability of the several internal baffles. (See Figures 300-4 and 300-5.) Vendors may use other criteria with or without other proprietary internals. Less conservative designs should not be accepted unless satisfactory performance has been demonstrated in a comparable application. […]

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Coalescers

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Coalescers

A knitted wire mesh pad coalescer may be used to improve separation of water from the hydrocarbon phase (Figures 300-4 and 300-7). Applications are based on experience. The pad acts by the same mechanism as a demister (Section 332). Use Yorkmesh Type 421 or equal, 1-foot thick. The pad is usually oriented vertically; liquid flow […]

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Separating hydrocarbon from water

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Separating hydrocarbon from water

Assume that a reflux drum operates at 100°F. The water leg should allow 100-micron oil droplets to “settle” upward. This will produce “good separation” of oil from water. If flow is laminar, we may substitute in Equation 300-5 and obtain the following equation (plotted in Figure 300-3) for allowable water velocity in the leg:

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Quality of Separation

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Measurement of droplet sizes (Dp) in industrial separators is impractical. We cannot verify the theoretical model; instead, we must rely on qualitative judgments. In general, when separators whose performance has been judged “good” are analyzed with the above terminal velocity correlations, it is found that the process conditions would theoretically allow 100-micron drops to settle. […]

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