Sizing of Vapor-Liquid Separators

Vapor-liquid separators (drums) are used to separate a liquid from a vapor-liquid stream with a minimum of liquid carryover. The separator size is determined by the vapor velocity which depends on the entrainment method used. The working equation is  

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For rough sizing check of vapor/liquid separators and accumulators, see the Fluor method in Chapter 8, Separators/Accumulators—Vapor/Liquid calculation method. 

The heating surface usually determines the evaporator cost and the vapor head the space requirements. The vapor—liquid separator must have enough horizontal plan area to allow the bulk of the initial entrainment to settle back against the rising flow of vapor and enough height to smooth out variations in vapor velocity and to prevent splashing directly into the vapor outlet. Separators are usually sized on the basis of the Souders-Brown expression ... 

R. Yamamoto and K Nakanishi, Computer Simulation of Vapor-liquid Phase Separation in two- and three-dimensional Fluids Growth Law of Domain Size, Phys. Rev. B 49 (1994) 14958-14966 II. Domain Structure, Phys. Rev. B 51... 

Control system. For subsequent selection and sizing of pumps and compressors, we need to map out the number and location of the control valves. Since the number of control valves is related to the number of control degrees of freedom, identify the control degrees of freedom. For example, a typical hydrodealkyllation process with a reactor, furnace, vapor-liquid separator, recycle compressor, two heat exchangers, and three distillation columns has 23 control degrees of freedom (Luyben et al., 1997). This requires 23 control valves whose location affects the rest of the design and the safety and hazards (see Section 16.7). 

A vapor-liquid separator is to be sized for a true vapor flow of 1.5 cfs. Vapor density is 0.65 pounds per cubic foot. Liquid density is 63 pounds per cubic foot. Use = 0.2 for this service. What diameter drum is required ... 

Now we can proceed to determine the CE of the separator. We start with the case of a monodisperse mixture with drops of the same size at the entrance. The volume concentration of liquid at the entrance Wo (for any given values of pressure and temperature, Wo can be determined from the equations of vapor-liquid balance) is given. To find the amount of the liquid phase settled in the separator, it is sufficient to consider a drop whose final position at the exit will be (0, L) and to determine its initial position at the entrance cross section. From (18.30), we find yo = VyL/ Uu- Now it is easy to find the volume concentration of the liquid phase at the exit Wi = (1 — yo)Wo and the CE of the separator ... 

This part, on applications, covers the following unit operations 8. Evaporation 9. Drying of Process Materials 10. Stage and Continuous Gas-Liquid Separation Processes (humidification, absorption) 11. Vapor-Liquid Separation Processes (distillation) 12. Liquid—Liquid and Fluid-Solid Separation Processes (adsorption, ion exchange, extraction, leaching, crystallization) 13. Membrane Separation Processes (dialysis, gas separation, reverse osmosis, ultrafiltration) 14. Mechanical-Physical Separation Processes (filtration, settling, centrifugal separation, mechanical size reduction). 

We work in a stagnant industry. It s true that vapor-liquid separation can be greatly improved by the use of vertical vortex tubes, which are a relatively new development. Yet most vapor-liquid separators are still empty vessels that depend on gravity settling and are sized in accordance with Stokes Law. 

These operations may sometimes be better kno Ti as mist entrainment, decantation, dust collection, filtration, centrifugation, sedimentation, screening, classification, scrubbing, etc. They often involve handling relatively large quantities of one phase in order to collect or separate the other. Therefore the size of the equipment may become very large. For the sake of space and cost it is important that the equipment be specified and rated to Operate as efficiently as possible [9]. This subject will be limited here to the removal or separation of liquid or solid particles from a vapor or gas carrier stream (1. and 3. above) or separation of solid particles from a liquid (item 4j. Reference [56] is a helpful review. 

The onset of flow instability in a heated capillary with vaporizing meniscus is considered in Chap 11. The behavior of a vapor/liquid system undergoing small perturbations is analyzed by linear approximation, in the frame work of a onedimensional model of capillary flow with a distinct interface. The effect of the physical properties of both phases, the wall heat flux and the capillary sizes on the flow stability is studied. A scenario of a possible process at small and moderate Peclet number is considered. The boundaries of stability separating the domains of stable and unstable flow are outlined and the values of the geometrical and operating parameters corresponding to the transition are estimated. 

Liquid-vapor separators designed by this method can be smaller than those sized via conventional means. This partly results from a fuller consideration of the mechanisms of vapor- and liquid-phase separations. 

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