Vapor-liquid separators Cyclones

Types of Equipment The three most commonly used types of equipment for handling emergency relief device effluents are blowdown drums (also called knockout drums or catch tanks), cyclone vapor-liquid separators, and quench tanks (also called passive scruh-hers). These are described as follows. 

Cyclone Separator with Separate Catch Tank This type of blowdown system, shown in Fig. 26-17 and 26-18, is frequently used in chemical plants where plot pan space is hmited. The cyclone performs the vapor-liquid separation, while the catch tank accumulates the hquid from the cyclone. This arrangement allows location of the cyclone knockout drum close to the reactor so that the length of the relief device discharge hne can be minimized. The cyclone nas internals, vital to its proper operation, which will be discussed in the following sections. 

Both Mitsubishi and Mitsui TLEs differ drastically from other designs. Mitsubishi offers a TLE with an integral steam dmm and cyclone for vapor—liquid separation. The pyrolysis gas flows in the shell side, and is claimed to accomplish the decoking of the furnace and the transferline exchanger in one operation. The Mitsui quench cooler uses three concentric tubes as the tube element, and requires steam—air decoking to clean the TLE (58,59). 

Figure 1 indicates the schematic flow of two-bed pyrolysis plant. This plant consists of the pyrolysis reactor and the regenerator through which fluidized medium circulates, the precombustion burner, the raw material feeder, the cyclones, the heat exchangers, the vapor-liquid separator, the gas recycle blower, the air feeder, the gas cleaner and the produced-gas combustion device. The plant also includes various auxiliary equipment, the devices for measuring and recording flow rate, pressure and temperature, as well as the automatic analysis for gas. 

Fig. 13.3.4. A Burgess-Manning multicyclone vapor/liquid separator unit (leftmost frame) and three different cyclone body designs Burgess-Manning type R-T, R-A and A-X, respectively. Courtesy Burgess-Maiming, Inc.

Foam-breaking cyclones can be installed in either vertical or horizontal vessels. In some offshore drilling operations, certain vapor-liquid separation vessels are routinely retrofitted with defoaming separators if there is a known or suspected foaming problem. This is usually possible since the individual tubes can pass through existing manways and be assembled inside the main separator vessel. If necessary, the separator assembly can be supported off the inside walls of the main vessel, as well as the vessel s inlet, thereby avoiding hotwork . 

FIGURE 3.2-7 Potential problems of vapor-liquid tangential separators. From Stem et al.. Cyclone Dust Collectors. American Petroleum Institute, New York, 1935. 

As mentioned above, a vapor-liquid cyclone of the conventional reverse-flow variety must be designed to handle liquid films attempting to make their way out the vortex tube (i.e., layer losses ). Additionally, the cyclone must be designed so that the vortex tail (the end of the vortex) is isolated or decoupled from any liquid that is allowed to collect in the lower section of the separator or from the liquid already flowing down the walls. See, for example. Fig. 13.1.1. Furthermore, proper underflow sealing is just as important with vapor-liquid cyclones as it is for gas-sohds cyclones. 

Fig. 13.3.2. Wright-Austin type TS vapor/liquid cyclone separator. Courtesy Hayward Industrial Products, Inc.

The catalyst travels to the top of the riser carrying heavy components and coke deposits from preceding reactions. The catalyst enters a stripping zone where some steam is added to further crack and remove the heavy hydrocarbons from the catalyst surface. The catalyst then enters the reactor section where a cyclone separates the catalyst from the product vapor. The separated product vapor is sent to the main fractionation column (Figure 4.2) that separates the product into gaseous and liquid products. The separated catalyst is piped into the regenerator where the coke on the catalyst is burned ofF. 

Poliak, A. and L. T, Work, The Separation of Liquid from Vapor, Using Cyclones, Amer. Soc. Mech. Engrs. 64, 1942, p. 31. 

From the sample solution to be analyzed, small droplets are formed by the nebulization of the solution using an appropriate concentric or cross-flow pneumatic nebulizer/spray chamber system. Quite different solution introduction systems have been created for the appropriate generation of an aerosol from a liquid sample and for separation of large size droplets. Such an arrangement provides an efficiency of the analyte introduction in the plasma of 1-3 % only.6 The rest (97 % to 99%) goes down in the drain.7 Beside the conventional Meinhard nebulizer, together with cooled or non-cooled Scott spray chamber or conical spray chamber, several types of micronebulizers together with cyclonic spray chambers are employed for routine measurements in ICP-MS laboratories. The solvent evaporated from each droplet forms a particle which is vaporized into atoms and molecules... 

The gas stream leaving the cyclone contains hot air, the excess ammonia, water evaporated from the nitric acid solution in the reactor and from the collected liquid in the cyclone, and 3% of the ammonium nitrate in the reactor effluent. The stream leaves the separator at 233°C, passes through the air preheater, and enters a partial condenser where some of the water and ammonia and essentially all of the nitrate are condensed. The equilibrium relationship between the compositions of the vapor and liquid streams leaving this unit may be expressed in the form... 

Spray dryers are normally used for liquid and dilute slurry feeds but can be designed to handle any material that can be pumped (see Figure 10.30). The material to be dried is atomized in a nozzle or by a disc-type atomizer positioned at the top of a vertical cylindrical vessel. Hot air flows up the vessel (in some designs downward) and conveys and dries the droplets. The liquid vaporizes rapidly from the droplet surface and open, porous particles are formed. The dried particles are removed in a cyclone separator or bag filter. 

Once the liquid phase is separated from the gas, it is diverted to impinge on the wall of a glass vessel like a simple test tube or collection bottle. The liquid runs down the wall while the gas exits the top. The carbon dioxide expands 500 times. Under typical operating conditions, 25-30 L/min of gas exits out the top of the test tube or bottle. The waste gas is diverted through a waste collection container and then vented outside. A small amount of the modifier, like methanol, is present in this waste stream (due to the vapor pressure of the compound). As with the cyclone separator, the user is never exposed to the effluent of the chromatograph. 

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