Flash drum

Figure 3.1a shows a flash drum used to separate by gravity a vapor-liquid mixture. The velocity of the vapor through the flash drum must be less than the settling velocity of the liquid drops. Figure 3.11) shows a simple gravity settler for removing a... 

Heater Detol reactors Flash drum Stabilizer Clay treater Distillation... 

For 2ibinary feed, specification of the flash-drum temperature and pressure fixes the equilibrium-phase concentrations, which are related to the values by... 

In Fig. 13-25, ifPg and the feed-stream conditions (i.e., F, Zi, T, Pi) are known, then the calculation of T9, V, L, yi, and Xi is referred to as an adiabatic flash. In addition to Eqs. (13-12) to (13-14) and the total mole balance, the following energy balance around both the valve and the flash drum combined must be included ... 

Flash-drum specifications in addition to (T9, T9) and (T9, adiabatic) are also possible but must be applied with care, as discussed by Michelsen [Comp. Chem. Engng., 17,431 (1993)]. Most computer-aided process design and simulation programs permit a wide variety of flash specifications. 

Blowdown systems utilize a series of flash drums and condensers to separate the blowdown into its vapor and liquid components. The liquid is typically composed of mixtures of water and hydrocarbons containing sulfides, ammonia, and other contaminants, which are sent to the wastewater treatment plant. 

Before desalters came into common use, crude pipe stills were frequently equipped with flash drums to minimize salt deposition on hot surfaces. In the flash drum system, the crude is heated to about 300 F. under enough pressure to suppress vaporization. The pressure is released as the crude enters the flash drum and all of the water (along with a small amount of crude) is flashed off, leaving the salt as a... 

While a desalter costs more to install than the flash drum system, it has the advantage of removing up to 95% of the salt from the oil permanently. Because less salt reaches the fractionating tower in a unit equipped with a desalter, a smaller quantity of corrosion products is formed due to high temperature breakdown and hydrolysis, and the salt content of the residual fuel oil is much lower. 

The Hj/400°FVT streams from each system are sent to separate flash drums where the bulk of the Cj and lighter material is removed. The virgin and cat cracker streams from the flash drums go to separate debutanizers while the Powerformer stream goes to an absorber-deethanizer followed by a debutanizer. The Q and lighter overhead streams from the virgin and cat cracker debutanizers are sent to this absorber- deethanizer for final deethanization. In the flow scheme shown this tower does not have a separate lean oil. It is called an absorber-deethanizer because the Powerformer stream serves in part to absorb the Cj and C4 components in the streams from the debutanizers. A separate lean oil stream is added in cases where higher Q and Q recoveries are justified. 

The CO2 rich solvent is drained from the bottom of the tower, and led first to a hydraulic turbo-expander and then to four flash drums connected in series, where CO2 is de-absorbed as the pressure is lowered. Lean solvent is pumped back to the top of the absorber tower... 

A - ABSORBER FD - FLASH DRUMS C - COMPRESSORS 1C - INTERCOOLED COMPRESSORS P- PUMP T - HYDRAULIC TURBINE D - DEHYDRATOR AC - AFTER COOLERS X- THROTTLE G GENERATOR... 

The acid-rich potassium carbonate solution from the bottom of the absorber is flashed to a flash drum, where much of the acid gas is removed. The solution then proceeds to the stripping column, which operates at approximately 245 °F and near-atmospheric pressure. The low pressure, combined with a small amount of heat input, drives off the remaining acid gases. The lean potassium carbonate from the stripper is pumped back to the absorber. The lean solution may or may not be cooled slightly before entering the absorber. The heat of reaction from the absorption of the acid gases causes a slight temperature rise in the absorber. 

Oxidized solution is delivered from the pumping tank to the top of the absorber tower, where it contacts the gas stream in a counter-current flow. The reduced solution flows from the contactor to the solution flash drum. Hydrocarbon gases that have been dissolved in the solution are flashed and the solution flows to the base of the oxidizer vessel. Air is blown into the oxidizer, and the solution, now re-oxidized, flows to the pumping tank. 

Each of the three process lines is supported within a structural steel framework that is 20 m tall. Each line contains a number of vessels (reactors, flash drums, separa-... 

Design a flash drum to separate liquid ethylene entrainment for the following conditions ... 

Notes Since this vessel will operate as a flash drum with a liquid level at approximately M of its height up from bottom, place the inlet at about center of vessel. See Figure 4-25. 

Figure 1-1. The Selexol process for acid gas removal (1) absorber, (2) flash drum, (3) compressor, (4) low-pressure drum, (5) stripper, (6) cooler.

Figure 3.15b. Similar to the first arrangement but with the water kept at high pressure to prevent vaporisation. The high-pressure water is flashed to steam at lower pressure in a flash drum. This system would give more responsive control of the reactor temperature. 

For the vapor pressure in a flash drum (and thus also vapor flow rate), we need a fast and tight response loop. We need at least a PI controller (c.f. the flow control). 

Flash steam recovery might also feature. Condensate or blowdown is fed to the flash drum, as illustrated in Figure 23.26. A material balance gives ... 

The flash drum pressure will be known as this will be set by the pressure of the main into which the flash steam will be recovered. The flash steam and condensate outlet enthalpies are set by saturation conditions. 

Once these pressures have been set, this sets the pressure difference across the compressor and the throttle, if the pressure drops in the heat exchangers, flash drums and the pipework are neglected. 

In the HTFT oil refinery the light oil and <345°C fraction of the decanted oil (obtained by passing the decanted oil through a vacuum flash drum) were clay treated. Clay treatment is similar to Bauxite treatment and is used to increase the octane number of the naphtha by acidic isomerization and to reduce the oxygenate content of the oil. Processing the LTFT and HTFT in separate (and different)... 

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