Absorber, counter-current

The term three-phase fluidization requires some explanation, as it can be used to describe a variety of rather different operations. The three phases are gas, liquid and particulate solids, although other variations such as two immiscible liquids and particulate solids may exist in special applications. As in the case of a fixed-bed operation, both co-current and counter- current gas-liquid flow are permissible and, for each of these, both bubble flow, in which the liquid is the continuous phase and the gas dispersed, and trickle flow, in which the gas forms a continuous phase and the liquid is more or less dispersed, takes place. A well established device for countercurrent trickle flow, in which low-density solid spheres are fluidized by an upward current of gas and irrigated by a downward flow of liquid, is variously known as the turbulent bed, mobile bed and fluidized packing contactor, or the turbulent contact absorber when it is specifically used for gas absorption and/or dust removal. Still another variation is a three-phase spouted bed contactor. 

A typical amine system is shown in Figure 7-4. The sour gas enters the system through an inlet separator to remove any entrained water or hydrocarbon liquids. Then the gas enters the bottom of the amine absorber and flows counter-current to the amine solution. The absorber can be either a trayed or packed tower. Conventional packing is usually used for 20-in. or smaller diameter towers, and trays or structured packing for larger towers. An optional outlet separator may be included to recover entrained amines from the sweet gas. 

Figure 7-5 shows a typical hot carbonate system for gas sweetening. The sour gas enters the bottom of the absorber and flows counter-current to the potassium carbonate. The sweet gas then exits the top of the absorber. The absorber is typically operated at 230°F therefore, a sour/ sweet gas exchanger may be included to recover sensible heat and decrease the system heat requirements. 

A physical solvent process is shown in Figure 7-6. The sour gas contacts the solvent using counter-current flow in the absorber. Rich solvent from the absorber bottom is flashed in stages to a pressure near atmos... 

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. 

The kinetics of the reactions taking place when contacting flue gas t ntaining NO and O2 with aqueous Fe (EDTA) solutior were detennined. With this information, a steady state, rate based BiodeNOx absorber model was developed for a counter current packed colunm djsorber unit. The model has been tqipli to determine the optimum reaction conditions for the absorber. Absorber perfiirmance is improved considerably when operating at the low end of the tempaature range. 

DDIF has been applied to understand two-phase flow (air and water) in a Berea sandstone sample and the relationship to the pore geometry [65], Several different states of saturation were studied full saturation and partial saturation by three methods, i.e., centrifugation, co-current imbibition and counter-current imbibition. Imbibition is a process in which a porous sample absorbs the wetting fluid through capillary force. In the case of co-current imbibition, the bottom of the rock sample was kept in contact with water, so the water is imbibed into the rock and the water and air flowed in the same direction. For counter-current imbibition, the whole sample was immersed and the water was drawn into the center of the rock as, the air was forced out in this case, the water and air flowed in opposite directions. 

Show that the steady- state and dynamic models for a double-pipe, counter-current heat exchanger can have the same form as the model of a packed bed absorber. Discuss the assumptions inherent in both the heat exchanger and the absorber models which might lead to significant differences in the kinds of model equations used to describe each system. 

Figure 6 shows a simplified C02 capture process with two major process units absorber and stripper Zhang et al., 2009. A lean amine solvent (low C02 loading) is fed into the top of the absorber and is in counter-current contact with the gas containing C02. The C02 is chemically absorbed by the amine solvent and the treated gas exits the top of the absorber. The rich (high C02 loading) amine leaves the bottom of the absorber and is preheated by a cross heat exchanger before... 

The off-gas from a chloral production unit contains 15 vol % Cl 75 vol % HC1, and 10 vol % EtCl2. This gas is produced at a rate of 150 cfm based on 70°F and 2 psig. It has been proposed to recover part of the Cl, by absorption and reaction in a partially chlorinated alcohol (PCA). The off-gas is to pass continuously through a packed absorption tower counter-current to the PCA, where Cl, is absorbed and partially reacts with the PCA. The gas leaving the top of the tower passes through an alcohol condenser and thence to an existing HC1 recovery unit. 

The hot reactor effluent is sent to a water absorber where it is quenched counter-currently, while unreacted ammonia is neutralized with sutfuric acid. The resulting ammonium sulfate can be recovered and used as a fertilizer. The off-gases containing N2, carbon oxides and unreacted hydrocarbon are sent to incineration. The solution of acetonitrile/acrylonitrile is a heteroazeotrope. After settling, an aqueous and an organic phase are obtained. The first is refluxed, while the latter, rich in acrylonitrile and HCN, is sent to the purification step. The aqueous aceto-... 

Kang, Y. T., and Christensen, R. N. (1994) Development of a Counter-Current Model for a Vertical Fluted Tube GAX Absorber, Proceedings of the International Absorption Heat Pump Conference, Jan 19-21 1994, New Orleans, LA, USA, ASME, New York, NY, USA, pp. 7-16. 

The openings in the bottom of each chamber act as pas- 1 sage for the ascending gas as well as overflows for the counter-current flow of the absorbing liquid. a... 

Consider a general-type absorber as diagrammed in Figure 13.6. Gas and liquid flow counter-currently through real or imagined stages. The usual specifications include (a) fraction of absorption of solute in the feed gas, (b) maximnm allowable concentration of solute in the exit gas, and (c) optimal ratio of solvent to feed gas. Based on mass balances,... 

The extractive distillation column has always two feeds the entrainer is sent to the upper position, few stages below the top, eventually slightly sub-cooled, while he mixture is fed in the lower position. The entrainer flows downwards in counter-current with the vapour, absorbing selectively the component that will leave in bottoms. 

Part of the stream is washed counter currently with a feed side stream in the vent absorber (9) for benzene recovery. The absorber overhead flows to the hydrogen purification unit (10) where hydrogen purity is increased to 90%+ so it can be recycled to the reactor. The stabilizer (11) removes light ends, mostly methane and ethane, from the flash drum liquid. The bottoms are sent to the benzene column (12) where high-purity benzene is produced overhead. The bottoms stream, containing unreacted toluene and heavier aromatics, is pumped to the recycle column (13). Toluene, Cg aromatics and diphenyl are distilled overhead and recycled to the reactor. A small purge stream prevents the heavy components from building up in the process. 

The stationary phase is allowed to flow down the column, while the sample and mobile phase enter continuously. Components with a relatively low solubility in the flowing liquid phase pass up the column counter-current to the sorbent flow and out at A. Components with higher solubility are retained in the moving bed and are stripped from the absorbent, as it passes B, by the mobile phase. 

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