Countercurrent scrubber

Wet scrubber for formaldehyde and methanol only afterburner for organic vent gases Venturi scrubber followed by cyclone separator and packed countercurrent scrubber... 

Schultes presented an absorption model for packed columns including simulations [81], while Eden [18] developed a non-equilibrium stage model describing the absorption of electrolytes in co-current and countercurrent scrubbers. The simultaneous view of phase and reaction equilibrium and the existence of solids in the liquid phase were emphasized in these reports. 

Tadient may be maintained per unit length of absorber in a cocurrent configuration. VII these considerations point to a need for careful qualification of the commonly iccepted rule of thumb concerning countercurrent scrubbers being more efficient or a given application. 

The Lurgi process requires the use of a degummed and deacidified feedstock. The refined vegetable oil and methanol are reacted in a two-stage mixer-settier arrangement in the presence of a catalyst. The glycerine produced in the reaction, dissolved in the surplus methanol, is recovered in the rectification column. Most of the entrained methanol and glycerine are recovered from the methyl ester in the countercurrent scrubber. The methyl ester can be further purified by distillation (6). 

Mass transfer driving forces are intermediate between vertical concurrent scrubbers and countercurrent scrubbers [1]. If the absorbed solute obeys Henry s Law in the liquid phase, the mass transfer driving force will limit maximum solute removal efficiency to about 90% of that obtained in a countercurrent scrubber for typical chemical fumes—assuming scrubbing water flow is limited. However, if the absorption of solute is followed by a rapid chemical reaction in the liquid phase, so that there is no appreciable vapor pressure of solute above the solution, the mass transfer driving force will be the same as for a countercurrent scrubber. 

Countercurrent scrubbers generally have these characteristics ... 

Countercurrent scrubber—Scrubber in which the gas and liquid flow in opposite directions. 

In the scrubbing of bigbly soluble/reactive gas/vapors (e.g. HCl vapor by water), the value of Hf may be at least an order of magnitude smaller than the ratio (W g/Wy). If the scrubbing liquid does not have any solute species as it enters a countercurrent scrubber, obtain a simplified expression for NTUog based only on the inlet gas-phase composition x,go and the outlet gas-phase composition Xi. Assume that (1) the gas is very dilute in the species to be scrubbed, (2) tbe scrubbing is very efficient and the gas is highly purified. 

Plate Towers Plate (tray) towers are countercurrent gas-atomized spray scrubbers using one or more plates for gas-liquid contacting. They are essentially the same as, if not identical to, the devices used for gas absorption and are frequently employed in apphcations in which gases are to be absorbed simultaneously with the removal of dust. Except possibly in cases in which condensation effects are involved, countercurrent operation is not significantly beneficial in dust collection. 

Packed-bed scrubbers m be construc ted for either vertical or horizontal gas flow. Vertical-flow units (packed towers) commonly use countercurrent flow of gas and liquid, although cocurrent flow is sometimes used. Packed scrubbers using horizontal gas flow usually employ cross-flow of liquid. 

Mobile-Bed Scrubbers Mobile-bed scrubbers (Fig. 17-51) are constructed with one or more beds of low-density spheres that are free to move between upper and lower retaining grids. The spheres are commonly 1.0 in (2.5 cm) or more in diameter and made from rubber or a plastic such as polypropylene. The plastic spheres may be solid or hollow. Gas and liquid flows are countercurrent, and the spherical packings are flmdized by the upward-flowing gas. The movement of... 

Figure 24, Countercurrent-flow packed Figure 25. Co-current-flow scrubber, scrubber.

Continuing further with the recovery aspects from coke oven gas reference may be drawn to the recovery of light oil (crude benzol). In a typical process used, the coke oven gas (from which benzol is to be recovered) after removal of tar, ammonia etc. is passed through the benzol scrubber where the benzol vapours are scrubbed by wash oil flowing countercurrent to the gas. Benzolised wash oil is then pumped to the recovery section where the crude benzol, absorbed in the wash oil is stripped off by steam. The steam vapour mixture, com-... 

Absorption is a commonly applied operation in chemical processing. It is used as a raw material or a product recovery technique in separation and purification of gaseous streams containing high concentrations of organics (e.g., in natural gas purification and coke by-product recovery operations). In absorption, the organics in the gas stream are dissolved in a liquid solvent. The contact between the absorbing liquid and the vent gas is accomplished in countercurrent spray towers, scrubbers, or packed or plate columns. 

An impingement-plate scrubber is a vertical chamber with plates mounted horizontally inside a hollow shell. Impingement-plate scrubbers operate as countercurrent PM collection devices. The scrubbing liquid flows down the tower while the gas stream flows upward. Contact between the liquid and the particle-laden gas occurs on the plates. The plates are equipped with openings that allow the gas to pass through. Some plates are perforated or slotted, while more complex plates have valve-like openings. 

For scrubbing of sulfur dioxide and a large portion of catalyst fines, a countercurrent spray tower with a multiple stage nozzle system is typically applied. The WESP is applied after the scrubber section to remove the residual particulate matter with a... 

While our focus has been on the treatment of wastewater, another technique known as biofiltering is intended to treat contaminated air. The most common technique and the one we will cite in the case studies is a subclass known as trickling filters. The general engineering design involves a countercurrent flow of air and water not unlike a scrubber. The exchange or extraction of the pollutant from the air into the water is the dominant step in the process. At steady state, the water is the vehicle within which remediation takes place. Thus while the pollution is resident in the air initially, the remediation takes place from the water and thus relates the process to the discussion above. 

Diffusion scrubbers are membrane-based denuders in which the sample air flows on one side of a membrane and a suitable scrubber liquid flows on the other side. The analyte gases of interest are collected in the scrubber liquid, and the effluent is subjected to analysis. The simplest geometry is that of a conventional single-tube denuder. Air is sampled through a tubular membrane while the scrubber liquid is pumped in a countercurrent fashion through an external jacket tube surrounding the membrane tube. 

The collection of particles is achieved in a countercurrent flow between the water droplets and the particulates. In a cyclonic scrubber, water is injected into the cyclone chamber from sprayers located along the central axis, as shown in Fig. 7.19. The water droplets capture particles mainly in the cross-flow motion and are thrown to the wall by centrifugal force, forming a layer of slurry flow moving downward to the outlet at the bottom of the cyclone. Another type of scrubber employs a venturi, as shown in Fig. 7.20. The velocity of the gas-solid suspension flow is accelerated to a maximum value at the venturi throat. The inlet of the water spray is located just before the venturi throat so that the maximum difference in velocity between droplets and particles is obtained to achieve higher collection efficiency by inertial impaction. A venturi scrubber is usually operated with a particle collector such as a settling chamber or cyclone for slurry collection. 

DAP solutions have a high partial pressure of ammonia, and the reaction is normally carried out in a two-stage reactor system with feed acid passing countercurrent to the flow of ammonia gas. Incoming acid reacts in the scrubber with ammonia from the main reactor and may also serve as a scrubber for dryer off-gases238. 

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