Vapor scrubbers

The volatile components, stripped during deodorization, are condensed and usually recovered in a direct condenser or vapor scrubber (Figure 15). 

E-1 Raw Flake Elevator E-2 Extractor Feed Convenor -3 Stationary Basket Extractor E-4 Spent Flake Elevator E-S Desolventiter Toaster E-6 Vapor Scrubber... 

Typical control measures used in pharmaceutical industry to reduce VOCs (including odors) are condensation, absorption (spray towers, venturi scrubbers, packed columns, and plate columns), adsorption (using activated carbon beds), thermal destruction (flares, boilers and process heaters, thermal incinerators, and catalytic incinerators), and vapor containment. Water- or brine-cooled condensers are the most common control devices, with carbon adsorbers in occasional use. Where the main objective is not solvent reuse but is the control of an odorons or toxic vapor, scrubbers or incinerators are used [86]. Typical spray dryer systems equipped with thermal and catalytic incinerators are shown in Figure 53.7. 

The excess of the low strength phosphoric acid is recycled to the reactor. The gases from LMS enter the BFL Vaporizer/Scrubber. 

Mol ratio (NH3 P20s), 1.6-2.0 Scrubbing liquor temperature, 85°C Recirculation ratio, 160 liters/100 Scrubber gas exit temperature, 82°- 90°C BFL vaporizer/scrubber Entering gas temperature, 82°- 90°C Exit gas temperature, 77 - 82 C Recirculation rate, 1.4 m /min Condensate composition 0.02-0.2% F... 

Vacuum-shelf dryers require auxiliary stream jets or other vacuum-producing devices, intercondensers for vapor removal, and occasionally wet scrubbers or (heated) bag-type dust collectors. 

Vapors (from drying) are removed at the feed end of the dtyer to the atmosphere through a natural-draft stack and settling chamber or wet scrubber. When employed in simple drying operations with 3.5 X 10 to 10 X 10 Pa steam, draft is controlled by a damper to admit only sufficient outside air to sweep moisture from the cylinder, discharging the air at 340 to 365 K and 80 to 90 percent saturation. In this way, shell gas velocities and dusting are minimized. When used for solvent recovery or other processes requiring a sealed system, sweep gas is recirculated throu a scrubber-gas cooler and blower. 

The other mechanism appears in scrubbers. When water vapor diffuses from a gas stream to a cold surface and condenses, there is a net hydrodynamic flow of the noncondensable gas directed toward the surface. This flow, termed the Stefan flow, carries aerosol particles to the condensing surface (Goldsmith and May, in Davies, Aero.sol Science, Academic, New York, 1966) and can substantially improve the performance of a scrubber. However, there is a corresponding Stefan flow directed away from a surface at which water is evaporating, and this will tend to repel aerosol particles from the surface. 

Another conditioning method, adaptable to scrubber systems, consists of inducing condensation of water vapor on the aerosol particles as nuclei, increasing the size of the particles and making them more susceptible to collec tion by inertial deposition. 

RooBng plants (asphalt saturators) Felt or paper saturators spray section, asphalt tank, wet looper Crushed rock or other minerals handling Asphalt vapors and particulates (liquid) Particulates (dust) Exhaust system with high inlet velocity at hoods (3658 m/s [>200 ft/min]) with either scrubbers, baghouses, or two-stage low-voltage electrostatic precipitators Local exhaust system, cyclone or multiple cyclones... 

Fhix-force-condensation scrubbers combine the effects of flux force (diffiisiophoresis and thermophoresis) and water-vapor condensation. These scrubbers contact hot, humid gas with subcooled liquid, and/or they inject steam into saturated gas, and they have demonstrated that a number of these novel devices can remove fine particulates (see Fig. 25-24). Although limited in terms of commercialization, these systems may find application in many industries. 

Some vent streams, such as light hydrocarbons, can be discharged directly to the atmosphere even though they are flammable and explosive. This can be done because the high-velocity discharge entrains sufficient air to lower the hydrocarbon concentration below the lower explosive limit (API RP 521, 1997). Toxic vapors must be sent to a flare or scrubber to render them harmless. Multiphase streams, such as those discharged as a result of a runaway reaction, for example, must first be routed to separation or containment equipment before final discharge to a flare or scrubber. 

Vapor recovery systems floating roof tanks pressure tanks vapor balance painting tanks white Cyclones-precipitator-CO boiler cyclones-water scrubber multiple cyclones Vapor recovery vapor incineration Smokeless flares-gas recovery... 

The suitability of gas absorption as a pollution control method is generally dependent on the following factors 1) availability of suitable solvent 2) required removal efficiency 3) pollutant concentration in the inlet vapor 4) capacity required for handling waste gas and, 5) recovery value of the pollutant(s) or the disposal cost of the unrecoverable solvent. Packed-bed scrubbers are typically used in the chemical, aluminum, coke and ferro-alloy, food and agriculture, and chromium electroplating industries. 

Other Considerations For organic vapor HAP control applications, low outlet concentrations will typically be required, leading to impractically tall absorption towers, long contact times, and high liquid-gas ratios that may not be cost-effective. Wet scrubbers will generally be effective for HAP control when they are used in combination with other control devices such as incinerators or carbon adsorbers. 

The discharge of copious quantities of chemicals directly to the atmosphere can give rise to secondary hazards, especially if the materials are toxic and can form a flammable atmosphere (e.g., vapor or mist) in air. In such cases, the provision of a knockout device (scrubber, dump tank) of adequate size to contain the aerated/foaming fluid is required. 

Provide vapor removal system to a scrubber or other emission control device. 

Packed-tower wet scrubber A gas scrubber that removes gases and vapors, by using either v/ater or a chemical liquid method. Efficient pollutant removal depends on the contact time between the entering gas stream and the wetted surface of the pack in the tower. This type of scrubber can be classified as... 

For MEA systeitis with a large gas flow rate, a scrubber should be considered for the outlet sweet gas. The vapor pressure of MEA is such that the separator may be helpful in reducing MEA losses in the overhead sweet gas. DEA systems do not require this scrubber because the vapor pressure of DEA is very low. 

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