Scrubbers spray cyclone scrubber

A typical device, known as spray cyclonic scrubber, consists on a cylindrical charnber with a conical bottom as illustrated in Figure 10.14. The scrubber... 

Types of equipment classified as spray contactors include countercurrent spray columns, venturi scrubbers, ejectors, cyclone scrubbers, and spray dryers. The use of spray dryers as absorbers is of particular interest in the removal of sulfur dioxide from hot flue gas (see Chapter 7). 

A wet cyclonic scrubber is a cyclone collector with centrally located, coarse water sprays. These water sprays are usually directed radially outward,... 

Cyclone Scrubbers The vessels of cyclone scrubbers are all in the form of cyclones, which provide for compact integral entrainment separation. The gas-liquid contacting section normally uses some sort of spray generator to disperse liquid throughout the gas. Performance is similar to other spray scrubbers. 

Almost all particle-separating devices can be converted into wet scrubbers by adding liquid spraying systems. Three types of commonly used scrubbers are the spray chamber, cyclonic scrubber, and venturi scrubber. Figure 7.18 shows a simple spray chamber in which water is sprayed through a series of nozzles into a settling chamber. The dust-laden gas is fed from the bottom of the chamber and exits from the upper portion of the chamber. 

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. 

Deodorization. The neutralized/bleached oil is pumped into a deaerator operated under a pressure of 500 Pa to evacuate entrained air. From the deaerator, the oil passes through a shell and tube economizer and is heated to a temperature of 240°C by means of a thermal oil heater. The stripper and deodorizing column operates under a pressure of 600-1000 Pa volatile components such as low-molecular-weight fatty acids, ketones, aldehydes, and other odoriferous substances are stripped off by live steam. The rising vapors laden with volatile components pass through a cyclone scrubber where fresh fatty acid oil is sprayed on top of the vessel to recover outgoing fatty acids. 

Figure 20.6. Wet scrubbers, (a) Wet cyclone scrubber, (b) Spray scrubber, (c) Venturi scrubber, (d) Orifice scrubber.

In a single-stage spray dryer the process is finished when most of the moisture in the pore space has dried. The agglomerates accumulate in the lower part of the spray-drying chamber and are removed by the suction of a fan driving a dust-collection system. The agglomerates are collected in a cyclone while dust is collected in a wet scrubber. Material-laden scrubber water may be recirculated and mixed with the liquid feed. 

Venturi Cyclonic. — This system consists of a venturi followed by a cyclonic spray scrubber. A low-pressure pamp circulates scrubber liquid to the venturi where it becomes atomized and thoroughly mixed with the gas by the extremely high velocity in the throat. Gas from the venturi enters the cyclonic scrubber... 

The proper operation of a spray dryer-scrubber also requires that a dry product be formed and subsequently removed from the gas stream. Pilot tests have shown that the product salts will be dry and collectable if the gas temperature at the dryer outlet is maintained about 20 °F above its dewpoint. This also tends to minimize plume formation. The cyclone collectors used in the pilot tests removed 89-99% of the product. Although this was excellent performance by mechanical collectors, particulate emission standards will require either replacement of the cyclones or additional collection devices in series with the cyclones. The system design presently favored involves using cyclones to remove the bulk of the product and adding a small electrostatic precipitator for final particulate removal. The sodium salts produced in the spray dryer-scrubber... 

Wet spinner scrubbers. Wet spinner scrubbers operate on the basis of the same principle as dry vortex separators, however, they are equipped with jets to spray water. The jets form a continuous film of water on the walls of the cyclone, thus making possible a removal of captured solid particles to the outlet neck of the scrubber. The gas temperature must not exceed 150° C. Types with an tangential inlet of the gas as weU as those with an axial inlet (with the use of a spinner) are used. The specific water consumption is between 0.1 and 0.41 m, in the case of wet scrubber with the spinner, the separation limit is below 1.5 /xm. The maximal input dust... 

The dried products that are entrained in the exhaust air from the drying chamber must be separated and collected. Generally, there are two main types of collectors, i.e., dry collectors and wet collectors. Dry collectors include cyclones, bag filters, and electrostatic precipitators, whereas wet collectors include wet scrubbers, wet cyclones, and spray towers. 

Wet scrubber wet cyclone or centrifugal scrubber, c/s, including housing and spray excluding fan, ductwork and instrumentation. FOB cost = 50000 at inlet gas flow rate = 10 Nm /s with n = 0.68 for the range 0.5-35 Nm /s. L-rM ... 

Air pollution control APC units (cyclone, venturi scrubber, tangential spray scrubber, spray tower, ID fans, chimney) This is required to absorb the gases evolved from reactor and den for air pollution control HF will be released into atmosphere and cause air pollution Monitor operation of APC units and exit gases all the time... 

Figure 7 Typical layout of the open-cycle spray dryer system (A) cyclone/scrubber and (B) bag filter, a, air f, feed p, spray-dried product. 1, spray dryer chamber 2, cyclone 3, wet scrubber 4, bag filter/collector. (Adapted from Ref 10.)...

For removing corrosive particulates and soluble gases from ducted exhaust air streams, wet cyclone scrubbers, or spray towers or chambers should be introduced into the system. 

Fig. 13.3.7. Left an irrigated cyclone scrubber. Right a cyclonic spray scrubber. Source US Environmental Protection Agency...

Unlike simple spray towers that operate at gas velocities on the order of 0.6 to 1.5 m/s (2 to 5 ft/s), cyclonic scrubbers are designed to operate at gas velocities of 60 to 180 m/s (200 to 600 ft/s). This makes cyclonic scrubbers much more efficient than spray towers in removing particulates due to the much greater particle-to-liquid relative velocity and turbulence. However, cyclonic type scrubbers are still not as efficient as ventmi scrubbers. 

Spray Dryers A spray diyer consists of a large cyhndrical and usu ly vertical chamber into which material to be dried is sprayed in the form of small droplets and into which is fed a large volume of hot gas sufficient to supply the heat necessary to complete evaporation of the liquid. Heat transfer and mass transfer are accomphshed by direct contact of the hot gas with the dispersed droplets. After completion of diying, the cooled gas and solids are separated. This may be accomplished partially at the bottom of the diying chamber by classification and separation of the coarse dried particles. Fine particles are separated from the gas in external cyclones or bag collectors. When only the coarse-particle fraction is desired for fini ed product, fines may be recovered in wet scrubbers the scrubber liquid is concentrated and returned as feed to the diyer. Horizontal spray chambers are manufactured with a longitudinal screw conveyor in the bottom of the diying chamber for continuous removal of settled coarse particles. 

---