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... 

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.

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... 

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.)...

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). 

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. 

Pot charging Particulates (dust), CO, HF, SO, CF4, and hydrocarbons High-efficiency cyclone, baghouse, spray towers, floating-bed scrubber, electrostatic precipitators, chemisorption, wet electrostatic precipitators... 

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... 

When the pollutant loading is exeeptionally high or consists of relatively large particles (> 2 /tm), venturi scrubbers or spray chambers may be used to reduce the load on the ESP. Much larger particles (> 10 /tm) are controlled with mechanical collectors such as cyclones. Gas conditioning equipment to reduce both inlet concentration and gas temperature is occasionally used as part of the original design of wet ESPs (AWMA, 1992 Flynn, 1999). 

Methods of dust removal depend mainly on the particle size of the dust and the temperature and moisture content of the gas. The methods used are broadly divided into dry methods and wet methods. The dry methods involve the use of gravity and baffle chambers, cyclones, filters, and electrostatic precipitators, while the wet methods involve the use of spray towers and venturi scrubbers. In principle, wet cleaning is preferred to dry cleaning because of the excessive wear associated with and the difficulty in handling the fine dusty material removed in the dry methods. The wet methods, however, must be followed by such operations as filtration, drying of filter cakes, and recycling of water. 

Venturi and orifice scrubbers are simple forms of wet scrubbers. The turbulence created by the venturi or orifice is used to atomise water sprays and promote contact between the liquid droplets and dust particles. The agglomerated particles of dust and liquid are then collected in a centrifugal separator, usually a cyclone. 

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