Dust-laden gas

Cooled dust-laden gas is dedusted in an electrostatic precipitator and sent to the cleaning unit to remove impurities such as arsenic, fluorine, and chlorine before being sent on to the sulfuric acid production plant. 

Fan, dust A purpose-designed fan that is capable of extracting a dust-laden gas. 

Pocket An extended-surface filter in which the medium is formed into pockets or hags through which the dust-laden gas flows. They may be supported by the air pressure or self-supporting. 

Cyclones are more efficient than gravity and baffle chambers, and also occupy less space. The dust-laden gas makes a tangential entry into a cylindrical or conical chamber. The dust particles travel outwards to the outer wall due to centrifugal forces there they collide with the wall and fall downwards to the receiver chamber, whilst the gases escape from an opening provided at the top. 

Cyclone Separators The most widely used type of dust-collection equipment is the cyclone, in which dust-laden gas enters a cylindrical or conical chamber tangentially at one or more points and... 

Example 7.1 In a test of the performance of a cyclone, a dust-laden gas with the particle mass flow rate of 600 kg/h is used. Given that the dust escape rate is 30 kg/h, what is the overall collection efficiency Plot the fractional efficiency curve to identify the cut-off size of this cyclone. The results of particle size analysis (by weight percentage [wt%]) at the inlet and outlet of the cyclone are given in Table E7.1. 

Example 7.2 Consider a dust-laden gas passing through an electrostatic precipitator. Assume that all particles have the same charge-to-mass ratio, q/m, and the electric field is uniform. Use the Deutsch equation to estimate the overall collection efficiency if the particle size distribution based on weight percentage (wt%) can be expressed by the mass density function, /M, as... 

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. 

It is interesting to note that the volume fraction and collection efficiency in cocurrent scrubbing are in the same form as those in countercurrent scrubbing even though the flow directions of the dust-laden gas in these two cases are opposite to each other. 

Cyclone Separators. The most commonly used equipment for the separation of dust particles from an air/gas stream is the cyclone separator. The literature on design and operation of cyclones has been extensively reviewed by Rietemer and Vetver (1961), Maas (1979), Zenz (1982), and Pell and Dunson (1999). A sketch of a cyclone separator and typical dimensional ratios are found in Figure 20.1(b). The dust-laden gas stream enters near the top of the collection chamber tangentially. The force on the larger particles is greater than the force on the smaller ones because the latter... 

Shaker filters have the drawback that they must be taken off stream to clean the bags. Since continuous on stream operation is required, several baghouse chambers are installed in parallel with dampers, permitting one section to be in the cleaning cycle while the rest of the baghouse is filtering the dust-laden gas stream. 

It is useful to note that certain types of reactors are automatically eliminated for certain situations, such as the packed-bed reactor for dust-laden gas. Further, reactor selection is usually straightforward for extreme situations such as reaction entirely in the bulk or in the film. In both cases, the quantity of bulk liquid is determined by the rate of production, but the extent to which the bulk phase is utilized for the reaction is minimal when the reaction is confined to the film and maximal when it occurs fully in the bulk. 

The cyclone is a mechanically simple, reliable device for the separation of PM from an air stream by the action of centrifugal forces. The centrifugal forces, resulting from the tangential velocity given to the dust-laden gas at the top of the cyclone. 

---