Diameter dust exit

The collection efficiency of cyclones varies as a function of particle size and cyclone design. Cyclone efficiency generally increases with (1) particle size and/or density, (2) inlet duct velocity, (3) cyclone body length, (4) number of gas revolutions in the cyclone, (5) ratio of cyclone body diameter to gas exit diameter, (6) dust loading, and (7) smoothness of the cyclone inner wall. Cyclone efficiency will decrease with increases in (1) gas viscosity, (2) body diameter, (3) gas exit diameter, (4) gas inlet duct area, and (5) gas density. A common factor contributing to decreased control efficiencies in cyclones is leakage of air into the dust outlet (EPA, 1998). 

Measurements on dust accumulation in a laboratory PPR module, carried out by Calis [6] with a silica powder and a fly ash (median particle diameter between 20 and 30 xm) at a solids concentration between 5 and 10 g/m in air at ambient conditions and a gas velocity of about 1 m/sec showed that about 10% of the dust introduced is trapped, the major part of 90% being entrained by the exit gas. 

A disadvantage of fluidized-bed reactors is that the equipment is large. So that the solid particles will not be blown out the top of the reactor, the gas velocity must be low. This in turn necessitates large-diameter vessels and increases the initial cost. There are also losses of cataly t fin s from the, reactor, necessitafing expMslve" dust-coIIection equipment in the exit streams. 

Carbon and sulfur are reacted (Reaction 4.1) in the absence of air in oval or cylindrical vessels called retorts. The vessels are approximately 3 ft in diameter and 10 ft in height [117] and are constructed from chrome alloy steel or cast iron. Usually, 1-4 retorts are installed in a furnace [118]. The furnace is heated by coal, gas or oil. Coal is intermittently added from the top of the retort while vaporized sulfur is continuously fed in from the bottom. Carbon disulfide is formed while the sulfur vapor works its way through the hot coal (800—1000 C) to the top of the retort. The reacted gases exit the top of the retort through a duct. Nonreactive ash and coal dust are periodically removed as they make their way to the bottom while fresh coal is added. Deposits are also removed from the inside walls of the retort, usually on a monthly or bimonthly basis. Because of the corrosive sulfur vapor, the retorts must be replaced every 1—2 years. 

The cyclones cannot remove all particles with satisfactory efficiency due to the generally wide variation in the dust particle size, weight, and properties, as well as variable gas flow rate in the process. However on the basis of known data, a design can be made and a major amount of dust can be separated. The author therefore suggests removable exit pipe pieces with different diameter and lengths. These can be fitted as a liner on the top nozzle. 

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