Cyclones in series

Connecting cyclones in series is often done in practice to increase recovery. Usually the primary cyclone would be of medium or low efficiency design and the secondary and subsequent cyclones of progressively more efficient design or smaller diameter. 

The size distribution of the overflow solids from stage I can be found by solving Eq. ( 3.2.6) for fe x)  

An example showing how to calculate the efficiency of two cyclone stages in series is included in Appendix 16.A. 

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Cyclones in series may be justified under some circumstances ... 

Most FCC unit regenerators employ 6-16 sets of primary and secondary cyclones in series, depending on unit size. These cyclones are designed to recover catalyst particles that are larger than 20 p. The recovered catalyst particles are returned to the regenerator via the diplegs. The flue gas exits the cyclones through a plenum chamber. 

Perhaps the most important concern in cyclone selection is that they have the required collection efficiency. In a large cat cracker, two stages of cyclones in series must have a combined efficiency of 99.99% to keep catalyst losses to an acceptable... 

Early fluid-catalyst units employed a bank of many small-diameter cyclones in parallel, but this practice was superseded by the use of a smaller number of large-diameter cyclones (97). These are typically 3 to 5 ft. in diameter and 10 to 15 ft. high, although rough-cut separators with diameters up to 8 ft. have been reported (272). Two stages of cyclones in series are ordinarily used in the reactor. In units without Cottrells, two stages are usually employed also in the regenerator. Three... 

A composed photograph of the plant is shown in Figure 5, Not visible in the photograph are the two cyclones in series between the pyrolysis reactor and the condenser and bio-fuel oil recycle loop of the condenser. 

The latter consists of 2 cyclones in series (5), 2 shell and tube heat exchangers (6), a packed bed scrubber (7), and a mist eliminator (8). 

As a graduate student you have been assigned the task of studying certain process factors in an operation that employs three cyclones in series to treat catalyst-laden gas at 25°C and 1 atm. The inlet loading to the cyclone series is 8.24gr/ft and the volumetric flowrate is 1,000,000 acfm. The efficiency of the cyclones are 93, 84, and 73%, respectively. Calculate the following ... 

Fig. 16.11. Cyclones in series at the Baterias de El Salvador plant in San Salvador. (By courtesy of Baterias de El Salvador S.A.) [26].

Operation mechanism, which can be (a) two or more cyclones in parallel, (b) two or more cyclones in series, (c) recycling portion of the gas outlet stream back to the feed, (d) the use of secondary air flow,... 

Particulate emission control equipment applicable to dryers in soda ash plants includes cyclones, wet scrubbers, ESPs, and baghouses. Venturi scrubbers are used to control emissions from rotary steam tube dryers. Cyclones in series with venturi scrubbers are used to control emissions from fluid-bed steam tube dryers. Both venturi scrubbers and ESPs have been used to control emissions from gas-fired dryers. However, the use of ESPs or baghouses can result in operation problems because of the high humidity of the dryer exit gas and the fact that the collected soda ash particles are quite soluble and hygroscopic. This wet, sticky dust adheres to the electrodes and hoppers of the ESP or blinds and cakes the fabrics in the baghouse. Controlled emission factors of total PM from rotary soda ash dryers and fluid-bed soda ash dryers are 0.25 and 0.019 kg/mg of product, respectively [85]. 

Figure 4.2 Schematic of main features of fluidized-bed reactor for production of acrylonitrile showing immersed serpentine heat transfer tubing, separate distributors for air and ammonia + propane or propene, and one representative cluster of internal cyclones in series.

Cyclone separators are often used in fluidized beds for separating entrained solids from the gas stream (see Chapter 9). Cyclones installed within the fluidized bed vessel would be fitted with a dip-leg and seal in order to prevent gas entering the solids exit. Fluidized systems may have two or more stages of cyclone in series in order to improve separation efficiency. Cyclones are also the subject of erosion and must be designed to cope with this. 

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