Cyclone stages

The Twister, produced in The Netherlands by Twister BV (Betting et al., 2007 van Eck et al., 2006), also incorporates a cyclone stage for gas/liquid separation, downstream of an expander and upstream of a recompression unit, packaged as shown in Figure 9.7. 

The dust content of the gas discharged from the preheater of a suspension preheater kiln is mainly governed by the dust collecting action of the top cyclone stage, its operational efficiency and the tightness of closure of its discharge locks. 

Energy loss through wall of cyclone stage 2 0,44 1 0.22... 

The operational behaviour of cement kilns is also determined by the cyclone preheater, in which part of the waste gas enthalpy is transferred to the kiln feed and thus recovered for the process. In addition to the gas mass flow, which in turn is governed by the fuel energy demand as well as by the air rate, the efficiency of the preheater is mainly dependent on the dust cycles in the preheater. It is normally between 50 to 65 % and may be markedly increased by the installation of additional dip tubes. Fig. 2 (2) indicates that by increasing the separation efficiency of both lower cyclone stages from 60 to 80 % each, the preheater energy loss may be cut by about 0.15 MJ/kg of clinker. In the past the installation of dip tobes was successfully effected in numerous plants. 

Fig. 2 Energy loss of a cyclone preheater with four cyclone stages in dependence on the separation efficiency of both lower cyclones.

Savings are mainly obtained by a reduction of radiation losses and false air amounts from direct or semi-indirect coal mill systems, reduction of reaction heat, improvement of the cooler efficiency, aHHitinnal cyclone stages, improvement of the cyclone efficiency and rednction of possible smoke gas losses due to injection of free water in the kiln system. 

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

The first step is to estimate the cut size needed to achieve the target emission. The required overall efficiency for the new cyclone stage is ... 

C, the second feed D, heat exchange E, staging and E, the cyclones and/or filters. 

The iron carbide process is alow temperature, gas-based, fluidized-bed process. Sized iron oxide fines (0.1—1.0 mm) are preheated in cyclones or a rotary kiln to 500°C and reduced to iron carbide in a single-stage, fluidized-bed reactor system at about 590°C in a process gas consisting primarily of methane, hydrogen, and some carbon monoxide. Reduction time is up to 18 hours owing to the low reduction temperature and slow rate of carburization. The product has the consistency of sand, is very britde, and contains approximately 6% carbon, mostly in the form of Ee C. 

For acid mists, the Brink impactor is often used (Fig. 10) (17). The mist is first drawn through a cyclone to remove particles larger than 3 fim. A five-stage impactor is used to classify mist particles of diameter 0.3—3.0 fim. 

To reduce catalyst losses even further, additional separation equipment external to the regenerator can be installed. Such equipment includes third-stage cyclones, electrostatic precipitators, and more recentiy the Shell multitube separator, which is Hcensed by the Shell Oil Co., UOP, and the M. W. Kellogg Co. The Shell separator removes an additional 70—80% of the catalyst fines leaving the first two cyclones. Such a third-stage separator essentially removes from the due gas stream all particles greater than 10 p.m (36). 

The cyclones are typically designed with diameters of 100—160 cm for ease of maintenance. Cyclone inlet velocities are usually restricted to 18—21 m /s in the first stage and to 20—26 m/s in the second stage to achieve satisfactory pressure drop and erosion characteristics (62). The number of sets of two-stage cyclones thus depends on the total gas flow. Finding room to house all the necessary cyclones within the regenerator frequently requires considerable ingenuity (62). 

W ste Hea.t Boilers. In a conventional FCCU flue gas system, the regenerator combustion gases pass through two stages of cyclonic separators, a sHde valve, orifice chamber, waste heat boiler, and electrostatic precipitator. The sHde valve and orifice chamber act in combination to reduce the flue gas to essentially atmospheric pressure. 

Recovered catalyst and blowdown gas (- 3% of the flue gas) exit from the bottom of the separator to an electrostatic precipitator or to a small, fourth-stage cyclone for further concentration of catalyst fines. The flue gas, with 70—90% of the catalyst particles removed, passes from the separator into the power expander. 

The product from each stage of grinding is classified by size, and the oversize material is recycled to be ground further. Wet cyclones are the most common type of classifier. 

The dust is relatively uniform, and the efficiency of the second-stage cyclone is not greatly lower than that of the first stage. 

Dependable operation is critical. Second-stage or even third-stage cyclones may be used as backup. 

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