Cyclone performance

Practically all cyclone performance data have been related to a present cyclone set of geometric ratios. One model for cyclone grade-efficiency curves has been tested against reported commercial cyclone efficiencies (159). A good fit was obtained. 

Cyclone Separator with Separate Catch Tank This type of blowdown system, shown in Fig. 26-17 and 26-18, is frequently used in chemical plants where plot pan space is hmited. The cyclone performs the vapor-liquid separation, while the catch tank accumulates the hquid from the cyclone. This arrangement allows location of the cyclone knockout drum close to the reactor so that the length of the relief device discharge hne can be minimized. The cyclone nas internals, vital to its proper operation, which will be discussed in the following sections. 

Other Considerations Cyclones perform more efficiently with higher pollutant loadings, provided that the device does not become choked. Higher pollutant loadings are generally associated with higher flow designs (Andriola, 1999). 

PSD is an important indicator of the fluidization characteristics of the catalyst, cyclone performance, and the attrition resistance of the catalyst. A drop in fines content indicates the loss of cyclone efficiency. This can be confirmed by the particle size of fines collected downstream of the cyclones. An increase in fines content of the E-cat indicates increased catalyst attrition. This can be due to changes in fresh catalyst binder quality, steam leaks, and/or internal mechanical problems, such as those involving the air distributor or slide vah es. 

C yciones. Changes in refractory anchor and material, the hanging system, longer L/D, and using more welds in the anchors have improved cyclone performance. 

Calculate the cyclone performance and overall efficiency (recovery of solids). If unsatisfactory try a smaller diameter. 

A cyclone will operate equally well on the suction or pressure side of a fan if the dust receiver is airtight. Probably the greatest single cause of poor cyclone performance, however, is the leakage of air into the dust outlet of the cyclone. A slight air leak at this point can result in a tremendous drop in collection efficiency, particularly with fine dusts. For a cyclone operating under pressure, air leakage at this point is objectionable primarily because of the local dust nuisance created. 

Knowlton and Bachovchin [Coal Processing Technol. 4 122-127 (1978)] studied the effect of pressure on cyclone performance and... 

The pressure drop across the cyclone is an important parameter in the evaluation of cyclone performance. It is a measure of the amount of work that is required to operate the cyclone at given conditions, which is important for operational and economical reasons. The total pressure drop over a cyclone consists of losses at the inlet, outlet and within the cyclone body. The main part of the pressure drop, i.e. about 80%, is considered to be pressure losses inside the cyclone due to the energy dissipation by the viscous stress of the turbulent rotational flow [9], The remaining 20% of the pressure drop are caused by the contraction of the fluid flow at the outlet, expansion at the inlet and by fluid friction on the cyclone wall surface. 

Aerosol concentrations affect cyclone performance with increased concentrations increasing efficiency (Ranz, 1985). Wheeldon and Bumard (1987) showed improved cyclone performance with very high particle concentration (50 g/m3). Detailed criteria for cyclone design have been summarized by Licht (1980) and include many of the considerations mentioned above. 

Lewnard, J. J., Herb, B. E., and Tsao, T. R. Effect of Design and Operating Parameters on Cyclone Performance for Circulating Fluidized Bed Boilers, in Circulating Fluidized Bed Technology IV (Amos A. Avidan, ed.), pp. 636-641. Somerset, Pennsylvania (1993). 

Highly friable particles may fracture and malleable particles may deform when thrown onto the cyclone wall. The nature of inertial separation based technologies impose the limitation that larger and more dense particles will be more readily separated from the continuum and therefore obtain higher collection yields compared to smaller less dense panicles. Various analytical semi-empirical and CFD-ba.sed methods exist for predicting cyclone fractional collection efficiency and yield (44). However, the ability to a priori predict full cyclone performance from first principles for applications involving inhalation panicles is still a considerable challenge. 

Units are sometimes placed in series to provide multiple stages of separation. Hydrocyclones are used on ships and drilling platforms for removing oil from water [Bednarski and Listewnik, Filtration and Sep., pp. 92-97 (March/April 1988)]. Numerical simulations ofhydro-cyclone performance and flow profiles are described by Bai and Wang [Chem. Eng. Technol., 29(10), pp. 1161-1166 (2006)] and by Murphy et al. [Chem. Eng. Sci., 62, pp. 1619-1635 (2007)]. 

In general, cyclones are used to separate particles from the gas stream, but recent developments have enabled cyclones to function as reactors. Some cyclone reactors can separate cracking catalyst from vaporized reaction products in the range of 950°F and 1,000°F, or can function as regenerators for flue gases between 1,250°F and 1,500°F. In both cases, the high particle velocities can cause rapid erosion of the cyclone material. This often results in poor performance of the cyclone. Other causes of poor cyclone performance are ... 

An approximate analysis of the particle motion and cyclone performance can be carried out by setting up a force bulance for Stokesian particles in the radial direction ... 

Two characteristics are used to define cyclone performance. They are the critical particle diameter (particle size that is completely removed from the air stream) and the cut size (the particle diameter for which 50% collection efficiency is achieved). A typical example of theoretically and experimentally obtained efficiency curves is shown in Figure 9.24. It is evident from this diagram that particles above 15 pm are removed with high efficiency in the cyclone. The pressure drop across the cyclone unit ranges between 700 and 2000 Pa. 

---