Micronization unit designs

The primai y distinguishing charac teristic of gas dispersoids is particle size. The generally accepted unit of particle size is the micrometer, [Lm. (Prior to the adoption of the SI system, the same unit was known as the micron and was designated by 1.) The particle size of a gas dis-persoid is usually taken as the diameter of a sphere having the same... 

The v.ct glycol from the separator flows through a sock filter to remove. solids and a charcoal filter to absorb small amounts of hydrocarbons that may build up in the circulating glycol. Sock filters are normally designed for the removal of 5-micron solids. On units larger than 10 gpm... 

Most FCC unit regenerators employ 4 to 16 parallel sets of primary and secondary cyclones. The cyclones are designed to recover catalyst particles greater than 20 microns diameter. The recovered catalyst particles are returned to the regenerator via the diplegs. 

Cyclone filters are effective at removing larger particles and can operate over a wide range of temperatures, limited primarily by the material of construction. Cyclone filters are often designed as multiple units in series (multi-clones). They can remove >90% of particulates above about 5 microns in diameter at minimal pressure drops of 0.01 atm. Partial removal of material in the 1.5 micron range is also possible, but cyclonic filters become ineffective with sub-micron particles. 

Figure 11.3 shows the entrainment flux measured at the outlet of the unit and the fines weight fraction (defined as particle sizes smaller than 44 microns) for the bed and entrained material as a function of time. As the fines concentration began to decrease in the bed, the entrainment rate increased rapidly to a peak approximately 10 times the initial rate. Further depletion of fines from the bed resulted in a subsequent drop in the entraimnent rate. For the commercial unit, the highly variable entrainment rates appeared to be due to the extreme sensitivity to the fines concentration. The dipleg was not designed to handle the presumed tenfold increase in the entrainment rate and often flooded as a result. 

The TSS has less potential for maximum emission control as the WGS and electrostatic precipitator (ESP). While all three technologies were designed to meet NSPS/ MACT, only the WGS and ESP can meet more stringent requirements. TSS performance can typically achieve d50 grade efficiency down to 2 microns. Most reported performance values result in emissions of 0.4-0.8 Ib/Mlb coke. Future PM2 5 regulations are a concern for TSS applications. By definition, TSS units cannot effectively remove small particles due to the cyclonic operation. 

Whether one uses millimeters, torr, microns, or millitorr, a unit of force is being determined by a unit of length. To maintain the relationship of force per unit of area used in pressure and vacuum, the SI decided on the term Pascal (one Newton per square meter) as a unit of vacuum. Regrettably, the acceptance of the Pascal has been as successful as metrics in the United States. The numeric relationship between all of these designation can be seen in Table 7.2. 

Vatavuk (1990) pointed out that a key dimension in the sizing of a cyclone is the inlet area. Properly designed cyclones can remove nearly every particle in the 20-30 micron range. Typically, cyclone separators have efficiencies in the range of 70-90%. Because of the low efficiency of these units, they are often used as a first stage of dust collection, or are referred to as primary collectors. 

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