Inlet target zone

Mills and Mason found, for instance, that for a solids-to-air mass ratio, Co, of 2 and for sand particles having an average size of 70 /xm, the run time, T, before a bend would fail due to wall penetration is strongly and inversely dependent upon the gas conve3dng velocity. They found  

We wish to point out that Mills and Mason s time-to-failure studies reveal a dependency of bend failure upon velocity that is not the same as the dependency of specific erosion (mass or volmne of material eroded per miit mass or volume of impacting solids) upon velocity. The specific erosion typically varies only as the 2 to power of velocity. Thus Mills and Mason s results indicate that the mass eroded from the bends at the point of failure is more sensitive to velocity than that foimd in more coimnonly reported specific erosion tests. 

Mills and Mason also report some rather interesting and, we believe, relevant results involving the dependency of time-to-failure of bends upon mean particle size and mass ratio. Without going into the details of their investigation, it was found that the time-to-failme, T, is very nearly proportional to the square root of particle size. 

Storch and Pojar (1970) performed an interesting and rare study of erosive wear within a variety of steel cylinder-on-cone cyclones with tangential inlets. Erosion rates in each cyclone s cylinder and cone sections were measured as a function of gas inlet velocity and solids concentration for two different types of abrasive dust. The experimental results are illustrated in Fig. 12.1.1, frames a through d. The wear reported is that after exposing the cyclone to a fixed total quantity of dust. 

As shown, erosion is very pronounced in the inlet target zone . It drops off rather rapidly with axial position below this zone and continues to drop, levelling off at some minimum value with increasing distance away from the inlet as long as there is no decrease in cross-sectional area of the cyclone body. Each of the erosion curves thereby assumes some minimum value above the cone section. 

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In low erosion applications, and in low pressure rating applications, cyclones are most commonly fabricated from sheet metal 10 or 12 gauge. Mild or galvanized steel is common for units smaller than about 1 meter in diameter. These units may have replaceable, flush mounted, metal wear plates affixed in areas that are prone to erosion. These areas normally include the inlet target zone and the lower cone section. 

Fig. 12.1.8. Cyclone wear plate consisting of a mild steel plate with an abrasion resistant metal overlay such as chromium carbide. Such a plate is typical of that which may be installed in the cyclone s inlet target zone (just downstream, and in the line of sight, of the inlet duct)...

Aside from generating turbulence, a poorly designed inlet transition section, namely one that is too short, can lead to particle fouling and to rapid erosion of the cyclone s inlet target zone (see Chap. 12). This is particularly true if the transition piece was installed, in part, to decelerate the incoming flow ahead of its entrance into the cyclone. 

As shown in Figs. 12.1.1 and 12.1.2 later in this section, several zones within a typical cyclone are especially vulnerable to erosive attack. These include the inlet Target area , the lower cone and the dust hopper and/or upper dipleg (if present). We will discuss each of these areas separately below. 

Gosling of UOP LLC patented the use of Raman spectroscopy to control a solid catalyst alkylation process.54 Based on the measured composition of the stream, specific process parameters are adjusted to bring the composition back to a targeted value. Multiple probes are placed in the process, for example, near a feed stock inlet, in the reaction zone, or after the reactor. In the process discussed, the catalyst can be deactivated faster than an on-line GC can produce a reading. This reason, coupled with obtaining greater process efficiency, is strong motivation for a fast on-line system like Raman. 

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