Cyclone system

Regardless of the source, the resultant oil slicks are essentially surface phenomena that are affected by several transportation and transformation processes. With respect to transportation, the principal agent for the movement of slicks is the wind, but length scales are important. Whereas small (i.e. relative to the slick size) weather systems, such as thunderstorms, tend to disperse the slick, cyclonic systems can move the slick essentially intact. Advection of a slick is also affected by waves and currents. To a more limited extent, diffusion can also act to transport the oil. 

Figure 4-48. A two-stage cyclone system. (Source Bill Dougherty, BP Oil Refinery Marcus Hook, PA.)...

A cyclone system is to be installed as a part of a bagging operation. The unit is shown in Figure 4-48. Determine the head required for purchase of the fan. The conditions are ... 

Mobil started installing closed cyclone systems in its FCC units. 

ABB Lummus s RTD consists of a two-stage reactor cyclone system (see Figure 9-2). The riser cyclones (the first stage) are hard-piped to the riser. Attached to the end of each riser cyclone dipleg is a conventional trickle valve as shown in Figure 9-3. Each trickle valve has a small opening to prevent catalyst defluidization, which can be a problem, especially during start-ups. 

SWEC offers a reactor quench system rather than a closed cyclone system. Their typical RTD is an external, rough-cut cyclone (see Figure 9-7). The vapors from the rough-cut cyclone enter the reactor vessel. 

In a fluidized bed reactor, entrained particles leaving in a dilute phase stream are conventionally and desirably either partially or wholly condensed into a bulk stream and returned to the bed via a centrifugally driven cyclone system. At equilibrium, or when steady state operation is attained, any particle loss rate from the cyclones, as well as the remaining bed particle size distribution, are functions of (a) the rate of any particle attrition within the system and (b) the smallest particle size that the cyclone system was designed to completely collect (i.e., with 100% efficiency), or conversely the largest size which the system cannot recover. These two functions result in an interdependency between loss rate and bed particle size distribution, eventually leading to an equilibrium state (Zenz Smith, 1972 Zenz, 1981 Zenz Kelleher, 1980). 

Case B. Suppose, more realistically, that the catalyst undergoes a known, experimentally determined, rate of attrition as a function of particle size (Zenz, 1971 Zenz Kelleher, 1980). The particle loss rate from the cyclone system will now approach and finally equal the rate of production of 0 to 10 micron particles by attrition from all the larger sizes. To maintain reactor inventory, this loss rate will be replaced, at an equal rate, with fresh catalyst. Since the rate of attrition of any size particle depends on its concentration in the stream subjected to the attrition (as finer particles effectively cushion the coarser), and since the loss is replaced with fresh catalyst (containing the coarsest), the bed size distribution will reach a steady state between 10 and 150 microns in which the mean size, as well as all sizes smaller than the largest, will now be decreased from what would have prevailed under conditions of zero attrition. 

The cyclone system pressure drop will increase... 

FIG U RE 7.3 Closed cyclone system. (Reprinted from Jack Wilcox, R., Published in Petroleum Technology Quarterly, Troubleshooting Complex FCCU Issues, http //www.ePTQ.com, Q3, 2009. With permission.)... 

In the process, a residuum is desulfurized and the nonvolatile fraction from the hydrodesulfurizer is charged to the residuum fluid catalytic cracking unit. The reaction system is an external vertical riser terminating in a closed cyclone system. Dispersion steam in amounts higher than that used for gas oils is used to assist in the vaporization of any volatile constituents of heavy feedstocks. 

The cyclone separates solid particles from the outlet gas. Several cyclones may be combined to form a multistage cyclone system. More than one multistage cyclone system can be placed inside or outside the bed. Other types of gas-solid separators (e.g., filters) are also used for gas-solid separation although the cyclone is most widely adopted in fluidized beds. The dipleg/standpipe returns the particles separated by the cyclone into the dense bed. The outlet of a dipleg may be located in the freeboard or immersed in the dense bed. 

Since the cyclone system is not 100% efficient, a certain amount of the catalyst used in the fluid-bed reactor is entrained in the off-gas and captured in the quench system. The loss is in the range 0.3-0.7kg/t acrylonitrile. 

The small amount of catalyst fines that pass through the highly efficient cyclone system are removed by a newly developed hot-gas catalyst filter or alternatively by wastewatertreatment that meets even the strictest regulations for copper, dioxins and furanes. The environmentally friendly process uses recycle gas, which is fed back to the reactor after condensing EDC and water. 

Low manufacturing costs The unlimited catalyst service is combined with the low losses via the highly efficient cyclone system (less than 20g catalyst per ton of produced EDC). High raw-material yields (98.5 % ethylene, 99 % anhydrous hydrochloride and 94 % oxygen) and the possibility to use low-cost oxygen from PSA units ensure a highly competitive process with low production costs. 

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