Cyclones flapper valve

No trickle or flapper valves are used on the first stage. The riser cyclone diplegs terminate with a splash plate (Figure 9-4A). The upper reactor cyclone diplegs use conventional trickle valves. Sealing the upper reactor cyclone diplegs with about two feet of catalyst provides... 

Flapper valves are used to seal both high and low solids-loaded cyclone underflows although the valve type shown on the left hand side of Fig. 11.1.4 is more commonly used with lightly-loaded, second-stage cyclones operating in a fluid bed environment. 

One may wonder why the flapper valve is ever used if the second-stage cyclone s dipleg is submerged (and therefore, sealed) below the surface of the... 

The second term is the manometer effect and accounts for the difference in solids densities in the bed outside the flapper valve and that inside the valve. If there is no difference in these densities, or if the dipleg is not submerged, this term vanishes. In lightly-loaded (that is, second or third-stage) cyclones for which Eq. (11.B.8) mainly applies, the dipleg solids density is normally less than that of the bed. This results in a positive contribution to the solids backup, h. We may note that the backup increases as the submergence increases and with a decrease in dipleg solids density. 

Finally, the last term accounts for the additional backup imposed by the suction of the cyclone to which the flapper valve is attached, relative to the pressure in the vessel itself. Here, Apcyc is the pressure difference between the dilute phase of the vessel and the dilute phase of the dipleg. As such, it accounts for the total pressure loss resulting from the pressure drop across any primary cyclone that may exist and the pressure drop from the inlet to the underflow of the cyclone for which h is being calculated. For the latter, if one... 

Entrainment Most fluidized bed reactors employ one or more cyclone, either inside the freeboard region at the top of the vessel or located externally, to capture entrained solids that are then returned continuously to the base of the fluidized bed via a standpipe and a mechanical (e.g., slide) valve or aerated nonmechanical valve (see Ref. ° for details of solid return systems). A flapper gate, acting as a check valve, is commonly employed to prevent backflow of gas up the standpipe. While cyclones are by far the most popular, other gas-solid separators like impingement separators, electrostatic precipitators, filters, and scrubbers are sometimes provided, especially as second- or third stage separators. 

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