Third stage separators

To reduce catalyst losses even further, additional separation equipment external to the regenerator can be installed. Such equipment includes third-stage cyclones, electrostatic precipitators, and more recentiy the Shell multitube separator, which is Hcensed by the Shell Oil Co., UOP, and the M. W. Kellogg Co. The Shell separator removes an additional 70—80% of the catalyst fines leaving the first two cyclones. Such a third-stage separator essentially removes from the due gas stream all particles greater than 10 p.m (36). 

Table 3. Particle-Size Distribution from a Shell Third-Stage Separator ...

The regenerator (Figure 4-80) is represented by a simplified model that ineludes the total volume and mass balanee ealeulation. The regenerator exit temperature is assumed eonstant for the duration of the transient. The third-stage separator is handled as a fixed volume and assoeiated pressure drop. Blow-down (bypass) flow is subtraeted from the input flow. 

As a first step in the driver analysis, the eapital required to make eaeh alternative operational is estimated. An orifiee ehamber is required to reduee the flue gas pressure for the steam turbine and motor alternatives. In this partieular ease, it is assumed that a third-stage separator is required for the power reeovery alternatives only and that an eleetrostatie preeipitator is used in all eases. Construetion and engineering are estimated as pereentages of total direet material and total material and eonstruetion, respeetively. An allowanee of 15% is made for eontingeney. Beeause the separator often ineludes a royalty fee, this item is added to the power reeovery alternates. As shown in Table 4-7, the motor alternative will require the least eapital. The power reeovery alternatives require additional eapital amounting to 4.63 and 4.75 per million respeetively. 

Other suggestions that address gas flow deviation include a retrofit of the stator-nozzle assembly or replacing rotors with shorter blades. However, it is easier to increase volume flow by lowering inlet pressure. Increased capacity of the third-stage separator and the auxiliary equipment avoids the possibility that excess catalyst will pass through the equipment. 

In some larger units, a turbo expander is used to recover this pressure energy. To protect the expander blades from being eroded by catalyst, flue gas is first sent to a third-stage separator to remove the... 

Increase in catalyst loading to the regenerator cyclones and third-stage separator... 

Continuous monitoring of the third-stage separator performance. If catalyst is showing up downstream, consider using more than the standard 3% flue gas underflow. The blowcase needs more attention than it usually gets. 

The majority of these units have a Third Stage Separator (TSS) or electrostatic precipitator (ESP) located before the SCR catalyst bed to protect against upsets in the FCC regenerator. The catalyst can easily be designed to handle the normal dust loading (60 mg-700 mg/Nm ), which is much lower than the typical coal fired boiler (5 g-9 g/Nm ). To handle a FCC upset (>15 g/Nm ) without a PM removal device, the catalyst volume would need to increase. 

Third stage separator (TSS) Electrostatic precipitator (ESP) Wet gas scrubber (WGS)... 

FIGURE 18.5 UOP third-stage separator. (With permission from UOP, LLC.)... 

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. 

Figure 7 Third stage separator, blow-up of swirl tube, emissions improvements.

Dries H, Patel M, van Dijk N. New advances in third-stage separators. World Refining 30-34, Oct. 2000. 

For flue gas from FCC regenerators, many licensors offer scmbbing technology. ExxonMobil offers wet-gas scmbbing (WGS), which removes particulates, SOx and NOx. UOP and Shell Global Solutions offer third-stage separator (TSS) technology, which removes PM in conjunction with flue-gas power recovery. ... 

Fig. 1.1.5. Examples of modern cyclones. From top left to bottom right Polutrol-Europe cyclone (excerpt from US Patent 3,802,570) Oneida wood shop cyclone cartridge filter Pentz/Mangano Clear-Vu cyclone two-stage LSR Core Separator-Butcher (2001) Shell Global Solutions Third-Stage Separator multiclone Dyson vacuum cleaner multiclone...

Fig. 16.2.2. Shell third-stage separator with swirl tubes working in parallel. Courtesy Shell Global Solutions International...

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