Third Stage Separators TSS

The flue gas passes through a number of small diameter high-efhciency cyclonic elements arranged in parallel and contained with the separator vessel. The UOP design uses an axial flow cyclone. After the catalyst particles are removed, the clean flue gas leaves the separator. A small stream of gas, called the underflow, exits the separator through the bottom of the TSS. In an environmental application, the underflow is diverted to a fourth stage separator (FSS) that is typically a barrier filter. The underflow rate is typically 2-5% of the total flue gas rate and is set by use of a critical flow nozzle. 

The particulate removal efficiency of a TSS is difficult to calculate with a single theoretical relationship. The technology licensors have utilized pilot plants and cold flow modeling to improve their removal efficiencies to meet stricter environmental regulations. While there is no theoretical relationship that exactly matches removal efficiencies, the following efficiency relationship from Rosin, Rammler, and Intehnann [2] is often used to understand cyclone fundamentals  

Dpmin = critical particle diameter p = gas viscosity B, = inlet duct width 

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

The above relationship shows that the opportunities for improved removal efficiency are by  

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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)... 

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. ... 

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