Regenerator cyclones

Even with proper operation of the reactor and regenerator cyclones, catalyst particles smaller than 20 microns still escape from both of these vessels. The catalyst fines from the reactor collect in the fractionator bottoms slurry product storage tank. The recoverable catalyst fines exiting the regenerator are removed by the electrostatic precipitator or lost to the environment. Catalyst losses are related to ... 

Process and Mechanical Design Guidelines for Reactor and Regenerator Cyclones... 

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

In nnits where a primary regenerator cyclone has failed, it is possible to cut the air back to a superficial velocity of 1.5 ft/sec and limp along nntil eqnipment is available for a shntdown. Feed rate wonld be proportioned to the rednction in air. This techniqne has been employed in sitnations where a nnit dropped a cyclone and when one of the primary diplegs was plngged with refractory. The pressnre drop throngh the air distribntor shonld not be less than 30% of the bed pressnre drop to prevent grid erosion. 

Regenerator cyclones have a typical life of 15-30 years depending upon erosion and mechanical fatigue. The base metal of the cyclones will deteriorate with time leading to graphitization. Once this happens, the metal cannot be welded upon and hence cannot be repaired during a normal unit TAR. This phenomenon is dependent upon time and temperature. COP is used to minimize the temperature to extend the cyclone life. 

Particulate management in the FCCU is critical because particulate emission rates can vary in response to upsets in the FCCU. For example, failure of the regenerator cyclones can lead to an order of magnitude increase in steady state particulate emission rates and pressure reversal upset incidents can result in massive, short-term particulate emission rates that must be accommodated by the SO2 scrubbing system. 

Catalyst recovery. Catalyst losses in downflow units are typically in the range of 0.2 to 0.4 Ib./barrel of feed (100,234). Cyclones recover most of the catalyst from vapors leaving the reaction vessels. Catalyst that escapes from the reactor cyclones is recovered in the bottoms from the fractionating tower. The upflow units and the early downflow units were equipped with Cottrell electrostatic precipitators to recover en-i rained catalyst from the flue gas leaving the regenerator cyclones. It... 

This behavior is illustrated in Figure 39. As a result, when cyclones are used in series, the catalyst recovered in the first stage is coarser than in the second. The particle size ( cut size ) above which recovery efficiency is good depends upon the physical dimensions of the equipment, gas velocity, particle density, and properties of the gas. High inlet velocities result in a greater separating force and a smaller cut size but also cause increased erosion of the equipment and attrition of the catalyst. The inlet-vapor velocity is normally limited to 60 ft./second in the reactor cyclones and 75 ft./second in the regenerator cyclones (97). 

Lieberman [15] has reviewed the causes of these maloperations, which often result in loss catalyst and reduced efficiency. A deficient cyclone reactor is identified by bottom sediment and water levels in the slurry oil product. For a regenerator cyclone, problems are visibly identified by the increased opacity of the regenerator flue gas or by reduced rates of spent catalyst withdrawal. 

First we consider fluidized bed reactors in general, then fluidized combustors or regenerators and then provide specifics for a fluid catalyst cracking unit, FCCU, which consists of a riser or fluidized bed reactor, cyclone separator, steam stripper, spend catalyst transport, air-oxidizing regenerator, cyclone separator and a regenerated catalyst return. ... 

Reactor cyclones are used to separate cracking catalyst from vaporized reaction products regenerator cyclones perform the same function for flue gas. In both services the erosive nature of the catalyst, combined with rapid gas velocities, may be highly destructive to the steel cyclones. Typically, the reactor cyclone is exposed to 950°F-1,000°F temperatures, while the regenerator cyclones must handle flue gas from 1,250°F to 1,500°F. Due to the temperature, the regenerator cyclones are especially prone to failure. 

A modern FCC unit may further include a power recovery system to recover energy from the regenerator flue gas, which is a high volumetric gas flow at an elevated temperature and a moderate pressure. It beeomes critical to control particulates in the flue gas in order to protect the blades of an expander in the power recovery system. However, most regenerator cyclone systems have a limited capability of removing particles around 10 microns. 

The regenerator cyclone model performs a two-phase, loading-based AP calculation. Flue-gas compositions are calculated and reported on a standard dry mole percent basis for parameterization purposes. The flue gas stream can be connected to the valve model between the regenerator and CO boiler, or to a downstream power recovery system. 

A cyclone is a simple device that uses centrifugal force to separate solids from a gas stream. A brief mention of cyclones is merited here because they are key to the successful operation of the regenerator and the reactor. FCCs can be forced to shutdown because of a small hole in a regenerator cyclone results in unacceptable plume of catalyst leaving the regenerator stack. 

Figures 1.3.3 a, b show two commercially available cyclones designed for light industrial use. An example of a much larger scale cyclone installation is presented in Fig. 1.3.4. This is a good example of a complete system— including cyclone, blower, rotary airlock valves and ducting—all supplied by the same manufacturer. Fig. 1.3.5 illustrates a huge spent catalyst regenerator cyclone system typical of today s modern FCCU installations. Such cyclones are used to capture and return the catalyst entrained off the vessel s fluidized bed. Fig. 1.3.6 illustrates where these and other cyclones are typically used in a commercial FCCU refinery process. The left- and right-hand frames in...

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