Catalyst distributor

The CRC is an important parameter for a unit operator to monitor periodically. Most FCC units check for CRC on their own, usually daily. The CRC is an indicator of regenerator performance. If the CRC shows signs of increasing, this could reveal malfunction of the regenerator s air/spent catalyst distributors. It should be noted that the MAT numbers reported on the E-cat sheet are determined after the CRC has been completely burned off. 

Air and spent catalyst distribution. Modifications to the air and spent catalyst distributors permit uniform dispersion of air and spent catalyst into the regenerator. Improvements are lower carbon on the catalyst and less catalyst sintering. The benefits are a cleaner and higher-activity catalyst, which results in more liquid products and less coke and gas. 

A schematic diagram of a typical industrial FCC regenerator is shown in Fig. 9.23. The spent catalyst particles are circulated through the regenerator. The orientation, size and location of the spent catalyst distributor are important parameters controlling solids mixing. The regenerated catalyst is withdrawn from the outlet located at the... 

In phot-scale DMTO fluidized bed reactor, the regenerated catalyst normally has very low coke content. As discussed above, such catalyst may not favor the selectivity to light olefins. Therefore, a counter-current fluidized bed configuration is adopted. In this configuration, the regenerated catalyst is injected into the reactor via catalyst distributor from the top of the dense bed, and the coked catalyst is taken from the draw-off bin beneath the gas distributor at the bottom. Thus, the methanol feed from the gas distributor first contacts the coked catalyst, by which a higher selectivity to light... 

The next step is to estimate transition pressure losses, whieh inelude riser liftpot, riser termination, cyclone, spent catalyst distributor, and other flow transitions. By subtracting these transition pressure losses from the hydraulic pressure, the remainder would be the pressure drop available for slide valve control. While other parameters in pressure balance seldom change much at all, it is not uncommon to have the standpipe apparent density lower than the typical... 

Both high CRC and afterburn in partial combustion regenerators can be overcome by proper design of the spent catalyst distributor and the air grid. Figure 6 shows one example of a modern spent catalyst distributor designed by Khouw et al. (1994), which distributes spent catalyst laterally through several horizontal arms. 

Figure 6 CCU spent catalyst distributor design. (From Khouw et al., 1994.)...

Quench Converter. The quench converter (Fig. 7a) was the basis for the initial ICl low pressure methanol flow sheet. A portion of the mixed synthesis and recycle gas bypasses the loop interchanger, which provides the quench fractions for the iatermediate catalyst beds. The remaining feed gas is heated to the inlet temperature of the first bed. Because the beds are adiabatic, the feed gas temperature increases as the exothermic synthesis reactions proceed. The injection of quench gas between the beds serves to cool the reacting mixture and add more reactants prior to entering the next catalyst bed. Quench converters typically contain three to six catalyst beds with a gas distributor in between each bed for injecting the quench gas. A variety of gas mixing and distribution devices are employed which characterize the proprietary converter designs. 

There are two regions in the regenerator the dense phase and the dilute phase. At the velocities common in the regenerator, 2-4 ft/sec, the bulk of catalyst particles are located in the dense bed immediately above the air distributor. The dilute phase is the region above... 

PSD is an important indicator of the fluidization characteristics of the catalyst, cyclone performance, and the attrition resistance of the catalyst. A drop in fines content indicates the loss of cyclone efficiency. This can be confirmed by the particle size of fines collected downstream of the cyclones. An increase in fines content of the E-cat indicates increased catalyst attrition. This can be due to changes in fresh catalyst binder quality, steam leaks, and/or internal mechanical problems, such as those involving the air distributor or slide vah es. 

Catalyst residence time in the stripper is determined by catalyst circulation rate and the amount of catalyst in the stripper. This amount usually corresponds to the quantity of the catalyst from the centerline of a normal bed level to the centerline of the lower steam distributor. A higher catalyst residence time, though it increases hydrothermal deactivation of the catalyst, will improve stripping efficiency. 

The main purpose of the regenerator is to produce a clean catalyst, minimize afterbum, and reduce localized sintering of the catalyst. For efficient catalyst regeneration it is very important that the air and the spent catalyst are evenly distributed. Although, in recent years, the design of air distributors has improved significantly, the same cannot... 

Two types of air distributors have been used in the past. In some of the original side-by-side units, both the air and the catalyst fltnvcd through the distributor. In virtually all the air distributors designed today, only air flows through the distributor. 

The pressure drop in the Y or J-bend section could be from improper fluidization or a flaw in the mechanical design. There are often fluffing gas distributors in the bottom of the Y or along the J-bend that are designed to promote uniform delivery of the cataly.st into the feed nozzles. Mechanical damage to these distributors or too little or too much fluffing gas affect the catalyst density, causing pressure head downstream of the slide valve. 

Improperly designed, eroded, or even missing restriction orifices used for steam purge or aeration nozzles could cause catalyst attrition. Catalyst attrition is also caused by broken air and stripping steam distributors. 

Design of mechanically robust spent catalyst and air distributors. 

Selective plugging/addition of air distributor jets to match the spent catalyst distribution... 

The catalyst must be fluidized to provide an effective seal for the diplegs. Fluidization is critical without it, the diplegs cannot discharge the catalyst and will plug, with possible massive carry-over to the main fractionator. To ensure this uniform fluidization, the system uses an additional steam distributor. 

Other more capital-intensive modifications include installing a dedicated air blower for the spent catalyst riser. The spent catalyst riser often requires a higher back-pressure than the main air blower to deliver the catalyst into the regenerator. Therefore, less total combustion air would be available if one common blower is used to transfer spent catalyst and provide combustion air to the air distributors. 

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