Reactor cyclone

Reduction of the catalyst/hydrocarbon time in the riser, coupled with the elimination of post-riser cracking, reduces the saturation of the already produced olefins and allows the refiner to increase the reaction severity. The actions enhance the olefin yields and still operate within the wet gas compressor constraints. Elimination of post-riser residence time (direct connection of the reactor cyclones to the riser) or reducing the temperature in the dilute phase virtually eliminates undesired thermal and nonselective cracking. This reduces dry gas and diolefin yields. 

The ash content of the DO is affected by the reactor cyclone s performance and catalyst physical properties. To meet the CBFS ash requirement (maximum of 0.05 wt%), DO product may need to be filtered for the removal of the catalyst fines. 

Higher catalyst circulation usually requires opening the regenerated and spent catalyst slide (or plug) valves. Higher circulation increases the pressure drop in the riser and in the reactor cyclones, lowering the differential pressure across the slide valves. This causes the valves to open further, until the unit finds a new balance. 

Sometimes insufficient differential across the regenerated catalyst slide valve is not due to inadequate pressure buildup upstream of the valve, but rather due to an increase in pressure downstream of the slide valve. Possible causes of this increased backpressure are an excessive pressure drop in the Y or J-bend section, riser, reactor cyclones, reactor overhead vapor line, main fractionator, and/or the main fractionator overhead condensing/cooling system. 

The pressure drop across the reactor cyclones, reactor vapor line, main fractionator, and main column overhead condensing/cooling system can be too high. The pressure drop is primarily a function of vapor velocity. Any plugging can increase the pressure drop. 

Compare the cyclone loading with the design. If the vapor velocity into the reactor cyclones is low, consider adding supplemental steam to the riser. If the mass flow rate is high, consider increasing the feed preheat temperature to reduce catalyst circulation. 

Follow proper start-up procedures. Introduce feed to the riser only when the reactor system is adequately heated up. Local cold spots cause coke to build up in the reactor cyclones, the plenum chamber, or the vapor line. 

ABB Lummus s RTD consists of a two-stage reactor cyclone system (see Figure 9-2). The riser cyclones (the first stage) are hard-piped to the riser. Attached to the end of each riser cyclone dipleg is a conventional trickle valve as shown in Figure 9-3. Each trickle valve has a small opening to prevent catalyst defluidization, which can be a problem, especially during start-ups. 

In the KBR system, as with the ABB Lummus design, the riser cyclones are hard-piped to the riser. The diplegs of both the riser cyclone and the upper reactor cyclone are often sealed with catalyst. This minimizes the carry-under of reactor vapors into the reactor housing and maximizes the collection efficiency of the riser cyclones. 

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... 

In KBR closed cyclone technology, each set of riser and upper reactor cyclones is connected via the use of a slip joint conduit. The stripper steam and hydrocarbons, as well as dome steam, exit the reactor housing by entering through this conduit as shown in Figure 9-5. 

Spent catalyst from the reactor/cyclones discharges into the stripper. Stripping steam displaces hydrocarbon vapors entrained with the catalyst and removes volatile hydrocarbons from the catalyst. 

Acoustic chemometrics has its greatest benefits in cases where haditional sensors and measurement techniques, such as flow, temperature and pressure transmitters cannot be used. In many processes it is preferable to use noninvasive sensors because invasive sensors may cause disturbances, for example fouling and clogging inside the process equipment such as pipelines, reactors cyclones, etc. In this chapter we concentrate mainly on new industrial applications for acoustic chemomehics, and only discuss the necessary elements of the more technical aspects of the enabling technology below - details can be found in the extensive background literature [3-5],... 

The upper (reactor) cyclone outlet temperature will increase... 

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). 

Cyclone reactors permit study of flow pattern and residence time distribution [6,7]. See for example, the studies by Coker [8,9] of synthetic detergent production with fast reaction. Reactor cyclones are widely used to separate a cracking catalyst from vaporized reaction products. 

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. ... 

In this case, it is the fluid medium, the fuel oil preheated to its evaporation point, that undergoes the value-adding conversion. Its long hydrocarbon chains are quickly cracked when encountering the catalyst particles in the fluid mix. The fluid is sent to a reactor. Cyclones at the top of the reactor separate the gaseous hydrocarbon fluid from the spent catalyst and transport it into a distillation unit. The solid catalyst particles are collected at the bottom of the reactor and sent to a regenerator, from where they are fed back into the catalytic riser in a continuous process. 

Schematic for the Chalmers pilot system for solids CLC (a) Air reactor (b) Riser (c) Air reactor cyclone (d) Fuel reactor.

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. 

Cyclone malfunctions result in catalyst loss. A deficient reactor cyclone may be identified by high BS W levels in the slurry oil product. Regenerator cyclone problems are visibly identified by the increased opacity of the regenerator flue gas or by reduced rates of spent catalyst withdrawal. 

High wet gas compressor suction pressure. An increase in the pressure at the suction to the wet gas compressor backs up through the fractionator overhead condensers and trays, the vapor line, and the reactor cyclones to the riser. Now, for the operator to maintain a proper regenerator slide valve AP (i.e., at least 3 psi), he must pinch back on the flue gas slide valve to raise the regenerator pressure. This, of course, translates directly into an increase in air-blower discharge pressure. 

At the termination of the riser it is important to have quick separation of reaction mix from spent catalyst. After the riser, the reaction mix can remain in the reactor vessel for over 20 seconds before it enters the reactor cyclones and is separated from the spent catalyst. Typically, catalyst densities between riser outlet and cyclone inlet average only 1 to 3 Lb/Ft. During that 20+ seconds additional conversion can occur, but since the catalyst is spent the conversion is thermal in nature and not selective to gasoline. Ross (1990) reports commercial information (Figure 15) for a simple riser turndown that shows a 4 LV % FF conversion gain between riser outlet and cyclone inlet. Even though conversion increased, gasoline yield went down. 

Reactors are now little more than holding vessels for the reactor cyclones. With efficient riser separators, reactor velocities of up to 3.5 Ft/S are not uncommon. A new reactor would be sized for about 2.5 Ft/S. Cyclone inlets are normally placed at least 15 Ft above simple riser turndowns to allow for any catalyst disengagement that might take place. 

One solution is to place the reactor cyclones very close to the riser outlet. This is the vented riser design offered by UOP — Figure 22. Catalyst from the end of the riser impacts the head of the reactor which now acts as a ballistic separator. The reaction mix turns 180 degrees as it leaves the riser to exit quickly through the cyclone inlets positioned right next to the riser. 

To reduce riser-outlet-to-cyclone-inlet times to a minimum, the reactor cyclones can be directly connected to the riser outlet as shown in Figure 22. Both Mobil (through Kellogg) and UOP offer this type of technology. These are more sophisticated devices than simple rough cut riser cyclones (vapor from rough cuts passes into the reactor dilute phase much like the vapor from a... 

Fig. 1.3.6. A typical Fluid Catalytic Cracking Unit (FCCU) with internal sets of regenerator and reactor cyclones...

Let us now try to estimate the overall pressure drop in the commercial reactor cyclone. The discussion in the main text of this chapter and in Chap. 4 leads us to expect the Eu number to be the same for the two. In addition, we can calculate Eu on basis of the inlet velocity ... 

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