Catalyst basket

Jankowski et al (1978) discuss in detail the great variety of gradientless reactors proposed by several authors with a pictorial overview in their paper. All of these reactors can be placed in a few general categories (1) moving catalyst basket reactors, (2) external recycle reactors, and (3) internal recycle reactors. 

In moving catalyst basket reactors, the flow regime is ill-defined and the contact between catalyst and gas can be poor even if well-mixed conditions for the fluid phase are achieved. Perhaps the most successful representative of this category is the Carberry reactor (1964, 1966). Even in this model only a single layer of catalyst can be charged in the cruciform catalyst basket because the fluid flows in a radial direction outward and... 

The most reliable recycle reactors are those with a centrifugal pump, a fixed bed of catalyst, and a well-defined and forced flow path through the catalyst bed. Some of those shown on the two bottom rows in Jankowski s papers are of this type. From these, large diameter and/or high speed blowers are needed to generate high pressure increase and only small gaps can be tolerated between catalyst basket and blower, to minimize internal back flow. 

The flow that is shown in these figures is the instrument flow measured as m/s in the measuring tube. Multiplied with the flow cross-section of 5.59 cm, this gives the volumetric flow in the 2.67-cm diameter flow tube. Using a different catalyst basket or measuring tube will change this ratio. The volumetric flow is the same in the basket. Because the small basket has a 3.15 cm diameter and 7.79 cm cross-section, the linear velocity will be 5.59/7.79 = 0.72 fraction of that in the tube. 

The catalyst should be the copper-based United Catalyst T-2370 in 3/16 , reduced and stabilized, in extrudate form. Initially, 26.5 g of this should be charged to the catalyst basket. This catalyst is not for methanol synthesis but for the low temperature shift reaction of converting CO to CO2 with steam. At the given conditions it will make methanol at commercial production rates. Somewhat smaller quantity of catalyst can also be used with proportionally cut feed rates to save feed gas. 

The experimental setup uses the ROTOBERTY internal recycle reactor. The catalyst basket of this is charged with W = 35.5 g or V = 44.3 cm of OXITOX that contains 0.25 mol, i.e., 26.5 g of sodium carbonate. 

The RR developed by the author at UCC was the only one that had a high recycle rate with a reasonably known internal flow (Berty, 1969). This original reactor was named later after the author as the Berty Reactor . Over five hundred of these have been in use around the world over the last 30 years. The use of Berty reactors for ethylene oxide process improvement alone has resulted in 300 million pounds per year increase in production, without addition of new facilities (Mason, 1966). Similar improvements are possible with many other catalytic processes. In recent years a new blower design, a labyrinth seal between the blower and catalyst basket, and a better drive resulted in an even better reactor that has the registered trade name of ROTOBERTY . ... 

Many ammonia synthesis converters operate at 150 to 200 bar and around 515°C. Under these conditions, nitriding and hydrogen embrittlement can occur. The pressure shell is a multi-layer or multi-wall carbon steel vessel. The internal catalyst baskets, contained in the shell, are made of SS 321 material88. 

Catalyst baskets and gauze supports (where the temperature may reach 900°C) must be resistant to oxidation, nitriding and distortion from high temperatures. Typical materials of construction are high strength alloys made of iron-nickel-chromium, nickel-chromium and nickel-chromium-tungsten-... 

PFR differential fixed bed PFR integral fixed bed PFR solids transport (riser) CSTR external recirculation CSTR internal fluid recirculation CSTR spinning catalyst basket Batch internal fluid recirculation... 

Internal recirculation would give better mixing in the catalyst baskets. 

Heat- and mass-transfer resistances in the catalyst basket could be significant. They may make data analysis difficult. 

The rotating-basket reactor (often known as the Carberry reactor) has been widely used for gas-solid as well as gas-liquid-solid reactions (see Fig. 5-6). Its construction is not very difficult, but it is more complex and expensive to build than a batch or fixed-bed reactor. The catalyst baskets can either be attached to the stirrer [Fig. 5-7(6)] or they can, themselves, be used as the stirrer paddles [Fig. 5-7(a)]. Furthermore, a small variety of rotating catalyst baskets are available (see Fig. 5-8). Baskets must, in general, be small in diameter, so that internal mass-transfer effects are minimized. 

Figure 5-6 Details of the CSTCR and the catalyst baskets (after Tajbl et a/.43).

The liquid reactant is in excess and its concentration is uniform in the catalyst basket. 

The important mass-transfer resistances are (a) liquid-film resistance at the gas liquid interface and (b) mass-transfer resistance within the catalyst basket. The mass-transfer resistance of the bulk liquid outside the basket can be assumed to be negligible. 

Solutions The differential material balance for hydrogen transfer within the catalyst basket (see Fig. 7-32) can be expressed as... 

In the previous section, it was recognized that for perfect fluid distribution flow direction has only a second order effect on conversion. In this section, the effects of maldistribution are investigated. In order to eliminate the influence of flow direction, a pseudo-homogeneous plug flow model is used with purely radial flow through the catalyst basket. The governing equation is thus Eqn. (14), which in more convenient form is... 

---