EQUIPMENT
New Catalytic Reactor Design Based on Sphere Untested design from Czechoslovakia promises a number of advantages over conventional cylindrical types Three Czechoslovakian engineers have come up with a new spherical design for a catalytic reactor. Featuring radial flow, either from the center out or from the outside in, the new concept breaks sharply with conventional cylindrical designs having axial flow. So far, only a model has been built. And there have been no tests. But the inventors feel that the new design will have a number of advantages over comparable cylindrical models: longer residence time, thinner wall, more efficient space utilization, lower pressure drop, and lower wall temperature. Although the design is unproved, a Czechoslovakian chemical plant— Severdceske Chemicke Zavody (North Bohemian Chemical Factory) located in Zaluzi u Mostu—has been suffi-
ciently impressed to order a 3meter-diameter production unit. It will be used to make aromatics (benzene, toluene, and xylene) from coal tar cuts, replacing a cylindrical unit presently in service. Design is scheduled to be completed in two to three months, construction in 1963. Z. Cimbalnik, who, with J. Prchal and C. Vermouzek, developed the design, described the unorthodox concept before the First International Congress on Chemical Engineering, Equipment Design, and Automation (CHISA) recently held in Brno, Czechoslovakia. The three engineers are with the Kralovopolska Strojirna Chemical Engineering Works of Brno, makers of chemical plant equipment. The new design consists of a spheri-
cal shell with inlet and outlet pipes mounted radially. In the basic design, the inlet pipe feeds to a perforated distribution ball in the center of the sphere. Within this distribution ball, specially designed ribs evenly distribute the reacting gases in all directions through the catalyst. Product gas leaves the catalyst bed at the circumference, enters meridian headers which convey gas to the outlet pipe. A spherical screen or sieve holds the catalyst in place. This screen is spotwelded to a system of meridian ribs welded to the inside of the sphere. The "poles" for these meridian ribs are at the outlet pipe and at a point directly opposite it. The spherical screen, mounted off center, is further away from the outlet pipe than it is
DETAILS OF SPHERICAL REACTOR POINT UP FEATURES
Meridian ribs onto which screen is welded
Insulation
Rrfa detail
Screen Distribution sphere
Pole for meridian ribs
Distribution dcvic ;
Catalyst support screen
Modified inlet for endothermic reactions Outlet for exothermic reactions (Inlet for endothermic reactions)
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Inlet for exothermic réactions (Outlet for endothermic reactions)
from the opposite "pole." Thus, each individual header increases in size to match the greater gas load as it converges on the outlet pipe. This gives a header system designed to equalize flow from all parts of the bed. The design includes a manhole at the top for installing catalyst and a hole at the bottom for removing it. The entire sphere will be insulated with magnesia. The designers feel that for exothermic reactions, center feed should be used. This will keep wall temperature down. And, although it may create a hot spot at the center which will kill some of the catalyst, they feel that only a relatively small portion will be affected. But for endothermic reactions, they believe that feeding from the outside in with discharge from the center is the best bet. This setup merely involves switching streams from, one pipe to another and a minor modification to what would then be the inlet pipe to ensure even distribution. But these are not hard and fast rules. Operating experience will give the final answers. Advantages. The new design stems from trouble experienced with cylindrical reforming units. Gas occasionally gets behind the refractory liner, causes hot spots in the metal wall and eventual structural damage. With the new design, it's hoped that no liner will be needed. The designers figure that the insulation value of the catalyst bed and of the space between screen and shell will make it unnecessary. But even if one is needed, they feel it will be thinner and easier to make gastight than that of a cylindrical reactor. Besides the no-liner feature, the design has a number of other advantages compared, to cylindrical units, according to Mr. Cimbalnik: • With radial flow, the mean velocity is about one third the inlet velocity. This means about three times the residence time, about one third the pressure drop of a standard cylindrical unit, for equal inlet velocities. • The spherical design gives from 80 to 95% usable volume for catalyst, whereas some cylindrical reactors used for reforming give only 40%. • Because of the inherent strength of a sphere, the wall can be thinner— about half that of a cylinder. • Velocity distribution along the radius vector should be about hyperbolic. Also, there is no shell effect and little chance of channeling.
• Cost estimates indicate a 30% saving for the sphere over a cylinder. In addition, the Czechoslovakian engineers see many other advantages for their new design. For example, the temperature of the wall should be constant, eliminating excessive temperature stresses. The sieve system holding the catalyst will distribute the weight evenly on a large area of reactor shell. Also, load on the screen due to pressure drop, will cancel out. Capacity can be increased with relatively small increases in diameter. And start-up and shut-down should be faster. The main disadvantage, according to the designers, is that the new design doesn't seem suitable for twophase reactions. They discount other potential trouble spots. For instance, they don't think coking will be any more of a problem than it is in conventional reactors. Nor are they concerned with uneven catalyst wear due to the changing gas velocity. Commercial Unit. The new unit to be built for the North Bohemian Chemical plant will be designed for 550° C. and 70 atm. Feed will be to the center. Diameter of the distribution sphere will be about 1 meter and that of the inlet pipe about 250 mm. Catalyst volume will be about 8 cubic meters. The reactor will be built without a refractory liner, although one can be added if necessary. Inlet velocity at the distribution sphere will be about 15 meters per second. The material of construction will be either 18-8 stainless steel with about 0.5% titanium or an austenitic steel with manganese. The new unit will replace a cylindrical reactor having an outside diameter of about 1400 mm. and an over-all length of about 10 meters. A refractory liner reduces the inner diameter to about 1200 mm. While the reactor is being built, flow tests will be made using a 50-cm. diameter model. Packed with acrylic packing (solid cylinders), the transparent model will be submerged in a solution of KCl in water designed to have a refractive index equal to that of acrylic plastic. The model will thus be visible. Motion pictures will be made of indigo dye in. KCl solution being fed into the model. At the same time, heat and mass transfer, pressure drop, and kinetic calculations will be made using an analog computer. A general Czechoslovakian patent has been applied for.
Sharp Markets Complete Carbon Dating Lab System includes sample conversion and counting apparatus using methane as counting gas A complete laboratory for carbon dating samples up to 45,000 years old has been introduced by Sharp Laboratories, La Jolla, Calif. Called the CDL-14 laboratory, the system is designed to give reliable results routinely, even in the hands of technicians who have had no special training in measuring radioactivity, according to the company. The CDL-14 includes not only a complete apparatus for converting the sample to the counting gas, methane, but also all necessary electronics, the sample detector, cosmic ray guard counter, and shielding. Cost of the entire system, $24,500, includes a training course by a company engineer at the customer's laboratory. Although counting electronics has been commercially available for many years, people interested in carbon dating have had to build much of their own sample conversion apparatus, detectors, and shields. This means that they must have a great deal of knowledge about the detector physics, the chemical procedures, their pitfalls, and limitations. Where specific skills are not available, they have relied on the services of laboratories that have experienced personnel and equipment. In marketing CDL-14, Sharp Laboratories hopes to solve the problem of those labs that have the need but not the experts. The company also expects labs that are well grounded in carbon dating to be interested in the new system. A practical system, says president Rodman Sharp, should not require a full-time physical chemist and an electronics man. Customers should be able to spend most of their time on the main problem, Dr. Sharp adds, not in "fighting a tricky sample preparation and instrumentation problem." The development that made the CDL-14 possible, Dr. Sharp says, is a method of easily converting the sample's carbon to methane, by way of carbon dioxide. This method, worked out by Fairhall, Schell, and Takashima at the University of Washington, involves burning the carbon to C 0 2 and then hydrogenating it to methane over a ruthenium catalyst. OCT. 8, 1962 C & E N
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