US2559069A - Choke for abrasive fluids - Google Patents

Description

Jul 3, 1951 F. E. ENGLAND CHOKE FOR ABRASIVE FLUIDS Filed July 30, 1949 000000 1g 0000000c Z 5 0000000 ,6 O

1/ Q i I 0 000 009000 O O O 0 INVENTOR. 000000000 0 FrederickEEng/and Patented July 3, 1951 CHOKE FOR ABR-ASIVE FLUIDS Frederick E. England, Homewood, Ill., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana Application July 30, 1949, Serial No. 107,714 2 -Claims. .(o1. 138-42) This invention relates to a muffler and pressurereducing choke for use with abrasive fluids. More particularly, it relates to a choke for flue gases containing suspended dusts, fly ash, siliceous outlet from a fluid catalytic cracking unit catalyst regenerator. Figure 2 is a schematic drawing of a modified form of the body of the choke.

One object of the invention is to provide a choke for reducing pressure on gaseous streams containing abrasive dusts in order to reduce the pressure of the escaping gas incrementally in a relatively noiseless manner without encountering destruction of the apparatus as a result of erosion. Another object of the invention is to provide an incremental pressure-reducing choke in which the parts thereof subject to erosion are readily replaceable. Other objects of the invention will become apparent from the following description thereof.

In the operation of the fluid catalyst cracking process, it is necessary to regenerate the catalyst in a large body by blowing airtherethru at combustion temperature, thereby eliminating carbonaceous deposits from the catalyst. Because of the fine state of subdivision of the catalyst, considerable quantities of the catalyst are carried from the regenerator with the waste gases which usually leave the regenerator at a temperature of about 950 to 1100 F. Because of the high temperature of the gases escaping from the regenerator and the large volume thereof, it has been a difiicult problem to devise a choke which will efiectually reduce the pressure from the regenerator pressure to the pressure of the atmosphere without serious erosion of the equipment and Without generation of an objectionable noise resulting from the vibration of the escaping gases.

Various types of slide valves, dampers, etc. have been tried for the purpose. Regenerator pressures are commonly of the order of 5 to 25 p. s. i. and the reduction of this pressure down to atmospheric pressure represents a large energy dissipation which has a destructive effect on any apparatus employed for the purpose.

In a typical cracking unit designed for the conversion of 20,000 barrels of oil per day, the amount of fluid catalyst in 'the regenerator is customarily about 200 to 500 tons and'the losses of catalyst fines carried out by the spent gas may amount to about 2 to 5 tons: per day or more.

The volume of air measured at standard condiof exhausting to the atmosphere.

tions required for the operation of such a unit may be about fifty million cubic feet per day, and the volume of spent regeneration gas will be several times this amount at the temperature The usual practice is to withdraw the spent regeneration gases from the upper part of the regenerator above the main body of catalyst therein and conduct them thru cyclone separators connected in series to recover as much catalyst as possible and return it to the body of catalyst in the regenerator. The cyclones for this purpose are usually placed inside the upper part of the regenerator.

Referring to Figure 1, spentregenerator gas enters the choke at the bottom as indicated by arrows I0, and passes upwardly and out the top of the choke apparatus, as indicated by arrows H. The choke in this case is in the form of a rectangular box or chamber equipped with header plates I2 and [3 on opposite sides thru which rods M are passed. The holes in the header plates are positioned so that the rods are substantially parallel and in successive rows. It is desirable to stagger the rods in adjacent rows to provide a distorted path for the escaping gases which pass upwardly around the rods on their way from the inlet to the outlet of the choke.

It is preferred to employ round rods which are slightly smaller than the holes in the header plates to facilitate removal and replacement. Tubing may be employed, and will be referred to herein as rods. The rods may be square, rectangular, hexagonal, etc., and may be placed either diagonally or in any other position.

By recessing the header plates somewhat, rods may be employed which extend slightly beyond the header plates, making it easy to remove them from the apparatus when desired. Doors [5 and 16, covering the header box, are shown in open position on one side of the apparatus. These doors serve to prevent leakage of gases around the rods where they pass thru the header plates, although, if desired, packing around each rod may be employed for thispurpose.

The entire apparatus may be constructed of ordinary boiler steel with the rods of the same or different composition, depending on the character of the service and erosion resistance of the metal employed. The inside of the box or case may suitably be lined with erosion resistant lining, such as firebrick, ceramic tile, gunite, etc. For service at moderate and low temperatures, the rods may be of elastic, noneroding materials, such as ebonite or plastics.

Figure 2 illustrates an arrangement in which header plates are employed on four sides of the choke instead of two sides, and provision is made for passing rods through from both directions at right angles in alternating layers. This arrangement, although more complicated to con- 2,559,069 T TV struct and service, has the advantage of providing more labyrinthine flow for the gases, thereby increasing the resistance to flow and pressure drop occurring in a given distance of travel.

In the operation of the apparatus, the gases passing through the first layer of baffle rods suffer a drop in pressure, for example 0.5 p. s. i., and a corresponding expansion in volume. Thus, in passing through the entire apparatus to the atmosphere, the volume of the gases will be substantially doubled for a pressure drop of 15 pys. i. Accordingly, to obtain constant uniform velocity and turbulence throughout the choke from ,end to end, it is preferred to design the choke with an increased spacing between the rods approaching the outlet end. This is not shown in the illustration in Figure 1.

After the choke has been in operation for some time, it will be observed that the desired pressure diiferential from inlet to outlet is no longer maintained, owing to erosion of the passages between the rods. This condition can be corrected in either of two ways, first, by inserting more rods in the choke in positions previously left vacant, or, second, by replacing rods which have suffered serious erosion and change in dimension. According to the first method,

the choke is only partially filled with baffle rods to the point where the pressure differential obtained for a given volume of gases released is a definite desired value. With change in gas volume load, or change in choke resistance due to erosion, additional bailie rods can be added, usually one complete layer at a time. If the volume of gases during the operation is increased for one reason or another, it will be desirable to re- 1 move some of the baflle rods. Thus it will be seen that the choke apparatus, according to this invention, is quite flexible with respect to meeting variations in operating requirements.

Where the battle rods have become seriously eroded, for example, where they have lost onehalf or two-thirds their diameter, they are replaced with new rods, an operation which can be done quickly, conveniently, and easily by opening the doors covering the headers and attaching the end of the new rod to the end of the old rod then quickly pushing it through the apparatus. The old rod in this case serves as a guide for the new rod entering the holes in the header plates.

Under most conditions, this operation can be-- performed without shuttingdown the apparatus -or interfering with the process in any way. The

new rods may be joined to the old rods by a tapered thread connection or other suitable easily manipulated junction device.

In order to determine which of the eroded rods require replacing, I may employ an electrical resistance detector which can be connected to. the rods at opposite ends, and resistance of the rods determined by passing low voltage electric square faces or on the end of the rod may be used to indicate the position of the rod in the apparatus.

The illustration in Figure 1 indicates an apparatus which is substantially square in transverse cross-section. However, the dimensions may be varied to provide for either a shorter or longer dimension in the direction of the battle rods, preferably longer. When used in high temperature service, the length of the rods is limited by the tendency of the rods to sag in the supports. Excessive sagging results in difficult replacement of the rods when worn, and

should. be avoided 'by making the rods shorter and/or of greater diameter. Intermediate headers of specially resistant alloy steel can be used to support the rods in the middle. In general, the diameter of the rods is approximately two to five times the width of the space between adjacent parallel rods in a given layer. Successive layers may be spaced equally close together.

Instead of employing-solid rods for the bafile elements in my choke apparatus, I may employ tubing, in which case the detection of excessive erosion is simply a matter of observing the escape of gases from theends of those tubes which have a portion of the walls eroded through. These may be detected by periodical observation or by an automatic alarm system which will respond to an increase in gas pressure within the header box. If it is desired to leave out some of the baffle rods, this may be done by capping the vacant holes in the header with suitable header caps well known in the art. Although the drawings show apparatus of rectangular cross-section, I may apply my invention to other forms of cases. Thus, I may arrange the rods in layers in a cylindrical case, the rods passing through the cylinder from end to end and the spent gases flowing through in transverse direction from side to side. Layers of rods provide a multitude of elongated slits to serve as escape ports for reducing pressure in increments.

Having thus described my invention, what I claim is:

1. A choke for abrasive fluids comprising a rectangular case provided with an inlet at one end .for entering gases and an outlet at the other end for leaving gases, perforated header plates on the four sides, the perforations in said plates being in alignment on opposing sides and baflle rods passing between opposing header plates forming a tortuous path therebetween for the passage of said abrasive fluids through said choke.

2. A choke for abrasive fluids which comprises a rectangular chamber having opposed'side walls and end walls, respectively, which chamber is open at its bottom to receive a fluid containing abrasive solids and open at its top for discharging said fluid and contained solids, the opposed side walls of the chamber being header plates with a plurality of staggered rows of closely spaced aligned openings in each header, rods removably inserted in said aligned openings, each rod being longer than the distance between the header plate so that at least one end of each rod protrudes outwardly from a header plate to facilitate removal and replacement of said rod,

and closure members for enclosing the protruding ends of the rods.

FREDERICK ENGLAND.

R NC S TED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Name Date

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