Tunnel-type bubble cap baffle

Sept 12, 1950

2,522,425

G. P. BAUMANN ET AL

TUNNEL-TYPE BUBBLE CAP BAFFLE

Filed Aug. 21, 1947

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Patented Sept. 12, 1950

2,522,425

UNITED STATES PATENT OFFICE

2,522,425

TUNNEL-TYPE BUBBLE CAP BAFFLE

George P. Baumann, Elizabeth, and Cyril O. Rhys, Jr., Cranford, N. J., assignors to Standard Oil Development Company, a corporation of Delaware

Application August 21,1947, Serial No. 769,860

Claims.

The present invention relates to an improved fractionating and distillation means. The invention is particularly concerned with an improved design for tunnel type bell caps used in connection with the plates of fractionating and distillation towers. A specific adaptation of the invention involves the use of longitudinal and/or transverse baffles internally of fractionating plate chimney members and bell caps therefor.

It is well known in the art to employ bell caps in conjunction with the trays or plates of fractionating and distillation towers. Ordinarily, in such equipment, a plurality of transverse plates are provided in a tower structure, dividing it into a plurality of chambers throughout its height. Liquids are introduced into the top of the tower to flow downwardly over the plates in succession. Gaseous elements are introduced lower down in the tower to flow upwardly thru chimney type openings in the plates. Bell caps, usually having slotted edges, are disposed telescopically over the chimney elements in such a manner that the gases are forced to escape around the lower edges of the bell caps through the liquid medium flowing over the plates.

A type of design presently employed involves the use of a comparatively small number of long, generally rectangular chimney openings in the fractionating plates, over which are telescopically disposed tunnel type bell caps. The chimneys and caps are usually arranged on the plates with their long axis parallel to the flow of liquid over the plates. Although chimneys and caps, according to such design, have many advantages, it has been found that in many instances they may perform inefficiently, due to a tendency for the vapors rising through the chimney to develop preferential flow, whereby the greater proportion of the flow of vapors escaping from beneath a bubble cap may be concentrated at one point or area thereof. Although the use of tunnel type bell caps is attractive because of the lower cost of construction, because of this characteristic of tunnel type bell caps, it has been necessary to use the more expensive form of construction involving the use of small round chimneys and bell caps in order to obtain proper distribution and flow of gases thru the plate liquid sealing the space between cap and chimney.

As indicated, regardless of the type of plate , construction, it is desirable to have equal vapor distribution over the area of each tray for maximum tower capacity and efficiency. In the ideal situation, the C. F. S. of the vapor per square foot of tray area rising thru the tower is the i

Ί. 261—114) same at all points on any one tray. Since plate distribution is a function of pressure drop through the caps, it can be shown that plate distribution depends upon the pressure drop of vapors escaping thru the plate liquid over the lower edges of the bubble cap. Using the long tunnel type bubble caps without the aid of the present invention, even though the initial distribution and pressure drop through the chimney i is regulated by means of chimney chokes, a preferential flow of vapors can occur from end to end, or side to side, within the bell cap after issuing from the chimney. When such swing action occurs, vapors will escape from under one side of the cap for a short time, and then the flow may switch to the other side or end of the cap. Such action causes the entire plate to swing or cycle. Chimney chokes alone have been found not effective in preventing such action.

It is an object of this invention to provide suitable baffle meaps associated with the chimney and the bubble cap in such a manner as to provide even vapor flow over the entire length of the edge portions of a tunnel type bubble cap.

The invention and its objects may be fully understood from the following description when read in conjunction with the accompanying drawings, in which:

Figure 1 is a plan view of a portion of a fractionating tower plate, showing a tunnel type bubble cap and chimney according to the invention with a portion of the cap broken away to show interior structure.

Figure 2 is a vertical section thru a portion of a tower plate showing a tunnel type cap and chimney according to Fig. 1, along the line Π—Π thereof.

Figure 3 is a side elevation of a combination chimney and cap baffle.

Figure 4 is an end elevation of the baffle.

Figure 5 is a side elevation of the longitudinal baffle.

Figure 6 is a side elevation of a transverse baffle. Referring again to the drawings, the numeral I designates a fractionating tower tray, having an elongated vapor chimney 2, over which is telescopically disposed a tunnel type bell cap 3. A longitudinal baffle is indicated by the numeral 4. This baffle is provided with upwardly extending slotted portions 4a adjacent to each end, and adapted to fit over and engage the end edge portions of the chimney 2. Slotted portions 4b are also provided in the baffle 4 to receive one or more transverse baffle members 5. Each such member, as particularly shown in Fig. 6. is provided with

9,823,43« downwardly extending slotted portions 5a, adjacent to the outer edges of the baffle adapted to fit over and engage the side edge portions of the chimney 2. A centrally disposed slotted portion 5b may be provided to coincide with the slotted portions of 4b of the baffle 4, in order to provide a combination baffle having longitudinal and lateral portions, the upper edges of which are in the same plane.

As shown in Fig. 2, when the baffles are disposed over the edge portions of the chimney 2, the tunnel type cap 3 will be supported by the upper edge portions of the baffles so that the lower edge of the bubble cap is disposed in spaced relation to the surface of the plate I, with the lower edge portions of the baffle members 4 and 5, which overlap and extend beyond the chimney 2, in engagement with the surface of the plate I. By means of the baffle arrangement described, there is provided within the chimney and the bell cap a series of compartments of which a portion of each compartment lies within the chimney element 2. Preferably the portions of these compartments which he within the chimney element 2 are of substantially equal volume. If desired a chimney choke 2a may also be used in conjunction with the baffle elements as described. Also where indicated by operating conditions, the number and type of baffle elements utilized may be varied without departing from the inventors’ concept. For example, longitudinal baffles or transverse baffles may be used alone, together or in combination with chimney chokes, and the number of transverse or longitudinal baffles used in combination with each other may be increased or decreased to suit operating conditions. The flow of vapors thru the compartmented chimney and bubble cap and their escape through the plate liquid surrounding and sealing the cap are illustrated in Figure 2.

In operation, vapors from the space below the plate as illustrated, flow upwardly through the chimney I, being divided in a substantially uniform fashion by the baffle members 4 and 5. In the chimney space, and in the space within the bell cap itself, preferential flow or swing action is likewise prevented by the baffle members 4 and 5, all the vapors entering any compartment being forced to escape over the comparatively limited lower slotted edge portions in that area of the bell cap.

While the invention is generally directed towards the improvement of the distribution of upflowing gases in a distillation or fractionating tower, wherein relatively large bell cape are employed, the invention has been set forth and described primarily with reference to the use of means for controlling the flow of vapors within the bell caps and chimneys associated with a fractionating tower plate. It is preferred to use a combination transverse and longitudinal baffle element but, as indicated, either may be used without the other, and some of the benefits of the invention will be obtained. Although illustrated and described in its preferred embodiments, it is to be understood that the invention is not considered as limited by such disclosure for the purpose of Illustration, but only by the appended claims.