GB1573745A

GB1573745A - Packing element for mass transfer devices

Info

Publication number: GB1573745A
Application number: GB3413277A
Authority: GB
Original assignee: Norton Co
Current assignee: Saint Gobain Abrasives Inc
Priority date: 1976-09-02
Filing date: 1977-08-15
Publication date: 1980-08-28
Also published as: AU509577B2; JPS5335144U; JPS5736249Y2; AU2809577A; DE7726885U1; CA1098028A

Description

(54) PACKING ELEMENT FOR MASS TRANSFER DEVICES (71) We, NORTON COMPANY. a corporation organized under the laws of the State of Massachusetts, United States of America, of 1 New Bond Street, Worcester, State of Massachusetts, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to packing elements for use in mass transfer towers.

Contact elements partially enclosing a space for fluid flow have found wide uses in mass transfer devices such as scrubber towers, absorption columns, distillation columns and the like. One example of a popular form of packing element is based on the cylindrical type described in U.S. Patent 3,266,787 to Eckert where contact fingers are punched out of the cylindrical wall and bent inwardly into the space defined by the cylinder. The type of packing described in the Eckert patent worked well in the smaller sizes of packings. However for the larger size packings, which are becoming increasingly important, for scrubber towers adapted to handle tremendous volumes of gas, such as encountered in the scrubbing of power plant stack gases, the efficiency falls off as the diameter of the packing element is increased. It is believed that this fall-off in efficiency results from the fact that, with the larger diameter of packing element, the gas has a tendency to flow axially of the packing element and parallel to the element surfaces. In this circumstance the contact between the gas and the wetted surfaces of the fingers extending into the fluid flow space is not as complete as desired. In the present invention the efficiency of the packing element is substantially increased since some of the fingers each have an elongate cross-section transverse to its length extending an angle at between 40 and 45" to the axis of the enclosed fluid flow space.

According to the invention there is provided a substantially cylindrical packing element, portions of the surface being cut from the cylinder to form fingers which are bent inwardly towards the cylinder axis, some of said fingers each having an elongate cross-section normal to its length extending at an angle of between 4" and 45" to the axis of the cylinder and extending along less than 35% of the axial length of the packing element, whereby the inwardly directed fingers create turbulent flow within the element of gases flowing past the fingers and generally parallel to the cylinder axis. This arrangement imparts a turbulence to the gas flowing along the axis of the space so as to provide more intimate contact between the flowing gas and the wetted surfaces projecting into this enclosed space as well as increasing contact with the wetted surface of the wall defining the space. The turbulence is not enough to provide aerodynamic shielding of the back surfaces of the fingers.

The exact amount of angle will depend on a number of factors including the spacing of the fingers, the amount of penetration of the fingers into the empty space, the width of the fingers parallel to the axis, the flow rate of the gas, etc. In one packing element, having a diameter of about 3+", it was found that a 10 angle seemed to give the highest efficiency. The efficiency started to fall off as the angle was increased to about 16 until it was about equal to the efficiency with the surfaces parallel to the axis. As far as is known, prior packing elements of the type described in the above mentioned Eckert patent have been made with surfaces either parallel to the axis of the cylindrical packing element or normal to the axis as shown in French patent 542,902. (See Figs. 5, 7 and 8). The only packing elements described in the prior art known to applicant having an inclined internal surface are the old spiral type rings. However these spiral rings were entirely different since their interior surfaces were not formed by fingers which were punched from the cylinder itself and bent inwardly, rather their spiral surfaces were completely enclosed by imperforate cylinders. A structure similar in performance to the old "spiral rings" is shown in Fig. 3 of British patent 1,385,672.

Another type of prior art packing is illustrated in German DAS 1,029,346 published May 8, 1958. This shows a saddle element having fingers punched from the surface and bent inwardly to the space partially defined by the curved saddle surface. In this DAS, however, the angle between the finger surfaces and the axis of gas flow approximates 900. While the recently issued U.S. Patent 3,957,931 contains the cryptic statement (col. 5 lines 13-14) that "these tabs may be angled to the longitudinal axis of the cylindrical member" there is no discussion of specific angles or how they are measured or the effect of the angulation.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a side view of one embodiment of the packing element having three rows of fingers punched from its surface and bent inwardly, and Fig. 2 is a downward sectional view along line 2-2 of Fig. 1 looking parallel to the axis of the cylinder.

Referring now to Fig. 1 the packing element, which is generally indicated at 10, is formed of a cylindrical surface 12 from which a number of fingers 14 and 14a are cut and bent inwardly to extend into the interior space 13 defined by the cylindrical surface 12. As indicated on Fig. 1 the finger 14 is formed by a roughly rectangular cut.

The normal finger 14 has an elongate cross section normal to its length extending at a 10 angle "a" with respect to the axis A. The hinge line 16, along which the finger 14 is bent inwardly, also conveniently has the same 10 angle "b" with the axis A. Thus the gas flowing down the cylinder parallel to the axis A is deflected somewhat by the fingers 14 to create turbulence which increases the amount of interaction between the flowing gas and the liquid on the wetted surfaces on the fingers 14 and the interior surface of the cylinder 12.

As viewed from the top (Fig. 2) the projected area of the bent fingers 14 intercepts an appreciable amount of the cross-sectional area of the empty space 13, thus substantially increasing the chance of interaction of the gas with the liquid on a wetted surface during its travel down the inside of the packing element. In Fig. 2 it is seen that fingers 14a are not twisted with respect to the axis.

Tests of packings made in accordance with the present invention by using humidification of air as a performance test showed considerable improvement over standard commercially available packing elements made in accordance with the prior art techniques where the finger surfaces were essentially parallel to the axis of the cylinder. It was found that a 3+" diameter ring packing element (90 millimeters) had a heat transfer efficiency equal to the 2" prior art packing element even though the pressure drop across a bed of the 3+" packing elements of the present invention was considerably less than the pressure drop across a bed of similar height of the 2" packing elements. In a preferred embodiment of the invention, the packing element made in accordance with Fig. 1 is formed of cylindrical elements approximately 3.54" high (90 millimeters) by 3.54" (90 millimeters) in diameter. Each element has three rows of fingers with eight fingers in each row of the approximate relative dimension shown in Figs. 1 and 2.

The center row of fingers 14a is parallel to the cylinder axis and the top and bottom rows are twisted so that the elongate crosssection of these fingers forms an angle of approximately 100 with respect to the axis of the cylinder. In Fig. 2 the bottom row of bent fingers is not visible since they would be shielded by the top row.

With the dimensions of the approximate size shown in Fig. 1 when the angle is somewhat greater than 15 (e.g. about 160) the performance falls off somewhat.

While actual tests have not been run with a narrower finger it is believed, on the basis of theoretical considerations, that when the width of the finger in the axial direction is about 5% of the total axial length of the packing element the angle "a" can be up to 45" and still provide improved performance.

In this latter case there will not be so much "shadowing" of the back side of the finger, i.e. the side which is down stream of the flowing gas. However, when the elongate cross-section of the finger normal to its length extends between about 25 S and 35Vn of the axial length of the packing element, then the angle is preferably between 4" and 8" with respect to the axis of the element. In the specific example mentioned above the elongate cross-section of the finger normal to its length extends along about 17 /" to 20 ,4 of the axial length of the packing element and the angle of the finger is preferably around 10 for improved performance.

While a preferred embodiment of the invention has been described above wherein the finger is more or less rectangular and is bent at a constant angle to the axis, considerable departure from this simple structure can be achieved without departing from the invention. For example the angle of the surface can change along the length, being relatively shallow near the cylinder wall and increasing towards the free end.

Similarly the shape of the finger can be triangular. elliptical, etc., provided it furnishes an elongate cross-section extending normal to its length at an angle of 4" to 45" to the axis of the cylinder.

WHAT WE CLAIM IS: 1. A substantially cylindrical packing element, portions of the surface being cut from the cylinder to form fingers which are bent inwardly towards the cylinder axis, some of said fingers each having an elongate cross-section normal to its length extending, at an angle of between 4 and 45" to the axis of the cylinder, and extending along less than 35n e of the axial length of the packing element, whereby the inwardly directed fingers create turbulent flow within the element of gases flowing past the fingers and generally parallel to the cylinder axis.

2. The element of claim 1, wherein each bent finger is formed by a generally rectangular cut, the sides of which are at an angle of 4" to 150 with respect to a plane normal to the axis of the cylinder.

3. The element of claim 1, wherein the majority of the fingers are bent inwardly at an angle to the axis.

4. The element of claim 1, wherein there are several rows of fingers spaced along the axis of the element and in at least one row the fingers are bent inwardly at an angle to the axis.

5. The element of claim 4, wherein the outer rows of fingers along the axis are bent inwardly at an angle to the axis.

6. The element of claim 1, wherein each inwardly bent finger has an elongate crosssection normal to its length of between 17 , to 20 /" off the axial length of the packing element and the finger has an angle of 10 to the axis.

7. An element according to claim 1, substantially is hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. being relatively shallow near the cylinder wall and increasing towards the free end. Similarly the shape of the finger can be triangular. elliptical, etc., provided it furnishes an elongate cross-section extending normal to its length at an angle of 4" to 45" to the axis of the cylinder. WHAT WE CLAIM IS:

1. A substantially cylindrical packing element, portions of the surface being cut from the cylinder to form fingers which are bent inwardly towards the cylinder axis, some of said fingers each having an elongate cross-section normal to its length extending, at an angle of between 4 and 45" to the axis of the cylinder, and extending along less than 35n e of the axial length of the packing element, whereby the inwardly directed fingers create turbulent flow within the element of gases flowing past the fingers and generally parallel to the cylinder axis.