This invention relates to internal structures, often referred to as "tower internals" that are used in vessels employed in chemical plant and oil refineries for mass transfer and heat transfer applications such as distillation, fractionation, absorption, scrubbing, contacting, stripping and quenching. It refers specifically to devices that distribute liquids at the tops of such towers in such fashion that the liquid is evenly spread over mass transfer surfaces. Such devices are commonly referred to as "sumps" or "troughs" and their function is to channel liquid and distribute it as uniformly as possible through perforations in the bottoms and sides of the sumps or troughs. Sumps are main conduits for the liquid and these usually distribute liquid to a series of lateral channels branching off from the sump called troughs. Where a tower has only one sump this usually extends all the way across the diameter of a tower and thus can be anything from about 1 meter to about 4 meters or more. Larger towers may have two parallel sumps that extend along chords of the cross-section of the tower and are shorter than the full diameter. This is because the sumps need to carry a large volume of liquid and the weight of this liquid can place excessive strains on the structure. The number of lateral troughs distributing liquid from the sump depends on the size of the tower but generally two of three lateral troughs extend on either side of the sump.
In cross-section sumps and troughs are usually U-shaped though they may also have a V-shaped bottom. The sumps are usually constructed in straight lengths making junctions, particularly junctions with the lateral distributor troughs at right angles to the line of the sump at frequent intervals. Typically these have been made by welding a flange on to the end of the lateral trough to be joined to the sump. This then is placed in register with an appropriate hole cut in the side of the sump and the flange is bolted to the sump with a gasket between the contacting surfaces to prevent leakages. This arrangement has a number of problems in that the material of the flange usually needs to be of a heavier gauge than the trough material to ensure the rigidity of the joint and prevent the kind of flexing that can cause failure of the welds. Weld failure is also a problem because it leads to leaks and the need for constant servicing of the distribution system.
A further disadvantage of welding a heavy gauge flange to a thin gauge trough is that this can lead to warping of the trough material. In addition there is difficulty in securing full allignment between the flange and the trough which is found to be critical to the ultimate liquid distribution characteristics of the system of troughs and sump. In the past any failure to allign the parts correctly has led to increased manufacturing rework costs or field installation costs. When the liquids distributed in the system are corrosive, (as is common in the refinery and chemical businesses), expensive non-corrosive metals must be used. The elimination of the heavy gauge metal flange and the reduction in the associated welding operations that need to be performed leads to substantial cost savings with no sacrifice in performance.
There is therefore a need to develop a trough jointing system that does not involve expensive and extensive welding or the use of heavy gauge flange materials to effect unions. Such a system is provided by the present invention.