Studies for improved vapour-liquid contacting

The object of the work was to attempt to propose an improvement in the process of vapour-liquid contacting with particular reference to commercial distillation. The literature was reviewed by considering both the overall performance data of the methods and devices used for contacting and the more fundamental studies of the mechanisms and effects taking place in them. It was concluded that the cross-flow Sieve tray with a high free area and many small holes would offer the best performance. This solution, however, is not commercially viable as the cost of producing a device to these specifications by conventional means would be excessive. To overcome this economic restraint and to retain the improved performance, a cheaper method of tray floor construction was proposed in which the material used was inherently porous. Many materials satisfy the requirements for use as a tray floor, for example, open cloths, meshes and gauzes and open cell foam and sintered materials. Sorting tests were, therefore, performed on a small scale, using an air-water system, to eliminate those materials which gave unsatisfactory hydraulic performance. A 68" x 14" column, also using an air-water system, was employed to test the feasibility and the hydraulic performance of the proposed tray floors on a large scale. The same apparatus was then used to determine the liquid mixing characteristics of the most promising material. To discover the performance of the new trays under actual vapour-liquid conditions, a 12” diameter, three tray distillation column was built and used experimentally. The separation efficiencies and tray pressure drops were evaluated for total reflux conditions at various vapour rates and outlet weir heights using the systems toluene n-heptane and toluene methyl-cyclo-hexane. The results for the new glass cloth trays showed that better performance could be obtained than conventional trays, particularly with regard to the flexibility. Various interesting phenomena manifested themselves in marked differences between the results obtained for the same material using the air-water and the hydrocarbon systems. The factors and their effects which produce these phenomena were, therefore, studied using various systems and glass cloths in a 3" diameter column