Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including solid – extended surface – fluid contact reaction...
Patent
1995-06-14
1997-05-27
Bhat, Nina
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Including solid, extended surface, fluid contact reaction...
422220, 422228, 261 792, 261 91, 261 97, 366337, 366339, B01J 1924, B01J 1002, B01D 5318, B01D 300
Patent
active
056329628
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a contacting column redistributor for use in effecting improved fluid distribution through a process vessel.
Columns with dumped or random packings, stacked packings or structured packings are widely used in the chemical, oil, gas and other process industries for separation processes (for example, absorption, desorption, rectification, stripping and distillation) and as reactors in which packings are used to bring gases and liquid into direct contact in order to transfer heat or constituents from one phase to the other. Two of the great advantages of packed columns are the low capital cost and the large contact area of packings.
Liquid and gas channelling and the difficulty of adding or removing heat are the main shortcomings of packed columns.
Packed columns suffer from liquid and gas channelling even when they are vertically positioned, and this channelling can cause a reduction in column efficiency, while packed columns which are used on board floating platforms and processing ships may suffer a much more serious liquid and gas channelling due to tilt and motion caused by marine waves. Channelling could cause a severe reduction of performance even under tilt of a few degrees.
The channelling type and severity could depend on whether the columuns are used onshore or offshore, as will be explained as follows:
The main short comings of the vertically positioned packed column (VPPC) is the non uniform distribution of the liquid and gas phase over the whole cross-sectional area of the column due to voidage variation near the wall area. The wall area width is equal to one packing diameter, (Gunn, D. J. 1980 Chem Eng Sci 35 2405).
The voidage near the wall is higher than that at the rest of the cross sectional area of the packed column. This voidage variation will lead to the channelling of liquid and gas phases through the wall area. More serious channelling could take place if the liquid distributor, located at the top of the column, was tilted, partially blocked or poorly designed or constructed.
It has been reported by Baker S. A. 1980 M Sc thesis, University of Wales and by Baker S. A. 1987, Ph D thesis, University of Wales that packed columns may suffer from liquid and gas channelling even with the supposedly good design criteria i.e. with high ratio of column diameter to packings diameter. This finding was valid for co-current and counter-current operations. Many workers, among them Morris G. A. and Jackson J. 1953, Absorption Towers, London: Butterworths Scientific publications and Mullin J. W. 1957, Industr Chem Mfr 33 408 have shown that liquid and gas maldistribution can effect the efficiency and performance of the packed column and reduce the number of mass transfer stages in a given depth of packing. The magnitude of this reduction varies with the degree of maldistribution being studied. It has been reported that very long, onshore used, packed columns which tilted under the effect of high wind, or their own weight or from thermal effects or which tilted when their foundation settled, suffered additional performance reduction similar to the performance reduction suffered by tilted packed columns used offshore on board floating production platforms and ships.
There are increasing demands for floating oil production platforms; as well as being cheaper than fixed production platforms, they can be relatively easily relocated after the depletion of the oil of the field. Also there are increasing demands for offshore chemical plants mounted on board ships, as they become more favourable than onshore chemical plants for certain duties due to rising expenses in construction of waste disposal and pollution control plants.
Floating platforms and processing ships permit some horizontal and vertical motion and tilt. This motion and tilt can cause severe liquid and gas channelling, which could lead to a severe reduction in the performance of the packed columns. The main cause of the reduction in the performance of the tilted packed columns is due to the severe liquid and gas channelli
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John A. Weedman et al, "Rectification of Liquid Air in a Packed Column", Industrial and Engineering Chemistry, vol. 39, No. 6, pp. 732-744.
D. J. Gunn, "Theory of Liquid Phase Dispersion in Packed Columns", Chemical Engineering Science, vol. 35, pp. 2405-2413, 1980.
J. W. Mullin, "The Effect of Maldistribution on the Performance of Packed Columns", The Industrial Chemist, Aug. 1957, pp. 408-417.
Baker Salah A.
Waldie Brian
Bhat Nina
British Technology Group Limited
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