Design Modification and Fatigue Life Analysis of Pressure Vessel Filter Tube Sheet

Abstract

Tube sheet in pressure vessel use to filter the natural gas during mining process for many petroleum industrial applications. During this process the natural gas contains many contaminating elements with sulphur as main ingredient, which can combines with sand or other carbon elements to create harmful effects of particulate impurities like slogging, clogging, fouling on the surface of the tubesheet. These impurities creates chemical reaction with tubesheet surface material which are normally made up of steel or ceramics. During working condition, the layer of clog is deposited on the filter tubes sheet surface and tubes. This clog layer creates increase in pressure inside the vessel. Once this pressure level exceeds the acceptable value, the filter tube sheet are cleaned either weekly or monthly basis. But this cleaning process needs to stop the entire plant working till the end of complete removal of clog, this creates reduction in efficiency parameters in terms of cost. In the present work design of pressure vessel filter tubesheet is performed on the basis of working conditions. Further it has been modified as per the corrections and suggestions given by end user. Number of holes for filtration and its pattern have been calculated on basis of modified design to get effective filtration with maximum efficiency. Another solution in terms of replacing filter unit has been proposed with which is divided into two sections and after every 4 to 5 seconds other section of tubesheet receives a back pressure of one seconds and washes out the other part of filter tubes. This modification in cleaning process gives efficient results without shutting down the plant production. Since it is a regular cycle so its needs to be shut down the plant once a year for full clean-up. This modification in working cycle creates cycling loadings on the tubesheet i.e. reverse pressure for cleaning and forwards pressure for working of pressure vessel. This compressive and tensile forces creates fatigue on the tubesheet and reduction in its fatigue strength. Therefore this tubesheet needs to analyse with modified concept for reduction in stresses and improved fatigue life. Dynamic analysis has been performed to evaluate fatigue life with modified thickness with dense meshing to get effective solution with respect to change in thickness of tubesheet.