Droplet removal in fibrous filters

Dave, N. C.

Title: Droplet removal in fibrous filters
Creator: Dave, N. C.
Relation: University of Newcastle Research Higher Degree Thesis
Resource Type: thesis
Date: 1987
Description: Research Doctorate - Doctor of Philosophy (PhD)
Description: Although, the knitted wire-mesh demisters have been commonly used as a low cost device for the removal of droplets from the gas or vapour streams in the industrial processes such as distillation, absorption and evaporation, the information on their general performance characteristics is rather lacking. The Souders-Brown expression, [formula could not be replicated] developed to estimate the superficial vapour velocity in a fractionating plate column which causes the entrainment of liquid droplets in the vapour stream has been generally accepted to predict the maximum allowable gas rate through the demister for a given duty. The value of K is usually taken to be from 0.06 to 0.13 ms-1. Though the value of K has been suggested to be a function of the geometry of the demister pad, droplet entrainment loads and the physical properties of the gas-liquid system, so far no formal attempt has been made to develop this functional relationship on any theoretical grounds. The primary aim of this study was therefore to investigate the general performance characteristics of the wire-mesh demisters and develop the functional relationship of K to the different variables. This investigation reports the performance characteristics of a demister when operating in air at atmospheric pressure and temperature. The variables considered in this programme of work are: (1) The geometry of the demister. ; (2) The velocity of gas at approach to the demister. ; (3) The drop size range of the entrained mist. ; (4) The liquid entrainment loading in the gas stream. ; (5) The wettability of wire surface material and the liquid properties of surface tension and viscosity. The performance characteristics are the resistance to the gas glow, the maximum allowable gas rate and the droplet capture efficiency of a demister. The collection efficiency was measured using a standard stack sampling method. The droplet size distribution at both the upstream and the downstream faces of the demister was measured in-situ using a Malvern Laser droplet sizer. The liquid retained in the mesh pad during the operation has considerable influence on both its flow resistance and efficiency of collection. The load cell method was employed to dynamically measure this liquid holdup. The interactions between the liquid holdup, the pressure gradient, liquid entrainment loading and the gas velocity are of extremely complex nature and hence macroscopic approach has been adopted to explain the maximum allowable gas velocity and flow resistance results. Based on the experimental results and semi-empirical modelling in terms of "flow through tubes" for wet filters, a simple design procedure for wire-mesh demisters has been developed.
Subject: droplet removal; vapour streams; gas streams; fibrous filters
Identifier: http://hdl.handle.net/1959.13/1312459
Identifier: uon:22396
Language: eng

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