Chemical Engineering Journal 138 (2008) 95–102

Chemical Engineering Journal138(2008)

Chemical Engineering Journal 138 (2008) 95–102

95–102

An experimental investigation of scrubber

internals at conditions of low pressure

Trond Austrheim a,Lars H.Gjertsen a,Alex C.Hoffmann b,?

a Statoil ASA,7005Trondheim,Norway

b Department of Physics and Technology,University of Bergen,Allegt.55,5007Bergen,Norway

Received20June2006;received in revised form11May2007;accepted22May2007

Abstract

This paper reports experimental results for the performance of natural gas demisting equipment(natural gas scrubbers),and on basis of this discusses possible improvements in the design of gas scrubbers.The separation ef?ciency and pressure drop of gas scrubber internals:a vane-type inlet,a mist mat and a cyclone deck,for two gas–liquid systems:air–water and air–Exxsol were determined at a range of gas and liquid?ows. To interpret results,a model for the cut size of an axial?ow cyclone is given.The results show that when reentrainment limits the separation performance of the scrubber the separation performance varies with the nature of the liquid injected,so that design on basis of an air–water system has to be done with caution.The results and the analysis presented further indicate that the K-value,although generally a good evaluation parameter, does not take into account some signi?cant effects,such as the nature of the?uids,changes in the free area for?ow,e.g.in the mist mat,and the action of scrubber internals in general.The separation ef?ciency is shown to be dominated by reentrainment from the cyclone deck at the liquid loadings and gas?ows used,loadings and?ows which are typical for an industrial scrubber.

©2007Elsevier B.V.All rights reserved.

Keywords:Gas scrubber;Souders–Brown equation;Inlet;Mist mat;Axial?ow cyclone;Experiments;Organic liquid

1.Introduction

1.1.Demisting in natural gas production

The exploration of oil and gas?elds is moving towards smaller and more remote?elds.To make this feasible more cost effective processing methods must be found.The goal is to per-form offshore gas/liquid and liquid/liquid separation sub-sea, as a high-pressure separation process,avoiding expensive top-side facilities,facilitating the separation processes themselves, reducing the amount of unwanted products to be transported and making it possible to to reclaim gas at a high pressure,making recompression before pipeline transport unnecessary.

Such a solution,however,requires improved separator design,since expenses related to unsatisfactory separator per-formance will be much higher.Also,due to higher installation costs,more compact separators will be needed,requiring more rigorous separator design.

?Corresponding author.Tel.:+4755582876;fax:+4755589440.

E-mail address:Alex.Hoffmann@ift.uib.no(A.C.Hoffmann).

Liquid is removed from the gas in all kinds of gas processing facilities for a number of reasons such as:

?prevent breakdown of rotating equipment like expanders, compressors and turbines;

?prevent foaming in gas dryers;

?prevent hydrate formation or other forms of fouling in down-stream equipment;

?to keep water or hydrocarbon dew point within sales gas or transport speci?cations;

?prevent loss of expensive and/or destructive chemicals such as,e.g.glycols or amines;

?protect burners,catalysts,etc.;

?air pollution control.

For the process of separating liquid and gas,two main types of vessel exist—the horizontally oriented and the vertically oriented.The former are mostly used when large amounts of liquid need to be handled,e.g.inlet separators on platforms. The vertical vessels,which are the focus of this article,are used when the?uid has a large gas to liquid ratio.These latter are often referred to as gas scrubbers.Such scrubbers mostly contain different types of separation equipment in series.

1385-8947/$–see front matter©2007Elsevier B.V.All rights reserved. doi:10.1016/j.cej.2007.05.048

Chemical Engineering Journal 138 (2008) 95–102

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