High pressure process technology: fundamentals and applications (industrial chemistry library)

The motivations of using high pressure today are summarized and a number of examples provided which relate to high- pressure production processes applied currently.. High pressure defin

High Pressure Process Technology: Fundamentals and Applications

Delft University of Technology, Delft, The Netherlands

(Edited by D.L Wise, Y.A Levendis and M Metghalchi) Advances in Organobromine Chemistry I

(Edited by J.-R Desmurs and B G6rard) Technology of Corn Wet Milling and Associated Processes (by P.H B lanchard)

Lithium Batteries New Materials, Developments and Perspectives (Edited by G Pistoia)

Industrial Chemicals Their Characteristics and Development (by G Agam)

Advances in Organobromine Chemistry II (Edited by J.-R Desmurs, B G6rard and M.J Goldstein)

The Roots of Organic Development (Edited by J.-R Desmurs and S Ratton) High Pressure Process Technology: Fundamentals and Applications (Edited by A Bertucco and G Vetter)

High Pressure Process Technology: Fundamentals and Applications

E d i t e d b y

A Bertucco

Universitgt di Padova, DIPIC- Department of Chemical Engineering,

Via F Marzolo 9, 1-35131 Padova PD, ltaly

P.O Box 211, 1000 AE Amsterdam, The Netherlands

9 2001 Elsevier Science B.V All rights reserved

This work is protected under copyright by Elsevier Science, and the following terms and conditions apply to its use: Photocopying

Single photocopies of single chapters may be made for personal use as allowed by national copyright laws Permission of the Publisher and payment of a fee is required for all other photocopying, including multiple or systematic copying, copying for advertising or promotional purposes, resale, and all forms of document delivery Special rates are available for educational institutions that wish to make photocopies for non-profit educational classroom use

Permissions may be sought directly from Elsevier Science Global Rights Department, PO Box 800, Oxford OX5 1DX, UK; phone: (+44) 1865 843830, fax: (+44) 1865 853333, e-mail: permissions@elsevier.co.uk You may also contact Global Rights directly through Elsevier's home page (http://www.elsevier.nl), by selecting 'Obtaining Permissions'

In the USA, users may clear permissions and make payments through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA; phone: (+1) (978) 7508400, fax: (+1) (978) 7504744, and in the UK through the Copyright Licensing Agency Rapid Clearance Service (CLARCS), 90 Tottenham Court Road, London WlP 0LP, UK; phone: (+44) 207 631 5555; fax: (+44) 207 631 5500 Other countries may have a local reprographic rights agency for payments

Derivative Works

Tables of contents may be reproduced for internal circulation, but permission of Elsevier Science is required for external resale or distribution of such material

Permission of the Publisher is required for all other derivative works, including compilations and translations

Electronic Storage or Usage

Permission of the Publisher is required to store or use electronically any material contained in this work, including any chapter or part of a chapter

Except as outlined above, no part of this work may be reproduced, stored in a retrieval system or transmitted in any form

or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior written permission of the Publisher

Address permissions requests to: Elsevier Science Global Rights Department, at the mail, fax and e-mail addresses noted above

Library of Congress Cataloging in Publication Data

A catalog record from the Library of Congress has been applied for

ISBN: 0-444-50498-2

The paper used in this publication meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper) Printed in The Netherlands

The application of elevated pressures in the manufacture of high technology products is permanently extending and offering new opportunities Nowadays this is true not only for reactions and separations during chemical processing, but also for other production activities such as jet-cutting, homogenization, micronization, pressing, plastification, spray-drying and for physico-biological treatments such as pasteurization, sterilization and coagulation At the dawn of the new century, it is quite evident that high pressure technology is one of the emerging tools and methods for improving product quality, both from the economic and the environmental viewpoints, and for the development of more sustainable processes and products for the future generations

Although the development of classical high pressure production dates back to the 1920s and 1930s (ammonia, low-density polyethylene, synthetic diamonds, etc.), research in this field has been particularly active in the last twenty-five years, leading to a number of new opportunities expanding to areas such as materials science and microbiology, and to the bulk production of foods, pharmaceuticals, cosmetics, and other products This is also due to the exploitation of the properties of fluids at the supercritical state, especially supercritical water and supercritical carbon dioxide, which are expected within a few years to offer alternatives to organic solvents in many widespread applications

On the other hand, high pressure technology is usually regarded as a highly specific field,

to which little space is devoted within scientific and technical curricula throughout the world,

so that a "high-pressure culture" is not widespread and the related expertise is difficult to find, even among physicists, chemists and chemical engineers In addition, the fear of dealing with high pressures in production plants always appears as a major issue, and therefore dissemination of the related knowledge and expertise among the manufacturing community deserves maximum attention

Of course, visions for and problems with the application of high pressure have been discussed and promoted by national and international working groups, both in Europe and overseas, for many years Within the European Federation of Chemical Engineering the working party on High Pressure Technology, now in its second decade and comprising members from twelve European countries, has developed initiatives for the transfer of scientific and technological knowledge in an outstandingly efficient manner

In Europe, one important pillar of these activities is represented by the institution of an Intensive Course on High Pressure Technology offered annually to European post-graduate students and funded by the European Union within the framework of the Socrates Programme The course has now been rotating for several years between major European universities Most of the working party members as well as other experts have contributed lectures, discussions and class-work problems as well as final examinations From the beginning of the course programme the firm intention was to publish the high-level teaching and educational documentation as a book for a larger community of users, and we are pleased

to present this work now

A special effort was made to organize and present the matter in such a way that a larger group of readers and experts can take advantage of it The book is intended to provide a comprehensive approach to the subject, so that it can be interesting not only for specialists,

such as mechanical and chemical engineers, but also beginners with high-pressures who would like to apply this kind of technology, but somehow are afraid of dealing with it either

on a research- or production s c a l e - biologists, chemists, environmental engineers, food technologists, material scientists, pharmacists, physicists, and others

The content of the book, structured into nine chapters, each being sub-divided into a number of sections, results from the long-term course presentations and the many connected discussions

In the first Chapter an overview of the general topic is presented The motivations of using

high pressure today are summarized and a number of examples provided which relate to high- pressure production processes applied currently

Chapter Two deals with the basic concepts of high-pressure thermodynamic and phase

equilibrium calculations Experimental methods and theoretical modelling are described briefly in order to give both a comprehensive view of the problems, and suggestions and references to more detailed treatments

The problem of the evaluation of kinetic properties is addressed in Chapter Three,

including both chemical and physical kinetic phenomena

Then, in the Fourth Chapter the design and construction of high pressure equipment is

considered, with reference to research and pilot units, and production plants as well This is a very important part of the book, as it clearly shows that running high pressure apparatus is neither difficult nor hazardous, provided some well established criteria are followed both during design and operation

Industrial reaction units are discussed in Chapter Five, where all the main issues related to

catalytic reactors are discussed, and a special emphasis is paid to polymeric reactors

The problems connected-with separation processes, units, and equipment are treated in the

Sixth Chapter, focusing the reader's attention on high-pressure distillation and on dense-gas

extraction from solids and liquids

Relevant safety issues arising in the design and operation of high-pressure plants are addressed in Chapter Seven After a general section where testing procedures, safe plant

operation, and inspection are summarized, two examples are dealt with in detail: dense-gas extraction units and polymerization reactors

Chapter Eight is concerned with a major question connected with the development of high

pressure technologies in the process and chemical industry, i.e., the economic evaluation of

production carried out at high pressures In this case, also, the matter is discussed in relation

to three important examples: dense gas extraction, polymerization and supercritical anti- solvent precipitation processes

Finally, Chapter Nine is a collection of currently used and (mostly) potential applications

Even though it cannot cover all possibilities and ideas put forward continuously by researchers and companies, the proposed examples provide a thorough view of the opportunities offered by the extensive use of high pressure technology in many fields

The book, written by experts in high pressure technology, is intended to act as a guide for those who are planning, designing, researching, developing, building and operating high pressure processes, plants and components The large number of references included will support the efficient transfer of the actual state of our knowledge The examples and problems, which illustrate the numerical application of the formulas and the diagrams, will provide the reader with helpful tools for becoming acquainted with high-pressure technology

We would like to thank all the contributors for their excellent co-operation, and Elsevier for their support during the editing procedure and for the readiness to publish the book A special acknowledgement is devoted to Ing Monica Daminato for her full commitment and precious help during the final editing of the manuscript and preparation of the camera-ready copy

The editors hope that the book will be well accepted and that it will help to promote the further development of high-pressure technology in the future

April 2001

Alberto Bertucco

University of Padova

Gerhard Vetter University of Erlangen-Ntirnberg

High pressure definitions and examples in nature

Early historical roots of high pressure technology

High pressure technology today - motivations for using high pressure

High pressure technology t o d a y - application survey and examples

Principles of phase equilibria

The Chemical potential and the phase rule of Gibbs

Fugacity and activity

Critical phenomena

Classification of phase equilibria

Fluid phase equilibria

Phase equilibria with the presence of solid phases

Calculation of high-pressure phase equilibria

Bubble point-, dew point- and flash calculations

Equations of state

Cubic equations of state

Non-cubic equations of state

Solubility of solids in Supercritical Fluids

Polymer systems

Glassy polymers

Chemical reaction equilibria

Homogeneous gas reactions

Kinetic properties at high pressure

Interesting features at high pressure

Kinetics of high-pressure reactions

Molecular theory of reaction rate constants

Activation volume

Terms contributing to AVR ~

Terms contributing to Avs #

Evaluation of the activation volume from experimental data

Single homogeneous reactions

Parallel reactions

Reactions in series

Chain reactions

Heterogeneous catalytic reactions

Reactions influenced by mass transport

Prediction of the activation volume

Activation volume as a tool for the elucidation of reaction mechanism

Change of reaction rate constant with pressure

Problems

Diffusivity in dense gases

Binary diffusivity data in different media

Thermal conductivity

Surface tension

Heat transfer mechanisms in dense fluids: calculation of heat-transfer

coefficients in different arrangements

Single phase convective heat transfer

Overall heat-transfer coefficient for exchangers

Mass transfer mechanisms in dense fluids

External mass transfer

Internal mass transfer

Mass transfer models

Design and construction of high pressure

equipment for research and production

High pressure machinery

Requirements and design concepts

Generation of pressure with pumps and compressors

Pumps

Reciprocating displacement pumps

Rotary displacement pumps

Centrifugal pumps

Compressors

Piston compressors

Turbo compressors

Special problems involving high-pressure machinery

Strength of the components

Seals

High-pressure piping equipment

Tubing and fittings

Isolation and control valves

Safety valves and other devices

References of sections 4.1 and 4.2

High-pressure vessels and other components

Calculation of vessels and components

The hollow cylinder under static loading

Strengthening the thick-walled hollow cylinder under static loading

Influence of temperature gradients on design

End pieces side-holes and surface influence

Closures and sealings

Design details - corrosion-protecting of inner surfaces

Heat exchangers and others

Laboratory-scale units

Reactors

Optical cells

Other devices

Small-scale high-pressure plants

Instrumentation of high pressure facilities

Industrial reaction units

Reactors for homogeneous reactions

Hydrodynamics and mass transfer in fixed-bed gas-liquid-solid reactors

operating at high pressure

Countercurrent gas-liquid flow in solid fixed-bed columns

Hydrodynamics in countercurrent fixed beds

Mass transfer in countercurrent fixed beds

Cocurrent gas-liquid downflow fixed-bed reactors"

Trickle-Bed Reactors (TBR)

Flow regimes

Flow charts

Models for the hydrodynamics of TBR

Two-phase pressure drop

5.2.2.7 Liquid-side mass-transfer coefficient

5.2.2.8 Gas-side mass-transfer coefficient

5.2.3 Some examples of industrial applications of gas-liquid-solid fixed beds

Processes carried out in slurry catalytic reactors

Process design issues

Interphase mass transfer and kinetics

Mechanically agitated tanks and three-phase sparged reactors

Design of bubble slurry column reactors (BSCR)

Hydrodynamic characteristics of BSCR

Design models for slurry bubble reactors

Scale-up of slurry catalytic reactors

Scale-up of mechanically stirred reactors (MSSR)

Scale-up of BSCR

Examples

References

5.4 Catalytic reactors for olefin polymerizations

5.4.1 History, catalysts, polymers and process elements

5.4.2.1 Modelling of polymerization kinetics

5.4.2.2 Modelling of the molecular weight distribution

5.4.2.3 Single particle modelling

Examples of pressure distillation

Interphase mass transfer and two-film theory

Two-film theory for distillation and dilute systems

Two-film theory for concentrate systems

Transfer Unit concept

HTU=Height equivalent to one transfer unit

HETP=Height equivalent to one theoretical plate

NTU=Number of transfer units

Efficiency

Effects of the total pressure

Packed towers: random and structured packings

Maximun column capacity

Efficiency

Tray columns

Flow regimes

Downcomer flooding and flooding

Liquid residence time

Process optimization by means of the T-S diagram

Separation of dissolved substances

Cascade operation and multi-step separation

Multistage cross-flow extraction

Multistage countercurrent extraction

Modelling of countercurrent high pressure extraction

Types of extraction columns

Extraction columns without internals

Safety and control in high pressure plant design and operation

General safety aspects in high-pressure facilities

7.2.3.4 Influence of decomposition sensitizers

7.2.5 9 Relief devices

7.2.5.2 Venting systems

References

Economics of high pressure processes

High-pressure extraction plants

Description of standardized units

Laboratory units

Medium scale units

Large scale units

9.1.7 Continuous organic reactions

Enzyme stability in supercritical fluids

Effect of water activity

Important process parameters

The supercritical single-phase hydrogenation

Single-phase conditions

Measurement of phase behavior in complex reaction mixtures

Connecting the different reaction systems

Impact of using supercritical single-phase hydrogenation technology

Supercritical water as a reaction media

Physical properties of supercritical water

Oxidation reactions in SCWO

Catalysis

SCWO process description

Feed preparation and pressurization

Deep-shaft wet-air oxidation

SCWO applications to wastewater treatment

Supercritical Fluid Extraction and Fractionation from Solid Materials

Decaffeination of coffee and tea and extraction of hops

Decaffeination of green coffee beans

Decaffeination of tea

Preparation of hop extracts with CO2

Extraction of spices and herbs

Description of a spice plant

Extraction of essential oils

Extraction of pungent constituents

Production of natural colorants

Production of natural antioxidants

Production of high-value fatty oils

Depestisation of vegetal raw materials

Decontamination of the rice

State of the art in polymer thermodynamics

Special polymer systems

Modelling polymer systems

Experimental methods in modelling polymer systems

Phase behaviour of polymer blends under pressure

State of the art of material processing using Supercritical Fluids

Crystallization from a Supercritical Solution (CSS)

9.9.2.2 Supercritical Fluid Chromatography

9.9.3 Extraction and purification (SFE)

9.9.4 Particle formation

9.9.4.1 Rapid Expansion

9.9.4.2 Recrystallization by Supercritical Anti-solvent

9.9.4.3 Impregnation with Supercritical Fluids

References

9.10 Treating microorganisms with high pressure

9.10.1 Introduction

9.10.2 Hydrostatic high pressure

9.10.2.1 State of the art

9.10.2.2 Equipment and methods

9.10.3 Supercritical CO2 treatment

9.10.3.1 State ofthe art

9.10.3.2 Equipment and methods

9.11.2.1 Conventional dry cleaning

9.11.2.2 Dry cleaning with liquid carbon dioxide

LIST OF CONTRIBUTORS

Alberto Bertueco

Dipartimento di Principi e Impianti di Ingegneria Chimica (DIPIC) Universit/l di Padova Via Marzolo, 91-35131 Padova Italy

Maria Jos~ Cocero

Departamento de Ingenieria Quimica, Universidad de Valladolid

Prado de la Madalena SP-47005 Valladolid, Spain

Nieola Elvassore

Dipartimento di Principi e Impianti di Ingegneria Chimica (DIPIC) Universit/t di Padova Via Marzolo, 9 1-35131 Padova Italy

Theo W De Loos

Faculty of Applied Science, Department of Chemical Technology

Laboratory of Applied Thermodynamics and Phase Equilibria

Delft University of Technology

Julianalaan 136 NL-2628 BL Delft, The Netherlands

Thomas Gamse

Institut fur Thermische Verfahrenstechnik und Umwelttechnik Erzherzog Johann Universit~it Infeldgasse, 25 A-8010 Graz, Austria

Sander van den Hark

Department of Food Science, Chalmers University of Technology

P.O Box 5401 SE-40229 Grteborg, Sweden

Magnus Hiirriid

Department of Food Science, Chalmers University of Technology

P.O Box 5401 SE-40229 Grteborg, Sweden

Z;eljko Knez

Department of Chemical Engineering University of Maribor

P.O Box 222, Smetanova 17, SI-2000 Maribor, Slovenia

Ireneo Kikic

Dipartimento di Ingegneria Chimica, dell'Ambiente e delle Materie Prime

Universitfi degli Studi di Trieste

Piazzale Europa, 1 1-34127 Trieste, Italy

Ludo Kleintjens

DSM Research and Patents

Postbus 18, NL6160 MD Geleen, The Netherlands

Eduard Lack

NATEX GmbH Prozesstechnologie

Hauptstrasse, 2 A-2630 Ternitz, Austria

Andr~ Laurent

Ecole Nationale Sup~rieure des Industries Chimiques (ENSIC)

B P No 451, 1 Rue Granville F-54001 Nancy Cedex, France

Gerhard Luft

Department of Chemistry, Darmstadt University of Technology

Petersenstr 20, D-64287 Darmstadt, Germany

Siegfried Maier

Formerly Research and Development, BASF AG,

D 67056 Ludwigshafen, Germany

Maj-Britt Macher

Department of Food Science, Chalmers University of Technology

P.O Box 5401 SE-40229 G6teborg, Sweden

Rolf Marr

Institut fur Thermische Verfahrenstechnik und Umwelttechnik Erzherzog Johann UniversiRit Infeldgasse, 25 A-8010 Graz, Austria

Nicola Meehan

School of Chemistry, University of Nottingham

University Park, Nottingham NG7 2RD England

School of Chemistry, University of Nottingham

University Park, Nottingham NG7 2RD England

Francisco Recasens

Universitat Polit~cnica de Catalunya

Departamento de Ingenieria Quimica

E.T.S.I.I.B Diagonal, 647 E-08028 Barcelona, Spain

Universitat Polit6cnica de Catalunya

Departamento de Ingenieria Quimica

E.T.S.I.I.B Diagonal, 647 E-08028 Barcelona, Spain

Enrique Velo

Universitat Polit6cnica de Catalunya

Departamento de Ingenieria Quimica

E.T.S.I.I.B Diagonal, 647 E-08028 Barcelona, Spain

Gerhard Vetter

Department of Process Machinery and Equipment,

University of Erlangen-Nuremberg, Cauerstr 4, D 91054 Erlangen, Germany

Guenter Weickert

P.O Box 217 NL-7500 AE Enschede, The Netherlands

Eekhard Weidner

Lehrstuhl fiir Verfahrenstechnische Transportprozesse, University Bochum

Universit~itsstr 150, 44780 Bochum, Germany

Federieo Zanette

Dipartimento di Principi e Impianti di Ingegneria Chimica (DIPIC) Universit~ di Padova Via Marzolo, 9 1-35131 Padova Italy

ABOUT THE EDITORS

Italy: Chairman of the Working Party High Pressure Technology of the European Federation

of Chemical Engineers, with long-term research activity in the field of Supercritical Fluids Applications

Nuremberg, Germany: many years of experience in High Pressure Plant Equipment and Process Machinery for Fluids and Bulk Solids

9 2001 Elsevier Science B V All rights reserved

C H A P T E R 1

I N T R O D U C T I O N

G Vetter

Department of Process Machinery and Equipment

University Erlangen-Nuremberg, Cauerstr 4, D-91058 Erlangen, Germany

The definition of high pressure, examples in nature, and the early historical roots of high pressure technology are explained The motivation of using high pressure today is based on chemical, physico-chemical, physico-bio-chemical, physico-hydrodynamical and physico- hydraulic effects A survey of today high pressure technology is given demonstrating the large range of applications and comprising many branches and processes of production A number

of examples like the production of polyethylene and fatty alcohols, the decaffeination of coffee beans, the homogenisation of foodstuffs, the water-jet cutting and cleaning, the polymer processing, the ultra-high pressure treatment for the aseptic processing as well as the hydrostatic pressure applications for pressing hydroforming and autofrettage are outlined shortly

around 0,25 bar on top of the highest mountain - up to a high pressure of around 1000 bar -

on the deepest ocean f l o o r - both exceeding the physiological limits of human beings more or less drastically

In general living beings on the planet earth are behaving very differently with respect to their compatibility towards pressurized environment Some species of microbes are able to suffer several thousand bar and there are sea mammals such as whales which dive down to a depth of 1000 m - equal to a pressure difference of 100 b a r - within short time intervals, a procedure which would kill human beings immediately

In the interior of our planet millions of bar are to be expected On the other hand we are able to develop hundreds of thousands of bar during the technical synthesis of diamonds Fundamental physical research about the behaviour of matter has now been extended beyond the level of one million bar

It is a characteristic feature of technical processes with high pressure conditions to exhibit absolutely artificial environments, far beyond those existing in nature High pressure machinery and containment are required to maintain these, "artificial conditions" With regards to the term "High Pressure" we should not become confused by linguistic terms such

as high blood pressure, high-pressure areas in weather forecasts, high political or moral psychological pressure, pressure exerted from above and below, etc

The "high pressure" this book is focused on represents the physical pressure defined as the force load per the unit of area (Newton/m2: N/m2; 105 N/m 2 - 1 bar) exhibiting the "normal" atmospheric pressure of our natural environment (ambient or barometric pressure)

1.2 Early historical roots of high pressure technology

The well-known first double-piston pumps of Ktesebios during Archimedes" time, water supply pipes in the ancient world together with Roman pump developments, as well as Agricola's (see: Twelve Books of Mining 1596) wooden "high pressure pumps" for the drainage of mines (100 m depth - 10 bar pressure) during the Middle Ages show early applications of high pressure

James Watt's steam engine (around 1785) working with several bar steam pressure only, innovated the world's energy supply and induced an industrial revolution This steam engine represented one of earliest high pressure processes for power generation

Starting in the Middle Ages, from the development of firearms and guns based on explosives emerged the problem of designing safe containments (gun barrels) against the high detonation pressure (today, several thousand bar)

As an early milestone of high pressure chemical processing should be mentioned the synthesis of ammonia by Haber and Bosch (Nobel prize 1918) This typical high pressure ( 3 0 0 - 700 bar) process already shows all the characteristics of the similar ones of today It should be regarded as the initiation of the very successful development of the high pressure chemistry during the last century, including the still up-to-date super-pressure polymerisation

of ethylene (3000 bar) Since the mid-20 th century diamonds have been synthesized by

process and special apparatus

the future The following effects of high pressure should be distinguished

The chemical effect of high pressure is to stimulate the selectivity and the rate of reaction together with better product properties and quality as well as improved economy This is based on better physico-chemical and thermodynamic reaction conditions such as density, activation volume, chemical equilibria, concentration and phase situation Many successful reactions are basically enhanced by catalysis

The physico-chemical effect of high pressure, especially in the supercritical state, to enhance the solubility and phase conditions of the components involved Supercritical hydrogenation, or enzymatic syntheses are offer new steps with high pressure Supercritical water oxidation at high pressure represents an efficient method for the decontamination of wastes

From the application of high pressure liquid or supercritical carbon dioxide as a solvent have emerged a number of promising or successful production processes such as supercritical extraction, fractionation, dyeing, cleaning, degreasing and micronisation (rapid expansion, crystallization, anti-solvent recrystallization) New material properties can be achieved by foam expansion, aerogel drying, polymer processing, impregnation and cell-cracking with high pressure supercritical CO2 [1, 2]

The physico-bio-chemical effect of the high pressure treatment predominantly of foodstuffs and cosmetics, is now emerging For the sterilization (pasteurisation, pascalisation) high pressure offers an alternative to high temperature Furthermore, treatment with static high pressure gives a promising improvement of certain organic natural products by advantageous swelling, gelation, coagulation and auto-oxidation effects in combination with fats or proteins This selection of high pressure effects actually is however only under increasing research however only and successful practical applications have not been achieved yet [3]

The physico-hydrodynamical effect of high pressure is based on the conversion of the potential (pressure) into kinetic energy (high speed fluid jetting: 100 - 1000 m/s) The main applications are the homogenisation of fluid mixtures by expanding them through very narrow clearances, water-jet cutting and water-jet cleaning, and the generation of sprays with fine droplets for efficient combustion or spray-drying of fine particles

The physico-hydraulic effect of high pressure is involved during the conveying of fluids against large differential pressures, for example the filtration of polymer melts, or pipeline transport over long distances The hydrostatic energy is applied for hydroforming of complex metal parts, isostatic pressing for sintered products, or the autofrettage treatment of high pressure components in order to generate beneficial residual stresses [4, 5]

pressure levels applied, and the products or results of the processes involved The survey is not complete, as the development is changing and progressing permanently

It should be pointed out at this stage that the application of high pressure as a beneficial tool for production procedures, from the experience of the past decades, is increasing and decreasing all the time High pressure equipment and plants are expensive in their development, investment, operation, and safety aspects So there is the general tendency to reduce the pressures as soon as the process development offers the chances (e.g by the introduction of new catalysts) to do so

Table 1.4-1

Applications of high pressure

propionic and acetic acid urea (fertilizers)

butanediol methanol

Hydroformylation

edible oils hydrogasification hydrocracking desulfurization catalytic cracking naphtha hydroforming coal liquefaction fatty alcohols 1-6-hexanediol 1-4-butanediol hexamethylenediamine C4 to C15 products

Extraction with supercritical fluids 8 0 - 3 0 0

(e.g., CO2)

decaffeinated coffee (tea) spices, hops

colours drugs oils, lecithine and fats tobacco (nicotine) perfumes

Micronization with supercritical

Dyeing with supercritical fluids

supercritical fluids (e.g., CO2)

Kinetic fluid (jet) energy with water up to 4000

Kinetic fluid energy

drying inhibition desulfurization, odorization secondary and tertiary production methods drilling support heavy water pipeline transport of ores and coal polymer spinning

polymer filtration polymer extrusion analytical chemistry chemical production jet cutting

jet cleaning jet treatment of fabrics foodstuffs

cosmetics pharmaceutical products chemical products bio-products autofrettage (residual stresses) hydroforming

isostatic pressing (sintered parts) fine powders of various products

Fuel injection 1000- 2000 diesel motors

(improved combustion)

Potential (pressure) energy effects up to 5000

on organic products

sterilization pascalisation coagulation gelation of various foodstuffs and other bio-products

The following examples of successful and well developed high pressure processes concentrate mainly on the general aspects and a consideration of the high pressure machinery involved The explanations will discuss primarily the general aspects and benefits of high pressure as a tool, and will not address details of the methodology

Example 1: Production of Polyethylene (PE)

The different available high pressure polymerisation processes of polyethylene (PE) yield LDPE (low density PE), LLDPE (linear low density PE) and copolymer features of the same The various process variations have been developed during recent decades and introduced a number of well developed steps and devices to achieve safe and economical operating conditions at the very high reaction pressures of 1500 to 3000 bar

The process (Fig 1.4-1) makes heavy demands on the pumps, compressors, reactors, piping, fittings and valves, as well as for other devices at the pressure range mentioned The monomer ethylene (storage tank, a) is compressed by a primary reciprocating compressor with several stages (b), up to around 300 bar, and then by a two-stage "hyper" reciprocating compressor (c) up to around 3000 bar Between the two piston-type compressors (b and c) is the main location for injecting modifiers, especially co-monomers, in order to achieve certain modifications of the polymer properties As these additives mainly represent solvents or liquified gases high pressure diaphragm pumps (m) must normally be applied

The polymerisation reaction takes place in tubular or stirred vessel reactors (d) under careful control of pressure and temperature, enhanced or initiated by the injection of initiator- solvents (e) (as well as co-monomers 1) which are frequently based on organic peroxides The typical injection pumps for this metering problem are of the two-cylinder amplifier types The further process comprises a number of further steps such as heat exchange (f, h), separation (g, j), gas recycling (k), and polymer discharge (i) The art of producing high pressure PE is based on an excellent understanding of the process and skill in designing and operating the high pressure equipment required

Example 2: Production of unsaturated fatty alcohols

This hydrogenation process (Fig 1.4-2) is, among others, the basis for the production of washing detergents

fatty acids catalyst /

Fig 1.4-2 Production of unsaturated fatty alcohols

(new) J

unsaturated fatty alcohols

fatty alcohols (reactor, a) Several high pressure steps such as heat exchange, separation, recycling catalyst feed (b to f) together with proper high pressure components, are required The dry hydrogen compression is avoids any contamination of the product with lubricants The diaphragm feed pumps offer the best service with respect to endurance and wear protection, with the lowest life-cycle costs

E x a m p l e 3: D e c a f f e i n a t i o n of coffee b e a n s

Of the various extraction processes the decaffeination with supercritical C 0 2 exhibits the most commercial advantages for bulk production The process is a discontinuous one Fig 1.4-3 shows a number of serially arranged extractors (5) charged with the supercritical CO2 feed by the centrifugal circulation pump (1)

Fig 1.4-3 Decaffeination of coffee beans

The supercritical solvent is expanded with the throttling valve (9) in order to remove the caffeine (separator 8) and to bring the solvent back to the liquid state (condenser 10) The gas- recycling (dry running) reciprocating compressor (7), the CO2 and the co-solvent feed (2, 3; diaphragm pumps) represent variable process components if required Heat exchangers (4) maintain the suitable thermodynamic conditions

the caffeine as valuable products

The supercritical extraction of hops, tea, and other foodstuffs can be performed in similar plants The challenge of the discontinuous extraction of bulk materials is in the design and automatic operation of high pressure extractors which can easily be opened and closed for the filling and discharging procedure

Example 4: Homogenisation of milk and other foodstuffs

Liquid foodstuffs, for example milk products must be submitted to homogenisation treatment in order to improve their long-term physical stability ("shelf life") The liquid is pumped at very high pressure by a multiplex reciprocating piston pump through the narrow clearances of a hydraulically controlled homogenisation valve (Fig 1.4-4, C, bottom)

By the action of hydraulic shear forces, cavitation, turbulence and impact owing to the very high flow velocity (several 100 m/s) or high differential pressure (low viscosity liquids, 300

to 400 bar, or more viscous liquids, up to 1500 bar) the liquid is turned into a very fine (homogeneous) dispersion

The homogenisation process is only one step (or sometimes two stages, see Fig 1.4-4, top) within the production line The feed (raw product) is adjusted in temperature by heat exchange (HE), passed through the homogeniser (H septic), then treated by ultra-high- temperature (UHT), homogenized a second time (H aseptic) and UHT-treated, ending with an aseptic final product

Homogenisation processes now extend up to 1500 bar differential pressures As the materials to be homogenized exhibit varying properties with respect to viscosity, corrosiveness and abrasiveness the high pressure components, such as homogenising pumps and valves, need very careful design and choice of materials

Example 5: High speed water-jetting as an efficient tool for production and other treatment steps

The growing demand for fully automated production processes must take benefit of new steps in order to achieve and secure the quality standards requested During continuous sheet steel production the permanent descaling of the sheet surfaces (Fig 1.4-5, S) is realized by high speed water-jetting (Fig 1.4-5, top) at suitable locations in the rolling-mill train (usually

600 bar water supply to the jetting nozzles, N) The high pressure plunger pumps (HP) should provide a smooth volume flow by multiplex design

Fig 1.4-5 Descaling, cleaning and jet-cutting with high pressure

A very similar process is the high speed water-jet cleaning applied during reconstruction of buildings, cleaning procedures in production processes, for ships, and especially in wastewater systems Depending on the nature of the surface layers to be removed the required water pressure can approach 2500 bar, and thus make outstanding demands on the high pressure pump design and the installation (Fig 1.4-5, bottom left side)

The prerequisite of the successful application of water-jet cleaning should be a proper understanding of the parameters involved in the jet-cleaning physics requiting profound case studies

Super-speed water-jets are further applied increasingly for the production steps requiting the cutting of pieces of material which should be kept at low temperature and which appear soft and restrictive towards mechanical tools The water-jet as a "hydrodynamic cutter" provides a number of advantages in cases which should be selected by case studies

Jet-cutting systems need to be compact and suitable for robotic action in automated trains

of production Usually the hyper-pressure plunger pumps for water-jet cutting purposes are based on hydraulic amplifiers, of double-cylinder design, and provide high pressure water of

up to 5000 bar

If very hard materials (e.g., natural stone, or metal sheets) must be cut, the injection of abrasives into the water jet will support and accelerate the cutting procedure (see Fig 1.4-5, bottom, fight side) The water-jet cutting represents a very flexible production method which can be regarded as supplementary to LASER methods if thermal influences on the materials involved cannot be accepted

Example 6: Polymer processing

During the production of polymers (e.g., polyolefins, polyamide, polystyrene), very viscous (up to 4.10 6 mPas) polymer melts have to be extracted with high pressure gear pumps (PGP) from the reactors (PR) or degasifiers (DG), then transferred through heat exchangers (HE), static mixers (MI), filters (F) and diverters (DI), depending on the process, onto spinning gear (SP) pumps (Fig 1.4-6)

Fig 1.4-7 Polymer extrusion

a, b foil extrusion c bottle extrusion

f co - extrusion

d cable extrusion e blow film extrusion

The viscosity of the transferred fluids increases from the monomer tank (M) to the polymer reactor (PR) and the degasifier (DG) The highest viscosity (occasionally over 106 mPas) is seen in the polymer extraction pump (PGP) behind the vacuum degasifier As the polymer melt has to pass mixers and filter systems its extreme viscosity requires very high pressures from the polymer gear pumps in order to force the material through the system (up to 400 bar)

to the spinningpumps (SP) During extrusion polymer processing the extruder (EX) is responsible for the homogenous melting and the following polymer gear pump (PGP) for generating the high and constant pressure for pressing the material through the extrusion tools (co-extrusion, foil extrusion, cable extrusion etc., Fig 1.4-7).The gear pumps for extremely viscous polymers must be designed accordingly, with very large inlet nozzles and crescent- shaped clearances in the suction area between the gear wheels and the pump housings

Example 7: The sterilization of fruit juices with high pressure

This method (ultra-high pressure treatment UHP) for the aseptic processing of food stuffs and other organic products still appears to be some way from extended application

From a number of pilot applications Fig 1.4-8 shows the quasi-continuous train for the sterilization of fruit juices with pulp contents The high pressure sterilization offers valuable advantages with respect to the quality of the final product compared to other sterilization procedures, especially if natural fractions of fruit pulp are desired by the consumers

The fruit juice enters the autoclaves (5) by the pumping action of the floating pistons (4) involved The drinking-water supply (vessel 1, low pressure pump 2, high pressure pump 3) is capable of submitting the fruit juice to the high pressure required (around 4000 bar), during a definite time period, through the floating piston Then the juice is discharged by the water hydraulic-control system At the same time, other parallel autoclaves perform the same steps

with a certain time shift so that quasi-continuous operation of the sterilization process can be achieved

Ind., Japan 1992)

Example 8: Hydrostatic pressure as an efficient tool for production

The high pressure treatment is growing rapidly for a number of productions steps

Traditional methods such as hot and cold isostatic pressing (HIP, CIP) for the production of

sintered metallic or ceramic parts have been developed further They are now also applied as a post-treatment for castings in order to eliminate or heal porosity or internal cracks and to improve the quality Isostatic pressing is a tool to produce intricately shaped parts demanding high density and homogeneity The process requires suitable presses to generate pressures of

internal fluid pressure (Fig 1.4-9, A) The untreated part may represent for example, a piece

of pipe which is fixed with appropriate joints in a swage body and closed at both ends By admitting an appropriate high internal pressure, various intricate geometrics can be achieved (1000 to 4000 bar) Another similar approach for the production of large fiat and curved parts from sheet material is the hydropressing by means of special presses transmitting pressure by appropriate diaphragms

The autofrettage treatment (Fig 1.4-9, B) is certainly one of the oldest, but still very

useful methods to create beneficial residual stresses in thick-walled components (e.g., pipes) The autofrettage pressure must be adjusted to a level so that the material in the thick wall is plastically strained within a certain percentage (e.g., 50 %), the rest staying only elastically strained

Fig 1.4-9 Hydro forming (A), Autofrettage (B)

After the removal of the autofrettage pressure (typically 3000 to 8000 bar) the plastically over-strained region exhibits compressive residual stresses, especially at the internal "surface (Fig 1.4-10) When submitting the thick-walled pipe to the desired operational pressure the compressive internal strains will reduce the operational ones effectively at the inner surface so the same pipe then can carry much more pressure before any failure can occur (compare Cyv and CYvA at the inner diameter) Autofrettage treatment, although first used for the gun-barrel reinforcement hundreds of years ago, is used today for high pressure components in the process industries as well as for appropriate components in common rail diesel injection systems for combustion motors The autofrettage method can be included in automated manufacturing sequences

tangential residual stress after autofrettage

References

Solvents, Blackie Academic & Professional, Glasgow, 1993

1998, Institut National Polytechnique de Lorraine

University of Heidelberg/Germany, Section Physical Chemistry, 1998

York, 1977