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DRY 1: Introduction to Drying Technology

DRY 1: Introduction to Drying Technology
     PART 1: Introduction
         1. THE MANUAL OF DRYING TECHNOLOGY
             1.1 Purpose
             1.2 Structure
             1.3 Contents of the Volumes
         2. LAYOUT OF VOLUME I
             2.1 PART 2 - DRYING FUNDAMENTALS
             2.2 PART 3 - INDUSTRIAL DRYING PRACTICE
         3. WHAT IS DRYING?
     PART 2: Drying Fundamentals
         1. INTRODUCTION
         2. MOISTURE IN MATERIALS
             2.1 Definition of moisture content
             2.2 Types of moisture
             2.3 Characteristic moisture content
             2.4 Enthalpy
             2.5 Practical measurements
         3. MOISTURE IN GASES
             3.1 Definitions of humidity and hygrometric terms
                 3.1.1 Absolute humidity, Y
                 3.1.2 Volumetric humidity, Yv
                 3.1.3 Molal humidity and partial pressure
                 3.1.4 Saturation pressure pYs and saturation humidity Ys*
                 3.1.5 Relative humidity,
                 3.1.6 Humid volume, vh
             3.2 Calculation procedures
             3.3 Enthalpy
             3.4 Psychrometric charts
             3.5 Saturation and dewpoint conditions
                 3.5.1 Dewpoint and frostpoint
                 3.5.2 Adiabatic saturation
                 3.5.3 Wet bulb temperature, Twb
                 3.5.4 Measurement techniques
         4. STAGES OF DRYING
             4.1 Drying rates
                 4.1.1 Mass-flow drying rate or evaporative load, Wev
                 4.1.2 Mass flux, J
                 4.1.3 Specific drying rate or moisture-loss rate, N
                 4.1.4 Characteristic drying rate, NC
             4.2 Basic mechanisms of drying
             4.3 Convection drying
                 4.3.1 Induction period
                 4.3.2 Constant rate or unhindered drying period
                 4.3.3 Falling rate or hindered drying period
                 4.3.4 Practical drying curves
             4.4 Contact drying
             4.5 Measurement of drying rates
                 4.5.1 Sampling method
                 4.5.2 Direct-weighing method
                 4.5.3 Humidity difference method
         5 HEAT TRANSFER
             5.1 Introduction
             5.2 Expressions for heat transfer rate to solids
             5.3 Heat transfer coefficients for convective drying
                 5.3.1 Heat transfer to particles
                 5.3.2 Heat transfer to sheets and films
             5.4 Calculation of critical moisture content
             5.5 Contact drying and conduction
             5.6 Radiative heat transfer
             5.7 Dielectric heating
             5.8 Heat transfer within the solids
         6 MASS TRANSFER AND DRYING KINETICS
             6.1 Introduction
             6.2 Mechanistic or theoretical models
                 6.2.1 Wetted surface models
                 6.2.2 Capillary model
                 6.2.3 Receding evaporative front models
                 6.2.4 Diffusion models
                 6.2.5 General theories of drying
             6.3 Scaling methods
                 6.3.1 The characteristic drying curve
                 6.3.2 Drying coefficient
                 6.3.3 The Biot number for mass transfer
                 6.3.4 The SPS design method for fluidised bed dryers
             6.4 Vapour phase mass transfer
                 6.4.1 Diffusion
                 6.4.2 Vacuum drying
         7 DRYING EQUILIBRIA
             7.1 Overview
             7.2 Forms of desorption isotherm
             7.3 Calculation of equilibrium moisture content
             7.4 Measurement of equilibrium moisture content
         8 HEAT AND MASS BALANCES
             8.1 Introduction to mass and energy balances
             8.2 Dryer system flowsheet
             8.3 Continuous dryers
                 8.3.1 Mass balance
                 8.3.2 Overall heat balance
                 8.3.3 Gas leaks
             8.4 Batch dryers
             8.5 Vacuum dryers
             8.6 Gas recycle
                 8.6.1 Basic flowsheet layout
                 8.6.2 Definition of recycle ratio
                 8.6.3 Mass and heat balances in circuit
                 8.6.4 Incorporation into overall flowsheet
                 8.6.5 Condenser conditions
             8.7 Heater and burner system
                 8.7.1 Dryer energy consumption
                 8.7.2 Heater duty in convective dryers
                 8.7.3 Indirect heaters
                 8.7.4 Direct-fired heaters
                 8.7.5 Combustion calculations for direct-fired heater
                 8.7.6 Short-cut calculation
                 8.7.7 Self-inerting dryers
                 8.7.8 Heaters for contact dryers
         9. PHYSICAL PROPERTIES
             9.1 Enthalpy and heat capacity
                 9.1.1 General principles
                 9.1.2 Heat capacity of gases
                 9.1.3 Heat capacity of liquids and vapours
                 9.1.4 Heat capacity of solids
             9.2 Saturation vapour pressure and temperature
             9.3 Dew point
                 9.3.1 Water vapour dew point
                 9.3.2 Acid dew point
             9.4 Estimation of physical properties
                 9.4.1 Worked example
             9.5 Psychrometric calculations
                 9.5.1 Adiabatic saturation temperature
                 9.5.2 Wet bulb temperature
                 9.5.3 Calculated values for air-water system
                 9.5.4 Psychrometric ratio
             9.6 Particle size and shape
                 9.6.1 Particle mean diameter, dP
                 9.6.2 Number-average mean diameter, dP(NA)
                 9.6.3 Volume diameter, dv
                 9.6.4 Surface-volume diameter, dsv
                 9.6.5 Median and mode
                 9.6.6 Shape effects
                 9.6.7 Sphericity or shape factor,
                 9.6.8 Measurement methods
         10 OTHER SOLIDS PROPERTIES
             10.1 Introduction
             10.2 Heat-sensitivity
             10.3 Measurement techniques
                 10.3.1 Physical properties
                 10.3.2 Stickiness, cohesion and adhesion
                 10.3.3 Attrition, dust and fines
                 10.3.4 Thermal effects
                 10.3.5 Safety and environmental factors
         11 SOME SOURCES OF FURTHER INFORMATION
             11.1 JOURNALS ON DRYING
             11.2 INTERNATIONAL DRYING SYMPOSIA
             11.3 GENERAL BOOKS ON DRYING
             11.4 BOOKS ON SPECIFIC DRYER TYPES
             11.5 BOOKS ON FOOD DRYING
             11.6 BOOKS ON PAPER DRYING
         12. REFERENCES
         13. NOMENCLATURE
         14. APPENDIX 1. ADDITIONAL CHARTS
         15. APPENDIX 2. CONVERSION FACTORS
     PART 3: Industrial Drying Practice
         1 INTRODUCTION
             1.1 Purpose
             1.2 Layout
         2 INDUSTRIAL DRYING EQUIPMENT
             2.1 Classification of drying equipment
                 2.1.1 Principal factors
             2.2 Types of dryer
             2.3 Dryer classification charts
             2.4 Layer dryers for particulate materials
                 2.4.1 Summary
                 2.4.2 Tray (oven) dryers
                 2.4.3 Rotating shelf dryers
                 2.4.4 Plate dryers
                 2.4.5 Band dryers
                 2.4.6 Tunnel dryers
                 2.4.7 Deep-bed through-circulation dryers
                 2.4.8 Rotating batch vacuum dryers
                 2.4.9 Vertical agitated dryers
                 2.4.10 Horizontal agitated dryers
                 2.4.11 Indirect rotary dryers
                 2.4.12 Rotary-louvre dryers
                 2.4.13 Drum dryers
             2.5 Layer dryers for sheets and films
                 2.5.1 Cylinder dryers
                 2.5.2 Stenters
                 2.5.3 Oven and belt dryers
                 2.5.4 Flotation dryers
                 2.5.5 Drying of bobbins
             2.6 Dispersion dryers
                 2.6.1 Summary
                 2.6.2 Fluidised bed dryers
                 2.6.3 Cascading rotary dryers
                 2.6.4 Pneumatic conveying dryers
                 2.6.5 Spouted bed dryers
                 2.6.6 Spray dryers
             2.7 Combinational dryers
                 2.7.1 Filter-dryers
                 2.7.2 Thin-film dryers
                 2.7.3 Mixer-dryers
             2.8 Flowsheet features and special types
                 2.8.1 Overview
                 2.8.2 Vacuum drying
                 2.8.3 Freeze drying
                 2.8.4 High humidity drying and gas recycle systems
                 2.8.5 Superheated steam drying
                 2.8.6 Inert gas drying
                 2.8.7 Radiofrequency and microwave drying
                 2.8.8 Induction drying
                 2.8.9 Infra-red drying and curing
                 2.8.10 Solar drying
                 2.8.11 Impinging streams drying
                 2.8.12 Pulsed combustion drying
                 2.8.13 The Carver Greenfield process
                 2.8.14 Solids recycle and backmixing
                 2.8.15 Non-thermal dewatering
                 2.8.16 Preforming
                 2.8.17 Size reduction
         3. CURRENT INDUSTRIAL PRACTICE
             3.1 Market data
             3.2 Breakdown by industrial sector
             3.3 Review of individual sectors
                 3.3.1 Iron and steel
                 3.3.2 Engineering and other metal trades
                 3.3.3 Chemicals
                 3.3.4 Food, drink and tobacco industry
                 3.3.5 Paper, printing and stationery
                 3.3.6 Textiles and leather
                 3.3.7 Bricks, tiles and building materials
                 3.3.8 Pottery and ceramics
                 3.3.9 Cement
                 3.3.10 Minerals
                 3.3.11 Timber
                 3.3.12 Laundries and fabric care
                 3.3.13 Wastes
         4. DRYER SELECTION
             4.1 Overview
             4.2 Drying in the context of the overall process
             4.3 The SPS dryer selection algorithm
                 4.3.1 Equipment and application factors
                 4.3.2 Stages in the algorithm
             4.4 Detailed description
                 4.4.1 Step 1 - Define problem and collect information
                 4.4.2 Step 2 - basic choices
                 4.4.3 Step 3 - Select suitable dryer types
                 4.4.4 Step 4 - Sub-types, refinements and flowsheet factors
                 4.4.5 Step 5 - Evaluation procedure
             4.5 Worked example
             4.6 Alternative dryer selection algorithm
                 4.6.1 Step 1 - Batch or continuous processing
                 4.6.2 Step 2 - Preliminary dryer selection
                 4.6.3 Step 3 - Dryer economic evaluation
                 4.6.4 Step 4 - Laboratory and pilot-plant tests
         5 PRELIMINARY DRYER DESIGN
             5.1 Introduction
             5.2 Mass and Energy Balances
                 5.2.1 Continuous dryers
                 5.2.2 Batch dryers
                 5.2.3 Use of psychrometric charts
             5.3 Scoping design calculations
                 5.3.1 Convective dryers
                 5.3.2 Worked example
                 5.3.3 Contact dryers
             5.4 Detailed Design Calculations
                 5.4.1 Equipment model
                 5.4.2 Material model
             5.5 General system models
                 5.5.1 Integral models
                 5.5.2 Incremental models
                 5.5.3 Number of transfer units (NTU) approach
             5.6 Scale-up
                 5.6.1 Scoping methods
                 5.6.2 Detailed methods
             5.7 Conclusions
         6 DRYER ANCILLARIES AND OPERATIONS
             6.1 Overview
             6.2 Safety
                 6.2.1 Introduction
                 6.2.2 Dust explosions
                 6.2.3 Hazard Assessment
                 6.2.4 Explosion precautions
             6.3 Environmental considerations
                 6.3.1 Introduction
                 6.3.2 Toxic and coloured particles
                 6.3.3 Toxic and harmful gases and odour prevention
                 6.3.4 Noise
             6.4 Control and instrumentation
                 6.4.1 Overview
                 6.4.2 Types of Control System
                 6.4.3 Microprocessor-assisted control systems
                 6.4.4 Control system design
                 6.4.5 Instrumentation
             6.5 Energy efficiency
                 6.5.1 Overview
                 6.5.2 Evaluation of dryer efficiency
                 6.5.3 Steps in a dryer survey
                 6.5.4 Performance assessment - dryer auditing
             6.6 Troubleshooting
                 6.6.1 Problem definition
                 6.6.2 Problems
                 6.6.3 Causes
                 6.6.4 Solutions
         7 DRYER ECONOMICS
             7.1 Drying costs
             7.2 Capital cost estimation
             7.3 Historical cost data for engineering equipment
             7.4 Operating costs
         8 PRODUCT QUALITY
             8.1 Introduction
             8.2 Particle Size; Attrition and Agglomeration
             8.3 Morphology of Dried Products
                 8.3.1 Shrinkage
                 8.3.2 Drying Stresses
                 8.3.3 Morphology of Spray-Dried Particles
                 8.3.4 Collapse during freeze drying
                 8.3.5 Case Hardening
             8.4 Bulk Density
             8.5 Powder stickiness and handling properties
             8.6 Reconstitution of solvent-soluble materials
             8.7 Odour - Loss of secondary volatile components
                 8.7.1 Losses from liquid feedstocks
                 8.7.2 Losses from frozen feedstocks
             8.8 Heat sensitivity
                 8.8.1 Introduction
                 8.8.2 Lipid autoxidation
                 8.8.3 Non-enzymatic browning
                 8.8.4 Protein Denaturation
                 8.8.5 Modelling of the Thermal Degradation Reactions
         9 REFERENCES
         10 NOMENCLATURE
             10.1 Part 1 - Generic Symbols
             10.2 Part 2 - Symbols and combinations used in text
     PART 4: Technological Update
         1 INTRODUCTION
             1.1 Contents of this Technological Update
             1.2 Summary of recent drying theoretical developments
                 1.2.1 Overview
                 1.2.2 Application of drying theory in practice
             1.3 Drying in the context of the overall process
         2 DRYING FUNDAMENTALS
             2.1 Existing material
                 2.1.1 Additional definitions and notes
             2.2 Humidity and psychrometry
                 2.2.1 Definitions and nomenclature
                 2.2.2 Advances in instrumentation
                 2.2.3 Theoretical developments
                 2.2.4 Formulae for physical properties
                 2.2.5 The psychrometer equation
                 2.2.6 Psychrometric calculations
                 2.2.7 Types of psychrometric chart
         3 DRYING SOFTWARE
             3.1 Overview
             3.2 Calculation and simulation programs
                 3.2.1 Psychic - Psychrometric chart plotting
                 3.2.2 DryScope - Dryer scoping calculation
                 3.2.3 FluBed - Fluidised bed dryer design
             3.3 Decision making tools and expert systems
                 3.3.1 DrySel - Dryer selection adviser
                 3.3.2 Assistants
             3.4 Previously released programs
                 3.4.1 DryCur - Drying curve data analysis
                 3.4.2 DryCon - Pneumatic conveying dryer design
                 3.4.3 Rotary - Cascading rotary dryer design
                 3.4.4 Spry - Spray dryer design
                 3.4.5 Hamblcon and Burner - Spreadsheets
                 3.4.6 Extensions in HYSYS and Aspen Plus
             3.5 Other drying software
             3.6 Websites
         4 INDUSTRIAL DRYING EQUIPMENT
             4.1 Existing material
             4.2 Developments in last 10 years
                 4.2.1 General trends
                 4.2.2 Centrifuge-dryers
                 4.2.3 Novel equipment
                 4.2.4 Good Manufacturing Practice (CGMP)
             4.3 Equipment for specific applications
                 4.3.1 Pharmaceuticals
                 4.3.2 Agriculture and foods
                 4.3.3 Sewage sludge drying
                 4.3.4 Paper drying
                 4.3.5 Textile drying
                 4.3.6 Wood drying
             4.4 Superheated steam and "Airless" drying
         5 DRYER DESIGN PROCEDURES
             5.1 Existing material
             5.2 Types of dryer model
                 5.2.1 The limiting factor for dryer performance
             5.3 Scoping design calculations
                 5.3.1 General points
                 5.3.2 Continuous convective dryers
                 5.3.3 Continuous contact (conduction) dryers
                 5.3.4 Batch dryers
                 5.3.5 Initial estimation of falling-rate drying kinetics
                 5.3.6 Use of literature data for drying kinetics and equilibrium moisture content
             5.4 Models incorporating experimental data
                 5.4.1 Integral model
                 5.4.2 Incremental model
                 5.4.3 Computational Fluid Dynamics (CFD)
             5.5 Interconversion of flowrates
                 5.5.1 Conversion between mass and volume-based flows
                 5.5.2 Dry and wet basis flowrates
                 5.5.3 Correction of flowrates to different conditions
                 5.5.4 Mass flow equivalents of standardized volume flowrates
         6 DRYER SELECTION
             6.1 Existing material
                 6.1.1 Alternative methods for dryer selection
             6.2 Selection algorithm
             6.3 Simplified selection methods
                 6.3.1 Published decision trees
                 6.3.2 New Aspen decision tree
                 6.3.3 Question-and-answer decision tree route
                 6.3.4 Rules for new decision tree
         7 FLUIDISED BED DRYERS
             7.1 Existing material
             7.2 Fluidised bed drying equipment
             7.3 Theoretical developments
                 7.3.1 The SPS analysis method for mean drying times
                 7.3.2 Residence time distribution for particles and outlet moisture content
                 7.3.3 Vertical variations within a fluidised bed
             7.4 Design and performance rating
         8 CASCADING ROTARY DRYERS
             8.1 Existing material
             8.2 Rotary drying equipment
             8.3 Theory for cascading rotary drying
                 8.3.1 Developments in the last 10 years
                 8.3.2 The SPS analysis method
                 8.3.3 Other theoretical problems
                 8.3.4 Other practical problems
                 8.3.5 Comparison of SPS model and previous theory
                 8.3.6 Experimental determination of particle motion
             8.4 Design methods
                 8.4.1 Practically-based design and scale-up methods
                 8.4.2 The SPS design method
                 8.4.3 Scale-up methods
                 8.4.4 Commissioning, optimisation and troubleshooting of rotary dryers
         9 SPRAY DRYERS
             9.1 Existing material
             9.2 Developments in spray drying equipment
                 9.2.1 Combination of spray dryers and other equipment
             9.3 Developments in theory and modelling
                 9.3.1 Numerical modelling and CFD in spray drying
                 9.3.2 Other aspects of modelling and operation
                 9.3.3 Troubleshooting spray dryers
         10 PNEUMATIC CONVEYING (FLASH) DRYERS
             10.1 Existing material
             10.2 Equipment developments
             10.3 Modelling of pneumatic conveying dryers
                 10.3.1 Basic modelling principles
                 10.3.2 Drying kinetics measurements for flash dryers
                 10.3.3 Air and particle flow patterns at the feedpoint
             10.4 Development of scale-up and other modelling procedures
             10.5 Solids residence time and drying in cyclones
                 10.5.1 The significance of the product removal cyclone for dryer performance
                 10.5.2 Particle residence times in cyclones
                 10.5.3 Optimising the overall duct-cyclone system
         11 LAYER AND CONTACT DRYERS
             11.1 Existing material
             11.2 Equipment developments in layer dryers
                 11.2.1 Cascade dryer
                 11.2.2 Spherical dryer
             11.3 Appropriate models for layer dryers
         12 RADIOFREQUENCY AND MICROWAVE DRYERS
             12.1 Existing material
             12.2 Developments in equipment
             12.3 Application of RF combinational drying to textile webs
             12.4 Microwave filter-dryer
         13 DRYING KINETICS AND EQUILIBRIA
             13.1 Existing material
             13.2 Simplified analysis of drying kinetics
                 13.2.1 First-order falling rate kinetics
                 13.2.2 Unhindered (constant rate) drying period
                 13.2.3 Induction period
                 13.2.4 Total drying time
             13.3 Drying kinetics models
                 13.3.1 Classical drying models
                 13.3.2 Distributed-parameter and lumped-parameter models
                 13.3.3 Choice of falling-rate model
             13.4 Processing of experimental data
                 13.4.1 Introduction
                 13.4.2 Methods for measuring drying kinetics
                 13.4.3 Types of data to be processed
                 13.4.4 Processing of weight-loss and moisture-time data
                 13.4.5 Processing of humidity-time data
                 13.4.6 Interpretation of the experimental data
                 13.4.7 Conclusions
             13.5 Moisture content profiles in materials
             13.6 Equilibrium moisture content and sorption isotherms: theory
                 13.6.1 Two-parameter isotherms
                 13.6.2 Three-parameter isotherms
             13.7 Equilibrium moisture content and sorption isotherms: measurement
                 13.7.1 Static method; salt solutions
                 13.7.2 Multiple dynamic equilibrium moisture measurements
         14 PRODUCT QUALITY AND SOLIDS PROPERTIES
             14.1 Existing material
             14.2 Powder stickiness
                 14.2.1 Caking (mobile liquid bridges)
                 14.2.2 Spider diagrams
                 14.2.3 Sticky-point (immobile liquid bridges)
             14.3 Thermal damage
             14.4 Freeze drying
                 14.4.1 Basic freeze drying principles
                 14.4.2 Equipment
                 14.4.3 Theory and research
                 14.4.4 The freeze drying cycle
                 14.4.5 Operation, control and instrumentation
         15 DRYER OPERATIONS
             15.1 Existing material
             15.2 Safety and the environment
             15.3 Control and instrumentation
                 15.3.1 Instrumentation
                 15.3.2 Control of dryers
             15.4 Troubleshooting
                 15.4.1 The troubleshooting algorithm
                 15.4.2 Problem categorisation
                 15.4.3 Debottlenecking convective dryers
                 15.4.4 Storage problems
             15.5 Energy efficiency
                 15.5.1 Overview
                 15.5.2 Classification of energy reduction methods
                 15.5.3 Direct reduction of dryer heat duty
                 15.5.4 Heater duty for a convective dryer
                 15.5.5 Pinch analysis of dryers
                 15.5.6 Heat recovery and heat exchange
                 15.5.7 Alternative utility supply systems
         16 RECOMMENDED PROCEDURES AND RESEARCH REPORTS
             16.1 Recommended Procedures
             16.2 Research Reports
         17 DRYING IN THE CONTEXT OF THE OVERALL PROCESS
             17.1 Introduction
             17.2 The overall solids process flowsheet
                 17.2.1 Conceptual design of processes
                 17.2.2 Processing steps in a typical flowsheet
             17.3 Particle formation and product properties
             17.4 Modelling the overall process
                 17.4.1 Refining the product specification
                 17.4.2 Particle size
                 17.4.3 Energy
             17.5 Overall process effects in troubleshooting

Volume DRY I   Part 1 Introduction.

This part defines the drying process and also reviews the drying manual volumes available throughout the field of drying technology and explains how to use them to best effect. It was issued in 1993.


Volume DRY I   Part 2 Drying fundamentals.

This part states the fundamental definitions used in drying and covers the underlying science in depth, including the following:

  • moisture in gases (psychrometry) and moisture in materials
  • stages of drying, mass transfer, drying kinetics and equilibria
  • physical, chemical and biological properties
  • heat transfer by conduction, convection, radiation and dielectric heating
  • generic heat and mass balances.

Section 2 describes how moisture is contained in materials. The various definitions of moisture content (wet and dry basis) and the binding mechanisms between moisture and solid are explained. Likewise, Section 3 covers moisture in gases, otherwise known as psychrometry. Humidity, saturation, wet bulb and dewpoint temperatures are defined and explained and the use of psychrometric charts is described.

Section 4 explains what factors regulate the overall drying process. The relationships between moisture content, drying rate and time are described and illustrated by means of drying curves. The section also categorises the various stages of drying and the fundamental mechanisms involved.

Section 5 covers the process of heat transfer to the solids to carry out evaporation, by convection, conduction, radiation and dielectric heating; the relevant correlations for heat transfer to single particles, sheets and beds are listed. Correspondingly, Section 6 describes mass transfer processes within the solids and the gas. Theoretical models for drying kinetics are briefly reviewed and practical representations such as the characteristic drying curve are explained. Section 7 covers the equilibria set up between moisture in the solids and vapour in the gas, and shows the effect of temperature and humidity on equilibrium moisture content.

Section 8 gives in detail the heat and mass balances around generic dryers, including convective, contact and vacuum units, and noting the effect of gas recycle, direct-fired burners and other refinements. Section 9 defines the physical properties of gas, solid and solvent and methods for their calculation. Heat capacity, enthalpy, dewpoint, psychrometric constants and diffusion coefficients are included. does likewise for materials handling, thermal and chemical properties.

The Part concludes with a list of useful additional sources and textbooks on drying, a comprehensive reference list and an explanation of the SPS standard nomenclature. The Appendices contain additional psychrometric charts and a list of conversion factors between SI and Imperial units for all parameters used in drying.


Volume DRY I   Part 3 Industrial drying practice.

This part covers, in general terms, the important features of actual dryers, and shows how the fundamentals discussed in Part 2 apply in real industrial situations. It includes the following;

  • Types of industrial dryers and their classification
  • Market data on the use of the different dryers in industry
  • Process configurations; detailed heat and mass balances
  • Preliminary dryer selection and preliminary dryer design
  • Dryer ancillaries and operations and product quality.

Industrially available dryers are classified in Section 2 in terms of the basic form of equipment (e.g. trays, fluidised beds, rotary dryers). All significant types of dryer are described and illustrated by line drawings and, in some cases, photographs. Flowsheet features, such as gas recycle, and novel dryers are mentioned.

Section 3, on market data, lists the different industries in which dryers are used, with details of typical processing duties and the types of dryers used for them. Energy use statistics for the UK are also included.

Section 4 is a very brief outline of the procedures used in selecting a dryer for a new application (the full method is in Manual Volume DRY II Part 1). Some consideration of how the dryer fits into the overall flowsheet is included.

Preliminary dryer design is covered in Section 5. This gives an outline of the basic methods for setting up heat and mass balances, use of psychrometric charts for calculating dryer inlet and outlet conditions and required air flow, and other rough initial sizing procedures. An outline of the principles of the main methods for detailed dryer design is also included.

Section 6 is on Dryer Operations, reviewing topics such as safety, control and instrumentation, troubleshooting and energy considerations. The discussion is in general terms; specific aspects are covered in the Manual Volumes on individual dryer types.

Section 7 covers costs and economics. The main factors governing capital and operating costs are noted, and scaling factors are provided for historical cost data.

Section 8 is an outline of product quality considerations, covering: particle size considerations, product morphology, bulk density, powder stickiness, reconstitution, odour and secondary volatiles, and heat sensitivity.


DRY I Part 4: Technological Update

The Drying Technological Update, released in 2004, is a comprehensive review of developments in theory and practice over the last 5-10 years, bringing the Drying technical area of the Process Manual fully up to date. It follows a similar structure to the Drying Manual itself, with most sections relating directly to a specific Process Manual volume.

Section 2 covers advances in drying fundamentals, especially in humidity and psychrometry.

Section 3 is a new review of the various drying software programs available, with descriptions of all the Aspen Process Tools covering drying.

Section 4 is an overview of the advances in drying equipment, including novel dryers introduced in the last 10 years, and industrial sectors in which notable developments have taken place.

Section 5 is a major update of dryer design procedures, which have been much better systematised and classified in recent years, enabling a more effective breakdown between generic and dryer-specific methods. Particularly important advances have been made on batch dryers.

Section 6 notes advances in techniques for dryer selection, particularly practical experience of applying the techniques recommended in DRY 2 Part 1, and short-cut methods which have been developed as a result.

Sections 7 to 12 cover new dryers and theoretical developments which apply to specific types of dryer. Examples of significant developments include analysis of fluidised bed dryers, particle motion in rotary dryers, drying in cyclones and computational fluid dynamics (CFD), especially for spray dryers.

Section 13 reviews developments in knowledge on drying kinetics and equilibria, and Section 14 looks at product quality aspects such as stickiness and polymorphism.

Section 15 covers dryer operations, including safety, control and instrumentation, and troubleshooting.

Section 16 lists and briefly reviews the Recommended Procedures and Research Reports.

Section 17 looks at the dryer in the context of the overall process, an important new field of analysis which has largely developed since the late 1990's, with close links to General Solids Processing (Mini-Manual) Volume 5. A comprehensive reference list of approximately 150 recent papers and publications is also included.