ABSTRACT
Introduction 1484 Mechanical Aeration 1484
Process Configurations 1484 Aerator Control Strategies 1485 Aeration Diffusers 1488 Aeration Blowers 1489 Air Distribution Control Valves 1493
Measurement of Do Concentration 1495 Galvanic Cell 1495 Polarographic Cell 1496 Galvanic and Polarographic Cell
Limitations 1496 Luminescent DO Sensors 1496
Miscellaneous Field Instruments 1497 Control of Diffused Aeration 1497
Parallel and Cascade Control of Blowers 1497 Aeration System Control 1498
Nitrogen Profile Analyzers for Wastewater 1503 Nitrogen Profile Analyzers 1503 Mechanical Aerator Control Application 1503 Diffused Aeration Control Application 1503
Acknowledgments 1505 References 1506
8.2 AIRHANDLER AND BUILDING CONDITIONING CONTROLS 1507
Introduction 1507 The Airhandler 1507
Airhandler Components 1508
Operating Mode Selection 1509 Fan Controls 1510 Temperature Controls 1512 Humidity Controls 1516 Outdoor Air Controls 1517
Optimizing Strategies 1519 Temperature Optimization in the Winter 1519 Temperature Optimization in the Summer 1520 AutoBalancing of Buildings 1521 Start-Up Algorithm 1522 Normal Algorithm for VAV Throttling 1522 Optimization of Air Supply Pressure and
Temperature 1523 Elimination of Chimney Effects 1524 Conclusions 1525 References 1526 Bibliography 1527
8.3 BATCH CONTROL DESCRIPTION, TERMINOLOGY, AND STANDARD S88 1528
Feature Summary 1528 Batch Process Classification 1528
Recipe Point of View 1528 Equipment Point of View 1529 Product Point of View 1529
Batch Automation 1530 Process/Product Management 1530 Production Management 1530 Batch Management 1534 Unit Supervision 1535
Process Control 1536 Safety Interlocking 1537
Engineering 1537 Conclusions 1541 References 1541 Bibliography 1541
8.4 BATCH PROCESSES AND THEIR AUTOMATION 1544
Introduction 1544 Batch Control Standards 1544
Part 1: Models and Terminology 1544 Part 2: Data Structures and Language
Guidelines 1545 Part 3: General and Site Recipes 1545 Part 4: Production Records 1546 The Benefits of Standards 1546
Definition of Batch Terms 1547 Models 1547
Physical Model 1547 Control Activity Model 1548 Procedure Model 1548
Batch Process Cell 1548 Physical Structure of a Plant 1548
Equipment for Batch Automation 1549 Batch Control Functions 1549
Interlock Functions 1549 Regulatory Control 1550 Discrete Control 1550 Sequential Control 1551 Unit, Batch, and Recipe Management 1551
From Analysis to Implementation 1552 Methods of Analysis 1553 Project Application Specification 1553
Reliability and Availability 1554 Control System Selection 1556 Acronyms 1557 References 1557 Bibliography 1557
8.5 BLENDING AND RATIO CONTROLS 1558
Introduction 1559 Blending Methods 1559
Rate Blending 1561 Totalizing Blending 1561 Optimizing Blending 1561
Analog Blending 1562 Mechanical Ratio Control 1563 Pneumatic Ratio Control 1564 Electronic Ratio Control 1564
Ratio Dial Setting 1566 Scaling Procedures 1566
Multiplying and Dividing 1566
Scaling a Multiplier 1566 Scaling a Heat-Transfer Calculation 1567
Ratio Controller Tuning 1568 Digital Blending System 1568 Trends in Blending Systems 1570
Application Examples 1570 Conclusions 1571 References 1571 Bibliography 1571
8.6 BOILER CONTROL AND OPTIMIZATION 1572
Introduction 1572 The Boiler 1573
Efficiency 1573 Equipment 1574 The Role of Sensors 1574 Safety Interlocks 1577 Soot Blowers 1580 Boiler Dynamics 1581 Air/Fuel Ratio Controls 1581
Basic Boiler Controls 1583 Boiler-Pressure and Firing Rate Controls 1583 Fuel Controls 1589 Air flow Measurement and Control 1594 Furnace Draft Control 1595 Air/Fuel Ratio 1596 Feedwater and Drum-Level Control 1599 Steam Temperature Control 1604 Flue-Gas Temperature 1606 Integration of Loops 1606
Pollution Control 1606 NOx Control 1607 SO2 Control 1608
Optimization of Boilers 1610 Excess Air Optimization 1610 Flue-Gas Temperature 1618 Fuel Savings through Optimization 1619 Steam Pressure Optimization 1621 Steam Temperature Optimization 1622 Water Side Optimization 1623 Load Allocation-Based Optimization 1623 Soot Blowing Optimization 1625 Model-Based Boiler Optimization 1627
Conclusions 1629 Acknowledgments 1629 References 1629 bibliography 1630
8.7 CENTRIFUGE CONTROLS 1632
Centrifuge Types 1632 Laboratory Centrifuges 1633
Industrial Centrifuges 1633
Sedimentation Centrifuges 1633 Filtration Centrifuges 1637
Conclusions 1639 Bibliography 1639
8.8 CHEMICAL REACTORS: BATCH SEQUENCING 1640
Introduction 1640 Batch Control Characteristics 1640 Batch Control Standards 1641
Standard Terminology 1641 Batch Reactor Control 1642
Control Concepts 1642 Recipe Types 1643 Programming Concepts 1644
Sequencing Logic Controls 1645 Recipe Procedures 1646 Procedure Function Chart Execution 1647 Equipment Control Sequence Logic 1647 Time-Sequence Diagrams 1647
Engineering a Batch Control Strategy 1649 Preparatory Steps 1649 Equipment-Related Requirements 1649 Process Sequencing and Supervision 1651 Exception Handling and Reporting 1651 Implementation 1651 Batch Charging 1652
Unit Operations Controllers 1652 Reactor Unit Controller 1653
Jacket Equipment Module 1653 Recipe Charging Module 1656 Stripping or Distillation Module 1656 Cleaning and Interting Modules 1657 Recipe Controls 1657 Equipment Phases 1658 Component or Device Control 1659
Conclusions 1662 References 1662 Bibliography 1662
8.9 CHEMICAL REACTORS: BASIC CONTROL STRATEGIES 1664
Introduction 1664 Reactor Designs and Characteristics 1664
Reaction Rates and Kinetics 1665 Reactor Time Constants 1666
Temperature Control 1667 Cascade Control 1668 Pressure-Compensated Temperature Control
1673 Model-Based Temperature Control 1675
Initial Heat-Up 1676 The Batch Unit 1677
Dual-Mode Controller 1677 Rate of Temperature Rise Constraint 1678 Model-Based Heat-Up Control 1679
Special and Optimizing Strategies 1680 Maximized Production by Constraint
Optimization 1680 Heat Release Control 1677 Stripping and Refluxing Controls 1682 Constant Reaction Rate 1682
Endpoint Detection 1683 Residence Time Control 1686 Analyzers for Endpoint Detection 1686 Product Quality Control 1687
Pressure Control 1688 Vacuum Control 1689 Vacuum Stripping 1689
Reactor Safety 1689 Runaway Reactions 1691 Glass Lining Protection 1691 Multiple Sensors 1692 Instrument Reliability 1693
Conclusions 1694 References 1694 Bibliography 1695
8.10 CHEMICAL REACTORS: CONTROL AND OPTIMIZATION 1697
Introduction 1697 Objectives 1697
Safety 1697 Maximizing Yield 1697 The Catalyst 1697
Chemical Reaction Kinetics 1698 Batch Reactions 1698 Continuous Plug-Flow Reactors 1698 Continuous Back-Mixed Reactors 1699 Effect of Temperature 1699
Exothermic Reactor Stability 1700 Steady-State Stability 1700 Unstable but Controllable 1701 Uncontrollable Reactors 1701
Temperature Control 1701 Measuring Temperature 1701 Manipulating Coolant Flow 1702 Tempering Loops 1702 Valve Selection 1703 Cascade Control 1703 Batch Reactor Start-Up 1704
Material Balance Control 1706 Stoichiometry 1706 Controlling Inventory 1706 Reactor Dynamics 1707 Batch End-Point Control 1707
Reactor Optimization 1708 Maximizing Production 1708 Supplemental Cooling 1709
References 1710 Bibliography 1710
8.11 CHEMICAL REACTORS: SIMULATION AND MODELING 1711
Introduction 1711 Model Building 1711
Simulation 1711 Control System Simulation 1712 Digital Control Simulation 1712 Control Valve Simulation 1713
Reactor Models 1713 Reaction Kinetics 1713 Perfectly Mixed Flow Reactor 1714 Plug Flow Reactor 1716 Nonideal Flow 1717 Heterogeneous Reactors 1718 Catalytic Reactors 1718
Conclusions 1718 Bibliography 1719
8.12 CHILLER CONTROL 1720
Introduction 1720 The Heat Pump 1720 Nomenclature 1720
The Cooling Process 1721 Coefficient of Performance 1721 Refrigerants and Heat Transfer Fluids 1722
Refrigerator and Chiller Designs 1723 Small Industrial Refrigerators 1723 Industrial Chillers 1725
Chilled Water Piping Configurations 1726 Adding Storage 1727
Conclusions 1728 References 1728 Bibliography 1728
8.13 CHILLER OPTIMIZATION 1729
Introduction 1729 The Total Cooling System 1729 Optimizing Mechanical Refrigeration
Systems 1730 Minimizing the Operating Cost 1731 Chilled Water Supply Temperature
Optimization 1732
Chilled Water Return Temperature Optimization 1733
Cooling Tower Supply Temperature Optimization 1735
Cooling Tower Return Temperature Optimization 1735
Heat Recovery Optimization 1736 Optimization by Operating Mode Selection 1737
Artificial Heat Sources 1737 Optimization by System Reconfiguration 1738
Indirect Free Cooling by Thermosiphon 1739 Indirect Free Cooling by Heat Exchanger 1740 Direct Free Cooling 1741 Operating Mode Reconfiguration 1742
Responsiveness and Prioritizing 1742 More Responsive Control 1742 Water Distribution Optimization 1743
Optimizing Storage and Load Allocation 1744 Optimized Storage 1744 Optimized Load Allocation 1745
Optimization of Special Chillers 1745 Optimized Commercial Chillers 1745 Multistage Chillers 1748 Optimized Control of Multiple Users 1749
Retrofit Optimization 1750 Surge Protection 1750 Low Evaporator Temperature 1750 Economizer and Steam Governor 1750
Conclusions 1751 References 1752 Bibliography 1752
8.14 CLEAN-ROOM CONTROLS AND OPTIMIZATION 1753
Introduction 1753 Semiconductor Manufacturing 1753
Subzone Optimization 1753 Optimization of the Zones 1756 Plantwide Optimization 1757
Conclusions 1761 Bibliography 1761
8.15 COMPRESSOR CONTROL AND OPTIMIZATION 1763
Introduction 1763 Centrifugal Compressors 1764
The Compression Process 1764 Characteristic Curves 1764 Compressor Throttling 1765 Surge Control 1768 Override Controls 1776 Optimized Load-Following 1777 Interaction and Decoupling 1778
Multiple Compressor Systems 1780 Multi-Inlet Compressor Control 1782 Installation 1782
Rotary Compressors, Blowers 1784 Reciprocating Compressors 1784
On/Off Control 1785 Constant-Speed Unloading 1785 The Stand-Alone Air Compressor 1786
Conclusions 1792 References 1792 Bibliography 1792
8.16 COOLING TOWER CONTROL 1794
Introduction 1794 Definitions 1794 The Cooling Process 1797 Mechanical Draft Cooling Towers 1798
Characteristic Curves 1798 Controls 1799
Load Controls 1799 Operating Interlocks 1799 Safety Interlocks 1800
Evaporative Condensers 1801 Secondary Controls 1801
Winter Operation 1801 Blowdown Controls 1802 Miscellaneous Controls 1802
Conclusions 1803 References 1803 Bibliography 1803
8.17 COOLING TOWER OPTIMIZATION 1805
Introduction 1805 Minimizing Operating Cost 1806
The Optimum Approach 1806 Cost Curves 1806 Supply Temperature Optimization 1807 Return Temperature Optimization 1807 Benefits of Optimization 1808 Starting Additional Pumps 1808 Return Water Distribution and Balancing 1808
Conclusions 1809 References 1809 Bibliography 1810
8.18 CRYSTALLIZER CONTROLS 1811
Introduction 1811 The Crystallization Process 1811
Crystal Size Distribution 1812 Degrees of Freedom 1812
Evaporative Crystallizers 1813 Indirectly Heated Crystallizers 1813 Advanced Controls 1814 Draft-Tube Baffle Crystallizer 1814 Multiple-Effect Operation 1814 Submerged-Combustion Crystallizers 1815
Cooling Crystallizers 1816 Controlled-Growth Magma Crystallizers 1816 Classifying Crystallizers 1816 Direct-Contact Crystallizers 1817
Vacuum Crystallizers 1817 Reaction Crystallizers 1818 Auxiliary Equipment 1819 Conclusions 1819 Bibliography 1819
8.19 DISTILLATION: BASIC CONTROLS 1820
Introduction 1820 General Considerations 1820
Distillation Equipment 1821 The Column 1821 Condensers 1823 Reboilers 1823 Interheaters/Intercoolers 1824 Column Variables 1824
Modeling and Control Equations 1825 Steady-State Model 1825 Dynamic Model 1827 Separation Equations 1828 Scaling 1828
Multiple Component Distillation 1830 Columns with Sidedraw 1831 Multiproduct Fractionators 1831 Superfractionators 1832 Batch Distillation 1832
Control Objectives and Strategies 1833 Alternative Control Strategies 1834
Control Loop Interaction 1834 Product Quality Control 1836
Inferring Composition from Temperature 1836 Control by Analyzers 1837
Pressure Control 1842 Liquid Distillate and Inerts 1842 Vapor Distillate and Inerts 1843 Liquid Distillate with Negligible Inerts 1843 Vacuum Systems 1845 Vapor Recompression 1846
Feed Controls 1847 Feed Flow Control 1847 Variable Column Feed 1847 Feed Temperature Control 1848
Feedforward Controls 1848 Conclusions 1849
References 1849 Bibliography 1850
8.20 DISTILLATION: CALCULATIONS OF RELATIVE GAINS 1855
Introduction 1855 Rga for Distillation 1855
Two-by-Two Subsets 1855 Choice of Manipulated Variables 1856
Column Model 1857 Material Balance 1857 Separation 1857 Operating Curves 1857
Relative Gain Calculations 1858 Slope Calculations 1858 Table of Relative Gains 1859 Interpreting the Results 1859
Sidestream Columns 1860 Pasteurization Columns 1860 Heavy-Ends Columns 1860 Small Sidestreams 1860
Open-Loop Gains in Terms of Relative Gains 1861 Reducing Matrix Models to 2 × 2 Subsets 1861 Simplified Model for Separation 1862 Formulas for Relative Gain 1863 Example 1 1863 Open-Loop Gains 1864 Example 2 1864
Conclusions 1864 Nomenclature 1864 Greek Letters 1865 References 1865 Bibliography 1865
8.21 DISTILLATION: OPTIMIZATION AND ADVANCED CONTROLS 1866
Introduction 1866 Definitions 1866
Advanced Process Control 1867 Model-Based Control 1868 Multivariable Control 1869 Dynamic Matrix Control 1870 Artificial Neural Networks 1870
Siso Control Advances 1872 Process Model 1873
Feedforward Systems 1875 Flow Control of Distillate 1876 Flow Control of Bottoms 1877 Constant Separation 1877 Maximum Recovery 1878
Composition Control of Two Products 1879 Two Products with Interaction 1880 Feed Composition Compensation 1881
Supervisory Control 1882 The Total Model 1883 Suboptimization 1883 Local Optimum Variables 1886
Optimization 1890 If Product Prices are Unknown 1890 If Products Prices are Known 1891 Optimizing Policies 1891 Operating Constraints 1891 Limited Market and Feedstock 1892 Control Equations 1893 Top Product Having Higher Value 1893 Bottom Product More Valuable 1894 Unlimited Market and Feedstock 1896
Conclusions 1899 References 1900 Bibliography 1901 For Pre-1990 Literature,
Refer to Section 8.19 1901
8.22 DRYER CONTROLS 1904
Introduction 1904 Adiabatic Drying 1904
The Psychrometric Chart 1904 Batch Drying 1905 Dryer Model 1907
Moisture Control 1907 Moisture Analyzers 1907 Controlling Batch Dryers 1908 Lumber Kilns 1908 Continuous Fluid-Bed Dryers 1909 Direct-Fired Dryers 1910 Countercurrent Dryers 1911
Nonadiabatic Dryers 1911 References 1912 Bibliography 1912
8.23 EVAPORATOR CONTROLS 1914
Introduction 1914 Evaporator Terminology 1914
Evaporator Modeling 1915 The Steady-State Model 1915 Scaling and Normalizing 1917
Evaporator Designs 1918 Evaporator Controls 1919
Feedback Control 1919 Feedforward Control 1921 Other Load Variables 1924
Auto-Select Controls 1926 Trimming Controls 1927
Product Density Measurement 1928 Boiling-Point Rise 1929 Conductivity 1929 Differential Pressure 1929 Gamma Gauge 1930 U-Tube Densitometer 1930 Buoyancy Float 1930 Oscillating Coriolis 1930
Conclusions 1930 References 1930 Bibliography 1930
8.24 EXTRUDER CONTROLS 1932
Introduction 1932 Extruder Production Rate 1932 Polymer Types and Characteristics 1932
Components of the Extruder System 1932 Blenders 1933 Cooling System 1933 Cutters 1934 Auxiliary Equipment 1935
Extruder Types and Subsystems 1935 Single-Screw Extruders 1935 Twin-Screw Extruders 1935 Extruder Dies and Barrels 1935 Cooling Systems 1936
Sensors, Variables, and Their Control 1937 Temperature Measurement 1937 Temperature Control 1937 Pressure Measurement 1938 Pressure Control 1938 Film Thickness Control 1939
Extruder Control Systems 1940 Basic Control 1940 Advanced Control 1940 Integrated Control 1944
Conclusions 1945 References 1945 Bibliography 1945
8.25 FAN CONTROLS 1946
Introduction 1946 Fan Types 1946 Fan Controls 1946
Fan Throttling 1946 Safety Interlocks 1947 Fan Controls in HVAC Applications 1948 Parallel Fan Balancing 1949 Optimizing Multiple Fans 1949
Optimizing the Discharge Pressure 1949 Conclusions 1950 References 1950 Bibliography 1950
8.26 FUEL CELL CONTROLS 1952
Introduction 1953 Efficiency and Pollution 1953 Historical Perspective 1954 High-Temperature Designs 1954 Polymer Technology 1954
Performance and Designs 1955 Electrical Performance 1955 Functional Requirements 1955
Fuel Cell Types and Features 1956 Fuel Cells Reactions 1956 Fuel Cell Design Features 1958
Fuel Cell Controls 1958 Oxidant and Fuel Flow Metering 1959 Thermal Control 1961
Control of the Auxiliary Systems 1961 Fuel Treatment Control 1961 Exhaust Systems Controls 1963 Inverter Controls 1964 Shutdown Control Requirements 1965
Conclusions 1965 Bibliography 1965
8.27 FURNACE AND REFORMER CONTROLS 1966
Introduction 1966 General Considerations 1967
Standards Applicable to Furnace Controls 1967 The Combustion Process 1967 Safety Considerations 1968 Pollution Abatement 1971 Analyzers for Furnace Control 1975 Furnace Instrumentation 1977
Furnace Types 1979 Start-Up Heaters 1979 Fired Reboilers 1979 Process and Crude Oil Heaters, Vaporizers 1980 Firing Controls 1982 Reformer Furnaces 1983 Cracking (Pyrolysis) Furnaces 1985
Advanced Controls 1987 Feedforward Control 1987 Coil Balancing Control 1988 Cross-Limiting Firing 1989 Severity Control 1990 Model-Based Control 1990
Conclusions 1991 Standards and Guidelines 1991 Bibliography 1992
8.28 HEADER-SUPPLIED DISTRIBUTION CONTROL 1993
Introduction 1993 Terminology and Coverage 1993
Valve Position Control 1993 The Most-Open Valve 1994 Energy Savings 1995 Valve and Damper Gain 1996
Supply-Demand Matching VPC (MOV1) 1998 MOV1 Controller Algorithm 1998
Distribution Controlling VPC (MOV2) 1999 Example 2001 Failure Modes and Applications 2002
Design, Start-Up, and Maintenance 2002 Actuators and Valves 2002 Control 2002 Blowers 2002 Fault Detection and Response 2003 Start-Up 2003
Conclusions 2003 Bibliography 2003
8.29 HEAT EXCHANGER CONTROL AND OPTIMIZATION 2004
Introduction 2004 General Considerations 2004
Temperature Detection and Transmission 2004 Process Characteristics 2005 Safety 2006
Basic Controls 2007 Liquid-Liquid Heat Exchanger Controls 2007 Steam Heater Controls 2011 Condenser Controls 2015 Reboilers and Vaporizers 2017
Advanced Controls 2019 Override Controls 2019 Cascade Control 2020 Feedforward Control 2021 Model-Based Controls 2022 Multipurpose Systems 2022
Conclusions 2023 References 2024 Bibliography 2024
8.30 INERT GAS BLANKETING CONTROLS 2025
Introduction 2025 Pollution and Personnel Safety 2025
The Combustion Process 2026
Inerting 2026 Alternatives to Inerting 2026 The Combustion Triangle 2026
Inerting Control Systems 2027 Flow-Controlled Inerting 2027 Pressure-Controlled Inerting 2028 Oxygen-Controlled Inerting 2028
Component Design Considerations 2030 Do Not Use “Fail-Safe” Solenoids 2030 Purge Flow Rate Variation 2030
Conclusions 2031 References 2031 Bibliography 2031
8.31 ORP CONTROLS 2032
Introduction 2032 ORP as a Process Variable 2032
The Nernst Equation 2032 Measurement 2033 Instrumentation 2033 Calibration 2034
ORP Control 2034 Chrome Waste Treatment 2035 Cyanide Waste Treatment 2036 Sodium Hypochlorite Production 2038 Paper Pulp Bleaching 2040 Other ORP Control Systems 2041
Conclusions 2042 References 2042 Bibliography 2043
8.32 pH CONTROL 2044
Introduction 2045 Titration Curves 2045
Strong Agents 2045 Buffering 2046
The Process 2047 Vessel Design 2047 Mixing 2048 Reagent Demand 2049 Reagent Rangeability 2049 Reagent Piping 2051 Multiple Stages 2052
The Control System 2052 Measuring pH 2052 The pH Characterizer 2053 PID Tuning 2054 Self-Tuning Control 2055 Batch pH Control 2055 Feedforward Control 2055
References 2056 Bibliography 2056
8.33 POWER PLANT CONTROLS: COGENERATION AND COMBINED CYCLE 2057
Introduction 2057 Cogeneration 2057
Cogeneration with Combined Cycles 2057 Cogeneration with Internal Combustion
Engines 2058 Combined Cycles 2058
Single-Shaft Arrangements 2058 Main Equipment Blocks 2061 Auxiliary Systems 2066
Auxiliary Equipment 2067 Demineralization Plant 2067 Fuel Gas System 2068 Liquid Fuel System 2068 Closed Circuit Cooling Water 2068
Control Equipment 2069 Central Control Room 2069 Monitoring and Control Loops 2070 Steam Drum Level Control 2071 Steam Temperature Control 2072 Pegging Steam Control 2073 Condensate Preheater (Economizer) Temperature
Control 2073 Supplementary Firing Control 2074 Steam Turbine Bypass Control 2075 Load/Frequency Control 2075 Running Permissives 2076 Safety Functions and Integrity Levels 2076
Start-Ups and Shutdowns 2077 Start-Up Procedures 2077 Short-Term Planned Stop 2079 Long-Term Planned Stop 2080 Emergency Shutdown 2080
Performance Tests 2081 Conclusions 2081 Abbreviations 2082 References 2082 Bibliography 2082
8.34 PUMP CONTROLS 2084
Introduction 2084 The Process 2084
System Curves 2084 Pump Types 2087
Displacement and Centrifugal Designs 2087 Pump Design Variations 2087
Centrifugal Pumps 2087 Pump Curves 2088 Adjusting the Pump Speed 2089 Cavitation 2092 Net Positive Suction Head 2093
Water Hammer 2095 Pump Stations 2096
Positive Displacement Pumps 2098 Reciprocating Pumps 2098
Control of Pumps 2101 On/Off Control 2101 Modulating Control 2104 Multiple-Pump Controls 2106
Conclusions 2109 References 2109 Bibliography 2109
8.35 PUMP OPTIMIZATION 2110
Introduction 2110 Nomenclature 2110 Pump Equations 2110 Model-Free Optimization 2111
Valve Position-Based Optimization 2112 Optimization Alternatives 2113 Calculating the Savings 2114
Model-Based Optimization 2114 Optimization of Pump Selection 2114 Starting or Stopping Pumps 2115
Conclusions 2115 References 2115
8.36 Rolling Mill Controls 2116
Introduction 2116 Multiple Drives in Strip Manufacturing 2117
Electrical Drive Systems 2118 Eddy-Current Drive 2118 DC Static Drives 2118 AC Variable-Frequency Drives 2118 Analog Multiple-Drive Systems 2118 Digital Control Techniques 2119
Bibliography 2122
8.37 SEPARATION CONTROLS, AIR 2123
Introduction 2123 Adsorption Technology 2123
The Process 2123 Control of the Adsorption Process 2124 Vacuum Swing Adsorption 2124 Pressure Swing Adsorption 2124
Membrane Air Separation 2126 Process Description 2126 Flux and Selectivity 2126
Membrane System Sizing 2127 Cryogenic Air Separation 2127
Front-End Air Purification 2127 Cryogenic Distillation (Cold Box)
Process 2130 Cryogenic Instrumentation 2130
Severe-Service Control Valves 2130 Impulse and Sample Lines 2130 Flow Elements 2131 Temperature Measurement 2131 Process Analysis in ASU 2131 Process Control Analyzers 2132
Regulatory and Feedforward Controls 2132 Main Air Compressor Flow 2132 Stabilization of Pressure Surge 2132 Sidearm Nitrogen Control 2133 Product Purity Control 2133 Oxygen Recovery Controller 2133 Front-End Purity and Hydrocarbon
Accumulation 2134 Hydrocarbon Concentration Factor 2134
Refrigeration Controls 2134 Expander Configuration 2134 Refrigeration Balance Controller 2134 Main Heat Exchanger Control 2134
Advanced Control 2135 Characterizers to Compensate Process
Nonlinearity 2135 Operating Close to Constraints 2135
Conclusions 2136 Abbreviations 2136 References 2136 Bibliography 2136
8.38 STEAM TURBINE CONTROLS 2137
Introduction 2137 Characteristics 2137
Operating Principles 2138 Steam Turbine Efficiency 2139 Advantages and Limitations 2139
Turbine Design Configurations 2140 Application Configurations 2140 Internal Design Configurations 2141
Steam Turbine Governors 2141 The Governor Valve 2141 The Early Speed Governors 2142 Hydraulic Droop Governors 2142 Electronic Governors 2143 Advanced Governors 2143
Controls and Optimization 2144 The Basic Turbine Controller 2144 Pressure Let-Down Control 2144 Extraction Turbine Control 2146
Safety Controls 2149 Sequential Controls 2150
Conclusions 2150 Bibliography 2150
8.39 WASTEWATER TREATMENT CONTROLS 2152
Introduction 2152 General Considerations 2152 Industrial Wastewater Treatment 2152
Chemical Oxidation 2153 Cyanide Destruction Process 2153
Chemical Reduction 2156 Reduction of Hexavalent Chromium 2156 Other Reduction Processes 2157
Neutralization Controls 2157 Equalization Tanks 2157 Single Reagent Control 2159 Two Reagent Control Systems 2160 Ratio Control 2160 Cascade Control 2161 Feedforward Control 2161 Precipitation and Filtering 2163 Lime Softening 2163 Hydroxyde Precipitation 2163 Filtering 2164
Chlorination 2165 Municipal Wastewater Treatment 2166
Tertiary Wastewater Treatment 2168 Safety 2169
Cooling Water Treatment 2169 Conclusions 2170 References 2171 Bibliography 2171
8.40 WATER SUPPLY PLANT CONTROLS 2172
Introduction 2172 Conventional Water Treatment Plants 2172
Filtration Hardware and Controls 2172 PLC Configuration 2172 Transfer Pumping and Ground Storage 2175 High-Service Pumping 2176
Ozonated Water Treatment 2176 Ozone Generator Controls 2177 Ozone Flow Distribution Control 2179 Control of Ozone Destruction 2179 Ozone Generator Start-Up Sequencing 2179 PLC Hardware 2182
Reverse Osmosis-Based Water Treatment 2182 Raw Water and Pretreatment 2182 R.O. Membrane Train Controls 2184 Pumping and Post-Treatment Controls 2187 Sequence of Operation Controls 2188
Ultrafiltration-Based Water Treatment 2189 Transmembrane Pressure 2189 Control Loops 2189
PLC Implementation of PID Loops 2191 In-Line Mixer Controls 2191 Override and Selective Control 2192
Conclusions 2193 References 2193 Bibliography 2193
8.41 WELL-SUPPLIED UNDERGROUND GAS STORAGE CONTROLS 2194
Introduction 2194 The Process 2195
The Operating Modes 2195 Injection Cycle 2195 Production Cycle 2196
Modeling and Simulation 2196 General Control Considerations 2197
Sensor Selection 2197
Control Valve Selection 2197 Controller Algorithms 2197 Pressure Correction 2198
Controlling the Injection Cycle 2199 Prestart-Up Settings 2199
Start-Up Mode 2199 Operator Actions in the Start-Up Mode 2200 Normal Operating Mode 2202 Manual, Automatic, and Cascade Control
Modes 2203 Controlling Valve Pressure Drops 2203 Protecting the Compressors 2203
Controlling Production Cycle 2203 Start-Up 2204 Continuous Operation 2205 Control Modes and Loops 2205 Controlling the Wells 2205 The Total Control System 2207 Existing DCS Hardware 2207
Conclusions and Comments 2207 References 2208 Bibliography 2208
INTRODUCTION
Aeration is mostly used in wastewater treatment facilities to introduce oxygen into the wastewater. Oxygen is necessary for biological treatment of carbonaceous matter (secondary treatment) and for oxidation of ammonia into nitrite and nitrate (nitrification). The transfer of oxygen is accomplished using two basic aeration methods. One method is the use of mechanical aerators (mechanical mixing), and the other method is the delivery of air through a network of pipes and diffusers located at the bottom of treatment basins (diffused aeration).
