Process Gas Chromatographs

Tony Waters owns Analyzer Consulting Engineers, LLC in USA and is an Elected Fellow of International Society of Automation. Since 2000, he has been a Consultant in Process Analysis assisting refiners and chemical processors to achieve optimal use of process analyzers. He has twenty-five years' experience of working in the industry before setting up his own company, Measurementation, Inc. in 1986 to manufacture process analyzer systems.

Preface xix

Contributors xxi

Acknowledgments xxvii

Part One PGC fundamentals 1

1 An introduction 3

Chromatographic separation 3

The gas chromatograph 4

The basic instrument 4

The process instrument 5

The oven 7

Temperature control 7

Temperature programming 7

The sample injection valve 8

Laboratory and online practice 8

Plug injection 8

Gas sample injection 9

Liquid sample injection 9

The column 10

The separating device 10

It takes time 10

Multiple columns 11

SCI-FILE: On Column Types 12

Introduction to SCI-FILEs 12

Two kinds of column 12

Packed columns 12

Open-tubular columns 12

The detector 13

Making the measurements 13

The chromatogram 14

Knowledge Gained 18

Did you get it? 19

Self-assessment quiz: SAQ 01 19

Student evaluation test: SET 01 20

References 21

Cited 21

Figures 22

New technical terms 22

2 Peakshape 25

How columns work 25

What happens inside the column 26

How gas and liquid interact 26

Troubleshooting tips 28

How peaks form 28

Forming an equilibrium 28

The effect of movement 30

A peak appears 31

Effect of more equilibria 33

Some conclusions 34

Identical molecules – different behavior 34

All peaks are symmetrical 35

More equilibria – narrower peaks 35

More equilibria – taller peaks 35

Retention at the apex 36

More equilibria – same retention time 36

SCI-FILE: On Solubility 36

Solubility 36

Partition 36

Distribution 37

Limitations 37

Knowledge Gained 37

Did you get it? 38

Self-assessment quiz: SAQ 02 38

Student evaluation test: SET 02 38

References 40

Figures 40

Equation 41

Symbols 41

New technical terms 41

3 Separation 43

How peaks get separated 43

A more realistic explanation 43

A challenge question 46

Significance of the air peak 47

The answer 48

Measurements from chromatograms 50

A practical task 50

Typical calculations 51

Knowledge Gained 52

Did you get it? 53

Self-assessment quiz: SAQ 03 53

Student evaluation test: SET 03 53

References 55

Figures 55

Equations 55

Symbols 55

New technical terms 55

4 Peakpatterns 57

Migration rate 57

Predictable patterns in peak position 57

Space or time 57

Spatial or temporal separation 58

Predictable patterns in peak width 59

Distance or duration 59

SCI-FILE: On Chemical Names 60

Hydrocarbons 60

Shorthand notation 61

Predictable patterns in retention 61

The doubling rule 61

Challenge question 62

A process of elimination 62

Temperature programming 64

Relative retention 66

Separation and resolution 67

Resolution 67

Predictable patterns in resolution 69

Knowledge Gained 71

Did you get it? 72

Self-assessment quiz: SAQ 04 72

Student evaluation test: SET 04 72

References 74

Figures 74

Equations 74

Symbols 74

New technical terms 74

Part Two PGC analytics 77

5 Industrial gas chromatographs 79

Process analyzers 79

Introduction to process analysis 79

The measurement of quality 80

Process gas chromatographs 81

Versatile and reliable 81

PGC development 82

The value of analysis 83

Competing technologies 84

Gas chromatograph or spectrophotometer? 84

Speed of response 86

The outlook 87

The PGC analytics unit 87

Introduction 87

Carrier gas supply system 88

Sample injection system 89

Chromatographic valves 89

Column system 89

Detectors 89

Temperature-controlled ovens 90

Knowledge Gained 90

Did you get it? 91

Self-assessment quiz: SAQ 05 91

Student evaluation test: SET 05 92

References 93

Cited 93

Table 93

Figures 93

Symbol 94

New technical terms 94

6 Carrier gas system 95

Choice of carrier gas 95

Carrier gas purpose 95

Choice of carrier gas 95

Mixed carrier gases 97

Carrier gas purity 97

Analytical effect of impurities 98

Damaging effect of impurities 100

Maintenance of gas cleaners 101

Carrier gas supply system 101

Carrier gas supply line 102

Pressure regulation 103

Mechanical pressure regulators 103

Electronic pressure controllers 104

Flow regulation 104

Measuring the carrier gas flow rates 104

Setting the flow rates 105

Optimum flow rate 106

Knowledge Gained 106

Did you get it? 107

Self-assessment quiz: SAQ 06 107

Student evaluation test: SET 06 108

References 109

Cited 109

Table 110

Figures 110

Symbols 110

New technical terms 111

7 Sample injection 113

Introduction 113

Injecting gas samples 114

Gas sample volume 114

Gas sample temperature 115

Gas sample pressure 116

Injecting liquid samples 118

Less preferred 118

Vaporizing a liquid sample 118

Liquid sample volume 119

Liquid sample temperature 120

Liquid sample pressure 121

Other techniques 122

Sample splitting 122

Remote sample injection 122

Normalization 122

SCI-FILE: On Analytic Units 123

A fable 123

Constant sample size 123

Different ratio units 124

Injected quantity 124

Conversion of units 125

Knowledge Gained 126

Did you get it? 127

Self-assessment quiz: SAQ 07 127

Student evaluation test: SET 07 128

References 130

Cited 130

Tables 130

Figures 130

Symbols 130

New technical terms 131

8 Chromatographic valves 133

Valve technology 133

Evolution 133

The strange effect of competition 134

Valve types 135

Solenoid instrument valves 135

Spool or piston valves 135

Slide valves 136

Rotary valves 139

Diaphragm valves 141

Plunger valves for liquid injection 143

Other switching techniques 145

Valve leaks 146

About leaks 146

Valve leak mitigation 148

Knowledge Gained 149

Did you get it? 151

Self-assessment quiz: SAQ 08 151

Student evaluation test: SET 08 151

References 153

Cited 153

Table 154

Figures 154

New technical terms 155

9 Column systems 157

Two fundamental issues 157

The general elution problem 157

The temperature ramp solution 158

The multiple column solution 159

The choice 160

Delayed injection 161

Four types of column system 161

Recognizing the functions performed 161

Type A: A single column 162

Type B: Multiple columns, single detector 163

Type C: Multiple detectors, single injector 164

Type D: Multiple sample injectors 166

Elemental column systems 168

Useful techniques 168

Backflush column system 168

Distribution column system 170

Heartcut column system 171

Trap-and-hold column system 173

The real power 174

Endnote 175

Knowledge Gained 176

Did you get it? 177

Self-assessment quiz: SAQ 09 177

Student evaluation test: SET 09 177

References 180

Cited 180

Table 180

Figures 180

New technical terms 181

10 Detectors 183

Introduction 183

Types of detector 183

Two measured variables 183

Concentration detectors 184

Rate-of-arrival detectors 185

Multiple detectors 186

Signal capture 186

SCI-FILE: On Detectors 187

Signal noise 187

Speed of response 187

Sensitivity 188

Thermal conductivity detector 189

TCD application 189

TCD basic function 190

TCD detection principle 191

TCD thermal elements 192

TCD electrical arrangement 194

TCD electrical improvements 194

TCD performance enhancement 195

Flame ionization detector 197

FID application 197

FID detection principle 198

FID makeup gases 199

FID sensitivity 199

FID vent arrangements 200

FID methanator 200

Flame photometric detector 202

FPD application 202

FPD detection principle 202

FPD concerns 203

Other detectors 205

Electron capture detector 205

Helium ionization detector 206

Photoionization detector 207

Pulsed discharge detector 207

Knowledge Gained 210

Did you get it? 213

Self-assessment quiz: SAQ 10 213

Student evaluation test: SET 10 214

References 216

Cited 216

Tables 217

Figures 217

Equations 217

Symbols 218

New technical terms 218

11 Temperature control 221

Need for stability 221

Sample volume 221

Retention times 221

The air-bath oven 223

Heating with air purging 223

The airless oven 225

Heating without air 225

The 2008 ABB PGC1000 227

The 2014 Rosemount Danalyzer 370XA PGC 227

The 2009 Rosemount 700XA PGC 227

The 2002 Maxum Edition II 228

Direct column heating 228

Resistive heating 228

The ABB approach 229

The Teledyne Falcon approach 230

A few cautions 231

Summary of heating methods 231

PGC standardization 231

Realities of the market 231

The applications engineering conundrum 232

MEMS technology 233

The 2002 siemens MicroSAM 234

A closing thought 234

Knowledge Gained 235

Did you get it? 236

Self-assessment quiz: SAQ 11 236

Student evaluation test: SET 11 237

References 238

Cited 238

Table 239

Figures 239

New technical terms 240

Part Three PGC control 241

12 Event scheduling 243

A sequence of actions 243

Program timing 243

Autozero 245

Atmospheric referencing 245

Sample injection 245

Step stream 246

Column switching 247

Peak gating 247

Initiate a calculation 248

Data transmission 248

Alarm notifications 248

End-of-cycle 248

Event markers 248

Calendar events 248

Timing mechanisms 249

Mechanical programmers 249

Electronic timers 249

Microprocessor control 250

The program or method 250

Control of analyzer operation 250

Temperature control 251

Pressure control 251

Peak identification 251

Fixed-time gating 252

Retention time tracking 253

Knowledge Gained 254

Did you get it? 256

Self-assessment quiz: SAQ 12 256

Student evaluation test: SET 12 256

References 258

Cited 258

Figures 258

New technical terms 259

13 Data display techniques 261

The chromatogram display 261

Detector signal 261

Digitized chromatograms 262

Chromatogram autozero 263

Peak height calibration 263

Peak area calibration 264

The bargraph display 265

The paper saver 265

The trend record 266

Analog peak processing 266

Digital signal processing 267

The minicomputer story 267

The ubiquitous microprocessor 268

A regression perhaps? 269

Central maintenance station 271

Continuous analyzer controllers 271

PGC function alarms 272

Indicators 272

Alarm notifications 272

Knowledge Gained 273

Did you get it? 274

Self-assessment quiz: SAQ13 274

Student evaluation questions: SET-13 275

References 276

Cited 276

Table 277

Figures 278

New technical terms 278

14 Peak area integration 279

Digital chromatogram processing 279

Pulse frequency digitization 279

Signal noise measurement 281

Signal noise reduction 281

Quantifying the analyte peaks 283

Forced integration 284

Slope detection 285

Errors from baseline disturbances 286

Troubleshooting aids 287

Measuring overlapping peaks 287

Avoiding the problem 287

Tackling the problem 288

Perpendicular drop method 289

Don’t integrate to a valley point 290

Angular drop or allocated area 292

Tangent skim method 292

Effect of setup mistakes 293

Knowledge Gained 294

Did you get it? 296

Self-assessment quiz: SAQ 14 296

Student evaluation test: SET 14 296

References 298

Cited 298

Figures 299

New technical terms 299

15 Calibration 301

Measurement principles 301

Terminology 301

Random error 302

Systematic error 302

Uncertainty 302

Accurate calibration 304

Calibration and validation 304

Calibration methods 307

External standard method 307

Normalization 308

Calibrating a composite peak 309

Grab sample calibration 310

Internal standard method 310

Area percentage method 311

SCI-FILE: On Response Factors 312

External standard 312

Normalization 312

Internal standard 312

Area percentage 313

Knowledge Gained 313

Did you get it? 314

Self-assessment quiz: SAQ 15 314

Student evaluation test: SET 15 314

References 317

Cited 317

Figure 317

Equations 317

Symbols 318

New technical terms 318

Answers to self-assessment questions 319

Bibliography 329

Glossary 331

Index 367