Types of Industrial Process Analyzers

1. TYPES OF PROCESS ANALYZERS

2. Analyzers – auto-analyzers Allows a sample stream to flow from the process equipment into an analyzer, sometimes conditioning the sample stream in between such as reducing pressure or changing the sample temperature.

3. Destructive and Non-destructive Analysis

4. Online vs. Inline Analysis

5. TUNABLE DIODE LAZER ANALYZERS SPECTROSCOPY (TDLAS) a technique for measuring the concentration of certain species such as methane, water vapor and many more, in a gaseous mixture using tunable diode lasers and laser absorption spectrometry Can achieve very low detection limits (of the order of ppb )  also possible to determine the temperature, pressure, velocity and mass flux of the gas under observation

6. Group IV-VI semiconductor material lasers Operate in 3 – 30 um spectral range A basic TDLAS setup consists of: tunable diode laser light source, transmitting (i.e. beam shaping) optics, optically accessible absorbing medium, receiving optics and detector/s

7. OXYGEN ANALYZERS ( Lambda Analyzers) an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analyzed Zirconia oxygen analyzer (ordinarily operate at a high temperature close to 800°C) Paramagnetic oxygen analyzer

8. Principle ( Zirconia Oxygen Analyzers) Reference gas on one side and sample gas on the other side O xygen ions move from the side with the highest concentration of oxygen to that with the lowest concentration. The movement of ions generates an EMF (Electro Motive Force) which can be measured to determine the oxygen content.

9. the EMF varies depending on the temperature of the zirconia sensor and the oxygen concentration of the reference gas (PR), in the actual device. the zirconia sensor is placed in a constant temperature oven air is generally used as the reference gas

10. Limitations Flammable gases cannot be used Sensor degradation occurs if corrosive gas ( fluorine-based gases, chlorine-based gases, sulfate-based gases )is measured In general, these analyzers cannot be used with closed loops (circulating systems) unless they are specially designed for that purpose. The sensor may be damaged by excess pressure.

11. Paramagnetic Oxygen Analyzers Magnetic susceptibility is a measure of the intensity of the magnetization of a substance when it is placed in a magnetic field

12. Limitations The difference in magnetic susceptibility between the dumbbell and the gas sample is very subtle for low oxygen concentrations, this method is used only when measuring percent levels of oxygen and not for trace levels

13. INFRA-RED GAS ANALYZER Gas detector doesn't directly interact with the gas Gas molecules only interact with a light beam Non-destructive analysis

14. Methods used for Detection

15. Structure and Operation

16. DUST MONITORING SYSTEMS Two basic methods of dust emission reporting

17. Mass concentration

18. Drawbacks A simple measurement becomes a complex measurement Cost of measuring the gas normalization parameters is greater than the cost of the primary dust measurement Schedule A processes: normalization data is already available as part of the gas analysis requirements Schedule B processes: which are only required to measure dust, the problem becomes severe

19. Mass Flow

20. Operating Principle (Grimm Aerosol DMS#365)

21. GAS CHROMATOGRAPHY used to separate organic compounds that are volatile consists of: a flowing mobile phase, an injection port, a separation column containing the stationary phase, a detector, and a data recording system .

22. P rinciple

23. Temperature Dependence of Partitioning Behavior A gas chromatography oven Partitioning behavior is depend ent on temperature the separation column is usually contained in a thermostat-controlled oven Separating components with a wide range of boiling points is accomplished by starting at a low oven temperature and increasing the temperature over time to elute the high-boiling point components

24. GC Detectors Separated components of the mixture must be detected as they exit the GC column Thermal-conduc. (TCD) and flame ionization (FID) detectors - two most common detectors on commercial GCs.

25. Thermal Conductivity Detector (TCD) Also known as Katharometer Bulk property detector and chemical specific detector Non-specific and non-destructive Universal detector – responds to all compounds

26. Limitations Less sensitive than other detectors Has a larger dead volume Cannot operate below 150 C temperature set Chemically active compounds may damage the filament

27. Flame Ionization Detector (FID) Measures the concentration of organic species in a gas stream Most sensitive gas chromatographic detector Has a low detection limit in the picogram or femtogram range Has a linear range of 6 to 7 orders of magnitude

28. Operating Principle

29. Detector Construction

30. Operation

31. Advantages Relatively inexpensive to acquire and operate Low maintenance requirements apart from cleaning and replacing of the FID jet Rugged construction Extensive linear and detection range

32. Limitations Cannot differentiate between organic compounds Cannot detect non-organic substances Presence of heteroatoms and oxygenates lower the response factor Carbon monoxide and carbon dioxide cannot be detected without a methanizer (bed of Ni catalyst used to reduce CO and CO 2 to methane) Destructive analysis – all components passing through the flame are oxidized

33. pH ANALYZERS pH is a measure of the acidity or alkalinity of water pH is defined as the negative logarithm of hydrogen ion activity ( a H + ) in water In practice, negative log of hydrogen ion concentration [H + ] is used

34. Electrode Chain pH Analyzer Two electrode setup – indicator electrode and reference electrode Measures the potential between reference electrode dipped in a solution of known pH and the indicator electrode

35. Electrode Construction

36. pH Meter Measures the potential difference between the electrodes and converts it to a display of pH

37. Buffer Solutions and Calibration Calibration is done using solutions which Have a precisely known pH value Are relatively insensitive to contamination from acidic and alkaline species (i.e. buffer solutions) Two different buffers are used for calibration which indicate electrode sensitivity

38. CONDUCTIVITY ANALYZERS Conductivity of a solution depends on: concentration of ions mobility of ions valence no. of ions temperature Two types of conductivity measurements: contacting inductive

39. Contacting Conductivity Two metal electrodes in contact with the solution are used Alternating current is applied at optimal frequency to the electrodes and output voltage is measured Cell constant – ratio of distance b/w electrodes to area of the electrodes Conductance of solution – input current / output voltage

40. Factors Influencing Measurement Polarization and Contamination of Electrode Surface – accumulation of ionic species near the surface and chemical reaction on the surface Field Effects – any interference with the field lines causes an error in signal measurement

41. Inductive Measurement Toroidal or electrode-less conductivity measure Two wire wound metal toroids enclosed on a corrosion resistant plastic body Ideal for measuring solutions having high conductivity Can tolerate high levels of fouling by suspended solids Does not come into contact with the electrolyte

42. Temperature and Conductivity Increasing the temperature of an electrolyte solution increases the conductivity 1.5% to 5% increase per degree C Conductivity readings are commonly corrected at a reference temperature, commonly 25 C Correction algorithms need to be applied Linear temperature coefficient high purity water or dilute sodium chloride high conductivity or dilute HCl

43. Linear Temperature Coefficient C 25 – conductivity at 25 C C t – conductivity at T C - linear temperature coefficient

44. High Purity Water (dilute NaCl ) Correction Assumes that the sample is pure water contaminated with NaCl Measured conductivity is the sum of conductivity of pure water and the conductivity from Na + and Cl - ions

45. Cation Conductivity (dilute HCl ) Correction Used in steam electric power industry Assumes the sample is pure water contaminated with HCl Contribution of water to the overall conductivity depends on the total amount of acid present