1. TYPES OF PROCESS ANALYZERS

2. An analyzer is an instrument or device which
conducts chemical analysis (or similar) on
samples or sample streams
• 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
Destructive Analysis: sample stream is modified by the
analyzer
• e.g. reducing the pressure, changing the sample temperature, addition of
reagents
• Sample stream cannot be returned to the process
Non-destructive Analysis: sample stream is not
substantially modified by the analyzer
• relies upon use of electromagnetic radiation, sound, and inherent
properties of materials to examine samples
• sample stream can be returned to the process

4. Online vs. Inline Analysis
Online analysis: analyzer is connected to a
process, and conducts automatic sampling
Inline analysis: a sensor can be placed in a
process vessel or stream of flowing material to
conduct the 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)
Determines oxygen concentration using the conductivity of
a zirconia ceramic cell. Zirconia ceramic cells only allow
oxygen ions to pass through at high temperatures.
• Reference gas on one side and sample
gas on the other side
• Oxygen 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
High magnetic susceptibility of oxygen
as compared to other gases allows it to
be attracted to a magnetic field
Magnetic susceptibility is a measure of the
intensity of the magnetization of a substance
when it is placed in a magnetic field

12. Focused magnetic field is
created
Nitrogen filled glass spheres are
mounted on a rotating suspension
within the field
Mirror mounted on the
suspension – detects the
displacement of the nitrogen
spheres as oxygen is attracted to
the strongest part of the field
Reflected light is directed on to a pair
of photocells – light intensity
converted to electrical signal - which
is fed to a feedback coil causing a
motor effect to keep the suspensions
in place

13. 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

14. INFRA-RED GAS ANALYZER
Measures trace gases by determining the
absorption of an emitted infrared light source
through a certain air sample
• Gas detector doesn't directly interact with the gas
• Gas molecules only interact with a light beam
• Non-destructive analysis

15. Methods used for Detection
Rise in temperature of
gas molecules
Photon detectors
(Absorption Spectrum)
Molecules resonate at
frequencies of radiation
matching with their natural
frequencies
Molecules of a specific gas
absorb radiations of
specific wavelengths
Increase in vibrations cause
an increase in temperature
of the gas
Transmitted spectrum
indicates the absorbed
wavelengths

16. Structure and Operation
The infrared light is
emitted and passes
through the sample
gas, a reference gas
with a known mixture
of the gases in
question and then
through the "detector"
chambers containing
the pure forms of the
gases in question.
When a "detector"
chamber absorbs some
of the infrared
radiation, it heats up
and expands. This
causes a rise
in pressure within the
sealed vessel that can
be detected either with
a
pressure transducer or
with a similar device.
The combination of
output voltages from
the detector chambers
from the sample gas
can then be compared
to the output voltages
from the reference
chamber.

17. DUST MONITORING SYSTEMS
Two basic methods of dust emission reporting
Mass concentration
(mg/cubic meter)
Mass flow (kg/hr)
Most commonly used
Total mass of dust
emitted per unit time
Assumes a
homogeneous mixture
of dust particles and air
Absolute measure of
dust emission

18. Mass concentration
Measurement of mass concentration depends factors that
change the volumetric characteristics of the carrier gas:
• Gas law effects: the effects of temperature and pressure.
• Dilution effects: the effects of excess air and water vapor levels.
Data normalization is required
• standard practice is to report the data as a mass per normal cubic meter
of dry gas, at a specified level of oxygen.

19. 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

20. Mass Flow
The measurement is related to mass concentration.
• Mass flow = mass concentration x volumetric flow
No normalization data is required
• Does not depend in any way on gas temperature, pressure, oxygen or water
vapor values, or on any form of dilution of the exhaust gases.
Mass flow can be directly related to the environmental impact

21. Operating Principle
(Grimm Aerosol DMS#365)
Single particle count – using light
scattering technology
Semiconductor laser as light source
Mirror reflects the scattered light beam to be
detected by a photodiode
Pulse height classifier classifies photodiode
signals in a multichannel size classifier
Counts are displayed and stored

22. 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.

23. Principle
The organic compounds are separated due to differences
in their partitioning behavior between the mobile gas
phase and the stationary phase in the column.

24. He
Injection
port
Oven
Detector
Recordercomputer
Carrier Gas
Column
Sample is injected
(using a syringe) into
the injection port.
Sample vaporizes and
is forced into the
column by the carrier
gas ( = mobile phase
which in GC is usually
helium or any other
inert gas)
Components of the
sample mixture interact
with the stationary
phase so that different
substances take
different amounts of
time to elute from the
column
The separated
components pass
through a detector.
Electronic signals,
collected over time, are
sent to the GC software,
and a chromatogram is
generated.

25. Temperature Dependence of
Partitioning Behavior
Partitioning
behavior is
dependent on
temperature
the separation
column is
usually
contained in a
thermostatcontrolled
oven
Process is similar to fractional distillation
A gas chromatography 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

27. 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.

28. Thermal Conductivity Detector (TCD)
Senses the changes in the thermal conductivity of
the column effluent with reference to a flow of
carrier gas
• Also known as Katharometer
• Bulk property detector and chemical specific
detector
• Non-specific and non-destructive
• Universal detector – responds to all compounds

29. TCD – an electrically heated filament in a
temperature controlled cell
• During elution of an analyte, thermal conductivity of
the column effluent reduces
• Filament heats up and changes resistance

30. 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

31. 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

32. Operating Principle
Ions formed during the combustion of organic
effluents in hydrogen flame is detected.
• Ion generation is directly proportional to the
concentration of organic species in the sample stream
• Presence of heteroatoms decreases the detector’s
response

33. Detector Construction
small volume chamber
gas chromatograph column capillary is directly
plumbed to the bottom of flame jet
column effluents are mixed with hydrogen and
air to be burned up in the flame jet
An electronic igniter (electrically heated
filament) lights on the flame
Charged particles created during combustion
create a current b/w the detector’s electrodes

34. Operation
positive electrode doubles as the nozzle head
where the flame is produced
negative electrode is positioned above the flame
(tubular electrode called collector plate)
ions attracted to collector, hit the plate and
induce current
current is measured with a high impedance
picoammeter and fed to an integrator
The response of the detector is determined by the number of
carbon ions hitting the detector per unit time. Thus, the
detector is sensitive to mass rather than concentration.

35. 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

36. 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 CO2 to methane)
• Destructive analysis – all components passing
through the flame are oxidized

37. pH ANALYZERS
• pH is a measure of the acidity or alkalinity of
water
• pH is defined as the negative logarithm of
hydrogen ion activity (aH+) in water
pH = -log10 aH+
• In practice, negative log of hydrogen ion
concentration [H+] is used

38. Electrode Chain pH Analyzer
Electrodes immersed in a solution form a galvanic cell due to
potential developed on both electrodes, which changes in
response to any change in pH of the solution
• 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

39. Electrode Construction

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

41. 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

42. 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

43. 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
Conductivity = Cell constant x Conductance of the Solution
Cell constant – ratio of distance b/w electrodes to area of the electrodes
Conductance of solution – input current / output voltage

44. 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

45. 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

46. Analyzer applies
an AC voltage to
the drive coil
A voltage is
induced in the
surrounding
liquid
An ionic current
flows
proportional to
the conductance
of the liquid
The ionic current
induces an
electronic
current in the
receiver coil
Electronic
current is
measured by the
analyzer

47. 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

48. Linear Temperature Coefficient
Conductivity of an electrolyte changes by about the
same percentage for every degree rise in temperature
C25 – conductivity at 25 C
Ct – conductivity at T C
- linear temperature coefficient

49. 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
Point 1 – raw
conductivity at
temp. ‘t’ degree
C
Conductivity of
pure water at ‘t’
– raw
conductivity =
conductivity of
Na+ and Cl- at ‘t’
(point 2)
conductivity of
Na+ and Cl- at ‘t’
is converted to
conductivity at
25 deg. C (point
3)
Add conductivity
of pure water at
25 deg. C corrected
conductivity
(point 4)

50. 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