Intro4u2u

Briefly I wil explain you the purpose of analysers:
Process Analysers are used to measure one or more components of the fluid it analyses. The instruments used in such analysis are called analytical instruments or anaysers; They can be used for continuous on-line and batch measurements
Examples are
1) To determine component gases such as CO, CO2, H2, O2, Butane, methane, H2S, Nitric oxide, chlorine etc content in gases.
2) To determine electrolytic conductivity of solutions, pH of a solution etc
3) To determine the density of fluid.
Purpose: The presence of such gas component may be or may not be desirable. After analysis, you can use processes to eliminate them or to control them to be within limits or to choose proper material to handle the presence of such components in fluid (if present in abnormal quantity). This will ensure that the end product you get meets the quality requirements of the purchaser
Sampling systems or samplers:
This systems will have to be installed upstream of analysers so that the sample is conditioned and transported to analyser in such a way it is acceptable to analysers. It may have also sequential controls between for multi sample analysis. Sometimes, the pressure and temp. have to be brought down before the sampling fluid enters the analyser and this is done in this sampling systems
In most cases, sampling systems have to be purchased along with the analysers.

Characteristic Benefit
Fast Speed of Response
• Minimize time on sample gas
• Most productive use of operator and instrument time
• Reduce emissions, in accordance with ISO environmental issues
• Reduce personal hazard to operator
• Provides ‘real time’ data for on-line operations – significant aid to
process control and fault diagnosis
Repeatability
• The analyzer should provide the ability to perform multiple tests
on the same sample, given constant sampling conditions and
methodology, and achieve consistent results within the stated
operating tolerances
• Good repeatability leads to increased operator confidence
• Increased validity of data
• Aids productivity in the commissioning of an instrument or on reactivation
following Plant interruption
Thermal Stability
• Any hygrometer, to produce accurate data, should be capable of
sampling in a wide range of ambient temperatures, with gases of
different temperatures
• The resistance of the analyzer to fluctuations in temperature
greatly simplifies the installation
• The reliability of, and confidence in, all data collected is vastly
increased
Heated Sensor
• A heated Sensor offers a very robust level of performance, as it
cannot easily be saturated or damaged by exposure to ambient
air / gases during the connection / disconnection process
• The heated Sensor provides a very high level of calibration
traceability, thereby greatly improving the validity of the sample
data
Flow Independence
• The hygrometer ought not to require a fixed flow level for each
measurement
• Productivity is aided through greater ease of operation
• Sampling set-up and methodology are simplified, hence reducing
the costs of ongoing service and maintenance
• Provides an additional level of diagnostic capability under Plant
equilibrium conditions
Flow Requirement
• A low flow level helps to minimize emissions of hazardous and /
or wastage of expensive sample gases
• Aids the user with regard to ISO emissions requirements and
Health & Safety requirements
• Low flow requires a less complex sampling methodology and
installation
• Low flow usage extends the operational life of the instrument and
increases the mean Service interval
Atmospheric Pressure
• A hygrometer should be calibrated, and operated, at atmospheric
pressure.
• A simpler methodology helps reduce data errors associated with
user sampling methodology
• Provides the only level of traceability to Internationally accepted
Standards
• Simple installation and methodology help to simplify the diagnosis
of any System or process faults
Contamination Resistance
• The instrument should display a high resistance to light volatile
contaminants
• The recovery from exposure to such contaminants should be fast
• A high resistance to contamination significantly increases the
validity of the collected data
Sensor Stability
• On a gas stream of a known moisture concentration, the analyzer
should show resistance to the effects of drift and hysteresis
• Provides higher significance of data
• Improved user confidence in data
• Helps negate cost penalties associated with inaccurate data and
associated Plant disruption
Specificity of Sample Gas
• The instrument should be capable of achieving a high level of
performance on a number of different sample gases
• The versatility of the analyzer will have a direct bearing on the
level of productivity it provides to the user
Self Diagnosis
• The instrument should provide the capability to verify
measurements while on-line.
• The user ought to be able to confirm both the functionality of the
Sensor and the electronics of the hygrometer.
• Such diagnostic features provide significant levels of user
confidence that the analyzer is functioning correctly, particularly in
on-line applications where stable moisture levels may be
experienced for extended periods of time
High Accuracy
• The hygrometer should have a traceable calibration from an
independent, accredited laboratory
• Helps in the reduction of commercial interfaces at the point of
supply / receipt
• Reduces uncertainty of data
• Increases operator confidence
• Increases flexibility and correlation of data
• Simplifies process control and management deliberation
• High accuracy in one measurement can help in determining the
criticality of other parameters
Inertness of Sensor
• The moisture Sensor should be chemically inert, and should not
degrade with time given ‘clean’ operating conditions
• The inert Sensor will not contribute contamination either to the
sample gas stream or the application process
• An inert Sensor will provide a long operating life for the analyzer
and will mean that the hygrometer will be capable of operating on
a variety of different applications
Warm-up Time
• The analyzer should be fast to respond on initial start-up and in
cases of recovery from power interruption
• The fast warm-up of the instrument in these events is critical to
the productivity of the analyzer and the audit trail of data collected
Graphical Display
• Provides the operator with the ability to quickly identify when an
sample equilibrium condition has been achieved
• Offers the benefit of being able to scrutinize the long-term
performance of the Sensor and in turn make a decision as to the
required frequency of recalibration
Datalogging
• Internal datalogging facilities are an excellent means of aiding
process and management control
• A date-stamped identification of each measured sample will
increase the integrity of the data audit trail
Portability
• The ease of transportation of any portable analyzer is critical to
the simplicity of use and hence overall productivity for the
operator.
Level of Technical Support
• Any hygrometer purchased should be fully supported by a high
level of after-sales care
• A fast instrument turnaround should be available for recalibration
• Spare parts, where required, should be readily available
• A fixed duration maintenance contract can be an extremely
reliable way of spreading capital investment and guaranteeing
reliable performance
Level of Supplier Knowledge
• The level of technical knowledge of the supplier should be of
paramount importance when buying a hygrometer
• Purchasing direct from a supplier, or recommended
representative, will provide a greater knowledge of hygrometry
and applications than will be available from a distributor
When assessing the relative merits of any analyzer, the following should also be
considerations. While not fundamental to the Sensor technology of a particular type of
hygrometer, all will affect the level of performance to some degree, and the effect of each
should be minimized to achieve accurate results.
These issues may include:
• Linearity of the analyzer
• Interference errors
• Electrical supply variations
• Output regulation
• Output ripple and noise
• Output terminal isolation
• Output insulation resistance
• Electrical supply interruptions
• Electrical supply transients
• Electrical supply insulation / isolation
• Radio frequency
• Vibration

Electrochemistry deals with cell potential as well as energy of chemical reactions. The energy of a chemical system drives the charges to move, and the driving force give rise to the cell potential of a system called galvanic cell. The energy aspect is also related to the chemical equilibrium. All these relationships are tied together in the concept of Nearnst equation.

Walther H. Nernst (1864-1941) received the Nobel prize in 1920 “in recognition of his work in thermochemistry”. His contribution to chemical thermodynamics led to the well known equation correlating chemical energy and the electric potential of a galvanic cell or battery.
Electric Work and Gibb’s Free Energy
Energy takes many forms: mechanical work (potential and kinetic energy), heat, radiation (photons), chemical energy, nuclear energy (mass), and electric energy. A summary is given regarding the evaluation of electric energy, as this is related to electrochemistry.
Electric Work

Energy drives all changes including chemical reactions. In a redox reaction, the energy released in a reaction due to movement of charged particles give rise to a potential difference. The maximum potential differenc is called the electromotive force, (EMF), E and the maximum electric work W is the product of charge q in Coulomb (C), and the potential DE in Volt (= J / C) or EMF.
W J = q DE C J/C (units)
Note that the EMF DE is determined by the nature of the reactants and electrolytes, not by the size of the cell or amounts of material in it. The amount of reactants is proportional to the charge and available energy of the galvanic cell.

Gibb’s Free Energy

The Gibb’s free energy DG is the negative value of maximum electric work,
DG = - W
= - q DE
A redox reaction equation represents definite amounts of reactants in the formation of also definite amounts of products. The number (n) of electrons in such a reaction equation, is related to the amount of charge trnasferred when the reaction is completed. Since each mole of electron has a charge of 96485 C (known as the Faraday’s constant, F),
q = n F
and,
DG = - n F DE
At standard conditions,
DG° = - n F DE°

The General Nernst Equation

The general Nernst equation correlates the Gibb’s Free Energy DG and the EMF of a chemical system known as the galvanic cell. For the reaction
a A + b B = c C + d D
and

[C]c [D]d
Q = ———
[A]a [B]b

It has been shown that
DG = DG° + R T ln Q
and
DG = - n FDE.
Therefore
- n F DE = - n F DE° + R T ln Q
where R, T, Q and F are the gas constant (8.314 J mol-1 K-1), temperature (in K), reaction quotient, and Faraday constant (96485 C) respectively. Thus, we have

R T     [C]c [D]d
DE = DE° - —– ln ———
n F     [A]a [B]b

This is known as the Nernst equation. The equation allows us to calculate the cell potential of any galvanic cell for any concentrations. Some examples are given in the next section to illustrate its application.

It is interesting to note the relationship between equilibrium and the Gibb’s free energy at this point. When a system is at equilibrium, DE = 0, and Qeq = K. Therefore, we have,

R T     [C]c [D]d
DE° = —– ln ———,    (for equilibrium concentrations)
n F     [A]a [B]b

Thus, the equilibrium constant and DE° are related.

The Nernst Equation at 298 K

At any specific temperature, the Nernst equation derived above can be reduced into a simple form. For example, at the standard condition of 298 K (25°), the Nernst equation becomes

0.0592 V     [C]c [D]d
DE = DE° - ——— log ———
n         [A]a [B]b

Please note that log is the logrithm function based 10, and ln, the natural logrithm function.

For the cell
Zn | Zn2+ || H+ | H2 | Pt
we have a net chemical reaction of
Zn(s) + 2 H+ = Zn2+ + H2(g)
and the standard cell potential DE° = 0.763.

If the concentrations of the ions are not 1.0 M, and the H2 pressure is not 1.0 atm, then the cell potential DE may be calculated using the Nernst equation:

0.0592 V     P(H2) [Zn2+]
DE = DE°  - ——- log ————
n           [H+]2

with n = 2 in this case, because the reaction involves 2 electrons. The numerical value is 0.0592 only when T = 298 K. This constant is temperature dependent. Note that the reactivity of the solid Zn is taken as 1. If the H2 pressure is 1 atm, the term P(H2) may also be omitted. The expression for the argument of the log function follows the same rules as those for the expression of equilibrium constants and reaction quotients.

Indeed, the argument for the log function is the expression for the equilibrium constant K, or reaction quotient Q.

When a cell is at equilibrium, DE = 0.00 and the expression becomes an equilibrium constant K, which bears the following relationship:

n DE°
log K = ——–
0.0592

where DE° is the difference of standard potentials of the half cells involved. A battery containing any voltage is not at equilibrium.

The Nernst equation also indicates that you can build a battery simply by using the same material for both cells, but by using different concentrations. Cells of this type are called concentration cells.

Example 1

Calculate the EMF of the cell
Zn(s) | Zn2+ (0.024 M) || Zn2+ (2.4 M) | Zn(s)

Solution

Zn2+ (2.4 M)  +  2 e  =  Zn     Reduction
Zn  =  Zn2+ (0.024 M) +  2 e    Oxidation
——————————————–
Zn2+ (2.4 M)  =  Zn2+ (0.024 M),  DE° = 0.00 - - Net reaction

Using the Nernst equation:

0.0592       (0.024)
DE = 0.00 - ——- log ——–
2          (2.4)

=  (-0.296)(-2.0)
=  0.0592 V

Discussion
Understandably, the Zn2+ ions try to move from the concentrated half cell to a dilute solution. That driving force gives rise to 0.0592 V. From here, you can also calculate the energy of dilution.

If you write the equation in the reverse direction,
Zn2+ (0.024 M) = Zn2+ (2.4 M),
its voltage will be -0.0592 V. At equilibrium concentrations in the two half cells will have to be equal, in which case the voltage will be zero.

Example 2

Show that the voltage of an electric cell is unaffected by multiplying the reaction equation by a positive number.

Solution
Assume that you have the cell
Mg | Mg2+ || Ag+ | Ag
and the reaction is:
Mg + 2 Ag+ = Mg2+ + 2 Ag
Using the Nernst equation

0.0592     [Mg2+]
DE  =  DE°  - —— log ——–
2        [Ag+]2

If you multiply the equation of reaction by 2, you will have
2 Mg + 4 Ag+ = 2 Mg2+ + 4 Ag
Note that there are 4 electrons involved in this equation, and n = 4 in the Nernst equation:

0.0592     [Mg2+]2
DE  =  DE°  - —— log ——–
4        [Ag+]4

which can be simplified as

0.0592     [Mg2+]
DE  = DE°  - —— log ——–
2        [Ag+]2

Thus, the cell potential DE is not affected.

Example 3

The standard cell potential dE° for the reaction
Fe + Zn2+ = Zn + Fe2+
is -0.353 V. If a piece of iron is placed in a 1 M Zn2+ solution, what is the equilibrium concentration of Fe2+?

Solution
The equilibrium constant K may be calculated using
K = 10(n DE°)/0.0592
= 10-11.93
= 1.2×10-12
= [Fe2+]/[Zn2+].
Since [Zn2+] = 1 M, it is evident that
[Fe2+] = 1.2E-12 M.

Example 4

From the standard cell potentials, calculate the solubility product for the following reaction:
AgCl = Ag+ + Cl-

Solution
There are Ag+ and AgCl involved in the reaction, and from the table of standard reduction potentials, you will find:
AgCl + e = Ag + Cl-, E° = 0.2223 V - - - -(1)
Since this equation does not contain the species Ag+, you need,
Ag+ + e = Ag, E° = 0.799 V - - - - - - (2)
Subtracting (2) from (1) leads to,
AgCl = Ag+ + Cl- . . . DE° = - 0.577
Let Ksp be the solubility product, and employ the Nernst equation,
log Ksp = (-0.577) / (0.0592) = -9.75
Ksp = 10-9.75 = 1.8×10-10
This is the value that you have been using in past tutorials. Now, you know that Ksp is not always measured from its solubility.

Confidence Building Questions

* In the lead storage battery,
Pb | PbSO4 | H2SO4 | PbSO4, PbO2 | Pb
would the voltage change if you changed the concentration of H2SO4? (yes/no)

Answer … Yes!
Hint…
The net cell reaction is
Pb + PbO2 + 2 HSO4- + 2 H+ ® 2 PbSO4 + 2 H2O
and the Nernst equation
DE = DE° - (0.0592/2)log{1/{[HSO4-]2[H+]2}}.

* Choose the correct Nernst equation for the cell
Zn(s) | Zn2+ || Cu2+ | Cu(s).
1. DE = DE° - 0.0296 log([Zn2+] / [Cu2+])
2. DE = DE° - 0.0296 log([Cu2+] / [Zn2+])
3. DE = DE° - 0.0296 log(Zn / Cu)
4. DE = DE° - 0.0296 log(Cu / Zn)

Answer … A
Hint…
The cell as written has
Reduction on the Right: Cu2+ + 2 e = Cu
oxidation on the left: Zn = Zn2+ + 2 e
Net reaction of cell is Zn (s) + Cu2+ = Cu (s) + Zn2+

* The standard cell potential DE° is 1.100 V for the cell,
Zn(s) | Zn2+ || Cu2+ | Cu(s).
If [Zn2+] = 0.01 M, and [Cu2+] = 1.0 M, what is DE or EMF?

Answer … 1.159 V
Hint…
A likely wrong result is 1.041 V.
The term that modifies DE is -(0.059/n)log{[Zn2+]/[Cu2+]} (n = 2 in this case).
Understandably, if the concentration of Zn2+ is low, there is more tendency for the reaction,
Zn = Zn2+ + 2 e.

* The logarithm of the equilibrium constant, log K, of the net cell reaction of the cell
Zn(s) | Zn2+ || Cu2+ | Cu(s) . . . DE° = 1.100 V
is
1. 1.100 / 0.0291
2. -1.10 / 0.0291
3. 0.0291 / 1.100
4. -0.0291 / 1.100
5. 1.100 / 0.0592

Answer … A
Hint…
Use the Nernst equation in the form
0 = 1.100 - 0.0296 log ([Zn2+] / [Cu2+])
The Nernst equation is useful for the determination of equilibrium constants.

Understanding is the key. Take time to understand it, there is no point in rushing

Analytical equipment has progressed over the years from analogue instruments born in the laboratory to new digital analytical equipment designed for specific applications. The analyser list has grown; we can now add flame ionisation detection gas analysers (FID), gas chromatography (GC), and mass spectrometry (MS). While there are other methods in use today and others under development, those mentioned here are the workhorse methods in process analytical chemistry and have been in everyday use, 24 hours per day, 365 days per year for making process analytical measurements. Some gases are difficult to measure just because they are hard to detect, but in general, reactive and condensable gases such as HCl, NH3, HF and formaldehyde, present the greatest measurement challenges. Such gases may react with other components within the stack gas stream; they may condense or be absorbed by liquid condensate within a cold extractive sampling system, they may adsorb onto surfaces, or they may polymerise before reaching the Analyser. Thus, depending upon the components making up the flue gas stream, special sampling equipment may be needed and special operation and maintenance procedures may be required to achieve reliable results. Thus, in addition to the measurement technologies of the instrumentation, one must also consider the technology of sample handling and transport.

A brief overview of these analytical techniques and advances in their technologies follows. Nondispersive infrared gas Analysers (NDIR) utilises several different detection techniques. Opto-pneumatic detectors, commonly known as Luft detectors (from their inventor, Karl Luft), interference filter photometers (IFC), and gas filter correlation (GFC) are the more predominant types. The theory of operation of these infrared methods is similar and is based upon absorption of infrared energy in the 2 to 11 micron wavelength range. Simple molecules with less than 5 or 6 atoms have infrared absorption spectra with fine structure. Gases fitting this description are ideal for Luft and GFC types of Analysers, which correlate the spectra of the sample gas with the spectra of the pure component of interest. Interference filter correlation is capable of measuring gases with either fine structure in the spectra or broadband absorption. Proximately 80 gases have been measured with NDIR. The capability list of all techniques mentioned herein is based on current availability in the marketplace and not theoretical considerations. Of the 80 gases, approximately 50% of the NDIR instruments sold are for measurement of Carbon Monoxide (CO).

Analytical equipment has progressed over the years from analogue instruments born in the laboratory to new digital analytical equipment designed for specific applications. The analyser list has grown; we can now add flame ionisation detection gas analysers (FID), gas chromatography (GC), and mass spectrometry (MS). While there are other methods in use today and others under development, those mentioned here are the workhorse methods in process analytical chemistry and have been in everyday use, 24 hours per day, 365 days per year for making process analytical measurements. Some gases are difficult to measure just because they are hard to detect, but in general, reactive and condensable gases such as HCl, NH3, HF and formaldehyde, present the greatest measurement challenges. Such gases may react with other components within the stack gas stream; they may condense or be absorbed by liquid condensate within a cold extractive sampling system, they may adsorb onto surfaces, or they may polymerise before reaching the Analyser. Thus, depending upon the components making up the flue gas stream, special sampling equipment may be needed and special operation and maintenance procedures may be required to achieve reliable results. Thus, in addition to the measurement technologies of the instrumentation, one must also consider the technology of sample handling and transport.

A brief overview of these analytical techniques and advances in their technologies follows. Nondispersive infrared gas Analysers (NDIR) utilises several different detection techniques. Opto-pneumatic detectors, commonly known as Luft detectors (from their inventor, Karl Luft), interference filter photometers (IFC), and gas filter correlation (GFC) are the more predominant types. The theory of operation of these infrared methods is similar and is based upon absorption of infrared energy in the 2 to 11 micron wavelength range. Simple molecules with less than 5 or 6 atoms have infrared absorption spectra with fine structure. Gases fitting this description are ideal for Luft and GFC types of Analysers, which correlate the spectra of the sample gas with the spectra of the pure component of interest. Interference filter correlation is capable of measuring gases with either fine structure in the spectra or broadband absorption. Proximately 80 gases have been measured with NDIR. The capability list of all techniques mentioned herein is based on current availability in the marketplace and not theoretical considerations. Of the 80 gases, approximately 50% of the NDIR instruments sold are for measurement of Carbon Monoxide (CO).

Recent developments in NDIR Analysers include the ability to have multiple optical benches in one Analyser and stacked detectors that result in as many as four (4) gases being measured in a single instrument. Microprocessors have added many capabilities to modern NDIR analysers, which include a platform, where a single system controller provides the user interface for as many as 3 analytical modules. The system controller provides industry wide interfaces to control systems and common computer networks. MODBUS is included for control systems and Ethernet is provided for interfacing to personal computers. The interference filter correlation (IFC) photometric analysers such as the Multiwave have been enhanced through microprocessor technology to measure multiple components and also operate over Analyser networks. These Analysers have also been successfully applied to hot wet measurement demands by heating to temperatures as high as 200 C. The IFC approach allows a spectroscopist to evaluate a complex sample matrix and select proper wavelengths of light to make successful analytical measurements of the component of interest. These Analysers are custom built for the application. Improvements have also been made in the calibration of NDIR gas Analysers. By using calibration cells, small optical cells with actual test gases encapsulated within, Analyser calibration can be checked without bottles of expensive test gases. Ultraviolet (UV) Analysers are in general more sensitive than NDIR Analysers. Another advantage of UV Analysers is that water (H2O) is transparent to UV. SO2 and NOx are frequently measured with this technology. Other possibilities are NO2, H2S, CS2, COS, Cl2, NH3, and other gases. The UV Analyser utilises a 4 beam optical approach so that a double quotient can be formed and removes variables such as dirty windows and ageing of components so that the result is a more robust and stable analyser.

Flame ionisation detection (FID) techniques are widely used to measure hydrocarbons. During the combustion of organic substances, in a hydrogen flame, electrically charged particles are produced. The resulting current of these ions is proportional to the organic carbon content. FIDs have very large dynamic ranges, from 10 to 100,000 mg of organic carbon / cubic meter. The hydrocarbon analyser utilises a heated system from the point of the sample interface throughout the entire analytical system to avoid cold spots where heavier hydrocarbons may be adsorbed and cause erroneous results. Modern FID Analysers feature self-monitoring, automatic fault recognition and logging functions. Some FID Analysers include options for a sparger, or water stripper to measure volatile organics in water. While FIDs respond to all hydrocarbons, it may be possible to use a FID type hydrocarbon analyser to measure a hazardous air pollutant if the pollutant is a hydrocarbon and no other hydrocarbons are present.

Gas Chromatography is a very versatile analytical technique that separates the sample stream into its individual components for measurement. The process or on-line gas chromatograph differs dramatically from its laboratory counterpart, the only common area being the separation concepts. In current practice, designs integrate a basic Analyser (chromatograph) with a controller & microprocessor package. These systems can perform as stand alone units or be interfaced with multiple chromatographs, distributed control systems, or a host computer. Significant changes have been made in valves, columns, column systems and detectors. Tough polyamide coated fused silica columns with stabilised stationary phases have reached a high level of reliability and are routinely used in Process Chromatographs. The most popular detectors for online chromatographs are still the thermal conductivity and flame ionisation detectors, but other component selective detectors are being used including electron capture, flame photometry, photoionisation, and chemiluminescence. Most gases can be measured by gas chromatography. The basic requirements are: the compound has a sufficient vapour pressure so that it will elute through the column, a chromatographic separation can be made, and the compound is stable thermally, i.e., does not crack at the oven temperature. Process chromatographs have been used in CEMS when the pollutant of interest is not one of the criteria pollutants, i.e.; there is not a standard off-the-shelf solution to the analytical need.

The CEMAS FTIR is based on the spectrometer MB 9100. It provides the high selectivity of the FTIR-technology and additional infrared components can easily be added if needed. The analysis system is used especially for the measurement of components like HCl, HF, NH3 or H2O that require hot & wet measurements. The measurement of O2 and THC can be integrated as well. Analysis systems must be serviced regularly to minimise failures and to increase life expectancy. The Analysers are measuring several components simultaneously. Advance Cemas-NDIR measures up to four gas components, e.g. CO, SO2, NO and O2, Advance Cemas-FTIR up to eight gas components, in individual cases even more. Furthermore, the analysis system Advance Cemas contains all components necessary for gas feed and conditioning, such as the cooler module with integrated gas feed unit. Due to the compact design of the systems especially short sample gas lines can be used and the number of connections minimised considerably. The simplified spare-parts stocking by using standard modules also results in a cost reduction.

Calibration concepts - convincing and cost-effective

Analysers have to be calibrated in certain intervals to ensure their accuracy and stability. The test gases and system components used for this calibration contribute considerably to the investment and operating costs. With the analysis system Advance Cemas-NDIR, can calibrate without test gases. The zero point or span point respectively for the oxygen measurement as well as the zero point for the infrared measurement is adjusted with ambient air. The span adjustment for oxygen measurement with the infrared Analyser Uras 14 are made by means of gas-filled, patented calibration cells. A long-time test over six years has proved the stability of these calibration cells. The calibration without test gases is run automatically. Due to its high stability the calibration costs of the Advance Cemas-FTIR are low. All instrument dependent factors are taken into consideration through the daily registration of the reference spectrum with zero gas. Because of this automatic zero point adjustment and the measuring principle, a calibration of zero and reference point every six months is sufficient to ensure smallest measuring ranges. The storage of test gas is not necessary. A calibration check with test gas can be carried out twice a year.

Everything under control

Usually, systems for emission monitoring are not installed at convenient locations. Therefore, normally an inspection on-site is required in regular intervals. Furthermore, you have to go to the analysis system to operate it. This is different with Advance Cemas; additional sensors in the Analyser and in the components for sample conditioning provide the status information centrally. Thus the gas flow is supervised, a condensate drain is recognised early, a message is displayed that the condensate bottle has to be emptied, or the complete optics is checked. Failures and frequent inspections can be avoided. All information is integrated into the status messages failure or maintenance required of the Analyser. Via the Ethernet interface detailed information can be obtained from a PC, e.g. in the control room, a diagnosis can be made or the Analyser can be remotely operated. Remote control becomes reality.

Advance Cemas-FTIR System Description

Measurement principle

The Advance Cemas FTIR is a multi-component emission monitoring system for simultaneously measuring HCl, HF, NH3, CO, NO, NO2, SO2, H2O, CO2 , O2 and total hydrocarbons. The infra-red-active measurement components are measured at high temperature (180oC) using an FTIR spectrometer (FTIR = Fourier Transform Infra Red). The O2 measurement is performed using an electrochemical oxygen sensor. The hydrocarbon content is measured using a flame ionisation detector (FID), when required.

The sample gas is piped via the heated sampling filter (2) and the heated sampling pipe (4) to the heated sample-gas feed (5)  . The heated cell of the FTIR spectrometer (11) protrudes directly into the heated sample-gas feed. Behind the gas outlet of the cell and FID (12) can be connected for measuring hydrocarbons within the sample-gas feed. A proportion of the sample gas stream is piped to the oxygen Analyser (13) from the heated sample-gas feed. Through the check valve  (3) on the sampling filter (2) dry compressed air is released automatically in the event of any problem , e.g. if the temperature falls below the permitted level in one of the heating circuits. The system is also purged of sample gas to avoid condensation. Through the second check valve (10) dry, CO2-free compressed air is automatically released for the purpose of recording zero-gas spectra. The molecular sieve unit (14) is used for conditioning the compressed air, i.e. drying it and reducing its CO2 content.

CEMAS FTIR system design
Sampling system

The sampling system comprises:

The probe tube, the filter device, and the sampling pipe

Probe tube

The probe tube (1) is made from special steel (316T) and can be supplied in either an unheated (probe 40) or a heated version (probe 42) and in lengths 1 m, 1.5 m and 2 m. A heated probe tube is only necessary in exceptional cases (e.g. cold bridge on the flange).

Filter device

The PFE2 filter device (2) contains a coarse filter (20 mm) that is heated to 180 C. The sampling pipe is connected directly to the filter device. For emergency purging of the entire sample-gas path from the inlet via the sample cell up to the outlet, cleaned compressed air is released through a heated check valve (3) on the filter device. For external installation of the sampling probe an optional protective probe case can be supplied. For situations with a high dust content a purging facility can be supplied for periodic cleaning of the coarse filter.

Sample Line

The sample line (4) can be heated to 180 C by a built-in fixed-resistance thermistor (90 W/m). The temperature is monitored using a Pt-100 sensor. The sample gas is transported in a PTFE hose (8 x 6 x 1mm). In order to avoid a long dead time the sample line should be no longer than 40 m.

Feeding and conditioning of sample gas

Sample-gas feed

The sample-gas feed comprises:

The needle valve, the sample-gas feed pump, the fine filter, the flow monitor, and the check valve for releasing zero gas and test gas. The sample-gas feed is housed in a heated cabinet.

Needle valve

The needle valve (6) is used for adjusting the sample-gas flow during commissioning of the measuring system.

Sample-gas feed pump

The motor for the sample-gas feed pump (7) is attached on rubber mounts to the right-hand side panel of the warming cabinet. The entire top of the diaphragm pump protrudes into the warming cabinet.

Fine filter

The ceramic fine filter (8) serves to separate out the finest particles. It has an average porosity of 0.05 m.

Flow monitor

The flow monitor (9) is based on a Reed contact with a magnetic piston seated in PTFE. The lower switching point is set to 250 l/h. If flow falls below this rate, the status signal Fault is output.

Check valve

Through a check valve (10) between the pump and the fine filter both zero gas and test gas can be released. An external magnetic valve controls this valve. An opening pressure of 10 psi (= 0.7 bar) is required.

Heated cabinet

The cabinet is heated to 180oC to prevent the temperature from falling below the dew point. An external temperature controller handles temperature control with a Pt-100 temperature sensor in the warming cabinet. For connecting the heated lines, mounting flanges are fitted on the left and right side panels of the heated cabinet in such a way that no cold bridge can develop. The internal piping in the sample-gas feed is in 6 x 4 x 1 mm PTFE. Transition pieces are made from special steel as Swagelok connections.

Spectrometer layout

The FTIR spectrometer, model MB9100, is installed suspended in the system cabinet. Its main components are as follows: The interferometer with the electronics for controlling the spectrometer and communicating with an external computer, the IR-ray source, the transfer optics and the IR detector, and the cell.

Interferometer

The interferometer modulates the IR light along with the light from the laser and from the white-light source. The latter two are used for scaling the spectrum. The complete interferometer unit comprises the above light sources, their power supplies, the detectors for laser light and white light, the beam splitter, the retroreflectors, the transfer mirrors and the interferometer arm. The interferometer arm is distinguished by its twin-pendulum design, which contributes to the spectrometers robustness and freedom from over sensitivity.

IR-radiation source

The source of the IR radiation is a glowbar, a resistor with positive temperature characteristics, made from silicon carbide.

IR detector

The IR detector is a DTGS detector (deuterized triglyceride sulphate).

Cell

Connected to the spectrometer is the heated long-path cell. Via an optical transfer device located above the cell, the IR ray passes into the cell. In the cell, it is reflected several times by three mirrors, increasing the length of the optical path before leaving the cell again and arriving at the detector. The optical path length is fixed in the factory through the setting of the mirrors. It is normally 6.4 m.

Processing of measured values

The digitised detector signal is evaluated in terms of concentration of the different sample-gas components by a computer that forms one of the system components.

Oxygen Analyser Sample-gas feed

A proportion of the sample gas stream is diverted and piped to the oxygen Analyser from the sample-gas feed. To prevent condensation the sample gas is passed along the heated cell and into the oxygen analyser.

Oxygen sensor

The type KE-25 electrochemical oxygen sensor in the oxygen analyser operates on the same principle as a lead acid battery. The cathode of the electrochemical cell is made of gold and the anode of lead. A weak acid is used as an electrolyte. At the cathode, the oxygen entering from the sample gas, is absorbed electrochemically; a process through which electrons are used up. At the anode, lead releases electrons and is oxidised to form lead oxide. The current flowing through the outer circuit in this process is proportional to the diffusing oxygen. A porous barrier limits the diffusion from the gas phase so that a linear signal results corresponding to the concentration of oxygen. The surface of the lead anode regenerates itself continuously as the lead oxide dissolves in the electrolyte.

Removal of condensate

In order to remove the condensate, the sample gas is passed over a condensate trap. The condensate is expelled from the filter housing by means of a peristaltic pump.

Flow monitoring

Monitoring the flow upstream of the oxygen sensor ensures a minimum flow of 10 l/h. If the flow rate falls below this value, then a status signal Fault is output.

Discharge of the condensation heat

The condensation heat is discharged through the cooling device in the system cabinet. For this purpose, a cold-air pipe passes from the cooling device into the oxygen Analyser.

Processing of measured values

The analogue sensor signal is digitised, incorporated into the processing of measured values from the Advance Cemas FTIR, and displayed on the screen. The measured value for oxygen, common with all other measured values, relates to the moist flue gas.

Adjustment

The oxygen Analyser is automatically adjusted during the daily recording of the zero spectrum.