ANALYTICAL INSTRUMENTS

WHY ANALYSERS ?

PROCESS CONTROL & MONITORING

- QUALITY

- OPTIMISATION

SAFETY - PERSONNEL - PLANT - ENVIRONMENTAL

ANALYTICAL INSTRUMENTSAnalytical instruments should ideally be:Reliable.Capable of fast analysis.Self-calibratingAble to withstand harsh environments.Able to tolerate different kinds of samples.Nondestructive so that the sample can be returned to the process as it was.Automated and capable of unattended operation.

ANALYTICAL INSTRUMENTSConsistent product quality Improved process efficiency Reduced equipment maintenance Plant and employee safety Compliance with environmental standards

ANALYTICAL INSTRUMENTSMajor Industries where analyzers are used: Power Generation Water and Wastewater Chemical Pulp and Paper Refining Pharmaceutical and Biotech Industrial Heating Semiconductor Food and Dairy

ANALYTICAL INSTRUMENTSProcess monitors that measure and transmit information about chemical composition, physical properties, or chemical properties are known as process analyzer . They are primarily used as continuous on-line analyzers. A process monitoring system usually requires a sample conditioning system, a process analyzer, and one or more data output devices. Process analyzers measure chemical concentrations or physical or chemical properties that can be used as control variables instead of relying on indirect physical parameters, such as pressure, temperature, and inferred data from computer models.

Analyzer Selection Design Requirements

A) ECONOMIC CONSIDERATIONS Analyzer systems can improve product qualityincrease product throughput and outputreduce energy costs.

Analyzer Selection Design Requirements

B) ENVIRONMENTAL AND SAFETY CONSIDERATIONS Analyzers are used to detect Hazardous plant conditionsFor monitoring government-mandated requirements concerning pollutants in ambient air, stack emissions, and effluent streams.

Analyzer Selection Design Requirements

C) APPLICATION REQUIREMENTS How the analyzer system will be used Quality controlProcess controlSafety/environmental regulations

ENVIRONMENTAL AND SAFETY CONSIDERATIONSContinuous Emission Monitoring SystemsContinuous emission monitors (CEM) commonly measure concentrations of pollutants prior to their release to the environment.

ENVIRONMENTAL AND SAFETY CONSIDERATIONSNon-dispersive Infrared Analyzers (NDIR) NDIR analyzers consist of an infrared light source, a sample cell and a detector system. Chromatography or non dispersive infrared techniques to analyze for carbon monoxide(CO), a product of incomplete combustion. Gas chromatographs are used to measure such pollutants as vinyl chloride, hydrogen sulfide, benzene, ammonia, and other sulfur, chlorinated, and hydrocarbon compounds.

ENVIRONMENTAL AND SAFETY CONSIDERATIONSThe following gases can be measured by NDIR analyzerssulfur dioxide (SO2), oxides of nitrogen (NO and NO2), carbon monoxide (CO) carbon dioxide (CO2).

CHEMICAL PROPERTY ANALYZERSpH ANALYSERSCONDUCTIVITY ANALYSERSDISSOLVED OXYGEN ANALYSER

CHEMICAL PROPERTY ANALYZERS

Common liquid electrochemical measurements include hydrogen ion concentration (pH), oxidation-reduction potential, electrolytic conductivityIonization is the basis for the measurement of pH, electrolytic conductivity, and oxidation-reduction potential (ORP).

CHEMICAL PROPERTY ANALYZERSTypical Applications: Wastewater and Pure Water Treatment pH Measurement in Food & Dairy Industries Corrosion Detection Dearator Efficiency Aeration, Effluent, Stream and Aquaculture Monitoring Industrial Drying Heat Treating Furnaces and Gas Generators Natural Gas Pipelines Turbine Monitoring Sterilization

CHEMICAL PROPERTY ANALYZERSTypical refinery applications for pH measurement include:a. Refinery wastewater.b. Cooling tower water.c. Boiler feed water.d. Crude tower overhead systems.e. Corrosion control in processing facilities.

pH AnalyzerpH is a measure of the hydrogen ion (H+) concentration in an aqueous solution. It is used widely as a measure of the degree of acidity or alkalinity of a solution.The electrode measuring system is comprised of three elements: the glass measuring electrode, the reference electrode, and the sensing element for automatic temperature compensation.

pH Analyzer

the pH value is determined by measuring the voltage potential developed between the process stream and the standard solution contained within the glass measuring electrode. This potential is developed because of the difference in hydrogen ion concentration of the two solutions.The reference electrode is designed to produce a constant potential regardless of the solution in which it is immersed.

pH Analyzer

There are two types of reference electrodes diffusion flowing. In the diffusion-type reference electrode, the electrolyte diffuses through a large porous area to contact the process. In flowing-type electrodes, a small amount of the electrolyte constantly flows out of the reference electrode creating a conductive path between the electrode and the process stream.

pH Analyzer

Temperature compensationDue to the fact that the electromotive force developed by the glass electrode will be affected by the temperature of the electrode itself, a temperature compensator is usually necessary. The compensator consists of a resistance thermometer built into the probe, which is immersed in the process stream.

pH Analyzer

Oxidation-Reduction Potential (ORP)

Ionized solutions contain particles that convey electrons. The development of an oxidation-reduction potential involves the transfer of electrons in a solution. When a voltage is applied to electrodes immersed in the solution, ions in the solution migrate. In this cell, the positive particle (M+) approaches the cathode and picks up an electron, reducing its positive charge. This is called reduction. At the anode, the negative particle (X) loses an electron to the anode and becomes more positive. This is called oxidation. These reactions are called oxidation-reduction or redox reactions.

Electolytic Conductivity Measurement

Electrolytic conductivity is the ability of a solution to conduct electric current. It is referred to as specific conductance or simply conductivity. Specific conductance is defined as the mho (siemen), which is the reciprocal of the resistance in ohms of 1 cubic centimeter of the liquid at a specified temperature. The common unit of measurement in conductivity is the micromho (microsiemen), which is one millionth of a mho (siemen).

Electolytic Conductivity Measurement

The electrical conductivity of a wastewater stream, usually measured in microsiemens per centimeter (mS/cm), is a measure of the dissolved ionized salts in the stream The conductivity of distilled water may be as low as 1 mS/cm, and that of sea water as high as 50 mS/cm. An increase in wastewater conductivity indicates an increase in ionized substances in the stream, which could be caused by strong acids or bases and indicates that specific analysis is required.

Electolytic Conductivity Measurement

CONDUCTIVITY CELLSThe conductivity cell typically consists of two metal plates or other electrodes firmly spaced within an insulating chamber that serves to isolate a portion of the liquid. Cell ConstantsThe conductance between two electrodes varies as follows:C A/L where.C = conductance, in mhos (siemens),A = area of electrodes, in square centimeters,L = distance between electrodes, in centimeters.

Electolytic Conductivity Measurement

Conductivity Sensors Conductivity measurements are widely used in industry. Most applications involve water treatment and range from desalination to the production of high purity water in the power and semiconductor business. Other applications include detecting leaks in the heat exchangers and sensing liquid interfaces

DISSOLVED OXYGEN IN WASTEWATER ANALYSIS

The quantity of dissolved oxygen in a wastewater stream, usually measured in parts-per-million, is a measure of the streams ability to support aquatic life.Typical analysis spans: 0 20 ppb up to 0 20 ppmTypical analyzer outputs: 0 1VDC, local meter, 4 20mA

TYPES OF OXYGEN ANALYZERS

There are two basic types of oxygen analyzers currently suitable for refinery process stream applications: electrochemical principleparamagnetic principle. Other methods of oxygen analysis include gas chromatography, oxygen/combustibles analyzers, and dissolved oxygen analyzers.

OXYGEN ANALYZERSOxygen analyzers may be used to ensure that sufficient oxygen to support life is available.Process conditions frequently require the use of an inert gas to purge or blanket vessels. Oxygen may be a contaminant that would cause degradation of the contents of the vessel or enable an explosive mixture to exist.

Electrochemical Oxygen AnalyzersElectrochemical oxygen analyzers consist of at least two metallic electrodes in good electrical contact with an appropriate electrolyte. The chemical reactions occurring in the cell produce an output current or voltage, which is a function of the number of oxygen molecules diffusing into the interface between the electrolyte and the measuring electrode

Electrochemical Oxygen AnalyzersThe various types of electrochemical analyzer cells are conveniently classified by the type of electrolyte used:a. Aqueous solutions of various metal salts and soluble organic compounds.b. Zirconia ceramic doped with combinations of calcia, yttria, and scandia.

Electrochemical Oxygen AnalyzersOxygen molecules diffuse through the membrane to the cathode. At the cathode, they are reduced to OH ions upon acceptance of four electrons produced by an appropriate reaction at the anode. The reactions occur in a cell comprised of a platinum cathode, silver anode, and potassium chloride electrolyte.

Electrochemical Oxygen AnalyzersThe materials used in these cells depend upon manufacturers designs and may be operated in a variety of modes at temperatures between 32F and 122F (0C and 50C)The output of the cell in the amperometric mode of operation is a current proportional to the number of oxygen molecules reaching and being reduced at the cathode/electrolyte Interface.

PARAMAGNETIC OXYGEN ANALYZER

PARAMAGNETIC OXYGEN ANALYZER

PARAMAGNETIC OXYGEN ANALYZER

Electrochemical Oxygen AnalyzersZirconia electrochemical type: High temperature zirconia electrochemical cells consist of a thin section of doped zirconia, usually a disk or a tube, whose opposite surfaces are coated with porous platinum electrodes. When operated at a temperature of about 1562F (850C), the voltage difference between the two electrodes is proportional to the log of the ratio of the partial pressures of oxygen existing at the two electrode/electrolyte interface. Instrument quality dry air is normally used as the reference gas on one side of the cell, while the other side is exposed to the sample gas.

Electrochemical Oxygen AnalyzersThese high temperature probes do not have heaters, but a temperature sensor is provided, and the analyzer output is temperature corrected.Any combustible gases present in the sample or reference gases will be burned completely before the gases reach the surface of the electrodes because 1562F (850C) is well above the ignition temperature of fuel gases.

Heated Probe-type Zirconia Electrochemical OxygenAnalyzer Schematic Diagram

ZIRCONIA OXYGEN ANALYZER

ZIRCONIA OXYGEN ANALYZER

Electrochemical Oxygen AnalyzersAvailable Ranges and Limits of Various Methods a. Electrochemical cells:1. Fuel cells, 0 2 ppm to 100% O2.2. Polarographic, 0 5 ppm to 100% O2.3. Coulometric, 0 1 ppm to 100% O2.b. Paramagnetic analyzers: 0 1% to 0 25%.c. Zirconium oxide: 0 2.5% to 0 25% (21% maximum output).

Electrochemical Oxygen AnalyzersThe zirconium oxide method is generally limited to flue gas analysis. The main advantage is that the sample system is reduced to a minimum.

Gas ChromatographySulfur content, which remains appreciable through the refining process, is generally an unacceptable contaminant and must be reduced or eliminated from the end product.To minimize pollution, most industrialized countries have adopted laws prohibiting the burning of fuels containing high sulfur concentrations.

Gas ChromatographyMost sulfur analyzers in common use today use the electromagnetic energy absorption characteristics of the various chemical forms of sulfur. Instruments used for sulfur content analysis include the gas chromatograph, the mass spectrometer the thermal conductivity

Gas ChromatographyThe accurate analysis of sulfur compounds in the gaseous state is commonly done with gas chromatography.The sulfur components most often monitored in stack emissions are SO2 and H2

Gas ChromatographyGas chromatography is a flexible method for analyzing several components in a gas discharge stream. For example, a gas chromatograph with a Flame Photometric Detector (FPD) can be used to analyze sulfur compounds such as H2S and SO2.

Gas ChromatographyThe gas chromatograph is used to obtain on-line composition information of selected process streams for current process operation. The gas chromatograph may be designed to determine concentration of one or more components in a multi-component stream. This type of chromatograph can determine component concentrations from parts-per-billion (PPB) ranges 100%.

Non-dispersive infrared absorbance system(NDIR)

Non-dispersive infrared absorbance system(NDIR)

GENERAL CONCEPTSGENERAL CONCEPTS ON

SAMPLE HANDLING SYSTEMS

CALIBRATION GASES/ LIQUIDS

ANALYSER HOUSES

SAMPLE HANDLING SYSTEM

Sample handling system of a process analyser is a device or combination of devices which transfers a sample from a process stream to the analyser in such a way as to minimise maintenance and to preserve or enhance the analytical information contained in the sample.

IDEAL SAMPLE HANDLING SYSTEM Contains no moving parts Contains no components which requires cleaning /servicing No transportation lag Preserve /enhance the analytical information contained in the sample.

SAMPLE HANDLING SYSTEMSAMPLE TAKE-OFF POINT.

SAMPLE TRANSPORT SYSTEM.

SAMPLE CONDITIONING SYSTEM.

SAMPLE RETURN AND/OR DISPOSAL SYSTEM

SAMPLE TRANSPORT SYSTEMSA SINGLE LINE TO THE ANALYSER

Vent / Drain

Used only if

THE SAMPLE LINE VOLUME IS SMALL COMPARED TO THE ANALYSER SAMPLE CONSUMPTION.

THE ANALYSERS ARE INSTALLED CLOSE TO THE SAMPLE TAKE-OFF POINT IN THE FIELD.

e.g. Conductivity or pH Analyser.

SAMPLE TRANSPORT SYSTEMSA SINGLE LINE WITH BYPASS STREAM Vent / Drain / Sample Recovery System

Vent / Drain / Sample Recovery System

This ensures a very high Velocity in the sample line. Hence a reduced Transportation lag.This system is applicable when no return point is found for a Fast Loop.The Bypass stream is connected to a vent or a drain or a sample recovery unit.

RESPONSE TIMEAnalyser response function contains a pure lag time & the time constant .

Lag is the time Delay between Input & the appearance of output.

Lag is due to Transmission lines

Lag time TL = Volume in m3/volume flow rate (m2/sec) = Line length / velocity

SAMPLE CONDITIONINGFILTRATIONSingle line to the analyser The filter shall be located at the sample take-off point itself. Used to remove particulate which causes interference (choking).All analysers should be fitted with a strainer near the sample take-off point so that the downstream components are protected from damage & blockage due to larger particles.

SAMPLE CONDITIONING

When sampling hot wet stack gas, a filter capable of withstanding the gas temperature is installed at the beginning of the sample line to prevent solids from entering the gas sample line.

After the sample is cooled the sample goes to coalescing filter to remove suspended liquids.

Cool the sample below ambient at the upstream of the coalscer to aid condensation & to heat the sample line gently at the downstream.

SAMPLE CONDITIONINGPressure regulators:Delivers sample at constant pressure & volume flow rate to the low pressure side , ie Analyser .

Why Pressure regulators ?

1. Analyser not rated for Process Pressure which is very high - Reduce pressure2. Analyser requires flow at constant pressure for accurate analysis - Maintain pressure

SAMPLE CONDITIONINGTEMPERATURE CONTROL Temperature control is effected by coolers & heaters

Temperature must be maintained above a dew point so that a representative sample is obtained at the analyser.

The sample lines must be traced.

Sample composition can be affected if the lines are heated or cooled excessively.

Gaseous samples containing condensables/ liquid samples will require the line to be heated up to prevent condensation in the first case & to prevent precipitation or freezing in case of the latter

SAMPLE DISPOSAL RETURNING THE LINE TO THE PROCESS .

Ensures no hazard to Environment Analyser Process RELEASING TO ATMOSPHERE Clean, non-flammable , non-toxic * Gas samples can be vented to the atmosphere. * Liquids to the chemical drain.

Corrosive or toxic gases * Scrubbed before disposal.

Flammable gases * Vented to flare stack . * Diluted to a safe level

SAMPLE DISPOSAL VENTS There are only seven flammable gases, which are lighter than air.

HydrogenMethaneAmmoniaAcetyleneHydrochloric acidEthyleneCarbon monoxide

All other flammable gases and all other flammable vapours are heavier than air. They can flow across the ground covering wide areas.

CALIBRATIONCALIBRATION GASES / LIQUIDS Calibration gases: shall be stored in mounted horizontally mounted cylinders which can be shaken . Calibration liquids: When mixtures of liquids are stored in cylinders these should only be partially filled. The rest of the portion shall be filled with an inert gas such as N2 at such a pressure as to not let the liquid vaporise and then fractionate.

CALIBRATIONCalibration fluids - Zero fluid & Span fluidZero Fluid : used for checking the Analyser Zero Zero fluid contains none of the component of interest , but has quality which correspond to the AnalyserE.g. Nitrogen of suitable purity is often used as the zero gas.Span / calibration Fluid : Used for checking the analyser span. It is an accurately made-up mixture containing only the components to be measured ,but may contain an inert diluent. Span fluid should have a quality corresponds to 70% of the analyser reading.

MOUNTING OF ANALYSERS

Field mounting of Analysers

Field mounting of analysers may only be considered when:

The cost of an analyser house would be disproportionate to the anticipated advantages

The selected location of the analyser house(s) would result in unacceptable time lags.

The sample is non-flammable and the proposed mounting position is in a safe area.

MOUNTING OF ANALYSERS Field mounted - 2 pipe mounting , wall mounting types

Cabinet mounted

Analyser house

Analyser shelter

MOUNTING OF ANALYSERSWeather protection

Field mounted analysers shall be provided with adequate protection against; Rain

Sun radiation

Process and water spills

In some cases, shielding against radiant heat from surrounding equipment must be provided.

ANALYSER HOUSE (AH) THE OBJECTIVES :

Create a non-hazardous atmosphere So that testing or calibration and maintenance of the analyser can be performed with casings opened and electrical circuits alive.

Create a good environment In which analysers and their associated equipment are adequately protected against adverse whether conditions.

ANALYSER HOUSE (AH)SAFETY :

External explosion hazards

Internal explosion hazards Flammable Gases / Vapours

Flammable Liquids

ANALYSER HOUSE (AH)The Analyser House should preferably be a separate building.When the ventilation system is in the operation of Under the specified conditions & the purging (if required ) has been completed , the atmosphere inside the AH shall be non-hazardous in spite of the external area classification.

ANALYSER HOUSE (AH)It is also necessary to take into account of the characteristics of non- explosion protected apparatus,which may affect the safety of Analyser Houses on ventilation failure. False ceiling/flooring shall be avoided.Cable trenches shall be avoided. All the pipes/tubes supplying flammable substances to the Analyser house should be capable of being isolated outside the Analyser House.

ANALYSER HOUSE (AH)Quantity of flammable material in the Analyser house to be kept minimum for the normal operation of the equipment installed.Provide efficient ventilation system to dilute the level of flammable gas or vapour in case of an internal release.Provide safe disposal of samples.All electrical equipment intended to remain in operation during ventilation failure shall have protection suitable for Zone 1.

ANALYSER HOUSE (AH) Lighting and emergency Tele phone shall confirm to Zone 2 requirement. Switch off power to non-explosion protected instruments on ventilation failure.Use gas detectors to detect leakage & Power shall be switched off on reaching 20 % of LEL.The sample conditioning equipment shall be mounted on the outside wall close to the location of the relevant analyser and be adequately weather protected Isolate the lines handling hazardous material to the Analyser House.

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