ANALYTICAL TECHNIQUES TO FULFILL AIR POLLUTION MONITORING REQUIREMENTS

Author

Marita du Toit

Company and address

ABB Analytical, 3 Eglin Road, Sunninghill, 2157, South Africa

email

marita.du_toit@za.abb.com

Keywords

atmospheric pollution, monitoring, control, analytical measurements, NDIR, FID, FTIR

ABSTRACT

A question often raised by plants facing new air pollution monitoring requirements is whether there are proven technologies for measuring the wide range of pollutants they are being asked to monitor and report. The only defensible answer to this question is a very strong yes. While environmental monitoring up to this time has been largely limited to a few targeted gases like SO2 and NOX, process engineers have for years been accurately measuring the same wide range of gases environmental managers are now being asked to monitor. The combinations of rapidly advancing technology and a need for greater automated process control have combined to allow process engineers of today to accurately monitor essentially any process variable or gas needed. This paper defines the wide range of monitoring technologies readily available. The reliability and accuracy of these systems/technologies are supported in actual field examples. This paper provides the material necessary to insure that plant environmental managers fully appreciate the well-documented capability of modern day instrumentation to provide whatever data is required by the plants permit. More specifically, this paper provides the plant environmental professional with a practical path forward for selecting and installing the most cost effective air pollution monitoring technology commensurate with the specific stake, liability and preferences of his or her site.

The Atmospheric Pollution Prevention Act

The Atmospheric Pollution Prevention Act (45) of 1965, as amended, is the primary mechanism in South Africa for the management and control of air pollution. This legislation provides for the following:

Control of noxious and offensive processes, commonly known as Scheduled Processes, of which there are 162 listed in schedule 2 of the Act. These processes are deemed to be subject to the practice of Best Practicable Means of pollution abatement ("BPM"). BPM is a set of guideline standards issued by the Department of Environmental Affairs and Tourism stipulating the level of technology that is the best, practicable means of preventing or reducing to a minimum the escape of noxious or offensive gases into the atmosphere at source. These guidelines are continually updated as new cleaner technologies are developed. The Chief Air Pollution Control Officer of the Department of Environmental Affairs and Tourism controls the application of the BPM approach.

The Department of Environmental Affairs and Tourism is currently in the process of revising the Act. Any amendments to the Act will need to be applied in the DMA.

Analytical Instrumentation History

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).

Figure 1

NDIR SCHEMATIC

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.

Figure 2

UV Analyser Schematic

Paramagnetic Analysers are commonly used to measure oxygen, and are normally used in CEMS to measure oxygen as the diluent gas. Newer analysers of this type are more resistant to corrosion and are smaller than their predecessors, which result in a faster and more stable response. There are several types of paramagnetic Analysers. The more widespread is the dumbbell type or more properly, magneto dynamic, which uses a small dumbbell shaped optical component to physically determine the oxygen concentration. These have the limitation of having moving parts and optical components exposed to the sample gas, which may be corrosive. Another type of paramagnetic is the Magnetic wind or thermomagnetic type of Analyser, where there are no moving parts and the construction is of highly corrosion resistant materials, which results in an extremely robust Analyser with a long service life. Microprocessor technology has also advanced paramagnetic Analysers by allowing for surrogate calibration mixtures for difficult or impossible to prepare gas mixtures or very toxic mixtures.

Figure 3

Figure 4

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.

Schematic layout of a total hydrocarbon analyser

Mass spectrometers have been a basic laboratory tool for many years. The mass spectra of a compound provide a positive fingerprint identification of that compound. Mass spectrometers also have inherently broad chemical applicabilities because the ionisation process is fairly uniform for all compounds. One instrument can measure many compounds providing a cost effective means of monitoring. They are inherently fast, sensitive, and capable of a wide dynamic range (parts per billion to 100%). The mass spectrometer is quantitative and linear since its output is directly proportional to the concentration of the species in the sample. It is a reliable, stable and low maintenance instrument because it is electronically based rather than chemically based, as are many single sensors. Finally, the mass spectrometer has maximum flexibility because its broad capabilities can be selectively used under programmable microprocessor control. Recent advances in technology have been made which provide the elements necessary for continuous online applications such as CEMS and air monitoring. These developments include: the turbo molecular vacuum pump, which allows operation in minutes, highly reliable, and low maintenance; the quadruple filter, which provides measurement of any mass from 0-400 amu; low cost computing power, and packaging for continuous operation environments.

Figure 6

The mass spectrometer is used often to measure hazardous air contaminants, which require fast analysis. In situations where many sample points are required, the speed of analysis allows a multistream-sampling concept to be used. As many as eighty (80) port valves can be used to monitor many sample points throughout a plant or process. Thus, the flexibility of this instrument makes it possible to monitor many different streams using several different methods for several different gases (up to 40).

Fourier Transform Infrared Analysers are another technology that has been taken from the laboratory and used online for CEMS. The advents of inexpensive and powerful microprocessors have made this possible. One advantage of this method is that several gases can be monitored at the same time by the same instrument. Heated versions are available that make it possible to monitor hard to handle gases like HCl and NH3 down to 10 ppm. These units are found in applications in the monitoring of combustion sources, toxic waste incinerators, and industrial processes as well as ambient monitoring applications for hazardous air pollutants.

Figure 7

Basically, the FTIR is able to produce very detailed infrared spectra over a range of typically 2.5 to 25 microns wavelength. Through the power of modern microprocessors, the spectra is calculated from an interference pattern and matched mathematically with the sample data held in memory. A variety of algorithms have been developed to obtain the concentration values from the wealth of data provided by this instrument. An interesting feature offered by this technique is the storing of digital spectra, not just the calculated values. Some time later, the stored spectra can be processed to determine concentrations of other gas components that were deemed unimportant at the time. For example, if a process upset caused the release of gases not normally present, the spectra could be evaluated to determine if the release actually occurred and to what extent. The operation of the FTIR system is controlled completely by the PC software, enabling the following functions:

Display of all measured results and status messages on the monitor, manual interactive operation of the system during commissioning and servicing, remote diagnosis by modem, self-diagnosis, and archiving of measured data and self-diagnosis data. Technology and products are available to make most measurements. The formula to the best and most successful monitoring project is to find the most cost-effective approach that has the best workable solution and is in the hands of the end user. Customers, suppliers, and government agencies must work together to achieve realistic and cost effective protection of our environment regardless of the methods chosen.

Some detailed examples of environmental applications directly applying some of the above technologies follow.

Example 1, (Emission)

Continuous Gas Analyser

Emission Monitoring of Air Pollinates in Recovery Boilers in Pulp and Paper Plant.

(See Analyser System Layout Drawing)

This analyser system was designed to measure SO2, CO, O2, NOx and H2S (TRS). The sampling method used is extractive. An extractive gas analysis system operates under standard conditions. The emission gas is sampled out of the stack with a heated probe. The sample gas lines are heated and always need to be kept at a minimum. The gas sample enters the analyser panel via a 3-Way solenoid and an acid filter is used as protection for the sampling system. The sample gas is cooled to 3C in the cooler. The cooler removes the water in the sample gas. The gas sample is then pumped to the analysers via a sample pump. The analysers can handle a max of 60l/h and a pressure below 10 Kpa. The sample system has to be designed with these limitations in mind.

The SO2, CO and O2 will be analysed using a NDIR analyser with two measuring benches, one for SO2 and the other for CO. The O2 is measured with an electrochemical cell. A UV Analyser is used to measure the TRS and the NOx.

The H2S and mercaptans is converted to SO2 and reported as TRS (total reduced sulphur). The SO2 in the sample gas is dosed out with 3% H2O2 in the sample gas cooler.

a) Mercaptan + x O2 = yCO2 + z SO2 + nH2O

b) H2S + 3/2 O2 = SO2 + H2O

The reaction takes place at 800oC in the presence of oxygen. The flow must be 60l/h and the sulphur components needs to be < 1000 ppm.

NOx measured as NO

NO2NO

The reaction takes place at 800C with the aid of LF 316 Catalyst. The flow must be 60l/h and the NO2 concentration has to be between 100-3000 ppm.

Figure 8

Example 2, (Emission)

Stack Monitoring by FTIR

Analytical process instrumentation with a modular system concept

Advance Cemas emission monitor

Higher demands and stricter limitations in environmental protection require the continuous measurement of a growing number of pollutants that are emitted in lower and lower concentrations. To meet these demands of environmental protection the effects of processes have to be monitored exactly. Consequently, reliable instruments for gas analysis are important to realise the analytical requirements and demands. However, the instruments alone are not sufficient. Another essential part of the analysis system is an adequate sampling and sample conditioning unit as well as the integration into the measuring and control system as a whole. A comprehensive know-how is absolutely necessary because of the individuality of the different measuring tasks. Not everyone has this specialised know-how. Therefore, a partner is needed providing services which considerably exceed the mere delivery of high-quality, powerful instruments but include advisory service to users, engineering, system engineering, assembly, commissioning and training as well as after-sales service.

System Concepts

Based on proved standard modules, customised solutions are provided including sample conditioning, Analysers, system control as well as analysis systems ready for measurement, which have been tested for their intended applications. Due to the worldwide presence of ABB, systems are in accordance with different regional requirements. The analysis systems can be integrated into already existing systems or be delivered as complete system solutions, e.g. with integrated data management. With Advance Cemas, two multi-component measuring systems are offered for emission monitoring and process control based on different measuring principles: Advance Cemas- NDIR is based on Advance Optima, a system for process analysis. The infrared Analyser Uras 14, the oxygen Analyser Magnos 16 or the electrochemical oxygen sensor is used. The Uras 14 is capable of measuring some 50 to 60 different gas components.

Figure 9

CEMAS FTIR system

CEMAS FTIR components

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.

Mode of operation

(See Figure below)

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.

FTIR spectrometer

(See Figure below)

Figure 12

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.

System design

System cabinet

All components of the system are housed in a system cabinet. In the upper, cooled section are the FTIR spectrometer, computer, control system and analogue outputs, temperature controller, and as an option the O2 Analyser. Located in the lower section of the cabinet is the heated sample-gas feed.

Control and monitoring of temperature

All the heated circuits, i.e. filter system, sample line, sample-gas feed and sample cell in the FTIR spectrometer are regulated and monitored to 18oC. If the temperature falls below this level, a Fault status signal is output and the complete sample-gas path is purged with dry air via the filter apparatus.

Operation, display and data output

During commissioning, shutting down or maintenance tasks the system is operated via a menu-driven user interface displayed on a PC monitor. A PC keyboard enables operations to be controlled, parameters to be set and the menu to be modified. All measured data is displayed on the screen in the units requested, as well as output in the form of analogue signals (420 mA). All measured values relate to moist sample gas.

Example 3, (Process)

Tasks for the Process Gas Analysis

Cement Industry

Measuring Task

Measuring Component

Fire-Optimisation

CO - O2

Thermal  Optimisation

NO

Safety

CO - O2

 

 

 

 Coal Fire Power Plants Industry

Measuring Task

Measuring Component

Fire-Optimisation

CO - O2

Fire Monitoring

CO - NO - CO2 - O2

DENOX Efficiency

NO

E Filter Monitoring

CO - O2

Milk of Lime Dosing

SO2

Flue Gas Desulphurisation Efficiency

SO2 - O2

 

 

 

 

 

Iron and Steel Industry

Measuring Task

Measuring Component

Blast Furnace gas

CO - H2O - CO2 - H2 CH4 - N2

Coke Oven Gas

NH3 NO - H2S

 

 

 

Conclusion

It is proven that process engineers, in all the different industry sectors have for years been measuring the same wide range of components that Environmental Managers are now being asked to monitor. The key to successful environmental monitoring systems is to design a simple, easy to maintain, accurate and reliable analysis system. This paper has shown that the technology is available. It is now for the Environmental Managers to insure the correct implementation thereof.

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