Extraction laser oxygen online analyzer

1、 Project Background and Requirements Analysis

1. Project BackgroundIn the industrial production process, oxygen content is a key process parameter, and its accurate measurement is of great significance for ensuring production safety, improving product quality, and optimizing energy consumption. Traditional electrochemical and magnetic oxygen analysis methods have problems such as slow response speed, large maintenance requirements, and susceptibility to interference, which make it difficult to meet the needs of modern industry for real-time, accurate, and stable monitoring.Extraction laser oxygen online analyzerBased on tunable semiconductor laser absorption spectroscopy（TDLAS）Technology has significant advantages such as good selectivity, high sensitivity, fast response speed, and low maintenance, and can be widely applied in gas analysis in fields such as power, petrochemicals, metallurgy, and environmental protection.

2. Requirements Analysis：

oMeasure components: Oxygen（O₂）

omeasurement range：0-1% O ₂The0-5% O ₂The0-10% O ₂The0-21% O ₂The0-100% O ₂(Select or customize according to the actual working conditions of the user)

omeasurement accuracy：≤±0.1%FSor≤±0.05%FS(Determined based on range and accuracy level)

orepetitiveness：≤±0.05%FS

oresponse time：T90 ≤ 5Seconds (depending on the lag time of the sample gas processing system)

oSample gas conditionsAccording to the actual situation on site, the sample gas may contain dust, water vapor, corrosive gases, high temperatures, etc., and pre-treatment is required.

oInstallation methodCabinet style installation inside the analysis cabin or control cabinet.

odata output：4-20mAAnalog signal (isolated output)RS485/RS232Digital signal（Modbus RTUProtocol), optional Ethernet interface.

oalarm functionHigh and low concentration alarm, instrument malfunction alarm (relay output).

oEnvironmental Requirements: Environmental temperature:-10℃~+50℃(Analyzer host); relative humidity≤90%RH(No condensation).

oPower supply requirements：AC 220V ±10%，50Hz.

2、 Technical principles

This analyzer is based on tunable semiconductor laser absorption spectroscopy technology（TDLAS）. The basic principle is that when a laser of a specific wavelength passes through the measured gas, the absorption intensity of the laser by the gas molecules and the gas concentration satisfy the Lambert equation-Bill's Law. By adjusting the operating current (or temperature) of the semiconductor laser, its emission wavelength is scanned across a specific absorption spectrum line of the measured gas molecule. The detector receives the transmitted light signal and processes it to obtain the absorption spectrum of the gas. By analyzing absorption spectra (such as peak detection method, second harmonic detection method, etc.), the concentration of the measured gas can be accurately calculated.

Laser oxygen analyzers typically select the absorption spectral lines of oxygen molecules in the near-infrared band, such as760nmThe nearby absorption band. This technology has the following characteristics:

·highly selectiveOnly absorb specific absorption lines of specific molecules, without interference from other gas components.

·high sensitivity: achievableppmevenppbLevel detection (depending on optical path length and detection technology).

·quick responseWithout the need for preprocessing, the response time can reach millisecond level, and with the addition of sample gas transmission and preprocessing system, it can still ensure a second level response.

·Low maintenance volumeLaser light sources have a long lifespan, simple optical path structure, and do not require frequent replacement of consumables.

3、 System composition

The extraction laser oxygen online analysis system mainly consists of the following parts:

1. Sampling probe and heat tracing pipeline：

oSampling probeA sampling point installed in process pipelines or equipment, used to extract representative sample gases from the process flow. The probe is equipped with a built-in filter (usually a metal sintered filter element) to preliminarily filter out large particles of dust in the sample gas. Select appropriate materials based on the temperature and corrosiveness of the sample gas (such as316LStainless steel).

oheat tracing lineUsing electric heat tracing composite tubes to maintain the temperature of the sample gas during transportation, prevent condensation of water vapor in the sample gas, and avoid certain easily condensable components (such as...)SO₃Condensation, blockage or loss of water vapor in pipelines. The heat tracing temperature is determined based on the dew point of the sample gas and is generally set above the dew point temperature of the sample gas10-20℃.

2. Sample gas pretreatment system：

oprimary filtrationFurther remove dust particles from the sample gas to protect the subsequent pretreatment unit. You can choose a cyclone separator or a precision filter (the filter element accuracy is usually1-5μm）.

oRefrigeration and dehumidification/dryIf the moisture content in the sample gas is high, dehumidification treatment is required. A commonly used compressor is a dehumidifier that cools the sample gas to a set temperature (such as5℃）By condensing and separating water vapor, the dew point of the outlet sample gas can reach5℃following. Or choose a membrane dryer as needed.

ofine filtrationRemoving trace droplets and residual dust that may be generated after dehumidification, the filter accuracy is usually0.1-0.5μm.

oVoltage and current stabilizationControl the pressure and flow rate of the sample gas entering the analysis unit through a pressure stabilizing valve and a flow stabilizing valve (or a mass flow controller) to ensure analysis accuracy. Usually, the sample gas flow rate is controlled within0.5-2L/min.

o(Optional) Chemical treatmentIf the sample gas contains gas components that interfere with laser absorption or corrode instrument components (such as...)H₂STheHClCorresponding chemical filters (such as activated carbon adsorption, neutralizing agent absorption, etc.) need to be added.

operistaltic pump/drain valveUsed for discharging condensed water generated during the pre-treatment process.

3. Laser gas analysis unit：

oLaser emission module: Contains specific wavelengthsDFBSemiconductor laser, laser driver circuit, and temperature control circuit. The laser is driven by a high-precision constant current source and cooled by a semiconductor cooler（TEC）Accurate temperature control ensures stable laser wavelength and narrow linewidth.

oGas absorption tankThe sample gas flows through the absorption cell, and the laser fully interacts with the sample gas in the absorption cell. Absorption tanks typically use multiple reflection structures (such asHerriottTo increase the optical path length and improve detection sensitivity, a pool is used. The material can be stainless steel or glass, with optical windows installed at both ends.

oLaser receiving moduleIncluding photodetectors (such asInGaAsPhotodiode and preamplifier circuit. The detector converts the received optical signal into an electrical signal and performs preliminary amplification.

oSignal processing and control unitIncludes high-speed data acquisition card, embedded microprocessor (or industrial control computer), and corresponding analysis software. Perform on the received electrical signalsA/DProcessing such as conversion, filtering, lock-in amplification (if harmonic detection technology is used), extracting gas absorption information, and based on Lambertian analysis-Bill's law calculates oxygen concentration. At the same time, this unit is responsible for monitoring and controlling the temperature, pressure, flow rate, and other parameters of the entire system, as well as communicating with the outside world.

4. Data display and communication unit：

oHuman computer interface（HMI）Usually a touch screen, it is used to display real-time measured concentration, historical data trend charts, instrument working status parameters, alarm information, etc., and can be used for parameter settings, calibration operations, etc.

oData output interface: Provide4-20mAAnalog outputRS485/RS232Digital communication interface, implementation andDCSThePLCWaiting for data exchange in the control system.

5. auxiliary unit：

ocabinetUsed to integrate the analyzer host, pre-processing module, and related electrical components, providing protection.

opower module: WillAC 220VConvert to the DC power required for each component of the system (such as+5VThe+12VThe+24V）.

oAlarm output moduleRealize relay output for concentration alarm and fault alarm.

4、 Technical parameters

5、 Installation and Debugging

1. Installation requirements：

oThe analysis cabin or installation location should avoid severe vibrations, strong electromagnetic interference, corrosive gases, and dust.

oEnsure good ventilation and heat dissipation.

oThe sampling point should be selected at a location in the process pipeline that is uniformly mixed, has a stable flow rate, and can represent the true state of the process.

oThe heat tracing pipeline from the sampling probe to the preprocessing system should be as short as possible to reduce transmission lag.

2. Installation steps：

oInstallation of sampling probeDrill holes on the pipeline according to the process requirements, weld flanges, and securely install the sampling probe to ensure sealing.

oConnection of heat tracing pipelineConnect the outlet of the sampling probe to the inlet of the heat tracing pipeline, and connect the outlet of the heat tracing pipeline to the inlet of the preprocessing system. Pay attention to interface sealing to prevent air leakage.

oThe analyzer cabinet is in placePlace the analyzer cabinet on a level and stable ground or platform, and secure the cabinet.

oPreprocessing system installationIf the preprocessing unit is designed modularly, install it in the designated location inside the cabinet and connect the internal air pipeline.

ocircuit connection: ConnectAC 220VPower line (pay attention to safety grounding), signal line（4-20mATheRS485Alarm output, etc.

3. debug content：

oGas path leak detectionConduct strict leak detection on the entire sampling, transmission, preprocessing, and gas chamber air circuit system to ensure no leakage.

oElectrical inspectionCheck the power supply voltage, whether the power supply of each module is normal, and whether the grounding is good.

oParameter SettingsSet the instrument measurement range, alarm value, sample gas flow rate, heat tracing temperature and other parameters through the touch screen.

ozero point calibrationIntroduce validated zero gas (such as high-purity nitrogen)N₂, purity≥99.999%）Perform zero point calibration.

oRange calibrationIntroduce standard gas of known concentration（O₂Perform range calibration using standard gas. The number of calibration points is determined according to the accuracy requirements, usually1-2Point.

osystem joint debuggingCheck whether the sample gas flow rate, pressure, and temperature are stable within the set range, observe whether the instrument measurement values are stable, and whether they are consistent with the standard gas concentration. Test whether the data output is normal and whether the alarm function is reliable.

oSimulated working condition testingIf possible, simulate actual operating conditions (such as temperature and humidity changes) and observe instrument performance.

6、 Operation and maintenance

1. Daily operation monitoring：

oRegularly check whether the measured values displayed by the analyzer are within a reasonable range and whether the trend is normal.

oCheck if the status indicator lights on the instrument panel are normal and if there are any alarm messages.

oCheck if the flow rate, pressure, and various components of the pre-treatment unit (such as filter pressure difference, refrigeration temperature, and drainage) are normal.

oRecord instrument operating parameters and calibration records.

2. regular maintenance：

odailyInspect, check the status of instruments, and discharge condensate water.

oweeklyCheck if the filter element is clogged (determined by differential pressure gauge or flow rate changes), and replace as needed. Check if the heat tracing pipeline is working properly.

omonthlyPerform a single point calibration or verification using zero gas and range standard gas to verify the accuracy of the instrument. Check if the air circuit connection is loose.

oquarterly/half a yearAccording to the cleanliness of the sample gas, replace the precision filter element and dryer adsorbent (if used). Check if the photodetector and laser head window are clean, and gently wipe them with anhydrous ethanol and lens paper if necessary.

oevery yearConduct a comprehensive performance check and calibration (multi-point calibration) on the analyzer. Check the sampling probe filter and replace it as needed. Check the heat tracing effect of the heat tracing pipeline and replace the aging heat tracing strip in a timely manner.

3. Fault handling：

oNo display or unable to startCheck the power supply, fuse, and power module.

oAbnormal measurement value (high)/low/Large fluctuationsCheck if the sample gas is normal (flow rate, pressure, leakage); Check if the preprocessing system is malfunctioning (filter blockage, poor dehumidification effect, pollution); Check if the light path is aligned and if the window is contaminated; Perform calibration verification; Check if there are any interfering components entering.

ocommunication failureCheck the communication line connection, communication parameter settings (baud rate, address, parity), and whether the communication interface is damaged.

oAlarm malfunctionCheck the alarm parameter settings, relay output circuits, and external alarm devices.

4. spare partsIt is recommended that users stock up on commonly used vulnerable parts and consumables, such as various specifications of filter cartridges, sealing rings, desiccants, standard gases, etc.

sevenConclusion:

Extraction laser oxygen online analyzeradoptedTDLASTechnology, combined with a sophisticated sample gas pretreatment system, enables continuous, accurate, and reliable online monitoring of oxygen content in industrial processes. Its high selectivity, fast response, and low maintenance make it an ideal choice to replace traditional analytical methods. This technical solution, through carefully designed system composition, strict installation and debugging, and standardized operation and maintenance, can ensure the long-term stable operation of the analyzer, provide accurate measurement data for users, meet the needs of production process control and safety monitoring, and have significant economic and social benefits.