Gas detection online pre-processing system

1、 System Overview

Gas detection online pre-processing systemIt is a key link connecting gas sampling points and analytical instruments, aimed at removing interfering components from the sample gas, adjusting the gas state, ensuring that the gas sample entering the analytical instrument is representative, stable, and clean, thereby ensuring the accuracy and reliability of monitoring data. This system is widely used in environmental monitoring, industrial process control, petrochemicals, metallurgy, power and other fields, targeting different monitoring objects (such as atmospheric environment)PM2.5TheSO₂TheNOxIn industrial waste gasVOCsRequirements for dust, acidic gases, etc. and analytical instruments require the configuration of corresponding pretreatment units.

2、 Core functions

1. Sample collection and transmissionCollect raw gas samples from fixed pollution sources or ambient air through sampling probes, and transport the samples to the pre-treatment system using heat tracing sampling pipelines or ordinary sampling pipelines. The heat tracing pipeline can prevent high humidity gases from condensing during transmission, avoiding loss of water-soluble components or accumulation of liquid pollution.

2. Particle filtrationUsing different accuracies (such asμmFilters (such as glass fiber filter membranes, metal sintered filter cartridges, polytetrafluoroethylene filter cartridges, etc.) are used to remove dust, aerosols, and other particulate matter from the sample, preventing them from blocking the gas path of the analytical instrument, damaging the sensor, or affecting the analysis accuracy.

3. dehumidify/dryWhen the humidity of the sample gas is high, dehumidification treatment is required. Common methods include:

oCondensation methodBy using semiconductor refrigeration or compressor refrigeration to lower the gas temperature below the dew point, water is condensed and precipitated, and then separated by a gas-liquid separator.

oAdsorption methodUsing desiccants such as silica gel, molecular sievesNafionThe tube adsorbs moisture.NafionThe tube can achieve continuous dehumidification when blowing dry gas, which is suitable for situations that are sensitive to moisture and require continuous monitoring.

4. Temperature and pressure regulationSome analytical instruments have specific requirements for the temperature and pressure of the sample entering, and the system needs to be equipped with temperature control devices (such as heating and insulation, cooling), pressure regulating valves, and stabilizers to control the temperature and pressure of the sample gas within the working range of the instrument.

5. Component removal and conversionSelective removal or conversion is required for components that may interfere with the analysis target in the sample. For example:

oUse chemical filters (such as activated carbon to adsorb organic interferents, alkaline adsorbents to remove acidic gases, and acidic adsorbents to remove alkaline gases).

oFor certain components that are difficult to measure directly, it may be necessary to convert them into measurable substances through catalytic conversion devices (such as...)NO₂convert toNO, orCOconvert toCO₂）.

6. Flow control and stability: Through a mass flow controller（MFC）Or the rotor flowmeter precisely controls and stabilizes the sample gas flow entering the analytical instrument, ensuring the repeatability and accuracy of the analysis results.

7. Backblowing and self-cleaningTo prevent clogging of the sampling probe and filter and extend the system maintenance cycle, the system usually has an automatic or manual blowback function, which uses clean air or inert gas to blow the sampling path.

3、 Main constituent units

1. Sampling probeDirectly inserted into the sampling point, the head usually comes with a primary filter, and the material is selected based on the corrosiveness of the gas (such as stainless steel, polytetrafluoroethylene).

2. Sampling pipelineTransport sample gas, divided into heat tracing type (with temperature control) and non heat tracing type, with materials that meet chemical compatibility and low adsorption requirements.

3. Preprocessing hostIntegrated filter and condenser/The casing of core components such as dryers, temperature controllers, pressure regulators, flow controllers, gas-liquid separators, and chemical converters.

4. Gas supply unitTo provide clean air sources (such as compressed air, nitrogen) for blowback, purging, driving pneumatic valves, etc., usually including air compressors, drying and purification devices, air storage tanks, etc.

5. Control and Display Unit: FromPLCOr it can be composed of embedded systems to achieve automatic control of various preprocessing units (such as temperature, flow rate, blowback cycle), and display system operating status parameters (temperature, pressure, flow rate, alarm information, etc.) through touch screens or upper computer software.

6. waste liquid/Waste adsorbent treatmentFor the waste liquid or saturated adsorbent generated by condensation dehumidification, corresponding collection and compliant treatment measures are required.

4、 Key technical considerations

1. representativenessThe preprocessing process should minimize the loss of the target analyte as much as possible, ensuring that the processed sample can truly reflect the composition and concentration of the original gas.

2. efficiencyEach processing unit (such as filtration, dehumidification, and interference removal) should have high processing efficiency to effectively remove interfering substances.

3. selectivityWhile removing interfering substances, avoid causing loss or impact on the target analyte.

4. Stability and reliabilityThe system should be able to operate stably for a long time, with long component life, easy maintenance, and low failure rate.

5. response speedThe lag time of the preprocessing system should be as short as possible to ensure rapid response to changes in gas concentration, especially suitable for process control or emergency monitoring.

6. compatibilityMatch with the interface, flow rate, pressure and other parameters of subsequent analytical instruments.

7. Automation and IntelligenceEquipped with automatic diagnosis, fault alarm, automatic blowback, remote control and other functions, reducing manual intervention and improving operation and maintenance efficiency.

5、 Application scenarios and selection criteria

1. Automatic monitoring of ambient air qualityTo cope with complex and changing meteorological conditions, the pretreatment system should focus on dehumidification, dust removal, anti condensation, and effective capture of low concentration pollutants. Usually, an online and continuous operation pretreatment scheme is adopted.

2. Fixed pollution source exhaust gas monitoringThe gas composition is complex (high temperature, high humidity, high dust, high corrosiveness), and the pre-treatment system needs to have high temperature resistance, corrosion resistance, efficient dust removal, and strong dehumidification capabilities. Sampling probes and pipelines often need to be accompanied to prevent tar and particulate matter from condensing and blocking.

3. Industrial process gas analysisAccording to specific process requirements, rapid response, high-precision flow and pressure control, as well as customized pre-treatment solutions for specific process gases (such as removing specific catalyst toxins) may be required.

4. Indoor air quality monitoringUsually, the concentration of pollutants is low and the environmental conditions are relatively mild. The pre-treatment system can be relatively simplified, with a focus on dust removal and minimal dehumidification.

When selecting, comprehensive consideration should be given to the properties of the monitoring target gas (composition, concentration, humidity, temperature, pressure, corrosiveness), the requirements of the analytical instrument, and the monitoring frequency (continuous)/If necessary, simulate and verify the pre-treatment plan based on factors such as intermittency, on-site environmental conditions, budget costs, and operational convenience.

Gas detection online pre-processing systemThe performance directly determines the quality of monitoring data, and its design, selection, installation, and maintenance must strictly follow relevant technical specifications and standards to meet the precision and intelligence needs of gas monitoring in different fields.