FID-Based Online VOCs Monitoring System

 

The Online VOCs Monitoring System is designed for continuous monitoring of organic emissions from industrial stacks and process exhaust lines. A heated sampling line transfers the sample to the conditioning and analysis unit, helping reduce condensation and sample loss before measurement. Online gas chromatography separates the target compounds, and a flame ionization detector measures their concentration.

 

The analyzer determines methane (CH4) and total hydrocarbons (THC). Non-methane hydrocarbons (NMHC) are reported from the difference between the THC and CH4 results, so these terms are related measurements rather than three unrelated monitoring items. Depending on the selected configuration, benzene, toluene, xylene, and other target compounds can also be measured.

 

Auxiliary instruments can record temperature, pressure, flow velocity, moisture, and oxygen for emission calculation and operating-condition assessment.

 

 

• Methane (CH4)
• Total hydrocarbons (THC), used together with the methane result
• Non-methane hydrocarbons (NMHC = THC - CH4)
• Selected aromatic compounds, including benzene, toluene, and xylene, depending on configuration
• Exhaust temperature, pressure, flow velocity, moisture, and oxygen through auxiliary instruments

 

 

A representative gas sample is extracted from the stack or exhaust duct and transferred through a heated sampling line. After sample conditioning, nitrogen carrier gas sends the sample into the chromatographic column. Gas chromatography (GC) separates the target compounds according to their retention time. The separated compounds then enter the flame ionization detector (FID), which converts the hydrocarbon response into an electrical signal. The software uses the calibration curve to calculate concentration results.

 

 

Sampling unit	Sampling probe and heated sample line for continuous extractive sampling.
Sample conditioning	Filtration, heated transfer, and related conditioning components selected for the site conditions.
GC-FID analyzer	GC separates the compounds; the FID detects the hydrocarbon response. The system reports CH4, THC, and calculated NMHC, with selected aromatic compounds available by configuration.
Auxiliary instruments	Temperature, pressure, flow, moisture, and oxygen measurement when required.
Gas supply	Hydrogen and clean-air supply for FID operation, with pressure control and safety functions.
Data system	Industrial computer, monitoring software, data storage, reports, and communication interfaces.

 

 

• Inert sampling pipes and flow components help reduce sample adsorption.
• The heated gas path is maintained at 120°C to reduce condensation before analysis.
• Automatic filter purging helps remove dust and extend filter service life.
• Gas chromatography separates the compounds, and the FID provides quantitative hydrocarbon detection.
• Automatic FID flame monitoring, gas shutoff, and alarm functions support safe operation.
• The interface displays monitoring results and supports historical data review and reports.
• Target compounds and auxiliary exhaust parameters can be configured for different industrial applications.

 

 

Item	Reference specification
Measurement range	0-200 mg/m3; the range can be expanded for the project
Indication error	Not exceeding +/-2% of full scale
Flue gas temperature range	0-300 C
Measurement repeatability	No more than 2%
Flue gas velocity range	4-40 m/s
Zero drift / span drift	Not greater than +/-3% of full scale
Gas renewal flow rate	1.5-2 L/min
Gas collection flow rate	70–100 mL/min
Cabinet ambient temperature	0–40°C
Cabinet ambient humidity	20–90% RH
Compressed air demand	250 L/min

 

 

Possible addition	Material-derived wording
Analysis method	Gas chromatography with flame ionization detection (GC-FID)
Target results	CH4, THC, calculated NMHC, and selected benzene-series compounds, depending on configuration
Measurement cycle	Up to 2 min for NMHC; up to 3 min for benzene, toluene, and xylene
Output units	ppm, ppb, and mg/m3
Signal outputs	4-20 mA, 0–10 V, and network output are listed in the supplied material
Power supply	220 VAC +/-10%, 50 Hz +/-1 Hz

 

 

The monitoring software displays real-time concentration data and supporting exhaust parameters. It can store historical data, generate reports and transmit results to the customer's control system. Keep the current webpage wording wherever possible and add only communication interfaces confirmed for the current equipment.

 

 

• Petrochemical and chemical production
• Pharmaceutical manufacturing
• Automotive and component coating
• Furniture and wood-product coating
• Printing and packaging
• Semiconductor and electronics manufacturing
• Other industrial processes with organized VOC exhaust outlets

 

 

The installation plan is prepared according to the stack or duct layout, sample conditions, distance to the analyzer shelter, and available utilities. The project normally requires a suitable sampling point, safe maintenance access, power, instrument air or nitrogen, grounding, signal cables, and a controlled environment for the analyzer cabinet.

 

Routine work includes checking the sampling path and filters, verifying gas pressure, reviewing alarms, confirming FID flame status, and performing zero/span calibration with certified gas. Maintenance frequency should be set according to site conditions and the final equipment manual.

 

 

 

 

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