ABB NGC8209 gas chromatograph maintenance

Hexane C6's 0.005-1 0.001 0.001

Heptane C7's 0.005-1 0.001 0.001

Octane C8's 0.005-0.5 0.001 0.001

Nonane and heavier C9+'s 0.005-0.5 0.001 0.001

Special key points for on-site installation and operation and maintenance

Even if the hardware design is excellent, the long-term stable operation of the chromatograph on site largely depends on the design of the sampling system and the standardization of daily maintenance.

3.1 Vaporization and Phase Management (Absolute Red Line)

When applying C6+or C9+heavy hydrocarbon analysis, the data manual provides an extremely strict warning: the maximum composition range of all calibrations must be established on the premise that the sample or calibration gas remains in the vapor state at all times in the probe, sampling cylinder, transmission tracing pipeline, sample processing module, GC interior, and injection module.

When on-site engineers are investigating faults such as "loss of heavy hydrocarbons" or "extremely low C6+readings", the primary suspect should be condensation caused by insufficient temperature in the heat tracing zone or Joule Thomson effect at the pressure reducing valve (regulator). Once the liquid is retained in the pipeline, it will not only cause component distortion, but also lead to column contamination.

3.2 Carrier gas consumption and H2S interference limitation

Under this application scheme, the typical consumption of helium carrier gas is 12 to 15 cc/min. For remote unmanned stations, operation and maintenance personnel need to calculate the replacement cycle of gas cylinders based on this.

In addition, the content of hydrogen sulfide (H2S) must be strictly controlled on site. H2S can interfere with the detector, and its concentration must be limited to 0.05 Mol% or 500 ppm. If the H2S in the process gas exceeds the standard, it will not only cause measurement errors, but also damage internal pipelines and valves due to its corrosiveness. It is recommended to install a desulfurization device or an online H2S analyzer for interlock protection in the sample processing system of the GC front-end.

Common troubleshooting strategies and calibration maintenance

When the chromatograph malfunctions, engineers can use its high-precision 24 bit ADC system to perform reverse inference through software chromatograms.

Baseline drift or flat peak:

Check if the constant bead temperature circuit is alarming. If the power supply of the detector circuit is abnormal, temperature fluctuations can cause baseline instability.

Insufficient purity of carrier gas or failure of purifier. Check if the carrier gas consumption (12-15 cc/min) is normal. If the flow rate drops sharply, it is necessary to investigate whether the gas path is blocked or leaking.

Deterioration of component separation (such as inability to separate C4/C5):

Check if the temperature of the chromatography column incubator is maintained at the set value of 140 ° F. Temperature fluctuations can directly alter the retention time of substances in the chromatographic column.

The valve or sample loop may be clogged with solid particles, resulting in inconsistent injection volumes. At this point, it is necessary to clean or replace the diaphragm/valve components of the injection system.

Poor repeatability of calorific value (deviation from ± 0.0125 index):

The standard gas has expired or the concentration is inaccurate. The exponential response factor of NGC is generated by four standard gases. If there is an error in the standard gas itself, the calibration will be invalidated. Four compliant mixed standard gases need to be reused to perform the calibration process.

Sample pressure fluctuations. If the pressure reducing valve of the sample processing system is not adjusted stably, causing the injection pressure to fluctuate, it will directly affect the repeatability of the measurement.

H2S interference investigation:

If a specific peak position is found to be abnormally elevated and cannot be eliminated through calibration, it is necessary to sample and test the H2S concentration in the gas source. Confirm if the tolerance limit of 500 ppm has been exceeded.