It is crucial to implement systematic daily maintenance to ensure the accuracy of LNG (liquefied natural gas) analysis data and the long-term stable operation of instruments. The maintenance work needs to cover the entire process from injection to testing.
1、 Gas system: the foundation of stability
The gas pathway is the "lifeblood" of chromatography, and its purity and stability are the primary prerequisites.
Gas source guarantee: Check the pressure of carrier gas (such as helium and hydrogen) and fuel gas daily to ensure sufficient supply. High purity gas (≥ 99.999%) must be used in conjunction with an efficient purifier and regularly replaced to remove moisture, hydrocarbons, and oxygen.
Leakage inspection: Regularly use leak detection solution to conduct tightness checks on all gas circuit joints, especially pressure regulating valves, injection ports, and chromatographic column joints, to prevent baseline instability and retention time drift caused by leaks.
Flow/pressure calibration: Regularly use electronic flow meters to calibrate the column front pressure and carrier gas flow rate to ensure the reproducibility of separation conditions.
2、 Sample injection and separation system: the source of precision
Injection port maintenance:
Spacer: Regularly (such as every 100 injections or according to the instructions) replace the injection spacer to prevent air leakage and debris contamination.
Lining: Regularly inspect and clean or replace the lining. High boiling point components in LNG samples are prone to remain and form active sites, leading to peak tailing or sample decomposition. It is crucial to use a deactivation liner and maintain its cleanliness.
O-ring: When replacing the spacer or liner, check and replace the sealing O-ring synchronously.
Column maintenance: Follow the manufacturer's recommended heating procedure to avoid exceeding the upper limit of column temperature. After completing the analysis, bake the chromatography column thoroughly to remove any residue. When shutting down, ensure that the chromatography column is at near room temperature and purged with carrier gas to prevent oxygen from entering.
3、 Detector: Sensitive Eye
FID (flame ionization detector): Check and optimize the flame state daily. Use high-purity gas and auxiliary gas. Regularly clean the nozzle to prevent carbon black or salt blockage, ensuring smooth ignition and high sensitivity.
TCD (Thermal Conductivity Detector): Absolutely avoid adding bridge current when no load gas is applied to prevent burning of rhenium tungsten wire. Ensure the stability of the detector's constant temperature chamber and avoid severe temperature fluctuations.
Summary:
By establishing and strictly implementing the entire process from gas path, sampling system to detector, and preventive maintenance checklist, the failure rate of LNG gas chromatography can be significantly reduced, ensuring the accuracy, repeatability, and long-term reliability of its analysis results, and providing solid data support for LNG trade delivery and process control.