The carrier gas purification unit of a transformer oil chromatography analyzer is a core component ensuring the accuracy of analytical results. Through multi-stage physical and chemical treatment technologies, it effectively removes impurities from the carrier gas, reduces background interference, and thus improves detection sensitivity. This process involves key steps such as gas purity control, impurity adsorption, and molecular sieve separation, collectively constructing a pure carrier gas supply system from source to end.
Carrier gas purity is a fundamental factor affecting chromatographic analysis. Transformer oil chromatography analyzers typically use high-purity nitrogen, helium, or hydrogen as carrier gases. Although these gases have reached high purity in the cylinders, they may still contain trace amounts of oxygen, moisture, hydrocarbons, and other impurities. The primary task of the carrier gas purification unit is to stabilize the gas flow pressure through the synergistic action of pressure reducing and regulating valves, avoiding changes in gas purity caused by pressure fluctuations. Subsequently, the gas enters the primary filtration unit, where the physical adsorption properties of activated carbon or molecular sieves intercept large molecular impurities and particulate matter, laying the foundation for subsequent deep purification.
Chemical adsorption is the core step in carrier gas purification. The gas, after primary filtration, enters the chemical adsorption tank, where specialized adsorbents (such as copper-loaded activated carbon, silica gel, or alumina) specifically remove reactive impurities such as oxygen, moisture, and sulfides. For example, copper-loaded activated carbon converts oxygen into copper oxide through the catalytic oxidation of copper ions, which is then fixed on the adsorbent surface. Silica gel, with its high specific surface area and microporous structure, efficiently adsorbs moisture, preventing it from reacting with the stationary phase after entering the chromatographic column and interfering with the separation of the target gas. This process significantly reduces the concentration of chemically active impurities in the carrier gas, avoiding detector baseline drift or signal noise.
Molecular sieve separation technology further improves the purity of the carrier gas. Molecular sieves are aluminosilicate materials with a uniform microporous structure whose pore size matches the diameter of gas molecules, enabling gas separation through molecular sieving. In the carrier gas purification device, the molecular sieve column selectively intercepts small molecule impurities such as carbon dioxide and methane, allowing only pure carrier gas that meets the requirements of chromatographic analysis to pass through. This physical separation method does not rely on chemical reactions and features high stability and long lifespan, maintaining the high purity of the carrier gas for extended periods.
The terminal processing unit of the carrier gas purification system ensures that the gas entering the chromatographic column fully meets analytical requirements through precision filtration and flow stabilization control. The precision filter uses PTFE or stainless steel membranes to further intercept any remaining microparticles, preventing contamination of the column or detector. Simultaneously, the combination of a flow stabilizing valve and a pressure gauge allows for real-time monitoring and adjustment of the carrier gas flow rate, ensuring it remains stable within the set range and preventing decreased separation efficiency or abnormal detection signals due to flow rate fluctuations.
Reduced background interference directly improves detection sensitivity. When the impurity content in the carrier gas is controlled at extremely low levels, the detector's response to the target gas is more accurate, baseline noise is significantly reduced, and the signal-to-noise ratio is improved. For example, in a flame ionization detector (FID), pure carrier gas avoids the additional ion flow generated by the combustion of impurities, thereby reducing baseline noise and allowing for the clear detection of trace amounts of hydrocarbon gases (such as acetylene and ethylene). This improved sensitivity is crucial for early fault diagnosis, effectively identifying trace amounts of fault-specific gases dissolved in transformer oil.
The maintenance and management of the carrier gas purification system also affect the reliability of analytical results. Regularly replacing the adsorbent, molecular sieve, and filter membrane is crucial for maintaining purification efficiency, while periodic testing of carrier gas purity ensures the purification unit is always operating at its optimal condition. Furthermore, operators must strictly adhere to procedures to avoid introducing external contamination during cylinder replacement or equipment maintenance, thereby guaranteeing the continued effectiveness of the carrier gas purification system.
