A carbon molecular sieve (CMS) is a core consumable in a pressure swing adsorption (PSA) nitrogen generation system, and its performance directly determines the purity of nitrogen and the stability of the equipment. Replacing a carbon molecular sieve is a highly specialized maintenance task with extremely strict requirements for the operating environment and process. The complete replacement process can be divided into four stages: preliminary preparation and safety, cleaning and inspection of the old carbon molecular sieve, filling the new molecular sieve, and subsequent commissioning and maintenance.
Preparation and Safety
Before replacement, the compressed air source must be cut off, all vent valves opened, and the pressure gauges of the adsorption tower and pipelines confirmed to be zero before power is cut off and flanges are removed. Carbon molecular sieves are extremely sensitive to moisture; moisture absorption and micropore blockage will lead to a permanent decrease in separation performance. Operators must wear protective equipment, and after opening the tank, dry nitrogen should be immediately introduced to purge and prevent humid air from entering.
Cleaning and Inspection of the Old Carbon Molecular Sieve
First, empty the old molecular sieve and the bottom activated alumina. Purge the inner wall of the tank and the distributor with dry air to ensure no oil or powder is present. Next, inspect the core components. Inspect the bottom and top support mesh for damage, and the palm gasket for rot or hardening. Replace any damaged parts; otherwise, the new molecular sieve will leak into the piping system, causing valve jamming and nitrogen purity degradation. Check that the cylinder clamping or spring clamping device operates smoothly, and replace all sealing rings. For the coconut gasket flange clamping, check the flange flatness. Pay special attention to the fillet welds at the connection between the inlet/outlet pipes and the tank; repair any cracks by welding. Apply anti-seize agent to all fastening bolts.
New Carbon Molecular Sieve Loading
The loading quality of the carbon molecular sieve directly determines the adsorption efficiency and service life of the PSA system. It must adhere to three principles: layered loading, dynamic compaction, and top overloading.
First, lay a layer of new palm gasket at the bottom of the tower, then evenly spread a 5-8 cm thick layer of activated alumina. This acts as a protective layer to adsorb oil and water, preventing high-velocity airflow from directly impacting the bottom of the carbon molecular sieve and causing pulverization. Secondly, the carbon molecular sieve must be filled within 30 minutes of opening and must not be exposed to humid air. Afterward, it should be filled in layers, compacting it with a vibrator on the outer wall of the tank every 15-20 cm to eliminate voids and prevent gas short-circuiting. Due to the pressure from the clamping mechanism and natural settling during initial operation, the filling height should be 5-10 cm above the design liquid level. Replace the gaskets and tighten the flanges symmetrically to compensate for natural settling after operation.
Subsequent Commissioning and Maintenance
After filling, an airtightness test is required. Charge the system with 0.8 MPa nitrogen and close all valves, maintaining the pressure for 24 hours. The acceptable standard is a pressure drop ≤ 0.01 MPa/h. If leakage exceeds the standard, the flange sealing surfaces and valve internal leakage must be re-inspected.
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