Cleaning and Maintenance of Supercritical Carbon Dioxide Equipment

Supercritical carbon dioxide equipment is crucial in the chemical, food, and pharmaceutical industries. It is highly efficient and environmentally friendly, serving as a precision operational partner. Daily cleaning and maintenance not only affect extraction results and product purity but also impact equipment service life and production safety. Proper cleaning and maintenance are essential for ensuring stable equipment operation, requiring meticulous attention to detail.

Daily cleaning focuses on addressing minor stains and potential hazards; it is not merely a simple wiping process. Cleaning needs to target potential risks based on the specific characteristics of each component. Extraction and separation vessels, as core containers, are in direct contact with raw materials and products, so they must be carefully cleaned after each batch. Residues from processed plant extracts tend to accumulate, and grease and impurities can adhere to the vessel walls. Delayed cleaning will affect product purity and may even cause pipeline blockages. After opening the vessel, wipe its interior clean with a neutral detergent and a soft brush to avoid scratching the inner surface. Finally, dry the vessel with high-pressure nitrogen to prevent rust caused by moisture.

The exterior and pipelines of the equipment also require cleaning. Dust accumulation on the exterior can hinder heat dissipation. Regularly wipe the area around the electrical control cabinet with a dry cloth to reduce the risk of electrical failures. Select the cleaning method for pipelines based on the characteristics of the processed materials. After extracting waxy components, flush the pipelines with an ethanol solution at a temperature slightly above the wax melting point to prevent crystallization and blockage. Generally, purge the pipelines with low-pressure carbon dioxide for 30 minutes to remove any residual substances. Before conducting any cleaning operations, always turn off the power and gas supply. Never operate the equipment under pressure, as high-pressure leaks pose extreme dangers.

Vulnerable parts are often the weak points of the equipment, among which seals and sensors are critical components. Long-term exposure to high pressure and high temperature-similar to a continuously stretched rubber band-makes these parts prone to wear and aging. The O-rings in extraction vessels may deform or crack, leading to carbon dioxide leakage. This not only reduces extraction efficiency but may also cause accidents. Inspect the seals monthly and replace any defective ones immediately, ensuring that the replacement seals match the required material and specifications. For food-grade equipment, fluororubber seals should be used to avoid product contamination.

Sensors act as the "eyes" of the equipment. Temperature and pressure sensors are responsible for controlling the supercritical state of carbon dioxide. If the temperature sensor deviates by more than 1 degree Celsius, carbon dioxide cannot maintain a supercritical state, resulting in reduced extraction efficiency. Calibrate the sensors quarterly using professional equipment. Before calibration, clean the sensor probe to remove dust and oil stains, ensuring accurate measurements. Flow meters should also be inspected regularly to prevent blockage by impurities, which could cause flow rate errors and affect mass transfer processes.

In addition to daily cleaning and component inspections, regular deep maintenance is necessary to extend equipment service life. Conduct a comprehensive inspection every six months or annually, which includes pressure testing and leak detection. Extraction and separation vessels are pressure-bearing components, so a hydraulic strength test should be performed at a pressure 1.25 times the design pressure, with the pressure maintained for 30 minutes. Check for fatigue cracks to prevent equipment failure.

To detect leaks, apply soapy water to pipeline connections and check for bubble formation; alternatively, use a helium mass spectrometer for accurate leak detection. Thorough maintenance of the electrical system is also crucial. Open the electrical control cabinet and inspect the wiring for signs of wear, ensuring that terminals are securely fastened to prevent short circuits and electrical leakage. Clean dust from the control cabinet, focusing on the cooling fan and vents to prevent overheating and damage to electrical components. Regularly inspect the grounding system to ensure the ground resistance meets safety standards, as this is essential for protecting operator safety.

Many maintenance errors stem from incorrect assumptions, such as using improper cleaning agents or adopting incorrect operating procedures. When cleaning electrical components, never use water-even a small amount can cause a short circuit. The correct method is to remove dust with a dry brush and then blow the components clean with compressed air. When replacing filter elements, relieve the pressure first; do not remove the filter element under pressure, as the airflow may dislodge the element.

Some operators neglect material pretreatment. Using materials with high moisture content can lead to moisture freezing in low-temperature environments, causing pipeline blockages. Therefore, materials must be dried before use, with the moisture content generally controlled at ≤5%. Maintaining an inventory of spare parts is critical. For vulnerable parts such as seals and filter elements, stock suitable models in advance. This ensures that replacement parts are available promptly in case of malfunction, preventing production disruptions.

In summary, the cleaning and maintenance of supercritical carbon dioxide equipment should prioritize prevention. This involves conducting thorough daily cleaning, inspecting key components regularly, and performing comprehensive maintenance on a scheduled basis. By following these practices, the equipment can operate efficiently, maintain stable product quality, avoid safety incidents, and provide reliable support for production activities.