Gas Chromatography Installation and Commissioning Guide
The installation of a gas chromatograph requires careful planning and attention to detail to ensure proper operation and safety. Below is a comprehensive guide covering the setup, gas preparation, and commissioning process.
1. **Chromatograph Analysis Room Requirements**
- The room must be free from strong magnetic fields, flammable gases, and corrosive substances.
- The ambient temperature should range between 5°C and 35°C, with humidity below 85% relative humidity. Good air circulation is essential, and air conditioning is recommended in factories with the necessary infrastructure.
- A sturdy working platform should be prepared to support the instrument. A cement platform (0.6–0.8 m high) is ideal, positioned at least 0.5–1.0 m away from the wall for ease of wiring and maintenance.
- The power supply should have a capacity of around 10KVA. The instrument’s power should not be shared with high-power equipment or devices that cause frequent voltage fluctuations. Proper grounding is crucial—ideally, a grounding rod (0.5–1.0 m long) driven into moist soil or salt solution with a resistance of less than 1 ohm. It's also recommended to ground both the power supply and the instrument case for optimal performance.
2. **Gas Source Preparation and Purification**
- **Gas Source Preparation**: High-pressure gas cylinders (available in large and medium cities) should be used. Each cylinder is color-coded for specific gases and must not be interchanged. Typically, nitrogen, hydrogen, and air are used, with two cylinders per gas preferred. Some labs use hydrogen generators or oil-free air compressors. When cylinder pressure drops to 1–2 MPa, it should be replaced. For electron capture detectors, gas purity of 99.999% or higher is required.
- **Gas Purification**: Before entering the instrument, all gases should be purified to remove moisture, dust, and organic impurities. Chromatographs may come with purifiers filled with 5A molecular sieve, activated carbon, and silica gel. For hydrogen generators, additional drying chambers with larger volumes (over 450 cm³) and 5A molecular sieve are recommended. Air compressors must be oil-free, and their intake should be filtered. A mixture of 5A molecular sieve and activated carbon is typically used in the purification chamber.
3. **Unpacking and Initial Setup**
After unpacking the chromatograph, check all accessories against the provided list and store spare parts carefully. Place the instrument on the prepared platform according to the manufacturer’s instructions, connect all wiring and plug-ins, and finally link the recorder and data processor. Avoid connecting any connectors without confirmation.
4. **External Gas Line Connection**
- **Pressure Regulator Installation**: Install appropriate pressure regulators for each gas cylinder. Use two oxygen and one hydrogen regulator. Ensure hydrogen regulators have reversed threads and include an O-ring seal. Tighten the nut, close the adjustment handle, and open the cylinder valve. Check for pressure indication and leaks.
- **Gas Tubing Connection**: Connect the gas source to the instrument using stainless steel or pressure-resistant plastic tubing. Plastic tubes are easier to handle but require stainless steel liners and sealing materials at joints. Keep the tubing length as short as possible.
- **Leak Detection**: Seal the main gas path and check for leaks by adjusting pressure settings and observing if the low-pressure gauge remains stable. If pressure drops, identify and fix the leak using soap solution or other sealing methods.
5. **Gas Path Leak Test**
A critical step before operation, this test ensures no gas leakage, which could lead to unstable readings or even explosions. Block the column, turn on the carrier gas, and monitor the pressure for 30 minutes. If the pressure decreases, locate and eliminate the leak. For internal leaks, inspect the unit’s side panel with soapy water.
6. **Instrument Commissioning**
- Turn on the carrier gas flow and adjust the flow rate to 20–30 ml/min.
- Power on the main unit and check for unusual noises. Some instruments perform self-diagnosis to indicate normal or abnormal operation.
- Verify all temperature controls (column, injector, detector) to ensure they maintain stability across different temperatures, especially for precise column temperature control.
Proper installation and commissioning of a gas chromatograph are essential for accurate and reliable results. Following these steps will help ensure safe and efficient operation of the equipment.
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