1、 Types of laboratory gases
The commonly used gases in laboratories include high-purity gases used in precision analysis instruments, experimental gases used in chemical reaction experiments (such as chlorine), and auxiliary experimental gases such as gas and compressed air. The high-purity gases used in precision instruments such as gas chromatography, gas chromatography-mass spectrometry, atomic absorption spectrometry, and ICP mainly include non combustible gases (nitrogen, carbon dioxide), inert gases (argon, helium), and flammable gases (hydrogen, acetylene) Combustion supporting gas (oxygen), etc. Laboratory gas is mainly provided by gas cylinders, and individual gases can be provided by gas generators.
2、 Laboratory gas supply method
The laboratory gas supply system can be divided into decentralized gas supply and centralized gas supply according to its supply mode.
Decentralized gas supply means that the gas cylinder or gas generator is placed in each Instrumental chemistry room, close to the instrument gas point, easy to use, gas saving and low investment; However, due to the proximity of gas cylinders to experimental personnel and poor safety, it is generally required to use explosion-proof gas cylinder cabinets with alarm and exhaust functions. The alarm is divided into combustible gas alarm and non combustible gas alarm. The cylinder cabinet should be equipped with cylinder safety warning signs and cylinder safety fixing devices.
Centralized gas supply refers to the centralized management of various gas cylinders that need to be used in various experimental analysis instruments, all of which are placed in independent gas cylinder rooms outside the laboratory. Various gases are transported through pipelines from the gas cylinder rooms to different experimental instruments in each laboratory according to the gas consumption requirements of different experimental instruments. The entire system includes a pressure control section for the gas source collection (manifold), a gas transmission pipeline section (BA grade stainless steel pipe), a secondary pressure regulation and distribution section (functional column), and a terminal section (joint, stop valve) connected to the instrument. The entire system is required to have good airtightness, high cleanliness, durability, and safety reliability, and can meet the requirements of the experimental instrument for uninterrupted and continuous use of various gases. During use, the overall or local gas pressure and flow rate are adjusted in full range according to the working conditions of the experimental instrument to meet the requirements of different experimental conditions.
Centralized gas supply can achieve centralized management of gas sources, keep away from the laboratory, and ensure the safety of experimental personnel; But the long gas supply pipeline leads to waste of gas, and opening or closing the gas source requires reaching the gas cylinder room, which is inconvenient to use.
3、 Code for design of gas pipelines
1. Hydrogen, oxygen, and gas pipelines, as well as various gas pipeline branches introduced into the laboratory, should be exposed. When hydrogen, oxygen and gas pipelines are laid in the pipeline shaft and pipeline technology layer, ventilation measures with Air changes per hour of 1-3 times per hour shall be taken.
2. For the general laboratory designed according to the combination of Standard cell, various gas pipelines shall also be designed according to the combination of Standard cell.
3. Gas pipelines passing through laboratory walls or floors should be laid in pre embedded sleeves, and the pipe sections inside the sleeves should not have welds. Non combustible materials should be tightly sealed between the pipeline and the casing.
4. Venting pipes should be installed at the ends and high points of hydrogen and oxygen pipelines. The vent pipe should be higher than the top of the layer by more than 2 meters and should be located in a lightning protection zone. Sampling and purging ports should also be installed on the hydrogen pipeline. The positions of the vent pipe, sampling port, and purging port should meet the requirements for gas purging and replacement in the pipeline.
5. Hydrogen and oxygen pipelines should have grounding devices that can conduct static electricity. The grounding and bridging measures for gas pipelines with grounding requirements should be implemented in accordance with the current relevant national regulations.
6. Pipeline laying requirements:
A. The pipeline for conveying dry gas should be installed horizontally, and the pipeline for conveying wet gas should not be less than 0. A slope of 3% towards the condensate collector.
B. Oxygen pipelines and other gas pipelines can be laid on the same frame, with a spacing of not less than 0. 25m, the oxygen pipeline should be above other gas pipelines except for the hydrogen pipeline.
C. When hydrogen pipelines are laid parallel to other combustible gas pipelines, their spacing should not be less than 0. 50m; When cross laying, the spacing should not be less than 0. 25m. When laying in layers, the hydrogen pipeline should be located above. Indoor hydrogen pipelines should not be laid in trenches or directly buried, and should not pass through rooms that do not use hydrogen.
D. Gas pipelines shall not be laid on the same frame as cables and conductive lines.
7. Seamless steel pipes should be used for gas pipelines. The gas purity is greater than or equal to 99. 99% of gas pipelines should use stainless steel, copper, or seamless steel pipes.
8. The connection section between pipelines and equipment should use metal pipelines. If it is a non-metallic hose, polytetrafluoroethylene pipes or polyvinyl chloride pipes should be used, and latex pipes should not be used.
9. Material of valves and accessories: Copper materials are not allowed for hydrogen and gas pipelines, while materials such as copper, carbon steel, and malleable cast iron can be used for other gas pipelines. The accessories and instruments used in hydrogen and oxygen pipelines must be specialized products for this medium and cannot be substituted.
10. The valve in contact with oxygen should be made of non combustible materials. The sealing ring should be made of materials such as non-ferrous metals, stainless steel, and polytetrafluoroethylene. The filler should be graphite asbestos or polytetrafluoroethylene treated with oil removal.
11. The material of flange gaskets in gas pipelines should be determined based on the medium conveyed inside the pipeline.
12. The connection of gas pipelines should be in the form of welding or flange connection. Hydrogen pipelines should not be threaded, and high-purity gas pipelines should be socket welded.
13. The connection between gas pipeline and equipment, valves and other accessories shall be flanged or threaded, and the thread packing of threaded joints shall be polytetrafluoroethylene film or Lead(II) oxide and glycerine blended packing.
14. The safety technology of gas pipeline design should comply with the regulations that flame arresters should be installed on the branch pipes and hydrogen vent pipes of each hydrogen equipment (group).
15. Various gas pipelines should be clearly marked.
4、 Referenced standards
GB 50029-2014 Code for Design of Compressed Air Stations
GB 50030-2013 Design Code for Oxygen Stations
GB 50031-1991 Code for Design of Acetylene Stations
GB 50073-2013 Code for Design of Clean Buildings
GB 50236-2011 Code for Welding Engineering and Acceptance of Field Equipment and Industrial Pipeline
GB 50316-2000 Design Code for Industrial Metallic Piping (2008 Edition)