Design of laboratory pneumatic system

Design of laboratory pneumatic system

1、 Types of laboratory gas used

The laboratory gas is mainly provided by gas cylinders, and some gases can be provided by gas generators. Common external color differentiation and labeling of steel cylinders: Oxygen cylinder (sky blue black text) Hydrogen cylinder (dark green red text) Nitrogen cylinder (black yellow text) Compressed air cylinder (black white text) Acetylene cylinder (white red text) Carbon dioxide cylinder (aluminum white black text, argon cylinder (gray green text) Helium cylinder (brown)

The commonly used gases in laboratories include high-purity gases used in precision analytical instruments, experimental gases used in chemical reaction experiments (chlorine gas), and auxiliary experimental gases such as coal gas and compressed air. High purity gases used in precision instruments such as gas chromatography, gas chromatography-mass spectrometry, atomic absorption spectroscopy, and 1CP mainly include non combustible gases (nitrogen, carbon dioxide), inert gases (argon, helium), and combustion supporting gases (oxygen).

2、 Laboratory gas supply method

The laboratory gas supply system can be divided into dispersed gas supply and centralized gas supply according to its supply method.

(1) Distributed gas supply refers to placing gas cylinders or gas generators separately in various instrument analysis rooms, close to the gas consumption points of the instruments, which is convenient to use, saves gas consumption, and requires less investment; However, due to the proximity of the gas cylinder to the experimental personnel, the safety is poor, and it is generally required to use explosion-proof gas cylinder cabinets with alarm and exhaust functions. Alarm devices are divided into combustible gas alarm devices and non combustible gas alarm devices. The gas cylinder cabinet should be equipped with gas cylinder safety warning signs and gas cylinder safety fixing devices.

(2) Centralized gas supply is the process of placing all types of gas cylinders required for various experimental and analytical instruments in separate cylinder rooms outside the laboratory for centralized management. Various gases are transported through pipelines from the cylinder rooms to different experimental instruments in each laboratory according to their gas requirements. The entire system includes a gas source collection pressure control section (manifold), a gas transmission pipeline section (EP grade stainless steel pipe), a secondary pressure regulation and diversion section (functional column), and a terminal section (joint, globe valve) connected to the instrument. The entire system requires good airtightness, high cleanliness, durability, and safety reliability, which can meet the requirements of uninterrupted and continuous use of various gases by experimental instruments. During use, the overall or local gas pressure and flow rate can be fully adjusted 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, away from laboratories, and ensure the safety of experimental personnel; However, the long gas supply pipeline leads to gas waste, and opening or closing the gas source requires going to the gas cylinder room, which is inconvenient to use.

3、 Safety regulations for gas cylinder rooms and gas cylinders

(1) Gas cylinders should be used exclusively for their own purposes and cannot be modified with other types of gases at will.

2) Gas cylinder rooms are strictly prohibited from being close to sources of fire, heat, or corrosive environments.

(3) Explosion proof switches and lighting fixtures must be used in the gas cylinder room, and open flames are prohibited in the surrounding area.

(4) The gas cylinder room should be ventilated and kept cool. There should be a leakage hole at the top of the gas cylinder room to prevent the accumulation of hydrogen gas.

(5) Empty bottles and solid bottles should be placed separately. Flammable and explosive gas cylinders in the gas cylinder room should be isolated from combustion assisting gas cylinders.

(6) The accessories such as bottle valves, connecting screws, and pressure reducing valves are intact and complete, without any dangerous situations such as air leakage, sliding wires, or loose gauge needles. Various pressure gauges should generally not be mixed.

(7) Gas cylinders must be stored and used upright. When the workplace is not fixed and they move frequently, they should be fixed on a dedicated handcart to prevent tipping over. It is strictly prohibited to use them lying down.

(8) Gas cylinders are strictly prohibited from being close to fire sources, heat sources, and electrical equipment. The distance from open flames should not be less than 10m. Oxygen cylinders and acetylene cylinders should not be placed together when used simultaneously.

(9) After use, empty bottles should be moved to the empty bottle storage area and labeled as empty bottles. It is strictly prohibited to mix empty bottles with real bottles.

(10) The gas in the cylinder cannot be used up completely, and a certain residual pressure must be maintained.

(11) Gas cylinders must be inspected regularly, and oxygen cylinders and acetylene cylinders must not be used beyond their expiration date. The inspection cycle for liquefied petroleum gas cylinders is 3 years, and the inspection cycle for argon cylinders and nitrogen cylinders is 5 years.

(12) Gas cylinders should be stored in the gas cylinder storage room outside the main building. For gases with a daily gas consumption of no more than one cylinder, a cylinder of that gas can be placed in the laboratory, but the cylinder should have safety protection facilities.

(13) The storage room for hydrogen and nitrogen gas cylinders should have ventilation measures with no less than three air changes per hour.

4、 Design Specification for Gas Pipeline

(1) Hydrogen, oxygen, and gas pipelines, as well as various gas pipeline branches introduced into the laboratory, should be laid openly. When hydrogen, oxygen, and gas pipelines are installed in pipeline wells and pipeline technical layers, ventilation measures should be taken for 1-3 hours of air exchange

(2) A general laboratory designed according to standard unit combinations should also have various gas pipelines designed according to standard unit groups.

(3) Gas pipelines passing through laboratory walls or floors should be laid in pre embedded sleeves, and there should be no welds on the pipe sections inside the sleeves. The pipeline and casing should be tightly sealed with non combustible materials.

(4) Vent pipes should be installed at the ends and high points of hydrogen and oxygen pipelines. The vent pipe should be at least 2 meters above the top of the layer and should be located within the 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 inside the pipeline.

5) Hydrogen and oxygen pipelines should have grounding devices to eliminate static electricity. The grounding and cross connection measures of gas pipelines with grounding requirements shall be implemented in accordance with the current relevant national regulations.

(6) Requirements for pipeline laying

1) Pipelines transporting dry gases should be installed horizontally, while pipelines transporting humid gases should have a slope of no less than 0.3% towards the condensate collector.

2) Oxygen pipelines can be laid on the same frame as other gas pipelines, with a spacing of no less than 0.25m. Oxygen pipelines should be located above other gas pipelines except for hydrogen pipelines.

3) When hydrogen pipelines are laid parallel to other combustible gas pipelines, the spacing should not be less than 0.50m; when laid cross over, the spacing should not be less than 0.25m. When laid in layers, hydrogen pipelines should be located above. Indoor hydrogen pipelines should not be laid in trenches or directly buried underground, and should not pass through rooms that do not use hydrogen.

4) Gas pipelines shall not be laid on the same rack as cables and conductive lines.

7) Seamless steel pipes should be used for gas pipelines. Gas pipelines with gas purity greater than or equal to 99.99% should use stainless steel pipes, copper pipes, or seamless steel pipes,

(8) The connection section between pipelines and equipment should use metal pipelines. If it is a non-metallic hose, it is recommended to use polytetrafluoroethylene pipes or polyvinyl chloride pipes, and latex pipes should not be used.

(9) Material of valves and accessories: Copper materials shall not be used for hydrogen and gas pipelines, while copper, carbon steel, and malleable cast iron materials may be used for other gas pipelines. The accessories and instruments used in hydrogen and oxygen pipelines must be specialized products for the medium and cannot be substituted.

(10) The contact part between the valve and 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 that has been treated with oil removal. (11) The material of flange gaskets in gas pipelines should be determined according to the medium transported inside the pipeline.

(12) Gas pipelines should be connected by welding or flange connection, while hydrogen pipelines should not be connected by threads. High purity gas pipelines should be welded by socket welding.

(13) The connection between gas pipelines and equipment, valves, and other accessories should be made using flanges or threaded connections, and the thread filling of threaded joints should be made of polytetrafluoroethylene film or a mixture of lead monoxide and glycerol filling.

(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 release pipes of each hydrogen equipment (group).

(15) Various gas pipelines should be clearly marked.

5、 Reference standards

GB50029-2003 "Design Code for Compressed Air Stations"

GB50030-1991 "Design Code for Oxygen Stations"

GB50031-1991 "Code for Design of Acetylene Stations"

GB50073-2001 (Code for Design of Cleanrooms)

GB50236-1998 "Code for Welding Engineering and Acceptance of Field Equipment and Industrial Pipelines"

GB503162000 "Design Code for Industrial Metallic Piping"

Design of laboratory pneumatic system