How should the air supply pipelines for pneumatic instruments in chemical plants be configured safely?

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In chemical processing plants, the piping arrangement for the air supply of pneumatic instruments is a crucial factor in ensuring their proper and safe operation. The piping configuration for pneumatic instruments involves various aspects, including the quality of the air source, the method of air supply, air supply to the control room, as well as the design and installation of the air supply system pipelines. 1. Quality requirements for the air source: The dew point of the air source in the supply system, under operational (online) pressure, should be at least 10°C lower than the local annual (seasonal) extreme minimum temperature in the working environment or historically recorded values. The particle size of dust in instrument air should not exceed 3 μm, and the dust concentration should be less than 1 mg/m³. The oil content in the instrument air should be less than 1 ppm. 2. Gas supply method for on-site instruments: The choice of gas supply method for chemical process instruments depends on the specific layout of the chemical plant, the location of the instruments, and the required gas consumption. In chemical processing plants, the methods of supplying air to pneumatic instrument pipelines mainly include the following: 1) Single-line air supply method: Suitable for situations where the instrument air consumption points are located in dispersed areas or require large amounts of air. The sample is usually taken from the main gas supply pipe or the gas supply trunk line. 2) Branch-type gas supply method: Suitable for situations where the gas consumption points for instruments are located in areas with high density. Typically, the source is taken from the main gas supply pipe. 3) Ring supply method: Suitable for applications where the gas supply points used in instruments require high stability in gas pressure. The ring-shaped gas supply method comes in two forms: main pipe ring shape and trunk pipe ring shape. The piping for ring-shaped gas supply from the gas source main pipe is installed by the piping specialists, while ring-shaped gas supply using trunk pipes usually takes its source from the gas source main pipe. Choosing the appropriate air supply method is crucial for ensuring the proper operation of pneumatic instruments and the stability of the system. 3. Air supply in the control room: Two sets of air filters and pressure regulators should be installed in parallel as the main air source in the control room, with the capacity of each set determined based on the total required capacity. The control room should be equipped with monitoring and alarm instruments for the gas supply system, including an indication of the pressure in the main gas pipeline and an alarm for low pressure. Nitrogen shall not be used as the second air source in the control room. On the outlet side of the filter pressure reducer, a pressure controller and a safety relief valve shall be installed; the discharge outlet shall be located outdoors. 4. The gas supply pipelines of the gas supply system should be installed overhead, to avoid being laid in unsafe environments such as those with high temperatures, radioactive radiation, corrosion, severe vibrations, or near discharge outlets of process pipelines or equipment. If it is difficult to avoid unsafe environments, appropriate measures should be taken to ensure the safety of personnel and equipment. In addition, the \"Design Code for Instrument Air Supply\" (HG∕T 20510-2014) and the \"Design Code for Instrument Air Supply in Petrochemical Industries\" (SH∕T 3020-2013) provide more detailed technical specifications and requirements, offering specific guidance and standards for the design of pneumatic instrument air supply pipelines in chemical plants. TIPS: It should be noted that currently, some chemical manufacturing companies use polyurethane (PU) plastic pipelines for the gas supply systems in their chemical equipment, but this may pose certain safety risks. The following safety reminders should be noted: The risks associated with using polyurethane (PU) plastic pipes as instrument control air supply lines mainly include insufficient pressure and temperature resistance, susceptibility to chemical corrosion, and potential safety issues. Firstly, the pressure and heat resistance of polyurethane plastic pipes are inferior to those of metal pipes. This may lead to pipe rupture or deformation in high-pressure or high-temperature working environments, thereby affecting the stability and safety of gas supply. (PU pneumatic hoses can maintain their physical properties and function reliably within a temperature range of -40°C to +90°C.) Secondly, polyurethane is sensitive to certain chemicals and may be corroded by them. In particular, under the influence of chemicals that might be present in the gas supply, polyurethane pipes could degrade or get damaged, which would in turn affect their service life and the overall safety of the system. Finally, polyurethane materials can pose safety issues under certain conditions; for example, in environments with static electricity, lightning, and stray currents, polyurethane pipelines can become potential sources of ignition, increasing the risk of fires or explosions. Therefore, although polyurethane plastic pipelines have advantages such as light weight and lower cost in certain applications, when used as gas supply pipelines for instrument control, it is necessary to fully consider the limitations of their physical and chemical properties as well as the potential safety risks, in order to ensure the safety and reliability of the system.