Design details of air separation unit
Insulation
In order to meet the needs of process production, maintain and exert production capacity, reduce cold loss, save energy, prevent surface condensation, and improve the working environment, low-temperature pipes need to be insulated. The insulation of this part of low-temperature pipes mainly adopts foam glass and vacuum insulation pipes.
Foam glass
Foam glass is an inorganic non-metallic glass material made by melting and foaming glass powder and foaming agent at high temperature. Its closed porous structure has good insulation performance, is non-flammable, has low water absorption, can be used at -196~400℃, and is widely used in the insulation of low-temperature pipes.
The pipeline insulation structure generally consists of an insulation layer, a moisture-proof layer and a protective layer.
A wear-resistant agent is usually applied to the inner layer of the foam glass to prevent the insulation material from wearing the metal outer wall and the contact surface between the insulation materials under temperature changes or mechanical vibrations.
Finished foam glass parts include pipe shells, curved plates, etc. The thickness of the insulation layer is graded in units of 10mm, with a minimum thickness of 30mm. When the foam glass cold insulation structure is used, the thickness of the cold insulation layer is relatively thick. Depending on the size of the pipe diameter, the thickness of the cold insulation layer varies from 150 to 250 mm. The outer diameter of the insulation requires a large space for the pipeline installation.
Vacuum insulation pipe
The pipelines from the liquid oxygen and liquid nitrogen distillation system to the storage tank, the atmospheric pressure liquid oxygen storage tank to the spare high-pressure liquid oxygen pump, the atmospheric pressure liquid nitrogen storage tank to the liquid nitrogen pump, and the spare medium-pressure liquid nitrogen pump to the vacuum liquid nitrogen storage tank all use vacuum insulation pipes. The vacuum insulation pipe consists of two concentric pipes, the inner and outer pipes are isolated by brackets, the outer surface of the inner pipe is wrapped with multiple layers of insulation materials, and the interlayer is in a high vacuum state.
Both the inner and outer pipes are made of stainless steel (06Cr19Ni10) seamless pipes.
The joints between the vacuum insulation pipe sections are flanged and welded. The vacuum pipe joints connected by welding are non-vacuum cold insulation, and pearl sand is filled in the joints for cold insulation. The nominal diameter of the vacuum insulation pipe provided by the process designer is generally the inner pipe diameter of the vacuum pipe. When selecting pipe supports and hangers, pipeline personnel should pay attention to the size of the outer pipe and leave enough space when laying the pipe. Vacuum insulated pipes are prefabricated in the factory and cannot be processed at the construction site. Once there is a deviation, the construction site cannot handle it, which is very likely to cause waste. Therefore, vacuum insulated pipes must be accurately prefabricated. In order to ensure the smooth progress of on-site construction, the supplier must provide the supplier with a pipeline axonometric drawing when ordering vacuum insulated pipes, and require the supplier to determine the final pipeline axonometric drawing after on-site measurement. After the equipment arrives at the construction site, the supplier's technicians and pipeline designers conduct on-site measurements to confirm the final vacuum insulated pipeline direction, bracket position and other issues. In the pipeline axonometric drawing, each section of the pipeline (straight pipe section, pipe fittings, etc.) is numbered, and the supplier marks the number in the pipeline axonometric drawing on each component to ensure the smooth installation of the vacuum insulated pipeline.
Regarding the manufacturing license for vacuum insulated pipes, JB/T 12665-2016 requires that cryogenic pipe manufacturers should obtain the AX-level cryogenic insulated pipe manufacturing license issued by the State Administration for Market Regulation, and engage in the manufacture of cryogenic pipe products within the level, variety range and validity period specified in the license. Article 3 of the "Notice of the General Office of the State Administration for Market Regulation on Issues Concerning the Safety Supervision of Pressure Pipeline Gas Cylinders" (Quality Inspection Office Special [2015] No. 675) stipulates: Cryogenic insulation pipes no longer need to obtain a special equipment manufacturing license. It is reported that the state will no longer issue AX-level cryogenic insulation pipe manufacturing licenses, which means that cryogenic insulation pipes are no longer special equipment and are no longer subject to administrative supervision and inspection.
