Device purging

For non-hydrogen pipelines, it is recommended to first purge them with steam and then wash them using water； Hydrogen pipelines or other gas pipelines can only be purged with nitrogen or unpurified air.

Are there any study materials on purging?

6.2 Purging of Pipeline Systems 6.2.1 After the pipeline system has passed the pressure test, it should be purged. Methods such as manual cleaning, water flushing, and air blowing can be used for purification. For pipelines with a nominal diameter greater than 600 mm, manual cleaning is recommended; for those with a nominal diameter less than 600 mm, clean water or air should be used for flushing or blowing. 6.2.2 Before purging the pipeline system, a purification plan should be prepared. Once approved, this plan should be presented to the personnel involved in the purification process for technical instructions. 6.2.3 Before purging the pipeline system, the following requirements must be met: 1. No orifice plates, flanged control valves, throttle valves, safety valves, or instruments should be installed. Appropriate protective measures should be taken for valves and instruments that are already welded to the pipelines. 2. Equipment and pipeline systems that are not part of the purification process should be isolated from the pipeline system being purified. 3. Pipeline supports and hangers must be secure; reinforcement may be necessary if required. 6.2.4 When flushing austenitic stainless steel pipeline systems, the chloride content in the water must not exceed 25 mg/L. 6.2.5 The purging pressure must not exceed the design pressure of the containers and pipeline systems. 6.2.6 When flushing pipeline systems with water, it is advisable to use the maximum flow rate, with a flow velocity of no less than 1.5 m/s. 6.2.7 After water flushing, the pipeline system can be checked by visually inspecting the color and transparency of the water at the outlet. It is considered satisfactory if the color and transparency are consistent with those at the inlet. 6.2.8 When purging pipeline systems with air, large compressors and storage tanks from the production facility can be used for intermittent purging. The maximum flow rate should be used, with an air flow velocity of no less than 20 m/s. 6.2.9 During air or steam purging, a white cloth or a target plate painted white should be placed at the outlet. It is considered satisfactory if there is no rust or other debris on the target plate after 5 minutes. 6.2.10 Pipeline systems with special cleaning requirements should be treated in accordance with specific technical procedures. 6.2.11 The purging process should be carried out in the order of main pipes, branch pipes, and drainage pipes. The dirt removed during purging must not enter equipment or pipeline systems that have already been cleaned, nor should it be discharged anywhere that could pollute the environment. 6.2.12 Pipeline systems that have been successfully purged should be restored to their original state promptly, and records of the purification process should be kept

Purging of hydrogen production equipment 1. Overview of purging 1.1 Purpose of purging Equipment purging is carried out after the construction of the equipment is complete and a thorough inspection has been done. Its purpose is to remove residues such as sediment and slag from the pipes and equipment, thereby preventing these substances from entering the catalyst beds as well as rotating equipment such as compressors and pumps during production. This helps to avoid a decrease in the catalytic activity of the catalysts and damage to the rotating equipment. It is also intended to examine the expansion of the pipelines under heating and pressure conditions, as well as to help the staff become more familiar with the process flow. 1.2 Purging preparation work a. The water, electricity, steam, air, and nitrogen pipelines are properly connected to the plant’s power system; there are measurement devices in place, as well as vent connections. b. Assign dedicated personnel to be in charge, familiar with the processes involved, and to identify the emission points as well as the gas (steam) supply points. c. Install blind flanges on the relevant pipelines and keep records. d. Close the inlet and outlet valves of each pump; install filters at the inlets to prevent dirt from entering the pumps during purging. Install blind flanges at the compressor inlets to stop impurities from getting inside the compressor during purging. e. Remove control valves, sharp orifice plates, flow-limiting orifice plates, flow meters, etc., from the pipelines, designate proper storage locations for them, and keep them safely to prevent loss. f. Contact the instrument technician to close the connection valves between the primary instruments and the pipelines, remove the bimetallic thermometers on those pipelines that are to be purged with steam and have a range of less than 250°C, and seal the thermometer openings with plugs. The removed thermometer should be stored properly, with proper records kept. g. Contact the dispatch team to prepare the media required for purging and flushing, and ensure that the steam pressure is ≮0.8 MPa, the industrial air pressure is ≮0.4 MPa, and the nitrogen pressure is ≮0.5 MPa. h. Contact relevant units such as maintenance, electrical, instrumentation, and construction teams, and assign security personnel to address any issues that may arise during the purging and flushing processes promptly. i. Prepare all the tools required for purging and flushing, such as: steam hoses, prefabricated splices, gaskets, blind flanges, target plates, etc. 1.3 Purging safety precautions a. During pipeline purging, no personnel other than those assigned to this facility are allowed to enter the site without permission. b. The personnel operating this equipment must wear the appropriate clothing as required, as well as safety helmets and protective gloves, to avoid being injured by debris blown out or scalded by steam. c. The steam hoses must be tied tightly, and the hoses used for temporary venting should be secured. d. When purging with steam, all remaining water must be drained to prevent water hammer from damaging the equipment and pipelines. e. A dedicated person should be assigned to monitor the intermittent drainage points to prevent steam from causing injuries. 1.4 Purging medium: a. The main process pipelines and equipment in systems such as desulfurization, conversion, medium-pressure transformation, and PSA are purged using industrial air or nitrogen. Due to its large supply volume and stable source, industrial air is the preferred medium for purging equipment. After the nitrogen lines and industrial air lines have been cleaned using their respective media, industrial air is connected via a temporary line to the main nitrogen line in order to purge the process pipelines within the equipment (steam must never be used for purging the conversion section, as the lower gas collection ducts are lined). b. After purging the device’s fuel line with 0.8 MPa steam, replace it with nitrogen ； After purging the solution system pipelines with 0.8 MPa steam, they are rinsed with demineralized water. c. The circulating water line, demineralized water line, deoxygenated water line, purified air line, unpurified air line, and the nitrogen line within the plant are purged and flushed with their respective media. d. The venting and sludge oil systems can be purged using steam; the pipelines connected to the equipment can be purged with the same medium used for purging the equipment itself. e. The steam system pipelines should be purged with steam of the appropriate pressure rating. f. The medium-pressure steam system needs to be subjected to shooting tests. 1.5 Precautions and requirements for purging: a. When introducing steam, it is necessary to first drain all the condensate water, and gradually warm up the pipelines to prevent water hammer. b. During cleaning, do not allow debris inside the pipelines to enter the tower and heat exchange equipment; instead, remove the inlet flanges or valves and insert thin iron plates as barriers for purging. Only after thorough purging should the tower and heat exchange equipment be reconnected. Equipment that crosses lines must also be purged along with those lines. c. When scanning to the control valve and meter, use a bypass line; remove the control valve and meter, and vent air from both the upstream and downstream ends of them until they are completely clear ； When purging the three-way valve, all the hot and cold flow tubes must be thoroughly cleaned. d. When purging the pump’s inlet and outlet, the inlet and outlet valves should be closed to prevent dirt from entering the pump; the pump’s return line should also be purged at the same time. e. When performing line cleaning, attention must be paid to the pressure of steam, nitrogen, and unpurified air; all teams should work together to adjust the distribution of gas flow across various system pipelines, ensuring that the gas used for cleaning has sufficient pressure to thoroughly clean the pipelines. f. All pipelines should be sorted by process to determine primary and secondary ones, and each system, line, and section must be thoroughly cleaned; no dead corners are allowed to remain. g. When the process on one side of the heat exchanger is purged with steam, the process on the other side must be emptied to prevent pressure buildup. h. When steam is introduced into the tower, both the vent at the top of the tower and the condensate drain at the bottom must be used for discharge; it is also essential to be careful and introduce the steam slowly to prevent the trays from being overturned. i. Steam should be used in a concentrated manner; having multiple steam supply points will lead to a decrease in pressure, thereby affecting the effectiveness of purging. j. All sampling points, relief valves, pressure gauge connections, instrument leads, and level gauges should be purged and leak-tested simultaneously with the pipeline equipment. k. When emptying a large amount, it should be done by a dedicated person to prevent injury. l. During pipeline purging, there must be sufficient pressure and flow rate; the purging pressure shall not exceed the design pressure, and the flow velocity shall be no less than 20 m/s. m. After the cleaning of a section of pipeline is completed, the removed valve flanges must be reinstalled, and the valves connected to that section of pipeline must be closed before proceeding with the cleaning of the next section. n. The pipeline that requires steam for purging must be supplied with steam only after the pipeline from which the steam is taken has been purged. o. During steam purging, the pipe should be heated slowly; after maintaining a constant temperature for one hour, purging is carried out. Then the temperature is lowered to ambient level, the pipe is heated again, and purging is done while keeping the temperature constant. This process is repeated at least three times. After steam purging, the pressure must be completely released, and the drain valve can only be closed after the temperature of the equipment or pipelines has dropped to room temperature. p. After flushing and purging are completed, all temporary installations installed must be removed to restore the system to its normal state, and the lowest points of the pipelines and equipment must be drained to remove any remaining water from the system. 1.6 Acceptance criteria for purging and flushing: a. During water flushing, it is considered acceptable if the color and transparency of the water at the discharge outlet of the pipeline appear identical to those at the inlet. b. During air or nitrogen purging, an inspection is carried out at the exhaust outlet using a target plate coated with white paint; it is considered satisfactory if no rust, dust, moisture, or other contaminants are found on the target plate within five minutes. c. Blow the pipeline with steam; use a sanded wooden board placed at the exhaust port to check – it is considered satisfactory if no rust or debris appears on the board within five minutes. d. When purging the pump inlet line (with filter), it is considered successful only if, after removing the filter, no debris remains attached to its surface.

Before a chemical processing plant is put into operation, all the process pipelines and equipment that have passed installation inspections must be purged and cleaned (hereinafter referred to as purging). The purpose of this is to use fluids such as air, steam, water, and various chemical solutions, along with purification and flushing methods as well as physical and chemical reactions, to remove debris such as sediment, grease, welding slag, and rust that remain within these components or are attached to their inner walls from the construction and installation process. This is done to prevent blockages in the pipelines and equipment during the commissioning phase of the plant； Damage to machines, valves, and instruments ； Contaminating catalysts and chemical solutions, affecting product quality, and preventing fires and explosions ； It is an important commissioning procedure to ensure the smooth commissioning of the equipment and its safe operation over a long period of time. In chemical plants, there are a wide variety of pipes and equipment, each with different operating conditions as well as varying materials and structures; consequently, the cleaning methods suitable for them also differ. But it usually includes the following methods: water flushing, air blowing, acid cleaning and passivation, oil cleaning, and degreasing, etc. Their main features and areas of application are summarized as follows. I. Water flushing: Water flushing is a method that uses water as a medium, pressurized by a pump, to clean pipes and equipment. It is widely used to remove residual dirt and debris from pipelines for transporting liquid media, as well as from equipment such as towers and tanks. Water flushing of pipes should be carried out at the maximum flow rate that can be achieved within the pipes, or at a flow velocity of not less than 1.5 m/s (this does not include high-pressure or ultra-high-pressure water jet cleaning equipment, nor methods for cleaning fouling on the inner and outer surfaces of pipe bundles). For general chemical processing equipment and pipelines, clear water with a turbidity of less than 10*106 and a chloride ion content of less than 100*106 is commonly used for flushing. However, for equipment and pipelines made of austenitic stainless steel, such as those in urea production facilities, deionized water must be used for flushing in order to prevent stress corrosion cracking (SCC) of the equipment and pipelines due to the accumulation of chloride ions (Cl-). Water flushing features ease of operation and no noise. II. Air Purging: Air purging is a method that uses air as the medium; after being pressurized by a compressor (usually to 0.6–0.8 MPa), this air is used to remove any residual debris from the pipes through which the gas is transported. When using air for purging, there must be an adequate volume of air such that the flow velocity of the purge gas is greater than that of the gas used in normal operation; generally, this velocity should be at least 20 m/s. This ensures that the purge gas has sufficient energy (or momentum) to remove any residual deposits in the pipes and equipment, thereby facilitating smooth commissioning of the system and ensuring safe operation. During air purging, the amount of air consumed is generally high, and a certain purging time is required. Therefore, air purging is usually provided by using the largest air compressor in the facility, or a large compressor capable of handling compressed air in the facility (such as the pyrolysis gas compressor in ethylene plants). For small and medium-sized chemical plants that lack the capability to supply large amounts of continuous purge air, a segmented purging method can also be employed. This involves dividing the system pipes into multiple sections, each of which is further divided into several sub-sections; purging is then carried out section by section, with each section being isolated from the system after it has been purged. In this way, the purging quality can be ensured even when the gas supply is limited. For large-diameter pipes or those in which dirt is difficult to remove, the explosive cleaning method can also be used. Oil-free air should be used for purging the oil-free pipeline and instrument air pipeline. Due to reasons such as source and cost, nitrogen is generally not used as a purging gas for ordinary pipelines and equipment; instead, it is commonly used for air purging, and for the protective displacement of pipelines and equipment after the system’s air has been dried to the required standard. III. Steam purging: Steam purging is a type of purging that uses steam with different parameters as the medium, with the steam source provided by a steam generator. Steam purging has a very high purging speed, and therefore possesses a large amount of energy (or momentum). The intermittent steam purging method causes the pipeline to contract and expand due to temperature changes, which facilitates the removal of deposits adhering to the inner wall of the pipeline; thus, it achieves the best purging results. Steam pipelines should be purged with steam, and this is especially necessary for power steam pipelines. When purging power steam pipes, it is necessary not only to thoroughly remove any dirt and debris attached to the inside of the pipes, but also to eliminate the rust on the metal surface; otherwise, if this rust gets carried along with the high-speed steam flow, it can cause severe damage to the rapidly rotating turbine blades, nozzles, and other components. Steam purging involves high temperatures, high pressures, and fast flow rates; as a result, the pipes expand when heated and contract when cooled. Therefore, steam pipes are equipped with compensators, steam traps, pipe supports, hangers, slides, etc., all of which are designed to account for these expansion movements. When air purging is not sufficient for cleaning non-steam pipelines, steam purging can also be used; however, it is necessary to consider whether the pipeline’s structure can withstand high temperatures and thermal expansion and contraction, and take appropriate measures to ensure the safety of personnel and equipment during the purging process. IV. Oil cleaning: For the lubrication oil, seal oil, and control oil pipeline systems of high-speed, high-load machinery such as steam turbines and centrifugal compressors, oil cleaning should be carried out after the equipment and pipelines have been successfully purged or pickled. Since such oil pipeline systems require an extremely high level of cleanliness, the presence of even tiny impurities in them can lead to damage to the bearing shells and seal rings of the machines in operation, as well as malfunctions in the control systems, resulting in serious accidents involving the machinery. The oil cleaning method involves circulating oil within the pipeline system; during this circulation process, the oil temperature must be raised and lowered 2–3 times every 8 hours within the range of 35–75°C, so that the particles attached to the pipe walls can fall off and be removed later by the oil as it passes through the filter elements. The cleaning oil should be high-quality oil suitable for that machine. Effective protective measures should be taken for pipeline systems that have passed the cleaning process. Qualified lubricating oil should be replaced before the machine is put into trial operation. The oil cleaning process takes a long time; it generally requires 40–50 days to be completed. To reduce the oil cleaning time, a mobile unit that uses a new type of fine filter to capture tiny ferromagnetic particles for high-flow oil flushing has been introduced to the market. Its oil cleaning time is nearly 2/3 shorter than that of the previous methods, which undoubtedly brings significant economic benefits to the commissioning of such devices. The criteria for determining whether oil cleaning is satisfactory: when the designer or manufacturer does not specify any particular requirements for the cleaning of the oil piping system, there are two methods to determine whether the oil cleaning meets the required standards. One method is to use the American MOOG Grade 4 standard for testing; this involves using the size of particulate impurities in 100 ml of oil as a criterion, and observing them under a 20x magnifying glass. If two consecutive samples meet the standards specified in Table 1-1-4-1, then it can be considered that the oil system has been properly cleaned. V. Degreasing: The degreasing of equipment and pipelines is a cleaning process intended for media such as oxygen, which may catch fire or explode if exposed to even small amounts of organic substances like oils during production, transportation, storage, or use; it is also used for other types of media whose contact with oils could affect product quality. To ensure the safety of testing and production, such equipment, pipelines (including fittings, valves, instruments, and sealing materials), as well as the tools and measuring devices used for installation, must all undergo strict degreasing treatment before being installed and put into use. Degreasing takes advantage of the fact that fats are soluble in certain chemical solvents; therefore, the process of degreasing is essentially a form of chemical cleaning. In addition, propanone, benzene, and alkaline solutions can also be used as degreasing agents. The most commonly used degreasing agent is carbon tetrachloride, as it has high degreasing efficiency, low toxicity and minimal corrosivity to metals, making it widely applicable.

During water washing, water is introduced into the tower – can it be fed in at the first tray at the top of the tower? ? Reason? ? ?