Purging scheme for low-temperature methanol washing

Ensure that every pipeline is thoroughly purged!

Blow out each device individually, blow out each pipeline individually, and ensure the appropriate amount of gas is used for blowing out.

I think the methanol wash is roughly divided into 3 stages for purging: high-pressure stage, medium-pressure stage, and low-pressure stage. However, this is relative; there are three sections: high-pressure section, medium-pressure section, and low-pressure section. During the purging process, attention should be paid to the pressure that the equipment in each section can withstand

(1) Purging Plan: To ensure the smooth commissioning of the low-temperature methanol washing unit, this purging and cleaning plan has been formulated. 1. Purpose of purging and cleaning: To prevent foreign substances such as cotton yarn, rust, iron shavings, sludge, and water that remain in the equipment and pipelines during manufacturing and installation from blocking the equipment, pipelines, and valves during operation, as well as from contaminating the liquid media within the system, it is necessary to purge and clean the interior of the equipment and pipelines to ensure the proper progress of system commissioning. During construction and installation, pipes and equipment retain various impurities such as rust, slag, sediment, and oil stains ； Through systematic purging, debris such as rust, dust, slag, sediment, and oil residues in the equipment and pipelines is removed, thereby creating the conditions necessary for chemical feeding. This prevents blockages in the equipment and pipelines, as well as damage to pumps and control valves caused by sand, gravel, and metal slag, ensuring that the feeding and commissioning process is successful on the first attempt. II. Conditions required for purging and cleaning: 2.1 Conditions to be achieved during construction: 2.1.1 The equipment and pipelines to be purged and cleaned must be constructed in strict accordance with the design requirements; all issues identified through the “three inspections and four confirmations” process must have been resolved, and any remaining tasks must have been completed. 2.1.2 The project quality inspection has passed, and the pressure test has been successful. 2.1.3 The device tag numbers, as well as the names of the pipeline media, flow directions, and identifiers, are all complete and meet the process requirements. 2.1.4 All equipment, pipelines, electrical systems, and instruments in the low-temperature methanol washing unit have been installed, meeting the technical requirements. 2.1.5 The utilities of water, electricity, steam, and gas are available for use. 2.1.6 The air separation unit has passed the commissioning tests and is ready to supply instrument air and nitrogen. 2.1.7 The floor inside the facility has been hardened in accordance with the design requirements, and the external drainage system is unobstructed, being in a usable condition. 2.1.8 The communication system and lighting system must meet the requirements of production. 2.1.9 Fire-fighting equipment and facilities are complete, and the emergency response system operates properly. 2.1.10 The purging and cleaning of temporary facilities have been completed in accordance with the requirements of the purging and cleaning plan. 2.1.11 The orifice plates, nozzles, transmitters, automatic control valves, thermocouples, etc. on the pipeline have been removed and stored properly. The instruments required for monitoring during the purging process (flow meters, pressure gauges) have been inspected and found to be of satisfactory accuracy; they are also properly protected. 2.2 Requirements for technical documents and materials: 2.2.1 The purging and cleaning plans have been thoroughly discussed, evaluated, and optimized, and have been approved by the competent authorities. 2.2.2 The purging and cleaning plan has been delivered to the staff involved in the purging and cleaning tasks, and discussed accordingly. 2.2.3 The operation records and various record forms are ready. 2.2.4 All types of tools and equipment required for purging and cleaning, as well as various other materials, are fully prepared. 2.3 Requirements for organizational structure and personnel involved in commissioning: 2.3.1 A leading group for equipment and pipeline purging and cleaning, comprising technical personnel for various positions as well as safety officers, should have been established, with clear divisions of responsibilities. 2.3.2 The personnel involved in purging and cleaning have received systematic training in safety, technical, and operational knowledge; they possess adequate safety knowledge, are familiar with this plan, have passed the relevant assessments, meet the requirements for taking up their duties, and hold safety operation certificates as well as qualification certificates for working on these tasks. 2.3.3 The personnel responsible for purging and cleaning are in place, and the scope of their responsibilities is clearly defined. III. Scope of purging and cleaning, as well as gas and water sources: 3.1. Scope of purging and gas source: 3.1.1. Rough and clean coal gas pipelines: Introduced from the high-pressure N2 pipeline at the low-temperature methanol washing unit; pipeline number: VHN15202 ； 3.1.2, CO2 pipeline gas source: Introduced from the high-pressure N2 pipeline entering C15202; pipeline number: VHN15203 ； From the C15203 low-pressure N2 pipeline, pipeline number: LPN15207 ； 3.1.3, Air source for exhaust pipeline: Introduced from the low-pressure N2 pipeline entering C15203; pipeline number: LPN15203 ； 3.1.4 Air source for the circulating gas pipeline: Introduced from the high-pressure N2 pipelines leading to C15201 and C15202; pipeline numbers: VHN15202, VHN15203 ； 3.1.5 Acidic gas pipeline gas source: Introduced from the low-pressure N2 pipeline entering C15204, pipeline number: LPN15208 ； 3.1.6 High-pressure N2 pipeline gas source: Supplied from the air separation unit via the high-pressure N2 pipeline; pipeline number: VHN15201 ； 3.1.7 Low-pressure N2 pipeline gas source: Supplied from the air separation unit via the low-pressure N2 pipeline; pipeline number: LPN15201 ； 3.1.8 Instrument air pipeline air source: Supplied from the air separation unit to the instrument air pipeline; pipeline number: IA15201 ； 3.1.9 Low-pressure steam pipeline gas source: Introduced from the low-pressure steam pipeline supplied by the thermoelectric plant; pipeline number: LS15201 ； 3.1.10、Gas source for the methanol-rich pipelines from C15201Ⅰ to C152011: Introduced from the high-pressure N2 pipeline of the air separation unit; pipeline number: VHN15201 ； 3.1.11、Gas source for the methanol-enriched pipelines from C15201Ⅱ to C15201Ⅲ, C15201Ⅳ, and C15202Ⅰ: Supplied by the high-pressure N2 pipeline from the air separation unit; pipeline number: VHN15201 ； 3.1.12、Gas source for the H2S-enriched methanol pipeline from C15202Ⅱ to C15203Ⅲ: Supplied via the high-pressure N2 pipeline from the air separation unit; pipeline number: VHN15203 ； 3.1.13、Gas source for the methanol vapor pipeline from C15204Ⅱ to C15205: Introduced from the low-pressure N2 pipeline entering C15204; pipeline number: LPN15208 ； 3.1.14、Gas source for the pipeline from C15205 to the wastewater treatment facility and C15206: It is supplied via the low-pressure N2 pipeline entering at C15204; pipeline number: LPN15208 ； 3.2 Cleaning Scope and Water Source: 3.2.1 For the cleaning of the methanol-poor pipelines from T15203 to C15205 and C15204Ⅱ, the water source is a temporary fire protection pipeline connected at T15203 ； 3.2.2 Source for cleaning the pure methanol pipelines from C15204Ⅱ to C15204Ⅲ, C15205, C15201Ⅰ, and C15202Ⅱ: Connect a temporary fire water pipeline at T15203, and start P15208 to continuously supply water to C15204Ⅱ ； 3.2.3、Water source for cleaning the methanol pipeline from C15204Ⅳ to C15205: Connect to temporary pipeline C15204Ⅳ for water supply ； 3.2.4、Water source for cleaning the sewage pipeline from C15206 to C15205: Connect to temporary pipeline C15206 for water supply ； 3.2.5 Source of cleaning water for the methanol return pipelines from T15201 to C15204 and the methanol drainage pipelines leading to the methanol tank area: Connect to temporary pipeline T15201 for water supply ； 3.2.6 Source of cleaning water for the methanol-enriched pipeline from C15203Ⅱ to C15201Ⅰ and the methanol spraying pipeline: Connect to temporary pipeline C15203Ⅱ for water supply ； 3.2.7, Water source for cleaning the H2S-rich methanol pipeline from C15203Ⅲ to C15203Ⅳ: Connect to temporary pipeline C15203Ⅲ for water supply ； 3.2.8 Source of cleaning water for the H2S-rich methanol pipelines from C15203Ⅳ to C15204Ⅰ and C15202Ⅱ: Connect to temporary pipeline C15203Ⅳ for water supply ； 3.2.9, Cooling water pipeline cleaning water source: Pipeline number CWS15201 ； 3.2.10, Water source for cleaning the boiler water pipeline at C15207: Pipeline number BFW15201 ； 3.3.11, Source for cleaning the desalination water pipeline up to C15206: Pipeline number DW15201 ； IV. Purging and cleaning control parameters: 4.1 The flow rate of the purging gas shall be no less than 20 m/s. 4.2 During water cleaning, the flow rate shall be set at the maximum flow rate that can be achieved in the pipe, or at a rate of not less than 1.5 m/s. 4.3 The purging pressure shall not exceed the design pressure. 4.4 The safety discharge cross-section for water flushing shall be no less than 60% of the cross-section being flushed. V. Qualification criteria upon completion of purging and cleaning: 5.1 The qualification criteria for cleaning the site, tanks, and equipment are as follows: “One flat, two clean, three visible, four absent, five not lacking”: One flat: The surface is level; Two clean: Door and window glass is clean, and the surrounding walls are clean; Three visible: The bottom of the trenches is visible, the interior of shafts is visible, and the equipment shows its original color; Four absent: There is no garbage, no weeds, no waste materials, and no unnecessary equipment; Five not lacking: There is a sufficient supply of paint, bolts, nuts, door and window glass, light bulbs and lampshades, as well as trench covers. 5.2 Qualification criteria for air purging: During air purging, a white cloth or a target board painted white is used at the exhaust outlet for inspection. It is considered satisfactory if no rust, dust, moisture, or other contaminants are found on it within five minutes. 5.3 Criteria for successful steam purging: The inspection is based on the aluminum target plate installed in the exhaust pipe; the surface of the target plate should be smooth, its width should be 5%–8% of the inner diameter of the exhaust pipe, and its length should equal the inner diameter of the pipe. After two consecutive replacements of the target plate for inspection, it is considered qualified if there are no more than ten visually visible impact marks on the target plate, and each mark is no larger than 1 mm. 5.4 Criteria for passing water flushing: It is considered successful if the color and transparency of the water at the outlet are visually consistent with those at the inlet (if there are specific inspection standards defined in the design, those standards shall apply). 5.5 After the purging and cleaning operations are completed and the pipes are restored to their original state, the construction unit shall, together with the project owner, conduct an inspection and fill out the \"Purging and Cleaning Record for the Pipeline System\". VI. Precautions for purging and cleaning: 6.1 Purging and cleaning should be carried out in sections after the pipeline system has passed the strength test, or before the pneumatic tightness test. 6.2 The purging method should be determined based on the requirements for using the pipeline, the working medium, and the degree of dirtiness on the inner surface of the pipeline. The order of purging is generally from the main pipes, to the branch pipes, and then to the drainage pipes. 6.3 Before cleaning, the instruments in the system should be protected, and orifice plates, nozzles, filters, filter elements, throttle valves, as well as the valve cores of check valves should be removed and stored properly to be reinstalled after the cleaning is complete. 6.4 Equipment and pipelines that are not allowed to be purged should be isolated from the purging system. 6.5 The dirt from cleaning the pipes must not enter the equipment downstream; the dirt that is blown out should generally not enter the pipes. 6.6 The pipeline purging should utilize sufficient flow rate; the purging pressure must not exceed the design pressure, and the flow velocity should be no lower than the operating flow velocity, generally not less than 20 m/s. 6.7 During purging, in addition to non-ferrous metals, wooden hammers should be used to tap the pipes; special attention should be paid to tapping the welds, dead corners, and the bottom of the pipes, but the pipes must not be damaged. 68. Before purging, the stability of pipe supports and hangers should be considered, and reinforcement should be provided if necessary. 6.9 The discharge pipe for water flushing shall be connected to a reliable well or ditch, ensuring smooth and safe discharge of the waste; the cross-sectional area of the discharge pipe shall not be less than 60% of that of the section being flushed. 6.10 Water with a chloride ion content exceeding 25 ppm shall not be used to flush austenitic stainless steel pipes. 6.11 For equipment such as towers, storage tanks, vessels, and containers, manual cleaning can be followed by purging. For heat exchangers, they can be purged together with the pipelines, but it is necessary to isolate the pipelines from the equipment’s manholes first; once the inlet pipelines have been successfully purged, the blocking plates should be removed, and after the pipelines are connected, the next section of pipelines can be purged. 6.12 For pipelines with larger diameters, purging is carried out using the intermittent method or the blasting method; if possible, equipment from this work order can be used as a storage tank. Once the pressure reaches a certain level, air is then introduced into the pipeline. A pressure gauge should be installed on the storage tank, and the pressure there should be kept below the operating pressure to ensure safe purging. 6.13 After flushing the pipeline, the water should be drained; if necessary, it can be dried with compressed air or other protective measures can be taken. 6.14 The purging gas for oil-free pipelines must be free of oil. 6.15 Before steam purging, the pipe should be heated slowly; condensate should be drained from the connection point, and after maintaining a constant temperature for a while, purging should be carried out. Then, the temperature should be allowed to drop naturally to ambient levels before heating again. The pipe should be kept at a constant temperature during the second purge, and this process should be repeated, usually no less than three times. 6.16 The exhaust pipeline for steam purging should be led outdoors and clearly marked; its outlet should be inclined upward to ensure safe discharge. The exhaust pipe must have secure support to withstand the reaction forces resulting from the evacuation process, and its diameter should not be smaller than that of the pipeline being purged. 6.17 Steam purging of insulated pipelines should generally be carried out before the insulation work begins; if necessary, local measures should be taken to protect workers from heat. 6.18 During cleaning and flushing, if it is necessary to work at heights, a high-altitude work permit must be obtained, and workers working at heights must wear safety belts. 6.19 Workers who enter towers, tanks, or vessels must obtain a permit to enter such containers, and there must be someone assigned to monitor them from outside. 6.20 Before sealing containers and pipelines, a thorough inspection must be carried out; they can only be sealed once no abnormalities are detected. 6.21 When performing manual cleaning, the following should be noted: ◆ Use a safe voltage for lighting ； ◆Ventilation should be considered for long-distance pipelines ； ◆If someone is cleaning inside the tower, cross-tasking must be avoided ； ◆When sealing the manhole, care should be taken to do so only after checking that all personnel and tools are present ； ◆When the purging is completed or comes to an end, the gas supply should be turned off promptly to prevent the system from…

One more thing: the process gas pipelines should be purged with instrument air or nitrogen； The steam pipeline should be purged with steam ； The liquid phase pipeline must be flushed with water!