Summary of Equipment Purging Work

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Summary of the purging work for the MTBE plant: Summary of purging the reaction, reaction separation, washing, and methanol recovery systems. To ensure the successful commissioning of the MTBE plant in just one attempt, we carried out comprehensive purging operations on the ether production reaction, reaction separation, washing, and methanol recovery systems. The summary is as follows: I. Basic information on the purging task (1) Conditions required prior to purging: 1. The pipelines and equipment in the process system must have been installed, and the strength tests must have passed. 2. The orifice plates, rotameters, etc. in the pipeline to be purged have had their internal components removed and then reinstalled in place; the root valves for differential pressure gauges, level gauges, pressure gauges, etc., are in the closed state. 3. Blind plates have been installed on the equipment, pipes, pumps, valves, etc. that are prohibited from being operated. 4. The construction and installation of temporary piping, valves, etc., for purging have been completed. 5. Process pipelines that require purging are generally not insulated temporarily (a wooden hammer is used to strike the outer wall of the pipeline during purging). 6. The external utility for supplying purge air has the capability for continuous gas supply. 7. The purging operators and installation/maintenance personnel have been assigned, and they are familiar with the purging plan. 8. Draw a schematic diagram of the purging process; this diagram should indicate the purging procedure, flow direction, exhaust outlets, temporary pipelines, temporary valves, etc., as well as any matters that need to be addressed in advance. 9. Prepare the purging record form to be signed by representatives from the user, the construction unit, and the commissioning department. (II) The equipment requiring purging and isolation includes: 5 material tanks ； 2 protection reactors ； 13 heat exchangers ； 20 pump units had their flow meters and control valves removed in 41 locations. (III) Tools and materials used for purging: 8″ pliers, 4 pieces ； Plum blossom wrenches, 17–34, 4 sets ； Pipe wrenches 12″, 4 pieces ； 4 steel-rubber handle screwdrivers ； Steel files, 14'' – 4 pieces; Sheet metal shears, 8'' – 4 pieces ； 8 rubber hammers with wooden handles ； 4 saw frames ； 5 scrub brushes ； 10 wire brushes ； Bolt loosener, 30 bottles ； Cleaning oil 20KG, grease 2 barrels ； Canvas gloves, 13 pairs ； Toolkit 4 pieces ； Goggles: 12 pairs, Earplugs: 20 pairs ； Dust masks, 20 pairs ； Target cloth 100 meters ； 1 barrel of white paint; 1 roll of asbestos sheeting for blasting and purging. II. Technical requirements for purging: (I) Purging principles: 1. When using air as the gas medium for purging pipelines, it is necessary to ensure an adequate flow rate of air, so that the flow velocity of the purging gas is greater than that during normal operation, or at least 20 m/s. 2. The pressure of the air used for purging process pipelines is generally required to be between 0.6 and 0.8 MPa; for applications where high purity in purification is required, the pressure can be increased slightly, but it should not exceed the operating pressure of the pipelines. Low-pressure and vacuum pipelines can be purged using a gas pressure of 0.15–0.20 MPa, as appropriate. 3. All instrument measuring components installed on the purging pipeline (such as flow meters, orifice plates, etc.) should be removed to prevent dirty debris flowing during purging from damaging these instrument components. At the same time, appropriate protective measures should also be taken for the control valve (in principle, it should only be passed after purge in front of the valve is successful; if necessary, it needs to be removed and connected with a temporary short pipe). 4. Before purging, blind flanges must be installed on the inlet side of equipment such as heat exchangers and towers; access to the equipment is permitted only after upstream purging is completed successfully. Under normal circumstances, the heat exchanger itself is not involved in the air purging process. 5. During purging, in principle, the control valves in the system shall not be used as the control valves for purging. When it is necessary to control the purging air volume, a temporary purging valve should be selected. 6. During purging, the connection between the safety valve and the pipeline should be disconnected, and a blind plate or baffle should be installed to prevent dirt and debris from reaching the bottom of the valve and causing wear to its sealing surface. 7. During system purging, all instrument pressure lead lines should be opened for purging, and they should be purged again during the comprehensive system purge test. 8. All vent flare lines and drain lines should be purged after the main pipe to which they are connected; the drains on the equipment housings, as well as the outlet pipes for level gauges and flow meters and the valves associated with them, must all be purged as well. 9. During the purging process, the purge air can enter the downstream system through the normal flow only after the upstream system is qualified. 10. For equipment with a pipe diameter greater than 500 mm and an inlet, manual cleaning should be carried out prior to purging, and any internal components that could interfere with the purging process must be removed. 11. All containers such as tanks, towers, and reactors should be manually cleaned again after the system has been purged successfully, and the corresponding internal components should be reset. When sealing them, the procedures specified for sealing work must be followed. (II) System purging air source: The air used for purging the pipelines and systems in chemical plants requires a large volume of flow, as well as a high flow rate through the pipelines and systems. Therefore, an adequate amount of air at sufficient pressure is necessary to meet the requirements for effective purging. To purge process pipelines with a diameter of 12”, an air compressor with a discharge pressure of 0.6–0.8 MPa and an air flow rate of around 7000 m3/h (standard) is required to continuously supply the purge air. Therefore, obtaining a purging gas source by utilizing a large compressor already present in or installable on the equipment to compress air is the best way to quickly complete system purging. For chemical plants that do not have air compressors with large capacity, purging operations generally employ methods such as sectional purging with industrial air and blast purging. (III) System purging method: 1. Purge each system one by one in the order indicated in the purging flowchart. During purging, purge the main pipes first; once the main pipes are satisfactory, then purge the individual branch pipes. During purging, the drain pipes, instrument pressure lead pipes, analysis sampling pipes, etc. must also be thoroughly purged to prevent the formation of dead zones. 2. Purging is carried out by intermittently releasing gas from various discharge ports, while the pipes are continuously struck with a wooden hammer. Special attention should be paid to welding seams and dead corners when striking, but the pipes must not be damaged, until purging is successful. 3. At the start of purging, air should be introduced into the pipeline slowly; once it is confirmed that air is being discharged from the outlet, the flow rate can be gradually increased to the required level in order to carry out the purging process, thereby preventing overpressure in the system due to issues such as faulty valves or blind flanges. 4. The container (tower) used as the gas source requires the openings of the associated pipelines to be sealed for blasting and purging ； The last time the gauge was removed from the equipment, it was sealed using a valve ； The glass plate level gauge only activates the drain valve. A system composed of closed equipment and associated pipelines to ensure the purging pressure and flow rate. 5. To ensure that the purging process is carried out in an orderly manner without any omissions, another flowchart of the purging process needs to be drawn. Colored markers should be used to indicate whether the preparations prior to purging have been completed, which stages of the purging have already been carried out, and the dates on which these tasks were performed. This allows all personnel involved in the purging process to clearly understand the progress and helps to prevent any areas from being overlooked during the system purging. This diagram should be archived for reference. 6. Pipeline purging is carried out using compressed air purging and blasting purging methods. For blast purging, 1.5-mm-thick asbestos boards are used as rupture discs. For pipelines undergoing blast purging along with the tower, the number of layers of asbestos boards should be determined based on the length of the pipeline, so as to minimize the gas injection time while ensuring the quality of the purging. Iron sheets are used as partitions between the pipeline purging outlet and the equipment nozzles as well as other nozzles, to prevent impurities from being blown into the equipment and other pipelines. The device serving as a gas storage tank should be equipped with a pressure gauge to ensure that the gas pressure inside the tank does not exceed 0.5 MPa. 7. During the system purging process, temporary reset should be carried out as required by the flowchart. After confirming that the purging is complete and satisfactory, the entire system should be reset in order to prepare for the subsequent comprehensive purging test of the system. (IV) Inspection methods and purge qualification standards. Whether the purging of each pipeline or system is successful should be jointly inspected by production and installation personnel. When the exhaust gas appears clean to the naked eye, with no colored impurities, a white cloth or a target plate coated with white lead paint should be placed at the exhaust outlet for inspection. If there is no rust, dust, moisture, other contaminants, or pitting on it within five minutes, then the purging is deemed successful. (5) Safety precautions: 1. Pay attention to personal safety during purging; clear markings should be placed on the exhaust outlets to prevent injuries. 2. Records should be kept of the temporary pipes, blind flanges, and gaskets added, so as to enable their restoration to their original state. 3. To accelerate the purging speed and effectiveness, use a wooden hammer or copper hammer to tap on the pipeline during purging, but be careful not to damage it. 4. For some important valves, strict internal leakage checks should be carried out; any leaks detected must be recorded, and the relevant personnel should be contacted to remove the faulty parts or replace them until the valves meet the required standards. 5. The purging personnel should be familiar with the process flow and PID diagram; during purging, they should follow the purging plan and refer to the PID diagram while keeping records. III. Status of purging 1. During the preliminary stage of purging, all process pipelines and equipment were subjected to hydraulic testing as well as water operation testing using pumps; as a result, there is a considerable amount of residual water and rust present. These are all the areas that need to be thoroughly purged at work, in order to minimize the risk of failures in the shielded pumps due to impurities. 2. All temporary facilities such as short pipes and valves used during purging, temporary filter screens and baffles at each suction inlet, etc., shall be removed, and all shall be restored to their original state after the purging is completed. 3. The shutdown points used during the purging of each heat exchanger, condenser, and reboiler shall have their original gaskets reinstated once the purging is complete, thereby reducing the workload for subsequent airtightness testing. 4. Count the number of gaskets lost or damaged due to purging operations, as well as the locations where new gaskets need to be installed, in order to provide first-hand data for the subsequent airtightness testing. 5. The purging work was essentially completed within 30 days, with all purging tasks in the system finished. 6. The process pipelines associated with other units are, due to reasons such as the need for coordination between parties, somewhat delayed compared to the scheduling of purging tasks within this unit. However, without affecting the overall work schedule, the purging of the relevant pipelines was essentially completed by the end of November. IV. Take advantage of this purging operation to enhance new employees’ practical independent operational skills and awareness. Master the key points of purging work, and gain a practical understanding of the technical requirements and characteristics of purging through actual work. For any issues with the process pipelines identified during the purging process, corrective action plans can be promptly submitted to the construction party. This helps to identify and resolve potential safety hazards at an early stage, laying a solid foundation for normal production in the future. Through the purging process, employees’ work capabilities and overall thinking skills were enhanced, helping to cultivate them into highly skilled and versatile workers, thereby laying a solid foundation. V. Existing shortcomings: The purge gas source used this time was the process air provided by the company. Due to the large number of users utilizing it during purging, the pressure in the pipeline network could reach at most 0.6 MPa. As a result, a stable and continuous pressure as well as airflow could not be maintained in the pipeline network of the purging system, which caused many difficulties in the purging process. In the end, most pipelines can only be cleaned using the blasting method, which increases the workload significantly. Furthermore, when purging the external pipeline network connected to this device and other devices, the timing cannot be adjusted according to our original plan, which results in a delay in the purging process.