Detection method for internal leakage in programmable valves of PSA systems

Thread Content

Detection method for internal leakage in programmable valves of PSA-CO2 systems. As the service life of PSA-CO2 systems increases, the valve spools in these programmable valves wear out severely, leading to increasing internal leakage. This results in cross-ventilation between the various adsorption towers, affecting their regeneration efficiency, reducing the production capacity of the PSA-CO2 systems, increasing power consumption, and lowering the recovery rate of useful gases. This becomes a bottleneck that limits the production capacity of the entire ammonia synthesis system. At the same time, it will lead to a decrease in the CO2 concentration at the air extraction outlet, as well as a deterioration in the gas quality, which affects the CO2 production capacity of the gas source and indirectly increases its production load. However, due to the characteristics of the PSA system’s process flow, the pipes and valves in each tower are interconnected and influence one another; it is somewhat difficult to determine which valve is leaking during production. Moreover, it is not possible to remove all of them for inspection, as this would be time-consuming and require too much effort, and replacing them all would be costly. As a result, the internal leakage issue in the PSA-CO2 system has not been resolved, and operating it in an impaired condition has restricted the production capacity of the ammonia system. Through observation and experimentation, I have developed a method that allows for rapid and accurate detection of internal leaks in the programmable valves of PSA-CO2 systems. Taking the PSA-CO2-833 system as an example, the specific steps for detection are as follows: 1. Method for detecting internal leaks in the programmable 4-5-pressure-equalization series valves: During periods of reduced load or short-term shutdown of the system, the 833 system is shut down first; the inlet and outlet valves of this system are closed, and one adsorption tower is selected as the tower for leak detection, with the pressure maintained at a constant level. The following example uses Tower A as a case study (the selection principle is to examine the pressure trend chart after parking; the adsorption tower with the smallest pressure fluctuations also has the least internal leakage, and thus it serves as the leak detection tower). ) The other 7 adsorption towers were depressurized to atmospheric pressure, and the 4–5–pressure equalization pipes were also brought to atmospheric pressure. To ensure the accuracy of testing, the inlet and outlet connection pipes of the 1–2–valve series must also be depressurized to atmospheric pressure during testing. The pressure inside the leak detection tower should be maintained at 0.6…0.7 MPa; if this level is not sufficient, the inlet valve 833 can be opened, along with valve 1A, to add pressure manually. Close the inlet valve, Valve 1A, and the connecting pipes of the Valve 1 series to bring the pressure to atmospheric level. First, test the Valve 5 series; open Valve 5A and use the pressure from the leak detection tower to fill the connecting pipes of the Valve 5 series, maintaining this pressure for a certain period of time. If there is internal leakage in the valve of series 5, the pressure in the corresponding adsorption tower will show an increase, which indicates that there is internal leakage in valve 5 of that tower. Record the internal leakage valves. After the testing is completed, except for the leak detection tower, all other pressurized adsorption towers are brought to atmospheric pressure, as are the connection pipes of series 5. If the pressure in the leak detection tower is insufficient, it is increased further. The testing for internal leakage in the programmable valves of series 4 is carried out using the same method; any valves that show internal leakage are recorded and sent for repair. 2. There are two methods for detecting internal leakage in the 1–2–inlet/outlet series of valves via programmed control: A: Using a leak detection tower, and applying pressure supplementation and release in accordance with the method used to determine internal leakage in the 4–5–pressure-equalization series of valves. For the range control 1 inlet series valves, valve 1A is opened to pressurize the series connection pipe, and any valves with internal leakage are identified and recorded. Release and reapply pressure once again, test the valves at outlet 2 of the control system; open outlet valve 2A and pressurize the connection pipe of series 2. Identify any valves with internal leaks and record them for repair. B: There’s no need to use the leak detection tower method; this method can only be applied when there is pressure in both the upstream and downstream sections. The 833 system is shut down; all 8 adsorption towers as well as the connecting pipes are brought to atmospheric pressure. First, the programmable valves of series 1 are tested. The inlet valve of the 833 system is opened, and the pressure from the previous processing stage is used to fill the connecting pipes of series 1. This pressure is maintained for a certain period of time; if there is any internal leakage, the pressure in the corresponding adsorption tower will increase. Record the internal leakage valves. Close the inlet valve of the 833 system, and bring all adsorption towers and connecting pipes to atmospheric pressure. To detect internal leakage in the programmable valves of Series 2, the automatic control valve at the outlet of the 833 system is activated; the pressure from the later stages of the system is used to fill the connection pipes of Series 2. This is maintained for a certain period of time, and if there is internal leakage, the pressure reading in the corresponding adsorption tower will increase. Record the internal leakage valves. Delivered for maintenance. 3. To detect internal leakage in the Series 3 valves that are under evacuation, it is necessary to first check and address any internal leakage in the Series 1–2–4–5 programmable valves; only then can the detection of internal leakage in Series 3 be carried out with accuracy. The method is as follows: Testing is carried out when the internal leakage in the 1-2-4-5 series of programmable valves has been resolved and there is pressure in the preceding process section. The 833 system is shut down; it is not necessary to release the pressure in the various towers. The inlet valve of the 833 system is opened, followed by manually opening inlet programmable valve 1 to repressurize each adsorption tower to a pressure of 0.6–0.7 MPa. Valve 1 and the system’s inlet valve are then closed, and reverse discharge valve 6 and valve 7 are opened. If the pressure in any adsorption tower drops, it indicates that there is internal leakage in the corresponding evacuation valve 3, and this should be recorded. Delivered for maintenance. 4. It is also necessary to check for internal leaks in valve 6 and valve 7 of the reverse exhaust system. If such leaks exist, air will be drawn back by the vacuum pump, which affects the vacuum level; moreover, the oxygen content in the evacuated air increases, impacting the gas supply and the production processes in related sections. For testing purposes, it is possible to use either tower A, C, E, or G to increase the pressure to 0.6–0.7 MPa, after which valve 3 for evacuation should be opened. If the pressure in the adsorption tower drops or if there is a sound of airflow coming from the reverse exhaust pipe, it indicates that there is an internal leak in valve 6. To test valve 7 for reverse discharge, select either B, D, F, or H; pressurize the corresponding tower to 0.6–0.7 MPa, then open valve 3 for evacuation. If the pressure in the adsorption tower drops, or if there is a sound of airflow coming from the reverse discharge vent, it indicates that there is an internal leak in valve 7. 5. To detect internal leaks in valves 8, 9, 10, and 11, it is necessary to ensure that all internal leaks in the programmable valves of the system have been resolved and that the butterfly valves at the inlet of each vacuum pump are properly sealed. The procedure is as follows: during testing, any one of towers A, C, E, or G can be selected to be pressurized to 0.6–0.7 MPa. First, open the exhaust butterfly valve of the evacuation system; then open valve 3 for evacuation. Next, slowly open butterfly valve 1 of the vacuum pump (e.g., vacuum pump No. 1). If the pressure drops, it indicates that there is an internal leak in valve 8. In that case, close valve 1 and open butterfly valve 3 of the vacuum pump; if the pressure drops again, it means there is an internal leak in valve 9. If internal leakage is detected in valves 10 and 11 during evacuation, replace them with either B, D, F, or H; then pressurize the corresponding tower to 0.6–0.7 MPa using the same method. During testing, it is important to note that when the vacuum pump is in operation and valves 1 and 3 are opened, this should be done slowly, and the degree of opening should not be too large, in order to prevent severe internal leakage in valves 8, 9, 10, and 11 from causing pressure spikes that could damage the pump. The above are the testing methods for various programmable control valves. Our company has a large number of PSA systems, but their process flows are similar. This method for detecting internal leaks in valves allows for testing to be carried out during short downtime periods, without affecting production. It also enables early detection of faults, allowing for timely arrangements for repairs and the restoration of the PSA system’s production capacity. This post was last edited by yang0570 on 2009-4-4 00:24]