【Q&A Question 015】2017.01.15
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This post was last edited by 955559 on 2017-7-21 at 12:54. [Q&A Question No. 015] January 15, 2017: What causes internal leakage in high-pressure heat exchangers? How to handle it? The reference answers will be visible after responding; points are awarded by identifying the key points. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) ) Phenomena: ① The color of the produced oil darkens, the impurity content increases, and quality parameters such as sulfur, hydrogen, and reaction-related aspects fail to meet the requirements; 2. The temperature rise in the reactor decreases. Treatment: 1. The quality of the produced oil is satisfactory, so production continues. ② If the quality of the produced oil is unsatisfactory and reducing the space velocity does not resolve the issue, the plant shall be shut down. 2017 Q&A Summary Thread (updates have begun) http://bbs.hcbbs.com/thread-1657793-1-1.html 2017 Daily Question Summary Thread (updates have begun) http://bbs.hcbbs.com/thread-1657794-1-1.html 2016 Q&A Summary Thread (updates completed) http://bbs.hcbbs.com/thread-1597792-1-1.html Xinchang Cup – 2016 Haichuan Top 10 Selection – Please recommend candidates http://bbs.hcbbs.com/thread-1654112-1-1.html Third Round of Haichuan Outstanding Management Members Selection http://bbs.hcbbs.com/thread-1655902-1-1.html (Source: Haichuan Chemical Forum)
1) The color of the produced oil darkens, the impurity content increases, and quality parameters such as sulfur, nitrogen, and reaction levels are not up to standard. (2) The reactor temperature rise decreases. Process; if the product is qualified, continue production. The product was substandard; reducing the air velocity had no effect, so production was halted.
After high conversion internal leakage. The product may exhibit abnormalities, with its performance parameters being abnormally high. Especially the sulfur content. If it is found that the product remains non-compliant over an extended period, and the standards cannot be met even by increasing the reaction temperature, a high internal leakage can be preliminarily inferred. So, we can take samples at the reactor outlet sampler for comparative analysis (it’s troublesome if there is no sampler). Through this comparative analysis, it is possible to determine whether there is internal leakage in the high-pressure exchanger.
Phenomena: ① The color of the produced oil darkens, the impurity content increases, and quality parameters such as sulfur, hydrogen, and reaction-related aspects fail to meet the requirements; 2. The temperature rise in the reactor decreases. Treatment: 1. The quality of the produced oil is satisfactory, so production continues. ② If the quality of the produced oil is unsatisfactory and reducing the space velocity does not resolve the issue, the plant shall be shut down.
Internal leakage refers to the phenomenon in heat exchanger equipment where the medium on the high-pressure side seeps into the low-pressure side due to certain reasons. Generally, internal leakage is very difficult to detect when it occurs. The main reasons for internal leakage in plate heat exchangers include plate perforation, cracks, and corrosion. To detect such leakage, it is necessary to regularly test the medium on the low-pressure side and make judgments based on changes in its composition. Plate heat exchanger manufacturers use the following methods for checking for internal leaks during shutdown: 1. Disassemble the plate heat exchanger, clean the dirt from the surface of the plates, dry them, and then reassemble the heat exchanger. Apply a water pressure of 0.2–0.3 MPa to one side; stop the test once water starts flowing out from the other side. Open the plate heat exchanger and carefully inspect the side that was not subjected to pressure testing – plates that are wet indicate that they have holes or cracks. 2. At the site, transparent and colored inspection methods can also be used to identify defective sheets. All defective sheets and gaskets identified in such inspections must be replaced; only after replacement and reassembly can they be used again.
Reduce output and suspend operations； If the sulfur content and color code of the product meet the requirements, seize the opportunity to shut down the production for treatment.
Phenomena of internal leakage in high-pressure heat exchangers: ① The color of the produced oil darkens, the impurity content increases, and quality parameters such as sulfur, nitrogen, and reaction levels are not up to standard. ②The reactor temperature rise decreases. Solution: ① The quality of the produced oil is satisfactory, so production should be continued. ②If the quality of the produced oil is unsatisfactory and reducing the space velocity does not resolve the issue, the plant shall be shut down.
Generally, circulating hydrogen leaks into the product oil, making it difficult to determine the issue. It can be assessed by checking the difference between the flow rate at the inlet of the circulating hydrogen heater and the flow rate at the inlet of the circulator. If high-pressure threaded lock rings are used and there is leakage in the tube or shell side, the internal bolts can be tightened to seal it； If it is a tube bundle corrosion leak, the only solution is to shut down the plant for repairs. If the impact on the hydrogen-to-oil ratio is minimal, it can be continued.