Our company’s PVC production line has recently experienced 3 batches of crude material in a row! Why? Please give me lots of advice! !
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The 5# reactor produced coarse material twice in a row! Monomer, water, and the amount of dispersion initiator are all normal! When the reaction progressed to 50–70 minutes, the stirring current curve dropped suddenly from 140 A to 130 A; on-site sampling revealed the formation of particles, so a terminator was added and the material was recovered After opening the cover for inspection, severe sticking to the inner wall was found in the upper part of the kettle. The cause of the rough material is unknown, and the workshop technicians and supervisor are still working to find it out. Shortly after, coarse material reappeared in Reactor 3#; the raw materials were normal, yet the stirring current showed abnormalities within 50–70 minutes. The stirring current suddenly increased from 140A to 150A and then to 190A, resulting in the formation of coarse particles; the reason for this is unknown. Inspection measures taken: the quality of the monomer (high-boiling and low-boiling types) was checked, water was drained from the monomer storage tank 8B, the pH value of the soft water used in the reactor was examined, and the dry basis amount and concentration of the dispersant were found to be normal. Additionally, with the same parameters and addition amounts, the reactions in the other reactors have proceeded normally so far. Possible causes: 1) There is a problem with the stirring in this reactor; 2) The TK5C liquid level was low when dispersant 1 was added (but it was normal in the other reactors). I hope everyone can provide more guidance – our PVC production team will be very grateful for any suggestions you have!
:):time: Since both the dry basis amount and concentration of the dispersant are normal, check the actual amount of dispersant added to the tank; there should be no issues with the tank’s mixing mechanism, as changes in current occur only before and after temperature elevation.
Are you using domestic dispersants? Our factory encountered the same issue; switching to imported dispersants resolved the problem, as the quality of domestic dispersants is not very stable
Which design institute designed you? Are there five kettles in total?
There will be no issues with stirring in the reactor; this can be seen from the stirring current. Verify that the dispersant level in each reactor is consistent between the DCS system and the actual conditions on site
It may be due to the dispersion system, related to the dispersant and buffer
I’m sorry, I don’t have a computer; I just got online. We have calibrated the dispersant flow meter, and the dosage is correct! Now, coarse material has appeared again in reactors No. 4 and No. 6 of my PVC process. It’s so annoying! ! The reasons I analyzed this time are as follows: On-site inspection: At 50–70 minutes after the reaction began, an inspection of the material discharged from the system showed that it contained only unevenly shaped coarse particles, along with water. After adding a terminator and discharging the material for sampling, it was found that the sample consisted almost entirely of uniform, normal fine particles! Suspicion: After adding Dispersant 1, the dispersion was uneven; layers formed inside the reactor, with more FSJ1 in the upper part and less in the lower part. The monomer was not fully dispersed, resulting in large liquid droplets. When the initiator was added to initiate the reaction, these large droplets turned into coarse particles, while the upper part contained normal material. Measure: Appropriately extend the mixing time after adding dispersant 1 to ensure uniform dispersion of the monomer in the reactor, or reduce the concentration of the dispersant (while keeping the amount added on a dry basis unchanged). Friends, take another look – is this okay?
Our company uses imported dispersant PVA
6 70-cubic-meter reactors. It seems to have been designed by Beierhua!
What effect does the buffer have on the reaction? Why are the remaining kettle reactions normal? Chance seems to imply necessity as well! I’m not very familiar with dispersed systems; I suspect that the concentration of the dispersant added is too high, which affects the rate at which the dispersant spreads after it is added, thereby leading to stratification. But why does it appear by chance? I don’t understand! What measures can be taken to remedy this?
The adverse effects of poor buffers include a decrease in pH, making it difficult to form a stable dispersion system and leading to the formation of coarse particles
The function of a buffer is to regulate the pH value of the entire reaction system! In my humble opinion, it’s necessary to check whether the pipelines for the dispersant and initiator are being flushed properly! This post was last edited by smallbilly on 2008-1-15 at 18:59
The formation of coarse particles is ultimately due to an inadequate establishment of the dispersion system; by focusing on this main issue to find the causes, it is definitely possible to identify the root problem. Although PVC technology in our country is now quite mature, the increasing number of new PVC manufacturers in recent years has given rise to many new problems. Experience is invaluable!
Oh, the buffer used in our company is an 10% aqueous solution of ammonium bicarbonate. If the buffer isn’t of good quality, then why have there been intermittent occurrences of coarse product recently? Since December, our company has produced 6 batches of coarse product (excluding Batch #1). So I would like to ask, apart from buffers, what else can affect a dispersion system? How does the pH value affect dispersion systems? I hope to get an accurate reply. Also, how is the pH value of the raw materials detected after they are added to the reactor? (On-site setting-out inspection?) ) The pH value of the soft water tested recently has been around 7.2.
Smallbilly, we have already carried out the checks you mentioned, and we’re still doing them now; yet just the day before yesterday, another batch of rough material appeared. For the monomer, rinse once before adding soft water to the tank for dispersion; rinse once after adding dispersant 2, once after adding dispersant 1, and once more after adding the initiator. The entire rinsing process proceeds normally without any issues, and the flow measurement is accurate. Is this normal?
Oh, recently in my PVC processing process I identified that the problem lies with the terminator. Finally, I would like to ask: what factors cause large fluctuations in the stirring current of the reactor? For example, it drops from 140A to 130A and then rises from 130A to 170A. What affects dispersion systems?
Why shouldn’t stirring be a problem? A poor mixing condition does not necessarily mean that the mixing current is also poor. Inadequate mixing (such as mixing intensity and number of cycles) can affect the flow of the fluid inside, resulting in the formation of stagnant layers in the tank. This can lead to droplet coalescence as well as the formation of larger particles This possibility shouldn’t be ruled out either, right?
Since several of your polymerization reactors have problems, it is unlikely that the mixing systems in all of them will fail at the same time. It is recommended that you measure the pH value of the slurry at the time of polymerization discharge; this pH value can be used to indirectly determine whether the polymerization system is stable.
The stirring power in the polymerization reactor should increase gradually during the reaction process. If there is an overall trend of the stirring power rising first, then falling, and rising again, it is very likely that coarse particles will be formed. I’m not sure whether by ‘coarse material’ you mean particles that are generally larger in size (like popcorn), or small pieces the size of eggs It is recommended to rinse the polymerization reactor thoroughly with high-pressure water, add materials strictly in accordance with the DCS procedures, and then check whether any coarse material is still produced.
What polymerization process? 1. The dispersion and monomer dispersion are not good. 2. Is the pH value too high? What should the PHZ value be in a normal system, and is there any unevenness? In a normal system, stirring should not be a problem. I wonder what the mixing intensity is.
Agreed; it is recommended to check the actual amount of dispersant added, as there might be leakage in the pipelines resulting in a lower addition amount!