In 2012, I wrote a process report on synthesis and distillation; it was discarded as soon as it was completed.

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This post was last edited by Small and on 2017-8-4 22:43. It contains an explanation for the adjustments made to the synthetic purge gas on April 19 and 20, 2012, as well as some personal views on the system’s operating conditions. To the workshop management: After this startup (4.7), some unusual phenomena occurred in the synthetic distillation process, phenomena that were different from what had been seen before. I have limited knowledge and am unable to understand the technical staff’s guiding principles, so it is difficult for me to keep in line with their instructions at work. Although attempts were made to learn and discuss in order to understand the underlying conceptual foundations of each other’s methods of operation, everyone stuck to their own views, and no common ground could be found. I am now submitting in writing my personal understanding as well as the reasons behind the manufacturing processes I carry out, hoping to clarify the situation and reduce errors and oversights in my work. The data listed below are based largely on memory; I also do not have access to the process data from the past few days. Moreover, limited by my own capabilities, it is inevitable that there will be inaccuracies. If anything I say is incorrect, I earnestly ask for the guidance and forgiveness of all leaders. Reasons and process for adjusting the synthetic purge gas on April 19 and 20, 2012: 1) It was found right after taking over that the synthetic production volume was decreasing day by day ； 2) Even when the inlet temperature remains unchanged or increases, the temperature of the synthetic catalyst bed still decreases ； 3) Under the same load, the synthesis pressure increased despite the vent gas emission being higher than a few days prior (12–14 days ago). It retains the same freshness as in the past: there is high circulation air, little off-gas, high production, and a low bed temperature. The C0304 (heater for starting up synthesis) has not been put into use, and the opening degree of valve PV1805A, which regulates the pressure from 4.0 MPA steam to 2.6 MPA steam in the medium-pressure steam network, is also much smaller ； 4) Analysis of the fresh gas and recycle gas in the synthesis system using S-304/305 showed that the CO/CO2 levels were very low, with their combined concentration being approximately 3.5% (on a volume basis). Even with the cold side lines of the synthesis tower completely closed, it was still not possible to maintain the bed temperature. During the previous shift, the PV1805A was operated at full capacity, allowing 4.0 MPa more steam to be supplied to the steam network at 2.6 MPA, thereby increasing the pressure in the synthesis drum; furthermore, C0304 was brought online in an attempt to counteract the downward trend in the temperature of the catalyst bed ； 5) On the 16th and 17th, other shifts adjusted the circulating water by reducing the flow rate of water returning to C0303 (the syngas cooler). By the time it was our shift, the temperature of the circulating gas had risen from 28°C to 34°C, and at one point even reached 35°C. The synthetic production volume began to show a downward trend on that day, and then declined more significantly day by day ； 6) The amount of flash vapor at the outlet of F0303 (synthesis flash tank) decreased; on the 12th it remained at 55% of the original level, with a flash vapor volume of 130 nm3/h, while by the 19th it had dropped to 89 nm3/h ； Based on the above phenomena, it is preliminarily concluded that the flow rate at the C0303 return water valve was reduced excessively, resulting in insufficient cooling of the synthesis gas; this led to an increase in uncondensed methanol gas, which, along with the circulating gas, entered the synthesis tower and suppressed the synthesis reaction, thereby reducing the synthesis efficiency. After searching through the S-304/305 data, no increase in the methanol content was found; immediately instructions were given to conduct an analysis to determine this value. At the same time, increase the venting volume slightly, and slightly open the return valve FV503 on the circulation section of J0301 (synthesis compressor) to reduce the amount of circulating gas and the space velocity, thereby offsetting the impact on temperature caused by the introduction of some methanol into the synthesis tower. It also enhanced the drainage from F308 (the separation tank in the synthetic compressor cycle section) in an attempt to lower the liquid level and create more separation space. Meanwhile, by opening the return valve FV503 in the J0301 cycle section, the flow was directed through the C0307 water cooler, with the hope that this would help condense some of the circulating gas. Increase the flow rate of C0303 return water to enhance methanol condensation. Analysis results at 10:00 on the 19th: S-304: 0.34% methanol; S-305: 1.75% methanol. Due to the unclear liquid level reading on the on-site gauge for F0308, and no liquid level display available on the ITCC, it was not possible to determine the exact liquid level; therefore, the discharge process was stopped after a short period of time. The temperature of the synthetic catalyst bed increased slightly on that day. On the 20th, analysis and sampling were ordered again for the middle shift: S-304 had a methanol content of 0.52%, while S-305 had 2.08%. As the methanol level continued to rise, the discharge valve of F308 was opened wider, and more vent gas was released. The volume of circulating gas and the space velocity were also reduced in order to help stabilize the temperature of the synthesis catalyst bed. Thereafter, the circulating gas temperature TI-1326 gradually decreased, while the catalyst bed temperature and inlet temperature gradually increased. Soon, enough capacity was available to take C0304 out of the system; the opening of valve PV1805A, which controls the steam pressure from 4.0 MPA to 2.6 MPA, was reduced, yet the steam pressure at 2.6 MPA increased instead. This should be a sign that things are gradually improving. On the afternoon of the 19th, after the technician arrived, he reported truthfully what he knew and the analysis data, but received no response; instead, he blamed our team for releasing gas excessively on our own, claiming it affected production. In fact, the decline in production has been going on for some time; there was a slight drop as soon as operations started. The increase in this decline began after the water adjustment on the 16th and 17th. The comparison is as follows: under the same load, the yield of primary alcohol was around 895 units per day from the 12th to the 16th, while it dropped to around 880 units per day from the 16th to the 20th. In my shift, the production volume was low on the 19th, mainly because the cooling system in C0303 was not functioning properly; the temperature of TI-1326 increased by about 7°C, which affected the synthesis process, and adjustments had to be made throughout that shift to address these issues ； The natural gas volume arriving at the gas distribution station is about 400 nm3/h less compared to other shifts. Moreover, the daily production on the 19th was the same as that on the 18th, at 895 T/day in total. This represents a reduction of about 15 T/day in primary alcohols compared to the levels on the 12th and 13th; it is unlikely that adding a few hundred cubic meters of vent gas by our team could achieve such a reduction. The technician believes that the activity of the synthesis catalyst has declined, and ordered that the control temperature of the synthesis catalyst be increased. I think it might be caused by an excessive amount of alcohol in the synthetic gas fed into the tower. The reasons are: 1) Compared to the early stage of driving, the output was much higher back then; it gradually decreased after a few days. If it is due to catalyst deactivation, what causes the catalyst to become deactivated within a few days? No obvious delay in the bed hotspot temperature was observed. 2) Previously, the circulation gas volume was as high as 600,000 nm3/h, while the purge gas volume was only 7,800 nm3/h; thus the space velocity was even higher than it is now. The bed temperature was almost the same as after water adjustment, but it was slightly lower at the inlet. The production rate was much higher – did the catalyst age within just a few days? Is it still an issue with the subsequent operations? 3) C0304 exited the system once normal operation was resumed, but it now needs to be put into use. The operation manual clearly states that the system should be exited once normal operation is resumed. In the past, at a load of 55%, there were also rare records of C0304 being put into use. This indicates that the reaction heat is no longer sufficient to compensate for the heat carried away by the same volume of cycle gas under the same load. 4) Is the extremely high level of alcohols in S-304/305, along with its ongoing increase, in any way unrelated to poor synthesis reactions? What should be the methanol content in the cooled and separated recycle gas? What was the alcohol content at the inlet of the synthesis tower previously? 5) At midnight on the 20th, the alcohol content in the vent gas after washing in S-312 reached a record level of over 800 PPM; it has since remained around 200 PPM for the past few days, showing an upward trend in a stepwise manner. Is it accidental, inevitable, or normal? 6) The flash vapor of F0303 decreases, and its components include by-products such as dimethyl ether from the synthesis reaction, as well as dissolved CO, CO2, H2, and some methanol. Generally, a decrease in catalyst activity is accompanied by an increase in by-products. In the later stage of using the catalyst synthesized in 2007, the amount of flash steam was very high, nearly 400 Nm³/h. If the activity declines, the ethanol content will also increase. If, however, the ethanol level in the crude alcohol does not increase but instead decreases, and this is taken into account along with the reduction in flash vapor, it is more likely that the issue lies not in catalyst activity but in inhibition of the reaction. Even under the previous anaerobic conditions, the flash vapor volume at 55% load was 85 nm3/h; why has it dropped now? 7) Currently, even when the return water valve C0303 is opened to its original degree of opening, it’s still impossible to achieve the previous daily production volume. Does this indicate a relationship between the decline in the heat exchange efficiency of C0303 and the increase in the alcohol content in the inlet gas? And what is the relationship between the alcohol content in the gas and the synthesis reaction? I once read in some materials that trace amounts of methanol have little effect on the synthesis reaction, but a significant increase in the methanol content in the gas is very detrimental to it. Once methanol is introduced into the catalyst bed, the most noticeable effect is a rapid drop in temperature at the top layer of the catalyst bed, which leads to a deterioration in the synthesis reaction. Liquid methanol is continuously vaporized, carrying away the heat of reaction and occupying part of the reaction space as well as the active surface of the catalyst; it even continues to react at high temperatures to produce various higher alcohols: CH3OH + CH3OH-----------C2H5OH + H2O; CH3OH + C2H5OH----------C3H7OH + H2O. If our estimates are correct, no measures can be taken to reduce the methanol content in the gas, and even if the temporarily increased temperature doesn’t last long, it will drop again, resulting in a further decrease in production. During this period, I have done my best to strengthen my operations following this approach. Increasing the purge gas flow is merely an auxiliary measure to raise the bed temperature; the most important operation is to enhance the discharge from F0308. The emission periods on the 19th and 20th were short, resulting in insignificant effects. On the day 24, during the day shift from 8:30 to 14:30, I continued working for nearly 5 hours after that shift ended. In total, it was 11 hours of work. The analytical results show a clear difference: the methanol content in samples S-304 and S-305 was 0.61% and 4.64% respectively at 10:00 on the 24th. At 8:00 on the 25th, it was 2% (it was something like 2.x%, but I can’t remember the exact figure). The sample taken on the 25th wasn’t prepared by my shift; it was the first sample of type 305 prepared by another shift that I saw. It was also the only instance where the methanol content decreased (there was no such decrease in sample S-304). This clearly indicates a significant reduction in methanol content. Even with such discharge, it is still not sufficient; in the past, the end of discharge was marked by an increase in F0303 pressure and flash flow rate, but now this phenomenon does not occur even after 11 hours of discharge. If persisted in, normal function can be restored within a few days of synthesis. But I discussed my views with the technician on many occasions; in each case, the analysis samples prepared were submitted to him, yet he gave no response – neither agreeing nor disagreeing, nor answering at all, as if his messages had sunk into the depths of the sea with no reply. For the distillation unit C0409 (atmospheric pressure shell-and-tube reflux cooler), technicians believe that dirt blocking the water side is causing poor heat exchange efficiency. C0409 is the largest water cooler aside from C0303 and the surface cooler; none of the others are blocked – is it only this largest one that’s having problems? I’m very puzzled. At midnight on the 12th, upon taking over shift, it was found that the vent at the top of the reflux tank of E0403 (at atmospheric pressure) was fully open; the tower pressure was as high as over 50 KPA. Large amounts of pure methanol vapor were being emitted from there, and the condensed methanol formed a mist that spread everywhere. At this time, C0409 was cooling well. Our team opened the return water valve to 2.5 turns, causing the tower pressure to drop rapidly; the on-site vent was closed to reduce the amount of extraction water, and the effective load was increased by 3 tons, after which the tower pressure dropped to around 30 KPA. 4:00 Analysis results: The ethanol content in S-406 (purified methanol from the pressurized tower) decreased from being out of specification to 11PPM; the moisture content in S-408 (purified methanol from the atmospheric pressure tower) was 0.01%, while the ethanol content dropped from 1710PPM to 1100PPM (E0404, the recovery tower, was not in operation). The distillation conditions have improved significantly compared to before, and the product quality has greatly enhanced. On the 14th, during the day shift, it was found that there were again abnormalities in the distillation process: the load decreased, the tower pressure was very high, and the reduced amount of low-pressure vapor led to a lower reflux ratio, resulting in a decline in product quality. The return water valve at C0409 was only open at 40–50%, and for some reason, the vent valve on site was opened again. After that, the distillation conditions deteriorated day by day, with the reflux temperature rising every day. By the 24th, during the day shift, E0403 produced as much as 24 T/H; however, the reflux rate was only 28 T/H. The tower pressure was as high as 66 KPA, the reflux temperature was 68°C, and the bottom temperature was 108°C. I determine that this operating condition will soon become unsustainable. As expected, after 9:00, the bottom temperature of E0403 dropped sharply, while the temperature at the top of the tower rose. The rising methanol vapor broke through the thin liquid film and reached the top of the tower, and the liquid took a shortcut to reach the bottom of the tower as well. Quickly transfer the load from E0403 to E0402; by the time of shift handover, C0409 was already fully open and the venting system was also in operation, leaving no means for adjusting E0403. Thus, it was necessary to use C0407 for reflux; in effect, this reduced the heat input to E0403, while allowing an increase in the reflux flow to E0402. This is one of the reasons why the load was shifted to E0402. By reducing the distillation load by 3T, normal distillation operations could still be maintained, and at the same time, the quality of the product from E0402 improved (at 15:30, the product met the AA grade standards). However, C0407 cannot replace the function of C0409. After the distillation adjustments were normalized and stabilized at 12:30 p.m., I accompanied a staff member from the distillation team to site C0409 to attempt to carry out the exhaust operation. More than an hour later, the pressure in tower E0403 dropped to near 55 KPA; the return water valve in C0409 was closed to 30%, and the distillation process was operating normally with a positive trend. It is afternoon now, and the temperature is much higher than in the early morning. Unexpectedly, while returning to the control room for a break, severe fluctuations in the desalinated water flow threatened the system’s safety. During that time, the pressure in tower E0403 increased; once the fluctuations in the desalinated water flow ceased, the pressure gradually decreased again, but all the work done to relieve pressure earlier was almost in vain. Before leaving work, I vented the system again; by reducing the backflow valve to 20%, I was able to maintain distillation stability, and I observed a downward trend in column pressure. Operations cannot continue because work is over. In summary, it appears that in C0409, insufficient venting occurred at the time of commissioning; during operation, the return water valve was blindly closed, resulting in excessively high return water temperature. Meanwhile, the pressure of the circulating water kept dropping. A small amount of vaporization occurred on the water side of C0409 and gradually accumulated, ultimately leading to air blockage. In recent days, the J0413 pump has also experienced frequent flow fluctuations; this is probably due to insufficient return water flow. The temperature at F0420 reached 41°C the day before yesterday. The above remarks merely represent my personal views; they are just expressions of the questions in my mind, and I have no intention of judging right or wrong. If there are any errors in reasoning or any rude or offensive aspects, I hope to reflect on them and offer my apologies. If any losses occur as a result of my work during this period, it is due to my own recklessness, and I am willing to take full responsibility; it has nothing to do with the other members of the team. I believe that the workshop supervisor can discern even the slightest details and make correct and fair judgments, thereby helping me to find the right direction. I wrote all this nonsense not to show off or seek attention; it’s probably just my immaturity and recklessness. I just work hard at my job because it’s my job. Best regards, 4/27/2012