The seven stages of chemical technology from concept to industrialization (Issue 25/100) -- Long-term operation

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This post was last edited by xiouxingzhe on 2026-6-11 at 11:42. The seven stages of chemical technology from concept to industrialization (Issue 25/100) —— Technology development: a long-term process. Dear friends: Hello everyone! In the previous issue, we discussed how to set up a continuous pilot plant, completing the entire process so that materials can flow from start to finish. But being able to make it work and being able to keep it running stably are two different things. In this issue, let’s talk about long-term operation. After the pilot continuous system is set up, the next step is to run it continuously for a sufficient length of time—starting with 72 hours—to expose those problems that would not arise in short-term experiments. I. Why run for such long periods of time? Hours versus dozens of hours – the problems faced by the device are completely different in each case. During batch operation, you clean, inspect, and refill the materials after each batch is completed. So some problems will never be exposed—because they are wiped out before they can accumulate to an observable level. But after continuous operation, as the material keeps flowing, those effects that accumulate slowly begin to show up. Will scale form on the inner wall of the pipe? How fast is the scaling rate? It’s not noticeable after a few hours, but after dozens of hours, it may be possible to detect the signal from changes in pressure drop. Does the catalyst experience slight activity degradation? Conduct a series of batch experiments, replacing the catalyst after each use; you’ll never know what condition it will be in after the tenth use. Only by running the catalyst continuously for dozens of hours can you observe the trend in its activity decline, whether there is any shift in selectivity, and whether the spectrum of by-products is changing slowly. Will the pump get clogged? A few hours might not be a problem, but after dozens of hours, some solid particles that gradually accumulate at the pump inlet may cause the flow rate to start fluctuating. These issues may not be apparent at all in short-term experiments. But on industrial installations—where they operate continuously for 8,000 hours per year—these cumulative effects are amplified infinitely. Therefore, exposing these potential issues during the pilot-scale continuous phase is one of the most valuable outputs of this stage. II. The 72-hour period isn’t chosen arbitrarily; many people think this figure is decided arbitrarily. Actually, it’s not. From a statistical perspective, 72 hours is sufficient to cover the rotation of multiple operating shifts, account for variations in day-and-night temperatures, and provide a sufficient number of sampling cycles and data points. Many cumulative problems—such as minor scaling, gradual carbon buildup on the catalyst surface, and material accumulation in pipe dead zones—take at least several dozen hours to reach a detectable level. From the perspective of engineering validation, 72 hours of continuous stable operation means that all the various units of the device, all control circuits, and all operational procedures have been tested over a certain period of time. It’s not that it was made to work just now, but that it has been running stably for some time now. 72 hours is just a starting point; it doesn’t mean that everything will be fine once 72 hours of running have been completed. Some problems may take longer to become apparent—such as early signs of certain types of corrosion, or fluctuations related to certain seasonal factors. However, at the pilot scale, 72 hours is a reasonable starting point. At the pilot scale stage, the operation time over a long period will be even longer—hundreds of hours or even thousands of hours, depending on the requirements of the specific process. III. What to focus on while running It is not sufficient to simply turn the device on and leave it unattended during long-term operation. There are a few areas that deserve special attention. The first is the pressure drop change. Is there a continuous upward trend in the pressure drop of pipes and equipment? If the pressure drop in a certain section of pipeline increases slowly over several hours—even by just a few kilopascals—it may be an early sign of scaling or blockage. This signal is more sensitive to changes in flow, as the flow rate can be compensated for automatically by the pump, but the pressure drop does not lie. The second is the temperature distribution. Has there been a gradual drift in the temperature at each temperature measurement point? If the temperature at a certain location continues to deviate gradually from the set value, it may be a sign of scaling on the heat exchange surface, changes in catalyst activity, or uneven distribution of the material. Third is the stability of product quality. During continuous operation, samples are taken at regular intervals to analyze key parameters—purity, impurity content, and critical physical properties. Check whether these indicators show any trendive changes over time. The level of some by-products may start low but gradually increase, indicating that something might be accumulating within the system. Fourth are abnormal noises and vibrations of the equipment. For rotating equipment such as pumps and compressors, does the bearing temperature rise during long-term operation? Has the vibration increased? Has the sound changed? These signals may indicate potential issues with the equipment earlier than gauge data. IV. What to check after running: After completing the 72-hour run, it’s not enough to simply turn off the device. There are a few actions worth taking. First, remove the pipe connections in the key areas to check whether there is scaling, corrosion, or color changes on the inner walls. Some things are invisible while in operation; they can only be seen by taking them apart. Take photos for documentation and keep the samples. Second, check the appearance and performance changes of the catalyst. If the catalyst is packed in a fixed bed, unload it to check its color, particle size distribution, and whether there is any fragmentation or pulverization. Take a sample to measure its activity and compare it with that of the fresh catalyst. Third, inspect areas prone to clogging such as filters, pump inlets, and instrument connections to check for any solid deposits. These areas are the weak points in the system where problems are more likely to occur. Fourth, organize and archive all operational data. Time series of temperature, pressure, flow rate, liquid level, and analysis data, with clear indication of which periods represented normal operation, which periods saw abnormalities, and which periods involved adjustments. These data will be used when preparing the pilot-scale data package later. V. How to address the identified issues: Every issue that arises as a result of long-term operation should be recorded. It’s not remembered in the mind, but in a notebook or spreadsheet. I usually keep three levels of records for each issue. The first layer is phenomenon description. When, where, what problem occurred, and what was the behavior at that time—objective records, without any judgment. The second layer is the preliminary analysis. Based on the information available at the time, what was the most likely cause? Which possibilities have been ruled out? This section can be used to write one’s own judgments, but it should be written separately from the first section, with a note indicating that it is an analysis rather than a fact. The third layer is handling and follow-up. What measures were taken at that time? Is it a temporary measure or a fundamental solution? If it wasn’t resolved at that time, what should be taken into account when scaling up later? Together, these three layers of records form a problem tracking file. These issues constitute the list of key points that need attention and resolution once entering the pilot-scale production phase. The more complete the list, the clearer the direction for pilot testing. VI. When to stop and when to continue: During long-term operation, various minor problems will always arise. Not every issue requires stopping to deal with it. The criterion is actually very simple: Does this issue affect safety? If it does not affect safety, will it impact the validity of the data? If it doesn’t affect the data either, then it can continue to run; the issue should be recorded and addressed collectively after it’s completed. But if there are signals indicating a safety hazard—such as a combustible gas leak alarm, abnormally high pressure, or abnormal intense vibration from the equipment—stop immediately without hesitation. Safety is the bottom line. Another situation in which it is necessary to stop is when there is a significant deviation from the process parameters, causing them to move outside the preset operating range; the data generated further on will no longer be meaningful – in such cases, it is also necessary to stop, adjust the conditions, and then start again. Preview of the next issue, Issue 26: Pilot-scale scale-up design – The purpose of pilot testing is not to produce products, but to verify the scaling-up principles. Once the small-scale tests run stably and continuously, the next step is pilot testing. What is the purpose of pilot testing? Many people think that pilot testing means “building a small production facility to make some money first” – this is a fairly common misconception. The true purpose of pilot testing is to verify scaling laws, identify engineering issues, and generate datasets. Next time, we will discuss several key issues in pilot-scale scale-up design: how to determine the scale, which scaling criteria to use, and what are the differences between the PID control systems used in pilot plants and those in industrial facilities.