The catalytic valve opening continues to decrease
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I installed the two devices in a coaxial configuration, and a major overhaul was carried out in 2020； After starting up, increase the valve opening to 34%, then to 30% ； It was found that the valve opening remained basically unchanged, while the valve opening continued to decrease. As of August 2021, the revalve opening was between 32-34% ； Reduce the valve pressure drop from 80 to 64 KPa ； There is no significant change in the nitrogen content in the dry gas. Based on our own analysis, it’s possible that the valve seat or valve stem is misaligned ； Valve head wear ； Pending riser leakage ； I’d like to ask everyone, what could be the possible reasons? If the situation continues to deteriorate and the valve opening keeps decreasing, how can it be maintained? How does the ventilation volume affect it – should it be adjusted up or down?
As a supplementary note, before maintenance, when the valve opening degree (34–38) was greater than that of the regenerative valve (34), analysis of past data showed cases where either the regenerative valve had a higher opening degree or the target valve had a higher opening degree; however, there was no occurrence of the target valve’s opening degree continuously decreasing.
If the inventory in the stripping section can’t increase, and it doesn’t increase, the likelihood of perforation in the standpipe is higher
It’s very difficult to increase the storage volume; when the valve is reduced to 20, it just manages to maintain the storage level – it can’t be reduced any further. There’s no problem increasing it instead
The startup riser, which was just replaced during last year’s major overhaul, has linings on both the inside and outside; based on past experience, perforations are very unlikely to occur. The previous one has been in use for over a decade without any signs of perforation
1. Logically, when the valve is closed, the flow rate should decrease. The prerequisite is that the density of the fluid remains constant. 2. However, if the fluid density changes – and it should increase here – then the valve should be closed more. 3. Another possibility is that the gap in the check valve increases; with the same degree of opening, the flow rate rises. To maintain an equal level of storage in the two vessels, it is necessary to close the valve slightly to ensure balance in their storage levels. You can observe whether there is a change in density before and after inserting the valve, and whether the trend of this change corresponds to the occurrence of the phenomenon.
Sorry, describing the oil stain; there is no lining inside
Firstly, there was no significant increase in the nitrogen content in the dry gas, which essentially rules out the possibility that perforations in the conical section of the stripper section within the regenerator are causing two-way leakage and leading to a gradual closure of the regenerative valve. At the same time, attention was paid to whether there was any periodic increase in the temperature of the gas collection chamber in the settler. Another possibility is that the weld joint at the upper part of the riser breaks and separates, allowing the raw catalyst to flow into the regenerator from this point; the raw catalyst plug valve then closes off the raw riser. This can be confirmed by parameters such as density inside the distributor. What is most desired is valve wear, as well as a valve-shutting action that enables high flow capacity due to the large cross-sectional area of the cone; this can be determined through measures such as the pressure difference across the plug valve, adjustments to the secondary air flow, and fine-tuning of the pressure difference between the two devices.
The plug valve was replaced in 2020; the lining of the valve head has a high hardness, so wear is highly unlikely. I have been analyzing this for some time now, and it is very likely that there is wear and perforation at the lower part of the riser.
Judging from the phenomena, the perforated catalyst should have come out of the perforation site prematurely. To determine this location, it is necessary to consider the operating conditions of the startup pipe and the startup sleeve; the density of the startup pipe decreases, while the density of the sleeve remains essentially unchanged, and the leakage point is located inside the sleeve ； If the density of the standpipe is abnormal, and at the same time the density of the catalyst bed sleeve is also abnormal (decreased), with the leakage occurring outside the sleeve, the most likely location of the leak is at the junction between the standpipe and the sleeve. It is also possible that it occurs in the riser section from the conical bottom end of the settler to the spent catalyst sleeve. It is likely that the loose point in the feed riser has broken, or that the backflow medium carrying catalyst has caused wear on the riser. If there are DCS screenshots (with density dots), it might be easier to make a clear judgment. For reference only