Why does catalyst scaling occur frequently with repeated double-acting slide valves?
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After operating the double-acting slide valve repeatedly for a period of time, its range of movement will decrease； During maintenance and inspection, it was found that the catalyst in the track assembly had formed clumps, which were quite solid ； But this does not happen with double action twice. It might be because of the repeated introduction of water vapor. Question: How can this be avoided?
Our company’s repeated urging mechanism is of the coaxial type, with a first repetition and a second repetition. After operating for six months within the double-acting slide valve guide grooves, milky white crystals form on the smoke-exhaust side of the valve plate, causing frequent jams. I’m not sure what causes this phenomenon
Changing the purge steam for the double-acting slide valve to purified air purge significantly reduces scaling.
But all of our special valves are purged with steam – so why does scaling occur only in those valves? Last edited by chengkang on 2009-3-23 18:29.]
Using purge air with the double-acting slide valve over and over again – I personally think it’s better to use purified air. The catalyst coming out of the settler, after being exposed to stripping steam, is inevitably subject to thermal decomposition; there is more fine powder in the first stage compared to the second. Meanwhile, the main air flow rate in the first stage is higher than that in the second stage, so losses are primarily associated with the first stage. At the double-acting slide valve, deposition occurs easily due to the effect of the pressure-reducing orifice plate and steam, leading to high-temperature sintering.
Is it a device with two-stage regeneration arranged side by side?
We have encountered sintered masses above and below the double-acting slide valve as well as on the valve channel; I believe they are sintered products of high-temperature catalysts.
It could be 1: Catalyst dust has caused scaling in the spool valve passage； 2. During normal production, the opening degree of the double-acting slide valve varies within a very narrow range; whether the additive components fuse to the valve passages of the double-acting slide valve at high temperatures ； As a result, to maintain an increased regenerator pressure, it is necessary to keep increasing the main air flow; at the same time, the amount of flue gas entering the flue gas turbine decreases, which hinders the recovery of flue gas energy and is not conducive to energy savings.
The result of mixing the purge steam and the regenerated flue gas.
There are slide valve structural materials in the sea channels; give it a search
Where does your facility use its catalysts from? What is the model? How long has it been in use? What is the approximate temperature at the double-acting spool? Anoxic, oxygen-rich regeneration? Was an additive to increase propylene production used? Some units have experienced similar issues due to problems with the catalyst formulation, and in some cases this has even led to severe scaling of the flue gas exhaust systems.
Some analyses suggest that metal melt at low temperatures was formed, which severely caused blockages in the three spinners and scaling in the flue gas fans.
The specific reason is unclear, but it is certain that the fine powder content is high. At that time, extensive cracks appeared in the secondary centrifugal gas lift cylinder of our unit, which caused significant loss of fine catalyst powder and led to scaling at the flue gas fan. Not only the smoke extractor, but also the double-acting slide valve became fouled at one point. During the renovation, the cracks were repaired, and several small cyclone tubes were added to the third-stage centrifugation system; the current condition is good. It is recommended to regularly operate the dual-acting slide valve
Recently, I’ve seen an increase in posts on forums discussing problems with sticking in the valve passages of double-acting slide valves; such issues seemed rare in the past. Let’s discuss the common problems so that everyone can analyze and identify the causes. In one company’s oxygen-poor regeneration catalyst unit, there were no issues before operation began, but excessive leakage occurred during operation. The double-acting slide valves stuck during the cigarette-cutting process. Similar problems had occurred in this unit before as well; upon inspection, it was found that catalyst scaling had blocked the valve passages. Moreover, scaling was quite severe in this unit’s cigarette cutter, and the catalyst used there was one designed for high propylene production. Two other companies’ threads: http://bbs.hcbbs.com/thread-419414-1-1.html Last edited by chengkang on 2009-3-23 18:24]
Regenerative and other types of slide valves are generally purged with clean air, while double-acting slide valves are purged with steam. If scaling occurs easily, it is necessary to carry out regular manual cleaning. If the flue gas extractor also suffers from severe scaling, then it is a problem with the catalyst, and the catalyst needs to be replaced. It is said that the catalyst contains phosphorus, which contributes to scaling; therefore, replacing the catalyst may yield better results
1. Catalyst thermal decomposition/melting deposition 2. The addition of additives has a significant impact 3. The introduction of water vapor exacerbates the formation of sulfites.
I would like to ask the experienced professionals here: in my company, there are serious problems with clogging and valve jamming in the channels of the catalytic double-acting slide valves, which significantly impacts safe production. I hope you can help analyze the causes. Additionally, I would like to know what the production time is for catalytic single-acting slide valves (DN400) and flue gas double-acting slide valves (DN600)
I will only answer the first question: The valve channel purge medium contains water.
What medium is flowing inside the pipeline?/