Gas-phase polyethylene plant: how to stabilize the reactor
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Our plant is a UCC gas-phase polyethylene facility. Recently, due to the replacement of the catalyst with one from another manufacturer, the bulk density of the resin used in the reaction decreased from 380 kg/m3 to the current level of 330 kg/m3. However, in order to maintain a reasonable material level in the reactor, the weight of the resin bed in the reactor was reduced from 95 t to 85 t, representing a decrease of 12%. At the same time, it was found that there were many small lumps in the reactor formed by the bonding of fine particles; I concluded that there must be hot spots inside the reactor! Please help – is there any way to stabilize the reactor’s operating conditions? Prevent caking, thank you!
There’s no other way; if the condition of the reactor continues to deteriorate, then we’ll have to replace the catalyst
Is there really no way? Leadership must be maintained continuously!
I think in this situation, the catalyst manufacturer should be informed to coordinate and find out the cause.
Reply to 1# 8914329: I think it’s not a matter of heat sensitivity, but rather the fact that fine powder tends to melt easily, and its static electricity is relatively high, which causes it to agglomerate! One can take a look at the particle size distribution of his catalyst, especially the small particles! Take another look at the comprehensive analysis of the powder, check the average particle size, especially the content of fine powder.
I also often observe the screening of the powder, and it is similar to that of the powder produced by the imported UCC; there isn’t much change in the fine powder. The biggest change is the decrease in pile density, as I mentioned above. I’ll upload a screenshot of the screening tomorrow. My current understanding is that the decrease in pile density leads to a reduction in the fluidization bulk density, which in turn results in decreased backmixing and heat removal capacity in the reactor.
Is bulk density not just loose density? They are the same concept.
Reply to 7# fastrong: The bulk density mentioned by the original poster is actually the loose density. The bulk density commonly referred to is the random bulk density of the particles themselves. A decrease in bed weight does indeed lead to a decline in heat removal capacity, and this is indeed a possible cause. The poster might as well check the temperature at the compressor outlet and the bonding temperature of the powder, especially the instantaneous bonding temperature of the powder. What is the basis for the original poster’s determination of the bed height? Has the density at the neck of the fluidized bed changed compared to before? Also, has there been any change in the amount of isopentane added compared to before?
Thank you all for your opinions! We control the bed height around the reactor neck, in order to counteract the scouring effect in the expansion section, as the polyethylene powder tends to agglomerate there. There is not much change in the density of the neck area; the ICA now controls 8% mol, compared to 7.5% before, so the change is not significant. It seems that this change is caused by the catalyst.
Control the amount of catalyst fed in; the evaporation of propylene serves mainly a heat removal function, so the propylene feed rate needs to be controlled.
Reply to 10# jbx1656: The ICA here is isopentane or n-hexane. If there is a high amount of n-hexane, it may also cause caking. Or has there been a change in your density control? The particle size of the catalyst is often observed.