Under such conditions, will the sulfur-resistant shift catalyst become sulfided? (Solved)
Thread Content
This post was last edited by 654262293 on 2010-10-23 06:54. The shift process used for methanol production involves an inlet temperature of 265°C in the shift reactor, with a peak temperature inside the reactor of 465°C. The water vapor-to-coal gas ratio at the reactor inlet is around 1.0; the H2S content in the coal gas is 0.1%, while the CO content is about 48%. The CO content at the reactor outlet is approximately 8%. To control the reactor temperature, cooling air is introduced into the reactor. As a result, the H2S content at the reactor outlet is slightly lower than at the inlet. Under such conditions, will cobalt-molybdenum-based sulfur-resistant shift catalysts suffer from sulfidation?
Is the moderator transformation process a full low-variation one? If it is a full low-temperature shift under the operating conditions specified by the moderator, the low-temperature shift catalyst will definitely experience reverse sulfidation.
The last edit to this post was made by 654262293 on 2011-1-23 at 16:26, in response to 2# Yan Qiusheng. The sulfur-resistant shift process is used, with all shift reactors equipped with cobalt-molybdenum-based sulfur-resistant shift catalysts. The above represents the current operating conditions in our facility. Initially, the H2S content in the water gas was between 0.2% and 0.3%, with little change in other parameters; sulfidation certainly would not occur under those conditions. However, now the H2S content in the water gas is only 0.1%, and this level is already close to the minimum amount of hydrogen sulfide required for sulfidation to take place under the current operating conditions. Do you think sulfidation will occur? What is the basis for your judgment?
This post was last edited by Yan Qiusheng on 2010-9-10 at 17:09. Please refer to this material. Minimum H2S content at various temperatures for different gas-to-vapor ratios: R T0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 200 225 250 275 300 325 350 375 400 425 450 14 25 41 65 98 143 202 279 375 493 637 21 37 61 97 147 214 303 418 562 740 955 28 50 82 129 195 285 404 557 750 987 1273 36 62 102 161 244 357 506 697 937 1233 1592 43 74 123 194 293 428 607 836 1125 1480 1910 50 87 143 226 342 500 708 976 1312 1727 2228 57 99 164 258 391 571 809 1115 1500 1973 2547 64 112 184 290 440 642 910 1254 1687 2220 2865 71 124 205 323 488 714 1011 1394 1874 2467 3183 78 136 225 355 537 785 1112 1533 2062 2713 3502 In the table, T represents the hottest temperature in the catalyst bed, while R is the gas-to-vapor ratio during reaction (not the inlet gas-to-vapor ratio). The units for the data in the table are dry gas in mg/m³. To ensure the proper operation of Co-Mo-based sulfur-resistant shift catalysts, an appropriate H2S content is necessary under different catalyst reaction temperatures and gas-to-vapor ratios, in order to prevent the catalyst from undergoing desulfurization reactions. The minimum H2S content in the gas can be calculated using the equilibrium constant equation for the desulfurization reaction of molybdenum sulfide.
This post was last edited by 654262293 on 2010-9-10 17:33. The table above shows the minimum hydrogen sulfide content required for desulfurization at different water vapor ratios and bed temperatures; but how can we determine the water vapor ratio at various temperatures? For example, what is the water vapor ratio at a bed temperature of 450°C? Everyone is welcome to actively participate in the discussion!
For the medium-string low or medium-low-low shift process, the CO level at the low-shift inlet is generally between 5% and 8%; the steam-to-gas ratio at the entrance to the shift system is kept around 0.5, while the steam-to-gas ratio at the low-shift inlet is approximately 0.2–0.3.
The last edit to this post was made by 654262293 on 2011-1-23 at 16:27. Reply to 6# Yan Qiusheng: You didn’t understand what I meant. What I’m saying is that, based on the data you provided, to determine whether reverse sulfidation will occur under operating conditions, it’s necessary to look at the lowest hydrogen sulfide level under those operating conditions (temperature, water vapor ratio). Then, it’s necessary to check whether the hydrogen sulfide content in the gas in question is higher than that value; if it is, then no reverse sulfidation will occur, otherwise reverse sulfidation will take place. Under the operating conditions I’ve specified, for example, if we want to determine whether desulfurization occurs when the bed temperature reaches 450 degrees, it is necessary to find out the lowest hydrogen sulfide concentration at a bed temperature of 450 degrees along with the corresponding water vapor ratio in the gas. But how can we calculate the water vapor ratio at a bed temperature of 450 degrees?
I’m using full low voltage here; the temperature at the hot spot ranges from 180 to 470. If it’s as you described, I personally don’t think reverse sulfidation will occur; reverse sulfidation means the release of sulfur, with the sulfur in the catalyst being emitted. From what you’ve said, I can understand this as the hydrogen sulfide level at the outlet being lower than that at the inlet, and I think this is sufficient to make such a judgment. Regarding the calculation of the gas-to-vapor ratio, it is rather complicated; one needs to know the temperature of the liquid exiting the saturated tower as well as the amount of steam added.
Reply to 7# 654262293: The question raised by the moderator is quite complex; given my current level of expertise, I am not able to answer it yet.
Reply to 8# OrdinaryPerson0011: Please read my post carefully. The overall vapor-to-gas ratio has already been explained to you; the key issue is that it’s difficult to calculate the vapor-to-gas ratio at the corresponding bed temperature!
It isn’t well explained in the ammonia synthesis section; I hope those who work on the purification section can help!