-----Could someone please give some advice on the issue with the synthesis tower?----

We use both single-tube baffled and quench-type synthesis towers. From the perspective of resisting minor poisoning, single-tube baffled synthesis towers are superior to cold-jet synthesis towers. I’m not sure whether your two synthesis processes are completely identical; the impact of even trace amounts of washing on the synthetic catalyst can be significant, and it depends on the location where the gas is added and the amount of ammonia used for washing.

Single-tube baffle-type internal component: when the catalyst is poisoned, the poisoning occurs gradually from top to bottom； In a cold-start synthesis tower, when the concentration of trace impurities in the feed gas is high, the catalysts in all sections of the reactor bed become poisoned, and the symptoms of poisoning are more pronounced and occur more rapidly than in a single-tube baffled design.

Compared with the internals of cold-jet synthesis towers, the single-tube baffle-type internals designed and manufactured by the Machinery Factory of Zhejiang University of Technology can also cause catalyst poisoning when there are high levels of trace toxic substances in the supplementary gas. However, the difference is that in the case of these single-tube baffle-type internals, catalyst poisoning starts at the surface layer; in severe cases, it progresses from top to bottom. Moreover, the proper arrangement of the upward and downward tubes in the cold-tube structure of this type of internal allows the reaction heat from the lower layers of the catalyst to be transferred to the upper layer, thereby compensating for the decrease in reaction heat resulting from the deactivation of the upper-layer catalyst and reducing the temperature drop, thus mitigating the damage caused by catalyst poisoning； In a cold-start type synthesis tower, when the concentration of trace elements in the make-up gas is high, the catalysts in all sections of the reactor bed become poisoned, and the symptoms of poisoning are more pronounced and occur more rapidly compared to that in a single-tube baffled type reactor.

Regarding the question raised by the original poster, I would like to provide answers through the following three points, in the hope that it will be helpful to them: First: Causes of catalyst poisoning. The main reasons for catalyst poisoning in synthesis processes are generally: 1. Trace amounts of CO, CO2, SO2, etc； 2. Oil spill ； 3. Impurities ； 4. The temperature changes too drastically ； Second: Cause analysis. The original poster mentioned that there are hardly any significant differences in the preceding processes for the two, which means that micro-level control should not be an issue; based on this, the possibility of micro-level poisoning can be ruled out ； Third: Possible sources of the problem 1. Micro-control may also merely be the owner’s assumption; detailed measurements need to be carried out through certain methods to ensure certainty in case anything goes wrong ； 2. Check for any oil leakage in the relevant process ； 3. Have there been any instances of sudden changes in catalyst temperature caused by issues such as process load or imbalances in the hydrogen-to-nitrogen ratio?

What are the differences in column temperature response for a three-axis-one-diameter column and a single-tube baffled column after catalyst poisoning?

Thank you all for your advice. Our plant’s two systems use the same process; the purification steps in the upstream section take place simultaneously, with gas being supplied in parallel. However, in cases of poisoning, it is always the cold shock tower that reacts first, while the baffled tower shows no reaction. Yet all the parameters from the upstream section are within the acceptable range, and the temperature during methanation remains completely unchanged. The hydrogen-to-nitrogen ratio and the ammonia cooling temperature in this section also fall within the specified limits. I hope you can help me figure out what might be the cause. This post was last edited by 52013145201314 on 2009-3-6 at 16:40

I’m not sure how many stages your compressor has. If it’s a three-stage compressor, to check for leaks, you can verify whether there are any leaks in the connections between stages 3 and 4, or if those connections aren’t properly sealed; it is only through these connections that a small amount of gas could leak out. Because from a broader perspective, methanation occurs earlier in the process; if trace amounts are present, they will first burn the methanation catalyst. I also don’t know whether your two towers are connected in parallel or in series.

Our plant uses six-stage compression, with two stages for pressure conversion. Three stages are dedicated to pressure swing adsorption and methanation. Leak detection valves are installed on both the two-way and three-way connections; it’s impossible for gas leaks to occur. We suspect that there is a leak in the heat exchanger used in the methanation process. But once the flow rate is reduced slightly, production can resume at full capacity. I’m really confused! ～～