What are the key points for cooling and removing a sulfur-resistant low-temperature shift catalyst?

Cool down using nitrogen, bring it to room temperature before unloading; when storing it, take measures to prevent spontaneous combustion of surface deposits, and have water ready

1# wlq1970’s question is too general. It is necessary to determine whether to use it after unloading or not. Methods vary. It’s simple if it’s not used after being unloaded. Lower the temperature to 100 degrees, open the manhole directly to remove the contents, and cool it down with water. But when removing manholes, protective clothing must be worn; if it is to be used, it should first be passivated. Careful operation is necessary to control the temperature properly. After installation, there are various ways to restore it to use.

Oxidation is required before unloading; otherwise, air convection will occur when the manhole is opened, leading to overheating and, in severe cases, damage to the equipment.

During the cooling process, care should be taken to prevent water from condensing, if it is still to be used. Try to use controlled compressed air to passivate the catalyst; otherwise, when the sulfided catalyst comes into contact with air, it oxidizes rapidly, releasing a large amount of heat. Danger

It’s a very simple thing! No passivation is required; simply cool the temperature below 50 degrees. Try to speed up the cooling process by increasing the circulation rate of the raw materials, and then it’s possible to consider removing it. However, the manhole must not be opened to avoid excessive temperature!

I. Deactivation of low-voltage catalysts 1. Ensure that the O2 level in the nitrogen system is ≤0.5%. 2, 3. Start the circulation system to pressurize the system, turn on the nitrogen blower, and start the electric heating furnace; feed material into the furnace once the outlet temperature is close to that of the catalyst bed. Cool the low-temperature shift catalyst according to the cooling curve, and shut down the heater as appropriate. 4. Begin oxygen supply once the bed temperature drops to room temperature; be sure to analyze the CH+H2 content in the circulating gas before adding oxygen

Fertilizer manufacturers that use Co-Mo sulfur-resistant shift catalysts often need to refill the catalyst beds due to problems such as flow imbalances, caking, and partial pulverization； Some manufacturers need to replace part of the catalyst or remove it in order to reactivate it. Once these situations occur, many manufacturers often struggle to figure out how to safely remove the catalyst in a non-oxidizing state. When some catalyst producers attempt to do this in practice, it is time-consuming and labor-intensive, resulting in high costs. To reduce the catalyst to room temperature or lower requires a significant amount of time and consumes plenty of semi-water gas; sometimes, the insulation material also has to be removed. Even so, when the temperature inside the conversion furnace is already very low (for example, below 40°C), the catalyst taken out often experiences a temperature rebound, rising even to 400–500°C, which causes the catalyst to switch to an oxidized state. Cooling it with water becomes necessary, and this inevitably leads to the catalyst becoming pulverized, rendering it unusable for regeneration – a great loss given all the efforts that have been made. So, are there any practical methods for non-oxidative discharge? The answer is yes. One of the prerequisites for using our company’s proprietary catalyst revival technology is that the old catalyst must be removed in a non-oxidized state, in order to maintain its sulfided condition. To this end, we conducted extensive laboratory work, and on that basis carried out practical applications in various fertilizer plants. As a result, we developed an effective method for the non-oxidative removal of catalysts. This method not only **reduces the cooling time** but also provides thorough protection to maintain the catalyst’s active state to the greatest extent possible. To solve the above problems, it is first necessary to identify the main reasons for these phenomena that occur during non-oxidative discharge, so that appropriate measures can be taken to find a fundamental solution to the issue. We know that when using semi-water gas to cool old catalysts, the sulfurized old catalysts are in a reducing atmosphere of H2, H2S, CO, and CO2; however, when they are removed, they come into contact with large amounts of O2 in the air, thus being in an oxidizing atmosphere. It is also during the transition from a reducing atmosphere to an oxidizing atmosphere that a strong exothermic reaction occurs. So, what are the main reactions that occur with O2 to produce strong exothermic reactions? We may list the relevant oxidation reactions and heat effects below to find an answer. H2S + 1/2O2 = S + H2O ΔH = -236 KJ/mol (1) CO + H2O = CO2 + H2 ΔH = -41.2 KJ/mol (2) It is easy to see from this that the main exothermic reaction during the non-oxidative discharge process is reaction (1), that is, the selective oxidation of hydrogen sulfide. In practice, it can also be observed that yellow smoke appears above the catalyst after unloading, and the color of the catalyst changes from pitch black to dark gray; this is actually gaseous sulfur formed during the selective oxidation reaction. In other words, the main causes of the rebound in the discharge temperature are H2S gas in the converter and hydrogen sulfide adsorbed on the catalyst; consequently, a solution was naturally developed, namely that when discharging the catalyst without oxidation, it is necessary to reduce the concentration of H2S in the gas as much as possible. Based on practical considerations, we propose the following specific procedures. (1) Use desulfurized semi-water gas to lower the temperature of the catalyst bed in the furnace below a certain level, ensuring that the O2 content in the semi-water gas is less than 0.5%. (2) Perform thorough displacement with nitrogen (or carbon dioxide) to ensure, in principle, that the hydrogen sulfide concentration at the outlet of the low-temperature converter remains as low as possible. At the same time, it is necessary to ensure that the O2 content in the inert gas used is less than 0.5%; otherwise, temperature spikes are likely to occur during the displacement process. (3) The area where the catalyst is unloaded must be dry and free of moisture; operations should be avoided on rainy days. A slight temperature rise occurs due to the escape of a small amount of adsorbed H2S and CO still present inside the catalyst during unloading. Therefore, it is required to seal the catalyst promptly after it has cooled down.

Catalyst removal: Studies have shown that used cobalt-molybdenum low-temperature catalysts cannot be deactivated with air in order to be removed and reused; the active component of these catalysts, cobalt sulfide, reacts with air to form cobalt sulfate, resulting in a permanent loss of their catalytic activity. Cooling should be achieved using dry gas circulation; the lower the temperature, the better. Cool it to around 20°C, then displace the air with nitrogen, and create an opening (an access hole or a discharge hole) to prevent convection. Unload (load) slowly; if the temperature rises, spray water while unloading (loading). It is better to submerge it in water in order to lower the temperature, otherwise the cobalt sulfide within the catalyst will oxidize into cobalt sulfate, losing most of its activity ； Then remove it, sieve it (if necessary), and put it into a new fertilizer bag with a lining ； If the temperature rises, pour in a little water, and tie the bag tightly to seal it and prevent air from entering. When maintaining the shift converter, the cooled and screened catalyst can be stored in a warehouse (but not piled up); however, it should not be kept there for too long, as this will affect its performance. The removed catalyst must be processed immediately and must not be exposed to air; the shorter the processing time, the better ； Once the converter is refilled (or partially replaced with new catalyst), it must be immediately purged with gas, followed by sulfidation (as appropriate). Its effectiveness depends on temperature and processing time; the lower the temperature and the shorter the time, the better the effect, so it is advisable to carry it out just before starting the vehicle. Since it is difficult in practical production to cool down to ~20°C, the following method can be used: (1) The catalyst temperature in the furnace must be reduced to below 50°C using semi-water gas, ensuring that the O2 content in the semi-water gas is ≤0.5%. (2) Perform thorough displacement with N2, ensuring that the O2 content in N2 is ≤0.2%, in order to keep the H2S level at the outlet of the conversion gas as low as possible or even eliminate it, thereby preventing oxidation of the catalyst. (3) Continuously remove it directly into the bag and tie up the bag opening. Spray water outside the bag and place it in a dispersed manner to reduce temperature (do not stack it). (4) During recharging of the furnace, sieve each bag one by one to replenish the lost amount, and immediately replace it with gas after completion. Its effectiveness depends on temperature and processing time; the lower the temperature and the shorter the time, the better the effect. If deactivation is caused by factors such as water or oxygen ingress, it should be addressed separately.

Catalyst removal and resulfurization: (1) Use dry gas to cool the low-temperature converter cyclically or directly to below 25°C, then remove the catalyst through a discharge hole and place it in plastic bags or iron drums for storage. It can be reused without sulfurization and operated directly in combination with gas flow. (2) The resulfurization scheme is the same as the original sulfurization scheme; both the temperature and the sulfurization time at each temperature must meet the specified requirements. The amount of CS2 used can be half of that used during the initial vulcanization; during re-vulcanization, H2S penetrates quickly, but the overall vulcanization time cannot be reduced. The decline in activity caused by factors such as anti-sulfidation can be restored through resulfidation.

Cobalt-molybdenum low-activation catalysts should not be discharged without being deactivated; they must first be thoroughly purged with nitrogen, cooled to below 30 degrees, and then quickly released and spread out. Otherwise, combustion will definitely occur as a result of temperature rise. It is best to pack them in containers or bags under nitrogen protection. The cost is also high. It can be released after passivation, is relatively safe, and has low construction costs; in case of incomplete passivation, simply spraying water will suffice. Safe and plenty. The key points to note are 1: it burns in the presence of oxygen. 2. Releasing S compounds is toxic. Accidents are likely to occur easily in these two areas, so extra caution is required.