What causes a sudden drop in the temperature of the catalyst layer in the synthesis tower?

1. Sudden decrease in the amount of supplementary gas – Solution: Shut off the cold bypass line to reduce the circulation volume. 2. Excessively high or low hydrogen-to-nitrogen ratio in the circulating gas. The hydrogen-to-nitrogen ratio in the circulating gas used in ammonia synthesis should generally be maintained within the range of 2.2–2.8, with appropriate adjustments made depending on the type of catalyst and the stage of its use. An improper control of this ratio, whether too high or too low, can cause a significant drop in the temperature of the catalyst bed. Among them, an excessively high hydrogen-to-nitrogen ratio has the greatest impact on the temperature of the catalyst bed; in severe cases, it can lead to a drop in the temperature of the catalyst bed and an abrupt increase in system pressure. Method 1: Check whether the hydrogen-to-nitrogen ratio of the synthetic cycle gas is displayed by the automatic analyzer. The hydrogen-to-nitrogen ratio can be calculated by analyzing the hydrogen and methane contents in the circulating gas on the analyzer. 2. A low hydrogen-to-nitrogen ratio results in a high current in the circulator and a large pressure difference in the system. A high hydrogen-to-nitrogen ratio results in a lower current in the circulator. This is because hydrogen has a lower density than nitrogen, resulting in less resistance as it passes through the pipes. The attractive force between hydrogen molecules (Edwards force) is also low, making it easier to compress. Thus, it consumes less power. Treatment method 1: Reduce the flow rate by closing the cold auxiliary valve. When reducing the flow rate, be sure to close the ammonia release valve as well to prevent low liquid levels from causing high-pressure gas to escape. Also monitor the pressure; if it rises too rapidly, use the vent valve to control the pressure or inform the compressor to reduce the amount of air supplied. If the temperature has dropped, the pressure should be reduced and the electric furnace turned on to raise the temperature. 2. Notify the gas generation unit to adjust the hydrogen-to-nitrogen ratio. When there are changes in the gas, before or after starting the tower, vent the circulating gas slowly to facilitate replacement, and gradually increase the circulation rate during operation to prevent a sudden rise in temperature. 3. The membrane separation hydrogen recovery unit should be fully utilized to assist in adjusting the hydrogen-to-nitrogen ratio in gas production. When the hydrogen-to-nitrogen ratio is low, the volume of the treatment gas should be increased. When the hydrogen-to-nitrogen ratio is too high, the volume of the treatment gas should be reduced. III. High levels of CO and CO2 in the make-up gas: Due to substandard refined gas or improper operation of the compressor, as well as the valve 56 not being closed properly or having internal leaks, the levels of CO and CO2 in the make-up gas increase. When large amounts of these gases enter the synthesis tower, CO, CO2, and H2 undergo the following reactions in the catalyst bed: CO + 3H2 → CH4 + H2O; CO2 + 4H2 → CH4 + 2H2O. The water vapor generated then reacts with the -Fe in the catalyst as follows: H2O + Fe → FeO + H2; 3H2O + 2Fe → Fe2O3 + 2H2O. As a result, the -Fe particles that play a role in activating the catalyst are oxidized to ferrous oxide and ferric oxide, leading to a decrease in catalyst activity, a rapid drop in the temperature of the catalyst bed, and an increase in system pressure – all symptoms of catalyst poisoning. High CO2 levels can not only poison the catalyst but also form crystals with substances such as ammonia in the system, causing blockages in the system’s pipes and equipment and increasing the pressure difference within the system. Method 1: The refined gas micro-automatic analyzer can display it clearly. If valve 56 of the high-pressure compressor is not fully closed or there is internal leakage, the automatic analyzer will not display any readings; in such cases, it is also possible to connect the analyzer’s sample gas pipe to the gas supply pipe used at the synthesis station. 2. When the catalyst becomes poisoned, the temperature in the upper layers of the catalyst bed drops first, while the temperature at the hot spots rises slightly. As the temperature at the hot spots begins to fall, the pressure also increases. If this is not addressed in time, when the hot spots reach the farthest point, it can lead to a collapse in the temperature of the catalyst bed. Treatment method 1: Quickly open the make-up gas vent valve to cut off the make-up gas, in order to prevent further poisoning of the catalyst, and immediately shut down the compressor to stop gas supply, so as to avoid the make-up gas pressure exceeding the specified limits. 2. Close the tower auxiliary valve to rapidly reduce the circulation volume significantly; depending on the degree of poisoning, stop the circulation pump or keep one running to maintain the temperature inside the tower. An electric heater can be used to raise the temperature if necessary. 3. If the poisoning causes only a slight drop in the temperature of the catalyst layer and the effect of poisoning is not significant, then once the refined gas meets the required standards, gas can be supplied again to restore normal operation ； In cases of severe poisoning, all pressure must be released first, and the area should be purged with qualified refined gas before the electric furnace is used to raise the temperature. To reduce the poisoned catalyst, within 2 hours after resuming normal production, the temperature can be raised above the normal operating temperature to facilitate the removal of the toxins. During accident handling, attention should be paid to the liquid levels in the ammonia separator and the heat exchanger to prevent high-pressure gas leakage. IV. Liquid ammonia is carried in the gas entering the synthesis tower due to improper adjustment of the liquid level in the cold exchanger or untimely ammonia release, which results in an excessively high liquid level and thus the entry of liquid ammonia into the synthesis tower. When liquid ammonia is introduced into the synthesis tower, it increases the ammonia concentration within the tower. This helps to suppress the synthesis reaction and reduce the heat generated by it. However, as the liquid ammonia evaporates in the tower, it absorbs heat, which leads to a decrease in the temperature of the catalyst bed. In severe cases, this can result in a drop in temperature to such an extent that it causes damage to the components inside the synthesis tower. Judgment method 1: The characteristics of liquid ammonia entering the synthesis tower are a decrease in the temperature at the inlet of the catalyst bed, a sharp rise in the ammonia concentration at the inlet, a rapid drop in the temperature in the upper part of the catalyst, and a swift increase in system pressure. 2. The liquid level in the cold exchanger is too high, resulting in a decrease in the ammonia release pressure. Treatment method 1: Quickly lower the liquid level in the cold exchanger; if the level gauge is faulty, notify the instrumentation team promptly for handling. In addition to the ammonia release valve on the valve frame, the cold exchanger is equipped with another ammonia release valve next to the root valve, which helps to lower the liquid level in the cold exchanger. 2. Close the cold bypass valve of the synthesis tower and reduce the circulation gas volume to suppress the temperature drop. If the temperature has dropped below the activation temperature of the catalyst, it is possible to stop supplying gas, reducing pressure, and applying power to raise the temperature. 3. When the temperature starts to rise normally, the circulation rate should be increased gradually to prevent a sudden spike in temperature. Generally, after the liquid ammonia-related fault is resolved, the temperature recovers quickly, so it needs to be controlled in advance. V. The intake gas to the synthesis tower containing copper melt is a serious accident; the main impacts are as follows: 1. Residual CO and CO2 in the copper melt can temporarily poison the catalyst. 2. A small amount of H2S in the copper melt can permanently poison the catalyst. 3. Introducing molten copper into the tower causes it to adhere to the surface of the catalyst, rendering it inactive. 4. Introducing molten copper into the tower can damage the internal components; if an electric furnace is also in use, the conductivity of the molten copper can cause a short circuit, thereby damaging the furnace filaments. Judgment method 1: When the copper melt is introduced into the synthesis tower, the temperature of the catalyst bed rises slightly before dropping sharply. This is particularly evident at the top layer, with temperatures decreasing in the other layers as well. The system pressure difference increases, causing the system pressure to rise. 2. The oil separator can discharge the copper melt. 3. The presence of molten copper in the gas increases the resistance to gas flow through the pipes, resulting in a high pressure difference in the circulation pump. 4. Blockage of sampling tubes or discharge of copper melt in the synthetic analysis laboratory. Treatment method 1: Immediately close the make-up air valve and open the make-up air vent valve to prevent further liquid carryover. 2. If the copper melt does not enter the synthesis tower but only goes into the heat exchanger and oil separator, the circulation pump should be stopped, the main inlet valve of the synthesis tower as well as the auxiliary cold valve should be closed, the copper melt in the heat exchanger and oil separator should be drained, and a purge should be performed before the tower to completely remove the copper melt from the system. 3. If the molten copper has entered the synthesis tower and poisoned the catalyst, it can be displaced and reduced using fresh gas at high temperature and low pressure to restore its activity. If the treatment is ineffective, the only option is to replace the catalyst. 4. Pay attention to pressure relief; it should be done first at the front of the tower, then at the back, and finally inside the tower. When turning on the circuit, it is necessary to check whether the insulation of the electric furnace is satisfactory. VI. High ammonia content in the gas entering the synthesis tower. Reasons for the high ammonia content in the gas entering the synthesis tower: 1. Leakage in the heat exchange section of the cold exchanger, causing the gas with high ammonia levels to leak into the gas flowing toward the synthesis tower after ammonia separation. 2. The ammonia separator section of the cold exchanger is damaged, or oil contamination causes low efficiency in ammonia separation; additionally, excessive level control leads to gas carrying liquid ammonia, thereby increasing the ammonia content in the gas entering the synthesis tower. 3. The high ammonia condensation temperature hinders the conversion of gaseous ammonia into liquid ammonia, resulting in an increase in the concentration of gaseous ammonia in the gas entering the synthesis tower. Solution 1: Inspect and repair the cold exchanger. 2. Strengthen oil drainage from the cold exchanger; stop the machine for hot washing if necessary. 3. Lower the ammonia condensation temperature. VII. Excessively high level in the waste heat boiler: A high level of liquid in the waste heat boiler can disrupt the thermal balance of the synthesis circuit, thereby reducing the temperature at the inlet of the synthesis tower. process ； Lower the heat waste boiler for synthesis and adjust it to the normal range. VIII. Excess methane content: Methane does not participate in the ammonia synthesis reaction, but it occupies partial pressure and carries away the heat of reaction. Therefore, an appropriate methane content should be controlled. IX. Improper operation such as ； The cold bypass is opened too much, the circulation rate is increased too rapidly, or the power of the electric furnace is insufficient when it is in use. X. In case of a thermometer malfunction, please have the instrumentation department handle it

Your question is too broad (it covers too many aspects). There are many reasons for a drop in temperature; the temperature in the middle section of the fresh gas will definitely drop. Be more detailed

1. First, check the fresh air flow rate. 2. Check the nitrogen flow rate to determine whether it is due to an inappropriate hydrogen-to-nitrogen ratio. 3. Check whether there is a problem with the gauge: If the pressure difference, flow rate, and make-up air volume are normal, and there are no significant fluctuations in the liquid levels of the condenser and separator as well as in the control valves, then it indicates that there is a problem with the temperature sensing element. 4. Check the liquid levels in the condenser and separator to determine if there is liquid present. 5. Check if there is any change in the pressure difference, to determine whether the circulation volume has increased. Check the opening degree of the line valve. 6. Check for trace amounts or notify the dispatch team to check the gas composition in the gas generation workshop. 7. Check whether the pressure difference increases or decreases to determine if there are any issues with the internal components of the tower.

If it’s not a disruption in gas supply, then it must be due to ammonia being present, as well as the cold line having been turned off. Other situations are not likely to cause a sudden drop in bed temperature.