How is the catalyst in the synthesis tower reduced? What issues should be considered during reduction?

This post was last edited by ZZJJAA70 on 2009-11-18 at 16:28. Principle: The ammonia synthesis catalyst can function as a catalyst only when Fe2+ and Fe3+ are reduced to α-Fe under certain temperature and pressure conditions; therefore, the new catalyst must be subjected to heating and reduction before use. Heat is supplied by an electric furnace or a start-up heating furnace to gradually reduce the catalyst at the top; the ammonia synthesis reaction takes place using the catalyst that has been reduced in the upper layer. The heat generated serves to compensate for any insufficient heat supply from the electric heaters, thereby enabling the catalyst in the lower layer to be reduced as well. At the same time, a certain pressure and space velocity are maintained to meet the requirements regarding the water vapor concentration at the outlet. 2. Reduction process: 1) During the reduction process, temperature, pressure, and water vapor concentration are the key control parameters. When the water vapor concentration exceeds the specified levels, increasing the circulation rate is used as a solution; if this approach is not sufficient, constant-temperature treatment should be employed. In special cases, it is necessary to reduce both temperature and pressure, ensuring that all moisture is removed from each layer of catalyst at the lowest possible temperature. 2) The reduction method employs segmented reduction; during the upper-stage catalyst reduction phase, a certain amount of gas flow must be allowed into the cold tube. 3) The gas circulation rate during the reduction period should be well controlled, with the principle being to increase the circulation rate as long as the reaction temperature does not drop. 4) Pressure increase should only be carried out after the upper catalyst has been reduced. The pressure increase should raise the temperature of the lower catalyst rather than causing it to drop; if the temperature drops, it indicates that the upper catalyst has not yet been fully reduced, and pressure increase should be stopped while maintaining a constant temperature. Note that pressure increase and temperature increase cannot occur simultaneously – either only pressure increase or only temperature increase is allowed. 5) Theoretical water output based on catalyst theory: In the catalyst, FeO accounts for approximately 22.5% and Fe2O3 accounts for approximately 45%; the total theoretical amount of water produced is calculated based on the total weight of the catalyst. Overall equation: Fe3O4 + 4H2 = 3Fe + 4H2O – 142.8 KJ. Determination of the reduction endpoint: Ammonia-iron catalysts are low-temperature catalysts; it is necessary to keep the peak temperature at ≤500°C, with the bottom layer temperature reaching 460°C for more than 10 hours. Once the actual water output reaches over 90% of the theoretical value, and the water vapor concentration remains at ≤0.2 g/Nm3 after two consecutive measurements, it is possible to enter the cooling phase, after which operation at reduced load can begin.

Heating reduction of synthetic ammonia catalyst: 1: First stage: The gas passes through 105-D, and the reduced gas is completely vented through the 4-inch vent valve in front of EMV-13, without being recycled； Ignite 102-B, and raise the temperature of the catalyst layer to 340 degrees at a rate of 25–30 degrees per hour ； 2: Within the allowable heat load of 102-B, the amount of reducing gas should be as large as possible in order to reduce the temperature difference across the catalyst layer. During the reduction process, it is essential to maintain stability in system pressure, flow rate, and temperature; only one parameter should change at a time, avoiding simultaneous changes in multiple factors, so as to ensure a steady increase in the temperature of the catalyst layer ； 3: When the temperature reaches 200 degrees, the reduction reaction begins and water is generated. It is necessary to conduct more frequent analyses of the water content in the gas exiting the tower; if the level exceeds the specified limits, the heating rate should be reduced or the temperature should be kept constant. Only after the water content falls within the acceptable range should heating be resumed ； 4: Phase 2: While ensuring that the water content in the gas exiting the tower does not exceed the specified limits, increase the temperature from 340 degrees to 400 degrees at a rate of 10~15 degrees per hour ； 5: Since 102-B is operating under maximum thermal load, ensure that the temperature of the gas exiting 102-B does not exceed 538 degrees, the temperature of the flue gas does not exceed 782 degrees, and the pressure does not exceed 1.2 kilograms ； When the temperature at outlet 123-C reaches 160 degrees, activate EMV-6; it is preferable to make manual adjustments on-site to avoid temperature fluctuations in the feedwater system and at 105-D ； 6: Based on the analysis of 105-D inlet, it is necessary to ensure that the hydrogen content is above 75%; at 400 degrees, the formation of ammonia begins simultaneously with the reduction process. Therefore, when analyzing the water content in the effluent stream, it is also necessary to conduct an analysis of the ammonia content ； 7: Phase 3: Increase the temperature from 400 degrees to 415 degrees at a rate of 5 degrees per hour, paying attention to the moisture content of the water exiting the tower ； Pay attention to the rise in the exit temperature at 105-D and the wall temperature of the tower; if necessary, increase HCV-16 and adjust by raising the air flow rate through the annular gap. Also, monitor the operating condition of the system carefully. 8: Phase 4: At a rate of 1–3 degrees per hour, the temperature increases from 415 degrees to 470 degrees. As the ammonia reaction intensifies and more heat is generated, it is necessary to adjust the temperature at the inlet of the catalyst layer in a timely manner, by increasing the amount of reducing gas or reducing the amount of 102-B fuel gas, in order to prevent the catalyst temperature from rising too rapidly or exceeding safe limits. The load on 102-B can be gradually reduced until it is extinguished. 9: At this point, the catalyst layer below the second layer is not yet fully developed. As the temperature of that layer increases, the temperature of the second layer also rises, and the amount of water generated increases accordingly. This can lead to an excessive moisture content in the gas exiting the tower; therefore, it is necessary to adjust the TCV-50 so as to keep the temperature of the second layer around 410 degrees. If the moisture concentration in the outlet gas does not exceed the specified limits, the temperature of the second layer can be increased slightly. 10: When the temperature of one layer reaches 470 degrees, the water vapor concentration in the gas exiting the tower is below 4000 PPM and shows a downward trend, then it is possible to proceed to heating the catalyst in the second layer ； If the ammonia concentration in the outlet gas of the synthesis tower is analyzed to be 2%–3%, the concentration of the ammonia water produced can be further determined to decide whether to proceed with the cycle heating process ； 11: Raise the temperature of the second catalyst layer by 1–3 degrees per hour until it reaches 460–465 degrees; pay attention to the vapor concentration exiting the tower. Keep the temperature of the third catalyst layer at 410 degrees, and follow the reduction process used for the second catalyst layer, raising the temperature by 1–3 degrees per hour until it reaches 450 degrees. Confirmation of ammonia concentration: 1: The ammonia content at the exit of the synthesis tower is 2%–3%. 2: Confirm that the replacement of the synthesis vent line is successful; the procedure is as follows: 3SG529~125-C~108-F~HCV-8~A-EA702~A-DA701 bypass line~PCV-44 vent ； 3: Start HCV-8 and gradually increase the FI-29 airflow to 5,000 cubic units; pay attention to the temperature of the synthesis tower and the operation of unit 103-J ； Use coolant ammonia in 125-C to keep the outlet temperature between -10 and -12 degrees; pay attention to the operation of 105-J and the liquid level in 109-F ； Adjust the outlet temperature of A-EA702 to be above 0 degrees ； 4: Once the level of 108-F is established, use LCV-29 to feed liquid into 107-F; as the level in 107-F rises, it is sent outside for treatment via valve LCV-47A ； Sample analysis shows that the ammonia concentration is greater than 25% ； Synthetic catalyst cycle heating: 1: Confirm that the pressure before EMV-13 is greater than the outlet pressure of stage 3 at 103-J ； 2: First turn on the EMV-13 auxiliary line, then gradually turn on EMV-13 and turn off the auxiliary line ； Meanwhile, gradually reduce the flow at the 4-inch outlet until EMV-13 is fully open and the 4-inch outlet is fully closed, after which the system enters circulation mode ； 3: During the switching process, pay attention to the temperature of 105-D and changes in gas flow, striving to maintain stability; also monitor the operation status of PCV-4, 103-J, and 105-J ； 4: Ammonia cooler 119-C was put into operation to control the outlet gas temperature at -5 degrees to -10 degrees ； 117-C, 118-C to be put into use as appropriate ； Pay attention to 109-F and the liquid levels in each flash tank, the operation status of 105-J, and the inlet temperatures of stage 1 and stage 2 ； Due to the decrease in the gas temperature at the 119-C outlet, the ammonia content at the 105-D inlet decreases, which will cause the temperature of the catalyst layer to rise; adjustments should be made promptly. 5: Stop 117-J, close the ammonia injection valve after EMV-5, and use 124-C or MCV-6 to maintain the inlet temperature of the circulation section of 103-J above 24 degrees ； 6: Pay attention to the rise in the level of 106-F; it is discharged to the outside through LCV-36 and then to 107-F. Points to note in cyclic reduction: 1: After starting cyclic reduction, it is necessary to strictly control the water vapor concentration in both the gas entering and exiting the tower ； 2: Due to the exothermic reaction involved in ammonia production, there is an excess of heat in the system; it is possible to increase the circulation rate or reduce the load on unit 102-B, while the operating pressure can be appropriately increased to 105–110 kilograms ； 3: To increase pressure, one can do so by raising the PCV-4 pressure ； Increase the speed of 103-J ； Adjust the settings of each anti-surge circuit. 4: Gradually provide a stable hydrogen-to-nitrogen ratio ； Pay attention to the wall temperature and outlet temperature of Tower 105-D, and gradually increase the opening degree of HCV-16 ； 123-C outlet temperature ； Sample and analyze data related to S-55, 35, and 47.

Scheme for heating and reducing the catalyst in the synthesis tower I. Preparatory work before heating 1. Notify the electrician to check the insulation of the electric furnace. 2. Notify the metrology department to check whether the instruments are sensitive and functioning properly. 3 Synthetic analysis: Conduct proper analysis of ammonia concentration and water vapor concentration. 4. For the synthesis position, conduct a thorough inspection of the equipment and process flow, and adjust the system valves to the state suitable for heating and reduction startup. 5 Prepare the circulation machine and ice machine. 6 The operators responsible for the heating and reduction process should have clear divisions of labor, and must be familiar with and thoroughly understand the principles behind this process. The position should be filled by individuals with proficient technical skills and a strong sense of responsibility. II. System ammonia charging III. Operating parameters for heating and reduction along with a table of the heating and reduction rates are provided separately. IV. Methods and principles for heating and reduction: Based on the characteristics of these internal components, an overall reduction method is employed; the cold shock valve and the cold feed valve remain closed throughout the heating and reduction process. Only when the process enters the light-load phase can these valves be gradually opened as needed in order to adjust the temperature of the catalyst bed. Adhere to the \"two highs and three lows\" principle, namely high gas velocity, high electric furnace power, low water vapor concentration, low pressure, and low temperature with excessive water output. V. Steps for heating and reduction process 1. Heating stage (from room temperature to 340°C) ⑴ Raise the system pressure to 7.0 MPa using refined gas, and start the circulator to enable circulation. ⑵Between room temperature and 340°C, the catalyst heating rate is controlled within the range of 35–40°C/h. ⑸When the temperature at the hot spot rises to 240°C, turn on the water cooler and release some water. When the temperature at the hot spot reaches 300°C, activate the ammonia cooler and gradually lower its temperature, keeping it within the range of 0–5°C. ⑹When the temperature rises to 320–340°C, continue to release physical water and continuously analyze the gas composition; measure and record the amount of physical water released as mentioned above, but do not calculate the amount of water produced through catalyst reduction. ⑺When the temperature rises to 340°C, the heating and reduction of the catalyst enters its initial stage; at this point, the concentrations of water vapor and ammonia are measured, and the hydrogen concentration is gradually increased. 2. Early reduction stage (340–440°C): ⑴ When the temperature at the hot spot rises to 340°C, water generation begins; measurement and recording activities must be carried out. During this stage, the ammonia cooling temperature is gradually adjusted to below -10°C, while the hydrogen content is kept within the range of 72–75%. ⑵During this stage, heat is supplied by an electric furnace; the circulation rate is gradually increased, and the power of the electric furnace as well as the temperature rise in the catalyst layer are adjusted according to the water vapor concentration. ⑶During this stage, it is necessary to maintain low temperature and pressure while allowing ample water output, and strictly control the temperature rise based on the water vapor concentration. The system pressure is maintained at the lower limit; in principle, the system pressure is not adjusted. ⑷During this stage, the catalyst effluent enters a period of peak performance, and it is necessary to strictly control the vapor concentration and H2 levels within the specified ranges. When the water vapor concentration exceeds the specified level, increase the circulation rate to make adjustments; if necessary, slow down the heating rate or employ a constant-temperature approach for treatment. When H2 is below the target value, gradually open the tower to allow replacement, thereby raising the H2 level back to the desired range. ⑸During this stage, it is important to control the temperature difference within the same plane; when this difference exceeds 10°C, measures should be taken to maintain a constant temperature in order to reduce it. If necessary, the system pressure should be lowered, and reduction processing can continue once the desired temperature difference is achieved. 3. Main reduction stage (440–485°C): ⑴ When the reduction temperature reaches 440°C, the heating-based reduction enters the main reduction stage, during which a large amount of reaction water is generated; it is necessary to increase the circulation rate at this stage and implement continuous water discharge. During this stage, important parameters such as the ammonia cooling temperature, hydrogen, and water vapor concentrations are strictly controlled. ⑵During the main period of water discharge, when the ammonia concentration reaches 95%, it can be discharged to the ammonia storage tank after being stabilized for 2–3 hours. ⑶When the hotspot temperature rises to 480°C, contact the instrument again to verify the hotspot thermocouple. ⑷During this stage of reduction, special attention should be paid to the temperature in the upper layer to ensure that it is fully reduced first. After the temperature of the upper catalyst reaches 480°C and is maintained for over 10 hours, control is achieved by adjusting the circulation rate, and if necessary, by adjusting the zero-meter temperature line. Late reduction stage (480–500–470°C): ⑴ In this stage, the temperature at the catalyst’s hot spots is gradually increased to 500°C, and it is essential to strictly control the relevant parameters during operation. When the temperature of the catalyst layer reaches 500°C, it is strictly prohibited to allow this condition to persist for more than 8 hours; if necessary, it should be controlled by adjusting the cold air supply and cold shock lines. ⑵At this stage, pressure-regulated reactions can be appropriately employed to control the furnace temperature as well as the temperature differences between the top and bottom of the catalyst layer and across the same plane; hydrogen concentration and ammonia cooling temperature are used to control the final reduction temperature. ⑶During this stage, the ammonia cooling temperature should be gradually increased to the range of 0–5°C, in order to provide suitable reduction conditions for the catalyst at the bottom and ensure thorough reduction of that catalyst. ⑷An analysis showing that the water vapor concentration remains ≤0.2 g/Nm3 for 3 consecutive hours indicates that the reduction process is essentially complete, and the system should be adjusted to operate under light-load conditions. ⑸During the light-load phase, the system pressure is gradually increased based on the furnace temperature, thereby reducing the role of the electric furnace until it is turned off; temperature is then regulated through means such as flow rate, zero-meter temperature control, and cooling shocks, so as to gradually adjust the system’s operating parameters to those suitable for normal production. ⑹Under normal operating conditions, the catalyst hotspot temperature is controlled at 470±5°C. Precautions for heating-based reduction: ⑴ During the heating-based reduction process, it is necessary to strictly control the level of trace refining gases (CO+CO2) at ≤25 PPm; once this level reaches 40 PPm, the system should implement constant-temperature measures and stop adding gas. ⑵The load of the electric furnace must be coordinated with the gas flow to ensure safe operation; if any abnormalities are detected in the furnace’s operation, contact an electrician promptly for inspection. ⑶Throughout the heating and reduction process, it is necessary to maintain a bottom-to-top temperature difference of ≤80°C. When this difference exceeds 80°C, measures such as maintaining a constant temperature or increasing the circulation rate should be taken to reduce the bottom-to-top temperature difference. ⑷When the water-cooling outlet temperature exceeds 40°C, water cooling should be activated; when the hotspot temperature in the catalyst layer reaches 280°C, ammonia should be added to the ammonia cooler to control its temperature. ⑸For operational safety, the pressure increase and decrease should be controlled at 0.3–0.5 MPa/min. ⑹Strengthen communication with the Ф1000 synthesis and high-pressure pump teams to stabilize the pressure in the main six-output pipeline, thereby facilitating stable system pressure. ⑺Entering the reduction phase, strictly control temperature parameters and prevent any drop in temperature. ⑻Throughout the reduction process, it is necessary to ensure thorough catalytic reduction while avoiding repeated oxidation and reduction of the catalyst; therefore, the water vapor concentration must be strictly controlled to guarantee the quality of catalyst reduction.