What are the characteristics of the so-called pre-reduction catalyst? Exactly how much should be restored?

It is recommended that the original poster take a look at the book titled “Practical Handbook of Fertilizer Catalysts”; you can download it by clicking on the link

Pre-reduced ammonia synthesis catalysts have a lower starting temperature; the A110-1-H type generally begins to reduce at 180°C to 200°C. First is to reduce the large amount of downtime in ammonia plants. For the use of a pre-reduced catalyst in the entire furnace, the reduction time required for the catalyst is only about 1/3 of that needed to reduce a catalyst in its oxidized state; this increases the effective production time for ammonia synthesis and reduces the startup costs. Secondly, the reduction of the pre-reduction catalyst is actually merely the removal of the passivation film. Since the oxygen content in the passivated portion accounts for only 8%–10% of that in the unreduced catalyst (with slight variations depending on particle size), and the bond between oxygen and iron in the passivation layer is relatively weak, it can be easily removed during catalyst reduction; thus, the reduction temperature is about 100°C lower than that of the oxidized catalyst. As reduction proceeds, the heat generated by the ammonia production reaction can be used to compensate for the insufficient capacity of the heater. Furthermore, since the pre-reduction catalyst produces little water during reduction, the amount of dilute ammonia generated is also limited, thus avoiding the troubles associated with dealing with large volumes of effluent ； Moreover, water vapor is also easy to control during the reduction process, reducing the possibility of catalyst poisoning by water vapor. The economic benefits obtained by using a pre-reduction catalyst are also significant. Based on a rough calculation of the overall energy consumption associated with the use of this type of catalyst, for a large ammonia plant producing 1,000 tons of synthetic ammonia per day, starting normal production one day earlier can generate benefits in the range of several million yuan ； Small and medium-sized factories will also earn revenues ranging from tens of thousands to several hundred thousand. Pre-reduction catalysts will become the main choice for ammonia production plants in the future. When loading the pre-reduction catalyst, pay attention to: 1) Avoid direct sunlight when screening the pre-reduction catalyst. 2) When loading the pre-reduction catalyst, a temporary temperature probe also needs to be installed to monitor the bed temperature. Usually, a trace amount of nitrogen is also introduced during charging to prevent the catalyst from oxidizing due to the destruction of the passivation film. 3) Safety measures must be in place when loading the pre-reduction catalyst into the tower. These are the temperature rise requirements for our company’s ammonia synthesis tower after adding some pre-reduction catalysts: Pressure at A is 5.0 MPa; there is 1 circulator with a capacity of 6 m3/min, and the short-circuit valve is used, with the acceleration controlled by the current in the electric furnace. At zero meters, the temperature rises to 480°C, with an increase rate of 40°C/h. The temperature at zero meter in C is 480°C–490°C; this temperature is achieved within 4 hours, and production can begin once the temperature remains constant for 4 hours. After being put into normal operation, everything worked perfectly, which indicates that the pre-reduction catalyst must have been fully reduced.