What are the catalyst reduction time, water vapor concentration, ammonia cooling temperature and pressure, as well as the circulating hydrogen volume in a large-scale ammonia synthesis tower?
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For example, 18W tons and 30W tons. Please, everyone, discuss it. At present, the 18W ton unit in our plant is in the reduction phase; it has been running for 6 days and another 7 days or so are required to complete the process.
The reduction methods for different types of catalysts vary, and catalyst manufacturers will provide detailed reduction protocols. The following two documents may be useful to you: 1. Temperature-raising reduction protocol for ammonia synthesis towers (click here) Catalyst reduction protocol (click here)
The reduction time varies from factory to factory. Main reasons: 1. Catalyst type; generally, pre-reduced catalysts require a shorter reduction time. 1. The operating time of the oxidized catalyst. 2. The reducing agent: whether to use process gas for reduction or cracking gas for premature reduction. 3. Whether the previous reduction process proceeds smoothly. 4. The amount of reducing gas used. 5. Control of the reduction temperature. Control of water vapor concentration: For pre-reduced catalysts, the water vapor concentration should be kept below 1000 ppm; for oxidized catalysts, it should be kept below 2500 ppm. Ammonia cooling temperature: The ammonia cooling temperature should be reduced gradually, with ammonia cooling taking place simultaneously with the reduction process – this allows ammonia to be released earlier and also prevents the ammonia cooler from freezing up and becoming clogged. The ammonia cooling temperature must be kept three degrees above the freezing point. Pressure control: It is increased gradually according to the requirements of the reduction process and the amount of reducing gas. The reduction start pressure is gradually increased from 80 atm to around 150 atm, with hydrogen flow being controlled; from a reduction perspective, a high hydrogen content is beneficial for the reduction process. However, toward the end of the reduction process, the heat required for reduction comes from the heat released by the reaction between hydrogen and nitrogen catalyzed by the already reduced catalyst; at this point, a high hydrogen-to-nitrogen ratio is detrimental to the reaction. Furthermore, at a hydrogen-to-nitrogen ratio of around 2.8–3.0, the pore structure of the reduced catalyst is the most optimal. Therefore, the hydrogen-to-nitrogen ratio is generally controlled at 3.0.