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Brief introduction to the characteristics of the Brown process: The energy-saving measures adopted by the American Brown Company involve reducing the amount of fuel gas used. This is achieved by decreasing the load on the first conversion furnace (raising the outlet CH4 content from 10% to around 30%), while increasing the load on the second conversion furnace and adding excess air there (which generates a large amount of reaction heat to supply the energy needed for the conversion of residual CH4). As a result, the temperature in the first furnace decreases, leading to reduced fuel gas consumption. At the same time, deep cryogenic purification is used to remove excess nitrogen, and a gas turbine drives the air compressor, resulting in an energy consumption of 28.4 GJ per ton of ammonia produced. In China, energy-saving technologies with a low water-to-carbon ratio have been applied to a section of the converter used in the imported Brown unit, while the ammonia synthesis process employs a three-tower and three-waste-heat boiler system to generate high-pressure steam from waste heat, thereby further reducing energy consumption. Cryogenic purification is the core technology of the Brown process. The cryogenic purification unit consists of 2 sets of plate-fin heat exchangers, an oil-braked turbine expander, and a distillation tower equipped with a top condensation evaporator. In the cryogenic purification unit, the difference in boiling points of the various components in the crude syngas is utilized to cause them to condense and be separated through distillation at low temperatures. As a result, the excess nitrogen, residual methane, and about half of the CO and Ar in the crude syngas are removed as waste gas, thereby achieving a hydrogen-to-nitrogen ratio of 3:1 in the syngas. Part of this waste gas is heated and used as gas for regenerating the molecular sieve, while the rest is used as fuel gas for the first-stage furnace. After cryogenic treatment, the H2 and N2 content in the fresh gas reaches 99.75%, which **improves the quality of the fresh gas** compared to other processes. The gas at 4.4°C at the outlet of the molecular sieve dryer (with H2:N2 ratio of approximately 2:1) is cooled to -129°C in the low-temperature Brown subcooling unit by heat exchange with the purified syngas and exhaust gases. It is then expanded through an expansion turbine and a throttle valve; due to isentropic expansion, the pressure drops and potential energy is converted into the cooling energy required for purification, allowing the gas to be cooled further to -132°C. The expanded gas is cooled to -175°C in a heat exchanger before entering the purified gas distillation column. The power extracted from the expander is varied as needed to control the liquid level at the bottom of the distillation column. The liquid coming from the bottom of the distillation tower is depressurized through a throttle valve and then sent to the shell side of the cooler at the top of the distillation tower as a cooling source; this cools the material at the top of the distillation tower and provides reflux fluid for it. The bottom product of the distillation tower consists mainly of excess nitrogen from the second-stage converter, methane in the gas, approximately 60% hydrogen, and about 50% of the remaining carbon monoxide. The partially vaporized liquid that leaves the condenser is reheated and vaporized after heat exchange with the purifier feed, and then exits as waste gas. Part of the exhaust gas is used as regeneration gas for the dryer, and then it goes together with the remaining exhaust gas to the conversion furnace as fuel. The purified syngas is heated to 2 °C after heat exchange for ammoxidation. The hydrogen-to-nitrogen ratio of the purified gas is precisely controlled at 3:1 by an on-line hydrogen analyzer. As a flexible connecting link between the front units (gas generation and decarburization) and the rear synthesis units, the cryogenic purification unit can absorb fluctuations such as increased nitrogen content due to excess air in the two-stage furnace at the front of the system, or increased methane content resulting from higher CO2 levels at the decarburization outlet. This is achieved by adjusting the operating conditions of the expander to increase the cooling capacity, thereby ensuring a stable gas composition at the output of the purification unit and preventing any disruption to the normal operation of the synthesis units.