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The ammonia synthesis unit of Zhongyuan Dahua Group adopts UHDE-AMV low-energy consumption process technology, uses natural gas from Zhongyuan Field as raw material, and has a daily output of 1,000 t of synthetic ammonia. In recent years, with the development of oil fields, the amount of natural gas has gradually decreased, and ammonia synthesis units rarely produce at full load, causing the cost of ammonia per ton to rise. In order to ensure the company's sustainable development, a new coal chemical project was built at the end of 2005, including a methanol unit with a production scale of 500 kt/a. In order to increase the synthetic ammonia load, it is planned to introduce the hydrogen-rich relaxation gas after methanol water washing into the ammonia synthesis unit, with the amount of about 30080m3/h (standard state). 1 Properties of synthetic ammonia conversion gas and methanol relaxation gas (1) After the natural gas undergoes the conversion reaction in the first-stage furnace and the second-stage furnace and recovers waste heat, the converted gas with a temperature of 370°C and a pressure of 4.2MPa enters the high-temperature shift furnace and the low-temperature shift furnace in sequence, and converts CO into CO2 under the action of the catalyst. The composition of the reformed gas before entering the high-temperature shift furnace is shown in Table 1. (2) The methanol relaxation gas after washing with water has a temperature of 55°C and a pressure of 7.49 MPa. Its composition is shown in Table 2. As can be seen from Table 1 and Table 2, the properties of ammonia conversion gas and methanol release gas are similar, with only differences in temperature and pressure. Methanol release gas must be heated and depressurized before being introduced into the ammonia synthesis unit before it can be connected to the grid. 2. Process flow and production organization. The process flow is shown in Figure 1. A new preheater is added at the outlet of the high-temperature shift furnace to use the high-temperature shift gas to preheat the methanol purge gas. The heat-exchanged shift gas then enters the waste heat boiler. ； The preheated methanol relaxation gas is combined with the ammonia reformed gas and then enters the high temperature shift furnace ； The new preheater is equipped with a bypass valve to control the inlet temperature of the high-temperature conversion furnace at 370°C. After the methanol release gas is introduced into the ammonia synthesis unit, production can be organized in two ways. Option 1: The output of synthetic ammonia remains unchanged at 1 000 t/d, that is, the amount of raw natural gas is reduced, but the amount of steam added to the first-stage furnace should be maintained so that the highly variable inlet steam-gas ratio is consistent with the original design value, that is, the water-to-carbon ratio of the first-stage furnace is higher than the design value. ； All the nitrogen required for ammonia synthesis comes from the process air added to the second-stage furnace, and the temperature of the high-variable furnace entrance basically remains unchanged from the original design. ； Compared with the original design, this solution can reduce raw natural gas consumption by about 25%. Option 2: The flow rate of raw natural gas is about 60% of the original design. Others are the same as the plan. ； Compared with the original design, this solution can maintain 80% to 85% of the operating load of the ammonia synthesis unit, that is, an ammonia output of 800 to 850t/d. Whether Option 1 or 2 is adopted, its impact on the ammonia synthesis unit is as follows:: ()) The load of the first stage furnace of both schemes is lower than the design index, and the steam production of the auxiliary boiler needs to be increased according to the requirements of steam balance. (2) Add more water vapor to the first-stage furnace to increase the water-to-carbon ratio and maintain the steam-to-gas ratio at the entrance of the high-variability furnace consistent with the original design. (3) The relative increase in the amount of air added to the second-stage furnace may slightly increase the temperature in the combustion zone of the second-stage furnace. However, due to the increase in the water-to-carbon ratio, it is beneficial to suppress the maximum temperature in the combustion zone of the second-stage furnace. (4) The heat required by the methanol purge gas preheater was originally used for the by-product steam of the high variable waste heat boiler, which means that the high variable waste heat boiler basically does not produce high-pressure steam, and the high-pressure steam that is missing in the ammonia synthesis unit needs to be found from another source. (5) The CO2 output of the two schemes can only meet 92% to 93% of the urea production load. Without additional CO2 supply, there will be 7% to 8% of liquid ammonia product. (6) If the output of synthetic ammonia remains unchanged at 1 000t/d, the amount of raw natural gas can be saved after grid connection ； If the supply of raw natural gas is insufficient, the production of synthetic ammonia can be increased after grid connection. (7) The natural gas consumption per ton of ammonia in both schemes has decreased, and the cost of synthetic ammonia has decreased. 3 Disadvantageous factors (1) The scheme has little impact on the subsequent heat recovery system, but changes in the relaxation gas and process gas flow from the first-stage furnace will affect the temperature of the process gas in the second-stage furnace, thereby affecting the normal operation and load regulation of the second-stage furnace, and may even affect safe operation. (2) In option 2, the operating load of the second-stage furnace is low, which may affect the uniform mixing and uniform combustion of the top air distributor, thus affecting the life of the top air distributor. (3) From the perspective of process calculation and material balance, neither scheme exceeds the original design scope, but the operation control indicators of some equipment will change, and it is necessary to explore and test in actual production operations to determine its feasibility and safety.