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Foreword The first synthetic ammonia plant of Linyi Branch of Shanxi Fengxi Fertilizer Industry (Group) Co., Ltd. was completed and put into operation in November 2001. The original design capacity was 120 kt/a. In order to improve production capacity and increase corporate benefits, this set of equipment has been transformed many times. The current production capacity has reached 193 kt/a, of which 40 kt/a of methanol is a by-product. The device uses anthracite as raw material and adopts fixed bed gas generation technology. The purification section uses tannin and DDS for desulfurization and NHD liquid cooling for decarburization. ； The conversion adopts full low-conversion technology ； The synthesis section adopts the double-methane synthesis process designed by Hunan Anchun Company. During the process of capacity expansion and transformation, problems that occurred in the Shuangjia section had a greater impact on production. Now we will briefly introduce the problems existing in the operation of the Double A section of the No. 1 Ammonia Branch Plant, the transformation situation and the effects after the transformation. 1 Main equipment and current operating parameters 1.1 Main equipment methanol tower: φ1400 mm ⅢJ99 three-axis two-diameter cold shock synthesis tower (two units) methanation tower: φ1200 mm J103 two-shaft one-diameter methanol tower preheater: φ800 mm methanation tower preheater: φ800 mm water cooler: 400 m3 methanation water cooler: 200 m3 circulation machine: 4.0 m3/min Three units 1.2 Current operating parameters 1.2.1 Flow supplementary air flow 65000 m3/h Circulating air flow 150000 m3/h 1.2.2 Pressure supplementary air pressure 13.4 MPa 1.2.3 Temperature raw gas 32℃ Hot spot of tower A 255℃ Water cooling inlet of tower A 75℃ Outlet 30℃ Cooling outlet of tower A 20℃ Tower B hot spot 245℃ Tower B water cooling inlet 70℃ outlet 30℃ Tower B cold exhaust outlet 20℃ Methanation tower hot spot 270±5℃ 1.2.4 Process operation status of towers A and B in series 1.2.5 Gas composition Raw gas CO 5% CO2 1.4% CH4 2.0% Tower A outlet CO 0.2% CO2 0.3% Tower B outlet CO 0% CO2 0.2% Alkane tower inlet CO 0% CO2 0.2% CH4 2.0% Alkane tower outlet CO 5.0×10-6 CO2 10.0×10-6 2 Situation before transformation 2.1 Process flow (Figure 1) http://www.nmtech.com.cn/jishuwang/upload1/080314932508292.jpg Figure 1 Simplified process flow diagram before transformation 2.2 There are problems. Because the water cooler is a horizontal tube heat exchanger, water goes through the shell side and the gas goes through the tube side. After long-term operation, scale and mud blockage will occur, and the temperature difference of the gas after water cooling is only 70 ℃ (the inlet gas temperature is 140 ℃, the outlet gas temperature is 70 ℃) ； The cooling water temperature difference is 1 to 2°C, and the heat exchange effect is poor, making it difficult to cool and separate the gas phase alcohol. Part of the unseparated methanol gas is circulated through the circulation machine in the system and enters the catalyst layer for decomposition and synthesis, consuming energy. ； The other part enters the methanation tower for decomposition, and H2, CO and CO react to generate CH4 and H2O, which increases energy consumption. Through measurement, the displacement of the methanation water separator is 400 kg/h, 300 kg exceeding the theoretical number. It is calculated that this part of water can consume 855 m3/h hydrogen, equivalent to 390 kg/h of standard coal, and generate 252 m3/h methane at the same time. This part of methane is sent to the synthesis system, and the venting volume increases by 1318 m3/h. 3 Transformation ideas In order to enhance the cooling and separation effects of alcohol, increase alcohol production, and reduce synthetic ammonia consumption, after repeated demonstrations by company leaders, technical departments, and Anchun Company, it was decided to add a 500 m3 cold radiator in front of the water cooler in Tower A. 4 Situation after transformation 4.1 Effect after transformation After the new cold radiator was put into operation on January 8, 2006, the cooling effect was obvious (inlet air temperature 140 ℃, outlet air temperature 30 ℃, temperature difference 110 ℃), the gas phase alcohol content was significantly reduced, the drainage volume of the methanation water separator was reduced to 100 kg/h, and the crude alcohol production increased from 105 t/d to 130 t/d. The comprehensive ammonia production increased from 520 t/d to 555 t/d, and the coal consumption per ton of ammonia decreased from 1205 kg to 1180 kg. 4.2 New problems that emerged after the transformation. Since there are still 0.1% CO and 0.2% CO2 in the post-alcohol gas, CH4 is generated after passing through the methanation tower. This part of methane is sent to the synthesis system, increasing the venting volume by 1300 m3/h. Carry 50 kg/h ammonia to isobaric recovery water and send it to urea analysis, bringing out 700 m3/h hydrogen, which is sent to the fourth inlet of the compressor after hydrogen recovery treatment. Not only does it increase the load of hydrogen recovery, this part of hydrogen is also circulated between the synthesis system (26.5MPa) and the fourth inlet of the compressor (1.7 MPa), occupying an effective volume. If there is no such hydrogen, the compressor will deliver fresh gas, and a ton of ammonia can save electricity 2 kW·h, as far as the ammonia synthesis system is concerned, it can produce 0.6 t more ammonia per hour. 4.3 Further transformation measures are based on the calculation of the amount of methane generated by the methanation tower and the investigation of the alcohol hydrocarbonization process of other manufacturers, especially Henan Xinlianxin Group, which has 32 machines (one machine at 36 m3/min), a daily production of total ammonia of 650 t, synthetic imported CH4 1.6%, and only one 2000 m3 hydrogen recovery system. In our branch plant (28 to 31.3 units), the synthesis system imports CH4 2.5%, and the synthesis vent volume reaches 8378 m3/h. Due to the limitations of coal type and gas production process, the adjustment of the methane content in the raw gas is not large. We envision converting the methane generated by methanation into other substances through process transformation without entering the synthesis system. This can not only purify the raw gas, but also reduce the synthesis vent volume, thereby increasing production and reducing energy consumption. According to our investigation and demonstration, the alcohol hydrocarbonization process has become the first choice, but we still need to further demonstrate the necessity and feasibility of process modification.