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Preface: In 2005, Shandong Mingshui Chemical Co., Ltd. entered into a strategic joint venture agreement with Shanxi Jinmei Group, enabling a strong alliance that strengthened the raw coal supply system for the \"18·30\" project. “The 18·30” project began its overall design at the end of 2005, with construction starting in April 2006. After a year of efforts, the civil work, installation tasks, and initial commissioning were completed, allowing the plant to start operating successfully. It has been in operation for nearly two years now, with stable production and advanced technical and economic performance, achieving the expected output and benefits. Currently, the total ammonia production at Nissan remains stable at 800–850 tons, of which 150–180 tons are methanol and 1150–1200 tons are large-grain urea. The coal consumption per ton of ammonia produced is ≤1150 tons (in physical terms), while the electricity consumption is ≤1200 kW·h. The company has achieved significant economic benefits through the implementation of the “18·30” project. “The 18·30” project utilizes coal as the feedstock for fixed-bed gasification; desulfurization is carried out using an atmospheric-pressure semi-water gas φ6000 mm desulfurization tower and the tannin wet oxidation method. The medium-low-pressure process takes place in a converter of 0.8 MPa and φ5400 mm, while wet conversion and desulfurization are conducted in a unit of φ4400 mm. Decarburization is achieved through the carbon-propane method in a unit of 2.7 MPa and φ3000 mm. Advanced desulfurization is accomplished using the JTC-4 φ3400 mm technology. Gas purification is carried out at 12.0 MPa through alcohol hydroformylation in units of φ1600–φ1600–φ1400. Ammonia synthesis is performed at 26.0 MPa using the ⅢJD φ2000 mm technology, and large-grain urea is produced using the Hydrotec process. Overall, the engineering design of the “18·30” project is reasonable and advanced; it has a certain margin for production capacity, and it makes extensive use of effective innovative achievements from the industry. The plant incorporates optimizations in the gas generation process, recycling of waste residues and gases, electrostatic dust removal for boiler flue gases, hydrogen recovery from decarboxylation flash vapor via PLA, energy savings through the recovery of potential energy from liquid in turbine units, widespread use of variable frequency drives to control the speed and volume of pump motors, utilization of low-grade waste heat, process optimizations to reduce ammonia synthesis pressure, passive ammonia and hydrogen recovery from vent gases, use of evaporation and condensation units in the refrigeration system, pressurized return of circulating cooling water along with utilization of its potential energy, reverse osmosis and mixed-bed processes for desalinated water, zero-discharge technology for wastewater generated in nitrogen fertilizer production, as well as biological treatment of final wastewater and control of NH4-N levels. All these measures enable optimal DCS control and centralized management of the plant. Summarizing the production operations over the past two years, the most significant achievements have been energy savings and reduced consumption, lower product costs, and improved environmental benefits. Notably, the alcohol hydrocarbonation process has replaced copper washing for purification, the ammonia synthesis process has been optimized, low-pressure synthesis has been adopted, and a JⅢDφ2000 mm synthesis tower has been used. It made the most significant contribution to improving the efficiency of the “18·30” device. 1 The main reasons for adopting the alcohol alkylation and IIIJDφ2000 mm synthesis technology are as follows: (1) The traditional copper washing process is an outdated technology that involves high consumption of materials and energy, poor environmental conditions, frequent production accidents, and low safety levels; it should definitely not be used in new installations. (2) Deep transformation methanation gas purification requires stringent process conditions, results in high consumption, and has poor stability, making it unsuitable for use. (3) “Shuangjia” gas purification is a technological advancement that has emerged in the recent development of the nitrogen fertilizer industry as an alternative to copper washing; it has demonstrated excellent performance in practical applications, offering advantages such as low energy and material consumption, low operating costs, and good environmental benefits. (4) Alcohol alkylation is an advancement and improvement of the “diamine” process, offering greater advantages over it. ① “The 18·30” project features a completely new type of unit; the purification units should be at the same pressure level, the process is simplified, there is a centralized layout, the circulation pumps are shared, installation is convenient, and this facilitates production coordination and scheduling. “In the \"dual-methyl\" process, the secondary alcoholation and alkylation steps must be carried out at the isobaric stage of ammonia synthesis; this not only complicates the pressure levels in the process, but also prevents ammonia synthesis from operating at the highest possible pressure, thereby hindering an increase in the ammonia synthesis rate. On the other hand, the alcoholation step can be carried out at medium pressures, allowing the synthesis tower to operate at the highest pressure level. ② The temperature maintenance of both the hydrocarbonation and alkylation catalyst beds relies on reaction heat as well as external heating. In the hydrocarbonation reaction, the CO+CO2 content in the feed gas can be increased appropriately to reduce the need for external heat supply, whereas in the alkylation reaction, the CO+CO2 content in the gas entering the reactor must be strictly controlled at 1×10‑6; otherwise, it will lead to an increase in methane in the alkylated gas, thereby increasing the amount of ammonia synthesis off-gas. Additionally, the temperature required for hydrocarbonation is lower than that for alkylation, which results in less heat supply being needed for hydrocarbonation and thus simplifies the process accordingly. ③ Although the CO+CO2 content in the alkylated gas, after heat exchange, is kept at the 10-6 level, the CH4 content in the alkylated gas still increases to the 10-3 level. According to available information, the gas entering the tower contains methanol, and the following reaction may occur during alkylation: CH3OH + H2 → CH4 + H2O. If the amount of pure alcohol is increased before alkylation, the process becomes more complex. ④ A new issue arising from hydrocarbonation is the formation of wax. It has been found that improving the quality of the catalyst and ensuring thorough reduction can prevent the formation of paraffin. Separating the hydrocarbon fraction from the water fraction in the hydrocarbonated gas can mitigate the effects of wax formation, without causing any harm to production. A comprehensive analysis indicates that both the alcohol hydrocarbonation process and the \"diamine\" process can meet the requirements for gas purification, with the alcohol hydrocarbonation process having overall advantages over the \"diamine\" process; therefore, there was consensus in favor of adopting the alcohol hydrocarbonation process. 2 Process flow for alcoholization gas purification. The alcoholization process consists of two-stage alcoholization and one-stage hydrocarbonation; the process flow of this unit system is roughly similar to that of the combined alcoholization process: the raw gas is preheated in a heat exchanger before entering the reaction tower after removing oil components. The gas emerging from the reaction tower is cooled in another heat exchanger before being sent for water cooling. Once the gas temperature drops to 35 °C, oil components are removed from it. Depending on the level of (CO + CO2) content, either a gas recirculation mechanism is used or the gas is directly sent to the next stage of the reaction process. The A and B alcoholization systems can be connected in series or in parallel, and adjustments are made according to the production load and the alcohol-to-ammonia ratio. The internal structures of towers A and B differ; tower A is designed primarily for alcohol production and is equipped with cooling tubes to transfer heat away, while tower B is mainly used for gas purification and does not have such cooling tubes. When Towers A and B are connected in series, Tower B is equipped with a feed gas bypass to adjust the (CO+CO2) content in the gas entering the tower, thereby facilitating the maintenance of the bed temperature. The hydrocarbonation process is similar to the alkylation process; only the heat-exchanged gas leaving the tower needs to be heated at the lower end of the hydrocarbonation tower, and then it passes through a secondary steam heater to reach a temperature of 210 °C. The gas then enters the catalyst bed directly via the central tube for reaction. The hydrocarbonized gas exiting the tower is cooled through heat exchange for hydrocarbonization; thereafter, water cooling and ammonia cooling are used to separate the water, hydrocarbons, and moisture, thereby allowing the hydrocarbons to be discharged as quickly as possible and reducing the total volume of the liquid mixture containing hydrocarbons. The gas after water separation is further purified before being fed into a compressor, where it undergoes final compression for ammonia synthesis. The external heat supply for the hydrocarbonation reaction is an important aspect of the alcohol hydrocarbonation process. Our company uses steam heaters to provide sensible heat with steam at a temperature of ≥250 ℃; steam at 180 ℃ is then used for gas production. The temperature of the hydrocarbonation bed can be adjusted easily, and this approach offers advantages in terms of convenience, stability, and energy efficiency. Moreover, the purity of the hydrocarbonation gases (CO + CO2) is high. 3 Equipment specifications for alcohol alkylation (see Table 1). Table 1: Equipment specifications for alcohol alkylation. 4 Temperature rise and reduction of the alcohol alkylation catalyst: The plan for temperature rise and reduction of this catalyst was developed through consultations among the technology development company Anchun, the catalyst manufacturers, and our company’s technical staff; it is shown in Tables 2 and 3. “The 18·30” project involves new units located away from the old plant area. The heating and reduction process in the hydrocarbonation tower uses decarburized feed gas as the source; the target value is to keep (CO + CO2) ≤ 1.2%. The reduction reaction of CO generates more heat than H2, so it is necessary to ensure that the circulation pump is available during the alcoholization and reduction process. A high space velocity is required to facilitate the removal of heat, with an actual space velocity of ≥ 4000/h. During the heating and reduction phase of alcohol alkylation, attention should be paid to the following aspects. (1) The temperature increase and reduction processes for the alcohol-to-hydrocarbon conversion and ammonia synthesis catalysts require a considerable amount of time during the initial startup. Since the alcohol-to-hydrocarbon conversion reactor is shared, it is not possible to carry out the reduction process simultaneously; therefore, by properly scheduling the reduction time and adjusting the operation of the reactor, work efficiency can be improved and the startup time shortened. Our company follows this approach: first, reduction is carried out in Alcoholization Tower A; then, the alcoholized gas is used to reduce the hydrocarbonation tower. Once qualified gas is produced through hydrocarbonation, ammonia synthesis reduction takes place. After production becomes stable, reduction is conducted in Alcoholization Tower B. ① The reduction of Tower A for alcoholization was carried out using decarburized feed gas, with a centralized circulation system employed. Thanks to the concentration of human and material resources, the safe and stable temperature rise and reduction process in Tower A was completed nearly 30 hours earlier than the planned reduction schedule. ② When the alcoholized gas (CO + CO2) is ≤0.3%, the alcoholized gas from Tower A is used to reduce the hydrocarbonation catalyst; during this process, 2 to 3 circulators are dedicated to the reduction process for hydrocarbonation, which ensures thorough layered reduction of the catalyst. ③ The hydrocarbonation system operates at light load, with the concentration of (CO + CO2) being as low as ≤10×10-6; the ammonia is then sent for reduction. The reduction of the catalyst in tower B for alcoholization is carried out once ammonia production is operating normally, which helps to shorten the overall startup time. (2) The reduction of the catalysts in towers A and B for alkylation follows a method similar to that of coupling alcohols. Adhering to the principle of controlling the heating rate based on the water output rate, it is necessary to maintain a stable increase in the temperature of the effluent by keeping the temperature as low and the pressure as low as possible. It is important to know the initial temperature of the effluent, so as to be able to properly control the heating rate. Using the decarburized feed gas as the gas source, it is essential to keep the concentration of (CO + CO2) stable and minimize any fluctuations. (3) The hydrocarbonation catalyst has an iron-based structure and similar properties to ammonia catalysts; it is normal for ammonia to be generated during the reduction process. Proper storage and treatment of the wastewater are necessary, and when the concentration of ammonia water increases over time, it can be sent to an ammonia storage tank for future use. (4) Hydrocarbonation catalysts exist in oxidized and pre-reduced states; in either case, thorough reduction is necessary. The bed temperature and hotspot temperature must be ≥490 °C, and the reduction process should last for more than 8 hours. Only by ensuring complete reduction of the catalyst can the formation of paraffin be avoided during production. (5) The ammonia cooling temperature in the hydrocarbonation system is an important means of controlling the gas water vapor concentration, which should be kept at or below 10 °C. 5 Operational status of the alcohol-to-hydrocarbon process: The alcohol-to-hydrocarbon process has been in operation for nearly two years now; the alcohol-to-ammonia ratio remains stable at 25%–30%, while the CO content in the feed gas to the system is controlled between 6.0% and 6.5%. The three towers involved in this process operate in series. “The 18·30” project compressor system operates with either 3 compressors of 305 m3/min and 3 compressors of 108 m3/min, or 4 compressors of 305 m3/min and 2 compressors of 108 m3/min, resulting in an overall ammonia production capacity of 800–850 t/d, of which 150–180 t/d is methanol. The actual production capacity exceeds that of the “18·30” system; in this case, two circulators are used in Tower A for alcoholization (with the inlet valves opened to 50%), and the raw gas flow rate is approximately 100,000 m3/h. Tower B for alcoholization and the hydrocarbonation gas pass through without the use of circulators, keeping the level of (CO+CO2) at a low value of ≤10×10-6. Since its commissioning, the system has operated stably, with a 100% compliance rate regarding the levels of (CO+CO2), and no abnormal incidents have occurred. Key operating parameters for alcoholization: Inlet pressure of alcoholization A system: 10.6 MPa; Outlet pressure of hydrocarbonization system: 10.1 MPa. Circulation rate at the inlet of alcoholization A tower: ~200,000 m3/h. CO+CO2 content in the feed gas: 6.0%–6.5%, of which CO constitutes 0.5%. CO+CO2 content in the gas after alcoholization: 0.3%. CO+CO2 content in the hydrocarbonized gas: ≤10×10-6. Temperatures in alcoholization A tower/°C: Inlet – 180, hot spot – 225, outlet – 195. Temperatures in alcoholization B tower/°C: Inlet – 120, hot spot – 220, outlet – 135. Temperatures in the hydrocarbonization tower/°C: Inlet – 207, hot spot – 220, outlet – 215. Moisture content: 134. Water cooling: 30. Ammonia cooling: 18. Hydrocarbon content: 18, 6. Gas composition and temperature control in the alcoholization process: (1) Alcoholization A tower is primarily used for alcohol production; when the CO content entering the tower is ≥6.0%, two circulators with a capacity of 12 m3/min each must be used. Production operations and adjustments are carried out by controlling the CO+CO2 content entering the tower as well as using bypass valves to maintain a stable bed temperature, so that the CO+CO2 content exiting alcoholization A tower is ≤2.0%. (2) Column B for alcoholization is primarily used for gas purification; no circulation pump is employed, and the gas passes through once. The temperature of the bed is regulated mainly by adjusting the CO+CO2 content in the feed gas via a bypass line, so that the CO+CO2 level at the exit of Column B is ≤0.3%. When production experiences fluctuations or the load is low, an electric furnace is used to assist in maintaining the furnace temperature. (3) The temperature of the hydrocarbonization bed is maintained by adjusting the amount of CO+CO2 entering the tower, as well as the flow rate of the steam heater and the power of the electric furnace. As long as the concentration of CO+CO2 in the hydrocarbonized gas remains low, it is appropriate to increase the CO+CO2 content in the gas exiting Tower B, thereby increasing the reaction heat and reducing the need for external heating. In the gas flow path, the incoming gas first passes through a heat exchanger at the bottom of the tower to be heated; then it enters the heater where it is heated with steam at ≥250 °C to reach a temperature of ≥205 °C. The gas then enters the reaction zone in the bed via the central tube. As long as the bed temperature remains at ≥210 °C, it is possible to keep the concentration of CO+CO2 at ≤10×10-6. The steam used in the heater is cooled to 180 °C before being used for gas production; the steam consumption per ton of ammonia produced is ≤10 kg, and the electricity consumption of the electric furnace is ≤6.0 kW·h. 7 Energy-saving and environmental benefits of the alcohol-to-hydrocarbon conversion process: (1) Isobaric alcohol-to-hydrocarbon conversion results in high-quality gas purification, stable trace elements, and safe production, thereby ensuring high yields and low consumption as well as long-term stable operation for the “18·30” project. (2) The alcohol alkylation technology is an excellent clean production process that eliminates the generation of \"three wastes,\" achieving zero emissions and removing contamination from copper melt and waste ammonia water in nitrogen fertilizer production. (3) In the alcohol alkylation process, the alcohol-to-ammonia ratio can reach 30%; this allows for the adjustment of the company’s product portfolio, and the ratio can be changed flexibly according to market demands, thereby improving the company’s profitability. Operation of the 8ⅢJDφ2000 mm synthesis system: The internal components of this ⅢJDφ2000 mm synthesis unit feature a two-axis, two-diameter, three-stage insulated structure; 80% of the filling volume corresponds to the radial sections. Bed temperature is regulated through cooling shocks and intermittent cooling. 30% of the fresh gas enters the three-stage cold tubes, and the gas enters the bed at 380 ℃. Due to the use of radial baskets as the main internal components along with a gas distribution mechanism, the resistance within the tower is low, and the three-stage insulation ensures a high ammonia recovery rate. The IIIJDφ2000 mm synthesis tower is loaded with approximately 100 t of catalyst, of which 80% is of the A110 series; only 20 t of DNCA catalyst is used at the top and bottom ends of the catalyst bed. Since its operation began nearly two years ago, this synthesis system has not only met the ammonia supply requirement of 1,150–1,200 t/d for urea production but also supplied an additional 20–30 t/d of liquid ammonia. The main process parameters for production operation are as follows: Fresh gas supply pressure – 24.0 MPa; inlet and outlet pressures of the recycler – 23.8/25.2 MPa, with △P ≤ 1.4 MPa. Fresh gas flow rate – ~85,000 NM3 (as per instruments); flow rate of gas entering the tower – ~373,000 NM3 (as per instruments). CH4 content in the recycler’s gas – 18%–19% (excluding Ar). Ammonia content upon entry into the tower – 2.45%; ammonia content upon exit from the tower – 13.78%. Temperatures: Stage 1 – 410–450°C; Stage 2 – 430–455°C; Stage 3 – 450–490°C; Stage 4 – 440–450°C. Temperature at the second outlet – 318°C; temperature at the waste heat boiler outlet – 198°C; temperature at the heat exchanger outlet – 70°C; temperature at the cold gas outlet – 20°C. Ammonia cooling temperature – -5°C. Waste heat boiler steam pressure – 1.5 MPa. The 9 IIIJDφ2000 mm ammonia synthesis system has a catalyst loading volume of 37 m3. Based on the economic operating intensity recommended by the Fertilizer Association, which is 20 t/(m3·day), the ammonia production capacity should be 740 t/day. The system can handle higher loads, with a production capacity exceeding 18×10^4 t/day. The actual operating pressure is ≤25.0 MPa. The total power consumption of the hydrogen-nitrogen compressor, the recycler, and the ammonia compressor is minimized during production. In practice, the CH4 content in the recycler’s gas has been increased appropriately. (2) The pressure at the outlet of the circulator is the highest at the location of the ammonia synthesis tower; meanwhile, the ammonia synthesis system also has its highest pressure at the end of the compressor. Additionally, since the internal components of the tower are designed with a three-stage adiabatic structure, the net ammonia value is relatively high. (3) The gas diversion process in the ammonia synthesis cycle system: 70% of the gas from the main tower passes through an exchanger outside the tower before entering the tower to exchange heat with the catalyst bed, while the remaining 30% of the gas goes directly into the three-stage cooling tubes and then returns to the zero-pressure zone. This diversion process results in high utilization of the high-pressure volume within the synthesis tower, high heat recovery efficiency, low tower resistance, a low temperature of the gas cooled by water, and a reduced load on the circulating cooling water. (4) The gas entering the ammonia synthesis tower is first purified by the catalysts in the alcohol hydrocarbonation towers, which significantly reduces the likelihood of poisoning of the ammonia synthesis catalysts. Nearly two years after the commissioning of the ⅢJDφ2000 ammonia synthesis tower, the catalyst temperatures in various sections of the bed remain at the levels they were at at the time of startup, and the location of the hot spots remains stable, indicating that the catalyst is still in good functional condition. It can be inferred that there should be no issues with the ammonia synthesis catalyst after five years of use. 10 Discussion (1) The three-stage radial cold-tube vapor valves are too small, resulting in higher temperatures in the three stages. Currently, this tower relies on increasing the circulation rate to keep the temperature at ≤490 ℃, which affects the optimal distribution of bed temperatures as well as the further optimization of ammonia purification and system resistance. (2) The synthetic supplementary fresh gas ammonia cooler was never activated for some reason; the introduction of fresh gas into the system has led to an increase in cooling resistance, requiring a thermal wash every six months. (3) 80% of the ammonia synthesis catalysts are of the A110 series; increasing the number of cobalt-containing series will yield even more significant results. 11 Conclusion The “18·30” project brings together the technical expertise accumulated over many years of production by our company, as well as various innovative energy-saving achievements from the industry in recent years. This project has demonstrated long-term benefits in terms of energy conservation, environmental protection, and efficiency; the various technical and economic indicators related to production have reached advanced levels, resulting in improved economic performance for the enterprise. From this, we realize that the core strength of a company lies in improving its technical capabilities and keeping its management methods up to date. By continuing to focus on energy conservation and emission reduction, as well as environmental protection, and by developing a circular economy, we will be on the right path.