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An overview of recent advancements in foreign urea production technologies: Currently, the competitive urea production technologies worldwide include the CO2 stripping process developed by Stamicarbon in the Netherlands, the NH3 stripping process used by Snam in Italy, the ACES process developed by Toyo in Japan, the isobaric dual stripping process (referred to as the IDR method) used by Montedison in Italy, and the MEC thermal cycle process developed by UTI in the United States. 1. CO2 stripping process 1. Main technical features: ① Simple process: The high stripping efficiency in the synthesis stage reduces the complexity of downstream processes. It is the only urea production process that has been industrialized and features a single low-pressure recovery step; it offers easy operation, low investment costs, high reliability, high operational efficiency, and low maintenance expenses ； ② Optimized combination for the high-pressure loop process: the operating pressure is 13.6 MPa, the ammonia/carbon ratio is 1:2.95, the synthesis temperature ranges from 180 to 183°C, the condensation temperature is 167°C, the stripping temperature is 190°C, and the stripping efficiency is over 80%. These parameters are relatively mild; the use of 25-22-2 CrNiMo material is sufficient to meet the requirements regarding corrosion resistance, and the costs associated with equipment manufacturing and maintenance are low ； ③Low power consumption: Due to the low operating pressure, the power consumption of high-pressure ammonia pumps and high-pressure ammonium methane pumps is also low. Due to the high stripping efficiency and the absence of a medium-pressure recovery section, there is no need for separate liquid ammonia to be recycled, and the amount of ammonium methylate that needs to be recycled is also low; as a result, the power consumption required for recycling ammonia and ammonium methylate is further reduced ； ④Pool-type condenser is used: As a primary reactor, the pool-type condenser reduces the volume of the synthesis tower by about 50%, and the height of the urea framework is around 76 m ； ⑤High safety factor: In the dehydrogenation converter, flammable gases such as H2 and CO in the feed CO2 are removed through passivated combustion, ensuring that both high-pressure and low-pressure vent gases remain outside the explosive range, thus providing high safety for the process equipment ； ⑥Low pollution: After hydrolytic decomposition of the process condensate, not only is ammonia loss reduced, but environmental pollution is also eliminated. 2. Technical advancements: The 2000+TM advanced process: To reduce investment costs, Stamicarbon Company has implemented technical improvements. The most representative of these is the urea 2000+TM advanced process, whose main advantages are as follows: ① It uses new, highly efficient trays; these trays are equipped with liquid rising pipes within a gas distribution system, which ensures uniform mixing of the gas and liquid phases on the trays, thereby eliminating the problems of channeling and backmixing that occur in conventional trays ； ②The horizontal tank-type condenser replaces the original vertical tank-type condenser and features submerged U-tube bundles ； ③The height of the urea main frame was further reduced: by using new types of efficient trays, horizontal pool-type condensers, reducing the volume of the synthesis tower and its height, and installing high-pressure ammonia injectors powered by liquid ammonia, the height of the main frame was decreased from 76 m to 38.5 m ； ④A CO2 H2 removal unit was added to reduce the volume fraction of H2 in the CO2 gas from 0.5% to below 0.005%. Large-particle urea fluidized bed process: The main features of the large-particle urea fluidized bed granulation technology developed by Norsk Hydro are as follows: ① Urea solution with a concentration of 95%–96% is used as the raw material; only one stage of evaporation and concentration is required for this urea solution, which simplifies the process flow in the urea production system ； ②By eliminating the two-stage evaporation system, steam used for heating in the two-stage evaporation process and for vacuum creation is saved, the amount of process condensate is reduced, which in turn lowers the hydrolysis load; it also reduces the consumption of cooling water ； ③The granulator uses a granulation technique that combines air atomization with fluidization, offering high efficiency, large production capacity, and high-quality finished products with strong strength ； ④Simple to operate, short processing time; the product can be obtained within 1 hour after feeding the materials ； High operational flexibility, with a load variation range of 30% to 110% ； ⑤Compared with other mechanical granulation devices, it has a lower return ratio, thereby enhancing the equipment’s capacity and reducing energy consumption during the granulation process ； ⑥Additives are used to reduce the dust generated in the fluidized bed, and the dust-containing exhaust gas is treated via wet scrubbing, which offers high absorption efficiency; as a result, the urea dust content in the exhaust gas released meets environmental regulations ； ⑦The device has high reliability; components such as granulators and dust washers, having no moving parts, can last for over 25 years. II. NH3 stripping process 1. Main technical features: ① The molar ratio of NH3 to CO2 in the feed to the synthesis tower is 3.3–3.6, resulting in a high CO2 conversion rate and reduced recycling load after the high-pressure stage ； ②Due to the high NH3/CO2 molar ratio in the synthesis system and the appropriate selection of equipment materials, **corrosion issues in the equipment are reduced; there is no need for special passivation of the high-pressure system equipment. Additionally, even in the event of an emergency shutdown, the tower can be sealed for several days without any need for discharge, and the urea product remains white even after restarting the system after 3 days of sealing.** ； ③Both the medium and low-pressure decomposition pressursizers are of the falling-film type, resulting in little accumulation of liquid during operation; even when shut down for discharge, there is minimal loss of NH3 and CO2 ； ④By using ammonium injection pumps, all high-pressure equipment can be installed on the ground level, eliminating the need for high-rise frameworks and thus saving costs, **accelerating the construction timeline ； ⑤The presence of a medium-pressure decomposition section enhances operational flexibility and resilience; by adjusting the gas lift efficiency and the amount of by-product steam generated by the high-pressure ammonium methoxide condenser, it is possible to regulate the steam balance of the entire plant and ensure it operates under optimal conditions ； ⑥After hydrolytic treatment, the process condensate not only has its contamination completely removed and losses of ammonia and urea are reduced, but the treated condensate can also be used as boiler feed water ； ⑦The granulation process was changed to drum granulation, overcoming the drawbacks of the original spray granulation method, such as low hardness of the urea, small particle size, tendency to caking, and environmental pollution caused by ammonia and urea powder emitted from the top of the tower. 2. Technical progress: The latest advancement in this process technology is the addition of absorption towers to recover ammonia released from the low-pressure system, which can reduce the ammonia consumption in urea production; it is estimated that 300–500 tons of ammonia can be recovered each year ； The heat exchange tubes in the air lift tower are made of zirconium-lined bimetallic stainless steel instead of titanium, a material that can effectively prevent erosion corrosion ； The BD vent pipelines and vent stacks are made of stainless steel instead of carbon steel ； Column-type high-pressure ammonia pumps use desalinated water instead of seal oil, saving 20 kL of oil per year ； By using the drum granulation technique, the hardness of the finished product can be increased, the particles can be made larger, and caking is less likely to occur. Three ACES process 1. Main technical features: ① Optimization of the operating conditions in the synthesis tower, a specially designed structure for the stripping tower, and no need for external heat supply for decomposition and separation, resulting in reduced energy consumption ； ②In this method, the NH3/CO2 molar ratio can reach as high as 4.0, with a corresponding conversion rate of up to 68% ； ③Double-phase stainless steel is used in areas with high corrosion, reducing corrosion and allowing the device to operate continuously ； ④It features a patented special stripping tower, providing an efficient CO2 stripping system. 2. Technical advancements: ACES21 process: To reduce investment costs, Toyoe Engineering Corporation has improved its existing ACES urea production process: ① The high-pressure vessels are arranged in a flat layout, facilitating installation ； ②The entire process integrates processes such as carbamate formation, heat recovery, and urea synthesis into a vertical buried carbamate condenser, reducing the number of high-pressure vessels and the heat transfer area ； ③Reduce the volume and mass of the reactor and the stripping tower, simplifying their installation ； ④Optimizing the different carbamate condenser reaction molar ratios and reactor reaction molar ratios under lower synthesis pressures reduced the design pressure for high-pressure vessels and rotating equipment, as well as energy consumption. Large-particle urea spray fluidized bed granulation technology: The key features of the large-particle urea spray fluidized bed granulation technology developed by Japan’s Toyo Engineering Company include: ① A relatively simple process flow and equipment design. This granulation process consists of two stages – fluidization and granulation – followed by cooling. The granulation nozzles are of the conventional pressure type, offering a simple structure and high capacity per unit. A dust washing tower is connected to the top of the granulator, which simplifies the process and reduces the number of required devices ； ②Short granulation time and high granulation efficiency: In this process, the recirculating seed crystals in the fluidized bed are successively coated with urine droplets in series-connected chambers, thereby growing larger; moreover, the thin fluidized bed layer facilitates particle formation ； ③The fluidized bed layer height in the granulator is low: within the 50%–100% load range, the layer height is only 400 mm. The resistance of the fluidized bed is low, the pressure required by the fan to aerate the bed is low, resulting in reduced power consumption ； ④Flexible and convenient production operation: the feedback ratio can be adjusted; the production control system is reliable, and it is simple to adjust the nozzle when the load changes ； ⑤Using about 95% of the urine as raw material can simplify the urine processing steps and save energy consumed in urine concentration ； ⑥The dust recovery system employs centralized dust collection along with efficient wet scrubbing and absorption, resulting in a low level of urea dust in the exhaust gases ； ⑦Set up an additive MMU self-provided system: The MMU solution is prepared from formaldehyde and urine; the process is simple, flexible, and convenient. There is no need to purchase UF85 externally, which helps to overcome the problem of uneven mixing of formaldehyde and urine that can affect product quality. Four-IDR process: ① The pressure and temperature in the synthesis system are high, the NH3/CO2 molar ratio is also high, and the conversion rate of CO2 exceeds 70% ； ②There are 2 stripping towers. The first stripping tower uses ammonia as the stripping agent; some of the ammonium that has not been converted into urea is decomposed and returned to the synthesis tower in gaseous form. The second stripping tower uses CO2 as the stripping agent, which facilitates the evaporation of most of the excess ammonia ； ③The high-pressure ammonium methoxide condensers are horizontal in design, and they offer the advantage of no stress-corrosion cracking between the tubes and the tube sections. There are two such condensers; the pressure of the by-product steam is relatively high, which allows for an increase in the heat transfer temperature difference across various pressurization devices. This, in turn, reduces the heat transfer area required for the heating devices, thus saving on investment costs ； ④To achieve corrosion protection for the equipment, a small amount of liquid passivator is added to the pipeline, which effectively solves the issue of equipment corrosion. The five-MEC thermal cycling process ① utilizes a specially designed \"isothermal synthesis tower\", which is equipped with a feed coil that runs through the tower and has an open interior ； ②Starting from the thermal balance of the entire system, 40% of the total CO2 is directly added to the medium-pressure absorption system, where it exchanges heat indirectly with the urea solution; this causes the ammonium carbamate contained in the solution to decompose, and the urea solution is concentrated to 88% ； ③The treatment of the condensate is carried out using a single hydrolysis stripping tower; the operating pressure of this tower is 0.9 MPa, and the lowest operating temperature is 180°C℃ ； ④The low content of biuret in urea products improves the quality of urea ； ⑤The diameter of the granulation tower is reduced and its height is lowered; air is blown in from the bottom of the tower and drawn out from the center of the top. The urea granulation nozzles are installed between the point where air is drawn out and the tower walls. This \"counterflow design\" increases the cooling efficiency inside the granulation tower by more than 2 times ； ⑥The equipment cost is low, and due to the high CO2 conversion rate, the investment in the corresponding synthesis tower equipment and circulation system equipment is reduced.