From Production Technology to Manufacturing Process: A Practical, Comprehensive Guide to the Upcoming Urea Futures

Most of China’s natural gas is concentrated in the northwest and southwest regions. During the first and fourth quarters each year, gas-based urea production facilities in these areas commonly experience widespread output reductions or shutdowns. Anticipated increases in natural gas prices—particularly sharp ones—cause a rapid decline in the competitiveness of gas-based urea production; ultimately, such facilities exit the urea market when cost increases outpace urea price increases. Coal-based urea producers face polarization: first, the proportion of urea produced from bituminous coal rises; second, numerous small-scale urea facilities with capacities below “1830” (i.e., 180,000 tons/year ammonia + 300,000 tons/year urea) will eventually withdraw from the market, while urea production using coke-oven gas for ammonia synthesis grows in significance. Globally, over 50 methods exist for producing urea, yet only two have achieved industrial application: the calcium cyanamide (nitrolime) process and the direct synthesis process from ammonia (NH₃) and carbon dioxide (CO₂). Of these, the NH₃–CO₂ direct synthesis method is now widely adopted due to the ready availability of its raw materials. Currently, China operates more than 200 urea production units, categorized by scale as large (≥480,000 tons/year), medium (≥110,000 tons/year), and small (≥40,000 tons/year). Medium- and small-scale units predominantly employ domestically developed aqueous solution full-recycle technology, whereas large-scale units mostly adopt foreign-introduced process technologies. Among domestic large-scale urea plants, CO₂-stripping and NH₃-stripping processes are currently designed and implemented; their ammonia consumption approaches theoretical levels, and their utility consumption (water, electricity, steam) is lower than that of traditional designs—resulting in reduced capital investment. Contemporary urea production—regardless of the specific process—comprises six fundamental process units: raw material supply; high-pressure urea synthesis; separation of urea-containing solution; recovery of unreacted NH₃ and CO₂; concentration of urea solution; and granulation, product conveying, and process condensate treatment. The basic flow is illustrated in the accompanying diagram. Compressed CO₂ and NH₃ feedstocks enter the high-pressure synthesis loop, where they react to form urea; CO₂ conversion rates range between 50% and 75%—this stage is termed the synthesis section. The separation and unreacted-material recovery sections jointly extract unconverted NH₃ and CO₂ from the solution and recycle them back to synthesis; thus, these two sections together constitute the recycle section. Finally, 70–75% urea solution is concentrated and processed into solid product via vacuum evaporation and granulation equipment—termed the final processing section. Although the fundamental process steps are similar across urea plants, differences persist in specific flows, operating conditions, and equipment configurations. To date, the vast majority of urea plants worldwide have been engineered and designed by a handful of major engineering firms, resulting in several established, representative process technologies—including Stamicarbon (Netherlands)’s aqueous solution full-recycle CO₂ stripping process; Snamprogetti (Italy)’s NH₃ stripping process; Montedison Group’s isobaric double-recycle (IDR) process; Mitsui Toatsu–Tyo Engineering (Japan)’s improved “C” and “D” full-recycle processes and ACES process; and UTI (U.S. Urea Technologies Inc.)’s thermal recycle (HR) urea process. However, regardless of the chosen process, the consumption of primary raw materials—NH₃ and CO₂—is essentially identical across all routes. The relative advancement of a given process is reflected primarily in its utility consumption (water, electricity, steam).

Urea: Part II — 'The Discovery of Urea and Its Industrialization'

Chapter Two: The Industrialization of Urea Section One: Historical Development of the Urea Industry At the beginning of the 20th century, large-scale industrial ammonia synthesis emerged, providing inexpensive raw materials for urea synthesis from NH₃ and CO₂. Researchers worldwide conducted comprehensive studies on reaction equilibrium conversion, kinetics, and key industrialization issues—including recovery of unreacted materials, commercial product forms, and corrosion-resistant materials—laying the foundation for industrialization and leading to the emergence of various urea production plants. Early industrial urea production faced two major obstacles: (1) Recovery and reuse of unreacted feedstocks. Because urea synthesis is equilibrium-limited, unreacted NH₃ and CO₂ remain in the reaction mixture. Early urea plants converted surplus NH₃ into other products: for every ton of urea produced, approximately seven tons of ammonium sulfate—or an equivalent quantity of other by-products—were generated. This necessitated large-scale auxiliary workshops for by-product processing, severely constraining the large-scale expansion of urea production. (2) Severe corrosion of equipment materials by process media during urea production. From the 1940s to the 1950s, urea process improvements focused primarily on overcoming these two challenges. First, efforts centered on maximizing recovery of unreacted NH₃ and CO₂, yielding successive innovations including the semi-recycle, high-efficiency semi-recycle, and full-recycle processes. Second, research addressed corrosion resistance of equipment materials. DSM (Dutch State Mines)’s subsidiary Stamicarbon pioneered the use of oxygen addition to prevent corrosion of austenitic stainless steel—enabling large-scale urea production. China’s urea industry began in 1958, when the Nanjing Yongli Ning Chemical Plant constructed and commissioned a pilot-scale semi-recycle urea workshop with a capacity of 10 tons per day. Concurrently, the Shanghai Research Institute of Chemical Industry conducted laboratory-level fundamental research, generating essential data required for industrial-scale expansion. Subsequently, the Shanghai Wujiang Chemical Plant built and operated China’s first industrial-scale semi-recycle urea plant, with an annual capacity of 15,000 tons. In 1965, the Shanghai Research Institute of Chemical Industry completed a pilot test of the ammonium carbamate aqueous solution full-recycle process. In 1967, China successfully commissioned its first domestically designed and manufactured full-recycle urea plant—rated at 110,000 tons/year—at the Shijiazhuang Fertilizer Plant. Thereafter, dozens of medium-scale urea plants were successively built and commissioned. In 1975, China completed design work for a 240,000-ton/year CO₂ stripping urea plant, which was subsequently constructed and commissioned at the Shanghai Wujiang Chemical Plant. Since the 1970s, China has imported over 20 large-scale urea plants—each rated at 500,000 tons/year—from abroad. Today, China possesses full capability to independently design and construct urea plants of all scales. Section Two: Industrialization of Urea Production and Evolution of Process Flows The world’s first industrial urea plant using NH₃ and CO₂ as feedstocks was built and commissioned in 1922 by I.G. Farben (Germany) at Oppau, employing a hot mixed-gas compression recycle method. Although this process suffered many deficiencies in both technology and equipment, it offered clear advantages over the then-existing calcium cyanamide hydrolysis route. In 1932, DuPont (USA) produced urea ammonium water via direct synthesis. Solid urea production began in 1935, with unreacted materials returned to the synthesis reactor as aqueous ammonium carbamate solution—a prototype of today’s aqueous solution full-recycle process. During the 1930s, Germany, the USA, the UK, and Japan successively constructed the first generation of large-scale, continuous non-recycle (i.e., once-through) urea plants. In the 1940s, semi-recycle and high-efficiency semi-recycle processes emerged: the former recovered excess unreacted NH₃, while the latter additionally recovered part of the ammonium carbamate.

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