Large-particle urea granule production – a comparison between Heidelu technology and Dongyang technology

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⑴Hydro’s fluidized bed granulation process a. Development overview and plant construction achievements This process was developed in 1974 by Stamicarbon, the patent holder for urea in the Netherlands; the scale of the experimental unit was 10 t/d. Pilot production was initiated in 1975, with a capacity of 150 t/d, and the product particle size ranged from φ2.1 to 2.9 mm. Subsequently, an industrial production plant with a capacity of 800 t/d was built in Sluiskil, the Netherlands, in 1978, producing products with particle sizes ranging from φ2.1 to 7 mm. To date, 25 large-scale urea production units have been built, with a maximum capacity of 3,000 t/d; the total annual production capacity exceeds 12.5 million tons. The particle size of the product ranges from φ2 to 8 mm, and as many as 15 of these units have a capacity of over 1,500 t/d. In addition, there are over 10 sets of equipment using this process for the production of other compound fertilizers and phosphatic ammonium fertilizers. In 1996, Hainan Fudao Chemical Co., Ltd. introduced the company’s fluidized bed granulation technology to produce large-grained urea with a particle size of 2.0–4 mm, at a capacity of 1,765 t/d; it is currently operating normally. In May 1998, Jiangsu Jinling Petrochemical Company used this technology to renovate a 2,000 t/d large-particle urea granulation unit, which is now operating normally. From September to November 1998, Hubei Yihua Group and Shandong Pingdu Fertilizer Factory used this technology to renovate and build 600 t/d large-grain urea granulation units, and both units are now in operation. b. Process technology features ● The process is mature and reliable, with a long history of industrial application and extensive experience. ●Urine with a concentration of 95–96% is used as the raw material, and urine processing requires only evaporation and concentration. ●By eliminating the two-stage evaporation concentration system, steam consumption is reduced. The amount of condensate in the corresponding process also decreases, and the hydrolysis and desorption loads are reduced as well. ●The granulator utilizes a combination of air atomization and fluidization, resulting in high granulation efficiency, large production capacity, good quality of the finished products, large particle size, and high strength. ●The fluidized bed granulation process is simple to operate and has a short startup time; products can generally be obtained within 1 hour after feeding the materials. The granulation unit is highly flexible in operation; it can handle load variations of 30–105%, offering great production flexibility and high adaptability. ●Compared with other mechanical granulation devices, it has a low granulation return ratio (0.5:1), thereby enhancing the equipment’s capacity and reducing energy consumption during the granulation process. ●By using additives and atomized fluidization granulation technology, the amount of dust generated in the fluidized bed is reduced. Moreover, the dust-containing exhaust gas is treated through wet scrubbing, which offers high absorption efficiency; as a result, the urea dust content in the exhaust gas released is less than 30 mg/Nm3. This not only reduces losses but also meets environmental protection requirements. ●The fluidized bed granulation process equipment has high operational reliability; the granulator, dust washer, and other units can operate for extended periods since they have no wearing parts. In rotating equipment such as fans, the medium is air, resulting in no wear or corrosion; conveyors, vibrating screens, crushers, and similar devices also operate under favorable conditions, offering high reliability. ●A new batch preparation system for the additive UF (Urea Formaldehyde) has been installed. By replacing formaldehyde with the additive UF in the urea solution, it is possible to overcome issues such as uneven mixing of formaldehyde and urine, which can affect product quality. ⑵Toyo Engineering Company’s jet fluidized bed granulation process: a. Development overview and plant construction achievements. The initial stage of research and development for this process was based on fluidized bed granulation technology, with a patent being filed in 1979. The scale of the test plant was 50 t/d, and it was later upgraded to 200 t/d. In 1983, the first industrial production facility was built at Kapuni Petrochemicals in New Zealand, with a production capacity of 470 t/d; the raw material used was molten urea with a concentration of 99.7%. To date, 5 units have been built worldwide, 3 of which utilize the improved jet fluidized bed granulation process. The largest of these units has a capacity of 1200 t/d and was put into operation in Piestritz, Germany, in 1996; this plant has since been expanded to an annual capacity of 2100 tons. In October 1997, the expansion project of Ningxia Chemical Plant’s facility for producing 1,740 tons per day of large-grain urea adopted the TEC process technology; for the first time, molten urea with a concentration of 95% was used as raw material. This facility came online at the end of September 1999. In May 1999, Sichuan Lutianhua (Group) Co., Ltd. adopted this technology in the renovation and expansion of a 2,000 t/d large-grain urea granulation unit in its second urea production workshop, and the unit is now in operation. b. Characteristics of the process technology ● The process flow and equipment structure are relatively simple. The nozzles used in the granulator are of the conventional pressure type; they have a simple structure and offer high capacity per unit. The granulator is divided into two parts: fluidized granulation and cooling. The dust washing tower is directly connected to the top of the granulator, simplifying the process and reducing the number of devices needed. ●The granulation time is short and the efficiency is high. The return particles in the fluidized bed are successively coated with liquid droplets in series-connected chambers, thereby growing larger; moreover, the fluidized bed layer is thin, which results in a short granulation time and high efficiency, as well as greater compressive strength of the final product. ●The production operation is flexible and convenient; during normal production, the return material ratio can be adjusted to obtain qualified products. The production control system is reliable, and it is simple to adjust the nozzles when the load changes. ●The bed height of the fluidized bed in the granulator is low; within the 50–100% load range, the bed height is 400–600 mm. The fluidized bed presents low resistance, requiring a low fan head pressure and thus saving electricity. ●Using 95% of the urine as raw material can simplify the urine processing procedures and save energy consumed for urine evaporation. However, in the plants built using this process, the urine concentration is usually over 98%; only in the large-grain urea production unit of the renovation project at Ningxia Chemical Plant was urine with a concentration of 95% used as a raw material. ●The dust recovery system employs centralized dust collection along with efficient wet scrubbing and absorption, resulting in a low urea dust content in the exhaust gases, below 30 mg/Nm3. ●In this process, an additive MMU preparation system is employed; the MMU solution (Mono Methylol Urea) is made from formaldehyde and urine, which offers greater flexibility and convenience. Compared to adding formaldehyde directly as an additive to urea solutions, this approach helps to overcome issues such as uneven mixing of formaldehyde and urine, which can affect product quality. ⑶Preliminary comparison and selection
a. Process development and performance comparison
Item: Hydrotreat process; Toyoe Engineering Corporation’s process
Patent filing for the process: 1975; 1979
Industrial production start: 1978; 1983
Number of plants built worldwide: 25; 6
Plants built in China: 6; 2
Maximum capacity of the plants: 3000 t/d; 2100 t/d

b. Preliminary comparison of process technologies
Item: Hydrotreat process; Toyoe Engineering Corporation’s process
Process maturity and advancement: Mature, advanced, reliable; good performance and extensive experience. Advanced and mature, but with fewer plants built.
Process flow: Relatively complex, involving staged cyclic absorption for dust washing. It’s simpler: centralized washing circulation is used at the outlet of the granulator for absorption. Number of process equipment – Total: 58 units. Granulators: 1 unit; Washers: 2 units; Fans and pumps: 18 units; Heat exchangers: 10 units; Storage tanks: 7 units; Powder processing equipment: 16 units; Others: 4 units. Total: 55 units. Granulators: 1 unit; Washers: 1 unit; Fans and pumps: 18 units; Heat exchangers: 10 units; Storage tanks: 4 units; Powder processing equipment: 16 units; Others: 5 units.

Requirements for the concentration of the urine raw material: >95%(wt); >95%(wt). Additives: Formalin solution, self-made UF solution, formalin solution, self-made MMU solution. The product contains 0.45%(wt) of formalin; 0.45%(wt). Feed ratio: 0.5:1; 0.5:1. Product quality: Particle size and strength meet the requirements; particle size and strength meet the requirements. Energy consumption (steam + water + electricity): 0.552×106 KJ; 0.535×106 KJ. Concentration of the returned urine: 44.8%(wt), with the amount of urea returned accounting for 4.5% of the product’s total weight; 41.6%(wt), with the amount of urea returned accounting for 4.4% of the product’s total weight. Amount of exhaust gas emitted and urea content therein: 6157 Nm3/t•ur, ≤30 mg/Nm3; 6303 Nm3/t•ur, ≤30 mg/Nm3.

c. Selection of granulation process: As mentioned above, both granulation processes belong to advanced fluidized bed granulation technologies. Hydril uses atomization + fluidized bed granulation, while Toyo Engineering uses spraying + fluidized bed granulation. Each method has its own characteristics and different granulation mechanisms, yet satisfactory results are achieved in both cases. In comparison, Hydrus has a large number of plants and extensive experience, especially in terms of building facilities that use urine with a 95% concentration as raw material ； The granulation process of Toyo Engineering Company has low power consumption, but high capital investment for plant construction.