Multiple large-scale units ensure stable operation and full production capacity; domestic technology for low-pressure ammonia synthesis leads the world”

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Multiple large-scale units ensure stable operation and full production capacity; China leads the world in low-pressure ammonia synthesis technology. Author/Source: China Chemical Industry News Date: 2016-08-15 Clicks: 28 China’s ammonia synthesis technology is evolving toward greater localization, larger scale, lower pressure, cleaner processes, and higher efficiency, with low-pressure and energy-efficient methods having become the mainstream in this field. Gu Zongqin, president of the China Nitrogen Fertilizer Industry Association, recently noted that new advances have been made in large-scale low-pressure ammonia synthesis plants. The domestically designed demonstration plants with a capacity of 600,000 tons per year are operating successfully at Cangzhou Zhengyuan and Shandong Ruixing, indicating that China’s fertilizer production technology is beginning to reach international advanced levels. 　 Zhang Rong, secretary-general of the China Nitrogen Fertilizer Industry Association, said that since the introduction of large-scale foreign ammonia synthesis technologies and equipment, the low-pressure ammonia synthesis technologies and equipment have been dominated by foreign countries. This situation did not change until the beginning of this century, when, by making use of foreign technologies and equipment to some extent, domestic efforts were made to develop domestic production systems for synthetic ammonia with capacities of 180,000 to 300,000 tons per year. According to Yu Zifang, a well-known expert in the domestic nitrogen fertilizer industry, the development of synthetic ammonia in China has progressed from low pressure to medium pressure and then to high pressure. The first version was developed at 12.5 Mpa, followed by 15 Mpa and 20 Mpa; the Fourth Research Institute eventually achieved 32 Mpa. Building on the knowledge of advanced ammonia synthesis technologies from abroad, China has reduced the pressure used in ammonia synthesis from 32 Mpa at high pressures to 25 Mpa. Many domestic research institutions have developed innovative low-pressure ammonia synthesis processes; some large-scale facilities operate at pressures of 22 Mpa or 20 Mpa or even lower, with some reaching pressures below 15 Mpa. Among the 15Mpa systems currently in use in the industry are Shandong Hongda’s 150,000 tons per year ammonia synthesis system, Xinjiang Hongji Coking’s 120,000 tons per year ammonia synthesis system, Sichuan Jinxiang Chemical’s 240,000 tons per year ammonia synthesis system, and Anhui Zhongneng (Linquan)’s 300,000 tons per year ammonia synthesis system; there is a clear trend toward lower pressure systems. Building on the 15Mpa level, Hualu Hengsheng and Nanjing Guochang jointly developed a more energy-efficient low-pressure ammonia synthesis technology at 11.5Mpa, and a 300,000-ton/year production facility was built by Hualu Hengsheng. The device passed the on-site assessment organized by the China Petroleum and Chemical Industry Federation, with all economic and technical indicators meeting or exceeding the design specifications. The average daily production is over 1,000 tons; at a low pressure of 11.4 MPa, an ammonia yield of 16.53% is achieved. For each ton of ammonia produced, 0.97 tons of superheated steam at 4.0 MPa are generated. The overall energy consumption is low, with the combined energy consumption for water, electricity, and steam per ton of ammonia being 73.04 MJ. According to the technical director of Nanjing Guochang Company, compared with the original low-pressure synthesis process, this system features a three-stage fully radial synthesis tower structure. It incorporates various new technologies such as a fish-scale tube radial distributor, a large reactor with a small-diameter central heat exchanger setup, as well as automatic catalyst removal, all of which help to achieve low resistance in the ammonia synthesis tower, high efficiency, pre-assembled equipment for easier maintenance, high reliability of the internal components, and automatic removal of the catalyst. Zhang Rong explained that domestically developed low-pressure synthesis technologies, which feature a more scientific structure, lower pressure levels, and better energy efficiency, have been successively applied to ammonia synthesis plants with capacities of 300,000 to 450,000 tons per year. Low-pressure synthesis systems with capacities of over 600,000 tons per year have also been put into industrial use. It is reported that the industrialization project of the 600,000 tons per year low-pressure ammonia synthesis process technology software package, independently developed by Nanjing Jutuo Chemical Technology Co., Ltd., has been successfully put into operation at Runyin Biochemical Co., Ltd. of Shandong Ruixing Group, opening up a new path for the scaling up and localization of ammonia synthesis processes in China. This is the first ultra-large-scale ammonia synthesis project in the country to utilize fully proprietary technology. The project was engineered based on a process that virtually eliminates the use of inert gases, with an ammonia production capacity of 900,000 tons per year, resulting in a daily ammonia output of over 2,400 tons. Among them, key equipment such as the DN3200 ammonia synthesis reactor, lotus-shaped direct-connected waste heat recovery unit, and modular ammonia cooler, which were independently developed, designed, and manufactured by the company, operated smoothly during the initial commissioning process; their performance met advanced technical standards, even exceeding the design specifications. The operation of this device marks a significant breakthrough in China’s technology for scaling up key equipment in ammonia synthesis systems.