Status of the Luxi DN2600 ammonia synthesis tower

On February 8, 2012, the successful first-commissioning of LuXi Chemical Group Co., Ltd.’s large-scale low-pressure ammonia synthesis plant with an annual capacity of 360,000 tons caused quite a stir in China’s nitrogen fertilizer industry. Many nitrogen fertilizer companies are highly interested in issues such as the operation status of this facility, its production technical parameters, and whether the domestic technology for ammonia synthesis can compete with advanced foreign technologies. With these questions in mind, a reporter recently visited Luxi Chemical Group and interviewed the responsible persons from the group’s technology center and ammonia synthesis facility. 　　Here, the reporter learned that the 360,000 tons per year ammonia synthesis plant also faced difficulties during its system commissioning process. Since all four units – air separation, gasification, purification, and ammonia synthesis – utilize entirely domestic proprietary technology, integrating them into such a large-scale facility is also the first time of its kind in China. Although there were some issues related to running in and tuning during the testing phase, thanks to the efforts of all parties, these problems were resolved quite quickly within just one month. In the ammonia synthesis unit, no other abnormalities occurred, aside from some effort required to connect the tower and the waste boiler during installation. Throughout the entire commissioning and running-in period, the ammonia synthesis circuit was the only part that encountered no problems, and its operation has been smooth over the past three months. 　　The reporter observed from the production report dated November 4, 2011, that the volume of fresh gas at that time was 90,991 standard cubic meters per hour (after liquid nitrogen washing). The pressure in the ammonia synthesis system was 11.7 megapascals, the system pressure difference was 0.58 megapascals, and the pressure difference within the synthesis tower was 0.16 megapascals. The inlet/heat spot temperatures of the catalyst bed were 363.9°C/469.8°C, 396.6°C/459.8°C, and 391.5°C/433.5°C respectively, while the maximum temperature differences across the same plane/along the cylinder surface of the bed were 9.1°C/5.6°C. The circulation rate of the synthesis system is 355,000 standard cubic meters per hour, the ammonia purity is 15.16%, and the liquid ammonia production rate is 34.5 tons per hour; these figures indicate that the plant is operating well. 　　At present, the ammonia synthesis system operates stably at 80% load, limited by the gas supply from the preceding process steps. Based on the aforementioned production data and load conditions, when the ammonia synthesis unit achieves a production capacity of 1,200 tons per day, its system pressure is ≤14.2 MPa, the system pressure difference is 0.90 MPa, the pressure difference in the synthesis tower is 0.25 MPa, and the pure ammonia content is ≥17.5%; meanwhile, the output of by-product medium-pressure steam exceeds 1.15 tons per ton of ammonia produced. 　　How should we view these indicators? A relevant person from the Technology Center of Luxi Chemical Group made a comparison: Both Topsφe S-300 and GC-R023 feature three radial beds plus two interlayer heat exchangers, while Casale 300B has three axial radial beds plus two interlayer heat exchangers. The pressures in the ammonia synthesis circuits of Topsφe S-300 and Casale 300B are 14.50 MPa and 14.43 MPa respectively; the pressure drop across the synthesis tower is 0.30 MPa and 0.25 MPa, while the circuit pressure drop is 1.0 and 0.9. The net ammonia content is 17.68% and 17.82% respectively. In comparison, the technical level of GC-R023 has reached that of advanced foreign ammonia synthesis tower technologies. 　　In the 1950s, the capacity of ammonia synthesis plants abroad was 200 tons per day; it increased to 1,000 tons per day in the 1960s, and has now reached 2,050 tons per day. The design pressure for these plants is usually 15 megapascals, and the raw materials used are mostly natural gas or naphtha, resulting in relatively low overall energy consumption for ammonia synthesis. The comprehensive energy consumption for ammonia synthesis using coal as a raw material is relatively high, and there are fewer such facilities. The more than 60 ammonia synthesis units introduced in our country also operate at a pressure of around 15 MPa, mainly using gas-phase processes, and have all functioned quite successfully. Small and medium-sized nitrogen fertilizer plants developed in China generally use coal as raw material, with a design pressure of 31.4 MPa. In recent years, their production capacity has been increased to 250,000 tons per year, and through technical improvements, the design pressure has been reduced from 31.4 MPa to 26–22 MPa ； Its comprehensive energy consumption per ton of ammonia is 45–48.5 GJ.

The DN2600 ammonia synthesis system was designed by Nanjing Guochang Company, and it is operating very well; the current maximum production rate is around 45 t/h (with a design capacity of 50 t/d). The system pressure is 12.2 MPa, and the resistance is 0.6 MPa.

It’s all exciting good news I hear; I really didn’t expect things to be going so well! It’s a breakthrough; this year it’s much cheaper compared to imported devices :victory:

If foreigners can do it, then Chinese people can do it as well, and they will even do it better. Bless Luci Chemicals!

I hope China will invest more funds in technological research and development to improve basic research even further

A blessing for the ammonia synthesis industry! Our original DN2400 model was also able to start up successfully on the first attempt

Generally speaking, the ammonia synthesis industry is a relatively traditional one; starting up the production process is simple. For large-scale facilities, the time required is mainly for the gas generation furnaces and air separation units; once those parts are operational properly, the rest is straightforward and there are no issues! :victory:

The DN2400 ammonia synthesis towers are now quite common, and there are several different pressure grades available. I’m not sure what pressure grade yours is – how is its operation, Ah Xianzi? Could you share some details for comparison?

What model of internal components does Guochang use? It’s clear without a doubt that it is a pioneer in domestic production. A successful drive is the result of a team’s effort – let’s do it! !

Sorry, we are still under construction; isobaric alcohol-alkane-ammonia synthesis at 26 MPa is being used. :$