Renovation of ammonia synthesis plants: an essential path to energy savings and reduced consumption

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Renovation of ammonia synthesis plants: an essential path to energy savings and reduced consumption. China is the world’s largest producer and consumer of fertilizers, with an annual ammonia synthesis capacity of 42.22 million tons. However, synthetic ammonia has always been a major energy consumer in the chemical industry. 　　 　　By the end of 2004, China’s annual production capacity for synthetic ammonia had reached 42.22 million tons, yet the energy consumption per ton of ammonia was 600 to 700 kilograms of standard coal higher than the international advanced level. Among the five high-energy-consuming industries in China’s chemical sector, synthetic ammonia accounts for 40% of the total energy consumption, with its energy intensity being 31.2% higher than that of internationally advanced levels; therefore, there is great potential for energy savings in this industry. However, the main factors restricting energy savings and consumption reduction in China’s synthetic ammonia industry remain raw materials, process technology, and funding. 　　The transformation of ammonia synthesis is an inevitable trend. In 2005, the **Energy Conservation Medium- and Long-Term Plan** issued by the National Development and Reform Commission designated ammonia synthesis as a key area and project for energy conservation and consumption reduction. In accordance with the planning requirements, over the next 15 years, **on the one hand, efforts will be accelerated to carry out industrial transformations that involve using clean coal or natural gas as alternatives to petroleum in the production of ammonia, in order to conserve these valuable petroleum resources ； On the other hand, significant efforts will be made to develop and promote energy-saving and consumption-reducing technologies, in order to reduce the energy consumption per ton of ammonia produced in large-scale facilities from the current 1,372 kilograms of standard coal per ton to 1,000 kilograms of standard coal per ton. By 2010, the energy-saving target for the synthetic ammonia industry was to raise the energy utilization efficiency from the current 42% to 45.5%, achieving energy savings of 5.7 to 5.85 million tons of standard coal, and reducing carbon dioxide emissions by 13.77 to 14.13 million tons. Therefore, accelerating the energy-saving upgrades of ammonia synthesis plants has become an essential path for many large fertilizer manufacturers to reduce energy consumption and waste. 　　In the 1970s, China introduced a total of 9 large-scale ammonia synthesis plants that used natural gas (or associated gas) as raw material. In the 1980s, another 6 large-scale ammonia synthesis plants with low energy consumption were brought online. Several years after these plants began operation, they underwent numerous modifications to their raw material supply routes as well as energy-saving upgrades, including changes from using oil to coal, from coal to oil, from oil to gas, and from anthracite to pulverized coal. Dozens of major renovations were carried out in areas such as the hydrocarbon steam conversion section, the shift reaction section, the decarburization section, and the control systems. Among these improvements, technical upgrades related to the gas generation furnaces, furnace operation monitoring and system optimization, and desulfurization systems were always of particular importance. Furthermore, various factors such as the raw material supply chain for the equipment, resource availability, transportation, as well as the maturity of funding and technology, also contribute to the significant energy-saving potential of technological upgrades in ammonia synthesis. With the continuous rise in energy prices, it has become a trend to carry out second and third rounds of systematic or partial technical upgrades to the production facilities, building on the aforementioned modifications, with the aim of saving energy, increasing output, and altering the raw material supply routes. 　　Reform measures for ammonia synthesis at Hubei Fertilizer Plant As early as 2004, Hubei Fertilizer Branch took advantage of the period between coal-based production and the switch to oil-based production to launch a project aimed at using natural gas as a substitute for oil. Amid high oil prices, it seized the opportunity provided by the availability of natural gas via the Zhongwu pipeline to maintain uninterrupted production, and completed in a very short time the design of processes that used natural gas as a fuel source, as well as the necessary modifications to the equipment. In 2005, production using gas instead of oil was achieved, resulting in a significant reduction in the production costs of synthetic ammonia. Recently, the company invested another 15 million yuan to carry out energy-saving upgrades to the synthesis circuit, enabling the plant’s production capacity to reach 110%. This not only **reduced the energy consumption in ammonia synthesis, resulting in annual savings of 54,700 tons of high-pressure steam and 27,700 tons of medium-pressure steam**, but also increased the ammonia production capacity by 20%, aligning it with the production capacity of the coal-based oil and gas conversion facility. As a result of these upgrades, energy savings alone can reduce production costs by over 10 million yuan per year. 　　During the equipment renovation, all the equipment in the existing ammonia synthesis loop was retained, except for the vent ammonia cooler and the vent separator. During pipeline renovation, only minor modifications are required to the pipes in the existing circuits, with an effort to change their original positions and piping as little as possible. The existing refrigeration compressors and turbine systems are not modified, and all heat exchangers in the refrigeration system remain in use. The existing instruments in the ammonia synthesis loop remain largely unchanged, with cost-effectiveness, practicality, and reliable quality serving as the guiding principles for instrument selection. 　　Through energy-saving upgrades to the ammonia synthesis loop, the circulation volume of the syngas compressor is reduced, the compression power consumption per unit of production is lowered, and the consumption of high-pressure steam is decreased, enabling the existing high-pressure steam pipelines from the power station to the synthesis units to meet the production requirements. By shifting ammonia separation from before the tower to after the tower, the amount of cooling energy required for separation per unit of ammonia produced is reduced, thereby saving energy consumption in the ice makers. At the same time, following the energy-saving upgrades, commercial liquid ammonia was added; its specifications meet the first-class standards set by the national standard GB536-88, and it can generate benefits for the enterprise.