In the industrial gas sector, argon, a widely used rare gas, is primarily obtained through cryogenic separation of air. Whether or not a large-scale cryogenic air separation unit is equipped with an argon system not only directly affects the unit's initial investment and long-term energy consumption, but also has a crucial impact on optimizing the plant's product mix and improving overall profitability. Especially during the planning phase of a new plant, a comprehensive analysis of the argon market supply and demand in the region, investment costs, and energy consumption data is necessary to select the optimal configuration for the project and fully unleash the potential of the air separation unit.
Based on its properties and application scenarios, argon is present in the atmosphere at approximately 0.932%, making it the most abundant rare gas. Its chemical properties are stable, it is non-flammable, and it does not support combustion. It plays an important role in manufacturing, electronics, metal smelting, and other fields. For example, argon is often used as a shielding gas in the welding of aluminum, magnesium, copper, their alloys, and stainless steel, effectively preventing oxidation or nitridation of welded parts due to contact with air, thereby ensuring weld quality. For example, a planned 50,000 Nm³/h oxygen production air separation unit for a large-scale coal chemical project in a certain region will utilize a process involving ambient temperature molecular sieve adsorption purification, air pressurization, and internal compression of oxygen and nitrogen products. This process will be combined with a structured packing upper tower and a full distillation argon production process, with the air compressor driven by an electric motor. The full distillation argon production process, currently the mainstream argon production method, offers significant advantages such as simplicity, ease of operation, safe and stable operation, and high argon extraction efficiency. Specifically, an argon-rich fraction is extracted from the middle and lower portions of the upper tower and fed into an argon distillation system. The crude argon column initially separates oxygen and argon, producing crude argon with an oxygen content of less than 1.5×10⁻⁶. This crude argon is then fed into a refined argon column for further separation of argon and nitrogen, ultimately producing a high-purity argon product with an argon content of 99.999%. Research into the region's argon market reveals a total of nine air separation units (ASUs) with a capacity of 6,000 Nm³/h or larger, operating, under construction, or planned. Six of these units are operational and capable of producing argon, with a total designed capacity of 5,860 Nm³/h (equivalent to 84,000 t/a). However, due to factors such as the inactivity of some projects' argon systems or substandard production, actual argon production is approximately 63,000 t/a, making overall regional production capacity relatively limited.
In terms of cost and market price, the unit transportation cost of liquid argon is 0.8-1.0 yuan per tonne/km. Based on this calculation, the theoretical price difference for markets within 200 km is approximately 160 yuan per tonne. For distances up to 500 km, the price difference exceeds 400 yuan per tonne, lowering supply barriers between different markets and enabling cross-connection. The regional argon market price fluctuates between 800 and 1,900 yuan per ton throughout the year. Calculated based on an annual average price of 1,000 yuan per ton, this leaves room for profitability.
Analyzing the production cost structure of argon, for a 50,000-class air separation unit, argon, as a byproduct, primarily consumes separation work and liquefaction work, with the compression work fully amortized into the costs of the oxygen and nitrogen products. The theoretical minimum liquefaction work for argon is 0.2391 kW·h/Nm³ (actually calculated as 0.3 kW·h/Nm³). The calculated liquefaction work is 560 × 0.3=168 kW·h/ton. Separation work is calculated using a specific formula, where R is the universal gas constant, T is the ambient temperature, n_O₂, n_N₂, and n_Ar represent the amounts of oxygen, nitrogen, and argon, respectively, p_O₂, p_N₂, and p_Ar are the pressures of each component, and p is the total pressure. Calculations show that the theoretical minimum separation work for complete separation of 1 Nm³ of air is approximately 0.01744 kW·h/Nm³ (calculated at 0.02 kW·h/Nm³). Since 8% of the separation work is concentrated in argon, the separation work is calculated to be 248,000 × 0.02 × 8% × (560 ÷ 1500)=148 kW·h/t. Overall, the production cost of argon is approximately 316 kW·h/t, equivalent to 139 yuan/t. If covering customers within a 200km and 500km radius, after adding corresponding transportation costs, the total argon cost is approximately 299 yuan/ton and 539 yuan/ton, respectively, maintaining a significant cost advantage compared to the local argon market price. Furthermore, the region is only 100km from the industrial zone of the provincial capital. With the advancement of the local "Strengthening the Provincial Capital" development strategy, the manufacturing industry, especially the electronics and photovoltaic industries, will usher in development opportunities, and the demand for argon will continue to grow accordingly, providing a broad market prospect for argon sales.
Regarding the risks and energy efficiency of argon production, the current full distillation argon production process is mature and reliable, without increasing plant safety risks. Furthermore, the addition of an argon system can increase oxygen extraction efficiency and achieve significant energy savings. For example, a 50,000-class air separation unit (ASU) can extract approximately 1,500 Nm³/h of argon (assuming a 70% extraction rate). Comparing the different configuration options, the oxygen extraction rate without the argon system is 90.4%, with no energy savings, no associated investment, and no returns. The option with the efficiency booster increases the oxygen extraction rate to 97%, with approximately 5% energy savings. The investment costs 8-10 million yuan, with an annual energy saving of 8 million yuan and a payback period of one year, but there is no argon product output or associated revenue. The option with the argon system achieves an oxygen extraction rate of 96.4%, with approximately 2.5% energy savings, an investment of approximately 15 million yuan, an annual energy saving of 4 million yuan, an annual argon production of 21,000 tons, an annual product benefit of 15 million yuan, and a payback period of one year. Furthermore, it can generate annual revenue of 15 million yuan during operation.
Further analysis of energy consumption data reveals that over 90% of the energy consumed by an air separation unit comes from the air compressor and booster. Taking the configuration of an argon system as an example, with a total compressor and booster power of 40,000 kW, assuming an annual operating time of 8,000 h and a budgeted electricity price of 0.44 yuan, the energy savings are calculated to be 40,000 × 8,000 × 0.44 × 2.5% ÷ 90%=3.91 million yuan. Regarding the benefits of liquid argon production, a single air separation unit produces 21,000 tons of liquid argon annually. Based on the local average annual price of argon of 1,000 yuan per ton, this generates over 15 million yuan in additional annual benefits. In terms of the payback period, if the argon system is configured but liquid argon product sales are not carried out, the investment cost can be recovered in approximately four years; if liquid argon product sales are carried out normally, the investment can be recovered in just one year. It is worth noting that if the air separation unit lacks an argon system and a booster tower, the oxygen extraction rate will be reduced, the air volume required to be handled by the air compressor will increase significantly, and the energy consumption of the air separation compressor unit will increase. Therefore, even without an argon system, conventional air separation unit designs typically require a booster tower to reduce compressor energy consumption.
In summary, deploying an argon system in large cryogenic air separation units is technically mature and reliable, poses no additional safety risks, and can improve oxygen extraction efficiency and reduce energy consumption. Economically, selling argon products in line with market demand can quickly recoup investment and significantly improve plant profitability. Furthermore, the argon system offers flexible adjustment capabilities, allowing the refined argon system to be switched in and out based on market fluctuations. The crude argon tower can then function as a booster tower, continuing to save energy and enabling dynamic adjustments to product production. For regions with a robust argon market, argon extraction equipment is recommended for large cryogenic air separation unit planning to optimize both economic benefits and energy efficiency.
