How to Achieve More Economical Oxygen Enrichment – Process Exploration of Pressure Swing Adsorption Oxygen Generation in Blast Furnaces

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An article reprinted from the China Metallurgical News is shared here for academic discussion. The content is as follows: How to Achieve More Economical Oxygen Enrichment – A Discussion on the Process of Using Pressure Swing Adsorption for Oxygen Production in Blast Furnaces, by Wang Hongqiang. Traditional blast furnace oxygen enrichment techniques rely on high-pressure oxygen produced through cryogenic oxygen production methods; however, due to the high investment required for cryogenic oxygen production, the oxygen used for blast furnace enrichment is usually high-pressure gas surplus from steelmaking processes. This means that the common method for oxygen enrichment in blast furnaces is post-machine oxygen enrichment. With the advancement of smelting technology, oxygen-enriched ironmaking has become an effective method for enhancing blast furnace operations. Obtaining stable and inexpensive oxygen is therefore the key to oxygen enrichment in blast furnaces. Advanced pressure swing adsorption oxygen production technology generates inexpensive oxygen, making it possible to significantly increase the oxygen enrichment level in blast furnaces. The application of the pre-machine oxygen-enrichment process further extends the use of pressure swing adsorption oxygen generation in blast furnaces. Principle and advantages of pressure swing adsorption for oxygen production. The pressure swing adsorption method, or PSA method, involves adsorption at higher pressures to achieve gas separation, and the regeneration of the adsorbent at lower pressures. This method relies on the selective adsorption of oxygen and nitrogen components in air by molecular sieves to separate air and obtain oxygen. When air is compressed and passes through an adsorption tower equipped with molecular sieve, nitrogen molecules are preferentially adsorbed, while oxygen molecules remain in the gas phase as oxygen. When adsorption reaches equilibrium, reduced pressure or vacuum is used to drive away the nitrogen molecules adsorbed on the surface of the molecular sieve, thereby restoring its adsorption capacity. To provide oxygen continuously, the device is typically equipped with two or more adsorption towers; one tower is used for oxygen production while the other is used for desorption, thereby achieving continuous oxygen generation. The PSA method can produce oxygen with a purity of 80% to 95%. The power consumption for oxygen production is generally between 0.32 kWh/m3 and 0.37 kWh/m3. The adsorption pressure is higher than atmospheric pressure, typically ranging from 30 kPa to 100 kPa. The process is simple, it operates at room temperature, features a high level of automation, allowing for unattended operation, and boasts excellent safety characteristics. In the vacuum desorption process, the operating pressure of the equipment is low, and containers and similar items are not subject to pressure vessel regulations. The pressure swing adsorption process is classified into single-tower, two-tower, three-tower, and five-tower configurations based on the number of adsorbers. The pressure swing adsorption process using a five-tower configuration is the most common; it involves 5 adsorption beds, 4 blowers, and 2 vacuum pumps. During each cycle, 2 beds are used for adsorption and vacuuming, which solves the technical challenges associated with large-scale oxygen production. The pressure swing adsorption oxygen production process has the following advantages: First, it utilizes automatic pressurization technology based on the pressure difference in the ambient air, which reduces the air flow required by the blower, extends the service life of the equipment, and lowers the cost of oxygen production. Secondly, the equipment is simple; the main components, namely the Roots blower and vacuum pump, operate stably and reliably. The molecular sieve has a service life of over 10 years and requires no maintenance. Thirdly, the amount and purity of the oxygen produced can be adjusted according to actual usage requirements; the stable purity level can reach 93%, while the economical purity range is 80%–90% ； The oxygen production time is fast; generally, a purity of over 80% can be achieved within 30 minutes ； The specific power consumption is only 0.32 kWh/Nm3 to 0.37 kWh/Nm3. Fourth, the comparison between pressure swing adsorption oxygen production and cryogenic oxygen production shows the following advantages: lower investment, simpler process, less space required, fewer equipment units, and fewer moving parts ； High degree of automation, enabling virtually unmanned operation ； It can meet the requirements of the oxygen-enriched blast furnace blowing process. Comparison of the two oxygen supply methods: The oxygen pressure generated by pressure swing adsorption for oxygen production is generally between 30 kPa and 100 kPa. Currently, there are two methods for oxygen supply: The first method involves post-machine oxygen enrichment, where the low-pressure oxygen coming out of the adsorption tower is pressurized to 600 kPa using a piston-type oxygen compressor; thereafter, it is regulated in pressure through an oxygen pressure control valve, and then fed into the cold air duct at the outlet of the blast furnace fan (the cold air duct between the fan and the hot blast stove) to mix with air thereby achieving oxygen enrichment ； It is generally equipped with a pressure regulating valve assembly and corresponding safety systems to meet the requirements of the production process. This approach requires large investment; in particular, the cost of each oxygen compressor ranges from several million to over several hundred million yuan, and the electricity consumption increases by 0.1 kWh/Nm3 after the oxygen is pressurized. More importantly, the pressurization and delivery of high-pressure oxygen impose higher safety requirements on various aspects of the equipment; if these standards are not met during installation, explosion accidents can easily occur. The second method is pre-machine oxygen enrichment, which involves using low-pressure oxygen coming directly from the adsorption tower and feeding it into the air intake before the fan as a means of supplying oxygen. In this method, the oxygen delivery pressure ranges from 5 kPa to 10 kPa; the low pressure results in a slow flow rate, so it is necessary to increase the diameter of the oxygen supply pipeline to meet the required flow volume. At the same time, in order to ensure thorough mixing of the oxygen drawn in through the fan’s intake with the air, an oxygen distributor is added at the inlet to meet the process requirements and achieve oxygen enrichment. This method eliminates the need for an oxygen compressor, reducing both cost and electricity consumption. Since oxygen is transported at low pressure, both its storage and transportation are carried out in accordance with low-pressure standards, which reduces the manufacturing costs of the equipment. Moreover, the construction requirements are also lower; there is no need to install pressure-reduction or explosion-proof devices, thus saving on construction costs and enabling better assurance of the safety of oxygen-enriched ironmaking in blast furnaces. The author suggests giving priority to promoting this process. Application Examples and Precautions: On April 19, 2011, Henan Wugang Sino-Canadian Steel Co., Ltd. entered into a technical cooperation agreement with Beijing Peking Pioneer Technology Co., Ltd. Construction of the 10,600 Nm3/h pressure swing adsorption oxygen production project began on August 10, and it was completed on May 9, 2012. This project is an independent oxygen production plant built by Sino-Canadian Company specifically for oxygen enrichment in 3 blast furnaces; it uses pre-machine oxygen enrichment to supply oxygen to the blast furnaces, and was put into operation successfully from the first attempt. The blast furnace achieved an oxygen enrichment rate of 5%, resulting in a 20% increase in production; the coal consumption increased by 35 kilograms per ton of iron, yielding good economic benefits. To date, through more than 2 years of operational experience, the equipment used by Zhongjia Company has proven to be stable in operation, safe and reliable; the purity and flow rate of oxygen exceed the design specifications, and noise levels are well controlled, with no complaints from residents living 40 meters away from the facility. The cost of producing oxygen is calculated as follows: the total amount of oxygen produced is 4,079,961 cubic meters per month, while the total electricity consumption is 1,372,601 kilowatt-hours. The electricity cost is 0.33643 kilowatt-hours per cubic meter multiplied by 0.65 yuan per kilowatt-hour, which equals 0.218679 yuan per cubic meter. The cost of salt used is 0.0012 yuan per cubic meter, compressed air costs 0.002167 yuan per cubic meter, labor costs 0.00598 yuan per cubic meter. Depreciation is calculated at 0.022 yuan per cubic meter, interest at 0.028 yuan per cubic meter, oil costs 0.0002253 yuan per cubic meter, and the cost of other materials is 0.0000751 yuan per cubic meter. The total cost, including taxes, is 0.2783269 yuan per cubic meter. Since this process uses rotary vane blowers, special attention must be paid to addressing noise and equipment vibration during the design and construction of the factory building. To reduce noise, various measures should be taken. These include installing silencers on the intake and exhaust fans in the factory building, using high-efficiency soundproofing materials inside the building, replacing the exhaust vents of vacuum pumps with silencing towers that provide effective noise reduction, and installing high-efficiency silencers at all vent points. Such measures help to significantly reduce noise generation, enabling the project to operate smoothly with noise levels that meet **the required standards in residential areas. To address the issue of excessive fan vibration, elastic flexible connections were installed at the fan’s inlet and outlet, and shock-absorbing pipes were designed for the outlet pipeline. However, since the heat exchanger at the fan outlet was selected in a square configuration, practical tests have shown that this design cannot effectively absorb vibrations, resulting in the shell of the heat exchanger frequently cracking. Through technical exchanges, it was found that circular-shaped heat exchangers can absorb vibrations better without being affected themselves, thereby fundamentally solving the vibration problem. Currently, due to cost pressures, the overall grade of ore fed into blast furnaces has generally decreased, while slag production has increased; therefore, the use of a high oxygen concentration has become the choice for major steel plants. However, relying solely on the excess oxygen from steelmaking is limited by quantity ； Oxygen produced using the cryogenic oxygen production process in large quantities is inevitably constrained by the cost of oxygen (it is not economical to have an oxygen concentration higher than 4%). The application of the cost-effective oxygen enrichment process based on pressure swing adsorption enables a high degree of oxygen enrichment in blast furnaces; it is now time to establish oxygen production plants specifically for these furnaces, and this pressure swing adsorption-based oxygen production method is likely to become the preferred choice. For selecting pressure swing adsorption oxygen production, it is recommended to use the pre-machine oxygen enrichment process.