In the past 20 years, China's economy has been developing steadily and rapidly. The continuous upgrading and innovation of production processes of iron and steel, non-ferrous metallurgy, chemical industry, furnace, environmental protection and other industries boosted the demand for oxygen, thus promoting the development of oxygen production technologies such as cryogenic air separation process, VPSA oxygen production and membrane separation technology. The low purity of product oxygen limits the adaptability of the membrane separation process while the cryogenic and VPSA process made great progress. After the localization of new lithium-based adsorbent and the breakthrough in the development of radial adsorption tower, the VPSA oxygen production process has been widely used and actively recognized by users in China.

Advancement of VPSA & PSA Oxygen Generation Technology

The VPSA (Vacuum Pressure Swing Adsorption) oxygen generation technology was developed in the 1960s and was industrialized in the USA and Japan successively in the early 1980s. In recent years, with the development of the permanent-magnet motor and the optimization of oxygen production process, the lowest power consumption overseas has been reduced to less than 0.3kWh/m3, and the largest capacity of dual-tower oxygen system has exceeded 6000Nm3/h. The cost of VPSA oxygen production was further reduced, and the capacity has been increasing year by year.

China started to explore the VPSA oxygen generation technology in the late 1980s, and only in the early 1990s did a small, industrialized oxygen unit became available. In early 2000, represented by PKU Pioneer, the high-efficiency lithium-based adsorbent production and VPSA oxygen generating process's industrialization using the lithium adsorbent made the technology achieve rapid progress and widespread popularity. At present, the flow rate of dual-tower oxygen units built by PKU Pioneer has reached 6000Nm3/h, and the power consumption (pure oxygen) is approaching 0.3kWh/m3.

In China, the capacity of VPSA oxygen plants has been increasing annually and the reliability has been steadily improving while the energy consumption was gradually cut down with the solution of some key issues such as stable production of high-efficiency lithium-based adsorbent, radial adsorber development, reliable high frequency, and large-diameter butterfly valve development. In addition, the specification has also been lifted from less than 1,000 Nm3/h of the initial single set of two-tower oxygen plant to 6,000 Nm3/h today, and the total capacity reaches more than 70,000 Nm3/h after the parallel connection of multiple towers while the unit power consumption has been reduced to less than 0.32 kWh/m3 and more than 98% of the oxygen plants were successfully and smoothly operated annually. The noise of the blower has met the requirement of less than 85dB and even below 70dB at 1m outside the factory through elimination measures. The failure-free rate of large-diameter butterfly valves has generally reached more than 8000h, and the service life of lithium molecular sieve has been extended to more than 5 years. Users have had a new understanding of China VPSA-O2 equipment and expanded its application. In 2018 alone, more than 70 sets of VPSA oxygen units with a capacity of more than 1000 Nm3/h were built.

Through continuous efforts, China enterprises such as PKU Pioneer changed the dependence on imported molecular sieves for VPSA oxygen production, made a breakthrough in lithium molecular sieves and other related products and realized the industrial application of new molecular sieve products. With the development and improvement of VPSA oxygen generation technology, it gradually showed many exclusive advantages compared with cryogenic technology, which further promoted the application of the technology in many industries in China.

Advantages of VPSA & PSA Oxygen Generation Technology

1. Low Energy Consumption and Operating Costs

Power consumption accounts for more than 90% of the total operating cost in the oxygen-generating process. With the continuous optimization of VPSA & PSA oxygen technology, its pure oxygen power consumption has dropped from 0.45kW·h/m3 in the 1990s to less than 0.32kW·h/m3 today, while even the lowest value of large-scale cryogenic ASU is around 0.42kW·h/m3. Compared with cryogenic technology, the VPSA & PSA oxygen technology has obvious economical advantages under working conditions where the user has no nitrogen demand and the oxygen process does not have too high requirements for oxygen purity and pressure.

2. Simple Process, Flexible Operation, Easy Start-Up and Shutdown

Compared with cryogenic oxygen generation technology, the VPSA process is relatively simple with comparatively brief operation and easy maintenance cause the main power equipment consists of the Roots blower and Roots vacuum pump.  As there is no cooling and heating process during the start-up and shutdown, it only takes only 30 minutes for the VPSA and PSA oxygen equipment to generate qualified oxygen from the beginning and a few minutes to regenerate after a short suspension. The shutdown is even simpler- just turn down the power equipment and control program. Thus, VPSA & PSA oxygen generation technology is easier than the cryogenic process, which also significantly reduces the operating cost of starting and shutting down the oxygen plant.

3. Lower Investment and Short Construction Period

The VPSA oxygen unit is mainly composed of a small number of components including the power system, adsorption system and valve switching system, etc., which can greatly save its once-off investment. The oxygen unit covers a small footprint and can reduce the civil engineering cost and the construction land. Also, the manufacturing and processing cycle is short, main equipment components can be delivered within only 4 months so as to achieve oxygen production requirements within 6 months under normal circumstances, thus significantly shortening the construction period of the oxygen system compared to that of nearly 1 year of cryogenic air separation units.

4. Simple Equipment Composition and Easy Maintenance

The equipment used in the VPSA oxygen plants, such as blowers, vacuum pumps and program control valves, can all be domestically produced, so spare parts can be conveniently replaced to cut costs and makes the construction period under control. With simple equipment maintenance and on-time after-sales services, VPSA oxygen plant users do not need too much cost and professional workers compared to the maintenance of large centrifugal compressors used in cryogenic air separators.

5. Easy Turndown Ratio Regulation

Compared with the cryogenic liquid oxygen technology, VPSA & PSA oxygen generation process can realize the rapid adjustment of product O2 capacity and purity with slight fluctuations in the pure oxygen power consumption. Generally, the capacity can be adjusted from 30% to 100%, and the purity from 70% to 95%, especially when several sets of VPSA & PSA oxygen generators are built in parallel, the load adjustment is even easier.

6. Higher Operational Safety

As the VPSA oxygen system is operated at low pressure and room temperature, there will be no liquid oxygen, acetylene enrichment and other phenomena, thus resulting in better safety compared with the low-temperature and high-pressure operation in the cryogenic oxygen generation process.

The Main Application Scenarios of VPSA & PSA Oxygen Generation Technology

With the increasing capacity and reliability and the gradual reduction of oxygen power consumption, as well as the advantages of flexible operation, simple turndown ratio adjustment, low power consumption, short construction period and high safety, VPSA oxygen generation technology has undoubtedly become an alternative to cryogenic oxygen generation for industries that need to utilize oxygen flexibly, and its application scope is expanding year by year. In recent years, the VPSA oxygen production process has been widely used in iron & steel, non-ferrous metallurgy, the chemical industry, furnaces and kilns, environmental protection and other industries.

1. Blast Furnace Oxygen Enrichment

With the development of blast furnace oxygen enrichment technology, blast furnace has become one of the main oxygen consumption sources in iron & steel enterprises. In the initial application stage of the technology, the blast furnace can be used as a regulator of oxygen supply, where the oxygen enrichment rate is higher with relatively large oxygen flow and lower contrarily. As the importance of blast furnace oxygen enrichment technology in the ironmaking process became clear to iron and steel mills, the stable blast furnace oxygen enrichment rate has become an important factor for low-cost and efficient ironmaking. Due to many oxygen supply processes in iron and steel enterprises, the turndown ratio fluctuates every week or even every day. Considering the weak turndown ratio regulation of cryogenic process and long start-up and shutdown time, the excessive oxygen needs to be liquefied and stored for later use or sale when the oxygen consumption flow is low, and sometimes even ventilation occurs. In view of the low pressure and relatively lower oxygen purity requirements for BF oxygen enrichment, many iron and steel enterprises can build VPSA oxygen units near the blast furnace directly. Meanwhile, as a regulator, when the oxygen volume by cryogenic air separation is surplus or insufficient, VPSA oxygen units can start and shut down at any time to lift or decrease the oxygen for the blast furnace. At present, after adopting VPSA oxygen technology for oxygen supply, many iron and steel manufacturers substantially cut their oxygen cost. Blast furnace's adoption of VPSA oxygen unit as an enriched-oxygen source has been a common understanding in most iron and steel enterprises.

2. EAF Steelmaking

In the past, most China steel enterprises believe electric furnace steelmaking need to use pure oxygen generated by cryogenic air separation units, while in Japan about 60%-70% of the steelmakers use 93% oxygen by VPSA-O2 system for steel manufacturing. Theoretically, EAF steelmaking mainly relies on electric arc smelting and oxygen only plays an auxiliary role, thus 93% oxygen by VPSA oxygen production can be fully applied to the electric furnace steelmaking. Up to now, China companies such as Luzhou Yixin Iron & Steel Co., Ltd., Zunyi Changling Special Steel Co., Ltd. and Chizhou Guihang Metal Products Co., Ltd. have already started to adopt VPSA oxygen plant to supply oxygen for EAF steelmaking. According to the users' feedback, utilizing the VPSA oxygen system has no negative impact on the quality of steel products, and can significantly reduce the steelmaking production cost.

3. Nonferrous Metallurgy

In the past 10 years, VPSA oxygen generation technology has been highly recognized in the smelting of copper, lead and zinc. Most of the non-ferrous metal smelting processes generally require oxygen of 24%~90% with large turndown ratio fluctuations, and N2 is hardly necessary for non-ferrous metal smelting enterprises, which makes VPSA oxygen production technology suitable for non-ferrous metal smelting with the characteristics of simpler operation and lower power consumption. At present, most China non-ferrous smelters such as Tongling Nonferrous Metals Group Co., Ltd., Zijin Mining Group Co., Ltd. and Yunnan Copper Co., Ltd. have chosen VPSA oxygen plants as the source of oxygen enrichment. With the increase in copper production and the improvement of the copper smelting process, Baotou Huading Copper Development Co., Ltd. has built 4 sets of VPSA oxygen units successively, and the total capacity reached over 25,000Nm3/h. In addition, Chuxiong Smelting Works in Yunnan has built 3 sets of VPSA oxygen generation units with the increase in copper production, and its total oxygen consumption volume has reached 30,000Nm3/h.

4. Chemistry

At present, some China small and medium nitrogen fertilizer factories use continuous enriched-oxygen generation process to improve the original intermittent gas production mostly by VPSA technology. Also, the oxygen-rich continuous gasification technology is highly applicable to coal by enhancing the capability of the gas production unit. Moreover, most paper enterprises both at home and abroad choose VPSA technology to generate oxygen. VPSA oxygen generation technology is also widely used in other areas, such as oxygen-enriched combustion for float glass in the glass fiber industry, cement kilns and waste incineration, wastewater oxygen-enriched aeration treatment and ozone.

Vision of the VPSA & PSA Oxygen Generation Technology Development

As a new oxygen generation technology that has been developing rapidly in the past 20 years, VPSA oxygen generation technology has gradually been recognized by many users as it continued to advance technologically and expanded its application fields. In order to reduce energy consumption, developing new adsorption materials and trying to coordinate with membrane or cryogenic process to expand more application areas by complementing each other is an important research and development direction for VPSA oxygen generation technology in the future. For example, the combination of VPSA and membrane oxygen technology can produce oxygen >99%, which is an alternative to cryogenic air separation units in remote areas or under some conditions requiring mobile equipment. China enterprises engaging in VPSA oxygen production such as PKU Pioneer have attached great importance to R&D, striving to take the lead in the future by enhancing investment. As the VPSA-O2 production technology is increasingly improved, it will possess a more extensive application prospect with various advantages and massive potential.