(1) Energy Saving

The vertical adsorption vessel is a radial cylindrical-grid-structure vessel. Compared with the axial adsorption vessel, the adsorbent bed is thinner, and the resistance is smaller, thus reducing the air flow pressure and leading to the discharge pressure & power decrease of rotary equipment correspondingly. By calculation and practice, energy consumption of VPSA oxygen plant can be reduced by 10% to 15% using a radial adsorber.

(2) Structural Advantages

The VPSA oxygen generation plant adopts a radial adsorption vessel where the gas flow direction is favorable for adsorption and desorption. Due to the direct influence of airflow velocity on adsorption and desorption for which slower airflow is more propitious. In the adsorption phase, as the feed gas flows from outside to the inside, nitrogen is gradually adsorbed with gradual volume reduction of the gas, and the flowing cross section of the radial adsorber is gradually narrowed from outside to the inside. This structure increases the comprehensive utilization efficiency of the adsorbent and improves the stability of the adsorbent bed at the same time. The direction of the airflow is perpendicular to that of gravity, which effectively reduces the washing-away of the adsorbent and increases its service life.

(3) Small Plot Area

The radial adsorption vessel adopts a cylindrical absorbent bed structure to make full use of the space. The covering area is only half as large as that of the axial adsorber of the same scale.

(4) Better Adaptability of Production Capacity

Radial adsorption vessel doesn’t have limitations of air volume. As the oxygen production capacity increases, it is necessary to increase the amount of feed gas and adsorbent, which can be solved by increasing the radial adsorber height When the equipment diameter is limited by transport or manufacturing.

Due to its low cost, flexible load adjustment, and simple start-up & shut-down, VPSA oxygen generation technology is widely used in industrial production. For example, in the steel industry whose market has improved in the past two years, in order to increase the oxygen enrichment rate of blast furnace, reduce the coke ratio and improve blast furnace production capacity, usually VPSA oxygen plant is chosen as the supplementary oxygen source to reduce the costs and increase production.

The pressure swing adsorption oxygen production plant has been widely used in non-ferrous metallurgy (copper, zinc, lead, gold, nickel smelting, titanium dioxide.,etc.), ferrous metallurgy (blast furnace oxygen-enriched coal injection ironmaking, electric furnace steelmaking, etc.), oxygen-enriched fuel combustion (industrial boilers, glass/glass fiber furnaces, electrolytic aluminum), chemical gas making (synthetic ammonia, methanol, ethylene glycol, etc.), health care, sewage treatment, pulp bleaching, hydrogen peroxide production, ozone generation, aquaculture, carbon black production and other fields.

The VPSA oxygen plant consists of power system, adsorption system, valve system, instrument control system, electronic control system and supporting public & auxiliary system, which are respectively described as follows:

The power system, consisting of Roots blower, Roots vacuum pump, electric motor, air filter, silencer, elastic joint and other ancillary parts, works to provide the positive pressure and vacuum level as required for adsorption and desorption of the adsorbent.

The adsorption system is made up by stuffing, adsorption vessel, and a buffer tank and heat exchanger matched thereto.

The valve system is composed of special regulating valves, switching valves and hand valves. The regulating and switching valves are all pneumatic butterfly valves controlled by PLC. Both adsorber-to-adsorber and adsorber-to-power equipment disconnecting and connecting can be realized by switching valves.

The instrument control system contains the control system and field instruments. The latter is composed of transmitter, oxygen analyzer, orifice flow-meter, vibration sensor, etc.

The electronic control system is made up by the inlet cabinet, PT cabinet, outlet cabinet, soft starting cabinet, uninterrupted power supply, etc.

The public auxiliary system, mostly provided by users, offers the necessary circulating water, soft water, electricity and instrument gas for the VPSA plant.

There are two ways to provide VPSA enriched oxygen to blast furnace:

The First approach is oxygen enrichment after the blower, i.e., the low-pressure oxygen at the outlet of VPSA oxygen plant is pressurized by an oxygen compressor to 6Bar(G), then mixed with ambient air in the cold air pipe at the blast furnace blower outlet to achieve enriched oxygen.

The second one is oxygen injection before the blower. Oxygen is directly fed into the blast furnace blower and then into the blast furnace making use of the pressure difference between the outlet of VPSA plant and the blower inlet. In order to fully mix oxygen and air, an oxygen distributor is required at the front of the blower inlet.

The advantages of oxygen injection before the blower are:

1. Energy Saving

The oxygen injection before the blower saves the energy needed for oxygen compression. Although it is still a controversial issue whether the oxygen injection before the blower shares the blower’s capacity, energy conservation of the technology is affirmative even though the saving amount shows slight differences for each company.

2. Investment Saving

Oxygen compressor is spared in oxygen injection before the blower, which reduces the one-time investment. At the same time, low-pressure oxygen as the conveying medium cuts the manufacturing and construction cost when implementing the low-pressure standards.

3. Safety Assurance

There is no need to install decompression and explosion-proof equipment. Thus, safety of the system is strengthened.

The VPSA oxygen generation plant is characterized by its short operating cycle (generally only tens of seconds), so the exhaust pressure of blower will change rapidly with large fluctuation ranges during operation. Based on the principle of vacuum pressure swing adsorption, the blower is required to satisfy the stability of gas volume under the circumstance, which is the essential condition for stabilizing the gas flow rate in adsorption vessel and ensuring the service life of the adsorbent and the performance of VPSA oxygen production plant.

The Roots blower is a volumetric rotary blower that keeps the two rotors meshed by the synchronizing gears at the shaft end. The concave curved surface of the rotor and the inner wall of cylinder constitutes a working volume. The gas is taken in from the suction port during the rotation of rotor, when moving near and connecting with the exhaust port, the pressure in the working volume suddenly rises and the gas is delivered to the exhaust passage due to the returning of the higher-pressure gas. The two rotors do not touch each other, and the gaps between them are tightly controlled to achieve encapsulation so that the discharged gas is free from lubricating oil.

The most prominent feature is that when the pressure is adjusted within the allowable range, the flow rate changes little. The pressure selectivity is flexible, thus it can transmit gases compulsorily. It has the advantages of simple structure, easy maintenance and long service life.

In addition, it is suitable for gas delivery and pressurization in low-pressure conditions and can also be used as a vacuum pump. Therefore, the Roots blower is suitable for VPSA oxygen production plant, which is a common consensus in the development of VPSA oxygen generation technology over the years.

VPSA oxygen plant suppliers usually provide overall materials including instructions for use, maintenance manuals and troubleshooting manuals. The structure of VPSA plant is simple- the rotary equipment only consists of a blower and a vacuum pump which are general-duty equipments with simple maintenance, therefore, maintenance of VPSA oxygen plant is generally composed of two parts: inspection (including fault handling) and replacement of vulnerable parts.

According to the information online,  VPSA oxygen plant has the advantage of simple and easy maintenance. At the same time, all the parts are controlled by PLC with high automation. In theory, unattended operation can be achieved.

The maintenance of VPSA oxygen plant is relatively simple, and it is easy to handle the faults. However, it is still recommended to replace the wearing parts such as valve seals on time in accordance with the requirements. Based on the association’s investigation, almost all domestic and foreign on-site gas production companies require regular maintenance on the VPSA plant, and regular replacement of the sealing ring whether it is worn or not.

Statistics have shown that regular maintenance is beneficial to reduce the long-term operation cost and prolong the service life of the VPSA oxygen plant.

The operating cycle of the VPSA oxygen production process is very short, generally less than 1 min. In one cycle, each adsorption vessel needs to experience the steps of adsorption, pressure reduction, desorption, purging, even pressure increasing, etc.

Key valves switch on and off once in each cycle, which is pretty frequent, so they are required to be switched quite fast in order to improve the working efficiency and effective utilization of the oxygen plant.

Therefore, the valves used in VPSA oxygen plant must feature the following characteristics:

1. high switching speed

2. good sealing performance

3. long service life under frequent and fast switching conditions

4. oil-free operation

At present, domestic VPSA plants generally adopt special double-eccentric pneumatic butterfly valves whose actuators and pneumatic components are made by famous brands such as Metso and SMC to improve the reliability of the valves. The valve has the following characteristics:

1. Wide Range of Caliber: DN100-to-DN900 diameter range

2. High Switching Speed: 0.3 to 0.8 second/time

3. Sealing Structure: lip-shape sealing structure with two-way zero leakage and self-repairing after wearing

4. Sealing Materials: reinforced PTFE material with high wearing resistance

5. Power Drive: driven by low-pressure, clean and oil-free instrument gas, which is relatively easy to obtain.

6. Maintenance: The valve is small in size, light in weight, easy to maintain. The maintenance cost is lower than that of other types of valves.

The VPSA plant is a complete set of systems. On the premise that the process design is reasonable, the supporting equipment is properly selected and the operation is smooth, the power consumption of the entire unit will be ensured the lowest. Specifically, related factors are as follows:

1. Whether the adsorbent is efficient.

The most efficient adsorbent currently on the market is the PU-8 lithium-based adsorbent, whose oxygen production per ton is the highest in the industry. The loading is less for the same oxygen production so that the resistance for the gas to pass through the adsorbent bed will be smaller, thus finally reaching a lower level of energy consumption.

2.Whether the process is reasonable.

The adsorbent is the core part of a plant and the maximum performance of the adsorbent can be ensured with reasonable process design, which includes adsorption temperature, pressure and cycle, desorption pressure and other indicators’ settings.

3.Whether the power equipment matches the whole VPSA plant.

The main power of the whole plant is consumed by power equipment. If the power equipment is too small, the oxygen production won’t meet the design specifications and if it is too large, the unit power consumption will be higher. In addition, smooth running of the supporting equipment is also important. If the valve leaks, the signal transmission of the instrument isn’t stable, etc., the operation of the entire system will be affected.

In summary, the power consumption of the VPSA oxygen production plant depends on the cooperative operation of the various components of the system.