Since 1985, China, as a major cement manufacturing country, has ranked first in the world in cement production for 37 consecutive years. The cement industry has also become one of the key sectors to be transformed for energy saving and emission reduction due to its high energy consumption attributes. In the cement manufacturing process, cement kilns as the core coal-fired calcining equipment account for a significant proportion of the total energy consumption and carbon emission of a cement plant. Oxygen-enriched combustion technology is a national key promotion project for energy saving and low-carbon emission in the cement industry. Upgrading the air supply system of cement kilns using the technology has a positive effect on the fuel combustion performance and the clinker output. The VPSA (Vacuum Pressure Swing Adsorption) and PSA (Pressure Swing Adsorption) oxygen generation system has been the preferred choice in those technological renovation projects due to its shorter construction period, adaptability to scale, flexibility in operation and convenience in start-up and shutdown.

1. The Direction of VPSA Oxygen Generation Application for Technological Transformation in Cement Production Industry

In cement production, energy consumption accounts for more than 50% of the total manufacturing costs, and the kiln, as the core calcining component, is also the most fuel-consuming equipment in the cement production process. Pulverized coal is usually fed into the burner and burned in the air from the blower as fuel. If adopting oxygen-enriched combustion technology, the oxygen content higher than that of air can help to achieve a better combustion-supporting effect by making the fuel burn more completely, increasing the burning temperature of pulverized coal and shortening the burn-out time, thus improving the overall fuel efficiency of the whole system. In addition, as oxygen-enriched combustion can lift the flame temperature and stabilize the combustion atmosphere, it's beneficial to enhance the strength of clinker and further improve the cement clinker production.

VPSA and PSA oxygen generation technology can be applied to cement kilns of various capacities, allowing one-to-one or one-to-many applications. It has obvious advantages in energy-saving renovation projects with shorter construction cycle, more flexible operation and better turndown ratio regulation adaptability.

2. Application of Two-Tower VPSA Oxygen Plant in a Cement Factory in Korea

In 2021, a cement plant in South Korea intended to carry out a transformation for its cement kiln with oxygen-enriched combustion technology. Due to the local energy structure, coal is mainly imported. To further reduce the cost, promoting alternative fuels and further improving combustion efficiency became an imminent need for technological improvement. Due to limited space in the plant, the area available for the oxygen equipment is only 21.6mx25.4m, and the total of 7 gas consumption points are relatively scattered. The cement plant decided to adopt PKU Pioneer's VPSA oxygen production technology to renovate the current gas supply system after thoroughly reviewing the cryogenic, membrane and VPSA air separation processes. Its oxygen capacity requirement is 5000Nm3/h with a purity of 90%.

The transformation project adopts a two-tower VPSA oxygen unit to upgrade the original gas supply system. After being pressurized to 150kPa, the product oxygen obtained from the oxygen system with a pressure of 20-30kPa, flow of 5000Nm3/h and purity of 90% is sent to 7 cement furnaces in a one-to-many form and is controlled and adjusted at each gas point according to the practical oxygen demands.

With the completion of the technical improvement, the cement system runs stably after starting up the oxygen-generating plant. The coal consumption was reduced compared with that before the improvement when using pulverized coal alone as fuel while the plastics burned more completely in an oxygen-rich atmosphere and the thermal efficiency was improved when using alternative fuels. In addition, clinker production increased by more than 10% year-on-year. Compared with the original production parameters, all manufacturing performances of the kilns are more stable after the renovation. After the technological transformation, the proportion of alternative fuels (plastic wastes) used increased, which not only reduced the cost of coal but also help to get the additional subsidy from the government due to plastic waste disposal, thus significantly cutting the overall fuel costs. The oxygen-enriched combustion retrofit by VPSA oxygen-generating technology brings obvious economic benefits by reducing the fuel cost of the cement production system, increasing the clinker output and stabilizing the kiln operation.

3. Characteristics and Advantages of VPSA Oxygen Generation Technology

This technological transformation adopts PKU Pioneer's radial-bed adsorber and the third-generation oxygen molecular sieve, the process has the following characteristics:

3.1 Simple Process and Fast Start-Up & Shutdown

The VPSA oxygen plant adopts blowers and vacuum pumps to feed and pump air respectively. The adsorption towers can be paralleled jointly in two or more and usually two vessels can generate the maximum oxygen of 7500Nm3/h. The impurity adsorption and the product oxygen discharge can be achieved by pressure equalization, oxygen purging, pressurization and adsorption, while the impurity desorption and adsorbent regeneration can be achieved through depressurization, vacuum extraction and purging. The overall process is simple: with a high degree of automation, the valves are opened and closed by the time sequence control. And it takes only 15 minutes to start to meet the oxygen requirements with flexible operation and convenient start-up and shutdown.

3.2 Easy Operation and Flexible Turndown Ratio Regulation

The VPSA oxygen unit can be adjusted by setting the sequence steps and controlling valve parameters to achieve the turndown ratio and oxygen purity adjustment. The load can be adjusted from 30%-100% and the purity from 70%-94% with slight changes in pure oxygen power consumption.

3.3 Stable Operation and Low Maintenance Cost

The oxygen system's power equipment (Roots blower, vacuum pump, as well as booster blower) results in its more stable operation and less daily maintenance. In addition, PKU Pioneer's advanced control system with a high degree of automation enables the production enterprises not to invest too much in operation and maintenance capital and civil costs.

3.4 Operation at Normal Temperature and High Safety

Since the VPSA oxygen unit is operated at room temperature and low pressure, there would be no enrichment of liquid oxygen and acetylene compared with the cryogenic ASUs, therefore, it has higher safety.

3.5 Low Operating Cost

The overall power consumption for pure oxygen of the VPSA and PSA oxygen plants is lower (0.29~0.33kWh/Nm3), resulting in less total operating costs.

3.6 Short Construction Period and Low Noise

The integrated steel structure mill with sound-proof walls whose construction cycle is shorter than the conventional concrete workshop can be used. Composite silencing materials are applied for noise reduction treatment and the noise 1m outside the plant is ≤85dB.

As a convenient and efficient oxygen generation system, the VPSA and PSA oxygen plant is more advantageous in the technological transformation projects of cement mills for its shorter construction period and more flexible operation. After the renovation of industrial kiln gas supply system by the oxygen-enriched combustion technology with VPSA and PSA oxygen generation method as the core can comprehensively achieve pulverized coal combustion efficiency and clinker production improvement. In the urgent context of energy saving and emission reduction, further promoting the application of oxygen-enriched combustion technology on industrial furnace gas supply systems can achieve better energy saving and carbon reduction effects.

As the largest VPSA and PSA oxygen plant manufacturer and supplier in the world, PKU Pioneer has built 300+ oxygen systems for customers in over 10 countries. With the highest capacity reaching 80,000Nm3/h, our high-performance oxygen units have been applied in 10+ industrial areas including iron & steel, nonferrous metallurgy, glass making, waste incineration, energy batteries, etc. We’ve received high recognition from leading enterprises in each field for the superior reliability, stability, safety as well as the sincere services we offer.