VOCs Molecular Sieve Adsorption Wheel Technology and Market
Volatile organic compounds (VOCs) are one of the main sources of air pollutants, especially smog. The World Health Organization and other institutions define VOCs as: a general term for organic compounds with a melting point lower than room temperature and a boiling point between 323.15 and 533.15 K, such as benzene, toluene, xylene, and naphthalene. VOCs originate from industries such as petrochemicals, pharmaceuticals, printing, shoemaking, automotive manufacturing, and electronic manufacturing. It is estimated that the total VOCs emissions in China amount to over 30 million tons. VOCs not only cause environmental damage but also pose a threat to human health.
Countries around the world have formulated relevant laws and regulations on VOCs emissions, aiming to minimize or eliminate their emissions. However, due to limitations in production technology and cost pressure, most methods for controlling VOCs emissions can only be implemented at the stage of treating exhaust gases. Currently, the methods for controlling VOCs emissions content mainly include recovery technology and destruction technology.
In practice, the choice of one or several combinations of these methods is often based on specific conditions such as the volume, concentration, type, and economic value of VOCs in the exhaust gas.
Molecular sieve wheel adsorption technology is one of the VOCs recovery technologies.
VOCs Molecular Sieve Wheel Adsorption Technology
VOCs Molecular Sieve Wheel Adsorption Technology originated from the wheel dehumidification technology invented by an American named Bryant in 1950. It was used for VOCs purification by a Japanese company in 1990. This technology can be used for both recovering and destroying VOCs. It is applicable to low-concentration VOCs exhaust gases. Through the molecular sieve wheel system, the exhaust gas is enriched and concentrated for recovery or destruction.
VOCs Molecular Sieve Wheel Adsorption System mainly consists of the adsorption molecular sieve wheel core (honeycomb-shaped block, Honeycomb Monolithic Adsorbent), gas filtration device, rotating device, fan, etc. The adsorption molecular sieve wheel core is the core part. The core can be divided into three areas: adsorption area, regeneration area, and cooling area. To prevent air leakage between the areas, each area is separated by partitions. The partitions use rubber sealing materials that are resistant to high temperatures and corrosion. The molecular sieve wheel rotates at a certain speed under the drive of a motor.
Air containing VOCs pollution is filtered and then sent by a fan to the adsorption area of the molecular sieve adsorption wheel, as shown in Figure 1. The adsorption rotor is driven by a motor through a belt and rotates at a certain speed slowly. Low-concentration organic gases are sent to the molecular sieve adsorbent of the molecular sieve wheel through the honeycomb pores and are purified. The purified gas is discharged from the other end of the honeycomb pores. As the adsorption continues, the part of the adsorbent in the molecular sieve wheel that is close to saturation is transferred to the regeneration area, where it is desorbed and decompressed by the hot air blowing from the opposite direction. The desorbed VOCs are collected for centralized treatment, and the part of the molecular sieve wheel adsorbent that is regenerated enters the cooling area, where it is cooled and reduced in temperature, and then transferred to the adsorption area for adsorption operation again. The molecular sieve wheel adsorbent undergoes the repeated process of adsorption - desorption - cooling. Generally, the air volume of the regeneration air is less than the processing air volume, so the concentration of VOCs at the regeneration outlet is concentrated, and therefore this method is also called VOCs Molecular Sieve Adsorption Concentration Technology.
Molecular sieve wheel adsorption has the advantages of stable operation, compact structure, small unit bed resistance, and small floor area. It has been used in production processes such as printing, integrated circuits, plastic processing, and spray painting lines that generate low-concentration and high-volume organic exhaust gas.
The preparation methods of the honeycomb structure adsorbents used in molecular sieve adsorption wheels mainly include coating type, immersion type and molding type. The adsorption materials commonly used include activated carbon, activated carbon fibers and zeolite molecular sieves.
Activated carbon has rich pores and a large specific surface area, and has good broad-spectrum applicability. Compared with zeolite molecular sieves, its adsorption capacity is larger. It is currently the most widely used adsorbent. However, humidity has a significant impact on its adsorption performance. When there is a large amount of water vapor in the exhaust gas, the adsorption performance will significantly decrease. Moreover, due to the high temperature during desorption, there are safety hazards such as flammability.
Activated carbon fibers are a new type of adsorbent developed after activated carbon. Commercial production began in the 1960s. Compared with granular and powder activated carbon, activated carbon fibers have high tensile strength and elasticity, and can be processed into various forms such as cloth, fabric, paper, and felt. Activated carbon fibers can be directly molded into honeycomb shapes and made into adsorption wheels. In addition, activated carbon fibers have a high specific surface area, with a BET specific surface area of up to 1000-2000 m2, and have narrow and uniform pore diameters, mainly consisting of micropores. They have large adsorption capacity, fast adsorption speed, easy regeneration, and excellent adsorption and desorption performance. The application fields of activated carbon fibers are also very extensive, and they are used in water treatment and air purification.
Zeolite molecular sieves have good flame retardancy and can withstand high temperatures. Using hydrophobic high-silicon molecular sieves, they still have good adsorption performance under the condition of relative humidity RH > 60%. Although the cost is higher than activated carbon, they are easy to desorb and can be recycled, making them more environmentally friendly.
VOCs Molecular Sieve Wheel Adsorption Market
The most stringent "Air Pollution Prevention and Control Law" was implemented on January 1, 2016, stipulating that the volatile organic compound content of raw materials and products used for production, import, sales and use shall comply with quality standards or requirements. The "13th Five-Year Plan" also includes VOCs in the total control target. With the gradual implementation of the pollution discharge fee collection policy and subsidy policy, VOCs treatment will gradually be liberalized.
Zhang Yonghong, the secretary-general of the China Environmental Protection Association, said that the VOCs treatment market is expected to experience a new round of explosive growth, and the "molecular sieve adsorption concentration wheel" is expected to have a market demand of tens of billions.
An authoritative institution estimates that assuming the density of VOCs gas is 0.8 g/L, the potential governance market space for VOCs in industrial parks could reach at least 40-60 billion yuan. Among them, the petroleum refining industry accounts for the largest market space, nearly 20 billion yuan, and the mechanical equipment manufacturing and printing industries also have a market space of 10 billion yuan. As of 2015, the already occurred market space of the VOCs treatment market was approximately 5 billion yuan, mainly concentrated in the petrochemical industry and the printing industry. By 2020, the remaining market space will be approximately 50 billion yuan, with considerable growth potential.
