Summary of VOCs waste gas treatment processes

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The following technologies are commonly used for the treatment of VOCs emissions, and they will be described in detail here based on our company’s expertise: 1) Low-temperature plasma technology. Principle of operation: Low-temperature plasma (Non-Thermal Plasma) technology generates corona discharge by applying ultra-high frequency and ultra-high voltage currents to a thin metal wire coaxial with a hexagonal metal tube; this results in the creation of a large number of high-energy electrons. These high-energy electrons collide with the surrounding gas molecules, producing chemically active radicals that help to decompose harmful gas pollutants. Figures 1-2 show the actual images of the low-temperature plasma power supply and generator. Technical advantages: 1. To meet the needs of treating large volumes of waste gas, high-power high-frequency high-voltage power supply technology (30kW/50kV) has been developed. High-voltage flashover factor detection and control technology is employed to keep the flashover factor at 10 times per minute; it features strong adaptability, high safety, low energy consumption, and stable and reliable operation ； 2. The new type of low-temperature plasma generator features a high energy efficiency ratio and a large discharge area, ensuring the efficiency and versatility of the device. Application industries: chemicals, material processing, tobacco, rubber, food, printing and dyeing, papermaking, leather, etc. Applicable operating conditions: Air volume: 3000~20000 Nm3/h ； Malodorous gases, industrial dust, and low-molecular-weight VOC emissions. 2) Catalytic oxidation technology: Principle of operation – This technology involves heating organic waste gases and malodorous gases to around 300°C; under the action of a catalyst, these gases are oxidized into small molecules such as N2, CO2, and H2O. The high-temperature gases generated are then used to preheat the cooler waste gases that need to be treated, thereby reducing the fuel consumption required to raise the temperature of the waste gases. Technical advantages: Stable performance, high efficiency, excellent economy and safety, compact structure with low space requirement; it can be equipped for waste heat utilization. The system can operate autonomously when the exhaust gas concentration is ≥5000 mg/m3 (or the self-heating temperature rise is ≥150°C), without the need for additional energy supply. Application industries: petrochemicals, spraying, chemicals, pharmaceuticals, printing, inks, and other industries. Applicable operating conditions: Air volume: 100~10000 Nm3/h ； Waste gas concentration: medium to high, 1000~6000 mg/Nm3. 3) Adsorption concentration technology: Principle of operation – Adsorption concentration technology makes use of the adsorption properties of adsorbent materials to concentrate waste gas with high flow rates and low concentrations into waste gas with lower flow rates and higher concentrations. This concentrated waste gas is then sent to subsequent treatment units such as (catalytic) oxidation or recovery processes, thereby reducing equipment investment and operating costs. Technical advantages: 1. Low equipment investment and operating costs, which can bring certain economic benefits to the owner ； 2. Other environmental protection companies do not possess the technology for recycling activated carbon. Our company’s activated carbon features a high adsorption capacity and a long service life of 1–2 years, which not only eliminates the costs associated with waste disposal for clients but also reduces their expenses related to replacing activated carbon ； 3. The process is mature and reliable, safe and stable, highly automated, and requires minimal maintenance. Application industries: petrochemicals, spraying, chemicals, pharmaceuticals, printing, inks, and other industries. Applicable operating conditions: Air volume: 1000~100,000 Nm3/h; exhaust gas concentration: ≤1000 mg/Nm3. Commonly used adsorption materials include activated carbon fibers, honeycomb activated carbon, and granular activated carbon; currently, granular activated carbon is the most widely used adsorption material. The commonly used form of adsorption bed is a fixed-bed, and multiple beds are usually operated in parallel to ensure continuous treatment of waste gas. 4) Condensation recovery technology: Principle of operation – Condensation recovery technology is primarily used for the recovery of VOCs exhaust gases that have value for recycling. It involves using chilled water or cooling water to condense high-concentration organic exhaust gases, thereby enabling their recovery and reuse; it is often used in combination with adsorption concentration technology. Technical advantages: It operates safely and stably, and can bring certain economic benefits to the owner. Application industries: Petrochemical, pharmaceutical, ink, and other industries that generate process exhaust gases containing simple components. Applicable operating conditions: Air volume: 100~100000 Nm3/h, VOCs concentration: high concentration (≥10000 mg/Nm3). 5) Regenerative Thermal Oxidation (RTO) technology: Principle – VOCs are oxidized at high temperatures (760–800°C) to produce pollution-free CO2 and H2O, and the heat generated by this oxidation reaction is recycled through a regenerative bed composed of ceramic heat storage materials. The VOC removal rate can reach 99%, with a heat exchange efficiency of over 90–95%. The RTO process flow diagram and equipment are shown in Figure 1-10. CnHm + (n+ )O2 → n CO2 + H2O + Q heat. Technical advantages: 1. Stable performance, with a VOC removal rate of ≥99% ； 2. High heat exchange efficiency (≥90%); the system can operate in a self-heating mode when the VOCs concentration is between 3000–4000 mg/m3 (or when the self-generated temperature rise is ≥80°C), resulting in low operating costs ； 3. RTO devices have good resistance to fluctuations and require little maintenance. Application industries: automotive, coating, semiconductors, machinery, and other industries. Applicable operating conditions: Air volume: 10,000~100,000 Nm3/h; VOCs concentration: moderate to low level, 3,000~4,000 mg/Nm3. 6) Regenerative catalytic oxidation (RCO) technology: Principle: A catalyst is added to the regenerative combustion technology, thereby reducing the reaction temperature to around 300–400°C. The VOC removal rate can reach 99%, while the heat exchange efficiency is around 90–95%. The schematic diagram of regenerative catalytic incineration is shown in Figure 1-11. Technical advantages: Stable performance, high efficiency, low operating costs, strong resistance to fluctuations, minimal maintenance requirements, and no generation of secondary pollutants such as nitrogen oxides. Application industries: automotive, coating, semiconductors, machinery, printing, inks, and other industries. Applicable operating conditions: Air volume: 10,000~100,000 Nm3/h; VOCs concentration: medium to low level, 3,000~5,000 mg/Nm3. 7) Direct combustion technology: Principle of operation – High-concentration VOCs waste gases are directly removed using combustion equipment; subsequently, water absorption devices are usually employed to eliminate secondary pollutants such as SO2. Technical advantages: simple process, stable performance, high efficiency, and low investment. Application industries: Waste incineration, coating, semiconductors, machinery, and other industries. Applicable operating conditions: Air volume: 1000~100000 Nm3/h; VOCs concentration: high concentration, 0~25 LEL%.