Currently, organic waste gases emitted by industries such as petrochemicals, light industry, plastics, and printing are treated using direct-fired incinerators and regenerative thermal oxidizers (RTOs). The honeycomb ceramic in RTOs can store the heat generated by the burner. When the temperature of the ceramic exceeds the ignition point of the organic waste gases, even if there is no flame inside the furnace, the hot honeycomb ceramic can still ignite the organic waste gases. RTOs offer advantages such as low energy consumption, high safety, and a wide range of applications, making them a promising VOCs treatment technology with great development potential.

　　1. Current Status of VOCs Waste Gas Treatment

　　Volatile Organic Compounds (VOCs) are among the most common pollutants emitted by petrochemical processes and various industries that use organic solvents, such as painting, printing, pharmaceutical manufacturing, and coal chemical industries. Most of these compounds have irritating odors and are toxic. Some have been classified as carcinogens; moreover, many VOC gases are flammable and explosive, posing a threat to workplace safety.

　　Due to the hazards posed by VOCs, many countries have enacted regulations to control their emissions. Around the 1990s, European and American countries imposed emission requirements on all facilities that use organic solvents. In 1990, the United States raised its air emission standards and listed 189 pollutants generated during industrial production as toxic pollutants, most of which are VOCs. China’s “Air Pollution Prevention and Control Law” requires that toxic gases produced during industrial processes be purified and treated, and flammable gases must be recovered and reused. China’s “Comprehensive Emission Standards for Air Pollutants” (GB16297-1996) specifies emission standards for 33 volatile organic compounds, treating most other volatile organic compounds as non-methane hydrocarbons and setting uniform emission limits for them.

　　2. Regenerative Thermal Oxidation Treatment Method

　　The thermal oxidation method is a technique that uses thermal oxidation and catalytic oxidation technologies to destroy organic compounds in emissions. What distinguishes the regenerative thermal oxidizer (RTO) from other thermal oxidation technologies currently used in China is its use of a bed made of ceramics or other high-density inert materials to absorb and store heat from the exhaust combustion gases, then release this heat to the cold incoming gas stream—rather than relying on shell-and-tube heat exchangers for heat transfer between the two fluids. As a result, RTOs can achieve a heat recovery efficiency of over 98%.

　　The working principle of a regenerative thermal oxidizer is as follows: Organic exhaust gases are preheated in the preheating chamber, absorbing heat and increasing in temperature. They then enter the combustion chamber, where they are subjected to high-temperature incineration (heated up to 800℃), causing the organic compounds to oxidize into carbon dioxide and water. Afterward, the treated gases pass through another heat-storage chamber, where they release their stored heat before being discharged. The heat stored in this chamber is used to preheat newly incoming organic exhaust gases. By periodically reversing the direction of gas flow, the furnace temperature is kept stable.

　　Typical regenerative thermal oxidation processes include the following: the integrated regenerative combustion process (single chamber), as shown in Figure 1 [2]; the split-regenerative combustion process (two chambers), as shown in Figure 2 [2]; and the integrated regenerative combustion process (three chambers), as shown in Figure 3 [3].

　　Characteristics of 3RTO

　　3.1 Large waste gas treatment capacity and high efficiency

　　RTO is particularly suitable for treating organic waste gases with concentrations ranging from 2 to 8 g/m³. For low-calorific gases (such as ethyl acetate), the concentration can reach up to 12 g/m³, making RTO especially well-suited for the incineration of compounds that are difficult to decompose [3]. Compared to other treatment technologies (such as regenerative thermal oxidizers), the primary advantage of RTO lies in its heat recovery rate, which can reach as high as 98%, whereas other systems typically achieve only about 70% heat recovery. This exceptionally high heat recovery rate significantly reduces the amount of supplemental fuel required, thereby lowering operating costs. The effect is even more pronounced when dealing with large volumes of industrial gases containing low concentrations of organic compounds.

　　To ensure a high destruction removal efficiency (DRE), RTO systems also benefit from their high heat recovery efficiency, which enables them to maintain elevated thermal oxidation temperatures. This makes it easier to treat difficult-to-decompose organic compounds while keeping the increase in system operating costs minimal. Achieving a DRE of 98% to 99% is typical for these systems. In RTO systems, the attainment of very high preheating temperatures within the packing bed means that the thermal oxidation process actually takes place right inside the bed itself. Typically, the preheating temperatures in these systems are significantly higher than the auto-ignition temperatures of most organic compounds.

　　3.2 Energy-saving, environmentally friendly, and easy to maintain

　　The application results show that, for an RTO of a given size, using structured packing offers the following advantages over using random packing: (1) Higher thermal efficiency can reduce annual fuel costs by 60% to 65%; (2) Lower pressure drop can reduce annual power costs by 14% to 78%; (3) Due to reduced clogging potential and enhanced cleaning performance, downtime and maintenance costs are also lowered. However, structured packing is more expensive to manufacture and install—its cost per unit volume is 5 to 10 times higher than that of traditional random packing. Therefore, the initial investment required for using structured packing is 5% to 20% higher than that for using random packing.

　　4. RTO's application in China

　　Currently, most of the waste-gas incinerators used in China’s insulation-material industry and copper-clad laminate manufacturing sector are direct-fired incinerators. Although these incinerators have relatively low initial costs, they also consume large amounts of fuel oil. In today’s context of continually soaring fuel prices, saving fuel and reducing costs have become critical concerns for every enterprise. In fact, simply adding a heat-storage medium (honeycomb ceramic) to a direct-fired incinerator can achieve significant fuel savings. After incorporating a heat-storage medium into a direct-fired waste-gas incinerator, not only does it serve as a heat accumulator, but it also acts as a secondary ignition source. When the combustion burner is “extinguished,” organic waste gases coming into contact with the hot honeycomb ceramic will spontaneously ignite and burn. The cost of converting a direct-fired waste-gas incinerator into a regenerative waste-gas incinerator is very low; therefore, it is both feasible and highly advisable to retrofit the direct-fired incinerators currently used in China’s insulation-material and copper-clad laminate industries.

　　5 Conclusion

　　Compared to the earlier direct-flame incineration technology, the regenerative thermal oxidation (RTO) treatment technology offers distinct advantages. This technology is already well-established abroad; however, due to cost considerations, it has yet to gain widespread adoption in China. The concept of RTO is currently only implemented in a small number of industrial kilns. Against the backdrop of soaring energy prices, organizing efforts to research, develop, and promote the use of this technology not only can help conserve energy and reduce environmental pollution but also bring about substantial economic benefits and significant social gains.