RTO promotes green metal printing and coating-also discusses the selection and evaluation criteria of air purification devices in the metal packaging industry

RTO helps green metal printing

——Also on the selection and evaluation criteria of air purification devices in the Metal Packaging industry

Text / Xu Haoran (Jiangsu Huayu Printing Equipment Group Co., Ltd.)

Figure 1 Huayu RTO in operation

Volatile Organic Compounds (VOCs) are the most common pollutants emitted by petrochemical processes and various industries that use organic solvents, such as paint spraying, printing, pharmaceuticals, and coal chemical industries. Most of these compounds have an irritating odor and toxicity, and some have been classified as carcinogens, such as benzene, polycyclic aromatic hydrocarbons, vinyl chloride, acetonitrile, etc., which endanger human health and pollute the air; in addition, most VOC gases are flammable and explosive Production safety poses a threat.

1. Environmental protection is under pressure, and the metal Packaging industry urgently needs to solve the effective management of VOCs

Due to the dangers of VOCs, many countries have issued laws to control VOC emissions. The "Air Pollution Prevention Law" promulgated by our country requires purification treatment of toxic gases generated in industrial production, and recycling of flammable gases. The "Comprehensive Emission Standards for Air Pollutants" (GB16297-1996) stipulates emission standards for 33 kinds of volatile organic compounds, treats most other volatile organic compounds as non-methane hydrocarbons, and stipulates a unified emission standard (

As far as the metal packaging industry is concerned, since the organic solutions in the paints used by most companies contain benzene, toluene, ethyl acetate, xylene, butanone, etc., they will exist in the process of surface coating and drying. Certain harmful volatiles are one of the major environmental protection governance. Under the high pressure of environmental protection, the metal packaging industry must solve the problem of "effective treatment of low-concentration, large-volume organic waste gas generated in color printing, coating and baking", use resources reasonably, protect the environment, significantly improve the industry's technical equipment and accelerate waste gas The replacement of purification equipment and other supporting equipment breaks the technology and market monopoly of foreign companies in this field, and improves China's competitiveness in the world packaging industry.

2. Comparison of the advantages and disadvantages of the three main VOCs processing technology routes

Methods for removing VOCs in industrial exhaust gas can be divided into destructive methods and non-destructive methods. Among the destructive methods, there are three types of technical routes: direct combustion method, catalytic combustion method and regenerative oxidation method. Among them, catalytic combustion technology and high temperature combustion technology are the most common and effective VOCs treatment technology.

The direct combustion method is the use of thermal combustion to oxidize and decompose odorous gases. At the appropriate temperature, it provides sufficient combustion oxygen and a certain residence time, which can efficiently deodorize and have a high purification rate. At the same time, the equipment host works stably without clogging. It is suitable for exhaust gas containing catalyst deactivated substances (S, heavy metals, halogens), as well as highly viscous substances such as asphalt exhaust gas. However, the equipment covers a large area and the cost is relatively high.

The catalytic combustion method uses a combined process of adsorption concentration + catalytic combustion. The entire system realizes a closed cycle of purification and desorption processes. Compared with the recovery type organic waste gas purification device, it does not require additional energy sources such as compressed air and steam. Secondary pollution, low equipment operating costs, suitable for normal temperature, large air volume, low and medium concentration, volatile organic waste gas. The one-time investment cost of equipment is relatively high.

The regenerative oxidation method adopts the preheating and regenerative switching technology, the heat exchange efficiency is as high as 90%, and the energy saving effect is remarkable. It has the functions of pre-sweep, fire stop protection, over-temperature alarm and automatic cut off of fuel supply. Adopt microcomputer automatic control and multi-point temperature control to realize a variety of protection actions, operation information retrieval and monitoring information feedback, so that the system operates safely, stably and reliably. Valve switching is more sensitive and rapid. The price of the catalyst is relatively expensive (120,000 yuan / m3), and the cost of burning auxiliary materials is also very high. It is suitable for medium and high concentration organic waste gas, as well as various organic compounds produced by coating lines, printing, chemical synthesis processes (ABS synthesis), and petroleum refining processes. Exhaust gas.

In general, the corresponding combustion temperature needs to be heated during the thermal catalytic combustion process. If the concentration of organic matter in the exhaust gas is high, the heat generated by the combustion of the exhaust gas can maintain the reaction temperature required for the decomposition of the organic matter, so the catalytic combustion method is a kind of Economically feasible method.

However, traditional catalytic combustion technology and high-temperature combustion technology have low heat transfer efficiency. When the concentration of organic matter in the exhaust gas is low, a large amount of energy consumption is required, and the operating cost is high. In order to improve the thermal efficiency of the equipment and reduce the operating cost of the equipment, in recent years, regenerative heating technology and regenerative catalytic combustion technology have emerged to combine the recovery of flue gas waste heat with efficient combustion and reduce NOx (thermal nitrogen oxides) emissions. Such technologies are organically combined to achieve the dual purpose of saving energy and reducing pollutant emissions.

3. Evaluation criteria for selecting exhaust gas treatment equipment

Industrial waste gas treatment equipment productivity and product quality Equipment productivity and product quality mainly refer to the product capacity per unit time and the engineering capability of equipment quality. The main features of high-efficiency equipment are: large-scale, high-speed, automated and electronic.

Investment cost When selecting equipment, after careful evaluation of the above factors, the initial investment of the equipment and a reasonable balance of investment must be considered, that is, the payback period of the equipment investment and the savings brought by the use of new equipment.

Processability is the ability of equipment to meet production requirements. In addition, the equipment must be easy to operate and flexible to control; equipment with large output should be highly automated; equipment for toxic and hazardous operations requires automatic control or remote monitoring.

Maintainability refers to the difficulty of preventing and eliminating failures of systems, equipment, parts, etc. through repair and maintenance. Generally speaking, if the equipment design is reasonable, the structure is simple, the parts are assembled reasonably, the parts are easy to disassemble and install during maintenance, the inspection is easy, the versatility of the parts is good, the standard and interchangeability are good, then the maintainability of the equipment is good .

When selecting equipment economically, the initial investment of the equipment is low, that is, the equipment purchase cost is low, the equipment productivity is high, the natural life is long, the maintenance and management costs are less, and labor can be saved.

Safety refers to the selection of safe and reliable equipment in production. For corrosive equipment, pay attention to the reliability of the protective facilities and whether the material of the equipment meets the design requirements. In addition, we should pay attention to whether the equipment structure is advanced, whether the assembly is reasonable and firm, and whether various safety devices for predicting and preventing equipment accidents are installed.

Environmental protection refers to the environmental pollution caused by harmful substances generated and discharged by equipment in compliance with national regulations. The equipment with no or little emissions of "three wastes" should be selected, or the equipment with corresponding treatment facilities for "three wastes" should be selected. It also comes with noise reduction and sound insulation devices.

Completeness is the matching situation between the equipment itself and various equipment. When choosing equipment, avoid the phenomenon of "large horse-drawn cart" or "small horse-drawn cart" between power equipment and production equipment, and the unmatched phenomenon of "top-heavy" among production equipment.

Reliability in a broad sense refers to the maintenance of the accuracy and accuracy of machine equipment, as well as the durability of machine parts, the reliability of executive functions, and whether the operation is safe.

4. Advantages of regenerative high-temperature air combustion technology

Regenerative high-temperature air combustion technology (High Temperature Air Combustion, HTAC) is a new combustion technology that has been popularized and applied in developed countries since the 1990s. It can preheat combustion air to 800 ~ 1000 ℃ or above, and the oxygen content of the air in the combustion zone is 2% -21%. Compared with the traditional combustion process, the biggest feature of high-temperature air combustion is to save fuel, reduce CO2 and NOX emissions, and reduce combustion noise.

The international community attaches great importance to the research and development of high-temperature air combustion technology, and the industry regards the promotion and application of high-temperature air combustion technology as one of the main tasks of energy conservation and environmental protection in the new century. In 2014, more than 50 companies in China adopted this technology to transform iron-and-paint coating ovens, with an average energy saving effect of 30%, and NOX emission targets in line with government environmental requirements.

The main characteristics of regenerative high-temperature air combustion technology are shown in the following aspects.

Significant energy saving and carbon reduction Adopting regenerative flue gas waste heat recovery device to maximize the recovery of physical heat of high-temperature flue gas, generally can save energy by 10% to 70%, improve the thermal efficiency of thermal equipment, and reduce greenhouse gas (CO2) emissions by up to 10% to 70%.

The temperature distribution in the furnace is even, which greatly reduces NOX. Through the organization of oxygen-depleted combustion, the flame combustion area is expanded to make the temperature distribution in the furnace uniform; at the same time, the emission of NOX in the flue gas is reduced by more than 40%.

Reduce equipment cost. As the average temperature in the furnace increases, the heat transfer in the furnace is strengthened, and the output of thermal equipment of the same size is increased by more than 20%, which greatly reduces the cost of the equipment.

The application range of low calorific value fuel is wider. Low calorific value fuel can obtain higher furnace temperature by means of high temperature preheated air or high temperature preheated gas, which expands the application range of low calorific value fuel.

5. Technical scheme of regenerative high-temperature air burner

Our company determines the following specific design schemes of regenerative burners according to the technical characteristics of customers: single air preheating, after preheating, the air temperature is greater than 800 ℃, the exhaust temperature is controlled at 100 ℃ ~ 200 ℃; the burner is sleeve type Structure, double burner design, one burner is used for combustion, and one burner is used for smoke exhaust; double regenerator design, the regenerator is located below the burner, using honeycomb regenerator (for details, see below); A rotary four-way reversing valve is used; the reversing time is set at 40s.

The design of the burner regenerative burner follows the basic technical principle of high temperature and low oxygen air combustion, that is, efficient recovery of flue gas waste heat, which greatly reduces the emission of pollutants, especially NOX.

The material of the heat storage body is for the purpose of high efficiency and energy saving. The heat storage body should have the functions of high-efficiency heat storage and high-efficiency heat exchange, as well as no temperature stress limitation, high-temperature structural strength, oxidation resistance, corrosion resistance, economy, and long life. The honeycomb regenerator (Figure 3) was finally selected as the filling material for the regenerator due to its many advantages, but its short switching time (30 ~ 70s) resulted in an increase in switching frequency, which inevitably increased the action of the directional valve Therefore, this point should be fully considered when making the directional valve.

Figure 2 Honeycomb regenerator

The directional valve can be a rotary four-way ordinary metal directional valve. Since frequent commutation is required during the operation of the burner, the life of the directional valve will directly affect the working performance of the burner.

6. Advanced regenerative thermal oxidizer RTO

Figure 3 As an advanced version of regenerative high-temperature air burner technology, RTO is considered to be the most economical, environmentally friendly treatment device with wide applicability and durability.

As an advanced version of regenerative high-temperature air burner technology, regenerative thermal oxidizer (RegenerativeThermal Oxidizer, RTO) is an energy-saving environmental protection device used to treat low- and medium-concentration volatile organic exhaust gas. Reliability, easy operation and low maintenance cost are widely concerned. Typical application areas include the printing iron coating industry and paint and ink manufacturing, textile and chemical electronics industries. It is considered to be the most economical, widely applicable and durable environmental treatment device.

Working principle The typical three-bed RTO main structure is composed of a combustion chamber, three ceramic packed beds and six switching valves (Figure 1). The exhaust gas is alternately switched between three regenerative oxidation beds, and VOCs are in a high-temperature environment ( ≥760 ℃) is decomposed and oxidized into CO2 and H2O. Regenerative ceramic packed bed heat exchangers can maximize the recovery of heat energy (heat recovery rate is greater than 95%), so that when processing VOCs, little or no fuel can be used.

Advantages RTO device has the following advantages.

First, the purification rate (DRE) is high. The purification rate of the three-bed RTO is above 99%, and after treatment, the exhaust gas fully meets the relevant national emission standards.

Second, the use of staged combustion technology releases heat energy under delayed combustion; the furnace has uniform temperature rise, low burning loss, and good heating effect. There is no local high temperature and high oxygen zone in the traditional combustion process, which suppresses the formation of NOX, without Secondary pollution.

Thirdly, it is especially suitable for high-volume, low-concentration organic waste gas, and the same production line, the composition of waste gas often changes due to different products.

Fourth, low operating costs and low fuel consumption operating costs. When the concentration of organic waste gas is above 2000PPM, the RTO device basically does not need to add auxiliary fuel.

Fifth, up to 97% of heat energy recovery (measured value). The temperature in the regenerator is evenly graded and increased, which enhances the heat transfer in the furnace and the heat exchange effect is better.

Sixth, it can realize fully automatic control, simple operation, stable operation, high safety and reliability. The small volume of the furnace reduces the cost of the equipment.

Seventh, the exhaust gas inlet is provided with inert alumina ceramic balls to protect, buffer and filter the regenerative ceramics, so that the service life of the regenerative ceramics is longer.

Eighth, fully automatic operation reduces power consumption, and there is no waste of energy consumption due to pressure changes.

Figure 4 The purification rate of the three-bed RTO is above 99%, and the exhaust gas after treatment fully meets the relevant national emission standards.

7. Conclusion

Among the organic waste gas treatment technologies that have been developed, applied and researched, the regenerative waste gas incineration treatment technology can not only effectively solve the problem that the traditional technology is not applicable to the treatment of low-concentration and atmospheric organic waste gas, but also has low investment and low operating cost. 1. The exhaust gas has a short residence time, high efficiency, stability, thorough reaction and no secondary pollution. In addition, it also overcomes the defects of traditional methods such as high operating cost and huge reactor. It has broad application prospects in the field of VOCs pollution control.

(Source of article: jargon)