Heat storage combustion technology in metal surface coating VOCs treatment applications!

Abstract: The heat storage combustion furnace (RTO) is to raise the temperature of the organic exhaust gas produced to 680-1050 degrees C, at this high temperature directly decomposed into carbon dioxide and water vapor, a large amount of heat energy from the flue gas transferred to the heat storage body, used to heat the next cycle of the organic exhaust gas to be decomposed. RTO operating costs, organic exhaust gas treatment efficiency can reach 95%-99%, the international more advanced equipment VOCS treatment more use this method. VOCs organic exhaust gas oxidation combustion is the use of high temperature, so that organic matter oxidation decomposition into carbon dioxide, water and some compounds, the general oxidation treatment efficiency can reach 95%-99%

. The combustion method is divided into direct oxidation combustion (TO) and heat storage combustion (RTO), RTO is more efficient and energy efficient than TO heat exchange.
1 Metal surface treatment overview
With the progress of science and technology, the development of industrial production and the improvement of people's living standards, the quality of products and industrial equipment has also changed. Products not only need corrosion resistance and durability, but also need to clean and beautiful appearance, beautiful and generous, with a certain ornamental value. Therefore, surface treatment technology has been widely used in a variety of manufacturing industries.
surface treatment technology has always played a huge role in protecting and adding value to metal materials. On the one hand, it can significantly reduce the rate of corrosion of metals (especially steel), save society a lot of wealth, and can be treated to give it a bright appearance. On the other hand, surface treatment technology can also try to give metals a variety of electrical, magnetic, optical, acoustic, chemical, mechanical and other related new functions.
Because most of the functions of the material are reflected in its surface layer, it is possible to make some low-cost metal materials after surface treatment to obtain wear resistance, reduce the mo, magnetization, conductivity, easy welding, chemical catalysis and other special functions, to multiply the value. This means that metal surface treatment technology can not only provide a flat, clean and beautiful surface for other processing processes, but also independently form a new type of surface material of great value. Its role in the development of manufacturing industry can not be ignored.
metal surface treatment technology covers a wide range of areas, the distance between disciplines is very small, very few people can master the whole content of surface treatment technology. In addition, as science and technology advance and demand grows, new technologies will be added to the list. However, this complex and important comprehensive technology has long been neglected by the academic community.
2 heat storage combustion technology works
heat storage combustion technology uses the heat exchange principle in the heat storage. When the flue gas is emitted, the high temperature flue gas is stored through the heat accumulator, the heat storage body releases heat, and the combustion air and gas are warmed up to a certain temperature, thus greatly reducing the fuel consumption of the heating furnace. This is a new technology to improve heat efficiency, energy saving and environmental protection of the furnace operation.
3 Heat Storage Incinerator (RTO) Process Principle
The two-bed RTO main structure consists of a high temperature oxidation chamber, two ceramic heat storage bodies and four switching valves. When the organic exhaust gas enters the heat storage body 1, the heat storage body 1 heats up, the organic exhaust gas is heated to about 800 degrees C after burning in the high temperature oxidation chamber after the high temperature clean gas through the heat storage body 2; Heat storage body 2 absorbs heat, high temperature gas is cooled by heat storage body 2, after switching valve discharge. After a period of time, valve switching, organic exhaust gas from the heat storage body 2 into, heat storage body 2 heating exhaust gas, exhaust gas is oxidized after combustion through the heat storage body 1, heat storage body 1 heat absorption, high temperature gas is cooled through the switching valve discharge. By switching periodically, organic exhaust gases can be treated continuously without the need for or a small amount of additional energy to achieve energy savings.
the VOC emission concentration and emission rate requirements are high, three or five heat storage beds can be designed, each heat storage bed in turn for heat storage - heat release - cleaning cycle process. For high concentrations (less than 20% LEL) of organic gases, the oxidized heat can be recovered from secondary heat, the recovery method can be: heating oil, steam, hot water, hot air, hot air filtered and directly reused, as shown in the figure.
3.1 Heat storage incinerator (RTO) process
4 VOCs exhaust gas treatment introduction
metal coating exhaust gas VOCs components are more complex, the main components are: toluene, xylene, ethyl acetate, cyclohexone, butyl ketone, isopropyl alcohol, butanol, etc., for aluminum coating with VOCs exhaust gas treatment, many domestic environmental protection enterprises developed a variety of equipment and processes.
4.1 Catalytic combustion method works by using VOCs in exhaust gases to effectively reduce the characteristics of oxidation conversion temperature under the action of catalysts, and adding catalysts as catalysts in equipment to reduce the oxidation conversion temperature of VOCs. First, the exhaust gas is heated by an external heat source to the catalytic combustion minimum temperature of 280 degrees C into the catalytic bed layer equipped with the catalyst, so that the exhaust gas containing VOCs is fully in contact with the catalyst and maintains sufficient dwell time. The heated VOCs rely on the active ingredients platinum Pt and palladium Pd in the catalyst to convert the organic matter in the exhaust gas into harmless water and carbon dioxide, thus purifying the exhaust gas.
disadvantage of this method is that with the extension of the equipment cycle, the performance of the catalyst is gradually reduced, and the processing effect is gradually reduced. At the same time, twice the maintenance cost is high, and the residue of non-methane total hydrocarbons exceeds the standard.
4.2 Thermal combustion method works by using VOCs in exhaust gases in the molecular chain at high temperatures easily hit by the principle of oxidation conversion, directly using external heat sources to heat the exhaust gas containing VOCs to the minimum oxidation conversion temperature of 750 degrees C. First of all, the exhaust gas containing VOCs is heated to the minimum oxidation conversion temperature of 750 degrees C, and stay enough decomposition time, so that the VOCs in the exhaust gas fully converted into water and carbon dioxide, so as to achieve the goal of purifying the exhaust gas. And under the right conditions can be used for residual heat, not only purifying the exhaust gas to protect the environment, at the same time, waste heat utilization to produce certain economic benefits. The method is suitable for any waste temperature of the occasion, the concentration of exhaust gas VOCs in the medium, high and low occasions can obtain a better treatment effect, due to the high lysing temperature of exhaust gas, fuel consumption, for heat can not be fully utilized in the occasion, resulting in high operating costs.
4.3 The method of adsorption of activated carbon (carbon fiber) works by using the physical adsorption of micropores inside activated carbon (carbon fiber) to absorb VOCs from the exhaust gas, so as to achieve the goal of purifying the exhaust gas. Since activated carbon adsorption only adsorption of VOCs, and does not really convert VOCs into harmless substances, and adsorption to a certain extent will reach saturation, so it is necessary to desorption regeneration. The methods of disenchonment include saturated steam dissoated solvent recovery method, normal pressure superheated steam de-attached catalytic purification method and direct catalytic combustion hot air continuous de-attachment.
the activated carbon adsorption/dissocing method is suitable for applications where the temperature <50 degrees C and the exhaust gas concentration <1,000 mg/m3. If the exhaust gas temperature is higher and the molecular thermal motion of organic matter is enhanced, the adsorption effect of activated carbon (carbon fiber) decreases significantly. If the exhaust gas concentration is high, the activated carbon (carbon fiber) will be rapidly saturated and must be continuously disassofiged. The disadvantage of this method is that ketones can be adsorbed but the regeneration effect is very poor, activated carbon is easy to saturate, relative purification efficiency is lower.
4.4 heat storage heat combustion its exhaust gas treatment principle and thermal combustion method is the same. The difference is that the heat storage method installed heat storage material instead of the heat combustion method heat exchanger, because the heat storage material has a large heat transfer area and heat capacity, so rely on the exhaust gas intake / exhaust direction of continuous switching, so that the heat storage material constantly absorb heat and release heat, to achieve energy-saving effect. The advantage of this method is that the installation of heat storage materials effectively improve heat exchange efficiency, usually up to more than 95%, far higher than the normal heat exchanger less than 60% heat exchanger heat exchange efficiency, in the lower exhaust gas concentration can achieve the lowest operating costs, exhaust gas concentration of 2g/m3 can achieve reactive operation, is currently the international common and the lowest energy consumption of the new treatment VCOs process method.
5 RTO Energy Saving and Emission Reduction Core
The key to using RTO energy saving and emission reduction is to optimize the intake and exhaust system of printing coating machines and coating equipment, increase the emission concentration of organic exhaust gas, and reduce the total exhaust volume. Therefore, the reactive loss of equipment is reduced, the investment in equipment is reduced, and the energy saving effect is more obvious.
Because, when the discharge of organic exhaust gas VOCs concentration is large, more than the RTO reactive operating balance point (general concentration of 3g/m2) or more heat, can be used back to the printing coating drying tank, as well as from the RTO discharge processing After the gas (temperature is more than 60 degrees C higher than the infested air), through the heat exchanger to preheat fresh air, and then the preheated gas to the oven, which can greatly save the energy consumption of the heating oven, for enterprises to create great economic benefits, energy conservation and emission reduction, worthy of great promotion.
for the steel drum manufacturing industry, the emission concentration is less than 2.5g/m2, also optional wheel or activated carbon adsorption concentration exhaust gas, and then the concentrated gas to RTO combustion.
6 Conclusion
Metal coating line exhaust gas using heat storage incineration process equipment for environmental protection treatment is very suitable and ideal, not only excellent treatment results, can fully meet the emission standards, but also the most economical operating energy consumption, is the metal coating enterprise environmental protection treatment of the best choice.