How do cigarette package printing enterprises deal with VOCs? Don't deal with it blindly!

Speaking of tobacco packaging, it broadly refers to the packaging materials used in the production of cigarettes, mainly including cigarette paper, filter rod forming paper, splicing paper, lining paper, frame paper, box packaging paper, strip packaging paper, label sealing paper, cigarette cartons, etc; In a narrow sense, it only refers to box wrapping paper and strip wrapping paper (commonly known as cigarette packs, decoration or trademark paper). It can be seen that the production of most tobacco packaging materials can not be separated from printing, which covers gravure printing, offset printing, screen printing, flexographic printing and other processes. Facing the decisive year of pollution prevention and control in 2020, and the general requirements of environmental protection governance of the country that "adhere to the same direction, do not reduce efforts, highlight the precise, scientific and legal pollution control, and promote the sustainable improvement of ecological environment quality", cigarette packaging and printing enterprises have become the key work to be solved urgently.
The author is in Wuxi ATI Group Technology Co., Ltd. (ATI), a Sino US cooperation high-tech enterprise specializing in the design and manufacture of waste gas treatment equipment, which has completed more than 80 VOCs waste gas treatment projects with a number of domestic cigarette package printing enterprises, and has achieved good ecological, environmental, economic and social benefits. Here we share our VOCs waste gas treatment experience with you.

VOCs (Volatile Organic Compounds) are volatile organic compounds, which participate in atmospheric photochemical reactions and are important factors to form ozone (O3) and affect air quality (PM2.5). VOCs waste gas from cigarette package printing enterprises is formed due to the volatilization of solvent based ink, alcohol water based ink, thinner and offset printing products using fountain solution, car wash water, etc. in the production process of cigarette packages. VOCs waste gas contains benzene, toluene, xylene, ethanol, ethyl acetate, n-propyl ester, n-propanol, isopropanol and other volatile organic compounds. Under the increasingly strict environmental protection requirements, the organized VOCs emission of cigarette package printing enterprises is the premise and guarantee to ensure the normal operation of enterprises.
According to printing methods, domestic cigarette package printing methods mainly include web gravure printing and sheet fed offset printing, including:
Web gravure printing mainly uses solvent based ink, supplemented by a small amount of alcohol water based ink. Its products account for more than 60% of the total number of cigarette packets, and a large amount of high concentration VOCs waste gas is generated in the process of gravure printing production;
Sheet fed offset printing mainly uses UV ink, and its products are mainly medium and high-end cigarettes, which generate low concentration VOCs waste gas during offset printing production;
Other printing methods, such as single concave printing and screen printing, are not the core printing methods of cigarette packs. With the goal of achieving special effects, they mainly use alcohol water based ink and UV ink, and generate very low concentrations of VOCs in the production process.
According to the emission mode, VOCs waste gas of cigarette package printing enterprises can be divided into two categories: organized emission waste gas and unorganized emission waste gas. Including:
The organized exhaust gas mainly comes from the printing process, especially the drying process of printing equipment. It is usually equipped with a special collection system and emission system. The exhaust gas has the characteristics of complex composition, high cleanliness, stable temperature and varying concentration due to different products;
The unorganized exhaust gas mainly comes from VOCs waste gas volatilized from various processes, which is distributed throughout the production workshop. The waste gas has the characteristics of wide distribution space and low concentration.
According to the concentration of waste gas, VOCs waste gas of cigarette package printing enterprises can generally be divided into two categories: high concentration VOCs waste gas and low concentration VOCs waste gas. Including:
▪ High concentration VOCs waste gas generally refers to VOCs waste gas discharged directly from the oven during the production of gravure printing machine, and the concentration of waste gas is generally not less than 2.0g/m3;
The low concentration VOCs waste gas generally refers to the exhaust gas from the gravure printing machine, offset printing machine, screen printing machine, single gravure machine and other equipment, and the exhaust gas from some places (such as ink warehouse, waste warehouse, ink mixing room, etc.). The concentration is generally lower than 300mg/m3.
Analysis of VOCs Waste Gas Treatment in Cigarette Packaging Printing Enterprises

At present, the most effective, reliable and popular treatment method for VOCs waste gas treatment in cigarette package printing field is thermal decomposition method, which uses RTO, also known as regenerative oxidation decomposer. Its basic principle is to fully react VOCs in waste gas with O2 under high temperature conditions, generate CO2 and H2O, and release heat at the same time:

The temperature of the RTO combustion chamber is generally around 820 ℃. Almost all VOCs in the exhaust gas fully react with O2 to generate CO2 and H2O, and release heat at the same time. Moreover, RTO is not sensitive to changes in the air volume, concentration, composition, etc. of VOCs in cigarette packets, and has high reliability. Its purification efficiency is more than 99%. It is one of the VOCs treatment equipment with the highest purification efficiency at present. The high-temperature clean gas directly discharged after the oxidation of waste gas is designed to flow through the ceramic heat storage body, and most of the heat energy contained in it is stored through the ceramic heat storage body, and then the gas is discharged. This regenerative chamber is used to preheat the subsequent normal temperature exhaust gas through valve switching. After repeated operation, its thermal efficiency can reach more than 95%, which can greatly save energy consumption.
Because RTO has high thermal efficiency and purification efficiency, the equipment can efficiently complete the treatment of VOCs waste gas under the condition of energy saving, and has high reliability and long life (can exceed 30 years). Therefore, RTO is the most typical equipment used to treat VOCs waste gas in the packaging and printing industry at home and abroad.

(1) Treatment of High Concentration VOCs Waste Gas from Gravure Printing Machine
Since more than 60% of cigarette packs are printed by web gravure printing machines, and solvent based inks are mainly used in the production process, even if some "water-based inks" are used, they also contain a high proportion of ethanol, and VOCs waste gas generated during the ink drying process is directly discharged through the oven.
If the concentration of VOCs waste gas discharged is high and above 1.8g/m3, such VOCs waste gas can be sent to RTO for direct combustion treatment, and RTO can be in a self-sustaining state (RTO equipment is in normal operation without additional energy consumption);
If the concentration of VOCs waste gas discharged is low but between 0.3~1.8g/m3, it can be given priority to implement the LEL air reduction and concentration enhancement transformation for the circulation air system of the gravure printing machine oven, and then input the enriched VOCs waste gas (in principle, the concentration is above 1.8g/m3) to RTO for direct combustion treatment;
If the concentration of VOCs exhaust gas is extremely low and below 0.3g/m3, when it is impossible to use the air reduction and concentration enhancement method to increase the concentration of exhaust gas, the runner can be considered for concentration treatment (not recommended under normal circumstances, because this method has the advantages of large investment, high energy consumption, high operation and maintenance and poor stability).
(2) Treatment of other low concentration VOCs waste gas
For the very low concentration VOCs waste gas generated during the production of such equipment as sheet fed UV offset printing, sheet fed gravure printing, screen printing and web paper gravure UV curing in cigarette packaging printing enterprises, due to the characteristics of complex components, extremely low concentration, large air volume and wide dispersion, when selecting the treatment method, it is necessary to consider the factors such as equipment investment cost, operating cost and stable compliance, It is also required to follow the relevant requirements of the national policy of "encouraging enterprises to adopt multiple technology combination processes to improve VOCs governance efficiency".
It is suitable for cigarette package printing enterprises to adopt a variety of technology combination processes to treat low concentration VOCs waste gas. The conventional choice of "photocatalysis technology+activated carbon adsorption technology (equipped with desorption process)" or "two-stage activated carbon adsorption desorption technology" can not only achieve effective treatment of low concentration VOCs waste gas and achieve standard emissions, but also achieve the goal of less investment, low operation and good results.
The reason why the zeolite runner concentration technology is not selected to treat such low concentration VOCs waste gas is that the UV ink used for offset printing, silk screen printing and gravure printing generates VOCs waste gas when it is dry. The special components contained in the UV ink will damage the zeolite runner, which will lead to frequent replacement of zeolite. The operation cost of waste gas treatment is too high, and the different inlet temperature or humidity of VOCs waste gas have a great impact on the removal efficiency, There is a potential risk that VOCs waste gas will not reach the standard after being adsorbed by the zeolite runner.
Greenization is the foundation and guarantee of sound coordination and high-quality interaction between the printing industry and resources and environment, and other industries, and is the only way for enterprises to develop with high quality. "The majestic road is like iron, and now we are stepping forward from the beginning". In the face of the new standards and requirements of national environmental protection governance, Wuxi ATI Group Technology Co., Ltd. is willing to cooperate with cigarette package printing enterprises to make more contributions to the stable and healthy development of the motherland's green mountains and rivers and cigarette package printing enterprises.