"Safety" is the first important problem in the production process of an enterprise. Safety production is related to the property of the enterprise and the life safety of employees, so it can not be ignored. However, safety production usually means more investment. How to invest less resources and obtain more profits under the premise of ensuring safety production is a key issue for every manufacturing enterprise.

For the packaging and printing industry, VOCs waste gas generated in the production process is the most important safety concern. In order to ensure safety, the concentration of VOCs waste gas generated in the production process should not exceed 25% (25% LEL) of its lower explosion limit. In the past, in order to ensure the safety of production, the packaging and printing industry often adopted the method of increasing the exhaust air volume and reducing the return air volume, which would lead to the increase of energy consumption and the invisible cost of enterprises. With the fierce competition in the industry, reducing hidden costs has become an important measure to increase profits! From the cooperation case between Guangdong huanbaojia Energy Saving Technology Co., Ltd. (hereinafter referred to as huanbaojia) and Shanghai Lingbo plastic packaging Co., Ltd. (hereinafter referred to as Shanghai Lingbo), we can confirm that the wind reduction and energy saving scheme can indeed bring new profit points for enterprises. After solving the problem of profit, many enterprises began to worry about solvent residue and production safety. Shanghai Lingbo's first ESO operation test report has proved to the industry that wind reduction and energy saving can also ensure product quality and reduce solvent residue. However, enterprises still have concerns about the safety of concentration effect caused by ESO wind reduction and energy saving. Next, we will make a detailed analysis on how to ensure production safety after the printing equipment is connected with ESO.

Generally speaking, the film printing process will include a white ink full plate and several color ink plates. Through a long-term user survey, huanbaojia company found that the total amount of solvent volatilization in most printing products is less than that of two full color inks. The solvent volatilization of full color ink is generally 30% - 50% of that of white ink, and the solvent volatilization of white ink full page is the most, which generally accounts for more than 50% of total solvent volatilization. It can be seen that the main link of producing high concentration VOCs waste gas in printing process is white ink full plate printing. Therefore, after the ESO is connected with the printing equipment, along the air flow direction in the main air inlet and exhaust pipe of ESO, the white ink full plate is arranged at the last place, as shown in Figure 1. Specifically, according to the difference between the surface printing and the inner printing, the white plate is in the last color, and the air flow direction in the ESO inlet and exhaust main pipe is from the unwinding end to the winding end; on the contrary, when the white plate is in the first color, the airflow direction in the ESO inlet and exhaust main pipe is from the winding end to the unwinding end.
The selection of ESO is based on the printing process parameters of the product with the largest solvent volatilization among the conventional products. For example, when a user's 8-color printing machine produces a product, the total amount of solvent volatilization is the largest, about 70kg / h, and the solvent components are ethyl acetate, n-propyl ester, etc. (here, for convenience, the ethyl acetate explosion limit is 85.7g/n.m3). Among them, the total amount of solvent volatilization of 7 color ink plates is about 30kg / h, and that of one white ink full plate is about 40kg / h.
Based on the above-mentioned specific data and combined with figure 1, we will explain how ESO can ensure production safety. From the overall analysis (the influence of oven leakage is not considered for the time being), the total amount of solvent volatilization is 70kg / h, to ensure safety (waste gas concentration ≤ 25% LEL, about 21.4g / n.m3), the total amount of exhaust air (i.e. fresh air supplement) should be more than 3300n.m3/h. Let's analyze the concentration in each section of the printing press when the fresh air supplement amount is 3300n.m3/h.
First of all, it is difficult to determine the solvent volatilization of each color and ink layout. Therefore, we consider the drying oven of all color and ink layout as a whole in series. The total amount of solvent volatilization is about 30kg / h, so as long as the fresh air of 1400n.m3/h can ensure that the concentration in the drying oven of any color and ink plate is ≤ 25% LEL, and the specific reconstitution According to figure 1, it is necessary to ensure that the fresh air supplement amount is not less than 1400n.m3/h, and the dry air volume of each color ink plate is not less than 1400n.m3/h. When the fresh air supply is 3300n.m3/h, as long as each drying air volume is ≥ 1400n.m3/h, the gas concentration in the oven of all color ink plates will have a large safety margin.
After analyzing the white ink full plate, it is not difficult to calculate that the gas flow rate in the main exhaust pipe (i.e. point a in Figure 1) before entering the drying oven of white ink full plate is 3300n.m3/h, and the concentration is 9.1g/n.m3 (10.6% LEL). This air flow is equivalent to the fresh air of the white ink full plate drying oven. Here, the solvent volatilization is 40kg / h. to ensure that the concentration in the oven does not exceed the standard during drying, the drying air volume of this oven must be It must be no less than 3300n.m3/h, i.e. the dry air volume must be greater than or equal to the fresh air supply.
Finally, the influence of oven leakage on the concentration is analyzed. In fact, it is difficult for the oven to be completely free of leakage. Therefore, in order to ensure the internal production environment of the workshop, the oven is in a micro negative pressure state during the actual work, which will make the air in the workshop enter into the ESO through the gap of the oven, which will lead to the increase of the final ESO exhaust air volume, increase energy consumption, but on the aspect of safety But it is a positive effect, because the increase of air volume will reduce the concentration of exhaust gas.
In the above analysis, the drying air volume is only analyzed from the perspective of safety. In fact, the drying air volume will be affected by the oven structure, drying quality requirements and other factors. Therefore, the final determination of the drying air volume should be based on the comprehensive consideration of various factors before taking the maximum value.
Through the above analysis, after the dryer of the printing machine is connected with its matching ESO, as long as the appropriate amount of fresh air is set according to the total amount of solvent volatilization, the safety of the whole drying process can be fundamentally guaranteed, which is the total amount control. As for how to realize ESO concretely, it involves three core technologies of ESO: wind pressure balance control technology, total amount control enrichment technology and intelligent algorithm control technology, which will not be discussed here. In addition, we can find that the highest concentration of the whole drying process is in the white ink full plate drying oven. Therefore, we only need to set a LEL detection point on the exhaust pipe of the drying oven (as shown in Figure 1) and linkage with the safety protection control program of ESO, we can get double security guarantee and realize the double effect balance of economy and safety.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service.
The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries.
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