Flexible packaging production safety concentration control is the most critical
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For the flexible packaging industry, VOCs generated during the production process are the most important safety concerns of the company. To ensure safety, the concentration of exhaust gas produced during production cannot exceed 25% of the lower explosion limit (25% LEL).
With the successful launch of ESO, the technology can help flexible packaging gravure companies reduce hidden costs and bring new profit points. According to the test, ESO can reduce the printing quality and reduce the solvent residue while reducing wind and energy. However, many current flexible packaging gravure companies still have concerns about the safety of ESO enrichment effects.
Below, the author on the gravure equipment after the connection of ESO, how to ensure production safety, detailed analysis and explanation, hope to help the industry to eliminate concerns and achieve VOCs standards discharge.
VOCs emission characteristics and control
In general, the film gravure process includes a white full version and a plurality of ink layouts. The total amount of solvent volatilization in the color ink layout of most printed materials does not exceed the amount of 2 full color inks, and the total amount of solvent volatilization in the full color version of the ink is generally 30% to 50% of the full version of the white ink.
It can be seen that in the gravure printing of the film, the solvent of the white ink full version has the largest amount of evaporation, and generally accounts for 50% or more of the total amount of solvent volatilization, that is, the main link of generating high concentration VOCs in the film gravure process is white ink full printing. Therefore, after the ESO is connected to the gravure printing device, the airflow in the air inlet and exhaust manifold of the ESO is directed, and the full version of the white ink should be ranked last, as shown in FIG. Moreover, according to the difference between the printing and the printing, the airflow direction of the ESO inlet and outlet air mains is set in a targeted manner. In the last color of the white ink in the printing, the airflow in the ESO inlet and exhaust manifold is from the unwinding end to the winding end; the opposite is printed, the white ink is in the first color, and the airflow in the ESO inlet and exhaust manifold is From the winding end to the unwinding end.
ESO selection
The ESO selection shall be determined according to the printing process parameters of a product with the largest amount of solvent volatilization in the conventional printed matter of the flexible packaging gravure printing enterprise. For example: an 8-color printing machine of a flexible packaging gravure printing company, when producing a certain printed matter, the total amount of solvent volatilization is the largest, about 70kg / h, the solvent component is ethyl acetate, n-propyl ester, etc. (here is convenient for calculation, all press Calculated by ethyl acetate, the lower limit of ethyl acetate explosion is 85.7g/N.m3), wherein the total amount of solvent evaporation of 7 color ink plates is about 30kg/h, and the evaporation amount of a white ink full version is about 40kg/h.
From the overall analysis (temporarily not considering the oven leak), the total amount of solvent volatilization is 70kg / h, to ensure safety (exhaust gas concentration ≤ 25% LEL, about 21.4g / N.m3), the total amount of exhaust air (ie fresh air replenishment) The amount should be guaranteed above 3300N.m3/h. At this time, the concentration of exhaust gas in the oven of each section of the gravure press is as follows.
(1) color ink layout
We consider all the ovens of the ink-coloured layout as a whole in series. The total amount of solvent evaporation of the seven ink-printed plates is about 30kg/h, so as long as the fresh air of 1400N.m3/h can guarantee any ink in the oven. Concentration ≤ 25% LEL (special case is considered). When the fresh air replenishment amount is 3300N.m3/h, as long as the dry air volume of each ink screen is ≥1400N.m3/h, the gas concentration in all the ink screen ovens will have a large safety margin.
(2) White ink full version
Before entering the white ink full version of the oven, the gas flow rate in the ESO inlet and exhaust manifold (point A in Figure 1) is 3300 N.m3/h, and the concentration is 9.1 g/N.m3 (10.6% LEL). In the fresh air of the white ink full version of the oven, the solvent evaporation amount is 40kg/h. To ensure that the concentration in the oven does not exceed the standard when drying, the drying air volume of the oven must be ≥3300N.m3/h, that is, the dry air volume ≥ fresh air filling amount .
(3) Oven leak
In the actual work, the whole oven is in a state of micro-negative pressure, so that the air in the workshop can enter the ESO through the gap of the oven. Although this will lead to an increase in the final exhaust volume of the ESO, it is beneficial to safety because of the increase in air volume. Will reduce the exhaust gas concentration.
In the above analysis, the dry air volume is only analyzed from a safety perspective. In fact, the dry air volume is also affected by factors such as the oven structure and the drying quality requirements. Therefore, the final determination of the dry air volume during ESO selection should consider various factors.
After the oven of the gravure printing machine is connected with the matching ESO, the safety of the whole drying process can be fundamentally ensured by setting the appropriate fresh air replenishment amount according to the total amount of solvent evaporation. This involves the three core technologies of ESO: wind pressure balance control technology, total control enrichment technology and intelligent algorithm control technology, which will not be described here.
In addition, the highest concentration of VOCs throughout the drying process is in the white ink full version of the oven, therefore, only need to set a LEL detection point on the oven exhaust line (as shown in Figure 1), and ESO safety protection control By linking the programs, you can get double security and achieve a balanced double balance between economy and safety.