The packaging and printing industry has become the first batch of pilot industries for VOCs sewage charges, allowing more and more enterprises to reach the crossroads of governance of VOCs. Up to now, among the 15 provinces and cities that have announced the charging standards, the charging standards vary from place to place, and the difference between the highest and the lowest is dozens of times. The charging standards for VOCs in Shanghai are comparable to those in Beijing. The high fees make printing companies even worse. If printing companies want to survive, they have to reduce VOCs emissions, including source reduction, process control and end management.
Gangbao Color Printing (Shanghai) Co., Ltd., the company where the author works, is a printing company mainly based on offset printing. According to DB31 / 872-2015 Shanghai "Air Pollution Emission Standards for Printing Industry" (see Table 1) Value requirements, the maximum allowable emission concentration of 50 mg / m3. To this end, according to the actual situation, the company has explored a set of treatment plans to effectively reduce VOCs emissions, and share it with industry insiders.
If the concentration of VOCs at the main nodes in the air of the company's offset printing workshop can be controlled below 50 mg / m3, then worrying end management is simple. Because the concentration of non-methane total hydrocarbons in the exhaust pipe after treatment is also required to be below 50 mg / m3. The author practiced this idea along the following path.
Step 1: External inspection
The main consumable materials of the offset press workshop include ink, fountain solution, and car wash water to be checked to confirm that it does not contain benzene, toluene, xylene and benzene series. If the supplier already has a corresponding test report, there is no need to repeat the test. After testing, all raw materials selected by the company are qualified.
Step 2: Instrument preparation
Purchase a VOCs detector. The author purchased the PGM-7300. This instrument has two shortcomings: (1) It cannot directly display how many milligrams per cubic meter, but must be converted by ppm. Usually, the ppm reading is multiplied by 2.5 to obtain an approximate result. ⑵ This detection instrument is PID (photoion gas detector), which is different from the official FID (hydrogen flame ionization detector), but it will not produce errors of orders of magnitude, and it is feasible as a reference. The advantage of this instrument is that it is easy to carry and cheap.
Step 3: On-site assessment
On the premise of not containing benzene, toluene, xylene and benzene series, the impact of VOCs of the main materials is evaluated, and the peak value of VOCs is tested in a closed workshop.
â‘ After the tank lid is opened, detect the concentration of VOCs above the tank.
â‘¡During the printing process, detect the concentration of VOCs above the ink roller.
â‘¢During the printing process, detect the concentration of VOCs near the layout.
â‘£After cleaning the blanket, check the concentration of VOCs between the units.
⑤Detect the color of VOCs above the ink roller when changing colors in car wash.
At this time, we must pay attention to the control of some details to reduce the negative effects as much as possible, including the cover of the container, do not use excessive amounts of car wash water, mix or cross-use car wash water, and use the fountain solution in the tank as little as possible alcohol.
Step 4: Set standards
In the third step only ⑤ when washing the car and changing the color, the peak value of VOCs concentration above the ink roller can be higher, but not higher than 200 ppm, and the other peaks of ①②③④ should not be greater than 20 ppm. Such standards may feel relatively high at the beginning of implementation, but after continuous improvement of suppliers or introduction of new suppliers, practice has shown that it is not particularly difficult. Over the mountain, the target is closer.
Step 5: Determine the plan
According to the requirements of one plant and one plan or one process and one plan, the closures, gas collection hoods, pipes, processing equipment, fans, and detection ports shall be designed and manufactured in accordance with the relevant requirements. Of course, there is a lot of choice at this time, for example, the workshop space is below 2 000 m3, then the air volume of 5 000 m3 / h is enough, and the 500 kg activated carbon treatment box can support more than three months. As long as you can continue to ensure that the workshop's own VOCs concentration has reached the standard, then it depends on your requirements, whether it is only up to the standard or 50% lower than the limit. Because according to the standard requirements, the VOCs concentration below 25 mg / m3 can be reduced by half. In production practice, it is actually not difficult to achieve VOCs below 25 mg / m3.
Step 6: Implement management, formulate procedures, and clarify responsibilities
Ensure the normal operation of the equipment, maintain and maintain records in a timely manner, and regularly invite third-party testing and acceptance testing by the environmental testing department.
To sum up the above six steps, it is actually a sentence: pay close attention to source reduction and implement end governance. Through detailed analysis of the company's VOCs production links, causes, scale and main emission sources, and then through the implementation plan shared in this article, the factory's various emission indicators are lower than the standard requirements, effectively reducing VOCs emissions.
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