With the increase of various environmental protection restrictions on heating methods, the cost of corporate thermal energy is getting higher and higher. Coupled with the collection of VOCs emission fees and strict restrictions on excessive emissions, the environmental protection costs of packaging and printing companies are also increasing. Energy saving and emission reduction through technology upgrade has become the only way for enterprises. How to choose the right technology route and equipment becomes the major issue for entrepreneurs. Proper choice can enhance competitiveness, gain sustainable development space, and make the enterprise stand out. If you choose it incorrectly, you will It is difficult for enterprises to continue to develop if they lose their competitiveness due to rising costs or continue to be under pressure from environmental protection.
First, the current common gravure printing machine drying system
Most gravure printing presses currently rely on the operator to manually adjust the operating status of the drying system based on practical experience. The air intake of each unit depends on the opening of the damper to balance the air pressure difference between the air inlets, thereby adjusting the air volume required by each unit. At the same time, in the case of multiple units exhausting in parallel, the exhaust valve needs to be adjusted to balance the air pressure of the exhaust outlets of each unit to achieve the exhaust demand of several drying units. However, because the exhaust air is adjusted at multiple points and affects each other, the air pressure difference between the points of the system is large, which is likely to cause leakage of the exhaust gas from the oven. The smaller the circulating air volume required by the drying unit, the more difficult it is to adjust the balance. The oven reduces leakage, and coupled with this feeling alone, manual manual adjustment is a tedious and difficult to grasp. Insufficient experience will fall into the dilemma of getting worse and worse, so production operators usually do not fine-tune in actual production. . In order to meet the improvement of most of the process air volume and the working environment, the air volume is generally adjusted to be relatively large. This not only increases the heating energy consumption and the exhaust fan operating power, but also increases the subsequent waste gas treatment input and operating costs. .
In addition, for the purpose of energy saving, most drying systems are equipped with return air. When the unit printing solvent volume is large or the return air ratio is large, even if the total exhaust air volume is large, the unit exhaust air volume may be insufficient, and dry gas may appear. If the solvent concentration exceeds the lower safety limit, there is a hidden danger of explosion.
To sum up, the problems of the existing system mainly include: difficulty in adjusting and matching the system, excessive exhaust volume, excessive heating energy consumption, hidden safety hazards, and high environmental protection costs.
Common current common solutions
In order to optimize the gravure drying system, many companies have adopted corresponding transformation measures.
First we analyze the relevant elements of gravure printing machine drying:
Purpose: To completely evaporate the solvent in the ink.
Countermeasure: Use hot air to fully contact the ink on the film surface to transfer heat and remove the solvent.
Objective: To ensure high speed and low energy consumption under the premise of ensuring safety and quality.
The controlling factors of the drying process are ink formula, speed, temperature, and air volume. The limiting factors are safety, appearance, residue, and energy consumption. The environmental factors include the leakage of oven exhaust gas. It is very difficult to balance so many factors to obtain a better result. For example, in order to obtain high speed, lengthening the oven and changing the air nozzle are used to lengthen the time and efficiency of heat and mass transfer, but the lengthening of the oven will also cause problems such as overprinting accuracy.
For existing equipment, we can analyze under the assumption that the ink formula and speed are the same:
1.The temperature is too high, causing problems such as bubbles, film deformation, and excessive energy consumption;
2.The temperature is too low, the product is not completely dried, and the solvent residue exceeds the standard;
3. The air volume is too large, causing problems such as film jitter, ink drag, and excessive energy consumption;
4. The air volume is too small, the drying is not thorough, the solvent residue exceeds the standard, and there are potential safety hazards.
Due to the large impact of energy consumption on production costs, many enterprises use low-temperature and large-volume air for production. The advantages are proper control of energy consumption under the premise of ensuring safety and quality, and low requirements for thermal energy grade. Solar energy, heat pumps, etc. can be used. Heating, further reducing heating costs.
However, the large air volume increases the difficulty and cost of exhaust gas treatment. The increase in investment and operating costs of exhaust gas treatment equipment will completely eat up the energy-saving benefits previously obtained, leading to a decline in corporate competitiveness. Therefore, the current mainstream method is not desirable.
Advantages of ESO system
ESO adopts a systematic method to study the problem, cracks the problem from the root, and focuses on the following key elements:
Preventing accidents caused by excessive solvent concentration is the first prerequisite. ESO uses the safe total control technology to determine the maximum solvent volatility of the gravure printing machine, calculate the safe air volume based on the 25% LEL required by the safety regulations, and control the total air volume. Keep the highest concentration in the system below 25% LEL to ensure safety.
Residual solvent is a key indicator of product quality. Residual is caused by incomplete solvent volatilization. Volatilization is carried out by mass and heat transfer. The fundamental factor affecting the volatilization rate is gas-liquid equilibrium. The difference between the gas phase equilibrium concentration and the actual concentration forms mass transfer. The driving force and the concentration difference are directly related to the temperature and air volume. Under a certain air volume, the higher the temperature, the larger the concentration difference, and the more thorough the drying.
The common ink formulations of gravure printing presses mainly include ethyl acetate, propyl acetate, and isopropanol. The saturation concentrations of the three solvents at different temperatures are shown in the table below. Because the relative volatility of ethyl acetate is much higher, the residual solvent is Propyl acetate and isopropanol were the main ingredients. The low content of propyl acetate and isopropanol was detected in the solvent condensed and recovered by the compound machine, which verified this conclusion.
At a safe air volume, the total volume concentration of the solvent is less than 0.5%. The effect of the air volume on the concentration difference is much lower than the temperature effect. Choosing the highest possible temperature can help reduce solvent residues. In other words, the concentration of dry gas The effect of residue is almost negligible, the key is temperature and drying time, and drying time is related to production speed and oven length.
Based on the above analysis, ESO uses the maximum temperature allowed by the material under safe air volume conditions, and gradually increases the solvent evaporation process to reduce the solvent residue and ensure the drying quality.
Since the oven cannot be completely closed, a negative pressure must be maintained to ensure that the exhaust gas does not leak. However, excessive negative pressure will cause excessive ambient air to be drawn into the oven, which not only increases the difficulty of exhaust gas treatment, but also causes uneven temperature and solvent residues. If the negative pressure is too small, it is difficult to overcome the influence of dry gas flow pressure, and exhaust gas leakage causes work The environment is harsh.
ESO adopts automatic pressure balancing technology, which automatically follows the pressure of the air sent and exhausted from the oven, so that the oven is stabilized at a set negative pressure state, and is not affected by other unit ovens and air exhaust fans, so that the amount of incoming and outgoing air is stabilized at the required drying. In terms of process air volume, a stable negative pressure in the tank can ensure that unnecessary external air intake is reduced without the exhaust gas leaking. The minimum intake air volume meets the need to prevent leakage, overcomes the problem of losing sight of each other when adjusting traditional equipment, and cooperates with successively increasing the solvent volatilization process, which not only meets the need for energy saving, but also achieves the goal of safe air volume control, while taking into account the reduction of exhaust emissions Total expectations.
The ESO air volume is equivalent to the air volume of a drying unit of a traditional drying system. The size is adjusted according to the requirements of the safe air volume. The unit air volume adjustment is simple and does not affect other units. The air and the heat contained are directly reused until the final drying unit is discharged from the drying system. The heating energy consumption is reduced. At the lowest point, in addition, the exhaust gas emission determines the subsequent exhaust gas treatment volume. ESO makes the subsequent exhaust gas treatment input cost and operating cost greatly reduced; the exhaust gas concentration at the unit exhaust port of the last group of drying units through which the dry gas flows through the system is the entire drying. The highest concentration point of the system, single-point online monitoring is implemented at the highest exhaust gas concentration point, making it easy for enterprises to implement and monitor the entire production process. The exhaust air volume of the drying system is adjusted according to the exhaust gas concentration to ensure that the exhaust gas concentration is below the safe limit. If the safety is a bit safe, the entire drying system is safe. , Completely eliminate the hidden dangers of explosion of production equipment; therefore, ESO has the advantages of simple and stable system, simple adjustment, small exhaust volume, low energy consumption, no hidden dangers, and low environmental protection and management costs.
Fourth, the conclusion
ESO captures the key elements to solve the problem, so the effect is significant and the cost is low. ESO has low implementation cost, short cycle and quick results. The launch of ESO is undoubtedly a boon for industries such as packaging and printing, and provides a fast way for the industry to save energy and reduce emissions. Taking a 9-color gravure printing press as an example, the renovation cost is less than 100,000 yuan, the renovation cycle is about one week, the energy saving efficiency in winter is more than 70%, and the product solvent residue is significantly reduced.
The owner of ESO's patent is Guangdong Huanjia Energy Saving Technology Co., Ltd. Huanjia Energy saves its patent licensing and technical services to promote ESO applications at an ultra-high cost performance. Comprehensive benefits, accelerate the transformation and upgrading of the industry, and quickly realize the social value of ESO.