As a gravure printing practitioner for many years, the author, from the perspective of gravure printing users, has some experience and suggestions on the end management of VOCs in gravure printing. I am here to share with you.

Application of terminal treatment technology of VOCs for gravure printing

From 2001 to 2007, in some large and medium-sized cities across the country, there were many projects for the end treatment of gravure VOCs, which basically focused on "activated carbon adsorption+catalytic combustion", but most of these projects did not actually operate. The main purpose of launching the project was to deal with the emission of VOCs after the environmental assessment acceptance, rather than to control VOCs.

From 2007 to 2012, various gravure printing enterprises above designated size started VOCs terminal treatment projects in succession, mainly focusing on "recovery". Ultra low emission dust meters such as activated carbon (carbon fiber) adsorption+recovery were launched for three main purposes: expected economic benefits of recovery, environmental assessment and acceptance, and enterprises' willingness to take the initiative in treatment.

From 2012 to 2014, many gravure printing enterprises took the initiative to launch VOCs terminal treatment projects, but they basically focused on "recycling", mainly because during the period when haze locked cities across the country, the country first proposed to include VOCs in pollution prevention, and the environmental pressure on gravure printing enterprises increased sharply.

Since 2015, the packaging and printing industry has been listed as a pilot industry of VOCs pollution charge by the state. The gravure printing industry is facing huge environmental pressure due to the use of a large number of organic solvents and direct discharge in the production process. Based on the substantial collection of VOCs pollution charges, the increasingly stringent emission standards for gravure printing, and the possibility of the installation of automatic online continuous detection in the future, the mainstream VOCs end treatment technology in the whole gravure printing industry began to rapidly shift to combustion (RTO). During the same period, a large number of combustion projects were rapidly promoted in large gravure printing enterprises across the country, spreading in a large area. However, up to now, the actual operation is still relatively small and remains to be observed. However, in the same period, many cities and prefectures put forward a request for short-term and rapid treatment within a specified time limit. Due to the situation, capital, and the complexity of technology and market, most gravure printing enterprises hastily chose temporary transitional measures such as plasma, photocatalysis, catalytic combustion, photolysis and other investment of hundreds of thousands, which is also a great waste.

Selection of Treatment Scheme for VOCs End of Gravure Printing

Based on the current economic, technological, environmental, market and other conditions, the author believes that gravure printing enterprises must pay attention to the following three aspects before choosing VOCs end treatment scheme.

1. Explore

Gravure printing enterprises must find out the overall situation of VOCs emission, concentration, composition, etc., and consider the scheme as a whole. In particular, the air volume, concentration, and law of waste gas at the inlet of the treatment facilities need to be repeatedly confirmed. This is the basis for the design and operation of all projects, and must be repeatedly confirmed in many ways.

2. Air reduction and site closure

Optimize the structure of the oven of the gravure printing machine, reduce, merge and concentrate waste gas, reduce the total amount of emissions, and control the total amount of waste gas per color to be less than 1000m3/min or less (but the internal circulation air volume and air pressure of the oven remain unchanged), which can be achieved through manual hot air recycling, automatic LEL hot air recycling and other measures. The concentration of waste gas after concentration is generally greater than 2.5g/m3, reaching the RTO self-sustaining concentration. After operation, the gravure printing enterprise only needs to bear the power cost of RTO inverter fan. However, the air reduction design of the gravure printing machine oven involves oven design, unorganized reduction, ink groove closure, system insulation, drying principle, gravure printing process, hot air recycling, etc., which requires scientific research institutes, gravure printing machinery plants, hot air system integrators Gravure printing enterprises and others have completed the overall planning (there are more than ten thousand gravure printing machines and hundreds of gravure printing machine factories in China, but most of the drying systems are based on the systems of foreign machine factories 20 years ago, and there is no system that can be developed and designed independently), so as to achieve the goal of effective drying at the given speed (but the exhaust gas concentration is lower than the safety value). Here, the author suggests that the gravure printing industry introduce energy consumption grades and energy efficiency labels, so that it can better make overall planning from the beginning of design, manage and utilize energy consumption, and greatly promote the progress of the industry.

Site sealing is an important measure to reduce unorganized emissions. Although there are few in foreign countries, there are domestic requirements. In addition to ink tank sealing, negative pressure in the oven, and cancellation or combination of ground ventilation, the relative sealing of the printing machine should also be included in the agenda.

3. Choose carefully

Based on the current environmental protection policies, governance technologies, and various complicated VOCs emissions of gravure printing enterprises, even if the gravure printing enterprises really invest in VOCs governance, it is extremely difficult to formulate a short-term effective and reasonable scheme. The author has seen too many failed cases, especially the current practice that some gravure printing enterprises directly outsource VOCs terminal governance to suppliers is extremely wrong. Gravure printing enterprises need to fully realize that even if suppliers participate and cooperate in the whole process from early research, design, processing to later installation and commissioning, there are still various uncertainties to ensure the success of the project, so gravure printing enterprises should be careful in their choice.

Below, based on the author's understanding and understanding of the existing VOCs end treatment technology, the following selection suggestions are given for your reference.

Scheme I: solvent recovery [not recommended]

The main problems are as follows:

(1) Up to standard

In the recovery scheme, it is difficult to adsorb the primary waste gas and discharge it to the standard, and the multi components of the waste gas (such as alcohol) and the adsorption material itself are non selective. The VOCs online monitoring system makes it very difficult to give consideration to the standard of various shapes of waste gas at the same time, and most of them need to add secondary VOCs treatment facilities to achieve the standard.

(2) Security

First, the solvent recycling process area needs operations such as water removal, odor removal, distillation, decolorization, purification, etc. It belongs to Class A explosion-proof area, which requires a site far away from the production area. In addition, purification and treatment of similar chemical processes have great potential safety hazards. In addition, whether the factory is allowed to deal with solvent recycling in this way, the local safety supervision and fire protection policies are unclear; Second, the composition of the waste gas from gravure printing is complex. In addition to solvents, there are also components of internal solvents such as ink and varnish. Repeated use of the original pure solvent process for gravure printing will lead to various potential product quality risks, especially for food packaging, which is very easy to have solvent migration risks.

(3) Technology

At present, the application of single solvent or two-component solvent ink is not yet mature. The mixed solvent is obtained from the recovery of gravure printing waste gas, which cannot be separated and purified on site for reuse. Moreover, if the enterprise has only one or two gravure printing machines, it will emit hundreds of tons of waste gas a year, which is too small to be suitable for recovery.

(4) Policy

The state defines the recycled solvent as hazardous waste, which needs qualified enterprises to deal with, making it more difficult to collect, store and circulate the recycled solvent. At present, it is not mature to transport the recycled solvent out for refining and reuse. In addition, with the current collection of VOCs pollution charges, the number of recovered solvents is clear and the links are transparent, so the pressure on gravure printing enterprises is greater.

(5) Economy

The cost of recovery is basically acceptable. If the electricity cost is 1 yuan/kilowatt hour and the steam cost is 200 yuan/ton, the cost of recovering 1 ton of solvent is about 1500 yuan/ton (the cost of pure solvent recovery, such as purification, will increase by 500~700 yuan/ton). However, due to the sharp price reduction of petrochemical products recently, the value of the recovered solvent has dropped sharply, the market has rapidly shrunk, and it is very difficult to sell. Previously, it could be sold without purification, and now few people want it after purification, It may be necessary to pay for hazardous waste, and the cost of hazardous waste treatment will increase by about 5000 yuan/ton, and the recovery cost will rise significantly.

Scheme II: runner enrichment [not recommended]

The main problems are as follows:

(1) Up to standard

The reasons are the same as above. Even though the runner is customized for various solvents, most gravure printing enterprises have several different ink systems, and the solvent composition added in the ink is complex. Considering the concentration ratio of 10, 90% of the waste gas is difficult to reach the standard directly when it is directly discharged through the runner concentration and primary adsorption purification, or it needs secondary runner purification, and it is also difficult to reach the standard when installing online detection and paying sewage charges in the future.

(2) Security

As the air volume and concentration at the intaglio printing exhaust gas inlet vary greatly, the difference can generally be 5-10 times. If the concentration of the runner can only be absorbed and analyzed at a fixed speed, the standard, energy consumption and safety of the exhaust gas with variable air volume, concentration and composition are all problems. For example, the original imported waste gas is 300mg/m3, and the concentration of 10 times is 3g/m3. However, if the order is switched, the runner part remains the same. If the import concentration reaches 3g/m3, it will become 30g/m3 after concentration, and the risk of waste gas explosion will increase dramatically.

(3) Energy consumption

Based on the characteristics of runner concentration, it can not adapt to the exhaust gas volume, concentration, and startup and shutdown very well, and the energy consumption can only match a narrow range, resulting in the actual full range of production conditions, and high operation and maintenance costs.

Scheme III: Activated carbon replacement [helpless choice]

This treatment scheme has a small investment, but generally one gravure printing machine emits 25~75kg of solvent per hour. In order to achieve the emission standard, the activated carbon needs to be replaced very frequently, and the replaced activated carbon is a hazardous waste, so it needs to pay for treatment. In particular, the technical transformation of waste gas treatment and new projects now have purification rate indicators. It is difficult for activated carbon to reach the standard, so it can only be discarded and has to be reinvested, so it can only be used as a helpless choice.

Scheme IV: Combustion [Suggestion]

It is recommended that the waste gas after concentration be directly sent to RTO, of course, it can also be sent to catalytic incineration, or RTO after the runner is concentrated. For other low concentration waste gases such as floor drain, workshop disorganization, ink warehouse, cleaning room, etc., it is recommended to try new technologies for treatment, or concentrate them before entering RTO. As for the comparison and selection of RTOs in China, it will not be expanded here.

Scheme V: Other technologies [suggest to keep trying]

Based on the huge environmental protection pressure and governance market in China, in recent years, new technologies have emerged in the field of gravure VOCs terminal governance, and some foreign countries have not yet (according to the analysis, the proportion of foreign gravure printing is very small, and the governance started more than ten years ago, which is basically mature at present, and few enterprises have invested in research and development), such as high-temperature plasma, low-temperature plasma, photolysis, photooxidation, biological method, and the combination of various technologies. It is recommended to keep trying.

Of course, the above scheme should be adjusted properly in combination with the specific conditions of gravure printing enterprises, as well as the environmental protection policies in different regions, and the collection of VOCs pollution charges.

From an economic perspective, the end treatment of gravure VOCs

(1) RTO is a relatively thorough and environmentally friendly solution for the end treatment of gravure VOCs at present, but it has large investment, large land occupation and high cost (about 500000~1 million yuan for 10000 exhaust air volume). Generally, the RTO with 60000 air volume is 22 meters long, 8 meters wide, 6 meters high and 100 tons heavy. It is recommended that large-scale gravure printing enterprises consider it, and it is also recommended to invest in stages.

(2) Concentration+catalytic combustion or concentration+RTO, the cost input and floor area will be slightly smaller, and there is no need to reduce wind, which has little impact on production. However, the author is negative about whether concentration is suitable for gravure printing process, for the reasons above.

(3) If the local environmental protection pressure is not great, gravure printing enterprises can observe first, or invest less, and adopt the transition plan first. At the same time, they should pay close attention to the changes in policies and the development of new technologies, until the gravure printing industry reaches an agreement, and the market introduces effective, mature and cost-effective technologies and plans. Objectively speaking, the ineffective consumption of investment and operation costs in failed cases is also not environmental protection, but also a secondary damage to the environment and gravure printing industry.

What needs to be clarified is that environmental protection must be done. Enterprises without strength during this period will inevitably be eliminated, and overcapacity will also be alleviated. However, this requires the cooperation of the state, associations, suppliers, enterprises and other parties, or the result will be the same as decades ago, and become a mere formality.

Future trend of gravure VOCs end treatment

(1) The gravure printing machine must be installed with VOCs treatment facilities. In the future, the gravure printing machine may be required to be equipped with VOCs end treatment facilities as standard before leaving the factory.

(2) In a short period of time, only qualified emission areas are required, and activated carbon replacement technology will also be the main response to the end treatment of gravure VOCs. However, in areas where purification rate and standard emission are required at the same time, various low-cost new technologies or combined technologies will be the mainstream.

(3) If there is a low-cost new technology for the end treatment of gravure VOCs, such as the investment of 100000 to 200000 yuan for 10000 exhaust air volume, it will replace the above mainstream technology.

(4) It is expected that the new technology for the end treatment of gravure VOCs will become the mainstream and be widely promoted, but if no new technology appears in the short term, the ultra-low CEMS system RTO will become the mainstream.

It should be noted that in the current solidified industrial pattern, gravure printing enterprises are the direct polluters in the entire industrial chain and must assume corresponding environmental protection responsibilities. Therefore, gravure printing enterprises must fully realize that environmental protection investment in the future is as routine as factory labor, water and electricity. Gravure printing environmental protection is not only for reaching the standard, but also for our own home. We need to work together to face it. We also hope that more gravure printing enterprises will actively invest in environmental protection. At the same time, as consumers, we should pay attention to the environmental performance of purchasing commodity packaging, cherish the purchasing right in our hands, force enterprises such as food, medicine and daily chemical products to reduce excessive packaging, restore functional packaging, and fundamentally guide and support green packaging.

Source: Printing technology