At present, the commonly used VOCs processing technology is combed.
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
There are two main types of processing for VOCs: recycling and destruction. Most of the more mature treatment methods use two types of combination to reduce VOCs pollution as much as possible. The recycling technology mainly treats VOCs by physical methods such as adsorption technology, condensation technology and membrane separation technology, and then recycles and reuses them; the destruction technologies include photocatalysis technology, thermal incineration technology, biotechnology, and plasma destruction technology.
1. Adsorption technology
The basic principle of the adsorption technology is to use the porous structure of the solid adsorbent (activated carbon, activated carbon fiber, zeolite) with a very large specific surface area to absorb and separate the VOCs mixed gas to achieve the purpose of purifying the air. The key to the adsorption method is the selection of adsorbent, adsorption equipment, regeneration medium and post-treatment process. Common adsorptions include fixed bed adsorption, fluidized bed adsorption and concentrated rotary adsorption.
(1) Fixed bed adsorption
The fixed bed adsorption is carried out on the same layer of adsorption and desorption. In order to ensure continuous adsorption, generally two or more adsorption beds are used alternately. There are two general processes for fixed bed adsorption: one is water vapor replacement regeneration, which is mostly used for low concentration VOCs recovery. When the organic waste gas concentration is high or the boiling point is high, the exhaust gas can be pretreated by condensation technology to partially recover the organic matter. At the same time reduce the concentration; the other is vacuum desorption regeneration, in the treatment of some high concentration of organic waste gas, can be combined with some large pore silica gel to treat organic waste gas, this method is suitable for the treatment of some high concentration organic waste gas, its operation specification Strictness has led to higher cost of use of the process.
(2) Fluid bed adsorption
The fluidized bed adsorption is mainly composed of separate adsorption units and desorption units. The organic waste gas first enters the adsorption unit, and then discharges the exhaust gas up to the standard; the adsorbent adsorbing the exhaust gas enters the desorption unit for desorption treatment, then the desorbed organic gas is condensed and recovered, and finally the adsorbent is sent back to the adsorption unit.
(3) Rotating zeolite adsorption
Rotating zeolite adsorption has been widely used in Europe, America, Japan, and Taiwan, and the technology is relatively mature. In recent years, China has also begun to introduce. Compared with the fixed bed adsorption technology, the rotary zeolite adsorption technology is more advantageous. The zeolite is used as an adsorbent, the dosage is small, the high-temperature desorption efficiency is high, and the cost is greatly saved.
In the process of adsorption of zeolite, the rotating wheel rotates at a constant speed, and the exhaust gas enters the runner and passes through three regions of the runner in turn, followed by the adsorption zone, the regeneration zone and the cooling zone. The gas passing through the zeolite is discharged after reaching the standard, and the molecules carrying the organic waste gas enter the regeneration zone from the adsorption zone, and the molecules are desorbed by the high-temperature gas stream. The desorbed molecules pass through the cooling zone from the regeneration zone and re-enter the adsorption zone after cooling. The equipment of the rotary zeolite process has a compact structure, a small footprint, and a stable discharge rate.
2. Condensation technology
The condensation technique is to reduce the VOCs to their boiling points through a condensing medium and liquefy them according to their boiling points. Common condensing media are cold water, chilled brine, and liquid nitrogen. Most of the volatile organic compounds have a relatively low boiling point and the recovery is relatively low when recovered using a condensing medium. In order to increase the recovery rate, it is necessary to use a low temperature condensing medium or high pressure, but due to the limitation of balance, the ideal recovery rate is still not obtained, the emitted gas is difficult to meet the standard, and the cost is also greatly increased. . Therefore, the current condensing technology is increasingly used as an auxiliary technology to pre-process other technologies, with other technologies to achieve the desired effect.
3. Membrane separation technology
Membrane separation technology is a clean treatment technology, that is, under the action of external force, VOCs pass through artificial membrane or natural membrane, and then discharge to the standard, and high-concentration VOCs gas enters the condensation section for recycling. The equipment used in this technology is relatively expensive, but the equipment loss has nothing to do with the gas concentration, but is related to the flow rate of the air, so the technology is suitable for the low-flow high-concentration exhaust gas generation industry. Because of its unique environmental protection and non-polluting characteristics, membrane separation technology is a development trend of future exhaust gas treatment, and European, American and Japanese technologies are more advanced. Compared with advanced membrane separation technology from abroad, China's membrane separation technology is still in a backward stage.
4. Photocatalysis technology
In theory, photocatalytic technology can completely convert VOCs into CO2 and H2O through ultraviolet light or other specific wavelengths of light. In actual production, many intermediate products such as aldehydes, ketones, acids, and fats are produced. Therefore, the photocatalytic technology cannot completely convert the VOCs gas, causing secondary pollution to the air, and the reaction rate is slow and the efficiency is low, which greatly limits the large-scale industrial application. Moreover, since the photocatalytic reaction itself has a strong dependence on the catalyst, the catalyst has a disadvantage of being easily deactivated. At present, many companies are trying to improve the production process by coupling technologies such as electrochemistry, ozone and microwave, and hope to improve production efficiency, increase conversion rate, and reduce secondary pollution, so as to treat low-concentration VOCs.
The characteristics of VOCs emissions in the printing industry are: the production lines of the enterprises are different, the equipment covers a large area, the production lines are dispersed, and the emission sources of VOCs are dispersed. Different inks or solvents produce different VOCs, so VOCs must be targeted and have limitations. And because the construction pattern of each printing plant is different, it is necessary to design a new installation according to the architectural style of each printing factory when installing the exhaust gas treatment equipment.