Zeolite runner concentration-storage incineration method for packaging and printing organic waste gas
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This paper introduces the process principle of the rotary enrichment-storage incineration technology. The purification device of the combined technology is used to treat the organic waste gas of the packaging and printing plant. The actual operation results show that the process and equipment can effectively handle the large air volume. The low-concentration organic waste gas has the effect of purifying and treating the new VOCs emission standards of the packaging and printing industry.
1 Overview
The discharge of volatile organic waste gases (VOCs, Volatile Organic Compounds) in packaging and printing plants mainly comes from solvent-based inks used in the production process of color printing and plastic film lamination processes, adhesives and organic solvents used for dilution. The organic solvents used mainly include Medium and high boiling solvents such as ethyl alcohol, esters, and aromatic hydrocarbons, such as ethyl acetate, butyl acetate, ethanol, isopropanol, toluene, and xylene, which are highly volatile in the production process. According to relevant data, the emissions of VOCs in China's packaging and printing industry are about 2 million to 3 million tons per year, accounting for more than 80% of the total emissions of the printing industry. The contribution of VOCs in the packaging and printing industry cannot be ignored. The data show [1~3] that VOCs are extremely harmful to people and the environment. Therefore, it is necessary to vigorously promote the comprehensive rectification of VOCs in packaging and printing enterprises, reduce VOCs emissions from the source, and adopt reasonable and effective treatment technologies for the discharged VOCs.
New environmental regulations and local VOCs emission standards have become more and more restrictive on VOCs emission standards, and have placed higher demands on VOCs emission companies and environmental protection equipment providers. Compared with the traditional activated carbon adsorption-catalytic oxidation process, the zeolite regenerative-regenerative combustion (RTO, RegenerativeThermalOxidizer) process has many advantages, such as high safety, small fluctuation of outlet concentration, high purification rate, etc. [4], zeolite Runner Concentration - RTO will soon be the mainstream process and processing equipment for such projects.
2 process and purification principle
purification principle
The technology is a combined process of zeolite runner adsorption and regenerative incineration technology. The purification system is mainly composed of dust filter device, zeolite runner concentrated adsorption device, RTO, fan, heat exchanger and PLC automatic control system. The combined technology concentrates the high-volume and low-concentration organic waste gas into a small air volume and a high-concentration concentrated gas through adsorption and concentration of the zeolite runner, and the high-concentration concentrated gas is decomposed into inorganic components such as CO2 and H2O by RTO high-temperature combustion. The zeolite runner concentrating device utilizes the adsorption-desorption-concentration three consecutive variable temperature adsorption and desorption procedures, and is completed simultaneously on the runner (divided into the adsorption zone, the desorption zone, the cooling zone) by the rotation of the runner. Adsorption and desorption regeneration of VOCs.
Combined technology process: When the organic waste gas after dust and particulate matter is removed by the dust filter device, the organic matter is adsorbed in the adsorption area of the runner, and the exhaust gas after adsorption purification (about 85% of the treated air volume) %~95%) is discharged into the atmosphere, and a small part of the exhaust gas (about 5%~15% of the treated air volume) is cooled by the heat exchanger to the desorption temperature of 180~220°C after the cooling zone is cooled. Flowing into the desorption zone, the organic matter in the desorption zone is separated from the adsorbent-zeolite into the heated gas stream, and the runner is regenerated. The desorbed high-concentration VOCs are sent to the RTO for high-temperature incineration, and the high-temperature flue gas after the reaction enters the regular honeycomb. In ceramic regenerators, 95% of the heat is absorbed and "stored" by the regenerator, and the temperature is reduced to near the RTO inlet temperature, usually no more than 50 °C. After the temperature of the regenerator rises, the flow direction of the airflow is switched by the switching valve or the rotating device, and heat storage and heat release are respectively performed to realize efficient recovery and utilization of heat.
This process has the following advantages:
(1) The outlet concentration is stable compared to the fixed bed activated carbon adsorption concentration. Since the runner is always in a rotating state, the zeolite transferred into the adsorption zone will be transferred to the desorption zone for desorption regeneration, so that the residence time of the adsorption zone is short.
(2) Zeolite is used as the adsorbent. Because zeolite has non-combustibility, it has better safety performance than coal/wood activated carbon.
(3) High temperature desorption, high desorption efficiency, and the problem of high boiling point residue can be solved.
(4) The system combination is compact, making full use of the heat source, saving equipment investment and operating costs. First, the concentration of VOCs after desorption is generally 6 to 25 times the concentration of the system, which can reach the RTO self-sustaining concentration. During normal operation, the RTO auxiliary heating system does not turn on. Secondly, the cooling air is used as the desorption wind (the temperature rises to 80~110 °C after the cooling air is cooled by the normal temperature), and a small amount of RTO furnace high temperature purification gas is taken to further heat the desorption wind to reach the desorption temperature, which can reduce the operating cost. .
(5) The oxidation system adopts regenerative incineration technology (RTO), which has higher purification efficiency (up to 99%) and high thermal efficiency (≥95%) compared with traditional catalytic combustion and direct-fired thermal oxidation furnace. Low cost and other characteristics, when the concentration is slightly higher, it can also carry out secondary waste heat recovery, greatly reducing operating costs.
3 practical application results
Taking a printing factory in Beijing as an example, the VOCs of the plant are derived from two printing lines (ten-color printing machines and eight-color printing machines). Each printing line has two main air outlets and two side air outlets. The amount is 40,000 m3/h, the main components of the exhaust gas are ethanol and butyl acetate, and the VOCS concentration is 300-600 mg/m3. For this large air volume and low concentration exhaust gas, the company adopted the rotary enrichment-RTO purification device for treatment. Since the first year of operation, the whole system has performed well. The monitoring results in Table 1 indicate that the VOCS outlet concentration is lower than 30mg/m3. It meets the national and local printing industry air pollutant discharge standards. In addition, the zeolite runner purification rate is over 95%, and the RTO purification rate is over 99%, which meets the design requirements.
The process first adopts the wheel adsorption and concentration to reduce the exhaust gas treatment amount of the RTO equipment, which makes the RTO scale smaller and reduces the equipment investment cost; although the organic waste gas concentration is relatively low, after the concentration, the organic waste gas concentration reaches the self-sustaining concentration, so In addition to the consumption of natural gas (RTO auxiliary fuel) for the first time, the RTO does not need to be turned on at other times. At the same time, the desorbed wind heat source is derived from the heat energy released by the oxidation of organic waste gas, and the operating cost of the system is low.
Zeolite Runner Concentration - The RTO Purification System is fully automated and equipped with a PLC touch screen display. The control program monitors all controllers, drives, pressure switches, pressure transmitters, thermocouples, limit switches, line-of-line signals, and instrumentation interlock signals. If any abnormality occurs, the display unit will display the fault information, and then take appropriate actions through program control to ensure the safety of the system.
4 Conclusion
The actual operation results show that the zeolite runner-RTO process has good purification effect on high air volume and low concentration organic waste gas, low operating cost, and purified exhaust gas emission meets the current strict VOCS emission standards. At present, more than 90% of domestic revolving system is imported from abroad. The technology and products are imported. The investment is high and the construction period is long. It is urgent to develop zeolite revolving technology to break the foreign monopoly of the revolving wheel, so as to better serve the VOCs in China. Governance.