In my country, there are relatively mature technologies for dust removal and desulfurization of flue gas, while the research on denitration technology is in the research and test stage. From the perspective of development trends, if sufficient attention is not paid to NOX, it is entirely possible that NOX will replace SO2 as the main substance of air pollution. As people pay more attention to the environment, as well as the scientific development concept and the requirements of building a socialist harmonious society, the future flue gas treatment should be integrated with desulfurization, denitrification and dust removal. In recent years, industrial development has continued to grow, but human living conditions have continued to deteriorate. "Energy saving and emission reduction" has become a focus topic in the industrial field. The ceramic industry has always been regarded as the "three highs" industry, and the government has repeatedly introduced The policy requires the ceramic industry to carry out rectification to achieve transformation and upgrading. Energy saving and emission reduction have become an important part of the ceramic industry. This article mainly describes the flue gas characteristics of ceramic industrial kilns, and proposes the use of modified SNCR low-temperature denitrification and semi-dry desulfurization and dust removal to treat the exhaust gas of ceramic kilns. The performance and structural characteristics of the technology are briefly analyzed.
1 Introduction
With the continuous development of the national economy, my country's ceramic industry has also developed rapidly. According to statistics, the production of ceramic wall and floor tiles has soared from 272 million m2 in 1991 to about 9 billion m2 in 2012, ranking first in the world, accounting for about 2/3 of the world, and the situation is very good. However, its negative impact-kiln flue gas pollution has become more and more prominent. 90% of SOX, 85% of CO2, 80% of ROX (dust) and 50% of NOX pollution in the atmosphere in our country come from ceramic kilns, steam boilers and various other industrial kilns. According to statistics, there are currently more than 3,000 kilns in the production of daily ceramics and architectural ceramics alone, accounting for 70% of the total number of kilns. Therefore, the treatment of ceramic kiln flue gas pollution has become a research direction.
Most of the current industries use wet desulfurization and dust removal tower systems. The result is that although the emission concentration of SO2 meets the standard, the dust emission concentration is difficult to meet the new ceramic industry emission standards ("Ceramic Industry Pollutant Emission Standard" (GB25464- 2010)), and the use of wet flue gas desulfurization will produce a large amount of desulfurization wastewater, and the area required for the sewage treatment system will be further expanded; the increase in the amount of wastewater, the majority of the previous industries will use wet desulfurization and dust removal towers The system and the further demand of the land area have further expanded the energy consumption required in the production process of the product [3]. In recent years, a desulfurization and dust removal technology suitable for the treatment of waste gas from ceramic industrial kilns has appeared on the market-spray semi-dry flue gas dust removal technology. This technology has been used commercially in the domestic desulfurization market, and the effect of dust removal and desulfurization is no less than that of wet desulfurization.
In my country, the control of flue gas pollution mainly focuses on the control of dust and SO2. With the increase of environmental pollution and the increase of air quality requirements, the control of NOx has been put on the agenda. At present, my country has also made strict regulations on the emission of NOx waste gas from industrial kilns, which are implemented in accordance with the "Comprehensive Emission Standard of Air Pollutants" GB25464-2010. At present, the suitable flue gas temperature of SCR denitration process is 300-420℃, the investment and operation cost are high, and the area is large, and it is not suitable for the flue gas denitration of ceramics enterprises with tight land use.
This article will combine the characteristics of ceramic industrial kiln flue gas, analyze and discuss from the perspective of practical application, and propose the use of modified SNCR low-temperature denitrification and semi-dry desulfurization and dust removal comprehensive technology to treat ceramic kiln tail gas.
2 Modified SNCR low-temperature denitrification and semi-dry desulfurization and dust removal comprehensive technology process introduction
Modified SNCR low-temperature denitration and semi-dry desulfurization and dust removal integrated technology is based on the full use of existing equipment, adding corresponding equipment to achieve simultaneous desulfurization, denitration and dust removal. The denitrification device is cleverly installed in the system, and some pipelines are added. The operating temperature of the system is 300-450°C to ensure the safe, stable and continuous operation of the system.
3 modified SNCR low temperature denitration technology system
3.1 Modified SNCR low temperature system process flow
Modified SNCR cryogenic system is actually a technology improved on the basis of SNCR. Its basic principle is the same as SNCR. It uses dry compound to reduce NOx in a certain temperature range (300～450℃). The main reaction is:
NOx+dry compound+O2→N2+H2O
Different from SNCR is that the modified SNCR cryogenic system sprays small droplets of modified reagent solution into the specific pipe area and distributes them evenly. The modified SNCR cryogenic system is a denitration reaction in a flue gas pipeline, and the fine distribution of the modified reagent solution droplets in the corresponding temperature window area of ??the pipeline is an important factor affecting the performance of the system. The system stores the modified agent solution of suitable concentration and circulates it to the pipeline side, and then uses the compressed air provided by the company to further dilute the modified agent solution to a preset concentration, and accurately measure the required denitration reaction through the metering module The modified agent solution is delivered to the spray gun. The spray gun uses mechanical atomization and carrying wind to spray the required modified chemical solution into the specific pipe area. During system optimization and commissioning, the atomization performance and flow rate of each gun should be further adjusted according to the actual operating load and NOx concentration in the pipeline to better meet the system requirements. The denitrification machine can be networked with online monitoring, and according to its feedback data (for example: concentration after treatment, NH3 escape concentration, etc.), it can automatically accurately adjust the spray volume, concentration of the solution and other parameters, in order to achieve a balanced discharge and save operating costs. .
The modified SNCR system is mainly composed of a medicament storage box, a medicament delivery adjustment system, a medicament feedback sensor component, a touch control panel, and an automatic adjustment medicament spray gun component.
3.2 Technical process characteristics
Compared with similar technology, this system has the following characteristics:
(1) Using modified agents as reducing agents, non-toxic, harmless, urea-free, and no ammonia escape;
(2) There is no need to store and handle the corresponding safety equipment for pressurized and dangerous anhydrous ammonia or ammonia;
(3) The use of liquid instead of gaseous reactant can more effectively control the reactant injection mode and reactant distribution, ensure good mixing with the flue gas, and at a suitable temperature, make the agent more fully utilized and effectively improve the reduction Agent utilization rate.
(4) The reducing reagent has strong permeability, reasonable droplet size, uniform distribution, and good mixing with NOx in the flue gas;
(5) The modified agent injection system of each project is specially tailored, including wall injectors, wall injectors with telescoping and multi-nozzle gun injectors, in areas that cannot be covered by short modified agent spray guns , Multi-nozzle gun sprayer can ensure good coverage of the sprayed modified chemical solution.
4 Semi-dry desulfurization and dust removal process
The flue gas of the ceramic industry kiln generally has the following characteristics. Because the tail gas of the firing kiln in production contains higher temperature, in order to utilize the waste heat, the exhaust gas of the firing kiln is generally transferred to the front-end process-the drying kiln, resulting in exhaust gas exhaust. The temperature is relatively low, and because the dust absorbs heat from the droplets in the process of spraying dry powder in ceramics, the SO2 in the flue gas is absorbed, and part of it is released during the kiln drying and firing process, and then in the firing process The SO2 generated by the combustion of medium fuel, the SO2 concentration in the kiln exhaust gas is relatively high, and the moisture generated during the drying process of the drying kiln is also discharged along with the exhaust gas, making the exhaust gas produced by the ceramic industry kiln have low temperature, high humidity and high concentration. Features [2].
The treatment system of the kiln flue gas "semi-dry desulfurization and dust removal technology" introduced in this article is mainly composed of two technological processes: "dry desulfurization" + "bag dust removal", as well as the matching fan piping system and electrical control System etc. Its basic process principle is: spray a certain amount of alkaline solution into the cooling desulfurization tower; the desulfurization mist will evaporate at a high temperature to form flue gas cooling and desulfurization, and the flue gas enters the dust collector, and the dust in the flue gas is combined with the dust collector. The desulfurization by-products are captured and purified, and then discharged through fans and chimneys up to standards. The specific process flow is shown in Figure 3.
4.1 Cooling desulfurization system
4.1.1 System composition and process
The cooling and desulfurization system adopts the "spray drying cooling and desulfurization technology". The system is mainly composed of a cooling and desulfurization tower, a cooling and desulfurization water system, and a compressed air system. The system process is shown in Figure 4.
4.1.2 System configuration and structure
(1) Cooling desulfurization tower
This system uses a cooling desulfurization tower as the cooling and desulfurization equipment, which consists of a cylinder, ash hopper, nozzle, deflector, water pipe, air pipe, etc.
After the flue gas enters the cooling desulfurization tower, it flows upwards evenly under the action of the deflector. The nozzle adopts a gas-water dual-flow nozzle, which can atomize the solution into 50μm droplets. When the droplets contact high-temperature flue gas, they can take away the heat in the flue gas and reduce the flue gas temperature. At the same time, the alkali in the solution and the flue gas During the SO2 reaction, the SO2 in the flue gas is absorbed and neutralized, so that the SO2 content reaches the relevant national emission standards. When the droplets are completely evaporated, the flue gas enters the dust collector again.
The dust in the flue gas falls into the ash hopper under the action of gravity, and is collected by the cloth bag and discharged through the ash discharge valve under the action of the vibrator.
(2) Preparation of cooling desulfurization solution
According to the requirements of the system for cooling and desulfurization, the concentration of the cooling and desulfurization solution is accurately prepared through the pump and the flow control valve. The cooling and desulfurization solution is sprayed into the temperature droplet through the air-water dual-flow nozzle under the pressure of the stainless steel multi-stage centrifugal pump. Inside the desulfurization tower.
4.3 System Features
(1) Unique structure, high cooling and desulfurization efficiency, meeting system requirements
Based on the flue gas treatment experience, the designed cooling tower combines the advantages of multiple cooling and desulfurization systems. Through the sensor and automatic control system, the accuracy of the relevant cooling and desulfurization operation can be effectively controlled, so that the flue gas can maintain a certain temperature and humidity stably.
(2) Small footprint
The cooling and desulfurization tower is a vertical structure, which occupies a small area. In addition, the solution tank and pump occupies a small area.
(3) Simple process, saving investment
According to the actual temperature of the high-temperature flue gas, the system automatically adjusts the flow rate, so that the temperature can be adjusted conveniently, which not only meets the system requirements, but also saves operating costs. And the operation of the cooling tower has no effect on the furnace pressure of the ceramic furnace.
(4) The system is stable and reliable, and easy to maintain
There are few moving parts in the whole system, clean tap water is used for the cooling and desulfurization solution, and there is no blockage problem in the system.
The flue gas after passing through the desulfurization tower enters the bag filter, which can reasonably and stably solve the problems of dust, desulfurization reactants, etc. that easily cause excessive flue gas dust.
The maintenance of all equipment on the cooling desulfurization tower does not need to enter the inside of the cooling tower, and the maintenance of the equipment does not affect the operation of the ceramic melting furnace, and whether it is online or not does not affect the pressure of the ceramic melting furnace.
So the system maintenance is very simple, the system failure rate is low, the equipment service life is long, saving a lot of manpower and financial resources.
(5) Tower products are easy to handle and no waste water is produced
The solution sprayed into the cooling desulfurization tower evaporates directly in the cooling desulfurization tower, part of the dust falls directly into the ash hopper of the cooling desulfurization tower, and the other part enters the next process flow, which is collected by the dust collector, and all by-products are dry State substance, stable in nature, non-toxic and harmless. Dust can be directly discarded. Convenient treatment, no secondary pollution such as waste water and waste gas.
Compared with other cooling desulfurization methods, the semi-dry cooling desulfurization process saves a lot of manpower, investment, maintenance, cooling product processing and other costs, so the comprehensive advantages of this cooling desulfurization technology are still relatively obvious.
In short, the advantages of the semi-dry process are: no water treatment system, no white smoke generation, low operating cost, convenient maintenance, no impact on quality and output, and can meet emission standards around the clock.
4.4 Dust removal system
In view of the characteristics of the kiln flue gas, the dust collector of the semi-dry dust removal system uses a bag filter. Currently, the more widely used bag filter on the market mainly include pulse line injection bag filter and box bag filter. Table 1 shows Analysis and comparison of two kinds of bag filter.
It can be seen from the above comparison that the pulse line injection bag filter is more suitable for kiln flue gas dust removal.
4.4.1 Dust removal-online pulse line jet bag dust collector
The gas purification method of the on-line pulse line jet bag filter is an external filter type. The dust collector is composed of upper box body, middle box body, ash hopper, filter bag assembly, blowing device, ash unloading valve, pulse valve and detection and control system. The filter bag is fixed on the flower hole plate through the bag cage. Each row of filter bags is equipped with a spray tube on the upper part, and there are small spray holes on the spray tube, corresponding to the center of each dust filter bag. A pulse valve connected with the air compressor is installed in front of the injection pipe, and the electromagnetic pulse valve is connected with the cylinder. The controller periodically sends out short-range pulse signals, and controls the opening of each pulse valve in an orderly manner through the control valve.
When working, the dust-containing waste gas enters the ash hopper of each unit through the air inlet through the lower part of the middle box. Large particles of dust fall directly into the ash hopper due to inertial collision and natural settlement, and the rest of the dust enters the filter area of ??the middle box with the airflow. Attached to the outer surface of the filter bag, the filtered clean gas is discharged through the filter bag through the upper box and the exhaust pipe to achieve the purpose of dust removal.
With the progress of the filtering conditions, the dust accumulated on the outer surface of the filter bag continues to increase, which causes the resistance of the dust collector itself to gradually increase. When the dust accumulated on the surface of the filter bag reaches a certain amount, the dust removal control device emits a clean The gray signal controls the opening of each pulse valve in an orderly manner through the control valve. When the pulse valve is opened, the injection pipe connected to the pulse valve communicates with the cylinder, and high-pressure air is ejected from the injection hole at a very high speed. The high-pressure airflow enters the filter bag, causing the filter bag to expand violently, causing shock and vibration. At the same time, in an instant, a reverse airflow from the inside to the outside is generated, so that the dust sticking to the outer surface of the filter bag and sucked into the inside of the filter bag is blown down. The purged dust falls into the ash hopper and is finally discharged through the unloader. Each row of filter bags takes turns to clean the dust, and after a period of time, it starts to take turns again.
4.4.2 Design characteristics of pulse line jet bag dust removal equipment
Its technical characteristics:
(1) The filter material has been technically improved to make the air permeability higher, less resistance, and more energy-saving.
(2) Anti-corrosion materials are updated to avoid the phenomenon of shell separation after long-term use and improve the service life.
(3) The spraying and cleaning solenoid valve of the dust collector is changed from the previous right-angle solenoid valve to the submerged pulse electric valve with better performance. Although the submerged valve is more expensive than the right-angle type, the submerged valve has instant ventilation Larger volume (can make dust cleaning cleaner, longer interval), small resistance, increase load driving capacity, expand the use range of air source pressure, and can be used in occasions with lower air source pressure (at least 3.5 kg/cm2 of compressed air pressure).
(4) After the control system of this dust collector has been optimized, it no longer adopts mechanical control elements for control, but adopts PLC control mode. At the same time, it is equipped with a touch control screen to display the working status and work of various equipment in real time. parameter. At the same time, the switches used for detecting the status of each valve are changed from the original mechanical stroke opening and closing to an inductive electronic switch, which can effectively reduce accidents caused by the opening and failure of the stroke.
5 Conclusion
In my country, there are relatively mature technologies for dust removal and desulfurization of flue gas, while the research on denitrification technology is in the research and test stage. From the perspective of development trends, if sufficient attention is not paid to NOX, it is entirely possible that NOX will replace SO2 as the main substance of air pollution. As people pay more attention to the environment, as well as the scientific outlook on development and the construction of socialism and