Analysis of flue gas purification process for hazardous waste incineration in chemical industry

　　At present, the techniques often used to dispose of hazardous wastes include marine disposal, incineration, chemical and biochemical disposal, solidification disposal, etc., aiming to achieve resource-based, harmless and reduction. In recent years, the application of incineration technology is more and more extensive. It is a kind of disposal technique that arranges hazardous wastes in incinerator to oxidize and release combustible factors. In the incineration technology, because of the characteristics of good continuity, long service life, stable operation and mature technology, the reverse kiln incineration technology shows a strong advantage. However, because of the rapid development of the reverse kiln incineration technology in recent years, and the lag of the joint development of the related technology, it brings the question that the flue gas emission is not up to the standard.

　　1. Production and control of filth in flue gas

　　1.1 production and control of acid gas

　　Acid gas fouling is mainly composed of nitrogen oxides, chlorides and sulfur oxides. During the incineration process, compounds such as Cl and s contained in solid waste will generate HCI and SO2. It is important to master the acid gases such as HCI and SO2 in the incineration flue gas by adopting wet, semi-dry and dry gas washing techniques.

　　The production mechanism of NOx mainly depends on self combustion fuel incineration to produce NOx, nitrogen oxidation to produce no in high temperature atmosphere and nitrogen factor in waste incineration to produce NOx. The key points of mastering NOx are as follows:

　　(1) Selective non catalytic recovery (SNCR)

　　When ammonia or urea is injected into the incinerator, it will eventually lead to CO2, water and nitrogen, and the nitrogen oxide in the flue gas will fall after recovery feedback.

　　(2) Selective catalytic recovery (SCR)

　　SCR system has a high denitration result. No in flue gas. Feedback with ammonia water and other reconstituting agents, under the use of catalyst, NOx in flue gas is converted into water and nitrogen.

　　(3) Burning control method

　　Maintain suitable furnace temperature and consolidate, temperature type No. The premise of production is that the temperature is more than 1400v, so in order to master its production, it can experience reasonable air supply (low oxygen concentration in the incineration plant), master the furnace temperature (reduce the generation of part of high temperature in the furnace).

　　1.2 production and control of dust and heavy metal pollution

　　Inert inorganic substances such as the filth and ash of the freezing gas are the important factors of the dust in the flue gas. Heavy metal contamination includes arsenic, chromium, lead and other elemental oxides and chlorides. After high temperature incineration, the heavy metal materials in the waste will volatilize into the flue gas and remain in the ash.

　　At present, the removal of heavy metals in the tail gas disposal system of incineration all accepts the skill of activated carbon adsorption, and finally experiences the safe landfill of bag filter network. After the bag filter, a small batch of heavy metal mercury with strong volatility and low boiling point still exists in the gas state, but because of its water-soluble characteristics, it is very eventually removed by washing liquid in the acid absorption tower.

　　1.3 production and control of dioxins

　　Dioxin is a general designation of PCDFs and PCDDs. The production mechanisms of dioxins are as follows: ① the mechanism of simply release; ② the mechanism of contrary feed of high temperature gas; ③ the mechanism of precursor synthesis; ④ the mechanism of feedback of re synthesis.

　　2. Flue gas purification process during hazardous waste incineration

　　2.1 process flow

　　In ancient times, the technology and technology of flue gas purification were flue gas quenching + dry deacidification + activated carbon adsorption + bag dust removal + wet deacidification.

　　The flue gas purification technology and process accepted by the project is flue gas high temperature denitrification + flue gas quenching + dry deacidification + activated carbon powder radiation + bag dust removal + two-stage wet deacidification + electrostatic demister + activated carbon adsorption bed.

　　2.2 optimization of flue gas purification process

　　2.2.1 master N0. Technology optimization of

　　(1) Mastering the temperature of reverse kiln

　　According to the historical data, the NOx production at 1000oC is 1 / 10 of that at 1300V. At the beginning, it is necessary to maintain the applicable furnace temperature and furnace incineration for consolidation, so as to master the production of NOx. In the reverse kiln, the project builds infrared thermometers to actively master the furnace temperature through long-distance monitoring. The project also adopts a combined incinerator to maintain the solid combustion of the furnace, and optimizes the layout of the air supply outlet of the reverse kiln head cover, which can reduce the emission of pollutants such as nitrogen oxides.

　　(2) Optimize the installation of secondary air

　　Accept 2 times of incineration, control the oxygen content in the reverse kiln at 6% - 10%, make the material burn once under the weak recovery atmosphere, activate the nitrogen compound to transform into N2, and sufficient incineration is carried out in the second combustion chamber, so that the unprofitable material is completely burnt out.

　　In order to reduce the production of no, it is necessary to install the secondary air reasonably. The project is to install secondary air diffusers in the straight section of the second combustion chamber. The venturi effect is applied to the growth of flue gas disturbance. At the same time, the uniform nozzle of the secondary air diffusers is arranged on the uniform section. When it cuts into the second combustion chamber, an assumption circle will be caused in the middle.

　　Under the disturbance of secondary air, the combustion flue gas spirals up, increasing the distance of flue gas activity, extending the pause time of flue gas in the secondary combustion chamber, and the flue gas retention time is more than 2.0S,

　　The useless materials in the smoke are thoroughly dissected.

　　(3) Optimization of denitrification system

　　The denitration feedback system is set in the first return of waste heat steam boiler. Denitration accepts SNCR method (non catalytic method) to master No. The joint of SNCR technology is the selection of temperature window.

　　Near the left side of the radiation port, a thermocouple is built in this project. The window temperature of 930c is very good, which is set at 900-1000 "C. At the same time, No. It is indicated that the system is built at the outlet of the boiler to monitor the NOx concentration in a timely manner, transmit the collected NOx concentration light number and credential concentration value to the PLC, and the PLC will mediate the radiation value of urea solution, output the radiation flow to master the light number, and finally spray the quantitative urea solution into the incinerator through the radiation system, heat dissect the urea solution in the boiler to release nitrogen, and at the appropriate temperature with the N in the boiler Ox

——Author：ebico