The flue gas from the cooling tower is neutralized by the slaked lime and activated carbon injection system, and then enters the bag filter and is discharged from the top of the compartment. The injected activated carbon and other particulate matter adhere to the surface of the filter bag to form a layer of filter cake; the acid gas in the flue gas further reacts with the excess reactant, which further improves the removal effect of the acid gas; the activated carbon is also The surface of the filter bag further plays an adsorption role. The fly ash attached to the surface of the filter bag is discharged into the dust removal hopper by the back blowing of the compressed air, and the fly ash is discharged through the ash conveying system.

The type, quantity and form of heavy metals contained in waste incineration flue gas are closely related to waste composition, properties, and incinerator operating conditions. Heavy metals mainly exist in the flue gas in the form of gas or adsorption.

When the flue gas passes through the waste heat utilization facility, the temperature gradually decreases, and some heavy metals with lower gasification temperature condense first to form small particles; Under the catalytic oxidation of the fly ash surface, the heavy metals are converted into metal oxides or chlorides that are more easily condensed; the remaining gaseous heavy metals will be adsorbed on the surface of the sprayed activated carbon powder or fly ash particles.

The above three forms of heavy metal particles (or particles with heavy metals adsorbed) can be separated in the dust collector. Taking Hg as an example, most of the Hg in the flue gas is gaseous, mainly in the oxidized form HgCl2, and a small part exists in the elemental form. The three forms of Hg can be effectively removed by activated carbon injection + bag filter.

Activated carbon powder is sprayed in the process of flue gas circulation. Using its porosity and adsorption capacity, it can effectively adsorb dioxins in flue gas, some ultra-fine particles that cannot be directly collected by dust removal, and heavy metals and their compounds adsorbed on these particles.

Usually, most of the flue gas treatment systems of domestic waste incineration enterprises use the activated carbon adsorption combined process with the bag filter. This combined process has a good removal effect on heavy metals, and the removal efficiency can reach 90%.

①Control the source. In order to reduce the production of dioxins during the incineration process, the combustible components in the garbage should be fully burned as much as possible. Through the classification and collection of domestic waste, resource recovery is strengthened to prevent substances containing PCDDs/PCDFs and substances containing high chlorine content from entering the incinerator.

②Reduce the generation in the furnace. The combustion chamber of the incinerator should maintain a sufficiently high combustion temperature (above 850°C); sufficient gas residence time (>2s); ensure that the exhaust gas has an appropriate oxygen content (6% to 12%), and maintain a large degree of turbulence.

③ Avoid low temperature resynthesis outside the furnace. When the incineration flue gas with a certain temperature (the temperature should not be lower than 500 ℃) is discharged from the waste heat boiler, the flue gas is rapidly cooled to below 200 ℃ within 0.2s by using the quenching technology, so as to avoid the easy formation of dioxins. temperature zone.

④Optimize boiler design and strengthen boiler purging.

⑤ Add dioxin production inhibitor. Including organic additives (urea, cyanamide and ethylene glycol, etc.) and inorganic additives (sulfur oxides, alkaline adsorbents, ammonia and strong oxidants hydrogen peroxide, ozone, etc.).

Acid gases HCl, SOx, HF are mainly removed by neutralization and absorption of alkaline substances such as Ca(OH)2 and NaOH in wet, dry or semi-dry methods.

The wet technology has high efficiency, up to more than 97%, but a large amount of sewage is discharged, which is easy to cause secondary pollution.

The dry technology has no sewage discharge, but the removal efficiency is only 60%~70%.

The semi-dry technology has high removal efficiency (about 90%), less drug dosage, and no sewage discharge, so it is the main applicable technology for flue gas deacidification. The semi-dry deacidification device is generally set before the dust collector, and mainly includes a feeding system, a mixing system and a reaction system. The deacidification agent CaO generates powdered Ca(OH)2 in the feeding system, and then enters the mixing system to be fully mixed with the flue gas and a small amount of water, and finally enters the reaction system in the form of a spray. Acidic components such as HCl, SOx, and HF are absorbed to form neutral and dry fine solid particles, which enter the next purification system with the flue gas. The main reactions are:
2HCl+Ca(OH)2=CaCl2+2H2O (1)
SO2+Ca(OH)2=CaSO3+H2O (2)

Since the odor is sensitive to the impact around the waste incineration plant, it must be treated effectively. The following measures can be taken:
① Closed garbage truck;
②Set the air curtain door at the entrance and exit of the garbage unloading platform;
③ The garbage storage pit is under negative pressure, and an air extraction device is installed above the pit to prevent the odor from overflowing. The gas in the pit is extracted and sent to the incinerator to support combustion;
④ Regularly clean up the old garbage in the garbage storage pit;
⑤Set up automatic discharge door to make the garbage storage pit airtight. Odor pollution control technologies include physical methods (sealing method, masking method, dilution method, etc.), chemical method (direct combustion method, catalytic combustion method, absorption method, etc.) and biological method (biological filter method, biological scrubber method).

(1) Semi-dry acid removal + activated carbon jet adsorption of dioxins + bag dust removal.

(2) SNCR denitrification + semi-dry acid removal + activated carbon jet adsorption of dioxins + bag dust removal.

(3) Semi-dry acid removal + activated carbon jet adsorption of dioxins + bag dust removal + SCR denitration.

(4) Semi-dry acid removal + activated carbon jet adsorption of dioxins + bag dust removal + wet acid removal + SCR denitration.

(5) Semi-dry acid removal + activated carbon jet adsorption of dioxins + bag dust removal + wet acid removal + activated carbon bed removal of dioxins.

At present, the first combined process is widely used, and this combined process is basically used in domestic waste incineration flue gas purification systems in my country. Requirements of “Standards for Pollution Control of Domestic Waste Incineration”. The second combined process adds the SNCR denitrification link on the basis of the first process to meet the requirements of the new emission standard and ensure that NOx is discharged up to the standard. However, Europe has higher requirements for acid gas (SO2, NOx, etc.) emissions. In recent years, wet acid removal + SCR denitration devices have been added.

“Low nitrogen combustion + SNCR + semi-dry method + dry method (slaked lime, activated carbon injection) + bag dust removal”, the technology and supporting equipment are relatively mature and economically feasible, and the pollutant removal efficiency is high, which can ensure the stable emission of flue gas pollutants. limit requirements.