Control countermeasures and measures of dioxin
Control Countermeasures of dioxin
In June, 1996, the Ministry of health and welfare of Japan established the discussion Committee on dioxin reduction countermeasures in waste treatment, and based on the recent dioxin reduction technology, the dioxin reduction countermeasures were divided into "emergency countermeasures" and "permanent countermeasures", with the goal of comprehensively promoting the reduction of dioxins, On January 23rd, 1997, the Japanese government rewritten the "guidelines on the prevention and control of dioxin production and other issues in the process of waste treatment" (commonly referred to as the "new guidelines"). The so-called "emergency response" is to use the latest technology to reduce the concentration of dioxin to the lowest level. Specifically, measures should be taken to ensure that the TDI (allowable daily intake per person) does not exceed 10pg/kg, even at the location with the maximum ground concentration that is most vulnerable to the impact of the waste incineration
plant D (TEQ) value, and the judgment standard for emergency countermeasures is 80pg/nm3 (TEQ). That is, if a waste incineration
plant cannot reach the emission concentration below 80pg/nm3 (TEQ), reduction measures should be taken immediately. Even if the emission concentration does not exceed this standard, the waste incineration plant should continue to implement permanent countermeasures and strive to control the emission of dioxins. The "permanent countermeasures" in the "new guidelines" stipulates that the dioxin emission concentration standard of the new fully continuous operation incinerator is set at 0.1ng/nm3 (TEQ).
Dioxin control measures
Research and practice at home and abroad have shown that the main method to reduce the concentration of dioxin in the flue gas of domestic waste incineration plant is to take effective measures to control the formation of dioxin. These control measures mainly include:
1. Choose a suitable furnace and grate structure to make the garbage fully burned in the incinerator. One of the important indicators to measure whether the garbage is fully burned is the concentration of CO in the flue gas. The lower the concentration of CO, the more sufficient the combustion is. The ideal index of CO concentration in the flue gas is less than 60mg/ Nm3;
2. Control the temperature of flue gas in the furnace and secondary combustion chamber, or in the flue before entering the waste heat boiler, not less than 850 ℃, the residence time of flue gas in the furnace and secondary combustion chamber is not less than 2S, and the O2 concentration is not less than 6%, and reasonably control the air volume, temperature and injection position of combustion supporting air, also known as "three T" control method;
3. Shorten the time when the flue gas is in the temperature range of 300 ~ 500 ℃ in the process of treatment and discharge, and control the exhaust gas temperature of waste heat boiler not to exceed about 250 ℃;
4. Select a new bag type dust collector, control the flue gas temperature at the inlet of the dust collector to be lower than 200 ℃, and set an injection device of activated carbon and other reactants on the flue entering the bag type dust collector to further absorb dioxins;
5 set up an advanced, perfect and reliable automatic control system in the domestic waste incineration plant, so that the incineration and purification process can be well implemented;
6. Control the substances with high content of chlorine and heavy metals in domestic waste to enter the waste incineration plant through classified collection or pre sorting;
7 because dioxins can be adsorbed or generated on fly ash, fly ash is collected in special containers and sent to a safe landfill for harmless disposal as toxic and harmful substances. If possible, fly ash can be heated and dechlorinated at low temperature (300 ~ 400 ℃), or sent to a safe landfill for disposal after melting and solidification treatment, so as to effectively reduce the emission of dioxins in fly ash.