At present, the methods of flue gas purification in waste incinerators can be divided into several kinds.
The spray drying method is to install a high-speed rotating spray head on the upper part of the absorption tower. When the slurry purifying acid gas is sprayed on the spray head, it is atomized and reacts with the flue gas entering the tower to neutralize, so harmful acid gas in the flue gas should be removed. The particulate matter in the flue gas is captured by the bag filter behind, so as to achieve the purpose of dust removal and acid removal.
1.2 suspended fluidized bed method
It is characterized by the use of boiler fly ash and the addition of deacidifiers (both reacted and not completely reacted) as circulating materials, large surface area, great reactivity and reaction surface area between gas, solid and liquid, good mixing and contact, strong heat and mass transfer. The residence time of the deacidifier in the absorber is prolonged by the repeated circulation of the dust, thus improving the utilization ratio of the deacidifier.
If a high deacidification effect is to be achieved, the amount of circulating ash is very large, and the dust concentration entering the bag filter is extremely high, reaching 1000g/m3. This bag filter on the high requirements, generally the best front set pre-precipitator, in order to reduce the bag filter dust load. Therefore, the requirements for filter bags are high and the resistance is low.
The NID method is also called the humidification and ash circulation desulphurization technology. It usually uses CaO as a desulfurizer, digests it into Ca (OH) 2 by adding water in a special digester, and then adds the circulating ash collected by the dust collector to the mixed humidifier, humidifies it with water and feeds it into the desulfurization tower, reacts with hot flue gas in the tower, and enters the dust collector together.
1.4 dry cleaning method -- pipe injection flue gas desulfurization technology
At present, this method can not only meet the requirements of environmental protection, but also is the most economical and convenient way to maintain and manage the waste incineration flue gas. Compared with semi-dry rotary spray drying, it does not need pulping system, nozzles are not easy to wear and tear, maintenance is simple; compared with fluidized bed deacidification tower, there is no large amount of circulating ash returned to deacidification tower, will not produce the danger of deacidification tower collapse, but also reduce the load of bag dust collector, reducing system resistance, saving energy consumption.
The composition of flue gas and soot produced by refuse incineration is different from that of coal-fired boilers. Although it changes with the original composition of refuse, the concentration of HCL in flue gas is the highest, generally up to 1000 mg/Nm3, and the content of SO2 is lower than that of coal-fired boilers, generally below 500 mg/Nm3, in addition to HF and other acidic gases. In smoke, there are some heavy metals and dioxins and other harmful substances.
There are several kinds of filter materials used in MSW incinerators.
SUPERFLEXTW "King of Incineration" is a kind of fabric membrane filter material developed by GORE Company in the United States. It is widely used in waste incinerators at present. It has good filtration performance, easy ash removal resistance stability, and in the fabric filter is a good resistance to mechanical bending fatigue strength filter material. However, in the manufacture, packaging, transportation, installation, use should pay attention to the protection of the surface of the film, so as not to damage the film and affect the use effect.
This filter material is used more widely in coal-fired boilers and is in good use. He maintains a stable chemical resistance to organic solvents, alkalis, and most acids (except certain oxidants, such as concentrated nitric acid), but is not resistant to oxidation at temperatures below 200 degrees Celsius. According to the practical application, in order to have a longer service life, it is necessary to operate at 150 C and with low oxygen content. Because of the high moisture content of the flue gas of domestic refuse incinerators, the higher superoxide coefficient during combustion and the higher exhaust temperature, if the acid in front of the incinerator can not be guaranteed to be removed well, the actual life is not long.
It is characterized by natural irregular blade-shaped hollow section, good dust trapping performance, in actual operation, to have a longer service life, the previous use should be below 200 C, when the temperature exceeds 140 C, a certain amount of water vapor, there will be hydrolysis problems. This filter material, like PPS, is not ideal for waste incinerators in China.
This kind of fiber has excellent chemical stability, no aging, poor physical strength, poor dimensional stability at high temperature, and high price. This filter material should be used for a long time in refuse incineration, because the imported filter material is too expensive to use less. At present, the production and performance of the company in China are still to be observed.
3.SP dry wet purification method -- selection of filter material for pipe injection flue gas desulfurization technology
Unlike the previous purification methods, the deacidification process takes place in pipes and bag filters. Further reaction on the bag surface is an important step. It does not increase the dust concentration at the inlet of bag filters too much. This method is aimed at the characteristics of waste incineration flue gas: the concentration of sulfur dioxide in the flue gas is lower than that of hydrogen chloride, and the removal of the latter is easier than the former.
4. about glass fiber filter media
GM800 is a double-sided fabric of glass fiber surface is PTEE membrane filter, micropore in 0.3-0.5 micron, 875 grams per square meter.
To sum up, we think that the filter material selection of MSW incinerator should be combined with the previous flue gas purification methods, comprehensive consideration is more appropriate. For example, in dry purification, the filter bag to maintain a moderate thickness of dust, to improve deacidification, removal of dioxins, heavy metals will be better. It is better to choose the glass fiber filter material with good performance and quality after treatment than the membrane filter material in terms of performance and economy. However, if the other semi dry flue gas purification systems are selected, they should be burned.