The bag type dust collector has a history of more than 100 years. Its biggest advantage is that the dust removal efficiency can reach more than 99.99%, the emission concentration can reach less than 10mg/m3, and its classification efficiency is also very high. For 2.5 μ Fine particles below m also have good trapping efficiency, so they are widely used. While the bag filter operates, it will also produce a large number of damaged waste and old filter bags. However, because most of these filter bags are made of synthetic chemical fiber raw materials, they have poor biodegradability and are difficult to be degraded in nature; At present, there is no effective disposal method, so random stacking has become a new pollution source. Therefore, how to effectively dispose of damaged waste filter bags has become an urgent problem to be solved.
At present, most of the filter materials are basically blended with two or more kinds of synthetic fibers, except for some manufacturers who want to reduce production costs and replace the inferior with the good. In order to improve the performance of filter material and the requirements of processing technology, for example, the key to the processing technology of needle felt filter material is the uniformity of fiber, and the key to the uniformity lies in the two processes of loosening and carding. Due to the short production process of needled felt, the evenness is difficult to control. Therefore, sometimes in order to facilitate processing, other fibers should be mixed into the fibers to ensure their uniformity. For example, PTFE fiber is difficult to be loosened and combed during processing due to its very large dielectric constant and large static electricity during loosening and carding. After adding 5% polyester, the opening and carding properties are greatly improved, and the processing becomes easier.
To sum up, modern filter materials are made of mixed spinning of various fibers. Therefore, when the cleaned waste filter bags are returned to the furnace for melting and wire drawing, the following problems are difficult to solve:
1) How to determine the melting temperature, because the melting temperature of various fibers is different;
2) The material of the re drawn wire is uncertain;
3) How to guarantee the physical and chemical properties of the new silk pulled out again.
Chemical changes in fiber composition of the original waste filter bag
The flue gas composition of the bag filter is complex and the operating environment is bad. After long-term use, the chemical composition of the filter bag material has also changed. The main reasons for the chemical change of filter bag material are as follows:
Oxidation is one of the main factors of filter bag damage. Fiber oxidation is a process in which the molecules in the fiber lose (or dissociate) electrons. This reaction will increase the oxygen atoms of the elements in the fiber. Polymeric compounds, such as polypropylene and polyphenylene sulfide, are easy to be oxidized in common fibers.
Hydrolysis is the reverse reaction of condensation. Fiber hydrolysis is a reaction in which water molecules intervene in the fiber to decompose the polymer into two. One part of the parent molecule obtains a hydrogen ion (h+) from the water molecule, while the other group gathers hydroxyl (oh-) from the water molecule, breaking its molecular chain to form new small molecular substances. As the molecular weight becomes smaller, the tensile strength of the fiber is weakened and damaged. Therefore, the synthetic fiber produced by polycondensation polymer is not resistant to hydrolysis. For example, commonly used polyester, polypropylene, Nomex and other filter materials are prone to hydrolysis.
Acid and alkaline corrosion
Corrosion is one of the most common causes of filter bag damage. The flue gas contains a variety of corrosive substances, which will cause greater corrosion in high temperature environment, thus causing damage to the filter bag.
The main reason for the corrosion of the filter bag is that the flue gas contains acid and alkaline components. With the change of the concentration of these chemicals, the dew point changes. For example, when the dust collector is started or shut down below the dew point, SO2 in the waste gas will form H2SO3 when encountering water, resulting in the carbonization of the filter bag fiber, the damage of the original molecular chain structure, and the formation of small molecular compounds.
Fiber degradation at high temperature
Since most filter bags work at high temperature, high temperature will cause the glass state of filter bag fiber, degrade the filter bag fiber and cause the fracture of fiber macromolecular chain. From the appearance, the high temperature causes the filter bag to shrink, deform and harden, the filter bag is tightly bound to the skeleton, and even the skeleton in the filter bag cannot be extracted, thus forming deep traces on the inner surface of the filter bag (as shown in Figure 4), and making the glass of the filter bag fiber extremely fragile and the strength reduced. Figure 5 shows the filter bag of the dust collector in a Guangzhou waste incineration plant. The filter bag is made of PPS fiber. The high temperature makes the PPS fiber extremely fragile and reduces its strength. A slight pull will tear a long hole.
Incineration is an effective means to realize the reduction and harmlessness of waste filter bags, and it is also one of the most effective methods to solve the problem of damaged and waste filter bags at present. Although there is the possibility of secondary pollution in the incineration process, the reduction, volume reduction and stabilization can be realized after incineration. After the waste filter bag is incinerated, the organic synthetic fiber will become CO2, H2O and other gases, while the fiber of the glass fiber filter bag will become SiO2 and other gases after high-temperature incineration, so as to achieve harmless.
Landfill is the most simple and practical method to solve the problem of waste filter bags, and it is also the most widely used method at present.
At present, there is no report that the waste filter bags have been applied in other aspects at home and abroad, but it is reported that some people have cleaned the waste filter bags and used them in fences to raise livestock. Therefore, it can be imagined that if the waste filter bag is used as the base cloth for lawn planting, it can replace the current base cloth for lawn planting. It is also a better use, but its pollution to groundwater should be prevented.
(1) Because the filter bag uses synthetic chemical fiber raw materials, its biodegradability is poor. The waste filter bag is difficult to be biodegraded in nature and will become a new pollution source;
(2) Incineration is a better way to dispose waste filter bags at present;
(3) Difficulties in the process of collection, transportation, cleaning, drying and melting are the key to the difficult recycling of waste filter bags;
(4) Economy is also one of the main problems that waste filter bags are difficult to recycle;
(5) The most ideal disposal method of waste filter bag is to melt and wire drawing after collection and reuse, but it is difficult to realize under the current technical conditions;
(6) Waste filter bags should be used to prevent groundwater pollution when planting lawns;
- Landfill is the most simple and practical method to dispose waste filter bags at present and it is also the most widely used method.
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