Bag filter used filter bags how to dispose of?

Bag filter used filter bags how to dispose of?

Bag filter has a history of more than 100 years, its biggest advantage is that the dust removal efficiency can be as high as 99.99% or more, and the emission concentration can reach below 10mg/m3, its classification efficiency is also high, and it has good capture efficiency for micro-particles below 2.5μm, so it is widely used.

Bag filter in its operation at the same time, will also produce a large number of broken waste, old filter bags, but because most of these bags are synthetic chemical fiber raw materials manufacturing, poor biodegradability, in nature is difficult to be degraded; and because there is no effective disposal method, randomly piled up and become a new source of pollution. Therefore, how to effectively dispose of the broken used filter bags has become an urgent problem.

1 China’s domestic filter bag market status

China’s early domestic bag filter bag for the use of ordinary industrial woven fabric, Wuhan Metallurgical Safety Research Institute in 1974 developed 208 industrial polyester cloth, has been widely used, until now there are still some occasions in use.

Early 1980s, Northeastern University and Fushun third woolen mill jointly developed needle felt non-woven filter media, from the traditional woven filter media to non-woven filter media, to achieve This revolutionary change of filter media has started the process of localization of filter media. Compared with woven filter media, non-woven filter media has short production process, high production efficiency, high degree of automation and low price, which can be widely used in various dust removal applications.

The performance of filter media depends on the characteristics of fibers, and the types of fibers are developing rapidly while generating process changes. From the early natural fiber, polyester fiber, glass fiber filter media, to synthetic fibers such as NOMEX, PPS, PTFE, etc., currently NOMEX, PPS, PTFE, P84 and other fibers have been localized.

While the varieties of filter media are constantly innovating, the output of filter media is also developing rapidly. In the 20 years from 1985 to 2005, the output of filter media in China has increased more than 23 times, and since the 21st century, the development of filter media has been even faster, and the output of filter media has almost doubled in just 3 years from 2005 to 2008.

There are 2 large enterprises with annual output of more than 5 million meters. It is expected that the domestic production of filter media in China will reach more than 90 million meters in 2010. As can be seen, the annual elimination of the number of used filter bags and the accumulation of broken over the years is also astronomical.

Bag filter used filter bags how to dispose of

2 broken used filter bag disposal methods

2.1 Furnace melting re-drawing

The broken used filter bags will be recycled, cleaned back to the furnace melting, drawing; re-made fiber, recycling. This is the best way to solve the broken used filter bags. However, in practice it is difficult to achieve, because of the following problems.

2.1.1 Collection, transportation problems

Over the years the accumulation of broken used filter bags, a huge number of these bags are distributed throughout the country, and in the case of damage time is uncertain, it is difficult to collect them all for unified treatment; secondly, due to the surface of the used filter bags attached to a large amount of dust, so in transport, especially in the long-distance transport process is difficult to ensure that the dust does not fly around, become a mobile source of pollution and pollution of the surrounding environment.

2.1.2 Cleaning problem

Cleaning of broken used filter bags is a very troublesome and difficult problem. As the surface of the used filter bag has a lot of dust sticky, and the composition of these dust complex (such as garbage incineration and other industries used filter bags, the surface contains heavy metals, dioxins and other toxic, harmful, corrosive substances), in the cleaning of used filter bags will produce a large amount of sewage and sludge.

And these sludge containing heavy metals, dioxins and other toxic, harmful and corrosive substances belong to the hazardous chemicals, and the disposal of hazardous chemicals is much more complicated. This makes the cleaning of used filter bags also becomes complicated.

2.1.3 Waste filter bag fiber composition complex

Early filter bag mainly using natural fibers: such as cotton, hemp and animal fibers, etc., simple structure, single component. And the current filter bag is basically a mixture of two or more synthetic fibers spun (some surfaces are also used to cover the film).

Such as gradient filter media, its structure from the outside to the inside: the surface layer: ultra-fine fibers; base layer: fine fibers; skeleton: coarse fiber layer after the surface layer of the base cloth. p84 + PPS gradient fiber composite filter media belongs to such a structure. Due to the low price of glass fiber filter media, the use of PTFE, PPS fiber + glass fiber (base cloth) made of gradient structure, can effectively reduce the price of filter media, improve the filtration performance and ash cleaning performance.

PTFE and PPS fine fibers as the windward layer of filter media can effectively trap dust particles, and also have a better effect on tiny particles; better ash cleaning effect; the bottom layer of base cloth is mainly used to support and resist skeleton friction corrosion. Therefore, the trapping ability of gradient filter media for tiny particles is significantly higher than that of ordinary filter media.

At present, in addition to individual manufacturers in order to reduce production costs, most of the filter media are basically made of two or more synthetic fibers mixed with spinning. In order to improve the performance of the filter media and processing process needs, for example, the key to the needle felt filter media processing process is the uniformity of the fiber, and the key to uniformity lies in the two processes of opening and carding. As the needle felt production process is short, it is difficult to control the uniformity.

Therefore, sometimes other fibers have to be mixed into the fiber to ensure its uniformity for the sake of processing. For example, PTFE fiber, due to its fiber dielectric constant is very large, when opening and carding generate a lot of static electricity, resulting in processing difficult to open and carding. And after adding 5% polyester, its performance of opening and combing is greatly improved, and processing becomes easy.

To sum up, as modern filter media is a mixture of many kinds of fibers spun into it. Therefore, when the cleaned waste filter bag back to the furnace melting, drawing and face the following difficult to solve the problem: 1) how to determine the melting temperature, because the melting temperature of various fibers is different; 2) redraw the material of the silk is uncertain; 3) redraw the new silk of the physical and chemical properties of how to ensure.

2.1.4 Chemical changes in the fiber composition of the original used filter bag

Bag filter flue gas composition is complex, the use of harsh environments, after a long period of use of the chemical composition of the filter bag material are also chemical changes. The main reasons for the chemical changes in the filter bag material are.

(1) oxidation

Oxidation is one of the main factors of damage to the filter bag. Fiber oxidation is the process of molecular loss (or dissociation) of electrons in the fiber, this reaction increases the oxygen atoms of the elements in the fiber. In the commonly used fibers are susceptible to oxidation is mainly polymeric compounds, such as polypropylene, polyphenylene sulfide, etc.. After oxidation, the large molecular chains of the fiber are broken up and turned into small molecular structures. The molecular structure has changed, and the fiber properties have changed.

(2) Hydrolysis

Hydrolysis is the reverse reaction of condensation. Fiber hydrolysis is due to the intervention of water molecules into the fiber and polymer decomposition into two reactions, a part of the parent molecule from the water molecule to obtain a hydrogen ion (H +), while another group from the water molecule gathered hydroxyl (OH-), so that its molecular chain breaks to generate new small molecules of the process. As the molecular weight becomes smaller, the tensile strength of the fiber is weakened and damaged. Therefore, synthetic fibers produced by condensation-type polymers are not resistant to hydrolysis. Such as the commonly used polyester type, polypropylene, Nomex and other filter media are very easy to hydrolysis.

Hydrolysis will destroy the main structure of the polymer, so that the fiber molecules become smaller. The higher the water molecule content and temperature in the flue gas, the more serious the hydrolysis of the filter bag. Different filter media have different hydrolysis temperatures. After hydrolysis, the strength of the filter bag is seriously reduced and easy to break, and after the hydrolysis of the sewing line, the filter bag cracks from the sewing line, so that the filter bag is no longer a cylinder and becomes a piece of cloth.

Bag filter used filter bags how to dispose of

(3) Acid and alkaline corrosion

Corrosion is one of the most common reasons for filter bag damage. Flue gas contains a variety of corrosive substances, the corrosion effect is greater in the high temperature environment, which will cause damage to the filter bag.

The main reason why the filter bag is corroded is that the flue gas contains acid and alkaline components, with the change of concentration of these chemicals and cause changes in the dew point, such as dust collector start or stop in the dew point below, the SO2 in the exhaust gas will form H2SO3 when it meets water, resulting in carbonization of the filter bag fiber, the original molecular chain structure is damaged, resulting in small molecular compounds.

Filter bag is corroded and damaged traces are mostly radial, and the formation of a large area of discoloration on the surface of the filter bag, resulting in the filter bag hardened, brittle and a small number of irregular holes, can be distinguished with the naked eye. Figure 3 for a magnesium oxide plant in Henan chlorination section was corroded filter bag, due to the very high content of HCl in the flue gas of the plant, PTFE filter bag average service life of less than 3 months was corroded to a lot of holes can not continue to use. Therefore, if pulse bag cleaning is carried out under this condition, it will accelerate the damage of filter bags.

Bag filter used filter bags how to dispose of

(4) Fiber high temperature degradation

As most of the filter bags are working at high temperature, high temperature will cause the filter bag fiber vitrification, so that the filter bag fiber degradation changes, resulting in fiber macromolecular chain breakage. From the outside, the high temperature causes the filter bag to shrink and deform, become hard, and the filter bag is tightly hooped on the skeleton, and even the skeleton in the filter bag cannot be withdrawn, thus forming deep traces on the inner surface of the filter bag, and making the filter bag fiber vitrification become extremely fragile and strength reduced.

The filter bag of a waste incineration plant dust collector, the filter bag material is PPS fiber, high temperature makes the PPS fiber become extremely fragile, strength reduced, gently pull, it will tear a long mouth.

2.1.5 Economy

In summary, due to the existence of waste filter bags collection, transportation, cleaning, secondary pollution and disposal costs are high, there are also difficulties in heating melting re-drawing and the performance and price of the newly pulled fiber yarn is difficult to determine, so the recycling of waste filter bags from the economic point of view, is time-consuming and difficult to do, no economic benefits.

2.2 Incineration

Incineration is an effective means to achieve the reduction of used filter bags, harmless, and is currently one of the most effective ways to solve the broken, used filter bags. Although there is also the possibility of secondary pollution in the incineration process, but the incineration can be achieved after the reduction of quantification, capacity reduction and stabilization. Organic synthetic fibers will become CO2 and H2O and other gases after the incineration of used filter bags, while glass fiber filter bags will become SiO2 and other fibers after high temperature incineration, thus achieving harmlessness.

2.3 Landfill

Landfill is the most simple and practical way to solve the waste filter bag, and is also the most applied method.

2.4 Other uses

At home and abroad, there is no used filter bags in other aspects of the application of the report, but it is also known to be used in the waste filter bag cleaning on the fence, captive livestock. This can be associated with, such as used filter bags as a base cloth used in the planting of lawn, can replace the current lawn planting used as a base cloth, is also a better use, but to prevent its pollution of groundwater.

3 Summary

(1) As the filter bag using chemical fiber synthetic raw materials, its poor biodegradability. Waste filter bags in nature is difficult to be biodegradable, and will become a new source of pollution.

(2) incineration is currently a better way to deal with used filter bags.

(3) collection, transportation, cleaning, drying, melting and other difficult processes, is the key to the difficulty of recycling of used filter bags.

(4) economics is also one of the main problems of used filter bags difficult to recycle.

(5) the most ideal disposal of used filter bags is collected, melting and drawing, reuse, but in the current technical conditions is difficult to achieve.

(6) used filter bags used in the planting of lawns to prevent pollution of groundwater.

(7) landfill is currently the most simple and practical way to dispose of used filter bags, but also the most applied method.

Hengke is a China trusted manufacture and supplier for dust filter bag in various countries. Hengke has designed and produced all types, sizes, and configurations of dust filter bag for more than 20 years. Being in the business for two decades, the company offers a wide range of products including dust filter bag, needle punched felts, dust collector bag, filter fabricfilter bag cagePulse valve etc. Till now, our products have been successfully exported to over 35 countries.

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