How to choose the filter material for boiler flue gas purification

Application fields:

Heat supply and power station boiler flue gas purification bag filter;

Coal-fired and gas-fired boiler flue gas purification bag filter;

Straw direct-fired power generation boiler flue gas purification bag filter;

Fuel co-fired boiler flue gas purification bag filter;

Garbage incineration and waste-coal co-firing boiler flue gas purification bag filter;

Domestic and medical waste incineration boiler flue gas purification bag filter.

SINO recommends:

PPS material filter material;

Composite filter material of PPS, P84, PTFE two or three fibers;

PTFE, glass fiber composite filter material.

Working condition analysis and filter material selection and determination:

The bag filter used for boiler flue gas purification is generally required to be synchronized with the overhaul period of boiler equipment. The service life of filter material (filter bag) of 30,000 hours has now become the basic service period required by thermal power plants. In addition to special requirements such as heating boilers and straw power generation boilers, the service life of filter materials is generally required to be 16,000 hours for straw power generation boilers, and 3 heating periods for heating boilers. However, for the flue gas dust removal of coal-fired power plant boilers, domestic application conditions are different from those of foreign countries, so when selecting filter materials, it is necessary to focus on analyzing the performance characteristics of flue gas, and the following points should be noted:

(1) Coal type: Foreign boilers usually use clean coal, while in my country, raw coal is mainly used, and there are differences in calorific value, ash content, S content, etc.;

(2) Equipment technology: boilers and other related equipment used in foreign developed countries have a high degree of automation, while domestic equipment generally has a combination of manual and automatic, which has a great impact on the stability of various characteristics of flue gas;

(3) Boiler equipment: Boiler equipment in developed countries abroad is relatively advanced, and there are still a large number of small and medium-sized equipment (especially early boilers) in China, and there are differences in the degree of old and new boilers;

(4) Comprehensive energy utilization: Blast furnace gas is burned, resulting in large fluctuations in flue gas volume and dust concentration, changes in gas composition, and rise in flue gas temperature.

(5) There are also certain differences in combustion methods and smoke exhaust methods.

Therefore, the application environment of the filter material is characterized by four highs, one large and one low (high exhaust gas temperature, high SO2 and NOX content in the flue gas; high oxygen content in the flue gas; high dust concentration; low filter bag resistance is required) . Due to the relatively harsh conditions of the flue gas emitted by coal-fired boilers, it will affect the service life of the filter material (filter bag). Therefore, when using filter materials in bag filters, we should learn from but not blindly copy the technology and experience of foreign counterparts. We should consider the actual situation of domestic boilers and choose filter materials in a targeted manner.

(1) General working conditions

At present, most of the filter bags of boiler bag filter bags in power plants are made of PPS needle felt filter material. There are also PPS+P84 composite fiber needle felt filter materials, and the P84 fiber content is about 20%. It is mainly aimed at boilers whose flue gas discharge temperature or dust collector inlet temperature is below 170°C and which use low-sulfur coal.

The scientific name of PPS is polyphenylene sulfide, referred to as PPS. PPS fiber is produced by only a few large chemical companies in the world, and the products of Japanese companies occupy the leading market. The registered trademark of TOYOBO Corporation is PROCON/General Resistance, the registered trademark of TORAY Corporation is TORCON/Telecom, and the registered trademark of PHILIP Corporation is RYTON/Leyton.

The scientific name of P84 is polyimide. Compared with the rod shape of PPS fiber, the cross section of P84 fiber is multilobal. Its irregular fiber cross section increases the surface area of the fiber, increases the air permeability of the needle felt, and has the effect of reducing resistance and increasing efficiency. P84 fiber is exclusively produced by LENZING Company in Austria.

Due to its good acid and alkali corrosion resistance, PPS fiber has been used in many working conditions, and the needle-punched filter felt made of it has played an important role in the field of boiler flue gas purification in power plants. PPS fiber can maintain good filtration performance in a certain environment and achieve an ideal service life due to its integrity retention of strength and inherent chemical resistance. It is widely used in the pulse bag filter in the fields of coal-fired boilers, garbage incinerators, dust collection and treatment of fly ash in power plants, etc. PPS filter felt exhibits excellent filtration performance under general working conditions, and its application conditions mainly depend on the performance of PPS fibers. The most suitable conditions for coal-fired flue gas dust removal are:

Working temperature: long-term working flue gas temperature 120-160 ℃;

Oxygen content: applicable to occasions where the oxygen content of flue gas is 8% or less;

Sulfur and nitrogen oxide content: SO2 content in flue gas<800mg/m3; NOx content<700mg/m3, NO2 content<15mg/m3;

Ash: coal ash <30%;

Flue gas humidity: moisture content in flue gas <12%;

Before starting the boiler operation, pre-coating is required;

It is not suitable to directly enter the bag filter when the fuel injection point furnace, the boiler tube bursts, and the flue gas exceeds the temperature, and a bypass flue is required;

The design filter wind speed of the bag filter is about 1.0m/min, and the design resistance of the filter is 1500Pa.

The filter bag of the bag filter bag in normal operation guarantees a service life of 30000h. In order to reduce the resistance of the filter material and increase the temperature resistance, PPS+P84 composite fiber needle felt is used.

(2) Special working conditions

In the traditional field of high-temperature dust collection, PPS fibers mainly appear in the form of needle-punched felts of single-specification PPS fibers. The filter bag made of it shows the good characteristics of PPS, mainly anti-acid and alkali corrosion, and good hydrolysis resistance. However, due to the special inherent characteristics of Chinese coal-fired boilers, such as high sulfur content, large dust, high oxygen content, and high moisture content, conventional PPS needle felts are not very effective when used in industrial and mining industries such as Chinese power plants. In order to solve these problems, filter material manufacturers around the world have successively developed various improved PPS needle-punched felt products, such as PPS film-coated filter material and our gradient special filter material. It is mainly aimed at the characteristics of high temperature, high humidity, and high sulfur at the inlet of the dust collector, or the simultaneous operation of the desulfurization device and the dust collector, and the exhaust gas temperature is above 170°C.

In order to reduce the resistance of the filter material, the filter material needle-punched felt made of PPS fibers with a single fineness (referred to as conventional filter material) was further improved into a filter material needle-punched felt with a fiber gradient structure made of PPS fibers of different finenesses (referred to as gradient filter).

The main technical features are:

(1) The cross-sectional structure of the needle felt adopts a gradient hierarchical structure in which the fiber fineness increases layer by layer. It consists of four layers: the superfine fiber layer, the fine fiber layer, the base cloth, and the thick fiber layer. The finer the fibers, the denser the ventilation channels. Gradient filter material features: The fiber in the filter material adopts a trend of gradually increasing fineness from the dust-facing surface to the clean air surface, forming a fluid channel that is dense at the front and sparse at the back, changing from the equal-width flow channel of traditional needle felt to the narrow front. The wide trapezoidal flow channel at the back makes the filter aperture in the filter material like a curved trumpet shape. The aperture on the dust-facing surface is very small, close to the film-coated filter material, and the filtration accuracy is very high. The closer to the clean air surface, the larger the aperture. , In this way, dust is not easy to block the tiny pores of the filter material during filtration, and the air permeability is good, thereby reducing the pressure drop of the filter material, reducing the frequency of cleaning, saving energy, and prolonging the service life of the filter material.

(2) The surface filtration technology of the film-coated filter material is used for reference. Transform the traditional needle-punched felt made of single fineness fiber or mixed fiber into gradient fiber needle-punched felt, and the filtration method is changed from "surface layer + deep layer" to "surface layer filtration", and the surface layer of filter material formed by ultrafine fibers blocks fine dust Increased grain capacity.

The trapezoidal channel with a narrow front and a wide rear makes it difficult for the inner layer of the filter material to collect dust, which keeps the filter material running for a long time and slows down the rate of rise and change of the inherent resistance of the filter material.

The superfine fiber layer is used for the surface layer, which makes the surface of the needle-punched felt denser, improves the ability to block fine dust particles, and is easy to clean the surface.

(3) The needle felt fiber is impregnated with PTFE (polytetrafluoroethylene), so that the surface of the fiber is coated with PTFE film. Improve the corrosion resistance, oxidation resistance and temperature resistance of the fiber, and enhance the water repellency of the filter material.

(4) The needle felt fiber is impregnated with silicone to enhance the wear resistance of the fiber, the water repellency of the filter material and the temperature resistance.

After adopting various technical improvements, the performance of the filter material has been significantly improved, which can prolong the service life of the filter material. The main technical indicators of the improved filter material are: flue gas temperature 120-180 ℃, SO2 content in flue gas<2000mg/m3, NOx content<1200mg/m3, oxygen content<10%, dust collector resistance 1200Pa.

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