Brief introduction of the hottest modern boiler du

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Introduction to modern boiler dust removal equipment

in recent years, with the rapid development of economy, the number of boilers using raw coal as fuel has increased a lot, and the air pollutants emitted by coal-fired boilers cause great harm to the surrounding environment. However, the main way to reduce or reduce the pollutants emitted by coal-fired boilers is all kinds of smoke and dust collectors matched with boilers, The performance and efficiency of the dust collector is the key to determine the degree of harm a boiler causes to the surrounding environment

since August 1st, 1992, the national maximum allowable emission concentration of boilers has been 200mg/n.m3 and 400mg/n in class I, class II and class III areas m3 、600 mg/N . M3, increased to 200 mg/n respectively m3、300 mg/N . m3、400 mg/N . m3。 Newly approved boilers for installation or replacement: the maximum smoke and dust emission concentration in class I area, class II area and class III area is 100 mg/N respectively m3、250 mg/N . m3、350 mg/N . m3。 In this way, the control standard is higher, and it is bound to produce a number of dust collectors that currently meet the current environmental protection standards, so as to achieve the purpose of smoke elimination and dust removal

the dust collectors installed in the boiler can be divided into two categories: ① dry dust collectors: including gravity settling chamber, inertia dust collector, electric dust collector, bag dust collector and cyclone dust collector. ② Wet dust collector: including spray tower, impact dust collector, venturi detergent, foam dust collector and water film dust collector. At present, cyclone separator, electrostatic precipitator and bag filter are commonly used

the following is a brief introduction to various dust collectors:

1 Gravity dedusting - purification equipment that uses the principle of different specific gravity of dust and gas to make the dust naturally settle down from the gas by its own gravity (gravity), which is usually called sedimentation chamber or birth chamber. It is a relatively primitive purification equipment with simple structure, large volume, small resistance, easy maintenance and low efficiency, which can only be used for rough purification. The working principle of the gravity dust chamber is shown in the following figure: the dusty gas enters the settling chamber at a uniform speed V in the horizontal direction from one side, and the dust particles sink and fall at the settling speed v. after running for t time, the dust particles settle at the bottom of the chamber. The purified gas is discharged from the outlet on the other side. (as shown in the figure below)

2 Inertia dust collector - inertia dust collector is also called inertia dust collector. Its principle is to separate dust from gas by using the difference of inertia force between dust and gas in motion. Generally, some form of obstacle is set in front of the dusty air flow, so that the direction of the air flow changes sharply. At this time, because the inertia force of dust is much greater than that of gas, the dust particles will be separated from the air flow, and the purified gas will be discharged after a sharp change of direction

the following figure shows several common weighted dust collectors. This dust collector has simple structure, low resistance (mm water column) and low purification efficiency (%). It is mostly used in the first stage of multi-stage purification, concentration equipment in purification or in combination with other purification equipment

the most commonly used inertial precipitator is the shutter type. (as shown in the figure below) it is suitable for purifying the air containing non viscous and non fibrous dust. It is usually used in combination with other kinds of dust collectors to connect with office and other office software to form a unit

3 Working principle of cyclone separator

the working principle of cyclone dust collector is shown in the figure below. The dusty gas is introduced from the inlet between the shell of the dust collector and the exhaust pipe to form a downward rotating outer swirl. The dust suspended in the outer swirl moves to the wall under the action of centrifugal force, and with the outer swirl, it turns to the lower part of the dust collector and is discharged from the dust discharge hole. The purified gas forms a rising internal swirl and is discharged through the exhaust pipe

application scope and characteristics: cyclone dust collector is suitable for purifying non viscous, non fiber dry dust greater than 5~10 microns. It is a purification equipment with simple structure, convenient operation, high temperature resistance, low equipment cost and resistance (80~160 mm water column). Cyclone dust collector is the most widely used in purification equipment

4. Working principle of bag dust removal technology:

⑴ gravity sedimentation effect - when the dusty gas enters the bag dust collector, the dust with large particles and large specific gravity will settle down under the action of gravity, which is exactly the same as the function of the sedimentation chamber

⑵ screening effect - when the particle diameter of the dust is larger than the gap between the fibers of the filter material or the gap between the dust on the filter material, the dust is blocked when the air flow passes through, which is called screening effect. When the accumulated dust on the filter material increases, this effect is more significant

⑶ inertia force effect - when the air flow passes through the filter material, it can pass around the fiber, while the larger dust particles still move in the original direction under the action of Zai inertia force, so they collide with the filter material and are captured

⑷ thermal movement effect - light and small dust (less than 1 micron) moves with the airflow, which is very close to the airflow streamline and can bypass the fiber. However, after they are collided by gas molecules with thermal motion (i.e. Brownian motion), they change the original direction of motion, which increases the contact opportunity between dust and fiber, so that dust can be captured. The finer the fiber diameter of the filter material, the smaller the void ratio, and the higher the capture rate, so it is more conducive to dust removal

bag filter has been widely used in various industrial departments for a long time, to capture non cohesive and non fibrous industrial dust and volatile matter, and capture dust particles up to 0.1 micron. However, when it is used to treat gas containing water vapor, condensation should be avoided. Bag filter has high purification efficiency, that is, the efficiency of capturing fine dust can reach more than 99%, and its efficiency is relatively stable. The schematic diagram of bag filter is as follows:

5 Electrostatic precipitator

working principle of electrostatic precipitator: when the gas containing dust particles passes through the high-voltage electric field formed between the cathode line (also known as corona electrode) connected with the high-voltage DC power supply and the grounded anode plate, due to the corona discharge of the cathode, the gas is ionized. At this time, the negatively charged gas ions, under the action of the electric field force, move towards the anode plate, and collide with the dust particles in the movement, so that the dust particles are negatively charged, Under the action of electric field force, the charged dust particles also move to the anode. When they reach the anode, they release the electrons they carry. The dust particles are deposited on the anode plate, and the purified gas is discharged out of the duster

according to the current common types of electrostatic precipitators in China, they can be roughly divided into the following categories: vertical and horizontal according to the direction of air flow, plate and tube according to the type of precipitation pole, dry and wet according to the dust removal method on the precipitation pole, etc

The sketch of

is as follows:

1- anode; 2-cathode; 3-Cathode upper bracket 4-anode upper bracket; 5-insulating support; 6-quartz insulating tube; 7-cathode suspension tube

8- cathode support frame; 9-top plate; 10 cathode rapping device; 11 anode rapping device; 12 cathode off the shelf; 13 anode hanging hammer

14- shell 15 - the first distribution plate at the inlet; 16 - the second distribution board at the inlet 17 - the distribution board at the outlet; 18 ash discharge device

advantages of electrostatic precipitator

⑴ high purification efficiency, capable of spreading fine dust of more than 0.01 micron. In the design, different operating parameters can be used to meet the required purification efficiency

⑵ the resistance loss is small, generally below 20mm water column. Compared with the cyclone, even considering the power consumption of the power supply unit and rapping mechanism, the total power consumption is still relatively small

⑶ the allowable operating temperature is high. For example, the allowable operating temperature of shwb circuit dust collector is 250 ℃, and other types reach 350~400 ℃ or higher

⑷ large range of gas treatment

⑷ automatic operation control can be fully realized

disadvantages of electrostatic precipitator:

⑴ the equipment is relatively complex, requiring a high level of equipment transportation, installation, maintenance and management

⑵ there is a certain requirement for automatic unloading of overload protection device for dust specific resistance, so there is a certain selectivity for dust, which can not make all dust obtain high purification efficiency

⑶ the operating conditions such as temperature and temperature are greatly affected. If the same kind of dust is operated at different temperatures and humidities, the effects are different. Some dust can be used effectively at a certain temperature and humidity, while the electrostatic precipitator can hardly be used at another temperature and humidity due to the change of dust resistance

⑷ the one-time investment is large, and the horizontal electrostatic precipitator covers a large area

(5) at present, the practical effect in some enterprises cannot meet the design requirements

6. High temperature ceramic dust collector:

for coal-fired combined cycle power generation system (IGCC), it is very important to develop a high-temperature gas purification system that can meet the requirements of both gas turbines and environmental protection. It is one of the most critical technologies for the true commercialization of coal-fired combined cycle power generation technology. High temperature ceramic filter is generally considered to be the most promising high temperature dust removal equipment at present. Ceramic filter filters the dust in high-temperature gas, and uses gravel layer (particle layer dust collector) or fiber layer (bag dust collector) to purify the gas, both based on the same filtration theory

At present, high-density materials are widely used as filter elements of ceramic filters, and the ceramic filter elements made mainly include rod type, steward type and cross flow type. The figure below shows a cross flow ceramic filter element, which is composed of thin porous ceramic plates, which are sintered to form a ribbed whole with channels. The dusty gas enters the filter from the short channel end, and then enters the long clean gas end of the channel after filtration in each channel. One end of the clean gas channel is sealed so that the clean gas flows into the clean gas collection tank, and the dust particles trapped in the short channel are regularly removed by reverse pulse air flow

7. Taking the water film dust collector as an example, the following introduces a wet dust collector:

using the dusty gas to impact the water film on the inner wall of the dust collector or other special components, so that the dust is captured by the water film and the gas is purified. This kind of purification equipment is called the water film dust collector. Including impact water film, inert (shutter) water film and centrifugal water film dust collector

the following is a schematic diagram of a CLS type water film dust collector:

the dusty gas is introduced tangentially from the lower part of the shell, rotates and rises, and the dust particles are separated by centrifugal force, thrown to the inner wall of the shell, absorbed by the water film flowing on the inner wall of the shell, and discharged with the water flow to the bottom cone through the dust outlet. The water film layer is formed by several nozzles arranged on the upper part of the future cylinder to spray water tangentially to the wall. In this way, the inner wall of the shell is always covered with a thin water film rotating downward to improve the dust removal effect. This kind of wet dust collector has simple structure and low metal consumption. It encourages children to move before, during and after class, with low water consumption. The disadvantage is that the height is large, the layout is difficult, and the phenomenon of water carrying is found in the actual operation

the above describes several common dust removal equipment in the project. Which one should be selected in practice should be determined according to their respective advantages and disadvantages and the actual situation. At present, electrostatic precipitators or bag filters are mostly used in large power stations. (end)

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