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Author of the application of wear-resistant ceramics in modern boiler dust removal equipment: Yao Yufei In recent years, with the rapid development of the economy, the number of boilers using raw coal as fuel has increased a lot. The air pollutants emitted by coal-fired boilers have caused great harm to the surrounding environment. However, the main way to reduce or reduce the pollutants emitted by coal-fired boilers is through various smoke elimination and dust collectors matched with the boilers. The performance and efficiency of the dust collector are the key to determining the degree of harm a boiler causes to the surrounding environment. From August 1, 1992, * * As for the maximum allowable emission concentration of boilers, the existing 200mg/N.m3, 400mg/N.m3, and 600 mg/N.m3 in Class I, II, and III areas have been increased to 200 mg/N.m3, 300 mg/N.m3, and 400 mg/N.m3 respectively. Newly installed or replaced boilers: The highest smoke emission concentrations in Class I, II and III areas are 100 mg/N .m3, 250 mg/N .m3 and 350 mg/N .m3 respectively. In this way, the standard of control is higher, and a batch of dust collectors that currently meet the current environmental protection standards are bound to be produced to achieve the purpose of smoke and dust removal. Dust collectors installed in boilers can be divided into two categories:: ①Dry dust collector: Including gravity settling chamber, inertial dust collector, electrostatic precipitator, bag dust collector and cyclone dust collector. ②Wet dust collector: Including spray towers, impact dust collectors, venturi detergents, foam dust collectors and water film dust collectors, etc. At present, the most commonly used ones are cyclone separators, electrostatic precipitators and bag dust collectors. Among them, the cyclone separator is seriously worn, and the most commonly used solution is to line the inner wall with wear-resistant ceramics. The following is a brief introduction to various dust collectors:: 1. Gravity dust removal - Purification equipment that uses the principle of different specific gravity of dust and gas to make dust naturally settle from the gas by its own gravity (gravity). It is usually called a settling chamber or a birth chamber. It is a relatively primitive purification equipment with simple structure, large volume, low resistance, easy maintenance and low efficiency, and can only be used for rough purification. The working principle of the gravity dust collection chamber is shown in the figure below: The dust-containing gas enters the settling chamber from one side at a uniform speed V in the horizontal direction, and the dust particles fall down at a 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 picture below) 2. Inertial dust collector - Inertial dust collector is also called inert dust collector. Its principle is to use the difference in inertial force between dust and gas in motion to separate dust from gas. Generally, some form of obstacle is set up in front of the dust-laden airflow to drastically change the direction of the airflow. At this time, the inertial force of the dust is much greater than that of the gas, so the dust particles break away from the air flow and are separated. The purified gas is discharged after changing its direction sharply. The picture below shows several common types of sexual dust collectors. This kind of dust collector has a simple structure, small resistance (10-80 mm water column), and low purification efficiency (40-80%). It is mostly used in the first stage of multi-stage purification, concentration equipment in purification, or used in conjunction with other purification equipment. The louver type is the most commonly used inertial dust collector. (As shown below) It is suitable for purifying air containing non-viscous and non-fibrous dust. It is usually used in combination with other types of dust collectors to form a unit. 3. Working principle of cyclone separator: The working principle of the cyclone dust collector is shown in the figure below. The dust-containing gas is introduced from the inlet between the dust collector casing and the exhaust pipe, forming a downward rotating external swirl flow. The dust suspended in the external swirling flow moves toward the wall of the device under the action of centrifugal force, and is transferred to the lower part of the dust collector with the external swirling flow, and is discharged through the dust discharge hole. The purified gas forms an upward swirling flow and is discharged through the exhaust pipe. Application scope and characteristics: Cyclone dust collector is suitable for purifying non-sticky, non-fibrous dry dust larger than 5~10 microns. It is a kind of purification equipment with simple structure, easy 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 - when dust-containing gas enters the bag dust collector, dust with large particles and heavy specific gravity will settle under the action of gravity, which has the same function as the sedimentation chamber. ⑵ Screening effect - When the particle diameter of the dust is larger than the gaps between the fibers of the filter material or the gaps between the dust on the filter material, the dust will be blocked when the airflow passes through, which is called the sieving effect. This effect becomes more significant when the amount of dust accumulated on the filter material increases. ⑶ The effect of inertia force - when the air flows through the filter material, it can pass around the fibers, but the larger dust particles still move in the original direction under the action of inertia force, and then collide with the filter material and be captured. ⑷ Thermal movement effect - light and small dust (below 1 micron) moves with the air flow, is very close to the air flow streamline, and can bypass the fiber. However, after being collided with gas molecules undergoing thermal motion (i.e. Brownian motion), they change their original direction of movement, which increases the chance of contact between dust and fibers, allowing dust to be captured. When the diameter of the filter fiber is smaller, the void ratio is smaller and the capture rate is higher, so it is more conducive to dust removal. Bag dust collectors have been widely used in various industrial sectors a long time ago to capture non-adhesive, non-fibrous industrial dust and volatile matter, and capture dust particles up to 0.1 micron. However, when using it to handle gases containing water vapor, condensation problems should be avoided. The bag dust collector has a very high purification efficiency. Even the efficiency of collecting fine dust can reach more than 99%, and its efficiency is relatively stable. The simplified diagram of bag dust collector is as follows: 5. Working principle of electrostatic precipitator: When the gas containing dust particles passes through the high-voltage electric field formed between the cathode wire (also called corona electrode) connected to the high-voltage DC power supply and the grounded anode plate, corona discharge occurs at the cathode and the gas is ionized. At this time, the negatively charged gas ions, under the action of the electric field force, It moves toward the sun plate and collides with the dust particles during the movement, so that the dust particles are charged with a negative charge. Under the action of the electric field force, the charged dust particles also move toward the anode. After reaching the anode, the electrons they carry are released, and the dust particles are deposited on the anode plate, and the purified gas is discharged out of the dust filter. According to the current common types of electrostatic precipitators in China, they can be roughly divided into the following categories:: According to the direction of air flow, it is divided into vertical and horizontal types, according to the type of precipitation electrode, it is divided into plate type and tube type, and according to the method of removing dust on the precipitation electrode, it is divided into dry type and wet type. The simplified diagram is as follows: 1-Anode ； 2-Cathode ； 3-Cathode upper shelf 4-Anode upper bracket ； 5-Insulation support ； 6-Quartz insulation tube ； 7-Cathode suspension tube ； 8-Cathode support frame ； 9-top plate ； 10-Cathode rapping device ； 11-Anode rapping device ； 12-Cathode removed from shelves ； 13-Anode lifting hammer ； 14-Shell 15-The first imported distribution board ； 16-Import second distribution board 17-Exit distribution board ； 18-Advantages of ash discharge device electrostatic precipitator ⑴ High purification efficiency, able to collect fine dust above 0.01 micron. Different operating parameters can be used in the design to meet the required purification efficiency. ⑵ The resistance loss is small, generally below 20 mm of water column. Compared with the cyclone dust collector, even if the power consumption of the power supply unit and the rapping mechanism is taken into account, the total power consumption is still relatively small. ⑶ The allowable operating temperature is high. For example, the SHWB type circuit dust collector is preferably allowed to operate at a temperature of 250°C, and other types can reach 350~400°C or higher. ⑷ Large range of gases to be processed. ⑸ Automatic operation control can be fully realized. Disadvantages of electrostatic precipitator: ⑴ The equipment is relatively complex and requires high levels of equipment transportation and installation as well as maintenance and management. ⑵ There are certain requirements for dust specific resistance, so there is a certain selectivity for dust, and high purification efficiency cannot be achieved for all dust. ⑶ It is greatly affected by operating conditions such as gas temperature and temperature. If the same kind of dust is operated at different temperatures and humidity, the effects will be different. Some dusts work well at a certain temperature and humidity, but at another temperature and humidity, it is almost impossible to use the electrostatic precipitator due to changes in the dust resistance. ⑷ The primary investment is relatively large, and the horizontal electrostatic precipitator occupies a larger area. ⑸ 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 systems (IGCC), it is very important to develop a high-temperature gas purification system that can not only meet the requirements of gas turbines but also meet environmental protection requirements. It is one of the most critical technologies for the true commercialization of coal-fired combined cycle power generation technology. High-temperature ceramic filters are currently generally considered to be the most promising high-temperature dust removal equipment. Ceramic filters filter dust in high-temperature gas and use gravel layers (granular layer dust collectors) or fiber layers (bag dust collectors) to purify gases, both based on the same filtration theory. The filter elements of ceramic filters are currently generally made of high-density materials. There are three main types of ceramic filter elements: rod type, tube type, and cross-flow type. The picture below shows a cross-flow ceramic filter element, which consists of thin porous ceramic plates that are sintered to form a ribbed whole with channels. Dust-containing gas enters the filter from the short channel end, and then enters the longer clean gas end of the channel after filtering in each channel. One end of the clean gas channel is sealed so that the clean gas flows into the clean gas collection box. The dust particles captured in the short channel are regularly removed by reverse pulse air flow. 7. The following uses a water film dust collector as an example to introduce a wet dust collector.: The dust-containing gas is used to impact the water film formed by some method 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 type of purification equipment is called a water film dust collector. Including impact water film, inert (louver) water film and centrifugal water film dust collector. The following is a simplified diagram of a CLS type water film dust collector: Dust-containing gas is introduced tangentially from the lower part of the cylinder, rotates and rises, and the dust particles are separated by centrifugal force and thrown to the inner wall of the cylinder. They are adsorbed by the flowing water film layer on the inner wall of the cylinder, flow to the bottom cone with the water, and are discharged through the dust discharge port. The water film layer is formed by several nozzles arranged on the upper part of the cylinder to spray water tangentially to the wall of the vessel. In this way, the inner wall of the cylinder is always covered with a very thin water film that rotates and flows downward, thereby improving the dust removal effect. This kind of wet dust collector has a simple structure, low metal consumption and low water consumption. Its disadvantages are its large height, difficulty in layout, and the phenomenon of water inclusion during actual operation. The above introduces several common dust removal equipment in projects. Which one should be selected in practice should be determined based on their respective advantages and disadvantages and the actual situation. At present, most large power stations use electrostatic precipitators or bag dust collectors.