In daily industrial and agricultural production, the use of storage warehouses for granular materials such as raw coal and ore powder is very common, and its role cannot be underestimated. However, during the process of discharging materials from the storage warehouse, material blockage often occurs, seriously affecting the normal operation of the equipment. Especially for large thermal power plants equipped with direct fired coal pulverizing systems such as raw coal bunkers and coking plant coal towers, once coal blockage occurs in the power plant, the generator units will be forced to urgently reduce output and load shedding, and even unstable boiler combustion may cause a large amount of oil injection, and more seriously, it may lead to boiler fire extinguishing and unplanned unit shutdown. Once a coal blockage occurs in a coking plant, the entire coal blending ratio becomes imbalanced, and in severe cases, it can cause coal transportation interruptions. The problem of coal blockage in the raw coal warehouse has become an industry wide challenge!
Analysis of the causes of blockage in the raw coal bin
1. The structural type of the bottom bin section of the raw coal silo
Material warehouse body - forms of blockage
The common structural types of the silo section include rectangular section oblique cone, cone, rectangular section hyperbolic, circular section hyperbolic, etc. But each has its own characteristics:
The raw coal near the four corners of the bucket wall of the rectangular section coal bunker is subjected to "double-sided friction" and compression, which makes it easy to adhere to the corners of the bucket wall for a long time. Under the same semi top angle, it is more prone to coal accumulation than the circular section coal bunker.
The cross-sectional area of the b-cone type raw coal bin (including cone and square cone types) gradually decreases along the flow direction of coal, the squeezing force increases, and the frictional force between coal particles and the bin wall, as well as between coal particles, also increases. The force of gravity that drives coal to flow along the wall remains unchanged. Therefore, as coal flows, the equivalent flow force inside the conical raw coal bin decreases. Especially in the case of high moisture content and strong agglomeration of coal particles, the flow of coal in the warehouse becomes more difficult, and the probability of arching and blockage greatly increases.
As the coal flows towards the outlet, the inclination angle of the bucket wall increases in the hyperbolic type raw coal bunker, which gradually increases the gravitational force that drives the coal to flow along the wall, and the compressive force of gravity on the wall gradually decreases. Compared with the conical type raw coal bunker, its equivalent flow dynamics decrease slower with the flow of coal. In principle, the probability of blockage in this form of raw coal silo is relatively small. However, in practice, when the water content of coal increases to a certain value (the washing of middling coal is more prominent), the probability of blockage will increase rapidly.
Half top angle and cross-sectional shrinkage rate of the inner wall of the raw coal silo
For conical raw coal silos, the smaller the half top angle of the silo wall, the more favorable it is for coal particle flow. For hyperbolic shaped coal bunkers, the smaller the cross-sectional shrinkage rate, the more favorable it is for coal particle flow.
At the initial design of the raw coal bunker, the semi top angle and area shrinkage rate of the raw coal bunker are determined based on the design coal type provided by Party A. In addition to considering the factors of warehouse volume and investment, the factor of preventing blockage in the raw coal warehouse is also taken into account. However, after the project is completed and put into operation, the coal quality of most power plants cannot be guaranteed at all, seriously deviating from the design coal. In addition, uncontrollable environmental factors such as rain, snow, and freezing have led to frequent coal blockages in coal bunkers that were originally designed to not block coal.
The flow state of coal inside the raw coal silo (funnel flow, overall flow) is not only determined by the half vertex angle and area shrinkage rate of the silo, but also by the coal quality itself. In the case of designing coal types, the flow of coal inside the raw coal bin is a whole flow, but after changes in coal quality (such as increased moisture and strong agglomeration), the flow of coal inside the raw coal bin changes from a whole flow state to a funnel flow state. The probability of blockage in the central flow raw coal bin is much higher than that in the overall flow raw coal bin.
Size of raw coal bin outlet
According to the theory of particle kinematics, for dry particles, the opening size of the silo that does not form arches should be at least 3 times the characteristic size of the particles, while for wet particles, the opening size of the silo should be at least 4 times the characteristic size of the particles. Although the silo is designed to prevent blockages as much as possible, due to the fact that materials such as raw coal come from different mining sites, their impurity content and viscosity are also different. In addition, during the rainy season, the materials are damp and prone to sticking, while during the cold winter, they are prone to freezing. Especially with the increase of water content in coal, the agglomeration of coal increases sharply. During the downward flow of coal in the raw coal silo, the pressure from the silo wall increases, and the originally loose particles are squeezed and agglomerated, resulting in larger characteristic sizes. When the characteristic size of the coal cluster reaches a certain critical value, blockages will occur. In addition, the contamination and agglomeration of damp coal on the walls of the discharge port also make the discharge port increasingly narrow, increasing the probability of blockage. Therefore, for a well-designed silo, it is almost impossible to prevent material blockage from occurring 24/7.
Coal type and composition
Different types of coal have varying degrees of agglomeration. For example, after crushing, oil shale has strong agglomeration, and bituminous coal has stronger agglomeration and water absorption than anthracite; Petroleum coke itself has weak agglomeration due to the presence of oil. The difference in coal agglomeration directly affects the coal blockage situation in the raw coal bunker.
Coal moisture is also an important factor affecting coal blockage in the raw coal silo. In actual production, it has been found that when the moisture content (external moisture) of coal reaches 8%, some poorly designed raw coal bunkers (rectangular raw coal bunker, central flow raw coal bunker) begin to experience coal blockage; When the moisture content of coal reaches 10%, coal blockage becomes more severe; When the moisture content of coal reaches 12%, coal blockage becomes quite severe. An increase in moisture will enhance the agglomeration of coal.
The smaller the average particle size of coal, the more fine powder, the larger the specific surface area, the higher the surface free enthalpy, the greater the force between particles, and the strong internal force. Its macro performance is the strong cohesiveness of coal, such as washing middling coal.
The main blockage location of the raw coal bin
According to investigation and research, over 90% of blockages in the raw coal bunker occur within a range of 1-2m above the outlet of the lower raw coal bunker. The main reason for the blockage in this section is that during the unloading of the silo, the material in the conical silo expands vertically and compresses horizontally, and the stress is in a passive plastic state. As the outlet size of the silo decreases, the pressure increases, and the frictional force between coal particles and between coal and the cylinder wall increases. The coal particles aggregate, and the characteristic size significantly increases, so the blockage mainly occurs in this section.
现阶段常用的原煤仓清堵措施
人力破堵
人工破堵费时费力！
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Manual breaking of blockages usually involves poking coal holes, striking the blocked coal area with a large hammer, and setting up a bell type heavy hammer outside the warehouse in areas prone to blockage to break through the arch.
Implementation status:
A、 Expensive manpower, unable to clear in a short period of time, limited effectiveness;
B、 Significant damage to the warehouse wall;
C、 When poking coal, a large amount of raw coal accumulates on site, causing serious environmental pollution;
D 、 Personnel working at heights pose safety hazards;
Warehouse wall vibrator
The principle of breaking the blockage of the silo wall vibrator is the same as manual striking, which gradually separates the coal adhered to the silo wall through the vibration of the silo wall, in order to achieve the purpose of breaking the blockage.
Implementation status:
The A silo wall vibrator must be in the position of the arch to play its role, as the arch and blockage positions of the raw coal silo are uncertain and constantly change due to factors such as coal quality. If the vibrator is in the arch position, it will make the coal denser as it vibrates.
The B vibrator can easily cause damage to the warehouse wall, such as cracking due to vibration.
air cannon
The working medium of an air cannon is compressed air, and its main components include an air storage tank, an electromagnetic quick closing valve, and a control system. When the quick closing valve is quickly opened, the compressed air in the air gun storage tank is compressed by the pressure difference, forming a strong airflow that sprays out at high speed. The high kinetic energy air directly impacts the blocked part in the compartment, causing the coal particles to flow again under the action of gravity.
Implementation status:
The A air cannon must be in the position of the arch to play its role, as the position of the arch and blockage in the raw coal bin is uncertain and constantly changes due to factors such as coal quality. When the air cannon is in the arch position, it will make the coal denser and more compact as it vibrates.
The baffle at the connection position between the B air cannon and the inner wall of the silo increases the friction coefficient of the wall and increases the probability of coal blockage.
C was covered in air cannons, and the walls of the warehouse were still heavily damaged from the impact.
Loosening machine
The raw coal silo loosening machine is usually driven by the mechanical energy generated by the hydraulic pump station through the hydraulic oil cylinder on the outer side of the silo wall, which drives the coal plow to move back and forth. At the same time, its coal plow blades scrape the raw coal in the blocked area, destroying its dense extrusion structure and restoring the flow of coal.
Implementation status:
Due to the influence of the baffle of the hydraulic cylinder and a large number of plow blades, the frictional resistance of the warehouse wall increases, which increases the probability of coal mining, especially at the outlet position of the warehouse body.
Due to the fact that the loosening machine can only move in a straight line, and the lower part of the raw coal bin is prone to coal blockage, the angle usually changes, making it impossible to clear the blockage in the lower part.
The C hydraulic system is prone to problems, causing the system to malfunction.
5. Adding stainless steel or PU board lining to the inner compartment wall and reducing the friction coefficient of the inner wall through special lining materials is one of the measures to prevent blockage.
Implementation status:
The inner lining of A is prone to detachment, causing uneven warehouse walls, increased friction, and blockage.
The thickness of the B PU lining plate is generally around 30, and adding an inner lining causes a reduction in the size of the coal outlet, resulting in blockage.
The C compartment wall with lining is only suitable for compartments with small half top angles. The warehouse with a larger half vertex angle belongs to the central flow warehouse, and the material on the wall does not flow, so its cleaning effect is not obvious.
Other measures to alleviate coal blockage
Many coal blockages are caused by changes in coal composition or low-temperature freezing in extremely cold regions. The following measures are usually taken to slow down the occurrence of coal blockages.
(1) Strengthen the control of moisture content in coal entering the furnace
Coal combustion, due to high external moisture content or seasonal or regional rainy weather, can cause a significant increase in external moisture content, resulting in high coal quality
Viscous and prone to coal blockage. In order to reduce the external moisture content, sufficient dry coal shed capacity can be configured during the design phase; in operation
On the premise of ensuring orderly stacking during the stage, try to increase the actual coal storage capacity of the dry coal shed as much as possible to ensure that the coal is fully dried before entering the furnace.
(2) Ensure proper heating of coal transportation systems and raw coal warehouses in cold regions to prevent low-temperature freezing of coal.
(3) In addition, there are a large number of equipment for clearing blockages in raw coal warehouses on the market, all of which play their respective roles to varying degrees. We won't introduce them one by one here
Rotating blockage clearing chamber
Rotating blockage clearing chamber
In order to solve the problem of blockage during the unloading process of raw coal bunkers and other material silos, our company officially recommends a "rotary cleaning machine", which is mainly used to solve the problem of blockage during the unloading process of raw coal bunkers and large material silos for other purposes in thermal power plants.
This product is mainly used for the overall design and manufacturing of the cone section of the raw coal silo in newly built power plants (in conjunction with the raw coal silo); The anti blocking renovation of large material warehouses used for operating power plant raw coal bunkers and other purposes, especially those with large semi top angles and mainly funnel flow inside.
Performance characteristics
1. The rotation of the warehouse completely breaks the balance formed when the material arches;
2. The easily clogged section installed at the bottom of the coal bunker has a clearing effect;
3. Changing the internal flow state of the entire warehouse, transforming the flow state into an overall flow, greatly reduces the probability of arching at the upper part of the warehouse;
4. Realize remote and on-site control conversion. It can be manually controlled and can also achieve timed start stop;
5. The sealing design adopts mature maze technology and sealing pre pressure compensation design, with no leakage phenomenon, preventing dust from overflowing and improving the working environment;
6. The warehouse adopts a suspended installation method, with gravity applied to the lifting arm and filler added to the sealing port to prevent damage to the sealing port;
7. The warehouse body is made of 12mm 16Mn steel material, which meets the on-site requirements;
8. The warehouse is equipped with a ball type positioning ring, which makes the cleaning equipment more stable during operation.
Working principle and structure
1. Change the material storage bin section from the original integrated bin to a rotary bin. The arch breaking and blocking knife installed in the wall of the rotary bin forms a relative motion system with the rotary bin. During this relative motion, the material cannot form a stable arch between the inner wall of the rotary bin and the bin wall, and the basic factors of blockage are timely destroyed and disintegrated, thus achieving the goal of better preventing material blockage and significantly improving the anti blocking effect.
It consists of three parts: the upper part is a fixed silo (with its upper opening connected to the silo); The central part is a rotary warehouse; The lower part is a fixed compartment (connected to the inlet of the coal feeder). The rotary warehouse section is located in the easily blocked section of the entire material warehouse and is a key component in solving the problem of blockage in the entire material warehouse.
The anti blocking device for the 3-revolving wall raw coal bin utilizes a high speed ratio reducer through gear transmission, and a ball type positioning ring is installed outside the bin to make the rotation of the revolving cone bin around the centerline of the raw coal bin more stable. Together with the anti blocking components installed inside the bin, it forms a special anti blocking and cleaning system. When the raw coal bin is blocked, the rotating bin body begins to rotate, and the material and the bin wall undergo relative motion. At this time, the material cannot form a stable arch with the bin wall on the inner side of the bin wall, and the foundation of the blockage is disintegrated. The collapse of the arch eliminates the blockage, ensuring that the entire material bin material flows as a whole, fundamentally solving the problem of coal blockage in the raw coal bin
