Analysis of Arrangement and Selection of Crushing Equipment for Circulating Fluidized Bed Boilers

Foreword

With the adjustment of the national energy structure and the continuous advancement of circulating fluidized bed boiler technology, domestic power plants using circulating fluidized bed boilers are on the rise. Circulating fluidized bed boilers have higher requirements for particle size grading of the incoming coal (fuel particle size grading: emphasis is on the particle size composition and distribution of the fuel, and it is necessary to ensure that the proportion of particles of various sizes is reasonable), due to the fuel particle size grading Unreasonable will lead to a series of problems such as boiler efficiency reduction, plant power consumption, and low boiler availability. Therefore, the choice of circulating fluidized bed boiler into the coal screening and crushing equipment is very important. With the increase of evaporation volume of circulating fluidized bed boilers, the coal consumption is also correspondingly increased. The small-output coal-fired screening equipment with more domestic applications is no longer applicable. Whether it is possible to find coal-fired sieving equipment suitable for 1000MW, 600MW or even 1000MW large-scale circulating fluidized bed boilers in the future, this poses a new topic for the fuel transportation profession.

1 Screening system layout

The selection of the circulating fluidized bed boiler sieving equipment should be determined according to the size of the incoming coal and the particle size of the incoming coal (the requirements of the boiler for the coal-fired particle size). At present, the coal-fired sifting system of the circulating fluidized bed power plant has the following arrangements. Option a: primary screening, primary crushing (or no screening equipment , directly using primary crushing). Option b: No screening equipment, secondary crushing, two-stage crushing equipment arranged in a coal crusher room. Option c: primary screening, secondary crushing arrangement. There are two coal crusher rooms in the coal conveying system. The first-stage coal crusher is equipped with coarse screening and coarse crushing equipment. After the first-stage screening, the coal-fired particle size reaches 30mm or less. Fine-grain crushing equipment is arranged in the secondary coal crusher. After fine crushing, the coal-fired particle size reaches the coal particle size requirement of the circulating fluidized bed boiler. Scheme d: the arrangement of secondary screening and secondary crushing, that is, on the basis of the scheme c, a first-stage fine screening device is added before the secondary crushing. Scheme e: three-stage screening and secondary crushing arrangement, that is, on the basis of the scheme d, after the secondary crushing, a first-stage fine screening equipment is added, and the sieved material can be returned to the crushing equipment to be broken or transported again. To the coal yard, the sieved material enters the boiler for combustion.

At present, the layout of scheme c and scheme d is usually adopted in large circulating fluidized bed boiler power plants in China, and scheme e has been applied more and more in recent years.

2 Requirements for coal-fired crushing equipment

Commonly used circulating fluidized bed boilers burn coal gangue, slime and washed coal, among which sieving and crushing are coal gangue and washing coal. Take the domestic conventional 300MW circulating fluidized bed boiler as an example: the coal consumption is about 250t/h, the coal particle size is about 300mm, the coal particle size is about 10mm, and the crushing ratio is 30 or higher; according to the “Code for Design of Thermal Power Plants” (GB50660-2011) stipulates that “the output of the belt conveyor of the upper coal system should not be less than 135% of the larger value of the coal consumption of the designed coal type and the nuclear type of coal for the maximum continuous evaporation of the corresponding unit” According to the "Technical Regulations for Coal Transportation Design of Thermal Power Plants Part 1: Coal Transportation System" (DL/T5187.1-2004), "the rated output of the circulating fluidized bed boiler crusher should not be lower than the coal handling system. Therefore, when two sets of 300MW circulating fluidized bed boiler power plants adopt a set of double-road coal system and no coal sieve, the output of single-channel system crusher should not be lower than 675t/h; circulating fluidized bed boiler Selection of coal crushing device in meeting the output of the broken, and should satisfy the circulating fluidized bed boiler fuel particle size distribution curve, crushing efficiency> 95%; circulating fluidized bed boiler for coal often contains iron block, wood There are many impurities such as stones, which requires the crusher to have anti-mesh The bad measures can make the difficult material pass smoothly through the inside of the crusher without damaging the crusher; the crushing equipment also needs to meet the physical properties of the broken material, mainly including the hardness of the material (the determining factor of the difficulty of crushing is the compressive strength of the material, due to the same The compressive strength data measured by the material varies greatly, so the hardness of the commonly used materials in actual work indicates its friability, water content, viscosity, density, explosiveness, corrosiveness, etc., and it is mainly required for coal gangue and washing coal. Its hardness and water content characteristics. Based on the above four points, the coal-fired crushing equipment of the circulating fluidized bed boiler should meet the requirements of large crushing ratio, large output, high efficiency, debris abd, and compliance with fuel physical properties.

To meet the requirements of the coal particle size of 10mm, it can be used for primary crushing or two-stage crushing. The primary crushing can meet the requirements of 300mm of incoming material size and 10mm of discharging size only by single-stage equipment. The grade equipment can be crushed to a certain value from 300mm, and then further crushed to 10mm by the second-stage equipment; to meet the crushing output, the output of a single crushing equipment can reach 675t/h, or two crushing equipments can be connected in parallel. Up to 675t/h, but the parallel connection of more than 2 crushing equipments will make the outdoor shape of the coal crusher too large, and any failure of any equipment in parallel will make the output of the crushing system unable to reach the rated value, and the whole system is reliable. To reduce the fuel particle size distribution curve and high crushing efficiency of the circulating fluidized bed boiler, it is related to the degree of fuel coalification, the crushing mechanism of the crusher (the main force applied to the crushed material), and the crushing mechanism that meets the incoming characteristics is possible. Breaking complex incoming materials into particles that meet the fuel particle size distribution curve of circulating fluidized bed boilers; to meet the function of debris removal, it is required that the broken parts of the crushing equipment have flexibility The characteristics of connection and operation are flexible; the Mo type hardness of coal gangue and washing coal is generally between 2 and 5, which is higher than that of common bituminous coal, and Mar (received base water) is between 10% and 15%. For materials with low hardness and moderate water content, most crushing equipment can meet the hardness and Mar requirements of coal gangue and washing coal.

3 Applicability analysis of main crushing machinery

Under the action of external force, the solid material overcomes the cohesive force of the material, and the process of breaking the large particles into small particles is called pulverization. The crushing machinery of materials is roughly classified into a crusher and a pulverizer. According to the different construction and working principle, the commonly used crushing machinery has the following types: jaw crusher , hammer crusher , cone crusher (gylon crusher), impact crusher, roller crusher; commonly used powder The mills are classified into the following categories: ball (rod) mills, medium-free mills, mills, vibratory mills, and jet mills. According to the particle size of the material after pulverization, the pulverization is usually divided into five stages, wherein the crushing can be divided into three stages, which are coarse crushing sections (injection granularity 300-1500 mm, discharge granularity 100-350 mm), and medium-grained sections ( Feeding particle size 100～350mm, discharge particle size 20～100mm), fine crushing section (feeding particle size 20～100mm, discharge particle size 5～20mm); grinding can also be divided into coarse grinding section and fine grinding section, generally A pulverizing section (feeding particle size 5 to 19 mm, discharge particle size 0.074 to 0.4 mm). It can be seen that the crushing stage required for the coal-fired crushing equipment of the circulating fluidized bed boiler is the middle crushing section and the fine crushing section, and no grinding equipment is needed. In the following, the applicability of several major crushing machines to coal combustion in a crushing circulating fluidized bed boiler is introduced.

3.1 Jaw Crusher

The jaw crusher relies on the eccentric shaft to drive the movable jaw for periodic reciprocating motion, crushing the material entering the fixed jaw and the movable jaw. The jaw crusher is suitable for coarse, medium and fine crushing of high and medium hardness materials with a Mohs hardness of 7 or less. The existing jaw crusher is divided into three types: simple swing type, complex swing type and mixed swing type according to the moving characteristics of the movable jaw. The simple swing type is divided into PJ type, JC56 type, PEJ type, PEXZ - 150 x750 fine crush type, and the complex swing type crusher is divided into PEF compound pendulum type, PE series compound pendulum type, PES series compound pendulum type, PEX complex. The split type, PEXS compound pendulum type, mixed swing type is divided into PEY type hydraulic protection type, PJQ strong type, PSH series double cavity rotary type. Among them, PEXZ - 150 x750 fine-cut type, PEF compound pendulum type, PE series compound pendulum type, PES series compound pendulum type, PEX compound pendulum type, PEXS compound pendulum type, PSH series double-cavity type can break the material to Below 10 mm, but its output does not exceed 50 t / h; due to its fracture mechanism, it is impossible to break the material to meet the fuel particle size distribution curve of the circulating fluidized bed boiler, and the crushing efficiency is low. In general, the jaw crusher cannot meet the fuel crushing requirements of large circulating fluidized bed boilers.

3.2 Roller Crusher

The roller crusher is an older crushing machine. The crushing mechanism of the roller crusher is a pair of pairs or pairs of cylindrical rollers horizontally mounted on the frame in parallel, the rollers rotate in opposite directions, and the material is added to the feeding box and falls on the rotating roller, and the friction on the surface of the roller Under the action, it is brought into the roller between the rollers, crushed by the roller, and the crushed material is pushed out by the roller and discharged downward. Therefore, the roller crusher is continuously operated and has the characteristics of forced discharge, and is often used for medium and fine crushing of medium and low hardness materials. According to the number of rollers, the roller crusher can be divided into four types: single roller, double roller, three roller and four roller; according to the shape of the roller surface, it can be divided into three types: smooth surface, groove surface and tooth surface roller crusher. . The main advantages are: simple structure, compact and light body; low price; convenient to adjust crushing ratio; less broken phenomenon; better crushing effect for wet and wet materials than jaw crusher and cone crusher . The main disadvantages are: low production capacity, the traditional two-roller and four-roller crusher can crush the material below 10mm under the condition of feed size of about 50mm, but the output can only reach 60t/h; due to its crushing mechanism Therefore, it is impossible to crush the material to meet the fuel particle size distribution curve of the circulating fluidized bed boiler, and the crushing efficiency cannot reach more than 95%; the roller teeth are easy to block when the discharge granularity is small; the large output roller type fine crusher has a long tooth roll and the equipment volume Larger, must ensure strict fabric uniformity, otherwise the uneven wear of the roller will lead to uneven particle size under the fine crusher, and the large output roller fine crusher will increase the maintenance due to the easy wear of the roller; the iron block, wooden block and other miscellaneous The dodge function of the object is poor. When there is debris in the coal, it is easy to cause the breaker to fail; the inferior fuel with high hardness of the vermiculite has poor adaptability. Conventional roller crushers are used in many slag crushers in power plants. The improved new roller crusher can crush 50mm of incoming material to less than 10mm, and the maximum output can reach 500~600t/h. However, due to the problems of poor adaptability of coal type and difficulty in controlling the granularity of discharge, it is only less. It has been applied in some circulating fluidized bed boiler power plants and has not been promoted.

In recent years, the four-tooth roller crusher independently developed by domestic manufacturers has two pairs of oppositely rotating toothed rollers. The coarse and fine two-stage crushing and combining are combined, and the large pieces of 300-500mm can be sieved without additional screening. Divided into the crusher, it can be broken to 8 ~ 13mm. Domestic equipment with a capacity of 600t/h and below has already been put into operation. The 800t/h four-tooth roller crusher is being installed, and the products that have been put into operation have a good response among the owners.

3.3 Cone Crusher

Cone crusher, its working parts are two truncated cones. One is a moving cone (inner cone) that is fixed to the main shaft; the other is a tapered cone (outer cone) that is part of the frame and is stationary. The moving cone rotates along the inner surface of the fixed cone. When the cone is pressed closer to the fixed cone, the material at that place is broken by the action of the moving cone and the bending. When the cone is deviated from the fixed cone, the broken material is affected by gravity. Just fall from the bottom of the cone. The working principle of the cone crusher is to apply a pressing force to the material, so that the material is crushed by the bending force and the shearing force between the two tapered surfaces, and the material is freely discharged after being broken. The crushing mechanism of the cone crusher determines that it can be used for coarse, medium and fine crushing of high or very high hardness materials. The cone crusher can be divided into coarse crushing and medium fine crushing according to the application; according to the structure and function, it can be divided into hanging type, support shaft type and vibration type. Among them PYB, PYD, PYZ, PYT spring type, PYX1600 single cylinder hydraulic type, PYS-B type, PYY-D multi-cylinder hydraulic type, PYY-T single-cylinder hydraulic type cone crusher under the condition of feeding particle size 40 ~ 130 mm The material can be crushed to less than 10 mm, but due to its crushing principle, its crushing speed is slow, the maximum production capacity can only reach 360 t/h, and the equipment has a large shape, such as PYD2200 spring cone crusher, the equipment dimensions are up to 7.7. m×3.43 m×5.06 m; due to its fracture mechanism, it is impossible to crush the material to meet the fuel particle size distribution curve of the circulating fluidized bed boiler, and the crushing efficiency is low. Which is commonly used in mine ore crushing ft, building stone crushing, metal ore crushing, solid waste treatment and other industries.

3.4 Horizontal Rotor Crusher

Horizontal rotor crushers, including hammer crushers, ring hammer crushers, impact crushers, cage crushers, chain crushers, etc.

3.4.1 Hammer Crusher

In the hammer crusher, the material is impacted by the hammer of the high-speed rotation and the material itself is impacted at a high speed on the fixed lining to break the material. The main working part of the hammer crusher is a rotor with a hammer (also called a hammer). The rotor consists of a main shaft, a disc, a pin and a hammer. The motor drives the rotor to rotate at high speed in the crushing chamber. The material is fed into the machine from the upper feed port and is broken by the impact, impact, shearing and grinding action of the high-speed moving hammer. The hammer crusher is mostly used for crushing medium and low hardness materials with moderate moisture content, and is suitable for crushing materials with strong fiber structure, elasticity and toughness. There are many types of hammer crushers. According to the number of rotors, they are divided into single-rotor hammer crushers and double-rotor hammer crushers. According to the rotor rotation direction, they are divided into reversible and irreversible. According to the number of hammer rows, they are divided into single rows and Multi-row type; according to the connection mode of the hammer on the rotor, it is divided into fixed hammer type and movable hammer type. Among them, the reversible hammer-type fine crusher has reasonable particle size distribution, high crushing efficiency, and the hammer head can smoothly pass the difficult-to-break material, the wearable parts have long service life, easy maintenance and maintenance, and convenient discharge particle size adjustment. The characteristics of small export volume are currently used in large circulating fluidized bed boiler power plants that have been put into operation or under construction in China. It can relatively easily break 50mm incoming material to below 10mm, and the output can also be 650t/h or more. The Sichuan Baima 600MW circulating fluidized bed boiler power plant uses a reversible hammer-type fine crusher.

In the early domestic large-scale circulating fluidized bed boiler project, more foreign reversible hammer-type fine crushers were used, and all of them were imported. More foreign imported fine crusher brands include: German FAM company, American crusher company, American Pennsylvania crusher company, Germany ZEMAG, Germany Aubema AUBEMA crushing company. It is understood that Mexico has been put into operation a fertilizer plant 1000t / h crushing rock phosphate ore reversible Hammer Crusher, which feed size 50mm, the particle size 9.5mm. Early domestic reversible hammer-type fine crusher mainly had problems such as poor wear resistance, short life, frequent maintenance and replacement, poor adaptability to coal moisture, and low crushing efficiency. With the continuous improvement of domestic manufacturers, more and more domestic reversible hammer-type fine crushers have been applied in recent years. The reversible hammer-type fine crushers with domestic output of 600t/h and below have already achieved a lot of operational results. The 800t/h domestic reversible hammer-type fine crusher is currently under construction.

Due to the diversity of coal-fired power plants in domestic power plants, it is recommended to design different reversible hammer-type fine crusher products according to the coal-burning characteristics of each power plant, so that the particle size distribution of the crushed materials is as close as possible to the circulating fluidized bed boiler. Requirements for the particle size characteristic curve of the coal.

3.4.2 Ring Hammer Crusher

The ring hammer crusher is an impact rotor crusher with a ring hammer. The ring hammer not only rotates with the rotor, but also rotates around the hammer pin. After the material enters the crusher, it is broken in the crushing chamber by the impact of the ring hammer rotating at a high speed with the rotor. The ring hammer crusher is mostly used for crushing medium and low hardness materials with moderate moisture content. The ring hammer crusher has been used in the early circulating fluidized bed boiler fuel crushing system. However, with the increase of the fuel volume of the circulating fluidized bed boiler, the ring hammer crusher is difficult to determine due to its crushing mechanism. Most materials are crushed to below 10mm, not to mention the fuel particle size distribution curve; due to the existence of the sieve plate, when the incoming water is large, it is easy to block; when used as a fine crusher, the ring hammer and the crushing plate are worn out. Large maintenance and high maintenance costs. Therefore, the ring hammer crusher gradually withdrew from the team of the circulating fluidized bed boiler fine crushing equipment.

3.4.3 impact crusher

The impact crusher is a deformation of the hammer crusher. The main changes are: the movable hammer head is changed to a fixed hammer head; and one or two counterattack plates are mounted on the casing in the tangential direction of the rotor hammer head. The impact crusher utilizes a plate hammer on a high-speed rotating rotor to generate high-speed impact and breakage of the material fed into the crushing chamber, and causes the broken material to be thrown at a high speed in the tangential direction toward the counterattack plate at the other end of the crushing chamber, again After being broken, then rebound from the counterplate to the hammer and continue the process. During the round trip, there is also a mutual impact between the materials. As the material is hit by the hammer, the impact of the counterattack and the collision of the materials, the material continues to crack, loose and smash. When the material particle size is smaller than the gap between the counterattack and the hammer, it can pass. The impact crusher has simple structure and low power consumption; the crushing ratio is large, generally about 40, and the maximum is 150; it is mostly used for crushing medium and low hardness and moderate moisture content; the feed size is ~50mm, and the discharge granularity is less than In the range of 10mm, the output of the impact crusher is below 100t/h, and due to its crushing mechanism, it is impossible to break the material into particles that meet the fuel particle size distribution curve of the large circulating fluidized bed boiler, and the crushing efficiency is low.

3.4.4 Other types of horizontal rotor crushers

Other types of horizontal rotor crushers, such as chain crushers (the main working part is a rotor with a steel chain, one end of the chain is connected to the rotor, and the other end of the chain is made of wear-resistant steel. The ring chain head breaks the impact of the block by the high-speed rotating chain), the cage crusher (the structure is composed of two relatively rotating cages, and the relatively high speed of the two cages after the material is moved in by the loading hopper It is also possible to crush 50 mm of incoming material to less than 10 mm by being broken under rotation. The output of the chain crusher is below 100t/h, which is mainly used for crushing medium hardness and wet adhesive materials. It is widely used in fertilizer production lines. Cage crusher is mostly used for fine crushing of medium and low hardness materials with moderate moisture content. The crushing ratio can reach 40. The crushing ratio can be adjusted by adjusting the speed of the cage rotor. Cage crushers have been widely used in early circulating fluidized bed boiler fuel crushing systems. For example, Pingding ft Ruiping Power Plant used two 500t/h cage crushers produced by American Steel Lake. However, due to the limitation of the crushing principle, the cage crusher meets the fuel requirement of the circulating fluidized bed boiler generally not more than 500t/h; the crushing granularity is difficult to control, and the discharge granularity is too fine; due to the severe wear of the broken strip, it is broken about 80,000. When the coal is used, the crushing strip needs to be replaced, and the equipment maintenance workload is large; the debris in the coal is seriously damaged by the high-speed running broken strip; the equipment is imported, and the price is 30% to 40% higher than that of the hammering crusher. Some domestic manufacturers also produce cage crushers, but the operation results are generally not ideal. The two cage crushers newly installed by Henan Shenhuo Coal and Electricity Co., Ltd. in 2009 have not been effective after being put into operation, and there are problems such as poor control of crushing granularity and easy overload of the motor. Therefore, the cage crusher is widely used only in brick factories where the proportion of fine powder particles is high.

In addition to the above several major crushing machines, other vertical shaft crushers, turbo crushers, etc. can not meet the requirements of large-scale circulating fluidized bed boilers.

4 Comparison of coal crushing equipment prices

Table 1 is applicable to the price of a reversible hammer crusher, a roller mill, a four-tooth roller crusher, a cage crusher, and a ring hammer crusher that can be used as a circulating fluidized bed boiler for coal-fired crushing equipment and the same output. Roughly compare.

As can be seen from the above table, the price of imported fine crusher is basically twice that of domestic equipment of the same specification. The use of imported fine crusher will increase engineering investment despite superior equipment performance. How to further improve the performance of domestic fine crushers and reduce the import of such equipment is also a topic facing the domestic technicians of fine crusher manufacturing in the future.

5 Conclusion Reversible hammer-type fine crusher, ring hammer crusher, cage crusher, roller crusher can be used as the fine crushing equipment of circulating fluidized bed boiler, in line with the physical properties of coal gangue and washing coal. Among them, the ring hammer crusher, cage crusher and roller mill are used in the early small-output circulating fluidized bed boiler fuel crushing system. Reversible hammer-type fine crusher is used in large, medium and small circulating fluidized bed boiler fuel crushing systems, and domestic engineering has the highest performance.

In the past, most of the domestic projects used large-capacity reversible hammer-type fine crushers imported from foreign machines. In recent years, the reversible hammer-type fine crushers with domestic output of 600t/h and below have been put into operation.

The performance of the reversible hammer-type fine crusher of 1000t/h crushed phosphate rock ore in the foreign fertilizer plant has been produced, and the 800t/h domestic reversible hammer-type fine crusher is currently being manufactured.

To break the 300mm incoming material to less than 10mm at a time, a four-tooth roller crusher can be used, and the crushing effect is better in the owner.

The degree of fuel coalification and the crushing mechanism of the crusher determine the particle size distribution curve of the crushed fuel. It is recommended that the manufacturer conduct a simulation experiment according to the coal-burning characteristics of each project, and design the different products of the reversible hammer-type fine crusher to make the broken product. The particle size distribution of the material is as close as possible to the particle size characteristic curve of the circulating fluidized bed boiler.

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