CFB boiler crusher industry development trend and equipment selection

Xuzhou Kalemite Anti-wear Engineering Institute Wang Dongshan Wang Guoping Chen Zhizhen, Tang Xu

Zhejiang Xizi United Engineering Co., Ltd. Liu Chengrong

[Abstract] Circulating fluidized bed boiler is a kind of equipment that utilizes fluidized combustion technology. It has the advantages of clean, high efficiency, wide adaptability of coal type, easy to realize mechanization and automation, and reduce environmental pollution. In China, circulating fluidized bed boilers have been used in some power plants since the 1960s. They have developed rapidly in recent years, and are increasingly used in small and medium-sized power plants and industrial enterprises, and their capacity is increasing. The circulating fluidized bed boiler has strict requirements on the particle size of the incoming coal, and the excessively large particles cause the wear area to expand and the wear speed to be accelerated. If the coal is too fine, the cycle effect will be poor, the burning will be poor, and the boiler efficiency will be affected. Therefore, the reliability of the crushing system in the operation of the coal handling system will directly affect the safe and economic operation of the boiler.

Key words: circulating fluidized bed boiler, crusher equipment selection, roller crusher

I. Analysis of the form and performance of domestic coal crushers

At present, the coal crushing equipment of the domestic circulating fluidized bed boiler mainly includes a ring hammer crusher, a reversible hammer crusher and a new four-tooth roller crusher. Each type of crusher differs in structure depending on the manufacturer, but its crushing origin is basically the same. Before the four-toothed roller crusher. Most of them use hammer crushers and ring hammer crushers, especially ring hammer crushers. However, with the development and popularization of the tooth roll crushing technology, and because the tooth roll crusher has unique advantages, the tooth roll crusher will gradually replace the ring hammer crusher and the reversible hammer crusher. The following is a comparative analysis of the structure, crushing principle and performance of the three crushers.

1. Ring hammer crusher is an impact rotor crusher with a ring hammer. The crusher is mainly suitable for materials with a compressive strength value of less than 150 MPa. After the material enters the crusher, it is firstly crushed by the impact of the high-speed rotating ring hammer, and the first broken material is further broken after hitting the crushing plate. When the crushed material falls between the sieve plate and the ring hammer, it is crushed to the specified particle size by the shearing, rolling and grinding of the ring hammer, and then discharged from the grid hole of the sieve plate, and a small amount can not be broken. The material is periodically removed after being thrown into the iron removal chamber by the centrifugal force by the centrifugal force. It relies on a fixed screen grid hole installed at the bottom to control the particle size of the discharge.

From the use of the ring hammer crusher currently configured for circulating fluidized bed boilers, the following problems exist:

a. The actual output does not reach the nameplate output. Under normal circumstances, the maximum output is only about 60% of the nameplate output.

b. Poor adaptability to the surface moisture of coal. Since the particle size of fluidized bed boiler fuel is generally below 10mm, the size of the mesh hole at the bottom of the ring hammer crusher is also small. When the surface water content of coal is more than 5%, it will be Blockage often occurs, directly affecting normal production.

c. The hammer ring and the broken sieve plate wear faster, the use time is short, the maintenance cost is high, and the workload is large.

The reasons are as follows:

a. Before the popularization of the circulating fluidized bed boiler, the ring hammer crusher is mainly used for the first-stage coarse-grained crushing of the coal-fired boiler feed coal system, and the raw coal entering the plant is broken into the particle size below 30mm and sent to the coal bunker. The coal mill prepares coal powder. When the application is carried out on a circulating fluidized bed boiler to prepare a particle size of 13 mm or less, and even if the boiler requires a particle size of 10 mm or less, the crushing particle size is ensured only by changing the pore size of the crushed sieve plate. Although the design theoretically ensures that the throughput of the perforation can meet the output requirements, the actual operation has a large difference, which is related to the crushing size and humidity of the coal and the hole size of the crushing sieve. The smaller the crushing granularity, the lower the output. The greater the humidity, the higher the clogging rate of the hole and the greater the decrease in output, the smaller the hole size, and the longer the time for the material to pass through the hole, resulting in a decrease in output.

b. The broken material of the ring hammer crusher is repeatedly hit and crushed in the crushing chamber. The material has a certain residence time in the crusher. When the broken coal has high humidity, the hammer ring hits and squeezes the coal. The pressure causes the coal to bond together, forming a coal plug, and is forced to stop the operation, especially in the winter and summer, when the coal quality is high, it brings great difficulties to the production operation. It is determined by operational experience that when the surface moisture of coal is more than 5%, the crusher will often become clogged.

c. The rotor speed of the ring hammer crusher is generally below 960r/min. In the process of crushing coal in the process of breaking the coal, the impact of the coal and the hammer ring is vertical impact except for the center, and the rest are different. The angle of impact, which causes the hammer ring to wear very quickly. The crushing screen is also subjected to similar impact during the crushing process, and the wear is also faster. In addition, the hammer ring often breaks during the operation process, and it is necessary to check and replace it frequently, so the maintenance workload is large. Hammer rings and crushing screens generally use special wear-resistant and impact-resistant materials, which are expensive.

2. Reversible Hammer Crusher: The basic structure of the reversible hammer crusher includes: machine casing, crushing plate, sieve plate, rotor and hammer. The hammer is directly hung on the rotor by a suspension rod, and has a single rotor, a double rotor, a sieve plate, a sieve plate and the like. The broken material enters the track of the rotary hammer from the inlet and is crushed by the hammer and rushed to the opposite crushing plate (or the hammer of the other rotor) for impact crushing. The material rebounded again enters the hammer track and is broken by the hammer until it is broken. Flush down from the hammer rail and drain from the discharge port or sieve hole. The size of the material crushing particle size mainly depends on the size of the gap between the top end of the hammer head and the crushing plate. The crusher with the sieve plate has the function of further impact crushing in the process of falling down the material, mainly Block some unbreakable substances into the next level of equipment, affect the operation of other coal feeding equipment, and remove these unbreakable debris after shutdown. The single rotor can be operated in both forward and reverse directions; the dual rotor can only be operated in one direction.

From the current situation of the use of reversible hammer crushers for circulating fluidized bed boilers, the following problems exist:

    a. Coal type adaptation, the coal type used in the domestic circulating fluidized bed boiler power plant, the hammer crusher can meet the crushing requirements, the crushing particle size is within the guaranteed range of 13mm, and even the adjustment hammer and the crushing plate can be adjusted. The spacing between the two makes the discharge size smaller or larger. The research and design of the coal-fired crushing equipment for circulating fluidized bed boilers comes from

    b. In terms of output: the rated output can be achieved when the coal quality is low, and the output is limited or even blocked when the water is high. The crusher of the toothed crushing plate is more likely to stick and block, which destroys the normal work of the crusher, resulting in a decrease in output and finer discharge; a sieve plate structure is prone to blockage of the sieve plate, causing damage to the overloaded equipment.

    c. The end of the hammer head wears faster. Although the linear velocity of the end of the hammer is 50-53m/s, the impact of the falling material and the hammer does not reach the appropriate impact surface. The impact surface is too small, and only concentrates on the top of the hammer to cause the transition wear to be accelerated, which needs to be adjusted frequently. Broken gap.

    d. For the hammer crusher without sieve plate, the size of the discharge particle size is determined by the gap between the lower half of the crush plate and the end of the hammer. The clearance can be adjusted to obtain the required particle size. There are unbreakable sundries such as iron blocks and stones, but the actual situation is that unbreakable debris in the coal is inevitable. This unbreakable debris is liable to cause damage to the hammer and the broken plate. As the broken coal enters the next-stage equipment and is sent to the boiler, it often happens that the boiler feed system is stuck due to the presence of these impurities, plugging failures, time increases, and these unbreakable iron blocks and stones A large amount of accumulation on the boiler bed surface affects the normal fluidized combustion of the boiler. Even if equipment such as iron remover is installed in the coal conveying system, these impurities in the coal cannot be completely removed, which indicates that some impurities such as iron blocks and stones are inevitably entered into the next stage.

3. The new four-tooth roller classification crusher, the double motor starts, the upper and lower two sets of tooth rollers, the two toothed rollers rotate in opposite directions, and the four toothed rollers rotate at different speeds. After the material enters the crusher, the material smaller than the gap between the two tooth rolls passes directly, which can effectively reduce the over-grinding phenomenon of the material. Materials larger than the gap between the two tooth rolls are broken or broken by the rotating teeth to a qualified particle size. The unique design makes it have the function of automatically removing the sticking material, and the material with high moisture content will not stick to the block, which can ensure the continuous operation of the equipment. The crusher is mainly suitable for materials with a compressive strength value of less than 100 MPa and a feed size of less than 300 mm. The material can be directly crushed from 300mm to less than 8mm, and the finished product particle size can be adjusted arbitrarily, which is suitable for the crushing of coal in circulating fluidized bed boiler.

Its main features are:

a. It has the dual effects of crushing and grading. The new four-tooth roller grade crusher has a spiral of spiral teeth arranged on the toothed roller. The relative movement of the two rollers is like a rotating sieve. The material with a smaller particle size is sieved to break up the bulk material and avoid the material entering the crusher. Noisy broken defects. With the dual functions of crushing and sieving, the crushing and screening operations can be completed separately within a certain range, without the need for screening equipment, simplifying the system and saving investment.

b low noise, low vibration and energy saving. Vibration noise is less than 80db (A) close to the asynchronous motor. The dynamic load is about 1.3 times the static load, which has little impact on the building and there is no need to set up a vibration damping platform. The difference in wind pressure between the inlet and outlet ports is extremely small, and there is almost no dust, and no dust removal equipment is required. In the case of the same output, the required motor power is only 40-70% of the same type of product.

c. Strictly guarantee the product granularity. The machine adopts a fixed center distance to forcibly crush the material. The structural size of the tooth roll is designed according to the product grain size requirements, and the space size through which the product passes is strictly controlled, and the crushing equipment is controlled as the final particle size. The product has uniform particle size, less pulverized coal output, energy saving and long service life. After the broken teeth are worn, the site can be directly repaired or replaced with a tooth cap, which is convenient and quick, and the production and maintenance costs are low.

d, the crushing is extremely low. By adopting the shearing principle, the material smaller than the required particle size passes directly, and only the material larger than the particle size requirement is crushed, thereby avoiding the defects of noisy crushing of the material entering the crusher, so that the material has an extremely low over-grinding rate. For medium and hard materials such as coal and coke, the over-grinding rate is generally below 5%.

e, simple structure, equipped with advanced overload protection device. The dovetail groove is connected between the tooth plate and the toothed roller for easy installation and maintenance. Elimination of long-tooth gear transmission and retraction systems in conventional crushers reduces intermediate energy consumption and points of failure. The whole machine is easy to operate and the two rolls are completely symmetrical with good interchangeability. In addition to the current overload protection system and belt drive protection, there is also a special spring-sensing automatic retraction device that automatically adjusts and restores the distance between the teeth to effectively protect the tooth plate. In order to ensure the uniform wear of the tooth plate, the whole machine runs reliably, and once the stall occurs, it will automatically stop and give an alarm to protect the machine and the whole system.

f, the center distance is adjustable. The first in China, the rigidity of the product can be adjusted under the premise of ensuring the granularity of the product, and can be adjusted conveniently and quickly according to the product granularity requirements.

Second, the development of the domestic five-generation roller crusher

The roller crusher is currently widely used in the crushing of materials below medium hardness, especially in the power industry, and the roller crusher is gradually replacing the ring hammer crusher and the reversible hammer crusher. However, its own development has gone through the following stages of development:

The first generation: light roller crusher

Advantages: 1. Solve the problem of crushing and blocking.

 2. Dismantle the crushing process of the material “Xintianyou”.

Disadvantages: 1. The roller is not wear-resistant.

 2, no retreat, easy to tear the bearing seat.

 3, only broken, no screening.

Second generation: surfacing type roller crusher

Advantages: 1. Solve the problem of crushing and blocking, basically wear-resistant,

Derived: "The Theory of Hard Surface Technology"

 2. Dismantle the crushing process of the material “Xintianyou”.

Disadvantages: 1. The roller is not wear-resistant.

  2, no retreat, easy to tear the bearing seat.

  3, only broken, no screening.

Third generation: fixed roller crusher

Advantages: 1 The contact surface with the material is made of wear-resistant materials.

 2. The material is broken and the sieve is broken.

 3, there is broken. There are sieves.

Disadvantages: 1, no concession, easy to tear the bearing seat.

 2. It is difficult to replace the toothed plate.

The fourth generation: the parallel retracting tooth roller crusher for hydraulic and mechanical transmission

Advantages: 1. The contact surface with the material is made of wear-resistant materials.

2. The material is broken and the sieve is broken.

3, there is broken. There are sieves.

Disadvantages: 1. Crusher in a company in Shandong in 1992

    In practice, it is found that the hydraulic mechanism is flat.

    The line of concession, the iron passed through no response.

2, using mechanical mechanism design parallel retreat, due to the parallel lead rust reaction slow results: one of the bearing seat was torn, and the second found the entire spindle deformation, the entire roller was scrapped.

  3. It is difficult to replace the toothed plate.

The fifth generation: combined roller crusher with V-type suspension retraction mechanism

Advantages: 1. The contact surface with the material is made of wear-resistant materials.

2. The material is broken and the sieve is broken.

 3, there are broken, there are screening.

 4. Make "flashback" be realized scientifically.

 5, the tooth plate can be quickly replaced.

Third, the comparative analysis of the roller crusher and the ring hammer crusher

After nearly 20 years of development, the roller crusher has reached a full-scale maturity stage. The breadth and depth of its use are increasingly accepted and promoted by the industry. After years of comparison with customers, the roller crusher has a big advantage over the ring hammer crusher in the following five aspects.

Special feature

Roller Crusher Advantages

Ring hammer crusher

1, the output is stable

     No sticking.

1, the output is 5mm-15mm, the particle size is adjustable.

2, completely solve the problem of blocking

3, no requirements for material moisture

1, the granularity can not be adjusted

2, sticking

3, the requirements for moisture and materials are relatively high

2. Saving investment

1. It has the dual functions of sieving and crushing: one machine is crushed (injection size ≤300mm discharge size ≤10mm), no need for screening equipment and heating equipment, saving investment costs.

2. Reduce the height of the broken building and save a lot of civil construction costs.

3, no need to build a shock absorption platform, saving some costs.

1. Purchase cylindrical sieve or spiral conveying sieve.

2. Design a layer of broken building than the tooth roller.

3, due to the vibration of the ring hammer, need to invest

   Construction of a damping platform.

3. Energy saving

1. The total power of the two motor of the roller crusher is smaller than that of the ring hammer.

   The power of the crusher and the no-load operation are smooth and energy-saving.

2. No breakage of particles below 5mm, full flow through, negative

   Load low and save energy.

1. The motor power is large and wastes energy.

2. For materials including pulverized coal, etc.

   The pellets need to be crushed, no

   Power consumption.

4. Promote environmental protection

1, low noise: (no load 1 meter ≤ 75dB)

2, the vibration is small: (vibration value within 0.05~0.1mm)

   Low ash: (the total amount of suspended particulates at the job site is less than 8mg/m3)

3, the sealing effect is good.

4, the tooth roller crusher uses a plate type distributor, uniform cloth

1. High noise (≥85dB at 1 meter)

2, large vibration (vibration