Description of Small Scaled Chain Grate

Wafangdian City Yongning Grate Manufacturing Co., Ltd.Founded in 1988, covering an area of 50,000 square meters, it is a professional manufacturer designated by the state for producing boiler auxiliary machines, located in southern Liaoning, south of Dalian, west of Bohai Bay, and east of the Shenda Expressway, with convenient transportation and a superior location.

In order to adapt to market needs, our factory can design and produce various grates according to user requirements. With strong technical strength and advanced and complete production equipment, we have laid a strong foundation for creating excellent products. For many years, we have supplied many domestic boiler manufacturers, and our products cover all parts of the country, with exports to neighboring countries such as Japan, Indonesia, and North Korea, receiving high praise.

Our main products include: beam-type chain grates, large flake chain grates, small flake chain grates, and chain belt grates. Various slag discharge machines, coal feeding machines, grate reducers, energy-saving coal bunkers, and various boiler accessories are also provided, and we undertake various projects for the design, transformation, installation, and maintenance of grates.

"Quality as the foundation, sincerity to the world" is the purpose of our factory's development. Factory director Wang Conghui is willing to work hand in hand with new and old friends at home and abroad for sincere cooperation and mutual development.

Technical characteristics of small flake chain grates

1. Usage range and requirements

Small flake chain grates are a mechanized staged combustion device that can be matched with boilers with an evaporation capacity of 2-40t/h and can also be used in various heating and drying equipment. They are suitable for burning bituminous coal, lignite, and peat. With special design, they can also be used as combustion equipment using raw materials such as bagasse, wood, and rice husks.

The coal quality used in this grate should meet the following requirements:

a. The maximum particle size of coal blocks should not exceed 40mm, and it is not advisable to burn coal dust below 0-6mm exceeding 50% of the total amount. Coal dust of 0-3mm should not exceed 25% of the total amount.

b. The moisture content of the coal should be less than 20%, preferably 8-10%.

c. The ash content of the coal should not exceed 30%, but should not be less than 10%, and the volatile matter should not be less than 20%.

d. The melting temperature of the coal ash should be greater than 1250.⁰C.

e. The caking property should not be strong.

f. The lower heating value of the coal should be greater than 4226kcal/kg.

g. If the above coal quality requirements conflict with the coal feeding settings, take the higher value between the two.

The primary air temperature used in this grate should not exceed 200.⁰C.

2. Structural characteristics of small flake chain grates:

Components: 1. Driving shaft; 2. Driven shaft; 3. Support; 4. Ash discharge device; 5. Air adjustment device; 6. Furnace chain; 7. Coal feeding hopper;

8. Front wind shield; 9. Side seal.

Technical characteristics:

a. The furnace chain consists of furnace bars, clamping plates, chains, double-headed bolts, liners, and rollers. The furnace bars are grouped in sets of five, inserted into the holes of the clamping plates, with overlapping front and rear furnace bars forming a fish scale pattern, allowing very little coal leakage. The ventilation cross-section of the grate surface is 8%, with uniform ventilation and stable combustion. The clamping plates are fixed to the chain with pins, and the parallel chains are connected together with double-headed bolts, with the double-headed bolts encased in liners to keep the parallel chains at the same distance apart. The liners are encased with rollers, which move along the upper guide rail during operation, transferring weight to the support.

b. Several independent air chambers are set along the longitudinal direction inside the grate. The primary air entering the air chamber slows down due to diffusion and can evenly fill the air chamber. The air volume of each air chamber can be adjusted through the air adjustment device.

c. Ash discharge devices are arranged inside each air chamber. At the bottom of the air chamber, ash discharge plates with ash discharge openings are arranged, and the movable doors connected to the ash discharge pull rods usually cover the ash discharge openings. By pulling the ash discharge handle at regular intervals, the ash falls from the ash discharge opening onto the furnace chain below, which carries it to the ash discharge door near the front ash hopper for manual removal.

d. A contact-type side seal structure is used between the sides of the grate and the support to prevent coal blocks from leaking into the sides of the grate and to prevent air leakage from the sides of the grate.

e. The slag blocking device is placed on the support behind the grate, relying on its own weight to press its head against the grate. Its main function is to shovel up ash and slag, preventing ash and slag from falling into the grate, protecting the rear axle rollers, and also creating obstacles for the movement of ash and slag, increasing the combustion time of combustible materials in the ash and slag on the grate, allowing them to burn out.

f. This grate has a compact structure, stable and reliable operation, and convenient installation and maintenance. It has been tested and operates normally in the factory, and the whole machine is shipped out. (It can also be shipped as loose parts according to user requirements.)

Usage of small flake chain grates:

1. On-site inspection and adjustment of the grate

This grate has undergone size adjustments in the factory and has passed an 8-hour cold state operation test. However, during transportation, vibrations may loosen the locking bolts, causing structural size changes. Therefore, after the entire boiler is assembled, the grate must be carefully inspected and subjected to a cold state no-load test.

a. Check whether the adjustment screw of the driving shaft is loose. If it is loose, the screw should be adjusted to tighten the driving bearing.

b. Fill the main and driven shaft bearings with lubricating oil.

c. Carefully check that no iron parts or other debris are lost or trapped anywhere in the grate.

d. Check whether the air adjustment device is flexible and troubleshoot any faults.

e. Check whether the ash discharge pull rod is flexible and troubleshoot any faults.

f.  Is the coal gate lifting flexible, and is the distance from both sides to the grate surface equal?

g.  The cover plate on the coal gate must be properly covered to prevent coal blocks from leaking in, which would affect the lifting of the coal gate.

h.  After the above checks and adjustments, a cold operation test should be conducted. If any abnormal phenomena are found, stop the machine immediately, eliminate the faults, and continue normal operation for more than 8 hours.

2. Ignition Use

Open the ignition door, place the igniter in, increase the induced draft, after the igniter burns, manually add coal on the igniter. This is to open the blower, and after the coal layer burns vigorously, close the ignition door, add coal to the coal hopper, intermittently operate the grate, and observe the ignition situation at the observation hole, making appropriate adjustments to the fire. Once the front arch is heated and the coal can ignite continuously, operate the grate and adjust the air volume to achieve normal combustion.

3. Grate Operation Management

a. The normal combustion condition on the grate is: the fire bed is flat, the flames are dense and uniform, bright yellow, with no cold air entering the fire mouth, the burnout section is neat and consistent, and the ash is dark, with the smoke emitted from the chimney being light gray.

b. It is strictly forbidden to introduce iron or other debris into the furnace to prevent the grate from getting stuck.

c. The coal layer should maintain a certain thickness, and only when the type of coal changes or the boiler load varies significantly should the thickness of the coal layer be adjusted. The thickness of the coal layer is generally 80-180mm, and for bituminous coal, the thickness is 90-120mm. When burning a mixture of bituminous coal or inferior bituminous coal with anthracite, the coal layer thickness should be 100-130mm. If the coal is too wet, a thicker coal layer should be used for slow combustion. (The above data is for reference only)

d. The coal hopper should not be lacking in coal, and the phenomenon of "burning coal bridges" in the coal hopper should be eliminated at all times.

e. When coal enters the furnace, it should ignite at a distance of 200-300 from the coal gate and should not burn under the coal gate, otherwise, it will damage the coal gate. If such a situation occurs, water can be added to the coal or the grate speed can be increased.

f. When coal enters the furnace, if it has not ignited at a distance of 200-300 from the coal gate, it is called "extinguishing fire." At this time, open the furnace door to adjust the fire, that is, push the burning coal to the coal layer near the coal gate, or add flammable materials to speed up the ignition.

g. If caking is found, the caking blocks should not exceed 200mm; otherwise, the furnace door should be opened to break the caking.

h. The combustion should be kept uniform across the grate. If there are fire mouths, black flames, or uneven coal layers, a fire poker can be used to level them.

i. The ash in the wind chamber and the ash cleaning area at the front of the grate must be cleaned 3-4 times per shift.

j. It is strictly forbidden to burn under positive pressure. At this time, the operation of the blower and induced draft should be checked, as well as whether the flue at the rear is blocked, and faults should be eliminated.

k. "Choking the furnace" should be avoided as much as possible to prevent damage to the grate plates.

l. When the boiler load increases and stronger combustion is needed, the induced draft should be increased first, then the blower, and then the grate speed should be increased. If necessary, the thickness of the burning coal should be increased. When the boiler load decreases and weaker combustion is needed, the air supply should be reduced first, and if necessary, the thickness of the coal layer can be reduced.

m. The shutdown of the grate is generally carried out in the following order.

1)   Stop supplying coal half an hour in advance and reduce the grate speed.

2)   Appropriately reduce the induced draft to allow the remaining burning coal on the grate to burn out before shutting down.

3)   After 2-3 hours, when the ash on the grate is unloaded, the ash in the ash equipment should be cleared, stop the air supply and induced draft, open the front windbreak and ash drop doors for natural ventilation.

4)   After unloading the fire, the grate continues to operate until the temperature in the furnace cools down to 150.⁰C.

n. The emergency shutdown of the grate is carried out in the following order.

1)   First stop the blower, then stop the induced draft.

2)   Rotate the arc plate under the coal hopper upwards to stop supplying coal.

3)   Reduce the grate speed until the ash is unloaded and then stop.

4)   Before the grate cools down, mechanical ventilation should be maintained.

4. Maintenance and Repair of the Grate

1). Regularly add lubricants to both sides of the main and driven shafts.

2). The grate must be adjusted and tightened in four stages at 3, 7, 15, and 30 days during the first month of operation. After that, regular checks should be made. If the grate chain is found to be loose or misaligned, the adjustment screw at the front axle should be adjusted in time, and the grate chain should be tightened to prevent arching.

3). If there are phenomena such as jamming or arching during operation, the faults should be eliminated in a timely manner according to the specific situation.

4). Grate plates that are burned out or deformed excessively should be replaced in a timely manner to avoid affecting operational safety. Solution: Open the front windbreak door and loosen the double-headed bolt nuts at the front of the wall panel, use a pry bar to open the grate clamp, replace the grate plates, then tighten the nuts of the double-headed bolts and lock them.

5). Grate misalignment. Generally, adjust the adjustment screw on the driving shaft.

6). If the lubrication oil path is blocked or the lubricant has solidified, the oil path should be cleaned, and the lubricant should be replaced.

7). If the furnace is stopped for a long time, the coal in the coal hopper and the collected ash in each wind chamber should be cleared.