Features and Advantages of Reciprocating Grates
The reciprocating grate is a commonly used boiler combustion device and has the following features and advantages:
Structural features
Grate bar arrangement: a reciprocating grate consists of fixed grate bars and moving grate bars arranged alternately, forming an obvious stepped shape with a certain inclination angle, generally between 15°-30°, which makes it convenient for the fuel to move downward under the action of its own gravity and the motion of the grate.
Ventilation gaps: there are longitudinal gaps between the grate bars, and also transverse gaps between the layers of grate bars, forming good ventilation passages; the ventilation open-area ratio is about 7%-12%, which allows air to enter the fuel layer evenly and provides sufficient oxygen for fuel combustion.
Drive mechanism: a motor drives the eccentric wheel, which drives the push-pull rod connected with the frame, so that the moving grate bars make back-and-forth reciprocating motion with the moving frame; the stroke is about 30-100mm and the reciprocating frequency is about 1-5 times/min, which can be adjusted by changing the motor speed.
Combustion process features
Strong fuel adaptability: the reciprocating grate has good adaptability to fuel and can adapt to many different types and qualities of fuel, such as low-grade coal, biomass fuel and so on. Especially for fuel with strong caking property, large ash content and difficulty in igniting, it can also achieve a good combustion effect, while a chain grate is relatively difficult when handling this kind of fuel.
Good ignition conditions: the relative motion between the grate and the fuel makes part of the new fuel be push-fed onto the hot glowing fire bed below that has already ignited, so the ignition conditions are improved artificially. At the same time, during the return process the moving grate bars also rake back part of the already ignited carbon particles to the bottom of the unburned fuel layer, becoming the ignition heat source of the bottom layer of fuel, which helps the fuel to ignite quickly and burn stably.
High combustion intensity: the fuel layer is continuously loosened under the raking and turning action of the moving grate bars, which enhances the air permeability and promotes the disturbance of the combustion bed. Moreover, the ash shell on the outer surface of coke lumps and fuel lumps is also broken or shed due to squeezing and turning, which greatly increases the contact area between fuel and air, thereby strengthening the combustion process, raising the combustion intensity and reducing the heat loss from chemical and mechanical incomplete combustion.
Staged combustion: the combustion process of the fuel on the grate proceeds in stages along the length direction of the grate, so staged air supply can be carried out; the air supply in the middle section of the grate is larger and the corresponding air pressure is also higher, while the air supply in the front and rear sections is less. At the same time, a reasonable arrangement of secondary air can strengthen the disturbance and mixing of the gas flow in the furnace, so that the combustible gas produced at the front part of the grate flows over the high-temperature combustion zone and mixes well with the excess air rising from the burnout zone for further burnout, improving the combustion efficiency.
