Reciprocating Type Grate

Product introduction

By structure, reciprocating grates are generally divided into inclined reciprocating grates and horizontal reciprocating grates. A reciprocating grate is stepped, being formed of fixed grate plates and movable grate plates arranged alternately. The movable grate moves back and forth so that the coal travels down evenly.

The stroke is usually 70–110 mm. A larger stroke should be chosen when the coal quality is poor.

When the movable grate moves, the coal bed is squeezed, rolled and stirred, and part of the fresh coal is pushed onto the hot burning coal bed below. On the return stroke of the movable grate, part of the hot burning coal particles is carried back to the bottom of the unburned coal bed, so the fuel bed ignites from both sides. Unlike a chain grate, the coal bed moves relative to the grate, which loosens the bed and increases its air permeability; the coal particles press and rub against each other, so the ash shell wrapping the hot particles comes off, which helps the coke burn.

The reciprocating motion of the grate also breaks coke lumps with weak bonding strength, which has a certain effect on combustion.

Scope of application and requirements

Scope of application

A reciprocating grate can be used in boilers of 1 t–200 t/h, and the choice of fuel is wider.

Operating requirements

The coal used in this grate shall meet the following requirements:

Particle size: the maximum lump size of the coal shall not exceed 40 mm, fine coal of 0–6 mm shall account for no less than 50% of the fuel, and the content of 0–3 mm coal powder shall be less than 25%.
The moisture of the coal shall be less than 15%, and 5–10% is best.
The ash content of the combustion shall not be less than 10%, and the ash melting point shall be above 1200℃.

Structure and characteristics

A reciprocating grate consists of a coal hopper, a support, movable beams, fixed beams, grate plates (movable grate plates and fixed grate plates), a front air baffle and a drive system.

The whole combustion surface of the grate is made up of movable grate plates and fixed grate plates, stacked alternately in a stepped pattern. The fixed grate plates are mounted on the fixed grate beams, and the fixed beams are fixed to the grate frame. The movable grate plates are set into the movable grate beams, the movable beams are mounted on the movable frame, and the movable frame rests on the supports of the grate frame. The movable frame is connected to the external drive mechanism through a connecting rod.
When the motor starts, the connecting rod, pulled by the reducer, moves the movable frame, so that the movable grate plates reciprocate back and forth over the fixed grate plates. The stroke is determined by the actual dimensions of the grate plates in the design and by the coal actually burned in the boiler, and is usually 70–180 mm.
The grate uses zoned air supply. Several mutually independent air chambers are arranged along the length of the grate, and air enters the chambers from the air boxes or ducts on both sides. The air flow into each chamber is regulated by an air regulating device.
The coal hopper is mounted on the wall plates on both sides of the support, and the coal bed thickness is adjusted by raising and lowering the coal gate.
The grate can be delivered in assembled or unassembled form, and users can choose as needed.
One of the main features that distinguish an inclined reciprocating grate from a chain grate is the relative movement between the grate and the coal. When the movable grate moves back and downwards, part of the fresh coal is pushed onto the top of the burning coal. When the movable grate moves forward and upwards, part of the burning coal returns to the bottom of the unburned coal and heats the fresh coal.

This ignition condition resembles a hand-fired furnace but is better than a chain grate. While being pushed, the coal is continuously squeezed, which breaks up coke lumps and ash shells. At the same time the coal rolls slowly, so the coal bed becomes loose and level, which favours combustion.

Model parameters

Boiler evaporation capacity	Effective grate area m²	Effective grate width mm	Air passage section ratio	Drive shaft torque N.m	Inclination angle
4 t/h	5.56	1600	6-8%	2000	user-defined
6 t/h	6.08	1600	6-8%	3000	user-defined
8 t/h	8.5	2100	6-8%	4000	user-defined
10 t/h	12.99	2020	6-8%	5000	user-defined
15 t/h	22.04	3300	6-8%	7500	user-defined
30 t/h	29.65	3730	6-8%	30000	user-defined
40 t/h	40	4630	6-8%	40000	user-defined
65 t/h	60.16	7020	6-8%	60000	user-defined
100 t/h	99.56	10480	6-8%	75000	user-defined
130 t/h	100	11580	6-8%	100000	user-defined
160 t/h	153	14700	6-8%	125000	user-defined
200 t/h	185	17780	6-8%	150000	user-defined
260 t/h	248	18400	6-8%	185000	user-defined
300 t/h	295	20700	6-8%	210000	user-defined

Operating features

The inclined reciprocating grate has a simple structure, is easy to machine and manufacture, is convenient to use and maintain, and has low metal consumption. Compared with a chain grate, it can burn low-grade fuels such as class II bituminous coal, class I bituminous coal, lignite and lean coal.
Compared with a chain grate, it is suitable for burning low-grade coal with high moisture, high ash, low calorific value (12560 kJ/kg) and a strong caking tendency.
When the air supply is reasonable and air leakage is small, the carbon content in the ash is usually 18%–20%, which is 5%–10% lower than the ash and slag of a hand-fired furnace, so coal is saved and black smoke is reduced.