How to Choose Between Chain Grates and Reciprocating Grates Based on Fuel?
The choice between a chain grate and a reciprocating grate depends mainly on fuel particle size, moisture, calorific value and slagging tendency, and on whether operation is continuous. When the fuel is regular, dry and stable in quality a chain grate fits better; when the fuel is wet, mixed, waste-heavy and unstable in calorific value a reciprocating grate fits better.
Fuels that favour a chain grate
Fuel with even particle size, moderate moisture, stable calorific value and little slagging tendency suits a chain grate. For coal, class II bituminous coal is suitable, with a particle size of 6-50mm, as-received moisture below 20%, ash fusion point above 1200℃ and weak caking property. Strongly caking coal, high-ash low-grade coal, lignite and raw coal carrying too much coal powder do not suit a chain grate. For biomass, pellets, briquettes and regular wood chips can be used with a moisture content of ≤20%, while wet sawdust, chopped straw and mixed waste easily stratify, cake and ignite poorly, so they are not recommended for direct firing on a chain grate.
A chain grate suits duties where the fuel source is stable, the fuel has been screened in advance and operation runs 24h continuously over the long term. Such duties usually also aim at long grate service life.
Fuels that favour a reciprocating grate
Fuel with higher moisture, irregular particle size, low calorific value, loose waste and easy slagging suits a reciprocating grate. For coal, low-grade bituminous coal, high-ash coal, lignite, low-calorific coal and mixed coal of uneven size can be used, the grate can take moisture of ≤30%, and lightly caking coal is also acceptable. Biomass waste is the strong field of the reciprocating grate: wet sawdust, saw powder, bark, straw, rice husk, bagasse and wood offcuts can all be handled, and loose agricultural and forestry waste has a moisture content of 25%-45%. Sludge co-firing, combustible light industrial residue and mixed fuels whose type changes often are equally suitable.
It is not suitable for long-term firing of large hard slag of high melting point only, and it does not suit very fine powder either. It fits duties with factory-generated waste, strongly fluctuating fuel quality, intermittent operation and no screening or pre-treatment of the fuel.
| Item | Chain grate | Reciprocating grate |
|---|---|---|
| Applicable coal | Class II bituminous coal, 6-50mm, weak caking coal | Low-grade bituminous coal, high-ash coal, lignite, low-calorific mixed coal |
| Moisture | As-received moisture below 20% | Coal can take moisture ≤30% |
| Ash fusion point and slagging | Ash fusion point above 1200℃, not suitable for strongly caking coal | Usable for lightly caking coal, not for long-term firing of large hard slag of high melting point |
| Suitable duty | Stable fuel, pre-screening, long-term 24h continuous operation | Factory waste, strongly fluctuating quality, intermittent operation |
Common misconceptions
A reciprocating grate is not necessarily more efficient: when fuel quality is good and stable a well-tuned chain grate boiler has higher thermal efficiency, and the advantage of the reciprocating grate only becomes clear with poor fuel. A reciprocating grate costs more to maintain, the hot movable bars are wearing parts that need regular replacement, while daily inspection work on a chain grate is lower. A chain grate is not unable to burn biomass, but loose wet biomass should not go straight onto a chain grate, because ignition difficulty, black smoke and insufficient output easily follow.
