Differences Between Chain Grates and Reciprocating Grates

The chain grate, also called a link-belt grate, is the most common type in stoker-fired boilers; reciprocating grates are divided into inclined and horizontal types. Both are moving-bed grates, and the core difference is whether the fuel moves relative to the grate surface.

Structure and pushing action

A chain grate has sprockets driving a complete chain belt or chain, with grate bars fixed to the chain, so the whole grate surface travels evenly backwards and the fuel lies on it with almost no relative sliding. A reciprocating grate alternates fixed and moving bars, and a drive swings the moving bars back and forth to push the fuel backwards step by step.

Ignition

The chain grate ignites from one side: fresh fuel entering the furnace is lit only by radiation from the furnace above and burns from top to bottom, while the grate runs through drying, volatile combustion, coke combustion and burnout with slag removal from front to rear. The reciprocating grate ignites from both sides: on the return stroke the moving bars turn hot glowing carbon under the fresh fuel, heating it from above and below and making wet or low-calorific fuel easier to ignite.

Fuel bed condition

The fuel bed on a chain grate is stable and rarely turned, so an ash shell formed after clinkering is hard to break and tends to block air. A reciprocating grate keeps squeezing and tumbling the bed, breaking coke lumps and the surface ash shell automatically and giving better bed permeability.