Effect of coal and air staging on the ignition plane movement and emissions during rapid large load changes on chain-grate stokers

Abstract

A major concern when operating stoker-fired boiler plant during rapid large load changes is maintaining stable ignition because 'burn-back' may occur or, at the other extreme, burning coal can be discharged from the end of the grate if the coal and air settings are not appropriately controlled. A suitable coal/air staging practice has been identified for chain-grate, stoker-fired boilers under rapid load-following conditions. The flame-front migration and carbon monoxide and oxygen concentrations in the flue gases were recorded during experiments on a test facility at Casella CRE. The findings were confirmed in tests on a full-scale industrial boiler and indicate that the coal feed should lead the air flow on load increase and vice versa on turndown in order to improve transient ignition stability and reduce carbon monoxide and smoke emissions.