Selective catalytic reduction (SCR)

Selective non-catalytic reduction (SNCR) a. Urea b. Ammonia

Fuel reburning

Combustion optimization

Inject oxidant Oxygen instead of air

Catalyst located in air flow and promotes reaction between ammonia and NOX

Injects reagent to react with NOX

High NOX removal

Injects fuel to react with NOX

Changes efficiency of primary combustion

Chemical oxidant injected into flow

Uses oxygen as oxidizer a. Low capital cost; moderate NOX removal; non-toxic chemical b. Low operating cost; moderate NOX removal

Moderate cost; moderate NOX removal

Minimal cost

Moderate cost

Moderate to high cost; intense combustion; eliminate thermal NOX

Very high capital cost; high operating cost; catalyst siting; increased pressure drop; possible water wash required a. Temperature dependent; NOX reduction less at lower loads b. Moderately high capital cost; ammonia storage, handling, injection system

Extends residence time

Extends residence time

Nitric acid removal

Eliminate prompt NOX; furnace alteration

Space requirements; ammonia slip; hazardous materials; disposal

All fuels

All fuels a. Furnace geometry; temperature profile b. Furnace geometry; temperature profile

Furnace temperature profile

Furnace temperature profile


Equipment to handle oxygen

All fuels

(pulverized solid)

All fuels

All fuels

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