Division 1.6.2 NOx emissions

United Kingdom

	Technique	Description
a	Burner design (low NO_x burner)	The low NO_x burners are useful for reducing the flame temperature and thus reducing thermal and (to some extent) fuel derived NO_x. The NO_x reduction is achieved by supplying rinsing air for lowering the flame temperature or pulsed operation of the burners. Low NO_x burners are designed to reduce the primary air portion which leads to lower NO_x formation whereas common multi-channel burners are operated with a primary air portion of 10 to 18 % of the total combustion air. The higher portion of the primary air leads to a short and intensive flame by the early mixing of hot secondary air and fuel. This results in high flame temperatures along with a creation of a high amount of NO_x formation which can be avoided by using low NO_x burners
b	Air staging	A reducing zone is created by reducing the oxygen supply in the primary reaction zones. High temperatures in this zone are particularly favourable for the reaction which reconverts the NO_x to elementary nitrogen. At later combustion zones, the air and oxygen supply is increased to oxidise the gases formed. Effective air/gas mixing in the firing zone is required to ensure that CO and NO_x are both maintained at low levels. In 2007, air staging had never been applied in the lime sector
c	SNCR	Nitrogen oxides (NO and NO₂) from the flue-gases are removed by selective non-catalytic reduction and converted into nitrogen and water by injecting a reducing agent into the kiln which reacts with the nitrogen oxides. Ammonia or urea is typically used as the reducing agent. The reactions occur at temperatures of between 850 and 1 020 °C, with the optimal range typically between 900 to 920 °C

Technique

Description

Burner design (low NO_x burner)

The low NO_x burners are useful for reducing the flame temperature and thus reducing thermal and (to some extent) fuel derived NO_x. The NO_x reduction is achieved by supplying rinsing air for lowering the flame temperature or pulsed operation of the burners. Low NO_x burners are designed to reduce the primary air portion which leads to lower NO_x formation whereas common multi-channel burners are operated with a primary air portion of 10 to 18 % of the total combustion air. The higher portion of the primary air leads to a short and intensive flame by the early mixing of hot secondary air and fuel. This results in high flame temperatures along with a creation of a high amount of NO_x formation which can be avoided by using low NO_x burners

Air staging

A reducing zone is created by reducing the oxygen supply in the primary reaction zones. High temperatures in this zone are particularly favourable for the reaction which reconverts the NO_x to elementary nitrogen. At later combustion zones, the air and oxygen supply is increased to oxidise the gases formed. Effective air/gas mixing in the firing zone is required to ensure that CO and NO_x are both maintained at low levels.

In 2007, air staging had never been applied in the lime sector

SNCR

Nitrogen oxides (NO and NO₂) from the flue-gases are removed by selective non-catalytic reduction and converted into nitrogen and water by injecting a reducing agent into the kiln which reacts with the nitrogen oxides. Ammonia or urea is typically used as the reducing agent. The reactions occur at temperatures of between 850 and 1 020 °C, with the optimal range typically between 900 to 920 °C