The oxides of nitrogen (NOx) are airborne pollutants that result from the combustion
of pulverised coal. The aim of this project is to identify operational methods that
reduce the NOx emissions from a coal fired boiler whilst maintaining satisfactory
performance.
This project describes important combustion properties and the processes occurring
during the combustion of pulverised coal. Detail is provided on the pulverisation
plant, draught plant and steam system of a large utility boiler. The dominant NOx
formation mechanisms in coal fired boilers are discussed and NOx reduction
strategies applicable to these boilers are described. Engineering models are
developed to describe initial flame temperature, furnace residence times, furnace
heat pickup and thermal NOx formation.
A series of tests were designed and undertaken to measure and assess the effect on
NOx formation and boiler performance to variations in:-
- The distribution of secondary air to each windbox, and
- The level of excess oxygen measure at the boiler exit.
During each test the following was undertaken:-
- Detailed temperature survey of the furnace region
- Coal sampling for laboratory analysis
- Fly Ash sampling to determine loss of ignition
- Logs of relevant data to determine plant performance.
Difficulties and shortcomings regarding the predictive models are discussed and the
performance of the boiler under each test is compared
