Nitrogen sulphur interactions in coal flames

The control of NOx emissions from coal combustion is a major factor in redu cing the environmental impact of coal-fired power plants. This paper invest igates the effect of sulphur on NO production in pulverised coal dames usin g an experimental approach. The NO emissions from a 20 kW down-fired combus tor were measured with and without SO: doping for a range of operating cond itions and coal types with total sulphur contents between 0.6 and 2.9%. Som e tests were repeated using coals that were acid-washed to remove pyritic s ulphur. The NO emissions were statistically correlated against 52 parameter s describing the physical and chemical properties of the coals. The experimental results show that the change in the NO emission due to SO2 addition is dependent upon the stoichiometry of the flame and that sulphur can interact with the production of NO in a heterogeneous coal flame in a manner similar to that reported previously for gaseous and liquid fuel flam es. For fuel-rich conditions, sulphur addition enhanced the production of N O from fuel-bound nitrogen by up to around 20%. The change was larger for c oals with a lower inherent fuel-S content (<0.5 wt%). The experimental tren ds also provide strong evidence that the in-flame sulphur nitrogen interact ions are controlled by the availability and production of inorganic (pyriti c) sulphur from the coal matrix. This is supported by statistical correlati on of the data which has identified specific coal properties, such as pyrit ic sulphur content and the total volatile yield, as being amongst the most influential parameters in predicting the NO emission for the system employe d. These parameters are the key indicators for the release of sulphur at lo w to intermediate temperatures and would imply that the NO enhancement mech anism under fuel-rich conditions appears to be associated with the early re lease of pyritic-S into the developing flame to subsequently interact with volatile nitrogeneous species. <(c)> 2001 Elsevier Science Ltd. All rights reserved.