Experimental Studey On Impact Of Preheating On Coal Combustion And NOx Release

Low combustion efficiency and high NO_x emission are the two outstanding obstacles for low volatile coal combustion in W style stove in China. These are urgent, and no effective measure has been adopted at present. This study suggested preheatment at the entrance of coal combustion stove, which on one hand benefited the volatile components to leave the surface and stimulate the burning process by enlarging the specific surface area, while both the reduction (NH₃ and HCN were reduced to N₂ in reduction atmosphere) and thermal decomposition of nitrogen-containing functional group in coal reduced the NO_x emission sharply on the other hand. The study mainly concerned the volatile component, semi-coke structure, combustion dynamics, nitrogen-containing function group, compounds prior to NO_x, which revealed the potential trend of the easy-burning, flame stability, fuel burn-out and the dynamic rules in combustion.First, the study stated that preheatment changed the physical-chemical structure of coal. Apparatus for BET surface, XRD, thermal gravity-ultra red chramotography were used to test the features in specific area, aromatic structure, and thermal gravity variation. The results showed that volatile content increased with the increasing in temperature for preheatment between 673 K与1273 K; and specific surface area and hole volume increased for bituminous coal, while high volatile coal showed reverse trends; Similar argraphite structure showed after preheatment, which leaded to better combustion properties compared with no preheatment; Heating rate showed obvious effect on volatile emission vilosity, but little effect could be found on the total amount of volatile components.Second, the study suggested that the conversion between the nitrogen-containing function groups reduced the NO_x emission. XPS analysis highlighted the possible conversion between nitrogen-containing conpounds. The results were, Nitrogen conversion efficiency in gaseous phase was improved by preheastment, thus the nitrogen residual in semicoke accumulated. HCN and NH3 played an important role in fuel nitrogen formation. N-Q was cut half after preheatment, which reduced the NO_x emission greatly. The greater the preheatment temperature was, the better the reducing effect on NO_x emission would be.