Flameless combustion behaviour of preheated pulverized coal

A method for stable flameless combustion of pulverized coal based on coal preheating was recently proposed. The method involves the initial heating of pulverized coal to a temperature above 800 degrees C. The heated coal is then transferred into a combustion chamber, where it is mixed with secondary air injected at a high velocity to achieve flameless combustion. The flameless combustion behaviour of the preheated pulverized coal was experimentally investigated in a lab-scale test apparatus. The results showed that stable flameless combustion of bituminous coal and two different anthracite coals could be achieved. The temperature of the combustion chamber was also observed to be homogeneous. The peak temperature was below 1250 degrees C, while the average combustion temperature was about 1150 degrees C. The normalized root mean square temperature fluctuation over the combustion chamber is 7.0%, 6.7%, and 6.8% for the three different coals. The colour of the entire combustion chamber was a faint yellow with no obvious flame front surface observed. Fuel preheating was found to be effective for improving the combustion efficiency, with values of 99.2%, 98.3%, and 97.9% achieved for bituminous coal and two different anthracite coals, respectively. The experimental data further revealed that the NOX emissions for all the considered coals were very low compared to the corresponding cases of traditional combustion, with the values for the different coal types also significantly varying. The NOX emissions were determined to be 232, 187, and 165mg/Nm(3) (6% O-2) for bituminous coal and two different anthracite coals, respectively.