Studies Of MILD Combustion Technology Applied To Pulverized Coal Boilers

MILD combustion is a well-known measure to reduce NOx emission, save energy and enhance flame stability. As an advanced combustion technology, MILD is expected to be an option for future pulverized coal boiler. The characteristics of pulverized coal in MILD combustion were studied by means of experimental investigations and numerical simulations. Effects of different elements such as the position and ratio of the tertiary air, excess air factor and heat load had been optimized for low NOx emissions and high burning efficiency. According to the experimental data, the pollutant emissions meet the national standard requirements.1. MILD combustion could decrease the pollutant emissions, especially combined with air staging combustion technology. In this way, it satisfied requirements both energy conservation and emissions reduction.2. The experiment was operated with supply position Z of tertiary air varying from 600 to 2600mm; NOx emissions were deduced with position Z. NOx emissions (119mg/Nm3@9%02) of air staging MILD combustion were greatly reduced compared with national standard (200mg/Nm3@9%O2) conducted in key areas when air allocation of total air varied from 0.6 to 0.7, excess air factor was 1.1 and the ratio of position Z and the total length of the boiler was 0.72. Combustion efficiency should be over 98%at this experimental condition.3. The CO/NOx emissions were supposed to increase when the experiment was operated with too large or too small air staging ratio. The air staging ratio should vary from 0.6 to 0.7 when the position Z=2600mm.4. Trace amounts of swirling air introduced into MILD combustion could effectively reduce CO emissions and increases combustion efficiency.5. MILD combustion can reach the furnace temperature uniformity. The air allocation causes little impact to the temperature field which is different from the impact of excess air factor and position Z.6. The PDF model was comparatively accurate for MILD combustion modeling and its temperature field, velocity profile and species concentrations, but it still need to be optimized.