What is the reburning effect of coal slurry? What are the features?

The water-coal slurry reburning technology, which can reduce NOx emissions, is an effective method for controlling nitrogen oxides; its effectiveness is directly related to the choice of fuel used for reburning. Water-coal slurry, as a reburning fuel, has the following characteristics: (1) Low pollution. It is made from coal with high volatiles and undergoes washing processes, which **reduces ash content, sulfur content, etc.; moreover, the low temperature during its combustion helps to minimize the formation of thermal and rapid-type NOx. (2) Higher activity: The active components in coal are beneficial for reducing NOx, and water vapor acts as an activator; reacting with coal can increase its activity. Therefore, the use of water spraying or water-coal slurry as a fuel represents a good option for re-ignition. (3) Larger specific surface area: After the moisture evaporates, the slurry droplets form particles with a porous, hollow structure, which increases the reaction-specific surface area of these particles, reduces the resistance to reactions within the particles, facilitates the ignition of the water-coal slurry droplets, and accelerates the reaction rates of volatiles and coke. Furthermore, the detonation of water-coal slurry droplets at high temperatures causes large voids to form on the particle surface or the particles to break into several smaller pieces, further increasing the reaction specific surface area. (4) The effect of water vapor: Firstly, since water-coal slurry contains a large amount of water, this water vaporizes into water vapor during combustion. The water vapor opens up the closed pores, thereby increasing the surface area and pore volume of the coke. The higher the temperature, the more pronounced the reaming effect, which helps to reduce the resistance to the precipitation of volatile nitrogen and facilitates its release, thereby lowering the content of pyrolytic nitrogen. Secondly, water vapor can react with coke at high temperatures to produce another reducing agent, CO, thereby facilitating the progress of homogeneous reactions and reducing NOx emissions. Again, water vapor at high temperatures can generate a large amount of H and OH free radicals, reducing NOx emissions; at the same time, it accelerates the decomposition of polycyclic nitrogen-containing structures, promoting the formation of HCN and increasing its release. The H radical can also activate nitrogen-containing functional groups, leading to nitrogen reduction and the release of more NH3. (5) It has a significant cost advantage: coal water slurry used for reburning can be produced without additives, resulting in lower slurry production costs.