Analysis on the influence of low nitrogen combustion transformation on boiler thermal efficiency and economy

The practical principle of low nitrogen combustion is to control NOx based on air fractional combustion technology. The technology works by burning coal, which actually burns at two temperatures: high oxygen and low oxygen. In this way, the co-occurrence of oxygen-rich and high-combustion temperature can be avoided, thus significantly hindering the formation of thermal NOx and fuel NOx to achieve the effect of NOx generation.

First, hypoxia in the main combustion zone of the lower layer presents an increasing trend. Burning area between the furnace exit and the formation of the corresponding burning distance is relatively short, at the same time the upper combustion temperature of burning zone in low temperature condition, the probability of pulverized coal, combustible gas combustion is not improved significantly, the fly ash carbon index in the boiler flue gas emissions and CO content exist the possibility of increasing, eventually increase the mechanical incomplete combustion loss of fly ash carbon content seems to use q4f refer to below), chemical use q3 refer to below is not completely lost like) the probability of ascension, the boiler thermal efficiency is coming down.

Second, the possibility of high temperature corrosion of water cooling wall increases gradually. In the denitrification reduction zone between the lower main combustion zone and the upper burnout zone, the production of reducing combustible gas (CO+H2) is the largest. The reducing gas reacts with S in the fuel to form HS. Under the reducing atmosphere, H5 gas reacts with the water cooling wall at high temperature. H2S reacts directly with metallic iron to form iron sulfide, some of which is further oxidized to iron oxide. This layer of iron sulfide and iron oxide is porous and does not protect the water cooling wall. H2S gas will continuously corrode the water cooling wall through this porous layer. The concentration of H2S has a linear relationship with the corrosion rate of metal.