| Coal is a kind of main energy source worldwide. China is a big country at coal production and consumption. Environmental pollution caused by industrial boilers is becoming more serious, nitrogen oxide emissions are highly valued. Along with the increasing demand for environmental protection, the development on highefficiency NOx emissions control technology for small and medium boiler is imperative. Carbonaceous material can be used as a direct reduction catalyst or catalyst carrier in NOx removal process. Strong activity char can reduce NOx emissions and increase burnout rate. The mechanism of char-NO reaction is not uniform, research on large-size coal particles and NO response characteristics are even fewer, which can not be obtained for industrial boilers. This paper select the appropriate nitriding coal char prepared to carry out experimental research, and establish a relationship between the different treatments and char-NO reactivity, having far-reaching significance on providing experimental support for the control of nitrogen oxide emissions.This paper explores a new char-urea coupling technology reducing NO for grate-fired boiler. We choose and analyze Shuozhou bituminous coal for nitriding coking at horizontal furnace under different conditions, including industrial analysis and elemental analysis, mercury testing, nitrogen adsorption test, SEM and EDS test, XPS testing of char elements, pore structure distribution, relative content of the functional groups and other physical parameters. After nitriding treatment, the relative content of nitrogen element in coal increased significantly, then decreased after NO reaction; pore structure of original char is undeveloped, water flashing and nitriding treatment lead to pore structure transformation and increase surface area. Nitriding process can promote the formation of nitrogen-containing functional groups, NH3 heating treatment have better nitriding effect, nitrogen by weight lifting 26.15%, respectively 15.22%; oxygen and oxygen-containing functional groups relative content reduced. After NH3 heat treatment, C-O,-C=O,-COOH relative content in coal decreased,-C-C-,-C-H content increased, the degree of graphitization deepened; N-6 and N-Q ratio rise while the ratio of N-5 and N-X fall; after nitriding, the relative content of N-6 and N-5 increased, N-Q and N-X fall; N-6 and N-Q probably played a key role in the reduction of NO among nitrogencontaining functional groups, N-5 is the largest proportion of existing form.By exploring the law of large particle size nitriding char to reduce NO on a vertical fixed-bed reactor, we believe that the char pore structure change, nitrogen agents and nitrogen-containing functional groups’ the formation and transformation after flashing are main factors to large diameter of the nitriding char’s NO reactivity during high temperature. As the temperature increases, NO reactivity of char rise; there are significant differences in reduction ability of NO at same temperature. 30 sflashing char’s reactivity is lower than 60s-flashing char. By nitriding treatment char’s NO reduction activity increased, especially above 700℃, when 850℃ up to 39.88%; the ability to reduce NO enhance in high-temperature zone within a certain range to improve the amount of urea; however, too much can hinder coal char coke porosity development, resulting in NO reduction effect decline. Below 725℃, ammonium bicarbonate nitrogen as nitriding agent char has a very good effect of NO reduction, 10% higher than urea, weaker above 725℃. After-treatment will reduce the impact to a certain extent, the overall trend unchanged. within the first 10 s flashing, the process occurs mainly is rapid vaporization of water, 10s-flashing nitriding char’s NO reducing effect is better than 30s-flashing char; but at 850℃ reduction effect is less than 30s-flashing char about 30%. Sodium carbonate as a synergistic, temperature range moves to lower in 500-800℃. For thermal state infusion, NO export concentration increased then decreased after nitrogen injection solution. |
