Dear All
As mention in subjected topic can give your point regarding following questions
1.) Main reasons for generation Nox (NO & NO2) and Sox (SO3 and SO2)?
2.) What is the measures to control them?
3.) Difference between Thermal and Rawmaterial Nox generation?
4.) what is the meaning of low Nox generation calciner, how calciner design help us to reduce no Nox generation?
best regards
raju verma
Hello Raju,
1.) NOx can be generated in kiln systems in two ways, primarily as thermal NOx due to oxidation of the nitrogen in the air as a result of the high temperature of the flame, and secondly due to the oxidation of nitrogen containing compounds in the raw materials, AFRs and fuels.
SOx is almost completely generated by pyrites (metal sulphides) in the raw materials.Sulphur in the fuels and sulphates in the raw materials are not normally volatile enough to escape the scrubbing effect of the preheater, as long as enough oxygen is present in the kiln and preheater,
2. NOx can be controlled by reducing the flame temperature of the main and calciner burners, by maintaining a small amount of CO at the back end of the kiln, or (if all else fails) by dosing of a reducing agent to chemically destroy the NOx eg. ammonia or urea solution.
SOx is normally controlled by minimising sulphide content in the raw materials and by keeping the O2 in the kiln inlet >2-3%
3.) Thermal NOx is generated from nitrogen and oxygen in the air at high temperature according to the equations;-
N2 + O2 ---> 2 NO
2 NO + O2 ---> 2NO2
Raw material NOx comes from the oxidation of nitrogen-containing compounds contained in the raw materials.
Fuel NOx comes from the oxidation of nitrogen-containing compounds contained in the fuel, particularly coal.
The largest contributers to NOx generation are thermal NOx and fuel NOx.
4.) Low NOx burners are designed to generate a small amount of CO which chemically reduces the NOx compounds to CO2 and N2. ie 2 NO2 + 4 CO ----> 4 CO2 + N2.
Regards,
Ted.
thanks ted.
any body have some opinion most welcome
regards
raju verma
As mentioned, Thermal NOx generation dominates at high temperature in the main kiln flame. Combustion in calciners can be designed to produce a lower concentration of NOx, particularly by having Fuel NOx generation as the dominant mechanism and/or by having a less-oxidising combustion regime than can be tolerated in the kiln burning zone. When kiln exhaust gases pass through the calciner combustion region, they attain the local equlibrium and NOx is "laundered" down to the lower concentration. Modern calciner furnace designs may have several points for injection of fuel and oxygen-bearing gases, and one or more of these may be used in various proportions to achieve lower NOx emissions, depnding upon the properties of the fuel being used and the local temperatures that prevail. A potential challenge whilst achiveing lower NOx emissions can be to avoid adversely changing the regions of the preheater/calciner in which sulfates decompose and recombine and subsequently become involved in either coatings or blockages or in SO2 emissions to air.