Discussion on the calculation of NOx processes in hazardous waste incinerators
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I would like to ask the experts in this field: when performing calculations related to incinerator processes in the hazardous waste industry (involving the incineration of waste gases and liquids containing hydrocarbons, NH3, H2S, and other hydrocarbon-based substances), how do you calculate the amount of NOx generated in the flue gases? Many people I asked said that using Aspen for such calculations is not reliable, and no one suggested any good algorithms or formulas； According to what I found, the mechanism behind NOx formation is quite complex; actual measurements are the only reliable way to determine it. I came across a formula commonly used in coal-fired boilers, but it doesn’t seem suitable for other industries either. If the system is to be upgraded to an out-of-stock system in the future, how do people calculate the NOx generation amount to set the requirements?
The formation of NOx occurs in three ways: the first is fuel-type, the second is rapid-type, and the third is thermal-type. The main sources of fuel-type NOx are nitrogen-containing compounds in the fuel or those formed by the combustion of organic substances ； The rapid type is primarily formed through the reaction of nitrogen in the air with CH groups during organic combustion ； The thermal type is formed by the direct reaction of nitrogen and oxygen in the air at high temperatures. Fuel-type NOx accounts for the largest proportion, generally ranging from 75% to 90%; rapid-type NOx makes up about 5%, while thermal-type NOx accounts for around 20%.
Thank you, I know the principle behind this; it’s just that I can’t find any guidance on how to calculate it specifically
Firstly, hazardous waste materials are complex and require blending to be handled. Generally, the amount of organic nitrogen is not set too high. In addition, the secondary combustion chamber for hazardous waste operates at temperatures of 1100–1200 degrees; the main gases involved are nitrogen from the raw materials and heat-generated nitrogen. It can be estimated based on experience that the temperature generally does not exceed 1000 degrees. To meet GB18484 requirements, installing an SNCR is sufficient. If ultra-low emissions are required in certain areas, then SNCR+SCR is needed.
Thank you. For one of our projects, the nitrogen content in the fuel is around 2.3% (by mass). Using Aspen’s data, we obtained a NOx value of 1200 mg/Nm3. When we showed this figure to the client, they said that our calculation was too low； Using the calculation formula for coal-fired boilers, I got a converted value of around 3000; it seems too high to me
If you want u, then okay, dear. Tonight it’s in Ouhai District
ASPEN performs calculations based on chemical equilibrium or minimum free energy, provided that there is sufficient and accurate property data available. There are too many organic impurities in your case; without relevant property data, accurate calculations cannot be carried out
If the fuel is stable, staged air supply can be used, and the temperature after combustion can be well below 1000.
The fact that substances can be input into Aspen indicates that all their physical property parameters are available, except for a few particularly complex substances. However, the Gibbs principle does not take into account factors such as the mechanism of NOx formation or reaction kinetics; it only considers minimizing Gibbs free energy. Therefore, its calculations of NOx production are not reliable
This falls under the design concept of low-nitrogen burners; with staged air supply, won’t the nitrogen in the fuel still turn into NOx? Generally speaking, low-nitrogen design focuses on how to avoid the formation of thermally induced NOx.
With such complex components, it’s not even clear what substances are involved; the substances that are fed in may not be correct, so of course the calculations will be inaccurate. If kinetic effects are not taken into account, ASPEN calculations give the upper limit that the reaction can reach. In other words, if the actual amount of nitrogen oxides produced is higher than what is calculated, it’s definitely because the component values entered were incorrect