One of the attractions of combustion equipment is that you can’t just let the flux go in the atmosphere! The subject of zero-emission has many aspects. Depending on what you burned and the temperature that what you burned reached, and those friends in combustion, what products they produced, the flux must be cleaned.
In this post, I want to explain one of the methods of cleaning flux from NOx out of a thousand and one cases that occur.
The name of this method is Selective Non-Catalytic Reduction (SNCR).
This system’s task is to reduce nitrogen oxides downstream of the combustion process using ammonia or urea. The duty of these two gentlemen is to convert NOx (in the absence of a catalyst) into nitrogen, water, and carbon dioxide.
This process is known as DENOX!
The normal DENOX temperature is between 900 and 1050 degrees Celsius. If the temperature goes above this range, the ammonia or urea itself oxidizes and produces NOx, and if the temperature drops, the reaction rate decreases so much that ammonia / urea does not enter the reaction and, as it is said, slips and directly enters the stack.
The advantages of urea-based systems are that urea is not toxic and the volatility of its solution is less than ammonia, and as a result, it can be stored more easily and safely. During evaporation, urea has a higher residence time due to lower vapor pressure in the spray. As a result, it has a higher penetration depth and better spread on the flux.
On the other hand, research on urea-based DENOX systems has reported N2O production up to about 36 ppm. This gas is a greenhouse gas that tends to produce in the lower temperature range of DENOX systems.
What are the challenges of the DENOX system designer?
We must be able to achieve high reduction efficiency and have the least amount of ammonia slip. Now how should we control this issue? We must be able to have the following:
- Uniform temperature distribution in the reaction chamber
- Minimum heat loss (quasi adiabatic reaction)
- Appropriate residence time
- Controlled and constant DENOX temperature
- Controlled dosing
- Proper mixing and momentum of ammonia / urea