Where did ammonia escape from cement plants
Date：2019-08-22 16:20 Source：cementepcViews:
Ammonia escape concentration actually refers to the comprehensive ammonia emission concentration of cement plant, not the ammonia emission concentration generated by SNCR denitrification of cement plant.Therefore, the escape concentration of ammonia stipulated in the standard = the actual ammonia emission concentration = the background ammonia emission concentration + the escape concentration of ammonia from SNCR process + the escape concentration of ammonia from waste disposal.
Now where does all this come from
1. Background ammonia emission concentration
The nitrate, ammonium salt and amino acid in the soil enter the cement production line with the form of limestone, and are decomposed by heat at different temperature ranges, releasing the background nitrogen oxide emission and background ammonia emission.The emission of nitrogen oxides and ammonia is unavoidable.In many cement plants, ammonia emission concentration in chimney is 0.5-2mg/m3 without SNCR denitrification
2. Ammonia escape from SNCR
This part of ammonia emission is the part of the limits proposed in the "standards for the emission of air pollutants in the cement industry".When ammonia enters the decomposing furnace, it reacts with nitrogen oxides to form nitrogen and water, a standard SNCR reaction.At the same time, excess ammonia reacts with oxygen in the flue gas to produce nitrogen, nitrogen oxides and water.However, the ignition point of ammonia in pure oxygen is 650℃, and the oxygen content in the flue gas of cement kiln is too low, so the reaction between ammonia and oxygen is relatively weak.So there's always some ammonia that doesn't react with nitrogen oxides, doesn't react with smoke, and goes off into the exhaust.This problem is especially serious when the overall oxygen concentration is low after the stage combustion reform of kiln tail system.
The SNCR system of many production lines is not reasonable. Although the nitrogen oxide emission concentration can be reduced to a very low level (such as 100mg/m3), a large amount of ammonia injection is required. This part of ammonia does not react and will run into the exhaust gas, resulting in excessive ammonia escape.
3. Ammonia escape from household waste disposal
There are more organic matter in household waste containing amines and ammonium salts.Due to the current way of disposal of domestic garbage, the residence time of bulk garbage in cement kilns is too short. With the release of amine and ammonium salts in the low-temperature area of flue gas, a large amount of ammonia is produced and finally discharged in the big chimney. The escaping emission concentration of ammonia can reach 10-30mg/m3.
As can be seen from the above, to solve the problem of excessive ammonia escape in cement plants, we need to start from the above three aspects:
1. Cement plant has few measures to deal with the ammonia emission concentration of the bottom, if it is possible to choose raw materials such as limestone, the raw material sources should be changed regularly, combined with ammonia emission flue gas analyzer to analyze the impact of different raw material sources on ammonia emission, and determine reasonable raw material resources.
2. Improve the existing SNCR system or replace the SCR system.The unreasonable SNCR system not only increases the consumption of ammonia water and raises the cost, but also increases the emission concentration of ammonia gas and thus faces the risk of environmental protection penalty.
3. Carefully deal with household waste, and make a decision after a detailed investigation of the production line of household waste disposal.
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