Excessive online nitrogen oxides in coal-fired boilers

This is a very practical topic; intermittent excess levels of nitrogen oxides in coal-fired boilers are indeed a common and tricky problem. I’ll briefly share a few of my thoughts: Regarding the reasons for exceeding limits, intermittent over-limit conditions are often related to fluctuations in combustion conditions, such as changes in load, unstable coal feeding rates, or errors in oxygen level control. Furthermore, if the ammonia injection rate in denitration systems (such as SNCR or SCR) is not adjusted in a timely manner to match the operating conditions, it can also lead to temporary exceedances of the limits. Fluctuations in the nitrogen content of coal are also one of the direct causes. Analysis of nitrogen in coal quality: Element analysis is generally required (industrial analysis can only provide estimates and is not accurate); if possible, the coal sample should be sent for a full element analysis (including N, C, H, S, etc.) to determine the actual nitrogen content. If the conditions on-site are not suitable, it is also possible to use historical data from the same mining area or of the same coal type as a reference for an approximate assessment; however, when there are large fluctuations, it is recommended to conduct analysis batch by batch. A small suggestion: You can try to examine the relationship between the periods of exceeding limits and factors such as coal batch types, load changes, and parameters of the denitration system, and conduct a simple statistical analysis; this often helps identify the main cause. Additionally, if there is a risk of environmental penalties, it is recommended to consult a qualified third party or the local environmental inspection agency, rather than relying solely on experience. The above are merely personal experiences; the specific reasons need to be determined by examining on-site data and equipment operation records. If it’s convenient, you could talk more about the approximate operating conditions when the limits are exceeded, so we can discuss it together.

The intermittent exceedance of NOx levels in coal-fired boilers is mainly due to fluctuations in fuel nitrogen, sudden changes in combustion conditions (start-up/shutdown of grinding units, low load, sudden increases in oxygen levels), and delayed responses in denitrification systems； The nitrogen analysis in coal shall be determined in accordance with GB/T 19227-2008, the semi-micro Kjeldahl method, or GB/T 30733-2014, the instrumental method.