NOx partition measurement method based on flow velocity weighting

Abstract

The invention discloses a NOx partition measurement method based on flow velocity weighting. The method comprises the following steps of: averagely dividing a denitration SCR outlet flue into a plurality of areas along the flow direction of flue gas, installing a multifunctional sampling probe (for multi-depth sampling of NOx and flue gas flow velocity) in each area, calculating flow velocity weighting coefficients by using flow velocity measurement values of different areas, subjecting measured NOx concentration values to flow velocity weighted correction, and allowing corrected calculated NOx concentration values to participate in denitration ammonia injection control. Thus, an ammonia-nitrogen mixing sufficiency degree is improved, and the purposes of efficient operation, low emission and stable operation of a denitration system are achieved under the condition of low ammonia escape. The measured NOx concentration values of different areas of an SCR outlet are dynamically correctedthrough a flue gas flow rate, and the corrected calculated NOx concentration values participate in denitration ammonia spraying control, so the ammonia-nitrogen mixing sufficiency degree can be improved to a greater extent, the purpose of ammonia spraying according to needs is achieved, and denitration operation effect is improved.

Description

Technical field[0001]The invention relates to a NOx sampling method for a denitration system of a thermal power unit, in particular to a NOx zone measurement method based on flow rate weighting.Background technique[0002]After the coal of a coal-fired power plant is burned in the boiler, the pollutants generated include dust, sulfur dioxide and nitrogen oxides (ie NOx). The conventional treatment of the first two pollutants is performed outside the furnace. The current technology is relatively mature and removes High efficiency. SCR flue gas denitration method is the main method for controlling NOx emissions of thermal power plants. The denitrification reaction zone is set in the boiler. If the ammonia injection is low, the efficiency will cause the NOx emission to be substandard, and the denitration efficiency will be high when the ammonia injection is excessive. However, it will increase ammonia escape, cause air preheater blockage, flue corrosion and other problems, which will ser...

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Problems solved by technology

[0004] To achieve the purpose of "on-demand ammonia injection" ammonia injection, it is very important to accurately measure the NOx concentration in different areas. At present, there are three common sampling methods: one is to install multiple sampling methods on the horizontal flue at the outlet of the SCR At the same time, it is sent to a "mixer" for physical mixing, and the mixed gas is sent to CEMS for analysis. This method can accurately measure the average value of NOx at the SCR outlet, but it cannot measure the actual value of each area. Cannot provide effective data support for partition control

The second is that the horizontal flue at the SCR outlet is divided into several areas on average. Each area is equipped with a set of flue gas analyzers to measure the real-time NOx values ​​of different areas at the same time. The ammonia injection in each area is adjusted according to the different NOx concentrations in each area. Ammonia injection control can achieve the purpose of zone control, but the investment is high and the application is limited

The third is to divide the horizontal flue at the SCR outlet into several areas on average, install a sampling probe in each area, and configure a set of NOx analyzers on one side. The flue gas sent to the analyzer is taken from different probes through control switching. Cycle switching between different probes, measure the actual value of NOx in different areas, and control the ammonia injection through the ammonia injection door in each area, to a certain extent achieve the purpose of zone control, but when the flow rates in different areas are different, only the real-time value of NOx is used to control the difference. The amount of ammonia sprayed in the area is obviously unscientific

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