Flue gas recirculation-based wide load-wide coal deep denitrification system for CFB (circulating fluidized bed) boiler

Abstract

The invention provides a flue gas recirculation-based wide load-wide coal deep denitrification system for a CFB (circulating fluidized bed) boiler. The system comprises the boiler, an SNCR (selective non-catalytic reduction) system, a primary air blower, a secondary air blower, an induced draft fan, a recirculation flue, a primary air recirculation adjusting valve, a secondary air recirculation adjusting valve and the like. One end of the recirculation flue is connected with an outlet of the induced draft fan, the other end is connected with an inlet of the primary air blower and an inlet of the secondary air blower by the aid of the primary air recirculation adjusting valve and the secondary air recirculation adjusting valve, low-temperature flue gas is led out of the outlet of the induced draft fan, the low-temperature flue gas with the proper flow is sent to different positions of a combustion chamber by the blowers through control by the adjusting valves, distribution of temperature fields in the boiler is optimized by fine controlling content of oxygen of primary air and content of oxygen of secondary air on the basis of SNCR, pollutant emission is reduced, and the CFB boiler can realize low emission of NOx under wide load-wide coal conditions.

Description

technical field [0001] The invention belongs to the field of circulating fluidized bed boilers, in particular to the field of wide load-wide coal type deep denitrification of circulating fluidized bed boilers. Background technique [0002] In recent years, more and more serious environmental pollution problems have attracted great attention from the society, and the country has become more and more strict on environmental protection indicators. The latest environmental protection requirements stipulate that by 2020, all coal-fired power plants that are eligible for transformation in the country will strive to achieve Ultra-low emissions (that is, under the condition of a reference oxygen content of 6%, the emission concentrations of soot, sulfur dioxide, and nitrogen oxides are not higher than 10, 35, and 50 mg / m3 respectively). [0003] In the actual operation of the traditional circulating fluidized bed boiler, due to the influence of coal quality and air distribution, the...

AI Technical Summary

Problems solved by technology

If the carbon content in the bed material is too high, if the air volume is not adjusted in time to control the bed temperature, the bed temperature will rise sharply, resulting in a sharp increase in NOx generation and a decrease in desulfurization efficiency

At the same time, when the bed temperature exceeds the ash melting point, high-temperature coking will occur, which will have a very negative impact on the stable, efficient and continuous operation of the unit

[0005] In addition, when the load of the circulating fluidized bed boiler changes, especially when the boiler is at low load, the outlet temperature of the furnace decreases, and it is difficult to ensure the progress of the SNCR reduction reaction (the reaction temperature range of SNCR is 850 ° C ~ 1150 ° C), resulting in NH3 reaction Incomplete, SNCR denitrification efficiency is greatly reduced, coupled with the difference in air distribution control during low-load operation, NOx emissions will increase. If the SNCR system's ammonia injection volume is only increased to reduce NOx emissions, it will inevitably increase ammonia emissions. Escape and generate ammonium bisulfate, causing corrosion and ash blocking on the heating surface of the tail

[0006] Therefore, when the coal type changes greatly and the load changes greatly, the removal of NOx by the SNCR system alone cannot meet the requirements of environmental protection. It is necessary to control the oxygen content in the primary air and secondary air on the basis of SNCR. Optimize the distribution of the temperature field in the furnace, reduce the emission of pollutants, and enable the circulating fluidized bed boiler to achieve low emission of NOx under the condition of wide load and wide coal type

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