Multi-stage high-efficiency low-nitrogen combustion method and combustion system for circulating fluidized bed boiler

Abstract

The invention relates to a multi-grade high-efficiency low-nitrogen combustion method and a multi-grade high-efficiency low-nitrogen combustion system for a circulating fluidized bed boiler. According to the method, combustion air enters a furnace hearth through corresponding inlets respectively to divide the furnace hearth into a less oxygen combustion area, a reduction area, an oxidative combustion area and a burning-out area; the excess air coefficients of each area are respectively controlled to be 0.55-0.95, 0.75-1.15, 1.05-1.25 and greater than or equal to 1.20, so that a fuel is dispersed and uniformly combusted in the furnace hearth. The burning-out area is positioned above the upper boundary of the oxidative combustion area and has the effective height which is not less than 2.5 times of a flue gas average velocity value in the area, the upper boundaries of the remaining areas are respectively 2.0-5.5 meters, 4.5-9.0 meters and 8.0-12.0 meters away from the surface of an air distribution plate. The system which is applicable to the method comprises the furnace hearth, the air distribution plate, a primary air inlet and a secondary air inlet; at least one layer of reducing air inlet, at least one layer of oxidative air inlet and at least one layer of burning-out air inlet are respectively formed in at least one wall of the corresponding area of the furnace hearth. By virtue of the method and the system, the generation capacity of nitrogen oxides can be reduced, and high-efficiency combustion of the fuel can also be realized.

Description

technical field [0001] The invention relates to a boiler combustion method and a combustion system, in particular to a multi-stage high-efficiency low-nitrogen combustion method and a combustion system for a circulating fluidized bed boiler. Background technique [0002] Nitrogen oxide is one of the main pollutants in atmospheric pollution, which endangers human health, affects plant growth, and participates in the destruction of the ozone layer. [0003] Nitrogen oxides mainly come from the direct combustion of solid, liquid and gas fuels. As a major emitter of nitrogen oxides, the control of nitrogen oxides emissions in thermal power plants is very important. In recent years, the low-nitrogen combustion technology to control the formation of nitrogen oxides in the fuel combustion process and the flue gas denitration technology to reduce the nitrogen oxides that have been formed have made great progress. [0004] The low-nitrogen combustion technology can greatly reduce th...

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Problems solved by technology

However, due to the unique low-temperature combustion and secondary air grading layout of the circulating fluidized bed boiler combustion technology, the nitrogen oxide generation is lower than that of ordinary pulverized coal boilers using the same fuel. Emission Standards of Air Pollutants "About Coal-fired Boilers 450-1100mg / Nm 3 Therefore, there are few researches and achievements on low-nitrogen combustion technology

However, the 2011 version of the emission standard raised the NOx emission limit for existing circulating fluidized bed boilers to 200mg / Nm 3 100mg / Nm is strictly enforced for new units 3 Therefore, the existing and new circulating fluidized bed boilers are faced with the problem of further reducing the amount of nitrogen oxides produced in the furnace

Especially for circulating fluidized bed boilers burning low-quality fuels with high volatile content and low ash melting point such as biomass, peat, oil shale, etc., there is a problem of uneven combustion and heat release of fuel along the furnace height direction, and the middle and lower parts of the furnace are generally There will be a relatively high combustion peak temperature, which increases the formation of thermal nitrogen oxides, and is also prone to slagging and high-temperature corrosion

[0005] In order to reduce the formation of nitrogen oxides, solutions are often adopted to reduce the combustion temperature in the furnace and increase the range of the reducing atmosphere in the furnace. However, this will affect the full combustion of fuel to a large extent, and will increase the mechanical capacity of the boiler. incomplete combustion loss

For circulating fluidized bed boilers that have already adopted air staged combustion technology, the greater the degree of air staging, the greater the degree of reduction of nitrogen oxides; however, as the degree of air staging increases, the furnace The larger the area in the reducing atmosphere, the greater the probability of slagging and high-temperature corrosion in these areas, the greater the carbon content of fly ash, which will affect the economical and safe operation of the boiler

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