Transformation of low nitrogen burner of coal-fired boiler - self recycling burner

Transformation of low nitrogen burner of coal-fired boiler
At present, China is still composed of coal-based resources, and its production and life rely heavily on traditional coal resources, causing great pollution to the atmospheric environment. The coal measures are mainly coal, which will produce sulfide, nitrogen oxide and other pollutants during combustion. In order to solve the contradiction between energy supply and environmental protection and reduce the denitration transformation and operating costs, the transformation of low nitrogen burner is imperative.
1、 Introduction to low NOx combustion technology
Reducing NOx emissions by changing combustion conditions is a low NOx combustion technology. Low-nitrogen combustion technology is the simplest and most economical method widely used to reduce NOx emissions. At present, low NOx combustion technologies mainly include the following:
1. Low excess air coefficient
Low excess air coefficient is a simple method to optimize combustion and reduce NOx production. The reduction of nitrogen content in flue gas can inhibit the formation of nitrogen oxides. Without changing the structure of the combustion device, the NOx emission is reduced and the operation economy of the device is improved. For coal-fired boilers, its limitations are mainly due to the low air excess coefficient, which will lead to binding slag and corrosion on the heating surface, temperature changes, and the increase of fly ash combustibles, resulting in a decline in economic efficiency. Therefore, the utility boiler cannot be significantly adjusted in actual operation.
2. Air staged combustion
The basic principle of gas staged combustion is to complete the fuel combustion process in stages. First, reduce the amount of air supplied by the main gas turbine to the furnace to 70-75% of the total amount of combustion air (equivalent to 80% of the theoretical amount of air), so that the fuel can be burned first under the condition of low oxygen and rich fuel combustion. This method makes up for the simple shortcomings of low excess air combustion. The smaller the excess air coefficient in the first stage combustion zone, the better the effect of inhibiting NOx generation, but the more combustion products, the lower the combustion efficiency, and the greater the possibility of slagging and corrosion. Therefore, in order to ensure NOx emission and the economy and reliability of boiler combustion, the air staged combustion process must be reasonably organized.
3. Fuel classification
When nitrogen oxides and hydrocarbon radicals, incomplete combustion products CO, H2, C and CnHm are generated during combustion, NO reduction reaction will occur. Using this principle, 80-85% of the fuel will be delivered to the primary combustion zone α> Carbon dioxide is produced by combustion at 1 hour. The fuel sent to the primary combustion zone is called primary fuel, and the remaining 15-20% of the fuel is sent to the secondary combustion zone at the upper part of the main burner α< A strong reducing atmosphere is formed under the condition of 1, so that NOx generated in the primary combustion zone is reduced to nitrogen molecules in the secondary combustion zone. The secondary combustion zone is also called the reburning zone. The fuel sent into the secondary combustion zone is also called the secondary fuel, or reburning fuel. The reburning zone can not only reduce the generated NOx, but also inhibit the generation of new NOx and further reduce the emission concentration of NOx.
4. Flue gas recirculation
At present, there is also flue gas recirculation method, which uses more low NOx combustion technology. It sends a part of low temperature flue gas directly into the furnace, or mixed with primary or secondary air and then sent to the furnace. This can not only reduce the combustion temperature, but also reduce the oxygen concentration, thus reducing the NOx emission concentration.
5. Low NOx burner
Burner is one of the key equipment of boiler combustion system. In the process of boiler combustion, the performance of the burner directly affects the reliability and economy of the boiler. According to the generation mechanism of NOx, most NOx is generated at the ignition stage of pulverized coal. Therefore, through the specially designed burner structure and the adjustment of the ratio of air and coal in the burner, the concentration of oxygen in the ignition zone and the temperature in the ignition zone can be reduced, so as to achieve the purpose of inhibiting the generation of NOx.
6. Low NOx combustion system
The low NOx burner and low NOx combustion (air classification, fuel classification and flue gas recirculation) are combined to form an ultra-low NOx combustion system, so as to better reduce NOx emissions and reduce the carbon content of fly ash.
2、 Problems to be noticed during transformation:
(1) In terms of fire safety: the gas boiler room belongs to Class A plant and the fire resistance rating is not lower than Class II, and the fire safety is far higher than that of the coal-fired boiler plant. Therefore, when transforming the coal-fired boiler into a gas boiler, the boiler plant should be reconstructed according to the specifications, and attention should be paid to the selection of explosion-proof and fire resistance rating.
(2) In terms of automatic control: special attention should be paid to the automatic interlock protection of boiler water level, the automatic interlock protection of gas boiler flameout, and the automatic interlock protection of steam pressure, gas pressure, and low air pressure. The degree of automatic control of gas boiler is much higher than that of coal-fired boiler.
(3) Two combustible gas alarm devices shall be set in the boiler room and surge chamber, and the alarm system shall be interlocked with the emergency shut-off valve and forced ventilation facilities.