It is summarized that after a large number of CFB low-nitrogen combustion boilers were put into operation, the serious ash accumulation problem in heating area gradually appeared. This paper analyzes the causes, characteristics and hazards of dust accumulation in heating areas. According to the above characteristics, the advantages and disadvantages of various soot blowers are analyzed, and finally the gas energy shock wave rotary soot blower is selected to solve this problem. At the end of the paper, the practical effect of applying gas energy shock wave rotary soot blower in the late stage of low nitrogen transformation is explained and recommended in the form of a case.
CFB (Circulating Fluidized Bed Boiler) low-nitrogen combustion is a necessary transformation project under the background of ultra-low emission, and the denitrification efficiency can generally reach 40-60%. At the same time, low-nitrogen combustion has achieved ideal results, but at the same time it has also brought negative effects that cannot be underestimated, such as load capacity, boiler combustion efficiency, ash tail heating surface and so on.
1 and analysis of the reasons for the influence of low nitrogen combustion reform on ash deposition
The optimum bed temperature for CFB low nitrogen combustion is 860 ~ 890℃, and the highest temperature should not exceed 920℃. The actual bed temperature is 930 ~ 1000℃, or even higher. Therefore, in the aspect of material circulation, the bed temperature is generally controlled within the temperature range suitable for low nitrogen combustion by improving the separation efficiency of the separator and increasing the return amount.
The direct effect of improving the separation efficiency of the separator is that the circulation rate of circulating ash increases and the amount of ash entering the tail heating surface increases. At the same time, the ash particles entering the tail heating zone are finer, and the finer ash particles have greater viscosity. Both of the above will aggravate the ash on the heated area.
2. The main characteristics of the increase of ash deposition caused by low nitrogen combustion reform.
The most direct phenomenon of ash aggravation in heating area is that the exhaust temperature increases, the main steam temperature decreases and the negative pressure decreases. When the boiler is stopped for inspection, it will be found that the heating area of the whole shaft flue is very gray.
Many units do not need to install soot blowers at all, or basically do not run after installing soot blowers. Now the soot blower must be put into operation. However, the soot blowers originally installed in some factories can meet the needs of soot blowing. Now, after low nitrogen combustion, the effect of the original soot blower becomes worse, which can not meet the needs of the current working conditions.
The main characteristics of ash deposition caused by low nitrogen combustion are: the particle size of ash becomes smaller, the amount of ash increases, and the adhesion of ash increases, which has a certain viscosity.
3. The ash accumulation after low nitrogen combustion transformation is serious to the boiler system.
3. 1, the serious ash on the heating area will lead to the increase of exhaust gas temperature and affect the boiler efficiency. According to the empirical data of the boiler, the boiler efficiency decreases by 65438 0% every time the exhaust temperature of the boiler increases by one degree.
3.2 Ash on the heating area, especially on the superheater, will affect the main flue gas temperature. The decrease of main steam temperature will affect the safe operation of steam turbine.
3.2 Ash on the heating area will affect the flow of flue gas and even the load capacity of the boiler in severe cases.
4. The soot blower selection for the ash problem in the heating area of low nitrogen combustion of boiler.
4. 1 sonic soot blower analysis: As mentioned above, the particles deposited under this working condition are fine and sticky. Acoustic soot blower is only suitable for dry ash and floating ash, but it is weak for fine ash with adhesion. So it is not recommended.
4.2 Analysis of traditional gas shock wave soot blower: This type of soot blower has strong directionality and blind spots for soot blowing. And there are inherent defects such as misfire, tempering and carbon deposition. High failure rate and high operating cost.
4.3 Analysis of gas energy shock wave rotary soot blower:
Pneumatic shock wave rotary soot blower uses compressed air or compressed nitrogen as the power of shock wave, which has low operating cost, no problems such as flameout and carbon deposition during tempering, and the equipment is maintenance-free.
Because of the strong impact of shock wave, the rotary soot blower with gas energy shock wave has a good effect on sticking ash and sticking ash. It can completely meet the characteristics of ash deposition caused by low nitrogen combustion.
The nozzle of gas energy shock wave rotary soot blower can rotate step by step, which can meet the requirements of soot blowing at different angles, and 360-degree rotation can realize soot blowing without dead angle.
Gas energy shock wave rotary soot blower can control the energy of shock wave by adjusting the pressure of gas source. When the installation position is close to the furnace wall, the pressure can be reduced to avoid damaging the furnace wall.
Gas energy shock wave rotary soot blower can control the energy of shock wave by adjusting the pressure of gas source. When the installation position is close to the furnace wall, the pressure can be increased, and the effective range and blowing intensity of the gas-energy shock wave rotary soot blower can be improved.
Through the comparison of various soot blowers, the gas energy shock wave soot blower is the most suitable for the soot deposition condition after the transformation of low nitrogen combustion. Specifically, according to the different installation parts and the requirements of working conditions, the gas energy shock wave fixed soot blower can be used.
5. Main measures to control dust accumulation and application examples.
A 75t CFB boiler in a thermal power plant in Wuxi, boiler model: UG-75/5.3-M 12. After the transformation of boiler low-nitrogen combustion, the separation efficiency of separator is improved, the fine ash particles become thinner with the increase of ring ratio, and the ash accumulation in the tail flue is serious. The exhaust gas temperature rose from 150 to 170, which seriously affected the thermal efficiency of the boiler and the safe operation of bag dust removal in the back, so it was forced to stop the boiler and transform it. After installing four fixed gas energy shock wave soot blowers and 14 gas energy excited rotary soot blowers in the superheater, economizer and air preheater of the boiler, the flue gas temperature dropped from 170 to 146, which was basically close to the design value of flue gas temperature. After low nitrogen combustion, the content of low oxides decreased from 450-500 to 150- 180, which achieved the expected goal of reducing nitrogen oxides. The boiler load capacity is improved, the exhaust temperature returns to normal, and the transformation has achieved the expected effect.