Cause analysis and Countermeasures of high carbon

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Cause analysis and Countermeasures of large carbon content in boiler ash

at present, although the unit consumption of boiler fly ash and pulverized coal has reached a good level, the unit consumption of fly ash, pulverized coal and pulverized coal fineness have always been tracked and adjusted, and the operation card has been issued. However, the problem of too large ash has not been fundamentally solved. The carbon content of large ash has improved, but it still can not be controlled within the national standard. The dry ash removal system adopted by our plant to save water will be put into full operation soon, and the fly ash brick plant with comprehensive utilization of ash will be put into operation soon, which is also faced with the problem of no raw materials. Therefore, we reorganized the combustion adjustment test in 5 furnace in order to find out the main factors affecting the high carbon content of large slag and the best operation mode The preparation and recycling technology of high molecular materials were analyzed

I. the combustion adjustment also puts forward a new challenge test:

1 Use the air distribution device to level the primary air according to the design wind speed (primary air speed 30m/s)

      2. Increase the primary wind speed of the lower row (primary wind speed 35m/s)

      3. Adjust the air volume, increase the secondary total air pressure and increase the oxygen content. Change the secondary air ratio, adopt the upper small and lower large air distribution mode, increase the rigidity of the lower secondary air, and increase the powder supporting capacity of the lower secondary air

      4. Adopt the air distribution mode of large at both ends and small in the middle

      5. Reduce the speed of the lower pulverized coal feeder: on the premise that the combustion condition is relatively stable, reduce the amount of pulverized coal fed to the lower pulverized coal feeder, control the speed of the lower pulverized coal feeder at 500-550rpm, reduce the pulverized coal concentration of the next primary air, and further improve the pulverized coal supporting capacity of the next secondary air

      6. Under various working conditions, measure the furnace temperature, take ash samples and coal samples, test the large and small ash percentages and pulverized coal fineness, and record various operating parameters

      7. Change the fineness of pulverized coal

through operation adjustment, the carbon content of large ash decreased from 18.5% to 13.8%. During this combustion adjustment, it was found that 2, 3 and when the load increased 4, the secondary air speed on the first floor was too low to support the lower primary air, and the boiler was contacted for treatment. After treatment, the secondary air speed of the first floor of 2 corner was increased from the original 27m/s to 37m/s, and the secondary air speed of the first floor of 2 and 4 corner was also increased. In April, the shutdown opportunity was used for thorough treatment. At present, the carbon content in large ash of 5 furnace is generally controlled below 10%

II. Analysis:

carbon content in large ash can be reduced through combustion adjustment, but the means are limited. Increasing the primary air speed and reducing the speed of the lower discharge pulverized coal feeder are limited by the unit load, and the adoption of such measures for load reduction will affect the combustion stability. At low load, the range of increasing the secondary air of the first floor is limited due to the limitation of the total air pressure, and increasing the secondary air of the first floor will affect the combustion stability. Reducing the fineness of pulverized coal will increase the unit consumption of pulverized coal production and affect the auxiliary power consumption rate. Increasing the secondary air pressure will increase the unit consumption of the fan and increase the air leakage of the preheater. At present, the induced air volume of 5 and 6 boilers in our plant is insufficient at high load, and the increase of air leakage rate will further aggravate the problem of air shortage at high load

however, all these measures can only reduce the carbon content of large ash, but can not fundamentally solve the problem of unqualified carbon content of large ash

the root cause of high carbon content in large ash is the problem of the lower burner. The primary air jet designed by our boiler is a direct current jet which is emitted horizontally. However, the primary air flow from the enrichment type or slotted bluff body burner currently used for the lower primary air in our plant is not a horizontal jet. After the primary air passes through the concentrator or slotted bluff body, the air flow is divided into three streams. The middle part of the air flow is horizontal jet, and the upper and lower parts of the air flow are inclined above and below respectively, and then change to the approximate horizontal direction after being oriented through the outlet horizontal section. Due to the short horizontal section, the emitted air flow is still not horizontal. The horizontal section of slotted bluff body burner is shorter than that of enrichment type burner, and the phenomenon of downward and upward impingement of gas flow is more serious. The secondary air on the first floor can not completely downrush the air flow, so that the pulverized coal can not be completely burned and fall into the cold ash hopper. At the same time, after the gas flow is ejected from the two burners, the capacity is expanded rapidly, the flow rate decreases, and the carrying capacity of the primary air decreases, resulting in the separation of air and powder, and part of the pulverized coal falls into the cold ash hopper almost without combustion. These reasons lead to the obvious increase of carbon content in large ash, and the carbon content in large ash of boilers with slotted bluff body burners is higher

therefore, if the carbon content of large ash is controlled within the qualified range in the whole load section, the burner must be transformed

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