At present, the operating load of the coal-water slurry gasification unit is generally 95%~110%, and the high-load operation has a great impact on the system. It has been found through recent operations that since the gasifier load has been raised to 15%, the service life of refractory bricks has been significantly shortened, and the service life of A/B gasifier cylinder bricks (burner chamber-K bricks) is only about 3700h, and in When replacing, the remaining refractory bricks are less, far less than 1/3 of the whole (refractory brick manufacturers require that the refractory bricks be replaced when the remaining 1/3), and the refractory bricks are seriously damaged.
Comprehensive analysis, in order to extend the service life of refractory bricks, should be adjusted from the following aspects.
flow field structure
As we all know, the quality of the atomization effect is determined by the speed and angle of the material exiting the burner, in which the main oxygen plays a crucial role. Refractory bricks cause severe scour. It is recommended that the main oxygen flow rate of the burner ranges from 120 to 150 m/s.
The data provided by the patentee are: the oxygen flow rate of 8949m³/h corresponds to the gasifier pressure of 6.3MPa, the main oxygen flow rate of 130m/s, and the central oxygen flow rate of 120m/s. With the increase of coal slurry concentration, the oxygen flow rate of furnace C has reached 9600m³/h. To ensure that the main oxygen flow rate is within the recommended range, the corresponding gasifier pressure should be 6.8MPa, but the pressure vessel does not allow overpressure operation. Unable to achieve (current pressure is 6.5MPa).
According to the current operating parameters, it is calculated that the main oxygen flow rate has reached 145m/s, and the central oxygen flow rate is 114m/s (calculation conditions: material ejection angle 50°, temperature 22°C, central oxygen ratio 16.6%). Due to the difference of each burner, there is a certain deviation in its flow velocity, but the range of deviation is less than 5m/s. During the operation of the gasification unit of a company, the refractory bricks were seriously damaged when the main oxygen flow rate was 95m/s and 145m/s. Based on the current conditions, when the system reaches 110% load, the main oxygen flow rate will reach 148m/s, which deviates greatly from the process index. When the temperature is higher in summer, the main oxygen flow rate will change more greatly (see Table 1 for the corresponding relationship between the oxygen flow rate and the temperature of the oxygen pipeline and the pressure of the gasifier).
According to the calculation of the oxygen pipeline temperature in 2014 (the highest temperature in summer is 37°C, and the lowest temperature in winter is 17°C), in summer, the main oxygen flow rate will reach 16m/s. In 2014, the operation time of furnace A was from May to October, basically in the season with higher temperature; while the operation time of furnace B was from August to December, and the temperature during operation was lower. Furnace A ran for 3716h in high temperature weather, while furnace B only ran for 1960h in high temperature weather. Under the same working conditions, the main oxygen flow rate of furnace A is 10m/s faster than that of furnace B. When replacing the refractory bricks, it was found that the thickness of the remaining refractory bricks in furnace B was 3 cm higher than that in furnace A.
In September 2012, the gasifier was operated at 100% load, the maximum oxygen flow rate was 8800m³/h, the system pressure was controlled at 6.5MPa, and the main oxygen flow rate was controlled at 120~125m/s. The effect of refractory bricks was good. Due to the low early load of the system , Refractory bricks have less erosion. From the start of operation to the first replacement of refractory bricks in furnace C, the load is basically at 95%~105%, and the life of the cylinder brick reaches 10,000h.
It can be seen from the actual operation that the main oxygen flow rate is high, the refractory brick is seriously corroded, and the service life is shortened. Through analysis, the oxygen flow rate can be further reduced only by changing the size of the burner.
operating temperature
Appropriate operating temperature is conducive to the formation of a certain thickness of slag film on the refractory bricks on the inner wall of the gasifier to protect the refractory bricks. It is generally believed that above the appropriate operating temperature, the erosion rate of high chrome bricks will increase by 4 times for every 100 °C increase. The ash melting point of coal increases, and the corresponding operating temperature of the gasifier increases. The ash melting point of coal is determined by the proportion of acid and alkali substances in the coal. The alkaline oxides have the effect of lowering the melting point of coal ash. The more alkaline oxides there are, the lower the ash melting point. However, the fastest erosion rate of refractory bricks is often alkaline oxides (the erosion rate of calcium oxide to refractory bricks is greater than that of iron oxide), so in gasification production, it is not that the lower the ash melting point, the better. A factory and our company are of the same type, the load is not much different, the oxygen flow is about 10000m³/h, the ash melting point of the raw coal used is 1180℃, and the operating temperature is 1250℃. At present, the operating temperature of our company’s gasifier is 1320~1350℃. Compared with it, the ash melting point of the raw coal used by our company is much lower, and there is still room for lowering the operating temperature. Even the operating temperature after coal blending should be ≤1250℃. Therefore, our company can reduce the current furnace temperature by 30~50℃, increase the effective gas content in the gas by 0.5%, the CO₂ content at 16.5%, and the methane content at 900×10⁻⁶.
In addition, it is too sensitive to the pressure difference at the slag port during operation. When the pressure difference at the slag port is found to rise, the oxygen flow rate is blindly increased, and the oxygen flow rate increases, resulting in an increase in the furnace temperature. Now add 1 oxygen (16m³) to each burner, the operating temperature of the gasifier will increase by 5 °C, adding 5 oxygen means the furnace temperature will increase by 20~30 °C, and the wear rate of the refractory bricks after 8 hours of operation is the same as that of the unoxygenated refractory bricks. 2d amount of wear.
How to judge whether the indication of the pressure difference at the slag outlet is true, you can refer to the changes of other process parameters and make a comprehensive analysis, so as to correctly judge the actual pressure difference at the slag outlet.
The slag port is blocked, the pressure difference of the slag port increases, and the secondary reaction time becomes longer, which will lead to an increase in the CO content. In the process of adding oxygen to the slag port pressure difference several times, it was found that although the slag port pressure difference increased, the CO content did not increase, but the CO2 content was close to 18%. According to the gas composition, the slag port pressure can be judged. The difference did not rise. In addition, whether the pressure difference of the slag port has increased can also be judged according to the pressure difference of the lock bucket, the pressure difference between the lock bucket and the gasifier, and the liquid level of the gasifier. . When the slag mouth is really blocked, it should be cooled down in time after normal treatment. Generally speaking, the cooling operation can be performed 8 hours after the pressure difference at the slag port returns to normal. Note that the cooling should not be too slow, because the cooling process continues for too long, which will lead to increased wear of the refractory bricks. If the rear system fluctuates too much in the control system pressure, this situation will cause the refractory bricks to fall off in lumps.
coal quality
Not all types of coal are suitable for gasifiers. Summarizing years of practical experience, it is concluded that in the process of coal blending, the difference between the ash melting points of the two coals should be less than 100 °C, because the greater the difference in the ash melting points of the two coals, the greater the impact on the gasifier. When the difference between the ash melting points of the two coals is too large, due to the inconsistent carbon content in the coal, the temperature in the gasifier will fluctuate greatly, and the gas composition will also fluctuate greatly. When the coal quality changes, the carbon content in the coal changes, and when the carbon content decreases, the actual oxygen-to-coal ratio of the gasifier increases under the condition that the original oxygen flow rate remains unchanged. The slag film of the refractory brick is relatively thin, which can not play a corresponding protective effect on the refractory brick, which will aggravate the erosion of the refractory brick. When the coal quality changes, the coal slurry concentration will change prior to the gasifier working condition for 8 hours. When the viscosity and concentration of the coal slurry change greatly (the fluidity of the coal slurry changes), the operator should pay attention to the slag Oral pressure difference and changes in slag samples.
production load
Changes in production load will have an impact on the life of refractory bricks, especially when starting and stopping, changes in temperature in the gasifier and changes in ambient atmosphere will have a serious impact on the life of refractory bricks, and the furnace temperature changes suddenly when the control is not good. , the thermal shock in the gasifier is severe, and the refractory bricks will fall off in blocks. Frequent start and stop, the gasifier will undergo severe thermal shock at the moment of charging, and the instantaneous temperature change of the refractory brick surface will be too large, which will cause the refractory brick to fall off. The production load was increased from 90% to 105%, and the life of the refractory bricks on the refractory surface was shortened by 18%.
Refractory brick quality and masonry quality
The quality of the refractory brick itself will have an impact on its life. By comparing the operation of 90 bricks and 95 bricks, it is not difficult to find that the higher the content of chromium in the refractory brick, the stronger the corrosion resistance, but the excessive chromium content will reduce the thermal shock resistance of the refractory brick and make it easy to make the refractory refractory. Bricks are falling off in lumps. At present, the use effect of 90 bricks is relatively good, and the use effect of 95 bricks is not very ideal.
If there is a problem with the masonry quality of the refractory bricks, the service life of the refractory bricks will be significantly shortened, and the refractory bricks may fall off in only one week. However, due to the gradual maturity of coal-water slurry gasification technology, the phenomenon of serious erosion of refractory bricks due to problems with masonry quality rarely occurs.
burner size
For the refractory bricks in the furnace, the local refractory bricks are seriously damaged instead of uniformly ablated, which indicates that the structure of the burner is unreasonable, and the size of the burner should be improved.
Through the inspection of the refractory bricks in the furnace, it is found that the damage of the refractory bricks is in the shape of steamed buns, that is, the middle is large and the edges are sunken. According to the analysis of the damage form of our company’s current refractory bricks, the size of the burner gap is seriously unreasonable. In order to prevent the steamed bread-like erosion of the refractory bricks, the epoxy channel of the burner should be transformed. In April 2014, the burner was reconstructed, and the diameter of the outer end of the outer channel of the nozzle was enlarged from the previous 41mm to 42mm. After the transformation, the main oxygen flow rate of the burner can be reduced to 10m/s, and the service life of the refractory brick is greatly prolonged.
Conclusion
By changing the size of the burner, the service life of the refractory brick is significantly improved. In order to further improve the service life of refractory bricks, efforts should be made to control the temperature, control the number of starts and stops, strictly control the operating temperature of the gasifier <1250 ° C, and prevent the furnace temperature from rising due to human judgment errors; Continue to change the size of the burner. Through theoretical calculation, the main oxygen channel of the burner is expanded to 43mm, and the main oxygen flow rate is expected to be reduced to 125m/s, which can play a decisive role in prolonging the service life of the refractory brick.
