The so-called tail temperature refers to the temperature of the kiln tail smoke chamber of the rotary kiln. The kiln end temperature is a window to observe the conditions in the kiln and a key parameter for judging coal consumption.
Some people think that it is a parameter of the rationality of the reaction kiln and furnace air ratio, some people think that it is affected by the secondary air temperature, and some people think that it can reflect the flame length and so on.
Tail temperature is a systemic problem. Many people do not know that tail temperature is also a key parameter of calcination. It is not only the ratio of head and tail coal, but also affects whether the kiln is normal.
1. Is the high tail temperature caused by more head coal or more tail coal
In many articles, people gravitate towards coal for the first time. In fact, both the first coal and coal feedings resulted in excessive tail temperatures. It should be said that, theoretically, the ratio of the first tailing coal is 40:60 through heat balance calculation. In fact, this ratio is not necessarily, it is affected by various factors and changes.
Experiments show that the coal gangue is mixed with the raw materials, and the coal gangue is added from the raw materials, which should theoretically save the first coal. However, due to excessive coal consumption, the amount of first coal is much larger than that of tailing coal. At this time, the operator will try to reduce the first coal, so the amount of the first coal will also be reduced.
Another example: in the case of normal calcination, the amount of coal used in tailings is artificially reduced. In order to ensure the normal current of the kiln, the operator will achieve normal calcination by adjusting the first coal. Of course, these circumstances are not enough to prove whether the ratio of 40:60 is reasonable, but ordinary cement workers will know whether it can save coal, equipment heat dissipation, and the heat taken by exhaust gas is not only operation, but determines the second wind temperature, not the first The proportion of primary coal. Therefore, the ratio of head and tail is not constant, but there is one parameter that is determined, that is, the lower the temperature of the smoke chamber, the better when the kiln current is normal in the calcination of the rotary kiln.
The so-called lower the better. First, the kiln in the high temperature zone is normal. Second, coal consumption is lower. The so-called normal in the kiln after the high temperature zone means that there is less skin formation in the kiln and it is not easy to form a circle. When the tail temperature is too high, the temperature of the carbonate decomposition zone and transition zone will be higher. Affected by the alkali and its harmful components, the liquid phase amount will appear earlier. As the temperature increases, the gas generated by the harmful components at the kiln end will intensify, and the circulating enrichment will increase.
In addition, with the early appearance of the liquid phase, the probability of the appearance of the sulphur-alkali circle in the kiln tail after the kiln will naturally increase. When the tail temperature is low, the time of the material at 1200-1350°C will naturally be shortened, the formation of harmful gas components will be less, the cycle enrichment will be less, and the probability of ring formation will be lower. That's why dealing with knot loops after 35 meters requires lowering the tail temperature to the bottom line. Many people know that when material leaks, the effect of reducing tail temperature calcination is obvious.
The reason for the low coal consumption is that the ratio of head to tail coal is better only when the temperature at the end of the rotary kiln is lower.
When the coal consumption at the head is large, especially when it is larger than the theoretical coal consumption in the kiln, the heat removal can only be discharged into the calciner through the kiln tail, so the tail temperature will increase (but not necessarily lead to high coal consumption, because the excess The heat can enter the decomposition furnace through the kiln tail).
When the consumption of tail coal is large, affected by the combustion process of the calciner, the tail coal will be burned from the calciner to the fifth-stage cylinder, and even continue to burn from the fifth-stage cylinder to the end of the kiln. Naturally, the temperature of the smoke chamber also increases.
In fact, when the tailing coal consumption is large, it is not necessary to enter the pulverized coal into the smoke chamber for combustion, and the temperature of the smoke chamber will also increase due to the increase of the material temperature. In order to ensure the normal current calcination of the rotary kiln, it must be ensured by increasing the consumption of tail coal. In theory, this is due to less head coal consumption, but an increase in tail coal consumption also increases the smoke chamber temperature.
When the coal consumption of the head coal and the secondary air is better, the temperature of the secondary air entering the smoke chamber is lower; when the coal consumption of the tail coal is better, it can ensure that the coal enters the fifth-stage pipe after normal calcination of the kiln, and the temperature of the feeding pipe is lower. Lower, both lower winds and materials must create lower smoke chamber temperatures.
Therefore, only when the tail temperature is lower is the time when the total amount of coal is lower and the best time for calcination (one of the measures to prevent the formation of sulfur rings in the kiln tail).
The relationship between tail temperature and flame
The temperature of the kiln tail smoke chamber is indeed related to the length of the flame. It is an indisputable fact that the secondary wind is strong and the wind speed is fast, while the secondary wind is small and the wind speed is slow. The wind speed is fast, the temperature moving distance is long, the pulverized coal burning time is short, and the kiln end temperature is high. That is to say, the temperature of the long tail of the flame is high, and the temperature of the short tail of the flame is low. Therefore, high winds are a key factor in causing the flames to grow longer.
A good process engineer must understand when tuning a burner that secondary air can also affect flame length and shape. To adjust the burner, the secondary air must be matched, and the relationship between the secondary air and the flame must be understood. The length of the flame is about the size of the secondary wind.
3. The relationship between tail temperature and scorchability of raw materials
Under the condition that the raw materials and process conditions are unchanged, the flammability of the raw materials depends on the relationship between KH and N (most people only focus on KH).
High KH, poor flammability; low KH, good flammability. Because the fluctuation of the normal component KH is often larger than the N value. The impression is that KH is more flammable than the N value. In fact, the result of many years of experimentation is that the N value is as important as the KH, which affects the burnability of clinker. The relationship is 0.01KH=0.1N.
When the flammability of the raw material is good, the amount of coal will be reduced, the combustion speed is fast under the same conditions, the decomposition of carbonate is fast, and the heat absorption is fast. So the temperature of the smoke chamber is very low.
When the flammability of the raw material is poor, more coal is needed, and the combustion speed is slowed down under the same conditions, the material needs a higher reaction temperature, and the decomposition furnace is prone to post-combustion. The firing zone is also extended in the kiln. It also causes high temperatures in the smoke chamber.
For example, if the KH of the clinker is 0.91 in the best production quality state, when the KH is mentioned as 0.93, the flammability of the raw material is very poor. If forced to reduce materials, coal consumption must be increased. According to the 5000t/d production line, the head and tail coal should be increased by more than 4 tons. You can calculate for yourself how much the coal consumption per ton of clinker has increased. You can imagine how much the tail temperature can increase.
Fourth, the relationship between tail temperature and pulverized coal combustion
Many people think that the pulverized coal does not burn well and the tail temperature will be very high. This cannot be said to be wrong, but the probability of high tail temperature due to poor combustion of pulverized coal is very low.
First, when the secondary air is large, the probability of pulverized coal entering the kiln end from the kiln head is extremely low in an oxygen environment above 1450 degrees.
Second, when the secondary air is small, the pulverized coal is also in the environment of 1450 degrees. Due to the reduced secondary air speed, the combustion time is more abundant. Even if the pulverized coal cannot burn, it will fall into the material instead of continuing to burn.
Of course, the above changes are extreme. When slight changes are not severe, changes in flame shape also affect changes in tail temperature. But does not affect the special changes in tail temperature. One is that the heat of pulverized coal combustion in the kiln cannot be reasonably absorbed by the material and runs away from the end of the kiln; the other is that the temperature of the smoke chamber rises sharply due to the combustion after the precalciner.
5. Relationship between carbonate decomposition rate and tail temperature
Many people ignore the problem of the carbonate decomposition rate of the five-stage feeding pipe material entering the kiln, and many people do not know the reason for controlling the carbonate decomposition rate of the kiln end material entering the kiln. In fact, the decomposition rate of carbonate entering the kiln has a great influence on the temperature at the end of the kiln. Excessive carbonate decomposition rate is not good.
As we all know, carbonate decomposition is a reaction process with large heat consumption in clinker calcination. After the carbonates decompose, very little heat is required to mature the material. Conversely, the solid phase reaction stage releases heat, and secondary air brings a lot of heat. After the material with excessive carbonate decomposition rate enters the kiln, the transition zone material absorbs very little heat. After the heat absorption reduces the secondary air temperature and reaches the kiln tail, the change is small, and the tail temperature is naturally higher. When the carbonate decomposition furnace of the material entering the kiln is low, it needs to absorb a lot of heat when entering the kiln, and the temperature of the secondary air will naturally drop when it reaches the end of the kiln. Therefore, the decomposition rate of carbonate entering the kiln is a problem that cannot be ignored, and it is expected to be controlled at 92-96, which should not be too high.