Summary of cement clinker calcination of rotary kiln and its advantages and disadvantages

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Advantages and disadvantages of rotary kiln

about Rotary kiln The research work of cement clinker calcination in China started in the early 1980s. With the cooperation and participation of the state and the research and design team, the research work of cement clinker calcination in rotary kiln is progressing smoothly. Up to now, the exploratory research work on cement clinker calcination of rotary kiln has achieved certain results. The following describes the working conditions, advantages and disadvantages of rotary kiln calcination.

 Calcination site of cement clinker in rotary kiln

1、 Calcination of cement clinker in rotary kiln

In the process of cement production, in order to meet the control requirements of cement clinker calcination, the raw material entering the kiln is repeatedly poured into the warehouse, which ensures the raw material and creates conditions for the system to stably calcine clinker. The raw meal rate value is controlled by high saturation ratio, high silica rate and high alumina oxygen ratio. Meanwhile, the raw meal stability is effectively controlled, and the fluctuation range is small, which can basically meet the control requirements of production. The change data of cement clinker rate after high-temperature calcination show that at first, the silica rate is high and the alumina oxygen rate is basically stable; then, when oil coal mixed combustion is used, the silica rate is reduced and the alumina oxygen rate is increased; then, with the completion of oil coal switching and the system stability, the three rate values are basically stable and controlled within the target range, which can also be verified by the fluctuation error of the rate value

In order to enhance the heat storage capacity and improve the anti temperature fluctuation ability of the feed, a large number of clinker meeting the requirements of particle size distribution have been injected before heating and feeding. Therefore, in the process of clinker sampling and analysis, in addition to controlling the sampling time, in order to prevent the clinker added into the system in advance, the sampling is mainly taken from the sampling hole in the L / V valve and fck. The strength of the clinker (early and late) is basically close to or slightly lower than that of the general rotary kiln clinker, except for some unqualified clinker samples. In the initial feeding stage, the temperature in the bed changes greatly, which is mainly due to the fact that there is no balance between the feed rate of raw meal and that of fuel. With the continuous feeding of raw meal and fuel, the thermal equilibrium stability relationship is established. The initial stable feed rate of raw meal was 45t / h (clinker output was 660t / D), and then the feed rate of raw meal was increased to 62t / h (clinker output was 950t / D). The feed rate of raw meal is relatively stable, and the bed temperature of 10 h is relatively stable during 24 h production operation; however, after the stable switching operation of oil coal for 2 h, the stability of pulverized coal supply becomes worse and worse, showing a large fluctuation, which leads to the temperature fluctuation. The direct cause of the fluctuation is that the moisture content of pulverized coal is high (> 4%), the discharge of pulverized coal bunker is not smooth, and then the pulverized coal bunker is blocked. In order to maintain the normal operation of the kiln, the fuel oil system was started again, and the production operation of the kiln system was terminated due to insufficient fuel oil preparation. During the whole production process, the pressure difference is basically stable at 18 kPa ± 7 kPa, which is due to the sufficient homogenization of raw meal. In the process of this round of trial production, the main focus is on production control, and there is no strict statistics on economic indicators; the statistical analysis of data in continuous operation time shows that the heat consumption of the sintering system is 3226.96kj/kg clinker (772kcal / kg clinker), and the power consumption is 37.3kwh/t clinker. Due to the limitations of clinker output, raw materials and fuel and operation control, the indicators are still improved Space. Therefore, using calcined cement clinker has certain advantages over the new dry preheating precalciner kiln. The energy consumption index of 1000 t / d rotary kiln is equivalent to that of 5000 t / D preheating precalciner kiln system.

2、 Advantages and disadvantages of calcined clinker

Compared with calcining cement clinker by rotary kiln, it has many advantages as follows

(1) By using static equipment instead of dynamic equipment, the equipment process is simplified, which is conducive to the improvement of gas-solid heat transfer efficiency and surface heat dissipation control; the clinker calcination temperature is reduced from 1425 ℃± 25 ℃ of solid phase temperature in rotary kiln to 1320 ℃± 15 ℃ of medium gas-solid mixed phase temperature demand, and the heat consumption is reduced by about 20%.

(2) Due to the decrease of heat consumption and clinker calcination temperature, emission reduction control of (10% - 25%) and X (40% or more) is beneficial.

(3) Due to the simplification of the firing system, the floor area is reduced by about 70%, and the equipment investment of the firing system is reduced by about 40%.

(4) The clinker particles calcined in rotary kiln are smaller, which is beneficial to reduce the power consumption of cement grinding, and the power consumption per ton of cement can be reduced by 15% ~ 20%.

(5) Due to the simplification of the system, the operation parameters to be monitored are reduced, which is conducive to the system operation control and production maintenance management, and the operation cost is reduced by about 25%.

(6) The gas-solid mixed combustion, heat exchange and reaction in rotary kiln can improve the heat exchange efficiency and lay a foundation for the use of bituminous coal, anthracite and even inferior coal.

(7) The production practice shows that the system can produce P · o52.5 and P · o62.5 high grade cement, which can meet the needs of engineering construction.

The so-called defects and constraints for future development are analyzed and compared as follows:

(1) The heat storage capacity of rotary kiln is small and its anti fluctuation ability is relatively poor. On the one hand, to improve the level of production control, such as strengthening raw meal homogenization and production operation control, it is necessary to meet the requirements of fine production control (KH, SM and im fluctuations should be controlled within 2.5%, 3.5% and 5.0% respectively, and the calcination temperature in the rotary kiln should be controlled within ± 15 ℃); on the other hand, it is necessary to meet the requirements of fine production control (KH, SM and im fluctuations should be controlled within 2.5%, 3.5%, 5.0%, respectively Due to the poor heat storage capacity of rotary kiln, it is particularly important to reduce the control range of system operation parameters (such as feed volume, air volume, coal consumption, etc.) in addition to putting enough clinker into the system as heat storage medium in the process of system startup and feeding, so as to facilitate the system stability and operation control. It is also the inevitable result and requirement of industrial production system control and development to change the operation control habit, from the original extensive operation mode to the fine control mode.

(2) Rotary kiln calcination is difficult to adapt to the use of extensive alternative fuels, especially the collaborative treatment of extensive municipal solid waste, which limits the expansion of extensive business. However, the system can still be used for collaborative disposal and utilization of various solid and liquid wastes after fine treatment.

After summarizing the above cement clinker calcination system of rotary kiln, it is concluded that the control process is simple, and there are only six important control point parameters of the whole sintering system, namely, oxygen content and temperature at preheater outlet, outlet temperature of calciner, mixing temperature and bed pressure of gas-solid reaction in rotary kiln, and gas phase temperature under porous plate of rotary kiln. These can meet the production control requirements, compared with the modern new dry preheating precalciner kiln system is simpler. However, the operation and control requirements are relatively high, mainly due to the poor impact resistance of the system. Therefore, the raw material and fuel preparation and homogenization control and system operation control requirements are relatively high, which can be passed completely and meet the control requirements of the system. There is still a lot of room for optimization, improvement and perfection, especially for the structure of preheater and the local structure of the system.

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