Energy-saving and emission reduction is the development trend of cement production industry. To reduce energy consumption can not only reduce the production cost of cement plant, but also reduce the environmental pollutants produced in the cement production process and slow down the global warming.
The cement calcining system mainly reduces energy consumption by saving coal and power. It is generally believed that in order to reduce energy consumption of the clinker production line, improvements should be made in the preheater outlet temperature, cooler outlet temperature, and clinker temperature out of the cooler.
The clinker cooler is a key device in the clinker production line. It quenches and transports the hot clinkers discharged from the rotary kiln, and supplies hot air for the rotary kiln and preheater system. As the first equipment where high-temperature clinker releases heat, it plays an indispensable role in reducing coal and power consumption, increasing secondary and tertiary air temperature, and improving heat recovery rate.
A good clinker cooler can help cement plant reduce energy consumption from two aspects: one is to improve the cooling efficiency and reduce the power consumption of clinker cooler itself; the other is to reduce the coal consumption of rotary kiln and preheating system by improving the heat recovery rate.
Clinker Cooler Working Principle
First, we need to analysis the working principle to the grate clinker cooler to fully understand how it helps save energy for cement plants.
The hot clinker from the rotary kiln falls on the grate bed. Under the push of the reciprocating grate plate, the hot clinker is spread on the grate bed to form a material layer.
The reciprocating grate plates are composed of the alternatively arranged fixed grate plates and movable grate plates. Driven by the transmission device, the movable grate plates located between the fixed grate plates in a row make horizontal reciprocating movement to push the clinker forward.
The cold air is blown into the material layer from the lower direction of the bed to cool the hot clinker.
The quenched clinker is then screened. After that, small pieces fell into the conveyor for transportation; large pieces are crushed into small pieces by the crusher and cooled another time before entering the conveyor.
The Clinker Cooling Process in Clinker cooler
In a reciprocating grate clinker cooler, the cooling of the clinker on the grate bed can be divided into three sections: high-temperature section, medium-high temperature section, and low-temperature section.
The high temperature section quenches the clinker and increases the temperature of the secondary and tertiary air; the medium-high temperature section is the heat recovery zone; the low temperature section can further cool the clinker and reduce the clinker temperature out of the clinker cooler.
The Air Volume Distribution of Clinker cooler
The cooling air is blown in by fans in each section. The air intake of the high temperature, medium-high temperature, and low-temperature section accounts for 31%, 50%, and 19% of the total air volume respectively.
After heat exchange, the air volume distribution of clinker cooler is as follows: the secondary air into the kiln accounts for about 15% ( air temperature is about 1050 ℃); the tertiary air into the calciner accounts for about 22% (standard condition and air temperature is about 950 ℃); the rest is discharged as exhausted gas.
Reduce Power Consumption of Cooling Fans
The main power consumption of a clinker cooler is its cooling fans. It usually takes 1.9-2.3 m3 under standard conditions to cool 1 kg clinker from 1400 ℃ to 65 ℃, and the power consumption of the whole system is about 7 kWh. If the air consumption per kilogram of clinker cooling is reduced from 2 m3 to 1.7 m3, the air consumption efficiency will be 15% lower than that of other cement plants, thus saving 2 kWh of electricity for the whole cement production process.
Improve Heat Recovery Rate of the System
In the whole process of clinker calcination, it needs 50-55 kg coal to generate enough calorific value for the calcination of 1 ton of clinker. How to effectively recycle this heat is the key to save coal consumption.
Raise the temperature of tertiary air can save coal consumption to a certain degree. At present, the tertiary air temperature of most cement plants’ calcining systems in the world is around 900 ℃. By reforming the clinker cooler to improve the reduction efficiency of the internal air, the temperature of the tertiary air can be increased to 1000-1100 ℃ (equivalent to about 3-3.5kg of standard coal), so as to improve the heat recovery efficiency of the whole calcining process.
Maintain Proper Material Layer Thickness
The difference of grate structure and grate outlet direction will directly affect the forward movement speed of the clinker, and thus affect the thickness of the material layer on the grate bed.
If the material layer is too thick and the air volume is too small, the clinker will not be fully quenched, which causes the temperature of the clinker and exhaust gas to be too high, and the material on the grate bed is easy to stack. This will not only decrease the cooling efficiency and heat recovery rate of the clinker cooler, but also decrease the temperature of the secondary and tertiary air, increase coal consumption. Therefore, it is crucial to maintain a proper thickness of the material layer.