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Grate cooler (abbreviated as grate cooler) is a kind of thermal equipment, which can promote sufficient heat exchange between high-temperature clinker and cold air in a short time, and quickly cool the cement clinker through quenching.
1. Rapid cooling of high temperature clinker
Quench of clinker can keep fine C3S crystal and form fine periclase crystal in liquid phase, which is conducive to the improvement of grindability and stability of clinker and the improvement of cement strength. At the same time, quench can solidify the liquid phase into glass, and most of C3A is in glass state, which is conducive to the improvement of chemical corrosion resistance of cement.
2. Heat recovery
While cooling the clinker, the temperature of the cooling air rises, but there is also a gradient in the temperature of the gas along the length of the grate cooler. The gas in the high-temperature section is used as secondary air to the kiln and as tertiary air to the decomposition furnace. The gas in the medium temperature section is used for waste heat power generation or drying materials, and the low-temperature residual air at the end is discharged into the atmosphere as waste gas after purification.
3. Be able to cool the clinker to meet the requirements of transportation, storage and cement grinding
If high-temperature clinker is transported, it needs to be made of high-temperature resistant materials, and it is also easy to wear, resulting in high cost and maintenance
The cost is also high, which is not conducive to the storage of clinker, cement grinding and cost reduction.
Working principle of grate cooler
The operation principle of clinker cooler is to realize the heat exchange between clinker and cooling air efficiently and quickly.
For the single cylinder or multi cylinder cooler used in the past, the cooling air is directly sucked from the cooler by relying on the negative pressure in the rotary kiln. Although the material is lifted by the lifting plate, which increases the gas-solid heat exchange area, the heat exchange efficiency is low because the relative speed between gas and solid is small, the contact area is small, and the countercurrent heat exchange value is small. The grate cooler has undergone three generations of technological innovation. The first generation fuller type promotes the grate cooler to ventilate the air chamber and operate in a thin material layer. Due to the separation of material particles and uneven distribution, the phenomena of "short circuit", "blowing through" of cooling air, as well as "Red River" and "snowman" often occur, and the thermal efficiency is not high. The second generation of push grate cooler still adopts air chamber for air supply. Although multi-stage grate bed is adopted to optimize the width of grate bed, distribute evenly, strengthen sealing and, most importantly, adopt improvement measures such as thick material layer operation, the phenomena of "short circuit" and "Red River" have not been completely solved. Until the third generation of flow control grate cooler with air beam and resistance grate plate appeared, the original problem was solved and the cooling air volume was greatly reduced.
Due to the use of "resistance grate plate" in the third generation grate cooler, the opening area of the grate plate, such as hole and air, is reduced by nearly half, which changes the ratio between the grate plate and the flow resistance of the clinker layer, and relatively reduces the influence of the change of the resistance of the clinker layer on the clinker cooling. The air beam and hot end grate bed are adopted to realize the grate plate in each block or community. The cooling air volume can be adjusted timely through the valve according to the change of resistance on the grate. At the same time, the high-pressure fan is used to reduce the amount of cooling air and increase the relative velocity and contact area between gas and solid, so as to greatly improve the convective heat transfer efficiency. In addition, due to the optimized design of the structure and material of the resistance grate plate and the improved uniform air flow through the grate plate, the service life of the grate plate and the operation rate of the cooler are improved.
"Resistance grate plate" solves many problems caused by uneven distribution of clinker layer, but due to its large resistance and high power consumption, the new generation of grate cooler is developing in the direction of "control flow". After canceling the "resistance grate plate", the air beam is used to blast in blocks or small areas, and the cooling air pressure and air volume are automatically adjusted according to the resistance of the charging layer of the grate, so as to realize efficient and rapid heat exchange between gas and solid.
Since the use of movable grate plates to promote the movement of clinker will cause wear between grate plates and relevant parts, the new generation (fourth generation) grate cooler uses push rods and parallel row conveying units to transport clinker, and uses self-adjusting flow valves to control the cooling air volume of each part of the grate bed, which greatly reduces the wear, operation and maintenance workload.
The continuous innovation of various types of new grate cooler technology not only greatly improves the heat exchange efficiency, reduces the cooling air volume, reduces the temperature of clinker out of the grate cooler, realizes the sudden cooling of clinker, further improves the temperature of secondary air and tertiary air into the kiln, and optimizes the production of precalciner kiln firing system.