Cement Kilns and the refractories

The original rotary cement kilns were called 'wet process' kilns. In their basic form they were relatively simple compared with modern developments. The raw meal was supplied at ambient temperature...

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Cement Kilns and the refractories

Refractories for Cement industry
1) Mg-Cr Directly Combined Bricks
2) Mg-Cr Semi-directly Combined Bricks
3) Ordinary Mg-Cr Bricks
4) Mg-Al Compound Bricks of fire-resistant and heat-insulate
5) Mg-Cr Compound Bricks of fire-resistant and heat-insulate
6) Periclase and Spinel Compound Bricks
7) MgO Bricks  Kyanite Bricks
9) High AUL Soft Bricks
10) Peel-off Proof high-Al Bricks
11) Phosphate high-Al Combined Bricks

Phosphate Composite Bricks

12) Aluminum Phosphate Combined Grinding Bricks
13) Alkali Resistant Bricks used in Cement Kilns
14) Steel Fiber Reinforced and Peel-off Proof Bricks
15) Steel Fiber Reinforced and Peel-off Proof Kyanite Bricks
16) New Dry Type Series of Refractory castable used in Cement Kilns
17) Steel Fiber Reinforced Refractory castable Materials

1 High Strength Quick Condensing Refractory castable

19) Light Heat-insulation Refractory castable
20) Series of High-Alumina Cement for Refractory Materials
21) Refractory Mud
22) High-Alumina Bricks
23) Acid Resistant Bricks
24) High-Alumina Heat-insulation Bricks
25) Clay Refractory Bricks
26) High-Alumina Bricks for Hot-blast Stoves
27) High-Alumina Bricks for top of Steelmaking Furnaces

2 High-Alumina Bricks for Furnaces
29) Clay Heat-insulation Bricks

Wet process kilns

The original rotary cement kilns were called ‘wet process’ kilns. In their basic form they were relatively simple compared with modern developments. The raw meal was supplied at ambient temperature in the form of a slurry.

A wet process kiln may be up to 200m long and 6m in diameter. It has to be long because a lot of water has to be evaporated and the process of heat transfer is not very efficient.

The slurry may contain about 40% water. This takes a lot of energy to evaporate and various developments of the wet process were aimed at reducing the water content of the raw meal. An example of this is the ‘filter press’ (imagine a musical accordion 10-20 metres long and several metres across) – such adaptions were described as ‘semi-wet’ processes.

The wet process has survived for over a century because many raw materials are suited to blending as a slurry. Also, for many years, it was technically difficult to get dry powders to blend adequately.

Quite a few wet process kilns are still in operation, usually now with higher-tech bits bolted on. However, new cement kilns are of the ‘dry process’ type.

Dry process kilns

In a modern works, the blended raw material enters the kiln via the pre-heater tower. Here, hot gases from the kiln, and probably the cooled clinker at the far end of the kiln, are used to heat the raw meal. As a result, the raw meal is already hot before it enters the kiln.

The dry process is much more thermally efficient than the wet process.

Firstly, and most obviously, this is because the meal is a dry powder and there is little or no water that has to be evaporated.
Secondly, and less obviously, the process of transferring heat is much more efficient in a dry process kiln.

An integral part of the process is a heat exchanger called a ‘suspension preheater’. This is a tower with a series of cyclones in which fast-moving hot gases keep the meal powder suspended in air. All the time, the meal gets hotter and the gas gets cooler until the meal is at almost the same temperature as the gas.

The basic dry process system consists of the kiln and a suspension preheater. The raw materials, limestone and shale for example, are ground finely and blended to produce the raw meal. The raw meal is fed in at the top of the preheater tower and passes through the series of cyclones in the tower. Hot gas from the kiln and, often, hot air from the clinker cooler are blown through the cyclones. Heat is transferred efficiently from the hot gases to the raw meal.

The heating process is efficient because the meal particles have a very high surface area in relation to their size and because of the large difference in temperature between the hot gas and the cooler meal. Typically, 30%-40% of the meal is decarbonated before entering the kiln.

A development of this process is the ‘precalciner’ kiln. Most new cement plant is of this type. The principle is similar to that of the dry process preheater system but with the major addition of another burner, or precalciner. With the additional heat, about 85%-95% of the meal is decarbonated before it enters the kiln.

Cement Rotray Kilns

Cement rotary is the main equipment in the dry production line of clinker cement. This series of rotary kiln consist of bowl, supporting part, supporting device with catch wheel, gearing rigging, flexible kiln hood, kiln hood and kiln end sealing device, nozzle device and so on. The rotary kiln is higher than the horizon as the whole body is supported by the riding wheel with the catch wheel controlling the up and down move of the kiln body. Besides the main transmission, the transmission system sets auxiliary transmission device which can keep the kiln body move when the main power is off to protect it from bending deflection. The kiln hood and kiln end sealing device adopts advanced technology which ensures the security of the sealing.

Cement rotary kiln is of solid structure, stable operation, and high quality output product.