Vertical Shaft Kiln Vs Rotary Kiln

Cement has been an indispensable construction material for a long time now. Kilns to produce cement are almost equally old. Now cement kilns can be divided mainly into 2 types: vertical shaft kiln and rotary kiln. The vertical kiln is the older type and its origin dates back to the 5th century AC. Rotary kilns were first used in 1880. Around the 20th century, they replaced vertical shaft kilns almost everywhere.

The Importance Of Cement KilnsA cement kiln is a device that finishes the process of clinker sintering. The kiln heats up the raw materials to a high temperature. As a result, several chemical reactions occur, resulting in the materials fusing together, thus forming the cement. The quality of this cement depends largely upon the features of the kiln, such as the kiln model, kiln speed, kiln diameter, cooling speed, etc.

Vertical Shaft KilnLet us take a look at how a vertical kiln functions. The kiln is placed upright on the ground, and unlike a rotary kiln, it doesn’t rotate. The raw materials flow from the top to the bottom of the kiln while combustion supporting air rises from the bottom to the top. As the materials heat up the air, it would prevent heat loss. Thus, the efficiency of the kiln depends largely upon the temperature profile. Burner types, firing rate, and degree of the draft are some of the factors which affect it.

Advantages Of Vertical Kiln:• The investment of capital is low.• Requires less ancillary equipment.• Available in different sizes.• Less ash produced.• Modern kiln designs reduce radiation loss.• Takes up less space.

Disadvantages Of Vertical Shaft Kiln:• Cannot be run on alternative fuels.• Requires higher heat, which in turn costs more fossil fuel.• Can pollute the environment highly.• The operating costs are high.

Rotary KilnThe function of rotary kiln is to calcine the bulk, the lump, and slurry materials. This kiln consists of a cylindrical vessel which is slightly inclined and rotates. After the materials are poured into the cylinder through an opening in the upper end, the rotation mixes up the materials together and gradually they move towards the lower end of the cylinder. At the lower end, they are stirred up and heated by passing hot gases in the opposite direction. These gases may be produced either in a separate kiln or by a flame inside the same kiln. In case if it is produced inside the kiln, the flame is projected from a burner pipe, using fuels such as pulverised petroleum coke, gas, pulverised coal, and oil.

Apart from cement, rotary kilns are also used to make industrial materials, ferrous metals, refractory materials, etc. Unlike the vertical kiln, heat transfer in a rotary kiln takes place via radiation.

Advantages Of Rotary Kiln:• Production costs are low.• Can be run on alternative fuels too.• The production process is much more dynamic.• Can calcine even the small lime particles.• Consumes less heat, and thus less fuel.• The cement produced is uniform and of higher quality.• Higher thermal efficiency.• Can produce cement in larger scales.• Convenient operation, easy blowing-down, and simple to restart the machine.

Disadvantages Of Vertical Kiln:• The initial investment required is higher.• Bulky in size and occupies too much space.• Requires more troubleshooting as it runs into issues often.

ConclusionBoth types of kilns have their upsides and downsides. While a vertical shaft kiln is cheaper, it also comes with several constraints. You may go for a vertical kiln if you need to produce only a small quantity of cement and the quality doesn’t matter much. But a rotary kiln would be better in the long run.

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