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The formation and characteristics of Cenosphere

Views: 86     Author: SEPPE     Publish Time: 2021-04-09      Origin: SEPPE Technologies

The formation principle of Cenosphere

Cenosphere is a new type of functional material newly developed in recent years. It has a wide range of applications in building materials, machinery, metallurgy, petroleum, and chemical industries and fields.

It has many excellent characteristics such as wear resistance, non-toxicity, dispersibility, fluidity, water resistance, acid and alkali resistance, high temperature resistance, electrical insulation, and low thermal conductivity. 

Generally speaking, Cenosphere refers to a kind of silico-alumina bead-like tiny glass particles extracted from the coal ash of thermal power plants. Its structure has the characteristics of thin and hollow walls and can float on water.

When pulverized coal is burned in a boiler, it generally needs to undergo several stages of decomposition, sintering, melting and cooling. 

In the decomposition stage, pulverized coal with a lower gasification temperature will volatilize and escape first, and burn to generate heat;

Under the action of combustion, the pulverized coal will form porous carbon particles (coke), and then after all the carbon is burned, it will further become a porous glass body, and the shape will remain the original irregular shape;

As the temperature rises (about 1400°C), after further combustion, it enters the melting stage. The porous glass body will begin to passivate from the sharp edges and corners, and gradually melt and shrink, the porosity continues to decrease, and the roundness continues to increase;

Under the action of cooling, dense glass beads with a higher density and a smaller particle size will eventually be formed, and some of them will form glass beads with a thin-walled hollow structure, which is called Cenosphere.

The output and quality of Cenosphere are related to factors such as coal type, coal fineness, boiler load, and combustion status.

1. Generally, bituminous coal with high calorific value and low sulfur content produces a large amount of Cenosphere;

2. There is little Cenosphere formed by anthracite, and there is very little or no Cenosphere formed by lignite;

3. If the temperature in the furnace is lower than 1400 degrees Celsius, Cenosphere is rarely formed;

4. 1400-1500 degrees Celsius, forming more Cenosphere;

5. Above 1500 degrees Celsius, the formed Cenosphere will burst into fragments.

Therefore, the furnace temperature is too high or too low will affect the formation of Cenosphere.

Coal-fired power plants mostly grind coal into pulverized coal and spray it into the furnace of a power-generating boiler to let it burn in suspension.

One of the products obtained is Cenosphere (wall thickness is one-tenth of the diameter). 

Another type of hollow sphere has a wall thickness of one-third of the diameter, even a solid sphere. Because it is very heavy, it is called "sink beads", Those with high iron content are called "magnetic beads".

The content of Cenosphere in coal ash is very small, generally only 0.2-0.5%, and a few can reach 1%. The amount of "sink beads" is very large, about 30-70% of coal ash.

Excellent performance and use of Cenosphere

1. High refractoriness:

The main chemical components of Cenosphere are oxides of silicon and aluminum, of which silicon dioxide is about 50-65%, and aluminum oxide is about 25-35%.

Because the melting point of silicon dioxide is as high as 1725 degrees Celsius, and the melting point of aluminum oxide is 2050 degrees Celsius, both are highly refractory materials.

Therefore, Cenosphere have extremely high refractoriness, generally reaching 1600-1700 degrees Celsius, making them an excellent high-performance refractory material.

2. Lightweight, thermal insulation:

Cenosphere has thin and hollow walls and a semi-vacuum in the cavity. There is only a trace amount of gas (N2, H2, CO2, etc.), and the heat conduction is extremely slow and minimal.

Therefore, Cenosphere is not only light in weight (bulk density 250-450 kg/m3), but also excellent in thermal insulation (thermal conductivity at room temperature 0.05-0.1). Cenosphere has great practicability in the field of lightweight thermal insulation materials.

3. High hardness and high strength:

Because Cenosphere is a hard glass body formed from the silicon-aluminum oxide mineral phase (quartz and mullite), the hardness can reach Mohs 6-7, the static pressure strength is as high as 70-140MPa, and the true density is 2.10-2.20 g/cm3. It is equivalent to a rock. Therefore, Cenosphere has high strength.

Generally, lightweight porous or hollow materials such as perlite, zeolite, diatomaceous earth, pumice, and expanded vermiculite have poor hardness. Thermal insulation products or lightweight refractory products made with them have the disadvantage of poor strength.

Their shortcomings are precisely the strengths of Cenosphere, so Cenosphere has more competitive advantages and wider uses.

4. Fine particle size and large specific surface area:

The natural particle size of Cenosphere is 1-250 microns. The specific surface area is 300-360g/cm2, which is similar to cement.

Therefore, Cenosphere does not need to be ground and can be used directly.

The fineness can meet the needs of various products. Other lightweight insulation materials generally have a large particle size (such as perlite, etc.). If they are ground, they will greatly increase the capacity and greatly reduce the thermal insulation.

In this regard, floating beads have advantages.

5. Excellent electrical insulation:

Cenosphere is an excellent insulating material and does not conduct electricity.

The resistance of general insulators decreases with the increase of temperature. While Cenosphere is the opposite, its resistance increases with the increase of temperature. This advantage is not available in other insulating materials.

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