Refractory for cement kiln - alkali-resistant brick
First, what is alkali-resistant brick?
The alkali-resistant brick for cement kiln refers to a clay refractory brick which is made of low-aluminum refractory clay as the main raw material and has alkali corrosion resistance in the cement kiln system. The main raw materials used in alkali-resistant bricks are coke gems, pyrophyllite, silica and the like. The alkali-resistant mechanism of alkali-resistant bricks is that they react with alkali metal oxides at high temperatures to form a high-viscosity liquid phase, forming a glazed protective layer covering the surface of the bricks to block surface pores to prevent alkali metal melts. The penetration and erosion play the role of alkali corrosion resistance.
Second, the application of alkali-resistant bricks in cement kiln
Ordinary type alkali-resistant bricks are mainly used in cement kiln preheaters, decomposition furnaces, and other air ducts.
High-strength alkali-resistant bricks are mainly used in cement kiln preheaters, decomposing furnaces, tertiary air ducts, vertical ascending flue, cyclone straight tubes and cones.
The arch-type alkali-resistant brick is mainly used for the cement kiln preheater and the tertiary air duct of the decomposition furnace.
The heat-insulating alkali-resistant brick is mainly used for the kiln mouth, kiln door cover and cooling machine of the cement kiln.

Alkali-resistant brick series products for cement kiln at home and abroad
The alkali-resistant brick is a semi-silica refractory material having an Al2O3 content of 25% to 30%. It is made of low-aluminum refractory clay as the main raw material. Due to its chemical composition, it can form a certain thickness of alkali-resistant protective layer on its surface, so it has wide application in cement precalcining furnace system.
In the production of cement rotary kiln, harmful components such as potassium, sodium, sulfur and chlorine from the original fuel are formed in the high temperature zone to form sulfate and chloride after the kiln gas, except for the alkalinity of the firing zone and the transition zone. In addition to the erosion damage of the kiln lining, the kiln tail gas chamber, the decomposition furnace, the preheater, etc. are condensed and enriched due to the temperature decrease, and can penetrate into the ordinary clay brick to chemically react with the refractory brick body to form potassium nepheline (KAS2). Expansive minerals such as leucite (KAS4) and feldspar (KAS6) cause the clay bricks to crack and form "alkali cracking" damage. In addition, due to the high temperature of the clinker from the kiln, the alkali continues to volatilize from the clinker, and the clay bricks of the hot end of the grate cooler, the kiln head chamber and the kiln door cover are eroded to form an "alkali crack". Therefore, it was once an obstacle to the development of human-type suspension preheating kiln in the 1960s. To this end, Germany first developed an alkali-resistant clay brick with an Al2O3 content of 25% to 28%, so that the alkali in the kiln gas chemically reacts with the brick surface after agglomerating on the brick surface to form a high-viscosity glaze layer. The pores in which the alkali continues to erode into the interior of the refractory brick body are closed, thereby preventing "alkali cracking". At the same time, when the kiln gas contains more chlorine, the SiO2 content in the refractory brick can be appropriately increased, and the ability of the refractory brick surface to bond with the chlor-alkali can be increased to form an alkali-resistant clay brick resistant to chlor-alkali erosion; In the secondary air duct, the high-speed airflow with clinker dust can wash the lining, and can also be made into high-strength alkali-resistant adhesive brick; in order to meet the heat insulation requirements of the kiln, it can also be made into light alkali-resistant adhesive brick (such as German brand Orylex brick, Japanese brand GlASil brick) and so on. These alkali-resistant bricks are widely used in suspension preheating kiln and precalcining kiln systems, with a dosage of 30% to 40%.
Since the 1990s, in order to meet the needs of large precalciner kiln, alkaline bricks have further improved the refractoriness and chemical corrosion resistance: further reducing the iron oxide content to 1.5%; in the non-moving equipment parts, there is replaced by castables. Potential.
Due to the large shrinkage and deformation of some refractory bricks during sintering, the dimensional deviation of the refractory bricks is large. For such alkali-resistant bricks with large deviations in outer dimensions, wet laying should be adopted on the masonry.

How to choose refractory materials for various parts of cement kiln
Pre-tropical zone and decomposition zone
The temperature of these two places is relatively low, and the thermal conductivity of the brick lining is required to be small, and the wear resistance is good. In this area, the alkali metal and the chlorinated alkali from the raw materials and fuels begin to volatilize, condense and enrich in the kiln, and penetrate into the brick. internal. Ordinary clay bricks react with alkali to form potassium nepheline and leucite, which makes the brick surface crisp, and the brick body expands and causes cracking and peeling. When the alkali-resistant brick or alkali-resistant heat-insulating brick containing Al2O325%~28% and SiO265%-70% reacts with alkali at a certain temperature, the surface of the brick immediately forms a high-viscosity glaze layer to prevent peeling. But this brick can't resist the use temperature above 1200 degrees Celsius. Therefore, the pre-tropical zone generally uses phosphate combined with high alumina bricks, anti-flaking high alumina bricks or alkali resistant bricks.
The decomposition zone generally adopts high-aluminum bricks with good anti-flaking properties. The silica-based bricks are superior in performance to the high-alumina bricks with good peeling resistance. The service life is about twice as high as that of the anti-flaking high-aluminum bricks, but the price is higher. Anti-skinning silicon carbide castables should be used for the tail feed.
2. Transition zone and firing zone
The transition zone kiln skin is unstable, and the kiln lining is required to resist the change of atmosphere, good thermal shock resistance, small thermal conductivity and wear resistance. Magnesium-aluminum spinel bricks are recommended in foreign countries, but the thermal conductivity of the bricks is large, the cylinder temperature is high, and the relative heat consumption is large, which is not conducive to reducing energy consumption. Domestic silicon molybdenum has a small thermal conductivity and wear resistance, and its performance is comparable to imported materials to a certain extent.
The firing zone has a high temperature and a strong chemical reaction. It requires brick lining to resist clinker erosion and strong resistance to SO3 and CO2. Magnesium-aluminum spinel bricks are generally used abroad, but the brick-hanging kiln skin is more difficult, and the dolomite bricks are not resistant to thermal shock and easy to hydrate; the foreign magnesium-iron spinel bricks have better effect on the hanging kiln skin. But the cost is too high. The newly used low chromium periclase composite spinel bricks in China are in good condition.
3. Cooling belt and kiln mouth
The temperature at the cooling zone and the kiln mouth is as high as 1400 degrees Celsius, the temperature fluctuates greatly, and the grinding of the clinker and the flushing of the airflow are serious. The brick lining is required to have small thermal conductivity, good wear resistance and thermal shock resistance; alkaline bricks excellent in thermal shock resistance, such as spinel bricks or high alumina bricks, are suitable for use in the cooling zone. Spinel bricks are generally recommended in foreign countries, but the spinel bricks have a high thermal conductivity and poor wear resistance. In recent years, most of the domestic use of silicon bricks and wear-resistant bricks with good peeling resistance.
The kiln mouth part is mostly made of castable material with good thermal shock resistance. For example, high-aluminum brick or steel fiber-toughened castables and low-cement high-aluminum castables that are resistant to thermal shock, but are used in large kiln with extremely high kiln temperature, using ordinary or steel fiber toughened corundum. Casting material.

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Henan hongtai kiln refractory co., LTD. Main products are high alumina brick, clay brick, fused zirconium corundum brick, fireproof ball lightweight insulation brick, wear-resistant pouring material, corundum pouring material, low cement high strength pouring material, impermeable material, self-flowing material, plastic material, and various types of refractory materials.For different industries, the cement industry with anti-flaking high-alumina bricks, alkali resistant bricks, phosphate bricks;Boiler industry USES all kinds of brand wear-resisting brick, corundum brick, mullite brick and other finalizing materials.The company insists on "product quality is the life, enterprise integrity is the foundation", in the fierce market competition, won many users' trust and praise.The products are sold all over the country, as far as Vietnam, India, Korea, Pakistan, kazakhstan, Iran and other southeast Asian countries and regions.

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