Magnesia-iron spinel bricks are a new generation of magnesia refractory bricks, which are an updated product of magnesia-chrome bricks for rotary kilns. This product has many advantages and has no impact on the environment. It is an alkaline refractory material. In addition to the excellent kiln-hanging properties of magnesia-chrome bricks, it also has high thermomechanical and thermochemical properties. In some European countries, it has been widely used in the burning zone and transition zone of cement rotary kiln to become a new chromium-free refractory material that may completely replace magnesia-chrome bricks.
The physical properties of magnesium iron spinel bricks
1. Excellent thermal shock stability. The periclase and spinel in the mafic-iron spinel bricks have different thermal expansion coefficients, so they form a part of micro-cracks during the firing process of the brick. The composition of this part of the micro-cracks, It plays a very important role in the thermal shock stability of the advancing brick. Using the interaction between periclase, magnesia-aluminum spinel, and mafic-iron spinel, select an appropriate ratio to achieve the thermal shock stability of the brick. The thermal shock stability of the brick (1100℃ water cooling) ≥10 times.
2. Excellent ability to hang "kiln skin" The bricks used in cement kiln firing belt contain a proper amount of Fe2O3, which can make it have excellent ability to hang "kiln skin". The Fe2O3 in the mafic spinel bricks participates in the way of mafic spinel. This kind of participation not only makes the bricks have excellent "kiln skin" capabilities, but also has excellent thermal shock stability.
3. Excellent corrosion resistance The main liquid phases in cement are C4AF and C3A. In the high-temperature firing zone, the main ingredient that penetrates into the bricks is C4AF. In the matching of bricks, multi-level ingredients are selected to optimize the matrix in the bricks. When the well-known liquid phase enters the surface of the brick, it forms a high-temperature refractory phase to block the further entry of the liquid phase, solves the problem of penetration, and advances the corrosion resistance of the brick.
4. The lining of the new dry-process cement kiln with low thermal expansion and low thermal conductivity is basically a single-layer structure. The high thermal conductivity of the lining bricks will cause the shell to overheat and deform and cause severe energy loss. Magnesium-iron spinel bricks have a lower coefficient of thermal expansion and lower thermal conductivity. The low thermal expansion coefficient can reduce the thermal stress of the furnace lining itself and the shell, reduce refractory material shedding and the damage of the kiln body; low thermal conductivity can reduce the thickness of the kiln skin and lower the surface temperature of the cylinder body, thereby reducing the load of the kiln and the operation of the rotary kiln. Rate and service life invent better conditions.
5. Better structural flexibility The microstructure, mineral composition and activation behavior of the mafic spinel bricks have caused better structural flexibility. In places with high mechanical stress, such as the tire belt and the upper transition zone, the structural flexibility of the mafic spinel brick can relieve the damage to the refractory brick caused by the mechanical stress caused by the deformation of the barrel, and extend the service life. In this respect, traditional magnesia-chrome bricks are incomparable with magnesia-iron spinel bricks.
The development trend of magnesium iron spinel bricks
Magnesium-iron spinel bricks are chromium-free alkaline refractory materials for the firing zone of a new generation of large rotary kilns. The product is made of artificially composed spinel materials and special processes. The product has high compressive strength and good thermal shock stability. It has the characteristics of good thermal creep function and high softening temperature under load. At the same time, it also has the characteristics of directly combining with magnesia chrome bricks and easy to stick to the kiln skin, which solves the problem of environmental pollution caused by magnesia chrome bricks for cement kilns in the process of use.
The development and application of magnesia-iron-aluminum spinel bricks are in line with the development trend that magnesia-chrome bricks will withdraw from the cement industry stage within a certain period of time, and meet the cement industry's market demand for environmentally friendly refractories for cement kilns under the new situation.
Magnesium-iron spinel refractory bricks have a long life and low thermal conductivity, reduce the heat dissipation loss of the cement kiln shell, improve the heat utilization rate of the kiln system, and have a significant energy-saving effect. Promote chromium-free refractory bricks for cement kilns.
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