Application of magnesia chrome brick in cement rotary kiln, RH furnace and copper smelting furnace

The finished magnesia chrome bricks (No. MC, fired bricks) before chrome free and magnesia spinel bricks (No. MS, unburned bricks) after chrome free used in the lower trough of RH furnace in a large domestic steel plant were selected for test. The chemical composition of sample MC and MS was measured by spectrometer; The phase composition of sample MC and MS was analyzed by X-ray diffractometer; According to GB/T2997-2000, GB/T5072-2008, GB/T5988-2007 and GB/T3002-2004, test the apparent porosity, bulk density, compressive strength, heating permanent line change rate and high temperature bending strength (1450 ℃ 1h) of sample MC and MS after treatment at 110 ℃ for 24h, 1000 ℃ 3h and 1600 ℃ 3h respectively; According to the standard GB/T7320-2008, RPZ-04 high temperature thermal dilatometer is used to test the thermal linear expansion rate from room temperature to 1500 ℃; The thermal shock resistance is tested according to the standard YB/T376.3-2004 (water cooling method). The test temperature is from room temperature to 1100 ℃. The sample is made into standard bricks, and the crack morphology on the surface of the sample after the thermal shock resistance test is compared;

The slag resistance is evaluated according to the standard GB/T8931-2007 (static crucible slag resistance method) and by comparing the corrosion morphology of the residual bricks removed from the tank wall at the lower part of the RH furnace. The chemical composition (w) of the test slag is: SiO2: 11.50%, Al2O3: 36.08%, Fe2O3: 10.15%, CaO: 22.50%, MgO: 7.71%, TiO2: 0.76%, Cr2O3: 0.16%, MnO: 9.97%; The microstructure of the reaction interface between the static crucible sample and the slag was observed by scanning electron microscope, and the micro composition of the reaction interface between the slag and the brick was determined by energy dispersive spectrometer, and then the respective corrosion mechanism was analyzed.

Compared with similar foreign products, domestic magnesia iron spinel brick has the advantages of short order cycle, low price, less reserve and convenient after-sales service.

(1) The magnesia iron spinel brick does not contain chromium, which saves the cement enterprises the cost of special treatment of chromium containing bricks, and also avoids the huge cost of national and social treatment of chromium pollution after chromium containing bricks cause chromium pollution.

(2) The service life of magnesia iron spinel brick is longer than that of magnesia chrome brick, and the direct economic benefit of the enterprise is obvious. Taking the price of magnesia iron spinel brick as 30% higher than that of magnesia chrome brick and taking two years of use as an example to compare the economic benefits, it has been more than a century since the rotary kiln produced cement clinker. In the early 1980s, the cement rotary kiln technology was basically finalized. At present, the new dry process kiln is the mainstream production technology. Its firing temperature is about 1450 ℃, and the temperature of combustion gas in the kiln can reach more than 1700 ℃, even close to 2000 ℃.

Refractories used in cement industry account for about 13% of all refractories. Refractory, as an indispensable lining material in the cement burning process, is also the material support condition of the second generation of new dry cement process, in which the refractory for burning belt is particularly important. The main mineral components of Portland cement are CaO · SiO2, 3CaO · Al2O3 and 4CaO · Al2O3 · Fe2O3. The most suitable refractory for the transition zone and firing zone of key parts of the cement kiln can only be alkaline magnesia refractory, as shown in Figure 1.

In the past, magnesia chrome bricks were widely used in the firing zone. The magnesia chrome bricks can resist the corrosion of cement components. CaO from cement clinker reacts with Fe2O3 in the bricks to form 4CaO · Al2O3 · Fe2O3, which makes the bricks easy to adhere to the clinker; Cr2O3 released from bricks can also stabilize 2CaO · SiO2 in the kiln skin, so chromite plays an important role in improving the refractoriness, corrosion resistance, thermal shock resistance and hanging kiln skin of basic refractories. The firing zone is in a high temperature chemical atmosphere. The furnace charge temperature is 1400~1500 ℃. With the production of molten liquid, the refractory is usually covered by raw materials. In addition to the rotation of the kiln body, the kiln skin often peels off. The reaction between the cement raw materials in the molten state and the bricks and the penetration of molten liquid into the bricks cause melting loss and structural peeling, and the transition zone is roughly the same