The closed blast furnace, front bed and continuous blowing furnace bottom of a small and medium-sized copper smelter were originally designed with silica sand-based siliceous refractory ramming material. The bottom is damaged quickly and the service life is short. The bottom structure of the furnace and the performance of the refractory ramming material used are analyzed according to the problem. It was found that there were a series of problems in the application of siliceous ramming material, so after the consistent research of experts and scholars, magnesia refractory ramming material was used instead.

1. Originally designed furnace bottom structure and refractory ramming material composition

1.1 The masonry structure of the original design of the closed blast furnace is shown in Figure 1. The surface layer in contact with the melt is magnesia-alumina brick, with a thickness of 230mm, staggered masonry, and a ramming material with a thickness of 70mm below. The material composition (weight ratio) is: 3~5mm quartz sand 70%, raw clay powder 30%, Add water glass with a modulus of 295, mix and wet, manually smash it, and dry it with firewood for 8 hours.

1.2 The original designed furnace bottom masonry structure is shown in Figure 2. The surface layer in contact with the high-temperature melt is magnesia-alumina brick, with a thickness of 230mm, and is built into a reverse arch. The thickness of the ramming material in the lower layer is 34mm (at the center line of the reverse arch), and the material composition (weight ratio) is: 3~8mm quartz sand 70%, raw clay powder 30%, mixed with water evenly, mixed with water glass 5%, after smashing drying.

1.3 "Continuous blowing furnace" The original design of the furnace bottom masonry structure is shown in Figure 3. The surface layer that contacts the high temperature melt is magnesia-alumina brick, with a thickness of 230mm, and is built into a reverse arch. The thickness of the ramming material below it is 140mm (at the center of the reverse arch), and the weight ratio of the material is the same as that of the front bed.

2. Analysis of the existing problems of siliceous ramming material

By carefully analyzing the structure of the above three furnace bottoms and the composition of the ramming material, it is not difficult to find the following situations and problems.

(1) The ramming materials in the three furnaces are all under the surface layer of magnesia-alumina bricks, and together with magnesia-alumina bricks, they have been subjected to high temperature and huge pressure of the melt for a long time. The magnesia-alumina brick on the opposite side of the ramming material layer is the support layer, and the lower side and the left and right sides of the brick body are the protective isolation layer.

(2) The composition of the ramming material in the three furnaces is basically the same as the original design, and all of them are mainly composed of quartz sand to form a water glass type siliceous ramming material. Quartz sand is an aggregate, which determines the quality of the ramming material bedding physical and chemical indicators: raw clay powder mainly acts as a filler, which can reduce the voids and increase the compactness of the ramming layer; water glass acts as a bonding agent.

(3) The ramming materials of the three furnaces are all siliceous and are acidic refractories; their surface layer is magnesia-alumina bricks, which are made of magnesia-alumina, which are basic refractories. Obviously, the two materials are different and have opposite properties.

(4) During the smelting process the furnace bottom of the third furnace, is subjected to a high temperature of 1200-1300 °C, and the SiO2 in the siliceous ramming layer and the MgO of the magnesia-alumina brick will react chemically to generate olivine 2MgO·SiO2 to the magnesia-aluminum brick. Bricks are damaged.

(5) During the three-furnace smelting process, the carried high-temperature melt contains basic components such as CaO, MgO, FeO, and Cu2O. When the magnesia-alumina bricks on the bottom surface of the furnace are defective due to the quality of bricks and masonry, the melt will penetrate downward. When its basic components touch the siliceous acid ramming material, there will be chemical interaction with each other, so that the ramming material will be eroded, resulting in problems such as looseness and penetration.

(6) The water glass type siliceous ramming material is mainly composed of quartz sand and adding raw clay powder and water glass, due to the weak cohesive force of water glass and no coagulant added, the integrity of the ramming and molding Density, firmness, and sintering effect are not ideal.

(7) Since the ramming material in the third furnace is siliceous, compared with the magnesia refractory, there is a big gap in refractoriness, compressive strength, bulk density, and apparent porosity, and resistance to alkaline oxides.

Improvement of refractory ramming material

The practice has proved that the use of magnesia sintering or magnesia-iron sintering furnace bottom (for direct contact with the melt) has greater mechanical strength, good compactness, high toughness, and good corrosion resistance, and the life of the furnace bottom is significantly prolonged. The method is to mix magnesia (MgO>83%, particle size <5mm), iron powder (Fe3O473%, Fe2O387%, FeO17%), and brine (MgCl2>45%) in proportion, and then tamping, and then ignited and heated to 1500 ° C., After 38h of constant temperature, a complete sintering furnace bottom will be formed. Based on the principle that the material selection of ramming material is similar to that of magnesia-alumina bricks, it was decided to change the originally designed water glass siliceous ramming material to brine plus magnesia, and to make it in the construction of a closed blast furnace, front bed and continuous blowing furnace at the same time. use. The weight ratio of the magnesia ramming material of this brine plus magnesia is 67% of 2-6mm magnesia, 33% of magnesium powder, and an appropriate amount of red iron oxide, mixed with brine (d ≥ 1.26), and then artificially mixed. Tamping, and drying with firewood for 24h. The material requirements are magnesia, MgO ≥ 80%, particle size 2-4mm and 4-6mm each 50%; magnesium powder, grade MF-82, particle size ≤ 0.088mm; brine with MgCl2 ≥ 45% brine powder deployment made; iron oxide red, standard H103, first-class product. During the construction, it was found that the magnesia ramming material has a good consolidation effect, can form a whole quickly without baking, and has good compactness, and the strength increases rapidly; the construction tool method is simple, and the operation is convenient and quick.