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In order to improve the alumina production process and technical equipment level, Chinalco Shandong Branch introduced a fluidized circulating boiling roaster with a capacity of 1600t/d alumina technology and high automation level from Luqi Company of Germany. In September 1997, the oven was ignited and put into operation. The subsequently installed set was fired in November 2001. This set of refractory lining apparatus used was calcium silicate boards, lightweight castable, refractory castable, refractory fiber and refractory clay brick and anchor.
I. Selection of alumina circulating boiling roaster and its refractory materials
1. Composition of alumina circulating boiling roaster
The alumina circulating boiling roaster is used for roasting aluminum hydroxide by a conical cyclone, a venturi dryer, a boiling roaster, a feed screw, a fluidization cooler, a circulating bed, a discharge tank, a discharge pipe, and The duct and the flue are composed. The shape of the equipment is basically cylindrical. The maximum outer diameter of the equipment is 5.8m and the height is 32m. The outer casing of the equipment is welded by steel plate. The inner lining is composed of unshaped refractory material, refractory brick, calcium silicate board and refractory fiber, and has anchor connection. Fixed, the entire device is connected to each other to form a sealed, holistic structural device.
2. Selection of refractory materials for alumina boiling roaster
The maximum furnace temperature of the device is about 1100 ° C, the highest pressure is about 12.5 kPa, the maximum flow rate is 48.5 m / s, and the roasting time is about 30 min, that is, the entire roasting process is completed at high speed and high temperature. Due to the high hardness and good fluidity of the processed alumina material, the quality of the alumina product is strict, and the mixing of any lining impurities directly affects the performance of the product. Therefore, the refractory material must meet the following conditions: high temperature resistance, It is resistant to abrasion, high strength, good thermal stability, and has excellent integrity and sealing.
In the selection of domestic alternative refractory materials, three principles should be followed: 1 to ensure that the physical and chemical indicators of the selected refractory materials meet the requirements of Luqi; 2 to ensure that the selected refractory materials have good construction performance, especially refractory burning materials; 3 The selected refractory material must be verified by practice. According to these three principles, after conducting on-the-spot investigations and comparisons on more than a dozen domestic refractory manufacturers, the final selection of six refractory materials plants, after comparison with various performance indicators of foreign refractories, selected The domestic refractory materials and Luqi's refractory performance indicators are close, and some performance indicators even exceed the foreign indicators.
Second, the application of refractory materials for alumina circulating boiling roaster
The total refractory material used in the whole process of the circulating boiling roaster is 762 tons, mainly including castables, refractory bricks, calcium silicate boards, aluminum silicate fibers and refractory clay, as well as fixed refractory anchors. [next]
1. Working layer refractory
The total number of refractory castables is 351t, which is used for the first-level venturi, cooling cyclone, fluidized bed cooler, all pipes, flue and the bottom of the boiling roaster and the cone part of the cyclone, mostly double or triple.
The refractory bricks share 269 tons and are mainly used in boiling roasters, circulating cyclones, secondary cyclones, secondary venturi dryers and flue.
According to the process characteristics of the boiling roaster and different process parameters and working conditions, the types and layers of refractory materials used in the working layer are different. According to the use temperature and material properties, all process pipes are configured for light and heavy pouring. The main equipment lining adopts the working layer configuration of heat insulation + heat insulation + refractory bricks to make the refractory energy saving effect better.
2, insulation refractory
Insulating refractories are lightweight castables, lightweight insulating bricks, calcium silicate boards and refractory fibers.
Castable
Mainly used in the top of all major equipment such as fluidized bed coolers, cooling cyclones, first-class venturi dryers and secondary venturi dryers and all pipes and flue.
Insulation brick
Insulation bricks share 41.76t, mainly used in fluidized bed coolers, first-class venturi dryers and secondary cyclones.
Calcium silicate board
The calcium silicate board shares 97.5m 3 and is available in 50mm thickness and 30mm thickness. It is mainly used in boiling roasters, circulating cyclones, cooling cyclones and first-class venturi dryers.
Refractory fiber
The refractory fiber shares 2.5t and is divided into plates, felts and blankets. It is mainly used in expansion joints, expansion joints, brackets and inlets, and around various process holes.
Anchor
The anchor is the main component of the lining and its function is to firmly bond the lining to the furnace wall. [next]
The distribution of the anchor is related to the furnace temperature, the nature of the refractory material, the thickness of the lining, the location of use and the shape and material of the anchor used. There are 15 types, 40 specifications, and the stress distribution of the anchor system with a weight of about 3000kg on the lining. And the balance of thermal expansion and contraction thermal stress, extending the life of the lining, plays a vital role.
Third, the effect and existing problems
1, effect and enlightenment
1 The furnace pays attention to the use of thermal insulation materials in the use of refractory materials. Five layers of refractory materials and four layers of thermal insulation materials are used on the high temperature equipment boiling roaster and the circulating cyclone cylinder, and the heat preservation effect is very good. Although the internal temperature of the furnace is as high as 1100 ° C, the external temperature of the furnace is only about 70 ° C. The other parts have two or three layers of insulation material, so the overall thermal efficiency of the furnace is very high.
2 Different equipment, different working conditions, different refractory materials are used to make the use of refractory materials more economical and reasonable, and have certain enlightenment for the selection of refractory materials in the future.
3 Different furnace temperatures, different refractory materials, different lining thicknesses, and different parts of use, the shape, distribution and material of the anchors used are different.
4 Boiling roaster, circulating cyclone, secondary cyclone separator, secondary venturi and other vaults are made of special-shaped bricks, and the joints between the rings and the rings ensure the overall performance of the spherical vault. It solves the problem that the pouring material is troublesome to construct, the curing time is long, and it is difficult to repair after the damage.
2, there is a problem
In less than three years of application, the boiling roaster was shut down for 4 times due to the secondary venturi dryer, flue, etc., for the following reasons.
Unreasonable structure
The passage from the second venturi to the secondary cyclone is 2.5m high and 1.7m wide. The brick thickness is only 180mm and is divided into two layers (65mm and 115mm). Although it is provided with anchors, it is still unstable and cannot be used. Falling bricks in one year.é‚ Improve during overhaul, keep the internal surface area unchanged, the height is unchanged, the outer casing is widened by 115mm, the refractory brick is thickened by 115mm, and it is changed to 65mm insulation brick and 230mm refractory brick. The modified operation is better. [next]
Large brick joints and expansion joints
The refractory brick designed by this furnace generally has 25mm expansion joints at intervals of 3.5m. According to the line change of refractory materials in China, at 1450°C, 2h insulation, the line shrinkage is generally +0～-0.2%, thermal expansion. The coefficient is 0.1% at 300 to 400 ° C, so the expansion joint of 25 mm is too large. The outer steel plate can be seen through all expansion joints when the furnace is shut down. Therefore, according to the theoretical requirements, the expansion joint stays 7 to 8 mm.
Venturi, secondary cyclone and refractory bricks connected to the aisle have low strength and are not wear resistant
For more than 2 years since the furnace was opened, the refractory brick of the secondary cyclone has been worn from 115mm thick to only 20mm. The wear of the secondary ventilated refractory brick is only about 70mm. The connected aisle refractory brick has been replaced twice. The strength of the brick is only 34 MPa, indicating that the refractory brick here does not meet the process requirements. In addition, the flow velocity of the airflow is large, and the erosion of the alumina is strict. High-strength wear-resistant bricks should be used. Therefore, wear-resistant aggregates are added to the high-alumina aggregate to enhance the wear resistance of the refractory bricks. Wear-resistant aggregates such as corundum and slab corundum have the advantages of high refractoriness, small creep, high density, good thermal shock resistance, good wear resistance, etc. In this part, trial use of high-strength wear-resistant bricks can significantly improve The service life of the lining.
Excessive construction gap between castables
The top of the aisle between the boiling roaster and the circulating cyclone is three layers of castable, two layers of insulating castable, one layer of refractory castable, and the anchor is ST-20-21. Due to excessive construction gap, alumina passes through. The construction seam scouring the anchor, causing the anchor to break and the castable to fall off, which affects production. The measures adopted include strengthening the welding strength of the anchor and improving the construction process; reducing the thickness of the thermal insulation castable, and changing both ends of the aisle to refractory castables to reduce construction joints.
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