Application of Alumina Cyclic Boiling Baking Furnace

Alumina> Alumina circulating boiling roaster and its choice of refractory materials

1. Composition of alumina circulation boiling roaster Alumina cycle Boiling roaster is used to roast aluminum hydroxide from conical cyclone, venturi dryer, boiling roaster, feeding spiral, fluidized cooling machine, circulation Beds, discharge chutes, feeding pipes, and ducts and flue ducts. The shape of the equipment is basically cylindrical. The maximum equipment has an outer diameter of 5.8m and a height of 32m. The outer shell of the equipment is made of welded steel plates. The inner lining is composed of unshaped refractory material, refractory brick, calcium silicate board and fire-resistant fiber, and has anchorage connection. Fixed, each device of the whole device is connected with each other to form a sealed, overall structural device.

2. Selection of Refractory Materials for Alumina Boiling Baking Furnace

The maximum furnace temperature of this device is about 1100°C, the maximum pressure is about 12.5kPa, the maximum flow rate is 48.5m/s, and the roasting time is about 30min, ie the whole roasting process is completed at high speed and high temperature. Due to the high hardness and good fluidity of the treated alumina, the quality of the alumina product is strictly required. Any mixing of the lining impurities directly affects the performance of the product. Therefore, the refractory material must meet the following conditions: high temperature resistance, Wear resistance, high strength, good thermal stability, integrity and tightness.

In the selection of domestic alternative refractories, three principles shall be followed: 1) ensure that the physical and chemical indicators of the selected refractories meet the requirements of the company; 2 ensure that the selected refractories have good construction performance, especially fireproof castables; 3 The selected refractories must be verified by practice. According to these three principles, after a dozen onsite fire-retardant material manufacturers in China have conducted on-the-spot inspections and comparative screening, they have finally selected six refractory materials factories, which have been compared with various foreign refractories' performance indicators. The domestic refractory materials and Luchi's refractories performance indicators are close, and some of the performance indicators even exceed the foreign indicators.

Second, the application of refractories of alumina circulating boiling roaster

A total of 762 tons of refractory materials were used in the entire cycle boiling roaster, including castables, refractory bricks, calcium silicate boards, aluminosilicate fibers and fire-resistant mud, as well as anchors for fixed refractory materials.

1. 351t refractory castables for working layer, used for primary Venturi, cooling cyclone, fluidized bed cooler, all pipelines, flue, and the cone part of the lower part of the boiling roaster and the cyclone drum. 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 ducts.

According to the process characteristics of 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 of temperature, material properties, all process piping for light and heavy pouring configuration, the main equipment lining insulation + insulation + fire brick working layer configuration, so that the energy-saving effect of refractories better.

2. Insulating refractory materials Insulating refractory materials include lightweight castables, lightweight insulating bricks, calcium silicate boards and refractory fibers.

The castables are mainly used in the top of the main equipment such as fluidized bed coolers, cooling cyclones, primary venturi dryers and secondary venturi dryers, and in all ducts and flue ducts.

The insulation bricks share 41.76 tons, which are mainly used in fluidized bed coolers, first-class Venturi dryers and secondary cyclones.

Calcium silicate board calcium silicate board share 97.5m3, 50mm thick and 30mm thick two specifications, mainly used in boiling roaster, circulating cyclone, cooling cyclone and a Venturi dryer.

Refractory fiber Refractory fiber is commonly used for 2.5t and is divided into panels, felts and blankets. It is mainly used in expansion joints, expansion joints, brackets, and entry holes and various process holes.

Anchor anchors are the main components of the liner, the role of which is to firmly bond the liner to the furnace wall.

The distribution of anchorage is related to the temperature of the furnace, the properties of the refractory, the thickness of the lining, the location of use, and the shape and material of the selected anchor. There are 15 types, 40 sizes, and the stress distribution of the anchor system with a weight of about 3000 kg to the lining The balance between thermal expansion and contraction and thermal stress, and extending the lining life, play a crucial role.

Third, the effect and existing problems

1. Effect and Revelation 1 The furnace focuses on the use of heat-insulating materials in the use of refractory materials. Five layers of refractory materials and four layers of heat-insulating materials are used in the high-temperature equipment boiling roaster and the recycling cyclones, and the heat preservation effect is very good. Although the internal temperature of the furnace is as high as 1100°C, the surface temperature of the furnace is only about 70°C. Other parts have two or three layers of heat insulation material, so the overall thermal efficiency of the furnace is high.

2 Different equipment and working conditions, the use of different refractory materials, so that the use of refractory materials is more economical and reasonable, there is a certain inspiration for the future selection of refractory materials.

3 Different furnace temperatures, different refractory materials, different lining thicknesses, and different locations of use, the shape, distribution, and material of the anchors used are different.

5 Boiling roaster, circulating cyclone, secondary cyclone separator, secondary venturi and other vaults are made of special-shaped bricks ring-by-ring masonry. The ring-to-ring interlocking between the ring and the ring ensures the overall performance of the spherical dome. It solves the problems of troublesome construction of castables, long maintenance time, and difficult repair after damage.

2. Problems exist In the application of less than three years, the red furnace in the boiling roaster due to the secondary Venturi dryer, flue, etc., has been shutdown and repaired four times for the following reasons.

Unreasonable structure The secondary venturi to the secondary cyclone channel has a height of 2.5m, a width of 1.7m, a brick thickness of only 180mm, and is divided into two layers (65mm and 115mm). Although an anchor is provided, it is still unstable. Use bricks less than a year away. During the overhaul, it was modified to keep the internal surface area constant and its height constant. The shell was widened by 115mm. The firebrick was thickened by 115mm and replaced with 65mm insulation bricks and 230mm firebricks. After the change, the operation effect is better.

Brick seams and expansion joints are larger. The firebricks designed in this furnace usually have 25mm swell joints at intervals of 3.5m at the position height. According to the line change of China's refractories, the line shrinkage is generally +0 at 1450°C and 2h. ～ -0.2%, 0.1% when the coefficient of thermal expansion is 300 to 400°C, so the 25mm expansion joint is too large. The outer steel plate can be seen through all expansion joints during furnace shutdown. Therefore, according to theoretical requirements, expansion joints remain 7 ~ 8mm.

The secondary venturi, secondary cyclones, and firebricks that connect the aisles have low strength and are not wear resistant. Since the furnace was opened more than two years ago, the refractory bricks of the secondary cyclones have been worn from a thickness of 115 mm to a local area of ​​only 20 mm. The wear of the refractory bricks is only about 70mm. The firebricks connected to the aisle have been replaced twice. The strength of the selected bricks here is only 34MPa, which means that the firebricks here do not meet the process requirements. In addition, the airflow velocity is large, and the alumina and alumina scouring is strict. High-strength wear-resistant bricks should be used. Therefore, wear-resistant aggregates are added to the high-aluminum aggregate to enhance the wear resistance of the refractory bricks. Wear-resisting aggregates such as corundum, plate-like corundum, etc. all have the advantages of high refractoriness, small creep, high density, good thermal shock resistance, good wear resistance, etc. Trial of high-strength wear-resistant bricks at this site can be significant. Improve the service life of the liner.

The construction gap between the pouring materials is too large The top of the aisle between the boiling roaster and the circulating cyclone is three layers of castables, two layers of thermal insulation castables, and one layer of refractory castables. The anchor is ST-20-21 type, due to construction If the gap is too large, alumina will wash the anchor through the construction joints, causing the anchor to break and the castable to fall off, which will affect production. The measures taken include strengthening the welding strength of the anchors and improving the construction process; reducing the thickness of the insulation castables, changing all the ends of the aisle into refractory castables, and reducing construction joints.