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Process design and control for high-silicon, calcium bauxite raw material smelting brown fused alumina
- Nov 30, 2018 -

Process design and control for high-silicon, calcium bauxite raw material smelting brown fused alumina


Brown fused alumina smelting production process, the choice of raw material source and raw material quality control is essential and a process must be strictly controlled; raw material selection To a certain extent, it determines the application range of its products; whether the quality of raw materials can be effectively controlled not only seriously affects product quality and performance, but also directly affects the manufacturing cost of brown corundum production; therefore, in brown corundum production In the process, the main raw materials, bauxite, iron filings and anthracite, must be strictly controlled. Especially for SiO2 and CaO, the amount of raw materials involved should be strictly controlled. The introduction of SiO2 and CaO not only brings difficulties to production, but also affects the manufacturing cost, reduces the content of valuable components of AL2O3 and TiO2, and also affects the product price of the product and the application range of the product because of the lack of product quality.

As a vitreous matrix material, excessive SiO2 entering the corundum matrix will greatly reduce the toughness and microhardness index of corundum, which will seriously affect the performance of corundum abrasives. However, a small amount of SiO2 and AL2O3 form a miscible phase. The state of stone (3 AL2O3.2 SiO2) is uniformly dispersed at the grain boundary of α-AL2O3, which is also beneficial to the self-sharpness of the abrasive. Therefore, the content of SiO2 in brown fused alumina is required to be less than 1%. The limitation of CaO on the crystallization of corundum Not large, as long as the CaO content does not exceed 8%, the first crystalline phase in the brown fused alumina smelting process is corundum. The experiment proves that when the CaO content reaches 3%, the CA6 (calcium hexaaluminate) formed in the corundum, its Excessive presence will not only reduce the microhardness of corundum, but also produce calcium aluminate low melting (C3A, CA, melting point around 1360 °C), which will seriously affect the thermal properties of corundum materials. Corundum is very harmful, so the content of CaO in brown fused alumina for refractory materials is generally less than 0.5%, and the content of CaO is 0.3% as high-quality refractory. [Fe2O3 in raw materials is made in smelting brown fused alumina For having The element is included; TiO2 is the main component of brown fused alumina coloring, and it can also promote the microcrystallization of corundum and increase the toughness of corundum; MgO is the microcrystalline promoter of microcrystalline corundum, and the amount of MgO (melting point 2800 ° C) can enter. Improve the toughness of corundum, and improve the overall performance of brown corundum].

Using the above principles, we can design and produce brown fused alumina for different purposes.

1. Smelting brown corundum with the main raw material technical conditions

for the production of ordinary (for abrasive or high temperature refractory) brown corundum, the main raw material quality requirements are as follows:

Table 1 The chemical composition of cooked bauxite should meet the following requirements:


Chemical Composition

Al2O3

TiO2

Fe2O3

CaO

Al/Si

Content %

Threshold %

>=85

>=80

2.5-5.5

3-6

<=0.5

>=15

>=12



Note: (1) The content of Fe2O3 and TiO2 when the content of SiO2 is less than 3% It can be controlled to less than 6%.

(2) In a batch of cooked bauxite, take one piece, and the ratio of aluminum to silicon should not be less than 10.

(3) The bauxite should not contain raw bauxite, bauxite, stones, Impurities such as dirt.

(4) CaO content is checked once a month for each mine.

(5) Size range 30-300mm, no more than 15% below 30mm, no more than 5% below 5mm.

Corundum smelting also has certain technical requirements for iron filings and anthracite (coke), otherwise, it will seriously affect brown corundum Technical and economic indicators. Smelting corundum are as follows  Anthracite (coke) and iron technical quality

Table2anthracite (coke) the chemical composition should meet the following requirements:


Chemical Composition

Fixed Carbon

Ash

Nonferrous

CaO

Valotiles

Weight %

80

12

=7

<=0.5

<=2



Note: Anthracite (coke) should not be mixed with obvious gangue, wood, mud, stones and other impurities.

Table 3, the chemical composition and quality of iron filings should meet the following requirements:


Chemical composition

Iron (Fe)

Si

non-ferro

non-magnetic

Weight %

>=88

<=3

<=0.1

<=1.8



Note: Do not mix cotton yarn into iron filings, wood, soil, sand and other impurities.

2. Analysis of the causes of high silicon and calcium bauxite raw materials The

smelting of brown alumina corundum with aluminum bauxite is different from the production of aluminum bauxite for metal aluminum and refractory raw materials. The bauxite clinker used for smelting brown corundum is selected. High-quality aluminum bauxite with high AL2O3, TiO2 and low SiO2, CaO, and bauxite for the production of metal aluminum and refractory raw materials have relatively lower requirements for the above-mentioned indicators, which can meet the production needs.

At present, there are about 170 manufacturing enterprises of corundum materials in China, and its production capacity is about 2 million tons. According to the production capacity, only high-alumina high-quality cooked bauxite for corundum production is about 2.4 million tons. Due to the rapid development of many basic industries and corundum manufacturing, the demand for bauxite is growing rapidly, and due to the lack of bauxite resources, coupled with the irregular behavior of some bauxite suppliers and intermediate links, brown fused alumina smelting The amount of cooked bauxite used was difficult to guarantee and the quality was seriously degraded; A/S dropped from 25-30:1 in the 1980s to 15-20:1 in the 1990s, and today's companies often use A/S 10-12:1 bauxite, and even some bauxite used in enterprises, sometimes the content of SiO2 exceeds 10%, which has not attracted the attention of corporate decision makers. How to get rid of the double dilemma of technology and economy is not generally considered. At present, the content of AL2O3, SiO2 and Fe2O3 in the south and north of the bauxite raw materials used for the production of ordinary (for abrasive or high-temperature refractory) brown corundum is similar.

The SiO2, CaO, which is a harmful impurity in the production of brown alumina for bauxite, is the solid material in the bauxite source; the second is brought along with the fine soil surface mixed with the bauxite clinker. The former is contained in the raw materials itself, and can be controlled as appropriate when selecting the source of the raw materials, or the mineral processing can be selected to ensure the quality of the raw materials, while the latter is a more important source of involvement, which requires the brown corundum manufacturing enterprises to strictly control themselves. It is. Due to the increasing tension of bauxite resources, the fine soil surface may become more and more serious when mixed with bauxite clinker, which makes the production enterprise in a dilemma of “abandoning, using and not being able to”, and also giving brown corundum Manufacturing companies have brought serious difficulties and challenges. In addition, from the above mathematical analysis of raw materials, it is known that the harmful impurities SiO2 and CaO brought in anthracite and iron filings should also be given sufficient attention and strict control. Due to the excessive mixing of SiO2 and CaO, the brown corundum production enterprises consume electricity and consume raw materials, which increases the manufacturing cost. More importantly, the product quality is seriously out of control and the performance is limited. It is economical and reasonable to find a solution. It must be done.

Third, process design and control

SiO2, CaO is very harmful to its brown fused alumina product quality and application range, must be strictly controlled in production and process technology. In the brown sapphire smelting process, SiO2 can be removed by gasification sublimation or reduction to form low-silicon iron, and CaO is very difficult to remove in the brown fused alumina smelting process, so it is necessary to strictly control the raw materials (aluminum bauxite, anthracite, iron filings). The amount of CaO in the process, and the design of a reasonable, appropriate process technology program, targeted to divert and control it.

a) Recovery and utilization of high SiO2 and CaO powders

1. Material recovery: Through mathematical analysis, excessive inferior bauxite mixed powder entering the charge is one of the main reasons for the serious exceeding of SiO2 and CaO in raw materials. Therefore, It is very necessary that this part of the inferior mixed powder is removed or effectively controlled. The purpose of separation of inferior powder and alumina can be achieved by dust collection or sieving treatment. The separated high SiO2 and CaO are separately stored and used for other purposes.

2. The spheronization treatment powder material is of the to make the smelting process smoothly, and it is necessary to ensure that the furnace material has a certain particle size, so as to achieve an ideal outgassing effect in the smelting process. The pulverized treatment of the recovered powder can achieve the purpose of smelting materials, and at the same time, an appropriate amount of composite additives are added in the process of spheronization to ensure the smooth progress of the smelting process, so that the quality of the corundum is reasonable. control.

1) The raw material preparation tool is simple and easy to maintain, and the drum mixing machine and the pellet forming machine are selected;

2) the drying heat energy is selected by the corundum package heat energy comprehensive utilization;

3) the pellet transportation is completed by the stereoscopic climbing.

3. Selection principle of composite additive

1) Technically feasible, no bad effect, does not affect the product quality of brown corundum;

2) Simple and easy to obtain, rich in resources and guaranteed;

3) Economical and reasonable, it is conducive to target cost control;

4) Consolidation High strength, no impact on the environment;

5) Conducive to improving smelting efficiency, easy to operate.

2) Process control

1. The source of the raw materials to be purchased is classified and controlled, so that the source is controlled. In the main raw material of smelting brown corundum, SiO2 is generally controlled within a range of less than 6%, while CaO should be controlled within a range of less than 0.5%.

2. The fine soil surface entrained in the bauxite has been pre-treated by sieving (or dust recovery) to ensure the purification and stability of the smelting raw materials.

3. Strictly control the content of impurities in anthracite (coke) and iron filings, and control the amount of impurities such as coal gangue and foundry sand from the source to ensure that the raw materials are in a controlled state.

4. Not only aluminum bauxite, anthracite, and iron filings should be strictly selected before batching, but also the chemical composition and particle size of the main raw material bauxite in the furnace should be rationally designed and strictly controlled to design the pre- and post-smelting phases. The reasonable proportion of the later materials, while strictly controlling the particle size range of the charge to ensure the smooth progress of the smelting process.

5. Reasonable design and utilization of the recovered fine powder. In the smelting process, according to the smelting principle, adjust the PH value of the corundum melt, and proportionate the reducing agent, clarifying agent, flux, accelerator and other raw materials. By processing into a spherical or a certain degree of composite material, and then smelting, the comprehensive benefits are better, which is not only economically reasonable, but also reduces the difficulty of smelting. More importantly, the quality of brown fused alumina is effectively controlled during the smelting process.

3) Process technology design

1. Process:

bauxite (anthracite, iron filings) raw materials into the warehouse inspection → preparation (classification control → pellet preparation → drying treatment) → ingredients → smelting → dumping → cooling → crush selection → Measurement and storage

2. Design and smelting process

smelting is an important process in the production of brown corundum. Through smelting, the appropriate smelting atmosphere is controlled to make the bauxite and reducing agent (anthracite or coke) and clarifying agent (iron scrap) at high temperature. The redox reaction is carried out to remove impurities and form α-Al 2 O 3 to obtain a corundum block satisfying the quality requirement.

1) The furnace material is designed to achieve reasonable control of the material entering the furnace; by rationally adjusting the pH value of the melt in the furnace, the design of the furnace material is optimized to obtain a good smelting index.

2) Main chemical reaction:
reactionin the furnace according to the thermodynamic analysis of the composition of the charge, the main chemical reactions in the smelting furnace are as follows:

After analyzing the composition of the dust-removing powder, SiO2 is about 40%, Al2O3 is about 40%, and K2O is about 10%. The rests are Fe2O3 and toner.

During the smelting process, about 50% of TiO2 is reduced, and elemental Ti enters the low Fe-Si alloy. The remaining TiO2 enters the corundum block with valuable components, while the valuable MgO and impurity CaO in the bauxite impurities retain their inherent nature. The content enters the corundum block.

3) Calculation of charge ratio respectively for carbon and iron:
calculating
where: SiO2%, Fe2O3%, TiO2% respectively represent the percentage of SiO2, Fe2O3, TiO2 in the raw material, and C% is the percentage of fixed carbon in anthracite. Fe% is the iron content in the iron filings, K is the iron-to-silicon ratio, (K is 5.5).

4) The smelting cycle design is

based on the capacity of the smelting equipment, and the batching preparation system of the charging materials is designed. The smelting furnace materials are divided into the front, middle and late respectively. The matching is a reasonable optimization process design to solve the difference of the furnace material, which is very beneficial to its technical and economic effects.

1 In the early stage of smelting: aiming at improving and ensuring that the furnace temperature is not lost, the mixture is mainly composed, and the addition amount is 60-70% of the total amount of the charge.

2 In the middle of smelting: In order to ensure the smooth progress of the whole smelting process, the middle of smelting must ensure that the gas escape effect in the furnace is good. This is the most important part of the whole process of smelting. Only the furnace material has good ventilation effect, and the excess SiO2 and SiO in the furnace. Exhaust gas can escape from the furnace to obtain satisfactory quality and good technical and economic indicators. It can be well controlled in the middle and late smelting; the addition amount is 30-20% of the total amount of charge.

3 Late smelting: In this stage, the objective of adjusting the quality of the furnace and increasing the output is particularly important. As the charge enters the refining period, it is very important to control the furnace temperature and shorten the smelting time. This period is the key to the whole process of the technology economy. The amount of charge added is 5-10% of the total charge.

3. Control of the smelting process

1) Pre-furnace adjustment: In the production process, according to the requirements of user quality indicators, the degree of smelting reduction can be appropriately controlled to achieve effective quality control. However, due to the batch quantity and quantity and sampling of the bauxite mine. The influence of factors such as methods and smelting operation methods, in the actual production process, sometimes need to pass the dipstick to make the pre-furnace judgment adjustment (after the processing ratio and process operation are familiar, the pre-furnace adjustment process can be canceled).

2) In-furnace reduction control: Due to the decrease of Al2O3 content and the increase of SiO2 content in bauxite, it is necessary to increase the amount of C involved in the smelting process, which strengthens the concentration of reducing atmosphere in the furnace and generates a large amount of high-temperature gas. , thereby increasing the difficulty of smelting operation and furnace control; in the case of increasing the amount of C and Fe, SiO2 can be effectively removed, but due to over-reduction, valuable components such as TiO2 in the mineral are also reduced. It enters the low-silicon iron in the form of metal Ti, which reduces the quality and performance of the brown fused alumina, and the application field is limited. Therefore, the proper open-arc exhaust gas is necessary for the effective escape of SiO2 and SiO exhaust gas.

3) Smelting parameter control: In order to obtain good technical and economic indicators, the smelting process should be adjusted according to the degree of material change. According to the molten pool situation, it is necessary to adjust the current and voltage gears of the smelting process reasonably. Control methods and means.

4. Smelting process control and operation skill

smelting is the main process of corundum production. Through smelting, the bauxite and reducing agent and clarifying agent are subjected to redox reaction at high temperature to remove impurities and form α-Al2O3, thereby obtaining quality requirements. Corundum block. For bauxite with high SiO2 and CaO content, from the theoretical and practical aspects, whether it is a fixed furnace or dumping furnace, its smelting process is different from traditional brown fused alumina smelting process.

1) Arcing: Arcing adopts technically feasible and economical carbon arcing block, without adding or adding iron filings as much as possible, which is safe and economical, and the cost of arcing can be saved by about 50%;

2) Installation ingredients: In the early stage of smelting (the first batch), relatively fewer iron filings are added on the basis of normal ingredients, and the required amount of iron filings is added successively in the middle and later stages, so that better technical and economic effects can be obtained;

3) charge Control: In the early stage of smelting, the in-furnace system is combined with coarse and fine materials, and the furnace is smelted to reduce the temperature loss in the furnace. In the medium term, the permeable pellets are used to make the SiO and SiO2 vapors escape smoothly from the furnace. In order to ensure the stability of the furnace conditions, save the amount of iron scraps, increase the smelting rate; after the medium-term open arc deflation, the later feeding should consider the appropriate use of fine furnace materials to ensure rapid melting of the charge, reduce heat loss, and improve the smelting rate; refining of high-quality bauxite powder or brown powder, softcover insulation process to ensure quality, increase furnace output;

4) metallurgical parameters Plan: in the case of the bath furnace reasonable, from safety From the perspective of increasing the output of single furnace, it is easy to use high voltage and low current in the early stage of smelting (relative), which is beneficial to enlarge the area of the molten pool in the furnace, so that it is safe and can increase the yield, and the melting effect is also It will be better; in the middle of smelting, the power (current, voltage) should be adjusted according to the condition of the furnace to ensure that the furnace is out of gas and smooth in smelting; it is necessary to increase the power transmission in the later stage of smelting, especially in the refining period, and at the same time with high-quality powder. The smelting economic indicators will be better.


5) Open arc outgassing: For high SiO2 low Al2O3 bauxite smelting, it is more beneficial to the smooth escape of SiO and SiO2 steam in the furnace by appropriately increasing the amount of reducing agent and the number and time of open arc outgassing. In this way, both harmful impurities and iron filings can be saved, which is also beneficial to product quality.

Fourth, the design of the smelting process of high silicon and calcium furnace materials:

smelting scheme 1: non-separate smelting. Process technology plan (slightly)

smelting plan 2: Separate single brown corundum smelting. Process technology plan (slightly)

smelting plan 3: According to the material chemical component, other corundum or special product production (SiO21.2-1.5; CaO1% or so), the process technology plan needs to be designed separately.

V. Economic Benefits and Feasibility of Production Organization

Any industrial production or any technical solution of any enterprise must be technically feasible, economically reasonable, and the production process is simple and convenient. Otherwise, it is not the best production or technical solution.

In the production process of brown corundum, the general smelting process requirements are: the early period is the heat preservation period; the medium period is the quality control period; the later stage (while shortening the smelting time as much as possible) is the quality and output double guarantee period; Technical and economic effects. Through the new design of the pretreatment of the incoming charge and the technical scheme of the process, it is expected that the following technical and economic effects can be achieved:

1. It is beneficial to the smooth operation of the smelting process, reducing the violent reaction in the furnace and improving the production efficiency. The production capacity during the smelting operation can be increased by about 5-10%.

2. Reduce or eliminate the power outage time in the furnace due to the reaction, which can reduce the labor intensity of the smelter, reduce the unit consumption, and shorten the smelting time.

3, can effectively improve or achieve intensified smelting operations, strengthen smelting rate, increase production capacity, improve the overall efficiency of enterprises, reduce costs;

4, can improve product quality, achieve effective quality control, lay a good foundation for improving corporate brand efficiency, It is conducive to creating markets, winning markets, increasing market share, and ultimately achieving good social and economic benefits.

5. The smelting part directly reduces the dust loss and the aluminum bauxite is about 2%. The preparation batching system can reduce the bauxite loss by about 3%. If this part of the bauxite dust is recycled, it will be calculated according to 5%. For example, 10,000 tons of corundum, about 12,000 tons of bauxite is needed, and 600 tons of bauxite can be saved annually. According to 900 yuan/ton, the annual benefit is 540,000 yuan. If you use the company to produce ten years of calculation, this will be a big benefit.

6. Purify the labor production environment and improve the health of employees.