Steel dust removal ash adhesive
An important use of adhesives in the field of dust removal and ash processing is the forming of mineral powder, especially the cold-fixing molding of powder. Its quality is directly related to the performance and quality of the cold-pressed pellets. Commonly used binders are bentonite, syrup, sodium humic acid, sodium carboxymethyl cellulose, sodium carboxymethyl starch, cement and the like.
Jianjie dust removal ash adhesive
Commonly used adhesives are classified
Regarding the classification of adhesives, different angles have different classification methods. According to the substance category of the main components, it can be divided into organic adhesives, inorganic adhesives and composite adhesives. This is shown in Table 1.
Table 1
At present, there are some insurmountable problems in inorganic binders, such as large addition, low ball forming rate, poor dry strength, large ash content, and many harmful impurities introduced. Forced everyone to seek new binders. As early as the beginning of the 20th century, we have achieved great results in the modification of natural polymers and the composition of polymer compounds. In addition to starch, we have successively developed organic binders such as coal tar, asphalt, pulp waste liquid, ammonium acrylate, peledo, and cellulose. An inherent advantage of organic binders is that they are burned away during the pellet roasting process, and some can significantly improve the mechanical strength of the pellet ore, and some can also make the pellet metallurgical function better. In 1995, Russia studied sodium carboxymethyl cellulose, and the results showed that the pellets with the addition of 1.5‰ sodium carboxymethyl cellulose could ensure that the dry pellet strength standard of the pellets added to about 1.5% bentonite was guaranteed. However, whether it is a natural polymer or an artificial compound, its internal structure is still relatively shallow. The industry needs more theoretical knowledge of polymer compounds to guide production, so this aspect of the research needs to be further developed.
Traditional inorganic adhesives such as bentonite, water glass, borate, etc., can be used as effective adhesives to help the molding of the pellet, but will increase the harmful elements in the dust removal ash, reduce the taste of iron, the metallurgical properties of the pellets become poor, and even cause secondary pollution of the environment. Organic binders such as starch, cellulose, sodium humic acid, coal tar, acrylamide, etc. are volatilized or burned and decomposed during the baking process of the pellets, which is beneficial to the iron taste of the pellets, but the price is high, the temperature resistance is poor, the pellets are easily explosive in the high-temperature furnace, endangering the safety of the blast furnace, affecting the smelting efficiency, and cannot meet the normal use requirements. Therefore, the research and development of composite adhesives can meet the shortcomings of the above two points. At present, everyone can understand the advantages of composite adhesives, but there are few suitable and cost-effective adhesives, so the right raw materials and the right combination are crucial in the development of composite adhesives.
3. Application of adhesive in the production of dust removal ash pellets
The common method of dust removal in the steel industry is to return to the raw material yard for re-blocking, such as the cold-pressed pellet method. First of all, the dust is mixed with reducing agents (pulverized coal), binders, etc. for ball making, and the raw balls with a certain strength are dried by the dryer to reduce the moisture of the raw balls to less than 3%, and then the dried raw balls are evenly arranged in the rotary bottom furnace through the vibrating cloth machine, and the temperature in the bottom furnace is controlled at 1100-1300 °C, and the direct reduction reaction occurs in the furnace.
At present, according to the different raw material composition and equipment situation, after a long period of experiments, a binder suitable for the molding of various steel dust removal ash has been developed. It overcomes the shortcomings of traditional adhesives and has the characteristics of strong applicability and high cost performance.
According to the different properties of the dust removal ash raw materials, it can be divided into two types: ore powder adhesive KF01 and mineral powder adhesive KF02.
Mineral powder binder KF01
Mineral powder binder KF01: The product is based on pre-gelatinized starch as the main material, adding bentonite, tackifier, reinforcer, modifier, high temperature resistance and other raw materials, through a series of processes to produce a composite adhesive. It has strong viscosity, activity and adsorption, and has certain high temperature and explosion resistance. Because of its unique characteristics, the effect in pellet production is very good, not only can achieve high pellet strength, but also does not reduce the grade of pellet ore, economical and practical.
2.1 Applicability of mineral powder adhesive KF01
The dust collection ash produced by steel enterprises has fine particle size, high iron content and high calcium oxide content. The iron content of blast furnace dust removal ash is generally between 20-30%, and the calcium oxide content is 3-5%. Converter dust removal ash contains more than 50% iron, fine particle size (about 5000 mesh), large specific surface area, and contains a large amount of CaO (about 10%). Below is an analysis table of the composition content in the dust removal ash of some steel mills, such as Table 2.
Table 2
From the composition of the dust removal ash, it contains quicklime (CaO), and the quicklime reacts with water to form calcium hydroxide. On the one hand, the reaction emits a lot of heat, and at the same time the volume expands (1.5 to 2.5 times). Therefore, before ball making, it must be infiltrated with water and fully digested, otherwise the finished cold pressed ball is very easy to powder, affecting the strength of ball making, and even cannot become a ball. The coarse ash containing high activity CaO and MgO is digested with water before forming into the ball, and the water addition is 18 to 20% of the mass of the mineral powder, and the air is isolated for more than 6 hours. A thorough condition takes 24 hours.
Therefore, when the mineral powder binder KF01 is applied in the dust collection ash containing calcium oxide, the raw material must first be completely digested. It is then machine-formed according to the normal process. At the same time, as a universal product, the product can also be applied to various steelmaking recycling materials such as returning to the mine (steel slag), dust removal ash (containing ash calcium has been digested or does not contain ash calcium), iron sludge, iron oxide sheet, OG mud, iron sand, iron ore powder and so on.
2.2 Application characteristics of mineral powder adhesive KF01
(1) The ball formation rate is as high as 96% and the initial strength is good, and the 2-meter free fall is not broken; the compressive strength of a single sphere after drying is ≥2000N.
(2) Do not increase ash, do not reduce calorific value, do not reduce the grade; strong adhesion, good molding effect, uniform and beautiful appearance.
(3) All indicators are in line with the requirements of steel mills.
2.3 Method of use and dosage
(1) The adhesive is uniformly added to the material, and the ratio of the material to the adhesive is determined according to the material composition, particle size and specific surface area, and the general increase is 2-3%.
(2) Wet the material and spray the appropriate amount of water according to the humidity of the material.
(3) After stirring well, hold the hand into a ball and press the ball.
Mineral powder binder KF02
If the active calcium oxide in the dust removal ash is not digested in advance, it will seriously affect the molding rate and cold strength of the pellets in the later stage, and even the phenomenon of chalking will occur. However, some manufacturers feel that early digestion will increase production costs and extend production time. Therefore, in the case of non-digestion of dust removal ash, the differentiation and lack of strength of cold pressing pellets have been developed, and a new adhesive KF02 has been developed.
3.1 Mechanism of mineral powder binder KF02 water absorption expansion and disintegration of calcium antioxidant
The calcium oxide in the dust removal ash absorbs water absorption and expands by 1.5 to 2.5 times, which is the key to the problem; only by preventing this expansion can the disintegration problem be solved; through the analysis of various raw material components, the problem is fundamentally solved.
The acidic environment formed and the alkaline environment of calcium oxide cancel each other out, and the dissolved SO and CaO form a film, and the hydration process of CaO is blocked, so that the curing shrinkage effect becomes the main role, and directly bypasses the link of calcium oxide digestion and expansion, and directly solidifies from calcium oxide to the comprehensive crystal lattice of calcium carbonate and other components.
3.2 Scope of Application
Used in dust removal ash containing uncaliminated calcium oxide, it can effectively counteract the decomposition and expansion of calcium oxide in contact with water, resulting in the phenomenon of cracking and disintegration of products. The adhesive can also be used in other calcium oxide-containing applications (such as building materials and other materials that need to be digested), and can also be used as a normal binder in materials that do not contain calcium oxide.
3.3 Application characteristics
Used in dust ash balls containing less than 45% of unconstituted calcium oxide, effectively offset the expansion of calcium oxide in contact with water digestion, and the compressive strength reaches more than 100kg (with the composition of dust removal ash, there is a certain change, the lowest effective dose, the minimum dry strength is not less than 50kg)
The product can fight digestion expansion for a long time (several months) without strength reduction or disintegration; in fact, when a sufficient amount of KF02 is added, the ball made of dust ash containing a high (up to 45%) of undissolved calcium oxide is left for a year without any signs of disintegration, and the compressive strength reaches and remains above 100 kg.
3.4 Method of use and dosage
Add 5 to 10% of the amount, use a feeder or directly add to the dust removal ash, mix well and add water to stir evenly to press the ball.
3.5 Precautions
The amount of water added by the product is slightly less than that of other adhesives (subject to the hand grasp into a ball and kneading can be scattered), the water mixing time should not be too long, in order to prevent early curing; the product is pressed into a slightly lower humidity strength, after 2 hours can have a certain pressure bearing capacity, 6 hours after reaching a higher initial strength, 24 hours basically reach the final strength.
4. Summary
Due to the continuous growth of steel production capacity, the demand for iron ore continues to rise, the contradiction between supply and demand is getting bigger and bigger; coupled with the increasingly stringent requirements of environmental protection; the secondary recycling of dust removal ash, sludge and steel slag is of great significance, which can not only reduce production costs and increase output, but also solve the problem of environmental pollution and alleviate resource shortages. The economic and social benefits are very obvious.