A method for carbon addition and pelletizing of stainless steel dust for improving the recovery rate of metal elements

Abstract

A method for carbon addition and pelletizing of stainless steel dust for improving the recovery rate of metal elements. Aiming at the problems of low briquetting quality, many broken materials, high powder rate during loading, easy dusting, unsatisfactory reduction kinetics conditions, low recovery rate of chromium, nickel and iron, and high cost of temperature increase by carbon addition with coke, a systematic process that synergizes low-cost briquetting and efficient use of pellets is developed. This process fully considers the physical and chemical properties of the materials, deeply grasps the key points of briquetting technology, and fully considers the process characteristics of the electric arc furnace. With low input and relatively simple operation, it realizes the improvement of the strength of stainless steel dust pellets and the reduction of powder and dust during handling. At the same time, it improves the reduction recovery rate of valuable metal elements in the pellets, and uses cheap powdered carbon (dry quenching coke dust) to replace the relatively expensive lump coke. It realizes the synergy of briquetting and improvement of metal recovery rate, the combination of utilization of dust and utilization of carbon powder, and overall significantly improves the economic benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy, and relates to a method for treating stainless steel dust, specifically a method for carbon addition and pelletizing of stainless steel dust to improve the recovery rate of metal elements. Background Art

[0002] During the stainless steel steelmaking process, a considerable amount of dust is generated. There is a type of 300 series dust with a typical composition as shown in Table 1 below.

[0003] Table 1 Composition Table of 300 Series Stainless Steel Dust

[0004]

[0005] The above dust has extremely fine particle size and contains relatively high amounts of iron oxide and chromium oxide. If it can be recycled in the metallurgical process to reduce and utilize chromium and iron metals, it is beneficial to reduce the enterprise cost while disposing of solid waste. At present, domestic stainless steel enterprises mainly adopt the following two modes for disposing of stainless steel dust:

[0006] First, set up a special bunker, and produce sinter ore in sintering batching together with stainless steel pickling sludge for supply to the steelmaking process. Most domestic stainless steel enterprises are independent stainless steel production lines with unified design and one-time construction for sintering, ironmaking, steelmaking, and rolling. This recycling mode can make full use of valuable elements and has relatively significant economic and environmental benefits. However, for enterprises with successive construction and commissioning of ironmaking and steelmaking blast furnaces, since there are no neatly arranged multiple independent sintering-ironmaking-steelmaking-rolling through production lines, after the blast furnace taps, the molten iron is cross-supplied to the carbon steel steelmaking or stainless steel steelmaking system, and the chromium-nickel-containing molten iron cannot be specifically supplied to stainless steel steelmaking. After a part of the molten iron is supplied to carbon steel, not only the chromium and nickel elements cannot be utilized, but also the quality risk of carbon steel products is increased. In this way, only the environmental benefits can be reflected, and the economic benefits cannot be reflected, and there are also problems such as fine material dusting and difficult discharging of stockpiled materials during sintering.

[0007] Second, build a cold pressing ball production line in the stainless steel plant of the enterprise, cold press the dust together with stainless steel acid sludge, and then supply it to the stainless steel electric arc furnace and de-P converter. When used in the electric arc furnace, due to the use of nickel iron blocks and high-carbon ferrochrome as metal materials, together with the addition of coke and injection of carbon powder, a high-carbon molten pool is formed, which can reduce most of the nickel and iron in the dust, and achieve a 50-60% reduction of chromium. Although the economy is not as good as using it in sintering, it realizes that the solid waste does not leave the factory, does not spread, and has self-circulation, which belongs to a relatively reasonable method that takes into account both economic and environmental benefits.

[0008] In addition, in order to ensure sufficient heat in the AOD furnace in the post-treatment process of the electric arc furnace, it is often necessary to add an additional part of coke while using high-carbon ferronickel and ferrochrome. While the electric arc furnace blows oxygen and burns to generate heat, the carbon content in the molten pool is increased, so that there is sufficient combustion heating agent during the argon-oxygen refining in the AOD furnace, the molten pool temperature in the AOD furnace is increased, and the effect of decarburization and chromium protection is improved. Although lump coke has high strength and appropriate particle size and is convenient to add through the bunker, its price is often above 2000 yuan, which is not economical enough.

[0009] Although the second method of stainless steel dust removal ash is feasible, due to the characteristics that the all-powder materials and high-calcium oxide materials are not easy to form balls, there are also problems of high briquetting cost (the high cost is mainly reflected in the high proportion of binder and the high binder cost) and large powder rate during loading and easy dusting. At the same time, only relying on the carbon in the molten pool to reduce metal oxides, the reduction atmosphere is insufficiently created, the reduction kinetic conditions are not ideal, and the recovery rates of iron, nickel, especially chromium are not high, and there is still a large room for improvement in the recovery rate. At present, there is no relevant technology application in the domestic field of stainless steel dust removal ash pelletizing to solve the above problems.

[0010] Therefore, it is very necessary to develop a system process that synergistically combines low-cost briquetting and efficient use of pellets. This process can fully consider the physical and chemical properties of the materials, deeply master the key points of briquetting technology, fully consider the process characteristics of the electric arc furnace, and achieve the improvement of the strength of stainless steel dust removal ash pellets with low investment and simple operation, reduce the powder and dust during the transfer process, further improve the reduction recovery rate of valuable metal elements in the pellets, and at the same time can utilize the characteristics that cheap carbon is mostly in powder form, add cheap carbon into the balls, which is convenient to add and replace the relatively expensive lump coke originally added to increase the carbon content in the molten pool of the stainless steel electric arc furnace, and achieve a significant improvement in the overall economic benefits. Summary of the Invention

[0011] In view of the problems existing in the above background technology, the present invention provides a carbon addition pelletizing and using method for stainless steel dust removal ash to improve the recovery rate of metal elements, and the specific content is as follows:

[0012] 1. Carbon addition pelletizing method for stainless steel dust removal ash

[0013] 1) Prepare materials and mix. The stainless steel dust removal ash, stainless steel scale, dry coke quenching dust, organic powder A, inorganic powder B and water after dissolution are placed in a large wheel-type mixer according to the ratio of 70:5:15:2:3:5 for mixing, and the number of rotations of the mixer rollers is not less than 100 circles; the mixed materials are transported to a large cone-bottom storage bin through a belt conveyor for material sealing, and the material sealing time is not less than 3 hours;

[0014] 2) Primary pelletizing: Electromagnetic vibration feeding is carried out from the bottom of the large conical-bottom storage bin. The material is transported by the feeding belt to the primary pair-roll pelletizing machine for the first-pass pelletizing. A spiral forced feeder is installed at the top of the pelletizing machine to ensure the filling rate of the ball sockets on the pair-roll surface.

[0015] 3) Final pelletizing: The pellets from the primary pelletizing enter the ball conveying belt through the inclined chute at the bottom of the pelletizing machine and supply the final pair-roll pelletizing machine. The final pair-roll pelletizing machine is the same as the primary pair-roll pelletizing machine but has deeper ball sockets. The pellets after final pelletizing enter the ball output belt through the inclined sieve plate at the bottom of the pelletizing machine. The crushed and powdered materials are transported by the under-sieve return belt to the primary pair-roll pelletizing machine for continued primary pelletizing, and so on in a cycle.

[0016] During the above pellet preparation process, the stainless steel dust removal ash is stainless steel 300 series dust removal ash, with a particle size of less than 100 mesh accounting for 70% - 80%. The typical components are: TFe: 36% - 40%, Ni: 1.5% - 2%, Cr: 10% - 15%, SiO2: 4% - 5%, CaO: 20% - 25%, MgO: 2% - 4%, S: 0.1% - 0.2%, P: 0.015% - 0.03%. Its functions are: to provide valuable elements Cr, Ni, and Fe in the form of oxides, and at the same time provide a part of CaO in the form of slaked lime, which can save the amount of lime used in the electric arc furnace, and realize partial carbonation consolidation through the reaction of slaked lime with carbon dioxide in the air, which is an auxiliary mechanism for ensuring pellet strength.

[0017] The main components of the stainless steel scale are: TFe: 58% - 64%, Cr2O3: 6% - 12%, NiO: 0.5% - 1.5%, SiO2: 0.8% - 1.6%, CaO: 0.1% - 0.5%, MgO: 0.01% - 0.1%, Al2O3: 0.1% - 0.5%, S: 0.04% - 0.06%, P: 0.01% - 0.03%; the particle size is 0 - 5 mm. Its functions are: to increase valuable elements Cr, Ni, and Fe in the form of oxides. Due to the relatively coarse particles, it can play the role of aggregate and improve the pellet strength.

[0018] The fixed carbon of the dry coke quenching dust removal ash is 78% - 80%, the ash content is 13% - 16%, the volatile matter is 1% - 2%, the sulfur is 0.9% - 1.2%, the moisture is less than 5%, and the particle size of less than 100 mesh accounts for more than 80%. Its functions are: to replace the original carbon-supplying material in the stainless steel electric arc furnace - lump coke to reduce the oxygen potential in the iron melt pool, and at the same time act as a reducing agent for metal oxides in the dust removal ash and a reducing atmosphere builder for the furnace gas near the pellet surface and slag surface.

[0019] Organic powder A is a preparation of modified starch and modified cellulose mixed in a ratio of 2:1. It is the main preparation for ensuring pellet strength. Through the unique aging hardening characteristics of the organic preparation, it ensures that the pellets have high late strength.

[0020] The inorganic powder B is a preparation made by mixing calcium-based bentonite and sodium-based bentonite in a ratio of 2:1. As an inorganic binder, it ensures that the newly pressed wet balls have a certain strength, facilitating the handling of the balls within a short period after pressing. It is an auxiliary mechanism for ensuring the strength of the pellets.

[0021] Water is a promoter for the full contact of the basic materials and the binder particles.

[0022] 2. Transfer of the stainless steel dust removal ash carbon-containing pellets

[0023] To reduce the proportion of carried powder and broken materials in the pellets, the following special transfer process is adopted:

[0024] 1) Ball discharging: Multiple groups of ball discharging belts are connected to convey the finished balls. Finally, the balls are stacked into an initial conical ball pile through an elevating angle adjustable ball discharging belt conveyor. The subsequent balls roll down successively with the initial ball pile as a buffer slope to reduce breakage. While discharging the balls, the elevating belt moves to one side, and finally a crater ridge-shaped ball pile is formed. After more than 12 hours of air drying and aging hardening, the balls are then shoveled and transported to a large pile for continued air drying. For production lines with sufficient space, more groups of belts are used to connect to control the distance of the circular ball pile. By using the elevating belt to create a quarter-circular short beam shape and stacking radially from the inside to the outside, the overturning can be reduced, and the amount of broken materials can be further reduced.

[0025] 2) The pellets in the large ball pile are taken according to the principle of first in, first out.

[0026] Mode 1 is to use a loader to load the balls into a vehicle with a well-sealed telescopic tarpaulin and transport them to the auxiliary material bin of stainless steel steelmaking. After starting the dust removal, the balls are dumped.

[0027] Mode 2 is to use a loader to feed the balls into a bin, and the bin uses electric vibration feeding to the conveyor belt under the bin. The conveyor belt directly delivers the pellets to the auxiliary material bin of the steelmaking process.

[0028] 3) The pellets in the bin are fed to the auxiliary material feeding belt through electric vibration and then transported to the steelmaking charging platform. They are charged into the high-level bin above the electric arc furnace by the charging trolley for standby.

[0029] 3. Use of the stainless steel dust removal ash carbon-containing pellets

[0030] On the basis of scientific pelletizing and transfer, in order to maximize the recovery rate of valuable metals in the stainless steel dust removal ash carbon-containing pellets, the following special feeding process is adopted under reliable theoretical support:

[0031] When the molten pool appears after the scrap steel and iron blocks in the electric arc furnace are melted under the action of the electric arc and oxygen lance, the stainless steel dust removal ash carbon-containing pellets are started to be added. The carbon-containing pellets are added in small amounts and multiple times. For a 100-ton electric arc furnace, 3 batches are added from the appearance of the molten pool to complete melting, with 1 ton in each batch; 3 batches are added during the molten pool heating-up stage after complete melting, with 1 ton in each batch, and no more pellets are added 10 minutes before tapping.

[0032] 4. Principle of Reduction of Stainless Steel Dust Removal Ash with Carbon Pellets and Improvement of Metal Recovery

[0033] The basic reaction of reducing chromium oxide in dust removal ash with solid carbon at a high temperature below 1600 °C in an electric arc furnace is as follows:

[0034] 2 / 3Cr2O3 + 2C = 4 / 3Cr + 2CO (1) ∆Gθ = 516890 - 339.5T The starting temperature of the reaction is 1250 °C

[0035] 2 / 3Cr2O3 + 26 / 9C = 4 / 9Cr3C2 + 2CO (2) ∆Gθ = 478234 - 347.15T The starting temperature of the reaction is 1100 °C

[0036] 2 / 3Cr2O3 + 18 / 7C = 4 / 21Cr7C3 + 2CO (3) ∆Gθ = 482281 - 343.54T The starting temperature of the reaction is 1130 °C

[0037] 2 / 3Cr2O3 + 54 / 23C = 4 / 69Cr 23 C6 + 2CO (4) ∆Gθ = 494369 - 341.72T The starting temperature of the reaction is 1175 °C

[0038] It can be seen that the reaction temperature for forming chromium carbides is lower than that for forming pure chromium, and the starting temperature of the reaction for forming carbides with a higher carbon content is lower than that for forming carbides with a lower carbon content. Therefore, the formation of carbides with a higher carbon content is more likely to occur preferentially. Due to the property of chromium and carbon to form stable carbides, the chromium obtained by reducing chromium oxide with a carbon reducing agent is Cr 23 Carbides of chromium in the form of C6, Cr7C3, and Cr3C2, etc. According to the principle of iron and steel metallurgy, the reduction temperature of Fe2O3 is about 900 °C. Therefore, the iron oxide in the dust removal ash is preferentially reduced at a lower temperature than Cr2O3. It is mutually melted with chromium carbide to form binary carbides such as (Cr, Fe)3C2, (Cr, Fe)7C3, (Cr, Fe) 23 C6 and enter the electric arc furnace molten bath. The formation of these composite carbides not only reduces the melting point of the alloy formed by iron, chromium, and carbon, but also, from the perspective of chemical equilibrium, reduces the activity of Cr, enabling the reduction reaction to proceed at a lower temperature. Therefore, the presence of iron in the dust removal ash is beneficial to the reduction of chromium oxide in the dust removal ash.

[0039] When the temperature of the electric arc furnace molten bath further increases, the later-reduced Cr2O3 decarburizes the carbides that have been reduced, and the reaction is as follows:

[0040] 14 / 5Cr3C2 + 2 / 3Cr2O3 = 4 / 3Cr + 6 / 5Cr7C3 + 2CO (5) ∆Gθ = 543609 - 309.45T The starting temperature of the reaction is 1490 °C

[0041] 2Cr7C3 + 2 / 3Cr2O3 = 2 / 3Cr 23 C6 + 2CO (6) ∆Gθ = 621315 - 328.13T The starting temperature of the reaction is 1620 °C

[0042] 1 / 3Cr 23 C6 + 2 / 3Cr2O3 = 9Cr + 2CO (7) ∆Gθ = 655173 - 326.67T The starting temperature of the reaction is 1730 °C

[0043] The decarburization temperature of chromium oxides is relatively high. In a stainless - steel electric - arc furnace, the temperature can only reach above 1600 °C before tapping. Therefore, the decarburization reaction of equation (5) mainly occurs, the reaction of equation (6) occurs very little, and the reaction of equation (7) only occurs in the high - temperature arc zone (accounting for less than 20% in all decarburization reactions). The metallic chromium or chromium carbide formed by the decarburization reaction becomes a part of the electric - arc - furnace bath.

[0044] Finally, through the impact of the electric arc, the stirring of injecting carbon powder, and the re - mixing during the tapping of the electric - arc furnace, a stainless - steel mother liquor containing elements such as chromium, nickel, iron, and carbon with a more uniform composition and temperature is formed and fed into the AOD refining furnace for subsequent process treatment of decarburization, chromium preservation, and impurity removal.

[0045] In summary, the initial stage of reduction of stainless steel dust starts with the reduction of iron oxides. As the temperature rises (above 1200°C), the part of chromium oxide in contact with the reducing agent begins to slowly reduce to form chromium and iron composite carbides. The chromium carbides generated by the reduction reaction, together with the carbonaceous reducing agent, continue to reduce the residual Cr2O3 at a higher temperature (above 1600°C), and the carbides are decarburized. Since the main charge in the electric arc furnace is high-carbon nickel-iron blocks with a small amount of high-carbon ferrochrome blocks, there are two types of reduction reactions after the metal material in the furnace melts and a molten pool appears. One is the reduction reaction of carbon inside the molten pellets (that is, part of the slag phase) to the oxides, and the other is the reduction reaction of carbon in the molten pool to the oxides in the slag phase (part of the carbon in the molten pool also comes from the dissolution of carbon in the carbon-matched pellets). Since the oxide and carbon particles in the carbon-matched pellets are extremely fine and in close contact, the reduction reaction is mainly controlled by the diffusion of the reduction products, and the mass transfer between carbon and metal oxides is not the main limiting link of the reaction rate during the entire reduction stage. Overall, the reduction kinetic conditions are improved, and the reduction rates of chromium and iron are increased. During the reduction process, C captures O in the oxides and part of the C is burned to form more CO, which strengthens the reducing atmosphere above the molten pool and around the pellets (CO is produced while being sucked by the exhaust system on the furnace cover, and there is a slight negative pressure in the furnace, so there is no need to worry about CO poisoning. In fact, metallurgical furnaces such as converters and electric furnaces produce CO every moment), which further promotes the improvement of the reduction rates of chromium, iron and nickel.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1) Taking into full account the physical and chemical properties of the materials, mastering the key points of the briquetting technology, and taking into full account the process characteristics of the electric arc furnace, the strength of the stainless steel dust ash pellets can be improved with reliable principles, low costs, and convenient operations, and the powder and dust in the transportation process can be reduced. The recovery rate of the valuable metal elements in the pellets can be further improved. At the same time, cheap carbon (CDQ dust ash) can be used to replace the expensive lump coke originally added to the stainless steel electric arc furnace to increase the carbon content of the molten pool, which has achieved a significant improvement in economic benefits overall;

[0048] 2) With a new idea, meticulous design and operation procedures, the company has achieved efficient utilization of stainless steel dust, iron oxide scale and dry quenching dust, which is difficult to handle solid waste, reducing the environmental pressure of the company, improving the company's benefits, and is conducive to the healthy and high-quality development of the company;

[0049] 3) After successful application, it can set up a model in the metallurgical industry, have a demonstration effect, and can drive the solid waste utilization work of metallurgical enterprises, with economic, social and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a process flow chart of the present invention. Detailed Implementation Manner

[0051] The following will explain the process of the present invention in detail with reference to the accompanying drawings.

[0052] Taking the stainless steel branch of a certain steel enterprise in the west as an example, the stainless steel smelting process of EAF (electric arc furnace) - AOD (refining furnace) - LF (refining furnace) - VOD (refining furnace) - CCM (continuous casting machine) is adopted, and the stainless steel dust removal ash and stainless steel scale generated during its production process are recycled. Among them, the stainless steel dust removal ash uses the stainless steel 300 series dust removal ash, and its main components are shown in Table 2 below.

[0053] Table 2 Composition Table of Stainless Steel 300 Series Dust Removal Ash

[0054]

[0055] The main components of the stainless steel scale are shown in Table 3 below, and the particle size is 0 - 5 mm.

[0056] Table 3 Composition Table of Stainless Steel Scale

[0057]

[0058] According to Figure 1 After pelletizing according to the shown process and putting it into the electric arc furnace for use, the effect is remarkable. The recovery rate of nickel increases from the original 70% - 80% to 80% - 90%; the recovery rate of Cr increases from the original 50% - 60% to 60% - 75%, with an increase of about 10% - 15%; the recovery rate of Fe increases from the original 55% - 65% to 70% - 80%, and the effect is remarkable. The only increase is the power consumption. The reason is that the reduction of Cr, Ni, and Fe oxides by C is an endothermic reaction, and the process of the present invention prolongs the reduction reaction in the furnace, which will inevitably cause an increase in power consumption.

[0059] Calculation Basis

[0060] The price of high-carbon ferrochrome containing 55% chromium locally is taken as 7000 yuan / ton, the price of low-nickel ferroalloy containing 16% Ni is taken as 16000 yuan / ton, the price of scrap steel is taken as 3000 yuan / ton, the price of self-produced coke is taken as 2700 yuan / ton, the market price of dry quenched coke ash is taken as 700 yuan / ton, and the local electricity price is 0.5 yuan / KWh; the ferrochrome contains 55% Cr and the recovery rate is 90%, the nickel ferroalloy contains 16% Ni and the recovery rate is 95%; the nominal capacity of the electric arc furnace is taken as 100 tons, and the addition amount of carbon pellets per furnace is 6 tons.

[0061] Assume that the carbon pellets contain 10% Cr and 1.5% Ni. Then when the recovery rates of Cr and Ni increase by 10%, the power consumption increases by 26 KWh. The calculation process is as follows:

[0062] 1) When the chromium recovery rate in the pellets increases by 10%, the corresponding chromium amount is 6×10%×10% = 0.06 tons. This is equivalent to using 0.06 / (55%×90%) = 0.121 tons less ferrosilicon chromium. The absolute benefit per furnace is 0.121×7000 = 847 yuan, and the cost per ton of steel is reduced by 847 / 100 = 8.47 yuan / ton.

[0063] 2) When the Ni recovery rate in the carbon ash pellets increases by 10%, the corresponding Ni amount is 6×1.5%×10% = 0.009 tons. This is equivalent to using 0.009 / (16%×95%) = 0.0592 tons less ferronickel. The absolute benefit per furnace is 0.0592×16000 = 947 yuan, and the cost per ton of steel is reduced by 947 / 100 = 9.47 yuan / ton.

[0064] 3) Replacing coke with low-cost carbon results in an absolute benefit of 6×15%×(2700 - 700) = 1800 yuan per furnace, and the cost per ton of steel is reduced by 1800 / 100 = 18 yuan / ton.

[0065] 4) The increase in power consumption causes the cost per ton of steel to increase by 26×0.5 = 13 yuan / ton, and the cost per furnace increases by 13×100 = 1300 yuan.

[0066] In summary, after using the process described in this patent, the benefit per furnace is 847 + 947 + 1800 - 1300 = 2294 yuan, and the cost per ton of steel is reduced by 2294 / 100 = 22.94 yuan / ton.

Claims

1. A method for carbon-containing pelletizing of stainless steel dust for improving the recovery rate of metal elements, characterized in that, It includes the following steps: 1) Prepare materials and mix them. Put the stainless steel dedusting ash after decoagulation, stainless steel scale, dry quenching coke dedusting ash, organic powder A, inorganic powder B and water in a large wheel mill mixer according to the ratio of 70:5:15:2:3:5 for mixing. The number of rotations of the mixer roller is not less than 100 circles. The mixed materials are transported to a large cone-bottom storage bin by a belt conveyor for material retting, and the retting time is not less than 3 hours. The stainless steel dedusting ash is the dedusting ash of stainless steel 300 series, with a particle size of less than 100 mesh accounting for 70% - 80%. The typical components are: TFe: 36% - 40%, Ni: 1.5% - 2%, Cr: 10% - 15%, SiO2: 4% - 5%, CaO: 20% - 25%, MgO: 2% - 4%, S: 0.1% - 0.2%, P: 0.015% - 0.03%. The main components of the stainless steel scale are: TFe: 58% - 64%, Cr2O3: 6% - 12%, NiO: 0.5% - 1.5%, SiO2: 0.8% - 1.6%, CaO: 0.1% - 0.5%, MgO: 0.01% - 0.1%, Al2O3: 0.1% - 0.5%, S: 0.04% - 0.06%, P: 0.01% - 0.03%; the particle size is 0 - 5mm. The fixed carbon of the dry quenching coke dedusting ash is 78% - 80%, the ash content is 13% - 16%, the volatile matter is 1% - 2%, the sulfur is 0.9% - 1.2%, the water content is less than 5%, and the particle size of less than 100 mesh accounts for more than 80%. The organic powder A is a preparation of modified starch and modified cellulose mixed according to 2:

1. The inorganic powder B is a preparation of calcium-based bentonite and sodium-based bentonite mixed according to 2:

1. 2) Primary pressure balling. Take materials by electric vibration from the bottom of the large cone-bottom storage bin. The materials are transported to the primary pressure pair-roller briquetting machine by a feeding belt for the first pass of briquetting. The pressure of the primary pressure pair-roller briquetting machine is 20 - 30 Mpa, and a spiral forced feeder is set at the top of the briquetting machine to ensure the filling rate of the ball sockets on the pair-roller surface. 3) Final pressure balling. The pellets coming out of the primary pressure enter the ball conveying belt through the inclined chute at the bottom of the briquetting machine and supply materials to the final pressure pair-roller briquetting machine. The final pressure pair-roller briquetting machine is the same as the primary pressure pair-roller briquetting machine but has deeper ball sockets. The pressure of the final pressure pair-roller briquetting machine is 30 - 40 Mpa. The pellets after the final pressure enter the out-ball belt through the inclined sieve plate at the bottom of the briquetting machine. The crushed and powdered materials are transported to the primary pressure pair-roller briquetting machine by the sieve-bottom return belt for continuous primary pressure, and so on in a cycle. The finished pellets after final pressure balling are oval, thick in the middle and thin at both sides, with a length of 40 mm, a width of 25 mm, and a thickness of 15 mm.

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