Method for preparing reduced iron powder from cold-rolled oil sludge

Abstract

The invention discloses a method for preparing reduced iron powder from cold-rolled oil sludge. The method comprises the following steps: drying the cold-rolled oil sludge, and then crushing and ball-milling to obtain cold-rolled oil sludge powder of less than 100 meshes; the obtained cold-rolled oil sludge powder is fed into a chain grate machine to be preheated and is fed into a high-level stock bin 1 of a secondary reduction furnace, and the stock bin is connected with a distributor 1; the preheated primary reduced iron powder is fed into an overhead bunker 2 of the secondary reduction furnace, and the overhead bunker 2 is connected with a distributor 2; in a material distribution section of the secondary reduction furnace, a cold-rolled oil sludge powder layer with the thickness of 1-3mm is arranged on a steel belt of the secondary reduction furnace through a material distributor 1; continuously arranging a primary reduced iron powder layer with the thickness of 15-27mm on the cold-rolled oil sludge powder layer through a distributor 2 to obtain a mixed material layer; and the obtained mixture layer is fed into a reduction section of a secondary reduction furnace along with the steel belt, secondary fine reduction is conducted in the H2 atmosphere, and the reduced iron powder is obtained after aftertreatment.

Description

Technical Field

[0001] The invention belongs to the resource utilization of solid waste, and specifically relates to a method for preparing reduced iron powder by utilizing cold rolling sludge. Background Art

[0002] Cold rolling sludge is a solid waste generated by the acid rolling process of cold rolling thin plate mills, and it requires a lot of cost to dispose of it harmlessly. Research and analysis show that cold rolling sludge mainly contains three phases: solid, water, and oil, which are emulsified and mixed together. The solid phase is generated by the friction between the steel plate and the roller. It is actually micron-level metal iron filings, which are high-quality ferrous resources. The oil phase is a plastic organic material. Although outsourcing the harmless disposal of cold rolling sludge solves the environmental protection problem, it is costly and a waste of high-quality resources.

[0003] CN 106281635A proposes a method for recovering and purifying silicon steel cold-rolled emulsion sludge, which includes pulping, demulsification, silicon removal, separation, and extraction of the sludge to obtain different iron powders, rolling oils, and other products, which are then used. The method has a long process, consumes a large amount of organic solvents, requires relatively complicated separation equipment, and has a high cost for processing the sludge itself.

[0004] CN 104946893B proposes a method for extracting ultrafine iron from cold rolling sludge, which is also based on the separation, oil replacement, and organic solvent extraction methods to separate and treat the cold rolling sludge and obtain ultrafine iron powder. The separation and treatment also has the problems of high cost and long treatment process.

[0005] CN 108558156A provides a method for resource processing of oil sludge rolled in a cold-rolled steel mill, wherein the oil sludge is heated and dehydrated, catalytically cracked, and condensed to obtain light cracking oil, heavy cracking oil, cracking dry residue and other products. The method focuses on oil sludge cracking and is suitable for occasions where the oil content in the oil sludge is high, with an emphasis on oil recovery.

[0006] CN 108863426A proposes a lightweight ceramsite of cold-rolled oil sludge and a preparation method thereof, which mainly uses fly ash, bentonite and cold-rolled oil sludge to mix in a certain proportion, granulate, dry, roast and cool to obtain ultra-light ceramsite. This method is mainly a harmless disposal method for oil sludge, and does not realize the valuable utilization of resources in oil sludge. Summary of the invention

[0007] Reduced iron powder is a high-grade raw material used in the powder metallurgy industry and is indispensable for the manufacture of automobile and motorcycle related metal parts. The two-step reduction method is a classic process for producing reduced iron powder. The iron ore powder or iron oxide scale with high purity is subjected to primary pre-reduction and secondary fine reduction to varying degrees. After magnetic separation and purification, qualified reduced iron powder can be obtained. Reduced iron powder is relatively expensive in the market, mainly because high-purity iron ore powder and iron oxide scale are difficult to obtain, and the reduction cost is also high. Cold rolling sludge contains a large amount of micron-sized metal iron filings with high purity, which has the potential to be used in the production of two-step reduced iron powder.

[0008] The purpose of the present invention is to provide a method for preparing reduced iron powder by using cold rolling sludge, and the cold rolling sludge is treated and used in a secondary reduction process to replace conventional raw materials, which not only saves disposal costs but also realizes high value-added resource utilization of steel solid waste.

[0009] In order to achieve the above purpose, the technical solution is as follows:

[0010] A method for preparing reduced iron powder from cold rolling sludge comprises the following steps:

[0011] 1) drying the cold rolled oil sludge, crushing and ball milling to obtain cold rolled oil sludge powder with a size of less than 100 meshes;

[0012] 2) The obtained cold-rolled oil sludge powder is sent to a chain grate for preheating, and then sent to a high-level silo 1 of a secondary reduction furnace, which is connected to a distributor 1;

[0013] 3) The preheated primary reduced iron powder is fed into the secondary reduction furnace high-level silo 2, which is connected to the distributor 2;

[0014] 4) In the secondary reduction furnace charging section, a cold-rolled oil sludge powder layer with a thickness of 1 to 3 mm is arranged on the secondary reduction furnace steel strip by the charging device 1; a primary reduced iron powder layer with a thickness of 15 to 27 mm is further arranged on the cold-rolled oil sludge powder layer by the charging device 2 to obtain a mixed material layer;

[0015] 5) The obtained mixed material layer is sent to the reduction section of the secondary reduction furnace along with the steel belt, and is subjected to secondary fine reduction in a H2 atmosphere, and then post-processed to obtain reduced iron powder.

[0016] In the above scheme, the cold-rolled sludge in step 1) is a solid-water-oil three-phase mixture, with a water content of 15% to 30%, an oil content of 5 to 20%, and a solid content of 60 to 80%; its solid phase chemical composition is: TFe≧92.0%, C≦3.0%, O≦5.0%; the remainder is other alloy elements or unavoidable impurity elements; and the content of particles below 200 mesh in the solid phase is greater than 90%.

[0017] In the above scheme, the drying temperature in step 1) is 150-180° C., and the drying time is 60-90 min.

[0018] In the above scheme, the preheating temperature in step 2) is 200-300° C., and the preheating time is 10-15 minutes.

[0019] In the above scheme, step 2) the chain grate preheating process is carried out in a N2 protective atmosphere, and the secondary reduction furnace high-level silo 1 and the transfer channel between it and the chain grate are both in a N2 protective atmosphere; step 3) the secondary reduction furnace high-level silo 2 and the transfer channel between it and the primary reduced iron powder are both in a N2 protective atmosphere.

[0020] In the above scheme, the once reduced iron powder in step 3) is an intermediate product obtained by a pre-reduction in a two-step reduced iron powder production process, wherein TFe≧90.0%, C≦5.0%, O≦5%, and the remainder is other alloy elements or unavoidable impurity elements.

[0021] In the above scheme, the temperature of the primary reduced iron powder after preheating in step 3) is 500-700°C.

[0022] In the above scheme, the thickness of the mixed material layer in step 4) does not exceed 30 mm.

[0023] In the above scheme, in step 5), the reduction temperature is 900-1100° C., and the reduction time is 180-300 min.

[0024] In the above scheme, the reduced iron powder obtained in step 5) has TFe≧98.0%, C≦1.0%, O≦0.5%, and the remainder is other alloy elements or inevitable impurity elements; the content of particles below 200 mesh is greater than 90%.

[0025] The cold rolling sludge used in the present invention has a solid-water-oil three-phase structure, wherein the solid phase mainly comes from the friction between the roller and the surface of the steel plate, and the metal iron scraps are generated. The roller and steel are both steel materials, so the chemical essence of the iron scraps is mainly steel and a small amount of iron oxide, and its particle size is in the micron level. The oil phase is mainly the lubricating oil used in the rolling process. The oil undergoes condensation and other reactions at high temperatures, and after losing water, it has thermosetting properties and is converted into a solid. The present invention uses a relatively high temperature for drying, and after the water in the sludge is evaporated, the material is converted into agglomerates, and the sludge can be further processed into powder by secondary crushing and grinding for reduction use.

[0026] Due to the physicochemical properties of the sludge solid phase, its TFe is higher than that of the primary reduced iron powder, and its particle size is equivalent to that of the primary reduced iron powder. Therefore, it can be directly subjected to secondary fine reduction, eliminating the need for a pre-reduction process and saving a lot of energy consumption and costs.

[0027] Secondary fine reduction usually uses hydrogen to further reduce and deoxidize the iron powder after the primary pre-reduction, as shown in Formula 1 and Formula 2, and then cooperates with subsequent magnetic separation and other processes to remove impurities to obtain high-purity reduced iron powder.

[0028] Fe2O3 + 3H2 = 2Fe + 3H2O Formula 1

[0029] FeO + H2 = Fe + H2O Formula 2

[0030] The present invention first lays an oil sludge layer on the steel strip through a distributor, and then lays a primary reduced iron powder layer on the oil sludge layer. The electric heater is arranged between the support rollers of the reduction section, and the steel strip first obtains heat and conducts it to the oil sludge layer. The oil sludge contains oil in addition to iron filings. In a non-oxidizing atmosphere, the oil material decomposes at high temperature to produce hydrocarbons, which react with oxygen in the iron filings and the primary reduced iron powder, as shown in Formulas 3 and 4, which helps to obtain high-quality reduced iron powder and realizes the harmlessness of the oil material.

[0031] Fe2O3 + C x H y = 2Fe + xCO2 + (y / 2)H2O Formula 3

[0032] FeO + C x H y = 2Fe + xCO2 + (y / 2)H2O Formula 4

[0033] H2 and hydrocarbons penetrate into the iron powder layer from the upper and lower directions respectively, ensuring the effect and quality of the secondary fine reduction process.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The method for preparing reduced iron powder from cold-rolled sludge of the present invention combines the solid waste of steel enterprises with the powder metallurgy industry, fully utilizes the generation principle of cold-rolled sludge and the essential characteristics of high solid-phase metallic iron content, and uses cold-rolled sludge as raw material, which not only solves the environmental protection problem of harmless disposal of solid waste and reduces disposal costs, but also reduces one reduction process compared to conventional raw materials such as oxidized iron scale, saves energy consumption and costs, and realizes high-value utilization of solid waste.

[0036] The present invention can be transformed by using the existing production line of reduced iron powder, with small additional investment and high technical and economic efficiency.

[0037] The oil substances in cold rolling sludge are environmental pollutants of this type of solid waste, but they are decomposed at high temperature to generate hydrocarbons in the secondary reduction process involved in the present invention. They have reducing properties and can be directly used in the iron powder reduction process to convert the pollutants into useful reducing agents. After oxidative decomposition, they are non-toxic and harmless, turning waste into treasure. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 : The present invention utilizes cold rolling sludge to prepare reduced iron powder process flow chart.

[0039] Figure 2 : Schematic diagram of the secondary reduction furnace structure used in the present invention. DETAILED DESCRIPTION

[0040] The following examples further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0041] A specific implementation method provides a cold rolling sludge, which, after detection and analysis, has a water content of 18.3%, an oil content of 12.1%, and a solid content of 69.6%; its solid phase chemical composition is: TFe 92.7%, C 2.5%, O 4.4%; the remainder is other alloy elements or unavoidable impurity elements; its solid phase particle content below 200 mesh is 91.8%.

[0042] The specific embodiment provides a method for preparing reduced iron powder using cold rolling sludge. Figure 1 As shown:

[0043] 1) The cold-rolled sludge is sent to a dryer and dried at 150-180°C for 60-90 minutes; the dried cold-rolled sludge is successively sent to a jaw crusher and an impact crusher for two-stage crushing, and the materials after crushing are screened, and the materials above 1.18 mm are returned to the impact crusher for re-crushing, and the materials below 1.18 mm are sent to a ball mill; the grinding time is 15-30 minutes, and the sieving is carried out after grinding, and the part above 100 mesh is returned to the ball mill for re-grinding, and the part below 100 mesh is sent to the material yard for storage and standby use;

[0044] 2) The cold-rolled sludge powder obtained in the previous step is sent to the chain grate for preheating at a temperature of 200 to 300° C. for a preheating time of 10 to 15 minutes. After preheating, the material is immediately sent to the secondary reduction furnace high-level silo 1, which is connected to the distributor 1;

[0045] 3) The preheated primary reduced iron powder is fed into the secondary reduction furnace high-level silo 2, which is connected to the distributor 2;

[0046] 4) In the secondary reduction furnace feeding section, the feeder 1 is used to feed the steel strip of the secondary reduction furnace, and the thickness of the cold rolling sludge powder layer is 1 to 3 mm. The feeder 2 is used to feed the primary reduced iron powder to the cold rolling sludge powder layer, and the thickness of the primary reduced iron powder layer is 15 to 27 mm.

[0047] 5) The mixed material after distribution is sent to the reduction section of the secondary reduction furnace along with the steel belt, and is subjected to secondary fine reduction in a H2 atmosphere at a reduction temperature of 900-1100°C and a reduction time of 180-300 minutes;

[0048] 6) After secondary fine reduction, the material is cooled, screened, magnetically separated, and packaged to produce reduced iron powder products.

[0049] Specifically, the primary reduced iron powder is an intermediate product obtained by a primary reduction in the two-step reduced iron powder production process, wherein TFe≧90.0%, C≦5.0%, O≦5%, and the remainder is other alloy elements or unavoidable impurity elements. The temperature of the primary reduced iron powder after heating is 500-700°C.

[0050] Specifically, the specific embodiment provides an improved secondary reduction furnace, the structural schematic diagram of which is shown in FIG. Figure 2 The secondary reduction furnace is a belt reduction furnace, with a steel belt as the material transfer carrier, and the transfer power is transmitted by the wheel head roller and the support roller; the secondary reduction furnace is divided into a distribution section and a reduction section, the distribution section is provided with a distributor 1 and a distributor 2, the horizontal spacing between the distributors 1 and 2 is 0.4-0.8m, the horizontal spacing between the distributor 1 and the wheel head roller is 0.2-0.3m, the reduction section is provided with a secondary reduction furnace cover, a hydrogen delivery pipeline and other equipment, and an electric radiation tube heater is provided between the support rollers of the reduction section.

[0051] Example 1

[0052] A method for preparing reduced iron powder from cold rolling sludge comprises the following steps:

[0053] 1) The cold-rolled oil sludge is sent to a dryer and dried at 155°C for 65 minutes; the dried cold-rolled oil sludge is successively sent to a jaw crusher and an impact crusher for two-stage crushing, and the materials after crushing are screened, and the materials above 1.18 mm are returned to the impact crusher for re-crushing, and the materials below 1.18 mm are sent to a ball mill; the grinding time is 15 minutes, and the sieving is performed after grinding, and the part above 100 mesh is returned to the ball mill for re-grinding, and the part below 100 mesh is sent to the material yard for storage for standby use;

[0054] 2) The cold-rolled sludge powder obtained in the previous step is sent to the chain grate for preheating at a temperature of 220° C. for 11 minutes. After preheating, the material is immediately sent to the secondary reduction furnace high-level silo 1, which is connected to the distributor 1;

[0055] 3) The preheated primary reduced iron powder is fed into the secondary reduction furnace high-level silo 2, which is connected to the distributor 2;

[0056] 4) In the secondary reduction furnace feeding section, the feeder 1 is used to feed the steel strip of the secondary reduction furnace, and the thickness of the cold rolling sludge powder layer is 0.5 mm. The feeder 2 is used to feed the primary reduced iron powder to the cold rolling sludge powder layer, and the thickness of the primary reduced iron powder layer is 18 mm.

[0057] 5) The mixed material after laying is sent to the reduction section of the secondary reduction furnace along with the steel belt, and is subjected to secondary fine reduction in a H2 atmosphere at a reduction temperature of 950°C and a reduction time of 190 minutes;

[0058] 6) After secondary fine reduction, the material is cooled, screened, magnetically separated, and packaged to produce reduced iron powder products.

[0059] Example 2

[0060] A method for preparing reduced iron powder from cold rolling sludge comprises the following steps:

[0061] 1) The cold-rolled sludge is sent to a dryer and dried at 165°C for 75 minutes; the dried cold-rolled sludge is successively sent to a jaw crusher and an impact crusher for two-stage crushing, and the crushed materials are screened, and the materials above 1.18 mm are returned to the impact crusher for re-crushing, and the materials below 1.18 mm are sent to a ball mill; the grinding time is 20 minutes, and the sieving is performed after grinding, and the part above 100 mesh is returned to the ball mill for re-grinding, and the part below 100 mesh is sent to the material yard for storage for standby use;

[0062] 2) The cold-rolled oil sludge powder obtained in the previous step is sent to the chain grate for preheating at a temperature of 250°C for 12 minutes. After preheating, the material is immediately sent to the secondary reduction furnace high-level silo 1, which is connected to the distributor 1;

[0063] 3) The preheated primary reduced iron powder is fed into the secondary reduction furnace high-level silo 2, which is connected to the distributor 2;

[0064] 4) In the secondary reduction furnace feeding section, the feeder 1 is used to feed the steel strip of the secondary reduction furnace, and the thickness of the cold rolling sludge powder layer is 1.5 mm. The feeder 2 is used to feed the primary reduced iron powder to the cold rolling sludge powder layer, and the thickness of the primary reduced iron powder layer is 23 mm.

[0065] 5) The mixed material after distribution is sent to the reduction section of the secondary reduction furnace along with the steel belt, and is subjected to secondary fine reduction in a H2 atmosphere at a reduction temperature of 1000°C and a reduction time of 240 minutes;

[0066] 6) After secondary fine reduction, the material is cooled, screened, magnetically separated, and packaged to produce reduced iron powder products.

[0067] Example 3

[0068] A method for preparing reduced iron powder from cold rolling sludge comprises the following steps:

[0069] 1) The cold-rolled oil sludge is sent to a dryer and dried at 180°C for 90 minutes; the dried cold-rolled oil sludge is successively sent to a jaw crusher and an impact crusher for two-stage crushing, and the materials after crushing are screened, and the materials above 1.18mm are returned to the impact crusher for re-crushing, and the materials below 1.18mm are sent to a ball mill; the grinding time is 30 minutes, and the sieving after grinding, the part above 100 mesh is returned to the ball mill for re-grinding, and the part below 100 mesh is sent to the material yard for storage for standby use;

[0070] 2) The cold-rolled sludge powder obtained in the previous step is sent to the chain grate for preheating at a temperature of 290° C. for 15 minutes. After preheating, the material is immediately sent to the secondary reduction furnace high-level silo 1, which is connected to the distributor 1;

[0071] 3) The preheated primary reduced iron powder is fed into the secondary reduction furnace high-level silo 2, which is connected to the distributor 2;

[0072] 4) In the secondary reduction furnace feeding section, the feeder 1 is used to feed the steel strip of the secondary reduction furnace, and the thickness of the cold rolling sludge powder layer is 3 mm. The feeder 2 is used to feed the primary reduced iron powder to the cold rolling sludge powder layer, and the thickness of the primary reduced iron powder layer is 27 mm.

[0073] 5) The mixed material after distribution is sent to the reduction section of the secondary reduction furnace along with the steel belt, and is subjected to secondary fine reduction in a H2 atmosphere at a reduction temperature of 1100°C and a reduction time of 300 minutes;

[0074] 6) After secondary fine reduction, the material is cooled, screened, magnetically separated, and packaged to produce reduced iron powder products.

[0075] The performance of the reduced iron powder obtained in Examples 1, 2 and 3 is shown in Table 1, and the product quality requirements are met.

[0076] Table 1

[0077] TFe C O Content of particles below 200 mesh Example 1 98.5％ 0.7％ 0.3％ 94.6％ Example 2 98.8％ 0.5％ 0.3％ 93.8％ Example 3 99.2％ 0.4％ 0.2％ 95.5％ .

Claims

1. A method for preparing reduced iron powder from cold-rolled oil sludge, characterized in that The steps include: 1) drying the cold rolled oil sludge, crushing and ball milling to obtain cold rolled oil sludge powder with a size of less than 100 meshes; 2) The obtained cold-rolled oil sludge powder is sent to a chain grate for preheating, and then sent to a high-level silo 1 of a secondary reduction furnace, which is connected to a distributor 1; 3) The preheated primary reduced iron powder is fed into the secondary reduction furnace high-level silo 2, which is connected to the distributor 2; 4) In the secondary reduction furnace charging section, a cold-rolled oil sludge powder layer with a thickness of 1 to 3 mm is arranged on the secondary reduction furnace steel strip by the charging device 1; a primary reduced iron powder layer with a thickness of 15 to 27 mm is further arranged on the cold-rolled oil sludge powder layer by the charging device 2 to obtain a mixed material layer; 5) The obtained mixed material layer is sent to the reduction section of the secondary reduction furnace along with the steel belt, and is subjected to secondary fine reduction in a H2 atmosphere, and then post-processed to obtain reduced iron powder.

2. The method for preparing reduced iron powder from cold-rolled sludge as claimed in claim 1, characterized in that Step 1) The cold rolling sludge is a solid-water-oil three-phase mixture, with a water content of 15% to 30%, an oil content of 5 to 20%, and a solid content of 60 to 80%; its solid phase chemical composition is: TFe≧92.0%, C≦3.0%, O≦5.0%; the remainder is other alloy elements or unavoidable impurity elements; and the content of particles below 200 mesh in the solid phase is greater than 90%.

3. The method for preparing reduced iron powder from cold-rolled oil sludge as claimed in claim 1, characterized in that Step 1) The drying temperature is 150-180° C. and the drying time is 60-90 min.

4. The method for preparing reduced iron powder from cold-rolled oil sludge as claimed in claim 1, characterized in that Step 2) The preheating temperature is 200-300°C and the preheating time is 10-15 minutes.

5. The method for preparing reduced iron powder from cold-rolled oil sludge as claimed in claim 1, characterized in that Step 2) The chain grate preheating process is carried out in a N2 protective atmosphere, and the secondary reduction furnace high-level silo 1 and the transfer channel between it and the chain grate are both in a N2 protective atmosphere; Step 3) The secondary reduction furnace high-level silo 2 and the transfer channel between it and the primary reduced iron powder are both in a N2 protective atmosphere.

6. The method for preparing reduced iron powder from cold-rolled oil sludge as claimed in claim 1, characterized in that Step 3) The once reduced iron powder is an intermediate product obtained by a pre-reduction in the two-step reduced iron powder production process, wherein TFe≧90.0%, C≦5.0%, O≦5%, and the remainder is other alloy elements or unavoidable impurity elements.

7. The method for preparing reduced iron powder from cold-rolled oil sludge as claimed in claim 1, characterized in that Step 3) The temperature of the primary reduced iron powder after preheating is 500-700°C.

8. The method for preparing reduced iron powder from cold-rolled oil sludge as claimed in claim 1, characterized in that In step 4), the thickness of the mixture layer does not exceed 30 mm.

9. The method for preparing reduced iron powder from cold-rolled oil sludge as claimed in claim 1, characterized in that In step 5), the reduction temperature is 900-1100° C. and the reduction time is 180-300 min.

10. The method for preparing reduced iron powder from cold-rolled oil sludge as claimed in claim 1, characterized in that Step 5) The reduced iron powder obtained has TFe≧98.0%, C≦1.0%, O≦0.5%, and the remainder is other alloy elements or inevitable impurity elements; the content of particles below 200 mesh is greater than 90%.

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