Method for strengthening reduction of dust and sludge containing iron and zinc through hydrocarbon coupling

Abstract

The invention discloses a method for strengthening reduction of iron-containing and zinc-containing dust mud by utilizing hydrocarbon coupling, which comprises the following steps: proportioning, mixing, forming / drying and roasting, the proportioning comprises the following steps: calculating materials, adding a reducing agent into the iron-containing and zinc-containing dust mud to obtain a uniformly mixed material, and the mixing comprises the following steps: adding a binder and water into the uniformly mixed material obtained by proportioning, uniformly mixing to obtain a mixed material, and molding / drying the mixed material to obtain the iron-containing and zinc-containing dust mud. And forming / drying: pressing the mixture into balls, drying to obtain dry balls, and determining the H / C molar ratio in the dry balls. And roasting: performing reduction roasting on the dry pellets in an inert atmosphere, and cooling to obtain metallized pellets. Biomass or pyrolytic carbon is adopted to partially replace coke powder to serve as a reducing agent, efficient reduction is achieved through a synergistic mechanism, the cost of the reducing agent is reduced, carbon emission is reduced, the hydrogen-containing reducing agent obtained through pyrolysis in the reaction process and a graded temperature regulation and control reduction technology can be utilized, the hydrogen-containing reducing agent participates in the reaction in the whole reduction process, and the reduction efficiency is improved. And traditional carbon thermal reduction is optimized into hydrocarbon coupling reduction, and the metallization ratio of the pellets is increased.

Description

Technical Field

[0001] The present invention relates to the field of recycling secondary resources in metallurgy, and particularly to a method for strengthening the reduction of iron-zinc-containing dust and sludge by carbon-hydrogen coupling. Background Art

[0002] China's crude steel output has exceeded 1 billion tons for many consecutive years, ranking first in the world. During the entire steel smelting process, a large amount of iron-zinc-containing dust and sludge is generated, and its generation amount is about 3% - 4% of the crude steel output, with the current annual output exceeding 30 million tons. The iron-zinc-containing dust and sludge have various types and complex compositions. They contain valuable elements required for steel production such as iron (20% - 50%), calcium (1% - 10%), carbon (5% - 20%), etc.; they also contain elements that are not conducive to steel production such as zinc (1% - 15%), potassium (0.1% - 2%), sodium (0.1% - 2%), etc., thus restricting its application in steel production. As a typical hazardous waste containing heavy metal elements, the stacking of iron-zinc-containing dust and sludge will cause great harm to the environment, so it must be properly disposed of.

[0003] Currently, the treatment of iron-zinc-containing dust and sludge mainly relies on carbothermal reduction. By adding pulverized coal or coke powder as a reducing agent, reduction roasting is carried out in a rotary hearth furnace or a rotary kiln. The zinc oxide in the iron-zinc-containing dust and sludge is reduced to volatile zinc vapor at high temperature, enters the condensation collector with the smoke and dust, and is oxidized again, and secondary zinc oxide is obtained through enrichment. The rotary kiln process is suitable for treating high-zinc dust and sludge, but has a low filling rate and a low metallization rate of direct reduced iron (DRI), and the phenomenon of ring formation often occurs during the production process. The rotary hearth furnace process has a large processing capacity, high metallization rate and dezincification rate; however, it also has the disadvantages of low thermal efficiency and high energy consumption. The energy required for both processes is provided by fossil energy, and a large amount of carbon dioxide will be emitted during the whole process. At the same time, most of the existing technologies use single coke powder or pulverized coal as a reducing agent and do not utilize the low-temperature advantage of hydrogen reduction; although there are also technologies that introduce hydrogen, they rely on external gas sources and have high costs. How to efficiently and environmentally utilize iron-zinc-containing dust and sludge is an urgent problem to be solved. Summary of the Invention

[0004] Aiming at the above problems existing in the prior art, the technical problem to be solved by the present invention is: how to efficiently and environmentally utilize iron-zinc-containing dust and sludge while reducing costs.

[0005] To solve the above technical problem, the present invention can be achieved through the following technical solutions: A method for strengthening the reduction of iron-zinc-containing dust and sludge by carbon-hydrogen coupling, comprising the following steps:

[0006] (1) Batching: Based on the main components of the iron-zinc-containing dust and sludge, batching calculations are carried out using the stoichiometric method, and a reducing agent is added to obtain a mixed material, wherein the weight ratio of the reducing agent to the iron-zinc-containing dust and sludge is 0.01 - 0.3.

[0007] (2) Mixing: Add a binder and water to the uniformly mixed material obtained in step (1). The addition amount of the binder is 0.5 wt% - 5 wt%. Mix the materials thoroughly to obtain a mixed material. The addition amount of the binder can be 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 4.0 wt%, 4.5 wt% or 5 wt%.

[0008] (3) Pelletizing / Drying: Press the mixed material obtained in step (2) into pellets, and the moisture content of the pellets can be controlled to 5 wt% - 12 wt%. Then dry the green pellets to obtain dry pellets.

[0009] (4) Roasting: Heat the dry pellets obtained in (3) from the lower limit temperature to the upper limit temperature of three temperature ranges of 500 °C - 800 °C, 800 °C - 1000 °C, and 1000 °C - 1300 °C at a heating rate of 5 °C / min - 60 °C / min. During the heating process in each temperature range, roasting is carried out at the corresponding temperature. The roasting time in each temperature range is 5 min - 20 min. After roasting in the three temperature ranges, cool to obtain metallized pellets. The entire roasting process is carried out in an inert atmosphere, and a hydrogen-containing reducing agent participates in the reaction throughout the reduction process. The contents of organic compounds and hydrogen elements in biomass and pyrolytic carbon are relatively high, and they will pyrolyze and gasify to generate hydrogen-containing reducing gases (such as H2, CH4, C2H4, etc.) under high-temperature conditions. The types of biomass and pyrolytic carbon will significantly affect the temperature range for generating hydrogen-containing reducing agents. For biomass without pyrolytic carbonization treatment, its carbon content is relatively low, and the pyrolysis gasification temperature of organic components is relatively low (200 - 400 °C). For the pyrolytic carbon obtained through the pyrolytic carbonization process, while its carbon content is relatively high, the pyrolysis gasification temperature of its hydrogen-containing reducing gas significantly increases (400 - 1300 °C). Based on this characteristic, by reasonably regulating the ratio of biomass to pyrolytic carbon, carbon-hydrogen coupling reduction throughout the process can be achieved.

[0010] Furthermore, the iron and zinc-containing dust and sludge used in step (1) include one or more of sintering ash, blast furnace ash, electric furnace ash, and iron and zinc-containing sludge.

[0011] Furthermore, the reducing agents used in step (1) include coke powder, biomass, or pyrolytic carbon of organic matter. The pyrolytic carbon of organic matter includes pyrolytic carbon of agricultural and forestry organic solid waste, pyrolytic carbon of domestic waste, pyrolytic carbon of industrial solid waste, power plant gasification ash, etc.

[0012] Furthermore, the reducing agent in step (1) is coke powder mixed with biomass or pyrolytic carbon. By utilizing the difference in the carbon reaction activity of coke powder, biomass, and pyrolytic carbon, the effect of enhanced reduction is achieved through reasonable proportioning. The H / C molar ratio in the uniformly mixed material is 0.1 - 0.8, and the carbon and hydrogen elements come from the iron and zinc-containing dust and sludge and the reducing agent.

[0013] Furthermore, the binder used in step (2) is an organic binder or an inorganic binder.

[0014] Furthermore, in the pelletizing process of step (3), the pressure is 10 - 20 Mpa, and the pellet size is 10 - 30 mm.

[0015] Furthermore, in step (4), hydrogen elements in biomass and pyrolytic carbon will pyrolyze to generate hydrogen-containing reducing agents such as hydrogen and methane in different temperature ranges. By optimizing the ratio, carbon-hydrogen coupling reduction throughout the process is achieved.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects:

[0017] The present invention uses biomass, organic pyrolytic carbon, and coke powder as reducing agents in the rotary hearth furnace process, which can not only effectively reduce the reducing agent cost for treating iron and zinc-containing dust sludge but also realize the recycling of carbon resources and reduce carbon emissions. At the same time, by utilizing the synergistic effect of the endogenous hydrogen in biomass and pyrolytic carbon and coke powder, the hydrogen-containing reducing agents pyrolyzed during the reaction process and carbon monoxide form a carbon-hydrogen coupling system, improving the reduction kinetic conditions and strengthening the reduction process. Combined with hierarchical temperature control and using the difference in the reaction activity of reducing agents, low-temperature and high-efficiency reduction is achieved. Specific Embodiments

[0018] The following will further elaborate on the present invention in combination with specific embodiments of the present invention.

[0019] The core technological innovation of the present invention lies in using biomass and pyrolytic carbon to partially or completely replace coke powder. Biomass and pyrolytic carbon will pyrolyze to produce hydrogen-containing gases such as hydrogen and methane as reducing agents during the reduction process, optimizing the traditional carbothermal reduction into a carbon-hydrogen coupling reduction system. Under the carbon-hydrogen synergistic effect, hydrogen-containing reducing gases such as hydrogen or methane can reduce iron and zinc oxides in a relatively low temperature range (~800℃), which means that the reaction time is extended under the same process conditions. Moreover, hydrogen molecules are small, and the mass transfer rate is higher than that of carbon monoxide, improving the reduction kinetic conditions. And by using the reasonable ratio of biomass and pyrolytic carbon and combining with hierarchical temperature control, carbon-hydrogen coupling reduction throughout the process is achieved. On the other hand, biomass and pyrolytic carbon have strong reactivity and can reduce iron oxides to iron oxide at a relatively low temperature range (~800℃), enabling more carbon monoxide to participate in the reduction of iron oxide and zinc oxide at high temperatures, thereby strengthening the metallization of iron and the removal of zinc and increasing the metallization rate and dezincification rate of the final pellets.

[0020] Example 1: A method for strengthening the reduction of iron and zinc-containing dust sludge by carbon-hydrogen coupling, comprising the following steps:

[0021] (1) Ingredients: Mix different types of iron- and zinc-containing dust and sludge in a certain proportion, and add a reducing agent to obtain a mixture. The weight ratio of the reducing agent to the iron- and zinc-containing dust and sludge is 0.05, and the ratio of biomass: corn straw charcoal: power plant gasification ash: coke powder is 3:3:4:2.

[0022] (2) Mixing: Add a binder and water to the mixture obtained in step (1). The addition amount of the binder is 2 wt%, and the addition amount of water is 6 wt%. Mix the materials evenly to obtain a uniformly mixed material. The H / C molar ratio in the uniformly mixed material is 0.05.

[0023] (3) Pelletizing / drying: Press the uniformly mixed material obtained in step (2) into pellets, and then dry the green pellets at 105 °C to obtain dry pellets.

[0024] (4) Roasting: Roast the dry pellets obtained in step (3) at a heating rate of 45 °C / min for 7 min, 5 min, and 7 min respectively under the conditions of 500 - 800 °C, 800 - 1000 °C, and 1000 - 1300 °C, and then cool to obtain metallized pellets. The whole process is carried out under an inert atmosphere.

[0025] Through Example 1, the metallization rate of iron is 85.98%, and the zinc removal rate is 97.81%.

[0026] Examples 2 - 13 have the same process steps as Example 1, only the process parameters are different, as shown in Table 1 specifically:

[0027] Table 1 Main process parameters of examples

[0028]

[0029] The implementation effects of Examples 1 - 13 are shown in Table 2:

[0030] Table 2 Implementation effects

[0031] Example Ferrous metallization rate / % dezincification rate / % 1 85.98 97.81 2 86.51 97.59 3 85.11 95.28 4 87.81 97.86 5 81.35 94.35 6 85.77 96.98 7 84.46 95.64 8 83.86 94.85 9 83.59 94.64 10 86.54 97.31 11 94.56 98.91 12 97.64 99.45 13 96.73 99.13

[0032] As can be seen from Table 2, by using biomass, pyrolysis carbon, and coke powder for synergistic reduction, the traditional carbothermal reduction process is optimized into a carbon-hydrogen coupling reduction process, strengthening the metallization rate of iron and the removal of zinc. After reduction roasting, the metallization rate and dezincification rate of the pellets are significantly improved.

[0033] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for strengthening the reduction of iron and zinc-containing dust and sludge by carbon-hydrogen coupling, characterized in that: It includes the following steps: S1 Batching: Based on the iron and zinc-containing dust and sludge, batching calculation is carried out by the stoichiometric method, and a reducing agent is added to obtain a mixed material, where the weight ratio of the reducing agent to the iron and zinc-containing dust and sludge is 0.01 - 0.3; S2 Mixing: Water is added to the mixed material obtained in step S1, and the materials are fully mixed evenly to obtain a mixed material; S3 Forming / Drying: The mixed material obtained in step S2 is pressed into balls, and then the green balls are dried to obtain dry balls; S4 Roasting: The dry balls obtained in step S3 are heated from the lower limit temperature to the upper limit temperature of the three temperature ranges of 500°C - 800°C, 800°C - 1000°C, and 1000°C - 1300°C at a heating rate of 5°C / min - 60°C / min. While completing the heating in each temperature range, roasting is carried out in this temperature range. The roasting time in each temperature range is 5 min - 20 min respectively. After roasting in the three temperature ranges, cooling is carried out to obtain metallized pellets. The entire roasting process is carried out in an inert atmosphere, and a hydrogen-containing reducing agent participates in the reaction throughout the reduction process.

2. The method for enhancing the reduction of iron and zinc-containing dust and sludge by carbon-hydrogen coupling according to claim 1, wherein In step S1, the iron and zinc-containing dust and sludge used includes one or several of sintering ash, blast furnace ash, electric furnace ash, and iron and zinc-containing sludge.

3. The method for enhancing the reduction of iron and zinc-containing dust and sludge by carbon-hydrogen coupling according to claim 1, characterized in that, In step S1, the reducing agent used includes coke powder, biomass, or pyrolytic carbon of organic matter, where the pyrolytic carbon of organic matter includes pyrolytic carbon of agricultural and forestry organic solid waste, pyrolytic carbon of domestic waste, pyrolytic carbon of industrial solid waste, or gasification ash of power plants.

4. The method for strengthening the reduction of iron and zinc-containing dust and sludge by carbon-hydrogen coupling according to claim 1, characterized in that In step S1, the H / C molar ratio in the mixed material is 0.1 - 0.8, and the carbon and hydrogen elements come from the iron and zinc-containing dust and sludge and the reducing agent.

5. The method for enhancing the reduction of iron and zinc-containing dust and sludge by carbon-hydrogen coupling according to claim 1, wherein In step S2, the binder used is an organic binder or an inorganic binder.

6. The method for strengthening the reduction of iron and zinc-containing dust and sludge by carbon-hydrogen coupling according to claim 1, characterized in that In step S3, for the ball pressing process, the pressure is 10 - 20 Mpa, and the pellet size is 10 - 30 mm.

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