Scrap steel preheating system and preheating method

Abstract

The invention relates to the technical field of electric arc furnace steelmaking. The invention relates to a preheating system, in particular to a waste steel preheating system and a preheating method. Aiming at the problems that the comprehensive cost of electric energy and chemical energy of an existing electric arc furnace is high, the economic cost between the electric energy and the chemical energy is not reasonably matched and optimally used, and the like, the invention provides the scrap steel preheating system and the preheating method, so that the electric furnace is promoted to be optimally and economically used between the electric energy and the chemical energy; and the extreme cost control of electric arc furnace smelting is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of electric arc furnace steelmaking, and more specifically, to a scrap steel preheating system and a preheating method. Background Art

[0002] The carbon emissions per ton of pure scrap steel short-process electric furnace steelmaking are about 1.5 tons lower than that of blast furnace-converter long-process steelmaking, and it is the most effective way for the steel industry to reduce carbon dioxide emissions. Vigorously promote the recycling of scrap steel and support the development of electric furnace short-process steelmaking to reduce carbon emissions and energy consumption. Therefore, in the future, one of the main ways for the steel industry to reduce carbon emissions is to develop electric furnace short-process steelmaking. The department has issued the "Special Action Plan for Energy Conservation and Carbon Reduction in the Steel Industry", and regards "increasing the proportion of short-process electric furnace steelmaking" as an important measure to promote the green and low-carbon development of the steel industry. It proposes that "by the end of 2025, the utilization of scrap steel will reach 300 million tons, and the proportion of electric furnace steel production in total crude steel production will strive to increase to 15%. In 2030, the proportion of electric furnace production in total crude steel production will reach 20%. However, due to the high overall cost of scrap steel prices, electricity costs and energy media, the cost of electric furnace smelting remains high, affecting the core competitiveness and industrial planning of electric furnaces. In the current situation of overcapacity in the steel industry and the continuous pressure on profit margins, the steel industry is facing a period of rapid development. In the case of shrinking, the pursuit of extreme energy efficiency and cost is the main way to solve the current difficulties of electric furnace companies. Therefore, the development of low-cost smelting equipment and process technology is of significant value to improving the technical level of electric furnace equipment and corporate competitiveness. At present, advanced electric arc furnaces at home and abroad all adopt the scrap steel preheating technology without opening the cover, using the waste heat of flue gas to achieve the purpose of energy saving and consumption reduction. The main technical indicators have been greatly improved compared with traditional open-cover electric arc furnaces. At present, domestic electric furnaces only use flue gas waste heat to preheat scrap steel, thereby improving the energy efficiency level of electric furnaces. Electric arc furnaces mainly use electrical energy and chemical energy to melt and heat scrap steel.

[0003] However, most companies currently do not make special optimization considerations in terms of energy efficiency and economy when pursuing economic benefits. For example, in the continuous production process of electric furnaces, electricity has peak, valley and flat time periods. Therefore, the price difference of electricity in different time periods is large. This poses a problem: in the process of heating scrap steel with electricity and chemical energy, there will be economic volatility. When the price of electricity is low, it is advisable to use electricity to melt scrap steel, and when chemical energy has energy efficiency and cost advantages, it is advisable to use chemical energy for electric furnace smelting. For example: during valley electricity, the price of electricity is generally 0.3 yuan / kWh. According to the analysis of the smelting data of electric furnaces, in general, 1Nm 3The oxygen added can reduce 3kWh / t, but in order to prevent the molten steel from overoxidation, about 0.8kg of carbon powder must be sprayed at the same time. According to the current market price of carbon powder of 3,000 yuan / t, the oxygen cost of the oxygen production station is 0.4 yuan / Nm3. Therefore, the chemical energy cost increased by spraying oxygen is 0.933 yuan / kWh, while the electric energy cost is only 0.3 yuan / kWh. If there is green electricity such as photovoltaics or waste heat generation in the factory, its economy will be more significant. At present, electric furnace manufacturers such as Tenon have proposed an enhanced scrap steel preheating system, which is mainly to heat the scrap steel by adding natural gas burners in the scrap steel preheating section and using the heat from the combustion of natural gas. However, due to the high price of natural gas and the problem of insufficient thermal efficiency, it is not economically advantageous, so it has not been used in China at present. Summary of the invention

[0004] In view of the problems that the comprehensive cost of electrical energy and chemical energy of the existing electric arc furnace is high, and the economic costs between electrical energy and chemical energy are not reasonably matched and optimized, the present invention provides a scrap steel preheating system and a preheating method to promote the best economical use of electrical energy and chemical energy in the electric furnace and achieve the ultimate cost control of electric arc furnace smelting.

[0005] In order to achieve these purposes and other advantages according to the present invention, a scrap steel preheating system is provided, comprising a scrap steel feeding section, a scrap steel preheating section and a scrap steel preheating section, wherein the discharge end of the scrap steel feeding section is connected to the feed end of the scrap steel preheating section, and the discharge end of the scrap steel preheating section is connected to the feed end of the scrap steel preheating section.

[0006] Furthermore, the scrap steel preheating system further comprises a dynamic sealing section, and the discharge end of the scrap steel preheating section and the feed end of the scrap steel preheating section are connected via the dynamic sealing section.

[0007] Furthermore, in the scrap steel preheating system, the scrap steel preheating section is an induction heating device.

[0008] The present invention also provides a method for preheating scrap steel, comprising the following steps:

[0009] S1, preheating the scrap steel for the first time through the scrap steel preheating section;

[0010] S2, preheating the scrap steel for the second time after the first preheating through the scrap steel preheating section.

[0011] Furthermore, in the scrap steel preheating method, the temperature of the scrap steel after the first preheating in S1 is not higher than 400°C.

[0012] Furthermore, in the scrap steel preheating method, the discharge end of the scrap steel preheating section and the feed end of the scrap steel preheating section are connected via a dynamic sealing section.

[0013] Furthermore, the method for preheating scrap steel further comprises:

[0014] S3, recovering the electric furnace flue gas preheated in the scrap steel preheating section and using it for waste heat power generation.

[0015] Furthermore, in the scrap steel preheating method, the scrap steel preheating section is an induction heating device, and the electric energy obtained by the waste heat power generation in S3 is supplied to the scrap steel preheating section.

[0016] Furthermore, in the scrap steel preheating method, the heating temperature of the first preheating in S1 is lower than 300°C, and the heating temperature of the second preheating in S2 is higher than 800°C.

[0017] Furthermore, in the scrap steel preheating method, waste heat power generation is performed by a waste heat power generation device in S3, and the air outlet of the scrap steel preheating section is connected to the air inlet of the waste heat power generation device.

[0018] The beneficial effects of the present invention are:

[0019] 1. The scrap steel preheating system of the present invention is mainly optimized, designed and modified for the scrap steel preheating scheme of the continuous charging type electric arc furnace. A scrap steel preheating section is added between the scrap steel preheating section and the scrap steel charging section. The scrap steel preheating section realizes the first preheating of the scrap steel by induction heating; the scrap steel after induction heating is transported to the scrap steel preheating section, and the flue gas is used to preheat the scrap steel for the second time; the scrap steel after the second preheating is transported to the electric furnace for smelting through a connecting trolley. The scrap steel preheating system of the present invention can selectively open the scrap steel preheating section according to the energy efficiency and economic fluctuation characteristics of electrical energy and chemical energy during the smelting process of the electric arc furnace and based on cost control requirements, optimize the energy matching system of the electric furnace, and realize low-cost smelting operation of the electric furnace;

[0020] 2. The present invention uses induction heating to preheat the scrap steel before the scrap steel is preheated by the electric furnace flue gas, thereby reducing the pressure of the electric furnace flue gas on the scrap steel preheating in the later stage;

[0021] 3. The present invention is mainly aimed at the continuous feeding type scrap steel preheating scheme, and can be designed and modified on the existing continuous feeding type scrap steel preheating equipment to achieve the high flue gas outlet temperature and the scrap steel preheating effect meeting the requirements, and finally achieve the win-win situation of greening and high efficiency of electric arc furnace smelting;

[0022] 4. The present invention controls the temperature of the preheated electric furnace flue gas to be above 800°C, thereby preventing the electric furnace flue gas from producing dioxins in the temperature range of 300-800°C; at the same time, waste heat power generation technology is adopted to utilize the preheated electric furnace flue gas, and the recovered electric energy is fed back to the early heating of scrap steel through waste heat power generation, thereby realizing the recovery and reuse of waste heat of the electric furnace flue gas.

[0023] 5. The present invention uses induction heating to preheat the scrap steel before the scrap steel is preheated by the electric furnace flue gas, thereby reducing the pressure of the electric furnace flue gas on the scrap steel preheating in the later stage, thereby making it easier to control the temperature of the preheated electric furnace flue gas to be above 800°C. At the same time, the heating temperature during induction heating is lower than 300°C, which can also reduce the possibility of dioxin generation. The present invention fully considers the generation range of dioxins and effectively avoids them.

[0024] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic structural diagram of an environmentally friendly scrap steel preheating system according to an embodiment of the present invention;

[0026] Figure 2 It is a schematic structural diagram of an environmentally friendly scrap steel preheating system according to another embodiment of the present invention.

[0027] Wherein, the reference numerals represent:

[0028] Electric furnace 1; connecting trolley 2; scrap steel preheating section 3; dynamic sealing section 4; waste heat power generation device 5; scrap steel preheating section 6; scrap steel charging section 7. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below in conjunction with embodiments so that those skilled in the art can implement the invention with reference to the description.

[0030] It should be noted that, in the description of the present invention, the terms "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc. indicating orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0031] like Figure 1 As shown, an embodiment of the present invention provides a scrap steel preheating system, comprising a scrap steel feeding section, a scrap steel preheating section and a scrap steel preheating section, the discharge end of the scrap steel feeding section is connected to the feed end of the scrap steel preheating section, the discharge end of the scrap steel preheating section is connected to the feed end of the scrap steel preheating section; the scrap steel preheating section is an induction heating device.

[0032] In this embodiment, the scrap steel is first hoisted into the trough of the scrap steel feeding section by means of a chain conveyor, a magnetic disk crane or a steel grabber, and then the scrap steel is evenly transported to the scrap steel preheating section by a vibrator. The scrap steel preheating section preheats the scrap steel machine for the first time; the scrap steel after induction heating is transported to the scrap steel preheating section, and the flue gas is used to preheat the scrap steel for the second time, and finally the scrap steel after the second preheating is transported to the electric furnace for smelting through a connecting trolley. In this embodiment, the scrap steel is heated by an induction heating device, the temperature of the scrap steel entering the furnace is increased, the smelting efficiency of the electric furnace is improved, and the energy consumption is reduced. The induction heating method is suitable for metal materials, which has the advantages of fast heating speed, high power utilization rate, and precise temperature control, so that the temperature of the scrap steel after preheating can be better controlled. The use of the induction heating device is based on the advantage of electric energy over chemical energy, which can reduce the smelting cost of the electric furnace. In order to illustrate the effect of the scrap steel preheating system in this embodiment on reducing the smelting cost of the electric furnace, a 100t continuous charging electric furnace in a steel plant is taken as an example. The electric furnace uses all scrap steel as raw material for smelting. Strong oxygen injection is used throughout the smelting process to improve the smelting efficiency of the electric furnace. The oxygen consumption reaches 36Nm 3 / t, the consumption of carbon-containing media such as carbon powder is 27kg / t, and the corresponding power consumption per ton of steel is 340kWh / t. Due to the high cost of carbon powder and the large amount of oxygen used, the comprehensive cost of electric furnace smelting is high under valley power conditions. Under the condition that the arc operation of the electric arc furnace is not affected, the consumption of oxygen and carbon-containing media is shortened as much as possible during valley power, and the energy lost by chemical energy is compensated by the electric energy of induction heating. After optimization, the oxygen consumption is reduced to 30Nm 3 / t, the injection volume of carbon medium is reduced to 23kg / t, and the power consumption per ton of steel increases from 340kWh / t to 365kWh / t. According to the current oxygen cost of the local industrial oxygen production station, it is 0.4 yuan / Nm 3 , the cost of carbon powder is 3,000 yuan / t. Considering that the local electric furnace is producing electricity in the valley, the electricity price is 0.3 yuan / kWh. Therefore, after adopting the economic efficiency evaluation method of electric arc furnace energy utilization, the cost saving of electric furnace smelting per ton of steel is [(36-30)×0.4+(27-23)×3.0-(365-340)×0.3)=6.9 yuan.

[0033] Preferably, as another embodiment of the present invention, it further comprises a dynamic sealing section, and the discharge end of the scrap steel preheating section and the feed end of the scrap steel preheating section are connected through the dynamic sealing section.

[0034] In this embodiment, the scrap steel advance heating section and the scrap steel preheating section are connected via a dynamic sealing section, and the connection between the two is sealed via the dynamic sealing section to prevent wild wind from entering the scrap steel preheating section.

[0035] The embodiment of the present invention also provides a scrap steel preheating system, such as Figure 2 As shown, it includes a scrap steel feeding section, a scrap steel preheating section, a scrap steel early heating section and a waste heat power generation device. The discharge end of the scrap steel feeding section is connected to the feed end of the scrap steel early heating section, the discharge end of the scrap steel early heating section is connected to the feed end of the scrap steel preheating section, and the air outlet of the scrap steel preheating section is connected to the air inlet of the waste heat power generation device.

[0036] In this embodiment, the scrap steel feeding section, the scrap steel preheating section, the scrap steel early heating section and the waste heat power generation device can all adopt existing technologies. The scrap steel feeding section, the scrap steel preheating section and the scrap steel early heating section are all equipped with conveying equipment. The scrap steel can be lifted into the material trough of the scrap steel feeding section by means of chain conveyors, magnetic disk cranes or steel grabbers. The conveying equipment in the scrap steel feeding section evenly transports the scrap steel to the scrap steel early heating section. The scrap steel early heating section preheats the scrap steel at a heating temperature lower than 300°C. During the heating process, the conveying equipment on the scrap steel early heating section drives the scrap steel forward until the scrap steel is transported to the scrap steel preheating section, that is, the early heating of the scrap steel is completed through the scrap steel early heating section. The high-temperature flue gas discharged from the electric furnace enters the scrap steel preheating section, and enters the waste heat power generation device from the outlet of the scrap steel preheating section. The scrap steel in the scrap steel preheating section is heated during the flow of the electric furnace exhaust gas through the scrap steel preheating section. The temperature of the electric furnace flue gas at the outlet of the scrap steel preheating section is controlled above 800°C to prevent the electric furnace flue gas from producing dioxins in the temperature range of 300-800°C. At the same time, the heat energy of the electric furnace flue gas discharged from the scrap steel preheating section is recycled through the waste heat power generation device. A connecting trolley is set at the discharge end of the scrap steel preheating section, and the discharge end of the scrap steel preheating section is connected to the connecting trolley, and the preheated scrap steel is sent into the electric furnace through the connecting trolley.

[0037] An embodiment of the present invention further provides a method for preheating scrap steel, comprising the following steps:

[0038] S1, preheating the scrap steel for the first time through a scrap steel preheating section; the scrap steel preheating section is an induction heating device;

[0039] S2, preheating the scrap steel after the first preheating for the second time through the scrap steel preheating section;

[0040] S3, recovering the electric furnace flue gas preheated in the scrap steel preheating section and using it for waste heat power generation;

[0041] The scrap steel preheating section is an induction heating device, and the electric energy obtained by the waste heat power generation in S3 is supplied to the scrap steel preheating section; the air outlet of the scrap steel preheating section is connected to the air inlet of the waste heat power generation device;

[0042] Preferably, as another embodiment of the present invention, the temperature of the scrap steel after the first preheating in S1 is not higher than 400°C.

[0043] In this embodiment, the temperature of the scrap steel after the first preheating is no higher than 400° C., so as to avoid excessive energy consumption in the scrap steel preheating stage when the temperature is too high, thereby ensuring the thermal efficiency of the electric energy.

[0044] Preferably, as another embodiment of the present invention, the discharge end of the scrap steel preheating section is connected to the feed end of the scrap steel preheating section via a dynamic sealing section.

[0045] In this embodiment, the scrap steel advance heating section and the scrap steel preheating section are connected via a dynamic sealing section, and the connection between the two is sealed via the dynamic sealing section to prevent wild wind from entering the scrap steel preheating section.

[0046] Preferably, as another embodiment of the present invention, the heating temperature of the first preheating in S1 is lower than 300°C, and the heating temperature of the second preheating in S2 is higher than 800°C.

[0047] In this embodiment, it is known from the prior art that the temperature range most likely to produce dioxins is 300 to 750°C. Within this temperature range, various activities may lead to the formation of dioxins, including steel and non-ferrous metal smelting, automobile exhaust emissions, and incineration of various types of waste, such as pharmaceutical wastewater, chemical waste, domestic garbage, and waste from coal-fired power plants. In particular, when the combustion temperature is lower than 300 to 400°C, leaded gasoline, coal, wood treated with preservatives, and petroleum products are more likely to produce dioxins. In addition, the production of polyvinyl chloride plastics, paper, chlorine, and certain pesticides may also release dioxins into the environment. The scrap steel in this application is mainly sourced from waste recycling. In addition to metal components, it may be mixed with various impurities. If the temperature of the scrap steel is greater than 300°C when it is heated in advance, dioxins may be generated during the heating process. Therefore, the heating temperature of the scrap steel when it is heated in advance is controlled within 300°C, which can minimize the generation of dioxins when the scrap steel is heated in advance.

[0048] The heating temperature of the second preheating is higher than 800℃, that is, the temperature of the electric furnace flue gas entering the scrap steel preheating section is controlled to be above 800℃; the length of the scrap steel preheating section of the general scrap steel preheating system is 30m at present, and the length of the scrap steel preheating section can be reduced to no more than 15m, shortening the residence time of the electric furnace flue gas in the scrap steel preheating section, thereby increasing the temperature of the electric furnace flue gas discharged from the scrap steel preheating section, so that the outlet temperature of the preheated electric furnace flue gas is not lower than 800℃, thereby preventing the generation of dioxins;

[0049] The temperature of the electric furnace flue gas discharged from the scrap steel preheating system is greater than 800℃, and it has high thermal energy. Directly discharging it will waste its thermal energy. At this time, waste heat power generation technology is used to recover the preheated electric furnace flue gas discharged from the scrap steel preheating system. The thermal energy of the electric furnace flue gas is recovered and utilized through waste heat power generation equipment, converted into electrical energy, and the waste heat of the electric furnace flue gas is recovered and reused.

[0050] Since the temperature of the electric furnace flue gas discharged from the scrap steel preheating system needs to be controlled above 800℃, the requirements for the scrap steel preheating system will be increased. At this time, the scrap steel entering the scrap steel preheating system is heated in advance to reduce the burden of the scrap steel preheating system and ensure its stable operation.

[0051] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the embodiments shown and described herein.

Claims

1. A scrap steel preheating system, characterized in that: It includes a scrap steel feeding section, a scrap steel preheating section and a scrap steel preheating section. The discharge end of the scrap steel feeding section is connected to the feed end of the scrap steel preheating section, and the discharge end of the scrap steel preheating section is connected to the feed end of the scrap steel preheating section.

2. A scrap steel preheating system as claimed in claim 1, characterized in that: It also includes a dynamic sealing section, through which the discharge end of the scrap steel preheating section is connected with the feed end of the scrap steel preheating section.

3. A scrap steel preheating system as claimed in claim 1, characterized in that: The scrap steel advance heating section is an induction heating device.

4. A method for preheating scrap steel, characterized in that: The following steps are involved: S1, preheating the scrap steel for the first time through the scrap steel preheating section; S2, preheating the scrap steel for the second time after the first preheating through the scrap steel preheating section.

5. A method for preheating scrap steel as claimed in claim 4, characterized in that: The temperature of the scrap steel after the first preheating in S1 is not higher than 400°C.

6. A method for preheating scrap steel as claimed in claim 4, characterized in that: The discharge end of the scrap steel preheating section is connected to the feed end of the scrap steel preheating section via a dynamic sealing section.

7. A method for preheating scrap steel as claimed in claim 4, characterized in that: Also includes: S3, recovering the electric furnace flue gas preheated in the scrap steel preheating section and using it for waste heat power generation.

8. A method for preheating scrap steel as claimed in claim 7, characterized in that: The scrap steel preheating section is an induction heating device, and the electric energy obtained by the waste heat power generation in S3 is supplied to the scrap steel preheating section.

9. A method for preheating scrap steel as claimed in claim 7, characterized in that: The heating temperature of the first preheating in S1 is lower than 300°C, and the heating temperature of the second preheating in S2 is higher than 800°C.

10. A method for preheating scrap steel as claimed in claim 7, characterized in that: In S3, waste heat power generation is performed by a waste heat power generation device, and the air outlet of the scrap steel preheating section is connected to the air inlet of the waste heat power generation device.

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