System and method for preheating scrap steel through heat accumulating type circulating gas

Abstract

The invention discloses a system and a method for preheating scrap steel by using heat accumulating type circulating gas, and belongs to the technical field of scrap steel preheating. The technical problem that in the prior art, high-temperature flue gas or flames are adopted for directly preheating the scrap steel, and consequently the scrap steel is overheated, softened and bonded is solved. The system comprises a heat accumulating type heat exchange unit, a high-temperature distribution unit, a waste steel preheating unit and a low-temperature distribution unit which are sequentially connected to form a closed loop, to-be-preheated scrap steel is arranged in the scrap steel preheating unit, and circulating gas can circulate among the heat accumulating type heat exchange unit, the high-temperature distribution unit, the scrap steel preheating unit and the low-temperature distribution unit in sequence; the heat accumulating type heat exchange unit can utilize heating gas to conduct indirect heat exchange on circulating gas. And the waste steel preheating unit can preheat the waste steel to be preheated by utilizing the heated circulating gas. The waste steel is indirectly preheated through high-temperature flue gas, so that overheating, soft melting and bonding of the steel are avoided, and the iron loss is reduced.

Description

Technical Field

[0001] The present invention relates to the field of metallurgical process technology and equipment technology, and in particular to a system and method for preheating scrap steel using heat storage circulating gas. Background Art

[0002] As an important pillar industry of the national economy under the background of dual carbon, the low-carbon transformation of the steel industry has become an urgent problem to be solved. Smelting with scrap steel as raw material has been recognized by everyone due to its inherent low-carbon advantages. Scrap steel preheating technology increases the heat contained in scrap steel by heating it, effectively raising the furnace temperature, has a good effect on both long and short process smelting, and has also been widely used.

[0003] Steel mills have adopted a variety of methods to preheat scrap steel, including preheating scrap steel in ladles, preheating scrap steel in converter scrap steel tanks, building special furnaces for scrap steel, and preheating scrap steel flue gas commonly used in short-process electric arc furnace smelting processes. While many scrap steel preheating technologies have increased the temperature of scrap steel entering the furnace, shortened smelting time, and improved smelting efficiency, they have also caused many problems, including overheating of scrap steel, overoxidation of scrap steel, and dioxin emissions.

[0004] Currently, the mainstream scrap steel preheating methods are divided into two categories. One is to use the high-temperature flue gas generated by the furnace to heat the scrap steel, and the other is to use an additional heat source to preheat the scrap steel.

[0005] Flue gas heating scrap steel technology is widely used in the electric arc furnace steelmaking process, and its representative equipment is the horizontal charging electric furnace, quantum electric furnace, and SHARC electric arc furnace. The advantage of flue gas preheating scrap steel is that it uses high-temperature dust-removing flue gas to preheat the scrap steel without the need for additional energy. While achieving scrap steel preheating, it can reduce the flue gas emission temperature, effectively utilize the heat therein, and improve the thermal efficiency of the entire smelting process. The disadvantage is that the flue gas temperature is difficult to control, and it is easy to overheat and cause the scrap steel to melt softly and stick together, affecting the stable operation of the equipment. At the same time, the chlorine contained in the flue gas has an important influence on the formation of dioxins, which limits the use of flue gas preheating scrap steel.

[0006] For the converter smelting process, due to its limited heat and lack of heating function, in order to increase the scrap steel ratio, additional heat sources will be used to preheat the scrap steel. Common heat sources include self-produced coal gas, purchased natural gas and electricity. Compared with flue gas preheating of scrap steel, the use of additional heat sources for preheating is convenient for controlling the preheating situation, and the specially designed heating device can achieve efficient preheating of scrap steel.

[0007] The existing scrap steel preheating method has the following problems:

[0008] (1) The flame directly heats the scrap steel, which results in excessive heat concentration and easily leads to overheating, softening and bonding of the scrap steel, thus affecting subsequent smelting. (2) The flame or high-temperature flue gas has a high oxygen content, which easily leads to oxidation of the scrap steel surface and reduces the scrap steel recovery rate. (3) The heating method is relatively extensive, resulting in uneven preheating of the scrap steel and poor effect. The exhaust gas temperature is high and the heating efficiency is low. Summary of the invention

[0009] In view of the above analysis, the present invention aims to provide a system and method for preheating scrap steel using regenerative circulating gas to solve at least one of the following problems:

[0010] (1) The existing preheating method uses high-temperature flue gas flames to directly heat the scrap steel, which causes excessive heat concentration and easily leads to overheating, softening and bonding of the scrap steel, affecting subsequent smelting;

[0011] (2) The flame or high-temperature flue gas used in the existing preheating method has a high oxygen content, which easily leads to oxidation of the scrap steel surface and reduces the scrap steel recovery rate;

[0012] (3) The existing preheating method is relatively extensive, the scrap preheating effect is uneven, the exhaust temperature is high, and the heating efficiency is low.

[0013] The purpose of the present invention is mainly achieved through the following technical solutions:

[0014] The present invention provides a system for preheating scrap steel using regenerative circulating gas, the system comprising a regenerative heat exchange unit, a high temperature distribution unit, a scrap steel preheating unit and a low temperature distribution unit which are sequentially connected to form a closed loop;

[0015] The scrap steel to be preheated is arranged in the scrap steel preheating unit, and the circulating gas can be circulated in sequence among the regenerative heat exchange unit, the high temperature distribution unit, the scrap steel preheating unit and the low temperature distribution unit;

[0016] The regenerative heat exchange unit can utilize the heated gas to indirectly exchange heat with the circulating gas; the scrap steel preheating unit can utilize the heated circulating gas to preheat the scrap steel to be preheated.

[0017] In one possible design, the regenerative heat exchange unit includes a regenerative heat exchanger;

[0018] The two ends of the heat storage heat exchanger are respectively the first end of the heat exchanger and the second end of the heat exchanger; a high-temperature flue gas inlet is provided on the first end of the heat exchanger, and the high-temperature flue gas inlet is connected to the high-temperature flue gas input pipeline; a high-temperature flue gas outlet is provided on the second end of the heat exchanger, and the high-temperature flue gas outlet is connected to the high-temperature flue gas output pipeline.

[0019] In a possible design, a first stop valve is provided on the high-temperature flue gas input pipeline; a second stop valve is provided on the high-temperature flue gas output pipeline; the first stop valve and the second stop valve are valves in the same group; and the valves in the same group have the same action.

[0020] In a possible design, a circulating gas inlet is further provided on the second end of the heat exchanger, and the circulating gas inlet is connected to the low-temperature distribution unit through the first section of the circulating gas delivery pipeline;

[0021] A circulating gas outlet is also provided on the first end of the heat exchanger, and the circulating gas outlet is connected to the high-temperature gas distribution unit through a second section of the circulating gas delivery pipeline.

[0022] In a possible design, the first section of the circulating gas delivery pipeline is provided with a third stop valve; the second section of the circulating gas delivery pipeline is provided with a fourth stop valve; the third stop valve and the fourth stop valve are valves of the same group, and the valves of the same group have the same action;

[0023] The third stop valve and the fourth stop valve are valves of different groups from the first stop valve and the second stop valve, and the valves of different groups have opposite actions.

[0024] In a possible design, a first forced gas circulator is also provided on the first section of the circulating gas delivery pipeline.

[0025] In a possible design, a first temperature sensor is provided near the first end of the heat exchanger; a second temperature sensor is provided near the second end of the heat exchanger;

[0026] When the temperatures of the first temperature sensor and the second temperature sensor tend to be consistent, the two groups of stop valves are switched.

[0027] In one possible design, the scrap steel preheating unit includes a scrap steel preheating bin;

[0028] The scrap steel preheating bin is connected to the high temperature distribution unit through the third section of the circulating gas delivery pipeline; the scrap steel preheating bin is connected to the low temperature distribution unit through the fourth section of the circulating gas delivery pipeline;

[0029] The third section of the circulating gas delivery pipeline is provided with a fifth stop valve; the fourth section of the circulating gas delivery pipeline is provided with a sixth stop valve.

[0030] In a possible design, a second forced gas circulator is further provided on the third section of the circulating gas delivery pipeline; and a third forced gas circulator is further provided on the fourth section of the circulating gas delivery pipeline.

[0031] The present invention also provides a method for preheating scrap steel using regenerative circulating gas, using the above-mentioned system for preheating scrap steel using regenerative circulating gas, the method comprises the following steps:

[0032] Step 1, introducing the heating gas into the heat storage heat exchange unit for heat exchange to store heat in the heat storage heat exchange unit; then introducing the circulating gas into the heat storage heat exchange unit for heat exchange to release heat in the heat storage heat exchange unit;

[0033] Step 2, transporting the heated circulating gas to a high temperature distribution unit;

[0034] Step 3: transporting the circulating gas in the high-temperature distribution chamber to the scrap steel preheating unit, and using the heated circulating gas to preheat the scrap steel in the bin;

[0035] Step 4: Introduce the circulating gas that has completed the heat exchange with the scrap steel into the low-temperature distribution chamber to complete the cycle; then, repeat steps 1 to 3.

[0036] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0037] (1) The present invention transfers the heat of external high-temperature flue gas or other heat sources to the scrap steel through a heat storage heat exchange unit and circulating gas, thereby achieving preheating of the scrap steel and avoiding direct contact between the scrap steel and the external flue gas. Therefore, the present invention can solve the problems of scrap steel composition changes and overoxidation.

[0038] (2) The circulating gas used in the present invention is composed of an inert gas; using the circulating gas composed of an inert gas to heat the scrap steel can avoid high-temperature oxidation of the scrap steel and reduce damage to the scrap iron.

[0039] (3) The present invention uses a heat storage heat exchanger to heat the circulating gas. The heating gas and the circulating gas are isolated from each other. The two only exchange heat without mixing, which can avoid changes in the circulating gas composition and thus avoid changes in the scrap steel composition.

[0040] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the embodiments of the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0042] Figure 1 It is a schematic diagram of the composition of the system for preheating scrap steel with regenerative circulating gas according to the present invention;

[0043] Figure 2 It is a schematic diagram of the composition of the heat storage heat exchange unit of the present invention;

[0044] Figure 3 It is a schematic diagram of the composition of the scrap steel preheating unit of the present invention.

[0045] Reference numerals:

[0046] 1-heat storage heat exchanger; 2-first temperature sensor; 3-second temperature sensor; 4-first stop valve; 5-second stop valve; 6-third stop valve; 7-fourth stop valve; 8-first forced gas circulator; 9-high temperature distribution chamber; 10-low temperature distribution chamber; 11-scrap preheating bin; 12-fifth stop valve; 13-sixth stop valve; 14-seventh stop valve; 15-eighth stop valve; 16-third temperature sensor; 17-fourth temperature sensor; 18-second forced gas circulator; 19-third forced gas circulator. DETAILED DESCRIPTION

[0047] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0048] In one aspect, the present invention provides a system for preheating scrap steel using regenerative circulating gas, such as Figure 1 As shown, the system includes a regenerative heat exchange unit, a high-temperature distribution unit, a scrap steel preheating unit and a low-temperature distribution unit which are sequentially connected to form a closed loop; the scrap steel to be preheated is placed in the scrap steel preheating unit, and the circulating gas can circulate in sequence among the regenerative heat exchange unit, the high-temperature distribution unit, the scrap steel preheating unit and the low-temperature distribution unit; the regenerative heat exchange unit can utilize the heated gas to indirectly exchange heat with the circulating gas; the scrap steel preheating unit can utilize the heated circulating gas to preheat the scrap steel.

[0049] Specifically, the circulating gas used in the present invention is an inert gas (referring to a gas that does not react with scrap steel); the heating gas used is high-temperature flue gas generated by smelting, flames generated by combustion, or hot air generated by other heat sources. The above-mentioned regenerative heat exchange unit uses the heat of the heating gas to indirectly heat the circulating gas, and the heated circulating gas enters the scrap steel preheating unit through the high-temperature distribution unit and exchanges heat with the scrap steel therein; the circulating gas after heat exchange returns to the regenerative heat exchange unit through the low-temperature distribution unit, completing a cycle.

[0050] Compared with the prior art, the present invention transfers the heat of external high-temperature flue gas or other heat sources to the scrap steel through a heat storage heat exchange unit and circulating gas, thereby achieving preheating of the scrap steel and avoiding direct contact between the scrap steel and the external flue gas. Therefore, the present invention can solve the problems of changes in the composition of the scrap steel and overoxidation.

[0051] It should be emphasized that the circulating gas used in the present invention is composed of inert gas; using the circulating gas composed of inert gas to heat scrap steel can avoid high-temperature oxidation of the scrap steel and reduce damage to the scrap iron.

[0052] In order to achieve indirect heat exchange between heating gas and circulating gas, such as Figure 2 As shown, the heat storage heat exchange unit of the present invention includes a heat storage heat exchanger 1; the two ends of the heat storage heat exchanger 1 are respectively a first end of the heat exchanger and a second end of the heat exchanger; a high-temperature flue gas inlet is provided on the first end of the heat exchanger, and the high-temperature flue gas inlet is connected to a high-temperature flue gas input pipeline; a high-temperature flue gas outlet is provided on the second end of the heat exchanger, and the high-temperature flue gas outlet is connected to a high-temperature flue gas output pipeline.

[0053] Specifically, when it is necessary to heat the circulating gas, the heating gas in the high-temperature gas input pipe is first introduced into the regenerative heat exchanger 1 through the high-temperature flue gas inlet and exchanges heat with the regenerative heat exchanger 1. After the heating gas completes the heat exchange, it is introduced into the high-temperature flue gas output pipe through the high-temperature flue gas outlet, and is thus completely discharged from the regenerative heat exchanger 1; then, the circulating gas to be heated is introduced into the regenerative heat exchanger 1 and exchanges heat with the regenerative heat exchanger 1. After the heat exchange, the circulating gas enters the scrap steel preheating unit through the high-temperature distribution unit to preheat the scrap steel therein. The circulating gas after the heat exchange with the scrap steel returns to the regenerative heat exchanger 1 through the low-temperature distribution unit and is reheated again.

[0054] In the prior art, flame or high-temperature flue gas is used to heat scrap steel. The flame or high-temperature flue gas has a high oxygen content, which easily leads to oxidation of the scrap steel surface and reduces the scrap steel recovery rate. Compared with the prior art, the present invention uses a regenerative heat exchanger 1 to heat the circulating gas. The heating gas and the circulating gas are isolated from each other. The two only exchange heat without mixing, which can avoid changes in the circulating gas composition, thereby avoiding changes in the scrap steel composition.

[0055] It should be noted that the number n of the thermal storage heat exchangers 1 of the present invention is multiple (n≥2), for example, n is 3, 4 or 5; the reduction of flue gas fluctuation and the control of heat storage effect are achieved by switching multiple thermal storage heat exchangers 1.

[0056] Specifically, a plurality of heat storage heat exchangers 1 are connected in parallel, and the amount of gas entering and exiting the heat storage heat exchanger 1 can be adjusted independently. The heat storage heat exchanger 1 has two working states: heat storage and heat release. When high-temperature flue gas enters the heat storage heat exchanger 1 (heat storage body), the heat storage body is in a heat storage state, and its temperature increases with time; when the temperature difference between the inlet and outlet of the heat storage body is small, it means that the heat storage of the heat storage body has reached an extreme value. At this time, the high-temperature flue gas pipeline is closed and the circulating gas pipeline is opened for heat release. Since the temperature of the incoming circulating gas is low, the heat storage body releases heat to the circulating gas. Therefore, the outlet temperature of the circulating gas is higher than the inlet temperature. As time goes by, the heat of the heat storage body decreases, and the difference between the two decreases. When the two tend to be consistent, it means that the heat stored in the heat storage body has been exhausted. At this time, the circulating gas pipeline is closed, and the high-temperature flue gas pipeline is opened to repeat the heat storage process.

[0057] The heat storage heat exchange unit of the present invention includes a first forced gas circulator, and the circulation power of the circulating gas comes from the first forced gas circulator (for example, a circulating fan); the switching action between different heat storage heat exchangers is manually realized by the corresponding control valves. The heat storage process is the process of heating the heat storage body after the high-temperature flue gas passes through the heat storage body. As the heat storage process proceeds, the temperature of the heat storage body continues to rise, and the exhaust gas temperature rises at the same time. When the difference between the two is small, it means that the heat storage capacity of the heat storage body is saturated. At this time, the first stop valve and the second stop valve are closed, and the third stop valve and the fourth stop valve of the circulating gas are opened to start the heat release process. In the heat release process, the low-temperature circulating gas passes through the heat storage body, and the two exchange heat. The temperature of the low-temperature circulating gas rises, and the temperature of the heat storage body drops. When the temperature of the circulating gas after heat exchange is lower than 800°C, it means that the heat of the heat storage body is insufficient to heat the circulating gas. At this time, the third stop valve and the fourth stop valve of the circulating gas are closed, and the flue gas valve is opened to carry out the heat storage process. The heat storage and heat exchange processes are operated alternately, and the switching standard is the gas temperature.

[0058] It should be pointed out that the structures of the multiple heat storage heat exchangers 1 are the same as each other, and the inlet and outlet positions of each heat storage heat exchanger 1 are provided with corresponding temperature sensors; for example, the number of heat storage heat exchangers 1 is four, namely the first heat storage heat exchanger, the second heat storage heat exchanger, the third heat storage heat exchanger and the fourth heat storage heat exchanger; the first heat storage heat exchanger, the second heat storage heat exchanger, the third heat storage heat exchanger and the fourth heat storage heat exchanger are all arranged in parallel, and are all connected to the high-temperature flue gas input pipeline through branch pipes, and each branch pipe is provided with a valve. When the indications of the temperature displays at both ends of the heat storage heat exchanger tend to be consistent, by controlling the valve switch, continuous switching between different heat storage heat exchangers can be achieved to reduce flue gas fluctuations.

[0059] Compared with the prior art, the present invention can reduce the flue gas fluctuation of the heating gas (high-temperature flue gas) by switching the multiple thermal storage heat exchangers 1. This is because the pipeline switching requires a certain amount of time. When there is only one set of thermal storage heat exchangers 1, the gas flow inside the pipeline will fluctuate greatly at the moment of switching the thermal storage heat exchanger 1. When multiple sets of thermal storage heat exchangers 1 are used, the switching time can be staggered, thereby greatly reducing the fluctuation amplitude of the airflow and achieving smooth operation.

[0060] It should be pointed out that the heat storage state of the heat storage body is judged according to the difference between the inlet temperature and the outlet temperature of the heated gas. In the heat storage heat exchanger 1, the exhaust gas temperature is controlled below 200°C, and the outlet temperature of the circulating gas is controlled within the range of 800-1000°C. At the same time, according to the characteristics of the high-temperature flue gas source, the influence of the periodic fluctuation of the flue gas temperature on the heat exchange is avoided by switching the states of multiple groups of heat storage heat exchangers 1.

[0061] In order to better control the heat exchange process between the heating gas and the circulating gas, a first stop valve 4 is provided on the high-temperature flue gas input pipeline of the present invention; a second stop valve 5 is provided on the high-temperature flue gas output pipeline; the first stop valve 4 and the second stop valve 5 are valves in the same group; and the valves in the same group have the same action.

[0062] Specifically, when it is necessary to store heat in the heat storage heat exchanger 1 (heat storage body), open the first stop valve 4 and the second stop valve 5 to allow the heating gas to enter the heat storage heat exchanger 1 for heat exchange; after the heat exchange is completed, close the first stop valve 4 and the second stop valve 5 in sequence to complete the heat storage of the heat storage heat exchanger 1.

[0063] In order to heat the circulating gas, a circulating gas inlet is also provided on the second end of the heat exchanger of the present invention, and the circulating gas inlet is connected to the low-temperature distribution unit through the first section of the circulating gas delivery pipeline; a circulating gas outlet is also provided on the first end of the heat exchanger, and the circulating gas outlet is connected to the high-temperature gas distribution unit through the second section of the circulating gas delivery pipeline. In addition, a third stop valve 6 is provided on the first section of the circulating gas delivery pipeline; a fourth stop valve 7 is provided on the second section of the circulating gas delivery pipeline; the third stop valve 6 and the fourth stop valve 7 are valves of the same group, and the valves of the same group have the same action; the third stop valve 6 and the fourth stop valve 7 are valves of different groups from the first stop valve 4 and the second stop valve 5, and the valves of different groups have opposite actions.

[0064] The working process of the thermal storage heat exchange unit is as follows: when storing heat, the first stop valve 4 and the second stop valve 5 are opened, and the third stop valve 6 and the fourth stop valve 7 are closed, and the heating gas (high-temperature flue gas) enters the thermal storage heat exchanger 1 from the high-temperature flue gas input pipeline and heats it; when releasing heat, the first stop valve 4 and the second stop valve 5 are closed, and the third stop valve 6 and the fourth stop valve 7 are opened, and the circulating gas enters the thermal storage heat exchanger 1 in the reverse direction (opposite to the flow direction of the heating gas), and the thermal storage heat exchanger 1 after heat storage heats the circulating gas; the two sets of valves are continuously switched, and the heating gas and the circulating gas alternately enter the thermal storage heat exchanger 1 to achieve heat exchange under mutual isolation.

[0065] It should be noted that the first section of the circulating gas delivery pipeline is also provided with a first forced gas circulator 8. The first forced gas circulator 8 is a forced circulation fan.

[0066] In order to detect the heat storage state of the heat storage heat exchanger 1 in real time, the present invention is provided with a first temperature sensor 2 near the first end of the heat exchanger; a second temperature sensor 3 is provided near the second end of the heat exchanger; when the temperature of the first temperature sensor 2 and the second temperature sensor 3 tend to be consistent, the two sets of stop valves are switched.

[0067] Specifically, the working process of the heat storage heat exchanger 1 includes a heat storage process and a heat release process; the heat storage process is: when the high-temperature flue gas passes through, the temperature of the heat storage body rises and the flue gas temperature drops; the heat release process is: when the circulating gas passes through, the temperature of the heat storage body drops and the circulating gas temperature rises.

[0068] During the heat storage process, when the temperatures detected by the first temperature sensor 2 and the second temperature sensor 3 tend to be consistent, it means that the heat inside the heat storage heat exchanger 1 is basically balanced, and the heat exchange efficiency between the heating gas and the heat storage heat exchanger 1 decreases. At this time, it is necessary to switch the valve, that is, close the first stop valve 4 and the second stop valve 5, and then open the third stop valve 6 and the fourth stop valve 7, and the heat storage heat exchanger 1 begins to release heat to the circulating gas. During this process, when the temperature detected by the first temperature sensor 2 (i.e., the outlet temperature of the heat storage body) is lower than the temperature of the high-temperature distribution chamber 9, it should be avoided to continue the heat exchange, so as not to cause the high-temperature distribution chamber 9 to cool down. This situation is caused by insufficient heat of the heating gas (high-temperature flue gas), and additional heat supplement is required. When the temperature detected by the second temperature sensor 3 is higher, it means that the temperature of the circulating gas output by the low-temperature distribution unit is higher, and it also means that the temperature in the scrap preheating bin 11 is higher. At this time, it is necessary to replace the low-temperature scrap for preheating.

[0069] For example, the target temperature of scrap preheating is 600-800°C. When the flue gas temperature in the low-temperature distribution chamber 10 reaches 600-800°C, it means that the scrap temperature has basically been reached and the low-temperature scrap should be replaced for further preheating.

[0070] Compared with the prior art, the present invention can timely replace new scrap steel for preheating by comparing the temperatures detected by the first temperature sensor 2 and the second temperature sensor 3 and by timely switching the two groups of valves.

[0071] The present invention sets a plurality of groups of parallel regenerative heat exchangers 1 and performs comprehensive judgment on the temperature sensors corresponding to each group of regenerative heat exchangers 1: when the inlet and outlet temperatures of the regenerative heat exchangers 1 tend to be consistent, the regenerative heat exchangers 1 are switched to ensure that the temperature of the circulating gas after heat exchange is 800-1000°C, and the temperature of the low-temperature flue gas after preheating of the scrap steel is lower than 600°C. The temperature of the circulating gas can be controlled, thereby solving the problems of local overheating, soft melting and adhesion of the scrap steel.

[0072] The system of the present invention further comprises a gas storage tank, in which inert gas at room temperature is stored, and the gas storage tank is used to make up for the circulating gas released during the circulation process.

[0073] It should be noted that the system of the present invention also includes a circulating gas treatment unit; the circulating gas treatment unit is connected to the scrap steel preheating unit through a pipeline; the circulating gas treatment unit includes a dust removal module and a harmful gas treatment module; wherein the harmful gas treatment module adopts a treatment method of high-temperature calcination or activated carbon adsorption; for flue gas with large dust, a dust removal module is used to capture solid particles therein; for harmful gases generated by preheating, high-temperature calcination or activated carbon adsorption is used for treatment; the gas treated by the circulating gas treatment unit is discharged from the system through an external exhaust pipe, and an eighth shut-off valve 15 is provided on the external exhaust pipe; the dust content of the gas during external discharge is ≤5mg / m 3 .

[0074] In the prior art, when the scrap steel is directly heated by flame, the excessive heat concentration may easily cause the scrap steel to overheat, soften and bond, thus affecting the subsequent smelting. Compared with the prior art, the present invention uses circulating gas composed of inert gas to heat the scrap steel, which can avoid the occurrence of high-temperature oxidation of the scrap steel.

[0075] It should be noted that the high temperature distribution unit and the low temperature distribution unit of the present invention are both used to provide a buffer space for the circulating gas entering therein, thereby reducing the pressure, flow and temperature fluctuations caused by gas switching.

[0076] Since the high and low temperature distribution chamber has a large pipe diameter, which is equivalent to a gas storage tank, it can reduce the fluctuations caused by gas switching under certain conditions.

[0077] Specifically, the high temperature distribution unit of the present invention is the high temperature distribution chamber 9, and the low temperature distribution unit is in the low temperature distribution chamber 10. Both the high temperature distribution chamber 9 and the low temperature distribution chamber 10 are cylindrical structures, and the inner walls of the high temperature distribution chamber 9 and the low temperature distribution chamber 10 are lined with refractory materials to resist high temperatures.

[0078] The scrap steel preheating unit of the present invention comprises a scrap steel preheating bin 11; the scrap steel preheating bin 11 is connected to a high temperature distribution unit through a third section of circulating gas delivery pipeline; the scrap steel preheating bin 11 is connected to a low temperature distribution unit through a fourth section of circulating gas delivery pipeline; a fifth stop valve 12 and a second forced gas circulator 18 are provided on the third section of circulating gas delivery pipeline; a sixth stop valve 13 and a third forced gas circulator 19 are provided on the fourth section of circulating gas delivery pipeline. Among them, the second forced gas circulator 18 is a high temperature circulation fan, and the third forced gas circulator 19 is a low temperature circulation fan, the high temperature circulation fan can force circulation of the heated circulation gas, and the low temperature circulation fan can force circulation of the low temperature circulation gas after heat exchange with the scrap steel.

[0079] Specifically, the high temperature distribution chamber 9 and the low temperature distribution chamber 10 contain circulating gases of different temperatures. When the scrap steel in the scrap steel preheating bin 11 needs to be preheated, the fifth stop valve and the sixth stop valve 13 are opened, and the high temperature circulation fan and the low temperature circulation fan are turned on at the same time, so that the circulating gas enters the scrap steel preheating bin 11 from the high temperature distribution chamber 9 through the third section of the circulating gas delivery pipeline, and preheats the scrap steel therein. The preheated circulating gas enters the low temperature distribution chamber 10.

[0080] It should be noted that the air volumes of the high-temperature circulation fan and the low-temperature circulation fan are the same, in order to reduce the mixing of external air or the escape of internal gas due to the different pressures of the two fans.

[0081] The existing heating method is relatively extensive, the scrap preheating effect is poor due to unevenness, the exhaust gas temperature is high, and the heating efficiency is low. Compared with the prior art, the present invention can improve the uniformity of scrap preheating by forcing circulating gas to penetrate the scrap through a high-temperature circulating fan.

[0082] It should be pointed out that the circulating gas enters from the bottom of the scrap steel preheating bin 11, and the scrap steel in the bin is preheated in a bottom-in-top-out manner. The circulating gas flow rate is 5 to 30 m / s. The bottom-in-top-out manner is beneficial to heat transfer, and high-speed gas is beneficial to improving the convection heat transfer coefficient. Gas circulation heating reduces the heat loss caused by smoke exhaust and improves the preheating efficiency. The high-temperature distribution chamber 9 makes the circulating gas temperature uniform to avoid overheating and soft melting caused by local high temperature.

[0083] It should be noted that the number of the scrap steel preheating bins 11 of the present invention is m (m≥1). When m>1, the functions of drying, heating and heat preservation can be achieved by distributing circulating gas among multiple bins.

[0084] For example, the number of scrap steel preheating bins 11 of the present invention is four, namely the first scrap steel preheating bin, the second scrap steel preheating bin, the third scrap steel preheating bin and the fourth scrap steel preheating bin; wherein the first scrap steel preheating bin, the second scrap steel preheating bin, the third scrap steel preheating bin and the fourth scrap steel preheating bin are arranged in parallel with each other, the first scrap steel preheating bin is connected to the third section of the circulating gas delivery pipeline through a first branch pipe, the second scrap steel preheating bin is connected to the third section of the circulating gas delivery pipeline through a second branch pipe, the third scrap steel preheating bin is connected to the third section of the circulating gas delivery pipeline through a third branch pipe, and the fourth scrap steel preheating bin is connected to the third section of the circulating gas delivery pipeline through a fourth branch pipe. In addition, a first valve is provided on the first branch pipe, a second valve is provided on the second branch pipe, a third valve is provided on the third branch pipe, and a fourth valve is provided on the fourth branch pipe.

[0085] Compared with the prior art, the present invention sets a plurality of scrap steel preheating bins 11 in parallel, and sets different valves on each branch pipe, thereby individually controlling the amount and speed of circulating gas entering the bin, which can realize efficient and continuous operation of multiple bins, efficiently utilize heat sources to realize scrap steel preheating, and at the same time reduce gas fluctuations and improve the preheating efficiency of circulating gas. It should be pointed out that scrap steel preheating includes baking, heat preservation and heating processes performed in sequence.

[0086] In view of the fluctuation of high-temperature flue gas, the present invention utilizes the heat storage characteristics of the heat storage heat exchanger 1 (heat storage body), stores more heat during peak hours and controls heat release during low hours, thereby maintaining the temperature of the high-temperature distribution chamber 9 stable.

[0087] It should be noted that the low-temperature distribution chamber 10 of the present invention is connected to the third-section circulating gas delivery pipeline through the fifth-section circulating gas delivery pipeline. The fifth-section circulating gas delivery pipeline is provided with a seventh stop valve 14. When the seventh stop valve 14 is opened, the low-temperature circulating gas in the low-temperature distribution chamber 10 can enter the scrap steel preheating bin 11 through the low-temperature forced fan.

[0088] In order to judge the preheating state in the scrap steel preheating bin 11, a third temperature sensor 16 is provided at the air inlet position of the scrap steel preheating bin 11 of the present invention, and a fourth temperature sensor 17 is provided at the air outlet position thereof, and the preheating state in the scrap steel preheating bin 11 is judged by the temperatures of the third temperature sensor 16 and the fourth temperature sensor 17; when the temperature of the third temperature sensor 16 exceeds 950°C, it indicates that the gas temperature is too high and the fifth stop valve 12 needs to be closed, and the seventh stop valve 14 needs to be opened to introduce low-temperature circulating gas into the scrap steel preheating bin 11 to lower its temperature and avoid overheating of the scrap steel to produce soft melting; when the temperature of the fourth temperature sensor 17 is higher than 600°C, it indicates that the scrap temperature in the scrap steel preheating bin 11 is relatively high, and the fan flow rate is reduced, and the excess circulating gas is allocated to other preheating bins to improve the preheating effect.

[0089] It should be noted that the temperature of the circulating gas entering the scrap steel preheating bin 11 is ≤ 950° C. to avoid overheating and softening of the scrap steel.

[0090] It should be noted that the present invention transfers heat from external high-temperature flue gas or other heat sources to the scrap steel, thereby achieving heating while avoiding direct contact between the scrap steel and the external flue gas, thereby solving the problems of composition change and overoxidation.

[0091] The present invention can control the temperature of the circulating gas by controlling the temperature of the high-temperature distribution chamber 9 within the range of 800-1000°C: when the temperature of the high-temperature distribution chamber 9 is too high (greater than 1000°C), inert circulating gas is added from the gas storage tank to the low-temperature distribution chamber 10 to cool the low-temperature circulating gas from the low-temperature distribution chamber 10; when the temperature of the high-temperature distribution chamber 9 is too low (lower than 800°C), the heat exchange of the heat storage heat exchanger 1 is enhanced; if the temperature of the high-temperature distribution chamber 9 is too low due to the low temperature of the high-temperature flue gas, an additional heat source can be used for supplementary heat to ensure the preheating effect of the scrap steel. The present invention can solve the problems of local overheating, soft melting and adhesion of scrap steel by controlling the temperature of the high-temperature distribution chamber 9.

[0092] On the other hand, the present invention also provides a method for preheating scrap steel with regenerative circulating gas using the above system, the method comprising the following steps:

[0093] Step 1: firstly introduce the heating gas into the heat storage heat exchange unit for heat exchange so as to store heat in the heat storage heat exchange unit; then introduce the circulating gas into the heat storage heat exchange unit for heat exchange so as to release heat in the heat storage heat exchange unit;

[0094] In the above step 1, the heat storage process of the thermal storage heat exchanger 1 includes: opening the first stop valve 4 and the second stop valve 5, closing the third stop valve 6 and the fourth stop valve 7, and introducing high-temperature flue gas, flames generated by combustion or hot air generated by other heat sources into the thermal storage heat exchanger 1 for heat exchange; when the temperatures of the first temperature sensor and the second temperature sensor 3 are close to each other, switching the two groups of stop valves, that is, closing the first stop valve 4 and the second stop valve 5, to complete the heat storage of the thermal storage heat exchanger 1.

[0095] In the above step 1, when the first stop valve 4 and the second stop valve 5 are closed, the third stop valve 6 and the fourth stop valve 7 are opened to introduce the circulating gas to be heated into the thermal storage heat exchange unit and complete the heat exchange between the circulating gas and the thermal storage heat exchanger 1.

[0096] In the above step 1, when heat storage is performed, when the temperature of the first temperature sensor 2 is 800-1000°C, heat storage is stopped; when heat storage is stopped, the exhaust temperature of the heating gas is controlled below 200°C.

[0097] In the above step 1, the circulating gas after heat exchange is heated to 800-1000°C.

[0098] Step 2, transporting the heated circulating gas to the high temperature distribution chamber 9;

[0099] In the above step 2, the fourth stop valve 7 is opened, and the heated circulating gas is transported to the high-temperature distribution chamber 9, which can provide a buffer space for the circulating gas entering therein, thereby reducing the pressure, flow and temperature fluctuations caused by gas switching.

[0100] In the above step 2, the temperature of the circulating gas in the high temperature distribution chamber 9 is 800-1000°C.

[0101] Step 3: transport the circulating gas in the high-temperature distribution chamber 9 to the scrap steel preheating unit, and use the heated circulating gas to preheat the scrap steel in the bin;

[0102] In the above step 3, the fifth stop valve and the sixth stop valve 13 are opened, and the high-temperature circulation fan and the low-temperature circulation fan are turned on at the same time, so as to force the circulating gas from the high-temperature distribution chamber 9 through the third section of the circulating gas conveying pipeline into the scrap steel preheating bin 11, and preheat the scrap steel therein.

[0103] In the above step 3, when the scrap steel is preheated, the circulating gas enters through the bottom of the scrap steel preheating bin 11, and the scrap steel in the bin is preheated in a bottom-in-top-out manner, and the circulating gas flow rate is 5 to 30 m / s.

[0104] The bottom-in-top-out method is beneficial to heat transfer, high-speed gas is beneficial to improving the convection heat transfer coefficient, gas circulation heating reduces heat loss caused by smoke exhaust, and improves preheating efficiency; the high-temperature distribution chamber 9 makes the circulating gas temperature uniform, avoiding overheating and soft melting caused by local high temperature.

[0105] In the above step 3, the scrap steel preheating process includes a baking mode, a heat preservation mode and a heating mode in sequence.

[0106] The baking mode is used to heat scrap steel below 200°C. When the scrap steel adopts the baking mode, the circulating gas flow rate is 3-5m / s and the heating rate is 50-100°C / min, which is used to slowly increase the temperature of the scrap steel. The baking mode is used to remove the oil stains mixed in the scrap steel; the flue gas in the baking mode is discharged after treatment and is not circulated.

[0107] The heating mode is used to heat the scrap steel within the range of 200°C to 800°C. At this time, the circulating gas flow rate is 10 to 30 m / s, and the high-speed circulating gas is used to heat the scrap steel at a high speed.

[0108] The insulation mode is used to keep scrap steel warm. At this time, the circulating gas flow rate is 5 to 15 m / s, and the circulating gas flow rate is reduced to maintain the temperature unchanged or slowly increase the temperature.

[0109] It should be noted that baking is a pretreatment and is only performed once, while heating and heat preservation can be repeated according to smelting needs.

[0110] Step 4: The circulating gas that has exchanged heat with the scrap steel is first introduced into the low-temperature distribution chamber 10 to complete a cycle; then, steps 1 to 3 are repeated.

[0111] In the above step 4, during the process of heating the circulating gas by the regenerative heat exchanger 1, when the temperature of the circulating gas after heating is lower than 800°C, the third stop valve 6 and the fourth stop valve 7 are closed, and the first forced gas circulator 8 is closed, and then the first stop valve 4 and the second stop valve 5 are opened, and the steps are repeated.

[0112] Compared with the prior art, the present invention utilizes circulating gas to perform indirect heat exchange with heating gas (eg, high-temperature flue gas) and direct heat exchange with scrap steel, and can transfer heat from high-temperature flue gas to scrap steel to achieve scrap steel heating.

[0113] Compared with the prior art, firstly, the high-temperature flue gas and circulating gas separation mode of the present invention can prevent the chlorine, copper and other ions contained in the flue gas from reacting with the organic components in the scrap steel to generate dioxins during the preheating process, thereby reducing environmental pollution. The circulating gas uses inert components, which can avoid oxidation during the preheating process of the scrap steel at high temperature and reduce iron loss.

[0114] Secondly, the present invention utilizes the second forced gas circulator 18 to force the heated circulating gas to circulate at high speed so as to penetrate the scrap steel at high speed, which can improve the heat transfer between the scrap steel and the preheating efficiency; the gas is in a circulating state to reduce the external exhaust volume and avoid heat loss caused by smoke exhaust.

[0115] Furthermore, the present invention homogenizes the temperature of the circulating gas through the high-temperature distribution chamber 9 and the low-temperature distribution chamber 10, thereby avoiding the occurrence of scrap steel soft melting caused by excessive local temperature.

[0116] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A system for preheating scrap steel using regenerative circulating gas, characterized in that: The system comprises a heat storage heat exchange unit, a high temperature distribution unit, a scrap steel preheating unit and a low temperature distribution unit which are sequentially connected to form a closed loop; The scrap steel to be preheated is arranged in the scrap steel preheating unit, and the circulating gas can be circulated in sequence among the regenerative heat exchange unit, the high temperature distribution unit, the scrap steel preheating unit and the low temperature distribution unit; The regenerative heat exchange unit can utilize the heated gas to indirectly exchange heat with the circulating gas; and the scrap steel preheating unit can utilize the heated circulating gas to preheat the scrap steel to be preheated.

2. The system for preheating scrap steel using regenerative circulating gas according to claim 1, characterized in that: The thermal storage heat exchange unit includes a thermal storage heat exchanger; The two ends of the heat storage heat exchanger are respectively the first end and the second end of the heat exchanger; the first end of the heat exchanger is provided with a high-temperature flue gas inlet, and the high-temperature flue gas inlet is connected to the high-temperature flue gas input pipeline; the second end of the heat exchanger is provided with a high-temperature flue gas outlet, and the high-temperature flue gas outlet is connected to the high-temperature flue gas output pipeline.

3. The system for preheating scrap steel using regenerative circulating gas according to claim 2, characterized in that: The high-temperature flue gas input pipeline is provided with a first stop valve; the high-temperature flue gas output pipeline is provided with a second stop valve; the first stop valve and the second stop valve are valves in the same group; the valves in the same group have the same actions.

4. The system for preheating scrap steel using regenerative circulating gas according to claim 3, characterized in that: The heat exchanger is also provided with a circulating gas inlet at the second end, and the circulating gas inlet is connected to the low-temperature distribution unit through a first section of circulating gas delivery pipeline; The first end of the heat exchanger is also provided with a circulating gas outlet, and the circulating gas outlet is connected to the high-temperature gas distribution unit through a second section of the circulating gas delivery pipeline.

5. The system for preheating scrap steel using regenerative circulating gas according to claim 4, characterized in that: The first section of the circulating gas delivery pipeline is provided with a third stop valve; the second section of the circulating gas delivery pipeline is provided with a fourth stop valve; the third stop valve and the fourth stop valve are valves of the same group, and the valves of the same group have the same action; The third stop valve and the fourth stop valve are valves of different groups from the first stop valve and the second stop valve, and the valves of different groups have opposite actions.

6. The system for preheating scrap steel using regenerative circulating gas according to claim 5, characterized in that: The first section of the circulating gas delivery pipeline is also provided with a first forced gas circulator.

7. The system for preheating scrap steel using regenerative circulating gas according to claim 5, characterized in that: A first temperature sensor is provided near the first end of the heat exchanger; a second temperature sensor is provided near the second end of the heat exchanger; When the temperatures of the first temperature sensor and the second temperature sensor tend to be consistent, the two groups of stop valves are switched.

8. The system for preheating scrap steel using regenerative circulating gas according to claim 1, characterized in that: The scrap steel preheating unit comprises a scrap steel preheating bin; The scrap steel preheating bin is connected to the high temperature distribution unit through the third section of the circulating gas delivery pipeline; the scrap steel preheating bin is connected to the low temperature distribution unit through the fourth section of the circulating gas delivery pipeline; The third section of the circulating gas delivery pipeline is provided with a fifth stop valve; the fourth section of the circulating gas delivery pipeline is provided with a sixth stop valve.

9. The system for preheating scrap steel using regenerative circulating gas according to claim 8, characterized in that: The third section of the circulating gas delivery pipeline is also provided with a second forced gas circulator; the fourth section of the circulating gas delivery pipeline is also provided with a third forced gas circulator.

10. A method for preheating scrap steel using regenerative circulating gas, characterized in that: The system for preheating scrap steel using regenerative circulating gas according to any one of claims 1 to 9 is adopted, and the method comprises the following steps: Step 1, introducing the heating gas into the heat storage heat exchange unit for heat exchange to store heat in the heat storage heat exchange unit; then introducing the circulating gas into the heat storage heat exchange unit for heat exchange to release heat in the heat storage heat exchange unit; Step 2, transporting the heated circulating gas to a high temperature distribution unit; Step 3: transporting the circulating gas in the high-temperature distribution chamber to the scrap steel preheating unit, and using the heated circulating gas to preheat the scrap steel in the bin; Step 4: Introduce the circulating gas that has completed the heat exchange with the scrap steel into the low-temperature distribution chamber to complete the cycle; then, repeat steps 1 to 3.

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