A method for preventing a denitration heating furnace from shutting down during blast furnace air shutdown

Abstract

The present invention belongs to the technical field of iron and steel smelting, and particularly relates to a method for preventing the denitration heating furnace from going out of fire during the process of shutting down the blast furnace. The method includes: alternately reducing pulverized coal and oxygen in the blast furnace to control the composition of the gas in the heating furnace, wherein during the process of shutting down the blast furnace, the lower calorific value of the blast furnace gas ≥ 2950 KJ / m3. By alternately reducing pulverized coal and oxygen in the blast furnace, the sharp fluctuation of the blast furnace gas composition is avoided, thereby preventing the calorific value of the gas from fluctuating too much, and ensuring that the heating furnace does not go out of fire.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a method for preventing a denitration heating furnace from shutting down during a blast furnace air stoppage process. Background Art

[0002] At present, environmental protection requires that steel enterprises must desulfurize and denitrify the flue gas from sintering and pelletizing. The flue gas can only be discharged into the atmosphere after passing the test. If the flue gas test fails, the machine must be shut down. Our company has built desulfurization and denitrification facilities in sintering and pelletizing according to the requirements: the main process flow of desulfurization is: the waste flue gas generated by sintering (pelletizing) is introduced through the desulfurization inlet flue, enters the absorption tower from the bottom, and removes the SO2 through the reaction of slaked lime and water. The flue gas enters the bag filter from the outlet of the absorption tower; the main process flow of denitrification is: the flue gas after desulfurization passes through the GGH and exchanges heat with the hot flue gas after denitrification. The flue gas after heat exchange is about 240~250℃, and then heated to 280℃ by the heating furnace, and then enters the SCR denitrification reactor. At the same time, the ammonia water from the ammonia water tank is transported to the ammonia water evaporator in the reaction zone by the delivery pump. The ammonia gas mixture after steam evaporation is sprayed into the inlet flue of the SCR reactor through the ammonia spray grid. Under the action of the SCR denitrification catalyst in the reactor, the ammonia gas removes NO in the flue gas. x Selective catalytic reduction to N2 and H2O completes NO x The clean flue gas after denitrification treatment undergoes secondary heat exchange at GGH to about 130~140℃, and the purified clean flue gas is discharged into the atmosphere through the chimney by the induced draft fan.

[0003] In the denitrification process, the heating furnace uses blast furnace gas (the 3# blast furnace gas and the 2# blast furnace gas are directly supplied to sintering desulfurization and denitrification after merging; the 2# blast furnace gas and the 1# blast furnace gas are mixed after the first phase of coking and gas tank and then supplied to 1# and 2# pellets) as fuel for combustion. The optimal reaction temperature of the SCR reactor is around 280℃, so the temperature control of the heating furnace is very important.

[0004] During the blast furnace shutdown process, the heating furnace is very likely to shut down, which will cause the temperature of the SCR reactor to drop rapidly, making it impossible to effectively spray ammonia for denitrification. The outlet nitrogen oxides will increase rapidly until they exceed the standard. The excessive nitrogen oxides will directly cause the pelletizing (sintering) production line to be forced to shut down, seriously affecting production and operations. Summary of the invention

[0005] The present application provides a method for preventing a denitration heating furnace from shutting down during a blast furnace air stoppage, so as to solve the technical problem of a heating furnace shutting down during a blast furnace air stoppage.

[0006] In a first aspect, the present application provides a method for preventing a denitration heating furnace from shutting down during a blast furnace air stoppage, the method comprising:

[0007] The blast furnace is alternately subjected to coal powder reduction and oxygen reduction to control the composition of the blast furnace gas to obtain a heating furnace, wherein during the air stop process, the low calorific value of the blast furnace gas is ≥2950KJ / m 3 .

[0008] During the blast furnace shutdown period, the main reason for the flameout of the heating furnace is that the calorific value of the gas decreases rapidly. The calorific value of the gas decreases greatly before the gas is shut down. At the same time, the nitrogen component in the gas increases significantly.

[0009] Optionally, the number of times of reducing coal powder is ≥2 times.

[0010] Optionally, the oxygen reduction is performed ≥ 3 times.

[0011] Optionally, the reduction of coal powder and oxygen specifically includes: reducing coal powder for the first time, reducing oxygen for the first time, reducing oxygen for the second time, stopping coal powder and stopping oxygen. Optionally, the method further includes: stopping the oxygen of the oxygen-coal gun when the blast furnace starts to stop blowing.

[0012] Optionally, the method further includes:

[0013] When the temperature of the blast furnace top drops to 200°C, the amount of nitrogen in the airtight box is reduced to 1 / 2 of the amount used in the working state.

[0014] Optionally, the method further includes:

[0015] When the blast furnace starts to shut down, reduce the amount of nitrogen purge to 1 / 2-3 / 4 times the amount used in the working state;

[0016] When the air volume of the blast furnace is reduced to 55.0% of the total air volume, the opening degree of the downcomer nitrogen is 1 / 4-1 / 2.

[0017] Optionally, the method further comprises: before the blast furnace stops blowing, controlling the inlet and outlet temperatures of the denitration reactor to 280-285° C. and the negative pressure of the heating furnace to -1.5 to -2.5 KPa;

[0018] Optionally, the method further comprises: before the blast furnace starts to shut down, NO X The concentration is 18~22mg / Nm 3 , X Is a positive integer.

[0019] Optionally, the method further comprises: after reducing the blast furnace air flow, starting high-pressure gas dissipation until the fluctuation of the furnace temperature of the heating furnace is ≤50°C.

[0020] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art: ;

[0021] The method provided in the embodiment of the present application comprises: alternately reducing pulverized coal and reducing oxygen in a blast furnace to control the composition of coal gas in the heating furnace to obtain a heating furnace, wherein during the air stop process, the low calorific value of the blast furnace is ≥2950KJ / m 3 ; By reducing coal powder and oxygen, the blast furnace gas composition can be prevented from fluctuating sharply, thereby avoiding excessive fluctuations in the calorific value of the gas and ensuring that the heating furnace does not shut down. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0024] Figure 1 A flow chart of a method for preventing a denitration heating furnace from shutting down during blast furnace air shutdown provided in an embodiment of the present application. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0026] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. If there is a conflict, the present specification takes precedence. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. For example, room temperature can refer to a temperature within the range of 10 to 35°C.

[0027] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0028] The technical solution of the embodiment of the present application is to solve the above technical problems, and the overall idea is as follows:

[0029] According to a typical embodiment of the present invention, a method for preventing a denitration heating furnace from shutting down during a blast furnace air stoppage is provided, the method comprising:

[0030] The blast furnace is alternately subjected to coal powder reduction and oxygen reduction to control the composition of coal gas in the heating furnace to obtain a stopped-air heating furnace, wherein during the stopped-air process, the low calorific value of the blast furnace is ≥2950KJ / m 3 .

[0031] In the embodiment of the present application, the low calorific value or calorific value variation of the blast furnace is controlled to be 2950-3850KJ / m 3 , which can avoid the denitrification heating furnace from shutting down due to excessive reduction in the calorific value of the gas during the blast furnace shutdown process. If it is not within the above range, it will have the adverse effect of stopping production due to excessive environmental protection indicators.

[0032] Generally speaking, the factors that affect the changes in the composition of coal gas during the blast furnace shutdown process include oxygen-enriched oxygen, nitrogen in the airtight box, nitrogen for coal injection, and nitrogen for purging, etc. When the blast furnace begins to reduce the wind, a large reduction in oxygen to the point of stopping oxygen will reduce the CO concentration in the coal gas and increase the nitrogen concentration, which will affect the composition of the coal gas in the heating furnace.

[0033] In some embodiments, the number of times of reducing coal powder is ≥2 times.

[0034] The reason for controlling the number of times of reducing pulverized coal to ≥ 2 times is to avoid reducing pulverized coal all at once, which will cause the composition of the coal gas in the heating furnace to change too much, thereby increasing the probability of flameout.

[0035] In some embodiments, the oxygen reduction is performed ≥ 3 times.

[0036] The reason for controlling the number of times of reducing pulverized coal to ≥ 3 times is to avoid stopping the oxygen supply after reducing the oxygen once or twice, causing the calorific value in the heating furnace to change too much, thereby increasing the probability of flameout.

[0037] In some embodiments, the reduction of coal powder and oxygen specifically includes: reducing coal powder for the first time, reducing oxygen for the first time, reducing oxygen for the second time, stopping coal powder and stopping oxygen.

[0038] The main factor affecting the composition of coal gas is the nitrogen content. Controlling the amount of coal reduction and oxygen reduction can effectively control the nitrogen content. Therefore, stopping coal and stopping oxygen must be carried out in steps to avoid sudden and large fluctuations in the composition of coal gas. The order of reducing coal and stopping oxygen is to stop the oxygen in the oxygen coal gun first, then reduce coal, and finally reduce oxygen. This not only reduces the nitrogen concentration in the coal gas, but also reduces the nitrogen transported into the furnace by the coal gun, and increases the theoretical combustion temperature before the tuyere. Stopping coal and stopping oxygen are carried out alternately in steps. Stopping coal is divided into two steps, and stopping oxygen is divided into three steps, to avoid a large increase in nitrogen in the coal gas due to direct oxygen cessation, and to avoid excessive increase in the combustion temperature. After stopping coal, stop blowing coal-transporting nitrogen. The coal gun cooling nitrogen stops when the gun is pulled out. The specific operation sequence is as follows:

[0039] Table 3 Coal and oxygen stop operations.

[0040]

[0041] In some embodiments, the method further comprises: stopping the oxygen of the oxygen-coal lance when the blast furnace starts to shut down.

[0042] In some embodiments, the method further comprises:

[0043] When the top temperature of the blast furnace drops to 200° C., the amount of nitrogen in the airtight box is reduced to 1 / 2 of the amount used in the working state.

[0044] In some embodiments, the method further comprises:

[0045] When the blast furnace starts to shut down, reduce the amount of nitrogen purge to 1 / 2-3 / 4 times the amount used in the working state;

[0046] When the blast furnace air volume is reduced to 55.0% of the full air volume, the opening degree of the downcomer nitrogen is 1 / 4-1 / 2 times;

[0047] In order to reduce the nitrogen content in the coal gas, controlling the amount of nitrogen purge and the degree of nitrogen opening in the downcomer can effectively reduce the changes in the coal gas composition and reduce the probability of flameout.

[0048] It is worth pointing out that: according to theoretical calculation, the set conditions are: Si=0.35%, S=0.045%, direct reduction degree rd=0.37, coke ratio 305kg / t, coal ratio = 204 kg / t, slag basicity 1.17, blast humidity 2g / m³, hot air temperature 1245℃, top gas temperature 200℃, molten iron temperature 1500℃. Based on this, the gas composition under different oxygen enrichment conditions is calculated.

[0049] Table 2 Gas composition.

[0050]

[0051] When the oxygen enrichment rate increased from 7% to oxygen cut-off, CO decreased by 4.48% and N2 increased by 9.1%.

[0052] Airtight box nitrogen: Under normal production conditions, the gas generation volume is 1363.73m 3 / t iron, nitrogen consumption in airtight box: 7.43 m 3 / t iron, the nitrogen content in the airtight box accounts for 0.55% of the gas volume. When the air volume is reduced to 1 / 2, the nitrogen content in the airtight box increases to about 1.10%.

[0053] Nitrogen for coal injection: Under normal production conditions, the nitrogen consumption for coal injection is 20.30m 3 / t iron, accounting for 1.49% of the gas volume. When the air volume is reduced to 1 / 2, the proportion of the gas volume increases to about 2.98%.

[0054] Purge nitrogen: The purge nitrogen used before gas outage is mainly gravity dust collector valve stem, valve seat and downcomer nitrogen. The valve stem and valve seat of the dust collector are in the open state, and the downcomer nitrogen is opened before gas outage to purge the downcomer (the purge nitrogen is not equipped with a flow meter, so the impact cannot be calculated).

[0055] In some embodiments, the method further comprises: before the blast furnace stops blowing, controlling the inlet and outlet temperatures of the denitration reactor to 280-285° C. and the negative pressure of the heating furnace to -1.5 to -2.0 KPa;

[0056] The temperature of the SCR reactor is controlled at 280-285℃ and the negative pressure of the heating furnace is -1.5~-2.5KPa. The reason is that the negative pressure is low, the combustion is stable, and it is not easy to flame out. Large negative pressure can easily cause the burner to flame out, which has a positive effect of preventing flameout.

[0057] In some embodiments, the method further comprises: before the blast furnace starts to shut down, NO X The concentration is 30~35mg / Nm 3 , X Is a positive integer.

[0058] Control NO X The concentration is 18~22mg / Nm 3 The reason is that if flameout occurs, there is enough time to re-ignite 1-2 times without exceeding emissions standards, which has the positive effect of preventing emissions from exceeding standards during ignition.

[0059] In some embodiments, the method further comprises: after reducing the blast furnace air flow, starting high-pressure gas dissipation until the fluctuation of the furnace temperature of the heating furnace is ≤50°C.

[0060] During the denitrification heating furnace shutdown process, after the blast furnace begins to reduce the wind, it is expected that the furnace temperature of the heating furnace will drop significantly after 20 minutes and the fire detection will flash. At this time, the 4-5 gear should be maintained and the gas flow should be increased. If the flameout occurs, re-ignition should be organized immediately (a single burner can be heated first) to reduce the probability of flameout.

[0061] The method of the present invention will be described in detail below with reference to embodiments, comparative examples and experimental data.

[0062] Example 1

[0063] A method for preventing a denitration heating furnace from shutting down during a blast furnace air stoppage, the method comprising:

[0064] The blast furnace is alternately subjected to coal powder reduction and oxygen reduction to control the composition of coal gas in the heating furnace to obtain a stopped-air heating furnace, wherein during the stopped-air process, the low calorific value of the blast furnace is ≥2950KJ / m 3 .

[0065] Specifically include:

[0066] The order of stopping coal and oxygen is to stop oxygen coal gun oxygen first, then reduce coal, and finally reduce oxygen. Stop coal and stop oxygen alternately in steps, stop coal in two steps, and stop oxygen in three steps. Stop blowing and transporting nitrogen after stopping coal. Stop cooling nitrogen when pulling out the gun.

[0067] During the air stop process, when the top temperature drops to 200℃, the amount of nitrogen in the airtight box is reduced to 1 / 2 of the usage.

[0068] When the blast furnace starts to reduce air volume, the nitrogen consumption of the gravity dust collector valve stem and valve seat is reduced to 1 / 2. When the air volume of the downcomer is reduced to 4500m3 / min, the nitrogen is opened 1 / 4 to maintain positive pressure, and fully opened after the gas is stopped.

[0069] According to the blast furnace air reduction time, the SCR inlet and outlet temperatures are maintained at 280-285°C half an hour before the air reduction. The negative pressure in the furnace is maintained at about -1.5 to -2.5 KPa. At the same time, NO X Controlled at 18~22mg / Nm 3 between.

[0070] After the blast furnace starts to reduce the wind, it is expected that the furnace temperature of the heating furnace will drop significantly after 20 minutes and the fire detector will flash. At this time, the 4th to 5th gear should be maintained and the gas flow should be increased. If the flameout occurs, re-ignition should be actively organized (a single burner can be heated first).

[0071] Comparative Example 1

[0072] The difference between this comparative example and the embodiment is that: on August 7, 2020, the fans of the 1# and 2# blast furnaces fell off, and the coal and oxygen were stopped instantly, causing the 1# and 3# ball heating furnaces to shut down.

[0073] Comparative Example 2

[0074] The difference between this comparative example and the embodiment is that: for example, on October 9, 2020, the No. 1 blast furnace was overhauled. During the wind reduction process, the No. 1 ball heating furnace had a basically stable blast furnace gas pressure due to a decrease in calorific value (2780KJ / m 3 ), the furnace temperature of the heating furnace dropped rapidly by 200 degrees Celsius in 10 minutes, which then caused the upper burner to flame out.

[0075] Comparative Example 3

[0076] The difference between this comparative example and the exemplary embodiment is that: on August 31, 2020, during the shutdown of the 3# blast furnace, the coal and oxygen were not reduced step by step, causing the sintering heating furnace to shut down.

[0077] It can be seen from the examples and comparative examples that the heating furnace alternately reduces coal powder and oxygen, and the low calorific value of the heating furnace is 2950KJ / m 3 , which is very important to avoid the heating furnace from stalling.

[0078] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0079] 1) Control the factors that affect the calorific value of blast furnace gas to avoid the denitrification heating furnace from shutting down.

[0080] 2) Avoid excessive nitrogen oxides in exhaust gas and protect the environment.

[0081] 3) Avoid shutdown accidents of pelletizing and sintering production lines.

[0082] 4) The calorific value of the gas generated during the air stop process is increased.

[0083] 5) Reduce nitrogen consumption during air stoppage and reduce production costs.

[0084] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or equipment including the elements.

[0085] The foregoing is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preventing a denitrification heating furnace from shutting down during a blast furnace shutdown process. Waste flue gas generated by sintering or pelletizing processes is introduced through a desulfurization inlet flue and enters an absorption tower from the bottom. SO2 is removed from the flue gas through a reaction between slaked lime and water. The flue gas enters a bag filter from the outlet of the absorption tower. The desulfurized flue gas passes through a GGH and exchanges heat with the hot flue gas after denitrification. The flue gas after heat exchange is 240-250°C. After being heated to 280°C by a heating furnace, it enters an SCR denitrification reactor. The method is characterized in that: The method comprises: The blast furnace is sequentially subjected to the first coal reduction, the first oxygen reduction, the second oxygen reduction, the coal pulverization stop and the oxygen stop to control the composition of the gas in the heating furnace, wherein the heating furnace uses blast furnace gas as fuel, and during the air stop process, the low calorific value of the blast furnace gas is ≥2950kJ / m 3 ; The method further comprises: before the blast furnace stops blowing, controlling the inlet and outlet temperatures of the denitration reactor to 280-285° C. and the negative pressure of the heating furnace to -1.5 to -2.5 kPa.

2. The method according to claim 1, characterized in that The method further comprises: stopping the oxygen of the oxygen-coal gun when the blast furnace starts to stop blowing.

3. The method according to claim 1, characterized in that The method further comprises: When the temperature of the blast furnace top drops to 200° C., the amount of nitrogen in the blast furnace top airtight box is reduced to 1 / 2 of the amount used in the working state.

4. The method according to claim 1, characterized in that: The method further comprises: When the blast furnace starts to shut down, reduce the amount of nitrogen purge to 1 / 2-3 / 4 times the amount used in the working state; When the blast furnace air volume is reduced to 55.0% of the total air volume, the opening degree of the downcomer nitrogen is 1 / 4-1 / 2.

5. The method according to claim 1, characterized in that The method further comprises: before the blast furnace starts to stop blowing, NO X The concentration is 18~22mg / Nm 3 , X Is a positive integer.

6. The method according to claim 1, characterized in that The method further comprises: after reducing the blast furnace air flow, starting the high-pressure gas release until the fluctuation of the furnace temperature of the heating furnace is ≤50°C.

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