Control method for preventing flue gas nitric oxide from exceeding standard in steel rolling heating furnace full-oxygen steel burning process

Abstract

A control method for preventing flue gas nitric oxide from exceeding standard for a steel rolling heating furnace total oxygen steel burning process belongs to the technical field of heating furnace nitric oxide emission reduction, and comprises the following steps: determining initial time intervals of cooling and heating as delta t11 and delta t12 respectively; detecting the temperature deviation of the furnace section; if the actual furnace section temperature is higher than the set furnace temperature and the cooling condition is met, the oxygen flow is reduced in an amplitude limiting mode, and after the time interval delta t11 is waited, the fuel gas flow is adjusted in an amplitude limiting mode according to the set oxygen-fuel ratio r. And if the actual furnace section temperature is lower than the set furnace temperature and the temperature rising condition is met, the gas flow is increased in an amplitude limiting mode, and after the time interval delta t12 is waited, the oxygen flow is adjusted in an amplitude limiting mode according to the set oxygen-fuel ratio r. In order to solve the problem that nitrogen oxide (NOx) of a full-oxygen-fired steel heating furnace exceeds the standard, when the furnace temperature is adjusted, it is guaranteed that an appropriate amount of fuel gas is always in a furnace section to digest oxygen input into the furnace.

Description

Technical Field

[0001] The invention belongs to the technical field of nitrogen oxide emission reduction in heating furnaces, and specifically relates to a control method for preventing excessive nitrogen oxides in flue gas from occurring in a full oxygen steel-sintering process in a steel-rolling heating furnace. Background Art

[0002] At present, the temperature control of heating furnaces commonly used in China mostly adopts double cross limit control technology. An important feature of this control technology is the combustion adjustment priority strategy, that is, when the temperature rises, the combustion air is increased first, and when the temperature drops, the gas is reduced first, in order to ensure that the input gas is fully burned.

[0003] With the full promotion of all-oxygen steelmaking technology, the high-intensity oxidizing property of pure oxygen has made the problem of excessive nitrogen oxides (NOx) increasingly prominent. Even if natural gas is used as the main heating raw material, excessive nitrogen oxides (NOx) still exist, thus becoming a major problem that plagues heating furnace production.

[0004] In addition, through a large amount of actual production process information analysis, it was found that although nitrogen (N2) is an inert gas, once there is no other combustible gas in the furnace, high-purity oxygen can still generate a large amount of nitrogen oxides (NOx). Summary of the invention

[0005] In order to solve the above problems, the present invention proposes: a control method for preventing excessive nitrogen oxides in flue gas from occurring in a steel rolling heating furnace full oxygen steelmaking process, comprising the following steps:

[0006] S1: Determine the initial time intervals for cooling and heating, respectively, Δt 11 , Δt 12 ;

[0007] S2: Detection of furnace section temperature deviation;

[0008] Assume that the oxygen-fuel ratio is r; the time intervals of the reverse double cross limiting control cooling and heating are Δt 11 , Δt 12 ; The waiting time from the start of cross adjustment to detection is Δt2(p), where p is the furnace section number where the billet is located, which is used to select different waiting times. The farther the furnace section is from the nitrogen oxide detection point, the longer the waiting time; the nitrogen oxide emission limit target value is NOx t ; The actual emission value of nitrogen oxides is NOx a ; make

[0009] ε≤NOx a -NOx t ≤0, (1).

[0010] Furthermore, the step S2 further includes the following steps:

[0011] S3: If the actual furnace temperature is higher than the set furnace temperature and meets the cooling condition, the oxygen flow rate is first limited and reduced, and the waiting time interval Δt is 11 After that, the gas flow rate is adjusted according to the set oxygen-fuel ratio r.

[0012] Furthermore, the method further comprises the following steps:

[0013] S4: If the gas flow rate starts to be reduced, after waiting for a period of time Δt2(p), nitrogen oxides (NOx) are detected; if the target deviation of nitrogen oxides (NOx) (NOx a -NOx t ) is less than the critical value ε, ε≤0, any fixed value, then reduce Δt 11 ; If the target deviation of nitrogen oxides (NOx) (NOx a -NOx t ) is greater than 0, then increase Δt 11 , return to execute S2.

[0014] Furthermore, in step S4, the optimal time interval Δt is generated. 11opt Given by formula (2), when the temperature drops

[0015] ε≤minΔ t11 =Δt 11opt (NOx a -NOx t )≤0 (2).

[0016] Furthermore, the step S2 further includes the following steps:

[0017] S5: If the actual furnace temperature is lower than the set furnace temperature and the temperature rise condition is met, the gas flow rate is first limited and increased, and the waiting time interval Δt is 12 After that, the oxygen flow rate is adjusted according to the set oxygen-fuel ratio r.

[0018] Furthermore, the method further comprises the following steps:

[0019] S6: If the oxygen flow rate is increased, after waiting for a period of time Δt2(p), nitrogen oxides (NOx) are detected; if the target deviation of nitrogen oxides (NOx) (NOx a -NOx t ) is less than the critical value ε, then reduce Δt 12 ; If the target deviation (NOx a -NOx t ) is greater than 0, then increase Δt 12 , return to execute S2.

[0020] Furthermore, in step S6, the optimal time interval Δt is generated. 12optGiven by formula (3), when the temperature rises

[0021] ε≤minΔ t12 =Δt 12opt (NOx a -NOx t )≤0 (3).

[0022] The beneficial effects of the present invention are as follows: the present invention aims at the problem of excessive nitrogen oxides (NOx) in an all-oxygen steel heating furnace. When adjusting the furnace temperature, the method ensures that there is always an appropriate amount of gas in the furnace section to digest the oxygen input into the furnace. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart of nitrogen oxide control and prediction in the heating furnace of the present invention. DETAILED DESCRIPTION

[0024] In order to make the technical means and objectives of the present invention easy to understand, the present invention is further described below in combination with specific embodiments. A control method for preventing excessive nitrogen oxides in flue gas from exceeding the standard in a steel rolling heating furnace full oxygen steel burning process is as follows: Figure 1 As shown, the following steps are included:

[0025] S1: Determine the initial time intervals for cooling and heating, respectively, Δt 11 , Δt 12 ;

[0026] S2: Detection of furnace section temperature deviation;

[0027] S3: If the actual furnace temperature is higher than the set furnace temperature and meets the cooling condition, the oxygen flow rate is first limited and reduced, and the waiting time interval Δt is 11 After that, the gas flow rate is adjusted according to the set oxygen-fuel ratio r.

[0028] S4: If the gas flow rate starts to be reduced, after waiting for a period of time Δt2(p), the nitrogen oxides (NOx) are detected. If the target deviation of nitrogen oxides (NOx) (NOx a -NOx t ) is less than the critical value ε, then reduce Δt 11 ; If the target deviation of nitrogen oxides (NOx) (NOx a -NOx t ) is greater than 0, then increase Δt 11 .

[0029] S5: If the actual furnace temperature is lower than the set furnace temperature and the temperature rise condition is met, the gas flow rate is first limited and increased, and the waiting time interval Δt is 12 After that, the oxygen flow rate is adjusted according to the set oxygen-fuel ratio r.

[0030] S6: If the oxygen flow rate is increased, after waiting for a period of time Δt2(p), the nitrogen oxides (NOx) are detected. If the target deviation of nitrogen oxides (NOx) (NOx a -NOx t ) is less than the critical value ε, then reduce Δt 12 ; If the target deviation (NOx a -NOx t ) is greater than 0, then increase Δt 12 .

[0031] S7: Return to execute S2.

[0032] Step S4 is used to generate the optimal time interval Δt 11opt It is given by formula (2).

[0033] Step S6 is used to generate the optimal time interval Δt 12opt It is given by formula (3).

[0034] Assume that the oxygen-fuel ratio is r; the time intervals of the reverse double cross limiting control cooling and heating are Δt 11 , Δt 12 ; The waiting time from the start of cross adjustment to detection is Δt2(p); The nitrogen oxide emission limit target value is NOx t ; The actual emission value of nitrogen oxides is NOx a ; When cooling or heating, adjust the time interval Δt 11 or Δt 12 , so that

[0035] ε≤NOx a -NOx t ≤0, (1)

[0036] When the temperature drops

[0037]

[0038] Or when the temperature rises

[0039]

[0040] Aiming at the problem of excessive nitrogen oxides (NOx) in an all-oxygen steel heating furnace, the present invention proposes a control method to prevent excessive nitrogen oxides (NOx) in flue gas. When adjusting the furnace temperature, this method ensures that there is always an appropriate amount of gas in the furnace section to digest the oxygen input into the furnace. The implementation method is as follows:

[0041] If you need to lower the furnace temperature, first reduce the oxygen flow rate; after Δt 11After (cooling waiting interval) time, the gas flow rate starts to be adjusted according to the set oxygen-fuel ratio r. The system waits for Δt2(p) (detection waiting time, where p is the furnace section number where the billet is located, used to select different waiting times. The farther the furnace section is from the nitrogen oxide detection point, the longer the waiting time) before starting nitrogen oxide (NOx) detection. If the target deviation of nitrogen oxide (NOx) (NOx a -NOx t ) is less than the critical value ε (ε≤0, any fixed value), then reduce Δt 11 The purpose is to reduce the excess gas input; if the target deviation (NOx a -NOx t ) is greater than 0, then increase Δt 11 The purpose is to reduce nitrogen oxide emissions and ensure that flue gas meets emission standards.

[0042] If you need to increase the furnace temperature, first increase the gas flow rate, then 12 (heating waiting interval) time. After the oxygen flow adjustment starts, the system starts nitrogen oxide (NOx) detection after waiting for Δt2(p) (detection waiting time, where p is the furnace section number where the billet is located, used to select different waiting times. The farther the furnace section is from the nitrogen oxide detection point, the longer the waiting time). a -NOx t ) is less than the critical value ε, then reduce Δt 12 ; The purpose is to reduce the amount of excess gas input. If the target deviation (NOx a -NOx t ) is greater than 0, then increase Δt 12 The purpose is to reduce nitrogen oxide emissions and ensure that flue gas meets emission standards.

[0043] 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 technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A control method for preventing excessive nitrogen oxides in flue gas from the full oxygen steelmaking process in a steel rolling heating furnace, characterized in that: The steps include: S1: Determine the initial time intervals for cooling and heating, respectively, Δt 11 , Δt 12 ; S2: Detection of furnace section temperature deviation; Assume that the oxygen-fuel ratio is r; the time intervals of the reverse double cross limiting control cooling and heating are Δt 11 , Δt 12 ; The waiting time from the start of cross adjustment to detection is Δt2(p), where p is the furnace section number where the billet is located, which is used to select different waiting times. The farther the furnace section is from the nitrogen oxide detection point, the longer the waiting time; the nitrogen oxide emission limit target value is NOx t ; The actual emission value of nitrogen oxides is NOx a ; Make ε≤NOx a -NOx t ≤0, (1)。 2. The control method for preventing excessive nitrogen oxides in flue gas from the full oxygen steelmaking process in a steel rolling heating furnace according to claim 1, characterized in that: The step S2 further includes the following steps: S3: If the actual furnace temperature is higher than the set furnace temperature and meets the cooling condition, the oxygen flow rate is first limited and reduced, and the waiting time interval Δt is 11 After that, the gas flow rate is adjusted according to the set oxygen-fuel ratio r.

3. The control method for preventing excessive nitrogen oxides in flue gas from the full oxygen steelmaking process of a steel rolling heating furnace according to claim 2, characterized in that: The following steps are also included: S4: If the gas flow rate starts to decrease, after waiting for a period of time Δt2(p), nitrogen oxides (NOx) are detected; if the target deviation of nitrogen oxides (NOx) (NOx a -NOx t ) is less than the critical value ε, ε≤0, any fixed value, then reduce Δt 11 ; If the target deviation of nitrogen oxides (NOx) (NOx a -NOx t ) is greater than 0, then increase Δt 11 , return to execute S2.

4. The control method for preventing excessive nitrogen oxides in flue gas from the full oxygen steelmaking process in a steel rolling heating furnace according to claim 3, characterized in that: Step S4 is used to generate the optimal time interval Δt 11opt Given by formula (2), when the temperature drops ε≤min Δt11 =Δt 11opt (NOx a -NOx t )≤0 (2)。 5. The control method for preventing excessive nitrogen oxides in flue gas from the full oxygen steelmaking process in a steel rolling heating furnace according to claim 1, characterized in that: The step S2 further includes the following steps: S5: If the actual furnace temperature is lower than the set furnace temperature and the temperature rise condition is met, the gas flow rate is first limited and increased, and the waiting time interval Δt is 12 After that, the oxygen flow rate is adjusted according to the set oxygen-fuel ratio r.

6. The control method for preventing excessive nitrogen oxides in flue gas from the full oxygen steelmaking process in a steel rolling heating furnace according to claim 5, characterized in that: The following steps are also included: S6: If the oxygen flow rate is increased, after waiting for a period of time Δt2(p), nitrogen oxides (NOx) are detected; if the target deviation of nitrogen oxides (NOx) (NOx a -NOx t ) is less than the critical value ε, then reduce Δt 12 ; If the target deviation (NOx a -NOx t ) is greater than 0, then increase Δt 12 , return to execute S2.

7. The control method for preventing excessive nitrogen oxides in flue gas from the full oxygen steelmaking process in a steel rolling heating furnace according to claim 6, characterized in that: Step S6 is used to generate the optimal time interval Δt 12opt Given by formula (3), when the temperature rises ε≤min Δt12 =Δt 12opt (NOx a -NOx t )≤0 (3)。

Images