Method for controlling concentration of nitrogen oxide in coke oven waste gas

Abstract

The invention belongs to the technical field of coke oven nitrogen oxide emission control, and particularly discloses a method for controlling the concentration of nitrogen oxide in coke oven waste gas, which comprises the following steps: firstly, setting the target concentration of nitrogen oxide concentration and the target temperature of furnace top heating standard temperature in a PLC (Programmable Logic Controller), and then reducing the proportion of coke oven gas in mixed gas; the temperature in the furnace is monitored in real time through a temperature sensor at the top of the furnace, and the temperature in the furnace is controlled by controlling the flow of coke oven gas and the flow of air introduced into waste gas, so that the generation of nitrogen oxides is reduced, and the concentration of nitrogen oxides in the waste gas is monitored through a nitrogen oxide sensor; the waste gas is diffused according to the concentration of the nitric oxide and enters a denitration system or circulates into the furnace to reduce the nitric oxide again, so that the problems that the coke oven gas proportion in the mixed gas is high, and the nitric oxide concentration of the waste gas exhausted by the coke oven is too high before entering the denitration system are solved.

Description

Technical Field

[0001] The invention relates to the technical field of nitrogen oxide emission control in coke ovens, and in particular to a method for controlling the concentration of nitrogen oxides in coke oven exhaust gas. Background Art

[0002] The heating medium for coking production is mainly rich coal gas (coke oven gas) and lean coal gas (blast furnace gas, producer gas and mixed coal gas). Among them, coke oven gas is produced in the coking process and comes from the dry distillation process of coal in the coke oven. Its components mainly include hydrogen, methane, carbon monoxide, etc., with a hydrogen content of about 55% and a high calorific value. Due to the fast combustion speed and short flame of hydrogen, the coke oven gas will be burned in a concentrated manner, thus easily forming a high-temperature zone; blast furnace gas is a by-product produced in the iron-making process and mainly comes from the chemical reaction in the blast furnace iron-making process. Its components mainly include carbon dioxide, carbon monoxide, nitrogen, a small amount of hydrogen, etc., of which carbon monoxide accounts for about 25%, and the content of carbon dioxide and nitrogen is about 70%. The calorific value is low and the theoretical combustion temperature is low. However, due to the uneven gas distribution in the combustion system, a high-temperature zone is easily formed in a local position, and a large amount of nitrogen oxides will be generated near the high-temperature zone.

[0003] Nitrogen oxides are one of the harmful substances that pollute the atmosphere. According to the "Emission Standards for Pollutants from Coking Chemical Industry" (GB16171-2012), the "Special Emission Limits for Air Pollution" stipulated in the standard sets the emission limit of nitrogen oxides from coke oven exhaust gas at 150mg / m 3 To reduce NO in conventional coke oven combustion exhaust gas X To meet the emission concentration, a large number of denitrification technologies have emerged, among which SCR and SNCR are the main representatives. SCR and SNCR are environmental protection technologies and measures for back-end management. The main principle is to remove the generated NO X It is recovered and decomposed into harmless gases and discharged into the atmosphere. However, it has the disadvantage of affecting the inlet NO X The concentration requirement is relatively high, among which the NO X Concentration ≤500mg / m 3 The design is only applicable to coke ovens heated by blast furnace gas. When the coke ovens are heated by coke oven gas or other high calorific value gas, the nitrogen oxide emissions from the coke oven exhaust gas will exceed the standard of 150mg / m 3 At this time, the only way to alleviate the discharge port NO is to lower the standard temperature and extend the turnover time. X The risk of exceeding the standard has seriously slowed down the productivity of the coke oven.

[0004] In actual production, when the purified blast furnace gas is introduced into the coke oven, due to the low calorific value of blast furnace gas, some coke oven gas needs to be introduced to increase the calorific value. At this time, a mixed gas is formed. If the proportion of coke oven gas in the mixed gas is high and the combustion temperature is higher than 1750℃, the NO in the coke oven exhaust gas discharged from the chimney will X The content will increase exponentially, and the concentration of nitrogen oxides in the discharged coke oven exhaust gas will be high, increasing the burden on the denitrification system. Summary of the invention

[0005] The object of the present invention is to provide a method for controlling the concentration of nitrogen oxides in coke oven exhaust gas, so as to solve the problem that the proportion of coke oven gas in the mixed gas is high and the nitrogen oxide concentration of the exhaust gas discharged from the coke oven is too high before entering the denitration system.

[0006] To achieve the above object, the present invention provides a basic solution: a method for controlling the concentration of nitrogen oxides in coke oven exhaust gas, comprising the following steps:

[0007] S1. The target concentration of nitrogen oxides and the target temperature of furnace top heating are set in the PLC controller for controlling coke oven production. The nitrogen oxide sensor detects the concentration of nitrogen oxides in the coke oven exhaust gas in real time, and the temperature sensor detects the furnace top temperature in real time, and transmits the furnace top temperature and nitrogen oxide concentration data to the PLC controller;

[0008] S2. The PLC controller controls the flow of coke oven gas and blast furnace gas in the mixed gas in real time, reducing the proportion of coke oven gas in the mixed gas from 4%-4.5% to 3.5%-3.9%;

[0009] S3.PLC controller controls the air flow according to the mixed gas flow;

[0010] S4. The coke oven exhaust gas is mixed with air, and the PLC controller controls the flow rate of the coke oven exhaust gas;

[0011] S5.PLC controller controls the furnace top temperature within the target temperature by increasing or decreasing the blast furnace gas flow and the coke oven exhaust gas flow;

[0012] S6. When the furnace top temperature is within the target temperature, the PLC controller controls the release of the coke oven exhaust gas, entry into the denitrification system or circulation back to S4 according to the concentration of nitrogen oxides in the coke oven exhaust gas.

[0013] The working principle of the present invention is: firstly, a target concentration of nitrogen oxide concentration and a target temperature of a furnace top heating standard temperature are set in a PLC controller, and then the proportion of coke oven gas in the mixed gas is reduced from 4%-4.5% to 3.5%-3.9%, so as to reduce the calorific value of the mixed gas, thereby reducing the temperature of the mixed gas during combustion, and the temperature in the furnace is monitored in real time by a temperature sensor on the furnace top, and the temperature in the furnace is controlled by controlling the flow rate of coke oven gas and the flow rate of coke oven exhaust gas into the air, and the temperature in the furnace is increased by controlling the flow rate of coke oven gas, and the air is depleted by controlling the mixing of coke oven exhaust gas into the air, so that the temperature in the furnace is reduced, and the concentration of nitrogen oxides in the coke oven exhaust gas is monitored by a nitrogen oxide sensor, and the coke oven exhaust gas is released, enters a denitration system or circulated to the furnace according to the concentration of nitrogen oxides.

[0014] The beneficial effects of the present invention are as follows: by reducing the proportion of coke oven gas in the mixed coal gas, the calorific value of the mixed coal gas is reduced, the combustion temperature in the furnace is controlled, thereby reducing the generation of nitrogen oxides in the furnace, and the coke oven exhaust gas with excessively high nitrogen oxide concentration is circulated to the air to deplete the air and reduce the combustion intensity of the mixed coal gas. By accurately controlling the flow rate of the coke oven exhaust gas introduced, the change of the temperature in the furnace is stabilized, thereby reducing the concentration of nitrogen oxides in the coke oven exhaust gas.

[0015] Scheme 2 is the preferred basic scheme. In step S1, the target temperature of the furnace top heating temperature is 1170-1210°C, and the target concentration of nitrogen oxides is 150-500 mg / m 3 ; If the heating temperature in the furnace is too high, it will affect the coking of the coke oven. If the heating temperature in the furnace is too low, a large amount of nitrogen oxides will be produced. If the concentration of nitrogen oxides is too high, it will increase the burden on the denitrification system, and the investment cost of denitrification needs to be increased to make the nitrogen oxides after denitrification meet the emission requirements. If the concentration of nitrogen oxides is too low, it can be released directly without entering the denitrification system.

[0016] Scheme 3, which is the preferred basic scheme, in step S2, when the mixed gas flow rate is 60000Nm 3 / h, the coke oven gas flow rate is reduced to 2100-2340Nm 3 / h; coke oven gas flow rate in mixed gas ranges from 2400-2700Nm 3 / h reduced to 2100-2340Nm 3 / h, reducing the calorific value of the mixed gas, thereby lowering the temperature of the mixed gas during combustion, and ultimately reducing the concentration of nitrogen oxides in the coke oven exhaust gas.

[0017] Scheme 4 is the preferred basic scheme. In step S3, when the mixed gas flow rate is 60000 Nm 3 / h, the air flow is 72000Nm 3 / h.

[0018] Scheme 5: This is the preferred basic scheme. In step S5, the mixed gas flow rate is 60000 Nm 3 / h, when the furnace top temperature is higher than 1210℃, the coke oven gas flow rate is reduced to 2100Nm 3 / h to lower the temperature. If the temperature is between 1170-1210℃, the exhaust gas flow rate of the coke oven in S4 is controlled to remain unchanged; if the temperature is still higher than 1210℃, the exhaust gas flow rate of the coke oven in S4 is controlled to increase. For every 1℃ increase in temperature, the exhaust gas flow rate of the coke oven increases by 500Nm 3 / h;

[0019] Mixed gas flow rate is 60000Nm 3 / h, when the furnace top temperature is lower than 1170℃, by increasing the coke oven gas flow rate to 2340Nm 3 / h to increase the temperature. If the temperature is between 1170-1210℃, the exhaust gas flow rate of the coke oven in S4 is controlled to remain unchanged; if the temperature is still below 1170℃, the exhaust gas flow rate of the coke oven in S4 is controlled to decrease. For every 1℃ decrease in temperature, the exhaust gas flow rate of the coke oven is reduced by 500Nm 3 / h;

[0020] Mixed gas flow rate is 60000Nm 3 / h, when the furnace top temperature is in the range of 1170-1210℃ and the coke oven gas flow rate is in the range of 2100-2340Nm 3 / h range, the flow rate of coke oven exhaust gas in S4 is controlled to remain unchanged; when the temperature in the furnace is too high, the flow rate of coke oven gas in the mixed gas is reduced to lower the temperature of combustion in the furnace to the minimum limit of coke oven gas. If the temperature is still too high, the temperature in the furnace can be lowered by increasing the coke oven exhaust gas introduced into the air. When the temperature in the furnace is too low, the flow rate of coke oven gas in the mixed gas is increased to increase the temperature of combustion in the furnace to the maximum limit of coke oven gas. If the temperature is still too low, the temperature in the furnace can be increased by reducing the coke oven exhaust gas introduced into the air. While controlling the temperature in the furnace, the generation of nitrogen oxides can be reduced.

[0021] Scheme 6, which is the preferred basic scheme, in step S6, when the nitrogen oxide concentration in the coke oven exhaust gas is lower than 150 mg / m 3 When the nitrogen oxide concentration in the coke oven exhaust gas is between 150-500 mg / m 3 When the concentration of nitrogen oxides in the coke oven exhaust gas is higher than 500 mg / m 3 When the concentration of nitrogen oxides is lower than 150mg / m 3 When the exhaust gas meets the emission standard of nitrogen oxides in coke oven exhaust gas, it can be directly released, and the concentration of nitrogen oxides is 150-500mg / m 3When the coke oven exhaust gas is passed into the denitration system, the nitrogen oxides in the coke oven exhaust gas can be further removed. The nitrogen oxide concentration is higher than 500mg / m 3 When the coke oven exhaust gas is introduced into the combustion air, the nitrogen oxides in the coke oven exhaust gas are further reduced.

[0022] Option seven is the preferred basic option. When the outdoor temperature is above -10℃, the fire-watching hole pressure is set to 0~5Pa. When the outdoor temperature is below -10℃, the fire-watching hole pressure is adjusted from 0~5Pa to 6~10Pa. Due to the different room temperatures in winter and summer, the furnace head temperature is increased and the coking temperature is lowered by changing the fire-watching hole pressure, thereby reducing the production of nitrogen oxides. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention is a flow chart of a method for controlling the concentration of nitrogen oxides in coke oven exhaust gas. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below through specific embodiments:

[0025] Example

[0026] like Figure 1 A method for controlling the concentration of nitrogen oxides in coke oven exhaust gas comprises the following steps:

[0027] S1. The nitrogen oxide sensor monitors the nitrogen oxide concentration in the coke oven exhaust gas. The temperature sensor detects the furnace top temperature in real time and transmits the furnace top temperature and nitrogen oxide concentration data to the PLC controller. The target concentration of nitrogen oxide concentration and the target temperature of furnace top heating temperature are set in the PLC controller. The target temperature of furnace top heating temperature is 1170-1210℃, and the target concentration of nitrogen oxide concentration is 150-500mg / m 3 When the outdoor temperature is above -10℃, the fire hole pressure is set to 0~5Pa. When the outdoor temperature is below -10℃, the fire hole pressure is adjusted from 0~5Pa to 6~10Pa.

[0028] S2.PLC controller controls the flow of coke oven gas and blast furnace gas in the mixed gas in real time, reducing the proportion of coke oven gas in the mixed gas from 4%-4.5% to 3.5%-3.9%. When the mixed gas flow is 60000Nm 3 / h, the coke oven gas flow rate is reduced to 2100-2340Nm 3 / h;

[0029] S3.PLC controller controls the air flow according to the mixed gas flow. When the mixed gas flow is 60000Nm 3 / h, the air flow is 72000Nm3 / h;

[0030] S4. The coke oven exhaust gas is introduced into the air, and the PLC controller controls the flow rate of the coke oven exhaust gas;

[0031] S5. Mixed gas flow rate is 60000Nm 3 / h, when the furnace top temperature is higher than 1210℃, the coke oven gas flow rate is reduced to 2100Nm 3 / h, if the temperature is within 1170-1210℃, the exhaust gas flow rate of the coke oven in S4 is controlled to remain unchanged; if the temperature is still higher than 1210℃, the exhaust gas flow rate of the coke oven in S4 is controlled to increase. For every 1℃ increase in temperature, the exhaust gas flow rate of the coke oven increases by 500Nm 3 / h;

[0032] Mixed gas flow rate is 60000Nm 3 / h, when the furnace top temperature is lower than 1170℃, by increasing the coke oven gas flow rate to 2340Nm 3 / h, if the temperature is within 1170-1210℃, the exhaust gas flow rate of the coke oven in S4 is controlled to remain unchanged; if the temperature is still below 1170℃, the exhaust gas flow rate of the coke oven in S4 is controlled to decrease. For every 1℃ lower temperature, the exhaust gas flow rate of the coke oven is reduced by 500Nm 3 / h;

[0033] Mixed gas flow rate is 60000Nm 3 / h, when the furnace top temperature is in the range of 1170-1210℃ and the coke oven gas flow rate is in the range of 2100-2340Nm 3 / h interval, the exhaust gas flow of the coke oven in S4 is controlled to remain unchanged;

[0034] S6. Determine whether the nitrogen oxide concentration in the coke oven exhaust gas is within the target range, control the coke oven exhaust gas to be released, enter the denitration system or circulate back to S4. When the nitrogen oxide concentration in the coke oven exhaust gas is lower than 150mg / m 3 When the nitrogen oxide concentration in the coke oven exhaust gas is between 150-500 mg / m 3 When the concentration of nitrogen oxides in the coke oven exhaust gas is higher than 500 mg / m 3 When the coke oven exhaust gas is controlled to circulate to S4.

[0035] The implementation method of this embodiment is as follows: before use, the target concentration of nitrogen oxides is set to 150-500 mg / m in the PLC controller that controls the coke oven production. 3 The target temperature of the furnace top heating temperature is 1170-1210℃, when the flow rate of the mixed gas is 60000Nm 3 / h, adjust the coke oven gas flow rate to 2100-2340Nm3 / h, the air flow rate is set to 72000Nm 3 / h, and then the coke oven exhaust gas is introduced into the air pipe, and the PLC controller controls the flow rate of the coke oven exhaust gas according to actual needs;

[0036] When in use, the temperature sensor monitors the furnace top temperature in real time. When the furnace top temperature is higher than 1210℃, the coke oven gas flow rate is reduced to 2100Nm 3 / h, if the temperature is within 1170-1210℃, the exhaust gas flow rate of the coke oven in S4 is controlled to remain unchanged; if the temperature is still higher than 1210℃, the exhaust gas flow rate of the coke oven in S4 is controlled to increase. For every 1℃ increase in temperature, the exhaust gas flow rate of the coke oven increases by 500Nm 3 / h; mixed gas flow rate is 60000Nm 3 / h, when the furnace top temperature is lower than 1170℃, by increasing the coke oven gas flow rate to 2340Nm 3 / h, if the temperature is within 1170-1210℃, the exhaust gas flow rate of the coke oven in S4 is controlled to remain unchanged; if the temperature is still below 1170℃, the exhaust gas flow rate of the coke oven in S4 is controlled to decrease. For every 1℃ lower temperature, the exhaust gas flow rate of the coke oven is reduced by 500Nm 3 / h; mixed gas flow rate is 60000Nm 3 / h, when the furnace top temperature is in the range of 1170-1210℃ and the coke oven gas flow rate is in the range of 2100-2340Nm 3 / h interval, the exhaust gas flow of the coke oven in S4 is controlled to remain unchanged;

[0037] At the same time, the nitrogen oxide concentration sensor detects the nitrogen oxide concentration in the coke oven exhaust gas in real time. When the nitrogen oxide concentration in the coke oven exhaust gas is lower than 150mg / m 3 When the nitrogen oxide concentration in the coke oven exhaust gas is between 150-500 mg / m 3 When the concentration of nitrogen oxides in the coke oven exhaust gas is higher than 500 mg / m 3 When the coke oven exhaust gas is circulated and mixed into the air.

[0038] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for controlling the concentration of nitrogen oxides in coke oven exhaust gas, characterized in that: The following steps are involved: S1. The target concentration of nitrogen oxides and the target temperature of furnace top heating are set in the PLC controller for controlling coke oven production. The nitrogen oxide sensor detects the concentration of nitrogen oxides in the coke oven exhaust gas in real time, and the temperature sensor detects the furnace top temperature in real time, and transmits the furnace top temperature and nitrogen oxide concentration data to the PLC controller; S2. The PLC controller controls the flow of coke oven gas and blast furnace gas in the mixed gas in real time, reducing the proportion of coke oven gas in the mixed gas from 4%-4.5% to 3.5%-3.9%; S3.PLC controller controls the air flow according to the mixed gas flow; S4. The coke oven exhaust gas is mixed with air, and the PLC controller controls the flow rate of the coke oven exhaust gas; S5.PLC controller controls the furnace top temperature within the target temperature by controlling the increase or decrease of the blast furnace gas flow rate and the coke oven exhaust gas flow rate mixed into the air; S6. When the furnace top temperature is within the target temperature, the PLC controller controls the release of the coke oven exhaust gas, entry into the denitrification system or circulation back to S4 according to the concentration of nitrogen oxides in the coke oven exhaust gas.

2. A method for controlling the concentration of nitrogen oxides in coke oven exhaust gas according to claim 1, characterized in that: In step S1, the target temperature of the furnace top heating temperature is 1170-1210°C, and the target concentration of nitrogen oxides is 150-500 mg / m 3 .

3. The method for controlling the concentration of nitrogen oxides in coke oven exhaust gas according to claim 1, characterized in that: In step S2, when the mixed gas flow rate is 60000Nm 3 / h, the coke oven gas flow rate is reduced to 2100-2340Nm 3 / h.

4. A method for controlling the concentration of nitrogen oxides in coke oven exhaust gas according to claim 1, characterized in that: In step S3, when the mixed gas flow rate is 60000Nm 3 / h, the air flow is 72000Nm 3 / h.

5. The method for controlling the concentration of nitrogen oxides in coke oven exhaust gas according to claim 1, characterized in that: In step S5, the mixed gas flow rate is 60000Nm 3 / h, when the furnace top temperature is higher than 1210℃, the coke oven gas flow rate is reduced to 2100Nm 3 / h to lower the temperature. If the temperature is between 1170-1210℃, the exhaust gas flow rate of the coke oven in S4 is controlled to remain unchanged; if the furnace top temperature is still higher than 1210℃, the exhaust gas flow rate of the coke oven in S4 is controlled to increase. For every 1℃ increase in temperature, the exhaust gas flow rate of the coke oven increases by 500Nm 3 / h; Mixed gas flow rate is 60000Nm 3 / h, when the furnace top temperature is lower than 1170℃, by increasing the coke oven gas flow rate to 2340Nm 3 / h to increase the temperature. If the temperature is between 1170-1210℃, the exhaust gas flow rate of the coke oven in S4 is controlled to remain unchanged; if the furnace top temperature is still lower than 1170℃, the exhaust gas flow rate of the coke oven in S4 is controlled to decrease. For every 1℃ lower temperature, the exhaust gas flow rate of the coke oven is reduced by 500Nm 3 / h; Mixed gas flow rate is 60000Nm 3 / h, when the furnace top temperature is in the range of 1170-1210℃ and the coke oven gas flow rate is in the range of 2100-2340Nm 3 / h range, the coke oven exhaust gas flow rate in S4 is controlled to remain unchanged.

6. A method for controlling the concentration of nitrogen oxides in coke oven exhaust gas according to claim 1, characterized in that: In step S6, when the nitrogen oxide concentration in the coke oven exhaust gas is lower than 150 mg / m 3 When the nitrogen oxide concentration in the coke oven exhaust gas is between 150-500 mg / m 3 When the concentration of nitrogen oxides in the coke oven exhaust gas is higher than 500 mg / m 3 When the coke oven exhaust gas is controlled to circulate to S4.

7. A method for controlling the concentration of nitrogen oxides in coke oven exhaust gas according to claim 1, characterized in that: When the outdoor temperature is above -10℃, the fire hole pressure is set to 0~5Pa. When the outdoor temperature is below -10℃, the fire hole pressure is adjusted from 0~5Pa to 6~10Pa.

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