Acetylene slag cement denitration ammonia escape control system and method

Abstract

The invention relates to the field of cement kiln flue gas treatment, in particular to a carbide slag cement denitration ammonia escape control system and method. The system comprises an SNCR + SCR denitration system, the ammonia gas control and regulation system comprises an ammonia water injection pump, a flue gas analyzer and a computer which is in signal connection with the flue gas analyzer and the SNCR ammonia water injection pump; the computer is configured to execute the following steps: a, calculating a critical judgment coefficient k = NH3 molecular weight / NO molecular weight = 17 / 30 approximately equal to 0.57; b, when A1 is smaller than or equal to kA2, the SCR ammonia water injection pump is controlled to supplement the ammonia injection amount; and c, when A1 is greater than kA2, calculating an SNCR ammonia water injection amount adjustment value delta q and controlling the SNCR ammonia water injection pump to reduce the ammonia injection amount. By testing the concentration of nitrogen oxide and the concentration of ammonia gas entering the SCR reactor, the ammonia spraying amount of SNCR denitration is adjusted, and meanwhile the concentration of nitrogen oxide and the concentration of ammonia gas in flue gas are adjusted, so that the ammonia-nitrogen ratio is in the optimal ammonia-nitrogen ratio state, and ammonia escape is reduced.

Description

Technical Field

[0001] The present invention relates to the field of cement kiln flue gas treatment, and specifically to a carbide slag cement denitration ammonia slip control system and method. Background Technique

[0002] Nitrogen oxides (NOx) are the main air pollutants, which are generated by fuel combustion in industrial production. The emission of nitrogen oxides has a great impact on the environment and health.

[0003] The ammonia-based denitration technology is a commonly used denitration method for cement kilns, including SNCR and SCR technologies. Ammonia reacts with nitrogen oxides to generate nitrogen and water. Conventional ammonia-based denitration adjusts the ammonia water injection volume by testing the nitrogen oxide concentration in the chimney, but there are problems such as system delay and excessive ammonia slip, resulting in unstable denitration efficiency and secondary pollution.

[0004] In the production process of carbide slag cement plants, due to the use of kiln tail flue gas to dry carbide slag, the release of ammonia is increased, thus increasing the risk of excessive ammonia slip in the chimney.

[0005] CN118594214A "A Denitration Ammonia Slip Emission Control System and Method" relates to a method, including data processing, data filling, concentration prediction, deviation prediction, and collecting ammonia slip concentration and second nitrogen oxide concentration through a monitoring device. This method can achieve ammonia slip emission control, reduce ammonia slip and air pollution, and improve the stability and safety of the denitration system.

[0006] Patent CN211928434U introduces an ammonia slip control device for a denitration system, which consists of an ammonia slip detection device and a control device. The ammonia slip detection device is installed at the outlet of the denitration system and is connected to the input end of the control device. In addition, it includes a slow-release adsorbent injection device, which is located at the inlet of the denitration system and includes a flow regulating solenoid valve and a nozzle. The solenoid valve is connected to the nozzle through a pipeline and is communicated with a storage device storing nano slow-release adsorbent, and the outlet of the nozzle points to the inside of the inlet flue of the denitration system.

[0007] CN 117065570 A "Denitration Ammonia Injection Control Method and System Based on Accurate Measurement of Ammonia Slip" discloses a denitration ammonia injection control method and system based on accurate measurement of ammonia slip, including the following steps: dividing the ammonia injection control area in the SCR inlet flue and dividing the same number of sampling areas in the SCR outlet flue; setting judgment conditions, if the judgment conditions are met, determine whether to adjust ammonia injection according to the ammonia slip concentration deviation or NOx concentration deviation at the SCR outlet, otherwise perform a purging operation on the sampling area and the catalyst or increase the flue gas temperature.

[0008] However, the above-mentioned literature and patents have a series of problems and disadvantages: ①The production process is not suitable for carbide slag cement and cannot solve the problem of ammonia escape in carbide slag cement plants: ② The method of adding ammonia adsorbent increases the cost: ③ The ammonia content in carbide slag is unstable, and the ammonia escape from the chimney fluctuates greatly. The above solutions cannot adapt to the problem of fluctuating ammonia release amount. Summary of the Invention

[0009] In order to solve the above-mentioned technical problems existing in the prior art, the present invention tests the concentrations of nitrogen oxides and ammonia entering the SCR reactor, adjusts the ammonia injection amount of SNCR denitration, and at the same time adjusts the concentrations of nitrogen oxides and ammonia in the flue gas to make the ammonia-nitrogen ratio in the optimal ammonia-nitrogen ratio state, reducing the generation of ammonia slip. One of the purposes of the present invention is to provide a control system for ammonia slip in carbide slag cement denitration, including: SNCR+SCR denitration system, including: Calciner, final cyclone, drying crusher, carbide slag cyclone dust collector, carbide slag dry powder silo, high-temperature fan, electrostatic bag precipitator, tail gas exhaust fan, chimney, SNCR spray gun, SCR reactor, SNCR ammonia water injection pump, ammonia water storage tank; Ammonia control and regulation system, including: An ammonia water injection pump connected between the ammonia water storage tank and the SCR reactor; A flue gas analyzer arranged at the inlet of the SCR reactor for real-time detection of NH3 concentration A1, NO concentration A2 and flue gas volume Q2; the flue gas volume Q1 is measured at the outlet of the preheater; a computer signal-connected to the flue gas analyzer and the SNCR ammonia water injection pump; the computer is configured to execute: a. Calculate the critical determination coefficient k = molecular weight of NH3 / molecular weight of NO = 17 / 30 ≈ 0.57; b. When A1 ≤ kA2, control the SCR ammonia water injection pump to supplement the ammonia injection amount; c. When A1 > kA2, calculate the adjustment value Δq of the SNCR ammonia water injection amount and control the SNCR ammonia water injection pump to reduce the ammonia injection amount.

[0010] Furthermore, the carbide slag in the drying crusher releases NH 3， as a supplementary ammonia source for SCR denitration.

[0011] Furthermore, in process c, the Δq is calculated by the following formula: ; In the formula: A1: Ammonia concentration before the SCR reactor, mg / m 3 ; A2: NO concentration before the SCR reactor, mg / m 3 ; Q1: Flue gas volume at the outlet of the preheater, m 3 / h; Q2: Flue gas volume at the inlet of the SCR reactor, m3 / h; η: The utilization rate of ammonia water for SNCR denitration, taking 75% - 90%; α: The concentration of ammonia water, %; Δq: The adjustment amount of SNCR ammonia water, Kg / h.

[0012] Furthermore, the ammonia-nitrogen ratio in the flue gas entering the SCR reactor reaches the optimal reaction range of 1 - 1.05.

[0013] Another object of the present invention is to provide a method for controlling ammonia slip in carbide slag cement denitration, including the following steps: S1: Install a flue gas analyzer at the inlet of the SCR reactor to detect the NH3 concentration A1, NO concentration A2 and flue gas volume Q2 in real time; the measured flue gas volume at the outlet of the preheater is Q1; S2. Calculate the critical determination coefficient k = 17 / 30 ≈ 0.57; S3. Perform dynamic adjustment: When A1 ≤ kA2, increase the ammonia injection amount of the SCR system; When A1 > kA2, calculate the adjustment value Δq of the SNCR ammonia injection amount and reduce the SNCR ammonia injection amount: S4. Loop through S1 - S3 until the ammonia slip concentration at the chimney outlet ≤ 5mg / m³.

[0014] Furthermore, the carbide slag in the drying crusher releases NH 3， as a supplementary ammonia source for SCR denitration.

[0015] Furthermore, the Δq is obtained by calculating the following formula: ; In the formula: A1: The ammonia concentration before the SCR reactor, mg / m 3 ; A2: The NO concentration before the SCR reactor, mg / m 3 ; Q1: The flue gas volume at the outlet of the preheater, m 3 / h; Q2: The flue gas volume at the inlet of the SCR reactor, m 3 / h; η: The utilization rate of ammonia water for SNCR denitration, taking 75% - 90%; α: The concentration of ammonia water, %; Δq: The adjustment amount of SNCR ammonia water, Kg / h.

[0016] Furthermore, Δq is obtained through the following calculation; (1) The molar amount M1 of ammonia in excess relative to nitrogen oxides, i.e., nitric oxide, at the SCR inlet: ; (2) Let the amount of ammonia water spray to be reduced in SNCR be Δq. Then, the reduction in the amount of nitrogen oxides, i.e., the molar amount, corresponding to the reduction in the ammonia water spray is: ; (3) The amount of ammonia slip reduced due to the reduction in the ammonia spray amount in SNCR, i.e., the molar amount: ; (4) The molar amount of ammonia in excess M1 - the reduced amount of ammonia slip = the reduction in the amount of nitrogen oxides, i.e., the molar amount, corresponding to the reduction in the ammonia water spray: ; (5) Formula rearrangement: .

[0017] Further, the ammonia-nitrogen ratio in the flue gas entering the SCR reactor reaches the optimal reaction range of 1 to 1.05.

[0018] The present invention has the following advantages and beneficial effects: 1. By adding a flue gas analyzer and a computer interlocking control system, a feedforward-feedback dynamic adjustment loop is established in the SNCR+SCR dual denitration system to realize real-time monitoring of the NH3 / NO concentration ratio at the SCR inlet. Based on the molecular weight ratio coefficient k = 0.57, a critical determination criterion for ammonia slip is established, and the adjustment amount of Δq is adjusted through iterative calculation to stably control the ammonia-nitrogen ratio within the optimal reaction range of 1 - 1.05; ensuring that the ammonia-nitrogen ratio at the inlet of the SCR denitration system is within a reasonable range, making full use of the denitration performance of the catalyst, and reducing the generation of ammonia slip. 2. For the special working condition of ammonia release during the drying process of carbide slag, the ammonia released from the carbide slag raw material itself is fully utilized as a supplementary denitration agent, reducing the overall ammonia water usage of the denitration system and the denitration operation cost.

[0019] 3. Breaking through the traditional independent operation mode of SNCR / SCR, through the redistribution of the ammonia spray amount, it is realized that: the SNCR section focuses on the regulation of ammonia source supply, and the SCR section strengthens precise control; the collaborative response time of the two-stage system is shortened to 15 minutes; This technical solution effectively solves the problem of ammonia slip control in the production of carbide slag cement. Compared with the traditional method, while ensuring ultra-low NOx emissions (<50 mg / m³), the control accuracy of ammonia slip is greatly improved, with significant technical progress and industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Ammonia slip control system for denitration of carbide slag cement Figure 2 This is the schematic diagram of the control method for ammonia slip in carbide slag cement denitrification in the present invention.

[0021] In the figure: 1, decomposition furnace; 2, final cyclone; 3, drying crusher; 4, carbide slag cyclone dust collector; 5, carbide slag dry powder silo; 6, high-temperature fan; 7, electric bag precipitator; 8, tail gas exhaust fan; 9, chimney; 10, SNCR spray gun; 11, SCR reactor; 12, SNCR ammonia injection pump; 13, ammonia storage tank; 14, SCR ammonia injection pump; 15, flue gas analyzer; 16, computer. Specific embodiments

[0022] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] Embodiment 1 As Figure 1 shown, this embodiment discloses a control system for ammonia slip in carbide slag cement denitrification, which is improved on the basis of the existing SNCR+SCR denitrification system. The existing SNCR+SCR denitrification system includes a decomposition furnace 1, a final cyclone 2, a drying crusher 3, a carbide slag cyclone dust collector 4, a carbide slag dry powder silo 5, a high-temperature fan 6, an electric bag precipitator 7, a tail gas exhaust fan 8, a chimney 9, an SNCR spray gun 10, an SCR reactor 11, an SNCR ammonia injection pump 12, and an ammonia storage tank 13.

[0024] The control system for ammonia slip in carbide slag cement denitrification adds an ammonia injection pump 14, a flue gas analyzer 15 and a computer 16 on the basis of the SNCR+SCR denitrification system. The SCR ammonia injection pump 14 is arranged between the ammonia storage tank 13 and the SCR reactor 11; the flue gas analyzer 15 is arranged at the inlet of the SCR reactor 11; the SNCR ammonia injection pump 12 and the flue gas analyzer 15 are respectively electrically connected to the computer 16; the computer 16 analyzes and calculates the data of the flue gas analyzer 15, and controls the ammonia injection amount of the SNCR ammonia injection pump 12 according to the result.

[0025] Embodiment 2 This embodiment is based on Figure 1 the control system for ammonia slip in carbide slag cement denitrification, and proposes a control method for ammonia slip in carbide slag cement denitrification, including the following steps: S1: Testing the flue gas composition at the inlet of the SCR reactor; Install a flue gas analyzer at the inlet of the SCR reactor to measure the concentrations of NO and NH3 and the flue gas volume at the SCR inlet; the ammonia concentration meter before the SCR reactor is A1 mg / kg; the NO concentration meter is A2 mg / kg, and the flue gas volume meter is Q2 m 3 / h; measure the flue gas volume meter at the outlet of the preheater as Q1 m 3 / h.

[0026] S2: Judgment of ammonia injection volume adjustment; (1) When A1 ≤ kA2, increase the ammonia injection volume of the SCR denitration system and adjust it normally so that the ammonia-nitrogen ratio in the flue gas entering the SCR reactor reaches the optimal reaction range of 1 to 1.05; (2) When A1 > kA2, reduce the ammonia injection volume of the SNCR denitration system to increase the concentration of nitrogen oxides entering the SCR reactor and reduce the ammonia concentration so that the ammonia-nitrogen ratio is in the optimal reaction range of 1 to 1.05; Specifically, according to the chemical reaction equation of the SNCR reaction: 4NH3↑ + 4NO↑ + O2↑ → 4N2↑ + 6H2O; NH3 and NO react in a molar ratio of 1:1 to judge whether the ammonia in the flue gas is excessive; Therefore, the coefficient k = molecular weight of NH3 / molecular weight of NO = 17 / 30 = 0.57; S3. Dynamically compensate and adjust the calculation of the ammonia injection volume of the SNCR denitration system; S31. Molar amount M1 of ammonia in excess of nitrogen oxides (nitric oxide) at the SCR inlet: ; S32. Let the amount of ammonia water injection to be reduced in SNCR be Δq, then the reduction in nitrogen oxide emissions (molar amount) corresponding to the reduction in ammonia water injection is: ; S33. Ammonia slip reduction (molar amount) due to reduced ammonia injection in SNCR: ; S34. Excess ammonia molar amount M1 - reduced ammonia slip = reduction in nitrogen oxide emissions (molar amount) due to reduced ammonia water injection: ; S35. Formula rearrangement ; In the formula: A1: Ammonia concentration before the SCR reactor, mg / m 3 ; A2: NO concentration before the SCR reactor, mg / m 3 ; Q1: Flue gas volume at the outlet of the preheater, m 3 / h; Q2: Flue gas volume at the inlet of the SCR reactor, m 3 / h; η: Utilization rate of SNCR denitrification ammonia water, generally 75% - 90% can be taken; α: Ammonia water concentration, %; Δq: Adjustment amount of SNCR ammonia water, Kg / h.

[0027] S4: According to the calculation results, adjust the ammonia water injection volume Δq of SNCR denitrification until the expected goal is achieved.

[0028] Working principle: Test the ammonia concentration and nitrogen oxide concentration at the inlet of the SCR reactor 11. When A1 ≤ kA2, use the SCR ammonia water injection pump for injection to supplement the ammonia concentration, so that the ammonia-nitrogen ratio in the flue gas entering the SCR reactor reaches the optimal reaction range of 1 - 1.05. When A1 > kA2, reduce the ammonia injection volume of the SNCR denitrification system through calculation. On the one hand, reduce the ammonia concentration escaping from the preheater, and on the other hand, increase the nitrogen oxide concentration at the outlet of the preheater; after adjustment, the ammonia-nitrogen ratio entering the SCR reactor is in the optimal range of 1 - 1.05, thereby reducing the ammonia escape concentration of the chimney. On the one hand, make the ammonia escape from the chimney up to the standard and reduce secondary pollution, and on the other hand, make full use of the ammonia released during the drying process of carbide slag, reducing the denitrification operation cost of the entire production system.

[0029] Example 3 In a certain carbide slag cement plant, due to the volatility of ammonia released during the drying and crushing of carbide slag, the ammonia escape concentration in the chimney is 20 - 80 mg / m 3 . To achieve ultra-low emissions of nitrogen oxides and ammonia escape in the flue gas, the ammonia escape control method for carbide slag cement denitrification in Example 2 was adopted. A flue gas analyzer was added at the inlet of the SCR reactor to detect the ammonia concentration and nitrogen oxide concentration of the flue gas entering the SCR reactor. When the ammonia concentration is greater than the nitrogen oxide concentration, the ammonia injection volume of the SNCR denitrification system is automatically adjusted through computer calculation, reducing the ammonia injection volume of the SNCR denitrification system and increasing the nitrogen oxide concentration at the outlet of the preheater, so that the ammonia-nitrogen ratio at the inlet of the SCR reactor is in the optimal reaction ratio of 1.05. The ammonia escape of the test chimney is reduced to 5 mg / m 3 , meeting the requirements of ultra-low emissions.

[0030] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention. It is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent substitutions on some or all of the technical features, and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A denitration ammonia slip control system for carbide slag cement, characterized in that, Comprising: SNCR+SCR denitration system, comprising: Calciner, final-stage cyclone, drying crusher, carbide slag cyclone dust collector, carbide slag dry powder silo, high-temperature fan, electrostatic bag precipitator, tail gas exhaust fan, chimney, SNCR spray gun, SCR reactor, SNCR ammonia water injection pump, ammonia water storage tank; Ammonia control and regulation system, comprising: An ammonia water injection pump connected between the ammonia water storage tank and the SCR reactor; A flue gas analyzer arranged at the inlet of the SCR reactor for real-time detection of NH3 concentration A1, NO concentration A2 and flue gas volume Q2; the flue gas volume Q1 is measured at the outlet of the preheater; a computer signal-connected to the flue gas analyzer and the SNCR ammonia water injection pump; the computer is configured to perform: a. Calculate the critical determination coefficient k = molecular weight of NH3 / molecular weight of NO = 17 / 30 ≈ 0.57; b. When A1 ≤ kA2, control the SCR ammonia water injection pump to supplement the ammonia injection amount; c. When A1 > kA2, calculate the SNCR ammonia water injection amount adjustment value Δq and control the SNCR ammonia water injection pump to reduce the ammonia injection amount.

2. The carbide slag cement denitration ammonia slip control system according to claim 1, wherein, The calcium carbide slag in the drying crusher releases NH during the drying process 3， as a supplementary ammonia source for SCR denitrification.

3. The carbide slag cement denitration ammonia slip control system according to claim 1, characterized in that In process c, the Δq is calculated by the following formula: ； In the formula: A1: Ammonia concentration before the SCR reactor, mg / m 3 ; A2: NO concentration before the SCR reactor, mg / m 3 ; Q1: Flue gas volume at the outlet of the preheater, m 3 / h; Q2: Flue gas volume at the inlet of the SCR reactor, m 3 / h; η: SNCR denitration ammonia water utilization rate, taking 75% - 90%; α: ammonia water concentration, %; Δq: SNCR ammonia water adjustment amount, Kg / h.

4. The carbide slag cement denitration ammonia slip control system according to claim 1, wherein, The ammonia-nitrogen ratio in the flue gas entering the SCR reactor reaches the optimal reaction range of 1 - 1.

05.

5. A method for controlling ammonia slip in denitrification of carbide slag cement, characterized in that, Including the following steps: S1: Install a flue gas analyzer at the inlet of the SCR reactor to detect the NH3 concentration A1, NO concentration A2 and flue gas volume Q2 in real time; the flue gas volume measured at the outlet of the preheater is denoted as Q1; S2. Calculate the critical determination coefficient k = 17 / 30 ≈ 0.57; S3. Perform dynamic regulation: When A1 ≤ kA2, increase the ammonia injection amount of the SCR system; When A1 > kA2, calculate the SNCR ammonia injection amount adjustment value Δq and reduce the SNCR ammonia injection amount: S4. Loop through S1 - S3 until the ammonia slip concentration at the chimney outlet ≤ 5mg / m³.

6. The method for controlling ammonia slip in carbide slag cement denitrification according to claim 5, wherein The calcium carbide slag in the drying crusher releases NH during the drying process 3， as a supplementary ammonia source for SCR denitration.

7. The method for controlling ammonia slip in carbide slag cement denitrification according to claim 5, wherein, The Δq is calculated by the following formula: ； In the formula: A1: Ammonia concentration before the SCR reactor, mg / m 3 ; A2: NO concentration before the SCR reactor, mg / m 3 ; Q1: Flue gas volume at the preheater outlet, m 3 / h; Q2: Flue gas volume at the inlet of the SCR reactor, m 3 / h; η: SNCR denitration ammonia water utilization rate, taking 75% - 90%; α: ammonia water concentration, %; Δq: SNCR ammonia water adjustment amount, Kg / h.

8. The method for controlling ammonia slip in carbide slag cement denitrification according to claim 7, wherein Δq is obtained through the following calculation; (1) The molar amount M1 of ammonia in excess of nitrogen oxides, i.e., nitric oxide, at the SCR inlet: ； (2) Let the amount of ammonia water sprayed by SNCR to be reduced be Δq, then the molar amount of nitrogen oxide emission reduction corresponding to the reduced ammonia water spray amount is: ； (3) The molar amount of ammonia slip reduced by SNCR due to the reduced ammonia injection amount: ； (4) The molar amount of excess ammonia M1 - the molar amount of reduced ammonia slip = the molar amount of nitrogen oxide emission reduction corresponding to the reduced ammonia water spray amount: ； (5) Formula rearrangement: 。 9. The method for controlling ammonia slip in carbide slag cement denitrification according to claim 5, wherein, The ammonia-nitrogen ratio in the flue gas entering the SCR reactor reaches the optimal reaction range of 1 - 1.05.

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