System and method for removing hydrogen cyanide in blast furnace gas

Abstract

The invention relates to a system and method for removing hydrogen cyanide in blast furnace gas, and belongs to the technical field of ferrous metallurgy waste gas purification. The system comprises a spray washing unit and a wastewater treatment unit, and the spray washing unit is provided with a multi-stage spray washing tower and is used for absorbing hydrogen cyanide in blast furnace gas through alkali liquor countercurrent washing. The wastewater treatment unit is provided with continuous stirred tank reactors connected in series, an inlet of the continuous stirred tank reactors is connected with a water outlet of the multi-stage spray washing tower, and the continuous stirred tank reactors are used for performing catalytic oxidation treatment on generated cyanide-containing wastewater. By integrating gas-phase washing and liquid-phase deep oxidation, hydrogen cyanide is efficiently removed from the source, secondary pollution is thoroughly eliminated, the system has the capacity of adapting to load fluctuation, and a complete technical scheme is provided for solving the problem of treatment of hydrogen cyanide in blast furnace gas.

Description

Technical Field

[0001] This application relates to the field of waste gas purification technology in the iron and steel metallurgical industry, and in particular to a system and method for removing hydrogen cyanide from blast furnace gas. Background Technology

[0002] Blast furnace gas is an important secondary energy source generated during steelmaking. Its combustible components (such as CO and H2) are commonly used for heating or power generation in equipment such as hot blast stoves and boilers. However, in the strongly reducing smelting environment of a blast furnace, nitrogen in the injected pulverized coal is partially converted into hydrogen cyanide (HCN) and present in the gas. As a highly toxic pollutant and a key reactive nitrogen precursor, HCN poses hazards in two main ways: First, direct emissions or leaks pose a serious threat to the environment and human safety; second, and more significantly, when blast furnace gas containing HCN is burned in equipment such as hot blast stoves, under high-temperature conditions, HCN will generate nitrogen oxides (NOx) at an extremely high conversion rate (usually exceeding 80%), becoming a major source of fuel-type NOx.

[0003] Currently, the mainstream technologies for treating HCN in blast furnace gas focus on denitrification of the flue gas produced after combustion, such as selective catalytic reduction (SCR) technology. However, blast furnace gas has a low calorific value, and its flue gas after combustion has characteristics such as a special temperature window, low initial concentration of pollutants but large total amount, and complex background composition. This leads to difficulties for end-of-pipe SCR technology, including easy catalyst poisoning and deactivation, large consumption of reducing agents (such as ammonia), and extremely high system investment and operation and maintenance costs, resulting in poor economic efficiency. Although removing HCN at the source is theoretically more fundamental, existing technologies are difficult to meet engineering requirements. Summary of the Invention

[0004] This application provides a system and method for removing hydrogen cyanide from blast furnace gas to solve the following technical problem: how to develop a source treatment method and system that can adapt to blast furnace gas operating conditions and efficiently and stably remove HCN.

[0005] In a first aspect, embodiments of this application provide a system for removing hydrogen cyanide from blast furnace gas, the system comprising:

[0006] The spray washing unit includes a multi-stage spray washing tower, which is provided from bottom to top with a drain outlet, a blast furnace gas inlet, multiple independent spray sections, and a purified gas outlet. The wastewater treatment unit has its inlet connected to the outlet of the multi-stage spray scrubbing tower. The wastewater treatment unit is equipped with at least two continuous stirred tank reactors connected in series. The continuous stirred tank reactors are equipped with a hydrogen peroxide dosing device and a copper ion catalyst dosing device. A control system is used to monitor the hydrogen cyanide concentration at the blast furnace gas inlet and adjust the number of spray sections in operation based on the hydrogen cyanide concentration.

[0007] Optionally, adjusting the number of spray sections in operation based on the hydrogen cyanide concentration includes: When the hydrogen cyanide concentration is at a normal level, a smaller number of the spray sections are operated to maintain a higher cyanide concentration in the cyanide-containing wastewater and promote subsequent catalytic oxidation reactions. When the hydrogen cyanide concentration is at its peak level, the number of spray sections in operation is increased to ensure that the hydrogen cyanide concentration in the purified gas meets the standard.

[0008] Optionally, the conventional level is no higher than 200 mg / Nm³. 3 The peak level is above 200 mg / Nm 3 ; When the concentration of hydrogen cyanide is ≤200 mg / Nm 3 At that time, the two-stage spray section is operated; When the concentration of hydrogen cyanide is >200 mg / Nm 3 When the number N of the spray sections is running, it satisfies: N = 2 + Ceil( (C - 200) / 100 ), where C is the concentration of hydrogen cyanide, in mg / Nm³. 3 Ceil() is the floor function; and N does not exceed the total number of spray stages.

[0009] Optionally, the number of spray sections is 2 to 5, and each spray section is independently equipped with a spray pipeline and a full-cone nozzle.

[0010] Optionally, the system further includes an alkali tank and an alkali circulation tank; The alkali tank is used to supply NaOH solution of a set mass concentration to the multi-stage spray scrubbing tower; The alkaline solution circulation tank is used to receive and store the treated wastewater from the wastewater treatment unit, and to return the treated wastewater to the multi-stage spray scrubbing tower as spray makeup water.

[0011] Optionally, the wastewater treatment unit further includes a pH adjustment device; The pH adjustment device includes a first pH adjustment sub-device and a second pH adjustment device; The first pH adjustment device is installed on the inlet pipe of the first-stage continuous stirred tank reactor and is used to adjust the pH value of the cyanide-containing wastewater entering the first-stage continuous stirred tank reactor to 10-11. The second pH adjustment device is installed on the inlet pipe of the last stage continuous stirred tank reactor and is used to adjust the pH value of the cyanide-containing wastewater entering the last stage continuous stirred tank reactor to 9.5-9.8.

[0012] Optionally, the copper ion catalyst dosing device is used to maintain the copper ion concentration in the reaction solution at 30 mg / L to 50 mg / L, and the hydrogen peroxide dosing device is used to add hydrogen peroxide at a ratio of 0.30 g / L cyanide-containing wastewater to 0.50 g / L cyanide-containing wastewater.

[0013] In a second aspect, embodiments of this application provide a method for removing hydrogen cyanide from blast furnace gas, the method being adaptable to the system described in any embodiment of the first aspect, the method comprising: Blast furnace gas containing hydrogen cyanide is introduced into the multi-stage spray scrubbing tower from the blast furnace gas inlet and subjected to countercurrent contact scrubbing with NaOH solution atomized through the spray section, so as to absorb the hydrogen cyanide in the blast furnace gas into the NaOH solution, thereby obtaining purified gas and cyanide-containing wastewater. The purified gas is discharged from the purified gas outlet, and the cyanide-containing wastewater is discharged from the drain outlet. The cyanide-containing wastewater is sequentially introduced into the series of continuous stirred tank reactors. Under the catalysis of copper ions, the cyanide-containing wastewater and hydrogen peroxide are subjected to catalytic oxidation treatment to oxidize and decompose the cyanide in the cyanide-containing wastewater, thereby obtaining the treated wastewater.

[0014] Optionally, during the countercurrent contact washing process, the liquid-to-gas ratio of the NaOH solution to the blast furnace gas is 0.7 L / m³. 3 ~10.2 L / m 3 The atomization pressure of the NaOH solution is 2.1 bar to 3.4 bar, and the mass concentration of the NaOH solution is 20% to 30%.

[0015] Optionally, the amount of hydrogen peroxide added is 0.30 g / L to 0.50 g / L of cyanide-containing wastewater.

[0016] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a system for removing hydrogen cyanide from blast furnace gas. The system includes: a spray scrubbing unit comprising a multi-stage spray scrubbing tower, the multi-stage spray scrubbing tower having a drain outlet, a blast furnace gas inlet, multiple independent spray sections, and a purified gas outlet from bottom to top; a wastewater treatment unit, the inlet of which is connected to the drain outlet of the multi-stage spray scrubbing tower, the wastewater treatment unit having at least two continuously stirred tank reactors connected in series, the continuously stirred tank reactors having a hydrogen peroxide dosing device and a copper ion catalyst dosing device; and a control system for monitoring the hydrogen cyanide concentration at the blast furnace gas inlet and adjusting the number of spray sections in operation based on the hydrogen cyanide concentration. Blast furnace gas enters the multi-stage spray scrubbing tower from the bottom blast furnace gas inlet. NaOH solution, after atomization, is sprayed from the spray section, contacting the rising blast furnace gas counter-currently. During this process, gaseous hydrogen cyanide in the gas undergoes a chemical neutralization reaction with the NaOH solution, being efficiently absorbed and converted into soluble cyanide that enters the liquid phase. This achieves the transfer of pollutants from the gas phase to the liquid phase, and the purified gas is sent out from the purified gas outlet. To cope with drastic fluctuations in the hydrogen cyanide concentration in the blast furnace gas, the control system monitors the hydrogen cyanide concentration at the blast furnace gas inlet and dynamically adjusts the number of spray sections in operation. This design allows the system's processing capacity to match changing pollution loads in real time, optimizing operating energy consumption and reagent consumption while ensuring stable removal efficiency. The cyanide-containing wastewater generated after hydrogen cyanide absorption is discharged from the drain outlet of the multi-stage spray scrubbing tower and enters the wastewater treatment unit via connecting pipelines. The cyanide-containing wastewater first enters the first stage of a series of continuous stirred tank reactors. Here, a pH adjustment device adjusts the wastewater to a strongly alkaline environment, creating optimal conditions for subsequent oxidation reactions. In the presence of a copper ion catalyst, hydrogen peroxide added to the cyanide-containing wastewater generates a highly reactive oxidizing agent, rapidly oxidizing cyanide into low-toxicity intermediate products. Before entering the final stage of the continuous stirred tank reactor, the cyanide-containing wastewater undergoes another pH adjustment to fine-tune the reaction environment to a weakly alkaline state, promoting the deep hydrolysis of intermediate products and ultimately completely decomposing cyanide into non-toxic and harmless substances such as nitrogen and carbonates, ensuring that the treated wastewater meets environmental discharge or reuse standards. This embodiment of the application efficiently removes hydrogen cyanide from blast furnace gas before combustion, fundamentally suppressing the potential for nitrogen oxide formation during subsequent combustion and avoiding expensive end-of-pipe flue gas treatment. The method of this embodiment allows the purified blast furnace gas to increase the hot blast temperature during combustion in the hot blast stove without increasing nitrogen oxide emissions, thereby reducing the blast furnace coke ratio and achieving indirect carbon dioxide emission reduction. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of a system for removing hydrogen cyanide from blast furnace gas provided in an embodiment of this application; Figure label: 1-Spray washing unit, 2-Wastewater treatment unit, 3-Multi-stage spray washing tower, 4-Spray section, 5-Continuous stirred tank reactor, 6-Control system, 7-Alkali tank, 8-Alkali circulation tank, 9-pH adjustment device. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0022] Figure 1 This is a schematic diagram of the system for removing hydrogen cyanide from blast furnace gas, provided in an embodiment of this application.

[0023] like Figure 1As shown, in a first aspect, embodiments of this application provide a system for removing hydrogen cyanide from blast furnace gas, the system comprising: The spray washing unit (1) includes a multi-stage spray washing tower (3), which is provided from bottom to top with a drain outlet, a blast furnace gas inlet, a multi-stage independent spray section (4), and a purified gas outlet; Wastewater treatment unit (2), the inlet of the wastewater treatment unit (2) is connected to the outlet of the multi-stage spray scrubbing tower (3), the wastewater treatment unit (2) is provided with at least two continuous stirred tank reactors (5) connected in series, the continuous stirred tank reactor is provided with a hydrogen peroxide dosing device and a copper ion catalyst dosing device; The control system (6) is used to monitor the hydrogen cyanide concentration at the blast furnace gas inlet and adjust the number of spray sections (4) in operation based on the hydrogen cyanide concentration.

[0024] The core equipment of the spray scrubbing unit (1) is the multi-stage spray scrubbing tower (3). The multi-stage spray scrubbing tower (3) is equipped with a blast furnace gas inlet, a purified gas outlet, a drain outlet, and key multi-stage independent spray sections (4). The spray scrubbing unit (1) undertakes the first stage of purification in the system. Its functional goal is to realize the transfer of pollutants from the gas phase to the liquid phase. That is, by using the principle of alkaline chemical absorption, gaseous hydrogen cyanide in the blast furnace gas is captured and transferred to the scrubbing liquid, thereby outputting purified gas and cyanide-containing wastewater.

[0025] The inlet of the wastewater treatment unit (2) is connected to the outlet of the multi-stage spray scrubbing tower (3), and the core equipment is at least two continuous stirred tank reactors (5) connected in series. The wastewater treatment unit (2) undertakes the second stage of the system's treatment task. Its functional goal is to achieve the harmless decomposition of pollutants in the liquid phase, that is, to completely degrade the cyanide in the cyanide-containing wastewater into non-toxic or low-toxic substances through catalytic oxidation, thereby outputting treated wastewater that can be reused or discharged in compliance with standards.

[0026] The core objective of the control system (6) adjustment mechanism is to maintain the hydrogen cyanide concentration at the outlet of the purified gas within a preset standard. Through a control logic combining feedforward and feedback (based on inlet concentration pre-adjustment, which can be combined with outlet concentration fine-tuning), the control system (6) can proactively and promptly offset the impact of fluctuations in the hydrogen cyanide concentration in the blast furnace gas on the final purification effect. This avoids the instantaneous exceedance of the hydrogen cyanide concentration at the outlet of the purified gas due to sudden load changes, transforming the static system that might have needed to be designed according to the maximum processing capacity into an adaptive system that can maintain stable output results, significantly improving process reliability.

[0027] In some embodiments, adjusting the number of spray sections (4) in operation based on the hydrogen cyanide concentration includes: When the hydrogen cyanide concentration is at a normal level, a smaller number of the spray sections (4) are controlled to maintain a higher cyanide concentration in the cyanide-containing wastewater and promote subsequent catalytic oxidation reactions; When the hydrogen cyanide concentration is at its peak level, the number of spray sections (4) in operation is increased to ensure that the hydrogen cyanide concentration in the purified coal gas meets the standard.

[0028] The control system (6) directly obtains the core, fluctuating processing load signal by continuously monitoring the hydrogen cyanide concentration at the blast furnace gas inlet. Based on this signal, the control system (6) issues instructions to increase or decrease the number of spray sections in operation in the multi-stage spray scrubbing tower (3). When the hydrogen cyanide concentration at the blast furnace gas inlet increases, increasing the number of spray sections in operation means simultaneously increasing the effective mass transfer area and the alkali circulation volume, thereby instantly improving the overall processing capacity of the multi-stage spray scrubbing tower (3) to cope with higher loads and ensure purification effect. Conversely, the number of operating sections is reduced to avoid overcapacity.

[0029] In some implementations, the conventional level is no higher than 200 mg / Nm³. 3 The peak level is above 200 mg / Nm 3 ; When the concentration of hydrogen cyanide is ≤200 mg / Nm 3 At that time, the two-stage spray section is operated; When the concentration of hydrogen cyanide is >200 mg / Nm 3 When the number N of the spray sections is running, it satisfies: N = 2 + Ceil( (C - 200) / 100 ), where C is the concentration of hydrogen cyanide, in mg / Nm³. 3 Ceil() is the floor function; and N does not exceed the total number of spray stages.

[0030] When the hydrogen cyanide concentration is ≤200 mg / Nm 3 At that time, two-stage spraying sections are operated; when the hydrogen cyanide concentration is >200mg / Nm³ 3 When the number of operating spray sections N satisfies: N = 2 + Ceil( (C - 200) / 100 ), where C is the hydrogen cyanide concentration in mg / Nm³. 3Ceil() is a rounding function; and N does not exceed the total number of spray stages. This technical feature provides the control system (6) with a precise, objective and automatically executable decision algorithm, defines the direct mathematical function relationship from the input variable "hydrogen cyanide concentration" to the output variable "number of operating spray stages N", and sets a clear decision boundary (200mg / Nm). 3 ) and incremental rule (for every 100 mg / Nm of concentration increase) 3 Theoretically, an additional spray stage is needed, which makes the response of the control system (6) no longer fuzzy or experience-based, but deterministic and predictable. When the hydrogen cyanide concentration is 280 mg / Nm 3 When, according to the formula N = 2 + Ceil( (280 - 200) / 100 ) = 2 + Ceil(0.8) = 2 + 1 = 3, the control system (6) will definitely instruct the operation of the three-stage spray section. This quantitative relationship is the basis of automated precision control.

[0031] In some embodiments, the number of spray sections (4) is 2 to 5, and each spray section is independently equipped with a spray pipe and a full cone nozzle.

[0032] The design of 2 to 5 spray stages (4) provides the necessary structural redundancy and capacity steps for the multi-stage spray scrubbing tower (3) to cope with the changing hydrogen cyanide concentration in blast furnace gas. If fewer than 2 spray stages are set, the basic processing capacity of the multi-stage spray scrubbing tower (3) will be insufficient, and there will be no room for adjustment under the normal fluctuation of hydrogen cyanide concentration, making it difficult to ensure that the hydrogen cyanide concentration at the outlet of the purified gas is stable and meets the standards. If more than 5 spray stages are set, although the theoretical processing capacity is stronger, the construction cost, space occupation and operating resistance (pressure drop) of the multi-stage spray scrubbing tower (3) will increase significantly, while the marginal improvement in processing efficiency will be limited, resulting in a decrease in economic efficiency. The range of 2 to 5 stages achieves an engineering balance between necessary processing capacity, equipment cost and operating energy consumption.

[0033] Each spray section is independently equipped with a spray pipeline and a full-cone nozzle, which is a necessary physical prerequisite for realizing the core control logic of "the control system (6) adjusting the number of spray sections in operation based on the hydrogen cyanide concentration". The independent spray pipeline means that the start-up, stop and addition of alkaline solution (NaOH solution) of each spray section can be controlled by the control system (6) individually. This allows the multi-stage spray scrubbing tower (3) to operate from the smallest 2-stage spray section. According to the increase of hydrogen cyanide concentration, more spray sections are activated step by step until the design upper limit of 5 stages is reached, thereby realizing precise and linear adjustment of the processing capacity to match the changing processing load and achieve the purpose of energy saving and high efficiency. Finally, the modular graded design of 2 to 5 stages and the equipment of independent spray pipelines and full-cone nozzles also improve the operational reliability and maintainability of the multi-stage spray scrubbing tower (3). When a certain spray section or its spray pipeline needs to be repaired or malfunctions, the stage can be shut down independently, and the other spray sections can continue to operate. The system does not need to be shut down as a whole, maintaining the stability of continuous production.

[0034] In some embodiments, the system further includes an alkali tank (7) and an alkali circulation tank (8). The alkaline tank (7) is used to supply the multi-stage spray scrubbing tower (3) with a set mass concentration of NaOH solution; The alkaline circulation tank (8) is used to receive and store the treated wastewater from the wastewater treatment unit (2) and return the treated wastewater to the multi-stage spray scrubbing tower as spray makeup water.

[0035] The alkali tank (7) serves as a centralized storage and supply unit for NaOH solution, ensuring that the multi-stage spray scrubbing tower (3) can continuously obtain sufficient absorbent with the required concentration during operation. The alkali tank (7) allows for unified storage, preparation, concentration monitoring, and replenishment of NaOH solution. This centralized management method is more economical, accurate, and safer than decentralized configuration. It ensures that the NaOH solution supplied to the multi-stage spray scrubbing tower (3) has uniform properties, thereby guaranteeing that the scrubbing effect of each spray stage is predictable and repeatable. At the same time, the buffer capacity of the alkali tank (7) ensures that the continuous operation of the multi-stage spray scrubbing tower (3) is not affected when replenishing fresh alkali solution or performing maintenance, thus improving the operational flexibility and online rate of the entire system.

[0036] The alkaline circulation tank (8) is a dedicated container for receiving the treated wastewater discharged from the wastewater treatment unit (2). This path connects the wastewater treatment unit (2) (the effluent after catalytic oxidation) with the operating medium replenishment point of the spray washing unit (1). This means that the effluent, which has been rendered harmless, meets the standards, and is usually still weakly alkaline, is no longer discharged as waste liquid, but is actively recycled by the system as a valuable process medium, forming an internal resource cycle closed loop of washing consumption → wastewater treatment → purification liquid reuse. This significantly reduces the fresh water consumption and wastewater discharge of the system, and improves environmental benefits and operational economy.

[0037] The "treated wastewater" stored in the alkali circulation tank (8) is mainly water, and contains trace amounts of unconsumed alkalinity and harmless salts. This liquid can be used as an ideal dilution solvent for preparing fresh absorbent (a high-concentration NaOH solution from the alkali tank (7)) or as direct makeup water. Pumping it back into the spray system of the multi-stage spray scrubbing tower (3) can effectively replenish the water lost during the washing process due to evaporation, entrainment, and sewage discharge. Since the reused liquid has undergone strict catalytic oxidation treatment and cyanide has been completely removed, its reuse will not bring pollutants back into the scrubbing tower, thereby maintaining the stability of the water balance of the spray scrubbing unit (1) while ensuring the safety of the circulation.

[0038] In some embodiments, the wastewater treatment unit (2) further includes a pH adjustment device (9); The pH adjustment device (9) includes a first pH adjustment sub-device and a second pH adjustment sub-device; The first pH adjustment device is installed on the inlet pipe of the first-stage continuous stirred tank reactor and is used to adjust the pH value of the cyanide-containing wastewater entering the first-stage continuous stirred tank reactor to 10-11. The second pH adjustment device is installed on the inlet pipe of the last stage continuous stirred tank reactor and is used to adjust the pH value of the cyanide-containing wastewater entering the last stage continuous stirred tank reactor to 9.5-9.8.

[0039] Precisely adjusting the pH of the cyanide-containing wastewater entering the first-stage continuous stirred tank reactor to 10–11 plays several crucial roles. Firstly, this strongly alkaline environment ensures that the cyanide in the wastewater is entirely converted to cyanide ions (CN). - The copper ion catalyst exists stably in this form, preventing cyanide ions from combining to form volatile hydrogen cyanide (HCN) gas, thus ensuring operational safety and preventing the escape of pollutants. Secondly, a pH of 10–11 is one of the optimal activity ranges for the highly efficient catalytic oxidation system composed of copper ion catalyst and hydrogen peroxide, effectively activating the reaction and promoting the rapid oxidation of cyanide to cyanate by hydrogen peroxide.

[0040] After the cyanide-containing wastewater undergoes the initial reaction, the second pH adjustment device fine-tunes the pH of the wastewater entering the final continuous stirred tank reactor to 9.5–9.8. Within this pH range, the cyanate (CNO3) generated in the first stage... - It can be further hydrolyzed at a better rate, and finally degraded into non-toxic nitrogen gas and bicarbonate, thus achieving complete harmlessness of cyanide.

[0041] By setting up two independent control points—the first pH adjustment sub-device and the second pH adjustment sub-device—a proactive and refined management strategy for the reaction process within the multi-stage series continuous stirred tank reactor (5) is established. This strategy acknowledges that the catalytic oxidation decomposition of cyanide is a multi-step series reaction, with each step having different pH requirements. By setting a pH value (10-11) at the beginning of the reaction that is most favorable for initiating oxidation and a pH value (9.5-9.8) at the end of the reaction that is most favorable for completing the final degradation, this design guides and optimizes the transformation path of the reactants throughout the wastewater treatment unit (2), ensuring the highest treatment efficiency and the most thorough degradation depth within the total residence time.

[0042] In some embodiments, the copper ion catalyst dosing device is used to maintain the copper ion concentration in the reaction solution at 30 mg / L to 50 mg / L, and the hydrogen peroxide dosing device is used to add hydrogen peroxide at a ratio of 0.30 g / L cyanide-containing wastewater to 0.50 g / L cyanide-containing wastewater.

[0043] The hydrogen peroxide dosing device and the copper ion catalyst dosing device are two independent functional units. The hydrogen peroxide dosing device is responsible for quantitatively adding hydrogen peroxide solution to the continuous stirred tank reactor (5) at a ratio of 0.30 g / L to 0.50 g / L of cyanide-containing wastewater. The copper ion catalyst dosing device (usually in the form of copper sulfate solution, etc.) is responsible for quantitatively replenishing copper ions to the continuous stirred tank reactor (5) to maintain the copper ion concentration in the reaction solution at 30 mg / L to 50 mg / L. The continuous or intermittent operation of the copper ion catalyst dosing device ensures that a certain concentration of catalytically active copper ions is always maintained in the reaction solution in the continuous stirred tank reactor (5). These copper ions, together with the hydrogen peroxide continuously supplied by the hydrogen peroxide dosing device, constitute a highly efficient catalytic oxidation system (Fenton-like system). In this system, copper ions catalyze the decomposition of hydrogen peroxide to produce active species with strong oxidizing power. These active species can efficiently and selectively oxidize cyanide to cyanate and further degrade it.

[0044] In a second aspect, embodiments of this application provide a method for removing hydrogen cyanide from blast furnace gas, the method being adaptable to the system described in any embodiment of the first aspect, the method comprising: Blast furnace gas containing hydrogen cyanide is introduced into the multi-stage spray scrubbing tower from the blast furnace gas inlet and subjected to countercurrent contact scrubbing with NaOH solution atomized through the spray section, so as to absorb the hydrogen cyanide in the blast furnace gas into the NaOH solution, thereby obtaining purified gas and cyanide-containing wastewater. The purified gas is discharged from the purified gas outlet, and the cyanide-containing wastewater is discharged from the drain outlet. The cyanide-containing wastewater is sequentially introduced into the series of continuous stirred tank reactors. Under the catalysis of copper ions, the cyanide-containing wastewater and hydrogen peroxide are subjected to catalytic oxidation treatment to oxidize and decompose the cyanide in the cyanide-containing wastewater, thereby obtaining the treated wastewater.

[0045] The countercurrent contact scrubbing step utilizes the weak acidity of hydrogen cyanide to rapidly neutralize it with the strong base NaOH, generating water-soluble sodium cyanide, thereby achieving chemical absorption. The countercurrent contact flow arrangement ensures that the gas and liquid phases maintain the maximum average concentration difference (mass transfer driving force) throughout the multi-stage spray scrubbing tower (3), thus achieving higher absorption efficiency. The atomized NaOH solution significantly increases the gas-liquid contact surface area, further enhancing the mass transfer process. The countercurrent contact scrubbing step directly produces two distinct outputs: "purified coal gas" and "cyanide-containing wastewater". The hydrogen cyanide concentration in the "purified coal gas" is significantly reduced to meet the requirements for subsequent combustion or utilization; the "cyanide-containing wastewater" becomes the carrier of pollutants in the liquid phase and is transported to the next treatment step.

[0046] The catalytic oxidation treatment step relies on a catalytic oxidation system composed of copper ions and hydrogen peroxide. Copper ions, as a catalyst, can effectively catalyze the decomposition of hydrogen peroxide to produce strong oxidizing species such as hydroxyl radicals. These species can sequentially oxidize cyanide ions and any possible complexed cyanides in cyanide-containing wastewater into less toxic cyanates, and ultimately degrade them into environmentally friendly substances such as nitrogen, carbon dioxide, and bicarbonates.

[0047] In some embodiments, during the countercurrent contact washing process, the liquid-to-gas ratio of the NaOH solution to the blast furnace gas is 0.7 L / m³. 3 ~10.2 L / m 3 The atomization pressure of the NaOH solution is 2.1 bar to 3.4 bar, and the mass concentration of the NaOH solution is 20% to 30%.

[0048] The liquid-to-gas ratio is less than 0.7 L / m³. 3 At this time, the amount of NaOH solution that can contact a unit volume of blast furnace gas is insufficient, the driving force for gas-liquid mass transfer decreases, resulting in incomplete absorption of hydrogen cyanide. The concentration of hydrogen cyanide at the purified gas outlet may exceed the design allowable value. The liquid-to-gas ratio is higher than 10.2 L / m³. 3While theoretically this can improve removal efficiency, the resistance loss within the multi-stage spray scrubbing tower (3) will increase significantly, and the energy consumption required to drive the blast furnace gas through the multi-stage spray scrubbing tower (3) will rise sharply; simultaneously, the transport load of the alkali circulation pump and the consumption of NaOH solution will also increase uneconomically. Therefore, 0.7L / m 3 ~10.2 L / m 3 The range defines an optimized operating window that balances high removal efficiency with low operating energy consumption.

[0049] The atomization pressure of NaOH solution is 2.1 bar to 3.4 bar to ensure that the NaOH solution forms atomized droplets with optimal size and distribution through the nozzle, thereby establishing an efficient and stable gas-liquid mass transfer interface with blast furnace gas in the multi-stage spray scrubbing tower (3), which is a key physical condition for achieving efficient absorption of hydrogen cyanide. When the atomization pressure is lower than 2.1 bar, the kinetic energy at the nozzle outlet is insufficient, the NaOH solution is not fully atomized, the droplet size is too large, the total specific surface area of ​​the large droplets is small, which limits the contact area between the gas and liquid phases, resulting in a decrease in the mass transfer rate of hydrogen cyanide diffusion from blast furnace gas to NaOH solution; when the atomization pressure is higher than 3.4 bar, although finer droplets can be generated and the specific surface area can be increased, the excessively fine droplets are easily entrained by the rising blast furnace gas flow, which may penetrate the demister in the multi-stage spray scrubbing tower (3), causing alkali loss and potentially affecting subsequent processes; at the same time, the excessively high pressure will unnecessarily increase the energy consumption of the alkali circulation pump. The pressure range of 2.1 bar to 3.4 bar is the equilibrium point for generating droplets with optimal specific surface area and sedimentation characteristics.

[0050] The NaOH solution has a mass concentration of 20%–30%, providing the optimal reaction driving force and material basis for the efficient chemical absorption of hydrogen cyanide. This balances operational safety and economy, and ensures coordinated operation of the spray washing unit (1) and the wastewater treatment unit (2). When the NaOH solution mass concentration is below 20%, the alkalinity of the solution is insufficient, reducing the driving force for the neutralization and absorption of hydrogen cyanide (HCN, a weak acid) in blast furnace gas. This may lead to a decrease in the absorption reaction rate, especially under conditions of high hydrogen cyanide concentration, making it impossible to ensure that hydrogen cyanide is completely converted into cyanide ions (CN). - However, when the hydrogen cyanide enters the liquid phase, the concentration of hydrogen cyanide at the purified gas outlet fails to meet requirements. When the mass concentration of NaOH solution exceeds 30%, although the alkalinity is higher, the corrosiveness of the NaOH solution to equipment and pipelines significantly increases, raising material costs and safety risks. Simultaneously, excessively high concentrations lead to increased viscosity of the NaOH solution, potentially affecting atomization and pumping performance, and unnecessarily increasing alkali consumption costs. A mass concentration range of 20%–30% achieves the optimal balance between efficient absorption and safe, economical operation.

[0051] In some embodiments, the hydrogen peroxide is added at a mass of 0.30 g / L to 0.50 g / L of cyanide-containing wastewater.

[0052] The dosage of hydrogen peroxide is 0.30 g / L to 0.50 g / L of cyanide-containing wastewater, meaning that 0.30 to 0.50 grams of hydrogen peroxide are required to treat each liter of cyanide-containing wastewater. Hydrogen peroxide is a key reactant in the oxidative decomposition of cyanide in cyanide-containing wastewater. When the hydrogen peroxide dosage is below 0.30 g / L of cyanide-containing wastewater, it is insufficient to effectively decompose cyanide (as expressed in CN). - The amount of cyanide required to completely oxidize the wastewater to cyanate and further degrade it into low-toxicity products such as nitrogen and bicarbonate is insufficient. This can lead to incomplete oxidation and the concentration of free cyanide in the treated wastewater may not be able to stably decrease to below the discharge standard. When the amount of hydrogen peroxide added is higher than 0.50 g / L of cyanide-containing wastewater, although it can ensure complete reaction, it will cause a significant excess and waste of hydrogen peroxide, needlessly increasing the operating cost of the wastewater treatment unit (2).

[0053] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0054] Example 1 In this embodiment, the flow rate of the blast furnace gas to be processed is 360,000 Nm³. 3 / h, at a temperature of 150°C.

[0055] Blast furnace gas enters the multi-stage spray scrubbing tower (3) from the blast furnace gas inlet and flows from bottom to top. A prepared 25% NaOH solution is transported from the alkali tank (7) to each spray section (4) through the supply pipeline and sprayed from top to bottom after being atomized by the full cone nozzle.

[0056] The control system (6) monitored that the concentration of hydrogen cyanide in the blast furnace gas was 140 mg / Nm³. 3 According to the preset program, the control system (6) automatically activates the two-stage spray section (4). Under this configuration, the liquid-to-gas ratio of NaOH solution to blast furnace gas is 4.0 L / m³. 3 The atomization pressure of the NaOH solution was 2.5 bar. Through countercurrent contact washing, the hydrogen cyanide in the blast furnace gas was absorbed by the NaOH solution, the purified gas was sent out from the purified gas outlet, and the cyanide-containing wastewater was discharged from the drain outlet. The HCN concentration of the purified gas was reduced to 25 mg / Nm³. 3 The concentration of free cyanide in the cyanide-containing wastewater was 28 mg / L.

[0057] The cyanide-containing wastewater discharged from the multi-stage spray scrubbing tower (3) enters the wastewater treatment unit (2), which is equipped with three continuous stirred tank reactors (5) connected in series. The hydrogen peroxide dosing device adds hydrogen peroxide at a ratio of 0.35 g / L of cyanide-containing wastewater, and the copper ion catalyst dosing device adds copper sulfate solution to maintain the copper ion concentration in the reaction solution at 35 mg / L.

[0058] The pH of the cyanide-containing wastewater entering the first-stage continuous stirred tank reactor was precisely adjusted to 10. After passing through the first-stage continuous stirred tank reactor, the overflowing cyanide-containing wastewater sequentially entered the second-stage and third-stage continuous stirred tank reactors for reaction. The pH of the cyanide-containing wastewater entering the third-stage continuous stirred tank reactor was finely adjusted to 9.6 to optimize the deep oxidation reaction environment. After passing through the third-stage continuous stirred tank reactor, the free cyanide concentration in the cyanide-containing wastewater was 0.2 mg / L. 95% of the treated cyanide-containing wastewater was returned to the alkaline circulation tank (8) for reuse, and the remainder was safely discharged.

[0059] The purified coal gas was sent to the hot blast stove, which increased the top temperature of the hot blast stove from 1320℃ to 1400℃, thereby increasing the hot blast temperature from 1150℃ to 1250℃. The coke ratio was reduced by 15 kg / t of molten iron, achieving a significant reduction in CO2 emissions while ensuring environmental compliance throughout the entire process.

[0060] Example 2 In this embodiment, the blast furnace gas flow rate to be processed is 260,000 Nm³. 3 / h, temperature is 190°C.

[0061] Blast furnace gas enters the multi-stage spray scrubbing tower (3) from the blast furnace gas inlet and flows from bottom to top. A prepared 25% NaOH solution is transported from the alkali tank (7) to each spray section (4) through the supply pipeline and sprayed from top to bottom after being atomized by the full cone nozzle.

[0062] The control system (6) monitored that the concentration of hydrogen cyanide in the blast furnace gas was 80 mg / Nm³. 3 According to the preset program, the control system (6) automatically activates the primary spray section (4). Under this configuration, the liquid-to-gas ratio of NaOH solution to blast furnace gas is 3.0 L / m³. 3 The atomization pressure of the NaOH solution was 2.5 bar. Through countercurrent contact washing, the hydrogen cyanide in the blast furnace gas was absorbed by the NaOH solution, the purified gas was sent out from the purified gas outlet, and the cyanide-containing wastewater was discharged from the drain outlet. The HCN concentration of the purified gas was reduced to 30 mg / Nm³. 3 The concentration of free cyanide in the cyanide-containing wastewater was 16 mg / L.

[0063] The cyanide-containing wastewater discharged from the multi-stage spray scrubbing tower (3) enters the wastewater treatment unit (2), which is equipped with three continuous stirred tank reactors (5) connected in series. The hydrogen peroxide dosing device adds hydrogen peroxide at a ratio of 0.35 g / L of cyanide-containing wastewater, and the copper ion catalyst dosing device adds copper sulfate solution to maintain the copper ion concentration in the reaction solution at 35 mg / L.

[0064] The pH of the cyanide-containing wastewater entering the first-stage continuous stirred tank reactor was precisely adjusted to 10. After passing through the first-stage continuous stirred tank reactor, the overflowing cyanide-containing wastewater sequentially entered the second-stage and third-stage continuous stirred tank reactors for reaction. The pH of the cyanide-containing wastewater entering the third-stage continuous stirred tank reactor was finely adjusted to 9.6 to optimize the deep oxidation reaction environment. After passing through the third-stage continuous stirred tank reactor, the free cyanide concentration in the cyanide-containing wastewater was 0.2 mg / L. 95% of the treated cyanide-containing wastewater was returned to the alkaline circulation tank (8) for reuse, and the remainder was safely discharged.

[0065] The purified coal gas was sent to the hot blast stove, which increased the top temperature of the hot blast stove from 1330℃ to 1400℃, thereby increasing the hot blast temperature from 1130℃ to 1170℃. The coke ratio was reduced by 5 kg / t of molten iron, achieving a significant reduction in CO2 emissions while ensuring environmental compliance throughout the entire process.

[0066] Example 3 In this embodiment, the flow rate of the blast furnace gas to be processed is 330,000 Nm³. 3 / h, temperature is 140°C.

[0067] Blast furnace gas enters the multi-stage spray scrubbing tower (3) from the blast furnace gas inlet and flows from bottom to top. A prepared 25% NaOH solution is transported from the alkali tank (7) to each spray section (4) through the supply pipeline and sprayed from top to bottom after being atomized by the full cone nozzle.

[0068] The control system (6) monitored that the concentration of hydrogen cyanide in the blast furnace gas was 180 mg / Nm³. 3 According to the preset program, the control system (6) automatically activates the secondary spray section (4). Under this configuration, the liquid-to-gas ratio of NaOH solution to blast furnace gas is 6.0 L / m³. 3 The atomization pressure of the NaOH solution was 2.5 bar. Through countercurrent contact washing, the hydrogen cyanide in the blast furnace gas was absorbed by the NaOH solution, the purified gas was sent out from the purified gas outlet, and the cyanide-containing wastewater was discharged from the drain outlet. The HCN concentration of the purified gas was reduced to 30 mg / Nm³. 3 The concentration of free cyanide in the cyanide-containing wastewater was 25 mg / L.

[0069] The cyanide-containing wastewater discharged from the multi-stage spray scrubbing tower (3) enters the wastewater treatment unit (2), which is equipped with three continuous stirred tank reactors (5) connected in series. The hydrogen peroxide dosing device adds hydrogen peroxide at a ratio of 0.35 g / L of cyanide-containing wastewater, and the copper ion catalyst dosing device adds copper sulfate solution to maintain the copper ion concentration in the reaction solution at 35 mg / L.

[0070] The pH of the cyanide-containing wastewater entering the first-stage continuous stirred tank reactor was precisely adjusted to 10. After passing through the first-stage continuous stirred tank reactor, the overflowing cyanide-containing wastewater sequentially entered the second-stage and third-stage continuous stirred tank reactors for reaction. The pH of the cyanide-containing wastewater entering the third-stage continuous stirred tank reactor was finely adjusted to 9.6 to optimize the deep oxidation reaction environment. After passing through the third-stage continuous stirred tank reactor, the free cyanide concentration in the cyanide-containing wastewater was 0.2 mg / L. 95% of the treated cyanide-containing wastewater was returned to the alkaline circulation tank (8) for reuse, and the remainder was safely discharged.

[0071] The purified coal gas was sent to the hot blast stove, which increased the top temperature of the hot blast stove from 1320℃ to 1400℃, thereby increasing the hot blast temperature from 1170℃ to 1250℃. The coke ratio was reduced by 10 kg / t of molten iron, achieving a significant reduction in CO2 emissions while ensuring environmental compliance throughout the entire process.

[0072] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: Indirect carbon emission reduction: After HCN removal, the hot blast stove can operate at a higher temperature without exceeding the standard, and the coke ratio of the blast furnace can be reduced, which indirectly reduces CO2 emissions.

[0073] Environmentally friendly: The embodiments of this invention use H2O2 oxidation to treat cyanide-containing wastewater. The process is clean, and the final products are low-toxicity cyanate, bicarbonate and N2. There is no secondary pollution, and the effluent can be reused or discharged in compliance with standards.

[0074] Flexible and economical operation: The system of this invention has the ability to operate under different conditions and can adapt to the drastic fluctuations in HCN concentration in blast furnace gas. By optimizing the operation strategy, reagent consumption and operating energy consumption are reduced.

[0075] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily 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 this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A system for removing hydrogen cyanide from blast furnace gas, characterized in that, The system includes: The spray washing unit (1) includes a multi-stage spray washing tower (3), which is provided from bottom to top with a drain outlet, a blast furnace gas inlet, a multi-stage independent spray section (4), and a purified gas outlet; Wastewater treatment unit (2), the inlet of the wastewater treatment unit (2) is connected to the outlet of the multi-stage spray scrubbing tower (3), the wastewater treatment unit (2) is provided with at least two continuous stirred tank reactors (5) connected in series, the continuous stirred tank reactor is provided with a hydrogen peroxide dosing device and a copper ion catalyst dosing device; The control system (6) is used to monitor the hydrogen cyanide concentration at the blast furnace gas inlet and adjust the number of spray sections (4) in operation based on the hydrogen cyanide concentration.

2. The system according to claim 1, characterized in that, The adjustment of the number of spray sections (4) in operation based on the hydrogen cyanide concentration includes: When the hydrogen cyanide concentration is at a normal level, a smaller number of the spray sections (4) are controlled to maintain a higher cyanide concentration in the cyanide-containing wastewater and promote subsequent catalytic oxidation reactions; When the hydrogen cyanide concentration is at its peak level, the number of spray sections (4) in operation is increased to ensure that the hydrogen cyanide concentration in the purified coal gas meets the standard.

3. The system according to claim 2, characterized in that, The standard level is no higher than 200 mg / Nm³. 3 The peak level is above 200 mg / Nm 3 ; When the concentration of hydrogen cyanide is ≤200 mg / Nm 3 At that time, the two-stage spray section is operated; When the concentration of hydrogen cyanide is >200 mg / Nm 3 When the number N of the spray sections is running, it satisfies: N = 2 + Ceil( (C - 200) / 100 ), where C is the concentration of hydrogen cyanide, in mg / Nm³. 3 Ceil() is the floor function; and N does not exceed the total number of spray stages.

4. The system according to claim 1, characterized in that, The number of spray sections (4) is 2 to 5, and each spray section is independently equipped with a spray pipeline and a full cone nozzle.

5. The system according to claim 1, characterized in that, The system also includes an alkali tank (7) and an alkali circulation tank (8). The alkaline tank (7) is used to supply the multi-stage spray scrubbing tower (3) with a set mass concentration of NaOH solution; The alkaline circulation tank (8) is used to receive and store the treated wastewater from the wastewater treatment unit (2) and return the treated wastewater to the multi-stage spray scrubbing tower as spray makeup water.

6. The system according to claim 1, characterized in that, The wastewater treatment unit (2) also includes a pH adjustment device (9); The pH adjustment device (9) includes a first pH adjustment sub-device and a second pH adjustment sub-device; The first pH adjustment device is installed on the inlet pipe of the first-stage continuous stirred tank reactor and is used to adjust the pH value of the cyanide-containing wastewater entering the first-stage continuous stirred tank reactor to 10-11. The second pH adjustment device is installed on the inlet pipe of the last stage continuous stirred tank reactor and is used to adjust the pH value of the cyanide-containing wastewater entering the last stage continuous stirred tank reactor to 9.5-9.

8.

7. The system according to claim 1, characterized in that, The copper ion catalyst dosing device is used to maintain the copper ion concentration in the reaction solution at 30 mg / L to 50 mg / L, and the hydrogen peroxide dosing device is used to add hydrogen peroxide at a ratio of 0.30 g / L cyanide-containing wastewater to 0.50 g / L cyanide-containing wastewater.

8. A method for removing hydrogen cyanide from blast furnace gas, the method being adapted to the system described in any one of claims 1 to 7, the method comprising: Blast furnace gas containing hydrogen cyanide is introduced into the multi-stage spray scrubbing tower from the blast furnace gas inlet and subjected to countercurrent contact scrubbing with NaOH solution atomized through the spray section, so as to absorb the hydrogen cyanide in the blast furnace gas into the NaOH solution, thereby obtaining purified gas and cyanide-containing wastewater. The purified gas is discharged from the purified gas outlet, and the cyanide-containing wastewater is discharged from the drain outlet. The cyanide-containing wastewater is sequentially introduced into the series of continuous stirred tank reactors. Under the catalysis of copper ions, the cyanide-containing wastewater and hydrogen peroxide are subjected to catalytic oxidation treatment to oxidize and decompose the cyanide in the cyanide-containing wastewater, thereby obtaining the treated wastewater.

9. The method according to claim 8, characterized in that, During the countercurrent contact washing process, the liquid-to-gas ratio of the NaOH solution to the blast furnace gas is 0.7 L / m³. 3 ~10.2 L / m 3 The atomization pressure of the NaOH solution is 2.1 bar to 3.4 bar, and the mass concentration of the NaOH solution is 20% to 30%.

10. The method according to claim 8, characterized in that, The hydrogen peroxide is added at a concentration of 0.30 g / L to 0.50 g / L of cyanide-containing wastewater.

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