A process to reduce fossil CO2 emissions

Abstract

1. A process for operating an oxidizable combustion gas cleaning unit in a metallurgical plant, comprising the steps of: (a) passing an oxidizable combustion gas from a metallurgical reactor, in particular blast furnace gas from a blast furnace, through a packed bed scrubber apparatus countercurrent to wash water or through a spray scrubber apparatus to remove cyanide compounds, in particular hydrogen cyanide, from the combustion gas by solubilizing the cyanide and chloride compounds in the wash water and increasing the removal of the chloride compounds, in particular hydrogen chloride; (b) collecting the wash water containing the solubilized cyanide and chloride compounds at the bottom of the packed bed or spray scrubber apparatus; and (c) collecting the purified oxidizable combustion gas at the top of the packed bed or spray scrubber apparatus, wherein a base is added to the wash water prior to step (a).

Description

[Technical field]

[0001] The present invention relates generally to the operation of metallurgical plants and in particular to the use of fossil CO 2 It concerns the process of reducing emissions. [Background technology]

[0002] CO released into the atmosphere today 2 The majority of emissions come from the burning of fossil fuels. The steel industry is a major contributor to greenhouse gases, especially CO 2 is one of the largest industrial emitters of anthropogenic CO 2 It accounts for 4% to 7% of emissions. Over the past 40 years, the European steel industry has reduced its energy consumption by around 50%, but further reductions are desirable from environmental and economic points of view and increasingly legally mandated.

[0003] The steel standard "Best Available Techniques" (BAT) and its conclusions are the gold standard regarding health and environmental limits and are applied in the national legislation of all European countries.

[0004] As an example, according to European regulations under the cap-and-trade mechanism, the European Trading Scheme (ETS, Directive 2003 / 87 / CE), the amount of avoided CO 2 Emissions can be sold to other companies 2 This represents the amount of quota. 2 Reduced emissions result in reduced costs or increased revenues in addition to positive climate effects.

[0005] Most parties are facing serious problems to comply with the above mentioned regulations, so this issue is very important to avoid undesirable consequences in proper plant operation. Moreover, all health and environmental issues are expected to become more and more important in the future, both in the most developed countries as well as in the newly industrialized and developing countries. In fact, some regulations are also to be implemented in important steel producing countries outside the EU (see for example Zero Liquid Discharge expected in the Indian MOEF draft dated 18 March 2016). Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, the object of the present invention is to 2 The object of the present invention is to propose a process for operating at least a part of a metallurgical plant in a manner that reduces emissions. [Means for solving the problem]

[0007] In order to achieve the above mentioned objectives, the present invention proposes in a first aspect a method for operating an oxidizable flue gas cleaning unit in a metallurgical plant, the method comprising the steps of: (a) passing oxidizable combustion gases from metallurgical reactors, in particular blast furnace gas from a blast furnace, through a packed bed scrubber apparatus in countercurrent with wash water or through a spray scrubber apparatus to remove said cyanide compounds, in particular hydrogen cyanide, from said combustion gases by solubilizing said cyanide and chloride compounds in said wash water, and to increase the removal of said chloride compounds, in particular hydrogen chloride; (b) collecting wash water containing solubilized cyanide and chloride compounds at the bottom of the packed bed or spray scrubber apparatus; and (c) collecting the purified oxidizable combustion gas at the top of a packed bed or spray scrubber device; Prior to step (a) a base is added to the wash water, said base being preferably an oxide or hydroxide of an alkali metal or alkaline earth metal, in particular NaOH, KOH, Ca(OH) 2 or mixtures thereof, most preferably the base is NaOH and is added in an amount of 3.5% to 6.5%, preferably 4.5% to 5.5% in excess of the stoichiometric amount relative to the cyanide and chloride compounds, particularly hydrogen cyanide and hydrogen chloride, being removed from the oxidizable combustion gas.

[0008] The inventors have found that by reducing the content of cyanide compounds, especially hydrogen cyanide, in oxidizable combustion gases, e.g. blast furnace gas, from a metallurgical reactor before use in a hot blast stove unit for hot blast production, the blast can be heated at higher temperatures without exceeding the NOx content permitted in the chimney if such burned gas is discharged to the atmosphere. The higher hot blast temperature significantly reduces the fuel / coke consumption in the metallurgical reactor. The inventors estimate that with the process of the invention, an increase of up to 150°C can be achieved in the operation of an otherwise identical metallurgical plant, depending on the average cyanide compounds in the blast furnace gas. A reduction in the coke rate of about 1 kg / t hot metal for every 10°C increase can be achieved, resulting in a reduction of up to 48 kg of CO per tonne of hot metal without prejudice to the proper operation of the metallurgical reactor. 2 Overall fossil CO 2 Emission reductions can be achieved. The benefits of reducing cyanide compounds from blast furnace gas may also be beneficial for other processes in which blast furnace gas is used as a fuel for combustion.

[0009] Furthermore, the removal of cyanide compounds prior to combustion in the hot blast stove unit allows for a more flexible control of hot blast production by taking into account the variations in the content of nitrogen sources in the fuel fed to the metallurgical reactor. Cyanide compounds in the context of the present invention are derived from the fossil fuel used in the metallurgical reactor or are formed during the metallurgical process from nitrogen containing compounds contained within said fuel. Cyanide compounds can be inorganic or organic. Inorganic compounds can be simple (e.g. HCN, KCN) or complexed by metal species.

[0010] The publication "Removal of cyanides from blast-furnace gas and wastewater" Steel in translation, Allerton Press, Inc, Heidelberg, vol. 42, no. 7, pages 606-610; October 26, 2012 describes a method for treating and purifying blast-furnace gas by removing cyanide compounds formed in the blast furnace. The blast-furnace gas is treated by a wet scrubber, which is capable of removing solid cyanide species, such as salts, by dissolving them in water. The resulting wash water is treated with ozone to remove the solubilized cyanides, CN. - and acidic components present in the blast furnace gas that can dissolve in water, e.g. CO 2 However, in contrast to the present invention, the method disclosed in this publication does not allow significant capture of the gaseous HCN already present in the blast furnace gas, nor effectively prevents the reformation of gaseous HCN in the wastewater.

[0011] In addition to the removal of cyanide compounds, an increase in the removal of chloride compounds, such as hydrogen chloride, from the oxidizable combustion gases is obtained with the proposed scrubber. Hydrogen chloride comes from coal combustion and is partially removed in the conventional cleaning systems of the oxidizable combustion gases, generally dedicated to dust removal. However, an increase in removal is desirable in order to reduce the corrosion of the equipment traversed by said gases.

[0012] In the context of the present invention, two scrubber devices can be applied: packed bed or spray.

[0013] Packed bed scrubber apparatus generally includes a tower containing one or more layers of variously shaped packing materials, e.g., Raschig rings, spiral rings, Berl saddles, etc., that provide a large surface area for liquid-gas contact. The bed packing may be held in place by a wire mesh retainer and is generally supported by at least one plate near the bottom of the scrubber apparatus. Wash water is introduced uniformly above the bed packing and flows down through the bed. The wash water establishes a thin film that coats the packing and provides an exchange surface for dissolution of cyanide and chloride compounds. Advantageously, the packed bed scrubber apparatus includes one or more intermediate plates that define a redistribution zone free of the packing bed, thereby dividing the packed bed into multiple overlapping packed bed zones, where a film of wash water is forced to drip down and redistributed to the next packed bed.

[0014] A spray scrubber device generally comprises a tower with different spray stages with different numbers and configurations of nozzles distributed on the slope. In particular, the size, number and configuration of the nozzles ensure the following requirements: a suitable size of the droplets allowing a high gas / liquid surface area, a compromise between the overlap of the sprays and the water losses at the spray tower walls, and a large amount of wash water in the spray stage, rich in hydrogen cyanide and hydrogen chloride, closest to the inlet of the gas to be treated. The wash water droplets in contact with the gas can absorb cyanide and chloride compounds. The multi-stage configuration allows each stage to be independently managed according to the amount of cyanide and chloride to be removed.

[0015] In both scrubber systems, the oxidizable combustion gases flow up the tower, i.e., countercurrent to the wash water which flows down by gravity. Additionally, a demister at the top of the tower is recommended to suppress entrained droplets.

[0016] In an advantageous embodiment, a packed bed scrubber apparatus usable in the process of the present invention comprises a tower comprising a random packed bed unit which may comprise a plurality of packed bed zones separated by redistribution zones, the packed bed unit being supported by at least one perforated support plate; a wash water spray distributor arranged above said packed bed for distributing wash water within the packed bed unit; a wash water collection unit arranged at the lower end of the packed bed scrubber apparatus below the packed bed, the wash water collection unit comprising a duct for discharging the wash water comprising cyanide and chloride compounds from the packed bed scrubber apparatus; a gas supply unit arranged to supply an oxidizable combustion gas into the tower below the packed bed unit; and an oxidizable combustion gas discharge unit at the top of the packed bed tower, the oxidizable combustion gas discharge unit comprising a duct for discharging the purified oxidizable combustion gas, preferably arranged after the mist eliminator.

[0017] In some embodiments, the packed bed scrubber apparatus has a wash water to oxidizable combustion gas ratio in the packed bed (including all packed bed zones in the case of one or more redistribution zones) in step (a) of 3.5 to 6.5 L / Nm 3 Preferably, the ratio is 4.5 to 5.5 L / Nm 3 , and most preferably said ratio is about 5.1 L / Nm 3 It is configured to be.

[0018] In some embodiments, the packed bed scrubber apparatus is configured such that the mean residence time of the combustion gas in the packed bed in step (a) is between 3.4 and 5.8 seconds, preferably between 4.1 and 5.1 seconds. Mean residence time has its ordinary meaning in the art and refers to the average time it takes for a given volume of gas to flow from the bottom of the packed bed unit to its top.

[0019] In some embodiments, the packed scrubber apparatus is configured such that the packed bed has a total (wet) contact surface, i.e., the total surface of the (wet) packed bed is between 0.09 and 0.15 m 2 / (Nm 3 / h), preferably 0.11 to 0.13 m 2 / (Nm3 / h) with the oxidizable combustion gas.

[0020] The packed bed scrubber apparatus is operated at near atmospheric pressure, for example 0.02-0.2 barg, preferably 0.06-0.1 barg. The temperature inside the packed bed is significantly below the boiling temperature of water, preferably between ambient and 70° C., in particular between 35-55° C. The packed bed scrubber apparatus can also be operated at higher pressures (up to 2.5 barg) and higher temperatures.

[0021] In an advantageous embodiment, the spray scrubber apparatus usable in the process of the present invention comprises a tower comprising at least four independent spray stages, composed of a set of nozzle units distributed along the height of the tower and arranged on a number of slopes, distributing wash water in the form of suitable droplets, said comprehensive spray section unit, a gas supply unit arranged to supply oxidizable combustion gas into the tower below the spray section unit, the gas supply unit giving priority to the tower unit by an external bypass to regulate the flow rate of oxidizable combustion gas treated in the spray scrubber towards the hot air stove, a wash water collection unit arranged at the lower end of the spray scrubber apparatus below the spray unit and the gas supply unit, said wash water storage unit comprising a duct for discharging wash water comprising cyanide and chloride compounds from the spray scrubber apparatus, and an oxidizable combustion gas discharge unit at the top of the spray tower, comprising a duct for discharging the purified oxidizable combustion gas, arranged after the mist eliminator.

[0022] In some embodiments, the spray scrubber apparatus has a ratio of wash water utilized in step (a) globally, i.e., the sum of all wash waters distributed to the different spray stages, to oxidizable combustion gases of 0.8 to 2.9 L / Nm3 depending on the amount of cyanide and chloride to be removed and the desired removal, and to manage the concentration of cyanide and chloride in the wash water. 3 The preferred ratio is 1.3 to 1.5 L / Nm 3 It is.

[0023] In some embodiments, the spray scrubber device is designed so that the average residence time of the combustion gas in the spray section unit in step (a) is 2-8 seconds, preferably 3-4 seconds. High variations depend on the amount of oxidizable combustion gas treated per hour and its temperature. In more typical conditions, the residence time is in the second range (3-4 seconds). The average residence time has its usual meaning in the field and represents the average time it takes for a given amount of gas to flow from the bottom of the spray section unit to its top.

[0024] In some embodiments, the nozzle of the spray scrubber device is an axial flow full cone nozzle that provides droplets having a Sauter mean diameter of 1100 to 1150 μm by appropriate setting of the nozzle pressure.

[0025] The spray scrubber unit operates at near atmospheric pressure, for example 0.03-0.2 barg, preferably 0.06-0.1 barg. The temperature inside the spray tower is significantly below the boiling temperature of water, preferably between ambient and 70° C., in particular 35-55° C. Spray scrubbers can also be operated at higher pressures (up to 2.5 barg) and higher temperatures.

[0026] In general, the wash water can be any industrial water available in the plant. The wash water can be any industrial water, but it is useful to adjust its pH before using it in step (a). Thus, a base is added to the wash water in step (a), said base being preferably selected from among the oxides and hydroxides of alkali metals and alkaline earth metals, in particular NaOH, KOH, Ca(OH) 2 or mixtures thereof. In some embodiments, it is particularly preferred that the base is NaOH, which is added in an amount of 3.5% to 6.5%, preferably 4.5% to 5.5%, in excess of the stoichiometric amount relative to the hydrogen cyanide and hydrogen chloride being removed from the oxidizable combustion gas.

[0027] In the case of plants which already incorporate a wet dust control unit for removing dust from the oxidizable combustion gases, it is particularly advantageous to add the following steps to the above process, whereby practical water consumption remains unchanged: (d) supplying the wash water from step (b) to a dust suppression unit (possibly supplemented with further water if the water used in step (a) is only a portion of the total available wash water) to reduce the dust content of the oxidizable combustion gas upstream of the scrubber unit of step (a); and (e) collecting dust suppression water from step (d) containing the dust rejected in the dust suppression unit.

[0028] In further preferred embodiments, it may be advantageous to (re)adjust the pH of the wash water from step (b) before it is used in step (d). Thus, in some embodiments, a base is added to the wash water before it is used in step (d), said base being preferably selected from among the oxides and hydroxides of alkali metals and alkaline earth metals, in particular NaOH, KOH, Ca(OH) 2 or mixtures thereof. In some embodiments, particularly preferred, the base is NaOH, which is added to reach a pH of 9.75 to 11, preferably closer to 11 which prevents volatilization of free cyanide. This (further) addition of base is more advantageous when the content of cyanide compounds is (expected or known to be) higher than average.

[0029] Such scrubber units achieve an adequate reduction of cyanide compounds in the oxidizable combustion gases, thereby enabling the downstream hot stove units to be operated at higher temperatures and thus reducing the fossil energy requirements in the metallurgical reactors and thus the fossil CO 2 It is particularly useful in the process of the present invention to reduce emissions.

[0030] These further objects of the invention are achieved in a second aspect of the invention which proposes a process for operating a metallurgical plant, in which oxidizable combustion gases from a metallurgical reactor, in particular blast furnace gas from a blast furnace, are purified with a scrubber for removing cyanides and chlorides as described herein and with a dedusting process as described herein, (h) fed to a hot stove unit and combusted in said hot stove unit configured to preheat a blast for blowing into said metallurgical reactor, the temperature of combustion of the purified oxidizable combustion gases being such that the temperature of the NO2 emitted to the atmosphere is reduced. x The preheated blast, which has been managed to control emissions, is then preferably injected into (i) a metallurgical reactor, in particular a blast furnace. x Emissions control is achieved by using purified oxidizable combustion gases with NO emissions lower than those obtained without purification. x without increasing the content and, more importantly, NO in the air x An enhancement is that higher combustion temperatures can be used without exceeding emission limits.

[0031] In other words, the second aspect of the present invention also comprises the first aspect relating to a process for purifying an oxidizable combustion gas as described in the previous paragraph, which is then used in a process for operating a metallurgical plant constituting the second aspect.

[0032] A third aspect of the invention relates to the treatment of wash water after removal of cyanide compounds from the oxidizable combustion gas to reduce its cyanide content, thereby making it possible to avoid cyanide accumulation in the wash water which can be so reused in the circuit, resulting in less fresh water being used, and furthermore, in the case of blowdown, regulatory limits being complied with.

[0033] In accordance with the third aspect of the present invention, in some embodiments, the process comprises: (f) treating the wash water from step (b) to remove cyanide compounds, in particular free cyanide.

[0034] The oxidation process is 2O 2 or SO 2 and based on the use of air and Cu catalyst. 2 O 2 The Cu-catalyzed oxidation process is preferred due to its lower CAPEX and OPEX, as well as easier management and less environmentally hazardous nature.

[0035] In an advantageous embodiment, H 2 O 2 The oxidation process based on the use of and Cu catalyst is carried out in a series of two continuous mixer reactor apparatuses, including the largest to the smallest reactor configurations in the series. Each reactor apparatus usable in the oxidation process of the present invention comprises a vertical tank including an impeller unit, an impeller engine unit, a baffle unit for better mixing and preventing the formation of vortexes, a duct for the supply of wash water, said wash water supply unit located near the top of the vertical tank unit, a duct located at the bottom of the vertical tank unit for discharging the treated wash water, said wash water outlet unit, and a reagent and catalyst supply unit located at the top of the reactor apparatus.

[0036] In some embodiments, the two series reactor systems are designed such that the residence time of the wash water in the reactors is 40-65 minutes in the first reactor system and 45-85 minutes in the second reactor system, respectively, preferably 50 minutes in the first reactor system and 60 minutes in the second reactor system.

[0037] In some embodiments, H 2 O 2 The dosage is 0.35-0.55 g of H per liter of wash water to be treated. 2 O 2 (30% wt.).

[0038] In some embodiments, the Cu in the wash water being treated 2+ A Cu-based catalyst is added to bring the concentration to 40 mg / L.

[0039] In some embodiments, the pH of the wash water to be treated is preferably adjusted to 10 (if the starting pH is lower) by the addition of a base, preferably NaOH.

[0040] In some embodiments, pitched blade impellers with a 45° blade angle are preferred to ensure a combination of radial and axial flow with higher shear levels. Impeller speeds of 20-25 rpm are preferred.

[0041] The reactor is operated at atmospheric pressure and the temperature inside it is generally 30°C.

[0042] In a further embodiment, the dust-free water from step (e) is then treated, typically in a water treatment unit, to separate the water from the dust and remove further contaminants. After treatment, the water is partially purged and recycled to the gas treatment after the addition of make-up water. The blowdown is preferably treated in step (g) to remove residual cyanide from step (e). The same oxidation process of step (f) is used, or preferably an activated carbon filter is utilized. [Brief description of the drawings]

[0043] Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a cross-sectional view of one embodiment of a packed scrubber apparatus useful in the present invention. [Diagram 2] FIG. 1 is a cross-sectional view of one embodiment of a spray scrubber apparatus useful in the present invention. [Diagram 3] FIG. 1 is a cross-sectional view of one embodiment of an oxidation reactor apparatus useful in the present invention. [Figure 4] 1 depicts a graph of some simulation data collected on the cleaning efficiency of two scrubber units. [Diagram 5] 1 depicts a graph of some simulation data collected on the cleaning efficiency of an oxidation reactor. [Figure 6]FIG. 1 is a block schematic process flow diagram of a metallurgical plant incorporating the solution described herein.

[0044] Further details and advantages of the invention will become apparent from the following detailed description of some non-limiting embodiments, taken in conjunction with the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] Figure 1 shows a cross-sectional view of a packed scrubber 1 useful for cleaning oxidizable combustion gases, such as blast furnace gas. The oxidizable combustion gases enter at an inlet 20 at the bottom of the scrubber tower 10 and flow through a packed bed 11 supported by support plates or baffles 12 toward a cleaned oxidizable combustion exhaust unit at the top of the tower 10. Wash water enters a wash water distribution unit 300 through a wash water duct 30, is distributed onto the packed bed by a wash water spray device 31, and flows by gravity from top to bottom countercurrent to the oxidizable combustion gases, passing through the packed bed 11 where cyanide and chloride compounds are absorbed by the wash water.

[0046] The packing of the packed bed 11 may be of any known type randomly oriented (random packing) in the column 10 above the perforated support plate 12, depending on the particular operating conditions and other constraints (the packing material may be a material having a specific surface area of ​​65 m 2 / m 3 , the free% may be 72% random).

[0047] The tower generally consists of a vertical cylindrical shell containing perforated support plates 12 for the packing material, and possibly further liquid distribution devices (not shown in FIG. 1) designed to provide more effective watering of the packed bed.

[0048] Further redistribution devices, such as intermediate baffles, may be provided at one or more different heights in the packed bed to redistribute the wash water into droplets and thus onto the underlying packed bed zones.

[0049] Moisture and liquid droplets carried by the purified oxidizable combustion gas are preferably removed by a mist separator 51, known in the state of the art of the present application, which allows the purified gas to flow through a dedicated duct via the purified oxidizable combustion gas exhaust port 50 to the hot air stove (not shown in FIG. 1).

[0050] Dissolved cyanide (mostly free CN - The wash water, containing iodides and chlorides, is drained into a wash water collection unit 400 forming a liquid reservoir 41 at the bottom of the chamber 10 and sent, for example by a pump, through a drain 40 to dedicated processing. The wash water collection unit 400 also preferably incorporates a pump suction 42 and an overflow orifice 43.

[0051] For installation and maintenance reasons, manholes, for example manhole 15 for the maintenance of the packed bed or manhole for the maintenance of the washing water spray distributor (unit) 32, are preferably provided in the shell of the chamber 10.

[0052] 2 shows a cross-sectional view of an atomizing scrubber 6, useful for cleaning oxidizable combustion gases such as blast furnace gas, which generally consists of a vertical cylindrical shell.

[0053] Oxidizable combustion gas enters the scrubber tower 60 at an inlet 70 near the bottom thereof and flows through a spray section unit 30 toward a cleaned oxidizable combustion exhaust unit 900 at the top of the tower 60 .

[0054] The wash water enters through a number of nozzles arranged on the slopes that make up the spray stages 61, 62, 63 and 64 and flows by gravity from top to bottom against the oxidizable combustion gases, forming droplets that allow the wash water to absorb cyanide and chloride compounds.

[0055] The nozzles of the spray stages 61, 62, 63 and 64 are preferably axial full cone nozzles providing uniform liquid distribution over the entire circular area. The nozzles are arranged according to an offset configuration to compromise between spray overlap and water loss at the wall of the spray section unit 600. The number of nozzles arranged in the spray stages 63 and 64 is generally greater than that of the spray stages 61 and 62 due to their greater proximity to the gas supply ducts corresponding to the highest content points of cyanide and chloride compounds in the oxidizable combustion gas.

[0056] Moisture and liquid droplets carried by the purified oxidizable combustion gas are preferably removed by a mist separator 91, well known in the state of the art of this application, such as a chevron type, so that the purified gas can flow to a hot blast stove (not shown in FIG. 1) via a purified oxidizable combustion gas exhaust duct 90. The pressure drop in the demister is generally monitored to control its purification, for which purpose a pressure loss sensor connection 93 and a liquid distributor for mist separator flushing 92 are provided.

[0057] Dissolved cyanide (mostly free CN - The wash water containing dimethylformamide, dimethyl ether, diethyl ether, dimethyl ether, and chloride is collected in a wash water storage unit 800 forming a liquid reservoir 80 at the bottom of the tower 60 and discharged through a wash water outlet 81 to flow, for example by a pump, to dedicated treatment. The wash water collection unit also incorporates a liquid level visual indicator 82 and a liquid level sensor connection 83.

[0058] For installation and maintenance reasons, personnel inspection holes 65 and 66 are preferably provided within the shell of tower 60 .

[0059] 3 is a cross-sectional view of a continuous mixed oxidation reactor for removing cyanide compounds, particularly free cyanide, from gas wash water. It generally consists of a vertical tank w10.

[0060] Wash water enters the reactor tank w10 through an inlet duct w40 near the top to a maximum allowable liquid level w65 (the level is monitored by sensors installed at connections w13 and w33) and is pumped through H 2 O 2 and possible antifoaming agents, as well as a Cu-based catalyst.

[0061] Mixing is provided by impellers w11 and w12, which are preferably pitched blade impellers with a blade angle of 45°, powered by a dedicated engine w200. Mixing is improved and vortexes are avoided by four baffles, e.g. the two baffles w31 and w32 shown in Figure 3.

[0062] The treated wash water is discharged from a drain duct w50 and sent to a dust prevention unit (not shown).

[0063] Possible gases and vapors are released through a dedicated vent w62 located at the top of the reactor tank w1, and a safety valve w63 is provided in case of emergency, for example due to pressure buildup in the reactor. At the top of the reactor w10, a pressure sensor connection w61 is provided, while pH and temperature sensor connections are provided near the bottom of the tank w10.

[0064] For installation and maintenance reasons, the personnel inspection holes w14 and w64 are preferably provided in the shell of the tank 10.

[0065] FIG. 4 shows the results obtained with the scrubbing of blast furnace gas with packed and spray scrubbers, using wash water doped with NaOH in an amount 5% greater than the stoichiometric amount for the hydrogen cyanide and hydrogen chloride removed.

[0066] As shown, by using a packed scrubber, up to 63% reduction of HCN in the blast furnace gas can be achieved, whereas with a spray scrubber up to 97% can be reached. The addition of NaOH aids in the absorption, which is selective towards cyanide and chloride compounds, and reduces the absorption of other acid components present in the blast furnace gas (e.g. CO, which is highly present in blast furnace gas). 2 , e.g. 20-24%). - Reacting with CN - and H 2 O. CN present in wastewater - In parallel, HCN can also react with acidic compounds that may have been initially present in the blast furnace gas and dissolved during the wet scrubbing process to form HCN. For example, this reaction can occur with CO 2 This can occur when dissolved CO is entrained in the wash water to form carbonate species that in turn will react with cyanide to form undesirable HCN. Adjustment of the base concentration is required to balance dissolved CO 2 Other acids such as CN - species to produce gaseous HCN again. Thus, the process can efficiently remove not only solid cyanide species but also HCN and HCl from the blast furnace gas.

[0067] CO and CO 2 The removal of is 0.10% and 0.70%, respectively, for the packed scrubber, but 0.24% and 0.07% for the spray scrub, confirming that the amount of base added is low enough to be selective towards cyanide and chloride.

[0068] HCl removal is not shown in the figure, but is nearly 100% for the packed scrubber and up to 96% for the spray scrubber.

[0069] Figure 5 shows the H 2 O 2The results obtained for the removal of free cyanide from gas wash water in an oxidation process based on the use of Cu-based catalysts are presented. Three different starting cyanide contaminations are reported, as well as the behavior of its content during the different stages of the process. 89.5-90.7% of the initial cyanide amount is removed in the first reactor, while values ​​of less than 1.5 mg / L and 0.2 mg / L are obtained after the second reactor and in the treated blowdown, respectively.

[0070] Figure 6 shows a process flow diagram of an embodiment of a metallurgical plant incorporating the solutions described herein. Three main sections can be observed: a blast furnace generating blast furnace gas (an oxidizable combustion gas), a gas treatment section, and a wash water treatment section.

[0071] The gas treatment section includes a first zone for dedusting (i.e. dust catcher, scrubber 1 and demister), a TRT for recovering energy from the expansion of the gas, and a scrubber 2 that allows the removal of cyanides and chlorides as described in the present invention. The treated gas from the scrubber 2 is then sent to the hot stove. The pre-treated gas leaving the first zone after dedusting contains cyanide and chloride species that are sent to the scrubber 2. One advantage of the first zone is that the gas sent to the scrubber 2 has a lower temperature when treated in the scrubber 2, thereby increasing the efficiency of the removal of cyanides and chlorides, more specifically the removal of HCN and HCl. The purified treated gas can be further sent to the hot stove and / or the gas network to be further used as fuel gas.

[0072] The wash water treatment section consists of two mixed series reactors 1 and 2 for removing absorbed cyanide compounds from the gas wash water and further subsections (i.e. clarifier, cooling tower, filter) for treating the water coming from the scrubber 1. A final blowdown treatment is provided, which consists of a further oxidation reactor (as shown in the figure) or preferably an activated carbon filter suitable for removing small amounts of residual cyanide. The absorbed cyanide compounds are oxidized by a suitable catalyst, e.g. a Cu-based catalyst, and a reagent, e.g. H2 O 2 in the mixed continuous reactors 1 and 2 in the presence of scrubber 1 to destroy cyanide compounds and thereby avoid the (re)formation of undesired HCN in the circulating water. The treated water is sent further to recycle / scrubber 1. The resulting wash water is then advantageously treated in a clarifier to remove sludge and cooled in a cooling tower. A portion is further returned to scrubber 1 and scrubber 2, and another portion is treated by oxidation or activated carbon filter in the mixed continuous reactor 3.

[0073] To better manage the process described in this invention, several tanks and pump systems are shown in the diagram. [Explanation of symbols]

[0074] 1. Filled scrubber equipment 10 towers 100 Packed Bed Units 11 Filled bed 12 Perforated support plate or baffle 15. Filling layer maintenance manhole 200 Gas Supply Unit 20 Gas supply duct 300 Cleaning water spray distributor (unit) 30 Cleaning water duct 31 Cleaning water spray device 32 Maintenance manhole for cleaning water spray distributor 400 Wash Water Collection Unit 40 Drain 41 Liquid storage unit 42 Pump suction 43 Overflow Orifice 500 Purifying and oxidizing combustion gas exhaust unit 50 Purified and oxidizable combustion gas exhaust duct 51 Mist separator 6. Spray scrubber equipment 60 towers 600 Spray Section Unit 61 Spray stage (nozzle on slope) 62 Spray stage (nozzle on slope) 63 Spray stage (nozzle on slope) 64 Spray stage (nozzle on slope) 65 Inspection hole for nozzle maintenance 66 Inspection hole for nozzle maintenance 700 Gas Supply Unit 70 Gas Supply Duct 800 Wash Water Storage Unit 80 Liquid storage unit 81 Discharge of washing water 82 Liquid Level Visual Indicator 83 Liquid level sensor connection 900 Purifying and oxidizing combustion gas exhaust unit 90 Purified and oxidizable combustion gas exhaust duct 91 Mist separator 92 Liquid distributor for mist separator flushing 93 Pressure loss sensor connection w1 Continuous mixed oxidation reactor equipment w10 vertical tank w100 impeller unit w11 impeller w12 impeller w13 Level sensor connection W14 Human Inspection Hole w200 impeller engine unit w300 baffle unit w31 baffle w32 baffle w33 Level sensor connection w400 cleaning water supply unit w40 Wash water inlet duct w500 cleaning water outlet unit w50 Purified cleaning water drain duct w51 pH sensor connection w600 Reagent and Catalyst Supply Unit w61 Reagent and catalyst inlets and pressure sensor connections w62 Vent w63 Safety valve w64 Human Inspection Hole w65 Maximum liquid level

Claims

1. 1. A process for operating an oxidizable flue gas cleaning unit in a metallurgical plant, comprising: (a) removing cyanide compounds, particularly hydrogen cyanide, from an oxidizable combustion gas from a metallurgical reactor, particularly blast furnace gas from a blast furnace, by passing said cyanide compounds, particularly hydrogen cyanide, from said combustion gas in countercurrent flow with wash water through a packed bed scrubber apparatus or through a spray scrubber apparatus, by solubilizing said cyanide compounds and chloride compounds in said wash water, and increasing the removal of said chloride compounds, particularly hydrogen chloride; (b) collecting the wash water containing solubilized cyanide and chloride compounds at the bottom end of the packed bed or spray scrubber apparatus; (c) collecting the cleaned oxidizable combustion gas at the top of the packed bed or spray scrubber apparatus; Prior to step (a) a base is added to the wash water, the base being preferably an oxide or hydroxide of an alkali metal or alkaline earth metal, in particular NaOH, KOH, Ca(OH) ２ or mixtures thereof, most preferably said base is NaOH, added in an amount of 3.5% to 6.5%, preferably 4.5% to 5.5% in excess of the stoichiometric amount relative to said cyanide and chloride compounds, particularly hydrogen cyanide and hydrogen chloride, removed from said oxidizable combustion gas.

2. 2. The process according to claim 1, wherein the packed bed scrubber apparatus comprises: a tower including a random packed bed unit, which may include a plurality of packed bed zones separated by redistribution zones, the packed bed unit being supported by at least one perforated support plate; a wash water spray distributor disposed above the packed bed for distributing the wash water within the packed bed unit; a wash water collection unit disposed at a lower end of the packed bed scrubber apparatus below the packed bed, the wash water collection unit including a duct for discharging the wash water containing cyanide compounds from the packed bed scrubber apparatus; a gas supply unit disposed to supply the oxidizable combustion gas into a chamber below the packed bed unit; and a purified oxidizable combustion gas discharge unit at the top of the packed bed tower, the purified oxidizable combustion gas discharge unit including a duct for discharging the purified oxidizable combustion gas, preferably disposed after a mist eliminator.

3. The ratio of the washing water to the oxidizable combustion gas in the packed bed in step (a) is 3.5 to 6.5 L / Nm ３ and preferably said ratio is 4.5 to 5.5 L / Nm ３ and most preferably said ratio is about 5.1 L / Nm ３ 3. The process according to claim 1 or 2,

4. The process according to any of claims 1 to 3, wherein the mean residence time of the combustion gas in the packed bed in step (a) is from 3.4 to 5.8 seconds, preferably from 4.1 to 5.1 seconds.

5. The packed bed has a total (wet) contact surface, i.e. the total surface of the (wet) packed bed is between 0.09 and 0.15 m ２ / (Nm ３ / h), preferably 0.11 to 0.13 m ２ / (Nm ３ 5. The process according to claim 1, wherein the oxidizable combustion gas is contacted with the oxidizable combustion gas at 0.5 to 1000 rpm for 24 hours.

6. A process according to any preceding claim, wherein the packed bed scrubber apparatus is operated at near atmospheric pressure, preferably from 0.02 to 0.2 barg, in particular from 0.06 to 0.1 barg.

7. The process according to any one of claims 1 to 6, wherein the temperature inside the packed bed is between ambient temperature and 70°C, in particular 35 to 55°C.

8. 2. The process according to claim 1, wherein the spray scrubber apparatus comprises a tower comprising at least four independent spray stages, each consisting of a set of nozzle units arranged on a plurality of slopes, distributed along the height of the tower, for distributing the wash water in the form of droplets; the oxidizable combustion gas is supplied from a gas supply unit into the tower below the spray section unit, the wash water is collected in a wash water collecting unit arranged at the lower end of the spray scrubber apparatus below the spray section unit and the gas supply unit, the wash water storage unit comprises a duct for discharging the wash water comprising cyanide and chloride compounds from the spray scrubber apparatus, and the purified oxidizable combustion gas passes through a mist eliminator and is then discharged to an oxidizable combustion gas discharge unit at the top of the spray tower, the duct comprising a duct for discharging the purified oxidizable combustion gas.

9. 9. The method of claim 1, wherein the flow of oxidizable combustion gas within the spray scrubber apparatus is regulated by diverting a portion of the flow of oxidizable combustion gas to the tower unit via an external bypass.

10. In step (a), the overall ratio of wash water to oxidizable combustion gas distributed to the different spray stages is between 0.8 and 2.9 L / Nm3 depending on the amount and desired removal of cyanide and chloride compounds to be removed and to control the concentration of cyanide and chloride compounds in the wash water. ３ and preferably said ratio is 1.3 to 1.5 L / Nm ３ The process according to any one of claims 1 and 8 to 9,

11. The process according to any of claims 1 and 8 to 10, wherein the average residence time of the oxidizable combustion gas in the spray section unit in step (a) is from 2 to 8 seconds, preferably from 3 to 4 seconds.

12. 12. The process of any of claims 1 and 8-11, wherein the nozzle of the spray scrubber apparatus is an axial flow full cone nozzle that provides droplets having a Sauter mean diameter of 1100 μm to 1150 μm by appropriate setting of the nozzle pressure.

13. A process as claimed in any one of claims 1 and 8 to 12, wherein the spray scrubber apparatus is operated at about atmospheric pressure, for example from 0.03 to 0.2 barg, preferably from 0.06 to 0.1 barg.

14. A process according to any of claims 1 and 8 to 13, wherein the temperature inside the spray tower is below the boiling temperature of water, preferably between ambient temperature and 70°C, in particular 35 to 55°C.

15. (d) supplying the wash water from step (b) to a dust suppression unit to reduce the dust content of the oxidizable combustion gas upstream of the scrubber apparatus of step (a); (e) collecting dust-proof water from step (d) containing the dust removed in the dust-proof unit; The process according to any one of claims 1 to 14.

16. Prior to step (d) a base is added to the wash water, the base being preferably an oxide or hydroxide of an alkali metal or alkaline earth metal, in particular NaOH, KOH, Ca(OH) ２ or mixtures thereof, most preferably said base is NaOH, which is added to reach a pH of 9.75-11, thereby preventing volatilization of free cyanide.

17. 17. The process according to any one of claims 15 or 16, further comprising the process step of (f) treating the wash water from step (b) to remove cyanide compounds, in particular free cyanide, and / or (g) further removing residual cyanide from the purification process blowdown of the dust water from step (e).

18. H, carried out in a series of two continuous mixed reactor apparatus. ２ O ２ and an oxidation step for removing cyanide from the wash water based on the use of Cu catalyst, each reactor apparatus comprising a vertical tank, preferably comprising an impeller unit, an impeller engine unit, a baffle unit for stirring and preventing vortex formation, a duct located near the top of said vertical tank unit for feeding wash water to a wash water feeding unit, a duct located at the bottom of said vertical tank unit for draining the treated wash water, a wash water outlet unit, and a reagent and catalyst feeding unit located at the top of said reactor apparatus.

19. 19. The process of claim 18, wherein the residence time of the wash water in the continuous mixing reactor system is from 40 to 65 minutes in the first reactor system and from 45 to 85 minutes in the second reactor system, preferably from 50 minutes in the first reactor system and from 60 minutes in the second reactor system.

20. H ２ O ２ The application amount is 0.35 to 0.55 g of H per liter of washing water. ２ O ２ (30% wt.).

21. Cu in the washing water ２＋ The process of any one of claims 18 to 20, wherein a Cu-based catalyst is dosed to achieve a concentration of 40 mg / L.

22. 22. The process of any one of claims 18 to 21, wherein a pitch blade impeller having a blade angle of 45° is used at an impeller speed of 20 to 25 rpm.

23. The process of any one of claims 18 to 22, wherein the reactor is operated at atmospheric pressure and 30°C.

24. The oxidizable combustion gas from a metallurgical reactor, in particular blast furnace gas from a blast furnace, purified by the process according to any one of claims 1 to 23, is (h) fed to a hot stove unit and combusted in said hot stove unit configured to preheat the blast to be blown into said metallurgical reactor, and the temperature of combustion of the purified oxidizable combustion gas is controlled to reduce the NOx emitted to the atmosphere. ｘ A process for operating metallurgical plants that controls emissions.

25. 25. The process according to claim 24, wherein (i) the preheated blast is injected into the metallurgical reactor, in particular the blast furnace.

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