Method of treating flue gas

Abstract

This invention relates to a method for treating flue gas. In particular, this invention relates to a method for reducing iodine from flue gas, thereby enabling the collection, recycling, or recovery of the iodine removed from the flue gas.

Description

[0001] This invention relates to a method for treating flue gas. In particular, this invention relates to a method for reducing iodine from flue gas, thereby enabling the collection, recycling, or recovery of the iodine removed from the flue gas.

[0002] Iodine is known to be used as a reactant or catalyst in chemical processes. Therefore, iodine is frequently found in waste streams. One example is flue gas, which is often generated as a waste stream and contains iodine. However, since iodine is a valuable feedstock, it is desirable to remove iodine from waste streams (especially from flue gas) and supply it for recycling.

[0003] DE 25 10 842 A1 discloses a method for recovering iodine from waste, in which waste adjusted to have an iodine content of 5% by weight is incinerated in a combustion chamber, and iodine or iodine compounds are extracted from the resulting combustion gas or exhaust gas using an alkaline aqueous solution of sodium thiosulfate or sodium thiosulfite, or iodine or iodine compounds are washed out from the combustion gas or exhaust gas.

[0004] CN 1 04 190 211 A and CN 1 03 011 084 also disclose methods for treating iodine-containing gases, in which the gas is introduced into a scrubber and washed with a washing aqueous solution containing a reducing agent.

[0005] However, there is still room for improvement in existing technologies, especially in flue gas purification, in order to more efficiently collect or recover iodine contained in flue gas.

[0006] Therefore, the object of this invention is to provide a solution for an improved flue gas purification method. In particular, the object of this invention is to achieve iodine recovery in the improved flue gas purification method.

[0007] According to the present invention, the solution to the above-mentioned problem is achieved at least in part by a method for treating flue gas having the features of claim 1. Preferred embodiments of the invention are described in the dependent claims, the specification, or the drawings, wherein other features described or shown in the dependent claims, the specification, or the drawings, whether individually or in any combination, constitute the scope of the invention unless the context clearly indicates otherwise.

[0008] This document provides a description of a method for treating iodine-containing flue gas to collect the iodine contained in the flue gas, wherein the method includes at least the following steps: a) Providing iodine-containing flue gas by burning iodine-containing waste with an iodine content of 8 to 40% by weight, thereby releasing flue gas; b) Cool the flue gas with a washing solution containing a reducing agent, especially in which the washing solution partially evaporates; c) The flue gas is washed with a washing solution in the first washing zone, wherein iodine from the flue gas is washed out into the washing solution, and wherein the iodine in the washing solution is reduced to iodide by a reducing agent; and d) Transfer the washing solution into the collection tank, wherein e) The washing solution is circulated between the collection tank and the first washing zone while the iodide is concentrated until the washing solution in the collection tank reaches the predetermined iodide concentration.

[0009] Compared with existing technologies, this method offers significant advantages in flue gas treatment or purification, particularly in the separation and collection of iodine from flue gas.

[0010] In particular, studies have shown that, depending on the quality of the wash water used, continuous recirculation of the wash solution can lead to so-called "salting out," the precipitation of salts contained in the original wash water. Therefore, conventional methods cannot be used to increase the iodide concentration in the wash water indefinitely.

[0011] Surprisingly, it has been found that when using iodine-containing waste with an iodine content of 8 to 40% by weight—higher than that in the prior art—the degree of salting out is less, thus enabling continuous recycling of the washing solution until the iodide concentration in the washing solution reaches ≥15% by weight. Furthermore, the method of the present invention can concentrate the iodide in the washing solution more quickly, thereby supplying it to recycling more rapidly.

[0012] Therefore, the method described herein is used to purify iodine-containing flue gas and to treat the flue gas in such a way that the iodine contained therein can be collected and reused. In the context of this invention, the collection of iodine means equivalently to the collection of reduced iodine, i.e., the collection of iodides.

[0013] Iodine-containing flue gas is generated in many processes, particularly in waste treatment. For example, waste streams are often subjected to heat treatment or incineration. The flue gas produced in these processes typically contains iodine. Because iodine must be removed from waste streams for environmental reasons, and because iodine is a valuable feedstock in many processes, it should be removed from the flue gas and collected for potential further use or recycling.

[0014] Therefore, the described method includes at least the following method steps.

[0015] According to step a), iodine-containing flue gas is provided. For example, the flue gas can be generated by burning iodine-containing waste or a stream of iodine-containing waste, thereby releasing the flue gas. In particular, iodine-containing waste is typically burned to generate iodine-containing flue gas. Furthermore, such gas streams are preferred for the method described herein because they contain a high concentration of iodine. This iodine should then be effectively removed from the flue gas.

[0016] In step a), the starting material used to provide iodine-containing flue gas is a material with an iodine content of 8 to 40% by weight, preferably 10 to 25% by weight, and particularly preferably 13 to 18% by weight, especially iodine-containing waste or iodine-containing waste streams.

[0017] As mentioned above, flue gas typically originates from waste streams or the thermal treatment or combustion of waste, resulting in flue gas that is typically at high temperatures. This temperature can be in the range of ≥100°C, for example ≥250°C, for example ≥500°C, or for example ≥1000°C.

[0018] According to step b), the flue gas is cooled using a washing solution containing a reducing agent. This method step can also be called quenching, and it is particularly used for rapidly cooling flue gas that is normally still at a high temperature. For example, the flue gas can be cooled to a temperature range below 100°C, typically around 80 to 85°C.

[0019] Furthermore, according to method step c), the flue gas is washed with a washing aqueous solution in the first washing zone, wherein iodine in the flue gas is washed out into the washing solution, and wherein the iodine in the washing solution is reduced to iodide by a reducing agent. Therefore, this step is specifically used to remove iodine from the flue gas. For this purpose, iodine is washed out of the flue gas by the washing solution, thereby accumulating in the washing solution. Furthermore, iodine is directly reduced to iodide by the reducing agent present in the washing solution, thereby accumulating in the washing solution in ionic form. This allows for the collection of a relatively harmless form of iodine, which can also be retained in the aqueous solution without problems.

[0020] In a particularly advantageous embodiment, the reducing solution is added through a scrubber nozzle to achieve the maximum possible surface area for the reduction reaction.

[0021] In principle, steps b) and c) can be performed in the same washing area, or these steps can be performed in different areas.

[0022] In addition, according to method step d), the washing solution is introduced into a collection tank. This collection tank is used to collect the iodide-containing washing solution and make it available for subsequent separation.

[0023] According to method step e), the washing solution is further configured to circulate between the collection tank and the first washing zone to concentrate the iodide until the washing solution in the collection tank reaches a predetermined iodide concentration. For example, the washing solution can circulate between the area where method step b) is performed and the collection tank.

[0024] Therefore, this method utilizes the fact that if the washing solution is continuously circulated, the same washing solution continuously washes the flue gas—specifically removing iodine from the flue gas and reducing it to iodide. This allows for the continuous concentration of the washing solution associated with iodide. Accordingly, the cycle can be maintained until the washing solution reaches a predetermined iodide concentration.

[0025] The concentration of iodine or iodide in the washing solution can be further increased by utilizing the fact that during iodine rinsing or before step b), the flue gas has not yet cooled below 100°C, and specifically, the flue gas temperature allows water to evaporate. Thus, it can be utilized that during the quenching period, i.e., during step b), water is always evaporated, thereby reducing the volume of washing water, wherein, as described, the concentration of iodine or iodide increases simultaneously. Of course, new water can be added, but care must be taken to ensure that the amount added is not excessive, so as not to unduly reduce the iodide concentration. For example, the volume of washing water can be kept constant.

[0026] In addition, it is preferable to add the reducing agent continuously or particularly in batches to the washing water to ensure that the reducing effect of the washing water is always maintained.

[0027] Therefore, continuous monitoring of at least one of the following in the wash water is generally advantageous: iodide content and reducing agent content. This monitoring can be performed, for example, according to a predetermined pattern, such as a time-based pattern, allowing for checks after a predetermined time period. Alternatively, such checks can be performed when a predetermined amount of flue gas has been washed or treated by the wash solution, or when a specific amount of iodide has accumulated in the wash water. This determination or check can be performed, for example, by radiometric analysis. As the iodide concentration in the wash solution increases, the load of other salts in the system also increases. This can also be monitored by radiometric density measurements. At an iodine content of 17% by weight, this density should be approximately 1.3 g / cm³. 3 Therefore, this can be a preferred configuration for continuous and easy monitoring of processes, especially regarding their progress.

[0028] This configuration ensures that iodine is always removed from the flue gas to the desired extent and reliably reduced to iodide in solution, since a sufficient amount of reducing agent remains in the washing solution. Consistent with the foregoing, it is particularly preferable that the specific reducing agent is continuously added to the washing solution, regardless of its type. Furthermore, this ensures that iodide accumulates at the desired concentration in the washing solution.

[0029] The method described above has the particular advantage of directly generating a concentrated iodide solution during the flue gas treatment process. This is especially advantageous because the concentrated solution is particularly beneficial for the further use or recovery of the iodide solution or for the recycling of iodine. This eliminates the need for subsequent concentration in later stages.

[0030] According to the present invention, this advantage can be achieved in a simple and highly explicit manner, and can also be achieved in existing systems.

[0031] Another advantage is that the relatively high concentration of iodide solution simplifies reuse, as transporting concentrated solutions is more efficient than transporting, for example, solutions with only low concentrations. In principle, the washing solution can be discharged from the collection tank for reuse.

[0032] The washing solution or the iodide it contains can, in principle, be used wherever iodine or iodide is required.

[0033] After the washing solution containing concentrated iodide is drained, a new washing solution can be added and a new cycle can be started, in which the washing solution is concentrated with iodide again.

[0034] Preferably, the pH of the aqueous solution or washing solution can be adjusted to a value in the range of 5 to 8. In particular, the washing solution can therefore be weakly alkaline, which can be easily achieved, for example, by adding sodium hydroxide or other bases (whether in solution or solid form). It is also preferable to continuously monitor the pH value, as explained above regarding the iodide concentration and the reducing agent concentration. The advantages of this arrangement can be seen from, for example, the fact that the reducing agent remains stable due to the relatively low acidity of the solution, and furthermore, no undesirable alkaline-catalyzed reaction of iodine occurs.

[0035] It may also be advantageous to implement step e) until the iodide concentration in the washing solution reaches ≥15 wt%. For example, step e) can be implemented until the iodide concentration in the washing water reaches ≥17 wt%. Studies have shown that such iodide concentrations in the washing water are particularly advantageous for achieving efficient reuse of iodides.

[0036] It may also be advantageous to wash the flue gas with an aqueous solution in a second scrubbing zone, which is specifically spatially separated from the first scrubbing zone. The second scrubbing zone may, for example, be located downstream of the first scrubbing zone and designed such that the scrubbing solution used in the second scrubbing zone does not participate in the circulation of the first scrubbing zone. However, it is also possible to at least partially transfer the solution from the second scrubbing zone into the circulation of the first scrubbing zone, and vice versa. Furthermore, it may be advantageous for the scrubbing water in the second scrubbing zone or the second scrubbing stage to also contain a reducing agent and / or have a pH value as described in the specification. Additionally, the concentration of reducing agent and / or iodide in the scrubbing water of the second scrubbing zone can be checked.

[0037] This configuration allows iodine remaining in the flue gas after the first scrubbing stage to be further washed out. Thus, the scrubbed flue gas can effectively remove or reduce iodine. Furthermore, iodine can be collected particularly effectively and as completely as possible, resulting in a particularly high level of economic efficiency.

[0038] It may also be advantageous to further purify the flue gas after step e) or after the iodine has been washed away by the washing solution. In this configuration, through further purification, other waste substances—especially other environmentally harmful substances—can be removed from the flue gas, thereby producing a clean gas that can preferably be released into the environment directly or after other standard purification steps.

[0039] Further purification steps can be specifically selected based on the substances to be removed from the flue gas contained in the system. For example, purification steps may include adding an absorbent and subsequent filtration. This allows, for example, the removal of dioxins or halogen residues from the flue gas. However, further purification steps are not limited to this in principle.

[0040] It may be further advantageous to implement the method under reduced pressure. In this configuration, the flue gas can pass through the equipment—for example, by a suction fan—from the supply or from the furnace (where the flue gas is generated) to a corresponding outlet, where the clean gas can, for example, leave the equipment. Therefore, the flue gas has only a limited residence time within the equipment (e.g., in a scrubber stage). By setting the reduced pressure (e.g., using a suction fan), very specific conditions regarding the flue gas residence time and the processing based thereon can be determined. Therefore, in this configuration, the iodide-containing solution can be collected in a specific and defined manner. Furthermore, this solution can be readily implemented in the apparatus.

[0041] Advantageously, the reducing agent may also include thiosulfate. Studies have shown that thiosulfate is stable under given conditions and is also electrochemically suitable for reducing iodine to iodide. Therefore, particularly in this configuration, this ensures the reliable removal of iodine from the flue gas and its collection as iodide.

[0042] For other advantages or technical features of the method, please refer to the device description, drawings, and description of the drawings.

[0043] The present invention also relates to an apparatus for treating iodine-containing flue gas to collect the iodine contained in the flue gas, wherein the apparatus comprises at least: i) Flue gas ducts, which are used to transport flue gas; ii) A scrubber having a first scrubbing zone for scrubbing flue gas, wherein the scrubber is connected to a supply line for supplying a scrubbing aqueous solution to the scrubber and the flue gas duct; iii) A collection tank connected to the scrubber via a fluid line; and (iv) A circulation line for supplying washing solution in the loop from the collection tank to the scrubber.

[0044] The device is specifically designed for implementing the method described above. Therefore, the advantages described in the detailed description of the method can also be achieved.

[0045] To implement this method, the apparatus therefore includes a flue gas duct for conveying flue gas. The flue gas duct may, for example, extend from a furnace used for incinerating iodine-containing waste, wherein the furnace may form part of the apparatus described herein, and the furnace may be configured, for example, as a rotary kiln with an afterburner.

[0046] The apparatus further includes a scrubber having a first scrubbing zone for scrubbing flue gas (e.g., flue gas within a flue gas duct), wherein the scrubber is connected to a supply line for supplying a scrubbing aqueous solution to the scrubber and the flue gas duct. Thus, the flue gas can be treated with a scrubbing solution in the scrubbing zone to remove iodine. If a reducing agent (e.g., sodium thiosulfate) is present in the scrubbing solution, the iodine in the scrubbing solution is immediately reduced to iodide. Furthermore, the flue gas duct may include a quench zone located at the transition from the furnace to the scrubbing zone, in which the flue gas can be rapidly cooled (e.g., by the scrubbing solution).

[0047] In addition, a collection tank, as part of the apparatus, is provided and connected to the scrubber via a fluid line. The collection tank collects a washing solution enriched with iodine or iodides. The collection tank may also include an outlet from which the iodine solution can be discharged.

[0048] To illustrate the method for enriching iodides in a washing solution, the apparatus further includes a loop for allowing the washing solution to flow in a loop from a collection tank to a washer. The washing solution can be fed directly into the washing zone or partially into the quenching zone. Therefore, the apparatus may preferably include a pump for conveying the washing solution in the loop.

[0049] The apparatus may also include a device for supplying alkali or a reducing agent. This allows the conditions of the washing solution to be maintained at a constant level.

[0050] In addition, to improve reaction control, the device may include a detector for detecting at least one of the following in the wash water: pH value and reducing agent concentration.

[0051] To reliably remove all iodine even when the iodine concentration in the flue gas flues, the apparatus may further include a second washing zone, which may be separate from the first washing zone. This second washing zone may, for example, be connected to the first washing zone, so that the aforementioned washing solution circulation may also include the second washing zone.

[0052] For other advantages or technical features of the device, please refer to the device description, drawings, and description of the drawings.

[0053] The invention is explained below by way of example with reference to the accompanying drawings and based on preferred embodiments, wherein the features described below may individually or in combination represent an aspect of the invention in each case. The drawings show: Figure 1 A schematic diagram of an apparatus for performing a method of treating iodine-containing flue gas to collect the iodine contained in the flue gas.

[0054] Figure 1 An apparatus 10 is schematically shown for performing a method of treating iodine-containing flue gas to collect the iodine contained in the flue gas.

[0055] The apparatus 10 includes a flue gas duct 12 through which flue gas from a combustion device 14 can be transmitted. The combustion device 14 can be, for example, a suitable furnace with an afterburner. Iodine-containing waste can be incinerated in the combustion device 14, thereby causing the flue gas transmitted through the flue gas duct 12 to contain iodine.

[0056] The flue gas duct 12 leads to a scrubber 16, in which the flue gas can be treated with a scrubbing solution. For this purpose, the scrubber 16 first includes a quench zone 18, in which the flue gas can be quenched or rapidly cooled by scrubbing water. The flue gas then flows into a first scrubbing zone 20, where iodine present in the flue gas can be washed out in a first stage. For this purpose, suitable nozzles 24 can be provided to spray scrubbing water into the flue gas. Subsequently, the flue gas flows through a second scrubbing zone 22, where more iodine can be removed from the flue gas. Therefore, additional nozzles 26 are provided for discharging the scrubbing solution. The nozzles 24 and 26 are supplied with the scrubbing solution via corresponding supply lines 28.

[0057] The apparatus 10 also includes a collection tank 30 connected to the scrubber 16 via a fluid line 32. The collection tank 30 is used to collect the washing solution. Specifically, the collection tank 30 may have an outlet 38 from which the washing solution can be removed from the apparatus 10. As a result, the washing solution can be supplied, for example, to other processing methods, or its composition can be analyzed.

[0058] To enrich the iodide-containing washing solution, the device 10 further includes a recirculation line 34 to supply the washing solution in a loop from the collection tank 30 to the scrubber 16. For example, the recirculation line 34 may extend from the collection tank 30 to the supply line 28, allowing the washing solution to be re-injected into the flue gas in the first washing zone 20, the second washing zone 22, and / or the quench zone 18. For this purpose, the washing solution can be discharged, for example, from the first washing zone 20 at the collection tank 40 or from the bottom 42 of the second washing zone 22.

[0059] In addition, in order to adjust the pH of the washing solution (especially to a value in the range of 7-8) and / or to provide reducing conditions in the washing solution, an inlet 36 may be provided through which an alkali (e.g., sodium bicarbonate) and / or a reducing agent (e.g., sodium thiosulfate) can be introduced into the washing solution.

[0060] To further purify the flue gas downstream of the scrubber 16, the device 10 may also include a purification unit, as illustrated below.

[0061] according to Figure 1 The configuration shown includes a condenser 44 downstream of the scrubber 16, which can be used to condense any iodine remaining in the flue gas after the scrubber 16.

[0062] In addition, according to Figure 1 The droplet separator 46 is located downstream of the condenser 44 and can supply fresh water or process water to the condenser 44 via inlet 48. The droplet separator 46 can be used to reduce the moisture content of the flue gas.

[0063] In addition, a heating chamber 50 is provided, which can be supplied with natural gas via inlet 52 to heat the flue gas. The flue gas heated in this way can be brought in through inlet 54 to contact a solid adsorbent for additional purification of the flue gas.

[0064] Accordingly, the adsorbent loaded can then be separated in a filter unit 56, which includes, for example, a fabric filter. Downstream of the filter unit 56, the gas has now been purified and can be conveyed via a ventilation duct 58 to a chimney 60 through which the gas exits the device.

[0065] It should be noted that, since the combustion process and flue gas scrubbing—and the resulting iodine recycling—are directly interconnected, it is preferable to monitor and regulate multiple parameters throughout the process. This makes the relevant operating conditions, at least to some extent, subject to control. These boundary conditions include, for example, negative pressure (which is preferably also present in the incinerator or combustion chamber), the amount of feed waste, the temperature in the combustion chamber, the flow rate and pressure in the scrubber nozzles and quench tangential feed lines, the pH of the scrubber stages, excess reducing agent (especially sodium thiosulfate), and any possible fluctuations in the composition of the feed waste (especially the content of iodine, chlorine, sulfur, etc.). However, this can be achieved without difficulty by those skilled in the art who are familiar with the appropriate apparatus.

[0066] Parts list 10 devices 12 flue gas ducts 14 Combustion Equipment 16 Washer 18 Cool Zone 20 First Washing Area 22 Second Washing Area 24 nozzles 26 nozzles 28 supply pipelines 30 collection tanks 32 fluid pipelines 34 Recycle 36 entrances 38 Exports 40 collection tanks 42 bottom 44 Condenser 46 Droplet Separator 48 entrances 50 heating chambers 52 entrances 54 entrances 56 filter units 58 ventilation ducts 60 chimneys

Claims

1. A method for treating iodine-containing flue gas, wherein iodine is collected from the flue gas, the method comprising at least the following steps: a) Providing iodine-containing flue gas by burning iodine-containing waste with an iodine content of 8 to 40% by weight, thereby releasing flue gas; b) Cool the flue gas with a washing solution containing a reducing agent; c) The flue gas is washed with a washing solution in the first washing zone (20), wherein iodine in the flue gas is washed out into the washing solution, and wherein the iodine in the washing solution is reduced to iodide by a reducing agent; and d) The washing solution is introduced into the collection tank (30), wherein e) The washing solution is circulated between the collection tank (30) and the first washing zone (20) while the iodide is concentrated until the washing solution in the collection tank (30) reaches the predetermined iodide concentration.

2. The method according to claim 1, characterized in that, The pH of the washing solution is adjusted to the range of 5 to 8.

3. The method according to claim 1 or 2, characterized in that, Step e) of the implementation method continues until the iodide concentration of the washing solution reaches ≥15wt%.

4. The method according to any one of claims 1 to 3, characterized in that, The flue gas is generated by burning iodine-containing waste with an iodine content of 10 to 25% by weight.

5. The method according to any one of claims 1 to 4, characterized in that, The flue gas is generated by burning iodine-containing waste with an iodine content of 13 to 18% by weight.

6. The method according to claims 1 to 5, characterized in that, Prior to step b), the temperature of the flue gas is ≥100°C.

7. The method according to claims 1 to 6, characterized in that, The flue gas is further purified after method step e).

8. The method according to any one of claims 1 to 7, characterized in that, The reducing agent includes thiosulfate.

9. The method according to any one of claims 1 to 8, characterized in that, The method is performed under reduced pressure.

10. The method according to any one of claims 1 to 9, characterized in that, The reducing agent is continuously added to the washing solution.

11. The method according to claims 1 to 10, characterized in that, Continuously monitor at least one of the iodide content and reducing agent content of the washing solution.

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