Method of offgas treatment

Abstract

The invention relates to a method of treating offgases with an offgas treatment system (10), comprising the following process steps: a) introducing an offgas stream into an offgas treatment system (10), where the offgas stream comprises water and at least one organic compound in the gas phase, b) introducing the offgas stream into a condenser (12) and separating out a portion of the gas phase as condensate to obtain a pretreated offgas stream, and c) treating the pretreated offgas stream with a nonthermal plasma or constituents of a nonthermal plasma to obtain a treated offgas stream.

Description

[0001] Waste treatment process

[0002] Description

[0003] The invention relates to a method for treating exhaust gases using an exhaust gas treatment system and a corresponding exhaust gas treatment system. Furthermore, the use of a corresponding exhaust gas treatment system for reducing the concentration of organic compounds in an exhaust gas stream is disclosed.

[0004] In many areas of technology, particularly in the chemical industry, it is often unavoidable that significant quantities of exhaust gases are produced, which must be released into the environment. These exhaust gases often include volatile organic compounds (VOCs) and fragrances. Many of the VOCs present, especially in high concentrations, are considered harmful to the environment and / or health, or, like fragrances, at least represent a potential source of unwanted odor nuisance. In addition to these factors, high VOC concentrations in exhaust gases can also pose a safety risk, as they can burn and / or even explode upon contact with an ignition source. Against this backdrop, many countries have regulations governing the maximum permissible concentrations of VOCs and / or fragrances in exhaust streams.In particular, due to the increasing awareness of the importance of more sustainable business practices and environmental protection, these requirements have become more stringent in many countries in recent years, with many companies also setting themselves ambitious targets with regard to emissions pollution.

[0005] An example of an industry where the contamination of exhaust gases with VOCs and / or odorous substances is regularly particularly high is the rubber processing industry, for example, tire manufacturing. Large quantities of VOCs can be released during the various steps of rubber processing, particularly the mixing of the often complex rubber compounds, but also during the vulcanization of these rubber compounds into vulcanizates. High concentrations of ethanol, in particular, regularly pose a major safety risk.

[0006] A state-of-the-art and established method for exhaust gas treatment in many industries is thermal afterburning (RTO). In this process, the exhaust gas to be treated is usually preheated with a heating element to partially oxidize its components before being fed into a combustion chamber where the VOCs are burned. Typically, the waste heat from the combustion process can be used to control the temperature of the heating element used for preheating. These systems consistently achieve high levels of purification, often removing up to 99.5% of VOCs.

[0007] Although RTO plants can achieve satisfactory purification levels in many cases, this technology is sometimes perceived as disadvantageous. This is particularly true because burners, which usually require fossil fuels, are typically used to operate the combustion chamber. Accordingly, the RTO process is generally not considered particularly energy-efficient and, in many cases, requires complex equipment and safety precautions due to the sometimes high combustion temperatures. The relatively high operating costs of RTO plants also indirectly impair the cost-effectiveness of the manufacturing processes.

[0008] The object of the present invention was to eliminate or at least mitigate the above-described disadvantages of the prior art. In particular, the object of the present invention was to provide a method for treating exhaust gases and an associated exhaust gas treatment system with which VOC-containing exhaust gases can be treated reliably and with high purification efficiency.

[0009] It was an object of the present invention that the method to be specified should be executable without the use of high temperatures or combustion steps.

[0010] It was a further object of the present invention that the method to be specified should also be able to reliably remove odorous substances from the exhaust gas stream.

[0011] In this respect, it was an object of the present invention to minimize the process costs associated with the removal of VOCs and / or odorous substances and the equipment required for this in the exhaust gas treatment system, whereby in particular the energy consumption and the need for fossil fuels should be reduced.

[0012] It was an object of the present invention that the method to be specified should be particularly suitable for the treatment of exhaust gas streams which occur in the rubber processing industry, in particular in the production of vulcanizable rubber mixtures.

[0013] It was desirable that the process to be specified and the associated exhaust gas treatment system should be easily combinable with other exhaust gas treatment processes in order to be able to further increase efficiency if necessary.

[0014] Furthermore, it was an object of the present invention that the exhaust gas treatment system to be specified should have the smallest possible space requirement and be easy to install and maintain. It was desirable that the specified method should be particularly easy to adapt to the treatment of large volumes of exhaust gas.

[0015] The inventors of the present invention have now found that the objects described above can surprisingly be achieved if, for a specific composition of the exhaust gas stream which comprises water and organic compounds in the gas phase, the combination of an upstream condenser for separating a condensate is combined with a downstream plasma treatment.

[0016] In such a process, excellent efficiency in VOC and / or odor removal can be achieved, while significantly reducing energy consumption, particularly fossil fuel consumption, and greenhouse gas emissions. The required exhaust gas treatment system relies on comparatively small components and, due to the simplicity of the components used and the absence of actual combustion processes, is easy to install and maintain, as well as being easily integrated into existing process lines.

[0017] The above-mentioned objects are accordingly achieved by the subject matter of the invention as defined in the claims. Preferred embodiments of the invention emerge from the subclaims and the following statements.

[0018] Such embodiments, which are designated as preferred below, are combined in particularly preferred embodiments with features of other embodiments designated as preferred. Combinations of two or more of the embodiments designated as particularly preferred below are thus very particularly preferred. Likewise preferred are embodiments in which a feature of one embodiment designated as preferred to any extent is combined with one or more further features of other embodiments designated as preferred to any extent. Features of preferred exhaust gas treatment systems and uses emerge from the features of preferred methods.

[0019] The invention relates to a method for treating exhaust gases with an exhaust gas treatment system, comprising the method steps: a) introducing an exhaust gas stream into an exhaust gas treatment system, wherein the exhaust gas stream comprises water and at least one organic compound in the gas phase, b) introducing the exhaust gas stream into a condenser and separating a portion of the gas phase as condensate to obtain a pretreated exhaust gas stream, and c) treating the pretreated exhaust gas stream with a non-thermal plasma or components of a non-thermal plasma to obtain a treated exhaust gas stream.

[0020] In the method according to the invention, an exhaust gas stream which, in the gas phase, comprises at least one organic compound in addition to water, is introduced into an exhaust gas treatment system according to the invention. In this exhaust gas treatment system, the exhaust gas stream first passes through a condenser. In this condenser, the temperature of the exhaust gas stream is reduced such that condensation of components in the exhaust gas stream occurs, in particular water. The method according to the invention advantageously utilizes the fact that water, which is particularly easy to condense compared to VOCs, at least partially dissolves the VOCs, so that a large proportion of them pass into the liquid phase with the condensed water, which is obtained as condensate from the condenser. This results in efficient pre-separation of VOCs from the exhaust gas stream, resulting in a pretreated exhaust gas stream.Only this pretreated exhaust gas stream is further treated in a specific manner downstream of the condenser, namely with a so-called non-thermal plasma. A typical example of this is a process according to the invention, in which the treated exhaust gas stream is released into the environment, preferably via a chimney.

[0021] The concept of a non-thermal plasma (NTP), also referred to as a non-equilibrium plasma, is familiar to those skilled in the art. Corresponding systems for treating exhaust gases with non-thermal plasma are commercially available. Non-thermal plasmas are in a state of thermal imbalance, which is usually achieved through the type of plasma generation. Compared to the systems available on the market for exhaust gas purification, which are based on the use of non-thermal plasmas, the inventive combination with the condenser can achieve a significant increase in efficiency. The reduced VOC concentration in the pre-treated exhaust stream makes it possible to use smaller plasma treatment devices and reduce energy consumption without having to compromise on the desired purification performance.In accordance with the expert understanding, the treatment can be carried out directly by interaction with the non-thermal plasma, but also merely by the action of active plasma components which are generated in a non-thermal plasma and then contacted with the pre-treated exhaust gas stream.

[0022] As explained above, in the process according to the invention, which relies on the combination of a condenser with a non-thermal plasma, the presence of water in the exhaust gas stream is of great importance, since the inventors believe this to be essential to the invention. The inventors believe that the efficiency of VOC removal by condensing water in the condenser is particularly high when the exhaust gas stream is as saturated with water as possible. Accordingly, a process according to the invention is preferred, wherein the exhaust gas stream in the gas phase has a relative water content in the range from 40 to 100%, preferably in the range from 60 to 100%, particularly preferably in the range from 80 to 100%, expressed as relative humidity, i.e. as the relative content of the mass of water per volume of the gas phase based on the maximum possible mass of water in the gas phase at complete saturation.In accordance with the expert understanding, the indication of the relative water content refers only to the gaseous part of the water, although it cannot be ruled out that, depending on the type of exhaust gas flow, small water droplets may also be present in the exhaust gas flow, whereby, in the opinion of the inventors, the efficiency of VOC removal can be further increased by this.

[0023] In principle, all typical VOCs are suitable organic compounds that can be removed using the process according to the invention. However, the inventors have succeeded in identifying selected organic compounds with which particularly good results and high deposition rates in the condenser can be achieved using the process according to the invention, with the process according to the invention being particularly suitable for the removal of ethanol. Thus, a process according to the invention is preferred in which the exhaust gas stream in the gas phase comprises at least one alcohol, preferably methanol, ethanol, or propanol, particularly preferably ethanol, as the organic compound.

[0024] The inventors have found that the process according to the invention is advantageously particularly suitable for the treatment of gas phases which have a high content of organic compounds. In these exhaust gas streams, the efficiency increases achievable by combining the condenser with the non-thermal plasma are particularly evident, wherein a high content of organic compounds in the gas phase can additionally promote condensation of the organic compounds in the condenser. In this respect, a process according to the invention is preferred, wherein the exhaust gas stream in the gas phase has a relative content of at least one organic compound, preferably an alcohol, in the range from 0.03 to 0.825%, preferably in the range from 0.3 to 0.7%, particularly preferably in the range from 0.33 to 0.625%, expressed as the relative content of the organic compound per volume of the gas phase.The concentration of organic compounds in the gas phase can be determined, for example, analogously to DIN ISO 16000-6:2020-08, DIN CEN / TS 13649:2015-03 or DIN EN 12619:2013-04 and using commercially available testing equipment, whereby the determination is preferably carried out in accordance with DIN ISO 16000-6:2020-08.

[0025] It can be seen as an advantage of the process according to the invention that it can reliably remove not only VOCs but also other odorous substances. Therefore, a process according to the invention is preferred wherein the exhaust gas stream in process step a) comprises at least one odorous substance in the gas phase. Without wishing to be bound by this theory, the inventors assume that the condensation of the water, which entrains a portion of the gaseous organic compound, also removes a large portion of the existing odorous substances even before treatment with the non-thermal plasma, so that the absolute reduction that must be achieved by the non-thermal plasma can be lower.

[0026] The advantages of the process according to the invention are particularly evident in cases where noticeable condensation occurs in the condenser. For this purpose, it is expedient if there is a sufficiently large difference between the temperature of the exhaust gas stream fed into the condenser and the temperature of the condenser. The inventors have succeeded in specifying ranges for these temperatures that allow advantageous energy efficiency to be achieved while simultaneously achieving good treatment performance. A process according to the invention is preferred in which the exhaust gas stream in process step a) has an average temperature in the range of 30 to 60 °C, preferably in the range of 30 to 50 °C, particularly preferably in the range of 30 to 40 °C.Likewise preferred is a process according to the invention, wherein the condenser is designed to reduce the temperature of the exhaust gas stream to a temperature in the range from 3 to 20 °C, preferably in the range from 5 to 15 °C, particularly preferably in the range from 7 to 12 °C.

[0027] Taking into account the above information, in particular the advantages of high water concentrations in the exhaust gas stream in combination with the excellent ethanol separation performance and the exhaust gas stream temperatures identified as efficient, a process according to the invention results which is particularly suitable for the treatment of exhaust gas streams such as those occurring in the rubber processing industry, in particular in mixing processes for the production of rubber compounds. The process according to the invention is therefore particularly predestined for use in these processes. Therefore, a process according to the invention is preferred wherein the exhaust gas stream comprises exhaust gases from a rubber processing process, preferably exhaust gases from a mixing process for the production of rubber compounds, in particular vulcanizable rubber compounds.

[0028] In the inventors' experiments, it was advantageously found that essentially all types of condensers are suitable in principle for use in the process according to the invention. However, it was identified that the use of tube bundle and / or plate heat exchangers, in particular, results in particularly efficient process configurations. Therefore, a process according to the invention is preferred in which the condenser comprises a heat exchanger, preferably a tube bundle heat exchanger or plate heat exchanger, particularly preferably a tube bundle heat exchanger. It can be seen as an advantage of the process according to the invention that the condensate obtained from the condenser comprises not only water but also organic compounds in the liquid phase.This advantageously makes it possible to recycle the condensate and recover the organic compounds, such as ethanol, for use in other processes, optionally directly as a mixture of organic compound and water, for example, as a solvent for other chemical reactions. A preferred method according to the invention is one in which the condensate is removed from the condenser via a fluid line system, with the condensate preferably being recycled.

[0029] The person skilled in the art will understand that the above statements mean that the treatment of the pretreated exhaust gas stream in process step c) comprises the oxidation of the at least one organic compound in the pretreated exhaust gas stream, wherein the oxidation is carried out by components of the non-thermal plasma, preferably by plasma-activated oxygen species. Relevant for most cases is a process according to the invention, wherein the pretreated exhaust gas stream is treated with a non-thermal plasma generated by a plasma generation unit. With regard to the treatment of the pretreated exhaust gas stream with the non-thermal plasma and the plasma generation unit used for this purpose, the inventors believe it is particularly advantageous to use a non-thermal plasma generated by electrical discharge between two electrodes.

[0030] The use of so-called plasma injectors is particularly preferred here. Corresponding non-thermal plasma injectors are known from the prior art and commercially available. These plasma injectors inject the components of the non-thermal plasma into the fluid stream of the pretreated exhaust gas, where they in turn lead to oxidation of the undesired components. Thus, a method according to the invention is preferred, wherein the plasma generation unit comprises one or more plasma injectors designed to contact the pretreated exhaust gas stream with a non-thermal plasma or components of a non-thermal plasma, wherein the pretreated exhaust gas stream is preferably guided past the plasma injectors.

[0031] One advantage of the method according to the invention is that in many cases it does not require the use of filter units to remove particles, since these can usually be largely captured in the condensate of the condenser anyway. Nevertheless, for certain applications it may be advantageous to install a corresponding particle filter upstream of the condenser, for example in order to reliably prevent clogging of the condenser and thus increase its service life. Accordingly, on the one hand, a method according to the invention is preferred in which the exhaust gas stream is filtered with a filter, preferably a particle filter, before being introduced into the condenser. Alternatively, a method according to the invention is preferred in which the pretreated exhaust gas stream and the treated exhaust gas stream are not filtered.

[0032] In order to ensure the most controlled process possible and to continuously monitor whether the treated exhaust gas complies with legal requirements, the inventors propose determining the content of the organic compound in the treated exhaust gas stream and, if necessary, adapting the process parameters for exhaust gas treatment in light of the determined values. A process according to the invention is therefore preferred, wherein the content of the organic compound in the treated exhaust gas stream is determined using a sensor unit. As explained above, the presence of water in the exhaust gas stream is essential for the process according to the invention, with excellent results being achieved in particular with high water contents, i.e. high relative humidities. This means that the purification efficiency may be reduced for exhaust gases that contain only small amounts of water.In order to address this problem and / or even expand the applicability of the method according to the invention to other, dry exhaust gas streams, the inventors propose the targeted provision of humidification devices designed to create the desired degree of humidity in the exhaust gas stream. This advantageously improves the purification efficiency even for exhaust gas streams that already contain certain amounts of gaseous water, with the spraying of water droplets into the exhaust gas stream also being able to result in an additional increase in efficiency. Therefore, a method according to the invention is particularly preferred for exhaust gas streams from processes that are not in the field of rubber production, wherein the exhaust gas stream is mixed with steam before or during process step a), preferably by means of a humidification device, in order to increase the water content in the exhaust gas stream.

[0033] The invention also relates to an exhaust gas treatment system, in particular for use in a method according to the invention, comprising: i) a condenser for separating a condensate from the gas phase of an exhaust gas stream, having an exhaust gas inlet and an exhaust gas outlet, and ii) a plasma generation unit fluidly connected to the exhaust gas outlet of the condenser for generating a non-thermal plasma. The exhaust gas treatment system is suitable for use in a method according to the invention. Those skilled in the art will understand that the above statements regarding preferred embodiments of the method according to the invention accordingly also apply to the exhaust gas treatment system according to the invention. Correspondingly preferred embodiments of the exhaust gas treatment system are addressed below.

[0034] According to the invention, the exhaust gas treatment system comprises a condenser and a plasma generation unit connected to the condenser. As explained above, in some cases it is advantageous to provide a particulate filter upstream of the condenser. Therefore, an exhaust gas treatment system according to the invention is preferred, wherein the exhaust gas treatment system additionally comprises: iii) a filter, preferably a particulate filter, wherein the filter is preferably arranged upstream of the exhaust gas inlet of the condenser, and particularly preferably, no filters are arranged between the condenser and the plasma generation unit.

[0035] In order to increase the water content, i.e. the relative humidity, of dry exhaust gas streams and thus to increase the efficiency of the exhaust gas treatment system according to the invention, an exhaust gas treatment system according to the invention is preferred, wherein the exhaust gas treatment system additionally comprises: iv) a humidification device for humidifying an exhaust gas stream introduced into the condenser.

[0036] Also preferred is an exhaust gas treatment system according to the invention, wherein the condenser comprises a fluid line system for removing condensate from the condenser. In principle, exhaust gas streams released into the environment must comply with applicable legal regulations, for example

[0037] Limit value specifications for VOCs and / or other fragrances. In order to avoid exceeding the limit values, an exhaust gas treatment system according to the invention is therefore preferred, wherein the exhaust gas treatment system additionally comprises: v) a sensor unit, preferably a sensor for determining the content of organic compounds, wherein the sensor unit is preferably fluidically connected to the exhaust gas outlet of the plasma generation unit, wherein the sensor unit is particularly preferably arranged at the exhaust gas outlet of the plasma generation unit.

[0038] To ensure efficient discharge of the exhaust gas flow from the

[0039] To enable an exhaust gas treatment system, an exhaust gas treatment system according to the invention is preferred, wherein the exhaust gas treatment system additionally comprises: vi) a chimney fluidly connected to an exhaust gas outlet of the plasma generation unit.

[0040] Also disclosed is the use of an exhaust gas treatment system according to the invention for reducing the concentration of organic compounds in an exhaust gas stream, preferably in an exhaust gas stream of a rubber processing process.

[0041] Preferred embodiments of the invention are explained and described in more detail below with reference to the accompanying figure. It shows:

[0042] Fig. 1 is a schematic representation of an exhaust gas treatment system according to the invention in a preferred embodiment. Fig. 1 shows an exhaust gas treatment system 10 according to the invention for treating exhaust gases. The exhaust gas treatment system 10 comprises a condenser 12 and a plasma generation unit 20. An exhaust gas stream can be introduced through an exhaust gas inlet 16 of the condenser 12, as illustrated by dashed arrows in Fig. 1. If necessary, the exhaust gas stream can be filtered by a particulate filter (not shown) before entering the condenser 12.

[0043] In the example shown, the exhaust stream comprises exhaust gases from a mixing process for the production of vulcanizable rubber compounds. It has a relative water content of approximately 85% in the gas phase (relative humidity) and comprises at least one fragrance and ethanol as an organic compound with a relative content of approximately 75%, expressed as the relative content of the mass of ethanol per volume of the gas phase based on the maximum possible mass of ethanol in the gas phase at complete saturation.

[0044] To separate a condensate from the gas phase of the exhaust gas stream, the condenser 12 is configured to reduce the temperature of the exhaust gas stream to a temperature of approximately 8°C. For this purpose, the condenser 12 comprises a heat exchanger 14, for example a tube-bundle heat exchanger. The condenser 12 may further comprise a humidification device for humidifying the exhaust gas stream (not shown) in order to increase the effectiveness of the exhaust gas treatment system. The condensate is discharged from the interior of the condenser 12 via a fluid line system 22 into a treatment unit (not shown). The thus pretreated exhaust gas stream leaves the condenser 12 via an exhaust gas outlet 18 and is guided past a plasma generation unit 20, which is designed as a plasma injector.

[0045] The plasma generation unit 20 is configured to generate a non-thermal plasma by an electrical discharge between two electrodes and is fluidly connected to the capacitor 12 so that the pretreated exhaust gas stream is treated in the area hatched in Fig. 1.

[0046] The plasma generation unit 20 comprises several plasma injectors for treating the pretreated exhaust stream, past which the pretreated exhaust stream is passed. The plasma injectors contact the pretreated exhaust stream with the non-thermal plasma or components of the non-thermal plasma to obtain a treated exhaust stream from the pretreated exhaust stream. After passing through the plasma injectors, the treated exhaust stream is tested for its content of organic compounds using a sensor unit (not shown) that is fluidly connected to the plasma generation unit 20. The treated exhaust stream is finally discharged to the environment via a chimney 24.

[0047] List of reference symbols

[0048] 10 Exhaust gas treatment system

[0049] 12 Capacitor

[0050] 14 Heat exchanger 16 Exhaust inlet

[0051] 18 Exhaust outlet

[0052] 20 Plasma generation unit

[0053] 22 Fluid line system

[0054] 24 Chimney

Claims

Claims 1. Method for treating exhaust gases with a Exhaust gas treatment system (10) comprising the process steps of: a) introducing an exhaust gas stream into an exhaust gas treatment system (10), wherein the exhaust gas stream in the gas phase comprises water and at least one organic compound, b) introducing the exhaust gas stream into a condenser (12) and separating a portion of the gas phase as condensate to obtain a pretreated exhaust gas stream, and c) treating the pretreated exhaust gas stream with a non-thermal plasma or components of a non-thermal plasma to obtain a treated exhaust gas stream.

2. The method of claim 1, wherein the exhaust gas stream comprises exhaust gases from a rubber processing process.

3. Method according to one of claims 1 or 2, wherein the exhaust gas stream in the gas phase comprises at least one alcohol as an organic compound.

4. Method according to one of claims 1 to 3, wherein the exhaust gas stream in process step a) comprises at least one odorant in the gas phase.

5. Method according to any one of claims 1 to 4, wherein the exhaust gas stream in the gas phase has a relative water content in the range of 40 to 100%, expressed as relative humidity.

6. Method according to any one of claims 1 to 5, wherein the exhaust gas stream in the gas phase has a relative content of at least one organic compound in the range of 40 to 98%, expressed as the relative content of the mass of the organic compound per volume of the gas phase based on the maximum possible mass of the organic compound in the gas phase at complete saturation.

7. Method according to any one of claims 1 to 6, wherein the condenser (12) comprises a heat exchanger (14), preferably a shell and tube heat exchanger or plate heat exchanger, particularly preferably a shell and tube heat exchanger.

8. Method according to any one of claims 1 to 7, wherein the condenser (12) is configured to reduce the temperature of the exhaust gas stream to a temperature in the range of 3 to 20 °C.

9. Method according to any one of claims 1 to 8, wherein the exhaust gas stream is mixed with steam before or during process step a).

10. Exhaust gas treatment system (10), in particular for use in a method according to any one of claims 1 to 9, comprising: i) a condenser (12) for separating a condensate from the gas phase of an exhaust gas stream with an exhaust gas inlet (16) and an exhaust gas outlet (18), and ii) a plasma generation unit (20) fluidly connected to the exhaust gas outlet (18) of the condenser (12) for generating a non-thermal plasma.

Images