RU2106183C1 - Method of cleaning of waste gases and installation for its realization - Google Patents

Abstract

FIELD: wood-pulp, petroleum refining, chemical industries, as well as power engineering for waste gas cleaning. SUBSTANCE: waste gas flow is influenced by a non-equilibrium low-temperature plasma and/or by radiation treatment by polymer, whose structure incorporates deterious components or their derivatives. Plasma and/or radiation treatment (for instance, ultraviolet one) accomplish reactions of activation of gas to be cleaned and polymer throughout the entire section of the reactor. Polymer is injected in the reactor in powdered state, and plasma is fed to the reactor at a supersonic speed from plasma generators. The reactor is connected to the waste gas pipeline, connected to which through a dehumidifier may be the plasma generators. The reaction products outlet device is made either with a separator of solid-phase components of reaction products, furnished with a collector of the latters, or with plates of polymer or with a coating of polymer located in the reactor. EFFECT: facilitated procedure. 18 cl, 5 dwg, 1 ex

Description

 The invention relates to the purification of exhaust gases of industrial and power plants from harmful gas components: sulfur oxides, nitrogen, as well as mercaptans, hydrogen sulfide, carbon disulfide, etc., and can be used to create treatment facilities in the oil refining, pulp and paper and chemical industries , as well as in the energy sector.

 Currently, various methods are known for removing harmful gas components that are part of the exhaust (flue) gases of industrial and power plants, mainly nitrogen oxides, sulfur.

 The known methods for purifying exhaust gases that have found application are divided into two types.

 The first includes chemical, absorption, catalytic.

 To the second - physical and chemical using electron beams, microwave discharges, plasma jets, corona discharges, etc.

 The most common chemical methods are methods using the introduction of various active substances into the gases to be cleaned, with the aim of creating processes of reduction, oxidation, catalysis, etc., which contribute to the removal of harmful substances from the exhaust (flue) gases.

Known industrial plasma cleaning method using NH ₃ and microwave discharge [1].

The specified known purification method involves introducing NH ₃ into the stream of gas to be purified while simultaneously creating a microwave discharge in the resulting mixture. In this case, the formation of radicals that react with nitrogen and sulfur oxides with the formation of nitric and sulfuric acids. Ammonia added to flue gases in the presence of free oxygen and water vapor forms ammonium nitrates and sulfates in the solid state.

The disadvantage of this known method is the high cost, multi-stage and toxicity of the introduced component of NH ₃ , as well as the inability to purify various sulfur compounds (except sulfur oxides).

A known installation for cleaning exhaust gases from SO _{2 by} exposure to plasma containing a reactor connected to a pipeline of exhaust gases and equipped with a section of gas plasma generators and a device for outputting reaction products [2].

 The specified installation limits the cleaning process by the decomposition of oxides and does not provide the necessary degree of purification of the exhaust gases from sulfur compounds and oxides before the exhaust gases into the environment. In addition, the known installation requires high energy costs per unit of gas to be cleaned and has a limitation on the consumption of gas to be purified.

 The closest analogue of the invention is a method of purification of exhaust gases from impurities and a device for its implementation [3].

 The method is carried out by passing through the reactor off-gas, into which a stream of hydrocarbon low-temperature non-equilibrium plasma is introduced, followed by separation of the solid-phase reaction products.

 The device comprises a reactor, a plasma generator and means for outputting the resulting solid phase.

 However, this technical solution has significant drawbacks: the use of hydrocarbon plasma makes the process technically explosive, especially with large volumes of gas to be purified, the purification process is carried out only for a limited composition of the gas to be purified, and large volumes of hydrocarbons are required for purification of the plasma, which is environmentally disadvantageous (low Efficiency) and is technically difficult to implement.

The purpose of the claimed inventions is to develop a method and create safe installations that ensure the purification of exhaust gases from various harmful components (SO ₂ , NO ₂ , CS ₂ , CH ₃ SH, CO _x ), actually present in industrial gas emissions, without disrupting the main technological process during low working voltage of plasma formation and high consumption of gas to be purified, as well as increased efficiency of plants at high concentrations of harmful components.

 The claimed technical result, according to the purification method, is achieved by the fact that a polymer or a polymerizable monomer is added to the reactor, incorporating harmful components or their derivatives into its structure, and they carry out activation reactions of the gas and polymer of gases to be purified and / or irradiation, while to intensify the purification process it is advisable to use ultraviolet radiation to irradiate the zone of interaction of the plasma with the gas and polymer being purified (or the polymerizable monomer). Nonequilibrium low-temperature plasma can be created from pre-dried exhaust (purified) gas, nitrogen, natural gas, or mixtures thereof, including with an inert gas.

The resulting plasma contains electronically excited neutral or charged particles (atoms, molecules, radicals, ions, etc.) (see Fig. 1) with internal excitation and ionization energies (from several units to tens of eV) exceeding the bond breaking energy of harmful components ( SO ₂ , NO ₂ , CH ₃ SN, H ₂ S) of the gas to be purified.

The effect of plasma jet components on harmful components is due to resonance conditions of the excitation reaction (or bond breaking) of particles, for example, SO ₂ molecules with the formation of SO $\genfrac{}{}{0ex}{}{\text{*}}{\text{2}}$ (in singlet or triplet states) and SO.

.Triplet SO ₂ can react with the olefin structures of the polymer, initiating radical processes and incorporating SO ₂ . For instance:

.

Especially intensive are unsaturated hydrocarbon-based polymers with high concentrations of paramagnetic centers, incorporating radicals SO, SH, S ₂ and others (see figure 4), and ultraviolet radiation increases the speed of incorporation.

.Purification of the exhaust gas from NO ₂ using the introduced polymer is due to various types of reactions, while NH, NH ₂ and NO ₂ radicals included in the polymer structure of the introduced polymer are recorded in the infrared absorption spectra, the incorporation of NO ₂ into the hydrocarbon-based polymer occurs by reaction:

.

 A mercaptan plays a positive role in the polymerization process due to the recoil of the hydrogen atom in interaction with a growing polymer radical, and its molecule becomes the initiator of the polymer chain.

 Thus, the polymerization mechanism is determined not only by high concentrations of excited particles in the plasma jet, but also by the structure of the introduced polymer, mainly by the presence of free radicals and paramagnetic centers in its composition.

 There are two installation options that implement the above method.

The claimed technical result according to the first embodiment of the installation for purification of exhaust gases is achieved by the fact that it further comprises a device for introducing into the reactor a polymer in the form of a powder incorporating harmful components into its structure: SO ₂ , NO ₂ , CO, SH, etc.

 According to the second variant, the device for outputting reaction products can be placed directly in the reactor and made in the form of surfaces such as plates made of polymer, incorporating these harmful components and their derivatives into its structure, or having a coating of the specified polymer in the form of a sprayed powder or film.

In both versions of the installation, a low-voltage plasma generator is connected to the exhaust gas pipeline and can be made in the form of a DC arc plasma torch with a low operating voltage U and its possible adjustment by changing the gap between the electrodes. In this case, E _b ≤U≤2E _i , where E _b is the excitation energy, E _i is the maximum ionization potential of the component of the plasma-forming gas. It is also possible to execute a part of the reactor in the form of a cascade plasmatron creating plasma from the dried off-gas with placement of a polymer injection device into the reactor after the plasma exits the cascade plasmatron.

 The installation in both cases may contain a source of ultraviolet radiation for irradiating the zone of interaction of gas, plasma and polymer to intensify the processes of excitation, polymerization and copolymerization.

 The invention is illustrated by the following material.

 Figure 1 shows the emission spectrum of excited radicals from the reaction zone of the plasma with the exhaust gases; figure 2 - absorption spectrum in the infrared region of the exhaust gas before cleaning; figure 3 - absorption spectrum in the infrared region of the exhaust gas after purification; figure 4 - absorption spectra in the infrared region of the polymer introduced into the reactor: I - before purification, II - after purification; figure 5 - diagram of the installation for purification of exhaust gases.

 Installation for purification of exhaust gases, which contains connected to the pipe 1 of the outlet of the latter from the industrial installation, reactor 2 with sections 3 of plasma generators 4 and a device 5 for outputting reaction products with a pipe 6 of the outlet for purified gas.

 According to the first embodiment, the installation is equipped with a device 7 for introducing into the reactor a polymer in powder form, incorporating into its structure the harmful components of the purified exhaust gas or their derivatives. In this case, the device 5 for outputting reaction products has a collection of 8 solid-phase reaction products with a pipe 9 for their removal.

 According to a second embodiment of the apparatus, the device 5 for outputting reaction products has plate-like surfaces (not shown in the drawing) installed directly in the reactor and made of a polymer incorporating the aforementioned harmful components and their derivatives, or having a coating of said polymer.

 In both versions of the installation, the latter may contain an ultraviolet radiation source 10 for irradiating the interaction zone of the exhaust gas, nonequilibrium low-temperature plasma and polymer, for example, through windows 11 made in the reactor 2.

 Windows 12 can be made in the walls of the reactor 2 to monitor the cleaning efficiency, in order to select the optimal mode of the cleaning process, through automatic software communication.

 To create a plasma from the gas to be purified, the installation can be equipped with a desiccant 13, through which the generators 4 are connected by their inlet to the pipeline 1.

 Gas purification is carried out as follows.

The cleaned gas supplied to the reactor 2 through the pipeline 1 from the devices 7 and the generator 4 is affected by the introduced polymer, a nonequilibrium low-temperature plasma with high speeds, respectively, the plasma can be created in the reactor itself and / or by irradiation, the plasma and / or irradiation, In particular (UV), they provide activation reactions and components of the gas and polymer being purified over the entire cross section of the reactor. In this case, ions and radicals are formed in the cavity of the reactor 2 during the interaction of these streams, for example, for a plasma based on nitrogen and an inert gas and a purified gas from the pulp and paper industry, ions: Na ₂ + CO ₂ + H ₂ S + CH ₃ SH + NO ₂ +, radicals: N, O, OH, CH ₃ SH, NO, N ^* , OH ^* , NO ^* , CH ^* , NH ^* , monomers: SO ₂ , C ₂ H ₂ , CS ₂ CO, which are involved in the copolymerization process with the incoming polymer, which results in the purification of the exhaust gas from harmful components: SO ₂ , CS ₂ , CH ₃ SN, NO ₂ , etc., for example, according to the above reactions or their analogs.

 When testing the inventive method for purification of exhaust gases, their composition at the inlet and outlet of the reactor was studied (installation of option 1 was used). As plasma-forming gases, mixtures of natural gas or nitrogen with inert gases were used. In the spectrum of radiation from the reaction zone, intense bands of excited radicals are observed (see Fig. 1). The polymer used was polymer powder obtained from a mixture of methane and argon by a plasma method, the structure of which is characterized by the presence of free radicals and high concentrations of paramagnetic centers.

 The composition of the exhaust gas was determined by the absorption spectra in the infrared region.

 The absorption spectra of the exhaust gas before and after purification are shown respectively in FIG. 2 and 3.

 From a comparison of the indicated spectra, it follows that the harmful components are removed from the gas phase, since the absorption bands of nitrogen oxides, sulfur, mercaptans, and other sulfur compounds are absent in the spectrum of exhaust gases after their purification (at the outlet of the reactor).

 Confirmation of the passage of the copolymerization process with incorporation of harmful components into the structure of the introduced polymer is illustrated in Fig. 4, which shows the absorption spectra of the polymer before the purification process and at the outlet of the reactor — curves I and II. Intense bands characteristic of sulfur and nitrogen compounds, previously absent from the spectrum of the introduced polymer, are observed in the absorption spectrum of the polymer.

The advantages of the inventions are the possibility of simultaneous purification of exhaust gases from oxides of sulfur, nitrogen, carbon, mercaptans, etc., sulfur compounds (for example, CS ₂ , H ₂ S) without the formation of secondary toxic products, a high degree of purification from oxides of sulfur, nitrogen, mercaptans and carbon disulfide, the use of low-voltage technology.

It should also be noted that the installation (in both of the presented versions) does not have complex and expensive components and equipment, is simple and safe to operate (due to the low voltage required for plasma formation), reliable in operation, has small dimensions and weight, it is easily mounted on the existing production without changing the technological process, it has the ability to increase the flow rate of the purified gas to several hundred thousand m ³ / h through the use of blocks from parallel reactors.

Claims (18)

 1. The method of purification of exhaust gases by exposing the gases in the reactor to non-equilibrium low-temperature plasma with the formation of solid reaction products, separating the latter and removing purified gas, characterized in that the polymer is additionally introduced into the reactor, which incorporates harmful components into its structure, or their derivatives, and is carried out activation reactions of the gas and polymer being purified by plasma and / or irradiation.  2. The method according to claim 1, characterized in that the introduction of the polymer is carried out by blowing it in a powder state.  3. The method according to claims 1 and 2, characterized in that the plasma is blown into the reactor at a supersonic speed.  4. The method according to claims 1 to 3, characterized in that ultraviolet radiation is used to irradiate the interaction zone of gases, plasma and polymer.  5. The method according to claims 1 to 4, characterized in that the plasma is created from a pre-dried purified gas.  6. The method according to claims 1 to 4, characterized in that the plasma is created from natural gas, nitrogen, inert gas or mixtures thereof.  7. Installation for purification of exhaust gases, containing a reactor connected to the exhaust gas pipeline with plasma generators and a device for outputting reaction products, made in the form of a separator with a collector of solid-phase components, characterized in that it is equipped with a polymer input device in the form of a powder incorporating into harmful components or their derivatives.  8. Installation according to claim 7, characterized in that each plasma generator is made in the form of a direct current plasma torch with an adjustable gap between its electrodes.  9. Installation according to claim 7, characterized in that the reactor with plasma generators is made in the form of a cascade plasmatron.  10. Installation according to claims 7 and 8, characterized in that each plasma generator is connected by its inlet to the exhaust gas pipe through a dryer.  11. Installation according to claims 7 to 10, characterized in that the device for introducing the polymer into the reactor is configured to change the direction of introduction of the polymer into the cavity of the reactor.  12. Installation according to claims 7 to 11, characterized in that it is equipped with a source of ultraviolet radiation for irradiating the zone of interaction of exhaust gases with plasma and polymer.  13. Installation of purification of exhaust gases, containing a reactor connected to the exhaust gas pipeline with plasma generators and a device for outputting reaction products, characterized in that the latter is placed directly in the reactor and is made in the form of surfaces such as plates of a polymer incorporating harmful components and their derivatives, or having a coating of the specified polymer in the form of a powder or film.  14. Installation according to claim 13, characterized in that each plasma generator is made in the form of an electric arc plasma torch with an adjustable gap between its electrodes.  15. Installation according to item 13, wherein the reactor with plasma generators is made in the form of a cascade plasmatron.  16. Installation according to claims 13 and 14, characterized in that each plasma generator is connected by its inlet to the exhaust gas pipeline through a desiccant.  17. The apparatus of claim 15, wherein the plasma torch is connected by its inlet to the exhaust gas pipe through a desiccant.  18. Installation according to claims 13-17, characterized in that it is provided with a source of ultraviolet radiation for irradiating the reaction zone.

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