RU2120328C1 - Method and device for cleaning gaseous emissions - Google Patents

Abstract

FIELD: chemical cleaning of exit gases of industrial process plants. SUBSTANCE: chemically active agent is introduced in gas, the latter is exposed to electrical diffusion discharge built up across electrodes, and reaction products are removed from exhaust gas; electrolyte is supplied to surface of at least one electrode facing the gas. Device implementing this method has reactor accommodating electrodes which form inner surface of channel passing clean gas and connected to electric power supply, as well as reaction product trap installed at reactor gas outlet; at least one of electrodes is provided with pipe connected to electrolyte heater and waste solution accumulator. EFFECT: facilitated procedure, improved efficiency. 6 cl, 4 dwg

Description

 The present invention relates to the field of chemical purification of exhaust gases during the operation of technological plants in various industries, in particular when burning organic fuel in boilers of power plants, in internal combustion engines.

 The purification of gas emissions and, in particular, the flue gases of industrial plants from nitrogen oxides and sulfur is an important environmental task.

A known method of purification of flue gases from nitric oxide, including the injection of water, lowering the temperature of the flue gases to 80-120 ^o C and mixing them with air, the introduction of a reagent in the form of an aqueous solution of carbonate and potassium nitrate at a molar ratio of 10: 1 and concentration, respectively 0.15-0.19 and 0.015-0.019 and subsequent exposure to an electron beam (see USSR author's certificate N 1662647 according to class B 01 D 53/34 of 03/03/1988).

 The known method of purification of gas emissions has insufficient energy efficiency due to the small degree of use of the generated free radicals, requires the use of electron accelerators, which is also associated with the need for radiation protection from washing high-voltage electron guns.

 A device for cleaning gas emissions, containing a reactor, an electronic gun, the trunks of which are placed on opposite walls of the reactor, an electronic accelerator connected to a power source and a device for introducing ammonia. A salt trap is installed at the gas outlet from the reactor. (see USSR author's certificate N 1472118 according to class B 01 J 19/08 of 09/09/1987).

 The disadvantages of the known devices are low energy efficiency and design complexity.

 A known method of cleaning gas emissions from oxides of nitrogen and sulfur, including passing gas emissions through the streamer corona area, formed by a system of electrodes "thread-cylinder" or "thread-plane", which are supplied with pulses of electric energy of a sufficiently high voltage, providing the transfer of sulfur oxides and nitrogen into acid fog (see US patent N 4695358 according to class B 01 D 53/34 publ. 03/22/1987).

 The implementation of the known method in a large reactor volume presents great technical difficulties, since the discharge develops from the electrodes in the form of separate conductive threads, occupying only a small part of the interelectrode space.

 A device for cleaning gas emissions using a pulsed streamer corona, comprising a cylindrical reactor with inlet and outlet nozzles for the inlet of the purified gas and the release of purified gas. A threadlike electrode connected to a pulsed high-voltage source is fixed on the axis of the reactor (see US Pat. No. 4,695,358, class B 01 D 53/34, publ. 09/22/1987).

 The disadvantages of the known device are significant technical difficulties in ensuring the existence of a discharge in a large reactor volume, erosion of the electrodes.

 The closest in technical essence to the problem being solved is a method of purifying gas emissions, including introducing a reagent into the gas, exposure to a diffuse electric discharge created between two electrodes, the surface of one of which (the cathode) is uniformly dotted with thin metal pins, each of which is loaded on an individual ballast resistance (see Akishev Yu.S., Levkin V.V., Napartovich A.P., Trushkin N.I. - The use of a glow discharge in a gas stream for the destruction of small impurities. - Materials of the seminar "Application of electric electron beams and pulsed discharges for cleaning flue gases ".- M.: IVTAN, 1991, S. 37-41).

 In the known method, the region intensively generating chemically active particles is the entire discharge volume, in contrast to the method using the streamer corona, however, this method is not without drawbacks: there is erosion of the electrodes, preliminary cooling of the gas to be purified and forced cooling of the electrodes are required to create diffuse electrical discharge it is necessary to apply a voltage of one polarity.

 A device for cleaning gas emissions, including a reactor in which there are flat electrodes, one of which is equipped with many tips directed perpendicular to the second flat electrode is known. The electrodes form the inner surface of the channel for the passage of the cleaned gas. The electrodes are connected to a direct current source through ballast resistance, the limits of which are selected in such a way as to, on the one hand, provide the necessary energy input, and, on the other hand, to avoid the arc discharge stage. At the outlet of the reactor there is a filter for trapping solid particles (see PCT application WO N 88/08325 according to class B 01 D 53/34, published 03.11.1988).

 The known device has a complex structure, requires forced cooling of the tips, erosion of the electrodes occurs in the device, there is no possibility of using an alternating voltage.

 The objective was to create such a method for purifying gas emissions and devices for its implementation, which would provide an increase in the energy efficiency of the purification process without additional energy input by increasing the contribution of cyclic reactions with the regeneration of free radicals, and simplify the design and apply alternating voltage.

 The problem is solved in that in a method for purifying gas emissions, including introducing a reagent into the gas, applying an electric diffusion discharge between the electrodes and removing reaction products from the exhaust gas, an electrolyte is supplied to the surface of the at least one electrode facing the gas, as which can be used with ordinary process water. The reagent (which may be a substance that binds harmful impurities in a gas, catalytic additives, etc.) can be introduced directly into the electrolyte supplied to the electrode surface. The electrolyte can also be applied to the facing surfaces of two electrodes, to which an alternating voltage is applied in this case.

 The problem is also solved by the fact that in the device for cleaning gas emissions, including a reactor, which contains electrodes that form the inner surface of the channel for passing the cleaned gas and connected to a power source, and a trap of reaction products installed at the gas outlet from the reactor, at least one of the electrodes is equipped with a nozzle connected to an electrolyte supercharger and a collector for receiving spent electrolyte. Two opposing electrodes may be provided with a nozzle for supplying electrolyte and a collector for receiving spent electrolyte. One of the electrodes can be made porous and directly connected to the pipe for supplying electrolyte.

 As a result of supplying the electrolyte to the surface of one of the electrodes facing the gas, a diffuse volume discharge arises between the surface of the liquid and the second electrode, while water vapor and electrolyte droplets are intensively introduced into the gas stream by evaporation and spraying of the electrolyte covering the electrode. All this significantly increases the intensity of the reactions of binding of solid impurities and the regeneration of free radicals in the droplet phase and, accordingly, increases the energy efficiency of purification. It becomes possible to use the electrolyte located on the surface of the electrode to cool the gas being cleaned, which simplifies the cleaning process. When a diffuse volume discharge is burned in the case of supplying an electrolyte to the electrode and introducing a reagent (reducing agent, catalytic additives, etc., depending on the composition of the impurities in the gas to be cleaned), it becomes possible to provide a metered introduction into the stream of gas being purified, which opens up new channels of reactions of binding of impurities and regeneration of radicals and leads to an increase in the energy efficiency of the process. When applying electrolyte to the facing surfaces of two electrodes, it becomes possible to use alternating voltage, which simplifies the implementation of the method. The supply of at least one of the electrodes of the device for cleaning gas emissions with a nozzle connected to an electrolyte supercharger and a collector for receiving spent electrolyte ensures reliable coating of the metal surface with an electrolyte layer and thereby stable combustion of a diffuse volume discharge, constancy of the electrolyte composition by replenishment with a fresh solution. With a liquid electrode, there is no erosion of the metal, since there is a spray of liquid, and not the metal of the electrode, as in the prototype method; at the same time, the electrode is also cooled, the occurrence of a contracted discharge is excluded. In addition, evaporation and spraying of the electrolyte can be used to cool the gas being cleaned. The supply of an electrolyte supply pipe and a collector for receiving the spent solution of two opposite electrodes allows working on alternating voltage, eliminating the need for rectifying devices. The execution of one of the electrodes porous and connecting it directly to the pipe for supplying electrolyte allows metered supply of electrolyte through the pores to the surface of the electrode, while simultaneously cooling its entire volume.

 It is known in the art to use liquid electrodes for metal etching (see Gaysin F.M., Son E.U. - Electrophysical processes in discharges with solid and liquid electrodes. - Sverdlovsk: Publishing House of Uralsk. University, 1989, 432 pp.) . In the claimed method of purification of gas emissions, on the contrary, there is no etching (erosion) of the metal, and as a result of supplying the electrolyte to the electrode, the gas being purified is cooled, the electrode is cooled, and the nature of the processes occurring in the discharge changes. Authors from the scientific and technical literature are not aware of the use of a discharge between solid and liquid electrodes for gas purification.

 A device for cleaning gas emissions is shown in the drawing, where Fig.1 schematically shows a General view of the device in section; figure 2 is one of the possible designs of the electrode assembly when water is supplied on the surface of two electrodes; figure 3 - the design of the electrode assembly to create an annular diffuse discharge; figure 4 - design of the electrode assembly with a porous electrode.

 The device for cleaning gas emissions includes a reactor 1, in which electrodes 2 and 3 are placed, which form the inner surface of the channel for passing the gas to be cleaned, the pipe 4 serves for supplying it. The electrode 3 is equipped with a pipe 5 connected to an electrolyte blower 6, connected in turn , pipeline 7 with a capacity of 8 for electrolyte. On the opposite side of the electrode pipe 5 of the electrode 3, a collector 9 is installed for receiving the spent electrolyte. When the electrolyte is supplied to both electrodes 2 and 3 (see Fig. 2), the electrode 5 is also provided with a nozzle 5 and a collector 2. The electrode 3 is provided on three sides (except for the side facing the collector 9) with a shoulder 10, which thus forms the walls of the bath to hold the electrolyte layer 11 on the surface of the electrode 3. The collector 9 is connected by a pipe 12 with a capacity 8. The electrode 2 is connected to a power source 13 and a voltmeter 14. In the case of supplying electrolyte to both electrodes 2 and 3 (see figure 2) they can be connected to a source 13 of alternating voltage. The electrode 3 when using unipolar voltage is usually grounded. The reactor 1 is equipped with outlet pipes 15 with filters 16 for trapping the reaction products. In the pipe 15, the sensor of the analyzer of gas composition 17 can be placed. The electrode 3 can be equipped with pores 18 for supplying electrolyte to its surface (see Fig. 4).

 A device for cleaning gas emissions works as follows. The electrolyte of the required composition from the tank 8 through the pipe 7 using the blower 6 through the pipe 5 is fed to the surface of the electrode 3. In the manufacture of the electrode 3 by porous electrolyte through the pores 18 enters its surface. The excess electrolyte through the collector 9 and the pipe 12 returns to the tank 8. When a high voltage is applied to the electrode 2 from the power supply 13 between the surface of the electrode 2 and the surface of the electrolyte 11, a diffuse volume electric discharge is generated, which forms chemically active free radicals. The gas purified from harmful impurities is supplied through the pipe 4 to the diffuse volume electric discharge region between the electrodes 2 and 3. As a result of the reaction of harmful gas impurities with free radicals in the presence, if necessary, of a catalyst or reducing agent, as well as evaporation and spraying of the electrolyte from the electrode for 3 s the initiation of cyclic reactions of absorption of oxides and regeneration of free radicals in the droplet phase, the gas is purified from harmful impurities with their transfer to the solid phase. At the same time, the gas to be purified is cooled. After passing through a diffuse volume discharge, the gas through the nozzles 15 enters the filters 16, where solid particles are separated from the gas, after which the purified gas is discharged from the reactor 1.

 The inventive method of cleaning gas emissions was tested on the layout of the device. The distance between the electrodes was equal to 1 cm, a potential difference of 2-4 kV was applied to the electrodes, depending on the qualitative and quantitative composition of the electrolyte. The speed of the gas being cleaned was in the interelectrode gap of the order of 10 m / s, the current in the diffuse discharge reached 1 A. Normal industrial water was supplied to the electrodes as an electrolyte. The experiments fully confirmed the advantages of the proposed cleaning method and device for its implementation over the method and device prototypes.

Claims (6)

 1. A method of purifying gas emissions, including introducing a reagent into the gas, applying a diffuse electric discharge generated between the electrodes, and removing reaction products from the exhaust gas, characterized in that an electrolyte is supplied to the surface of the at least one electrode facing the gas.  2. The method according to claim 1, characterized in that the reagent is introduced into the electrolyte supplied to the surface of the electrode.  3. The method according to claim 1, characterized in that the electrolyte is fed onto the facing surfaces of two electrodes to which an alternating voltage is applied.  4. A device for cleaning gas emissions, comprising a reactor in which electrodes are placed that form the inner surface of the channel for passing the gas to be cleaned and connected to a power source, and a catcher of reaction products installed at the gas outlet from the reactor, characterized in that at least one of the electrodes are equipped with a pipe connected to an electrolyte supercharger, and a collector for receiving the spent solution.  5. The device according to claim 4, characterized in that the pipe for supplying the electrolyte and the collector for receiving the spent solution are equipped with two opposite electrodes.  6. The device according to claim 4, characterized in that at least one of the electrodes is made porous and directly connected to the pipe for supplying electrolyte.

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