RU2264852C1 - Catalytic reactor for purification of gaseous outbursts from nitrogen oxide with the help of ammonia, combined with a spiral countercurrent heat exchanger-recuperator - Google Patents

Abstract

FIELD: chemical industry; catalytic reactors for gaseous outbursts purification.

SUBSTANCE: the offered reactor is pertaining to chemical industry and used for purification of gases from nitrogen oxide impurities by means of ammonia. The reactor has an electrical cabinet of control and a catalytic section which contains plug-in catalytic blocks heated up by plug-in electric heaters based of a foam-metal with a catalytic coating out of metal oxides. The catalytic section is placed inside the spiral countercurrent heat exchanger-recuperator. The spiral of the heat exchanger-recuperator with the catalytic section are located horizontally. The upper part and the ends of a heat exchanger-recuperator are protected by a layer of a heat insulation. In the catalytic section there is a safety fuse de-energizing the catalytic reactor at reaching the temperature of 660°C in the catalytic section. The catalytic blocks have different thickness and sizes of meshes. The electric heaters are divided into two separately adjustable assemblies, pressing to which of the catalytic blocks is exercised under their own weight, and in the catalytic reactor feed a controlled by a small amount of ammonia flow rate meter. The technical result of the invention is an increased effectiveness and safety of the catalytic process.

EFFECT: the invention ensures an increased effectiveness and safety of the catalytic process.

3 dwg, 1 tbl

Description

The invention relates to techniques for purifying process and ventilation gases from impurities of nitrogen oxides with the help of ammonia and can be used in the chemical, electrical, engineering and any other industries where work is underway with these chemical compounds.

Known catalytic oxidation apparatus, consisting of a catalytic section, an electric heater, a spiral heat exchanger-recuperator, where the spiral channels are made of corrugated semi-cylindrical shells of the same diameter, offset from each other by the width of the channel, and the corrugated folds are made across the movement of the gas stream (RF patent No. 1762459, C. B 01 J 8/04, publ. 10.10.1998).

The disadvantages of this apparatus are its large dimensions, weight and energy consumption, since it uses the principle of heating the entire gas stream by electric heaters to a bulk catalyst to ensure the required temperature of the catalytic process. In addition, the design does not provide for the safe conduct of the process in case of emergency release of neutralizable compounds into the cleaned gas stream.

The closest in technical essence to the proposed invention (prototype) is disclosed in the patent of the Russian Federation No. 2180869, class. B 01 D 53/86, publ. 03/27/2002, a device for gas purification with a current-heating catalytic unit and a heat exchanger, in which air is purified from organic substances by catalytic oxidation on blocks based on foam metals. Energy losses in the reactor are minimized by lowering the temperature of the gases, since the operating temperature is maintained only on the catalytic units where the reaction proceeds. The use of open-cell foam nickel-based block catalysts provides intensive mass and heat transfer over the entire volume of the catalyst, increases the contact time of the gas with the working surface and its uniform gas-dynamic and thermal load due to low hydraulic resistance and turbulization of the gas flow.

The disadvantages of the prototype are the high energy costs in the case of low concentrations of neutralizable compounds, due to the fact that the hot stream of purified gas is in contact with the upper end wall of the heat exchanger, significantly increasing its temperature and creating a danger during operation due to the high temperature of its surface. In addition, in this device it is impossible to simultaneously carry out both oxidative and reduction reactions necessary in the case of neutralization of nitrogen compounds in air.

The objectives of the invention are to increase the efficiency and safety of the catalytic process, which are solved in the proposed catalytic reactor due to its design, which allows to obtain technical results consisting in simplifying the design, expanding the possibilities of application, reducing heat loss and ensuring operational safety.

The catalytic reactor for purifying gas emissions from nitrogen oxides using ammonia (hereinafter referred to as the catalytic reactor, shown in FIG. 1) consists of a current-heating catalytic section 1 located inside a spiral counter-current heat exchanger-recuperator 2, and from a control cabinet 3.

The catalytic section 1 is formed by a housing 4 with a thermocouple 5 and a fuse 6. In the catalytic section 1 there are replaceable catalytic blocks 7 with different thickness and cell sizes based on foam metal with a catalytic coating of metal oxides, heated by two clamped, separately regulated assemblies of electric heaters 8, 9 which are also interchangeable.

The spiral countercurrent heat exchanger-recuperator 2 consists of a housing 10 with an inlet 11, an outlet 12 and a heat insulation layer 13. The spiral channels 14 of the heat exchanger-recuperator 2 are made of semi-cylindrical shells 15, 16 of the same diameter, offset from each other by the channel width and connected to end walls of the housing 10.

A controlled amount of ammonia is fed to the inlet of the catalytic reactor: an ammonia feed meter 17 connected to the ammonia feed line is located at the inlet 11 of the housing 10.

The proposed catalytic reactor eliminated the disadvantages of the prototype, and solved the tasks with the following technical results.

The efficiency and possibilities of interaction of the gas stream with the catalytic layer are increased, as well as the efficiency of neutralizing the gas to be cleaned is increased due to the fact that the catalytic units 7 of the catalytic section 1 have different thickness and cell sizes and the required amount of gaseous or liquefied ammonia is fed to the inlet of the catalytic reactor or its aqueous solution, adjustable using a flow meter 17.

The design and maintenance of the catalytic reactor is simplified due to the fact that the catalytic blocks 7 are pressed to the electric heater assemblies 8, 9 due to their own weight, and not by means of belt springs, as in the prototype, and the electric heaters are divided into two separately adjustable electric heater assemblies 8, 9: to achieve the required temperature at the start of the catalytic process and to maintain the temperature of the catalytic process, which increases the efficiency of the catalytic reactor, extends the working life Heating resistor and facilitates replacement of the catalyst units 7 and assembly of electric heaters 8, 9.

The heat losses of the catalytic process are reduced due to the fact that the upper parts of the catalytic blocks 7 and the catalytic reactor are not overheated, since the catalytic section 1 and the spiral channels 14 of the heat exchanger-recuperator 2 are located horizontally (in the prototype - vertically, which leads to overheating), and the upper part and ends of the housing 10 of the heat exchanger-recuperator 2 are protected by a layer of thermal insulation 13. With this design of the proposed catalytic reactor, due to convection of the heat flux, a greater its uniform temperature distribution over the catalytic blocks 7, while the surface temperature of the catalytic reactor is reduced, and heat loss to the environment is reduced.

The operational safety of the catalytic reactor is improved due to the fact that there is a fuse 6 in the catalytic section 1, which mechanically disconnects the limit switch when the temperature reaches 660 ° C in the catalytic section 1 during the catalytic process or in case of malfunction of the control cabinet 3 and thereby de-energizes the catalytic reactor.

The catalytic reactor operates as follows.

A fan (not shown in FIG. 1) delivers process and ventilation gases through the inlet of the catalytic reactor. The incoming gas enters the heat exchanger-recuperator 2, comes into contact with its walls and is heated to a temperature below the beginning of the catalytic oxidation process, and falling on the catalytic blocks 7 heated by means of an electric heater assembly 8, it is heated to a temperature corresponding to the beginning of the catalytic reduction-oxidation process. The thermocatalytic reduction of nitrogen oxides with ammonia in the presence of air oxygen occurs on the catalytic blocks 7 of foam nickel with a deposited layer of metal oxides according to the reactions:

4NO + 4NH ₃ + O ₂ = 4N ₂ + 6H ₂ O;

4NO ₂ + 4NH ₃ + O ₂ = 3N ₂ + 6H ₂ O;

NO + NO ₂ + 2NH ₃ = 3N ₂ + 6H ₂ O.

Ammonia as a reagent is added to the gas stream leaving the manganese nitrate synthesis reactor and reacts with nitrogen oxides to form water and nitrogen with the release of reaction products into the atmosphere.

The efficiency of the process occurring in the proposed catalytic reactor, depending on the conditions, is shown in the diagrams of Figure 2 and Figure 3. In this process, both gaseous or liquefied ammonia and a solution of ammonia in water can be used. The catalytic blocks 7 operate in an optimal temperature range from 350 to 450 ° C, ensuring maximum conversion of ammonia and nitrogen oxides.

After the catalytic units 7, the purified gas again enters the heat exchanger-recuperator 2 and gives off heat to the incoming gases. The assembly of electric heaters 8 is switched off after entering the operating mode, and the temperature recorded by the thermocouple 5 through the control cabinet 3 is then automatically maintained at the required level by the assembly of electric heaters 9. Energy losses in the catalytic reactor are minimized by lowering the temperature of the passing gases, since the operating temperature It is supported only on the catalytic blocks 7, on which the reaction proceeds, and also due to the thermal insulation of the housing 10 of the heat exchanger-recuperator 2 of the catalytic about the reactor. The use of different types of foam-nickel catalytic blocks 7 along the gas flow allowed to reduce the hydraulic resistance and cost of the catalytic reactor while maintaining its high efficiency and resource.

Technical solutions, sequentially, one after another, used in the proposed catalytic reactor, give a synergistic effect, which ensures high efficiency of purification of gases, including air, from nitrogen oxides, increase the safety of operation and provide significant savings in energy consumption with low material consumption.

Figure 1 schematically represents a catalytic reactor device.

Figure 2 graphically represents the conversion process of nitrogen oxides depending on the quantitative ratio between ammonia and nitrogen oxides at a certain gas temperature.

Figure 3 graphically represents the conversion process of nitrogen oxides depending on the gas temperature at a certain quantitative ratio between ammonia and nitrogen oxides.

The present invention is confirmed and implemented on an industrial scale at OJSC Elecond, Sarapul. The results obtained during industrial tests of a catalytic reactor when performing a specific process for cleaning gas emissions are shown in the table.

Substance Inlet concentration, mg / m ³ The concentration at the exit, mg / m ³ The temperature of the catalytic blocks, ° C Nitrogen oxide 10 400 Nitrogen dioxide 5000 42 400 Ammonia 550 0,0 400

Claims (1)

A catalytic reactor having a control cabinet and a catalytic section, which contains replaceable catalytic blocks heated by replaceable electric heaters based on foam metal with a catalytic coating of metal oxides and is placed inside a spiral counter-flow heat exchanger-recuperator having a body with inlet and outlet openings and spiral channels made of semi-cylindrical corrugated shells of the same diameter, offset relative to each other by the width of the channel and connected to the end body casing, characterized in that the coil of the heat exchanger-recuperator with the catalytic section is horizontal, the upper part and the ends of the spiral counter-flow heat exchanger-recuperator are protected by a thermal insulation layer, there is a fuse in the catalytic section to de-energize the catalytic reactor when the temperature in the catalytic section reaches 660 ° C, the catalytic blocks have different thicknesses and cell sizes, the electric heaters are divided into two separately adjustable assemblies, which are pressed to The lithium blocks are carried out under their own weight, and a small amount of ammonia, controlled by a flow meter, is fed into the catalytic reactor.

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