RU2194570C2 - Reactor for catalytic cleaning of gases - Google Patents

Abstract

FIELD: manufacture of chemical equipment; cleaning gases from nitrogen oxides and decontamination of waste gases from organic admixtures. SUBSTANCE: reactor has bottom and cover with inlet and outlet pipe unions. Interior of reactor is divided by blind horizontal partition into two chambers; each chamber is provided with packing placed on grate with catalyst laid over it; electric heaters are mounted between them. Said partition is located between upper and lower chambers which are communicated by means of vertical tube-mixer located along axis of upper chamber. Fitted in upper portion of each chamber are horizontal mixers with electric heaters located inside them. Tube-mixer is provided in its center portion with reductant spraying manifold for selective reduction of nitric oxides; reductant is fed in form of liquid or vapor phase. EFFECT: reduced usage of metal; low cost of reactor; simplified construction; enhanced reliability. 4 cl, 2 dwg, 2 ex

Description

 The invention relates to chemical apparatus engineering and can be used for catalytic purification of exhaust gases from nitrogen oxides, as well as gases generated during the production of nitric acid, separation of sulfuric and nitric acids, etc. In addition, the reactor can be used for catalytic neutralization of gases from organic impurities.

 Known contact devices for the neutralization of exhaust gases from organic substances and nitrogen oxides in the so-called non-stationary mode [RF Patent 1829173, B 01 D 53/34, 1997; RF patent 2058186, 09/10/999, ed. testimonial. USSR 1011950, B 01 D 53/34, 04/15/1983, ed. St. CCCP 1535619, 1/15/90, pat. PL 154894, B 01 D 53/36, 02/28/1992; RF patent 2064331, B 01 J 8/04, 03.16.1994].

 A characteristic feature of such devices is the need to supply heat to the chemical reaction zone for carrying out the process in an autothermal mode. As a rule, the exhaust gases have low concentrations of components to be neutralized, their adiabatic heating is relatively low, and the neutralization process in a stationary mode is impossible. The additional heat introduced into the reaction zone increases the adiabatic heating to the value necessary to maintain the neutralization process in an autothermal mode.

 The closest is the contact apparatus described in [Pat. PL 154894, B 01 D 53/36, 02.28.1992]. The apparatus (Fig. 1) consists of a vertical cylindrical metal case with a flat bottom and a lid, on which electric heaters are mounted below. The casing of the apparatus is divided by a vertical partition into two chambers, in which two inert layers of equal volume are placed on the grate grids, on which catalyst layers of the same volume are poured on top. Below, under the grate, there are gas inlet and outlet fittings.

 During the operation of the contact apparatus, the catalyst is heated to the temperature of the onset of the chemical reaction, the gas to be purified is first supplied to one chamber, and removed from the apparatus through another chamber. After a certain time, called a half-cycle, the gas supply in the chambers is reversed, thereby implementing an unsteady mode of neutralization. In this case, the heat of the chemical reaction is constantly in the catalyst beds. At low concentrations of gases to be rendered harmless, when the intrinsic heat of the chemical reaction is insufficient to carry it out in autothermal mode, additional heat is introduced by switching on the electric heaters.

The design of the contact apparatus according to the prototype does not allow gas purification in a more economical mode due to the relatively large heat loss to the environment - especially in the high temperature zone (~ 400 ^o С above the catalyst bed), through the roof of the apparatus. In addition, due to the switching of the gas supply direction, one half of the cylindrical wall of the housing along the perimeter and the other half operate in a variable temperature regime, i.e. the cylinder is heated unevenly over the cross section, which causes alternating stresses and reduces its mechanical strength and stability. For complete mixing of the entire volume of the reaction mixture in the area where the electric heaters are installed, a mixing device is needed, which is not in the prototype. Its absence is compensated by an excess amount of catalyst, which is not economically feasible.

 The invention solves the problem of simplifying the design of the apparatus and increasing the reliability of its operation.

 The problem is solved by the following reactor design.

 The reactor (Fig. 1) consists of a vertical cylindrical body 1 with gas inlet / outlet fittings 2, a conical cover 3 and a flat bottom 4. The inner space is divided by a blank horizontal partition 5 into two chambers - upper I and lower II, interconnected by a central support with a mixer pipe 6 with internal turbulent partitions 7. In each chamber on the grate 8 there is a layer of an intermediate nozzle 9 (for example, a Raschig ring) and a catalyst layer 10 on top of the nozzle 10. On top of each chamber, above the catalyst layer p removable packages of electric heaters are placed in the form of electric heaters placed in cassettes, in each of which, from below and at the end, there are windows 12 for gas passage, the rest of the reactor cross section is blocked by a blank partition 13. In the upper chamber II, the cover 3 is shielded from heat losses by an additional partition 14. For selective catalytic purification of gases from nitrogen oxides in the middle of the mixer 6, a gas collector-sprayer 16 with holes is installed, connected by a pipe 15 to the reducing agent supply fitting 17 (ammonia, ammonia water). For the catalytic purification of gases from organic and other impurities, the installation of parts 15, 16 and 17 is not required.

 Moreover, the technical result achieved by using the entire combination of the essential features described above is to reduce the metal consumption and the cost of the reactor, reduce heat loss to the environment and, as a result, reduce the amount of heat entering the reaction zone.

 The operation of the reactor is as follows.

Before starting, the catalyst layers and the adjacent part of the inert nozzle are heated to 280-380 ^{° C.} by supplying atmospheric air alternately through nozzles 2 to chamber I, then exhaust gas is supplied at a temperature of 60-80 ^° C. (The gas flow during the first half cycle is shown figure 2 solid arrows). The cold cleaned gas passing through the inert packing layer 9 and the catalyst layer 10 in the chamber I is heated, as in a regenerative heat exchanger, to a temperature at which the selective reduction reaction proceeds at a sufficiently high speed at 280-380 ^o C. Simultaneously into a gas stream containing nitric oxide, a reducing agent is supplied through the spray manifold 16, which is mixed upstream in the mixer 6, then through the packages of heaters 11 and window 12, the reaction mixture is additionally mixed and enters chamber II catalyst 10, where nitrogen oxides are finally reduced, the heat of the reacted mixture is absorbed in an inert nozzle 9, after which the mixture leaves the apparatus through the side nozzle 2 into the atmosphere.

 After a certain period of time, the direction of movement of the gas stream being cleaned is reversed (the second half-cycle) and the reaction mixture goes the same way, but in the opposite direction (shown by dashed arrows in Fig. 1). After a predetermined period of time, the direction of supply of cold gas is again reversed, thereby realizing continuous operation of the reactor in the so-called non-stationary mode. The amount of heat introduced into the reaction mixture is controlled by the heaters 11 depending on the concentration of impurities in the gas being purified.

 The present invention has similar features with the prototype.

 The contact apparatus is designed for the selective purification of gases from nitrogen oxides, from organic impurities, etc.

 The contact apparatus includes a vertical cylindrical body, a bottom and a cover.

 The contact apparatus has two grates, on which layers of inert packing and catalyst layers are placed on them.

 The contact apparatus has fittings for the inlet of the purified gas and the outlet of the purified gas.

 In the area between the catalyst layers installed electric heaters.

 The casing of the device is divided by a partition into two chambers.

Distinctive features are as follows:
the case of the device is divided into two chambers by a horizontal partition;
cameras are located in the housing one above the other;
chambers are connected to each other by a vertical pipe-mixer, placed along the axis of the upper chamber;
removable electric heaters are placed in horizontal mixers with holes for gas to pass through them;
For the process of selective reduction of nitrogen oxides in the central part of the mixer pipe, a collector-sprayer is installed, to which the reducing agent is supplied in the form of a liquid or vapor phase.

 Example 1

 Figure 1 shows the design of a reactor designed for the selective catalytic purification of gases from nitrogen oxides.

Gas productivity 5-10 thousand m ³ / h.

The amount of catalyst AVK-10 -6 m ³ (5.4 t).

The amount of inert nozzle -14 m ³ (9.8 t).

The concentration of nitrogen oxides 2-3 g / m ³ ,
The temperature of nitrous gases 20-30 ^o With
Gas temperature in the device:
- maximum, in the reaction zone, 450 ^o C,
- working, in the catalyst bed, 320-350 ^o C,
- at the inlet-outlet of the gas into the apparatus variable for a half-cycle of 20-200 ^o C,
- the beginning of the chemical reaction 180-200 ^o C.

 Estimated hydraulic resistance of 400 mm of water. Art.

 The total rated power of the electric heater is 56 kW.

 To carry out the process under given conditions - gas volume, impurity concentration, amount of catalyst and inert packing, hydraulic resistance and other requirements, the diameter of the reactor was 2.8 m with a total height of 7.4 m.

The calculated heat loss from the apparatus to the environment is up to 10,500 kcal / h (at ambient air with a temperature of 40 ^o C), which is ~ 21% of the installed capacity of electric heaters.

 Example 2 (prototype). Same as in example 1.

 The calculated heat loss to the environment is 32% more than in the apparatus in example 1, and is ~ 13860 kcal / h.

 Thus, the proposed reactor design is more compact, which reduces heat loss to the environment. The metal walls of the body in each section along the perimeter experience the same temperature stresses.

Claims (4)

 1. A reactor for the catalytic purification of gases from nitrogen oxides, neutralization of exhaust gases from organic and other impurities, containing a bottom and a cover with inlet and outlet fittings, divided by a partition into two chambers, in each of which layers of an inert nozzle with a catalyst are placed on the grate grids between them, electric heaters are installed, characterized in that the partition dividing the internal volume of the reactor is made horizontal blind and is located between the upper and lower chambers, which are connected enes between a riser-mixer situated upper chamber axis.  2. The reactor according to claim 1, characterized in that horizontal mixers are installed in the upper part of each chamber.  3. The reactor according to claim 1 or 2, characterized in that the electric heaters are located in horizontal mixers.  4. The reactor according to any one of paragraphs. 1-3, characterized in that for the process of selective reduction of nitrogen oxides in the Central part of the mixer pipe is additionally installed collector-spray reducing agent supplied in the form of a liquid or vapor phase.

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