RU2367594C1 - Method for preparation of sulphur trioxide and device thereof - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: initial reaction gas mixture containing sulphur dioxide and oxygen passes through at least two arranged in-line catalyst layer with alternately changing in cyclic mode the direction of the reaction gas mixture inlet and outlet to/from every layer. The feed of reaction gas mixture to one of the catalyst layers is increased up to maximal value with following feed decrease up to complete cease in the moment of the gas movement direction change in the layer; the feed of reaction gas mixture is simultaneously decreased in the same cycle up to complete cease, then direction of gas movement is changed and cycle is repeated. The total flow of reaction gas mixture fed and withdrawn to/from corresponding catalyst layers is maintained constant due to time displacement of the moment of the gas movement direction change in every layer. Method is implemented in contact apparatus containing body 1 with connections 12 and 13 for reaction gas mixture inlet and outlet, central column 5 coaxially positioned in the body and connected with connections as well as at least two gridworks 3 with catalyst located between body and column throughout the height. The vertical power shaft 9 is coaxially located in the cavity of the central column 5 and provided with control valves 6 fixed on the shaft The amount of the control valves 6 is equal to amount of the gridworks with catalyst separated with separating partition-wall 11. Every valve is designed as hollow cylinder with windows 10 connected with connections for reaction gas mixture inlet and outlet and provided with inclined inner partition-wall 8 separating the valve cavity In two neighbour valves the windows and inclined partition-walls are turned about on the shaft relative to each other at angle 90°.

EFFECT: quality enhancing of the obtained sulphur trioxide.

2 cl, 3 dwg

Description

The invention relates to a method and apparatus for conducting exothermic oxidative reactions in the chemical industry, in particular the oxidation of sulfur dioxide to trioxide in sulfuric acid production.

From SU No. 994400, C01B 17/76, 1975, a method is known comprising oxidizing sulfur dioxide by cyclic alternately changing the places of entry and exit of the reaction mixture from the catalyst bed. The method allows the process of non-stationary oxidation of sulfur dioxide to trioxide under conditions when the contact layer is spaced at least two sublayers with intermediate cooling of the reaction gas and averaging the temperature of the gases for each layer.

The disadvantage of this method is that the switching direction of the gas flow is carried out by valves through the "fully open" position, i.e. at the time of switching, a volley release of unreacted sulfur dioxide into the atmosphere occurs.

The closest analogue to the developed method is a method for the oxidation of sulfur dioxide into trioxide, comprising passing the initial reaction gas mixture through at least two successive catalyst beds with alternating changes in the direction of supply and removal of the reaction gas mixture to each layer (SU, No. 1535619 A1 B01J 8/04, 1988).

During the operation of such a system, a decrease in the degree of conversion of sulfur dioxide in a gas is observed as the moment of switching the direction of gas movement in the layer approaches due to a decrease in the thickness of the heated catalyst participating in the oxidation reaction.

This method is carried out in the device, which is the closest analogue to the developed contact apparatus. The device comprises a housing with nozzles for supplying and discharging the reaction gas mixture, a central column coaxially located in the housing and connected to the nozzles, as well as at least two grates with a catalyst located between the housing and the column in height.

The disadvantage of this device is the presence of an external switching device in relation to the contact apparatus, therefore, at the moment of switching the direction of gas movement in the contact apparatus there are volley emissions of unreacted sulfur dioxide into the atmosphere, bypassing the contact apparatus, which negatively affects the quality of the finished product.

The objective of the invention is to improve the quality of the finished product by obtaining a stably high degree of oxidation of sulfur dioxide into trioxide throughout the entire cycle of the apparatus and stopping the discharge of unreacted sulfur dioxide with gases at the moment of switching the direction of movement along the contact layer.

The task in terms of the method is achieved by the method for producing sulfur trioxide by catalytic oxidation of sulfur dioxide, comprising passing the initial reaction gas mixture through at least two successive catalyst beds with an alternate change in the direction of supply and removal of the reaction gas mixture to each reaction layer the gas mixture is fed to the catalyst layers in a cyclic mode, while the feed of the reaction gas mixture is increased to a maximum on one of the catalyst layers values with a subsequent decrease in its supply until it stops at the moment of changing the direction of gas movement in the layer, and on the other catalyst layer simultaneously in the same cycle, reduce the flow of the reaction gas mixture until it stops completely, then change the direction of gas movement and repeat the cycle, and the total flow the reaction gas mixture supplied and discharged from the respective catalyst layers is kept constant due to the time displacement of the moment the direction of movement of the gases in each layer changes.

When two parallel contact layers are working on each of them, a cyclic change in gas loads is organized in the following order. When approaching the moment of switching the direction of gas motion along the layer, the gas load on this layer decreases and becomes equal to zero at the moment of switching the direction of gas motion across the layer. At this moment, the entire gas load of the apparatus is assumed by the parallel working layer. Working according to a time-shifted program of gas loads of two parallel working layers, they achieve a constant gas load in the combined inlet and outlet ducts, excluding volley gas emissions past the contact layers at the moment of switching the direction of gas movement in each layer.

The task in part of the device is achieved by the fact that in the contact apparatus comprising a housing with nozzles for supplying and discharging the reaction gas mixture, a central column coaxially located in the housing and connected to the nozzles, and at least at least one height between the housing and the column two grates with a catalyst, according to the invention, the central column is equipped with a vertical drive shaft coaxially located in its cavity and bypass valves fixed to it according to the number of grates brushes with a catalyst, with each valve made in the form of a hollow cylinder with windows communicating with the nozzles for supplying and discharging the gas mixture and separating the valve cavity with an inclined internal partition, and in two adjacent valves the windows and inclined partitions are deployed on the shaft in a plane of rotation each other at 90 °.

Figure 1 schematically shows a contact apparatus (in section) with two reaction chambers with a catalyst, figure 2 is a section along aa in figure 1 and figure 3 is a section along bb in figure 1.

The contact apparatus comprises a housing 1 with two reaction chambers 2 bounded by grate grids 3, in which two contact layers of catalyst 4 are placed. The grids are supported on one side of the housing 1, and on the other, on the central column 5. In the latter, two rotating bypass valves 6 are mounted in the form of hollow cylinders with windows 7 for gas passage cut through on their diametrically opposite sides and an inclined internal partition 8. The valves are rigidly attached to the vertical drive shaft 9 and are deployed with their windows and 7 and baffles 8 90 ° from each other. In the central column 5 above and below each contact layer, four inlet and outlet windows 10 are made.

The internal space of the contact apparatus is divided into two parts by a gas-tight insulating partition 11.

In the casing there are mounted pipes 12 connected to the valve cavity 6 for introducing gas and nozzles 13 for removing gas from each layer. The nozzles of the gas inlet 12 to both catalyst layers are combined by the collector 14, and the nozzles of the output 13 by the collector 15 respectively.

Mounted on the drive shaft 9, the inner cylindrical parts of the valves 6 during continuous rotation of the drive shaft 9 also continuously rotate.

The gas ports 7 on the cylinder of the valve 6 at certain times coincide with the cavity of the nozzles 12, and at this moment the valve has minimal resistance, which means that it passes through itself the entire flow of gas entering the contact device. As the windows are mutually displaced during rotation of the movable cylinder of the valve, the gas inlet and outlet cross-section through the valve 6 decreases, and, accordingly, the resistance of the valve 6 increases, which leads to a decrease in the gas flow moving through the valve 6 and the corresponding contact layer.

When the bypass valves rotate 90 °, its windows and the windows on the central column 5 do not completely coincide, and the movement of gases through the corresponding valve and layer is completely stopped.

Since the bypass valves attached to a single rotating shaft are rotated 90 ° relative to each other, at the time of passage of any of the valves to the “fully closed” position, the other valve is in the “fully open” position and the entire gas flow rushes through this valve and associated contact layer. The peculiarity of the internal inclined partition is such that, depending on the position of the valve, the gas flow exiting the valve can be directed up or down. Accordingly, the gas flow entering the valve after passing through the layer can be directed from below or from above, thereby providing alternating movement of gases in each layer, then from top to bottom or from bottom to top, and at the moment of switching the direction of gas movement through the layer, gas through this layer generally does not pass.

The presence of an insulating partition between the layers eliminates the mutual flow of gases from one layer to another inside the contact apparatus.

The method according to the invention is as follows.

Example 1

The initial reaction gas mixture, consisting of 4% sulfur dioxide, 10% oxygen and 86% nitrogen, is fed into the contact apparatus through a collector 14 with a temperature of 200 ° C, and then the mixture is diluted through nozzles 12 to each of two parallel catalyst beds . The full cycle of valve switching 6 was 38 min. A stable degree of conversion of sulfur dioxide to trioxide achieved in the contact apparatus was 98%. The maximum temperature in the area of the temperature front is 605 ° C.

The height of the catalyst layer was 1.7 m, and the height of the layer of the upper and lower bedding of lump quartz was 0.5 m. The maximum gas velocity in each layer was 0.4 m / s, while the nature of the change in gas load in each layer was close to sinusoidal with overlapping gas movement at the moment of switching the direction of gas movement. The total degree of load stability of the combined stream was 98%. The temperature of the gases at the outlet of the apparatus exceeded the temperature of the gases at the entrance to it by 110 ° C.

Processing gas in the traditional way (prototype), it is not possible to raise the degree of conversion of sulfur dioxide above 94%. In the developed method, the degree of conversion is increased to 98%, the emissions of residual sulfur dioxide are reduced by 3 times and amount to only 0.08% by volume of residual sulfur dioxide.

Example 2

The initial reaction gas mixture, consisting of 1% sulfur dioxide, 8% oxygen, 12% carbon dioxide and 79% nitrogen by volume, is supplied to the contact apparatus through a manifold 14 with a temperature of 330 ° C, and then the mixture is diluted through nozzles 12 for each of two parallel catalyst beds. The full cycle of valve switching 6 was 22 min. A stable degree of conversion of sulfur dioxide to trioxide, achieved in the contact apparatus, was 97.5%. The maximum temperature in the area of the temperature front is 495 ° С.

The height of the catalyst layer was 1.5 m, and the height of the layer of the upper and lower bedding of lump quartz was 0.3 m. The maximum velocity of the gases in each layer was 0.35 m / s. The nature of the change in gas load in each layer is close to “sawtooth” with a peak in the middle of the period and a decline before and after switching by the overlap of the gas movement at the moment of switching the direction of gas movement. Fluctuations in the total gas flow over the load was not more than 1.5%. The temperature of the gases at the outlet of the apparatus exceeded the temperature of the gases at the entrance to it by 25 ° C.

Using a well-known non-stationary contact apparatus on gases with a concentration of ~ 1% sulfur dioxide, it is possible to obtain a degree of conversion not higher than 93%. In the invention, the degree of conversion is 97.5%, that is, it is possible to reduce the residual dioxide content in gases by 2.8 times, and sulfur dioxide in the exhaust gases is only 0.025-0.03 vol.%.

Example 3

The initial reaction gas mixture, consisting of 2.5% sulfur dioxide, 7.5% oxygen, 6% carbon dioxide, 5% water vapor and 79% nitrogen by volume, is supplied to the contact apparatus through a manifold 14 with a temperature of 280 ° C, and the mixture is then diluted through nozzles 12 to each of two parallel catalyst beds. The full cycle of valve switching 6 was 30 minutes The stable degree of conversion of sulfur dioxide to trioxide achieved in the contact apparatus was 98.5%. The maximum temperature in the area of the temperature front is 580 ° С.

The height of the catalyst layer was 1.7 m, and the height of the layer of the upper and lower bedding of lump quartz of fraction 50 was 0.5 m each. The maximum gas velocity along the section of the layer was 0.38 m / s. The nature of the change in gas load in each layer is close to sinusoidal with a shift of the load program between the layers by a quarter of the period. Oscillations of the combined gas load from the nominal indicator did not exceed 2%. The temperature of the gases at the outlet of the apparatus exceeded the temperature of the gases at the inlet by 70 ° C.

The best known non-stationary apparatus systems working with 2% gas were able to achieve a conversion rate of 96%. When using the invention, it is possible to raise this indicator to 98.5%, thereby reducing the residual sulfur dioxide content in the gas to 0.03% or to improve the situation with emissions by 2.6 times.

The location of the partition 8 in the upper valve 6 creates a movement of incoming gases of the upper layer up the column, then the gases through the windows 10 from the column 5 go into the space above the catalyst layer, pass through the latter, where sulfur dioxide is oxidized to sulfur trioxide. Gases enter the space under the layer, then through the windows 7 enter the column, rise into the valve 6 and through the pipe 13 are removed from the apparatus. In the collector, the gases coming from the upper catalyst layer are combined with the gases of the parallel contact lower layer and through the collector 15 are removed from the system for absorption.

In a similar way, the gas flow moves in the lower contact layer. Since the location of the baffle in the lower valve is the inverse of the upper valve, the incoming gas flow is first directed down the column, then through the windows in it, goes into the space under the catalyst layer. Then the gas passes from bottom to top through the layer where sulfur dioxide is oxidized to trioxide, enters the column windows in the space above the layer, lowers down into the valve and from there through the nozzle 13 it is removed from the apparatus for combining with the gases going to the absorption through the collector 15. Thus , gases in the upper contact layer at a particular moment in time move along the layer from top to bottom, and in the bottom - from bottom to top. The direction of gas movement in the layers is reversed after half the period compared with the direction shown in figure 1.

The amount of gas entering at any moment on any of the parallel working layers depends on the resistance of the corresponding valve at each moment, i.e. from the relative position of the windows of the movable and fixed cylinders that make up the main parts of the valve. At the moments when the cylinder windows are rotated 90 ° relative to each other, one of the valves is closed for the passage of gases through it and the corresponding layer and vice versa, when the windows coincide, the gases experience minimal resistance from the valve side, i.e. in this case, all the gas passes through the corresponding layer. The position of the tilted internal partition inside the valve determines the movement of the incoming gas flow up and down the central column.

Thus, in the claimed method and device for its implementation, the following positive effects are achieved:

- volley emissions of sulfur dioxide are excluded at the moment of switching the direction of gas movement through the layer, since at this moment, as a result of design features, the valves pass through the "absolutely locked" position,

- there is no decrease in the degree of contacting of sulfur dioxide at the moments of approaching switching the direction of gas movement through the layer, since the valves at this moment sharply reduce the gas flow passing through the valve.

Claims (2)

1. A method of producing sulfur trioxide by catalytic oxidation of sulfur dioxide, comprising passing the initial reaction gas mixture through at least two successive catalyst beds with alternately changing the direction of supply and removal of the reaction gas mixture to each layer, characterized in that the reaction gas mixture the catalyst layers are fed in a cyclic mode, while on one of the catalyst layers the supply of the reaction gas mixture is increased to a maximum value and then reduced we feed it until it stops completely at the moment of changing the direction of gas movement in the layer, and simultaneously on the other catalyst layer, in the same cycle, reduce the flow of the reaction gas mixture until it stops completely, then change the direction of gas movement and repeat the cycle, and the total flow of the reaction gas mixture , supplied and discharged from the respective catalyst layers, is kept constant due to the time displacement of the moment of change in the direction of gas movement in each layer. 2. A contact apparatus for implementing the method, comprising a housing with nozzles for supplying and discharging the reaction gas mixture, a central column coaxially located in the housing and connected to the nozzles, and at least two reaction chambers with a catalyst located between the housing and the column in height bounded by grate grids, characterized in that the central column is provided with a drive vertical shaft coaxially located in its cavity and bypass valves fixed to it by the number of grate gates gratings with a catalyst, which are separated by an insulating partition, each valve being made in the form of a hollow cylinder with windows communicating with the nozzles for supplying and discharging the gas mixture and separating the valve cavity with an inclined internal partition, moreover, in two adjacent valves there are windows and inclined partitions deployed on the shaft in a plane of rotation relative to each other by 90 °.

Images