FI69046C - PROCEDURE FOR OIL ANALYSIS OF CATALYTIC OXIDERING AV SWINE - Google Patents

Description

69046

This invention relates to a process for the catalytic oxidation of sulfur dioxide in several stages by passing hot sulfur dioxide-containing gases sequentially through a plurality of solid catalyst beds and cooling the gases between the stages. The present invention further relates to an apparatus for carrying out the above process, comprising at least one inlet chamber having one or more successive horizontal gratings in the flow direction of sulfur dioxide-containing gases on which there is a particulate fixed catalyst bed and a gas exchange device between each catalyst bed. between the catalyst mattresses. Cooling of the gas between the catalyst beds can take place by external or internal heat exchangers of the reactor, by blowing cold raw gas or air.

Sulfur dioxide oxidation reactors commonly used in the sulfuric acid industry are large, partially masonry steel sheet cylinders with a plurality of overlapping and, in the gas flow direction, successive solid catalyst beds, usually 3-5 mounted on a horizontal grate, usually consisting of cylindrical holes, usually cylindrical holes projections. Alkali-vanadium pyrosulfate is generally used as the active ingredient in these catalyst bodies. Because the reaction of sulfur dioxide with oxygen is exothermic and the reactor is adiabatic, gas must be cooled between the mattresses, with a heat exchanger or cold gas blast arranged after each mattress to intercool the gases heated in the contact reaction before passing them to the next mattress. Sulfur dioxide-containing gases are passed practically from top to bottom through the catalyst mattresses. A major disadvantage of these previously known methods and devices is that the contaminants carried by the gas, such as dust, iron oxides and sulfates, clog the catalyst mats over time and the first catalyst mat is exposed to the greatest danger.

Another disadvantage is that when external heat exchangers are used at the inlet and outlet openings of the catalyst chamber, a significant change in flow rate occurs, which in turn causes a pressure difference in the gas space near the catalyst bed, especially if the gas space is aerodynamically unfavorably shaped and close to the catalyst bed. The pressure difference due to one orifice can be 150-200 Pa. With modern catalysts, the first layer pressure drop is 500-1000 Pa when new. Thus, channelization can occur in the catalyst bed, especially in the vicinity of such openings, and thus local overheating of the catalyst as the gas flows unevenly through the catalyst bed, especially when treating concentrated sulfur dioxide-containing gases. As a result, catalyst utilization is inefficient in places, and in addition, the activity of vanadium catalysts drops over time at high temperatures.

It is known from DE 138 695 to pass sulfur dioxide-containing gases from the bottom upwards through several successive platinum-based catalyst layers. However, there are no means for separating dust in this solution, as is the case with the device according to U.S. Pat. No. 3,997,655, although the catalyst mattresses in the latter solution are arranged in separate chambers with intercoolers.

Fluidized bed reactors have also been tried for the industrial oxidation of sulfur dioxide. Their disadvantage is at least the rapid wear of the catalyst.

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It is an object of the present invention to obviate or reduce the above-mentioned drawbacks and to provide a method and apparatus for the catalytic oxidation of sulfur dioxide in which clogging of the catalyst bed due to dust and local overheating due to channeling are avoided or substantially reduced.

The main features of the invention appear from the appended claims.

According to the present invention, the oxidizable sulfur dioxide-containing gases are passed, at least in a first step, under a grate supporting the catalyst bed and removed above the catalyst bed so that the gases have to flow through the catalyst bed from the bottom upwards. From the gases passed under the solid catalyst bed, the separated dust is periodically removed from the space under the catalyst bed.

The free space above the catalyst bed is preferably 1.3 to 6 times the volume of the catalyst bed and the gas outlet is preferably at least at the distance of the thickness of the catalyst bed from the surface of the catalyst bed.

Thus, the channeling of the catalyst bed as well as its local overheating is significantly reduced.

Also, solid and potential liquid contaminants accompanying the gas do not automatically enter the catalyst bed, as has been the case to date, but accumulate in the chamber bottom below the catalyst bed (from which they can be removed) because the gas flow slows significantly as it enters the chamber. This allows the screening and replacement interval of the catalyst to be significantly extended.

4,69046

By fitting a flow diffuser in front of the gas inlet below the catalyst bed in its vicinity, the channeling of the catalyst bed can be further reduced. The structure of the diffuser depends on the curved parts of the inlet pipe, the shape of the nozzle between the inlet pipe and the reactor chamber and the ratio of the inlet pipe to the inner diameters of the reactor chamber. The optimal structure in question can be retrieved, for example, by means of model experiments. The flow diffuser reduces the otherwise uneven pressure on the lower surface of the catalyst bed due to the ejection effect of the inlet and promotes the separation and settling of non-gaseous contaminants at the bottom of the chamber.

Modern large catalyst particles (pellets) in the upstream catalyst beds of sulfur dioxide contact reactors do not circulate with normal flow and the arrangement described above, although the gas flows abnormally from the bottom up through the catalyst bed. However, this can still be ensured by fitting a denser metal mesh or heavy and / or interlocking ceramic pieces on top of the catalyst bed.

Any dust that may have accumulated on the catalyst bed can be removed by passing reaction gases or air momentarily in the opposite direction through the catalyst bed, e.g. during downtime. The reverse gas flow removes any dust that may have adhered to the catalyst droplets and falls to the bottom of the chamber.

Dust can be easily removed from the bottom of the chamber through an opening hatch fitted to its wall below the grate.

It is clear that the solid impurities entrained in the gas are much easier to remove from the bottom of the catalyst bed at the bottom of the reactor chamber than from the catalyst itself, as in previously known methods. In the solution according to the invention, the dust accumulated on the bottom of the chamber can be removed either mechanically or by suction even when the process is running or at least during a short downtime.

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An additional advantage of the process according to the invention is that when placing one of the conventional chambers of the subsequent reaction steps under the first step according to the invention, the bottom between these steps does not need to be thermally insulated by masonry, since the gas inlet temperatures to the catalyst layers are approximately the same.

The invention will be described in more detail below with reference to the accompanying drawings, in which Figure 1 shows a cross-sectional elevational view of a conventional contact reactor and Figure 2 shows a cross-sectional elevational view of a preferred embodiment of the invention.

The contact reactor shown per se in Fig. 1 has three overlapping chambers 1, 1 'and 1 "separated from each other by intermediate bases 11. Sulfur dioxide-containing gases are introduced into the upper or first chamber 1 from the inlet 2 and led in the chamber 1, above the horizontal grate 4. through a fixed catalyst bed 5 from top to bottom into the free space between the grate 4 and the base 11 and further through the outlet 3 to the intercooler 6 and from there to the next chamber 1 'below the chamber 1 through its inlet 2'. Finally, the gases are removed from the lowest chamber 1 " through the 3 "outlet at the bottom.

In this previously known solution, all the dust and liquid impurities carried by the sulfur dioxide-containing gases end up in the catalyst bed, leaving most of them in the mattress, causing blockages. In addition, the location of the outlets 3 and 3 'causes a significant pressure difference in the space below the grate in its vicinity due to the relatively small pressure drop of the upstream mattresses. Likewise, the location of the inlet 2 'and also the inlet 2, if the first stage of the 6 69046 is not at the top, causes a significant pressure difference in the space above the mattress in its vicinity. As a result, the catalyst mattress is easily channeled in the vicinity of the openings, which can cause the catalyst mattress to overheat locally and its use is not efficient enough.

The solution according to the invention shown in Fig. 2 differs from the solution shown in Fig. 1, known per se, in that sulfur dioxide-containing gases are introduced into at least the first stage chamber 1 below the grate 4, the gas inlet 2 being below the grate 4 and the outlet 3 above the catalyst mattress 5. The gases can then be led through the intercooler 6 to the next stage, i.e. chamber 1 ', where the inlet 2' can be arranged above the catalyst bed 5 in a conventional manner, since at this stage the gases are not so dusty as to cause inconvenience in the catalyst bed 5.

Most of the dust contained in the sulfur dioxide-containing gases and the liquid contaminants of the start-up are already separated in the space between the grate 4 and the intermediate base 11 and fall to the intermediate base 11, and thus do not enter the catalyst bed 5, as in Figure 1.

An opening is formed in the side wall of the chamber 1 below the grate 4 with an openable door 10 through which dust and impurities dropped on the bottom 11 can be removed from the chamber 1.

The ejector effect of the outlet 3 is also easy to eliminate in the solution shown in Fig. 2, since the free space 9 above the catalyst mattress 5 of the chamber 1 can easily be made so large, preferably 1.3 to 6 times the volume of the catalyst mat 5 and the outlet 3 so far that no significant ejector effect and no catalyst-bed channelization. In addition, a flow is arranged in the chamber 1 in front of its inlet opening 2 at a distance therefrom.

It 7 69046 its diffuser 7, which distributes the gas evenly over the entire surface area of the catalyst bed 5, reducing the ejector effect below and thus further channeling.

In addition, ceramic pieces or a metal mesh 8 are arranged on the surface of the catalyst mat 5, which prevents the catalyst parts from floating if the flow rate through the catalyst mat becomes too high.

In both the solutions according to Figures 1 and 2, a layer of a few 10 mm thick ceramic bodies is normally used between the catalyst bed and the grate.

Claims (8)

A process for catalytic oxidation of sulfur dioxide in several stages by passing hot sulfur dioxide-containing gases in succession through several solid catalyst beds and cooling the gases between the steps, the hot sulfur dioxide-containing gases being conducted in the at least the first step below the solid catalyst bed and removed above it. , characterized in that dust separated from the sulfur dioxide-containing gases discharged under the solid catalyst bed is removed from a space under the solid catalyst bed. Process according to Claim 1, characterized in that, for the purification of the solid catalyst bed, there is thus conducted intermittently from below uptake of sulfur dioxide containing gases or other gas such as air. Process according to Claim 1 or 2, characterized in that the sulfur dioxide-containing gases carried under the solid catalyst bed are caused to impinge on a control plate or plates for dispersion and even distribution of the gas stream over the catalyst bed. Apparatus for oxidizing sulfur dioxide comprising a chamber (1, 1 ') provided with at least one inlet (2, 2') and outlet (3, 3 ') for gas, which chamber comprises one or more of the sulfur dioxide containing gases. flow direction followed by substantially horizontal grids (4) with a fixed catalyst bed (5) consisting of particles thereon, there being between each catalyst bed (5) a cooling device (6) and in which the gas inlet (2) is located The first catalyst bed (5) is characterized below the dining table, characterized in that in the chamber (1) there is an openable hatch (10) below the grate (4) for removal of dust collected from the gases from the bottom (11) of the chamber (1). ). Device according to claim 4, characterized by a flow disperser (7) arranged in front of the gas inlet (2). Il