DE2300695B2 - Recombiner for the catalytic combustion of radiolysis gases contained in steam-gas mixtures - Google Patents

Description

The exhaust gases produced during the operation of nuclear power plants consist for the most part (approx. 90%) of the Radiolysis gases oxygen and hydrogen.

Since the entire amount of exhaust gas has to be processed before it is released into the atmosphere, and the size of the treatment plants depends on the amount of exhaust gas, is sought before actual treatment to remove or delay radioactive substances to the amount of exhaust gas to decrease. From this Gn.'ide the exhaust gases are passed through a recombiner in which the Radiolysis gases are subjected to catalytic combustion and thus converted into water.

Such recombiners consist of one Container with a side or central gas supply and a mostly centrally arranged discharge line. Within the container is a grid-like intermediate floor on which the catalyst in the form Small balls or cylinders with a diameter of approx. 3 - 8 mm are piled up during the operation of a nuclear power plant Accruing exhaust gases are generally with the help of steam jet pumps from the Turbine condenser withdrawn. The exhaust gases then pass through dehydrators together with the motive steam and preheater in the recombiner. The steam-gas mixture flowing in through the inlet pipe arrives here first in a so-called inlet apron, which the mixture flow in the upper free space of the container diverts. From there, the mixture flows downwards, deflected by the container lid, and hits the ground in the process on the catalyst. In operation it has now been found that the so in the upper Adjust the flow forming the container part to unfavorable conditions. The one from the side on the The flow that hits the catalyst sets it in motion at certain flow velocities, moves the catalyst bulk material, and creates accumulations and valley formations, which in turn The reason for the resulting different flow resistance results in an uneven loading lead of the catalyst. Furthermore, the flow-related movement of the bulk catalyst material leads to its abrasion and thus reduces the amount of catalyst present and increases the pressure loss dusty deposits. Destruction of the catalyst particles is also caused by the entrainment these corpuscles through the inflowing vapor-gas mixture and the impact on the container lid and caused the container wall. All of these phenomena have an adverse effect on the performance of the recombiner.

The object of the invention is to dit; Flow conditions in recombiners of the initially described

ic nen way to improve so that the disadvantages mentioned above are avoided.

This object is achieved by a arranged above the bulk catalyst material and up to about 70% of its height filled with catalyst surface, honeycomb-like flow guide grille, as well as an above the insertion pocket attached perforated baffle, which is oriented such that the inflowing Steam-gas mixture in a partial flow flowing above and below the guide plate is divided.

The invention improves the recombiner performance due to greater possible throughputs that can be achieved by a more uniform application of the catalyst bulk material are made possible. At the same time results in

Gentle treatment of the bulk catalyst during operation, an extended service life of the Catalyst. For example, practical Sirömungsversuche in a test facility have shown that recombiners with the internals according to the invention up to 60%

jo allow higher flow velocities of the bulk material, as shown later on the basis of a diagram is explained in more detail. Therefore, the cross section of the recombiner can be significantly reduced, so that an inexpensive slim design results

j5 An embodiment of the invention is in the Drawing shown and explained below It shows

F i g. 1 shows a longitudinal section of a recombiner according to the invention,

F i g. 2 shows a cross section of the recombiner according to FIG. 1 along the line AA,
F i g. 3 details of the invention,
F i g. 4 is a diagram showing the effect of the invention.

In the container 1 with the lateral inlet connection 2 and the inlet pocket 3 adjoining this inlet connection, the catalyst 5 is piled up on a support grid 4 in the form of small spheres or cylinders. Above the inlet pocket 3 there is a perforated guide plate 6. This guide plate 6 is attached above the inlet pocket 3 in such a way that the incoming steam-gas mixture flow 9 is divided into two partial flows 9a, 9b , so that one partial flow 9a is above and the other ( 9b) flows past below the guide plate 6. The openings 10 in the baffle plate 6 have the task 9b to below this sheet extending part-stream, in turn, be divided (partial flows 96'und 9b "), wherein a part of the steam-gas mixture flows through the apertures and thus a

bo cross flow 9b ″ to the partial flow 9a running above the guide plate. This cross flow 9b ″ causes turbulence and a delay in the upper partial flow. The two partial flows combine in the free space 7 above the bulk catalyst material and, as has been confirmed in model tests, are significantly more favorable in their overall effect than is the case with free formation of the flow.
To further improve the flow ratio

A honeycomb-like flow guide grille 8 is attached above the catalytic converter 5. It has proven to be expedient to pour the catalyst so high that the grid positions are filled with bulk catalyst material up to a certain height, which depends on the type and size of the catalyst bodies. This grid, in combination with the baffle 6 described above, has the consequence that the mixture ^{flow hits the catalytic converter 5 almost uniformly and perpendicularly, and thus a movement of the catalytic converter 1} bodies and the associated disadvantages are largely avoided. After flowing through the catalyst, the gas-vapor mixture leaves the container 1 through the central lower nozzle 11. ι =>

The diagram according to FIG. 4 shows the behavior of the catalyst bodies in a curve form, in which on the abscissa 12 the strength of the movement of the catalyst body is shown, while on the Ordinate 13 is the steam speed in m / sec in the> o Recombiner, based on the free one The cross section is indicated. The catalyst bodies have the two mentioned above different shapes of balls cJer cylinders (tablet shape).

The increasing strength of the movement from the rest position (movement 0) is shown on the abscissa represented by three characteristic values:

1. At the value represented by the vertical line 15, the catalyst bodies begin a shaking movement.

2. With the value represented by the vertical 16, the shaking movement is in a rolling movement passed over.

3. With the value J indicated by the vertical 17 ^:> the catalyst bodies lift off, ie they are whirled up by the gas flow

The curve 20 shows the movements in the form of tablets Flow velocities assigned to the catalyst body if there are none according to the invention in the recombiner There are internals. They are a maximum of about 1.5 m / sec

The dashed curve 21 shows the flow velocities under the same conditions for spherical catalyst bodies, which because of their more aerodynamically favorable shape to the flowing through Medium offer less attack surface. Here, too, undesirable movements can be seen at 1.5 m / sec.

With the internals according to the invention, however, there is a significant increase in the permissible Flow velocity, namely lie in the area 24 shown in dashed lines between üen Boundary lines 25 and 26 show the flow rates for tablet-shaped catalyst bodies in a recombiner with internals. It can be clearly seen that the area 24 forms the curve 21 for the more flow-favorable enclosing spherical catalyst body approximately in the middle. The boundary lines 25 and 26 result from different angles of incidence of the guide plate 6.

An even further overlying area 28 between the curves 29 and 29 shown in dashed lines 30 includes the flow velocities applicable to internals for movements of spherical shapes Catalyst body. The area 28 lies well above the curve 21, which shows the flow velocities for represents the case that no internals are present.

In the diagram of FIG. 4, the straight line 32 in a solid line shows the value that results in a first nuclear power plant, which is practically executed and a recombiner with tablet-shaped Catalyst bodies and dimensions according to the following table: The value of the flow rate at 1.46 is well above curve 20, as can be seen

The straight line 33 shown in dashed lines applies to another practically implemented nuclear power plant B with spherical catalyst bodies and the speed value 1.66. This value is also higher than could be used according to curve 21 for recombiners without internals.

Dim.

Gas-steam throughput
Inside diameter
Free cross-section
Gas vapor velocity

rn ^J / s 2.75 3.14 mm 1548 1552 m ² 1.89 1.89 m / s 1.46 1.66

For this purpose 2 sheets of drawings

Claims (1)

Claim: Recombiner for the catalytic combustion of radiolysis exhaust gases contained in steam-gas mixtures Oxygen and hydrogen with the formation of water, this recombiner from one Containers with the side of the bulk catalyst lying inlet nozzle, which has a Bag is protected in a known manner against the catalyst masses, characterized through an above the catalyst bulk material (5) arranged and up to about 70% of its height filled with catalyst mass honeycomb-like flow guide grid (8), as well as a perforated guide plate attached above the insertion pocket (3) (6), which is oriented in such a way that the inflowing vapor-gas mixture into a top and a partial flow flowing below the baffle is divided.