DE2300695C3 - 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. For this reason, 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 a container with a side or central gas supply and a mostly centrally arranged discharge line. Inside the container there is a grid-like one Intermediate floor on which the catalyst is in the form of small spheres or cylinders of approx. 3-8 mm Diameter is heaped up. The exhaust gases generated in the operation of a nuclear power plant are generally withdrawn from the turbine condenser with the help of steam jet pumps. The exhaust gases arrive then together with the motive steam via dehydrator and preheater into the recombiner. That through the The steam-gas mixture flowing into the inlet pipe first enters a so-called inlet skirt, which is the Diverts mixture flow into the upper free space of the container. From there the mixture flows through the Container lid deflected downwards and hits the catalytic converter in the process. In operation has now It has been found that unfavorable conditions arise in the flow thus forming in the upper part of the container to adjust. The flow hitting the catalytic converter from the side induces it certain flow velocities in motion, shifts the catalyst bulk material, and generates Accumulations and valley formations, in turn, give way due to the resulting different flow resistance lead to uneven loading of the catalyst. Furthermore, the Flow-related movement of the bulk catalyst material to its abrasion and thus reduces the existing Amount of catalyst and increases the pressure loss due to dusty deposits. A destruction of the Catalyst corpuscles are also carried away by the entrainment of these corpuscles by the inflowing vapor-gas mixture and caused the impact on the container lid and the container wall. All these Phenomena have an adverse effect on the performance of the recombiner.

The object of the invention is to determine the flow conditions in recombiners of the type described at the outset Kind 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 stuffed with catalyst mass

honeycomb-like flow guide grille, as well as a perforated one above the insertion pocket Baffle, which is aligned so that the incoming 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. Practical flow tests in a similar 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.

An embodiment of the invention is shown in the drawing and is explained below. It shows

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

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 is a perforated baffle plate 6. This guide plate 6 is so mounted above the inlet pocket 3 that the inflowing steam-gas mixture stream 9 is divided into two part streams 9a, 9b, so that a partial stream 9a 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 9ft'und 9b "), wherein a part of the steam-gas mixture flows through the apertures and thus a

W) 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 substreams combine in the free space 7 above the catalyst bulk

bi good and are in their overall effect, as confirmed in model tests, much more favorable than is the case with free development of the flow.
To further improve the flow ratio

se a honeycomb-like flow guide grille 8 is attached above the catalytic converter 5. It has sieve proven to be useful to pour the catalyst so high that the lattice sites up to one certain height, depending on the type and size of the catalyst particles, with bulk catalyst material are filled. This grid has in «Combination with the baffle 6 described above that the Mixture flow impinges almost uniformly and perpendicularly on the catalyst 5 and so a movement of the ι ο Catalyst bodies and the associated disadvantages are largely avoided. After this Flowing through the catalyst, the gas-vapor mixture leaves the container 1 through the central one lower nozzle 11.

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 shows the steam speed in m / sec in the recombiner, based on the free one The cross section is indicated. The catalyst bodies have the two already mentioned above different shapes of spheres or 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. At the value represented by the vertical 16, the shaking movement is in a rolling movement passed over.

3. At the value indicated by the vertical 17, the catalyst bodies lift off, i. H. you will be whirled up by the gas flow.

Curve 20 shows the flow velocities associated with the movements of tablet-shaped catalyst bodies, if there are no internals according to the invention in the recombiner. They are a maximum of about 1.5 m / sec.

The dashed curve 21 shows among those for spherical catalyst bodies, because of their A more streamlined shape offers the flowing medium less surface to attack. Here too unwanted 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 rate and that lie in the area 24 shown in dashed lines between the 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 is significantly above the curve 21, which the flow velocities for represents the case that there are no internals.

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 that 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. A B

Gas-vapor throughput Internal diameter Free cross-section, the flow velocities are the same as 45 gas-vapor velocity

m7s 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 catalytic combustion of radiolysis gases contained in steam-gas mixtures, oxygen and hydrogen are formed of water, this recombiner from a container with the side of the catalyst bulk material lying inlet pipe consists, the upper a pocket in a known manner against the catalyst masses is protected, characterized by 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 steam-gas mixture into one above and one below the baffle Partial flow is divided.