CA1310768C - Apparatus for the recombination of hydrogen and oxygen - Google Patents

Abstract

Abstract of the Disclosure:
An apparatus for the recombination of hydrogen and oxygen with the aid of a catalyst includes a vertically extending tube having end surfaces. A catalyst body is disposed in the tube. Stoppers close the end surfaces of the tube and open as a function of at least one parameter from the group consisting of pressure and temperature.

Description

13~7B~

VPA ~7 P 6073 APPARAT~S FOR THE RECOMBINATION OF HYDROGEN AND OXYGEN

Specification:
The invention relates to an apparatus for the recombination of hydrogen and oxygen with the aid of a catalyst.

As described in German Patent DE-PS 30 04 677, such an apparatus is used in par~icular for the breakdown of the hydro~en trapped in the containment of a water-cooled nuclear reactor plant. In ~lle device disclosed in that patent, ignition sources/ which may ba ~ a catalytic nature, are distributed in the containment.
The hydrogen that ~ight be produced during a malfunction is incended to be burned off with the igni~ion sources upon attain-~en~ of the lower ignition limit. The term "burning off" is intended to refer to an open combustion.

In German Patent DE-PS 30 04 677, burning off is said to be unobjeetionable, because gas cloud temp~-atures of a maximum of 500~e that are briefly produced cannot cause any damage. Howev-a~, chis process is quite expensive and does not limit combustion ~o ~ha vicinity of the catalyst body, I~ is accordingly an object of the invention to provide an ~pparaCu~ for the recombination of hydrogen and oxygen, which ov~rco~e~ the ~ereinafore-mentioned disadvantages of the hereto-fore-known devices of this general type and which recombines ~ 3 ~

hydrogen and oxygen with the aid of a catalyst in an apparatus in which free gas clouds are ~voided.

With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for the recombina-tion of hydrogen and oxygen with the aid of a catalyst, compris-ing a vertically extending tube having end surfaces, a catalyst body disposed in the tube, and stoppers closing the end surfaces of the tube including means for opening the stoppers as a func-tion of at least one parameter from the group consisting of pressure and/or temperature.

In the apparatus according to the invention, a recombinat~on already takes place in the range of non-ignitabla concentrations of hydrogen with the aid of the catalyst body which contains palladium or platinum as a catalyst material. In this recombina-tio~, known as "cold ignition", although hea~ing does occur, it is substantially less extensive than in the conventional burning off process. Above all, with low hydrogen prop~ tions, the recombination is limited in its heating to the vicinity of the catalyst body which is virtually shielded from the outside by the tube~ In accordance with another feature of the invention, the tube has an inner wall surface, and the catalyst body is spaced apart from the inner wall surface. Nevertheless, the heating assures the stimulation of a gas flow, which carries further gas through the tube and through the catalyst body, as long as the gas contains low percentages of hydrogen.

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C.erman Patent DE-PS 30 35 103 does disclose the provision of shafts havin~ recombination devices for hydrogen and oxygen in the containment of a nuclear power plant, and heating devices in the shafts which set a gas flow into motion by a chimney effect.
However, these shafts, which may also include shutoff devices, are supposed to extenà over at least one-half the height of the containment, in other words 2Q meters or more. In the shafts, elec~ric heaters should attain temperatures of over 600C with appro~imately 50 kW of power, in order to combust existing hydrogen. On the other hand, an apparatus according to the invention which does not need to be supplied with energy and which has tube lengths of no ~ore than 2 meters, is so small and so simple to install that it can be favorably used virtually an~here, and above all for retrofitting purposes.

In accordance with a further feature of the invention, there is p~o~ided ca~alyst material coating the inner wall surface. This is done in order to improve the catalyst action. The resultant heating that then occurs there is~ow in comparison with the cooling surface area of the tube.

In accordance with an added feature o~ the invention, there is p~ovided a porous substance containing silver nitrate being disposed below the catalyst body. Due to this provision, it is possible to keep the effectiveness of the catalyst from being affected by air-borne catalyst poisons.

~ 3 ~ 8 ~ ccordance with an additional feature of the invention, the porous subscance containing silver nitrate is a ceramic body.
~l~is is done, ~or e~ample, by being dipped in a silver nitrate solution ~

.
In accordance with yet another feature of the inven~ion, there are provided wires enveloped by catalyst material being secured LO ~he cacalyst body and protruding into a free space b~low the c.l~aly3t body in ~he tube.

In accordance with yet a further feature of ~he invention, the wires axtend through the porous substance. The wires, which may axtand through the porous substance having silver nitrate, are in turn heated by the heating of the catalyst body, The free ends o~ ~he wires therefore form an ignition source, with which the ~s i~ combusted whenever the concentration of appro~imately 4%
o~ hydrogen, which is sufficien~ for an ignition, is attained.
~ha combustion occurs before the gas passes through the catalyst body. In~çontrast to the prior art apparatus, the tube pr~ides 3hieldin~ ~or combustion purposes as well, so that large bufers ar~ not raquired~

In accord~nce with yet an added feature of the invention, the ~atalyst body has a honeycomb structure and is coated with ~atalyst material. The honeycomb body may be formed of a metal or ceramic carrier material, which is manufactured in cubic or cylindrical form. The channels extending parallel to the tube ~3~76~

a~is in the incerior of the body are coated with palladium orplatinum in a conventional ~anner.

In accordance with yet a further feature of the invention, the catalyst body includes wire meshes being stacked on one an~ther in axial direction of the tube and having individual wires intersecting each other at given points, and ~here are provided other wires woven into the meshes at the given points and extend-ing in axial direction of the tube. The wire meshes may be coated with the catalyst material, for example by electrodeposition, either before or after they are joined togeth-er.

In accordance with yet an added feature of the invention, the catalyst body is a metal sheet carrying the catalyst material, the metal sheet has at least one folded over edge region, and at least one of the wires is in thermally conductive contact with the metal sheet in the folded over edge region. This permits the dimensions of the o~erall apparatus to be reduced because it has been unexpectedly found that at the low hydrogen concentrations to be processed, even flat metal sheets of relatively small sur~ace area are sufficient to attain a reliable recombination, The lecombination causes a heat buildup to be generated so that a forceful gas flow is thermally set into motion. The rapid heating, which can lead to temperatures of 800C, becomes greater as the carrier mass to be heated by the reaction becomes smaller.

1 3 ~ 6 8 Therefore the chimney effect u~ilized to sti~ulate a gas flow can be at~ained even with relatively short tubes.

In accordance with yec an additional feature of the invention, the at least one folded over ed~e region of the metal sheet is in the ~orm of two parallel folded over edge regions each being provided with one of the wires. The result then is a symmetrical embodiment, which is convenient to manufacture.

In accordance with still another fea~ure of ~he invention, the metal sheet is disposed vertically, and the wire extends upward and downward beyond the metal sheet.

In accordance with still a further feature of the invention, the ~etal sheet has a lower edge extending at an angle and tapering to a runoff point, from which water produced in the recombination can drip of~ without impeding the wires.

In view o the high temperatures of up to 800C, in accordance wi~h still an added feature of the invention, the folded over edge region is fi~ed by a metallurgical bond, preferably produced by spot welding. This metallurgical bond can also improve the t~ans~ission of heat between the sheet and the wires.

T~e stoppers at the ends of the tube assure that the catalyst ~etion is not diminished by the ambient atmosphere before a recombination is necessary. To this end, in accordance wi~h 11 3 ~

still an addi~ional feature of the invention, the stoppers are membranes formed of a plastic that melts at temperatures above a gi~en level. If an elevated temperature arises, the stoppers liberate the catalyst material during a malfunc~ion in which hydrogen is produced. Another possibility is for membranes to be ruptured by the overpressure produced during a malfunction.

In accordance with again another feature of the invention, the stoppers are bime~allic sheets. The deformation produced by changes in temperature is utilized in this case to open flow cross sections.

In accordance with again a further feature of the invention, the sheets are a multiplicity of sheet-metal strips covering the cross section of the tube. In this way, a large cross section can be exposed, even at slight temperature chan~es.

In accordance with again an added feature of the invention, the catalyst body is a~metal sheet seated in the tube, the stoppers `~`~
are caps covering the end surfaces of the tube, and there are provided ~eans for subjecting the caps to spring biasing in an opening direction, and a bond with solder absorbing the spring biasing~ With this structure, temperature~dependent opening of the tube is obtained, so that the catalyst becomes effective in the case of a malfunction. Prior to opening, the tube is pro-tecced against becoming soiled and the like.

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In accordance with a concomitant feature of the invention, there is provided a bar transverse to the axial direction of the tube, the metal shee~ being secured in the middle of the tube on the bar. With this fastening structure, only a limited dissipation of heat is obtained, so ~hat the desired high temperature of the metal sheet is not impaired. However, it is also possible to select other fastenings, for instance a suspension, which is both stable and at the same time is not very thermally conductive.

Other features which are considered as rharacteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in an apparatus for the recombination of hydrogen and oxygen, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, ho~ever, together with additional objects and advantages thereof will be best understood from the following description of specif-ic embodiments when read in connection with the accompanying drawings.

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rtly brok~n aw~y ~nd sec~ional, dia~ramlTiacic p~-s~ tiv~ w ol ~n apparatus accordin~ to the invention;

~ ' is a ~ragmencary, perspective view of ano~her embodiment .> t` ~he ca cc~ lys t boày;

is perspective view oL a third embodiment of the catalyst body;

a vertical-sectional view of a further apparacus a~or~in~ to che invention; and . 5 is a horizontal-sectional view of the apparatus shown in ~i~. 4~

R~erring now to the figures of the drawing in detail and irst, par~icularly, to Fig. 1 thereof, there is seen an apparatus ~cording to the invention including a vertically extending metal ~e 1, Eor instance a s~eel tube, having a diameter of 200 mm ~and a len~th of 600 mm. The length and diameter are accordingly ~tC -~ ra~io of 3:1. The wall thickness is approximately 3 mm.

A ~a~alyst body 2 which is disposed in the upper portion o~ the ~be 1, ha3 a diameter that is approximately 30 mm smaller than ~ insidc diameter of the tube 1. The length of ~he catalyst b~dy ' is 150 mm. The catalyst body 2 is fixed in position by protrusions 3 of the inner wall of the tube, which assure that _9_ . .

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clle cr~ mission of heat b~tween the ~ lysc bod~ . ~nd ~he tube i is as low as possible. l`he protrusions may be punctiform or formed of points and can be produced from outside by indenting che cube.

The catalyst body 2 in ~he embodiment of Fig. 1 is formed of a ceramic material having a honeycomb structure, producing a great number of channels 4 extending parallel to the tube axis and having a ~quare cross section in the illustrated embodiment.
However, the channel cross section could also be triangular, hexagonal or round, as long as a large surface area in proportion ~o che voiume is attained. The catalyst body is coated in the vicinity of the channels 4 as well as on the outer surface ~hereof with palladium and/or platinum as a catalyst material.
This coating is also applied to the inner surface 5 of the tube 1.

~ A porous substance in the form of a ceramic body 7 is provided .
,~elow the catalyst body 2 and fills the tube cro~s!section, but is only 30 mm high. The body 7 serves to chemically neutrali~e catalyst poisons and is provided with silver nitrate. Instead of the ceramic body 7, a compressed fiber structure,~for example in ~le form of steel wool or asbestos cloth, could be used. The important factor is that the flow resistance be relatively low.

A broken-away portion of the catalyst body 2 shows that a wire 9, which is partly or entirely formed catalyst material, is secured .. . .

I~L07~

r~) clle w~11 of one O r the channel~ 4. The bond between the wire '3 a~d the catalys~ material should have good ~hermal conductivity ~It that location. The wire 9 is therefore wound inco a coil 10 at ~he fastenillg point. The coil 10 is joined to the catalyst mc~terial of the wall by welding, soldering, or gluing.

~s the drawing shows, a plurality of wires 9 distributed-over the ~ube cross section protruàe downward through the porous substance 7 into a free space 12. In this space, free ends 11 of the wires ean f~me~ion as ignition sources, which ignite inflowing hydrogen whenever the hydrogen concentration is greater than 4%. Before that occurs, catalytic recombinations in the vicinity of the ca~alyst body 2 bring about heating of the catalyst body itself and of the wire coils 10 that are bonded to the catalyst body in a thermally conductive manner.
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Sto~pers 14 which open as a function of temperature are provided on the end surfaces of the tube 1, as shown at the top of Fig. 1.
In the illustrated embodiment, four segments of mutually par~`~lel bimetallic strips 15 are provided, which bulge outward upon a cempera~ure chan~e and thus enable a gas flow, which is stim~llat-ed by the heating of gas in the tube 1. An identical stopper on the lower end surface is not visible.

The novel apparatus functions entirely-without external energy sources~ It requires no maintenance and can therefore be used at arbitrary locations inside the containment of a water-cooled , -11-.;

~L311 ~7~

us1~ rea~cvl, in p~cicuiar a pressuriz~d water reactor. I~
Lh~ ~ven~ oL` a ma1tuilction, th~ resultant elevatea pressures and ~emp~r.3tures open ~he scoppers 14 of ~he tube 1. During this roce~s, the medium in the cc~ntainment gains access to the in~erior of the tube. In ~he vicinity of thè catalyst body 2, hydro~en present in this medium is catalytically recombined with t~e o~ygen that is also presenc to form water. In this ~xothermic reaction, the cataiytic body is heated. This sets a ~3 ~low i~l~o motion, which leads from below through the verti-~lly e~tendin~ tube in the direction indicated by an arrow 16.
New mediulll havin~ a hydrogen content which is reduced by recombi-n~cion, is chus delivered to the catalyst body 2~

If the hydrogen content exceeds the ignition limit of 4%, then ~e wires 9 which are heated with the eatalyst body 2 cause an ignition, so that only uncombusted hydrogen needs to be recom-bined in the vicinity of the catalyst body itself. The tube 1 ~3sure3 ~hac the aforementioned combustion as well as the cata-lytic heating take place in a shielde~ space and do not lead to u~oncr~lled consequences.

In Ghe embodiment illustrated in Fig. 2, a catalyst body 2' is in ~h~ ~orm o a coil formed of a sheet-metal strip 16', which is p~-o~iled w.iCh longitudinal beads in the direction of the axis of th~ coil, as the drawing shows. The sheet-metal winding of the b~dy ~ provided with catalyst material. The catalyst ~ 3~7~8 rllcit~rial also e~cen~s to th~ protrusions ~t the coil which thlnccion as i~nition wires 9'.

ln the embodimen~ illu~trated in Fig. 3, a catalys~ body 2'' i9 ~ormed of stac~ed wire meshes 17 having the circular cross section shown in the drawing. Ignition wires ~'' extending CrarlSversely tO the plane of the meshes are woven into the wire meshes. The meshes 17 and ignition wires 9'' can be coated in common with catalyst material.

The apparatus according to the invention shown in Figs. 4 and 5 includes a housing 21 which is formed of a steel tube 22 having a diameter D of 100 mm, for example, and a length L of 180 mm, for e~ample, and also lncludes caps 24 and 25 on both end surfaces 26 and 27. Two fastening brackets 28 and 29 having screw holes 30, are secured to the left side of the housing 21. The housing 21 may be secured with the fastening brackets to a core pad or carrier in the interior of the containment of a water-cooled nuclear re~ctor. ~

The bottom cap 24 and the top cap 25 are under the influence of springs 31, which tend to spread them apart and thus away from che end surfaces 26, 27. The magnitude of the motion is limited by ~ nut 32 on a bolt 33 supporting the spring 31. In Fig. 1, only one spring 31 acting upon the cap 25 is shown, while the springs 31 acting upon ~he cap 24 are mounted underneath a guide 34~ but are otherwise identically constructed.

11 3 ~ 8 This ~prin~ c~ counteracced by bracin~ me~ns 35, which surr~ulld ~ wlr~ 36 havirlg à solder fuse 37. The solder fuse 37 has A response tempera~ure of 70C, for example. If the braeing me~ns, whiell are aajustable with a lock 38, should loosen, then ~he illcerior 40 of the ~ube is exposed and allowed to communicate wi~h the ambient air, i~ catalys~ 42 is disposed in the middle of the tube cross sec-ti~n, as shown in Fig. 4. The catalyst 42 includes a vertically excending fla~ metal sheet 43 of largely rectangular cross n, which is 40 mm in width and approximately 75 mm in l~ngch~ Tlle lower edge 44 o~ the flat metal sheet 43 tapers to a p~int 45, ~he angle of the edges being 45.

The metal sheet 43 is formed of stainless steel which is used as a catalyst carrier and is coated with platinum. Parallel edge ~eghons 47 and 48 of the metal sheet 43 are folded over into ~old~d regions 46 with a width of a few millimeters. Platinum wires 49 and 50 in the folded re~-ons 46 protrude upward and d~wnward out of ~he metal sheet 43 by approximately 40 mm each.
~he ~olded l~egions 46 are fixed by spot welding at least at two poin~s 5~ and 53 in the lower and upper regions of the metal she~t 43, pruducing a highly thermally conduceive bond of the wir~s 4~ and 50 to the metal sheet 43. As can be seen, the metal 3h~et 43 is secured with two bars 55 and 56 which extend trans-ver3e to che tube axis through bores 57 and 58 in the metal sheet ~3. The metal sheet 43 is firmly clamped at the bores with nuts ~L3~07~8 60, whiell are disposed in ~airs and thus checked. The bars 55, 56 are seated in threâded bushes 61 ~hat are welded OlltO the tub~
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Claims (19)

1. Apparatus for the recombination of hydrogen and oxygen with she aid of a catalyst, comprising a vertically extending tube having end surfaces, a catalyst body disposed in said tube, and stoppers closing said end surfaces of said tube including means for opening said stoppers as a function of at least one parameter from the group consisting of pressure and temperature.

2. Apparatus according to claim 1, wherein said tube has an inner wall surface, and said catalyst body is spaced apart from said inner wall surface.

3. Apparatus according to claim 2, including catalyst material coating said inner wall surface.

4. Apparatus according to claim 1, including a porous substance containing silver nitrate being disposed below said catalyst body.

5. Apparatus according to claim 4, wherein said porous substance containing silver nitrate is a ceramic body.

6. Apparatus according to claim 4, including wires enveloped by catalyst material being secured to said catalyst body and pro-truding into a free space below said catalyst body in said tube.

7. Apparatus according to claim 6, wherein said wires extend through said porous substance.

8. Apparatus according to claim 1, wherein said catalyst body has a honeycomb structure and is coated with catalyst material.

9. Apparatus according to claim 1, wherein said catalyst body includes wire meshes being stacked on one another in axial direction of said tube and having individual wires intersecting each other at given points, and including other wires woven into said meshes at said given points and extending in axial direction of said tube.

10. Apparatus according to claim 6, wherein said catalyst body is a metal sheet carrying said catalyst material, said metal sheet has at least one folded over edge region, and at least one id wires is in thermally conductive contact with said metal sheet in said folded over edge region.

11. Apparatus according to claim 10, wherein said at least one folded over edge region of said metal sheet is in the form of two parallel folded over edge regions each being provided with one of said wires.

12. Apparatus according to claim 10, wherein said metal sheet is disposed vertically, and said wire extends upward and downward beyond said metal sheet.

13. Apparatus according to claim 12, wherein said metal sheet has a lower edge extending at an angle and tapering to a runoff point.

14. Apparatus according to claim 10, wherein said folded over edge region is fixed by a metallurgical bond.

15. Apparatus according to claim 1, wherein said stoppers, are membranes formed of a plastic that melts at temperatures above a given level.

16. Apparatus according to claim 1, wherein said stoppers are bimetallic sheets.

17. Apparatus according to claim 16, wherein said sheets are a multiplicity of sheet-metal strips covering the cross section of said tube.

18. Apparatus according to claim 1, wherein said catalyst body is a metal sheet seated in said tube, said stoppers are caps covering said end surfaces of said tube, and including means for subjecting said caps to spring biasing in an opening direction, and a bond with solder absorbing said spring biasing.

19. Apparatus according to claim 10, including a bar transverse to the axial direction of said tube, said metal sheet being secured in the middle of the tube on said bar.