NO742918L - - Google Patents
Info
- Publication number
- NO742918L NO742918L NO742918A NO742918A NO742918L NO 742918 L NO742918 L NO 742918L NO 742918 A NO742918 A NO 742918A NO 742918 A NO742918 A NO 742918A NO 742918 L NO742918 L NO 742918L
- Authority
- NO
- Norway
- Prior art keywords
- sulfur
- gas
- acid
- mercury
- added
- Prior art date
Links
- 239000007789 gas Substances 0.000 claims description 56
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 37
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 34
- 229910052717 sulfur Inorganic materials 0.000 claims description 31
- 239000011593 sulfur Substances 0.000 claims description 31
- 239000002253 acid Substances 0.000 claims description 24
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 claims description 24
- 229910052753 mercury Inorganic materials 0.000 claims description 24
- 238000000034 method Methods 0.000 claims description 15
- 238000004519 manufacturing process Methods 0.000 claims description 12
- 238000000746 purification Methods 0.000 claims description 10
- 238000010521 absorption reaction Methods 0.000 claims description 9
- 238000004140 cleaning Methods 0.000 claims description 8
- 239000012141 concentrate Substances 0.000 claims description 6
- 238000001816 cooling Methods 0.000 claims description 6
- 238000001035 drying Methods 0.000 claims description 6
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 claims description 5
- 238000006243 chemical reaction Methods 0.000 claims description 4
- 150000001875 compounds Chemical class 0.000 claims 1
- 238000007792 addition Methods 0.000 description 10
- RAHZWNYVWXNFOC-UHFFFAOYSA-N Sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 150000002731 mercury compounds Chemical class 0.000 description 4
- JPJALAQPGMAKDF-UHFFFAOYSA-N selenium dioxide Chemical compound O=[Se]=O JPJALAQPGMAKDF-UHFFFAOYSA-N 0.000 description 4
- AKEJUJNQAAGONA-UHFFFAOYSA-N sulfur trioxide Chemical compound O=S(=O)=O AKEJUJNQAAGONA-UHFFFAOYSA-N 0.000 description 4
- 239000012717 electrostatic precipitator Substances 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- QXKXDIKCIPXUPL-UHFFFAOYSA-N sulfanylidenemercury Chemical compound [Hg]=S QXKXDIKCIPXUPL-UHFFFAOYSA-N 0.000 description 2
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 239000005864 Sulphur Substances 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000003546 flue gas Substances 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 239000011133 lead Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000012453 solvate Substances 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 150000004763 sulfides Chemical class 0.000 description 1
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical class S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 description 1
- 229910052815 sulfur oxide Inorganic materials 0.000 description 1
- 210000002435 tendon Anatomy 0.000 description 1
- 231100000331 toxic Toxicity 0.000 description 1
- 230000002588 toxic effect Effects 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B17/00—Sulfur; Compounds thereof
- C01B17/69—Sulfur trioxide; Sulfuric acid
- C01B17/74—Preparation
- C01B17/76—Preparation by contact processes
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Treating Waste Gases (AREA)
- Gas Separation By Absorption (AREA)
Description
Fremgangsmåte ved fremstilling av konsentrert kontaktsvovelsyre Procedure for the production of concentrated contact sulfuric acid
Oppfinnelsen angår en fremgangsmåte for å senke kvikksolvinnholdet i svovelsyre under fremstilling av denne, ved at kvikksolv fjernes fra gasstrommen hvorfra syren skal fremstilles. Ifolge en foretrukken utforelsesform angår oppfinnelsen behandling av gasser ■ The invention relates to a method for lowering the mercury content in sulfuric acid during its production, by removing mercury from the gas drum from which the acid is to be produced. According to a preferred embodiment, the invention relates to the treatment of gases ■
som inneholder svoveloxyder og kvikksolv, slik at' kvikksolvinn-which contain sulfur oxides and mercury, so that mercury
holdet i svovelsyre fremstilt fra disse gasser synker sterkt.the content of sulfuric acid produced from these gases falls sharply.
Svovelsyre fremstilles vanligvis fra svoveldioxyd erholdt ved rosting av sulfidkonsentrater av sink, kobber, jern eller bly etc. Sulfuric acid is usually produced from sulfur dioxide obtained by roasting sulphide concentrates of zinc, copper, iron or lead etc.
Når slike konsentrater inneholder kvikksolv eller kvikksølvforbindel-ser, er den erholdte syre forurenset med kvikksolv eller kvikksølv-forbindelser. When such concentrates contain mercury or mercury compounds, the acid obtained is contaminated with mercury or mercury compounds.
Det er blitt påvist at kvikksolv som slippes ut til omgivel-It has been proven that mercury that is released into the environment
sene, kan akkumulere i forskjellige organismer som, hvis de benyttes som mat, kan være giftige for mennesker. Da svovelsyre anvendes ved fremstilling av gjodningsmidler, kan et eventuelt kvikksolvinnhold i disse til slutt komme over i matvarer for mennesker. Det er derfor sterkt onskelig å kunne fremstille svovelsyre slik at forurensningen;i denne av kvikksolv bli så lav som mulig. tendons, can accumulate in various organisms which, if used as food, can be toxic to humans. As sulfuric acid is used in the production of fertilisers, any mercury content in these can eventually end up in foodstuffs for humans. It is therefore highly desirable to be able to produce sulfuric acid so that the pollution in this by mercury is as low as possible.
En rekke fremgangsmåter for dette formål er blitt beskrevet. A number of methods for this purpose have been described.
Således kan syren efter fremstilling behandles med 'sulfider for å ut-felle kvikksiilvsulf id. Svoveldioxydgassen kan ledes over materiallag som inneholder selendioxyd. Dessuten kan gassen vaskes med varm, konsentrert svovelsyre alene eller i nærvær av selendioxyd eller to-verdige kvikksølvforbindelser. Alle disse metoder er kostbare og krever' omfattende forandringer eller tillegg til anlegg for fremstilling av svovelsyre. Thus, after production, the acid can be treated with sulphides to precipitate mercury sulphide. The sulfur dioxide gas can be passed over layers of material containing selenium dioxide. In addition, the gas can be washed with hot, concentrated sulfuric acid alone or in the presence of selenium dioxide or divalent mercury compounds. All these methods are expensive and require extensive changes or additions to facilities for the production of sulfuric acid.
Det tas ved oppfinnelsen sikte på å tilveiebringe en fremgangsmåte for å kontrollere kvikksolvinnholdet i kontaktsvovelsyre på en .enkel og pålitelig måte, idet fremgangsmåten lett_skal kunne utfores i nye eller eksisterende anlegg for fremstilling av syre. The aim of the invention is to provide a method for controlling the mercury content in contact sulfuric acid in a simple and reliable way, the method being easy to carry out in new or existing facilities for the production of acid.
Ved fremstillingen av kontaktsvovelsyre ledes varme gasser erholdt ved rosting av sulfidkonsentrater gjennom kjole- og rensetrinn, fulgt av torking-, omdannelses- og absorpsjonstrinn for er-holdelse av svovelsyre.• ■ In the production of contact sulfuric acid, hot gases obtained by roasting sulphide concentrates are passed through dressing and cleaning steps, followed by drying, conversion and absorption steps to obtain sulfuric acid.• ■
Vanligvis er syrefremstillingsanlegg hvor gasser fra rosting av sulfidiske konsentrater benyttes, utstyrt med det folgende utstyr for avkjoling og rensing av gassene for svoveldioxydet omdannes til svoveltrioxyd: (a,) Våtskrubbere hvori den varme gass vaskes med vann eller med fortynnet syre dannet ved omsetning av. gassen med vannet. Stov fjernes, og gassen avkjoles.. (b) Elektrostatiske utfellere hvori ytterligere faste partikler, Usually, acid production plants where gases from the roasting of sulphidic concentrates are used are equipped with the following equipment for cooling and cleaning the gases before the sulfur dioxide is converted to sulfur trioxide: (a,) Wet scrubbers in which the hot gas is washed with water or with dilute acid formed by reaction of. the gas with the water. Dust is removed, and the gas is cooled.. (b) Electrostatic precipitators in which additional solid particles,
svoveltrioxyd og en del vann fjernes.sulfur trioxide and some water are removed.
(c) Et torketårn hvori den fuktige gass efter å ha passert gjennom de forutgående to trinn, bringes i kontakt med konsentrert svovelsyre for å fjerne vann. Da denne seksjon av anlegget står i direkte forbindelse med absorpsjonsseksjonen for SO^(c) A drying tower in which the moist gas, after passing through the preceding two stages, is brought into contact with concentrated sulfuric acid to remove water. As this section of the plant is in direct connection with the absorption section for SO^
(syre fra dette tårn pumpes til absorpsjonstårnet for SO^), ér det•nodvendig å hindre at kvikksolv kommer inn i torketårnet. (acid from this tower is pumped to the absorption tower for SO^), it is necessary to prevent mercury from entering the drying tower.
Andre metoder for gasskjoling og rensing kan anvendes.Other methods of gas stripping and cleaning can be used.
Det har nu overraskende vist seg at hvis elementært svovel injiseres i den varme gasstrom for rensesystemetforbedres fjernel-sen av kvikksolvet i gassen sterkt. It has now surprisingly been shown that if elemental sulfur is injected into the hot gas space for the purification system, the removal of the mercury in the gas is greatly improved.
Oppfinnelsen angår således en fremgangsmåte ved fremstilling av konsentrert kontaktsvovelsyre, hvor . 'varme gasser erholdes ved rosting av sulfidkonsentrater som inneholder kvikksolv eller kvikk-sølvforbindelser og gassene derefter ledes gjennom avkjølings- og rensetrinn, fulgt av torke- omdannelses- og absorpsjonstrinn, og fremgangsmåten er særpreget ved at svovel settes til den varme gasstrom for denne kommer inn i avkjølings- og rensetrinnene, slik at kvikksolvinnholdet i gassene fra rensetrinnet og i den fremstilte syre nedsettes. The invention thus relates to a method for the production of concentrated contact sulfuric acid, where . 'hot gases are obtained by roasting sulphide concentrates containing mercury or mercury compounds and the gases are then led through cooling and purification steps, followed by drying, conversion and absorption steps, and the method is characterized by the fact that sulfur is added to the hot gas stream for which it enters in the cooling and cleaning steps, so that the mercury content in the gases from the cleaning step and in the produced acid is reduced.
Svovelet settes fortrinnsvis til gassen når denne har en tempera-tur på 150-^00°C, helst l80-<!>+00°C. The sulfur is preferably added to the gas when it has a temperature of 150-^00°C, preferably 180-<!>+00°C.
Det er gunstig å tilsette svovelet i en mengde av 5 x 10"^ -It is advantageous to add the sulfur in an amount of 5 x 10"^ -
5 x 10 kg svovel pr. m- gass målt i normaltilstanden.5 x 10 kg of sulfur per m- gas measured in the normal state.
Avhengig av den tilstedeværende kvikksolvmengde i gassen kan svovelet også tilsettes i en mengde av 5 x 10 -6 - 5 x 10 -i+ kg svovel-pr. m<J>gass målt i normaltilstanden. Depending on the amount of mercury present in the gas, the sulfur can also be added in an amount of 5 x 10 -6 - 5 x 10 -i+ kg sulfur-per. m<J>gas measured in the normal state.
Oppholdstiden for det tilsatte svovel i den varme rokgass er fortrinnsvis 0,5 - 20 s.. The residence time for the added sulfur in the hot flue gas is preferably 0.5 - 20 s..
Eksempel• 1Example• 1
Elementært svovel ble ved hjelp av en skrue innfort i gass-Elemental sulfur was inserted into the gas by means of a screw
. ledningen til et vanlig kontaktanlegg for fremstilling av svovelsyre (med et gassrensesystem som beskrevet ovenfor). Svovelet ble tilsatt i en mengde av ca. 10 kg/h i 9'+,5 timer, med unntagelse av tiden mellom den 10,5 - 1^,5 time da intet svovel ble tilsatt. Gasstemperaturen ved svoveltilsetnings.stedet var 260°C, gassvolumet., 31 000 m-Vh beregnet i normaltilstanden og oppholdstiden for det injiserte svovel i den varme gass 2,0 s for den varme gass kom inn i våtskrubberne. De elektrostatiske utfellingsenheter ble vasket med vann en gang pr. 2h timer. Kvikksolvkonsentr as jonene i. prover av kontaktsyreproduktet (98,6$) tatt til forskjellige tider er gjengitt i tabell 1. . the line to a conventional contact plant for the production of sulfuric acid (with a gas cleaning system as described above). The sulfur was added in an amount of approx. 10 kg/h for 9'+.5 hours, with the exception of the time between 10.5 - 1^.5 hours when no sulfur was added. The gas temperature at the sulfur addition location was 260°C, the gas volume, 31,000 m-Vh calculated in the normal state and the residence time for the injected sulfur in the hot gas 2.0 s before the hot gas entered the wet scrubbers. The electrostatic precipitator units were washed with water once per 2h hours. The mercury concentration ions in samples of the contact acid product (98.6$) taken at different times are reproduced in table 1.
Variasjoner på 2 - 3PPm i kvikksolvinnholdet i .produktsyren er mulig på grunn av variasjoner i sammensetningen av gassen som Variations of 2 - 3 PPm in the mercury content of the product acid are possible due to variations in the composition of the gas which
r. leveres til kontaktsyreanlegget. Den samlede syrekapasitet for torke- og absorpsjonstårn, tanker og ledninger etc. er anslått som" r. delivered to the contact acid plant. The total acid capacity for drying and absorption towers, tanks and lines etc. is estimated as"
en 2h timers produksjon (200 tonn syre) for en gassgjennomgang på 31000 m-yh; gass beregnet i normaltilstanden. Svovel må derfor tilsettes kontinuerlig i over 2h timer for denne syre er blitt erstattet. a 2h hour production (200 tons of acid) for a gas throughput of 31000 m-yh; gas calculated in the normal state. Sulfur must therefore be added continuously for over 2 hours because this acid has been replaced.
Intervallet A ifolge tabell 1 viser at et hurtig fall i kvikksolvinnholdet i produktkontaktsyren (98,6$) forekommer under den begynnende periode for svoveltilsetningen, dvs. mellom 0 og 30,5 timer. Den hastighet som kvikksolvinnholdet i produktsyren minsker med, er 0 mellom den 6,5 og l<*>+,5 time på grunn av at svoveltilsetningen stanses mellom den 10,5 og 1^,5 time. Under intervallet A fylles den samlede syrekapasitet for kontaktsyreanlegget i det vesentlige fullstendig med syre med lavt kvikksolvinnhol. The interval A according to table 1 shows that a rapid drop in the mercury content of the product contact acid (98.6$) occurs during the beginning period of the sulfur addition, i.e. between 0 and 30.5 hours. The rate at which the mercury sulfur content in the product acid decreases is 0 between 6.5 and 1<*>+.5 hours due to the fact that the sulfur addition is stopped between 10.5 and 1^.5 hours. During the interval A, the total acid capacity for the contact acid plant is essentially completely filled with acid with a low mercury content.
Intervallet B ifolge tabell 1 viser at i en periode på 6^ timer efter intervallet A bevirket en fortsatt svoveltilsetning at det ble erholdt en produktsyre som inneholdt et gjennomsnittlig kvikksolvinnhold på ^-,8 ppm med et standard avvik på 1,1. The interval B according to table 1 shows that in a period of 6^ hours after the interval A a continued addition of sulfur caused a product acid to be obtained which contained an average mercuric sulfur content of ^-.8 ppm with a standard deviation of 1.1.
Eksempel 2Example 2
Elementært svovel ble ved hjelp av en mateskrue innfort i gass-ledningen til et vanlig kontaktsvovelsyreanlegg (med et'gassrensesystem som beskrevet ovenfor). Svoveltilsetningen var 12 kg/h, gasstemperaturen ved svovelinjiseringsstedet 250°C, gassvolumet 31 000 m-yh beregnet i normaltilstanden og oppholdstiden for injisert svovel' i den varme gass 1,9 s. Hver elektrostatisk utfellingsenhet ble renset en gang hver tolvte time ved vasking .ned vann. Produktsyren (98,6$ H^SO^) inneholdt 29 ppm kvikksolv straks for svoveltilsetningen ble påbegynt. Under svoveltilsetningen sank kvikksolv-konsentrasjonen•i produktsyren til h ppm og holdt seg konstant på dette nivå i 2h timer. Elemental sulfur was introduced by means of a feed screw into the gas line of a conventional contact sulfuric acid plant (with a gas purification system as described above). The sulfur addition was 12 kg/h, the gas temperature at the sulfur injection site 250°C, the gas volume 31,000 m-yh calculated in the normal state and the residence time for injected sulphur' in the hot gas 1.9 s. Each electrostatic precipitator unit was cleaned once every twelve hours by washing .down water. The product acid (98.6$ H^SO^) contained 29 ppm mercury immediately before the sulfur addition was started. During the sulfur addition, the mercury solvate concentration in the product acid dropped to h ppm and remained constant at this level for 2h hours.
EksempelExample
Elementært svovel ble ved hjelp av en mateskrue innfort i et gassledningssystem for tilforsel av gass til et kontaktsvovelsyreanlegg som omfattet tre gassrensesystemer av den ovenfor beskrevne type koblet i parallell. Gass fra disse rensesystemer ble tilfort til fire konvertere og tre absorpsjonstårn (to av konverterne hadde et felles absorpsjonstårn). Elemental sulfur was introduced by means of a feed screw into a gas line system for the supply of gas to a contact sulfuric acid plant which comprised three gas purification systems of the type described above connected in parallel. Gas from these purification systems was supplied to four converters and three absorption towers (two of the converters had a common absorption tower).
Elementært svovel ble tilfort' til gassledningene for rense-systemene i en mengde av 11 kg/h i<>>+0 timer. Gasstemperaturen ved tilsetningsstedet var 250°C, den samlede gasstrom til anlegget 113 000 m-Vh beregnet i normaltilstanden, og oppholdstiden for tilsatt svovel 'i den varme gass varierte fra 1,^- til h , k s for de tre forskjellige rensesystemer. Fordelingen av svovel mellom gass som ble fort til de tre rensesystemer var hverken jevn eller konstant under tilsetjingsperioden. Elemental sulfur was supplied to the gas lines for the purification systems in an amount of 11 kg/h for <>>+0 hours. The gas temperature at the point of addition was 250°C, the total gas volume of the plant 113,000 m-Vh calculated in the normal state, and the residence time for added sulfur in the hot gas varied from 1.^- to h , k s for the three different purification systems. The distribution of sulfur between the gas that was passed through the three purification systems was neither even nor constant during the addition period.
Kvikksolvkonsentrasjonen i produktsvovelsyren (98,6% HgSO^) fra absorpsjonstårnet var lk ppmfor svovelet ble tilsatt, og ved slutten av forsoket var kvikksolvkonsentrasjonen blitt redusert til 3 ppm, 2 ppm og 5 ppm i syren fra de tre adskilte adsorpsjons-tårn. The mercury sol concentration in the product sulfuric acid (98.6% HgSO^) from the absorption tower was 1 ppm before the sulfur was added, and by the end of the experiment the mercury sol concentration had been reduced to 3 ppm, 2 ppm and 5 ppm in the acid from the three separate adsorption towers.
Claims (6)
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AUPB533973 | 1973-10-22 |
Publications (1)
Publication Number | Publication Date |
---|---|
NO742918L true NO742918L (en) | 1975-04-23 |
Family
ID=3765793
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
NO742918A NO742918L (en) | 1973-10-22 | 1974-08-14 |
Country Status (10)
Country | Link |
---|---|
JP (1) | JPS5067796A (en) |
BE (1) | BE819361A (en) |
DE (1) | DE2441208A1 (en) |
ES (1) | ES430053A1 (en) |
FI (1) | FI251274A (en) |
FR (1) | FR2248234A1 (en) |
NL (1) | NL7412004A (en) |
NO (1) | NO742918L (en) |
SE (1) | SE7410462L (en) |
ZA (1) | ZA745333B (en) |
-
1974
- 1974-08-14 NO NO742918A patent/NO742918L/no unknown
- 1974-08-16 SE SE7410462A patent/SE7410462L/xx unknown
- 1974-08-20 ZA ZA00745333A patent/ZA745333B/en unknown
- 1974-08-27 FI FI2512/74A patent/FI251274A/fi unknown
- 1974-08-28 DE DE2441208A patent/DE2441208A1/en active Pending
- 1974-08-29 BE BE148050A patent/BE819361A/en unknown
- 1974-09-06 FR FR7430287A patent/FR2248234A1/en active Granted
- 1974-09-10 NL NL7412004A patent/NL7412004A/en unknown
- 1974-09-14 ES ES430053A patent/ES430053A1/en not_active Expired
- 1974-10-01 JP JP49113235A patent/JPS5067796A/ja active Pending
Also Published As
Publication number | Publication date |
---|---|
FR2248234A1 (en) | 1975-05-16 |
JPS5067796A (en) | 1975-06-06 |
FI251274A (en) | 1975-04-23 |
NL7412004A (en) | 1975-04-24 |
SE7410462L (en) | 1975-04-23 |
ZA745333B (en) | 1975-08-27 |
BE819361A (en) | 1974-12-16 |
DE2441208A1 (en) | 1975-04-24 |
FR2248234B3 (en) | 1977-06-17 |
ES430053A1 (en) | 1976-10-16 |
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