GB2132406A

GB2132406A - A method of manufacturing positive tube plates for accumulators

Info

Publication number: GB2132406A
Application number: GB08333502A
Authority: GB
Inventors: Dr Reiner Kiebling; Karl-Friedrich Zimmermann
Original assignee: Hagen Batterie AG
Current assignee: Hagen Batterie AG
Priority date: 1982-12-23
Filing date: 1983-12-16
Publication date: 1984-07-04
Also published as: NO155747C; JPS59132560A; DE3247787A1; DE3247787C2; IT1206334B; NO155747B; GB8333502D0; NO834760L; FR2538623B1; GB2132406B; FR2538623A1; IT8324271A0

Abstract

In a method of manufacturing positive tube plates for accumulators a mixture containing essentially Pb and Pb compounds is filled into the tubes of the tubular pockets, which contain a lead core connected to the terminal strip, from the ends of the tubes remote from the terminal strip, until the tubes are full, whereupon the filling openings of the tubes are closed. In this method lead dust is granulated in a granulator (12) with the addition of H2SO4 and H2O in the form of diluted sulphuric acid, and with oxygen being supplied. The still moist granulate (14) is subjected to post oxidation and to size classification matched to the filling chambers in the tubular pockets. The tubes are then filled with the post- oxidised, classified and still moist fine granulate (14') which forms the mixture (Fig. 2). <IMAGE>

Description

SPECIFICATION A method of manufacturing positive tube plates for accumulators The invention relates to a method of manufacturing positive tube plates for accumulators wherein each tube plate comprises a plurality of tubular pockets each containing a respective lead core, with said lead cores being connected at one end to a terminal strip, and wherein said tubular pockets are filled with a mixture containing essentially lead and lead compounds.

It is already known to fill positive tube plates of accumulators with lead containing, powder-like mixtures. Such mixtures are for example minium, mixtures of lead dust and minium in various proportions and also pure lead dust. Pure lead dust consists generally of from 65 to 80%, and in particular approximately 75% PbO and 20 to 35%, in particular approximately 25% Pb.

The tamping density of these mixtures, from which the bulk density in the formed condition can be directly derived, is the prime determining factor for the usability of these mixtures in the tube plates. The second important criterion for the suitability of the mixture as a filling for positive tube plates is the formability of the mixture, i.e.

the electrochemical efficiency having regard to the conversion of the starting mixture into PbO2 by electrochemical oxidation. This efficiency is greatest for minium; moreover the degree of oxidation in this material in the initial state is very favourable. However, having regard to the high cost of this material, increasing use is being made directly of lead dust as it occurs in the mills.

Lead dust is basically very suitable as a material for filling the tubular pockets of positive tube plates as a result of its favourable price. Lead dust can namely be obtained with the aid of simple chemical reactions.

It is however problematic when using lead dust that even minor irregularities in the production of the dust can lead to problems during fabrication because they directly effect the tamping density.

Differential tamping densities have in turn an effect on the capacity of the finished accumulator.

A further disadvantage of the use of lead dust for filling tubular plates lies in the fact that considerable dust generation is unavoidable during the filling process. This makes extensive measures necessary to ventilate the working areas, in order to keep the health damaging effects of the highly reactive lead compounds on the workers within limits. All previous efforts at improving the construction and in automating these places of work have proved to be relatively ineffective. One continues to be forced to equip workers in these areas with special dust protecting masks and to take further expensive measures as a result of the regulations for the protection of workers.

One has also already attempted to form pastes by mixing the lead dust with water, these pastes are however only suitable for filling grid plates.

The pastes are subjected in the grid to a maturing process in order to reduce the content of lead metal and to generate basic sulfate. These pastes are not however suitable for the filling of the relatively narrow tubes of tube plates, the diameters of which amount to approximately 8 mm, with the filling chamber however being reduced by the lead core which is approximately 3 mm thick and by the centering vanes.

The object underlying the present invention is now to provide a process of the initially named kind by means of which the disadvantages of using lead dust, in particular the fluctuating tamping density and the generation of dust, are avoided, without the considerable advantages of the lead dust for the filling of positive tube plates being reduced.

In order to satisfy this object the invention provides that lead dust is granulated in a granulator with the addition of H2SO4 and H2O, preferably in the form of diluted sulphuric acid, and with oxygen being supplied, preferably in the form of air; in that the still moist granulate is subjected to post-oxidation and to size classification matched to the filling chambers in the tubular pockets; and in that the tubes are filled with the post-oxidised, classified and still moist granulate which forms the mixture and which, as a result of the size classification, only contains granules which fit smoothly in the filling chamber.

It is important for the process of the invention that the granulate taken from the granulator is subjected to post-oxidation still in the moist condition, with the post-oxidation preferably being continued until a residual lead content of from 10 to 15%, and in particular approximately 1 1% is reached. Furthermore, it is also important that the post-oxidised fine granulate is not dried but is instead filled into the tubes of the tubular pockets in the moist condition. In this way it is ensured that the lead dust is extensively converted into tribasic and tetrabasic lead sulphate, with the initially tetragonal PbO being transformed as a result of the reaction with water into orthorhombic PbO.

It is particularly advantageous for the important post-oxidisation step to be carried out simultaneously with the size classification, which preferably consists of a sieving process.

An advantageous embodiment of the invention provides that water is added during the granulation and that the temperature in the granulator is controllable during the granulation and preferably reaching a maximum value in the range from 75 to 850C. A suitable water addition avoids a specified temperature being exceeded and the associated destruction of the tribasic lead sulphate. The addition of water may however not be allowed to be so great that a paste is formed and no longer a granulate.

In the practical realisation of the method of the invention one expediently proceeds in such a way that the addition of H2SO4 and H20 takes place in a first phase of the granulation process, and that the granulation is subsequently continued without further additions until a mixture of tribasic and tetrabasic lead sulphate and orthorhombic lead oxide with admixtures of tetragonal PbO is formed. Furthermore, it is expedient for the first phase to be followed by a second phase with a higher intensity of movement, which substantially concludes the granulation and which is then followed by a third phase with a reduced intensity of movement, which serves for completion of the reaction, i.e. the post-reaction in which the residual metal content reduces and the desired formation of basic lead sulphate is promoted.

With this arrangement the addition of acid and water in the first phase should take place within a period of from 0.5 to 5 min. The granulation in the second phase expediently takes place in a period of from 1 to 6 min. and in particular of approximately 3 min. duration. The post-reaction in the third phase should be carried out for a period of 6 to 8 min., and in particular of approximately 7 min. duration.

In order, on the one hand, to obtain an ideal chemical conversion of the lead compounds contained in the lead dust and, on the other hand, to maintain the temperature within limits and also to obtain a good granule, 4 to 6% by weight of H2SO4 and 7 to 9% by weight of H20 should be added to the lead dust in the first phase.

The diluted sulphuric acid that is used has a density of from 1.2 to 1.5, and in particular of approximately 1.3 g/ml.

Whereas the previously described method ensures a yield of well-sieved fine granulate of 65 to 75%, the total yield of the method of the invention can be increased to practically 100% if the granulate which is separated off as being too large during the size classification is comminuted and is regranulated in the granulator with the addition of water, and also post-oxidised and classified, with the resulting fine granulate likewise being used to fill the tubes. This process can always be repeated until all the lead dust has been converted into fine granulate.

The invention will now be described by way of example and with reference to the drawings which show: Fig. 1 a schematic side view of a positive tube plate for an accumulator, wherein only the tubes of the tubular pockets provided at the two ends are shown, the intermediate, identically constructed, tubes have been omitted in order to simplify the drawing, Fig. 2 an enlarged section on the line Il-Il of Fig. 1. and Fig. 3 a schematic partly sectioned side view of a granulator usable for the method of the invention.

As seen in Fig. 1 mutually spaced lead cores 1 6 with a diameter of approximately 3 mm extend from the lead terminal strip 15 into the tubes 17 of a tubular pocket 1 1 which consist of a textile mesh and have an internal diameter of ca. 8 mm.

Centering vanes 18, which contact the inner wall of the tubes 17 and thus ensure a central position of the lead cores 1 6 within the tubes 17, are provided at specified longitudinal spacing around the lead cores 16. Whereas in the drawing shows respective pairs of diametrically oppositely disposed centering vanes 18 which are alternately displaced by 90C it is preferred to provide three centering vanes uniformly distributed around the periphery twice over a length of 0.5 m.

The fine granulate 14' (Fig. 2) manufactured in accordance with the later described example is filled into the tubes 17 of the tubular pockets 11 in the manner illustrated in Fig. 1 by the arrows f, with the tube plate being clamped in the inverted position. As soon as all the tubes 17 are filled a synthetic strip 19 which is schematically illustrated in Fig. 1 is secured to the lower ends of the tubes 17 as a closure member. The tube plate can then be turned back into its normal position for use and inserted into an accumulator. It is important that the fine granulate 14' is sufficiently fine to fit in the filling chamber 13 between the lead core 16 and also the centering vanes 18 and the tube 17, and to be able to flow without problem into this filling chamber, so that a good tamping density is obtained.The compaction can be improved by vibrating the tube plate during the filing process.

The granulation process of the invention is schematically illustrated in Fig. 3. The granulator 12 is rotatablyjournalled by its rotational axle 20 in bearings 21 with the rotatable shaft 20 being arranged inclined by an angle a equal to ca.

60C relative to the horizontal. The granulator consists essentially of a correspondingly inclined vessel which is closed at the top by a lid 22, which is however stationary relative to the granulator 12. This is intended to be made clear by a support 23 which is indicated to the left of Fig. 3 and is secured to the machine frame.

An inlet stub 24 for air and lead dust and also a diametrically opositely disposed outlet stub 25 for the addition of diluted sulphuric acid and the extraction of exhaust air and water vapour are arranged through the lid 22. Furthermore, the shaft 26 of a stirrer passes between these two connection stubs with the stirrer preferably rotating in the opposite direction to the rotating shaft 20 of the granulator 12.

The granulate 14 which forms is schematically illustrated in the granulator.

The method of the invention takes place as illustrated by the following example.

Lead dust with for example 25% Pb and 75 PbO is put into the granulator 12 through the inlet stub 24.

It is assumed that the weight of the quantity of dust added is 100 kg.

After the total quantity of lead dust has been fed into the slowly rotating granulator (speed of rotation equal to 100 Rpm) the addition of diluted sulphuric acid takes place over a period of approximately 60 to 80 sec with the stirrer working at a speed of 1000 r.p.m.

With the assumed weight of 100 kg of lead dust 30 kg of sulphuric acid with a density of 1.3 g/ml are added and this corresponds to an admixture of 5.16 kg H2SO4 and 7.84 kg H20.

The heat of neutralisation and the heat of oxidation, and also the heat generated by the mechanical movement of the material would normally cause the temperature of the granulate 14 to increase rapidly in an impermissible manner. As a result of the vaporisation of water of the thermal capacity of the granulate and of the air passing through the granulator 12 it is however possible to keep the maximum temperature of the granulate below 850C.

During granulation no notable reaction with the air can take place.

The actual granulation takes place after the addition of the acid for a period of approximately 3 min during which the stirrer runs, now as previously, at 1000 r.p.m.

It is important that, following this, a postreaction takes place for approximately 7 min during which the stirrer only runs at 10 to 20% of the original speed of rotation, which in the present case corresponds to a speed of rotation of 100 to 200 r.p.m. A further quantity of water is able to vaporise during this post-reaction with the temperature falling to approximately 600C A vapour thus emerges from the granulator which has to be appropriately drawn off through the outlet stub 25.

The granulate 14 is subsequently taken out of the granulator 12 and subjected to a sieving process so that a fine granulate 14' (Fig. 2) is obtained which is adequately flowable within the tubular pockets. As this sieving process takes place in air a post-oxidation takes place from a rest content of approximately 20% Pb to approximately 11%. At the same time the water content drops to a rest moisture of 3.5%. Thus, during sieving, at least 0.9% water is once again evaporated.

It has been found that as a result of the method of the invention, and with a uniform initial dust, the bulk density and the tamping density of the fine granulate are very reproducable. Both values can be varied by changing the acid concentration and the quantity of liquid. This possibility of variation is an important advantage of the invention because in this way one can readily meet the requirements of different types of accumulator.

The ventilation of the granulating drum after the actual granulating process and at low speed allows, as a result of the high granulate temperature and of the thereby resulting further oxidation of the material, such an extensive postreaction effect to be obtained that a sievable product is directly created.

The sieving of the product is expedient because oversize granules with diameters from 1 to 5 mm always occur. The percentage of the oversize granules can be reduced by the nature of the acid addition.

The sieved-off oversize granules can be broken down with an increase speed of the stirrer in the granulator (in the present example, for example 2000 r.p.m.) can be subsequently regranulated at normal speed with water, and can finally be posttreated as previously. The yield of good, sieved fine granulate obtained for a one stage process amounts to ca. 65 to 75%. By re-using the oversize granules the total yield of the process can be increased to approximately 100%.

The chemical reactions which takes place during the method of the invention are as follows: PbO FH2SO4=PbS04+H20 (1) 2Pb+02=2PbO (2) These are the processes of the method of the invention which deliver heat of neutralisation and heat of oxidation.

As a result the following complexes are formed: 3Pb0 ~ pBSO4. 2H2O (tribasic lead sulphate) 4PbO pBSO4 (tetrabasic lead sulphate).

The PbO in the lead dust, which is initially tetragonal, is converted by the reaction with water to orthorhombic PbO.

The rest content of lead metal amounts to ca.

11%. As a result of the fact that the sieved off oversize granules are broken down and regranulated with the addition of water, which can be multiply repeated, the rest metal content is indeed broken down to less than 0.5%.

The sieving off of the granulate takes place so that the maximum grain size of the fine granulate 14' amounts to 1 mm.

Commercial tubular pockets can be used.

The current yields with the tube plates in accordance with the invention are at least as good as with the normal lead powder mixtures, however the problems associated with the filling of the tube plates when using lead dust are completely avoided.

After formation charging the PbO2 content lies between 81 and 86.6%. The quantity of current charged lies at approximately 11 3% of the theoretically necessary charging quantity.

The PbO2 is primarily present as -PbO2 together with smaller quantities of a-PbO2.

The minimum granule size of the granulate is approximately 25 ym. The surface of the individual granules is covered with microcrystals approximately 4 ym long and 1 Mm thick.

These microcrystals are exceptionally fine for tetrabasic lead sulphate. The granule size distribution in the granulate obtained from the oversize granules is considerably less uniform.

The fines are clearly only held together by water and break up when being prepared for investigation. Plate-like structures (tribasic lead sulphate) can be found on the surface together with the already described prismatic microcrystals.

The life of accumulators equipped with tube plates in accordance with the invention is actually slightly better than that of the known accumulators equipped with positive tube plates.

An essential reason why the method of the invention is successful is the fact that lead dust can be rapidly and effectively granulated in intensive mixing devices by the addition of diluted sulphuric acid. The term "granulation" will be understood to mean a process in which the individual grains of a powder are baked together to form an agglomerate which cannot be destroyed under moderate mechanical loading.

Decisive for the formation of such agglomerates is the combination of the action of a liquid with a chemical reaction between the components of this liquid and of the solid material. It is the formation of a new phase which enables an agglomeration which goes beyond the effects of the adhesive forces.

Claims

1. A method of manufacturing positive tube plates for accumulators wherein each tube plate comprises a plurality of tubular pockets each containing a respective lead core, with said lead cores being connected at one end to a terminal strip, and wherein said tubular pockets are filled with a mixture containing lead and lead compounds, characterised in that lead dust is granulated in a granulator (12), with H2SO4, H20 and oxygen being supplied to form a moist granulate (14); in that the still moist granulate (14) is subjected to a post-oxidation process and is graded (classified) to single out granules which will fit into said tubular pockets (11) around said lead cores (16); and in that said post-oxidised and graded granulate is filled into said tubular pockets (11) while still in the moist condition.

2. A method in accordance with claim 1, characterised in that said tubular pockets are filled via filling openings at their ends remote from the terminal strip.

3. A method in accordance with claim 2, characterised in that said filling openings are subsequently closed.

4. A method in accordance with any one of the preceding claims, characterised in that the graded granulate consists of granules with a maximum dimension of substantially 1 mm or less.

5. A method in accordance with any one of the preceding claims, characterised in that said H2SO4 and said H20 are supplied in the form of diluted H2SO4.

6. A method in accordance with any one of the preceding claims, characterised in that said oxygen is supplied in the form of air.

7. A method in accordance with claim 1, characterised in that water is added during granulation; and in that during the granulation the temperature in the granulator is controllable (12) and preferably reaches a maximum value in the range from 75 to 850C.

8. A method in accordance with any one of the preceding claims, characterised in that the addition of H2SO4 and H20 takes place in a first phase of the granulating process; and in that granulation is subsequently continued without further additions until a mixture of tribasic and tetrabasic lead sulphate and orthorhombic lead oxide with a content of tetragonal PbO is formed.

9. A method in accordance with claim 8, characterised in that the first pulse is followed by a second phase with a higher intensity of movement, which substantially concludes the granulation and which is followed by a third phase of reduced intensity of motion, which serves for the post-reaction.

10. A method in accordance with claim 8 or claim 9, characterized in that the acid and water addition in the first phase takes place within a period from 0.5 to 5 min. and preferably within a period of approximately 2 min.

11. A method in accordance with one of the claims 8 to 10, characterised in that the granulation in the second phase takes place in a period of from 1 to 6 and in particular of approximately 3 min. duration.

12. A method in accordance with one of the claims 8 to 11, characterised in that the postreaction in the third phase takes place in a period of from 4 to 10 and in particular of approximately 7 min. duration.

13. A method in accordance with one of the preceding claims, characterised in that 4.0 to 6.0% by weight H2SO4 and 7.0 to 9.0% by weight H20 are added to the lead dust in the first phase.

14. A method in accordance with one of the preceding claims, characterised in that the diluted sulfuric acid that is used has a density of from 1.2 to

1.5 and in particular of approximately 1.3 g/ml.

1 5. A method in accordance with one of the preceding claims, characterised in that the postoxidation takes place during the size classification.

16. A method in accordance with claim 5, characterised in that the size classification consists of a sieving process.

1 7. A method in accordance with one of the preceding claims, characterised in that the postoxidation is continued until a residual lead content from 5 to 15%, and in particular of approximately 11% is reached.

18. A method in accordance with one of the preceding claims, characterised in that the granulate separated off as being too large during the size classification is comminuted and regranulated in the granulator (12) with the addition of water, and also post-oxidised and classified; and in that the resulting fine granulate (14') is likewise used for filling the tubes (11).

19. A method substantially as herein described with reference to and as illustrated in the drawings.