CA1191198A

CA1191198A - Multiple stage multiple filter hydrate store

Info

Publication number: CA1191198A
Application number: CA000419350A
Authority: CA
Inventors: Harry K. Bjorkman, Jr.
Original assignee: Energy Development Associates Inc
Current assignee: Energy Development Associates Inc
Priority date: 1982-04-16
Filing date: 1983-01-12
Publication date: 1985-07-30
Also published as: EP0092297A2; MX160700A; ES8406800A1; JPS58188069A; ES519371A0; JPH0427676B2; EP0092297A3; US4386140A

Abstract

ABSTRACT OF THE DISCLOSURE An improved hydrate store for n metal halogen battery system is disclosed which employs a multiple stage, Multiple filter means for separating the halogen hydrate from the liquid used in forming the hydrate. The filter means is constructed in the form of three separate sections which combine to substantially cover the interior surface of the store container. Exit conduit means is provided in association with the filter means for transmitting liquid passing through the filter means to a hydrate former subsystem. The hydrate former subsystem combines the halogen gas generated during the charging of the battery system with the liquid to form the hydrate in association with the store. Relief valve means is interposed in the exit conduit means for controlling the operation of the separate sections of the filter means, such that the liquid flow through the exit conduit means from each of the separate sections is controlled in a predetermined sequence. The three separate sections of the filter means operate in three discrete stages to provide a substantially uniform liquid flor to the hydrate former subsys em during the charging of the battery system. The separation of the liquid from the hydrate causes an increase in the density of the hydrate by concentrating the hydrate along the filter means.

Description

MU _IPLP STAGE ~LlIPLE PILTER HYDRAT5 5TORE
BACRGROUND OF THE INV~NTION
The present invention relates to improveme~ts in metal halogen battery systems. More particula~ly the invsntion r~lates to a new multiple stage, multiple filter hydrate store for these battery systems.
The electrical energy storage systems of the type referred to herein (9 . g ., a zinc chlorine battery system or o~her metal-halogen battery system) utili2e a halogen hydTate as the source ~f halogen components ~or reduction at a normally positive electrode, and an oxidi-2abls metal adapted to become oxidized at a normally - negative electrode during the normal discharge of the storage system. An aqueous electrolyte is eJnployed for replenishing the supply of the halogen components as it becomes reduced at the positi~e electrode. The electTD-lyt~ contains the dissolved ions of the oxidized metal and the reduced halo~en and is circulated between the electrode area and a storage area containing halogen hydrate, which progressively decomposes during a normal discha~e of the electrical energy system, ~iberating additional elemental halogen to be consumed at the positi~e electrode.
The state of the art in electrical energy storage systems or battery systems of this type is describsd in the ~ollowing cited references owned by ~,', .

t]le Sarlle aSS:iCJIlee LIS the p.recent :invent:i.on, ~;uch ar-; Syrrlonc;
U.S. ratent. 3,713,888 enti.tLed "Process ~'or E:l.ectrical Enerc3y Using Soli.d l-Ialogen Hydrates"; Symons ~.S. Patent 3,809,578 entitled "Process :Eor Forming and Stoxing llalocJen EIydrate in a Bat-tery"; and Bjorkrnan U.S. Patent 3,814,630 entitled "Fil-tex/Store For Electric Energy Sto:raye Device"O
The new multiple sta-te, multiple hydrate store disclosed herein has wide applica*ion for use in nurnerous metal halogen battery systems.
The basic operation of a zi.nc chloride battery system is as follows. In charge, an electrolyte pump ~eli~ers aqueous elec-trolyte to pocket, between pairs of porous graphite-chlorine electrodes in a battery stack comprised oE a plurality of cells. The electrolyte passes through the porous chlorine electrodes into a charnber be-tween opposite polarity electrodes, flows up between the electrodes, then ~lows back into -the battery sump.

sb/ -Ch1Orille ga-; liberatecl ~rolll porous g-lQphite elcctrode substrat.es is pumped by a gear p~lmp, otherw:i.se referred to as the gas pump, and be~ore entering the gas pump, ~he chlorine is mixed with electrolyte chilled by a chiller unit. The chlorine and chilled electrolyte are mixed in the gear pump, chlorine hydrate forms in a process analogous to the water freezing process ~ith chlorine included in the ice crystal, and the chlorine hydrate-electrolyte mixture is deposited in the store.
lD In discharge, chlorine is liberated from the hydra~e hy decomposition of the chlorine hydrate in the store in a process aIlalogous to ~he melting o ice, by injectio of warm electrolyte for the sump. On development of the ~equired chlorine gas pressure in the store, the chlorine is injected and mixed wi.thand dissolved in the electrolyte, which is then fed to ~he porous electrodes in the bat~0ry stac~. The battery stack is then dis-charged, wherein the electrode dissolution of zinc occurs a~ the zinc electrode, reduction o:E the dissolved chlorine occurs at the chlorine electrode, power is available from ! the battery ~erminals, and zinc chloride is formed in the elec~rolyte by reaction of zinc and chlorine to form zinc c~loride.
Further discussion of the structure and operation ~5 of zinc chloride battery system may be found in cnmmonly assigned copending Cdn. patent applicati.ons of Fong et al., 1.'9~

Ser:i.a:l. N~. ~12,~S0, ~.il.ed Sep-tembe:r 30, 1982, ent.i-tl.ed "Metal llcl:Logen Ba ttery Cons-truc-tion With Irnproved Technique For Proclucing Halogell Hydrate"; o:E Ki.walle et al., Serlal ~o. 419,024, filed January 6, 1983, enti.tled "Me-tal Halogen Battery Sys-tem," and of Hacha, Serial No. 420,731, filed February 2, 1983, entitled "Halogen Hydrate Storaye Device for Mobile Zinch-Chloride Battery Sys-terns." Such systems are also described in published xeports prepared by the assignee herein, such as "Development of the Zinc-Chloride Battery for Utility Applications,i' Interim Repor-t EM-1417, May 1980, and "DeveIopment of the Zinc-Chloride Battery for Utility App].ications," Interim Report EM-105., April 1979, both prepared for the Electric Power Research Institute, Palo Alto, California.
During the development of the zinc-chloride battery system, several single stage filter designs for use in the hydrate store have been tested, including a rectangular filter across the top of -the store, an L-shape filter across one side and the bottom of the store, a combinàti.on of these two filters in a single stage, a basket-type filte:r seated in the store, and a bag like filter substantially overlying the interior walls of the store (as described in U.S. Patent No. 3,814,630). The purpose of the filter in the hydrate store is to separate the compressible particulate chlorine hydrate from the liquid used in the hydrate formation process.
As the chloride hydrate enters the store r it is in the form of a dilute slurry, of which approximately seven ~7) percent is hydrate crystal. However, due to the amount of chlorine sb/~

yas wh:icil :i.s l:ibera~ecl durin(l Lhe char(JillcJ of thc battery, :it i.s not p.racti.cal to store the chLo:rine h~drclte p~l:rticLes in this clil~lte slurry. Accord:ing:l.y, a :E.i:L-ter is used to provicle a hydra-te concentration system Eor rernovincJ as much of the excess liquid as possible. It ~7ill be apprecia-ted that the increase ln the density of -the hydrate particles in the store will resul-t in a decrease in the size and weight of the battery system. This advantageous result is particularly important where the battery system is employed in a battery-powered vehicle.
The present invention therefore resides in a metal haloyen baLtery system, ir.cluding at least one cell having a positive electrode and a negative electrode contac-ted by aqueous electrolyte containing the material of the me-tal and halogen, store means whereby a compressible particulate haloyen hydrate is :Eormed during the chargi.ncJ of the battery sys-tem from the halogen gas libera-ted at the positive electrode and a chilled liquid, and conduit means for transmitting the haloyen yas and the liquid to a hydrate former means for forming the halogen hydrate in association ~iith the store means. The store means is constructed in the form of a container, and multiple filter means is provided for separating the halogen hydrate from the liquid, the filter means being constructed in the form oE separate sections which combine to substantially cover the interior surface of the container. Exit conduit means is provided in association with the filter means for transmitting the liquid passing through the filter means to the hydrate former means.

sb/

Relie:~ va:lve meclnc~ inl~rr.)o.sed :in l:he ex:i~ concluit meanC;
~or contro:l:L:Lng the operatiorl oE the separaLe sect.l.ons of the ~il.ter means, such -that the liquid flow through che e~i-t conduit means from each of the separate sections i5 controlled in a predetermined sequence.
It is an object of a speciEic embodiment of the present invention to provide a multiple stage, multipl.e filter hydrate s-tore for a zinc-chloride battery sys-tem which more effectively concentrates the chlorine hydra-te particles during the charging of the battery system.
In one form of the present invention there is prov ded a hydrate store filter decign having three separa_e sections and which operates in three discrete stages to achieve a substantially uniform liquid flow through the store during the charging of the battery sys-tem whi:l.e maintaining a hydraulically compressive load on the hyd.rate. A rnultipJ.e stage, multiple filter hydrate store filtration or hydrate concentration system .is adapted to maintain the pressure in the hydrate store within acceptable levels during the charging of the battery.
Additional advantages and features of the present invention will become apparent from a reading of the detailed description of the preferred embodiments which makes reference to the following set of drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a simplified schematic of a metal halogen battery system employing the present invention, and particularly illustrating a multiple stage, multiple sb/:-l :ELlle:r hyclr~ e store ac(oK(linq to thf3 pr-3sr.-rlt invenl:i.c~n.
I~'.igurf;~ 2 :Ls a ~op elevat:i.orl v:iew, pcl:rtial.ly in cross-sect:i.on, o:~ -the~ muL-tip:le stage, mult:i.p:Le fllter hydrate store illus-trated in F:i.gure 1.
Figure 3a is a cross sect:i.onal vie~ of the multiple s-tac3e, multiple filter hydrate store .illustrated in Figure 1, taken generally along lines A-A oE Figure 2.

- 6a -sb/ ~

) ) ~iguTe 3b is ~ partial plan elevation view of the interior side wall of the multiple stage, multiple f~r hydrate store, taken gerlerally al~ng lines B
of Figure 3a Figure 4a is a cross-sectional ~iew of ~n~ther embodiment of a multiple stage, multiple filter hydr~te store according to the present invention.
Figure 4b is an enlarged cross-sectio~al view of a portion of the multiple stage, multiple filter hydrate store embodiment of Pigure 4a, particularly illustrating a technique of securing the filter cloth end in a sealing relationship with the side wall of the hydrate store.
Figure 5 is a plan elevation view, partially in cross-section, of a valve assembly for the multiple stage, multiple filter hydrate store illustrated in Figure 1.
SUM~RY OF THEi INVENTIO
The invention concerns an improved hydrate ~tore for a metal halogen battery system wherein a multiple stage, multiple Eilter means is employed for separating ~he halogen hydratefrom the liquid used in forming the hydrate. The filter means is constructed in the form of three separate sections ~hich combine to substantially cover the interior surface of the stDre container. F~it csnduit means is provided in association with the filter ~eans for transmitting liquid passing through the filter means ko a hydrate former subsystem. The hydrate former subsystem combines the halogen gas generated during the chargirlg of th0 batt~ry system ~ith the liquid to form the hydrate in ass~ciation with the store. Relief valv~
~eans is interposed in the exit conduit means for controlling the operation of the separate scctions of the filter means, such that the liquid flow through the ~xit conduit means from each of the separate scctions is controlled in a predetermined sequence. The three sepa-rate sections of the filter means operate in three discrete stages to provide a substantially uniform liquid flow t~
the hydrate former subsystem during the charging of the battery sys~em. The separation of the liquid from the hydsate causes an increase in the density of the hydrate by concentrating the hydrate along ~he filter mea~s.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Filtration has been developed as a prati al art rather than as a science, possibly because the large number of variables involved in any particular type of filtration reisult in analytical situations that can be solved more economically by experimental rather than theoretical methods (Perry's Chemical Engineer's Handbook, 5th Ed., McGTaw-~ill7 19659 pp. 19-57-60). Thè use of filtration theory is limited by the fact that filtering characteristics must always be determined on the actual slurry in question, as the data obtainedon one type of slurry is generally not applicable to another because of distribution and packing characteristics.
Filtration proceeds by the formation of a layer or cake of sPlid particles on the surface of a porou~
filter media. Once this layer has formed, its surace acts ~s the filter media. As solids are deposited, they ~dd ~o the thickness of the cake and the liquid is 8 i~ `.

,. .. . .

3~. t~

~iltered-out. The liquid passes par~ially thro~lgh bulky mass oE particlcs of irregular shape ~nd p~rti~lly through small channels that tend to form in the cQke.
The liquid flow through both the packed particle bed and the small channel is laminar. Therefore, the Poiseuille equation, which is the analytical expres-sion applicable to laminar flow, is frequently used as a basis for the semi.empirical characterization of the bed-flow parameters. In this instance, parameters that cannot be determined separately are collected or "lumped." The parameters that are know are then applied to the equaticn to e~tract the lumped parameters that are known are ~he~
applied to the equation to extract the lumped parameters.
Applied to filtration, the Poisuille equation becomes:
dV = ~c P (1 dtA y a(W/A + r) where V = Volume of filtrate (solution) ~O A c Area of filtering surface t ~ Ti~e p = Total pressure drop across the filter ~edia and ~he cake deposited on it ~ = Viscosity of filtrate W = MASS of dry cake solids corresponding to V
~ = Specific cake resistance r = Other resistance losses in the system across which P is the pressure drop.
W is related to V by:

( ~ (2 - m 9 i~, (~

~here Mass of ~ry c~ke solids per unit ~oluMe ~f filtrate p ~ Density of ~he filtra~e C = Mass fraction of cake solids i~ the ~lurry m = Mass satio Df wet cake to dry cake The symbol u representing the a~erage specifir resistance of the filteT is i constant for the particulate cake in its in~ediate condition at a particular operating value of P.
The variable ~ is related to pressure P by the empirical expression:
_ ~-p (3) here ~' D Bed resis~ance coefficient, a constant deter-mined by parkicle size and shape S = Cake compressibility, 0.0 for rigid incompres-sible particles and 1.0 for ~ery highly com-pressible cakes If the pressure is constant, equations 1 and 2 may be combined to give _t~ w ~V ~ ~r t4) V/A 2g~P ~AJ P
If the provisio~ is made to measure the pressure drop across the cake independent of the filter media, the constant r can be neglected to give:
t Z ~ ~V~2 2gcp ,A3 (5) Dividing both sides by t~ and rear~anging:
p lla~.~t (~2 ` (6 2g~ ~,At .
' .

-~0- ,.... .
..

Substituting equation 3 into equation 6 p(l-S) ~ (V ~ 2 gc ~At~

Equation 7 is ~ standard form used to describe continuous filtration where P is the pressure drop açross the filter cake. ~See, Unit Operations of Chemical , W. L. McCabe and J. C. Smith, McGraw-Hill, 3rd Ed., 1976, pp. 942-946). The parameters ~, ' and are constants. If ~he volume rate of solids filtrAtion V/t is held constant, measurements of pressure as a function of time can be sued to directly determine the apparent cake compressibility~ S.
In experiments conducted to deteTmine the charac-teristics oF chlorine hydrate filtration, the value o the compressibility coef$icient S was found to be 0.73 when water was used for the hydrate forming liquid media. This compressibility coefficient value indicates that the hydrate in ~he store behaYes as a highly compressible filter c3ke.
The value of the bed resista~e coefficient ~ ~as al50 found to be approxima~ely 2.73 x 105 (cm, g, sec.). This bed resistance coefficient value indicates that ~ithin the range of hydrate concentration tested ~8 to 23 percent) 9 the chloTine hydrate cake is highly porous or channeled.
These experiments suppDrted the hypothesis that the pre-~iously achie~ed hydrate storage density could be increased by modifications to the me~ns of filtration in ordeT t~
take advantage of the cake porosity and compressibility.

? `

ReferIing to Figure 1, a simplified schematic of a ~inc chloride battery system 10 according to tho present invention is shown. The battery system 10 g&nerally comprises a battery stack 12, a sump 14, and S a hydrat~ store 16. The stack 12 comprises a plurslity of cells each having a positi~e electrode and a negative electrode. The detailed description of a typical cell construction may be found in U.S. Patent No. 4,100,332 to Peter Carr, issued July 11, 197~, assigned to th~
assignee of the presentinvention. The sump 14 comprises an electrolyte reservoir which feeds an electrolyte pump 18 used to circulate ~he electrolyte to all the cells in the battery s~ack.
During the charging of the battery system 10 chlorine gas is generated or liberated at the positive electrodes in the battery stack 12. The formation o~
chlorine hydrate in the battery is accomplished by mixing the chlorine gas with an aqueous liquid which has been chilled to a temperature compatible with the formation of hydrate for that liquid (typically between -8~ to 46C).
This liquid or hydrate forming media may be comprised of the battery electrolyte itself, water, or other suitabl~
liquids. In battery System 10 a portion of the hydrate forming liquid is pro~ided by the battery electrolyte ~ia eonduit 20, and the remaining p~rtion is provided by the ~iltered ~iquid through conduit 22. Conduit 22 includes an orifice 24 which is used to regulate the flow of the liquid through the conduit. The liquid or electrolyte from conduits -12~ ,~

_. ' ' ' J

20 arld 22 combirle ancl 1OW tllrougll a heat exchln~er 26 W}l:iC]I :iS used to decreasc tlle temperatllre of th~ electrolyte ~o the level rcquired for ~he Eormation of hydrate. In one ~orm oE the p~sent invention, the heat exchanger 26 comprises a tube-shell type heat exchanger ha~ing on the Drder of one hundred and fifty thin wall titanium tubes arranged -in par--allel. A more detailed discussion of this type of heat ex-changer may be found in "Development of the Zinc-Chlorine Battery for Utility Applications, " Interior Report EM-lOSl April 1979, pp. 15-g, 15-10. The chlorine gas generated in ~he battery stack 12 is m;xed with the chilled electro-lyte in conduit 28, and pumped into the hydrate store 16 via a Jas pum~ 30 conduit 32. In onc ~orm of the present inJen-tion~ the gas pump 30 comprises of G-10 gear pump manufac-tured by Eco Rump, Corp., New Jersey. A detailed discussion of the structure and operation of the*G-10 pump may be ~ound in "Development o the 7;nc hlorine ~attery for Utility Applications," Interim Report EM-1051 April, 1979, pp. 17-7 17-8. The heat exchanger 26 and the gas pump 30 comprise the hydrate former subsystem for the battery system 10.
The solution o the chilled electrolyte and the chlorine gas is mixed undeT turbulent condit;ons to form a finely divided particulate chlorine hydrate by the reaction of CL~(g) ~ H2O(L) = CL2 XH2O(S), where x is approximately 6-8 for chlorine hydrate under normal conditions.
At the begining o charge, the hydrate store 16 is filled with the hydrate forming liquid. Du~ to its density~ the paTticulate ch~o~ine hydrate expelled from * - Trade Mark ,j!, 13 the pump outlets 34 and 36 will normally ~ise through the liquid until it reaches a top filt~r section 3B. 'rhe flow of the newly ormed hydrate slurry into the store 16 will cause liquid ~low through the top filter section 38 into ~op intake conduit 40. The top intake conduit 40 is ~onnected to a manifold conduit q2 which serves (as part of an exit condui~ subsystem) to return the liquid used in the hydrate formation process to the heat exchanger 26 in order to be recycled. The battery system 10 also includes a liquid/gas separater 44 which permits any gas leaving the hydrate store 16 to return tothe battery stack 12. As will be more fully discussed below, the hydrate filter means arcording to the presentinvention is constructed so as to pesmit gas and liquid 10w, but to prevent the particulate hydrate from escaping a store container 45.
As the charging of the battery system 10 pr~-gresses, the particulate chlorine hydrate will gradually form as a compressible cake along the top filte-r section 38. This ilter cake will be supported in part by the upward fluid flow and by very small residual attached gas b~lbbles. As the thickness of this filter cake increases during charge, the pressure drop through ~he cake increases.
The hydrate cake itself 'becomes a filter, and the cake will compress as the liquid attempts to find its way through the cake under the hydraulic pressure load. This will in turn, decrease the pore volume available for flow9 thereby adding further resistance to liquid flow and increasing the pressure drop across the hydrats cake. Although a positive pressure ~14 , ; .

in the store 16 will serve to compress snd compact the hydr~te, at some point in the hydrate bed depth the pressure drop across the hydra~e bed or cake will exceed the pratical design limits for the store:container 45 and the gas pump 30. Additionally, the liquid flow through the intake conduit 4D, and hence ~he liquid flow to the heat exchanger 26, will gradually begin to decrease as the hydrate cake becomes more resistant to liquid flow. This will, oE course, affect the $ormation of the hydrate by upsetting the balance of liquid to gas ~low. This situation is furth~ complicated by the fact that the particle size of the hydrate is believed to be in~ersely proportional to the concentration of the zinc chloride electrolyte. The sizes of the hydrate particules appear to be much smaller with the 25~ zinc chloride solu-tion concentration normally employed at the beginning of the charge. Larger particle sizes occur with the 5~ ~inc chloride solution concentration normally encountered at the end of ~he charge. Accordingly, as ~he zinc chloride concentration in the electrolyte changes during the charge, the particle size of the hydrate will also vary. Additional-ly9 the viscosity of the electrolyte being used to form the hydrate will also vary due to the gradually changin~ electro-lyte concentration during the charging of the battery system.
In order ~o ~chieve advantageous results of the present invention9 batteTy system 10 is also pro~ided with a side section filter 46, and a bottom section filter 48.
Each of the fil~ers 38, 46 and 48 are completely separate and operate in 3 discrete s~ages. In the firs~ stage only ~he ~15~

(. ) .,,) top filter section 38 operates to cuncentrate the hydrat~
by filtering out th~ e~cess liquid. In the seoDnd st~ge both thc top filter section 3B and the side filter ~ection 46 are operable, and in the thiTd stage all three of the filter sections are operable. The sequence and timing of ehese stages are controlled by a pair of relief valves S0 and 52 which are interposed in the mani~old conduit 42.
In the first stage, the excess liquid from the hydrate store 16 flows freely through the top intake conduit 40 and out to the manifold conduit 42. However, fluid flow through the side filteT section 46 and the bottom filter sec-tion 48 is prevented by the pressure responsive ~elief valves 50 and 52. The side filter section 46 is provided with a side int~ke conduit 54 which has an inlet port S6 disposed in the space betw~en the filter section and a side portion 58 of the store means container. Similarly, the bottom filter section 48 is provided with a bottom intake conduit 60 which has an inlet port 62 disposed in the space between the filter section and a bottom portion of the container.
The intake conduit 54 is connected to the mainfold conduit 42 between ~he relief valve 50 and relieve valve 52, while the intake conduit 60 is connected to the inlet port side of the relief valve 52. The relief valve 50 is adapted to permit liquid flow through the side intake conduit 54 above a first predetermined pressure in the store Means container.
Similarly, the relief valve 52 operates to permit liquid flow through the bottom intake conduit 60 above a second .
.

3.~ 3 predctermin~id pressuTe in ~he store mcans container, In ~ onc form of ~hc prcsent invrntion, the first predcitermined press~re lies in a ran~e between 2 psi to 6 psi, with ~
preferred pTess~re level of 4 psi in the store contai~er.
The second predetermined pressure al90 lies within a range of 3 psi to 8 psi, with a preferred pressure level of 6 psi.
In operation, the top filter section 3B coopeTates with the relief Yalve 50 in the first stage to concent~ate the hydrate along the top filter section of the filter ~eans until the pressure in the store containeT rises abo~e the first predetermined pressure. This allows compression ~f the hydrate on the primaly or top filter section 38 until such time that the pressure rises to such a point the hydrate ca~e is optimumly compressed along the top filter section. In the lS second state the pressure responsive relief valve 5~ opens to permit flow through the side intake conduit 54, thereby peTmitting the side ~ilter section 46 to operate. In this stage, both the top filter section 38 and the side filter section 46 will operate to filter the excess liquid. However~
the hydrate will quickly form a cake along the side ~ er section 46 due to ~he lower ~esistance to liquid flow.
Accordingly, even though both these filt~r sections will be operating, the side filter section 46 will become the primary filter doing the substantial portion of the work until the c~ke forms and compresses to the bed depth along the ~op filter section 38. In the third stage, both of the reli~f ~alves 5D and 52 will open to permit liquid flow through all three of the filter section of the filt~Ting means. However, as in the case of the second sta~e, the bottom filter section 48 will become the primary filter during the initial portion of th~ third s~age. It will also bei appreciated ~hat during i~ :

' , ,, ." _ the ~hird st~ge the manifold conduit 42 will operate tD
receive liquid fl~w fron~ the first~ second and third intake conduits9 40, 54, 60, respectively, and transmit this liquid to the hydrate forming means, that is the heat exchanger Z6 and gas pump 30.
The above described operation of the hydrate store 16 achieves several advantageous results over previous single fil~er or single stage hydrate store designs. Firstly, the multiple stage9 multiple filter hydrate store according to the present invention pro~ides a controlled compation or compre5sion of the hydrate in the store during the charging of the battery system.
In a single stage filter design little hydrate compaction occurs until a fil~er cake forms along the entire filter means, whereas in bat~ery system 10 hydrate compaction occurs veTy quickly along the top ~ilter section 38.
Thus, the hydrate store 16 is adapted to maintain a hydraulicly compressive load on the hydrate substsn-tially during tlle entire charging of the battery system 10. Additionally, the hydrate store 16 also operates to achieve a substantially uniform liquid flow to the heat exchanger 26 during the charging of the battery system by providing for 3 separate intake conduit portions whicb are operable in 3 distinct stages. It will also be appreciated that this hydrate concentration system i5 ~dapted to maintain the pressure in the hydrate sto~e within acceptable levels during the charging ~f the ba~tery system 10 by pro~iding for 2 con~rolled pressure ~elie~ levels.

;~ .
~18- -..

Turning now to Figure 2, a top elevation vi~w, partially in cross-section, of the hy~rate stor~e 16 is shown.
As is ~eadily apparent from this figure, the hydrate store 16 is generally cylindrical in nature. Accordingly, the store container ~5 comprises the generally vertically disposed ~nnular side portion 46, a generally horizontally disposed circular top portion 66, and the a generally horizontaily disposes circular bottom portion 64. As may best be seen with reference to Figure 1, both the top portion 66 and the bottom portion 64 aTe deformed or bowed outwardly to reduce the effective pressure on these portions of the container 46.
To prevent the escape of gas or liquid from the store con-tainer 45, both the top portion 66 and the bottom portion 64 are secured to the side portion 58 in a sealing relationship.
Specifically, a pair of anmllar collar members 68 snd 70 are employed to secure the top portion 66 and the botto~l portion 64 *o the side portion 58 via a plurality of elong-ated horizontally disposed bolts 72. HoweYer, it should be appreciated that this method of attachment is intended to be exemplary only, and that other suitable methods of attachment may be employed in the appropriate application.
Although the principles of the present invention may be applie~ to a variety of store container shapes, such as a ~pherical shape, it has been found advantageous in a cylindrical configuration to provide a predetermined geometri-cal relationship between the magnitude of the height of the side por~ion 58 of the container and the magnitude of the diameter of the top and bottom portions 66 and 64 of the container. Specifically, it is preferred that the TatiO of the side portion height to the top/bottom poAtion diameter ;f 19 , ~ , should be between 0.~5 and 0.9. The renson for thi~
specific geometrical relationship is derived from the packing characteristics of the chlorine hydrate. It is believed that a relatively greater side portion height with respect to the top/bottom portion dia~eter may lead to premature dense packiDg of the hydrate along that portion uf the side filter section nearest to the pu~p outlets during the second state of operation.
This situation could arise because the hydrate cake along the 20p filter secti~n may foTm a downwardly projecting colu~n which orerlaps the upper portion of the side filter section and impedes the formation of dense hydrate on this portion of the side filter section.
Since the densest packing occurs at the filter surf~ce, excessive side poTtion container heights may result in non-uniEorm hydrate formation and packing along the side filter section of the filter means. It should also be noted that the heat exchanger 26, the gas pump 30, and the relief valves 50 and 52 are all disposed outside the hydrate stoTe container 45. This is intended to reduce any interference with the packing of the hydrate within the store container 45. Howe~er, these components may also be suitably disposed within the container 45 in the appropriate application.
Referring ~o Figure 3a, a cross-sectional ~iew ~f the hydra~e store 16 is illustrated, the section being taken generally along line AA of Figure 2. Figure 3a pasticulaTly illus~rates a ~pace 74 between the side -20- ' -,, , , , , -.. ~, ( ! rv~

section fllter 46 ~nd an inter:ior surface 76 of the side portion SB of the container 45. ~he filter section 46 is supported by a scre0n 78 which has ~ plurality of perferations therethrough to permit liquid flow f~o~
the interior of the store 16 to the space 7~. A plural-ity of spacer bars 80 provide a predetermined dist~nce between the screen 78 and the in~erior surface 76 of the side portion S8. The relative length of the spacer bars 80 may best be seen with reference to Figure 3b~ which is a partial plan elevation Yiew Df the interior side portion of the store container 45. The arrows in Figure 3b indi-cate that the liquid flow through the side filter section 46 travels ver~ically around the spacer bars 80 toward the side intake conduit 54. The spacer bars 80 may be cemented, welded or otherwise conventionaliy secured to the side por-tion 58 of the container 45 (at reference numeral 80), depending upon the materials used for the container and the spacer bars. The predeter~ined distance provided by the .
spacer bars 80 is preferably between l/8th and 1/4th inches, but ~his distance may be varied so long as a sufficient distance is provided to permit the necessary gas and liq~id ~low in the space 74.
As illustrated in Figures l and 3a + b, the fil~er sections 38, 46 and 48 combine to substantially cover the ?S interior surface of the container 45, and it is preferred that the space between the filter sections be minimized in order tD provide as ~uch filter surface area as possible uithin the store container. Each of the filter sections ~re secured to their respective container portions around the periphery thereof i~ ~ particle-tight sealin~

,'',-, ...... ...

relati~nship. It should be appreciated that ~ gas tight o~ liquid tight seal is not ~equired ~s the filter sec-tions need only be adapted to ~etain the hydrate pa~ticles within ~he xtore container. One form of securing the filter sec~ions to the container portions is illustrated in the Pigures 3a ~ b. Specifically, the filter ~loth 46 is folded over an end spacer bar 84 and anchoTed there-to via a plurality of bolts 86.
Referring to Figures 4a ~ b, a cross-sectio~al view of a po~tion of another hydrate store 88 is shown.
~hese figures particularly illustrate an alternative technique of securing the filteT sections of thei~ respec-tive container portions. Firstly, the hydrate store 88 illustrates that a container portion 90 may be provided with a suitable liner 92 which may be operable to both protect tlle container from corrosion and protect the interior of the store from contamination. With respect to the technique of sealing, an end spacer bar 94 is provided with an inwardly expanding, outwardly ope~ing channel 96 which is adapted to receive the end of a filter cloth wrapped around a resilient, deformable bead 100. During the inseTtion of the filter section end in bead 100 into the channel 96, the bead 100 will deform and contract to permit the bead and the filter end to be translated past the opening of the channel and beco~e nestingly received within ~he channel. It will be app~e-ciated that once the bead 100 is received within the channel 96 it will again expand to its normal diametes -9~
r ) and operate to retain the end of the Eiltor section 98 wi~hin the channel.
Referring to Figure 5, a plan elevation vi~w, partially in cross-section, of the relief ~alve 50 shown in Figure 1 is illustrated. The Telief Yal~e 50 gen~rally comprises Q housing 102 having an inlet port 104 and one or more outlet po~ts 106, a ball 108 operably associated with theinlet port 104, and a weighted rod 110 for con-trolling the position of ~he ball 108 in response to the pressure at the inlet port 104. When the ball 108 is in - i~s seated position, as shown in ~igure 5, it will sealably engage a seal element 112 preventing any gas or liquid from passing from the inle~ port 104 to the outlet port 1~6.
However, when the pressure at the inlet port 104 exceeds the first predetermined pressure the ball 108 will be forced upwardly against the wieRht of the wei~hted rod 110 to permit the fluid flow throu~h the outlet ort 106.
It should be noted that the contruction of the relief valve S0 is intended to be exemplary only, and that otheT
suitable relief valve constructions may be employed, such as spring loa~ed relief valves or elec~rically operated Te1ief Yalves. For example, one electrically operated relief valve is exemplified by Model No. DY2-146NCAl~
manufactured by the Flourocarbon Company, Anaheim,

2~ California.
In terms of materials which may be employed for the hydrate stores according to the present inventiDn, it should first be noted that the materials should be chemically resistan~ or inert ~o ~he electrolyte and other chemical ;~:

. -~3.
, ell`tit:iCS W; t}l wh:ieh they will come into c~tact ~Jith respe~t t~ the filter sect:ion, it is pre~erred th~t l)uP~r *Armalon c:loth having one o~ the following ~odel numbers he employed: X12363, XT2663, E9223-7-l, E9223--17-l, E922~-20.
IYith respec~ to possibIe materials for the store container por-~ions and spacer bars, one or rnore of t~t following ma~erials may be employed DuPont*IEFLON, ~TFE)polytetra-~louroethy1ene,(FEP~Flourona~ed Ethylene Pr~palene co-pol~ner,~PFA)(EPE)Perflouro alkoxy resin, D~Pont*Tedlar, (PVF)Polyvinyl Flouride, DuPont*Tefyel,~CT~E) Chlorotri-flouroethylene, (Allied)*Halar, ~ECTFE) Ethylene-Chlorotri-1Ouroe~hylene, (Pennwalt)*Kynar~ ~PVDF~ Polyvinylidine Flouride, (General Tire ~ Rubber Corp.~ Bo~on (PVC~
Polyvinylchloride (4008~21~4), glass fiber, ca-r~on. With ~espect to the screen supporting the ilter sections~ such as screen 78, it is preferred that titanium expanded screen be employed. However; sne or more of the above-identified plastic materiaIs may also be employed.
The ~arious embodimen~s which hav~ been set forth above were for the purpose of illustration and were not in~ended to limit the invention. It will be appreciated by those skilled in the art that various changes and modifications may be made to these embodiments described in this specification without departing fro~ the spiri~
~5 and scope of ~he invention as def7ned by t~e appended c7aima.
* Trade Mark

Claims

I CLAIM: ,

1. In a metal halogen battery system, including at least one cell having a positive electrode and a negative electrode contacted by aqueous electrolyte containing the material of said metal and halogen, store means whereby a compressible particulate halogen hydrate is formed during the charging of said battery system from the halogen gas liberated at said positive electrode and a chilled liquid, and conduit means for transmitting said halogen gas and said liquid to a hydrate former means for forming said halogen hydrate in association with said store means, said store means being constructed in the form of a container, the improvement comprising:
multiple filter means for separating said halogen hydrate from said liquid, said filter means being constructed in the form of separate sections which combine to substan-tially cover the interior surface of said container;

exit conduit means in association with said filter means for transmitting the liquid passing through said filter means to said hydrate former means; and relief valve means interposed in said exit conduit means for controlling the operation of said separate sections of said filter means, such that the liquid flow through said exit conduit means from each of said separate sections is controlled in a pre-determined sequence.

2. The invention of Claim 1, wherein said separation of said liquid from said halogen hydrate causes an increase in the density of said halogen hydrate by concentrating said halogen hydrate along said filter means.

3. The invention of Claim 2, wherein said separate sections of said filter means are spaced a predetermined distance away from the interior surface of said container to provide a space between said filter means and the interior surface of said container.

4. The invention of Claim 3, wherein said filter means comprises three separate sections which operate in three discrete stages to provide a substan-tially uniform liquid flor to said hydrate former means during the charging of said battery system.

5. The invention of Claim 4, wherein said three separate sections of said filter means further operate to provide a hydraulically compressive load on said halogen hydrate substantially throughout the charging of said battery system.

6. The invention of Claim 5, wherein said store means container is substantially cylindrical in shape, and comprises a generally vertically disposed annular side portion, a generally horizontally disposed circular top portion, and a generally horizontally disposed circular bottom portion, said top and bottom portions being secured to said side wall portion in a sealing relationship.

7. The invention of Claim 6, wherein said three separate sections of said filter means comprises a first section substantially covering said side portion of said store means container, a second section sub-stantially covering said top portion, and a third section substantially covering said bottom portion.

8. The invention of Claim 7, wherein said exit conduit means includes a first intake conduit portion having an inlet port disposed in the space between said first section of said filter means and said side portion of said store means container, a second intake conduit portion having an inlet port disposed in the space between said second section of said filter means and said top portion of said container, and a third intake conduit portion having an inlet port disposed in the space between said third section of said filter means and said bottom portion of said container.

9. The invention of Claim 8, wherein said exit conduit means further includes manifold conduit means for connecting said first, second and third intake portions of said exit conduit means and for collecting the liquid flow therefrom.

10. The invention of Claim 9, wherein said relief valve means comprises a first pressure responsive valve interposed in a portion of said manifold conduit means between said first and second intake conduit portions, and a second pressure responsive valve interposed in portion of said manifold conduit means between said first and third intake conduit portions.

11. The invention of Claim 10, wherein said first pressure responsive valve operates to permit liquid flow through said first intake conduit portion above a first predetermined pressure in said store means container, and said second pressure responsive valve operates to permit liquid flow through said third intake conduit portion above a second predetermined pressure in said container.

12. The invention of Claim 11, wherein said filter means cooperates with said relief valve means in a first stage to first concentrate said halogen hydrate along said second section of said filter means until the pressure in said store means container rises above said first pre-determined pressure.

13. The invention of Claim 12, wherein said filter means cooperates with said relief valve means in a second stage to substantially concentrate said halogen hydrate along said first section of said filter means between said first and second predetermined pressures in said store means container.

14. The invention of Claim 13, wherein said filter means cooperates with said relief valve means in a third stage to substantially concentrate said halogen hydrate along said third section of said filter means when said pressure in said store means container rises above said second predetermined pressure.

15. The invention of Claim 14, wherein said manifold conduit means operates to receive the liquid flow from said first, second and third intake conduit portions and transmit said liquid to said hydrate former means.

16. The invention of Claim 15, wherein said store means container is constructed such that a pre-determined geometrical relationship exists between the magnitude of the height of said side portion and the magnitude of the diameter of said top and bottom portions of said container.

17. The invention of Claim 16, wherein said liquid comprises said electrolyte of said battery system.

18. In a zinc-chloride battery system, in-cluding at least one cell having a positive electrode and a negative electrode contacted by aqueous zinc-chloride electrolyte, store means whereby a compressible particulate chlorine hydrate is formed during the charging of said battery system from the chlorine gas liberated at said positive electrode and a chilled liquid, and conduit means for transmitting said chlorine gas and said liquid to a hydrate former means for forming said chloride hydrate in association with said store means, said store means being constructed in the form of a container, the improvement comprising:
multiple filter means for separating said chlorine hydrate from said liquid, said filter means being constructed in the form of separate sections which combine to substan-tially cover the interior surface of said container;

exit conduit means in association with said filter means for transmitting the liquid passing through said filter means to said hydrate former means; and relief valve means interposed in said exit conduit means for controlling the operation of said separate sections of said filter means, such that the liquid flow through said exit conduit means from each of said separate sections is controlled in a pre-determined sequence.

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19. The invention of Claim 18, wherein said separation of said liquid from said chlorine hydrate causes an increase in the density of said chlorine hydrate by concentrating said chlorine hydrate along said filter means.

20. The invention of Claim 19, wherein said separate sections of said filter means are spaced a predetermined distance away from the interior surface of said container to provide a space between said filter means and the interior surface of said container.

21. The invention of Claim 20, wherein said filter means comprises three separate sections which operate in three discrete stages to provide a substan-tially uniform liquid flow to said hydrate former means during the charging of said battery system.

22. The invention of Claim 21, wherein said three separate sections of said filter means further operate to provide a hydraulically compressive load on said chlorine hydrate substantially throughout the charging of said battery system.

23. The invention of Claim 22, wherein said store means container is substantially cylindrical in shape, and comprises a generally vertically disposed annular side portion, a generally horizontally disposed circular top portion, and a generally horizontally dis-posed circular bottom portion, said top and bottom portions being secured to said side portion in a sealing relationship.

24. The invention of Claim 23, wherein said three separate sections of said filter means comprises a first section substantially covering said side portion of said store means container, a second section sub-stantially covering said top portion, and a third section substantially covering said bottom portion.

25. The invention of Claim 24, wherein said exit conduit means includes a first intake conduit portion having an inlet port disposed in the space between said first section of said filter means and said side portion of said store means container, a second intake conduit portion having an inlet port disposed in the space between said second section of said filter means and said top portion of said container, and a third intake conduit portion having an inlet port disposed in the space between said third section of said filter means and said bottom portion of said container.

26. The invention of Claim 25, wherein said exit conduit means further includes manifold conduit means for connecting said first, second and third intake portions of said exit conduit means and for collecting the liquid flow therefrom.

27. The invention of Claim 26, wherein said relief valve means comprises a first pressure responsive valve interposed in a portion of said manifold conduit means between said first and second intake conduit portions;
and a second pressure responsive valve interposed in a portion of said manifold conduit means between said first and third intake conduit portions.

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28. The invention of Claim 27, wherein said first pressure responsive valve operates to permit liquid flow through said first intake conduit portion above a first predetermined pressure in said store means container, and said second pressure responsive valve operates to permit liquid flow through said third intake conduit portion above a second predetermined pressure in said container.

29. The invention of Claim 28, wherein said filter means cooperates wish said relief valve means in a first stage to first concentrate said chlorine hydrate along said second section of said filter means until the pressure in said store means container rises above said first predetermined pressure.

30. The invention of Claim 29, wherein said filter means cooperates with said relief valve means in a second stage to substantially concentrate said chlorine hydrate along said first section of said filter means between said first and second predetermined pressures in said store means container.

31. The invention of Claim 30, wherein said filter means cooperates with said relief valve means in a third stage to substantially concentrate said chlorine hydrate along said third section of said filter means when said pressure in said store means container rises above said second predetermined pressure.

. . -33-

32. The invention of Claim 31, wherein said manifold conduit means operates to receive the liquid flow from said first, second and third intake conduit portions and transmit said liquid to said hydrate former means.

33. The invention of Claim 32, wherein said store means container is constructed such that a pre-determined geometrical relationship exists between the magnitude of the height of said side portion and the magnitude of the diameter of said top and bottom portions of said container.

34. The invention of Claim 33, wherein said liquid comprises said electrolyte of said battery system.

35. In a zinc-chloride battery system adapted to provide electrical power during the discharging of said battery system for an electrically powered vehicle, said battery system including a plurality of cells each having a positive electrode and a negative electrode con-tacted by aqueous zinc-chloride electrolyte, store means whereby a compressible particulate chlorine hydrate is formed during the charging of said battery system from the chlorine gas liberated at said positive electrodes and a portion of said electrolyte, means for circulating electrolyte through said cells, and conduit means for transmitting said halogen gas and said electrolyte to a hydrate former means for forming said chlorine hydrate in .
association with said store means, said store means being constructed in the form of a container, the improvement comprising:
multiple filter means for separating said chlorine hydrate from said electrolyte, said filter means being constructed in the form of three separate sections which combine to sub-stantially cover the interior surface of said container;

exit conduit means in association with said filter means for transmitting the electrolyte passing through said filter means from said store means to said hydrate former means; and relief valve means interposed in said exit conduit means for controlling the operation of said separate sections of said filter means a such that the electrolyte flow through said exit conduit means from each of said separate sections is controlled in a pre-determined sequence.

36. The invention of Claim 35, wherein said separation of said electrolyte from said chlorine hydrate causes an increase in the density of said halogen hydrate by concentrating said chlorine hydrate along said filter means.

37. The invention of Claim 36, wherein said separate sections of said filter means are spaced a pre-determined distance away from the interior surface of said container to provide a space between said filter means and the interior surface of said container.

38. The invention of Claim 37, wherein said three separate sections operate in three discrete stages to provide a substantially uniform electrolyte flow to said hydrate former means during the charging of said battery system.

39. The invention of Claim 38, wherein said three separate sections of said filter means further operate to provide a hydraulically compressive load on said chlorine hydrate substantially throughout the charging of said battery system.

40. The invention of Claim 39, wherein said store means container is substantially cylindrical in shape, and comprises n generally vertically disposed annular side portion, a generally horizontally disposed circular top portion, and a generally horizontally disposed circular bottom portion, said top and bottom portions being secured to said side portion in sealing relationship.

41. The invention of Claim 40, wherein said three separate sections of said filter means comprises a first section substantially covering said side portion of said store means container, a second section sub-stantially covering said top portion, and a third section substantially covering said bottom portion.

42. The invention of Claim 41, wherein said exit conduit means includes a first intake conduit portion having an inlet port disposed in the space between said first section of said filter means and said side portion of said store means container, a second intake conduit portion having an inlet port disposed in the space between said second section of said filter means and said top portion of said container, and a third intake conduit portion having an inlet port disposed in the space between said third section of said filter means and said bottom portion of said container.

43. The invention of Claim 42, wherein said exit conduit means further includes manifold conduit means for connecting said first second and third intake portions of said exit conduit means and for collecting the electrolyte flow therefrom.

44. The invention of Claim 43, wherein said relief valve means comprises a first pressure responsive valve interposed in a portion of said manifold conduit means between said first and second intake conduit portions, and a second pressure responsive valve interposed in a portion of said manifold conduit means between said first and third intake conduit portions.

45. The invention of Claim 44, wherein said first pressure responsive valve operates to permit electrolyte flow through said first intake conduit portion above a first predetermined pressure in said store means container, and said second pressure responsive valve operates to permit electrolyte flow through said third intake conduit portion above a second predetermined pressure in said container.

46. The invention of Claim 45, wherein said filter means cooperates with said relief valve means in a first stage to first concentrate said chlorine hydrate along said second section of said filter means until the pressure in said store means container rises above said first predetermined pressure.

47. The invention of Claim 46, wherein said filter means cooperates with said relief valve means in a second stage to substantially concentrate said chlorine hydrate along said first section of said filter means between said first and second predetermined pressures in said store means container,

48. The invention of Claim 47, wherein said filter means cooperates with said relief valve means in a third stage to substantially concentrate said chlorine hydrate along said third section of said filter means when said pressure in said store means container rises above said second predetermined pressure.

49. The invention of Claim 48, wherein said manifold conduit means operates to receive the electrolyte flow from said first, second and third intake conduit portions and transmit said electrolyte to said hydrate former means.

50. The invention of Claim 49, wherein said store means container is constructed such that a pre-determined geometrical relationship exists between the magnitude of the height of said side portion and the magnitude of the diameter of said top and bottom portions of said container.