Abstract:
The invention concerns a cooling system for a high intensity electric circuit designed to power an electrolysis vessel with high intensity current. Said system comprises a tube ( 18 ) made of conductive metal in series and/or in parallel in the electric circuit, conveying the high intensity current and liquid circulating circuit ( 34 ) comprising a pump with variable flow rate ( 28 ) maintaining a liquid flow in the tube for recovering the heat released by the passage of high intensity current in said tube and a heat exchanger ( 30 ) for evacuating the heat recovered in the tube and restore it to the electrolysis vessel for maintaining its temperature above a crystallisation threshold of the electrolysis, the variable flow rate of the pump being able to be adapted based on the value of the intensity of the high intensity current.

Description:
TECHNICAL FIELD  
         [0001]    This invention concerns cooling systems for high intensity electric circuits and particularly a liquid cooling device for high intensity electric circuits supplying power namely to electrolysis vessels.  
         BACKGROUND ART  
         [0002]    High intensity electric circuits are used in applications such as electrolysis facilities. These circuits generally convey currents ranging from 10 to 400 kiloamperes (kA). These high intensity circuits release a significant amount of heat owing to the Joule effect. It is thus necessary to implement cooling systems which allow this heat to be dissipated. This cooling action is essentially obtained using air cooling systems. This air may be ambient air or pulsed air which creates a current within the exchange zones. Natural cooling in the air requires having a low current density so as not to raise conductor temperature above approximately 100° C. Excessive conductor temperature may prove to be dangerous, not only for the operators but also for the thermal stability of the circuit. The increase in the resistivity of conductive metals combined with the increase in temperature may lead to irreversible damage. This energy, released in the form of heat transmitted to the air, is highly penalising and difficult to recover. It generates significant facility air-conditioning and ventilation costs and may draw dust or pollutants outside. Furthermore, exchange zones must be quite large in order to ensure efficient cooling. In this manner, for high intensity electric circuits which release large amounts of heat, the equipment required for cooling are quite large which makes installation difficult and their dimensions quite penalising. Another major drawback of these air cooling systems is that they cannot be adapted to the current intensity used in the circuit. If such a system is designed to enable the cooling of a circuit having a specific current intensity, this system would no longer be adapted if the current intensity in the circuit is increased. Possible increases in current intensity must be anticipated when initially designing the cooling system so that such modifications can be incorporated.  
           [0003]    For the high intensity electric circuits, at least one part of the circuit has been designed in the form of a conductive tube in which a coolant flows, as described in documents U.S. Pat. No. 3,067,278 or GB 465,342. In such a device, the cooled tube generally forms part of the coolant&#39;s circulation circuit featuring a pump and a heat exchanger designed to recover the heat released in the tube caused by the electrical current passing through it.  
           [0004]    When supplying power to electrolysis vessels, another problem inherent to this type of application must be overcome. The electrolyte located inside the electrolysis vessels must be maintained at a temperature above a minimum temperature, failing which the electrolyte crystallises. This requires a secondary circuit which enables the necessary amount of heat to be produced in order to maintain the electrolyte at the correct temperature. High intensity electric circuits featuring cooling systems enabling the energy produced to be dissipated (although not enabling its recovery), and heating systems enabling the electrolyte to be maintained at a sufficient temperature to avoid crystallisation are thus generally seen.  
           [0005]    Finally, another problem is encountered when several electrolysis vessels are connected in series and one of these vessels must be disconnected. In conventional electric disconnect one. Once it has been isolated, the other vessels are returned to operation. This operation is thus very restricting as the entire electrolysis device must be immobilised for a relatively long period of time. This immobilisation results in significant production losses and very high restart costs for the company which uses these electrolysis vessels.  
         DISCLOSURE OF THE INVENTION  
         [0006]    The object of the invention is to thus provide a liquid cooling system capable of absorbing the energy released by the high intensity electric circuit powering an electrolysis vessel and to use the heat recovered to heat the vessel and prevent its temperature from dropping below a predetermined threshold.  
           [0007]    Another object of the invention is to provide a liquid cooling system for at least one part of an electric circuit supplying several electrolysis vessels in series enabling one electrolysis vessel to be rapidly isolated without immobilising the other vessels.  
           [0008]    This invention concerns a cooling system for a high intensity electric circuit featuring a conductive metal tube in series and/or parallel in the electric circuit, transporting the high intensity current and a liquid circulating circuit featuring a pump with variable flow rate which circulates the liquid in the tube designed to recover the heat released by the high intensity current passing through this tube and a heat exchanger to dissipate the heat recovered in the tube. The high intensity electric circuit supplies an electrolysis vessel featuring at least two electrodes of different polarity and the heat exchanger transmits the heat recovered in the tube to the electrolysis vessel so that the temperature of the vessel does not drop below a predetermined temperature.  
           [0009]    According to another characteristic of the invention, the high intensity electric circuit supplies a plurality of electrolysis vessels in series, each of the electrolysis vessels being associated with a portion of tube and to a heat exchanger to transmit the heat recovered in the portion of tube to the electrolysis vessel so that the temperature of the vessel does not drop below a predetermined temperature. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0010]    The purposes, objects and characteristics of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which:  
         [0011]    [0011]FIG. 1 represents a front view of the cooling device according to the invention adapted to a high intensity electric circuit powering an electrolysis vessel.  
         [0012]    [0012]FIG. 2 represents a top view of the cooling device according to the invention, adapted to a high intensity electric circuit powering an electrolysis vessel, and  
         [0013]    [0013]FIG. 3 represents a block diagram of the supply of several electrolysis vessels in series according to the principles of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    According to FIG. 1, the high intensity electric circuit supplies several electrolysis vessels in series. The current enters or leaves the previous electrolysis vessel by a supply bar  10 , made of a conductive metal which may be copper or aluminium, connected to the electrode  12  of the electrolysis vessel (not shown). This supply bar is connected to a circuit breaker  13 . The electrode  12  thus serves as the inlet for the high intensity current. After passing through the electrolyte, the current is divided into two parts. Half of it passes into electrode  14  and the other half in electrode  16 . These two electrodes thus act as the output for the high intensity current. According to another embodiment, the direction in which the current flows in the electrodes may be reversed. In the same respect, according to other embodiments, the vessel may have only one output electrode or more than two output electrodes. The current which passes through the output electrode  14  then enters a tube  18 , connected to this electrode, belonging to the cooling device according to the invention. For example, if the current supplied to the electrolysis vessel is 50 kA, at its output, 25 kA enters the output electrode  14  and the cooling tube  18  and 25 kA enters the output electrode  16 . The tube  18  is made of a conductive metal. According to a preferred embodiment, copper or aluminium is used. This tube is also used to convey the liquid, thus enabling the high intensity electric circuit to be cooled. The liquid used may be water with or without additives, oil or glycol. The connection of the tube to the cooling circuit is detailed in FIG. 2. The fraction of current which passes through the tube  18  joins with the current which passes through the output electrode  16  at the level of the supply bar  22 . This bar allows current to flow into the next electrolysis vessel by means of a circuit breaker  24 . In this manner, a 50 kA current is supplied to the next vessel. The current returns via the supply bar  20 .  
         [0015]    When the electrolysis vessel must be short-circuited to undergo maintenance, for example, one simply has to close the switch  11  and open the circuit breaker  13 . The supply bar  10  nor the electrolysis vessel are thus no longer energised. All of the current coming from the previous tank flows directly into the tube  18  and supplies the next vessel, via the circuit breaker  24 . As a result, in this configuration, the 50 kA current flows into the tube  18 . The electrolysis vessel short-circuiting operation is thus much easier and does not require the immobilisation of the entire electrolysis device.  
         [0016]    According to FIG. 2, the cooling tube  18  is connected to a cooling circuit featuring a pump  28  which circulates the coolant, enabling an exchanger  30  to transmit the energy recovered in the cooling tube  18  in the form of heat, to the electrolysis vessel  32 . These various cooling system components are interconnected by insulated flexible hoses or rigid pipes  34 . The liquid arrives at the pump  28  and joins the cooling tube  18 . At this level, the liquid has temperature t 1 .  
         [0017]    While the liquid circulates in the cooling tube, its temperature increases until it reaches a temperature t 2 . This reheating is due to the heat released being conveyed to the liquid which flows through the cooling tube and which comes from the output electrode  14 . When the electrolysis vessel is in operation, the current intensity transmitted to the cooling tube is equal to 50% of the current intensity transmitted to the vessel  32  by the input electrode  12 , connected to the supply bar  10 . The remaining 50% are conveyed by the second output electrode  16 . In this case, the energy recovered by the liquid in the form of heat thus corresponds to the energy released by 50% of the high intensity current. If the vessel is short-circuited, all of the current is transmitted to the cooling tube. It is thus capable of absorbing the energy released by all of the current. Even if the intensity of the current flowing in the cooling tube may double, it is easy to ensure constant liquid temperature by simply varying its flow rate in the cooling circuit. It is not even necessary to vary the flow rate in the cooling circuit, as the temperature variation of the liquid is minimal in the case where the vessel is short-circuited.  
         [0018]    For example, if the cooling tube is formed by a copper tube with a total surface area of 8,200 mm 2 , when the vessel is operating, a current equal to 25 kA, the density of which is 6 A/mm 2 , produces a power of 1.3 kW per meter of tube. The corresponding increase in the temperature of the water, used as coolant, is 2.3° C. per meter of tube, for a water flow rate of 0.5 m 3 /h. When the vessel is short-circuited, the current intensity is 50 kA. For the same current density and the same water flow rate, the circuit produces 5.2 kW/m, that is a temperature increase of approximately 9° C.  
         [0019]    The liquid which enters the exchanger  30  has thus been subjected to a temperature increase which varies depending on whether the vessel is connected or short-circuited. The exchanger allows the transfer of the energy corresponding to the increase in the liquid&#39;s temperature toward the electrolytic solution. The electrolytic solution needs to be maintained at a minimum temperature, for example 40° C., to prevent the electrolyte from crystallising. This heating energy may represent up to 10% of the total energy. When the vessel is in operation, part of this energy is introduced by the electrolysis itself. The other part is introduced by the heat recovered by the cooling circuit. When the vessel is short-circuited, the electrolyte must be maintained at the same temperature. However, we no longer have the energy released by the electrolysis. All of the energy is thus introduced by the cooling circuit. The short-circuiting circuit measures 4 meters in length while the vessel&#39;s supply circuit measures 8 meters in length. In this manner, when the vessel is short-circuited, the overall energy produced in the cooling tube is double that of the normal amount and thus compensates for the lack of electrolysis energy to maintain the electrolyte at the desired temperature.  
         [0020]    In the embodiment example illustrated in FIG. 3, two electrolysis vessels  40  and  40 ′ are supplied in series by a 50 kA current supplied by the electrical source  42 . For each vessel, the current supplies the solution by means of two anodes  14  and  16  ( 14 ′ and  16 ′ for the other vessel) supplying a current of 25 kA each. An output current of 50 kA is thus supplied by the vessel&#39;s cathode. During normal operation, the 50 kA current exiting the cathode  12  supplies, owing to the closed switch  11 , the anode  16 ′ and the cooling tube  18 ′ of the electrolysis vessel  40 ′ by supplying both a current of 25 kA. The other end of the cooling tube  18  is connected directly to the anode  14 ′ of the vessel  40 ′.  
         [0021]    If, for any reason whatsoever (maintenance in particular), the vessel  40  must be short-circuited, the switch  12  is opened and the circuit breaker  13  is closed (while during normal operation, this circuit breaker is open). In this way, no current flows into the electrolysis vessel  40 , and the 50 kA current thus flows into the cooling tube  18 .  
         [0022]    It should be noted that in the example illustrated in FIG. 3, the electrolysis vessel  40  is the first of the chain and, as a result, the anode  16  and the cooling tube  18  are not supplied via the switch or the circuit breaker.  
         [0023]    In another embodiment, the cooling tube may be in contact with the supply bar of the high intensity electric circuit in order to cool it. The cooling tube is thus connected in parallel with the supply bar, in the high intensity circuit. One part of the high intensity current that usually flows through this bar, is transmitted into the cooling tube. The energy which is released in the supply bar is thus less significant. Furthermore, this energy is transferred to the fluid circulating in the cooling tube. The energy produced by the fraction of current flowing in the cooling tube is equally transferred to the fluid flowing in this tube. This adaptation thus allows the electrical capacity of the supply bar to be increased and to thus lower its temperature while enabling the energy produced at the level of this bar to be recovered. In particular, this system adapts to high intensity electric circuits by a traditional air cooling system. When cooling is no longer optimal and the cooling system must be replaced, the adaptation of the liquid cooling system according to the invention for compensating this shortcoming appears to be a much less costly solution.  
         [0024]    Although the cooling system according to the invention is applied, in the examples, to a high intensity electric circuit of 50 kA, this system applies more generally to electric circuits having current intensities ranging from 10 to 400 kA.  
         [0025]    In the case of a traditional air cooling system, the cooling bars must have sufficient surface area to be able to dissipate the energy released by the current, the intensity of which is maximal when the vessel is short-circuited, even if the short-circuiting operation only lasts a few hours per year. In addition, the current density in the cooling bars is limited. The density in aluminium bars is approximately 0.5 A/mm 2 . The cooling surface is thus 100,000 mm 2  for a 50 kA current, or approximately 300 kg per meter of conductor. Such an installation is thus highly expensive. Such an investment is not very profitable as an installation of this type is used at its maximum potential only very rarely, when the electrolysis vessel is short-circuited.  
         [0026]    The device according to the invention thus allows the costs related to manufacturing and installing the cooling system of the electric circuit to be significantly lowered. By using a cooling tube representing a significant portion of the electric circuit, its size can be significantly reduced as well. Furthermore, it allows an electrolysis vessel to be short-circuited easily. Finally, this device especially enables the energy produced to by recycled by the high intensity electric circuit in order to supply an electrolysis vessel and to particularly maintain the solution of the electrolysis vessel at a desired temperature, thus avoiding the crystallisation of the electrolyte contained in the solution.