Abstract:
A flush and fill process is used to ready a fuel cell cooling circuit for initial use. An external flushing system relasably connected to the cooling circuit circulates flushing coolant through the cooling circuit to remove contaminants from the wetted surfaces of the cooling circuit before the fuel cell is put into use. The flushing system includes a pump for circulating the flushing coolant through the cooling circuit, filters for removing contaminants from the coolant and a heater for elevating the temperature of the coolant. Following the flushing process to remove contaminants, the flushing system is disconnected from the cooling circuit and the cooling circuit is filled with fresh coolant.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention broadly relates to cooling circuits used in fuel cells, and deals more particularly with a method and apparatus for cleansing and filling the cooling circuit for initial use.  
       BACKGROUND OF THE INVENTION  
       [0002]     Fuel cells are electro-chemical energy conversion devices that generate electricity and heat by converting the chemical energy of fuels, such as hydrogen and oxygen. A single fuel cell normally consists of an electrolyte sandwiched between two thin electrodes, a porous anode and a cathode. While a variety of differing fuel cell types have been developed, all operate on essentially the same principles. The fuel cell reaction produces heat which must be extracted from the fuel cell in order to maintain optimum operating efficiency. Sophisticated cooling and temperature control circuits have been developed for fuel cells which closely control operating temperatures. These cooling circuits typically include channelized plates or passageways within the fuel cell through which a coolant such as de-ionized water may flow to carry heat away from the fuel cell to a heat exchanger or other device for dissipating the heat.  
         [0003]     In the case of fuel cells used to power vehicles such as an automobile, the cooling circuit is located on-board the vehicle and may include a variety of subsystems such as filters and temperature controllers for conditioning the coolant. The condition of the coolant, and particularly its purity, affect the efficiency of the coolant to conduct heat away from the fuel cell. Ideally, the coolant should not contain particulate contaminants greater than a very small size and should have near zero electrical conductivity. As a practical matter however, the coolant picks up small particulates contaminants and conductive ions as it flows through the cooling circuit. Various types of on-board particulate filters and de-ionization filters have been devised to remove these contaminants, however these devices are often limited in their ability to remove contaminants, and in any event must be periodically serviced or replaced due to contaminate buildup. Part of the inefficiency of prior filters and rapid contaminate buildup is due to the fact that a certain amount of the contaminants is present on the wetted surfaces of the component parts of the cooling system at the time of their installation and assembly. Consequently, on initial start-up of the fuel cell, the coolant flowing through the cooling circuit carries these initial contaminants away, resulting in an immediate buildup of contaminates in the filters, in turn reducing the overall efficiency of the cooling circuit.  
         [0004]     It would therefore be desirable to reduce the level of contaminants present in the cooling circuit before it is filled with coolant and put into use. The present invention is directed towards satisfying this need.  
       SUMMARY OF THE INVENTION  
       [0005]     A method is provided for readying a fuel cell cooling circuit for use, comprising flushing the cooling circuit to remove contaminants from the wetted surfaces of the cooling circuit, and then filling the cooling circuit with a volume of fresh coolant. The cooling circuit is flushed using an external flushing system which is removal removably connected to the cooling circuit at the time the fuel cell is being readied for its initial use. The flushing system includes a supply of coolant, filters for removing contaminants from the coolant and a series of valves for controlling the flow of coolant between the flushing system and the cooling circuit. Particulate contaminants and conductivity increasing ions present within the component parts of the cooling circuit are carried away by the flushing coolant to filters forming part of the flushing system where they are filtered out of the flushing coolant. The temperature and pressure of the flushing coolant is regulated to enhance contaminant removal and protect fuel cell components against excessive pressure. The cooling circuit is flushed for a pre-selected time period, following which all coolant is removed from the cooling circuit and the flushing system is disconnected from the cooling circuit. After the flushing coolant is removed from the cooling circuit, fresh coolant is introduced into the cooling circuit to ready the fuel cell for use.  
         [0006]     Apparatus is provided for cleansing a fuel cell cooling circuit, comprising a flushing system removably connected to the cooling circuit for flushing the cooling circuit of contaminants. The flushing system includes a supply of flushing coolant, a filtering system for removing contaminants from the flushing coolant, and a pump for circulating a volume of coolant between the cooling circuit and the flushing system. The filtering system desirably includes both particulate filters and a de-ionization filter. The flushing system further includes a pressure regulator for regulating the pressure of the coolant circulated from the flushing system to the cooling circuit, and optionally also includes a heater for heating the coolant to a temperature that is sufficient to promote the removal of contaminants from component parts of the cooling circuit. The flushing system also includes a series of shut-off valves which may be controlled manually or automatically to control the flow of flushing coolant between the flushing system and the cooling circuit.  
         [0007]     The invention advantageously reduces the level of contaminants present in the cooling circuit when the fuel cell is initially put into service, thereby increasing fuel cell efficiency and fuel cell temperature control.  
         [0008]     Another advantage of the invention is that the contaminant filters forming part of the cooling circuit are not used to filter out contaminants that are present in the coolant upon start-up of the fuel cell, consequently, the filters are capable of operating with greater efficiency and longer service life.  
         [0009]     A further advantage of the invention is that larger contaminating particles present in the coolant circuit at the time of manufacture are flushed from the cooling circuit before the start-up of the fuel cell.  
         [0010]     These, and other advantages of the invention will be made clear or will become apparent during the course of the following description of a preferred embodiment of the present invention. In the course of this description, reference will frequently be made to the attached drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a combined schematic and diagrammatic view of a flushing system connected to a cooling circuit for a fuel cell, according to the preferred embodiment of the invention;  
         [0012]      FIG. 2  is a block diagram of a control system for the flushing system shown in  FIG. 1 ; and  
         [0013]      FIGS. 3   a  and  3   b  taken together, form a flow chart of the steps used to carry out the method for readying a fuel cell according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]     Referring first to  FIG. 1 , a vehicle  10  includes an on-board fuel cell system  12 , including a fuel cell  14  which generates electrical power used to drive the vehicle  10  or operate auxiliary electrical systems on-board the vehicle  10 . The fuel cell  14  may be of any of various types which convert fuels such as hydrogen and oxygen into electricity through electro-chemical conversion. A by-product of the conversion process is heat generated within the fuel cell  14  which must be dissipated or carried away from the fuel cell  14 . Accordingly, the fuel cell system  12  includes a cooling circuit which typically will include heat exchangers (not shown), coolant carrying lines, valves and other control devices for controlling the flow of a coolant, such as de-ionized water through the cooling circuit in order to carry heat away from the fuel cell  14 . Such on-board circuits typically include a particulate filter  16  for filtering contaminants from a coolant, and a de-ionization filter  18  for removing conductivity increasing ions from the coolant.  
         [0015]     In accordance with the present invention a flushing system is provided external to the vehicle  10  which is removably connected to the cooling circuit by releasable coolant line connections (not shown) located at points on the vehicle  10 , designated by the letters “A” and “B”.  
         [0016]     The flushing system broadly includes a coolant storage tank  30 , pump  46 , particle filter tank  40 , de-ionization filter  26 , coolant heater  28  and a series of later discussed valves which control flow of coolant between the flushing system and the on-board cooling circuit. The fluid connections coupling the flushing system to the cooling circuit at points “A” and “B” are of preferably of the quick-release type which is well known in the art.  
         [0017]     The coolant storage tank  30  is filled with a fixed volume of a suitable coolant such as de-ionized water. Pump  46  draws the coolant from the tank  30  into the particle filter tank  40 . The flow rate into the filter tank  40  is controlled by a shut-off valve  44 . The filter tank  40  is pressurized, and a pressure gage  42  is provided to indicate the pressure of the coolant in the tank  40 , and therefore the flushing system lines. The filter tank  40  is connected to the coolant storage tank  30  through a shut-off valve  48  which, when in the open position, allows any remaining coolant in filter tank  40  to flow back into storage tank  30 . The pump  46  together with the filter tank  40  and shut-off valve  44 ,  48  form a flushing machine  24 .  
         [0018]     Coolant present in filter tank  40  is delivered under pressure through line  56  through a shut-off valve  38  to both a by-pass line  50  and another shut-off valve  36  immediately upstream of the de-ionization filter  26 . The by-pass line  50  allows a desired amount of the coolant to by-pass the de-ionization filter, as determined by the opening position of shut-off valves  36  and  38 . Valve  36  specifically limits the flow through the filter  26  so that the capacity of this filter to remove and process the coolant is not exceeded. Coolant exiting the filter  26  is delivered by line  58  through a three-way valve  34  to an optional coolant heater  28 . As will become apparent later, the three-way valve may be actuated at the end of the flushing cycle to allow coolant present in line  58  to flow back into the storage tank  30 . During the flushing cycle, however, valve  34  is switched to a position that forces all flow of coolant in line  58  to be delivered to the coolant heater  28 .  
         [0019]     Although satisfactory results may be realized when the flushing coolant is at ambient temperature, it has been found that superior results may be achieved if the coolant is heated to a temperature sufficient to oromote the removal of contaminants from the wetted surfaces of the components that make up the cooling circuit. Superior contaminant removal has been achieved when the coolant is heated to a temperature of approximately 80° C. A temperature gage  32  and related temperature sensor (not shown) are provided at the exit of the coolant heater in order to sense and indicate the temperature of the coolant exiting the heater  28 . The heated coolant is delivered by flushing line  60  to a connection at “A” which feeds into an on-board particulate filter  16 . Although some contaminants may be filtered out by the filter  16 , most of the particulates have been previously filtered in the filter tank  40 . The flushing coolant passes from the particulate filter  16  through the heat exchanging passageways in the fuel cell  14  and are carried away from the fuel cell by cooling circuit line  62 .  
         [0020]     Normally, the coolant exiting the fuel cell  14  in line  62  is delivered to the on-board de-ionization filter  18 . However, in accordance with the present invention, a pair of shut off valves  20 ,  22  are provided which block the flow of coolant to the filter  18 , and instead, re-route the flow so as to by-pass the filter  18  and deliver the coolant back through the flushing system line  65  to the storage tank  30 .  
         [0021]     When the flushing system is initially connected to the on-board cooling circuit at points “A” and “B”, the cooling circuit is empty of coolant and is ready for a flushing cycle. A fixed quantity of the flushing coolant is stored in tank  30 . The shuttle valve  44  is adjusted between its fully open and fully closed positions to regulate the pressure in the system to keep it below the safe limits that can be tolerated by the fuel cell  14 . Initially, shut-off valve  38  is closed to allow the filter tank  44  to be filled with coolant drawn from the storage tank  30 . Once filled, shut-off valve  38  is opened and coolant flows both through shut-off valve  36  to the filter  26  and through the by-pass line  50 . Shut-off valve  36  regulates the amount of coolant which flows through the filter  26 . The on-board particulate filter  16  removes any particles that may have entered the coolant between the time it flows from the filter tank  40  to the vehicle  10 .  
         [0022]     Although the flushing system described above may be operated manually, it may be desirable in some applications to use a partially or fully automated control system. In this respect, attention is now directed also to  FIG. 2  which shows a controller  64  for operating the flushing system. The controller  64  may be a conventional, programmable logic controller (PLC) operating under programmed instructions to carry out the various control functions in accordance with real-time information supplied to the controller  64 . The controller  64  delivers output control signals to operate the coolant heater  28 , pump  46  and the various, previously described shut-off valves which, for sake of simplicity, are collectively shown in  FIG. 2  as a valve system  72 . The controller  64  receives real time data from a pressure sensor  66 , storage tank level sensor  68 , flow sensor  69 , coolant quality sensor  71  and temperature sensor  70 .  
         [0023]     The pressure sensor  66 , as previously mentioned, senses the pressure within the filter tank  40  which is also displayed on the pressure gauge  42 . A conventional level sensor  68  may be provided in the storage tank  32  to verify that the correct amount of coolant is present in the tank  30  before the flushing cycle commences and to verify that the proper flow rates are being achieved, as determined by the rate of coolant returned to the tank  30  and via line  65 . Although not shown in  FIG. 1 , one or more flow sensors  69  may be incorporated into various flushing system and cooling circuit lines to measure flow rates. One or more coolant quality sensors  71  may be provided to determine certain characteristics of the coolant indicating its purity or quality. One such device would be a conductivity sensor for determining the level of conductivity increasing ions present in the coolant. The various components forming the control system shown in  FIG. 2  are conventional, commercially available items, consequently their details need not be described here.  
         [0024]     Reference is also now made to  FIGS. 3   a  and  3   b  which, taken together, depict success steps used in carrying out the inventive method by which the fuel cell coolant circuit  12  is readied for use. The method starts at step  74  with a fixed volume of flushing coolant present in the storage tank  30 . The flushing system is connected to the cooling circuit at step  76 . This involves connecting the cooling carrying lines of the flushing system to quick release couplings on-board the vehicle, at points “A” and “B”, as previously described. Next, shut-off valves  20  and  22  are closed at step  78 , thereby causing the flushing coolant flowing out of the fuel cell  14  on line  62  to bypass the filter  18 . Next, at step  80 , shut-off valve  38  is closed and shut off valve  44  is partially opened. Then, at step  82 , pump  46  is activated, causing coolant in tank  32  to flow through lines  52  and  54  into the filter tank. This filling procedure is continued until the tank is full at step  84 , following which shut off valve  38  is opened at step  86 .  
         [0025]     At step  88 , the shuttle valve  44  is opened slightly further to increase the flow of coolant entering the tank  40 , until coolant within the tank  40  is within desired pressure levels indicated at  90 . If the pressure is above or below the desired limits, shut-off valve  44  is adjusted as required, at step  92 . Once the desired pressure within the tank is achieved, shut-off valve  36  is adjusted to achieve a desired flow rate through the deionization filter  26 . Because the de-ionization filter  26  represents a flow constriction that creates fluid back pressure, there is a limit to the amount of coolant that may be passed through the filter  26 . In step  96 , the level of coolant in the storage tank  30  is assessed, and when it is determined that sufficient coolant is returning to the tank  30  (via line  65 ) as evidenced by the fluid level in the tank, the coolant heater  28  is activated at step  102 . In the event that insufficient coolant is being returned to the tank  30 , the shut-off valve  36  is adjusted to increase the flow, at step  100 .  
         [0026]     At step  104 , a previously described temperature sensor  70  determines whether the temperature of the coolant has been elevated to a desired level, for example 80° C. If the temperature is out of range, the heater  28  is adjusted at step  106 , otherwise a determination is made at  108  of whether the flow of flushing coolant through the flushing system and the coolant circuit has stabilized, i.e. proper coolant temperature, pressure and flow rates. If the flushing system does not stabilize, steps are taken to adjust the control parameters at step  110 . Otherwise, at step  112 , the flushing coolant is allowed to circulate from the flushing system to the coolant circuit for a period of time necessary to remove coolant contaminants at a specified level. In one application, it was found that a circulation period of approximately  40  minutes was appropriate, however the exact duration will depend on a variety of factors unique to each specific fuel cell application. The circulation period may be adjusted upwardly of downwardly depending upon real time information gathered by sensors measuring the purity and quality of the coolant, such as the previously mentioned conductivity sensor.  
         [0027]     At the end of the circulation period, the pump  46  is turned off at step  114 , following which the flushing system may be disconnected from the coolant circuit in step  116 . With the flushing system disconnected from the vehicle  10 , all of the flushing coolant present within the flushing system must be removed. Consequently, first, shut-off valve  48  is opened at step  118 , and at step  120  the three-way valve  34  is switched to a position which drains coolant in lines  58  and  60  back into the storage tank  30 . Shut-off valves,  20 ,  22  on-board vehicle  10  are opened, at step  122 , thereby re-connecting filter  18  into the on-board cooling circuit.  
         [0028]     Next, at step  124 , the on-board cooling circuit is filled with fresh coolant, thereby readying the fuel cell system  12  for initial use. At step  126 , all of the coolant present in storage tank  30  is removed and may be subjected to reclamation or re-cycling processes to renew the coolant for future use. A fresh quantity of flushing coolant is then introduced into the tank  30 , thereby readying the flushing system for flushing the next fuel cell system  12 , and completing the last step in the process, as indicated at block  128 .  
         [0029]     From the foregoing, it may be appreciated that the method and apparatus for readying a fuel cell cooling circuit described above not only provide numerous advantages, but do so in a particularly simple and economic manner. It is recognized, of course, that those skilled in the art may make various modifications or additions to the preferred embodiment chosen to illustrate the invention without departing from the spirit and scope of the present contribution to the art. Accordingly, it is to be understood that the protection sought and to be afforded hereby should be deemed to extend to the subject matter claimed and all equivalents thereof fairly within the scope of the invention.