Patent Publication Number: US-2011061833-A1

Title: Stationary engine coolant circuit

Description:
TECHNICAL FIELD 
     The present invention relates to a coolant circuit for a stationary engine having a waste heat recovery device such as might be employed in a GHP (gas heat pump) or a cogeneration system. 
     BACKGROUND ART 
     Disclosed conventionally as a coolant circuit for a stationary engine having a waste heat recovery device, in the context of an engine coolant circuit having a waste heat recovery device, is a constitution in which a coolant pump suction region communicates with a region vented to atmosphere (see, for example, Patent Reference No. 1). 
     That is, the engine coolant circuit described in Patent Reference No. 1 is equipped with a waste heat recovery device constituted such that a radiator is in contact with an outdoor heat exchanger. Moreover, the inlet region side of the coolant pump is connected to a reserve tank, and the coolant pump suction port communicates with atmosphere by way of a vent hole provided at the reserve tank. 
     PRIOR ART REFERENCES 
     Patent References 
     PATENT REFERENCE NO. 1: Japanese Patent Application Publication Kokai No. H09-88602 (1997) 
     SUMMARY OF INVENTION 
     Problem to be Solved by Invention 
     With the constitution of the engine coolant circuit of the aforementioned Patent Reference No. 1, pressure at the coolant pump suction region will be more or less equal to head pressure at the reserve tank, and so long as the coolant pump is not arranged at a location higher than the reserve tank, it will not be possible to set the pressure at the pump suction region so as to be the same or less than the head pressure. 
     However, an engine coolant circuit having a waste heat recovery device is equipped with an exhaust gas heat exchanger for causing engine heat to be absorbed by engine coolant from exhaust gases prior to supply of engine waste heat by way of engine coolant at the waste heat recovery device. Because it heats engine coolant, there is a possibility that such an exhaust gas heat exchanger might be treated as a type of boiler. Where the exhaust gas heat exchanger is thus treated as a boiler, there will be a desire to keep the pressure of that engine coolant as low as possible. 
     The present application therefore addresses the problem of making it possible, in the context of an engine coolant circuit having a waste heat recovery device, to adjust pressure as required at a coolant pump suction region, which is where pressure in the circuit is lowest, so as to be any desired pressure that is the same or less than head pressure, for the purpose of setting pressure within the coolant circuit of an exhaust gas heat exchanger or the like so as to be a prescribed pressure. 
     Means for Solving Problem 
     The present invention, being conceived in order to solve the aforesaid problem, is a stationary engine coolant circuit having a waste heat recovery device that supplies engine waste heat by way of engine coolant; a radiator that dissipates engine waste heat by way of engine coolant; an exhaust gas heat exchanger that supplies engine waste heat from exhaust gas to engine coolant; and a coolant pump that causes engine coolant to circulate, the constitution being such that a coolant pump suction region is made to communicate with a region vented to atmosphere; a location upstream with respect to the pressure drop equipment is made to communicate with the region vented to atmosphere; a restrictor is arranged in a communication passage between the region vented to atmosphere and the location upstream with respect to the pressure drop equipment; and the region vented to atmosphere is capable of being kept in communication with atmosphere. 
     In such present invention, the pressure drop from the pressure drop equipment makes it possible to cause pressure at the coolant pump suction region to be lower than head pressure. Furthermore, by adjusting flow rate at the restrictor in the passage communicating with the region vented to atmosphere, it is possible to adjust pressure so as to be any desired pressure within a range from a negative pressure below atmospheric pressure to the head pressure at the region vented to atmosphere. This being the case, it is possible to set pressure within the coolant circuit to be a prescribed pressure while maintaining engine coolant flow rate so as to be equal to (pump suction region pressure+pump discharge pressure+pressure drop to measurement location). 
     The exhaust gas heat exchanger in the aforesaid present invention is arranged at a location that is at a discharge side of the coolant pump and that is downstream with respect to the engine. In such present invention, it is possible to cause pressure at the inlet port of the exhaust gas heat exchanger to be (pump suction region pressure+pump discharge pressure+pressure drop across flow passages within engine), this being lower than (pump suction region pressure+pump discharge pressure) by an amount corresponding to (pressure drop across flow passages within engine). 
     In the aforesaid present invention, a motor-driven three-way valve having an adjustable opening is arranged at a region where a radiator downstream passage and a waste heat recovery device downstream passage meet. In such present invention, because a motor-driven three-way valve is arranged at a location in the engine coolant circuit at which coolant temperature is lowest, heat resistance of the motor-driven three-way valve is improved. Note that the motor-driven three-way valve corresponds to one example of the aforesaid pressure drop equipment. 
     In the aforesaid present invention, a thermostat is arranged at a discharge side of the coolant pump; the waste heat recovery device is arranged at a passage on a high-temperature side of said thermostat; and a radiator is arranged at a location downstream with respect to the waste heat recovery device. In such present invention, when engine coolant temperature is at or above the thermostat setpoint temperature, all coolant flow will be directed to the waste heat recovery device. This being the case, when calculating the amount of heat supplied from the engine coolant, as compared with a constitution in which there is control of divided flow with respect to the waste heat recovery device and the radiator, calculation is simplified to the extent that there is no need to take engine coolant flow ratio into account. 
     In the aforesaid present invention, the region vented to atmosphere is constituted such that a vent pipe is provided at an upper region of a coolant tank, the coolant pump suction region and at least one of either the exhaust gas heat exchanger or the radiator being made to communicate with a watersealed region of the coolant tank. In such present invention, because a location in the coolant circuit at which there is high probability of air pocket formation is vented to atmosphere by way of a watersealed region, it is possible to definitively carry out gas-liquid separation on bubbles so that only engine coolant is returned to the circuit. 
     In the aforesaid present invention, the constitution is such that two of the coolant tanks are provided; the vent pipe being provided at one of the tanks; and further, an air pocket region at one of the tanks being made to communicate with an air pocket region at the other tank; the coolant pump suction region and at least one of either the exhaust gas heat exchanger or the radiator being made to communicate with a watersealed region at the other tank; a watersealed region at one of the tanks being made to communicate with a watersealed region at the other tank; and a bottom of the tank provided with the vent pipe being arranged at the same height or elevation as a bottom of the other tank. In such present invention, because a constitution is adopted in which two tanks are provided, it is possible to divide these in terms of function such that one serves as reserve tank while the other serves to allow gas-liquid separation of high-temperature bubbles that rise up from within the circuit, permitting prevention of elevated reserve coolant temperature as a result of gas-liquid separation. 
     BENEFIT OF INVENTION 
     In the present invention, because the pressure drop from the pressure drop equipment and adjustment of the opening at the restrictor make it possible to adjust the pressure at the coolant pump suction region so as to be any desired pressure that is the same or less than head pressure, this can be set as required so as to be the same or lower than atmospheric pressure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a circuit diagram showing an engine coolant circuit in a cogeneration apparatus associated with one embodiment of the present invention. 
         FIG. 2  is a front perspective view showing the entirety of same cogeneration apparatus. 
         FIG. 3  is a rear perspective view showing the entirety of same cogeneration apparatus. 
         FIG. 4  is a schematic drawing of a coolant tank. 
     
    
    
     EMBODIMENTS FOR CARRYING OUT INVENTION 
     Below, embodiments of the present invention are described with reference to the drawings. 
     In the present embodiment, description is carried out in terms of a situation in which the present invention is applied to a cogeneration apparatus  1 . Note that cogeneration apparatus  1  refers to a system, where a commercial electric power subsystem of an external commercial power supply and an electric power generation subsystem of an electric generator are connected to an electric power delivery subsystem that delivers electric power to electric power consuming equipment (load), that meets the electric power demand of said load, that recovers waste heat generated in accompaniment to electric power generation, and that utilizes said recovered heat. 
       FIG. 1  shows a circuit diagram of an engine coolant circuit in the cogeneration apparatus,  FIG. 2  shows a front perspective view of same apparatus, and  FIG. 3  shows a rear perspective view of same apparatus. 
     As shown in  FIG. 2  and  FIG. 3 , cogeneration apparatus  1  associated with the present embodiment is equipped with shell  2  serving as enclosure. The interior of this shell  2  is divided vertically into two regions, the lower region comprising engine chamber  3  and equipment housing chamber  5 , and the upper region comprising radiator chamber  7 , intake chamber  8 , and exhaust chamber  9 . 
     Arranged within the aforesaid engine chamber  3  there are an engine  10 , an electric generator  11  driven by this engine  10 , and an oil tank  12  storing lubricating oil. 
     The aforesaid equipment housing chamber  5  is arranged to the side (right side as shown in  FIG. 2 ) of engine chamber  3 . Arranged within equipment housing chamber  5  there are an inverter  14  and a control box  17  equipped with a control apparatus  16  for controlling engine drive equipment and so forth. 
     The aforesaid radiator chamber  7  is arranged above equipment housing chamber  5 , radiator  18  and coolant tank  20  being arranged within this radiator chamber  7 . Heat-dissipating radiator fan  19 , driving of which is controlled by the aforesaid control apparatus  16 , is arranged above radiator chamber  7 . 
     Respectively arranged at intake chamber  8  are air cleaner  22  and intake silencer  23 . Arranged at exhaust chamber  9  is exhaust silencer  24 . 
     Next, referring to  FIG. 1 , the engine coolant circuit will be described. This engine coolant circuit  30  is equipped with coolant pump  32 , which is the drive source for causing circulation of engine coolant. Connected in order as one proceeds downstream from the discharge side (coolant pump discharge region  32   a ) of this coolant pump  32  there are coolant passages (water jacket) internal to engine  10 , exhaust gas heat exchanger  33 , and thermostat  35 . 
     Engine  10  might be a stationary gas engine using municipal gas or the like as fuel, the exhaust system thereof being equipped with the aforesaid exhaust gas heat exchanger  33  and the aforementioned exhaust silencer  24 . Furthermore, engine coolant passing through engine  10  is sent to exhaust gas heat exchanger  33 , and after heat from exhaust gas is removed therefrom at exhaust gas heat exchanger  33 , is made to flow into thermostat  35  by way of passage  31 . 
     Thermostat  35  is equipped with passage  35   a  on the low-temperature side thereof and passage  35   b  on the high-temperature side thereof, the downstream end of low-temperature passage  35   a  being connected to the inlet side (coolant pump suction region  32   b ) of coolant pump  32 . Furthermore, the downstream end of high-temperature passage  35   b  is connected to liquid-liquid heat exchanger  37  serving as waste heat recovery device. 
     Thermostat  35  is such that when temperature of engine coolant is below a prescribed temperature (e.g., when the engine is first started), engine coolant is made to flow to low-temperature passage  35   a ; and such that when engine coolant reaches a temperature that is at or above a prescribed temperature, engine coolant is made to flow to high-temperature passage  35   b  and liquid-liquid heat exchanger  37 . 
     Liquid-liquid heat exchanger  37  supplies heat removed from engine coolant to the exterior, supplying heat to water flowing in the secondary-water side  38  of a hot water supply, for example. Respectively provided at locations upstream and downstream from liquid-liquid heat exchanger  37  are temperature sensors  43 ,  44  for detecting temperature of engine coolant. 
     Engine coolant that has passed through liquid-liquid heat exchanger  37  is made to flow to radiator  18  and motor-driven three-way valve  34 . That is, motor-driven three-way valve  34  comprises a motor valve controlled by the aforesaid control apparatus  16 , and has three ports, these being first coolant inlet  34   a , second coolant inlet  34   b , and coolant outlet  34   c.    
     Furthermore, connected to first coolant inlet  34   a  is the downstream end of waste heat recovery device downstream passage  39 , which extends from liquid-liquid heat exchanger  37 . Moreover, connected to second coolant inlet  34   b  is the downstream end of radiator downstream passage  40 , which extends from radiator  18 . Accordingly, motor-driven three-way valve  34  is arranged at a region where waste heat recovery device downstream passage  39  and radiator downstream passage  40  meet. Note that waste heat recovery device downstream passage  39  is connected by way of passage  42  to radiator  18 . 
     Furthermore, coolant outlet  34   c  is connected by way of coolant supply pipe  41  to the aforesaid low-temperature passage  35   a.    
     Motor-driven three-way valve  34  is such that the ratio between the degree to which first coolant inlet  34   a  and second coolant inlet  34   b  are opened is capable of being changed (adjustment of opening), the opening ratio being determined in correspondence to the amount of heat exchange occurring at liquid-liquid heat exchanger  37 . Specifically, when the amount of heat exchange occurring at liquid-liquid heat exchanger  37  is large, i.e., when the amount of heat being dissipated by engine coolant is large, the degree to which first coolant inlet  34   a  is opened will be large; and when the amount of heat exchange occurring at liquid-liquid heat exchanger  37  is small, i.e., when the amount of heat being dissipated by engine coolant is small, the degree to which second coolant inlet  34   b  is opened will be large. 
     The aforesaid coolant tank  20  comprises two tanks, one tank (reserve tank)  20   a  being made of synthetic resin, and the other tank (gas-liquid separation tank)  20   b  being made of metal. Connected to the one tank  20   a  is a vent pipe  48  that is capable of being kept in communication with atmosphere. The bottom of the coolant at the one tank that is provided with vent pipe  48  is arranged at the same height or elevation as the bottom of the other tank, and moreover, respective air pocket regions at the one tank  20   a  and the other tank  20   b  are made to communicate by means of communication pipe  46 . Furthermore, watersealed regions of the two tanks  20   a ,  20   b  (the portions thereof at which engine coolant is stored) are made to communicate by way of communication pipe  47  which extends to the respective lower portions of the tanks. 
     The lower portion of the other tank  20   b  is connected by way of communication pipe  45  to the upper portion  18   a  of radiator  18 . Furthermore, communication pipe  49  is connected between the lower portion of the other tank  20   b  and plumbing (not shown), through which engine coolant flows, within exhaust gas heat exchanger  33 . Radiator  18  and exhaust gas heat exchanger  33  are arranged at elevation(s) higher than engine  10 , the reason being that they are locations within the coolant circuit that are susceptible to formation of air pockets. By thus providing an air purge circuit leading to a gas-liquid separation tank at location(s) where there is danger of air pocket formation, this allows gas-liquid separation to be carried out so that only engine coolant is returned for intake by coolant pump  32 . 
     Moreover, restrictors  60  and  61  are provided so as to prevent excessive flow of engine coolant to communication pipes  45  and  49  and so as to adjust pressure at the inlet side of coolant pump  32  to any desired pressure that is the same or less than head pressure. 
     However, if it should become necessary to drastically reduce pressure at coolant pump suction region  32   b , the diameters of restrictors  61 ,  60  may be increased, or the restrictors might be removed from communication pipes  45 ,  49  and a restrictor  51  might be provided at communication passage  50 , so as to allow pressure within the circuit to be adjusted to a lower value. 
     Cogeneration apparatus  1  of the present embodiment having the foregoing constitution, operation with respect to circulation in the coolant circuit will next be described. 
     Upon causing coolant pump  32  to operate, engine coolant discharged from coolant pump  32  is supplied to engine  10 , its temperature becoming elevated as it cools cylinders and various other locations while passing through the interior of engine  10 , and it moreover passes through exhaust gas heat exchanger  33  to arrive at thermostat  35 . At thermostat  35 , when coolant temperature is below a prescribed temperature, engine coolant is returned to coolant pump  32 . 
     Furthermore, when engine coolant reaches a temperature that is at or above a prescribed temperature, thermostat  35  causes engine coolant to flow to liquid-liquid heat exchanger  37 . Here, in the event that there is desire for supply of hot water, at liquid-liquid heat exchanger  37 , heat from engine coolant is extracted to the exterior as it is used to heat water flowing in the secondary-water side  38  of a hot water supply. Furthermore, the amount of engine coolant flowing to radiator  18  is adjusted in correspondence to the amount of heat exchange occurring at liquid-liquid heat exchanger  37 . When the amount of heat exchange is large, the degree to which first coolant inlet  34   a  of motor-driven three-way valve  34  is opened is greater than the degree to which second coolant inlet  34   b  thereof is opened, and the amount of coolant flowing through waste heat recovery device downstream passage  39  and bypassing radiator  18  is large. 
     When the amount of heat exchange is small, the degree to which second coolant inlet  34   b  of motor-driven three-way valve  34  is opened is greater than the degree to which second coolant inlet  34   a  thereof is opened, and the amount of coolant flowing to radiator  18  is large. 
     Furthermore, the passage which goes from coolant pump suction region  32   b , through communication passage  50  and coolant tank  20 , to vent pipe  48  constitutes a line vented to atmosphere; and because both the communication pipe  49  from exhaust gas heat exchanger  33  and the communication pipe  45  from radiator  18 , at which the pressure within the coolant circuit is higher than at coolant pump suction region  32   b , go through restrictors  61 ,  60  before meeting at coolant tank  20 , it is possible to cause the pressure at coolant pump suction region  32   b  to be the same or less than head pressure. 
     Furthermore, by providing exhaust gas heat exchanger  33  downstream with respect to engine  10 , this makes it possible to reduce the pressure drop by an amount corresponding to the contribution from engine  10  and thus reduce the pressure acting at exhaust gas heat exchanger  33 . 
     By providing motor-driven three-way valve  34  at the suction location of the pump, which is the location within the coolant circuit where temperature is lowest, reliability with respect to the part(s) employed for motor-driven three-way valve  34  is improved. Moreover, with improved reliability it becomes possible to use motor-driven three-way valve  34  over a long period and achieve cost reduction. 
     When engine coolant temperature increases and the state of thermostat  35  becomes such that the high-temperature side thereof is opened, because all flow constantly goes through liquid-liquid heat exchanger  37 , it will be possible to calculate the amount of heat exchange occurring at liquid-liquid heat exchanger  37  by detecting the change in water temperature at temperature sensor  43  at the inlet side of liquid-liquid heat exchanger  37  versus temperature sensor  44  at the outlet side thereof. This being the case, as compared with the situation in which radiator  18  and liquid-liquid heat exchanger  37  are arranged in paralleled fashion, because computation of the amount of heat exchange no longer requires a flowmeter at the passage leading to liquid-liquid heat exchanger  37 , cost reduction is made possible. Alternatively, as compared with use of the ratio of opening relative to liquid-liquid heat exchanger  37  at motor-driven three-way valve  34  to calculate flow rate to liquid-liquid heat exchanger  37 , computational load is reduced. 
     Also, an air purge circuit leading to a gas-liquid separation tank is provided at location(s) where there is danger of air pocket formation, such as at exhaust gas heat exchanger  33  and radiator  18 . This being the case, bubbles mixed with engine coolant at exhaust gas heat exchanger  33  and radiator  18  are, as shown at  FIG. 4 , made to pass through communication pipe  49  and communication pipe  45 , to flow into the other tank  20   b . Moreover, only air passes through communication pipe  46  and enters the one tank  20   a , the air traveling through vent pipe  48  to be discharged to atmosphere. Thus, because the constitution is such that gas-liquid separation is carried out, with only engine coolant being returned to the circuit interior, it is possible to reduce the size of radiator  18 , and it is also possible to prevent cavitation at coolant pump  32 . Note that engine coolant within the one tank  20   a  moves as appropriate to the interior of the other tank  20   b  by way of communication pipe  47 . 
     By carrying out gas-liquid separation of high-temperature bubbles at the other tank (gas-liquid separation tank)  20   b , which is different from the one tank (reserve tank)  20   a , it is possible to prevent increase in water temperature at the reserve tank. In addition, because increase in water temperature is prevented thereat, the reserve tank may be manufactured easily and cheaply from synthetic resin. 
     The present invention is not limited to the foregoing embodiment. For example, as indicated by the imaginary line at  FIG. 1 , it is possible for the bottom of the coolant at the one tank that is provided with vent pipe  48  to be arranged so as to be at higher elevation than the bottom of the other tank. In such case, it will be possible to more easily cause engine coolant within the one tank  20   a  to move to the interior of the other tank  20   b  by way of communication pipe  47 . 
     Furthermore, it is also possible to employ the present invention in an engine-driven heat pump. The present invention may be embodied in a wide variety of forms other than those presented herein without departing from the spirit or essential characteristics thereof. The foregoing embodiments and working examples, therefore, are in all respects merely illustrative and are not to be construed in limiting fashion. The scope of the present invention being as indicated by the claims, it is not to be constrained in any way whatsoever by the body of the specification. All modifications and changes within the range of equivalents of the claims are, moreover, within the scope of the present invention. 
     Moreover, this application claims priority based on Patent Application No. 2008-121521 filed in Japan on 7 May 2008. The content thereof is hereby incorporated in the present application by reference. 
     POTENTIAL INDUSTRIAL USE 
     The stationary engine coolant circuit associated with the present invention is effective as a coolant circuit for a stationary engine having a waste heat recovery device, and is particularly suited to use in a GHP (gas heat pump) or a cogeneration system. 
     EXPLANATION OF REFERENCE NUMERALS 
     
         
           1  Cogeneration apparatus 
           2  Shell 
           10  Engine 
           18  Radiator 
           20  Coolant tank 
           20   a  The one tank 
           20   b  The other tank 
           30  Engine coolant circuit 
           32  Coolant pump 
           32   a  Coolant pump discharge region 
           32   b  Coolant pump suction region 
           33  Exhaust gas heat exchanger 
           34  Motor-driven three-way valve 
           35  Thermostat 
           37  Liquid-liquid heat exchanger (waste heat recovery device) 
           39  Waste heat recovery device downstream passage 
           40  Radiator downstream passage 
           41  Coolant supply pipe 
           42  Passage 
           43  Temperature sensor 
           44  Temperature sensor 
           45  Communication pipe 
           46  Communication pipe 
           47  Communication pipe 
           48  Vent pipe 
           49  Communication pipe 
           50  Communication passage 
           51  Restrictor 
           60  Restrictor 
           61  Restrictor