JP2011242039A - Waste heat recovery system and cogeneration system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance efficiency of waste heat recovery and suppress fluctuation of water temperature during waste heat recovery.SOLUTION: This waste heat recovery system includes: a heat exchanger 4 generating hot water by heating water by waste heat of an engine 2; a water supply tank 6 storing the hot water and supplying water to a boiler 5; a circulation pipe line 7 having a going pipe line 7a supplying water within the water supply tank 6 to the heat exchanger 4 and a return pipe line 7b returning hot water generated by the heat exchanger 4 to the water supply tank 6; a branch pipe line 12 interconnecting the going pipe line 7a and the return pipe line 7b in the middle of the pipe lines; a three-way valve 11 diverging hot water within the return pipe line 7b to the water supply tank 6 side and the branch pipe line 12 side; and a controller 14 controlling the three-way valve 11 based on detection output by a water temperature sensor 13 for detecting water temperature on the downstream side from a connection part of the going pipe line 7a with the branch pipe line 12.

Description

  The present invention relates to a waste heat recovery system that recovers waste heat of a heat source such as a prime mover or a fuel cell, and a cogeneration system including the same.

  Conventionally, feed water to the boiler is preheated with high-temperature exhaust gas from the engine, the preheated feed water is flushed to form deaerated water from which dissolved oxygen has been removed, and this deaerated water is further preheated with the exhaust gas and supplied to the boiler Such a waste heat recovery system is known (see, for example, Patent Document 1).

JP 2005-140376 A

  However, in the waste heat recovery system of Patent Document 1 described above, the feed water preheating flow path is arranged in the exhaust gas passage from the engine to preheat the feed water to the boiler with the exhaust gas, so that the water level in the boiler is within a predetermined range. When the boiler is not supplying water, the supply water stays in the feed water preheating flow path, and the recovered waste heat cannot be immediately consumed by the boiler, so the recovered waste heat can be used without waste. However, there is a problem that the utilization efficiency of waste heat is reduced.

  In addition, depending on the combustion state of the boiler burner, such as high combustion or low combustion, or the presence or absence of water supply to the boiler, the amount of heat heated by the exhaust gas in the feed water preheating channel changes, and the water temperature fluctuates. There is also a problem that it ends up.

  This invention is made | formed in view of the above-mentioned subject, Comprising: While improving the recovery efficiency of waste heat, it aims at enabling it to suppress the fluctuation | variation of the water temperature in waste heat recovery.

  In order to achieve the above object, the present invention is configured as follows.

  (1) A waste heat recovery system according to the present invention is a waste heat recovery system that recovers waste heat from a heat source, wherein a heat exchanger that heats water with the waste heat to generate hot water, and water in a tank A forward path that supplies the heat exchanger, a circulation path that includes a return path that returns the hot water generated in the heat exchanger to the tank, a branch path that connects the forward path and the return path in the middle of the path, A diversion unit for diverting the hot water in the return path to the tank side and the branch path side, and a control unit for controlling the diversion of the diversion unit are provided.

  As the heat source, a prime mover such as a gas engine, a diesel engine, or a gas turbine, a fuel cell, or the like can be used.

  The hot water returned to the tank via the return pipe and stored in the tank is preferably used for boiler water supply, hot water supply or heating, for example.

  According to the waste heat recovery system of the present invention, waste heat from a heat source is recovered by a heat exchanger to generate hot water, and the generated hot water can be stored in a tank and used for boiler water supply, hot water supply, etc. When heat is not being supplied or when hot water is not being supplied, waste heat from the heat source can be recovered with a heat exchanger and stored in the tank via the circulation path, increasing the efficiency of waste heat recovery. it can.

  Furthermore, since the diversion means diverts the hot water in the return path from which the waste heat has been recovered by the heat exchanger to the tank side and the branch path side, the hot water diverted to the branch path side To the outgoing route, where it is mixed with the cold water from the tank. Therefore, by controlling the diversion ratio of the diversion means, the temperature of the water supplied to the heat exchanger is controlled by controlling the ratio of mixing the low temperature water from the tank and the high temperature hot water from the branch path in the forward path. Can be adjusted. As a result, even if the temperature of the hot water in the tank fluctuates due to the usage state of the boiler or hot water supply equipment that uses the hot water stored in the tank, for example, the presence or absence of water supply to the boiler, it is supplied to the heat exchanger Fluctuation of the water temperature can be suppressed.

  (2) In a preferred embodiment of the waste heat recovery system of the present invention, the heat source is an engine that drives a generator, and the heat exchanger is at least one of exhaust of the engine and a cooling medium of the engine. And heat exchange between the water supplied from the tank.

  According to this embodiment, while the generator is driven by the engine to generate electricity, the waste heat can be recovered from the exhaust and cooling medium of the engine and stored in the tank, so that the overall efficiency of the cogeneration system can be improved. it can.

  (3) In another preferred embodiment of the waste heat recovery system of the present invention, the waste heat recovery system includes a water temperature sensor that detects a water temperature circulating in the circulation path, and the branching means is a branch between the return path and the branch path. The three-way valve provided in the connecting portion is configured such that the control means controls the flow dividing ratio by the three-way valve based on the detection output of the water temperature sensor.

  The water temperature sensor preferably detects the water temperature downstream from the junction where the low-temperature water from the tank and the high-temperature hot water from the branch path merge in the forward path.

  According to this embodiment, the temperature of the low-temperature hot water supplied to the heat exchanger is controlled to the set temperature by controlling the diversion ratio by the three-way valve so that the water temperature detected by the water temperature sensor becomes the set temperature. be able to.

  (4) In another embodiment of the waste heat recovery system of the present invention, the tank is a water supply tank that supplies water to the boiler, and the water supply tank includes at least a high-temperature tank having a high water temperature and a low-temperature tank having a low water temperature. In addition to having two tanks, the return path and a water supply path for supplying water to the boiler are connected to the high temperature tank, and the forward path is connected to the low temperature tank.

  The boiler may be a standard boiler having a combustion device or a waste heat boiler not having a combustion device.

  The high temperature tank and the low temperature tank are preferably communicated with each other through a communication path so that the water level of each tank can be maintained at the same level.

  A water supply tank may comprise three or more tanks, such as an intermediate temperature tank, in addition to a high temperature tank and a low temperature tank.

  When the water supply tank is composed of a single tank, the hot water returning from the heat exchanger to the water supply tank via the return path is mixed with the low temperature water in the water supply tank to equalize the water temperature. The water temperature supplied from the water supply tank to the heat exchanger via the outgoing path rises, and the waste heat utilization efficiency decreases.

  On the other hand, according to this embodiment, the water supply tank includes a high-temperature tank and a low-temperature tank, and the high-temperature hot water generated by recovering the waste heat of the heat source with the heat exchanger passes through the return path. Hot water from the high-temperature tank is supplied to the boiler via the water supply path, while water having a low water temperature from the low-temperature tank is supplied to the heat exchanger via the forward path and is used as a heat source. It will be heated by the waste heat of, and the utilization efficiency of waste heat will improve.

  (5) In the embodiment of the above (4), the high temperature tank and the low temperature tank are each tank in which the interior of the water supply tank is divided into two by a partition plate erected from the bottom wall of the water supply tank. Each partition is configured, and the partition plate is provided with a communication path communicating the two tanks.

  According to this embodiment, the high-temperature tank and the low-temperature tank can be easily configured by partitioning the water supply tank with the partition plate having the communication path.

  (6) The cogeneration system of the present invention includes the waste heat recovery system of the present invention according to the above (1) to (5), a prime mover such as an engine, and a generator driven by the prime mover. .

  According to the cogeneration system of the present invention, the generator is driven by the prime mover to generate power, while the waste heat of the prime mover can be recovered and stored in the tank, so that the overall efficiency can be improved. Furthermore, the fluctuation | variation of the water temperature supplied to the heat exchanger which collect | recovers waste heat can be suppressed.

  According to the present invention, waste heat from a heat source is recovered by a heat exchanger to generate hot water, and the generated hot water can be stored in a tank and used for boiler water supply or hot water supply, while not supplied to the boiler When the hot water is not supplied, the waste heat from the heat source can be collected by the heat exchanger and stored in the tank via the circulation path, so that the efficiency of waste heat recovery can be improved.

  Furthermore, the temperature of the water supplied to the heat exchanger is controlled by controlling the diversion ratio of the diversion means for diverting the hot water in the return path from which the waste heat has been recovered by the heat exchanger to the tank side and the branch path side. Therefore, the temperature of the water supplied to the heat exchanger varies depending on the state of use of the boiler or hot water supply equipment that uses the hot water stored in the tank, for example, the presence or absence of water supply to the boiler. Can be suppressed.

FIG. 1 is a diagram showing a schematic configuration of a cogeneration system including a waste heat recovery system according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  In FIG. 1, the outline of a structure of a cogeneration system provided with the waste heat recovery system which concerns on embodiment of this invention is shown.

  The cogeneration system is an energy saving system that generates power using fuel and uses waste heat generated at that time. The cogeneration system in this embodiment is a micro cogeneration system with a power generation output of about 300 kW or less, particularly for general households or business customers such as hotels, hospitals, stores, and the like.

  A cogeneration system 1 according to this embodiment includes, as a system main body 24, an engine 2, a generator 3 connected to an output shaft 2a of the engine 2 and driven by the engine 2 to generate AC power, and generated by the engine 2. A heat exchanger 4 that recovers waste heat and generates hot water. The engine 2 is, for example, a gas engine that uses city gas as fuel. The generator 3 is driven by the engine 2 to generate electric power, and the generated electric power is supplied to a load via a grid interconnection inverter (not shown).

  The cogeneration system 1 includes a waste heat recovery system. The waste heat recovery system recovers the waste heat of the engine 2 to generate hot water, and the heat exchanger 4 generates the heat heat. The water supply tank 6 that stores the heated water as supply water to the boiler 5, the circulation pipe (circulation path) 7 that connects the water supply tank 6 and the heat exchanger 4, and water is supplied from the water supply tank 6 to generate steam. A boiler 5.

  In the heat exchanger 4, cooling water flowing through a water cooling jacket (not shown) of the engine 2 is circulated through the pipe lines 8 and 9. That is, the cooling water flowing through the water cooling jacket is heated by the waste heat of the engine 2 to become high-temperature cooling water, supplied to the heat exchanger 4 through the pipe line 8 and radiated by the heat exchanger 4, The engine 2 is cooled again by being supplied to the water cooling jacket through the pipe 9.

  A circulation line 7 that connects the heat exchanger 4 and the water supply tank 6 includes a forward line 7a that is provided with a circulation pump 10 and forms a forward path, and a return pipe that is provided with a three-way valve 11 and forms a return path. And a road 7b. By driving the circulation pump 10 in the outgoing pipe 7a, the low-temperature water from the water supply tank 6 is mixed with the hot hot water from the branch pipe 12 through the outgoing pipe 7a to the heat exchanger 4. The heat is exchanged with the high-temperature cooling water from the water-cooling jacket of the engine 2 in the heat exchanger 4 to increase the temperature, and the increased temperature of the high-temperature hot water passes through the three-way valve 11 in the return line 7b. It is returned to the water supply tank 6. Such warm water circulation is performed at a constant flow rate. Due to the circulation of the hot water, the circulation pump 10 is driven to recover the waste heat of the engine 2 while the engine 2 is being operated.

  Furthermore, in this embodiment, in order to suppress fluctuations in the temperature of hot water supplied from the water supply tank 6 to the heat exchanger 4 via the forward pipe 7a, the following configuration is provided.

  That is, the forward pipeline 7a and the return pipeline 7b of the circulation pipeline 7 are connected by the branch pipeline 12 as described above, and the connection portion of the return pipeline 7b with the branch pipeline 12 is not heated. A three-way valve 11 is provided as a diversion means for diverting hot hot water from the exchanger 4 to the water supply tank 6 side and the branch pipe line 12 side. Further, a water temperature sensor 13 for detecting the temperature of the hot water in the forward pipe 7 a is installed on the downstream side of the connecting part of the forward pipe 7 a with the branch pipe 12. Based on this, a controller 14 is provided as control means for controlling the three-way valve 11.

  The three-way valve 11 mixes the hot water, which is diverted to the outgoing pipe 7a side via the branch pipe 12, with the low-temperature water from the water supply tank 6 to adjust the water temperature, and the water temperature is adjusted. Hot water is supplied to the heat exchanger 4 via the circulation pump 10.

  The controller 14 controls the diversion ratio by the three-way valve 11 so that the temperature of the hot water in the outgoing pipe 7a detected by the water temperature sensor 13 becomes a preset temperature.

  Therefore, according to this embodiment, for example, even if the temperature of the hot water stored in the water supply tank 6 fluctuates depending on the combustion state of the burner of the boiler 5 supplied from the water supply tank 6 or the presence or absence of water supply to the boiler 5, The temperature of the hot water supplied from the water supply tank 6 to the heat exchanger 4 via the outgoing pipe 7a is adjusted to become a set temperature by controlling the diversion ratio of the three-way valve 11, thereby Variations in the temperature of the water supplied to the heat exchanger 4 can be suppressed. The water temperature sensor 13 is provided on the upstream side of the circulation pump 10, but may be provided on the downstream side of the circulation pump 10.

  In this embodiment, as described above, if the circulation flow rate by the circulation pump 10 is constant and the load of the engine 2 is constant, the temperature of the engine 2 is raised by the heat exchanger 4, and the water supply tank 6 is connected via the return line 7b. The temperature of the high-temperature hot water that returns to is, for example, 75 ° C. to 85 ° C., and the temperature of the low-temperature water taken out from the water supply tank 6 to the outgoing pipe 7a is, for example, 2 to 30 ° C. And hot hot water divided by the three-way valve 11 are mixed, adjusted to a set temperature of, for example, 70 ° C. to 80 ° C., and supplied to the heat exchanger 4. In this embodiment, the water temperature difference Δt between the inlet and the outlet of the heat exchanger 4 is approximately 5 ° C.

  In the waste heat recovery system of this embodiment, the hot water of the water supply tank 6 is stored by a metal partition plate 15 such as SUS standing from the bottom wall except for the upper space. The high-temperature tank 6a and the low-temperature tank 6b in which low-temperature hot water is stored are partitioned into two tanks, and a communication hole 15a that communicates both tanks 6a and 6b is formed below the partition plate 15.

  The forward line 7a of the circulation line 7 is connected to the lower part of the low temperature tank 6b, while the return line 7b of the circulation line 7 is connected to the upper part of the high temperature tank 6a. The low-temperature water stored in the low-temperature tank 6b is supplied to the heat exchanger 4 through the forward pipe 7a and heated by the high-temperature cooling water from the water-cooling jacket of the engine 2 in the heat exchanger 4 to raise the temperature. The high temperature hot water whose temperature has been raised is configured to return to the high temperature tank 6a through the return pipe 7b.

  A water supply line 16 to the boiler 5 is connected to the lower portion of the high-temperature tank 6 a of the water supply tank 6, and a water supply pump 23 is installed in the water supply line 16. When this water supply pump 23 is driven, the hot hot water in the high temperature tank 6 a is supplied to the boiler 5.

  In addition, a replenishment water pipe 19 in which a water softener 17 and a deoxygenation device 18 are arranged is connected to the lower part of the low temperature tank 6b of the water supply tank 6, for example, degassed soft water at 2 ° C to 30 ° C is supplied with water. Tank 6 is replenished.

  The water softener 17 treats make-up water with, for example, a sodium-type cation exchange resin, and replaces the hardness contained in the make-up water, that is, calcium ions and magnesium ions with sodium ions to soften the water. Moreover, the deoxygenation device 18 removes dissolved oxygen contained in the soft water obtained by the water softener 17, and removes dissolved oxygen using, for example, a separation membrane (hollow fiber membrane).

  The water supply tank 6 is provided with a water level detector (not shown). Based on the detection signal from the water level detector, the deoxygenation device 18 is controlled so that the water level in the water supply tank 6 is maintained within the set range. Make-up water is supplied. In this embodiment, the water level in the water supply tank 6 is maintained above the partition plate 15. A large number of beads 20 are floated on the water surface of the water supply tank 6 in order to prevent oxygen from being dissolved again when the degassed soft water comes into contact with air.

  In this embodiment, the water supply tank 6 is partitioned into a high-temperature tank 6a and a low-temperature tank 6b by a partition plate 15, and the high-temperature hot water heated by the high-temperature cooling water in the heat exchanger 4 is heated to the high-temperature tank 6a. Therefore, it is possible to suppress the low temperature water in the lower part of the low temperature tank 6b from being mixed with the high temperature hot water in the high temperature tank 6a, and to prevent the water temperature of the high temperature hot water from being lowered. And while the hot water of the high temperature tank 6a can be supplied to the boiler 5 via the water supply line 16, the low temperature water of the low temperature tank 6b can be supplied to the heat exchanger 4 to recover waste heat. Therefore, the utilization efficiency of waste heat is improved. Although the upper space of the water supply tank 6 is not partitioned by the partition plate 15 as described above, the temperature of the hot water in the water supply tank 6 is higher at the upper portion. Since relatively high temperature hot water circulates, a decrease in the water temperature of the high temperature hot water is suppressed.

  In the boiler 5 fed from the feed water tank 6, the burner combustion is controlled to a high combustion state or a low combustion state according to the steam pressure. Further, the water level in the boiler 5 is detected, and based on the detected water level, the water supply pump 23 is driven or stopped, the water supply from the water supply tank 6 is controlled, and the water level in the boiler 5 is within a predetermined range. Maintained within. The steam generated in the boiler 5 is stored in the steam header 21 and then supplied from the steam header 21 to a load device 22 such as a heat exchanger that uses the steam. Since the load device 22 uses the heat of the steam, the steam is deprived of heat and condensed to be drained and discharged from the load device 22. In this embodiment, the drain discharged from the load device 22 is collected in the water supply tank 6.

  In the cogeneration system 1 having the above configuration, the engine 2 is operated to drive the generator 3 to generate AC power. At the same time, the circulation pump 10 installed in the forward pipeline 7 a of the circulation pipeline 7 is driven to supply low temperature water from the water supply tank 6 to the heat exchanger 4. In the heat exchanger 4, the low-temperature water from the outgoing pipe 7 a is heated by exchanging heat with the high-temperature cooling water heated by the waste heat of the engine 2, and the high-temperature hot water that has been heated is The water is supplied to the water supply tank 6 through the return pipe 7b of the path 7 and stored. At this time, the hot water from the heat exchanger 4 is diverted to the outgoing pipeline 7a side via the branch pipeline 12 by the three-way valve 11 provided in the return pipeline 7b, and the low temperature from the water supply tank 6 is reduced. The temperature of water mixed with water and supplied to the heat exchanger 4 is adjusted to a set temperature.

  The hot hot water stored in the water supply tank 6 is supplied to the boiler 5 when the water supply pump 23 is driven. During the combustion of the boiler 5, the boiler water is boiled by heating to generate steam. This steam is supplied to the load device 22 via the steam header 21. Drain generated in the load device 22 is collected in the water supply tank 6.

  As described above, the heat exchanger 4 that recovers the waste heat of the engine 2 and the water supply tank 6 are connected by the circulation line 7, and low-temperature water is supplied from the water supply tank 6 to the heat exchanger 4. Therefore, even when the water level in the boiler 5 is within a predetermined range and water is not supplied to the boiler 5, the hot water heated by the waste heat is returned to the water supply tank 6. Heat can be stored, and the efficiency of waste heat recovery is improved.

  Further, the temperature of the hot water supplied from the water supply tank 6 to the heat exchanger 4 via the forward pipe 7a is adjusted to the set temperature by controlling the diversion ratio by the three-way valve 11, so that, for example, the boiler 5 Even if the temperature of the hot water stored in the water supply tank 6 fluctuates depending on the combustion state of the burner and the presence or absence of water supply to the boiler 5, the temperature of the hot water supplied from the water supply tank 6 to the heat exchanger 4 varies. Without being performed, the temperature is controlled to the set temperature.

  Furthermore, since the water supply tank 6 is divided into the high temperature tank 6a and the low temperature tank 6b by the partition plate 15, the high temperature hot water returned to the high temperature tank 6a from the heat exchanger 4 is the low temperature water of the low temperature tank 6b. Mixing is suppressed from making the temperature uniform, and hot water in the high-temperature tank 6a can be supplied to the boiler 5, while low-temperature water in the low-temperature tank 6b is supplied to the heat exchanger 4 and discarded. Since heat can be recovered, the utilization efficiency of waste heat is improved.

  In the above-described embodiment, the three-way valve 11 is provided as the diversion unit. However, the diversion unit is not limited to the three-way valve, and for example, two normal two-way valves may be provided to control the diversion ratio.

  In the above-described embodiment, a single tank is partitioned to form a high-temperature tank and a low-temperature tank. However, as another embodiment of the present invention, a high-temperature tank and a low-temperature tank are configured by two individual tanks, respectively. In this case, it is preferable that the tanks communicate with each other through a communication pipe.

  In the above-described embodiment, the heat exchanger 4 is provided in the cooling water flow path of the engine 2 to perform heat exchange. However, as another embodiment of the present invention, a heat exchanger is provided in the exhaust gas flow path of the engine 2. Heat exchange with the exhaust gas may be performed, or heat exchangers may be provided in the cooling water flow path and the exhaust gas flow path of the engine 2 to exchange heat with the cooling water and the exhaust gas.

  In the above-described embodiment, the hot water stored in the water supply tank 6 is boiler water supply, but may be used for hot water supply or heating.

  The present invention is useful as a waste heat recovery system or a cogeneration system.

DESCRIPTION OF SYMBOLS 1 Cogeneration system 2 Engine 3 Generator 4 Heat exchanger 5 Boiler 6 Water supply tank 6a High temperature tank 6b Low temperature tank 7 Circulation line (circulation path)
7a Outward route (outward route)
7b Return pipeline (return route)
10 Circulating pump 11 Three-way valve 12 Branch path (branch line)
13 Water temperature sensor 14 Controller 15 Partition plate

Claims (6)

A waste heat recovery system for recovering waste heat from a heat source,
A heat exchanger for generating hot water by heating water with the waste heat;
A circulation path including a return path for supplying water in the tank to the heat exchanger and a return path for returning the hot water generated in the heat exchanger to the tank;
A branch path connecting the forward path and the return path in the middle of the path;
A diversion means for diverting the warm water in the return path to the tank side and the branch path side;
Control means for controlling the diversion of the diversion means;
A waste heat recovery system comprising: The heat source is an engine driving a generator;
The heat exchanger performs heat exchange between at least one of the engine exhaust and the engine cooling medium and water supplied from the tank;
The waste heat recovery system according to claim 1. Comprising a water temperature sensor for detecting the water temperature circulating in the circulation path;
The diversion means is constituted by a three-way valve provided at a branch connection portion between the return path and the branch path,
The control means controls a diversion ratio by the three-way valve based on a detection output of the water temperature sensor.
The waste heat recovery system according to claim 1 or 2. The tank is a water supply tank for supplying water to a boiler,
The water supply tank comprises at least two tanks, a high temperature tank having a high water temperature and a low temperature tank having a low water temperature,
The return path and a water supply path for supplying water to the boiler are connected to the high-temperature tank,
The forward path is connected to the low temperature bath,
The waste heat recovery system according to any one of claims 1 to 3. The high-temperature tank and the low-temperature tank are each constituted by each tank in which the interior of the water supply tank is divided into two by a partition plate erected from the bottom wall of the water supply tank,
The partition plate is provided with a communication path that communicates the two tanks.
The waste heat recovery system according to claim 4. The waste heat recovery system according to any one of claims 1 to 5,
A prime mover such as an engine,
A generator driven by the prime mover;
A cogeneration system comprising:

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