JPH0631717B2 - Method and apparatus for controlling low temperature fluid in heat exchanger - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat exchanger, and more particularly to a cryogenic fluid control method and apparatus for a heat exchanger that recovers heat from exhaust gas of an internal combustion engine.

PRIOR ART A conventional heat exchanger is used to recover heat from the exhaust gas of an internal combustion engine, for example as shown in FIG. That is, the heat exchanger 10 is connected to the gas engine 11 by the pipe 12 serving as the first passage, and the catalytic converter 13 is arranged therebetween. Further, a silencer 14 is connected to the heat exchanger 10 on the outlet side of the first passage. The gas engine 11 is operatively connected to a compressor 15, as indicated by the dotted line 16, which compresses refrigerant, such as air conditioners, through tubes 17 and 18. The cooling water of the gas engine 11 is sent to the hot water storage tank 20 through the pipe 19 and exchanges heat with other fluids passing through the pipes 21 and 22. The cooling water is supplied from the hot water storage tank 20 to the pipe 23.
Through the pump 24 and the pipes 25 and 26, and is again sent to the gas engine 11. The cooling water of the pipe 25 is also sent to the heat exchanger 10 through the pipe 27.

Problems to be Solved by the Invention In the apparatus shown in FIG. 4, the exhaust gas of the gas engine 11 which is a high temperature fluid is discharged to the outside through the pipe 12 through the catalytic converter 13, the heat exchanger 10 and the silencer 14. In the heat exchanger 10, the heat of the hot exhaust gas passing through the pipe 12 is
Recovered by cooling water passing through. In this device, when the exhaust gas passing through the heat exchanger 10 is generally below 150 ° to 200 ° C, a condensation phenomenon occurs in which the water vapor contained in the exhaust gas becomes condensed water. That is, the exhaust gas is cooled to a temperature below the dew point by the inner wall of the heat exchanger. Water vapor in the exhaust gas,
Since sulfur or nitrogen is contained and the steam pressure is reduced to a saturated steam pressure or less by this cooling, steam is condensed on the inner wall of the heat exchanger 10 to generate condensed water containing corrosive components such as sulfuric acid or nitric acid. .

More specifically, the gas engine 11 includes city gas or LP.
Gas fuel such as G is used. These fuels include mercaptans composed of SH groups, which react with steam to produce sulfuric acid during combustion. Further, the air supplied to give oxygen during combustion contains nitrogen, and this nitrogen reacts with water vapor to form nitric acid. Although the sulfuric acid or nitric acid is weakly acidic, the temperature inside the heat exchanger is high, so it is highly active, and therefore the corrosion weight loss per unit time that corrodes the inner surface of the heat exchanger is large.

Therefore, it becomes necessary to develop a heat exchanger that does not generate condensed water containing corrosive components. In the conventional heat exchanger, a method of measuring the outlet temperature of the cryogenic fluid and controlling the flow rate of the cryogenic fluid has been proposed, but in this method, the cryogenic fluid is not sufficiently cooled when the heat exchanger is restarted. Since the flow rate control device does not perform the intended function, there is a drawback that the condensed water is generated.

It is an object of the present invention to provide a low temperature fluid control method for a heat exchanger and an apparatus thereof that can be implemented without changing the structure of a conventional heat exchanger.

SUMMARY OF THE INVENTION A cryogenic fluid control method for a heat exchanger according to the present invention is a cryogenic fluid control method for a device for exchanging heat between exhaust gas discharged from an engine and a circulating cryogenic fluid, wherein a part of the circulating cryogenic fluid is , The flow is divided before it is made to flow into the engine, it is made to flow into a heat exchanger provided in the exhaust pipe of the engine, and the flow rate of the low-temperature fluid is divided so that the temperature of the exhaust gas becomes a predetermined value or more. In addition, the device of the present invention provides a circulating low temperature fluid path between the engine and the hot water storage tank via a pump, and provides a heat exchanger in the exhaust pipe of the engine to connect the engine and the pump. A low temperature fluid circulating between the engine and the hot water storage tank is connected by a pipe, the heat exchanger is interposed in the middle of the pipe, and the low temperature fluid flows in the pipe in accordance with the exhaust gas temperature. With a flow control device that controls the amount of fluid is there.

Embodiments Embodiments of the present invention will be described below with reference to the drawings. In FIG. 4 and FIGS. 1 to 3, the same parts are designated by the same reference numerals.

FIG. 1 showing an embodiment of the present invention is basically the same as the fourth embodiment.
It has the same device as that shown in the figure. Therefore, description of the same device is omitted.

In the present invention, the engine such as the gas engine 11 or the internal combustion engine and the hot water storage tank 20 are connected by the pipes 19, 23 and 25 via the pump 24 to form a circulating low temperature fluid passage.
A flow rate control device 28 is attached to a pipe 27 that connects the heat exchanger 10 with the heat exchanger 10, and a temperature sensitive element 31 is attached to an outlet portion 12a of the high temperature fluid of the heat exchanger 10 provided in the exhaust pipe of the engine, for example. To be The temperature sensitive element 31 is a part of the temperature sensor 30 that converts the temperature of a high temperature fluid into an electric signal, and is a thermistor, particularly a negative characteristic thermistor (NTC thermistor) or chromel-.
Various side temperature devices such as alumel (CA) thermocouples are used. The temperature sensor 30 converts the signal from the temperature sensitive element 31 into a signal corresponding to the outlet temperature of the high temperature fluid, and converts this into a control circuit 32.
Supply to. The temperature sensitive element 31 is mounted at the above-mentioned outlet portion.
It may be other than 12a. For example, the output of the temperature sensing element 31 may be attached to the inlet portion or an intermediate portion between the inlet and the outlet, but in any case, the output of the temperature sensitive element 31 has a constant relationship with the hot fluid temperature and includes a level representing the hot fluid temperature. The control circuit 32 receives the signal from the temperature sensor 30 and electrically determines the level of the outlet temperature, and generates a drive signal corresponding to this level. This drive signal is sent to the flow rate control device 28, and the flow rate control device 28 supplies the low temperature fluid to the heat exchanger 10 through the pipe 29 at a flow rate corresponding to the drive signal. That is, when the outlet temperature of the exhaust gas discharged from the heat exchanger 10 is, for example, about 150 ° to 200 ° C. or higher, the flow rate control device 28 supplies the low temperature fluid to the heat exchanger 10 at a flow rate proportional to the outlet temperature. . In other words, when the outlet temperature is high, the flow rate of the low temperature fluid to the heat exchanger 10 is high, and conversely, when the outlet temperature is low, this flow rate is low. However, due to the performance of the gas engine, the temperature upper limit and the maximum discharge flow rate of the exhaust gas passing through the pipe 12 are set, so that the flow rate control device 28 does not operate until the exhaust gas outlet temperature reaches a constant temperature, for example, 400 ° C. to the upper limit temperature. The low temperature fluid may be supplied to the heat exchanger 10 at a constant maximum flow rate. On the contrary, when the outlet temperature of the exhaust gas is the lower limit temperature of about 120 ° C. or less, the control device 32 does not generate a drive signal and the operation of the flow rate control device 28 is stopped. The upper limit and the lower limit temperature of the exhaust gas are determined according to the performance of the gas engine. These upper and lower temperatures are much higher when the temperature sensitive element 31 is attached to the inlet of the heat exchanger 10 than when it is at the outlet.

An example of the details of the control circuit 32 and the flow control device 28 is shown in FIG. The control circuit 32 includes an amplifier 33 connected to the temperature sensor 30, and a differential amplifier 34 that receives the output of the amplifier 33 and determines whether the output is equal to or higher than a predetermined level. The differential amplifier 34 has a non-inverting input terminal 40 connected to the amplifier 33 and an inverting input terminal 41 connected to the constant voltage power supply 36.

The flow rate control device 28 is a servo valve 28 that is a variable flow rate control valve that is operated by a torque motor 35 that receives a drive signal of a differential amplifier 34 and a flapper (not shown) of the torque motor 35.
have a. For the torque motor 35 and the servo valve 28a, known type devices can be used.

The operation of the apparatus shown in FIG. 2 will be described. The differential amplifier 3
Reference numeral 4 determines whether or not the output from the temperature sensor 30 is higher than that of the power supply 36. When this output is high, a drive signal corresponding to this output is generated to move the flapper of the torque motor 35 to the corresponding position, and the servo valve Increase the opening amount of 28a. Therefore, from the pump 24 to the pipes 25 and 27, the servo valve 28
The flow rate of cryogenic fluid through a and tube 29 is increased. If the temperature of the high temperature fluid is high but the temperature does not reach the upper limit temperature, the temperature sensor 3
The output provided from 0 to the non-inverting input terminal 40 is below its maximum level but above the power supply 36 so that the differential amplifier 34 produces a relatively low level drive signal. Therefore, the amount of movement of the flapper of the torque motor 35 is small, and the amount of opening of the servo valve 28a is also small. Therefore, the low temperature fluid flow rate through the servo valve 28a is low.

When the exhaust gas outlet temperature is equal to or lower than a certain temperature, the signal supplied from the temperature sensor 30 to the non-inverting input terminal 40 is lower than that of the power source 36. Therefore, since the differential amplifier 34 does not generate a drive signal, the torque motor 35 does not operate and the servo valve
28a is not released either.

FIG. 3 shows another embodiment of the flow rate control device 28. The flow rate control device 28 includes an acceleration / deceleration motor 37 that receives the output of the differential amplifier 34 and a pump 28 that is driven by the motor 37.
with b and. The pump 28b is connected to the pipes 27 and 29, but the pipe 27 may be directly connected to the hot water storage tank 20. The motor 37 is driven by a drive signal of the differential amplifier 34 corresponding to the temperature of the exhaust gas, and is a pump operatively connected to the motor 37.
28b supplies the low temperature fluid to the heat exchanger 10 at a flow rate corresponding to the above temperature.

The cryogenic fluid control device has been described as an example of the heat exchanger that recovers heat from the exhaust gas of the gas engine, but the embodiment of the present invention can be variously modified. For example, the present invention can be implemented in a heat exchanger that recovers heat from the exhaust gas of an internal combustion engine mounted on a vehicle. In the control circuit 32,
It is also possible to connect an A / D converter instead of the differential amplifier 34, generate a drive signal digitally at regular time intervals, and operate the digital signal torque motor 35 or the acceleration / deceleration motor 37. It is also possible to operate these by combining a differential amplifier and an A / D converter.

As described above, according to the method and apparatus of the present invention, the circulating low temperature fluid is controlled to a predetermined temperature or higher, and a part of the low temperature fluid is divided and heated by the heat exchanger before being returned to the engine, Further, since the remaining portion is not heated but is allowed to flow into the engine, it prevents generation of condensed water causing corrosion in the heat exchanger without impairing the cooling action of the engine.

[Brief description of drawings]

FIG. 1 is a block diagram of a cryogenic fluid control device for a heat exchanger according to the present invention; FIG. 2 is a block diagram showing details of a control circuit and a flow rate control device used in the device of FIG. 1; FIG. 4 is a block diagram showing another embodiment similar to FIG. 2; FIG. 4 shows a block diagram of a conventional cryogenic fluid control device. 10: Heat exchanger, 28: Flow control device, 30: Temperature sensor, 32: Control circuit

Claims (2)

[Claims] 1. A low-temperature fluid control method for an apparatus for exchanging heat between an exhaust gas discharged from an engine and a circulating low-temperature fluid, wherein a part of the circulating low-temperature fluid is split before flowing into an engine. A method for controlling a low temperature fluid in a heat exchanger, wherein the flow rate of the low temperature fluid is controlled so that the temperature of the exhaust gas is equal to or higher than a predetermined value. 2. A circulating low-temperature fluid path is provided between the engine and the hot water storage tank via a pump, and a heat exchanger is provided in the exhaust pipe of the engine.
A circulating low-temperature fluid path between the engine and the pump and a circulating low-temperature fluid path between the engine and the hot water tank are connected by a pipe, and the heat exchanger is interposed in the middle of the pipe and the temperature of the exhaust gas is adjusted according to the exhaust gas temperature. A low temperature fluid control device for a heat exchanger, which is provided with a flow rate control device for controlling the flow rate of the low temperature fluid flowing in the pipe.