JPH01117909A - Cooling water controller of heat-exchanger - Google Patents

Abstract

PURPOSE:To prevent moisture from being concentrated inside the inner wall of an exhaust pipe and improve the durability in a system wherein heat- exchange is executed between exhaust gas and cooling water by measuring the moisture of exhaust gas and the temperature of exhaust pipe and controlling the flow rate of cooling water according to the measurements. CONSTITUTION:Exhaust gas passing through the exhaust pipe 12 of an engine 11 is heat-exchanged with cooling water passing through a cooling pipe 13 with a heat-exchanger 10. The cooling water, as a result, increased in temperature is fed into a secondary heat-exchanger 14 to heat the cooling water inside a secondary cooling pipe 16. The hot cooling water is then used as hot water in an air conditioner. A moisture measuring apparatus 21 measuring the moisture of exhaust gas inside the exhaust pipe 12 and a temperature measuring apparatus 22 measuring the temperature of the exhaust pipe 12 are incorporated in such system. When the measured moisture of exhaust gas is decided to be higher than the saturated moisture corresponding to the temperature of the exhaust pipe 12, a flow rate control circuit 24 controls a flow rate controller 23 to make control for the flow rate of cooling water for the heat-exchanger 10.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to the prevention of deterioration of heat exchangers, particularly heat exchangers connected to the exhaust pipe of an engine.

A conventional heat exchanger for a gas engine will be explained with reference to FIG. The heat exchanger 10 exchanges heat between an exhaust pipe 12 of an engine 11 such as a gas engine and cooling water (subcooling water) flowing through a cooling pipe 13 from the engine 11.
1 and the cooling water in the cooling pipe 13 heated by the heat exchanger 1° is further connected to a second heat exchanger 14. In the second heat exchanger 14, heat exchange is performed between the cooling water flowing in the cooling pipe 13 and the cooling water flowing in the second cooling pipe 16.

The cooling pipe 13 is provided with a thermostatically sealed switching valve 15, and the cooling water passing through the cooling pipe 13 is transferred to the second heat exchanger 14.
A passage through which the heat exchanger passes through and supplies the engine 11, or a passage which flows directly into the engine 11 without passing through the second heat exchanger 14 is formed.

In the above configuration, the heat exchanger 10 receives the heat of the exhaust gas discharged from the engine 11 and passing through the exhaust pipe 12 by the cooling water passing through the cooling pipe 1.

This heat is supplied to the second heat exchanger 14 and is recovered from the second cooling pipe 16. The heated high-temperature cooling water of the second cooling pipe 16 is used for hot water or hot water for an air conditioner. The exhaust gas passing through the exhaust pipe 12 flows into the first heat exchanger 10, where heat is removed by the cooling water of the cooling pipe 13, and then released into the atmosphere.

The primary cooling water passing through the cooling pipe 13 is circulated by a pump (not shown), and after passing through the heat exchanger 10, the flow direction is controlled by a thermostatic seal switching valve 15. The thermostatic seal switching valve 15 is, for example, 80°C.
When the temperature is set above and the secondary cooling water has a water temperature of 80° C. or lower, it is directly returned to the gas engine 11 without passing through the second heat exchanger 14. However, when the temperature of the secondary cooling water exceeds 80° C., a flow path is formed for the secondary cooling water to pass through the second heat exchanger 14 and return to the gas engine 11.

In the exhaust pipe 12 of the gas engine 11, when heat is exchanged with the cooling water, the exhaust gas cools down excessively, which promotes the adhesion of moisture, soot, etc. Deterioration such as corrosion or clogging has occurred in the passages. That is, the exhaust gas passing through the heat exchanger 10 generally has a temperature of 150°C to
When the temperature is below zOO°C, a phenomenon of condensation occurs in which water vapor contained in the exhaust gas becomes condensed water. The exhaust gas is cooled to a temperature below the dew point by the inner wall of the heat exchanger 10.

The exhaust gas contains water vapor, sulfur, or nitrogen, and when the air pressure is reduced to below the saturated vapor pressure, the water vapor condenses on the inner wall of the heat exchanger 10 and becomes sulfuric acid or nitric acid. , condensate water containing corrosive components such as acids is produced.

The gas engine 11 uses gas fuel such as city gas or LPG. These fuels contain mercaptans composed of SH groups, which upon combustion react with water vapor to produce sulfuric acid. Also.

Nitrogen is included in the air that provides oxygen during combustion.

Nitrogen reacts with water vapor to form nitric acid. Although the generated sulfuric acid or nitric acid is weakly acidic, since the temperature inside the heat exchanger 10 is high, it is highly active, and therefore the corrosion loss per unit of time during which it corrodes the inner surface of the heat exchanger 10 is large. Furthermore, when the temperature of the exhaust pipe was low, carbon contained in the exhaust gas adhered to the inner wall of the exhaust pipe, causing clogging of the exhaust pipe.

In order to eliminate such drawbacks, Japanese Patent Application Laid-Open No. 61-1497
As shown in Japanese Patent No. 96, a method has been proposed in which the temperature of exhaust gas is measured and cooling water is caused to flow in accordance with the temperature level. As shown in this publication, low-temperature fluid control detects the temperature of exhaust gas flowing through a heat exchanger for exhaust heat recovery for gas engines and controls the flow rate of cooling water flowing through the heat exchanger in accordance with this temperature. The law is known.

While the invention is trying to solve 1. a However, with conventional low-temperature fluid control devices, the flow rate of cooling water to the heat exchanger is controlled by detecting the engine exhaust gas temperature, which sufficiently prevents moisture condensation and carbon adhesion in the exhaust gas. I couldn't do that. That is, the conditions for water droplets and carbon to adhere to the inner wall of the exhaust pipe are mainly caused by not only the temperature of the exhaust gas but also the saturated humidity. Even if the temperature of the exhaust pipe is low, if the humidity in the exhaust gas does not reach the saturated humidity, water droplets will not adhere to the inner wall of the exhaust pipe. Conversely, if the temperature of the exhaust pipe is high, the humidity in the exhaust gas will not reach the saturated humidity. When the humidity exceeds the saturated humidity, water droplets adhere to the inner wall of the exhaust pipe. Carbon in the exhaust gas adheres to the inner wall of the exhaust pipe along with water droplets that adhere to the inner wall of the exhaust pipe, and accumulates as the engine operates.

Since such a phenomenon actually occurs, it is not possible to sufficiently prevent corrosion and clogging of the heat exchanger by simply measuring the temperature of the exhaust gas as in the past.

SUMMARY OF THE INVENTION Accordingly, the present invention provides a cooling water control device for a heat exchanger that can eliminate the above-mentioned conventional drawbacks and control the flow rate of cooling water in accordance with the humidity in exhaust gas and the saturated humidity at the temperature of the exhaust pipe. The purpose is to

Depth 2 points J” 1 means to fall prone A cooling water control device for a heat exchanger according to the present invention is a cooling water control device for a heat exchanger.

A heat exchanger that is connected to the engine exhaust pipe and exchanges heat between engine exhaust gas and cooling water, a flow control device that controls the flow rate of the cooling water in the heat exchanger, and measures the humidity of the exhaust gas. a humidity measuring device that measures the temperature of the exhaust pipe; and a temperature measuring device that measures the temperature of the exhaust pipe; and a temperature measuring device that measures the temperature of the exhaust pipe; At this time, the heat exchanger has a configuration including a flow rate control circuit that controls the flow rate control device to control the flow rate of cooling water to the heat exchanger.

The operating flow rate control circuit controls the flow rate control device to control the cooling water when the humidity of the exhaust gas measured by the humidity measuring device is higher than the saturated humidity corresponding to the temperature of the exhaust pipe measured by the temperature measuring device. The flow rate of the cooling water is controlled, and when the humidity of the exhaust gas is lower than the saturated humidity corresponding to the temperature of the exhaust pipe, the flow rate of the cooling water is not controlled.

EXAMPLE Hereinafter, an example of a cooling water control device for a heat exchanger according to the present invention will be described with reference to FIGS. 1 to 3.

In these drawings, the same parts as shown in FIG. 4 are designated by the same reference numerals, and their explanation will be omitted.

The cooling water control device 2 for a heat exchanger according to the present invention includes a humidity Jf1 measuring device 21 that measures the humidity of exhaust gas flowing in the exhaust pipe 12, and a temperature measuring device v that measures the temperature of the exhaust pipe.
122, a flow rate control device 23 that controls the flow rate of the cooling water of the heat exchanger, and a humidity of the exhaust gas measured by the humidity measuring device relative to the saturated humidity corresponding to the temperature of the exhaust pipe measured by the temperature measuring device. A flow control circuit 24 is provided which controls the flow rate control device to control the flow rate of cooling water to the heat exchanger when the temperature is high.

As the humidity measuring device 21, various humidity measuring devices such as a psychrometer, a dew point meter, a hair hygrometer, an infrared absorption hygrometer, and an electrical resistance hygrometer can be used. Infrared absorption hygrometers utilize the fact that specific infrared rays are absorbed by water vapor. In addition, electrical resistance hygrometers use hygroscopic substances (mainly Li)
This method utilizes the characteristic that the electrical resistance of the thin layer C1) changes depending on humidity.

As the temperature measuring device 22, various temperature measuring devices such as a thermocouple, a negative or positive thermistor, or a bimetal can be used.

The flow rate control device 23 is a pump that circulates the cooling water flowing through the cooling pipe 13, a flow rate control valve, or a switching valve that limits the flow rate to the heat exchanger 10 and returns it to the engine 11 or the second heat exchanger 14.

The flow rate control circuit 24 can be created using an integrated circuit such as a microcomputer. In any case, the flow rate control circuit 24 includes a saturated humidity determining means that is connected to the temperature measuring device 22 and calculates the saturated humidity, and a saturated humidity determining means that is connected to the saturated humidity determining means and the humidity measuring device 21 and uses the output of the saturated humidity determining means. When the output of the humidity measuring means is large, a control output is provided to the flow rate control device to control and compare the flow rate of the cooling water. This operation will be explained with reference to the flowchart of FIG.

First, in step 30, a signal from the humidity measuring device 21 is received to detect the humidity of the exhaust gas flowing through the exhaust pipe 12.Next, in step 31, a signal is received from the temperature measuring device 22, and the humidity of the exhaust gas flowing through the exhaust pipe 12 is detected. The temperature of the exhaust pipe 12 is detected. In the flow control circuit 24.

An arithmetic circuit is provided, and in step 32, the saturated humidity at the temperature of the exhaust pipe 12 is determined. This saturated humidity can be easily determined using a psychrometric diagram. In step 33, the comparing means determines whether the humidity of the exhaust gas is higher than the saturated humidity. When the humidity of the exhaust gas is greater than or equal to the saturated humidity, the process proceeds to step 34, where the flow rate control device 23 controls the flow rate of the cooling water. This flow rate control is performed by reducing the flow rate of the cooling water to the heat exchanger 10 by using a pump, a flow control valve, or a switching valve that circulates the cooling water flowing through the cooling pipe 13, reducing the flow rate to a zero flow state, or reducing the flow rate to a zero flow state or a non-increasing state. It will be done. but.

When the humidity of the exhaust gas is less than the saturated humidity, the flow rate of the cooling water is not controlled in step 35.

After controlling or not controlling the flow rate of the cooling water in steps 34 and 35, the process returns to step 33 to check whether the engine 11 is running or not. During Fll, the humidity in the exhaust gas and the saturated humidity are always compared.

FIG. 3 shows a specific circuit of the flow rate control circuit 24. Humidity al that measures the humidity of exhaust gas flowing inside the exhaust pipe 12
The ll determining device 21 is connected to a differential amplifier 28 via an amplifier 25.
is connected to the inverting input terminal of Also, a temperature measuring device 22 that measures the temperature of the exhaust pipe.

It is connected to a non-inverting input terminal of an operational amplifier 27 via an amplifier 26 . The inverting input terminal of operational amplifier 27 is connected to a suitable power supply. The operational amplifier 27 calculates the saturated humidity at the temperature of the exhaust pipe 12. The output of operational amplifier 27 is supplied to a non-inverting input terminal of differential amplifier 28. The output of the operational amplifier 2B is sent to a driver circuit 29 such as a transistor.

When the driver circuit 29 is turned on, it operates the flow control device 23 that controls the flow rate of cooling water to the heat exchanger.

In the configuration of FIG. 3, based on the output of temperature measuring device 22, operational amplifier 27 provides an output representative of saturated humidity to a non-inverting input terminal of operational amplifier 28. Furthermore, the humidity measuring device 21 provides an output to the inverting input terminal of the differential amplifier 28. When the output of the operational amplifier 27 is smaller than the output of the amplifier 25, the differential amplifier 28 supplies an output to the driver circuit 29 to operate the flow control device 23 and circulate the cooling water.

However, when the output of the operational amplifier 27 is greater than or equal to the output of the amplifier 25, the flow control device 23 is controlled to reduce the flow rate of the cooling water, to a zero flow state, or to a non-increasing state.

As mentioned above, the flow control circuit 24 controls the temperature measurement device 22
When the humidity of the exhaust gas measured by the humidity measuring device 21 is higher than the saturated humidity corresponding to the temperature of the exhaust pipe measured by When the humidity of the exhaust gas is lower than the saturated humidity corresponding to the temperature, the flow rate of cooling water is not controlled.
Therefore, when the temperature of the exhaust pipe is low and the humidity in the exhaust gas does not reach the saturated humidity, cooling water is circulated. Further, even if the temperature of the exhaust pipe is high, when the humidity in the exhaust gas exceeds the saturated humidity, the flow rate of the cooling water is restricted. For this reason,
A phenomenon in which water droplets adhere to the inner wall of the exhaust pipe and a phenomenon in which carbon in the exhaust gas adheres to the inner wall of the exhaust pipe together with the attached water droplets does not occur.

In this invention, the humidity of the exhaust gas and the temperature of the exhaust pipe are adjusted to 1 liter.
The flow rate of the cooling water flowing to the heat exchanger is controlled based on the specified temperature. By controlling the flow rate of cooling water and preventing water droplets from adhering to the inner wall of the exhaust pipe, corrosion of the exhaust pipe of the heat exchanger due to corrosive substances and clogging due to adhesion of carbon can be prevented.

In this way, the deterioration of the heat exchanger is prevented.

It becomes possible to prevent a decrease in heat exchange efficiency.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a cooling water control device for a heat exchanger according to the present invention, Fig. 2 is a flowchart showing the operation of the flow rate control circuit, Fig. 3 is a circuit diagram of the flow rate control circuit, and Fig. 4 is a conventional heat exchanger cooling water control device. FIG. 2 is a block diagram of an exchanger. 110. Engine, 101. heat exchanger, 126.
Exhaust pipe, 20. , cooling water control device, 21°, humidity measuring device, 220. Temperature measurement device, 23°, flow rate control device, 240. Flow control circuit, Figure 1 Figure 2

Claims (3)

[Claims] (1) A heat exchanger connected to the engine exhaust pipe and exchanging heat between engine exhaust gas and cooling water; a flow rate control device controlling the flow rate of the cooling water in the heat exchanger; A humidity measuring device for measuring humidity, a temperature measuring device for measuring the temperature of the exhaust pipe, and a temperature measuring device for measuring the temperature of the exhaust gas measured by the humidity measuring device against the saturated humidity corresponding to the temperature of the exhaust pipe measured by the temperature measuring device. 1. A cooling water control device for a heat exchanger, comprising a flow rate control circuit that controls a flow rate control device to control the flow rate of cooling water to the heat exchanger when humidity is high. (2) The flow control circuit includes a saturated humidity determining means connected to the temperature measuring device and calculating saturated humidity, and an output of the humidity measuring means connected to the saturated humidity determining means and the humidity measuring device and based on the output of the saturated humidity determining means. A cooling water control device for a heat exchanger according to claim 1, further comprising comparison means for controlling the flow rate of cooling water to the heat exchanger by giving a control output to the flow rate control device when the flow rate is large. (3) The cooling water control device for a heat exchanger according to claim (1), wherein the flow rate control device is a pump, a flow control valve, or a switching valve that circulates the cooling water.