JPS60240996A - Method of controlling surface temperature of heat transfer tube of evaporator in waste heat recovering device - Google Patents

Abstract

PURPOSE:To continuously change in available heat transfer area to improve the heat recovery ratio by controlling a liquid level within a condenser. CONSTITUTION:A liquid level control valve 19 is interposed in a condensate tube 8 between an outlet side header 18a of a condenser 6 and a liquid tank 16. With the lowering of the temperature of waste gas, when the temperature of a lower temperature side heat transfer tube 9a within an evaporator 3 or the temperature of steam is lowered to draw near to a dew point temperature, a valve opening contracting signal is generated from controller 20 to operate a liquid level control valve 19 to the closed side by an actuator. As a result, the flow quantity of a liquid heat medium is throttled to raise the liquid level of the heat transfer tube 9 within the condenser 6 and to reduce the available heat transfer area for steam condensation of the heat transfer tube 9. That is, when the height (h) of the liquid level becomes high, the available heat transfer area is reduced. As a result, the condensation quantity of steam is reduced. Hence, the reduction of the load of the evaporator is prevented and the lowering of the surface temperature of the heat transfer tube within the evaporator 3 to a temperature less than the dew point is also prevented, and is maintained at a temperature more than the dew point of acid or the like.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a method for controlling the surface temperature of a heat transfer tube in an evaporator in a separated heat pipe type waste heat recovery device, and particularly relates to a method for controlling the surface temperature of a heat transfer tube in a heating side. The surface temperature of the heat exchanger tube in the evaporator can always keep the surface temperature of the evaporator above the dew point temperature when the temperature decreases and there is a risk that the surface temperature of the heat exchanger tube in the evaporator will fall below the dew point temperature of the exhaust gas. Regarding control method.

[Technical background of the invention and its problems] Generally, in a hot blast furnace installed in parallel with a blast furnace, etc., a separate heat pipe type exhaust heat recovery device, for example, is installed in order to effectively recover the sensible heat of exhaust gas. There is.

To explain this example based on FIG. 3, this exhaust heat recovery device includes an evaporator installed in an exhaust gas passage 2 extending from a hot air stove 1, a combustion air pipe 4, and a combustion air pipe 5. Each of them is composed of an interposed condenser 6, and each of them houses, for example, 1000 heat exchanger tubes. The heat medium (steam) vaporized by the sensible heat of the exhaust gas in the evaporator 3 is sent to each condenser 6 via the steam pipe 7, where the combustion air and fuel gas are heated. The heat medium (water) condensed and liquefied by this heating is returned to the evaporator 3 via the condensate pipe 8 and used for circulation to recover heat from the exhaust gas.

Incidentally, the combustion heat in the combustion chamber 1a is stored in the heat storage chamber 1b, and the exhaust gas after storing the heat exhibits the following characteristics of this type of heat exchanger. That is, the temperature of this exhaust gas tends to be low at the beginning of combustion, and the humidity tends to increase toward the end of combustion. The heat transfer area of each of the evaporator 3 and condenser 6 is determined by the most efficient part of this temperature change, but depending on the operating method of the hot air stove, the exhaust gas temperature on the evaporator outlet side becomes low. As a result, there is a risk that the humidity on the heat transfer surface of the heat transfer tube on the low temperature side of the evaporator will reach the dew point temperature of the acid in the exhaust gas, so it is necessary to maintain the humidity on the heat transfer surface above the dew point temperature from the perspective of preventing corrosion of the heat transfer tube. arise.

Therefore, in order to meet this demand, in the past, methods such as those shown in FIGS. 4 and 5 have been typically adopted.

Incidentally, the same parts as in FIG. 3 are given the same reference numerals and the description thereof will be omitted.

As shown in Figure 4, the evaporator 3 that recovers heat from exhaust gas and the condenser 6 that heats the gas to be heated (combustion air, etc.) with the recovered heat (only one unit is shown for simplicity) are vertically connected. A large number of rows (three rows in the illustrated example) of heat transfer tubes 9 and 10 arranged in the direction of In order to reduce the effective heat transfer area of the condenser 6 and reduce the load, a required number of rows of the heat transfer tube group provided in multiple rows are closed by the stop valve 11 so that they do not operate as a condenser. The temperature of the heat exchanger tube on the low temperature side of the evaporator 3 was kept at or above the dew point temperature.

However, in this type of conventional method, the effective heat transfer area of the condenser 6 can only be increased or decreased in stages because the stop valve 11 operates in a 0N10FF manner. There were cases where 1q was not collected effectively.

In addition, a large number of stop valves 11 are required, and the structure becomes ml-sized, and there is also the problem that steam hammering tends to occur when the valves are opened and closed.

In the conventional method shown in FIG. 5, a heating gas passage 12 (including a fuel gas pipe and a combustion air pipe) through which fuel gas or combustion air flows, bypasses a condenser 6 installed therein. A bypass pipe 13 is provided, and when the temperature of the low temperature side heat transfer pipe (not shown) in the evaporator 3 reaches the dew point temperature, the bypass valve 14 provided in the bypass pipe 13 is opened and a part of the gas to be heated is condensed. By bypassing vessel 6, the load on the condenser is reduced. As a result, the temperature of the low-temperature side heat exchanger tube of the evaporator 3 increases by the amount that the load decreases, and this temperature is maintained above the dew point temperature.

However, in this method, a separate bypass pipe 1
3 and a bypass valve 14 must be provided, and the diameter of these must also be 800 to 14 mm due to the need to flow the heated gas.
The power must be increased to 200w+m, which necessitates a rise in equipment costs.

[Object of the Invention] The present invention focuses on the above-mentioned problems and has been devised to effectively solve the problems.

5. An object of the present invention is to improve the temperature of the heat exchanger tubes without complicating the structure by controlling the liquid level of the heat exchanger tubes in the condenser or by introducing non-condensable gas into the heat exchanger tubes. It is an object of the present invention to provide a method for controlling the surface temperature of a heat transfer tube in an evaporator in an exhaust heat recovery device, which can continuously increase and decrease the effective heat transfer area, thereby improving the efficiency of heat recovery from exhaust gas.

[Summary of the invention] The present invention was made based on the finding that the effective heat transfer area can be changed continuously by controlling the liquid level in the condenser, and the temperature of the heat transfer tubes of the evaporator Alternatively, the vapor temperature of the heat medium is detected, the detected temperature value is compared with a preset dew point temperature value to calculate the temperature difference, and the detected temperature value is made to exceed the dew point temperature value based on this temperature difference. The main idea is to continuously increase and decrease the effective heat transfer area of the heat transfer tubes in the condenser, thereby improving heat recovery efficiency.

61 [Embodiments of the invention] The method of the present invention will be explained in detail below based on the accompanying drawings.

FIG. 1 is a schematic perspective view showing an example of an exhaust heat recovery apparatus for carrying out the method of the present invention.

As shown in the figure, this exhaust heat recovery device includes an evaporator 3 installed in an exhaust gas passage 2 from a hot air stove, etc., for recovering exhaust heat, and an evaporator 3 through which heated gas such as combustion II gas or combustion air flows. The condenser 6 is provided in the heated gas passage 12 and heats the heated gas using the recovered heat (see FIGS. 3 and 4). These evaporator 3 and condenser 6 are connected to a circulation system 15 that circulates a heat medium such as water.
This circulation system 15 includes a steam pipe 7 that sends steam from the evaporator 3 side to the condenser 6 side, and a condensate pipe 8 that sends condensed liquid from the condenser 6 side to the evaporator 3 side. It is mainly composed of.

A liquid tank 16 for storing condensed liquid and a circulation pump 17 for circulating this liquid within the system are successively installed in the condensed liquid pipe 8 on the downstream side of the condenser 6.

Inside the evaporator 3 and condenser 6, there are provided a large number of rows of heat transfer tubes 9 arranged in the vertical direction, and each header section 18 connected to the end of each heat transfer tube 9 is a steam pipe. 7 and condensate pipe 8.

In particular, in this device, the outlet side header section 18 of the condenser 6
The condensate pipe 8 between the liquid tank 16 and the liquid tank 16 is provided with a liquid level control valve 19 that increases or decreases the height h of the liquid level in the heat transfer tube 9 in the condenser by controlling the flow rate of the condensate flowing into the condensate pipe 8. is interposed. The control valve 19 is configured to be able to take any valve opening degree from a fully open state to a fully open state based on a command signal from a controller 20. In addition, in the circulatory system 15,
In order to maintain a pressure balance between the upstream and downstream sides of the control valve 19, a pressure balance pipe 21 is provided that connects the upstream side of the condenser 6 and the downstream side of the valve 19.

Low-temperature side heat transfer tube of the evaporator 3 (the most downstream side of the exhaust gas) 9
A is provided with a temperature sensor 22 for detecting this temperature, and the steam pipe 7 is also provided with a temperature sensor 23 for detecting the steam temperature of the heat medium flowing therein, and each detected temperature value is sent as an electric signal. The signal is input to the controller 20 as follows.

In this controller 20, a dew point temperature value is input and set in advance, and this set value and the above-mentioned detected temperature value (lower temperature value) are compared and calculated to calculate the concentration difference. Based on this, a command signal is issued to the liquid level control valve 19 so that the detected temperature value exceeds a preset temperature value. Note that the dew point temperature value can be set to any value.

Further, as described above, the two temperature sensors 23 and 24 may not be provided (although only one of the temperature sensors may be provided).

The method of the present invention will be specifically explained based on the above configuration.

First, during normal operation, the sensible heat of the exhaust gas flowing in the exhaust gas passage 2 is recovered by heating and vaporizing the heat medium in the evaporator 3, and this steam flows through the circulation system 15 and is introduced into the condenser 6. and heats the gas to be heated. Through this heat exchange, the steam is re-liquefied, and the liquid tank 16 and circulation pump 17
The liquid is transferred to the evaporator 3 again via the .

9- Here, as the temperature of the exhaust gas decreases, the temperature of the low temperature side heat transfer @ 9a in the evaporator 3 or the steam temperature decreases and approaches the dew point humidity, the controller 20 issues a valve opening reduction signal. Then, the liquid level control valve 19 is operated to the closed side by an actuator (not shown). This reduces the flow rate of the liquid heat medium to raise the liquid level in the heat transfer tubes 9 in the condenser 6, thereby reducing the effective heat transfer area of the heat transfer tubes 9 for vapor condensation. That is, as the height h of the liquid level increases, the effective heat transfer area decreases.

As a result, the amount of condensed and liquefied steam is reduced, so the square tube of the evaporator 3 is reduced, and the surface of the heat exchanger tube in the evaporator 3 is prevented from falling below the dew point temperature, and the dew point of the acid etc. Hold above temperature.

The controller 20 stores in advance the correlation between the temperature difference and the corresponding optimal liquid level height h that provides the best heat recovery efficiency, and continuously adjusts the valve opening based on this. This will lead to a significant change.

Therefore, when the exhaust gas temperature changes continuously, the effective heat transfer area could only be changed stepwise in the past, but according to this embodiment, the liquid By changing the opening degree of the surface control valve 19, the effective heat transfer area of the heat transfer tube 9 can be continuously changed, and as a result, the surface temperature of the heat transfer tube in the evaporator 3 can be maintained above the dew point temperature. Effective heat recovery is possible by constantly increasing heat recovery efficiency.

Further, when the temperature of the low temperature side heat transfer tube 9a of the evaporator 3 rapidly decreases, the liquid level may not rise rapidly even if the liquid level control valve 19 is rapidly closed (if the amount of condensed liquid is small). In consideration of such a case, the condensate pipe 1 on the outlet side of the circulation pump 17 is
A branch pipe 28 is provided from 5 to allow a portion of the condensate to always flow upstream of the liquid level control valve 19. By doing this, more condensed liquid than can be condensed in the condenser 6 flows upstream of the liquid level control valve 19, and even when the temperature of the evaporator low temperature side heat transfer tube 9a rapidly decreases, By adjusting the liquid level control valve 19, the liquid level rises rapidly and the evaporator low temperature side heat transfer tube 9a
It is possible to obtain the heat transfer area of the condenser 9 depending on the temperature.

In addition, in the conventional example, a large number of stop valves 11 (fourth
However, according to this embodiment, the liquid level control valve 19 controls the flow rate of the condensate. The diameter of the condensate pipe 8, which is conventionally used, is sufficient, and the equipment cost can be reduced.

In addition, to reduce the effective heat transfer area, conversely to the above, the valve 19
By increasing the opening degree and increasing the flow rate, the height of the liquid level h
Make smaller.

In the above device example, a method of controlling the height h of the liquid level was adopted as a method of increasing/decreasing the effective heat transfer area, but the method is not limited to this, and as shown in FIG. It may also be controlled by introducing a toxic gas.

That is, as shown in the figure, the outlet side header section 1 of the condenser 6
A non-condensable gas introduction pipe 24 for introducing non-condensable gas into the condensate pipe 8 and a non-condensable gas discharge pipe 25 for discharging gas are connected to the condensate pipe 8 between 8a and the liquid tank 16, respectively. At the same time, a non-condensable gas injection control valve 26 and a non-condensable gas discharge control valve 27 are provided in the introduction pipe 24 and the discharge pipe 25, respectively. As the non-condensable gas used here, for example, a gas such as radon or xenon whose specific gravity is larger than the specific gravity of the heat medium is used.

The opening degrees of these eight valves 26 and 27 are controlled by a controller (not shown) similar to that described above to determine the amount of non-condensable gas to be filled in and the amount to be discharged. Note that the correlation between the height of the gas column of the heat transfer tube in the condenser 6 (and the temperature difference calculated by the controller) is stored and set in advance in the controller 20.

In such a configuration, first, the non-condensable gas filling control valve 26 is opened in response to a command from the controller 20, and the non-condensable gas is introduced into or sealed into the condensate pipe 8. Since the enclosed non-condensable gas is heavier than the heat medium vapor, it begins to accumulate above the liquid level in the liquid tank 16 and over time reaches the header portion 18a at the lower part of the heat transfer tube of the condenser 6. When the non-condensable gas reaches the header portion 18a, the enclosure control valve 26 is closed to maintain this gas state.

In this state, as described above, as the temperature of the exhaust gas 13 decreases, the temperature of the heat exchanger tube of the evaporator 3 (see Figure 1) decreases and approaches the dew point temperature, and the detected temperature value and the preset temperature decrease. Since the temperature difference from the dew point temperature value becomes small, the controller 20 issues a valve open signal based on this temperature difference, and the enclosure control valve 26 is opened. As a result, the non-condensable gas located below the heat transfer tubes 9 in the condenser 6 rises.

Then, the height β of the gas column is raised by opening the valve 26 and continuing to fill in the non-condensable gas until the required effective heat transfer area of the heat transfer tube is reached. As a result, the heat exchanger tube 9
The effective heat transfer area can be continuously reduced, and the heat recovery efficiency can be maintained at a high level at all times.

Furthermore, when it is desired to increase the effective heat transfer area of the heat transfer tubes 9, the non-condensable gas discharge control valve 27 is opened. As a result, the non-condensable gas in the condenser 6 is discharged.

By repeating the above-described operations, the effective heat transfer area can be continuously increased or decreased. Incidentally, in the above embodiment, a case where the present invention is applied to exhaust gas heat recovery 14- from a hot air stove has been described, but it is needless to say that the present invention is not limited to this.

[Effects of the Invention] In summary, according to the present invention, the following excellent effects can be achieved.

[1] By controlling the condensate level in the condenser or by controlling the height of the gas column of non-condensable gas, the effective heat transfer area can be continuously changed, so the low temperature of the evaporator can be changed. Even if the temperature of the side heat exchanger tube approaches the dew point temperature, the temperature of the heat exchanger tube can be continuously maintained above the dew point temperature.

(2) Therefore, since the effective heat transfer area is changed continuously instead of stepwise as in the conventional example, the effective heat transfer area can always be maximized at temperatures above the dew point temperature, improving heat recovery efficiency. I can do it.

(3) It is not necessary to provide many stop valves as in the conventional case (one is sufficient for one condenser, and even when non-condensable gas is used, the number of valves is small, and the overall It can contribute to reducing equipment costs.

[Brief explanation of drawings]

Fig. 1 is a schematic perspective view showing an example of an exhaust heat recovery device for carrying out the method of the present invention, Fig. 2 is a partial perspective view showing another embodiment, and Fig. 3 is an exhaust heat recovery device installed in a hot blast stove. FIG. 4 is a schematic plan view showing the device, FIG. 4 is a schematic perspective view showing a conventional waste heat recovery device, and FIG. 5 is a schematic perspective view showing another conventional waste heat recovery device. In addition, in the figure, 3 is an evaporator, 6 is a condenser, 9 is a heat exchanger tube, 15 is a circulation system, 19 is a liquid level control valve, 20 is a controller, 22.23
is a temperature sensor. Patent applicant: Ishikawajima-Harima Heavy Industries Co., Ltd. Attorney and Attorney
Kinu Tani Nobu Yuki Q6 My sister's printing group Gakbiomi district

Claims (1)

[Claims] The circulation system that circulates the heat medium is equipped with an evaporator and a condenser, each with a built-in heat transfer tube, and the heat medium vapor generated in the evaporator is condensed in the condenser to recover heat from exhaust gas, etc. In the waste heat recovery device, the temperature of the heat transfer tube of the evaporator or the vapor temperature of the heat medium is detected, the detected temperature value is compared with a preset dew point temperature value, the temperature difference is calculated, and the temperature difference is calculated. Evaporation in the exhaust heat recovery device, characterized in that the effective heat transfer area of the heat transfer tube built in the condenser is continuously increased or decreased so that the detected temperature value exceeds the dew point temperature value based on Method for controlling the surface temperature of heat transfer tubes inside the vessel.