JPS6373092A - Heat exchanger - Google Patents

Abstract

PURPOSE:To effectively prevent a low temperature corrosion by connecting heat transfer tubes having a possibility of producing the low temperature corrosion, of heat transfer tubes constituting an evaporation tube group, to each other by a medium circulation system separate from other heat transfer tube group, and closing the medium circulation system of the heat transfer tubes upon lowering of the temperature of a heating gas. CONSTITUTION:A plurality of stages of heat transfer tube panels PA are arranged within a duct 1 through which a heating gas 17 passes in the shifting direction of the heating gas. When the measured temperature of the heating gas 17 becomes lower than a predetermined value, and a possibility of producing a low temperature corrosion is produced in heat transfer tube panels PA1 and PA2, a temperature controller 14 closes valves 12a and 12b and stops the supply of a heating fluid to a liquid lifting heater. Thus, air bubbles are not produced from a medium in a liquid connecting tube, and the circulation of the liquid is stopped. Accordingly, since the heat absorption in the heat transfer tube panels PA1 and PA2 is stopped, the surface temperature of heat transfer tubes constituting these heat transfer tube panels is kept at a value higher than a predetermined value, thus preventing the low temperature corrosion.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat exchanger, and particularly to a separate heat pipe type heat exchanger that can effectively prevent low-temperature corrosion.

[Conventional technology]

Heat pipes have excellent advantages such as simple structure, wide adaptability, controllable heat transfer, and ability to transport heat over long distances with little heat. Because of these characteristics, they are widely used as heat transfer elements in a variety of fields, from small household devices to large industrial devices. The basic structure of a heat pipe is that a fluid, which is a working medium, is sealed in a single sealed space, and the fluid changes its phase from vapor to liquid between an evaporating part (heat absorption part) and a condensing part (heat radiation part). Heat is transferred by circulating flow. However, in large-scale industrial heat pipes, separate type heat pipes in which the evaporating section and the condensing section are installed separately have been put into practical use.

FIG. 2 shows a popular separated heat pipe commonly called a gas-gas heater, which is used to effectively utilize waste heat in thermal power plants and chemical plants. In the same device, in a duct 1 through which heated gas (high temperature gas) 17 passes, heat transfer tube panels PA in which a plurality of heat transfer tubes are integrated with upper and lower headers are arranged in multiple stages in the direction of movement of the heated gas. These panels PA as a whole form an evaporation tube group 3.

On the other hand, for the duct 2 through which the heated gas (low-temperature gas) 18 passes, heat exchanger tube panels PB having the same configuration as the aforementioned panels are arranged in multiple stages in the direction of gas movement, and these heat exchanger tube panels The entire PB constitutes a condensing tube group 8. These tube groups 3 and 4 are connected by a steam communication tube 5 and a liquid communication tube 6, and constitute a closed loop as a whole.

In this configuration, the heat transfer medium in the evaporator tube group 3 (e.g.
water") is evaporated by the heat of the heating gas 17, and
, and reaches the condensing pipe group 8 via the steam pipe 5. Here, the heat transfer medium releases latent heat to heat the gas to be heated 18, and condenses itself.

The condensed liquid returns to the evaporation tube group 3 via the liquid communication tube 6. In this manner, the heat transfer medium circulates and flows while changing its phase between vapor and liquid, thereby transferring the heat of the heating gas 17 to the heated gas 18 side.

[Problem to be Solved by the Invention 3] In the above configuration, when the heating gas 17 is waste gas from a combustion device, there is a possibility that low-temperature corrosion will occur in the heat transfer tubes due to the sulfur content in the waste gas.

That is, while the heated gas 17 passes through the evaporation tube group 3, heat is removed and the temperature decreases, but in this case, if the temperature of the heated gas 17 is originally lower than the specified temperature, the downstream heat exchanger tube panel, For example, as the surface temperature of the heat exchanger tube panel PAI in the figure decreases, moisture in the gas condenses on the surface of the heat exchanger tubes, and the sulfur content in the gas reacts to produce corrosive liquids such as sulfuric acid. Pipes are corroded. If the heat transfer tube were to break due to corrosion and the internal fluid should leak, there is a risk of a major accident. For this reason, conventionally, the heat transfer area of the evaporator tube group arranged in the flow path of the heating gas 17 is set small in advance to cope with the case where the flow rate of the heating gas 17 decreases or the temperature decreases. This prevented low-temperature corrosion. However, since this configuration limits the heat transfer area of the evaporator tube group in advance, if the flow rate of the heated gas increases or the temperature rises, it becomes impossible to absorb enough heat from the heated gas. , the efficiency of the heat exchanger as a whole becomes poor.

[Means for solving problems]

The present invention is configured to eliminate the problems of the conventional configurations described above.

That is, the present invention connects the heat exchanger tubes that are likely to cause low-temperature corrosion among the heat exchanger tubes constituting the evaporator tube group through a medium circulation system that is separate from the other heat transfer tube groups, and in this medium circulation system. is a heat exchanger configured to control the flow of a heat transfer medium in accordance with the temperature of heated gas.

[Effect]

If there is a risk of low-temperature corrosion due to a drop in the temperature of the heated gas, etc., the medium circulation system of the heat exchanger tube that may cause low-temperature corrosion is closed, the circulation of the medium is stopped, and the temperature of the heat exchanger tube is lowered. Maintain the temperature at a temperature that does not cause low-temperature corrosion. Further, when the heated gas is at a predetermined temperature or higher, the medium circulation system is opened and all heat transfer tubes are used for heat transfer.

[Implementation row]

Examples of the present invention will be described in detail below.

First, the arrangement of the heat exchanger tube panel and the evaporator tube group, condensation tube group, etc. that are constituted by these panels is basically almost the same as the conventional structure. That is, in the duct 1 through which the heated gas (high-temperature gas) 17 passes, heat transfer tube panels PA in which a plurality of heat transfer tubes are integrated by upper and lower headers 4 are arranged in multiple stages in the direction of movement of the heated gas. , these panels PA as a whole form an evaporation tube group 3.

On the other hand, for the duct 2 through which the heated gas (low-temperature gas) 18 passes, heat exchanger tube panels PB having the same configuration as the aforementioned panels are arranged in multiple stages in the direction of gas movement, and these heat exchanger tube panels The entire PB constitutes a condensing tube group 8. These tube groups 3 and 8 are connected by a steam communication tube 5 and a liquid communication tube 6, and constitute a closed loop as a whole.

Next, among the heat transfer tube panels PA forming the evaporation tube group 3, PAL located at the most downstream position and PA2 located upstream thereof constitute a medium circulation system separate from other heat transfer tube panels. First, the heat exchanger tube panel FAI will be described. This panel PAI is connected to the most downstream heat exchanger tube panel FBI among the heat exchanger tube panels PB constituting the condensing tube group 8 through the liquid communication pipe 7a. However, the medium outlet side is connected to the steam communication pipe 5 like other heat exchanger tube panels. Similarly, evaporator tube group 3
The side heat exchanger tube panel PA2 and the heat exchanger tube panel PB2 of the eight condensing tube groups are connected by separate liquid communication pipes 7b, and independent medium circulation loops are established between these heat exchanger tube panels PAI and PBI and between PA2 and PH1. Configure. As shown in the figure, the liquid communication tubes 7a and 7b connecting these heat exchanger tube panels are once raised vertically higher than the upper end of the evaporator tube group 3, and then lowered and positioned at the bottom of each heat exchanger tube panel. It is configured to connect to a media storage compartment. 1
0a and 10b are pumping liquid heaters arranged at the rising portions of these pipes 7a and 7b. Further, reference numerals 15a and 15b are gas venting pipes, which connect the upper ends of the liquid communication pipes 7a and 7b and the steam communication pipe 5. Reference numeral 11 denotes a pipe line for supplying heating fluid to the pumped liquid heaters, and control valves 12a and 12b control the supply of heating fluid to each pumped liquid heater.

Reference numeral 14 denotes a temperature control device, and a temperature sensor 13 that measures the gas temperature near the most downstream heat transfer tube panel PA1 of the evaporator tube group 3 is connected to this temperature control device.
Answers 12a and 12b are determined according to the temperature of the heated gas measured in 4.
is operated to drive and stop the liquid pumping heaters tOa and 10b. Furthermore, the reference numeral 16 is a communication pipe, and this communication pipe 16
A liquid reservoir 9 is arranged in the area.

In the above configuration, the heat transfer medium (for example, "water") in the evaporator tube group 3 is evaporated by the heat of the heating gas 17, and each header 4
, and reaches the condensing pipe group 8 via the steam communication pipe 5. Here, the heat transfer medium releases latent heat to heat the gas to be heated 18, and condenses itself. The condensed liquid returns to the evaporation tube group 3 via the liquid communication tube 6. In this way, the heat transfer medium is steam,
The heat of the heated gas 17 is transferred to the heated gas 18 side by circulating the liquid and its phase while changing it.

During this heat exchange, the temperature control device 14 constantly monitors the temperature of the heated gas 17 downstream of the evaporator tube group 3 using the temperature sensor 13. As a result, the heat exchanger tube panel PAI
and controls the medium circulation loop of PBI, PA2, and PH1. That is, when the measured temperature of the heated gas 17 is a predetermined value or higher, the temperature control device 14 responds to the answer 12a,
12b is opened to supply heating fluid to pumped liquid heaters 10a and 10b. As a result, the heat transfer medium remaining in each liquid communication pipe 7a, 7b is heated and generates bubbles. These bubbles rise up the rising portion of each liquid communication pipe, and the liquid serving as the medium also rises due to this rising force. In this way, when the steam reaches the upper end of the liquid communication pipe, the gas vent pipes 15a, 1
5b, it flows into the water connecting pipe 5 to ensure the subsequent flow of liquid.

On the other hand, the liquid flowing through the descending portions of the liquid communication pipes 7a and 7b flows into the respective heat transfer tube panels PAI and PA2, and generates steam by the heat of the heating gas 17, and the generated steam passes through the steam communication pipe 5 and into the condensing tube group. 8. That is, these independent media vIi
The ring system also transfers heat in the same way as other heat exchanger tube panels when the measured temperature of the heated gas 17 is a predetermined value or higher.

Next, the measured temperature of the heating gas 17 becomes below a predetermined value,
If there is a possibility that low temperature corrosion will occur in the heat exchanger tube panels PAL and PA2, the temperature control device 14 will control the valves 12a and 12b.
is closed and the supply of heating fluid to the pumped liquid heater is stopped. As a result, no bubbles are generated from the medium in the liquid communication tube, and the flow of the liquid stops. Therefore, heat transfer tube panel PA
Since heat absorption in L and PA2 is stopped, the surface temperature of the heat exchanger tubes constituting these heat exchanger tube panels is maintained at a predetermined value or higher, and low-temperature corrosion is prevented. In this case, depending on the measured temperature of the heated gas, it may be necessary to stop the flow of the medium only in the most downstream heat exchanger tube panel PAL, so in this case, only the valve 10a is closed and the heat exchanger tube panel PAL is closed.
A2 can also be controlled to circulate the medium.

Note that in order to smoothly circulate the flow between the evaporator tube group 3 and the condenser tube group 8, the condenser tube group 8 is arranged at a higher position than the evaporator tube group 3; Simply stopping the heater cannot completely stop the circulation of the medium. For this reason, as mentioned above, the liquid communication pipes 7a and 7b are once raised to a higher position than the evaporation pipe group 3, and are configured to create a gas space at this high position, thereby ensuring that the liquid flow stops when the liquid pumping heater is stopped. It is configured to do so. Note that the medium in the heat exchanger tube panel of the loop where the flow of the medium has stopped is evaporated by the heated gas and flows into the steam communication pipe 5, so the amount of liquid medium becomes relatively surplus. Adjustment is made by adjusting the liquid level in reservoir 9.

In the above configuration, the pumping liquid heater is used as the device for starting and stopping the flow of the medium, but in the pumping liquid heater, the heating fluid circulation path and the liquid communication pipe are completely separated, and the airtightness of the pumping liquid heater installation part is extremely high. It is highly suitable for On the other hand, in control devices such as valves, the part that operates the valve body is always located outside the liquid communication pipe, which reduces airtightness and may reduce the performance of the heat pipe as a whole, which is not so desirable. .

〔effect〕

As the configuration of the present invention has been shown above, among the heat exchanger tubes constituting the evaporator tube group, the heat exchanger tubes that are likely to cause low-temperature corrosion are connected by a separate medium circulation system from the other heat exchanger tube groups. death,
In addition, this medium circulation system is configured to control the flow of the heat transfer medium in accordance with the temperature of the heated gas, and if there is a risk of low-temperature corrosion occurring due to the temperature reduction ring of the heated gas, this low-temperature corrosion can be prevented. It is possible to close the medium circulation system of the heat transfer tube, which may cause corrosion, to stop the circulation of the medium, and to maintain the temperature of the heat transfer tube at a temperature at which low temperature corrosion does not occur, thereby effectively preventing low temperature corrosion. Can be done.

In addition, if the heated gas is at a predetermined temperature or higher, this medium circulation system is opened and all heat transfer tubes are used for heat transfer, and if there is a possibility of low-temperature corrosion, some By stopping the flow of the medium in the heat transfer tube, the heat transfer area can be adjusted according to the temperature and flow rate of the heating gas, so unlike the conventional configuration, the heat transfer area can be set to a small value in advance to prevent low-temperature corrosion. There's no need to. Therefore, high heat exchange efficiency can be maintained at all times regardless of the temperature of the heated gas.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a heat exchanger showing the configuration of the present invention, and FIG. 2 is a system diagram of a heat exchanger with a conventional configuration. 3... Evaporation tube group 5... Steam communication pipes 7a, 7b.
...Liquid communication pipe 8...Condensing pipe group 9...Liquid reservoir 10a, 10b...Hyper heater 11...Heating fluid 12a, 12b...Control valve 13...Changing degree sensor 15a, 15b...Gas vent pipe 16...Transmission pipe 17...Heating gas l8...Heated gas PA, PAI, PA2...Evaporator tube group side heat exchanger tube panel PB, PBI, PB2.・Condenser tube group side heat transfer tube panel

Claims (4)

[Claims] (1) An evaporation tube group consisting of a plurality of heat transfer tubes is arranged on the heating fluid side, and a condensation tube group consisting of a plurality of heat transfer tubes is arranged on the heated fluid side, and these evaporation tube group and condensation tube A heat exchange system in which a medium circulation system is constructed by connecting the groups with steam communication pipes and liquid communication pipes, and heat is transferred from the heated fluid side to the heated fluid side by circulating and flowing the medium through these pipe groups. In the heat exchanger tube group, among the heat transfer tube groups that make up the evaporator tube group, the tube group that may cause low-temperature corrosion and a part of the tube group that makes up the condensing tube group are separated from the liquid communication tubes of other tube groups. is connected with another independent liquid communication pipe, and a device for controlling the medium flow is arranged for this independent liquid communication pipe, and this control device is operated according to the temperature of the heating fluid side. A heat exchanger characterized in that it is configured to prevent low-temperature corrosion of heat exchanger tubes in a heat exchanger. (2) The independent liquid communication pipe is arranged to stand up in a substantially vertical direction so that its top is higher than the upper end of the evaporation tube group, and the top of the independent liquid communication pipe and the steam communication pipe are connected to each other for gas. 2. The heat exchanger according to claim 1, wherein the heat exchanger is connected to a discharge pipe and further includes a pumping liquid heater as a device for controlling the flow of the medium to the rising portion of the liquid communication pipe. (3) A temperature sensor is arranged in the heated fluid flow path on the downstream side of the evaporation tube group, and this temperature sensor is connected to a control device, and the control device is connected to the control valve of the pipe that supplies the heated fluid of the pumped liquid heater. 2. The heat exchanger according to claim 2, wherein the heat exchanger is connected by a command signal circuit, and the control device is configured to operate the control valve in accordance with the temperature of the heating fluid. (4) By connecting the steam communication pipe and the liquid communication pipe with a communication pipe, installing a liquid reservoir for this communication pipe, and adjusting the liquid level in this liquid reservoir, an independent medium circulation loop can be created. Claim No. 1 is characterized in that the structure is configured to cope with fluctuations in the required medium liquid amount due to the flow or stoppage of the medium in the medium.
) to (3).