JPH02309101A - Waste heat recovery heat exchanger - Google Patents

Abstract

PURPOSE:To prevent water hammering or instability in the quantity of feed water to a steam drum from occurring and enable a uniform distribution of exhaust gas temperature to be obtained at an outlet of an economizer, by a construction wherein all flows of feed water in heat exchanger tubes on the upstream side with respect to an exhaust gas flow on which steam bubbles might be generated in the heat exchanger tubes during a low-load operation are upward flows, and downward flow of the feed water is permitted in non-heating connection tubes. CONSTITUTION:Feed water 4 first flows upward through heat exchanger tubes 51 in a heat exchanger tube panel 54b into an upper header, then flows through a connection tubes 55a into an upper header 52 of an adjacent heat exchanger tube panel 54b on the upstream side with respect to an exhaust gas flow, and flows downward through heat exchanger tubes 51. Then the feed water 4 flows upward and downward repeatedly in the panels 54b, and flows through a connection tube 55b or 55c into a lower header 53 of a heat exchanger tube panel 54a. The feed water 4 then repeats upward flow through the heat exchanger tubes 51 and downward flow through the connection tube 55b or 55c, and is fed out from an economizer 23 to a stream drum. Variations in the flow of feed water due to generation of steam bubbles and the accompanying water hammering or instability in the quantity of feed water supplied to the steam drum can be prevented from occurring, and a substantially uniform temperature distribution on a practical basis can be obtained at an outlet of the economizer 23.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an exhaust heat recovery heat exchanger that generates steam using exhaust gas from a gas turbine, and particularly during low load operation. The present invention also relates to an exhaust heat recovery heat exchanger having a fuel economizer that allows stable flow in the pipes without causing water hammer.

(Conventional technology) In recent years, from the perspective of effective energy use, combined cycle power generation and cogeneration power generation have been developed to generate exhaust heat from gas turbines and diesel engines and their exhaust gas, which is used as a high-temperature heat source to generate drive steam for steam turbines and process steam. Power generation systems that combine a recovery heat exchanger are attracting attention.

FIG. 3 shows an example of the configuration of a conventionally known combined cycle power generation system. This system includes a gas turbine device 10, an exhaust heat recovery heat exchanger 20 that generates steam using its exhaust gas as a heat source. A steam turbine device 30 driven by steam generated in the exhaust heat recovery heat exchanger 20 and a generator 40 directly connected to both the turbine devices IO and 30.
and 41. Gas turbine device 10
is composed of a compressor 11, a combustor 12, and a gas turbine 13. Combustion air 1 is pressurized by a compressor 11 and sent to a combustor 12, where it is mixed with fuel 2 and combusted to become high-temperature combustion gas. After this combustion gas is sent to the gas turbine 13 and does work, it becomes exhaust gas 3 and is led to the exhaust heat recovery heat exchanger 20.

The exhaust heat recovery heat exchanger 20 includes, for example, a superheater 21, an evaporator 22, and a economizer 23 in order from the upstream side of the flow of the exhaust gas 3, and the exhaust gas 3 exiting the economizer 23 is sent to the atmosphere from a chimney (not shown). released inside.

On the other hand, exhaust steam exiting the steam turbine 31 is condensed in a condenser 32, then pressurized by a water supply pump 33 and supplied to the energy saver 23. This feed water 4 is superheated to near the saturation temperature in the economizer 28 and then introduced to the canned water section of the steam drum 24. The canned water in the steam drum 24 is sent to the evaporator 22, where a part of it becomes steam, and then returns to the steam drum 24 again, where moisture is removed and sent to the superheater 21. The steam superheated in the superheater 21 is sent as main steam 5 to the steam turbine 31, where it expands and performs work, and then is discharged to the condenser 32.

(Problem to be solved by the invention) One of the characteristics of the combined cycle power generation system configured as described above is that it is capable of efficient operation in a wide range of load bands. There is a problem.

As mentioned above, in the economizer, the water fed by the water pump is heated to a temperature close to the saturation temperature of the steam drum relative to the internal pressure. The difference between the water supply temperature at the exit of the economizer and the saturation temperature (hereinafter referred to as "F approach point temperature difference") is often designed so that it is generally 6 to 10 degrees Celsius at rated load. However, the approach point temperature difference decreases as the load decreases. When the load falls below a certain level, this temperature difference becomes 0°C, and steam bubbles occur in the heat exchanger tubes of the economizer, so-called steaming. The relationship between the water supply temperature and the heat transfer area in the economizer at this time will be explained in more detail using FIG. 4. Figure 4 shows how the feed water temperature changes in the economizer, with the horizontal axis representing the heat transfer area along the flow of the feed water, and the vertical axis representing the temperature of the feed water at saturation within the economizer. It is shown relative to the temperature difference between the temperature and the inlet water supply temperature. The feed water that has flowed into the economizer exchanges heat with the exhaust gas, and is heated as the heat transfer area increases as it passes from the inlet to the exit of the economizer. In order to prevent steaming from occurring within the economizer heat transfer tubes during rated load, the approach point temperature difference is generally set to 6 to 10°C as described above. However, when the load decreases, the temperature and flow rate of the exhaust gas decrease, but the flow rate of the feed water also decreases as the amount of evaporation decreases, and the pressure inside the steam drum also decreases, so the difference between the saturation temperature and the inlet feed water temperature decreases. The rate of increase in feed water temperature per unit heat transfer area relative to increases. For this reason, as the load decreases, the approach point temperature difference decreases, and below a certain load level, the feed water temperature reaches the saturation temperature before it reaches the economizer outlet, causing the This causes steam bubbles to form inside.

On the other hand, the structure of a conventional energy saver of an exhaust heat recovery heat exchanger in which exhaust gas flows horizontally is as shown in FIG. 5, for example. The plurality of heat transfer tubes 51 are an upper header 52 and a lower header 5.
3 to form a heat exchanger tube panel 54. The economizer is constituted by a plurality of heat exchanger tube panels 54, and the upper header 52 or the lower header 53 between adjacent heat exchanger tube panels 54 are connected by a connecting pipe 55a. The feed water 4 that has entered the energy saver configured in this way first rises (descends) inside the heat transfer tube, enters the upper header 52 (lower header 53), passes through the connecting pipe 55a, and then flows into the adjacent header. Heat exchanger tube panel 5 on the upstream side of the flow of exhaust gas 3
4 is sent to the upper header 52 (lower header 53). Thereafter, the feed water 4 descends (rises) through the heat transfer tubes 51, enters the lower header 53 (upper header 52), passes through the connecting pipe 55a, and further passes through the lower header 53 of the heat exchanger tube panel 54 on the upstream side of the gas flow.
(upper header 52). Thereafter, the feed water 4 flows through the heat exchanger tube of the economizer by repeating rising and falling in the same manner, and then reaches the outlet of the economizer (for example, Utility Model No. 61-13
5105, etc.).

If steam bubbles are generated during low-load operation in the heat transfer tube where the feed water of such a economizer flows downward (for example, the second heat transfer tube panel from the upstream side of the exhaust gas flow in Figure 5), the feed water will flow downward. In contrast, vapor bubbles tend to rise due to buoyancy. This contradictory movement between the feed water and the steam bubbles causes fluctuations in the flow of the feed water in the economizer, causing so-called water hammer or making the flow rate of the water feed to the steam drum unstable.

To solve this problem, an energy saver having a structure as shown in FIG. 6, for example, has been used so far.

As in the case of FIG. 5 described above, the economizer is constituted by a plurality of heat exchanger tube panels 54 formed by heat exchanger tubes 51, upper header 52, and lower header 53. However, the connections between the heat exchanger tube panels 54 are different, and the upper pipe header 52 is connected to the connecting pipe 55b passing through the gas passage on the downstream side of the gas flow of the economizer or through the communicating pipe 55c passing outside the gas passage.
and the lower header 53 of the adjacent heat exchanger tube panel 54 on the upstream side of the gas flow.

In the economizer with this structure, the water supply 4 ascends through the heat exchanger tubes 51, enters the upper header 52, descends through the connecting pipe 55b or 55c, and flows through the lower header 52 of the adjacent heat exchanger tube panel 54.
Sent to 3. Thereafter, the feed water 4 repeats the flow of rising in the heat exchanger tube of the economizer and descending in the communication pipe, and then reaches the outlet of the economizer. That is, in this structure, all of the water supply flow within the heat exchanger tube becomes an upward flow. Therefore, in an energy saver with this structure, even if steam bubbles are generated in the heat transfer tubes during low-load operation, the direction of the feed water flow and the direction of the buoyant force acting on the steam bubbles are the same, so the water supply as described above is Fluctuations in the flow and related problems do not occur, and although the flow in the connecting pipe is downward, it is not heated by the exhaust gas, so no new steam bubbles are generated and the supply water descends smoothly ( For example, JP-A-57-188904, JP-A-81-2
52401, etc.).

As described above, if the energy saver having the structure as shown in FIG. 6 is adopted, various problems caused by steaming of the water supply during low load operation can be solved, but on the other hand, the following problems occur. In other words, as shown in Fig. 2 as an example, when a economizer having the structure shown in Fig. 6 is adopted, the temperature distribution of the exhaust gas at the exit of the economizer is such that the temperature distribution between the upper part of the gas passage and the lower part thereof is This results in a large temperature difference, which has a negative impact on the heat transfer performance of the heat exchanger installed downstream of the gas flow of the economizer. This is because all the flows in the heat exchanger tubes are upward flows, so the temperature distribution of the feed water in all the heat exchanger tubes is high at the upper part of the gas passage section and low at the lower part thereof.

The purpose of this invention is to eliminate the above-mentioned problems, and even if steam bubbles are generated in the heat transfer tubes during low-load operation, fluctuations in the flow of water supply and accompanying instability in the flow rate of water supply to the water hammer and steam drum occur. An object of the present invention is to provide an exhaust heat recovery heat exchanger having a cost saving device that does not cause the heat transfer performance of the heat exchanger on the downstream side of the gas flow to be adversely affected by non-uniform distribution of outlet exhaust gas temperature. be.

[Structure of the invention]

(Means for solving the problem) In order to achieve this object, in the present invention, high-temperature exhaust gas flows horizontally, and heat transfer tubes installed in the gas passage are connected by an upper header and a lower header. In an exhaust heat recovery heat exchanger that has an energy saver made up of a plurality of heat exchanger tube panels, some of the heat exchanger tube panels installed upstream of the gas flow have heat exchanger tubes installed upstream of the feed water flow. By connecting the upper header of the panel and the lower header of the adjacent heat exchanger tube panel on the downstream side of this water supply flow with a connecting pipe, all the flow in the pipe is configured to be an upward flow.
For the remaining downstream heat exchanger tube panels, the upper headers or the lower headers of adjacent heat exchanger tube panels are connected along the water supply flow by connecting pipes, so that the flow inside the tubes becomes an upward flow.

It is characterized in that the heat tube panels and the downward flow heat transfer tube panels have economizers arranged alternately along the exhaust gas flow.

(Function) That is, in the present invention, for the heat exchanger tube panels on the upstream side of the exhaust gas flow of the economizer, where steam bubbles may occur in the heat exchanger tubes during low-load operation, the space between adjacent heat exchanger tube panels is By connecting the upper header of the panel on the downstream side of the exhaust gas flow and the lower header of the panel on the upstream side of the exhaust gas flow by a descending connecting pipe, all the water flow in the heat exchanger tubes belonging to the heat exchanger tube panel is made to be an upward flow. In addition, for the remaining heat exchanger tube panels on the downstream side of the gas flow, the upper headers of adjacent heat exchanger tube panels or the lower headers of adjacent heat exchanger tube panels are connected with connecting pipes, so that the water flow in the heat exchanger tubes becomes an upward flow. Panels and heat exchanger tube panels that flow downward are arranged alternately along the exhaust gas flow.

(Example) Hereinafter, an example of the present invention will be described using the drawings. 1st
The figure shows a system of a economizer which is an embodiment of the present invention. The plurality of heat exchanger tubes 51 are connected by an upper header 52 and a lower header 53 to form heat exchanger tube panels 54a, 54b, and the energy saver is connected to the heat exchanger tube panels 54a, 54b.
54b (five in the case of FIG. 1). Among these heat exchanger tube panels, the heat exchanger tube panels 54b on the upstream side of the water supply flow are connected by providing communication pipes 55a between the upper headers 52 or between the lower headers 53. Further, between the heat exchanger tube panels 54a on the downstream side of the water supply flow and between the heat exchanger tube panels 54b and 54a adjacent along the water supply flow, the upper header 52 of the heat exchanger tube panels on the upstream side of the water supply flow and the same downstream It is connected to the lower header 53 by providing a communication pipe 55b passing through the gas passage on the downstream side of the exhaust gas flow of the economizer or a communication pipe 55c passing outside the gas passage.

The number of panels from the upstream side of the exhaust gas flow to be used as the panel 54a described above among the heat exchanger tube panels constituting the economizer is determined as follows. That is,
As shown in Figure 4, steam bubbles are generated in the heat exchanger tubes only in the heat exchanger tube panels on the downstream side of the feed water flow, that is, on the upstream side of the exhaust gas flow, during low load operation. The heat exchanger tube panel where steam bubbles start to be generated is predicted, and all the panels located upstream from the heat exchanger tube panel are designated as panels 54a.

In the energy saver with such a configuration, the water supply 4 first rises through the heat exchanger tubes 51 of the heat exchanger tube panel 54b and enters the upper header, and then passes through the connecting pipe 55a to the adjacent exhaust gas flow on the upstream side. The heat tube panel 54b enters the upper header 52 and descends through the heat transfer tubes 51. After that, the water supply 4 is connected to the heat exchanger tube panel 54b.
After repeating the rise and fall within the connecting pipe 55b or 55c
and enters the lower header 53 of the heat exchanger tube panel 54a.

After the feed water 4 repeats the process of rising in the heat transfer tube 51 and descending in the communication pipe 55b or 55c, it exits the economizer and is sent to a steam drum (not shown).

In the energy saver of this embodiment described above, even if steam bubbles are generated in the heat transfer tube during low load operation, the feed water flow on the upstream side of the exhaust gas in the heat transfer tube is all upward flow, and the feed water flow is downward flow. Because there is no heat exchange with the exhaust gas in the connecting pipe, and no new steam is generated, fluctuations in the water supply flow due to the generation of steam bubbles and the accompanying water supply to the water hammer and steam drum It is possible to prevent the amount from becoming unstable. In addition, in the heat exchanger tube group on the downstream side of the exhaust gas flow where there is no risk of generating steam bubbles, the feed water flow alternately rises and falls, so the exhaust gas temperature distribution at the exit of the economizer reaches its maximum as shown in Figure 2. The temperature distribution between the upper part of the gas passage section and the lower part thereof, which is the lowest, is as small as 3°C, and in practical terms, a nearly uniform temperature distribution is obtained, which adversely affects the heat transfer performance of the heat exchanger on the downstream side of the exhaust gas flow. There isn't.

[Effects of the Invention] As explained above, according to the present invention, in the heat exchanger tubes on the upstream side of the exhaust gas flow where steam bubbles may be generated in the heat exchanger tubes during low-load operation, all feed water flows are upward flows, and the feed water flows downward.・Since this is done using an unheated connecting pipe, a stable water supply flow is achieved by preventing fluctuations in the water supply flow due to the generation of steam bubbles and the resulting instability in the amount of water supplied to the water hammer and steam drum. In addition, since the feed water flow alternately rises and falls in the heat exchanger tube downstream of the exhaust gas, where there is no risk of generating steam bubbles, a sufficiently uniform exhaust gas temperature distribution can be obtained at the outlet of the economizer, and the exhaust gas Good heat exchange can also be achieved with the heat exchanger on the downstream side.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of the economizer of the waste heat recovery heat exchanger according to the present invention, Fig. 2 is the exhaust gas temperature distribution at the outlet of the present invention and the conventional economizer, and Fig. 3 is the main part of the combined cycle power plant. Fig. 4 is a diagram showing the relationship between the feed water temperature and heat transfer area in the energy saver, and Figures 5 and 6 are the energy economizer of a conventional exhaust heat recovery heat exchanger. This is a system diagram of 3... Exhaust gas 4... Water supply 23... Energy saver 51... Heat exchanger tube 52... Upper header 53... Lower header 54.54a, 54b
... Heat exchanger tube panels 55a, 55b, 55c ... Liaison management agent Patent attorney Yudo Nori Chika Ken Daishimaru Figure 1 Figure 5

Claims (1)

[Claims] 1. High-temperature exhaust gas flows horizontally, and it has an economizer made up of a plurality of heat transfer tube panels formed by connecting heat transfer tubes installed in the gas passage section with an upper header and a lower header. In the waste heat recovery heat exchanger, for some heat exchanger tube panels installed upstream of the gas flow, there is a By connecting the lower pipe header of the heat pipe panel with a connecting pipe, all the flow in the pipe is configured to be an upward flow, while the remaining heat pipe panels on the downstream side are connected with the lower pipe header along the water supply flow. By connecting the upper headers or the lower headers of heat exchanger tube panels with connecting pipes, the heat exchanger tube panels in which the flow in the tubes is upward flow and the heat exchanger tube panels in which flow is downward can be alternated along the gas flow. An exhaust heat recovery heat exchanger characterized by having a disposed energy saver.