JPS63310626A - Heat exchanger for steam power plant - Google Patents

Abstract

PURPOSE:To obtain the same rectifying effect as obtained when a rectifying lattice is used, and to reduce the drift loss in a gas turbine, etc., by disposing an injection lattice injecting a reducing agent to the rear part of pipe cluster provided to the front part of a denitrating catalyst layer. CONSTITUTION:The denitrating catalyst layer 11 is formed in plural pipe clusters constituting a heat exchanging part, and the injection lattice 12 injecting the reducing agent into exhaust gas or burned gas entering the denitrating catalyst layer 11 is provided in the upstream side of the denitrating catalyst layer 11. And, the injection lattice 12 is furnished between the denitrating catalyst layer 11 and the pipe clusters 2, 3 with a specified distance from the rear part of the pipe clusters. As a result, the pipe cluster of its own functions as a rectifying mechanism to reduce the drift loss in a gas turbine, etc.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention provides a steam power system incorporating a denitrification catalyst layer for reducing nitrogen oxides contained in the exhaust gas or combustion gas of a cast turbine. It relates to a heat exchanger for equipment.

(Prior art) Generally, an exhaust heat recovery heat exchanger is used in a steam power plant (consisting of a steam turbine and a condensing device) in a combined cycle power plant.
used for the purpose of producing steam for This exhaust heat recovery heat exchanger simultaneously reduces a large amount of nitrogen oxides (NOx) in the exhaust gas released from the gas turbine to harmless nitrogen using a reducing agent such as ammonia.
For this purpose, the exhaust heat recovery heat exchanger is usually equipped with a denitrification device. There are two types of denitration wrestling: dry and wet, with the dry method being preferred.

Among the dry processes, the one used in the exhaust heat recovery heat exchanger is called the dry catalytic reduction method. This method uses ammonia etc. as a reducing agent, and the exhaust gas temperature is 250~250℃.
This system uses a catalyst installed in the 450'C range to reduce and decompose NOx into nitrogen and steam. By the way,
The wet process uses a sulfate or the like as an absorption liquid, and oxidizes and reduces NOx within this absorption liquid. These two types of denitrification processes each have their advantages and disadvantages, and should be used depending on the situation.

As mentioned above, the optimum reaction temperature of the catalyst in the dry catalytic reduction method is 250 to 450°C. In the case of an exhaust heat recovery heat exchanger, the position of the denitrification catalyst layer is determined from the above reaction temperature as follows. That is, as shown in FIG. 9, the exhaust heat recovery heat exchanger has five components in the shell 1: a superheater 2, a high-pressure evaporator 3, a high-pressure economizer 4, a low-pressure evaporator 5, and a low-pressure economizer 6. Exhaust gas is introduced into the shell 1 at a temperature of approximately 500' (: 'C and is discharged outside the vessel. Therefore, since any of the five heat exchange parts is within the optimum reaction temperature range of the denitrification catalyst, the space between the five heat exchange parts 7.8. 9.10, a catalyst suitable for each temperature is selected, and the denitrification catalyst layer 11 is formed at the most preferable location.

On the other hand, a reducing agent such as ammonia must be injected upstream of the denitrification catalyst rS layer 11. This is to ensure that the reducing agent is diffused to every corner of the flow of exhaust gas containing NOX and brought into contact with the denitrification catalyst once the concentration distribution is uniform. An injection grid 12 is installed for injecting the reducing agent. Normally, this injection grid 12 is constructed by fixing a plurality of injection tubes 13 placed parallel to each other with a support beam 14 placed perpendicular to the injection tubes 13, as shown in FIGS. 1Q (a) and (b). It is formed as a whole or in the form of a grid. Roughly speaking, a rectifying grid 15 is provided upstream of the injection grid 12. This is because if the flow of exhaust gas toward the injection grid 12 becomes large, the injection of the reducing agent becomes uneven, making it impossible to obtain a uniform concentration distribution, so the flow of the gas is changed to rectification through the rectification grid 15. be.

(Problems to be Solved by the Invention) When trying to obtain a uniform concentration distribution of the reducing agent in the denitrification process using the dry catalytic reduction method described above, the function of the rectifying grid 15 that rectifies the flow of waste gas is especially ignored. I can't. Generally, the flow of exhaust gas is disturbed by the operating conditions of the gas turbine, the shape of the exhaust duct, etc., resulting in uneven flow.

In most cases, it is possible to convert this drift into rectification using the rectifier grating 15, and there is almost no question about the movement of the rectifier grating 15.

However, there is a problem in that the flow of exhaust gas is temporarily stagnated in the heat exchanger section due to the rectifying grid 15, and the occurrence of drift loss becomes unavoidable, resulting in a decrease in the output of the gas turbine.

The purpose of the present invention is to provide a heat exchanger for a steam power plant that has a novel rectification mechanism that has a rectification effect equivalent to that of using a rectifier grid and has no chance of causing drift or loss. [Structure of the Invention] (Means for Solving the Problems) The heat exchanger for a steam power plant according to the present invention has an injection grid located at the rear of the tube group placed before the denitration catalyst layer. It is characterized by being placed at a certain distance from the tube group.

(Function) Hereinafter, the results of an experiment conducted using an actual machine model will be explained in order to clarify the basis on which the present invention is established.

In other words, FIGS. 4(a) and 4(b) show the configuration of a group of tubes prepared for the experiment, and the reference numeral 16 in the figure is provided with spiral-shaped fins on the outer periphery. represents a heat exchanger tube,
As shown in the figure, the heat transfer tubes 16 are arranged in a staggered manner to form a tube group with eight stages. Air is caused to flow through this tube group from the direction indicated by the arrow, and the velocity distribution behind the tube group is measured.

By the way, the above-mentioned number of stages is determined based on the following considerations regarding the flow within the tube group. Generally, the air that has flowed into the tube group collides with the surface of the heat exchanger tubes 16 and becomes turbulent flows such as flows Fl and F2, but then settles down and becomes a regular flow such as flow F3. The number of stages that can obtain this regular flow is eight. In other words, it can be seen that the heat transfer at each stage of the tube group corresponds to the flow state in that region, and the flow state can be considered from the results of observing heat transfer as shown in Figure 5. It is possible. It is clear from this figure that the heat transfer is approximately equal to the saturation value after the 8th stage, and it is expected that the flow will be regular from this point onwards, so the number of stages is set to 8.

The results of an experimental investigation of the flow outside the tube group are shown in FIGS. 6 to 8.

The test results will be explained in detail below.

In Fig. 6, reference numeral 17 indicates a polygonal line indicating the flow velocity of turbulent air intentionally created at the inlet of the tube group, and it is measured at the upper end of the tube group (see code X in Fig. 4 (b)). It is based on the value given. Line 1 showing this inlet velocity distribution
The changes at each measurement point 18a, 18b, 18c, and 18d indicate the respective flow velocities.
Here, the measurement point 18d is located at a distance corresponding to 8 stages of the tube group (symbol L in Fig. 4(b)).
Hereinafter, the measurement point 18a is set at 1/4 of this, and 18C is set at 3/4 of this. The measurement point 18b is set slightly ahead of 2/4, or more precisely at point 7716. Further, V/Vavc on the horizontal axis represents a dimensionless velocity ratio obtained by dividing the velocity V at the measurement point by the average flow velocity v ave at the measurement point.

The air flow passing through the last row of heat transfer tubes 16 in the tube group has a regular uneven velocity distribution at the measurement point 18a, as shown by the polygonal line 19. That is, the gap 23 between the heat exchanger tubes 16.
24. The velocity of the point corresponding to 25 is that the air flow is a heat transfer tube.
Because it is not obstructed by 6, it is faster than other measurement points. On the other hand, the air flow at the position overlapping with the heat exchanger tube 6 is disturbed by the collision with the heat exchanger tube 16, and is slower than at other measurement points.

Roughly speaking, when the air flow advances to the measurement point 18b, the air flow begins to mix in the width direction, so the polygonal line 20
As shown in Figure 1, the unevenness is relaxed and the velocity distribution becomes relatively flat, but some unevenness is still visible. At the position of measurement point 18G, the remnants of unevenness disappear as shown by polygonal line 21, resulting in a fairly flat velocity distribution, and at measurement point 18d, that is, a distance equivalent to 8 stages of the tube group, the flattening of the velocity distribution is almost completed as shown by polygonal line 22. It appears that he did.

Figures 7 and 8 show the central part and lower end (fourth part) of the tube group.
This is the result in Figure (b) (see symbols Y and Z). As is clear from the figure, the results are almost the same as those in FIG. 6, and it can be seen that the air velocity valve A5 has completely flattened at the measuring point 18d.

From the above experimental results, it has been verified that the tube group itself is equipped with a rectifier structure, and it is possible to function as an alternative to the conventional rectifier grid. Therefore, as long as the injection grid is placed in an appropriate position behind the tube bank to be worked before the denitrification contact RR layer, no rectification grid is required. That is, this position minimizes the distance equivalent to 8 stages of the tube group based on the experiment described above. A tube bank flow straightener instead of a flow straightener grid helps reduce drift losses, thereby increasing gas turbine power output.

(First example) FIG. 1 shows an example of application to an exhaust heat recovery heat exchanger.

Here, the injection grid 12 is provided on the downstream side of the high-pressure evaporator 3, and its position is at a distance corresponding to the 8th stage of the tube group from the end of the tube group of the high-pressure evaporator 3 shown in FIG. (b) is at a distance L) far away.

In this embodiment, the injection grid 12 is arranged at a distance corresponding to 8 stages of the tube group from the end of the tube group. The flow of exhaust gas leaving the afu has already become regular after the afu, and the flow of exhaust gas is changed into a rectified flow before the injection grid 12.

(Second Embodiment) A second application example of the present invention is a case where a denitrification catalyst layer 26 is formed in the exhaust flue 25 of a combustion wheeler shown in FIG. Here, the denitrification catalyst layer 26 is installed downstream of the economizer 27, 28, but this is because the optimum reaction temperature of the catalyst is 25.
Needless to say, this takes into account the temperature range of 0 to 450°C. The injection grid 29 in this embodiment is installed at a distance corresponding to eight stages of the tube group from the last end of the tube group constituting the superheater 30 and the reheater 31.

In the present embodiment, since the number of stages of the tube group in the reheater 31 is eight or more, the flow of combustion gas exiting the last stage is already a regular flow from the eighth stage onward, and a rectifying grid is used. It is possible to reduce the rectification effect by 1 w, which is equivalent to the case where the

The method of applying the present invention when the number of tube group stages is less than 8 is as follows. That is, the position of virtual 8 stages counting from the 1st stage of the tube group is determined, and the position corresponding to the 8 stages ahead is set as the installation location of the injection grid. In this way, since the injection grating is placed in the same position as in the first and second embodiments, the same effects as in the first and second embodiments can be obtained. I can do that.

[Effects of the Invention] As explained above, in the present invention, the injection grid for injecting the reducing agent is arranged behind the tube group provided before the denitration catalyst layer, so the tube group itself has a flow rectification mechanism. It has the excellent effect of reducing drift loss in gas turbines and the like.

[Brief explanation of the drawing]

1 and 2 are a configuration diagram of an exhaust heat recovery heat exchanger and an arrangement diagram of an injection grid according to a first embodiment of the present invention, and FIG. 3 is a configuration diagram of a combustion boiler according to a second embodiment of the present invention. 4(a) and (b) are a plan view and an elevation view of the heat exchanger tube group used in the experiment of the present invention, and FIG. 5 is a line showing the relationship between the number of stages of the tube group and the heat transfer coefficient. Fig. 6, Fig. 7, and Fig. 8 are state diagrams showing air velocity distribution, Fig. 9 is a configuration diagram showing a conventional exhaust heat recovery heat exchanger, and Fig. 10 (a>(b) 1 is a front view and a side view showing an example of a conventional injection grid. 1...Channel 2...Superheater 3...High pressure Evaporator 4...High pressure economizer 5...Low pressure evaporator 6...Low pressure economizer 11.26...Denitrification Catalyst layer 12.2... Injection grid 16... Heat exchanger tubes 17.19.2Q, 21.22... Broken lines 18a, 18b, 18c, 18 indicating air flow velocity d...Measurement point 27
．． 28...Coal economizer 31...Reheater Applicant: Tokyo Electric Power Co., Ltd. Applicant: Toshiba Corporation Representative Patent Attorney: Satoshi Suyama - Figure 1 Figure 2 Figure 3 Figure 4 Figure 1t Calendar Yakusanl Figure 5 ■／■C Figure 6 Figure 7 Figure 8 Figure 9 (al (b) Figure 10

Claims (2)

[Claims] (1) A denitrification catalyst layer is formed in a plurality of tube groups constituting the heat exchange section, and a reducing agent is injected into the upstream side of the denitrification catalyst layer for the exhaust gas or combustion gas heading toward the denitrification catalyst layer. In a heat exchanger provided with an injection grid, the injection grid is arranged behind a group of tubes placed before the denitrification catalyst layer, with a certain distance between the group of tubes. Features of heat exchanger for steam power equipment. (2) The heat exchanger for a steam power plant according to claim 1, wherein the injection grid is arranged at a distance corresponding to at least eight stages of the tube group from the end of the tube group.