JPH0763305A - Exhaust heat recovery boiler - Google Patents

Abstract

PURPOSE:To feed superheat steam, generated by an exhaust heat recovery boiler, at temperature adjusted to a proper value. CONSTITUTION:A superheat steam generating part SH to change steam fed from a high pressure drum 20 of an exhaust heat recovery boiler 1 to superheat steam. The superheat steam generating part SH is divided into a superheat steam first generating part 26 and a superheat steam second generating part 25 and the generating parts 25 and 26 are individually connected in series to the high pressure drum 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an exhaust heat recovery boiler which generates steam by using exhaust gas (exhaust heat) emitted from a prime mover such as a gas turbine.

[0002]

2. Description of the Related Art Conventionally, a steam turbine used in a thermal power plant requires a large-scale boiler as a steam source for its operation. There has been a demand for the appearance of a new power plant from the viewpoint of energy saving without increasing the thermal efficiency.

Recently, the appearance of a so-called combined cycle power plant, which is a combination of a gas turbine and a steam turbine, has come to the fore, and this field is in the limelight. This combined cycle power plant emerged due to measures such as high thermal efficiency and large output capacity of the plant.The combustion gas at the gas turbine inlet was heated to a high temperature, and the exhaust heat recovery boiler was changed accordingly. The temperature of the guided exhaust gas is also increasing. Due to the high temperature of the exhaust gas, the steam generated in the exhaust heat recovery boiler has also become high.

On the other hand, the steam turbine that receives steam from the exhaust heat recovery boiler has a working steam temperature of 538 ° C to 566 ° C.
Although heat-resistant steel that can withstand the high temperatures of the above is used for the turbine rotor and the turbine casing made of cast steel is also thick, when the operating steam temperature exceeds this, the material of each component There is concern about weakness or lack of toughness. For this reason, a temperature reduction device is installed in the exhaust heat recovery boiler that sends steam to the steam turbine, and the upper limit of the steam temperature sent from the exhaust heat recovery boiler to the steam turbine is within a certain range regardless of the power generation output. The technology to try to fit in has already been proposed.

FIG. 4 is a schematic view showing a typical embodiment of an exhaust heat recovery boiler equipped with a temperature reducing device. The exhaust heat recovery boiler indicated by reference numeral 1 is a compound pressure type having a horizontally long cylinder. The exhaust heat recovery boiler 1 has a high-pressure second superheater 2, a high-pressure first superheater 3, and a high-pressure evaporator 4 including a high-pressure drum 20 in the following order along the flow of exhaust gas (exhaust heat) from the gas turbine:
Denitration device 9, high pressure economizer 5, low pressure superheater 6, low pressure drum
A low-pressure evaporator 7 and a low-pressure coal economizer 8 each having 13 are arranged, and the superheated steam is finally created by preheating, evaporating, heating, and repeating vaporization, which is so-called stepwise heating and pressurization. is there.

That is, the feed water guided to the low pressure economizer 8 through the water supply pipe 10 becomes saturated water preheated by the exhaust gas (exhaust heat), and a part of the saturated water passes through the low pressure pipe 11 and the adjusting valve 12. It is sent to the low-pressure drum 13. The remaining saturated water is sent to the high-pressure economizer 5 via the pipe 15, the water supply pump 16, and the high-pressure water pipe 17.

The saturated water collected in the low pressure drum 13 is
The low-pressure evaporator 7 evaporates, and this evaporation is repeated to separate water and water, and the saturated steam having a relatively high degree of wetness is again sent to the low-pressure superheater 6 via the pipeline 14, where the degree of wetness is low. It is sent to the steam turbine low pressure stage as saturated steam.

On the other hand, the saturated water collected in the high-pressure economizer 5 exchanges heat with the exhaust gas (exhaust heat) here, and becomes saturated vapor having a relatively low degree of wetness through the high-pressure pipe 18 and the adjusting valve 19 to the high-pressure drum. Has been sent to 20.

The high-pressure drum 20 once sends the saturated steam to the high-pressure evaporator 4 for re-evaporation, and after vapor-water separation, the saturated steam having a very low degree of wetness is passed through the steam pipe 21 and the high-pressure first superheater 3 It is being sent to the second superheater 2. Then, the high-pressure first superheater 3 and the high-pressure second superheater 2 generate superheated steam and supply it to the steam turbine high-pressure stage as working steam.

[0010]

If the temperature of the working steam supplied from the exhaust heat recovery boiler to the high pressure stage of the steam turbine is too high, the strength of each member constituting the high pressure stage will decrease. Because of concern, a temperature reducing device 22 is provided at the inlet of the high-pressure second superheater 2 as shown in FIG. The temperature reducing device 22 receives saturated water from a spray pipe 23 that branches the high-pressure water pipe 17 of the water supply pump 16, and lowers the superheated steam produced from the high-pressure first superheater 3 to an appropriate temperature by this saturated water. There is. That is, the temperature of the superheated steam produced from the high-pressure second superheater 2 is constantly detected by the temperature detecting end 25. When the detected temperature exceeds the reference value, the regulating valve 24 is opened and the temperature reducing device 22 is opened. The saturated water is provided in the form of mist and mixed so that the temperature of the hot steam of the high-pressure first superheater 3 is preferably lowered.

Therefore, since the superheated steam sent to the steam turbine high-pressure stage is adjusted to a preferable mixed state, the high-pressure stage has a material strength due to external factors such as excessive thermal stress and thermal strain. There is little concern about the decline.

However, since a mixture of superheated steam and saturated water having extremely different temperature differences passes through the temperature reducing device 22,
If it is used for a long period of time, it suffers severe wear due to overheating stress and thermal strain, often resulting in malfunction, and there is a problem that saturated water flows into the high-pressure second superheater 2 in the form of water droplets. When the steam turbine has a command to rapidly increase or decrease the output, the supply of saturated water to the superheated steam may be insufficient, but the superheated steam of the high-pressure first superheater 3 may be lowered to an appropriate temperature although it is transient. It is sent to the high-pressure second superheater 2 without being able to do so, and an abnormal event may occur there.

The present invention is an improvement made in view of the above-mentioned circumstances. Instead of the conventional temperature reducing device, the high pressure first and second superheaters are properly arranged to thereby generate superheated steam at an appropriate temperature. The purpose is to announce the exhaust heat recovery boiler.

[0014]

In order to achieve this object, the invention described in claim 1 has a high pressure second superheater and a high pressure first
A superheater, a high-pressure evaporator equipped with a high-pressure drum, a denitration device, a high-pressure economizer, a low-pressure superheater, a low-pressure evaporator equipped with a low-pressure drum, and a low-pressure economizer are arranged, while the preheated water supply by the low-pressure economizer is used. Part of the water is guided to the low-pressure drum and evaporated, and the evaporated steam is further evaporated by the low-pressure superheater and sent out to the low-pressure stage of the steam turbine, while the remaining part of the feed water is saved in the high-pressure economizer. Through the high pressure drum to evaporate, the vaporized steam is generated into superheated steam by the high pressure first superheater, the superheated steam is adjusted to an appropriate temperature by the temperature reducing device, and the superheated steam after the adjustment is pressurized to high pressure. In the exhaust heat recovery boiler that sends to the steam turbine high pressure stage through the second superheater,
A superheated steam generating part is provided for converting the steam sent out from the high-pressure drum into superheated steam, and the superheated steam generating part is divided into a superheated steam first generating part and a superheated steam second generating part, and each of these generating parts has the high pressure. The drums are individually connected in series.

In addition to the invention described in claim 1,
In the invention described in claim 2, the first superheated steam generating part and the second superheated steam generating part are continuously arranged in the following order along the flow of the exhaust gas, and the invention according to claim 3 is the superheated steam first part. The generator and the second superheated steam generator are arranged in parallel across the flow of the exhaust gas.

[0016]

In the exhaust heat recovery boiler according to the first and second aspects of the present invention, there is provided a superheated steam generating section for converting the steam sent from the high-pressure drum into superheated steam, and the superheated steam generating section is the superheated steam first generating section. It is divided into a superheated steam second generation section, and each of these generation sections is connected in series to a high-pressure drum, while the superheated steam first generation section and the superheated steam second generation section are arranged continuously along the flow of exhaust gas. Therefore, the temperature of the superheated steam generated from the second superheated steam generating section is higher than the temperature of the superheated steam generated from the first superheated steam generating section. This difference in temperature is due to the difference in the amount of heat of the exhaust gas temperature, because the exhaust gas flows to the first superheated steam generation unit via the second superheated steam generation unit.

However, the allowable temperature value of the superheated steam sent from the exhaust heat recovery boiler to the steam turbine exists between the superheated steam temperature of the second superheated steam generating section and the superheated steam temperature of the first superheated steam generating section. Therefore, if the superheated steam of the second superheated steam generating unit and the superheated steam of the first superheated steam generating unit are combined, the combined steam can be kept within the above allowable temperature value. Therefore, the exhaust heat recovery boiler can send the superheated steam at an appropriate temperature to the steam turbine high-pressure stage, and the conventional problems do not occur.

Further, in the exhaust heat recovery boiler according to the third aspect of the present invention, since the first superheated steam generating section and the second superheated steam generating section are arranged in parallel across the flow of the exhaust gas, each generating section The superheated steam can be suppressed to a relatively low level by sending different quantities of steam to. Generally, when equal amounts of steam are flown through two superheated steam generators arranged in parallel, the superheated steam temperature generated from these generators is high.

However, when a relatively large amount of steam is caused to flow to one superheated steam generating part and a relatively small amount of steam is caused to flow to another one of the superheated steam generating parts, the superheated steam temperature when these are combined is It is lower than the combined superheated steam temperature when an equal amount of steam is passed through the vessel.

The cause of this will now be described in a little more detail. Since the heat transfer area of the superheated steam generation part is constant, when a relatively large amount of steam is flown through one superheated steam generation part, the exchange heat amount does not change when the heat quantity of the exhaust gas is constant. When a relatively small amount of steam is caused to flow through the other superheated steam generating portion, the temperature of the superheated steam generated here does not exceed the temperature of the exhaust gas.

Therefore, even if the temperatures of the superheated steam generated from the respective generating parts are different, the temperature of the combined superheated steam obtained by combining these steams is lower than the temperature of the equal amount of the combined superheated steam of the respective generating parts. Become.

As described above, when a relatively large amount of steam is caused to flow to one of the superheated steam generating units arranged in parallel and a relatively small amount of steam is caused to flow to the other one of the superheated steam generating units, the combined superheated steam is generated. Since the temperature is lower than the equivalent combined superheated steam, it can be sent to the steam turbine high pressure stage as the proper superheated steam temperature.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Exhaust heat recovery boiler according to the present invention will be described below with reference to the drawings. The same components as those shown in FIG. 4 are designated by the same reference numerals, and the duplicate description thereof will be omitted.

FIG. 1 is a schematic diagram of an exhaust heat recovery boiler according to the present invention. This invention, among the exhaust heat recovery boiler,
This is an improvement of the part that produces superheated steam. That is, the superheated steam generating section SH is provided at the inlet of the exhaust heat recovery boiler 1 (the portion where the exhaust gas from the gas turbine is first guided). The superheated steam generating section SH is divided into a superheated steam first generating section 26 and a superheated steam second generating section 25,
The first superheated steam generator 26 is provided on the high-pressure drum 20 with the adjustment valve 30 provided on the communication pipe 28, and the second superheated steam generator 25 is provided on the communication pipe 27 with the adjustment valve 29. The high-pressure drums 20 are individually connected in series. And each of these superheated steam generators
In the exhaust heat recovery boiler 1, 26 and 25 are continuously arranged along the flow of exhaust gas.

In such a structure, the exhaust gas and the steam exchange heat according to the graph shown in FIG. First, a part of the saturated steam having a very low degree of wetness generated while reciprocating between the high pressure evaporator 4 and the high pressure drum 20 is sent to the superheated steam first generation section 26, where the superheated steam is generated. And its temperature is T ₁ . The other part of the saturated steam that has exited the high-pressure drum 20 is guided to the superheated steam second generation section 25, where superheated steam is produced and its temperature is T ₂ . In this way, although the superheated steam temperatures produced by the generators 26, 25 are different, the superheated steam temperature set value T ₀ required by the steam turbine high-pressure stage is the above-mentioned generators 26, 25.
It exists between the vapor temperatures T ₁ and T ₂ of 25. For this reason, if the superheated steam produced by each of the generation units 26 and 25 is merged, the temperature of the merged superheated steam approaches the set value T ₀ .

Therefore, the superheated steam sent from the exhaust heat recovery boiler 1 to the high-pressure stage of the steam turbine can be sent out at an appropriate temperature so that the strength of each member of the turbine does not decrease.

FIG. 3 is a schematic view showing another embodiment of the exhaust heat recovery boiler according to the present invention. In this embodiment, a superheated steam first generation part 31 and a superheated steam second generation part 32 are arranged in parallel across the flow of exhaust gas, and each generation part 31, 32 is connected to a connecting pipe 33,
The high pressure drum 20 is connected in series to the high pressure drum 20 via the adjusting valves 34 and 36 on the 35.

According to such a configuration, saturated steam can be flowed from the high-pressure drum 20 to the first superheated steam generating section 31 and the second superheated steam generating section 32 in a quantitatively different manner. As described above, the confluence of the superheated steam created by the difference does not reach a high temperature, and therefore the strength of the turbine member does not decrease from the exhaust heat recovery boiler 1 to the steam turbine high pressure stage. It can be delivered as superheated steam at a temperature. Note that the quantitative difference between the saturated steam sent to the first superheated steam generating section 31 and the second superheated steam generating section 32 is
It is controlled by 34 and 36.

[0029]

As described above, the exhaust heat recovery boiler according to the present invention is provided with the superheated steam generating section for converting the steam sent from the high-pressure drum into the superheated steam, and the superheated steam generating section produces the first superheated steam. Section and a superheated steam second generation section, and these generation sections are individually connected in series to the high-pressure drum, and the confluent value of the superheated steam generated from each generation section has a relatively low temperature. From the exhaust heat recovery boiler, it can be sent to the steam turbine high pressure stage as superheated steam at an appropriate temperature.

In addition, the first superheated steam generation section and the second superheated steam second section
Since the generator and the generator are arranged parallel to each other across the flow of exhaust gas, by flowing different amount of steam to each generator,
The confluence of the superheated steam generated from each generation section has a relatively low temperature, so that it can be sent to the steam turbine high-pressure stage as superheated steam at an appropriate temperature.

[Brief description of drawings]

FIG. 1 is a schematic view of an exhaust heat recovery boiler according to the present invention.

FIG. 2 is a graph showing heat settlement of an exhaust heat recovery boiler according to the present invention.

FIG. 3 is a schematic view showing another embodiment of the exhaust heat recovery boiler according to the present invention.

FIG. 4 is a schematic diagram showing an embodiment of a conventional exhaust heat recovery boiler.

[Explanation of symbols]

 1 Exhaust heat recovery boiler 2 High pressure second superheater 3 High pressure first superheater 4 High pressure evaporator 5 High pressure economizer 6 Low pressure superheater 7 Low pressure evaporator 8 Low pressure economizer 9 Denitration equipment 13 Low pressure drum 20 High pressure drum 22 Reduction Warming device SH Superheated steam generator 25 Superheated steam second generator 26 Superheated steam first generator

Claims (3)

[Claims] 1. A high-pressure second superheater, a high-pressure first superheater, a high-pressure evaporator equipped with a high-pressure drum, a denitration device, a high-pressure economizer, and a low-pressure superheat in the following order along the flow of exhaust gas guided as a heat source: A low-pressure evaporator equipped with a low-pressure drum and a low-pressure economizer are arranged, while part of the feedwater preheated by the low-pressure economizer is guided to the low-pressure drum to evaporate, and the vaporized vapor is further heated to low-pressure overheat. Vaporizer and sends it to the steam turbine low pressure stage, and guides the remaining part of the feed water through the high pressure economizer to the high pressure drum to vaporize the vaporized steam by the high pressure first superheater. In the exhaust heat recovery boiler that produces superheated steam, adjusts the superheated steam to an appropriate temperature by a temperature reducing device, and sends the adjusted superheated steam to the steam turbine high pressure stage through the high pressure second superheater, The steam delivered from the high-pressure drum An overheated steam generating part for converting to overheated steam is provided, and this overheated steam generating part is divided into an overheated steam first generating part and an overheated steam second generating part, and these generating parts are individually connected in series to the high pressure drum. Exhaust heat recovery boiler characterized by 2. The exhaust heat recovery boiler according to claim 1, wherein the first superheated steam generating section and the second superheated steam generating section are continuously arranged in the following order along the flow of the exhaust gas. 3. The exhaust heat recovery boiler according to claim 1, wherein the first superheated steam generating section and the second superheated steam generating section are arranged in parallel across the flow of the exhaust gas.