JP4934738B2 - High temperature steam turbine plant - Google Patents

Description

  The present invention relates to a high-temperature steam turbine power plant having a main steam temperature of 675 ° C. or higher and an output of 100 MW or higher.

  In order to improve the power generation efficiency of the steam turbine power plant, it is effective to improve the main steam temperature. At present, a steam turbine power plant having a main steam temperature exceeding 600 ° C. is in commercial operation, and a steam turbine having a main steam temperature of 650 ° C. is being developed. Development of a steam turbine with a main steam temperature of 700 ° C. or higher is also being promoted with the aim of further improving efficiency.

  In a steam turbine aiming at a main steam temperature of 700 ° C. or higher, since the service temperature of steel materials conventionally used for rotor materials is about 650 ° C., it is necessary to make the rotor materials etc. Ni-based superalloys. Ni-base superalloys are high in strength but expensive compared to steel materials, and it is difficult to produce large forgings. Currently, the development, selection and demonstration of Ni-base superalloys that excel in the production of large forgings are underway, and some Ni-base superalloys are expected to be able to produce forgings with a weight of 10 tons. It has been. However, the weight of a general large steam turbine rotor is 30 to 40 tons. For this reason, a welded rotor system in which a plurality of forged materials are connected by welding to form a rotor has been studied. Further, a top turbine type in which only a portion having a high temperature is divided into a small high-temperature turbine has been studied (for example, see Patent Document 1).

E. Saito, et al., “Development of the Ultra-Supersritical Steam Turbine for Large Coal-fired Power Plants”, Proc. Power-Gen International, (2004).

  In a steam turbine plant aiming at a main steam temperature of 700 ° C or higher, Ni is more expensive than conventional steel materials, in addition to the technology of forming high-temperature parts of turbines and boilers using Ni-base superalloys. Reducing the amount of expensive Co and Mo contained in a large amount of Ni-base superalloys is a major issue.

  In the welded rotor system, if all 30-40 ton rotors are made of Ni-based superalloys, the amount of Ni used becomes enormous, so the high temperature part (equivalent to about 10 tonnes) is superalloy, and the low temperature part is 12Cr steel, etc. As a steel material, it is necessary to join both parts. Since the portion having a high temperature weighs about 10 tons at most, the amount of Ni used can be reduced.

  However, since bonding of dissimilar materials occurs, the bonding portion is deteriorated by diffusion of elements caused by a difference in composition between materials in use at a high temperature for a long time, so it is difficult to ensure reliability. Also, ferritic steel with excellent high-temperature strength will be used as the steel, but the ferritic steel and the Ni-base superalloy have a larger thermal expansion coefficient than the Ni-base superalloy, and the thermal expansion coefficients of the two differ. As a result, cracks due to thermal stress during joining and fatigue failure due to thermal stress during use may become a problem. For this reason, it is necessary to use a Ni-base superalloy having a small thermal expansion.

  Among Ni-base superalloys, there are Ni-Fe-base superalloys having high strength while containing a large amount of Fe. However, since Fe increases the coefficient of linear expansion, Ni—Fe based superalloys are not preferred as welded rotor materials. In order to make the linear expansion coefficient of the Ni-base superalloy similar to that of ferritic steel, in addition to not adding inexpensive Fe, it is necessary to add a large amount of Mo that reduces thermal expansion.

  A Ni-base superalloy containing a large amount of Mo is suitable as a welded rotor material, but it does not contain cheap Fe and contains a lot of Mo that is more expensive than Ni. In the top turbine type, since there is no welded portion, the reliability is high and a low-cost Ni—Fe base superalloy can be used. However, the cost increase due to the addition of one turbine is a problem.

  Next, problems on the boiler side that generates high-pressure steam to be supplied to the steam turbine will be described.

  Boilers of large steam turbine plants generally have a height of 70 m or more, and the upper part is hotter, and the high temperature and high pressure steam piping supplied to the steam turbine is routed from the upper part of the boiler to the turbine building on the ground. The length will be over 100m.

  In a steam turbine plant having a main steam temperature of 675 ° C. or higher, since the service temperature of the steel material is about 650 ° C., it is necessary to manufacture the high-temperature and high-pressure steam pipe using a Ni-base superalloy. This steam pipe has an outer diameter of about 600 mm and a thickness of about 100 mm, and its length reaches 100 m or more. Therefore, the total weight of the pipe is much larger than the amount of Ni-base superalloy used in the turbine.

  In addition, as a boiler material, at a main steam temperature of 700 ° C. or lower, Ni—Fe base superalloys such as HR6W, which are excellent in cost and manufacturability, can be used as Ni base superalloys. In addition, it is necessary to use a solid solution strengthened Ni-base superalloy such as IN617, and a precipitation strengthened Ni-base superalloy such as Nimonic 263 having excellent strength characteristics at 720 ° C. or higher. IN617, Nimonic 263, etc. are not only high in cost but also poor in manufacturability, so it is impossible to produce a long pipe having an outer diameter of about 600 mm. Therefore, it is necessary to supply high-temperature and high-pressure steam from the boiler building to the turbine building using multiple pipes with small outer diameters.However, when multiple pipes are used, the weight per flow area increases, which increases the pipe weight. This further increases the cost.

  Against this background, attempts have been made to lay down the vertical boiler sideways for the purpose of shortening the piping between the turbine building and the boiler building, but the combustion efficiency decreases and the installation area increases significantly. That is a problem.

  An object of the present invention is to provide a high-temperature steam turbine power plant having a main steam temperature of 675 ° C. or more and an output of 100 MW or more, which is composed of a vertical boiler having both reliability and cost and excellent combustion efficiency.

  In the present invention, a high-temperature steam turbine plant having a main steam temperature of 675 ° C. or more and an output of 100 MW or more is set as a top turbine type and configured as follows.

  In other words, a boiler building including a vertical boiler with a VHT (Very high temperature) turbine installed at the top, and a turbine building installed on the ground, the inlet temperature of the VHT turbine is 675 ° C. or more, and the outlet temperature is It is 550 degreeC or more and 650 degrees C or less, the VHT turbine is installed in the upper part of a vertical boiler, and the total Ni equivalent combining the VHT turbine and the high pressure piping between a boiler building and a turbine building is 4 tons or less.

  According to the present invention, it is possible to provide a high-efficiency high-temperature steam turbine plant that achieves both cost and reliability.

It is a schematic block diagram of the high temperature steam turbine plant by one Example of this invention. It is a schematic block diagram of the high temperature steam turbine plant by the other Example of this invention. It is the schematic block diagram which showed the reference example of the high temperature steam turbine plant. It is the schematic block diagram which showed the prior art example of the high temperature steam turbine plant. It is the schematic block diagram which showed another conventional example of the high temperature steam turbine plant. It is the schematic block diagram which showed the comparative example of the high temperature steam turbine plant. It is a schematic block diagram of the high temperature steam turbine plant by another comparative example. It is a schematic block diagram of the high temperature steam turbine plant by another comparative example.

  A VHT turbine means a top turbine. In order to make the material of the highest pressure steam pipe between the boiler building and the turbine building be ferritic steel or austenitic steel containing 50% by weight or more of Fe, since the upper limit of the service temperature of these materials is 650 ° C., the VHT turbine The outlet temperature must be below 650 ° C. As a result, the highest pressure steam pipe between the turbine building and the boiler building, which has been conventionally made of a Ni-base superalloy, can be made of a steel material, so that the amount of Ni used can be greatly reduced.

  However, ferritic steel having a service temperature exceeding 630 ° C. has high melting and forging costs. Therefore, considering the costs of the downstream piping and the turbine rotor, the VHT turbine outlet temperature is preferably 630 ° C. or lower.

  In order to obtain high reliability, it is desirable to integrate the VHT turbine with a Ni-base superalloy. However, it is difficult to produce a forged product greatly exceeding 10 tons with a Ni-base superalloy, and the size of the VHT turbine is limited. When the outlet temperature of the VHT turbine is lowered, the number of turbine stages increases, the rotor becomes longer, and the weight increases. Increasing the outlet temperature of the VHT turbine shortens the rotor and reduces the weight. From the production limit of Ni-base superalloys, it is desirable that the inlet temperature is 690 to 720 ° C. and the outlet temperature is 600 ° C. or higher and 620 ° C. or lower in an integrated VHT turbine made of Ni-base superalloy.

  For the rotor having a length exceeding the production limit of the Ni-base superalloy, the outlet temperature is 620 ° C. or lower, so it is preferable to weld ferritic steel. However, in this case, a Ni—Fe base superalloy with a low Ni content can be used if it is an integral type, but it is necessary to use not only Ni but also a Ni base superalloy containing a large amount of expensive Mo in the welding rotor. Therefore, the cost increases. There is also a method of increasing the length by welding the superalloys, but the amount of Ni used increases as the superalloy increases, resulting in an increase in cost.

  If it is steam of 620 ° C. or lower, it is preferable to feed the ferritic turbine in the boiler building with a ferritic steel pipe. However, if the main steam temperature exceeds 700 ° C and the rotor is made of a 10 ton class forged product and the outlet temperature cannot be made 630 ° C or higher and 650 ° C or lower, the superalloy forged products are welded together to increase the rotor length. It is necessary to make the outlet temperature 630 ° C. to 650 ° C. or less. That is, a high-temperature steam turbine plant composed of the above-described VHT having a VHT turbine inlet temperature of 720 ° C. or higher and an outlet temperature of 630 ° C. to 650 ° C. manufactured by a superalloy welded rotor is also within the scope of the present invention. It is. In the present invention, the turbine in the turbine building has a maximum pressure steam inlet temperature of 550 to 600 ° C., and has a structure equivalent to a steam turbine plant having a main steam temperature of 550 to 600 ° C. currently in commercial operation. It is also suitable to replace a steam turbine plant having a main steam temperature of 550 to 600 ° C. class to a 700 ° C. class, and such a replaced steam turbine plant is also within the scope of the present invention.

  An example in which the present invention is applied to a one-stage reheat steam turbine plant with an output of 500 MW class and a main steam temperature of 700 ° C. is shown below together with a reference example and a comparative example.

  Table 1 shows the composition (% by weight) and Ni equivalent of the materials used for the VHT turbine, HP turbine, high-pressure piping between the turbine building and the boiler building of the steam turbine plant of this example. Since the object of the present invention is to achieve both cost and reliability, it is necessary to minimize the amount of expensive Ni used. In addition to Ni, the superalloy contains expensive elements such as Mo, Co, and W. In some cases, the Ni equivalent shown in Table 1 was used as the material cost index of the superalloy. Table 2 shows the total Ni equivalent.

  FIG. 4 shows a conventional example in which an HP turbine is configured by a welding rotor, and is assumed to be a conventional A. In the steam turbine plant having this configuration, the superalloy used for the welding rotor 41 is superalloy A having a linear expansion coefficient close to that of ferritic steel. Since the high-pressure pipe 16 is also high-temperature and high-pressure, it is necessary to use the superalloy A from the balance between strength and workability. In this case, the sum of the Ni equivalents of the high-pressure piping and the HP turbine is 54.6 tons.

FIG. 5 shows a conventional example of a top turbine type steam turbine plant.
In this case, since a welded structure is not used, the material used for the VHT turbine 51 does not need to match the linear expansion coefficient with that of ferritic steel, and a superalloy B that is rich in Fe and excellent in manufacturability can be used. . In this case, the Ni equivalent is 49.5, which is smaller than the conventional value A, but there is a problem of an increase in cost due to the addition of one turbine.

  FIG. 1 shows an embodiment of the present invention, which is referred to as the present invention A1. The steam turbine plant of the present invention A1 includes a boiler building 14 including a vertical boiler 11 in which a VHT turbine 12 and a generator 13 are installed at an upper portion, and a turbine building 15 installed on the ground. A VHT turbine 11 is installed on top of the vertical boiler 11, and a generator 13 connected to the VHT turbine 11 is further installed. By setting the inlet temperature of the VHT turbine 12 to 650 ° C. or less, the high-pressure pipe 16 between the turbine building 15 and the boiler building 14 that conventionally used a superalloy of about 50 tons is replaced with ferritic steel.

  In the present invention A1, since the outlet temperature is 610 ° C., steel C can be used for the high-pressure pipe 16 and steel A can be used for the rotor of the HP turbine 17.

  When the difference between the inlet temperature and the outlet temperature of the VHT turbine 12 increases, the total length of the VHT turbine becomes longer and the weight of the rotor increases, so that the production limit of the superalloy A and the superalloy B exceeds 10 tons. become unable. The weight of the VHT turbine rotor in the present invention A1 is a marginal weight that does not exceed the production limit of the superalloy B, and is a VHT turbine rotor having an integral structure. In this case, the total Ni equivalent is 4, which is significantly lower than those of Conventional A and Conventional B. Compared with the conventional A, the Ni equivalent is reduced by 50 tons or more, and there is much to compensate for the cost disadvantage of increasing one small turbine and one small generator, which is superior in cost to the conventional A, Since the rotating part does not include the welded part, the reliability is high.

  FIG. 2 shows a case where the outlet temperature of the VHT turbine 12 is higher than that of the present invention A1, and is referred to as the present invention A2. It is said that ferritic steel can be used up to about 650 ° C. However, in order to use it at a temperature exceeding 620 ° C., it is necessary to add Co and B, which increases material cost and manufacturing cost. Steel B has a strong tendency to deteriorate in strength when used for a long time. Steel A is superior when the reliability of steel A at about 620 ° C. and the reliability of steel B at a temperature exceeding 630 ° C. are compared.

  In the present invention A2, since the VHT outlet temperature exceeds 620 ° C., steel B in which Co and B are added to the rotor of the high-pressure pipe 16 and the HP turbine 17 is used. In the present invention A2, the superalloy B is used for the VHT turbine 12, and since the outlet temperature is higher than that of the present invention A1, the total length of the rotor is shortened and the rotor weight is lightened. It becomes lower than the present invention A1.

  However, for high-pressure pipes and HP turbines that are heavy in weight, the ferritic steel is expensive, and it is necessary to use B steel, which is less reliable for a long time compared to steel A. Therefore, the present invention A1 is more costly and reliable. Is excellent in terms of.

  FIG. 3 shows a case where the inlet temperature of the VHT turbine is increased to 730 ° C. and is used as a reference example. In order to make the material of the high-pressure pipe 16 and the HP turbine 17 into steel A and steel C that achieve both cost and reliability, the outlet temperature of the VHT turbine needs to be 630 ° C. or lower. In this case, the total length of the VHT turbine becomes long, and the superalloy B cannot be integrated. Further, since the superalloy B has insufficient strength at 730 ° C., the superalloy C is welded to the high temperature portion to form the VHT turbine 30 having a welded rotor structure. The total amount of Ni in this case is about 14 tons, which is a value significantly lower than those of Conventional A and Conventional B in which the VHT turbine inlet temperature is 700 ° C.

  Compared with the present invention A1 and the present invention A2, the Ni equivalent is a slightly high value, but considering the improvement in efficiency due to a 30 ° C. increase in the VHT turbine inlet temperature, the reference example is also a sufficiently effective configuration. It can be said.

  Comparative Example 1 shown in FIG. 6 is a case where the outlet temperature of the VHT turbine is 675 ° C. In this case, the high-pressure pipe 16 needs to be a superalloy, and the HP turbine needs to be a welded structure of superalloy and ferritic steel. Therefore, the total Ni equivalent is about the same as that of Conventional A and Conventional B, and there is no effect at all considering the cost of increasing the number of small generators.

Comparative Example 2 shown in FIG. 7 is a case where the outlet temperature of the VHT turbine is lowered to 500 ° C.
In this case, the VHT turbine rotor becomes large and becomes a welded rotor of superalloy A and steel A. Although a welded structure of ferritic steel and superalloy is formed, the total Ni equivalent is higher than that of the present invention A1 and the present invention A2, and there is no merit. In addition, since the total weight of the VHT turbine increases, the installation of the boiler on the top of the boiler involves costs such as reinforcement. For this reason, the VHT turbine outlet temperature must be 550 ° C. or higher.

  Although the comparative example 3 shown in FIG. 8 is a case where all HP turbines are raised on the boiler, since the HP turbine is a structure having a weight exceeding 150 tons, it cannot be installed on the upper part of the boiler. Is not realistic.

  From the above results, the effectiveness of the present invention is clear.

  According to the present invention, a high-temperature steam turbine power plant having a main steam temperature of 675 ° C. or more and an output of 100 MW or more, which is composed of a vertical boiler having both reliability and cost and excellent combustion efficiency, can be configured. It is likely to be applied to future high-temperature, high-output power plants.

  DESCRIPTION OF SYMBOLS 11 ... Vertical boiler, 12 ... VHT turbine, 13 ... Generator, 14 ... Boiler building, 15 ... Turbine building, 16 ... High pressure piping, 17 ... HP turbine, 30 ... VHT turbine of welding rotor structure.

Claims (3)

A boiler building including a vertical boiler with a VHT turbine installed on the top, a first turbine installed on the ground and working with the VHT turbine through a first steam pipe, the first turbine; A first turbine driven by the first turbine and the second turbine, which is obtained by reheating the steam worked in the turbine through a second steam pipe after being reheated by the vertical boiler in the boiler building; The VHT turbine has an inlet temperature of 675 ° C. or higher, an outlet temperature of 550 ° C. or higher and 650 ° C. or lower, and is connected to the VHT turbine and the VHT turbine at an upper portion of the vertical boiler . 2 generators are installed,
A high-temperature steam turbine plant characterized in that a total Ni equivalent of the VHT turbine and the boiler building and the high-pressure piping between the turbine building is 4 tons or less.   The said VHT turbine is comprised from the rotor made from an integrated Ni base superalloy which does not include a welding joint part in a steam flow path, The inlet_port | entrance temperature is 690 to 720 degreeC, and outlet temperature is 600 to 620 degreeC. High temperature steam turbine plant.   2. The main steam temperature of 700 ° C. or more, wherein a steam flow path between the vertical boiler and the VHT turbine is composed of a plurality of pipes having an outer diameter of 300 mm or less, and a material thereof is a precipitation strengthened Ni-base superalloy. High temperature steam turbine plant.

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