JPS6267239A - Power generating method for gas turbine - Google Patents

Abstract

PURPOSE:To improve the thermal efficiency by utilizing a part of steam produced by a waste heat boiler for cooling blades so as to allow the rest of the steam to be mixed with combustion gas. CONSTITUTION:An intermediate cooler 15 is provided between an intermediate pressure compressor 12 and a high pressure compressor 13. Heat is exchanged by a regenerative preheater 33 between air from the high pressure compressor 13 and air from a low pressure compressor 32. A part of steam produced by a waste heat boiler 66 is utilized to cool blades of the high pressure turbine 31, and is subsequently fed into combustion gas. And then the rest of the steam is allowed to flow into a combustor 20 so as to be mixed with combustion gas. This configuration enables the thermal efficiency of a cycle to be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a power generation method using a gas turbine. More specifically, the present invention relates to a superior power generation method using a combined cycle that combines a gas turbine cycle and a steam cycle generated using the exhaust gas of the gas turbine.

[Prior art and its problems] Gas turbine cycles are often used in combination with steam cycles. There are many examples of this combination, but one example is shown in Figure 2.

This example adds fuel to the gas turbine exhaust and burns it.
This increases the steam pressure and temperature, and also places a reheater in front of the steam low-pressure turbine to further increase the thermal efficiency of the steam cycle.

By doing so, the cycle thermal efficiency is increased and there is a certain effect, but the disadvantage is that the device becomes complicated and the cost becomes considerably high. That is, the waste heat boiler performs auxiliary combustion, and therefore requires a combustion device, a steam high-pressure turbine, a steam low-pressure turbine, a generator, a reheater, a condenser, a cooling water facility, etc.

By performing auxiliary combustion, the proportion of power generated by the steam cycle increases, but the thermal efficiency of this steam cycle cannot be made that high due to the restriction of being an exhaust heat boiler, and in the end the overall thermal efficiency is not that good. It won't happen.

In order to avoid complicating the device and increasing costs, some systems inject the generated steam directly into the combustor, so that all the power is generated by a gas turbine. The dilution air gap is reduced by the amount of steam that enters the combustion gas, ie, the excess air ratio is reduced, and the power of the air compressor is significantly reduced.

However, when looking at the injected steam, it is released at atmospheric pressure, meaning that the energy up to the vacuum is not utilized, resulting in very poor thermal efficiency. Therefore, the overall efficiency cannot be said to be good.

Our invention aims to maintain the simplicity of the device by injecting the generated steam into the combustor, while pursuing overall thermal efficiency comparable to the gas turbine and steam turbine combined cycle described above.

SUMMARY OF THE INVENTION A disadvantage of the method of mixing generated steam with combustion gas and processing it in a gas turbine is that its thermal efficiency, with respect to steam, is very poor. In order to prevent this poor thermal efficiency, one solution is to increase the temperature of the hot air.

Steam and combustion gas are mixed, but approximately the thermal efficiency of both can be considered separately. Considering this, it is possible to achieve steam temperatures that would not be possible in a normal steam cycle.

Therefore, it can be seen that if the gas temperature and pressure at the gas turbine inlet become high, the thermal efficiency will not be as good as that of a normal steam cycle above a certain level.

In addition, as in this case, a ``special steam cycle'' in which generated steam is processed by a gas turbine is different from a normal steam cycle, but at Honmoesaiten, we do not particularly distinguish between the two, and refer to them as ``steam cycles.'' We will call it ′°.

For example, as a rough guide, steam pressure temperature exhaust pressure thermal efficiency 22 aha
400℃ 0.05a[a 34%22
400 1.00 2422 1400 1.
00 35 If the steam pressure and temperature are higher than those shown in the table above, the thermal efficiency will further increase. On the other hand, in the case of such a waste heat boiler in a normal steam cycle, it is difficult to further increase the above value, that is, about 34%, so if the steam temperature (that is, the temperature of the gas turbine inlet gas) is high, the generated It can be said that the thermal efficiency will be higher if the steam is injected directly into the combustor.

In such a case, when the gas temperature and pressure at the gas turbine inlet increase, the thermal efficiency of the gas turbine cycle becomes considerably higher than that of the steam cycle, so it is desirable that the proportion of power generated by the steam cycle as a whole is as low as possible. That is, it is better to minimize the amount of steam mixed into the combustion gas. Of course, this is based on the premise that the maximum amount of heat can be recovered from the gas turbine exhaust gas.

In order to reduce the amount of steam injected into the turbine combustion gas,
First, it is necessary to reduce the amount of steam generated. Second, if there is a more effective use for the generated hot air, it should be used for that purpose. For example, if there is a demand for power to reduce the pressure of the steam and for heating to meet the low-pressure steam generated, it is considered to be the most effective use.

In summary, in order to make the process of injecting generated steam into combustion gas more attractive, it is necessary to do the following.

(1) To make it possible to keep the gas turbine inlet gas temperature at 8 temperatures as much as possible.

As for pressure, there is an optimal repulsion ratio according to this temperature, so
You can think of it as a process. However, this optimum pressure ratio also increases with temperature.

The advantages of high turbine input log gas are (a) increased cycle thermal efficiency, (b) dilution gas (excess air, steam)
(C) Therefore, the total amount of gas decreases, so the retained heat i of the exhaust gas decreases. (d) Therefore, the amount of steam generated using the exhaust gas decreases. (e) The device becomes more compact because the amount of gas decreases. The point is that it produces the effect that it can be done.

N) Reduce the amount of steam generated by reducing the amount of heat held by the gas turbine exhaust as much as possible.

The gas conditions immediately after the gas turbine exit are naturally determined by the cycle. The amount of heat held by this exhaust gas can be reduced by lowering its temperature through heat exchange with other gases (for example, combustor inlet air). In addition, the amount of diluting gas decreases due to the increase in combustion gas temperature, the total amount of gas decreases, and the retained heat group also decreases.

(Ii) If the generated steam has an effective use, it is used preferentially, and the amount of steam injected into the combustion gas is reduced as much as possible. This is understandable given the poor thermal efficiency of the steam cycle compared to the gas turbine cycle.

The specific means for realizing the above points are summarized as follows.

■ The air compressor is divided into multiple compressors each consisting of a pressure stage, and intermediate cooling is performed at least before the intake of the final stage compressor, and the air flowing out from this compressor and the gas flowing out from the gas turbine are exchange heat.

■ The moving and stationary blades of the gas turbine pressure section are cooled by steam. The steam used for cooling is allowed to flow into the combustion gases.

■ Mix the remaining steam with the combustion gas as part of the dilution gas.

In order to explain this in more detail, the first example of the plan of this invention
This will be explained using figures.

(2) In this example, the air compressor is divided into three parts: a low pressure compressor 11, an intermediate pressure compressor 12, and a high pressure compressor 13. Since the pressure ratio of this air compressor is as large as 22, the pressure ratio of each compressor is kept at 4 or less, which is enough to operate in a single shaft as an axial flow compressor without any countermeasures.

Intermediate cooling is performed between the intermediate pressure compressor 12 and the high pressure compressor 13 by a heat exchanger 14 and an intermediate cooler 15. Intercooling is meant to reduce the power required by the compressor, but
At the same time, the regeneration preheater 33 has the meaning of ensuring sufficient heat exchange between the air at the compressor outlet and the exhaust gas at the gas turbine outlet. The temperature of the gas turbine outlet exhaust gas decreases, m(i
) is very effective in reducing the retained heat m of the turbine exhaust gas.

■ Cooling of the rotor blades and stationary blades of the gas turbine high pressure section 31 is performed using steam.

Currently, all cooling in this area is done by air. Cooling with steam is in principle no different from cooling with air. The advantage of using steam is that its specific heat is approximately twice that of air, so it has a good cooling effect. Therefore, compared to air-cooled blades, it is easier to design for high-temperature gases.

The concept of cooling the blades with steam has already been introduced and is well known. However, there are no examples of it being actually used. In non-aviation turbines where steam is available, there is nothing that prevents the use of steam. The steam used to cool the blades flows into the combustion gas and becomes part of the working fluid, so it is not wasted at all. Since the pressure, temperature and amount of steam used can be selected arbitrarily, the cooling effect can be maximized. Furthermore, since steam is used to cool the cylinder, it has the effect of reducing the amount of steam injected into the combustor.

■After the above-mentioned measures have been taken, the remaining steam is blown into the combustion gas as part of the dilution gas.

Since the specific heat of steam is about twice that of air, the effect of temperature regulation is large, the amount of excess air is significantly reduced, and the power and equipment for air compression are eventually reduced. Additionally, the equipment after the gas turbine also becomes smaller because the amount of gas decreases.

Since the temperature of the gas at the gas turbine inlet is sufficiently high and the amount of steam is kept to a minimum, there is little risk that the high thermal efficiency of the gas turbine cycle will be diluted by the low efficiency of the steam cycle.

In other words, the high thermal efficiency that the combined cycle aims for can be achieved by processing the generated steam with a gas turbine, without investing in equipment such as a steam turbine.

All of the three specific means described above belong to known techniques. However, what I would like to emphasize here is that it is only when these measures are used in combination in this manner that particularly remarkable effects can be achieved.

The example of FIG. 1 will be explained in more detail.

This example was planned using methane as the fuel (100%), the pressure ratio of the air compressor at 22, and the temperature of the log gas entering the turbine at 1430°C.

The air compressor has a low pressure 11 each consisting of three pressure stages.
, a medium pressure compressor 12, and a high pressure compressor 13. The low pressure compressor is connected to the low pressure turbine together with a generator 51.

The medium pressure and high pressure compressors are each driven by separate high pressure gas turbine shafts. Although the gas turbine casing is integrated, it is of course possible to use separate casings. Temperature-controlled steam is introduced to cool high-pressure gas turbine blades.

An intercooler consisting of a heat exchanger 14 and an intercooler 15 is provided between the medium pressure and high pressure compressors. This heat exchanger exchanges heat with boiler water and generates some steam.

The air exiting the air compressor exchanges heat with the gas turbine exhaust gas in the regenerative preheater 33 and is introduced into the combustor 20. The gas turbine exhaust gas is cooled and introduced into the thermal boiler 60, where the exhaust heat is recovered as steam and then released to the atmosphere.

The amount of steam generated decreases by the amount of temperature lowered by the regeneration preheating hole.

Boiler water is replenished by a boiler water pump 61,
Boiler drum 67 via feed water preheater 63 and deaerator 64
will be introduced in It is further evaporated in the boiler 66, superheated in the superheater 68, and then flows out. The pressure of steam is 25k (]
/cnfG, temperature is 300°C. The temperature of the steam for cooling the turbine is adjusted to a desired level before being introduced into the turbine. Note that special care must be taken to prevent scale build-up with this steam. That is, it is desirable to use pure water, for example, pure water, which has few scale components, as the boiler feed water.

With the above process, the overall thermal efficiency is about 50%.

This is superior to the one using a normal steam turbine as shown in FIG. 2, which is about 48% under the same conditions. The basic reason for this is, as explained earlier, that the thermal efficiency of the steam cycle is slightly higher in the present invention.
This is also because the proportion of power generated by the steam cycle is smaller in the present invention.

The quantitative balance of this process can be summarized as follows.

Theoretical air 110, Air amount 23, 700 Pkd/Kr Fuel Methane 100% 1.050 〃Steam generation amount 3
, for 700 kCI / 1ljr injection
2.200 〃For blade cooling 1.500 8 Generated power 5,200Kw If the gas temperature and pressure ratio entering the turbine are even higher than in this example, this type of gas turbine equipment will show even better thermal efficiency than conventional ones. However, the one shown in Figure 1 has an air compressor pressure ratio of 1
6-64, turbine input log gas temperature 1300-1700℃
Particularly suitable for degree conditions.

If the temperature and pressure ratio are below this level and the proportion of power generated by steam is relatively large, the equipment cost will be low, but the thermal efficiency cannot be said to be particularly superior compared to conventional ones. Moreover, if the temperature exceeds this level, further measures are required such as countermeasures against hot gas and increasing the pressure of steam and compressor.

[Brief explanation of drawings]

FIG. 1 Gas turbine power generation equipment 70-sheet of the present invention FIG. 2 Conventional gas-steam turbine combined cycle 70-sheet 10 Air compressor 11 Low-pressure compressor 12 Intermediate-pressure compressor 13 High-pressure compressor 14 Heat exchanger 15 Intermediate Cooler 20 Combustor 30 Gas turbine 31 High pressure turbine 32 Low pressure turbine 33 Regeneration preheater 40 Steam turbine 41 Steam high pressure turbine 42 Steam low pressure turbine 43 Condenser 51 Gas turbine generator 52 Steam turbine generator 60 Waste heat boiler 61 Boiler water pump 62 Boiler Feed water pump 63 Feed water preheater 64 G-hole 65 Economizer 66 Boiler 67 Boiler drum 68 Superheater 69 Reheater

Claims (1)

[Claims] Air is compressed by an air compressor, fuel and compressed air are combusted in a combustor, and the generated combustion gas is expanded in a gas turbine to generate power. The air compressor is driven by the gas turbine, and the remaining power is supplied to the outside.The gas that flows out of the gas turbine is exchanged with heat in the waste heat boiler and used to generate steam, and then released into the atmosphere. In the power generation method, the air compressor is divided into a plurality of compressors each having its own pressure stage, intercooling is performed at least at the inlet of the final stage compressor, and this final stage compressor is heat exchange between the air flowing out from the gas turbine and the gas flowing out from the gas turbine,
and a part of the steam generated in the waste heat boiler,
After being used to cool the rotor blades and stationary blades in the high-pressure part of the gas turbine, the steam is introduced into the combustion gas, and the remaining steam is mixed with the combustion gas as part of the dilution gas of the combustion gas. Gas turbine power generation method.