JPH0445641B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a gas turbine device, an exhaust heat recovery boiler device that heats a fluid using the exhaust gas of the gas turbine as a heat source, and a heat recovery boiler device that is operated by the heated fluid. The present invention relates to a combined cycle power plant comprising a steam turbine device.

[Background of the invention]

This type of plant uses the exhaust gas of the gas turbine as a heat source to generate steam in the exhaust heat recovery boiler, so depending on the fuel used to drive the gas turbine, it may be significantly affected by the substances contained in the fuel exhaust gas. . Typically, if the fuel has a high sulfur content, the exhaust gas will contain a large amount of acid corrosive components, leading to the problem that the exhaust heat recovery boiler will be corroded by this. This problem is more or less unavoidable in combined cycle power plants that recover and utilize heat from exhaust gas.

Furthermore, in the past, combined cycle power generation plants were mainly non-auxiliary combustion types in which the exhaust heat recovery boiler used only exhaust heat as a heat source and did not use any other auxiliary fuel, but recently some plants have been increasing their output. There are cases where this is required, and it has become necessary to adopt an auxiliary combustion type that has a higher output capacity than a non-auxiliary combustion type, that is, a type that uses auxiliary fuel in addition to exhaust heat.
In the case of auxiliary combustion, the above becomes an even bigger problem. In other words, it is of course preferable to use a fuel that does not contain acid-corrosive components such as sulfur as an auxiliary fuel, but in recent years, due to cost and petroleum issues, it has become necessary to use residual oil with a high sulfur content. In many cases, poor quality fuel must be used. If such inferior fuel is used, there are many causes of trouble such as clogging of the burner chip during auxiliary combustion in the exhaust heat recovery boiler, and the fuel may eventually become unusable. In addition to this basic problem, there is also the problem that if fuel containing acid-corrosive components is used, corrosion will occur below a certain temperature, so the temperature of the heat source of the waste heat recovery boiler cannot be lowered very much. . For this reason, even if an attempt is made to lower the temperature to a certain extent in order to increase efficiency, it is not possible to do so, and thus efficiency and acid corrosion become contradictory problems. This becomes a significant problem when adopting the auxiliary combustion method, but as mentioned above, the gas turbine itself that generates exhaust gas often has to use fuel containing sulfur, etc., and therefore, combined cycle plants This is a common problem for many people.

This problem will be explained in more detail with reference to the drawings as follows.

Figure 1 shows a conventional auxiliary combustion combined cycle power plant. This is a conventional example of a single pressure type steam turbine having one steam inlet.

The gas turbine device 110 includes a compressor 11, a combustor 12, and a gas turbine 13, and drives a generator 14.

The exhaust heat recovery boiler 20 includes, from the upstream side of the gas, a superheater 22, an evaporator 22, a economizer 23, and a drum 2.
4, and an auxiliary combustion device 26.

Further, the steam turbine device 30 includes a steam turbine 3
1, generator 35, condenser 32, condensate pump 33,
It is constituted by a deaerator 36.

The superheater 21 of the exhaust heat recovery boiler 20 and the steam turbine device 30 are connected by a high-pressure and high-temperature steam pipe 4. The steam turbine 31 and the condenser 3
2. Deaerator 36, energy saver 2 of exhaust heat recovery boiler 20
3 are connected by a condensate pipe 5 and a water supply pipe 6, and a water supply pump 34 is installed on the upstream side of the water supply pipe 6.

Air 1 is compressed by the compressor 11 and burns fuel 7 in the combustor 12 to generate high temperature gas 2, which is injected into the gas turbine 13 and drives the generator 14. The exhaust gas 3 discharged from the turbine 13 flows into the exhaust heat recovery boiler 20.

In the exhaust heat recovery boiler 20, the feed water 6 is supplied,
As it passes through the economizer 23, evaporator 22, and superheater 21, the heat of the exhaust gas 3 is recovered, and the auxiliary combustion device 26 turns it into high-temperature steam 4, which is injected into the steam turbine 31 and drives the generator 35. do.

Further, a part of the steam is extracted from the middle of the steam turbine 31 through the bleed pipe 8, and the steam is extracted from the deaerator 36.
It is a heat source for

The overall efficiency of such a combined cycle power plant is higher as the feed water temperature is lower. That is,
In the conventional combined cycle power plant described above, the relationship between the temperature of the feed water supplied to the waste heat recovery boiler and the efficiency of the entire combined cycle power plant is as shown in FIG.

In FIG. 2, as for the steam turbine plant cycle, the higher the feed water temperature is as shown in the graph, the higher the efficiency is, but as for the exhaust heat recovery boiler efficiency, as shown in the graph, the lower the feed water temperature is, the higher the efficiency is. As shown in the graph, the lower the feed water temperature, the higher the efficiency of the overall combined cycle power plant.

However, due to the above-mentioned problem, the temperature of the exhaust heat recovery boiler to which feed water is supplied cannot be lowered much because acid corrosion occurs when the temperature falls below a certain temperature (referred to as the "acid dew point"). In other words, depending on the amount of corrosive components contained in the gas turbine exhaust gas,
In general, the general relationship between the corrosion rate due to the acid dew point of sulfur content and the feed water temperature at low temperatures is as shown in FIG. As is clear from this figure 3,
It can be seen that acids such as sulfur in the exhaust gas become below the dew point at approximately 120°C to 140°C, and the corrosion rate increases rapidly.

Therefore, in the past, despite the reduction in overall combined cycle power plant efficiency as explained in FIG. , a deaerator, and a feedwater heater were installed to raise the temperature of the feedwater to above the acid dew point using the extracted air from the steam turbine as a heat source.

Furthermore, in the combined cycle power plant shown in FIG. 1, if a steam turbine output greater than the capacity of the exhaust heat recovery boiler is required, a fuel firing device such as the one described above may be added to the conventional exhaust heat recovery boiler. It is possible to improve the steam turbine output by using the auxiliary combustion system provided, but in this case, as mentioned above, if fuel with a high acid content such as sulfur is used, it becomes necessary to install the acid dew point prevention device mentioned above. come. In addition, when using inferior fuel as described above, there are problems with the boiler characteristics due to the design of the duct boiler and unreliability such as burner chip clogging, as described above.

[Purpose of the invention]

In view of the above-mentioned problems of the prior art, the present invention makes it possible to prevent corrosion due to acid dew point on low-quality fuel, improve main steam conditions to high temperature and high pressure conditions, increase output, and improve plant performance. The objective is to provide a combined cycle power plant that can improve efficiency.

[Summary of the invention]

In order to achieve the above object, the present invention introduces feed water into an exhaust heat recovery boiler, exchanges heat with the exhaust gas of a gas turbine and preheats it using a preheater installed in the exhaust heat recovery boiler, and converts the preheated feed water into exhaust heat. The structure is such that steam generated in a fuel-fired boiler installed separately from the recovery boiler is guided to the steam turbine inlet.

[Embodiments of the invention]

The present invention will be further explained below by describing some of its embodiments in detail with reference to the drawings. In the description of the embodiments, components similar to those of the above-mentioned conventional ones will be referred to as No. 1 in the drawings.
The same reference numerals as those in the figure are given, and detailed explanation thereof will be omitted.

FIG. 4 shows an embodiment in which the present invention is applied to the typical combined cycle power plant shown in FIG. 1 described above.

In FIG. 4, the feature of the present invention is that the feed water is introduced into the waste heat recovery boiler 20, and is exchanged with the exhaust gas 3 of the gas turbine device 10 by the preheater 25 in the waste heat recovery boiler 20, and is preheated. The supplied water is led to a fuel-fired boiler 40 located separately from the exhaust heat recovery boiler 20, and the steam generated from the fuel-fired boiler is introduced into the steam turbine device 30.

To explain this example in more detail,
It is as follows. Reference numeral 5 in the figure indicates a condensate system, and the condensate from the condenser 32 is passed through the condensate pump 33 to the energy saver 2 provided in the exhaust heat recovery boiler 20.
3. After passing through the evaporator 22 and drum 24 in this order, it is introduced into the superheater 21. Generated steam superheated by the superheater is introduced into the steam turbine 31 through the steam pipe 9.

On the other hand, in the above condensate system 5, the condensate pump 3
The feed water branched from the system that is supplied to the exhaust heat recovery boiler 20 through the exhaust heat recovery boiler 20 is introduced into the exhaust heat recovery boiler 20, and the feed water is heat exchanged with the exhaust gas 3 of the gas turbine device 10 by the preheater 25 to 120°C to 140°C. The temperature is raised to ℃. This temperature increase is also to raise the temperature higher than the acid dew point and prevent acid corrosion.
Therefore, by installing the present preheater 25, it is possible to prevent corrosion due to the acid dew point even in the case of a fuel-fired boiler that uses fuel with a high acid content such as sulfur content, which will be described next.

That is, with this configuration, even if inferior fuel containing sulfur or the like is used, corrosion caused by the acid content can be prevented. This is because the temperature of the feed water is raised by the exhaust gas 3 of the gas turbine device 10 and kept above the acid dew point, so corrosion that occurs below the acid dew point does not occur.

The feed water whose temperature has been raised by the preheater 25 is
The fuel is introduced into the fuel economizer 44 of the fuel-fired boiler 40, which includes the economizer 44, the evaporator 43, the drum 45, and the superheater 42. Furthermore, an evaporator 43 and a drum 4
5, and is heated by a superheater 42. The generated steam here passes through the high-pressure and high-temperature main steam pipe 4 and joins with the generated steam 9 from the exhaust gas recovery boiler mentioned above,
It is introduced into the steam turbine 31 as main steam.

As a result of the above configuration, thermal efficiency can be improved in this embodiment. This improvement in thermal efficiency is one of the effects of the present invention, and will be explained with reference to FIG. 5 in accordance with the present example.

Figure 5 shows the Rankine cycle, which is the simplest theoretical cycle using steam as the working fluid.
An S diagram is shown.

In this Rankine cycle, superheated steam generated in a boiler is guided to a turbine, expanded, and cooled in a condenser to become saturated water.The water pump increases the pressure and sends it to the boiler, where it is heated. In this cycle, the steam is returned to the superheated steam state again via the →→ route.

The area represents the amount of heat supplied by the boiler, the area represents the amount of heat equivalent to the work generated (effective amount of heat), and the area represents the amount of heat discarded to the condenser (reactive amount of heat). The theoretical thermal efficiency is expressed by the following formula.

η _R = AL/QB Where, η _R : Rankine cycle theoretical thermal efficiency (%) AL: Effective amount of heat (kcal/h) QB: Supplied amount of heat (kcal/h) Therefore, in order to improve the cycle thermal efficiency, , it is necessary that the increase in the amount of effective heat exceeds the increase in the amount of reactive heat.

Now, when the exhaust vacuum level is constant in Figure 5,
A Rankine cycle under conventional steam conditions is shown, and a Rankine cycle in which the steam temperature is increased by installing the fuel-fired boiler according to the present invention is shown.
Denoted by 1′ b′.

It is clear from this figure that as the superheating temperature rises, the increase in the amount of effective heat exceeds the increase in the amount of reactive heat, and the thermal efficiency is improved.

As described above, the effects of this embodiment include, firstly, that it is possible to prevent corrosion caused by the acid content of inferior fuel containing sulfur, etc., which could not be solved with an auxiliary combustion type exhaust heat recovery boiler. That is, in this configuration, by raising the temperature of the water supply using the exhaust gas 3 of the gas turbine device 10, it is possible to prevent corrosion due to the acid dew point. Furthermore, the second
By installing a fuel-fired boiler 40 separately from the waste heat recovery boiler 20, the main steam conditions were improved by converting the low-temperature steam generated by conventional gas turbine exhaust gas into high-temperature steam, thereby improving the efficiency of the combined cycle power plant. Improvements will be made.

Next, as an application example, an example in which the present invention is applied to a double pressure combined cycle power plant is shown in FIG.

In contrast to the example shown in FIG. 4 described above, FIG. 6 shows that the low-temperature, low-pressure steam generated from the exhaust heat recovery boiler 20
The steam is introduced into the intermediate stage of the steam turbine 31 through the steam pipe 9 .

On the other hand, the water supply branched from the condensate system 5 is pressurized by the water supply pump 34, and the pressure is increased to the exhaust heat recovery boiler 20.
The fuel is then introduced into the fuel-fired boiler 40 via the preheater 25. The high temperature and high pressure steam generated here is introduced into the steam turbine 31 as main steam.

The present invention can also be applied to a double-pressure combined cycle power plant as in this application example, and by such application, higher temperature and high pressure steam can be generated than in a single-pressure combined cycle power plant. Therefore, it is possible to improve the plant efficiency of the entire combined cycle power plant.

It goes without saying that the present invention is not limited to the illustrated embodiments.

〔Effect of the invention〕

As described above, in the present invention, firstly, the feed water is used in the preheater in the waste heat recovery boiler to handle low-quality fuel containing sulfur, etc., which could not be dealt with in the conventional auxiliary combustion type waste heat recovery boiler. Corrosion due to acid dew point can be prevented by preheating by exchanging heat with the exhaust gas of the gas turbine device and raising the temperature of the feed water. Secondly, by installing a fuel-fired boiler separate from the waste heat recovery boiler and introducing the preheated feed water mentioned above, we were able to improve the main steam conditions to high temperature and high pressure, allowing combined cycle power generation. It becomes possible to improve the plant efficiency of the plant.

[Brief explanation of drawings]

Figure 1 is a diagram showing the overall configuration of a conventional general single-pressure combined cycle power plant, Figure 2 is a diagram showing the relationship between feed water temperature and thermal efficiency of a combined cycle power plant, and Figure 3 is a diagram showing the relationship between metal FIG. 3 is a diagram showing trends in temperature and corrosion rate. FIG. 4 is a diagram showing the overall configuration of a single-pressure combined cycle power plant that is an embodiment of the present invention. FIG. 5 is a diagram for explaining the thermal efficiency improvement on the theoretical Rankine cycle T-S diagram according to the present invention with respect to the example of FIG. 4. FIG. 6 is a diagram showing the overall configuration of a double pressure combined cycle power plant according to another embodiment of the present invention. 3...Exhaust gas, 10...Gas turbine device, 20...
Exhaust heat recovery boiler, 30...Steam turbine device, 40
...Separate fuel-fired boiler.

Claims (1)

[Claims] 1. A combined cycle power generation system comprising a gas turbine device, an exhaust heat recovery boiler that generates steam using the exhaust gas of the gas turbine device as a heat source, and a steam turbine device driven by the steam generated by the boiler. In the plant, a preheater is installed in the steam exhaust heat recovery boiler and preheats the feed water by exchanging heat between the exhaust gas and the feed water, and a preheater is installed separately from the waste heat recovery boiler and the preheater is heated from the preheater. A combined cycle power generation plant characterized by being equipped with a fuel-fired boiler that heats feed water, generates steam, and introduces the steam into a steam turbine device. 2. In the combined cycle power plant set forth in claim 1, the turbine is constructed as a double-pressure turbine having a plurality of steam inlets, and the steam generated on the heat-fired boiler side is heated at a higher temperature and pressure than the steam generated by the waste heat recovery boiler. A combined cycle power generation plant characterized in that: is injected into the high pressure side of the double pressure turbine.