JPH0415364B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a coal gasification combined cycle power plant. In particular, a combined coal gasification combined power generation plant that combines a coal gasification plant comprising a coal gasification furnace, a gas cooler, and a gas purification section with a combined power generation plant comprising a gas turbine, an exhaust heat recovery boiler, and a steam turbine. The present invention relates to a coal gasification combined cycle power plant that has improved thermal efficiency by improving its heat cycle.

[Prior art]

In such coal gasification combined cycle power generation plants, the steam supplied to the steam turbine is used to generate steam by combining the amount of heat recovered in the gas turbine waste heat recovery boiler and the amount of heat recovered in the gas cooler. It is considered to be the amount of heat. Therefore, improving the thermal efficiency of the entire plant is
It all depends on how effectively the heat cycle is configured for the entire plant.

This point will be explained in more detail with reference to the prior art. FIG. 1 shows an example of the heat cycle of a conventional coal gasification combined cycle power plant.

In this conventional example, coal 1 is gasified in a gasifier 3 using air or oxygen as a gasifying agent 2. The crude gas 4 at the outlet of the gasifier is cooled by a gas cooler 7. The sensible heat of this crude gas 4 is recovered as high pressure steam 6. That is, a cooling water supply 32 (indicated by a reference numeral) cools the crude gas 4 and at the same time is heated by the gas 4 to vaporize it and become high-pressure steam 6 which is led to the high-pressure drum 25 . Gas cooling outlet crude product gas 8 is heat exchanged with purified gas 12 by gas/gas heat exchanger 9, cooled to a temperature required for purification in gas purification section 11, and then gas purified. The purified gas 12 undergoes heat exchange and is heated in the gas/gas heat exchanger 9, and then is supplied to the gas turbine combustor 14 as a fuel gas 13. The fuel gas 13 is mixed with the air 16 compressed by the compressor 15 in the combustor 14 and combusted to become high-temperature, high-pressure gas, which performs the work of rotating the gas turbine 17 . Gas turbine 17 drives gas turbine generator 18, thereby generating electrical energy.

The heat recovery system has the following configuration. Sensible heat of the gas turbine exhaust gas 19 is recovered in an exhaust heat recovery boiler 20, where steam is generated. At the same time, the crude product gas 4 at the gasifier outlet
The sensible heat is recovered in the gas cooler 7, and steam (high-pressure steam 6) is generated here as described above. Generally, in this type of plant, these are combined to form a heat recovery system. The steam generated by such a system is superheated by a superheater 27 and works in steam turbines 44, 45,
A steam turbine generator 48 generates electrical energy.

The steam that has passed through the steam turbine 45 is transferred to the condenser 4
7, it is cooled to become condensate 41. This condensate 41
is sent as water supply to the exhaust heat recovery boiler 20 by the water supply pump 43. In the figure, 40 indicates the feedwater pump outlet water supply, and 37 indicates the exhaust heat recovery boiler water supply.

In the example shown in FIG. 1, in such a water supply system, the low pressure economizer 21 inlet water supply 37 of the exhaust heat recovery boiler 20
A feed water heater 42 is installed to heat the water. This is to prevent if the temperature of the water supply 37 is too low, dew condensation will occur on the inner surface of the exhaust heat recovery boiler 20, causing corrosion.

As a method of heating the water supply 37, the low pressure economizer 2
Although the method of recirculating the feed water at the outlet 1 is also considered, the heating method using the feed water heater 42 is superior to the method of recirculating the feed water from the point of view of thermal efficiency. This is because it is known.

On the other hand, the water supply 32 (indicated by the reference numeral in the figure) to the gas cooler 7 is also heated in advance, and is heated by the exhaust heat recovery boiler 20 and the low-pressure economizer 21 . That is, the condensate 41 becomes the exhaust heat recovery boiler feed water 37 and is heated by the low pressure economizer 21, but this is branched and one is sent to the low pressure drum 22, and the other is further sent to the feed water pump inlet water 29 and the gasifier. The water supply pump inlet water supply 29 is pressurized by the high-pressure boiler feed water pump 39, and this water pump outlet water supply 31 is also branched, one of which is connected to the high-pressure energy saver. The water supply 33 is led to the high-pressure economizer 24, and the other becomes the gas cooler supply water 32.

In this way, in the example shown in FIG. 1, the method of heating the water supply 32 to the gas cooler 7 using the low-pressure economizer 21 is adopted, but in addition to this, heating the water supply 32 is performed using the gas purification unit. 11, or in systems using air as the gasifier 2, a method that involves heat exchange with the gasifier air compressor inlet air, and a combination of these methods have been proposed. .

The purpose of heating the cooling water supply 32 to the gas cooler 7 is to recover the sensible heat of the gasifier crude gas 4 as effectively as possible to obtain high-pressure steam 6. That is, the temperature of the inlet gas 4 to the gas cooler 7 generally varies depending on the type of gasifier 3 used, but
When the type of gasifier 3 is limited, it is constant.
On the other hand, this gasifier outlet crude gas 4 needs to be purified for environmental reasons, and therefore it is necessary to cool the crude gas 4 to a temperature required for purification. How to effectively recover the sensible heat between the gas purification inlet gas 10 and the crude gas 4 at the gasifier outlet is one of the keys to the cycle configuration of a coal gasification combined cycle power plant. By preheating the cooling water supply 32 using the low-pressure economizer 21, it is effectively converted into high-pressure steam 6, thereby increasing thermal efficiency.

Generally, the amount of heat exchanged by the gas/gas heat exchanger 9 is increased to increase the temperature of the fuel gas at the inlet of the thermal burner 14.
It is known that the plant efficiency improves as the value of 3 is increased, but in this case, the amount of heat exchanged by the gas cooler 7 decreases, and the efficiency decreases due to a decrease in the amount of high-pressure steam 6, resulting in an improvement in efficiency. The gain of
The plant as a whole was small.

Rather, a heat cycle has been commonly used in the past, in which water that is fed to a boiler is heated by steam that has already done work in a steam turbine, thereby improving thermal efficiency. The configuration is adopted. This configuration corresponds to using the extracted air 46 from the medium/low pressure turbine 45 as a heat source for the feed water heater 42 when the aforementioned condensate 41 is heated by the feed water heater 42 to become the exhaust heat recovery boiler feed water 37. It is something to do.

As mentioned above, a number of configurations have been adopted to improve thermal efficiency, but by further increasing thermal efficiency,
Currently, research is being carried out to develop plants that are even slightly advantageous.

[Purpose of the invention]

In view of the above-mentioned current situation, an object of the present invention is to provide a coal gasification combined cycle power generation plant that improves the heat cycle of the coal gasification combined cycle power plant and thereby further improves thermal efficiency. be.

[Summary of the invention]

In order to achieve the above object, in the present invention, a feed water heater using steam turbine extraction air as a heating source is installed in the water supply system to the gas cooler, thereby increasing thermal efficiency by heating the feed water. Adopt a configuration that enhances the results.

In the present invention, similarly to a general coal gasification combined cycle power plant, the steam supplied to the steam turbine combines the amount of heat recovered in the gas turbine waste heat recovery boiler and the amount of heat recovered in the gas cooler of the coal gasification plant. However, as mentioned above, in such a combined cycle power generation plant, how effectively the heat cycle is configured for the coal gasification combined cycle power plant as a whole is an important key to improving the plant thermal efficiency. Therefore, in the present invention, in the heat cycle, the feed water to the gas cooler of the coal gasification plant is heated by the feed water heater installed with steam turbine bleed air as the heating steam source, thereby heating the entire plant. This is intended to improve thermal efficiency.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. This example is an improvement of the prior art shown in FIG. 1 by applying the present invention. In the figure, the same reference numerals as in FIG. 1 refer to parts having the same configuration or performing similar functions.

This coal gasification combined cycle power generation plant includes a coal gasification plant including a coal gasification furnace 3, a gas cooler 7, and a gas purification section 11, and a combined coal gasification plant including a gas turbine 17, an exhaust heat recovery boiler 20, and steam turbines 44, 45. It consists of a power generation plant.
In such a plant, a feed water heater 51 is installed in the water supply system to the gas cooler 7, using the extracted air 49 of the steam turbine 44 as a heating steam source (see the reference numeral in the figure). Newly provided systems compared to the conventional example shown in FIG. 1 are particularly illustrated with thick lines).

According to the above configuration, the water supply 3 sent to the cooler 7
2 is preheated by bleed air 49, and then the crude product gas 4 is cooled in a gas cooler 7 and effectively vaporized by the heat of this gas 4 to become high-pressure steam 6. Therefore, thermal efficiency is further improved than in the conventional configuration.

Next, a more specific configuration and operation of this embodiment will be described in detail.

Fuel produced by coal gasification plants13
After being combusted in a combustor 14 with air compressed by a compressor 15, the gas is used as a high-temperature gas to perform work in a gas turbine 17, and a generator 18 generates electrical energy.

In this embodiment, the heat recovery system includes a heat recovery system in which gas turbine exhaust gas 19 is recovered in a gas turbine exhaust heat recovery boiler 20 to generate steam, and a gasification furnace in a gas cooler 7 of a coal gasification plant. A system configuration is adopted in which a heat recovery system for recovering the sensible heat of the crude gas 4 at three outlets is combined.

The exhaust heat recovery boiler 20 includes a low pressure economizer 21, a low pressure drum 22, a low pressure evaporator 23, a high pressure economizer 24,
High pressure drum 25, high pressure evaporator 26, superheater 27,
It is composed of a reheater 28.

The condensate 41 is pressurized by the water supply pump 43 and heated by the low-pressure water heater 42, and then supplied to the low-pressure energy saver 21. The water supply branches at the outlet of the low pressure economizer 21 into a low pressure drum 22, a coal gasifier cooling water 30, a high pressure water supply pump 39, and a water supply 29. Water supply 2
9 is pressurized by a high-pressure water supply pump 39 and then branches into a high-pressure economizer water supply 33 and a gas cooling water supply 32. The water supply 33 to the high-pressure economizer 24 is sent to the high-pressure drum 25 through the high-pressure economizer 24 to generate steam.

On the other hand, the water supplied to the gas cooler 7 is heated by the high-pressure feed water heater 51 and then supplied. In this embodiment, the feed water heater 51 extracts air from the high-pressure turbine exhaust gas. The bleed steam 49 is typically
The temperature is 340-350℃ or slightly higher. This extracted steam 49 undergoes heat exchange in the high pressure feed water heater 51, and its latent heat is recovered. Here, the feed water 32 at about 180℃ is heated to 220℃ due to the latent heat.
It is heated to about 230°C and then led to the cooler 7. The extracted steam 49 from which the latent heat has been recovered is transferred to the drain 5
0 and is led to the low pressure feed water heater 42.

The bleed air is not only from the high pressure turbine exhaust as in this example, but also from the high pressure turbine exhaust.
This can be achieved by extracting air from each stage of the high pressure turbine 44 (indicated by 44' in FIG. 2) and the steam inlet stage of the low pressure turbine 45 (also shown by 45').

Continuing the explanation of the illustrated embodiment, the high pressure steam generated in the exhaust heat recovery boiler 20 and the high pressure evaporator 26 and the high pressure steam 6 generated in the gas cooler 7 are superheated by the superheater 27 and sent to the high pressure steam turbine 44. Sent. The high pressure steam 34 performs work in a high pressure steam turbine 44 and generates electrical energy in a generator 48 . After the high-pressure steam 34 performs work in the high-pressure turbine 44, the steam generated in the low-pressure drum and heat are recovered in the gasifier, mixed with the generated steam, and sent to the intermediate-pressure turbine through a reheater. . This performs work on the medium and low pressure turbine, which drives the generator 48 to generate electrical energy.

Next, the effects of this embodiment will be explained using FIG. 3. Figures 3a to 3c are state diagrams showing the states of gas, water supply, and steam inside the gas cooler, where a and b represent the conventional system, and c represents the system of the present invention shown in Figure 2. represents data in the example system. In each figure, the crude product gas enters the gas cooler 7 at a gas cooler inlet gas temperature T ₁ , indicated by reference numeral 54, and undergoes heat exchange to reach a gas cooler outlet gas temperature T ₂ or temperature T, indicated by 55 or 57. Leave in ₃ .
On the other hand, the water supply side enters the gas cooler 7 at the gas cooler inlet feed water temperature t ₁ or temperature t ₂ indicated by 56 or 58;
Temperature t ₄ , temperature t ₅ or temperature t ₆ at the economizers 21 and 24
It enters the drum and exits as steam.

FIG. 3a shows the state in the conventional heat cycle shown in FIG. FIG. 3b shows a case where the gas cooler outlet gas temperature is increased in order to increase the fuel gas temperature under the same water supply conditions in the conventional example. FIG. 3c shows the heat cycle of this embodiment shown in FIG.

This will be explained below.

The amount of steam generated in the gas cooler is determined by the drum pressure. Saturation temperature at drum pressure
Assuming _t3 , the difference between the crude product gas temperature _T4 and the cooler inlet gas temperature _T1 , which is expressed by the relationship _t3 + about 20°C, is the sensible heat used for evaporation in the drum. This is because the design of the gas cooler is T ₄ −
Generally, T ₂ >about 20°C. Also, in order to bring T ₄ as close to t ₂ as possible, it is necessary to make the heat transfer area of the evaporator infinitely large.

Therefore, it can be seen that in order to increase the amount of evaporation in the dom, it is necessary to increase the water supply temperature _t4 , _t5 , or _t6 to the drum when the drum pressure is constant.

FIG. 3a is a temperature diagram of the conventional basic heat cycle shown in FIG. From the state shown in Figure 3a, if the gas cooler outlet temperature is increased by approximately 70°C from _T2 to _T3 in order to raise the fuel temperature, the amount of heat exchanged Q in the gas cooler will increase to Approximately in the state of Figure 3 a
90%, so the steam generation amount G also decreases by about 90%. This is because the amount of heat exchanged in the economizer decreases, and the temperature of the water supplied to the drum decreases from t ₄ to t ₅ by approximately 35℃.
This is because it has decreased. In the state shown in Figure 3b, the amount of heat exchanged by gas cooling decreases and the amount of steam generated decreases, but the fuel temperature increases, so the thermal efficiency is approximately 0.1% (relative value) compared to the case in Figure 3a. (The heat cycle in FIG. 3b is also the same as that shown in FIG. 1, that is, the same as in FIG. 3a).

Furthermore, when the present invention is applied and the feed water temperature is increased by about 70°C from t ₁ to t ₂ , the amount of heat exchanged becomes 3rd as shown in Figure 3c.
For the situation in Figure 3a, the same as in Figure b, about
90%, but the amount of evaporation is about 10% compared to Figure 3 a.
It increases by about 20% compared to Figure 3b. By heating the feed water, the drum inlet temperature changes from t ₅ to t ₆ by approximately 70℃.
This is because the amount of evaporation increases as the amount increases.
The heat cycle in this case is shown in FIG. 2, which is an embodiment of the present invention.

Therefore, in the embodiment shown in FIG. 2, the high pressure steam at the inlet of the steam turbine increases by about 5 to 10% compared to the conventional heat cycle. As a result, the steam turbine generator output increases by approximately 0.6 to 1.2% due to the effect of heating the feed water. This results in an improvement of 0.3 to 0.6% in terms of thermal efficiency for coal gasification combined cycle power plants, but this is supplemented by an efficiency improvement of approximately 0.1% due to the rise in fuel gas temperature.
is added, resulting in a total improvement of approximately 0.4% to 0.7%, and the larger the output, the greater the contribution from the efficiency improvement, which is extremely advantageous.

The thermal efficiency of a combined cycle power plant is generally defined as below.

(Electric output (KW) x 860 ÷ {(Fuel heat input (kcal/Kg)) x (Fuel consumption (Kg/H)}) Fig. 3 shows another example of the implementation of the present invention.
This is a modification of the embodiment explained in FIG. Water supply 3 to charcoal generator 24
3 and a gas-cooled water supply 32, and the gas-cooled water supply 32 is heated by the high-pressure water heater 5 and sent to the gas cooling system, whereas in this embodiment, the water supply 2
9 is pressurized by a high-pressure water pump 39, heated by a high-pressure water heater 51, and branched into a water supply 33 to a high-pressure economizer 24 and a gas cooling water supply 32.

In this example as well, the output of the steam turbine is approximately
Relative value improved by 0.6-1.2%.

As explained above, each embodiment of the present invention can increase the amount of high-pressure steam generation by heating the water supplied to the gas cooler by steam turbine extraction.
Improved thermal efficiency can be achieved. This efficiency improvement is the fifth step.
The explanation is as follows using a diagram. FIG. 5 is a graph in which the horizontal axis shows the temperature rise of the gas-cooled feed water caused by the high-pressure feed water heater, and the vertical axis shows the relative change in thermal efficiency of the coal gasification combined cycle power plant.

By heating the water supplied to the gas cooler, the amount of steam generated in the gas cooler increases. The improvement in plant efficiency due to this increase in the amount of high-pressure steam is shown at 61 in FIG.

On the other hand, the steam turbine output decreases due to air extraction for heating the feed water. This effect is shown in 62.

As a result, the efficiency improvement value 63 of the coal gasification power plant is expressed as the above-mentioned (improvement value 61 due to increase in high-pressure steam - decrease value 62 due to bleed air). This improvement in thermal efficiency is approximately 0.3 to 0.6% when the feed water temperature rises to 70°C.

In this heat cycle, as a result, the gas cooler outlet temperature is raised to a temperature approximately equal to the feed water temperature, and the combustor inlet temperature of the fuel gas increases. The increase in efficiency due to this increase in fuel temperature is 0.1%/60
~70°C, this heat cycle has an overall efficiency improvement of about 0.4 to 0.7% compared to the conventional heat cycle.

〔Effect of the invention〕

As described above, according to the present invention, in a coal gasification combined cycle power generation plant, a feed water heater that uses steam turbine extraction air as a heating steam source is installed, and this heats the feed water to the gas cooler, thereby increasing high pressure. Since the amount of steam generated can be increased, thermal efficiency can be improved.

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

[Brief explanation of drawings]

FIG. 1 shows an example of a heat cycle of a conventional coal gasification combined cycle power plant. FIG. 2 shows a heat cycle of a coal gasification combined cycle power plant according to an embodiment of the present invention, and FIG. 4 shows a heat cycle of a modified example of the embodiment. Figure 3 shows
FIG. 5 is a graph showing changes in the state of gas, water supply and steam inside the gas cooler, and showing the effect of the above embodiment of the present invention. 3...Coal gasifier, 7...Gas cooler, 11
...Gas purification department, 17...Gas turbine, 20...
...Exhaust heat recovery boiler, 44, 45...Steam turbine, 49...Bleed air, 51...Feed water heater.

Claims (1)

[Claims] 1. A coal gasification plant comprising a coal gasification furnace, a gas cooler, and a gas purification section, a gas turbine,
In a coal gasification combined cycle plant that combines a combined cycle plant with an exhaust heat recovery boiler and a steam turbine, the water supply system to the gas cooler is
A coal gasification combined cycle power generation plant characterized by installing a feed water heater that uses steam turbine extraction air as a heating steam source.