JP2808456B2 - Steam turbine power plant - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor thermoelectric converter applied to a steam turbine power plant, particularly to a turbine exhaust duct (exhaust line).

2. Description of the Related Art A basic plant system configuration of a conventional steam turbine power plant will be described with reference to FIG. 8. In the figure, reference numeral 01 denotes a condenser, 02 denotes a feedwater pump, 03 denotes a feedwater heater, and 04 denotes a boiler. , And 05 are steam turbines, and the condensate in the condenser 01 is pressurized by a water supply pump 02 and processed by a water supply processing device (not shown).

Thereafter, the water is heated by the water supply heater 03, supplied to the boiler 04 via the water supply pipe 06, and turned into steam by overheating.

The generated steam is introduced into the steam turbine 05 through the main steam pipe 07, drives the turbine 05 by expansion work, and turns a generator 05 'connected to the turbine to generate electric power.

Therefore, the steam that has worked in the steam turbine 05 becomes low-pressure wet steam having a slight degree of wetness, is re-entered into the condenser 01 as described above via the exhaust duct 08, and is cooled by cooling water and condensed.

Further, the above steam cycle will be described based on the is-line diagram (enthalpy-entropy diagram) of the steam turbine plant shown in FIG. 9, and the pressure P ₁ generated in the boiler 04,
Temperature te, high-temperature, high-pressure steam enthalpy ie (point a) is expanded in a steam turbine 05 outlet to a pressure P _2, the temperature tl, wet steam enthalpy il, the words turbine exhaust (point b).

Then, the exhaust gas is condensed by cooling in the condenser 01 and becomes condensed water (point c) with enthalpy, and condensed water is supplied to the feed pump 02
(Point d) and overheated by the boiler 04 via the feed water heater 03 (point a).

Problems to be Solved by the Invention The conventional steam turbine power plant described above, however, has the following problems.

A steam turbine plant expands high-temperature, high-pressure steam, which holds thermal energy, with a turbine, converts it into mechanical energy, and turns a generator to generate electricity.More than 60% of the energy held by the steam is latent heat. Cannot be converted to mechanical work.

That is, assuming that the steam flow rate in this case is W, the total heat input of the steam turbine plant is W · (ie-ic) (see FIG. 9), of which the condensation latent heat corresponding to W · (il-ic) Is discarded to the condenser 01, more specifically, to the cooling water passing through the condenser 01.

Therefore, even in a state-of-the-art power plant, (turbine plant efficiency η _TP ) = (ie-el) / (ie-ic) × 100% is 5
At present, power generation efficiency is low at less than 0%.

For example, a high-performance steam turbine adopts a reheat regeneration method, which expands to an exhaust pressure of about 0.05ata, and about 55% of the heat input is discarded by a condenser with about 10% wetness of saturated steam.
The turbine plant efficiency η _TP is about 45%.

Therefore, an object of the present invention is to provide an apparatus for improving the efficiency of a total turbine plant by converting the heat into electric power and extracting it in order to recover and effectively use a large amount of waste heat in the above condenser. It is.

Means for Solving the Problems In order to solve such a conventional problem, a steam turbine power plant according to the present invention includes a steam turbine, an exhaust duct which receives steam expanded by the steam turbine and exhaust gas, and the steam turbine. A high-temperature section that uses the exhaust gas as a high-temperature heat source and a low-temperature section that uses cooling water as a low-temperature heat source. A semiconductor thermoelectric converter connected to the section and the high-temperature section so as to generate a potential difference based on a temperature difference between the low-temperature section and the high-temperature section.

A part of the latent heat of the turbine exhaust is discarded by the cooling water as a low-temperature heat source, but the remainder is converted into electricity by the semiconductor thermoelectric conversion means and supplied to the load. Therefore, heat energy corresponding to the electron energy is recovered, thereby improving the overall turbine plant efficiency η _TC . Moreover, since the exhaust temperature of the steam turbine can be easily adjusted to an exhaust temperature at which the thermoelectric performance of the semiconductor thermoelectric conversion means becomes an optimum value, the thermoelectric conversion rate of the semiconductor thermoelectric conversion means itself is maximized, and the overall turbine plant efficiency is increased. Bring further improvement.

Embodiment An embodiment of the present invention will be described below in detail with reference to FIGS. Note that the same reference numerals as those used in FIG. 8 indicate the same or equivalent members, and a description thereof will be omitted to avoid duplication.

Thus, according to the present invention, in the basic steam turbine cycle shown in FIGS.
(See FIG. 8) is not required, and instead, the semiconductor thermoelectric converter 1 using the exhaust gas of the steam turbine 5 as a high-temperature heat source and the cooling water as a low-temperature heat source is installed in the turbine exhaust duct 8.

The semiconductor thermoelectric converter 1 converts latent heat of exhaust gas into electricity and condenses turbine exhaust gas.

That is, the present invention focuses on the fact that the semiconductor thermoelectric conversion device requires a heat source of a constant temperature (with a small temperature change) as a high-temperature heat source, while the turbine exhaust is saturated steam or superheated steam having a slight degree of superheat. The semiconductor thermoelectric converter uses the latent heat (condensation heat) to generate electricity, and the turbine exhaust is condensed to eliminate the need for a condenser.

Next, the structural composition of the semiconductor thermoelectric converter 1 will be described with reference to FIGS. 3 to 6. FIG. 3 shows an overview of the converter, and FIGS. 4 and 5 show heat exchangers in the converter. 4 shows a turbine exhaust side contact surface (FIG. 4) and a cooling water side contact surface (FIG. 5). FIG. 6 shows the semiconductor element material,
That is, it shows an example of the arrangement of the thermoelectric conversion materials and the connection method thereof. Similar to the plate type heat exchanger, a large number of heat exchange means as a heat exchange means having a grooved or honeycomb structure 2a or the like to enhance heat transfer efficiency. The heat exchanger 2 (see FIGS. 3 to 5) also includes passages 3 and 4 for a turbine exhaust provided for a high-temperature heat source and a cooling water provided for a low-temperature heat source, which also flow in opposition from the viewpoint of thermal efficiency.
Are arranged in the conversion device 1.

At the bottom of the converter 1, a condensate tank (reservoir) 1 'communicating with the turbine exhaust passage 3 is provided.

N-type and P-type semiconductor elements (semiconductor thermoelectric conversion means) 6 are alternately arranged in these plate-type heat exchangers, that is, flat heat exchangers 2 (see FIG. 6). When one of these two elements is placed on the high-temperature part (turbine exhaust passage 3) side and the other is on the low-temperature part (cooling water passage 4) side, when connecting the two high-temperature parts, the N-type and P-type elements are used. Since the difference causes a potential difference (voltage) between the two low-temperature portions, the load 7 on the power demand side is connected between them.

In the drawing, reference numeral 6a indicates a high-temperature junction of each element, 6b indicates a low-temperature junction, and 6c indicates a connection electrode. N-type and P-type semiconductors are provided so that a predetermined voltage can be obtained through the connection electrode 6c. A large number of elements 6 are connected in series, and a high-temperature heat source temperature T'l
And the low-temperature heat source temperature Tc, a part of the heat flowing from the high-temperature side to the low-temperature side via the heat exchanger 2 is N-type.
The P-type semiconductor element 6 directly converts the electricity into electricity, and the remaining heat is discarded by the cooling water.

Accordingly, the thermoelectric converter 1 including the heat exchanger 2, the cooling water passage 4, and the condensate tank 1 ', which includes the semiconductor element 6, is a power generator and a conventional condenser 01.
It also serves as a condenser.

In addition, as shown in FIG.
Regarding the thermoelectric conversion performance of various thermoelectric conversion materials A to F
(However, since it is not the purpose of specifying the material, the names of the materials are omitted in this case.) The figure of merit Z and the temperature (difference) T
In order to obtain a high thermoelectric conversion efficiency η _TE , an optimum value based on the performance of the element material itself and the quality of the combination thereof, that is, a high performance index Z and an optimum temperature T as large as possible in a wide temperature range are required. It is necessary to make a selection.

 Next, the operation will be described.

On one contact surface of a large number of heat exchangers 2 similar to plate heat exchangers in the semiconductor thermoelectric converter 1, turbine exhaust as a high-temperature heat source flows through the exhaust duct 8 into the turbine exhaust passage 3, At the same time, cooling water as a low-temperature heat source is caused to flow into the cooling water passage 4 opposite to the turbine exhaust gas on the other contact surface.

Due to the difference between the heat source temperatures, the N-type and P-type semiconductor elements arranged in series in each heat exchanger 2 before a part of the latent heat of the turbine exhaust is introduced into the condensing tank 1 '. 6, the voltage is directly converted into a DC voltage applied to the low-temperature junction 6b side, so that the voltage, that is, the electric energy, together with the generator 5 '(similar to the conventional generator 05'), is transferred to the power demand side. It can be supplied to the load 7.

In other words, the total turbine plant efficiency η _TC can be increased by a part of the amount of latent heat effectively extracted (recovered) as electric energy.

In this case, for example, the turbine plant efficiency when the turbine exhaust temperature is tl which has been conventionally set is η _TP ,
The converter 1, when strictly to the ratio of the electrical output to heat input of the total heat exchanger 2 (thermoelectric conversion) and eta _TE, the eta
_TC is _calculated by the following equation.

η _TC = η _TP + (1.0−η _TP ) × η _TE (1) However, the value of (1.0−η _TP ) indicates the ratio of the loss (exhaust heat) of latent heat discarded to the cooling water in the cooling water passage 4 and removed. .

Thereafter, the exhaust gas that has passed through the turbine exhaust passage 3 is condensed, stored as condensate water in a condensate tank 1 ′ provided at the bottom of the converter 1, and supplied again to water supply.

Thus, as the semiconductor element (thermoelectric conversion material) 6 used in the heat exchanger 2, an element B covering the vicinity of the turbine exhaust temperature tl is selected as shown in FIG.

However, the actual turbine exhaust temperature tl is 100 ° C.
In the following, in such a low temperature range, there are not so many thermoelectric conversion materials having high thermoelectric exchange performance, and even if the element B can be selected, the turbine exhaust temperature is determined by the performance index Z of the element B itself. In many cases, the temperature is lower than the ideal turbine exhaust temperature t'l at which the optimum value can be obtained.

Therefore, even if the thermoelectric exchange device 1 of this embodiment is installed in a state-of-the-art high-efficiency steam turbine plant (usually the exhaust gas temperature is 50 ° C. or lower), the effect of improving the efficiency of the overall turbine plant is extremely small.

Therefore, as a countermeasure, according to the present embodiment, the steam turbine 5 is raised so that the turbine exhaust temperature is raised from Tl to T′l (see FIG. 2 b ′) at the expense of some turbine plant efficiency η _TP . The design can increase the overall turbine plant efficiency.

That is, the exhaust temperature t'l is a saturation temperature which is obtained by increasing the exhaust pressure higher than the conventional value and substantially corresponds to the exhaust pressure P ₂ '. Then, the turbine plant efficiency at this exhaust temperature t′l is represented by η ′ _TP = (ie−i′l) / (ie
-Ic) × 100%, also 'When _TE, such reasons First described above, P _2' the conversion of electrical output for heat input eta> P _2,
Under i′l> il, η _TC > η _TP ≧ η ′ _TP (2) (However, when Tl = T′l, η _TP = η ′ _TP ).

From this, although η ′ _TP is usually lower than η _{TP, in} order to eliminate the gap, the thermoelectric conversion rate is close to the maximum when the thermoelectric conversion performance (performance index Z) of the semiconductor element 6 is highest. Is increased from η _TE to η ′ _TE , so that η _TC = η ′ _TP + (1.0−η ′ _TP ) × η ′ _TE (3) The value of the turbine exhaust temperature T′l that satisfies the following condition may be determined.

Effects of the Invention As described in detail above, according to the invention, the following effects can be obtained.

(1) The overall turbine plant efficiency can be improved.

(A) Since the turbine waste previously discarded in the condenser is used as a high-temperature heat source and the cooling water is used as a low-temperature heat source, a part of the latent heat of the turbine exhaust is directly converted to electricity by a semiconductor thermoelectric converter. Therefore, the efficiency of the turbine plant is improved.

As one example, the turbine waste heat (loss) of a steam turbine with a turbine plant efficiency η _TP = 45% is (1.0−η _TP )
≒ 0.55 or about 55%. Even if this converter is installed in this plant instead of a condenser, the high-temperature heat source temperature (turbine exhaust temperature) is as low as about 40 ° C, and the temperature difference between the low-temperature heat source temperature (cooling water temperature) and about 20 ° C Few.

For this reason, the thermoelectric conversion efficiency η _TE is low, and is about several% (for example, about 2%).

Therefore, from the equation (1), it can be seen that the efficiency of the total turbine plant is improved by η _TC = 0.45 + (1.0−0.45) × 0.02 ≒ 0.46, that is, about 45 to 46%.

(B) In consideration of the fact that the thermoelectric conversion performance depends on the heat source temperature, in particular, the turbine exhaust temperature t'l is set to be higher than the conventional temperature tl, and it is optimal for the thermoelectric conversion performance of the semiconductor element used. By adopting a turbine design capable of expanding to a saturation pressure, the thermoelectric conversion rate η ′ _TE itself can be improved, and the overall turbine plant efficiency can be further improved.

That is, if this is explained according to the above example, t′l>
By setting tl, the thermoelectric conversion performance η ′ _TE of the semiconductor element is greatly improved, and it is possible to achieve about 10% of the above 2% or the like.

Here, for simplicity, the turbine exhaust has a temperature t'l = 10
In the case of the saturated steam at 0 ° C., the turbine plant efficiency η ′ _TP is naturally reduced as compared with the above η _TP to about 41%.

On the other hand, the total turbine plant efficiency is η _TC = 0.41 + (1.0−0.41) × 0.1 ≒ 0.47 or 47% from the equation (3). As a result, it is possible to further improve the overall turbine plant efficiency.

(2) The required equipment of the steam turbine plant can be rationalized.

(B) A condenser is not required on the condensate line, and the peripheral equipment can be simplified.

(B) Since the amount of hot waste water can be reduced, it is possible to reduce the power source such as a pump, the energy, and the effective use of the space.

(C) In (b) of the above item (1), since the turbine exhaust pressure is high, the low pressure stage installed under operating conditions of, for example, 1 ata or less can be eliminated. Therefore, the steam turbine can be significantly reduced in size, and the production period and cost of the turbine can be reduced.

In addition, as described above, the efficiency of the turbine plant is improved, and the effect of preventing erosion due to the reduction of wet steam is obtained, so that the reliability and life of the entire steam turbine plant are improved.

[Brief description of the drawings]

FIG. 1 is a basic plant system diagram showing an example of a steam turbine power plant according to the present invention, and FIG.
FIG. 3 is an external view and a partial cross-sectional view showing the structure of the semiconductor thermoelectric converter, and FIG. 4 is an outer surface of a heat exchanger disposed in the thermoelectric converter, which contacts a turbine exhaust (high-temperature heat source). FIG. 5 is a schematic view showing an outer surface in contact with the cooling water (low-temperature heat source), FIG. 6 is a cross-sectional view taken along line VV in FIGS. 4 and 5, and FIG. FIG. 8 is a basic plant system diagram showing a conventional steam turbine power plant, and FIG. 9 is its is diagram thereof. DESCRIPTION OF SYMBOLS 1 ... Semiconductor thermoelectric converter, 2 ... Heat exchanger (heat exchange means), 3 ... Turbine exhaust passage (high temperature part), 4 ... Cooling water passage (low temperature part), 5 ... Steam turbine, 6 ... ... semiconductor element (semiconductor thermoelectric conversion means), 8 ... turbine exhaust duct.

────────────────────────────────────────────────── (5) References JP-A-63-163746 (JP, A) JP-A-63-29964 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) F01K 19/10 F01K 17/04 Z F01K 11/00 F28B 1/02 F01K 9/00 Z

Claims (1)

(57) [Claims] A steam turbine, an exhaust duct for receiving steam expanded by the steam turbine as exhaust gas, a high-temperature portion using the exhaust gas from the steam turbine as a high-temperature heat source, and a low-temperature portion using cooling water as a low-temperature heat source. A heat exchange means for condensing the exhaust gas with the cooling water to supply water, and generating a potential difference in the low temperature part and the high temperature part of the heat exchange means based on a temperature difference between the low temperature part and the high temperature part. And a semiconductor thermoelectric converter connected to the steam turbine power plant.