JPH02238104A - Steam turbine type power generation plant - Google Patents

Abstract

PURPOSE:To permit the conversion of the latent heat of the turbine exhaust to electricity and eliminate the need of a condenser by arranging a semiconductor heat-electricity converter which uses the exhaust of a steam turbine as high temperature heat source and uses cooling water as low temperature heat source onto a turbine exhaust duct. CONSTITUTION:A steam turbine 5 is driven by the steam generated in a boiler 04 into which water is supplied from a water feeding pump 02, and a power generator 5' is driven by the generated power, and a semiconductor heat- electricity converter 1 which uses the exhaust of the steam turbine 5 as high temperature heat source and uses cooling water as low temperature heat source at the part where a condenser is arranged in the conventional is arranged in a turbine exhaust duct 8. The semiconductor heat-electricity converter 1 is equipped with a number of heat exchangers 2 having each honeycomb structure which are installed so as to be interposed in each passage 3, 4 for the turbine exhaust and cooling water and N-type and P-type semiconductor elements 6 are arranged alternately in the heat exchanger 2. The latent heat of the exhaust is converted to electricity, and the turbine exhaust is condensed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor-to-thermoelectric conversion device for use in a steam turbine power plant, in particular in a turbine exhaust duct (exhaust line).

BACKGROUND OF THE INVENTION The basic plant system configuration of a conventional steam turbine power plant will be explained based on FIG. 8. In the figure, 01 is a condenser, 02 is a feed water pump, 03 is a feed water heater,
04 is a boiler, and 05 is a steam turbine, in which condensate in a condenser Ol is pressurized by a feed water pump 02 and treated by a feed water treatment device (not shown).

Thereafter, the water is heated by the feed water heater 03, supplied to the boiler 04 via the water feed pipe 06, and becomes steam due to overheating.

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

Therefore, the steam that has done work in the steam turbine 05 becomes low-pressure wet steam with a slight degree of humidity, is reinjected into the aforementioned condenser 01 via the exhaust duct 08, is cooled by cooling water, and is condensed and condensed.

Moreover, when the above steam cycle is explained based on the i-s diagram (enthalpy enthrobi diagram) of the steam turbine plant shown in FIG. 9, the pressure P1 generated in the boiler 04 is
, temperature te, enthalpy ie, high-temperature, high-pressure steam (point a) expands at the steam turbine 05 outlet to pressure P, and temperature t
I2, the enthalpy i (2) becomes wet steam, that is, the turbine exhaust (point b).

Then, the exhaust gas is cooled and condensed in condenser 01 to become enthalpic condensate (point C), and the condensate is pressurized in feed water bomb 02 (point d), passes through feed water heater 03, and is heated in boiler 04. (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 contains thermal energy, in a turbine and converts it into mechanical energy, which then turns a generator to generate electricity. Approximately 60% or more of the energy contained in steam is latent heat. cannot be converted into mechanical work.

That is, if the steam flow rate in this case is W, the total human heat of the steam turbine plant is W・(ie-ic) (9th
．． (see figure), of which the latent heat of condensation corresponding to W·(k-10) is discarded to the condenser Ol, more precisely to the cooling water passing through the condenser 01.

Therefore, even in the most advanced power plants, (turbine plant efficiency η7p) = (ie − i1J)/(ie
-ic)X 10G% is less than 50%, and the power generation efficiency is currently low? .

For example, high-performance steam turbines use a reheat regeneration system, which expands to an exhaust pressure of about 0.05 ata and a humidity level of about 10.
% of the heat input is wasted in the condenser, and the turbine plant efficiency η■ is about 45%.

Therefore, an object of the present invention is to provide a device that improves overall turbine plant efficiency by converting the heat into electric power and extracting it in order to recover and effectively utilize the large amount of waste heat in the condenser. It is.

Means for Solving the Problems In order to solve these conventional problems, the present invention provides a semiconductor thermoelectric conversion device in a steam turbine power generation plant that uses the exhaust of the steam turbine as a high-temperature heat source and uses cooling water as a low-temperature heat source. It is installed in the turbine exhaust duct and converts the latent heat of the turbine exhaust into electricity, as well as condensing the turbine exhaust, eliminating the need for a condenser.

Effect? According to such a method, the effective latent heat of the still-hot turbine exhaust, which was conventionally discarded in the condenser, is converted into electricity by the semiconductor thermoelectric conversion device, so the thermal energy equivalent to that electrical energy is converted into electricity. By recovering the total turbine plant efficiency η■.

can be increased.

EXAMPLE Hereinafter, an example of the present invention will be described in detail with reference to FIGS. 1 to 7.

According to the present invention, however, in the basic steam turbine cycle shown in FIGS. 1 and 2, the conventional condenser 01 (
(see Figure 8) is not required, and instead the steam turbine 5
A semiconductor thermoelectric conversion device 1 is installed in the turbine exhaust duct 8, using the exhaust gas as a high-temperature heat source and cooling water as a low-temperature heat source.

This semiconductor thermoelectric conversion device 1 converts the latent heat of exhaust gas into electricity and condenses turbine exhaust gas.

That is, the structural composition of the converter 1 will be explained based on FIGS. 3 to 6. FIG. 3 shows an overview of the converter, and FIGS. 4 and 5 show the turbine exhaust side contact of the heat exchanger in the converter. surface(
Figure 4) and cooling water side contact surface (Figure 5) are shown, respectively. Further, FIG. 6 shows an example of the arrangement of the semiconductor element material, namely the thermoelectric conversion material, and its connection method, and similar to a plate type heat exchanger, a grooved or honeycomb structure 2a etc. is used to improve heat transfer efficiency. A large number of heat exchangers 2 (see Figs. 3 to 5) having a large number of heat exchangers 2 (see Figs. 3 to 5) are interposed in each passage 3, 4 for the turbine exhaust gas for the high temperature heat source and the cooling water for the low temperature heat source, which flow oppositely from the point of view of thermal efficiency. Come on, the conversion device! arranged within.

Note that the converter 1 is provided with a condensate tank (reservoir) connected to the turbine exhaust passage 3.

These plate heat exchanger type flat heat exchangers 2 (
(see Fig. 6), N-type and P-type semiconductor elements 6 are arranged alternately, and the principle is that one of these two types of elements is placed on the high threat part (turbine exhaust passage 3) side, and the other When connecting both high-temperature tubes on the low-temperature section (cooling water passage 4) side, a potential difference (voltage) is connected between the two low-temperature sections due to the difference in N-type and P-type elements.

In the figure, reference numeral 6a indicates a high-temperature junction of each element, 6b indicates a low-temperature junction, and 6c indicates a connection electrode.
A large number of N-type and P-type semiconductor elements 6 are connected in series so that a predetermined voltage can be obtained through the heat exchanger. The heat flowing from the high temperature side to the low temperature side through the N-type and P-type semiconductor elements 6 is directly converted into electricity, and the remaining heat is discarded into the cooling water.

Therefore, the heat exchanger 2 made of the semiconductor element 6 in this way,
The thermoelectric conversion device 1, which includes the cooling water passage 4 and the condensate tank 1', is not only a power generation device but also a condenser that performs the function of the conventional condenser 01.

In addition, as shown in FIG. 7, regarding the thermoelectric conversion performance of the N-type and P-type semiconductor elements 6, various thermoelectric conversion materials A to F (however, the main purpose is not to specify the material, so in this case, each material name is (omitted) depends on the figure of merit Z and temperature (difference) T, so the thermoelectric conversion efficiency is high. In order to obtain this, it is necessary to select an optimum value based on the performance of the element materials themselves and the quality of their combinations, that is, a high figure of merit Z and an optimum temperature T that is as large as possible over a wide temperature range.

Next, its effect will be explained.

At one contact surface of a large number of heat exchangers 2 similar to plate-type heat exchangers in the semiconductor thermoelectric conversion device 1, turbine exhaust gas, which serves as a high-temperature heat source, flows through an exhaust duct 8 into a turbine exhaust passage 3, and at the same time On the other contact surface, cooling water serving as a low-temperature heat source is made to flow in the cooling water passage 4, facing the turbine exhaust gas.

Due to the generation of this difference in heat source temperature, in particular, before the latent heat retained in the turbine exhaust gas is introduced into the condensing tank, the voltage of the generator 5' arranged in series in each heat exchanger 2 is That is, electrical energy can be supplied to the load 7 on the power demand side.

In other words, is the total amount of heat equivalent to the amount of latent heat effectively extracted (recovered) as electrical energy? This makes it possible to increase the plant efficiency η1o.

In this case, for example, the turbine plant efficiency when the turbine exhaust temperature is tX, which is conventionally set, is set to η. , 4, and to be more precise, the ratio of electrical output to total heat exchanger 2 heat input (thermoelectric conversion rate) is η■. Then,
The above η1o is determined by the following equation.

η = η + (1.0-η)×η ・ ・
φ(1)TC TF TP
TE? The value of (1.0-η■,) indicates the rate of latent heat loss (exhaust heat) that is discarded to the cooling water in the cooling water passage 4.

After that, the exhaust gas that passed through the turbine exhaust passage 3 is condensed and converted into a converter! The water is stored as condensate in a condensate tank 1' provided at the bottom, and is supplied to the water supply again.

Therefore, as the semiconductor element (thermoelectric conversion material) 6 used in the heat exchanger 2, an element B that covers around the turbine exhaust temperature tQ is selected as shown in FIG.

However, the actual turbine exhaust temperature tQ is 100
℃ or below, and there are not many thermoelectric conversion materials that have high thermoelectric conversion performance in such a low temperature range, and even if element B can be selected, the turbine exhaust temperature will be lower than the figure of merit Z of element B itself. Even if the thermoelectric conversion device 1 of this embodiment is installed in a turbine plant (usually, the exhaust temperature thereof is 50° C. or lower), the effect of improving the overall turbine plant efficiency is extremely small.

Therefore, as a countermeasure to this problem, according to this embodiment, the turbine plant efficiency η. , the overall turbine plant efficiency can be increased by designing the steam turbine 5 to raise the turbine exhaust temperature from Tl2 to T'& (see Figure 2 b'), even at the expense of .

That is, the exhaust temperature t'C is a saturation temperature obtained by raising the exhaust pressure above the conventional value and approximately corresponds to the exhaust pressure P,'. Then, the turbine plant efficiency at this exhaust temperature t'g is η'T, = (ie − i'Q
) / (ie - ic) 〉 ηTP≧η'TP...(2) (However, when T& = T'ff, "TP=""TP)
becomes.

From this, η′. , is usually higher than ηT, and the thermoelectric conversion rate increases from ηTE to η'TE.
Since the value increases, ηTC - η'TP + (1.0 - η'TP) × η'TE・
...(3), it is sufficient to determine the value of the turbine exhaust temperature T'g that satisfies the equation (3)>(1).

Effects of the Invention As detailed above, according to the present invention, the following effects can be obtained.

(1) Overall turbine plant efficiency can be improved.

(a) Turbine waste that was conventionally disposed of in the condenser? Since the turbine is used as a high-temperature heat source and the cooling water is used as a low-temperature heat source, the semiconductor thermoelectric conversion device can directly convert a portion of the latent heat held in the turbine exhaust into electricity, improving turbine plant efficiency.

As an example, the turbine exhaust heat (loss) of a steam turbine with a turbine plant efficiency ηTP - 45% is (1.0-η
■, )40.55, or about 55%.

The converter is installed in this plant instead of a condenser.The high-temperature heat source temperature (turbine exhaust temperature) is as low as approximately 40°C, and the low-temperature heat source temperature (cooling water temperature) is approximately 20°C.
There is also little difference in temperature from ℃.

For this reason, the thermoelectric conversion efficiency η■6 becomes low, on the order of several percent (for example, 2%).

Therefore, from equation (1), the overall turbine plant efficiency is ηTc = 0.45+ (1.0- 0.45)X 0
．． 02# 0.46, that is, an improvement of about 45 to 46% is observed.

(Example) Furthermore, considering that the thermoelectric conversion performance depends on the heat source temperature, it is particularly important that the turbine exhaust temperature t'g is lower than the conventional temperature tI2.
The thermoelectric conversion rate η′. 6 itself, and the overall turbine plant efficiency can be further improved.

That is, to explain this according to the above example, t'c >
By setting tc, the thermoelectric conversion performance η'T of the semiconductor element
E is significantly improved, and it is possible to achieve about 10% compared to the above-mentioned 2%.

Here, for simplicity, the temperature of the turbine exhaust is t'a=i
In the case of saturated steam at oo°C, the turbine plant efficiency η′
is naturally lower than the above-mentioned ηTP to 4;rP, which is about 1%.

On the other hand, the overall turbine plant efficiency is calculated as follows from equation (3): ηTc=0.41+(1.0-0.41)xo. 1=
0.47 or 47%, resulting in a greater overall turbine plant efficiency improvement.

(2) The required equipment for a steam turbine plant can be rationalized.

(a) A condenser is no longer required on the condensate line, and the surrounding equipment can be simplified.

(Example) Since the amount of heated waste water can be reduced, it is possible to reduce the power source and energy for pumps, etc., and to make effective use of space.

(C) Regarding item (1), since the turbine exhaust pressure is high, it is possible to eliminate the need for a low-pressure stage that has been installed under operating conditions of, for example, 1 ata or less. Therefore, the steam turbine can be made significantly more compact, and the manufacturing period and cost of the turbine can be reduced.

Moreover, as described above, the reliability and life of the entire turbine plant are improved.

[Brief explanation of drawings]

Fig. 1 is a basic plant system diagram showing an example of a steam turbine power generation plant according to the present invention, and Fig. 2 is an i-
s diagram, Figure 3 is an overview and partial structural cross-sectional view of a semiconductor thermoelectric conversion device, and Figure 4 shows the outer surface of a heat exchanger placed in the thermoelectric conversion device that comes into contact with the turbine exhaust (high-temperature heat source). Schematic diagram, Figure 5 is a schematic diagram showing the outer surface in contact with the cooling water (low-temperature heat source), Figure 6 is a sectional view taken along the ■-V line in Figures 4 and 5, and Figure 7 is a diagram showing the outer surface in contact with the cooling water (low-temperature heat source). A correlation diagram of a general figure of merit Z and a heat source (turbine exhaust) temperature T, FIG. 8 is a basic plant system diagram showing a conventional steam turbine power generation plant, and FIG. 9 is an i-s diagram thereof. ■...Semiconductor thermoelectric conversion device, 2...Heat exchanger, 3...Turbine exhaust passage, 4...Cooling water passage, 5...Steam turbine, 6...Semiconductor element, 8...Ta (and other names) Figure 1' Tank Figure B Figure 1'

Claims (1)

[Claims] A semiconductor thermoelectric conversion device that uses steam turbine exhaust as a high-temperature heat source and cooling water as a low-temperature heat source is installed in the turbine exhaust duct to convert latent heat in the turbine exhaust into electricity.
A steam turbine power generation plant characterized by condensing turbine exhaust gas and eliminating the need for a condenser.