JPH01184304A - Variable pressure operating plant - Google Patents

Abstract

PURPOSE:To enable an efficiently of a pressure reduction turbine to be kept at a high value within a wide range of load by a method wherein a steam outlet of a high pressure turbine to be driven by a steam generated from a secondary superheater is communicated with an inlet of a steam compressor. CONSTITUTION:A valve 29 and a pressure reduction turbine 4 are arranged in parallel in the midway of a pipe line connecting a primary superheater 3 and a secondary superheater of a boiler. A steam compressor 6b driven by the pressure reduction turbine 4 is arranged and a steam outlet of a high- pressure turbine 9 driven by steam from the secondary superheater 8 is communi cated with an inlet of the steam compressor. With this arrangement, the steam compressor 6b with a variable speed is driven by the pressure reduction turbine 4 so as to compress a high pressure discharged gas of a main turbine 9. Accord ingly, the number of rotation of the pressure reduction turbine is not fixed and the pressure reduction turbine can be kept at its high efficiency over a wide range of load.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention maintains the efficiency of a thermal power plant operating at variable voltage at a high level over a wide range of loads.

[Conventional technology] In thermal power plants, the steam conditions have been improved to increase the efficiency of the plant, and currently the main steam pressure is 246 kg.
/mP, a main steam temperature of 538°C, and a reheat steam temperature of 538°C to 566°C. Many supercritical pressure plants have been constructed. If these plants are operated continuously at the rated load, there will be no problem under the above steam conditions, but there will be frequent start-stops and load fluctuations to low loads (this means that if the steam conditions above remain the same, the turbine's governor stage will be affected). The temperature change at the outlet is large (
This brings up the problem of thermal stress in the rotor.

In order to reduce temperature changes at the outlet of the turbine governor stage due to load changes, a method of changing the main steam pressure according to the load is suitable. This method is called variable voltage operation method.

When the variable pressure operation method is applied to the entire plant including the boiler,
The gain of reducing feed water pump power due to the drop in feed water pressure at low loads can be obtained, so in addition to reducing the throttling loss of the steam control valve and other gains, the turbine side also gains gains in efficiency improvement in addition to thermal stress reduction. . However, for the boiler side,
Changing the furnace pressure changes the furnace temperature, creating boiler thermal stress problems.

Therefore, the turbine operates at variable pressure to reduce the thermal stress on the rotor, and the boiler furnace operates at constant pressure to reduce the thermal stress in the furnace.
A pressure reducing valve device has been installed between the secondary superheater (8) and the secondary superheater (8). In this case, there is no gain in plant efficiency improvement due to power reduction of the feed water pump (although there remains a variable pressure operation gain due to reduction in throttling loss of the steam regulating valve, etc.). In addition to the loss caused by steam pressure reduction, there was also the problem that erosion occurred in the pressure reducing valve due to the high differential pressure, making it difficult to shut off.

As an improvement plan for this point, as shown in Fig. 5, instead of the pressure reducing valve device, a pressure reducing turbine (4) installed in parallel with the pressure reducing valve device is installed.
It has been devised to flow steam to drive a generator (6a) and recover power.

In Figures 4 and 5, (1) is the economizer, (2) is the furnace, (5) is the pressure reducing turbine steam control valve, (power is the auxiliary superheater, (9) is the high pressure turbine, and αQ is the main turbine steam control valve,
αυ is a high-pressure bypass valve, α2 is a low-temperature reheat steam pipe check valve,
0 is the reheater, I is the intercept valve, ←9 is the medium pressure turbine, αQ is the low pressure bypass valve, η is the condenser, (I1 is the low pressure turbine, (19 is the generator, ■ is the condensate pump, r2υ is a low pressure heater, (c) is a deaerator, (c) is a water supply pump, (
(Fi) is a high-pressure heater, (C) and (B) are shut-off valves.

[Problem to be solved by the invention] When a generator is driven by a pressure-reducing turbine, the pressure turbine has a large flow rate when the plant is under high load, as shown in Figure 6 (an example of a 100 OMW class hybrid variable voltage operation plant). Low differential pressures, low flow rates and high differential pressures when the plant is at low load, make it extremely difficult to maintain high efficiency levels throughout the entire range with a constant speed turbine.

Also a pressure reducing turbine and generator? When placed on the ground, the superheater is located at the top of the boiler, so the steam pipes at the inlet and outlet of the pressure reducing turbine are long, resulting in a pressure drop in the pipes.

However, if the pressure reducing turbine is placed near the superheater,
Since the heavy generator must also be placed above the boiler, problems arise in terms of placement, such as reinforcing the boiler steel frame and routing the generator bus duct.

[Means for Solving the Problems] In order to solve the above-mentioned conventional problems, the present invention provides a system in which a valve and a pressure reducing turbine are arranged in parallel in the middle of a pipe connecting a primary superheater and a secondary superheater of a boiler. and a steam compressor driven by the pressure reducing turbine, the steam outlet of the high pressure turbine driven by the steam from the secondary superheater communicating with the inlet of the steam compressor. This paper proposes a plant with variable pressure operation.

[Effect]

The present invention is configured as described above, and uses a pressure reducing turbine to
Instead of driving a constant speed generator, a variable speed vapor compressor Z is driven. The steam compressor then compresses the high-pressure exhaust gas from the main turbine.

〔Example〕

FIG. 1 shows a system diagram Z of an embodiment of the present invention. The same parts as those of the conventional device explained with reference to FIGS. 4 and 5 are given the same reference numerals, and the explanation thereof will be omitted. In this example, the boiler's primary superheater (3) and secondary superheater (8)
In the middle of the pipe connecting the and via the auxiliary superheater (7),
A pressure reducing valve device and a pressure reducing turbine (4) are arranged in parallel. A steam compressor (6b) is provided which is driven by this pressure reducing turbine (4), and a high pressure turbine (9) is driven by steam from the secondary superheater (8).
) is in communication with the inlet of the vapor compressor (6b). Further, the outlet of the vapor compressor (6b) communicates with the inlet of the reheater. (5), @ is a cutoff valve, and (to) is a bypass valve.

Steam that has been superheated through the plant odors, boiler economizer (1), furnace (2), and heat generator (3) in such a system is led to a pressure reducing turbine (4).

The steam control valve (5) of the pressure reducing turbine is controlled so that the steam pressure at the inlet of the pressure reducing turbine becomes a constant value.

As a result, the pressures in the furnace (2) and the heating device (3) are kept constant. The pressure reducing turbine (4) is a steam compressor (6b
) to drive.

The exhaust gas of the pressure reducing turbine (4) passes through an auxiliary superheater (8), is further increased in superheat degree Z, and is led to the high pressure turbine (9) of the main turbine.Auxiliary superheater (The power is -Next week, the steam leaving the heater (3) is transferred to the decompression turbine (4)
This is provided to compensate for the temperature drop caused by the work being done in the boiler, but due to the characteristics of the boiler, it may not necessarily be provided.

The main turbine steam control valve aQ is used to adjust the output of the main turbine. Steam control valve (lOl) during variable pressure operation
There are various control methods as typified below, and any of them may be used.

■ Steam regulating valve opening - original method: This is a method in which the opening of the steam regulating valve is fixed and the turbine output is uniformly determined by the main steam pressure. Therefore, it is difficult to precisely control the main steam pressure during transients such as when the load changes in degrees Celsius, and therefore it is difficult to precisely control the turbine output.

■ Steam control valve opening fine adjustment method 2 As in the above ■, the steam control valve opening is not completely fixed, but is finely adjusted to 5 until the turbine output reaches the required value. Turbine output can be precisely controlled even at times. Since the steam temperature at the governor stage outlet changes as much as the opening degree of the steam control valve changes, it is difficult to say that it is a perfect variable pressure operation, but it is a disaster-saving method.

■ Main steam pressure/governing stage outlet pressure ratio constant control method: This is a method in which the steam regulating valve is controlled so that the ratio between the main steam pressure and the governor stage outlet pressure is constant. This is a foot system with a partial front pressure control function added during transient periods. In this method, there are fewer transient fluctuations in the main steam pressure than in the method (2) above (although the transient output changes are large).

A high-pressure bypass valve αυ is provided at the inlet of the high-pressure turbine (9), and when the high-pressure turbine inlet pressure exceeds a predetermined value, main steam is bypassed to the high-pressure exhaust. The steam discharged from the high-pressure turbine (9) passes through the low-temperature reheat steam pipe reverse valve (1) and is guided to the steam compressor (6b).The steam compressed by the steam compressor (6b) is , is reheated by the reheater αJ, and is introduced into the intermediate pressure turbine α9 through the main turbine intercept valve Q41.A low pressure bypass valve (
161 is provided, and when the intermediate pressure turbine inlet pressure exceeds a predetermined value, the high temperature reheated steam is transferred to the condenser αη. The steam discharged from the intermediate pressure turbine a4 passes through the low pressure turbine αQ, is guided to the condenser αD, and becomes condensed water. High pressure turbine (
9) A generator a1 is driven by a main turbine consisting of an intermediate pressure turbine αω and a low pressure turbine α barrel.

Condensate from the condenser a is sent to the condensate pump and low pressure heater Qυ
, the deaerator, the water supply pump (c) Z, the water is supplied, passes through the high pressure heater @, and returns to the economizer (1) of the boiler.
sent to.

When the pressure reducing turbine (4) and steam compressor (6b) are not in use, such as during the early stages of plant startup, the shutoff valve (c) is used.

(c) Close @, @, pressure reducing valve - and bypass valve -
open.

In Figures 1, 4 and 5, low pressure heater Qυ
, one high-pressure heater (good) is shown, but there may be more than one of these. Further, the main steam stop valve and reheat steam stop valve of the main turbine are not shown. Also, depending on the characteristics of the plant, the high-pressure bypass valve aυ, the low-pressure bypass valve (Le, and the low-temperature reheat steam pipe check valve α21) may not necessarily be provided. It is not a valve (it may also be a shutoff valve).

FIG. 2 shows an example of the relationship between main turbine output and main steam pressure. The solid line in the diagram indicates what is called "hybrid variable pressure operation (compound variable pressure operation)," in which the first to sixth of the eight steam control valves in the main turbine open simultaneously, and the seventh and subsequent valves open simultaneously. For those that open sequentially, the 7th valve starts to open (at a load of A point 9 or above, constant pressure operation, and at a load below that, the main steam pressure is changed with the 1st to 6th valves fully open). This is a combination of variable voltage operation that changes the load.

However, at low loads (below point B), the main steam pressure is approximately 100
The steam control valve throttle operation is performed by maintaining the pressure at about Kg/mP and simultaneously opening the first to sixth valves. In FIG. 2, the relationship between the output and the main steam pressure in the case of constant pressure operation and in the case of wide range variable pressure operation with the first to eighth valves fully open are also shown by broken lines and dashed-dotted lines, respectively.

FIG. 3 shows the effect of this embodiment, that is, the efficiency improvement rate of a variable pressure operation plant, calculated using a 10100O supercritical pressure plant as an example. The broken line in this figure shows the pressure reducing turbine output and the plant efficiency improvement rate of the variable pressure operating plant shown in Figure 5, which uses a pressure reducing turbine to drive the generator (plant efficiency of the variable pressure operating plant shown in Figure 4 using a pressure reducing valve). (relative value to) indicates heat. Moreover, the solid line in FIG. 3 shows the characteristics of the embodiment of the invention shown in FIG. 1, which uses a pressure reducing turbine to drive the steam compressor. The vapor compressor reduces the exhaust pressure of the high pressure turbine relative to the inlet pressure of the intermediate pressure turbine, increasing the heat drop of the high pressure turbine, increasing the main turbine output and reducing the heat input to the reheater. , plant efficiency is improved.

Since the efficiency of the vapor compressor is lower than the efficiency of the generator, the plant efficiency improvement of 4A according to this embodiment is lower than that in the case of FIG. 5 in which the generator is driven by a pressure-reducing turbine.
In this example, the decompression turbine and steam compressor set is relatively light in weight (and can be easily installed near the superheater or reheater in the upper part of the boiler, so it can be installed in the upper part of the boiler, which is a heavy generator). It is advantageous in terms of the boiler structure because there is no need to install it in the boiler or run large steam piping.
Also, the pressure loss in the pipeline is small. Furthermore, since the rotational speed of the pressure reducing turbine is not fixed, the efficiency of the pressure reducing turbine can be maintained at a high level over a wide range of loads.

〔Effect of the invention〕

According to the present invention, the following effects can be achieved.

■ Since the rotation speed of the pressure reducing turbine is not fixed, it is possible to maintain high efficiency of the pressure reducing turbine over a wide range of loads.

■ The relatively light decompression turbine and steam compressor set can be easily installed on top of the boiler where the superheater and reheater are located, making piping easier and reinforcing the boiler steel frame for use in heavy generators. There is no need to install the boiler at a high place or route large steam piping, which is advantageous in terms of the structure of the boiler, and the lateral force loss of the piping is also reduced.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an embodiment of the present invention, FIGS. 2 and 3 are diagrams showing its effects, and FIGS. 4 and 5 are system diagrams showing an example of a conventional variable voltage operation plant. FIG. 6 is a diagram showing the conditions of the pressure reducing turbine. (1)...Economizer (2)...Furnace (
3)...-Next week's heater (4)...Reducing turbine (5)...Reducing turbine steam regulator

Claims (1)

[Claims] A valve and a pressure-reducing turbine are arranged in parallel in the middle of the pipe connecting the primary superheater and the secondary superheater of the boiler, and a steam compressor driven by the pressure-reducing turbine is installed to achieve the above-mentioned secondary superheating. A variable pressure operation plant, characterized in that a steam outlet of a high pressure turbine driven by steam from a steam compressor is communicated with an inlet of the steam compressor.