JPS6217308A - Drain device for thermal power plant - Google Patents

Abstract

PURPOSE:To prevent the drain valve from corrosion by providing a strainer in the upper course side of the drain valve and an orifice i the lower course side and further providing a bypass orifice to the drain valve. CONSTITUTION:A strainer 24 is provided between a main steam pipe 15 and a drain valve 21 and then a multi-stage orifice 27 is provided on the lower course side of the drain valve 21. Further, a bypass orifice 31 is provided to the drain valve for bypassing said drain valve 21. Therefore, scale and dirt which are fed to the drain valve 21 are removed by the strainer 24 and the flow velocity of drain is reduced by the orifice so that it is possible to prevent the drain valve from corrosion.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a thermal power plant, and more particularly to an improvement in a drain device for a thermal power plant.

[Background of the invention]

As the demand gap between day and night expands, thermal power plants tend to be operated under DSS (daily startup and shutdown), and each component is required to adapt to the high frequency of startup and shutdown. Significant efforts are being made to shorten the length, strengthen the strength of the steam turbine, and improve starting characteristics.

・ However, the drain valve in the drain device connected to the main steam has been eroded over time by the drain (second lotion).
However, there are still no sufficient hardening measures available, and only by replacing the drain valve at every regular inspection. The current situation is that it is being dealt with.

[Purpose of the invention]

The present invention aims to improve the reliability of thermal power plants by protecting drain valves from erosion, and for this purpose provides an improved drain device for thermal power plants.

[Summary of the Invention] The drain device for a thermal power plant of the present invention includes, in a drain circuit, a strainer located between a main steam pipe and a drain valve, and a bypass orifice that connects an upstream side and a downstream side of the drain valve. and an orifice located on the downstream side of the drain valve, and the strainer removes scale and dirt, and the former orifice allows drain to constantly leak out during operation to reduce the amount of drain to be flushed. Furthermore, the latter orifice can reduce the flow rate of condensate passing through the drain valve, thereby minimizing erosion of the drain valve during power plant start-up, thereby improving the reliability of thermal power plants in DBS operation. This is what I did.

Embodiments of the drain device for a thermal power plant according to the present invention will be described below with reference to the accompanying drawings.

[Embodiments of the invention]

FIG. 1 is a system diagram of the vicinity of a high-pressure turbine of a thermal power plant equipped with this drain device, in which reference numeral 11 indicates a boiler, 12 indicates a high-pressure turbine, 13 indicates a drain discharge device, and 14 indicates a condenser. There is.

The boiler is connected to a high pressure turbine by a main steam pipe 15. A main steam stop valve 16 is provided in the main steam pipe. This valve has a built-in strainer that removes scale and other substances from the steam generated by the boiler before supplying it to the turbine. Furthermore, the steam control valve 17
is provided in the main steam pipe, located downstream of the main steam stop valve.

The drain device drains the drain from the main steam pipe 15 into a drain discharge bag [1
3 and the condenser 14 for flushing. The drain device itself consists of a drain circuit including a drain pipe 18 that connects a portion of the main steam pipe upstream of the main steam stop valve 16 and the drain discharge device, and a drain valve 21 disposed in this drain pipe; Steam stop valve 1
A drain circuit having a drain pipe 19 connecting the front side of the strainer 6 and the condenser 14 and a drain valve 22 disposed on this drain pipe, and a drain circuit having a drain pipe 19 connecting the front side of the strainer of the main steam stop valve 16 and the condenser 14; It includes a drain circuit having a drain pipe 20 connecting the drain pipe and a drain valve 23 disposed in the drain pipe. Among the drain circuits, the drain circuit with drain valves 21 and 22 flushes the drain in front of the valve seat of the main steam stop valve 16 to the drain discharge device 13, and the drain circuit with the drain valve 23 flushes the drain in front of the valve seat of the main steam stop valve 16. The drain after the seat is flushed to the condenser 14.

In the present invention, each drain circuit includes a strainer located between the main steam pipe and the drain valve, an orifice located downstream of the drain valve, and a bypass orifice connecting the upstream and downstream sides of the drain valve. Equipped with

FIG. 2 shows details of the drain valve 21 for flushing the drain in front of the valve seat of the main steam stop valve. The strainer 24 is arranged on the upstream side of the drain valve 21 in the drain pipe 18. The orifice 27 is composed of a multi-stage orifice, and is arranged downstream of the drain valve 21 in the drain pipe 18. The bypass orifice 31 is provided in a bypass pipe 35 for the drain valve 21. The bypass pipe is located upstream of the drain valve 21 in the drain pipe 18 and between the drain valve 21 and the strainer 24, and the first orifice in the multi-stage orifice 27, that is, the orifice 27A closest to the drain valve 21.
is connected to the downstream side.

The remaining two drain circuits are similarly equipped with strainers, multi-stage orifices, and bypass orifices. In Figure 1, each strainer is designated by the number 2.
5.26, each multi-stage orifice is 28.29,
Each bypass orifice is designated 32.33 respectively.

To start up this thermal power plant, drain valves 21 to 23,
This is done by opening the main steam stop valve 16 and the steam control valve 17. The steam generated in the boiler 11 enters the main steam pipe 15, where scales and the like are removed by a strainer in the main steam stop valve 16, and then flows into the high-pressure turbine 12 via the steam control valve 17. and rotate this. When the turbine reaches a predetermined rotation, the drain valves 21 to 23 are closed, the steam control valve 17 is adjusted, and the rotation of the turbine 12 is maintained constant. To stop the operation, the main steam stop valve 16 and the steam control valve 17 are closed to stop the supply of steam to the turbine 12, and the drain valves 21 to 23 are opened to drain the drain into the drain exhaust system [1].
3 and condenser 14.

When the drain device according to the present invention is started, the drain valve 2
Erosions 1 to 23 are eliminated, and even if they do exist, they are minimized. explain in detail.

In this type of drain device, steam in the main steam pipe is converted into drain and discharged through drain valves 21-23. Among them, the drain in front of the valve seat of the main steam stop valve 16 is led to the drain pipes 18, 1'9, passes through the drain valves 21, 22, and then flushed to the drain discharge device 13. Further, the drain after the valve seat of the main steam stop valve 16 is flushed to the condenser 14 via the drain pipe 20 and the drain valve 23. At this time, the drain valves 21 to 23 have a high differential pressure and are subjected to impact by the drain passing through them, so that the valve seats and valve stems are eroded.

Furthermore, when the operation starts, the drain valves 21 to 23 are fully closed to prevent the steam passing through the main steam pipe 15 from flowing out to the drain discharge device 13, so that the drain is on the upstream side of each drain valve. It is always staying there. Therefore, when the drain valve is opened at the next startup, the drain valve will be subject to greater erosion due to the addition of this accumulated drain. In particular, the drain valves 21, 22 are connected to the main steam stop valve 16.
Because it is located in front of the valve seat and strainer, it not only receives a greater impact than the drain valve 23, but also is directly hit by the scale contained in the steam, resulting in severe erosion of the valve seat and valve stem. As a result, the valve function may sometimes be lost with just one activation.

In the drain device according to the present invention, when the drain valves 21 to 23 are opened during startup, scale and dirt heading towards the drain valves 21.22 are removed by the strainers 24.25 and passed through the strainer of the main steam stop valve 16. In addition, the strainer 26 removes dirt and the like heading toward the drain valve 23, thereby preventing erosion of the drain valve by scale and dirt.

In addition to this, in the drain device of the present invention, the bypass orifices 31 to 33 continuously allow a small amount of steam to flow out to the drain discharge device 13 during operation, and the drain is transferred to the drain piping 18 to 2.
This prevents the condensate from accumulating on the upstream side of the drain valve at o, reducing the amount of condensate to be flushed, and the flow rate of condensate passing through each drain valve is reduced by the multi-stage orifices 27 to 29, so that the condensate Erosion of the valve can be minimized.

In the embodiments described above, the orifice located downstream of the drain valve is a multistage orifice, but when the drain pressure is low, it may be a normal orifice.

〔Effect of the invention〕

As described above, the drain device for a thermal power plant of the present invention prevents scale and dirt from reaching the drain valve, and also reduces the amount of drain that passes through the drain valve when the drain valve is opened. In addition, by reducing the flow rate of condensate passing through the drain valve, erosion of the drain valve can be significantly reduced compared to conventional ones, and as a result, power plants can avoid frequent startups and shutdowns. Even if this is done, the drain valve will not lose its valve function in a short period of time, and the reliability of the power generation plant can be significantly enhanced.

[Brief explanation of the drawing]

The drawings show an embodiment of the drain device for a thermal power plant according to the present invention, and FIG. 1 is a system diagram of a thermal power plant equipped with the drain device of the present invention, and FIG. 2 is a partial system diagram of the drain device. It is a diagram. 11... Boiler, 12... High pressure turbine, 13...
- Drain discharge device, 14... Condenser, 15... Main steam pipe, 16... Main steam stop valve, 17... Steam control valve, 18-20... Drain pipe, 21-23 ...Drain valve, 24-26...Strainer, 27-29...Multi-stage orifice, 31-33...Bypass orifice.

Claims (1)

[Claims] 1. A drain circuit that has a drain valve with a shutoff function in a pipe connected to a portion of the main steam pipe between the boiler and the steam turbine to flush the drain in the main steam pipe. In the drain device for a thermal power plant, the drain circuit includes a strainer located between the main steam pipe and the drain valve, a bypass orifice connecting the upstream side and the downstream side of the drain valve, and a drain valve located downstream of the drain valve. A drain device for a thermal power plant, characterized by comprising an orifice located on the side. 2. A patent in which the orifice located downstream of the drain valve is a multi-stage orifice, and the orifice that bypasses the drain valve is arranged between the upstream side of the drain valve and the downstream side of the first orifice in the multi-stage orifice. A drain device according to claim 1.