JPH06221107A - Heat impact prevention for valve seat drain pipe of steam stopping valve - Google Patents

Abstract

PURPOSE:To eliminate production of drain so as to prevent flash back by providing a warming pipe in a valve seat drain pipe for making drain from a steam stopping valve in high-temperature steam system so as to allow overheated steam extracted on the upper stream side to make flowing motion. CONSTITUTION:Steam from a boiler flows into a steam turbine via a steam stopping valve 32 and a steam adjustment valve 33. In the case of warming, valve seat front drain valves 34, 35 are opened so that drain produced in the steam stopping valve 32 and a steam adjustment valve 33 is discharged from a valve seat drain 36. After completion of warming, the valve seat front drains 34, 35 are closed so that steam flows from the valve seat rear drain pipe 36 to an governor leak pipe 39 via a warming pipe 37 and a reducing orifice 38. During this process the valve seat rear drain pipe 36 is heated by steam so as to be same level of as that of the main steam stopping valve 32. Thus, the drain pipe 36 can be always held in a overheateds range without producing drain, heat impact on the main steam stopping valve can be eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steam stop valve attached to a high temperature steam pipe (main steam, reheated steam, etc.) of a steam power plant, etc. The present invention relates to a method of preventing thermal shock when the steam stop valve is rapidly cooled.

[0002]

2. Description of the Related Art A drain in a branch pipe from a steam stop valve causes self-evaporation, so-called flushing, to flow back to the steam stop valve when the pressure in the plant system fluctuates, and the high temperature steam stop valve is rapidly cooled to cause thermal shock. Is well known. This thermal shock forces a severe situation inside the valve,
At times, it can fall into corruption. Attempts to mitigate this have been proposed by various methods. 2 and 3
Figure 2 shows a proposal of a conventional method for preventing thermal shock of a mother pipe by flashback of a branch pipe.

FIG. 2 shows a self-evaporation prevention method for the drain in the branch pipe, in which the length H of the falling portion of the drain pipe from the steam pipe 1 is set to a certain length or more, and the heat insulation 14 in the horizontal portion of the drain pipe 2 is made thin (burn injury prevention Degree), or the method of limiting the flashback range of the drain generated after the drain valve 4 is closed due to the lack of construction to the falling portion.

FIG. 3 shows a branch pipe, which is a drain pipe 2 from a steam pipe 1.
In order to prevent flashback, a cooling fin 15 is provided to quickly cool the drain generated after the drain valve 4 is closed. In all of the above conventional methods, the generated drain is cooled after a certain period of time, and it is expected that the flashback amount at the time of a sudden pressure drop is reduced.

[0005]

However, the above-mentioned conventional method has the following drawbacks. It takes a certain amount of time to cool the drain. In other words, since the saturation temperature is maintained during the generation of drain, the pressure drop in the mother pipe occurs after the drain is full in the drain pipe and before it drops to the temperature at which it does not flash because it begins to fall from the saturation temperature of the drain. If there is, a flashback will occur.

Further, since the temperature in the vicinity of the boundary with the steam does not drop below the saturation temperature of the steam pressure in the mother pipe due to heat conduction from the branch, there is always flashback if there is a pressure drop in the mother pipe. Occurs. Thus, the conventional method cannot be expected to have the effect of completely preventing the occurrence of flashback.

Therefore, an object of the present invention is to provide a method for preventing the thermal shock by preventing the drain itself from being generated by warming the inside of the drain pipe by utilizing the latent heat of the steam in the steam stop valve.

[0008]

According to the present invention, a warming pipe is provided in a valve seat drain pipe discharged from a steam stop valve used in a high temperature steam system such as a steam power plant, and is extracted upstream thereof. Characterized by flowing superheated steam.

[0009]

According to the present invention, in the branch pipe in which the valve seat drain of the steam stop valve attached to the high temperature steam pipe (main steam, reheated steam, etc.) is blocked, the drain always stays due to heat dissipation. This can be achieved by introducing the warming steam and circulating the steam having a high enthalpy to warm it, thereby eliminating the generation of drain itself which is the root of the flashback.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is characterized in that warming is performed by utilizing a differential pressure.

Steam coming from a boiler (not shown) passes through a steam pipe, a steam stop valve 32, a steam control valve 33, and flows into a steam turbine (not shown). During warming in the starting process of the plant, the drain valves 34 and 35 before the valve seat are open, and the drain generated by the steam stop valve 32 and the steam control valve 33 is discharged from the drain 36 after the valve seat to a condenser (not shown). After the warming is completed, the drain valves 34 and 35 before the valve seat are closed. After the valve seat is closed, the drain valves 34 and 35 are closed, and then the steam is exhausted from the valve seat after the drain pipe 36 to the warming pipe 37 through the decompression orifice 38.
After that, it flows into the regulator valve leak pipe 39. In this process, after the valve seat, the drain pipe 36 is heated by steam in a certain section and reaches the same temperature as the main steam stop valve 32. Adjustable valve leak pipe 36
Is connected to an extraction pipe (not shown) or the like and effectively uses heat energy.

[0012]

As described above, according to the present invention,
Drain itself is not generated, it can be always maintained in the superheated steam region, and it is possible to eliminate thermal shock in the main steam stop valve. Although the drain of the main steam stop valve has been described, the use is not limited to this and can be applied to a pipe having a drain in another steam valve.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory view of a conventional branch pipe equipped with a heat insulating material.

FIG. 3 is an explanatory view of a conventional branch pipe provided with a radiation fin.

[Explanation of symbols]

1 ... Steam pipe, 2 ... Drain pipe, 4 ... Drain valve, 14 ... Heat insulation,
15 ... Cooling fins, 31 ... Steam pipe, 32 ... Steam stop valve, 33 ... Steam control valve, 34 ... Drain valve before valve seat, 35 ... Drain valve before valve seat,
36 ... Drain valve after valve seat, 38 ... Pressure reducing orifice, 39 ... Adjustable valve leak-off pipe.

Claims (1)

[Claims] 1. A warming pipe is provided in a valve seat drain pipe discharged from a steam stop valve used in a high temperature steam system such as a steam power plant, and superheated steam extracted upstream of the warming pipe is made to flow. A method to prevent thermal shock from the valve seat drain pipe of a steam stop valve.