STEAM TURBINE PLANT

Abstract

A steam turbine plant includes an extraction system and a control system for controlling the steam extraction. The extraction system includes an extraction steam flowmeter and a stop valve. The control system sets a warning flow and an extracted steam stop flow for the extracted steam. When the extracted steam flow reaches the warning flow, a warning is issued and after a lapse of a predetermined time period, the stop valve is opened to restrict the extracted steam flow. When the extracted steam flow reaches the extracted steam stop flow, the stop valve is closed to stop steam extraction. A steam turbine plant can thus exercise extraction control to stably supply extracted steam while avoiding turbine trip, even if not equipped with a high-performance and expensive valve device such as an extraction steam control valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a system configuration of an extraction steam turbine plant according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a steam extraction control system.

FIG. 3 is a diagram illustrating the relationship between a steam extraction structure and stage inlet/outlet steam differential pressure due to steam extraction.

FIG. 4 is a chart illustrating the relationships between the steam condition and a turbine expansion line and between a difference between a turbine steam extraction point and turbine thermal stress restriction value, and the steam condition.

REFERENCE NUMERALS ARE BRIEFLY EXPLAINED BELOW

1 . . . extraction steam turbine, 3 (3a, 3b) . . . extraction system, 4 (4a, 4b) . . . extraction steam supply pipe, 5 (5a, 5b) . . . extraction steam flowmeter, 6 (6a, 6b) . . . extraction steam stop valve, 7 . . . steam extraction control system, 8 . . . extracted steam demander, 9 . . . warning device, 11 . . . restriction flow value setting unit

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below. FIG. 1 is a systematic diagram of a configuration of an extraction steam turbine plant according to an embodiment of the present invention. The extraction steam turbine plant is for power generation and includes an extraction steam turbine 1 and a generator 2 connected thereto. The extraction steam turbine 1 is composed of a high-pressure turbine 1a and a reheat turbine 1b. The high-pressure turbine 1a and the reheat turbine 1b are each provided with an extraction system 3 (3a, 3b). The reason why the extraction system 3 is composed of two extraction systems 3a, 3b is that the extraction systems 3a, 3b are selectively used according to the pressure state of main steam to more stably supply extracted steam. More specifically, the extraction system 3b is used to supply extracted steam in the normal state and the extraction systems 3a, 3b are used when the pressure of main steam drops lower than a predefined level. Thus, the stability of the extracted steam supply is enhanced.

The extraction system 3 includes an extraction steam supply pipe 4 (4a, 4b) connected to an intermediate stage of the extraction steam turbine 1 (high-pressure turbine 1a, reheat turbine 1b); an extraction steam flowmeter 5 (5a, 5b) provided in the middle of the extraction steam supply pipe 4; and an extraction steam stop valve 6 (6a, 6b) provided in the middle of the extraction steam supply pipe 4. Extracted steam is delivered to an extracted steam demander 8 under the control of an extracted steam control system 7.

The extraction steam flowmeter 5 measures the flow volume of extracted steam flowing in the extraction steam supply pipe 4 and inputs the measurement to the steam extraction control system 7.

The extraction steam stop valve 6 is driven in an openable and closable manner by e.g. an electric motor. This stop valve 6 is an inexpensive valve device that is simply configured so as to take three states: a fully-closed state, a fully-open state and a predefined intermediate-open state. Such three valve states set the steam extraction states of the extraction system 3.

The steam extraction control system 7 controls the extraction steam stop valve 6 based on the extracted steam flow measurement value obtained by the flowmeter 5. The steam extraction control system 7 is configured as shown in FIG. 2 by way of example to exercise such control. This steam extraction control system 7 includes restrictive flow setting unit 11, comparator 12, and opening instruction/warning instruction generating unit 13.

The restrictive flow setting unit 11 sets two restrictive flow values, a warning flow D3 and an extracted steam stop flow D4, based on an extracted steam flow measurement value D1 and extracted steam flow parameter D2. The extracted steam flow parameter D2 uses the flow of main stream delivered to the extraction steam turbine 1 or a turbine output corresponding thereto, or post-turbine-first-stage pressure. Thus, an instrument for measuring the main stream flow is provided; however, it is not shown in the figure. The extracted steam flow parameter D2 such as the main steam flow and the restrictive flow resulting from the extracted steam flow are set as above. This is because the permissible amount of extracted steam in the extraction steam turbine 1 is correlated with the main steam flow. Specifically, the stage inlet/outlet steam differential pressure in the extraction steam turbine 1 is correlated with the main steam flow. If the main steam flow is small, the inter-state differential pressure decreases. The percentage of the permissible amount of extracted steam can be increased accordingly. Thus, steam extraction that accounts for the permissible range at a maximum can be performed by correlating the restrictive flow with the main steam flow.

The comparator 12 compares the extracted steam flow measurement value D1 with the warning flow D3 and with the extracted steam stop flow D4 to provide a comparison result D5, which is output to the opening instruction/warning instruction generating unit 13.

Based on the comparison result the opening instruction/warning instruction generating unit 13 creates an opening instruction D6 for the extraction steam stop valve 6 and a warning instruction D7 for the warning device 9 (FIG. 1).

Under the control of the steam extraction control system 7 as described above, the normal steam extraction is performed with the extraction steam stop valve 6 brought into the fully-open state. The extracted steam flow corresponding to the demand of the extracted steam demander 8 is extracted. In this state, when the extracted steam flow increases and the extracted steam flow measurement value D1 obtained by the flowmeter 5 reaches the warning flow, the control system 7 issues the warning instruction D7 to allow a warning device 9 to give an alarm. In addition, the control system 7 notifies the demander 8 of the fact that since the extracted steam flow is excessive, the extracted steam flow is likely to be restricted or the steam extraction is likely to be stopped. The extracted steam flow measurement value may have still reached the warning flow after a lapse of a predetermined period time after the extracted steam flow excessive warning has been issued. The predetermined period time is a time period that the demander 8 approximately takes to appropriately deal with restriction of the extracted steam flow or with the stoppage of steam extraction. In this case, the control system 7 sends a signal of an intermediate opening instruction as the opening instruction D6 to the extraction steam stop valve 6. Thus, the extraction steam stop valve 6 is intermediately opened to appropriately restrict the extracted steam flow.

In the state where the extraction steam stop valve 6 is intermediately opened, if the extracted steam flow is increased and the extracted steam flow measurement value D1 reaches an extracted steam stop flow, the control system 7 sends a fully-closed instruction signal as an opening instruction D6 to the extraction steam stop valve 6 to be fully closed for stopping steam extraction.

As described above, in the present invention, the two restrictive flow values for the warning flow and the extracted steam stop flow are set to control steam extraction, when the extracted steam flow is about to exceed the warning flow, a warning is issued to the extracted steam demander for advance notice, and thereafter the extracted steam valve 6 is intermediately opened to appropriately restrict steam extraction. In this state, if the extracted steam flow is further increased and then is about to exceed the extracted steam stop flow, the extraction steam stop valve 6 is fully closed to stop steam extraction. With such steam extraction control, a steam turbine plant can exercise extraction control capable of stably supplying extracted steam while it is primarily intended that the turbine can continuously be operated by avoiding occurrence of the turbine trip due to steam extraction even if the steam turbine plant is not equipped with a high-performance and expensive valve device such as an extraction steam control valve and adopts high-pressure steam condition where it is difficult to exercise control based on the pressure difference reference method.

Claims

1. A steam turbine plant comprising: an extraction system which extracts a portion of main steam from an intermediate stage of a steam turbine and delivers the extracted steam to a demander; and a steam extraction control system for controlling steam extraction of the extraction system; wherein the extraction system includes an extraction steam flowmeter and an extraction steam stop valve; andthe steam extraction control system is configured to set a warning flow and an extracted steam stop flow as restrictive flow values with respect to a flow of the extracted steam whereby when an extracted steam flow measurement value from the flowmeter reaches the warning flow, a warning is issued and after a lapse of a predetermined time period an opening instruction is sent to the stop valve so as to bring the stop valve into a fixed open state for restriction of the extracted steam flow, and when in the restriction state the extracted steam flow is further increased and the extracted steam flow measurement value reaches the extracted steam stop flow, a fully-closing instruction is sent to the stop valve so as to fully close the stop valve for stoppage of steam extraction.

2. The steam turbine plant according to claim 1, wherein the extraction steam stop valve selectively takes any one of three valve-states comprising a fully-closed state, a fully-opened state and an intermediate-open state as a fixed open state.

3. The steam turbine plant according to claim 1, wherein the steam extraction control system includes restrictive flow value setting means for setting said restrictive flow values; and the restrictive flow value setting means comprises any one of a main steam flow, turbine output and post-turbine-first-stage pressure in the steam turbine as an extracted steam flow parameter and sets the restrictive flow values on the basis of the parameter and the extracted steam flow measurement value.