Power plants – Motive fluid energized by externally applied heat – Power system involving change of state
Reexamination Certificate
2001-10-01
2002-12-24
Nguyen, Hoang (Department: 3748)
Power plants
Motive fluid energized by externally applied heat
Power system involving change of state
C060S653000, C060S677000
Reexamination Certificate
active
06497099
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for controlling a steam turbine with a steam bleed. The invention also relates to a control device for such a steam turbine.
A control of a steam turbine with bleed steam, called a bleeder turbine for short, is described in the book having the title “Regelung von Dampfturbinen” [“Closed-loop control of steam turbines”] by Adolf Brücher, 2nd edition, 1972, Kraftwerkunion AG, Mülheim/Ruhr, from page 53 in the Chapter “Reglereinstellblatt bei gesteuerten Entnahmeturbinen” [“Regulator adjustment sheet for controlled bleeder turbines”]. In the case of a bleeder turbine, steam for normal operational purposes is bled off from a specific stage. If steam is bled off to condensation or feed-water preheaters, only one connection is provided from the stage to these preheaters, without any closed-loop control element. This is a so-called uncontrolled bleeding or tapping. The pressure at a tap is governed by the flow rate or amount of the steam passing through the turbine.
In contrast to this, it may be necessary to provide steam at a specific pressure, irrespective of the magnitude of the turbine steam flow rate, and thus the electrical power. However, this requirement can be satisfied only if it is possible to maintain pressure. In this case, the steam turbine is a controlled bleeder turbine. For example, steam flows into the high-pressure section of such a bleeder turbine. At the end of the high-pressure section, the steam flows on the one hand into a steam bleed line, and on the other hand into a low-pressure section of the turbine. The steam which flows through the low-pressure section can then be supplied not only to a condenser but also, once again, to a bleed line. The latter configuration is referred to as a backpressure bleeder turbine. Thus, the function of a bleeder turbine is not only to drive a generator, but also to provide so-called process steam for operational purposes.
Depending on the desired amount of electrical power or the desired amount of process steam, different operational tasks arise with regard to the closed-loop control of the bleeder turbine. These tasks are characterized by different types of controlled variables that are used for closed-loop control. The controlled variables may be, for example, a bleed steam flow rate, a power level emitted from the turbine, a rotation speed of the turbine shaft, a backpressure in the steam flowing out of the turbine, or an initial pressure in the steam flowing into the turbine. One operational task would thus be characterized, for example, by closed-loop control on the basis of the bleed steam flow rate and the power. Another operational task would be characterized, for example, by closed-loop control on the basis of the bleed steam flow rate and the backpressure.
U.S. Pat. No. 4,146,270 discloses a control device for a steam turbine with speed and power control coupled on the output side. A fuzzy controller described in the article “Dampfturbinenregelung mit Fuzzy-Logik” [steam turbine regulation with fuzzy logic], R. Hampel, N. Chaker, in ATP Automatisierungstechnische Praxis [automation engineering in practice], 37 (1995), June, No. 6, Munich, Germany, is intended to permit such regulation in the case of a steam turbine with steam bypass stations. Nevertheless, until now, a specific control structure has been used for each operational task. Parameters obtained empirically are in this case linked so that the desired control response is obtained for the operational task. Both the parameters and the linking of the parameters thus differ from one another, so that use is always made of different control structures.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for controlling a steam turbine with a steam bleed which overcomes the above-mentioned disadvantages of the heretofore-known methods of this general type and which is matched in a simple and operationally reliable manner to the operational tasks of the steam turbine. It is a further object of the invention to provide a control device for a steam turbine with a steam bleed that carries out the operational tasks of the steam turbine in a simple and operationally reliable manner.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for controlling a steam turbine, the method includes the steps of:
regulating a steam feed via a feed valve, and regulating a steam bleed via a bleed valve;
supplying, with a first regulator or a second regulator, a first control signal and a second control signal to a regulating structure as a function of controlled variables fed to the first regulator or the second regulator;
linking, when there is a task-specific change between the first and second regulators, by using always a same regulating structure including a parameter set subdivided into subgroups, each subgroup having a first parameter and a second parameter, a result of a conversion of the first control signal with the second parameter and a result of a conversion of the second control signal with the first parameters to one another;
determining a first actuating signal with a first one of the subgroups and determining a second actuating signal with a second one of the subgroups; and
feeding the first actuating signal to the feed valve and feeding the second actuating signal to the bleed valve.
In other words, a method for controlling a steam turbine is provided in which a steam feed is regulated via a feed valve and a steam bleed is regulated via a bleed valve, wherein a first regulator or a second regulator emits a first control signal and a second control signal to a regulating structure as a function of the controlled variables respectively fed to them, wherein, during a task-specific change between the regulators by using a regulating structure which is always the same and has a parameter set subdivided into subgroups each having a first parameter and a second parameter, within each subgroup, the result of a conversion of the first control signal using the second parameter and the result of a conversion of the second closed-loop control signal using the first parameters are linked to each other, and wherein a first actuating signal fed to the feed valve is determined with a first subgroup, and a second actuating signal fed to the bleed valve is determined with a second subgroup.
There may also be a plurality of feed valves or else a plurality of bleed valves, and corresponding regulators. A bleed valve may also at the same time be a feed valve. For example, a steam bleed from a first stage of the steam turbine may be controlled by adjusting a feed steam quantity or flow rate (feed flow rate for short) for a second stage in the steam turbine, following the first stage, such that the desired bleed steam quantity or flow rate (bleed flow rate for short) is obtained from the difference between the respective feed flow rate supplied to the first stage and that supplied to the second stage.
A steam feed or else a steam bleed may be supplied to or taken from any point on the steam turbine, depending on the requirement. The operational tasks are characterized by the nature of the controlled variables, depending on the desired emission of power from the turbine or the desired bleed steam flow rate. For example, one operational task is characterized by a (closed-loop) control based on the steam bleed flow rate the rotational speed of the turbine.
The control structure is used to convert the control signals from the regulators into actuating signals for actuating elements for the feed or bleed valve. Depending on the operational task, this conversion must be carried out in a manner matched to the operational task, since each operational task is based on a different operating envelope for the feed or bleed valve.
In the invention only a single control structure is now used for this purpose for all the operational tasks. In this case, each operational task is now in each
Greenberg Laurence A.
Locher Ralph E.
Nguyen Hoang
Siemens Aktiengesellschaft
Stemer Werner H.
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