Rotary kinetic fluid motors or pumps – With control means responsive to non-cyclic condition... – Plural diverse condition responsive
Reexamination Certificate
2001-01-08
2003-05-06
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
With control means responsive to non-cyclic condition...
Plural diverse condition responsive
C415S118000
Reexamination Certificate
active
06558113
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to a process for regulating a turbocompressor to prevent surge in which a difference signal is generated from a continuously determined actual value of an operating variable of the compressor and a set point which depends on the position of the working point in the characteristic diagram and an input signal for the controller, which controller controls a valve branching off from the compressor outlet, is obtained from the difference signal using a time element, as well as to a device for carrying out the process.
BACKGROUND OF THE INVENTION
The jerky or periodic backflow of medium being delivered from the delivery side to the intake side in compressors is called pumping or surge. This state occurs, e.g., if the end pressure is too high and/or the throughput is too low. A surge limit line, which separates a stable range of the characteristic diagram from an unstable range to the left of the surge limit line, can therefore be defined in the characteristic diagram. Operation in the unstable range to the left of the surge limit is not permissible, because severe damage to the machine may occur within a very short time. To avoid surge, i.e., the operation in the unstable range, a anti-surge controller is used, which controls a valve at the compressor outlet, which is connected as a anti-surge valve to the atmosphere or as a recycle valve to the intake side of the compressor. By opening the valve, the flow through the compressor is increased to the extent that the working point always remains within the stable range of the characteristic diagram. A control line (anti-surge or recycle curve) is defined for such a control in the characteristic diagram at a safety margin from the surge limit line. When the instantaneous working point is approaching the control line, the anti-surge or blow-by valve (hereinafter called anti-surge valve only) is more or less opened.
More precisely, such a control operates such that the set point for the flow control is determined from the compressor pressure or from the pressure ratio between the outlet pressure (end pressure) and the inlet pressure, or from a variable derived from this pressure ratio. This set point corresponds to the control line. The measured compressor intake flow is compared with the set point, and the anti-surge valve is adjusted in case of a deviation. If the working point of the compressor is on the control line, the control deviation of the surge limit controller is zero and the anti-surge valve remains in its position. If the working point exceeds the control line in the direction of the surge limit, the controller opens the valve wider, and if the working point is located to the right of the control line, the controller closes the valve.
During normal operation of the compressor, the working point of the compressor is markedly to the right of the control line (the design point is typically 20% to 30% to the right of this) and the anti-surge valve is completely closed. In case of a shift of the working point from this operating state in the direction of the surge limit, a conventional controller begins to open only when the actual value drops below the set point, i.e., when the working point has exceeded the control line in the direction of the surge limit.
Processes of the aforementioned kind for controlling a turbocompressor to prevent surging are described in the present Inventor's earlier U.S. Pat. Nos. 4,298,310, 4,789,298, 4,810,163 and 4,968,215, the entire contents of which are incorporated herein by way of reference.
The aforementioned U.S. Pat. No. 4,298,310 discloses a process in which a difference signal is generated from a continuously determined actual value of an operating variable of the compressor and a set point, which depends on the position of the working point in the characteristic diagram and an input signal for the controller, which controller controls a valve branching off from the compressor outlet, is obtained from the difference signal using a time element. In this prior-art process, the difference signal from the set point and the actual value is sent once without delay and, in parallel thereto, with a delay to a subtraction point, from which the input signal is taken for the controller. This has the advantage that the control circuit can also process rapid, transient changes of the working point with sufficient reliability. The effect of the system is that an additional signal, which causes such a shift of the control line during transient working point shifts that when the working point approaches the control line, the safety margin between the surge limit and the control line is increased and the controller responds sooner as a result, is added to the set point of the controller. The control line is shifted quasi dynamically and a new “dynamic control line” is in effect. The consequence of this is that the safety margin between the control line and the stability limit is markedly greater under transient conditions than under steady-state conditions and the compressor is protected considerably better under such critical conditions.
However, the prior-art process has the drawback that even though the safety margin is increased during transient working point shifts which take place from a steady state in the direction of the surge limit, the controller can follow changes with a delay only, with the time constant set on the time element. The prior-art process is fully effective only when the working point is shifted in the direction of the surge limit from a steady-state working point. By contrast, the prior-art process works only unsatisfactorily in the case of disturbances that lead first to a shifting of the working point away from the surge limit and then again in the direction of the surge limit. When the working point is moving away from the surge limit, the control line is first shifted transiently to the left, with the tendency of being again set at the steady-state value according to a set time constant, i.e., normally over several minutes. A new steady state can be assumed and the prior-art process can show its full effectiveness only after this state has subsided. Until the subsidence of this transient state, the dynamic control line (this is the effective control line) is located to the left of the steady-state control line. The surge limit controller therefore interferes only with the delay, because the working point must be transiently shifted farther in the direction of the surge limit until the controller comes into action.
SUMMARY AND OBJECTS OF THE INVENTION
The basic object of the present invention is to improve a process and a device of the prior-art type such that the advantage of the increase in the safety margin can always be utilized to the full extent, regardless of whether the working point is located before the beginning of the disturbance in a steady operating state or whether transient working point shifts had already taken place before.
According to the invention, a process is provided for regulating a turbocompressor to prevent surge. A difference signal is generated from a continuously determined actual value of an operating variable of the compressor. A set point, which depends on the position of the working point in the characteristic diagram and an input signal for the controller, which controller controls a said valve branching off from the compressor outlet, is obtained from the difference signal using a time element. The difference signal is delayed with different time constants, depending on the direction in which it changes (increase or decrease). The controller responds more slowly to working point shifts in the direction of the surge limit line and more rapidly to working point shifts in the opposite direction.
The invention also provides a device for regulating a turbocompressor to prevent surge, with a measuring transducers for determining the actual value of one or more operating variables characteristic of the working point of the said compressor. A set point transducer is provided with a preset co
Kershteyn Igor
Look Edward K.
Man Turbomaschinen AG GHH Borsig
McGlew and Tuttle , P.C.
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