JPS6024284B2 - Steam turbine back pressure control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to reduce power consumption in a process line of a chemical plant by installing a compressor or the like that is simultaneously driven by a steam turbine and a transfer motor having slip at sufficient output. This relates to a method for controlling the back pressure of a steam turbine using one governor when a turbine is installed.The steam turbine control system uses an isochronous speed governing system and a droop governor for stable operation of the pressure regulating system. This is what I did.

BACKGROUND ART Conventionally, as a back pressure control mechanism for a steam turbine in a process line of an industrial plant, a system that separately performs speed regulation and back pressure control, as shown in FIG. 1, has been adopted.

That is, the steam control valve 12 connected to the speed regulating governor 11 only controls the speed, and the opening degree of the flow control valve 13 provided in the steam inlet line is detected, and the back pressure of the steam turbine 15 is detected by the pressure detector 14. Back pressure control is performed by air control based on this detected value. In the figure, 16 is a speed sensor. However, in the case of a machine, (i') the size of the flow rate control valve is selected for the maximum flow rate, so the throttling loss becomes large compared to the normal flow rate, and the thermal efficiency of steam decreases significantly.

Since the flow rate control valve is operated in a fair manner, there is likely to be a time delay in this operation.

(iii) There is a great tendency for interference to occur between the speed governing system and the pressure concession system.

It had some disadvantages such as:

The present invention relates to a back pressure control method for a steam turbine that can eliminate the above-mentioned problems, and provides a smooth load control method for the steam turbine and induction motor in response to load fluctuations of the driven machine and fluctuations in process steam demand. The idea is that in a system that connects a steam turbine, a driven motor, and an induction motor, steam from the steam source is branched and one side is supplied to the steam turbine. The other side controls the amount of steam supplied by a steam control valve and makes it merge into the steam demand point, and the steam control valve, which is built into the steam inlet line of the steam turbine and connected to the governor, is connected to the steam turbine. Controlling the back pressure of the steam turbine by detecting the back pressure and sending the detection signal as a feedback back pressure signal to the governor, and adjusting the steam control valve via the governor using the output of the induction motor. It is in.

Embodiments of the present invention will be described with reference to the drawings.

Reference numeral 1 in FIG. 2 is a steam turbine, and a steam control valve 2 is built into the steam inlet line of the steam turbine. This steam control valve 2 is connected to a governor 3 so that it is regulated by the governor 3. It has become.

Further, 4 is a speed sensor which detects the rotational speed of the steam turbine 1 and sends this detection signal to the governor 3, and 5 is a pressure sensor which detects the back pressure of the steam turbine and sends this detection signal. is sent to governor 3, and 6
is a driven motor such as a compressor, and is connected to the rotating shaft of the steam turbine 1 via a coupling, and is connected to the gear mechanism 8 of the induction motor 7.
and are connected via a coupling, and this driven machine 6
are driven simultaneously by the steam turbine 1 and the induction motor 7. Furthermore, 9 is an output detector that detects the output of the transfer motor 7 and sends this detection signal to the governor 3. 9 is a steam control valve that supplies steam directly from the steam source (for example, a boiler) to the steam demand point. It is installed in the line that supplies steam and can control the steam supply as appropriate. Furthermore, when backup by the induction motor 7 is not required in a low load state, the power to the transfer motor 7 can be cut off to perform speed control operation. A mechanism for changing the back pressure within a preset range (for example, a mechanism for providing a steam detector in the steam discharge line of the boiler and controlling the steam control valve 2 based on a detection signal from the detector) is provided. Steam is supplied as live steam from a boiler at a pressure P, and an amount G2, or an amount of steam G2 from a power generation turbine, etc., is supplied to a steam generator through a steam control valve 2, and work is performed in the steam turbine. This back pressure P2 is supplied to the process.

When the driven machine load is constant, when the process demand quantity G4 becomes greater than the quantity C2, the steam passes through the steam control valve 10 and the steam reaches the output terminal C3.
Conversely, when the required amount of steam C4 decreases below the supplied steam amount G, the back pressure P2 rises above the set value, and this change is detected by the pressure detector 5 and this detection signal is sent to the governor 3. The governor 3 is actuated to limit the function of the steam control valve 2, and the output of the steam turbine 1 is reduced, thereby increasing the load on the induction motor 7. As shown in FIG. 3, the speed of the steam turbine 1 is controlled isochronously by the governor 3 (100
)% (while the system is running at the speed of the induction motor 7 and is in a state of backpressure control, the set speed of the steam turbine 1 is set to 100 Q% to kill the regulating action of the governor 3). During normal operation, the number of revolutions (operating speed) nr of the steam turbine 1 becomes equal to the speed of the induction motor 7, the speed regulating system is inactive, and only the pressure regulating system is in the operating state. The relationship of the steam control valve 2 is maintained so that the back pressure of the engine 1 is maintained within a set pressure range, and the required power of the driven machine 6 is the shortfall LN due to the output LT of the steam turbine (= during normal operation Since the total load (L-LT) is shared by the induction motor 7, it is possible to save energy. 6 in Figure 3. 6r indicates the slip when the induction motor 7 has an output of 0 [KW], and 6r indicates the slip when the induction motor 7 has the rated output. As mentioned above, in order to perform pressure regulating operation, the relationship between the amount of steam used by the steam turbine and this back pressure is adjusted as shown in Figure 4 (droop), and if the steam demand of the process decreases during pressure regulating operation, The back pressure changes from A to B, and the load sharing of the steam turbine 1 and induction motor 7 respectively (LT
+LM)→(LT″10LM″)→(LT′+L,).

In addition, when the load on the driven machine 6 decreases and the steam demand amount G4 of the process increases, the output of the steam turbine is automatically reduced when the minimum load of the induction motor 7 is reached to prevent the induction motor 7 from generating electricity. 04-(G.-
The amount of steam (Gloss) is replenished from the steam control valve 10. If the load on the driven motor 6 increases in this state, the output of the induction motor 7 is detected by the output detector 9, and the steam control valve 2 is operated based on this detection signal to automatically release the output restriction of the steam turbine 1. can be obtained. In Fig. 4, Go is the minimum steam base required to cool the steam turbine 1 when the steam demand of the process decreases and the induction motor 7 alone shares the load, and GLT, is the minimum value of the regular steam demand of the process. , GLT2 is the steam consumption of the steam turbine 1 corresponding to the minimum load of the driven machine 6, and GLT3 is the maximum value of the regular steam demand of the process. Also LT,,LT2 and L,3
is the output of the steam turbine 1 when the steam amounts GH, , GLT2 and GLT3 are given, and L1 (mln) is the maximum load to be shared by the electric motor 7 to prevent this power generation. Now, when the back pressure increases during operation with the total load L=LT+LM, the output of the steam turbine 1 decreases and the load on the induction motor 7 increases as shown in (LT'+LM'→(LT^+LMr)).

Conversely, if the back pressure decreases during operation at a point such as (LTr + LM''), the steam regulating valve 2 is opened and the output of the steam turbine 1 increases and returns to (LT' + LN'). All of these are pressure regulating operations. Also, if the total load suddenly decreases during operation such as (L, 10LM) or (LT'+LM' and the load on the electric motor 7 becomes L1 (min), the load on the steam turbine LT
Alternatively, the load is automatically reduced from LT' to LT2 and reaches point C, after which the load distribution becomes (LT river + LM river). Next, a pressure regulating operation of the steam turbine 1 performed by driving the induction motor 7 after starting the steam turbine 1 will be described. After the steam turbine 1 and the driven machine 6 are started up to about 20% rotation speed using only the steam generator, the driven machine 6 is warmed up at a rotation speed sufficiently lower than the critical rotation speed of the steam turbine 1 and the driven machine 6, and then the governor 3 is started.
The speed setting of the induction motor 7 is manually operated to increase the speed to nS, and the induction motor 7 is powered on to be driven.

At this time, if the amount of steam is sufficient and the power required to increase the speed of the driven motor 6 is small, the speed of the steam turbine 1 alone is increased to (100 Q)% of the rated speed to drive the induction motor 7,
Conversely, if the amount of steam is insufficient and the amount of movement required to increase the speed of the driven motor 6 is large, the speed of the driven motor 6 is rapidly increased from low rotation to the rated rotation speed of the induction motor 7. After driving the induction motor 7 as described above (corresponding to Figure 5 A), in order to prevent the induction motor 7 from generating electricity, the output of the steam turbine 1 is changed to the output LT^ (corresponding to Figure 5) corresponding to the minimum amount of steam. ), and when the induction motor 7 continuously shares the load LN^ (corresponds to C in Figure 5), the steam turbine 1 is
automatically removes the load limit of the output LT^ and enters competitive pressure operation (corresponding to Figure 5 2). During this pressure operation, if the load on the induction motor 7 becomes less than LNB (minimum output shared to prevent the induction motor 7 from generating power) (corresponds to E in Figure 5),
This is detected by the output detector 9, and the governor 3 is appropriately driven to limit the maximum output of the steam turbine 1 to an output LTc that is less than the maximum load of the driven machine 6 (corresponding to Fig. 5), and the induction motor 7 If the load exceeds LNc and continues for a time Tc (corresponding to Figure 5), the limit is automatically released and at the same time, the steam control valve 10 is instantaneously fully opened to prevent the back pressure from rising momentarily. The load on the steam turbine 1 is increased (corresponding to Fig. 5, h), and the load on the induction motor 7 is decreased. In this manner, after the steam turbine 1 is started, the induction motor 7 can be driven to perform pressure regulating operation of the steam turbine 1. In FIG. 5, Lmjn indicates the minimum required power of the driven machine 6. Note that the present invention is not limited to the illustrated and described embodiments;
Of course, various changes can be made without departing from the gist of the invention.

As described above, according to the steam turbine back pressure control method of the present invention, (1) the control system can be simplified and the time delay in operation can be reduced.

(b) The steam throttling loss in the steam turbine can be significantly reduced compared to the conventional method, and the thermal efficiency can be improved.

(m) The back pressure of the steam turbine can be quickly controlled within a set pressure range in response to changes in process steam demand.

(W) Stable operation can be performed at all times while saving energy.

Demonstrates excellent effects such as

[Brief explanation of the drawing]

Fig. 1 is an explanatory system diagram showing a conventional steam turbine back pressure control mechanism, Fig. 2 is an explanatory system diagram showing a mechanism implementing the steam turbine back pressure control method of the present invention, and Fig. 3 is the main system diagram. FIG. 4 is a diagram showing the output and speed of the steam turbine and transfer motor in the invention; FIG. The figure is a diagram showing a state in which the steam turbine performs pressure regulating operation by driving the induction motor after starting the steam turbine according to the present invention. 1...Steam turbine, 2...Steam control valve, 3...
Governor, 4...Speed sensor, 5...Pressure detector,
6... Driven machine, 7... Induction motor, 9... Output detector, I0... Steam control valve. Figure 2 Figure 3 Figure 4 Town boat

Claims (1)

[Claims] 1 In a system that connects a steam turbine, a driven machine, and an induction motor, steam from a steam source is branched, one side supplies it to the steam turbine and then guides it to the steam demand point, and the other side controls the amount of steam supplied by a steam control valve. A steam control valve is connected to the steam inlet line of the steam turbine and connected to the governor to detect the back pressure of the steam turbine and send the detected signal to the governor as a feedback back pressure signal. 1. A method for controlling back pressure of a steam turbine, characterized in that the back pressure of the steam turbine is controlled by adjusting the steam control valve by transmitting the steam and adjusting the steam control valve via the governor using the output of the induction motor.