JPS58206812A - Device for adjusting discharged gas of steam turbine with vacuum - Google Patents

Abstract

PURPOSE:To improve a thermal efficiency by a method wherein a maximum vacuum (limit pressure) allowable in a performance of condenser type steam turbine is calculated by its operating time in response to its actual operating condition and the pressure in a condenser is automatically adjusted when the turbine is operated under a pressure less than the limit pressure. CONSTITUTION:A turbine is provided with a pressure sensor 1 for use in sensing a differential pressure in the midway of the turbine, the discharged volume of turbine is calculated in a calculater 2 in response to its output and then a limit discharging pressure Pc is calculated. A discharged valcuum sensor 3 is connected to the discharged pressure of the turbine, the actual discharged pressure P2 calculated at the sensor is sent to a comparator 4 along with said limit pressure Pc and then both of them are compared. In case of P2<Pc, a signal for adjusting a volume of cooling water in the condenser is produced in such a way as a relation of P2=Pc is applied and then an angle of pump vane of circulation pump is controlled through the control device 5 in response to the signal. With this arrangement, it is made possible to get the most appropriate discharged vacuum in correspondense with the turbine load or a variation of temperature of cooling water.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention calculates in real time the maximum vacuum (limit pressure) allowable for the performance of a condensing steam turbine according to the actual operating conditions, and calculates the maximum vacuum (limit pressure) that is allowable for the performance of a condensing steam turbine, and calculates the maximum vacuum (limit pressure) that is allowable for the performance of a condensing steam turbine, The invention relates to a device for automatically adjusting condenser vacuum to a critical pressure.

Conventionally used exhaust vacuum adjustment devices for steam turbines are designed to reduce the turbine load and restore vacuum when the exhaust vacuum drops due to some abnormality in the condensing equipment during operation. There was no suitable device for automatically regulating the condenser vacuum.

Note that in the past, the adjustment was made appropriately based on the operator's judgment, so it was not always optimal, and there were drawbacks such as energy loss.

The purpose of the present invention is to provide an adjustment device for obtaining an optimal exhaust vacuum according to changes in cooling water temperature and turbine load, and to improve thermal efficiency and save energy by operating at the optimal vacuum. shall be.

According to the present invention, a pressure detector and a computing unit are connected in series to the turbine intermediate stage pressure side, an exhaust vacuum detector is connected to the turbine exhaust pressure side, and the output side and exhaust vacuum of the operator are connected in series. It consists of a comparator connected to the output side of the detector and a control device for controlling the circulating water pump blade angle, etc. connected to the output side of the comparator. Conventionally, the optimum vacuum according to the turbine load is calculated in advance. There is provided a steam turbine exhaust vacuum adjustment device in which what was estimated from a previously prepared performance curve is directly calculated from the actual operating state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below as illustrated in the accompanying drawings.

The drawing shows a circuit diagram of the combined state of the device of the present invention, where reference numeral 1 is a pressure detector for calculating the turbine displacement, and 2 is a device that calculates the displacement from the detected pressure and calculates the limit exhaust pressure. A computing unit is connected in series to the turbine mid-stage pressure side.

Reference numeral 3 denotes an exhaust vacuum detector connected to the turbine exhaust pressure side. Symbol 4 is the limit pressure Pc determined by the calculator 2
5 is a control device connected to the output side of the comparator 4; It is operated by the output and controls the circulating water pump blade angle etc. so that P2=pc when P2<Pc.

As the turbine exhaust pressure (turbine final stage outlet pressure) is lowered, the outlet steam flow rate gradually increases, but once it reaches the speed of sound, the flow rate does not increase any further and the turbine exhaust pressure (outlet pressure) remains constant. It becomes a constant value (limit pressure),
Even if the condenser pressure decreases, there is only a loss in the exhaust chamber and the turbine output does not increase.

Therefore, increasing the condenser vacuum below the critical pressure will only lead to a decrease in thermal efficiency, and it is rather preferable to control the vacuum so that it does not fall below the critical pressure.

More specifically, the outlet steam flow rate (axial flow rate) C2 is expressed by the following equation.

C2=GV2/A (1) where G is the exhaust flow rate, A is the exhaust area (blade ring area), and v2 is the exhaust specific volume.

On the other hand, the sound velocity a2 at the exit is expressed by the following equation.

a2=f T also -(2) However, T2 is the absolute exhaust temperature, R is the steam gas constant, k is the steam specific heat ratio, and g is the gravitational acceleration.

Here, if PC is the critical pressure at which the steam flow velocity C2 at the outlet is equal to the sound velocity a2 at the stage mouth, then (1) i and (2)
From the equation, Gvo/A = W (3), and on the other hand, from the ideal gas equation, P(vc=RT
c (4). (3) and (
4) Limit pressure P from equation. Hato becomes. Here, even if the exhaust vacuum changes somewhat, it can be regarded as the constant exhaust value. Therefore, when this is expressed by a constant Kl, it becomes as follows. On the other hand, the flow rate in a turbine stage is approximately proportional to the inlet pressure P1 of that stage, so the exhaust flow rate G is G = K
,・P□ (7) Here, K2 is a constant.

(6) From equation (7), limit pressure P. It is represented by .

Here K is a constant. That is, the critical pressure P. is obtained from equation (8) as a function of the inlet pressure P0 of the final stage (or any suitable stage above it). Therefore, by measuring the appropriate (usually final extraction stage) stage population pressure P1 in place of the difficult-to-detect displacement, the critical pressure PC of the turbine can be determined using equation (8), and the actual exhaust pressure ( When P2iN P is compared to P2, the condenser vacuum is lowered so that P2 becomes PC.

In recent large-capacity thermal power plants, movable blade mixed-flow pumps are often used as circulating water pumps to supply condenser cooling water, so the amount of cooling water can be adjusted by changing the installation angle of the blades. Therefore, P2 and P. Compare P2<P. If P2
A comparator 4 is provided that emits a signal so that = Po, and the control device 5 that receives the signal changes the blade mounting angle of the circulating water pump (using an appropriate servo mechanism) to adjust the condenser pressure to match the turbine load. The pressure can be automatically controlled to the optimum pressure.

According to the present invention, since the blade angle can be controlled to an appropriate angle commensurate with the amount of cooling water, the pump efficiency can be improved and the power consumption of the pump can also be reduced.

') ff * i

[Brief explanation of drawings]

The drawing is a block diagram showing a steam turbine exhaust vacuum regulating device according to the present invention. 1. Pressure detector, 2. Arithmetic unit, 3. Exhaust vacuum detector, 4. Comparator, 5. Control device.

Claims (1)

[Claims] A pressure detector (11) that detects the turbine midway stage pressure and a calculator (2) that calculates the limit pressure from the detected pressure.
and an exhaust vacuum detector (3) that detects the turbine exhaust pressure.
and the output of the arithmetic unit (2) and the exhaust vacuum detector (3).
a comparator (4) that outputs a signal when the actual exhaust pressure is below the calculated limit pressure based on the output of the comparator (4);
control device ( ) that adjusts the condenser pressure according to the output signal of
5) A steam turbine exhaust vacuum adjustment device comprising: