JP2569079B2 - Expansion turbine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an expansion turbine, and more particularly to an expansion turbine suitable for use with a hydrodynamic gas bearing.

[Conventional technology]

2. Description of the Related Art Conventionally, a protection system for an expansion turbine is generally provided with the following.

(1) Rotational speed overspeed (2) Shaft vibration abnormality (3) Bearing temperature abnormality (4) Oil supply pressure or bearing gas pressure drop However, in these protection systems, bearing wear of the expansion turbine using a dynamic pressure gas bearing However, no consideration has been given to problems such as an increase in the starting torque due to the above, a sudden acceleration rotation of the starting portion, and bearing damage due to this.

It should be noted that related devices of this type include, for example, JP-A-59-147803, JP-A-61-110850, and JP-A-61-1687.
No. 56 and the like.

[Problems to be solved by the invention]

Tilt pad type dynamic pressure gas journal bearing
When the rotating shaft is stationary, a preload is applied to the pad to forcefully contact the pad.

This is to apply a preload in order to obtain a stable bearing performance when the rotating shaft rotates and a gas film is formed between the pad and the rotating shaft by a wedge film effect.

Therefore, when rotating the rotating body, the rotating body does not rotate unless a force that overcomes the static frictional force of the journal bearing portion caused by the preload is applied as a starting torque.

On the other hand, in the dynamic pressure / pressure bearing, since the rotating body and the pad surface of the journal bearing portion always contact at the time of startup and at rest, the contact surface gradually wears, and the static friction force increases as the operation progresses.

When the static frictional force of the journal bearing increases, the starting torque must be increased. Therefore, the turbine inlet pressure must be increased accordingly.

However, when the turbine inlet pressure is high at the time of starting the turbine, the increase in the number of rotations increases in a rapidly accelerating state, and in some cases, the overspeed may be reached instantaneously. When such a state is exhibited, there is a problem that the bearings and the rotating body of the turbine are burned and suffer large damage.

SUMMARY OF THE INVENTION An object of the present invention is to provide an expansion turbine using a tilting pad type dynamic pressure gas bearing, which detects that wear of a pad portion has progressed and static friction force has increased to a specified value or more, thereby starting the turbine. An object of the present invention is to provide an expansion turbine capable of stopping operation and preventing major damage.

[Means for solving the problem]

The object is to provide a means for calculating a starting torque at the time of starting the rotating body, and a control means for fully closing the turbine inlet valve when the rotating body does not rotate even if the starting torque is equal to or more than the set value. Is achieved.

[Action]

The starting torque of the rotating body is calculated by means for calculating the starting torque at the time of starting the rotating body, and if the starting torque is larger than the preset starting torque set value by the control means, the turbine inlet valve is fully closed. So
Since the rotating body does not rotate with the set starting torque or more, the rotating body does not over-rotate and the bearing is not damaged.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to FIG.

First, the configuration will be described. A turbine inlet valve 1, an inlet pressure gauge 2, and an inlet thermometer 3 are provided in a turbine inlet line, a pressure gauge 4 is provided at an outlet of a turbine nozzle 7, a pressure gauge 12 is provided at an outlet of a rotor 8, and a rotation speed of the rotating shaft 9 is detected. Tachometer 5 is provided. Further, a computing unit 6 is provided which calculates the starting torque based on the detected values of the pressure gauges 2, 4, 12 and the temperature 3 and the tachometer 5, compares the starting torque with the allowable starting torque, and gives an operating signal to the inlet valve 1.

A rotor 8 and a brake wheel 10 are mounted on both ends of a rotating shaft 9 of the turbine, and the rotating shaft 9 is supported by dynamic pressure journal bearings 11a and 11b.

Next, the operation of the protection system for the expansion turbine configured as described above will be described.

At the time of starting the turbine, the turbine inlet valve 1 is gradually opened to increase the pressure of the turbine inlet line to increase the turbine starting torque. When the starting torque of the turbine becomes larger than the static friction torque of the journal bearings 11a and 11b (tilting pad type dynamic pressure bearing), the turbine rotates and the tachometer 5 is instructed.

However, in this start-up operation, the start-up torque calculated by the calculator 6 from the measured values of the pressure gauges 12 and 2 at the turbine entrance and exit, the thermometer 3 at the turbine entrance, and the pressure gauge 4 at the exit of the nozzle 7 is set in advance. A comparison is made with the allowable starting torque, and if the detected value of the tachometer 5 is not higher than the allowable starting torque, a signal for closing the turbine inlet valve 1 is given to the turbine inlet valve 1.

Here, the torque TB acting on the turbine rotor is:
According to the literature (Report of Institute of Industrial Science, The University of Tokyo: Radial Gas Turbine Researcher Nagao Mizumachi), it is expressed by equation (1).

In the equation (1), (U ₂ −W ₂ cosr) ₂
Values be about 1/10 or less of the value of _{C 1 · cos α · R 1} , torque TB have been shown to mainly given by _{C 1 · cos α · R 1} .

Here G: process fluid flow rate (variable) g: gravitational acceleration (constant) C _1: nozzle exit velocity (variable) alpha: nozzle outlet angle (turbine eigenvalues) R _1: Rotor outer radius (turbine eigenvalue) Thus (1) Neglecting the term on the right side of Next, variables in this and G, and C _1, the other can be considered as unique value for each turbine. (However, the turbine outlet pressure is sufficiently lower than the nozzle outlet pressure.) Here, the processing fluid flow rate G is the same as the flow rate passing through the nozzle, and the nozzle passing flow rate GN is GN = AN × C ₁ × PN... 3) where AN: nozzle area (turbine eigenvalue) C _1: nozzle outflow rate PN: represented by the nozzle velocity factor (0.9 to 0.95).

Furthermore, the nozzle exit velocity C ₁ can be determined from a nozzle inlet pressure and outlet pressure and inlet temperature. (Refer to P11-63 of the 5th revised edition of Mechanical Engineering Service Run) Therefore, the nozzle inlet pressure = turbine inlet pressure P ₁ , inlet temperature T ₁ , and nozzle outlet pressure P ₂ can be measured to grasp turbine specific values in advance. In this case, the torque acting on the rotor can be calculated from equations (2) and (3).

On the other hand, the resistance torque accompanying the increase in the static friction force of the bearing is
Since the calculation can be performed based on the preload and the static friction coefficient for forcibly bringing the bearing and the rotating shaft into contact with each other, if the upper limit of the static friction coefficient is grasped in advance, the allowable starting torque can be calculated and set.

Therefore, the the permissible starting torque, the P _1, T _1, can be calculated is P ₂ than the starting torque, compared with the permissible starting torque which is set in advance, even if the above permissible starting torque, rotation speed detection Since it is detected that the operation is not performed, the turbine inlet valve is closed, so that the turbine can be prevented from rotating at an allowable starting torque or more.

According to the present embodiment, since the turbine does not rotate at the allowable starting torque or more, it is possible to prevent the turbine from rapidly accelerating and rotating at the time of starting and becoming overspeed.

Further, it is possible to know the abnormality of the bearing portion before the wear of the bearing portion progresses, and the bearing portion is burned and damages various parts of the rotating body. This also has the effect of facilitating maintenance.

Further, in addition to the present embodiment, only the turbine inlet pressure is monitored under the starting conditions in which only the inlet pressure changes among the starting conditions of the turbine and the turbine inlet temperature and the outlet pressure become substantially constant. The turbine inlet valve 1 may be fully closed when it does not rotate even if it exceeds the set value.

〔The invention's effect〕

According to the present invention, the start-up operation of the turbine can be stopped by detecting that the wear of the bearing portion has progressed and the static friction force of the bearing portion has increased to a specified value or more. is there.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an expansion turbine according to an embodiment of the present invention. 1 ... Turbine inlet valve, 2 ... Inlet pressure gauge, 3 ... Inlet thermometer, 4 ... Nozzle outlet pressure gauge, 5 ... Revolving gauge, 6 ...
... Calculator, 7 ... Nozzle, 8 ... Rotor, 9 ... Rotary shaft, 10 ... Brake wheel, 11a, 11b ... Journal bearing, 12 ... Rotor outlet pressure gauge

Claims (1)

(57) [Claims] 1. An expansion turbine employing a tilting pad type hydrodynamic gas bearing for applying a preload to a journal bearing for supporting a rotating body having a turbine wheel provided at an end of a rotating shaft. Means for calculating torque;
A control means for completely closing the turbine inlet valve when the rotating body does not rotate even when the starting torque exceeds a set value.