JPH0120281B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an expansion turbine, and particularly to a thrust control device for a high-pressure turbine or the like that tends to undergo thrust fluctuations during operation.

[Background of the invention]

Expansion turbines used for generating refrigeration in air separation devices and the like are used under a wide range of operating conditions from normal temperature conditions to extremely low temperature conditions in plants. Therefore, since the pressure and temperature at the entrance and exit of the expansion turbine change under each operating condition, the thrust load acting on the rotating bodies (impeller, rotating shaft, etc.) of the expansion turbine also changes. Therefore, it is necessary to incorporate a thrust bearing into the expansion turbine that can sufficiently support this thrust load.

Generally, in an expansion turbine having a full-shrouded impeller, the axial thrust acting on the rotating body is calculated from the pressure on the front and back surfaces of the impeller and the ratio of the pressure-receiving area on which this pressure acts, as shown in FIG. (Mechanical Engineering Handbook Revised 5th Edition P9-44) F=P ₁ ×A ₁ +P ₂ ×A ₂ −P ₃ ×A ₃ −P ₄ ×A ₃
...(1) Here, F = Thrust acting on the rotating shaft P ₁ = Impeller inlet pressure P ₂ = Impeller outlet pressure P ₃ , P ₄ = Impeller back pressure A ₁ ~ _{A 4} = Pressure P ₁ ~ _{P 4} acting Pressure-receiving area The pressure-receiving areas A ₁ to _{A 4} are determined by the impeller shape, but the pressures of P ₁ and P ₄ vary depending on the expansion turbine operating conditions. Therefore, in an expansion turbine that processes high-pressure process gas, there are operating conditions ranging from low pressure to high pressure, so the shaft thrust changes greatly depending on the operating conditions. For this reason, a thrust bearing with a high load capacity is required, resulting in disadvantages such as increased bearing loss, increased amount of bearing lubricating oil, and, in power recovery type expansion turbines, a decrease in the amount of recovered power.

[Purpose of the invention]

An object of the present invention is to provide a thrust control device for an expansion turbine that maintains the thrust acting on the rotating shaft within a certain range under any operating conditions.

[Summary of the invention]

The magnitude of the axial thrust generated in an expansion turbine is determined by the difference between the impeller back pressure and front pressure, as shown by equation (1) above. This pressure difference varies depending on operating conditions, and this variation is particularly large in expansion turbines that process high-pressure process gas, making it necessary to increase the load capacity of the thrust bearing.

Therefore, the present invention maintains the axial thrust generated by the impeller within a certain range by controlling the pressure on the back surface of the impeller, thereby reducing the load capacity of the thrust bearing.This reduces bearing loss and reduces bearing loss. By reducing the amount of bearing lubricating oil and increasing the amount of recovered power in power recovery expansion turbines, it is possible to improve the unit consumption during plant operation.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. FIG. 2 shows a cross section of the impeller portion of the expansion turbine. The process gas in the scroll 1 passes through the nozzle 2, expands adiabatically, becomes a jet gas, enters the impeller 3, rotates the impeller, and then flows to the differential user 4. A labyrinth 5 is provided at the front outlet of the impeller 3 to prevent a shot path of the process gas. Further, a labyrinth 6 is provided on the outer periphery of the back surface of the impeller 3, and a labyrinth 7 is provided on the inner periphery portion, and a portion surrounded by the labyrinths 6 and 7 forms a back pressure chamber 8. The pressures in the back pressure chamber 8 and the impeller outlet are detected by a differential pressure gauge 9.

The upper limit of the differential pressure gauge 9 is the specified value when the axial thrust according to equation (1) above acts in the front direction of the impeller, and this upper limit signal causes the control valve to send the high-pressure process gas from the scroll 1 to the back pressure chamber 8. A line marked with 10 is attached. Conversely, the lower limit of the differential pressure gauge 9 is the specified value when the axial thrust according to equation (1) above acts on the back side of the impeller 3, and this lower limit signal causes the back pressure chamber 8 to
A line is provided with a control valve 11 for sending the gas from this part to the differential user 4.

The specified upper and lower limits of the differential pressure gauge 9 are determined from the load capacity of the thrust bearing.

With the above configuration and operation, it is possible to maintain the axial thrust generated by the impeller within a certain range under any operating conditions, and any thrust bearing suitable for expansion turbines can be designed. can.

〔Effect of the invention〕

According to the present invention, since the load capacity of the thrust bearing can be set arbitrarily, a thrust bearing suitable for an expansion turbine can be designed, the thrust bearing can be made more compact, bearing loss can be reduced, and the amount of bearing lubricating oil can be reduced. The power recovery type expansion turbine has the effect of increasing the amount of recovered electric power.

[Brief explanation of drawings]

FIG. 1 is an explanatory view showing a cross section of an impeller and the types of pressures acting on the impeller, and FIG. 2 is a cross-sectional view of an embodiment of the present invention. 1...Scroll, 2...Nozzle, 3...Impeller, 4...Diff user, 9...Differential pressure gauge,
10... Control valve, 11... Control valve, 8... Back pressure chamber.

Claims (1)

[Claims] 1 In an expansion turbine equipped with a rotating shaft supported by a bearing, an impeller provided at the end of the rotating shaft, and a nozzle for supplying process gas to the impeller from a scroll section, a back pressure is applied to the back surface of the impeller. providing a chamber, and providing a line connecting the back pressure chamber with the scroll portion and the impeller outlet portion through control valves, respectively;
A thrust control device for an expansion turbine, comprising a differential pressure gauge that detects a pressure difference between the back pressure chamber and the impeller outlet and operates the control valve.