JPH04295104A - Method and device for minimizing heat-rate deterioration in steam turbine - Google Patents

Abstract

PURPOSE: To provide a method and a device for incrementally controlling a flow of a first stage of 9 turbine without adding or throtting a flow control valve. CONSTITUTION: In an atomic power steam turbine 18, deterioration of a heat consumption ratio is generated due to excessive flow margine. For minimizing this, a plug member 48 selectively disconnects a flow passage for steam passing a first stage nozzle ring 20. The plug member 48 is selectively inserted before the flow passage between adjacent nozzle blades 30 of the nozzle ring 20 by detection of a timing when a flow of steam passing a control valve to supply steam to the steam turbine 18 exceeds a desired flow value to the steam turbine 18 by a monitoring device. The plug member 48 effectively reduces the flow passing the nozzle ring 20 without throttling steam by the control valve to prevent deterioration of efficiency.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION Steam turbines are delivered with a warranty of rated output. For fossil fuel systems, the power rating is related to the power output of the turbine. However, in nuclear powered systems, the Nuclear Regulatory Commission (NRC) in the United States certifies power generation systems based on thermal energy input to the turbine. In either type of system, rated output can be achieved by oversizing the turbine, i.e. by giving it more flow capacity than is calculated to be necessary to produce the guaranteed rated output. It is customary to do so. This extra flow capacity is commonly referred to as flow margin and is often selected to be about 5%. In the case of fossil fuel systems, this flow margin works to the user's advantage, simply providing greater power output capability. However, in nuclear field systems, flow margins may require throttling the valves at full operating power to limit thermal energy input to NRC approved specifications for the system. Unfortunately, throttling the valve reduces the efficiency of the turbine system.

One way to overcome the efficiency loss caused by throttling the valves is to provide partial arc control of the steam turbine. Partial arc delivery is accomplished by dividing the steam entering the turbine inlet into multiple isolated and separately controllable delivery arcs. In this method, the first
The number of nozzles in a stage is changed in response to changes in load. Part-arc feed turbines achieve relatively high ideal efficiencies by sequentially pumping steam through individual nozzle chambers with minimal throttling, rather than throttling the entire feed arc.

In nuclear steam turbines, where the maximum allowable steam flow rate is limited by the authorized reactor power, excess flow margin results in reduced efficiency. Furthermore, in many nuclear steam turbine designs, the effects of two-phase flow are often inadequately predicted, which can reduce turbine first stage outlet pressure or increase flow capacity, resulting in The performance of the first stage will deviate from the design. These effects require excessive throttling of control valves to maintain authorized reactor power. Also, these 2
The phase effect reduces the turbine feedwater heater bleed pressure and therefore the final feedwater temperature and enthalpy. These latter effects result in a reduction in steam generator flow and further throttling of the control valve in order to maintain the rated output at the approved output level. If the flow margin is reduced, the risk of inadequate output increases.

[0004] By increasing the number of valve points or valve installation locations, the flow rate that is throttled at the rated output can be reduced. Referring to FIG. 1, if we consider valve curves 10 and 12 compared to valve curves 14 and 16, we find that 87.5% flow rate and 62%
．． It is shown that increasing the valve placement at 5% flow rate improves the heat dissipation rate. However, each valve location requires the addition of a control valve and associated steam piping, which significantly increases capital costs.

[0005] In general, partial arc delivery allows a limited range of control and is combined with some throttling of the input steam. For example, the flow area of the turbine first stage is divided into 4, 6 or 8 sub-arcs, with the smallest sub-arc being 12% of the first stage nozzle area. Obviously, if the flow margin is set to a maximum of 5% and the flow rate is to vary in increments of less than 12%, some throttling is required and there is an attendant loss in efficiency. In the case of part-arc inlet turbines, each inlet part-arc, whether it is 25% or 12.5%, cooperates with a separately controllable steam control valve, thus controlling the steam flow rate for each part-arc. can be controlled. Each control valve is relatively large and connected to steam piping several inches in diameter to accommodate the large flow rates in the power plant turbine. Most turbines with partial arc feed are so complex with control valves and piping that it is impractical to add valves and their associated steam piping, so the partial arc It is prohibited to use valves that can be controlled in fractions of less than %. Accordingly, it would be desirable to provide a method and apparatus for regulating steam flow in less than 5% increments without throttling the steam and without adding control valves and piping.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for incrementally controlling first stage flow without adding or throttling flow control valves.

The foregoing and other objects and advantages include, in one form, a first stage nozzle block with a plurality of nozzles, for example 100; This is accomplished in a steam turbine in which the nozzles of the nozzles are selectively blocked to prevent steam flow from passing through the nozzles. Preferably, the plug is inserted radially to a predetermined position that blocks steam from entering the space or spaces between adjacent nozzle vanes. 10
In the case of a nozzle block with 0 nozzles, using 4 such plugs makes it possible to reduce the flow area by up to 4%. These plugs are
It is possible to operate by a hydraulic cylinder, a pneumatic cylinder or an electromagnetic coil. Springs can be used to ensure retraction of these plugs. Preferably, these plugs are individually insertable and removable to allow incremental control of the flow field. Control is simplified by positioning the plug in either a fully closed or fully open position.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A partial arc feed steam turbine is disclosed in U.S. Pat. No. 4,780,057, the disclosure of which is incorporated herein by reference. In the above US patent, a simple partial arc delivery system has six partial arc segments, six corresponding nozzle chambers and six control valves, one for each nozzle chamber. Each is provided. Steam passing through each control valve is directed into a corresponding arcuate group of nozzle fixed vanes. Six nozzle blade groups form one nozzle ring. The nozzle vanes direct the steam to a rotating array of vanes connected in driving relation to the turbine shaft.

During turbine startup, the control system simply opens the steam control valves and directs steam through the multiple nozzle chambers in a predetermined sequence. Steam can be throttled by gradually opening each control valve. The valve point is set at each steam flow rate when the valve is in the fully open position. Referring to FIG. 1, for a turbine system with eight control valves, the valve points are 100% delivery, 87.
It is set to 5% inflow, 75% inflow, 62.5% inflow, etc. For a turbine with four control valves, the valve point is 25%;
Can be set to 50% and 75% feed. In the graph of FIG. 1, the reduction in efficiency during throttling is evident by the higher heat dissipation rate when gradually opening (or closing) each control valve. For example, 87.5 cm corresponds to a steam flow rate of 3.4 pounds per hour (1.54 kg/hour).
For a 5% feed, the heat rate for a four control valve turbine system is approximately 7933 BTU/KWH. Valve curves 10, 12, for a turbine system with eight control valves
Each of 14 indicates a deviation from the ideal curve indicated by 16.

As is clear from the above description, the reference numeral 16
An ideal curve in can be achieved in a turbine containing an infinite number of control valves and corresponding nozzle segments. However, as discussed above, the practical limit for most turbines is simply in the range of eight control valves due to limitations on the number and size of steam piping that can be connected to the turbine. Regarding the provision of separate control valves for small increments of the nozzle ring, e.g. Same problem occurs.

[0011] The inventor has discovered that when the control increments are small, for example about 1% increments, such incremental control can be applied fully or completely without creating undesirable shock loads on the downstream rotor blades. It was confirmed that the turbine system could be operated or controlled by fully closing it. Furthermore, using only a limited number of such incremental controls,
The thermal energy input to a nuclear steam turbine can be adjusted to its desired value without the use of throttling and thus avoiding the efficiency losses associated with throttling.

FIG. 2 shows a simplified partial cross-sectional view of the steam turbine 18 in the vicinity of the first stage nozzle ring and the downstream rotating blade row in which the teachings of the present invention are implemented. ing. An annular nozzle ring 20 is held in an operational position within the turbine between an outer casing 22 and an inner casing 24. Nozzle ring 20 has an outer annular shroud 26 and an inner annular shroud 28. A plurality of equally circumferentially spaced nozzles 30 extend between the shrouds 26,28. These nozzles (nozzle vanes) 30 are sometimes referred to as nozzle guide vanes or simply stator vanes. Outer and inner casings 22, 24
The intervening space 32 forms a nozzle chamber that receives steam from a control valve (not shown) and directs the steam to the nozzle 30. These nozzles 30 direct the steam described above to the first stage rotary vanes 34 . These rotating vanes 34 are arranged in an annular group between an outer shroud member 36 and an inner root member 38. This root member 38 is coupled to a portion 40 of a turbine shaft (not shown) so that steam impinging on the rotating blades 34 causes the turbine shaft to rotate. Seal 42 prevents leakage of steam around rotating vanes 34, while seal 44 prevents leakage of steam around rotary vanes 34.
leakage between the inner cylinder 46 and the inner cylinder 46 is prevented.

The present invention utilizes a plurality of plug members 48, for example four, and positions the plug members 48 within outer casing 22 near selected ones of the spaces between adjacent nozzles 30. place in position. In a preferred embodiment, the plug members 48 have a circumferential width that corresponds to the nozzle pitch, so that vapor flow between adjacent pairs of nozzles 30 can be interrupted by a single plug member. can. However, it will be appreciated that the width of the plug member may be selected to block one or more such spaces. Plug member 48 may be forced into the closed position shown in FIG. 2 using high pressure fluid, ie hydraulic or pneumatic, introduced into cavity 52 via piping 50. The plug member 48 is formed with a head 54 that acts as a piston and has a sealing ring 56 between the head 54 and the inner wall of the cavity 52. When fluid pressure is released from above the head 54, the spring 58 under the head 54 retracts the plug member 48. The body 60 of the plug member 48 slides within a guide cylinder 62 formed within the outer casing 22 .

FIG. 3 shows a radial view of the inlet partial arc. In this partial arc, two plug members 48 are shown in position to block flow through the selected nozzle passage. The plug members 48 are spaced several nozzles apart to minimize the effects of shock when the rotating vanes 34 pass by already blocked nozzle passages (and thus enter and exit the reduced flow region). can be opened.

While the principles of the invention have been illustrated in the illustrated embodiments, it will be apparent to those skilled in the art that the invention can be practiced without departing from the spirit and scope of the invention as set forth in the claims. Many variations in structure, arrangement, and components in the embodiments described above may be possible to develop alternative embodiments suitable for operating conditions.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between heat consumption rate and throttle flow rate in a steam turbine under high load.

FIG. 2 is a cross-sectional view showing a nozzle blocking structure operated by hydraulic pressure.

FIG. 3 is a cross-sectional view of a portion of the inlet arc into which two plug members have been inserted.

[Explanation of symbols]

18 Steam turbine 20 Nozzle ring 30 Nozzle vane (nozzle) 34 Rotating vane 48 Plug member

Claims (2)

[Claims] 1. A steam turbine having a first stage nozzle ring comprising a plurality of circumferentially spaced nozzle vanes defining a steam flow path between each adjacent pair of the nozzle vanes. , having a plurality of plug members each insertable in a position to interrupt a steam flow path, and at least one control valve for throttling the steam flow entering the steam turbine, the volume of the steam flow passing through the nozzle ring In a method of minimizing heat rate deterioration resulting from excess flow margin in said steam turbine whose output is at least partially determined, determining when a steam flow rate through said control valve exceeds a desired flow value for said steam turbine. measuring and inserting a selected one of the plug members into an operative position of the plug member in the vicinity of the nozzle ring to reduce the steam flow rate to the desired flow value. A method for minimizing heat consumption rate deterioration in steam turbines. 2. A steam turbine comprising a first stage nozzle ring consisting of a plurality of circumferentially spaced nozzle vanes, with which the nozzle vanes direct steam flow in a predetermined direction toward a first row of rotating vanes. Apparatus for minimizing heat dissipation rate deterioration resulting from excess flow margin in a turbine arrangement, the apparatus comprising: blocking steam flow through at least one passageway between adjacent nozzle vanes to reduce steam flow without throttling a valve; A device for minimizing heat dissipation rate deterioration in a steam turbine, comprising at least one plug member selectively insertable into the steam turbine in the vicinity of the inlet side of the nozzle ring to reduce heat dissipation rate deterioration.