Steam turbine rotating speed control method based on valve characteristic curves under extreme working condition

Abstract

The invention discloses a turbine rotating speed control method based on a valve characteristic curve under an extreme working condition. The turbine rotating speed control method comprises the following steps: setting a set pressure P0 of main steam and a set pressure PREH0 of reheated steam; obtaining an actual pressure value P1 of the main steam and an actual pressure value PREH of the reheated steam according to a steam turbine control system; comparing the actual pressure value P1 of the main steam with the set pressure P0, and if P1 is larger than or equal to P0, fixing the opening degree of a high-pressure bypass valve and adjusting the opening degree of a low-pressure bypass valve; and if P1 is smaller than P0, fixing the opening degree of the low-pressure bypass valve and adjusting the opening degree of the high-pressure bypass valve. Steam flow of a reheat steam cold section and a reheat steam hot section can be distributed according to the unit condition under the extreme working condition, and impulse rotation and constant speed of a rotor are automatically maintained under the condition that steam inlet flow of a high-pressure cylinder and a medium-pressure cylinder is guaranteed. The monitoring and operation workload of operators is greatly reduced, the grid-connected time of a unit is shortened on the basis of ensuring the safety and stability of the unit and a power grid, and the overall improvement of the safety and economy of the unit is facilitated.

Description

technical field [0001] The invention relates to the technical field of thermal power generation, in particular to a steam turbine speed control method based on a valve characteristic curve under extreme working conditions. Background technique [0002] With the continuous improvement of the installed capacity and steam parameter level of thermal power units in my country, the unit working conditions under extreme working conditions mainly include unit load shedding, hot state or extremely hot state start-up, and generally there is a high steam quality of the steam turbine unit (steam In the case of high pressure and high temperature), it is very easy to cause speed overspeed or instability when backlashing and maintaining stable speed. In extreme cases, the units are all controlled by the unit DEH (Digital Electric Hydraulic Control System) in the automatic control mode, using automatic (load shedding, rotor over-critical speed) or manual setting of the target value (3000r / mi...

AI Technical Summary

Problems solved by technology

[0004] (1) At present, thermal power units generally have large capacity and high parameters, and the rotor time constant of the units is relatively small. Under extreme working conditions, it is very easy to cause fluctuations in the speed of the unit or overspeed, which is harmful to the safety and stability of the power grid and the unit itself. is a great threat

The emergence of these working conditions not only tests the dynamic characteristics of the steam turbine regulating system, but also tests the parameter matching ability of the unit under extreme conditions. The small amount of steam not only affects the safety of the reheater of the boiler and the low-pressure cylinder of the steam turbine

[0005] (2) The flow of a typical steam turbine control valve is non-linear, as shown in the attached figure 2 , while the total valve position command is a combination of several regulating valves (and is a single valve control method attached image 3 ), there is a problem of poor linearization in both the low valve position range and the large valve position range by the valve management, especially in the low valve position range of a single valve; when the steam quality is high and the rotor time constant is relatively low, the unit When rushing and constant speed, it is easy to cause large fluctuations in speed

[0006] (3) When the high and low pressure bypass valves are manually adjusted, the steam flow in the reheater is likely to be insufficient, resulting in dry burning of the reheater; or the steam flow in the reheater is too large, and the quality of the reheated steam drops too quickly, It increases the safety risk of the unit; at the same time, when the high and low pressure bypass valves are manually adjusted, they are prone to jamming, which seriously delays the start-up time of the unit

[0007] (4) The high energy generated by high-quality steam causes the opening of the regulating valve to be small when the unit is running, and the characteristics of the regulating valve itself are not good at low opening, which is easy to cause speed fluctuations; at the same time, the high-quality steam Under normal circumstances, after the unit load is shed or when it runs again, it is easy to cause the pressure difference between the front and rear of the valve to be too large, and the main steam valve cannot be opened (for example, the main steam valve of Harbin steam medium pressure is a plate structure) often occurs, which not only delays The normal grid connection and load process of the unit will be accompanied by many vicious accidents such as pipeline resonance

[0008] (5) Under the existing technical conditions, the unit can recover quickly under extreme conditions such as constant speed or tripping after load shedding, and the unit can be connected to the grid at a constant speed of 3000r / min in a short period of time. High, on the one hand, it is necessary to run, constant speed and grid connection of the extremely hot state or hot state units, on the other hand, it is necessary to make timely adjustments to boilers, steam turbines, thermal engineering and other related systems (boilers need to prevent superheaters, reheaters Overpressure, boiler flameout, maintenance of water supply, condensed water, shaft seal steam and other systems on the machine side are normal, and thermal electrical equipment needs to verify relevant signals and protection inputs to prepare for the re-connection of the unit to the grid), so the requirements for operating personnel are extremely high At the same time, the workload, work risk and work pressure are also extremely high; in addition, when the unit is idling, the high-quality steam rushes to the steam turbine, which will easily cause the final stage blast of the low-pressure cylinder to increase, which will easily cause the rotor and structure of the low-pressure cylinder to resonate, and the occurrence of blades Events that cause damage to the steam turbine such as damage or friction of the static parts of the steam turbine

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