Gas Turbine Compressor Inlet Guide Vane Control During Shutdown

Solution Overview

Problem

Gas turbine shut down is plagued by compressor instabilities, particularly rotational stalls at low speeds, leading to shaft vibrations and potential damage due to unsatisfactory vane position regulation methods in existing technologies.

Innovation Solution

Initiate closure of compressor inlet guide vanes at a shaft speed 5-15% above the stall-induced vibration peak, closing them by 15-35° at a rate of 5-10° per second to reduce aerodynamic braking and susceptibility to rotating stall, thereby decreasing shaft vibrations and compressor pressure ratio.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If compressor inlet guide vanes are kept open during gas turbine shut down, then mass flow is maintained and convective cooling is improved, but compressor instabilities and rotational stalls occur at low speeds

Engineering Contradiction:

Improvecooling of compressor componentsVSAvoidcompressor stability

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The guide vanes are closed in advance before the gas turbine reaches critical low speeds. By initiating closure at a predetermined speed threshold (5-15% above the stall-induced vibration peak), the system prevents rotational stalls from occurring while maintaining adequate cooling during the shutdown process.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The guide vane position is dynamically adjusted during the shutdown process rather than remaining fixed. The system transitions from an open state (for cooling) to a closed state (for stability) based on real-time speed conditions, optimizing both cooling effectiveness and compressor stability at different stages of shutdown.

Inventive Principle:

Principle #15Dynamics

2Reliability

If compressor inlet guide vanes are closed to prevent rotational stall, then compressor stability is improved, but aerodynamic braking on the shaft increases

Engineering Contradiction:

Improvecompressor stabilityVSAvoidaerodynamic braking force

Core Design Contradiction:

ReliabilityVSForce

Solution Approach 1:

The guide vanes are closed in advance before the gas turbine reaches critical low speeds. By initiating closure at a predetermined speed threshold (5-15% above the stall-induced vibration peak), the system prevents rotational stalls from occurring while maintaining adequate cooling during the shutdown process.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The aerodynamic braking effect, which is normally harmful during shutdown, is converted into a beneficial control mechanism. By closing the guide vanes at the optimal moment, the resulting aerodynamic braking helps control the shutdown speed and prevents rotational stalls, transforming a potentially harmful force into a useful control tool.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Reliability

If guide vane closure is initiated early during shut down, then rotational stall is prevented, but the time for convective cooling is reduced

Engineering Contradiction:

Improvecompressor stabilityVSAvoidcooling time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The guide vanes are closed in advance before the gas turbine reaches critical low speeds. By initiating closure at a predetermined speed threshold (5-15% above the stall-induced vibration peak), the system prevents rotational stalls from occurring while maintaining adequate cooling during the shutdown process.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The closure angle of the guide vanes is precisely controlled and varied during the shutdown process. By adjusting the closure angle dynamically (closing by 15-35° at a rate of 5-10° per second), the system optimizes the balance between preventing rotational stalls and maintaining adequate cooling time.

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Effectively reduces rotational stall risk, minimizing compressor damage and increasing convective cooling, leading to decreased vibrations and extended vane opening time for enhanced cooling during gas turbine shut down.

Implementation Method 1

the compressor airfoils have an aerodynamic braking effect on the shaft, which results in a compressor pressure rise across the airfoil stages

Methodology Applied

Scientific EffectAerodynamic braking: Drag

Implementation Method 2

Effectively, it is then the gas turbine shaft rotational energy that drives the compressor

Methodology Applied

Scientific EffectRotational energy transfer: Angular Momentum

Implementation Method 3

the increased mass flow resulting from allowing the vanes to remain open for a longer period of time during the shut down causes an increased convective cooling of the flow path and metal parts

Methodology Applied

Scientific EffectConvective cooling: Convection

Data Source

PatentEP1999354B1Method of operating a gas turbine power plant

Publication Date: 2009.07.01 ALSTOM TECH LTD

Figure 1a~1b

AI summary

In a method of operating a gas turbine during shut down the gas turbine is decelerated and closure of compressor inlet guide vanes (1) is initiated at a shaft speed at least 5% above the shaft speed where a (stall incuced) vibration peak occurs. The compressor inlet guide vanes (1) are closed by an angle in the range from 15°- 35° , preferably at a rate between 5° and 10° per second. The method effects a reduction of the risk of rotational stall.