Gas Turbine Shutdown Thermal Soak-back Mitigation
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Solution Overview
Problem
Thermal soak-back in gas turbine engines leads to residual heat transfer, causing physical deterioration of internal components, such as coking, seal deterioration, thermal stresses, and compressor tip rubbing, resulting in early degradation of engine performance and increased maintenance needs.
Innovation Solution
A method of operating a gas turbine engine involving a shutdown procedure that includes idle and cranked rotation operations, where a controller determines thermal parameters to assess thermally stabilised conditions, allowing for controlled heat removal and redistribution using a thermal management system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If active cooling with powered fans and adapted ducts is used to mitigate thermal soak-back, then component protection is improved, but energy consumption, mass, size and complexity increase
Solution Approach 1:
The gas turbine engine performs self-cooling during shutdown through its own operational characteristics. The turbine continues to expand hot combustion products to drive the spool at idle rotation speed, creating natural convection currents that remove residual heat from components without requiring external cooling systems.
Solution Approach 2:
The invention extracts and utilizes the existing hot combustion products and spool rotation mechanism to create a cooling effect. By allowing the turbine to expand hot gases during idle rotation, the system extracts thermal energy that would otherwise cause soak-back and redirects it to provide beneficial cooling airflow through the engine components.
2Ease of operation
If the gas turbine engine is left stationary after shutdown, then operational simplicity is maintained, but thermal soak-back causes component deterioration
Solution Approach 1:
The controller initiates idle rotation operation immediately upon shutdown, performing the cooling action before thermal soak-back can occur. This preliminary action of continuous expansion and airflow generation prevents residual heat from transferring to surrounding components and air cavities.
Solution Approach 2:
The system implements periodic idle rotation operations at predetermined intervals during the shutdown sequence. The controller activates and deactivates the idle rotation mode based on thermal condition monitoring, creating periodic cooling cycles that effectively manage thermal soak-back without requiring continuous operation.
3Reliability
If idle rotation operation is performed continuously during shutdown, then thermal soak-back is mitigated, but energy consumption increases
Solution Approach 1:
The controller continuously monitors thermal parameters of the gas turbine engine during shutdown and uses this feedback to determine when idle rotation should be activated or deactivated. The system adjusts operation based on real-time thermal conditions, ensuring energy is consumed only when and where thermal soak-back risk exists.
Solution Approach 2:
The idle rotation operation is dynamically adjusted based on actual thermal conditions rather than running continuously at fixed speed. The controller modulates the rotation speed and duration of idle operation to match the cooling requirements, optimizing energy consumption while maintaining effective thermal management.
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
This approach effectively mitigates thermal soak-back, reducing component degradation, maintaining engine performance, and minimizing maintenance requirements by optimizing the shutdown procedure based on real-time thermal conditions.
Implementation Method 1
a turbine of the gas turbine engine expands hot combustion products from a combustor to drive the spool to rotate
Implementation Method 2
performing a heat removal operation comprising controlling the thermal management system to cause heat to be removed from the gas turbine engine
Implementation Method 3
performing a heat redistribution operation comprising controlling the thermal management system to cause heat to be redistributed within the gas turbine engine
Implementation Method 4
thermal inertia of heated components of the gas turbine engine such as a compressor disc and/or a turbine disc may lead to residual heat being transferred to other components of the gas turbine engine
Implementation Method 5
residual heat being transferred to other components of the gas turbine engine and/or into surrounding air cavities within the gas turbine engine
Data Source
AI summary
A method of operating a gas turbine engine having a spool includes executing, by a controller, a pre-shutdown procedure. The pre-shutdown procedure includes: determining a parameter associated with a thermal condition of the gas turbine engine; and calculating an idle period for an idle rotation operation to be performed in a shutdown procedure. Calculation of the idle period is based on the determined parameter.