Reversible Turning Gear for Thermal Energy Conservation in Combined Cycle Plants

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Solution Overview

Problem

During turning-gear operation of combined cycle gas turbines, thermal energy is lost from the heat recovery steam generator due to cooler ambient air flowing through the system, leading to increased start-up times and thermal stresses on components, negatively impacting overall power plant performance.

Innovation Solution

A reversible turning gear system is implemented to counter-rotate the gas turbine rotor shaft, reversing the flow of combustion exhaust gas back through the heat recovery steam generator, thereby conserving thermal energy by utilizing the hotter exhaust gas to reduce heat transfer with the working fluid, and a method to measure and control the exhaust gas temperature to optimize energy conservation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the gas turbine is shut down during non-peak periods and the rotor shaft is turned via turning gear, then the gas turbine rotor is protected from bowing, but thermal energy is lost from the working fluid in the heat recovery steam generator to the cooler exhaust air

Engineering Contradiction:

Improvegas turbine rotor protectionVSAvoidthermal energy loss from working fluid

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The turning gear is made reversible to rotate the rotor shaft in the opposite direction during turning gear operation. This reverse rotation reverses the flow direction of exhaust gases through the heat recovery steam generator, allowing hot exhaust gases to flow through the heat exchanger and prevent heat loss to the cooler ambient air that would otherwise occur during standard turning gear operation

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The ambient air that would normally cause harmful heat loss from the working fluid is converted into a beneficial flow path. By reversing the rotor shaft rotation, the ambient air flow is redirected to follow the exhaust gas path through the heat recovery steam generator, transforming it from a heat-sinking harmful factor into a flow carrier that maintains thermal energy conservation

Inventive Principle:

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

2Reliability

If the gas turbine is shut down and turned via turning gear, then the rotor is protected from bowing, but additional time is required to bring the working fluid back to operating temperature

Engineering Contradiction:

Improvegas turbine rotor protectionVSAvoidstart-up time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

During turning gear operation following shutdown, the reversible turning gear immediately initiates reverse rotation to establish reverse flow of exhaust gases through the heat recovery steam generator. This preliminary action maintains the thermal energy in the working fluid by preventing heat loss to ambient air, thereby preparing the system for faster restart and reducing the time required to reach operating temperature

Inventive Principle:

Principle #10Preliminary action

3Reliability

If the gas turbine is shut down and turned via turning gear, then the rotor is protected from bowing, but thermal stresses are imposed on HRSG components due to temperature differential

Engineering Contradiction:

Improvegas turbine rotor protectionVSAvoidthermal stress on HRSG components

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

By making the turning gear reversible and rotating the rotor shaft in reverse direction, the flow direction of exhaust gases through the heat recovery steam generator is inverted. This reverse flow ensures that hot exhaust gases pass through the heat exchanger, maintaining temperature uniformity and eliminating the temperature differential that would otherwise create harmful thermal stresses on HRSG components during standard turning gear operation

Inventive Principle:

Principle #13The other way round (Inversion)

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 reduces thermal energy loss, shortens start-up times, and minimizes thermal stresses on components, enhancing the efficiency and performance of the combined cycle power plant by maintaining a higher temperature differential within the heat recovery steam generator.

Implementation Method 1

Thermal energy from the hot combustion exhaust gas is transferred via the heat exchanger(s) to a working fluid such as water

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 2

The reversible turning gear counter rotates the rotor shaft during turning gear counter rotation operation of the gas turbine and reverses flow of combustion exhaust gas from the exhaust stack through the heat exchanger

Methodology Applied

Scientific EffectFluid flow reversal: Convection

Data Source

PatentUS9945266B2Combined cycle power plant thermal energy conservation

Publication Date: 2018.04.17 GE INFRASTRUCTURE TECH LLC

AI summary

A combined cycle power plant includes a gas turbine having a primary flow passage, a heat recovery steam generator having a heat exchanger disposed downstream from the primary flow passage, an exhaust stack in fluid communication with the primary flow passage and disposed downstream from the heat recovery steam generator and a reversible turning gear coupled to a rotor shaft of the gas turbine. The reversible turning gear counter rotates the rotor shaft during turning gear counter rotation operation of the gas turbine and reverses flow of combustion exhaust gas from the exhaust stack through the heat exchanger and back into the primary flow passage of the gas turbine, thereby conserving thermal energy stored in the heat recovery steam generator. A method for conserving thermal energy of a combined cycle power plant during counter rotation turning gear operation of the gas turbine is also disclosed.