Active Draft Control for CCPP Shutdown Heat Loss

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Solution Overview

Problem

Combined cycle power plants face inefficiencies and rapid cooling issues during turbomachine shutdowns due to naturally induced airflow, leading to tighter tip clearances and increased heat loss, which hinder quick restarts and reduce efficiency.

Innovation Solution

Implementing a recirculated exhaust gas system that measures and adjusts airflow through the HRSG to control draft, using a bypass fan and controller to maintain a setpoint pressure difference, thereby reducing heat loss and optimizing clearances during shutdown and restart cycles.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If inlet guide vanes are left open during shutdown to allow natural cooling airflow, then cooling efficiency is improved, but heat loss from stator casing increases and tip clearances become tighter

Engineering Contradiction:

Improvestator casing temperatureVSAvoidheat loss

Core Design Contradiction:

TemperatureVSLoss of energy

Solution Approach 1:

The system dynamically adjusts the position of inlet guide vanes and outlet dampers based on measured temperature differentials and pressure conditions. By changing the flow parameters (open/closed states) based on real-time conditions, the system optimizes the balance between cooling effectiveness and heat loss prevention during shutdown transitions.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Temperature sensors monitor the stator casing temperature throughout the shutdown process, and this feedback is used by the control system to adjust vane positions and damper settings. The system continuously adapts its control strategy based on the measured temperature evolution, preventing excessive cooling that would lead to tight clearances.

Inventive Principle:

Principle #23Feedback

2Temperature

If natural convection cooling is allowed during shutdown, then cooling of turbomachine and HRSG is improved, but tip clearances become tighter due to faster exterior cooling

Engineering Contradiction:

Improveturbomachine temperatureVSAvoidtip clearance

Core Design Contradiction:

TemperatureVSLength of moving object

Solution Approach 1:

The control system modifies the airflow parameters by adjusting inlet guide vane angles and outlet damper positions based on the thermal state of the turbomachine. This dynamic parameter adjustment prevents excessive exterior cooling that would cause the stator case to contract and reduce tip clearances.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The system takes preliminary action by closing inlet guide vanes and outlet dampers before the shutdown is complete, anticipating the harmful effect of excessive cooling. This preemptive control prevents the stator casing from cooling too rapidly and contracting, thereby maintaining adequate tip clearances for hot restart conditions.

Inventive Principle:

Principle #9Preliminary anti-action

3Loss of energy

If inlet guide vanes and outlet dampers are closed to prevent cooling during shutdown, then heat loss is reduced, but cooling requirement is not met

Engineering Contradiction:

Improveheat lossVSAvoidturbomachine temperature

Core Design Contradiction:

Loss of energyVSTemperature

Solution Approach 1:

The system transitions from static closed positions to dynamic adjustable positions for the inlet guide vanes and outlet dampers. During shutdown, the system dynamically opens these components to controlled degrees based on real-time temperature measurements, allowing necessary cooling while minimizing heat loss. This dynamic control enables the system to meet cooling requirements without excessive energy loss.

Inventive Principle:

Principle #15Dynamics

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 reduces heat loss from the stator casing and HRSG, allowing for larger clearances during hot restarts, preventing tip rub and improving turbine efficiency by maintaining optimal operational conditions.

Implementation Method 1

ambient air infiltration can be naturally induced through the compressor and hot gas path by natural convection of the hot gas contained in the turbomachine, HRSG, flue gas stacks

Methodology Applied

Scientific EffectConvection: Convection

Implementation Method 2

air may continue to pass into the compressor. The induced air travels along the length of the turbomachine, with flow being supported by the angular momentum of the rotor

Methodology Applied

Scientific EffectAngular momentum: Angular Momentum

Implementation Method 3

the stator case may cool and contract toward the interior

Methodology Applied

Scientific EffectThermal contraction: Thermal Contraction

Data Source

PatentUS10215059B2Active draft control for combined cycle power plant shutdown

Publication Date: 2019.02.26 GE INFRASTRUCTURE TECH LLC

AI summary

A system and method for active draft control through a combined cycle power plant (CCPP) can initiate a CCPP shutdown, activate the recirculated exhaust gas (REG) system for the turbomachine; measure a HRSG airflow through the HRSG; communicate the HRSG airflow to a controller configured to condition a control signal; and adjust a recirculated exhaust gas volume in accordance with the control signal.