Molten Salt Combined Cycle Start-Up Without Heat Transfer Fluid Freezing

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Solution Overview

Problem

Combined cycle power plants face challenges in efficiently storing and rapidly deploying renewable energy due to the 'Duck Curve' phenomenon, leading to curtailment and steep load variations, which affects profitability and emissions.

Innovation Solution

A liquid salt energy storage combined cycle system integrates thermal energy storage with gas and steam turbines, using molten salt to store and superheat steam, enabling fast start-up and improved efficiency by removing heat transfer constraints and optimizing steam turbine flow.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If thermal energy storage system uses heat transfer fluid to transfer heat from storage to boiler, then energy storage efficiency is improved, but during start-up the fluid may freeze causing system failure

Engineering Contradiction:

Improvesystem start-up reliabilityVSAvoidheat transfer fluid freezing

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The startup feedwater heater preheats feedwater using a third heat source before the heat transfer fluid is introduced into the boiler. This preliminary heating action ensures that when the heat transfer fluid circulates during start-up, the boiler and associated piping are already above the freezing point of the fluid, preventing freeze-up and enabling reliable system start-up.

Inventive Principle:

Principle #10Preliminary action

2Speed

If combined cycle plant rapidly ramps up to meet steep load variations, then grid responsiveness is improved, but fuel consumption and emissions increase

Engineering Contradiction:

Improveload response speedVSAvoidfuel consumption

Core Design Contradiction:

SpeedVSLoss of energy

Solution Approach 1:

The thermal energy storage system preheats feedwater and generates steam in advance during periods of low demand or excess renewable generation. When rapid load increase is required, the stored thermal energy is quickly deployed to generate steam for the steam turbine, enabling fast ramp-up without immediately increasing fuel consumption in the combustion turbine.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system maintains continuous operation of the steam turbine by using stored thermal energy to sustain steam generation even when the combustion turbine is ramping up or down. This continuity allows the plant to respond rapidly to load changes while optimizing fuel usage by decoupling steam generation from immediate fuel combustion.

Inventive Principle:

Principle #20Continuity of useful action

3Reliability

If excess renewable energy is curtailed to maintain grid stability, then grid reliability is maintained, but energy waste increases

Engineering Contradiction:

Improvegrid stabilityVSAvoidrenewable energy curtailment

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

During periods of excess renewable generation and low grid demand, the system uses the available thermal energy (from renewable sources or low-cost periods) to preheat feedwater and charge the thermal energy storage system. This preliminary energy capture and storage prevents curtailment by storing the energy for later use, thereby maintaining both grid reliability and energy utilization.

Inventive Principle:

Principle #10Preliminary action

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

The system achieves low fuel heat rates, reduces greenhouse gas emissions, and enhances operational flexibility, making it more economical to use renewable energy, while minimizing storage costs and maintaining system readiness for rapid power adjustments.

Implementation Method 1

a startup feedwater heater configured to use heat from the third heat source to heat feedwater from the feedwater reservoir to a temperature greater than a freezing point of a heat transfer fluid

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 2

a feedwater preheater configured to heat feedwater from the feedwater reservoir with heat exclusively from the combustion turbine exhaust gases

Methodology Applied

Scientific EffectHeat transfer: Convection

Implementation Method 3

a boiler configured to boil feedwater from the feedwater preheater with heat exclusively from the thermal energy storage system to generate steam

Methodology Applied

Scientific EffectPhase change: Boiling

Implementation Method 4

a superheater configured to heat steam from the boiler exclusively with heat from the combustion turbine exhaust gases to generate the superheated steam

Methodology Applied

Scientific EffectHeat transfer: Convection

Implementation Method 5

a steam turbine generator that expands superheated steam across a steam turbine to generate electricity

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 6

a thermal energy storage system that stores heat from the second heat source

Methodology Applied

Scientific EffectThermal energy storage: Thermal Energy Storage

Data Source

PatentUS12584424B2Start-up and control of liquid salt energy storage combined cycle systems

Publication Date: 2026.03.24 PINTAIL POWER LLC

AI summary

The invention relates generally to methods and apparatus for start-up and control of liquid salt energy storage combined cycle systems.