sulfur based thermochemical heat storage for baseload ...€¦ · the combined cycle power plant...
TRANSCRIPT
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Sulfur Based Thermochemical Heat Storage for
Baseload Concentrating Power
General Atomics (GA)German Aerospace Center (DLR)
Staff
Award Number: DE-EE0003588
CSP Program Review 18th May, 2011
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Outline
• Project Description and Objectives
• Thermodynamic Modeling
• Laboratory Results
• Process Pathways and System Efficiency
• Summary
• Future Work
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Project Goals
• Demonstrate the engineering and economic feasibility of using sulfur to support baseload operation of a solar electricity plant
Reaction Temp ( C) ∆H (kJ/mole)
Sulfuric Acid Decomposition
2H2SO4 → 2H2O(g) + 2SO3(g) 450 – 500 560
2SO3 → O2 (g) + 2SO2(g) 700 – 800
Disproportionation Reaction
2H2O(l) + 3SO2(g) → 2H2SO4(aq) + S(s,l) 50 – 200 -260
Sulfur Combustion S(s,l) + O2(g) → SO2(g) 500 – 1200 -300
• All chemical reactions have been demonstrated
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The baseline concept decouples thermochemcialprocess from electricity generation
•storage of sulfur and H2SO4 is simple and inexpensive
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Disproportionaton
Improve Kinetics
ThermodynamicsModeling
Verify Process Feasibility
• Catalysts• Sulfur Extraction
Phase I Objective – Maximize the sulfur generation rate and establish a baseline system design
GO NOGO
Flowsheet
Process Pathways Comparison
System DesignDecomposition (DLR)
Decomposer Selection
ConcentrationConstruction
Materials
Project Performance
Capacity Factor
LCOE
Phase I began in September 2010 and the duration is 18 months
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Thermodynamic modeling is used to guide disproportionation reaction experiments
HSC Chemistry Aspen Plus Aspen Plus
OLI
• Design of Experiments– HSC Chemistry– Aspen Plus advanced sulfuric acid model
• Preliminary optimization– Aspen Plus advanced sulfuric acid model– OLI Systems electrolytes model
• Final optimization– Custom model based on experimental data
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Aspen Plus results showed sulfur yield is suppressed by temperature but enhanced by pressure
• Optimal H2O: SO2 ratio enhances sulfur yield• Too much water can reduce SO2 activity resulting in
lower sulfur yield• Too little water suppresses reaction resulting in lower
H2SO4 formation
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H2O:SO2 ratio and pressure effects predicted by thermodynamic model were qualitatively verified
• High H2O:SO2 ratio enhance sulfur generation • A minimum pressure is required for sulfur generation
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Catalysts have been used to enhance sulfur generation
• Thiosulfates, metal sulfates and hydroxides have all shown catalytic activities in this system
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Disproportionation reaction is affected by a number of factors
Sulfur
High Pressure>200psi
H2O:SO2ratio >2
Temperature>100°C
CatalystsThoisulfates
MnSO4NH4OHSolution pH
SO2 solubility
• Laboratory studies to find the optimal parameters for fast reaction kinetics is on going
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Several process pathways were considered in devising the initial Sulfur TES flowsheet
• Rankine steam power cycle High process heat available (~900⁰C) not an
optimal fit for steam cycle alone
• Supercritical CO2 power cycle Large gas-gas heat exchangers may be required
for high efficiency Development work remains
• Methods for sulfuric acid concentration Solar trough heat SO2 conversion to SO3
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The current Sulfur TES flowsheet is based upon a combined-cycle power plant with SO2 conversion
Solar Cavity
SO2
O2
Air
H2ODisproportionate
Reactor
S
H2SO4Decomposer
Sulfur Combustor
dilute
H2SO4
SO2
Air
H2SO4Concentrator
S
Conc.H2SO4
S
Steam Turbine
Generator
Gas Turbine
Generator
SO2
Air
SO3
Air
Air
S
On Sun24 hour
S Storage
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The combined cycle power plant concept is well established and is very efficient
• Electrical conversion efficiency of heat supplied to the power plant is ~50%
• Overall efficiency of electricity generation from solar heat supplied to thermochemical process is about 27%
• Losses in disproportionation reactor and in sulfuric acid decomposer account for the difference
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Sulfuric acid concentration can be done via conversion of SO2 to SO3
• Avoids construction of a separate solar trough plant
• Allows this process to leverage established sulfuric acid production equipment and techniques
• SO2 converter units generate recoverable heat, increasing efficiency
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TES is done via storage of dry sulfur
• Hot (molten) sulfur storage not necessary
• Dry sulfur delivered via hopper to combustor
• Sulfur is melted in combustor before atomizing/spraying into burner
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Summary
• Process parameters boundaries were defined by thermodynamic models
• Laboratory results qualitatively agreed with thermodynamic models
• Sulfur yield was enhanced by using catalysts
• Flowsheet design focused on minimizing impact of thermochemical losses
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Future Work
• Define the pressure, temperature and H2O:SO2ratio for optimal reaction kinetics and system design
• Identify the catalyst(s) to be used
• Demonstrate a sulfur extraction methodology
• Establish reactor and system design concepts
• Determine the economics of the proposed system
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Sulfur as a TES medium is truly unique
• Provides process heat at temperatures higher than collected at solar receiver
• Uncomplicated storage method
• Allows for seasonal storage if desired