www.dlr.de Slide 1 Joule-Enhanced Compact Porous Heat Exchanger for Solar Hydrogen Production Institute for Solar Research, German Aerospace Center, Cologne, Germany Dr. Moises Romero, Dennis Thomey, Martin Roeb, Christian Sattler
www.dlr.de Slide 2 Overview - Background -H 2 SO 4 considerations - Simulations - Mechanical Design
www.dlr.de Slide 3 Background - Development and demonstration of key components of Solar Hybrid Sulphur Cycle for Hydrogen Production - Many components in development: Pilot Plant Layout, Balances, catalytic reactors, solar receiver, spectroscopic analysis. - this work focuses on the Joule-Boosted Sulphuric Acid boiler. The electric evaporator is a milestone for the engineering of the Concentrated Solar Acid Boiler, as this reproduces similar boundary conditions for a solar powered equipment. - But what is the chemistry behind the project?
The Sulphur Family of Cycles SI Cycle H 2 SO 4 Decomposition HyS Cycle (our project) Boiling acid to produce H 2 O*H 2 SO 4 to produce SO 2 -O 2 -H 2 O
www.dlr.de Slide 5 SOL2HY2 Demo Diagram H2 Pilot plant for solar sulphuric acid splitting H2SO4 H2O Electrical evaporator
www.dlr.de Slide 6 Challenges Operational difficulties - Amount of acid to be decomposed (1 liter per minute) - Sizing of scrubbing unit (80 kg/h of NaOH 40%) - Water make-up - 40 hours of operation Material Challenges - Leakage avoidance and detection - Corrosion resistant materials are few - Thermal stress between different material types (SS and SiC) Heat Transfer Challenges - How to heat up 1 l/min acid without having to recur to a $30,000 TEMA Hastelloy heat exchanger? - Data on sulphuric acid boiling and porous media unavailable to our knowledge
www.dlr.de Slide 7 Boiler Design Criteria For the boiling of H 2 SO 4 before the solar receiver, the objectives set in the beginning were the following - Electrically Operated - Silicon Carbide - Modular/Tubular configuration - Minimise Size/Cost - Safe operation
www.dlr.de Slide 8 Design Methodology - Thermodynamic Analysis of the System - Energy & Mass Balance - Heat Transfer Calculations - CFD Simulations - Experimental Data - Then to Mechanical Design and Construction! (we re in the last two stages, the project will be operated in Jülich in July 2015)
www.dlr.de Slide 9 Previous work by General Atomics Not applicable to our work: - Massive heat fluxes (~1 to 0.6 MW/m 2 ) - High Helium Temperatures (700 900 C) - High Pressures (1-8 MPa)
www.dlr.de Slide 10 Thermodynamics of the system: How does H 2 SO 4 behave at high temperatures? Acid Boiling Boiler Operating Temperatures 20 to 400 Centigrade Water boiling SO 3 formation in the gas phase
www.dlr.de Slide 11 Physical Data & Energy Balance HO, T 330 C T 2 f T S L S S L S Q Q H2SO4 H 2 O Q ( l) H2 O Q ( l) H2 O Q (g) H2SO Q 4( l) H2SO Q 4( l) H2SO4(g) ambient 100 C 100 C 100 C 330 C 330 C f Cp 2.43 1, 430 0.001 kj kg K kg m Pa s Sequence: 1) Heat the solution 2) Boil the water 3) Heat the acid 4) Boil the acid 5) Superheat the vapours 3 Temperature 350 300 250 200 150 100 50 0 Temperature vs. Heat input Heat Input Stages Needed: >30 kw in ideal scenario Reality: 56 kw including insulation losses, non homogeneity, safety factor
www.dlr.de Slide 12 Heat Transfer Media: Alumina Jacket - 4 tubes of 88mm Ø 2mm thick SiC in contact with ceramic heaters. - Packed with a SiSiC foam of 0.87 porosity, bulk conductivity of 80 W/m 2. - Surface area of >550 m 2 /m 3. - Mass flow: 0.0057 kg/sec acid
www.dlr.de Slide 13 Heat Transfer Enhancement Principle Increased heat transfer surface Optimized heat flow in radial direction (relevant to our conditions) Ceramic Heater
www.dlr.de Slide 14 FLUENT calculations in Post Boiling Front (3D ss dp) T ( ) t (0, t) T s Velocity Profile (2D axisymmetric dp) ( ) ( ) S
www.dlr.de Slide 15 Temperature profiling Boiling Front + Temp. Profile On yz plane Temperature vs. Boiler lenght (3D ss dp)
www.dlr.de Slide 16 Conclusions - A state of the art 30 kw joule-boosted ceramic HX was designed and will be comissioned within the next couple of months, after detailed system characterisation both experimentally and mathematically - Electrically operated (30 kw of power, for little less than EUR 2,500) - Material compatibility and solid previous experience with SiC - Scalable via modular configuration - Heat Transfer enhancement via packed ceramic foams - Extremely small in comparison to TEMA-designed heat exchangers with superheated steam service - Safety included as a priority in the design - Most important: could be used with virtually any other chemical and in a wide range of conditions, or for use with catalytic reaction processes.
www.dlr.de Slide 17 Acknowledgements
www.dlr.de Slide 18 Questions