Introduction Acoustic to electric power conversion Kees de Blok, Aster Thermoacoustics Pawel Owczarek, Future energy management-University of Wraclow Maurice Francois, Hekyom Brief introduction Thermoacoustic engine Multistage traveling wave themoacoustics High power applications Acoustic to electric conversion (movie) Full scale design Conclusions 23 juni 2014 1 Introduction What is thermoacoustics? •A key enabling energy conversion technology based on "classic" thermodynamic cycles in which compression, displacement and expansion of the gas is controlled by an acoustic wave rather then by pistons and displacers. •Characteristics n n n n n n n n n No mechanical moving parts in the thermodynamic process Maintenance free Simple construction Large freedom of implementation Low noise High efficiency (>40% of the Carnot factor) Large temperature range Scalable from Watt’s to MegaWatt’s Inert gas like helium, argon or even air as working medium 23 juni 2014 2 Introduction What can we do with thermoacoustics? Heat supply at high temperature Converting heat into acoustic energy (= mechanical energy) Þ Heat engine n n n Heat supply at high temperature from arbitrary heat source Onset temperature difference » 30ºC Operating temperature differerence >100ºC TAEC Acoustic output power Heat sink at a low temperature Converting the acoustic output power into electricity n Linear alternator (loudspeaker) n Bi-directional turbine Heat sink at a high temperature Converting acoustic energy into a temperature lift (By reversal of the thermodynamic cycle) Þ Heat pump or refrigerator n n Acoustic power Temperature lift: > 80ºC Temperature range: -200ºC up to 250ºC TAEC Heat taken at low temperature 23 juni 2014 3 Introduction Thermoacoustic Heat Engine Typical operating characteristics •Low onset and operation temperature n No wear and mechanical friction •Large temperature range n No phase change working gas Thermoacoustic cooler 23 juni 2014 Thermoacoustic heat pump 4 Thermoacoustic engine Basic geometry of a thermoacoustic engine n Above onset temperature acoustic power gain exceeds losses and oscillation start n Oscilllation frequency is set by (acoustic) length of the feedback tube n At increasing input temperature (above onset) part of the acoustic loop power can be extracted as net output power Acoustic output power can be converted to n electricity … n or drive a termoacoustic heat pump 23 juni 2014 5 Multi-stage traveling wave thermoacoustics Utilizing low and medium temperature heat sources •Waste heat •Solar (vacuum tube collectors) •Geothermal •……. •. Multi stage traveling wave thermoacoustic engine n Increase of acoustic power gain proportional with 4-stage thermoacoustic traveling wave engine (THATEA project) number of stages n Less acoustic loop power relative to the net acoustic output power (more compact design) n Oscillation frequency set by the acoustic length n Onset temperature difference < 30°C n Operating temperature difference > 100 °C 23 juni 2014 6 High power applications 100 kW T Thermo Acoustic Power generator Thermoacoustic power (TAP) Conversion of industrial waste heat into electricity •SBIR project phase2 nDesign and built of a TAP converting 100 kW waste heat at 160ºC into 10 kW electricity nLocation: Smurfit Kappa Solid Board, Nieuweschans(Gr) Other (industrial) applications •Heat transformer 3m nUpgrade waste heat above the pinch •Gas liquefaction nStorage and transport of LNG 23 juni 2014 7 High power applications Conclusions of the TAP project in 2011 •Thermoacoustic energy conversion itself can be scaled up in power succesfully •Upscaling toward high power applications is blocked by the linear alternators Practical issues n Piston stroke limited by stroke of the springs n Size and weigth of moving mass more than proportional with power (Larger TA system Þ lower frequency Þ less induction) n Sensitive for overload n Vibration Economic issues n Cost > 3000 € / kW n No mass production n Per kW electrictricity relativelly large amont of magnetic materiaal n Availability and cost of raw materials for strong magnets (neodynium) 23 juni 2014 8 The TAP Linear alternator Acoustic to electric conversion Acoustic wave motion 1) Using the acoustic wave pressure component Convert periodic pressure variation into periodic bi-directional linear motion (piston, membrane) Pressure amplitude Mean pressure n Linear alternators n MHD n Piezo electric effect 2) Using the acoustic wave velocity component 0 0 Convert periodic bi-directional velocity into unidirectional rotation n Bi-directional turbine Gas displacement amplitude 23 juni 2014 9 Acoustic to electric conversion Bi-directional turbines Guide vanes Guide vanes Rotation is independent of flow direction Rotor Know embodiments •Lift based turbines Wells turbine Darrieus rotor (wind turbine) •Impulse based turbines Savonious rotor (ventilation) Axial impulse turbine Radial impulse turbine Existing technology used for oscillating water column (OWC) wave power plants (30-500kWe) Bron: Limpet 500 23 juni 2014 10 Acoustic to electric conversion Axiale impuls turbine Acoustic experiments on scale models • Radial impuls turbine (100mmÆ) • Axial impuls turbine (72mmÆ) Both manufactured in SLA-SMS 3-D printing. brushless DC elektromotor used as generator Observations: • Radial turbine n • Relation rotor efficency and frequency Higher torque at lower rotational speed Axiale turbine n Lower torque at higher rotational speed • Better efficiency for AC flow • Output power and efficiency observed to be hardly dependent of acoustic frequency 23 juni 2014 11 Acoustic to electric conversion Scaling experiment at the 100 kW TAP SKSB Radiale impuls turbine voor de TAP (Drotor =300 mm) Linear alternator replaced by radial bi-directional inpulse turbine •Measured rotor efficiency of 75% at 0.8MPa •Efficiency proportional with fluid density Radiale impuls turbine in position in engine stage #2 23 juni 2014 12 Acoustic to electric conversion Test axial turbines in the 100kW TAP Turbine in preparaton Manufactured by AGAN italy Axial turbine : Rotor diameter: 200mm Rotational speed : 2700rpm Power: 2 kW Generator : Outer runner permanent magnet motor Turbine position inside the TAP Aim of this experiment •Validate turbine model •Acoustic impedance •Avoid radial induced streaming •Confirm feasible turbine effciency •Starting point for manufacturing and turbine optimization Efficiency in air at 0.8MPa of this axial bi-directional turbine is measured to be 80% 23 juni 2014 13 Full scale design 1MW T • Basic thermoacoustic engine stage High temperature heat exchanger Regenerator Low temperature heat exchanger Bi-directional turbine + generator Acoustic power out Low temperature cooling circuit 15-40°C (Waste) heat in (140-250°C) Acoustic power in Electricity out 23 juni 2014 14 Full scale design 1MW T Looped heat-pipe circuits Flue gas heat exchanger 2m Roof section or mounting platform Heat sink terminals 23 juni 2014 15 Conclusions •The TAP concept is theroretical and experimentally validated and recognized as a compatitive technology for converting waste heat into electricity. •Upscaling in power toward industrial levels however was blocked by the increasing cost, mass and complexity of linear alternators •As a practical and economic viable alternative for linear alternators at increasing power levels the concept of a bi-directional turbine, converting acoustic power into rotation and from there into electricity, is introduced and tested succesfully •Rotor efficiency defined as shaft output power over acoustic input power is a function of fluid density, and is measured to raise from about 30% at atmospheric pressure up to 80% for air at 0.8MPa. •As a major achievement, the initial limitation in upscaling the thermal and electric power levels is abrogated, paving the way for full scale application of thermoacoustic waste heat recovery in industry up to MW scale 23 juni 2014 16
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