Thermal Energy Storage : Methods and Materials

Transcription

1 Thermal Energy Storage : Methods and Materials Dr. P. Muthukumar Associate Professor Department of Mechanical Engineering Indian Institute of Technology Guwahati Guwahati , INDIA pmkumar@iitg.ernet.in 1

2 About IITG Located in the Gateway of North Eastern Part of India Started 1995, established during Beautiful campus among other IITS. Located on the river bank on Brahmaputra. Campus is surrounded by many Hills and Lakes. Campus size about 700 acr. 8 Engg and 4 Science Departments About 6000 students, 300 faculty and 500 supporting staffs Over million migratory birds, wild cats, etc. IIT M 2 Dept. of Mechanical Engineering, Indian Institute of Technology Guwahati

3 Dept. of Mechanical Engineering, Indian Institute of Technology Guwahati 3

4 Out line of Presentation TES concepts and methods Types TES techniques Steam accumulator Reversible chemical heat storage (Metal hydride based thermal energy storage) World wide status of TES systems Proposed TES system for Solar PAN IIT 4 Dept. of Mechanical Engineering, Indian Institute of Technology Guwahati

5 Thermal Storage Systems Thermal energy storage (TES) systems correct the mismatch between the supply and demand of energy. Types : Sensible, Latent and Reversible Chemical Storage Benefits Increase system reliability: To reduce the peaks of energy generation Increase generation capacity: The excess generation available during low demand periods can be used to charge a TES in order to increase the effective generation capacity during high-demand periods. The result is a higher load factor for the plants, helping to generate energy in a stable way. Reduction of costs of generation: Seasonal demands can be matched with the help of TES systems that operate synergistically. 5

6 Sensible Heat Storage Materials Essential requirements o High thermal capacity (ρc p ) o High melting point (large operating temperature) o High thermal conductivity o Stability o Low cost Commonly used sensible storage materials (Solid) Storage medium Operating temperature, C Heat capacity, kj/kg-k [k] Reinforced concrete [1.5] NaCl (solid) [7] Cast iron [37] Cast steel [40] Silica fire bricks [1.5] Magnesia fire bricks [5] Low cost High thermal conductivity and volumetric storage capacity

7 Molten Salts (Sensible liquid Heat Storage Materials) Best: 60% NaNO % KNO 3 Solar Salt : Freezing point 220 C Source: Hoshi et al., Solar Energy 79; , A t H t t f fl id f l t t t t o Acts as Heat transfer fluid from solar concentrator to steam generator and also heat storage medium o Heat storage : Active storage

8 Latent Heat Storage Materials Requirements # High heat of fusion # High thermal conductivity #Low cost MgCl 2 /KCl/NaCl; KOH; KNO 3 ;KNO 3 /KCl; NaNO 3 Yet to be explored Suffer from low thermal conductivity Integration of graphite enhance k up to 10 W/mK. Source: Hoshi et al., Solar Energy 79; , Features: High energy density ; Temperature ranges are flexible, Optimal utilization of the storage materials

9 Proposed phase change materials (PCM) for cascade heat storage in the temperature range up to 380 C are NaNO 3, KNO 3 / KNO 3,KOHandMgCl 2 is proposed. A schematic of the cascade latent heat storage 9

10 Techniques of Thermal Storage Active Heat storage : o o o o Characterized by forced convection heat transfer. Heat storage medium circulates in the solar field High heat transfer rate, more effective But, high cost; freezing in solar panels Direct Active storage : Heat transfer fluid itself serves as storage (Hot and cold tank) Indirect Active storage : Heat transfer fluid which is circulated in the solar panel is different from the one used in storage. i.e. heat transfer fluid transfer heat to secondary fluid, which acts as storage Passive Heat Storage : Storage medium is fixed. Heat transfer fluid passes through h storage medium only during charging and discharging time. e.g. solid storage and PCM.

11 Direct active Two Tanks Thermal Storage System o Hot and cold fluids are stored separately o No additional heat exchanger o Fast heat transfer ~450 C ~450 C o Freezing of salt ( C) o Auxiliary heater is required to maintain the temperature 60% NaNO % KNO 3 above freezing during night time and adverse weather conditions Schematic of Solar Thermal Power Plant with direct active two tanks thermal storage system (Solar Tres, Sevilla; source: Gil et al. (2010), Renewable and Sustainable Energy Reviews 14; )

12 Active indirect single tank thermal storage system o Hot and cold fluids are stored in the same tank o Hot and cold fluids are separated because of the stratification effect o Controlled charging and discharging are necessary to maintain the stratification o Filler material such as quartzite and silica sand used to help thermocline 12 Gil et al. (2010), Renewable and Sustainable Energy Reviews 14; 31-35

13 STEAM ACCUMULATORS Steam accumulators are specially suited to meet the requirements for buffer storage in solar steam systems, providing saturated steam at pressures up to 100 bar. Direct steam generation (DSG) in parabolic troughts with integrated steam accumulator (Direct heat storage) DSG with integrated steam accumulator also used as phase separator W.D. Steinmann and M.Eck, Solar Energy 80 (2006)

14 STEAM ACCUMULATORS Steam accumulators provide saturated steam. If superheated steam is needed, a second storage system must be connected to the exit of the steam accumulator During the discharge there is a drop in the pressure of the steam. To avoid this, the integration of PCM into the storage vessel to replace partly the liquid water Saturated Steam Steam accumulator and sensible Steam accumulator with integrated t storage material latent heat storage material W.D. Steinmann and M.Eck, Solar Energy 80 (2006)

15 Ammonia-based solar thermochemical energy storage system 2NH 3 + Heat N 2 +3H 2 (Charging mode) N 2 +3H 2 2NH 3 + Heat (Discharging i mode) Operating temperature: C Operating pressure : Mpa 15 H. Kreetz and K. Lovegrove, Solar Energy Vol. 73, No. 3, pp , 2002

16 Reversible Chemical Heat Storage: Metal Hydride Intermetallic compounds formed alloying of different metals by ball milling or melting. Absorption (Exothermic) Intermetallic + H Metal Hydride + Heat Desorption (Endothermic) 2 2 Intermetallic + H Metal Hydride + Heat Metal Hydride Applications kj/mole H 2 Absorption Desorption Hydrogen Storage Hydrogen Compressor H 2 Refrigerator Heat pump Thermal Energy Storage Heat transformer Heat Heat Heat driven mass transfer phenomenon

17 Metal Hydride Based Heat Storage o High storage capacity up to 2.2 MJ/kg of hydride o No thermal insulation o Long term storage o Easy regeneration H t h o High exergy efficiency Heat exchange MH Reactor Alloy ΔH (kj/mol. H 2 ) P d V 1 Mg+2% -74 V P 2 r Ni P s MgNi Mg H 2 Supply 17

18 Schematic of a Metal Hydride Reactor 18

19 Test Setup of Heat Storage Device

20 Effect of supply pressure on the amount of heat stored 4 30 bar Amount of heat stored (kj J/kg) bar 20 bar 15 bar 10 bar Mg + 30%MmNi 4 T a = 150 C m = 280 g Time (min) 20

21 Effect of supply pressure on thermal energy storage coefficient 0.8 Thermal en nergy stora age coeffic cient (TESC C) T a = 150 o C T a = 140 o C T a = 130 o C 0.4 T = o a 120 C 0.3 Mg + 30%MmNi 4 m = 280 g Supply pressure (bar) 21

22 Schematic of a Pre-industrial Sacle Metal Hydride Reactor for Heat Storage Application i 22

23 4 450 Hydogen stora age capacity (w wt%) Hydogen storag ge capacity (wt t%) Mg 2 Ni T a = 250 C m a = kg P s 20 bar 15 bar 10 bar 20 bar 15 bar 10 bar Absorption time (s) Hydrogen storage capacity Average bed temperature P s =20 bar 15 bar 10 bar P s =20 bar 15 bar 10 bar C) Av verage bed te emperature( Average bed temperature e( C) Effect of supply pressure on hydrogen storage capacity and average bed temperature (T a = 250 C) Carried out at IIT Madras, 2004 Effect of supply pressure on hydrogen storage capacity and average bed temperature (T a = 300 C) Mg 2 Ni 100 Hydrogen storage capacity T a = 300 C Average bed temperature (Muthukumar et al., J. Alloys and m a = 0375kg Compd., 452, 2008) Absorption time(s) 150 0

24 r (MJ/kg of allo oy) Q r bar 3 bar 4 bar Effects of heat release temperature and supply pressure on heat stored (Q r ) m r = 1.5 T h = 650 K T a = 298 K Heat release temperature (K) Qr vs Tr for Mg2+%Ni at different supply pressures l o y) (M J/kg of all Qr ( bar 3 bar 4 bar m r = 1.5 T h = 650 K T a = 298 K Heat release temperature (K) Qr vs Tr for MgNi at different supply pressures Qr (MJ/kg of alloy) bar 3 bar 4 bar m r = 1.5 T h = 650 K T a = 298 K Heat release temperature (K) 24 Qr Vs Tr for Mg at different supply pressures

25 Comparison of performances at 3 bar supply pressure N (mo oles/kg of alloy y/cycle) Mg Mg + 2% Ni MgNi lloy) (M J/kg of a 2.5 m r = 1.5 T h = 650 K T a = 298 K P S = 3 bar Heat release temperature (K) Qin Mg Mg2%Ni MgNi m r = 1.5 T h = 650 K T a = 298 K P S = 3 bar Heat release temperature (K) No Of hydrogen moles transferred Vs Tr Heat input Vs heat release temperature J/kg of alloy y) Qr (M Mg Mg+2%Ni Mg2Ni m r = 1.5 T h = 650 K T a = 298 K P S = 3 bar Heat release temperature (K) 25 Heat release vs Heat release temperature

26 Operating temperature ranges of different metal hydrides Material Usable temperature range ( o C) Mg±Ni/Mg g 2 NiH 4 250±350 Mg/MgH 2 +2 wt% Ni 290±420 Mg/MgH 2 350±450 Mg/MgH wt% Fe 350±450 Mg±Fe/Mg 2 FeH 6 450±550 Mg±Co/Mg 2 CoH 5 450±550 26

27 Storage characterictics of different metal hydrides Properties Mg/MgH 2 +2 wt%ni Mg/ MgH 2 Mg-Fe/ Mg 2 FeH 6 Mg- Co/Mg 6 CoH 1 Mg- Co/Mg 2 CoH 5 1 Enthalpy, kj/mol Filling Density, g/cm 3 Capacity, wt% Energy to weight, kj/kg Energy to volume, kj/dm Storage properties of Mg; (25 40) µm, Temperature ( o C) Absorption Desorption Source: pressure (bar) pressure (bar) Bogdanovic et al., J Alloys and Compounds,282; ,

28 Operational solar thermal power station in the world Country Location Plant Features/Technology capacity Applied USA Mojave Desert 354 parabolic trough California Spain Sevilla 150 parabolic trough Spain Granada 100 parabolic trough USA Boulder City, Nevada 64 parabolic trough Spain Puertollano, Ciudad 50 parabolic trough Real Spain Badajoz 50 parabolic trough Spain Torre de Miguel 50 parabolic trough Sesmero (Badajoz) Spain Alvarado (Badajoz) 50 parabolic trough Spain Sevilla 20 solar power tower Iran Yazd 17 parabolic trough Spain Sevilla 11 solar power tower USA Bakersfield, California 5 fresnel reflector USA Lancaster, California 5 solar power tower Italy near Siracusa, Sicily 5 parabolic trough Australia New South Wales 2 fresnel reflector USA Peoria, Arizona 1.5 dish stirling Germany Jülich 1.5 solar power tower Spain Murcia 1.4 fresnel reflector USA Red RockAi Arizona 1 parabolic trough USA Hawaii 2 parabolic trough Iran Shiraz 0.25 CSP

29 Summary of different thermal storage technologies and materials used in the solar power plant (Trough plant) Storage concept Experiences/ projects Passive system LS3-SSPS-PSA, Spain Active Indirect system (Two- Tanks) Active Indirect system (Two- Tanks) Active Indirect system (Two- Tanks) n.a. ANDASOL I- SENER/Cobra, Guadix, Spain ANDASOL II- SENER/Cobra, Guadix, Spain EXTRESOL I- SENER/Cobra SOLANA, Phoenix, AR, USA Year Thermal Total Operating HTF capacity capacity temperatu (MWh th ) (MWe) re ( C) TES media n.a. n.a. Mineral Hightemperatur Oil e concrete n.a Steam Molten salts (60% NaNO n.a % KNO 3 ) 2009 n.a. n.a. n.a. Steam Molten salts 2010 (12 h) 50 n.a. Synthet Molten ic Oil salts 2011 n.a. 280 n.a. n.a. n.a. Source: Medrano et al., Renewable and Sustainable Energy Reviews 14; 56-72, 2010.

30 Summary of different thermal storage technologies and materials used in the solar power plant (Central receiver plant) Active Indirect system (Two- Tanks) Active Indirect system (Two- Tanks) Active Direct system (Two- CESA I-PSA, Spain CERS-SSPS PSA, Spain Steam Molten salts 1982 n.a. 1 n.a. Steam Molten salts (nitrate) Steam (100 bar) Molten salts n.a. Molten salt Molten salt (liquid sodium) (sodium) THEMIS, Molten salt (High Molten salt Targasonne, technology) (High Tanks) France technology) Active Direct system PS10- Abengoa, (50 min) 11 n.a. Steam Steam ceramic (Direct steam Sevilla, Spain generation) Active Direct system (Direct steam generation) Active Direct system (Two- Tanks) PS20- Abengoa, Sevilla, Spain SOLAR TRES-PSA, Spain (SENER) 2007 n.a. 20 n.a. Steam Steam ceramic (16 h) Molten salts (NaNO 3 + KNO 3 ) Molten salts (NaNO 3 + KNO 3 ) Source: Medrano et al., Renewable and Sustainable Energy Reviews 14; 56-72,

31 Solar PAN IIT : Research Proposal Schematic of proposed 1 MW Solar Thermal Power Plant

32 Objectives of Heat Storage To ensure continuous generation of stream for 8 hrs with 95% reliability and to extend the possibility of steam generation during night time Proposed Heat Storage Capacity Technique Capacity App. Cost (USD) Steam Accumulator 14 GJ 4,20,000 Sensible Heat Storage 1 GJ 1,20,000 Latent Heat Storage 1 GJ 1,80,000 32

33 Proposed Thermal Energy Storage Systems o It is proposed to store the excess energy absorbed during the day time in the form of high pressure water up to 80 bar. The approximate capacity of high pressure steam storage vessel is 150 m 3 andtheestimatedamountofheatstoredintheformof high pressure water is about 14 GJ. o Heat generated from the parabolic solar collector is first stored in the form of sensible heat in the temperature range up to C. This storage module is also used to generate super heated steam. o It is also proposed to store 1 GJ heat in the form of latent heat using phase change materials (PCM) of temperature range up to 400 C. Cascade latent heat storage consists of NaNO 3, KNO 3/ KNO 3, KOH and MgCl 2 is proposed. The use of a cascade of multiple phase change materials (PCM) shall ensure the optimal utilization of the storage material. o Application of metal hydrides as heat storage will be also tested. 33

34 Thanks for your kind attention 34