Direct Steam Generation in Linear Receivers: overview and key issues

Transcription

1 SFERA-2 Summer School (Almería 9-10 June, 2016) HEAT TRANSFER FLUIDS FOR CONCENTRATING SOLAR THERMAL SYSTEMS Direct Steam Generation in Linear Receivers: overview and key issues Eduardo Zarza Moya CIEMAT-Plataforma Solar de Almería

2 Direct Steam Generation in Linear Receivers Contents Introduction Advantages and disadvantages of the DSG process Thermo-hydraulic issues Current status of the DSG technology

3 Direct Steam Generation in Linear Receivers Contents Introduction Advantages and disadvantages of the DSG process Thermo-hydraulic issues Current status of the DSG technology

4 Steam Production with Linear Solar Concentrators Steam production with linear solar concentrators Steam P1 P1 >> P2 P2 Solar Field T1 Steam Generator T2 T1 T K Process Solar Field Expansion valve Water recirculation Flash Tank Process Proceso Industrial Feed pump Oil expansion tank Liquid water Feedwater pump a) using a Heat Transfer Fluid b) Flashing

5 Steam Production with Linear Solar Concentrators Steam Solar Field Process Liquid water Feed water pump c) with Direct Steam Generation (DSG)

6 Direct Steam Generation Different sections in the rows of a DSG solar field m Solar Radiation L1 L2 L3 Preheating Evaporation Sperheating To Po

7 Steam Production with Linear Solar Concentrators Solar Field Feed water pump Steam Liquid water Process c) with Direct Steam Generation (DSG) Superficial liquid velocity / (m/s) ,1 0,01 0,001 0,01 Two-phase Flow Pattern Map for an horizontal pipe Bubbly Intermittent Stratified 0, Superficial steam velocity / (m/s) v l = m (1-x) / (A tube ρ l ) vg = (m x) / (Atube ρ g ) Annular 100

8 Direct Steam Generation in Linear Receivers Two dif ferent Bub b ly confi gu rations A A Disperse-Bubbly Flow Section A-A A A Foggy-Bubbly Flow Sección A-A A Section A-A

9 Direct Steam Generation in Linear Receivers Two dif ferent Intermittent confi gu rations A A Plug-Intermittent Flow Section A-A A A Slow-Intermittent Flow Section A-A

10 Direct Steam Generation in Linear Receivers Solar Field Feed water pump Steam Liquid water Process c) with Direct Steam Generation (DSG) Superficial liquid velocity / (m/s) ,1 0,01 0,001 0,01 Two-phase Flow Pattern Map for an horizontal pipe Bubbly Intermittent Estratified 0, Superficial steam velocity / (m/s) v l = m (1-x) / (A tubo ρ l ) vg = (m x) / (Atubo ρ g ) Annular 100

11 Direct Steam Generation in Linear Receivers Contents Introduction Advantages and disadvantages of the DSG process Thermo-hydraulic issues Current status of the DSG technology

12 The Direct Steam Generation Process Comparison between the DSG and the HTF (oil) technologies Advantages of the DSG technology: Smaller environmental risks because oil is replaced by water Higher steam temperature (maximum steam temperature with oil = 385ºC)

13 Typical HTF Solar Thermal Power Plant Thermal oils currently available have a thermal limits of 398ºC. There is a significant degradation above 400ºC 395 ºC Oil Superheated Steam (104bar/380ºC) Steam turbine Solar Field Steam generator Deaerator Condenser G G 295 ºC Oil Reheated steam 17bar/371ºC Reheater Oil expansion vessel Scheme of a typical HTF plant with parabolic trough collectors Preheater

14 The Direct Steam Generation Process Comparison between the DSG and the HTF (oil) technologies Advantages of the DSG technology: Smaller environmental risks because oil is replaced by water Higher steam temperature (maximum steam temperature with oil = 385ºC) The overall plant configuration is more simple

15 Direct Steam Generation versus HTF Technology Simplified Scheme of typical HTF and DSG solar thermal power plants Steam at104 bar/371 ºC Oil at 390 ºC Superheater Steam turbine Solar Field Oil Circuit Condenser Steam Generator GDV Plant Steam at 104 bar/400 ºC Steam turbine Auxiliary heater Oil at 295 ºC Degasifier Reheater Oil expansion tank Auxiliary boiler HTF Plant Degasifier Condenser Liquid water at 114 bar / 120 ºC

16 The Direct Steam Generation Process Comparison between the DSG and the HTF (oil) technologies Advantages of the DSG technology: Smaller environmental risks because oil is replaced by water Higher steam temperature (maximum steam temperature with oil = 385ºC) The overall plant configuration is more simple Lower investment and O&M costs and higher plant efficiency

17 Lower LCOE of DSG versus HTF Plants A comparative study of HTF and DSG performed by DLR for a 100 MWe plant with a 9-hour TES has shown that: Scaling-up beyond a certain limit is not recommended for DSG plants (two 50 MWe plants together have a lower LEC than a single 100 MWe plant) The size and type of TES has a great impact on the LEC LEC changes by different DSG options compared to oil reference (TES = storage, OT = once-through, PCM = PCM storage).

18 The Direct Steam Generation Process Comparison between the DSG and the HTF (oil) technologies Advantages of the DSG technology: Smaller environmental risks because oil is replaced by water Higher steam temperature (maximum steam temperature with oil = 385ºC) The overall plant configuration is more simple Lower investment and O&M costs and higher plant efficiency Disadvantages of the DSG technology: Solar field control under solar radiation transients is more complex

19 The Direct Steam Generation Process Influence of solar radiation transients on feed-water flow distribution Radiación solar m L1 L2 L3 T P Radiación solar m L1' L2' Radiación solar L3' T < T P > P m 1" L L 2" L3" T > T P < P

20 The Direct Steam Generation Process Comparison between the DSG and the HTF (oil) technologies Advantages of the DSG technology: Smaller environmental risks because oil is replaced by water Higher steam temperature (maximum steam temperature with oil = 385ºC) The overall plant configuration is more simple Lower investment and O&M costs and higher plant efficiency Disadvantages of the DSG technology: Solar field control under solar radiation transients is more complex Instability of the two-phase flow inside the receiver tubes

21 The Direct Steam Generation Process Comparison between the DSG and the HTF (oil) technologies The Ledinegg instability Pressure drop versus mass flow in a row of linear collectors with DSG at constant intel temperature, outlet pressure and heat gain Pressure drop, P P Steam only P P ( P) m ) < 0 E d =cte Characteristic curve of a centrifugal pump Liquid only Mass flow, m

22 The Direct Steam Generation Process Comparison between the DSG and the HTF (oil) technologies Advantages of the DSG technology: Smaller environmental risks because oil is replaced by water Higher steam temperature (maximum steam temperature with oil = 385ºC) The overall plant configuration is more simple Lower investment and O&M costs and higher plant efficiency Disadvantages of the DSG technology: Solar field control under solar radiation transients Instability of the two-phase flow inside the receiver tubes Temperature gradients at the receiver pipes

23 Direct Steam Generation in Parabolic Troughs Uneven heat transfer at the steel absorber pipe h liquid Receiver pipe Parabolic trough concentrator h liquid

24 Direct Steam Generation Uneven heat transfer at the steel absorber pipe Temperature gradients in the steel absorber pipes

25 DSG with Linear Solar Concentrators DSG-related projects and studies since 1980 Theoretical studies by SERI (1982) The ATS (Advance Trough System) project by LUZ,( ) Experiments by ZSW at the HIPRESS test facility ( ) The GUDE project experiments at Erlangen ( ) The project PRODISS The project ARDISS ( ) R+D activities at UNAM (Mexico, up to date) The DISS project ( ) The INDITEP project ( ) The RealDISS project ( ) The DUKE project ( )

26 Direct Steam Generation in Linear Receivers Contents Introduction Advantages and disadvantages of the DSG process Thermo-hydraulic issues Current status of the DSG technology

27 DSG Thermo-hydraulic Issues Assessment of pressure drop, P, in pipes with two-phase flow Experimental results gathered at the PSA DISS test facility within the pressure range 3-10 MPa have shown that correlation proposed by Friedel in 1975¹ provides pressure drop values with an acceptable accuracy. The basic concept of Friedel s model is the application of a 2-phase-multiplier, R, to the single phase pressure drop that would occur if the total mass flow would pass as liquid through the pipe, Pl : P2F = R Pl Pl = v = l f l 2 ρ v m total ρ l x (d/2) 2 Re l = v l x ρ l x d /µ l l 2 l L d (f l = Moody s friction factor assuming that total mass flow is liquid) m total d µ l ρ l v l = total water mass flow (liquid+steam) = inner diameter of pipe = dynamic viscosity of liquid phase = density of liquid phase = fluid velocity if total mass flow is in liquid phase ¹ Friedel, L. Modellgesetz für den Reibungsdruckverlust in der Zweiphasenströmug. VDI-Forschungsheft 572, 1975

28 DSG Thermo-hydraulic Issues Moody s diagram (friction factor)

29 Assessment of pressure drop, P, in pipes with two-phase flow Once the single phase pressure drop that would occur if the total mass flow would pass as liquid through the pipe has been calculated, the 2-phase-multiplier, R, has to be calculated also. For this, the auxiliary parameter A, and the Froude, Fr l, and Weber, We l, numbers must be previously calculated: R l 0.8 g 0.22 g = A x (1 x) ( ) ( ) (1 ) Frl Wel ρ g µ l µ l A = (1 x) x = steam quality σ = surface tension between water and steam = dynamic viscosity of steam phase = density of steam phase µ g ρ g g = acceleration by gravity = 9.81 m/s 2 f g 2 + x DSG Thermo-hydraulic Issues 2 ρ l ( f g ρ ( f g / 4) / 4) = Moody s friction factor assuming that total mass flow is steam l ρ Fr l = µ 2 16 qm 2 π ρ g d 2 l µ 5 i We l = 2 3 π di 2 16 qm σ ρ l

30 DSG Thermo-hydraulic Issues Assessment of pressure drop, P, in two-phase flow pipes Practical consideration concerning Friedel s correlation: Since for high steam quality values, Friedel s correlation can deliver pressure drop values that are higher than the pressure drop when all the mass flow is in steam phase, Pg, a limit must be imposed to the values obtained with Friedel s correlation for high steam quality values: P2F Pg

31 Assessment of pressure drop, P, in bends with two-phase flow Experimental results gathered at the PSA DISS test facility within the pressure range 3-10 MPa have shown that correlation proposed by Chisholm in 1980¹ provides pressure drop values with an acceptable accuracy. The basic concept of Chisholm s model is the application of a 2-phase-multiplier, R, to the single phase pressure drop that would occur if only the liquid mass flow would pass through the pipe, Pl,only : P2F = F Pl,only Pl,only = 1+ ( ρl / ρ g F = DSG Thermo-hydraulic Issues 2 2 qml ( 8 π ) ζ d 4 i ρ 1) ( B x (1 x) + x 2 (1 x) 2,2 B = 1+ ζ (2 + R / d i ) ¹ Chisholm, D. Two-phase flow in bends, International Journal of Multiphase Flow, Vol. 6, 1980, pp l 2 ) ζ = the pressure loss coefficient usually known as a function from the ratio between radius, R, of the bend and its inner diameter, d i. For standard 2,5 90º elbows with R/d =3 ζ = 0.17

32 DSG Thermo-hydraulic Issues Assessment of pressure drop, P, in bends with two-phase flow Practical consideration concerning Chisholm s correlation: For high steam quality values (X>0.85), Chisholm s correlation can deliver pressure drop values that are too low. To overcome this problem for x >0.85 it is recommended to use the pressure drop value p ' according to the following correlation: Where: ' p = p 2 F (1 x) + p g x p 2 F = Pressure drop calculated according to Chislhom s correlation p g = Pressure drop assuming that the total mass flow is in steam phase

33 Direct Steam Generation in Linear Receivers Contents Introduction Advantages and disadvantages of the DSG process Thermo-hydraulic issues Current status of the DSG technology

34 Current Status of DSG with Linear Collectors Curent Status Technical feasibility of the DSG process in linear solar concentrators has been proven. There are several DSG solar thermal power plants in operation

35 Current Status of DSG with Linear Collectors Plant TSE-1, Thailand 5 MWe 34 bar, 340 C Technology by Solarlite

36 Current Status of DSG with Linear Collectors Plant Puerto Errado-2, Spain 30 MWe 55 bar, 270 C Technology by Novatec&ABB

37 Current Status of DSG with Linear Collectors Curent Status Technical feasibility of the DSG process in linear solar concentrators has been proven. There are several DSG solar thermal power plants in operation Accurate simulation&design tools for DSG solar fields have been developed

38 Current Status of DSG with Linear Collectors Comparison between experimental and simulation results for the PSA DISS test facility Temperature / (ºC) Pressure (experimental data) Pressure (simulation results) Temperature (experimental data) Temperature (simulation results) Collector # ,0 6,8 6,6 6,4 6,2 6,0 5,8 5,6 5,4 5,2 5,0 Pressure / (MPa) Date: 17/07/2001 Temperature / (ºC) Pressure (experimental data) Pressure (simulated data) Fluid temperature(experimental data) Fluid temperature (simulated data) Collector # Test day at 10 MPa ,0 10,8 10,6 10,4 10,2 10,0 9,8 9,6 9,4 9,2 9,0 Pressure / (MPa) Date 05/04/2001

39 Current Status of DSG with Linear Collectors Curent Status Technical feasibility of the DSG process in linear solar concentrators has been proven. There are several DSG solar thermal power plants in operation Accurate simulation&design tools for DSG solar fields have been developed Ball-joints for water/steam at 100bar/500ºC have been successfully tested. The best configuration for commercial DSG solar fields is a mixture of injection and recirculation. This configuration has been experimentally evaluated at PSA

40 Current Status of DSG with Linear Collectors Scheme of a DSG row of collectors with Recirculation Preheating + Evaporation Steam superheating Feed water Water/steam separator Water recirculation ( 20%) Water inyection ( 7%)

41 Current Status of DSG with Linear Collectors Curent Status Technical feasibility of the DSG process in linear solar concentrators has been proven. There are several DSG solar thermal power plants in operation Accurate simulation&design tools for DSG solar fields have been developed Ball-joints for water/steam at 100bar/500ºC have been successfully tested. The best configuration for commercial DSG solar fields is a mixture of injection and recirculation. This configuration has been experimentally evaluated at PSA Compact and cost-effective water/steam separators have been developed

42 Current Status of DSG with Linear Collectors Water/steam separators for DSG Classic water/steam separator Compact water/steam separator

43 Current Status of DSG with Linear Collectors Curent Status Technical feasibility of the DSG process in linear solar concentrators has been proven. There are several DSG solar thermal power plants in operation Accurate simulation&design tools for DSG solar fields have been developed Ball-joints for water/steam at 100bar/500ºC have been successfully tested. The best configuration for commercial DSG solar fields is a mixture of injection and recirculation. This configuration has been experimentally evaluated at PSA Compact and cost-effective water/steam separators have been developed A cost-effective thermal energy storage technology for DSG still to be developed Technical feasibility of the Once-Through option must be fully investigated

44 Current Status of DSG with Linear Collectors Upgraded PSA DISS Facility for Once-Through mode (The DUKE project)

45 Current Status of DSG with Linear Collectors Curent Status (II) Liquid water stratification is not so dangerous as initially assumed, because the maximum temperature difference in a cross section of the receiver tubes is always <70ºC within the usual range of operational parameters

46 Current Status of DSG with Linear Collectors Circumferential heat conduction in the DSG receiver tubes Receiver tube R 1 R 2 T T 2 T 1 Receiver tube cross section Parabolic trough concentrator

47 SFERA-2 Summer School (Almería 9-10 June, 2016) HEAT TRANSFER FLUIDS FOR CONCENTRATING SOLAR THERMAL SYSTEMS Direct Steam Generation in Linear Receivers: overview and key issues End of the Presentation Thank you very much for your attention!! Eduardo Zarza Moya CIEMAT-Plataforma Solar de Almería