Applications de l'analyse exergétique pour la conception des systèmes de conversion d'énergie intégrés

Transcription

1 Applications de l'analyse exergétique pour la conception des systèmes de conversion d'énergie intégrés F.Marechal LENI-ISE-STI-EPFL 2005 François Marechal Laboratoire d énergétique industrielle Institut de Génie mécanique Sciences et techniques de l ingénieur Ecole Polytechnique fédérale de Lausanne mailto:francois.marechal@epfl.ch

2 Process system integration Environment Air Energy Water - solvent Energy Conversion Production support Raw materials Processes Energy Products By-products Waste heat Emissions Waste treatment Water Solids 2 3

3 Exergy and process intergation Process unit analysis Analyse the requirements Energy conversion integration Polygeneration and utility integration Evaluate the results 3

4 4 Process description : list of process units francois.marechal@epfl.ch - LENI ISE-STI-EPFL Marsh 2006

5 5 The heat transfer requirement interface Electricity Process unit operation Heat transfer Heat-Temperature Heat at the lowest temp. - LENI ISE-STI-EPFL Marsh 2006 Material streams Material & mechanical conversion Heat transfer Material streams Heat-Temperature Cool at the highest temp.

6 6 Unit operation analysis Water 35 kg/s 80 C Water 35 kg/s 10 C 72 kg/s 60 C Mixing tank 2 kg/s 110 C francois.marechal@epfl.ch - LENI ISE-STI-EPFL Marsh 2006 d E = d Q * (1 T a T ) Ė = Q(1 T a T lm ) T lm = T 1 T 2 ln T 1 T kwth Exergy consumption Steam production 1252 kwe Tank heating 795 kwe

7 7 Analyse unit operation Water 37 kg/s 80 C Water 35 kg/s 10 C 0 kg/s 110 C 60 C 60 C 72 kg/s 60 C Mixing tank francois.marechal@epfl.ch - LENI ISE-STI-EPFL Marsh 2006 Exergy production 512 kwe Exergy consumption 612 kwe

8 7 - LENI ISE-STI-EPFL Marsh 2006 Analyse unit operation Water 37 kg/s 80 C Water 35 kg/s 10 C 0 kg/s 110 C Exergy production 512 kwe 60 C 60 C 72 kg/s 60 C Exergy consumption 612 kwe Mixing tank Heat req. : 5335 kwth Steam production :1252 kwe Tank heating : 795 kwe Heat transfer req. : 100 kwe

9 Process integration Hot & cold composite curves Minimum energy requirement Hot Cold Refrigeration Heat recovery T(K) Cold composite curve Hot composite curve DTmin/ DTmin/ Q(kW) 8

10 Carnot composite curves of a process 1 1-T0/T Hot composite curves Carnot composite curves hot composite hot composite cor Exergy losses corresponding to the DTmin/2 of the hot streams Exergy delivered by the hot streams to the system Exergy losses corresponding to the DTmin/2 of the hot streams Exergy required by the hot streams of the system E 0 Cold Utility Heat recovery Hot Utility -0.2 Refrigeration Q(kW) FM_07/ 2000

11 Carnot composite curves of the process 1 1-T0/T 0.8 Cold composite curves Carnot composite curves cold composite cor. cold composite 0.6 Exergy losses corresponding to the DTmin/2 of the cold streams Exergy required by the cold streams of the system Heat recovery Hot Utility E -0.2 Q(kW) FM_07/ 2000

12 Table 3 Exergy of the hot and cold process composite curves Energy Exergy Exergy Name Total T min corrected Table 4 Hot streams [kw] Ėq hota below T 0 [kw] Ėq hotr Cold streams[kw] Ėq colda below T 0 [kw] Ėq coldr T min losses [kw]

13 Carnot composite curves 12

14 Hot and cold composite 1-T0/T Cold composite curve Hot composite curve + Exergy delivered - Exergy to supply + Cold utility losses + refrigeration exergy requirement Q(kW) + Heat exchange exergy losses - Hot utility requirement FM_07/ 2000

15 Energy conversion integration Grand composite curve Hot utility Cold utility Refrigeration CHP Cycles T(K) Hot Utility : 6854 kw Self sufficient "Pocket" Cold utility : 6948 kw Refrigeration : 1709 kw Ambient temperature Q(kW) 14

16 Carnot Grand composite curve 0.6 Carnot Grand composite Carnot Grand composite curve 600 Exergy requirement Exergy requirement as a function of the temperature 0.5 T(K) 550 (1-T0/T) Q(kW) Exergy (kw, T0 : 298.1K) 15

17 Requirements Table 2 Minimum energy and exergy requirements of the process Energy Exergy Name Heating [kw] Ė heat Cooling [kw] Ė cool Table 3 Refrigeration [kw] Ė frg Balance [kw]

18 Exergy requirement above the pinch Utility composite curve 1-T0/T (T0=298K) Exergy requirement Q(kW) Process composite curve 17

19 Exergy by combustion 1-T0/T (T0=298K) Exergy losses chimney Exergy combustion Exergy requirement Q(kW) Utility composite curve Process composite curve 18

20 Exergy composite Heat exchange losses 1-T0/T (T0=298K) Exergy losses chimney Exergy loss combustion Exergy loss - Heat exchange Exergy requirement Q(kW) Utility composite curve Process composite curve 19

21 Exergy composite -self-sufficient pockets 1-T0/T (T0=298K) Exergy losses chimney Exergy loss combustion Exergy loss - Heat exchange Exergy requirement Q(kW) Utility composite curve Process composite curve Process Exergy 20

22 CHP : define the steam network T(K) T v T c Grand composite curve q c Q(kW) Grand composite curve E = q c T v T c T v T η v T c c ( ) Fuel consumption = 21 A T v ( T η v T c ) c ṁ fuel LHV fuel = Q MER + n CHP i=1 η comb Ė i [1] F. Marechal and B. Kalitventzeff. Identification the optimal pressure levels in steam networks using integrated combined heat and power method. Chemical Engineering Science, 52(17): , 1997.

23 Integration of the energy conversion system Creative engineers? 22

24 Integration of the energy conversion system Technology w with nominal flow Hot/cold streams Tw,i,P in in w,i, ṁ w,i,x w,i q w = ṁ w,i (h in w,i h out w,i) T out w,i,p out w,i, ṁ w,i,x w,i Mechanical power/electricity e w Costs C1 w,c2 w, CI1 w, CI2 w Creative engineers? 22

25 Integration of the energy conversion system Technology w with nominal flow Hot/cold streams Tw,i,P in in w,i, ṁ w,i,x w,i q w = ṁ w,i (h in w,i h out w,i) T out w,i,p out w,i, ṁ w,i,x w,i Mechanical power/electricity e w Costs C1 w,c2 w, CI1 w, CI2 w Creative engineers? Decision variables Level of usage of w f w Buy/use technology w? y w 22

26 MILP formulation nw min R r,y w,f w,e +,E ( w=1 C2 w f w + C el +E + C el E ) t + n w w=1 Subject to : Heat cascade constraints Feasibility Fixed maintenance n w w=1 f w q w,r + n s s=1 C1 w y w + 1 τ ( n w w=1 Q s,r + R r+1 R r =0 (CI1 w y w + CI2 w f w )) R r 0 r =1,..., n r ; R nr+1 = 0; R 1 =0 Operating cost Investment r =1,..., n r E + 0; E 0 Electricity consumption n w w=1 f w e w + E + E c 0 Energy conversion Technology selection Electricity production n w w=1 f w e w + E + E c E =0 fmin w y w f w fmax w y w y w {0, 1} 23

27 Consider exergy losses New objective function Min Ṙ r,y w,f w n w w=1 L w = n w w=1 Thermal exergy : (f w (Ė+ w n r r=1 (Ėq w,r) Tmin = (Ėq w,r) Tmin Ė w )) ns w s=1 Q s,r (1 T 0 ln( T r+1 T r ) T r+1 T r ) Chemical Exergy : Work : Ė + w = n fuel,w Ṁ f,w k 0 f f=1 hot and cold streams (the Ė w ) 24

28 Application Maximum energy recovery Energy Exergy Heating (kw) Cooling (kw) Refrigeration (kw) Hot utility Boiler house : NG (44495 kj/kg) Air Preheating Gas turbine : NG (el. eff = 32%) Steam cycle Header P T Comment (bar) (K) HP superheated HP superheated HPU condensation MPU condensation LPU condensation LPU condensation LPU condensation DEA deaeration T(K) Heat pumps Fluid R P low T low P high T high COP kwe (bar) ( K) (bar) (K) - Cycle Cycle Cycle Hot Utility : 6854 kw Cold utility : 6948 kw Self sufficient "Pocket" Ambient temperature 250 Refrigeration : 1709 kw Q(kW) Refrigeration Refrigerant R717 Ammonia Reference flowrate 0.1 kmol/s Mechanical power 394 kw P T in T out Q!T min/2 (bar) ( K) ( K) kw ( K) Hot str Cold str

29 Results Opt Fuel GT CHP Cooling HP kw LHV kwe kwe kw kwe Comb. + frg Comb. + stm + frg GT + stm + frg hpmp + frg hpmp + stm + frg 26

30 Results Opt Fuel GT CHP Cooling HP kw LHV kwe kwe kw kwe Comb. + frg Comb. + stm + frg GT + stm + frg hpmp + frg hpmp + stm + frg Share between heat pumps HP1 : 34 kwe HP2 : 323 kwe HP3 : 129 kwe 26

31 Balanced composite curves (option 5) Balanced Grand composite curve BalancedCarnot Grand composite Grand composite 1 (1-T0/T) T(K) Q(kW) Q(kW) 27

32 Integrated composite curves T(K) Utility composite Process composite curve Q(kW) 28

33 Integrated composite curve : steam network 29

34 Visualising the results : Carnot efficiency Tricks for creative engineers : reduce the green area! 1 1-T0/T Option 1 : Carnot composite curves Process composite curve Utility composite curve 1 1-T0/T Option 5 : Carnot composite curves Process composite curve Utility composite curve Q(kW) Q(kW) 30

35 Carnot integrated composite curves 1200 T(K) Integrated composite curves of the steam network Others (STMNET) Mech. power Carnot integrated composite curves of the steam network 1 1-T0/T Others (STMNET) Mech. power Q(kW) Q(kW) 31

36 Comparing results Energy efficiency NGCC equivalence of electricity T otal1 = ṁ fuel LHV fuel + (E+ E ) (= 55%(NGCC)) EU mix for electricity T otal2 = ṁ fuel LHV fuel + (E+ E ) (= 38%(EUmix)) η el η el Exergy efficiency Ėq colda + η ex = Ėq hot r + Ė grid Ė + + Ėq cold r + Ėq with Ė + = hot a n fuels fuel=1 Ṁ + fuel k0 fuel + Ė+ grid L = (1 η ex )(Ė+ + Ėq cold r + Ėq hot a ) 32

37 Results T otal1 = ṁ fuel LHV fuel + (E+ E ) (= 55%(NGCC)) η el T otal2 = ṁ fuel LHV fuel + (E+ E ) (= 38%(EUmix)) Table 9 Energy consumption and exergy efficiency of the different options Option Fuel Ė + grid Total 1 Total 2 η ec η ex Losses [kw LHV ] [kwe] [kw LHV ] [kw LHV ] % % [kw] Comb. + frg Comb. + stm + frg η el GT + stm + frg hpmp + frg hpmp + stm + frg

38 Shares of Exergy losses 34

39 Sensitivity of the grid electricity mix Comb. + frg Comb. + stm + frg GT + stm + frg hpmp + frg hpmp + stm + frg option 1 option 2 option 3 option 4 option 5 (i.e. when c fuel (e/kj) c grid (e/kj e) t cogenerat

40 Power plant design - LENI ISE-STI-EPFL Mai 2005 STI ISE LENI 36

41 Power plant : steam cycle integration Integrated composite curves francois.marechal@epfl.ch - LENI ISE-STI-EPFL Mai 2005 STI ISE LENI [1] F. Marechal and B. Kalitventzeff. Targeting the minimum cost of energy requirements : a new graphical technique for evaluating the integration of utility systems. Computers chem. Engng, 20(Suppl.):S225 S230,

42 Visualising the integration Carnot composite curves - LENI ISE-STI-EPFL Mai 2005 STI ISE LENI 38

43 Conventional cycles Air Air preheating and draw off - LENI ISE-STI-EPFL Mai 2005 STI ISE LENI Fuel

44 Nuclear power plant Efficiency : 33% Based on the thermal energy francois.marechal@epfl.ch - LENI ISE-STI-EPFL Mai 2005 STI ISE LENI 40

45 Conclusions Energy conversion system integration Satisfy the process requirement with minimum ressources Valorise the available process exergy Combined exergy - Process integration Analyse the requirements Unit operation analysis : the heat transfer interface heat at the coldest Temp cool at the highest Temp Opportunities for energy conversion integration (Carnot composite) Generate optimal integrated systems MILP method with Exergy objective Evaluate & compare solutions Graphical representations : Carnot composite & area Integrated composite curves 41