Post on 11-May-2018
transcript
Delft, 22nd – 23rd September 2011
POTENTIAL OF WATER SPRAYEDPOTENTIAL OF WATER-SPRAYED CONDENSERS IN ORC PLANTS
Stefano Filippini, Umberto Merlo (LU-VE Group)
Matteo C Romano Giovanni Lozza (POLITECNICO DI MILANO)Matteo C. Romano, Giovanni Lozza (POLITECNICO DI MILANO)
Heat rejection in ORC
In ORC cycles, 75In ORC cycles, 75--90% of inlet heat must be rejected 90% of inlet heat must be rejected to the environmentto the environmentto the environmentto the environment
Air cooled condenser is often the preferred choice:Air cooled condenser is often the preferred choice:Air cooled condenser is often the preferred choice:Air cooled condenser is often the preferred choice:large condensing surface and footprintlarge condensing surface and footprinthi h i t t t ( b t 20% f th ORC d l )hi h i t t t ( b t 20% f th ORC d l )high investment cost (about 20% of the ORC module)high investment cost (about 20% of the ORC module)high auxiliary electric consumptionhigh auxiliary electric consumptionl i fl f bi t diti ORC fl i fl f bi t diti ORC flarge influence of ambient conditions on ORC performancelarge influence of ambient conditions on ORC performanceEconomic optimization of condenser design and operation is Economic optimization of condenser design and operation is importantimportantimportantimportant
Heat rejection in ORC
This presentation illustrates an alternative solution to This presentation illustrates an alternative solution to traditional air cooled condenser able to lower electrictraditional air cooled condenser able to lower electrictraditional air cooled condenser able to lower electric traditional air cooled condenser able to lower electric consumption and to improve ORC performance and consumption and to improve ORC performance and efficiency.efficiency.efficiency.efficiency.The solution is applied from several years in The solution is applied from several years in refrigeration and air conditioning fields showingrefrigeration and air conditioning fields showingrefrigeration and air conditioning fields showing refrigeration and air conditioning fields showing excellent results excellent results
Product description
Water spray condenser is a fin-and-tube heat exchanger, operating with dry surface when h bi i l hthe ambient temperature is lower than a
selected design value.
For higher ambient temperatures, the water spray system is activated allowingspray system is activated, allowing significant performance improvements.
R & D activity – Heat exchanger simulation with CFD – dry mode
PathPath lineslines of of Fin design improved by
ComputationalComputational FluidFluidwavywavy finsfins
ComputationalComputational FluidFluidDynamicsDynamics analysis.
PP S dS d T tT tDistributionsDistributions ofof
PressurePressure SpeedSpeed TemperatureTemperature
R & D activity – Heat exchanger simulation with CFD – wet mode
Application of COMPUTATIONAL FLUID DYNAMICS ANALYSIS on a sprayed fin: “WET” application“WET” application.
Water droplets distribution
S S o a sp ayed fi : W applicatioW applicatio .
0.7500
1.0000Diameter Distibution
0.5000
0.0000
0.2500
0 20 40 60 80 100
droplets diameter μm
Quantity Quantity distribution of the distribution of the
•• min diameter 3.5 µmmin diameter 3.5 µm•• max diameter 87.5 µmmax diameter 87.5 µm
di t 17 5di t 17 5Flow of the Flow of the
evaporated evaporated
droplets diameter, μm
distribution of the distribution of the evaporated waterevaporated water
•• avg. diameter 17.5 µmavg. diameter 17.5 µm•• distribution field distribution field 1.251.25
evaporated evaporated waterwater
DRY and SPRAY - Performance DRY and SPRAY - Performance
Performance of DRY and SPRAY related to EHLD1S Performance of DRY and SPRAY related to EHLD1S
range, with 30%range, with 30% Ethylene GlycolEthylene Glycol andand ΔΔTwTw=5K=5Krange, with 30% range, with 30% Ethylene Glycol Ethylene Glycol and and ΔΔTwTw 5K5K
Case study: R134a recuperative supercritical ORC cycle for geothermal application
140
160
49
80
100
120
ratu
re, °
C
10
40
60Tem
per
2
1 7
63
0
20
1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9Entropy, kJ/kg/K
1
PerformanceDesign conditionsηcyc,gross=16.4%ηheatr rec =91.7%ηnet=11.6%
•Tw=150°C•Treinj-min=70°C•Tamb=23,5°C ηnet 11.6%
Qcond=85.6% of Qin-ORC
Tamb 23,5 C•Tcond=35°C
Calculation model
Given the cycle operating conditions at design point, off-design performance are estimated considering constraints imposed by components design:components design:
• Main heat exchanger heat transfer surface• Recuperator heat transfer surfaceRecuperator heat transfer surface• Turbine nozzle critical section• Condenser design: tube and fin geometry + fan
h i icharacteristic curve
Dependent variables used to respect the given constraints:• Turbine inlet temperature• Recuperator effectiveness• Turbine inlet pressure• Turbine inlet pressure• Condensing temperature
Turbine efficiency corrected by taking into account the isentropicTurbine efficiency corrected by taking into account the isentropic enthalpy drop and outlet volume flow rate.
Influence of ambient temperature
Tamb=35.6°C, fans speed at design value (670 RPM):increased condensing temperatureg preduced heat recovery efficiency (recup. cycle)
140
160
49
80
100
120
ture
, °C
610
40
60
80
Tem
pera
1
2
37
0
20
40
1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9Entropy, kJ/kg/K
Influence of ambient temperature –dry operation
Effect of fans speed:Effect of fans speed:ambient temperature = 23 5°Cambient temperature = 23.5 C
5016
4514
e, °C%
Heat recovery loss
G l ffi i
4012
mpe
rature
Efficiency, Gross el. efficiency
Condensing temperature
3510
Te
308
300 400 500 600 700 800 900
fans speed, RPM
Influence of ambient temperature –dry operation
Efficiency decay at ambient temperature = 23.5°C
16
14
16fans efficiency loss
pump efficiency loss
Net efficiency
12
14
10
12
η, %
8
10
i l f d i i i ffi i b f d
800650500350
fans speed, RPM
An optimal fan speed maximizing net efficiency can be found
Influence of ambient conditions –wet operation
0.14dry operation spray=22mc/h
Tamb= 23.5°C; RH=68%
0.13
Tamb= 35.6°C; RH=31% (summer peak)
0.13
ency
spray=45mc/h spray=67mc/h
0.11
0.12
ency
0.11
0.12
Net efficie
0.09
0.10
Net efficie
0.10
300 400 500 600 700 800 900
0.07
0.08
300 400 500 600 700 800 900
dry operation spray=22mc/h
spray=45mc/h spray=67mc/h
fans speed, RPM fans speed, RPM
Thanks to wet operating net efficiency increases by 13% p g y y(Tamb 23,5°C) and by 33% (Tamb 35,6°C).
Also in these cases there is an optimal fan speed maximizing net efficiency
Influence of ambient conditions –wet operation
Net electric efficiency vs. ambient conditions at optimal fan speed
0.16
Rel Humidity0.14
Rel.Humidity=81% 82%
80%76%
0.12
efficiency
76%
68%55%
46%0.10
Net e
dry operation spray 22mc/h 38%31%
0.08
0 5 10 15 20 25 30 35 40
dry operation spray=22mc/h
spray=45mc/h spray=67mc/h
0 5 10 15 20 25 30 35 40
Ambient temperature, °C
Water spray injection improves the net efficiency by 7 ÷ 33%, according to ambient temperature
Economic calculation
Increase of water injection always enhances net electric efficiencyOptimal operations should be optimized to maximize cash flowThe trade-off between water cost and price of electricity is very
dependent on site conditions and local costs
15Cw=1.0€/mc; EE=15c€/kWh
Tamb= 23.5°C; RH=68%
9
12
e, %
Cw=0.5€/mc; EE=15c€/kWh
Cw=0.1€/mc; EE=15c€/kWh
6
flow increase
0
3
Cash f
0 20 40 60 80
Water consumption, mc/h
Economic calculation
Increase of water injection always enhances net electric efficiencyOptimal operations should be optimized to maximize cash flowThe trade-off between water cost and price of electricity is very
dependent on site conditions and local costs
35
40Cw=1.0€/mc; EE=15c€/kWh
Tamb= 35.6°C; RH=31%
25
30
35
, %
Cw=0.5€/mc; EE=15c€/kWh
Cw=0.1€/mc; EE=15c€/kWh
15
20
flow increase
0
5
10
Cash f
0 20 40 60 80
Water consumption, mc/h
Economic calculation
By considering an annual temperature distribution (Central Italy case), an annual calculation can be undertaken at optimized (maximum cash flow) working conditions, for different costs of water
3 512
3.0
3.5
10
12t, %
2.0
2.5
6
8
time, years
mprovem
ent
1.0
1.5
4
Pay back
al cash flo
w im
0.0
0.5
0
2
0 0 2 0 4 0 6 0 8 1 1 2
Ann
ua
0 0.2 0.4 0.6 0.8 1 1.2
Water cost, €/mc
Conclusions
• Dry & spray technology can be an effective system to improve power output and profitability of ORC plantsp p p p y p
• Actual performance should be evaluated on a annual basis and are strongly dependent on the installationbasis and are strongly dependent on the installation site (climate, water cost and electricity price)
I h i ti i ti ff t f• In a comprehensive optimization process, effects of the investment costs should also be considered, defining the proper condenser size considering thedefining the proper condenser size considering the water spray option
Dry & spray technology will be more convenient in• Dry & spray technology will be more convenient in solar power generation plants, where production is concentrated during the hot hours of the dayconcentrated during the hot hours of the day