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Sensitivity analysis of the total reinjection geothermal plant in Castelnuovo

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Abstract

The results of surface equipment design for the Castelnuovo geothermal power plant including the facilities required for the power cycle and the complete reinjection of the two-phase geothermal fluid (H2O + non-condensable gases (NCGs)) are showed. Steady-state and dynamic simulations were performed. The study includes the sensitivity analysis of the surface design. The dynamic simulation model provides information on the unsteady behaviour of the process with relevant info on how to manage two-phase flow conditions at the reinjection well head.
Sensitivity analysis of the total
reinjection geothermal plant
in Castelnuovo
1Department of Industrial Engineering (DIEF)
University of Florence
Florence, Italy
lorenzo.talluri@unifi.it
Daniele Fiaschi1, Giampaolo Manfrida1,
Pouriya Niknam1 and Lorenzo Talluri1
Sensitivity analysis of the total reinjection geothermal plant in Castelnuovo 2
Table of contents
Resource conditions
Power plant schematic
Thermodynamic model
Results
Sensitivity Analysis
Exergo-economic model
Results
Dynamic Simulation
Response time of the reinjection well
Flow-pressure variations in the reinjection
well
Conclusions
Sensitivity analysis of the total reinjection geothermal plant in Castelnuovo 3
Resource conditions
Heat flow distribution expressed in mW/m2(Bellani et al., 2004)
The Montecastelli Pisano area (in which the "Castelnuovo"
permit falls) is characterized by values between 100 and 300
mW/m2on average.
Saturated vapour at a pressure within the 60-80 bar range,
280°Ctemperature at about 3500 m depth.
At well head, the expected resource conditions are 10.3 bars
pressure and 180 °Ctemperature.
The NCG mass content is estimated at about 8%, of which
about 7.8% is CO2and 0.2% H2S.
Bellani, S., Brogi, A., Lazzarotto, A., Liotta, D., Ranalli, G., 2004. Heat flow, deep temperatures and extensional structures in the
Larderello geothermal field (Italy): constraints on geothermal fluid flow. J. Volcanol. Geotherm. Res. 132, 1529.
Sensitivity analysis of the total reinjection geothermal plant in Castelnuovo 4
41
42
43
44 45
46
50
51
5253
54
55
A
30 31
40
12
3
6
7
8
9
20 21
45
MHE
T
RHE
CON
P
PreC
C1
IC1
C2
IC2
C3
Reinjection well
56 PC 57
Production well
Power plant schematic
The well layout consists of 2
production and 1 reinjection
wells.
The ORC is a recuperative
power cycle using
R1233zd(E) as working
fluid.
A three-stage compressor
with intercoolers to reduce
the power consumption is
considered.
Sensitivity analysis of the total reinjection geothermal plant in Castelnuovo 5
  
    
  
Thermodynamic models
All the processes for system and sub-
systems are steady state.
Turbines and pumps are considered as
adiabatic devices.
For design point conditions, the mass flow
rate of the ORC was obtained fixing the
net power output of the turbine at 5MWe.
Geothermal fluid are
considered as a mixture of
H2O and CO2.
CO2-H2O mixture properties
are estimated with a third-
order EOS model.
A CO2Solubility model
(Duan and Sun, 2003) is
implemented in the in-house
code for THD properties.
Duan Z., Sun R., An improved model
calculating CO2solubility in pure water and
aqueous NaCl solutions from 273 to 533 K
and from 0 to 2000 bar, Chemical Geology,
193, 2003, 257 271
Sensitivity analysis of the total reinjection geothermal plant in Castelnuovo 6
Thermodynamic model results
Parameter
Unit
Value
Geothermal mass flow rate kg/s 11.82
CO2mass flow rate kg/s
0.9452
Power plant efficiency % 18.56
Heat input from Geothermal Fluid
kW 26855
-1.25 -1.00 -0.75 -0.50 -0.25 0.00
0
20
40
60
80
100
120
140
s [kJ/kg-K]
T [°C]
CarbonDioxide
p[40]=1 000 [kPa]
p[41]=1 000 [kPa]
p[42]=1 817 [kPa]
p[43]=1 817 [kPa]
p[44]=3 302 [kPa]
p[46]=6 000 [kPa]
P[47 ]=6000 [kPa] p[45]=3 302 [kPa]
T[40]=89 [C]
T[41]=60 [C]
T[42]=11 4.8 [C]
T[43]=60 [C]
T[44]=11 5.3 [C]
T[45]=60 [C]
T[46]=11 6 [C]
T[47]=50 [C]
Sensitivity analysis of the total reinjection geothermal plant in Castelnuovo 7
0 1 2 3 4 5 6 7 8
1000
2000
3000
4000
5000
6000
7000
8000
CO2 [%]
WNet [kW]
1.461 20.85 40.24
59.63
79.02 98.41
117.8
137.2
156.6
176
WcTot [kW]
Cases


 
[kW]
[kg/s] [kW] -- --
%CO2
Variation
Wnet = 5 MW
Preinj = 60
bar
c= 0.82
0.5%CO
2
7.307
0.05384
26221
0.1906
0.5443
1%CO214.7
0.1083 26260
0.1903
0.5462
2%CO2
29.76
0.2193 26339
0.1897
0.5498
4%CO2
61.02
0.4496 26503
0.1884
0.557
6%CO2
93.89
0.6918 26675 0.187
0.5645
8%CO2
128.5
0.947 26856
0.1856
0.5721
1000 2000 3000 4000 5000 6000 7000 8000
4000
4500
5000
5500
6000
6500
7000
7500
8000
Wnet [kW]
Preinj [kPa]
29.64 49.39 69.14 88.89 108.6 128.4 148.1
167.9
187.6
207.4
227.1
WcTot [kW]
Sensitivity Analysis (CO2content)
Lower %CO2=> lower 𝑾𝒄=> higher 𝜼𝑰.
Conversely, due to the better match between the main heat
exchanger curves, the exergy efficiency increases with an
increase of CO2content within the geothermal fluid stream
(the input exergy is lower).
Sensitivity analysis of the total reinjection geothermal plant in Castelnuovo 8
k
Component
Cost balance equations Auxiliary equations
1P
 

=
2RHE

=
+
+
  
3MHE

 
  
+
+
   
  
4T

 
+
 
5CON

  
 

 =0
  
6PreC 
+
  
 

 =0
  
7C1 
  
+
+
 =
8IC1 
+
  
 

   
  
9C2 
  
+
+
 =
10
IC2 
+
  
 

   
  
11 C3 
  
+
+
 =
  



Exergo-Economic model
Exergy is defined as the maximum
work that can be obtained by bringing
the state of a system to equilibrium
with the environment (Kotas, 1985).
Exergy cost balance
Exergy destruction ratio
The Exergo-Economic Analysis (EEA) combines the exergy and the economic
analyses, in order to provide a clear and efficient evaluation of the cost
effectiveness of each component of the power plant, introducing the costs per
exergy unit (Bejan et al., 1996).
Bejan A., Tsatsaronis G., Moran M.J.: Thermal Design and
Optimization, John Wiley & Sons, (1996).
Kotas, T., The Exergy Method of Thermal Plant Analysis, Elsevier,
1985.
Sensitivity analysis of the total reinjection geothermal plant in Castelnuovo 9
0
0.1
0.2
0.3
0.4
0.5
0.6
Xk
P
RHE
MHE
T
CON
0
0.0003
0.0006
0.0009
0.0012
0.0015
Xk
PreC
C1
C2
C3
IC1
IC2
Component PEC
(€)
P193464 0.001558 0.0008032 0.07148 0.1056
RHE 438204 0.00353 0.00242 0.05154 0.1009
MHE 2.920E+06 0.02352 0.009514 0.01804 0.03419
T2.651E+06 0.02136 0.008596 0.05154 0.07148
CON 656282 0.005286 0.01634 0.05538 0.2662
PreC 181662 0.001463 0.000003835 0.01804 1.819
C1 126231 0.001017 0.0001109 0.07148 0.1835
IC1 185022 0.00149 0.000053 0.05869 0.8226
C2 120236 0.0009685 0.0001071 0.07148 0.1837
IC2 219831 0.001771 0.00006767 0.08384 1.008
C3 113008 0.0009102 0.0001005 0.07148 0.1834
Exergo-economic Results
PEC = Purchased Equipment Cost
= Sum of the cost rates associated with investments and
operation and maintenance for the k-th component
 = Exergy destruction cost rate
 = costs per exergy unit of fuel
 =costs per exergy unit of product
Exergy destruction ratio
Sensitivity analysis of the total reinjection geothermal plant in Castelnuovo 10
TP
TT
Dynamic Simulation of the Reinjection Well
The model was developed in Honeywell
UniSim®, including control of the flow rate by
valve throttling and estimation of the water level.
Two approaches are considered for the simulation
of the drain injection process.
In the first design (Tank-Tank: TT), the well is
simplified with two cascade tanks and a valve.
In the second design a preliminary cylindrical
tank and a pipe segment are utilized (Tank-Pipe:
TP).
Sensitivity analysis of the total reinjection geothermal plant in Castelnuovo 11
Stabilization time of water level in the start-up phase. Water level change as the result of reducing valve opening in
three steps 10% each.
Response time of the reinjection well
Sensitivity analysis of the total reinjection geothermal plant in Castelnuovo 12
MTP
Flow-pressure variations in the reinjection well
Multi-stage array of tanks (MTP) for the
preliminary section => water level analysed over a
wide range
The safe lower pressure limit for re-injection is
determined by saturation conditions.
It is possible to guarantee adequate pressure at
wellhead either by hydrostatic head or using a
circulation pump on the condensate line.
Psat
Sensitivity analysis of the total reinjection geothermal plant in Castelnuovo 13
Conclusions
A
A model of the Castelnuovo power plant was presented with a focus on power generation performance
(design) and on the reinjection process (including transients/dynamic simulation).
Sensitivity analyses were performed: the performance of the system for the power generation (CO2
content) and the compression train (delivery pressure and 2-phase reinjection depth) were assessed over a
wide operating range.
The dynamic simulation model provided information on the unsteady behaviour of the process with
relevant info on how to manage two-phase flow conditions at the reinjection well head.
Sensitivity analysis of the total
reinjection geothermal plant
in Castelnuovo
1Department of Industrial Engineering (DIEF)
University of Florence
Florence, Italy
lorenzo.talluri@unifi.it
Daniele Fiaschi1, Giampaolo Manfrida1,
Pouriya Niknam1 and Lorenzo Talluri1
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