ca-looping process for low emission power plants
TRANSCRIPT
Ca-looping process for low emission power plants:
integration with a cement plant
M.C. Romano, M. Spinelli, S. Campanari, S. Consonni – Politecnico di Milano
M. Marchi, G. Cinti – C.T.G. Italcementi Group
4th IEAGHG Network Meeting - High Temperature Solid Looping Cycles
21-22nd August 2012, Tsinghua University, Beijing
2Ca-looping power plant
Purge
Purge
3Ca-looping power plant
AIR BLOWN CFB BOILER
Operating temperature, °C 850
Desulphurization efficiency, % 90
Gas temperature at economizer outlet, °C 350
CARBONATOR
Operating temperature, °C 650
CALCINER
Operating temperature, °C 950
Recycle gas temperature, °C 350
Oxygen concentration in oxidant stream, %vol. 50
COAL & AMBIENT CONDITIONSAmbient conditions: 15°C 101325 Pa 60% UR
Coal: sub-bituminous – LHV=26.4 MJ/kg; Ash 4.6%wt., S 0.65%wt.
4Ca-looping power plant
CO2 compression and purification unit
Number of intercoolers 5
Intercooling temperature, °C 28÷30
Flash temperature, °C -54
Flash pressure, bar 23
Minimum ∆T in cryogenic HE °C 2
Final CO2 purity, %mol 97
Final CO2 pressure, bar 150
5Ca-looping power plant
STEAM CYCLE
Live steam temperature SH/RH, °C 600 / 620
Live steam pressure SH/RH, °C 290 / 60
RH/SH piping thermal losses, °C 2
Condensing pressure, bar 0.048
Number of preheaters 9
STEAM TURBINE
Last stage turbine blade height, m 1.1
Last stage peripheral velocity, m/s 500
Exhaust steam velocity, m/s 220
Rotational speed, RPM 3000
Number of HP/IP/LP parallel flows 1 / 2 / 4
Isentropic efficiency, % calculated
6Simulation tools
GS code:
� Modular structure: very complex schemes can be reproduced by
assembling basic modules
� Efficiency of turbomachineries evaluated by built-in correlations
accounting for operating conditions and the machine size
� Stage-by-stage calculation of steam and gas turbines
� Chemical equilibrium
� Thermodynamic properties of gases � NASA polynomials
� Thermodynamic properties of water/steam � IAPWS-IF97
Matlab:
� Carbonator model
Aspen Plus:
� CO2 compression and purification
Carbonator model 7
Carbonator calculated by means of a core-annulus + freeboard K-L model
CO2 capture efficiency function of solid inventory and properties of solid population (sorbent ‘‘age’’, carbonation degree, sulfation, ash)
M.C. Romano, 2012: Modeling the carbonator of a Ca-looping process for CO2
capture from power plant flue gas; Chem Eng Sci, 69, 257-269
Example output for:
Ws = 570 kg/(m3/s)
FS/FCO2 = 0.0075
Fash/FCO2 = 0.0125
Sensitivity analysis on:
• Limestone makeup: F0/FCO2 (0.04-0.25)
• Sorbent recycle rate: FR/FCO2 (4-12)
• Solid inventory: Ws/Vg (150-525 kg/(m3/s)).
Two possible carbonator designs were considered:
• ‘‘Standard’’ design: h=40 m, u0=5 m/s
• ‘‘Compact’’ design: h=20 m, u0=10 m/s
8Power plant simulation
9Sensitivity analysis: overall performance
10Economic analysis
Equipment cost estimated with exponential laws and data from the literature (IEA & NETL reports):
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for example, fluidized bed cost as function of volume (f=0.69):
Other economic assumptions agrees with the «European Benchmarking Task Force» (EBTF) document.
11Economic analysis: results
12Economic analysis: results
FR/FCO2=6
Reference cement plant13
3600 tpdclk plant, with precalciner and suspension preheater
Utilization of CaL process purge in the cement plant14
Effects of feeding CaO-rich CaL purge:- Reduction of fuel consumption for limestone calcination- Reduction of CO2 emission from fuel oxidation and calcination- Reduction of gas and solid flow rate in the suspension preheater
Level of integration defined by the substitution rate:
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Maximum substitution rate limited by the presence of solids species other than CaO/CaCO3, i.e. fuel ash and CaSO4 in the CaL purge
� Important influence of composition of fuel used in the calciner of the CaL process
� Cases with lower FR/FCO2 lead to higher purity purge and may be preferred
15Effects of different substitution rates
0
200
400
600
800
1000
Fu
el in
pu
t,
kca
l LH
V/k
gck
0
150
300
450
600
750
900
0% 20% 40% 60% 80% 100%
EC
O2, kg/t
on
ck
Substitution rate
Total emissions
Emissions from fuel
combust. in the kiln
16
Hot air from clinker cooler (tertiary air) entirely used in the suspension preheater despite well overstoichiometric for combustion in the precalciner
� reasonable variations of gas velocities (-17%) and gas/solid ratio (-8%)at SR=100%
0.83
0.84
0.85
0.86
0.87
0.88
0.89
0.90
0.91
70
75
80
85
90
95
100
105
0% 20% 40% 60% 80% 100%
mg
as/m
so
lids
V g
as, m
3/s
Substitution rate
Operating conditions of the suspension preheater
17Overall emission from the complete system
Power plantCement Plant
Complete cement + power plant system with maximum allowable SR (cases with FR/FCO2=6)
34%
35%
36%
37%
38%
39%
40%
0 0.05 0.1 0.15 0.2 0.25 0.3
Ele
ctr
ic e
ffic
ien
cy,
%
F0/FCO2
18
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!"#$%&,()( � !"#$%&,�)1�.� 2&( + !"#$%&,,�+�&(� 2&(
(771 kcal/kgck)-1
Equivalent electric efficiency
FR/FCO2=4
FR/FCO2=6
η
ηeq
19
4 ,56,�� =+,56,()( − +,- ∗ 4,56,,-,.�/
��
-200
-100
0
100
200
300
0 0.05 0.1 0.15 0.2 0.25 0.3
EC
O2,
g/k
Wh
e
F0/FCO2
FR/FCO2=4
FR/FCO2=6
ECO2
ECO2,eq
ΔE~190 g/kWhe
Equivalent CO2 emission
885 gCO2/kgck
20Cost of CO2 avoided of the whole system
Assuming no variation in the clinker price:
21Conclusions
Acknowledgments:
CTG – Italcementi is greatly acknowledged for the the technical and
financial support
• The potential of this cement & power production system in reducing the emissions from power and cement sector at competitive cost is huge:
• possibility of retrofitting on the cement plant with minimal modifications
• reduced fuel consumption in the cement plant
• A proper selection of CaL process parameters and of the fuel used in both the calciner and the cement plant is important for high substitution rates:
• F0/FCO2 higher than usually considered
• Benefits arise by using a low sulfur fuel in the cement plant
NB: Definitive and more detailed results will be presented in forthcoming journal papers and at GHGT-11.