Prof. Joe Wood Dr Yu Rong, Dr Jiawei Wang * School of Chemical Engineering University of Birmingham, UK * School of Chemical Engineering and Applied Chemistry, University of Aston, Birmingham, UK April 2014 Studies of Hydrotalcite Clays for CO 2 Adsorption
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Studies of Hydrotalcite Clays for CO2 Adsorption · • Temperature of solid phase ( ) ... • Downstream CO 2 capture using NiMgAl N2 adsorption Overall: Process Modelling ... Mohammad
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Prof. Joe Wood Dr Yu Rong, Dr Jiawei Wang*
School of Chemical Engineering University of Birmingham, UK
*School of Chemical Engineering and Applied Chemistry, University of Aston, Birmingham, UK
April 2014
Studies of Hydrotalcite Clays for CO2 Adsorption
STEPCAP Project: Step Change Adsorbents for Post-Combustion Carbon Capture
Aim: To develop advanced adsorbents for post-combustion CO2 capture
Adsorbents should have desirable kinetics, capture capacity, stability and ability to be regenerated
Performance Parameter Target Operating Temperature
Adsorbents: NiMgAl N2 Kinetic models: Avrami and Lagergen’s pseudo-fist order models; Parameters in the kinetic model were calculated from experimental data through linear regression.
( )teFt qqk
tq
−=∂∂
( )te1nn
At qqtk
tq AA −=∂∂ −
1st order:
Avrami:
Time
CO
2 upt
ake
(mm
ol/g
)
7/22
Temperature swing adsorption using NiMgAl N2 Performance Parameter Target NiMgAl N2 Operating Temperature
: adsorption 40 – 80 °C 65-85 °C : desorption 85 – 160 °C ~140 °C
Step 1: Adsorption is operated at ~80 oC; pressure close to ambient.
Step 2: Operating temperature is raised to ~ 140 oC.
Step 3: Desorption continues until meet the recovery target.
Step 4: Cooling returns back to Tad.
1 3 Tde = ~140 oC
Tad = 65-85 oC
2
4
8/22
Cyclic operating conditions
Fixed bed reactor (L/D = 5~9) 100~200 ml/min CO2/N2 mixture 10~15% CO2 in feed gas 80 °C for adsorption 140 °C for desorption ~1 bar pressure
Experimental Procedure
Tem
p (o
C)
CA/
C0
Adsorbents- NiMgAl N2
9/22
Fixed bed model Gas concentration
C = concentration of component (mol/m3) DL = axial dispersion coefficient (m2/s) H = heat of adsorption (J/mol) P = pressure (Pa) T = temperature (K) us = superficial velocity (m/s) µ = viscosity (Pa·s) ρ = density (kg/m3)
( )t
qερε
zC
εu
zC
Dt
C isisiL
i
∂∂−
−∂∂
−∂∂
=∂∂ 1
2
2
• Temperature of gas phase
• Temperature of solid phase
( ) ∑
∂∂
−+−=∂∂
tq
HρTTdh
tT
Cρ iissg
p
fsss Δ
6
( )t
TCρε
zT
uCCzT
ελt
TCCε s
ssg
sg,fg
Lg
v,f ∂∂
−−∂
∂−
∂
∂=
∂
∂12
2
( ) ( )wgint
wiis TT
dh
tq
Hρε −−
∂∂
−−+ ∑ 41 Δ
Energy balance
( ) ( )3
2
32
2 11εd
uερB
εduεμ
AzP
p
sg
p
s −+
−=
∂∂
−
Pressure drop
T.L.P. Dantas et al., 2011, Chemical Engineering Journal 169, 11-19
R. Serna-Guerrero, 2010, Chemical Engineering Journal 161, 173-181
10/22
Assumptions: The gas phase follows the ideal gas law; Constant gas flow rate and uniform void fraction along the column; The mass and temperature gradients in the bed radial direction are negligible.
Model validation A dynamic fixed bed model has
been developed for
Gas separation simulation
Process evaluation
Optimisation
Feed gas: F0 = 105 ml min-1 CO2 = 14.3 %
Validated by experimental-simulation fit
Feed gas: F0 = 150 ml min-1 CO2 = 15 %
Feed gas: F0 = 200 ml min-1 CO2 = 10 %
11/22
• Base case: No CO2 capture • Downstream CO2 capture using NiMgAl N2 adsorption
Overall: Process Modelling
Constraints: • Downstream flue gas properties • CO2 capture and recovery target • Operating condition (temperature, pressure and residence time)
Cycle design: • Dimension of the column(s) • Operating conditions
Performance: • Power for steam/gas stream fed into column(s) • Steam for desorption processes • Cost of fuel (and CO2 emissions) for supplementary energy • Operating cost per unit of CO2 avoided
12/22
Adsorption-desorption cycle
Target Adsorption:
Capture: 90% of feed CO2
Desorption: Recovery: 85% of adsorbed CO2
Flue gas Pressure (bar) 1.4 Temperature (oC) 93.1 Gas flow (mol/s) 200 Composition (mol%, dry) CO2 14.3 N2 80.7 O2 5
J. Zhang et al., 2008, Energy Conversion and Management, 49, 346 -356
SEQUESTRATION
13/22
Adsorption step
Constraints (Retention time, pressure) Gas-adsorbent interaction Breakthrough curve
Cyclic operating
Fixed bed column - Internal diameter : 3.1 m - Length : 6.34 m
16.3 ton NiAlMg N2 do=2.5 mm
14/22
Steam temperature 120~270 oC
Steam flow rate 100~300 mol/s Pressure 1.1~1.4 bar Desorption time < 60 mins
Desorption step
To recover 80% of adsorbed CO2
Initial point:
Saturated NiMgAl N2 q = 0.82 mol kg-1
Column temperature T = ~95 oC
Bounds set based on industrial practices and material limitations
Fixed bed
Steam
Steam +CO2 Flue gas
Emission
Separation & compression
Cyclic operating
15/22
Mohammad R. M. Abu-Zahra, Carbon Dioxide Capture from Flue Gas, 2009
• Base case: CO2 emissions 100 ton per day • Desorption operating • Flue for supplementary energy: coal
Effect of steam temperature
16/22
Effect of steam flowrate • Base case: CO2 emissions 100 ton per day • Desorption operating • Constraints: operating time; pressure
17/22
Optimize cyclic operating • compare performance to base case (no CO2 emissions avoided)
Objective function: Minimizing energy penalty per unit of CO2 emissions avoided