Design of a dual fluidized beds system for hydrogen production with CO2 capture
based on calcium looping process
Doctoral candidate: Wang Dong Supervisor: Xiang Wenguo
Contents
Background
Conventional CLHP route
A novel CLHP method
Future work
Discussion
Previous experiment
Background
CO2CO2
6%2%
17%75% Coal Oil
Others
NG
China
Fig.1 The structure and status of power consumption
World
10%
24%40%
26%
Oil
Coal
NG
Others
Background
Fossil fuel
Conventional method
Coal gasification
Biological hydrogen production
Fig.2 Technology roadmap for hydrogen production
Water electrolysis
Photocatalytic water splitting
Background
Fig.3 The schematic of calcium looping hydrogen production (CLHP) from coal
Calciner
Gasifier
CO2
Coal/ steam
O2
CaO
Char/ CaCO3
H2-rich gas The main reactions occur in the two reactors: (1)Gasifier char gasification: C+H2O→CO+H2 water-gas shift reaction: CO+H2O→CO2+H2 carbonation: CO2+CaO→CaCO3 The net reaction: C+2H2O+CaO→CaCO3+2H2
(2)Calciner char combustion: C+O2→CO2 decarbonation: CaCO3→CO2+CaO
Conventional CLHP route
Fig.4-CO2 partial pressure versus temperature
• PCO2;eq increases with the increase in equilibrium temperature; • T<Teq, carbonation reaction takes place; • T>Teq, calcination reaction occurs, and carbonation reaction is inhibited. • Typical CO2 concentration in atmospheric gasifier is <20vol.%, the temperature of gasifier is required to <750℃.
[ ] [ ]2 ,8308log atm 7.079co eqPT K
= −
The relationship between temperature and CO2 partial pressure is given as follows:
The advantages of calcium looping hydrogen production:
• Exhibit great potential for hydrogen production, and obtain a high concentrated CO2 stream simultaneously;
• Large absorption capacity, abundant reserves, widely distributed, cost-effective, low cost of operation;
• Sulfur removal, reduce the pollutants emission.
Conventional CLHP route
Single fluidized bed is usually employed as conventional gasifiers, the range of temperature is between 600 and 750℃, but due to heat and mass transfer, and the chemical kinetic limitations, char gasification and water-gas shift reaction are limited by this above-mentioned unexpected factors, when thermodynamic equilibrium is achieved, the range of H2 concentration in product gas is only 65-85vol.%.
Therefore, an innovative compact fluidized bed is proposed to produce H2-rich syngas.
Discussion
Fig.5-The schematic of a compact fluidized bed
Coal
H2-rich gas
C+CaCO3
CaCO3 Absorber
GasifierSteam
CaO
A novel CLHP method
Fig.6-The prototype of the novel CLHP
O2
CO2
Char+CaCO3
CaO
H2+H2O
CaO/CaCO3
Abs
orbe
r
Gasifier
Cal
cine
r
steam
coal
Components:H2:95%; CO:0.71%;CO2:0.53%; CH4:2.91%;Others:0.63%
Components:H2:81.33%; CO:10.68%;CO2:6.48%; CH4:0.95%;Others:0.57%
Pressure 1bar
Gasifier temperature 600-700℃
Absorber temperature 600-650℃
Calciner temperature 850-1150℃
Calciner atmosphere O2/steam,O2/CO2
Mean particle size 0.35mm
Particle size range (0.1-0.5)mm
Gasifier (6-10)umf
Absorber (4-10)ut
Calciner (4-10)ut
Table1. Main design parameters
Fig. 8 Hydrogen production (kg/h) varying with steam/C and Ca/C of gasifier, gasifier at 700℃,
calciner at 900℃,absorber at 600℃, carbon conversion 0.55
0.5 1.0 1.5 2.0 2.5 3.0200
250
300
350
400
450
500
550
Hyd
roge
n pr
oduc
tion
(kg/
h)
Ca/C in gasifier
0.5 1 1.5 2 2.5 3
Fig. 7 Hydrogen purity (day basis) varying with steam/C and Ca/C of gasifier, gasifier at 700℃,
calciner at 900℃,absorber at 600℃, carbon conversion 0.55
Simulation results
0.5 1.0 1.5 2.0 2.5 3.060
65
70
75
80
85
90
95
100
Ca/C in gasifier
Hyd
roge
n co
ncen
tratio
n (v
ol%
)
0.5 1 1.5 2 2.5 3
Simulation results
450 500 550 600 650 700
0
200
400
600
800
1000
1200
1400
1600
1800
H2O CO CO2
H2
CH4
Gas
yie
lds
/kg
s-1
The absorber temperature/℃
0.75
0.80
0.85
0.90
0.95
1.00
H2 c
once
ntra
tion
(dry
)
Fig. 9 Gas yields varying with different absorber temperature, gasifier at 700℃, regenerator at 900℃, coal feed rate=1 kg/s,
steam flow=60 mol/s, total CaO recycle rate=30 mol/s.
0.5 1 1.5 2 2.5 3
0.5
1
1.5
2
2.5
3
b. CaO /C
Stea
m/C
0.5 1 1.5 2 2.5 3
0.5
1
1.5
2
2.5
3
a. CaO /C St
eam
/C
Simulation results
Fig. 9 Feasible regimes for hydrogen production varying with steam/C and Ca/C molar ratios (mol/mol) of gasifier,
carbon conversion: a) 0.7, b) 0.65, c) 0.5
0.5 1 1.5 2 2.5 3
0.5
1
1.5
2
2.5
3
c. CaO /CSt
eam
/C
Carbonator:600-700℃
Calciner:>900 ℃
Absorber:600-650℃
Carbon conversion:0.5-0.65
Hydrogen concentration:95%
Condenser
GT
HP IP LP
Steam
O2
Air
C
CO2
Coal Preparation
Hopper
Coal
Gasifier
Regenerator
Absorber
Waste Boiler
H2 HRSG IP saturated steam
From Condenser Stack
CO2 HRSG
From Condenser
To HP
Syngas
CaO/CaCO3CaO
Water/SteamSorbent
Cooler
H2 Compressor
Hydrogen-rich Gas
CO2 Sequestration
Reactors Unit
Power Generation
Water
C.W
C.W
Char/CaCO3
Fig.12 The flowsheet diagram of proposed integrated gasification hydrogen-fueled power plant
Fig.13 The 2kW bench-scale hot rig
Fig.14 The photographs of a fixed bed
Previous experiment
Table 2. Proximate analysis and ultimate analysis of Xuzhou natural coke and Xuzhou bituminite
Sample
Proximate analysis /%(mass, air dry) Ultimate analysis /%(mass, daf)
Qnet,ad (MJ·kg)
M A V FC C H O N S
Xuzhou natural coke 0.81 16.15 9.05 73.99 93.12 1.99 3.21 1.10 0.58 26.59
Xuzhou bituminite 1.77 23.52 28.73 45.98 80.47 5.10 2.19 1.46 0.78 23.08
Previous experiment
650 700 750 8000
10
20
30
40
50
60
70
Temperature (°C)
Gas
frac
tion
(vol
%)
H2
CO2
CO CH4
Results
650 700 750 800 8500
10
20
30
40
50
Gas
frac
tion
(vol
%)
Temperature (°C)
H2
CO2
CO CH
4
Fig.15 Volume fraction of main gas component versus
temperature (without CaO)
Fig.16 Volume fraction of main gas component versus
temperature (with CaO)
650 700 750 800 8500.0
0.5
1.0
1.5
2.0
Temperature (°C)
Gas
yie
ld (L
)
H2
CO2
CO CH
4
0.0
0.5
1.0
1.5
2.0
2.5
Gas
yie
ld (L
)
Temperature (°C) 800750700650
H2
CO2
CO CH
4
Fig.17 Main component yield versus temperature (without CaO)
Fig.18 Main component yield versus temperature (with CaO)
0.0
0.4
0.8
1.2
1.6
2.0
2.4
2.8
1.21.00.70.60.5
Gas v
olum
e (L
)
Ca/C molar ratio
Total H2 CO2 CO CH4
Results
Fig.19 The effect of Ca/C molar ratio on gas production
2 3 4 5 60
10
20
30
40
50
60
H2
CO2
CO CH4
Gas
frac
tion
(vol
%)
Steam flow rate (L/min)
Fig.20 The effect of steam flow rate on gas component volume
fraction (without CaO)
Results
2 3 4 5 60
10
20
30
60
70
Gas
frac
tion
(vol
%)
Steam flow rate (L/min)
H2
CO2
CO CH4
Fig.21 The effect of steam flow rate on gas component volume
fraction (with CaO)
Results
2 3 4 5 6 70.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8 H2
CO2
CO CH4
Total
Steam flow rate (L/min)
Gas
yie
ld (L
)
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
Total yield (L)
Fig.22 The effect of steam flow rate on gas yield (without CaO)
2 3 4 5 6 70.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
H2
CO2
CO CH4
Total
Steam flow rate (L/min)
Gas
yie
ld (L
)
2.63
2.64
2.65
2.66
2.67
2.68
Total yield (L)
Fig.23 The effect of steam flow rate on gas yield (with CaO)
Results
Fig.24 The comparison of gas yield between natural coke and bituminite
0.0
0.4
0.8
1.2
1.6
2.0
2.4
2.8
CH4COCO2H2
0.1120.0520.240.148
0.8920.756
2.757
1.712
Com
pone
nt y
ield
(L)
Natural coke Bituminite
Fig.25 The comparison of gas volume fration between natural coke and bituminite
0
10
20
30
40
50
60
70
2.86
22.3
68.9
25.5
28.3
64.2
H2 CH4COCO2
Com
pone
nt fr
actio
n (v
ol.%
) Natural coke Bituminite
Fig.27 CO2 volume in syngas as a function of calcination time and
carbonation time
Fig.26 CO2 volume in syngas as a function of calcination temperature and carbonation time
0 10 20 30 40 50 60 70 80 90 100
0.024
0.027
0.030
0.033
0.036
0.039
0.042
0.045
Carbonation time (min)
CO
2 vol
ume
(L)
120min 90min 60min 30min 200min
0 10 20 30 40 50 60 70 80 90 1000.021
0.024
0.027
0.030
0.033
0.036
0.039
CO
2 vol
ume
(L)
Carbonation time (min)
850℃ 950℃ 1050℃ 1250℃
Results
• The main aspects of our investigation is listed as follows:
• (1) Continuous operation;
• (2) Investigate the effect of CaO/C, H2O/C and temperature on H2 concentration and yield during gasification;
• (3) The effect of calcination atmosphere and temperature on the CaCO3 decomposition characteristics in the calciner;
• (4) The effect of the total solid inventory, the solid circulating rate on the performance of overall system;
• (5) The sulfur migration characteristic;
• (6) The activity decay of calcium oxide sorbent under realistic fluidized bed conditions, and improve the carbonation conversion.
Future work
Thank you!