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!