- Email: [email protected]
Development of In-situ CO2 Capture Coal Utilization Technologies
Available online at www.sciencedirect.com
Energy Procedia 37 (2013) 99 – 106
GHGT-11
Development of In-Situ CO2 Capture Coal Utilization Technologies Shiying LIN * Japan Coal Energy Center, 3-2-1 Nishishinbashi, Minato-ku, Tokyo 105-0003,Japan
Abstract In-situ CO2 capture in coal utilization captures CO2 during coal combustion or gasification such as Oxygen fuel combustion or Chemical looping coal gasification processes. Japan coal energy center (JCOAL) have proposed a chemical looping coal gasification method. This method utilizes a chemical looping with the calcium cycle, in which CaO (or Ca(OH)2) captures CO2 during coal gasification to form CaCO3 and release heat for gasification to produce hydrogen in one gasifier. This paper introduces the current developing status of the method, mainly including the experimental examination of the transition of sorbent particle size distribution, ash and sulfur concentration of materials at several locations of gasification and calcination system for the process. As results it is shown that, the product gases from the chemical looping coal gasification only contained nearly 80% H2 with 20% CH4 with dry base. It was also found that coal ash and sulfur concentrated highly in the process of calcination after cyclone. And the plant cold gas efficiency which should be affected by ash separation was also analyzed. If it is possible, separate and remove ash and sulfur by applying devices like filter or/and cyclone separator, the plant coal gas efficiency may raise 2 points than that in the previous study in which a part of recycled sorbent was rejected without separation. As an application of the chemical looping coal gasification, exergy regeneration type IGFC power generation was proposed. Exhaust heat of FC can be used for reforming of CH4 which produced by coal gasification. This system was analyzed by use AspenPlus. The result shown that, hydrogen cold gas efficiency was about 10% higher than the cold gas efficiency of the chemical looping coal gasification. © 2013 The TheAuthors. Authors.Published PublishedbybyElsevier Elsevier © 2013 Ltd.Ltd. Selection and/orpeer-review peer-reviewunder underresponsibility responsibility GHGT Selection and/or of of GHGT Keywords: CO2 sorbent, Reactivity, Exergy regeneration, Chemical looping, Calcium
1. Introduction Coal is a major energy source and supports our social activities. Main utilizations of coal are combustion for power generation, gasification for fuel gas and cokes for iron manufacturing. However, coal utilization produces carbon dioxide, CO2 of the green house gas. In-order to reduce CO2 emission dramatically from coal combustion or coal gasification, some efforts are necessary to capture CO2 from these plants, though CO2 capture consumes a lot of energy.
* Corresponding author. Tel.:+81-3-6402-6103; fax: +81-3-6402-6111 E-mail address:[email protected]
1876-6102 © 2013 The Authors. Published by Elsevier Ltd.
Selection and/or peer-review under responsibility of GHGT doi:10.1016/j.egypro.2013.05.089
100
Shiying Lin / Energy Procedia 37 (2013) 99 – 106
JCOAL had proposed an In-Situ CO2 capture coal gasification method named-HyPr-RING (Hydrogen Production by Reaction-Integrated Novel Gasification) with AIST (National Institute of Advanced Industrial Science and Technology). The HyPr-RING method utilizes a chemical looping with the calcium cycle, in which CaO (or Ca(OH)2) captures CO2 during coal gasification to form CaCO3 and release the heat for gasification to produce hydrogen in one gasifier. Fig. 1 shows the concept of the In-situ CO2 capture coal gasification (HyPr-RING) method. Coal, steam and CaO as CO2 sorbent are injected in to gasifier directly. In gasifier, coal gasifies with steam to form CO and H2, and the CaO reacts with CO to form CaCO3 and H2 again. From the gasifier, H2 is only gas product and the carbon as CO2 will be fixed by CaO into CaCO3. By calcination in a calciner, the CaCO3 will be regenerated into CaO and releases CO2. Heat is needed for he calcination of CaCO3, however, more than 2/3 calcination heat will become to CaO chemical energy and be reuse to the coal gasification. 104
Ca Looping gasification C+2H2 3+2H2
Gasifier C(coal + H2O(steam) + Heat
H2 + CO2 + C
CaO absorb CO2
CaO + CO2
CaCO3 + Heat
CaO absorb H2S
CaO + H2S
CaS
Combustor (Calciner) CaCO3 decompositi
CaCO3 + Heat
Char combustion
C Char + 2O2
CaS combustion
CaS + 2O2
Reactions in gasifier and Calciner
CaO + CO2 CO2 + Heat CaSO4
1000 100
KC=Exp ( -
Gasification
10
G<0
1
0.1
G>0
0.01 500
Steam gasification C+H2 2
670 600
700
800
900
1000
Reaction constants vs. temperature
Fig.1 Concept of the In-Situ CO2 capture (chemical looping ) coal gasification method The In-Situ CO2 capture gasification have several advantage features: (1) High efficiency CO2 remove; (2) Sulfur remove in gasifier; (3) Can use low rank coal; (4) Cheap circulating material. During the past about ten years, the HyPr-RING method was studied by experiment (bench scale facilities) and by process analysis. Main results were obtained: (1) Gas product mainly contains H2 80% and CH4 20%; (2) CaO had enough strength during cycle; (3) Ash and Sulfur compounds can be separated by cyclone; (4) CaO also improve tar steam reforming; (5) Under pressure condition, CaCO3 can be calcined at1000 oC. We are planning to use the In-Situ CO2 capture coal gasification technology into a new high efficiency coal utilization system: An exergy regeneration coal gasification power system. As shown in Fig.2, it is possible to dramatically enhance the generation efficiency by implementing an exergy regeneration system in which coal is gasified at low temperatures (between 700 C and 850 C) with the recycled waste heat from the high-temperature gas turbines (around 1700 C) or fuel cells. Substituting steam as gasifying agent will reduce the necessary motor power for producing oxygen in the plant. Another important challenge is to develop a brown/subbituminous coal utilization technology. Recycle the exhaust heat of gas turbine or fuel cell to the endothermic reactions of coal gasification or methane reforming to produce hydrogen. by Exergy Regeneration, high power efficiency can be made. The exergy regeneration power generation system needs a low temperature coal gasification 700 850
Shiying Lin / Energy Procedia 37 (2013) 99 – 106
In this study, we build a exergy regeneration system proposed by combined of fuel cell with In-situ coal gasification (Chemical looping coal gasification), and then analysis the system proposed by using the AspenPlus model. % QPEGRVQHVJG'ZGTI[ 4 GIGPGTCVKQP% QCN2 QY GT) GPGTCVKQP # +) % % CPF# +) (% * GCV Coal
Gasifier
A-IGCC
GT
* GCV Coal
Gasifier
ST
A-IGFC
FC energy exergy
Gasifier Low temperature gasification (700-850
'ZJCWUVJGCVTGE[ENG
A-IGFC energy conversion flow
Fig. 2 Concept of the Exergy regeneration coal power generation (A-IGCC, A-IGFC)
2. System proposed Fig. 3 shows concept of exergy regeneration power generation combined chemical looping coal gasification with fuel cell. Product gases of Chemical looping coal gasification mainly contain hydrogen with CH4. Hydrogen is fuel for Fuel cell power generation and the waste heat of fuel cell is used for CH4 reforming. CH4 + H2O + waste heat 2 + CO2 Waste heat become to hydrogen energy means exergy regeneration.
Points in the proposed system: Ca Looping coal gasification CH4 content in gasification gas 10 20%
Low temperature gasification about 750 catalyst, If needed 30%-40% FC exhaust heat be used for CH4 reforming
Gasifier type used in the proposed system: Circulating Fluidized Bed Unreacted char in low temperature gasifier can be burned in combustor to calcine CaCO3 and to heat bed materials. Can separate the exhaust gases of combustor and gasifier, to obtain high concentration CO2 and H2/CH4 Gasification rate improvement at lower temperature: Ca looping + Catlyst (if needed) Using CaO as heating material can largely reduced the amount of heating material like SiO2.
101
102
Shiying Lin / Energy Procedia 37 (2013) 99 – 106
Using Ca looping and catalyst can obtain enough gasification rate and purity of H2/CH4 at low temperature. CO2 absorbed by CaO can improve steam gasification reaction equilibrium constant, KC for Ca Looping steam gasification (see Fig.1) % CNQQRKPIEQCNICUKHKECVKQP(% RQY GTU[UVGO HNQY CO2 CaSO4 Ash
CaO
Limestone make-up
Combustor Calciner 950 1100
Coal Catalyst
FC heat exergy reneration
H2 80%, CH4 20%
H2 CH4 H2 Gas clean up separation reforming separation
Tar reforming
Heat changer
H2
Gasifier
Off gas
H2
700 800
Q1 Steam
Water
(FCQ:0.3-0.4)
Q2
FC Power system
O2
Fig. 3 Exergy regeneration power generation system proposed by combined FC with the In-situ CO2 capture (chemical looping) coal gasification.
Main results studied until now: Gas products : mainly H2 80%; CH4 20% CaO had enough strength during cycle. Ash and Sulfur compounds can be separated by cyclone and filter (see Fig.4). CaO also improve tar steam reforming Under pressure condition, CaCO3 can be calcined at1000 oC (see Fig. 5). Concept of Ca Looping coal gasification
40
Real limestone decomposition Temperature
CO2
O2 or 1000 Air
Filter
CaO
CaCO3 /CaS/
Char
30
CaCO3
CO2 20 atm
cyclone
Gasifier
% QO DWUVQT
% CNEKPGT
CaO/ Ash /CaSO4
750
Ash /CaSO4 H2/CH4
Coal
CaO
20 10
Theoretical Decomposition curve
CO2 6 atm Q %
0
Steam 1000
1100
1200
1300
1400
1500
Temperature [K]
Fig. 4 Ca looping coal gasification process.
Fig.5 Calcination temperature of limestone under high CO2 pressure. It was found that the decomposition temperature of natural limestone is lower than theoretical decomposition temperature of CaCO3.
103
Shiying Lin / Energy Procedia 37 (2013) 99 – 106
Increase impurity content in material, decrease the decomposition temperature of material.
Gasification Part
Gas Reforming Part
FC Heat Recycle Part
3. AspenPlus Process Model Fig. 6 shown an AspenPlus model structured for the process combined chemical looping coal gasification with fuel cell. IGFC Exhaust heat recycle
IGFC power Generation
H2 Separation 2
CO Shift CH4 reforming
Product gas Heating value
H2 Separation 1
Coal Heating value Coal supply
CH4 reforming Steam generation
Gasification Steam generation
Gasifier and cyclone
Gasification Residue heating
Calciner and Cyclone
Fig. 6 AspenPlus model structured for the process combined chemical looping coal gasification with fuel cell Calculation conditions: Coal supply 42t/h S/Coal=1/1 Limestone making up 4.2t/h Pressure 20 atm Gasifire T 500-850 Material circulating: enough heat supply for gasification Analysis points Gasification product gas Cold gas efficiency Hydrogen cold gas efficiency FC Power generation efficiency Material circulating ratio 4. Analysis results and discussion Gas products of Ca chemical looping coal gasification with T and P Fig.7 shown the gas products from Ca chemical looping coal gasification with different temperature and pressure.
104
Shiying Lin / Energy Procedia 37 (2013) 99 – 106
100
H
2
80 60
atm CO
40 CH4
20
CO
2
0 400
500
600
700
800
Gasification temperature [
]
900
Gas procts concentr. [dry%]
Gas procts concentr. [dry%]
Under 1atm and 500 650 temperature area, gas products can be obtained about 10% CH4. Over 650 , CH4 and H2 were decreased. Under 10 atm, 500 750 temperature area, gas products can be obtained about 20% CH4. Over 750 , CH4 and H2 were decreased. 100 H
2
80 60
atm
40
CO
CH
4
20 0 400
CO2 500
600
700
800
Gasification temperature [
1 atm
]
900
10 atm
Fig. 7 Analysis results of gas products from Ca chemical looping coal gasification with different T and P. This is caused by that, with pressure, CaO can absorbs CO2 at comparatively high temperature as shown in Fig. 8. ]
40 40
CO2 Concentration [vol
35
* GCVECRCEKV[MI
30 30
CaCO3
25
SiO2(950
750
: 270 kJ
CaO (950
750
187 kJ
20 20
CaO
15
1 atm 5 atm
10 10
55 00
700 700
CaO(950 10 atm
750 800 750 800 Temperature [ ]
)
CaCO3 (750 3,186 kJ
850 850
CaO-CO2 absorption equilibrium Fig. 8 CO2 absorption equilibrium by CaO with temperature and pressure.
Fig. 9 The heat capacity of sensible heat and reaction hest of materials
FC exhaust heat exergy regeneration hydrogen cold gas efficiency can be raised 10% than gasification cold gas efficiency (see Fig.10). Used a part of FC exhaust heat to generate steam, and to pre-heat supply materials, gasification cold gas. efficiency can be obtained as 85 %. Used a part of FC exhaust heat to reform CH4, hydrogen cold gas efficiency can be obtained as high as 95% . However, over 750 , the area which CaO can not absorb CO2, hydrogen cold gas efficiency decreased.
105
Shiying Lin / Energy Procedia 37 (2013) 99 – 106
At CaO absorbs CO2 area (<750 the material circulating ratio is about 1.7 (see Fig. 11) At the area which is difficult for CaO absorbing CO2 (>750 , the material circulation ratio quickly increased, as about 36 at 900 .
100
Hydrogen cold gas efficiency
Efficiency [%]
95
Exergy regeneration effect
90 85 80 75
Gasification cold gas efficiency IGFC power generation efficiency
70 65 400
500
600
700
800
Gasification temperature [
]
900
Fig. 10 Analysis results of cold gas efficiency, hydrogen efficiency and exergy regeneration.
/ CVGTKCNEKTEWNCVKQPTCVKQ
This is caused by that, the CO2 absorption heat with CaO is much larger than the sensible heat of materials (see Fig.9)
40 35 P: 10 atm 30 Material circulation ratio 25 Amount of material circulation 20 = Amount of coal supply 15 10 1.7 5 0 500 600 700 800
36
Gasification temperature [
900
]
Fig. 11 Analysis results of material circulation ratio with temperature.
5. Conclusion Ca looping coal gasification /FC power system with exergy regeneration was analyzed by using Aspen model. The results are shown as follows. 750 temperature area, Ca looping coal gasification can obtained product (1) Under 10 atm, 500 gases about 20% CH4 with 80% H2. (2) A part of FC exhaust heat can be used for CH4 reforming. The hydrogen cold gas efficiency was obtained as 95%, is 10% higher than gasificaiton cold gas efficiency. (3) At the temperature area witch CaO absorbs CO2, since the absorption heat can be supply to coal gasification, the material circulating ratio was low as 1.7. However, at the temperature area witch CaO can not absorb CO2, the material circulation ratio become higher as 36 at 900 oC.
Acknowledgements The authors give their great thanks to NEDO for their financial support.
References [1] . Shiying LIN, Takashi KIGA, Yin Wang and Katsuhiro Nakayama, Energy analysis of CaCO3 calcination with CO2 capture, the 10th International Conference on Greenhouse Gas Control Technologies GHGT-10, Amsterdam, The Netherlands, 2010.9
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Shiying Lin / Energy Procedia 37 (2013) 99 – 106
[2] Shiying LIN, Takashi KIGA, Katsuhiro Nakayama and Yoshizo Suzuki, Coal Power Generation with In-Situ CO2 Capture Effect of Ash Separation on Plant Efficiency , the 10th International Conference on Greenhouse Gas Control Technologies GHGT-10, Amsterdam, The Netherlands, 2010.9.
Energy Procedia 37 (2013) 99 – 106
GHGT-11
Development of In-Situ CO2 Capture Coal Utilization Technologies Shiying LIN * Japan Coal Energy Center, 3-2-1 Nishishinbashi, Minato-ku, Tokyo 105-0003,Japan
Abstract In-situ CO2 capture in coal utilization captures CO2 during coal combustion or gasification such as Oxygen fuel combustion or Chemical looping coal gasification processes. Japan coal energy center (JCOAL) have proposed a chemical looping coal gasification method. This method utilizes a chemical looping with the calcium cycle, in which CaO (or Ca(OH)2) captures CO2 during coal gasification to form CaCO3 and release heat for gasification to produce hydrogen in one gasifier. This paper introduces the current developing status of the method, mainly including the experimental examination of the transition of sorbent particle size distribution, ash and sulfur concentration of materials at several locations of gasification and calcination system for the process. As results it is shown that, the product gases from the chemical looping coal gasification only contained nearly 80% H2 with 20% CH4 with dry base. It was also found that coal ash and sulfur concentrated highly in the process of calcination after cyclone. And the plant cold gas efficiency which should be affected by ash separation was also analyzed. If it is possible, separate and remove ash and sulfur by applying devices like filter or/and cyclone separator, the plant coal gas efficiency may raise 2 points than that in the previous study in which a part of recycled sorbent was rejected without separation. As an application of the chemical looping coal gasification, exergy regeneration type IGFC power generation was proposed. Exhaust heat of FC can be used for reforming of CH4 which produced by coal gasification. This system was analyzed by use AspenPlus. The result shown that, hydrogen cold gas efficiency was about 10% higher than the cold gas efficiency of the chemical looping coal gasification. © 2013 The TheAuthors. Authors.Published PublishedbybyElsevier Elsevier © 2013 Ltd.Ltd. Selection and/orpeer-review peer-reviewunder underresponsibility responsibility GHGT Selection and/or of of GHGT Keywords: CO2 sorbent, Reactivity, Exergy regeneration, Chemical looping, Calcium
1. Introduction Coal is a major energy source and supports our social activities. Main utilizations of coal are combustion for power generation, gasification for fuel gas and cokes for iron manufacturing. However, coal utilization produces carbon dioxide, CO2 of the green house gas. In-order to reduce CO2 emission dramatically from coal combustion or coal gasification, some efforts are necessary to capture CO2 from these plants, though CO2 capture consumes a lot of energy.
* Corresponding author. Tel.:+81-3-6402-6103; fax: +81-3-6402-6111 E-mail address:[email protected]
1876-6102 © 2013 The Authors. Published by Elsevier Ltd.
Selection and/or peer-review under responsibility of GHGT doi:10.1016/j.egypro.2013.05.089
100
Shiying Lin / Energy Procedia 37 (2013) 99 – 106
JCOAL had proposed an In-Situ CO2 capture coal gasification method named-HyPr-RING (Hydrogen Production by Reaction-Integrated Novel Gasification) with AIST (National Institute of Advanced Industrial Science and Technology). The HyPr-RING method utilizes a chemical looping with the calcium cycle, in which CaO (or Ca(OH)2) captures CO2 during coal gasification to form CaCO3 and release the heat for gasification to produce hydrogen in one gasifier. Fig. 1 shows the concept of the In-situ CO2 capture coal gasification (HyPr-RING) method. Coal, steam and CaO as CO2 sorbent are injected in to gasifier directly. In gasifier, coal gasifies with steam to form CO and H2, and the CaO reacts with CO to form CaCO3 and H2 again. From the gasifier, H2 is only gas product and the carbon as CO2 will be fixed by CaO into CaCO3. By calcination in a calciner, the CaCO3 will be regenerated into CaO and releases CO2. Heat is needed for he calcination of CaCO3, however, more than 2/3 calcination heat will become to CaO chemical energy and be reuse to the coal gasification. 104
Ca Looping gasification C+2H2 3+2H2
Gasifier C(coal + H2O(steam) + Heat
H2 + CO2 + C
CaO absorb CO2
CaO + CO2
CaCO3 + Heat
CaO absorb H2S
CaO + H2S
CaS
Combustor (Calciner) CaCO3 decompositi
CaCO3 + Heat
Char combustion
C Char + 2O2
CaS combustion
CaS + 2O2
Reactions in gasifier and Calciner
CaO + CO2 CO2 + Heat CaSO4
1000 100
KC=Exp ( -
Gasification
10
G<0
1
0.1
G>0
0.01 500
Steam gasification C+H2 2
670 600
700
800
900
1000
Reaction constants vs. temperature
Fig.1 Concept of the In-Situ CO2 capture (chemical looping ) coal gasification method The In-Situ CO2 capture gasification have several advantage features: (1) High efficiency CO2 remove; (2) Sulfur remove in gasifier; (3) Can use low rank coal; (4) Cheap circulating material. During the past about ten years, the HyPr-RING method was studied by experiment (bench scale facilities) and by process analysis. Main results were obtained: (1) Gas product mainly contains H2 80% and CH4 20%; (2) CaO had enough strength during cycle; (3) Ash and Sulfur compounds can be separated by cyclone; (4) CaO also improve tar steam reforming; (5) Under pressure condition, CaCO3 can be calcined at1000 oC. We are planning to use the In-Situ CO2 capture coal gasification technology into a new high efficiency coal utilization system: An exergy regeneration coal gasification power system. As shown in Fig.2, it is possible to dramatically enhance the generation efficiency by implementing an exergy regeneration system in which coal is gasified at low temperatures (between 700 C and 850 C) with the recycled waste heat from the high-temperature gas turbines (around 1700 C) or fuel cells. Substituting steam as gasifying agent will reduce the necessary motor power for producing oxygen in the plant. Another important challenge is to develop a brown/subbituminous coal utilization technology. Recycle the exhaust heat of gas turbine or fuel cell to the endothermic reactions of coal gasification or methane reforming to produce hydrogen. by Exergy Regeneration, high power efficiency can be made. The exergy regeneration power generation system needs a low temperature coal gasification 700 850
Shiying Lin / Energy Procedia 37 (2013) 99 – 106
In this study, we build a exergy regeneration system proposed by combined of fuel cell with In-situ coal gasification (Chemical looping coal gasification), and then analysis the system proposed by using the AspenPlus model. % QPEGRVQHVJG'ZGTI[ 4 GIGPGTCVKQP% QCN2 QY GT) GPGTCVKQP # +) % % CPF# +) (% * GCV Coal
Gasifier
A-IGCC
GT
* GCV Coal
Gasifier
ST
A-IGFC
FC energy exergy
Gasifier Low temperature gasification (700-850
'ZJCWUVJGCVTGE[ENG
A-IGFC energy conversion flow
Fig. 2 Concept of the Exergy regeneration coal power generation (A-IGCC, A-IGFC)
2. System proposed Fig. 3 shows concept of exergy regeneration power generation combined chemical looping coal gasification with fuel cell. Product gases of Chemical looping coal gasification mainly contain hydrogen with CH4. Hydrogen is fuel for Fuel cell power generation and the waste heat of fuel cell is used for CH4 reforming. CH4 + H2O + waste heat 2 + CO2 Waste heat become to hydrogen energy means exergy regeneration.
Points in the proposed system: Ca Looping coal gasification CH4 content in gasification gas 10 20%
Low temperature gasification about 750 catalyst, If needed 30%-40% FC exhaust heat be used for CH4 reforming
Gasifier type used in the proposed system: Circulating Fluidized Bed Unreacted char in low temperature gasifier can be burned in combustor to calcine CaCO3 and to heat bed materials. Can separate the exhaust gases of combustor and gasifier, to obtain high concentration CO2 and H2/CH4 Gasification rate improvement at lower temperature: Ca looping + Catlyst (if needed) Using CaO as heating material can largely reduced the amount of heating material like SiO2.
101
102
Shiying Lin / Energy Procedia 37 (2013) 99 – 106
Using Ca looping and catalyst can obtain enough gasification rate and purity of H2/CH4 at low temperature. CO2 absorbed by CaO can improve steam gasification reaction equilibrium constant, KC for Ca Looping steam gasification (see Fig.1) % CNQQRKPIEQCNICUKHKECVKQP(% RQY GTU[UVGO HNQY CO2 CaSO4 Ash
CaO
Limestone make-up
Combustor Calciner 950 1100
Coal Catalyst
FC heat exergy reneration
H2 80%, CH4 20%
H2 CH4 H2 Gas clean up separation reforming separation
Tar reforming
Heat changer
H2
Gasifier
Off gas
H2
700 800
Q1 Steam
Water
(FCQ:0.3-0.4)
Q2
FC Power system
O2
Fig. 3 Exergy regeneration power generation system proposed by combined FC with the In-situ CO2 capture (chemical looping) coal gasification.
Main results studied until now: Gas products : mainly H2 80%; CH4 20% CaO had enough strength during cycle. Ash and Sulfur compounds can be separated by cyclone and filter (see Fig.4). CaO also improve tar steam reforming Under pressure condition, CaCO3 can be calcined at1000 oC (see Fig. 5). Concept of Ca Looping coal gasification
40
Real limestone decomposition Temperature
CO2
O2 or 1000 Air
Filter
CaO
CaCO3 /CaS/
Char
30
CaCO3
CO2 20 atm
cyclone
Gasifier
% QO DWUVQT
% CNEKPGT
CaO/ Ash /CaSO4
750
Ash /CaSO4 H2/CH4
Coal
CaO
20 10
Theoretical Decomposition curve
CO2 6 atm Q %
0
Steam 1000
1100
1200
1300
1400
1500
Temperature [K]
Fig. 4 Ca looping coal gasification process.
Fig.5 Calcination temperature of limestone under high CO2 pressure. It was found that the decomposition temperature of natural limestone is lower than theoretical decomposition temperature of CaCO3.
103
Shiying Lin / Energy Procedia 37 (2013) 99 – 106
Increase impurity content in material, decrease the decomposition temperature of material.
Gasification Part
Gas Reforming Part
FC Heat Recycle Part
3. AspenPlus Process Model Fig. 6 shown an AspenPlus model structured for the process combined chemical looping coal gasification with fuel cell. IGFC Exhaust heat recycle
IGFC power Generation
H2 Separation 2
CO Shift CH4 reforming
Product gas Heating value
H2 Separation 1
Coal Heating value Coal supply
CH4 reforming Steam generation
Gasification Steam generation
Gasifier and cyclone
Gasification Residue heating
Calciner and Cyclone
Fig. 6 AspenPlus model structured for the process combined chemical looping coal gasification with fuel cell Calculation conditions: Coal supply 42t/h S/Coal=1/1 Limestone making up 4.2t/h Pressure 20 atm Gasifire T 500-850 Material circulating: enough heat supply for gasification Analysis points Gasification product gas Cold gas efficiency Hydrogen cold gas efficiency FC Power generation efficiency Material circulating ratio 4. Analysis results and discussion Gas products of Ca chemical looping coal gasification with T and P Fig.7 shown the gas products from Ca chemical looping coal gasification with different temperature and pressure.
104
Shiying Lin / Energy Procedia 37 (2013) 99 – 106
100
H
2
80 60
atm CO
40 CH4
20
CO
2
0 400
500
600
700
800
Gasification temperature [
]
900
Gas procts concentr. [dry%]
Gas procts concentr. [dry%]
Under 1atm and 500 650 temperature area, gas products can be obtained about 10% CH4. Over 650 , CH4 and H2 were decreased. Under 10 atm, 500 750 temperature area, gas products can be obtained about 20% CH4. Over 750 , CH4 and H2 were decreased. 100 H
2
80 60
atm
40
CO
CH
4
20 0 400
CO2 500
600
700
800
Gasification temperature [
1 atm
]
900
10 atm
Fig. 7 Analysis results of gas products from Ca chemical looping coal gasification with different T and P. This is caused by that, with pressure, CaO can absorbs CO2 at comparatively high temperature as shown in Fig. 8. ]
40 40
CO2 Concentration [vol
35
* GCVECRCEKV[MI
30 30
CaCO3
25
SiO2(950
750
: 270 kJ
CaO (950
750
187 kJ
20 20
CaO
15
1 atm 5 atm
10 10
55 00
700 700
CaO(950 10 atm
750 800 750 800 Temperature [ ]
)
CaCO3 (750 3,186 kJ
850 850
CaO-CO2 absorption equilibrium Fig. 8 CO2 absorption equilibrium by CaO with temperature and pressure.
Fig. 9 The heat capacity of sensible heat and reaction hest of materials
FC exhaust heat exergy regeneration hydrogen cold gas efficiency can be raised 10% than gasification cold gas efficiency (see Fig.10). Used a part of FC exhaust heat to generate steam, and to pre-heat supply materials, gasification cold gas. efficiency can be obtained as 85 %. Used a part of FC exhaust heat to reform CH4, hydrogen cold gas efficiency can be obtained as high as 95% . However, over 750 , the area which CaO can not absorb CO2, hydrogen cold gas efficiency decreased.
105
Shiying Lin / Energy Procedia 37 (2013) 99 – 106
At CaO absorbs CO2 area (<750 the material circulating ratio is about 1.7 (see Fig. 11) At the area which is difficult for CaO absorbing CO2 (>750 , the material circulation ratio quickly increased, as about 36 at 900 .
100
Hydrogen cold gas efficiency
Efficiency [%]
95
Exergy regeneration effect
90 85 80 75
Gasification cold gas efficiency IGFC power generation efficiency
70 65 400
500
600
700
800
Gasification temperature [
]
900
Fig. 10 Analysis results of cold gas efficiency, hydrogen efficiency and exergy regeneration.
/ CVGTKCNEKTEWNCVKQPTCVKQ
This is caused by that, the CO2 absorption heat with CaO is much larger than the sensible heat of materials (see Fig.9)
40 35 P: 10 atm 30 Material circulation ratio 25 Amount of material circulation 20 = Amount of coal supply 15 10 1.7 5 0 500 600 700 800
36
Gasification temperature [
900
]
Fig. 11 Analysis results of material circulation ratio with temperature.
5. Conclusion Ca looping coal gasification /FC power system with exergy regeneration was analyzed by using Aspen model. The results are shown as follows. 750 temperature area, Ca looping coal gasification can obtained product (1) Under 10 atm, 500 gases about 20% CH4 with 80% H2. (2) A part of FC exhaust heat can be used for CH4 reforming. The hydrogen cold gas efficiency was obtained as 95%, is 10% higher than gasificaiton cold gas efficiency. (3) At the temperature area witch CaO absorbs CO2, since the absorption heat can be supply to coal gasification, the material circulating ratio was low as 1.7. However, at the temperature area witch CaO can not absorb CO2, the material circulation ratio become higher as 36 at 900 oC.
Acknowledgements The authors give their great thanks to NEDO for their financial support.
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