Principal Research Results

Proposal of Advanced Integrated Coal Gasification Combined Cycle
Power Generation System with CO2 Capture
BackgroundCO2 emissions control from coal fired power plants is an important issue for global warming prevention. Electric powerindustries are advancing various measures such as the improvement of power generation efficiency and the introduction of carbon
neutral fuels such as biomass fuels to this problem. On the other hand, discussion for the application of CO2 capture and storage (CCS)
to coal fired power plants has been active internationally. However, if power plants with the current CO2 capture technology are introduced, it will be impossible to avoid great decreases of the power generation efficiency and rises in power generating cost. For thisreason, the development of new highly efficient power generating systems is desired.

Objectives
To improve the power generation efficiency and reduce the generation cost, this study aims to propose a highly efficient
integrated coal gasification combined cycle power generation system with CO2 capture, and to clarify the advantage of our proposed
IGCC system through numerical analysis.

Principal Results
1.

Features of proposed IGCC system with CO2 capture (Fig. 1)
The system has a new O2-CO2 blown coal gasifier where captured CO2 is effectively used. The synthesis gas is burned withthe mixed gas of O2 and CO2-rich recycled exhaust gas in the oxy-fuel gas turbine (closed gas turbine) system. Non-recycled exhaustgas is directly compressed and CO2 is liquefied. In this system, the gasification performance and power generation efficiency improve
greatly. Furthermore, CO2 separation process (CO2 absorption process, etc.) is not needed.
2. Expected effects(1) It was estimated that O2-CO2 blown coal gasifier improves the carbon conversion and cold gas efficiency as compared to thecurrent O2 blown (O2-N2 blown) coal gasifire and air blown coal gasifire because CO2 enhances the gasification reaction (Table 1).
These effects allow us to realize a compact gasifier and a simple char recycle system ＊ 1.
(2) The gas turbine is compacted because the inlet gas of the gas turbine is CO2-rich and the specific gravity of CO2 is higher than thatof air. Furthermore, the CO2-rich gas which has a low specific heat ratio, and the addition of a regenerative heat exchanger
improve the power generation efficiency in the gas turbine.
(3) CO2 separation process (CO2 absorption process etc.) is not needed because the exhaust gas of the gas turbine is directly
compressed and CO2 can be liquefied. Furthermore, the proposed system is expected to have the efficiency of 42% (HHV) in asystem with a 1300 ℃-class gas turbine and 45% in a system with a1500 ℃-class gas turbine because the addition of a regenerative heat exchanger improves the power generation efficiency (Table 2). If the molten carbonate fuel cell instead of the gas turbine
is applied to this system, efficiency of near 60 % is obtained.
3.

Development items
The following development items are enumerated to put this system into practical use.
・ Optimization of the total system
・Realization of the compact gasifier and simple gasification system (char recycle system etc.) by making the best use of great
improvement of the gasification performance
・ Measures for carbon deposition in the gas cooling process and the gas cleaning process
・ Optimization of the design and control method in the oxy-fuel gas turbine (closed gas turbine) system

Future Developments
It is scheduled to conduct the feasibility study (F.S.) of this system to clarify the power generating cost, and confirm thegasification performance using 3ton/day coal gasifier.
Main Researcher: Hiromi Shirai, Ph. D.,
Senior Research Scientist, Plant Engineering Sector, Energy Engineering Research Laboratory
Reference
H. Shirai, et.al., 2007, “Proposal of a highly efficient system with CO2 capture and the task on integrated coal gasification combined
cycle power generation”, CRIEPI Report M07003 (in Japanese)＊1：the system where collected particles (char) containing unburnt carbon from raw coal gas are recycled to the gasifire

1006. Fossil Fuel Power Generation

N2
Coal
OxygenorAir

Reformer

SteamturbineGascleaning

CO+H2O→CO2+H2

Coal
gasifier

CO2Separator

GasTurbine

HRSG

Gas cooler

AirStack

Steam

Steam
turbine
Steam

Steam
Coal

Coal
gasifier

OxygenCondensed water

Gas
TurbineHRSG

OxygenGascooler

Hot gascleaning

CO2

To CO2 liquefaction

Condensed water

To CO2 liquefaction

1) Current IGCC system with CO2 capture2) Proposed advance IGCC system with CO2 capture

Fig.1 Comparison between IGCC systems with CO2 capture
In the current system, the carbon monoxide (CO) in the synthesis gas is reacted with steam in a catalytic reactor, called a shiftconverter, to yield CO2 and more hydrogen. CO2 is then separated by a physical or chemical absorption process. On the otherhand, in the advanced system, the oxy-fuel gas turbine (closed gas turbine) system is applied, and CO2 separation process is notneeded because the synthesis gas is burned with the mixed gas of O2 and the recycled exhaust gas instead of air to obtain CO2-richexhaust gas whose components are CO2 and steam.

Table 1 Comparison of the gasification performance in three gasifire types
Gasifier type

O2-CO2O2-N2

Air%

10069.9

69.5

Generated Char

t/h

13.9

51.8

58.1

Carbon content.

wt%

072.9

66.3

Ash content

wt%

10027.1

23.7

t/h

274.6

274.6

536.3

MJ/m3N

11.1

10.3

5.7

Carbon conversion
CharSynthesis gas
Flow rate
Calorific value
CH4

vol%

000

H2

vol%

21.3

24.4

12.9

COvol%

66.5

56.9

31.8

CO2vol%5.402.0

H2O

vol%

5.302.2

N2

vol%

1.5

18.7

51.1

Cold gas efficiency

%80.8

78.8

76.5

It is estimated that the carbon conversion was 100% for the O2-CO2 blown gasifier. It means that coal is gasified perfectly. The
cold gas efficiency, which is the ratio of the energy of the synthesis gas to the energy of supplied coal, is 80% which is thehighest out of the three gasifier types. Therefore, the O 2-CO 2 blown gasification system presents the possibility of greatly
contributing to the improvement of the gasification performance as compared to conventional gasification systems.

Table 2 Comparison of the efficiency between the O2-N2 blown IGCC system and the O2-CO2 blown
IGCC system
Gasifier typeO2 -N2*2Gas turbine typeo

O2-CO21300 Coo

1300 C

1300 C

1500 oC090

Over 99 Over 99

CO2 recovery ratio％

Gross efficiency (HHV/LHV)％

47.7/49.8 42.7/44.7 56.9/59.6

60.0/62.8

Net efficiency％

42.5/44.5 34.9/36.5 42.1/44.1

45.1/47.2(HHV/LHV)*2 NEDO report No. 04002145-0, 2005.3 (in Japanese)In the O2-CO2 blown IGCC system (1300℃ class gas turbine), the efficiency of 42.0% at capturing CO2 by 99% or more can beobtained and the improvement of power generation efficiency is expected. On the other hand, the efficiency in the O2-N2 blown
IGCC system (1300℃ class gas turbine) decreases up to 34.9% when 90% of CO2 is captured.

1016