Project Subjects
Thermal Power Generation Systems with CO2 Capture
Background and Objective
The reduction of CO2 emission in coal thermal power generation for global warming control is an important problem for the electric utilities. Therefore, the high-efﬁciency technology and biomass utilization are promoted in power generation systems. In recent years, CO2 Capture and Storage (CCS) as an effective global
warming control measure has been attracting attention. In Europe and the United States, many plans for CCS
projects have been announced. However, current CCS technology has many problems such as signiﬁcant reduction of power generation efﬁciency and high cost.
To offer a futuristic option that solves these problems, CRIEPI have proposed highly efﬁcient IGCC
system with CO2 capture (Fig. 1). In this project, we evaluate the feasibility of this system, the development issues
for practical use, and advance the development of the elemental technology.

Main results
1. Modeling of char gasiﬁcation for the O2-CO2 blown gasiﬁer
The O2-CO2 blown gasiﬁer is used in this system. The gasiﬁcation reaction is promoted by high partialpressure CO2 and H2O in this gasiﬁer. It is necessary for the analytical evaluation to construct a char*1 gasiﬁcation model that can be applied under the condition where CO2 gasiﬁcation competes with H2O gasiﬁcation. We
constructed a new char gasiﬁcation reaction model according to the amount of active sites*2 that CO2 and H2O areabsorbed. This model can express the char gasiﬁcation rate with a high degree of accuracy (Fig. 2). In addition,
simple numerical analyses of reductor parts of the gasiﬁers were performed using this model. It was found thatthe carbon conversion efﬁciency of O2-CO2 blown gasiﬁer is 10 point larger than that of Air blown gasiﬁer (Fig.
3) [M09014].
2. Optimization of the dry gas desulfurization process
Consideration of the optimized process to prevent carbon deposition, which may cause deterioration
effect on the desulfurization performance, is an extremely important issue, because the coal derived gas in thispower plant contains a very high concentration of carbon monoxide (around 60% vol.). Retardation of the carbon
deposition by steam addition to the process gas was evaluated from its effect on the reaction rate of desulfurization sorbent at various temperature and steam concentration. (Fig. 4) Prevention of carbon deposition required
steam concentration of 10% vol. at 500°C to retain the reaction rate over than base condition (450°C, steam
concentration of 5% vol.) This result enabled us to design optimization by considering the operating condition of
the desulfurization process [M09015].
3. Fundamental issues and guideline for design of Gas Turbine(GT) combustor
This system is different from the conventional GT, and is a fuel-oxygen combustion closed GT cycle
using the recycled gas mainly composed of CO2 and steam. To establish this system, reducing O2 and unburned
fuel in the exhaust is required, thus the fundamental issues for design of the GT combustor were reviewed (Table1). In addition, fundamental combustion analyses were conducted focusing O2 concentration at the reaction zone.
As a result, it has been clariﬁed that the fundamental outlines of design the GT Combustor for IGCC with CCS,
for example the conventional design methods of GT combustors can be applied utilizing O2 concentration aroundthe burner as a loadstar [M09009].
*1 : Char is the solid material including combustible content and ash that remains after coal pyrolysis.
*2 : Active site is the point or carbon at which CO2 or H2O molecules are adsorbed.

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Oxygen–1

Steam
SteamTurbine
TurbineSteam

Gasifier
Gasifier

Gas
Gas
Clean
Clean UpUp

CO2GasGas
TurbineTurbine
OxygenCO2HRSGHRSG
CO2Compression
Compression

StorageFig. 1 Concept of high efﬁcient IGCC with CO2
CaptureThis system consists of O2-CO2 blown gasiﬁer and O2
combustion closed GT with exhaust CO2 circulation. It is
expected to have higher thermal efﬁciency (more over 40%: HHV Net) and the system simpliﬁcation, compared withthe existing IGCC with CO2 capture.

80CCER(Air blown)
CCER(O2/CO2blown)

1500
1400

60

1300

40

1200

20T(O2/CO2blown) T
1100(Air blown)

00

1000
512
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Residence time [s]Fig. 3 Simple numerical analysis results of thereductor (the part where char gasiﬁcation
mainly progress) of the 2 stage entrained
bed gasiﬁer
Carbon conversion of O2/CO2 blown gasiﬁer is expected tobe much higher than that of air blown gasiﬁer because ofhigh CO2 part pressure.

0.00060.0004
conventionalmodel20.0002
00

proposedmodel

20 40 60 80 100
H2O concentration [%]Fig. 2 Char gasiﬁcation rate in CO2/H2O coexistence(measured by TG, American coal, 900°C)
Proposed model express the char gasiﬁcation rate better
than conventional models.

Temperature (T) [℃]

Carbon conversion efficiency
in the reductor (CCER) [%]100

CO2concentration [%]100 80 60 40 20
00.001experimental
conventional data
0.0008 model1

Relative desulfurization rate [－]CoalChar gasification rate dx/dt| x=0.5 [s ]Stable Power Supply Technology* Carbon deposition was prevented
in all condition except at 500 C andH2O 5vol%.

1.5

Target level ofthe reaction rate.

1.0

0.5

0.0

500℃
450℃
400℃
051015

Steam concentration [vol%]Fig. 4 Relative desulfurization rate of the sorbent at
varied steam concentration (Base condition is0.98 MPa, 450°
C, steam concentration of 5% vol.)Operating temperature has to be raised to retain reaction
rate of desulfurization to compensate negative effect fromthe steam addition for prevention of carbon deposition.

Table 1 Comparison of the Combustor characteristic between GT for IGCC with CCS and Natural Gas Burning GT.
Fundamental issues written in red for design have been clariﬁed by comparing with conventional GT combustors.

Working Medium
O2 Concentration atCombustion Zone
Local Maximum
Temp.
Equivalence Ratio(at Combustor Exit)NOx

GT Combustor for IGCC with CCS（Closed Cycle GT）*
Burned Gas (CO2+H2O)
diluent
Oxygen O2
FuelCoal Gasification Gas

Natural Gas Burning GT Combustor（Air Breathing Open Cycle GT/Conventional GT）
OxygenAirFuel

Natural Gas (Major Conp.:CH4)

0～100 % vol.(Controllable)

21 % vol.(Not Controllable)

Lower than 3080℃（Controllable by O2 Concentration）

2219℃ (Not Controllable)φ≒1 (Stoichiometric Combustion)
Reducing O2 in exhaust is needed for CO2 separation.

φ≒0.5 (Oxygen Rich Combustion)

Thermal NOx

Even if the flame temperature is high, NOx formation
is little for the low N2 partial pressure.→Countermeasures not necessary. (Non Premixed combustion)

Fuel NOx

Ingenuity for reducing NOx conversion ratio isrequired when the fuel includes nitrogen.

If the flame temperature is high, NOx formation
increases.→Some measures necessary (PremixedCombustion/Stratified Combustion)
The little nitrogen content in the fuel eliminate theneed for reducing NOx.

*Diluent is needed to control the flame temperature in fuel-oxygen combustion system.

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