Integration of Oxygen Transport Membranes in an IGCC power plant with CO2 capture

Integration of Oxygen Transport
Membranes in an IGCC power plant with
CO2 capture

Rahul Anantharaman1 and Olav Bolland2
1
SINTEF Energy Research, Energy Processes
2
Department of Energy and Process Engineering, NTNU

PRES 2011, Florence
May 9, 2011

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SINTEF Energy Research s s s s s s 1

Overview of Presentation

Introduction
Motivation
Oxygen Transport Membranes
Objective
Project Framework

Integration of oxygen membranes in an IGCC
Membrane operating methods
Air integration

Summary

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concluded that the performance penalty associated with using E-class gas t
technology would be a barrier to successful deployment of pre-combustion capture.
Integrated Gasiﬁcation Combined Cycle
These processing steps are shown in the outline flow scheme in Figure 3.1:
(IGCC)

DYNAMIS D5.3.2:IGCC with pre-combustion CO2
Figure 3.1: Recommendations for HYPOGEN Initiative capture for co-production of electricity and hyd
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from coal and lignite. SINTEF Energy Research s s s s s s 3

Air Separation Unit

I ASU supplies O2 at 95% purity.
I Theoretical minimum work consumption: 49 kWh/ton of O2
produced.
I State-of-the-art cryogenic ASU consumes: 175-200 kWh/ton of
O2 produced.
I Cryogenic ASU development prospects: 145-160 kWh/ton of O2
produced.

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Oxygen Transport Membranes
I Dense ceramic membranes (metal oxides).
I Membrane operation based on mixed conduction of ions and
electrons.
I Separates O2 from air with 100% selectivity.
I Operating temperature range: 800-1000°C.

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Integration of OTM in an IGCC

I OTM are a promising technology that present a major source of
efficiency improvement
I Challenge lies in efficient integration of such membrane in an
IGCC to realize this potential

Objectives

I Develop efficient cycles integrating an Oxygen Transport
Membranes as an ASU in an IGCC plant to reduce efficiency
penalty.
I Insight into considerations for such an integration.

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Framework
I This work was done as part of the EU FP7 project DECARBit.
I DECARBit investigates several advanced pre-combustion capture
technologies, both at a fundamental and more applied level.

SP1 System integration and optimisation
including application
to other industries
SP2 Advanced Pre-
combustion CO2 separation CO2 to
Coal storage
Gasifier, Shift CO2 CO2
Reformer reactors H2, separation compression
Natural CO2
gas

O2 SP4 Enabling
H2
technologies for
(fuel
pre-combustion
gas)

Air Electric
Air Separation N2 Gas Steam power
Unit turbine Cycle

SP3 Advanced oxygen
separation technologies

SP5 Pre-combustion pilots

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Reference cases

I European Benchmarking Task Force (EBTF) established between
3 EU FP7 projects - CESAR, CAESAR and DECARBit.
I EBTF developed and published document on benchmarking
reference cases with and without capture for
1. Advanced Supercritical Pulverized Coal (post-combustion).
2. Integrated Gasiﬁcation Combined Cycle (pre-combustion).
3. Natural Gas Combined Cycle (post-combustion).
I Reference case for IGCC without capture: 46.88 %.
I Reference case for IGCC with 90% CO2 capture: 36.66 %.
I Relevant assumption: 50% air integration between GT and ASU.

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Membrane system design

I The driving force is the partial pressure difference (pO2 = xO2 · P )
between the oxygen rich feed side and the permeate side.
I The oxygen flux across the membrane is given by modified
RT ln pO ,perm σel σion
Wagner’s equation: JO2 = − 16F 2 L 2
ln pO ,feed σel +σion
∂ ln pO2
2

I Give a feed side oxygen partial pressure, to increase flux
1. xO2 ,perm should decrease, and/or
2. Pperm should should decrease.

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Membrane operating method
with sweep gas

I Advantages:
– Improved mechanical stability.
– O2 is produced at higher pressure and hence compression work to
gasiﬁer condition is reduced.
I Disadvantages:
– Sweep gas temperature should be close to that of the feed side.
– Sweep gas requirement.

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Sweep gas

I Sweep gas will dilute the O2 .
I Sweep gas can either be Steam or CO2 .
I Large ﬂow of sweep gas are required.

I Steam
– Extracted from bottoming cycle.
– Leads to large efﬁciency penalty.
I CO2
– Recycled after separation from syn-gas and requires compression.
– CO2 sweep increases CO2 captured, thus increasing energy
penalty.
– This is partly offset by the increased partial pressure of CO2 in the
acid gas removal section.

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Sweep gas - efﬁciency penalty

120 37
Steam flow (kg/s)
110
Energy penalty (MW) 32

nergy Penalty (MW)
100
Steam flow (kg/s)

90 27

80 22
70

En
17
60

50 12
10 12 14 16
Sweep gas pressure (bar)

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Membrane operating method
without sweep gas

I Advantages:
– No efﬁciency penalty associated with sweep gas.
I Disadvantages:
– O2 produced at lower pressure leading to increased compression
penalty.
– Mechanical stability of membrane system.

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50% air integration - Scheme 1

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I Efficiency lower than reference case with cryogenic ASU

Reasons for low efficiency

I Raising the OTM feed temperature to 900°C results in losses from
the extra fuel conversion to H2 and eventual combustion in this
process.
I Transport limitation: The overall plant efficiency depends on the
degree of O2 separation - mO2 ,perm /mO2 ,feed . The degree of
separation for the process under consideration is 0.45.
I A separate ASU required for N2 production. Nitrogen required for
gas turbine fuel dilution and coal transport is supplied by a
cryogenic ASU.
I Improper integration!

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Reference case - Temperature proﬁle

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50% Integration - Scheme 2

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I Efficiency lower than reference case with cryogenic ASU

Reasons for low efficiency

I Turbine Inlet Temperature (TIT) is reduced compared to the
reference case leading to increased efficiency penalty.
I Transport limitation.
I Need for seprate ASU for N2 production.
I Improper integration!

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100% Integration

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Figure 3: Process block diagram for OTM integrated IGCC plant with CO2 capture
100% Integration - Performance
Table 1: Overall plant performance of OTM integrated IGCC plant with CO2 capture
Coal flow rate 138.9 Tph
Thermal energy of fuel (LHV) 969.7 MWth
Thermal energy for coal drying 8.23 MWth
Gas turbine output 280.5 MWe
Steam turbine output 176.6 MWe
Gross electric power output 457.1 MWe
Total ancillary power consumption 92.1 MWe
Net electric power output 365.0 MWe
Net electric efficiency 37.3 %
CO2 capture rate 90.9 %

5. Conclusions
System considerations for integration of an oxygen transport membrane based air
separation unit are presented. Arguments for selection of membrane operating mode and
I Heat and mass GT is selected. detail. An integrated IGCC shows anand 100% airwith heating
air integration are discussed in
integration with
integration removewithout sweep gas efficiency gain of
The OTM
OTM
losses associated side
fuel to0.7% points over the reference IGCC plant with cryogenic ASU. However, the trade-off
900°C and transport limitation.
is the tighter integration and reduced flexibility of the plant. Also, the number of plant
I This also required a separate to the OTM based ASU for O2 production a
components is increased as in addition cryogenic ASU, but with smaller
cryogenic ASU is required for N2 production.
capacity.
I Complete integration could lead to start-up/shut-down and
availability issues.
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Summary

I An overview of the considerations when integrating an oxygen
transport membrane as an ASU in an IGCC is presented.
I An OTM with out sweep gas and 100% air integration is shown to
have 0.7% points higher efﬁciency than the reference case cycle.
I The trade-off is tighter integration - reduced ﬂexibility.
I Other cycles, e.g. combination of pre- and oxy-combustion
concepts, are being evaluated.

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Acknowledgement

The research leading to these results has received funding from the
European Community’s Seventh Framework Programme
(FP7/2007-2013) under grant agreement nˇ 211971 (The DECARBit
r
project).

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Integration of Oxygen Transport Membranes in an IGCC power plant with CO2 capture

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