(317b) Electrochemical Membrane for Carbon Dioxide Separation and Power Generation

Electrochemical
Membrane for Carbon Dioxide Separation and Power Generation

Stephen
Jolly, Hossein Ghezel-Ayagh, Jennifer Hunt, Dilip Patel

FuelCell Energy, Inc., 3 Great Pasture Road,
Danbury, CT 06813

William
A Steen, Carl F Richardson

URS Corporation, 9400 Amberglen Blvd, Austin, TX
78729

Olga
A Marina

Pacific Northwest National Laboratory, 902 Battelle
Blvd., Richland, WA 99352

FuelCell Energy, Inc. (FCE) has developed a novel system concept for
separation of carbon dioxide (CO₂) from greenhouse gas (GHG) emission sources
using an electrochemical membrane (ECM). The salient feature of the ECM is its
capability to produce electric power while capturing CO₂ from flue
gas, such as from an existing pulverized coal (PC) plant. Laboratory scale
testing of the ECM has verified the feasibility of the technology for CO₂
separation from simulated flue gases of PC plants as well as combined cycle
power plants and other industrial facilities. Recently, FCE was awarded a
contract (DE-FE0007634) from the U.S. Department of Energy to evaluate the use
of ECM to efficiently and cost effectively separate CO₂ from the
emissions of existing coal fired power plants. 
The overarching objective of the project is to verify that the ECM can
achieve at least 90% CO₂ capture from flue gas of an existing PC
plant with no more than 35% increase in the cost of electricity (COE) produced
by the plant.  The specific objectives
and related activities planned for the project include: 1) conduct bench scale
tests of a planar membrane assembly consisting of ten or more cells of about
0.8 m² area each, 2) develop the detailed design for an ECM-based CO₂
capture system applied to an existing PC plant, and 3) evaluate the effects of
impurities (pollutants such as SO₂, NO_x, Hg) present in
the coal plant flue gas by conducting laboratory scale performance tests of the
membrane. The results of this project are anticipated to demonstrate that the
ECM is an advanced technology, fabricated from inexpensive materials, based on
proven operational track records, modular, scalable to large sizes, and a
viable candidate for >90% carbon capture from existing PC plants. In this
paper, the fundamentals of ECM technology including: material of construction,
principal mechanisms of operation, carbon capture test results and the benefits
of applications to PC plants will be presented.

SYSTEM CONCEPT

To address the concerns about
climate change resulting from emission of CO₂ by coal-fueled power
plants and other industrial plants, FCE has developed Combined Electric Power and Carbon-dioxide Separation (CEPACS) system concept, as a novel solution (US Patent 7,396,603 B2) for greenhouse
gas emission reduction. The CEPACS system utilizes the Company's well-established
Direct FuelCell^® (DFC^®) technology. The system concept
works as two devices in one:  it
separates the CO₂ from the exhaust of other plants such as an
existing coal fired plant and simultaneously, using a supplementary fuel,
produces clean and environmentally benign electric power at a very high
efficiency.

Figure
1.   CEPACS CO₂ Separation and
Power System Concept:

The system can be used with a variety of CO₂-containing greenhouse
gases (GHG)

A simplified diagram of the CEPACS
system concept is shown in Figure 1.  CO₂-containing
flue gas from a coal-fired (combustion-based) power plant, such as the exhaust
from a PC power plant or other industrial sources, is utilized as the oxidant
for the DFC cathode.  The key feature is
that the DFC utilizes the CO₂ of the flue gas as a reactant for the
electrochemical reaction to produce power, while synergistically transferring
CO₂ from the flue gas to the anode exhaust stream.  A supplementary fuel such as natural gas,
biogas from a digester, or syngas from a biomass/coal gasifier is internally
reformed in the fuel cell anode to provide the hydrogen needed to complete the
electrochemical power generation cycle. CEPACS separates the CO₂
from the flue gas because of the unique underlying mechanism of DFC operation.
The operating principle of the DFC is shown in Figure2, along with
the electrochemical reactions involved. In addition to CO₂, H₂O
is produced at the anode as H₂ is consumed by the chemical reaction.
Overall, the operating mechanism of the DFC results in the separation and
transfer of CO₂ to the anode exhaust stream with a much reduced
flow, compared to the original flue gas. The CO₂ rich anode exhaust
also contains water vapor which can be condensed, and a small amount of unused
fuel (H₂) which can be easily separated and either recycled to the
fuel cell for achieving ultra-high efficiencies or sold as a byproduct. The
captured CO₂ can then be processed for sequestration.

Figure
2.   Separation of CO₂ in a
Carbonate Fuel Cell:
Carbon dioxide is used at the cathode as an oxidant and
transferred to the anode via the carbonate electrolyte

TECHNOLOGY
STATUS

The fuel
cells used in the CEPACS system are built from the same material and by the
same fabrication processes as those used in the Company's DFC-based power plant
products. DFC technology has reached commercial maturity and is readily
available as a manufactured product used in building fuel cell stacks.  Figure 3 shows a picture of a unitized fuel
cell assembly produced at the Company's manufacturing plant in Torrington,
Connecticut.

Figure
3.  DFC Fabricated at Manufacturing Plant in Torrington, CT

Currently, the mass produced cells
of about 9000 cm² area, suitable for large-scale applications, are
commercially available.  These cells have
already been engineered for multi-layer stacking as shown in Figure 4.  The stacks of DFCs are incorporated in
modules, which make up the MW scale building blocks for large power plants and
CEPACS Systems.

Figure  4.  DFC
Stack: Four hundred cells are stacked to form
the building blocks usable in a CEPACS system

The CEPACS
enabling technology has been deployed in MW-scale power plants for stationary
power applications in three sizes: 300 kW, 1.4 MW, and 2.8 MW units.  A 1 MW (nominal) unit (DFC1500) installed at
a customer site is shown in Figure 5. 
FCE services over 50 DFC power plant sites around the globe.

 

Figure 5. DFC1500 Direct FuelCell Power Plant:

The DFC products are
suitable for large multi-MW systems

CEPACS
TECHNO-ECONOMIC EVALUATION

Monoethanolamine
based scrubbing technology (MEA) is considered to be the state-of-the-art for
separating CO₂.  However, the
energy and efficiency penalties of using amines for CO₂ capture in
PC plants are substantial.  About 22-30%
of plant gross power is used up by the amine system, dropping the plant
efficiency to <30%.  Operation of the
CEPACS system is set apart from other technologies by generation of electric
power rather than consuming it, resulting in an increase in the power output of
the retrofitted power plant.  

A
preliminary Technical and Economic Feasibility Study is being performed. The
study includes assessments of cost and performance of ECM-based CO₂
capture and compression system for retrofitting a 550 MW (net AC) PC plant. While
the ECM-based CEPACS system captures 90% of CO₂ from the PC plant
flue gas, it generates additional (net AC) power after compensating for the
auxiliary power requirements of CO₂ capture and compression. The net
electrical efficiency of the retrofitted PC plant (with CO₂ capture)
was estimated to be 39.8% (based on higher heating values of coal and natural
gas fuels used by PC plant and CEPACS system, respectively).

A
first iteration cost estimate for the CO₂ capture system has been
generated. The CEPACS plant cost and incremental cost of electricity for
ECM-based CO2 capture are being finalized. The CEPACS technology has the
potential to meet/exceed DOE's goal of <35% increase in COE.