(158d) Performance Analysis of a Staged Pressurized Oxyfuel Combustion (SPOC) Power Plant With Minimal Flue Gas Recycle

Power
plant CO₂ emissions account for a major portion of the anthropogenic
greenhouse gases emitted to the atmosphere. Presently, the costs associated
with the capture of carbon dioxide from coal-fired power plants using
first-generation oxy-combustion technology are prohibitively high. The U.S.
Department of Energy (DOE) has set a goal of developing technologies that can
lead to more than 90% capture of carbon dioxide, with an increased cost of
electricity of no more than 35%, as compared to a similar plant without carbon
capture. One approach that has shown promise to both reduce capital costs and
improve power plant efficiency is pressurized oxy-combustion.

Pressurizing
the combustion process increases the dew point of the flue gas moisture and
allows for condensation at high temperatures. The large latent energy
associated with the flue gas moisture can be effectively integrated with the Rankine
cycle to increase the efficiency of the process. It also reduces equipment
sizes, and eliminates air ingress, resulting in higher CO₂ purity in
the raw flue gas.

There
have been some studies in recent years to analyze the effect pressurization has
on the overall performance of an oxy-combustion power plant [1-3].
Results have shown that an improvement in net efficiency of about 3% points can
be gained over what has been reported for first-generation oxy-combustion
plants[2, 4].

In
this presentation, a new DOE-funded project under the Advanced Oxy-Combustion
Technology Development and Scale-up for New and Existing Coal-Fired Power
Plants program will be introduced. The goal of the project is to optimize the
design of a unique pressurized oxy-combustion process that incorporates fuel
staging to minimize the cost of electricity (COE).

A
fuel staging approach allows for increased control of the temperature and heat
transfer during combustion. This eliminates the need for other temperature
control processes, such as flue gas recycle or water/steam injection. The
potential benefits of fuel staging which may lead to improved cycle efficiency
are: reduced process gas volume, increased average radiation heat transfer,
reduced oxygen demands, increased CO₂ purity, and reduced auxiliary
power demands.

In
the Staged, Pressurized Oxy-Combustion (SPOC) process, combustion is carried
out initially at very high stoichiometric ratio, enabling control of
temperature even with minimal flue gas recycle. To enable combustion under
non-stoichiometric conditions, fuel is brought into the combustion chamber in
stages. In the first stage, the coal is burned in nearly pure oxygen. However,
the amount of coal is small and the amount of excess O₂ is very
large. With proper mixing rates, the temperature of the combustion products of
the first stage can be controlled since there is a large amount of excess O₂,
which effectively acts as a diluent. Also, the amount of coal consumed in the
first stage is relatively small.  The products of the first stage, a mixture of
O₂, CO₂ and H₂O, enter stage 2, where more
fuel is injected and more O₂ is consumed. Since the O₂ is
diluted with the products and the products have been cooled, the peak flame
temperature in this stage can be lower than the first stage. This process
continues in multiple stages until nearly all of the O₂ is consumed.

In
this work, the performance and costs of a 550MW_e (net) power plant
employing the SPOC process are investigated. An integrated pollutant control
method was used to remove the NO_x and SO_x. Process and
systems modeling was performed using ASPEN Plus software. Sensitivity studies
to understand the effect of pressure and the effect of the excess oxygen
concentration in the flue gas on the overall performance are also presented.

This
study shows that with the SPOC process, a net plant efficiency can be achieved
that is similar to that of a sub-critical, air-fired PC power plant that does
not have carbon capture. It is also concluded that a more advanced Rankine
cycle, with higher throttle pressure and temperature results in an efficiency similar
to that of a super-critical, air-fired PC power plant. The increased
efficiency, compared to a first-generation oxy-fired plant, is due to both an
increase in pressure allowing for the recovery of the latent heat in the flue
gas moisture, and the staged process allowing for a significant reduction of the
auxiliary load for recycling flue gas.

Acknowledgements

·        
This material
is based upon work supported by the Department of Energy under Award Number
DE-FE0009702.

·        
Ameren
advising team: Rich Smith, Tom Callahan, George Mues.

·        
Engineering,
consulting, and cost estimation services provided by Burns & McDonnell.

Disclaimer:

This
report was prepared as an account of work sponsored by an agency of the United
States Government. Neither the United States Government nor any agency thereof,
nor any of their employees, makes any warranty, express or implied, or assumes
any legal liability or responsibility for the accuracy, completeness, or
usefulness of any information, apparatus, product, or process disclosed, or
represents that its use would not infringe privately owned rights. Reference
herein to any specific commercial product, process, or service by trade name,
trademark, manufacturer, or otherwise does not necessarily constitute or imply
its endorsement, recommendation, or favoring by the United States Government or
any agency thereof. The views and opinions of the authors expressed herein do
not necessarily state or reflect those of the United States Government or any
agency thereof.

References:

1.         Fassbender, A.G., Analysis of ThermoEnergy integrated
power system for new power facilities using Alaskan and reference coal types,
2009, AEA.

2.         Hong,
J., et al., Analysis of oxy-fuel combustion power cycle utilizing a
pressurized coal combustor. Energy, 2009. 34(9): p. 1332-1340.

3.         Hong,
J., Techno-economic analysis of pressurized oxy-fuel combustion power cycle
for CO2 capture, 2009, MIT: Cambridge.

4.         DOE/NETL-2007/1291.
Pulverized Coal Oxycombustion Power Plants. Vol. 1: Bituminous Coal to
Electricity, rev. 2, 2008, U.S. Department of Energy National Energy
Technology Laboratory.