1. Introduction - Firenze University Press

Abstract:
PROCEEDINGS OF ECOS 2012 - THE 25 TH INTERNATIONAL CONFERENCE ON
EFFICIENCY, COST, OPTIMIZATION, SIMULATION AND ENVIRONMENTAL IMPACT OF ENERGY SYSTEMS
JUNE 26-29, 2012, PERUGIA, ITALY
Design and Optimization of ITM Oxy-Combustion
Power Plants
Surekha Gunasekaran a , Nicholas D. Mancini a and Alexander Mitsos a
a Massachusetts Institute of Technology, Cambridge, United States
surekhag@mit.edu, mancini@mit.edu, amitsos@alum.mit.edu (CA)
Oxy-fuel combustion using an oxygen ion-transport membrane (ITM) is a promising alternative to the existing
cryogenic air separation method, which incurs heavy thermodynamic and economic penalties. The
performance of ITM-based power plant systems depends on the operating conditions, geometric structure of
the reactor and the integration approach of ITM to the existing power plant system. A detailed study of these
factors is required to perform an optimization analysis. In this paper, an intermediate-fidelity ITM model is
used to study the performance of ITM reactors under different operating conditions and flow configurations.
Using this model, ITM-based oxy-combustion power cycles are investigated. This article focuses on the
results of an optimization analysis of the AZEP 100 cycle, which consists of a Brayton-like topping cycle and
a triple pressure heat recovery steam generation bottoming cycle. The effects of power plant operating
parameters are analyzed, namely the outlet pressure of pumps, turbines, valves and de-aerator, the split
fractions of splitters, flow rates, and the outlet temperatures of heat exchangers. The optimization study has
resulted in an increase of 2.92 percentage points which is important with respect to the feasibility of ITMbased
oxy-combustion power plants compared to alternatives.
Keywords:
Oxy-fuel combustion, Ion-transport membrane, Zero-emission power cycle, Power cycle efficiency.
1. CCS and ITM Technology
Global warming and anthropogenic emissions of CO2 have motivated the search for more efficient
and economically feasible environment-friendly technologies for power generation, which
contributes to about 65% of total anthropogenic CO2 emissions [1]. Carbon-dioxide capture and
sequestration (CCS) allows for the use of fossil fuels for power generation without the detrimental
effects of associated CO2 emissions. The most conventional CCS technique is post-combustion
capture, which is energy-intensive and expensive [2].
In the oxy-combustion method, O2 is separated from air prior to the combustion of the fuel-air
mixture and fuel oxidation occurs in a nitrogen free environment, typically with large recirculation
of exhaust gases to control the temperature. The flue gas consists only of CO2 and H2O, from which
CO2 can be separated simply by condensation. Thus, the penalty associated with separation of CO2
from the flue gas is greatly reduced [3]. At present, large scale separation of O2 from air is done
using cryogenic air separation methods. The major disadvantages of this method are that it is energy
intensive, and has low second law efficiency [4]. A promising alternative is the use of ion-transport
membranes (ITM), which operate based on chemical potential differences, and use a high
temperature mixed-conducting (ionic and electronic) ceramic membrane [5]. This technology is
motivated by the fact that the penalties incurred are much lower than the additional power
requirement for cryogenic air separation [6].
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