(542d) Novel Solvent Selection and Solvent Stripping for CO2 Capture From Power Plants

Novel Solvent Selection and
Solvent Stripping for CO₂ Capture from Power Plants

Juan
Salazar and Urmila Diwekar

Center
for Uncertain Systems: Tools for Optimization & Management

Vishwamitra Research Institute

Clarendon
Hills, IL 60514

E-mail:
urmila@vri-custom.org; Tel: 630-886-3047

And

Kevin
Joback

Molecular
Knowledge Systems, Inc.

Bedford,
NH  03110-0755

And

Abhoyjit
S. Bhown

Electric
Power Research Institute, Inc.

Palo
Alto, CA 94304

This paper presents a new
approach to solvent selection for post-combustion CO₂ capture from
fossil fuel fired power plants.  Two main questions arise in a
solvent capture process: how to select an effective separating agent and how to
design and synthesize this separation process. In previous studies, few
solvents were considered for CO₂ capture. Further, researchers
arrived at these solvents using experimental methods with limited capacity to
screen a large number possible candidates.  In this work, we are using computer aided
molecular design (CAMD) method to obtain a large number of possible solvent
candidates. These candidates are then evaluated by integrating the solvent
selection and CO₂ capture process to ensure improved energy,
environmental, and economic performance. In this paper we present the first
attempt at using group contribution based CAMD to derive new solvents for CO₂
capture.  

CO₂ absorption in a
solvent-based capture process is essentially based on the reversible, selective
nature of the chemical reaction between the liquid solvent and CO₂
in the flue gas. The process flow diagram shown in Figure 1 has been widely
used in literature.  Flue gas from the
boiler is brought into contact with the solvent in the absorber after the
removal of impurities such as NOx, SOx and particulate matter using processes that also cool
the flue gas.  A blower is used to
compensate the pressure drop experienced in the absorber. In the absorber, CO₂
selectively absorbs into the solvent, and flue gas leaving the absorber is
relatively free of CO₂. The CO₂-rich solvent from the
absorber is then pumped to the top of a stripper (or regeneration vessel), via
a heat exchanger. Solvent is regenerated in the stripper at elevated
temperatures and near atmospheric pressure. The desorption heat required for
removing the absorbed CO₂ is provided to the reboiler
section of the stripper.  The CO₂-lean
solvent, containing far less CO₂ is then pumped back to the absorber
via a lean-rich heat exchanger to cool it to the operating temperature of the
absorber.  We used this process diagram
to evaluate new solvents.

Figure  SEQ Figure \* ARABIC \s 1 1

Base Absorption Process Flowsheet for CO₂
Capture 

 In our CAMD approach, we concentrated on amines.  In order to use group contribution methods,
at first we analyzed the equilibrium performance for these new amines for
absorption (CO₂ capture) and for regeneration (solvent
stripping).   The CAMD resulted in a list
that included a group of more than 50 alkyl alcohol amines whose CO₂
solubility properties have not been experimentally determined as far as we
know.  We evaluated these solvents using ASPEN
Plus models and group contribution methods like UNIFAC to evaluate the nonideality.  Figure
2 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003300320033003000320037003400390030000000
shows the preliminary results of these solvents.
The figure shows the energy requirement versus boiling point for 18 solvents
simulated both as ideal an nonideal
solvents.   In general, we observe the nonideality
related to these solvents reduces the energy consumption.   We will be generating and evaluating additional
solvents in order to determine optimum solvents.

Figure  SEQ Figure
\* ARABIC \s 1 2

Energy Requirements for the New Solvents