Post-combustion CO 2 -capture from coal-fired power plants: Preliminary evaluation of an integrated chemical absorption process with piperazine-promoted potassium carbonate Jochen Oexmann a, *, Christian Hensel b , Alfons Kather a a Institute of Energy Systems, Hamburg University of Technology, Denickestr. 15, D-21073 Hamburg, Germany b Evonik Energy Services GmbH, Rellinghauser Str. 1-11, D-45128 Essen, Germany 1. Introduction Growing public awareness of the ongoing climate change has led to increasing research activity in the field of greenhouse gas (GHG) mitigating technologies. Since it is envisaged that renewable and nuclear energy will only provide part of the world’s energy needs in the next decades, fossil fuels will remain a key energy source. Of all fossil fuels, coal resources are the largest and show a wide global distribution. The continuing use of coal ensures a diversification of the energy supply and thus safeguards security of supply, especially in countries lacking their own natural gas and oil resources. However, coal-fired power plants show the highest specific CO 2 -emissions, currently about twice as large as those of natural gas-fired combined cycle power plants. CO 2 -emissions from coal-fired power plants can be reduced by increasing the energy conversion efficiency or by capturing and storing the emanating CO 2 . The latter is commonly international journal of greenhouse gas control 2 (2008) 539–552 article info Article history: Received 11 December 2007 Received in revised form 21 March 2008 Accepted 1 April 2008 Published on line 19 May 2008 Keywords: CO 2 capture Chemical absorption Potassium carbonate Piperazine ASPEN Plus 1 EbsilonProfessional 1 abstract The simulation tool ASPEN Plus 1 is used to model the full CO 2 -capture process for chemical absorption of CO 2 by piperazine-promoted potassium carbonate (K 2 CO 3 /PZ) and the sub- sequent CO 2 -compression train. Sensitivity analysis of lean loading, desorber pressure and CO 2 -capture rate are performed for various solvent compositions to evaluate the optimal process parameters. EbsilonProfessional 1 is used to model a 600 MW el (gross) hard coal- fired power plant. Numerical equations for power losses due to steam extraction for solvent regeneration are derived from simulation runs. The results of the simulation campaigns are used to find the process parameters that show the lowest specific power loss. Subsequently, absorber and desorber columns are dimensioned to evaluate investment costs for these main components of the CO 2 -capture process. Regeneration heat duty, net efficiency losses and column investment costs are then compared to the reference case of CO 2 -capture by monoethanolamine (MEA). CO 2 -capture by piperazine-promoted potassium carbonate with subsequent CO 2 -com- pression to 110 bar shows energetic advantages over the reference process which uses MEA. Additionally, investment costs for the main components in the CO 2 -capture process (absorber and desorber columns) are lower due to the enhanced reaction kinetics of the investigated K 2 CO 3 /PZ solvent which leads to smaller component sizes. # 2008 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +49 40 42878 2771; fax: +49 40 42878 2841. E-mail address: [email protected](J. Oexmann). Abbreviations: CCS, carbon capture and storage; FGD, flue gas desulphurisation; GHG, greenhouse gas; K 2 CO 3 , potassium carbonate; MEA, monoethanolamine; PZ, piperazine; RPP-NRW, Reference Power Plant North-Rhine-Westphalia. available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/ijggc 1750-5836/$ – see front matter # 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijggc.2008.04.002
Post-combustion CO2-capture from coal-fired power plants: Preliminary evaluation of an integrated chemical absorption process with piperazine-promoted potassium carbonate
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i n t e r n a t i o n a l j o u r n a l o f g r e e n h o u s e g a s c o n t r o l 2 ( 2 0 0 8 ) 5 3 9 – 5 5 2
Post-combustion CO2-capture from coal-fired power plants:Preliminary evaluation of an integrated chemical absorptionprocess with piperazine-promoted potassium carbonate
Jochen Oexmann a,*, Christian Hensel b, Alfons Kather a
a Institute of Energy Systems, Hamburg University of Technology, Denickestr. 15, D-21073 Hamburg, GermanybEvonik Energy Services GmbH, Rellinghauser Str. 1-11, D-45128 Essen, Germany
a r t i c l e i n f o
Article history:
Received 11 December 2007
Received in revised form
21 March 2008
Accepted 1 April 2008
Published on line 19 May 2008
Keywords:
CO2 capture
Chemical absorption
Potassium carbonate
Piperazine
ASPEN Plus1
EbsilonProfessional1
a b s t r a c t
The simulation tool ASPEN Plus1 is used to model the full CO2-capture process for chemical
absorption of CO2 by piperazine-promoted potassium carbonate (K2CO3/PZ) and the sub-
sequent CO2-compression train. Sensitivity analysis of lean loading, desorber pressure and
CO2-capture rate are performed for various solvent compositions to evaluate the optimal
process parameters. EbsilonProfessional1 is used to model a 600 MWel (gross) hard coal-
fired power plant. Numerical equations for power losses due to steam extraction for solvent
regeneration are derived from simulation runs. The results of the simulation campaigns are
used to find the process parameters that show the lowest specific power loss. Subsequently,
absorber and desorber columns are dimensioned to evaluate investment costs for these
main components of the CO2-capture process. Regeneration heat duty, net efficiency losses
and column investment costs are then compared to the reference case of CO2-capture by
monoethanolamine (MEA).
CO2-capture by piperazine-promoted potassium carbonate with subsequent CO2-com-
pression to 110 bar shows energetic advantages over the reference process which uses MEA.
Additionally, investment costs for the main components in the CO2-capture process
(absorber and desorber columns) are lower due to the enhanced reaction kinetics of the
investigated K2CO3/PZ solvent which leads to smaller component sizes.
# 2008 Elsevier Ltd. All rights reserved.
avai lab le at www.sc iencedi rec t .com
journal homepage: www.e lsev ier .com/ locate / i jggc
1. Introduction
Growing public awareness of the ongoing climate change has
led to increasing research activity in the field of greenhouse
gas (GHG) mitigating technologies. Since it is envisaged that
renewable and nuclear energy will only provide part of the
world’s energy needs in the next decades, fossil fuels will
remain a key energy source. Of all fossil fuels, coal resources
are the largest and show a wide global distribution. The
Abbreviations: CCS, carbon capture and storage; FGD, flue gas desuMEA, monoethanolamine; PZ, piperazine; RPP-NRW, Reference Power1750-5836/$ – see front matter # 2008 Elsevier Ltd. All rights reserveddoi:10.1016/j.ijggc.2008.04.002
continuing use of coal ensures a diversification of the energy
supply and thus safeguards security of supply, especially in
countries lacking their own natural gas and oil resources.
However, coal-fired power plants show the highest specific
CO2-emissions, currently about twice as large as those of
natural gas-fired combined cycle power plants.
CO2-emissions from coal-fired power plants can be reduced
by increasing the energy conversion efficiency or by capturing
and storing the emanating CO2. The latter is commonly
The calculation of the column height is based on the film
theory, in which a bulk liquid and gas phase and an interface
between the two phases are distinguished. The column height
of each theoretical stage is mainly determined by mass
transfer between the gas and the liquid phase, where the main
driving force is the difference in the partial pressure of CO2 in
the gas and in the liquid phase.
The required packing surface AP,i and the total packing
volume can be calculated from
AP;i ¼FCO2 ;iRTi
Ji; (A.5)
where FCO2 ;i is the CO2 mole flow on stage i going from the gas
into the liquid phase (absorption) or vice versa (desorption),
and Ji is the mass transfer flux which is determined from
Ji ¼ D pCO2 ;iKtot;i; (A.6)
where D pCO2 ;iis the change in the logarithmic CO2 partial
pressure difference between gas and liquid phase from stage
i to stage i + 1. The values for D pCO2 ;iare taken from the
simulation results.
Ktot,i is the mass transfer coefficient which comprises the
mass transfer coefficient of the gas phase KG and of the liquid
phase taking into account the chemical reactions.
Ktot;i ¼1
ð1=KGÞ þ ð1=ðL E KLÞÞ: (A.7)
KG depends on the diffusion of CO2 in the gas phase, a packing
specific equivalent diameter deq (MELLAPAK 125Y:
deq = 0.018 m) and the Sherwood number Sh which represents
the ratio of the characteristic length of the system to the
diffusive boundary layer thickness.
L is the temperature-dependent solubility of CO2 in
aqueous PZ solutions. Following the Bravo Fair’s correlation
(Kister, 1992), the physical mass transfer coefficient KL is a
function of the effective velocity of the liquid, the diffusion of
CO2 in the liquid phase and a packing specific length S
(MELLAPAK 125Y: S = 0.017 m).
Following Westerterp et al. (1993) the enhancement factor E
can be determined iteratively taking into account the
dimensionless Hatta number Ha, which compares the rate
of absorption of a solute in a reactive system to the rate of
absorption of the same solute in the case of physical
i n t e r n a t i o n a l j o u r n a l o f g r e e n h o u s e g a s c o n t r o l 2 ( 2 0 0 8 ) 5 3 9 – 5 5 2 551
absorption. As the carbamate reactions are dominant for the
determination of the overall absorption rate (Cullinane and
Rochelle, 2006), only the following reactions are considered:
PZþ CO2 þ
OH� @kPZ�OH�
PZCOO� þH2O
H2O @
kPZ�H2O
PZCOO� þH3Oþ
PZ @kPZ�PZ
PZCOO� þ PZHþ
CO32�
@
kPZ�CO3
2�
PZCOO� þHCO3�
PZCOO� @kPZ�PZCOO�
PZCOO� þHPZCOO
26666666664
37777777775
(A.8)
PZCOO� þ CO2
þ
H2O @
kPZCOO��H2O
PZðCOO�Þ2 þH3Oþ
PZ @kPZCOO��PZHþ
PZðCOO�Þ2 þ PZHþ
CO32�
@
kPZCOO��CO3
2�
PZðCOO�Þ2 þHCO3�
PZCOO� @kPZCOO��PZCOO�
PZðCOO�Þ2 þHPZCOO
266666664
377777775
(A.9)
With the rates of reaction kj taken from Cullinane and Rochelle
(2006), the Hatta number and with it the enhancement factor E
can be calculated.
Finally, with the column diameter the packing volume for
each equilibrium stage i is determined fromAP,i. A safety factor
of 25% and additional spacing for any additional equipment
such as distributors is added to determine the total packing
volume which is needed to reach equilibrium conditions on
each stage.
A.3. Investment costs
Total cost for absorber and desorber columns (Ctot) can be
divided into three groups:
Ctot ¼ CCJ þ CCP þ CCE; (A.10)
where CCJ is the cost for the column jacket, CCP the investment
cost for the packing and CCE is additional cost for any external
devices such as ladders and platforms. Costs are determined
following the strategy of Vatavuk and Neveril (1982) and scaled
to s in 2007 by taking into account the change in the M&S
index and s–US$ exchange rate.
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