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Björk, H. och Aronsson, J. (2011) Process Integration and Performance of Chilled Ammonia CO2 Capture Technology. Göteborg : Chalmers University of Technology (Examensarbete. T - Institutionen för energi och miljö, Avdelningen för energiteknik, Chalmers tekniska högskola, nr: ).
BibTeX
@mastersthesis{
Björk2011,
author={Björk, Henric and Aronsson, Jesper},
title={Process Integration and Performance of Chilled Ammonia CO2 Capture Technology},
abstract={Global environmental concern with possible near-term political policies to increase cost for
greenhouse gas emissions and an inclusion of aluminium production in the European emissions
trading system have sparked an interest for CO2 capture within the aluminium industry.
The aluminium manufacturing process produces large quantities of CO2 emissions through a noncombustion
process, this limits the potential technologies for CO2 capture to post combustion
only. A commercially available post combustion technology utilizes a solvent that is degraded in
an oxidising environment, as is the case in aluminium manufacturing. The CO2 capture
technology investigated in this study uses ammonia as solvent. Ammonia is not degraded by
oxygen. The process integration of the chilled ammonia process CO2 capture technology in a
novel aluminium manufacturing plant was investigated from a required reboiler duty and
available heat from an integration point of view. The process gas leaving the aluminium
manufacturing process is characterised by low CO2 concentration and high flow rates compared to
applications such as coal-power plants and sour-gas removal from natural gas. The effects on
performance and behaviour of the chilled ammonia process for these low CO2 concentrations
have not been fully established and have therefore been investigated.
The process integration was performed for a case with varying process gas flow rate and CO2
concentration. Gas properties were obtained from Hydro, the company operating the
Sunndalsøra aluminium manufacturing plant studied in this report. To isolate and investigate the
effects of varying CO2 concentration, a case with constant process gas flow rate was also studied.
The CO2 concentration was varied between 4, 7, 10 and 15 vol%. To determine the amount of
surplus heat available for process integration, a model of the process gas treatment train was
created using the process simulation software Ebsilon Professional. The model consists of the
existing process gas treatment train with the addition of two heat extractions for the top and
bottom cycle process integration.
The chilled ammonia process was described in two separate models in order to determine the
required reboiler duties, one for CO2 capture in the bottom cycle and another for ammonia
recovery in the top cycle. The simulation software Aspen Plus, handling heat and mass transfer,
chemical reactions and complex solutions, was used for modelling. All components, except the top
and bottom cycle absorbers, were modelled using an equilibrium calculation approach that
assumes infinitely fast mass transfer and reaction kinetics in reactors. The absorbers were
modelled using a rate-based approach in which also kinetics is considered, creating limiting
factors for the speed and performance of the process. The CO2 capture rate was predetermined to
85% with a maximum ammonia slip of 10 ppmv.
Through simulations it was observed that CO2 only has a moderate effect on the bottom cycle
specific reboiler duty, in kJ/kg CO2 captured, but that the absolute reboiler duty increases as CO2
concentration and total CO2 content increases. The opposite effect was observed for the top cycle;
with the absolute reboiler duty remaining relatively unchanged and the specific reboiler duty
decreasing with increasing CO2 concentration. The reboiler temperatures were found to be 111°C
for the top cycle and between 194-207°C for the bottom cycle.
Through simulations of the process gas treatment train, it was established that surplus heat is
available at temperatures sufficient for integration with the chilled ammonia process. It was found
that the total heat demand for the chilled ammonia process could be covered to 50% by process
integration for the best case scenario. The highest share of heat demand covered through process
integration was achieved for the 4 vol% CO2 concentration case. The share then decreases with
increasing CO2 concentration to 32% heat demand covered through integration for the 15 vol%
case.
The study concluded that increasing the CO2 concentration not necessarily will be economically
favourable. The lower process gas flow rate associated with the higher CO2 concentration allows
for the use of smaller process equipment, lowering investment costs. The lower share of heat
demand covered through process integration will however increase operational costs meaning
that the most economically feasible CO2 concentration is a trade-off between investment costs
and operational costs.},
publisher={Institutionen för energi och miljö, Energiteknik, Chalmers tekniska högskola},
place={Göteborg},
year={2011},
series={Examensarbete. T - Institutionen för energi och miljö, Avdelningen för energiteknik, Chalmers tekniska högskola, no: },
note={40},
}
RefWorks
RT Generic
SR Electronic
ID 145515
A1 Björk, Henric
A1 Aronsson, Jesper
T1 Process Integration and Performance of Chilled Ammonia CO2 Capture Technology
YR 2011
AB Global environmental concern with possible near-term political policies to increase cost for
greenhouse gas emissions and an inclusion of aluminium production in the European emissions
trading system have sparked an interest for CO2 capture within the aluminium industry.
The aluminium manufacturing process produces large quantities of CO2 emissions through a noncombustion
process, this limits the potential technologies for CO2 capture to post combustion
only. A commercially available post combustion technology utilizes a solvent that is degraded in
an oxidising environment, as is the case in aluminium manufacturing. The CO2 capture
technology investigated in this study uses ammonia as solvent. Ammonia is not degraded by
oxygen. The process integration of the chilled ammonia process CO2 capture technology in a
novel aluminium manufacturing plant was investigated from a required reboiler duty and
available heat from an integration point of view. The process gas leaving the aluminium
manufacturing process is characterised by low CO2 concentration and high flow rates compared to
applications such as coal-power plants and sour-gas removal from natural gas. The effects on
performance and behaviour of the chilled ammonia process for these low CO2 concentrations
have not been fully established and have therefore been investigated.
The process integration was performed for a case with varying process gas flow rate and CO2
concentration. Gas properties were obtained from Hydro, the company operating the
Sunndalsøra aluminium manufacturing plant studied in this report. To isolate and investigate the
effects of varying CO2 concentration, a case with constant process gas flow rate was also studied.
The CO2 concentration was varied between 4, 7, 10 and 15 vol%. To determine the amount of
surplus heat available for process integration, a model of the process gas treatment train was
created using the process simulation software Ebsilon Professional. The model consists of the
existing process gas treatment train with the addition of two heat extractions for the top and
bottom cycle process integration.
The chilled ammonia process was described in two separate models in order to determine the
required reboiler duties, one for CO2 capture in the bottom cycle and another for ammonia
recovery in the top cycle. The simulation software Aspen Plus, handling heat and mass transfer,
chemical reactions and complex solutions, was used for modelling. All components, except the top
and bottom cycle absorbers, were modelled using an equilibrium calculation approach that
assumes infinitely fast mass transfer and reaction kinetics in reactors. The absorbers were
modelled using a rate-based approach in which also kinetics is considered, creating limiting
factors for the speed and performance of the process. The CO2 capture rate was predetermined to
85% with a maximum ammonia slip of 10 ppmv.
Through simulations it was observed that CO2 only has a moderate effect on the bottom cycle
specific reboiler duty, in kJ/kg CO2 captured, but that the absolute reboiler duty increases as CO2
concentration and total CO2 content increases. The opposite effect was observed for the top cycle;
with the absolute reboiler duty remaining relatively unchanged and the specific reboiler duty
decreasing with increasing CO2 concentration. The reboiler temperatures were found to be 111°C
for the top cycle and between 194-207°C for the bottom cycle.
Through simulations of the process gas treatment train, it was established that surplus heat is
available at temperatures sufficient for integration with the chilled ammonia process. It was found
that the total heat demand for the chilled ammonia process could be covered to 50% by process
integration for the best case scenario. The highest share of heat demand covered through process
integration was achieved for the 4 vol% CO2 concentration case. The share then decreases with
increasing CO2 concentration to 32% heat demand covered through integration for the 15 vol%
case.
The study concluded that increasing the CO2 concentration not necessarily will be economically
favourable. The lower process gas flow rate associated with the higher CO2 concentration allows
for the use of smaller process equipment, lowering investment costs. The lower share of heat
demand covered through process integration will however increase operational costs meaning
that the most economically feasible CO2 concentration is a trade-off between investment costs
and operational costs.
PB Institutionen för energi och miljö, Energiteknik, Chalmers tekniska högskola,PB Institutionen för energi och miljö, Energiteknik, Chalmers tekniska högskola,
T3 Examensarbete. T - Institutionen för energi och miljö, Avdelningen för energiteknik, Chalmers tekniska högskola, no:
LA eng
LK http://publications.lib.chalmers.se/records/fulltext/145515.pdf
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