O objetivo desse trabalho foi o estudo da utilização do carbonato de potássio para a absorção de CO2, tendo como principal foco o uso dessa tecnologia para o beneficiamento de biogás em instalações de pequeno e médio porte. O estudo foi dividido em três partes. Na primeira, realizou-se um projeto fatorial, baseado em resultados obtidos por meio de simulação via ASPEN Plus, com o intuito de quantificar a influência da vazão de líquido, da vazão de gás, da concentração da solução e da temperatura do líquido na quantidade de gás carbônico absorvida. Na segunda, foram realizados ensaios de absorção de CO2 em coluna recheada com anéis de Raschig de vidro, utilizando soluções de carbonato de potássio, com objetivo de comparar os resultados obtidos pelo projeto fatorial e estudar o seu potencial para o processo de beneficiamento de biogás. Na terceira, quatro substâncias foram separadamente utilizadas em mistura com solução de carbonato de potássio, de maneira a verificar seu poder como promotores da reação de gás carbônico com carbonato de potássio. Os resultados do projeto fatorial apresentaram a temperatura, vazão e concentração de líquido como as variáveis independentes de maior influência positiva na absorção de CO2, enquanto que a vazão de gás teve influência negativa de baixa intensidade. A quantidade de gás carbônico absorvida em solução sem promotores e em pressão ambiente foi baixa, como relata a literatura. A utilização de promotores possibilitou um aumento substancial da absorção, principalmente com o uso da piperazina. / The objective of this work is to study the use of potassium carbonate for CO2 absorption, aiming to use this technology for biogas upgrade for small and medium scale plants. The study was divided in three parts. In the first one, a factorial design was done, based in results obtained by simulation via ASPEN Plus, to verify the influence of four process variables, namely: liquid volumetric flow rate, gas volumetric flow rate, solution concentration and liquid temperature. Secondly, CO2 absorption experiments were run in columns packed with glass Raschig rings, using potassium carbonate, in order to compare the results obtained by the factorial design and to study the solution\'s potential for biogas upgrade. Lastly, four substances were separately mixed into potassium carbonate solutions, aiming to verify their potential as CO2 absorption promoters. The results of the factorial design presented the liquid temperature, the liquid volumetric flow rate and the solution concentration as the most positively influential independent variables in carbon dioxide absorption, while the gas volumetric flow rate had a negative influence with low intensity. The amount of CO2 absorbed in solution without promoters and in ambient pressure was low, fact that is mentioned by other researchers. The use of promoters allowed a substantial increase in efficiency of CO2 absorption, mainly with the use of piperazine.

O objetivo desse trabalho foi o estudo da utilização do carbonato de potássio para a absorção de CO2, tendo como principal foco o uso dessa tecnologia para o beneficiamento de biogás em instalações de pequeno e médio porte. O estudo foi dividido em três partes. Na primeira, realizou-se um projeto fatorial, baseado em resultados obtidos por meio de simulação via ASPEN Plus, com o intuito de quantificar a influência da vazão de líquido, da vazão de gás, da concentração da solução e da temperatura do líquido na quantidade de gás carbônico absorvida. Na segunda, foram realizados ensaios de absorção de CO2 em coluna recheada com anéis de Raschig de vidro, utilizando soluções de carbonato de potássio, com objetivo de comparar os resultados obtidos pelo projeto fatorial e estudar o seu potencial para o processo de beneficiamento de biogás. Na terceira, quatro substâncias foram separadamente utilizadas em mistura com solução de carbonato de potássio, de maneira a verificar seu poder como promotores da reação de gás carbônico com carbonato de potássio. Os resultados do projeto fatorial apresentaram a temperatura, vazão e concentração de líquido como as variáveis independentes de maior influência positiva na absorção de CO2, enquanto que a vazão de gás teve influência negativa de baixa intensidade. A quantidade de gás carbônico absorvida em solução sem promotores e em pressão ambiente foi baixa, como relata a literatura. A utilização de promotores possibilitou um aumento substancial da absorção, principalmente com o uso da piperazina. / The objective of this work is to study the use of potassium carbonate for CO2 absorption, aiming to use this technology for biogas upgrade for small and medium scale plants. The study was divided in three parts. In the first one, a factorial design was done, based in results obtained by simulation via ASPEN Plus, to verify the influence of four process variables, namely: liquid volumetric flow rate, gas volumetric flow rate, solution concentration and liquid temperature. Secondly, CO2 absorption experiments were run in columns packed with glass Raschig rings, using potassium carbonate, in order to compare the results obtained by the factorial design and to study the solution\'s potential for biogas upgrade. Lastly, four substances were separately mixed into potassium carbonate solutions, aiming to verify their potential as CO2 absorption promoters. The results of the factorial design presented the liquid temperature, the liquid volumetric flow rate and the solution concentration as the most positively influential independent variables in carbon dioxide absorption, while the gas volumetric flow rate had a negative influence with low intensity. The amount of CO2 absorbed in solution without promoters and in ambient pressure was low, fact that is mentioned by other researchers. The use of promoters allowed a substantial increase in efficiency of CO2 absorption, mainly with the use of piperazine.

Thesis (MScEng)--Stellenbosch University. / ENGLISH ABSTRACT: Carbon dioxide (CO2) is classified as the main greenhouse gas (GHG) contributing to global warming. Estimates by the Intergovernmental Panel on Climate Change (IPCC) suggest that CO2 emissions must be reduced by between 50 to 85% by 2050 to avoid irreversible impacts. Carbon capture and storage (CCS) strategies can be applied to de-carbonize the emissions from fossil-fueled power plants. Compared to other CCS techniques, post-combustion capture (PCC) is most likely to be implemented effectively as a retrofit option to existing power plants. At present however CCS is not yet commercially viable. The main challenge with CCS is to reduce the inherent energy penalty of the CO2 separation stage on the host plant. Seventy-five to eighty percent of the total cost of CCS is associated with the separation stage. There are several technologies available for separating CO2 from power plant flue gas streams. Reactive absorption with aqueous amine solutions has the ability to treat low concentration, low pressure and large flux flue gas streams in industrial-scale applications. It is most likely to be the first technology employed commercially in the implementation of CCS. The energy required for solvent regeneration however, is high for the standard solvent used in reactive absorption processes, i.e. MEA. This leads to a reduction in thermal efficiency of the host plant of up to 15%. Alternative solvent formulations are being evaluated in an attempt to reduce the energy intensity of the regeneration process. The main objective of this study was to establish a novel, simplified thermodynamic method for solvent screening. Partial solubility parameters (PSPs) were identified as the potential basis for such a method. The major limitation of this approach is that the model doesn’t account for effects from chemical reaction(s) between materials, e.g. CO2 reacting with aqueous alkanolamine solutions; considering only the effects from dissolution. The EquiSolv software system was developed based on PSP theory. The Hansen 3-set PSP approach was used to describe the equilibrium behaviour of CO2 absorbing in task specific solvents. The Hansen theory was expanded to a 4-set approach to account for contributions from electrostatic interactions between materials. The EquiSolv program was used successfully to screen large sets of solvent data (up to 400 million formulations) in the search for suitable alternative solvent formulations for CO2 absorption. The secondary objective of this study was to evaluate the ability of the proposed PSP model to accurately predict suitable alternative solvents for CO2 absorption through preliminary experimental work. A series of CO2 absorption experiments were conducted to evaluate the absorption performance of predicted alternative solvent formulations. The predicted alternative solvent formulations exhibited a significant improvement in absorption performance (up to a 97% increase in the measured absorption capacity) compared to conventional solvent formulations. Statistical analysis of the experimental results has shown that there is a statistically significant concordant relationship between the predicted and measured rankings for the absorption performance of the predicted solvent formulations. Based on this it was concluded that PSP theory can be used to accurately predict the equilibrium behaviour of CO2 absorbing in task specific solvents. Recently ionic liquids (ILs) have been identified as potential alternatives to alkanolamine solutions conventionally used for CO2 absorption. Absorption experiments were conducted as a preliminary assessment of the absorption performance of ILs. Results have shown ILs to have significantly improved performance compared to conventional alkanolamine solvents; up to a 96% increase in the measured absorption capacity compared to conventional solvents. Future work should focus on developing task specific ionic liquids (TSILs) in an attempt to reduce the energy intensity of solvent regeneration in CO2 absorption processes. / AFRIKAANSE OPSOMMING: Koolsuurgas (CO2) word geklassifiseer as die vernaamste kweekhuis gas (GHG) wat bydra to globale verwarming. Beramings deur die Interregeringspaneel oor Klimaatsverandering (IPKV) toon aan dat CO2 emissies teen 2050 verminder moet word met tussen 50 en 85% om onomkeerbare invloede te vermy. Verskeie koolstof opvangs en bergings (KOB) strategieë kan toegepas word ten einde die koolstof dioksied konsentrasie in die emissies van kragstasies wat fossielbrandstowwe gebruik, te verminder. Naverbranding opvangs (NVO) is die mees aangewese KOB tegniek wat effektief toegepas kan word op bestaande kragstasies. Tans is KOB egter nog nie kommersieël lewensvatbaarvatbaar nie. Die hoof uitdaging wat KOB in die gesig staar is om die energie boete inherent aan die CO2 skeidingstap te verminder. Tussen vyf-en-sewentig en tagtig persent van die totale koste van KOB is gekoppel aan die skeidingstap. Daar is verskeie metodes beskikbaar vir die skeiding van CO2 uit die uitlaatgasse van kragstasies. Reaktiewe absorpsie met waterige oplossings van amiene kan gebruik word om lae konsentrasie, lae druk en hoë vloei uitlaatgasstrome in industriële toepassings te behandel. Dit is hoogs waarskynlik die eerste tegnologie wat kommersieël aangewend sal word in die toepassing van KOB. Die oplosmiddel wat normalweg vir reaktiewe absorpsie gebruik word (d.w.s. MEA) benodig egter ‘n groot hoeveelheid energie vir regenerasie. Dit lei tot ‘n afname in die termiese doeltreffendheid van die voeder aanleg van tot 15%. Alternatiewe oplosmiddelstelsels word tans ondersoek in ‘n poging om the energie intensiteit van die regenerasieproses te verminder. Die hoof doelwit van hierdie studie was om ‘n nuwe, ongekompliseerde termodinamiese metode te vestig vir die keuring van alternatiewe oplosmiddels. Parsiële oplosbaarheidsparameters (POPs) is geïdentifiseer as ‘n moontlike grondslag vir so ‘n metode. Die model beskryf egter slegs die ontbindings gedrag van materiale. Die effekte van chemise reaksie(s) tussen materiale, bv. die tussen CO2 en waterige oplossings van alkanolamiene, word nie in ag geneem nie. Die POP teorie het gedien as grondslag vir die ontwerp van die EquiSolv sagteware stelsel. Die Hansen stel van drie POPs is gebruik om die ewewigsgedrag te beskryf van CO2 wat absorbeer in doelgerig-ontwerpte oplosmiddels. Die Hansen teorie is verder uitgebrei na ‘n stel van vier POPs om die bydrae van elektrostatiese wisselwerking tussen materiale in ag te neem. Die EquiSolv program is verskeie kere met groot sukses gebruik vir die sifting van groot stelle data (soveel as 400 miljoen formulasies) in die soektog na alternatiewe oplosmiddels vir CO2 absorpsie. Die sekondêre doelwit van die studie was om die vermoë van die voorgestelde POP model om geskikte alternatiewe oplosmiddels vir CO2 absorpsie akkuraat te voorspel, te ondersoek deur voorlopige eksperimentele werk. ‘n Reeks CO2 absorpsie eksperimente is gedoen ten einde die absorpsie werkverrigting van die voorspelde alternatiewe oplosmidels te ondersoek. ‘n Verbetering in absorpsie werkverrigting van tot 97% is gevind vir die voorspelde oplosmiddels vergeleke met die van oplosmiddels wat tipies in die industrie gebruik word. Statistiese ontleding van die eksperimentele resultate het getoon dat daar ‘n beduidende ooreenstemming tussen die voorspelde en gemete rangskikking van die voorspelde oplosmiddels se werkverrigting bestaan. Dus kan POP teorie gebruik word om die absorpsie van CO2 in doelgerig-ontwerpte oplosmiddels akkuraat te beskryf. Ioniese vloeistowwe (IVs) is onlangs geïdentifiseer as moontlike alternatiewe oplosmidels vir die alkanolamien oplossings wat normaalweg gebruik word vir CO2 absorpsie. Absorpsie eksperimente is gedoen ten einde ‘n voorlopige raming van die absorpsie werkverrigting van IVs te bekom. Daar is bevind dat IVs ‘n beduidende verbetering in werkverrigting toon in vergelyking met die alkanolamien oplosmiddels wat normaalweg gebruik word. ‘n Verbetering in absorpsie werkverrigting van tot 96% is gevind vir die voorspelde IV-bevattende oplosmiddels vergeleke met die van oplosmiddels wat tipies in die industrie gebruik word. Die fokus van toekomstige navorsing moet val op die ontwikkeling van doelgemaakte ioniese vloeistowwe (DGIVs) in ‘n poging om die energie intensiteit van oplosmiddel regenerasie in CO2 absorpsie prosesse te verminder.

Les procédés de captage de CO2 par absorption chimique engendrent une importante pénalité énergétique sur la production électrique des centrales à charbon, constituant un des principaux verrous technologiques au déploiement de la filière. L'objectif de cette thèse est de développer et valider une méthodologie à même d'évaluer précisément le potentiel d'un procédé de captage aux amines donné. La phénoménologie de l'absorption chimique a été étudiée en détail et représentée par des modèles à l'état de l'art. Le modèle e-UNIQUAC a été utilisé pour décrire les équilibres chimiques et de phases des solutions électrolytiques et les paramètres du modèle ont été régressés pour quatre solvants. Un modèle hors-équilibre a été utilisé pour représenter le transfert couplé de matière et de chaleur, accéléré par les réactions chimiques. Les modèles ont été validés avec succès sur des données expérimentales d'un pilote industriel et d'un pilote de laboratoire. L'influence des phénomènes sur les efficacités de séparation a été explicitée afin d'isoler les phénomènes les plus impactants. Une méthodologie a alors été proposée pour évaluer la pénalité énergétique, incluant les consommations thermiques et électriques, liée à l'installation d'un procédé de captage sur une centrale à charbon supercritique. Une méthode d'estimation du coût de l'électricité est proposée pour quantifier les dépenses opératoires et d'investissement d'un tel procédé. L'environnement de simulation et d'évaluation de procédés obtenu a ensuite été couplé à une méthode d'optimisation afin de déterminer les paramètres opératoires et les dimensions des équipements maximisant les performances énergétiques et économiques / CO2 capture processes by chemical absorption lead to a large energy penalty on efficiency of coal-fired power plants, establishing one of the main bottleneck to its industrial deployment. The objective of this thesis is the development and validation of a global methodology, allowing the precise evaluation of the potential of a given amine capture process. Characteristic phenomena of chemical absorption have been thoroughly studied and represented with state-of-the-art models. The e-UNIQUAC model has been used to describe vapor-liquid and chemical equilibria of electrolyte solutions and the model parameters have been identified for four solvents. A rate-based formulation has been adopted for the representation of chemically enhanced heat and mass transfer in columns. The absorption and stripping models have been successfully validated against experimental data from an industrial and a laboratory pilot plants. The influence of the numerous phenomena has been investigated in order to highlight the most limiting ones. A methodology has been proposed to evaluate the total energy penalty resulting from the implementation of a capture process on an advanced supercritical coal-fired power plant, including thermal and electric consumptions. Then, the simulation and process evaluation environments have been coupled with a non-linear optimization algorithm in order to find optimal operating and design parameters with respect to energetic and economic performances

The thermodynamic properties of CO2-mixtures are essential for the design and operation of CO2 Capture and Storage (CCS) systems. A better understanding of the thermodynamic properties of CO2 mixtures could provide a scientific basis to define a proper guideline of CO2 purity and impure components for the CCS processes according to technical, safety and environmental requirements. However the available accurate experimental data cannot cover the whole operation conditions of CCS processes. In order to overcome the shortage of experimental data, theoretical estimation and modelling are used as a supplemental approach.   In this thesis, the available experimental data on the thermodynamic properties of CO2 mixtures were first collected, and their applicability and gaps for theoretical model verification and calibration were also determined according to the required thermodynamic properties and operation conditions of CCS. Then in order to provide recommendations concerning calculation methods for engineering design of CCS, totally eight equations of state (EOS) were evaluated for the calculations about vapour liquid equilibrium (VLE) and density of CO2-mixtures, including N2, O2, SO2, Ar, H2S and CH4.   With the identified equations of state, the preliminary assessment of impurity impacts was further conducted regarding the thermodynamic properties of CO2-mixtures and different processes involved in CCS system. Results show that the increment of the mole fraction of non-condensable gases would make purification, compression and condensation more difficult. Comparatively N2 can be separated more easily from the CO2-mixtures than O2 and Ar. And a lower CO2 recovery rate is expected for the physical separation of CO2/N2 under the same separation conditions. In addition, the evaluations about the acceptable concentration of non-condensable impurities show that the transport conditions in vessels are more sensitive to the non-condensable impurities and it requires very low concentration of non-condensable impurities in order to avoid two-phase problems.   Meanwhile, the performances of evaporative gas turbine integrated with different CO2 capture technologies were investigated from both technical and economical aspects. It is concluded that the evaporative gas turbine (EvGT) cycle with chemical absorption capture has a smaller penalty on electrical efficiency, while a lower CO2 capture ratio than the EvGT cycle with O2/CO2 recycle combustion capture. Therefore, although EvGT + chemical absorption has a higher annual cost, it has a lower cost of electricity because of its higher efficiency. However considering its lower CO2 capture ratio, EvGT + chemical absorption has a higher cost to avoid 1 ton CO2. In addition the efficiency of EvGT + chemical absorption can be increased by optimizing Water/Air ratio, increasing the operating pressure of stripper and adding a flue gas condenser condensing out the excessive water. / QC 20100819

Coal-fired power plants are the largest anthropogenic point sources of CO2 emissions worldwide. About 40% of the world's electricity comes from coal. Approximately 49% of the US electricity in 2008 and 23% of the total electricity generation of Canada in 2000 came from coal-fired power plant (World Coal Association, and Statistic Canada). It is likely that in the near future there might be some form of CO2 regulation. Therefore, it is highly probable that CO2 capture will need to be implemented at many US and Canadian coal fired power plants at some point. Several technologies are available for CO2 capture from coal-fired power plants. One option is to separate CO2 from the combustion products using conventional approach such as chemical absorption/stripping with amine solvents, which is commercially available. Another potential alternative, membrane gas separation, involves no moving parts, is compact and modular with a small footprint, is gaining more and more attention. Both technologies can be retrofitted to existing power plants, but they demands significant energy requirement to capture, purify and compress the CO2 for transporting to the sequestration sites. This thesis is a techno-economical evaluation of the two approaches mentioned above along with another approach known as hybrid. This evaluation is based on the recent advancement in membrane materials and properties, and the adoption of systemic design procedures and optimization approach with the help of a commercial process simulator. Comparison of the process performance is developed in AspenPlus process simulation environment with a detailed multicomponent gas separation membrane model, and several rigorous rate-based absorption/stripping models. Fifteen various single and multi-stage membrane process configurations with or without recycle streams are examined through simulation and design study for industrial scale post-combustion CO2 capture. It is found that only two process configurations are capable to satisfy the process specifications i.e., 85% CO2 recovery and 98% CO2 purity for EOR. The power and membrane area requirement can be saved by up to 13% and 8% respectively by the optimizing the base design. A post-optimality sensitivity analysis reveals that any changes in any of the factors such as feed flow rate, feed concentration (CO2), permeate vacuum and compression condition have great impact on plant performance especially on power consumption and product recovery. Two different absorption/stripping process configurations (conventional and Fluor concept) with monoethanolamine (30 wt% MEA) solvent were simulated and designed using same design basis as above with tray columns. Both the rate-based and the equilibrium-stage based modeling approaches were adopted. Two kinetic models for modeling reactive absorption/stripping reactions of CO2 with aqueous MEA solution were evaluated. Depending on the options to account for mass transfer, the chemical reactions in the liquid film/phase, film resistance and film non-ideality, eight different absorber/stripper models were categorized and investigated. From a parametric design study, the optimum CO2 lean solvent loading was determined with respect to minimum reboiler energy requirement by varying the lean solvent flow rate in a closed-loop simulation environment for each model. It was realized that the success of modeling CO2 capture with MEA depends upon how the film discretization is carried out. It revealed that most of the CO2 was reacted in the film not in the bulk liquid. This insight could not be recognized with the traditional equilibrium-stage modeling. It was found that the optimum/or minimum lean solvent loading ranges from 0.29 to 0.40 and the reboiler energy ranges from 3.3 to 5.1 (GJ/ton captured CO2) depending on the model considered. Between the two process alternatives, the Fluor concept process performs well in terms of plant operating (i.e., 8.5% less energy) and capital cost (i.e., 50% less number of strippers). The potentiality of hybrid processes which combines membrane permeation and conventional gas absorption/stripping using MEA were also examined for post-combustion CO2 capture in AspenPlus®. It was found that the hybrid process may not be a promising alternative for post-combustion CO2 capture in terms of energy requirement for capture and compression. On the other hand, a stand-alone membrane gas separation process showed the lowest energy demand for CO2 capture and compression, and could save up to 15 to 35% energy compare to the MEA capture process depending on the absorption/stripping model used.

Coal-fired power plants are the largest anthropogenic point sources of CO2 emissions worldwide. About 40% of the world's electricity comes from coal. Approximately 49% of the US electricity in 2008 and 23% of the total electricity generation of Canada in 2000 came from coal-fired power plant (World Coal Association, and Statistic Canada). It is likely that in the near future there might be some form of CO2 regulation. Therefore, it is highly probable that CO2 capture will need to be implemented at many US and Canadian coal fired power plants at some point. Several technologies are available for CO2 capture from coal-fired power plants. One option is to separate CO2 from the combustion products using conventional approach such as chemical absorption/stripping with amine solvents, which is commercially available. Another potential alternative, membrane gas separation, involves no moving parts, is compact and modular with a small footprint, is gaining more and more attention. Both technologies can be retrofitted to existing power plants, but they demands significant energy requirement to capture, purify and compress the CO2 for transporting to the sequestration sites. This thesis is a techno-economical evaluation of the two approaches mentioned above along with another approach known as hybrid. This evaluation is based on the recent advancement in membrane materials and properties, and the adoption of systemic design procedures and optimization approach with the help of a commercial process simulator. Comparison of the process performance is developed in AspenPlus process simulation environment with a detailed multicomponent gas separation membrane model, and several rigorous rate-based absorption/stripping models. Fifteen various single and multi-stage membrane process configurations with or without recycle streams are examined through simulation and design study for industrial scale post-combustion CO2 capture. It is found that only two process configurations are capable to satisfy the process specifications i.e., 85% CO2 recovery and 98% CO2 purity for EOR. The power and membrane area requirement can be saved by up to 13% and 8% respectively by the optimizing the base design. A post-optimality sensitivity analysis reveals that any changes in any of the factors such as feed flow rate, feed concentration (CO2), permeate vacuum and compression condition have great impact on plant performance especially on power consumption and product recovery. Two different absorption/stripping process configurations (conventional and Fluor concept) with monoethanolamine (30 wt% MEA) solvent were simulated and designed using same design basis as above with tray columns. Both the rate-based and the equilibrium-stage based modeling approaches were adopted. Two kinetic models for modeling reactive absorption/stripping reactions of CO2 with aqueous MEA solution were evaluated. Depending on the options to account for mass transfer, the chemical reactions in the liquid film/phase, film resistance and film non-ideality, eight different absorber/stripper models were categorized and investigated. From a parametric design study, the optimum CO2 lean solvent loading was determined with respect to minimum reboiler energy requirement by varying the lean solvent flow rate in a closed-loop simulation environment for each model. It was realized that the success of modeling CO2 capture with MEA depends upon how the film discretization is carried out. It revealed that most of the CO2 was reacted in the film not in the bulk liquid. This insight could not be recognized with the traditional equilibrium-stage modeling. It was found that the optimum/or minimum lean solvent loading ranges from 0.29 to 0.40 and the reboiler energy ranges from 3.3 to 5.1 (GJ/ton captured CO2) depending on the model considered. Between the two process alternatives, the Fluor concept process performs well in terms of plant operating (i.e., 8.5% less energy) and capital cost (i.e., 50% less number of strippers). The potentiality of hybrid processes which combines membrane permeation and conventional gas absorption/stripping using MEA were also examined for post-combustion CO2 capture in AspenPlus®. It was found that the hybrid process may not be a promising alternative for post-combustion CO2 capture in terms of energy requirement for capture and compression. On the other hand, a stand-alone membrane gas separation process showed the lowest energy demand for CO2 capture and compression, and could save up to 15 to 35% energy compare to the MEA capture process depending on the absorption/stripping model used.

Made available in DSpace on 2014-12-17T15:01:56Z (GMT). No. of bitstreams: 1 LuizFSF_TESE.pdf: 2382677 bytes, checksum: 16f0fd92d4efa3b045a66f19b62ab2ea (MD5) Previous issue date: 2013-09-09 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Natural gas, although basically composed by light hydrocarbons, also presents contaminant gases in its composition, such as CO2 (carbon dioxide) and H2S (hydrogen sulfide). The H2S, which commonly occurs in oil and gas exploration and production activities, causes damages in oil and natural gas pipelines. Consequently, the removal of hydrogen sulfide gas will result in an important reduction in operating costs. Also, it is essential to consider the better quality of the oil to be processed in the refinery, thus resulting in benefits in economic, environmental and social areas. All this facts demonstrate the need for the development and improvement in hydrogen sulfide scavengers. Currently, the oil industry uses several processes for hydrogen sulfide removal from natural gas. However, these processes produce amine derivatives which can cause damage in distillation towers, can cause clogging of pipelines by formation of insoluble precipitates, and also produce residues with great environmental impact. Therefore, it is of great importance the obtaining of a stable system, in inorganic or organic reaction media, able to remove hydrogen sulfide without formation of by-products that can affect the quality and cost of natural gas processing, transport, and distribution steps. Seeking the study, evaluation and modeling of mass transfer and kinetics of hydrogen removal, in this study it was used an absorption column packed with Raschig rings, where the natural gas, with H2S as contaminant, passed through an aqueous solution of inorganic compounds as stagnant liquid, being this contaminant gas absorbed by the liquid phase. This absorption column was coupled with a H2S detection system, with interface with a computer. The data and the model equations were solved by the least squares method, modified by Levemberg-Marquardt. In this study, in addition to the water, it were used the following solutions: sodium hydroxide, potassium permanganate, ferric chloride, copper sulfate, zinc chloride, potassium chromate, and manganese sulfate, all at low concentrations (?10 ppm). These solutions were used looking for the evaluation of the interference between absorption physical and chemical parameters, or even to get a better mass transfer coefficient, as in mixing reactors and absorption columns operating in counterflow. In this context, the evaluation of H2S removal arises as a valuable procedure for the treatment of natural gas and destination of process by-products. The study of the obtained absorption curves makes possible to determine the mass transfer predominant stage in the involved processes, the mass transfer volumetric coefficients, and the equilibrium concentrations. It was also performed a kinetic study. The obtained results showed that the H2S removal kinetics is greater for NaOH. Considering that the study was performed at low concentrations of chemical reagents, it was possible to check the effect of secondary reactions in the other chemicals, especially in the case of KMnO4, which shows that your by-product, MnO2, acts in H2S absorption process. In addition, CuSO4 and FeCl3 also demonstrated to have good efficiency in H2S removal / O g?s natural, embora seja composto basicamente de hidrocarbonetos leves, apresenta tamb?m em sua composi??o gases contaminantes como o CO2 (Di?xido de carbono) e o H2S (Sulfeto de hidrog?nio). O H2S, que comumente ocorre nas atividades de explora??o e produ??o de ?leo e g?s, danifica as tubula??es de transporte do petr?leo e do pr?prio g?s natural. Por isso, a elimina??o do sulfeto de hidrog?nio levar? a significativa redu??o dos custos de opera??o e a uma melhor qualidade do ?leo destinado as refinarias, resultando assim num beneficio econ?mico, ambiental e social. Tudo isso demonstra a necessidade de desenvolvimento e aprimoramento de sequestrantes que removam o sulfeto de hidrog?nio da ind?stria de petr?leo. Atualmente existem v?rios processos para o tratamento do g?s natural, utilizados pela ind?stria petrol?fera para remo??o do H2S, no entanto, eles produzem derivados de aminas que danificam as torres de destila??o, formando precipitados insol?veis que provocam entupimento dos dutos e originam res?duos de grande impacto ambiental. Por isso, a obten??o de um sistema est?vel em meio reacional inorg?nico ou org?nico capaz de remover o sulfeto de hidrog?nio sem formar subprodutos que afetem a qualidade e o custo do processamento, transporte e distribui??o do g?s natural ? de grande import?ncia. Para estudar, avaliar e modelar a transfer?ncia de massa e a cin?tica da remo??o do sulfeto de hidrog?nio (H2S) montou-se uma coluna de absor??o contendo an?is de raschig, por onde o g?s natural contaminado com H2S atravessava uma solu??o aquosa de compostos inorg?nicos estagnada, sendo por esta absorvida. A essa coluna foi acoplado a um sistema de detec??o de H2S com interface com o computador. Os dados e Equa??es do modelo foram resolvidos pelo m?todo de m?nimos quadrados modificado de Levemberg-Marquardt. Neste estudo al?m da ?gua foram utilizadas as solu??es de hidr?xido de s?dio, permanganato de pot?ssio, sulfato de cobre, cloreto f?rrico, cloreto de zinco, cromato de pot?ssio, sulfato de mangan?s, a baixas concentra??es, na ordem de 10 ppm, com o objetivo ? avaliar a interfer?ncia entre par?metros f?sicos e qu?micos da absor??o, ou mesmo buscar um melhor coeficiente de transfer?ncia de massa como ? o caso dos reatores de mistura e colunas de absor??o operando em contra corrente. Nesse contexto a avalia??o da remo??o do H2S surge como um procedimento valioso para o tratamento do g?s natural e destino dos subprodutos do processo. Os estudos das curvas de absor??o obtidos permitiram determinar a etapa controladora da transfer?ncia de massa dos processos envolvidos, os coeficientes volum?tricos de transfer?ncia de massa e as concentra??es de equil?brio, assim como, efetuar um estudo cin?tico. Os resultados mostraram que a cin?tica de remo??o do H2S ? maior para o NaOH, mas como o estudo foi realizado em baixas concentra??es de reagente pode-se verificar o efeito das rea??es secund?rias nos outros reagentes, principalmente no caso do KMnO4, que mostra seu sub produto, MnO2, tamb?m atua na absor??o do H2S. O CuSO4 e o FeCl3 tamb?m apresentaram boa efici?ncia de remo??o

This degree project studies the integration of carbon capture system into biomass fired combined heat and power (bio-CHP) plants. The key disturbances from bio-CHP plants include flue gas flow rate, carbon dioxide (CO2) concentration and available heat for the reboiler because the use of versatile biomass and the dynamic operation of CHP plants results in large fluctuations in the properties of flue gas and the heat input for CO2 capture. To clearly understand the impacts of these disturbances on the performance of CO2 capture, a dynamic CO2 capture model is developed in Aspen Plus Dynamics by using monoethanolamine (MEA) based chemical absorption. Proportional-Integral (PI) feedback controllers are then implemented to further study and compare the performance of the CO2 capture process under different control strategies, the performance with general control settings and fine-tuned controllers are obtained and compared, including both the control performance and system performance. The control performance includes the maximum deviation and settling time, which could reflect only the performance of the controllers.  The system performance includes Captured CO2, reboiler duty and Energy penalty per unit CO2 captured, which could reflect CO2 capture system performance. An equilibrium stage steady state model is first developed for the key components in the CO2 capture plant in Aspen Plus, consisting of the absorber, the stripper, and lean-rich heat exchanger. By sizing the components and employing the pressure driven mode, the steady state model is enabled to be a dynamic model. The disturbances about flue gas and reboiler heat are taken from a real bio-CHP plant in Sweden. Considering the higher flue gas flowrate, the model has been scaled up to meet the requirement of this bio-CHP plant. The addition of controllers are done for the flexible operation of the CO2 capture system and the controlled variables considered in this study are the percentage of CO2 absorbed in the absorber column, reboiler temperature and rich solvent flow in the stripper column. The results show the effects of fluctuations in the key influencing factors on the control performance and the system performance . The fine-tuned controller implemented system showcases better performance when the quantity of CO2 captured is compared with that of the system in the absence of controllers, where a 1.1% increase in the amount of captured CO2 is observed when the flue gas flow rate is increased by 30%. The system also maintains a 1.8% higher capture rate when controllers are implemented. This showcases better system performance when controllers are implemented in the system. To further analyse the effects of control strategies two different control strategies are compared where controllers with general settings are compared to the controllers which are fine-tuning achieved by implementing tuning parameters which were obtained through Internal Model control (IMC) based on the system requirements. The fine tuning of the controllers results in improved system performance where the amount of captured CO2 increases by 1.4% when the reboiler duty is increased by 30% and a 1.7% decrease in the energy penalty per unit CO2 captured. Additionally, the results show that the settling time and maximum deviation are different for the two controllers where the controller which underwent fine tuning maintained the steady set point whereas the controller with general controller tuning showcases deviation before it attained stability. Therefore, the fine-tuned controller is more efficient to enable the flexible operation of CO2 capture when facing disturbance. It is studied that the tuning parameters implemented in the controllers affect the transient operation of the plant and improved the dynamic performance of the capture system. The tuned controllers offered more stability to the capture system while attaining their respective set points in a shorter time frame. It is also found that there exists a big difference between the system’s performance without controllers and that with finely tuned controllers. The difference in captured CO2 amount is approximately 26 ton/h when flue gas flow rate increases by 30%. The percentage difference is 1.1%, 7.7% and  5.9% for Captured CO2, reboiler duty and Energy penalty per unit CO2 captured respectively. In conclusion the control of the transient operation of the CO2 capture system needs the control system implemented and requires fine tuning parameters to achieve the desirable performance.

De 20 största massabruken i Sverige släpper tillsammans ut ungefär 20 miljoner ton CO2 per år. Dessa utsläpp har biogent ursprung och anses därför vara klimatneutrala. Massa- och pappersindustrin är därmed en lämplig kandidat för implementeringen av BECCS (eng. Bioenergy with Carbon Capture and Storage) och har en betydande potential att nå de, av den svenska regeringen, uppsatta klimatmålen som säger att Sverige inte ska några nettoutsläpp av växthusgaser till atmosfären senast år 2045. I detta examensarbete simulerades kemiska absorptions- och desorptionsprocesser med MEA som lösningsmedel genom att tillämpa den hastighetsbaserade metoden i en rigorös modell i Aspen Plus. Stripper- och absorptionsmodellerna validerades innan standardprocessen modifierades till en konfiguration som möjliggör värmeintegration av koldioxidinfångningens överskottsvärme med, exempelvis, ett sulfatmassabruk. Avskiljningsgraden och laddning hos den mättade lösningen användes som prestandaindikatorer för att validera absorptionskolonnerna. Återkokarens energiåtgång och laddning hos den omättade lösningen användes somprestandaindikatorer för att validera stripperkolonnerna. Samtliga kolonner dimensionerades för att erhålla 90 vikt% avskiljningsgrad. Olika flödeshastigheter av lösningsmedlet testades för att säkerställa effektivt nyttjande av packningen i absorptions- och stripperkolonnerna. Lämpliga temperaturnivåer för värmeintegration, inom och utanför, koldioxidinfångningen erhölls genom att utvärdera olika varianter av en stripper-overhead-kompression konfiguration. Utvärderingen av den modifierade MEA processen tog hänsyn till potentialen för ångbesparing och energieffektivisering. Resultat från simuleringarna tyder på att den modifierade strippern skulle kunna ge besparingar på upp emot 11 % i ånganvändning. Energibesparingar i samma storleksordning kunde även erhållas genom värmeintegration mellan koldioxidinfångningen och en särskild process i ett referensbruk. Implementering av BECCS-konceptet på det här sättet skulle därmed kunna bli ett mer attraktivt alternativ för den svenska massa- och pappersindustrin att bekämpa klimatförändringarna. / The 20 largest pulp mills in Sweden emit around 20 million tonnes of CO2 per year. These emissions are considered carbon-neutral since they originate from biogenic sources. The pulp and paper industry is therefore a good candidate for the application of BECCS (Bioenergy with Carbon Capture and Storage) and has the potential to play a significant role for reaching the long-term mitigation target set by the Swedish government that Sweden should be climate-neutral by year 2045. In this thesis, a MEA-based chemical absorption and desorption process was rigorously modelled in Aspen Plus using the rate-based method. Validation of the absorber and stripper model was conducted before the standard process was modified to a configuration that enables heat integration of a significant amount of excess heat from the capture process in, for example, a Kraft pulp mill. CO2 removal rate and rich solvent loading were used as performance indicators to validate the absorber columns. The reboiler duty and lean solvent loading served as performance indicators in the stripper validation. The columns were dimensioned considering 90 wt% capture rate. Efficient use of the entire packing in the absorber and stripper columns was ensured by testing different solvent flow rates. Suitable temperature levels for heat integration, within and across the capture plant, were obtained through an assessment of different versions of a stripper overhead compression configuration. The evaluation of the modified MEA processes took into account the steam conservation potential and energy efficiency potential. The simulation results indicate that the modified stripper may lead to savings of up to 11% in steam consumption. Heat integration between the capture plant and a specific process in a reference Kraft pulp mill resulted in energy savings of the same order of magnitude. Thereby, making the BECCS concept a more attractive solution for the Swedish pulp and paper industry to mitigate climate change.