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Viability of Technologies for CO2 Capture and Reuse in a FPSO: Technical, Economic and Environmental Analysis
Krist V.Gernaey, Jakob K.Huusom and RafiqulGani (Eds.), 12th International Symposium on Process Systems Engineering and 25th European Symposium on Computer Aided Process Engineering. 31 May – 4 June 2015, Copenhagen, Denmark © 2015 Elsevier B.V. All rights reserved.
Viability of Technologies for CO2 Capture and Reuse in a FPSO: Technical, Economic and Environmental Analysis Bruna C de S Limaa, Ofélia Q F de Araújoa, José Luiz de Medeirosa, Cláudia R V Morgadoa a
Federal University of Rio de Janeiro (UFRJ), Av. Athos da Silveira Ramos, 149, Rio de Janeiro, 21941-909, Brazil [email protected]
Abstract The recent discoveries of Pre-Salt layers in Brazil require process developments for enhanced sustainability as these reservoirs have oil with associated natural gas exhibiting an expressive amount of CO2. Monetization of CO2 by offshore production of methanol in a dedicated FPSO – MFPSO – is a potential alternative to sustainable E&P. Two process alternatives for an MPFSO were previously investigated by the authors, consisting of physical absorption of CO2 with propylene carbonate and its conversion to yield methanol. Alternative 1 combines dry and steam reforming in one reactor (BiReforming), while Alternative 2 segregates the two reactions - dry reforming occurs in one reactor and water gas-shift reaction in a subsequent reactor. Both alternatives considered Enhanced Oil Recovery (EOR) as a parallel path for CO2 destination. The economic evaluation employed the software Capital Cost Estimation (CAPCOST) for calculations of CAPEX and OPEX. The software Waste Reduction Algorithm (WAR, EPA) was used to evaluate the potential environmental impacts. The analysis indicated that the performance of Alternative 1 was superior to the performance of Alternative 2: (a) methanol production (17.9 t/h) 4 times higher, (b) lower CAPEX, (c) sales revenue 181% greater, and (d) the potential environmental impact (PEI) 47.7% lower (868 PEI/h). In the present work, Alternative 1was modified by eliminating the EOR step, resulting in enhancement of methanol production as CO2 was integrally designated to chemical conversion. The modified process (Alternative 3) inherits the environmental feasibility of Alternative 1 and, through elimination of the EOR compression train, has the potential of positive impacts on CAPEX. Keywords: CO2 Capture and Utilization, Physical Absorption, Bi-Reforming, Methanol Synthesis, FPSO
1. Introduction This work approaches the production of remote natural gas exhibiting high CO2 contents where the separated CO2 is utilized in situ to produce methanol resulting in monetization of CO2 in an FPSO – MFPSO. The concept of an MFPSO is particularly relevant in the context of Brazilian pre-salt oil reservoirs, 300km distant from the continent and exhibiting high CO2 - reaching 70% in Jupiter reservoir (Guzzetti, 2010). The sought monetization could contribute to sustainability of natural gas production from such remote fields. The study evaluates three process alternatives where CO2 is captured from natural gas, by physical absorption with propylene carbonate (PC), producing a natural gas stream poor in CO2 and a stream consisting of a mixture of CO2
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and hydrocarbons. The evaluated routes for CO2 conversion to methanol includes BiReforming (Alternative 1 and 3) and Dry-Reforming (Alternative 2). In Alternatives 1 and 2, presented by Lima et al. (2014), part of the captured CO2 is destined for EOR while Alternative 3 (proposed in the present work) integrally converts CO2 to methanol. It is worth noting PC was selected as absorption solvent due to its easiness of regeneration, involving a simple expansion valve and a flash vessel. Also relevant in the scope of the downstream processing of the CO2 rich stream is that PC has also affinity for hydrocarbons, yet lower than its affinity for CO2. This benefit is explored by the proposed alternative processes, where absorbed hydrocarbons (CH4 and, in a lesser extent, heavier molecules) react with CO2 in dry reforming reactions (e.g., CH 4 CO 2 o 2CO 2 H 2 ), steam reforming reactions (e.g., CH 4 H 2O o CO 3H 2 ) and bi-reforming reactions (e.g., 3CH 4 2 H 2O CO 2 o 4CO 8 H 2 ). When CO2 reforming occurs simultaneously with steam reforming, coke deposition is drastically reduced (GANGADHARAN et al., 2012). This combination, named bi-reforming, generates syngas with a H2/CO ratio of 2, ideal for methanol synthesis (OLAH et al., 2009). Although dry reforming generates syngas with a suboptimal H2/CO ratio, the water gas-shift reaction (WGS) adjusts the ratio to favour further methanol synthesis (GANGADHARAN et al., 2012). Alternatives 1 and 3 combine dry and steam reforming in one reactor, while Alternative 2 segregates dry reforming in one reactor and WGS reaction in a subsequent reactor. The Alternatives are evaluated with Aspen HYSYS® simulator for calculation of energy and mass balances necessary to assess economic and environment performances. The economic evaluation employed Capital Cost Estimation Software (CAPCOST) for calculations of CAPEX and OPEX, and the Waste Reduction Algorithm Software (WAR) was used to evaluate the potential environmental impacts.
2. Process Simulation Bi-Reforming (Alternatives 1 and 3) and Dry Reforming (Alternative 2) were evaluated with Aspen HYSYS® simulator. The first process steps relates to CO2 capture and are common to all evaluated alternatives, which is fed with raw natural gas (NG) stream exhibiting the following molar composition: 60% CH4, 20% CO2, 12% C2H6, 6% C3H8 and 2% N2. The adopted process premises are: (a) the natural gas, previously dehydrated, enters at 70 bar and 40 oC with a volumetric flow rate of 1MMNm3/d; (b) the treated gas meets selling Brazilian specifications (< 3% in CO2), and (c) PC flow of 435t/h, necessary to obtain the molar ratio between CH4 and CO2 at treated stream suitable for reforming reactions (obtained by successive simulations). Figure 1 shows the Aspen HYSYS® process flow diagram for CO2 PC absorption. NG enters at the bottom of absorber column (T-100), countercurrent to PC. NG correctly specified is obtained as the top product of absorber, and PC regeneration occurs at the flash vessel (V-100).
Figure 1. Process flow diagram for CO2 absorption with PC
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2.1. Bi-Reforming Process with CO2-EOR(Alternative 1) The stream ‘CO2 + CH4’ is divided into two parts: one goes to a compression train, for CO2-EOR, and the other is destined to a reactor where both dry and steam reforming reactions occur, shown in Figure 2.
Figure 2. Process flow diagram for EOR and Bi-Reforming process – Alternative 1
With CO2/CH4 molar feed ratio of 1:1, GBR-100 operates at 900oC and 1 bar and water vapour is added in reactor at 10.81 t/h. After reaction, the stream ‘SYNGAS’ passes through a sequence of compressors, heat exchangers and vessels, in order to eliminate water and pressurize gas to 70 bar for methanol synthesis. These heat exchangers utilize seawater for refrigeration. Liquid methanol is recovered at V-101, V-103 and V106.The remaining hydrocarbons and syngas return to Methanol reactor. 2.2. Dry Reforming Processwith CO2-EOR (Alternative 2) Similarly to the Bi-Reforming process, the stream ‘CO2 + CH4’ is divided into two parts. However, the stream ‘To Reaction’ proceeds to the GBR-100 reactor, where occurs exclusively the dry reforming. GBR-100 operates at 870oC and 1 bar. After reaction, stream ‘SYNGAS’ passes through a compression and intercooler train. This stream is pressurized to 70.5 bar before entering the Adjust reactor (WGS), where water vapor is added at a rate of 2 t/h. In the sequence, stream “feed” enters in the Methanol reactor. The stream that leaves the Methanol reactor has a high quantity of unreacted methane, which, after methanol recovery, is recycled to GBR-100. Methanol is recovered at V-102, and residual hydrocarbons are recycled (Figure 3). 2.3. Bi-Reforming Process without CO2-EOR (Alternative 3) The stream ‘CO2 + CH4’ is integrally directed to methanol conversion, accordingly to Figure 4. Reaction section proceeds as described for Alternative 1.
3. Economic and Environmental Analysis – Alternatives 1 and 2 Alternatives 1 and 2 were evaluated economically, for decision of which reaction path would be more attractive, through CAPEX and OPEX calculations. Equipment sizing
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was performed according to procedures described in the literature (e.g., CAMPBELL, 2004; PERRY, 1997; TOURTON et al., 2009). For the economic analysis, the MS Excel spreadsheet CAPCOST, developed by Turton et al (2009), was employed. Table 1 presents the main results from Bi-Reforming (Alternative 1) and Dry-Reforming (Alternative 2) Processes, indicating the resulting CAPEX, OPEX and revenue for each alternative. Alternative 1 has the highest revenue as methanol production (17960 kg/h) was 4 times higher than for the Dry-Reforming Process (Alternative 2).
Figure 3. Process flow diagram for EOR and Dry-Reforming process – Alternative 2
Figure 4. Process flow diagram Bi-Reforming process without EOR – Alternative 3
Table 1. Results of CAPEX, OPEX and Revenue Sales – Alternatives 1 and 2 Cost (U$$) CAPEX OPEX Revenue Sales
Bi-Reforming 25,165,709 122,575,216 144,890,686
Dry-Reforming 32,145,906 101,189,415 51,463,757
The WAR Algorithm (CABEZZAS et al.,1999) was used to comparatively quantify the environmental performance of Alternatives 1 and 2, based on eight categories of environmental impacts, equally weighted. The categories are: Human Toxicity Potential
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by Ingestion, Human Toxicity Potential by Exposure, Aquatic Toxicity Potential, Terrestrial Toxicity Potential, Global Warming Potential, Ozone Depletion Potential, Smog Formation Potential, Acidification Potential. WAR measures performance as output rate of PEI (Potential of Environmental Impact). PEI can be described through rates of inlet (Îin), outlet (Îout) and generation (Îgen) of impact in a given system. The mass flow and composition obtained from ASPEN HYSYS simulations were used in the WAR algorithm. Comparing the total impact for these processes two Alternatives (both employing CO2-EOR), Bi-Reforming (Alternative 1) has a lower impact (868 PEI/hr) than Dry-Reforming (Alternative 2) (1661 PEI/hr).
4. Alternatives 1 and 3 - Bi-Reforming with and without EOR The comparative economic and environmental analysis indicate that Alternative 1 (BiReforming) is technically, economically and environmentally superior to Alternative 2. Considering the main objective of an MFPSO of enhanced methanol production, Alternative 3 was proposed with removal of the CO2-EOR section (Figure 4). Based on the conclusion of superior performance of Alternative 1 over Alternative 2, Alternative 1 is the basis of Alternative 3. A preliminary economic analysis (exclusively based on revenue increase) shows enhancement of methanol production of around 2 times over the production achieved in Alternative 1 (35,497.56 kg/h). Consequently, Alternative 3 presents revenue of U$$ 251,502,365, (Alternative 1 showed revenue of US$144,890,686). Furthermore, Alternative 3 and Alternative 1 were compared considering the generation rate of PEI, calculated through WAR Algorithm. It was observed that Alternative 1 (Bi-Reforming) has a negative rate, higher than Alternative 3 (Bi-Reforming without EOR), what means that the first alternative is environmentally superior to Alternative 3, as shown in Figure 5. It is worth noting that methanol contributes to all impact categories evaluated while CO2 most exclusively impacts in global warming. Consequently, WAR penalises the increase in methanol production achieved in Alternative 3.
Figure 5. Generation rate of PEI for Bi-Reforming with and without EOR step
5. Discussion and Conclusions The proposed processes are potentially amenable to methanol floating production system, MFPSO, where the regeneration of PC would present a competitive advantage over alternative CO2 capturing technologies, since weight and space are the key considerations for floating plants. The treated natural gas stream (248.7 m3/h) composition is (in molar basis): 90.19% CH4, 1.67% CO2, 3.31% C2H6, 0.63% C3H8 and
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4.20% N2. The main difference of the proposed processes is the fact that at Bi-Reforming (Alternatives 1 and 3) just one reactor is utilized, where occur both dry and steam reforming. On the other hand, for Dry-Reforming (Alternative 2) two reactors are conceived: one for dry reforming and other for WGS reaction. This difference poses a large discrepancy of methanol productivity, as methanol production by Bi-Reforming was 17905 kg/h, 4 times higher compared to Dry-Reforming. Dry reforming occurs not only for methane, but also for ethane and propane, and these last reactions are more favoured than the first one. In consequence, methane is not consumed, but rather produced in the Dry-Reforming alternative, explaining the associated low production of methanol. Since the preliminary conclusions indicate that Bi-Reforming is technically, economically and environmentally superior to Dry-Reforming, a third flowsheet was proposed, considering the elimination of CO2-EOR section, with dedicated production of methanol. Analysis showed that methanol production in Alternative 3 (35,497.56 kg/h) present revenues around 2 times higher than Alternative 1. Regarding the environmental aspect, Bi-Reforming (Alternative 1) shows superior environmental performance over Bi-Reforming without EOR step (Alternative 3) due to the penalty attributed by WAR algorithm to producing methanol, which contributes to all considered impact categories. However, both alternatives presented negative generation of PEI, which turns Alternative 3 the most sustainable alternative. Although a more detailed economic analysis for Alternative 3 (CAPEX and OPEX) is necessary to reinforce this conclusion, it is foreseen a superior economic performance since the increase in revenues is significant and compression costs associated to CO2-EOR are eliminated.
Acknowledgments The authors acknowledge the financial support of PETROBRAS S.A., ANP (PRHANP/MCT, PRH-41) and CNPq research grants.
References H. Cabezas, J. Bare, S. Mallick, 1999, Pollution prevention with chemical process simulators: the generalized waste reduction (WAR) algorithm - full version. Computers and Chemical Engineering, 23, 4–5, 623–634. J. M. Campbell, 2004, Gas conditioning and processing: the equipment modules. Norman: John M Campbell & Company, 2, 8. J. Formigli, 2007 Pre-salt reservoirs offshore Brazil: perspectives and challenges, Miami. C. Guzzetti, Gaffney, Cline & Associates, 2010, Review and evaluation of ten selected discoveries and prospects in the pre-salt play of the deepwater santos basin, Brazil. www.anp.gov.br/?dw=39137. P. Gangadharan,; K. Kanchi,; H. Lou, 2012, Evaluation of the economic and environmental impact of combining dry reforming with steam reforming of methane. Chem. Eng. Res. Des., 90, 11, 1956–1968. B. Lima, O. Araújo, J. L. Medeiros, C. Morgado, 2014, Technical, Economic and Environmental Viability of Offshore CO2, Proceedings of 2014 AICHE Annual Meeting, Atlanta, GA, USA. G. A. Ola et al., 2013, Bi-reforming of methane from any source with steam and carbon dioxide exclusively to metgas (CO–2H2) for methanol and hydrocarbon synthesis, J. Am. Chem. Soc., 135, 2,648–650. R. Perry, D. Green, 1997, Perry’s Chemical Engineers’s Handbook, McGraw-Hill, 1, 7. R. Turton et al., 2009, Analysis, Synthesis, and Design of Chemical Processes, New Jersey: Prentice Hall, 1, 3.
Viability of Technologies for CO2 Capture and Reuse in a FPSO: Technical, Economic and Environmental Analysis Bruna C de S Limaa, Ofélia Q F de Araújoa, José Luiz de Medeirosa, Cláudia R V Morgadoa a
Federal University of Rio de Janeiro (UFRJ), Av. Athos da Silveira Ramos, 149, Rio de Janeiro, 21941-909, Brazil [email protected]
Abstract The recent discoveries of Pre-Salt layers in Brazil require process developments for enhanced sustainability as these reservoirs have oil with associated natural gas exhibiting an expressive amount of CO2. Monetization of CO2 by offshore production of methanol in a dedicated FPSO – MFPSO – is a potential alternative to sustainable E&P. Two process alternatives for an MPFSO were previously investigated by the authors, consisting of physical absorption of CO2 with propylene carbonate and its conversion to yield methanol. Alternative 1 combines dry and steam reforming in one reactor (BiReforming), while Alternative 2 segregates the two reactions - dry reforming occurs in one reactor and water gas-shift reaction in a subsequent reactor. Both alternatives considered Enhanced Oil Recovery (EOR) as a parallel path for CO2 destination. The economic evaluation employed the software Capital Cost Estimation (CAPCOST) for calculations of CAPEX and OPEX. The software Waste Reduction Algorithm (WAR, EPA) was used to evaluate the potential environmental impacts. The analysis indicated that the performance of Alternative 1 was superior to the performance of Alternative 2: (a) methanol production (17.9 t/h) 4 times higher, (b) lower CAPEX, (c) sales revenue 181% greater, and (d) the potential environmental impact (PEI) 47.7% lower (868 PEI/h). In the present work, Alternative 1was modified by eliminating the EOR step, resulting in enhancement of methanol production as CO2 was integrally designated to chemical conversion. The modified process (Alternative 3) inherits the environmental feasibility of Alternative 1 and, through elimination of the EOR compression train, has the potential of positive impacts on CAPEX. Keywords: CO2 Capture and Utilization, Physical Absorption, Bi-Reforming, Methanol Synthesis, FPSO
1. Introduction This work approaches the production of remote natural gas exhibiting high CO2 contents where the separated CO2 is utilized in situ to produce methanol resulting in monetization of CO2 in an FPSO – MFPSO. The concept of an MFPSO is particularly relevant in the context of Brazilian pre-salt oil reservoirs, 300km distant from the continent and exhibiting high CO2 - reaching 70% in Jupiter reservoir (Guzzetti, 2010). The sought monetization could contribute to sustainability of natural gas production from such remote fields. The study evaluates three process alternatives where CO2 is captured from natural gas, by physical absorption with propylene carbonate (PC), producing a natural gas stream poor in CO2 and a stream consisting of a mixture of CO2
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and hydrocarbons. The evaluated routes for CO2 conversion to methanol includes BiReforming (Alternative 1 and 3) and Dry-Reforming (Alternative 2). In Alternatives 1 and 2, presented by Lima et al. (2014), part of the captured CO2 is destined for EOR while Alternative 3 (proposed in the present work) integrally converts CO2 to methanol. It is worth noting PC was selected as absorption solvent due to its easiness of regeneration, involving a simple expansion valve and a flash vessel. Also relevant in the scope of the downstream processing of the CO2 rich stream is that PC has also affinity for hydrocarbons, yet lower than its affinity for CO2. This benefit is explored by the proposed alternative processes, where absorbed hydrocarbons (CH4 and, in a lesser extent, heavier molecules) react with CO2 in dry reforming reactions (e.g., CH 4 CO 2 o 2CO 2 H 2 ), steam reforming reactions (e.g., CH 4 H 2O o CO 3H 2 ) and bi-reforming reactions (e.g., 3CH 4 2 H 2O CO 2 o 4CO 8 H 2 ). When CO2 reforming occurs simultaneously with steam reforming, coke deposition is drastically reduced (GANGADHARAN et al., 2012). This combination, named bi-reforming, generates syngas with a H2/CO ratio of 2, ideal for methanol synthesis (OLAH et al., 2009). Although dry reforming generates syngas with a suboptimal H2/CO ratio, the water gas-shift reaction (WGS) adjusts the ratio to favour further methanol synthesis (GANGADHARAN et al., 2012). Alternatives 1 and 3 combine dry and steam reforming in one reactor, while Alternative 2 segregates dry reforming in one reactor and WGS reaction in a subsequent reactor. The Alternatives are evaluated with Aspen HYSYS® simulator for calculation of energy and mass balances necessary to assess economic and environment performances. The economic evaluation employed Capital Cost Estimation Software (CAPCOST) for calculations of CAPEX and OPEX, and the Waste Reduction Algorithm Software (WAR) was used to evaluate the potential environmental impacts.
2. Process Simulation Bi-Reforming (Alternatives 1 and 3) and Dry Reforming (Alternative 2) were evaluated with Aspen HYSYS® simulator. The first process steps relates to CO2 capture and are common to all evaluated alternatives, which is fed with raw natural gas (NG) stream exhibiting the following molar composition: 60% CH4, 20% CO2, 12% C2H6, 6% C3H8 and 2% N2. The adopted process premises are: (a) the natural gas, previously dehydrated, enters at 70 bar and 40 oC with a volumetric flow rate of 1MMNm3/d; (b) the treated gas meets selling Brazilian specifications (< 3% in CO2), and (c) PC flow of 435t/h, necessary to obtain the molar ratio between CH4 and CO2 at treated stream suitable for reforming reactions (obtained by successive simulations). Figure 1 shows the Aspen HYSYS® process flow diagram for CO2 PC absorption. NG enters at the bottom of absorber column (T-100), countercurrent to PC. NG correctly specified is obtained as the top product of absorber, and PC regeneration occurs at the flash vessel (V-100).
Figure 1. Process flow diagram for CO2 absorption with PC
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2.1. Bi-Reforming Process with CO2-EOR(Alternative 1) The stream ‘CO2 + CH4’ is divided into two parts: one goes to a compression train, for CO2-EOR, and the other is destined to a reactor where both dry and steam reforming reactions occur, shown in Figure 2.
Figure 2. Process flow diagram for EOR and Bi-Reforming process – Alternative 1
With CO2/CH4 molar feed ratio of 1:1, GBR-100 operates at 900oC and 1 bar and water vapour is added in reactor at 10.81 t/h. After reaction, the stream ‘SYNGAS’ passes through a sequence of compressors, heat exchangers and vessels, in order to eliminate water and pressurize gas to 70 bar for methanol synthesis. These heat exchangers utilize seawater for refrigeration. Liquid methanol is recovered at V-101, V-103 and V106.The remaining hydrocarbons and syngas return to Methanol reactor. 2.2. Dry Reforming Processwith CO2-EOR (Alternative 2) Similarly to the Bi-Reforming process, the stream ‘CO2 + CH4’ is divided into two parts. However, the stream ‘To Reaction’ proceeds to the GBR-100 reactor, where occurs exclusively the dry reforming. GBR-100 operates at 870oC and 1 bar. After reaction, stream ‘SYNGAS’ passes through a compression and intercooler train. This stream is pressurized to 70.5 bar before entering the Adjust reactor (WGS), where water vapor is added at a rate of 2 t/h. In the sequence, stream “feed” enters in the Methanol reactor. The stream that leaves the Methanol reactor has a high quantity of unreacted methane, which, after methanol recovery, is recycled to GBR-100. Methanol is recovered at V-102, and residual hydrocarbons are recycled (Figure 3). 2.3. Bi-Reforming Process without CO2-EOR (Alternative 3) The stream ‘CO2 + CH4’ is integrally directed to methanol conversion, accordingly to Figure 4. Reaction section proceeds as described for Alternative 1.
3. Economic and Environmental Analysis – Alternatives 1 and 2 Alternatives 1 and 2 were evaluated economically, for decision of which reaction path would be more attractive, through CAPEX and OPEX calculations. Equipment sizing
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was performed according to procedures described in the literature (e.g., CAMPBELL, 2004; PERRY, 1997; TOURTON et al., 2009). For the economic analysis, the MS Excel spreadsheet CAPCOST, developed by Turton et al (2009), was employed. Table 1 presents the main results from Bi-Reforming (Alternative 1) and Dry-Reforming (Alternative 2) Processes, indicating the resulting CAPEX, OPEX and revenue for each alternative. Alternative 1 has the highest revenue as methanol production (17960 kg/h) was 4 times higher than for the Dry-Reforming Process (Alternative 2).
Figure 3. Process flow diagram for EOR and Dry-Reforming process – Alternative 2
Figure 4. Process flow diagram Bi-Reforming process without EOR – Alternative 3
Table 1. Results of CAPEX, OPEX and Revenue Sales – Alternatives 1 and 2 Cost (U$$) CAPEX OPEX Revenue Sales
Bi-Reforming 25,165,709 122,575,216 144,890,686
Dry-Reforming 32,145,906 101,189,415 51,463,757
The WAR Algorithm (CABEZZAS et al.,1999) was used to comparatively quantify the environmental performance of Alternatives 1 and 2, based on eight categories of environmental impacts, equally weighted. The categories are: Human Toxicity Potential
Viability of Technologies for CO2 Capture and Reuse in a FPSO: Technical, Economic and Environmental Analysis
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by Ingestion, Human Toxicity Potential by Exposure, Aquatic Toxicity Potential, Terrestrial Toxicity Potential, Global Warming Potential, Ozone Depletion Potential, Smog Formation Potential, Acidification Potential. WAR measures performance as output rate of PEI (Potential of Environmental Impact). PEI can be described through rates of inlet (Îin), outlet (Îout) and generation (Îgen) of impact in a given system. The mass flow and composition obtained from ASPEN HYSYS simulations were used in the WAR algorithm. Comparing the total impact for these processes two Alternatives (both employing CO2-EOR), Bi-Reforming (Alternative 1) has a lower impact (868 PEI/hr) than Dry-Reforming (Alternative 2) (1661 PEI/hr).
4. Alternatives 1 and 3 - Bi-Reforming with and without EOR The comparative economic and environmental analysis indicate that Alternative 1 (BiReforming) is technically, economically and environmentally superior to Alternative 2. Considering the main objective of an MFPSO of enhanced methanol production, Alternative 3 was proposed with removal of the CO2-EOR section (Figure 4). Based on the conclusion of superior performance of Alternative 1 over Alternative 2, Alternative 1 is the basis of Alternative 3. A preliminary economic analysis (exclusively based on revenue increase) shows enhancement of methanol production of around 2 times over the production achieved in Alternative 1 (35,497.56 kg/h). Consequently, Alternative 3 presents revenue of U$$ 251,502,365, (Alternative 1 showed revenue of US$144,890,686). Furthermore, Alternative 3 and Alternative 1 were compared considering the generation rate of PEI, calculated through WAR Algorithm. It was observed that Alternative 1 (Bi-Reforming) has a negative rate, higher than Alternative 3 (Bi-Reforming without EOR), what means that the first alternative is environmentally superior to Alternative 3, as shown in Figure 5. It is worth noting that methanol contributes to all impact categories evaluated while CO2 most exclusively impacts in global warming. Consequently, WAR penalises the increase in methanol production achieved in Alternative 3.
Figure 5. Generation rate of PEI for Bi-Reforming with and without EOR step
5. Discussion and Conclusions The proposed processes are potentially amenable to methanol floating production system, MFPSO, where the regeneration of PC would present a competitive advantage over alternative CO2 capturing technologies, since weight and space are the key considerations for floating plants. The treated natural gas stream (248.7 m3/h) composition is (in molar basis): 90.19% CH4, 1.67% CO2, 3.31% C2H6, 0.63% C3H8 and
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4.20% N2. The main difference of the proposed processes is the fact that at Bi-Reforming (Alternatives 1 and 3) just one reactor is utilized, where occur both dry and steam reforming. On the other hand, for Dry-Reforming (Alternative 2) two reactors are conceived: one for dry reforming and other for WGS reaction. This difference poses a large discrepancy of methanol productivity, as methanol production by Bi-Reforming was 17905 kg/h, 4 times higher compared to Dry-Reforming. Dry reforming occurs not only for methane, but also for ethane and propane, and these last reactions are more favoured than the first one. In consequence, methane is not consumed, but rather produced in the Dry-Reforming alternative, explaining the associated low production of methanol. Since the preliminary conclusions indicate that Bi-Reforming is technically, economically and environmentally superior to Dry-Reforming, a third flowsheet was proposed, considering the elimination of CO2-EOR section, with dedicated production of methanol. Analysis showed that methanol production in Alternative 3 (35,497.56 kg/h) present revenues around 2 times higher than Alternative 1. Regarding the environmental aspect, Bi-Reforming (Alternative 1) shows superior environmental performance over Bi-Reforming without EOR step (Alternative 3) due to the penalty attributed by WAR algorithm to producing methanol, which contributes to all considered impact categories. However, both alternatives presented negative generation of PEI, which turns Alternative 3 the most sustainable alternative. Although a more detailed economic analysis for Alternative 3 (CAPEX and OPEX) is necessary to reinforce this conclusion, it is foreseen a superior economic performance since the increase in revenues is significant and compression costs associated to CO2-EOR are eliminated.
Acknowledgments The authors acknowledge the financial support of PETROBRAS S.A., ANP (PRHANP/MCT, PRH-41) and CNPq research grants.
References H. Cabezas, J. Bare, S. Mallick, 1999, Pollution prevention with chemical process simulators: the generalized waste reduction (WAR) algorithm - full version. Computers and Chemical Engineering, 23, 4–5, 623–634. J. M. Campbell, 2004, Gas conditioning and processing: the equipment modules. Norman: John M Campbell & Company, 2, 8. J. Formigli, 2007 Pre-salt reservoirs offshore Brazil: perspectives and challenges, Miami. C. Guzzetti, Gaffney, Cline & Associates, 2010, Review and evaluation of ten selected discoveries and prospects in the pre-salt play of the deepwater santos basin, Brazil. www.anp.gov.br/?dw=39137. P. Gangadharan,; K. Kanchi,; H. Lou, 2012, Evaluation of the economic and environmental impact of combining dry reforming with steam reforming of methane. Chem. Eng. Res. Des., 90, 11, 1956–1968. B. Lima, O. Araújo, J. L. Medeiros, C. Morgado, 2014, Technical, Economic and Environmental Viability of Offshore CO2, Proceedings of 2014 AICHE Annual Meeting, Atlanta, GA, USA. G. A. Ola et al., 2013, Bi-reforming of methane from any source with steam and carbon dioxide exclusively to metgas (CO–2H2) for methanol and hydrocarbon synthesis, J. Am. Chem. Soc., 135, 2,648–650. R. Perry, D. Green, 1997, Perry’s Chemical Engineers’s Handbook, McGraw-Hill, 1, 7. R. Turton et al., 2009, Analysis, Synthesis, and Design of Chemical Processes, New Jersey: Prentice Hall, 1, 3.