Again we return to what seems an issue of contention among some of our readers. But, the reasoning behind the concept of recycling the carbon dioxide by-product of our coal use, as opposed to, at great expense, attempting to stuff it all down leaky geologic storage rat holes, seems so self-evident to us that we can't abstain from dwelling on it.
Our excerpt, below, from the enclosed link and attached file is lengthy, and we haven't attempted to edit it very much. But, it is well-worth a careful read.
You will find within it some concepts that we have touched on previously. One, which shouldn't escape you, is the proposal that, yes, we should harness environmental energy; but, we could use that wind or water power as a means to capture and recycle carbon dioxide into a more portable energy storage medium - such as methanol.
The authors of this report refer to such practice as the "chemical storage of renewable energy". Such "chemical storage" media would also be a lot more portable, and a lot more versatile, as well.
Remember: Once methanol has been synthesized from carbon dioxide, and from hydrogen electrolyzed from water, using wind, water or solar power, it can be further processed, as we have amply documented, into gasoline and plastics.
The same is true of ethanol, as well, again as we have documented. And, ethanol, too, as these United Kingdom scientists reveal, and as we have also thoroughly documented, can be directly synthesized from carbon dioxide, without wasting food crops, and a great deal of additional energy, and creating more carbon dioxide, through the processes of fermentation and distillation.
Another point they make, but somewhat obliquely, is that there is a huge energy cost involved in capturing carbon dioxide from flue gas for the purposes of geologic sequestration. And, remember, these researchers are very close to the North Sea oil field. They touch on that subject lightly, though, as we have also been "encouraged" to do.
Without further comment, the excerpt follows. Everyone in US Coal Country should read it carefully, and ponder all of the implications; the main one being, from our point of view, that carbon dioxide, as arises in part from our use of coal, is a valuable raw material resource. We shouldn't be fooled into allowing it to be hijacked from us, and we shouldn't allow our vital, critically important, coal industries to be taxed out of existence because they produce it for us. We can use it.
SQUARING THE CIRCLE: SEQUESTRATION OF CO2 AS LIQUID FUEL
Dimitri.Mignard and Colin Pritchard
Institute for Energy Systems, University of Edinburgh, UK
ABSTRACT
The case for using CO2 as a feedstock to fix electrolytic hydrogen is presented. Advantages include the avoidance of small scale reforming and associated un-recovered CO2 emissions for the production of hydrogen; the possibility for a large penetration of renewable generators of variable output into the electricity grid; and the production of clean fuel utilising CO2 emissions. A preliminary analysis based on integrated
heat balances indicates that the methanol-to-gasoline process uses less energy than the production of methanol or ethanol fuel.
heat balances indicates that the methanol-to-gasoline process uses less energy than the production of methanol or ethanol fuel.
WHY USE CO2 AS RAW MATERIAL FOR FUEL?
1. Challenges for the attainment of a high proportion of wind and marine power -
The long term-necessity for the world economy is to achieve a sustainable pattern of energy use. In Britain, a significant contribution is expected from resources such as wind and wave power, but the intermittency and variability of these sources limits their penetration into existing electricity grids to a maximum of 15-20%. Besides power conditioning, there are issues of continuity of supply, and of matching demand and supply. For example, Denmark met 14% of its 33 TWh/yr internal electricity demand from wind in 2002, but the variability of this supply meant it had to import 8.94 TWh from neighbouring countries, and export 11.01 TWh [1]. For a country such as Britain, the Danish example would suggest that a contribution of 14% from wind power in the future would make available at least 115 TWh of additional electricity. Continuity of supply can also be a serious issue, since imports may not be an option for Britain at times of supply shortage. Within this context, the chemical storage of electrical power appears to be an attractive option for the supply of fuels or power back-up.
2. Chemical storage of renewable energy – large scale, seasonal or remote production -
Electrolysis of water is an established technology for producing hydrogen fuel from electricity, but centralised production, storage and distribution of H2 on a large scale or for long periods may be very costly. In Britain, where a high proportion of renewable energy is expected to come from remote locations on islands or at sea, the production of a liquid fuel could be more convenient than hydrogen for shipping to the mainland. The decentralised production of H2 on the mainland using the electricity grid (e.g. with electrolysis at vehicle refuelling stations) has been proposed, but the very large infrastructure cost suggests that this scheme would not be able to develop in the short timescale required to reduce CO2 emissions. It would require network management and control of the hydrogen production, in order to avoid using grid electricity
when it is needed elsewhere. More importantly, hydrogen vehicles and appliances would have to be as economical as conventional ones, with ubiquituous refuelling stations.
3. Recycling of CO2 as hydrogen carrier fuel -
Meanwhile, it is usually assumed that the expansion of the “hydrogen economy” will rely on decentralised fossil-fuel reforming for the production of hydrogen. This option would lead to the generation of considerable quantities of CO2 which could be difficult to collect. On the other hand, the development of electrolytic capacity would need to be given a head start if a truly sustainable energy economy is to emerge within 30 years. Perhaps a worthwhile approach would be to shift some of the emphasis away from the ‘demand’ side of the future hydrogen economy, and to generate truly “zero emission” fuels over a timescale of years rather than decades.
A possible solution is the centralised production of electrolytic hydrogen, to be used on-site in the synthesis of a liquid fuel (hydrocarbon or alcohol) from recycled CO2. Such a fuel could be readily used in existing distribution networks, appliances and vehicles. This scheme would permit a substantial penetration of renewable power and deliver large cuts in CO2 emissions, on a short timescale. The CENS project, which
involves the UK, Denmark and Norway (government bodies and companies), is currently planning a CO2 infrastructure in and around the North Sea for sequestration and EOR. 29 Mt/yr of CO2 would come from coal-fired power stations in the UK and Denmark [2].
involves the UK, Denmark and Norway (government bodies and companies), is currently planning a CO2 infrastructure in and around the North Sea for sequestration and EOR. 29 Mt/yr of CO2 would come from coal-fired power stations in the UK and Denmark [2].
TECHNOLOGY OVERVIEW: ELECTROLYSIS AND RECYCLED CO2 FOR THE PRODUCTION OF FUELS
1. Electrolysis using variable and intermittent current Recent developments have made available on the market alkaline electrolysers that can operate at 25 or 30 bar ([3] and [4], resp.), and in intermittent or variable conditions. Appropriate industrial electrodes can be found that do not need a protective voltage in these conditions [5]. Advanced designs for alkaline pressure electrolysers include the IMET® technology, which is commercialised by Stuart Energy for capacities up to 1MW ([3] and [6]), and the Pressure Module Electrolyser (PME) technology, which is being developed by a consortium including MTU-Friedrichshafen, Norsk Hydro, and PMT (Prime Membrane Technology, Belgium) [4]. The PME technology is at the demonstration stage [4]. Both technologies do not require lye pumps, and use separate catholyte and anolyte streams preventing any mixing of O2 and H2, an advantage for operation at low load. The modular construction of the PME pressurised shell allows the electrolyser to be scalable beyond several MW [7]. Capital costs for the PME electrolyser are 500 Euro/kW installed or less [4].
Anglesey Wind and Electricity Ltd (AWEL) is promoting electrolysis as a ‘dispatchable’ load for grid power management [8]. The technology may help electricity suppliers to offset any excess production caused by the unpredictability of embedded generation and intermittent power sources. Following the Balancing and Settlement Code (BSC), electricity providers in Britain are charged for any imbalance between supply and demand on the National Grid. In a favourable case (detailed on the company website, [8]) AWEL claims that a 10MW electrolysis plant can produce 5.84 MNm3/yr H2, and make £1,350,000 from a licence fee and industrial sales of the hydrogen. This shows that the cost of power may actually be negative in a grid management context.
2. CO2 recovery
The CENS project claims a cost of 35 $/t for CO2 recovered from flue-gas, which represents ca. $ 33 /t CO2 after subtracting the CAPEX of the 1500 km pipeline [2]. This cost is kept low due to the use of high-pressure, superheated steam at the reboiler of the CO2 amine-absorption stripper, and the exclusive use of existing ‘ultra clean’ flue-gas at 14-16% CO2 from a coal-fired power station which has heat co-generation for district heating. Energy consumption may be improved further with the flue-gas scrubbing technology and the KS-1 solvent that were developed by Mitsubishi Heavy Industries, Ltd (MHI), and Kansai Electric Company (KEPCO) [9]. A 160 tCO2/day plant in Malaysia has been using the KS-1 solvent since 1999. Solvent consumption there is 0.35 kg/t of CO2 recovered, with solvent stability over at least 5,700 hours; LP steam consumption is 1.5t per t CO2 recovered, which compares to 2.7 t with the Kerr-McGee/ABB Lummus Global process [10].
3. Fuel synthesis
The following three options were considered:
3.1. Process A. Methanol synthesis
Methanol synthesis from pure CO2 has been shown to be feasible on existing Cu/ZnO/Al2O3 catalysts used for making methanol from synthesis gas [11], according to the reaction CO2 + 3H2 7 CH3OH + H2O(g) (1) DH298K, 1bar = - 49.16 kJ/mol The observed equilibrium yield when using CO2 + 3H2 was ca. 22% for methanol, due to the inhibitory effect of the water product. Deactivation of the catalyst by water is known to be a problem, but better catalysts have been developed. For instance, Cu/ZnO/ZrO2/Al2O3/Ga2O3 showed excellent longevity, selectivity and activity [12]. Its space-time-yield was stable at 600 g MeOH/l(catalyst)/h after 2500 hours, 46% better than for a commercial Cu/ZnO/Al2O3 [12]. Mignard et al. [13] modelled the adiabatic operation of a tubular reactor with ICI 51-2 catalyst (Cu/ZnO/Al2O3). Modelling for a minimum 99% yield predicted minimum compression requirements (including recycle) at 227oC, 30 bar; recycle ratio of 7.9.
3.2. Process B. Ethanol synthesis
Ethanol has the advantage that it is less toxic than methanol, and could be handled more safely by the general public. However, the reactor may ‘run away’ and requires cooling with careful control. The reactions are CO2 + H2 7 CO + H2O(g) (2) DH298K, 1bar = 41.21 kJ/mol of C 2CO + 4H2 7 CH3CH2OH(g) + H2O(g) (3) DH298K,1bar = - 256.1 kJ/mol ethanol Until recently, reaction (3) was not possible with good yields or good selectivity. However, Pearsons Technologies Inc. (PTI) [14, 15] now claims the invention of a Fischer-Tropsch catalyst capable of converting synthesis gas to ethanol with a yield of 99+% to ethanol after recycle the single pass conversion was 15-60%, depending on the conditions. It is claimed that the process and catalyst can be adapted to run at temperatures and pressures typical of methanol processes [14], although higher pressures and temperatures are favourable. Details on the composition of a synthesis gas feedstock could be found in [16]: 51.1% H2, 23.7% CO, 17.1% CO2, and 6.3% CH4. This indicates that a ratio CO2 /(CO2+CO) of 42% is acceptable, and that the catalyst must have a strong reverse Water-Gas Shift (WGS) activity. The light ends were returned to the reactor [14,15]. The Pearson process is marketed by Kwikpower Inc. under the name KPI Ethxx, Ethxx being the owner of PTI in 2001 [17]. PTI has built and operated a 50 t/day pilot plant processing woodwaste to produce ethanol in Aberdeen, North Mississippi[14]. A reverse Water-Gas-shift reactor may be needed if the feedstock is pure CO2. A Cu/ZnO/ZrO2/Ga2O3 catalyst for reverse WGS was proposed [18]. Using the table provided by these authors, it was found that operating the RWGS reactor at 400oC, 30 bars and no recycle would permit a ratio CO2/(CO2+CO) of 61%.
3.3. Process C. Methanol to gasoline (MTG)
Methanol reacts on the ZSM-5 zeolite catalyst to produce DME, which then gives hydrocarbons with up to ten carbon atoms [19]. The Mobil fluid bed process demonstrated in Wesseling, Germany, was able to produce 15.9 m3/day of gasoline. 99+% methanol was converted to 88% gasoline, 6.4% LPG and 5.6% fuel gas when operating at 413oC and 2.75 bar. The feed was raw methanol with 27% mol. water and 73% mol.
methanol. The heat evolved was 1.74 MJ/kg methanol, recovered through heating oil tubes immersed within the bed. [19].
METHODOLOGY
The processes were compared according to their overall net energy requirements. A preliminary heat integration was carried out, and then the need for additional high grade heat for product purification was compared with that made available from the reaction. The feed was taken to be CO2 + 3H2 at 30 bar, 25oC. Methanol product was fuel grade at 98% wt, while ethanol was also fuel grade at 99.4%. In process B, a reverse water-gas-shift reactor was operated at 30 bar, 500oC inlet and 383oC outlet, CO2 conversion 39% and no recycle. The ethanol reactor was operated at 30 bars, 500oC inlet and 570oC outlet, CO conversion was 30%, and the reverse WGS reaction was assumed to maintain the CO2/CO ratio constant. Ethanol separation was first effected at atmospheric pressure to yield a 90% azeotropic condensate, which was sent to a drying unit. In process C, the gaseous product from process A was partly condensed to yield a 40% mol. methanol feed for distillation, and the remainder of the gas was separately condensed to yield a 73% methanol liquid. Distillation to upgrade the 40% product to 73% may be carried out in one stage. This scheme saved up to a third of the reboiler duty, and two thirds of the MTG reactor feed vaporisation duty. A debutaniser column was also required to separate the light gases from the raw product.
DISCUSSION
The methanol process was not producing much surplus high-grade heat, due to the lower heat of reaction. The ethanol process generated more heat, but demanded more energy for distillation. The MTG process seemed to need no net heat input, due to its integration with the methanol process, and reduced distillation loads. In all cases, the extraction of CO2 using amine technology was not considered and would require 10.95 kWh/kmol (CO2 + H2 ) feed.
CONCLUSION
The methanol to gasoline process seemed the most promising candidate from the point of view of heat inputs. Future work will look at the integration of this scheme with a fossil-fuel power technology requiring the less energy for CO2 extraction, in particular the chemical looping process.
ACKNOWLEDGEMENTS
EPSRC funded this work through the SUPERGEN marine energy research consortium.
REFERENCES
1. Danish Energy Authority, Energy in Denmark. 2002, http://www.ens.dk
2. Markussen P., J.M. Austell, C.-W. Hustad. 2003. A CO2 infrastructure for EOR in the North Sea (CENS): macroeconomic implications for host countries, Greenhouse Gas Control Technologies, GHGT6, Kyoto, J. Gale and Y. Kaya Eds., Pergamon, Vol. II: 1077-1082
3. Stuart Energy website. Accessed 06/2004. http://stuartenergy.com
4. European Commission. 2003. EUR 20718 - European and Fuel Cell Projects 1999-2002, Luxembourg: Office for Official Publications of the European Communities p. 90
5. EUHYFIS website. Accessed 06/2004. http://www.euhyfis.com/indexgb2.html?/konzept.html~mainFrame
6. Vandenborre H. 2002. High Pressure Electrolyser Module, Patent EP0995818
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13. Mignard D., M. Sahibzada, J. Duthie, and H.W. Whittington. 2003. Methanol synthesis from flue-gas CO2 and renewable electricity: a feasibility study, International Journal of Hydrogen Energy, 28: 455-464
14. Pearson S.R. 2001. The manufacture of synthetic gas and ethanol from biomass using the Pearson thermo-chemical steam reforming and catalytic conversion processes, 5th International Biomass Conference of the Americas, Sept. 17-21 2001, Orlando, USA
2. Markussen P., J.M. Austell, C.-W. Hustad. 2003. A CO2 infrastructure for EOR in the North Sea (CENS): macroeconomic implications for host countries, Greenhouse Gas Control Technologies, GHGT6, Kyoto, J. Gale and Y. Kaya Eds., Pergamon, Vol. II: 1077-1082
3. Stuart Energy website. Accessed 06/2004. http://stuartenergy.com
4. European Commission. 2003. EUR 20718 - European and Fuel Cell Projects 1999-2002, Luxembourg: Office for Official Publications of the European Communities p. 90
5. EUHYFIS website. Accessed 06/2004. http://www.euhyfis.com/indexgb2.html?/konzept.html~mainFrame
6. Vandenborre H. 2002. High Pressure Electrolyser Module, Patent EP0995818
7. Kliem E. 1995. Dispositif d’électrolyse (sous pression) en structure modulaire, Linde AG patent FR2710076
8. AWEL website, accessed 06/2004. http://www.anglesey-wind.co.uk/HydrogenSystems/Index1.htm
9. Iijima M. and T. Kamijo. 2003. Flue gas CO2 recovery and compression cost study for CO2 enhanced oil recovery, GHGT6, Kyoto, Vol. I: 109-114
10. CO2 Recovery. April 2000. Hydrocarbon Processing, April 2000, p. 63.
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12. NEDO and RITE. 1998. Project of CO2 fixation and utilization using catalytic hydrogenation reaction, , report obtained from NEDO, Japan
13. Mignard D., M. Sahibzada, J. Duthie, and H.W. Whittington. 2003. Methanol synthesis from flue-gas CO2 and renewable electricity: a feasibility study, International Journal of Hydrogen Energy, 28: 455-464
14. Pearson S.R. 2001. The manufacture of synthetic gas and ethanol from biomass using the Pearson thermo-chemical steam reforming and catalytic conversion processes, 5th International Biomass Conference of the Americas, Sept. 17-21 2001, Orlando, USA
15. Pearson S.R. 2003. The manufacture of synthesis gas from biomass and production of alcohols and electric power using the Pearson thermo-chemical steam reforming and catalytic conversion processes, Poster Presentation 5-18, 25th Biotechnology Symposium, Breckenridge, Colorado May 4-7 2003, http://www.nrel.gov/biotech_symposium/session5_pp.html
16. Vantine B. 2004. Pearson technologies is making ethyl alcohol from “almost anything” a reality. Presented at the New Mexico Green Fuels Symposium, Santa Fe Community College, May 12-13, 2004, New Mexico Energy, Minerals and Natural Resources Department http://www.emnrd.state.nm.us/ECMD/html/
16. Vantine B. 2004. Pearson technologies is making ethyl alcohol from “almost anything” a reality. Presented at the New Mexico Green Fuels Symposium, Santa Fe Community College, May 12-13, 2004, New Mexico Energy, Minerals and Natural Resources Department http://www.emnrd.state.nm.us/ECMD/html/
17. Kwikpower Inc. website, http://www.kwikpower.com, flowsheet is ©2000
18. Joo O.-S., K.D. Jung, I. Moon, A.Y. Rozovskii, G.I. Lin, S.H. Han, and S.J. Uhm. 1999. Carbon Dioxide Hydrogenation to form methanol via a reverse-water-gas-shift reaction (the CAMERE process), Industrial Engineering and Chemistry Research, 38: 1808-1812
19. Keil F.J. 1999. Methanol-to-hydrocarbons: process technology, Microporous & Mesoporous Materials, 29: 49-66
18. Joo O.-S., K.D. Jung, I. Moon, A.Y. Rozovskii, G.I. Lin, S.H. Han, and S.J. Uhm. 1999. Carbon Dioxide Hydrogenation to form methanol via a reverse-water-gas-shift reaction (the CAMERE process), Industrial Engineering and Chemistry Research, 38: 1808-1812
19. Keil F.J. 1999. Methanol-to-hydrocarbons: process technology, Microporous & Mesoporous Materials, 29: 49-66