The global mean surface temperature increase from the 1860s to 1994 is between 0.3 to 0.6° C. and the temperature rise by the year 2100 is expected to be in the range of 1 to 3.5° C., with a best estimate of 2° C. Carbon dioxide is one of the greenhouse gases that enhances radiative forcing and contributes to this global warming. The concentration of CO2 in Earth's atmosphere prior to industrialization was 270-280 ppmv while in 1994 it had risen to 354 ppmv and is expected to double within the next century. Burning of fossil fuels, the main source of CO2, produces around 21.3 billion tons of carbon dioxide per year, but it is estimated that natural processes can only absorb about half of that amount, so there is a net increase of 10.65 billion tons of atmospheric carbon dioxide per year. World energy consumption was growing about 2.3% per year and world carbon dioxide emissions are expected to increase by 1.8 percent annually between 2004 and 2030. Halmann et al. describes the effects of a global temperature increase to include: “(1) a rise in sea level, due to melting of the glaciers and the Antarctic ice caps and (2) increasing desert formation in the tropical zone”.
Energy Information Administration estimated that in 2006 primary sources of energy consisted of petroleum 36.8%, coal 26.6%, and natural gas 22.9%, amounting to an 86% share for fossil fuels. The Reserves-to-production ratio (RPR or R/P) is the remaining amount of a non-renewable resource, expressed in years. Based on International Energy Outlook 2009 from EIA, R/P ratios of the world's main fossil energy sources are: Crude oil—40 to 44 years, Natural Gas—55 to 57 years, Coal (2006)—137 years. The R/P ratio might decrease drastically over time as the consumption of many resources typically increases as the population grows and becomes more prosperous. This leaves a huge challenge for mankind to search for alternative energy sources. This trend of rapid consumption of fossil fuels brings two major challenges to mankind—global warming and depletion of fossil energy resources.
Halmann et al. and George Olah et al. proposes 3 main strategies to solve the problems of global warming and diminishing fossil resources: 1) Increase Energy efficiency to reduce CO2 and fossil fuel use 2) Use of renewable energy to replace fossil energy usage in both the fields of electricity generation and liquid fuel utilization 3) Direct reduction of CO2 through capture, storage or re-use. Efficiency of current processes consuming fossil fuels can be improved to increase the amount of useful energy per unit of CO2 emitted. Halmann et al. in 1999 concludes that by 2050 a 60% reduction in energy consumption and CO2 emissions is possible with improved energy efficiency from mid-1970s. The study does however, not consider the rise in population and thus the foreseeable increase in energy demand. Population rose from 4 billion in 1975 to 6.8 billion by 2008, with expected population rise to 10 billion by 2050. Thus, savings due to increased energy efficiency can only extend the availability of needed and accessible fossil fuels in the relative short term.
Increased utilization of renewable energy is another strategy as it produces very little or zero carbon emissions and is replenished naturally. In 2006, about 18% of global final energy consumption came from renewable energy, with 13% coming from traditional biomass, and 3% from hydro power. The storages and flows of renewable energy on the planet are very large relative to human needs. The amount of solar energy intercepted by the Earth every minute is greater than the amount of energy the world uses in fossil fuels each year. The energy in the winds that blow across the United States each year could produce more than 16 billion GJ of electricity—more than one and one-half times the electricity consumed in the United States in 2000. According to Hoffert et al., stabilization of CO2 at twice the preindustrial concentration in the atmosphere requires that by the year 2050, 100-300% of today's global power (˜10 TW) come from carbon-emission-free sources. Main shortcomings of renewables are their low areal power densities. 10 TW from biomass (power density ˜0.6 W m−2) requires greater than 10% of Earth's land surface, comparable to all of human agriculture. Photovoltaic and wind energy (power density ˜15 We m−2) need less land, but other materials can be limiting. For solar energy, the electrical equivalent of 10 TW (3.3 TWe) requires a surface array of 220,000 sq. km. However, all the PV cells shipped from 1982 to 1998 would only cover ˜3 km2. A massive, but not insurmountable, scale-up is required to get 10 to 30 TW equivalents. Also, energy from most of the renewable sources is harnessed dynamically and will not be as useful as fossil carbon until it can be stored and transported with similar ease. With intermittent renewables such as solar and wind, the output may be fed directly into an electricity grid. At penetrations below 20% of the grid demand, this does not severely change the economics; but beyond about 20% of the total demand, external storage will become important. Current and emerging technologies in the field of energy storage, according to the National Renewable Energy Laboratory of United States, include: batteries, hydrogen, compressed air energy storage (CAES), flywheels, pumped hydropower, super capacitors, and superconducting magnetic energy. Of particular interest to the present disclosure, PCT/EP2008/059866, submitted by Werner Leonhard, discloses a method for achieving energy sustainability by converting energy into hydrogen, and using this gas as the means for energy storage. But hydrogen has very low volumetric energy density which creates problems for physical storage. Also, concerns of safety and the requirement of massive infrastructural changes hinder the use of hydrogen for energy storage. Though much work is also being done on energy storage through batteries, the energy densities of these storage techniques are not sufficient to replace fossil energy sources. For example today's lead acid batteries can store about 0.1 mega-joules per kilogram, or about 500 times less than crude oil. Those batteries, of course, could be improved, but any battery based on the standard lead-oxide/sulfuric acid chemistry is limited by foundational thermodynamics to less than 0.7 mega-joules per kilogram.
One approach to support global warming mitigation is direct reduction of CO2 through Carbon Capture and Storage (CCS), a process comprising of the separation of CO2 from industrial and energy-related sources, transport to a storage location and long-term isolation from the atmosphere. In most scenarios for stabilization of atmospheric greenhouse gas concentrations between 450 and 750 ppmv CO2 the economic potential of CCS would amount to 220-2,200 GtCO2 (60-600 GtC) cumulatively, which would mean that CCS contributes 15-55% to the cumulative mitigation effort worldwide until 2100, averaged over a range of baseline scenarios. Uncertainties in these economic potential estimates are significant. For CCS to achieve such an economic potential, several hundreds to thousands of CO2 capture systems would need to be installed over the coming century, each capturing some 1-5 MtCO2 per year. The actual implementation of CCS, as for other mitigation options, is likely to be lower than the economic potential due to factors such as environmental impacts, risks of leakage and the lack of a clear legal framework or public acceptance. CCS is a costly process, leading to reduced plant efficiencies and is not economically favorable unless incentives are provided.
Another approach for direct CO2 reduction is carbon capture and re-use. Commercial applications of CO2 reuse are currently limited to refrigeration for food (PCT/US1999/5974826 Novak et al), carbonated beverages, enhanced oil recovery and chemicals. In 1980, the total US market consumption of 2.3 million tons carbon represents only 0.18% of the US total emission. Halmann et al. concludes that as a sink for CO2 the market demand would have to grow by at least two factors of 10 to become a major factor in reducing man made CO2. Another CO2 reduction scheme is disclosed in PCT/US2001/6237284 by Stewart E. Erickson where CO2 storage and distribution underground to plant soil for enhancing plant growth is proposed. Iceland patent IS 2300, Shulenberger et al., presents a process which combines industrially captured CO2 with H2 from renewable energy driven electrolysis for the production of methanol by means of a low pressure and temperature process. PCT/IT2008/000559, submitted by A.S.T. Engineering s.r.l., presents a system closely modeled on the Carnol Process in which the CO2 from industrial flue gas is separated from other emission components and mixed with H2 from natural gas for methanol production. US 2008/0319093 A1, submitted by George Olah, aims to use industrial CO2, not necessarily from industrial exit stacks, along with methane or natural gas for the production of methanol and methanol byproducts using “bi-reformation”, a combination of steam reformation and dry reformation. PCT/BE2003/000016, submitted by Félicien Absil, discusses a method for the recovery of CO2 from industries like cement plants or coal fired power stations for the production of syngas for heat energy and carbon nanotube production. US2008/0072496 A1 submitted by A. Yogev et al. relates to the thermochemical capture of CO2 from gas by reaction with K2CO3 and producing methane or methanol fuel by releasing the captured CO2 and reacting it with hydrogen. Commercial application of these processes is yet to be seen. It is to be noted that in most CCS or CO2 reuse systems, the cost of CO2 capture could be the largest cost component. A number of systems for the removal and recovery of CO2 are described by Halmann et al. including, amine absorption, oxy-combustion, potassium carbonate absorption, molecular sieves, refrigeration, seawater absorption, pressurized, fluidized bed combustor, and membrane separation. On this topic, it is noted that both thermal and electrical energy are needed to remove and recover CO2. PCT/EP2009/050205, PCT/EP2008/068212, PCT/US2008/084463, and PCT/US2008/084457, submitted by Alstom Technology, describe methods for the capture of CO2 either through compressive means, solid materials or specialty systems. PCT/US2008/081998, submitted by Powerspan Corporation, describes a system in which a synergistic system removes CO2 from a flue gas. WO 2008137815 A1 submitted by Clark describes a process where biomass feedstock is converted to synthesis gas streams where one is converted to CO2 and steam for producing electricity and another is converted to fuel in a Fischer-Tropsch reactor.
US2008/0303348A1 submitted by Witters describes a process for continuously generating baseload electrical energy from renewable resources utilizing biomass in boilers and capturing CO2 to produce algae fuel.
Biomass utilization is a natural cycle of CO2 capture and reuse. Biomass provides a potentially CO2-neutral source of energy as the CO2 released during processing and combustion is taken up by the next crop. Biomass is majorly used for transport fuel production through biochemical (fermentation, transesterification, and anaerobic digestion) or thermochemical (gasification, pyrolysis and conversion) methods. At present, the main transportation fuel available from biomass is ethanol. Haroon et al. studies that current ethanol production techniques from fermentation consume fossil carbon for energy and chemical inputs and it is these fossil carbon inputs that result in positive full-fuel-cycle emissions. Each liter of ethanol saves 1.85 kg of CO2 by replacing gasoline, but at the same time releases 1.39 kg of CO2 as produced in the US and 0.24 kg of CO2 in Brazil. Thus the full-fuel-cycle analysis shows that current ethanol fuel systems are only partially successful at recycling CO2 and being CO2-neutral sources of energy. Full-fuel-cycle CO2 emissions from corn ethanol in the USA nearly wipe out all of the CO2 advantage of replacing gasoline. Another disadvantage of this process is that only a fraction of the biomass is converted to the final desired liquid fuels. This problem is also associated with proposed biofuel production from algae, which is currently un-economical and will likely remain so for the foreseeable future due to fundamental thermodynamic constraints (Krassen Dimitrov, 2007 Case Study). Thermochemical production pathways of biofuels from biomass could use biomass with higher efficiency. This process happens through an intermediate called synthesis gas, also known as syngas, which consists of a variable ratio mixture of H2, CO, and CO2. The conventional thermochemical process for liquid fuel production from biomass is presented in FIG. 1. Depending on the type of biomass and the conditions of syngas production, CO2 concentration of the raw syngas output may vary from 6 to 40 mol % on dry basis. To obtain the required ratio of CO/H2, water gas shift reaction is employed in which CO is reacted with H2O to generate more hydrogen thus releasing further CO2. For example, methanol production processes from biomass produce around 600 to 1200 pounds of CO2 per ton of methanol. The Hynol Process is employed for the conversion of carbonaceous materials into methanol via a syngas intermediate. Steam reformation and hydrogasification are performed in parallel in this system, and high conversion efficiency to the production of methanol is achieved. The Hynol Process causes a reduction of CO2 emissions on the order of 30% relative to conventional processes for methanol production, but still causes the emission of approximately 103 pounds of CO2 for each MMBTu of methanol produced (Halmann 249). U.S. Pat. No. 6,736,955B2 by Shaw, US2008/0115415A1 by Agrawal et al., US1995/5416245 by MacGroger et al. further overcome the problem of excess CO2 generation by offsetting the stoichiometric imbalance of syngas with H2 produced from off peak electricity. While Shaw and Agrawal et al. uses Reverse Water Gas Shift (RWGS) to reduce CO2, MacGroger et al. plans to dissociate CO2 to CO with energy generated from a Partial Oxidation (PDX) reactor to reduce CO2. All the three methods use partial oxidation reactor or gasification system for syngas production either to produce methanol or any other liquid synthetic fuels. FIG. 2 depicts these modifications to the conventional prior art in addition to stable electrical power generation from hydrogen and syngas, proposed by Boyapati et al US2004/0265158A1. The success of the above processes to solve the problem of internal CO2 generation and release is dependent on the availability, adaptability and effective utilization of carbon free energy sources for H2 production, which has its own limitations as discussed previously.
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