Patent Application
20080289499
The present invention relates to systems and methods for removing greenhouse gases from an atmosphere, and in particular to systems and methods for removing carbon dioxide from an atmosphere.
There is much attention currently focused on trying to achieve three energy related and somewhat conflicting energy related objectives: 1) provide affordable energy for economic development; 2) achieve energy security; and 3) avoid the destructive climate change caused by global warming. Many different approaches are being considered to address climate change, including increasing the use of clean, non polluting renewable energy sources such as biofuels, solar, wind and nuclear, attempting to capture and sequester the carbon dioxide emissions from fossil fuel plants, as well as increased conservation efforts. Some of these approaches, such as solar power, have had their large scale implementation blocked due to their current high costs as compared to the cost of fossil based electricity, and other approaches, such as nuclear, are restrained by their environmental and security risks. In fact, the infrastructure and supply for renewable energy is so underdeveloped (e.g., only about 0.01% of our energy is provided by solar) that there is no feasible way to avoid using fossil fuels during the rest of this century if we are to have the energy needed for economic prosperity and avoid energy shortfalls that could lead to conflict.
The climate change threat caused by global warming and the more general recognition of our need to use renewable resources that do not harm our planet has grown steadily since the first Earth Day in 1972. It is mostly undisputed that an increase in the amount of so-called greenhouse gases like carbon dioxide (methane and water vapor are the other major greenhouse gases) will increase the temperature of the planet. These greenhouse gases help reduce the amount of heat that escapes from our planet into the atmosphere. The higher the concentrations of greenhouse gases in the atmosphere the warmer the planet will be. There are complicated feedbacks that cause the amount of carbon dioxide and other greenhouse gases to change naturally even in the absence of human impact. Climate change throughout geological history has caused many extinctions. The concern about the threat of human induced climate change (i.e., global warming) resulted in the Kyoto Protocol that has been approved by over 165 countries and is an international agreement that commits the developed countries to reduce their carbon emissions.
One reason global warming is thought by the Intergovernmental Panel on Climate Change (IPCC) to be a threat is because of the sea level rise resulting from the melting of glaciers and the expansion of the ocean as our planet becomes hotter. Hundreds of millions of people who live just above sea level on islands or on the coasts are threatened by destructive flooding requiring relocation or the building of sea walls if the sea level rises even a meter. There is also a threat to other species from climate change which will destroy ecosystems that cannot adjust to the fast rate of human caused climate change. Additional threats include increased infectious diseases and more extreme weather as well as direct threats from extreme heat.
We can demonstrate the challenge of dealing with global warming using a simple model. Let CCA(YN) represent the carbon dioxide added to the atmosphere in year YN in gigatonnes per year. Similarly, let CEX(YN) equal the amount extracted, CEM(YN) the amount emitted by humans and CN(YN) be the amount either added or removed due to natural variations in the carbon cycle. Today, the land stores each year approximately 1.8 gigatonnes (109 tonnes) of carbon dioxide and the ocean approximately 10.5 gigatonnes (note carbon dioxide is 3.66 times heavier than carbon), while the amount humans add by emissions is about 24 gigatonnes of carbon dioxide. More generally, we have:
CCA(YN)=—CEX(YN)+CEM(YN)+CN(YN) (1)
CA(YN+1)═CA(YN)+CCA(YN) (2)
where CA(YN) is the amount of carbon in the atmosphere in year YN, 2780 gigatonnes of carbon dioxide today. Other forms of carbon contribute to global warming, most notably methane, although by weight they represent a small component
If CEX(YN) is set to zero than the only way one could possibly stop adding carbon dioxide to the atmosphere would be to reduce our emissions to be equal to the natural uptake. However, CN(YN) itself varies greatly and can be a net addition to the atmosphere from the much larger natural carbon cycle which adds and subtracts carbon at about 750 gigatonnes of carbon per year. It is the shifts in this natural balance that has caused climate change before our species existed and will also continue to do so in the future. Thus, it is clear that there is no solution that only reduces human contributions to carbon dioxide emissions that can remove the risk of climate change. With air extraction and the capability to increase or decrease the amount of carbon dioxide in the atmosphere one can in principle compensate for other greenhouse gases like methane that can change their concentrations and cause climate change.
Accordingly, there is a broadly recognized need for a system and method for reducing the amount of carbon dioxide in the atmosphere created by burning of fossil fuels and for providing a low cost, non-polluting renewable energy source as a substitute for fossil fuels.
A system for removing carbon dioxide from an atmosphere to reduce global warming and increase availability of renewable energy according to an exemplary embodiment of the present invention includes: an air extraction system that collects carbon dioxide from the atmosphere through a medium and removes carbon dioxide from the medium; a sequestration system that isolates the removed carbon dioxide to a location for at least one of storage and generation of a renewable carbon fuel; and one or more power supplying units that supply heat to the air extraction system to remove the carbon dioxide from the medium, at least one of the one or more power supplying units being a concentrated solar power supplying unit.
In at least one embodiment, the air extraction system comprises an air contactor that includes the medium to absorb carbon dioxide from the atmosphere.
In at least one embodiment, the air contactor is selected from the group of air contactors consisting of: convection towers, absorption pools and packed scrubbing towers.
In at least one embodiment, the medium is selected from the group of mediums consisting of: a liquid, a porous solid, a gas and mixtures thereof.
In at least one embodiment, the medium is an NaOH solution.
In at least one embodiment, the medium comprises an amine.
In at least one embodiment, the solar-power supplying unit comprises solar power cells selected from the group of solar power cells consisting of: concentrated solar power parabolic mirrors and concentrated solar power towers.
In at least one embodiment, the one or more power supplying units comprise at least one energy supplying unit selected from the group of energy supplying units consisting of: thermal energy supplying units, nuclear energy supplying units and chemical energy supplying units.
In at least one embodiment, the air extraction system collects carbon dioxide and the sequestration system isolates the removed carbon dioxide using the heat supplied by the one or more power supplying units.
In at least one embodiment, the sequestration system isolates the removed carbon dioxide to a location that is underground.
In at least one embodiment, the location is at a remote site upwind from one or more other components of the system.
A method for removing carbon dioxide from an atmosphere to reduce global warming and increase availability of renewable energy according to an exemplary embodiment of the present invention comprises the steps of: collecting air from the atmosphere; removing carbon dioxide from the collected air; and isolating the removed carbon dioxide to a location for at least one of storage and generation of a renewable carbon fuel, wherein at least one of the collecting, removing and isolating steps is performed using solar energy.
In at least one embodiment, the step of removing comprises absorbing the carbon dioxide using an absorber.
In at least one embodiment, the absorber is an NaOH solution.
In at least one embodiment, the absorber comprises an amine.
In at least one embodiment, the step of isolating comprises at least one of mineral sequestration and injection into geologic formations.
A global thermostat for controlling average temperature of a planet's atmosphere according to an exemplary embodiment of the present invention comprises: one or more first systems for extracting greenhouse gases from the atmosphere at a rate slower than the greenhouse gases are increasing in the atmosphere and at least one of storing the greenhouse gases and generating a renewable carbon fuel using the greenhouse gases; one or more second systems for extracting greenhouse gases from the atmosphere at a rate faster than the greenhouse gases are increasing in the atmosphere and at least one of storing the greenhouse gases and generating a renewable carbon fuel using the greenhouse gases; one or more third systems for extracting greenhouse gases from the atmosphere at the same rate as the greenhouse gases are increasing or decreasing in the atmosphere and at least one of storing the greenhouse gases and generating a renewable carbon fuel using the greenhouse gases; and a solar energy source for providing heat to at least one of the first, second and third systems.
In at least one embodiment, the greenhouse gases comprises carbon dioxide, and the at least one of the first, second and third systems comprises: an air extraction system that collects carbon dioxide from the atmosphere through a medium and removes carbon dioxide from the medium; and a sequestration system that isolates the removed carbon dioxide to a location for at least one of storage and generation of a renewable carbon fuel, wherein the heat provided by the solar energy source is used by the air extraction system to remove the carbon dioxide from the medium.
In at least one embodiment, the air extraction system comprises an air contactor that includes the medium to absorb carbon dioxide from the atmosphere.
In at least one embodiment, the air contactor is selected from the group of air contactors consisting of: convection towers, absorption pools and packed scrubbing towers.
In at least one embodiment, the medium is selected from the group of mediums consisting of: a liquid, a porous solid, a gas and mixtures thereof.
In at least one embodiment, the medium is an NaOH solution.
In at least one embodiment, the medium comprises an amine.
In at least one embodiment, the solar energy source comprises solar power cells selected from the group of solar power cells consisting of: concentrated solar power parabolic mirrors and concentrated solar power towers.
In at least one embodiment, the air extraction system collects carbon dioxide and the sequestration system isolates the removed carbon dioxide using the heat supplied by the solar energy source.
In at least one embodiment, the sequestration system isolates the removed carbon dioxide to a location that is underground.
In at least one embodiment, the location is at a remote site upwind from one or more other components of the system.
These and other features of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of this invention.
Various exemplary embodiments of this invention will be described in detail, with reference to the following figures, wherein:
The solar collector 10 may be any known or future-discovered solar energy collection system, which may include solar energy collection units, such as, for example, concentrated solar power parabolic mirrors, and concentrated solar power towers. As is known in the art, the solar collector 10 converts solar energy to thermal energy, which may be used to drive the power generator 30. Residual thermal energy (i.e., process heat) may be used to drive the air extraction system 42 and/or the sequestration system 50. For example, the process heat may be used to improve the efficiency of chemical and/or physical reactions used in the air extraction system 42 to absorb CO2 from the air and/or to drive off the CO2 from the medium. In addition, in other exemplary embodiments, as shown by the dashed arrows in
The power generator 30 may be, for example, a thermal power generator that converts the thermal energy provided by the solar collector to electricity. As is known in the art, the suns heat may be focused on a medium, such as molten salts, that is then used to generate high temperature, high pressure steam that drives a turbine to generate electricity. The generated electricity may then be used to power the other components of the system 2, in addition to providing power to the general population as part of a power grid. In this regard, the thermal energy provided by the solar collector 10 may be supplemented by energy generated by the supplemental energy source 20. For example, the supplemental energy source 20 may be a waste incineration plant, which provides additional thermal energy to drive the power generator 30. Also, it should be appreciated that any other type of renewable energy source may be used in addition to solar energy, and preferably a renewable energy source that produces heat as a precursor to the generation of electricity. Other potential renewable energy sources to be used in addition to solar energy include, for example, nuclear, biomass, and geothermal energy sources.
In this embodiment, at the air contactor 41, CO2 may be absorbed into an NaOH solution forming sodium carbonate (Na2CO3). Of course, other known or future-developed absorbers may also be used as an alternative or in addition to an NaOH solution. The generated Na2CO3 is then sent to the causticizer 43, where the NaOH is regenerated by addition of lime (CaO) in a batch process. The resulting CaCO3 solid is sent to the calciner 47 where it is heated in a kiln to regenerate the CaO, driving off the CO2 in a process known as calcination. The regenerated CaO is then sent through the slaker 45, which produces slaked lime Ca(OH)2 for use in the causticizer 43.
The capture unit 49 captures the CO2 driven off at the calciner 47 using any know or later-discovered CO2 capturing method that is effective in the low concentrations in which CO2 is present in the atmosphere and that needs only low temperature heat for regeneration. For example, the capture unit 49 may use an amine based capture system, such as the system described in U.S. Pat. No. 6,547,854, incorporated by reference herein. The capture unit 49 may also compress the captured CO2 to liquid form so that the CO2 may be more easily sequestered.
The sequestration system 50 may use any known or future-discovered carbon storing technique, such as, for example, injection into geologic formations or mineral sequestration. In the case of injection, the captured CO2 may be sequestered in geologic formations such as, for example, oil and gas reservoirs, unmineable coal seams and deep saline reservoirs. In this regard, in many cases, injection of CO2 into a geologic formation may enhance the recovery of hydrocarbons, providing the value-added byproducts that can offset the cost of CO2 capture and sequestration. For example, injection of CO2 into an oil or natural gas reservoir pushes out the product in a process known as enhanced oil recovery. The captured CO2 may be sequestered underground, and according to at least one embodiment of the invention at a remote site upwind from the other components of the system 2 so that any leakage from the site is re-captured by the system 2.
In regards to mineral sequestration, CO2 may be sequestered by a carbonation reaction with calcium and magnesium silicates, which occur naturally as mineral deposits. For example, as shown in reactions (1) and (2) below, CO2 may be reacted with forsterite and serpentine, which produces solid calcium and magnesium carbonates in an exothermic reaction.
½Mg2SiO4+CO2═MgCO3+½SiO2+95 kJ/mole (1)
⅓Mg3Si2O5(OH)4+CO2═MgCO3+⅔SiO2+⅔H2O+64 kJ/mole (2)
Both of these reactions are favored at low temperatures. In this regard, both the air capture and air sequestration processes described herein may use electricity and/or thermal energy generated by the solar collector 10 (or other renewable energy source) to drive the necessary reactions and power the appropriate system components. In an exemplary embodiment of the present invention, a high temperature carrier may be heated up to a temperature in a range of about 400° C. to about 500° C. to generate steam to run a generator for electricity, and the lower temperature steam that exits from the electrical generating turbines can be used to drive off the CO2 and regenerate the sorbent (e.g., NaOH). The temperature of the high temperature heat, the generated electricity and the temperature of the lower temperature process heat remaining after electricity production can be adjusted to produce the mix of electricity production and CO2 removal that is considered optimal for a given application. In addition, in exemplary embodiments, still lower temperature process heat that emerges out of the capture and sequestration steps may be used to cool equipment used in these steps.
One or more systems for removing carbon dioxide from an atmosphere may be used as part of a global thermostat according to an exemplary embodiment of the present invention. By regulating the amount of carbon dioxide in the atmosphere and hence the greenhouse effect caused by carbon dioxide and other gas emissions, the system described herein may be used to alter the global average temperature. According to at least one exemplary embodiment of the present invention, several carbon dioxide capture and sequestration systems may be located at different locations across the globe so that operation of the multiple systems may be used to alter the CO2 concentration in the atmosphere and thus change the greenhouse gas heating of the planet. Locations may be chosen so as to have the most effect on areas such as large industrial centers and highly populated cities, or natural point sources of CO2 each of which could create locally higher concentrations of CO2 that would enable more cost efficient capture. For example, as shown in
While this invention has been described in conjunction with the exemplary embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.
