Patent Application
20130202516
I. Field of the Invention
The present invention generally relates to the field of removing carbon dioxide from a source, such as the waste stream (e.g. flue gas) of a power plant, whereby Group 2 silicate minerals are converted into Group 2 chloride salts and SiO2, Group 2 chloride salts are converted into Group 2 hydroxide and/or Group 2 hydroxychloride salts. These in turn may be reacted with carbon dioxide to form Group 2 carbonate salts, optionally in the presence of catalysts. These steps may be combined to form a cycle in which carbon dioxide is sequestered in the form of carbonate salts and byproducts from one or more steps, such as heat and chemicals, are re-used or recycled in one or more other steps.
II. Description of Related Art
Considerable domestic and international concern has been increasingly focused on the emission of CO2 into the air. In particular, attention has been focused on the effect of this gas on the retention of solar heat in the atmosphere, producing the “greenhouse effect.” Despite some debate regarding the magnitude of the effect, all would agree there is a benefit to removing CO2 (and other chemicals) from point-emission sources, especially if the cost for doing so were sufficiently small.
Greenhouse gases are predominately made up of carbon dioxide and are produced by municipal power plants and large-scale industry in site-power-plants, though they are also produced in any normal carbon combustion (such as automobiles, rain-forest clearing, simple burning, etc.). Though their most concentrated point-emissions occur at power-plants across the planet, making reduction or removal from those fixed sites an attractive point to effect a removal-technology. Because energy production is a primary cause of greenhouse gas emissions, methods such as reducing carbon intensity, improving efficiency, and sequestering carbon from power-plant flue-gas by various means has been researched and studied intensively over the last thirty years.
Attempts at sequestration of carbon (in the initial form of gaseous CO2) have produced many varied techniques, which can be generally classified as geologic, terrestrial, or ocean systems. An overview of such techniques is provided in the Proceedings of First National Conference on Carbon Sequestration, (2001). To date, many if not all of these techniques are too energy intensive and therefore not economically feasible, in many cases consuming more energy than the energy obtained by generating the carbon dioxide. Alternative processes that overcome one or more of these disadvantages would be advantageous.
The referenced shortcomings are not intended to be exhaustive, but rather are among many that tend to impair the effectiveness of previously known techniques for removing carbon dioxide from waste streams; however, those mentioned here are sufficient to demonstrate that the methodologies appearing in the art have not been altogether satisfactory and that a significant need exists for the techniques described and claimed in this disclosure.
Disclosed herein are methods and apparatuses for carbon dioxide sequestration, including removing carbon dioxide from waste streams.
In one aspect there are provided methods of sequestering carbon dioxide produced by a source, comprising:
In certain embodiments, the MgCl2 of step (a) is a MgCl2 hydrate (e.g., MgCl2.6(H2O)). In some embodiments, the MgCl2 of step (a) is greater than 90% by weight MgCl2.6(H2O). In still further embodiments, some or all of the MgCl2 formed in step (b) and/or step (c) is the MgCl2 used in step (a). Thus, in certain embodiments, some or all of the water in step (a) is present in the form of a hydrate of the MgCl2 or is obtained from the water of step (c) or step (b). In certain embodiments, some or all of the water in step (a) is present in the form of steam or supercritical water. In some embodiments some or all of the hydrogen chloride of step (a) is admixed with water to form hydrochloric acid. In a further embodiment the first step (a) product comprises greater than 90% by weight Mg(OH)Cl. In certain embodiments step (a) occurs in one, two or three reactors.
In some embodiments, a defined quantity of water is maintained in the second product mixture of step (b). For example, in some embodiments, the molar ratio of water to MgCl2 in the second product mixture is between about 6 and about 10, between about 6 and 9, between about 6 and 8, between about 6 and 7 or is about 6. In certain embodiments, a method comprises monitoring the concentration of MgCl2 in the second product mixture, the quantity of water in the second product mixture or both. In still further embodiments, the amount MgCl2 and/or water in step (b) (or the flow rates of MgCl2 and/or water into the second admixture) is adjusted based on such monitoring.
In a further embodiment, a method comprises separating the step (b) products. For example, the Mg(OH)2 product of step (b) can be a solid and separating the step (b) products can comprise separating some or all of the solid Mg(OH)2 from the water and MgCl2 solution. Thus, in some embodiments, the MgCl2 product of step (b) is aqueous MgCl2.
In yet a further embodiment step (b) comprises reacting some or all of the Mg(OH)Cl from step (a) with MgCl2 and a quantity of water in a second admixture under conditions suitable to form a second product mixture comprising a first step (b) product comprising Mg(OH)2 and a second step (b) product comprising MgCl2, wherein the quantity of water is sufficient to provide a molar ratio of water to Mg of greater than or equal to 6 to 1 in said second admixture. In some embodiments, the some or all of the MgCl2 for the reaction of step (b) is the MgCl2 product of step (c).
In a further embodiment, step (c) further comprises admixing sodium hydroxide salt in the third admixture.
In still yet a further embodiment, a method comprises:
For example, in some cases, some or all of the HCl in step (e) is obtained from step (a). In certain embodiments, step (e) further comprises agitating the calcium silicate mineral with HCl. In some embodiments, some or all of the heat generated in step (e) is recovered. In certain embodiments, some or all of the CaCl2 of step (c) is the CaCl2 of step (e). In further embodiments, a method comprises a separation step, wherein the silicon dioxide is removed from the CaCl2 formed in step (e). In yet further embodiments, some or all of the water of step (a) and/or (b) is obtained from the water of step (e).
Certain aspects of the embodiments comprise use of a calcium silicate mineral, such as a calcium inosilicate. In some embodiments, the calcium silicate mineral comprises diopside (CaMg[Si2O6]), tremolite Ca2Mg5{[OH]Si4O11}2 or CaSiO3. In some embodiments, the calcium silicate further comprises iron (e.g., fayalite (Fe2-[SiO4])) and or manganese silicates.
In some embodiments, the carbon dioxide is in the form of flue gas, wherein the flue gas further comprises N2 and H2O.
In some embodiments, suitable reacting conditions of step (a) comprise a temperature from about 200° C. to about 500° C. In some embodiments, the temperature is from about 230° C. to about 260° C. In some embodiments, the temperature is about 250° C. In some embodiments, the temperature is from about 200° C. to about 250° C. In some embodiments, the temperature is about 240° C.
In some embodiments, suitable reacting conditions of step (b) comprise a temperature from about 140° C. to about 240° C.
In some embodiments, suitable reacting conditions of step (c) comprise a temperature from about 20° C. to about 100° C. In some embodiments, the temperature is from about 25° C. to about 95° C.
In some embodiments, suitable reacting conditions of step (e) comprise a temperature from about 50° C. to about 200° C. In some embodiments, the temperature is from about 90° C. to about 150° C.
In further aspect there are provided methods of sequestering carbon dioxide produced by a source, comprising:
In some embodiments, the first cation-based halide sulfate or nitrate salt or hydrate thereof of step (a) is a first cation-based chloride salt or hydrate thereof, and the second step (a) product is HCl. In some embodiments, the first cation-based halide, sulfate, or nitrate salt or hydrate thereof of step (b) is a first cation-based chloride salt or hydrate thereof.
In some embodiments, the first cation-based chloride salt or hydrate thereof of step (a) is MgCl2. In some embodiments, the first cation-based chloride salt or hydrate thereof of step (a) is a hydrated form of MgCl2. In some embodiments, the first cation-based chloride salt or hydrate thereof of step (a) is MgCl2.6H2O. In some embodiments, the first cation-based hydroxide salt of step (a) is Mg(OH)2. In some embodiments, the first cation-based hydroxychloride salt of step (a) is Mg(OH)Cl. In some embodiments, the first step (a) product comprises predominantly Mg(OH)Cl. In some embodiments, the first step (a) product comprises greater than 90% by weight Mg(OH)Cl. In some embodiments, the first step (a) product is Mg(OH)Cl. In some embodiments, the first cation-based oxide salt of step (a) is MgO.
In some embodiments, the second cation-based halide, sulfate or nitrate salt or hydrate thereof of step (b) is a second cation-based chloride salt or hydrate thereof, for example, CaCl2. In some embodiments, the first cation-based chloride salt of step (b) is MgCl2. In some embodiments, the first cation-based chloride salt of step (b) is a hydrated form of MgCl2. In some embodiments, the first cation-based chloride salt of step (b) is MgCl2.6H2O.
In some embodiments, some or all of the water in step (a) is present in the form of steam or supercritical water. In some embodiments, some or all of the water of step (a) is obtained from the water of step (b). In some embodiments, step (b) further comprises admixing sodium hydroxide salt in the second admixture.
In some embodiments, the methods further comprise:
In some embodiments, some or all of the HCl in step (d) is obtained from step (a). In some embodiments, the methods of step (d) further comprises agitating the Group 2 silicate mineral with HCl. In some embodiments, some or all of the heat generated in step (d) is recovered. In some embodiments, some or all of the second cation-based chloride salt of step (b) is the Group 2 chloride salt of step (d). In some embodiments, the methods further comprise a separation step, wherein the silicon dioxide is removed from the Group 2 chloride salt formed in step (d). In some embodiments, some or all of the water of step (a) is obtained from the water of step (d).
In some embodiments, the Group 2 silicate mineral of step (d) comprises a Group 2 inosilicate. In some embodiments, the Group 2 silicate mineral of step (d) comprises CaSiO3. In some embodiments, the Group 2 silicate mineral of step (d) comprises MgSiO3. In some embodiments, the Group 2 silicate mineral of step (d) comprises olivine (Mg2[SiO4]). In some embodiments, the Group 2 silicate mineral of step (d) comprises serpentine (Mg6[OH]8[Si4O10]). In some embodiments, the Group 2 silicate mineral of step (d) comprises sepiolite (Mg4[(OH)2Si6O15].6H2O), enstatite (Mg2[Si2O6]), diopside (CaMg[Si2O6]), and/or tremolite Ca2Mg5{[OH]Si4O11}2. In some embodiments, the Group 2 silicate further comprises iron and or manganese silicates. In some embodiments, the iron silicate is fayalite (Fe2[SiO4]).
In some embodiments, some or all of the first cation-based chloride salt formed in step (b) is the first cation-based chloride salt used in step (a).
In some embodiments, the carbon dioxide is in the form of flue gas, wherein the flue gas further comprises N2 and H2O.
In some embodiments, suitable reacting conditions of step (a) comprise a temperature from about 200° C. to about 500° C. In some embodiments, the temperature is from about 230° C. to about 260° C. In some embodiments, the temperature is about 250° C. In some embodiments, the temperature is from about 200° C. to about 250° C. In some embodiments, the temperature is about 240° C.
In some embodiments, suitable reacting conditions of step (a) comprise a temperature from about 50° C. to about 200° C. In some embodiments, the temperature is from about 90° C. to about 260° C. In some embodiments, the temperature is from about 90° C. to about 230° C. In some embodiments, the temperature is about 130° C.
In some embodiments, suitable reacting conditions of step (a) comprise a temperature from about 400° C. to about 550° C. In some embodiments, the temperature is from about 450° C. to about 500° C.
In some embodiments, suitable reacting conditions of step (a) comprise a temperature from about 20° C. to about 100° C. In some embodiments, the temperature is from about 25° C. to about 95° C.
In some embodiments, suitable reacting conditions of step (a) comprise a temperature from about 50° C. to about 200° C. In some embodiments, the temperature is from about 90° C. to about 150° C.
In another aspect, the present invention provides methods of sequestering carbon dioxide produced by a source, comprising:
In some embodiments, some or all of the hydrogen chloride of step (a) is admixed with water to form hydrochloric acid. In some embodiments, some or all of the magnesium hydroxide, magnesium oxide and/or Mg(OH)Cl of step (b)(i) is obtained from step (a)(i). In some embodiments, some of all the water in step (a) is present in the form of a hydrate of the magnesium chloride salt. In some embodiments, step (a) occurs in one, two or three reactors. In some embodiments, step (a) occurs in one reactor. In some embodiments, the magnesium hydroxide, magnesium oxide and/or Mg(OH)Cl of step (a)(i) is greater than 90% by weight Mg(OH)Cl. In some embodiments, the magnesium chloride salt is greater than 90% by weight MgCl2.6(H2O).
In some embodiments, the methods further comprise:
In some embodiments, some or all of the hydrogen chloride in step (d) is obtained from step (a). In some embodiments, step (d) further comprises agitating the Group 2 silicate mineral with the hydrochloric acid. In some embodiments, some or all of the magnesium chloride salt in step (a) is obtained from step (d). In some embodiments, the methods further comprise a separation step, wherein the silicon dioxide is removed from the Group 2 chloride salt formed in step (d). In some embodiments, some or all of the water of step (a) is obtained from the water of step (d). In some embodiments, the Group 2 silicate mineral of step (d) comprises a Group 2 inosilicate.
In some embodiments, the Group 2 silicate mineral of step (d) comprises CaSiO3. In some embodiments, the Group 2 silicate mineral of step (d) comprises MgSiO3. In some embodiments, the Group 2 silicate mineral of step (d) comprises olivine. In some embodiments, the Group 2 silicate mineral of step (d) comprises serpentine. In some embodiments, the Group 2 silicate mineral of step (d) comprises sepiolite, enstatite, diopside, and/or tremolite. In some embodiments, the Group 2 silicate further comprises mineralized iron and or manganese.
In some embodiments, step (b) further comprises admixing CaCl2 and water to the second admixture.
Other objects, features and advantages of the present disclosure will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present disclosure. The invention may be better understood by reference to one of these drawings in combination with the detailed description of specific embodiments presented herein.
1st Chamber: MgCl2.6H2O→MgCl2.4H2O+2H2O 100° C.
2nd Chamber: MgCl2.4H2O→MgCl2.2H2O+2H2O 125° C.
3rd Chamber: MgCl2.2H2O→MgCl2.H2O+H2O 160° C.
4th Chamber: MgCl2.H2O→Mg(OH)Cl+HCl 130° C.
The first three reactions above may be characterized as dehydrations, while the fourth may be characterized as a decomposition. Results from this simulation, which is explained in greater detail in Example 2, indicate that at lower temperatures (130-250° C.) the decomposition of MgCl2.6H2O results in the formation of Mg(OH)Cl instead of MgO. The Mg(OH)Cl then reacts with H2O to form MgCl2 and Mg(OH)2, which then reacts with a saturated CaCl2/H2O solution and CO2 from the flue gas to form CaCO3, which is filtered out of the stream. The resulting MgCl2 formed is recycled to the first reactor to begin the process again.
1st Chamber: MgCl2.6H2O→MgCl2.4H2O+2H2O 100° C.
2nd Chamber: MgCl2.4H2O→MgCl2.2H2O+2H2O 125° C.
3rd Chamber: MgCl2.2H2O→Mg(OH)Cl+HCl+H2O 130° C.
3rd Chamber: MgCl2.2H2O→MgCl2.H2O+H2O 130° C.
The first, second and fourth reactions above may be characterized as dehydrations, while the third may be characterized as a decomposition. As in the embodiment of
MgCl2.6H2O→MgO+5H2O+2HCl 450° C.
Additional details regarding this simulation are provided in Example 4 below.
MgCl2.6H2O→Mg(OH)Cl+HCl+5H2O 250° C.
The reaction was modeled at 250° C. In some embodiments, the preferred range is from 230° C. to 260° C. Additional details regarding this simulation are provided in Example 5 below.
FIG. 18—CaSiO3—Mg(OH)Cl Process, Cases 10 & 11. This figure shows a process flow diagram providing parameters and results from a process simulation using Aspen Plus process software. The net reaction is the capture of CO2 from flue gas using inexpensive raw materials, CaSiO3, CO2 and water, to form SiO2 and CaCO3. Results from this simulation indicate that it is efficient to use heat from the HCl reacting with CaSiO3 and heat from the flue gas emitted by a natural gas or coal fired power plant to carry out the decomposition of MgCl2.6H2O to form Mg(OH)Cl. The Mg(OH)Cl then reacts with H2O to form MgCl2 and Mg(OH)2, which then reacts with a saturated CaCl2/H2O solution and CO2 from the flue gas to form CaCO3, which is filtered out of the stream. The resulting MgCl2 formed is recycled to the first reactor to begin the process again. In this embodiment, the magnesium chloride hexahydrate is dehydrated to magnesium chloride dihydrate MgCl2.2H2O in the first chamber using heat from the HCl and CaSiO3 reaction and decomposed in a second chamber at 250° C. using heat from the flue gas. Thus the decomposition goes partially to Mg(OH)Cl. The main reactions occurring in this chamber can be represented as follows:
FIG. 19—CaSiO3—MgO Process, Cases 12 & 13. This figure shows a process flow diagram providing parameters and results from a process simulation using Aspen Plus process software. The net reaction is the capture of CO2 from flue gas using inexpensive raw materials, CaSiO3, CO2 and water, to form SiO2 and CaCO3. Results from this simulation indicate that it is efficient to use heat from the HCl reacting with CaSiO3 and heat from flue gas emitted by a natural gas or coal fired power plant to carry out the decomposition of MgCl2.6H2O to form MgO. The MgO then reacts with H2O to form Mg(OH)2, which then reacts with a saturated CaCl2/H2O solution and CO2 from the flue gas to form CaCO3, which is filtered out of the stream. The resulting MgCl2 formed is recycled to the first reactor to begin the process again. In this embodiment, the magnesium chloride hexahydrate is dehydrated to magnesium chloride dihydrate MgCl2.2H2O in the first chamber using heat from the HCl and CaSiO3 reaction and decomposed in a second chamber at 450° C. using heat from the flue gas. Thus the decomposition goes completely to MgO. The main reactions occurring in this chamber can be represented as follows:
FIG. 20—MgSiO3—Mg(OH)Cl Process, Cases 14 & 15. This figure shows a process flow diagram providing parameters and results from a process simulation using Aspen Plus process software. The net reaction is the capture of CO2 from flue gas using inexpensive raw materials, MgSiO3, CO2 and water, to form SiO2 and MgCO3. Results from this simulation indicate that it is efficient to use heat from the HCl reacting with MgSiO3 and heat from the flue gas emitted by a natural gas or coal fired power plant to carry out the decomposition of MgCl2.2H2O to form Mg(OH)Cl. The Mg(OH)Cl then reacts with H2O to form MgCl2 and Mg(OH)2, which then reacts with CO2 from the flue gas to form MgCO3, which is filtered out of the stream. The resulting MgCl2 formed is recycled to the first reactor to begin the process again. In this embodiment, the magnesium chloride remains in the dihydrate form MgCl2.2H2O due to the heat from the HCl and MgSiO3 prior to decomposition at 250° C. using heat from the flue gas. Thus the decomposition goes partially to Mg(OH)Cl. The main reactions occurring in this chamber can be represented as follows:
FIG. 21—MgSiO3—MgO Process, Cases 16 & 17. This figure shows a process flow diagram providing parameters and results from a process simulation using Aspen Plus process software. The net reaction is the capture of CO2 from flue gas using inexpensive raw materials, MgSiO3, CO2 and water, to form SiO2 and MgCO3. Results from this simulation indicate that it is efficient to use heat from the HCl reacting with MgSiO3 and heat from the flue gas emitted by a natural gas or coal fired power plant to carry out the decomposition of MgCl2.2H2O to form MgO. The MgO then reacts with H2O to form Mg(OH)2, which then reacts with CO2 from the flue gas to form MgCO3, which is filtered out of the stream. In this embodiment, the magnesium chloride remains in the dihydrate form MgCl2.2H2O due to the heat from the HCl and MgSiO3 prior to decomposition at 450° C. using heat from the flue gas. Thus the decomposition goes completely to MgO. The main reactions occurring in this chamber can be represented as follows:
FIG. 22—Diopside-Mg(OH)Cl Process, Cases 18 & 19. This figure shows a process flow diagram providing parameters and results from a process simulation using Aspen Plus process software. The net reaction is the capture of CO2 from flue gas using inexpensive raw materials, diopside MgCa(SiO3)2, CO2 and water, to form SiO2 and dolomite MgCa(CO3)2. Results from this simulation indicate that it is efficient to use heat from the HCl reacting with MgCa(SiO3)2 and heat from the flue gas emitted by a natural gas or coal fired power plant to carry out the decomposition of MgCl2.6H2O to form Mg(OH)Cl. The Mg(OH)Cl then reacts with H2O to form MgCl2 and Mg(OH)2, which then reacts with a saturated CaCl2/H2O solution and CO2 from the flue gas to form MgCa(CO3)2 which is filtered out of the stream. The resulting MgCl2 formed is recycled to the first reactor to begin the process again. In this embodiment, the magnesium chloride hexahydrate is dehydrated to magnesium chloride dihydrate MgCl2.2H2O in the first chamber using heat from the HCl and CaSiO3 reaction and decomposed to Mg(OH)Cl in a second chamber at 250° C. using heat from the flue gas. The main reactions occurring in this chamber can be represented as follows:
FIG. 23—Diopside-MgO Process, Cases 20 & 21. This figure shows a process flow diagram providing parameters and results from a process simulation using Aspen Plus process software. The net reaction is the capture of CO2 from flue gas using inexpensive raw materials, diopside MgCa(SiO3)2, CO2 and water, to form SiO2 and dolomite MgCa(CO3)2. Results from this simulation indicate that it is efficient to use heat from the HCl reacting with MgCa(SiO3)2 and heat from the flue gas emitted by a natural gas or coal fired power plant and/or other heat source to carry out the decomposition of MgCl2.6H2O to form MgO. The MgO then reacts with H2O to form Mg(OH)2, which then reacts with a saturated CaCl2/H2O solution and CO2 from the flue gas to form MgCa(CO3)2 which is filtered out of the stream. The resulting MgCl2 formed is recycled to the first reactor to begin the process again. In this embodiment, the magnesium chloride hexahydrate is dehydrated to magnesium chloride dihydrate MgCl2.2H2O in the first chamber using heat from the HCl and CaSiO3 reaction and decomposed to MgO in a second chamber at 450° C. using heat from the flue gas. The main reactions occurring in this chamber can be represented as follows:
FIG. 30—MgCl2.6H2O Decomposition at 500° C. after One Hour. This graph shows the normalized final and initial weights of four test runs of MgCl2.6H2O after heating at 500° C. for one hour. The consistent final weight confirms that MgO is made by decomposition at this temperature.
FIG. 31—Three-Chamber Decomposition. This figure shows a process flow diagram providing parameters and results from a process simulation using Aspen Plus process software. In this embodiment, heat from cold flue gas (chamber 1), heat from mineral dissolution reactor (chamber 2), and external natural gas (chamber 3) are used as heat sources. This process flow diagram illustrates a three chamber process for the decomposition to Mg(OH)Cl. The first chamber is heated by 200° C. flue gas to provide some initial heat about ˜8.2% of the total required heat, the second chamber which relies on heat recovered from the mineral dissolution reactor to provide 83% of the needed heat for the decomposition of which 28% is from the hydrochloric acid/mineral silicate reaction and 55% is from the condensation and formation of hydrochloric acid, and finally the third chamber, which uses natural gas as an external source of the remaining heat which is 8.5% of the total heat. The CO2 is from a combined cycle power natural gas plant, so very little heat is available from the power plant to power the decomposition reaction.
FIG. 32—Four-Chamber Decomposition. This figure shows a process flow diagram providing parameters and results from a process simulation using Aspen Plus process software. In this embodiment, heat from cold flue gas (chamber 1), heat from additional steam (chamber 2), heat from mineral dissolution reactor (chamber 3), and external natural gas (chamber 4) are used as heat sources. This process flow diagram illustrates a four chamber process for the decomposition to Mg(OH)Cl, the first chamber provides 200° C. flue gas to provide some initial heat about ˜8.2% of the total required heat, the second chamber provides heat in the form of extra steam which is 0.8% of the total heat needed, the third chamber which relies on heat recovered from the mineral dissolution reactor to provide 83% of the needed heat for the decomposition of which 28% is from the hydrochloric acid/mineral silicate reaction and 55% is from the condensation and formation of hydrochloric acid, and finally the fourth chamber, which uses natural gas as an external source of the remaining heat which is 8.0% of the total heat. The CO2 is from a combined cycle natural gas power plant, so very little heat is available from the power plant to power the decomposition reaction.
FIG. 33—Two-Chamber Decomposition. This figure shows a process flow diagram providing parameters and results from a process simulation using Aspen Plus process software. In this embodiment, heat from mineral dissolution reactor (chamber 1), and external natural gas (chamber 2) are used as heat sources. This process flow diagram illustrates a two chamber process for the decomposition to Mg(OH)Cl, the first chamber which relies on heat recovered from the mineral dissolution reactor to provide 87% of the needed heat for the decomposition of which 28% is from the hydrochloric acid/mineral silicate reaction and 59% is from the condensation and formation of hydrochloric acid, and the second chamber, which uses natural gas as an external source of the remaining heat which is 13% of the total heat. The CO2 is from a combined cycle natural gas power plant, so very little heat is available from the power plant to power the decomposition reaction.
FIG. 34—Two-Chamber Decomposition. This figure shows a process flow diagram providing parameters and results from a process simulation using Aspen Plus process software. In this embodiment, heat from mineral dissolution reactor (chamber 1), and hot flue gas from open cycle natural gas plant (chamber 2) are used as heat sources. This process flow diagram illustrates a two chamber process for the decomposition to Mg(OH)Cl, the first chamber which relies on heat recovered from the mineral dissolution reactor to provide 87% of the needed heat for the decomposition of which 28% is from the hydrochloric acid/mineral silicate reaction and 59% is from the condensation and formation of hydrochloric acid, and the second chamber, which uses hot flue gas as an external source of the remaining heat which is 13% of the total heat. The CO2 is from an open cycle natural gas power plant, therefore substantial heat is available from the power plant in the form of 600° C. flue gas to power the decomposition reaction.
The present invention relates to carbon dioxide sequestration, including energy-efficient processes in which Group 2 chlorides are converted to Group 2 hydroxides and hydrogen chloride, which are then used to remove carbon dioxide from waste streams. In some embodiments, hydrogen chloride may be further reacted with Group 2 silicates to produce additional Group 2 chloride starting materials and silica.
In some embodiments, the methods and apparatuses of the invention comprise one or more of the following general components: (1) the conversion of Group 2 silicate minerals with hydrogen chloride into Group 2 chlorides and silicon dioxide, (2) conversion of Group 2 chlorides into Group 2 hydroxides and hydrogen chloride, (3) an aqueous decarbonation whereby gaseous CO2 is absorbed into an aqueous caustic mixture comprising Group 2 hydroxides to form Group 2 carbonate and/or bicarbonate products and water, (4) a separation process whereby the carbonate and/or bicarbonate products are separated from the liquid mixture, (5) the reuse or cycling of by-products, including energy, from one or more of the steps or process streams into another one or more steps or process streams. Each of these general components is explained in further detail below.
While many embodiments of the present invention consume some energy to accomplish the absorption of CO2 and other chemicals from flue-gas streams and to accomplish the other objectives of embodiments of the present invention as described herein, one advantage of certain embodiments of the present invention is that they provide ecological efficiencies that are superior to those of the prior art, while absorbing most or all of the emitted CO2 from a given source, such as a power plant.
Another additional benefit of certain embodiments of the present invention that distinguishes them from other CO2-removal processes is that in some market conditions, the products are worth considerably more than the reactants required or the net-power or plant-depreciation costs. In other words, certain embodiments are industrial methods of producing chloro-hydro-carbonate products at a profit, while accomplishing considerable removal of CO2 and incidental pollutants of concern.
As used herein, the terms “carbonates” or “carbonate products” are generally defined as mineral components containing the carbonate group, [CO3]2−. Thus, the terms encompass both carbonate/bicarbonate mixtures and species containing solely the carbonate ion. The terms “bicarbonates” and “bicarbonate products” are generally defined as mineral components containing the bicarbonate group, [HCO3]1−. Thus, the terms encompass both carbonate/bicarbonate mixtures and species containing solely the bicarbonate ion.
As used herein “Ca/Mg” signifies either Ca alone, Mg alone or a mixture of both Ca and Mg. The ratio of Ca to Mg may range from 0:100 to 100:0, including, e.g., 1:99, 5:95, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, 95:5, and 99:1. The symbols “Ca/Mg”, “MgxCa(1-x)” and CaxMg(1-x)” are synonymous. In contrast, “CaMg” or “MgCa” refers to a 1:1 ratio of these two ions.
As used herein, the term “ecological efficiency” is used synonymously with the term “thermodynamic efficiency” and is defined as the amount of CO2 sequestered by certain embodiments of the present invention per energy consumed (represented by the equation “∂CO2/∂E”), appropriate units for this value are kWh/ton CO2. CO2 sequestration is denominated in terms of percent of total plant CO2; energy consumption is similarly denominated in terms of total plant power consumption.
The terms “Group II” and “Group 2” are used interchangeably.
“Hexahydrate” refers to MgCl2.6H2O.
In the formation of bicarbonates and carbonates using some embodiments of the present invention, the term “ion ratio” refers to the ratio of cations in the product divided by the number of carbons present in that product. Hence, a product stream formed of calcium bicarbonate (Ca(HCO3)2) may be said to have an “ion ratio” of 0.5 (Ca/C), whereas a product stream formed of pure calcium carbonate (CaCO3) may be said to have an “ion ratio” of 1.0 (Ca/C). By extension, an infinite number of continuous mixtures of carbonate and bicarbonate of mono-, di- and trivalent cations may be said to have ion ratios varying between 0.5 and 3.0.
Based on the context, the abbreviation “MW” either means molecular weight or megawatts.
The abbreviation “PFD” is process flow diagram.
The abbreviation “Q” is heat (or heat duty), and heat is a type of energy. This does not include any other types of energy.
As used herein, the term “sequestration” is used to refer generally to techniques or practices whose partial or whole effect is to remove CO2 from point emissions sources and to store that CO2 in some form so as to prevent its return to the atmosphere. Use of this term does not exclude any form of the described embodiments from being considered “sequestration” techniques.
In the context of a chemical formula, the abbreviation “W” refers to H2O.
The pyroxenes are a group of silicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems. Pyroxenes have the general formula XY(Si,Al)2O6, where X represents calcium, sodium, iron (II) and magnesium and more rarely zinc, manganese and lithium and Y represents ions of smaller size, such as chromium, aluminium, iron(III), magnesium, manganese, scandium, titanium, vanadium and even iron (II).
In addition, atoms making up the compounds of the present invention are intended to include all isotopic forms of such atoms. Isotopes, as used herein, include those atoms having the same atomic number but different mass numbers. By way of general example and without limitation, isotopes of hydrogen include tritium and deuterium, and isotopes of carbon include 13C and 14C.
The use of the word “a” or “an,” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”
Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.
The terms “comprise,” “have” and “include” are open-ended linking verbs. Any forms or tenses of one or more of these verbs, such as “comprises,” “comprising,” “has,” “having,” “includes” and “including,” are also open-ended. For example, any method that “comprises,” “has” or “includes” one or more steps is not limited to possessing only those one or more steps and also covers other unlisted steps. The term “effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.
The above definitions supersede any conflicting definition in any of the reference that is incorporated by reference herein. The fact that certain terms are defined, however, should not be considered as indicative that any term that is undefined is indefinite. Rather, all terms used are believed to describe the invention in terms such that one of ordinary skill can appreciate the scope and practice the present invention.
In the embodiment shown in
(Ca/Mg)Cl2+2 H2O→(Ca/Mg)(OH)2+2HCl (1)
The water used in this reaction may be in the form of liquid, steam, a crystalline hydrate, e.g., MgCl2.6H2O, CaCl2.2H2O, or it may be supercritical. In some embodiments, the reaction uses MgCl2 to form Mg(OH)2 and/or Mg(OH)Cl (see, e.g.,
Carbon dioxide from a source, e.g., flue-gas, enters the process at reactor 20 (e.g., a fluidized bed reactor, a spray-tower decarbonator or a decarbonation bubbler), potentially after initially exchanging waste-heat with a waste-heat/DC generation system. In some embodiments the temperature of the flue gas is at least 125° C. The Group 2 hydroxide, some or all of which may be obtained from reactor 10, reacts with carbon dioxide in reactor 20 according to the reaction represented by equation 2.
(Ca/Mg)(OH)2+CO2→(Ca/Mg)CO3+H2O (2)
The water produced from this reaction may be delivered back to reactor 10. The Group 2 carbonate is typically separated from the reaction mixture. Group 2 carbonates have a very low Ksp (solubility product constant). So they be separated as solids from other, more soluble compounds that can be kept in solution. In some embodiments, the reaction proceeds through Group 2 bicarbonate salts. In some embodiments, Group 2 bicarbonate salts are generated and optionally then separated from the reaction mixture. In some embodiments, Group 2 oxides, optionally together with or separately from the Group 2 hydroxides, are reacted with carbon dioxide to also form Group 2 carbonate salts. In some embodiments, the flue gas, from which CO2 and/or other pollutants have been removed, is released to the air.
Group 2 silicates (e.g., CaSiO3, MgSiO3, MgO.FeO.SiO2, etc.) enter the process at reactor 30 (e.g., a rock melter or a mineral dissociation reactor). In some embodiments, these Group 2 silicates are ground in a prior step. In some embodiments, the Group 2 silicates are inosilicates. These minerals may be reacted with hydrochloric acid, either as a gas or in the form of hydrochloric acid, some or all of which may be obtained from reactor 10, to form the corresponding Group 2 metal chlorides (CaCl2 and/or MgCl2), water and sand (SiO2). The reaction can be represented by equation 3.
2HCl+(Ca/Mg)SiO3→(Ca/Mg)Cl2+H2O+SiO2 (3)
Some or all of the water produced from this reaction may be delivered to reactor 10. Some or all of the Group 2 chlorides from equation 3 may be delivered to reactor 20. In some embodiments, some or all of the Group 2 chloride is delivered to reactor 20 as an aqueous solution. In some embodiments, some or all of the Group 2 chloride is delivered to reactor 20 in an aqueous suspension. In some embodiments, some or all of the Group 2 chloride is delivered to reactor 20 as a solid. The net reaction capturing the summation of equations 1-3 is shown here as equation 4:
CO2+(Ca/Mg)SiO3→(Ca/Mg)CO3+SiO2 (4)
In another embodiment, the resulting MgxCa(1-x)CO3 sequestrant is reacted with HCl in a manner to regenerate and concentrate the CO2. The Ca/MgCl2 thus formed is returned to the decomposition reactor to produce CO2 absorbing hydroxides or hydroxyhalides.
Through the process shown in
In some embodiments, and depending on the concentration of CO2 in the flue gas stream of a given plant, the methods disclosed herein may be used to capture 33-66% of the plant's CO2 using heat-only as the driver (no electrical penalty). In some embodiments, the efficiencies of the methods disclosed herein improve with lower CO2-concentrations, and increase with higher (unscrubbed) flue-gas temperatures. For example, at 320° C. and 7% CO2 concentration, 33% of flue-gas CO2 can be mineralized from waste-heat alone. In other embodiments, e.g., at the exit temperatures of natural gas turbines approximately 100% mineralization can be achieved.
These methods and devices can be further modified, e.g., with modular components, optimized and scaled up using the principles and techniques of chemistry, chemical engineering, and/or materials science as applied by a person skilled in the art. Such principles and techniques are taught, for example, in U.S. Pat. No. 7,727,374, U.S. Patent Application Publications 2006/0185985 and 2009/0127127, U.S. patent application Ser. No. 11/233,509, filed Sep. 22, 2005, U.S. Provisional Patent Application No. 60/718,906, filed Sep. 20, 2005; U.S. Provisional Patent Application No. 60/642,698, filed Jan. 10, 2005; U.S. Provisional Patent Application No. 60/612,355, filed Sep. 23, 2004, U.S. patent application Ser. No. 12/235,482, filed Sep. 22, 2008, U.S. Provisional Application No. 60/973,948, filed Sep. 20, 2007, U.S. Provisional Application No. 61/032,802, filed Feb. 29, 2008, U.S. Provisional Application No. 61/033,298, filed Mar. 3, 2008, U.S. Provisional Application No. 61/288,242, filed Jan. 20, 2010, U.S. Provisional Application No. 61/362,607, filed Jul. 8, 2010, and International Application No. PCT/US08/77122, filed Sep. 19, 2008. The entire text of each of the above-referenced disclosures (including any appendices) is specifically incorporated by reference herein.
The above examples were included to demonstrate particular embodiments of the invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.
In the embodiment shown in
MgCl2.x(H2O)+yH2O→z′[Mg(OH)2]+z″[MgO]+z′″[MgCl(OH)]+(2z′+2z″+z″)[HCl] (5)
The water used in this reaction may be in the form of a hydrate of magnesium chloride, liquid, steam and/or it may be supercritical. In some embodiments, the reaction may occur in one, two, three or more reactors. In some embodiments, the reaction may occur as a batch, semi-batch of continuous process. In some embodiments, some or all of the magnesium salt product may be delivered to reactor 200. In some embodiments, some or all of the magnesium salt product is delivered to reactor 200 as an aqueous solution. In some embodiments, some or all of the magnesium salt product is delivered to reactor 200 in an aqueous suspension. In some embodiments, some or all of the magnesium salt product is delivered to reactor 200 as a solid. In some embodiments, some or all of the hydrogen chloride (e.g., in the form of vapor or in the form of hydrochloric acid) may be delivered to reactor 300 (e.g., a rock melter). In some embodiments, the Mg(OH)2 is further heated to remove water and form MgO. In some embodiments, the MgCl(OH) is further heated to remove HCl and form MgO. In some variants, one or more of Mg(OH)2, MgCl(OH) and MgO may then be delivered to reactor 200.
Carbon dioxide from a source, e.g., flue-gas, enters the process at reactor 200 (e.g., a fluidized bed reactor, a spray-tower decarbonator or a decarbonation bubbler), potentially after initially exchanging waste-heat with a waste-heat/DC generation system. In some embodiments the temperature of the flue gas is at least 125° C. Admixed with the carbon dioxide is the magnesium salt product from reactor 100 and CaCl2 (e.g., rock salt). The carbon dioxide reacts with the magnesium salt product and CaCl2 in reactor 200 according to the reaction represented by equation 6.
CO2+CaCl2+z′[Mg(OH)2]+z″[MgO]+z′″[MgCl(OH)]→(z′+z″+z′″)MgCl2+(z′+1/2z′″)H2O+CaCO3 (6)
In some embodiments, the water produced from this reaction may be delivered back to reactor 100. The calcium carbonate product (e.g., limestone, calcite) is typically separated (e.g., through precipitation) from the reaction mixture. In some embodiments, the reaction proceeds through magnesium carbonate and bicarbonate salts. In some embodiments, the reaction proceeds through calcium bicarbonate salts. In some embodiments, various Group 2 bicarbonate salts are generated and optionally then separated from the reaction mixture. In some embodiments, the flue gas, from which CO2 and/or other pollutants have been removed, is released to the air, optionally after one or more further purification and/or treatment steps. In some embodiments, the MgCl2 product, optionally hydrated, is returned to reactor 100. In some embodiments, the MgCl2 product is subjected to one or more isolation, purification and/or hydration steps before being returned to reactor 100.
Calcium silicate (e.g., 3CaO.SiO2, Ca3SiO5; 2CaO.SiO2, Ca2SiO4; 3CaO.2SiO2, Ca3Si2O7 and CaO.SiO2, CaSiO3 enters the process at reactor 300 (e.g., a rock melter). In some embodiments, these Group 2 silicates are ground in a prior step. In some embodiments, the Group 2 silicates are inosilicates. In the embodiment of
2HCl+(Ca/Mg)SiO3→(Ca/Mg)Cl2+H2O+SiO2 (7)
The net reaction capturing the summation of equations 5-7 is shown here as equation 8:
CO2+CaSiO3→CaCO3+SiO2 (8)
These methods and devices can be further modified, optimized and scaled up using the principles and techniques of chemistry, chemical engineering, and/or materials science as applied by a person skilled in the art. Such principles and techniques are taught, for example, in U.S. Pat. No. 7,727,374, U.S. Patent Application Publications 2006/0185985 and 2009/0127127, U.S. patent application Ser. No. 11/233,509, filed Sep. 22, 2005, U.S. Provisional Patent Application No. 60/718,906, filed Sep. 20, 2005; U.S. Provisional Patent Application No. 60/642,698, filed Jan. 10, 2005; U.S. Provisional Patent Application No. 60/612,355, filed Sep. 23, 2004, U.S. patent application Ser. No. 12/235,482, filed Sep. 22, 2008, U.S. Provisional Application No. 60/973,948, filed Sep. 20, 2007, U.S. Provisional Application No. 61/032,802, filed Feb. 29, 2008, U.S. Provisional Application No. 61/033,298, filed Mar. 3, 2008, U.S. Provisional Application No. 61/288,242, filed Jan. 20, 2010, U.S. Provisional Application No. 61/362,607, filed Jul. 8, 2010, and International Application No. PCT/US08/77122, filed Sep. 19, 2008. The entire text of each of the above-referenced disclosures (including any appendices) is specifically incorporated by reference herein.
The above examples were included to demonstrate particular embodiments of the invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.
Disclosed herein are processes that react a Group 2 chloride, e.g., CaCl2 or MgCl2, with water to form a Group 2 hydroxide, a Group 2 oxide, and/or a mixed salt such as a Group 2 hydroxide chloride. Such reactions are typically referred to as decompositions. In some embodiments, the water may be in the form of liquid, steam, from a hydrate of the Group 2 chloride, and/or it may be supercritical. The steam may come from a heat exchanger whereby heat from an immensely combustible reaction, i.e. natural gas and oxygen or hydrogen and chlorine heats a stream of water. In some embodiments, steam may also be generated through the use of plant or factory waste heat. In some embodiments, the chloride salt, anhydrous or hydrated, is also heated.
In the case of Mg2+ and Ca2+, the reactions may be represented by equations 9 and 10, respectively:
MgCl2+2 H2O→Mg(OH)2+2HCl(g) ΔH=263 kJ/mole** (9)
CaCl2+2 H2O→Ca(OH)2+2HCl(g) ΔH=284 kJ/mole** (10)
**Measured at 100° C. The reactions are endothermic meaning energy, e.g., heat has to be applied to make these reactions occur. Such energy may be obtained from the waste-heat generated from one or more of the exothermic process steps disclosed herein. The above reactions may occur according to one of more of the following steps:
CaCl2+(x+y+z)H2O→Ca2+.xH2O+Cl−.yH2O+Cl−.zH2O (11)
Ca+2.xH2O+Cl−.yH2O+Cl−.zH2O→[Ca2+.(x−1)(H2O)OH−]++Cl−.(yH2O)+Cl−.(z−1)H2O+H3O+ (12)
[Ca2+.(x−1)(H2O)OH−]++Cl−.(yH2O)+Cl−.(z−1)H2O+H3O+→[Ca2+.(x−1)(H2O)OH−]++Cl−.(yH2O)+zH2O+HCl(g)↑ (13)
[Ca2+.(x−1)(H2O)OH−]++Cl−.(yH2O)→[Ca2+.(x−2)(H2O)(OH−)2]+Cl−.(y−1)H2O+H3O+ (14)
[Ca2+.(x−2)(H2O)(OH−)2]+Cl−.(y−1)H2O+H3O+→Ca(OH)2↓+(x−2)H2O+yH2O+HCl↑ (15)
The reaction enthalpy (ΔH) for CaCl2+2H2O→Ca(OH)2+2HCl(g) is 284 kJ/mole at 100° C. In some variants, the salt MgCl2.6H2O, magnesium hexahydrate, is used. Since water is incorporated into the molecular structure of the salt, direct heating without any additional steam or water may be used to initiate the decomposition. Typical reactions temperatures for the following reactions are shown here:
MgCl2.6H2O→MgCl2.4H2O+2H2O (16)
MgCl2.4H2O→MgCl2.2H2O+2H2O (17)
MgCl2.4H2O→Mg(OH)Cl+HCl+3H2O (18)
MgCl2.2H2O→MgCl2.H2O+H2O (19)
MgCl2.2H2O→Mg(OH)Cl+HCl+H2O (20)
MgCl2.H2O→MgCl2+H2O (21)
MgCl2.H2O→Mg(OH)Cl+HCl (22)
Mg(OH)Cl→MgO+HCl (23)
In certain aspects, Mg(OH)2 can be more efficiently generated from MgCl2 (via Mg(OH)Cl) by adjusting the proportion of MgCl2 and water in the presence of Mg(OH)Cl. In order to optimize production of Mg(OH)2, the amount of water in the chamber is adjusted to favor Mg(OH)2 precipitation, while preventing formation of MgCl2.6(H2O) hydrates. Specifically, the amount of water in a Mg(OH)Cl solution is maintained at a water to MgCl2 molar ratio of greater than or equal to 6, such as a ratio of between about 6 and 7. Under these conditions Mg(OH)2, which is virtually insoluble, whereas the magnesium chloride remains in an aqueous solution. See, for example page 52 of de Bakker 2011, the entire disclosure of which is incorporated herein by reference.
Thus, to reach a product mixture of MgCl2.6H2O and Mg(OH)2 Mg(OH)Cl is reacted with an aqueous MgCl2 solution, such as that from the bubble column. That reaction would be:
CaCl2(aq)+CO2+Mg(OH)2=>MgCl2(aq)+CaCO3↓+H2O
MgCl2(aq)˜MgCl2.13-16H2O(liquid)
Boiling the mixture MgCl2.13-16H2O(liquid)+ΔH=>MgCl2.6H2O(solid)+7-9H2O(gas)↑ would require significant energy usage. Thus, a solution more dilute than MgCl2.6H2O shall cause the disproportionation of Mg(OH)Cl, a solution of MgCl2.xH2O(liquid) where x≧12 should also be able to cause the disproportionation of Mg(OH)Cl. The equation is written as follows:
Mg(OH)Cl+1/2MgCl2.13-16H2O(liquid)=>1/2Mg(OH)2+MgCl2.6.5-8H2O
Such as: Mg(OH)Cl+1/2MgCl2.12H2O(liquid)=>1/2Mg(OH)2+MgCl2.6H2O
The MgCl2(aq) is being reconstituted to half of the original MgCl2.6H2O by water removal and the remaining half of the MgCl2.6H2O forms from the disproportionation of Mg(OH)Cl by addition of water.
An example of a system that utilizes Mg(OH)2 generated as detailed above is shown in
In another aspect of the present disclosure, there are provided apparatuses and methods for the decarbonation of carbon dioxide sources using Group 2 hydroxides, Group 2 oxides, and/or Group 2 hydroxide chlorides as CO2 adsorbents. In some embodiments, CO2 is absorbed into an aqueous caustic mixture and/or solution where it reacts with the hydroxide and/or oxide salts to form carbonate and bicarbonate products. Sodium hydroxide, calcium hydroxide and magnesium hydroxide, in various concentrations, are known to readily absorb CO2. Thus, in embodiments of the present invention, Group 2 hydroxides, Group 2 oxides (such as CaO and/or MgO) and/or other hydroxides and oxides, e.g., sodium hydroxide may be used as the absorbing reagent.
For example, a Group 2 hydroxide, e.g., obtained from a Group 2 chloride, may be used in an adsorption tower to react with and thereby capture CO2 based on one or both of the following reactions:
Ca(OH)2+CO2→CaCO3+H2O (24)
Mg(OH)2+CO2→MgCO3+H2O (25)
In some embodiments of the present invention, most or nearly all of the carbon dioxide is reacted in this manner. In some embodiments, the reaction may be driven to completion, for example, through the removal of water, whether through continuous or discontinous processes, and/or by means of the precipitation of bicarbonate, carbonate, or a mixture of both types of salts. See example 1, below, providing a simulation demonstrating the ability to capture CO2 from flue gas using an inexpensive raw material, Ca(CO)2 derived from CaCl2, to form CaCO3.
In some embodiments, an initially formed Group 2 may undergo an salt exchange reaction with a second Group 2 hydroxide to transfer the carbonate anion. For example:
CaCl2+MgCO3+→MgCl2+CaCO3 (25a)
These methods and devices can be further modified, optimized and scaled up using the principles and techniques of chemistry, chemical engineering, and/or materials science as applied by a person skilled in the art. Such principles and techniques are taught, for example, in U.S. Pat. No. 7,727,374, U.S. patent application Ser. No. 11/233,509, filed Sep. 22, 2005, U.S. Provisional Patent Application No. 60/718,906, filed Sep. 20, 2005; U.S. Provisional Patent Application No. 60/642,698, filed Jan. 10, 2005; U.S. Provisional Patent Application No. 60/612,355, filed Sep. 23, 2004, U.S. patent application Ser. No. 12/235,482, filed Sep. 22, 2008, U.S. Provisional Application No. 60/973,948, filed Sep. 20, 2007, U.S. Provisional Application No. 61/032,802, filed Feb. 29, 2008, U.S. Provisional Application No. 61/033,298, filed Mar. 3, 2008, U.S. Provisional Application No. 61/288,242, filed Jan. 20, 2010, U.S. Provisional Application No. 61/362,607, filed Jul. 8, 2010, and International Application No. PCT/US08/77122, filed Sep. 19, 2008. The entire text of each of the above-referenced disclosures (including any appendices) is specifically incorporated by reference herein.
In aspects of the present invention there are provided methods of sequestering carbon dioxide using silicate minerals. The silicate minerals make up one of the largest and most important classes of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group. Silicate minerals all contain silicon and oxygen. In some aspects of the present invention, Group 2 silicates may be used to accomplish the energy efficient sequestration of carbon dioxide.
In some embodiments, compositions comprising Group 2 inosilicates may be used. Inosilicates, or chain silicates, have interlocking chains of silicate tetrahedra with either SiO3, 1:3 ratio, for single chains or Si4O11, 4:11 ratio, for double chains.
In some embodiments, the methods disclosed herein use compositions comprising Group 2 inosilicates from the pyroxene group. For example, enstatite (MgSiO3) may be used.
In some embodiments, compositions comprising Group 2 inosilicates from the pyroxenoid group are used. For example, wollastonite (CaSiO3) may be used. In some embodiments, compositions comprising mixtures of Group 2 inosilicates may be employed, for example, mixtures of enstatite and wollastonite. In some embodiments, compositions comprising mixed-metal Group 2 inosilicates may be used, for example, diopside (CaMgSi2O6).
Wollastonite usually occurs as a common constituent of a thermally metamorphosed impure limestone. Typically wollastonite results from the following reaction (equation 26) between calcite and silica with the loss of carbon dioxide:
CaCO3+SiO2→CaSiO3+CO2 (26)
In some embodiments, the present invention has the result of effectively reversing this natural process. Wollastonite may also be produced in a diffusion reaction in skarn. It develops when limestone within a sandstone is metamorphosed by a dyke, which results in the formation of wollastonite in the sandstone as a result of outward migration of calcium ions.
In some embodiments, the purity of the Group 2 inosilicate compositions may vary. For example, it is contemplated that the Group 2 inosilicate compositions used in the disclosed processes may contain varying amounts of other compounds or minerals, including non-Group 2 metal ions. For example, wollastonite may itself contain small amounts of iron, magnesium, and manganese substituting for calcium.
In some embodiments, compositions comprising olivine and/or serpentine may be used. CO2 mineral sequestration processes utilizing these minerals have been attempted. The techniques of Goldberg et al. (2001) are incorporated herein by reference.
The mineral olivine is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. When in gem-quality, it is called peridot. Olivine occurs in both mafic and ultramafic igneous rocks and as a primary mineral in certain metamorphic rocks. Mg-rich olivine is known to crystallize from magma that is rich in magnesium and low in silica. Upon crystallization, the magna forms mafic rocks such as gabbro and basalt. Ultramafic rocks, such as peridotite and dunite, can be residues left after extraction of magmas and typically are more enriched in olivine after extraction of partial melts. Olivine and high pressure structural variants constitute over 50% of the Earth's upper mantle, and olivine is one of the Earth's most common minerals by volume. The metamorphism of impure dolomite or other sedimentary rocks with high magnesium and low silica content also produces Mg-rich olivine, or forsterite.
Group 2 silicates, e.g., CaSiO3, MgSiO3, and/or other silicates disclosed herein, may be reacted with hydrochloric acid, either as a gas or in the form of aqueous hydrochloric acid, to form the corresponding Group 2 metal chlorides (CaCl2 and/or MgCl2), water and sand. In some embodiments the HCl produced in equation 1 is used to regenerate the MgCl2 and/or CaCl2 in equation 3. A process loop is thereby created. Table 1 below depicts some of the common calcium/magnesium containing silicate minerals that may be used, either alone or in combination. Initial tests by reacting olivine and serpentine with HCl have been successful. SiO2 was observed to precipitate out and MgCl2 and CaCl2 were collected.
In some embodiments, the conversion of carbon dioxide to mineral carbonates may be defined by two salts. The first salt is one that may be heated to decomposition until it becomes converted to a base (hydroxide and/or oxide) and emits an acid, for example, as a gas. This same base reacts with carbon dioxide to form a carbonate, bicarbonate or basic carbonate salt.
For example, in some embodiments, the present disclosure provides processes that react one or more salts from Tables A-C below with water to form a hydroxides, oxides, and/or a mixed hydroxide halides. Such reactions are typically referred to as decompositions. In some embodiments, the water may be in the form of liquid, steam, and/or from a hydrate of the selected salt. The steam may come from a heat exchanger whereby heat from an immensely combustible reaction, i.e. natural gas and oxygen or hydrogen and chlorine heats a stream of water. In some embodiments, steam may also be generated through the use of plant or factory waste heat. In some embodiments, the halide salt, anhydrous or hydrated, is also heated.
For Tables A-D, the numerical data corresponds to the energy per amount of CO2 captured in kWh/tonne, NC=did not converge, and NA=data not available.
This same carbonate, bicarbonate or basic carbonate of the first salt reacts with a second salt to do a carbonate/bicarbonate exchange, such that the anion of second salt combines with the cation of the first salt and the cation of the second salt combines with the carbonate/bicarbonate ion of the first salt, which forms the final carbonate/bicarbonate.
In some cases the hydroxide derived from the first salt is reacted with carbon dioxide and the second salt directly to form a carbonate/bicarbonate derived from (combined with the cation of) the second salt. In other cases the carbonate/bicarbonate/basic carbonate derived from (combined with the cation of) the first salt is removed from the reactor chamber and placed in a second chamber to react with the second salt.
This reaction may be beneficial when making a carbonate/bicarbonate when a salt of the second metal is desired, and this second metal is not as capable of decomposing to form a CO2 absorbing hydroxide, and if the carbonate/bicarbonate compound of the second salt is insoluble, i.e. it precipitates from solution. Below is a non-exhaustive list of examples of such reactions that may be used either alone or in combination, including in combination with one or more either reactions discussed herein.
2NaI+H2O→Na2O+2HI and/or Na2O+H2O→2NaOH
MgCl2.6H2O→MgO+5H2O+2HCl and/or MgO+H2O→Mg(OH)2
2NaOH+CO2→Na2CO3+H2O and/or Na2CO3+CO2+H2O→2NaHCO3
Mg(OH)2+CO2→MgCO3+H2O and/or Mg(OH)2+2CO2→Mg(HCO3)2
Examples of a Carbonate exchange with a Salt-2:
Na2CO3+CaCl2→CaCO3↓+2NaCl
Na2CO3+2AgNO3→Ag2CO3↓+2NaNO3
Ca(OH)2+Na2CO3→CaCO3↓+2NaOH*
* In this instance the carbonate, Na2CO3 is Salt-2, and the salt decomposed to form Ca(OH)2, i.e. CaCl2 is the Salt-1. This is the reverse of some of the previous examples in that the carbonate ion remains with Salt-1.
Known carbonate compounds include H2CO3, Li2CO3, Na2CO3, K2CO3, Rb2CO3, Cs2CO3, BeCO3, MgCO3, CaCO3, MgCO3, SrCO3, BaCO3, MnCO3, FeCO3, CoCO3, CuCO3, ZnCO3, Ag2CO3, CdCO3, Al2(CO3)3, Tl2CO3, PbCO3, and La2(CO3)3. Group IA elements are known to be stable bicarbonates, e.g., LiHCO3, NaHCO3, RbHCO3, and CsHCO3. Group HA and some other elements can also form bicarbonates, but in some cases, they may only be stable in solution. Typically rock-forming elements are H, C, O, F, Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Mg and Fe. Salts of these that can be thermally decomposed into corresponding hydroxides by the least amount of energy per mole of CO2 absorbing hydroxide may therefore be considered potential Salt-1 candidates.
Based on the energies calculated in Tables A-D, several salts have lower energies than MgCl2.6H2O. Table E below, summarizes these salts and the percent penalty reduction through their use relative to MgCl2.6H2O.
The following salts specify a decomposition reaction through their respective available MSDS information.
In aspects of the present invention there are provided methods of sequestering carbon dioxide in the form of limestone. Limestone is a sedimentary rock composed largely of the mineral calcite (calcium carbonate: CaCO3). This mineral has many uses, some of which are identified below.
Limestone in powder or pulverized form, as formed in some embodiments of the present invention, may be used as a soil conditioner (agricultural lime) to neutralize acidic soil conditions, thereby, for example, neutralizing the effects of acid rain in ecosystems. Upstream applications include using limestone as a reagent in desulfurizations.
Limestone is an important stone for masonry and architecture. One of its advantages is that it is relatively easy to cut into blocks or more elaborate carving. It is also long-lasting and stands up well to exposure. Limestone is a key ingredient of quicklime, mortar, cement, and concrete.
Calcium carbonate is also used as an additive for paper, plastics, paint, tiles, and other materials as both white pigment and an inexpensive filler. Purified forms of calcium carbonate may be used in toothpaste and added to bread and cereals as a source of calcium. CaCO3 is also commonly used medicinally as an antacid.
Currently, the majority of calcium carbonate used in industry is extracted by mining or quarrying. By co-generating this mineral as part of carbon dioxide sequestration in some embodiments, this invention provides a non-extractive source of this important product.
In aspects of the present invention there are provided methods of sequestering carbon dioxide in the form of magnesium carbonate. Magnesium carbonate, MgCO3, is a white solid that occurs in nature as a mineral. The most common magnesium carbonate forms are the anhydrous salt called magnesite (MgCO3) and the di, tri, and pentahydrates known as barringtonite (MgCO3.2H2O), nesquehonite (MgCO3.3H2O), and lansfordite (MgCO3.5H2O), respectively. Magnesium carbonate has a variety of uses; some of these are briefly discussed below.
Magnesium carbonate may be used to produce magnesium metal and basic refractory bricks. MgCO3 is also used in flooring, fireproofing, fire extinguishing compositions, cosmetics, dusting powder, and toothpaste. Other applications are as filler material, smoke suppressant in plastics, a reinforcing agent in neoprene rubber, a drying agent, a laxative, and for color retention in foods. In addition, high purity magnesium carbonate is used as antacid and as an additive in table salt to keep it free flowing.
Currently magnesium carbonate is typically obtained by mining the mineral magnesite. By co-generating this mineral as part of carbon dioxide sequestration in some embodiments, this invention provides a non-extractive source of this important product.
In aspects of the present invention there are provided methods of sequestering carbon dioxide that produce silicon dioxide as a byproduct. Silicon dioxide, also known as silica, is an oxide of silicon with a chemical formula of SiO2 and is known for its hardness. Silica is most commonly found in nature as sand or quartz, as well as in the cell walls of diatoms. Silica is the most abundant mineral in the Earth's crust. This compound has many uses; some of these are briefly discussed below.
Silica is used primarily in the production of window glass, drinking glasses and bottled beverages. The majority of optical fibers for telecommunications are also made from silica. It is a primary raw material for many whiteware ceramics such as earthenware, stoneware and porcelain, as well as industrial Portland cement.
Silica is a common additive in the production of foods, where it is used primarily as a flow agent in powdered foods, or to absorb water in hygroscopic applications. In hydrated form, silica is used in toothpaste as a hard abrasive to remove tooth plaque. Silica is the primary component of diatomaceous earth which has many uses ranging from filtration to insect control. It is also the primary component of rice husk ash which is used, for example, in filtration and cement manufacturing.
Thin films of silica grown on silicon wafers via thermal oxidation methods can be quite beneficial in microelectronics, where they act as electric insulators with high chemical stability. In electrical applications, it can protect the silicon, store charge, block current, and even act as a controlled pathway to limit current flow.
Silica is typically manufactured in several forms including glass, crystal, gel, aerogel, fumed silica, and colloidal silica. By co-generating this mineral as part of carbon dioxide sequestration in some embodiments, this invention provides another source of this important product.
Separation processes may be employed to separate carbonate and bicarbonate products from the liquid solution and/or reaction mixture. By manipulating the basic concentration, temperature, pressure, reactor size, fluid depth, and degree of carbonation, precipitates of one or more carbonate and/or bicarbonate salts may be caused to occur. Alternatively, carbonate/bicarbonate products may be separated from solution by the exchange of heat energy with incoming flue-gases.
The exit liquid streams, depending upon reactor design, may include water, CaCO3, MgCO3, Ca(HCO3)2, Mg(HCO3)2, Ca(OH)2, Ca(OH)2, NaOH, NaHCO3, Na2CO3, and other dissolved gases in various equilibria. Dissolved trace emission components such as H2SO4, HNO3, and Hg may also be found. In one embodiment, removing/separating the water from the carbonate product involves adding heat energy to evaporate water from the mixture, for example, using a reboiler. Alternatively, retaining a partial basic solution and subsequently heating the solution in a separating chamber may be used to cause relatively pure carbonate salts to precipitate into a holding tank and the remaining hydroxide salts to recirculate back to the reactor. In some embodiments, pure carbonate, pure bicarbonate, and mixtures of the two in equilibrium concentrations and/or in a slurry or concentrated form may then be periodically transported to a truck/tank-car. In some embodiments, the liquid streams may be displaced to evaporation tanks/fields where the liquid, such as water, may be carried off by evaporation.
The release of gaseous products includes a concern whether hydroxide or oxide salts will be released safely, i.e., emitting “basic rain.” Emission of such aerosolized caustic salts may be prevented in some embodiments by using a simple and inexpensive condenser/reflux unit.
In some embodiments, the carbonate salt may be precipitated using methods that are used separately or together with a water removal process. Various carbonate salt equilibria have characteristic ranges where, when the temperature is raised, a given carbonate salt, e.g., CaCO3 will naturally precipitate and collect, which makes it amenable to be withdrawn as a slurry, with some fractional NaOH drawn off in the slurry.
Because certain embodiments of the present invention are employed in the context of large emission of CO2 in the form of flue-gas or other hot gases from combustion processes, such as those which occur at a power plant, there is ample opportunity to utilize this ‘waste’ heat, for example, for the conversion of Group 2 chlorides salts into Group 2 hydroxides. For instance, a typical incoming flue-gas temperature (after electro-static precipitation treatment, for instance) is approximately 300° C. Heat exchangers can lower that flue-gas to a point less than 300° C., while warming the water and/or Group 2 chloride salt to facilitate this conversion.
Generally, since the flue-gas that is available at power-plant exits at temperatures between 100° C. (scrubbed typical), 300° C. (after precipitation processing), and 900° C. (precipitation entrance), or other such temperatures, considerable waste-heat processing can be extracted by cooling the incoming flue-gas through heat-exchange with a power-recovery cycle, for example an ammonia-water cycle (e.g., a “Kalina” cycle), a steam cycle, or any such cycle that accomplishes the same thermodynamic means. Since some embodiments of the present invention rely upon DC power to accomplish the manufacture of the reagent/absorbent, the process can be directly powered, partially or wholly, by waste-heat recovery that is accomplished without the normal transformer losses associated with converting that DC power to AC power for other uses. Further, through the use of waste-heat-to-work engines, significant efficiencies can be accomplished without an electricity generation step being employed at all. In some conditions, these waste-heat recovery energy quantities may be found to entirely power embodiments of the present invention.
As noted above, some embodiments of the apparatuses and methods of the present disclosure produce a number of useful intermediates, by-products, and final products from the various reaction steps, including hydrogen chloride, Group 2 carbonate salts, Group 2 hydroxide salts, etc. In some embodiments, some or all of these may be used in one or more of the methods described below. In some embodiments, some or all of one of the starting materials or intermediates employed in one or more of the steps described above are obtained using one or more of the methods outlined below.
A. Use of Chlorine for the Chlorination of Group 2 Silicates
In some embodiments the chlorine gas may be liquefied to hydrochloric acid that is then used to chlorinate Group 2 silicate minerals. Liquefaction of chlorine and subsequent use of the hydrochloric acid is particularly attractive especially in situations where the chlorine market is saturated. Liquefaction of chlorine may be accomplished according to equation 27:
Cl2(g)+2H2O(l)+hv(363 nm)→2HCl(l)+1/2O2(g) (27)
In some embodiments, the oxygen so produced may be returned to the air-inlet of the power plant itself, where it has been demonstrated throughout the course of power-industry investigations that enriched oxygen-inlet plants have (a) higher Carnot-efficiencies, (b) more concentrated CO2 exit streams, (c) lower heat-exchange to warm inlet air, and (d) other advantages over non-oxygen-enhanced plants. In some embodiments, the oxygen may be utilized in a hydrogen/oxygen fuel cell. In some embodiments, the oxygen may serve as part of the oxidant in a turbine designed for natural gas power generation, for example, using a mixture of hydrogen and natural gas.
B. Use of Chlorine for the Chlorination of Group 2 Hydroxides
In some embodiments the chlorine gas may be reacted with a Group 2 hydroxide salts to yield a mixture of a chloride and a hypochlorite salts (equation 28). For example, HCl may be sold as a product and the Group 2 hydroxide salt may be used to remove excess chlorine.
Ca/Mg(OH)2+Cl2→1/2Ca/Mg(OCl)2+1/2Ca/MgCl2+H2O (28)
The Group 2 hypochlorites may then be decomposed using a cobalt or nickel catalyst to form oxygen and the corresponding chloride (equation 29).
Ca/Mg(OCl)2→Ca/MgCl2+O2 (29)
The calcium chloride and/or the magnesium chloride may then be recovered.
In addition to removing CO2 from the source, in some embodiments of the invention, the decarbonation conditions will also remove SOx and NOx and, to a lesser extent, mercury. In some embodiments of the present invention, the incidental scrubbing of NOR, SON, and mercury compounds can assume greater economic importance; i.e., by employing embodiments of the present invention, coals that contain large amounts of these compounds can be combusted in the power plant with, in some embodiments, less resulting pollution than with higher-grade coals processed without the benefit of the CO2 absorption process. Such principles and techniques are taught, for example, in U.S. Pat. No. 7,727,374, U.S. patent application Ser. No. 11/233,509, filed Sep. 22, 2005, U.S. Provisional Patent Application No. 60/718,906, filed Sep. 20, 2005; U.S. Provisional Patent Application No. 60/642,698, filed Jan. 10, 2005; U.S. Provisional Patent Application No. 60/612,355, filed Sep. 23, 2004, U.S. patent application Ser. No. 12/235,482, filed Sep. 22, 2008, U.S. Provisional Application No. 60/973,948, filed Sep. 20, 2007, U.S. Provisional Application No. 61/032,802, filed Feb. 29, 2008, U.S. Provisional Application No. 61/033,298, filed Mar. 3, 2008, U.S. Provisional Application No. 61/288,242, filed Jan. 20, 2010, U.S. Provisional Application No. 61/362,607, filed Jul. 8, 2010, and International Application No. PCT/US08/77122, filed Sep. 19, 2008. The entire text of each of the above-referenced disclosures (including any appendices) is specifically incorporated by reference herein.
The following examples are included to demonstrate some embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.
One embodiment of the present invention was simulated using Aspen Plus v. 7.1 software using known reaction enthalpies, reaction free energies and defined parameters to determine mass and energy balances and suitable conditions for capturing CO2 from a flue gas stream utilizing CaCl2 and heat to form CaCO3 product. These results show that it is possible to capture CO2 from flue gas using inexpensive raw materials, CaCl2 and water, to form CaCO3.
Part of the defined parameters includes the process flow diagram shown in
Constraints and parameters specified for this simulation include:
The results of this simulation indicate a preliminary net energy consumption of approximately 130 MM Btu/hr. Tables 2a and 2b provide mass and energy accounting for the various streams (the columns in the table) of the simulated process. Each stream corresponds to the stream of
The process consists of two primary reaction sections and one solids filtration section. The first reactor heats MgCl2/water solution causing it to break down into a HCl/H2O vapor stream and a liquid stream of Mg(OH)2. The HCl/H2O vapor stream is sent to the HCl absorber column. The Mg(OH)2 solution is sent to reactor 2 for further processing. The chemical reaction for this reactor can be represented by the following equation:
MgCl2+2H2O→Mg(OH)2+2HCl (30)
A CaCl2 solution and a flue gas stream are added to the MgCl2 in reactor 2. This reaction forms CaCO3, MgCl2 and water. The CaCO3 precipitates and is removed in a filter or decanter. The remaining MgCl2 and water are recycled to the first reactor. Additional water is added to complete the water balance required by the first reactor. The chemical reaction for this reactor can be represented by the following equation:
Mg(OH)2+CaCl2+CO2→CaCO3(s)+MgCl2+H2O (31)
The primary feeds to this process are CaCl2, flue gas (CO2) and water. MgCl2 in the system is used, reformed and recycled. The only MgCl2 make-up required is to replace small amounts that leave the system with the CaCO3 product, and small amounts that leave with the HCl/water product.
This process is a net energy user. There is cross heat exchange to recover the heat in high temperature streams to preheat the feed streams. Significant heat recovery may be obtained by reacting the concentrated HCl thus formed with silicate minerals.
Results from the simulation suggest that it is efficient to heat a MgCl2.6H2O stream in three separate dehydration reactions, each in its own chamber, followed by a decomposition reaction, also in its own chamber, to form Mg(OH)Cl and HCl, i.e. total of four chambers. The Mg(OH)Cl is reacted with H2O to form MgCl2 and Mg(OH)2, which then reacts with a saturated CaCl2/H2O solution and CO2 from the flue gas to form CaCO3, which is filtered out of the stream. The resulting MgCl2.6H2O formed is recycled along with the earlier product to the first reactor to begin the process again.
This process is not limited to any particular source for CaCl2. For example, it may be obtained from reacting calcium silicate with HCl to yield CaCl2.
Constraints and parameters specified for this simulation include:
The results of this simulation indicate a preliminary net energy consumption of 5946 kwh/tonne CO2. Table 3 provides mass and energy accounting for the various streams of the simulated process. Each stream corresponds to the stream of
The process consists of two primary reactors and one solids filtration section. The first reactor heats MgCl2.6H2O causing it to break down into a HCl/H2O vapor stream and a solid stream of Mg(OH)Cl. The HCl/H2O vapor stream is sent to a heat exchanger to recover extra heat. The Mg(OH)2 formed from the Mg(OH)Cl is sent to reactor 2 for further processing. Chemical reaction(s) occurring in this reactor include the following:
MgCl2.6H2O+Δ→Mg(OH)Cl+5H2O↑+HCl↑ (32)
2Mg(OH)Cl(aq)→Mg(OH)2+MgCl2 (33)
A CaCl2 solution and a flue gas stream are added to the Mg(OH)2 in reactor 2. This reaction forms CaCO3, MgCl2 and water. The CaCO3 precipitates and is removed in a filter or decanter. The remaining MgCl2 and water are recycled to the first reactor. Additional water is added to complete the water balance required by the first reactor. Chemical reaction(s) occurring in this reactor include the following:
Mg(OH)2+CaCl2+CO2→CaCO3↓(s)+MgCl2+H2O (34)
The primary feeds to this process are CaCl2, flue gas (CO2) and water. MgCl2 in the system is used, reformed and recycled. The only MgCl2 make-up required is to replace small amounts that leave the system with the CaCO3 product, and small amounts that leave with the HCl/water product.
This process is a net energy user. The amount of energy is under investigation and optimization. There is cross heat exchange to recover the heat in high temperature streams to preheat the feed streams.
The steps for this process (Case 1) are summarized below:
Part of the defined parameters includes the process flow diagram shown in
Constraints and parameters specified for this simulation include:
The results of this simulation indicate a preliminary net energy consumption of 4862 kwh/tonne CO2. Table 4 provides mass and energy accounting for the various streams of the simulated process. Each stream corresponds to the stream in
The process consists of two primary reactors and one solids filtration section. The first reactor heats MgCl2.6H2O causing it to break down into a HCl/H2O vapor stream and a solid stream of Mg(OH)Cl. The HCl/H2O vapor stream is sent to a heat exchanger to recover extra heat. The Mg(OH)2 formed from the Mg(OH)Cl is sent to reactor 2 for further processing. Chemical reaction(s) occurring in this reactor include the following:
MgCl2.6H2O+Δ→Mg(OH)Cl+5H2O↑+HCl↑ (35)
2Mg(OH)Cl(aq)→Mg(OH)2+MgCl2 (36)
A CaCl2 solution and a flue gas stream are added to the Mg(OH)2 in reactor 2. This reaction forms CaCO3, MgCl2 and water. The CaCO3 precipitates and is removed in a filter or decanter. The remaining MgCl2 and water are recycled to the first reactor. Additional water is added to complete the water balance required by the first reactor. Chemical reaction(s) occurring in this reactor include the following:
Mg(OH)2+CaCl2+CO2→CaCO3↓(s)+MgCl2+H2O (37)
The primary feeds to this process are CaCl2, flue gas (CO2) and water. MgCl2 in the system is used, reformed and recycled. The only MgCl2 make-up required is to replace small amounts that leave the system with the CaCO3 product, and small amounts that leave with the HCl/water product.
This process is a net energy user. The amount of energy is under investigation and optimization. There is cross heat exchange to recover the heat in high temperature streams to preheat the feed streams.
The steps for this process (Case 2) are summarized below:
Part of the defined parameters include the process flow diagram shown in
Constraints and parameters specified for this simulation include:
The process consists of two primary reactors and one solids filtration section. The first reactor heats MgCl2.6H2O causing it to break down into a HCl/H2O vapor stream and a solid stream of MgO. The HCl/H2O vapor stream is sent to a heat exchanger to recover extra heat. The Mg(OH)2 formed from the MgO is sent to reactor 2 for further processing. Chemical reaction(s) occurring in this reactor include the following:
MgCl2.6H2O+Δ→MgO+5H2O↑+2HCl↑ (38)
MgO+H2O→Mg(OH)2 (39)
A CaCl2 solution and a flue gas stream are added to the Mg(OH)2 in reactor 2. This reaction forms CaCO3, MgCl2 and water. The CaCO3 precipitates and is removed in a filter or decanter. The remaining MgCl2 and water are recycled to the first reactor. Additional water is added to complete the water balance required by the first reactor. Chemical reaction(s) occurring in this reactor include the following:
Mg(OH)2+CaCl2+CO2→CaCO3↓(s)+MgCl2+H2O (40)
The primary feeds to this process are CaCl2, flue gas (CO2) and water. MgCl2 in the system is used, reformed and recycled. The only MgCl2 make-up required is to replace small amounts that leave the system with the CaCO3 product, and small amounts that leave with the HCl/water product.
This process is a net energy user. The amount of energy is under investigation and optimization. There is cross heat exchange to recover the heat in high temperature streams to preheat the feed streams.
The steps for this process (Case 3) are summarized below:
Part of the defined parameters include the process flow diagram shown in
Constraints and parameters specified for this simulation include:
The results of this simulation indicate a preliminary net energy consumption of 4681 kwh/tonne CO2. Table 6 provides mass and energy accounting for the various streams of the simulated process. Each stream corresponds to the stream of
The process consists of two primary reactors and one solids filtration section. The first reactor heats MgCl2.6H2O causing it to break down into a HCl/H2O vapor stream and a solid stream of Mg(OH)Cl. The HCl/H2O vapor stream is sent to a heat exchanger to recover extra heat. The Mg(OH)2 formed from the Mg(OH)Cl is sent to reactor 2 for further processing. Chemical reaction(s) occurring in this reactor include the following:
MgCl2.6H2O+Δ→Mg(OH)Cl+5H2O↑+HCl↑ (41)
2Mg(OH)Cl(aq)→Mg(OH)2+MgCl2 (42)
A CaCl2 solution and a flue gas stream are added to the Mg(OH)2 in reactor 2. This reaction forms CaCO3, MgCl2 and water. The CaCO3 precipitates and is removed in a filter or decanter. The remaining MgCl2 and water are recycled to the first reactor. Additional water is added to complete the water balance required by the first reactor. Chemical reaction(s) occurring in this reactor include the following:
Mg(OH)2+CaCl2+CO2→CaCO3↓(s)+MgCl2+H2O (43)
The primary feeds to this process are CaCl2, flue gas (CO2) and water. MgCl2 in the system is used, reformed and recycled. The only MgCl2 make-up required is to replace small amounts that leave the system with the CaCO3 product, and small amounts that leave with the HCl/water product.
This process is a net energy user. The amount of energy is under investigation and optimization. There is cross heat exchange to recover the heat in high temperature streams to preheat the feed streams.
The steps for this process (Case 4) are summarized below:
A sample of Mg(OH)Cl, produced by the heated decomposition of MgCl2.6H2O, was dissolved in water and stirred for a period of time. Afterwards, the remaining precipitate was dried, collected and analyzed. By the formula of decomposition, the amount of Mg(OH)2 could be compared to the expected amount and analyzed. The chemical reaction can be represented as follows:
2Mg(OH)Cl(aq)→Mg(OH)2+MgCl2 (44)
The solubility data for Mg(OH)2 and MgCl2 is as follows:
Theoretical weight of recovered Mg(OH)2:
Given weight of sample: 3.0136 gm.
Expected amount of Mg(OH)2
Precipitate collected=1.1245 gm
% of theoretical collected=(1.1447÷1.1245)*100=98.24%
Analytical data:
Next the sample of Mg(OH)2 was sent for analysis, XRD (X-ray-diffraction) and EDS. Results are shown in
The EDS analysis reveals that very little chlorine [Cl] was incorporated into the precipitate. Note, this analysis cannot detect oxygen or hydrogen.
Approximately 20 grams of Mg(OH)2 was placed in a bubble column with two liters of water and CO2 was bubbled though it for x minutes period of time. Afterwards some of the liquid was collected to which a solution of CaCl2 was added. A precipitate immediately formed and was sent through the XRD and EDS. The chemical reaction can be represented as follows:
Mg(OH)2+CO2+CaCl2→CaCO3↓+H2O (45)
The XRD analysis (
The EDS analysis indicates almost pure CaCO3 with only a 1.55% by weight magnesium impurity and almost no Chlorine from the CaCl2.
The same test was performed, except that Mg(OH)Cl from the decomposition of MgCl2.6H2O was used instead of Mg(OH)2. Although Mg(OH)Cl has half the hydroxide [OH−], as Mg(OH)2 it is expected to absorb CO2 and form precipitated CaCO3 (PCC).
The XRD analysis (
Note: Results do not include elements with Z<11 (Na). Again the results indicate almost pure CaCO3, almost no Mg or Cl compounds.
Samples of olivine (Mg,Fe)2SiO4 and serpentine Mg3Si2O5(OH)4 were crushed and reacted with 6.1 molar HCl over a period of approximately 72 hours. Two sets of tests were run, the first at room temperature and the second at 70° C. These minerals have variable formulae and often contain iron. After the samples were filtered, the resulting filtrand and filtrate were dried in an oven overnight. The samples then went through XRD and EDS analysis. The filtrates should have MgCl2 present and the filtrand should be primarily SiO2.
Olivine Filtrate Reacted with HCl at Room Temperature
Olivine Filtrate Reacted with HCl at 70° C.
Serpentine Filtrate Reacted with HCl at Room Temperature
Serpentine Filtrate Reacted with HCl at 70° C.
The filtrate clearly for both minerals serpentine and olivine at ambient conditions and 70° C. all illustrate the presence of MgCl2, and a small amount of FeCl2 in the case of olivine.
Olivine Filtrand Reacted with HCl at Room Temperature
Olivine Filtrand Reacted with HCl at 70° C.
Given that the formula for olivine is (Mg,Fe)2SiO4, and this is a magnesium rich olivine. The raw compound has a Mg:Si ratio of 2:1. However the filtrand, that which does not pass through the filter has a (Mg+Fe:Si) ratio of (37+5.5:52) or 0.817:1. (Atom % on the chart), evidently more than 50% of the magnesium passed through the filter.
Serpentine Filtrand Reacted with HCl at Room Temperature
Serpentine Filtrand Reacted with HCl at 70° C.
Given that the formula of serpentine is (Mg,Fe)3Si2O5(OH)4 the initial 1.5:1 ratio of (Mg+Fe) to Si has been whittled down to (37+9.3:56.5)=0.898:1.
Pressure and temperature was varied, as shown below (Table 7) and in
The following remaining examples are concerned with obtaining the necessary heat to perform the decomposition reaction using waste heat emissions from either coal or natural gas power plants. In order to obtain the necessary heat from coal flue gas emissions, the heat source may be located prior to the baghouse where the temperature ranges from 320-480° C. in lieu of the air pre-heater. See Reference: pages 11-15 of “The structural design of air and gas ducts for power stations and industrial Boiler Applications,” Publisher: American Society of Civil Engineers (August 1995), which is incorporated by reference herein in its entirety. Open cycle natural gas plants have much higher exhaust temperatures of 600° C. See Reference: pages 11-15 of “The structural design of air and gas ducts for power stations and industrial Boiler Applications,” Publisher: American Society of Civil Engineers (August 1995), which is incorporated by reference herein in its entirety. Additionally, the decomposition reaction of MgCl2.6H2O may also run in two different modes, complete decomposition to MgO or a partial decomposition to Mg(OH)Cl. The partial decomposition to Mg(OH)Cl requires in some embodiments a temperature greater than 180° C. whereas the total decomposition to MgO requires in some embodiments a temperature of 440° C. or greater.
Additionally the incoming feed to the process can be represented as a continuum between 100% Calcium Silicate (CaSiO3) and 100% Magnesium Silicate (MgSiO3) with Diopside (MgCa(SiO3)2) (or a mixture of CaSiO3 and MgSiO3 in a 1:1 molar ratio) representing an intermediate 50% case. For each of these cases the resulting output will range in some embodiments from calcium carbonate (CaCO3) to magnesium carbonate (MgCO3) with Dolomite CaMg(CO3)2 representing the intermediate case. The process using 100% calcium silicate is the Ca—Mg process used in all of the previously modeled embodiments. It is also important to note that the 100% magnesium silicate process uses no calcium compounds; whereas the 100% calcium silicate incoming feed process does use magnesium compounds, but in a recycle loop, only makeup magnesium compounds are required.
Further details regarding the Ca—Mg, Mg only, Diopside processes, for example, using complete and partial decomposition of hydrated MgCl2 to MgO and Mg(OH)Cl, respectively, are depicted below.
Overall reaction CaSiO3+CO2→CaCO3+SiO2
Overall reaction MgSiO3+CO2→MgCO3+SiO2
Note, in this embodiment no recycle of MgCl2 is required. The value of x, the number of waters of hydration is much lower than 6 because the MgCl2 from the rock melting reaction is hot enough to drive much of the water into the vapor phase. Therefore the path from the rock melting runs at steady state with “x” as modeled with a value of approximately 2.
Note, in this embodiment half of the MgCl2 is recycled. The value of x, the number of waters of hydration is somewhat lower than 6 because half of the MgCl2 is from the rock melting reaction which is hot enough to drive much of the water into the vapor phase and the remaining half is recycled from the absorption column. Therefore the number of hydrations for the total amount of MgCl2 at steady state will have a value of approximately 4, being the average between the MgCl2.6H2O and MgCl2.2H2O.
III) Diopside or Mixed process:
Note diopside is a mixed calcium and magnesium silicate and dolomite is a mixed calcium and magnesium carbonate.
Overall reaction: 1/2CaMg(SiO3)2+CO2→1/2CaMg(CO3)2+SiO2
1The temperature range of 320-550° C. includes models run at 320, 360, 400, 440 and 550° C. respectively.
2The CO2 percentage of flue gas 7.2%-18% includes models run at 7.2%, 10%, 14% and 18% respectively.
The CaSiO3—MgO and CaSiO3—Mg(OH)Cl decomposition processes are further divided into two stages, the first step consists of a dehydration reaction where MgCl2.6H2O is converted to MgCl2.2H2O+4H2O and the second step in which the MgCl2.2H2O is converted to Mg(OH)Cl+HCl+H2O if partial decomposition is desired or required and MgO+2HCl+H2O if total decomposition is desired or required.
The MgSiO3—MgO and MgSiO3—Mg(OH)Cl processes consists of a one chamber decomposition step in which the HCl from the decomposition chamber reacts with MgSiO3 in the rock-melting reactor and the ensuing heat of reaction leaves the MgCl2 in the dihydrate form MgCl2.2H2O as it leaves the rock-melting chamber in approach to the decomposition reactor where it is converted to either MgO or Mg(OH)Cl as described earlier. This process may be preferred if calcium silicates are unavailable. The HCl emitted from the decomposition reacts with MgSiO3 to form more MgCl2. The magnesium silicate process follows a different path from the calcium. The process starts from the “rock melting reaction HCl+silicate”, and then moves to the “decomposition reaction (MgCl2+heat),” and lastly the absorption column. In the calcium silicate process, all the magnesium compounds rotate between the decomposition reaction and the absorption reaction.
The intermediate process Diopside-MgO and Diopside-Mg(OH)Cl also involve a two stage decomposition consisting of the dehydration reaction MgCl2.6H2O+Δ→MgCl2.2H2O+4H2O followed by the decomposition reaction MgCl2.2H2O+Δ→MgO+2HCl+H2O (full decomposition) or MgCl2.2H2O+Δ→Mg(OH)Cl+HCl+H2O partial decomposition.
The ensuing HCl from the decomposition then reacts with the Diopside CaMg(SiO3)2 in a two step “rock melting reaction.” The first reaction creates CaCl2 through the reaction 2HCl+CaMg(SiO3)2→CaCl2(aq)+MgSiO3↓+SiO2↓+H2O. The solids from the previous reaction are then reacted with HCl a second time to produce MgCl2 through the reaction MgSiO3+2HCl→MgCl2+SiO2↓+H2O. The CaCl2 from the first rock melter is transported to the absorption column and the MgCl2 from the second rock melter is transported to the decomposition reactor to make Mg(OH)Cl or MgO.
All of these examples assume 50% CO2 absorption of a reference flue gas from a known coal fired plant of interest. This was done to enable a comparison between each example. The emission flow rate of flue gas from this plant is 136,903,680 tons per year and the CO2 content of this gas is 10% by weight. This amount of CO2 is the basis for examples 10 through 21 which is:
Amount of CO2 present in the flue gas per year:
136,903,680 tons per year*10%=13,690,368 tons per year
Amount of CO2 absorbed per year.
13,690,368 tons per year*50%=6,845,184 tons per year of CO2.
Since the amount of CO2 absorbed is a constant, the consumption of reactants and generation of products is also a constant depending on the reaction stoichiometry and molecular weight for each compound.
For all the examples of both the CaSiO3—MgO and the CaSiO3—Mg(OH)Cl process (examples 10-13) the overall reaction is:
CaSiO3+CO2→CaCO3+SiO2
For all the examples of both the MgSiO3—MgO and the MgSiO3—Mg(OH)Cl process (examples 14-17) the overall reaction is:
MgSiO3+CO2→MgCO3+SiO2
For all the examples of both the Diopside-MgO and the Diopside-Mg(OH)Cl process (examples 18-21) the overall reaction is:
1/2CaMg(SiO3)2+CO2→1/2CaMg(CO3)2+SiO2
The Aspen model enters the required inputs for the process and calculates the required flue gas to provide the heat needed for the decomposition reaction to produce the carbon dioxide absorbing compounds MgO, Mg(OH)2 or Mg(OH)Cl. This flue gas may be from a natural gas or a coal plant and in the case of coal was tested at a range of temperatures from 320° C. to 550° C. This flue gas should not be confused with the reference flue gas which was used a standard to provide a specific amount of CO2 removal for each example. A process with a higher temperature flue gas would typically require a lesser amount of flue gas to capture the same amount of carbon dioxide from the basis. Also a flue gas with a greater carbon dioxide concentration would typically result in greater amount of flue gas needed to capture the carbon dioxide because there is a greater amount of carbon dioxide that needs to be captured.
The consumption of reactants and generation of products can be determined from the basis of CO2 captured and the molecular weights of each input and each output for each example.
The CaSiO3 consumption is:
6,845,184 tons per year*(116.16/44.01)=18,066,577 tons per year.
The CaCO3 production is:
6,845,184 tons per year*(100.09/44.01)=15,559,282 tons per year.
The SiO2 production is:
6,845,184 tons per year*(60.08/44.01)=9,344,884 tons per year
The same type of calculations may be done for the remaining examples. This following table contains the inputs and outputs for examples 10 through 21. Basis: 6,845,184 tons CO2 absorbed per year.
Running the Aspen models generated the following results for the heat duty for each step of the decomposition reaction, dehydration and decomposition. The results for each example are summarized in the table below.
A value of over 100% means that excess heat is available to produce more Mg(OH)Cl or MgO.
The thermal decomposition of other salts has been measured in lab. A summary of some test results are shown in the table below.
Table 23 (see below) is a comparison of the four configurations corresponding to
In this case study involving flue gas from a coal-based power plant, Table 24 illustrates that the volume of mineral outputs (limestone and sand) are 83% of the volume of input minerals (coal and inosilicate). The results summarized in Table 24 are based on a 600 MWe coal plant; total 4.66 E6 tonne CO2, includes CO2 for process-required heat.
In this case study summarized in Table 25 (below) involving flue gas from a natural gas-based power plant, the “rail-back volume” of minerals is 92% of the “rail-in volume” of minerals. The results summarized in Table 25 are (based on a 600 MWe CC natural gas plant; total 2.41 E6 tonne CO2, which includes CO2 for process-required heat.
Mg(OH)2 can be used in the following reaction to produce limestone from CO2 gas.
CaCl2(aq)+CO2+Mg(OH)2=>MgCl2(aq)+CaCO3↓+H2O
In order to optimize production of Mg(OH)2, upon conversion of MgCl2 to Mg(OH)Cl, the amount of water in the reaction chamber will be adjusted to favor Mg(OH)2 precipitation. Specifically, when Mg(OH)Cl and MgCl2 is provided in a large enough volume of water, the magnesium hydroxide precipitates, as it is virtually insoluble, whereas the magnesium chloride forms an aqueous solution. Thus the two compounds may be efficiently separated. Note the water (H2O) in the reaction below, does not become part of the products, it merely solvates the Mg2+ and Cl− so they become an ionic solution.
Mg(OH)Cl(H2O)=>1/2Mg(OH)2↓+1/2MgCl2(aq)
If the amount of water is reduced until the a ratio of about 6 to 1 relative to magnesium, it would be possible to form MgCl2.6H2O instead of MgCl2(aq). The equation would be as follows:
Mg(OH)Cl+3H2O=>1/2Mg(OH)2↓+1/2MgCl2.6H2O
Thus, by maintaining a MgCl2 to water ratio of greater than or equal to 6 to 1, production of aqueous MgCl2 and solid Mg(OH)2 is favored. Thus, an example set of CO2 capture reactions can be represented as:
i) MgCl2.H2O=>Mg(OH)CL+H2O+HCl
ii) HCl+CaSiO3=>CaCl2+H2O+SiO2
iii) Mg(OH)Cl+MgCl2+H2O=>Mg(OH)2+MgCl2+H2O
iv) H2O+Mg(OH)2+CO2+CaCl2=>MgCl2+CaCO3+H2O
With an overall reaction of: CaSiO3CO2=>CaCO3+SiO2.
This system is shown in the Aspen diagram of
All of the methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of particular embodiments, it will be apparent to those of skill in the art that variations may be applied to the methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.
The following references, to the extent that they provide exemplary procedural or other details supplementary to those set forth herein, are specifically incorporated herein by reference.
This application claims priority to U.S. Provisional Patent Application No. 61/585,597, filed Jan. 11, 2012, the entire contents of which are expressly incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61585597 | Jan 2012 | US |
