Systems and methods for the purification of carbon dioxide are generally described, which are particularly suited, in some embodiments, for processing the exhaust of oxy-combustion systems for carbon dioxide sequestration.
Growing concerns over the impact of greenhouse gas emissions on the global climate have spurred widespread research studies focused on limiting carbon dioxide emissions. Many researchers have focused their efforts on the sequestration of carbon dioxide, which involves storing the carbon dioxide (e.g., in geological formations) after it has been produced in, for example, a fossil-fuel power production process. For sequestration applications, the concentration of contaminants such as NOx, SOx, O2, and H2O must be limited to avoid adverse consequences, such as, for example, corroding or otherwise damaging transport pipelines and/or storage areas. For these reasons, among others, there exists a need for effective systems and methods for purifying streams of carbon dioxide.
Inventive systems and methods for the purification of carbon dioxide are described. Also described are systems and methods of reducing the parasitic energy load using novel heat integration techniques, while producing carbon dioxide that is sufficiently pure to be sequestered. The subject matter of the present invention involves, in some cases, interrelated products, alternative solutions to a particular problem, and/or a plurality of different uses of one or more systems and/or articles.
In one set of embodiments, a method of purifying a carbon dioxide containing fluid inlet stream by removing NOx and SOx is described. The method can comprise, in some embodiments, feeding the fluid inlet stream comprising carbon dioxide, NOx, and SOx to a single reactive absorption column; and within the single reactive absorption column, removing at least a portion of the NOx and SOx to create a fluid outlet stream enriched in carbon dioxide and lean in SOx relative to the fluid inlet stream, and comprising less than about 50 ppm NOx.
In some cases, the method can comprise feeding the fluid inlet stream comprising carbon dioxide, NOx, and SOx to a single reactive absorption column operated at a pressure of between about 20 bar and about 50 bar; and within the single reactive absorption column, removing at least a portion of the NOx and SOx to create a fluid outlet stream enriched in carbon dioxide, lean in SOx, and lean in NOx relative to the fluid inlet stream.
The method can comprise, in some instances, feeding the fluid inlet stream comprising carbon dioxide, NOx, and SOx to a single reactive absorption column; and within the single reactive absorption column, removing at least a portion of the NOx and SOx to create a fluid outlet stream enriched in carbon dioxide, lean in SOx, and lean in NOx relative to the fluid inlet stream, wherein the removal step comprises feeding an acid condensate stream to the absorption column, the acid condensate stream originating from a condenser unit upstream of the reactive absorption column relative to the fluid inlet stream.
In some embodiments, the method can comprise feeding the fluid inlet stream comprising carbon dioxide, NOx at a concentration of less than about 4000 ppm, and SOx to a single reactive absorption column; and within the single reactive absorption column, removing at least a portion of the NOx and SOx to create a fluid outlet stream enriched in carbon dioxide and lean in SOx relative to the fluid inlet stream, and comprising a molar concentration of NOx that is at least about 20 times smaller than the molar concentration of NOx in the fluid inlet stream.
In one set of embodiments, a method of purifying carbon dioxide is provided. The method can comprise feeding a fluid inlet stream comprising carbon dioxide and a contaminant to a distillation column to create a distillate stream comprising a first portion of the contaminant and a first portion of the carbon dioxide, wherein the distillate stream is enriched in the contaminant relative to the fluid inlet stream; forming from the distillate stream a vapor stream comprising a second portion of the contaminant and a second portion of the carbon dioxide; forming from the vapor stream a recycle stream comprising a third portion of the carbon dioxide; and transporting at least a portion of the recycle stream to the distillation column.
In some cases, the method can comprise feeding a fluid inlet stream comprising carbon dioxide and a contaminant to a distillation column to create a distillate stream comprising a first portion of the contaminant and a first portion of the carbon dioxide, wherein the distillate stream is enriched in the contaminant relative to the fluid inlet stream; forming from the distillate stream a vapor stream comprising a second portion of the contaminant and a second portion of the carbon dioxide; forming from the vapor stream a recycle stream comprising a third portion of the carbon dioxide; and performing a Joule-Thompson expansion of at least a portion of the recycle stream.
In one set of embodiments, a system for purifying carbon dioxide is described. The system can comprise a distillation column constructed and arranged to distill a fluid inlet stream comprising carbon dioxide and a contaminant to create a distillate stream comprising a first portion of the contaminant and a first portion of the carbon dioxide, wherein the distillate stream is enriched in the contaminant relative to the fluid inlet stream; a first separator fluidically connected to the distillation column constructed and arranged to form from the distillate stream a vapor stream comprising a second portion of the contaminant and a second portion of the carbon dioxide; a second separator fluidically connected to the first separator constructed and arranged to form from the vapor stream a recycle stream comprising a third portion of the carbon dioxide; and a fluidic pathway constructed and arranged to transport at least a portion of the recycle stream to the distillation column.
The system can comprise, in one set of embodiments, a distillation column constructed and arranged to distill a fluid inlet stream comprising carbon dioxide and a contaminant to create a distillate stream comprising a first portion of the contaminant and a first portion of the carbon dioxide, wherein the distillate stream is enriched in the contaminant relative to the fluid inlet stream; a first separator fluidically connected to the distillation column constructed and arranged to form from the distillate stream a vapor stream comprising a second portion of the contaminant and a second portion of the carbon dioxide; a second separator fluidically connected to the first separator constructed and arranged to form from the vapor stream a recycle stream comprising a third portion of the carbon dioxide; and an expander fluidically connected to the second separator constructed and arranged to perform Joule-Thompson expansion of at least a portion of the recycle stream.
In one set of embodiments, a method of combusting a fuel to produce a combustion exhaust stream and purifying carbon dioxide in the combustion exhaust stream is provided. In some cases, the method can comprise feeding an air stream to an air separation unit to produce a fluid oxidizing stream comprising between about 92 mol % and about 95 mol % oxygen; combusting a fuel in the presence of the fluid oxidizing stream within a combustor to produce a combustion exhaust stream comprising carbon dioxide; and purifying the combustion exhaust stream to produce a carbon dioxide containing stream comprising at least about 90 mol % carbon dioxide; wherein heat provided by the combustor is used to produce power from a power production unit, and wherein the overall system efficiency is at least about 98% of the overall system efficiency of a power system without the at least one carbon dioxide purification unit, but under otherwise essentially identical conditions.
In some instances, the method can comprise feeding an air stream to an air separation unit to produce a fluid oxidizing stream comprising between about 92 mol % and about 95 mol % oxygen; combusting a fuel in the presence of the fluid oxidizing stream within a combustor to produce a combustion exhaust stream comprising carbon dioxide; purifying the combustion exhaust stream to produce a carbon dioxide containing stream comprising at least about 90 mol % carbon dioxide; wherein heat provided by the combustor is used to produce power from a power production unit, and wherein the Rankine system efficiency is at least about 35%.
Other advantages and novel features of the present invention will become apparent from the following detailed description of various non-limiting embodiments of the invention when considered in conjunction with the accompanying figures. In cases where the present specification and a document incorporated by reference include conflicting and/or inconsistent disclosure, the present specification shall control.
Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. In the figures:
Inventive systems and methods for the purification of carbon dioxide are described. Also described are systems and methods of reducing the parasitic energy load using novel heat integration techniques, while producing carbon dioxide that is sufficiently pure to be sequestered. In at least a portion of the inventive carbon dioxide purification methods, a carbon dioxide-containing fluid stream is purified by removing NOx and SOx, using a single reactive absorption column.
In some cases, a fluid inlet stream containing carbon dioxide and at least one non-condensable gas is purified by feeding the fluid inlet stream to a gas separation unit operation. In one set of embodiments, the gas separation unit may comprise a distillation column that forms a distillate stream. In some cases, a vapor stream (and, optionally, a reflux stream) can be formed from the distillate stream, a portion of which can be further used to form a recycle stream comprising a portion of the carbon dioxide originally present in the fluid inlet stream. In some cases, at least a portion of the recycle stream can be transported to the distillation column, which can enhance the degree to which carbon dioxide is purified.
Heat integration may be used in certain embodiments to increase the efficiency with which carbon dioxide can be purified and/or the efficiency of other functions or unit operations of an inventive system. For example, at least a portion of the recycle stream mentioned above can be used in certain embodiments to perform a Joule-Thompson expansion, which can be used, for example, to provide cooling duty to another component of the system (e.g., a condenser used to recover CO2 from a vapor stream, other heat exchanger, etc.). In addition, in some cases, the distillation column can be used to form a relatively cool bottoms stream (e.g., a carbon dioxide-rich bottoms stream), which can be used to pre-cool the mixture of carbon dioxide and non-condensable gases fed to the distillation column and/or can be made to undergo Joule-Thompson expansion to provide cooling duty to other system component(s).
Certain embodiments of the inventive systems and methods described herein can provide certain advantage(s) over traditional carbon dioxide purification techniques in certain applications. For example, in some embodiments, the amounts of NOx and SOx within a carbon dioxide containing stream can be reduced to very low levels using a single reactive absorption column, thereby requiring significantly lower costs relative to systems that use two or more reactive absorption columns and relative to conventional and widely-deployed low-pressure systems, including Flue Gas Desulfurization (FGD) for SOx removal and Selective Catalytic Reduction (SCR) for NOx removal. In addition, the inventive systems and methods described herein may in certain embodiments be used to generate power at a relatively high efficiency while producing carbon dioxide sufficiently pure to be sequestered.
The carbon dioxide purification systems and methods described herein can be used in a variety of applications. For example, in some embodiments, the carbon dioxide containing stream that is to be purified can originate from an oxy-combustion plant (e.g., an oxy-coal combustion plant). The purified carbon dioxide stream produced by certain embodiments of the inventive systems and methods can, in some cases, be sequestered or used as part of an enhanced oil recovery (EOR) process or an enhanced gas recovery processes. The purified CO2 stream can be used in other applications where carbon dioxide is a useful component such as, for example, soda production. It should be understood, however, that the inventive carbon dioxide purification systems and processes are not limited to the exemplary applications described herein, and may be used with any suitable system in which the removal of NOx, SOx, and/or non-condensable gases from a carbon dioxide containing stream is desired.
In some embodiments, the feed fluid stream to a carbon dioxide purification system/process of the invention may consist essentially of carbon dioxide, NOx, and SOx, while in other cases, the feed fluid stream may contain additional components (e.g., oxygen, nitrogen, carbon monoxide, argon, etc.). The inventive purification techniques described herein may be particularly useful for purifying carbon dioxide streams containing relatively low amounts of NOx (e.g., less than about 1.5 mol %, less than about 0.1 mol %, less than about 2000 parts per million (ppm), less than about 1000 ppm, between about 100 ppm and about 1.5 wt %, or between about 100 ppm and about 2000 ppm), which can require relatively expensive and/or complex systems to purify to sequestration standards using traditional methods. In some cases, the systems and methods can be used to purify carbon dioxide containing stream containing relatively low amounts of SOx (e.g., less than about 3 mol %, less than about 1.5 mol %, less than about 0.1 mol %, less than about 2000 parts per million (ppm), less than about 1000 ppm, between about 100 ppm and about 1.5 wt %, or between about 100 ppm and about 2000 ppm). It should be understood, however, that the invention is not so limited, and the carbon dioxide containing inlet stream can contain, in other embodiments, higher concentrations of NOx and/or SOx.
The carbon dioxide stream can originate from any suitable source. For example, in some cases, at least a portion of the carbon dioxide stream might originate from a combustion source, such as, for example, an oxy-combustion process (e.g., an oxy-coal combustion process) which can be used, for example, as part of a power production system. In some embodiments, the feed fluid stream can be pressurized to a pressure substantially greater than standard ambient pressure (e.g., at least about 5 bar, at least about 10 bar, at least about 20 bar, between about 5 bar and about 50 bar, between about 20 bar and about 50 bar, or between about 25 bar and about 35 bar) prior to introduction into the carbon dioxide purification system.
In the illustrated embodiment, water containing stream 114 is also fed to the reactive absorption column. The water within this stream can participate in one or more chemical reactions that results in the removal of NOx and/or SOx within the reactive absorption column, described in more detail below. The water containing stream can originate from any suitable source. In some cases, the water containing stream can originate from a stand alone water tank, pond, or other such source. In other embodiments, the water containing stream can originate from another process within a system comprising the reactive absorption column. For example, in some embodiments, carbon dioxide containing stream 112A can be fed to optional acid condenser 120 at a location upstream (relative to inlet stream 112) from the reactive absorption column. The acid condenser can be used to remove water and, in some cases, one or more components from stream 112A (e.g., one or more acids) to produce carbon dioxide containing stream 112 and water containing stream 122. In some embodiments, water containing stream 114 can comprise at least a portion of water containing stream 122 originating from the acid condenser. Such a pretreatment may be particularly advantageous when stream 112A comprises flue gas from a combustion/oxy-combustion process.
At least a portion of the NOx and/or SOx may be removed within the single reactive absorption column 110, in some instances, to create a fluid outlet stream 116 depleted in at least one of NOx or SOx. Reactive absorption columns in general are known to those of ordinary skill in the art, and, given a set of design specifications (including, for example, a desired throughput, residence time, operating pressure, and/or number of equilibrium stages within the absorber) and the guidance provided herein, those skilled in the art would be capable of constructing the absorption columns described herein as useful for practicing certain embodiments of the invention. In certain embodiments, a column containing a plurality of theoretical stages is employed for reactive absorption column 110. In certain embodiments, the column includes at least 9 theoretical stages or between about 7 stages and about 13 theoretical stages. One of ordinary skill in the art would be capable of determining the number of theoretical stages in a column based upon the actual number of stages by multiplying the actual number of stages by the stage efficiency. In certain embodiments, the reactive absorption column includes packing to enable multi-stage separations. In certain embodiments, the column will include at least 3 theoretical stages. In alternative embodiments, the column instead of being a packed column, may be a multi tray column. In yet other embodiments, the column may comprise both packing and trays.
Removal of SOx can be accomplished, in some instances, via a combination of the following gas phase reactions:
NO+1/2O2→NO2 [1]
2NO2←→N2O4 [2]
NO2+SO2←→NO+SO3 [3]
and/or the following liquid phase reaction:
SO3+H2O←→H2SO4 [4]
In some cases, removal of NOx can be accomplished via a combination of Reactions 1 and 2, the following interfacial reaction:
N2O4(g)←→N2O4(l) [5]
and the following liquid phase reactions:
N2O4+H2O←→HNO3+HNO2 [6]
3HNO2←→HNO3+2NO+H2O [7]
It may be advantageous, in some cases, for the reactive absorption column to be pressurized to a pressure substantially greater than standard ambient pressure (e.g., at least about 3 bar, at least about 10 bar, at least about 20 bar, between about 3 bar and about 50 bar, between about 20 bar and about 50 bar, or between about 25 bar and about 35 bar). One of ordinary skill in the art would recognize that such reactive absorption columns might require the use of one or more design features to accommodate such high operating pressures such as, for example, relatively thick walls, high pressure conduit connections, one or more emergency pressure relief valves, and the like.
In the set of embodiments illustrated in
In some instances, the step of removing at least a portion of the NOx and SOx from fluid inlet stream 112 can result in the formation of acidic stream 124. The acidic stream can contain, for example, any of the acidic products outlined in Equations 1-7 above such as, for example, sulfuric acid (H2SO4) and/or nitric acid (HNO3).
In addition to or instead of removing NOx and/or SOx from a carbon dioxide containing stream, one or more other contaminants of a carbon dioxide containing stream can be removed in certain embodiments. In some cases, a carbon dioxide containing stream can contain one or more non-condensable gases. The phrase “non-condensable gas,” as used herein, refers to any gas that does not condense at temperatures above 123 K at atmospheric pressure (i.e., 1 atm) nor under the conditions expected to prevail in the gas separation system employed systems. A carbon dioxide containing stream can include, for example, non-condensable gases such as oxygen (O2), nitrogen (N2), argon (Ar), and/or carbon monoxide (CO).
In some embodiments, a carbon dioxide containing stream containing at least one contaminant gas (e.g., one or more non-condensable gases) can be purified by feeding it to a distillation column.
It can be advantageous, in some circumstances, to provide a relatively low-temperature inlet stream 212 to the distillation column. For example, in some embodiments in which it is desired to remove a contaminant with a relatively low boiling point relative to carbon dioxide (e.g., a non-condensable gas), relatively low temperatures can be used to condense the carbon dioxide prior to feeding it to column 210. Accordingly, in some cases, optional heat exchanger 214 can be used to cool carbon dioxide containing stream 212A to produce carbon dioxide liquid containing stream 212. Stream 212A may originate from any of the sources mentioned above with respect to stream 212.
The distillation column can be constructed and arranged to distill the fluid inlet stream comprising carbon dioxide and the contaminant gas(es) to create a distillate stream 216. One of ordinary skill in the art would be capable of constructing a distillation column, given a set of design parameters (e.g., number of stages, feed stage location, desired throughput, operational temperatures and pressures, etc.). In certain embodiments, the distillation column includes packing to enable multi-stage separations. In certain embodiments, the distillation column will include at least 3 theoretical stages. In alternative embodiments, the distillation column instead of being a packed column, may be a multi tray column. In yet other embodiments, the distillation column may comprise both packing and trays. The distillation column can include, in some cases, between 3 and 20 theoretical stages, or between 7 and 13 theoretical stages. One of ordinary skill in the art would be capable of determining the number of theoretical stages in a column based upon the actual number of stages by multiplying the actual number of stages by the stage efficiency.
In some cases, at least a part of the distillation column might be constructed and arranged to operate at relatively low temperatures (e.g., below about 0° C., below about −20° C.) or at relatively high pressures (e.g., above about 5 bar, above about 10 bar, above about 20 bar). One of ordinary skill in the art would be capable of providing suitable heat exchangers to achieve these low temperatures. In addition, one of ordinary skill in the art would be capable to designing the column (e.g., by incorporating relatively thick walls, by incorporating high-pressure fluidic connections, etc.) to withstand these relatively high pressures.
While the formation of a distillate stream using a distillation column has been primarily described, it should be understood that, in other embodiments, other unit operations can be used to form a purified carbon dioxide containing stream from the inlet stream. For example, in some cases, a membrane separation unit or a pressure swing absorption unit could be used in place of or in addition to the distillation column.
In the set of embodiments illustrated in
A vapor stream comprising a second portion of the contaminant and a second portion of the carbon dioxide can be formed from the distillate stream, in some embodiments. The vapor stream can be relatively rich in contaminant, relative to the distillate stream, in some embodiments. Formation of the vapor stream can be achieved, for example, using a separator fluidically connected to the distillation column. Two components are said to be “fluidically connected” when they are constructed and arranged such that a fluid can flow between them. In some cases, two components can be “directly fluidically connected,” which is used to refer to a situation in which the two components are constructed and arranged such that a fluid can flow between without being transferred through a unit operation constructed and arranged to substantially change the temperature and/or pressure of the fluid. One of ordinary skill in the art would be able to differentiate between unit operations that are constructed and arranged to substantially change the temperature and/or pressure of a fluid (e.g., a compressor, a condenser, a heat exchanger, etc.) and components are not so constructed and arranged (e.g., a transport pipe through which incidental heat transfer and/or pressure accumulation may occur).
The set of embodiments illustrated in
Any suitable separator can be used to form vapor stream 222. In some embodiments, the separator can comprise a condenser. One of ordinary skill in the art, given a set of design parameters (e.g., temperature, pressure, heat duty, etc.), could select or construct a condenser suitable for use in forming vapor stream 222. In some cases, separator 220 can be the first condenser of a two-stage condenser.
A recycle stream 232 comprising a third portion of the contaminant and a third portion of the carbon dioxide may be formed from the vapor stream from the second separator, in some embodiments. Formation of the recycle stream 232 can be achieved, for example, using a second separator fluidically connected (e.g., directly fluidically connected) to the first separator. In the set of embodiments illustrated in
Any suitable separator can be used to form recycle stream 232. For example, the second separator can comprise a condenser in some cases (e.g., the second stage of a two-stage condenser). In some embodiments, the second separator can comprise a separate heat exchanger and flash drum. For example, the vapor stream 222 can be partially condensed in a heat exchanger (not shown in
Recycle stream 232 can be relatively cool and/or relatively highly pressurized. In some instances, a Joule-Thompson expansion can be performed on at least a portion of the recycle stream, which can generate a cold stream that can provide cooling duty elsewhere in the system. In the set of embodiments illustrated in
The recycle stream 232 can comprise the fluid product of the second separator and, in some embodiments, can be relatively rich in carbon dioxide relative to the vapor stream from the first separator. In some cases, at least a portion 237 of the recycle stream can be transported to the distillation column (e.g., an intermediate stage of the distillation column. For example, in the embodiments illustrated in
Referring back to the distillation column, in some cases, the fluid inlet stream can be separated within the distillation column to form the distillate stream and a bottoms stream (e.g., bottoms stream 240 in
In certain embodiments, the bottoms stream can be relatively cool and/or relatively highly pressurized. In some such cases, the bottoms stream can be used to provide cooling duty to another component of the system. In some embodiments, a Joule-Thompson expansion can be performed on at least a portion of the bottoms stream to further cool it for use elsewhere in the system. In the set of embodiments illustrated in
The bottoms stream can be, in some instances, relatively rich in carbon dioxide relative to the fluid inlet stream. For example, in some embodiments, the bottoms stream can contain at least about 90 mol %, at least about 95 mol %, at least about 98 mol %, at least about 99 mol %, at least about 99.9 mol %, at least about 99.99 mol %, at least about 99.99 mol %, between about 90 mol % and about 99.999 mol %, between about 90 mol % and about 99.999 mol %, between about 95 mol % and about 99.999 mol %, between about 95 mol % and about 99.99 mol %, or between about 98 mol % and about 99.999 mol % carbon dioxide. In some instances, the molar concentration of the non-carbon dioxide components of the bottoms stream (e.g., the molar concentration of the non-condensable gases in the bottoms stream) can be at least about 10 times, at least about 100 times, at least about 1000 times, at least about 10,000 times, between about 10 times and about 105 times, between about 100 times and about 105, or between about 1000 times and about 105 times smaller than the molar concentration of the non-carbon dioxide components in the fluid inlet stream.
After optionally providing a cooling load to another component of the system, bottoms stream 240 can be compressed to a pressure suitable for sequestration, in some cases, and pumped to the sequestration location via pump 250. While a single pump is illustrated in
Some embodiments of the invention are directed to the use of one or more purification systems (e.g., system 100 of
Combustor 312 can be used as part of an energy generation process (e.g., in an oxy-combustion energy generation process, such as an oxy-coal combustion process). For examples, combustor 312 can be part of the energy generation process described in Hong, et al., “Analysis of Oxy-Fuel Combustion Power Cycle Utilizing a Pressurized Coal Combustor,” Energy, 2009, which is incorporated herein by reference. The combustor can be used to combust a fuel to produce heat, which can be used to produce power with a power production unit (e.g., by heating a stream of fluid that powers a turbine). In addition to oxidizing stream 316, fuel stream 320 may also be fed to combustor 312. Any suitable fuel can be used in system 300 including, but not limited to, coal, light or heavy oils, petcoke and other refinery products, biomass, waste streams, natural gas, and the like. The fuel can be combusted in the presence of the fluid oxidizing stream within the combustor to produce heat and a combustion exhaust stream 322 comprising carbon dioxide and NOx, SOx, and/or another contaminant (e.g. the non-condensable contaminant gases separated with system 200).
Combustion exhaust stream 322 can be purified to produce carbon dioxide stream 324. Carbon dioxide stream 324 can include a relatively high amount of carbon dioxide (e.g., at least about 95 mol %, at least about 98 mol %, at least about 99 mol %, at least about 99.9 mol %, at least about 99.99 mol %, at least about 99.99 mol %, between about 95 mol % and about 99.999 mol %, between about 95 mol % and about 99.99 mol %, or between about 98 mol % and about 99.999 mol % carbon dioxide).
In the set of embodiments illustrated in
System 300 can be capable of achieving relatively high efficiencies, in some embodiments, despite the fact that relatively low amounts of oxygen might be present (e.g., between about 92 mol % and about 95 mol %) in oxidizing stream 316 and despite the fact that relatively pure carbon dioxide stream can be produced (e.g., at least about 90 mol %, at least about 95 mol %, at least about 98 mol %, at least about 99 mol %, at least about 99.9 mol %, at least about 99.99 mol %, between about 90 mol % and about 99.999 mol %, between about 90 mol % and about 99.99 mol %, between about 95 mol % and about 99.999 mol %, between about 95 mol % and about 99.99 mol %, between about 98 mol % and about 99.999 mol %, or between about 98 mol % and about 99.99 mol %).
In some embodiments, a purified carbon dioxide stream (e.g., at any of the purities mentioned in the preceding paragraph) can be produced and pressurized to a pressure of at least about 110 bar using a single-column NOx/SOx purification unit and/or a contaminant purification unit (e.g., a non-condensable gas purification unit), while maintaining an overall system efficiency that is at least about 98% of the overall system efficiency of a power system without the carbon dioxide purification units, but under otherwise essentially identical conditions. “Essentially identical conditions,” in this context, means conditions that are substantially the same or identical other than the use of the carbon dioxide purification system(s) (e.g., a single-column NOx/SOx purification unit and/or a contaminant (e.g., non-condensable gas) purification unit). For example, otherwise identical conditions may mean a power production system that is identical, but where it is not constructed to purify and compress carbon dioxide to at least about 110 bar (e.g., for sequestration). One of ordinary skill in the art would be capable of calculating the overall system efficiency as:
wherein Pout is the power produced by the power production unit, Pin,ASU is the power input to the air separation unit, Pin,PPU is the power input to the power production unit, Pin,pur is the power input to the CO2 purification system(s) including pressurizing the purified stream to at least about 110 bar, {dot over (m)}fuel is the mass flow rate of the fuel, and SEfuel is the specific energy (i.e., energy per unit mass based on the lower heating value) of the fuel.
In some cases, system 300 can be capable of achieving Rankine system efficiencies of at least about 35%, at least about 36%, or between about 35% and about 36.2% at any of the conditions mentioned herein. The Rankine system efficiency is generally calculated as:
wherein Pout,Rankine is the power produced when a supercritical Rankine cycle is employed as the power production unit, Pin,ASU is the power input to the air separation unit, Pin,Rankine is the power input to the supercritical Rankine cycle power production unit, Pin,pur is the power input to the CO2 purification system(s) including pressurizing the purified stream to at least about 110 bar, {dot over (m)}fuel is the mass flow rate of the fuel, and SEfuel is the specific energy (i.e., energy per unit mass based on the lower heating value) of the fuel. In some embodiments, any of the above efficiency numbers can be achieved using coal as a fuel.
U.S. Provisional Patent Application No. 61/330,860, filed May 3, 2010, and entitled “Carbon Dioxide Purification” is incorporated herein by reference in its entirety for all purposes.
The following examples are intended to illustrate certain embodiments of the present invention, but do not exemplify the full scope of the invention.
This example describes a simulation of an exemplary single reactive absorption column NOx/SOx purification system. Oxy-combustion takes place in an environment consisting mainly of oxygen and recycled combustion gases. The product of combustion consists primarily of carbon dioxide and water, with contaminants like NOx and SOx (addressed in this example) and non-condensable gases like argon, oxygen and nitrogen (addressed in Examples 2-6). Most of the water in the oxy-combustion exhaust stream can be removed using an acid condenser, resulting in a CO2-rich stream. Table 2 includes a typical flue gas composition for a pressurized oxy-coal combustion system leaving an acid condenser.
The single-column NOx and SOx removal system described in this example (and illustrated schematically in
Aspen Plus version 7.1 (Aspen Technology, Inc.) was used to perform the simulations described in Examples 1-6. In addition, process inputs for Examples 1-6 were based upon the overall base power cycle described in detail in Hong, J., et al., “Analysis of Oxy-Fuel Combustion Power Cycle Utilizing a Pressurized Coal Combustor,” Energy, 2009. The base power cycle was a pressurized oxy-coal plant designed with a coal flow rate of 30 kg/s (HHV: 874.6 MWth, LHV: 839.1 MWth) with a flue gas flow rate of 87.4 kg/s, operating at a pressure of 10 bar.
The single-column NOx and SOx removal unit was simulated using the ElecNRTL Property Method, which is suitable for the dilute acid concentrations expected in the column. Table 1 includes the design parameters used for the reactive absorption column. Table 2 shows the CO2 flue stream data. The design parameters were chosen to achieve NOx and SOx exit stream concentrations of less than about 10 ppm.
The use of acid condensate from an upstream acid condenser was also investigated as a means of reducing water usage by the oxy-fuel power plant. It was believed that such a design would be feasible, given that the acid concentration of this stream would be very low in practice and, therefore, would be suitable for use directly in the NOx and SOx removal column. Table 3 includes the results of a simulation obtained using the same column and inlet specifications outlined in Tables 1 and 2, but replacing fresh water with acid water. The composition of the acid water used to obtain the results in Table 3 is shown in Table 4.
A sensitivity analysis was performed to determine the impact of vapor holdup, water flow rate and pressure on column performance. From
Adopting the single column design can lead to savings in process energy requirements as well as equipment cost. In addition, the pressure sensitivity plot (
For purposes of comparison, a simulation was also performed using a dual-reactive absorption column system, as illustrated schematically in
From Table 5, it can be seen at the two-column process removed similar amounts of SOx, and removed less NOx, relative to the single-column process. The power requirements of the single-column and dual-column processes were also compared. It was determined that the dual-column arrangement required 7.22 MW of power to perform the separation, while the single-column arrangements only required 7.07 MW.
Finally, the effect of increasing the NOx and SOx concentrations in the flue gas on the performance of the single column system was investigated. Table 6 includes the inlet and outlet stream compositions for two simulations of the single-column process (a first simulation using Inlet 1 to produce Exit 1, and a second simulation using Inlet 2 to produce Exit 2) where relatively large concentrations of NOx and SOx, relative to the concentrations in the previous examples.
This example describes a simulation of a first system, illustrated in
For the non-condensable gas removal units described in Examples 2-6, the RK-Aspen property method was selected. Since oxygen was considered to be the most important non-condensable contaminant (because of the stringent concentration restrictions usually applied to pipeline, EOR, and sequestration specifications), PTXY simulations were carried out for CO2—O2 binary systems, and the results were shown to be comparable to those described in the literature (See, e.g., Zenner, et al., Chem. Eng. Progr. Symp. Ser. 59, No. 44, 36 (1963); Muirbrook, et al., A.I.Ch.E. J., 11, 1092 (1965); and Fredenslund, et al., J. Chem. Eng. Data, 1970, 15 (1), pp 17-22). High predictive accuracy was achieved using data regression.
Table 8 includes detailed stream compositions for each of the streams contained in
Dried CO2 stream 1 was first cooled to −6° C. by heat exchange with evaporating fluid in the reboiler (M1) before further cooling to about −23° C. by the cold box (M2) and supplemental refrigeration (M7). Cooling in the cold box was provided by the evaporation of depressurized high purity (99.99%) CO2 streams 7 and 12 at 14 bar (−31° C.) and 21.3 bar (−18° C.), respectively. Bottoms stream 6 was used to provide the required evaporative cooling in the condenser (M4). More CO2 was recovered from the vapor distillate stream 17 by partially condensing it in the cold box (M5) to yield a two-phase stream 18. Two-phase stream 18 was then separated in the flash drum (M6). The low temperature vapor stream 24 (−42° C.) and the throttled stream 20 (−50° C., 12.2 bar) provided the requisite cooling in M5. The 96% pure CO2 stream 21 was first compressed then cooled and fed back into the distillation column. The cooling duty was provided by the low temperature streams 25, 9 and 13a. Stream 10 was then compressed up to 21.3 bar to match the pressure of stream 13b, and the two streams were combined, compressed to 75 bar (safely in the supercritical state) and then pumped up to a pipeline pressure of 110 bar, making it suitable for sequestration.
This example describes a simulation of an alternate arrangement (
This examples describes a simulation of a second system used to purify a carbon dioxide stream to remove non-condensable gases.
This process also utilizes a distillation column for the purification of the CO2 stream. One advantage of this system is that the purified CO2 is extracted as bottoms liquid and pumped directly to sequestration, eliminating the energy penalty of gas phase compression of the purified stream. Previous systems designed to extract liquid CO2 utilize large external refrigeration cycles for cooling the inlet gas and also for providing cooling duty to the condenser. This configuration was developed to replace the use of external refrigeration for providing cooling duty to the condenser and to lower the overall energy requirement by innovative use of internal heat integration. The cooling load for the condenser is now provided in part by the reboiler and in part by a joule-Thompson expansion of the distillate reflux distillate stream. Ordinarily, the condenser temperature is lower than that of the reboiler, making it impossible to integrate the two units. To overcome this limitation, the distillate vapor is compressed to a pressure high enough to ensure that condensation will take place at a higher temperature than the evaporation in the reboiler. The balance cooling is then provided by the Joule-Thompson effect. The two phase reflux stream is separated and fed into appropriate stages in the distillation column.
In the simulation outlined in
This example describes a simulation of a first alternate arrangement (
This example describes a simulation of a second alternate arrangement (
This example describes simulations performed upon integrating the single-column NOx/SOx purifier outlined in Example 1 and various non-condensable gas purification schemes with the base power cycle described in Hong, J., et al., “Analysis of Oxy-Fuel Combustion Power Cycle Utilizing a Pressurized Coal Combustor,” Energy, 2009. Table 10 includes the results of simulating various integration options, using the base simulation described in Example 2 above. The “No Vent expansion” case describes a simulation in which the vent stream 26 was not expanded to recover power. The “Vent Gas Expansion” case describes a simulation where vent stream 26 was expanded to recover power. The “50% Vent Gas Recycle” case describes a simulation where the vent stream 26 (see
While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present invention.
The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”
The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to “A and/or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.
As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.
As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.
In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.
This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/330,860, filed May 3, 2010, and entitled “Carbon Dioxide Purification,” which is incorporated herein by reference in its entirety for all purposes.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US11/34948 | 5/3/2011 | WO | 00 | 1/22/2013 |
Number | Date | Country | |
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61330860 | May 2010 | US |