The present invention relates to articles for extracting at least one component from a fluid stream. The present invention also relates to a method of forming such articles and methods and systems including same.
It is often desirable to extract or capture a component or components from a fluid stream, particularly where the fluid stream is a gas emission from a process which contains compounds which are harmful to humans and/or the environment. Examples of such compounds are carbon dioxide (CO2) and methane (CH4), which have been attributed as the two major sources of the greenhouse effect. CO2 is emitted into the atmosphere from various sources, including fossil fuel (coal, oil and gas etc.) fired power stations, and heating furnaces. Fugitive CH4 emissions occur from coal, oil and gas production as well as transport, mining, agriculture, waste disposal, livestock, and land use (forestry). Whilst much development is currently being made on reducing CO2 and CH4 emissions, an alternative approach to mitigating the effects of these gases is to capture them for sequestering or, in the case of CH4, utilisation as a fuel source.
To this end, several different technologies have evolved to separate and capture CO2 from flue gas and CH4 from mine ventilation air, such as amine scrubbing, cryogenic separation, membrane separation and absorption. However, these technologies have encountered problems in specifically targeting and capturing CO2 and CH4. Furthermore, these technologies do not excel in treating gas emissions produced in high dust environments such as exhibited in flue gas from coal-fired power stations or ventilation air from coal mines. Furthermore, in order for a stream of captured CH4 to be useful as a fuel source for conventional gas engines, the concentration of CH4 should be approximately 30% or higher. This requirement has proven difficult for the aforementioned technologies to satisfy, particularly as the untreated gas emissions typically have a CH4 concentration of less than 1%. Removal of CO2 or N2 from natural and mine drainage gases is also required during purification to indirectly increase the CH4 concentration of the gas.
Another approach to capture components from a fluid stream has been through adsorption of the components on activated carbon structures. Bulk, typically cylindrical, or flat plate carbon monoliths have been formed from carbonisable binders and subsequently dried, cured, carbonised and activated. The formed activated carbon monolith is quite porous, and can therefore be used for adsorbing a component or components from a fluid by passing the fluid over the monolith. For example, U.S. Pat. No. 6,258,300 and U.S. Pat. No. 6,030,698 (both to Burchell et al.) disclose an activated carbon fibre composite made up of rigidly bonded carbon fibres to form an open, permeable, rigid monolith with a controlled pore structure. U.S. Pat. No. 6,090,477 (Burchell et al.) teaches a series of hybrid carbon fibre monoliths made from a blend of isotropic and mesophase pitch derived carbon fibres which possess enhanced thermal conductivity over conventional activated carbon fibre composites and granular activated carbons. U.S. Pat. No. 5,972,077 (Judkins et al.) teaches an apparatus and method that involves the adsorption of CO2 and H2S onto a carbon fibre composite molecular sieve. The adsorbed gas is then desorbed via an electric swing technique. U.S. Pat. No. 5,925,168 (Judkins et al.) discloses a method for separating gases, in particular N2 and O2, the method involving application of a electrical and magnetic field to a carbon fibre composite adsorption material to preferentially attract certain gases. Desorption of the gas is affected via either an electric or pressure swing process.
Alternative structures have also been proposed including a monolith substrate coated or impregnated with carbon materials that are subsequently dried, cured, carbonised and activated. The substrates are typically ceramics, metals or other materials which provide sufficient strength for the activated carbon. However, the substrates in these monoliths are relatively expensive, in particular ceramic monolith substrates. Furthermore, the metal substrates are particularly susceptible to a loss of performance and durability through poisoning by sulphur, trace lead and other compounds which may be present in the fluid flowing through the monolith. Additionally, the carbon coating may erode from the substrate, creating uneven surfaces inside the monolith and concomitant blockage of pores within the structure.
The present invention aims to provide alternative articles for capturing one or more components from a fluid stream, in particular CO2 from flue gases and CH4 from mine ventilation air. Furthermore, the invention aims to provide methods for forming the articles and systems employing the articles.
According to a first aspect of the present invention there is provided an article for extracting a component from a fluid stream, the article including a body portion having a plurality of bores extending therethrough, the bores facilitating the flow of the fluid stream through the body portion in use, wherein the body portion is formed from a mixture of a binder and at least one component selected from the group consisting of carbon fibres, carbon nanotubes and mixtures thereof.
As used herein the term “bore” includes within its scope individual discrete channels extending through the body portion and includes connected channels that form a network extending within and through the body portion.
The term includes channels formed subsequent to formation of the body portion, for example by drilling or the like, and also includes channels formed during formation of the body portion, for example during extrusion or moulding of the body portion.
The structure of the body portion may take any suitable form. Preferably, the body portion is a honeycomb monolith structure.
The component that is to be extracted from the fluid stream may be captured anywhere on the body portion by adsorption. More preferably, the component to be extracted is captured onto the inner surfaces of the bores of the body portion of the article by adsorption.
The bores may be arranged in any way that is suitable for flow therethrough of the fluid stream. This will be appreciated from the above definition for the bores.
The width, which as used herein includes reference to diameter, of each bore is preferably from about 1 mm to about 40 mm. More preferably, the width of the bores is from about 1 mm to about 10 mm and even more preferably from about 1 mm to about 8 mm or from about 1 mm to about 6 mm. Most preferably, the width of the bores is from about 3 mm to about 6 mm. It will be appreciated by one skilled in the art that the width of some or all of the bores may or may not be constant across the length of the bores. Preferably, the width of the bores is constant across the length of the bores. Furthermore, the width of bores within the body portion may or may not be uniform. In certain embodiments it may be desirable that all of the bores in the body portion be of identical or similar width. In other embodiments, it may be desirable that some bores have a larger width than others. This may be somewhat dependent on the particular field of use, or volume of fluid to be extracted.
The bores may be of regular or irregular cross sectional shape. Preferably, the bores are regular in cross sectional shape and extend from one face of the body portion to an opposing face of the body portion. Preferably, the bores are substantially parallel to one another. The cross sectional shape of the bores is not intended to be limited in any way. For example, the bores may have a square, triangular, circular, hexagonal, octagonal or pentagonal cross sectional shape. Preferably, the bores have a circular or square cross sectional shape.
The body portion includes internal walls that define the bores and that separate them from one another. The width of the internal walls is preferably from about 1 mm to about 150 mm. More preferably, the width of the internal walls is from about 2 mm to about 30 mm, and even more preferably from about 2 mm to about 10 mm. It will be appreciated that the width of the internal walls may or may not be constant along their length.
Preferably, the width of the internal walls is constant along the length of the internal walls. Moreover, the width of individual internal walls may differ compared with other internal walls. Preferably, all of the internal walls are of identical or similar width. Of course, it will be appreciated that the width and cross sectional shape of the plurality of bores will affect the width and shape of the internal walls (and vice versa).
The shape and configuration of the body portion is not particularly limited. For example, the body portion may be cubic, cylindrical or prismatic in shape. In certain embodiment, it is envisaged that the body portion may be a prism of triangular, square, pentagonal, hexagonal, or octagonal shape. Generally, the body portion is cylindrical such that the body portion complements a chamber in which it is fitted.
The carbon fibres may, for example, be pitch based, activated pitch based, polyacrylonitrile (PAN) based, rayon (viscose) based or any combination thereof. In the case of pitch based carbon fibres, the pitch based carbon fibres may be isotropic and/or mesophase pitch based. Further, the pitch based carbon fibres may be derived from petroleum or coal tar.
In addition, the carbon fibres may be chopped or milled. It is also possible to incorporate a mixture of chopped and milled carbon fibres into the body portion.
The carbon fibres may be of any length, but are preferably from about 5 μm to about 5000 μm in length. More preferably, the carbon fibres are from about 100 μm to about 2000 μm in length. Similarly, the diameter of the carbon fibres is not particularly limited. Typically, the carbon fibres have a diameter of from about 5 μm to about 50 μm and more preferably from about 10 μm to about 30 μm.
The carbon nanotubes may be single walled or multiwalled. In addition, the carbon nanotubes may be chopped or milled. It is also possible to incorporate a mixture of chopped and milled carbon nanotubes into the body portion.
The carbon nanotubes may be from about 10 nm to about 100 nm in diameter. Alternatively, the diameter of the carbon nanotubes may be from about 10 nm to 40 nm, or 40 nm to 70 nm, or even from about 70 nm to 100 nm.
The carbon nanotubes are typically between about 100 μm to 2500 μm in length. Optionally, the length of the carbon nanotubes is between about 100 μm to 600 μm, or 600 μm to 1300 μm, or 1300 μm to 1800 μm, or even from about 1800 μm to 2500 μm.
Without wishing to be bound by any theory, it is believed that including carbon nanotubes in the mixture provides an article with a relatively more open structure and uniform pore size which is preferential to CO2 or CH4 than articles prepared from mixtures that only include carbon fibre.
The binder serves to bind the carbon fibres together enabling the formation of the body portion. The binder may be a resin selected from phenolic resin, polyethylene, epoxy resin, vinyl ester resin or any combination thereof. If the resin is a phenolic resin, this may be formed from phenol, methylphenol, ethylphenol, propylphenol, isopropylphenol or dimethylphenol. Phenolic resins are especially suitable for withstanding temperatures up to about 150° C. which may be required during drying and curing of the article, as described below. In a preferred embodiment the resin is a carbon based resin so that it is carbonisable during further treatment of the body portion. A mixture of different types of resins may also be used.
The ratio of carbon fibre to binder in the mixture used to form the body portion is not particularly limited. For example, the ratio may range from about 9:1 to 1:9. Preferably, the ratio of carbon fibre to binder is from about 4:1 to 1:4. More preferably, the ratio of carbon fibre to binder ranges from about 2:1 to 1:2.
Similarly, the ratio of carbon nanotube to binder in the mixture used to form the body portion is not particularly limited. For example, the ratio may range from about 9:1 to 1:9. Preferably, the ratio of carbon nanotube to binder is from about 4:1 to 1:4. More preferably, the ratio of carbon nanotube to binder ranges from about 2:1 to 1:2.
As stated above, both carbon fibres and carbon nanotubes may be included in the mixture used to form the body portion. In this case, the ratio of carbon fibres to carbon nanotubes is not particularly limited. For example, the ratio of carbon fibres to carbon nanotubes may be about 9.5:0.5. Alternatively, the ratio of carbon fibres to carbon nanotubes may be about 9:1 or 8.5:1.5 or 7:3 or 6:4 or 1:1.
It will be appreciated that carbon fibres, carbon nanotubes and a binder may be included in the mixture. The ratio of carbon fibres, carbon nanotubes and binder is again not particularly limited. For example, the ratio of carbon fibres to carbon nanotubes to binder may be about 0.99:0.01:9 or 9.9:0.1:1 or 0.99:0.01:2 or 0.99:0.01:0.5 or 0.9:0.1:2 or 0.9:0.1:0.5 or 0.5:0.5:2 or 1:1:1.
The article may be used to extract any particular component, or components, from the fluid stream. In one embodiment, the article extracts CO2 from the fluid stream. Alternatively, the article may extract CH4 from the fluid stream. More preferably, however, the article extracts CO2 and CH4 from the fluid stream.
The source of the fluid stream, and therefore the source of the CO2 and/or CH4, is not particularly limited. Preferably, the article is capable of extracting CO2 from flue gas derived from a coal fired power station. With respect to CH4, the article is advantageously capable of extracting CH4 from the ventilation air of a coal mine.
Accordingly, in a second aspect the invention provides a system for extracting a component from a fluid stream including:
Generally, as will be appreciated from the above discussion, the system is a system for extracting CO2 from flue gas derived from a coal fired power station or a system for extracting CH4 from ventilation air derived from a coal mine.
The system may include one article or more than one article. The number of articles will depend on what is desired or required for a particular application. In a system which includes two articles, during operation one article may receive the fluid stream for extraction of the desired component, for example by adsorption, while a second article is undergoing desorption of the extracted component and is readied for adsorption again. As, such, each of the two articles may cycle between an adsorption stage and desorption stage, each stage being offset relative to one other. Once desorption of the second article is completed and ready for adsorption, the fluid feed is re-directed from the first article to the second article when the first article is saturated at a predetermined level. Desorption of the first article may then commence. As noted above, and as will be readily appreciated by those of skill in the art, the system of the invention may include many more articles as necessary for a particular application. For example, where the system includes three articles, during operation of the system one article may receive the fluid stream for extraction of the desired component, while a second article desorbs the extracted component and the third article is either kept on stand-by to receive the fluid stream or is being readied for another adsorption cycle.
The swing apparatus may effect a thermal, electrical or pressure/vacuum swing across the at least one article. A thermal swing may be achieved by any suitable heat source, for example by passing a hot flue gas over the article or contacting the article with an electrical heating element. Optionally, a coolant source is included to lower the temperature of the article following thermal desorption. The article may be cooled prior to or simultaneously with re-introduction of the fluid stream. An electrical swing may be brought about under the influence of an electrical current supplied by wires connected to opposing ends of the article. A pressure/vacuum swing may be achieved by using a vacuum pump to create a pressure drop over the article in order to effect desorption. It will be appreciated that the system may include one or more thermal, electrical or pressure/vacuum swing apparatuses or a combination thereof.
If heat exchange is desired, whether during an adsorption or desorption stage, the system may include at least one conduit, more preferably a plurality of conduits, which extends through a bore of the article. A heat exchange fluid may be passed through the conduit(s) as desired such that it is brought into indirect contact with the article along the length of the article. This may advantageously facilitate heat exchange between the article and the heat exchange fluid. According to this embodiment of the invention, the conduit may optionally be larger in diameter or width and pass through an annulus formed in the article. In that case, the bores extending through the article are located in the annulus surrounding the conduit through which the heat exchange fluid may pass.
The at least one article is preferably positioned such that the bores extending through the article are parallel with the flow of the incoming fluid stream. Thus, resistance to the flow of the fluid stream through the article(s) is minimised. Other than with regard to the direction of flow of the fluid stream as mentioned above, the orientation of the article(s) is not particularly limited. For example, the article(s) may be horizontally or vertically mounted to facilitate either substantially horizontal or vertical introduction of the fluid stream into and through the bores of the article(s). Generally, the at least one article is orientated so that the fluid stream flows substantially vertically through the bores in the body portion of the at least one article.
The system, in use, may operate continuously or non-continuously. Preferably, the system operates continuously.
If desired, the system may further include a source of purge fluid for flushing the desorbed component from the article(s). The source of purge fluid may be used in conjunction with an electrical, thermal or pressure/vacuum swing apparatus to assist desorption. Preferably, the purge fluid is a gas such as argon, nitrogen, helium, air and the like. Ideally, the at least one component desorbed from the at least one article into the purge fluid is at a higher concentration than as present in the fluid stream.
According to a third aspect of the invention there is provided a method of extracting CO2 from flue gas derived from a coal fired power station, the method including:
According to a fourth aspect of the invention there is provided a method of extracting CH4 from ventilation air derived from a coal mine, the method including:
It will be appreciated that any feature described above in relation to the first aspect of the invention will be equally applicable to the second, third and fourth aspects of the invention.
The articles of the invention may be prepared by any suitable method. However, there is further provided a method of forming an article for extracting a component from a fluid stream, the method including:
The method may also include the step of chopping or milling the carbon fibres. If so, this preferably occurs prior to mixing the carbon fibres with the binder to form the slurry. It will also be appreciated that the carbon fibres may be both chopped and milled prior to mixing with the binder. Optionally, the method includes the step of blending different types of carbon fibres. Again, such blending preferably takes place prior to mixing the carbon fibres with the binder.
The method may also include the step of chopping or milling the carbon nanotubes. If so, this preferably occurs prior to mixing the carbon nanotubes with the binder to form the slurry. It will also be appreciated that the carbon nanotubes may be both chopped and milled prior to mixing with the binder. Optionally, the method includes the step of blending different types of carbon nanotubes. Such blending preferably takes place prior to mixing the carbon nanotubes with the binder.
It will of course be appreciated that the method may include the step of mixing chopped or milled carbon fibres with chopped or milled carbon nanotubes. Preferably, this occurs prior to mixing with the binder to form the slurry.
Generally, the slurry is formed by adding water to a mixture of the binder and the carbon fibres and/or carbon nanotubes. Further additives may be added to the carbon fibres and/or carbon nanotubes and binder to enhance the selectivity of the body portion towards adsorption of the component from the fluid stream.
Shaping of the slurry may include, for example, vacuum moulding or extrusion. During vacuum moulding or extrusion of the slurry, excess water present is removed.
The method also advantageously includes the step of drying the body portion once it has been shaped. Any suitable temperature may be used to dry the body portion. Preferably, however, during drying the body portion is heated from about 50 to about 100° C. and more preferably from about 50 to about 70° C. Drying may take up to 24 hours, but more preferably takes only 1 to 3 hours.
Advantageously, the method also includes the step of curing the body portion. Curing may involve either constant or gradual stepwise increases in temperature. For example, the body portion may be heated to from about 100 to about 150° C. In general, curing may take up to 24 hours. Preferably, curing may take between about 1 to 10 hours and even more preferably 1 to 5 hours.
The method may also include the step of carbonization of the body portion. During carbonization, the temperature of the body portion is slowly raised to from about 500° C. to 1000° C. and more preferably from about 650° C. to 850° C. Carbonization ordinarily occurs over a period of 1 to 10 hours, preferably in the presence of an inert gas such as nitrogen or argon.
Without wishing to be bound by any theory, it is thought that during carbonisation the resin matrix of the body portion is transformed into a glassy carbon. Furthermore, it is believed that the porosity of the body portion depends inter alia on the carbonisation conditions.
The method may also include the step of activation of the body portion. During activation, the body portion is heated from about 600° C. to 1500° C. in the presence of an activating agent. More preferably, the body portion is heated from about 650° C. to 950° C. Activation may result in the formation of narrower pores with a concomitant increase in the adsorption capacity of the article. During the step of activation, the body portion may lose up to 75% of its mass. The mass lost during the step of activation may be referred to as burn-off.
The activating step may be a thermal or chemical activation step. Examples of thermal activation steps include flowing thermal activating agents such as steam, carbon dioxide, nitrogen, moisture saturated helium or any combination thereof through the body portion. Alternatively, the step of chemical activation includes impregnating the body portion with chemical activating agents such as alkaline hydroxides (e.g. sodium or potassium hydroxide), phosphoric acid, metal chloride (e.g. zinc chloride), potassium sulphide or any combination thereof. Moreover, chemical activation may also include heating the body portion impregnated with the chemical activating agent at a first temperature for a first period of time followed by heating at a second temperature for a second period of time. Preferably, the second temperature is higher than the first temperature. For example, the first temperature may be approximately 120° C. and the first period of time approximately 10 hours. Optionally, heating at the first temperature occurs in the presence of an inert gas such as nitrogen or argon. This is advantageously followed by treatment at a second temperature of from about 500° C. to 800° C. for the second period of time which is approximately 30 minutes.
Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Referring firstly to
Advantageously, it has been found that articles 10 formed from a binder and carbon fibres and/or carbon nanotubes are substantially easier to handle relative to, for example, granular activated carbon or non-bound carbon fibres. Furthermore, because of the inclusion of the bores 12, the pressure drop across the article 10, in use, is relatively low compared with the prior art. Still further, the article 10 has a further advantage over various prior art substrates in that it contains a comparatively high surface area to volume ratio.
As noted above, the body portion includes internal walls 13 that define and separate the plurality of bores 12 from one another. The bores 12 extend from a first end face 14 of the body portion 11 to a second end face 15 of the body portion 11. The plurality of bores 12 are shown substantially parallel to one another, although they need not be. It is also noted that although in
The width, or in the case of circular bores diameter, of each of the plurality of bores 12 is from 1 mm to 40 mm. The width of the internal walls 13 which define the bores 12 is from 1 mm to 150 mm. However, it is noted that the width of the bores 12 (and hence of the internal walls 13) need not be constant across the length of the bores 12. Likewise, the bores need not be of uniform cross sectional shape within the matrix of bores 12.
In
The ratio of carbon fibres and/or carbon nanotubes to binder and the type of carbon fibres and/or carbon nanotubes employed, and in what ratios, may be decided depending on the desired properties of the article 10. For example, properties of interest may include strength, porosity, size, volume and size distribution of pores, size of bores and side walls, and adsorption capacities. The desired properties for a particular article may be somewhat dependent on the component or components which the article is to extract from the fluid stream and the conditions in which it is intended to operate. For example, selection of the above properties may be dependent on the operating temperature or pressure in use, levels of dust in the fluid stream, fluid stream flow rate, the concentration of the component(s) in the fluid stream, and the presence of various impurities in the fluid stream. Table 1 below shows some suitable carbon fibre-binder combinations which may be used in making the article for the capture of CO2 and/or CH4.
The article 10 for capturing at least one component from a fluid may be formed in a method which includes the steps of mixing the carbon fibres and/or carbon nanotubes with the binder to form a slurry, shaping the slurry of fibres and binder into the body portion 11 with the plurality of bores 12 which extend through the body portion 11. The mixture of carbon fibres and binder may be any of the combinations of different types of carbon fibre and binders as described above. The ratio of carbon fibre to binder is not limited to any specific range. Typically, the step of shaping the mixture occurs by vacuum moulding or extrusion.
In an embodiment, the method may also include the step of introducing additives to the mixture of carbon fibres and/or carbon nanotubes and binder to enhance the selectivity of the body portion 11 towards adsorption of the at least one component.
The method of forming the article also typically includes the steps of drying, curing, carbonisation and/or activation. The step of drying includes heating the body portion 11 to 50 to 100° C. (preferably 50 to 70° C.) in an oven for approximately 24 hours. The step of curing, which follows the step of drying, includes further heating of the body portion 11 to 100 to 150° C. for approximately 1 to 24 hours. More preferably, the curing step takes approximately 1 to 10 hours and even more preferably 1 to 5 hours. Curing occurs in a muffle furnace with a stepwise gradual increase in temperature.
Following the step of curing, the step of carbonisation includes slowly raising the temperature of the body portion to 500-1000° C. over a period of 1 to 10 hours. The step of carbonisation is carried out in the presence of an inert gas (for example nitrogen or argon).
The step of activation, which follows the step of carbonisation, includes heating the body portion at 600 to 1500° C. (preferably 600 to 1000° C.), in the presence of an activating agent. During the step of activation, the body portion 11 may lose 0-75% of its mass (“burn-off”). The step of activation may include a thermal or chemical activation step. Thermal activation may include flowing thermal activating agents such as steam, carbon dioxide, nitrogen, moisture saturated helium or any combination thereof through the body portion 11. Chemical activation may include impregnating the body portion 11 with chemical activating agents such as alkaline hydroxides (e.g. sodium or potassium hydroxide), phosphoric acid, metal chloride (e.g. zinc chloride), potassium sulphide or any combination thereof. During chemical activation, the impregnated body portion 11 is first heated to approximately 120° C. for approximately 10 hours before being heated to 500-800° C. up to 30 minutes.
The choice of activating agent, its concentration and flow rate may be chosen to achieve a particular desired property (or properties) of the article 10. Likewise, the temperature employed during activation and the “burn off” percentage may also dictate desired properties of the article 10. Such properties may include strength, surface area, porosity, size of pores and adsorption capacity.
The article 10 may be used to extract at least one component from a fluid stream by adsorption onto inner walls 13 of the bores 12 of the article 10. The captured component(s) can be subsequently desorbed from the article 10 by a pressure/vacuum, thermal or electrical swing to produce a concentrated stream of the captured component(s). The concentrated stream of captured component(s) may be subsequently utilised or stored (i.e. in the case of CH4), or may be sequestered (i.e. in the case of CO2).
Referring now to
Each of the adsorption chambers 23 contains an article 10 as described above for capturing the component(s) from the fluid. The articles 10 are arranged in the chambers 23 so that the fluid flows substantially vertically through the bores 12 in the body portion 11 of each of the articles 10. However one of ordinary skill in the art will appreciate that the orientation of the articles 10 is not particularly critical to the operation of the system. For example, the chambers 23 and articles 10 therein may be arranged so that the fluid flows substantially horizontally through the bores 12. In
The system 20 may also include particle separators 25 at the outlets of the adsorption chambers 23 to remove any dust or other particulate matter from fluid flowing out of the adsorption chambers 23, which is subsequently collected in dust hoppers 26. The particle separators 25 may be filters or inertial separators for example. Although each adsorption chamber 23 is shown having its own particle separator 25 and dust hopper 26. A single particle separator and a single dust hopper may be used to treat the fluid flowing from all the adsorption chambers 23. It is noted also that the system 20 may not require the particle separators 25 and dust hoppers 26 either because the fluid feed 21 does not contain any dust or other particulate matter or because any such matter has been removed from the fluid in the pre-treatment stage 22.
The system 20 also includes an outlet control valve 27 for each of the adsorption chambers 23 which directs spent fluid to waste 28 (to vent where the fluid is a gas) following capture of the component(s) in the adsorption chamber 23.
The system 20 also includes a swing apparatus 29 for providing a thermal, electrical or pressure swing across the articles 10 located in the adsorption chambers 23. A switch 30 controls the operation of the swing apparatus 29.
During operation of the system 20, the inlet control valve 24 directs the fluid feed 21 to one of the adsorption chambers 23 for capture of the component(s) from the fluid by the article 10. As the article 10 approaches a saturation point the adsorption rate decreases. At a predetermined level of adsorption, the inlet control valve 24 closes flow of the fluid feed 21 to that adsorption chamber and directs it to another. The switch 30 triggers operation of the swing apparatus 29, which subsequently provides a thermal swing (effects a higher or lower temperature), electrical swing (effects a reversal in polarity or a change from being neutral to polar or vice versa) or a pressure swing (effects a change in the pressure) across the article 10. This causes the captured component(s) to desorb from the article 10.
A source of purge fluid 31 is provided to flush the desorbed component(s) from the chamber 23. The purge fluid 31 may be a gas such as argon nitrogen, helium, air and mixtures thereof. The flow rate of purge fluid 31 is typically selected to ensure the concentration of the captured component(s) exiting the chamber 23 is not excessively diluted. The outlet control valve 27 subsequently directs the concentrated component(s) stream 32 to a further system (not shown) for sequestration, use and/or storage.
The system 20 also includes a gas analyser 33 for detecting the concentration of the component(s) in stream 28, thereby helping to ensure a specified concentration of the component(s) in stream 28 by, for example, sending one or more signals (not shown) to the control valve 24 for closing flow of the fluid feed 21 to one adsorption chamber and directing the fluid feed 21 to another adsorption chamber. The signals may also change the state of swing apparatus 29 and/or alter the purge fluid 31 flow rate and the time taken for desorption.
This system 20 is suitable for capturing CO2 from the flue gas of power stations or capturing CH4 from ventilation gas from coal mines. The system may also be useful in the purification of natural gas and mine drainage gas by removing CO2 and possible other gaseous components from these gases to increase the CH4 concentration of the gases. The treated gases having increased CH4 content may then find use as fuels.
Furthermore, in situations where the gas streams to be treated have relatively high particulate concentration, more particularly high dust content, substantially uninhibited flow of the gas stream through the article 10 may be achieved due to the bores 12 extending through the article which are aligned with the flow of the gas stream. This is because the dust particles, or other particulate matter, can flow through the bores 12 in the body portion 11 of the article 10 without causing significant blockages. In addition, this system 20 can be used to produce concentrated streams 32 of CH4 and/or CO2 from a fluid feed 21 in which these components could be highly diluted (e.g. less than 1% for the CH4 in mine ventilation air). Such concentrated streams 32 can be successfully sequestrated or utilised as mentioned above.
A back pressure regulator 520 may also be included between the separator 512 and valve 516 to prevent backflow of unadsorbed components into the chamber 506 and increase the pressure inside the chamber 506, if required. Another gas analyser 522 with a vent 524 may also be connected to the vent 518 in order to measure the contents of the unadsorbed components. As the article 10 approaches saturation, the adsorption rate decreases. At a certain predetermined low level of adsorption, the inlet control valve 510 closes flow of the fluid feed 502 to that adsorption chamber and directs it to another. At the same time the thermal swing device 532 is activated. The device 532 preferably includes a heat source such as a hot flue gas which passes through or over article 10 thereby causing an increase in temperature with concomitant desorption of the captured component(s). Optionally, a source of purge fluid 530 is provided to flush the desorbed component(s) from the chamber 506. Separator 512 and valve 516 subsequently direct the concentrated component(s) stream to a common chamber 526 where the component(s) can be stored or directed through line 528 to a further system (not shown) for sequestration and/or use.
If desired, after desorption the temperature of article 10 may be lowered under the influence of a coolant source provided by cooling medium 534 and cooling tower 536. Any suitable coolant may be utilised, for example water, nitrogen, helium, argon, air or condensed gases. The article 10 is then ready to receive a fresh fluid feed 502. Ideally, the process operates continuously so that one chamber is receiving the fluid feed 502 while the other chamber is undergoing desorption of captured components.
As discussed above, the preferred system of the invention illustrated in
An alternative embodiment 800 for heating and/or cooling the article is illustrated in
Although not illustrated, the article may also be of annular form, including a plurality of bores in the annular ring. In that embodiment, a central conduit may be provided that passes through the annulus and that is in contact with the inner surface of the annulus. In a similar vein to embodiment 800, the conduit may be used to pass heat exchange fluid into indirect contact with the article to effect heating or cooling of the article.
Articles for capturing at least one component from a fluid, specifically, CO2 and/or CH4 have been successfully prepared in the laboratory by vacuum moulding, drying, curing, carbonization and activation (thermal or chemical) in accordance with the flow sheet of
Tests have been carried out on the articles to identify their surface area, pore characteristics and CO2 and CH4 adsorption capacities, using a Tristar analyser (Micromeritics). All the gases used for testing are of research grade (more than 99.99% purity). Table 2 gives the characteristics of various articles.
It was observed that both carbonisation time and temperature had little effect on the characteristics of the article. In particular, burn-off, surface area, pore width, and CO2 and CH4 adsorption capacities showed only minor changes under different carbonisation conditions.
As evidenced in Table 4, varying the activation parameters had a significant effect on the characteristics of the article. An increase in activation time produced a linear increase in the N2 BET surface area, pore volume and pore width. The surface area (based on CO2 analysis) increased as the activation time increased. However, in relation to CO2 and CH4 adsorption capacity, it would be preferable to perform the activation step at a higher temperature (for example 950° C.) for a shorter duration (1 hour), rather than at lower temperature (such as 850° C.) for a longer duration (8 hours).
The effect of burn-off was studied to evaluate the characteristics of the article and its CO2 adsorption capacity.
Activation of the composites resulted in the formation and development of pores. However, activation also affected the weight loss (burn-off) in the material. An increase in the degree of burn-off was found to initially increase the pore volume, pore width and surface area (
Experiments to measure adsorption kinetics were performed. Simulated gas mixtures were passed through the article and their concentration upon exit of the material was recorded with respect to time. Characteristics of the three articles selected for the kinetic experiments are shown in Table 6 and the simulated gas mixtures are given in Table 7.
With respect to the coal tar pitch based article, it was found that a CH4 adsorption efficiency of 96 to 97% was achieved under the influence of VAM1 and VAM2 (
In the specification the term “comprising” shall be understood to have a broad meaning similar to the term “including” and will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. This definition also applies to variations on the term “comprising” such as “comprise” and “comprises”.
The reference to any prior art in this specification is not, and should not be taken as an acknowledgement or any form of suggestion that the referenced prior art forms part of the common general knowledge in Australia.
It will of course be realised that the above has been given only by way of illustrative example of the invention and that all such modifications and variations thereto as would be apparent to those of skill in the art are deemed to fall within the broad scope and ambit of the invention as herein set forth.
Number | Date | Country | Kind |
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2007904651 | Aug 2007 | AU | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/AU2008/001269 | 8/28/2008 | WO | 00 | 12/27/2010 |