Patent Application
20250198697
Carbon dioxide emissions, particularly from the combustion of fossil fuels and other industrial processes have been identified as potential contributors to environmental issues ranging from local pollution to global climate change. Thus, over the years, various efforts to mitigate and re-capture these emissions have been identified and attempted. For larger industrial processes, particularly where a flue is utilized to facilitate emissions, these efforts may include absorption with amines, adsorption, the use of membranes, calcium looping, biological-focused efforts and even cryogenic efforts.
Cryogenic carbon dioxide capture efforts have proven promising. However, given that efforts are directed at a stream of flue gas, such as through a flue, this means that a flue channel with physical inner walls is exposed to the stream throughout the process. So, for example, cryogenically cooling the flue gas means that the carbon dioxide within the stream will begin to condense as a solid at pressures and temperatures below the triple point at about 5.17 bara and −56.56° C. This effectively facilitates a transition of the carbon dioxide from a gas to a solid state as dry ice. In theory, and in practice, this renders separation and collection of the carbon dioxide from the stream of flue gas as a practical undertaking.
Unfortunately, the described process involves a form of carbon dioxide condensation wherein the dry ice tends to accumulate at the inner walls of the flue. Further, even where other equipment is utilized, such as directing the stream of flue gas through heat exchangers or other equipment still renders a gas stream where condensing carbon dioxide has a tendency to accumulate at sidewalls of the channel utilized to direct the stream. This leads to clogging of the flue or other equipment which then requires system shutdown, maintenance and considerable expense along with loss of production time. Furthermore, utilizing more complex equipment or techniques that are not standard industry practice, may also present a variety of cost and training obstacles. Therefore, while cryogenic carbon capture techniques appear promising, operators often avoid the hassle of implementing such techniques in spite of the promising potential.
Embodiments of a cryogenic-based carbon dioxide capture system embodiments are detailed herein. For one embodiment an exhaust line for channeling a gas stream to a work extraction mechanism is taught. The work extraction mechanism may be utilized to cool the gas stream and condense carbon dioxide from the gas stream into a solid form in absence of surface accretion within the system. To this end, the mechanism may include a housing for receiving the gas stream with a moving implement therein. A heating device is coupled to one of the housing and the implement to target one of an interior surface within the housing and the implement to keep temperature thereat above a de-sublimation temperature of the carbon dioxide.
Implementations of various structure and techniques will hereafter be described with reference to the accompanying drawings. It should be understood, however, that these drawings are illustrative and not meant to limit the scope of claimed embodiments.
Embodiments are described with reference to a particular cryogenic-based carbon capture system. Specifically, the embodiments depict a system where work extraction is utilized to condense carbon dioxide from a gas stream. In this manner, obtaining carbon dioxide in solid form may be achieved in a manner that avoids surface accretion. However, other configurations of the system may be utilized. For example, there may be options in utilizing multiple compressors, the extracted carbon dioxide in solid form may be liquified and re-used through the system for continued operation and a host of other system layout possibilities. Regardless, so long as the system achieves carbon-capture with a work extraction mechanism, as opposed to being a surface temperature based reduction, at the time of condensation, appreciable benefit may be realized in the substantial absence of surface accretion.
Referring now to
Ultimately, it is the work extraction mechanism 185, such as a turbo-expander, that presents a volumetric effect to the received gas stream to cool and condense without reliance on a cooling surface to achieve the condensation. As a result, condensate or accretion of carbon dioxide is not promoted at system surfaces. Thus, once the stream begins to present as a partially solid carbon dioxide stream 197, clogging or blocking of the flow with buildup is not promoted. Indeed, as illustrated at 195, upon routing through a mechanical separator 190, solid carbon dioxide may be drawn from the system for practical management and removal from the system 100. This leaves a clean emission 180 available for venting or other uses. As used herein, the term “clean” emission is meant only to infer a substantially carbon-free form of emission as is the nature of the system 100.
Continuing with reference to
For the embodiment of
For the depicted embodiment, this circulation targets reaching a clearance 186 between the turbine 188 and the inner surfaces of the housing 188. Therefore, while the colder portion of the gas stream 182 is delivered to the work extraction mechanism 185 for processing into solid carbon dioxide as described herein, this warmer portion of the gas stream is utilized to target surfaces where accretion might be likely to occur. Of course, there are other types of hydraulic network layout options available as discussed further below which may target heating at the moving implement, interior housing surfaces or other components within the work extraction mechanism. So long as a targeted heating is applied, appreciable benefit may be realized.
Continuing with reference to
Once reaching this initial cooling temperature, the stream may be directed to a mechanical separator 145 where newly formed liquid water 150 may be removed. Additional water 150 may be removed by flowing the stream through a process dryer 155. With water 150 substantially removed, the stream may be directed to a second cooling assembly in the form of a recuperator 170 as noted above. The recuperator 170 may be a heat exchanger where additional cooling may take place down to a working temperature that remains above a de-sublimation temperature for the carbon dioxide in the stream. The use of two-stage cooling allows for the removal of water at a practical temperature short of ice formation followed by additional cooling to facilitate later carbon dioxide solidification.
By this point, just prior to reaching the work extraction mechanism 185 and even with two stages of cooling, the stream remains at a temperature that is still above a condensation temperature for the carbon dioxide, generally between about −80° C. and −120° C., depending on the carbon dioxide concentration in the stream. The cold pressurized stream, still above this condensation temperature for carbon dioxide, may now be directed to the work extraction mechanism 185 described above (see 182). It is of note that when the stream reaches the work extraction mechanism 185, a substantial amount of cooling has already occurred and the stream is within about 10° C.-50° C. of the condensation temperature for the carbon dioxide, perhaps entering at about −110° C. This means that the degree to which the work extraction mechanism 185 is relied upon to achieve the solidification of the carbon dioxide is within a manageable range that does not rely on surface-based temperature reduction to achieve the solidification. As a result, the work extraction which occurs in the mechanism 185 may reasonably attain the necessary condensation temperature of less than about −120° C. without encouraging accretion of solid carbon dioxide at surfaces of the mechanism 185 or anywhere else within the system 100 for that matter. The use of targeted heating as described above may further this avoidance of such surface accretion.
The work extraction mechanism 185 may then be utilized to convert the stream to a partially solid carbon dioxide stream 197. At this point, the stream 197 may be directed to a mechanical separator 190 for separation of the solid carbon dioxide 195 from the stream to achieve the sought carbon capture. The remainder of the stream may be considered a clean emission 180 that is vented or, as illustrated, re-utilized back to the recuperator 170 where the cooled gas may further facilitate the process. Of course, other types of routing for the clean emission 180 may also be incorporated into the layout.
For the embodiment shown, the work extraction mechanism 185 may constitute a dynamic working device such as a condensing turbine. However, a positive displacement device such as a piston or other volumetric affecting device may also be utilized to extract work through a moving boundary as opposed to inducing a dramatic temperature variation in order to achieve the sought degree of de-sublimation for solidifying the carbon dioxide. Indeed, the likelihood is that the boundary surfaces of the moving portions of the work extraction mechanism 185 will actually be warmer than the cooling of the stream. Therefore, accretion of de-sublimating carbon dioxide may actually be discouraged thereby keeping the system 100 substantially free of clogging for sake of continued operation. As noted above, the power available from the work extraction mechanism 185 may also naturally be a candidate for supplementing power to the shaft 125 for further driving the initial compressor 120 or for other supplemental purposes.
Referring now to
The interior of the housing may include various airfoils or blades 288, along with the rest of the turbine 188, along with shrouds above the blades 288, flow-path casings, stationary nozzles and other components. Therefore, avoiding accretion may involve a host of surfaces within the housing that otherwise might be prone to such an occurrence. For the present embodiments, the sequence of temperature applications, followed by use of a work extraction mechanism 185 to complete the carbon dioxide solid transformation avoids this risk, particularly where the mechanism 185 itself employs targeted heating as described herein.
Referring now to
Referring now to
Referring now to
Instead of returning the warmer gas stream from premature locations of the recuperator 170, this warmer gas stream is circulated through the turbine 188. Allowing this warmer portion of the gas stream to enter the main flow path may expose more interior components to encounter the effects of this warming fluid. This may be particularly beneficial for the rotating or moving parts of the work extraction mechanism 185. That is, the particular layout of the hydraulic network 484 for this warmer portion of the gas stream may be tailored to the configuration of the work extraction mechanism 185 itself and operator preferences. Regardless, once managed by the mechanism 185, this stream will still exit as a partially carbon dioxide solid stream at 197 for the carbon dioxide present within the stream.
Referring now to
Such a dedicated hydraulic layout may be supported by a circulating device such as a pump and the fluid may be propane or another suitable fluid that remains in liquid form within the temperature range of interest. That is, as described above, the gas stream for processing from the recuperator 470 may reach the work extraction mechanism 185 at a working temperature of between about −80° C. and −120° C. Thus, fluids which may remain in reliably liquid form at such temperatures may be suitable candidates for use in this dedicated circulating network 485. Again, the particular layout of the hydraulic network 485 for this dedicated warming fluid may be tailored to the configuration of the work extraction mechanism 185 itself and operator preferences.
Referring now to
Referring now to
As indicated at 560, the work extraction mechanism may now be utilized to extract work for solidifying carbon dioxide from the stream. Thus, the solidified carbon dioxide may be diverted from the stream (see 570). Further, this occurs with the additional assurance from the targeted heat that surface accretion will not take place at surface locations within the housing of the work extraction mechanism (see 580).
Embodiments described hereinabove include a system and techniques for achieving carbon extraction from an industrial gas through a cryogenic process that avoids accretion of carbon dioxide at system surfaces. Thus, dry ice accumulation at the inner walls of a flue or other channeling is avoided. Additionally, the equipment utilized may be readily available and scalable, industry standard components that do not require a complete re-configuration of system layouts that would be unfamiliar to those in the field. Use of a heated turbine as the primary component for the work extraction mechanism may even present a compact assembly that opens up additional space in the facility footprint. Once more, the addition of amines or other unique chemicals, consumables or process materials is not required as with other carbon extraction methods is not required. Ultimately, a system of familiar industry equipment that is uniquely arranged and includes a work extraction mechanism for the eventual carbon dioxide solidification allows for effective carbon removal from industrial gas without surface accretion and clogging that could lead to the expenses of considerable downtime and/or the need for regular equipment replacement.
The preceding description has been presented with reference to presently preferred embodiments. Persons skilled in the art and technology to which these embodiments pertain will appreciate that alterations and changes in the described structures and methods of operation may be practiced without meaningfully departing from the principle, and scope of these embodiments. Furthermore, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.
