By a News Reporter-Staff News Editor at Life Science Weekly — From Washington, D.C., NewsRx journalists report that a patent application by the inventors GUIDOLIN, Sandra (Belfort, FR); KOSS, Ulrich (Baden, CH); KNIESBURGES, Peter (Weisbaden, DE), filed on February 28, 2014, was made available online on July 3, 2014 (see also Patents).
No assignee for this patent application has been made.
News editors obtained the following quote from the background information supplied by the inventors: “In the combustion of a fuel, such as coal, oil, peat, waste, natural gas, etc., in a combustion plant, such as a power plant, a hot process gas is generated, such process gas containing, among other components, carbon dioxide, CO.sub.2. The negative environmental effects of releasing carbon dioxide to the atmosphere have been widely recognized, and have resulted in the development of processes adapted for capturing carbon dioxide from the hot process gas generated in the combustion of the above mentioned fuels. One such system and process has previously been disclosed and is directed to a Chilled Ammonia based system and method for capture of CO.sub.2 from a post-combustion flue gas stream using an ammoniated solution and/or slurry for capturing CO.sub.2 from a flue gas stream. WO 2009/055419 discloses a process and system using three absorbers to improve efficiency of the CO.sub.2 capture process. The system disclosed in WO 2009/055419 is, however, complicated from a technical point of view, and has a high operating cost.”
As a supplement to the background information on this patent application, NewsRx correspondents also obtained the inventors’ summary information for this patent application: “The above drawbacks and deficiencies of the prior art are overcome or alleviated by means of a method of capturing CO.sub.2 from a flue gas stream in a CO.sub.2-absorber, the method comprising: contacting, in a first absorption stage of the CO.sub.2-absorber, the flue gas stream with a mixture of CO.sub.2-lean ammoniated solution and recirculated CO.sub.2-enriched ammoniated solution to form a partly cleaned flue gas stream, contacting, in a second absorption stage of the CO.sub.2-absorber, the partly cleaned flue gas stream with the recirculated CO.sub.2-enriched ammoniated solution to form a cleaned flue gas stream, forming a collected CO.sub.2-enriched ammoniated solution by collecting the mixture of CO.sub.2-lean ammoniated solution and recirculated CO.sub.2-enriched ammoniated solution after having passed through the first absorption stage, passing a first portion of the collected CO.sub.2-enriched ammoniated solution for regeneration for removing CO.sub.2 from the first portion of the collected CO.sub.2-enriched ammoniated solution to form the CO.sub.2-lean ammoniated solution, and utilizing a second portion of the collected CO.sub.2-enriched ammoniated solution to form the recirculated CO.sub.2-enriched ammoniated solution.
“An advantage of this method is that carbon dioxide can be efficiently captured, without an undue slip of ammonia, with lower operating cost and capital costs compared to the prior art.
“According to one embodiment the method further comprises forwarding the recirculated CO.sub.2-enriched ammoniated solution first through the second absorption stage, and then through the first absorption stage. An advantage of this embodiment is that the recirculated CO.sub.2-enriched ammoniated solution acts as a barrier to gaseous ammonia and serves to collect not only carbon dioxide, but also ammonia from the flue gas, before the flue gas is forwarded from the second stage to a water wash vessel or an ammonia polishing stage, as the case may be.
“According to one embodiment the method further comprises forwarding the CO.sub.2-lean ammoniated solution through the first absorption stage without forwarding the CO.sub.2-lean ammoniated solution through the second absorption stage. An advantage of this embodiment is an improved mass transfer of CO.sub.2 from the gas phase to the liquid phase by achieving a concentration profile with regard to CO.sub.2 in the ammoniated solution which varies in an optimum manner along the CO.sub.2-absorber.
“According to one embodiment the recirculated CO.sub.2-enriched ammoniated solution and the CO.sub.2-lean ammoniated solution are kept at a temperature, while passing through the first and second absorption stages, which is above a temperature at which ammonium bicarbonate particles may start to precipitate from the respective ammoniated solution. An advantage of this embodiment is that the absorber operates entirely in solution mode, with no, or almost no, formation of solid carbonate particles. This reduces risks of clogging in the absorber and makes absorber operation more robust. It is also possible to reduce the liquid to gas ratio, L/G, in the absorber since operating with solid formation in accordance with the prior art requires high liquid to gas ratios to reduce risks of solids accumulating in unwanted locations inside the absorber.
“According to one embodiment the partly cleaned flue gas stream is passed vertically upwards from the first absorption stage to the second absorption stage, and wherein the recirculated CO.sub.2-enriched ammoniated solution is passed vertically downwards from the second absorption stage to the first absorption stage. An advantage of this embodiment is that gas distribution of the partly cleaned flue gas stream entering vertically upwards into the second absorption stage becomes very even and efficient, and so does the liquid distribution of the recirculated CO.sub.2-enriched ammoniated solution entering vertically downwards into the first absorption stage.
“According to one embodiment the method further comprises contacting, in a third absorption stage, being an ammonia polishing stage, of the CO.sub.2-absorber, the cleaned flue gas stream coming from the second absorption stage with a polishing portion of the recirculated CO.sub.2-enriched ammoniated solution to form a further cleaned flue gas stream, the polishing portion of the recirculated CO.sub.2-enriched ammoniated solution being cooled, prior to being supplied to the third stage, to a polishing temperature which is lower than an absorbing temperature of the absorbing portion of the recirculated CO.sub.2-enriched ammoniated solution supplied to the second stage. An advantage of this embodiment is that a very low equilibrium pressure of ammonia, beneficial for low slip of ammonia, is achieved in the third absorption stage. Still further, only a small amount of the recirculated CO.sub.2-enriched ammoniated solution needs to be cooled to the low temperature for ammonia capture in the third absorption stage, which reduces the need for installed cooling power, and in particular the need for installed refrigeration unit capacity.
“According to one embodiment the method further comprises mixing the polishing portion of the recirculated CO.sub.2-enriched ammoniated solution, after having passed through the third absorption stage, with the absorbing portion of the recirculated CO.sub.2-enriched ammoniated solution to form the recirculated CO.sub.2-enriched ammoniated solution passing through the second absorption stage. An advantage of this embodiment is that the polishing portion of the recirculated CO.sub.2-enriched ammoniated solution is utilized in an efficient manner for absorbing ammonia in both the third and second absorption stages in a counter-current mode in relation to the flue gas flow.
“According to one embodiment the R-value, being the molar concentration of NH.sub.3 divided by the molar concentration of CO.sub.2, of the recirculated CO.sub.2-enriched ammoniated solution supplied to the second absorption stage is within the range of 1.75 to 2.00. An advantage of this embodiment is that efficient capture of carbon dioxide is achieved, still at a low slip of ammonia, and with little, or no, formation of solid ammonium bicarbonate. More preferably, the R-value of the recirculated CO.sub.2-enriched ammoniated solution supplied to the second absorption stage may be within the range of 1.81 to 1.96.
“According to one embodiment, the temperature of the recirculated CO.sub.2-enriched ammoniated solution supplied to the second absorption stage is controlled to be within the range of 8-30.degree. C., more preferably 20-25.degree. C. An advantage of this temperature range is that efficient capture of carbon dioxide, low slip of ammonia, and little, or no, formation of solid ammonium bicarbonate is achieved.
“According to one embodiment, the R-value of the ammoniated solution is within the range of 1.70 to 2.80 throughout the entire first absorption stage. An advantage of this embodiment is that very efficient capture of carbon dioxide is achieved, still with no, or only little, formation of solid ammonium bicarbonate.
“According to one embodiment, the R-value of the recirculated CO.sub.2-enriched ammoniated solution entering to the second absorption stage is lower than the R-value of the mixture of recirculated CO.sub.2-enriched ammoniated solution and the CO.sub.2-lean ammoniated solution entering the first absorption stage. An advantage of this embodiment is that efficient capture of carbon dioxide is achieved in the first absorption stage, and a very low slip of ammonia is achieved from the second absorption stage.
“According to one embodiment, the temperature of the mixture of recirculated CO.sub.2-enriched ammoniated solution and CO.sub.2-lean ammoniated solution entering the first absorption stage is higher than the temperature of the recirculated CO.sub.2-enriched ammoniated solution entering the second absorption stage. An advantage of this embodiment is that kinetics beneficial for efficient absorption of CO.sub.2 are improved in the mass transfer device of the first stage, which significantly reduces the need for height of the mass transfer device packing of the first absorption stage.
“According to one embodiment, the liquid to gas ratio, L/G, on a mass basis is 5 to 16, more preferably 7 to 12, and most preferably 8 to 10 kg solution/kg flue gas in the first absorption stage. The L/G is 3 to 10, and more preferably 4 to 8, kg solution/kg flue gas in the second absorption stage. Such liquid to gas ratios have been found to result in efficient capture of carbon dioxide, with low energy consumption. Additionally, the relatively low L/G increases the temperature inside the absorber, in particular in the first absorption stage, since the exothermic absorption of CO.sub.2 has to heat a smaller amount of solution. An increased temperature in the absorber is beneficial for the kinetics of the capture of CO.sub.2. Furthermore, the relatively low L/G reduces back-mixing, i.e., occasional entrainment upwards of solution, which further increases the CO.sub.2 capture due to a more stable counter-current flow between solution and gas.
“According to one embodiment the first portion of the collected CO.sub.2-enriched ammoniated solution comprises 30 to 70% by weight of the collected CO.sub.2-enriched ammoniated solution, and wherein the second portion of the collected CO.sub.2-enriched ammoniated solution comprises 70 to 30% by weight of the collected CO.sub.2-enriched ammoniated solution. An advantage of this embodiment is that efficient balance between recirculation and regeneration of the collected CO.sub.2-enriched ammoniated solution is achieved, resulting in efficient operation of the first and second absorption stages, and low total liquid to gas ratio.
“According to one embodiment 4-30% of the total flow of the CO.sub.2-lean ammoniated solution forwarded to the CO.sub.2-absorber is forwarded to the second absorption stage for contacting the partly cleaned flue gas stream. An advantage of this embodiment is that an enhanced removal of CO.sub.2 in the second absorption stage may be achieved.
“The above mentioned drawbacks and deficiencies of the prior art are also overcome or alleviated by means of a system for capturing CO.sub.2 from a flue gas stream which comprises: a CO.sub.2 absorber comprising a first absorption stage and a second absorption stage, an inlet for forwarding a flue gas stream to the first absorption stage, first contacting means for contacting, in the first absorption stage, the flue gas stream with a mixture of CO.sub.2-lean ammoniated solution and recirculated CO.sub.2-enriched ammoniated solution to form a partly cleaned flue gas stream, a transfer device for transferring the partly cleaned flue gas stream from the first absorption stage to the second absorption stage, second contacting means for contacting, in the second absorption stage, the partly cleaned flue gas stream with the recirculated CO.sub.2-enriched ammoniated solution to form a cleaned flue gas stream, an outlet for cleaned flue gas stream forwarded from the second absorption stage, a device for collecting the mixture of CO.sub.2-lean ammoniated solution and recirculated CO.sub.2-enriched ammoniated solution after having passed through the first absorption stage to form a collected CO.sub.2-enriched ammoniated solution, a CO.sub.2-enriched solution pipe for passing a first portion of the collected CO.sub.2-enriched ammoniated solution for regeneration for removing CO.sub.2 from the first portion of the collected CO.sub.2-enriched ammoniated solution to form the CO.sub.2-lean ammoniated solution, a CO.sub.2-lean solution pipe for passing the CO.sub.2-lean ammoniated solution from regeneration to the first absorption stage, and a recirculation pipe for passing a second portion of the collected CO.sub.2-enriched ammoniated solution to the second absorption stage to form the recirculated CO.sub.2-enriched ammoniated solution.
“An advantage of this system is that it is robust and has lower operating and capital costs compared to the prior art systems.
“According to one embodiment, the system comprises a heat exchanger arranged on the recirculation pipe for cooling the recirculated CO.sub.2-enriched ammoniated solution prior to being supplied to the second absorption stage. An advantage of this embodiment is that cooling to a suitable temperature for the second absorption stage can be achieved efficiently. Often a relatively simple water cooled heat exchanger is sufficient. At the relatively high temperature level of the second absorption stage much of the heat that needs to be cooled away can be rejected using cooling water, for example from a cooling tower, thus reducing the heat load on a refrigeration unit involving, for example, compression stages and organic cooling media. If cooling water is available at low temperatures, such as 5-10.degree. C., the need for refrigeration can be eliminated so that the capacity of the refrigeration unit is significantly reduced.
“According to one embodiment, the absorber comprises a single tower housing the first and the second contacting means, with the second contacting means being located vertically above the first contacting means inside the tower. An advantage of this embodiment using a single tower which is common to the first and second contacting means is that a simple absorber design can be utilized. Furthermore, the transfer of partly cleaned flue gas and recirculated CO.sub.2-enriched ammoniated solution between the first and second absorption stages can be made efficient, in a ‘plug flow’ manner and in a way which ensures good distribution of flue gas and solution within packing material of the respective stage. Optionally, when a third absorption stage is included in the absorber for polishing ammonia, a third contacting means of the third absorption stage may be arranged within the single tower housing together with the first and the second contacting means. In such case the third contacting means would be located vertically above the second contacting means.
“Further objects and features of the present invention will be apparent from the following detailed description and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
“The invention is described in more detail below with reference to the appended drawings in which:
“FIG. 1 is a schematic side view of a boiler system.
“FIG. 2 is a schematic side view of a CO.sub.2-absorber.
“FIG. 3 is a diagram illustrating the composition of ammoniated solution in various positions of the CO.sub.2-absorber of FIG. 2.
“FIG. 4 is a diagram illustrating the temperature of ammoniated solution in various positions of the CO.sub.2-absorber of FIG. 2.
“FIG. 5 is a diagram illustrating the molar fractions of carbon dioxide and ammonia of the flue gas stream in various positions of the CO.sub.2-absorber of FIG. 2.”
For additional information on this patent application, see: GUIDOLIN, Sandra; KOSS, Ulrich; KNIESBURGES, Peter. Absorber for Capturing Co2 in Ammoniated Solution. Filed February 28, 2014 and posted July 3, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=3762&p=76&f=G&l=50&d=PG01&S1=20140626.PD.&OS=PD/20140626&RS=PD/20140626
Keywords for this news article include: Ions, Patents, Chemistry, Electrolytes, Carbon Dioxide, Nitrogen Compounds, Inorganic Chemicals, Ammonium Bicarbonate, Inorganic Carbon Compounds.
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