Patent Publication Number: US-2015072393-A1

Title: Flue gas treatment and permeate hardening

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to flue gas treatment and water desalination more particularly, to a synergetic connection of a power plant and a desalination plant. 
     2. Discussion of the Related Art 
       FIG. 1  is a schematic illustration of a prior art system for treating flue gas and providing CO 2  to acidify product water (permeate) from a desalination plant, such as a reverse osmosis (RO) plant  130 . 
     The prior art system comprises a power plant with CO 2  regenerator  61  followed by a stripper tower  62 . Power plant  61  produces flue gas  81 , including CO 2 , N 2 , O 2  and other gases. Some of the flue gas is processed in a cooler and scrubber unit  71  and in an absorber tower  72 . For production of CO 2 , flue gas  81  goes through a processing chain comprising KMnO 4  bubblers  64 , a purification tower  65  and a CO 2  drying tower  66 , to be finally condensed by a CO 2  condenser  67  and stored as a liquid in a liquid CO 2  container  68 . 
     For acidifying RO product water, liquid CO 2  is mixed with the permeate, or CO 2  is bubbled into the permeate. The acidified permeate is then added limestone for hardening the water. 
     The process is an elaborate and expensive one. 
     BRIEF SUMMARY 
     One aspect of the invention provides a system comprising: a compressor connected to a flue gas outlet of a plant and arranged to compress flue gas obtained therefrom to a specified pressure, the flue gas comprising CO 2 , a water source supplying pressurized water, an absorber connected to the water source and arranged to spray water therefrom, further connected to the compressor and arranged to inject the compressed flue gas into the sprayed water to dissolve over 50% of CO 2  in the flue gas in the resulting water, and a water receiving unit connected to the absorber and arranged to receive the water with dissolved flue gas therefrom and to remove dissolved CO 2  from the resulting water into an organic or a mineralized form. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of embodiments of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings in which like numerals designate corresponding elements or sections throughout. 
       In the accompanying drawings: 
         FIG. 1  is a high level schematic block diagram illustrating a prior art system for treating flue gas; 
         FIG. 2  is a high level schematic block diagram illustrating a system for flue gas treatment according to some embodiments of the invention; 
         FIG. 3  is a high level schematic block diagram illustrating a system for flue gas treatment combined with a reverse osmosis (RO) plant according to some embodiments of the invention; 
         FIG. 4  is a high level schematic block diagram illustrating a system for flue gas treatment comprising a permanganate cleaning unit according to some embodiments of the invention; and 
         FIG. 5  is a high level flowchart illustrating a method for flue gas treatment according to some embodiments of the invention. 
     
    
    
     The drawings together with the following detailed description make apparent to those skilled in the art how the invention may be embodied in practice. 
     DETAILED DESCRIPTION 
     With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. 
     Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is applicable to other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. 
       FIG. 2  is a high level schematic block diagram illustrating a system  100  according to some embodiments of the invention. 
     System  100  comprises a compressor  112 , an absorber  110  and a water receiving unit (depicted in  FIG. 2  as power exchanger  120  and water reservoir  80 ). 
     Compressor  112  is connected to a flue gas outlet of a plant  90  and is arranged to compress flue gas  81  obtained therefrom to a specified pressure e.g.  20  bar that allows dissolving flue gas  81  into water sprayed in absorber  110 . Flue gas  81  comprises CO 2 , N 2 , O 2  and other gases. 
     Absorber  110  is connected to a water source that supplies pressurized water (e.g. at 20 bar). The water source may comprise pumped seawater serving as cooling water  82  in power plant  90 , as illustrated in  FIG. 2 . Pressurization of the water supplied to absorber  110  may be carried out by a pressure exchanger  120  as explained below, to preserve the built up pressure while exchanging liquids in the high pressure loop. 
     Absorber  110  is arranged to spray the pressurized water in inject into the water compressed flue gas  81  from compressor  112 . A large part of the CO 2  in the injected flue gas, e.g. over 50%, dissolves under the pressure into the sprayed water, to produce resulting water enriched with dissolved gases, mainly CO 2 . System  100  utilizes the high dissolvability of CO 2  in water (ca. 1200 ppm) in respect to the dissolvability of the other flue gas constituents (e.g. O 2  ca. 10 ppm, N 2  ca. 1 ppm, at 20 bar). 
     The water receiving unit is connected to absorber  110  and is arranged to receive the water with dissolved flue gas therefrom and to remove dissolved CO 2  from the resulting water into an organic or a mineralized form. For example, in  FIG. 2 , the resulting water is removed over power exchanger (to maintain their high pressure) and dispensed to water reservoir  80  such as the sea. 
     In the sea, dissolved CO 2  is turned into organic matter by algae, and other gas constituents may evaporate. 
     System  100  thus removes CO 2  from the flue gas and makes the CO 2  available for biological and mineralization processes within water reservoir  80  (such as the sea), thereby reducing CO 2  emissions of power plant  90  to the atmosphere. 
     Power exchanger  120  has a low pressure (LP) inlet  120 A, a low pressure outlet  120 B, a high pressure inlet  120 C and a high pressure outlet  120 D, as illustrated in  FIG. 2 . Power exchanger  120  is arranged to exchange fluid between a low pressure loop and a high pressure loop while maintaining the respective pressures. 
     Power exchanger  120  is connected to the water source, for example a cooling water source  93  (arranged to cool a condenser  92  receiving steam from a turbine  91  in power plant  90 ) and is arranged to receive water therefrom in low pressure inlet  120 A. 
     Power exchanger  120  is connected to a pump  111  that is arranged to receive and pressurize the resulting water from absorber  110 . Power exchanger  120  is arranged to receive the pressurized resulting water from pump  111  in high pressure inlet  120 C. 
     Power exchanger  120  is arranged to discharge, from high pressure outlet  120 D, water from low pressure inlet  120 A that is pressurized by the pressurized resulting water from high pressure inlet  120 C and to discharge, from low pressure outlet  120 B, depressurized pressurized resulting water from high pressure inlet  120 C. 
     Absorber  110  is connected to high pressure outlet  120 D of power exchanger  120  to receive therefrom the water for spraying. 
     When the water fed to absorber  110  is cooling water  82  of the same plant  90  producing flue gas  81 , system provides a solution for CO 2  removal and sequestration. The sea may be the source for cooling water  82  as well as the water reservoir  80  into which CO 2  enriched water is disposed for organic CO 2  utilization. 
       FIG. 3  is a high level schematic block diagram illustrating system  100  according to some embodiments of the invention. 
     System  100  comprises compressor  112 , absorber  110  and a water receiving unit (depicted in  FIG. 3  as the hardened product water  85 B). 
     Compressor  112  is connected to a flue gas outlet of a plant  90  and is arranged to compress flue gas  81  obtained therefrom to a specified pressure e.g. 20 bar that allows dissolving flue gas  81  into water sprayed in absorber  110 . Flue gas  81  comprises CO 2 , N 2 , O 2  and other gases. 
     Absorber  110  is connected to a water source that supplies pressurized water. The water source may comprise permeate or product water  84  from a reverse osmosis (RO) plant  130 , as illustrated in  FIG. 3 . Product water  84  are pressurized by pump  111  before entering absorber  110 , e.g. to a pressure of 20 bar. 
     Absorber  110  is arranged to spray the pressurized product water in inject into the water compressed flue gas  81  from compressor  112 . A large part of the CO 2  in the injected flue gas, e.g. over 50%, dissolves under the pressure into the sprayed water, to produce resulting water enriched with dissolved gases, mainly CO 2 . System  100  utilizes the high dissolvability of CO 2  in water (ca. 1200 ppm) in respect to the dissolvability of the other flue gas constituents (e.g. O 2  ca. 10 ppm, N2 ca. 1 ppm). 
     The water receiving unit is connected to absorber  110  and is arranged to receive the product water enriched with dissolved CO 2  therefrom and to mineralize the CO 2  as CaCO 3  or MgCO 3  to harden the product water. 
     System  100  not only removes CO 2  from flue gas  81 , but also synergetically acidifies permeate  84  of RO plant  130  to spare the necessary addition of expensive liquid CO 2  (see  FIG. 1 ). 
     When seawater  80  is the source of cooling water  82  for plant  90  providing flue gas  81 , brine  83  from RO plant  130  may be disposed into sea  80 , or mixed with disposed cooling water to reduce its salinity, hence providing a second synergy with plant  90 . 
       FIG. 4  is a high level schematic block diagram illustrating system  100  according to some embodiments of the invention. 
     System  100  comprises a cleaning unit  117  connected between compressor  112  and absorber  110  or before compressor  112  (not shown in  FIG. 4 ). 
     Cleaning unit  117  is connected after a blower  113  conducting flue gas  81  (comprising e.g. 6-17% CO 2 ) to a direct contact cooling tower  114  for cooling. Cleaning unit  117  comprises a permanganate cleaning unit  115  arranged to bring the flue gas into gas-liquid contact with a permanganate solution, to generate a first stage treated flue gas in which all toxic gases (e.g. NO 2 ) are oxidized. 
     Cleaning unit  117  further comprises an activated carbon unit  116  arranged to bring the first stage treated flue gas into gas-solid contact with activated carbon that adsorbs organic matter from the flue gas, to generate a cleaned CO 2  in air mixture  81 A. Cleaned CO 2  in air mixture  81 A is dissolved in RO permeate  84  to yield acidified product  85 A. 
     System  100  may further comprise a limestone reactor  140  connected to absorber  110 , and arranged to bring received resulting CO 2  enriched product water  85 A into contact with limestone, to mineralize the CO 2  to harden the product water  85 B. Excess CO 2  from product water  85 B may be removed in a desorber tower  145  by a stripping air stream. Residual CO 2  may be treated, returned to CO 2  in air mixture  81 A or dissolved in water disposed to water reservoir  80 . 
     In exemplary projects, power plant  90 &#39;s CO 2  production of  30 - 56  tons CO 2  per day, may provide 19-36 ton CO 2  per day used in associated desalination plants, thereby simultaneously sequestering CO 2  from flue gas  81  and sparing the expensive addition of CO 2  in the post treatment of permeate. 
       FIG. 5  is a high level flowchart illustrating a method  200  according to some embodiments of the invention. 
     Method  200  comprises the following stages: compressing obtained flue gas that comprises CO 2  to a specified pressure (stage  201 ), e.g. 20 bar, spraying pressurized water (e.g. at 20 bar) in an absorber (stage  210 ), injecting the compressed flue gas into the sprayed water (stage  215 ) to dissolve over 50% of the CO 2  in the flue gas in the resulting water (stage  217 ), and removing dissolved CO 2  from the resulting water into an organic or a mineralized form (stage  220 ). 
     In embodiments, method  200  comprises using pressurized cooling water as sprayed water (stage  221 ), and removing cooling water with dissolved CO 2  to the water reservoir (stage  222 ), e.g. into a reservoir in which CO 2  is consumed by algae. 
     In embodiments, method  200  further comprises pumping (stage  223 ), over a power exchanger, cooling water from a reservoir for spraying in the absorber. Removing the cooling water (stage  222 ) is carried out over the power exchanger and back into the reservoir. The cooling water and the flue gas may be associated with the same power plant. The reservoir may be a sea and the water seawater. The dissolved CO 2  may be consumed by algae in the sea. 
     Method  200  may comprise separating a high pressure loop supplying pressurized cooling water and a low pressure loop removing the cooling water with dissolved CO 2  to conserve pumping power (stage  224 ). 
     In embodiments, method  200  comprises using RO permeate as sprayed water (stage  230 ) by pumping (stage  231 ) product water from a reverse osmosis (RO) plant for spraying in the absorber (stage  210 ). 
     Method  200  may comprise processing and cleaning flue gas with an elevated level of CO 2  (stage  202 ) and generating a clean CO 2  in air mixture from the flue gas (stage  204 ) by bringing the flue gas into gas-liquid contact with a permanganate solution (stage  206 ) and bringing the flue gas into gas-solid contact with activated carbon (stage  208 ) (see  FIG. 4 ). 
     In embodiments, method  200  comprises infiltrating the cleaned CO 2  in air mixture into reverse osmosis (RO) permeate (stage  232 ) to generate CO 2  enriched acidified permeate (stage  234 ) and generating remineralized product by bringing the CO 2  enriched acidified permeate into contact with limestone and allowing excess CO 2  to escape (stage  240 ) such that removing of dissolved CO 2  (stage  220 ) is carried out by mineralization to CaCO 3  to harden the product water. 
     Method  200  may further comprise mixing brine from the RO plant with cooling water associated with a plant producing the flue gas to dilute the brine prior to disposal (stage  242 ). 
     In the above description, an embodiment is an example or implementation of the invention. The various appearances of “one embodiment”, “an embodiment” or “some embodiments” do not necessarily all refer to the same embodiments. 
     Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment. 
     Furthermore, it is to be understood that the invention can be carried out or practiced in various ways and that the invention can be implemented in embodiments other than the ones outlined in the description above. 
     The invention is not limited to those diagrams or to the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described. 
     Meanings of technical and scientific terms used herein are to be commonly understood as by one of ordinary skill in the art to which the invention belongs, unless otherwise defined. 
     While the invention has been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of some of the preferred embodiments. Other possible variations, modifications, and applications are also within the scope of the invention.