Patent Publication Number: US-2022226781-A1

Title: Improved gas exchange system and method

Description:
FIELD 
     The invention relates to a system and method of exchanging gas with a solvent, said gas including CO2 and H2S, both to laden said solvent with said gas, and to strip a gas-laden solvent of said gas. 
     BACKGROUND 
     For clarity, reference to CO2 will further apply to H2S and other acidic gases unless the application would make such an extension unworkable. 
     The use of membrane cartridges involve placing gas permeable/liquid impermeable hollow membrane within a cylinder and passing high temperature gas, such as steam, into the membrane. The solvent is injected into the cartridge so as to fill the interstitial spaces around the membrane whereby the steam strips the acidic gas from the solvent, which subsequently passes into the membrane and exits the cartridge with the condensed steam. The solvent, having the acidic gas removed, is then removed from the cartridge for subsequent downstream use. 
     It will be appreciated that the process is reversible whereby the acidic gas is passed into a cartridge with the solvent injected about the membrane. The acidic gas then permeates through the membrane to be absorbed by the solvent which subsequently exits the cartridge. 
     The difficulty in this process is scalability, for those application where the volume of gas and solvent exceeds that of a reasonable cartridge size. A typical cartridge may be 9 inches in diameter, and arranged to process a solvent mass flow rate of the order of 0.8 to 1 kilogram per second. To scale the process by, say, an order of magnitude would involve 10 times the number of cartridges with a weight of the cartridges approaching 10 tonnes. 
     Alternatively, several membranes could be placed into a single module and thus reducing the weight of the steel casing of individual cartridges. However, the efficiency of a multi-cartridge arrangement is substantially reduced as membranes coinciding with the flow path of the solvent from the inlet to the outlet may be efficiently used. However, membranes outside the flow path may be subject to low flow or no flow conditions and therefore incapable of being fully utilized to receive high gas transfer due to a lack of replenishment of solvent about the fiber. 
     SUMMARY 
     In a first aspect, the invention provides a gas exchange system, said system comprising: a plurality of cartridges, each having a casing, said casing having a cartridge inlet adjacent to a first end and a cartridge outlet adjacent to an opposed second end; each casing having a bore in which is placed a gas permeable, liquid impermeable, hollow membrane; each hollow membrane having a membrane inlet arranged to receive a gas from an inlet chamber and a membrane outlet for venting said gas; each cartridge inlet in communication with a concentration zone, and arranged to receive a solvent from said concentration zone, so as to exit said solvent through said cartridge outlet; wherein said bore is arranged to flow said solvent adjacent to said hollow membrane so as to permit the exchange of gas through said gas permeable, liquid impermeable membrane. 
     Therefore, by providing a concentration zone for receiving the solvent which is discrete from the solvent outlet, the flow path for the solvent is confined to being proximate to the membranes thus maintaining an efficient gas transfer. This may lead to substantially improved scalability with no clear limitation of the size of the regeneration plant. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible and consequently, the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention. 
         FIGS. 1A to 1D  show various views of a regeneration module according to one embodiment of the present invention, and; 
         FIGS. 2A and 2B  are various views of a concentration zone for a module according to a further embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In general terms, the invention involves placing a concentration zone in fluid communication with inlets for a plurality of cartridges, the cartridges having hollow membranes within a bore of the cartridges, for transporting gas. The hollow membranes are gas permeable but liquid impermeable. By passing the solvent through the bore of the cartridges, so as to be proximate with the external surface of the membranes, a more efficient exchange of gas will occur. The gas is then vented from the membranes, and the solvent flowing out of the cartridges. 
       FIGS. 1A to 1D , and  FIGS. 2A and 2B , show a solvent regeneration module  5  according to one embodiment of the present invention. It will be appreciated that whilst reference is made to the module being used for regeneration, it is equally applicable to the reverse process whereby new solvent is infused with acidic gas. Therefore, whilst the following description makes reference to regeneration, the invention is not limited to the use with a regeneration process but is also applicable to the gas infusion process. 
       FIG. 1A  shows an elevation view of a module  5  having a housing  10  with end caps  15 ,  20 . The end caps  15 ,  20  include a gas inlet  25  and a gas outlet  30 , respectively. Further, the housing  10  includes an inlet  35  for receiving liquid solvent and outlet  40  for exiting said liquid solvent. 
       FIGS. 1B and 1C  show a plurality of cartridges  55  which are grouped in parallel and held in place by support plates  67 ,  75 . The inlet end cap  15  and inlet support plate  67  define an inlet chamber into which the gas is injected through the inlet  25 . Each cartridge  55  includes an open end  57  which permits the gas from the inlet chamber to enter into the cartridge  55  and specifically through hollow longitudinal membranes  77 . Each cartridge may have one or more membrane located within, depending upon the required flow rate and optimal size of the membrane. 
     The cartridge  55  further includes interstitial spaces  59  within the bore of the cartridge for receiving solvent, as will be discussed below. The entire cartridge  55  is then sealed around the periphery by a casing  53 . The gas is permitted to vent  51  into an outlet chamber defined by outlet support plate  75  and outlet end cap  20  which feed the gas through to the outlet  30 . 
     The solvent enters the housing  10  through the inlet  35  which allows the liquid solvent to flow about the cartridges  55 , within an interstitial space  80 . The cartridge housing  53 , however, prevents direct contact between the solvent within the interstitial space  80  from contacting the membranes  77 . According to the present invention, the solvent entering  45  the housing  10  is directed to flow into ingress apertures  65  so as to flow through the cartridge  55  within the interstitial space  59  and thus contact with the membrane  77  before exiting the cartridge  55  through ingress apertures  70 . 
     This arrangement provides a fluid path for the solvent that places the solvent in close proximity to the membranes, and so solves the issue of having a sufficient flow for an efficient gas transfer. 
     In a further embodiment, the invention provides baffle plates  60  which define concentration zones. 
     With reference to  FIGS. 2A and 2B , the baffle plates  60  define a concentration zone  85  that separates the interstitial spaces  90  near the inlet, ensuring all the solvent flows  95  into the ingress apertures  65  without the solvent escaping directly through the outlet  40 . Thus, the use of baffle plates  60  defines a concentration zone  85  which is discrete from the outlet  40 , ensuring a flow path for the solvent that is in close proximity to the membranes and thus fully utilizing each of the membranes within the group of cartridges. Once the solvent has flowed through the length of the cartridge  55  it exits from the ingress apertures  70  flowing  100  into the interstitial space  95  proximate to the outlet  40 . 
     It will be appreciated that whilst  FIG. 1B  shows the position of the baffle plate  60  at approximately two thirds the length of the module  5 , in fact the position will be a function of the flow rate  45  into the module  5 , the size of the apertures  65 ,  70  and the desired gas flow rate during the gas transfer within the cartridges. Accordingly, the size of the concentration zone may vary from application to application, subject to various design parameters based upon permeability, flow rate etc. 
     Further still, in  FIG. 1B  the baffle plate  60  also acts as an intermediate support plate. The invention is not limited by the number of intermediate support plates and only those intermediate support plates defining a concentration zone may be considered a baffle plate.