Patent Publication Number: US-10307709-B2

Title: Method and apparatus for continuous removal of water vapors from gases

Description:
This invention was made with government support under DE-FE0028697 awarded by The Department of Energy. The government has certain rights in the invention. 
    
    
     BACKGROUND 
     Field of the Invention 
     This invention relates generally to the field of purification of gases. Our immediate interest is in the removal of water vapor, from a gas stream, such as combustion flue gas, natural gas, and air. 
     Related Technology 
     The art of gas purification has been part of industry for many years. This includes the removal of entrained solids and liquids, as well as separation of gases. The process of removing vapors from carrier gas streams is especially of interest to hydrocarbon suppliers, combustion gas producing facilities, purified gas suppliers, and many others. Vapor removal is primarily conducted by either chemical complexing, condensation, or desublimation. 
     Chemical complexing in solids occurs by passing the gas stream through a bed of desiccants or related solids that chemically bind the vapor. Chemical complexing in liquids occurs in brine solutions, near-eutectic solutions, or other systems where the liquid has the ability to complex with the vapor. 
     Condensation occurs when the partial pressure of the vapor is reduced below the vapor&#39;s condensation point, allowing the vapor to condense into a liquid form. Desublimation is considered a form of condensation, as it brings a gas to a condensed state, namely to a solid. 
     The greatest difficulty in gas purification is energy costs. Standard techniques are costly, requiring large amounts of energy for distillation, reconstitution of solid desiccants, and similar processes. Further, the solutions used for vapor removal can be highly toxic, difficult to work with, or simply expensive. 
     As the separation of gases becomes more prevalent in technology, new methods are needed to address any limitations that exist. 
     United States patent publication number 2008/7314502 to Kelley teaches a method for the separation of a single component from a multi-component gas stream. This disclosure is pertinent and could benefit from vapor removal methods disclosed herein and is hereby incorporated for reference in its entirety for all that it teaches. 
     United States patent publication number 2011/0203174 to Lackner teaches a method and apparatus for extracting carbon dioxide from air. This disclosure is pertinent and could benefit from vapor removal methods disclosed herein and is hereby incorporated for reference in its entirety for all that it teaches. 
     United States patent publication number 9067173 to Alban teaches a method and equipment for treating carbon dioxide-rich smoke. This disclosure is pertinent and could benefit from vapor removal methods disclosed herein and is hereby incorporated for reference in its entirety for all that it teaches. 
     United States patent publication number 8088197 to Wright teaches a method for removing carbon dioxide from air. This disclosure is pertinent and could benefit from vapor removal methods disclosed herein and is hereby incorporated for reference in its entirety for all that it teaches. 
     Other current technologies include methods for heat and mass transfer utilizing gas streams. These methods are affected by the limitations discussed above, namely cost and energy requirements. 
     SUMMARY 
     A method for continuously removing water vapor from a carrier gas is disclosed. This method includes, first, causing direct contact of the carrier gas with a liquid mixture in a separation chamber, the carrier gas condensing at a lower temperature than the water vapor. A combination of chemical effects cause the water vapor to condense, complex, or both condense and complex with the liquid mixture. The liquid mixture is chosen from the group consisting of: first, a combination of components that can be maintained in a liquid phase at a temperature below the water vapor&#39;s condensation point, whereby the water vapor condenses into the liquid mixture; second, a combination of components where at least one component forms a chemical complex with the water vapor and thereby extracts at least a portion of the water vapor from the carrier gas; and third, a combination of components that can both be maintained in a liquid phase at a temperature below the water vapor&#39;s condensation point, and wherein at least one component forms a chemical complex with the water vapor and thereby extracts at least a portion of the water vapor from the carrier gas. The liquid mixture is then reconstituted after passing through the separation chamber by a chemical separation process chosen to remove an equivalent amount of the water vapor from the liquid mixture as was removed from the carrier gas. The reconstituted liquid mixture is restored to temperature and pressure through heat exchange, compression, and expansion, as necessary, in preparation for recycling back to the separation chamber. The liquid mixture is then returned to the separation chamber. In this manner, the carrier gas leaving the exchanger has between 1% and 100% of the water vapor removed. 
     The liquid mixture may consist of a mixture of water and a compound from either of the following two groups: i) ionic compounds including potassium carbonate, potassium formate, potassium acetate, calcium magnesium acetate, magnesium chloride, sodium chloride, lithium chloride, and calcium chloride; and, ii) soluble organic compounds including glycerol, ammonia, propylene glycol, ethylene glycol, ethanol, and methanol. The carrier gas may consist of combustion flue gas, moist air or similar light gas streams, or a hydrocarbon with higher volatility than water. 
     The separation chamber may be either a counter-current, direct-contact exchanger or a co-current, direct-contact exchanger. 
     The chemical separation process for reconstituting the liquid mixture may be distillation, pressure-swing separation, liquid extraction, reverse osmosis, forward osmosis, filtration, stripping, or a combination of these. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through use of the accompanying drawings, in which: 
         FIG. 1  shows a general process flow diagram in accordance with an embodiment of the invention; 
         FIG. 2  shows a process flow diagram for dehydrating combustion flue gas, in accordance with an embodiment of the invention; 
         FIG. 3  shows a process flow diagram for dehydrating natural gas, in accordance with an embodiment of the invention; 
         FIG. 4  shows a process flow diagram for dehydrating propane gas, in accordance with an embodiment of the invention; 
         FIG. 5  shows a process flow diagram for dehydrating nitrogen gas, in accordance with an embodiment of the invention; 
         FIG. 6  shows a phase diagram for ionic compounds that include a subset of useful compounds in accordance with some embodiments of the invention; 
         FIG. 7  shows a phase diagram for inorganic and organic compounds that include a subset of useful compounds in accordance with some embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the invention, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of certain examples of presently contemplated embodiments in accordance with the invention. 
     Referring to  FIG. 1 , a process flow diagram  100  is shown. A carrier gas  102 , containing a water vapor  104  to be removed, enters a separation chamber  106 . A cold liquid mixture  108  enters separation chamber  106  flowing counter-current to the carrier gas  102 /water vapor  104  combination. Carrier gas  102  exits separations chamber  106  with substantially less water vapor  104 . In some embodiments, this can mean a removal of between 1% and 100% of water vapor  104 . Liquid mixture  108  and extracted water vapor  104  exit separations chamber  106  and are conveyed to a separations system  110  where captured water vapor  104  is removed as a liquid or vapor, and liquid mixture  108 , now at the same composition as required for separation chamber  106 , is sent to a heat exchanger, compressor, or expander  112  for cooling to the required temperature for separations chamber  106 . 
     The chemical separation process for reconstituting the liquid mixture may be distillation, pressure-swing separation, liquid extraction, solid extraction, reverse osmosis, forward osmosis, filtration, stripping, or a combination of these. 
     In some embodiments, the liquid mixture consists of water and a compound from either of the following two groups: i) ionic compounds including potassium carbonate, potassium formate, potassium acetate, calcium magnesium acetate, magnesium chloride, sodium chloride, lithium chloride, and calcium chloride; and, ii) soluble organic compounds including glycerol, ammonia, propylene glycol, ethylene glycol, ethanol, and methanol. Carrier gas  102  may be combustion flue gas, syngas, producer gas, natural gas, steam reforming gas, any hydrocarbon that has higher volatility than water, or light gases. 
     Combustion flue gas consists of the exhaust gas from a fireplace, oven, furnace, boiler, steam generator, or other combustor. The combustion fuel sources include coal, hydrocarbons, and biomass. Combustion flue gas varies greatly in composition depending on the method of combustion and the source of fuel. Combustion in pure oxygen produces little to no nitrogen in the flue gas. Combustion using air leads to the majority of the flue gas consisting of nitrogen. The non-nitrogen flue gas consists of mostly carbon dioxide, water, and sometimes unconsumed oxygen. Small amounts of carbon monoxide, nitrogen oxides, sulfur dioxide, hydrogen sulfide, and trace amounts of hundreds of other chemicals are present, depending on the source. Entrained dust and soot will also be present in all combustion flue gas streams. The method disclosed applies to any combustion flue gases. 
     Syngas consists of hydrogen, carbon monoxide, and carbon dioxide. 
     Producer gas consists of a fuel gas manufactured from materials such as coal, wood, or syngas. It consists mostly of carbon monoxide, with tars and carbon dioxide present as well. 
     Steam reforming is the process of producing hydrogen, carbon monoxide, and other compounds from hydrocarbon fuels, including natural gas. The steam reforming gas referred to herein consists primarily of carbon monoxide and hydrogen, with varying amounts of carbon dioxide and water. 
     Light gases include gases with higher volatility than water, including hydrogen, helium, carbon dioxide, nitrogen, and oxygen. This list is for example only and should not be implied to constitute a limitation as to the viability of other gases in the process. A person of skill in the art would be able to evaluate any gas as to whether it has higher volatility than water. 
     In some embodiments of the present invention, liquid mixture  108  is conveyed from separation chamber  106  by a pump. While an appropriate pump can be chosen by one of normal skill in the art, the pump chosen would preferentially be a cryogenic-style pump, capable of handling temperatures significantly below the freezing point of water. The pump chosen could be a centrifugal, piston, pressure-recovery, propeller, circulator, slurry, positive-displacement, diaphragm, progressive-cavity, screw, or vane pump. The internals of the pump would again be chosen based on the specifics of liquid mixture  108 , but would have to be chosen to be resistant to whatever materials were conveyed. They would need to be cold resistant, but may also need to be acid or corrosive resistant. The possibility of particulates, especially in cases where the carrier gas may have contaminants like soot or dust, would also indicate an erosion resistant material, such as ceramic or stainless steel. 
     Referring to  FIG. 2 , one embodiment of the present invention is disclosed, with a process flow diagram  200  shown. In this embodiment, a combustion flue gas  202 , containing a water vapor  204  to be removed, enters a counter-current direct contact exchanger  206 . A cold liquid mixture  208  enters exchanger  206  flowing counter-current to the combustion flue gas  202 /water vapor  204  combination. Liquid mixture  208  is chosen to consist of water and sodium chloride at an appropriate concentration and temperature, as per  FIG. 6 . Combustion flue gas  202  exits exchanger  206  with all water vapor  204  removed in the liquid phase. Liquid mixture  208  and extracted water  204  exit exchanger  206  and are conveyed to a forward-osmosis system  210  where the captured water  204  is removed, and liquid mixture  208 , now at the same composition as required for exchanger  206 , is sent to a heat exchanger  212  for cooling to the required temperature for exchanger  206 . 
     Referring to  FIG. 3 , another embodiment of the present invention is disclosed, with a process flow diagram  300  shown. In this embodiment, natural gas  302 , containing a water vapor  304  to be removed, enters a co-current direct contact exchanger  306 . A cold liquid mixture  308  enters exchanger  306  flowing co-current to the liquefied natural gas  302 /water vapor  304  combination. Liquid mixture  308  is chosen to consist of water and ethanol at an appropriate concentration and temperature, as per  FIG. 7 . Liquefied natural gas  302  exits exchanger  306  with all water vapor  304  removed in the liquid phase. Liquid mixture  308  and extracted water  304  exit exchanger  306  and are conveyed to a stripping system  310  where the captured water  304  is removed, and liquid mixture  308 , now at the same composition as required for exchanger  306 , is sent to a heat exchanger  312  for cooling to the required temperature for exchanger  306 . 
     Referring to  FIG. 4 , one embodiment of the present invention is disclosed, with a process flow diagram  400  shown. In this embodiment, propane gas  402 , containing water vapor  404  to be removed, enters a counter-current direct contact exchanger  406 . A cold liquid mixture  408  enters exchanger  406  flowing counter-current to the propane  402 /water vapor  404  combination. Liquid mixture  408  is chosen to consist of water and potassium acetate at an appropriate concentration and temperature, as per  FIG. 6 . Propane gas  402  exits exchanger  406  with all water vapor  404  removed in the liquid phase. Liquid mixture  408  and extracted water  404  exit exchanger  406  and are conveyed to reverse-osmosis system  410  where the captured water  404  is removed, and liquid mixture  408 , now at the same composition as required for exchanger  406 , is sent to a heat exchanger  412  for cooling to the required temperature for exchanger  406 . 
     Referring to  FIG. 5 , one embodiment of the present invention is disclosed, with a process flow diagram  500  shown. In this embodiment, nitrogen gas  502 , containing water vapor  504  to be removed, enters a counter-current direct contact exchanger  506 . A cold liquid mixture  508  enters exchanger  506  flowing counter-current to the nitrogen gas  502 /water vapor  504  combination. Liquid mixture  508  is chosen to consist of water and potassium acetate at an appropriate concentration and temperature, as per  FIG. 7 . Nitrogen gas  502  exits exchanger  506  with all water vapor  504  removed in the liquid phase. Liquid mixture  508  and extracted water vapor  504  exit exchanger  506  and are conveyed to a flash separation system  510  where the captured water vapor  504  is removed, and liquid mixture  508 , now at the same composition as required for exchanger  506 , is sent to a heat exchanger  512  for cooling to the required temperature for exchanger  506 . 
     Referring to  FIG. 6 , a phase diagram for various ionic compounds that are acceptable for use as part of liquid mixture  108 ,  208 , or  408  with water is shown. This diagram is prior art. While this list includes very useful ionic compounds in solution with water, this chart should not be interpreted as limiting the selection of compounds useful in the present invention. Those of ordinary skill in the art can determine the desired concentration and temperatures for liquid mixtures  108 ,  208 , and  408  based on reference charts and phase diagrams for different combinations of compounds. In the case of the phase diagram in  FIG. 6 , the concentration chosen will determine the temperature that liquid mixture  108 ,  208 , or  408  can reach. Depending on how much water vapor is to be removed, different concentrations will be required. Therefore, liquid mixtures  108 ,  208 , or  408  are chosen to have a combination of one or more of the following properties: (i) Liquid mixture  108 ,  208 , or  408  are at a temperature and pressure such that the partial vapor pressure is below the condensation point of water vapor  104 ,  204 , or  404 , and thus water vapor  104 ,  204 , or  404  desublimates. (ii) Liquid mixtures  108 ,  208 , or  408  contain at least one compound that can form complexes with water vapor  104 ,  204 , or  404 , the system being at such a concentration that any of water vapor  104 ,  204 , or  404  passing through will be complexed. iii) Liquid mixtures  108 ,  208 , or  408  contain a combination of components wherein at least one component absorbs water vapor  108 ,  208 , or  408  and thereby extracts at least a portion of water vapor  108 ,  208 , or  408  from carrier gas  102 ,  202 , or  402 . iv) A combination of the above. 
     Referring to  FIG. 7 , a phase diagram for various inorganic and organic compounds that are acceptable for use as part of liquid mixture  108 ,  208 ,  308 ,  408 , and  508  with water is shown. This diagram is prior art. While this list includes very useful organic compounds in solution with water, this chart should not be interpreted as limiting the selection of compounds useful in the present invention. Those of ordinary skill in the art can determine the desired concentration and temperatures for liquid mixtures  108 ,  208 ,  308 ,  408 , and  508  based on reference charts and phase diagrams for different combinations of compounds. In the case of the phase diagram in  FIG. 7 , the concentration chosen will determine the temperature that liquid mixture  108 ,  208 ,  308 ,  408 , and  508  can reach. Depending on how much water vapor is to be removed, different concentrations will be required. Therefore, liquid mixture  108 ,  208 ,  308 ,  408 , and  508  are chosen to have a combination of one or more of the following properties: (i) Liquid mixture  108 ,  208 ,  308 ,  408 , and  508  are at a temperature and pressure such that the partial vapor pressure is below the condensation point of water vapor  104 ,  204 ,  304 ,  404 , or  504 , and thus water vapor  104 ,  204 ,  304 ,  404 , or  504  desublimates. (ii) Liquid mixtures  108 ,  208 ,  308 ,  408 , and  508  contain at least one compound that can form complexes with water vapor  104 ,  204 ,  304 ,  404 , or  504 , the system being at such a concentration that any of water vapor  104 ,  204 ,  304 ,  404 , or  504  passing through will be complexed. iii) Liquid mixtures  108 ,  208 ,  308 ,  408 , and  508  contain a combination of components wherein at least one component absorbs water vapor  108 ,  208 ,  308 ,  408 , and  508  and thereby extracts at least a portion of water vapor  108 ,  208 ,  308   408  or  508  from carrier gas  102 ,  202 ,  302 ,  402  or  502 . iv) A combination of the above.