Patent Publication Number: US-2019170440-A1

Title: Pressure-Regulated Melting of Solids

Description:
GOVERNMENT INTEREST STATEMENT 
     This invention was made with government support under DE-FE0028697 awarded by the Department of Energy. The government has certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     The devices, systems, and methods described herein relate generally to melting of solids. More particularly, the devices, systems, and methods described herein relate to melting of solids that sublimate at ambient pressures. 
     BACKGROUND 
     Cryogenic solids of various varieties have phase diagrams that do not permit transitions between solid and liquid phases at ambient or near-ambient pressures. Handling these materials as solids is a challenge, as they require the solids handling be done under high pressure conditions, which is logistically difficult and costly. Devices, systems, and methods capable of handling cryogenic materials with minimal solids handling would be beneficial. 
     SUMMARY 
     Devices, systems, and methods for pressure-regulated melting are disclosed. A vessel includes a solids inlet, a fluids outlet, a cavity, and an energy source. Solids enter the vessel through the solids inlet. The cavity has an internal pressure. A backpressure is induced in the solids inlet. The energy source heats the vessel, the contents of the vessel, or a combination thereof. The rate of heating of the energy source is matched to a feed rate of the solids such that the solids are melted directly to a product liquid at the internal pressure. The product liquid passes through the fluids outlet through a restriction that maintains the internal pressure in the cavity. 
     The energy source may comprise a melting device, a warm fluid, or a combination thereof. The solids inlet may include a screw press. The fluids outlet may include a heat exchanger that further heats the product liquid, producing a heated product liquid. The fluids outlet may further include a gas/liquid separator that receives the heated product liquid from the heat exchanger and separates a final product liquid and a product gas. The gas/liquid separator may include a pump that pumps a portion of the final product liquid from the gas/liquid separator to the vessel, the portion of the final product liquid being the warm liquid. 
     The restriction may be one or more valves. The vessel may have an internal heating element. The solids inlet may include a reducer which induces the backpressure on the solids inlet. The reducer may be a concentric reducer, an eccentric reducer, or a nozzle. 
     The solids may include water, hydrocarbons, ammonia, solid acid gases, or a combination thereof, and wherein solid acid gases comprise solid forms of carbon dioxide, nitrogen oxide, sulfur dioxide, nitrogen dioxide, sulfur trioxide, hydrogen sulfide, or a combination thereof. The warm liquid may include water, hydrocarbons, liquid ammonia, liquid acid gases, cryogenic liquids, or a combination thereof, and wherein liquid acid gases comprise liquid forms of carbon dioxide, nitrogen oxide, sulfur dioxide, nitrogen dioxide, sulfur trioxide, hydrogen sulfide, or a combination thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the advantages of the described devices, systems, and methods will be readily understood, a more particular description of the described devices, systems, and methods 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 described devices, systems, and methods and are not therefore to be considered limiting of its scope, the devices, systems, and methods will be described and explained with additional specificity and detail through use of the accompanying drawings, in which: 
         FIG. 1  shows a process flow diagram for melting solids. 
         FIG. 2  shows an isometric side elevation cutaway view of a vessel and screw press for use in the process of  FIG. 1 . 
         FIG. 3  shows a process flow diagram for melting solids. 
         FIG. 4  shows a process flow diagram for melting solids. 
         FIG. 5  shows an isometric side-front elevation view of a vessel for use in the process of  FIG. 4 . 
         FIG. 6  shows a method for melting solids. 
     
    
    
     DETAILED DESCRIPTION 
     It will be readily understood that the components of the described devices, systems, and methods, 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 described devices, systems, and methods, as represented in the Figures, is not intended to limit the scope of the described devices, systems, and methods, as claimed, but is merely representative of certain examples of presently contemplated embodiments in accordance with the described devices, systems, and methods. 
     Many cryogenic solids act in ways seemingly contradictory to that which is expected for solids. Normally, solids melt into a liquid, which then vaporizes into a gas. Many cryogenic liquids, such as carbon dioxide and other acid gases, have phase diagrams that, at ambient pressures, will sublimate from solid directly to gas. In materials handling, liquids are simple to transport when compared to both solids and gases. Gases typically require large equipment to transport similar masses in comparison to liquid. On the other hand, solids have to be moved by conveyance devices that are, with only a few exceptions, open to ambient pressures. The devices, systems, and methods disclosed herein overcome these challenges by avoiding the issue entirely. Cryogenic solids, or any solids that can be melted, are passed into a vessel against a backpressure and an energy source melts the solids directly to a liquid as they enter the vessel, resulting in a product liquid. This product liquid then leaves the vessel through a restriction, resulting in an internal pressure in the cavity of the vessel, allowing the solids to transition from solid to liquid instead of liquid to gas. This is due to the pressure increase moving the product to a different portion of the phase diagram—specifically, from the pressure at which solids transition by desublimation to gases to the pressure at which solids transition by melting to liquids. The energy source can be a melting device or a warm liquid. The melting device can be a resistance-style heater, or can be a hot liquid in a tube (any indirect-contact heat exchanger). The means by which the solids are passed into the vessel depend entirely upon the solids being passed, whether as fine ‘fluid-like’ solids, or suspended in slurries. Of special note are screw conveyors and peristaltic pumps. Each provides a benefit that traditional systems cannot. In the case of peristaltic pumps, solids are entirely blocked from backing up in the system, and so solids will not be forced backwards. In the case of screw conveyors, specialized filtering screw presses can be used that remove liquids from slurries before forcing the solids into the vessel for melting. 
     Referring now to the Figures,  FIG. 1  shows a process flow diagram  100  for melting solids that may be used in the described devices, systems, and methods. A slurry stream  150  is fed to a filtering screw press  104 . The slurry stream  150  consists of a liquid, such as, isopentane, and an entrained solid, such as carbon dioxide. The slurry stream  150  passes through filter screw press  104  and a backpressure on the slurry stream  150  from a solids inlet  116  causes substantially all the liquid to leave the filter screw press  104  as a contact liquid  154 . Any gas evolved in the filtering screw press  104  leaves as off-gas stream  152 . The solid stream  156 , now substantially pure solid carbon dioxide, passes through the solids inlet  116 . 
     The energy source in this example is a warm fluid stream  164  of liquid carbon dioxide. The warm fluid stream  164  passes through the vessel fluids inlet  118  into the vessel  102 . The inlet pressure of this warm fluid stream  164  from pump  110  contributes to the backpressure on the solid stream  156  in the solids inlet  116 , and therefore on the slurry stream  150  in the filter screw press  104 . As the warm fluid stream  164  encounters the solid stream  156 , the solid stream  156  is melted, resulting in a first product liquid stream  158 . The vessel outlet  120  is restricted, in this case downstream by valves  112  and  114 , such that an internal pressure is maintained in the cavity of the vessel  102 . The warm fluid stream  164  is pumped into the vessel  102  at a rate that matches the rate required to melt the solid stream  156  and at an inlet pressure that will maintain the internal pressure of the vessel  102  in a range that the solid stream  156  can transition directly from solid to liquid. Deviation from pressure can result in sublimation rather than melting, which can be dangerous and inefficient. Also, impurities, such as isopentane from the filter screw press  104 , can be introduced into the vessel  102  if the melting rate and pressure are not balanced. 
     The first product liquid stream  158  leaves through the vessel outlet  120  and is heated passing through a first heat exchanger  106 , resulting in a warmed product stream  160 . Warmed product stream  160  enters a gas-liquid separator  108 , splitting into a second product liquid stream  166  and a product gas stream  168 . Product liquid stream  166  leaves through valve  112  and product gas stream  168  leaves through valve  114 . A portion  162  of product liquid stream  166  is diverted through pump  110  and passed into the vessel  102  as the warm fluid  164 , as described above. 
     In other embodiments, a lesser amount of liquid may be removed from the filtering screw press  104 , resulting in some contamination of the product liquid stream  158  by the liquid. 
     Referring to  FIG. 2 ,  FIG. 2  shows an isometric side cutaway elevation view  200  of a vessel and screw press that may be used in the described devices, systems, and methods. In this example, the vessel and screw press may be used in the process of  FIG. 1 , and will be described accordingly. Vessel  102  includes the solids inlet  116 , the vessel fluids inlet  118 , and the vessel outlet  120 . Filtering screw press  104  includes a screw  236  with a rotor  237 , a slurry inlet  230 , a filter  238 , a gas outlet  232 , and a liquid outlet  234 . In this case, the outlet for the filtering screw press  104  is the solids inlet  116 . 
     The slurry  150  is conveyed through the filtering screw press  104  by screw  236 , driven by rotor  237 . The slurry  150  is pushed through the outlet, solids inlet  116 . Solids inlet  116  is restricted, in this case, an orifice, resulting in a first back-pressure on the slurry  150  in the screw press that drives the liquid out of the slurry and through the filter  238 . The liquid leaves out of the liquid outlet  234  as a substantially pure liquid stream  154 . Some portion of the liquid and the solid may leave in the gas phase through gas outlet  232 . The solid stream  156  passes through solids inlet  116  and is met by warm fluid stream  164 , which melts the solid stream  156  at the rate it enters the vessel  102 . The warm fluid stream  164  also provides a portion of the backpressure on the solids inlet. The resultant first product liquid stream  158  passes out the vessel outlet  120 , which is restricted, providing the internal pressure on the first product liquid stream  158 . 
     Referring to  FIG. 3 ,  FIG. 3  shows a process flow diagram  300  for melting solids that may be used in the described devices, systems, and methods. A solid stream  350  (e.g.,  150 ) is fed to a peristaltic pump  304 . The solid stream  350  is of a fine enough particle size that it can be made to “flow” through the peristaltic pump  304 . The resultant pressurized solid stream  356  ((e.g.,  156 ) passes through a reducer  317  and into the solids inlet  316  (e.g.,  116 ) into the vessel  302  (e.g.,  102 ). The reducer  317  causes a backpressure on the pressurized solid stream  356 . In this example, the solid stream  350  may be a mixture of frozen acid gases and the warm fluid stream  364  may be liquid carbon dioxide. Acid gases include carbon dioxide, nitrogen oxide, sulfur dioxide, nitrogen dioxide, sulfur trioxide, hydrogen sulfide, and other acidic gases. The solid stream  356  is melted by the heat from the melting device  344 , resulting in a first product liquid stream  358  (e.g.,  158 ). The vessel outlet  320  ((e.g.,  120 ) is restricted, in this case by a valve  312 , such that an internal pressure is maintained in the cavity of the vessel  302 , the internal pressure being such that the solid stream  356  can transition directly from solid to liquid. The melting device  344  provides heat at a rate that matches the rate required to melt the solid stream  356 . In some embodiments, the melting device  344  is a resistive heating element. In other embodiments, the melting device  344  is a tube through which a hot fluid is passed. 
     Referring to  FIG. 4 ,  FIG. 4  shows a process flow diagram  400  for melting solids that may be used in the described devices, systems, and methods. This method utilizes the energy sources of both  FIGS. 1 and 3 . A solid stream  456  (e.g.,  156 ,  356 ) is passed through a flow meter  444  into the vessel  402  (e.g.,  102 ,  302 ). A warm fluid stream  464  (e.g.,  164 ,  364 ) passes through the vessel fluids inlet  418  (e.g.,  118 ) into the vessel  402 . The inlet pressure of the warm fluid stream  464  produces a backpressure on the solid stream  456 . The flow meters  444  and  446  are shown as coriolis-style flow meters, but other flow meters may be used, as appropriate to the solid or fluid being measured. A melting device  440  provides a portion of the heat required for melting the solid stream  456 . The warm fluid stream  464  encounters the solid stream  456  and provides the balance of the heat needed to melt the solid stream  456 , resulting in a first product liquid stream  458  (e.g.,  158 ,  358 ). The vessel outlet  420  ((e.g.,  120 ,  320 ) is restricted, in this case by a valve  412  (e.g.,  312 ), such that an internal pressure is maintained in the cavity of the vessel  402 , the internal pressure being such that the solid stream  456  can transition directly from solid to liquid. The heating rate from the melting device  440  is controlled, along with the warm fluid stream  464  flow rate, to match the heating rate required to melt the solid stream  456 . In some embodiments, the melting device  440  may be a resistive heating element. In other embodiments, the melting device  440  may be a tube through which a hot fluid is passed. 
     Pressure transmitter  442  and temperature transmitter  444  measure pressure and temperature, respectively, in vessel  402 , and transmit the information to a process controller  446 . Flow meters  444  and  446  measure flow in their respective streams and transmit this information to the process controller  446 . Process controller  446  evaluates this information and then controls heating rates for melting device  440  and flow rates for solid stream  456  and warm liquid stream  464  and balances these against valve  412  to maintain pressure, temperature, and melting rate in vessel  402 . 
     Referring to  FIG. 5 ,  FIG. 5  shows an isometric side-front elevation view  500  of a vessel that may be used in the described devices, systems, and methods. In this example, the vessel may be used in the process of  FIG. 4 , and will be described accordingly. Vessel  502  includes solids inlet  416 , warm fluids inlets  418 , vessel outlet  420 , pressure transmitter  442 , melting device  440 , and temperature transmitter  444 . 
     Referring to  FIG. 6 ,  FIG. 6  shows a method  600  for melting solids that may be used in the described devices, systems, and methods. At  601 , solids are passed through a solids inlet into a vessel. The vessel includes the solids inlet, an energy source, a cavity, and a fluid outlet. At  602 , an energy device heats up the solids. At  603 , a backpressure is induced in the solids inlet. At  604 , the heating rate of the energy source is matched to the feed rate of the solids such that the solids are melted, producing a product liquid. At  605 , the fluid outlet is restricted such that an internal pressure is maintained in the cavity of the vessel, the internal pressure being such that the solids transition directly from solid to liquid. At  606 , the product liquid is bled out the fluid outlet past the restriction. 
     In some embodiments, the solid and the warm liquid are the same compound. In other embodiments, the solid or liquid stream may include impurities or be varying mixtures of compounds. 
     In some embodiments, the solids may include water, hydrocarbons, ammonia, solid acid gases, or a combination thereof, and wherein solid acid gases comprise solid forms of carbon dioxide, nitrogen oxide, sulfur dioxide, nitrogen dioxide, sulfur trioxide, hydrogen sulfide, or a combination thereof. 
     In some embodiments, the warm liquid may include water, hydrocarbons, liquid ammonia, liquid acid gases, cryogenic liquids, or a combination thereof, and wherein liquid acid gases comprise liquid forms of carbon dioxide, nitrogen oxide, sulfur dioxide, nitrogen dioxide, sulfur trioxide, hydrogen sulfide, or a combination thereof.