Abstract:
A batch process and apparatus for producing a pressurized liquid carbon dioxide stream includes distilling a feed stream of carbon dioxide vapor off of a liquid carbon dioxide supply; introducing the carbon dioxide vapor feed stream into at least one purifying filter; condensing the purified feed stream within a condenser to form an intermediate liquid carbon dioxide stream; introducing the intermediate liquid carbon dioxide stream into at least one high-pressure accumulation chamber; heating the high pressure accumulation chamber to pressurize the liquid carbon dioxide contained therein to a delivery pressure; delivering a pressurized liquid carbon dioxide stream from the high-pressure accumulation chamber; and, discontinuing delivery of the pressurized liquid carbon dioxide stream for replenishing the high pressure accumulation chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority from Provisional Patent Application No. 60/415,641 filed Oct. 2, 2002, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a method and apparatus for producing a purified and pressurized liquid carbon dioxide stream.  
       BACKGROUND  
       [0003]     Highly pressurized, purified liquid carbon dioxide is required for a variety of industrial processes. Such highly pressurized liquid is produced by purifying industrial grade liquid carbon dioxide that is available at about 13 to 23 bar (1.3 to 2.3 MPa) and then pumping the liquid to a pressure of anywhere from between about 20 and about 68 bar (2 to 6.8 MPa). The problem with pumping, however, is that impurities such as particulates or hydrocarbons can be introduced into the product stream as a byproduct of mechanical pump operation.  
         [0004]     U.S. Pat. No. 6,327,872, incorporated by reference herein, and assigned to The BOC Group, Inc., the assignee of the present application, is directed to a method and apparatus for producing a pressurized high purity liquid carbon dioxide stream in which a feed stream composed of carbon dioxide vapor is purified within a purifying filter and then condensed within a condenser. The resulting liquid is then alternately introduced and dispensed from two first and second pressure accumulation chambers on a continuous basis, in which one of the first and second pressure accumulation chambers acts in a dispensing role while the other is being filled.  
         [0005]     High purity CO 2  can be used for the cleaning of optical components using the solvation and momentum transfer effects of CO 2  when sprayed onto the optics. These benefits are achieved only if the purity of the CO 2  is very high and the CO 2  is delivered at a high pressure.  
       SUMMARY  
       [0006]     The present invention relates to a method and apparatus for producing a purified and pressurized liquid carbon dioxide stream in which a feed stream composed of carbon dioxide vapor is condensed into a liquid that is subsequently pressurized, such as by being heated within a chamber.  
         [0007]     A batch process is provided for producing a pressurized liquid carbon dioxide stream comprising:  
         [0008]     distilling a feed stream comprising carbon dioxide vapor off of a liquid carbon dioxide supply;  
         [0009]     introducing the carbon dioxide vapor feed stream into at least one purifying filter;  
         [0010]     condensing the purified feed stream within a condenser to form an intermediate liquid carbon dioxide stream;  
         [0011]     introducing the intermediate liquid carbon dioxide stream into at least one high-pressure accumulation chamber;  
         [0012]     heating said high pressure accumulation chamber to pressurize the liquid carbon dioxide contained therein to a delivery pressure; and,  
         [0013]     delivering a pressurized liquid carbon dioxide stream from the high-pressure accumulation chamber; and,  
         [0014]     discontinuing delivery of the pressurized liquid carbon dioxide stream for replenishing the high pressure accumulation chamber.  
         [0015]     The process may include venting the high-pressure accumulation chamber to the condenser to facilitate introduction of the intermediate liquid stream into the accumulation chamber. In certain embodiments, the intermediate liquid carbon dioxide stream is accumulated in a receiver prior to introduction into the high-pressure accumulation chamber, and in certain embodiments, the condenser is integral with the receiver.  
         [0016]     In one embodiment, the process includes passing the pressurized liquid carbon dioxide stream through a particle filter prior to delivery to a cleaning process.  
         [0017]     An apparatus is provided for producing a purified, pressurized liquid carbon dioxide stream comprising:  
         [0018]     a bulk liquid carbon dioxide supply tank for distilling off a feed stream comprising carbon dioxide vapor;  
         [0019]     a purifying filter for purifying the carbon dioxide vapor feed stream;  
         [0020]     a condenser for condensing the carbon dioxide vapor feed stream into an intermediate liquid carbon dioxide stream;  
         [0021]     a receiver for accumulating the intermediate liquid carbon dioxide stream;  
         [0022]     a high-pressure accumulation chamber for accepting the intermediate liquid carbon dioxide stream from the receiver;  
         [0023]     a heater for heating the high-pressure accumulation chamber for pressurizing the carbon dioxide liquid contained therein to a delivery pressure;  
         [0024]     a sensor for detecting when the high-pressure accumulation chamber requires replenishment of liquid carbon dioxide;  
         [0025]     a flow network having conduits connecting the bulk supply tank, the condenser, the receiver and the high-pressure accumulation chamber and for discharging said pressurized liquid carbon dioxide stream therefrom;  
         [0026]     the conduits of said flow network including a vent line from the high-pressure accumulation chamber to the condenser to facilitate introduction of the intermediate liquid carbon dioxide stream into the accumulation chamber; and, the flow network having valves associated with said conduits to allow for isolation of components of the apparatus.  
         [0027]     In one embodiment, a particle filter is connected to the flow network to filter the pressurized liquid carbon dioxide stream.  
         [0028]     In certain embodiments, the condenser includes an external refrigeration circuit having a heat exchanger to condense the vapor feed stream through indirect heat exchange with a refrigerant stream. In certain embodiments, the condenser is integral with the receiver. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]      FIG. 1  is a schematic view of an apparatus for carrying out the process according to one embodiment.  
         [0030]      FIG. 2  is a schematic view of an alternative embodiment of an apparatus for carrying out the process. 
     
    
     DETAILED DESCRIPTION  
       [0031]     An apparatus and process are provided including introducing a feed stream comprising carbon dioxide vapor into a purifying filter, such as for carrying out gas phase purification; condensing the purified CO 2  stream, such as by use of mechanical refrigeration or cryogenic refrigerants; isolating the high purity liquid CO 2 ; and, vaporizing a portion of the liquid CO 2 , such as by using a heater element, to achieve the target pressure.  
         [0032]     In one embodiment, the apparatus and process operating cycle is designed to maintain a continuous supply of high-pressure pure liquid carbon dioxide for a period up to about 16 hours, with about 8 hours to reset the system, that is, to replenish the high purity liquid carbon dioxide available for delivery. An example of the operating cycle and corresponding “Modes”, and the logic controlling the cycle of the system is presented below in Table 1.  
         [0033]     By way of example, in one embodiment, gaseous carbon dioxide is withdrawn from a bulk tank of liquid carbon dioxide, where single stage distillation purification occurs, removing a majority of the condensable hydrocarbons. From the bulk tank, the gaseous carbon dioxide passes through a coalescing filter, providing a second level of purification. The gaseous carbon dioxide is re-condensed in a low-pressure accumulator, providing the third level of purification by removing the non-condensable hydrocarbons. The low-pressure liquid is then transferred to a high-pressure accumulator. Once filled, an electric heater pressurizes the accumulator up to the desired pressure set-point. Upon reaching the pressure set point, the accumulator enters Ready mode (Mode 4, as in Table 1). In one embodiment, the process maintains high purity liquid carbon dioxide to the point of use for a period of up to about 16 hours. After the liquid has been expended, the system may return to Mode 1 and repeat the operating sequence.  
         [0034]     With reference to  FIG. 1 , a carbon dioxide purification and supply apparatus is shown generally at  1 . From a bulk supply of liquid carbon dioxide  10 , a feed stream  11  comprising carbon dioxide vapor is distilled in a first purification stage, and is introduced into a purifying particle filter  13  and a coalescing filter  14  which can be any of a number of known, commercially available filters, for a second stage purification. Valves  12  and  15  are provided to isolate the purifying filter(s)  13 , 14 . The bulk supply may be a tank of liquid CO 2  maintained at about 300 psig (2.1 MPa) and about 0° F. (−18° C.). As carbon dioxide vapor is drawn out of the bulk supply tank, a portion of the liquid carbon dioxide in the bulk tank is drawn through conduit  16  and introduced to a pressure build device  17  such as an electric or steam vaporizer or the like, to maintain the pressure relatively constant within the bulk supply tank even though carbon dioxide vapor is being removed. The vaporizer takes liquid CO 2  from the supply tank and uses heat to change the CO 2  from the liquid phase to the gas phase. The resulting CO 2  gas is introduced back into the headspace of the supply tank.  
         [0035]     The feed stream  11  after having been purified in the second stage is introduced into a condenser  18  that is provided with a heat exchanger  21  to condense the carbon dioxide vapor into a liquid  19 . Such condensation is effected by an external refrigeration unit  22  that circulates a refrigeration stream through the heat exchanger, preferably of shell and tube design. Isolation valves  28  and  29  can be provided to isolate refrigeration unit  22  and its refrigerant feed line  26  and return line  27 . The liquid carbon dioxide  19  is temporarily stored in a receiver vessel  20 , that is, a low pressure accumulator. The level of liquid in the receiver vessel  20  is controlled by a level sensor  44  (such as a level differential pressure transducer) and a pressure sensor  54  (such as a pressure transducer) via a controller (not shown), such as a programmable logic computer.  
         [0036]     An intermediate liquid stream comprising high purity CO 2  liquid  24  is introduced from the receiver vessel  20  into a high-pressure accumulation chamber  30 . The high-pressure accumulation chamber  30  is heated, for example, by way of an electrical heater  31 , to pressurize the liquid to a delivery pressure of the pressurized liquid carbon dioxide stream to be produced by apparatus  1 .  
         [0037]     An insulation jacket  23 , such as formed of polyurethane or the equivalent, can be disposed about the condenser  18 , the conduit for carrying the liquid CO 2    19 , the high pressure accumulation vessel  30 , and the outlet conduit  32  and associated valves to maintain the desired temperature of the liquid CO 2 .  
         [0038]     A valve network controls the flow within the apparatus  1 . In this regard, fill control valve  25  controls the flow of the intermediate liquid stream from the receiver vessel  20  to the high-pressure accumulation chamber  30 . Control of the flow of the high pressure liquid carbon dioxide through outlet conduit  32  is effected by product control valve  34 . Drain valve  33  also is connected to outlet conduit  32  for sampling or venting, as needed. The venting of the high-pressure accumulation chamber  30  via vent line (conduit)  51  to the condenser  18  is controlled by vent control valve  52 . A pressure relief line  55  from the condenser  18  to the receiver vessel  20  passes vapor from the receiver vessel  20  back to the condenser  18  as liquid carbon dioxide  19  enters the receiver vessel  20 .  
         [0039]     A pressure sensor  53  (such as a pressure transducer) monitors the pressure and a level sensor  45  (such as a level differential pressure transducer) monitors the level of liquid carbon dioxide within the high-pressure accumulation chamber  30  in order to control the heater  31  for vaporizing a portion of the liquid carbon dioxide, so that a desired pressure of the liquid carbon dioxide can be supplied therefrom. A temperature sensor (not shown) can monitor the liquid carbon dioxide temperature in the heater  31  or accumulation chamber  30 .  
         [0040]     The process has six operating sequences, or modes, for the high-pressure carbon dioxide accumulator (AC-1). The cycle logic controls the valves, heaters and refrigeration according to these modes. Table 1 lists the possible operation modes.  
                                           TABLE 1                           High-Pressure Accumulator Status Modes.            Mode   Designation   Description                    Offline   0   All valves closed, heaters off,               refrigeration off.       Vent   1   Depressurize accumulator 30 prior to               refilling with low-pressure liquid. Vent               valve 52 open. Fill valve 25 and product               valve 34 closed. Refrigeration on.       Fill   2   Filling accumulator 30 with low-               pressure liquid. Vent valve 52 and fill               valve 25 open. Product valve 34 closed.               Refrigeration on.       Pressurize   3   Pressurizing accumulator 30 up to the               set point (i.e. using electric immersion               heater 31). Vent, fill and product valves               closed.       Ready   4   System hold at pressure awaits               dispensing high pressure liquid. Vent,               fill and product valves closed.       Online   5   System supplying high-pressure liquid.               Product valve 34 open. Vent valve 52               and fill valve 25 closed.                  
 
         [0041]     High pressure carbon dioxide from the high pressure accumulator travels through outlet conduit  32  and may be again purified in a further purification stage by one of two particle filters  41  and  42 . The particle filters  41  and  42  can be isolated by valves  35 , 36  and  37 , 38  respectively, so that one filter can be operational while the other is isolated from the conduit by closure of its respective valves, for cleaning or replacement. The high pressure, purified liquid carbon dioxide stream  43  emerges from the final filtration stage for use in the desired process, such as cleaning of optic elements.  
         [0042]     The optical component to be processed is contacted with high purity CO 2  directly in a cleaning chamber, such that the contamination residue is dissolved and dislodged by the CO 2 . The liquid CO 2  may be supplied to the cleaning chamber at about 700 psig to about 950 psig (4.8 MPa to 6.6 MPa) or higher.  
         [0043]     When the high-pressure accumulation chamber  30  is near empty, as sensed by level sensor  45  and/or the pressure sensor  53 , vent control valve  52  opens to vent the high-pressure accumulation chamber. Fill control valve  25  opens to allow intermediate liquid stream  24  to fill the high-pressure accumulation chamber  30 . When the differential pressure sensor indicates the completion of the filling, control valves  25  and  52  close, and the liquid carbon dioxide is heated by electrical heater  31  to again pressurize the liquid within the high-pressure accumulation chamber  30 .  
         [0044]     Pressure relief valves  46 , 47 , 48  may be provided for safety purposes, in connection with the high-pressure accumulation chamber  30 , receiver vessel  20 , and condenser  18 , respectively.  
         [0045]     Other exemplary embodiment(s) of the apparatus are shown in  FIG. 2 . Elements shown in  FIG. 2  which correspond to the elements described above with respect to  FIG. 1  have been designated by corresponding reference numbers. The elements of  FIG. 2  are designed for use in the same manner as those in  FIG. 1  unless otherwise stated.  
         [0046]     With reference to  FIG. 2 , an alternative carbon dioxide purification and supply apparatus is shown generally at  2 . From a bulk supply of liquid carbon dioxide  10 , a feed stream  11  comprising carbon dioxide vapor is distilled in a first purification stage, and is introduced into a purifying particle filter  13  and a coalescing filter  14  which can be any of a number of known, commercially available filters, for a second stage purification. Valves  12  and  15  are provided to isolate the purifying filter(s)  13 , 14 .  
         [0047]     The feed stream  11  after having been purified in the second stage is introduced into the receiver vessel  20  that is provided with a heat exchanger  21  to condense the carbon dioxide vapor into a liquid. Such condensation is effected by an external refrigeration unit  22  that circulates a refrigeration stream through the heat exchanger, preferably of shell and tube design. Isolation valves  28  and  29  can be provided to isolate refrigeration unit  22  and its refrigerant feed line  26  and return line  27 . The liquid carbon dioxide is temporarily stored in the receiver vessel  20 , that is, a low pressure accumulator.  
         [0048]     As may be appreciated, since vapor is being condensed within receiver  20 , a separation of any impurities present within the vapor might be effected by which the more volatile impurities would remain in uncondensed vapor and less volatile impurities would be condensed into the liquid. Although not illustrated, sample lines might be connected to the receiver vessel  20  for sampling and drawing off liquid and vapor as necessary to lower impurity concentration within the receiver.  
         [0049]     An intermediate liquid stream comprising high purity liquid  24  is introduced into first and second pressure accumulation chambers  30   a  and  30   b . First and second pressure accumulation chambers  30   a  and  30   b  are heated, preferably by way of electrical heater  31 , to pressurize the liquid to a delivery pressure of the pressurized liquid carbon dioxide stream to be produced by apparatus  2 .  
         [0050]     A valve network controls the flow within the apparatus. In this regard, fill control valve  25  controls the flow of the intermediate liquid stream from the receiver  20  to the high-pressure accumulation chambers  30   a  and  30   b . Control of the flow of the high pressure liquid carbon dioxide through outlet conduit  32  is effected by product control valve  34 . Drain valve  33  also is connected to outlet conduit  32  for sampling or venting, as desired. The venting of the high-pressure accumulation chamber  30  via vent line (conduit)  51  to the condenser  18  is controlled by vent control valve  52 .  
         [0051]     First and second high pressure accumulation chambers  30   a  and  30   b  may be interconnected by conduit  39  without an isolation valve interposed there between, so that both act effectively as a single unit, at lower cost.  
         [0052]     A pressure sensor  53  (such as a pressure transducer) monitors the pressure and a level sensor  45  (such as a level differential pressure transducer) monitors the level of liquid carbon dioxide within the high-pressure accumulators  30   a  and  30   b  in order to control the heater  31  for vaporizing a portion of the liquid carbon dioxide, so that a desired pressure of the liquid carbon dioxide can be supplied therefrom.  
         [0053]     High pressure carbon dioxide from the high pressure accumulator travels through outlet conduit  32  and is again purified in a further purification stage by one of two particle filters  41  and  42 . The particle filters  41  and  42  can be isolated by valves  35 , 36  and  37 , 38  respectively, so that one filter can be operational while the other is isolated from the conduit by closure of its respective valves, for cleaning or replacement. The high pressure, purified liquid carbon dioxide stream  43  emerges from the final filtration stage for use in the desired process as described above. When the requirement for the purified carbon dioxide stream  43  is no longer needed, or can no longer be met, the apparatus begins a replenishment cycle. That is, after Mode 5 is complete, the system can return sequentially to Mode 1, Mode 2, and so on, as set forth in Table 1.  
         [0054]     Further features of the apparatus and process include a fully automated microprocessor controller which continuously monitors. system operation providing fault detection, pressure control and valve sequencing, ensuring purifier reliability, while minimizing operator involvement. By way of example and not limitation, level sensors  44 , 45 , pressure sensors  53 , 54 , and temperature sensors can provide information for the controller, in order to provide instructions to flow control valves  15 , 34 , 52 , or pressure relief valves  46 , 47 , 48 . The valves in the apparatus may be actuated pneumatically, by pulling a tap off of the CO 2  vapor conduit such as at valve  57 , to supply gas for valve actuation.  
         [0055]     The apparatus may include system alarms to detect potential hazards, such as temperature or pressure excursions, to ensure system integrity. Alarm and warning conditions may be indicated at the operator interface and may be accompanied by an alarm beeper. A human machine interface displays valve operation, operating mode, warning and alarm status, sequence timers, system temperature and pressure, heater power levels, and system cycle count.  
         [0056]     In summary, industrial grade CO 2  gas may be pulled off of the head space of a supply tank where the supply tank acts as a single stage distillation column (Stage 1). The higher purity gas phase is passed through at least a coalescing filter, reducing the condensable hydrocarbon concentration and resulting in a higher level of purity (Stage 2). Stage 3 includes a mechanical or cryogenic refrigeration system to effect a phase change from the gas phase back to the liquid phase. All non-condensable hydrocarbons and impurities are thus removed from the operative carbon dioxide liquid stream.  
         [0057]     The subject apparatus and process permits cyclic operation of the process, rather than continuous feed operation. The apparatus and process is also of a more economical design (by approximately half) due to the reduction from continuous or multi-batch to single batch operation. The apparatus and process is further of a more economical design than prior art systems, due to the omission of accessory equipment like boilers and condensers. The reduced footprint allows for location of the apparatus closer to the point of use, resulting in less liquid carbon dioxide boil-off.  
         [0058]     It will be understood that the embodiment(s) described herein is/are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the invention. All such modifications and variations are intended to be included within the scope of the invention as described herein. It should be understood that the embodiments described above are not only in the alternative, but can be combined.