Abstract:
An electrostatic spray drying system includes an electrostatic spray nozzle having a spray tip assembly arranged to discharge a supply of fluid into a drying chamber. The electrostatic spray nozzle is responsive to a duty cycle signal that determines periods at which the electrostatic spray nozzle is open to inject the fluid. A controller is programmed to activate a pulse width modulation (PWM) mode of operation for the electrostatic spray assembly, initiate a first timer, provide a first duty cycle signal to the electrostatic spray nozzle at a first PWM activation frequency while the first timer has not reached a first pulse duration, initiate a second timer when the first timer has reached the first pulse duration, and provide a second duty cycle signal to the electrostatic spray nozzle at a second PWM activation frequency while the second timer has not reached a second pulse duration.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims the benefit of U.S. Patent Application No. 62/250,318, filed Nov. 3, 2015, which is incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to spray dryers, and more particularly to an apparatus and methods for spray drying liquids into dry powder form. 
       BACKGROUND OF THE INVENTION 
       [0003]    Spray drying is a well known and extensively used process in which liquid slurries are sprayed into a drying chamber into which heated air is introduced for drying the liquid into powder. The slurry commonly includes a liquid, such as water, an ingredient, such as a food, flavor, or pharmaceutical, and a carrier. During the drying process, the liquid is driven off leaving the ingredient in powder form encapsulated within the carrier. Spray drying also is used in producing powders that do not require encapsulation, such as various food products, additives, and chemicals. 
         [0004]    Spray drying systems commonly are relatively massive in construction, having drying towers that can reach several stories in height. Not only is the equipment itself a substantial capital investment, the facility in which it is used must be of sufficient size and design to house such equipment. Heating requirements for the drying medium also can be expensive. 
         [0005]    While it is desirable to use electrostatic spray nozzles for generating electrically charged particles that facilitate quicker drying, due to the largely steel construction of such sprayer dryer systems, the electrostatically charged liquid can charge components of the system in a manner, particularly if unintentionally grounded, that can impede operation of electrical controls and interrupt operation, resulting in the discharge of uncharged liquid that is not dried according to specification. 
         [0006]    While it is known to form the drying chamber of electrostatic spray dryers of a non metallic material to better insulate the system from the electrically charged liquid, particles can adhere to and build up on the walls of the drying chamber, requiring time consuming cleanup which interrupts the use of the system. Moreover, very fine dried powder within the atmosphere of heating air in the drying chamber can create a dangerous explosive condition from an inadvertent spark or malfunction of the electrostatic spray nozzle or other components of the system. 
         [0007]    Such spray dryer systems also must be operable for spray drying different forms of liquid slurries. In the flavoring industry, for example, it may be necessary to operate the system with a citrus flavoring ingredient in one run, while a coffee flavoring ingredient is used in the next operation. Residual flavor material adhering to the walls of the drying chamber can contaminate the taste of subsequently processed products. In the pharmaceutical area, of course, it is imperative that successive runs of pharmaceuticals are not cross-contaminated. 
         [0008]    Existing spray dryer systems further have lacked easy versatility. It sometimes is desirable to run smaller lots of a product for drying that does not require utilization of the entire large drying system. It further may be desirable to alter the manner in which material is sprayed and dried into the system for particular applications. Still in other processing, it may be desirable that the fine particles agglomerate during drying to better facilitate ultimate usage, such as where more rapid dissolution into liquids with which it is used. Existing sprayers, however, have not lent themselves to easy alteration to accommodate such changes in processing requirements. 
         [0009]    Spray dryers further tend to generate very fine particles which can remain airborne in drying gas exiting the dryer system and which must be filtered from gas exiting the system. Such fine particulate matter can quickly clog filters, impeding efficient operation of the dryer and requiring frequent cleaning of the filters. Existing spray dryers also have commonly utilized complex cyclone separation and filter arraignments for removing airborne particulate matter. Such equipment is expensive and necessitates costly maintenance and cleaning. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0010]    It is an object of the present invention to provide a spray dryer system adapted for more efficient and versatile operation. 
         [0011]    Another object is to provide an electrostatic spray dryer system as characterized above that is relatively small in size and more reliable in operation. 
         [0012]    A further object is to provide such an electrostatic spray dryer that has a control effective for more efficiently controlling operation of the electrostatic spray nozzle for particular spray applications. A related object is to provide a spray dryer control of such type which is effective for enabling fine particles to agglomerate into desired form for specific applications. 
         [0013]    Still another object is to provide an electrostatic spray dryer system that is relatively short in height and can be installed and operated in locations without special building or ceiling requirements. 
         [0014]    A further object is to provide an electrostatic spray dryer system of the foregoing type that is effective for spray drying different product lots without cross-contamination. 
         [0015]    Yet another object is to provide an electrostatic spray dryer system of the above kind that is easily modifiable, both in size and processing techniques, for particular drying applications. 
         [0016]    Still another object is to provide an electrostatic spray dryer system that can be effectively operated with lesser heating requirements, and hence, more economically. A related object is to provide a spray dryer system of such type that is operable for effectively drying temperature sensitive compounds. 
         [0017]    Another object is to provide a modular electrostatic spray dryer system in which modules can be selectively utilized for different capacity drying requirements and which lends itself to repair, maintenance, and module replacement without shutting down operation of the spray dryer system. 
         [0018]    Yet another object is to provide an electrostatic spray dryer system of the above type that is less susceptible to electrical malfunctions and dangerous explosions from fine powder and the heating atmosphere within the drying chamber of the system. A related object is to provide a control for such spray dryer system that is effective for monitoring and controlling possible electrical malfunctions of the system. 
         [0019]    Another object is to provide a spray dryer system of such type which has a filter system for more effectively and efficiently removing airborne particulate matter from drying gas exiting the dryer and with lesser maintenance requirements. 
         [0020]    A further object is to provide a spray dryer system as characterized above in which the drying gas filter system includes means for automatically and more effectively removing the buildup of particulate matter on the filters. 
         [0021]    Still a further object is to provide such an electrostatic spray dryer system that is relatively simple in construction and lends itself to economical manufacture. 
         [0022]    Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a side elevational view of the powder processing tower of the illustrated spray dryer system; 
           [0024]      FIG. 2  is a vertical section of the powder processing tower shown in  FIG. 1 ; 
           [0025]      FIG. 3  is an exploded perspective of the illustrated powder processing tower; 
           [0026]      FIG. 3A  is a plan view of an unassembled flexible non-permeable liner usable with the illustrated powder processing tower; 
           [0027]      FIG. 3B  is a plan view of an alternative embodiment of a liner similar to that shown in  Fig. A1  but made of a permeable filter material; 
           [0028]      FIG. 3C  is a plan view of another alternative embodiment of liner, in this case made in part of a non-permeable material and in part of a permeable filter material, usable with the illustrated powder processing tower; 
           [0029]      FIG. 3D  is a plan view of another alternative embodiment of liner, in this case made of a non-permeable non-conductive rigid material, usable with the illustrated powder processing tower; 
           [0030]      FIG. 4  is an enlarged top view of the top cap or lid of the illustrated powder processing tower with an electrostatic spray nozzle centrally supported therein; 
           [0031]      FIG. 5  is a side view of the top cap and spray nozzle assembly shown in  FIG. 4 ; 
           [0032]      FIG. 6  is an enlarged vertical section of the illustrated electrostatic spray nozzle assembly; 
           [0033]      FIG. 7  is an enlarged fragmentary section of the nozzle supporting head of the illustrated electrostatic spray nozzle assembly; 
           [0034]      FIG. 8  is an enlarged fragmentary section of the discharge end of the illustrated electrostatic spray nozzle assembly; 
           [0035]      FIG. 8A  is a fragmentary section, similar to  FIG. 8 , showing the spray nozzle assembly with the discharge spray tip altered for facilitating spraying of more viscous liquids; 
           [0036]      FIG. 9  is a transverse section of the illustrated electrostatic spray nozzle assembly taken in the line of  9 - 9  in  FIG. 8 ; 
           [0037]      FIG. 10  is an enlarged fragmentary section of the powder collection cone and filter element housing of the illustrated powder processing tower; 
           [0038]      FIG. 10A  is an exploded perspective of the powder collection cone and filter element housing shown in  FIG. 10 ; 
           [0039]      FIG. 11  is a side elevational view, in partial section, of an alternative embodiment of filter element housing for use with the illustrated powder processing tower; 
           [0040]      FIG. 11A  is an enlarged fragmentary section of one of the filters of the filter housing shown in  FIG. 11 , showing a reverse gas pulse filter cleaning device thereof in an inoperative state; 
           [0041]      FIG. 11B  is an enlarged fragmentary section, similar to  FIG. 11A , showing the reverse gas pulse air filter cleaning device in an operating condition; 
           [0042]      FIG. 12  is a side elevational view of an alternative embodiment of a filter element housing and powder collection chamber; 
           [0043]      FIG. 12A  is a top plan view of the filter element housing and powder collection chamber shown in  FIG. 12 ; 
           [0044]      FIG. 12B  is an enlarged partial broken away view of the filter element housing and powder collection chamber shown in  FIG. 12 ; 
           [0045]      FIG. 12C  is an exploded perspective of the filter element housing and an associated upstream air direction plenum shown in  FIG. 12 ; 
           [0046]      FIG. 13  is a fragmentary section showing the fastening arrangement for securing the top cover to the drying chamber with an associated upper liner standoff ring assembly; 
           [0047]      FIG. 13A  is a fragmentary section, similar to  FIG. 12 , but showing the fastening arrangement for securing the drying chamber to the powder collection cone with an associated bottom liner standoff ring assembly; 
           [0048]      FIG. 14  is an enlarged fragmentary view of one of the illustrated fasteners; 
           [0049]      FIG. 15  is a schematic of the illustrated spray dryer system; 
           [0050]      FIG. 15A  is a schematic of an alternative embodiment of a spray dryer operable for spray chilling of melted flow streams into solidified particles; 
           [0051]      FIG. 16  is a fragmentary section showing the fluid supply pump and its associated drive motor for the illustrated spray drying system; 
           [0052]      FIG. 16A  is a vertical section of the illustrated fluid supply pump supported within an outer non-conductive housing; 
           [0053]      FIG. 17  is an enlarged top view of the illustrated insulting liner and its standoff ring support assembly; 
           [0054]      FIG. 18  is an enlarged top view, similar to  FIG. 17 , but showing a standoff ring assembly supporting a smaller diameter insulating liner; 
           [0055]      FIG. 19  is an enlarged side elevational view of the top cap of the illustrated powder processing tower supporting a plurality of electrostatic spray nozzle assemblies; 
           [0056]      FIG. 20  is a top view of the top cap shown in  FIG. 19 ; 
           [0057]      FIG. 21  is a vertical section of the illustrated powder processing tower, modified for supporting the electrostatic spray nozzle centrally adjacent a bottom of the drying chamber thereof for the upward direction of sprayed liquid for drying; 
           [0058]      FIG. 22  is a diagrammatic side elevational view of the bottom mounting support of the electrostatic spray nozzle assembly shown in  FIG. 21 ; 
           [0059]      FIG. 23  is a top view of the electrostatic spray nozzle assembly and bottom mounting support shown in  FIG. 22 ; 
           [0060]      FIG. 24  is an enlarged section of one of the support rods for the spray nozzle bottom mounting support shown in  FIGS. 22 and 23 ; 
           [0061]      FIG. 25  is a chart showing alternative configurations for the illustrative powder drying system; 
           [0062]      FIG. 25A  is a schematic of an alternative embodiment of a spray dryer system in which fresh nitrogen gas is introduced into the gas recirculation line of the system; 
           [0063]      FIG. 25B  is a schematic of another alternative embodiment of a spray dryer system that utilizes a cyclone separator/filter bag assembly for filtering particulate matter from a recirculating drying gas stream; 
           [0064]      FIG. 25C  is an alternative embodiment, similar to  FIG. 25B , and which dried fine particles separated in the cyclone separator are reintroduced into the drying chamber; 
           [0065]      FIG. 25D  is another alternative embodiment of the spray dryer system that has a plurality of fluid bed filters for filtering particulate matter from recirculating drying gas; 
           [0066]      FIG. 26  is a flowchart for a method of operating a voltage generator fault recovery method for use in an electrostatic spray dryer system in accordance with the disclosure; 
           [0067]      FIG. 27  is a flowchart for a method of modulating a pulse width in an electrostatic spray nozzle for use in an electrostatic spray dryer system in accordance with the disclosure; 
           [0068]      FIG. 28  is a top view, diagrammatic depiction of a modular spray dryer system having a plurality of powder processing towers; 
           [0069]      FIG. 29  is a front plan view of the modular spray dryer system shown in  FIG. 28 ; and 
           [0070]      FIG. 30  is a top view of the modular spray dryer system, similar to  FIG. 28 , but having additional powder processing towers. 
       
    
    
       [0071]    While the invention is susceptible of various modifications and alternative constructions, certain illustrative embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0072]    Referring now more particularly to the drawings, there is shown an illustrative spray drying system  10  in accordance with the invention which includes a processing tower  11  comprising a drying chamber  12  in the form of an upstanding cylindrical structure, a top closure arrangement in the form of a cover or lid  14  for the drying chamber  12  having a heating air inlet  15  and a liquid spray nozzle assembly  16 , and a bottom closure arrangement in the form of a powder collection cone  18  supported at the bottom of the drying chamber  12 , a filter element housing  19  through which the powder collection cone  18  extends having a heating air exhaust outlet  20 , and a bottom powder collection chamber  21 . The drying chamber  12 , collection cone  18 , filter element housing  19 , and powder collection chamber  21  all preferably are made of stainless steel. The top cover  14  preferably is made of plastic or other nonconductive material and in this case centrally supports the spray nozzle assembly  16 . The illustrated heating air inlet  15  is oriented for directing heated air into the drying chamber  12  in a tangential swirling direction. A frame  24  supports the processing tower  11  in upright condition. 
         [0073]    Pursuant to an important aspect of this embodiment, the spray nozzle assembly  16 , as best depicted in  FIGS. 6-9 , is a pressurized air assisted electrostatic spray nozzle assembly for directing a spray of electrostatically charged particles into the dryer chamber  12  for quick and efficient drying of liquid slurries into desired powder form. The illustrated spray nozzle assembly  16 , which may be of a type disclosed in the International application PCT/US2014/056728, includes a nozzle supporting head  31 , an elongated nozzle barrel or body  32  extending downstream from the head  31 , and a discharge spray tip assembly  34  at a downstream end of the elongated nozzle body  32 . The head  31  in this case is made of plastic or other non conductive material and formed with a radial liquid inlet passage  36  that receives and communicates with a liquid inlet fitting  38  for coupling to a supply line  131  that communicates with a liquid supply. It will be understood that the supply liquid may be any of a variety of slurries or like liquids that can be dried into powder form, including liquid slurries having a solvent, such as water, a desired ingredient, such as a flavoring, food, a pharmaceutical, or the like, and a carrier such that upon drying into powder form the desired ingredient is encapsulated within the carrier as known in the art. Other forms of slurries may also be used including liquids that do not include a carrier or require encapsulation of the dried products. 
         [0074]    The nozzle supporting head  31  in this case further is formed with a radial pressurized air atomizing inlet passage  39  downstream of said liquid inlet passage  36  that receives and communicates with an air inlet fitting  40  coupled to a suitable pressurized gas supply. The head  31  also has a radial passage  41  upstream of the liquid inlet passage  36  that receives a fitting  42  for securing a high voltage cable  44  connected to a high voltage source and having an end  44   a  extending into the passage  41  in abutting electrically contacting relation to an electrode  48  axially supported within the head  31  and extending downstream of the liquid inlet passage  36 . 
         [0075]    For enabling liquid passage through the head  31 , the electrode  48  is formed with an internal axial passage  49  communicating with the liquid inlet passage  36  and extending downstream though the electrode  48 . The electrode  48  is formed with a plurality of radial passages  50  communicating between the liquid inlet passage  36  and the internal axial passage  49 . The illustrated electrode  48  has a downstream outwardly extending radial hub  51  fit within a counter bore of the head  31  with a sealing o-ring  52  interposed there between. 
         [0076]    The elongated body  32  is in the form of an outer cylindrical body member  55  made of plastic or other suitable nonconductive material, having an upstream end  55   a  threadably engaged within a threaded bore of the head  31  with a sealing o-ring  56  interposed between the cylindrical body member  55  and the head  31 . A liquid feed tube  58 , made of stainless steel or other electrically conductive metal, extends axially through the outer cylindrical body member  55  for defining a liquid flow passage  59  for communicating liquid between the axial electrode liquid passage  49  and the discharge spray tip assembly  34  and for defining an annular atomizing air passage  60  between the liquid feed tube  58  and the outer cylindrical body member  55 . An upstream end of the liquid feed tube  58  which protrudes above the threaded inlet end  55   a  of the outer cylindrical nozzle body  55  fits within a downwardly opening cylindrical bore  65  in the electrode hub  51  in electrical conducting relation. With the electrode  48  charged by the high voltage cable  44 , it will be seen that liquid feed to the inlet passage  36  will be electrically charged during its travel through the electrode passage  49  and liquid feed tube  58  along the entire length of the elongated nozzle body  32 . Pressurized gas in this case communicates through the radial air inlet passage  39  about the upstream end of the liquid feed tube  58  and then into the annular air passage  60  between the liquid feed tube  58  and the outer cylindrical body member  55 . 
         [0077]    The liquid feed tube  58  is disposed in electrical contacting relation with the electrode  48  for efficiently electrically charging liquid throughout its passage from the head  31  and through elongated nozzle body member  32  to the discharge spray tip assembly  34 . To that end, the discharge spray tip assembly  34  includes a spray tip  70  having an upstream cylindrical section  71  in surrounding relation to a downstream end of the liquid feed tube  58  with a sealing o-ring  72  interposed therebetween. The spray tip  70  includes an inwardly tapered or conical intermediate section  74  and a downstream cylindrical nose section  76  that defines a cylindrical flow passage  75  and a liquid discharge orifice  78  of the spray tip  70 . The spray tip  70  in this case has a segmented radial retention flange  78  extending outwardly of the upstream cylindrical section  71  which defines a plurality of air passages  77 , as will become apparent. 
         [0078]    For channeling liquid from feed tube  58  into and though the spray tip  70  while continuing to electrostatically charge the liquid as it is directed through the spray tip  70 , an electrically conductive pin unit  80  is supported within the spray tip  70  in abutting electrically conductive relation to the downstream end of the feed tube  58 . The pin unit  80  in this case comprises an upstream cylindrical hub section  81  formed with a downstream conical wall section  82  supported within the intermediate conical section  74  of the spray tip  70 . The cylindrical hub section  81  is formed with a plurality of circumferentially spaced radial liquid flow passageways  83  ( FIG. 8 ) communicating between the liquid feed tube  58  and the cylindrical spray tip passage section  75 . It will be seen that the electrically conductive pin unit  80 , when seated within the spray tip  70 , physically supports in abutting relation the downstream end of the liquid feed tube  58 . 
         [0079]    For concentrating the electrical charge on liquid discharging from the spray tip, the pin unit  80  has a downwardly extending central electrode pin  84  supported in concentric relation to the spray tip passage  75  such that the liquid discharge orifice  78  is annularly disposed about the electrode pin  84 . The electrode pin  84  has a gradually tapered pointed end which extends a distance, such as between about ¼ and ½ inch, beyond the annular spray tip discharge orifice  78 . The increased contact of the liquid about the protruding electrode pin  84  as it exits the spray tip  70  further enhances concentration of the charge on the discharging liquid for enhanced liquid particle breakdown and distribution. 
         [0080]    Alternatively, as depicted in  FIG. 8A , when spraying more viscous liquids, the discharge spray tip assembly  34  may have a hub section  81 , similar to that described above, but without the downwardly extending central electrode pin  84 . This arrangement provides freer passage of the more viscous liquid through the spray tip, while the electrostatic charge to discharging liquid still enhances liquid breakdown for more efficient drying of such viscous liquids. 
         [0081]    The discharge spray tip assembly  34  further includes an air or gas cap  90  disposed about the spray tip  70  which defines an annular atomizing air passage  91  about the spray tip  70  and which retains the spray tip  70 , pin unit  80 , and liquid feed tube  58  in assembled conductive relation to each other. The air cap  90  in this instance defines a conical pressurized air flow passage section  91   a  about the downstream end of the spray tip  70  which communicates via the circumferentially spaced air passages  77  in the spray tip retention flange  78  with the annular air passage  60  between the liquid feed tube  58  and the outer cylindrical body member  55  for directing a pressurized air or gas discharge stream through an annular discharge orifice  93  about the spray tip nose  76  and liquid discharging from the spray tip liquid discharge orifice  78 . For retaining the internal components of the spray nozzle in assembled relation, the air cap  90  has an upstream cylindrical end  95  in threaded engagement about a downstream outer threaded end of the outer cylindrical member  55 . The air cap  90  has a counter bore  96  which receives and supports the segmented radial flange  78  of the spray tip  70  for supporting the spray tip  70 , and hence, the pin unit  80  and liquid feed tube  58  in electrical conducting relation with the upstream electrode  48 . 
         [0082]    The spray nozzle assembly  16  is operable for discharging a spray of electrostatically charged liquid particles into the drying chamber  12 . In practice, it has been found that the illustrated electrostatic spray nozzle assembly  16  may be operated to produce extremely fine liquid particle droplets, such as on the order of 70 micron in diameter. As will become apparent, due to the breakdown and repelling nature of such fine liquid spray particles and heated drying gas introduced into the drying chamber, both from the heating air inlet  15  and the air assisted spray nozzle assembly  16 , the liquid particles are susceptible to quick and efficient drying into fine particle form. It will be understood that while the illustrated electrostatic spray nozzle assembly  16  has been found to have particular utility in connection with the subject invention, other electrostatic spray nozzles and systems could be used, including electrostatic hydraulic rotary spray nozzles and high volume low pressure electrostatic spray nozzles of known types. 
         [0083]    Pursuant to a further important feature of the present embodiment, the drying chamber  12  has an internal non-metallic insulating liner  100  disposed in concentric spaced relation to the inside wall surface  12   a  of the drying chamber  12  into which electrostatically charged liquid spray particles from the spray nozzle assembly  16  are discharged. As depicted in  FIG. 2 , the liner has a diameter d less than the internal diameter d 1  of the drying chamber  12  so as to provide an insulating air spacing  101 , preferably at least about 2 inches (about 5 cm), with the outer wall surface  12   a  of the drying chamber  12 , but other dimensions may be used. In this embodiment, the liner  100  is non-structural preferably being made of a non-permeable flexible plastic material  100   a  ( FIGS. 3 and 3A ). Alternatively, as will become apparent, it may be made of a rigid non-permeable non-conductive material  100   c  ( FIG. 3D ), a permeable filter material  100   b  ( FIG. 3B ), or in part a non-permeable material  100   a  and in part a permeable filter material  100   b  ( FIG. 3C ). 
         [0084]    According to another aspect of the present embodiment, the processing tower  11  has a quick disconnect assembled construction that facilitates assembly and the mounting of the annular liner  100  in electrically insulated relation to the outer wall of the drying chamber  12 . To this end, the annular insulating liner  100  is supported at opposite ends by respective upper and lower standoff ring assemblies  104  ( FIGS. 1, 3, 13, 13A, 14 and 17 ). Each ring assembly  104  in this case includes an inner cylindrical standoff ring  105  to which an end of the liner  100  is attached and a plurality of circumferentially spaced non-conductive, polypropylene or other plastic, standoff studs  106  fixed in outwardly extended radial relation to the standoff ring  105 . In the illustrated embodiment, the upper end of the liner  100  is folded over the top of the standoff ring  105  of the upper ring assembly  104  and affixed thereto by an annular U configured rubber gasket  108  positioned over the folded end of the liner  100  and the standoff ring  105  ( FIG. 13 ). The lower end of the liner  100  is similarly trained about the bottom of the standoff ring  105  of the lower ring assembly  104  and secured thereto by a similar rubber gasket  108  ( FIG. 13 ). Similar rubber gaskets  108  also are supported on the opposite inner ends of the cylindrical standoff rings  105  of the ring assemblies  104  for protecting the liner  100  from damage by exposed edges of the standoff rings  105 . 
         [0085]    For securing each standoff ring assembly  104  within the drying chamber  12 , a respective mounting ring  110  is affixed, such as by welding, to an outer side of the drying chamber  12 . Stainless steel mounting screws  111  extend through aligned apertures in the mounting ring  110  and outer wall of the drying chamber  12  for threadably engaging the insulating standoff studs  106 . A rubber o-ring  112  in this instance is provided about the end of each standoff stud  106  for sealing the inside wall of the drying chamber  12 , and a neoprene bonded sealing washer  114  is disposed about the head of each retaining screw  111 . 
         [0086]    For securing the drying chamber top cover  14  in place on the drying chamber  12  in sealed relation to the upper standoff ring assembly  104 , an annular array  120  ( FIGS. 1 and 2 ) spaced releasable latch assemblies  121  are secured to the mounting ring  110  ( FIGS. 13-14 ) at circumferentially spaced locations intermediate the standoff studs  106 . The latch assemblies  121  may be of a known type having an upwardly extending draw hook  122  positionable over a top marginal edge of the cover  14  and drawn down into a locked position as an incident to downward pivotal movement of a latch arm  124  into a latching position for retaining the top cover  14  against the U-shaped gasket  108  about the upper edge of the standoff ring  105  and a similar large diameter annular U shaped gasket  126  about an upper edge of the cylindrical drying chamber  12 . The latch assemblies  121  may be easily unlatched by reverse pivotal movement of the latch hooks  124  to move the draw hooks  122  upwardly and outwardly for permitting removal of the top cover  14  when necessary. A similar annular array  120   a  of latch assemblies  121  is provided about a mounting ring  110  adjacent the bottom of the drying chamber  12 , in this case having draw hooks  124  positioned downwardly into overlying relation with an outwardly extending flange  129  of the collection cone  18  for retaining the flange  129  of the collection cone  18  in sealed relation with rubber gaskets  108 ,  126  about the bottom edge of the standoff ring  105  and the bottom cylindrical edge of the drying chamber  12  ( FIG. 13A ). It will be understood that for particular applications the liner  100 , o-rings and other sealing gaskets  108 , 126  may or may not be made of FDA compliant materials. 
         [0087]    During operation of the electrostatic spray nozzle assembly  16 , liquid supplied to the electrostatic spray nozzle assembly  16  from a liquid supply, which in this case is a liquid holding tank  130  as depicted in  FIG. 15 , is directed by the electrostatic spray nozzle assembly  16  into an effective drying zone  127  defined by the annular liner  100 . Liquid is supplied from the liquid supply holding tank  130  through a liquid supply or delivery line  131  connected to the liquid inlet fitting  38  of the spray nozzle assembly  16  via a pump  132 , which preferably is a peristaltic dosing pump having a liquid directing roller system operable in a conventional manner. The peristaltic dosing pump  132  in this case, as depicted in  FIG. 16A , comprises three plastic electrically isolated pump rollers  33  within a plastic pump housing  37 . The liquid supply or delivery line  131  in this case is an electrically shielded tubing, and the stainless steel drying chamber  12  preferably is grounded by an approved grounding line through the support frame  24  to which it is secured with metal to metal contact. 
         [0088]    An electronic controller  133  is operably connected to the various actuators and electric or electronic devices of the electrostatic spray dryer system such as an electric motor  134 , the pump  132 , the liquid spray nozzle assembly  16 , a high voltage generator providing electrical voltage to the high voltage cable  44 , and others, and operates to control their operation. While a single controller is shown, it should be appreciated that a distributed controller arrangement including more than one controller can be used. As shown, the controller  133  is capable of operating in response to a program such as a programmable logic controller. The various operable connections between the controller  133  and the various other components of the system are omitted from  FIG. 15  for clarity. 
         [0089]    Pursuant to a further aspect of the present embodiment, the pump  132  is operated by the electric motor  134  ( FIG. 16 ) disposed in electrically isolated relation to the pump  132  and the liquid supply line  131  coupling the pump  132  to the spray nozzle assembly  16  for preventing an electrical charge to the motor  134  from liquid electrostatically charged by the spray nozzle assembly  16 . To that end, the drive motor  134  has an output shaft  135  coupled to a pump head drive shaft  136  by a non-electrically conductive drive segment  138 , such as made of a rigid nylon, which isolates the pump  132  from the electric drive motor  134 . The nonconductive drive segment  138  in the illustrated embodiment has a diameter of about 1.5 inches (about 3.8 cm) and an axial length of about 5 inches (about 12.7 cm). The electric motor drive shaft  135  in this case carriers an attachment plate  139  which is fixed to the nonconductive drive segment  138  by screws  141 . The pump head drive shaft  136  similarly carries an attachment plate  140  affixed by screws  141  to the opposite end of the nonconductive drive segment  138 . 
         [0090]    An electrostatic voltage generator  222  is electrically connected to the nozzle assembly  16  via an electrical line  224  for providing a voltage that electrostatically charges the sprayed liquid droplets. In the illustrated embodiment, the electrical line  224  includes a variable resistor element  226 , which is optional and which can be manually or automatically adjusted to control the voltage and current provided to the spray nozzle assembly  16 . An optional grounding wire  228  is also electrically connected between the liquid supply line  131  and a ground  232 . The grounding wire  228  includes a variable resistor  230  that can be manually or automatically adjusted to control a voltage that is present in the fluid. In the illustrated embodiment, the grounding wire is placed before the pump  132  to control the electrical charge state of the fluid provided to the system. The system may further include sensors communicating the charged state of the fluid to the controller  133  such that the system may automatically monitor and selectively control the charge state of the liquid by controlling the resistance of the variable grounding resistor  230  to bleed charge off from the liquid line in the system. 
         [0091]    The drive motor  134 , which also is appropriately grounded, in this instance is supported within a nonconductive plastic motor mounting housing  144 . The illustrated liquid holding tank  130  is supported on a liquid scale  145  for enabling monitoring the amount of liquid in the tank  130 , and an electrical isolation barrier  146  is provided between the underside of the liquid holding tank  130  and the scale  145 . It will be understood that in lieu of the peristaltic pump  132 , plastic pressure pots and other types of pumps and liquid delivery systems could be used that can be electrically insulated from their electrical operating system. 
         [0092]    Pressurized gas directed to the atomizing air inlet fitting  18  of the spray nozzle assembly  16  in this case originates from a bulk nitrogen supply  150  which communicates with the atomizing air inlet fitting  18  of the spray nozzle assembly  16  via a gas supply line  151  ( FIG. 15 ). A gas heater  152  is provided in the supply line  151  for enabling dry inert nitrogen gas to be supplied to the spray nozzle assembly  16  at a controlled temperature and pressure. It will be understood that while nitrogen is described as the atomizing gas in connection with the present embodiment, other inert gases could be used, or other gasses with air could be used so long as the oxygen level within the drying chamber is maintained below a level that would create a combustive atmosphere with the dry powder particles within the drying chamber that is ignitable from a spark or other electrical malfunction of the electrostatic spray nozzle assembly or other electronically controlled elements of the drying system. 
         [0093]    Pursuant to a further important aspect of the present embodiment, heated nitrogen atomizing gas supplied to the spray nozzle assembly  16  and directed into the drying chamber  12  as an incident to atomization of liquid being sprayed into the drying chamber  12  is continuously recirculated through the drying chamber  12  as the drying medium. As will be understood with further reference to  FIG. 15 , drying gas introduced into the drying chamber  12  both from the drying gas inlet  15  and the spray nozzle assembly  16  will circulate the length of the drying chamber  12  efficiently drying the electrostatically charged liquid particles sprayed into the drying chamber  12  into powder form. The dried powder will migrate through the powder collection cone  18  into the powder collection chamber  21 , where it can be removed by appropriate means, either manually or by other automated means. 
         [0094]    The illustrated powder collection cone  18 , as best depicted in  FIGS. 10 and 10A , has an upper cylindrical section  155 , an inwardly tapered conical intermediate section  156 , and a lower cylindrical powder delivery section  158  that extends centrally through the filter element housing  19  for channeling dried powder into the powder collection chamber  21 . The filter element housing  19  in this case has a pair of vertically stacked annular HEPA filters  160  mounted in surrounding outwardly spaced relation to the lower sections of the powder collection cone  18 . The illustrated powder collection cone  18  has an outwardly extending radial flange  161  intermediate its ends positioned over the upper filter  160  in the filter element housing  19  with an annular seal  162  interposed between the radial flange  161  and the filter element housing  19 . While the bulk of the dried powder will fall downwardly through the collection cone  18  into the powder collection chamber  19 , only the finest particles will remain entrained in the drying gas as it migrates upwardly around the bottom sections of the powder collection cone  18  and then outwardly through the HEPA filters  160  which restrain and filter out the fine powder, prior to exiting through the exhaust gas outlet  20  of the filter housing  19 . 
         [0095]    Alternatively, as depicted in  FIGS. 11, 11A and 11B , a filter element housing  19   a  may be used that comprises a plurality of circumferentially spaced cylindrical filters  160   a  that are mounted in depending vertical relation from an intermediate transverse support panel  163  of a housing  19   a . Gas latent with powder particles directed from the collection cone  18  into a lower collection chamber flows transversely through the filters  160   a  into a common exhaust plenum  164  within the filter element housing  19   a  above the transverse support panel  163  for communication through an outlet port  20   a  with the particles being restricted from the air flow by the filters  160   a . For periodically cleaning the filters  160   a , the filters  160   a  each have a respective reverse pulse air filter cleaning device  167  of a type disclosed in U.S. Pat. No. 8,876,928 assigned to the same applicant as the present application, the disclosure of which is incorporated herein by reference. Each of the reverse pulse air filter cleaning devices  167  has a respective gas supply line  167   a  for coupling to a pulsed air supply. 
         [0096]    The illustrated the reverse pulse air filter cleaning devices  21 , as depicted in  FIGS. 11A and 11B , each includes a reverse pulse nozzle  240  having a gas inlet  241  in an upper wall of the exhaust plenum  164  fixed by an annular retainer  242  for connection to the compressed gas supply line  167   a  coupled to a pressurized gas source, such as nitrogen. The nozzle  240  has a cylindrical closed bottom construction which defines a hollow inner air passageway  244  extending from the inlet  241  through the exhaust plenum  164  and substantially the length of the filter  160   a . The nozzle  240  is formed with a plurality of relatively large diameter discharge holes  246  in a section within the exhaust plenum  164  and a plurality of smaller sized air discharge holes  248  in the length of the nozzle  240  within the filter  160   a.    
         [0097]    For interrupting the flow of process gas from the filter element housing  19   a  to the exhaust plenum  164  during operation of the reverse pulse nozzle  240 , an annular exhaust port cut off plunger  249  is disposed above the reverse pulse nozzle  160   a  for axial movement within the exhaust plenum  164  between exhaust port opening and closing positions. For controlling movement of the plunger  249 , a bottom opening plunger cylinder  250  is mounted in sealed depending relation from the upper wall of the exhaust plenum  164 . The illustrated plunger  249  includes an upper relatively small diameter annular sealing and guide flange  252  having an outer perimeter adapted for sliding sealing engagement with the interior of the cylinder  250  and a lower larger diameter valve head  254  disposed below the lower terminal end of the cylinder  250  for sealing engagement with an exhaust port  253  in the panel  163 . The plunger  249  preferably is made of a resilient material, and the upper sealing and guide flange  252  and lower valve head  254  have downwardly tapered or cup shaped configurations. 
         [0098]    The plunger  249  is disposed for limited axial movement along the reverse pulse nozzle  240  and is biased to a normally open or retracted position, as shown in  FIG. 3 , by coil spring  256  fixed about the outer perimeter of the reverse pulse nozzle  240 . With the valve plunger  249  biased to such position, process gas flows from the filter element housing  19   a  through the filter  160   a , exhaust port  253  and into the exhaust plenum  164 . 
         [0099]    During a reverse pulse gas cleaning cycle, a pulse of compressed gas is directed through the reverse pulse nozzle  240  from the inlet line  167   a . As the compressed gas travels through the nozzle  160   a , it first is directed through the larger diameter or plunger actuation holes  246  into the plunger cylinder  250  above the plunger sealing and guide flange  252  and then though the smaller reverse pulse nozzle holes  248 . Since the larger holes  249  provide the path of less resistance, gas first flows into the plunger cylinder  250  and as pressure in the plunger cylinder  250  increases, it forces the plunger  249  downwardly against the biasing force of the spring  256 . Eventually, the pressure builds to a point where it overcomes the force of the spring  256  and forces the plunger  249  downwardly toward the exhaust port  253  temporarily sealing it off After the plunger  249  seals the exhaust port  253  the compressed gas in the outer plunger cylinder  250  can no longer displace the plunger  249  and gas pressure in the plunger cylinder  250  increases to a point that the compressed gas is then forced through the smaller nozzle holes  248  and against the filter  160   a  for dislodging build up particulate matter about its outside surface. 
         [0100]    Following the reverse compressed air pulse and the dislodgement of the accumulated particulate on the filter  160   a , pressure will dissipate within the plunger cylinder  250  to the extent that it will no longer counteract the spring  256 . The plunger  249  then will move upwardly under the force of the spring  256  to its retracted or rest position, unsealing the exhaust port  253  for continued operation of the dryer. 
         [0101]    Still another alternative embodiment of an exhaust gas filter element housing  270  and powder collection chamber  271  mountable on a lower end of the drying chamber  12  is depicted  FIGS. 12-12B . In this case, an upper powder direction plenum  272  is mountable on an underside of the elongated drying chamber  12 , the filter element housing  270  includes a plurality of vertically oriented cylindrical filters  274  and is disposed below the powder direction plenum  272 , a powder direction cone  275  is coupled to the underside of the filter element housing  270 , and the powder collection chamber  271  is supported on an underside of the powder direction cone  275 . 
         [0102]    The illustrated powder direction plenum  272  comprises an outer cylindrical housing wall  289  mountable in sealed relation to an underside of the drying chamber  12  and having an open upper end for receiving drying gas and powder from the drying chamber  12  and drying zone  127 . Housed within the powder direction plenum  272  is a downwardly opening conically configured exhaust plenum  281  which defines on its underside an exhaust chamber  282  ( FIG. 12B ) and on its upper side directs drying gas and powder from the drying chamber  12  downwardly and outwardly around an outer perimeter of the conical exhaust plenum  281 . 
         [0103]    The filter element housing  270  comprises an outer cylindrical housing wall  284  mounted in sealed relation by means of an annular seal  285  to a bottom peripheral edge of the powder direction plenum  272  and an inner cylindrical filter shroud  286  mounted in sealed relation by means of an annular seal  288  to the bottom peripheral edge of the conical exhaust plenum  281 . The conical exhaust plenum  281  and the inner cylindrical filter shroud  286  are supported within an outer cylindrical housing wall  289  of the gas directing plenum  272  and filter element housing  270  by the plurality of radial supports  290  ( FIG. 12A ) so as to define air passageways  291  communicating about the bottom perimeter of the conical exhaust plenum  281  and an annular gas passageway  292  between the inner cylindrical filter shroud  286  and outer cylindrical housing wall  284  such that gas and powder passing through the powder direction plenum  272  is directed by the conical exhaust plenum  281  outwardly about the filter element shroud  281  into the underlying powder direction cone  275  and collection chamber  271 . 
         [0104]    The cylindrical filters  274  in this case are supported in depending relation to a circular support plate  295  fixedly disposed below the underside of the downwardly opening conical exhaust plenum  281 . The circular filter support plate  295  in this case is mounted in slightly recessed relation to an upper perimeter of the cylindrical shroud  286  and defines a bottom wall of the exhaust chamber  282 . The illustrated cylindrical filters  274  each are in cartridge form comprising a cylindrical filter element  296 , an upper cylindrical cartridge holding plate  298 , a bottom end cap and sealing plate  299  with interposed annular sealing elements  300 ,  301 ,  302 . For securing the filter cartridges in assembled relation, the upper cartridge holding plate  298  has a depending U-shaped support member  304  with a threaded lower end stud  305  positionable through a central aperture in the bottom end cap  299  which is secured by a nut  306  with a o-ring sealing ring  308  interposed therebetween. The upper holding plate  298  of each filter cartridge is fixed in sealed relation about a respective circular opening  310  in the central support plate  295  with the filter element  296  disposed in depending relation to an underside of the support plate  295  and with a central opening  311  in the holder plate  298  communicating between the exhaust chamber  282  and the inside of the cylindrical filter element  296 . The filter element cartridges in this case are disposed in circumferentially spaced relation about a center of the inner shroud  274 . 
         [0105]    The filter element housing  270  in this instance is secured to the powder direction plenum  272  by releasable clamps  315  or like fasteners to permit easy access to the filter cartridges. The inner filter shroud  286  also is releasably mounted in surrounding relation to the cylindrical filters  274 , such as by a pin and slot connection, for enabling access to the filters for replacement. 
         [0106]    During operation of the dryer system, it will be seen that drying gas and powder directed into the powder direction plenum  272  will be channeled about the conical exhaust plenum  281  into the annular passageways  291 ,  292  about the inner filter element shroud  274  downwardly into the powder direction cone  275  and collection chamber  271  for collection in the chamber  271 . While most of the dried powder remaining in the gas flow will migrate into the powder collection chamber  271 , as indicated previously, fine gas borne particulate matter will be separated and retained by the annular filters  274  as the drying gas passes through the filters into the drying gas exhaust plenum  282  for exit through a drying gas exhaust port  320  and recirculation to the drying chamber  12 , as will be become apparent. 
         [0107]    For cleaning the cylindrical filters  274  of buildup of powder during the course of usage of the dryer system, the cylindrical filters  274  each have a respective reverse gas pulse cleaning device  322 . To this end, the gas direction plenum  272  in this case has an outer annular pressurized gas manifold channel  321  coupled to a suitable pressurized air supply. Each reverse air pulse cleaning device  322  has a respective pressurized gas supply line  325  coupled between the annular pressurized gas manifold channel  321  and a respective control valve  326 , which in this case mounted on an outer side of the air direction plenum  272 . A gas pulse direction line or tube  328  extends from the control valve  326  radially through the air direction plenum  272  and the conical wall of the exhaust plenum  329  and then with a right angle turn downwardly with a terminal discharge end  329  of the gas pulse directing line  328  disposed above and in aligned relation to the central opening  311  of the filter cartridge holding plate  298  and underlying cylindrical filter element  296 . 
         [0108]    By appropriate selective or automated control of the control valve  326 , the control valve  26  can be cyclically operated to discharge pulses of the compressed gas from the line  328  axially into the cyclical filter  274  for dislodging accumulated powder on the exterior wall of the cylindrical filter element  296 . The discharge end  329  of the pulse gas directing line  328  preferably is disposed in spaced relation to an upper end of the cyclical filter  274  to facilitate the direction of compressed gas impulses into the filter element  296  while simultaneously drawing in gas from the exhaust chamber  282  which facilitates reverse flow impulses that dislodge accumulated powder from the filter element  296 . Preferably the discharge end  329  of the air tube  328  is spaced a distance away from the upper end of the cylindrical filter element such that the expanding air flow, depicted as  330  in  FIG. 12B , upon reaching the filter cartridge, has an outer perimeter corresponding substantially to the diameter of the central opening  311  in the cartridge holding plate  298 . In the exemplary embodiment, the air direction tube  28  has a diameter of about one inch and the discharge end  329  is spaced a distance of about two and a half inches from the holding plate  298 . 
         [0109]    The powder collection chamber  271  in this case has a circular butterfly valve  340  (shown in  FIG. 12B  in breakaway fashion within the powder collection chamber  271 ) mounted at an upper end of the collection chamber  271  operable by a suitable actuating device  341  for rotatable movement between a vertical or open position which allows dried powder to be directed into the collection chamber  271  and a horizontal closed position which blocks the passage of dried powder into the collection chamber  271  when powder is being removed. Alternatively, it will be understood that the powder collection chamber  271  could deposit powder directly onto a moveable conveyor from an open bottom end. 
         [0110]    For enabling recirculation and reuse of the exiting drying gas from the filter element housing  19   a , the exhaust outlet  20  of the filter housing  19  is coupled to a recirculation line  165  which in turn is connected to the heating gas inlet port  15  of the top cover  14  of the heating chamber  12  through a condenser  166 , a blower  168 , and a drying gas heater  169  ( FIG. 15 ). The condenser  170  removes any water vapor from the exhaust gas flow stream by means of cold water chilled condensing coils  170   a  having respective cold water supply and return lines  171 ,  172 . Condensate from the condenser  170  is directed to a collection container  174  or to a drain. Dried nitrogen gas is then directed by the blower  168  through the gas heater  169  which reheats the drying gas after cooling in the condenser  170  to a predetermined heated temperature for the particular powder drying operating for redirection back to the heating gas inlet port  15  and into the heating chamber  12 . An exhaust control valve  175  coupled to the recirculation line  165  between the blower  168  and the heater  169  allows excess nitrogen gas introduced into the system from the electrostatic spray nozzle assembly  16  to be vented to an appropriate exhaust duct work  176 . The exhaust flow from the control valve  175  may be set to match the excess nitrogen introduced into the drying chamber  12  by the electrostatic spray nozzle assembly  16 . It will be appreciated that by selective control of the exhaust flow control valve  175  and the blower  168  a vacuum or pressure level in the drying chamber  12  can be selectively controlled for particular drying operations or for the purpose of controlling the evaporation and exhaust of volatiles. While a cold water condenser  170  has been shown in the illustrated embodiment, it will be understood that other types of condensers or means for removing moisture from the recirculating gas flow stream could be used. 
         [0111]    It will be appreciated that the drying gas introduced into the effective drying zone  127  defined by the flexible liner  100  both from the electrostatic spray nozzle assembly  16  and the drying gas inlet port  15 , is a dry inert gas, i.e. nitrogen in the illustrated embodiment, that facilitates drying of the liquid particles sprayed into the drying chamber  12  by the electrostatic spray nozzle assembly  16 . The recirculation of the inert drying gas, as described above, also purges oxygen from the drying gas so as to prevent the chance of a dangerous explosion of powder within the drying chamber in the event of an unintended spark from the electrostatic spray nozzle assembly  16  or other components of the system. 
         [0112]    Recirculation of the inert drying gas through the spray drying system  10 , furthermore, has been found to enable highly energy efficient operation of the spray drying system  10  at significantly lower operating temperatures, and correspondingly, with significant cost savings. As indicated previously, emulsions to be sprayed typically are made of three components, for example, water (solvent), starch (carrier) and a flavor oil (core). In that case, the object of spray drying is to form the starch around the oil and dry off all of the water with the drying gas. The starch remains as a protective layer around the oil, keeping it from oxidizing. This desired result has been found to be more easily achieved when a negative electrostatic charge is applied to the emulsion before and during atomization. 
         [0113]    While the theory of operation is not fully understood, each of the three components of the sprayed emulsion has differing electrical properties. Water being the most conductive of the group, will easily attract the most electrons, next being the starch, and finally oil being the most resistive barely attracts electrons. Knowing that opposite charges attract and like charges repel, the water molecules, all having the greatest like charge, have the most repulsive force with respect to each other. This force directs the water molecules to the outer surface of the droplet where they have the greatest surface area to the drying gas which enhances the drying process. The oil molecules having a smaller charge would remain at the center of the droplet. It is this process that is believed to contribute to more rapid drying, or drying with a lower heat source, as well as to more uniform coating. Testing of the spray dried powder produced by the present spray drying system operated with an inlet drying gas temperature of 90 degrees C. found the powder comparable to that dried in conventional spray drying processes operable at 190 degrees C. Moreover, in some instances, the subject spray drying system can be effectively operated without heating of the drying gas. 
         [0114]    Encapsulation efficiency, namely the uniformity of the coating of the dried powder, also was equal to that achieved in higher temperature spray drying. It further was found that lower temperature drying significantly reduced aromas, odors and volatile components discharged into the environment as compared to conventional spray drying, further indicating that the outer surface of the dried particle was more uniformly and completely formed of starch. The reduction of discharging aromas and odors further enhances the working environment and eliminates the need for purging such odors that can be irritating and/or harmful to operating personnel. Lower temperature processing also enables spray drying of temperature sensitive components (organic or inorganic) without damage or adversely affecting the compounds. 
         [0115]    If during a drying process any particles may stick or otherwise accumulate on the surface of the liner  100 , a liner shaking device is provided for periodically imparting shaking movement to the liner  100  sufficient to remove any accumulated powder. In the illustrated embodiment, the drying chamber  12  has a side pneumatic liner shake valve port  180  which is coupled to a pneumatic tank  181  that can be periodically actuated to direct pressurized air through the pneumatic liner shake valve port  180  and into the annular air space between the liner  100  and the outer wall of the drying chamber  12  that shakes the flexible liner  100  back and forth with sufficient force to dislodge any accumulated powder. Pressurized air preferably is directed to the pneumatic liner shake valve port  180  in a pulsating manner in order to accentuate such shaking motion. Alternatively, it will be understood that mechanical means could be used for shaking the liner  100 . 
         [0116]    In order to ensure against cross contamination between successive different selective usage of the spray dryer system, such as between runs of different powders in the drying chamber  12 , the annular arrays  120 ,  120   a  of quick disconnect fasteners  121  enable disassembly of the cover  14  and collection cone  18  from the drying chamber  12  for easy replacement of the liner  100 . Since the liner  100  is made of relatively inexpensive material preferably it is disposable between runs of different powders, with replacement of a new fresh replacement liner being affected without undue expense. 
         [0117]    In keeping with another important feature of this embodiment, the drying chamber  12  is easily modifiable for different spray drying requirements. For example, for smaller drying requirements, a smaller diameter liner  100   a  may be used to reduce the size of the effective drying zone. To that end, standoff ring assemblies  104   a  ( FIG. 18 ), similar to that described above, but with a smaller diameter inner standoff rings  105   a , can be easily substituted for the larger diameter standoff ring assembly  104 . The substitution of the ring assemblies may be accomplished by unlatching the circumferentially spaced arrays  120 ,  120   a  of latches  121  for the top cover  14  and collection cone  18 , removing the larger diameter ring assemblies  104  from the drying chamber  12 , replacing them with the smaller diameter ring assemblies  104   a  and liner  100   a , and reassembling and relatching the top cover  14  and collection cone  18  onto the drying chamber  12 . The smaller diameter liner  100   a  effectively reduces the drying zone into which heated drying gas and atomizing gas is introduced for enabling both quicker and more energy efficient smaller lot drying. 
         [0118]    In further enabling more efficient drying of smaller lot runs, the drying chamber  12  has a modular construction that permits reducing the length of the drying chamber  12 . In the illustrated embodiment, the drying chamber  12  comprises a plurality, in this case two, vertical stacked cylindrical drying chamber modules or sections  185 ,  186 . The lower chamber section  186  is shorter in length than the upper chamber section  185 . The two cylindrical drying chamber sections  185 ,  186  again are releasably secured together by an array  102   b  of circumferentially spaced quick disconnect fasteners  121  similar to those described above. The mounting ring  110  for this array  102   b  of fasteners  121  is welded to the upper cylindrical drying chamber section  185  adjacent the lower end thereof and the fasteners  121  of that array  102   b  are oriented with the draw hooks  122  downwardly positioned for engaging and retaining an underside of a top outer radial flange  188  ( FIGS. 1 and 2 ) of the lower cylindrical drying chamber section  186 . Upon release of the two arrays  102   a ,  102   b  of fasteners  121  affixing the lower cylindrical section  186  to the upper cylindrical section  185  and the collection cone  18 , the lower cylindrical section  186  can be removed, the lower standoff ring assembly  104  repositioned adjacent the bottom of the upper chamber section  185 , and the liner  100  replaced with a shorter length liner. The upper cylindrical dryer chamber section  185  can then be secured directly onto the powder collection cone  18  with the lower standoff ring assembly  104  therebetween by the fasteners  121  of the array  102   b  which then engage the outer annular flange  129  of the collection cone  18 . This modification enables use of a substantially shorter length effective drying zone for further reducing heating requirements for smaller lot drying. 
         [0119]    It will be appreciated that additional cylindrical drying chamber modules or sections  186  could be added to further increase the effective length of the drying chamber  12 . For increasing the quantity sprayed liquid into the drying chamber  12 , whether or not increased in size, a plurality of electrostatic spray nozzle assemblies  16  can be provided in the top cover  14 , as depicted in  FIGS. 19 and 20 . The plurality of spray nozzle assemblies  16 , which may be supplied from the common liquid and nitrogen supplies, preferably are supported in a circumferential spaced relation to each other in respective, previously capped, amounting apertures  190  in the top cover  14  ( FIG. 4 ). The then unused central mounting aperture  192  ( FIG. 20 ) may be appropriately capped or otherwise closed. 
         [0120]    According to still another feature of this embodiment, the modular quick disconnect components of the drying tower  11  further enables relocation of the electrostatic spray nozzle assembly  16  from a position on top of the drying chamber  12  for downward spraying to a position adjacent a bottom of the drying chamber  12  for the upward direction of an electrostatically charged liquid spray into the drying chamber  12 . To this end, the spray nozzle assembly  16  may be removed from the top cover  14  and secured in a bottom spray nozzle mounting support  195  ( FIGS. 21-24 ), which in this case is mounted within the upper cylindrical wall section  155  of the powder collection cone  18  immediately adjacent the bottom of the drying chamber  12  for orienting the electrostatic spray nozzle assembly  16  for spraying charged spray pattern upwardly into the drying chamber  12 , as depicted in  FIG. 21 . The illustrated bottom nozzle mounting support  195 , as depicted in  FIGS. 22-24 , includes a central annular mounting hub  196  for supporting the spray nozzle assembly  16  adjacent an upstream end which, in turn, is supported in the upper cylindrical section  155  of the powder collection cone  18  by a plurality of radial mounting rods  198  made of a non-conductive material. The radial mounting rods  198  each are secured to the cylindrical wall section  155  by respective stainless steel screws  199  ( FIG. 24 ) with a rubber bonded sealing washing  200  between the head of the screw  199  and the outer wall surface of the powder collection cone  18  and a sealing o-ring  201  is interposed between the outer end of each mounting rod  198  and the inside wall surface of the powder collection cone section  18 . Non-conductive Teflon or other plastic liquid and atomizing gas supply lines  205 ,  206  respectively connect radially outwardly to insulated fittings  208 ,  209  by powder collection cone  18 , which in turn are connected to the atomizing air and liquid supply lines  151 ,  131 . A high voltage power cable  210  also connects radially with the nozzle assembly through an insulated fitting  211 . 
         [0121]    With the electrostatic spray nozzle assembly  16  mounted adjacent the underside of the drying chamber  12 , a central spray nozzle mounting aperture  192  in the cover  14  may be appropriately capped, as well as the gas inlet port  15 . The powder collection cone  18  further has a tangentially oriented drying gas inlet  215 , which may be uncapped and connected to the drying gas recirculation line  165 , and the cover  14  in this case has a pair of exhaust ports  216  which also may be uncapped for connection to the heating gas return line. 
         [0122]    With the spray nozzle assembly  16  mounted on the underside of the drying chamber  12 , electrostatically charged liquid spray particles directed upwardly into the drying chamber  12  are dried by drying gasses, which in this case are tangentially directed through the bottom heating gas inlet  215  and by heating atomizing gas from the spray nozzle assembly  16 , which again both are dry inert gas, i.e. nitrogen. 
         [0123]    Pursuant to this embodiment, the annular liner  100  in the drying chamber  12  preferably is made of a filter media  100   b  ( FIG. 3B ) for enabling the drying gas to ultimately migrate through the filter media for exit out from the upper exhaust ports  216  in the cover  14  to the recirculation line  165  for recirculation, reheating, and redirection to the bottom gas inlet port  215 , as explained above. The powder dried by the upwardly directed drying gas and atomizing gas will ultimately float downwardly into and through the powder collection cone  18  into the collection chamber  19 , as described above, with only the finest particles being filtered by the filter media liner  100 . The pneumatic liner shaker again may be periodically actuated to prevent the accumulation of powder on the liner  100 . 
         [0124]    From the foregoing, it can be seen that the processing tower can be easily configured and operated in a variety of processing modes for particular spray applications, as depicted in the table  220  in  FIG. 25 . The drying chamber length may be electively changed by adding or removing the cylindrical dryer chamber section  186 , the material of the liner may be selectively determined, such as non-permeable or permeable, the electrostatic spray nozzle orientation may be changed between top spraying downwardly or bottom spraying upwardly, and the processed gas flow direction can be changed between downward or upward directions based upon the desired configuration. 
         [0125]    While in the foregoing embodiments, nitrogen or other inert drying gas, is introduced into the system as atomizing gas to the electrostatic spray nozzle assembly  16 , alternatively, the nitrogen gas could be introduced into the recirculating gas. In the spray dry system as depicted in  FIG. 25A , wherein parts similar to those described above have been given similar references numerals to those described above, nitrogen or other inert gas is introduced into the gas heater  169  from a nitrogen injection line  169   a  for direction to the drying chamber  100  via the gas delivery and supply line  169   a  and recirculation from the drying chamber  100  through the condenser  170 , and blower  168  as described previously. In that embodiment, nitrogen gas can also be supplied to the electrostatic spray nozzle assembly  16  as atomizing gas, as described above, or air, or a combination of an inert gas and air, can be supplied to the electrostatic spray nozzle assembly  16  as the atomizing gas so long as it does not create a combustive atmosphere within the drying chamber. Operation of the drying system depicted in  FIG. 25A  otherwise is the same as in previously described. 
         [0126]    With reference to  FIG. 25B , there is shown another alternative embodiment drying system similar to that described above, except that a powder collection cone  18   a  directs powder to a conventional cyclone separator/filter bag housing  19   a  in which dried product is discharged from a lower outlet  19   b  and exhaust air is directed from an upper exhaust port line  165  for recirculation through the condenser  170 , the blower  168 , drying gas heater  169  and the drying chamber  11 . In  FIG. 25C , there is shown an alternative embodiment of drying system similar to that shown in  FIG. 25B  but with a fine powder recirculation line  19   c  between the cyclone separator and filter bag housing  19   a  and the upper end of the drying chamber  11 . Dried fine particulates separated in the cyclone separator  19   a  are recirculated through the fine powder recirculation line  19   c  to the drying chamber  11  for producing powers having agglomerations of fine particles. Again, the system otherwise operates the same as previously described. 
         [0127]    Referring now to  FIG. 25D  there is shown another alternative embodiment in the form of a fluidized bed powder drying system. The powder drying system again has a cylindrical drying chamber  12  with a non-permeable liner  100  concentrically disposed therein and an electrostatic spray nozzle assembly  16  for directing electrostatically charged liquid particles into the effective heating zone  127  defined by the liner  100  as described above. In this case, a conically formed collection container section  18   b  communicates powder from the drying chamber  12  into a collection chamber  19   b  through a fluid bed screen separator  19   c  of a conventional type. In this embodiment, a plurality of fluid bed cylindrical filter elements  160   b , similar to those described in connection with the embodiment of  FIG. 11A , are supported from an upper transverse plate  163   b  which defines an exhaust plenum  164   b  adjacent a top of the drying chamber  12 . A blower  168  in this case draws air from the exhaust plenum  164   b  from which powder and particulate matter has been filtered out for direction via the line  165  through the condenser  170  and heater  169 , for reintroduction into the bottom collection chamber  19   b  and recirculation upwardly through the drying chamber  12 . The filters  16   b  again have reverse pulse air filter cleaning devices  167   b  of the type as disclosed in the referenced U.S. Pat. No. 8,876,928, having respective air control valves  167   c  for periodically directing pressurized air to and through the filters  16   b  for cleaning the filters  16   b  of accumulated powder. 
         [0128]    While the non-permeable liner  100  of the foregoing embodiments, preferably is made of flexible non-conductive material, such as plastic, alternatively it could be made of a rigid plastic material, as depicted in  FIG. 3D . In that case, appropriate non-conductive mounting standoffs  100   d  could be provided for securing the liner in concentric relation within the drying chamber  12 . Alternatively, as depicted in  FIG. 3C  the permeable liner can be made in part, such as one diametrical side, of a permeable filter material  100   b  which allows air to flow through the liner for exhaust and in part, such as on an opposite diametric side, of a non permeable material  100   a  that prevents dried particles from being drawn into the liner. 
         [0129]    As a further alternative embodiment, the illustrated spray dryer system can be easily modified, as depicted in  FIG. 15A , for use in spray chilling of melted flow streams, such as waxes, hard waxes, and glycerides, into a cold gas stream to form solidified particles. Similar items to those described above have been given similar reference numerals. During spray chilling, a feedstock with a melting point, slightly above ambient conditions, is heated and placed in the holding tank  130  which in this case is wrapped in an insulation  130   a . The feed stock is pumped to the atomizing nozzle  16  thru the feed line  131  using the pump  132 . The molten feedstock again is atomized using compressed gas such as nitrogen  150 . During spray chilling melted liquid feedstock may or may not be electrostatically charged. In the latter case, the electrode of the electrostatic spray nozzle assembly is deenergized. 
         [0130]    During spray chilling, the atomizing gas heater  152  is turned off so that cool atomizing gas is delivered to the atomizing nozzle  16 . During the spray chilling, the drying gas heater  169  also is turned off delivering drying gas that has been cooled by the dehumidification coil  170   a  to the drying chamber  12  through the drying gas line  165 . As the atomized droplets enter the drying gas zone  127  they solidify to form particles that fall into the collection cone  18  and are collected in the collection chamber  19  as the gas stream exits for recirculation. The removable liner  100  again aids in the cleaning of the dryer chamber since it can be removed and discarded. The insulating air gap  101  prevents the drying chamber  12  from becoming cold enough for condensation to form on the outside surface. 
         [0131]    In carrying out still a further feature of this embodiment, the spraying system  10  may operate using an automated fault recovery system that allows for continued operation of the system in the event of a momentary charge field breakdown in the drying chamber, while providing an alarm signal in the event of continued electrical breakdown. A flowchart for a method of operating a voltage generator fault recovery method for use in the spraying system  10  is shown in  FIG. 27 . The illustrated method may be operating in the form of a program or a set of computer executable instructions that are carried out within the controller  133  ( FIG. 15 ). In accordance with the illustrated embodiments, the method shown in  FIG. 26  includes activating or otherwise starting a liquid pump at  300  to provide a pressurized supply of fluid to an injector inlet. At  302 , a verification of whether a voltage supply is active is carried out. In the event the voltage supply is determined to be inactive at  302 , an error message is provided at a machine interface at  304 , and a voltage generator and the liquid pump are deactivated at  306  until a fault that is present, which may have caused the voltage supply to not be active as determined at  302 , has been rectified. 
         [0132]    At times when the voltage supply is determined at  302  to be active, a delay of a predefined time, for example, 5 seconds, is used before the liquid pump is started at  308 , and the liquid pump is run at  310  after the delay has expired. A check is performed at  312  for a short or an arc at  312  while the pump continues to run at  310 . When a short or arc is detected at  312 , an event counter and also a timer are maintained to determine whether more than a predefined number of shorts or arcs, for example, five, have been detected within a predefined period, for example, 30 seconds. These checks are determined at  314  each time a short or arc is detected at  312 . When fewer than the predefined shorts or arcs occur within the predefined period, or even if a single short or arc is detected, the liquid pump is stopped at  316 , the voltage generator producing the voltage is reset by, for example, shutting down and restarting, at  318 , and the liquid pump is restarted at  310  after the delay at  308 , such that the system can remediate the fault that caused the spark or arc and the system can continue operating. However, in the event more than the predefined number of sparks or arc occur within the predefined period at  314 , an error message is generated at a machine interface at  320  and the system is placed into a standby mode by deactivating the voltage generator and the liquid pump at  306 . 
         [0133]    In one aspect, therefore, the method of remediating a fault in an electrostatic spray drying system includes starting a pump startup sequence, which entails first determining a state of the voltage generator and not allowing the liquid pump to turn on while the voltage generator has not yet activated. To accomplish this, in one embodiment, a time delay is used before the liquid pump is turned on, to permit sufficient time for the voltage generator to activate. The liquid pump is then started, and the system continuously monitors for the presence of a spark or an arc, for example, by monitoring the current drawn from the voltage generator, while the pump is operating. When a fault is detected, the voltage generator turns off, as does the liquid pump, and depending on the extent of the fault, the system automatically restarts or enters into a standby mode that requires the operator&#39;s attention and action to restart the system. 
         [0134]    Finally, in carrying out a further aspect of the present embodiment, the spray drying system  10  has a control which enables the charge to the liquid sprayed by the electrostatic spray nozzle assembly to be periodically varied in a fashion that can induce a controlled and selective agglomeration of the sprayed particles for particular spray applications and ultimate usage of the dried product. In one embodiment, the selective or controlled agglomeration of the sprayed particles is accomplished by varying the time and frequency of sprayer activation, for example, by use of a pulse width modulated (PWM) injector command signal, between high and low activation frequencies to produce sprayed particles of different sizes that can result in a varying extent of agglomeration. In another embodiment, the selective or controlled agglomeration of the sprayed particles may be accomplished by modulating the level of the voltage that is applied to electrostatically charge the sprayed fluid. For example, the voltage may be varied selectively in a range such as 0-30 kV. It is contemplated that for such voltage variations, higher voltage applied to charge the fluid will act to generally decrease the size of the droplets, thus decreasing drying time, and may further induce the carrier to migrate towards the outer surfaces of the droplets, thus improving encapsulation. Similarly, a decrease in the voltage applied may tend to increase the size of the droplets, which may aid in agglomeration, especially in the presence of smaller droplets or particles. 
         [0135]    Other embodiments contemplated that can selectively affect the agglomeration of the sprayed particles include selectively changing over time, or pulsing between high and low predetermined values, various other operating parameters of the system. In one embodiment, the atomizing gas pressure, the fluid delivery pressure, and the atomizing gas temperature may be varied to control or generally affect particle size and also the drying time of the droplets. Additional embodiments may further include varying other parameters of the atomizing gas and/or the drying air such as their respective absolute or relative moisture content, water activity, droplet or particle size and others. In one particular contemplated embodiment, the dew point temperature of the atomizing gas and the drying air are actively controlled, and in another embodiment, the volume or mass airflow of the atomizing gas and/or the drying air are also actively controlled. 
         [0136]    A flowchart for a method of modulating a pulse width in an electrostatic spray nozzle to selectively control the agglomeration of sprayed particles is shown in  FIG. 27 . In accordance with one embodiment, at an initiation of the process, a voltage generator is turned on at  322 . A determination of whether a PWM control, which will selectively control the agglomeration, is active or desired is carried out at  324 . When no PWM is desired or active, the process controls the system by controlling the voltage generator to a voltage setpoint at  326 , and the fluid injector is operated normally. When PWM is desired or active, the system alternates between a low PWM setpoint and a high PWM setpoint for predefined periods and during a cycle time. In the illustrated embodiment, this is accomplished by controlling to the low PWM setpoint at  328  for a low pulse duration time at  330 . When the low pulse duration time has expired, the system switches to a high PWM setpoint at  332  until a high pulse duration time has expired at  334 , and returns to  324  to determine if a further PWM cycle is desired. While changes in the PWM setpoint are discussed herein relative to the flowchart shown in  FIG. 27 , it should be appreciated that other parameters may be modulated in addition to, or instead of, the sprayer PWM. As discussed above, other parameters that may be used include the level of voltage applied to charge the liquid, the atomizing gas pressure, the liquid delivery rate and/or pressure, the atomizing gas temperature, the moisture content of the atomizing gas and/or drying air, and/or the volume or mass air flow of the atomizing gas and/or drying air. 
         [0137]    In one aspect, therefore, the agglomeration of sprayed particles is controlled by varying the injection time of the sprayer. At high frequencies, i.e., at a high PWM, the sprayer will open and close more rapidly producing smaller particles. At low frequencies, i.e., at the low PWM, the sprayer will open and close more slowly producing larger particles. As the larger and smaller particles make their way through the dryer in alternating layers, some will physically interact and bind together regardless of their repulsing electrical charges to produce agglomerates by collusion. The specific size of the larger and smaller particles, and also the respective number of each particle size per unit time that are produced, can be controlled by the system by setting the respective high and low PWM setpoints, and also the duration for each, to suit each specific application. 
         [0138]    In accordance with still a further feature, a plurality of powder processing towers  10  having drying chambers  11  and electrostatic spray nozzle assemblies  16  as described above, may be provided in a modular design, as depicted in  FIGS. 28 and 29 , with the powder discharging onto a common conveyor system  340  or the like. In this case, a plurality of processing towers  10  are provided in adjacent relation to each other around a common working platform  341  accessible to the top by a staircase  342 , and having a control panel and operator interface  344  located at an end thereof. The processing towers  10  in this case each include a plurality of electrostatic spray nozzle assemblies  16 . As depicted in  FIG. 28 , eight substantially identical processing towers  10  are provided, in this case discharging powder onto a common powder conveyor  340 , such as a screw feed, pneumatic, or other powder transfer means, to a collection container. 
         [0139]    Such a modular processing system has been found to have a number of important advantages. At the outset, it is a scalable processing system that can be tailored to a users requirements, using common components, namely substantially identical processing powder processing towers  10 . The system also can easily be expanded with additional modules, as depicted in  FIG. 30 . The use of such a modular arrangement of processing towers  10  also enables processing of greater quantities of powder with smaller building height requirements (15-20 feet) as compared to standard larger production spray dryer systems which are 40 feet and greater in height and require special building layouts for installation. The modular design further permits isolation and service individual processing towers of the system without interrupting the operation of other modules for maintenance during processing. The modular arrangement also enables the system to be scaled for energy usage for particular user production requirements. For example, five modules could be used for one processing requirement and only three used for another batch. 
         [0140]    From the foregoing, it can be seen that a spray dryer system is provided that is more efficient and versatile in operation. Due to enhanced drying efficiency, the spray dryer system can be both smaller in size and more economical usage. The electrostatic spray system further is effective for drying different product lots without cross-contamination and is easily modifiable, both in size and processing techniques, for particular spray applications. The spray drying system further is less susceptible to electrical malfunction and dangerous explosions from fine powder within the atmosphere of the drying chamber. The system further can be selectively operated to form particles that agglomerate into a form that better facilitates their subsequent usage. The system further has an exhaust gas filtration system for more effectively and efficiently removing airborne particulate matter from drying gas exiting the dryer and which includes automatic means for removing the buildup of dried particulate matter on the filters which can impede operation and require costly maintenance. Yet, the system is relatively simple in construction and lends itself to economical manufacture.