Abstract:
A high-pressure system and method utilizing an input fluid. The system includes a reactor treating a material to produce an effluent having an energy content, a plurality of stages compressing the input fluid in a stepwise manner providing a high-pressure reactor input stream to the reactor, and a cascading effluent energy recovery system mechanically communicating with the plurality of stages. The cascading effluent energy recovery system imparts a portion of the energy content of the effluent into each of the plurality of stages powering that stage. The method includes receiving an input fluid, compressing the input fluid over a plurality of stages producing the high-pressure stream, providing the high-pressure stream to the reactor, recovering a portion of the energy content of the effluent at each of the plurality of stages, and using each the portion of the energy in compressing the input fluid at a corresponding respective stage.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    The present disclosure generally relates to the field of pressurizing systems for use in thermo-chemical processes. In particular, the present disclosure is directed to a high-pressure compression system utilizing cascading effluent energy recovery. 
       BACKGROUND 
       [0002]    High-pressure air and steam are used in various industrial applications. For example, extremely high-pressure air may be used on submarines for clearing main ballast tanks. High-pressure water vapor (commonly referring to water molecules with or without air or other gas molecules present) can also be used to create a very effective high-pressure chemical reaction with a purpose of reducing various components of the reaction down to their fundamental constituents of water and carbon dioxide. For example, this technique is used in the process of supercritical water oxidation (SCWO), wherein diverse waste streams, including sewage, commercial waste, old munitions, and the like, are converted to basic oxidized constituents with minimal harmful waste effluent from the process. 
         [0003]    Conventional forms of compression for such high-pressure applications have been accomplished with positive displacement compressors originally designed for submarines and that provide pressures in the order of 5,000 psi. Such conventional compressors limit the possibilities of efficient recapture of waste energy and reinsertion of the energy back into the cycle. 
         [0004]    Various processes for treating a feedstock require process materials to be maintained at elevated pressures. Additionally, conventional processes may require the feedstock to be at an elevated temperature. In such treatment processes, obtaining a high-pressure rise with minimum energy consumption presents a continuing problem. One of the efforts to recover waste energy in current systems involves the use of conventional turbines to expand the high-pressure gas effluent stream once the reaction is complete. The energy recaptured is then delivered to an electric generator. The electric power created in the generator is either used to drive the high-pressure positive displacement compressors or is returned to the grid. 
         [0005]    Inefficient use of waste energy has been particularly acute in the hydrothermal treatment of organic waste products using SCWO techniques. In a typical SCWO process, the materials in a reaction chamber are preferably maintained at a pressure of over 200 bar and a temperature of over 700° Celsius. Processes may have a preferred reaction pressure of 1000 bar. Conventional positive displacement compressors, as described above, are used to help achieve such high-pressures in the reaction chamber. 
         [0006]    In SCWO processes, oxidation of waste organics can be achieved by pumping an oxidizer, such as air, into the reaction chamber for mixing with other constituents of the reaction, such as supercritical water, raw wastes, and additives such as a fuel to assist in maintaining suitable temperatures. Such processes are described in U.S. Pat. No. 4,338,199 issued to Model on Jul. 6, 1982, U.S. Pat. No. 5,106,513 issued to Hong on Apr. 21, 1992, and U.S. Pat. No. 6,519,926 issued to Hazlebeck on Feb. 18, 2003, which are all hereby incorporated by reference in their entirety. 
         [0007]    Multiple stage turboccharging of internal combustion engines is a technique well known in the art. For examples, such multiple stage turbocharging of internal combustion engines may be found in U.S. Pat. No. 7,000,393 issued to Wood et al. Additionally, multiple stage turbocharging of internal combustion engines is also provided in  Turbocharging the Internal Combustion Engine,  by N. Watson and M. S. Janota, at sections 11.5 and 11.6, published by Wiley-Interscience Division, John Wiley &amp; Sons, Inc., New York (1982). However, the recovery of energy in such conventional systems has generally been inefficient. 
       SUMMARY OF THE DISCLOSURE 
       [0008]    In one embodiment of the present disclosure, a system utilizing an input fluid is disclosed. The system includes a continuous reaction reactor for converting an input material using the input fluid so as to produce an effluent having an energy content of a first energy type. A plurality of compression stages are located in series with one another for compressing the input fluid in a stepwise manner so as to provide a pressurized reactor input stream to the continuous reaction reactor. A cascading effluent energy recovery system mechanically communicates with each of the plurality of compression stages. The cascading effluent energy recovery system imparts a portion of the energy content of the effluent into each of the plurality of compression stages so as to power that one of the plurality of compression stages. 
         [0009]    In another embodiment of the present disclosure, a system utilizing an input fluid is provided. The system comprises a reactor for converting a material using the input fluid so as to produce an effluent having an energy content of a first energy type. The system also comprises a first early compression stage that includes a first early stage compressor for compressing the input fluid and a first early stage expansion turbine for recovering a portion of the energy content of the effluent. The first expansion turbine is mechanically linked to the first early stage compressor for at least partially driving the first compressor. A first motor/generator is mechanically linked to each of the first early stage compressor and the first early stage expansion turbine. The first motor/generator selectively powers the first early stage compressor during periods of insufficient power from the first early stage expansion turbine and converting an excess of the energy content into electricity during periods of excess power from the first early stage expansion turbine. A latter compression stage is located downstream from the first early compression stage and upstream from the reactor. The latter compression stage comprises a latter stage compressor for further compressing the input fluid and a latter stage expansion turbine for recovering a second portion of the energy content of the effluent. The latter stage expansion turbine is mechanically linked to the latter stage compressor for driving the latter stage compressor. 
         [0010]    In yet another embodiment of the present disclosure, a method of providing a pressurized stream of an input fluid to a continuous reaction reactor so as to produce a non-pulsed effluent having an energy content is disclosed. The method includes the steps of receiving an input fluid and compressing the input fluid over a plurality of compression stages so as to produce the pressurized stream. The pressurized stream is provided to the continuous reaction reactor. A portion of the energy content of the effluent is recovered at each of the plurality of compression stages. Each portion of the energy content is used in compressing the input fluid at a corresponding respective one of the plurality of compression stages. 
         [0011]    In a further embodiment, a method of providing a pressurized stream of al input fluid to a reactor so as to produce a non-pulsed effluent having an energy content is disclosed. The method includes the steps of receiving an input fluid and compressing the input fluid over a plurality of compression stages so as to produce the pressurized stream. The pressurized stream is provided to the reactor. A portion of the energy content of the effluent is recovered at each of the plurality of compression stages. The portion of the energy content at at least one of the plurality of compression stages is supplemented with additional energy to supplement the compressing of the input fluid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    For the purpose of illustrating the disclosure, the drawings show aspects of one or more embodiments of the disclosure. However, it should be understood that the present disclosure is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein: 
           [0013]      FIG. 1  is a schematic diagram of the components of a high-pressure system in accordance with the present disclosure; and 
           [0014]      FIG. 2  is a schematic diagram of a later compression stage of a high-pressure system in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Referring to the drawings,  FIG. 1  illustrates an efficient high-pressure system  100 . At a high level, system  100  includes a pressurized chemical reaction system  110  and a cascading energy recovery system  112 . As can be readily seen in  FIG. 1 , cascading energy recovery system  112  interacts with pressurized system  110  to recover at least a portion of the initial energy content from effluent  114  and uses this energy to produce, or aid in producing, a high-pressure stream  118 , e.g., air and/or steam, that is input into pressurized system  110  as part of the reaction process. 
         [0016]    High-pressure system  100  includes a series of compression and expansion stages, here stages  124 ,  126 , and  128 , for compressing an input fluid  122 , e.g., vapor and/or gas, through the series of stages to produce high-pressure stream  118  for reactor  116  on a compression side and for expanding effluent  116  through the series of stages to produce power for each associated stage on an expansion side. It is noted that while  FIG. 1  shows three compression and expansion stages  124 ,  126 , and  128 , the present disclosure contemplates a lower or greater number of stages while keeping within the scope and spirit of the present disclosure. The number of compression and expansion stages utilized may depend upon the actual pressure requirements for high-pressure stream  118  and upon the actual energy content available from reactor effluent  114 . Generally, three or more stages will typically be required to achieve necessary levels of pressure on the input side of pressurized chemical reaction system  110  and to successfully recapture high amounts of waste energy on the output side, as will be described below. 
         [0017]    In the illustrative embodiment shown, pressurized chemical reaction system  110  includes a reactor  116  that may perform a continuous self-sustaining process for converting an uninterrupted continuous feed of input materials, as discussed further below, into effluent  114  with an initial energy content. The self-sustaining process of reactor  116  provides a thermally self-sustaining continuous flow of energy to system  100 , wherein the reactor includes but is not limited to a supercritical water oxidation (SCWO) reactor, or other type of continuous chemical process reactor. In these cases, reactor  116  may be referred to as a “continuous reaction reactor.” It is noted that the present disclosure also contemplates that reactor  116  may be of a “pulsed reaction” type in which the on going process involves a series of intermittent reactions, e.g., combustions. Examples of such pulsed reaction reactors include reciprocating type internal combustion engines, e.g., spark-ignition engines or diesel engines, among others. Input materials may include any of a variety of materials which may be treated and/or converted to usable end products, as will be discussed below. 
         [0018]      FIG. 1  illustrates reactor  116  as an SCWO reactor in which SCWO reactions occur under high-pressure and high-temperature conditions. (Again, although the illustrated embodiment is directed to SCWO, those skilled in the art will readily appreciate that the scope of this disclosure covers systems beyond SCWO.) Reactor  116  may process a mixture of a feedstock  130 , an additive  132 , and high-pressure stream  118 . Reactor  116  generally gasifiers the mixture of water and organics under hydrothermal treatment conditions to produce effluent  114  with the initial energy content. Effluent  114  may include a high-temperature and high-pressure gaseous mixture of steam and combustible gases containing particulates, salts and corrosive species, among other things. Moreover, effluent  114  may include compounds resulting from the broken chemical bonds of organics during the reaction in reactor  116 . Additionally, reactor  116  may include mechanical systems and/or purging systems (not shown) for helping transport materials through the reactor. 
         [0019]    Feedstock  130  generally includes organic wastes. Additive  132  may include one or more waste materials or fuel, including but not limited to, an oil-based hydrocarbon or diesel. Additive  132  may also include, but is not limited to, neutralizing agents to neutralize acids formed in reactor  116 , inert solids to aid in salt transport, salt-forming agents, corrosion inhibitors, minerals, and combustible material for use as an auxiliary fuel. Generally, burning additive  132  helps maintain appropriate elevated temperatures in reactor  116  for the desired reactions. For example, elevated temperatures may generally be in the range of 350° Celsius to 800° Celsius, but are not limited to this range. High-pressure stream  118  generally includes pressurized steam and air for use in reactor  116 . 
         [0020]    As shown, the compression side of first stage  124  may include a first compressor  134  having a moderate pressure ratio, such as a pressurization in the range of but not limited to 2 to 9, for compressing input fluid  122 . First compressor  134  may be mechanically linked with a first expansion turbine  136  of energy recovery system  112 , e.g., via a first shaft  138  on the expansion side of first compression and expansion stage  124 . First expansion turbine  136  generally powers first compressor  134  as effluent  114  expands through the turbine. The input:output pressure ratios for both first compressor  134  and first expansion turbine  136  are preferably chosen so as to balance the thrust to a reasonable first order, with residual thrust being handled by bearings or a thrust collar (not shown). Additionally, first compression and expansion stage  124  may also include a first motor/generator  140  coupled to first shaft  138  so as to selectively drive first compressor  134 , either alone or in combination with first expansion turbine  136 , during periods of insufficient power from the first expansion turbine or to generate electricity when the amount of energy needed to drive the first compressor is less than the energy recovered by the first expansion turbine. 
         [0021]    The compression side of second compression and expansion stage  126  may include a second compressor  142  for further compressing/pressurizing input fluid  122 , which may be received as a cooled second-stage input  166  as described below. Second compressor  142  is mechanically linked with a second expansion turbine  144 , via a second shaft  146 . Second expansion turbine  144  generally powers second compressor  142  as effluent  114  expands through the second turbine. Additionally, second compression and expansion stage  126  may also include a second motor/generator  148  coupled to second shaft  146  so as to selectively drive second compressor  142 , either alone or in combination with second expansion turbine  144 , during periods of insufficient power from the second expansion turbine or to generate electricity when the amount of energy needed to drive the second compressor is less than the energy recovered by the second expansion turbine. 
         [0022]    Third compression and expansion stage  128  may include a third compressor  150  oil the compression side for yet further compressing input fluid  122  so as to produce high-pressure stream  118  that enters reactor  116 . Third compressor  150  may be driven by a third expansion turbine  152  via a third shaft  154 . In the present example, each compression and expansion stage  124 ,  126 ,  128  achieves a gain of approximately, but not limited to, 6 to 7 times in pressure exiting that stage relative to the input of that stage. 
         [0023]    Since third turbine  152  of third compression and expansion stage  128  is the first of three expansion turbines  136 ,  144 , and  152  to expand effluent  114 , the third turbine will typically output sufficient power to drive third compressor  150  without the need of an associated motor/generator in the stage, as in first and second stages  124 ,  126 . Moreover, typical optimal speeds of operation of the later compression stage(s), i.e., stage(s) closest to reactor  116 , are so high that it is often problematic, at least under contemporary technology, to employ a motor rotating at such high speeds. 
         [0024]    For startup of one or more later compression stages, i.e., the stage(s) closest to reactor  116 , and/or where additional motive force in steady-state is needed, a motive system without additional rotating parts may be provided, e.g., in the form of a bootstrap, or bypass  156 , that bypasses reactor  116  and utilizes pressurized flow from one or more lower stages, here, compression and expansion stages  124 ,  126 . The bootstrap driving of third compression and expansion stage  128  by bypass  156  utilizes a portion of input fluid  122  after compression/pressurization by second compression and expansion stage  126 . In other embodiments, e.g., one or more bootstrap drives similar to bypass  156  may replace the motor/generators of two or more stages after first compression and expansion stage  124  or other early compression stages. 
         [0025]    Pressurized system  110  may also include one or more intercoolers, or heat exchangers, e.g., heat exchangers  158 ,  160 , that may serve one or more purposes. For example, in some processes, inter-stage cooling of compressed input fluid  122  may be required to satisfy temperature requirements for a cycle. Inter-stage cooling helps achieve improved downstream stage compressor performance and thermodynamic efficiency. Additionally, lower temperatures allow compressors, such as compressors  134 ,  142 , and  150 , and related components to be constructed from less expensive materials and/or surface-coated with materials having lower temperature limits that provide less stringent design constraints. Alternatively, the material characteristics of the particular compressors and related components selected may require inter-stage cooling. Inter-stage cooling may be accomplished by providing heat exchangers  158 ,  160  between corresponding respective successive compression and expansion stages. For example, first heat exchanger  158  may be fluidly located between first compression and expansion stage  124  and second compression and expansion stage  126 , and second heat exchanger  160  may be fluidly located between the second compression and expansion stage and third compression and expansion stage  128 . Heat exchangers (intercoolers)  158  and  160  capture and remove heat and energy from the input fluid following compression at the corresponding respective compression and expansion stages. The removed heat and energy may be used within high-pressure system  100  as described below or elsewhere. 
         [0026]    During operation of high-pressure system  100 , input fluid  122  enters first compressor  134  at first compression and expansion stage  124 . First compressor  134  imparts energy to input fluid  122  by raising tie pressure and temperature of the input fluid to produce a first-stage output  162  for introduction into second compressor  142  of second compression and expansion stage  126 . As discussed below in more detail, first compressor  134  is powered by either first expansion turbine  136 , first motor/generator  140 , or both, depending upon the particular operating characteristics and state of operation of high-pressure system  100 . 
         [0027]    When first heat exchanger  158  is present, first-stage output  162  enters the first heat exchanger, wherein heat and energy is removed from the first-stage output, e.g., using a coolant  164 . First heat exchanger  158  provides a cooled second-stage input  166  to second compressor  142 . The heat and energy removed from first-stage output  162  may be utilized, e.g.,.to assist in pre-heating feedstock  130  and/or additive  132  for receipt by reactor  116 , or for another purpose. 
         [0028]    Cooled second-stage input  166  (or first-stage output  162  if first heat exchanger  158  is not present) enters second compressor  142  for additional compression so as to output a second-stage output  168  with a higher pressure and temperature than the cooled second-stage input. For example, if the output:input pressure ratio for first compressor  134  is slightly greater than 7, and the output:input pressure ratio for second compressor  142  is also slightly greater than 7, then an output:input pressure ratio of approximately 50 or more for the two stages together may be achieved. As discussed below in more detail, second compressor  142  is powered by either second expansion turbine  144 , second motor/generator  148 , or both, depending upon the particular operating characteristics of high-pressure system  100 . 
         [0029]    When second heat exchanger  160  is present, second-stage output  168  enters the second heat exchanger, wherein heat and energy is removed from the second-stage output, e.g., using a coolant  170 . Second heat exchanger  160  provides a cooled third-stage input  172  to third compressor  150 . The heat and energy removed from second-stage output  168  may be transferred to and utilized in another part of system  100  or used elsewhere. 
         [0030]    Cooled third-stage input  172  (or second-stage output  168  if second heat exchanger  160  is not present) enters third compressor  150  for additional compression so as to output high-pressure stream  118 . Which has a higher pressure and temperature than the cooled third-stage input. In one example, the output:input pressure ratio for first compressor  134  may be slightly greater than 7, the Output:input pressure ratio for second compressor  142  may be slightly greater than 7, and the output: input pressure ratio for third compressor  150  may be approximately 5, resulting in a combined output:input pressure ratio for the three stages of approximately 250, which if input fluid  122  has an initial pressure of about 14 psi results in high-pressure stream  118  having a pressure of about 3,500 psi. 
         [0031]    It is noted that high-pressure system  100  may not include a heat exchanger (intercooler) downstream of third compressor  150 . This is so because it may be desirable to retain the full temperature of high-pressure stream  118  exiting third compressor  150  (or other final stage(s) in other embodiments) in order to keep heat (enthalpy) in the system to promote the reaction in reactor  116 . In any case, the materials from which the later stage compressor(s) are typically constructed must be able to operate for long periods of time at highly elevated temperatures. It is also noted that first, second, and third compressors,  134 ,  142 ,  150  are illustrated with progressively smaller impellers  180 ,  182 ,  184  respectively, to indicate that smaller physical dimensions of these machines may be needed due to higher gas density and to keep up with the peripheral speed of the respective compressor&#39;s rotating elements within the tolerances of the materials available for their construction. 
         [0032]    Turning to the expansion side of cascading energy recovery system  112 , in this illustrative embodiment third expansion turbine  152  expands effluent  114  to provide sufficient power to drive third compressor  150  generally without the need for additional power from an associated motor. (While this is true for this embodiment, it is to be understood that other embodiments may indeed include a motor/generator if needed or desired.) As mentioned above, during startup of high-pressure system  100 , bypass  156  from downstream of second compressor  142  may be used to help drive third expansion turbine  152  along with effluent  114 . Bypass  156  may be closed and/or the flow therein may be adjusted via a valve  174 , e.g., a balancing valve or similar device, that may work in conjunction with one or more other devices (not shown), e.g., a timer, pressure sensor in the bypass, and/or a speed sensor associated with third expansion turbine  152  or third shaft  154 , among others. Valve  174  may work to reduce bootstrap driving of third expansion turbine  152  as is appropriate as effluent  114  gains sufficient energy to drive the third expansion turbine. 
         [0033]    Effluent  114  expands and cools through third expansion turbine  152 . If effluent  114  contains a vapor, upon cooling some of the vapor may condense, resulting in a third-stage liquid output  176  and a third-stage vapor output  178  from third expansion turbine  152 . In the context of SCWO, third-stage liquid output  176  will typically be principally water, entrained salts, and precipitants. Third-stage liquid output  176  may be removed via a liquid removal collector and channel (not shown). In the SCWO context, third-stage vapor output  178  typically includes simpler compounds produced in reactor  116  from feedstock  130 . Due to the expansion through third expansion turbine  152 , the removed compounds are at a reduced temperature and reduced pressure relative to effluent  114 . Generally, third-stage vapor output  178  retains large amounts of energy in the form of elevated temperature and pressure, even with the temperature and pressure drop across third expansion turbine  152 . 
         [0034]    Third-stage vapor output  178  cascades into second expansion turbine  144  of second compression and expansion stage  126 , where it expands and helps drive second compressor  142 . If the power needed to drive second compressor  142  is greater than the power provided by second expansion turbine  144 , second motor/generator  148  will act as a motor to help drive the second compressor. If, on the other hand, the power needed to drive second compressor  142  is less than the power provided by second expansion turbine  144 , second motor/generator  148  may act as a generator to produce electricity. If the power requirement of second compression  142  and the power output by second expansion turbine  144  balance, second motor/generator  148  may not operate in either a motor or generator capacity. Third-stage vapor output  178  expands and cools in second expansion turbine  144  to produce a second-stage vapor output  186  and, typically, a second-stage liquid output  188 , which may be removed via a liquid removal collector and channel (not shown). In the SCWO context, second-stage liquid output  188  may include simpler compounds produced from third-stage vapor output  178  in second expansion turbine  144 . By virtue of the expansion through second expansion turbine  144 , the removed compounds are at a reduced temperature and reduced pressure relative to third-stage vapor output  178 . Second-stage output vapor  180  retains large amounts of energy in the form of elevated temperature and pressure, even with the temperature and pressure drop across second expansion turbine  144 . 
         [0035]    Second-stage vapor output  186  cascades into first expansion turbine  136  of first compression and expansion stage  124 , where it expands and helps drive first compressor  134 . If the power needed to drive first compressor  134  is greater than the power provided by first expansion turbine  136 , first motor/generator  140  will act as a motor to help drive the first compressor. It on the other hand, the power needed to drive first compressor  134  is less than the power provided by first expansion turbine  136 , first motor/generator  140  may act as a generator to produce electricity. If the power required by first compression  134  and the power output by first expansion turbine  136  balance, first motor/generator  140  may not operate in either a motor or generator capacity. First expansion turbine  136  expands and cools second-stage vapor output  186  to produce a first-stage output  190 , which may include vapors and liquid of lower temperature and pressure and suitable for final energy extraction with a heat exchanger (not shown) or for inputting to a separator (not shown) that isolates the components of the effluent for disposal or other use, such as fuel for reactor  116  or elsewhere. 
         [0036]      FIG. 2  illustrates an alternative embodiment of a latter compression and expansion stage  200 , generally a stage located directly upstream or closest to a reactor  218 , of the present disclosure. Generally, latter compression and expansion stage  200 , e.g., third compression and expansion stage  128  in the illustrative embodiment of  FIG. 1 , may include a latter stage compressor  202  and an additional compressor  204  mounted on, e.g., a common shaft  206  that may also be shared with a respective latter stage expansion turbine  208 . Additional compressor  204  may provide additional compression of an input  272  from a previous stage to stage  200 , e.g., cooled third-stage input  172  of  FIG. 1 , when required by process requirements. Latter stage expansion turbine  208  may receive a bootstrap bypass drive stream  210  from latter stage compressor  202 . A valve  212  may be provided for controlling the flow of bypass drive stream  210  into latter stage expansion turbine  208 . A heat exchanger  214  may be included to reduce the temperature of a portion of bypass drive stream  210  to provide a cooled drive stream  216  to drive additional compressor  204 . The heat and energy recovered by heat exchanger  214  may be used, e.g., to preheat materials supplied to a reactor  218  or for other purposes in the corresponding system (not shown). 
         [0037]    As will be appreciated, ally stage of a high-pressure system made in accordance with the present disclosure, such as any one of first, second, and third compression and expansion stages  124 ,  126 ,  128  of high-pressure system  100  of  FIG. 1 , may include multiple compressors in the manner illustrated in  FIG. 2 , while keeping within the scope and spirit of the present disclosure. Multiple compressors in a stage of such a system may improve that stage&#39;s efficiency and reduce mechanical stress on each compressor. 
         [0038]    Moreover, it will be appreciated that the use of a multiplicity of turbocharger-type stages to provide a pre-reaction compression process may be desirable for use with other reaction systems that utilize supercritical water oxidation. In any such system the compression arrangement of the present disclosure achieves various beneficial results, such as reduced size of motor/generators needed, elimination of positive displacement equipment, the availability of design methodologies for radial flow compressors and turbines, minimal interfacing with an external electric grid, reduction in size of the compression and energy recovery systems, and simplification of maintenance. 
         [0039]    Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present disclosure.