Abstract:
The present invention relates to online analysis of crude oil from desalting processes. Online analysis of the crude oil that has been desalted will allow for real time adjustments to process operating parameters such that the salt concentration of the crude oil is maintained within acceptable parameters. This online analysis can yield a more efficient process, reduce energy consumption of the desalting process, and maintain corrosion rates within acceptable limits.

Description:
REFERENCE TO CROSS-RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. application Ser. No. 14/077,389 filed on Nov. 12, 2013, which claims priority to and the benefit of U.S. Provisional Application Ser. No. 61/725,145 filed on Nov. 12, 2012, which is incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention generally relates to the field of analyzers for salt in crude. 
         [0003]    More specifically, it relates to the online analysis of crude oil from desalting processes. 
       BACKGROUND 
       [0004]    Currently, salt content measurement in the crude oil production and refining industry follows either the standard reference method ASTM D3230 or ASTM D6470, both of which are incorporated herein by reference. ASTM D6470 is not practical for online measurement as it requires extraction steps. ASTM D3230 requires the utilization of a combination of three chemicals: methanol, butanol, and xylene, to reduce the crude oil resistivity to a measurable range for traditional sensors and common instrumentation. However, these solvents are extremely toxic, volatile, and flammable, which makes them particularly difficult to handle in facilities located in hot environments. 
         [0005]    The principle of the method outlined in ASTM D3230 is to dilute a crude oil sample in an alcoholic mixture in order to allow for conductivity readings and to compare the readings to reference values. This method can be applied either off-line on a collected sample or online. Off-line measurements are susceptible to errors due to unequal gas desorption, which can be attributed to time lag between sampling and measurement and/or variations of the external temperature and/or the crude oil temperature, improper mix of chemicals, measurement errors, and data reporting. Online measurements avoid manual sampling and prevent some potential errors. However, in high temperature environments, the use of volatile solvents is inadvisable because it can lead to fires, explosions, or intoxication. Another disadvantage of ASTM D3230 is the limitation in solvent quantity stored on site due to flammability concerns and risks of explosion. 
         [0006]    Furthermore, xylene, methanol, and butanol must be added in precise proportions, as any minimum alteration in their volumetric ratio, which is even more likely to occur at high temperatures due to their volatile nature, disturbs the homogeneity and causes erroneous measurement readings. This leads to a complicated measurement procedure, thereby introducing potential errors. Moreover, these issues also require bulky equipment with frequent and careful maintenance. 
         [0007]    Currently, there are no effective, efficient, and easy to use online analyzers for monitoring salt content in treated crude. The available online salt-in-crude analyzers are generally expensive and require high maintenance, as well as the use of solvents, as required by the ASTM standards. The frequent replacements of chemicals and the presence of moving parts in the analyzer make the analyzer labor-intensive and requires constant maintenance. Currently available online nuclear and radioactive-based salt-in-crude analyzers also require high maintenance and provide unreliable measurement. Additionally, off-line monitoring requires laboratory sampling to monitor the PTB. However, it is very easy to miss the product specification based on the timing of sampling collections and using an off-line monitoring system. 
         [0008]    Therefore, it would be beneficial to provide a method and apparatus that is capable of measuring the salt concentration online and also modifying operating conditions such that salt concentration is maintained. 
       SUMMARY 
       [0009]    The present invention relates to online analysis of crude oil from desalting processes. Online analysis of the crude oil that has been desalted will allow for real time adjustments to process operating parameters such that the salt concentration of the crude oil is maintained within acceptable parameters. This online analysis can yield a more efficient process, reduce energy consumption of the desalting process, and maintain corrosion rates within acceptable limits. 
         [0010]    In some embodiments, the present invention provides a process for monitoring salinity of a dry crude stream. The process includes the steps of feeding a recycled water stream using at least one recycled water pump having a predetermined range of operating conditions and at least one emulsion breaking chemical using an emulsion breaking chemical injection system having a predetermined range of operating conditions, to a wet crude stream to produce an enhanced wet crude stream with water and emulsion breaking chemicals. The wet crude stream with water and emulsion breaking chemicals is then fed to a first mixing apparatus having a predetermined range of operating conditions to produce a mixed wet crude stream. The mixed wet crude stream is then fed to a dehydrator vessel having a predetermined range of operating conditions to produce a reduced water content crude stream and a waste water stream. The waste water stream is then fed to a waste water facility using at least one waste water stream pump having a predetermined range of operating conditions. A wash water stream is then fed using at least one wash water pump having a predetermined range of operating conditions to the reduced water content crude stream to produce a hydrated crude stream. The hydrated crude stream is then fed to a second mixing apparatus having a predetermined range of operating conditions to produce a mixed hydrated crude stream. The mixed hydrated crude stream is then fed to a desalter vessel having a predetermined range of operating conditions to produce a dry crude stream and the recycled water stream. The dry crude stream is fed to an analyzing unit for determining the basic sediment and water (BSW) of the dry crude stream. The recycled water stream is fed to an analyzing unit for determining total dissolved solids (TDS) of the recycled water stream from a desalting unit. A salt concentration in the dry crude stream is determined based on a predetermined correlation of BSW and TDS. A multivariable controller is used to assess the operating parameters within the predetermined range of operating conditions of any of the wet crude stream pump, recycled water pump, emulsion breaking chemical injection system, first mixing apparatus, dehydrator vessel, waste water stream pump, wash water pump, second mixing apparatus, and desalter vessel. The multivariable controller then adjusts one or more of operating parameters within the predetermined range of operating conditions to maintain the salt concentration in the dry crude stream within a predetermined range such that power usage of the process is minimized. 
         [0011]    In other embodiments, the present invention provides an apparatus for controlling content of impurity in a crude oil stream. The apparatus includes at least one mixing apparatus for receiving a water stream and a wet crude stream and for mixing the water and wet crude stream to provide a wet crude stream with water. The apparatus also includes at least one emulsion breaking chemical injection system for injecting an emulsion breaking chemical into the wet crude stream with water. The apparatus also includes at least one dehydrator vessel for receiving the wet crude stream with water for removing an amount of water to provide a reduced water content crude stream and a waste water stream. The apparatus also includes at least one water pump for pumping the water stream. The apparatus further includes at least one desalter vessel for removing salt from the reduced water content crude stream to produce a dry crude stream and a second waste water stream. The apparatus also includes a first impurity analyzer for measuring BSW of the dry crude stream and operable to provide a measurement of a BSW value to a controller. The apparatus further includes a second impurity analyzer for measuring TDS of the water stream and is operable to provide a measurement of a TDS value to the controller. The apparatus also includes a multivariable controller operable to perform an assessment of the BSW value and the TDS value using a predefined correlation. The controller is further operable to adjust at least one operating parameter of at least one of the mixing apparatus, the emulsion breaking chemical injection system, water pump, desalter vessel, first impurity analyzer, and second impurity analyzer, such that the power consumption of the apparatus for controlling content of impurity in a crude oil stream is optimized. 
         [0012]    The features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of the preferred embodiments that follow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    So that the manner in which the features and advantages of the invention, as well as others, which will become apparent, may be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof, which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the invention and are therefore not to be considered limiting of the invention&#39;s scope as it may include other effective embodiments as well. 
           [0014]      FIG. 1  shows a conventional salt in crude analyzer. 
           [0015]      FIG. 2  shows an apparatus for measuring crude salinity in accordance with an embodiment of the invention. 
           [0016]      FIG. 3  shows an apparatus for measuring crude salinity in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Although the following detailed description contains many specific details for purposes of illustration, it is understood that one of ordinary skill in the relevant art will appreciate that many examples, variations, and alterations to the following details are within the scope and spirit of the invention. Accordingly, the exemplary embodiments of the invention described herein are set forth without any loss of generality, and without imposing limitations, relating to the claimed invention. 
         [0018]    In desalting processes known in the art, analysis of samples of the dry crude stream is usually done offline, such as in laboratories. As shown in  FIG. 1 , which is one version of known desalting processes, wet crude stream  100  and water stream  110  are fed, along with emulsion breaking chemicals, to first mixing apparatus  120  to produce mixed wet crude stream  125 , which is then fed to dehydrating vessel  130 . The dehydrating vessel then separates waste water stream  140  from reduced water content crude stream  150 . Reduced water content crude stream  150  is then combined with wash water stream  160  using second mixing apparatus  170  to create mixed hydrated crude stream  175 , which is fed to desalter vessel  180 . From the desalter vessel, water stream  110  is produced which can be recycled to be fed to wet crude stream  100 . Dry crude stream  190  is also produced from desalter vessel  180 . In the various configurations of the desalting processes known in the prior art, samples  200  are taken from dry crude stream  190 . These samples usually monitor the BSW of the dry crude stream off line in a laboratory setting. From the BSW, the concentration of salt in the dry crude stream is determined. This process does not allow for online monitoring of the salt content of the dry crude stream. Additionally, the known processes do not allow for continuous monitoring and real time adjustments of various operating parameters to adjust the salt concentration of the dry crude stream to required levels. 
         [0019]    The online analysis provided by the impurity analyzers of embodiments of the present invention will allow for automation of the operations of a desalter operation such that the energy consumption of the desalter operation is minimized, water use is minimized, and the use of emulsion breaking chemicals is minimized, such that costs associated with producing desalted crude to set specifications will be reduced. This is accomplished by use of a multivariable controller, which is operable to adjust operating parameters in response to information provided by the online impurity analyzers which determine the BSW of the dry crude stream and the total dissolved solids TDS of the recycled water stream from a desalting unit. A salt concentration in the dry crude stream is determined based on a predetermined correlation of BSW and TDS. The invention can be used for continuous monitoring and control of the salt concentration of the crude stream. 
         [0020]    In some embodiments, the present invention provides a process for monitoring salinity of a dry crude stream. The process includes the steps of feeding a recycled water stream using at least one recycled water pump having a predetermined range of operating conditions and at least one emulsion breaking chemical using an emulsion breaking chemical injection system having a predetermined range of operating conditions, to a wet crude stream to produce an enhanced wet crude stream with water and emulsion breaking chemicals. The wet crude stream with water and emulsion breaking chemicals is then fed to a first mixing apparatus having a predetermined range of operating conditions to produce a mixed wet crude stream. The mixed wet crude stream is then fed to a dehydrator vessel having a predetermined range of operating conditions to produce a reduced water content crude stream and a waste water stream. The waste water stream is then fed to a waste water facility using at least one waste water stream pump having a predetermined range of operating conditions. A wash water stream is then fed using at least one wash water pump having a predetermined range of operating conditions to the reduced water content crude stream to produce a hydrated crude stream. The hydrated crude stream is then fed to a second mixing apparatus having a predetermined range of operating conditions to produce a mixed hydrated crude stream. The mixed hydrated crude stream is then fed to a desalter vessel having a predetermined range of operating conditions to produce a dry crude stream and the recycled water stream. The dry crude stream is fed to an analyzing unit for determining the BSW of the dry crude stream. The recycled water stream is fed to an analyzing unit for determining TDS of the recycled water stream from a desalting unit. A salt concentration in the dry crude stream is determined based on a predetermined correlation of BSW and TDS. A multivariable controller is used to assess the operating parameters within the predetermined range of operating conditions of any of the wet crude stream pump, recycled water pump, emulsion breaking chemical injection system, first mixing apparatus, dehydrator vessel, waste water stream pump, wash water pump, second mixing apparatus, and desalter vessel. The multivariable controller then adjusts one or more of operating parameters within the predetermined range of operating conditions to maintain the salt concentration in the dry crude stream within a predetermined range such that power usage of the process is minimized. 
         [0021]    As shown in  FIG. 2 , one embodiment of the invention is a desalting process which feeds wet crude  100  and recycled water stream  110  along with emulsion breaking chemicals to first mixing apparatus  120  to produce mixed wet crude stream  125  which is fed to dehydrator vessel  130 . The dehydrator vessel then separates waste water stream  140  from reduced water content crude stream  150 . Reduced water content crude stream  150  is then combined with wash water stream  160  using second mixing apparatus  170  to create mixed hydrated crude stream  175  which is fed to desalter vessel  180 . From desalter vessel  180 , water stream  110  is produced which can be recycled and fed to wet crude stream  100 . Dry crude stream  190  is also produced from desalter vessel  180 . In the embodiment shown in  FIG. 2 , the TDS of recycled water stream  110  is analyzed using impurity analyzer  210 . The BSW of the dry crude stream  190  is also assessed using impurity analyzer  200 . The salt concentration in the dry crude stream is then assessed by an online analyzer  220  using a predetermined correlation of TDS and BSW. 
         [0022]    As shown further in  FIG. 3 , online analyzer  220  can communicate with multivariable controller  230 . In some embodiments, online analyzer  220  and multivariable controller  230  can be a single unit. Emulsion breaking chemicals  260  can be added to wet crude stream  100  at the same time as the recycled water stream  110 , as shown in  FIG. 3 . The multivariable controller  230  is operable to assess operating parameters of first mixing apparatus  120 , second mixing apparatus  170 , dehydrator vessel  130 , desalter vessel  180 , and emulsion breaking chemical injection systems  240  and  250  and to adjust operating parameters of one or more of first mixing apparatus  120 , second mixing apparatus  170 , dehydrator vessel  130 , desalter vessel  180 , and emulsion breaking chemical injection systems  240  and  250  in order to adjust the salt concentration in the dry crude and to reduce overall chemical, wash water, and power consumption of the process. Additionally, a person of skill in the art will understand that the wash water stream and recycled water streams will be pumped using a wash water pump and a recycled water pump, respectively. The multivariable controller can also be operable to assess operating parameters of the wash water pump and the recycled water pump and adjust the operating parameters in order to adjust the salt concentration in the dry crude and to reduce overall power consumption of the process. 
         [0023]    In some embodiments, the predetermined range of the salt concentration in the dry crude stream is less than 10 lb/1000 barrels. In another embodiment, the predetermined range of the salt concentration in the dry crude stream is less than 5 lb/1000 barrels. 
         [0024]    The at least one emulsion breaking chemical fed to the wet crude stream can be a single chemical or a mixture of several emulsion breaking chemicals. Emulsion breaking chemicals for use in the process are well-known in the art. 
         [0025]    In further embodiments, the at least one emulsion breaking chemical is injected using the emulsion breaking chemical injection system at a lowest injection rate required to maintain the salt concentration in the dry crude stream at less than 10 lb/1000 barrels. In further embodiments, the at least one emulsion breaking chemical is injected using the emulsion breaking chemical injection system at a lowest injection rate required to maintain the salt concentration in the dry crude stream at less than 5 lb/1000 barrels. 
         [0026]    In yet a further embodiment, the injection rate of the emulsion breaking chemical injection system is such that it results in a concentration of emulsion breaking chemical of 3-10 ppm of the mixed wet crude. 
         [0027]    In other embodiments, additional emulsion breaking chemicals can be fed to the wash water stream using a second emulsion breaking chemical injection system. The emulsion breaking chemicals fed to the wash water stream can be the same as or different than the emulsion breaking chemicals fed to a wet crude stream. The emulsion breaking chemicals fed to the wash water stream can be a single chemical or a mixture of several emulsion breaking chemicals. 
         [0028]    In further embodiments, the additional emulsion breaking chemicals are injected using the second emulsion breaking chemical injection system at a lowest injection rate required to maintain the salt concentration in the dry crude stream at less than 10 lb/1000 barrels. In further embodiments, the additional emulsion breaking chemicals are injected using the second emulsion breaking chemical injection system at a lowest injection rate required to maintain the salt concentration in the dry crude stream at less than 5 lb/1000 barrels. 
         [0029]    In some embodiments, the at least one wash water pump is operated within a predetermined range of operating conditions at a lowest level of flow required to maintain the salt concentration in the dry crude stream at less than 10 lb/1000 barrels. In other embodiments, the at least one wash water pump is operated within a predetermined range of operating conditions at a lowest level of flow required to maintain the salt concentration in the dry crude stream at less than 5 lb/1000 barrels. 
         [0030]    In some embodiments, the first mixing apparatus is operated within a predetermined range of operating conditions at a lowest mixing efficiency and for the least amount of time required to maintain the salt concentration in the dry crude stream at less than 10 lb/1000 barrels. In other embodiments, the first mixing apparatus is operated within a predetermined range of operating conditions at a lowest mixing efficiency and for the least amount of time required to maintain the salt concentration in the dry crude stream at less than 5 lb/1000 barrels. 
         [0031]    In other embodiments, the dehydrator vessel is operated within a predetermined range of operating conditions at a lowest level of energy consumption required to maintain the salt concentration in the dry crude stream at less than 10 lb/1000 barrels. In further embodiments, the dehydrator vessel is operated within a predetermined range of operating conditions at a lowest level of energy consumption required to maintain the salt concentration in the dry crude stream at less than 5 lb/1000 barrels. 
         [0032]    In other embodiments, the at least one waste water stream pump is operated within the predetermined range of operating conditions at a lowest level of flow required to maintain the salt concentration in the dry crude stream at less than 10 lb/1000 barrels. In further embodiments, the at least one waste water stream pump is operated within the predetermined range of operating conditions at a lowest level of flow required to maintain the salt concentration in the dry crude stream at less than 5 lb/1000 barrels. 
         [0033]    In other embodiments, the at least one recycled water pump is operated within the predetermined range of operating conditions at a lowest level of flow required to maintain the salt concentration in the dry crude stream at less than 10 lb/1000 barrels. In further embodiments, the at least one recycled water pump is operated within the predetermined range of operating conditions at a lowest level of flow required to maintain the salt concentration in the dry crude stream at less than 5 lb/1000 barrels. 
         [0034]    In another embodiment, the wet crude stream pump is operated within a predetermined range of operating conditions at a lowest level of flow required to maintain the salt concentration in the dry crude stream at less than 10 lb/1000 barrels. In further embodiments, the wet crude stream pump is operated within a predetermined range of operating conditions at a lowest level of flow required to maintain the salt concentration in the dry crude stream at less than 5 lb/1000 barrels. 
         [0035]    In another embodiment, the second mixing apparatus is operated within a predetermined range of operating conditions at a lowest mixing efficiency and for the least amount of time required to maintain the salt concentration in the dry crude stream at less than 10 lb/1000 barrels. In further embodiments, the second mixing apparatus is operated within a predetermined range of operating conditions at a lowest mixing efficiency and for the least amount of time required to maintain the salt concentration in the dry crude stream at less than 5 lb/1000 barrels. 
         [0036]    In another embodiment, the desalter vessel is operated within a predetermined range of operating conditions at a lowest level of energy consumption required to maintain the salt concentration in the dry crude stream at less than 10 lb/1000 barrels. In further embodiments, the desalter vessel is operated within a predetermined range of operating conditions at a lowest level of energy consumption required to maintain the salt concentration in the dry crude stream at less than 5 lb/1000 barrels. 
         [0037]    In another embodiment, the desalter vessel is operated within a predetermined range of operating conditions at a temperature of between about 50-150° C. 
         [0038]    In a further embodiment, the multivariable controller adjusts one or more of the operating parameters within the predetermined range of operating conditions of the wet crude stream pump, recycled water pump, emulsion breaking chemical injection system, first mixing apparatus, dehydrator vessel, waste water stream pump, wash water pump, second mixing apparatus, and desalter vessel such that the energy consumption of the process is at a minimum level required to maintain a salt concentration in the dry crude stream of less than 10 lb/1000 barrels. 
         [0039]    In a further embodiment, the multivariable controller adjusts the operating parameters within the predetermined range of operating conditions of the wet crude stream pump, recycled water pump, emulsion breaking chemical injection system, first mixing apparatus, dehydrator vessel, waste water stream pump, wash water pump, second mixing apparatus, and desalter vessel such that the energy consumption of the process is at a minimum level required to maintain a salt concentration in the dry crude stream of less than 5 lb/1000 barrels. 
         [0040]    In other embodiments, the present invention provides an apparatus for controlling content of an impurity in a crude oil stream. The apparatus includes at least one mixing apparatus for receiving a water stream and a wet crude stream for mixing water and wet crude stream to provide a wet crude stream with water. The apparatus also includes at least one emulsion breaking chemical injection system for injecting an emulsion breaking chemical into the wet crude stream with water. The apparatus also includes at least one dehydrator vessel for receiving the wet crude stream with water for removing an amount of water to provide a reduced water content crude stream and a waste water stream. The apparatus also includes at least one water pump for pumping the water stream. The apparatus further includes at least one desalter vessel for removing salt from the reduced water content crude stream to produce a dry crude stream and a second waste water stream. The apparatus also includes a first impurity analyzer for measuring BSW of the dry crude stream and operable to provide a measurement of a BSW value to a controller. The apparatus further includes a second impurity analyzer for measuring TDS of the water stream and operable to provide a measurement of a TDS value to the controller. The apparatus also includes a multivariable controller operable to perform an assessment of the BSW value and the TDS value using a predefined correlation. The controller is further operable to adjust at least one operating parameter of at least one of the mixing apparatus, the emulsion breaking chemical injection system, water pump, desalter vessel, first impurity analyzer, and second impurity analyzer, such that the power consumption of the apparatus for controlling content of impurity in a crude oil stream is optimized. 
         [0041]    In some embodiments, the impurity in the crude oil stream that is controlled is salt. 
         [0042]    In a further embodiment, the BSW in the dry crude stream is less than about 0.2% by volume of the dry crude stream, or less than about 0.1% by volume of the dry crude stream. 
         [0043]    In some embodiments of the apparatus, the multivariable controller is operable to control one or more operating parameters of the mixing apparatus, the emulsion breaking chemical injection system, water pump, desalter vessel, first impurity analyzer, and second impurity analyzer so as to maintain the BSW value of the dry crude stream at a maximum of about 0.2% volume of the dry crude stream. 
         [0044]    In some embodiments of the apparatus, the multivariable controller is operable to control one or more operating parameters of the mixing apparatus, the emulsion breaking chemical injection system, water pump, desalter vessel, first impurity analyzer, and second impurity analyzer so as to maintain the BSW value of the dry crude stream at a maximum of about 0.1% volume of the dry crude stream. 
         [0045]    In further embodiments of the apparatus, the multivariable controller is operable to control one or more operating parameters of the mixing apparatus, the emulsion breaking chemical injection system, water pump, desalter vessel, first impurity analyzer, and second impurity analyzer to maintain a salt concentration in the dry crude stream of less than 10 lb/1000 barrels. 
         [0046]    In further embodiments of the apparatus, the multivariable controller is operable to control one or more operating parameters of the mixing apparatus, the emulsion breaking chemical injection system, water pump, desalter vessel, first impurity analyzer, and second impurity analyzer to maintain a salt concentration in the dry crude stream of less than 5 lb/1000 barrels. 
         [0047]    In some embodiments of the apparatus, the multivariable controller can be used to control one or more operating parameters of the mixing apparatus, the emulsion breaking chemical injection system, water pump, desalter vessel, first impurity analyzer, and second impurity analyzer so as to maintain a salt concentration in the dry crude stream of less than 10 lb/1000 barrels and to maintain the BSW value of the treated dry crude stream at a maximum of 0.2% volume of the dry crude stream. 
         [0048]    In some embodiments of the apparatus, the multivariable controller can be used to control one or more operating parameters of the mixing apparatus, the emulsion breaking chemical injection system, water pump, desalter vessel, first impurity analyzer, and second impurity analyzer so as to maintain a salt concentration in the dry crude stream of less than 5 lb/1000 barrels and to maintain the BSW value of the dry crude stream at a maximum of 0.1% volume of the dry crude stream. 
         [0049]    In some embodiments, the predetermined correlation of BSW and TDS is based on the equation below: 
         [0000]      PTB=350.5*ρ desalter outlet water (1500 BSW/100−BSW)*(TDS desalter outlet water /10 6 )/(combined mixing efficiency of desalter 180 and mixing valve 170)
 
         [0050]    It will be understood by a person of skill in the art that the optimization of the described invention will be dependent on a number of factors, including the mixing efficiency of the water and crude. Various methods are known to improve mixing efficiency including commercially available mixing valves which have improved mixing efficiencies. 
         [0051]    Embodiments of the present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step. 
         [0052]    Unless defined otherwise, all technical and scientific terms used have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. 
         [0053]    The singular forms “a,” “an,” and “the” include plural referents, unless the context clearly dictates otherwise. 
         [0054]    As used herein and in the appended claims, the words “comprise,” “has,” and “include” and all grammatical variations thereof are each intended to have an open, non-limiting meaning that does not exclude additional elements or steps. 
         [0055]    Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within the range. 
         [0056]    Although the present invention has been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereupon without departing from the principle and scope of the invention. Accordingly, the scope of the present invention should be determined by the following claims and their appropriate legal equivalents.