reference will now be made in detail to the various aspects of the present invention . the method and corresponding steps of the invention will be described in conjunction with the detailed description of the compositions . the present invention will now be described in greater detail in connection with the figures . the present invention aims to reduce fouling in heat exchangers and other components located within a refinery . this aim is achieved by a blended base crude oil , which can consist of a whole crude oil , a blend of two or more crude oils or fractions thereof with a predetermined amount of a high solvency dispersive power ( hsdp ) crude oil . the addition of hsdp crude oil mitigates both asphaltene induced fouling and particulate induced / promoted fouling . the high s bn of these hsdp crude oils allows for the enhanced solubility of any asphaltenes in the rest of the crude oils and / or blends . a measured tan is believed to indicate the presence of molecules that help disperse the particulates in the crude oil blend which prevents them from adhering to the heated surface . in order to achieve the reduction in fouling , the hsdp crude oil should have a total acid number ( tan ) of at least 0 . 3 mg koh / g . higher tan levels can result in improved fouling reduction and mitigation . the hsdp crude oil should have a solubility blending number ( s bn ) of at least 90 . higher s bn levels can result in improved fouling reduction and mitigation . the volume of hsdp crude oil necessary in the blended crude oil will vary based upon the tan and / or s bn values of the hsdp crude oil . the higher the tan and / or s bn values of the hsdp crude oil , the lower the volume of hsdp crude oil necessary to produce a blended crude oil that will reduce and / or mitigate both asphaltene induced fouling and particulate induced fouling and / or promotion in refinery components , including but not limited to heat exchangers and the like . the hsdp crude oil preferably makes up between three percent and fifty percent of the total volume of the blended crude oil . the blended crude oil is then processed within the refinery . the blended crude oil exhibits improved characteristics over the base crude oil . specifically , the blended crude oil exhibits a significant reduction in fouling over base crude which contain particulates . this results in improved heat transfer within the heat exchanger and a reduction in overall energy consumption . fig1 depicts an alcor testing arrangement used to measure what the impact the addition of particulates to a crude oil has on fouling and what impact the addition of a hsdp crude oil has on the reduction and mitigation of fouling . the testing arrangement includes a reservoir 10 containing a feed supply of crude oil . the feed supply of crude oil can contain a base crude oil containing a whole crude or a blended crude containing two or more crude oils . the feed supply can also contain a hsdp crude oil . the feed supply is heated to a temperature of approximately 150 ° c ./ 302 ° f . and then fed into a shell 11 containing a vertically oriented heated rod 12 . the heated rod 12 can be formed from a carbon steel . the heated rod 12 simulates a tube in a heat exchanger . the heated rod 12 is electrically heated to a predetermined temperature and maintained at such predetermined temperature during the trial . typically rod surface temperatures are approximately 370 ° c ./ 698 ° f . and 400 ° c ./ 752 ° f . the feed supply is pumped across the heated rod 12 at a flow rate of approximately 3 . 0 ml / minute . the spent feed supply is collected in the top section of the reservoir 10 . the spent feed supply is separated from the untreated feed supply oil by a sealed piston , thereby allowing for once - through operation . the system is pressurized with nitrogen ( 400 - 500 psig ) to ensure gases remain dissolved in the oil during the test . thermocouple readings are recorded for the bulk fluid inlet and outlet temperatures and for surface of the rod 12 . during the constant surface temperature testing , foulant deposits and builds up on the heated surface . the foulant deposits are thermally degraded to coke . the coke deposits cause an insulating effect that reduces the efficiency and / or ability of the surface to heat the oil passing over it . the resulting reduction in outlet bulk fluid temperature continues over time as fouling continues . this reduction in temperature is referred to as the outlet liquid δt or δt and can be dependent on the type of crude oil / blend , testing conditions and / or other effects , such as the presence of salts , sediment or other fouling promoting materials . a standard alcor fouling test is carried out for 180 minutes . the total fouling , as measured by the total reduction in outlet liquid temperature is referred to as δt180 or dt180 . fig1 and fig2 illustrate the impact that the presence of particulates in a crude oil has on fouling of a refinery component or unit . there is an increase in fouling in the presence of iron oxide ( fe 2 o 3 ) particles when compared to similar crude oils that do not contain particulates . the present invention will be described in connection with the use of a low - sulfur , low asphaltene or lsla whole crude oil and a high - sulfur , high asphaltene or hsha crude oil blend as base crude oil examples . these oils were selected as being representative of certain classifications of crude oil . the lsla crude oil represents a low s bn , high reactive sulfur and low asphaltenes crude oil . the hsha blend crude oil represents a crude oil that is both high in asphaltenes and reactive sulfur . the use of these crude oils is for illustrative purposes only , the present invention is not intended to be limited to application only with lsla crude oil and hsha crude oil . it is intended that the present invention has application with all whole and blended crude oils and formulations of the same that experience and / or produce fouling in refinery components including but not limited to heat exchangers . the presence of fouling reduces the heat transfer of the heating tubes or rods contained within a heat exchanger . as described above , the presence of fouling has an adverse impact of heat exchanger performance and efficiency . the present inventors have found that the addition of a crude oil having a high tan and high s bn to the base crude oil reduces particulate - induced fouling . the degree of fouling reduction appears to be a function of the tan measured on the overall blend . this is believed to be due to the ability of the naphthenic acids to keep particulates present in the blends from wetting and adhering to the heated surface , where otherwise promoted and accelerated fouling / coking occur . most high tan crude oils also have very high s bn levels , which have been shown to aid in dissolving asphaltenes and / or keeping them in solution more effectively which also reduces fouling that would otherwise occur due to the incompatibility and near - incompatibility of crude oils and blends . these crude oils are classified as high solvency dispersive power ( hsdp ) crude oils . there is a notable reduction in fouling when a predetermined amount of hsdp crude oil is added to the base crude , where the hsdp crude oil has a tan as low as 0 . 3 mg koh / g and a s bn as low as 90 . the predetermined amount of hsdp crude oil can make up as low as three percent ( 3 %) of the total volume of the blended crude oil ( i . e ., base crude oil + hsdp crude oil ). sample tests were performed to determine the effect the addition of hsdp crude oils a and / or b to a hsha base crude oil has on the fouling of the base oil . the results are illustrated in fig3 . fig3 is a variation of fig2 where the reduction in fouling associated with the addition of a predetermined amount of hsdp crude is blended with a base crude oil containing the hsha crude oil . in one example , the base crude oil containing hsha is blended with a hsdp crude oil , which accounts for twenty five percent ( 25 %) of the total volume of the blended crude oil . the hsdp crude oil is labeled hsdp crude oil a having an approximate tan of 4 . 8 mg koh / g and a s bn of 112 . as shown in fig3 , a significant reduction in fouling is achieved when compared to both base crude oil containing particulates and a base oil without particulates . in another example , the base crude oil containing hsha is blended with a hsdp crude oil , which accounts for fifty percent ( 50 %) of the total volume of the blended crude oil . the hsdp crude oil is hsdp crude oil b having an approximate tan of 1 . 1 mg koh / g and a s bn of 115 . while the impact of the hsdp crude oil b on the fouling of the base crude oil is not as significant as the hsdp crude oil a , the hsdp crude oil b nonetheless produces a marked decrease in the fouling of a base crude oil containing particulates . sample tests were performed to determine the effect the addition of hsdp crude oils a and b on the fouling of the base oil . the results are illustrated in fig4 . fig4 is a variation of fig1 where the reduction in fouling associated with the addition of a predetermined amount of hsdp crude is blended with a base crude oil . in the illustrated examples , the base crude oil is a lsla crude oil and is blended with hsdp crude oil a , which accounts for twenty five percent ( 25 %) of the total volume of the blended crude oil . like the addition of hsdp crude oil a to the hsha crude oil , a significant reduction in fouling is achieved when compared to both base crude oil containing particulates and a base oil without particulates . in the other illustrated example , the lsla base crude oil is blended with hsdp crude oil b , which accounts for fifty percent ( 50 %) of the total volume of the blended crude oil . while the impact of the hsdp crude oil b on the fouling of the base crude oil is not as significant as the hsdp crude oil a , the hsdp crude oil b again produces a marked decrease in the fouling of a base crude oil containing particulates . sample tests were also performed to determine the effect the addition of the hsdp crude oil a to a base oil containing either lsla whole crude oil or hsha blended crude oil has on the fouling of the base oil . the hsdp a crude oil having an approximate tan of 4 . 8 mg koh / g and a s bn of 112 . the results associated with the impact of the hsdp a on the hsha blend are illustrated in fig5 . the results associated with the impact of the hsdp a on the lsla whole crude oil are illustrated in fig6 . for both base oils , the addition of the hsdp a crude as the hsdp crude oil produced a reduction in fouling . as shown in fig5 - 8 , the reduction in fouling increased as the predetermined amount of hsdp crude oil content in the blended crude oil increased . the above illustrative examples of the benefits of the present invention were based upon the use of examples a and b crude oils as the hsdp crude oil . the present invention is not intended to be limited to only these examples of hsdp crude oils . other hsdp crude oils having an approximate tan of at least 0 . 3 mg koh / g and a s bn of at least 90 will achieve reductions in fouling . fig9 illustrates the impact beneficial impact on fouling that the addition of various hsdp crude oils on a base oil of lsla whole crude oil . as summarized in table 1 below , the addition of hsdp crude oils resulted in a reduction in fouling when compared to base crude oil containing particulates . in accordance with another aspect of the invention , a method is provided for on - line cleaning of a fouled crude oil refinery component . on - line cleaning of a fouled crude oil refinery component provides that the component does not need to be removed from service and it is not necessary to re - route crude oil to other refinery components . the method generally includes operating a fouled crude oil refinery component , and feeding a blended crude oil to the fouled crude oil refinery component . the blended crude oil including a base crude oil and a predetermined amount of a high solvency dispersive power ( hsdp ) crude oil , the hsdp crude oil having a total acid number ( tan ) of at least 0 . 3 mg koh / g and a solubility blending number ( s bn ) of at least 90 . laboratory fouling simulation tests have been performed to demonstrate and measure the differences in the capabilities of many hsdp crude oils to mitigate fouling . those with a higher degree of effectiveness ( measured at similar concentrations ) are referred to as “ top - performing ” hsdp crude oils , wherein lower amounts of these crude oils generally are needed to achieve the desired fouling mitigation . higher amounts of the other less effective (“ moderate - performing ”) hsdp crude oils are required for blending to achieve the same levels of fouling reduction . the s bn and tan properties identify whether or not a crude oil is an hsdp . alcor fouling simulation tests carried out with hsdp crude oils blended with known fouling crudes can be used to define relative hsdp performance , as well as to estimate the preferred concentrations desired to mitigate whole crude blend fouling . table 2 provides a list of crude oils that have been determined to have hsdp capability . the tested s bn and tan levels are provided in table 2 . the relative performance of each hsdp crude oil was determined using alcor fouling simulation tests following co - blending at 25 % of the total volume with two different fouling control blends having 200 wppm particulates (& lt ; 0 . 5 micron ). the hsdp crude oils listed in table 2 are provided for purpose of illustration and not limitation ; additional hsdp crude oils also can be suitable for the present invention . refinery evaluations can be used to define concentrations needed to facilitate on - line cleaning behavior . the effectiveness of each of the hsdp crude oils listed in table 2 were determined using alcor testing procedures , as described above . fig1 and 12 provide the alcor dimensionless delta t from tests carried out on two different fouling control blends with 25 % of the total volume of each hsdp blend a through r . as above , any known or suitable technique can be used to blend an hsdp crude oil with a base crude oil . dimensionless delta t factors in heat transfer characteristics ( viscosity , density , heat capacity , etc .) of the oil and environmental conditions ( e . g ., fluctuating room temperatures ) that could have a slight impact on the maximum oil outlet temperatures achieved . dimensionless dt corrects for these different heat transfer impacts . this correction is achieved by dividing δt ( i . e ., toutlet − toutletmax ) by a measure of heat transferred from the rod during each experiment , which is simply the rod temperature minus maximum outlet temperature , as shown below : fig1 and 14 illustrate the performance difference between top - performing and moderate - performing hsdp crude oils . as shown in fig1 , the top - performing hsdp crude oil is effective to reduce fouling with concentrations as low as three percent ( 3 %). it is contemplated that still lower concentrations can be used with a lower reduction in fouling . the reduction in fouling increases when the concentration is increased to ten percent ( 10 %) or twenty five percent ( 25 %) of the total volume of the blend . the present invention is not intended to be limited to the concentrations illustrated in fig1 ; rather , concentrations of top performing hsdp crude oil between the concentrations identified in fig1 are well within the scope of the present invention , as well as concentrations greater than twenty five percent ( 25 %). to achieve more effective levels of reduced fouling using a “ moderate - performing ” hsdp crude oil , a relatively higher concentration of the hsdp crude oil is necessary than when using a “ top - performing ” hsdp crude oil . as shown in fig1 , higher concentrations of the moderate performing hsdp crude oil are required in order to reduce fouling . concentrations of twenty five percent ( 25 %) and fifty percent ( 50 %) of a moderate performing hsdp crude oil are effective to reduce fouling . the present invention is not intended to be limited to the concentrations illustrated in fig1 ; rather , concentrations of moderate performing hsdp crude oil between the concentrations identified in fig1 are well within the scope of the present invention , as well as concentrations greater than fifty percent ( 50 %). as shown in fig1 and 16 , performance of hsdp crude oils in reducing fouling is dependent upon the concentration of the hsdp crude oil . fig1 and 16 plot final alcor dimensionless δt levels after 180 minutes of run time . as shown in fig1 , top - performing hsdp crude oil is effective to reduce fouling with as little as about 2 percent of hsdp crude oil a in the blend . the concentration of hsdp crude oil suitable to effectively mitigate fouling of other crude oils was determined using the alcor testing approach described above . as demonstrated by the alcor testing of top and moderate performing hsdp crude oils , low levels of top - performing crude oils are effective for mitigating fouling of crude oil refinery components . levels of top performing hsdp crude oil as low as 2 - 25 percent the total volume of the blend are effective . for example , as shown in fig1 , as little as two percent ( 2 %) of top performing hsdp crude oil is effective to significantly reduce fouling . higher levels of moderate performing hsdp crude oil of from about 10 - 50 percent of the total volume of the blend are similarly effective . for example , as shown in fig1 , at least about twenty - five percent ( 25 %) of moderate performing hsdp crude oil is effective to significantly reduce fouling . preferably one or more hsdp crude oils are blended into a blended crude oil in an amount of from 2 to 50 percent of the total volume of the blend . more preferably , the one or more hsdp crude oils are blended in an amount of from 3 to 25 percent of the total volume of the blend . in accordance with another aspect of the invention , the one or more hsdp crude oils can be blended in an amount of from about 5 to 10 percent of the total volume of the blend or from 10 to 50 percent of the total volume of the blend . in accordance with another aspect of the present invention , a system is provided that is capable of experiencing fouling conditions associated with particulate or asphaltene fouling . the system generally includes at least one crude oil refinery component and a blend in fluid communication with the crude oil refinery component . the blend includes a blend of a base crude oil and a predetermined amount of a high solvency dispersive power ( hsdp ) crude oil , the hsdp crude oil having a total acid number ( tan ) of at least 0 . 3 mg koh / g and a solubility blending number ( s bn ) of at least 90 . particularly , it has also been discovered to use hsdp crude oils to perform on - line cleaning of already fouled crude pre - heat train exchangers and other refinery components to improve heat transfer efficiencies and recovered furnace coil - inlet - temperatures ( cits ). cit levels of both atmospheric and vacuum pipestill furnaces have been found to increase dramatically when running hsdp crude oils , resulting in energy savings and environmental benefits as a result of reduced fired heating needs . as with co - blending for fouling mitigation , the on - line heat exchanger cleaning efficiency is dependent on the hsdp crude oil and its concentration . as shown in fig1 and 18 , varying levels of hsdp crude oils have been shown to be effective in cleaning an already fouled crude oil refinery component , such as a heat exchanger . fouled exchangers result in reduced furnace ( atmospheric and vacuum ) coil - inlet - temperatures ( cits ), which requires additional firing resulting in increased energy demands and costs . the hsdp crude oils of the present invention have been shown to remove the foulant from already fouled refinery components . as shown in fig1 and 18 , addition of a top - performing hsdp crude oil to a fouled heat exchanger resulted in recovered cit levels , thereby reducing the energy required to fire the furnace . the recovery in cit shown in fig1 was 40 ° c . and occurred within a period as short as about 1 to 2 days of introducing the hsdp crude oil into the blend . fig1 shows heat exchanger performing improvement upon addition of hsdp crude oil b in amounts varying from 2 to 20 percent . as shown in fig1 , a moderate performing hsdp crude oil is effective in cleaning an already fouled heat exchanger . the improvements in cit observed were up to 20 ° c . when adding between about twenty percent ( 20 %) and forty percent ( 40 %) of moderate performing hsdp crude oil k . as shown in fig1 and 19 , higher levels of moderate performing hsdp crude oils are required to obtain the same heat exchanger recovery obtained with lower levels of top performing hsdp crude oil . it will be apparent to those skilled in the art that various modifications and / or variations can be made without departing from the scope of the present invention . it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense . while the present invention has been described in the context of the heat exchanger in a refinery operation , the present invention is not intended to be so limited ; rather it is contemplated that the present invention is suitable for reducing and / or mitigating fouling in other refinery components including but not limited to pipestills , cokers , visbreakers and the like . furthermore , it is contemplated that the use of a hsdp crude oil , as described in connection with the present invention , can be combined with other techniques for reducing and / or mitigating fouling . such techniques include , but are not limited to , ( i ) the provision of low energy surfaces and modified steel surfaces in heat exchanger tubes , as described in u . s . patent application ser . nos . 11 / 436 , 602 and 11 / 436 , 802 , the disclosures of which are incorporated herein specifically by reference , ( ii ) the use of controlled mechanical vibration , as described in u . s . patent application ser . no . 11 / 436 , 802 , the disclosure of which is incorporated herein specifically by reference ( iii ) the use of fluid pulsation and / or vibration , which can be combined with surface coatings , as described in u . s . patent application ser . no . 11 / 802 , 617 , filed on jun . 19 , 2007 , entitled “ reduction of fouling in heat exchangers ,” the disclosure of which is incorporated herein specifically by reference ( iv ) the use of electropolishing on heat exchanger tubes and / or surface coatings and / or modifications , as described in u . s . patent application ser . no . 11 / 641 , 754 , the disclosure of which is incorporated herein specifically by reference and ( v ) combinations of the same , as described in u . s . patent application ser . no . 11 / 641 , 755 , filed on dec . 20 , 2006 , entitled “ a method of reducing heat exchanger fouling in a refinery ,” the disclosure of which is incorporated herein specifically by reference . thus , it is intended that the present invention covers the modifications and variations of the method herein , provided they come within the scope of the appended claims and their equivalents . while a particular form of the invention has been described , it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention . accordingly , it is not intended that the invention be limited except by the appended claims . while the present invention has been described with reference to one or more particular embodiments , those skilled in the art will recognize that many changes can be made thereto without departing from the spirit and scope of the present invention . each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the claimed invention , which is set forth in the following claims .