Patent Grant
7951340
The present invention relates to processing of whole crude oils, blends and fractions in refineries and petrochemical plants. In particular, the present invention relates to the reduction of particulate induced crude oil fouling and asphaltene induced crude oil fouling. The present invention relates to the blending of atmospheric and/or vacuum resid fractions of a high-solvency-dispersive-power (HSDP) crude oil with a base crude oil or crude oil blends to reduce fouling in pre-heat train exchangers, furnaces, and other refinery process units.
Fouling is generally defined as the accumulation of unwanted materials on the surfaces of processing equipment. In petroleum processing, fouling is the accumulation of unwanted hydrocarbon-based deposits on heat exchanger surfaces. It has been recognized as a nearly universal problem in design and operation of refining and petrochemical processing systems, and affects the operation of equipment in two ways. First, the fouling layer has a low thermal conductivity. This increases the resistance to heat transfer and reduces the effectiveness of the heat exchangers. Second, as deposition occurs, the cross-sectional area is reduced, which causes an increase in pressure drop across the apparatus and creates inefficient pressure and flow in the heat exchanger.
Fouling in heat exchangers associated with petroleum type streams can result from a number of mechanisms including chemical reactions, corrosion, deposit of insoluble materials, and deposit of materials made insoluble by the temperature difference between the fluid and heat exchange wall. For example, the inventors have shown that a low-sulfur, low asphaltene (LSLA) crude oil and a high-sulfur, high asphaltene (HSHA) crude blend are subject to a significant increase in fouling when in the presence of iron oxide (rust) particulates, as shown for example in
One of the more common root causes of rapid fouling, in particular, is the formation of coke that occurs when crude oil asphaltenes are overexposed to heater tube surface temperatures. The liquids on the other side of the exchanger are much hotter than the whole crude oils and result in relatively high surface or skin temperatures. The asphaltenes can precipitate from the oil and adhere to these hot surfaces. Another common cause of rapid fouling is attributed to the presence of salts and particulates. Salts/particulates can precipitate from the crude oils and adhere to the hot surfaces of the heat exchanger. Inorganic contaminants play both an initiating and promoting role in the fouling of whole crude oils and blends. Iron oxide, iron sulfide, calcium carbonate, silica, sodium and calcium chlorides have all been found to be attached directly to the surface of fouled heater rods and throughout the coke deposit.
Prolonged exposure to such surface temperatures, especially in the late-train exchanger, allows for the thermal degradation of the organics and asphaltenes to coke. The coke then acts as an insulator and is responsible for heat transfer efficiency losses in the heat exchanger by preventing the surface from heating the oil passing through the unit. Salts, sediment and particulates have been shown to play a major role in the fouling of pre-heat train heat exchangers, furnaces and other downstream units. Desalter units are still the only opportunity refineries have to remove such contaminants and inefficiencies often result from the carryover of such materials with the crude oil feeds.
Blending of oils in refineries is common, but certain blends are incompatible and cause precipitation of asphaltenes that can rapidly foul process equipment. Improper mixing of crude oils can produce asphaltenic sediment that is known to reduce heat transfer efficiency. Although most blends of unprocessed crude oils are not potentially incompatible, once an incompatible blend is obtained, the rapid fouling and coking that results usually requires shutting down the refining process in a short time. To return the refinery to more profitable levels, the fouled heat exchangers need to be cleaned, which typically requires removal from service, as discussed below.
Heat exchanger in-tube fouling costs petroleum refineries hundreds of millions of dollars each year due to lost efficiencies, throughput, and additional energy consumption. With the increased cost of energy, heat exchanger fouling has a greater impact on process profitability. Petroleum refineries and petrochemical plants also suffer high operating costs due to cleaning required as a result of fouling that occurs during thermal processing of whole crude oils, blends and fractions in heat transfer equipment. While many types of refinery equipment are affected by fouling, cost estimates have shown that the majority of profit losses occur due to the fouling of whole crude oils, blends and fractions in pre-heat train exchangers.
Heat exchanger fouling forces refineries to frequently employ costly shutdowns for the cleaning process. Currently, most refineries practice off-line cleaning of heat exchanger tube bundles by bringing the heat exchanger out of service to perform chemical or mechanical cleaning. The cleaning can be based on scheduled time or usage or on actual monitored fouling conditions. Such conditions can be determined by evaluating the loss of heat exchange efficiency. However, off-line cleaning interrupts service. This can be particularly burdensome for small refineries because there will be periods of non-production.
The need exists to be able to prevent the precipitation/adherence of particulates and asphaltenes on the heated surfaces before the particulates can promote fouling and the asphaltenes become thermally degraded or coked. The coking mechanism requires both temperature and time. The time factor can be greatly reduced by keeping the particulates away from the surface and by keeping the asphaltenes in solution. Such reduction and/or elimination of fouling will lead to increased run lengths (less cleaning), improved performance and energy efficiency while also reducing the need for costly fouling mitigation options.
Some refineries and crude schedulers currently follow blending guidelines to minimize asphaltene precipitation and the resultant fouling of pre-heat train equipment. Such guidelines suggest blending crude oils to achieve a certain relationship between the solubility blending number (SBN) and insolubility number (IN) of the blend. The SBN is a parameter relating to the compatibility of an oil with different proportions of a model solvent mixture, such as toluene/n-heptane. The SBN is related to the IN, which is determined in a similar manner, as described in U.S. Pat. No. 5,871,634, which is incorporated herein by reference. Some blending guidelines suggest a SBN/IN blend ratio>1.3 and a delta (SBN−IN)>10 to minimize asphaltene precipitation and fouling. However, these blends are designed for use as a passive approach to minimizing asphaltene precipitation.
Attempts have been made to improve the method of blending two or more petroleum oils that are potentially incompatible while maintaining compatibility to prevent the fouling and coking of refinery equipment. U.S. Pat. No. 5,871,634 discloses a method of blending that includes determining the insolubility number (IN) for each feedstream and determining the solubility blending number (SBN) for each stream and combining the feedstreams such that the SBN of the mixture is greater than the In of any component of the mix. In another method, U.S. Pat. No. 5,997,723 uses a blending method in which petroleum oils are combined in certain proportions in order to keep the SBN of the mixture higher than 1.4 times the IN of any oil in the mixture.
These blends do not minimize both fouling associated with asphaltene and particulate induced/promoted fouling. There is a need for developing a proactive approach to addressing organic, inorganic and asphaltene precipitation and thereby minimize the associated foulant deposition and/or build up.
According to one aspect of the present invention, a method for reducing fouling in a crude oil refinery component is disclosed having the steps of providing a base crude oil, providing a high solvency dispersive power (HSDP) crude oil, the HSDP crude oil having an Sbn>90 and a total acid number (TAN) of at least 0.3 mg KOH/g, distilling the HSDP crude oil to isolate atmospheric and vacuum resid fractions, blending the base crude oil with an effective amount of the atmospheric or vacuum resid fractions to create a blended crude oil, and feeding the blended crude oil to a crude oil refinery component. The crude oil refinery component can be a heat exchanger, furnace, distillation column, scrubber, reactor, liquid-jacketed tank, pipestill, coker, or visbreaker. The effective amount of HSDP crude oil resid fractions can be at least about five percent (5%) of the total volume of the blended crude oil. The base crude oil can be one of a whole crude oil or a blend of at least two crude oils. The HSDP crude oil atmospheric resid fraction can have a solubility blending number (SBN) of at least 105. The HSDP crude oil vacuum resid fraction can have an SBN of at least 182.
According to another aspect of the present invention, a blended crude oil is disclosed including a base crude oil and an effective amount of an atmospheric resid fraction and a vacuum resid fraction of a high-solvency-dispersive-power (HSDP) crude oil, the HSDP crude oil having an Sbn>90 and a total acid number (TAN) of at least 0.3 mg KOH/g. The effective amount of HSDP crude oil resid fractions can be at least about five percent (5%) of the total volume of the blended crude oil. The base crude oil can be one of a whole crude oil or a blend of at least two crude oils. The HSDP crude oil atmospheric resid fraction can have a solubility blending number (SBN) of at least 105. The HSDP crude oil vacuum resid fraction can have an SBN of at least 182.
According to yet another aspect of the present invention, a system is disclosed that is capable of experiencing fouling conditions associated with particulate or asphaltene fouling. The system including at least one crude oil refinery component, and a blend in fluid communication with the crude oil refinery component, the blend including a base crude oil and an effective amount of an atmospheric resid fraction and/or a vacuum resid fraction of a high-solvency-dispersive-power (HSDP) crude oil, the HSDP crude oil having an Sbn>90 and a total acid number (TAN) of at least 0.3 mg KOH/g. The crude oil refinery component can be a heat exchanger, furnace, distillation column, scrubber, reactor, liquid-jacketed tank, pipestill, coker, or visbreaker. The effective amount of HSDP crude oil resid fractions can be at least about five percent (5%) of the total volume of the blended crude oil. The base crude oil can be one of a whole crude oil or a blend of at least two crude oils. The HSDP crude oil atmospheric resid fraction can have a solubility blending number (SBN) of at least 105. The HSDP crude oil vacuum resid fraction can have an SBN of at least 182.
According to another aspect of the present invention, a method for on-line cleaning of a fouled crude oil refinery component is disclosed, having the steps of operating a fouled crude oil refinery component, and feeding a blended crude oil to the fouled crude oil refinery component, the blended crude oil comprising a blend of a base crude oil and an effective amount of an atmospheric resid fraction and a vacuum resid fraction of a high solvency dispersive power (HSDP) crude oil, the HSDP crude oil having an Sbn>90 and a total acid number (TAN) of at least 0.3 mg KOH/g. The crude oil refinery component can be a heat exchanger, furnace, distillation column, scrubber, reactor, liquid-jacketed tank, pipestill, coker, or visbreaker. The effective amount of HSDP crude oil resid fractions can be at least five percent (5%) of the total volume of the blended crude oil. The base crude oil can be one of a whole crude oil or a blend of at least two crude oils. The HSDP crude oil atmospheric resid fraction can have a solubility blending number (SBN) of at least 105. The HSDP crude oil vacuum resid fraction can have an SBN of at least 182.
These and other features of the present invention will become apparent from the following detailed description of preferred embodiments which, taken in conjunction with the accompanying drawings, illustrate by way of example the principles of the present invention.
The invention will now be described in conjunction with the accompanying drawings in which:
In the drawings, like reference numerals indicate corresponding parts in the different figures.
While the invention is capable of various modifications and alternative forms, specific embodiments thereof have been shown by way of the process diagrams and testing data shown in
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 SBN 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 (SBN) of at least 90. Higher SBN 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 SBN values of the HSDP crude oil. The higher TAN and/or SBN 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.
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.
The present inventors have found that the addition of a crude oil having a high TAN and/or high SBN 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 SBN 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 SBN 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
Sample tests were performed to determine the effect the addition of HSDP Crude Oils A and B have on the fouling of the base oil. The results are illustrated in
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 SBN of 112. The results associated with the impact of the HSDP A on the HSHA blend are illustrated in
As shown in
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 SBN of at least 90 will achieve reductions in fouling.
In accordance with another aspect of the invention, a method is provided for reducing fouling in a crude oil refinery component. The method generally includes providing a base crude oil and a high solvency dispersive power (HSDP) crude oil, the HSDP crude oil having an Sbn>90 and a total acid number (TAN) of at least 0.3 mg KOH/g. The method includes distilling the HSDP crude oil to isolate atmospheric and vacuum resid fractions, blending the base crude oil with an effective amount of the atmospheric and/or vacuum resid fractions to create a blended crude oil, and feeding the blended crude oil to a crude oil refinery component.
Hydrocarbon feedstocks, whether derived from natural petroleum or synthetic sources, are composed of hydrocarbons and heteroatom containing hydrocarbons which differ in boiling point, molecular weight, and chemical structure. High boiling point, high molecular weight heteroatom-containing hydrocarbons (e.g., asphaltenes) are known to contain a greater portion of metals and carbon forming constituents (i.e., coke precursors) than lower boiling point naphtha and distillate fractions. It is known to fraction the crude oil into different components, as described for example, in U.S. Pat. No. 6,245,223, filed on May 9, 2000, entitled “Selective Adsorption Process for Resid Upgrading (LAW815),” the disclosure of which is incorporated herein specifically by reference. Residuum is defined as that material which does not distill at a given temperature and pressure. Atmospheric resid is that fraction of crude petroleum that does not distill at approximately 300° C. at atmospheric pressure. Atmospheric resid is further fractionated under vacuum and that fraction that does not boil at greater than approximately 500° C. is called vacuum residuum (vacuum resid fraction).
The SBN and TAN properties identify whether or not a crude oil is an HSDP oil. Alcor fouling simulation tests carried out with atmospheric and vacuum resid fractions of HSDP crude oils blended with known fouling crudes can be used to define relative performance, as well as to estimate the preferred concentrations desired to mitigate whole crude blend fouling.
To demonstrate the effectiveness of atmospheric and vacuum resid fractions of an HSDP crude oil in reducing fouling of crude oil refinery equipment, laboratory fouling simulation tests were performed. Two control blends of crude oils (Crude Blend A and Crude Blend B) were prepared. Each control blend contained a different level of asphaltenes, but both contained over 300 wppm of particulates. The particulates were filterable solids known to increase the fouling potential of many crude oils. Each of the control blends was tested using the Alcor fouling simulation described above and can be seen in
dimdT=(TOUTLET−TOUTLETMAX)/(TROD−TOUTLETMAX)
Table 2 provides the relevant physical properties of an HSDP crude oil, having SBN of 100 and TAN of greater than 0.3 mg KOH/g, in accordance with the present invention. This HSDP crude oil was distilled to isolate its vacuum gas oil (VGO, 650° F.-1050° F.; 343° C.-565° C.), atmospheric resid fraction (650° F.; 343° C.), and vacuum resid fraction (1050° F.; 565° C.). The values for each fraction of the exemplary HSDP crude oil SBN and Insolubility Number (IN) are shown in Table 2.
Addition of an effective amount of atmospheric and vacuum resid fractions of an HSDP crude oil are shown to be effective to reduce fouling of another crude oil. For example, by way of illustration and not limitation, tests were performed using about five percent (5%) of the total volume of HSDP resid fractions and resulted in significant decreases in fouling as shown in
Each of control blend A and control blend B was re-tested after blending as five percent (5%) of the total weight, each of the HSDP crude oil resid fractions shown in Table 2. As above, any known or suitable technique can be used to blend the atmospheric and vacuum resids of HSDP crude oil with a base crude oil.
As shown in
In accordance with another aspect of the present invention, a blended crude oil is provided including a base crude oil and an effective amount of an atmospheric resid fraction and a vacuum resid fraction of an HSDP crude oil, the HSDP crude oil having an Sbn>90 and a TAN of at least 0.3 mg KOH/g.
In accordance with yet 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 includes at least one crude oil refinery component and a blend in fluid communication with the crude oil refinery component. The blend includes a base crude oil and an effective amount of an atmospheric resid fraction and a vacuum resid fraction of an HSDP crude oil, the HSDP crude oil having an Sbn>90 and a TAN of at least 0.3 mg KOH/g.
In accordance with a further aspect of the present invention, a method is provided for on-line cleaning of a fouled crude oil refinery component. The method includes operating a fouled crude oil refinery component and feeding a blended crude oil to the fouled refinery component. The blended crude oil includes a blend of a base crude oil and an effective amount of an atmospheric resid fraction and a vacuum resid fraction of an HSDP crude oil, the HSDP crude oil having an Sbn>90 and a TAN of at least 0.3 mg KOH/g.
Particularly, it has also been discovered to use HSDP crude oil atmospheric and vacuum resid fractions 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 a blend including atmospheric and vacuum resid fractions of HSDP crude oils, resulting in energy savings and environmental benefits as a result of reduced fired heating needs.
The concentration of atmospheric and vacuum resid fractions 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, low levels of atmospheric and vacuum resid fractions of HSDP crude oil are effective for mitigating fouling of crude oil refinery components. For example, levels as low as five percent (5%) of the total volume of the blend are effective. It is contemplated that still lower concentrations can be used with a lower reduction in fouling. It is preferable that the atmospheric resid fraction of HSDP crude oil has an SBN of at least 105. It is preferable that the vacuum resid fraction of HSDP crude oil has an SBN of at least 182.
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 atmospheric and vacuum resid fractions of an 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.
This application is a divisional application of U.S. patent application Ser. No. 12/222,761, filed on Aug. 15, 2008, which relates to and claims priority from U.S. patent application Ser. No. 11/506,901, now U.S. Pat. No. 7,833,407, entitled “Method of Blending High TAN and High SBN Crude Oils and Method of Reducing Particulate Induced Whole Crude Oil Fouling and Asphaltene Induced Whole Crude Oil Fouling” filed Aug. 21, 2006, which is incorporated by reference in its entirety.
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