Crude Oil E. Product data are generally known more accurately than feed data. Moreover, light gases pro- duced by cracking appear in the products. Hydrocarbon Distillation Workbook 19 If the samples were cut into fractions by the laboratory, the gravities of the individual fractions can be supplied at the mid-volume percents of the fractions on the TBP curve. Such a gravity curve can also be con- structed when the yields and gravities of the distilled products are available.
This is important for high altitude locations to generating good pseudocomponents. D dis- tillations are almost always corrected by the reporting lab to a mm Hg basis. It is always good practice to ascertain this, however. It can be easily detected by plotting the distillation on probability paper. The slope of the distillation curve changes slope and becomes very flat as cracking occurs. The uncracked results can be estimated by continu- ing the slope prior to the cracking as a straight line on probability paper.
This is not adequate for problems in which some streams are virgin stocks and some are cracked stocks. Assay Blending When your flowsheet contains more than one user-defined assay stream i. This set of petrocomponents is called a blend. The large number of petrocomponents would lead to great slowing of the flowsheet calculations. Note that the summation is over the assay streams con- taining the cut range of interest.
Consider a flowsheet that has several user-defined assay streams, as shown in Figure 7. Only three of assay streams contain material boiling in this range so they will be the only ones participating in the blending procedure for this cut range. Likewise the gravities and molecular weights for this cut range will probably differ in each of the assay streams.
The differences may be due to errors in lab data or calculational approximations. Or they may indicate genuine physical differences in the assay streams. Hydrocarbon Distillation Workbook 21 The blending proce- dure is really a form of data reconciliation.
Its properties are closest to those of feed 2, because the greatest contribution of material in this cut range comes from feed 2. From this point on, all three of these streams will be characterized by this petro- component in this boiling range. The blends are named after the cutpoint sets. The fol- lowing slide discusses why you would want to use multiple blends. This is commonly done for assay streams that are used as initial estimates for a recycle.
Since the initial estimate can be significantly in error, you would not want the initial estimate to influence the blend properties. When to Use The main reason to use multiple blends is for property differentiation. Multiple For example, if your flowsheet contains both virgin and cracked feed- stocks, then you would want to use two different blends to account for Blends the different properties of the virgin and cracked streams.
Using multiple blends preserves these differences in the simulation and gives a more realistic representa- tion of their processing requirements. The price of using multiple blends is that flowsheet calculations must be performed on a larger number of components. This always leads to longer execution times. Property Differentiation In the flowsheet shown below, imagine you are designing processes to treat low and high sulfur feeds.
Naturally the processing requirements differ for each feed because of their differing sulfur content. Using a single blend for this problem would be a mistake. Using different blends for each feed provides you with a means to track the fate of each stream. This is useful for refinery planning and for checking designs for their tol- erance to feedstock changes. Crude Oil Crude oil is a very complex mixture of hydrocarbons. An API project begun in has isolated more than 16, distinct compounds in one barrel of Oklahoma crude oil.
The huge number of components occur- ring in crude oil gives it a very continuous TBP distillation. Obviously, representing crude oil with 50 components or even does not allow perfect matching of the tray temperatures and product compositions in a crude column simulation.
Crude oil varies widely in composition, both by location, and with time. Moreover, a given crude oil mix, for example, West Texas Sweet, may vary in composition from day to day because of the individual wells in production. Because of allocations, not all wells are produced each day. Different crude oils are best for making certain products. Some crude oils have a high asphaltene content and are used to produce asphalt.
Oth- ers may be light enough that the heaviest portion may be charged directly to the FCC unit. Kerosene yield and quality are an important consideration since this material is sold as commercial jet fuel. Some crude oils have light naphtha components more suited to reforming than others, and so forth.
Crude oil gravity varies widely, with the lighter crude oils generally being more valuable since they can be more readily converted to higher priced products, such as gasoline, jet fuel and distillates. Historically crude oil price was based on gravity alone, however, it did not take long for individuals to beat this system by spiking the crude oil with cheap LPG gas. Certain data are reported on laboratory assays for crude oil. The boiling points for the remainder of the mixture are unknown and you should use probability paper to estimate a typical tail for the mixture.
A chromatographic analysis of the light ends is usually given. This is rarely an accounting of the light ends in the crude column, which include light gases created in the furnace by cracking. The crude oil is broken into distinct product cuts which correspond to the products from the crude still.
The TBP still products are more precise than the products from the crude still, because of the superior fraction- ation in the TBP still. An alternate method to simulate a crude oil mixture is to combine the products. Product data are accurately known for most of the products, 24 Assay Blending Sometimes, the laboratory will run a low pressure D distillation for this material that can be used to develop pseudocomponents.
Thermo Follow the application guidelines and the water decant options outlined Methods in the following section when selecting the appropriate thermodynamic method for your simulation. Application Guidelines How do you determine which method is most suitable for your problem? In short, the best way to select the appropriate thermodynamic method is to understand the assumptions, features, and limitations built into each of the different models.
A certain portion of all of our thermo- dynamic methods is empirical. For example, the PR method is tuned i. While it can represent heavy hydrocarbon systems, you would not expect the results to be as accurate as light hydrocarbon systems.
The basic PR method would do a poor job at predicting equilibrium for polar systems, such as the Moon- shiner's ethanol-water system, for the simple reason that it was not designed for polar systems. The kij's are binary interaction coefficients. Their presence usually indi- cates that certain experimental data have been incorporated into the ther- modynamic model, and you can expect an extra degree of accuracy for these components. The absence of some binary interaction coefficients their values will be zero is not necessarily a cause for alarm, it just indicates that you might want to provide your own values or look for a thermodynamic method that includes values.
The Grayson-Streed method usually works best for heavy ends columns operating at low pressures less than 50 psia or 3. Grayson-Streed can also be used for the downstream processing in an FCC gas plant if it is desired to simulate the main fractionator and all downstream process- ing in one model.
Both methods have numerous sup- plied binary interaction parameters, and are capable of accurately pre- dicting vapor liquid equilibria for sour gas systems. Because the Hydrocarbon Distillation Workbook 25 Grayson-Streed method has special liquid fugacity curves for methane and hydrogen, it usually does an adequate job of predicting hydrogen rich operations such as reforming and hydrocracking.
The SOUR method is designed for the simulation of sour water strippers. Note that the electrolytic chemistry is not considered by the calculations, therefore, the answers must suffer some inaccuracy. Handling of Water For the free water or decant option, water is considered as forming an immiscible phase with the hydrocarbon liquid. The free water option is a convenient, efficient method to simulate the three phase behavior exhibited by hydrocarbon- water systems when dis- solution of hydrocarbons in the liquid water phase is small.
Thus, refin- ery columns with stripping steam and natural gas streams saturated with water can generally be simulated adequately with this method. The free water technology is a semi-rigorous three phase VLLE calcu- lation. The vapor is first saturated with water at its vapor pressure. Water is then dissolved in the hydrocarbon liquid up to its solubility limit, and any remaining water is decanted as a free water phase.
The solubility of water in the hydrocarbon liquid is based on data in the component library. The water solubility can also be cal- culated with an equation of state.
The free water phase contains no dissolved hydrocarbons or light gases. If these were an important consideration for the problem being analyzed, e. Water K-values are computed from the water vapor pressure PW , the mole fraction water in the hydrocarbon liquid phase XS , and the system pressure PI.
For natural gas systems at pressures greater than psia bars , a chart from the GPSA Data Book that relates the partial pres- sure of water vapor in natural gas to temperature and pressure gives more accurate K-values for the water. Rigorous three phase calculations must be performed for hydrocarbon- water systems where the dissolution of hydrocarbons and light gases in 26 Assay Blending Therefore, these methods are preferred for three phase calcula- tions unless you have some interaction parameters to supply.
It is good practice to inspect the reprint of interaction parameters and verify that parameters are present for components for which accurate calculations are needed. When the standard SRK or PR methods are selected for three phase cal- culations, the free water decant option must be deactivated. Hydrocarbon Distillation Workbook 27 An algorithm is a mathematical procedure, or strategy, for solving the col- umn equations.
Although all of these algorithms will produce identical results, some are better suited for certain problems.
It may, however, require more user intervention to obtain a solution than the other algorithms. A column with total pumparounds and water draws on several trays, for example, can only be solved with the Sure algorithm. Later in this workbook, you will learn some of the details of the various algorithms. In doing so, you will gain an appreciation of each algo- rithm's strengths and weaknesses; this information will help you select the appropriate algorithm for your problems.
By clicking on the appro- priate buttons and following the prompts, you can build complex Data Entry distillation columns. What follows is a quick introduction to this screen's Window features. Most will be discussed in greater detail later on. The Overall mode is the easiest way to define a pressure profile. Simply provide the top tray pres- sure and then specify a per-tray or total-column pressure drop.
If you want to provide pressure values on some or all stages, select By Individ- ual Trays and enter data. This is accomplished through the Tray Hydrau- lics dialog box. Feeds and Products Click this button to enter the locations, flowrates, and phases of the feed and product streams. For multiphase feeds, you have the option of plac- ing the vapor portion on the stage above the designated feed stage. You can also define product pseudostreams in this dialog box.
Pseudostreams are copies of tray liquid, vapor, or pumparound streams and do not affect column calculations. They are simply a tool that gives you access to internal column streams. Note that it is your responsibility to maintain the material balance for the flowsheet when you use pseudostreams. Convergence Data Adjust convergence parameters, tolerances, and request diagnostic infor- mation via this button. The diagnostic information is particularly useful for troubleshooting non-converging columns.
Hydrocarbon Distillation Workbook 29 You can also adjust the damping factor to less than one which can be used to improve convergence when the outer loop is oscillating.
Refinery complex fractionators are given a default damping factor of 0. Chemi- cals columns may require more severe damping. Larger systems can be simulated, but a large number of calculations can be expected. Thermodynamic Systems Click this button to change the default thermodynamic model. Or, select different models for different sections of the column.
Use this option when a single thermodynamic method cannot accurately characterize the wide range of conditions that are possible throughout the column. You can choose from partial, bubble point, and two types of subcooled condensers. It is here that you supply the condenser's operating conditions. Heaters and Coolers You can place side heaters and coolers on any tray in the column. Also called alkenes.
This information is also important in characterizing petroleum fractions and products from catalytic reforming and from thermal and catalytic cracking as blending components for motor and aviation fuels.
This information is also important as a measure of the quality of fuels. The aromatic hydrocarbon content of motor diesel fuels is a factor that can affect their cetane number and exhaust emissions. The aromatic hydrocarbon content and the naphthalenes content of aviation turbine fuels affect their combustion characteristics and smoke-forming tendencies.
R egulations place limits on the total aromatics content and polynuclear aromatic hydrocarbon content of motor diesel fuel. After the sample has been adsorbed on the gel, alcohol is added to desorb the sample down the column to separate the hydrocarbons. The fluorescent dyes are selectively separated into aromatic, olefin, and saturate zones, which are visible under ultraviolet light. Each boundary in the column is calculated by volume percentage from the length of each zone in the column.
Monoaromatics and polynuclear aromatics in the sample are separated from nonaromatics and detected using a flame ionization detector. Alternative test methods: IP for jet kerosine and EN for aromatics. ASTM D for olefins. Typical specifications: Gasoline: Aromatics: Max Jet Kerosine: Aromatics: Max Aromatics: Cyclic ring-shaped , planar flat molecules with a ring of resonance bonds that exhibits more stability than other geometric or connective arrangements with the same set of atoms.
Why: The aromatic hydrocarbon content of motor diesel fuels is a factor that can affect their cetane number and exhaust emissions. Regulations place limits on the total aromatics content and polynuclear aromatic hydrocarbon content of motor diesel fuel. Typical specifications: Diesel: Max 2. What: Ash: The non- gaseous , non-liquid, solid residue after a complete combustion with air.
The determination of ash in the range 0. It is limited to petroleum products which are free from added ash-forming additives. Why: Knowledge of the amount of ash-forming material present in a product can provide information as to whether or not the product is suitable for use in a given application.
Ash can result from oil or water-soluble metallic compounds or from extraneous solids such as dirt and rust. Typical specifications: Diesel: Max 0. What: Test method covering the following concentration ranges for the preceding aromatics: benzene, 0.
Benzene: The most simple aromatic molecule, with the formula C 6 H 6. Why: Regulations limiting the concentration of benzene and the total aromatic content of gasoline have been established in order to reduce the ozone reactivity and toxicity of automotive evaporative and exhaust emissions. Test methods to determine benzene and the aromatic content of gasoline are necessary to assess product quality and to meet fuel regulations.
Typical specifications: Gasoline: Max 1. What: Determination of the amount of carbon residue "coke" formed after evaporation and pyrolysis of petroleum materials. Why: he carbon residue value of the various petroleum materials serves as an approximation of the tendency of the material to form carbonaceous type deposits under degradation conditions similar to those used in the test method.
It can be used to provide some indication of the relative coke forming tendency of such materials. The sample undergoes coking reactions, and volatiles formed are swept away by the nitrogen. It is a supplementary tool for estimating cetane number when a result by Test Method D is not available and if cetane improver is not used.
Within the range from Why: The Calculated Cetane Index is useful for estimating ASTM cetane number when a test engine is not available for determining this property directly and when cetane improver is not used. It may be conveniently employed for estimating cetane number when the quantity of sample available is too small for an engine rating.
Procedure A has been developed for diesel fuels meeting the requirements of Specification D Grades No. Procedure B has been developed for diesel fuels meeting the requirements of Specification D Grade No. Typical specifications: Diesel: Min What: A test method covering the determination of the rating of diesel fuel oil in terms of an arbitrary scale of cetane numbers.
The cetane number scale covers the range from zero 0 to , but typical testing is in the range of 30 to 65 cetane number. Why: The cetane number provides a measure of the ignition characteristics of diesel fuel oil in compression ignition engines. The method is used by engine manufacturers, petroleum refiners and marketers, and in commerce as a primary specification measurement related to matching of fuels and engines. It s using a standard single cylinder, four-stroke cycle, variable compression ratio, indirect injected diesel engine.
Back to Content. What: Cloud point: The temperature of a liquid specimen when the smallest observable cluster of hydrocarbon crystals first occurs upon cooling. Why: For petroleum products and biodiesel fuels, cloud point of a petroleum product is an index of the lowest temperature of their utility for certain applications.
Typical specifications: Diesel: Equal to or lower than the lowest expected ambient temperature where used. What: C FPP: Highest temperature, at which a given volume of fuel fails to pass through a standardized filtration device in a specified time when cooled. The test method covering the determination of the CFPP temperature of diesel and domestic heating fuels, including those containing a flow-improving or other additive.
Why: The CFPP of a fuel is suitable for estimating the lowest temperature at which a fuel will give trouble-free flow in certain fuel systems. Why: Determination of the color of petroleum products is used mainly for manufacturing control purposes and is an important quality characteristic since color is readily observed by the user of the product. In some cases the color may serve as an indication of the degree of refinement of the material. When the color range of a particular product is known, a variation outside the established range may indicate possible contamination with another product.
How: ASTM D Standard Test Method for Saybolt Color of Petroleum Products: The height of a column of sample is decreased by levels corresponding to color numbers until the color of the sample, when viewed through the length of the column, is unmistakably lighter than that of the standard. The color number above this level is reported, regardless of whether the sample was darker, questionable, or a match at the higher level.
Typical specifications: Jet kerosine: The requirement to report Saybolt Colour shall apply at the point of manufacture, thus enabling a colour change in distribution to be quantified. Unusual or atypical colours should be noted and investigated. What: Test methods covering the determination of the electrical conductivity of aviation and distillate fuels with and without a static dissipator additive. The test methods normally give a measurement of the conductivity when the fuel is uncharged, that is known as the rest conductivity.
Conductivity: A measure of a material's ability to conduct an electric current. Why: The ability of a fuel to dissipate charge that has been generated during pumping and filtering operations is controlled by its electrical conductivity, which depends upon its content of ion species.
If the conductivity is sufficiently high, charges dissipate fast enough to prevent their accumulation and dangerously high potentials in a receiving tank are avoided. With portable meters, the current measurement is made almost instantaneously upon application of the voltage to avoid errors due to ion depletion. Ion depletion or polarization is eliminated in dynamic monitoring systems by continuous replacement of the sample in the measuring cell.
What: Determination of the corrosiveness to copper of aviation gasoline, aviation turbine fuel, auto-motive gasoline, cleaners solvent, kerosine, diesel fuel, distillate fuel oil, lubricating oil, and natural gasoline or other hydrocarbons having a vapor pressure no greater than kPa at Why: Crude petroleum contains sulfur compounds, most of which are removed during refining.
However, of the sulfur compounds remaining in the petroleum product, some can have a corroding action on various metals and this corrosivity is not necessarily related directly to the total sulfur content.
The effect can vary according to the chemical types of sulfur compounds present. The copper strip corrosion test is designed to assess the relative degree of corrosivity of a petroleum product. How: ASTM D Standard Test Method for Corrosiveness to Copper from Petroleum Products by Copper Strip Test: A polished copper strip is immersed in a specific volume of the sample being tested and heated under conditions of temperature and time that are specific to the class of material being tested.
At the end of the heating period, the copper strip is removed, washed and the color and tarnish level assessed against the ASTM Copper Strip Corrosion Standard. What: Detection of the corrosiveness of aviation turbine fuels on silver. The silver strip corrosion test is designed to assess the relative degree of corrosivity of a petroleum product towards silver and silver alloys.
Typical specifications: Jet kerosine: Max 1. Its application is restricted to liquids with vapor pressures below 80 kPa and viscosities below about 15 cSt at the temperature of test.
Density: Mass of a substance per unit volume. Why: Density is a fundamental physical property that can be used in conjunction with other properties to characterize both the light and heavy fractions of petroleum and petroleum products. Density is important for consistency and good fuel economy. Higher density produces more power and more smoke.
How: ASTM D Standard Test Method for Density and Relative Density of Liquids by Digital Density Meter: A small volume of liquid sample is introduced into an oscillating sample tube and the change in oscillating frequency caused by the change in the mass of the tube is used in conjunction with calibration data to determine the density of the sample. What: Atmospheric distillation of petroleum products using a laboratory batch distillation unit to determine quantitatively the boiling range characteristics of such products as light and middle distillates, automotive spark-ignition engine fuels, aviation gasolines, aviation turbine fuels, diesel fuels, special petroleum spirits and naphthas.
Test results are commonly expressed as percent evaporated or percent recovered versus corresponding temperature, either in a table or graphically, as a plot of the distillation curve. Why: Distillation volatility characteristics of hydrocarbons are important for their safety and performance. The boiling range gives information on the composition, properties and behavior during storage and use. Volatility is the major determinant of the tendency of a hydrocarbon mixture to produce potentially explosive vapors.
Distillation characteristics are critically important for gasolines, affecting starting, warm-up, and tendency to vapor lock at high operating temperature or at high altitude. High boiling point components in fuels can significantly affect the degree of formation of solid combustion deposits. Volatility is an important factor in the application of many solvents. Distillation limits are often included in petroleum product specifications. This basic test method of determining the boiling range of a petroleum product has been in use as long as the petroleum industry has existed.
Then, a tremendous number of historical data bases exist for estimating end-use sensitivity on products and processes.
Apparatus arrangement, condenser temperature, and other operational variables are defined by the group in which the sample falls. The distillation is performed in a laboratory batch distillation unit at ambient pressure under conditions that provide one theoretical plate fractionation.
Systematic observations of temperature readings and volumes of condensate are made. The volume of the residue and the losses are also recorded. Typical specifications:. What: Determination of ethers and alcohols in gasolines by gas chromatography. Individual ethers are determined from 0. Individual alcohols are determined from 0. The method includes a relative bias correlation for ethanol in spark-ignition engine fuels for the U.
Alcohols: Organic compounds in which a hydroxyl functional group —OH is bound to a saturated carbon atom. Ethers: Organic compounds that have the general group R-O-R'. R and R' can be smilar or different alkyl substituents. Why: Ethers, alcohols, and other oxygenates can be added to gasoline to increase octane number and to reduce emissions. Type and concentration of various oxygenates are specified and regulated to ensure acceptable commercial gasoline quality.
Drivability, vapor pressure, phase separation, exhaust, and evaporative emissions are some of the concerns associated with oxygenated fuels. Alternative test methods:.
What: Determination of the existent gum content of aviation fuels, and the gum content of motor gasolines or other volatile distillates in their finished form, including those containing alcohol and ether type oxygenates and deposit control additives at the time of test.
Gum: Viscous material that is formed from degradation of oil. Why: The primary purpose of the test method, as applied to motor gasoline, is the measurement of the oxidation products formed in the sample prior to or during the comparatively mild conditions of the test procedure. Since many motor gasolines are purposely blended with nonvolatile oils or additives, the heptane extraction step is necessary to remove these from the evaporation residue so that the deleterious material, gum, may be determined.
With respect to aviation turbine fuels, large quantities of gum are indicative of contamination of fuel by higher boiling oils or particulate matter and generally reflect poor handling practices in distribution downstream of the refinery. It has been proved that high gum can cause induction-system deposits and sticking of intake valves, and in most instances, it can be assumed that low gum will ensure absence of induction-system difficulties.
For aviation gasoline and aviation turbine fuel, the resulting residue is weighed and reported as milligrams per mL. For motor gasoline, the residue is weighed before and after extracting with heptane and the results reported as milligrams per mL. Alternative test methods: IP , IP It is applicable to concentrations from 1.
The procedure is applicable only to FAME. Why: The test method is applicable for quality control in the production and distribution of diesel fuel and biodiesel blends containing FAME. A beam of infrared light is imaged through the sample onto a detector, and the detector response is determined.
Wavelengths of the absorption spectrum that correlate highly with biodiesel or interferences are selected for analysis. A multivariate mathematical analysis converts the detector response for the selected areas of the spectrum from an unknown to a concentration of biodiesel.
The absorption spectrum shall be used to calculate a partial least square PLS calibration algorithm. Typical specifications: Diesel: Non-detectable.
Add text or edit existing text Make layout adjustments Insert, move or delete images. Get it Free. Edit PDF. Save and Share PDF.
Choose from three options to sign a PDF: Draw your signature using your mouse Add an image of your signature Type your signature Multiple handwriting fonts are included so that you can choose the best font to create your digital signature.
Download Now. Mac OS X Change or add text, images and more.
0コメント