Petroleum Refining PDF

## Petroleum Refining ### Processes * **Chemical Reactions:** include chemical reactions. * **Operations:** do not include chemical reactions. Examples include distillation. ### Petroleum Refining/Distillation * Represents an operation. * In India, 18% production and 180MMT imported from other c...

## Petroleum Refining ### Processes * **Chemical Reactions:** include chemical reactions. * **Operations:** do not include chemical reactions. Examples include distillation. ### Petroleum Refining/Distillation * Represents an operation. * In India, 18% production and 180MMT imported from other countries. * 60% of oilfields are offshore, 40% onshore. * Mature oilfields are known as "Brown oilfields." * 3 petrochemical industries are located in Dibrugarh: BCPL, NPE, PE. * **Virion 2080** (Hydrocarbon mission 2030). * **Reasons for declining oil production in Assam:** * Mature old fields * Limited Technology * Using the same old fields. * Solid state of Petroleum: Pitch (semi-solid form), Bitumen (finished product) ### Petroleum * Occurs in Earth's crust in all possible states. * Ranges in color from light brown to dark brown, or black. * Mixture of various hydrocarbons, primarily of homologous series: paraffins, napthenes (cyclo alkenes), aromatics (PAN). * Main elements are C (84-86%), H (11-16%). * Other elements include oxygen, nitrogen, and sulfur. * Metal constituents are about 8%. * Metals + SON -> 8% (hardly). * Inorganic Compounds in crude oil: SON * More homogeneous than coal and occur mainly in sedimentary rocks. ### Pitch * A solid or semi-solid petroleum is called Pitch. * The famous pitch lake in Trinidad is an example of this kind of petroleum. (Located in the Caribbean Sea; 5th largest island of the West Indies) * **Composition:** * Not only depends on the origin of formation, but also changes with the time of formation, storage, and migration * Impurities: other properties like color, odor, and corrosiveness ### Petroleum and Hydrocarbons * Bulk of petroleum is made up of hydrocarbons (saturated compounds like paraffins and napthenes, and unsaturated aromatics). * Highest carbon atom present in a group is C70 but generally up to C35. * **Hydrocarbon range:** * C1-C2: Gas * C3-C5: Gas (contain all 3 states and so on distillation, we get all different types of products) * C6-C7: Liquid * C8: Liquid * C9..... * C70: Solid or semi-solid * C1 and C2: dry gas * C3 and C4: wet gas * Upon increasing weight, atmospheric pressure changes to liquid and vice versa. When pressure is released, the liquid turns into gas. ### Sulphur Content in Petroleum * **Depends on the:** * Crude to crude * Country to country * Reservoir to reservoir * Assam Crude oil: very low sulfur which is good crude. * Gulf Countries: Russian crude contains up to 5% of sulfur (very high) * East: crude oils from East possess very less amount of sulfur, e.g. Indian, Indonesian, Libyan (contains up to 0.5%); whereas Assam contains in terms of PPM. ### Paraffins * Up to 3 carbon atoms have an inclination to form hydrates (ice line solid structures) by reacting methane, ethane, propane with water vapor. * Blockage on clogging oil lines, causing slush forming. * Structures: * C1H4 - 7H20 between methane and water vapor. * C1H6 - 10H20 between ethane and water vapor ### Paraffin Properties * **Viscosity**: Lower than aromatics, but Viscosity Index is high * **Rate of change of viscosity** with respect to temperature is low. * **Pour Point**: The minimum temperature which crude oil stops flowing. * **General formula**: CnHan ### Other properties of hydrocarbons * The first 4 core gases, up to C19, are liquids and beyond C19 are solids or semisolid. * Unsaturates are mainly formed during cracking. ### Refining vs Petrochemicals | | Refining | Petrochemicals | | -------- | -------- | -------- | | Products | Saturated | Unsaturated | | Example | LPG | Pen, Bagpains al | ### Thermal Cracking * **Process**: Use around 1000°C heat to crack higher hydrocarbons. * **Result**: Gasoline produced by BCPL has some unsaturated compounds mixed with it as they are produced from the cracking process. * **Use**: 100% saturated petrol in cars * **Sulfur in Crude Oil**: Occurs in different forms: * Elemental sulfur (solid) * Free sulfur * H2S (gaseous) * Mercaptan * Thiophenes ### Sulfur's role in refining * Occupies a prominent position due to problems with pet corrosion. ### Acid Gas * **Composition**: N2, H2S, CO2 plus brines in contact with H2O forming carbonic acid. ### Natural Gas (NG) * Elements: * CO (84-92%) * C2 * C3-C4 (LPG WET) * C5+ * C6+ * CO2 * H2S * H2O * Types of N.G: * Dry * Wet * Type of coil: * Dry * Wet ### Steam reforming reaction * **CH4 +1/2O-> CO + CO2 + 4H2** * Reaction of N.G. with steam: N.G. hydrates when methane enters the void space of water vapor particles, forming some ice-like structures called hydrates. ### Crude Oil Classification * Classified into 3 categories: * Paraffinic * Intermediate/ Mixed * Napthenic * **Assam Crude Oil** - Intermediate/Mixed base ### API Gravity * **Formula:** API = 141.5 - 131.5 / specific gravity * **Units:** degrees * **Method of classification:** * **Basis**: Residuum. * **Steps:** 1. Reduced crude oil (RLO) that is not defined or distilled: Distill in two-stages, one atmospheric and one vacuum. 2. Products from atmospheric distillation are further distilled in vacuum. * **Major components produced in ADU**: * Residuum * Naptha, Kerosene, Diesel are produced in VDU #### Residuum * Contains more than 5% of paraffins - paraffinic base * Contains less than 2% of paraffins - napthenic base * Contains between 2-5% of paraffins - intermediate or mixed base **US Bureau of Mines' Technique/Method** * **Basis:** Key Fraction I and II * **Study**: Chosen products out of the 5 products of ADU * **Key Fraction I (Kerosene):** 250-278°C at 760 mmHg (ADU) * **Key Fraction II (Kerosene ):** 275 to 300°C at 40 mm of Hg. (ADU) * API gravity of AFI and KFD are worked out and then characterization of crude oil is done. * **API gravity for KF-I:** * 40 or more - Paraffinic * Less than 33 - Napthenic * Between 33-40 - Intermediate/mixed * **API gravity for KF-II:** * 30 or more - Paraffinic * 20 or less - Napthenic * Between 20-30 - Intermediate/mixed ### UOP Characterization (Salon) * **Formula:** UOP = 3√R = 6.8278 * specific gravity/156/150°C. * **Classification**: * 12.5 and above: Paraffinic base. * Less than 10: Napthenic base. * 10-12.5: Intermediate/Mixed ### UOP Correlation Index * **Formula:** CI = 48640 + 473.75 - 456 * 6^8 / (Specific Gravity * Boiling point in °K) * **Classification:** * 0-15: Predominantly PB. * 15-50: Napthenic base. * 50: Aromatic **True Boiling Point (TBP) Experiment** * **Purpose:** to access distillation characteristics of crude oil. * **Benefits:** * Enlightens refiners with all possible information; * Identifies the quantum of fraction, and * Highlights difficulties to be faced during refining. * **Process**: * Determine the range of compounds/products that can be obtained from a batch of crude oil ~100ml crude oil is taken: * 20 ml petrol * 2 ml oil * 10 ml distillate **ASTM Distillation** * **Purpose**: to test crude oil * **Key terms:** * **Viscosity:** * Absolute * Kinematic * **Viscosity Index** (refinery product, cut, fraction, distillates) **Refining Products** * **Volatile Products:** C1 - C4 [C1H4 (LPG)] * **Light Distillates:** * MS/Naphtha/ Solvent / Spirit/ Spilood/ Raw Somm * Raw material for bags, raincoats, water bottles, etc. and other finished products. * **J.P - Written:** * In water bottles in polyethylene terephthalate (PET) * from 0.7 ortho -> 6% styrene * then polystyrene, naptha, polyester, and other materials. * **Aromatic:** * From para * **HBPA source:** bisphenol A (added in plastics to increase strength, but when it comes in contact with sunlight, it emits vapor which causes cancer. * **Middle Distillates:** * ATF/ Diesel / Kerosene (HSA/LSA) * High speed diesel/low speed diesel (based on RPM of vehicle) * **Lube Base Stock:** engine oil, gear oil, lube oil * **Wax:** food grade, monocrystalline, needle type * **Lactolose 50/77:** contains food-grade wax and is related to constipation medications. * **Residue/Heavy Products:** fuel oil/bitumen, 151/s (low sulfur heavy stick). ### Dehydration & Desalting of Crude Oil * **Description:** All crude oils contain moisture and salts to varying degrees. * **Problem:** Water in crude oil is likely to occur in emulsion when crude oils are basically naphthenic and sulfurous. * **No harm to distillation column:** due to the presence of moisture; there is always steam in distillation. * **Solution:** crude oils have to be dehydrated to remove salts. Water is a very good solvent for salts. Salt removal is very crucial. * **Salts:** chlorides of calcium and magnesium play an inevitable role in overhead corrosion * **Salts Present in Crude:** * Na2CO3, NaCl, CaCl2, MgCl2, FeSO4, Na2/CO3 * **Other salts (Ca,Mg) in presence of steam:** * easily hydrolyze generating hydrochloric vapor, causing corrosion. * **Salt content:** * crude oil that contains more than 5 gallons of total salts per 1000 barrels can be regarded as salty crude oil. * 1,59,000 liters of CO. ### Dehydration * **Purpose:** To remove water. * **Stages:** 1. Site of mine 2. Refinery * **Long standing of crude oil:** * may permit separation of the aqueous phase along with some amount of salts and other suspended impurities. * Free water * Emulsified water ### Dehydration Methods * **Methods:** 1. **Gravity Setting/Settling:** 2. **Chemical Treatment:** 3. **Centifugal Separation:** 4. **Electrical Resalting:** **Salt Removal from the Oilfield** * **Method:** Settling or by a combination of two. * **Problem:** Crude oil processing and emulsifying characteristics are not responsive to the settling method. * **Solution:** Emulsifying agents are necessary to increase the coalescence of water droplets. NaOH, salts of fatty acids, and petroleum sulphonates are such chemicals. * **Process:** 1. Add the chemicals and water to the crude mixture. 2. Allow it to stand at 75 to 80°C, and a pressure of 15 kg force per cm² in huge tall tanks * **Results:** * High pressure ensures the retention of volatiles in the crude oil. * Good separation into hydrocarbon and aqueous phase results when crude oil is allowed to stand for 48 hours. * **Centifugal Separation:** * Not economically viable due to high energy consumption and less quantity to handle. ### Electrical Desalting * **Process:** * Simultaneous desalting and dehydration * **Results:** Spectacular removal of more than 90% of salts from crude oil within half an hour. * **Description**: * Apply a potential difference of 20-30kV between electrodes through which crude oil is passed. * Water present in the form of emulsion forms ions that move toward the steam and trap all the salts. * **Results:** Salts collect at the bottom of the desalting column and form separate steam. * **Benefits:** * Compactness * Efficiency * Ease of operation, which induce refinery operations to adopt such desalting techniques **Pumping of Wary Crude Oil:** * **Process:** * Crude from the desalting column collects at the bottom of the desalting column and forms a separate steam. * This process is compact, efficient, and easy to operate. This makes it a desirable technique for refineries.