Ops Final Exam Revision Doc PDF

ADNOC Classification: Internal Ops Final Exam Revision Doc 1) Oil & Gas Production Operations Crude oil chemistry Crude oil is a mixture of hydrocarbon molecules, which are organic compounds containing carbon and hydrog...

ADNOC Classification: Internal Ops Final Exam Revision Doc 1) Oil & Gas Production Operations Crude oil chemistry Crude oil is a mixture of hydrocarbon molecules, which are organic compounds containing carbon and hydrogen atoms that may include from one to more than sixty carbon atoms. Crude oil contains mainly three classes of hydrocarbons: paraffins, Naphthenes and aromatics. Paraffins : Naphthenes : Aromatics : ADNOC Classification: Internal Main crude oil properties Cloud Point Cloud point is the temperature at which dissolved solids are no longer completely soluble, precipitating as a second phase giving the fluid a cloudy appearance. In the petroleum industry, cloud point refers to the temperature below which wax in crude oil form a cloudy appearance. Pour Point Pour point is the temperature at which the crude oil becomes semi solid and ceases to flow. Reid Vapor Pressure Apparatus for Crude Oil Floating Production System (FPS) Consists of a semi-submersible unit which is equipped with drilling and production equipment. ADNOC Classification: Internal Floating Production, Storage & Offloading System (FPSO) FPSO consists of a large tanker type vessel moored to the seafloor. Sections of Main Processing Facility The main objective of a production facility is to process the well fluids into clean, marketable products. A typical oil, natural gas production facility consists of the following systems. Well head Manifolds Production and Test separators Gas compression Storage Tanks Shipping pumps Water treatment plant Natural flow wells: This type of well uses the natural pressure from the formation to force the oil or gas from the reservoir to the surface without requiring a pump. ADNOC Classification: Internal CRUDE OIL DEHYDRATION, DESALTING, & STABLIZATION To separate the saltwater droplets, four different treatments are used. These are: 1- Heating 2- Chemical Injection 3- Wash water Injection 4- Electrostatic Coalescence Heating crude oil lowers its viscosity, makes it thinner. Thin crude oil cannot hold water droplets in suspension. Scale inhibitor : is a chemical treatment used to control or prevent scale deposits in heat exchangers. Chemical injection: A demulsifier is added to dissolve the oil film around the saltwater droplets in the crude which makes them easier to separate. Wash water Injection: its purpose is to dilute the salt concentration in crude oil. Mixing Valves are used to mix the demulsifier and wash water with the wet crude oil. Electrostatic Coalescence: A high voltage is applied to the electrical grid (coalescer) to create a strong electrostatic charge. The electrostatic charge attracts the saltwater droplets in the crude, causing them to rise and join together (coalesce) and finally settle at the bottom of the vessel by gravity. Crude oil stabilization the process of crude stabilization and sweetening aims: To separate light hydrocarbon gases (C1 to C4) that are dissolved in the crude oil. To remove acid gas Hydrogen Sulphide (H2S) from the crude oil. When H2S has been removed, the crude oil is referred to as sweet crude. ADNOC Classification: Internal Spheroid Sour Crude oil NATURAL GAS SWEETENING PROCESS Sour Gas : Natural gas containing acid gases (CO2 and H2S) Sweet Gas: Natural gas free from acid gases CO2 & H2S Gas Sweetening process includes two sections ABSORPTION & REGENERATION Amine Contactor operates at High Pressure & Low Temperature Amine Regenerator operates at Low Pressure & High Temperature Lean Amine: fresh amine free from acid gases and contaminants Rich Amine : Amine containing H2S and CO2. ADNOC Classification: Internal Amine Contactor Column NATURAL GAS DEHYDRATION PROCESS Dehydration of natural gas is very important, as it is required to: Prevent hydrates formation in equipment and pipelines, Prevent corrosion and erosion of equipment and pipelines, Meet water content specification as per sales gas agreement Gas Hydrates are solid, ice-like crystallized compounds formed of hydrocarbons and water. ADNOC Classification: Internal Gas Dew point : By lowering the gas temperature, water vapor in the wet gas stream condenses & forms a dew. This temperature is called the "dew point" Technologies used for natural dehydration : two types of dehydration techniques are commonly used nowadays: Adsorption by solid desiccants. Absorption by liquid desiccants. 2) PIPING SYSTEMS & VALVES PIPE MATERIALS : the material used for pipe manufacture must be able to: Resist chemical attack (chemical corrosion) of the fluid (medium) inside the pipe and chemical corrosion from outside due to the surrounding environment. Withstand the maximum working pressure in the piping system. Copper and copper alloys are used for instrument lines and heat transfer equipment. Stainless steels are used in chemical, pharmaceutical and food processing industries. PIPE CORROSION PREVENTION TECHNIQUES Barrier protection: isolating the metal from the atmosphere to stop the electrons moving. Paint or coating is a corrosion barrier that stops air and water from reaching the iron to start the rusting process. Passive cathodic protection (Sacrificial Protection): In this method, a sacrificial metal which loses electrons and corrode instead of the protected metal. Blocks of magnesium or zinc are attached at intervals to the protected structure. In time, they will disappear and therefore, they will need to be regularly replaced. ADNOC Classification: Internal PIPELINE INSPECTION GAUGE (PIG) A pipeline inspection gauge, commonly referred to as a ‘pig’, is a device used to clean and/or inspect a pipeline from the inside to ensure long life for the pipe and smooth flow for the fluid. Pipe thermal Insulation reduces heat flow from one surface to another. ADNOC Classification: Internal Hot Insulation is applied on the hot surfaces of the piping system to reduce heat loss. Mineral Wool, Glass Wool, Calcium Silicate, etc are normally used as Hot insulating material. Cold Insulation is used on cold surfaces of the piping system to avoid heat gain from outside. Polyurethane Foam, Expanded Perlite Foam, Expanded Polystyrene Foam are the widely used cold insulating materials. ADNOC Classification: Internal Fittings Reducers are used to join pipe Reducer of different diameters. Bushings are used to make the diameter of a pipe fitting smaller. They differ from Bushing reducers in that they make abrupt changes in diameter and take very little space. Are used to join two straight Coupling pieces of pipe of the same diameter. Used to close the end of a dead- Cap end pipe. Short lengths (under 12") of Nipple pipe threaded at both ends. Used to join pieces of pipe where pipes cannot be turned Union or when a piece of equipment may have to be removed for maintenance or replacement. ADNOC Classification: Internal Valves Rising Stem Gate Valve Non-Rising Stem Gate Valve ADNOC Classification: Internal Globe Valves Needle Valves : Used to Throttle or block fluid flow to Instruments or in chemical systems ADNOC Classification: Internal Check Valves ( Non return valves) : allow the flow only in one direction.( prevent backflow ) Split Disc Check Valves Pressure Safety / Relief Valves: to release excess pressure from a system (pipe or vessel) Actuators Pneumatic (Air Operated) Used for moving block and throttle valves in most plants. Hydraulic Actuator (Oil operated) Electric Motor (Electric Actuator) ADNOC Classification: Internal 3) Process Diagrams Block Flow Diagram is the simplest drawing of a process plant. It consists of a series of blocks representing different equipment or unit operations connected by input and output streams. PTP Block Flow Diagram PROCESS FLOW DIAGRAM (PFD) PFDs will always contain the following: A title block identifying the unit, the author and the date drawn. All the major equipment showing their names and their identification numbers (Tag Numbers) Major lines showing the flow of process fluids. Major bypass lines which are important for understanding the process A table listing the variables at different points of the system called process variables table. ADNOC Classification: Internal Each piece of equipment is identified by a unique number commonly called “Tag Number”. For example, the tag number of the pump P-101A/B provides the following information: P-101A/B means that the equipment as a pump P-101A/B means that the pump is located in the area 100 of the plant P-101A/B means that the specific pump is number 01 of the area 100 P-101A/B means that there are two pumps: P-101A and P-101B. Process Variables Table Stream Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Vapour Fraction 1.00 1.00 1.00 1.00 1.00 1.00 NOTE 2 0.00 0.00 0.00 0.0119 0.0120 1.00 1.00 0.00 0.00 0.00 0.00 0.00 Pressure bar g - 4.40 4.40 4.40 4.40 4.10 0.06 4.30 4.15 4.10 3.90 3.90 - 3.90 1.30 0.25 0.06 1.50 Temperature °C 49.00 59.00 59.00 59.00 59.00 58.49 49.00 49.00 49.00 53.22 53.23 53.23 51.85 53.23 53.23 49.0 49.00 49.00 Liquid m3/hr - - - - - - 23 23 20 20 20 - - 20 20 20 3 3 Vapour Am3/hr 375.0 72.4 2.8 2.8 69.6 69.6 - - - - 75.3 75.3 363.7 - - - - - Total flow m3/hr 375.0 72.4 2.8 2.8 69.6 69.6 23.0 23.0 20.0 20.0 95.3 75.3 363.7 20.0 20.0 20.0 3.0 3.0 Gives Pressure, Liquid flow, Vapor flow, Total Flow & Temperature in different streams PTP Process Flow Diagram H-001: Electrical Heater / Heater; V-001: Two-phase separator; P-002: Chemical dosing pump / Corrosion inhibitor pump; V-003 A/B: Filters; E-001 A/B: Fin fan Coolers ADNOC Classification: Internal PIPING AND INSTRUMENT DIAGRAM (P&ID) A P&ID gives a complete and detailed representation of a process plant. Legend: shows symbols and names used in the drawing. Title Block: shows the plant name, drawing number, date, scale, and revision number. Equipment Data Block: provides detailed information about the equipment. Diagram: shows the process piping together with the equipment and instrumentation. Equipment coding, symbols, and their identification Each equipment in the plant has a unique code and is represented in same way in the P&ID. The standard equipment number consists of four main parts as shown below: 654: Refers to plant area number P: for pump. 2800: Pump sequence number in the plant. A: Refers to pump A. (This means that there is more than one pump with the same sequence number). ADNOC Classification: Internal Line Identification Each process line shown on a P&ID will have line identification data written next to the line on the drawing. There many standard methods for writing the line identification. The one used in ATA pilot plants is the following: SG—1—AC2GAO—0023 SG: Stripping Gas; 1: Size in “inch”; AC2GAO: Pipe specification; 0023: Line Number Note: there is no insulation for this pipe, so the insulation code is not mentioned. Identification of instruments and their Symbols Instrument mounted locally in the field. Instrument mounted in the main control panel Symbol of an instrument Located behind the control panel. ADNOC Classification: Internal Process Line Symbols: 4) Static Equipment TWO PHASE SEPARATOR A vessel that separates the feed fluids into a gas stream and a total liquid one is called two-phase separator. A two-phase separator can be horizontal or vertical. The liquid stream leaves the vessel at the bottom; however, the gas leaves the vessel at the top, passing through a mist extractor to remove the small liquid droplets from the gas. ADNOC Classification: Internal THREE PHASE HORIZONTAL SEPARATOR In a horizontal three-phase separator, fluid enters the vessel through an inlet, and immediately hits an inlet diverter. This sudden impact provides the initial separation of liquid and vapor and begins the gas- oil separation process. In the liquid collection section of the vessel, the oil and emulsion separate, forming a layer above the free water. A weir maintains the oil level, while an interface liquid level controller maintains the water level. The oil spills over the top of the weir, and then a level controller, which operates the oil dump valve, controls its level. Slug Catcher Demister Vortex Breakers Distillation Towers/ Columns There are two main types of columns: Packed and Tray columns. Packed Columns Packed columns are used for gas absorption and liquid-liquid extraction. The liquid flows down in the column over a packing surface and the vapor (or the gas) moves counter- currently, up the column. Packing Function: The packing material is used to increase the surface area for mass transfer between gas and liquid phases during the distillation process. ADNOC Classification: Internal Tray Columns These are tall columns equipped a series of plates (trays), one above the other. Tray Function: The trays are used to bring the rising vapour and falling liquid into close contact. Tray type distillation columns operate on the same principle as packed columns; however, instead of using packed material they use trays situated at various heights within the tower. The trays have a weir to maintain a layer of liquid across the surface. Hot vapour bubbles through the liquid to strip out light components. As the liquid flows over the weir, it is directed to the tray below by down comers. The down comers direct the fluid from one tray to the next lower tray in the tower. MAIN SECTIONS OF A DISTILLATION COLUMN 1. Feed Section / Flash Zone The flash zone is the feed section area where the crude oil changes into a mixture of liquid and vapour Rectifying Section are the trays that are above the feed nozzle. a. The light vapours flash out of the feed fluid and rise up the tower. b. The reflux flows down across the trays and re-absorbs any liquid droplets from the rising vapours. 2. Stripping Section These are the trays below the feed nozzle. In this section, the light vapour components are stripped (removed) out of heavier liquids. ADNOC Classification: Internal INTRODUCTION TO HEAT EXCHANGERS Heat Transfer Modes Conduction: is an exchange of energy by direct interaction between molecules of a substance with temperature differences. Heat transfer in a solid or a stationary fluid (gas or liquid) due to the random motion of its constituent atoms, molecules and /or electrons. Convection: Heat transfer due to the combined influence of bulk and random motion for fluid flow over a surface. It is caused by the movement of fluids. Radiation: Energy that is emitted by matter due to changes in the electron configurations of its atoms or molecules and is transported as electromagnetic waves (or photons). Figure 3.1 Heat Transfer Modes HEs CLASSIFICATION BASED ON TYPE OF CONSTRUCTION Shell and tube HE, Plate HE, Fin fan cooler and Fired heater Shell and tube HE ADNOC Classification: Internal Plate HE Fired Heater / Furnace Fin Fan Coolers / Air cooled Heat Exchangers ADNOC Classification: Internal STORAGE TANKS Selection criteria for a fixed roof tank. Fixed roof tanks are suitable for low vapor pressure liquid hydrocarbon (1.5 psi) Class C Liquids which have higher flash point (above 65 °C) A pressure-vacuum relief valve (PVRV) also called as breather valve is commonly installed on many fixed roof tanks, and allows the tank to operate at a slight internal pressure or partial vacuum. This valve prevents the release of vapours during very small changes in temperature, barometric pressure, or liquid level. Pressure/vacuum relief valves ((PVRV) are protection devices which are typically mounted on a nozzle opening on the top of a fixed roof atmospheric storage tank to protect the tank against bursting or imploding (collapsing due to vacuum) during loading/ unloading operation. ADNOC Classification: Internal Selection Criteria for Floating Roof Tank Floating roof tanks are suitable for vapor pressure hydrocarbon 16.8 psi Class A and B Liquids which have Low flash points. External floating roof tank Internal floating roof tank Liquid Petroleum Products classification based on flash point. Class-A Petroleum: Liquids which have flash point below 23°C. Class-B Petroleum: Liquids which have flash point of 23°C and above but below 65°C. Class-C Petroleum: Liquids which have flash point of 65°C and above but below 93°C. ADNOC Classification: Internal 5) ROTATING EQUIPMENT Centrifugal Force. Centrifugal means moving outwards from the centre. Centrifugal force is a force caused by rotating an object. This force is used in centrifugal pumps by rotating an impeller. Centrifugal Force Concept Suction Head System If the liquid to be pumped is at a higher level than the pump, then this is called a 'suction head' system. Suction Lift System If the liquid to be pumped is at a lower level than the pump, then this is termed a 'suction lift' system. ADNOC Classification: Internal Positive Displacement Action Positive displacement happens when a liquid is forced to move by the movement of a solid object into it. Series and Parallel Pumps Operation. Pumps are combined in series to obtain an increase in pressure (head ) or in parallel for an increase in flow rate.. ADNOC Classification: Internal Pumping System Pressure Control. The Figure below shows a simple pressure control system using a Pressure Recording Controller (PRC) and a Pressure Control Valve (PCV). Depending on the pressure situation in the discharge line, the PRC sends a signal to the PCV which will open or close to bring back the pressure value to set point. In case of a pressure increase, the PCV will open more and send back liquid excess to the storage tanks. Pumping System Flow Control The Figure below shows a simple flow control system using a Flow Recording Controller (FRC) and a Flow Control Valve (FCV). The flow of liquid from the pump is sensed by the FRC which is fitted directly to the pump discharge pipeline. A signal from the FRC causes the FCV to open or close which in turn controls the flow to the downstream process. ADNOC Classification: Internal Pump Protection systems. It is very important to protect the pump from damage due to abnormal operating conditions. So almost every pump in process plants is associated with a protection control system. Listed below are some of the main automatic shutdown systems which will trip the pump once it exceeds the safe operating conditions. ✓ Low Level in the suction tank. ✓ Low pressure in the suction line. ✓ High pressure in the pump discharge line. ✓ High bearing temperature. ✓ High vibration. ✓ Low Lubrication oil Level and Pressure. Compressors The main function of a compressors is to increase the pressure of a gas. ✓ Compression Ratio: It is the ratio between the compressor discharge pressure and the compressor suction pressure. If the discharge pressure is 20 psig and the suction pressure is 5 psig then the compression ratio is 4:1. That is, 20 divided by 5. Compressors are classified based on their operating principles into the following types: Dynamic - Centrifugal compressors are the most suitable to handle high volumes. Positive Displacement – Reciprocating compressors are best for high pressures. Rotary compressors experience less vibration than reciprocating ones ADNOC Classification: Internal Centrifugal Compressor Capacity Control. In a continuous gas process the flow of gas through the process may not be constant. There may be changes in either the supply of gas or the demand for gas. If a compressor is installed as part of a continuous gas process, we need to be able to control the capacity of the compressor to suit changes in gas flow. Capacity can be controlled by any of the below mentioned method. By controlling the speed of the compressor. By using the recycle loop. By adjustable inlet guide vanes. By throttling the compressor suction valve. Speed Control. Centrifugal compressors which are driven by a steam turbine, a gas turbine or an internal combustion engine can have their capacity controlled easily by adjusting the speed of the prime mover by the governor of the prime mover. Recycle Loop. A recycle loop is used to recycle gas from the discharge side of the compressor to the suction side to control the capacity of the compressor. Compressor Recycle Loop. ADNOC Classification: Internal Adjustable Inlet Guide Vanes. To direct incoming gas to the impeller some centrifugal compressors are fitted with inlet guide vanes. The inlet guide vanes can be made adjustable so that they control the amount of gas entering the compressor. This controls the capacity of the compressor. Adjustable Inlet Guide Vanes. Prime Movers In oil and gas industry the main types of prime movers used are: ✓ Electric motor. ✓ Gas turbine. ✓ Steam turbine ✓ Internal combustion engine Electric Motor. Electric motors used as prime movers are either direct current (DC) or alternating current (AC). A DC motor is normally used where the speed of the prime mover must be changed but they are very expensive compared to most AC motors. For this reason, AC motors are more common in process plants. ADNOC Classification: Internal Typical Electric Motor Parts. The main parts of an electric motor are: 1. The casing: Holds the rotor shaft with bearings and the stator windings 2. The rotor: Contains wire coils which creates the magnetic field 3. The stator: Contains wire coils which creates the magnetic field. These two magnetic fields interact with each other to rotate the shaft. 4. The drive shaft: This shaft can be coupled to drive pumps and compressors. Steam Turbine. When one or more of the following conditions exist in a plant a steam turbine prime mover is the best option. ✓ Explosive atmospheres are present in the surrounding area. ✓ Variable speed drives are needed. ✓ High speed operation is needed. ADNOC Classification: Internal Typical Steam Turbine Parts A: Steam Inlet port: allows steam to enter inside the turbine. B: Casing contains the other parts of the turbine and provides passage for steam flow. C: Throttle Valve regulates the amount of steam that is allowed into the turbine. A. D: Turbine rotor the steam hits the rotor blades causing them to rotate with the shaft. Hazards associated with Electric Motor operation. When working with electricity, especially when operating machinery or equipment in large industrial environments, there is always an element of risk. Normal electrical hazards are: ✓ ELECTRIC SHOCK. When a person comes into contact with energized conductors, he will receive an electrical shock due to the current flowing through their skin, muscles and vital organs. ADNOC Classification: Internal ✓ ELECTRIC BURNS. An electrical burn is a burn that results from electricity passing through the body causing temporary or permanent damage to the skin, tissues, and major organs. ✓ EXPOSURE TO ARC-FLASH. An Arc-Flash is an unexpected sudden release of heat and light energy produced by electricity traveling through air, usually caused by accidental contact between live conductors. Hazards associated with Steam Turbine operation. ✓ WET STEAM HAZARD. ✓ HEAT AND HIGH-PRESSURE HAZARD. ✓ WARM UP HAZARD. ✓ OVER SPEEDING. ✓ SLIPS AND FALLS HAZARD. Due to steam leak or when condensate is released into the atmosphere, it can make the floor wet and slippery which can cause slip and fall hazards. ADNOC Classification: Internal Safety checks associated with Steam Turbine operation. Safe operation of steam turbine requires careful observance of all safety rules and safety procedures to protect serious injury to personal and prevent damage to equipment. Steam turbines are operated by high pressure high temperature steam, hence extreme measures ought to be taken to prevent accidental injuries and equipment damage. Always keep the work area clean. Make sure all the locks and tags are removed and all Permit to Works (PTWs) are closed. Thoroughly inspect the turbine, coupling, and driven load for solid, firm mounting. Look for any loose parts, poor grouting, and adequate base components. Complete all alignment tests. Before starting, securely fasten pulleys, belts, couplings, gears, etc. and install proper guards. Make sure no steam leaks around the area. 6. PROCESS CONTROL ✓ Manufacturers use process control for the following main reasons: Reduce process variability (Changes) Increase efficiency Ensure safety. Reduce environmental impact ✓ Process efficiency can be increased by: Increasing production rate.: producing more Decreasing energy consumption: using less energy (electricity, steam, water.) Decreasing off specification products: less waste. Extending the life of equipment: equipment used for longer time before replaced. ✓ Process control should be able to run the process with minimum environmental problems. Bad or poor process control may cause serious environmental problems (pollution). ✓ Ensuring safety is one important goal of process control because poorly controlled process may result in serious accidents. ✓ Automatic Control is a control system done totally by the controller. In automatic control, the valve actuator receives a corrective signal from a controller to keep the control variable at set point. ADNOC Classification: Internal O/ P Automatic control of furnace coil outlet temperature Set point (SP) It is the value of a process variable that needs to be maintained to keep the process at the required conditions. The desired room temperature is an example of set point. Offset (Error) It is the difference between the measured variable (actual value of process variable) and the set point (desired value of process variable). Process Variables the most common process variables are Level, Pressure, Temperature and Flow Level Control Loop in PTP The main components of the separator level control loop are: Transmitter (LT-015): Measuring means Controller (LIC-015): Control element Control valve (LCV-015): Adjusting element ADNOC Classification: Internal LCV-015 is an air to open fails close valve (A/O; FC) which remains closed in case of emergency. This will prevent the separator from being emptied from water. Pressure Control Loop in PTP The main components of the separator pressure control loop are: Transmitter (PT-012) continuously monitors the pressure and sends it as an electrical signal to the pressure indicator controller PIC-012. Controller (PIC-012) Control valve (PCV-012) PCV-012 is an air to close, fails open valve (AC/ FO). This valve type selection is crucial, because the pressure in V-001 should be vented in any emergency. Temperature Control Loop The main components of the separator level control loop are: Temperature Transmitter (TT-009): measuring means. Controller (TIC-009): Controlling element. Electrical heater H-001: Adjusting element / final control element. ADNOC Classification: Internal LEVEL / FLOW CASCADE CONTROL Primary Loop: Level Control Loop Secondary Loop: Flow Control Loop The secondary controller (FC) should be three times faster than the primary controller (LC). Split Range Pressure Control ADNOC Classification: Internal Controller output 0% - both valves are closed. Controller output 25% - valve A is 50% open and valve B still closed. Controller output 50% - valve A is fully open and valve B closed. Controller output 75% - valve A is fully open and valve B 50% open. Controller output 100% - both valves are fully open. Low Selector Switch (LSS) Override Control The following example shows an LSS override control system used to protect the heating coil from damage. This is done by constantly keeping it immersed in water. If liquid level falls below the lower limit, the LSS switches the control action from pressure control to level control in order to maintain the required water level in the boiler drum. This protects the coil from damage by overheating. ADNOC Classification: Internal High Selector Switch (HSS) Override Control The discharge of the compressor has two control loops: Flow control loop (loop 1) Pressure control loop (loop 2) The HSS transfers the control action from the flow control to the pressure control loop (loop2) whenever the discharge pressure exceeds the upper limit. Both loops use the motor speed to control the flow or the pressure. 7. UTILITIES Inert Gas System is required in process plants for the following main reasons: ✓ Purging: removing air or hydrocarbon gases from vessels and pipe works. ✓ Inerting & blanketing: Inert gases such as nitrogen or carbon dioxide (CO2) are used to bring oxygen concentrations down to a safe level in environments with the potential for fire and explosions. ✓ Leak pressure testing: A special nitrogen/helium mixture is supplied to detect even tiny leaks and leakage rates at operating conditions with pressures of up to 250 bar. The two commonly used inert gases in process plants are CO2 and N2. ADNOC Classification: Internal Steam System The process of steam generation, distribution and condensate recovery is summarized in below process steam cycle figure. Steam is usually provided at three pressure levels: High pressure (40 barg or 600 psig): to drive the big steam turbines. Medium pressure (10 barg or 150 psig): to drive small steam turbines. Low pressure (4 barg or 60 psig): used for heating and stripping purposes. Gaseous Fuel There two main types of gas mixtures used as fuel gas in refineries and petrochemical plants: ✓ Refinery fuel gas (RFG): is a mixture of mainly methane, light hydrocarbons, and hydrogen. ✓ Natural gas: consists of a high percentage of methane (generally greater than 85%) and varying amounts of ethane, propane, butane, nitrogen, carbon dioxide. ADNOC Classification: Internal Pre-treatment of Desalination Plant Feed Water ✓ Screening The first step of pre-treatment is called Screening. Here, the suspended solids are removed. Screening takes place at the mouth of the intake pipe. It consists of three steps: stop gate, bar screen, and fine screening as shown in the following figure. Seawater Screening Equipment ✓ Settling Tank and Chlorine Injection. After the step of screening, the feed water passes into large holding tanks, called “Settling Tanks”. The feed water moves very slowly in these tanks. Very small solid particles that have managed to get through the screening process fall to the bottom of the settling tank. The particles settle in the bottom because of gravity. Water stays in the settling tank for 2 to 3 days. The final stage of the process is to kill small marine animals. Chlorine is injected into the feed water to kill any small marine animals that are still present in the water. The chlorine is added to the water in the settling tank as shown in the below figure. ADNOC Classification: Internal Settling Tanks and Chlorine Injection Demineralization Demineralization means removing the minerals or dissolved solids from the raw water, which will cause scale formation on the boiler tubes. The demineralizer works on an ion exchange process. An ion is an atom or group of atoms that carry a positive (+) or negative (–) charge. Positive ions are called cations, and negative ions are called anions. The demineralization process consists of three units as shown in the below Figure. Cation unit removes the cations such as Ca+2, Mg+2, & Na+ by exchanging them with positive Hydrogen ions (H+). Degasifier is used to remove different gases such as CO2 from water. This will increase the capacity of the anion exchanger and helps in improving the process of ion exchange. Anion unit removes the anions such as SO4-2 and Cl- by exchanging them with negative Hydroxide ions (OH-). ADNOC Classification: Internal Water Demineralization Process Boiler Feed Water Deaeration The deaerator is a large vessel that removes dissolved gases from the boiler feed. Dissolved gases, especially oxygen (O2) and carbon dioxide (CO2 cause corrosion to boiler internal parts due to the high operating temperatures. A second function of the deaerator is to preheat the boiler feed water. This happens because the feed water absorbs heat from the low-pressure steam that is used to strip (remove) dissolved O2 and CO2 from the feed water. The boiler feed water must be heated to a high temperature (near the temperature of the water inside the boiler) to prevent thermal shock which can damage piping systems and operating equipment. The commonly used type of deaerator is the “SPRAY AND TRAY” type. Low pressure steam is used to strip off the harmful gasses (O2 and CO2) from the boiler feed water because: It is available throughout the plant. It does not contaminate the feed water. ADNOC Classification: Internal Boiler Feed Water Deaeration Internal Chemical Treatment of Boiler Feed Water Chemical treatment is done to the feed water inside the deaerator and inside the boiler by using chemicals. This chemical treatment ensures that the water inside the boiler is kept clean and kept within the manufacturers specification to prevent scale build-up and corrosion. Oxygen Scavengers Oxygen scavengers are chemicals that are added to the feed water to absorb any free oxygen that is remaining in the feed water. The oxygen scavenger (hydrazine) is added to the deaerator storage tank to absorb any free oxygen. Hydrazine (N2H4) will combine with the free oxygen (O2) to produce nitrogen (N2) plus two water molecules (2H2O). See chemical exchange below: Hydrazine + Oxygen Water + Nitrogen N2H4 + O2 2H2O + N2 ADNOC Classification: Internal APP Air System Air System for the PTPPs consists of two Plant Air Screw Compressors 700-K-1501A/B (2 X 100%) (one working and one standby), each with a capacity 3.7 m3/min, supply compressed air to the Process Air and Instrument Air systems. Air Compressor discharge is routed to the Air Receiver 700-V-1502 via After Cooler. The Compressed air from the Air Receiver is supplied to the Process Air header from where it is distributed to the mixing manifold in Utility area and to all 4 PTPPs. Process air is supplied at a pressure of 6.0 barg and 40 oC. Compressed Air from the Air Receiver 700-V-1502 is supplied to the Instrument Air Dryers 700-A- 1503A/B. The compressed air from the Air Receiver is preferentially routed to the Instrument Air Dryers. The Instrument Air Dryer package consists of two Refrigerated type dryers 700-A-1503A/B. Air Dryers are supplied by Ingersoll Rand. Dried air from the dryer package is supplied to the Instrument Air distribution header. The Air Receiver has up to 5 minutes capacity between normal and minimum operating pressures to allow safe operation and shutdown of the plant in the event of loss of air. The instrument air is supplied at a pressure of 7.0 barg and 30oC. A simplified process flow diagram of air system is shown below. PCV 2251 Air Dryer Instrument Air 700-A-1503A/B To Distribution Ambient SDV PCV Air 7151 2252 After Process Air Cooler To Air Manifold Air Compressor 700-K-1501A/B PCV 2253 Process Air To Distribution Air Receiver 700-V-1502 Drain Air System Simplified Flow Diagram ADNOC Classification: Internal Air Compressors After coolers Air Receiver Air Dryers