7/29/2019 Petroleum.ppt [Recovered] http://slidepdf.com/reader/full/petroleumppt-recovered 1/42 A refinery is a factory. Just as a paper mill turns lumber into legal pads or a glassworks turns silica into stemware, a refinery takes a raw material--crude oil--and transforms it into gasoline and hundreds of other useful products .
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• An "average" crude oil contains about 84% carbon, 14% hydrogen, 1%-3%
sulfur, and less than 1% each of nitrogen, oxygen, metals, and salts. Crude oilsare generally classified as paraffinic, naphthenic, or aromatic, based on thepredominant proportion of similar hydrocarbon molecules. Mixed-base crudeshave varying amounts of each type of hydrocarbon. Refinery crude base stocksusually consist of mixtures of two or more different crude oils.
Petroleum refining processes and operations can be separated into five basic areas:•Fractionation (distillation) is the separation of crude oil in atmospheric and vacuum distillation towersinto groups of hydrocarbon compounds of differing boiling-point ranges called "fractions" or "cuts.“
•Conversion Processes change the size and/or structure of hydrocarbon molecules. These processesinclude:
•Decomposition (dividing) by thermal and catalytic cracking;•Unification (combining) through alkylation and polymerization; and• Alteration (rearranging) with isomerization and catalytic reforming.
•Treatment Processes are intended to prepare hydrocarbon streams for additional processing and toprepare finished products. Treatment may include the removal or separation of aromatics andnaphthenes as well as impurities and undesirable contaminants. Treatment may involve chemical orphysical separation such as dissolving, absorption, or precipitation using a variety and combination of
•Formulating and Blending is the process of mixing and combining hydrocarbon fractions, additives,and other components to produce finished products with specific performance properties.
•Other Refining Operations include: light-ends recovery, sour-water stripping, solid waste andwastewater treatment, process-water treatment and cooling, storage and handling, product movement,hydrogen production, acid and tail-gas treatment and sulfur recovery.
• Auxiliary Operations and Facilities include: steam and power generation, process and fire watersystems, flares and relief systems, furnaces and heaters, pumps and valves, supply of steam, air,nitrogen, and other plant gases, alarms and sensors, noise and pollution controls, sampling, testing, andinspecting and laboratory, control room, maintenance, and administrative facilities
•Crude oil often contains water, inorganicsalts, suspended solids, and water-soluble trace metals.• As a first step in the refining process, toreduce corrosion, plugging, and foulingof equipment and to prevent poisoning
the catalysts in processing units, thesecontaminants must be removed bydesalting (dehydration).•The two most typical methods of crude-oil desalting, chemical and electrostaticseparation, use hot water as the
extraction agent.
•The feedstock crude oil is heated to between 150° and 350°F to reduce viscosity and surfacetension for easier mixing and separation of the water.•The temperature is limited by the vapor pressure of the crude-oil feedstock. In both methods otherchemicals may be added.
• Ammonia is often used to reduce corrosion. Caustic or acid may be added to adjust the pH of thewater wash.•Wastewater and contaminants are discharged from the bottom of the settling tank to thewastewater treatment facility.•The desalted crude is continuously drawn from the top of the settling tanks and sent to the crudedistillation (fractionating) tower.
Atmospheric Distillation•The desalted crude feedstock is preheated using recovered process heat.•The feedstock then flows to a direct-fired crude charge heater where it is fed into the verticaldistillation column just above the bottom, at pressures slightly above atmospheric and at
temperatures ranging from 650°
to 700°
F (above these temperatures undesirable thermal crackingmay occur).• All but the heaviest fractions flash into vapor. As the hot vapor rises in the tower, its temperatureis reduced.•Heavy fuel oil or asphalt residue is taken from the bottom.• At successively higher points on the tower, the various major products including lubricating oil,heating oil, kerosene, gasoline, and uncondensed gases (which condense at lower temperatures)
•The ADU feed is pumped by P-100 (HS-100) and controlled by FIC-100. It is preheated in the bottoms feed exchanger (E-100) before entering the Feed Furnace (F-100). TIC-100 controls the crude oil temperature entering the ADU (T-100) byadjusting fuel gas flow to the furnace.
•Bottoms liquid is collected and sent to the VDU by LIC-114 through the Bottoms Pump P-114 (HS-114). This flow isindicated by FI-124. Stripping steam is injected into the ADU bottoms by FIC-134.
•Hot gas oil flows by gravity to the Gas Oil Stripper (T-113) through FIC-113. The gas oil enters the stripper at the top andflows downward over six trays. Stripping steam is introduced into the bottom of the stripper through FIC-133. The gas oilproduct is pumped from the base of the stripper by the Gas Oil Product Pump P-113 (HS-113) to storage. The gas oil productflow is controlled by LIC-113 and the flow rate is indicated by FI-123. The gas oil product's 95% point is monitored by AI-
123.
•Hot kerosene flows by gravity to the Gas Oil Stripper (T-112) through FIC-112. The kerosene enters the stripper at the topand flows downward over six trays. Stripping steam is introduced into the bottom of the stripper through FIC-132. Thekerosene product is pumped from the base of the stripper by the Gas Oil Product Pump P-112 (HS-112) to storage. The gasoil product flow is controlled by LIC-112 and the flow rate is indicated by FI-122. The kerosene product's 95% point ismonitored by AI-122.
•Hot naphtha flows by gravity to the Naphtha Stripper (T-111) through FIC-111. The naphtha enters the stripper at the topand flows downward over six trays. Stripping steam is introduced into the bottom of the stripper through FIC-131. Thenaphtha product is pumped from the base of the stripper by the Naphtha Product Pump P-111 (HS-111) to storage. Thenaphtha product flow is controlled by LIC-111 and the flow rate is indicated by FI-121. The naphtha product's 95% point ismonitored by AI-121.
• A naphtha pump around is drawn from tray 6, pumped through P-115 (HS-115) and controlledby FIC-115. The pump around return temperature is controlled by TIC-115 which modulatescooling water flow to E-115.
• The ADU overhead vapor flows through the overhead condenser E-110 (HV-110), whose outlettemperature is indicated by TI-120, into the Overhead Reflux Drum D-111. The hydrocarbonsare partially condensed and the two phases (vapor and liquid) enter the overhead reflux drumwhere the condensed water separates from the hydrocarbon liquid by gravity.
• The reflux is returned to tray 1 of the tower from the reflux drum via pump P-110 (HS-110).The reflux flow is controlled by FIC-110 which is reset by TIC-110 to control the toweroverhead temperature. The level of the overhead drum is maintained by LIC-110 which sendsthe gasoline product to storage, whose rate is indicated by FI-120.
• Water collects in the boot of the overhead reflux drum, and is transferred to the water systemfor treating. LIC-120 maintains a constant sour water level. The sour water is sent totreatment through pump P-120 (HS-120).
• The uncondensed gas (FI-130) is sent to fuel gas through PIC-120, which maintains the ADUback pressure. Analyzers are present to monitor the C3 composition of the off gas (AI-130) andvapor pressure (AI-120) of the gasoline.
• ADU overhead pressure is indicated by PI-110 and bottoms pressure is indicated by PI-114.
• The ADU tower temperature profile is indicated by TI-120 (overhead), TI-110 (gasoline), TI-111(naphtha), TI-112 (kerosene), TI-113 (Gas Oil), and TI-114 (ADU residuum).
•In order to further distill the residuum or topped crude from the atmospheric tower at higher temperatures,
reduced pressure is required to prevent thermal cracking.
•The process takes place in one or more vacuum distillation towers. The principles of vacuum distillationresemble those of fractional distillation except that larger diameter columns are used to maintain comparablevapor velocities at the reduced pressures.
•The equipment is also similar. The internal designs of some vacuum towers are different from atmospheric
towers in that random packing and demister pads are used instead of trays.
• A typical first-phase vacuum tower may produce gas oils, lubricating-oil base stocks, and heavy residual forpropane deasphalting.
• A second-phase tower operating at lower vacuum may distill surplus residuum from the atmospheric tower,which is not used for lube-stock processing, and surplus residuum from the first vacuum tower not used fordeasphalting.
• Vacuum towers are typically used to separate catalytic cracking feedstock from surplus residuum.
•Atmospheric and vacuum distillationareclosed processes and exposures areexpected to be minimal.
•When sour (high-sulfur) crudes areprocessed, there is potential for exposureto hydrogen sulfide in the preheatexchanger and furnace, tower flash zoneand overhead system, vacuum furnace andtower, and bottoms exchanger.
•Hydrogen chloride may be present in thepreheat exchanger, tower top zones, andoverheads.
•Wastewater may contain water-solublesulfides in high concentrations and otherwater-soluble compounds such as
ammonia, chlorides, phenol, mercaptans,etc., depending upon the crude feedstockand the treatment chemicals.
•The VDU (Vacuum Distillation Unit) takes the residuum from the ADU (Atmospheric
Distillation Unit) and separates the heavier end products such as vacuum gas oil, vacuumdistillate, slop wax, and residue.
•Heavy crude oil is preheated by the bottoms feed exchanger, further preheated andpartially vaporized in the feed furnace, and passed into the vacuum tower where it isseparated into slop oil, vacuum gas oil, vacuum distillate, slop wax, and bottomsresidue.
•This tower contains a combination of 14 fractionation trays and beds. It is equippedwith three side draws and pump around sections for vacuum gas oil, vacuum distillate,and slop wax products.
•The liquid from the feed furnace enters the tower bottoms, where it is collected andsent for further processing.
•Steam is injected into the base of the tower to reduce the hydrocarbon partialpressure by stripping some light boiling components from the bottoms liquid. The vaporsfrom the feed heater enter the tower below tray 14.
• At tray 14, a draw pan is located from which slop wax product is drawn. The slop waxproduct and pump around are cooled, with the slop wax product going to storage,while the pump around is returned to the tower at tray 11.
• The next product draw is located at tray 8, where the draw for vacuum distillate
product is located. The vacuum distillate draw tray is a total draw tray, where thereflux from the tray is pumped under flow control to the tray below.
• The product and pump around are cooled, with the vacuum distillate product going tostorage, while the pump around is returned to the tower at tray 7.
• The last product draw is located at tray 4, where the draw for vacuum gas oil productis located.
• The vacuum gas oil draw tray is also a total draw tray, where the reflux from the trayis pumped under flow control to the tray below.
• The product and pump around are cooled with the vacuum gas oil product going tostorage, while the pump around is returned to the tower at tray 1.
• The overhead from the VDU is condensed and combined with the vacuum steam. Theslop oil and water are separated by gravity in the vacuum drum.
• The water is drained to disposal, while the slop oil is accumulated and occasionallydrained to slop collection.
•The purpose of solvent extraction is to prevent corrosion, protect catalyst in subsequent processes, and improvefinished products by removing unsaturated, aromatic hydrocarbons from lubricant and grease stocks.
•The solvent extraction process separates aromatics, naphthenes, and impurities from the product stream by dissolving
or precipitation.
•The feedstock is first dried and then treated using a continuous countercurrent solvent treatment operation.
• In one type of process, the feedstock is washed with a liquid in which the substances to be removed are more soluble
than in the desired resultant product.
•In another process, selected solvents are added to cause impurities to precipitate out of the product. In the adsorption
process, highly porous solid materials collect liquid molecules on their surfaces.
•The solvent is separated from the product stream by heating, evaporation, or fractionation, and residual trace amountsare subsequently removed from the raffinate by steam stripping or vacuum flashing.
•Electric precipitation may be used for separation of inorganic compounds. The solvent is then regenerated to be used
again in the process.
•The most widely used extraction solvents are phenol, furfural, and cresylic acid. Other solvents less frequently used are
liquid sulfur dioxide, nitrobenzene, and 2,2' dichloroethyl ether.
•The selection of specific processes and chemical agents depends on the nature of the feedstock being treated, the
contaminants present, and the finished product requirements.
•Catalyt ic cracking breaks complex hydroc arbons into sim pler molecules in order to
increase the qual i ty and q uant i ty of l igh ter, more desirable produc ts and d ecrease the
amoun t of residuals.
•This process rearranges the mo lecular structure of hydroc arbon com pou nds to con vert
heavy hydro carbon feedstock into l ighter fract ions s uch as k erosene, gasol ine, LPG,
heating o i l , and petrochem ical feedstock.
•Catalyt ic cracking is simi lar to th ermal cracking except that catalysts faci l i ta te the
conv ers ion of the heavier molecules into l ighter produc ts.
•Use of a catalyst (a mater ial that assists a chemical react ion bu t do es not take part in i t )
in the cracking react ion increases the yield of impro ved-quali ty pro ducts u nder much
less severe operat ing co ndi t ions than in thermal cracking.
•
•Typ ical tem per atu res are fr om 850°-950°F at muc h l ow er p ressu res o f 10-20 ps i.
•The catalysts used in ref inery c racking u ni ts are typical ly so l id m ater ia ls (zeol i te,alumin um hyd ros i l icate, treated bento nite clay, ful ler 's earth, baux ite, and sil ica-alumina)
that come in the form of powders, beads, pel lets or shaped mater ia ls c al led extrudi tes.
There are three basic functions in the catalytic racking process:•Reaction - Feedstock reacts with catalyst and cracks into different hydrocarbons;
•Regeneration - Catalyst is reactivated by burning off coke; and
•Fractionation - Cracked hydrocarbon stream is separated into various products.
The three types of catalytic cracking processes are fluid catalytic cracking (FCC),moving-bed catalytic cracking, and Thermofor catalytic cracking (TCC).
Fluid Catalytic Cracking•The most common process is FCC, in which the oil is cracked in the presence of a finelydivided catalyst, which is maintained in an aerated or fluidized state by the oil vapors.
•The fluid cracker consists of a catalyst section and a fractionating section that operatetogether as an integrated processing unit.
•The catalyst section contains the reactor and regenerator, which, with the standpipe andriser, form the catalyst circulation unit.
•The fluid catalyst is continuously circulated between the reactor and the regeneratorusing air, oil vapors, and steam as the conveying media.
•A typical FCC process invo lves mixin g a preheated hyd rocarbo n charge with h ot, regenerated catalyst as it enters the
riser leading to the reactor.
•The charg e is com bin ed wi th a recyc le stream wit hin the ris er, vapo rized, and raised to r eactor temperatu re (900°-
1,000°F) by the ho t c ataly st .
•As the m ixture travels up th e riser, the charge is crack ed at 10-30 psi. In the more mod ern FCC units, all cracking takes
place in the ris er.
•The "reactor" no longer funct ions as a reactor ; i t merely serves as a hold ing vessel for the cyclones. This cracking
con tinues unti l th e oil vapors are separated from the catalyst in the reactor cyc lones.
•The resultant prod uct stream (cracked produc t) is then charged to a fractionating column w here it is separated into
fractions , and som e of the heavy oil is recycled to the riser.
•Spent catalyst is regenerated to get rid of co ke that collects on th e catalyst during the pro cess.
•Spent catalyst f lows thro ugh th e catalyst str ipp er to the regenerator, where mos t of the coke deposits burn off at the bottom wh ere preheated air and spent catalyst are mixed.
• Fresh catalyst is added and w orn-out catalyst removed to opt imize the cracking process.
•The moving-bed catalytic cracking process is similar to the FCC process.
•The catalyst is in the form of pellets that are moved continuously to the top of the unit by conveyor or pneumatic lift tubes to a storage hopper, then flow downward by gravity through the reactor, and finally to a regenerator.
Thermofor Catalytic Cracking
•In a typical thermofor catalytic cracking unit, the preheated feedstock flowsby gravity through the catalytic reactor bed.
•The vapors are separated from the catalyst and sent to a fractionating tower.
•In the first stage, preheated feedstock is mixed with recycled hydrogenand sent to the first-stage reactor, where catalysts convert sulfur and nitrogen compounds to hydrogen sulfide and ammonia.
•Limited hydrocracking also occurs. After the hydrocarbon leaves the first
stage, it is cooled and liquefied and run through a hydrocarbon separator.
•The hydrogen is recycled to the feedstock. The liquid is charged to a fractionator.
•Depending on the products desired (gasoline components, jet fuel, and gasoil), the fractionator is run to cut out some portion of the first stage
reactor out-turn.
•Kerosene-range material can be taken as a separate side-draw product or included in the fractionator bottoms with the gas oil.
•The fractionator bottoms are again mixed with a hydrogen stream and
charged to the second stage.
•Since this material has already been subjected to some hydrogenation,cracking, and reforming in the first stage, the operations of the second stage are more severe (higher temperatures and pressures).
• A catalytic reformer comprises a reactor section and a product-recovery section. Most processes use platinum as the active catalyst. Sometimes platinum is combined with a second catalyst (bimetalliccatalyst) such as rhenium or another noble metal.•There are many different commercial catalytic reforming processes including platforming, powerforming,ultraforming, and Thermofor catalytic reforming.
•In the platforming process, the first step is preparation of the naphtha feed to remove impurities fromthe naphtha and reduce catalyst degradation.•The naphtha feedstock is then mixed with hydrogen, vaporized, and passed through a series of alternating furnace and fixed-bed reactors containing a platinum catalyst.•The effluent from the last reactor is cooled and sent to a separator to permit removal of the hydrogen-rich gas stream from the top of the separator for recycling. The liquid product from the bottom of theseparator is sent to a fractionator called a stabilizer (butanizer).•It makes a bottom product called reformate; butanes and lighter go overhead and are sent to the
Alkylation combines low-molecular-weight olefins (primarily a mixture of propylene and butylene) with isobutene in the presence of a catalyst, either sulfuric acid or hydrofluoric acid.
The product is called alkylate and is composed of a mixture of high-octane,
branched-chain paraffinic hydrocarbons.
Alkylate is a premium blending stock because it has exceptional antiknock properties and is clean burning.
•Feedstock from various refinery units are sent to gas treating plants where butanesand butenes are removed for use as alkylation feedstock, heavier components are sentto gasoline blending, propane is recovered for LPG, and propylene is removed for usein petrochemicals. Some mercaptans are removed by water-soluble chemicals.
•Caustic liquid (sodium hydroxide), amine compounds (diethanolamine) or fixed-bed catalyst sweetening also may be used.
•Drying is accomplished by the use of water absorption or adsorption agents to removewater from the products.
•Some processes simultaneously dry and sweeten by adsorption on molecular sieves.