Refinery Operations Furfural Extraction

7/30/2019 Refinery Operations Furfural Extraction

1/15

Refinery Operations

The previous section described the manner in which the crude oil is received, passed through the variousunits to produce finished products or finished components that are blended to make finished products.

The purpose of this section is to describe in a little more detail how each of these processing isaccomplished and its overall work by practical application of the many principles covered earlier.

Refinery has 13 process units and each has a specific function to purify or to rearrange the molecular

structure or crack the molecules to make more desirable products. In all the units great emphasis isplaced on the conservation of heat by the use of heat exchangers.The steam used in the process units is served by three headers under different pressures. The high

pressure (H.P.) steam header will have a pressure of 31'2 kg. per sq. cm., the medium pressure (M. P.)steam will be under pressure of 10-5 kg. per sq. cm. and the low pressure (L. P.) steam will be under apressure of 3'5 kg. per sq. cm. The air required for pneumatic instruments and control valves and thecooling water are supplied from a central source for all the plants.

Crude distillation unit - Plant No. I.The crude unit is the starting point for all refinery operations. The separation of crude oil into rawproducts is accomplished in the crude unit by fractional distillation in fractionating columns, based ontheir distillation range. The process does not involve any chemical changes. The unit consists of an

electrostatic desaker, an atmospheric distillation tower and a two stage vacuum distillation sections. Theunit is designed to process Darius crude having a specific gravity of 0'855 at a rate of 348-6 m3 /hr.

A schematic representation of the crude oil and product flow is attached. The two crude feed pumps,located near the crude storage tanks, supplies the feed to the unit. The feed to the unit is passedthrough a desalter where the chlorides of calcium, magnesium and sodium are removed. These saltsform corrosive acids during processing and therefore are detrimental to process equipments. Byinjecting water to the crude oil stream these salts are dissolved in the water and the solution isseparated from the crude by means of an electrostatic separator in a large vessel. The electrically

charged grids coalesces the water and aids separation from the crude. After desalting the crude isheated through a series of heat exchangers and then by a furnace to a temperature of 393C and

admitted to the flash zone of the atmospheric distillation tower.

Four fractions are separated in the atmospheric tower. The overhead vapours are condensed in a twostage system. The condensed liquid from the first stage is used as reflux to the tower. The second stageliquid together with the compressed and condensed vapours from the second stage is collected in thestablilizer feed accumulator. The liquid in the stabilizer feed accumulator is the feed to the VapourRecovery unit. The uncondensed vapours from the stabilizer feed accumulator is routed to fuel gas

system after removal of H 2 S in the sulphur plant. The other three products separated are heavynaphtha, kerosene and diesel. The heavy naphtha is drawn from tray 28 and is steam stripped toimprove flash. The majority of this product is line blended with diesel from HSD desulphurisation unit

(Plant No. 5) and raw diesel to make finished High Speed Diesel oil. A small amount of the heavynaphtha is sent to Merox treater. This treater oxidises mercaptans to disulphi-des thereby eliminating

the unpleasant odour. The treated stream is used for blending JP-4.

Kerosene drawn from tray No. 20 is steam stripped and is charged hot to kerosene hydro-desulphuriserplant (Plant No. 4). When this unit is shut down, kerosene is cooled and sent to intermediate storagetank through the kerosene product cooler at Plant No. 4.Diesel oil is drawn from plate 10. Approximately 50% of the diesel oil is routed to H. S. D.Hydrodesulphuriser (Plant 5) after heat exchange with crude and the balance is cooled and blended with
http://www.geocities.ws/alfiefernandes/images/ref100.jpghttp://www.geocities.ws/alfiefernandes/images/ref98.jpg


2/15

the desulphurised diesel oil to produce HSD product. When Plant No. 5 is shut down, the total stream iscooled in the product cooler at Plant 5 and sent to storage.The stripped overhead liquid streams from kerosene hydrode-sulphuriser, HSD desulphuriser and lube oilhydrofinisher are sent to the atmospheric distillation tower after separating the water in a dewateringdrum.

The hot reduced crude from the bottom of atmospheric distillation tower is further fractionated in thetwo stage vacuum distillation section. The vacuum maintained in these fractionators makes it possible tofractionate the reduced crude at much lower temperatures. But for this vacuum, the highertemperatures required to fractionate reduced crude will result in cracking of the products. The reducedcrude from atmospheric tower bottoms is further heated in presence of steam in the first stage vacuum

heater and introduced into the first stage vacuum tower. Three side-stream products spindle oil, lightneutral and intermediate neutral and an overhead productgas oil are separated in the first stage

vacuum tower. Spindle oil, light neutral and intermediate neutral are sent to the Lube Oil Extractionplants as feed stock or to storage. The distillates in excess of the lube oil requirements is sent hot as

charge stock to Vacuum Distillate Desulphuriser (Plant 13) prior to thermal cracking of theseintermediate products. The gas oil is routed to thermal cracker feed tank or directly to Plant 13.

The bottoms product from first stage vacuum tower is reheated along with steam and fractionated toyield heavy neutral stream. Flash zone vapours of the second stage vacuum tower pass through ademister pad to prevent entrainment of asphaltenes into the heavy neutral stream. The heavy neutralstream is cooled and sent to intermediate storage tank as charge to Furfural

Extraction unit (Plant 8).A part of the second stage vacuum tower bottoms, vacuum residuum, is cooled and sent to Bitumen AirBlowing Unit (Plant 7). Another part is charged to the Visbreaker (Plant 6) and the balance is routed to

light fuel oil blending.

Plant 2 - Vapour Recovery UnitThe vapour recovery unit consists of two sections (a) vapour recovery section and (b) merox treatingsection. The function of vapour recovery section is to separate gas, LPG, light gasoline and light

naphtha from the overhead naphtha of atmospheric tower in plant 1. The merox treating section is forsweetening of LPG, a mixture of light gasoline and light cracked gasoline for gasoline blending, a mixture

of light naphtha and heavy naphtha for JP-4 blending.The Vapour Recovery section is designed to process 75.8m3/hr. atmospheric tower overhead fromcrude unit. This section consists of a stabilizer with an LPG stripper and a splitter tower. The productyields from the unit are:(a) LPG 4-9 m3/hr.(b) Light gasoline 37-3 m3/hr.(c) Light naphtha 30-1 m3/hr.The feed to the unit from the stabilizer feed drum in the crude unit is preheated by exchangers and is

admitted to the stabilizer column. The stabilizer separates the feed into gas, LPG and C^ bottoms. Theheat required is obtained from a reboiler by exchanging heat with the bottom pump around of the

atmospheric tower. LPG is drawn from tray No. 31 or 33 and the light hydrocarbons are stripped in astripper. The stripped LPG is sent to merox extraction plant to remove mercaptans. The overhead gassent partly to fuel gas treating system in the sulphur plant (Plant 12) and partly as feed to hydrogenplant after amine treating.

The bottoms of the stabilizer is fed to the naphtha splitter to produce light gasoline and light naphtha.The light gasoline is taken overhead and part of this is sweetened in Merox treating section to meet therequirements of gasoline blending and the balance is sent to raw naphtha storage tank. The light


3/15

naphtha is taken as bottoms product. This product is split into three streams. The first part isdesulphurised in Unifmer and sent to Platformer as feed. The second part is sweetened in a Meroxtreater along with heavy naphtha according to the JP-4 blending requirement. The balance is diverted tothe raw naphtha storage tanks.

The Merox treating facilities has three treaters for processing three different streams. The streamsprocessed are (a) LPG, (b) a mixture of light gasoline and light cracked gasoline for motor spirit blendingand (c) a mixture of light naphtha and heavy naphtha for blending JP-4. Merox treating utilizes aproprietory process developed by Universal Oil Products Company. The treating can be classified intotwo categoriesextraction and sweetening. In the extraction system the mercaptans are removed fromthe feed stream whereas in the sweetening system the mercaptans are oxidised to disulphides and are

left in the product stream.

The LPG Merox treating is an extraction system designed to process 4-9 m3/hr. of LPG from VapourRecovery section. The feed stream is treated with MEA and passed through a caustic scrubber toremove H2S from the feed stream. The N2 S free LPG then flows to the extractor where it meets a

counter-current flow of Merox solution in a caustic soda medium. The mercaptans in the feed areextracted by the merox solution and the treated LPG is sent to storage. The spent Merox solution is sent

to the oxidiser where the extracted mercaptans are oxidised to disulphides. The regenerated Meroxsolution is then pumped to the extractor. The extracted disulphides are pumped to the crude feed inPlant I.

The light gasoline Merox treater is designed for a feed rate of 6-8 m^hr. consisting of a mixture of light

gasoline from vapour recovery section and light cracked gasoline from visbreaker fractionacor in Plant 6.The Merox solution is regenerated in the common system for LPG and Merox. The treated gasoline issent to storage and is blended with Reformate from Plant 3 to make motor gasoline.

The Merox treatment of light naphtha is a sweetening process. The Merox catalyst is impregnated in a

bed of activated charcoal using methanol and made alkaline by circulating caustic soda solution as apreparation to receive the feed stock. This treating unit is designed for a feed rate of 4'2 m^rir.consisting of light naphtha from Vapour Recovery section and heavy naphtha from Plant I. The treatednaptha is sent to storage and later blended with other components to make JP-4. The naphtha feed

stream is caustic scrubbed to remove naphthenic acids. Air is then injected to the feed stream and thefeed stream is admitted to the top of the solid bed reactor. The mercaptans are oxidised to disulphideswhile passing through the bed and are carried along with the product stream. The sweetened naphthapasses through a caustic settler to remove entrained caustic. Periodically the caustic from the settler is

recirculated through the catalyst bed to remove the absorbed traces of phenols, naphthenic acid andbasic nitrogen compounds. The caustic when spent attains a brown colour and is discarded,

Plant No. 3 - Uni finer and PlatformerPlant No. 3 consists of two inter-dependant sections (I) A Unifiner to remove sulphur and nitrogencompounds and saturate olefins in the light naphtha prior to reforming and (2) A Platformer to upgradethe low octane light naphtha to a high octane product. The Unifiner uses the hydrogen from Platformerto remove the undesirable compounds and supplies the feed to the Platformer.

The feed stock for the Unifiner is a mixture of cracked naphtha from visbreaker fractionator in Plant 6and light naphtha from the splitter in the Vapour Recovery unit. The feed stock is combined withhydrogen and heated to the reaction temperature of 347C. The vapourised feed is passed through acatalyst filled reactor. In the reactor the organic sulphur compounds are combined with hydrogen to

form hydrogen sulphide and the nitrogen compounds are converted to ammonia. The unsaturated olefinsare saturated with hydrogen to form haphthenes and paraffins.

The reactor effluent is cooled and the ammonia, hydrogen sulphide and excess hydrogen are separatedfrom the product. These separated gases are partly recycled and balance is sent to HSpO

desulphurisation unit as treat gas. The liquid is sent to Platformer as feed after stripping dissolvedhydrogen sulphide in a stripper.
http://www.geocities.ws/alfiefernandes/images/ref108.jpg


4/15

Over a period of time the catalyst in the unifiner reactor will be coated with a deposit called coke. It isnecessary to burn off the coke to reactivate the catalyst. For this purpose the unit will be shutdown andthe deposited coke will be burnt by circulating inert gas through the reactor and injecting air at acontrolled rate. This reactivation is common to all the hydrodesulphurisers and Platformer reactors.

The platforming unit converts the low octane naphtha from Unifiner to high octane reformate by

convertion of straight chain compounds into cyclic compounds. The reaction is endothermic andtherefore the feed stream is reheated after each reactor. The unitconsists of three reactors operating inseries with heaters before each reactor, a product separator, a debutinizer and hydrogen recyclefacilities.

The feed from the Unifmer is mixed with hydrogen, passed through three sets of heaters and reactors.The reactor effluent from the final reactor is cooled by heat exchange and is sent to a separator drum.

The reaction produces hydrogen which is separated from the hydrocarbons and is partly recycled to thefeed stream and balance is routed to the Unifiner. The separated effluent is then sent to a debutinizer.The overhead product of debutinizer is supplied as a part of feed gas to hydrogen plant and the bottomproduct, the reformate is sent to storage tank.

Plant 4 -Kerosene Hydrodesulphurisation Unit

The purpose of the plant is to reduce sulphur content of the raw kerosene by treating with hydrogen.During the treatment some of the aromatic hydrocarbons are converted to cycloparaffins which results in

an increase in the smoke point. The plant is designed to process 62-5 n^/hr. of raw kerosene from PlantI or from intermediate storage. The hydrogen requirement is met by the hydrogen rich gas from HSDO

desulphuriser and balance is made up from Plant II. The feed mixed with hydrogen is passed throughthe reactor after heating to the required reaction temperature in the charge heater. After separation of

the reaction gases and excess in a two stage separators, the effluent is sent to the stripper. The stripperbottoms is the finished product which is sent to the product storage after cooling. The hydrogen rich gas

from the separator is sent as feed to hydrogen plant or to fuel gas after recovering the Hi S by aminetreating in sulphurplant.

Plant 5 - Diesel Oil Hydrodesulphurisation Plant

The function of this plant is to desulphurise the part of the diesel (approximately 50%) produced in PlantI by catalytic hydrogenation. The desulphurised diesel and the balance of the raw diesel

and heavy paphtha are line blended in this unit to produce HSD product. The plant is designed toprocess 31'5 m^hr. of feed. The hydrogen gas is supplied from Unifmer, Lube oil Hydrofinisher andVacuum Distillate HDS units. The hydrogen requirement over and above that supplied by these units ismet from the hydrogen plant.The feed mixed with recycle gas and make up hydrogen is heated in a furnace and passed through thereactor. The effluent from the reactor is cooled and the excess hydrogen and other products of reactionare separated in a separator drum. The liquid Is steam stripped in a stripper. The overhead system ofthis stripper is common to the stripper in Plant 13 also. The desulphurised diesel is yielded from the

bottom of the stripper. The hydrogen rich recycle gas from the separatordrum is treated with 15% MEA solution to remove Hi S before recycling. A portion of the separator off-

gas is sent to Plant 5 as treat gas. The liquid from the overhead system of the stripper is sent to IC-22in Plant I and the vapours to the overhead system of atmospheric tower.


5/15

Plant 6 - Visbreaker and Thermal CrackerThe function of the Visbreaker and Thermal cracker units is to process high viscosity Vacuum Residuumand desulphurised vacuum distillate from Plant 13 respectively into lower viscosity products. Thisprocess therefore helps to upgrade the product directly by producing low viscosity gas oils andnaphthas. Visbreaker is essentially a thermal cracking unit operated under mild condition i.e., lower

severity. In a thermal cracking unit a heavy oil is heated and maintained at a high temperature for aperiod of time. This breaks up the larger molecules into smaller molecules falling in the range of gas to

gas oils. The main disadvantage of the process is that the products obtained by thermal cracking tend tobecome unstable due to the olefihic compounds.

The unit consists of a thermal cracker furnace, a visbreaker furnace, a visbreaker flash tower, a commonfractionator and other facilities.

The products obtained are:Light gasoline .... 2-3 m3/hrCracked naphtha .... 3-8 m3/hr.Cracked gas oil .... 35-2 m3/hr.Thermal tar ... 137 m3/hr.Visbreaker tar ... 31-4 m3/hr.

The design feed rate for the Thermal Cracker is 47.0 m3/hr of a mixture of vacuum distillates from Plant13 and feed rate of the Visbreaker 50.6 m3/hr. of Vacuum Residuum from Plant I. The Thermal crackerfeed is heated to a temperature of 493C under a back pressure of 18.6 kg/cm2 and is admitted to thevisbreaker fractionator. The furnace is designed to provide sufficient residence time for effecting thecracking of the molecules. The visbreaker feed is heated to atemperature of 493C under a pressure of 15.1 kg/cm2. The visbreaker tar is separated from the

furnace effluent in the visbreaker flash tower. The overhead vapour of the flash tower is routed to thevisbreaker fractionator for fractionation. The visbreaker tar is routed to Heavy Fuel after adding cracked

gas oil as cutter stock to maintain the desired viscosity. The product yielded from the Fractionator arethermal tar, cracked gas oil, cracked naphtha and cracked light gasoline. The thermal tar is cooled in atempered water cooling system in Plant I and is routed to light fuel oil rundown. The gas oil draw offfrom the tower is used for three different purposes.They area) to provide quench for the furnace effluents of both furnaces, b) to provide lean oil to absorber torecover the gasoline fractions in the gas and c) to provide tray wash for the visbreaker fractionator. Theheat available in these streams are utilised to produce steam or to heat up other streams. The net gas

oil is steam stripped and routed to the light fuel oil rundown along with thermal tar. Cracked naphtha isdrawn from tray No. 19 and is sent to the Unifiner as feed stock. The overhead vapours are condensed

and collected in the fractionator overhead drum. The liquid is pumped to a debutinizer tower and thegases are routed through an absorber to recover the gasoline fractions. The lean oil for the absorber are

gas oil and naphtha. The absorbed gases are routed to fuel gas system through Plant 12. Thedebutinizer tower yields light cracked gasoline as bottom product and the overhead gases are sent alongwith the gases from the absorber to fuel gas system. The light cracked gasoline is sweetened in theMerox treater in Plant 2 along with light gasoline and later blended to gasoline.

Plant 7 - Bitumen Air Blowing Unit

The Bitumen Air Blowing plant is designed to process 9-4 T/hr. of vacuum residuum from the crude unit

to produce 204 metric tons per stream day of 80/100 penetration asphalt and 24.2 T/SD of 30/40penetration asphalt. The feed stock is expected to have a penetration of 160 mm.The vacuum residuum feed is split into two streams (a) converter feed and (b) blending stock. In theconverter the aromatics in the feed are oxidised to asphaltenes by air and the product from theconverter will have a penetration between 30-40 mm. The feed to the converter enters in the top sectionand meets a counter-current air stream supplied by a compressor. The stock yielded from the converter


6/15

meets the specification of 30/40 penetration grade. A portion of this is sent to the 30/40 asphalt storagetank and the balance is blended with the blending stock to produce 80/100 penetration asphalt.The off-gases from the converter are cooled by direct contact with water to remove oil and then burnt inthe heater I F-3.

Plant 8-Furfural Extraction Unit

The Furfural Extraction Unit processes portions of all vacuum distillates in blocked out operations as thefirst step in converting these distillates into lubrication oil blending components. The extraction processremoves aromatic and oxygenated compounds which have low viscosity index and tend to becomeunstable. The viscosity index of a component is based on a comparison of viscosity of the component

with that of two reference oils which have the same viscosity at 210F as that of the component.Viscosity index gives an indication of the reduction in viscosity of the component at higher temperatures

in comparison with that of the reference oil.The components in the feedstock that have low viscosity index form the smaller percentage of the feed.Furfural has an affinity for the aromatic and oxygenated compounds and, therefore, it is used forextracting them from the feed. The extracted aromatics are called extract and the refined stream istermed as raffmate.

The plant is designed to process four feed stocksspindle oil, light neutral, intermediate neutral andheavy neutral, into two grades each of high viscosity index (HVI) and medium viscosity index (MVI)products. These feed stocks are run on a blocked out operation. The feed rates for the different stocksare tabulated below.Stock. Rate for HVI operation. Rate for MVI operation

1. Spindle Oil 37 m^hr. 33 m^hr.2. Light neutral 32-6 n^/hr. 33 m3/hr.

3. Intermediate neutral 27 m^hr. 36 mi/hr.4. Heavy neutral 23 m^hr. 33 ms/hr.

The raffinates from this unit are sent as the feed stock to the MEK dewaxing unit through intermediatestorage tanks.For the purpose of discussion the unit may be divided into foursections. They are; a) Feed Extraction system, b) Raffinate system, c) Extract system, d) Furfural

recovery and drying system.

The air in the feedstock is removed by passing the feed through a deaerator. The deaeration of the feedstock is necessary to prevent oxidation of the furfural which will result in furfural losses and causefouling and corrosion of the equipments. The deaerated feed is then heated to the required temperature

and introduced in the extraction column. The temperature of the feed is maintained low enough tominimise the solubility of the paraffinic components in furfural solvent. The extraction is effected in the

extraction column known as rotating disc contactor in which the furfural and feed are mixed thoroughly.Furfural is introduced at the top section of the extraction column and the feed at or near the bottomsection. The extract mix is drawn from the bottom of the column and is routed to the extract recoverysection and raffinate mix is routed to the raffinate recovery section to recover furfural from therespective streams.

The major portion of furfural from the raffinate mix is recovered by heating the mixture in a heater andseparating the furfural in the Raffinate vacuum flash tower. The bottom stream of the raffinate flashtower is then steam stripped to recover the residual solvent in raffinate stripper. The solvent freeraffinate is then routed to storage. The furfural from the extract mix is recovered in a three stage

system operating under different pressures. The solvent recovered from both of the systems aresegregated into two streams called dry solvent, which does not come in contact with steam and wetsolvent which comes in contact with steam.

The solvent recovery system consists of two fractionators A and B and the CBM surge drum. The waterand furfural mixture from the overhead of the raffinate and extract strippers are separated


7/15

in the CBM surge drum. The separated furfural is dried in the fractionator A and the furfural from wateris recovered in fractionator B. The dry furfural collected in the bottom of the A fractionator is pumpedback to the extraction column.The Raffinate from this unit is the feed stock for the MEK dewaxing unit. The extract is mixed withvacuum distillates and supplied to Thermal Cracker as feed stock.

Plant 9 - Dewaxing Unit

The function of this unit is to improve the pour point of the feed stock by removing wax from the feedstock. The unit is designed to process 8 grades of furfural raffinates and unextracted light netural,

intermediate neutral and heavy neutral vacuum distillates. The dewaxing is carried out on a blocked outoperation. The dewaxing operation removes enough of heavy paraffins from the feed stock to lower the

pour point of the product to meet the specification.

The table given below indicates the design feed rates for thedifferent feed stocks.

Stock. HVI stock MVI stock LVI stock

feed rate. feed rate. (unextracted)feed rate.

1. Spindle oil 41-2 mS/hr. 42-6 rn^hr. 2. Light neutral 34.3 m^hr. 36.3 m^hr. 36.6 m^hr.

3. Intermediate 36.9 mS/hr. 39.6 m'/hr. 38.4m3/hr.4. Heavy Neutral 29.4 m^hr. 29.3 m^hr. 27.5 m^hr.

The dewaxing is accomplished by mixing the waxy charge with a solvent oil consisting of equal

proportions of Methyl Ethyl Ketone (MEK) and Toluene, chilling the mixture to precipitate the wax andthen filtering the resultant slurry to separate the wax.The feed stock is line mixed with the solvent and is chilled in a series of exchangers using vapourisingammonia as a cooling agent. The chillers are specially designed to scrape out the wax deposits on theheat transfer surface so as to have efficient heat transfer. After passing through the chillers thetemperature of the solvent and feed mixture is lowered to18 to21C at which all the waxcomponents crystallise.The scream is passed through the Vacuum Rotary filters. The filter consists of a shell and a cylindricaldrum with the filter cloth. By means of a vacuum maintained inside the filter drum through a system of

internal pipes, the solvent and oil are drawn through the filter cloth leaving a layer of wax on the cloth.The filter drum is continuously rotated by an electric motor and a rotary valve at the end of the filter

drum subjects the filter cloth to vacuum or pressure. The wax layer

is removed. The wax mix and the dewaxed oil are pumped to their respective section where the solventis recovered and re-used.

The facilities for solvent recovery from the wax mix and dewaxed oil are identical. The charge is heated

using steam and is admitted to a flash tower where most of the solvent is recovered. Theflash tower bottoms is then admitted to a stripper where it is steam stripped to remove the balance ofthe solvent. The solvents separated from the stripper and flash tower are segregated.

The stripped wax is routed to a storage tank and is blended with other components to produce fuel oil.

The dewaxed oil is sent tothe Lube Oil Hydrofmisher (Plant 10) as feed stock. The wet solvent from theoverhead of the stripper is collected in the solvent decanter where the water and solvent are separated.To minimise solvent losses the water from the decanter is passed through a MEK fractionator where the

dissolved solvent is steam stripped and separated.


8/15

Plant 10 - Lube Oil Hydro finishing UnitThe lube oil hydrofinisher employs a hydrogenation process to improve colour stability and lengthens theoxidation period of the finished lube stocks. The hydrogenation reduces sulphur, oxygen, nitrogen and

undesirable carbon forming compounds without damaging the other properties of the lube oils.

The plant is designed to process all the eleven lube oil stocks from MEK unit on a blocked-out operation.

The feed rate for the spindle oil HVI and MV1 will be 30.6 m3 /hr. and for all other stocks will be 27.8m^hr. The products from this unit are the finished lube oil blending components and are delivered to

off-plot storage tanks.The process flow through this unit is similar to the other hydrogen treaters. The feed is mixed with

hydrogen, heated in heater and passed through a three bed reactor. Recycle gas is added to thesecond and third bed to control the temperature. The effluent is cooled and separated from the excesshydrogen and the other gases formed by reaction. The off-gas from the separator is MEA treated toremove Hz S and is recycled to the reactor and the feed stream, and part of it sent to Plant 5 as make-up gas. The make-up hydrogen for this plant is supplied from Hydrogen plant (Plant No. II). The liquid

from the separator is steam stripped in a vacuum stripper and then driedin a vacuum drier to remove traces of water. The product from the vacuum drier is cooled and then sentto~storage. The overhead liquid from the stripper is pumped to IC-22 in Plant I.

Plant 11 - Hydrogen PlantThe function of Plant II is to produce enough hydrogen for the use in the hydrofinishers. The plantconverts the light hydrocarbon gas feed into hydrogen by reaction with steam in presence of catalyst at

a temperature of 815C. The reaction proceeds as follows:CH4 + H2 0 - CO + 3H2

CO + H2 0 CO2 + H2Heavier hydrocarbons and steam react to form CH4 , CO and CO2 , and then CH4 reacts with steam as

shown above.

The hydrogen plant is designed for a feed rate of 1680 m3 /hr. of hydrocarbon gas not heavier than

butane to produce 11,160 m3/hr. of hydrogen. The normal feed to the plant consists of all theplatformer stabilizer off-gas plus a mixture of off-gas from Plant 4, stabilizer off-gas from Plant 2. During

Platformer shutdown, all the feed gas will be supplied by Plant 2. The feed gas from Plant 4 and plant 2are combined and MEA treated in Plant 12 to remove 1-h S before it Is sent to the hydrogen plant.The process can be divided into three sections (a) reforming (b) shift conversion and (c) methanation.

The feed gas is desulphurised by passing through two zinc oxide beds. The desulphurised feed is thenmixed with sufficient steam to complete the reaction through the shiftconversion and passed through the reforming furnace. The radiant tubes in the furnace are filled withreforming catalyst. The temperature is maintained at 815C. Reaction (I) is completed when it leavesthe reforming furnace and reaction (2) is partially attained. Therefore, the reforming is followed by a

catalytic conversion at lower temperature, which is known as shift conversion. In the shift converter thesteam and CO react to form COz and Hi.

The gas leaving C02 absorber contains small amount of carbon monoxide and carbon dioxide which aredetrimental to the catalyst in hydrodesulphurisers as they form corrosive acids during the processing.

Therefore CO and C02 are reconverted to methane by a catalytic reaction with hydrogen which is calledmethanation. The reaction proceeds as follows :CO2 + 4H2 - CH4 +2H20

CO + 3H2--CH4 + H20The reaction takes place over a nickel catalyst at a temperature of 315C. The methanator effluent gasis hydrogen of 95% purity and sent to the two stage compression system. Hydrogen requirements of

Plants 4 and 5 are met after the first stage compression and that of Plant 13 and 10 after second stagecompression.
http://www.geocities.ws/alfiefernandes/images/rerf128.jpghttp://www.geocities.ws/alfiefernandes/images/ref126.jpg


9/15

The heat in the reformer effluent is used to produce steam in a waste-heat boiler and this steam is usedfor the process. Supplementary requirement is obtained from H.P. steam and excess, if any, isrouted to the MP steam header.

Pant 12-Sulphur Recovery Plant

The hydrogen treating of kerosene, diesel, vacuum distillates nd lube oil component produces hydrogen

sulphide. Hydrogen sulphide is also present in crude which is evolved with gases fromPlant I and Plant 2. In the sulphur plant, the hydrogen sulphide is recovered by absorption by a 15%solution of MEA.

The absorbed H2S is then recovered from MEA solution and is converted into sulphur. The conversion ofHz S to elemental sulphuris accomplished in two stages-first in the thermal reaction boiler andsecondly by in the catalytic converter. The reaction proceeds as follows:

2H2 S + 3H2 0- 2 S02 + 2H2 0 (I)S02 + 2H2 S 3S + 2H2 0 (2)

Reaction No. (2) is partially completed In the reaction boiler and is completed in the converters.

The Hi S stream from the MEA regenerator is mixed with proper proportion of air and is reacted in the

reaction boiler. The reaction is exothermic. The heat evolved is utilised to produce MP steam. The gasesare then passed through the two converters. The gas from the convertor is passed through a coalescer

which removes entrained sulphur from the gases. Liquid sulphur is withdrawn from reaction boiler,converters and the coalescer into a pit. The sulphur is shipped in a liquid state from the pit or is sent tothe refrigeration system for solid ification. The tail gas from the coalescer is burnt in the stack of theheater in Plant 8 or alternatively in the flare stack.

Sulphur plant has the facilities to process all the sour water collected from various plants. In this sectionthe water is stripped off all hydrogen sulphide in the sour water stripper and the strippedwater is drained to sewer.

Plant 13 - Vacuum Distillate Hydrodesulphurisation Unit

The Vacuum Distillate HDS unit processes the vacuum distillates in excess of that needed to meet the

lube oil product requirements. The desulphurised product is the feed to the Thermal Cracker in Plant 6.The plant Is designed to process 43.6 m3 /hr. of feed which is a mixture of the following components.

(a) First stage vacuum tower gas oil from Plant I 4.3 m3/hr.(b) Spindle oil distillate from Plant I 10.8 m3hr.

(c) Light neutral distillate from Plant I 8.8 m3/hr.(d) Intermediate Neutral distillate from Plant I 15.95 m3/hr.(e) Furfural unit extracts 3.75 m3/hr.

Total 43.6 m3/hr.

The process flow through the HDS unit is similar to that in the other HDS units. The reactor has threebeds of catalyst proportioned to give approximately equal rise in temperature. Recycle gas isadmitted in between the beds to limit the temperature rise across the bed. The recycle gases are aminetreated to remove H2S. The reactor effluent is steam stripped to remove light hydrocarbons.

The stripper overhead vapours are condensed in the common overhead condenser of the HSDO stripperin Plant 5. The desulphurised vacuum distillate is fed directly to Plant 6 as feed or cooled and sent to thevisbreaker feed storage tank.


10/15

Utilities System

Utilities are the common requirements that are necessary for the refining of crude oil. These commonitems, that are necessary for the proper operation of the refinery, are required in such quantities that itis economical to supply them from a central source rather than provide separate facilities for individualplant. The items that come under utilities are steam, electricity, cooling water, boiler feed water, fuelsand compressed air facilities.Water supply to the refinery comes from the wells located 14 to 20 kilometers away from the refinery.These wells are operated by the State Water Supply department. Adequate facilities to ensureuninterrupted water supply are provided at the site.

Boiler Feed Water Treating and Steam Generation

A schematic representation of the treated water system and steam is shown in the accompanying figure.

To prevent scale formation in the tubes of the steam generating equipment the feed water must betreated. Salts of silica, magnesium, calcium and iron in the water form scales. Oxygen, carbon dioxide,hydrogen sulphide are corrosive gases. The raw water from the fresh water pond containing hardness ofabout 210 ppm is first softened in a cold lime softener to about 115 ppm. Water is then passed through

a set of cat-ionic softeners.The ion-exchange softeners are filled with resins. The cat-ionic softener removes the calcium

magnesium and sodium ions by exchanging place with hydrogen ion. The bed is regenerated periodicallyby dilute hydrochloric acid. The anionic softener removes the sulphate, chlorate and silica ions by

replacing the hydroxyl ions in the anionic resin. The bed is regenerated with a weak solution of sodiumhydroxide.

The demineralised water is used as feed water to the main boilers and waste heat boilers in the units.

The steam to the units is supplied by means of common headers running through the plants and to thetank farm. There are three systems of steam supply (a) the high pressure steam under a pressure of31-5 kg. per sq. cm. (b) the medium pressure steam at a pressure of 10-5 kg. per sq. cm. (c) the lowpressure steam of 3.5 kg. per sq. cm. pressure.

There are three boilers to supply the steam requirements of the units and for power generation. Inaddition to these boilers steam is also produced in Plants 6, 7, II and 12. The main boilers are operatedat a pressure of 50 kgs per sq. cm. This very high pressure steam is used for (a) driving two turbo-generators to produce electricity (b) to drive the turbines of two of the cooling water pumps (c) tosupply H. P. steam and (d) to make-up the requirements of MP steam and LP steam. The HP steamobtained by desuperheating the steam from the boilers is used for turbine drives in the boiler and watertreatment sections. The MP steam is supplied from turbines of the generator and from the boilers in the

unit. The balance is made up by desuperheating steam from the main boiler. The low pressure steam isderived from the generator turbine exhaust steam from the cooling water pump turbines, exhaust of the

turbine drives in the boiler plant and from the boilers in Plant 12. The low pressure steam is used fordeaeration of the boiler feed water, for heatingproducts in storage tanks and in some strippers in the unit.

Fuel System

The fuel supply for the heaters in the process plants and boilers comes from the fuel gas system and thefuel oil system. Fuel gas is primarily produced from the vapour Recovery unit and the

desulphurisers. The fuel oil is supplied from a tank of 790 cubic meters capacity by means of a pump.The pump discharges into a header that runs to all the heaters and boilers. To maintain a steady

pressure and an even flow a circulation line returns part of the fuel oil back to the tank. The fuel oil tankis filled with the visbreaker tar from Plant 6.

Fire Water System


11/15

Water for fire fighting requirements is supplied from the oxidation basin of the effluent water from theAPI separator. The system has one low pressure pump and two pumps of higher capacityand greater discharge pressure. Normally the smaller pump will be kept running to maintain the firewater header under pressure and also to supply minor requirements from the header. For firefighting, the higher capacity pumps will be used. One of the pumps can be started remotely from thecontrol room. The fire water lines are run around the process units and throughout the refinery

and is provided with hydrants and monitors at suitable locations.

Drinking Water

The drinking water is served through a 2' line from the discharge of the raw water pumps at the freshwater pond. The water is properly chlorinated and is served by a separate header running to placeswhere needed.

Compressed Air Facilities

The compressed air required for the operation of the instruments and for driving the pneumatic tools issupplied by two compressors. Normally only one compressor is required for meeting

the consumption. The air supplied to the instruments is dried through air driers to remove moisture. Theair driers are filled with dessicants to adsorb the moisture and are regenerated periodically. A back

pressure controller is provided in the service air line to preferentially supply the instrument airrequirement in case the total air requirement is higher than the input.

OIL MOVEMENTS & STORAGE

The storage and shipments of crude, intermediate and finished products is a necessary part of the

refining operations. The purpose of the storage tanks is to ensure the availability of the stocks inadequate quantities for continuous operation or provide storage for the feed stocks to the units on

blocked out operation or to have sufficient quantities for the bulk shipments. The storage and shippingoperations are carried out by the Oil Movement and Storage Division (0. M. & S).

The broad functions of the 0. M. & S Division are: (a) receiving and storing crude oil, (b) feeding theunits with respective feed stocks and receiving the products into tanks, (c) blending of the components

produced in the units into finished products, (d) moving finished porducts and (e) oil recovery from theAPI separator system.

The storage tanks of the products can be broadly classified into two categories: (a) Pressure tanks, (b)Atmospheric tanks. The high vapour pressure products like LPG are stored in the pressure tanks and the

low vapour pressure products are stored in atmospheric tanks. The products like gasoline naphtha whichhave vapour pressure not high enough for pressure tanks, but high enough to have losses due toevaporation are stored in floating roof tanks to minimise the lossof product due to evaporation. The relative advantages and needs for the type of storage will bediscussed in Equipment Fundamentals.

The crude oil is brought from Persian Gulf by tankers and is pumped from the harbour by a 30" crude oilline to the crude tanks. The crude is then pumped to Plant No. I after settling and water draw off. The oilis processed into different fractions in the various units.The LPG, naphtha, kerosene and ATF-50 are received from the units directly in the product tanks. Theraw diesel, desulphurised diesel and heavy naphtha are line blended in Plant 5 and is received in thediesel storage tank. The kerosene and diesel are provided with a common intermediate tank for storingthe raw products during the shut down of Plants 4 and 5.

The reformate from Plant No. 3 and treated gasoline (light gasoline) are also provided with a surge tankas a cushion for the gasoline blending requirements.

Product BlendingThe products that are made by blending are (a) gasoline, (b) JP-4, (c) light diesel oil and (d) fuel oil.

The table given below indicates the components of each of these products.Product Components

Gasoline Treated gasoline and Reformate.LDO Diesel oil and Heavy fuel oil.


12/15

Fuel oil Light fuel, heavy fuel, heavy neutral extract and slack wax.

The treated gasoline is merox treated mixture of light gasoline from Vapour Recovery unit and the light

cracked gasoline from Visbreaker and Thermal Cracker unit (Plant 6).Heavy fuel oil consists of mainly visbreaker tar, vacuum residuum and small portion of cracked gas oil asit leaves Plant I. The light fuel oil is a mixture of thermal tar and cracked gas oil. These components areline mixed before leaving Plant I. The slack wax and heavy neutral extract are received in the nominatedtanks from the units.The blending of the above mentioned products are carried out by Oil Movements and Storage Division inproper quantities to meet specification of the product.

Product Movements

The products other than LPG, Asphalt and Sulphur are moved by pipelines to the marketing terminals ofIndian Oil Corporation, Esso Standard Eastern, Burmah - Shell and Caltex Oil Company. Thesemarketing terminals distribute the products in the nearby areas by tank trucks and railway tank wagons.The major portion of the production is despatched by pipeline shipments. The products are also shippedby tankers to other parts of the country. LPG is filled into cylinders andasphalts into drums before they are moved by trucks and railway box wagons from the refinery.Facilities exist for loading LPG and asphalts in tank wagons. Most of the sulphur produced will be

despatched by special type tank trucks.API Separator

All the process water that has been in contact with oil and small quantities of oil from the packing glandsof pumps and the draining from the sample points from the units are collected in sewerbasin, by means of a common underground sewer system.In the sewer basin oil and water are separated. The separated oil is pumped to the wet slop tanks 801,803 and 804. The water from the sewer basin is pumped by two electric pumps to the separator box for

the recovery of oil. The oil separates from the water while flowing through the API separator and isskimmed off by an adjustable skimmer.

The collected oil is pumped to the wet slop tanks. The skimmed water then flows to the oxidation basin

which also serves as water reservoir for fire fighting purposes. The oxidation pond provides enoughresidence time for oxidation of any traces of oil that elude separation at the API Separator bymicrobiological organisms. The water overflowing from the oxidation pond is routed to the Buckinghamcanal. Provision is made to collect any oil that accumulates in the oxidation pond at the outlet of thepond.

One must not get an impression that all the oil that is drained in the sewer is recovered. Some of the oildrained is lost to atmosphere by vapourisation, some by adhering to the sludge and someby oxidation in the pond. Very small quantity of oil is also lost via the effluent going to the canal fromthe oxidation pond. These losses may even be as high as 1.5% to 2 %. Therefore, it is very importantthat operators take special care not to drain oil to the sewer except when it is unavoidable andabsolutely necessary. Draining of sample point before sampling should be limited to the extent

necessary to obtain a representative sample. Drips and leaks from the joints in thepipelines and equipments should be repaired promptly. Remember that part of the oil drained is always

lost to the atmosphere by evaporation, through the sludge and by oxidation in the pond and this oilcould have been a valuable product. Remember that considerable sum of money can be lost by these

types of non - recoverable oil loss.

Corrosion Inhibitors And Additives Used In Process Units

In the various phases of operation suitable inhibitors and chemicals for corrosion protection, foulingprevention and foam prevention are added depending on the nature of the stream. These chemicals are

added in very small quantities and are usually expensive. The purpose of the addition of the inhibitorsand chemicals is to achieve longer lengths of operation and longer life of the equipment. The addition of

these chemicals and inhibitors are therefore very important and should be done within specified limitsand conditions. The various chemicals and inhibitors are used.


13/15

Need a Web site? GetYourOwnWebsite.com FREE!More than 1000 Websites templates, Unlimited Hosting Starting at $1.45

Powered by: Geocities.ws

Process Units from Refinery

* 13,000 tpd Refinery

* Naptha Refinery

* Hydrotreater* Lube Oil Refinery

Process Units from 13,000 tpd (100,000 BPD) refinery

Process Units

1. 8500 tpd (60,000 bpd) Naphtha Minus Complex, NMC, with Hysomer and sieve section to increase

octane from 66 to 88. built in 1991 as PAUs (pre-assembled units) Feed Naphtha, final product 90+octane petrol Shell Technology.

2. 3500 tpd (26,000 bpd) Hydocraker to produce naphtha from VDU bottoms. (2) 150 bar reactors, low

pressure side 10-15 bar, high pressure side 150 bar. Including (3) 2400 kw H2 compressors, 150 bar.

3. 2000 tpd (15,000 bpd) Keromode unit to upgrade cut of Naphtha from Hydrocraker to Kerosene for jet
http://www.gridhoster.com/web-hosting-features.php?footer=geocities.wshttp://www.gridhoster.com/web-hosting-features.php?footer=geocities.wshttp://www.gridhoster.com/web-hosting-features.php?footer=geocities.wshttp://www.gridhoster.com/web-hosting-features.php?footer=geocities.wshttp://www.gridhoster.com/web-hosting-features.php?footer=geocities.wshttp://www.gridhoster.com/web-hosting-features.php?footer=geocities.wshttp://www.gridhoster.com/web-hosting-features.php?footer=geocities.wshttp://www.gridhoster.com/web-hosting-features.php?footer=geocities.wshttp://www.gridhoster.com/web-hosting-features.php?footer=geocities.wshttp://www.gridhoster.com/web-hosting-features.php?footer=geocities.wshttp://www.gridhoster.com/web-hosting-features.php?footer=geocities.wshttp://www.usedplants.com/component/mailto/?tmpl=component&link=aHR0cDovL3d3dy51c2VkcGxhbnRzLmNvbS9wcm9jZXNzLXVuaXRzLWZyb20tcmVmaW5lcnkuaHRtbA%3D%3Dhttp://www.usedplants.com/equipment-for-sale/213-process-units-from-refinery.html?tmpl=component&print=1&page=http://www.gridhoster.com/web-hosting-features.php?footer=geocities.wshttp://www.gridhoster.com/web-hosting-features.php?footer=geocities.wshttp://www.gridhoster.com/web-hosting-features.php?footer=geocities.ws


14/15

fuel.

4. 4500 tpd (34,000 bpd) Kerosene Hydrotreater, to remove sulfur and H2S from kerosene.

5. (2) 10 MW steam turbine generators, pass through turbine, 100 bar inlet, 17 bar exhaust, 2,800 tpd

steam for each turbine.

Back to top

Units from Naphtha Refinery

1. 7,250 BPD cyclohexane plant, feedstock toluene, benzene, hydrogen

2. Tank farm (tanks and spheres) from 50,000 bpd naphtha refinery For Lease

Back to top

Hydrotreater

4,500 B/D Hydrotreater for desulphurization of diesel or gasoline, 600 psi pressure, dual reactor, built late

1980s. Previously used for niche application by major international oil company.

Back to top

Process units from 30,000 barrels per day Lube OIL refinery

Process Units:

The manufacture of lubricating oil basestock/bitumen is done through five (5) distinct unit processes,

namely:

High Vacuum Unit (HVU). The HVU processes the reduced crude (long residue) feedstock into four (4)

distillate products. It also produces gas oil and a short residue bottoms product. Distillation is done by

heating the feedstock to about 380C and then feeding it into a vacuum tower where high vacuum is

maintained.

Propane Deasphalting Unit (PDU). The PDU processes short residue (vacuum residue) from the High

Vacuum Unit. The process employs the principle of solvent extraction to separate the lighter paraffinic

fraction from the heavier asphaltic fraction of the charge stock. Liquid propane is used as the solvent whichremoves the deasphalted oil (DAO), leaving an asphalt stream behind for use in the manufacture of bitumen

and fuel oil which are sold as secondary products. Propane extraction is accomplished in two extraction

towers operated at about 30 bar.

Furfural Extraction Unit (FEU). The FEU processes distillates and DAO and uses furfural solvent to remove

the aromatic molecules from the feed. A high level of aromatic components is detrimental to lube oil

performance and so the majority is removed in this unit and blended into the refinery fuel oil pool.

MEK Dewaxing Unit (MDU). The MDU processes raffinates from the FEU and deasphalted oil (DAO) from

the PDU. It uses a mixture of MEK (Methyl Ethyl Ketone) and Toluene as solvent in extracting wax from

the lubeoil and makes it suitable for low temperature applications. The wax that is removed is either blendedinto fuel oil or sold as secondary product.

Bitumen Blowing Unit (BBU). The BBU and its attendant facility, was constructed to produce high quality

bitumen that meets Shell brand specifications. The Bitumen Blowing Unit (BBU) improves the quality of the


15/15

present paving grade production through oxy-conversion.

Back to top

Documents

Refinery Operations Furfural Extraction