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Jawaban PIK

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Jawaban PIK
A. Industri amoniak
1. Jelaskan secara garis besar proses pembuatan amoniak beserta diagram alirnya !
Jawab
:
Short Description of the Process Units
The process steps necessary for production of ammonia from the above mentioned
raw material are as follows
:
1. Hydrocarbon feed is completely desulphurized in the desulphurization section.
2. The desulphurized hydrocarbon is reformed with steam and air into raw
synthesis gas (process gas) at a pressure 30-37kg/cm2 g. The gas contains
mainly hydrogen, nitrogen, carbon dioxide and carbon monoxide.
3. In the gas purification section, CO is first converted into CO2 and H2 with
steam (shift reaction), in order to increase the H2 yield. The CO2 is removed in
the CO2 removal section. The residue CO and CO2 are converted into CH4
using H2 (methanation), before the gas is sent to ammonia synthesis loop.
4. The purifiedsynthesis gas is compressed to about 220 kg/cm2 and sent to the
ammonia synthesis loop where it is converted into ammonia.
2.
Mengapas dalam industry amoniak terdapat primary reformer dan secondary
reformer?
Jawab :
Primary reformer berfungsi untuk mengkonversi metana menjadi hidrogen
secara cepat yang dibutuhkan sebgai bahan baku dalam proses pembuatan amoniak.
Proses yang dilakukan mengguanakan gas metanan yang telah diproses pada
adiabatic reformer. Gas metana ini akan direaksikan dengan steam pada temperature
tinggi 700C dan tekanan tinggi 700 psig menggunakan katalis nikel alumina yang
dibuat packing rashig ring dan didukungg dengan pertambahan panas pada boiler.
Namun exhaust gasses dari primary reformer masih mengandung ammoniak sekitar
10-13% dalam basis kering. Pada secondary reformer berfungsi untuk mereaksikan
kembali sisa ammoniak dari primary reformer serta menyediakan pasokan nitrogen
dari udara untuk bahan dasar pembuatan amoniak dan juga mengambil oksigen
sebagai bahan baku pembakaran gas hidrogen untuk proses konversi sisa amoniak
menjadi hidrogen dan CO.
3.
jelaskan mengapa pada industry amoniak ada low temperature shift converter dan
terdapat high temperature shift converter !
Jawab
:
Reaksi pengubahan gas karbon monoksida menjadi gass karbon dioksida pada
shift converter adalah reaksi yang bersifat eksotermis dan berkesetimbangan balik
denga reaksi karbon dioksida dan hidrogen. Sehingga untuk konversi yang optimum
dibutuhkan kondisi operasi reaksi pada suh rendah. Namun pada suhu rendah, laju
reaksi sangat lambat. Maka dari itu HTS dibuat untuk mempercepat laju reaksi dan
setelah gas umpan dimasukkan kedalam HTS, untuk memperbesar konversi gas
karbondioksida dan gas hidrogen maka terdappat LTS. Sehingga proses produksi
menjadi lebih cepat dan efisien.
4.
Berapa rasio gas hydrogen dan gas nitrogen yang diumpankan ke reactor pada
industry ammonia?
Jawab :
1:3 by volume, karena menurut hukum Avogadro, tiap—tiap gas yang berbeda
jenisnya pada kondisi suhu dan tekanan yang sama maka memiliki jumlah mol yang
sama untuk tiap volume yang sama. Lalu jumlah mol yang dibutuhkan dalam reaksi
pembentukkan satu mol ammonia adaalah 3 mol hidrogen dan 1 mol nitrogen,
sehingga dibutuhkan rasio volume umpan gas nitrogen dan hidrogen 1:3. Disisi lain,
dalam reaksi pembetukkan ammonia, tidak dibutuhkan excess reaktan untuk
menekan penghabisan reaktan. Cara excess ini hanya digunakan untuk reaktatnreaktan dengan harga mahal supaya penggunaannya dapat maksimal, namun jika
diterapkan pada reactor ammonia maka hanya akan mengurangi konversi karena
reaktan yang berlebih tidak bereaksi.
B.
Industri pulp and paper
1. Jelaskan proses pembutan pupl and paper beserta diagram alir prosesnya !
Jawab
:
1. Wood preparation(chipping)
Potongan kayu dari hutan tanaman industri denngan panjang 2-3 meter dan
diameter 30 cm diangkut dan ditumpuk di penumpukkan kayuu sementara. Lalu
setelah 3 bulan, diangkut dan dikupas kulitnya. Lalu dilakukan penyaringan utama
(main screening) untuk dipisahkaan berdasarkan kriteria.
2. Pulping = merupakan metode untuk membebaskan serat/fiber selulosa pada kayu
dari matriks lignin. Metode pulping ada
a. Chemical pulping = menggunakan bahan kimia dan biasanya disertai proses
pemanasan. Yield 40-50%, proses bleached mencapai 92%. Cocok untuk kertas
printing dan tissue.
Yang paling banyak digunakan adaalh chemicall pulp. Ada 2 tipe chemical
pulping, yaitu dengan basa/alkali/kraft dan denga asam atau sulfat.
Pulp making :
Cooking/digesting process : untuk memisahakan fiber dari lignin dengan
perlakuan bahan kimia dan panas. Bahan kimia yang diguanakan adalah white
liquor yg mengandung NaOH dan Na2S. Chipped wood dimasukkan kedalam
digester pada suhu … dan tekanan … selama …. Menit. White liquor yang
telah digunakan akan menjadi black liquor yang kemudian akan dibakar dalam
boiler untuk menghasilkan panas yang digunakan dalam industi dan menjadi
green liuor. Green liquor direcovery menjadi white liquor.
Washing : untuk memisahkan bahan terlarut seperti lignin dalam pulp
O2 delignifikasi : untuk mengurangi liginin yang masih menempel pada pulp,
menggurangi konsummsi bahan kimia proses bleaching, serta mengurangi
dampak lingkungann dari proses bleaching
Bleaching : untuk membuang lignin dan menaikkan kecerahan pulp. Prinsip
dari proses bleaching adalah mengeluarkan sisa liginin untuk mendaaptkan
kecerahan yang tinggi.
Reaktan yang digunakan :
Cl2. Cl02, naoh, naclo, o2,o3, h202,
b. Semichemical pulping = untuk melarutkan selulosa yang sedikit dengan yield
45-50%, proses bleach hanya mencapai 75%. Cocok untuk bahan kertas box.
c. Mechanical Pulping = yield yang dihasilkan kotor karna masih mengandung
wood. 55-85% yield dg hasil blached nya kurang dari 70%. Cocok untuk kertas
Koran.
3. Paper making
a. Wet End adalah proses persiapan, pencampuran aditif, dan pembentukkan
lembaran kertas dimana kadar air yang terkandung masih cukup tinggi.
b. Dry End adalah proses lanjutan yang dapat mengeluarkan kandungan air yang
tersisa.
c. Rewinder adalah proses penggulungan ulang kertas dari gulungan kertas besar
(jumbo roll) menjadi gulungan yang lebih kecil dan memotongnya dengan
lebar tertentu.
Stock preparation/ Wet End, yaitu, menyiapkan campuran bubur kertas yang
homogen, proses ini terdiri dari beberapa tahap;
Repulper : Menguraikan lembaran pulp menjadi single fibre dengan
mencampurkan air sehingga menjadi bubur kertas.
Cleaning : Memisahkan kotoran dengan melewatkannya pada alat
berbentuk cone, dengan prinsip pemisahan berdasarkan perbedaan berat jenis
dengan gaya sentrifugal. Kotoran yang dipisahkan biasanya adalah kawat, pasir
dsb.
Refining : Mengkondisikan serat melalui aksi mekanis (penggilingan)
untuk mendapatkan lembaran dengan sifat yang diinginkan, meningkatkan
kontak ikatan atar serat.
Proportioning & Blending : Pada proses ini sejumlah stock akan dilakukan
pencampuran dengan stock yang lain dari jenis pulp yang berbeda, kemudian
ditambahkan sejumlah chemicals.
Beberapa chemicals yang digunakan pada industri kertas adalah:
Starch: ditujukan
penggunaanya.
untuk meningkatkan
sifat
kualitas
kertas
dalam
Filler : meningkatkan opacity kertas dan daya cetak dalam penggunaan tinta.
Pada umumnya filler yang digunakan adalah CaCO3
Retention aid: untuk menahan furnish agar tidak terbuang saat pembentukan
lembaran kertas
Biocide: untuk menghilangkan slime
Dyes: memberikan warna dan shade pada kertas
Brightener agent: meningkatkan kecerahan kertas
Sizing agent: untuk melapisi fiber agar tidak mudah tembus cairan
Defoamer: untuk menghilangkan busa pada stock
Approach flow : Bertujuan untuk mengencerkan stock serta membersihkannya
dari kontaminan, serta mengukur kebutuhan stock untuk setiap gramatur kertas
yang akan diproduksi. Beberapa proses utamanya yaitu:
?Cleaning : Sama seperti Proses Cleaning sebelumnya, yaitu memisahkan stock
dari kotoran berdasarkan berat jenisnya.
?Screen : Memisahkan kotoran berdasarkan perbedaan ukuran dengan
mengalirkan stok pada basket screen yang berputar.
?Headbox : Headbox akan Menyebarkan dan meratakan bahan secara
homogen, kemudian Menjaga dan mengendalikan stock agar tetap seragam.
Stock dari headbox dikirim ke mesin kertas dengan kecepatan sesuai dengan
kecepaan mesin tanpa adanya gangguan aliran agar diperoleh kertas yang sama.
Selain itu juga headbox dapat mengatur gramatur kertas yang akan diproduksi.
?Forming : Merupakan tempat pembentukan lembaran kertas, dimana stock
yang dikirim dari headbox akan disemprotkan diatas wire, sehingga terbentuk
lembaran kertas yang merata. Selain itu juga wire berfungsi sebagai media
drainase air, sehingga kadar air yang melewati proses ini akan tersisa sekitar
60%.
?Press part : Lembaran yang yang telah terbentuk pada forming section dengan
kadar air sekitar 60% akan melewati press part. Bagian ini akan meembuat
lembaran kertas menyisakan kadar air sekitar 35-40% saja. Prinsip kejanya
adalah melewatkan lembaran kertas pada dua roll yang berputar dan saling
menekan sehingga air ayang terkandung dalam lembaran kertas akan keluar
dari lembaran itu. Sampai bagian ini tahap Wet End berakhir
Dry End
Setelah tahapan Wet End lembaran kertas akan melewati proses selanjutnya
diantaranya yaitu:
?Drying : Karena propertis kertas yang diinginkan adalah memiliki kadar air
yang kecil dibawah 10% maka dilakukanlah proses pengeringan di dryer. Pada
proses ini lembaran kertas akan dilewatkan dan ditempelkan pada beberapa
drum silinder panas yang dipanaskan oleh steam.
?Calender : Berfungsi untuk menghasilkan kertas dengan smoothness dan
caliper (ketebalan) sesuai standar.
?Pope reel : Menggulung kertas hingga didapat gulungan raksasa yang akan
dipotong sesuai ukuran di proses selanjutnya. Setiap jumbo roll yang
dihasilkan maka akan di cek kualitasnya, sehingga kualitas kertas yang
dihasilkan harus dipastikan bernilai baik.
Rewinder
Proses penggulungan ulang kertas dari gulungan kertas besar (jumbo roll)
menjadi gulungan yang lebih kecil dan memotongnya dengan panjang dan
lebar tertentu.
Finishing
Pada proses ini gulungan dari rewinder akan dipotong dan diconvert menjadi
berbagai ukuran sesuai dengan ukuran dan jenis kertas yang diinginkan serta
dilakukan pengemasan untuk dikirim ke customer.
C. Petrochemical
1. Jelaskan yang dimaksud dengan industry petrochemical !
Jawab
:
Industri Petrokimia adalah industri yang berkembang berdasarkan suatu pola yang
mengkaitkan suatu produk-produk industri minyak bumi yang tersedia, dengan
kebutuhan masyarakat akan bahan kimia atau bahan konsumsi dalam kehidupan
sehari-hari. Contoh produk-produk industri petrokimia hulu antara lain Methanol,
Ethylene, Propylene, Butadine, Benzene, Toluene, Xylenes, Fuel Coproducts, Pyrolisis
Gasoline, Pyrolisis Fuel Oil, Raffinate dan Mixed C4. Industry Pertokimia merupkan
industry yang bergerak dalam bidang penglolahan bahan kimia yang berbahan baku
minyak bumi dan gas alam dan mengolahnya menjadi produk yang bermanfaat bgi
keterlangsngan akivitas manusia.
2. Jelaskan 3 proses utama yang ada pad aindustri petrokimia
Jaawab :

Upstream proses
Bertindak sebagai proses pengolahan produk dasar (primer) yang akan
menghasilkan produk setengah jadi mauppun yang dpat langsung dolah pada
industry hulu sebgai produk jadi. Contoh produknya : propilena, benzene,
touluena, etilena, methnol dsb. Inti dari tahapan ini adalah mengubah bahan
dasar/produk primer menjadi prodk setengah jadi.

Mid stream proses
Produk dari ini adalah berbahan dari produk hasil tahapan industry hulu dan
selanjutnya akan diproses menjadi produk jadi oleh industry hilir. Contoh dari
produk nya adaalh : polietilenna, ammonia, butena, dikloroetilen-vinil klorida dan
sebagainya.

Downstream proses
Pengolahan produk antara menjadi produk jadi. Produknya adaalah : pupuk, serat
pakaian, kosmetik, pelarut, cat, lilin, karet, nilon dsb. Inti dari proses ini adalah
mengolah hasil dari proses sebelumnnya menjadi barag yang siap dipakai oleh
masyarakat.
3. Jelaskan dengan diagram alir proses dari atmosferik dan vacuum destilation unit pada
industry petrokimia :
Jaawab :
Process Objective:
– To distill and separate valuable distillates (naphtha (on the overhead of CDU
column), kerosene(sidecuts, i.e. light gasses oil and heavy gasses oil), diesel) and
atmospheric gas oil (AGO) from the crude feedstock by its different boiling point
range.
• Primary Process Technique:
– Complex distillation
• Process steps:
– Preheat the crude feed utilizing recovered heat from the product
Streams the temperature required is 100C-137C.
– Desalt and dehydrate or inorganic salt compound in the crude oil using
electrostatic enhanced liquid/liquid separation (Desalter)
– Heat the crude to the desired temperature using fired heaters until approximatly
350C
– Flash the crude in the atmospheric distillation column
– Utilize pumparound cooling loops to create internal liquid reflux
– Product draws are on the top, sides, and bottom
Merupakan unit proses pertama dalam seluruh unit proses petroleum refinary.
Process Objective:
– To recover valuable gas oils from reduced crude via vacuum distillation.
• Primary Process Technique:
– Reduce the hydrocarbon partial pressure via vacuum and stripping steam and prevent
decomposizing/ cracking/ degrading (nearly 770F) of component with high boiling point
by reducing the pressure into vacuum, and minimize the cost and energy.
• Process steps:
– Heat the reduced crude to the desired temperature using fired heaters
– Flash the reduced crude in the vacuum distillation column
– Utilize pumparound cooling loops to create internal liquid reflux
– Product draws are top, sides, and bottom
Temperature the top of the tower is approximately 150F at 10mmHg
Temperature the bottom of the tower is slightly less than 770F at 20mmHg..
4. Jelaskan apa yang dimaksud dan kegunaan dari absorpsion daan adsorpsion proses
pada indstri petrokimia 1
5. Jelaskan apa yang dimaksud dengan coking prose !
Jawab : Coking proses adaalah proses untuk mengubah residu dari CDU dan VDU
menjadi produk yang lebih berhharga dengan bobobt molekul yang lebih rendah
seperti naphta, petroleum coke, light and heavy gass oil, and hydrocarbon gasses,
prinsip kerja dari coking proses adaalah dengan meng-crack residu hidrokarbon pada
suhu dan tekanan tinggi (900F/450-500C dan tekanan diatas tekkanan atmosfer).
Produk dari coking proses dapat berupa fuel grade oil (high sulphur and metals) atau
anode grade oil (low sulphur and metals). Ada 3 type coking process yaitu :

Delayed coking process :
Process Objective:
– To convert low value resid to valuable products (naphtha and diesel) and
coker gas oil.
• Primary Process Technique:
– Thermocracking increases H/C ratio by carbon rejection in a semi-batch
process.
• Process steps:
– Preheat resid feed and provide primary condensing of coke drum vapors by
introducing the feed to the bottom of the main fractionator and then mkxed
with steam to prevent cracking occurred in the preheater
– Heat the coke drum feed by fired heaters to 475C a
– Flash superheated feed in a large coke drum at pressure 10-30psi where the
coke remains and vapors leave the top and goes back to the fractionator
– Off-line coke drum is drilled and the petroleum coke is removed via
hydrojetting
Fluidic coking process
Process Objective:
– To convert low value resid to valuable products (naphtha and diesel and
coker gas oil.
• Primary Process Technique:
– Thermocracking increases H/C ratio by carbon rejection in a continuous
process.
• Process steps:
– Preheat resid feed, scrub coke particles, and provide primary and steam to
prevent the thermocracking on the preheater condensing of reactor vapors by
introducing the feed to the scrubber
– Resid is atomized into a fluid coke bed and thermocracking occurs (475C and
pressuere is 10-30psi) on the particle surface
– Coke particles leaving the reactor are steam stripped to remove remaining
liquid hydrocarbons
– Substoichiometric air is introduced to burner to burn some of the coke and
provide the necessary heat for the reactor
– Reactor vapors leave the scrubber and go to the fractionator
Fluid coking and flexi-coking are fluid-bed processes developed from the basic
principles of FCC, with close integration of endothermic (cracking, coking, or
gasification) and exothermic (coke burning) reactions. In fluid coking and
flexi-coking processes, part of the coke product is burned to provide the heat
necessary for coking reactions to convert vacuum residua into gasses, distillate
liquids, and coke. Flexi-coking, as a variation of fluid coking, provides the
options of partial or complete gasification of the coke product to produce a fuel
gas with some or no coke in the product slate. Different from the bulk liquidphase coking in delayed coking, coking takes place on the surface of circulating
coke particles of coke heated by burning the surface layers of accumulated coke
in a separate burner. Figure 6.8 shows a schematic flow diagram of the fluid
coking process. The preheated vacuum residue is sprayed onto the hot coke
particles heated in the burner by partial combustion of coke produced in the
previous cycle. Using fluid beds in the reactor and burner provides efficient
heat transfer and fast coking on a collectively large surface area of the small
coke particles circulating between the reactor and burner. The products of
coking are sent to a fractionator (similar to that used in delayed coking after
recovery of fine coke particles). Steam is also added at the bottom of the
reactor (not shown in the figure) in a scrubber to strip heavy liquids sticking to
the surface of coke particles before they are sent to the burner. This steam also
provides fluidization of coke particles in the reactor. The reactor and the burner
operate at temperatures of 510–570°C and 595–675°C, respectively.
Higher temperatures and short residence times in the reactor lead to higher liquid and lower coke
yields compared with those of delayed coking. Coke is deposited layer by layer on the fluidized
coke particles in the reactor. Air is injected into the burner to burn 15–30 % of the coke produced
in the reactor, part of the particles are returned to the reactor, and the remainder is drawn out as
the fluid coke product. Fluid coking can process heavier VDR and gives a higher distillate yield
(and lower coke yield) than delayed coking.
Figure 6.9 shows a schematic diagram of flexi-coking. A gasifier is added for conversion of some
or all coke produced in the coker in reaction with air and steam to produce a synthesis gas. The
hot coke particles from the combustor are circulated back to the coking reactor to provide the
heat necessary for coking. The distillate products from the coker are sent to the fractionator, as is
done in the fluid coking process. On the gasifier outlet, after removing the fine particles from the
gas by cyclones, the gas is cooled in a direct-contact cooler to condense the sour water and
recover the flexi-gas. The product gas can be used as fuel gas in the refinery. Depending on the
demand, the flexi-coking process can produce both fluid coke and fuel gas, or gasify all the coke
to produce only fuel gas.
What the petroleum it is?
Answer
Petroleum (/pəˈtroʊliəm/) is a naturally occurring, yellowish-black liquid found in geological
formations beneath the Earth's surface. It is commonly refined into various types of fuels.
Components of petroleum are separated using a technique called fractional distillation, i.e.
separation of a liquid mixture into fractions differing in boiling point by means of distillation,
typically using a fractionating column.
It consists of naturally occurring hydrocarbons of various molecular weights and may contain
miscellaneous organic compounds.[1] The name petroleum covers both naturally occurring
unprocessed crude oil and petroleum products that are made up of refined crude oil. A fossil
fuel, petroleum is formed when large quantities of dead organisms, mostly zooplankton and
algae, are buried underneath sedimentary rock and subjected to both intense heat and pressure.
Petroleum includes not only crude oil, but all liquid, gaseous and solid hydrocarbons. Under
surface pressure and temperature conditions, lighter hydrocarbons methane, ethane, propane and
butane exist as gases, while pentane and heavier hydrocarbons are in the form of liquids or
solids. However, in an underground oil reservoir the proportions of gas, liquid, and solid depend
on subsurface conditions and on the phase diagram of the petroleum mixture.[50]
An oil well produces predominantly crude oil, with some natural gas dissolved in it. Because the
pressure is lower at the surface than underground, some of the gas will come out of solution and
be recovered (or burned) as associated gas or solution gas. A gas well produces predominantly
natural gas. However, because the underground temperature and pressure are higher than at the
surface, the gas may contain heavier hydrocarbons such as pentane, hexane, and heptane in the
gaseous state. At surface conditions these will condense out of the gas to form "natural gas
condensate", often shortened to condensate. Condensate resembles gasoline in appearance and is
similar in composition to some volatile light crude oils.[citation needed]
The proportion of light hydrocarbons in the petroleum mixture varies greatly among different oil
fields, ranging from as much as 97 percent by weight in the lighter oils to as little as 50 percent in
the heavier oils and bitumens.[citation needed]
The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various aromatic
hydrocarbons, while the other organic compounds contain nitrogen, oxygen and sulfur, and trace
amounts of metals such as iron, nickel, copper and vanadium. Many oil reservoirs contain live
bacteria.[51] The exact molecular composition of crude oil varies widely from formation to
formation but the proportion of chemical elements varies over fairly narrow limits as follows:[52]
The alkanes, also known as paraffins, are saturated hydrocarbons with straight or branched
chains which contain only carbon and hydrogen and have the general formula CnH2n+2. They
generally have from 5 to 40 carbon atoms per molecule, although trace amounts of shorter or
longer molecules may be present in the mixture.
The alkanes from pentane (C5H12) to octane (C8H18) are refined into gasoline, the ones from
nonane (C9H20) to hexadecane (C16H34) into diesel fuel, kerosene and jet fuel. Alkanes with more
than 16 carbon atoms can be refined into fuel oil and lubricating oil. At the heavier end of the
range, paraffin wax is an alkane with approximately 25 carbon atoms, while asphalt has 35 and
up, although these are usually cracked by modern refineries into more valuable products. The
shortest molecules, those with four or fewer carbon atoms, are in a gaseous state at room
temperature. They are the petroleum gases. Depending on demand and the cost of recovery, these
gases are either flared off, sold as liquefied petroleum gas under pressure, or used to power the
refinery's own burners. During the winter, butane (C4H10), is blended into the gasoline pool at
high rates, because its high vapour pressure assists with cold starts. Liquified under pressure
slightly above atmospheric, it is best known for powering cigarette lighters, but it is also a main
fuel source for many developing countries. Propane can be liquified under modest pressure, and
is consumed for just about every application relying on petroleum for energy, from cooking to
heating to transportation.
The cycloalkanes, also known as naphthenes, are saturated hydrocarbons which have one or
more carbon rings to which hydrogen atoms are attached according to the formula C nH2n.
Cycloalkanes have similar properties to alkanes but have higher boiling points.
The aromatic hydrocarbons are unsaturated hydrocarbons which have one or more planar sixcarbon rings called benzene rings, to which hydrogen atoms are attached with the formula CnH2n6. They tend to burn with a sooty flame, and many have a sweet aroma. Some are carcinogenic.
These different molecules are separated by fractional distillation at an oil refinery to produce
gasoline, jet fuel, kerosene, and other hydrocarbons. For example, 2,2,4-trimethylpentane
(isooctane), widely used in gasoline, has a chemical formula of C8H18 and it reacts with oxygen
exothermically:[59]
2C
8H
+
→
+
18(l)
2(g)
2(g)
2O(g)
25 O
16 CO
18 H
(ΔH = −5.51 MJ/mol of octane)
The number of various molecules in an oil sample can be determined by laboratory analysis.
The molecules are typically extracted in a solvent, then separated in a gas chromatograph,
and finally determined with a suitable detector, such as a flame ionization detector or a mass
spectrometer.[60] Due to the large number of co-eluted hydrocarbons within oil, many cannot
be resolved by traditional gas chromatography and typically appear as a hump in the
chromatogram. This Unresolved Complex Mixture (UCM) of hydrocarbons is particularly
apparent when analysing weathered oils and extracts from tissues of organisms exposed to
oil. Some of the component of oil will mix with water: the water associated fraction of the
oil.
Incomplete combustion of petroleum or gasoline results in production of toxic byproducts.
Too little oxygen during combustion results in the formation of carbon monoxide. Due to the
high temperatures and high pressures involved, exhaust gases from gasoline combustion in
car engines usually include nitrogen oxides which are responsible for creation of
photochemical smog.
Process Objective of fcc:
– To convert low value gas oils to valuable products (naphtha and diesel) and
slurry oil.
• Primary Process Technique:
– Catalytic cracking increases H/C ratio by carbon rejection in a continuous
process.
• Process steps:
– Gas oil feed is dispersed into the bottom of the riser using steam
– Thermal cracking occurs on the surface of the catalyst
– Disengaging drum separates spent catalyst from product vapors
– Steam strips residue hydrocarbons from spent catalyst
– Air burns away the carbon film from the catalyst in either a
“partial-burn” or “full-burn” mode of operation
– Regenerated catalyst enters bottom of riser-reactor
FCC, a fluidized-bed (or fluid-bed) of catalyst particles is brought into contact with the gas oil feed
along with injected steam at the entrance (called the riser) of the reactor. The hot catalyst particles
coming from the regenerator unit evaporate the feed gas oil upon contact in the riser, and the
cracking starts as the gas oil vapors and the catalyst particles move upward in the reactor. The
temperature of the catalyst particles drops as the evaporation of gas oil and endothermic cracking
reactions proceed during the upward movement. Cracking reactions also deposit a significant
amount of coke on the catalysts, leading to the deactivation of the catalyst. After removing the
adsorbed hydrocarbons by steam stripping, the coked catalyst is sent to the regeneration unit to burn
off the coke with air. Heat released from burning the coke deposit increases the temperature of the
catalyst particles that are returned to the riser to complete the cycle. Burning off the rejected carbon
(coke) in the regenerator provides the energy necessary for cracking without much loss, thus
increasing the thermal efficiency of the process. The cracking products are sent to the fractionator for
recovery after they are separated from the catalyst particles in the upper section of the reactor [3].
In the reactor, the cracking reactions initiate on the active sites of the catalysts with the formation of
carbocations and the subsequent ionic chain reactions produce branched alkanes and aromatic
compounds to constitute the crackate (cracked gasoline with high octane number), light olefins, cycle
oils, and slurry oil that are sent to the fractionator. A carbon-rich byproduct of catalytic cracking,
termed “coke,” deposits on catalyst surfaces and blocks the active sites. FCC is considered a carbon
rejection process because the coke deposited on the catalyst surface and eventually burned off for
heat is rich in carbon and thus enables the production of large quantities of a light distillate (crackate)
in the process without the addition of hydrogen.
Two different configurations of the commercial FCC processes exist depending on the positions of
the reactor and the regenerator: they can be side by side or stacked, where the reactor is mounted
on top of the regenerator. Major licensor companies that offer FCC processes with different
configurations include Kellogg Brown & Root, CB&I Lummus, ExxonMobil Research and
Engineering, Shell Global Solutions International, Stone & Webster Engineering Corporation, Institut
Francais du Petrole (IFP), and UOP. Figure 7.8 shows examples of Exxon and UOP designs [1,4].
The UOP design of high-efficiency two-stage regenerator units offer advantages of uniform coke
burn, higher conversion of CO to CO2 and lower NOx emissions among others. Another modification
to FCC plants could be the installation of a catalyst cooler, which may provide better control of the
catalyst/oil ratio; the ability to optimize the FCC operating conditions, increase conversions, and
process heavier residual feedstocks; and better catalyst activity and catalyst maintenance [3].
In the link below (external link), the animation of an explosion in an FCC unit in 2015 (7:12 minute
long) provides a good review of the FCC process, and points out the potential hazards of working
with hydrocarbons exposed to high temperatures in refinery units:
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