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:
