Urea is manufactured by reacting ammonia and carbon dioxide in autoclave to form ammonium 0 carbamate. The operating temperature is 135 C and 35 atm pressure, the chemical reaction is endothermic reaction and so ammonia is maintained in excess to shift the equilibrium towards urea formation. Urea production consists of main two reactions. 1. Formation of ammonium carbamate 2. Dehydration of ammonium carbamate to produce molten urea Description of flow sheet: 1. Ammonia pumping : Liquid ammonia is pumped from the multistage pump which maintain the reaction pressure in the vertical stainless steel vessel 2. Carbon dioxide compression: ammonia plant directly boost the carbon dioxide from the compression section as it readily form at the CO 2 section of ammonia production plant. 3. Urea synthesis tower: It is lined with film of oxides to protect form corrosion. Catalyst bed is placed in the inner side of the autoclave structure and 180- 200 atm pressure at temperature about 180-200 deg centigrade is maintained. Plug flow operation take places and molten urea is removed from the top of the tower. 4. Distillation tower and Flash drum: This high pressure slurry is flashed to 1 atm pressure and distilled to remove excess ammonia and decomposed ammonia carbamated salts are removed and recycled. 5. Vacuum Evaporator: The solution is fed to vacuum evaporator for concentrating the slurry. 6. Prilling Tower: It is dryer where the molten slurry is passed from top of the tower into a bucket which rotates and sprinkles the slurry and air is passed from the bottom. All the moisture is removed as the urea form into granules during it journey to the bottom of the tower. This granules are sent by conveyor to the bagging section.
Urea Production from NH3 and CO2
A simple description which give an idea of the urea manufacturing process with plant layout:: layout
Low pressure section for urea production REACTOR EFFLUENT: The reactor effluent which consists of a liquid phase along with a certain percentage inerts and reactants in a vapour phase, fed to the H.P. stripper where the first carbamate decomposition occurs. The vapour phase containing most of the inert gases then flows to the carbamate condenser together with the carbamate recycle from the medium pressure section. Only before re-injecting the carbamate into the reactor, the inert gases are separated from the liquid phase-in the carbamate separator and fed to the MP decomposer. H.P. STRIPPER: It is the falling film type heat exchanger. It containing 2429 tubes with some space above the tubes and below the tubes. In the above space a 0.315m height pall rings bed arranged. A sieve tray is fitted above the packed bed. The tubes are fitted with ferrules have three tangentially drilled distribution holes. Tubes are made with titanium and shell side fluid is the medium pressure saturated steam. The reaction product leaving the reactor flow to the steam heated falling film stripper which operates at about 144-146Kg/cm2 pressure. The liquid from the feed distributor pipe is evenly distributed onto the packed bed by means of preheated sieve having 1400 holes. The mixture is heated up as it flows into the vertical tubes of the falling film exchanger. The CO 2 content of the solution is reduced by the stripping action of the ammonia as it boils out of the solution. The carbamate decomposition heat is supplied by medium pressure saturated steam, where the latent heat of condensation of saturated steam is taken by carbamate solution. In the falling film exchanger, the principle advantages are high rate of heat transfer, no internal pressure drop, short time of contact. Decomposition is promoted by heating and stripping CO 2 by vaporized excess NH 3, under the same pressure level as urea reactor. Stripper used is falling film type, decomposed and vaporized gases and liquid effluent are therefore in countercurrent contact and CO 2 concentration in liquid is gradually reduced from the top to bottom of the stripper tube. As NH 3 rich gas (CO 2lean gas) rises from the lower parts of the tube, then the gas at upper parts of the tube becomes an NH 3 rich gas as compared with the equilibrium composition and the decomposition reaction in liquid phase corrects the deviation from the equilibrium (the stripping effect). Decomposition at high pressure requires high temperature which means that much biuret has formed and the liquid becomes corrosive, but excess ammonia and the use of titanium in the stripper permit minimizing the problems. The urea solution with part of inerts is coming from the bottom of the stripper enters into the medium pressure decomposition in urea purification section. The overhead gases from the top of the stripper mixed with recovered solution from medium pressure absorber and then pressurized
2
to 180kg/cm in H.P. carbamate pumps and preheated in carbamate pre-heater by using steam condensate flowing to battery limits then this mixture enters tube side of carbamate condenser where heat of reaction of reaction-1 and condensation of carbamate gases is removed by 2 production of steam at 3.5 to 4.5 kgf/cm on the shell side by vaporization of water. The condensate from the condenser with few inert gases is entered into the carbamate into the carbamate separator. Carbamate separator is the cylindrical empty vessel in which separation of carbamate solution from inert gases will take place, carbamate solution from bottom of separator is recycled to reactor by means of ejector. The non-condensate gases from the top of the separator consist mainly of inert gases, with a small amount of NH 3 and CO2 are passed through the split range controller to the medium pressure decomposer holder to utilize the heat of these for that decomposition.
UREA PURIFICATION:
Urea purification takes place in three stages at decreasing pressures as follows: First stage at 18kgf/cm2 Second stage at 4.5kgf/cm2 Third stage at 0.35kgf/cm2 It is pointed out that the exchangers where the urea purification occurs are called decomposer. the upper part of the medium pressure inert washing tower consists of three valve trays. Where the inert gases are subjected to a final scrubbing or washing by means of some absorption water. In this way the inerts are sent to vent stack practically free from ammonia. PREVENTION OF EXPLOSION HAZARD IN GASES VENTED TO THE ATMOSPHERE: CO2 fed to the reactor normally contains a small percentage of H 2,CH4 and CO in addition to inerts like N2 and Ar. These gases plus the small quantity of gases introduced into the plant with NH3 coming from B.L together with CO 2 contained in passivation sir could give rise to explosively problems when vented into atmosphere from MP inerts washing tower. As a matter of fact, this problem is minimized in Snamprogetti urea plants. Since the quantity of passivation air used is far lower than the one used in other processes. Thus the O 2 to flammable gases ratio in the vented gases does not justify the use of a H 2 removal system on the CO 2 stream from B.L 2
PURIFICATION AND RECOVERY STAGE AT 4.5 kg/cm : L.P.Decomposer: This is also the falling film type heat exchanger. It is also constructed same as to MP decomposer, the packed bed height, equipment divisions and construction are same. The lower the pressure , the better the prevention of NH 3 and CO2 loses from the system, but the recovered solution becomes weaker.Which means that excess water is recycled to the synthesis loop, the operating conditions of L.P decomposer are selected at 3.5kgf/cm2 pressure
decomposer (falling film type). The gases leaving the top separator are mixed with the dilute carbon solution coining from waste water treatment and sent to the ammonia preheater, where they are practically absorbed and condensed. The ammonia preheater is the shell and tube(1-4 pass) heat exchanger, in which LPD vapours are condensed and feed NH 3 to reactor is heated. While depressurizing(drawing tube side NH 3 loop, case must be taken to avoid freezing of water) solution on shell side of this preheater. From the above condensate wit uncondensed gases then enter the LP condenser, where the residue absorption and condensation heat is removed by cooling water. The liquid phase , with remaining inert gases, is sent to the carbonate solution vessel. The carbonate solution tank is a horizontal cylindrical vessel. It is constructed with inerts washing tower above the tank, and is located slightly taper to the ground to maintain the solution head for pumps at low level also. In shutdown followed by emptying of high pressure equipment, the recovered NH 3, CO2 in low pressure stage is also stored in their tank. The level of this tank should be maintained low in order to recover all carbonate in case of shutdown. The inert gases leaving from carbonate solution tank enters into low pressure inerts washing tower which is located on the tank with packed bed. The inerts are washed in this tower by using water in the counter current flow. The inerts which are leaving from the washing tower are vented to stack, which are practically free from NH 3.
PURIFICATION AND RECOVERY STAGE AT 0.35 kgf/cm2 VACUUM PRE CONCENTRATOR: This is also the falling film type heat exchanger. It is also constructed same as to above decomposers with bell distributor. The solution leaving(the bottom of low pressure decomposer is expanded at 0.35 kgf/cm2 a pressure and enters the vacuum pre-concentrator) falling film types as with the help of tangentially inlet duct. Top separator where the released flash gases are removed before the solution enters the tube bundle. Decomposition section where the last residual carbamate is decomposed and the required heat is supplied by the condensation of the gases coming from the medium pressure decomposer separator. The gases leaving the pre-concentrator top are routed to the vacuum duct where condensation takes place. The urea solution, collected at the bottom of pre-concentrator holder is sent to the vacuum section by using centrifugal pump. The pre-concentrator is able to save a lot of pressure stream in the evaporator permits to concentrate the urea solution from 70-75% to about 85-88% wt.
UREA CONCENTRATION : As it is necessary , in order to prill urea, to concentrate the urea solution up to 99.8% wt. The
simplest and most widely used method is direct concentration , which consists in heating the solution under vacuum to remove water. Direct concentration is operated on the basis of the equilibrium vapour pressure of the urea solution. Theoretically to concentrate the solution without the deposit of crystals, the operating pressure 0 should be kept over 0.3kh/cm2 abs.., 136 C int eh second vacuum system.The urea solution coming from vacuum pre-concentrator holder is sent to the first vacuum concentrator where it is heated up to above the boiling point of that liquid at the pressure of separator. The mixed phase coming out of concentrator enters the gas-liquid separator from where vapours are extracted by the second vacuum system, while the solution fed to the prilling section by using centrifugal pump. Both the 70-72% wt.urea solution from the L.P decomposer and the urea melt from the vacuum separator can be directed to the urea solution tank, so as to face any emergency situation in both the vacuum and prilling sections.
UREA PRILLING: PRILL TOWER:
It is a cylindrical vertical tower with a height of 100m, in which urea prilling takes place. It consists of prill section the top and scrapper at bottom. Prill tower contains bottom lowers(window) and top lowers(windows) also. In the prill section bucket (Tuttle type) is there. The tower is coated inside with anti corrosive plant. This is a natural draft Prill tower. The molten urea leaving the second vacuum holder is sent to the prilling bucket by means of centrifugal pump. Bucket contains no. of holes to the wall. The urea coming out of the rotating bucket in the form of drops fall along the prilling tower and arid encounters cold air flow which causes its solidification. 0 The molten urea drops coming from bucket contains is at a temperature of133 C There will be heat transfer from drops to air , thus reducing the temperature of drops and increasing the temperature of air. The heated air try to go up, due to that flow of air, some vacuum is created at the glass. The bottom air will try to cover the above vacuum thus creating the natural draft. The air will enter the prill tower through bottom lowers and vented to the atmosphere through top lowers. The heated air with a few parts of urea dust enters the scrubbing section where the urea dust will recover from air by scrubbing of air with DM water and the free from urea dust is vented to atmosphere. The molten urea drops from bucket falls down along the prilling tower. Due to the counter current flow of air the temperature of molten urea will decrease and form as a prill. The solid prills falling to the bottom of the prilling tower are fed to a belt conveyor by a rotary scrapper. From here they are sent to the automatic weighing machine and to the urea storage, bagging section.
Biuret Formation: Two moles of urea are converted into one mole of biuret and one mole of NH 3 by hetaing. 2 NH2CONH2-------------> NH 2CONHCONH2 + NH3 Because the biuret is injurious to germinating seeds, and pine apple and citrus trees wither when the fertilizer is sprayed on the leaf. The biuret content in fertilizer grade urea on the world market is required to be below 1.0%. biuret forms almost everywhere in urea production steps. The following conditions are favorable for biuret formation. • High residence times. • High temperature. • Low amount of water. Process Water Treatment: As already pointed out in the process description, the liquid effluent treatment section consists mainly of a distillation column to purify the waste water, a hydrolyserto decompose the small percentage of urea into ratio NH 3and CO2 which are eventually stripped in the lower section of the same column. The condensed vapors from first and second vacuum systems, containing urea, ammonia and CO2 are collected in the process condensate tank. In this tank the carbonate close drain is also fed by the centrifugal pump and are recycled . UREA PURIFICATION AT M.P. DECOMPOSER: This is falling film type heat exchanger is divided into three parts. Top separator where the released flash gases are separated, middle decomposer where the carbamate decomposition will take place and bottom holder where the concentrated urea solution will holding. The decomposer tubes are fitted with ferrules having four tangentially distribution holes with equispaced. Packing bed of pall ring with 1.3m height and sieve plate for distribution is provided above the decomposer in separator. To promote more decomposition it is necessary to that higher temperatures or to reduce to lower levels. M.P. Decomposed is operated at 17kgf/cm2 (g) and O 156-158 C decomposed heat is being supplied from outside of tube by M.P. steam and M.P. condensate.
Urea medium pressure section flow sheet The solution with a low residual CO 2 content, leaving the bottom of the stripper is expanded at the pressure of 18kgf/cm2 and enters at the top of the M.P. decomposer where the released flash gases are removed before solution enters the tube bundle. Where the residual carbamate is decomposed and the required heat is supplied by means of medium pressure saturated steam and medium pressure steam condensate which is coming from the stripper. Distribution of falling film is obtained by ferrules. After decomposition of carbamate, the concentrated urea solution with part of inert is collected in the holder and then flows to L.P. decomposer. The NH3 and CO2 rich gas leaving the top of separator are sent to vacuum pre concentrator,where
they are partially absorbed in the aqueous carbonate solution coming from the urea purification section at 4.5kgf/cm2. The absorption and condensation of gases are removed by evaporating water from urea solution, thus allowing a considerable saving of L/P/ steam in the evaporation stages. Then the gases enter the M.P. condenser where the residue absorption and condensation of heat of gases is removed by cooling water. In the condenser CO 2 is almost totally absorbed. The mixture from M.P. condenser flows to the medium pressure absorber. M.P. Absorber: It is the bubble cap tray type column contains 4 numbers of trays having bubble cap risers fitted with bell caps. It contains sparger pipe distributor at bottom. The absorber perform CO 2 absorption and NH 3 rectification. Reflux NH3 is drawn as part from the NH 3 booster pump and fed to the absorber on top tray and the aqueous ammonia solution which in coming from M.P.inerts washing tower is fed on the third tray by means of centrifugal pump and tray washing provision is also there.
Image of medium pressure section of urea production Partially condensed NH 3 -CO2-H2O mixture from M.P. condenser enters the bottom of the column, where it is distributed is carbamate solution by means of sparger pipe distributor. Uncondensed gases consisting of NH 3 , CO2, H2O and inerts rising from the bottom are absorbed by cold liquid NH 3 reflux in the upper section of the column. Most of the CO 2 and H2O condenses as ammonium carbamate and fall back to the bottom. Condensation heat is removed by evaporation of ammonia. Thus a stream of inert gases saturated with NH 3 leaving the top of the absorbers rectification section. The bottom solution is recycled to urea synthesis and high pressure recovery section by H.P. carbonate pump. Ammonia vapours with inert gases leaving the top of column is partially condensed in ammonia condenser by heat exchange with cooling water and then the liquid and gaseous ammonia phases are returned to ammonia receiver.
Ammonia Receiver: It is the horizontal cylindrical vessel fitted with ammonia recovery tower. The tower is installed on the receiver with 3m packing bed height of pall rings and contain distribution sieve tray above the packed bed. The receiver is located slightly tapper to the ground. The ammonia which is received from battery limits containing 5PPM oil. It causes the foaming in synthesis section, to avoid this foaming the oil should be separated from ammonia. In the above receiving tank, the oil will separate by density separation and comes towards the down end of the tank. This oil will drain periodically. • The function of this receiver tank is to receive and act as a s a buffer storage for ammonia received from battery limit. • To receive ammonia recovered during plant shut down. • To receive ammonia condensed in the recovery system.
The inert gases containing residual ammonia leaving the receiver, enters the ammonia recovery tower, where the pure ammonia coming from B.L. is fed at the top of the tower. In the tower the inert gases containing NH 3 and pure liquid NH 3 are brought in contact with each other in a counter current flow to recover some ammonia from inerts. The inert gases containing residual ammonia are sent to the medium pressure falling film absorber(inert washing tower) where they meet in a counter current water flow which absorbs gaseous ammonia. The heat of absorption is removed by cooling water. From the bottom of the absorber water-NH 3 solution is recycled back to the medium pressure absorber by means of centrifugal pump. Tower operating at a pressure 2.5 kgf/cm2 before entering the distillation tower the process condensate is preheated in the exchangers where the heating medium is the purified condensate flowing out the tower. Since the solution is contaminated by urea, after a first stripping in the upper part of the tower, it is pumped into the hydrolyser where the urea is decomposed by means of stream at 37 kgf/cm2 , 370oC. Before entering the hydrolyser , the solution is preheated in the exchanger with the solution coming out from the hydrolyser. The hydrolysis reaction of urea is the opposite of that occurring in the reactor. NH2CONH2 + H2O ------->2NH 3 + CO2 + Heat Therefore urea decomposition is favored by high temperature, low pressure and NH 3 & CO2 deficiency. Also a sufficient long residence time has proved to be an important parameter. In order to eliminate NH 3 and CO2 as far as possible before feeding the hydrolyser the waste water coming out from the vacuum condensers is first stripped in the column. Moreover a series of baffles in the hydrolyser provided a plug flow effect, thus avoiding back mixing. Also the continuous removal of hydrolysis reaction and this encourages the decomposition of urea.
Urea High Pressure section The vapours leaving the hydrolyser, jointly with the vapours coming from the distillation tower are condensed in the distillation tower overhead condenser. Where the condensation heat is removed by cooling water. From this condenser the carbonate solution flows to the reflux accumulator from part of the solution fed to the distillation column by using pump. The purified waste from the bottom of distillation tower is cooled. DEDUSTING SYSTEM: The urea melt coming out of the bucket in the form of droplets and while falling inside the prill tower encounters a countercurrent flow of cold air causes solidification . Hot air leaving prill tower top consists of fine urea dust and free ammonia. In order to prevent pollution caused during the process of prilling . During system has been incorporated at prill tower top. The system also recovers urea, which is recycled back into the system.
OPERATION: In dedusting tank air travels in two chambers and a stainless steel partition wall which is hanging fro the top separates these two chambers. The three recirculation pumps take suction deduction chamber with the help of scrubber nozzles with an angle of 10 deg and due to this spraying action, sir is sucked into the first chamber (annual scrubbing chamber). Urea gets dissolved while exhaust air traveling from top to bottom in annular scrubber chamber and then it enters the second chamber of dedusting sump, where demister pads are provided at the top. Process condensate pump is sprayed on demister pads. By nozzles with 90deg.angle, and this system is operated by PLC (programmable logic control). Before taking DDS in line top louvers are be kept closed. Make up liquid for dedsuting sump is done by a control valve and after attaining required concentration the solution is drained to urea lumps dissolving tank. Maximum allowable urea dust to atmospheric air is 3Omg/Nm2 of air. An energy-efficient process for urea synthesis must fulfill the following parameters. • High conversion efficiency of CO2 in urea synthesis reactor, in order to minimize the heat required for decomposition of unconverted carbamate.(Achieved by optimization of parameters in the urea reactor). • Efficient decomposition of carbamate and efficient separation of ca rbamate decomposition products(CO 2 and NH3 ), as well as of excess ammonia .(Optimization of process parameters in the stripper and decomposer) • Maximum recovery and efficient utilization of heat formed by absorption and reaction of NH3 and CO2 released from the stripper and decomposition. (Optimization of process parameters in the carbamate condenser ,the MP decomposes and MP absorber).
Urea formation and high pressure section photo
http://rindafera.blogspot.com/2011/04/makalah-peral http://rindafera.blogsp ot.com/2011/04/makalah-peralatan-industri-kimia.html atan-industri-kimia.html
MAKALAH PROSES INDUSTRI KIMIA INDUSTRI NITROGEN PEMBUATAN UREA Disusun Oleh : Kelompok 3
Nama : Rr.Rinda Fera E Nim
: 0609 3040 1028
Kelas : 3 KIC
Dosen Pengajar Ir. Erlinawati, M.T
JURUSAN TEKNIK KIMIA POLITEKNIK NEGERI SRIWIJAYA 2010
BAB IV INDUSTRI NITROGEN 3. Urea
3.1. Pendahuluan
Kedengaran amat sederhana bahwa pupuk Urea terbuat dari gas alam, air dan udara. Udara tersedia tidak terbatas sedang gas alam terdapat banyak di Indonesia. Dengan sendirinya bagi Indonesia bukanlah menjadi masalah yang berat untuk dapat memproduksi sendiri pupuk buatan bagi kepentingan pertaniannya. Namun tidaklah sesederhana itu proses pembuatan pupuk Urea yang dibuat di Pabrik Pusri yang dikenal sebagai jenis pupuk tunggal berkadar Nitrogen 46%. Urea(NH2CONH2) Pupuk urea adalah pupuk buatan senyawa kimia organic dari CO(NH 2)2, pupuk padat berbentuk butiran bulat kecil (diameter lebih kurang 1 mm). Urea larut sempurna di dalam air 46. Pupuk ini mempunyai kadar N 45 dan tidak mengasamkan tanah. Sifat urea lain yang tidak menguntungkan adalah sangat higrokopis dan mulai menarik air dari udara pada kelembaban nisbi 73 persen(Hasibuan,2006).
3.2.
Klasifikasi Klasifikasi Proses Amonia dan karbondioksida dikompres dan bereaksi pada tekanan 100-200 atm dan pada suhu
170-190 oC. Didalam autoclave akan membentuk ammonium carbamate (UREA). Urea akan terbentuk secara dehidrasi pada tekanan rendah. Proses pembuatan Urea dibuat dengan bahan baku gas CO2 dan liquid NH3 yang disupply dari Pabrik Amoniak. Proses pembuatan Urea tersebut dibagi menjadi 6 unit, yaitu : 1. Sintesa Unit 2. Purifikasi Unit
3. Kristaliser Unit 4. Prilling Unit 5. Recovery Unit 6. Proses Kondensat Treatment Unit
(1) Sintesa Unit
Unit ini merupakan bagian terpenting dari pabrik Urea, untuk mensintesa Urea dengan mereaksikan liquid NH3 dan gas CO2 di dalam Urea reaktor dan ke dalam reaktor ini dimasukkan juga larutan recycle karbamat yang berasal dari bagian recovery. Tekanan operasi di sintesa adalah 175 Kg/cm2 G. Hasil sintesa Urea dikirim ke bagian Purifikasi untuk dipisahkan ammonium karbamat dan kelebihan ammonianya setelah dilakukan stripping oleh CO2. (2) Purifikasi Unit
Ammonium karbamat yang tidak terkonversi dan kelebihan ammonia di unit sintesa diuraikan dan dipisahkan dengan cara tekanan dan pemanasan dengan dua step penurunan tekanan, yaitu pada 17kg/cm2 G dan 22,2 kg/cm2 G. Hasil peruraian berupa gas CO2 dan NH3 dikirim ke bagian recovery, sedangkan larutan ureanya dikirim ke bagian kristaliser. (3) Kristaliser Unit
Larutan urea dari unit Purifikasi dikristalkan dibagian ini secara vacum. Kemudian kristal ureanya dipisahkan di Centrifuge. Panas yang diperlukan untuk menguapkan air diambil dari panas sensibel larutan urea, maupun panas kristalisasi urea dan panas yang diambil dari sirkulasi Urea Slurry ke HP absorber dari recovery. (4) Prilling Unit
Kristal urea keluaran Centrifuge dikeringkan sampai menjadi 99,8% berat dengan udara panas, kemudian dikirimkan ke bagian atas Prillign Tower untuk dilelehkan dan didistribusikan merata ke seluruh distributor, dan dari distributor dijatuhkan ke bawah sambil didinginkan oleh udara dari bawah dan menghasilkan produk urea butiran (prill). Produk urea dikirim ke bulk storage dengan belt conveyor.
(5) Recovery Unit
Gas ammonia dan gas CO2 yang dipisahkan dibagian purifikasi diambil kembali dengan 2 step absorbsi dengan menggunakan mother liquor sebagian absorbent kemudian di recycle kembali ke bagian sintesa. (6) Proses Kondensat Treatment Unit
Uap air yang menguap dan terpisahkan dibagian kristaliser didinginkan dan dikondensasikan. Sejumlah kecil urea, NH3, dan CO2 ikut kondensat kemudian diolah dan dipisahkan di stripper dan hydrolizer. Gas CO2 dan gas NH3nya dikirim kembali ke bagian purifikasi untuk direcover. Sedang air kondensatnya dikirim ke utilitas.
3.3. Data Kuantitatif
a.
Basis : 1 ton prilling urea ( 99 +%)
One Through
Partial recycle
Total recycle
NH
1.15 1.15
0.88 0.88
0.60 0.60
CO
1.47 1.47
0.91 0.91
0.77 0.77
Power KWH
210
165
145
Cool Coolin ing gH O
120 120
70
110 110
Uap ton
1.8
2.0
2.4
b. Kapasitas : 1000-1500 ton/ hari
3.4. Sifat Fisik dan Kimia Bahan Baku
Bahan dasar pembuatan urea adalah amoniak (NH3) dan Karbondioksida (CO2). Karbondioksida dihasilkan dari hasil sampingan dari Unit Amoniak.
1. Amonia (NH3) Sifat Fisik dan Kimia
Gas tidak berwarna
Berbau
Iritan
Mudah larut dalam air
Titik leleh - 77.7oC
Titik didih – 33.4oC
Tekanan uap : 400mmHg
Berat jenis 0.682 gr/ml
Berat jenis uap 0.6 gr/ml
Suhu kritis 133oC
Titik bakar : 650oC
Berat molekul : 17,3 gr/mol
Spesific gravity pada acuan udara : 0,5971
Kelarutan dalam air panas (100 oC) : 7,4/100
Kelarutan dalam air dingin (0 oC) : 89,9/100
Viscositas (25 oC) : 13,35 Cp
2. Karbondioksida ( CO 2) Sifat fisik CO 2
gas CO2 memiliki bau yang sedikit mengganggu, tidak berwarna dan lebih berat daripada udara.
Titik beku -78,5 ° C untuk membentuk karbon dioksida
Massa jenis cair: 1032 kg/m3 ,massa jenis gas 1,98 g/L
Tanpa warna
Tidak mudah terbakar
°C (216 K) (di bawah tekanan) Titik leleh −57
Titik didih −78
°C (195 K)
(menyublim menyublim))
Sifat Kimia CO 2
Dalam larutan air membentuk asam karbonat, yang terlalu stabil akan mudah terisolasi.
Tekanan uap: 58,5 bar
Kelarutan dalam air 1,45 g/L
Keasaman (pK a) 6,35
Pada keadaan STP STP,, rapatan karbon dioksida berkisar sekitar 1,98 kg/m³, kira kira 1,5 kali lebih berat dari udara udara..
Molekul karbon dioksida (O=C=O) mengandung dua ikatan rangkap yang berbentuk linear.
3.5. Sifat Fisik dan Kimia Produk Sifat-sifat Urea (NH 2CONH2)
Urea berupa kristal berwarna putih, tidak mudah terbakar, menghantarkan listrik dan sifat fisis sebagai berikut: o Densitas (padat pada suhu 20o C) : 1335 kg/m3 o Titik lebur : 132,6o C o Panas peleburan (titik lebur) : 13,6 kJ/mol o Berat Molekul : 60,056 gr/mol o Spesific heat (lebur) : 126 J/mol/ o C 3.6. Reaksi Kimia yang Terjadi
Reaksi pembuatan urea (NH2CONH2) terdiri atas dua tingkat yaitu reaksi pembentukan Ammonium Karbamat (NH2COONH4) dan reaksi penguraian Ammonium Karbamat menjadi urea dan air.
Ammonium Karbamat dibuat dari Amoniak (NH3) dan Karbondioksida (CO2) menurut reaksi sebagai
berikut: a. CO2 + 2NH3
NH4.COO.NH2
H0 = - 37.4 Keal
ammonium carbamate b. NH4.COO.NH2
NH2.CO.NH 2 + H2O
H0 = +6.3 Keal
Urea Reaksi samping c. 2NH2.CO.NH 2 + H2O
NH3.CO.NH.CO.NH 2.H2O + NH3
Biuret
3.7. Uraian Proses
Amoniak (NH3) dan karbondioksida (CO2) masuk kedalam Urea Syntesis Autoclave, pada tekanan 180 atm dan suhu 185oC. Untuk menjaga kestabilan suhu pada Autoclave dilengkapi dengan pendingin. Kemudian gas tersebut dipanaskan dengan steam, setelah itu dimasukkan kedalam Flash Evaporator pada tekanan 27 atm dan suhu 140oC, dan akan menghasilkan 3 keluaran yaitu air yang akan direcycle, gas dan reaktan yang berlebih akan direcycle, dan gas yang dipanaskan dengan steam akan dialirkan kedalam Flash drum dengan tekanan 1 atm. Kemudian akan dipanaskan lagi dengan steam, dan dimasukkan pada Vacum Evaporator 60 cmHg dengan suhu 135oC. Keluaran dari Flash Drum berupa NH3 dan CO2 dan direcycle. Pada Flash Drum dibagian bawah akan keluar 80% aquoeous urea dari N 2 cair. Pada Vacum Evaporator setelah terjadi pemanasan dengan steam menghasilkan 99% molton urea, lalu mengalir masuk kedalam Prilling Tower yang dilengkapi dengan pendingin. Produk yang dikeluarkan dari Prilling Tower yang telah ditambah udara dingin akan menghasilkan urea granules sebesar 1% buiret. 3.8.
Flowsheet (terlampir)
3.9. Kegunaan Produk * Kegunaan pupuk Urea
Bahan dasar pembuatan urea adalah amoniak (NH3) dan Karbondioksida (CO2). Karbondioksida dihasilkan dari hasil sampingan dari Unit Amoniak. Beberapa kegunaan dari urea adalah: Pupuk Tanaman
Bahan dasar Melamine
Urea Formal Dehyde Consentrate
Nutrisi untuk binatang mamalia
Unsur hara Nitrogen yang dikandung dalam pupuk Urea sangat besar kegunaannya bagi tanaman untuk pertumbuhan dan perkembangan, antara lain: 1. Membuat daun tanaman lebih hijau segar dan banyak mengandung butir hijau daun (chlorophyl) yang mempunyai peranan sangat panting dalam proses fotosintesa 2. Mempercepat pertumbuhan tanaman (tinggi, jumlah anakan, cabang dan lain-lain) 3. Menambah kandungan protein tanaman 4. Dapat dipakai untuk semua jenis tanaman baik tanaman pangan, holtikultura, tanaman perkebunan, usaha peternakan dan usaha perikanan.
3.10. Fungsi Alat 1. Autoclave Sintesis urea : untuk tujuan sterilisasi alat yang akan digunakan untuk terjadinya reaksi antara bahan baku pembuatan urea, seperti NH3 dan CO2. Dan tempat bereaksinya bahan baku. 2. Flash Evaporator : Tempat terjadinya proses penguapan, tempat pemisahan antara uap dari cairan. 3. Flash Drum : Tempat proses penguapan dari hasil keluaran pada alat Flash Evaporator yang berupa gas yang telah dipanaskan pada steam. Dan pada alat ini akan menghasilkan keluaran berupa Amoniak dan karbondioksida kar bondioksida hasil recycle.
4. Prilling Tower : Tempat proses pembutiran produk urea, dengan bentuk produk yang keras, padat, putih dan berbentuk butiran. 3.11. Kesimpulan
1. Pupuk urea adalah pupuk buatan senyawa kimia organic dari CO(NH 2)2, pupuk padat berbentuk butiran bulat kecil (diameter lebih kurang 1 mm). 2. Sifat-sifat Urea (NH2CONH2) Urea berupa kristal berwarna putih, tidak mudah terbakar, menghantarkan listrik dan sifat fisis sebagai berikut: o Densitas (padat pada suhu 20o C) : 1335 kg/m3 o Titik lebur : 132,6o C o Spesific heat (lebur) : 126 J/mol/ o C o Berat Molekul : 60,056 gr/mol
3.12. Daftar Pustaka
eruler.multiply.com/journal/item/4/proses_ pembuatan _urea
okleqs.wordpress.com/2009/03/16/amoniak-nh3 /
www.gas-plants.com/ co2 co2-properties.html
www.ekodokcell.co.cc/.../sek www.ekodokcell.c o.cc/.../seksi-pemurnian-purifikasi si-pemurnian-purifikasi-di-pupuk.html -di-pupuk.html
autobliz.wordpress.com/2008/05/22/ kondensor kondensor /
rioardi.wordpress.com/2009/01/21/pupuk-nitrogen/
pusri.wordpress.com/2007/09/22/mengenal-pupuk-urea / pusri.wordpress.com/2007/09/22/mengenal-pupuk
www.pusri.co.id › Produksi › Profil Pabrik
id.wikipedia.org/wiki/ Karbon_dioksida Karbon_dioksida
mbahinox.wordpress.com/.../karakteristik-sen mbahinox.wordpress.com /.../karakteristik-senyawa-dalam-pembuatanyawa-dalam-pembuatan- urea-dan-reaksi/
Diposkan oleh RindaFera di 18:54
