Presentation Topic
UREA PRODUCTION For more chemical engineering ebooks and solution manuals visit here www.chemicallibrary.blogspot.com
UREA
Urea is an organic compound with the
chemical formula (NH2)2CO. Urea is also known as Carbamide
HISTORY
Urea was first discovered in urine in 1773 by the French chemist Hilaire Rouelle. It was the first organic compound to be artificially synthesized from inorganic starting materials, material s, in 1828 by Friedr Friedrich ich Wöhler, who prepared it from silver sil ver isocyanate through a reaction with ammonium chloride:
AgNCO + NH4Cl
(NH2)2CO + AgCl
FUNDAMENTAL STEPS
OF PROCESS
The process for manufacturing urea involves a combination combinatio n of up to 7 major unit operations. Solution
concentration.
Solid formation. Solid cooling. Solid screening.
Clay coating
Solid bagging.
Bulk shipping.
Solution
concentration concentratio n
In th the e so solu luti tion on sy synt nthe hesi siss op oper erat atio ion, n, am ammo moni nia a (NH3) and carbon dioxide (CO2) are reacted to form fo rm amm mmon oniu ium m ca carb rbam amat ate e (N (NH H2C 2CO2 O2NH NH4) 4).. Typical operating conditions include temperatures from 180 to200°C (356 to 392°F), pressures from 140 to 250 atmospheres (14,185 to 25,331 25,331 kilopasca kilopascals) ls) NH3:CO2 NH3:CO2 molar ratios ratios from 3:1 to 4:1.The carbamate is then dehydrated to yield 70 to 77 percent aqueous urea solution. These re rea act ctio ions ns are as fol ollo lows ws:: 2NH3 +CO2 NH2CO2NH4 NH2CO2NH4 NH2CONH2 + H2O
Solid
formation
The concentration concentration process p rocess furnishes urea "melt for solids formation. Urea solids are produced from the urea melt by 2 basic methods: prilling and granulation g ranulation..
PRILLING Prill Pri lliing is a pr proc oces esss by wh whiich so sollid pa part rtic iclles ar are e produced from molten urea. Molten urea is sprayed from the top of a prill tower. As the droplets fall thro th roug ugh h a co coun unte terc rcur urre rent nt ai airr fl flow ow,, th they ey co cool ol an and d solilidi so dify fy in into to nea nearl rly y sp spher heric ical al par parti ticl cles. es. There are 2 types of prill towers: fluidized bed and nonf no nfllui uidi dize zed d bed ed.. The majo jorr di diff ffer eren encce is th tha at a separate solids cooling operation may be required to produc pro duce e ag agri ricul cultur tural al gr grad ade e pr prilills ls in a no nonf nflui luidi dize zed d bed be d pr pril illl to towe werr.
GRANULATION ran nulati tio on Gra
is used more frequently than prilli lin ng in producing solid urea for fertilizer. fertilizer. Granular urea is generally stronger than prilled urea, both in crushing strength and abra ab rasi sion on re resi sist stan ance ce.. Th Ther ere e ar are e 2 granu granula latio tion n me meth thod ods: s: dr drum um granu gra nula lati tion on an and d pa pan n gr gran anul ulat atio ion. n. In dr drum um gra granu nula lati tion on,, soli so lids ds ar are e buil builtt up in layers on seed granules placed in a ro rottating drum granu gra nulat lator/c or/cool ooler er app approxi roximat matel elyy 4.3 met meters ers (14 fee feet) t) in dia di ame metter er.. Pa Pan n gr gra anula lato tors rs als lso o fo form rm th the e pr prod odu uct in a laye la yeri ring ng pr proc oces ess, s, bu butt di diff ffer eren entt eq equi uipm pmen entt is us used ed an and d pan pa n gr gran anul ulat ator orss ar are e not not co comm mmon only ly us used ed in the the U. S.
SOLID
COOLING
The so sollids cool oliing ope perrati tio on is ge gen neral allly accomplished during solids formation, but for pan granulation processes and fo forr some agricultura agric ulturall grade prill prills, s, some suppleme supplementary ntary cooliling coo ng is provid provided ed by aux auxililiar iary y rotary rotary dru drums. ms.
SOLID SCREEN REENI ING
The solids screening operation removes offsize product from solid urea. The offsize material may be returned to the process in the solid phase or be redissolved redissolved in water and returned to the solution concentration process.
LAY Y COATING CLA
Clay coatings are used in the urea industry to redu re ducce pro rodu ducct ca caki kin ng and ur urea ea du dust st for orma mattio ion. n. The coating also reduces the nitrogen content of the product. The use of clay coating has dim di min inis ish hed con onsi sid dera rabl bly y, be bein ing g re rep place ced d by inje in jeccti tion on of for orma mald ldeh ehyd yde e ad addi diti tive vess in intto th the e liquid or molten urea before solids formation. Formaldehyde reacts with urea to from meth me thyyle len ned ediu iurrea, wh whic ich h is th the e cond ndit itio ioni ning ng agen ag ent. t. Ad Addi diti tive vess re redu duce ce so soli lids ds ca cak kin ing g du duri ring ng storage and urea dust formation during tran tr ansp spor ortt an and d ha hand ndlin ling. g.
SOLID SHIPING AN AND D
AGG GING BAG
The ma majo jorrity of so soli lid d urea product is bul ulk k shipped in trucks, enclosed railroad cars, or barges, but approximately 10 percent is bagged.
FLOW
CHART
EMISSI EM ISSIONS
Emissions from urea manufacture are mainly ammonia and particulate p articulate matter. (Particulate matter are tiny particles of solid or liquid suspended in a gas or liquid). Ammonia is emitted during the solution synthesis and solids production pr oduction processes. Particulate matter is emitted during all urea process.
CONTROLS Urea manufacturers presently control particulate matter emissions from prill towers, coolers, granulators, and bagging operations. With the exception of bagging operations, urea emission sources are usually controlled with wet scrubbers.
Scrubber systems are preferred over dry
collection systems primarily for collection f or the easy recycling of dissolved urea collected in the device. Scrubber liquors are recycled to the solution concentration concentration process to eliminate waste disposal problems and to recover the urea collected collected..
USES
OF
UREA
Urea is used as
a nitrogen-release fertilizer, fertilizer, as it hydrolyses back to ammonia and carbon dioxide, but its most common impurity, biuret, must be present at less than 2%, as it impairs plant growth. It is also used in many multi-component solid fertilizer formulations.
Biuret: [NH2.CO.NH.CO.NH2] condensation A condensation
product of urea. Colorless needles that are soluble in hot water,, and decomposes at 190 C water Also known as ; allophan amide carbamyl urea Di carbamyl amine
stabilizer A stabilizer
in explosives. A component of fertilizer and animal feed, providing a relatively cheap source of nitrogen to promote growth.
A raw material for the manufacture of
plastics. A raw material for the manufacture of various glues (urea-formaldehyde or urea-melamineformaldehyde);; the latter is waterproof . formaldehyde) An alternative to rock salt in the de-icing of
roadways and runways; it does not promote metal corrosion to the extent that salt does.
An additive ingredient in cigarettes, designed
to enhance flavour A browning agent in factory-produced pretzels h air conditioners, An ingredient in some hair facial cleansers, bath oils, and lotions A reactant in some ready-to-use cold compresses for first-aid first-aid use, due to the endothermic reaction it creates when mixed with water water..
HAZARD AZARDS S
Urea can be irritating to skin ski n and eyes. Too high concentrations in the blood can cause damage to organs of the body. Low concentrations of urea, such as are found in typical human urine, are not dangerous with additional water ingestion. Many animals (e.g., (e.g., dogs) have a much more concentrated urine and it contains a higher urea amount than normal human urine; this can prove dangerous as a source of liquids for consumption in a life-threatening situation (such as in a desert).
Repeated or prolonged contact with urea in
fertilizer form on the skin may cause dermatitis. The substance also irritates the eyes , the skin and the respiratory tract.
The substance decomposes on heating above melting point, producing toxic gases and reacts violently causing fire and explosion hazard.
For more chemical engineering ebooks and solution manuals visit here www.chemicallibrary.blogspot.com
REFENCES www.google.com. Manuf acturing Industry: Technical Document, Do cument, Urea Manufacturing EPA-45 EP A-450/3-81-001, 0/3-81-001, U. S. Environmental Triangle Park, NC, Protection Agency, Research Triangle January 1981. 2. D. F. Bress and M. W. Packbier, "The Startup Of Two Major Urea Plants", C hemical hemical Engineering Progress, May 1977. Written communication from Gary McAlister, U. S. 3. Written Environmental Protection Protect ion Agency, Agency, Research
Triangle Park, NC, to Eric Noble, U. S.
Environmental Protection Agency, Research Triangle Park, NC, July 28, 1983. ormaldehyde Use In Urea-Based Urea-Based F ertilizers, ertilizers, 4. F ormaldehyde Report Of The The F ertilizer ertilizer Institutes ormaldehyde F ormaldehyde Task Group, The Fertilizer Institute, Washington, DC, February 4, 1983