Urea Engineers Guide
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ENGINEERS GUIDE The Snamprogetti Urea Process Description The Sna mpr oget ti Ure a Pro ces s is basicall y a tot al rec ycl e stripping pro ces s usi ng ammonia as self stripping agent. The Snamprogetti process used the excess ammonia present in the urea solution leaving the reactor to strip CO2 from urea solution in a falling film steam heated heat exchanger operated at the urea reactor pressure . The separated CO2 and NH3 are recombined as ammonium carbamate in the carbamate condensers, also operati ng at urea reactor press ure and then returne d to the reactor for conversi on to urea. The overall result of this scheme is that an internal recycle of both NH3 and CO2 in the urea reactor system is established without having to pump either component , as in previous total recycle process in which NH3 and CO2 were separated from the solution at lower pressure. This substantially reduces the high pressure pumping requirements for both the NH3 and ammonium carbamide solution, since in the Snamprogetti stripping process approximately 80% of the CO2 fed is converted to urea within high pressure synt hesi s loop and only about 20% of it must be pumped back to the reactor as ammonium carbamate solution from lower pressure. In addition to the reducing pumping requirements, this process permits a substantial saving in steam requirement, since the operating temperature level of the ammonium carbamate condenser by utilizing the heat released by the condensing vapor. The NH3 to CO2 ratio used in Snamprogetti process is 3.3-3.6 : 1which combines with a temperature of 186-189deg C and pressure of 155 Kg/cm2g approximately, permits a conversion yield in the reactor of 62 to 65%.
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Transcript of Urea Engineers Guide
8/4/2019 Urea Engineers Guide
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ENGINEERS GUIDE
The Snamprogetti Urea Process Description
The Snamprogetti Urea Process is basically a total recycle stripping process usingammonia as self stripping agent. The Snamprogetti process used the excess ammonia
present in the urea solution leaving the reactor to strip CO2 from urea solution in a falling
film steam heated heat exchanger operated at the urea reactor pressure . The separated
CO2 and NH3 are recombined as ammonium carbamate in the carbamate condensers,also operating at urea reactor pressure and then returned to the reactor for conversion to
urea.
The overall result of this scheme is that an internal recycle of both NH3 and CO2 in the
urea reactor system is established without having to pump either component , as in previous total recycle process in which NH3 and CO2 were separated from the solution atlower pressure. This substantially reduces the high pressure pumping requirements for
both the NH3 and ammonium carbamide solution, since in the Snamprogetti stripping
process approximately 80% of the CO2 fed is converted to urea within high pressuresynthesis loop and only about 20% of it must be pumped back to the reactor as
ammonium carbamate solution from lower pressure. In addition to the reducing pumping
requirements, this process permits a substantial saving in steam requirement, since the
operating temperature level of the ammonium carbamate condenser by utilizing the heatreleased by the condensing vapor.
The NH3 to CO2 ratio used in Snamprogetti process is 3.3-3.6 : 1which combines with atemperature of 186-189deg C and pressure of 155 Kg/cm2g approximately, permits a
conversion yield in the reactor of 62 to 65%.
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Block diagram of total recycle of ammonia stripping in urea production
Urea production takes place through the following main reactions:
Urea synthesis and high pressure recovery.
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Urea purification in the medium, low pressure decomposers, Pre vacuum concentrators.
Urea concentration.
Urea Prilling.
Flow sheet of Urea prilling system
Block diagram of urea prilling section
UREA SYNTHESIS:(FLOW SHEET) a complete urea process description with
flow sheet
The liquid ammonia coming from the battery limit at a temperature of 120C and 18
Kg/cm2(g) is collected in a ammonia receiving vessel which is operated at a medium
pressure(17Kg/cm2). From the ammonia receiver, the liquid ammonia is pumped to thereactor by two pumps. The first pump is the ammonia booster pump which is centrifugal
type and supplies the liquid ammonia at 22Kg/cm2 to second pump suction. The second pump is the high pressure ammonia pump which is a reciprocating-plunger type. Due to
the reciprocating motion of second pump pulsating takes place in the discharge of booster
pump and those cause the change of loads on booster pump to avoid these booster pump
and those cause the change of loads on booster pump to avoid these pulsations a damper is provided in the suction of second pump. In the H.P. ammonia pump, the ammonia
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pressure is increased to 239Kg/cm2 and then goes to a ammonia pre heater where it is
preheated to 750C by L.P. decomposer outlet gases, H.P. ammonia is used as pressure
section contains first and second stage another one is the high pressure section containsthird and fourth stage. First and second stages contains three, third stage contains four
and fourth stage two numbers of closed type impellers. Carbon dioxide gas enters first
stage suction at 1.5kg/cm2 and 400
C and compressed to 160 Kg/cm2 in four stages.Intercoolers are provided after first, second and third stages to cool the carbon dioxide
using cooling water. Along with coolers knock out drums are provided between each
stage in which moisture gets separated. Lube oil system provides the lubrication of therotating parts. The superheated steam and saturated LS steam is used as a driving fluid for
steam turbine. Superheated HS steam is extracted and part of steam is condensed in
condenser. Condensate is then pumped to D.M. plant.
Block diagram of total recycle of carbon dioxide stripping in urea production
