Prilled Urea, Molten Urea, Liquid Ammonia and Carbon Dioxide Gas

 ØUrea:  3.15 ton/ton
 NH3:  0.6 ton/ton
 Catalyst:  4.0 kg/ton

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Melamine

 ØShape:  White Powder

Quality:
     Purity: 99.9% min.
     Moisture:0.1% max
    Color:as APHA 20 max
    Iron:1 ppm max
    Ash:20 ppm max
    pH:7.5 ~ 9.5
    Ammeline + Ammelide:0.01% max

Melamine A/B plants were revamped in 2002. 
The improving contents before and during the revamping respectively.

Before Revamping

  1. B Plant Reactor

• Optimization of Reactor Cyclone
  • Increase the catalyst charge amount
  • Production capacity increased (B : 38 -> 50 T/D)
  • Product quality was improved

  2. The prolonging of short shut-down interval

•  A : 40 -> 60 days, B : 85 -> 100 days 
• Operation condition change
  • Melted urea circulation flow rate, Crystallyzer outlet temperature etc.

  During Revamping (A : 25 -> 33 T/D,   B : 50 -> 65 T/D)

   1. Process

• Catalyst Change : Gamma Alumina -> Silica Alumina (High Efficiency)
• Increase catalyst charge amount
• Increase system pressure
• Change other operation conditions

  2. Equipment

• Reactor 
  • Increase the height of reactor
  • Increase the salt heater and heat exchanger capacity
  • Improve the reactor cyclone
• Urea Circulation 
  • Urea washer improvement and capa up
  • Change Urea separator type (high efficiency)
  • Cooling gas blower capa up
• Crystallyzer : increase the height
• Others : Product packer, off-gas treatment capa up etc

  After Revamping

• B plant F-4 filter was improved. 
  •  Product quality was improved drastically(Color/Turbidity : 15/5 -> 6/1)
    
    

 Process Flow

• Ø Urea feed is introduced to melamine synthesis reactor (A-1) while urea is stored and maintained for reaction in urea solution tank (B-16)
• Ø
In the reactor (A-1), the catalyst is charged and the heated carrier gas goes through and forms catalyst fluidization.  Owing to endothermic melamine forming reaction, it is necessary to keep the temperature between 350°C to 400°C in the reactor by heating coil installed in the fluiding bed of the catalyst to which the molten salt is introduced
• Ø
As the reactants pass through the reactor, the molten urea is vaporized and reacted to melamine, carbon dioxide and ammonia
• Ø
The melamine-rich effluent gas from the reactor is cooled down to about 320°C in the hot gas cooler (W-12A/B) and introduced to hot gas filter (F-4A/B) where the by-products and catalyst dust carried out from the reactor (A-1) are separated
• Ø
The product gas is cooled down again to about 210°C in the crystallizer (A-2) by contacting the gas effluent (140°C) and very fine melamine particle is formed
• Ø
The cyclone separator (F-6 A/B) is used for the separation of melamine product and consecutive cooling and packing system is installed for final treatment
• Ø The remaining gas from the cyclone separator (F-6A/B) is introduced to urea washer (K-1) and cooled down to 140°C by contacting with the spray of molten urea
• Ø The gas containing ammonia and carbon dioxide serves as carrier gas in the melamine reaction and cooling medium in the crystallizer (A-2)
• Ø The temperature of the molten urea should be strictly controlled by the urea cooler system (W-14) for washing and cooling the gas
• Ø The molten urea is then mixed with fresh urea feed in the urea storage tank (B-15)
• Ø The yield of melamine by the above whole treatment is over 90% (on the basis of dry and theoretical) 

Off Gas Recovery

• The off gas from the melamine plant, mixture of NH 3 , CO 2 , H 2 0 and a small amount of inert gas is pressured by the off gas blower (V-8) and sent to the off gas absorber (B-18)
• In the absorber (B-18), most of the NH 3  and CO 2  in the off gas is absorbed in water fed from the battery limit for off gas absorber
• The produced ammonium carbonate solution is then transferred to the battery limit by the off gas solution pump
• In consequence of feeding, the ammonium carbonate solution to the existing urea plant shall be made to keep the designed production capacity of the urea plant