Stamicarbon

At this time over 95% of all new urea plants are Hcensed by Snamprogetti, Stamicarbon, or Toyo Engineering. SNAM utilizes thermal stripping while STAC (Stamicarbon) and Toyo use CO2 stripping. Only these three processes are, therefore, covered in detail. Process flow sheets are included for others at the end of this section. 

Stamicarbon GO2 Stripping Process. In the early 1960s, Stamicarbon introduced the first stripping process. One of the main... 

Fig. 3. Stamicarbon CO2 stripping process. TCW — tempered cooling water.

Fig. 5. Pool condenser vessel for Stamicarbon CO2 stripping process.

The Stamicarbon wastewater system consisting of two desorbers, hydrolyzer, hydrolyzer heater, reflux condenser, desorber heat exchanger, and a wastewater cooler is very efficient. Also, in many plants, as the water contains less than 1 ppm of NH and of urea, it can be used as cooling water make-up, or boiler-feed water. 

In 1994 Stamicarbon introduced a pool condenser in the synthesis section (see Figs. 4 and 5). This allowed a 34% decrease in reactor volume and a 45% decrease in carbamate heat-exchange area, thus reducing costs considerably for equipment, stmctural steel, and constmction. 

In late 1997, DSM (Stamicarbons parent company) will start up a new plant utilizing, the next step, a pool reactor (see Figs. 6 and 7). In 1999 this process should be offered for licensing. 

All process Hcensors also feature wastewater treatment systems. Stamicarbon guarantees the lowest NH —urea content and has plants in operation confirming the low NH —urea (1 ppm NH —1 ppm urea). This water is very satisfactory to use as boiler feed water. See Figures 16 and 17 for this system. 

Jonckers, V. Mermen, J. Meesen, and W. Lemmen, Stamicarhon Neu> Process Urea 2000 and Stamicarhon, WastewaterProcess, Stamicarbon AB Geleen, The Netherlands, Feb. 1997. 

The patent Hterature indicates that the AUiedSignal process uses lower boiling solvents such as chlorofluorocarbons as the cooling/extraction baths (16), whereas the processes of Stamicarbon indicate the use of decalin solvent followed by cooling and slow removal of the decalin in successively hotter chambers while stretching (17). 

An additional mole of ammonium sulfate per mole of final lactam is generated duting the manufacture of hydroxylamine sulfate [10039-54-0] via the Raschig process, which converts ammonia, air, water, carbon dioxide, and sulfur dioxide to the hydroxylamine salt. Thus, a minimum of two moles of ammonium sulfate is produced per mole of lactam, but commercial processes can approach twice that amount. The DSM/Stamicarbon HPO process, which uses hydroxylamine phosphate [19098-16-9] ia a recycled phosphate buffer, can reduce the amount to less than two moles per mole of lactam. Ammonium sulfate is sold as a fertilizer. However, because H2SO4 is released and acidifies the soil as the salt decomposes, it is alow grade fertilizer, and contributes only marginally to the economics of the process (145,146) (see Caprolactam). 

The Stamicarbon (22) and Kaltenbach high concentration processes are designed to use the evaporated water vapor produced by pressure neutralization to heat the evaporator used for concentration. The Kaltenbach neutralizer operates at 350 kPa (3.5 bar) and 175°C, and produces steam used to concentrate the solution to 95% in a vacuum evaporator. A recent variation uses a final atmospheric evaporator to produce a 99.7% melt (22). 

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