Stamicarbon urea process

Jonckers, V. Mennen, J. Meesen, and W. Lemmen, Stamicarbon New Process Urea 2000 and Stamicarbon, Wastewater Process, Stamicarbon AB Geleen, The Netherlands, Feb. 1997. 

The synthesis section of the Stamicarbon (STAC) process is shown in Figure 11.3. An updated version of this process, Urea 2000plus, is offered by DSM (Stamicarbon s parent company)108,110. In this process NH3 and CO2 are converted to urea via ammonium carbamate at a pressure of 140 bar and a temperature of lSt/ C to 185°C. An NH3-to-C02 molar ratio of 2.95 is used in the reactor to give a CO2 conversion of 60%, and an NH3 conversion of 41%. The reactor is lined with 316L stainless steel. It contains sieve trays to provide... 

This was followed by the Stamicarbon 11 process, based on the decomposition of ammoniiun carbamate by carbon dioxide stripping (Fig. U3.). The urea synthesis loop features four main steps in this case ... 

Commercial plants The AVANCORE urea process is a new urea synthesis concept that incorporates all the benefits of Stamicarbon s earlier proven innovations. The AVANCORE urea process combines the advantages of Urea 2000Plus technology, Safurex and innovations and experiences gained from many revamp projects. No AVANCORE Urea plants are yet in operation. 

Figure 19.8. Stamicarbon bv s Urea Process Water Treatment.

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. 

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. 

Stamicarbon [Staatsmijnen carbon] Stamicarbon bv is the licensing subsidiary of the Dutch chemical company DSM. It offers a number of processes, including HPO and HSO. Historically, the process for which the company was best known was a coal carbonization process today, a urea-manufacturing process is probably its most important one. 

Technical information brochures on the Urea 2000plus process can be obtained from Stamicarbon B.V., the licensing company of DSM. 

Because of the high conversions in the synthesis, the recycle section of the plant is very small. An evaporation stage with vacuum condensation system produces urea melt with the required concentration either for the Stamicarbon fluidized-bed granulation or for prilling. Process water produced in the plant is treated in a desorbtion/hydrolyzer section. This section produces an effluent, which is suitable for use as boiler feedwater. 

Urea 2000plus A process for making urea from ammonium carbamate, using a novel pool reactor. Developed by DSM and first offered for license in 1996. Stamicarbon is the licensing arm of DSM and now offers the technology. Over 200 plants had been built by 2005. 

Stamicarbon bv Urea Ammonia and carbon dioxide C02 stripping technology using proven, innovative Urea 2000 Plus synthesis process for prilled or granulated urea 115 2001... 

In the Stamicarbon process, the NH3/CO2 molar ratio in the reactor (operated at 140bar and 180-185°C) is 2.95. In this step, approximately 60% of C02 and 40% of NH3 are converted, leading to an NH3/C02 ratio of about 4.5 in the unreacted gas. The effluent solution from the reactor is stripped at high pressure and temperature with C02 (reestablishing the proper NH3/C02 ratio) and the gases are recycled to the reactor. The urea solution is further purified from residual NH3 and C02 and finally taken through an evaporation step yielding 99.7% urea melt. 

With Stamicarbon s pool condenser technology, condensation can be done very efficiently by reversing the former high-pressure carbamate condenser s process and steam side. The entire heat exchanging part is submerged in condensed carbamate. This pool-type condensation enables higher heat transfer, while staging two-thirds of the entire synthesis section s urea conversion in its liquid holdup. Thus, the urea reactor... 

All processes still require use of oxygen for pasava-tion in the synthesis loop. Metallurgical advances have reduced the amount required. Snamprogetti now utilizes a bimetallic zirconium/25-22-2 (Ni, Cr, Mo) tube in its stripper. The corrosion rate for zirconium in urea service is nil. Toyo utilizes a duplex alloy (ferrite-austenite), which requires less ojqjgen. Stamicarbon working with the Swedish steel producer Sandvik, has patented a proprietary material called Saferex, which requires very little oxygen future plants wnll use this new material,... 

There now are three prevailing process designs for urea manufacture, licensed by Stamicarbon, Mitsui Toatsu, and Snampro-getti. The main differences between these processes are in the methods used to handle the converter effluent, to decompose the carbamate and carbonate, to recover the urea, and to recover the unreacted ammonia and carbon dioxide for recycle, with the objective being minimum expenditure of energy and a maximum recovery of heat. In some processes, a liquid is used to recycle a solution of carbamate, carbon dioxide, ammonia, and water. In others, the amount of water recycled is minimized, and only carbon dioxide and ammonia are recycled. In the older plants, or once-through plants, the off-gases are used as feed to ammonium nitrate or ammonium sulfate plants. 

Fig. 28.19. Stamicarbon process for urea. (Hydrocarbon Processing, 58, No. 11, 1979, copyright by Gulf Publishing Company and used by permission.)...

The first reaction is exothermic and goes almost to completion, while the second, endothermic, reaction converts less than 70% of feedstocks to urea. Consequently, the once-through process of urea synthesis had to be combined with production of other nitrogen compounds. Modern syntheses use a more expensive total recycle process in which all the unreacted CO2 and NH3 is separated from the effluent solution and returned to the reactor. Conversion rates range between 65 and 67% for each pass, and the overall reaction yield is on the order of 99%. Three commercial processes—Dutch Stamicarbon, Italian Snamprogetti, and Japanese Toyo—dominate today s world market for large (up to 2,000 t/day) urea plants using the total recycle process. ... 

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