Urea stripping process

Kaasenbrood, P.J.C., arxi H.A.G. Chermin. 1977. The Urea Stripping Process, Stripping Technology, Phase EquiDbria, and Thermodynamics, Proceedings of the Fertiliser Society (London), No. 167. 

The urea produced is normally either prilled or granulated. In some countries there is a market for Hquid urea—ammonium nitrate solutions (32% N). In this case, a partial-recycle stripping process is the best and cheapest system. The unconverted NH coming from the stripped urea solution and the reactor off-gas is neutralized with nitric acid. The ammonium nitrate solution formed and the urea solution from the stripper bottom are mixed, resulting in a 32—35 wt % solution. This system drastically reduces investment costs as evaporation, finishing (priQ or granulation), and wastewater treatment are not required. 

Application To produce urea from ammonia and carbon dioxide (C02) using the C02 stripping process. 

Fig. 2.2-3. Flow sheet for urea manufacture by the stripping process. [Taken from Fromm, D. and Liitow, D., Modern Processes in the Heavy-Chemicals Industry f/ren , Chemie in un.sererZcit 13,78-81 (I979).l...

Toyo Engineering Corp. (TOYO) Urea Ammonia (NH3) and carbon dioxide (CO ) Process produces urea from NH and CO using CO stripping process 100-1- NA... 

The key process unit is an FW Evaporative Scrubbing System (ESS). The raw process condensate from the urea unit is first steam stripped to reduce ammonia content. The stripped process condensate is mixed with a circulating stream of urea solution and enters the distribution system of the ESS, which also acts as a cooling tower. The air from the finishing process (prilling or granulation) is introduced into the bottom of the ESS. Particles entrained in the air are dissolved in the urea... 

Figure 3.9 Block flow diagram of stripping process for urea synthesis with consecutive production...

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. 

Fig. 1. Snamprogretti thermal stripping urea process. BL = battery limits.

A plant is to be designed for the production of 300,000 kg per day of urea by the reaction of ammonia and carbon dioxide at elevated temperature and pressure, using a total-recycle process in which the mixture leaving the reactor is stripped by the carbon dioxide feed (DSM process, references 1 to 4). 

Urea in kidney dialysate can be determined by immobilizing urease (via silylation or with glutaraldehyde as binder) on commercially available acid-base cellulose pads the process has to be modified slightly in order not to alter the dye contained in the pads [57]. The stopped-flow technique assures the required sensitivity for the enzymatic reaction, which takes 30-60 s. Synchronization of the peristaltic pumps PI and P2 in the valveless impulse-response flow injection manifold depicted in Fig. 5.19.B by means of a timer enables kinetic measurements [62]. Following a comprehensive study of the effect of hydrodynamic and (bio)chemical variables, the sensor was optimized for monitoring urea in real biological samples. A similar system was used for the determination of penicillin by penicillinase-catalysed hydrolysis. The enzyme was immobilized on acid-base cellulose strips via bovine serum albumin similarly as in enzyme electrodes [63], even though the above-described procedure would have been equally effective. 

The urea-product solution, leaving the first decomposition stage and still containing some unreacted carbamate and excess NH3, is let down in pressure and steam heated in the second-staged decomposition section, which operates at about 2 atm and 120°C. Practically all of the residual carbamate is decomposed and stripped from the urea-product solution together with the residual excess ammonia. The 74—75 wt % urea solution thus obtained is further processed to solid urea... 

Figure 11J. Snamprogretti thermal stripping urea process. (This material is used by permission of John Wiley Sons, Inc.)...

The Isobaric Double-Recycle (IDR) urea process was developed by Montedison. In this process most of the unconverted material leaving the reactor is separated by heating and stripping at synthesis pressure using two strippers in series. The unconverted ammonia, C02, and carbamate in the urea solution are recycled to the synthesis loop.108110... 

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... 

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 ... 

Montedison, which originally participated in the Momecaiini-Fauser joint venture to market a number of total-recycle variants, and now presents its IDR (Isobaric Double Recycle process) technique. TTiis process operates at 20.10 Pa absolute, around 190 to 200, with an N/C ratio of4 to 5 in the reactor. Unconverted carbamate is decomposed in two successive gas stripping steps, one with ammonia, and the second with CO 2. in the pressure conditions of urea s nthesis, i.e.. 10 Pa absolute. 

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. 

In the Edeleanu process, waxy feed is mixed (Figure 9.15) in one of several reactors with urea and with recycled and fresh methylene chloride whose vaporization controls the exothermic reaction with urea. Prior to filtration, the adduct passes through a series of baffles to encourage complete reaction. After washing, the adduct is filtered from the oil, which proceeds to a stripper (to remove the methylene chloride) and then to product storage. The separate adduct stream from the filter is decomposed by steam at 75°C, then sent to a separator and subsequently stripped of solvent to yield the n-parafflns. The dewaxed oils disengage from the aqueous phase in a separator. 

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