Urea plant

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. 

The technology of urea production is highly advanced. The raw materials requited ate ammonia and carbon dioxide. Invariably, urea plants ate located adjacent to ammonia production faciUties which conveniently furnish not only the ammonia but also the carbon dioxide, because carbon dioxide is a by-product of synthesis gas production and purification. The ammonia and carbon dioxide ate fed to a high pressure (up to 30 MPa (300 atm)) reactor at temperatures of about 200°C where ammonium carbamate [111-78-0] CH N202, urea, and water ate formed. 

Because an excess of ammonia is fed to the reactor, and because the reactions ate reversible, ammonia and carbon dioxide exit the reactor along with the carbamate and urea. Several process variations have been developed to deal with the efficiency of the conversion and with serious corrosion problems. The three main types of ammonia handling ate once through, partial recycle, and total recycle. Urea plants having capacity up to 1800 t/d ate available. Most advances have dealt with reduction of energy requirements in the total recycle process. The economics of urea production ate most strongly influenced by the cost of the taw material ammonia. When the ammonia cost is representative of production cost in a new plant it can amount to more than 50% of urea cost. 

This ammonia is recycled to the reactor via a compressor and a heater. Liquid ammonia is used as reflux on the top of the absorber. The net amount of carbon dioxide formed in the reactor is removed as bottom product from the absorber in the form of a weak ammonium carbamate solution, which is concentrated in a desorber-washing column system. The bottom product of this washing column is a concentrated ammonium carbamate solution which is reprocessed in a urea plant. The top product, pure ammonia, is Hquefted and used as reflux together with Hquid makeup ammonia. The desorber bottom product, practically pure water, is used in the quench system in addition to the recycled mother Hquor. 

Urea Plants - In urea plants, wet scrubbers or fabrie filters are used to control fugitive emissions from prilling towers fabric filters are used to eontrol dust emissions from bagging operations. These equipment are an integral part of the operations, to retain product. New urea plants should achieve levels of particulate matter in air emissions of less than 0.5 kg/t of product for both urea and ammonia. 

Urea Plant 6. Use total recycle processes in the synthesis process reduce microprill formation and carryover of fines in prilling towers. 

P. J. Nightingale, Major Incident Following the Failure of an Ammonia Injector on a Urea Plant, Paper presented at AIChE Ammonia Symposium, Aug. 1990. 

Heaven, D. et al., Synthesis gas purification in gasification to Ammonia/Urea plants, Gasification Technologies Conference, Washington, 2004. 

Christensen LK, Thinggaard K (1999) Solarization of greenhouse soil for prevention of Pythium root rot in organically grown cucumber. J Plant Pathol 81 137-144 Chun D, Lockwood JL (1985) Reduction of Pythium ultimum, Thielaviopsis basicola, and Macrophomina phaseolina populations in soil associated with ammonia generated from urea. Plant Dis 69 154-158... 

In July of 1997, a cooling tower at an ammonia and urea plant, originally constructed in 1968, caught fire and was destroyed. The plant produced 1,450 tons/day (1,315 tonnes/day) of ammonia and 240 tons/day (218 tonnes/day) of urea. The coolingtowerwasa 5-cell, induced draft, cross flow unit. It was constructed of redwood with steel supports and fiberglass fill. The capacity of the cooling tower was 50,000 gallons (190,000 liters). 

Table 19 Characteristics of Urea Plant, Pharmaceutical Plant, and Combined Wastewater [63]...

Parameter Urea plant Pharmaceutical plant Combined wastewater... 

According to the literature [3,17,33], the heterogeneous nature of fertilizer production plants precludes the possibility of presenting a typical case study of such a facility. Nevertheless, the wastewater flows, the characteristics, and the treatment systems for a phosphoric acid and N-P-K fertilizer plant were parts of a large fertilizer manufacturing facility. The full facility additionally included an ammonia plant, a urea plant, a sulfuric acid plant, and a nitric acid plant. The typical effluent flows were 183 m /hour (806 gpm) from the phosphoric plant and 4.4 m /hour (20 gpm) from the water treatment plant associated with it, whereas in the N-P-K plant they were 420 m /hour (1850 gpm) from the barometric condenser and 108 m /hour (476 gpm) from other effluent sources. 

Notes 1) The structure, consisting of the plenum chamber filter, shall be of such design that it can be supported by means of four (4) steel columns, one (1) at each corner. 2) Plenun chamber shall be of sufficient strength bracing to prevent wall, floor or ceiling from pulsating or oscillating. 3) For ammonia/urea plants or other installations with ammonia in the atmosphere, no copper, alianinum or their alloys shall be used for parts exposed to the air. 4) Seals filter material shall be resistant to vapors present in the inlet air (ammonia, hydrocarbons, etc.). 5) Unit shall be completely assembled and shipped as one unit. 6) Instruments controls to be conpletely piped and wired. 7) Outlet connection screen (0.25 in.) (6 mm) wire mesh, with back up bars to withstand seven (7) psi/0.5 kg/cm Press, across the screen. 

Installation of first pool reactor, largest single-line urea plant in operation... 

Shown in Figure 10, this ammonia plant is a major part of the overall fertilizer site complex. Other major facilities include urea plant, steam system, and cooling water system. Most of the ammonia is used to make granulated urea product. The other raw material for urea synthesis is C02 from the C02 capture system in the ammonia plant, supplemented with a small stream from an adjacent business. The ammonia production and the C02 available from the ammonia plant are never precisely in balance, in part because of the overall stoichiometric yields of ammonia and C02 from the natural gas feedstock. C02 is the limiting feedstock for the urea plant and its production rate in the ammonia plant sets the urea plant production rate since there is no intermediate C02 storage to buffer the urea production from the C02 production rate. Ammonia that is produced in excess of that which is used to make urea... 

Since urea is made from ammonia and carbon dioxide (both of which are produced in an ammonia plant), all urea plants are located adjacent to or in close proximity to an ammonia plant. Figure 11.1 shows how ammonia and urea plants can be connected111. 

Duplex stainless steel alloys are a mixture of ferritic (400 series) and austenitic (300 series) metals. They provide 1) resistance to stress corrosion and fatigue, 2) pitting resistance, 3) are suitable for a wide temperature range (-50°C to 280°C) and 4) are cost effective. In urea plants, duplex stainless steel is used to construct strippers, decomposers, condensers and pipe lines88. 

In the United States poor profitability resulted in the closure of five urea plants between 1999 and the end of 2002. These plants had a total capacity of 725 thousand tons per year - about 7 percent of the total US capacity in 1999. During this same period, about one-half of the operating plants were either idled for extended periods or turned down in their output because of natural gas price spikes that drove up the cost of ammonia230. 

Beginning in 1997, urea prices fell precipitously as China (who used to be a major buyer) began producing urea domestically. Between 1994 and 1997, China opened nine new urea plants and raised domestic production by 50 percent. This shifted world export product toward the US and lowered prices. At the end of 2001, China officially joined the World Trade Organization and re-entered the urea import market. The effect was to pull product away from the United States, which resulted in higher prices230. Historical urea prices are shown in Figure 11.10154. 

Nair, M.P.S., Control Corrosion Factors in Ammonia and Urea Plants , Hydrocarbon Processing, 80 (1), pp. 85-93, January 2001. 

Christensen, P.V., Revamping Ammonia Plants to Follow Feedstock Situation and Market Demands, Haldor Topspe Ammonia Publications, Presented at FAI Symposium on Improving Productivity of Ammonia and Urea Plants in New Delhi, India, www.haldortopsoe.com, Lyngby, Denmark, April 2001. 

For NH3 adsorption, experimental evidence has shown that the main interaction mechanism is H bonding of Si-OH to the N atom in NH3 [124], Ammonia gas is a widely used chemical in industry, and it has to be removed to less than one ppm, for instance, from the gaseous effluents of ammonia fertilizer plants, urea plants, and other sources [127], It is evident that silica is an excellent adsorbent of NH3 [124-126], Also, adsorption of ammonia on silica gel has received considerable attention recently, owing to its potential use in solar energy cooling cycles [128],... 

In 2001 most new urea plants are licensed by Snamprogetti (SNAM), Stamicarbon (STAC), or Toyo. SNAM utilizes thermal stripping whereas STAC and Toyo use C02 Stripping. At the end of 1996, about 70 SNAM plants, 125 STAC, and 7 Toyo plants had been built. STAC will design plants for over 3000 tonnes per day SNAM designs plants for about 2800 tonnes per day and Toyo designs plants for about 2300 tonnes per day as single train units.108... 

Three urea plants with Stamicarbon s new Granulation technology are under construction. 

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