Application Example Conveying and Storage of …

1 1 Smart Feeding & Conveying SolutionsApplication ExampleConveying and Storage of UreaIntroductionUrea is produced in prills, gran-ules, flakes, pellets, crystals and solutions, but it is traditionally marketed as prills or granules. The choice of the commercial pre-ferred form is normally associated with its Application , solubility, crushing strength and free-flowing pneumatic Conveying and Storage of urea must take into consideration the abrasive, hygro-scopic and heat-sensitive charac-teristics of this of a compound is defined as the moisture absorp-tion proper ties under specif ic conditions of temperature and humidity.

2 This value is repor ted as critical relative humidity (CRH). Urea s CRH value ranges from 70 to 75 at 30 C (86 F). The table below provides the CRH values of urea at different kg/m3 depending on the size of the process for manufacturing urea involves a combination of several major unit operations as illustrated in the diagram to the right. The shaded section deals with the solids formation, solids cooling, solids screening, solids coating and bagging, and/ or bulk is commercially produced from ammonia and carbon dioxide and takes place in two reactions. The first reaction (exothermic) of liquid ammonia with dry ice produces an intermediate product called ammonium carbamate.

3 The second reaction (endother-mic) produces urea and + CO2 (NH4)2CO3(NH4)2CO3 H2 NCONH2 + H2 Omoisture pick up, caking, dusti-ness and particle factors that most affect the moisture absorption-penetration characteristics of urea are its chemical composition, par ticle porosity, par ticle sur face area, and degree of is the formation of salt bridges or adhesive points of contact between the par ticles. Product related factors that influ-ence caking include: chemical composition and impurity con-tent, moisture content, size and shape of par ticles, mechanical strength and resistance to break-down, hygroscopicity, and Storage temper atur e.

4 Exter nal factor s that inf luence caking include: warehouse Storage temperature, atmospheric humidity, length of Storage and the pressure from stacking or being at the bottom of a C10152025304050 CRH % Urea is one of the most important nitrogen-containing fer tilizers in the world. It is also one of the raw materials for the manufacture of urea formaldehyde resins and ur ea-melamine-f or maldehyde * Optional with individual manufacturing practicesOFFSIZE RECYCLEUrea Manufacturing Process Schematicare produced from molten urea that is sprayed from the top of a prill tower. As the droplets fall through a counter current air flow, they cool and solidify into nearly spherical is a method where solids are built in layers on seed granules that are placed in a rotating drum granulator, cooler or Formation & HandlingThe urea solution that results in the second reaction can be used as an ingredient of nitrogen solu-tion fertilizers, or it can be con-centrated further to produce solid urea.

5 There are three methods for concentrating the urea solution: vacuum concentration, crystalli-zation, and atmospheric evapora-tion. The most common method is evaporation. The concentration process furnishes urea "melt" for solids solids are produced from the urea melt by two basic methods: prilling and granulation. Prilling is a process by which solid particles Also known as carbamate, urea is a white odorless solid with a density of 1333 kg/m3 at room temperature and a melting point of about 134 C (273 F). Urea s loose bulk density ranges from 700 to 800 kg/m3 and the tapped bulk density ranges from 820 to Pneumatic Conveying & StorageThe handling and Storage of urea requires special attention to sev-eral product related proper ties and external factors.

6 Most com-mon problems are associated with AMMONIACARBONDIOXIDESOLUTIONSYNTHESISADD ITIVES *SOLUTIONCONCENTRATIONSOLIDSFORMATIONSOL IDSCOOLINGSCREENINGCOATINGS *BULK LOADINGBULK LOADINGBAGGING2 Exhaust fansBin vent filtersDesiccantbed dryersBinunloaderAerolockAfter coolerScale hopperson load cellAeropass valvewith flexible hoseconnections A ValvesSlide gatesSlide gates located aboveeach reactorFlexPressure blowerTwo waydiverter valveFilterreceiverIn-linefilterRailcarM anifoldconveyinglinesVacuum blowerAerolockTw o waydiverter valvesTransportation The majority of solid urea product is bulk shipped in trucks, enclosed railroad cars, or barges, but ap-proximately 10 percent is bagged.

7 The flow diagram above shows the rail-unload and in-plant transfer operations in a melamine and urea resin production facility for the production of break-resistant melamine tableware. Urea is received in railcars and unloaded into one of two Storage tanks. Upon demand, the material is conveyed by pressure to one of two scale hoppers providing mate-rial to six Unload SystemThe system consists of a dual blower rail unload system with a filter receiver group capable of handling up to 9,000 kg/hr (20,000 lbs/hr) or more. The vacuum side of the system moves the material from the railcar to a filter receiver that ef fectively separates the material from the Conveying air.

8 Mounted below the receiver is a K-Tron Premier heavy-duty (HD) Aerolock rotary valve that meters the material into the pressure side of the system for final delivery to Storage . The Aero-lock is constructed of stainless steel and includes relieved tips to reduce material smearing. Automatic bin vents are placed on the top of each Storage tank to trap the airborne particles of material inside the tank while allowing the Conveying air to escape from the tank as it is filled. The trapped par-ticles are removed from the unit s filter bags by timed, compressed air pulses. The conveyed material remains in the Storage tank and clean air exhausts through the bin vent into the atmosphere.

9 After coolers are normally in-stalled at the discharge of the pressure blower s to keep the temperature of the Conveying air from reaching excessive levels and avoid changing the material s Premier filter receiver group Conveying urea from railcar to a Storage tank and blower assembly with silencers and after coolerPneumatic Conveying of Urea in a Melamine Production FacilityTime-Proven Pneumatic Conveying SystemsHigh level indicatorStorage TankLow level indicator3K-Tron Premier scale hoppers with Aeropass valvesStorageDue to urea s hygroscopic nature, the Conveying line from the railcar to the filter receiver is insulated to eliminate condensation in the line that can result from ambient temperature changes.

10 Desiccant Bed Dryers (DBD) also provide a blanket of dry air on the material while it remains in Storage . Diverter valves are used to allow a single Conveying line to be used to provide the dry blanket of air and the delivery of material. During the unloading of the railcar, the valve diverts to the line Conveying mate-rial. Following the unloading cycle, it automatically diverts back to the supply of dry air. Desiccant bed dryers provide fast, efficient drying while urea is TransferThe second phase of the system is the pressure Conveying system that allows the customer to trans-fer urea from either of the Storage tanks to one of two scale hoppers located above the reactors.