Construction Details of Urea Reactor (UR-211) Presented By : Imran Khan Apprentice Engineer P. No. 20320 Batch # 14 Objective Multi-layered vessel fabrication Welding and fabrication techniques Modifications in Reactor Stamicarbon Urea Synthesis Process
Outlines Urea Synthesis Process Specifications of Urea Reactor (UR-211) Mechanical Construction - Shell - Leak Detection System - Hemispherical Heads - Sieve Trays - Top Cover & Nozzles - Insulation Installation of Siphon Jet Pump Current Status - Stamicarbon Inspection - Lining Repair Job Urea Synthesis Process Urea is produced from carbon dioxide and ammonia and
composed of two chemical reversible reactions 1) 2NH3 + CO2 NH4COONH2 (-28.4 Kcal/ Mole) 2) NH4COONH2 NH2CONH2 + H2O (+5.97 Kcal/ Mole) The first reaction is fast and takes place in very short period of time, whereas second reaction is relatively slow and requires longer time Off Gases Off Gases to Vent thru UC-291 4kg/cm2 Absorber Reactor
HPCC UR-211 UH-241 Scrubbe rUH-221 Carbamate Solution from UP-271 HV-221.09 Gas HV-231.02 UJ-221 34% Urea Solution Ejector
Liquid Stripper NH3 from HP-Pump (UP211) UH-231 CO2 In from CO2 Compressor HV-231.07 HV-221.10 LV-231.04 Urea Solution 54% to LP Section Specifications of Urea Reactor (UR-211) Internally lined/overlayed multilayered vertical vessel with sieve trays & overflow pipe as internals. Fabricated by M/s. Nooter Corporation USA in year
1997-98. Process Design Codes & Standards Construction Details Reactor Shell Hemispherical Heads Inlet Nozzles Reactor Overflow R8 R8 R7 R7 R 66 R R 55 R Sieve Trays Top cover & Outlet Nozzles
R 44 R Insulation Modifications Siphon jet pump Installation R 33 R R2 Provision of Manholes in Trays R1 R2 R2 Shell Can 3 Plates per Wrap, Total 39 Plates per Shell Can Wrap Plates (13 Nos.) Width = 3042mm , Length= 3669 mm Thickness = 7.94mm
Material = SA-724 Gr. B Liner Nos.) Core Plate (01 Nos.) Width = 3669 mm , Length = 9242 mm Thickness = 19.1 mm (01 Reactor Shell Core Plate Machining of Leak detection grooves and barrier layer faces Weld seam barrier layer is overlayed on premachined faces by using 310 MoL (25:22:2) through plasma arc welding (PAW) on inside of core plate
Longitudinal welding : SMAW with E- 9018-D1 as filler rod Groove Barrier faces 3669 mm 9242 mm 19 mm for layer Leak Detection Grooves(35 mm) Welding of Wrap Plates Drilling of vent holes prior to welding for venting of welding gases Qty
: 04 (Both ends of each Shell Can ) Dia. : 9.5 mm up to core plate in first 3 wrap plates and 19.5 in the remaining 10 Nos. of plates At 90 degrees apart radially drilled in wrap plates Longitudinal seams : SMAW process Electrode : E-9018-D1 Liner Welding 04 plates are rolled, welded and inserted in each shell can - 03 longitudinal butt welding of rolled plates -
Final Liner weld seam after insertion in shell can - Welding technique Welding) : PAW (Plasma Arc Shell Cans Welding Both ends of each Shell Can are build-up using SMAW and E-9018-D1 as Electrode for integrating core and all wrap plates Circumferential welding joint Root pass : SMAW & E-9018D1 as Electrode (at core plate ) 02 barrier layers welded by using plasma arc welding with 310 MoL prior to final circumferential weld joint of the liner Leak Groves & Liner Welding B A
A B See Details Hemispherical Heads Material : A-516 Gr-70 Plate thickness : 135 mm Process : Hot forging Thickness after forging : 119mm Heat treatment : Normalizing (To relieve work hardening stresses) After dimensional checks bevels were made on circumferential ends as per drawing (at 8). Hemispherical Heads Manhole and nozzles are fabricated and installed by full
penetration welding Manhole is welded by SMAW using E- 9018 D1 as Electrode. After this welding the inside surface of heads is strip overlayed by Plasma Arc Welding technique using 310 MoL as filler in 03 layers. Head to Shell Weld Seam STD. 8 U-Bevel 3 To 1 Taper Weld Build up Hemi. Head Core Plate 25 Min. Liner Plate 30 Head Overlay SIEVE TRAYS Total No. of Sieve Trays : 10 EA
Overflow Pipe No. of segments per tray : 06 EA Material : 316 L (BC01) Thickness : 10 mm Clamping Nut Bolts : M14 (25/22/2) # Tray No. No. of Holes Hole Dia.
3 7, 8, 9, 10 570 8 79 Top Cover & Bolting Top cover Outside Diameter : 1220 mm Thickness of Cover : 331 mm Material of Cover : A-266 class 2 Top Cover Weight : 2.5 Tons Number of Nozzles : One 6 and other is 3 Overlay
: 9.5 mm (310 Mol , PAW) Number of Holes : 16 (diameter: 96 mm) Gasket : 804 mm I.D x 854 mm O.D (Serrated type with PTFE envelope, BC-03) Detail of bolting Number of bolts : Size of bolts : Length of Bolts Material of Bolts : 16 each M-90 X 6 : 632 mm A-193 Grade B7 Top Cover Siphon Jet Pump Skirts Reduction of HS steam consumption
(25-60 Kg/hr) in stripper Improvement in urea conversion Improvement in gas-liquid mixing Improvement in equal temperature distribution throughout the reactor Reduction in stagnant zones in reactor Easy to install on conventional trays
TRAY OVERFLOW PIPE MANHOLES Installation Details 900 mm Siphon Skirt 08 Segments 500 mm Guide Ring Siphon Jet Pump Skirts Inspection History of UR-211 TA-2000 &TA-2001 : Jointly executed by FFBL & Stamicarbon Revealed no major abnormality UT of Liner revealed a corrosion rate of about 0.05 mm/yr.
TA-2004 Siphon jet skirts were installed Minor repair of pinholes defects was carried out using pencil grinder TA-2006 Minor repairs were carried out as previously But increase corrosion rate of liner observed as compared to previous years TA-2007 To confirm the thickness monitoring results achieved during TA-2006 Increase in corrosion rate i.e. 0.15mm/yr and 0.213 mm/yr Minimum thickness of 7.41mm at top compartment Inspection History of UR-211 TA-2009 Inspection and Eddy Current thickness measurement by Stamicarbon SIIC cracks found by Eddy Current testing just below the top head to shell circumferential weld Surface was ground smooth using pencil grinder. DPT revealed cracking and subsequent grinding indicated the ~4mm deep crack
Liner Thickness Measurement: Compartmen t 1997 Average(m m) 2009 (mm) Min Max. . Avg. Corrosion Rate (mm/ yr) 1 (Top) 8.61 7.1 7.6
7.35 0.15 5 (Middle) 8.67 7.5 8.2 7.78 0.11 Inspection History of UR-211 Stamicarbon TA-09 Inspection Recommendations: Partial Relining of the top compartment within 1-2 years Lower the liquid level in the reactor up to meter
below the top circumferential weld seam Improve insulation gas phase area in top Next inspection after 4 years effective on-stream time But, relining to be checked after 1 year THANK YOU Questions-Answers Shell Liner Plates are hot rolled, solution annealed and pickled. dimensions Length Width : 3680 mm : 2292 mm (radius) Thickness : 8.4 mm Quantity : 04 plates per shell can (total 32 plates in 08 shell cans) Material : SS-316 LN (Stamicarbon BC. 01)
BACK Liner long Weld seam Section A-A Core Plate 38mm 16mm Leak detection Grooves 5mm 5 mm 30 Liner PAW Weld seam barrier layer overlaid on premachined faces (PAW). 60
8 Min. Gap Liner long Weld seam BACK Circumferential Weld seam 152 mm 4 Nos. Vent Holes located 90 apart thru each end of each Shell Can -3000# Half coupling 128.5 mm Wrap Plates 30 Core Plate 19.05 mm 3 mm
Liner 8.4 mm Liner Circumferential Weld Seam BACK Leak Groove and Hole SCH-160 Pipe SS-316L Circ. Leak Groove -NPT with SS Plug 10mm Leak Groove Long. Leak Groove BACK Strain Induced Integranular Cracking (SIIC)
SIIC is an electrochemical corrosion mechanism in combination with deformation (strain). The following conditions are a pre-requisite for occurrence of these cracks : The presence of an electrolyte as a result of condensation of ammonium carbamate in the gas phase or liquid phase. If the liquid level is extremely high, such cracks are also observed in the liquid phase because an electrolyte is always present. Plastic deformation (=strain) of the liner material. Plastic deformation of the liner plates will always occur during start up of the plant (heating the synthesis section with steam). Other conditions can enhance this failure mode, such as : inferior liner material and/or weld quality ; presence of chloride and/or sulphur in the porous oxide layer ; an increased gap between the liner plates and the shell ; and large number of pressure cycles (start/stops). BACK SIIC-(Grinding using Pencil grinder) BACK Chemical Compositions
Material C (max ) 0.03 Cr Ni Mo Si Mn N 18-20 8-12 ---
11.5 / 11.5 184 BACK Safurex Corrosion Resistance Low overall cost Low weight BACK Plasma Arc Welding (PAW) Plasma.arc welding (PAW) is a advanced version of the gas tungsten arc welding (GTAW). GTAW has a free-burning arc, which is unstable and tends to wander in the low current range. With increase in current, the arc power increases and the arc diameter also increases. This leads to a lack of concentrated power in the workpiece, which results in a bigger seam and a larger heataffected zone. Unlike GTAW-welding torches, PAW uses a constricting nozzle and employs two separate gas flows, which give rise to a concentrated plasma arc having a narrow
columnar shape. The plasma column is now stabilized along the axis of the electrode and is more intense than the GTAW-welding arc. The column temperature in PAW is 10,000-24,000 K as compared to 8,000-18,000 K in case of GTAW BACK Process Design Type of Reactor : Plug Flow Reactor Density of Inlet Liquid Density of Inlet Gas : 990-1130 Kg/m3 : 114.7-126 Kg/m3 Operating Temperature : 170.2 C at inlet & 183 C at outlet Flow Rate of Inlet Gas: 198 m3/hr
Flow Rate of Inlet Liquid : 219 m3/hr Reactor Hold up Volume : 192 m3 Residence Time : 60 minutes (at 100 % load) Inside Diameter of Reactor Number of Sieve Trays : 2917 mm : 10 Height of Reactor : 29100mm Codes& Standards Design Code : ASME Boiler & Pressure Vessel Code, Section VIII, Division-2. 1995 Design Pressure : 162 Kg/cm2 (2304 psig)
Design Temp : 190 C (374 F) Hydro test Pressure : 2880 psig Corrosion allowance : 1mm Ext. on Head & Shell, 2mm Int. & Lining Wind Loading : Per UBC 88, Wind Speed = 150 Km/hr, Exposure C Radiography : 100 % all liner, Shell can and shell to head weld joints PWHT : Heads only Leak Detection System
8 Nos. of Inlet air lines Leak Detection Grooves Ammonia Analyzer HP Urea Synthesis Loop M90 Studs Construction Details (16 nos) Reactor Shell Multilayer Shell Can, R8 Hemispherical Heads (Typical) 3670 mm (Typical)
R7 Sieve Trays R6 Reactor Overflow R5 Inlet / Outlet Nozzles R4 Modifications Siphon Jet Pump Installation Provision of Manholes in Trays Top Hemispherical Head Sieve Trays (10 Nos.) Overflow Pipe
R3 R2 R1 Bottom Hemispherical Head 34% Urea Liquid Inlet Gas Inlet
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