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 2NH3 + CO2 NH4COONH2 (-28.4 Kcal/ Mole) 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

Carbamate Solution from UP-271 Off Gases Off Gases to Vent thru UC-291 4kg/cm2 Absorber HPCC UH-241 Reactor UR-211 ScrubberUH-221 Carbamate Solution from UP-271 HV-221.09 HV-231.02 Gas Liquid HV-221.10 Ejector UJ-221 34% Urea Solution StripperUH-231 NH3 from HP-Pump (UP-211) CO2 In from CO2 Compressor Urea Solution 54% to LP Section HV-231.07 LV-231.04

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 Sieve Trays Top cover & Outlet Nozzles Insulation Modifications Siphon jet pump Installation Provision of Manholes in Trays R 6 R 5 R 4 R 3 R 2 R1 R 2

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 (01 Nos.) Core Plate (01 Nos.) Width = 3669 mm , Length = 9242 mm Thickness = 19.1 mm Material = SA-724 Gr. B

Reactor Shell Core Plate Machining of Leak detection grooves and barrier layer faces Weld seam barrier layer is overlayed on pre-machined 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 3669 mm Groove for Barrier layer faces Leak Detection Grooves(3×5 mm) 9242 mm 19 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 : PAW (Plasma Arc Welding)

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 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. 8⁰ U-Bevel 3 To 1 Taper Weld Build up Hemi. Head Core Plate 25 Min. 30 ̊ Liner Plate Head Overlay

  SIEVE TRAYS Total No. of Sieve Trays : 10 EA No. of segments per tray : 06 EA Material : 316 L (BC01) Thickness : 10 mm Clamping Nut Bolts : M14 (25/22/2) Overflow Pipe # Tray No. No. of Holes Hole Dia. (mm) Pitch (mm2) 1 1, 2, 3 1270 8 52 2 4, 5, 6 920 62 3 7, 8, 9, 10 570 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 : 16 each Size of bolts : M-90 X 6 Length of Bolts : 632 mm Material of Bolts : 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 with minor modifications

Sieve Trays after Modification S.No Tray No. No. of Holes Hole Dia. (mm) Pitch (mm2) No. of Holes after Modification 1 1, 2 1270 8 52 730 2 3 600 4 920 62 5, 6 480 5 7, 8, 570 79 400 345 6 9, 10

Siphon Jet Pump Skirts SIPHON SKIRT GUIDE RING OVERFLOW PIPE EXISTING SIEVE TRAY 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: Compartment Average(mm) 2009 (mm) Corrosion Rate (mm/yr) Min. Max. Avg. 1 (Top) 8.61 7.1 7.6 7.35 0.15 5 (Middle) 8.67 7.5 8.2 7.78 0.11 10 (Bottom) 8.5 8.38 1.04

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 ½ 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 BACK Plates are hot rolled, solution annealed and pickled. dimensions Length : 3680 mm Width : 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 Leak detection Grooves 16mm 5mm 30⁰ 5 mm PAW 8 Min. Gap 60 ⁰ Liner Weld seam barrier layer overlaid on pre-machined faces (PAW).

Liner long Weld seam BACK

Circumferential Weld seam 4 Nos. Vent Holes located 90 apart thru each end of each Shell Can 152 mm ½’’-3000# Half coupling 128.5 mm Wrap Plates 30 ̊ 3 mm Core Plate 19.05 mm Liner 8.4 mm

Liner Circumferential Weld Seam BACK

Leak Groove and Hole BACK ¾ ’’ SCH-160 Pipe SS-316L ½’’-NPT with SS Plug Circ. Leak Groove 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) Cr Ni Mo Si Mn N 304L 0.03 18-20 8-12 --- 0.75 2 0.10 304L U.G (BB) 17-20 1 0.22 316L 16-18 10-14 2-3 316L U.G (BC.01) 17-18.5 13-15 2.2-3 X2CrNiMo 25 22 2 (BC. 05) 0.02 24.5-25.5 21-23 1.9-2.3 0.40 0.1-0.16 Safurex (BE. 06) 28-30 5.8-7.5 1.5-2.6 0.5 0.8-1.5 0.3-0.4 BACK

Mechanical Properties Material Yield strength (Mpa) 20 ̊/225 ̊C Tensile strength (Mpa) Elongation (%) Thermal Expansion* 10-6/ ̊C Module of Elasticity N/mm2 at 20 ̊/225 ̊ C. Steel 248 / 202 482 / 482 >16 12.5 / 12.5 190 BC.01 190 / 135 490 / 412 > 40 16.5 / 16.5 184 BC.05 270 / 195 580 / 495 > 30 Safurex 650 / 465 800 / 717 > 25 11.5 / 11.5 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 work-piece, which results in a bigger seam and a larger heat-affected 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 : 990-1130 Kg/m3 Density of Inlet Gas : 114.7-126 Kg/m3 Operating Temperature : 170.2º C at inlet & 183º 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 : 2917 mm Number of Sieve Trays : 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 : 190º C (374º 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

Construction Details Reactor Shell Hemispherical Heads Sieve Trays Multilayer Shell Can, R8 (Typical) M90 Studs (16 nos) Liquid Inlet 3670 mm (Typical) Top Hemispherical Head R7 R6 R5 R4 R3 R2 R1 Bottom Hemispherical Head Sieve Trays (10 Nos.) Overflow Pipe Gas Inlet 34% Urea Reactor Shell Hemispherical Heads Sieve Trays Reactor Overflow Inlet / Outlet Nozzles Modifications Siphon Jet Pump Installation Provision of Manholes in Trays