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Figure 4: Pressure Letdown StationTwo control valves in series are required to reduce the import pressure of 100barg to 5.7barg based on thesizing criteria for control valves and because of the large pressure differential required.Apart from the pressure letdown station the outlet of the fuel gas coil is controlled to a minimum of 15oC bya three-way TCV. The first coil inlet is uncontrolled. Both of the controls are traditional feed forward PIDcontrollers.Figure 5: Temperature Control ValveHeaterTCOutlet Header4.6Inlet HeaderProcess Safeguarding4.6.1 DepressurizationAll process equipment operating above 7barg or containing at least 4m³ of butane or a more volatile liquidunder normal operating conditions shall need to be provided with remotely operated vapourdepressurisation valves (Ref. 4).The BDV is also actuated automatically by a signal from the emergency shutdown system, initiated by fireor gas detection. A restriction orifice is usually used in conjunction with a BDV to restrict flow.The Scrubber is operated at 83 psig (5.7barg) and the pressure of the inlet stream is controlled by twopressure control valves in series.Under emergency conditions the fuel gas system (i.e., fuel gas inlet line, heater, PCVs and scrubber) can beisolated. The fuel gas scrubber is blown down to atmosphere via a 2” ball valve (Ref. 13).4.7IChemE Technical Report August 2009

The scrubber operates at pressures below 7barg and would not ordinarily require depressurization; howeverthe blowdown of the vessel via the provided valve is examined.The BDV and vent sizing has been based on the total inventory as a worst case. This is estimated to be40Sm3 of gas (See Appendix C). Depressurisation calculations have been carried out for the design as it isand also with the use of a restriction orifice.Aspen HYSYS is used to determine the maximum vent rate obtainable and minimum temperatures. Therequirement is to blowdown this inventory to 2.86barg (50% of the operating pressure of 5.7barg) within15mins. The depressurisation profiles are attached in Appendix C.The minimum temperature obtained is -9.4 C. The piping specification for ASME Class 150 (carbon steel)pipework has a minimum operating temperature of -29 C (Ref. 8). Thus carbon steel piping will beadequate for depressurisation requirements.4.6.2 DispersionDispersion modelling has been carried out for the vented gases using PHAST. The vented gases comprise amixture of hydrocarbons which can form a potentially flammable mixture when mixed with air, i.e.,between 5% and 15% methane in air; the lower and upper flammability limits (LFL and UFL). Thedispersion calculation determines the location of the vent.PHAST is third-party consequence modelling software used to analyse hazards resulting from leaks andemissions of fluids.PHAST is used to determine the hazardous area around the vent, i.e., the horizontal and vertical distancefrom the vent to the edge of the LFL gas cloud (Ref. 12). The scenarios for gas dispersion are given inTable 9.Table 9: Relief/Blowdown Scenarios – Fuel Gas SystemCaseScenarioFlowrate (kg/s)Pressure(barg)Temp. C)A1Fuel Gas Scrubber fire case0.3418.34107A2Fuel Gas Scrubber closed outlet0.6587.5876.2A3Fuel Gas Scrubber control valve failure0.6365.730.7A4Fuel Gas Scrubber blowdown - without relief orifice2.4665.730.7A5Fuel Gas Scrubber blowdown - with relief orifice0.0265.730.7Case A4 is the worst case scenario. Modelling was carried out under the worst case weather conditionsobtainable on site with the following results:Table 10: Fuel Gas Venting Dispersion Distances from Vent Outlet (Case A4)Horizontal distance to dispersion (m)Vertical distance to dispersion (m)100% LFL50% LFL100% LFL50% LFL1.774.66 9.74 13.371.824.49 10.81 15.172.416.11 5.42 7.292.947.07 3.47 4.564.8IChemE Technical Report August 2009

Graphical output from the dispersion calculations are shown in Appendix C.4.6.3 Radiation: Fuel Gas VentDuring venting there is a possibility that the vented gases could ignite with resultant damage topersonnel/equipment from radiation.Ref. 4 specifies the allowable radiation levels as a function of time. Solar radiation of 0.9kW/m² is assumedfor the location.Table 11: Recommended Design Total RadiationPermissible design levelConditions1.58 kW/m² (500 Btu/h ft²)Location where personnel with appropriate clothing may be continuously exposed4.73 kW/m² (1500 Btu/h ft²)Areas where emergency actions lasting several minutes may be required bypersonnel without shielding but with appropriate clothing6.31 kW/m² (2000 Btu/h ft²)Areas where emergency actions lasting up to one minute may be required bypersonnel without shielding but with appropriate clothing9.46 kW/m² (3000 Btu/h ft²)Value at design flare release at any location to which people have access; exposureshould be limited to a few seconds, sufficient for escape15.77 kW/m² (5000 Btu/h ft²)Structures/areas where operators are not likely to be performing duties and whereshelter from radiant heat is availableThe radiation levels from an ignited vent were modelled using FLARESIM - a third-party software used forthe design and rating of flare stacks.The height of the vent will be determined based on the radiation level measured at grade being below4.73kW/m² in order to protect personnel. Case A4 is used as basis and the vent is a simple 4” NBunimpeded pipe work vent stack venting to atmosphere.Appendix C contains the radiation contour plots for Case A4. It was determined that a 10.25m high ventwould be required. The 4.73 kW/m², 6.31 kW/m² and 15.7 kW/m² radiation contours would sit at theirlowest point at approximately 0m, 3m and 7.5 m above grade, respectively. The flame length wasestimated to be approximately 23.65 m. The horizontal distances (i.e. the radii) to radiation levels of4.73kW/m² and 6.3kW/m² were estimated to be approximately 17.1m and 10.2 m (at “head” height).The distances to these radiation contours may affect personnel on location and thus the vent height mayneed to be increased. The rate of “decay” of the radiation was also investigated with the following results.Table 12: Radiation Decay (Case A4)Time (sec)Mass Flow (kg/s)Volume Flow (m3/s)02.4665Distance(m)4.7 kW/m²6.3 kW/m²9.46 5--150.8050.9353---200.6050.7536Notes: The distances are the horizontal radii from the centre of the vent stack at head height (2 m above grade).4.9IChemE Technical Report August 2009

Table 12 shows that despite the fact that the initial distance to radiation level of 4.7kW/m² and 6.3kW/m²are high, this configuration of the vent stack may still be acceptable because the intensity of the radiationdecreases rapidly. The radiation intensity around the vent stack decreases to within acceptable levels within20 seconds because the vented flow is unrestricted.Radiation modelling was also carried out for Case A2, Fuel Gas Scrubber closed outlet. It was determinedthat the 4.73 kW/m², 6.31 kW/m² and 15.7 kW/m² radiation contours would sit at their lowest point atapproximately 2.2 m, 3.5 m and 9 m above grade, respectively. The flame length was estimated to beapproximately 12.6 m. This result was for the same vent stack of 10.5 m. On further investigation if thestack height were to be reduced to 9m, the 4.73 kW/m², 6.31 kW/m² and 15.7 kW/m² radiation contourswould sit at their lowest point at approximately 1.4 m, 3 m and 6.3 m above grade, respectively.However, the Case A2 vent radiation scenario is only applicable if the relief/vent piping is modified toinclude a restriction orifice downstream the blowdown valve thus restricting its flow.4.6.4 Over-Pressure ProtectionIn addition to the blowdown system there is a PSV on both the Fuel Gas Scrubber inlet line and thescrubber itself, both are set at 100psig.The over-pressure relief devices (PSVs) protecting the fuel gas system have been sized in accordance withAPI RP 520 (Ref. 5) and API RP 521 (Ref.4) for the most severe individual relief condition. Table 13identifies the applicable relief conditions considered for the sizing of the PSVs.Table 13: PSV Relief ConditionsCase1.Closed / blocked outlet2.Control valve malfunction3.Excess heat input/vapour generation4.External fireThe relief valve has been selected in accordance with API Standard 526 (Ref. 6).The operating pressure of the scrubber is 83psig (5.7bar). The PSVs are 3” x 4” and calculations are carriedout to determine the suitability of these safety valves for the process. The minimum size of PSV required is1.5” x 3” thus the pre-installed PSVs are adequate. See Appendix B3 for detailed calculations.4.7Line SizingThe sizing of lines for the project was done as per company practice and principles which were based onengineering standards (Ref 8 and Ref 9). The equations and correlations used are as follows:vπd 2Line velocities are estimated using: Q 4Eqn 4-4Where:Q Flowrate (m3/s)V velocity (m/s)D inside pipe diameter (mm)4.10IChemE Technical Report August 2009

The pressure drop for liquid or gas lines are calculated using the Darcy formula: P100 m w2 62530 f ρ d5 Eqn 4-5Where:ΔP100m Pressure drop (kPa/100m)W Mass flow (kg/hr)ρ Density (kg/m3)f Moody friction factord internal diameterThe Moody friction factor is a function of the Reynolds number and the surface roughness of the pipe. TheMoody diagram (Ref. 8) may be used to determine the friction factor once the Reynolds number is known:Re ρdvµEqn 4-6Where:Re Reynolds numberρ Density (kg/m3)v Velocity (m/s)d internal diameter (mm)μ Viscosity (cP)Finally, erosional velocities are calculated as per Ref. 7: Ve Cρ m 0.5Eqn 4-7Where:V e Erosional velocity (ft/s)C Constant (100 for continuous flow)ρ m Gas/Liquid density (lb/ft3)The inlet line to the fuel gas system is 4”, ASME CL 900. From calculations this size is adequate. Theinter-connecting lines within the process are also 4” (and ASME CL 150) and the distribution lines are 2”ASME CL 150 lines. The line sizing and calculations are given in Appendix B4.4.11IChemE Technical Report August 2009

5.5.1CONCLUSIONS AND RECOMMENDATIONSConclusions1. Fuel gas demand is expected to be 2.39MMscfd, which is within the design rate of 2.5MMscfd.2. The supplied scrubber is adequate for project requirements.3. The supplied heater is adequate for project requirements.4. The minimum temperature on blowdown is -9.4oC which does not exceed the ASME CL 150 pipingspecification.5. Dispersion - the 50% LFL from the Fuel Gas Vent was estimated to be 7m horizontally. This is notexpected to pose a hazard to personnel or equipment so long as the fuel gas vent is higher than anyequipment within 7m of the vent.6. Radiation - A Fuel Gas Vent of 10.25m high will expose personnel and equipment to radiation levels ofnot more than 4.73kW/m². This radiation level has a radius of approximately 17.1 m and will last forless than 20 seconds.5.2Recommendations1.A minimum Fuel Gas Vent height of 10.25m above grade is recommended.2.Modifying the vent piping downstream of the BDV to include a restriction orifice will mean that thevent height can be reduced to 9 m.5.12IChemE Technical Report August 2009

6.REFERENCES1. Client Scope of Work and Vendor Data2. Perry’s Chemical Engineering Handbook, Vol. 1 & 2, 7th Ed.3. Coulson and Richardson’s Chemical Engineering, 5th Ed.4. American Petroleum Institute: “API RP 521: Guide for Pressure Relieving and DepressurisingSystems”, 4th Ed, March 1997.5. American Petroleum Institute: “API RP 520: Sizing, Selection and Installation of PressureRelieving Devices”, 7th Ed, January 2000.6. American Petroleum Institute: “API Standard 526: Flanged Steel Pressure Relief Valves”, 5th Ed,June 2002.7. American Petroleum Institute: “API RP 14: Design and Installation of Offshore ProductionPlatform Piping Systems, 5th Ed, Oct 1991.8. GPSA: “Engineering Data Book”, 12th Ed. 2004.9. Woodhill Frontier Engineering Standards10. Masoneilan Control Valve Sizing Handbook, bulletin OZ1000, 200011. The Centre for Marine and Petroleum Technology (CMPT): “A Guide to Quantitative RiskAssessment for Offshore Installations”, Publication 99/100.12. Energy Institute: “Model Code of Safe Practice Part 15: Area classification code for installationshandling flammable fluids”, 3rd Edition, July 2005.13. Fisher Vee Ball Rotary Valves, Doc. No. D350004X012/MS11-CD171/4-066.13IChemE Technical Report August 2009

APPENDICESA1: FUEL GAS SYSTEM - PFD6.14IChemE Technical Report August 2009

A2 - FUEL GAS BALANCETable 14: Heat and Mass .265.71.723415.6818.9628.3701.515.70.7VAPOUR FLOW (kg/hr)VAPOUR DENSITY (kg/m3)VAPOUR MWLIQUID FLOW (kg/hr)LIQUID DENSITY (kg/m3)PRESSURE (barg)TEMPERATURE 5.08912NORMAL DESIGNVAPOUR VAPOUR7235.3818.795.715.013NORMAL DESIGNVAPOUR 8.785.715.010NORMAL DESIGNVAPOUR AL DESIGNVAPOUR VAPOUR325.3818.795.715.0335.3818.785.715.011NORMAL DESIGNVAPOUR 698.7327.9707.840.0-1.56.15IChemE Technical Report August 2009

B1 - CALCULATION: FUEL GAS SCRUBBERFeed data under normal case and worst case (Fuel gas with heater failure) scenarios.ValueNormal caseWorst caseTemperature (T)Pressure (P)Fluid PropertyoCKpaUnit0.70673-26.11673Liquid Density (ρ l )kg/m³701.6688.0Vapor Density (ρ v )kg/m³5.688.78Mixed Density (ρ m )kg/m³5.756.45Liquid Mass Flow (F L )kg/h28.359.6Vapor Mass Flow (F V )kg/h23412302Inlet Mass Flow (F M )kg/h23702362Liquid Volume Flow (Q L )m³/h4.03E-028.65E-02Vapor Volume Flow (Q V )m³/h412.4366.2 ρ ρv Using Stokes law, Ref 3: VV K l ρv A 0.5Eqn. B1-1QVQ Tand Ll lVVAEqn. B1-2, B1-3Where:VV K ρv A max allowable vap vel (m/s)constantρl liquid density (kg/m³)T holdup time (mins)Ll liquid depth (m)QV Ql vap density (kg/m³)cross sectional area (m²)vap volumetric flowrate (m³/s)liquid volumetric flowrate (m³/s)For a vertical separator of height 3 m,K 0.037m/s, From (Eqns. 10 - 12), the following is calculated:UnitNormal caseWorst .38E-025.10E-02Sketch 600mm0.15 (Min)0.4m Min (1)D (1.0m Min) (2)D/2 (0.6m Min) (3)1 2 3 4 0.410.600.15mmmmTan-Tan 2.15mLiquid Level0.15m (Min) (4)6.16IChemE Technical Report August 2009

B2 - CALCULATION: PRESSURE REDUCTION STATIONThe control valve sizing is carried out as per GPSA (Ref. 8) and (Ref. 10)Gas lines:The valve sizing equations used is: Cv where,wN 8 FP P1YT1ZXMEqn. B2-1q, fluid volumetric flowrate in m3/hrw, fluid mass flowrate in kg/hrN 8 , numerical constant 94.8F p , pipe geometry factorP 1 , fluid inlet pressure in baraP 2 , fluid outlet pressure in baraM, fluid molecular weightT, gas inlet temperature in KZ, compressibility factorY, expansion factor is calculated by: Y 1 X3Fk X TEqn. B2-2(Y should not be less than 0.67. Also X should not exceed FkXc for gas)Where, Fk, ratio of spec. heats is calculated by: Y 1 Xand X T ( P / P1 )3Fk X TEqn. B2-3, B2-4Two-phase flows:The valve sizing equation used is: Cv where,wN 6 Fpff p f γ f fg p g γ g Y 2Eqn. B2-5w, fluid mass flowrate in kg/hrN 6 , numerical constant 27.3F p , pipe geometry factorf f , weight fraction of liquid phasef g , weight fraction of vapor phase p f , pressure drop for liquid phase in bara p g , pressure drop for vapor phase in baraγ f specific weight (mass density) in kg/m3 (for liquid phase)γ g specific weight (mass density) in kg/m3 (for vapor phase)Actual pressure drops are used for Dpf and Dpg, but with individual limiting pressures: p f FL ( p1 FF pv ) and p g Fk xT p12Eqn. B2-6, B2-7Summary of results:Inlet temperatureOutlet temperatureInlet pressureOutlet pressureCVValve typeoCoCbargbar-PCV 144.849.33100191.51GlobePCV 29.330.70195.738.33Globe6.17IChemE Technical Report August 2009

B3 - CALCULATION: PRESSURE SAFETY VALVESDesign DataOperating pressureDesign pressureRelieving pressure set pointOperating temperatureAllowable over pressureRelieving pressureRelieving temperature83.0100100492.6psigpsigpsig 01107.6629.276.4169.5%psigbarg R C Fbargbargbarg C P Relieving temperature: T1 1 Tn Pn Eqn. B3-1Where:P 1 Relieving pressureP n Operating temperatureT n Operating temperatureClosed Outlet Case: Relieving rate (vapour relief)k 1WA CK d P1 K b K cTZ 2 k 1, where C 520 k M k 1 W (relief load)k (ratio of specific heats)C (co-efficient)Kd (co-efficient of discharge)Kb (capacity correction factor)Kc (rupture disc correction)Z (compressibility)M (molecular weight)T (relieving temperature)P1 (relieving pressure)A (effective discharge 50.711kg/hrRpsiain²Eqn. B3-2, B3-35,161lb/hrAPI RP 520 [3.6.2.1.1]API RP 520 [3.6.2.1.1]API RP 520 [3.6.2.1.1]76.4 CClosed Outlet Case: Relieving rate (liquid relief)A Q38 K d K w K c K vGp1 p2Q (flow rate)Kd (co-efficient of discharge)Kw (back pressure correction)Kc (combination correction)Kv (viscosity correction)G (specific gravity)p 1 (relieving pressure)p 2 (back pressure)A (preliminary discharge area)Eqn. gin²6.3bbl/d0.2USGPMAPI RP 520 [3.8.1.2]API RP 520 [3.8.1.2] - assuming P2 / P1 0.15API RP 520 [3.8.1.2]API RP 520 [3.8.1.2] - preliminary estimateat flowing temperature(assumed)6.18IChemE Technical Report August 2009

Re Q(2800 G )µ AEqn. B3-5μ (absolute viscosity)A (effective discharge area)Re (Reynold's Number)0.5550.111.95E 3cPin²-Kv (viscosity correction)A (effective discharge area)0.9410.001in²0.712in²0.712H1501.5 x 3in²Ref. 6lbMinimum sizeat flowing temperaturefrom API Std 526 (standard orifice areas)N Re adjusted valueClosed Outlet Case: PSV sizingA (total discharge area)(vapor liquid relief)PSV selectionA (maximum discharge area)Relief orifice designationValve body ratingValve body sizeNote: the PSV was sized for other cases such as fire and control valve failure. The closed case was thelargest relief load.

The fuel gas will be required to be treated to ensure that the fuel gas specification requirements advised by the heater and generator vendors is met , such that no power loss occurs due to fuel gas quality . The system in designed for 2.5MMscfd gas. The scope of work is to design the fuel gas treatment and distribution for the pumping station.