3.2.3Mechanical Design of Separator3.2.3.1Design PressureIt is known that the design pressure must be designed to withstand the maximum pressure to which it is likely to be subjected in operation. The design pressure is normally taken as the pressure at which the relief device is set. This will normally be 5 to 10% above the normal operating pressure (Sinnot and Towler,2009).Therefore, the design pressure will operate 10% above the operating pressure as a safety factor. Operating pressure = 1atm = 1.013bar

Design Temperature = 105 C105 C = 378K; at 378K, Maximum Allowable Design Stress is 16.48ksi by doing interpolation (from Table 3.21)Temperature (K)Maximum Allowable Stress

30015.0

37814.2

50012.9

S, Maximum Allowable Design Stress

14.18ksi X = 97.77 E, Welding Efficiency = 1

3.2.3.2 Material for ConstructionThe process chemicals which deal with nitric acid and sulfuric acid solution are corrosive chemical. Hence, according to Sinnot and Towler (2009) the most suitable material use to construct the separator is stainless steel 304 which it is highly corrosive resistance.

3.2.3.3 Maximum Allowable Design StressAccording to Table 3.21, the typical maximum allowable design stress,S after being interpolate at 105oC (378K) for Stainless Steel 304L is 14.18ksi (97.77 ).

Table 3.21 Typical Maximum Allowable Stresses

3.2.3.4Minimum Wall Thickness, tIn order to ensure that vessel is sufficient to rigid to withstand its own weight and any incidental load, there will be a minimum wall thickness. According to Sinnot and Towler, 2009,the minimum thickness equation is : ................................................................................ (3.2.23)where,t = minimum thickness of the plate required Pi = internal pressure, 0.869 N/mm2 Di = internal diameter, 1190 mm S = design stress, 97.77 N/mm2E = Joint efficiency,1

Taking into consideration that the corrosion allowance is 2mmt=0.33m= 2.33 3

3.2.3.5Head and ClosureThere are several types of head and closure of a cylindrical vessel including hemispherical, ellipsoidal, torispherical and flat plate. According to Sinnot and Towler (2009), the most suitable head and closure for vassel in which the the operating pressure less than 15 bar is torispherical and ellipsoidal head. Since the operating pressure is 5 bar both of it were chose to be compared with.

Figure 3.6: Domed heads. (a) Hemispherical. (b) Ellipsoidal. (c) Torispherical

a)Ellipsoidal Head The calculation of minimum thickness of ellipsoidal head was based on equation below: ................................................................ (3.2.24)

Taking into consideration that the corrosion allowance is 2mmt=0.33= 2.33 3

b)Torispherical Head The calculation of minimum thickness of torispherical head was based on equation below: .......................................................................... (3.2.25)Where:Crown Radius, Rc = Di =

Taking into consideration that the corrosion allowance is 2mmt=0.295= 2.295mm 3

3.2.3.6Dead weight of Vessela)Weight of ShellFor preliminary calculation the approximate weight of a cylinder steel vessel with domed end, and uniform wall thickness can be calculate by using the following equation: ............................................. (3.2.26)Where: The average wall thickness, tThis value is calculated based on 5 separated section where build up by adding 2mm, from vessel minimum thickness as a much thicker wall will be needed at the column base to withstand the wind and dead weight load.

The mean diameter of vessel, DM

A factor, CwTake 1.08 for vessels with only a few internal fittings.

b)Height or length between tangent lines, HvTake 2.685 m as the height (as calculated in chemical design section) Therefore,

3.2.3.7 Weight of Insulation, Generally, all equipment in the contact section of an acid plant is insulated for the purpose of heat conservation and process temperature maintenance.Insulating material: Mineral wool Mineral wool density: 130 kg/m3Insulation thickness: 70mm (Harish, 2011)

a)Approximate volume of insulation,

..................................... (3.2.27)

b)Weight of insulation

c)Coupling weight for fittings,

................................................... (3.2.28)

1. 2. 3. 3.1. 3.2. 3.2.1. 3.2.2. 3.2.3. 3.2.3.1. 3.2.3.2. 3.2.3.3. 3.2.3.4. 3.2.3.5. 3.2.3.6. 3.2.3.7. 3.2.3.8. Weight of Demister, Stainless steel 304L wire mesh is selected as material of construction of demister pad due to its excellent resistance against acid, alkali, heat and corrosion. a)Approximate volume of demister pad,

............................................................ (3.2.29)

Where:, 1.04m, 0.15m

b)Weight of demister pad, .................................................................................. (3.2.30)

c)Total Vessel Weight,

+ + ................................................. (3.2.31) + +

3.2.3.9 Wind LoadA vessel must be designed to withstand the weight bending stress cause by the highest wind speed that is likely to be encountered at the site during the life of the plant. For a preliminary design, a wind speed of 160km/h can be used equivalent to wind pressure PW, 1280N/m2.a)Mean diameter, Dm ...................................... (3.2.22)

b)Loading (per linear meter), Fw ................................................................. (3.2.23)

c)Bending moment, Mx ........................................................ (3.2.24)

3.2.3.10 Analysis of the StressesThe stress analysis of separator is analyzed to determine the stress exert on a body vessel. This section will show the analysis of primary stress, dead weight stress, bending stress and resultant and longitudinal stress.a)Longitudinal, and Circumferential Pressure Stress, Longitudinal pressure stress,Use the maximum thickness

............................................................................. (3.2.25)

Circumferential Pressure Stress, ....................................................................... (3.2.26)

b)Dead Weight Stresses,It is a direct stress due to the weight of the vessel, its content and any attachment. The weight dead stress is significant compared to the other stress. .................................................... (3.2.27)

c)Bending Stresses,Bending moment is a vital in stress analysis as this stress will cause by the wind load of tall self supported vessels, dead weight and wind loading on piping and equipment Outer Diameter, Do...................................................... (3.2.28)

Second Bending Moment, ..................................................... (3.2.29)

Bending Stresses, ................................................... (3.2.30)

d)The resulted longitudinal stress, ...................................................... (3.2.31)is compressive and therefore negative value

The difference between the principles stresses will be on the down-wind side: .................................. (3.2.32)

Because of this value smaller than design stress, 112.38 N/mm2 it means the design is satisfactory.

e)Critical Elastic Stability, The critical buckling stresses are given as: ............................................................. (3.2.33)

The maximum compressive stress will occur while the vessel is not under pressure;

resulting a value which is less than critical buckling stress, thus the design is acceptable.

1. 2. 3. 3.1. 3.2. 3.2.1. 3.2.2. 3.2.3. 3.2.3.1. 3.2.3.2. 3.2.3.3. 3.2.3.4. 3.2.3.5. 3.2.3.6. 3.2.3.7. 3.2.3.8. 3.2.3.9. 3.2.3.10. 3.2.3.11. Vessel SupportType of support used usually depends on the orientation of the vessel. There are some factors need to be considered during the support design including the weight of the vessel and contents, and any superimposed loads. The support design also must have easy access to the vessel and fitting for maintenance and inspections (Sinnot and Towler, 2009). In this design, the skirt support are recommended as the vertical vessels support because this type of support are the most economical (Brownell and Young, 1959) and they do not impose concentrated loads on the vessel shell (Sinnot and Towler, 2009).Type of Support: Straight cylindrical skirt Base angle of a conical skirt, s : 90 Material of Construction: Stainless steel 304Design Stress: 137.9 N/mm2 at ambient temp. 20 C Youngs Modulus: 193000N/mm2

a)Approximate Skirt Weight, The maximum dead weight load on the skirt will occur when the vessel is full of water; Approximate Weight, ................................................... (3.2.34)

Total Weight, ........................................................... (3.2.35)

Bending moment of the skirt base, ................................................................. (3.2.36)where is the skirt height, and take its value as 1m height

Bending stresses in skirt,As first trial, take skirt thickness,ts as the same as bottom of vessel,7mm ............................................................. (3.2.37)

Dead Weight in the Skirt, ................................................................ (3.2.38)

0.017N/

23.51N/

Resulting the maximum stress in the skirt,

Take the joint efficiency E as 1.Cateria for design: .......................................... (3.2.39)

Both criteria are satisfied, add 2mm for corrosion, and give the design thickness,

1. 2. 3. 3.1. 3.2. 3.2.1. 3.2.2. 3.2.3. 3.2.3.1. 3.2.3.2. 3.2.3.3. 3.2.3.4. 3.2.3.5. 3.2.3.6. 3.2.3.7. 3.2.3.8. 3.2.3.9. 3.2.3.10. 3.2.3.11. 3.2.3.12. Pipe Size Selection for NozzleOptimum diameter for the pipe can be calculated using the following equation below. .................................... (3.2.40)

Where,

Feed inlet nozzle sizingThe calculation for the theoretical diameter of inlet nozzle, D1 is: .............................................................. (3.2.41)

The calculation of feed pipe optimal diameter is:

Gas outlet nozzle sizing

The calculation of gas outlet optimal diameter is:

Liquid outlet nozzle sizingThe calculation of gas outlet optimal diameter is:

1. 2. 3. 3.1. 3.2. 3.2.1. 3.2.2. 3.2.3. 3.2.3.1. 3.2.3.2. 3.2.3.3. 3.2.3.4. 3.2.3.5. 3.2.3.6. 3.2.3.7. 3.2.3.8. 3.2.3.9. 3.2.3.10. 3.2.3.11. 3.2.3.12. 3.2.3.13. Standard FlangeStandard flanges will be specified for most applications. Standard flanges are available in a range of types, sizes and materials and are used extensively for pipes, nozzles and other attachments to vessels body. Flanges used in this design were chosen from the standard flanges. The standard flanges are adapted from Standard Flanges of Steel welding neck flange.

Table 3.22: The standard flanges are adapted from Standard Flanges of SteelPipeD optimum (mm)Nominal Size Use

AFeed Inlet2630

BGas Outlet2930

CLiquid Outlet29.430

3.2.3.14. Manways for Column AccessManholes are design for entrance into vessel column. It should be position so that it can be accessed to the internal parts of the column. It should be sufficiently large to allow workers to rapidly climb out through them without cutting themselves. According Rahimi (2011), normally manway is 0.6m. therefore, in this separator design we take 0.03m as manways diameter.

Table 3.23: Mechanical Design for SeparatorPressure Vessel

Operating Pressure, Po0.790 N/mm2

Design Pressure, P10.869 N/mm2

Operating Temperature105oC

Design Temperature816 oC

Column MaterialStainless Steel 304

Safety Factor10%

Design Stress97.77N/mm2

Head and Closure

TypesTorispherical Head

Crown Radius, Rc0.749 m

Joint Factor, J1

Minimum thickness, e3 mm

Column Weight

Dead weight of Vessel, Wv

Weight of Insulation, Wi

Weight of Demister,Wd

Total Weight, Wt

Bending Moment, Mx

Insulation MaterialMineral Wool

Insulation Thickness70 mm

Skirt Support

Type of SupportStraight Cylindrical Skirt

Material of ConstructionStainless Steel

Youngs Modulus193000N/mm2

Bending Moment, Mx

Skirt Thickness, ts7 mm

Skirt Height, Hs1 m