t-402 report.docx

8/10/2019 T-402 report.docx

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T- 401: Introduction:The absorption column that will be design will be used in a carbon dioxide capture process usingDGA as the main amine.

Column Sizing:

Finding the flow rate of each streams:

The basis flow rate given to our group is 55000 kg/h. We will take that as the flow rate for stream 33.Doing the water mass balance, solvent mass balance and hydrogen mass balance as shown in theappendix will give the flow rate of each streams:Streamnumber

Mass flowrate (kg/h)

34 68793.284436 9688.246116 14288.314017 73244.0092

Finding the number of stages required:

Using Figure 1, the number of stages required at different mG m/L m will be determine:mG m/L m 0.8 1.0 1.1 1.2 1.3

NOG 2.2 2.8 3.2 4 6

We will chose the N OG of 6 as this will give a higher flow rate, hence the column will not be under-

designed.

Calculating column diameter:

The physical properties of the gas as found in HYSYS:Molar flow

rate (kmol/h)Mass flowrate (kg/s)

Density(kg/m 3)

Viscosity(Pa.s)

Gas flow 1308 3.97 12.71 1.610 - Liquid flow 2915 19.11 1015.12 1.110 -

Pressure drop given is 25 kPa or 2549.29 mmH 2O, the packed bed height is 6 m, so the pressure drop/height will be 425 mmH 2O. The highest pressure drop per height in the Figure 11.54 is around 125mmH 2O, so we will take that and the column will be over-designed, which is good for safety

precaution or to upscale the process in the future.3 sizes of Pall rings packing will be considered, which are 25 mm, 32 mm and 51 mm. Pall rings

packing will be used as it is the most suitable packing for absorption of hydrocarbons.Packing

size (mm)F p (m

- ) V w*(kg/m 2s)

Diameter(m)

Percentageflooding (%)

Packing size to columndiameter ratio

25 160 3.63 2.6 91 10432 92 4.79 2.3 88 7251 66 5.65 2.1 90 41

The lowest percentage flooding is 88%. It is high, but still satisfactory. Furthermore, the column is

already deliberately over-designed to counter this type of problem. The diameter of the column will be 2.3 meter.


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H OG estimation:

Cera mic packing will be used as it is the first choice for corrosive liquid. The Cornells method and

the Ondas method will be used to estimate the H OG . These two methods have been found to bereliable for preliminary design work and with the absence of practical values can be used for the finaldesign with a suitable factor of safety.The result are:

Method H L H G H OGCornells 0.18 1.23 1.46Ondas 0.56 0.05 0.78

The shown that Cornells method will give a higher value of H OG and this value will be taken to sizethe height of the packed bed.With the value of H OG and N OG that are found, the height of the packed bed will be 8.8 meters.

Stress Calculation:

Parameters:

HeightDiameterHemispherical HeadSkirt Support ,heightCorrosion allowance

Insulation, Mineral WoolMaterial of construction, carbon steelOperating pressureVessel to be fully radiographed

8.8m2.3m

1.38m2mm

70mm thick88.9N/mm 2 at design temperature 200 degrees30bargE=1

Justification of materials

Based on preliminary calculations, the thickness was calculated to be 45.35mm thick and rounded to46mm. The inclusion of the allowance for corrosion gives an overall thickness of 48mm. It was foundin accordance to the Clause 1.6 and 1.7 of the AS-1210 that the vessel design could be considered as aclass 1 pressure vessel due to the presence of highly volatile and flammable compounds within thevessel and that it is a major component for the process plant.The material selected for the design of the vessel should meet all the criteria in accordance to the 2010version of the Australian Standards AS-1210 and the ASME. The metal was chosen based on itsstrength, ductility, corrosion resistance and maintenance frequency. As the working fluid within thevessel is not corrosive, carbon steel was chosen as the material for construction instead of stainlesssteel. Although stainless steel has a slightly higher allowable stress of 135N/mm 2, it is lesseconomical to use stainless steel as it is much more expensive as compared to carbon steel. Carbonsteel has a high allowable stress of 88.9N/mm 2 and is able to withstand the calculated stresses, it isalso more economical.A corrosion allowance of 2mm was allowed to ensure that the functionality of the vessel does notdegrade over time. Although the working fluid is not corrosive, it is typically safer to allow a fewmillimetres to ensure safe and long term operation.


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The type of head chosen was the hemispherical head as it is the strongest shape, capable resistingabout twice the pressure of a torispherical head of the same thickness. It is used when operating

pressures are high. The thickness required for the head and closure were made in accordance to theASME BPV Code Sec. VIII D.1.The skirt support is chosen as the column is vertical and they do not impose concentrated loads on thevessel shell with conformity to the clause 3.24 in the AS-1210. As the vessel if 8.8m high, it is subjectto wind loading and skirt supports are more suitable as compared to saddle supports.Operating temperatures range from 45degres Celsius to 75 degrees Celsius, insulation is required. Athickness of 70mm was chosen as the operating temperatures are relatively low. Mineral wool ischosen as it provides good insulation by trapping air within the small pores present in the wool. It hasthe capability of withstanding up to 800 degrees Celsius and has a low thermal conductivity of0.08W/mK at 298K. It also acts as a flame retardant in the event of a breakout of fire.A double welded butt joint is required for a class 1 pressure vessel with a maximum efficiency of 1.0as stated by the clause 3.5 of the AS1210. 2 platforms with an outer radius of 1m and a ladder isincluded in the calculations for dead weights.The dead weights before and after hydro testing are tabulated in table 1.1

Dead Weights Value

Vessel and Head 302.73kNLadder 0.42kNPlatforms 17.62kNInsulation 9.57kNHydro Testing (waterfilled in column

358.67kN

Total (Before Test) 330.34kNTotal (After Test) 689.01kN

Table 1.1: Dead weightsWind loading was calculated using a wind speed of 160km/h and a drag coefficient of 0.07 to accountfor attachments such as ladders or platforms.Wind Loading 5627N/mBending Moment 219818.1654Nm

Table 1.2: Wind Loading & Bending MomentThe pressure stresses, dead weight stress and bending stresses before hydrostatic testing were thencalculated and tabulated in table 1.3Longitudinal Stress 47.437 Hoop Stress 94.875 Dead Weight Stress 0.974 Bending Stress 0.129 Resultant Longitudinal Stress ( upwind) 45.541 Resultant Longitudinal Stress (downwind) 48.282 Elasticity Stability 384.615

Maximum compression Stress 1.103 Table 1.3: Stresses on vessel before hydrostatic testingThe greatest difference is the difference between Hoop Stress and Resultant downwind longitudinalstress. The difference gives a value of 46.59 which is much lower than the maximumallowable stress of 88.9 which means that copper steel at this thickness is able to withstandexternal and internal stresses before hydrostatic testing is carried out. The maximum compressionstress is also much lower than the elasticity stability, signifying the strength and stability of the vessel.

45.541 48.282 94.875 85.56 MPa 94.875


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Up-wind Down-windResultant longitudinal stresses

Hydrostatic testing is carried out to test the integrity of the vessel under high stresses and pressures toensure the safe operation of the vessel even under extreme conditions.The stresses were thenrecalculated after pressure testing and tabulated into table 1.4Longitudinal Stress 64.47 Hoop Stress 128.94 Dead Weight Stress 2.032 Bending Stress 0.1294 Resultant Longitudinal Stress ( upwind) 66.633 Resultant Longitudinal Stress (downwind) 63.374 Elasticity Stability 384.6154 Maximum compression Stress 2.1617

Table 1.4 Stresses after hydrostatic testingEven after hydro testing was carried out, the vessel was much able to withstand the stresses with no

problem. The greatest difference between Hoop Stress and Resultant downwind longitudinal stressgives a value of 62.569 , which is much lower than the allowable stress of 88.9 . Thevessel is fit and strong to be used even under extreme conditions as there is a large margin betweenthe allowable stress and the greatest difference between stresses. The maximum compressive stress isonly a mere 2.16188 , which is much lower than the elastic stability of 384.6154 .

66.633 63.374 128.94

85.56 MPa 128.94

Up-wind Down-wind

Skirting

A straight cylindrical skirt of plain carbon steel with maximum allowable stress of 89 and a

youngs modulus of 200,000 was used. Through careful iteration, the optimal thickness of theskirt was selected to be 20mm. The skirt height of 1.38m was carefully chosen based on the diameterof the vessel.Skirt Height 1.38mSkirt Thickness 20mmBending moment at base of skirt 291.56kNmDead weight on skirt 671.4kNBending Stress 3.4485

Dead Weight Stress (test) 4.605

Dead Weight Stress (normal) 2.342


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79.56

223.5

Maximum tensile stress ( ) 8.0535 Maximum compressive stress ( ) 2.263 Table 1.5 Stresses on skirt support and parametersUnder the worst combination of wind and dead-weight loading, the calculated values are able towithstand such stresses as the maximum tensile stress and maximum compressive stress is

significantly lower than and respectively. As a straight skirt is chosen,

the angle use is 90degrees.

Optimization

The vessel thickness of 46mm proved to be incredibly stable and strong. Through thorough inspectionand iteration, a thickness of 38mm was shown to provide adequate support and strength. However, thevessel thickness was left at 46mm for ease of fabrication as the outer diameter of the vessel would be2.376m as compared to 2.396m which would have been rounded up to 2.4m anyway.

2.0 T-402 Solvent Regeneration Tower

2.1 Simulation of the process in HYSYSHYSYS was utilized to design and simulate the distillation column while Amine Package wasused as the fluid package at the specified operating conditions. The primary purpose of the

distillation column is to remove the CO 2 via the distillate (Stream 29) and at the same timeregenerate the solvent to be returned into the system via the bottom stream (Stream 25)

Firstly, to obtain the relevant mass flows for the streams involved in the distillation column,simple mass balances were conducted and the mass flow rates of the streams were obtained asfollows:

Table 2.1.1: Mass flow rates of the streams involvedStream Mass flow rate (kg/hr)25 (given) 5500021 (inlet) 73168.91

29 18168.91

Next, the distillation column was then simulated in HYSYS whereby the condenser was set tooperate at full reflux to achieve the desirable process. The operating conditions and streamproperties were only defined for the feed stream (Stream 21). Various parameters were thenadjusted to achieve the desirable component fractions and conditions of the outlet streams aslisted in the PFD drawing provided. However, in this simulation, the primary goal is to attain thecomposition that is as close as possible to those specified in the PDF given; specifically for theCO2 fraction in Stream 29 and the solvent fraction in Stream 25.

The number of trays and its inlet stage can be varied to achieve the desirable goals. Besides, theoperating pressures of the condenser and reboiler can also be varied but within a considerablerange. The simulation can be carried out using a trial-and-error basis to iterate towards theoptimum parameters that provides for the desirable outcomes. The table below shows the


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process data obtained for the overhead and bottom product from the designed distillationcolumn in HYSYS.

Table 2.1.2: Stream properties of the overhead and bottom productProperties Overhead (Stream 29) Bottom (Stream 25)

Temperature ( ) 104.8 123.8Pressure (kPa) 136 208Mass fraction:CO2 0.2403 0.001895Water 0.7597 0.6421Solvent 0 0.356

2.2 Maximum operating levelsTo determine the maximum operating level for the distillation column, several data wereextracted from the HYSYS file simulated. Firstly, the feed inlet stream to the vessel was

identified as the stream having the highest volumetric flowrate as follows:

The design hold up time for the distillation was assumed to be 5 minutes. Hence, the hold upvolume can be calculated as follows:

The design vessel diameter was determined to be . Hence, the cross sectional area of thevessel can be obtained as follows:

Finally, the maximum operating level of the distillation column can be determined as follows:

2.3 Mechanical Design

2.3.1 Height of the Distillation ColumnIn essence, there is a total number of 22 trays in the distillation column; each having a traythickness of 0.005m and a tray spacing of 0.75m. In the calculation of the height of column,space for disengagement is also taken into consideration whereby a height of 1.5m was


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assumed for both vapour disengagement at the top of the column and liquid accumulation at thebottom of the column.

Besides, the torispherical head selected for the distillation column is also taken into account.The internal height of the head is obtained via a series of calculations. (Slawinski, 2014) Thethickness of the vessel material, the insulation applied, being mineral wool and the aluminiuminsulation cover are also taken into account for the calculation of the height of column.However, the supports of the column are not taken into account.

As aforementioned, a number of elements contribute to the total height of the distillationcolumn, which is shown as below:

Table 2.3.1.1: Height elements and total height of the columnHeight Elements Height (m)

Total tray thickness 0.11Total tray spacing 15.75Total space for disengagement 3Total height of torispherical heads 0.939Total torispherical head wall thickness 0.018Total insulation and insulation cover thickness 0.2

Total Height 20.017

Hence, the height of the distillation column is determined to be 20.02m.

2.3.2 Diameter and tray of the distillation column

The feed inlet is positioned at the 10 th tray, which is located between the 9 th and 11 th tray froma Top-down stage numbering. Hence, the 9 th tray is taken as the top tray while the 11 th tray istaken as the bottom tray. Several stream properties were required for the determination of thediameter and were extracted from HYSYS as shown below:

Table 2.3.2.1: Stream properties for stages 9, 10 and 11

The column diameters for the bottom and top were obtained as 2.222m and 2.0626mrespectively, whereby the larger diameter is then chosen and rounded up to the neareststandard column diameter size, which was found to be 2.286m (90 inches). This columndiameter will be used above and below the feed.

In this case, the flooding percentage was assumed to be 85% at maximum flow rate. Theflooding percentage calculated was found to be 80.3%, hence showing that the magnitude of thediameter selected is feasible.

Stage

Liquid component Vapour componentSurface Tension

( 10 -3 N/m)Mass flow(kg/hr)

Density(kg/m3) Mass flow (kg/hr) Density (kg/m3)

9 19905.66 952.3 38056.34 1.016 55.8910 94687.62 990.6 38069.34 0.9979 50.1911 94774.02 977.4 39682.4 1.003 50.02


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As mentioned earlier, trays with thickness of 5mm and tray spacing of 0.75m are adopted. Theweir height is also designed as 50mm and the hole diameter is designed to be 5mm each, eachhaving an area of 1.9635E-05 . The tray spacing chosen can be said to be appropriate as theback-up in downcomer, was found to be 396.96mm, being less than 0.5 (plate spacing + weirheight). Moreover, the residence time of the designed distillation column is also larger than 3

seconds. Hence, proving that sufficient residence time is allowed for the vapour disengagementfrom the liquid stream.

The design of the bottom and top trays are similar in dimension and only differ in the number ofholes, to account for the difference in the column diameter required; whereby the bottom trayhas 12710 holes and the top tray has 13839 holes.

2.3.3 Thickness of vessel

The ASME BPV Code Sec. VIII D.1 specifies minimum wall thicknesses for various vesseldiameters, regardless of its dimensions and material of construction. In accordance to this, for avessel diameter of 2 to 2.5m, the minimum thickness required is 9mm, which also alreadyincludes a corrosive allowance factor of 2mm.

The thickness of the torispherical head and the vessel were calculated but failed to meet theminimum thickness specified for the range of diameter. Hence, the thickness of the vessel istaken to be 9mm , and the thickness of the torispherical head is assumed to be the same as thatof the vessel.

Insulation for the column is also introduced, mainly to reduce heat loss from the distillationcolumn to the surroundings. For our distillation column design, mineral wool with a density of130kg/m 3 is chosen, owing to its economical cost and simplicity of application. However, it

may potentially cause skin irritation.

Hence, for safety purposes, an insulation cover is applied,being an aluminium cover with density of 2700 kg/m 3 .The thickness of both the insulation andthe insulation cover were taken to be 0.05m each. Therefore, the total thickness of the vesselwall, inclusive of the insulating elements is found to be 0.109m.

2.3.4 Design Temperature, Pressure and Material ChoiceThe design temperature and pressure were calculated from HYSYS whereby the designconditions are taken to be 10% higher than the maximum operating conditions. This is toprovide optimal design parameters and to ensure that safety is not compromised under anycondition. From HYSYS, the maximum operating temperature was and the maximum operatingpressure was obtined at the reboiler. The design operating conditions are as follows:

Table 2.3.4.1: Design operating conditionsMaximum operating temperature ( ) 123.8Design operating temperature ( ) 136.2Maximum operating pressure (kPa) 208Design operating pressure (kPa) 228.8

The vessel material was chosen based on the design conditions calculated. Based on the designtemperature, Carbon Steel A285 Grade A was chosen under the ASME BPV Code Sec. VIII D.1.The maximum tensile strength that the material can withstand was obtained to be 88.94MPa .

2.3.5 Dead Weight LoadingsThe total dead weight of the column encompasses all the dead weights involved in every part ofthe column and the table below presents the summation of these weights.


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Table 2.3.5.1: Dead weight components and the total dead load

2.3.6 Combination of loads on the column for Hydrotesting

A key assumption was made in the conduct of hydrotesting to ensure that the vessel can sustaingreater loading. It was assumed that the density of the liquid in the vessel is that of water, whichis 1000kg/ m 3 . The combination of dead weight on the distillation column during hydrotestingoperating conditions can be determined by summing up the total dead weight of the vessel ascalculated earlier and the total weight of the liquid filled furing hydrotesting operatingconditions. In short, the weight of the liquid was calculated to be 805.95kN and the combinedloads on the column for hydrotesting is calculated to be 1851.95kN .

2.3.7 Wind LoadingThe wind speed was assumed to be 160km/h and the wind pressure due to the columnattachments and increase in drag can be calculated. The effective column diameter was alsocalculated to take the platform, caged ladder and insulation into consideration. The calculationsand results can be summarized as follows:

Table 2.3.7.1: Results for wind loadingComponent ValueWind Pressure (N/m2) 1792Effective column diameter (m) 4.904Loading per unit length column (kN/m) 8.79Bending moment, Mx (kNm) 1760.58

2.3.8 Analysis of stressSeveral stresses were evaluated and calculated for the purpose of analysing the feasibility andsuitability of material chosen (Carbon Steel A285 Grade A) . The summary of the stressescalculated are shown as below:

Table 2.3.8.1: Summary of the components of stress

Dead Weight Component Weight (kN)Volumetric vessel 125.58Vessel heads 207.87

Internal fittings:Trays 425.29External fittings:Steel caged ladder 7.21Steel platform (x3) 56.14Insulation 18.88Insulation cover 204.37

Total dead load 1046

Components of Stress Symbol Stress (Mpa)Maximum tensile strength f 88.95Longitudinal stress 14.53Circumferential stress 29.06

Dead weight stress 16.12Bending stress 47.48


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As mentioned earlier, the maximum tensile strength that can be withstand by the materialchosen is 88.94MPa . Several stress analysis were carried out as follows:

1. Check if the equivalent tensile stresses are lower than that of the maximum tensilestrength of the chosen material.

2. Check if the upwind and downwind resultant longitudinal stresses are lower than thatof the maximum tensile strength of the chosen material.

The results from the tensile strength tests evidently show that the material chosen, Carbon SteelA285 Grade A satisfies all the respective stress requirements of different aspects. Hence, it canbe said that the material chosen is suitable for the design.

2.3.9 Buckling TestFor this test, the maximum compressive stress, in the vessel wall must not exceed thecritical buckling stress, and the maximum tensile strength of the chosen material.

The critical buckling stress, was calculated to be 78.13MPa ; the maximum compressivestress, From the calculations shown above, it can be deduced that the design of the vessel is safe andoperable.

2.3.10 Hydrostatic TestingFor this test, the design pressure, must not exceed the hydrostatic pressure, . In this case, itis assumed that the design strength at the test temperature and design temperature are thesame, which is 88.94MPa. The hydrostatic pressure is calculated to be 0.343MPa. Besides, the thickness of the design vessel is evaluated to check if it is able to withstand themaximum hydrostatic pressure, .The minimum wall thickness required to resist the hydrostatic pressure was calculated as2.19mm . Since the thickness of the vessel is 9mm ,

Resultant longitudinal stress (upwind) 45.89Resultant longitudinal stress (downwind) -49.07Equivalent membrane stress (upwind) 16.83Equivalent membrane stress (downwind) 78.13


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Next, the stress due to hydrostatic pressure, must not exceed the maximum tensilestrength. In accordance to the results obtained from hydrostatic testing, the design appears to be

satisfied in various aspects.

2.3.11 Support Type: SkirtThe criteria for skirt design is evaluated for when the distillationcolumn is at hydrotesting condition as the dead weight stresses are at its maximum, hencegiving a safer design.The maximum compressive stress and maximum tensile stress are calculated and are used todetermine if the skirt design is satisfactory.Since,

i)

s(tensile) sin

s = 34.23MPa < 88.94MPa ii)

s(compressive ) 0.125 ( ) sin s = 91.31MPa < 103.35MPa

Since both criteria are satisfied, the skirt design is said to be satisfactory. With an additional2mm for corrosion allowance, the total skirt thickness is determined to be 11mm.

2.4 Design Decision Criteria2.4.1 Selection of materialCarbon steel (A285 Grade A) is chosen as the design material for the entire distillationcolumn. The main reason for this selection is because it is cheaper compared to othermaterials such as stainless steel. Furthermore, it has a high resistance to corrosion, hencemaking the vessel wall more long lasting. Carbon steel is also favoured among othermaterials as it does not interact with the amine group present in the DGA solvent, unlike theother materials. Another reason for the selection of this material is because carbon steel is astrong material and has a relatively high maximum tensile strength; it can also withstand hightemperatures and pressures. Since the conditions they can sustain are much higher than thedesign temperature and pressure of the distillation column, which are 136.18 oC and 228.8kPa respectively, this allows for some overheating and over-pressure protection fromuncontrolled process parameters, which increases the safety of the vessel. Hence, carbon steel

is suitable material as it fulfils all the required parameters and also is a safe and economicalmaterial.

2.4.2 Type of endThere are four different types of heads for process vessels, which are flat heads,hemispherical heads, ellipsoidal heads and torispherical heads. Flat heads are mainly used forlow-pressure and small-diameter vessels, and are also the cheapest type of heads.Torispherical heads, also known as dished ends, are commonly used for columns operating at

pressures below 15 bar. On the other hand, ellipsoidal heads are more economical for vesselsoperating at pressures above 15 bar. Lastly, hemispherical heads are the strongest type ofheads as they can withstand high pressures. However, hemispherical heads are also the most

expensive compared to the other type of heads. Torispherical heads are used for thedistillation column because the design pressure of the vessel, which is 2.08 bar, is much


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lower than 15 bar. Since there is allowance for over-pressure, this type of head is sufficient.Furthermore, it is more economical to use this type of head as it is cheaper compared to theellipsoidal and hemispherical heads.

2.4.3 Insulation

Heat losses from a distillation column affects the amount of heat added to andremoved from the reboiler and condenser respectively. The main purpose of thermalinsulation in the chemical industry is to reduce heat losses from a vessel. This is necessary asit protects the operators from injury in the case of accidental contact with the hightemperature vessel, making the column safer to operate. Furthermore, heat loss from thevessel should be minimized as it may affect the required process temperature, which wouldaffect the product quality and process efficiency. Additionally, reduced heat loss lowers theenergy input required for the process, which results in a lower operating cost of the vessel,hence making the column more efficient and economic. Mineral wool, which is a mineralfibre insulation, is chosen to insulate the distillation column because of its low thermalconductivity and excellent water-repellent properties. It also has a good corrosion resistance,is less costly, light-weight and easy to install. The thickness of insulation used in the designwas 0.05mm. However, mineral wool can potentially cause skin irritation. A layer ofaluminium of thickness 0.05mm is added to reduce this risk.

2.4.4 Plate thickness for the cylindrical and end sectionsA minimum wall thickness is required so that the vessel can withstand its own weight andany incidental loads. The minimum thickness of the plate for the distillation column isdetermined to be 9mm. Corrosion allowance is also accounted for to allow any loss ofmaterial by corrosion, erosion or scaling. A small corrosion allowance of 2mm is used forthe carbon steel plates because this material will not corrode severely due to its highcorrosion resistance. Furthermore, sieve plates are used for this distillation column mainly

because of their lower costs compared to bubble-cap plates. Sieve plates with a good designalso give a satisfactory operating range. Hence the use of this type of plates is moreeconomical. All the plates in the column have the same size and thickness. However, the top

plates have more holes as compared to the bottom plates.

2.4.5 Support typeThe type of support used for a vessel depends on many factors such as the shape, size andweight of the vessel. Cylindrical skirt supports are used for the distillation column as they arecommonly used for tall, vertical columns. This type of support consists of a cylindrical or

conical shell welded to the base of a vessel. The load is transmitted to the foundations using aflange at the bottom of the skirt. An advantage of using this type of support is that it does notexert concentrated loads on the shell of the vessel. It distributes the load uniformly over theentire shell. Therefore, skirt supports are suitable when the vessel is subjected to windloading. The skirt needs to have sufficient thickness to be able to withstand the dead-weightloads and bending moments exerted on it by the column. The skirt thickness in this designwas calculated 11mm. Bracket supports are not used mainly because they cannot resistsignificant bending moments. Fire-resistant supports may also be used to increase protectionagainst fires.

2.4.6 Requirements for welding and stress relief

Fusion welding is commonly used for the construction of process vessels. There are manydifferent forms of welded joint. A good welded joint is one that provides good accessibility


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for welding and inspection, and requires a minimum amount of weld metal to minimize cost.A good welded joint should also give good penetration of the weld metal from both sides andincorporate sufficient flexibility to avoid cracking due to thermal expansion. The strength ofa welded joint depends on the type of joint and the welding quality; the number of welded

joints in the vessel should be kept to a minimum. Stress corrosion cracking may occur if a

vessel is subjected to stress and corrosion, which may lead to premature failure of the vesselwall. Stress relief is therefore necessary for materials that are susceptible to stress corrosioncracking. Pressure-relief devices are also installed in the distillation column to prevent over-

pressure, which may result in failure of the vessel. This device is set to the design pressure,and when the vessel pressure exceeds this set value, the relief valves are opened and theexcess pressure is released.

2.4.7 PaintingProtective paints for metals are commonly used for providing protection to vessels. Manytypes of protective paints are available which protect metals from many different factors, forinstance, epoxy- based paints. These paints are used to protect the metal from atmosphericcorrosion and rust. Fire-proof paints may also be used to provide protection to the vessel inthe case of a fire. Another purpose of coating vessels with this type of paint is to protectmetals from extreme weather conditions and chemical attacks. This type of paint also

provides protection from high temperatures. These paints usually consist of chemically inertmaterials and give a smooth and non-sticky surface after use. The main purpose of these

paints is to protect the vessel wall from any damage, which will reduce the futuremaintenance cost, hence making the column more durable and economical.

2.4.8 Insulation and claddingMineral wool is selected for insulating the distillation column because it is a good insulator,has a low conductivity and good corrosion resistance. Insulation is necessary to reduce heatlosses from the column as well as to cool the surface of the column to prevent any injury tothe operators. Cladding is a process where a metal or composite is bonded onto anothermetal. The purpose of cladding is mainly to protect metals from corrosion as well as toenhance its toughness and durability. Cladding is very economical as it involves adding a thin

plate of an expensive cladding material to a thicker inexpensive metal solid, which is muchcheaper compared to constructing the vessel entirely out of the cladding material. Stainlesssteel plates are selected for cladding mainly because of the high mechanical strength of thematerial. Hence, it can withstand high temperatures and pressures. Stainless steel also has afairly high resistance to corrosion, stains and rust, as well as to environmental factors andstress corrosion cracking. Furthermore, stainless steel is very durable and recyclable, making

it an economical and sustainable material.

2.4.9 FireproofingIn the event of an external fire, the vessel may overheat which would lead to a rise in

pressure. This can weaken the carbon steel wall, which may even result in failure of thestructure. Therefore, fireproofing is obligatory to reduce damage and prevent loss ofexpensive, valuable equipment in an industry. Fireproofing is a passive fire protectionmeasure used to protect equipment by making a structure more resistant to fire. Fireproofingdelays the damaging effects caused by the high temperature during a fire for a specific periodof time, which depends on the thickness of the material. The fireproof material should bedurable and provide a good corrosion resistance. A layer of concrete can be used to fireproof

the distillation column as it is an excellent fire protection material due to its high mass andlow thermal conductivity. Stainless steel jacket and bands may also be used to protect the


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vessel as it can retain its strength at high temperatures due to its high melting point. Hence, itcan provide fire-resistance for a long period of time. Besides, pressure relief valves can also

be installed to minimize the pressure rise in the vessel. Moreover, water sprinkler systemscan also be established to put out any small fires.

3.0 S-401 CO2 Separator3.1 Introduction

Separators are usually part of an instrument in industrial process. The type of separators usedare usually Vapour-liquid separators. It is an industrial unit used to separate gases and liquid to

produce a number of products in vapour and liquid form respectively for different purposes.The vapour in the vapour stream will travel through the outlet of the separator at a velocity

which will reduce the entrainment of any liquid droplets in the vapour as it leaves the vessel. Usuallyit is liquis that is partially flashed into vapour and liquid that is fed into the separator. Vapour-liquidseparators can also be called as knock-out drum, knock-out pot, compressor suction drum orcompression inlet drum. Vapour-liquid separators has a very high usages at industries as stated below.

- Oil refineries- Natural gas processing plants- Petrochemical and chemical plants- Geothermal Power Plants- Combined cycle power plants- Paper mills and so on

3.2 Horizontal Separation Design Calculation 1.) Calculation of Vapour flow rate and Fluid flow rate

Given,

Vapour fraction 0.0006 at inlet, stream 18


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2.) Calculate Vertical terminal vapour velocity,

Given that no mist eliminator pad is used Separator K value can be calculated using formulae (1) in appendix , K= 0.13

Set for conservative design. Note that for secondary separation, allowable velocity must be calculated so that the disengagementarea can be determined. Besides, the design U T must be always greater than U v for the droplet to settleout. Hence as shown above.

3.) Calculate Holdup Volume, V H and Surge Volume, V S

Since our outlet of S-401 separator is connected to T-402 column vessel, following table 2 apenddixholdup time(NLL-HLL) and surge(NLL-LLL) time should be 5 minutes(T H) and 3 minutes(T S)respectively.

Holdup time is based on the reserve required to maintain a stable control and safer operation of down

stream facilities. Where else surge time is normally based on accumulation of liquid as a result ofupset variation flow in downstream or upstream. In the absence of specific requirement, surge timecan be assume to be one half of holding time.

4.) Diameter and Area of the Separator

Where (L/D) can be estimated using the operating pressure of separator. Refer to table 5 ratio guidelinesAssume negligible change in operating pressure, Average pressure of For vessel operating pressure of (L/D)= 3

When sizing separator for horizontal setup, usually the diameter is assume , then LLL is determined.


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5.) Low Liquid height H LLL and A LLL

Figure 1.0 horizontal 2 phase separatorSince vessel diameter is under 2.43m(8ft) use 0.274m (11in.) value in table 3 appendix hence, To find A LLL, use relation of ) where,

6.) Calculating minimum length to accommodate liquid holdup/surge

If there is no mist climinator pad, the minimum height of the vapour disengagement area, is largerof 0.2D or 0.305m(1ft). If there is mist eliminator pad, minimum height of the vapour disengagementarea is the larger of 0.2 D or 0.610m(2ft). Hence, since no mist eliminator pad, H V = 0.2(2.36m) =0.472m.

Using the same relation in part (5.),

The length of vessel is calculated to accommodate the holdup ,surge and as well as to facililate vapourliquid separation. Since L/D is more than 1.5 and below 6 , no iteration calculation required.

7.) Minimum Length required for vapour liquid disengagement, L MIN


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Where, is actual vapour velocity and is liquid drop out time:

The calculation shows , which indicate that the design is acceptable for vapor/ liquidseparation. Besides that , the shows that liquid holdup is controlling , L can only bedecreased and increased if H V is decreased. H V may be decreased if it is greater than theminimum specified in step (6.). Since L/D is less than 6, the range is acceptable.

8.) Design parameters and Wall thickness

Assumptions The material chosen to build the separator is select as carbon steel of grade A285 Gr A.

Material data can be found in ( Sinnot page 1001, table 13.2) . Operating temperature for the process is constant at 67.91 Celsius. At this temperature, the Maximum allowable stress is at 88.94 N/mm2 Internal diameter, is calculated as Joint efficient = 1 Total Internal length of horizontal separator = 5.76m Operating pressure = Assume Corrosion allowance = 2mm (rule of thumb)

Design pressureThe separator must be design to withstand the maximum pressure which it is likely to handle inoperation, therefore to avoid spurious operation of the relief valve during minor process upset, an

extra 30% margin of working pressure is selected. Hence, Minimum thickness of separatorDuring operation for a pressurized vessel, there must a minimum amount of thickness of vessel wallto contain the pressure without deforming , HenceFor Minimum wall thickness of shell, Therefore the minimum thickness of separator shell wall is 9.25mm Selection of type headFrom table 9 appendix, for the selection of head type, dished heads with knuckle radius =0.6D areselected as it is typically used when D is lesser than 15ft ( 2.36m in this case) and design pressure islower than 100psig (64.54psig


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Weight of separator, From table 9,

Therefore the weight of separator is estimated to be 3720kg.(without component in separator) 9.) Calculate normal and high liquid levels

Using table 6 relationship,

10.) Dead weight loadings:

To simplify the calculations and also due to safety factor, the thickness of the column is madeuniform. Hence, a minimum required wall thickness of 12mm was used for calculations (Sinnot page1004, Table 13.4.8).Outer diameter required, Total Outer diameter = =2.384m From the diameter value, it can be said that the separator is large enough for easy maintenance asworkers can enter the separator and clean it within.

a.) Weight of vessel(with all the component in it):

= Approximate weight of vessel shell excluding fittings,N= Factor to account for weight of nozzles, manways, internal supports (1.08 for separator) = Height of cylindrical column, m

t= wall thickness, mm 11.) Stress analysis

Pressure vessel are subjected to other loads in addition to pressure. The maximum allowable stress incompression is different from the maximum allowable

a.) Pressure stress


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b.) dead weight stress

c.) The result longitudinal is:

The greatest different between the principal stress is on the downwind side

12.) Saddle support

For the support of separator, 2 saddles are the most commonly used and it is used to support forhorizontal separator for this case. If more than 2 saddles is used, the distribution of weight isunknown. For a uniform distribution, it can be done by placing the supports at 21% of the span fromeach ends. However, the supports will usually be nearer to the end in real case to utilize the stiffeningeffect of the ends. There are stresses applied to the vessel supported by the saddles which includeslongitudinal stress and to circumferential bending stress. Few assumption made while selecting thesaddles dimension and maximum weight support.

Only longitudinal and circumferential stress in consider .

assume the position od both saddles is at 21% of each sides. the material chosen for saddle is standard steel saddles the contact angle should not be less than 120 degrees. Maximum allowable stress for carbon steel at ambient temperature of 69C, Total dead weight =

From table 13.23 standard steel saddles (Sinnot page 1034, Table 13.23), the supporters can be choose based on the vessel diameter and maximum weight it can hold. In our design, since our diameter ofvessel is 2.384m with the wall thickness, dimension for saddles is chosen at 2.4 meter with t1 and t2equal to 12 and 16 mm respectively and bolt diameter and bolt holes are 27mm and 33mmrespectively.

81.2

-

53.5

Up downwin


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3.3 Discussion3.3.1 Two phase separator typeThe two phase separator can be oriented either by vertically or horizontally. Vertical separator are

preferred when separating vapour from liquid with high ratio of vapour/liquid while horizontal is preffered when the ratio vapour to liquid. In our design, horizontal two phase separator is chosen to process the stream is because the vapour flow to liquid flow is so small that the construction forvertical separator is not feasible (calculation can be found in the appendix) . Besides that, separatormat be designed with or without mist eliminator pads, and in our design we started without misteliminator.

3.3.2 Separator multi stage designIn the design, our separation are divided into 3 stages which consist of primary stages, gravity stage,and mist elimination stage. Primary stage involve the use of diverter to change the direction ofmomentum of fluid entrained in vapour that enter the separator, which then cause the droplet impingeon the diverter and drop by gravitation force. At the second stage, gravitation force plays a big rolehere as gravity separates smaller droplets while the vapour flows through the disengagement area.Final stage is mist elimination where the smallest droplet cannot be separate by gravitational force are

coalesced to form a bigger droplet to be separate by gravity.3.3.3 Stress analysisFor horizontal stress analysis we only consider a certain stress applied to the vessel as stress involvein horizontal is different from vertical vessel. First of all, unlike vertical vessel, horizontal vessel inthis design we do not have to consider wind load as it will not affect significantly as the height of theseparator is relatively low. Therefore , we do not need to include torque calculation and bending stress

by wind load. Besides that, earthquake loading is exempted as well, due to the fact that earthquake phenomenon is assumed non exist in the plant area. Only dead weight stress and pressure stress isconsider in the design.

3.4 Specification Sheet

SEPARATORDATA SHEET

Sheet No. 1 CompanyCHE3166 Process Design Group 14

Equipment No. S-401Function

Separating Liquid Water from Process Fluid

DATA PER UNIT SPECIFICATION OPERATING CONDITIONS

Design Orientation Horizontal Operating Temperature ( oC) 67.91

Minimum Column Diameter (m) 0.517 Maximum allowable stress(N/mm 2)

88.94

Column Diameter (m) 2.36 Operating Pressure (kPa) 44200

Column Height (m) 1.450 Design Pressure (kPa) 54600

Domed Head Type Dished Corrosion allowance (mm) 2

Domed Head Height (m) 0.0084 Construction MaterialCarbon steel of grade A285 Gr A


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LIQUID PROPERTIES VAPOUR PROPERTIESMass Flow Rate (kg/s) 0.026 Mass Flow Rate (kg/s) 1.262

Density (kg/m ) 967.1 Density (kg/m ) 0.6367

Volumetric Flow Rate (m /s) 0.0158 Volumetric Flow Rate (m /s) 0.0108

PREPARED BYYian Tee Phang

Date 12 th October 2013

CHECKED BY Ang Tze Jian Date 13 th October 2013


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AppendixNomenclatures

A Vertical vessel cross sectional area, ftALLL Cross section for LLL (horizontal vessel), ftAT Total cross sectional area (horizontal vessel), ft

AVD Vapor disengagement area required, ftC D Drag coefficientD Vessel diameter, ft or inDP Droplet diameter, ftDN Nozzle diameter, in (inlet or outlet vapor/liquid

as specified)DVD Vapor disengagement diameter, ft

E Welded joint efficiencyF D Drag force, lb f F G Gravity force, lb f g Gravitational constant, 32.17 ft/s 2 gc 32.17 (lbm/ft)(lbs

-2)H D Disengagement height, ftH H Holdup height, ft

H LIN HLL to inlet nozzle centerline height, ftHLL High Liquid LevelH LLL Low liquid level height, ftH ME Mist eliminator to top tank height, ftH S Surge height, ftH T Total vertical separator height, ftH V Vapor disengagement area height, ftK Terminal velocity constant, ft/sL Vessel length, ft

LLL Low Liquid LevelL MIN Vapor/Liquid separation minimum length, ftM P Droplet mass, lb f

NLL Normal Liquid LevelP Pressure, psig or psia

Q L Liquid volumetric flow, ft3/min

Q M Mixture volumetric flow, ft f/min, ft /sQ V Vapor volumetric flow, ft /s, ft /minS Vessel material stress value, psi

T H Holdup time, mintH Head thickness, in

t s Shell thickness, inUAH Allowable horizontal velocity, ft/sUT Terminal velocity, ft/sUm Mixture velocity, ft/sVH Holdup volume, ft

3

VLLL LLL volume, ft3

VS Surge volume, ft3

VT Total volume (horizontal vessel), ft3

W Vessel weight, lb m

Greek Letters Table Mixture liquid fraction

Vapor viscosity, cP Liquid density, lb/ft 3


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Mixture density, lb/ft 3

Vapor density, lb/ft

Liquid dropout time, s

T-401 and T-402 have similar calculations methods

Number of stages

1st selection, 25-mm (1 in) Pall rings (Pall rings is the typical packing for absorption of hydrocarbons)From Table 11.2, F p = 160 m

-1

So, Figure 11.54 will give K 4 = 0.85, and at flooding, K 4 = 1

So, From equation

* + * +

Round off to 2.6 m Estimation of H OG

Using Ondas method: R = 0.08314 bar m 3/ kmol.KSurface tension of liquid (from HYSYS), L = 6.010

-2 N/mg = 9.81 m/s 2 Size of packing, d p = 0.032 mFrom Table 11.3, for 32-mm Pall rings: = 128 m 2/m3 c for ceramics = 0.061 N/mDL = 1.510

-9 m2/s (estimated using Wilke-Chang equation)Dv = 1.310

5 m2/s (estimated using Fuller equation)Using equation:


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Design Pressure given allowance of 1.1

Minimum thickness

Dead Weight of Vessel Wv

Weight of insulation

Weight of Ladder

Weight of platform

Total Weight


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Wind Loading

Bending Moment

Analysis of StressesAt bottom tangent line

Pressure stresses :

Dead weight Stress:

Bending Stresses:

where

( )

Resultant longitudinal Stress:

Elastic Stability

Hydro-testing

[ ] [ ] At bottom tangent linePressure stresses:


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Dead weight Stress:

Bending Stresses: where ( ) Resultant longitudinal Stress:

Elastic Stability

Skirting

Initial guess is equal to the thickness of the vessel. Iterations are carried out to obtain a suitablethickness.

The skirt thickness is accepted if And


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Tables of Data

Table 1: Values of K for Separators


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Table 2: L iqui d Holdup and Sur ge times

Table 3: L ow liqui d level height table


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Tabl e 4: Tables of i nl et nozzle sizin g

Table 5: Table of guidelines for L/D r atio

Table 6: T able of cyli ndri cal height and area conversions.


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Tabl e 7: Table of wall thi ckness, sur face area and approx imate height of vessels

Table 8: T ables of conditions for hori zontal separator

Table 9: Tables of selecti on of head types


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4.0 ReferencesCarpentier, P.I.,Important Parameters for Cost Effective Separator Design., Shell Oil Company-Head Office Facilities Engineering, Facilities/Chemical Engineering Conference (1988).Geruda, Arthur, How To Size Liquid Vapor Separators, Chem Eng., p. 81 -84 (1981)ASME Pressure Vessel Code, Section VIII, Division I, Table UCS-23, p. 270-21771 (1986)Sinnott, R. & Towler, G. (2009) Chemical Engineering Design. Fifth Edition. Oxford: Butterworth-Heinemann

Kennedy, P., Ryan 2007, A Study on the effects of insulation on the glass distillation column ofGoddard Hall Lab

Williams, John, Evans, Owen 2010, The Influence of Insulation Materials on corrosion underinsulation, Northern Area Western Conference, February 15-18, Calgary, Alberta

Industrial column insulation, viewed 11 October 2014, http://guide.rockwool-rti.com/applications/column-insulation/industrial-column-insulation.aspx?page=2156

Hart, L., Fred, Jaber, David 2002, Best Practices in Steam System Management

Iris NV Expands Use of TSA Coatings and Metal Spraying for Refinery Vessel, viewed 11 October2014, http://www.metallisation.com/applications/iris-nv-expands-use-of-metal-spraying-for-refinery-vessel.html

2013, The Advantages of Choosing Stainless Steel Cladding, viewed 11 October 2014, http://ath-stainless.com/the-advantages-of-choosing-stainless-steel-cladding/

Kondo, J., Nagae, M., Tsuji, M., Izawa, T., Urne, K., Hirano, O 1992, 316L Type Stainless Steel CladPipe Manufactured By Uoe Process, The Second International Offshore and Polar EngineeringConference, 14-19 June, San Francisco, California, USA

Whittaker, Gary 2005, The Fundamentals of Fire-Protective Insulation

Slken, Werner 2014, Explore the world of piping, viewed 11 October 2014,http://www.wermac.org/materials/fireproofing.html

Slawinski & Co. GmbH, Torispherical head according to DIN 28011, viewed 11 October 2014,http://www.slawinski.de/en/products/torispherical-heads/

2005, Mechanical Insulation Best Practices Guide

Sinnot, R. & Towler, G., (2009), Chemical Engineering Design, 5th

ed., USA: Elsevier Inc.
http://guide.rockwool-rti.com/applications/column-insulation/industrial-column-insulation.aspx?page=2156http://guide.rockwool-rti.com/applications/column-insulation/industrial-column-insulation.aspx?page=2156http://www.metallisation.com/applications/iris-nv-expands-use-of-metal-spraying-for-refinery-vessel.htmlhttp://www.metallisation.com/applications/iris-nv-expands-use-of-metal-spraying-for-refinery-vessel.htmlhttp://ath-stainless.com/the-advantages-of-choosing-stainless-steel-cladding/http://ath-stainless.com/the-advantages-of-choosing-stainless-steel-cladding/https://www.onepetro.org/search?q=dc_creator%3A%28%22Kondo%2C+J.%22%29http://www.wermac.org/materials/fireproofing.htmlhttp://www.slawinski.de/en/products/torispherical-heads/http://www.slawinski.de/en/products/torispherical-heads/http://www.wermac.org/materials/fireproofing.htmlhttps://www.onepetro.org/search?q=dc_creator%3A%28%22Kondo%2C+J.%22%29http://ath-stainless.com/the-advantages-of-choosing-stainless-steel-cladding/http://ath-stainless.com/the-advantages-of-choosing-stainless-steel-cladding/http://www.metallisation.com/applications/iris-nv-expands-use-of-metal-spraying-for-refinery-vessel.htmlhttp://www.metallisation.com/applications/iris-nv-expands-use-of-metal-spraying-for-refinery-vessel.htmlhttp://guide.rockwool-rti.com/applications/column-insulation/industrial-column-insulation.aspx?page=2156http://guide.rockwool-rti.com/applications/column-insulation/industrial-column-insulation.aspx?page=2156


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