chapter 8 sizing and costing

CHAPTER 8

EQUIPMENT SIZING AND COSTING

8.1INTRODUCTIONAmong the most important parts for the success of production of 100,000 MTA of MMA are the sizing of the chosen equipment followed by preliminary costing for every one of them. Equipment sizing will affects the profitability of a plant where the choice of material used and the size of the units determine the feasibility of a plant. For this purpose, the calculations are based on the throughput into the equipment and its corresponding operating parameters. The results will be needed for the cost correlations to estimate the equipment cost. Sizing and costing for a plant is important factor that should be done in good manner because its determined the whole plant profitability besides ensure that the plant run smoothly without any problem during the operation.

Generally, the units including main units comprises of Reactor, Distillation Column, Flash Column and some side units of Mixer, Compressor, Heat Exchanger,Heater, Cooler, Pump and Storage Tank. For the preliminary calculation of sizing and costing, parameters that important such as flow rate, temperature, pressure and density. And generally, determination of volume, diameter and length has been carried out using the parameters simulated from results of simulation and manual mass balance results.

The exchange rate used for the calculation is from US dollar ($) to Ringgit Malaysia: $ 1 US dollar = RM 3.20. The costing index is based on the Chemical Engineering Plant Cost Index (CE Plant cost Index). When using Product and Process Design Principle, the base cost index (2006) is CE500 and for present cost index (2010) is CE532.9. When using the reference of Chemical Engineering Volume 6, the base cost index (mid of 2004) of CE444.2 is used for the costing calculation.

In this plant design, most of the equipment sizing and costing will be referred to Chemical Engineering Volume 6, Product and Process Design Principle, A Guide to Chemical Engineering Process Design and Economics and Systematic Methods of Chemical Engineering Process Design.

The sizing and costing calculation for each unit operation will be enclosed in Appendix A. Only the summary will be considered here. The equipment and the unit operation used in the process plant are listed in Table 8.1 below. However, the sizing for divider is not calculated since it involves in gas phase, which needs only pipeline. Due to the low cost of valves compared to other equipment, the sizing and costing of 3 main valves also neglected.

Table 8.1: The Equipment ListEQUIPMENTQUANTITY

Pump2

Mixer3

Compressor2

Heat Exchanger4

Reactor2

Flash Column4

Distillation Column1

Storage Tank3

Cooled 3

Heater1

Pervaporation membrane1

In this chapter, the summary result of all equipment will be shown and the detailed calculation can be found in Appendix A. The result of this chapter will be used in the calculation of mechanical design in Chapter 10. The base cost all equipment is based on the methods in Chemical Engineering Volume 6 (Sinnott, 1983), Product and Process Design Principle (Seider, 2010), Systematic Methods of Chemical Process Design (Biegler, 1997) and A Guide to Chemical Engineering Design & Economics (Ulrich, 1984)

8.2PUMP

The pump used in the plant is centrifuge pump with electric motor. The calculation was done based on the Product and Process Design Principle (Seider, 2010). The summary of pump sizing is shown in Table 8.2.

Table 8.2: Summary on Sizing and Costing for PumpIdentification Pump 1Pump 2

Item no.P-1P-2

Liquid Flow rate, kg/hr9926.854382.84

Liquid Density, kg/m3810790

Pressure inlet, bar3.039751.01325

Pressure outlet, bar5.066255.06625

Power, kW406.82368.48

Equipment cost, RM44314.5153758.45

8.3MIXER

The function of mixer is to mix the different components from different stream into one stream. Turbulent flow is important to make sure that the component mixes well. In theory, turbulent flow can be achieve when the Reynolds Number >2000. Therefore, a space-time assumption of 5 second (M-1) and 30 second (M-2 and M-3) is made in the calculation in order to achieve a Reynolds Number >2000. Detailed calculations of mixer as shown in Appendix A and for MMA plant three mixers are used. Mixer-1 is used to well mix the raw material, isobutylene with the air and steam. Mixer-2 is used to mix the air, methanol and intermediate product (methacrolein) stream from second stage separation while for Mixer-3 is used to well mix the raw material, pure methanol with the methanol in recycle stream.

Table 8.3: Summary on Sizing and Costing For MixerIdentificationMixer 1Mixer 2Mixer 3

Item noM-1M-2M-3

Type of mixerAgitators with propellerAgitators with propellerAgitators with propeller

Material of constructionCarbon steelCarbon steelCarbon steel

Flow rates, kg/ hr.50323.2641010.474254.82

Volume, m3100.19147.138470.04469

Tank Diameter, m5.7624.4820.440

Agitator Diameter, m1.7291.3450.132

Blast Pitch, m3.1122.4200.238

Tank Height, m5.7624.4820.440

Power, kW3.1409.2870.673

Equipment Cost, RM28,741.1441,039.5022,118.57

8.4COMPRESSOR

Compressor is used to compress gases from one low pressure to high pressure. Three type of compressor widely use in the process industries namely, centrifugal, reciprocating and axial flow compressor. Each compressor is generally a function of the gas capacity, action and discharge head. In this MMA plant, there are 2 compressors used to increase the pressure for the next separation system. The methods used to calculate the sizing and costing is show in Appendix A

Table 8.4: Summary on Sizing and Costing For CompressorIdentificationCompressor 1Compressor 2

Item noC-1C-2

Flow rate, kgmol/h1935.56924.88

Inlet Temperature, K623.15383.15

Pressure inlet, atm33

Pressure outlet, atm33

Actual work, kW546464.91085929

Equipment cost, RM552094.7

544265.1

8.5HEAT EXCHANGER

Type of heat exchanger used in this plant is shell and tube exchanger with one shell pass and two tube passes. The reasons for using this type of heat exchanger is because the surface area per volume is larger compared to other heat exchanger and the easier cleaning procedure. Besides, it can be constructed from a wide range of materials with well-established fabrication techniques and design procedures.

There are many kinds of shell and tube heat exchangers such as fixed-tube plate, U-tube type, internal floating head and external floating head. Split-ring internal floating head type is chosen as the model of the heat exchangers in this plant because of the following features.

Its suitable for high temperature differentials between shell and tubes Its easier to be cleaned as the tubes can be nodded from end to end and the bundle removed It can be used for fouling liquids

The way to allocate the fluid in the shell and tubes plays a very important role in the heat exchanger design. Where no phase change occurs, the following factors provide the basic guidelines in the allocation of the fluid stream to the shell or tubes.

Corrosive fluid should be allocated to the tube-side Higher fouling tendency fluid should be placed in the tube because tubes are easier to be cleaned than shell Higher temperature fluid should be allocated in the tube to reduce the overall cost The higher-pressure stream should be allocated to the tube-side For the same pressure drop, higher heat-transfer coefficients will be obtained on the tube-side than the shell-side More viscous fluid should be placed in the shell-side Locating the fluids with the lowest flow-rate to the shell side will give the most economical design

The general specification of shell and tubes heat exchanger is as follow:

Tube length between 2.44m and 8.88m Tube with outer diameter between 15.88 to 19.05 mm and inner diameter of 10.33 to 16.56 mm One shell pass and two tube passes

The designing procedures are based on the Kerns and Bells method (Sinnott, 1991). The design produce is as below:

i. Define the duty: heat transfer rate, fluids flow rate and temperatureii. Collect the fluid physical required: density, viscosity and thermal conductivityiii. Decide the type of exchanger to be usediv. Select the trial value for the exchanger to be usedv. Calculate the mean temperature different, Tlmvi. Calculate the area requiredvii. Decide the exchanger layoutviii. Calculate the individual coefficientsix. Calculate the overall coefficient and compare with the trial value. If the calculated value differ from the estimate value, substitute the calculated value and return to step (vi)x. Calculate the heat exchanger pressure drop: if unsatisfactory return to step (vii) or (iv) or (iii) in that order of procedure

Table 8.5: Sizing Specification Sheet of Heat Exchanger, X-1Sizing Specification Sheet Heat Exchanger, X-1

Identification:Item Heating Heat ExchangerDate: 03-5-2014

Item No. X-1 No required 1

Function :Heat-exchange

Operation :Continuous

Type:Horizontal Shell and Tube Heat Exchanger -Split-ring floating head type

Duty: 13278.584 kW

Tube Side:Tube:

Outer diameter 19.05 mmInner diameter 15.75 mm

Flowrate 53.063 kg/sNumber of tube 1968

Cross Flow Area194.85 mm2Length 2.44 m

Temperature110.00 oC to 340.00 oC1 Passes

Head MaterialCarbon steelTube Material Carbon steel

Shell Side:Shell:

Flowrate 5.08E+04 kg/h1.1964 m diameter

Cross Flow Area0.2863 m2

Temperature350.00 C to 347.42 CShell Material:

Carbon steel







Duty: 2896.40 kW

Tube Side:Tube:






Shell Side:Shell:




Carbon steel







Duty: 1555.405 kW

Tube Side:Tube:






Shell Side:Shell:




Carbon steel







Duty: 96.919 kW

Tube Side:Tube:






Shell Side:Shell:




Carbon steel

Table 8.9: Sizing Specification Sheet of Cooler, C-1Sizing Specification Sheet Cooler, C-1


Item No. C-1 No required 1

Function :Cooler



Duty: 15275.138 kW

Tube Side:Tube:





Head MaterialCarbon steelTube Material: Carbon steel

Shell Side:Shell:




Carbon steel




Function :Cooler



Duty: 1571.832 kW

Tube Side:Tube:






Shell Side:Shell:




Carbon steel




Function :Cooler



Duty: 702.875 kW

Tube Side:Tube:




Temperature25.00 oC to 48.00oC1 Passes


Shell Side:Shell:




Carbon steel

Table 8.12: Sizing Specification Sheet of Heater, H-1Sizing Specification Sheet Cooler, H-1


Item No. H-1 No required 1

Function :Heater



Duty: 295.446 kW

Tube Side:Tube:






Shell Side:Shell:




Carbon steel

Table 8.13: Summary on Sizing and Costing for Heat ExchangerTypeItem No.Material of ConstructionUtility Cost(RM/ year)Equipment Cost (RM)

Shell SideTube Side

Heat ExchangerX-1Carbon steelCarbon steel0128580.98




CoolerC-1Carbon steelCarbon steel433,430,077.90

64227.37


80579.81


56804.23

HeaterH-1Carbon steelCarbon steel9,730,650,837.29

32552.08

8.6REACTOR

There are two main reactors in the MMA plant. The first reactor is used to synthesis isobutylene to methacrolein and gases. Meanwhile, the second reactor is used to convert the intermediate product from first reactor to MMA by adding methanol, air and catalyst.

As the reactor is a type of continuous stirred tank reactor, method in Systematic Methods of Chemical Process Design (for vessel pressure) is used for sizing and costing. The reactor-sizing summary is shown in Table 5.6 below.

Table 8.14: Summary on Sizing and Costing for ReactorIdentificationReactor 1Reactor 2

Item noR-1R-2

Material constructionCarbon steelCarbon steel

Type of vessel Horizontal pressure vesselVertical pressure vessel

Catalystpalladium5% palladium-lead containing on alumina

Temperature (C)35080

Pressure (atm)35

Flowrate (kg/h)50332.423013.73

Density (kg/m3)847.0813.65

Molecular weight (kg/kmol)70.07818.02

Residence time (hour)510

Reactor volume (m3)356.581011.66

Diameter (m)6.7146.85

Height (m)396.4627.42

Volume of catalyst (m3)178.29

Equipment Cost (RM)1,859,929.711,713,345.3

8.7VAPOR- LIQUID SEPARATOR COLUMN

The separator column is simply a pressure vessel to phase-split between liquid and vapor phase. The chemical engineering design of the separator column is calculate as similar as flash drum based on the method found in Chemical Engineering Volume 6 (Sinnott, 1983) and Product and Process Design Principle (Seider, 2010). Detailed calculation is shown in Appendix A.

Table 8.15: Summary on Sizing and Costing for Separator Identification Separator 1Separator 2Separator 3Separator 4

Item no.F-1F-2F-3F-4

MaterialCarbon SteelCarbon SteelCarbon SteelCarbon Steel

Type of vesselVerticalVerticalVerticalVertical

Temperature, 0C110404030

Pressure, atm3351

Flowrate of vapor, kg/hr32147.34022225.25024909.130227.530

Density of vapor, kg/m33.3303.3205.7201.630

Flowrate of liquid, kg/hr18185.0809922.10013100.670214.970

Density of liquid, kg/m3907.620813.630917.470802.540

Residence time, min10101010

Volume, m33.3392.0322.3800.04464

Diameter, m4.6662.0791.8640.252

Length, m2.4314.0173.9681.572

Equipment cost, RM203,553.93168,468.32156,134.31131,274

8.8DISTILLATION COLUMN

Distillation is the most common method of separating homogenous mixtures. The separation of liquid mixtures by distillation depends of the differences in volatility between the components. The greater the volatility of a component compared to other component, the easier it is to be separated. Vapour flows up to the top column and the liquid flows counter currently down to the bottom of the column. The vapour is brought into intimate contact with the liquid on every plate. The design of distillation columns in this production of 100 000 MTA of MMA is based on the typical design procedures as stated in the Product and Process Design Principle (Seider, 2010). This is for the convenient of costing calculation. However, the more detail mechanical design of the plate is calculated in chapter 8 when designing the mechanical drawing.

For the column sizing and costing, it included the column vessel, tray stack, column condenser and column reboiler. The detail calculation for each of the columns is shown in Appendix A

8.8.1Choosing a Plate or Packed Column

There are two common types of distillation column used in the industries that are plate or packed column. It is important to choose the right type of distillation column in order to obtain the most efficient and cost effective for separation process. The most suitable type of column must be determined for the desired separation process because each of the columns has its own function. In this project, a sieve plate has been selected because:

1. Its modernization compared to bubble cap and other related plates as well as the economic value.2. It is more effective than other plate in bringing the vapour and liquid flows to be in intimate contact for achieving the desired separation.3. It satisfactory for most application.4. It can be designed to give a satisfactory operating range typically from 50% to 100%.5. It gives the lowest pressure drop.6. It gives the best capacity among the valve plate and bubble cap.

8.8.2 Plate Spacing

Plate spacing is the most important part for determining the overall height of the column. Plates spacing ranges from 0.15 m to 1 m are normally used. The spacing chosen depends on the column diameter and operating conditions. For columns above 1 m diameter, plate spacing 0.3 to 0.6 m will normally be used and 0.45 m can be taken as initial. This will be revised as necessary.

8.8.3Column Diameter

The principle factor in determining the column diameter is the vapour flow rate. The column diameter can be calculated by calculating the top and the bottom net area at its maximum volumetric flow rate. The velocity is normally between 70 to 90% of what which could cause flooding.

8.8.4Height of Column

The height of column in the distillation column is calculated by knowing the number of actual stages. The height of the column can be calculated by multiplying the number of the actual stages with tray spacing value.

Table 5.8 shows the calculation summary of three distillation columns. For further information, please refer to Appendix A.

Table 8.16: Summary on Sizing and Costing for Distillation ColumnIdentificationDistillation Column

Item no.DC-1

Material of construction? Steel

Type of plateSieve tray

Temperature, 0C

Pressure, atm1

Number of Tray

Reflux Ratio, R

Q condenser, kW

Q reboiler, kW

Column Height, m

Diameter, m

Tray Stack Cost, RM

Column Vessel Cost, RM

Column Condenser Cost, RM

Column Reboiler Cost, RM

Total Equipment cost, RM

Utility cost, RM / year

8.9 STORAGE TANK

Storage tank is needed for storing the product (MMA) and raw material (isobutylene and methanol) before entering to mixer. These components are in liquid form at the atmospheric pressure. The type of storage tank that has been chosen is fixed-cone roof, atmospheric pressure storage tank. Table 8.17 shows the summary of the storage tank.

HR

Stored liquid

Hs

HL

Diameter, D

Figure 5.1: Storage Tank Design.

Table 8.17: Summary on Sizing and Costing for Storage TankIdentificationStorage tank 1Storage tank 2Storage tank 3

StoredIsobutyleneMethanolMMA

Type of roofFixed-cone roofFixed-cone roofFixed-cone roof

Storage ClassificationHorizontalHorizontalHorizontal

Material of constructionStainless SteelCarbon SteelCarbon Steel

Day of Inventory3 days7 days7 days

Liq flowrate, m3/hr13.64755.0914.91

Storage volume, m31080.882844.122504.88

Diameter, m14.01412.90018.54

Height of tank (Hs), m7.0076.4509.270

Liquid space (HL), m5.9915.3717.649

Vapor space (HR), m1.2341.1401.630

Wall thickness, m0.2020.18560.267

Equipment cost, RM699,638.59527,309.541,306,350.74

8.10 PERVAPORATION MEMBRANE

By referring to Product and Process Design Principles book by Seider etc (2010), the cost for pervaporation membrane is typically $38/ft2. Therefore, the cost had been calculated together with the cost for the second reactor (R-2).

Table 8.19: Summary on Sizing and Costing for pervaporation membraneIdentificationMembrane

Area (ft2)397.25

8.11Summary of Equipment Total Costing

The total costing including the equipment cost and the utility cost for all the equipment used is listed in the Table 8.18 below.

Table 8.18: Summary of Equipment Total CostingEquipmentEquipment Cost (RM)Utility Cost (RM/yr)

P-148289.430

P-252672.230

M-128,741.140

M-241,039.500

M-322,118.570

COMP-1472198.70

COMP-2465502.10

X-1128580.980

X-220167.570

X-3382860.360

X-46317.110

C-164227.37433,430,077.90

C-280579.81418,855,584.97

C-356804.23387,228,424.36

H-132552.089,730,650,837.29

R-11,859,929.710

R-20

F-1203,553.930

F-2168,468.320

F-3156,134.31

F-4131,2740

DC-1

Pervaporation membrane

Isobutylene Storage Tank699,638.590

Methanol Storage Tank527,309.540

MMA Storage Tank1,306,350.740

Total