Chapter 5 - Equipment Sizing and Costing

CHAPTER 5

EQUIPMENT SIZING AND COSTING

5.1 Introduction

This section covered the chemical design of the equipment and unit operation

in the acrylic acid plant. The equipment and the unit operation used in the process

plant are listed as below :

Table 5.1: The Equipment List

UNIT QUANTITY

Compressor 2

Mixer 1

Heat Exchanger 1

Heater 1

Cooler 3

Reactor 2

Flash 1

Extraction Column 1

Pump 3

Distillation Column 3

Group 39 200,000 MTA Acrylic Acid

Chapter 5-1

Refrigeration System 2

Condenser 1

Reboiler 3

Storage Tank 3

In this chapter, the summary result of every equipment will be shown and the

detailed calculation can be found in Appendix E. The result of this chapter will be

used in the calculation of mechanical design in Chapter 8. The base cost of every

equipment is based on the methods in Systematic Methods of Chemical Process

Design (L.T Biegler, I.E. Grossmann and A.W. Westerberg, 1997) and A Guide to

Chemical Engineering Design & Economics (Gael D. Ulrich, 1984)

5.2 Compressor

5.2.1 Introduction

Compressor is used to compress gases from one point to another point. There

are three type of compressor widely used in the process industries namely,

centrifugal, reciprocating and axial flow compressor. Axial flow compressor used for

high flowrate and moderate differential pressure and centrifugal compressor for high

flowrate and by staging for high differential pressure. Reciprocating compressor can

be used over a wide range of pressures are required at relatively low flowrate. Each

compressor is generally a function of the gas capacity, action and discharge head.

The work of compressor and single stage compressor can be calculated by

assumed the compressor is operated ideally under adiabatic compressor with three

stage compressor.

Ws = ( (-1) ) RTinlet [ (Poutlet Pinlet( (-1) ) - 1]

With :

Ws = Compressor work (kJ/ hr)


Chapter 5-2

= Molar gas flowrate (kmol/ hr)

= Cp / Cv = 1.4

R = Gas constant

= 8.314 kJ/ kmol K

Tinlet = Inlet temperature (K)

Poutlet = Outlet pressure (atm)

Pinlet = Inlet pressure (atm)

The actual compressor work is

Wactual = W / (c x m)

With :

Wactual = Actual compressor work (hp)

W = Compressor work (kW)

c = Compressor efficiency

m = Motor efficiency

5.2.2 Chemical Design and Costing Summary

Detailed calculation as shown in Appendix E

Identification Compressor 1 Compressor 11

Item no. 1 11

Function To provide system

pressure required

To provide system

pressure required

Material of construction Stainless Steel Stainless Steel

Type of equipment Air Compressor Centrifugal Motor

Flowrates (kmol/hr) 4937.6 753.3

Pressure inlet (atm) 1 0.0526

Pressure outlet (atm) 3 1.5


Chapter 5-3

Temperature in (C) 25 12.4

Actual work (kW) 1218.8 3874.4

Equipment Cost (RM) 48423354.39 22533319.22

Total Cost 70,956,673.62

5.3 Mixer

5.3.1 Introduction

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

mix well. In theory, turbulent flow can be achieve when the Reynolds Number

>2000. Therefore, a space-time assumption of 60 seconds is made in the calculation

in order to achieve a Reynolds Number >2000.



Identification Mixer 9

Item no 9

Function Mixed fresh ethyl

acetate with recycle

stream 20

Material Stainless Steel

Flowrates, kmol/ hr. 804.23

Volume, m3 1.0590

Pressure, atm 1.5

Temperature, C 30.0

Equipment Cost (RM) 560642.95


Chapter 5-4

Total Cost 560642.95

5.4 Heat Exchanger

5.4.1 Introduction

Heat exchanger can be classified in a number of ways depending on their

construction or on how the fluid moves relatively to each other through the device.

The most common type is one in which the hot and the cold come separated by a

tube wall or a flat or curved device. For this chemical design, the heat exchanger

that transferred heat from the hot stream to the cold stream and from the cold stream

to hot stream will be considered.

5.4.2 Design Procedure

The design procedure follows as below :

i. Define the duty: heat transfer rate, fluids flow rate and temperature

ii. Collect the fluid physical properties required : density, viscosity and

thermal conductivity.

iii. Decide the type of heat exchanger to be used.

iv. Select the value for the overall coefficient, U.

v. Calculated the mean temperature different, Tlm

vi. Calculated the heat transfer area required

vii. Decide the heat exchanger layout

viii. Calculated the individual coefficient

ix. Calculated the overall coefficient and compare with the trial value. If the

calculate value is above the estimated value, than the overall coefficient is

satisfy

x. Calculated the heat exchanger pressure drop; if the pressure drop is less than

1 atm, this mean that the pressure drop for heat exchanger is acceptable.


Chapter 5-5

5.4.3 Summary for Heat Exchanger Design


Identification Heat Exchanger

Item no 19

Function Exchange Heat Between Stream

5 and Stream 9

Heat Duty, Q (kW) 14,155.16

Hot Fluid Properties

Flowrates (kg/s)

Inlet temperature (C)

Outlet temperature (C)

62.81

220

59.7

Cold Fluid Properties



149

315

Heat transfer area, A (m2) 721

Number of tubes, Nt 2350

Tube inside diameter, dI (mm) 16

Tube outlet diameter, do (mm) 20

Length of tube, L (m) 4.88

Bundle diameter, Db.(mm) 1.352

Shell diameter, Ds.(m) 1.448

Tube Pressure Drop (atm) 0.3

Shell Pressure Drop (atm) 3.1

Cost, RM 5,045,787

Total Cost, RM 5,045,787


Chapter 5-6

5.4.4 Summary for Heater Design


Identification Heater

Item no 4

Function Heating Stream 28

Heat Duty, Q (kW) 852.72


Flowrates (kg/s)



16.16

321

295




315

Heat transfer area, A (m2) 210.1


Tube inside diameter, dI (mm) 16

Tube outlet diameter, do (mm) 20




Tube Pressure Drop (atm) 3.8

Shell Pressure Drop (atm) 3.7

Cost, RM 728,836.00

Total Cost, RM 728,836.00


Chapter 5-7

5.4.5 Summary for Cooler Design


Identification Cooler Cooler Cooler

Item no 6 8 12

Function Cooling

Stream 29

Cooling

Steam 7

Cooling

Stream 19

Heat Duty, Q (kW) 852.28 9708.97 2339.36


Flowrates (kg/s)



36.61

59.7

50

62.73

325

220

14.50

131

30




25

40

25

50

25

50

Heat transfer area, A (m2) 116.3 673.2 176.1

Number of tubes, Nt 379 2195 574

Tube inside diameter, dI (mm) 16 16 16

Tube outlet diameter, do (mm) 20 20 20

Length of tube, L (m) 4.88 4.88 4.88

Bundle diameter, Db.(mm) 0.592 1.311 0.714

Shell diameter, Ds.(m) 0.683 1.407 0.806

Tube Pressure Drop (atm) 2.4 0.5 0.0013

Shell Pressure Drop (atm) 0.0024 0.1 0.0029

Cost, RM 560,643 1,569,800 672,772

Total Cost, RM 2749215.00


Chapter 5-8

5.4.6 Summary for Reboiler Design


Identification Reboiler Reboiler Reboiler

Item no 10 14 17

Function Heating out

stream from

distillation 10

Heating out

stream from

distillation 14

Heating out

stream from

distillation 17

Equipment Type Kettle Reboiler Kettle Reboiler Kettle Reboiler

Heat Duty, Q (kW) 8142.750 6138.125 2932.708


Flowrates (kg/s)



85.7718

150

100

664.6561

150

100

153.7625

150

140




23.2

33.4

32.3

40.3

59.4

59.70

Heat transfer area, A (m2) 95.8293 79.0865 38.1778

Number of tubes, Nt 201 166 80

Tube inside diameter, dI (mm) 28.45 28.45 28.45

Tube outlet diameter, do (mm) 31.75 31.75 31.75

Length of tube, L (m) 4.8 4.8 4.8

Bundle diameter, Db.(mm) 723.2039 665.2634 0.714

Shell diameter, Ds.(m) 1.4464 1.3305 0.806

Cost, RM 688297.04 615844 398487.76



Chapter 5-9

5.4.7 Summary for Condenser Design


Identification Condenser

Item no 17

Function Cooling out

stream from

distillation 17

Equipment Type Floating head

Heat Duty, Q (kW) 2530.8889




28.5

28.3


Flowrates (kg/s)



605.2007

25

26

Heat transfer area, A (m2) 979.8716


Tube inside diameter, dI (mm) 22.10

Tube outlet diameter, do (mm) 25.40




Cost, RM 2934318.96


5.5 Refrigeration


Chapter 5-10

5.5.1 Refrigeration system

If a process stream needs to operate below about 300 K, some sort of

refrigeration is required and a refrigeration cycle needs to be considered. Often,

refrigeration can be purchased from an off-site facility.

In designing a refrigeration system , we first consider the refrigeration cycle

and the pressure-enthalpy diagram. As with staged compression, there is a trade-off

between capital and operating costs in choosing the number of refrigeration cycles. A

single cycle requires the maximum work and cooling water while a large number of

cycles require minimum work and cooling water. To relate the work (W) and heat

rejected for refrigeration (Q), a coefficient of performance is defined, CP = Q/ W. As

with staged compression, CP~4 is selected for design purposes. Thus, in a typical

cycle :

W = Q/ 4

Qc = W + Q ~ 5/ 4 Q

And for the compressor driven with an electric motor,

Wb = W/ mc

= W/ 0.72

(Assume c = 0.8 and m = 0.9)

5.5.2 Designing a Refrigeration System

By using these simplified sizing relationship, the work requirements for each

refrigeration cycle will be evaluated. This is done by considering that CP is the same

for all N cycles, and T = 30K/ cycle. The simplified relationships are :

W = Q [(5/ 4)N – 1 ]

Qc = (5/ 4)N Q

Wb = W/ (mc)


Chapter 5-11

The costing of a refrigeration system can be done by using the mechanical

refrigeration configurations which had been specified directly in Guthrie. The basic

configuration includes centrifugal compression, evaporators, condensers, field

erection, and subcontractor indirect costs.

5.5.3 Sizing and Costing Summary of Refrigeration System


No. of

cycles

Qc (kW) Wb (kW) S (ton) Price

RM

Condenser 10 1 162.65 45.1801 37.00 1438590.40

Condenser 14 1 7554.17 2098.3796 1718.40 21124826.58

Total 22563416.98

5.6 Reactor


Chapter 5-12

5.6.1 Introduction

In term of reactor design, decisions must be made due to the type of reaction,

concentration, temperature, pressure, phase and catalyst. Then a practical reactor is

selected, approaching as nearly as possible the ideal in order that the design can

proceed.

Practical reactor deviate from the three idealized models, which are idealized

batch model, continuous well-stirred model and plug-flow model. The practical

reactor can be classified to stirred tank reactor, tubular reactor, fixed bed catalytic

reactor, fixed bed non-catalytic reactor, fluidized bed catalytic reactor, fluidized bed

non catalytic reactor and kiln.

5.6.2 Chemical Design Summary


Reactor First-stage (R-3) Second-stage (R-5)Type Fixed-bed Multi-Tubular Reactor

Operating conditions :Temperature, oC 325 220Pressure, atm 2.5 2.5Space velocity, h-1 1625 2160Residence time, s 2.22 1.67Volume, m3 124 93Diameter, m 3.4 3.1Length, m 13.6 12.4Cross-sectional area, m2 9.1 7.5Catalyst :Basic components Mo, Co, Ce, Ni oxidesAppearance Grey tablets with dimensions 5x5 mm Bulk density, kg/m3 1200 1200Total mass, kg 74296 55921Mass in tube, kg 15.6 14


Chapter 5-13

Tube properties :Nominal size, in 2 2Outside diameter, mm 60 60Inside diameter, mm 42.25 42.25Wall thickness, mm 5.4 5.4Inside cross-sectional area, m2 0.001905 0.001905Number of tube 4776 3952Length, m 7 6Bundle diameter, m 5.34 4.89Shell inside diameter, m 5.4 4.94Baffle spacing, m 2.16 1.98Number of baffle 3 3Heat removal system :Heat transfer area, m2 3468.6 3005.1Cooling media Molten SaltCoolant flowrate, m3/h 411.4 698.9Total cost, RM 3,135,000 2,810,690

5.7 Flash Column

5.7.1 Introduction


Chapter 5-14

The flash drums are simply a pressure vessel to phase-split between liquid

and vapor phase. The chemical engineering design of the flash drum are based on the

method found in Chemical Engineering Volume 6 (Sinnott, 1991).


Detailed calculation as shown in Appendix E.

Identification Flash

Item no. 7

Function Purge The Residual Gas

Material Stainless Steel

Temperature (C) 30

Pressure (atm) 1.5

Cross sectional Area (m2) 11.8417

Inside Diameter (m) 3.8827

Height for Vapor Phase (m) 3.8827

Light Liquid Height (m) 2.2414

Liquid Depth (m) 1.3862

Cost 2458203.71


5.8 Pump

5.8.1 Introduction


Chapter 5-15

Pump are devices for supplying energy or head to a flowing liquid in order to

overcome head losses due to friction and also if necessary, to raise the liquid to a

higher level. The different types of pump commonly employed in industrial

operations can be classified as follows :

Reciprocating or positive-displacement pump with valve action : piston pumps,

diaphragm pumps, plunger pumps.

Rotary positive-displacement pumps with no valve action:gear pumps, lobe

pumps, screw pumps, metering pumps.

Rotary centrifugal pumps with no valve action : open impeller, closed impeller,

volute pumps and turbine pumps.

Air-displacement systems : airlifs, acid eggs or blow cases, jet pumps, barometric

legs.

The centrifugal pumps are the major types that used in the chemical plant

nowadays. Centrifugal pumps are used so extensively and for such a wide variety of

services that need for standardization of dimensions and operating characteristic has

long been evident. Pump selection is made depending on the flow rate and head

required, together with other process considerations.




Chapter 5-16

.

Identification Pump Pump Pump

Item no 15 16 18

Function Pump the effluent

to D-10

Pump the

effluent to D-14

Pump the fresh

solvent

Type Centrifugal Pump Centrifugal

Pump

Centrifugal Pump

Material of

construction

Stainless Steel Stainless Steel Stainless Steel

Inlet Flowrates,

(kmol/hr)

877.2 455.9 50.9

Outlet Flowrates,

(kmol/hr)

877.2 455.9 50.9

Pressure Inlet (C) 0.526 0.039 1

Pressure Outlet

(C)

1 1 1.5

Temp. Inlet (C) 33.4 40.3 30

Temp. Outlet (C) 33.3 40.3 30

Shaft power (kW) 1.3973 1090.3283 0.1346

Differential head

(m) 9.6917 9.7003 5.8351

Equipment Cost

(RM) 88552.84 2728.79 336.83


5.9 Distillation Column


Chapter 5-17

Industrial scale of production of chemical product concerns purity of the

product. Higher purity gives higher market price. In each operation, separator plays

a major and important task to separate products from side products in order to obtain

the desired specification. Chemical can be divided into miscible and immiscible

phases. Immiscible phase can be isolated using physical separation methods, while

separating of miscible phase mostly deals with surface contacting devices. Among

the equipment used are distillation column, absorption column and stripping column.

5.9.1 Introduction

Distillation is a process of heating a liquid until its more volatile constituents

pass into the vapor phase, and then cooling the vapor to recover such constituents in

liquid form by condensation. The main purpose of distillation is to separate a

mixture of several components by taking advantage of their volatilities, or the

separation of volatile materials from nonvolatile materials. The design of distillation

columns in this production of 200,000 MT/ year of acrylic acid has based on the

typical design procedures as stated in Chapter 11 of Chemical Engineering, Volume

6, by J.M Coulson and J.F Richardson.

For the column sizing and plate design, a trial and error approach has been

used to obtain an optimum and satisfactory design. Each design variable is set and

calculated from the design formula and based on the recommended values. By

checking the key performance factors, the design parameters have been revised or

other wise determined. Some designs parameters are obtained from the simulation

generate report by the ChemCAD Simulator. In addition, the design calculation is

done for above feed point and below separately.

5.9.1.1 Choosing A Plate or Packed Column


Chapter 5-18

There are two common types of distillation column used in the industries that

are palate or packed column. It is important to choose the right type of distillation

column in order to obtain the most efficient and cost effective separation process.

The most suitable type of column must be determined for the desired separation

process because these two columns have their own uses. In this project, a sieve plate

has been selected.

5.9.1.2 Plate Spacing

Plate spacing is the important for determined the overall height of column.

Plates spacing from 0.15m to 1m are normally used. The spacing chosen depends on

the column diameter and operating conditions. For column above 1m diameter, plate

spacing 0.3 to 0.6m will normally be used, and 0.5m can be taken as initial. This

will be revised as necessary.

5.9.1.3 Column Diameter

The principle factor on determining the column diameter is the vapor flow

rate. The column diameter can be calculated by calculating the top and bottom net

area at its maximum volumetric flow rate. The velocity is normally between 70 to

90% of what which cloud cause flooding

5.9.1.4 Height of Column

The height of column in the distillation column is calculated by knowing the

number of actual stages. Theoretical stages is given by ChemCAD Simulator was

used to obtained the number of actual stages required. The height of column can be

calculated by multiplying the number of the actual stages with tray spacing value.

5.9.1.5 Design Procedure


Chapter 5-19

The general outlines of the design procedures are as below;

i. Determine the vapor and liquid rate, based on the reflux ratio and feed

condition

ii. Collect or estimate the system physical properties

iii. Select a trial plate spacing

iv. Based on the flooding condition, the column diameter is determined.

v. Decided the liquid flow pattern on the plate.

vi. Try to make a plate layout with downcomer area, active area, hole diameter,

hole area, weir height, weir length and plate thickness.

vii. Check the weeping rate.

viii. Check the plate pressure drop.

ix. Check the down-comer backup.

x. Determine plate layout details.

xi. Confirm on the percentage flooding based on the chosen column diameter.

xii. Check for entrainment.

xiii. Optimize the design parameters for column diameter and plate spacing.

xiv. Determine the column wall thickness and column head selection.

xv. Finalize the design with the drawing and data specification sheet.



Chapter 5-20


Identification Distillation Distillation Distillation

Item no. 10 14 17

Operating pressure, barg 0.0533 0.0935 0.0404

Column Sizing

a) Tray Spacing (m)

b) Diameter of column, Dc (m)

c) Area of column, Ac (m2)

d) Total height of column, HT (m)

0.61

3.93

12.1627

12.64

0.61

2.78

6.0884

23.49

0.61

2.31

4.2025

23.49

Provisional plate design

a) Plate thickness (mm)

b) Plate area

i. Downcomer area, Ad (m2)

ii. Net area, An (m2)

iii. Active area, Aa (m2)

iv. Hole area, Ah (m2)

3

1.4595

10.7031

9.2436

0.9244

3

0.7306

5.3578

4.6272

0.4627

3

0.5043

3.6982

3.1939

0.3194

Weir Design

a) Weir length, Iw (m)

b) Weir height, Hw (m)

c) Weir liquid crest

i. Maximum, how (mm liquid)

ii. Minimum, how (mm liquid)

2.9868

12

30.2929

23.8821

2.1128

12

21.9503

17.3051

1.7556

12

24.5746

19.3509

Weep Point

a) Minimum Uh (m/s)

b) Actual Ua (m/s)

30.0833

62.9164

52.9122

127.1840

37.5584

83.2073

Hole Design

a) Hole diameter (mm)

b) Hole area (m2)

c) Number of holes

5

1.964x 10-5

47066

5

1.964x 10-5

23561

5

1.964x 10-5

16263

Total plate pressure drop

(mm Liquid)

175.6899 169.2340 150.0615


Chapter 5-21

Equipment Cost (RM) 4601987.36 5164815.38 4122882.02


5.10 Storage Tank Specification



Storage Tank Propylene (raw material)Day of inventory, days 3Vessel type Cylindrical (Bullet) TankNumber of Bullet 2Volume, m3 1383Pressure, bar 30.0Temperature, oC 40.0Stored materials LiquidDiameter, m 7.60Length, m 30.0Orientation Axis horizontalCorrosion allowance, mm 2.0Wall thickness, mm 6.0Material of construction Carbon SteelCost, RM 6,037,693

Storage tank Ethyl Acetate (solvent) Acrylic Acid (product)Day of inventory, days 5 5Vessel type Floating-roof Floating-roofVolume, m3 654 3190Pressure, atm 1 1Temperature, oC 25 25Stored materials Liquid LiquidDiameter, m 8.22 13.94Height of tank :

HS

4.11 6.97

HL 3.7 6.27HR 0.72 1.23


Chapter 5-22

Orientation Axis vertical Axis verticalCorrosion allowance, mm 2 4Wall thickness, mm 12 21Material of construction Carbon Steel Stainless SteelCost, RM 306,485 1,707,805


Chapter 5-23

Chapter 5 - Equipment Sizing and Costing

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