Design

SEPARATOR DESIGN

ISSUED FOR
APPROVAL
March 07, 2021

A Issued for Approval 07/03/2021 Muhammad Usman

Client
Rev Description Date Prepared by
Approval

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Design

Table of Contents
1. OBJECTIVE 3
2. INTRODUCTION 3
2.1 Settling Laws 3

3. THEORY AND EQUATION 4

3.1 Retention Time 4

4. PROCESS DESCRIPTION 5
5. MATERIAL BALANCE 6
6. SEPARATOR CALCULATIONS 7
6.1 Design Conditions 7

6.2 Superficial Velocity 7

6.3 Volumetric Flow Rate 8

6.4 Flow Area 8

6.5 Diameter 8

6.6 Standard Separator Sizes 8

6.7 Liquid Volume 9

7. MECHANICAL DESIGN OF SEPARATOR 10

7.1 Design Pressure 10

7.2 Design Temperature 10

7.3 Minimum practical wall thickness 10

7.4 Heads and closures 11

7.5 Types of supports 11

7.6 Weight of shell 12

8. ECONOMIC AND SUSTAINABILITY 12

8.1 Separator: 12

9. DATA SHEET 16
10. PIPING AND INSTRUMENTATION DIAGRAM 17
11. REFERENCES 18

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Separator design

1. Objective
Separator are design in such a way that it optimizes the separation of Gas, solid and water
emulsion. The separator is design to handle the capacity of Vapour 812.17 kg/hr, solid 116.91
kg/hr and water 361.19 kg/hr. The recommended L/D ratio is 3 and droplet size is 150 mm.
The detailed process description along with P&IDs and Economic analysis are also the part of
scope
The GPSA handbook and API 12J is followed to design the separator with different empirical
methods [1] [2].

2. Introduction
The separation is based on the density difference, greater the difference easier will be the
separation. Residence time is required to settle the droplets of heavy liquid from the light one,
Liquid droplets will settle out of a gas phase if the gravitational force acting on the droplet is
greater than the drag force of the gas flowing around the droplets, These forces are described
by the terminal or finite settling velocity calculations

Figure 1: Forces on liquid droplets in gas stream

2.1 Settling Laws
Three settling laws is applicable for separator design
• Stokes law When the Reynold number is less than 2
• Intermediate Law when the Reynold number is between 2 and 500
• Newtons law when the Reynold number is between 500 – 200,000

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• Liquid droplet size and distribution is another factor for the selection of appropriate law

3. Theory and Equation

From the modification of stokes law, gas capacity of the separator may be determined. The
separation capacity is based on the minimum droplet size of particle which need to be removed
from the gas phase at the given velocity. The equation used to calculate the maximum allowable
velocity of gas at operating conditions is given below [1]:

𝑑𝐿 − 𝑑𝐺
𝑣𝑎 = 𝑘√
𝑑𝐺

Where
Va: Maximum allowable superficial veleocity
dL: Density of liquid (lb/ft3)
dG : Density of Gas (lb/ft3)
K: Constant, based on operating and design condition

Table 1: K factor for Separators

Height or length
Type Separator Typical K-factor Range
L (ft)
5 0.12 to 0.24
Vertical
10 0.18 to 0.35
10 0.40 to 0.50
Horizontal
Other lengths 0.40 to 0.50 (l/10)0.56

Spherical All 0.2 to 0.35

The rate calculated from the above equation allow the droplets greater than 10 microns to settle
from gas.
3.1 Retention Time
The capacity of the liquid is dependent on the retention time of liquid in the vessel. The enough
residence time should be provide to obtain equilibrium between gas and liquid at the operating
condition[1].
1440 (𝑉)
W=
𝑡

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Where
W : Liquid capacity bbl/day
V: Settling volume of liquid
t: Retention time

4. Process Description
Feed is flow into the separator, Feed temperature is measured by TI-001, which is 358 C. The
Feed flow rate is measured by FIT-001, the flow is controlled by feed forward controller, FIT
transmit the Electric signal to Flow controller, Flow controller send the pneumatic signal to
final control element (Valve), Valve is open and closed according to the set pressure of 1290
kg/hr. Emergency shutdown valve is installed on the feed line to isolate the equipment in case
of emergency.
In the separator flashing cause the gas, liquid and solid to separate, due to light density gases
moves upward, the gas temperature and flow is measured by TI-002 & FI-002, the temperature
of the stream is 358 C and Flow is 812 kg/hr. The pressure is measured by PIT-001, the pressure
is controlled by feed forward controller, PIT transmit the Electric signal to Pressure controller,
Pressure controller send the pneumatic signal to final control element (Valve), Valve is open
and closed according to the set pressure of 1 atm. Emergency shutdown valve is installed on
the gas line to isolate the equipment in case of emergency.

The liquid flow over through the baffle installed inside the separator, the level of the liquid in
separator is controlled by feedback ward control loop. The LIT sense the level and controller
take action according to the set point. The liquid is pumped by P-100. The pump speed is
adjusted by the variable frequency drive. XI indicator is also installed on pump which indicate
the on/off position of the pump. Hand switches are also mounted on the field for operator
assistance. Non return valve is installed at the downstream of pump to avoid back flow in the
pump. The Liquid temperature and flow is measured by TI-003 & FI-003, which is 358 C and
361.19 kg/hr.

Solid stream consist of ash and carbon its separated in the vessel due to gravitational force. The
solid settle down and flow out to the separator. The Solid temperature and flow is measured by
TI-004 & FI-004, which is 358 C and 116 kg/hr.

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The pressure safety valve is also installed on the separator for its safety. Its set pressure is 1.5
atm. If the pressure inside the vessel is greater than 1.5 atm due to mishap in the operation then
the PSV is popup and Safe the apparatus to rapture.

5. Material Balance
The material balance of the stream are given below

Table 2: Stream Composition From Aspen Plus Simulation

Unit Feed Gas Solid Liquid

Mass Flows
kg/hr 1290.354 812.17 116.9938 361.19

Mass Fraction

O2 0.1336 0.2123

CO2 0.2635 0.4187

CO 0.1677 0.2665

CH4 0.0045 0.0071

H2S 0.0010 0.0015

ASH 0.0515 0.0000 0.5684

H2 0.0504 0.0801

WATER 0.2799 0.0000 1

NH3 0.0040 0.0064

C 0.0391 0.0000 0.4316

HCL 0.0046 0.0074

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6. Separator Calculations
Steps that involve in the separator design is:
1. Calculate the superficial velocity
2. Calculate the Volumetric flow rate
3. Calculate the minimum gas flow area by using superficial velocity and volumetric flow
rate.
4. Calculate the Diameter by using flow area
5. Select the one size above then the calculated diameter from the standard separator sizes
6. Calculate the liquid Volume and Liquid capacity of the vessel.
7. Calculate the design pressure and temperature conditions for the separator
8. Calculate the minimum practical wall thickness
9. Select the type of Head and Closure.
10. Select the type of support for separator structure
11. Calculate the weight of shell
6.1 Design Conditions
The design parameters are given in table below:
Parameters Units Value
Gas flow rate MMSCFD 1.191
Water and ash flow rate BPD 55.99
Operating Pressure PSIG 14.7
Operating Temperature F 99.37 (37.42 C)
Flowing gas Density, Dg lb/ft3 0.0557 (0.89 kg/m3)
Molecular w8 of gas - 15.17
Flowing water and Ash density, dL lb/ft3 65.70 (1052 kg/m3)
Separator type - Vertical

For initial guess assume that the length of the vessel will be 5 feet so the K factor from table
1 is 0.24.
6.2 Superficial Velocity
To calculate the diameter of the vessel superficial velocity of gas is required. Increase in
superficial velocity increases the gas holdup. The maximum allowable gas superficial
velocity is

𝑑𝐿 − 𝑑𝐺
𝑣𝑎 = 𝑘√
𝑑𝐺

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Design

65.7 − 0.0557
𝑣𝑎 = 0.24√
0.0557

Va = 8.23 ft/sec (2.50 m/sec)

6.3 Volumetric Flow Rate
Actual volume flow rate of gas
(1.191∗106 𝑠𝑐𝑓/𝑑𝑎𝑦)∗15.17 𝑙𝑏/𝑚𝑜𝑙
=
379.5 𝑠𝑐𝑓/𝑚𝑜𝑙∗86400𝑠/𝑑𝑎𝑦∗0.0557𝑙𝑏/𝑓𝑡3
= 9.89 ft3/sec (0.28 m3/sec)
6.4 Flow Area
Minimum Gas flow area = Actual volume flow rate of gas / Maximum allowable gas
superficial velocity
Minimum Gas flow area = 9.89/8.23 = 1.2007 ft2 (0.112 m2)

6.5 Diameter
Minimum internal diameter of separator =
𝜋 𝑑2
Area =
4

1.2007∗144
Diameter = √
0.7854

Diameter = 14.83 inch

6.6 Standard Separator Sizes
Standard Separator sizes are given below:
STANDARD SEPARATOR SIZES AS PER
API
D [in] x H or L [ft]
12¾ in x 5 ft
12¾ in x 7½ ft
12¾ in x 10 ft

16 in x 5 ft
16 in x 7½ ft
16 in x 10 ft

20 in x 5 ft

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STANDARD SEPARATOR SIZES AS PER

API
20 in x 7½ ft
20 in x 10 ft

24 in x 5 ft
24 in x 7½ ft
24 in x 10 ft

30 in x 5 ft
30 in x 7½ ft
30 in x 10 ft

36 in x 5 ft
36 in x 7½ ft
36 in x 10 ft
36 in x 15 ft

42 in x 7½ ft
42 in x 10 ft
42 in x 15 ft

48 in x 7½ ft
48 in x 10 ft
48 in x 15 ft

54 in x 7½ ft
54 in x 10 ft
54 in x 15 ft

60 in x 7½ ft
60 in x 10 ft
60 in x 15 ft

As the calculated diameter is 14.38 inch so the above standard size is 16 in x 10 ft.
Retention time according to API 12J is 1 min.
6.7 Liquid Volume
162 ∗0.7854 𝑖𝑛𝑐ℎ2 ∗3 𝑓𝑡
Liquid Volume, V =
144 𝑖𝑛𝑐ℎ2 𝑓𝑡2 ∗5.615 𝑓𝑡3/𝑏𝑏𝑙

V= 0.748 bbl
1440∗ 0.746
Liquid capacity of the separator =
1
W = 1074 BPD

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Liquid capacity is satisfactory for design based on 16-in. ID x 10 ft vertical size.

7. Mechanical Design of Separator

7.1 Design Pressure
Operating pressure = 14.7 psi = 1 bar
Design pressure = 5-10 % of operating pressure
Design pressure= 1*0.10+1
Design pressure= 1.10 bar
7.2 Design Temperature
Operating temperature = 99.37 oC
Design temperature = 5-10 % of operating temperature
Design temperature = 99.37 * 0.10 + 99.37
Design temperature = 9.937 + 99.37
Design temperature = 109 oC
7.3 Minimum practical wall thickness
A less wall thickness needed to assure that any of the vessel is enough rigid to stand at its own
weight and any accidental loads. From general guidelines, the wall thickness of a vessel must
not be lesser than the values given below and these values are with a corrosion allowance of 2
mm[3].
Table 3: Wall thickness of vessel [4]

Vessel Diameter (m) Minimum thickness (mm)

1 5

1 to 2 7

2 to 2.5 9

2.5 to 3 10

3 to 3.5 12

Since the diameter of the vessel is 0.40 m (16inch), so from the above table the thickness of
shell is 0.4*5 = 2 mm. Verify the thickness with the mathematical correlation.
Thickness of the Separator shell [3]=

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Pi= 1.10 bar or 0.11 N/mm2

J =1 (for no joints in the head)
f= stress factor =80 N/mm2 (for carbon steel)[3].
Di = 406.4 mm
0.11∗406.4
e=
(2∗1∗80)−0.11

e = 0.27 mm
By adding the corrosion allowance
e = 0.27 + 2 = 2.27 mm
7.4 Heads and closures
The ends of a cylindrical vessel are closed by heads of various shapes. The principal types used
are[3]:
1. Flat plates and formed flat heads;
2. Hemispherical heads
3. Ellipsoidal heads
4. Torispherical heads
Table 4: Comparisons of Heads

Hemispherical
Flat Head Torispherical heads Ellipsoidal heads
heads
Above 15 bar
Applicable to low Used up to operating Used for very high
ellipsoidal head is
pressure pressure of 15 bar pressures
used
Above 10 bar their
cost should be
Cheapest from all Economical with in
compared with that Capital cost is high
types pressure limits
of an equivalent
ellipsoidal head

Flat head is applicable for Separator.

7.5 Types of supports
• Saddle supports ( for horizontal vessels)
• Brackets supports ( for vertical vessels )
• Skirt support (for vertical vessels, particularly where the length is high and effect of
wind is prominent).
For the desired separator, I used “Bracket Supports”

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Figure 2: Brackets supports

7.6 Weight of shell
Wv = 240 * Cv *Dm*(Hv+0.8*Dm)*t [3].
W= Total weight of shell
Cv = A factor to account for the weight of nozzles, manways, internal supports, etc.; which
can be taken as = 1.08 for vessels with only a few internal fittings,
Dm = Mean diameter = (Di+t) = 0.40+0.00027 = 0.40027 m
Hv = height of vessel = 3.048 m
t = thickness of shell = 0. 27 mm
Wv = 240*1.08*0.40027*(3.048+0.8*0.40027)*0.27
Wv = 94.35 N

8. Economic and Sustainability

Cost estimation is a specific subject and a business itself. A design engineer required to capable
to evaluate a time efficient and rough cost details to take a decision between the alternative
designs and for project assessment. Chemical plants are generally construct to generate a great
profit and an estimation of investment needed and cost of producing the product required before
the profitability of project can be evaluated [4].
8.1 Separator:
Design conditions
Diameter = 0.4064 m
Length = 3.048 m
From figure 6.5 b (Colson and Richardson Vol-6)

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As the length is 3.048 m and diameter is 0.4064 m so from the graph the equipment cost is
Bare cost= 6*1000 =6,000 $
Purchased cost= Bare cost from fig * Material factor * Pressure factor [3]
Material factor = C.S = 1.0
Pressure factor = 1-5 bar = 1
Purchased cost= 6,000 * 1.0 * 1.0
Purchased cost= 6,000 $ at 1998
To update the historical cost to the present cost, chemical engineering plant cost index is used.
The average yearly based cost index is given in table below:
YEAR CEPCI
1950 73.9
1953 84.7
1955 88.3
1958 99.7
1959 101.8
1960 102
1961 101.5
1962 102

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YEAR CEPCI
1963 102.4
1964 103.3
1965 104.2
1966 107.2
1967 109.7
1968 113.6
1969 119
1970 125.7
1971 132.3
1972 132.3
1973 144.1
1974 164.4
1975 182.4
1976 192.1
1977 204.1
1978 218.8
1979 238.7
1980 261.2
1981 297
1982 314
1983 316.9
1984 322.7
1985 325.3
1986 318.4
1987 323.8
1988 342.5
1989 355.4
1990 357.6
1991 361.3
1992 358.2
1993 359.2
1994 368.1
1995 381.1
1996 381.7
1997 386.5
1998 389.5
1999 390.6
2000 394.1
2001 394.3
2002 395.6
2003 401.7
2004 444.2
2005 468.2
2006 499.6
2007 525.4
2008 575.4
2009 521.9
2010 550.8

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YEAR CEPCI
2011 585.7
2012 584.6
2013 567.3
2014 576.1
2015 556.8
2016 541.7
2017 567.5
2018 603.1
2019 607.5
2020 656.1

1998 indexes = 389.5

2020 Indexes = 656.1
Cost in 2020 = Cost in 1998 * (Cost index in 2020/ cost index in 1998)
Cost in 2020 = 6,000 * (656.1/389.5)
Cost in 2020 = $ 101,06

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9. Data Sheet

Separator
10 feet
V-100

1.33 feet
16 inch

Separator
Item No. V‐100
No. Required 1
Function: To separate gas from Ash and water emulsion
Operation: Continuous
Design Parameters
Units Values

Design Temperature C 109

Design Pressure bar 1.10
Superficial Velocity m/sec 2.50
Volumetric flow rate m3/sec 0.28
m2
Minimum gas flow area 0.112
Diameter inch 16
Length ft 10
Liquid Capacity BPD 1074
Wall Thickness mm 2.27
Type of head - Flat Head
Type of support - Brackets Support
Weight of Shell N 94.35
Cost $ 101,06

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10.Piping and Instrumentation Diagram

SEPERATOR V-100 PUMP P-100

Capacity: 1290 kg/hr Power:

Height: 10 feet Capacity:

Diameter: 16 inch Head: PC

001
MOC: Carbon steel MOC: Carbon steel

TI FI
002 002 PIT
001

Gas
PCV-001 SDV-002 TO CO MP RESSOR

TO VEN T
001
PSV-001

TI
001
001
V-100
LIT LC
FEED 001 001
SDV-001 FCV-001
FROM PRODUCT COOLER Lo cal/ Start/ Start/
Remote Sto p Sto p
Ru nning
XI VFD HS HS HS
Sto p

TI FI
003 003

M
Liqu id
SDV-003 WATER

LC V-001

P-100

TI FI
004 004

Solid
ASH

LEGEND: NOTES: USMAN ENGINEERING

Electric Signal Shutdown Valve Globe Valve

Con trol Valve

VFD Variable Frequ en cy Drive THREE PHASE SEPERATOR
Pneu matic Signal
Piping & Instrumentation Diagram
HS Hand Switch SIZE FSC M NO DWG NO REV
Process Line Gate Valve
A3 1 A
19/04/2020 SCALE 1:1 SHEET 1 OF 1

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11.References
[1] E. Edition, “API specification for oil and gas separators.,” no. October 2008, 1973.
[2] G. P. S. Association, “ENGINEERING DATA BOOK,” FPS VERSION, pp. 1–771,
2011, doi: 10.1002/9781444341294.
[3] “RICHARDSONS AND COLSON VOL 6.”
[4] R. K. Sinnott, “Coulson & Richardsons Chemical Engineering Design,” ELSEVIER -
Coulson Richardson’s Chem. Eng. Ser., vol. 6, no. 4, pp. 440–445, 2005, doi:
10.1016/S1385-8497(00)00184-4.

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