Design of Heat Exchanger Network for VCM Distillation Unit Using Pinch Technology

VISHAL G. BOKAN Int. Journal of Engineering Research and Applications www.ijera.com
ISSN : 2248-9622, Vol. 5, Issue 6, ( Part -2) June 2015, pp.80-86
www.ijera.com 80 | P a g e
Design of Heat Exchanger Network for VCM Distillation Unit
Using Pinch Technology
VISHAL G. BOKAN 1
, M.U.POPLE2
1
Student of M.E. chemical, Department of Chemical Engineering, MGM’S jawaharlal Nehru College of
Engineering, Aurangabad, India.
2
Associate Professor, Department of Chemical Engineering, MGM’S Jawaharlal Nehru College of Engineering,
Aurangabad, India.
Abstract
In process industries, heat exchanger networks represent an important part of the plant structure. The purpose of
the networks is to maximize heat recovery, thereby lowering the overall plant costs. In process industries, during
operation of any heat exchanger network (HEN), the major aim is to focus on the best performance of the
network As in present condition of fuel crises is one of the major problem faced by many country & industrial
utility is majorly depend on this. There is technique called process integration which is used for integrate heat
within loop so optimize the given process and minimize the heating load and cooling load .In the present study
of heat integration on VCM (vinyl chloride monomer) distillation unit, Heat exchanger network (HEN) is
designed by using Aspen energy analyzer V8.0 software. This software implements a methodology for HEN
synthesis with the use of pinch technology. Several heat integration networks are designed with different ΔT
min and total annualized cost compared to obtain the optimal design. The network with a ΔT min of 90
C is the
most optimal where the largest energy savings are obtained with the appropriate use of utilities (Save 15.3764%
for hot utilities and 47.52% for cold utilities compared with the current plant configuration). Percentage
reduction in total operating cost is 18.333%. From calculation Payback Period for new design is 3.15 year. This
save could be done through a plant revamp, with the addition of two heat exchangers. This improvement are
done in the process associated with this technique are not due to the use of advance unit operation, but to the
generation of heat integration scheme. The Pinch Design Method can be employed to give good designs in rapid
time and with minimum data.
Key Words: VCM Process, Process Integration, Synthesis of HEN, Aspen Energy Analyzer V 8.0
I. INTRODUCTION OF INTEGRATION
Today in the industry, the design and
optimization procedures have the trend to identify
the configurations where, less energy consumption
can be achieved. The possibilities for energy savings
resulting in environmental and economic saving for
various industrial applications can be diverse and
very useful nowadays, when the search of new
energy resources because the scarcity of traditional
fuels and instability in the global markets, demands
to maximize their efforts in energy consumption
optimization. The use of Pinch Technology allows to
finding balance between energy and costs as well as
correct location of utilities and heat exchangers. The
procedure first predicts the minimum requirements
of external energy network area and number of units
for given process at the pinch point. Next heat
exchanger network design that satisfies these targets
synthesized. Finally the network is optimized by
comparing energy cost and the capital cost of the
network, so that the total cost is minimized. Thus the
prime objective of pinch analysis is to achieve
financial savings by better process heat integration.
[3, 4]
.
II. MATERIALS AND METHODS
2.1 Concept of Pinch Analysis
Pinch Analysis is also known as process
integration, heat integration, energy integration, or
pinch technology. This method for minimizing the
energy costs of a chemical process by reusing the
heat energy in the process streams rather than
outside utilities. The process requires three pieces of
data from each process stream: the heat load
(enthalpy) in kW or Btu, the source temperature in
°C or °F, and the target temperature in °C or °F. The
data from all streams are combined in order to create
plots of enthalpy against temperature, called
composite curves. Composite curves are needed for
the hot and cold process streams, a combined plot of
both the hot and cold composite curves, and the
grand composite curve. From the combined curve
plot we can see the region where the distance
between the hot and cold curves is minimum this
RESEARCH ARTICLE OPEN ACCESS

region is called the pinch point. Pinch point provides
an important constraint for the design of our heat
exchanger network, it is only after the constraint is
determined that we can design a heat exchanger
network that can meet our ideal minimum energy
requirements. [5, 8, 11]
By adjusting the minimum approach distance,
known as ΔTmin, then find a balance between ideal
minimum utility requirements and total surface area
of our heat exchanger network. As the value of
ΔTmin is made smaller our utility needs go down,
but at the same time the required total surface area of
our heat exchanger network is increased in order to
achieve the necessary amount of heat transfer
between our process streams. Therefore, ΔTmin
indicates a bottleneck in the heat integration system.
From the combined composite curve and grand
composite curve plots we can easily see the
temperature that the pinch point falls on, as well as
the ideal minimum heating and cooling utility
requirements. It is very important to know the pinch
temperature in order to maximize the process-to
process heat recovery and minimize the utility
requirements, as process-to-process heat exchange
should not be occurring across the pinch. This
constraint is applied automatically in this program,
allowing the user to only place heat exchangers
between process streams on only one side of the
pinch or the other, but not on both sides at the same
time. The important questions is, are these targets
achievable in real industrial practice, or are they
confined to paper theoretical studies?
Within a short time, the team had calculated
targets showing that the process could use much less
energy even with expansion; Targets were lower
than the current energy use moreover, they quickly
produced practical designs for a heat exchanger
network, which would achieve this. As a result,
saving of over a million pounds per year was
achieved on energy, and the capital cost of the new
furnace with its associated problems was avoided.
Although new heat exchangers were required, the
capital expenditure was actually lower than for the
original design, so that both capital and operating
costs had been slashed. [6]
III. PROCEDURE
In this work data required for the design of heat
exchanger network was taken from “Cosmo films
limited,waluj,Aurangabad” in VCM Plant datasheet.
The specific heat capacity for the stream component
is known to be significantly dependent on
temperature. The components that are present in
comparatively large amount haves the significant
effect on specific heat capacity of mixture. Hence
components like hydrogen chloride (HCl), low boils,
high boils and other non condensable are neglected
in the specific heat capacity calculations.
3.1 Process description
The product from the cracking unit consists of
VCM, HCl, unconverted ethylene dichloride (EDC)
and By-products of various chemical structures.
Hydrogen chloride is recovered in the HCl column
and fed to the oxychlorination unit. Vinyl chloride is
obtained at the top of the VCM column. Any traces
of HCl are removed from the VCM in the HCl
column. The bottom product of the VCM column,
i.e. unconverted EDC, was returned to the EDC
distillation process after the low-boiling compounds
have been converted by chlorination to high-boiling
compounds. Thus the difficult and energy-
consuming separation of recycle EDC from other
low-boiling components is avoided.
3.2 Data Extracted from VCM Process Unit:
With consistent heat and mass balance
available, stream data are extracted. Here only those
flows, which require heating or cooling, are
extracted from given process. This leaves four actual
streams whose characteristics are listed in table
1.From below table it has been found that total heat
load for the cold streams is 2173152.186 KJ/hr. and
for the hot streams is 1881156.938 KJ/hr. This
implies that current hot utility and cold utility
demands, reducing the hot utility and cold utility
targeting procedure is applied. There are two
targeting procedure applied for utility reduction. One
is to draw “composite curve” and other is to form
“problem table algorithm”. For drawing the
composite curve, understanding of pinch concept is
very essential and here we are targeting on
composite curve. [10]
164oC 110oC
79oC
49oC
50oC
77oC
77oC
37oC
Vent VCM Column
VCMColumn
HClColumn
T-48oC
P-6.1kg/cm2
Bottom VCM Column
Bottom HCl Column
Feed VCM
Feed HCl Column
Overhead HCl Column
S-1
S-2
S-3
S-4
Fig. 1. Data extraction from VCM Process Flow
diagram

Table no.1 Extracted data from VCM PFD for Pinch
analysis
IV. PINCH ANALYSIS USING ASPEN
ENERGY ANALYZER V8.0
Heat integration in Aspen Energy Analyzer
(formerly called HX-Net) is designed for analyzing
and improving the performance of HEN. Aspen
Energy Analyzer focuses on analyzing the networks
from operations' as well as design's point of view.
HEN operations features are designed to provide you
with an understanding of current plant operation and
related issues such as fouling. Furthermore fouling
mitigation strategies can be studied and simulated in
Aspen Energy Analyzer. HEN design features assist
the designer in understanding the gap between
current operation and the thermodynamic optimum
operation. Furthermore, the designer can use Aspen
Energy Analyzer to identify and compare options to
improve the performance and reduce the gap
between current and thermodynamic optimum
operations. To perform any heat integration study
from a design or operations perspective, Aspen
Energy Analyzer needs the process requirements and
the HEN that achieves the process requirements. The
terminology that is used in Aspen Energy Analyzer
is "scenario" for process requirements and "design"
for the HEN.
4.1 Data Entry to Aspen Energy Analyzer
The Process Streams tab allows us to specify
information about the process streams in the HEN.
Here we were provided stream data extracted from
above flow diagram. Considering ethylene
dichloride and vinyl chloride as Low Molecular
Weight Hydrocarbon we were selected heat transfer
coefficient from aspen energy analyzer database as
2713.2 kJ/(h.m2
.0
C). [2]
The Utility Streams tab
allows us to specify the utilities used in the HEN to
cool or heat the process streams. Here we were
provided cooling utility as cooling water available at
200
C and hot utility as a low-pressure (LP) steam
available at 1250
C. The cost index of LP steam and
cooling water are and respectively[2]
The Economics
tab allows us to modify the cost calculations. We
were considered heat exchanger capital cost index
parameters for calculation of heat exchanger capital
cost index values were as follows: a=100000, b=800,
c=0.8. Here we were assumed rate of return was
10%, plant life was 5 years, and hours of operation
were 8765.76 hours/years. [2]
4.2 Process streams tab
The Process Streams tab allows us to specify
information about the process streams in the HEN.
Here we are providing stream data extracted from
above flow diagram. Considering ethylene
dichloride and vinyl chloride as Low Molecular
Weight Hydrocarbon we are selecting heat transfer
coefficient from aspen energy analyzer database as
2713.2 kJ/(h.m2
.0
C).
Figure 2 Process streams tab [2]
4.3 UTILITY STREAMS TAB
The Utility Streams tab allows us to specify the
utilities used in the HEN to cool or heat the process
streams. Here we are providing cooling utility as
cooling water available at 200
C and hot utility as a
low-pressure steam available at 1250
C. The cost
index of LP steam and cooling water are
and respectively.
Stream
no.
Name Type Tin(0
C) Tout(0
C)
MCp
(KJ/hr)
Cp
KJ/(Kg.
K)
1
Bottom
of
column 1
HOT 164 110
17734.
457
0.9427
2
Bottom
of
column 2
HOT 77 37
23087.
4065
1.5393
3
Feed of
column
1
Cold 50 79
43286.
3278
1.2004
4
Feed of
column
2
Cold 49 77
32780.
31
1.2009

Figure 3 Utility stream tab[2]
4.4 ECONOMICS TAB
The Economics tab allows us to modify the cost
calculations. We are considering heat exchanger
capital cost index parameters for calculation of heat
exchanger capital cost index value are as follows
a=100000, b=800, c=0.8. Here we are assuming rate
of return is 10%, plant life is 5 years, hours of
operation are 8765.76 hours/years.
Figure 4 Economics tab
[2]
4.5 TARGETS VIEW
The Targets view allows us to observe all the
target values for the values specified on the HI Case
view. From the targets view tab we get following
information,
Minimum heating load =
(kJ/hr)
Minimum cooling load =
(kJ/hr)
Pinch temperature = (58-49) 0
C
Total minimum no of units = 5
Total annual cost = (cost/sec)
Figure 5 Targets view tab
[2]
4.6 HEAT EXCHANGER NETWORK VIEW
The HEN view allows us to build the network
based on all of the parameters entered in the main
view. The network can be manipulated through the
Grid Diagram or the Worksheet.
Figure 6 Heat Exchanger Network View[2]
4.7 Optimum ΔTmin in comparison with
operating cost index and capital cost index

Based on the capital cost index and operating
cost index with respect ΔTmin value we got
optimum value equals to 90
C.[2]
4.8 Composite curve
Following composite curve, displays both the
hot composite curve and cold composite curve on
the same plot. The closest temperature difference
between the hot and cold composite curves is known
as the minimum approach temperature, i.e. ΔTmin.
The composite curves was moved horizontally such
way that minimum approach temperature on the plot
equals to minimum approach temperature we
specified.
Fig. 7 Composite Curve at OPTIMUM Tmin [2]
4.9 COSTING OF HEAT EXCHANGERS
AFTER NETWORK DESIGN
Heat Exchanger Capital Cost Index Parameters
are as follows,
a = 10000
b = 800
c = 0.8
CC = a + b NShell
Annualization Factor (A) =
Total annualized cost (TAC) =
(A
Where; CC = Installed capital cost of a heat
exchanger ($)
a = installation cost of heat
exchanger ($)
b,c = duty/area –related cost set
coefficient of the heat exchanger
Area = heat transfer area of heat
exchanger
NShell = number of heat exchanger shells
in the heat exchanger
ROR = rate of return (percent of capital)
PL = plant life (yr)
Using above equation, capital cost of each heat
exchanger is as follows,
Table 2 Capital cost of each heat exchanger
Assuming, 1$ = 54 Rs.
Operating cost of minimum heating & cooling
utilities are as follows;
For heating utility,
Cost = QHmin cost index
=776800
=1.47592 $/hr
= 80 Rs/hr
Cost for 1 year considering hours of
operations = 8765.76 (hrs/year)
Cost = 80 8765.76
= 7,01,260.8
Rs/year
 For cooling utility,
Cost =
484800
= 0.10302 $/hr
= 5.563 Rs/hr
cost for 1 year considering hours of
operations = 8765.76 (hrs/year)
cost = 5.563 8765.76
= 48763.923
Rs/year
 Total operating cost = operating cost of
heating + cooling utilities
=7,01,260.8 +
48,763.923
= 7,50,024.723
Rs/year
Now we calculate Annualization Factor as
follows,
Annulization Factor =
= 0.3221
Sr No. Heat exchanger Capital cost ( ) ,$
1 E-102 1.4820
2 E-103 1.1670
3 E-104 1.4598
4 E-105 2.5740
5 E-106 1.2260
Total capital cost 8.0510

 Capital cost per year = total capital cost
of all HE annualization factor
=
= 25932.271
$/year
=
14,00,342.634
Rs/year
 Total annualized cost = total capital cost
+ total operating cost
= 14,00,342.634 +
7,50,024.723
= 21,50,367.337
Rs/year
 Calculation of Payback Period,
PBP =
The 0.85 value it obtained by assuming that the
working capital is 15% of Total capital
investment.[15]
=
= 3.15 yr.
4.10 COSTING OF EXISTING HEAT
EXCHANGERS
Table 3 Capital Cost Index of Existing Heat
Exchanger
Total Capital Cost = (cost)
Operating cost for existing heating & cooling load
are as follows,
 For heating utility,
Cost = QHmin cost index
= 917948
= 1.7439 $/hr =
8,25,476.9 Rs/year
 For cooling utility,
Cost = QCmin cost index
= 923496
= 0.19624 $/hr = 92,917 Rs/year
 Total operating cost = operating cost of
heating + cooling utilities
= 8,25,476.9 + 92,917
= 9,18,393.9 Rs/year
Annualization factor = 0.3221
 Capital cost per year = total capital cost of
all HE annualization factor
=
= 22099.6031
$/year = 11,93,378.6
Rs/year
 Total annualized cost = total capital cost +
total operating cost
= 9,18,393.9 +
11,93,378.6
= 21,11,772.5
Rs/year
 Percentage reduction in heating load,
% Reduction =
 Percentage reduction heating utility cost,
% Reduction =
 Percentage reduction in cooling load,
% Reduction =
 Percentage reduction cooling utility cost,
% Reduction =
 Percentage reduction in total operating cost,
% Reduction =
V. RESULTS AND DISCUSSION:
1. Minimum heating load = 7.768 × 105
(kJ/hr)
2. Minimum cooling load = 4.848 × 105
(kJ/hr)
3. Pinch temperature = 58-490
C
4. Total minimum no of units = 5
5.1 Final design of flow sheet based on grid
Based on the above design of HEN by using
methodology of aspen energy analyzer software and
use of pinch technology actual arrangement of heat
exchanger in VCM distillation process flow diagram
as shown in fig. 3. Here we added some extra heat
exchangers (HE) to recover the process to process
heat and to save addition heating or cooling load of
utilities.
Sr
No.
Heat
exchanger
Area(m2
) Capital cost($)
1 E-1512 20.04
2 E-1506 23.94
3 E-1513 54.72

Feed VCM
Vent VCM Column
VCMColumn
HCl
Column
Overhead HCl Column
P- 6.1kg/cm2
T- 48oCBottom VCM Column
Bottom HCl Column
Feed HCl
Column
110oC
164oC
50oC 72.1o
C
79o
C
49 o
C
62.4 o
C
77 oC
77 o
C
58oC
37oC
CW
LP
Steam
LP
SteamE-102
E-103
E-105
E-106
E-104
Fig.8 Specification of heat exchangers in final
design
5.2 Specification of heat exchangers in final
design
Specification of heat exchangers appeared in the
final VCM PFD is tabulated as follow Table 2.
Specification of Heat Exchangers in Final Design
HE
Heat
Load
(kJ/hr)
Area(m2
)
HTC
KJ/(m2
K)
LMTD(0
C)
E-
102
957660.7 9.4 1356.6 74.81
E-
103
297642.8 2.5 2410.4 49.18
E-
104
484835.5 8.9 2259.2 24.12
E-
105
438660.7 34.8 1356.6 11.58
E-
106
479188.0 3.7 2410.4 49.18
Table 4 Specification of heat exchangers in final
design
VI. CONCLUSION:
In present case study of VCM distillation unit of
heat exchanger network was designed by use of
methodology of aspen energy analyzer software
V8.0 and pinch technology. Several HEN are
designed at different ΔTmin values and by
comparing the total annualized costs to obtain the
optimum design was selected and among the various
values ΔTmin at 90
C gives the most optimal results.
Whereas the largest energy savings were obtained
with the appropriate use of utilities (Saves 15.3764%
of hot utilities and 47.52% of cold utilities compared
with the current plant configuration). Percentage
reduction in total operating cost is 18.333%. From
calculation Payback Period for new design is 3.15
year. This save could be done through a plant
revamp, with the addition of two heat exchangers.
Additionally it is possible to realize a detailed study
with a rigorous design methodology of Heat
Exchanger Network. This improvement are done in
the process associated with this technique are not
due to the use of advance unit operation, but to the
generation of heat integration scheme. The Pinch
Design Method can be employed to give good
designs in rapid time and with minimum data.
ACKNOWLEDGEMENTS:
I am especially grateful to my guide Prof.M.U.
Pople Sir for their time and much needed valuable
guidance and without their moral support and
cheerful encouragement my synopsis would not have
been successful.
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Design of Heat Exchanger Network for VCM Distillation Unit Using Pinch Technology