CHAPTER 5
PROCESS INTEGRATION
5.1ABSTRACTThis plant is designed to produce product of 45,000
metric tonne per year of polytetrafluoroethylene. The production
rate of the product was determined by break even analysis.
Generally, PTFE has many unique properties that made their chemical
is in highest ranking of applications. It involves in material
coating, use in laboratory equipment that can resist corrosive and
can be an insulator. PTFE also can used to insulate much data
communication cable, and also can act in manufacture of
semi-conductors, as their properties that low electrical
conductivity. In this plant, there are two processes in which
preparing the monomer which is tetrafluoroethylene and the
polymerisation process. For, monomer preparation, pyrolysis
reaction took place while suspension polymerisation type was
chosen. As for the market demand and supply,
polytetrafluoroethylene is monopoly by Asian Countries. By
comparing the demand in Asia, Japan has largest demand of PTFE
compared to other Asian Country. However, the main producer and
manufacturer of PTFE is comes from China. Although the demand for
PTFE is high at Japan, the new plant is decided to build in China
because the availability of raw material supply. Therefore, the
plant is to be built in Suzhou National New & Hi-Tech
Industrial Development Zone because the area provide low land cost
and many facilities. In process flow diagram, there are seven major
equipments which have been detailed design to ensure it suitable
for the process. Besides, the process control systems have been
designed in all equipments in PTFE plant to make sure that the flow
in each process runs in desired condition. In economic analysis,
all costs involved in the plant had been calculated and
profitability analysis had been done. The payback period for this
PTFE plant is about 5 years which is in the range of industrial
payback period. In environmental aspect, waste water treatment and
waste gas treatment involved in the process. For gas treatment,
incineration is used. Last but not least, some hazards analysis had
been done and plant layout had been sketched to ensure the safety
of the process condition, people, and environment.
5.2 INTRODUCTION OF HEAT EXCHANGER NETWORKSEnergy conservation
is very important in process design. Energy can be conserved by
using process integration method. In recent years, much work has
been done in developing a perfect method for energy integration and
the efficient design of heat exchanger networks (Gundersen and
Naess, 1988). However, Bodo Linnhoff had successfully developed a
method that had been usually used until now: pinch technology. The
term was derived from the fact that in a plot of the system
temperature versus the heat transferred. A pinch usually occur
between the hot stream and cold stream curve. It has been shown
that the pinch represent a distinct thermodynamic break in the
system and that, for minimum energy requirements, heat should not
be transfer across the pinch. (Linnhoff and Townsend,1982)
Figure 5.2 Hot and cold stream composite curve
5.3 PINCH TECHNOLOGYPinch Technology provides a systematic
methodology for energy saving in processes and total sites. The
methodology is based on first and second law thermodynamic
principles. Pinch Technology gives three rules that form the basis
for practical process design:a) No external (utility) cooling above
the Pinch Temperature.b) No external (utility) heating below the
Pinch Temperature.c) No heat transfer between process streams
across the Pinch Temperature.By using Pinch Technology, appropriate
changes in the core process conditions that can have an impact on
energy savings can be identified. After the heat and material
balance is established, targets for energy saving can be set prior
to the design of the heat exchanger network. The Pinch Design
Method ensures that these targets are achieved during the network
design. In PTFE production plant, there are nine streams with five
hot streams and 4 cold streams that need to be considered for the
problem of integrating the utilization of energy. The heat capacity
flow rate of each stream is shown as CP. For streams where the
specific heat capacity can be taken as constant, and there is no
phase change, CP will be given by:
Wherem = mass flow rate, kg/sCp = average specific heat capacity
between
16 | Page
PropertiesStream 1Stream 2Stream 3Stream 4Stream 5Stream 6Stream
7Stream 8Stream 9
Temperature, T (oC)2577102308850-357529350
Temperature difference, T ( oC )131312214.5890162675301330
Mass flow, m
(kg/h)1.45x1048.66x1048.66x1042.58x1043.52x1042.58x1049.41x1038.71x1046.39x105
Mole Heat capacity, Cp (J/kg
oC)2.87x103786.49x1028.47x1022.49x1038.74x1023.29x1031.89x1023.41x102
Heat capacity, mCP (kW/oC)
11.61.8815.65.8211.96.268.594.5760.3
Table 5.3.1 Aspen Data Properties
5.3.1 ENERGY TARGETING PROCEDUREPinch Analysis provides a target
for the minimum energy consumption. There are two procedures to
achieve the energy targets for the process, which are: a) Problem
Table AlgorithmCalculates the process heat surpluses and deficits
within some specified temperature intervals.
b) Composite Curves The cumulative process heat availability
(surplus) and heat requirement (deficit)
5.3.2 PROBLEM TABLE METHOD Problem table method (PTA) was
developed by Linnhoff & Flower (1978) as a mean of determining
the utility needs of a process and the location of the process
pinch. The procedure for PTA is as follows: 1. Convert the actual
stream temperatures, Tact, into interval temperatures, Tint. The
use of the interval temperature rather than the actual temperatures
allows the minimum temperatures difference to be taken into account
(Tmin = 10 K).
2. Note that any duplicated interval temperatures.
3. Rank the interval temperatures in order of magnitude, showing
the duplicated temperatures only once in the order.
4. Carry out a heat balance for the streams falling within each
temperature interval.
For mixture: (Where (Cp) mix = heat capacity mixture yi =
mass/mole fraction of i-component Cpi = heat capacity of
i-component
For the nth interval:
Where Hn = net heat required in the nth intervalCPc = sum of the
heat capacities of all the cold streams in the interval CPh = sum
of the heat capacities of all the hot streams in the interval Tn=
interval temperature difference = (Tn-1 Tn)
5. Cascade the heat surplus from one interval to the next down
the column of interval temperatures.
6. Introduce just enough heat to the top of the cascade to
eliminate all the negative values.
Construct table by calculate:
Since, Tmin = 10 oC
Therefore:
Hot streams,
Cold streams, Stream no.Stream typeTactual ( oC )Tinterval( oC
)Tinterval( oC )mCP (kW/ oC )
TinitialTfinal
1-2Hot251230-171311.6
5-6Cold779072-85131.88
7-8Hot10290107-951215.6
13-14Cold35522.530-7457155.82
16-17Hot850-40905- -3594011.9
19-23Cold-35127-40-1221626.26
20-21Cold7575070-7456758.59
27-28Cold2933024-3253014.57
25-29Hot 35020355-2533060.3
Table 5.3.2.1 Summary Process Data for Each Stream
Then, draw temperature interval to shows the series of
temperature intervals for hot and cold stream.
Figure 5.3.2.1 Temperature Interval1 3 5 9 2 4 6 7 8 11.6 15.6
11.9 60.3 1.88 5.82 6.26 8.59 4.57 845 755 1.99x104 527.5 1.06x104
345 1.87x102 335 1.50x102 132 1.37x103 97 95 5.80x103 85 82 80 40
34 20 1.01x103 15 2.84x103 7 -30 2.44x101 -45 Hot Hot Hot Hot
ColdCold Cold Cold Cold
Cp (kW/k)StreamQ=CpT (W)
Tranked (oC)Tint (oC)CP(kW/K)=CPC-CPH
H(kW)=CP x Tint
845---
7559011.91.071x103
527.5227.53.317.53x102
345182.5-2.51-4.581x102
3351057.795.779x102
13220353.221.08x104
973546.961.644x103
95262.561.251x102
851060.686.068x102
82345.081.352x102
80246.9693.9
404055.552.222x103
34661.373.682x102
201465.949.232x102
15577.543.877x102
7817.241.379x102
-30375.642.087x102
-451511.91.785x102
Table 5.3.2.2 Problem Table Method
Interval T (oC)Grand Composite net heat, H (kW)Hot and Cold
Cascaded heat (kW)
845-0
7551.071x1031.071x103
527.57.53x1021.824x103
345-4.581x1021.366x103
3355.779x1021.944x103
1321.08x1041.275x104
971.644x1031.439x104
951.251x1021.452x104
856.068x1021.512x104
821.352x1021.526x104
8093.91.535x104
402.222x1031.757x104
343.682x1021.794x104
209.232x1021.887x104
153.877x1021.925x104
71.379x1021.939x104
-302.087x1021.960x104
-451.785x1021.978x104
Table 5.3.2.3 Cascading Heat Table AnalysisCascading the heat
from one interval to the next indicates that the temperature
difference is such that the heat can be transferred between the hot
and the cold streams. As the value is all positive, there is no
pinch occur as it is thermodynamically feasible. From Table 5.4:
Hot and Cold Cascaded heat (kW) 1. At interval temperature, T = 750
oC
2. At interval temperature, T = 350 oC
Cascade Diagram Pinch temperature
Heat Load (W)
Temp (oC)HOT UTILITYCOLD
UTILITY0
1.071x103
1.071x103
1.824x1037.53x102
-4.581x102
1.366x103
1.944x1035.779x102
1.08x104
1.275x1041.644x103
1.439x104
1.452x104441.251x102
6.068x102
1.512x104
1.526x1041.352x102
9.392x101
1.535x104
2.222x103
3.682x1021.757x104
1.939x1041.925x1041.887x1041.794x1041.379x1023.877x1029.232x102
2.088x102
QC=1.978 x104
1.960x104
1.785x102
1.978x104
Figure 5.3.2.2 Cascaded DiagramTherefore, 1. Minimum amount of
heat must be Removed by Cold Utilities is 1.978x104 kW.
2. Pinch Point at interval, T = 845oC.
a) Cold Stream, T = 850 oC.
b) Hot Stream, T= 840 oC.
5.3.3 GRAND COMPOSITE GRAPH A graph of net heat flow against
shifted temperature can be plotted from the data of the Problem
Table (heat cascade). This graph is known as the Grand Composite
Curve (GCC). GCC is done to highlight the difference between heat
available from the process hot streams and the heat required by the
process cold streams, relative to the pinch, at a given shifted
temperature Temperature (oC)Grand Composite net heat, H (kW)
8450
7551.071x103
527.51.824x103
3451.366x103
3351.944x103
1321.275x104
971.439x104
951.452x104
851.512x104
821.526x104
801.535x104
401.757x104
341.794x104
201.887x104
151.925x104
71.939x104
-301.960x104
-451.978x104
Table 5.3.3.1 Data for plotting the grand composite curve
Figure 5.3.3.1 Grand Composite Curve5.3.4 Design for Heat
Exchanger Network (HEN)5.2.4.1 Grid RepresentationGrid
representation is a method to present a heat exchanger as a grid.
Heat exchangers are drawn as circles connected by a vertical line.
The circles connect the two streams that are in between heat being
exchanged. Thus, the streams would flow through the actual
exchanger. Heaters or coolers will be drawn as a single circle,
connected to the appropriated utility (Sinnot et. al, 2013).In PTFE
production process, only below pinch grid diagram is needed. The
network design below the pinch is as follows:
CPHOT CPCOLD
Figure 5.3.4.1 Grid diagram of PTFE production processFCPH
H12511.6150.8 H210215.6 187.2 H385011.9 10591 H435060.3 19899
C1901.88 24.44 C2522.55.822837.25 C31276.26 1014.12
C47508.595798.25
C53304.571375.5719778.372837.25150.8187.2676.125798.2524.441254.94120.63
5.2.5 Minimum Number of Heat Exchangers For simple networks,
Holmann (1971) has shown that the minimum number of exchangers is
given by;
Where; Zmin= NHE= minimum number of exchangers needed, including
heaters and coolers N= Ns+Nu-1= the number of streams, including
the utilities NHE= Number of Heat Exchanger NS= Number of stream
NU= Number of Utilities
Therefore, Above Pinch:
Below Pinch:
Figure 5.3.4.2 Process flow diagram of PTFE production before
heat integration
Figure 5.3.4.3 Process flow diagram of PTFE production before
heat integration
5.3.6 Comparison Before and After Heat Integration5.3.6.1 Total
Energy Can Be Saved
By implementing the heat integration, the heat removal from
condenser can be utilized to heat up the reactant
mixture.UtilityBefore integrationAfter integration
Hot (kW)3.142x1040
Cold (kW)1.237x1041.978x104
Total (kW)4.379x1041.978x104
Table 5.3.6.1 Comparison Before and After IntegrationTherefore,
percentage (%) total energy can be saved:
5.4 ConclusionAs a conclusion, by doing heat integration, the
energy requirement can greatly be reduced as shown at the step
above. By reducing the energy requirement it will help reduced the
cost and the payback period of the plant.
5.5 References
Gary Smith, Ajit Patel. (1987, November). Step by step through
the pinch. Energy Integration, pp. 26-31.Richard Turton. (2012).
Analysis, Synthesis, and Design of Chemical Processes. Pearson.