Total Site Targeting Approach for Heat Recovery at a Paper Factory
JUAN PEDRO HERNÁNDEZ TOUSET1,a, JOSÉ ULIVIS ESPINOSA MARTÍNEZ2,b
1Departamento de Ingeniería Química,
Universidad Central Marta Abreu de Las Villas,
Alemán 120 y San Cristóbal, Santa Clara,
CUBA
2Departamento de Ingeniería Industrial,
Universidad Central Marta Abreu de Las Villas,
Carretera a Camajuani, km 5.5, Santa Clara
CUBA
aORCiD: https://orcid.org/0000-0002-0032-8685
bORCiD: https://orcid.org/0000-0003-0558-7843
Abstract: - The total Site heat integration approach has been used extensively in the industry, including process
services and heat exchanger network design integrated with the site service system. This work aims to propose
a design for the heat recovery network in the paper factory through Total Site targeting. A procedure that
includes the energy analysis and Pinch Analysis methodologies, with the use of Aspen Energy Analyzer is
applied. The heat exchanger network design through total site heat integration shows that the rehabilitation of
the heat recovery system of the paper machine and boiler blowdown is feasible, with a potential annual saving
of 259 t of fuel oil and 116 000 m3 of water, which make it feasible to invest in the factory's heat recovery
system, whose project budget is estimated to recover in a year. Heat exchanger network retrofit design allows
to recover 46.2% of the maximum energy recovery.
Key-Words: - heat integration, total site, paper mill, energy analysis, blowdown, drying.
Received: May 14, 2023. Revised: October 15, 2023. Accepted: December 6, 2023. Published: December 31, 2023.
1 Introduction
Thermal energy recovery represents a key aspect of
the sustainable design and operation of processing
plants, as minimizing energy consumption translates
into reduced environmental impacts and costs. Heat
recovery in an industrial process takes place through
the heat recovery system, a set of units where the
exchange of thermal energy between two or more
mediums occurs, [1]. Instead improved energy
efficiency should be aiming at increased mechanical
dewatering in the press section and increased waste
heat recovery from the exhaust moist air, [2].
During industry operations, large portion of the
energy input is dissipated as waste heat to the
ambient in different forms, resulting in severe
energy waste. Recovering such waste heat can
provide power, heat or cooling output without extra
energy input. This increases the energy utilizing
efficiency and is considered to be a significant
“technology wedge” with the potential to contribute
a particular figure for the emission reduction, [3].
Thermal drying is often responsible for more
than 80% of the total steam use. The paper machine
drying section and its operating principles have
remained almost unchanged since their initial
development; contact drying with steam-heated
cylinders is still the dominant method for drying
paper and board, [4]. To decrease energy costs
different forms of heat recovery are applied to
energy-dense flows, such as exhaust air from paper
machines, where excess energy may be transferred
into secondary energy such as warm water which
may be utilized for low or partial heating of
incoming flows. Due to several improvements and
reconstruction of equipment, the heat recovery
systems may be operating far from their original
design, and opportunities for improvement might
exist. In a typical paper machine, 60 % of energy
may be expected to be recovered in heat recovery,
while the rest is exhausted outside, [5].
A large amount of heat energy is required at the
drying section of a paper factory for the removal of
the large quantity of water present in the paper web
WSEAS TRANSACTIONS on HEAT and MASS TRANSFER
DOI: 10.37394/232012.2023.18.20
Juan Pedro Hernández Touset,
José Ulivis Espinosa Martínez
E-ISSN: 2224-3461
246
Volume 18, 2023
by evaporation. The majority of the heat then would
be available as latent heat of vaporization. The
means of recovery of the waste heat and its cost-
effectiveness can only be established if one can
quantify the amount of the heat with an acceptable
degree of accuracy, [6].
In paper drying thermal conductivity is a
fundamental property that has a determining
influence on the temperature distribution and heat
flux density during thermal heating, [7], and
convective heat transfer must meet the requirements
in terms of improving thermal performance and
energy efficiency, [8].
The goal of Pinch Analysis (PA) is to maximize
energy recovery in industrial processes to reduce
their need for external energy sources. In this
method, all streams are categorized into either hot or
cold streams. The pinch analysis aims to provide the
required energy of cold streams by the hot streams.
One of the most important goals of PA is to
minimize the total annual cost of the plant without
negatively affecting the thermodynamic
performance of the system. To do so, the total area
of heat exchangers should be minimized, [9]. For
optimal heat transfer, it is sufficient to know all the
streams involved, without needing to make a priori
assumptions about how they will be connected.
PA has been successfully used in a great
number of industrial applications. Limitations of the
method have motivated the search for more efficient
mathematical techniques for handling HEN
optimization problems, where genetic algorithms
have been used for synthesizing a process including
HEN, [10]
The PA tool has been extended to consider
energy integration across several plants or processes
using indirect heat transfer, termed Total Site (TS)
heat integration, [11].
Total Site Profile (TSP) analysis can identify the
opportunities for Inter-Process Integration via the
utility system and the preparation of the appropriate
integration strategy, [12].
Potentials for heat recovery have not been
properly identified in the paper mill, which affects
the energy performance indicators. This work aims
to propose a design for the heat recovery network in
the paper mill through TS targeting.
2 Methodology
Energy management in the paper manufacturing
process is based on the Cuban standard ISO 50001:
2019 and a methodology for energy usage, [13]. By
applying energy analysis and Heat Integration,
energy performance indicators (EnPIs) are
determined. Pinch Analysis methodology is applied
to determine network targets, minimum temperature
difference, and maximum energy recovery (MER),
[14]. Data processing was performed by Aspen
Energy Analyzer, [15].
3 Results and Discussion
3.1 Energy Usage Analysis in the Paper
Factory
The paper factory produces kraft paper, cardboard,
and liner from old corrugated containers (OCC).
The steam utility consists of one water-tube boiler
with a superheated steam generation capacity of 20
t/h at 2.5 MPa and 398 o C, which consumes Fuel
Oil. The steam pressure for the process is 0.054 –
0.5 MPa. The dryer section is enclosed by a semi-
open hood, where the top half of the cylinders is
covered with an insulated hood but not covered at
the bottom of the cylinders.
Figure 1 shows the paper factory steam network
diagram.
Mass and energy balances are applied for the
production of 3,965 kg/h of liner with a basic weight
of 200 g/m2 and a paper machine speed of 90
m/min. Table 1 shows the results of the steam, heat,
and water balances in the factory and the heat
balance in the drying section, [16]. The result of the
boiler blowdown calculation is added.
Fig. 1: Paper factory steam network diagram.
Energy balance provides vegetable vapor flow and
boiler blowdown, which constitute essential streams
for the application of the Pinch Analysis Method.
WSEAS TRANSACTIONS on HEAT and MASS TRANSFER
DOI: 10.37394/232012.2023.18.20
Juan Pedro Hernández Touset,
José Ulivis Espinosa Martínez
E-ISSN: 2224-3461
247
Volume 18, 2023
Table 1. Energy usage analysis
3.2 Heat Recovery Network Analysis and
Design
Figure 2 shows the process flowsheet and stream
data is presented in Table 2. The streams considered
in the analysis are: Vegetable vapor (H1); Cylinder
condensate (C1); Wet paper streams (C2 – C31);
Boiler blowdown (H2); Feed water (C32); Fuel
(C33); film coefficients for hot and cold utilities are
5,000W/m2oC and 3,000W/m2oC, [17]. Process
equipment are boiler (2), and dryers (1). There are
41 cylinders; in 10 cylinders there is a temperature
drop in the paper sheet at the exit of the cylinder,
caused by a temperature decrease of the steam in the
cylinder; therefore, they are not taken into account
as cold streams, since they are hot currents that cool
without receiving external cooling service, which
introduces an error in the application of Pinch
Analysis Method.
Fig. 2: Process flowsheet
Nomenclature: cp = specific heat capacity
(kJ/kg °C), Tf= final temperature (°C), Ti= initial
temperature, m = flowrate (kg/h), CP = heat
capacity flowrate (kW/ o C), h = film heat transfer
coefficient (kW/m2 o C), ΔH = heat load (kJ/h).
Steam properties are calculated for 0.4 MPa.
The global minimum temperature difference
(ΔTmin) in this case is set at 20 °C, because is de
minimum temperature difference between process
streams. There is one Pinch point, at 52 o C, with a
hot and cold pinch at 62 o C and 42 o C. The
minimum hot and cold duties are 1,653,000 kJ/h and
931,200 kJ/h. The Composite Curves in Figure 3
show the minimum hot and cold duties. There is an
energy potential (MER) of 3,810,606.64 kJ/h,
feasible to be recovered.
Table 2. Streams data
Fig. 3: Composite curves diagram
Figure 4 and Figure 5 show the location of the
heat exchangers in the feasible combinations.
According to the algorithms for stream splits, [17];
above the pinch, the number of hot streams (Nh) has
to be less than the number of cold streams (Nc) and
it is verified that CPh ≤ CPc (above pinch), that is,
34,240. 68 kJ/h°C<63,352.8 kJ/h°C, therefore, the
combination of streams H1 and C1 (heat exchanger
E101) is feasible. The second possible exchange
occurs between streams H2 and C32, which comply
Parameter
Value
Heating duty, kW
8,871
Steam consumption, kg/h
15,134
Heat losses , kW
3,016
Drying section thermal efficiency, %
66.0
Vegetable vapor, kg/h
8,172
Sensible heat from vegetable vapor, kW
456.0
Latent heat from vegetable vapor, kW
5,239
Boiler blowdown, kg/h
2,857
Condensate, kg/h
817.0
Water make up, kg/h
6,912
Fuel oil consumption, kg/h
740.0
Specific steam consumption, t / t paper
3.8
Stream
Ti
(°C)
Tf
(°C)
m
( kg/h)
cp
(kJ/kg°C)
CP=m·cp
(kJ/h°C)
ΔH
(kJ/h)
h
(kJ/m²°C)
H1
80
32
8,172
4.19
34,240.68
1,643,552.64
10,800
C1
42
90
15,134
4.19
63,352.8
3,040,934.4
10,800
C2
33
37
4,212
1.3
5,475.6
21,902.4
3,600
C3
37
50
4,212
1.3
5,475.6
71,182.8
3,600
C4
48
58
4,212
1.3
5,475.6
54,756
3,600
C5
58
63
4,212
1.3
5,475.6
27,378
3,600
C6
62
63
4,212
1.3
5,475.6
5,475.6
3,600
C7
70
72
4,212
1.3
5,475.6
10,951.2
3,600
C8
71
76
4,212
1.3
5,475.6
27,378
3,600
C9
76
76.3
4,212
1.3
5,475.6
1,642.68
3,600
C10
76
80
4,212
1.3
5,475.6
21,902.4
3,600
C11
80
82
4,212
1.3
5,475.6
10,951.2
3,600
C12
81
82
4,212
1.3
5,475.6
5,475.6
3,600
C13
82
83
4,212
1.3
5,475.6
5,475.6
3,600
C14
82
83
4,212
1.3
5,475.6
5475,6
3,600
C15
60.7
79.7
4,212
1.3
5,475.6
104036,4
3,600
C16
79
95
4,212
1.3
5,475.6
87609,6
3,600
C17
94.6
96
4,212
1.3
5,475.6
7665,84
3,600
C18
92
93
4,212
1.3
5,475.6
5475,6
3,600
C19
72.6
79.1
4,212
1.3
5,475.6
35,591.4
3,600
C20
70
79.7
4,212
1.3
5,475.6
53,113.32
3,600
C21
67.7
92.5
4,212
1.3
5,475.6
135,794.88
3,600
C22
72
82
4,212
1.3
5,475.6
54,756
3,600
C23
78
95
4,212
1.3
5,475.6
93,085.2
3,600
C24
60
63
4,212
1.3
5,475.6
16,426.8
3,600
C25
62.8
78.3
4,212
1.3
5475.6
3,943,527.12
3,600
C26
76
77.2
4,212
1.3
5,475.6
6,570.72
3,600
C27
60.4
64.3
4,212
1.3
5,475.6
21,354.84
3,600
C28
64
67
4,212
1.3
5,475.6
16,426.8
3,600
C29
57
64
4,212
1.3
5,475.6
38,329.2
3,600
C30
63,3
63.4
4,212
1.3
5,475.6
547.6
3,600
C31
63.2
72.9
4,212
1.3
5,475.6
53,113.32
3,600
C32
32
75
6,912
4.19
28,961.28
1,245,335
720.0
H2
300
40
2,844
4.19
11,916.36
3,098,254
720.0
C33
30
86
770.0
2.09
1,609.3
90,120.8
720.0
WSEAS TRANSACTIONS on HEAT and MASS TRANSFER
DOI: 10.37394/232012.2023.18.20
Juan Pedro Hernández Touset,
José Ulivis Espinosa Martínez
E-ISSN: 2224-3461
248
Volume 18, 2023
with the CP inequality rule (E102). Below the pinch,
there are no feasible combinations.
Table 3 presents the heat exchanger data as a
result of HEN design.
Table 3. Heat Exchangers data
Fig. 4: HEN design
Fig. 5: HEN above Pinch
Table 4 shows hot and cold utility duties from
energy analysis, minimum hot and cold utilities,
energy recovery, and the energy and financial
resources potential savings of the heat recovery
system in the paper mill. A net caloric value of the
fuel of 43,157 kJ/kg, 300 days of operation per year,
20 hours/day, and fuel (FO) and water prices of
$512.9 /t and 0.1 $/m3 are assumed. Potential
savings to estimate the feasibility of investment
projects are based on the energy recovered. In the
heat exchange between the vegetable steam and the
condensate from the cylinders, the temperature of
the boiler condensate is raised by 12.5 o C. In the
heat exchange between the purge condensate stream
and the make-up water, the temperature rises from
42 o C to 75 o C. Through the two exchanges, annual
savings of 259 t of fuel and 115,776 m3 of cooling
water are achieved. For the purposes of estimating
the investment cost, fuel and cooling water savings
are considered. The cold utility is saved in the
exchange between process streams by using 7.78
m3/h of condensed vegetable steam that is recovered
and recirculated for condensation and cooling
vegetable steam stream. In the boiler heat recovery
system, savings in hot utility are achieved by
combining the boiler blowdown stream with water
make-up. The modified Total Site heat recovery
network design allows to recover 46.2% of the
maximum energy recovery. This methodology is
feasible to be applied in processes where vapor
stream waste heat can be used. It was recently
applied in a raw sugar refinery with significant fuel
and water savings, which motivates the continuity of
research in this field, [18].
Table 4. Fuel and water savings
4 Conclusion
The design of the heat recovery system through
Total Site heat integration shows that the
rehabilitation of the heat recovery system of the
paper machine and the steam generator is feasible,
with a potential annual saving of 259 t of fuel oil
and 115,776 m3 of water. There is a high excess of
current hot utility duty about the minimum hot duty,
a behavior that is associated with the data extraction
system. Total Site Heat exchanger network retrofit
allows 46.2 % of the maximum recoverable energy
to be recovered. Fuel and water savings make it
feasible to invest in the heat recovery system. This
study allows us to continue the research to
rehabilitate hot air system to the hood.
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Equipment
Cold
stream
Ti
oC
Tf
oC
Hot
stream
Ti
oC
Tf
oC
Load
kJ/h
Area
m2
∆T
min
cold
oC
E-101
C1
42
52.5
H1
81.5
62
665,9
5.43
20
E-102
C32
42
75
H2
142.2
62
955,7
44.1
20
Sum
1,621,6
Duty
Energy analysis
Heat Integration
ΔTmin = 20oC
Savings
kW
t/h
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energy
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t/y
m3/y
$/y
kW
m3/h
t/h
Hot (steam)
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15,13
459
-
0,8
450
259
-
110,8
Cold (water)
-
-
259
11,13
-
450
-
115,776
11,6
Sum
122,4
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Volume 18, 2023
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DOI: 10.37394/232012.2023.18.20
Juan Pedro Hernández Touset,
José Ulivis Espinosa Martínez
E-ISSN: 2224-3461
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Volume 18, 2023
Contribution of Individual Authors to the
Creation of a Scientific Article (Ghostwriting
Policy)
- Juan Pedro Hernández Touset was responsible for
research methodology.
- José Ulivis Espinosa Martínez was responsible for
data extraction.
The authors equally contributed to the present
research, at all stages from the formulation of the
problem to the final findings and solution.
Sources of Funding for Research Presented in a
Scientific Article or Scientific Article Itself
No funding was received for conducting this study.
Conflict of Interest
The authors have no conflicts of interest to declare
that are relevant to the content of this article.
Creative Commons Attribution License 4.0
(Attribution 4.0 International, CC BY 4.0)
This article is published under the terms of the
Creative Commons Attribution License 4.0
https://creativecommons.org/licenses/by/4.0/deed.en
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WSEAS TRANSACTIONS on HEAT and MASS TRANSFER
DOI: 10.37394/232012.2023.18.20
Juan Pedro Hernández Touset,
José Ulivis Espinosa Martínez
E-ISSN: 2224-3461
251
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