1 Restructuring of a Parabolic Rolling Production Line of Frauenthal to Improve its Energy and Production Efficiency GUILHERME DE CAMPOS MATIAS VENDEIRINHO Under supervision of Prof. Viriato Sérgio de Almeida Semião Mechanical Departmenent, IST, Lisbon, Portugal November, 2014 ABSTRACT This paper focused on the identification and analysis of three main measures to reduce the energy consumption of Frauenthal factory, with significant impacts on the improvement of its energy and production efficiency. The first suggested measure aims to conceive a more efficient forging procedure by changing the parabolic hot rolling process. To achieve this, a numerical simulation was performed using ANSYS® commercial code to characterize the thermomechanical phenomena during rolling of steel bars, in order to enable the design of a new rolling mill capable of processing simultaneously both ends of the steel bars. The second measure is intended to achieve the direct use of the energy contained in the exhaust gases of an annealing furnace for subsequent injection into the inlet of a tempering furnace. The third measure is related to the recovery of thermal energy contained in the hot quenching oil and tempering furnace exhaust gases to meet the heat demand in different parts of the plant. With the assistance of an application software developed in MATLAB®, which allows the characterization and monitoring of different energy and productivity aspects, it is concluded that the three measures are economically viable, enabling an effective final energy saving of 30% and an energy bill reduction of 25%. Computational modelling of the rolling process has shown the main factors influencing the heat exchange and temperature distribution on the billet, as well as the major forces that occur during rolling. KEYWORDS: Final energy saving, Energy efficiency, Hot rolling mill, Finite element method, Temperature distribution, Energy management software 1. Introduction It is essential to create favorable conditions for automotive companies to be competitive, so they can anticipate the challenges of competition and respond to them in a socially responsible and innovative way. Thereby, the main objective of this work is the energetic and economic assessment of the implementation of three measures that promote energy and productive efficiency of the Frauenthal factory, after the restructuring of one of its parabolic rolling lines. The purpose of this work includes the development of a software that estimates the of costs associated with the energy consumption of the factory. On the other hand,
10
Embed
Restructuring of a Parabolic Rolling Production Line of ... · that year corresponded to a consumption of 2566 kWh/ton of produced stock, resulting in a production cost of 124,8 €/ton.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1
Restructuring of a Parabolic Rolling Production Line of Frauenthal to
Improve its Energy and Production Efficiency
GUILHERME DE CAMPOS MATIAS VENDEIRINHO
Under supervision of Prof. Viriato Sérgio de Almeida Semião
Mechanical Departmenent, IST, Lisbon, Portugal
November, 2014
ABSTRACT
This paper focused on the identification and analysis of three main measures to reduce the energy
consumption of Frauenthal factory, with significant impacts on the improvement of its energy and production
efficiency.
The first suggested measure aims to conceive a more efficient forging procedure by changing the parabolic hot
rolling process. To achieve this, a numerical simulation was performed using ANSYS® commercial code to
characterize the thermomechanical phenomena during rolling of steel bars, in order to enable the design of a
new rolling mill capable of processing simultaneously both ends of the steel bars.
The second measure is intended to achieve the direct use of the energy contained in the exhaust gases of an
annealing furnace for subsequent injection into the inlet of a tempering furnace.
The third measure is related to the recovery of thermal energy contained in the hot quenching oil and
tempering furnace exhaust gases to meet the heat demand in different parts of the plant.
With the assistance of an application software developed in MATLAB®, which allows the characterization and
monitoring of different energy and productivity aspects, it is concluded that the three measures are
economically viable, enabling an effective final energy saving of 30% and an energy bill reduction of 25%.
Computational modelling of the rolling process has shown the main factors influencing the heat exchange and
temperature distribution on the billet, as well as the major forces that occur during rolling.
KEYWORDS: Final energy saving, Energy efficiency, Hot rolling mill, Finite element method, Temperature
distribution, Energy management software
1. Introduction It is essential to create favorable conditions for automotive companies to be competitive, so they can
anticipate the challenges of competition and respond to them in a socially responsible and innovative way.
Thereby, the main objective of this work is the energetic and economic assessment of the implementation of
three measures that promote energy and productive efficiency of the Frauenthal factory, after the
restructuring of one of its parabolic rolling lines. The purpose of this work includes the development of a
software that estimates the of costs associated with the energy consumption of the factory. On the other hand,
2
it is also intended to carry out a numerical simulating of the hot rolling process, in order to evaluate the
benefits provided by the first measure, which is the largest one.
The Finite Element Method (FEM) simulates the rolling process of steel bars with a high level of certainty and
proved to be a useful tool in the study of severall hot rolling parameters, improving not only industrial planning
but also the design of new rolling lines with the increasing productivity in perspective [1].
It is known that the geometrical parameters are directly associated with the rolling forces, while the
thermomechanical and structural parameters are related also to the temperature distribution on the bar after
the passage of the roll [2]. The influence of those parameters on the modelling of the rolling process will be
presented in detail on chapter three.
The factory studied in the present work, Frauenthal Automotive Azambuja, produces parabolic leaf springs for
the automotive industry. The primary energy consumption of the factory in 2012 reached 4306 TEP, which for
that year corresponded to a consumption of 2566 kWh/ton of produced stock, resulting in a production cost of
124,8 €/ton.
Figure 1.1 - Flowchart of the productive process in the forging area, where 1-Bar cutting lines, 2,3 – Parabolic rolling lines,
4,5 – Eye forming lines and with the heat treatment lines at the end [3]
As shown on the figure 1.1, the processing of steel bars starts at the cutting lines (1 in figure 1.1), followed by
the individual rolling on each side of the blade. Subsequently, each eye is formed individually (4 e 5 in figure
1.1) and finally the heat treatment of the parts is carried out. Each process requires partial heating of the bar
followed by a forced cooling before entering in the next line.
2. Energy Efficiency Measures 2.1. Dimensioning of the New Hot Rolling Single Line – Hot Zone
A MATLAB® application was conceived allowing the analysis of energy data collected manually, and the
correlation of these elements with the production data. The table 2.1 shows some energy data obtained with
this software for the production lines that will be covered by this first measure, among which it should be
noted the low efficiency and high annual cost of the furnaces for each production line.
Table 2.1 - Production and energy data of the lines that will be merged into the new PR single line
The huge waste of energy that occurs in some furnaces, the fact that there is a forced cooling of hot steel bars
between each of 5 forging processes and both the slowness and the complexity of the forging process reveals a
high potential for improving energy and productive efficiency.
Production
Line
Monthly
Production (ton)
Monthly Natural Gas
Consumption (m3)
Specific Consumption
(Wh/kg)η
Average working
days (days)
Natural Gas
Annual Cost (€)
Weighted
Consumption (%)
Average efficiency
of furnaces (%)
325 601 11110 3550 5% 20 97322 7% 20,9%
405 527 9992 728 25% 20 87529 7%
406 623 16595 1023 18% 20 145369 11%
407 109 3905 1378 13% 11 34211 3%
3
The proposed solution intends to the reduce energy waste and the above mentioned productive inefficiencies
by designing a single production line where the entire forging process of the steel, with the exception to the
eye forming lines, is done in a continuous line. So, the main goal is to merge the cutting line 325, and the
parabolic rolling lines 405, 406 and 407, shown in the figure 2.1(a), into one single line as shown in the figure
2.1(b).
Figure 2.1 - Forging area with light springs processing lines (blue) and heavy springs processing lines (red), as well as
some of the possible routes for light springs (blue arrows) (a) and location shown in blue for the new single line without 405, 406, 407 and 325 lines (b)
The biggest barrier to implementing this measure lies in the design of a mill capable of processing both sides of
the bar simultaneously. The equations 2.1, 2.2 e 2.3, developed in accordance with the Slab Method [4], are
the starting point for the chosen bar profile (or thickness) that will be used in the numerical simulation of the
rolling process, whose results will be presented in chapter 4.
Figure 2.2 - Schematic representation of the variables involved in the sizing of a rolling process
Table 2.2 – Equations used to calculate the rolling load, P, in accordance with Slab Method
𝑃 =2
√3𝜎0 [
𝑏
𝑄(𝑒𝑄 − 1)√𝑅𝛥ℎ] (2.1) 𝑃[𝑁] is the rolling load, σ0 [MPa] is the steel flow stress, b [m] is the width of the bar, μ
is the friction coefficient between the bar and the roll, R [m] is the roll radius, Δh [m] is
the absolute thickness reduction, ℎ̅ [m] is the average thickness in each roll passage and
T [N.m] is the torque in the rolls.
𝑄 =𝜇𝐿𝑝
ℎ̅ (2.2)
𝑇 = 𝑃𝐿𝑝 (2.3)
After performing the calculation of the daily productive capacity of the new line it turned out that this single
line will have a capacity that is 25% greater than the lines 325, 405, 406 and 407 altogether, summing up a total
of 2646 springs/day. In order for this to be achieved, a 1024 kW induction heating furnace was dimensioned.
2.2. Recovering of the thermal energy in the furnace 537 exhaust gas to inject in the 541 tempering furnace
This measure intends to directly forward the exhaust gases from the furnace 537 to the fresh air inlet of
furnace 541, which will be achieved through the installation of an air duct that will capture the hot exhaust
gases in the entrance of furnace 537. Figure 2.3 illustrates how to achieve this benefit.
4
Figure 2.3 - Representation of the reutilization of the exhaust gases from furnace 537 (left) to furnace 541 (right)
The available power, 𝑃𝑜𝑡𝑒𝑥ℎ𝑎𝑢𝑠𝑡_537, to inject in furnace 541 can be calculated with an ordinary energy balance.
Thus, after finding the flow rate of the exhaust gases available at the inlet of the furnace 537, the following
parameters were calculated: the heat received by the new air duct for passing near the hot surface of the
furnace 537; the heat loss from the duct to the environment; and the main inlet’s (figure 2.3) fresh air flow,
�̇�𝑓𝑟𝑒𝑠ℎ 𝑎𝑖𝑟, shown in table 2.3, that ensures a temperature inside the furnace 541 slightly above 300 ° C.
Table 2.3 - Power available in the exhaust gases and fresh air admitted in the main inlet
𝑃𝑜𝑡𝑒𝑥ℎ𝑎𝑢𝑠𝑡_537 (kW) 474,8
�̇�𝑓𝑟𝑒𝑠ℎ 𝑎𝑖𝑟 (kg/s) 0,7
2.3. Quenching Oil and Furnace 538 Heat Recovery In this measure will be analysed two solutions to recover the heat contained both in the exhaust gases of the
538 tempering furnace and in the quenching oil of the heat treatment lines.
In the first solution the use of air-fluid heat exchangers (i.e. finned tubes) will be studied, while in the second
the use of radiant panels will be studied only in the paint ovens. In both measures the heat will be transported
to the cold zone of the factory with a thermal fluid.
The heat exchange between the thermal fluid and the exhaust gases of 538 furnace will be made using a coil
formed by tube banks, while the heat exchange with the quenching oil is made with a plate heat exchanger
2.3.1. Liquid-to-Air Heat Exchangers The purpose of this measure is to transform the current circuit, shown on the left side of figure 2.4, in the
circuit of the right side of the same figure.
Figure 2.4 - Schematic representation of the initial circuit (left) and the circuit to be installed (right)
Three circuits will be designed, where the first transports the heat to the paint ovens, the second one to
electrical heaters in the warehouse and showers, while the third circuit transports the heat to the domestic hot
water central (DHW).
5
First, the heat requirements of each paint oven, �̇�𝑎𝑖𝑟_𝑑𝑟𝑦𝑖𝑛𝑔, were evaluated by an energy balance, taking into
account the desired temperature inside each oven. Subsequently, it was evaluated the temperature at which
the thermal fluid needs to reach the paint ovens, 𝑇𝑛𝑒𝑐𝑒𝑠𝑠𝑎𝑟𝑦_𝑖𝑛𝑙𝑒𝑡, with equation (2.4):
𝜀 =
(𝑡𝑜 − 𝑡𝑖)
(𝑇𝑛𝑒𝑐𝑒𝑠𝑠𝑎𝑟𝑦_𝑖𝑛𝑙𝑒𝑡 − 𝑡𝑖) (2.4)
On the previous equation, 𝜀 refers to the design efficiency of the heat exchangers to be installed in the paint
ovens and the DHW central (𝜺 = 𝟎, 𝟕𝟓), 𝑡𝑜 [K] is the outlet temperature of the fluid with the lower heat
capacity rate, �̇�𝐶𝑝 (Air and Water, in the paint ovens and DHW central, respectively), 𝑡𝑖 [K] is the inlet
temperature of the fluid with the lower �̇�𝐶𝑝, 𝑇𝑛𝑒𝑐𝑒𝑠𝑠𝑎𝑟𝑦_𝑖𝑛𝑙𝑒𝑡 [K] is the temperature of the fluid with the higher
�̇�𝐶𝑝, in order to satisfy the heat required, �̇�𝑎𝑖𝑟_𝑑𝑟𝑦𝑖𝑛𝑔 (Thermal fluid).
Through an iterative method, knowing the available energy by radiation and convection in the exhaust gases of
538 furnace and quenching oil, discounting the heat losses from the thermal fluid that come from the heat
treatment area until it reaches every heat exchange point in the cold zone of the factory, and knowing the
mass flow in the piping, it is possible to calculate the total length of the tube bank to be installed in 538 furnace
(84m) and the heat recovered in the furnace 538 and in the quenching oil (table 2.4)
Table 2.4 - Summary of energy recovered in the 538 furnace and in the quenching oil
448 kW to Pain ovens, 60kW to DHW and 52 kW to Electric heaters
Total needs
Circuit 1 (kW)
Total needs
Circuit 2 (kW)
Total needs
Circuit 3 (kW)
�̇�𝑐𝑖𝑟𝑐𝑢𝑖𝑡 1 (𝑘𝑔
𝑠) �̇�𝑐𝑖𝑟𝑐𝑢𝑖𝑡 2 (
𝑘𝑔
𝑠) �̇�𝑐𝑖𝑟𝑐𝑢𝑖𝑡 3 (
𝑘𝑔
𝑠)
Heat recovered in the Furnace
(kW)
Heat recovered in the
Quenching oil (kW)
448,0 60,0 63,4 2,59 0,426 1,169 347,6 168,0
2.3.2. Radiant Panels Solution The solution proposed in this section is similar to the previous one, since it was considered the use of radiant
panels instead of air-fluid heat exchangers. Equation (2.5) shows the used method to compute the energy
required to dry the ink in the steel bar, which was then used to design the radiant panels to be installed.
𝐸𝑣𝑎𝑝 = 𝑚𝑝𝑎𝑖𝑛𝑡ℎ𝑓𝑔 + 𝑚𝑝𝑎𝑖𝑛𝑡𝐶𝑝𝑤𝑎𝑡𝑒𝑟(𝑇𝑓 − 𝑇𝑖) (2.5)
Where, 𝐸𝑣𝑎𝑝 [J] is the necessary energy to evaporate the water in the bar surface, 𝑚𝑝𝑎𝑖𝑛𝑡 [kg] is the mass of ink
applied on the bar surface, ℎ𝑓𝑔 [kJ/kg] is the latent heat of vaporization of water and 𝑇𝑖 and 𝑇𝑓 [K] are the initial
and final temperature of the bar, respectively. The heat recovered in the furnace 538 with this second solution
is, approximately, 248 kW and the necessary length of the tube bank is significantly reduced to 46m.
It should be noted that this solution provides a significant reduction in the insulation and piping, since it is
possible to suppress the circuit 2 (DHW) because there is still enough energy available in the thermal fluid after
all thermal exchanges that occur at the end of the circuit 1.
3. Modelling of the Rolling’s Thermo-Mechanical Process The hot rolling process was simulated using ANSYS® code, based on the finite element method (FEM).
To simplify the mathematical and physical modelling of the rolling process, the following assumptions were
taken into account: (i) the simulation was considered two-dimensional (2D); (ii) the temperature in the roll axis
direction is assumed to be constant; (iii) the rolling load, P, in both rolls, upper and lower, as well as the
6
geometry of the steel bar, are symmetrical relative to its center plane (as shown in figure 3.1); (iv)
Thermoplasticity effects and the heat generated by the friction force were ignored. [1,2,5]
Figure 3.1 - Symmetry plane representation, rolling load, P, initial, hi, final, hf, and absolute thickness reduction, Δh
3.1. Mathematical Rolling Mill Modelling The behaviour of the steel was assumed to be elastic-plastic after being assumed that the strain-rate of the
steel during its parabolic rolling is reduced and, therefore, negligible. The thermal and mechanical properties of
the steel bar and the roller are defined as temperature dependent functions. Figure 3.2 (b) shows the
temperature dependency of the 0,2% tensile yield strength for a similar steel to that to be used in this
modelling (51CrV4).
Table 3.1 summarizes the constitutive and thermal equations employed in this model.
Table 3.1 - Summary of thermal and constitutive equations used in the model