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FUEL SAVING SCENARIOS ANALYSED BY MATHEMATICAL MODELLING

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Fuel savings have been increasingly climbing the priority agenda of a diversity of companies and the recent development of global economy speeds up the pace. Energy intensive industries are particularly engaged in finding out creative solutions towards efficiency. On addressing the trade-off between shortage of resources and the need for R&D investments, mathematical modelling arises as a sure solution. The present study applies GS-GFM (CFD software from Glass Service) to analyse several scenarios for the temperature hold of coke ovens, culminating on possible 40,8% savings in fuel consumption, compared to the common practice.
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FUEL SAVING SCENARIOS ANALYSED WITH MATHEMATICAL MODELLING
Isis Santos Costa, Caroline Satye Martins Nakama, Ricardo Leite Passos
Æstus Industrial Services | Thermojet do Brasil
Abstract
Fuel savings have been increasingly climbing the priority agenda of a diversity of companies and the
recent development of global economy is speeding up the pace. Energy intensive industries are
particularly engaged in finding out creative solutions towards efficiency. On addressing the trade-off
between shortage of resources and the need for R&D investments, “mathematical modelling” rises as
a sure solution. The present study consists of the analysis of several scenarios developed with GS-
GFM for the temperature hold of coke ovens, culminating on possible 40,8% savings in fuel
consumption, compared to the common practice.
INTRODUCTION
This study consists of a method of utilizing the thermal energy from waste gases produced
on holding the temperature of coke ovens. The method enables the collection of the energy
usually emitted through the chimney and their reuse for holding the temperature of ovens not
equipped with burners. Forced exhaustion allows the gas to flow in the opposite route to that
in normal operation of the ovens.
During the normal operation of these ovens, combustion of coal volatiles usually takes place
maintaining the temperature of the whole refractory structure adequate for operation, without
the need for external burners. Thereafter, once the operational temperature has been
achieved, around 1.110°C, the ovens remain permanently heated as a result of the operation
itself.
This feature of thermal self-sustaining contributes to the structural integrity of the coke ovens.
Usually lined in silica, they endure high temperatures, but are sensitive to cooling down, so
that steadily high energy levels are desirable. In extreme events, the constitutive materials
may undergo property changes so that they become unusable.
As a result, in times of suspension of operation for inspection or for cleaning the ducts or the
boiler, or because of demand reduction, for instance, strategies are necessary for the
conservation of temperature of the coke ovens.
The state of the art observed in addressing that issue corresponds to a method for keeping
the coke oven chamber (A) hot by installing at least one external burner at the oven, from
which combustion fumes (H or R), after heating up the corresponding coke oven chamber
are converted into waste gases (J). These gases flow through a collecting line (B) and are
emitted directly into the atmosphere through the chimney (C). The gases discharged through
the chimney according to this method are usually at high temperatures, corresponding,
therefore, their issuance to waste of thermal energy.
A. Coke oven
B. Collecting line that connects the ovens and conducts the gases to the chimney
C. Chimney
D. Collecting line that connects the ovens and conducts the gases to the boiler
E. Heat recovery boiler
F. Pusher side door of oven
G. Element blocking the flow of gases to the boiler
H. Combustion fumes of burner installed at the pusher side
I. Combustion fumes of burner installed at the coke side
J. Waste gases
K. Element blocking the flow of gases to the chimney
Figure 1 presents the common practice illustrating the top view of a set of ovens connected
by a collecting line (B) with temperature regulation by external burners positioned at each
oven (A), producing combustion fumes at the pusher or coke side (H and I, respectively) or
on both sides simultaneously. The waste gases (J) are prevented from leaking into the boiler
(E) by the locking element (G) and are exhausted through the chimney (C).
Figure 1: Common practice.
As an alternative for the strategy presented, Thermojet / Æstus tested the possibility of
diverting the flow of gases from the chimney into ovens not equipped with burners. Systems
were projected to be disposed for supplemental energy, as necessary. The criterion used to
limit the amount of energy injected into the oven was the expansion level of silica. Figure 2
presents the result obtained for the common practice scenario. This baseline model was
developed and validated on the basis of results from the heating up of 464 ovens, during
5.904 hours, using 1.683 thermocouples (Table 1).
0017
96.3274 %
0016
96.3283 %
0018
92.633 %
0030
95.6084 %
Slice X, I
Perc_Exp.dir [%] - C:\Users\caroline.martins\Doc uments\GFM\Thermojet\CoqueriaCSA_12-2012\Case7\Perc_Exp.dir
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
13600; 213
800°C 800°C
Figure 2: Simulation of expansion levels at common practice.
Table 1: Field data used for validation.
Field Data Ovens Hours Thermocouples
Sol Coqueria 320 3.312
TKCSA 144 2.592
1.683
(data validation)
The fuel saving scenario was then modelled and the results were compared to the baseline,
with adjustments being made up to achievement of the set-up expansion levels (Figure 3). A
30,5% reduction on gas consumption was firstly achieved. Combined with some changes in
the process, it summed up to 40,8% of fuel savings.
0016
95.3977 %
0018
90.2341 %
0017
95.7311 %
0030
92.9081 %
Slice X, I
Perc_Exp.dir [%] - C:\Users\caroline.martins\ Documents\GFM\Thermojet\CoqueriaCSA_12-2012\Case7\Perc_Exp.dir
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
13600; 213
800°C 800°C
Figure 3: Simulation of of expansion levels at tested scenario.
CONCLUSIONS
The present study illustrates the use of mathematical modelling for cost-effective testing of
scenarios allowing the reduction of up to 40,8% of fuel consumption in a project involving the
use of around 7.000 ton of LPG/month.
ACKNOWLEDGEMENTS
The authors are thankful for the constant support and on demand customization from the
Glass Service team, allowing the use of GFM software outside the boundaries of the Glass
Industry.
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