The flow of thermal energy from gases of electric furnace in the charge of rotary furnace.
Terziqi, Avni Kahriman ; Mulliqi, Ismet Sejdi ; Bajraktari, Bekim Veli 等
Abstract: Increased of fuels prices and environmental pollution
highlights the necessity to become their maximum utilization. Even
during the process of obtaining ferronickel in electric furnaces such a
possibility exists. In this case the energy which contains gases at the
exit of electric furnace can be used for heating and various before
heating within the complex of the "New Company Ferronickel".
In this paper is developed the model of using these gases for the
purpose of heating in rotary furnace. Working model can be used in
expansion of general model for rationalization of energy use in electric
furnaces process for obtaining ferronickel.
Key words: electrical furnace, rotary furnace, gases, heating
1. INTRODUCTION
Electric furnace gases (EF) in the industrial complex of
"Ferronickel" in Kosovo, currently cast directly into the
atmosphere, without any preliminary treatment. In this way, the thermal
energy contained in these gases remains untapped.
In order to model of use of the thermal energy of these gases to be
more accurate, will be used measures taken of the parameters of gases in
the chimney. Results of measurements of the concentration of the
components of gases, and the gas flows to the regime for electric
furnaces 24MW and 33MW are given as input value of model.
Measurements of concentrations of gases components are made with
the instrument "Maihack" with detector with infrared ray and
with instrument IMR. Gas flow measurements are made with the
Pitott--Prandlt tube.
2. TEMPERATURE OF GASES OF EF AT THE EXIT OF CONVEYOR TUBE
The concentration of the thermal energy flows (Beqiri, 1996) in
electric furnace gases (EF) in entrance and exit of conveyer tube with
length L is:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1)
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (2)
Meanwhile for the tube through which transported the gases of
electric furnace with length L, the flow of the thermal energy in its
output will be calculated according to equations:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (3)
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (4)
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (5)
where are: [q.sub.c+c+r]--heat flow which loses in the environment
with conduction, convection and radiation, [q.sub.L,c+c+r]--Heat flow,
in units of length, which loses in the environment with conduction,
convection and radiation, [([E.sub.[tau]).sub.1]--the thermal energy
flow in the entrance of the conveyor tube, [([E.sub.[tau]).sub.2]--the
thermal energy flow in the exit of the conveyor tube, From equation (2)
determined the gases temperature at the exit of conveyor tube, according
to equation:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (6)
Based on the equations (1) and (2), for the regime 24MW and 33MW
can be determined the dependence of the thermal energy flow and
temperature of gases of electric furnace in the exit of conveyor tube
for different lengths of this tube up to the entrance of rotary furnace
(RF) (fig. 1 and fig. 2).
While the reduction of value of the gases temperature depending on
the length of the conveyor tube is given in fig. 3.
3. THE FLOW OF THE THERMAL ENERGY FROM THE EF GASES IN THE CHARGE
OF RF
The charge which enters into rotary furnace consists of nickel ore,
limestone and lignite, is with average temperature during the year
[T.sub.sh.] = 283.15 K.
While the flow of the heat, which is carried from gases of electric
furnace in rotary furnace can be computes by the following equation
(Sacadura, 1993):
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (7)
The decrease of heat flows of gases in rotary furnace, depending on
the length of conveyor tube, for regime 24MW and 33MW is shown in fig.4.
Total energy of gases brought by EF in RF not consists only in the
thermal energy which is contained in gases, but also by their thermal
capacity, which is the result of carbon monoxide contained in these
gases.
The low thermal ability of fuel and low thermal ability of gases
(Coulson, & Richardson 1978) determined by equation:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (8)
[H.sub.lgFE] = 12644co (9)
Total energy that gases bring from electric furnaces in the rotary
furnace consists of heat generated, from low thermal ability and thermal
energy contained in the unit of measure:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (10)
Based on equation (10) can be determined the total energy values
that electric furnace gases bring in rotary furnace for various lengths
of conveyor tube (see figure 5).
In the case when will be used only thermal energy equivalence with
low thermal ability of electric furnace gases, saving of fuel for the
working regime 24MW and 33MW will be compute:
[H.sub.lg.EF]/[H.sub.lfuel] (11)
If used the total energetic flow of EF gases, the fuel savings will
depend on the length of conveyor tube between EF and RF (fig. 6).
4. CALCULATIONS AND RESULTS
Input values in the model are: [[lambda].sub.st.]=59.313 W/mK.
[[lambda].sub.ins] =0.037 W/mK, [[delta].sub.ins..] = 0.05m;
[[lambda].sub.int.] =229.111W/mK, [[lambda].sub.int] =0.0008m,
[d.sub.1]=0.16m, [d.sub.2]=0.17m, [d.sub.3]=0.270m, [d.sub.4]=0.2716m,
[T.sub.envir.]=283.15 K, [T.sub.internal] = 303.15K, [d.sub.chimney]
=0.735m, [W.sub.1] =11.67m/s, [[rho].sub.1] =0.365 kg/[m.sup.3],
[[lambda].sub.geF] = 0.09575WJmK, [p.sub.g]=101325 Pa, [T.sub.g.33MW]
=1123.15K, [T.sub.g.24MW]=1149.15K, [DELTA]T=20K, [beta]=0.00341,
[[epsilon].sub.1]=0.055, C=0.135, n=0.3333, [M.sub.CO]=28,
[M.sub.CO2]=44, [M.sub.SO2]=64; [M.sub.O2]=32; [M.sub.NO]=30;
[M.sub.NO2]=46; [[upsilon].sub.air] = 15.06 [10.sup.6] [m.sup.2]/s,
[[lambda].sub.air] = 0.02593 W/mK, [Pr.sub.air]=0.703, [[rho].sub.air] =
1.205 kg/[m.sup.3], [Cp.sub.CO] = 114.425J/kgK,
[Cp.sub.CO2]=1094.85J/kgK, [Cp.sub.O2] = 1020.75 J/kgK,
[Cp.sub.SO2]=767.25J/kgK, [[mu].sub.CO] = 4.5x[10.sup.5]Pa,
[[mu].sub.CO2]=4.6x[10.sup.-5]Pa, [[mu].sub.O2] = 5.1x[10.sup.-5]Pa,
[[mu].sub.SO2]=3.8x[10.sup.-5] Pa (Michael & Howard 2004). While the
results calculated by the model are given in figure 1--fig. 6.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
5. CONCLUSION
The flow of the total thermal energy, including the power generated
from thermal capacity that electric furnace gases submit charges in RF
marks a decrease depending on the length of tube.
While the flow of the total thermal energy delivered during the
working regime 33MW is higher than for working regime 24MW.
In the case when will be used only thermal energy equivalence with
low thermal ability of electric furnace gases, the fuel savings for
working regime 24MW will be compute 12.9%, while for working regime 33MW
this savings will be compute 15.5%.
In the case when will be used as thermal energy equivalence with
low thermal ability of electric furnace gases, as well as the
significant energy of these gases, the fuel savings for working regime
24MW will be compute about 15%, while for working regime 33MW savings
will be compute about 18%.
6. REFERENCES
Coulson, J. & Richardson, F. (1978). Chemical Engineering, 3rd
Edition, Vols. 1, 2, Pergamon, Oxford
Michael, J. & Howard, N. (2004). Fundamental of Engineering
Thermodynamics, John Wiley, ISBN 0-471-27471-2, Hoboke
Beqiri, E. (1996). High Course of heat transmissions, Prishtina
Sacadura, J. (1993) Knowledge for thermal transfer, TEC&DOC,
ISBN 2-85206-618-1, Paris