IDEAL OPERATIONAL PARAMETERS OF FeSi75 FURNACES - FACTOR J1

L. R. Jaccard

ANTECEDENTS

We verified that the C3 equations ( I = C3 . P2/3 and V = P1/3 / C3 ), commonly used to define the submerged arc ideal parameters, are wrong.

Based on theoretical principles, confirmed by experiences made in cassiterite reduction furnaces, we concluded that, for a determined electrode spacing, the voltage that promotes the electrode ideal position is a function of the electrodes diameter and the active power: V = J0 . D / P1/4, where D is the electrode diameter, P is the active power and J0 is a factor dependent of the processed material and electrode space.

It was also suggested for the tests that, inside a certain range, the ideal voltage is proportional to the electrode spacing square root: V = J1 . D . S1/2 / P1/4, in which S is the electrode spacing and J1 is a factor proportional to the resistivity of the processed material ( J1 = V . P1/4 / D . S1/2 ).

APPLICATION OF FACTOR J1 TO FESI75 FURNACES

In order to calculate the J1 factor of the FeSi75 furnaces, we considered three real cases of furnaces with known dimensions, operational parameters and performances. The furnace number 1 operates with an energy consumption of 7800 kWh/t and without SiC deposition problems at the hearth, the second furnace consumes 8000 kWh/t but suffers with a high SiC deposition rate and the third furnace operates with energy consumption of 8500 kWh/t ( SiC deposition rate was not informed ).

That is, it is possible to inferred that the furnace 1 operates close to the ideal position, the furnace 2 operates with the electrode in a position a little apart from the ideal and the electrodes of the furnace 3 operate far from the ideal position.

For each one of these furnaces we calculate J1 and C3.

Furnace
Energy
SiC Deposit
D
S
I
V
P 3 phase
Factor C3
Factor J1
Error by C3
Error by J1
No
(kWh/t)
-
(cm)
(cm)
(kA)
(V)
(MW)
-
-
(%)
(%)
1
7.800
NÃO
106
250
51,0
74,7
11,4
10,07
0,350
0
0
2
8.000
SIM
115
275
65,0
83,3
16,2
10,13
0,375
+0,006
+7,1
3
8.500
?
130
291
72,9
95,6
20,9
9,60
0,394
-4,7
+11,25

It is possible to conclude that factor J1 evaluated very precisely the different performance of the three furnaces and the C3 evaluation failed. However, the three furnaces are operating in a relatively good condition and the performance differences are tenuous. Let see what it would happen if a strong power increase were made at furnace number 2 maintaining the C3 reference factor ( 10,07 ). Suppose that a power increase to 20 MW be made without increasing the electrode diameter and the electrode space. Following C3 equation, to maintain electrode position, the current should be increased to: I = 10,07 . 202/3 = 74,12 kA. But, in this case, the J1 factor would be: 90 V . (20.000 kW / 3 )1/4 / 115 cm . ( 276 cm )1/2 = 0,425. Taking as a reference the furnace 1, the ideal J1 factor would be 0,350 and the J1 factor for the new type of operation would be 21,4 % higher than the ideal. In this case, trusting in J1 factor, we can expect a very poor performance with higher energy and electrode consumption, higher SiC deposition and lower productivity.

We can conclude that the J1 factor value that defines the ideal operation of the FeSi75 furnaces must be equal to approximately 0,350 ( using Watts, cm and Volts ) ( furnaces operating in Brazil with coal charge ).

Using J1 factor, it is possible, for each active power, to choose the ideal voltage, electrode diameter and electrode space.

Contact Mr. L R Jaccard

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