JP2003073719A - Method for controlling surplus air in metal-oxide reducing furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply a reasonable quantity of surplus air without employing an analyzer. SOLUTION: This method comprises measuring a quantity of a material fed into the furnace with time, which contains metallic oxide, calculating total amount of difference between the oxygen gas, which is released from the material passing in the furnace out of the measured materials, and the oxygen gas which is consumed, and supplying the furnace with surplus air so as to offset fluctuations of the total amount of the calculated difference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling excess air in a metal oxide reduction furnace, and more particularly to a method for properly controlling the amount of excess air in the furnace without using an oxygen analyzer or the like.

[0002]

2. Description of the Related Art In order to reuse steel-making dust, powder ore, etc., a binder and a reducing material are mixed with steel-making dust, which is a metal oxide, and kneaded, and then granulated into pellets. Floor-type metal oxide reduction furnace (hereinafter referred to as reduction furnace)
And heat treatment such as heating and reduction is performed. In this case, a combustible gas is generated from the binder and the reducing material while passing through the furnace, and the burner is burned with an air-fuel ratio of less than 1 in order to maintain a reducing atmosphere in the reducing zone of the furnace. Combustible gas containing, for example, is discharged from the furnace without burning. When such a flammable gas is caused to flow into the exhaust gas passage, there is a risk that it will explode by being mixed with invading air in a heat exchanger or a cooling tower provided in the exhaust gas passage. Therefore, conventionally, surplus air is supplied to the heating zone of the reduction furnace to which the exhaust gas passage is connected to burn the combustible gas in advance before flowing out to the exhaust gas passage. Here, if the excess air is less than the appropriate value, the danger of explosion in the exhaust gas passage remains, and if it is more than the appropriate value, excess air will enter the reduction furnace, so It causes a decrease and both are not preferable. To prevent this, the excess air is supplied by installing an oxygen analyzer or a CO analyzer at the upstream end of the exhaust gas passage so that the oxygen (O2) gas concentration reaches a predetermined value Do as shown in FIG. The amount of air Fo is controlled to CO
The combustible gas concentration is sufficiently low, and the furnace temperature and thermal efficiency are not lowered, or the amount of exhaust gas is not increased.

[0003]

However, the use of an analyzer is costly because it is relatively expensive, and the analyzer is used for eliminating clogging of filters associated with the analyzer. There was a problem that it took time to maintain and adjust.

Therefore, the present invention solves such a problem, and provides a surplus air control method for a metal oxide reduction furnace which can supply an appropriate amount of surplus air without using an analyzer. The purpose is to

[0005]

In order to achieve the above object, in the present invention, the supply amount of a material containing a metal oxide into a furnace is measured over time, and the measured amount of the above material in the furnace is measured. The total amount of the difference between the oxygen gas released by the material passing through and the consumed oxygen gas is calculated, and surplus air is supplied into the furnace so as to cancel the variation in the total amount of the difference. In this case, the calculation of the total amount of the difference between the oxygen gas to be released and the oxygen gas to be consumed is obtained by determining the change over time in the amount of oxygen gas to be released and the amount of oxygen gas to be consumed while the material of unit mass passes through the furnace It can be performed by adding these to the product of the amount of material charged into the furnace at each time. Further, in the calculation of the total amount of the difference between the released oxygen gas and the consumed oxygen gas, it is possible to introduce a delay time until the material is actually put into the furnace after measuring the supply amount of the material. .

In the present invention, the total amount of the difference between the oxygen gas released by the material passing through the furnace of the reduction furnace and the oxygen gas consumed is calculated, and excess air is added so as to cancel the variation in the total amount. Since it is supplied into the furnace, the total amount of oxygen gas (oxygen gas concentration) at the exhaust gas outlet of the reduction furnace can be maintained at an appropriate constant value without using an oxygen analyzer. Therefore, the reduction treatment of the material containing the metal oxide can be carried out at low cost, and the maintenance and adjustment work for eliminating the clogging of the filter can be reduced.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a feed system of pellets, which is a material, of a reducing furnace to which the method of the present invention is applied. The pellets cut out from the weighing hopper 1 are transferred to a plurality of conveyors 2
Rotary hearth type reduction furnace 3 while being transferred onto A, 2B and 2C
The metal oxide in the pellets is reduced to a metal under the reducing atmosphere of the reduction zone by being fed into the heating zone of the reduction furnace 3 and fed to the intermediate zone and the reduction zone. The exhaust gas containing combustible gas generated from the pellets in this process is discharged to the exhaust gas passage through the heating zone, but the heating zone is supplied with an appropriate amount of excess air determined by the calculation described later, and the exhaust gas passage The flammable gas is completely burned prior to its outflow.

The weight m (t) of the pellets cut out from the weighing hopper 1 onto the conveyor 2A fluctuates with time as shown in FIG. 2 (1) due to fluctuations in granulation conditions and the like.
Pellets cut out at time to are conveyor 2A
After being conveyed over ~ 2C, it is put into the furnace after a time Tf, remains in the furnace for a time τ, is reduced, and is discharged.
The I02M (t) in Fig. 2 (2) shows the change over time in the amount of oxygen gas released from the oxides contained in the pellet of unit weight, and is 0 until the pellet is charged into the furnace. After it is charged into the furnace, it gradually increases and reaches a peak, then decreases, and becomes close to 0 again immediately before being discharged to the outside of the furnace. Further, OO2M (t) in FIG. 2 (3) shows a time-dependent change in the amount of oxygen gas burned and consumed by the combustible gas generated from a unit weight of the pellet, and shows the same tendency as the above-mentioned generated oxygen gas amount. As shown in the figure, it is 0 until the pellets are put into the furnace, and after the pellets are put into the furnace, it gradually increases and reaches a peak, then decreases, and becomes close to 0 again immediately before being discharged out of the furnace. In addition, I02M (t), OO2M in the furnace
The change curve of (t) is obtained by an actual machine test or the like.

The total amount of oxygen gas TO at the exhaust gas outlet of the reduction furnace is represented by M, where M is the total amount of pellets charged into the furnace.
It is represented by formula (1). Here, I02B is the amount of oxygen gas contained in the combustion air of the burner, O02B is the amount of oxygen gas consumed by the fuel of the burner, and I02A is the amount of oxygen gas contained in the excess air.

[0010]  TO = IO2B-OO2B + IO2A + (IO2M-OO2M) * M ... (1)

In the formula (1), (IO2B-OO2B) is a manageable amount, and the fluctuation amount is the oxygen gas balance (I
O2M-OO2M) x M, so if this amount can be accurately calculated, the total amount of oxygen gas (oxygen gas concentration) at the exhaust gas outlet of the reduction furnace is adjusted by adjusting I02A, that is, the amount of excess air so as to offset the fluctuation. TO can be maintained at an appropriate constant value.

Therefore, the term of (IO2M-OO2M) * M will be examined below. In FIG. 3 (1), when a pellet of weight m (to) cut out at time to is supplied into the furnace after time Tf and reaches the exit of the furnace after time τ,
The time-dependent change of IO2M (t) is shown. In FIG. 3, the change curve of I02M (t) in the furnace is approximated by a substantially triangular shape.
Further, in FIGS. 3 (2) to 3 (4), time to + Δ
Weights m (to + Δt), m (to + 2Δt), ..., M cut out at t, to + 2Δt, ..., To + τ
IO2M (t) when (to + τ) pellets are fed into the furnace after time Tf and reach the exit of the furnace after time τ
Shows the change with time.

Here, when the total amount of released oxygen gas TMI (t) in the furnace at this time is calculated with reference to the time t when the pellets cut out at the time to reach the exit of the furnace,
This is at each time to, to + Δt, to + 2Δt, ..., T
It is the total amount of oxygen gas generated from each pellet cut out at o + τ and put into the furnace, and is represented by the equation (2). Note that t = to + Tf + τ.

[0014]  TMI (t) = IO2M (t-to) · m (to) Δt + IO2M (t-to-Δt ) ・ M (to + Δt) ・ Δt + IO2M (t-to-2Δt) ・ m (to + 2Δt ) Δt + ... + IO2M (t-to-τ) · m (to + τ) Δt  = IO2M (to + Tf + τ-to) ・ m (to) Δt + IO2M (to + Tf + τ -To-Δt) ・ m (to + Δt) ・ Δt + IO2M (to + Tf + τ-to-2 Δt) ・ m (to + 2Δt) Δt + ... + IO2M (to + Tf + τ-to-τ) ・ m (to + τ) Δt (2)

When the expression (2) is expressed in a continuous form, the expression (3) is obtained.
Becomes

[0016]

[Equation 1]

Total oxygen gas consumption T in the furnace at time t
MO (t) can also be calculated by the same calculation as Equation (4), and eventually, the oxygen gas balance (the difference between the released oxygen gas and the consumed oxygen gas) derived from the pellets in the reducing furnace at the time t by the charged pellets. The total amount) TM (t) is represented by the equation (5).

[0018]

[Equation 2]

[0019]

[Equation 3]

Therefore, when TM (t) fluctuates as shown by the chain line in FIG. 4, the oxygen gas amount IO2A in the excess air, that is, the excess air amount is changed so as to cancel it (see FIG. 4), the total oxygen gas amount TO at the exhaust gas outlet of the reduction furnace can be maintained at a predetermined constant value as shown by the solid line in FIG.

Incidentally, it is preferable that IO2A, that is, the surplus air amount is continuously changed so as to cancel the fluctuation of the oxygen gas balance TM (t), but as shown in FIG. In some cases, it cannot be changed. In this case, the total amount TO of oxygen gas fluctuates to some extent, but the fluctuation amount can be suppressed within an allowable range.

In the above embodiment, IO2M (t) and OO
The change curve of 2M (t) is individually calculated, and the total amount of generated oxygen gas TMI (t) and the total amount of consumed oxygen gas TMO (t) are calculated individually. However, in the actual machine test, etc., (IO2M (t) -OO2M
If the change curve of (t) is obtained, TMI (t)
Oxygen gas balance TM by the procedure similar to the procedure for calculating
(T) can be calculated directly.

[0023]

As described above, according to the surplus air control method for a metal oxide reduction furnace of the present invention, it is possible to supply an appropriate amount of surplus air without using an oxygen analyzer, resulting in low cost. Thus, the combustible gas in the exhaust gas can be completely burned and removed without any trouble.

[Brief description of drawings]

FIG. 1 is a diagram showing a material supply path of a metal oxide reduction furnace to which the method of the present invention is applied.

FIG. 2 is a diagram showing changes over time in the pellet cutout amount, the generated oxygen gas amount, and the consumed oxygen gas amount.

FIG. 3 is a diagram showing changes over time in the amount of oxygen gas generated from pellets cut out at various times.

FIG. 4 is a diagram showing changes over time in the oxygen gas balance, the amount of oxygen gas in excess air, and the total amount of oxygen gas at the exhaust gas outlet.

FIG. 5 is a diagram showing changes over time in the oxygen gas balance, the amount of oxygen gas in excess air, and the total amount of oxygen gas at the exhaust gas outlet in another example of the present invention.

FIG. 6 is a graph showing C with respect to a change in the amount of surplus air supplied into the furnace.
It is a figure which shows the change of O density | concentration and O2 density | concentration.

[Explanation of symbols]

1 ... Weighing hopper, 2A, 2B, 2C ... Conveyor, 3 ... Metal oxide reduction furnace.

Claims (3)

[Claims] 1. A supply amount of a material containing a metal oxide into a furnace is measured with time, and among the measured materials, an oxygen gas released by a material passing through the furnace and an oxygen gas consumed are consumed. A surplus air control method for a metal oxide reduction furnace, comprising calculating a total amount of difference and supplying surplus air into the furnace so as to cancel a variation in the total amount of difference. 2. The change with time of the amount of oxygen gas released and the amount of oxygen gas consumed while a unit mass of material passes through the furnace is determined, and these are multiplied by the amount of material charged into the furnace at each time. The surplus air control method for a metal oxide reduction furnace according to claim 1, wherein the total amount of the difference between the released oxygen gas and the consumed oxygen gas is calculated by adding things. 3. In calculating the total amount of difference between the released oxygen gas and the consumed oxygen gas, a delay time after the material supply amount is measured and before the material is actually charged into the furnace is introduced. The method for controlling excess air in a metal oxide reduction furnace according to claim 1 or 2, wherein.