JP2595590B2 - Exhaust gas treatment method after scrap preheating - Google Patents

Description

The present invention relates to a method for treating exhaust gas after preheating of scrap.

Electric furnaces are widely used for melting metals, but from this kind of electric furnace, due to the property of melting raw materials by arc heat,
Hot exhaust gas is generated. The exhaust gas is post-combusted by a so-called self-combustion in a combustion tower, further detoxified through a cooler and finally through a dust collector, and then released into the atmosphere. However, if the sensible heat of the exhaust gas from such an electric furnace is released into the atmosphere without particularly effective use, heat energy is extremely wasted.

Therefore, the sensible heat of the exhaust gas from the electric furnace is used for preheating of the scrap as a raw material. Particularly, when the scrap is a low-grade scrap such as Dalai powder or shredder, particularly after the preheating. The exhaust gas contains a large amount of malodorous components such as hydrogen sulfide, acetaldehyde, and styrene due to the oil content of the low-grade scrap and the paint. If such malodorous components are directly discharged into the atmosphere via a dust collector, they will have an adverse effect on the dust collector and cause serious secondary pollution. It is strongly required to remove odorous components from the exhaust gas after the preheating of the scrap before introducing it into the waste gas.

The present invention responds to the above demand, and in particular, since the preheating of scrap originally takes a viewpoint of effectively utilizing the sensible heat of exhaust gas from an electric furnace, so as not to go back to such a viewpoint, The present invention relates to a method for deodorizing exhaust gas after scrap preheating under energy-saving conditions, and treating the exhaust gas after deodorization with a dust collector.

<Prior art and its problems> Conventionally, as a treatment method for deodorizing exhaust gas after preheating scrap, the exhaust gas after preheating is returned to a combustion tower for post-burning exhaust gas from an electric furnace. ing. However, according to this conventional method, the combustion atmosphere in the combustion tower is greatly affected by the operating conditions of the electric furnace, and the malodorous components contained in the exhaust gas after the preheating of the scrap are sufficiently burned in the combustion tower ( Without being oxidatively decomposed, it may be sent to the dust collector as it is, and may be released to the atmosphere, so that the odorous component has an adverse effect on the dust collector and causes serious secondary pollution. There is a problem.

Therefore, conventionally, as another treatment method for deodorizing the exhaust gas after the preheating of the scrap, a method of installing a decomposition furnace separately from the combustion tower and burning the exhaust gas after the preheating by the decomposition furnace has been proposed (Japanese Patent Application Laid-Open No. H10-163873). No. 56-155379). However, according to this conventional method, despite the fact that the contents (type and concentration of the odor component) contained in the exhaust gas after the preheating of the scrap vary greatly depending on the properties of the scrap, etc., the scrap does not matter. Since the exhaust gas after preheating is burned with fuel in the cracking furnace, the fuel is often used in vain in practice. Therefore, the original method of preheating scrap by effectively utilizing the sensible heat of the exhaust gas from the electric furnace. There is a problem that it greatly contradicts the purpose.

<Problems to be Solved by the Invention, Means for Solving the Problems> The present invention provides an improved method for treating exhaust gas after scrap preheating, which solves the above-mentioned conventional problems.

Thus, the present invention provides a method of deodorizing exhaust gas after scrap preheating by supplying fuel and burning it, and discharging the exhaust gas after deodorization to the atmosphere via a dust collector,
The present invention relates to a method for treating exhaust gas after preheating of scrap, characterized in that a supply amount of fuel for burning the exhaust gas after preheating of scrap is controlled according to the properties of the scrap and / or the properties of exhaust gas after preheating of scrap.

In the present invention, the exhaust gas after preheating of the scrap is deodorized by supplying and burning the fuel, and the exhaust gas after the deodorization is detoxified by the dust collecting device and then released to the atmosphere. Deodorizing by burning the exhaust gas after preheating the scrap according to the proportion of oil and paint in the scrap which is almost quantified by the type and combination thereof and / or according to the total hydrocarbon concentration in the exhaust gas after preheating the scrap To supply the minimum amount of fuel necessary and sufficient to

Hereinafter, the configuration of the present invention will be described in more detail with reference to the drawings. FIG. 1 is a system diagram schematically showing an operation procedure of the present invention. After the exhaust gas from the electric furnace 11 is post-combusted in the combustion tower 21 and branched at the valves 31 and 32, part or all of the exhaust gas is introduced into the scrap preheating device 41, and the scrap preheating device 41
The exhaust gas after preheating the scrap as specified in the deodorization tower 51
Has been introduced to. Further, a detection pipe 61 for detecting the total hydrocarbon concentration is branched in a system path between the scrap preheating device 41 and the deodorization tower 51, and the exhaust gas after the scrap preheating taken out through the detection pipe 61 is taken out through the detection pipe 61. Is analyzed by the total hydrocarbon analyzer 62, and the opening degree of the control valve 64 incorporated in the fuel supply line is determined by a signal issued from the arithmetic unit 63 under the influence of the total hydrocarbon analyzer 62. Regulated and deodorized tower 51
Is controlled. Thus, the exhaust gas after being oxidized and decomposed by the deodorization tower 51 is combined with the exhaust gas branched off by the valve 31 by the supply of a minimum amount of fuel necessary and sufficient to deodorize the exhaust gas after the scrap preheating by combustion, and is sucked. After being rendered harmless by a dust collector 81 via a fan 71 and a cooler (not shown) or the like, the dust is discharged to the atmosphere.

In the case of the drawing, the fuel supply amount to the deodorization tower 51 is controlled according to the total hydrocarbon concentration in the exhaust gas after the scrap preheating, but the control of the fuel supply amount depends on the ratio of oil and paint in the scrap. It can be done accordingly. Depending on the type of scrap, such as Dalai powder, shredder, A-press, C-press, Kayama, etc., the ratio of oil and paint contained in the scrap is almost constant, so depending on the type of preheated scrap and its combination (use ratio) The ratio of oil and paint contained in the scrap is also almost quantified. On the other hand, a minimum and sufficient amount of fuel necessary and sufficient to oxidatively decompose the odorous components in the exhaust gas after the preheating of the scrap generated by the oil and the paint by combustion can be predicted. Utilizing it, the fuel supply is controlled according to the ratio of oil and paint in the scrap. If the control according to the properties of the scrap and the control according to the total hydrocarbon concentration in the exhaust gas after the preheating of the scrap as described above are used together, the exhaust gas after the preheating of the scrap is more preferably and purposefully deodorized. be able to.

<Example> According to the system diagram of Fig. 1 described above, the mixed scrap was preheated, and the exhaust gas after preheating was deodorized, and then discharged to the atmosphere via a dust collector. The following Examples 1 and 2 are cases in which the amount of fuel supplied to the deodorization tower was controlled according to the properties of the mixed scrap, and Example 3 below was determined according to the total hydrocarbon concentration in the exhaust gas after preheating the mixed scrap. This is a case where the fuel supply amount to the deodorization tower is controlled.

Example 1: 10,000 kg of Dalai powder (2% by weight of oil, 0% by weight of paint), 20,000 kg of shredder (0.5% by weight of oil, 1% by weight of paint), and 10,000 kg of C press (1% by weight of oil, 2% of paint)
Wt%) of the mixed scrap was preheated. 15 fuel supply
As a result of controlling at 0 / h, no odor was found in the exhaust gas from the deodorization tower (sensory test and gas chromatographic analysis, the same applies hereinafter).

Example 2: Using the same raw material as in Example 1, Dalai powder 5000
A mixed scrap of Kg, 10,000 kg of shredder and 10,000 kg of C-press was preheated. As a result of controlling the fuel supply amount to 115 / hour, no odor was found in the exhaust gas from the deodorization tower.

Example 3: The total hydrocarbon concentration in the exhaust gas after preheating is 30 ppm
Was preheated. As a result of controlling the fuel supply rate to 65 / h, no odor was found in the exhaust gas from the deodorization tower.

<Effect of the Invention> As described above, the present invention has an effect that the exhaust gas after the preheating of the scrap can be deodorized and treated under the most energy-saving condition.

[Brief description of the drawings]

 FIG. 1 is a system diagram schematically showing an operation procedure of the present invention. 11: Electric furnace, 21: Combustion tower 31, 32: Valve 41: Scrap preheating device, 51: Deodorizing tower 62: Total hydrocarbon analyzer, 63: Calculation device 64: Control valve, 81 …… Dust collector

Claims (3)

(57) [Claims] 1. A method for deodorizing exhaust gas after scrap preheating by supplying fuel and burning the exhaust gas, and discharging the exhaust gas after deodorization to the atmosphere via a dust collector, the exhaust gas after scrap preheating is burned. A method for treating the exhaust gas after the preheating of the scrap, characterized in that the supply amount of the fuel is controlled according to the properties of the scrap and / or the properties of the exhaust gas after the preheating of the scrap. 2. The method for treating exhaust gas after preheating of scrap according to claim 1, wherein the supply amount of fuel is controlled according to the ratio of oil and paint in the scrap. 3. The method for treating exhaust gas after preheating of scrap according to claim 1, wherein the supply amount of fuel is controlled according to the total hydrocarbon concentration in the exhaust gas after preheating of scrap.