JPH11281041A - Method for operating plasma-type ash melting furnace and plasma-type ash melting furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve stable operation and decomposition of dioxin by raising the temperature of an exhaust gas. SOLUTION: A plasma-type ash melting furnace is operated such that a plasma power is impressed on a carbon electrode 4 in an inert gas atmosphere which has been blown into a melting chamber 1a as a working gas to generate a plasma arc between a base metal 2 and the electrode, followed by heating and melting the ash fed onto the base metal 2, and that the resultant exhaust gas is discharged to a secondary combustion chamber for recombustion. At the time of operation, a predetermined amount of air for heating the exhaust gas is blown into the melting chamber 1a from an air nozzle 21 for heating the exhaust gas, so that the concentration ratio of oxygen to carbon monoxide of the exhaust gas at the exit of the melting chamber 1a does not exceed 0.30, thereby combusting a portion of the combustible matters in the exhaust gas in the furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of operating a plasma type ash melting furnace and a plasma type ash melting furnace.

[0002]

BACKGROUND ART In a conventional plasma ash melting furnace, for example when using a carbon electrode, because the furnace is severe depletion becomes an oxidizing atmosphere electrode, not of ₂ such as Ar and N as the plasma working gas Activated gas is blown into the furnace to make it into a reducing atmosphere and perform heating and melting. For this reason,
Exhaust gas containing a large amount of combustible components such as CO, H ₂ and hydrocarbon gas is generated in the furnace. At present, this exhaust gas is introduced into the secondary combustion chamber and heated by the exhaust gas combustion burner, and the combustible components in the exhaust gas are completely burned by the secondary air blown from the secondary air nozzle arranged downstream. .

[0003]

The main heat input in this plasma type ash melting furnace is due to the plasma power because the combustion heat is small in a reducing atmosphere, while the plasma power is generated by the refractory in the furnace. The temperature of the exhaust gas (atmosphere in the furnace) was controlled depending on the temperature of the molten slag for the purpose of protection of the slag.

When the temperature of the exhaust gas in the furnace becomes low, a molten salt layer is formed on the surface of the molten slag, and the molten salt layer has a low electric resistance and short-circuits the current. This causes instability of the plasma power and interruption of the plasma arc. Also, when the temperature of the exhaust gas is low, the temperature becomes high due to heating on the downstream side of the exhaust gas combustion burner, but since the temperature is low on the upstream side of the exhaust gas combustion burner, the residence time at the high temperature necessary for the decomposition of dioxin is sufficient. There was a problem that it could not be taken.

An object of the present invention is to provide a method of operating a plasma type ash melting furnace and a plasma type ash melting furnace capable of solving the above problems and increasing the temperature of exhaust gas to achieve stable operation and decomposition of dioxin. With the goal.

[0006]

In order to achieve the above object, a method of operating a plasma type ash melting furnace according to the present invention comprises a method of operating a plasma ash melting furnace on a carbon electrode in an inert gas atmosphere blown into a melting chamber as a plasma working gas. Plasma arc is generated between the base metal by applying electric power, the ash charged on the base metal is heated and melted, and this exhaust gas is discharged to the secondary combustion chamber to re-burn, and the plasma ash melting furnace is used. During operation, oxygen for exhaust gas heating or air for exhaust gas heating is blown into the melting chamber so that the concentration ratio of oxygen: carbon monoxide of the exhaust gas at the outlet of the melting chamber becomes 0.30 or less, and the combustible component in the exhaust gas is blown. A part is burned in a furnace.

In a plasma type ash melting furnace, a plasma arc is generated between a base metal by applying plasma power to a carbon electrode in an inert gas atmosphere blown into a melting chamber as a plasma working gas. In a plasma ash melting furnace that heats and melts the ash charged on the metal, discharges this exhaust gas to the secondary combustion chamber, and reburns it,
The concentration ratio of oxygen: carbon monoxide in the exhaust gas at the outlet of the melting chamber is 0.
A nozzle for injecting exhaust gas heating oxygen or exhaust gas heating air for burning a part of the combustible content in the exhaust gas in the furnace so as to be 30 or less is provided.

[0008] According to the above-described configurations, the temperature of the exhaust gas can be increased by burning part of the combustible components in the exhaust gas in the furnace with the oxygen for heating the exhaust gas or the air for heating the exhaust gas. Generation of a molten salt layer that causes instability and interruption of a plasma arc can be prevented, and stable operation can be achieved. Further, since the high temperature state of the exhaust gas can be maintained on the upstream side of the reburning burner in the secondary combustion chamber, the decomposition of dioxin can be promoted. Furthermore, since the concentration ratio of oxygen: carbon monoxide in the exhaust gas, that is, the reducing atmosphere value is set to 0.30 or less, it is possible to suppress the consumption of the electrodes and prevent an increase in the operating cost.

According to a third aspect of the present invention, there is provided a plasma type ash melting furnace, wherein a nozzle for supplying oxygen for heating exhaust gas or air for heating exhaust gas is disposed near a discharge port for discharging molten slag from a melting chamber. .

[0010] According to the above structure, a combustion zone by combustion oxygen or combustion air can be formed in the vicinity of the discharge port, and the molten slag is heated to increase the fluidity and discharge can be performed more smoothly. Can be.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, an embodiment of a plasma type ash melting furnace according to the present invention will be described with reference to FIGS.

As shown in FIGS. 1 to 3, this plasma type ash melting furnace accommodates a base metal 2 at the bottom of a melting chamber 1a of a furnace body 1 and an electrode insertion hole 3 formed in a top wall. 3 is a carbon electrode (negative electrode and positive electrode)
4 is suspended vertically. A working gas, for example, N ₂ gas, is supplied into the furnace body 1 from a working gas supply hole 4a formed in the carbon electrode 4 and a gas supply hole (not shown) formed in the furnace body 1, The furnace is configured to be kept in a reducing atmosphere.

An ash supply port 5 is provided at one end of the furnace body 1.
Is formed, and the ash A can be supplied from the ash hopper 7 into the furnace main body 1 by a predetermined amount by the ash supply device 6 including the push cylinder 6a and the push block 6b. Further, on the other end side of the furnace body 1, a discharge port 8 for discharging the molten slag MS generated by heating and melting the ash in an overflow manner is formed. And a slag heating burner 10 for preventing solidification of the molten slag MS. The waste port 8
Is provided below the cooling water tank 11a for cooling the molten slag MS with water.
And a scraper conveyor 11b for discharging the granulated slag generated by water cooling is provided.

An exhaust gas port 1 is provided on one side wall of the melting chamber 1a.
2 is connected through an exhaust duct 13 to a secondary combustion chamber 14a formed by a refractory wall 14a, and a reburn burner is provided on a side wall of the secondary combustion chamber 14a facing the exhaust gas duct 13. 15 is arranged, and a secondary air nozzle 16 is arranged thereon. Reference numeral 17 denotes an exhaust gas outlet where the exhaust pipe 18 is connected to the secondary combustion chamber 14a.

In FIG. 1, reference numeral 21 denotes an exhaust gas heating air nozzle, which is a nozzle for injecting exhaust gas heating air according to the present invention, and is provided near the upper portion of the discharge port 8, for example, through the top of the cover wall 9. Exhaust gas heating air supplied from the air supply fan 22 is supplied via the flow control valve 23. This exhaust gas heated air is introduced into the melting chamber 1a from the discharge port 8, and a part of the combustible portion of the exhaust gas is burned between the carbon electrode 4 and the discharge port 8 while maintaining a reducing atmosphere within a predetermined range. f
As a result, the temperature of the exhaust gas is raised, and the molten slag MS at the discharge port 8 is heated from the carbon electrode 4 to improve the fluidity.

In place of the exhaust gas heating air, high-purity oxygen for heating the exhaust gas is supplied from an oxygen cylinder 32 through a flow control valve 33 and an exhaust gas heating oxygen nozzle (a nozzle for blowing exhaust gas oxygen) 31. Is also good. According to this, the amount of exhaust gas discharged from the secondary combustion chamber 14a can be reduced as compared with the exhaust gas heated air, and there is no need to increase the amount of exhaust gas treatment equipment and increase the capacity.

An exhaust gas thermometer 24 for measuring the temperature of the exhaust gas at the exhaust gas port 12 of the melting chamber 1a is provided on the upstream side of the exhaust gas duct 13, and an exhaust gas analyzer for measuring the component amount of the exhaust gas further downstream. A vessel 25 is provided therethrough. 2
Reference numeral 6 denotes an operation control device for controlling the flow control valve 23 (33) based on the detection value of the exhaust gas analyzer 25.

Next, a method of operating the plasma type ash melting furnace will be described. N from the working gas supply hole 4a and the gas inlet hole
^{The two} gases are supplied into the melting chamber 1a and maintained in a reducing atmosphere, and plasma power is supplied to both carbon electrodes 4 and 4 from a plasma power supply device (not shown) so that a plasma arc is generated between the two carbon electrodes 4 and 4. The ash A of the ash hopper 7 is formed and heated by the ash supply device 6 so that the base metal 2
It is supplied above and melted by heating. Exhaust gas heating air is supplied from the exhaust gas heating air nozzle 21 by a predetermined amount, and a portion of the combustibles in the exhaust gas is burned around the combustion zone f, where carbon monoxide is burned and its concentration decreases. To increase the temperature of the exhaust gas,
The fluidity is improved by heating S. Then, the molten slag MS overflows from the discharge port 8 and is discharged to the slag cooling device 11, where it is further cooled to form granulated slag WS.

During this operation, the flow control valve 23 is controlled by the operation control device 26 on the basis of the oxygen concentration and the carbon monoxide concentration of the exhaust gas at the outlet of the melting chamber 1a detected by the exhaust gas analyzer 25, and the exhaust gas is heated. The amount of exhaust gas heating air supplied from the air nozzle 21 to the melting chamber 1a is adjusted. That is, the exhaust gas heated air amount is controlled such that the oxygen: carbon monoxide concentration ratio (reducing atmosphere value) of the exhaust gas at the outlet of the melting chamber 1a is 0.30 or less. As a result, the temperature of the exhaust gas can be raised by about 50 ° C. as compared with before the blowing of the exhaust gas heated air, the exhaust gas temperature can be kept high, and the generation of a molten salt layer can be prevented and the plasma arc can be stably maintained. Further, the exhaust gas is allowed to stay at a high temperature for a long time until it is heated from the melting chamber 1a by the reburning burner 15 of the secondary combustion chamber 14, so that dioxin in the exhaust gas can be sufficiently decomposed. The consumption of the carbon electrode 4 can be suppressed by the reducing atmosphere value of 0.30 or less.

Here, an experimental ash melting furnace (capacity: 0.25 t)
/ Hr), the experimental result of injecting the exhaust gas heated air amount into the melting chamber 1a is shown in Table 1 and FIG.

[0021]

[Table 1]

At this time, the blowing of the exhaust gas heating air is started after a lapse of 24 hours when the operation of the furnace is started and the operation becomes stable. When the exhaust gas heating air is not blown, the exhaust gas temperature in the exhaust duct 13 is about 650 on average.
On the other hand, when the exhaust gas heated air is blown into the melting chamber 1a at 10 Nm ³ / h from the exhaust gas heated air nozzle 21, the exhaust gas temperature rises to about 700 ° C. on average. Further, the exhaust gas heating air is supplied to the melting chamber 1 at 20 Nm ³ / h.
In the case of blowing into a, it has been confirmed that the exhaust gas temperature rises to an average of about 750 ° C. Therefore, even if the plasma power is controlled based on the temperature of the molten slag for the purpose of protecting the refractory in the furnace, the exhaust gas temperature (atmospheric temperature of the melting chamber) ) Can be raised to control and raise the temperature of the melting chamber 1a. As a result, it was found that there was no generation of a molten salt layer, the plasma arc could be stably maintained, and stable operation was possible.

FIG. 5 shows the consumption of the carbon electrode with respect to the ratio of the oxygen concentration of the exhaust gas at the outlet of the melting chamber 1a to the carbon monoxide concentration, and the oxygen: carbon monoxide concentration ratio of the exhaust gas at the outlet of the melting chamber 1a. Exceeds 0.30, it was confirmed that the consumption of the carbon electrode 4 was greatly increased. Therefore, by setting the ratio of the oxygen concentration of the exhaust gas to the carbon monoxide concentration to 0.30 or less, the consumption of the carbon electrode 4 can be suppressed.

FIG. 6 shows the relationship between the exhaust gas temperature at the exhaust gas outlet 17 of the secondary combustion chamber 14 and the amount of dioxin contained in the exhaust gas at the inlet of a bag filter (not shown) interposed in the exhaust pipe 18. It has been found by experiment.
Here, it is understood that when the exhaust gas temperature at the exhaust gas outlet 17 decreases, dioxin is not decomposed. In the secondary combustion chamber 14a, the amount of combustion (fuel and combustion air) of the reburn burner 15 and the temperature of the secondary air nozzle 16 are adjusted so that the exhaust gas temperature at the exhaust gas outlet 17 becomes approximately 850 ° C. for the purpose of exhaust gas treatment. Is controlled, and the exhaust gas temperature downstream of the reburn burner 15 is 850 ° C. or higher. However, in the secondary combustion chamber 14a, the residence time from the reburning burner 15 to the exhaust gas outlet 17 is about 3 seconds, whereas the residence time from the melting chamber 1a to the reburning burner 15 is about 4.5 seconds. If the exhaust gas temperature during this period is low, the decomposition of dioxin is not promoted. Therefore, as in the present invention, by directly blowing the exhaust gas heating air into the melting chamber 1a, the reburning burner 1 is discharged from the melting chamber 1a.
By increasing the exhaust gas temperature up to 5, the decomposition of dioxin can be effectively promoted.

[0025]

As described above, according to the first and second aspects of the present invention, a part of the combustible components in the exhaust gas is burned in the furnace by the oxygen for heating the exhaust gas or the air for heating the exhaust gas to reduce the amount of the exhaust gas. By halving the concentration of carbon oxide, the temperature of the exhaust gas can be raised, preventing the formation of a molten salt layer that causes instability of plasma power and interruption of the plasma arc, enabling stable operation. Become. Further, since the high temperature state of the exhaust gas can be maintained on the upstream side of the reburning burner in the secondary combustion chamber, the decomposition of dioxin can be promoted. Furthermore, since the concentration ratio of oxygen: carbon monoxide in the exhaust gas, that is, the reducing atmosphere value is set to 0.30 or less, it is possible to suppress the consumption of the electrodes and prevent an increase in the operating cost.

Further, according to the third aspect of the invention, a combustion zone by combustion oxygen or combustion air can be formed in the vicinity of the discharge port, and the molten slag is effectively heated to increase the fluidity and discharge. Can be performed more smoothly.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a plasma type ash melting furnace according to the present invention.

FIG. 2 is a sectional view taken along line BB shown in FIG.

FIG. 3 is a plan sectional view of the plasma type ash melting furnace.

FIG. 4 is a graph showing blowing of exhaust gas heating air and a change in exhaust gas temperature in the experimental furnace.

FIG. 5 is a graph showing changes in the exhaust gas reducing atmosphere value and the amount of electrode consumption in the experimental furnace.

FIG. 6 is a graph showing changes in the exhaust gas temperature at the outlet of the secondary combustion chamber and the change in the dioxin content of the exhaust gas at the inlet of the bag filter in the experimental furnace.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Furnace main body 1a Melting chamber 2 Base metal 4 Carbon electrode 4a Working gas supply port 5 Ash supply port 6 Ash supply device 8 Drainage port 9 Slag heating burner 10 Cover wall 11 Slag cooling device 13 Exhaust gas duct 14a Secondary combustion chamber 15 Re Combustion burner 16 Secondary air nozzle 21 Exhaust gas heating air nozzle 23 Flow control valve 24 Exhaust gas thermometer 25 Exhaust gas analyzer 26 Operation controller 31 Exhaust gas heating oxygen nozzle A Ash MS Melt slag f Combustion zone

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Tadashi Kono 1-7-89 Minami Kohoku, Suminoe-ku, Osaka-shi, Osaka Inside Hitachi Zosen Corporation (72) Inventor Tsuneharu Sakakibara 1-chome Minami-Kohoku, Suminoe-ku, Osaka-shi, Osaka No. 7-89 Within Hitachi Zosen Corporation (72) Inventor Katsuya Noritomi 1-89, Minami Kohoku, Suminoe-ku, Osaka City, Osaka Prefecture Within Hitachi Zosen Corporation

Claims (3)

[Claims] 1. A plasma arc is generated between a carbon electrode and a base metal by applying a plasma power to a carbon electrode in an inert gas atmosphere blown into a melting chamber as a plasma working gas. Heat and melt the ash,
When operating a plasma type ash melting furnace in which this exhaust gas is discharged into the secondary combustion chamber and reburned, the concentration ratio of oxygen: carbon monoxide in the exhaust gas at the outlet of the melting chamber is 0.
A method for operating a plasma type ash melting furnace, characterized in that oxygen for exhaust gas heating or air for exhaust gas heating is blown into a melting chamber so as to be 30 or less, and a part of combustible components in the exhaust gas is burned in the furnace. . 2. A plasma arc is generated between a carbon electrode and a base metal by applying plasma power to the carbon electrode in an inert gas atmosphere blown into a melting chamber as a plasma working gas, and is injected onto the base metal. Heat and melt the ash,
In a plasma type ash melting furnace in which this exhaust gas is discharged into the secondary combustion chamber and recombusted, the concentration ratio of oxygen: carbon monoxide in the exhaust gas at the outlet of the melting chamber is 0.
A plasma type ash melting furnace, comprising a nozzle for blowing exhaust gas heating oxygen or exhaust gas heating air for burning a part of the combustible content in the exhaust gas in the furnace so as to be 30 or less. 3. The plasma type ash melting method according to claim 2, wherein a nozzle for supplying exhaust gas heating oxygen or exhaust gas heating air is disposed near a discharge port for discharging molten slag from the melting chamber. Furnace.