JPH11248134A - Method for operating ash melting furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lengthen a lifetime by preventing a corrosion of a wall of an ash melting furnace. SOLUTION: The method for operating a DC electric resistance type ash melting furnace 1 for melting an ash by an electric resistance heat, by supplying a current between a furnace bottom electrode 2 provided at a furnace bottom and an upper electrode 3 inserted from a furnace cover, comprises the steps of regulating a basisity of the ash 7 supplied to the furnace 1 to a range of 0.9 to 1.1; sequentially forming from below to above a molten metal layer 9, a molten slag layer 10, a molten transfer layer 11 in which the molten slag and solid ash coexist, and an ash solid layer 12 in the furnace 11; and controlling current and voltage values, so that a current density per sectional area of the furnace becomes 0.1 to 5 A/cm<2> and a power consumption amount per weight of the ash to be treated is 500 to 1,000 kwH/t.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ash melting furnace for processing a fly ash containing a large amount of an alkali salt such as salt in a melting furnace, and more particularly, to actively reducing an alkali salt contained in the fly ash during ash melting. The present invention relates to a method of operating an ash melting furnace, which can be electrolyzed and can reduce deterioration of a refractory material of a furnace wall due to an alkali salt.

[0002]

2. Description of the Related Art Various wastes such as municipal waste and sewage sludge are
Incineration ash and dust generated by incineration in the incineration facility
Previously, it was landfilled. However, due to the problem of depletion of landfill sites and the problem of groundwater contamination due to elution of harmful metals, the necessity of weight reduction / melting by melting and detoxification is increasing.

[0003] Under such a background, a melting treatment method using a residual carbon in ash, coke, kerosene, and electric power as a heat source has been proposed.
Actual processing is performed in part. Among them, there are a plasma arc heating method and a resistance heating method as a melting furnace using electric power as a heat source.

The resistance heating type ash melting furnace has a counter electrode disposed in a melting slag and heats and melts the ash by electric resistance heat (Joule heat) caused by direct current or alternating current.
It is characterized by 1) high thermal efficiency, 2) little generated gas, 3) no flicker due to no arc generation, and 4) separate slag that separates molten slag and molten metal.

An example of such a resistance heating ash melting method is disclosed in JP-A-7-77318. FIG. 2 shows a cross section of the ash melting furnace and a flow sheet of the front and rear facilities disclosed in the above publication. In the figure, a
Is an ash melting furnace, b is a top electrode, c is a furnace bottom electrode, d is a power supply device, e is a molten metal layer, f is a molten slag layer, g is a molten salt layer, h is a CO gas combustion furnace, i is a dust collector, j is a dust collecting fan, k is a chimney, and m is an electrode burying position adjuster. The feature of the invention is a method of melting and processing incineration ash generated from a refuse incineration plant, soot and dust, or a mixture of the two, using electric resistance heat as a heat source. g in the molten slag layer f between the molten metal layer e and the molten salt is melted without electrolysis by flowing electricity between the furnace bottom electrode c in the vertical direction by direct current or two-phase current. The purpose is to stably form a molten salt layer g above the slag layer f to prevent generation of harmful chlorine gas, hydrogen chloride gas and the like.

However, when an operation is performed to form a molten salt layer g in the ash melting furnace a as described above, the molten salt has a very strong property of invading the furnace wall material. You need to use wall material. Further, since the molten salt having good electric conductivity penetrates into the furnace wall, a short circuit accident is likely to occur. Therefore, as a result of earnest research, the applicant of the present application has found that when electricity is supplied between the cathode at the bottom of the furnace and the anode inserted from the furnace lid to melt the ash by electric resistance heat, an alkaline salt such as sodium chloride (NaCl) is used. Decided to adopt an operation method that actively electrolyzes. According to this operation method, for example, salt is electrolyzed into chlorine gas and metallic sodium. Chlorine gas reacts with water vapor to form hydrogen chloride and hypochlorous acid, but hypochlorous acid releases oxygen to form hydrogen chloride. Also, the metallic sodium evaporates and becomes sodium oxide in an oxidizing atmosphere. These substances are contained in the exhaust gas and released to the outside. Note that the metallic sodium partially remains in the molten metal layer e.

[0007]

SUMMARY OF THE INVENTION The inventors of the present application have used a pilot plant of a DC electric resistance type ash melting furnace,
When operated under various conditions, it was found that, depending on the operating conditions, the electrolysis of the alkali salt was sometimes actively performed or was hardly performed. According to experimental findings, the melting point of the ash itself must be kept below 1250 ° C,
It is important to maintain a ash solid layer above the molten slag layer with a temperature gradient in the furnace and to have a molten transition layer where solid ash and molten slag coexist between the molten slag layer and the ash solid layer It turned out to be.

The present invention has been devised in view of the above-mentioned problems and findings, and is directed to a direct current resistance type ash melting furnace in which electrolysis of alkali salts such as salt is actively performed. It is intended to provide a driving method.

[0009]

In order to achieve the above object, a method for operating an ash melting furnace according to the present invention is characterized in that electricity is supplied between a furnace bottom electrode provided on a furnace bottom and an upper electrode inserted from a furnace lid. A method of operating a DC electric resistance type ash melting furnace for melting ash by resistance ripening, wherein the basicity of ash supplied to the ash melting furnace is set to 0.1.
The molten metal layer, the molten slag layer, the molten transition layer in which the molten slag coexists with the solid ash, and the ash solid layer are sequentially adjusted from the bottom to the top in the ash melting furnace while adjusting to the range of 9 to 1.1. And the current density per cross section of the furnace is 0.1 to 5
A / cm ² , power consumption per weight of ash to be treated is 50
The current / voltage value is controlled so as to be 0 to 1000 KwH / t. The basicity refers to the weight ratio (CaO / SiO ₂ ) between calcium oxide (CaO) and silicon dioxide (SiO ₂ ) in the ash.

[0010] The current density is 0.7 to 1.3 A / cm.
^2. Most preferably, the power consumption is 700 to 800 KwH / t.

Next, the operation of the present invention will be described. First, the basicity of the ash supplied to the ash melting furnace is adjusted. When the ash is fly ash, the basicity is 1.3 to 1.5, and the basicity is 0.9 to 1. 1 by adding silicon dioxide (silica sand).
Set to the range of 1. Adjustment of the basicity is described in, for example, Japanese Patent Application No. 8-1.
As disclosed in Japanese Patent No. 42632, the measurement is performed by continuously measuring the basicity with a basicity measuring device such as a fluorescent X-ray analyzer and adjusting the amount of silica sand or lime. The reason for setting the basicity to 0.9 to 1.1 is that at this time, the melting point of the ash becomes the lowest and becomes about 1100 ° C.
(Ishikawajima-Harima Technical Report 1997 Vol.37 No.3 P2
15-220).

In the furnace, metal layers are arranged in order from bottom to top,
A molten slag layer, a molten transition layer in which molten slag and solid ash coexist, and an ash solid layer are formed. At this time, the operation is performed with a temperature gradient such that the temperature decreases in the order of the molten slag layer, the molten transition layer, and the ash solid layer. The temperature of the molten slag layer is 110
0 to 1250 ° C. The temperature of the molten transition layer is maintained at the temperature of the melting point of the ash.

In order to achieve the above temperature, the current density per sectional area of the furnace is 0.1 to 5 A / cm ² , preferably 0.7
The power consumption per weight of ash is 500 to 1000 KwH / t, preferably 700 to 80 A / cm ^2.
The current and voltage values are controlled so as to be 0 KwH / t.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a DC electric resistance type ash melting furnace used in the embodiment of the present invention. In the figure, 1 is an ash melting furnace. Reference numeral 2 denotes a furnace bottom electrode provided on the furnace bottom 1a, and reference numeral 3 denotes an upper electrode inserted from the furnace lid 1b. The furnace bottom electrode 2 and the upper electrode 3 are connected to a cathode and an anode of a power supply 4, respectively, and are energized with direct current. Reference numeral 5 denotes an ash inlet to which incineration ash and fly ash 7 are supplied. Ash 7 has a basicity of 0.
It is adjusted in the range of 9 to 1.1. Adjustment of basicity
For example, as disclosed in Japanese Patent Application No. 8-142632, a silica sand input hopper and a lime input hopper are provided in front of an ash feeder, and a basicity measuring device such as a fluorescent X-ray analyzer is provided at an outlet of the ash feeder. The measurement may be performed by continuously measuring the basicity by attaching a filter and adjusting the input amount of silica sand or lime. In addition, 6 is a gas outlet, and 8 is an exhaust gas.

In the ash melting furnace 1, a molten metal layer 9, a molten slag layer 10, a molten transition layer 11 in which molten slag and solid ash coexist, and an ash solid layer 12 are formed in this order from bottom to top. ing. The temperature of the molten slag layer 10 is 1100-1.
It is kept at 250 ° C.

In order to achieve the above temperature, the current density per sectional area of the furnace is 0.1 to 5 A / cm ² , preferably 0.7
The power consumption per weight of ash is 500 to 1000 KwH / t, preferably 700 to 80 A / cm ^2.
The current / voltage value of the power supply 4 is controlled so as to be 0 KwH / t. In addition, 13 is a slag discharge port, 14 is a metal discharge port, 15 is a molten slag to be discharged, and 16 is a molten metal to be discharged. The molten metal 16 is discharged after discharging the molten slag 15 when the thickness of the molten metal layer 9 becomes too thick, and then generating an arc to melt the molten metal layer 9.

Next, the operation of the present embodiment will be described. In order for electrolysis to be actively performed in the molten slag layer 10 and the molten transition layer 11, it is necessary to conduct electricity by positively moving cations such as sodium ions and anions such as chlorine ions. . When the temperature of the molten slag is 1250 ° C. or lower, such an energization is performed. On the other hand, when the temperature exceeds 1250 ° C., the electrolysis mainly occurs due to the movement of electrons in the molten slag. Will not be done. In the present invention, the basicity is adjusted to about 1 to lower the melting point of the ash 7 and lower the current density, so that the calorific value is reduced and the temperature in the molten slag layer 9 is maintained at 1250 ° C. or less. It was done. Further, the temperature in the molten transition layer 11 is maintained at the melting point of the ash, and electrolysis is most actively performed in this portion.

The present invention is not limited to the embodiment described above, and various changes can be made without departing from the gist of the invention.

As described above, the method for operating the ash melting furnace of the present invention reduces the temperature of the molten slag layer by setting the basicity of the ash supplied to the ash melting furnace to around 1 and keeping the current density low. Since it was kept at 1250 ° C or less,
The electrolysis of the alkali salt contained in the fly ash is actively performed, and there is an excellent effect that the furnace wall material is hardly invaded by the alkali salt and a long life can be maintained.

[Brief description of the drawings]

FIG. 1 is a sectional view of an ash melting furnace for carrying out the present invention.

FIG. 2 is a sectional view of an ash melting furnace shown as a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ash melting furnace 2 Furnace bottom electrode 3 Upper electrode 4 Power supply 9 Metal layer 10 Molten slag layer 11 Melt transition layer 12 Ash solid layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiro Umeda 2-1-1 Toyosu, Koto-ku, Tokyo Ishikawajima-Harima Heavy Industries Co., Ltd. Tokyo 1st Plant (72) Inventor Naoto Yoshinari 2-chome, Toyosu, Koto-ku, Tokyo No. 1 Ishikawajima Harima Heavy Industries Co., Ltd.

Claims (2)

[Claims] 1. A method of operating a DC electric resistance type ash melting furnace in which electricity is supplied between a furnace bottom electrode provided on a furnace bottom and an upper electrode inserted from a furnace lid to melt ash by electric resistance heat, The basicity of the ash supplied to the ash melting furnace is adjusted to the range of 0.9 to 1.1, and the molten metal layer, the molten slag layer, and the molten slag are sequentially arranged in the ash melting furnace from bottom to top. And a solid ash coexist with the molten transition layer and the ash solid layer, the current density per cross section of the furnace is 0.1-5 A / cm ² , and the power consumption per ash weight to be treated is 500-1000 KwH.
A method for operating an ash melting furnace, characterized in that current / voltage values are controlled so as to be / t. 2. A current density of 0.7 to 1.3 A / cm ² ,
2. The power consumption is 700 to 800 KwH / t.
An operating method of the ash melting furnace described in the above.