JP3918280B2 - Operation method of ash melting furnace - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ash melting furnace that treats fly ash containing a large amount of alkali salt such as salt, etc., in particular, by electrolyzing the alkali salt contained in the fly ash during ash melting, The present invention relates to a method for operating an ash melting furnace that can reduce deterioration of a refractory material on a furnace wall.
[0002]
[Prior art]
Various types of waste such as municipal waste and sewage sludge were incinerated at incineration facilities, and the resulting incinerated ash and dust were conventionally disposed of in landfills. However, there is a problem of depletion of landfill sites and groundwater contamination due to leaching of toxic metals, so the need for weight reduction, melting and detoxification by melting is increasing.
[0003]
Against this background, a melting treatment method using residual carbon in ash, coke, kerosene, and electric power as heat sources has been proposed, and some actual treatments have been performed. Among these, there are a plasma arc heating method and a resistance heating method as a melting furnace using electric power as a heat source.
[0004]
The resistance heating type ash melting furnace has a counter electrode in the molten slag and heats and melts the ash by electric resistance heat (Joule heat) by direct current or alternating current. 1) High thermal efficiency 2) Generated gas 3) Since no arc is generated, flicker does not occur, and 4) it is possible to divide molten slag and molten metal separately.
[0005]
As such a resistance heating type ash melting method, there is one disclosed in JP-A-7-77318. FIG. 2 shows the cross section of the ash melting furnace and the flow sheet of the front and rear equipment disclosed in the above publication. In the figure, a is an ash melting furnace, b is an upper 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 buried position adjuster. A feature of the above invention is a method of melting waste made of incineration ash, dust, or a mixture of the two from a waste incineration facility using electrical resistance heat as a heat source, wherein the tip position of the upper electrode b is a molten salt layer. Molten salt is not electrolyzed by electrification in the vertical direction by direct current conduction or alternating current two-phase conduction between the bottom electrode c positioned in the molten slag layer f between g and the molten metal layer e. The molten salt layer g is stably formed above the slag layer f to prevent generation of harmful chlorine gas, hydrogen chloride gas, and the like.
[0006]
However, when the operation is performed to form the 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. It is necessary to use it. In addition, since a molten salt having good electrical 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 conducted an energization 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, and thus an alkaline salt such as sodium chloride (NaCl). We decided to adopt an operation method that positively electrolyzes. According to this operating 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. Metal 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 part of the metal sodium remains in the molten metal layer e.
[0007]
[Problems to be solved by the invention]
The inventors of the present application, when operated under various conditions using a pilot plant of a direct current electric resistance type ash melting furnace, depending on the operating conditions, there are cases where the electrolysis of the alkali salt is actively performed and rarely performed. I found out. According to experimental findings, the melting point of the ash itself is kept below 1250 ° C., the temperature gradient is set in the furnace, the ash solid layer is maintained on the upper part of the molten slag layer, and the molten slag layer and the ash solid layer It was found that it is important to have a molten transition layer between which solid ash and molten slag coexist.
[0008]
The present invention has been devised in view of the problems and knowledge described above, and provides a method for operating an ash melting furnace in which electrolysis of alkali salts such as salt is actively performed in a direct current electric resistance type ash melting furnace. The purpose is to provide.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the method of operating the ash melting furnace of the present invention is a direct current electric method in which ash is melted by ripening electric resistance by energizing between a furnace bottom electrode provided at the furnace bottom and an upper electrode inserted from the furnace lid. A resistance type ash melting furnace operating method, wherein the basicity of the ash supplied to the ash melting furnace is adjusted to a range of 0.9 to 1.1, and the bottom of the ash melting furnace is directed upward from the bottom. In order, a molten metal layer, a molten slag layer, a molten transition layer in which molten slag and solid ash coexist, and an ash solid layer are formed, and the current density per cross-sectional area of the furnace is 0.1 to 5 A / cm ² . The current / voltage value is controlled so that the power consumption per weight of ash is 500 to 1000 KwH / t. The basicity refers to the weight ratio (CaO / SiO ₂ ) between calcium oxide (Ca 2 O) and silicon dioxide (SiO ₂ ) in ash.
[0010]
Most preferably, the current density is 0.7 to 1.3 A / cm ² and the power consumption is 700 to 800 KwH / t.
[0011]
Next, the operation of the present invention will be described. First, the basicity of the ash charged into the ash melting furnace is adjusted. When the ash is fly ash, the basicity is 1.3 to 1.5, so the basicity is adjusted to a range of 0.9 to 1.1 by adding silicon dioxide (silica sand). For example, as disclosed in Japanese Patent Application No. 8-142632, the basicity is continuously measured by a basicity measuring device such as a fluorescent X-ray analyzer, and the amount of silica sand or lime input is adjusted. By adjusting the. The reason why the basicity was set to 0.9 to 1.1 is that the melting point of ash is the lowest at this time and is about 1100 ° C. (Ishikawajima Harima Technical Report 1997 Vol.37 No. 3 P215-220).
[0012]
In the furnace, a metal layer, a molten slag layer, a molten transition layer in which molten slag and solid ash coexist, and an ash solid layer are formed in order from bottom to top. 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 a molten slag layer shall be 1100-1250 degreeC. The temperature of the melting transition layer is kept at the melting point of ash.
[0013]
In order to achieve the above temperature, the current density per cross-sectional area of the furnace is 0.1-5 A / cm ² , preferably 0.7-1.3 A / cm ^2, and the power consumption per ash weight is 500- The current / voltage value is controlled to be 1000 KwH / t, preferably 700 to 800 KwH / t.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of a DC electric resistance ash melting furnace used in the practice of the present invention. In the figure, 1 is an ash melting furnace. 2 is a furnace bottom electrode provided on the furnace bottom 1a, and 3 is an upper electrode inserted from the furnace lid 1b. The furnace bottom electrode 2 and the upper electrode 3 are connected to the cathode and the anode of the power source 4 and are DC-energized. Incineration ash and fly ash 7 are supplied to the ash inlet 5. Ash 7 has a basicity adjusted to a range of 0.9 to 1.1. For adjusting the basicity, for example, as disclosed in Japanese Patent Application No. 8-142632, a silicate feeder and a lime feeder are provided in front of the ash feeder, and a fluorescent X-ray analyzer is provided at the outlet of the ash feeder. A basicity measuring device such as the above may be attached to measure the basicity continuously and adjust the amount of silica sand or lime input. In addition, 6 is a gas discharge port and 8 is exhaust gas.
[0015]
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 order from bottom to top. The temperature of the molten slag layer 10 is maintained at 1100 to 1250 ° C.
[0016]
In order to achieve the above temperature, the current density per cross-sectional area of the furnace is 0.1-5 A / cm ² , preferably 0.7-1.3 A / cm ^2, and the power consumption per ash weight is 500- The current / voltage value of the power source 4 is controlled to be 1000 KwH / t, preferably 700 to 800 KwH / t. Note that 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. When the molten metal layer 9 becomes too thick, the molten metal 16 discharges the molten slag 15 and then generates an arc to melt and discharge the molten metal layer 9.
[0017]
Next, the operation of this embodiment will be described.
In order to perform electrolysis actively in the molten slag layer 10 and the molten transition layer 11, it is necessary to be energized by the active movement of cations such as sodium ions and anions such as chlorine ions. . When the temperature of the molten slag is 1250 ° C. or lower, such energization is performed, whereas at a temperature exceeding 1250 ° C., the electrolysis is actively performed because electrons mainly move through the molten slag. No longer done. In the present invention, the basicity is adjusted to around 1 to lower the melting point of the ash 7 and the current density is lowered so that the heat generation amount is reduced and the temperature in the molten slag layer 9 is kept at 1250 ° C. or lower. It is a thing. Further, the temperature in the molten transition layer 11 is maintained at the melting point of ash, and electrolysis is most actively performed in this portion.
[0018]
The present invention is not limited to the embodiments described above, and various modifications can be made without departing from the scope of the invention.
[0019]
As described above, the operation method of the ash melting furnace of the present invention sets the basicity of the ash supplied to the ash melting furnace to around 1 and keeps the current density low, thereby reducing the temperature of the molten slag layer to 1250 ° C. or less. Therefore, the alkaline salt contained in the fly ash is actively electrolyzed, and the furnace wall material is less likely to be invaded by the alkali salt.
[Brief description of the drawings]
FIG. 1 is a cross-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.
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 Molten transition layer 12 Ash solid layer

Claims (3)

A method for operating a direct current electric resistance type ash melting furnace in which an ash containing an alkali salt is melted by electric resistance heat by energizing between a furnace bottom electrode provided on the furnace bottom and an upper electrode inserted from the furnace lid, The basicity of the ash is adjusted to a range of 0.9 to 1.1 so that the melting point of the ash supplied to the ash melting furnace is the lowest, and the temperature of the molten slag layer is adjusted to a melting point of the ash of 1250 ° C. range kept, in order from bottom to top in the ash melting furnace, molten metal layer, the molten slag layer, melt transition layer ash molten slag and solid coexist, by forming the ash solid layer, an alkali salt A method of operating an ash melting furnace characterized by controlling the current value so that the current density per cross-sectional area of the furnace becomes a required value in order to actively carry out electrolysis of the molten metal to prevent generation of a molten salt layer . The method of operation ash melting furnace according to claim 1, wherein the current density per cross-sectional area of the furnace is 0.1~5A / cm ^2. Current density per cross-sectional area of the furnace is 0.7 to 1.3 A / cm ² The method for operating an ash melting furnace according to claim 1, wherein:

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