JP2008292072A - Level measuring method and device for ash melting furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a level measuring method and a device applied to an ash melting furnace such as a plasma electric melting furnace which melts molten objects such as incinerated ash, reduced in initial cost and in running cost. <P>SOLUTION: The method comprises steps for measuring the back pressure of inactive gas A supplied into a furnace body 51 while moving an electrode 53 down in the ash melting furnace 50 supplying the inactive gas A into the furnace body 51 through a hollow hole 52 of the electrode 53 movable up and down, and detecting a molten slag level SL and a molten metal level ML from a change in the increasing rate of the back pressure. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an improvement in a level measuring method and a level measuring apparatus applied to an ash melting furnace such as a plasma electric melting furnace that melts a material to be melted such as incinerated ash.

Conventionally, as a method for measuring a molten slag level or a molten metal level in an ash melting furnace, for example, those described in Patent Documents 1 to 7 are known.
Further, although not used in an ash melting furnace, there is also known one that detects a change in the back pressure of a gas fed from a gas pipe and measures a molten metal level (see Patent Documents 8 to 11).

JP-A-8-271319 JP-A-8-320111 Japanese Patent Laid-Open No. 10-9555 JP 10-122544 A JP 10-332268 A JP 2001-50528 A Japanese Patent Laid-Open No. 2003-42428 JP-A 63-196820 JP-A-6-588 JP-A-6-589 JP-A-9-126858

  However, since all of them were measured using a dedicated measuring device, there was a problem that the initial cost and the running cost were excessive.

  The present invention was devised in view of the above-mentioned problems, and was devised to solve this problem. The process to be performed is a method for measuring the level of an ash melting furnace capable of reducing initial costs and running costs, and To provide a level measuring device.

  In the ash melting furnace according to the present invention, the level measurement method of the ash melting furnace supplies the inert gas to the furnace body while lowering the electrode in the ash melting furnace that supplies the inert gas into the furnace body from the hollow hole of the electrode that can be raised and lowered. The feature is that the back pressure of the inert gas is measured and the molten slag level and the molten metal level are detected from the change in the increase rate of the back pressure.

  The level measuring apparatus for an ash melting furnace of the present invention is provided in the furnace main body through an electrode provided with a hollow hole that can be moved up and down in the furnace main body, a lifting means for moving the electrode up and down, and a hollow hole of the electrode. Gas supply means for supplying inert gas, back pressure detection means for detecting the back pressure of the inert gas, and the molten slag level and the molten metal from the change in the increase rate of the back pressure due to the back pressure detection means It is characterized by the fact that it is composed of calculation means for calculating the level.

  It is known that when a gas is blown into a liquid, the back pressure of the gas changes according to the specific gravity and immersion depth of the liquid. When this principle is applied and the electrode is lowered while injecting an inert gas such as nitrogen from the tip of the electrode, the gas part, the molten slag, and the molten slag are caused by the difference in specific gravity of the gas in the furnace, the molten slag, and the molten metal. The increase rate of the back pressure of the inert gas changes in each boundary layer of molten metal. The molten slag level and the molten metal level can be detected from these changing points.

The thickness of the molten slag layer can be calculated from the moving distance of the electrode from the molten slag level to the molten metal level.
The thickness of the molten metal layer can be calculated from the distance from the lower end of the electrode to the height of the slag outlet and the moving distance of the electrode to the molten metal level, based on the height of the slag outlet.

According to the present invention, the following excellent effects can be achieved.
(1) Back pressure of inert gas supplied into the furnace body while lowering the electrode in an ash melting furnace that supplies inert gas into the furnace body from the hollow hole of the electrode that can be raised and lowered Since the molten slag level and the molten metal level are detected from the change in the increase rate of the back pressure, the initial cost and the running cost can be reduced.
(2) Since the ash melting furnace electrode, lifting and lowering means and gas supply means are used, the structure of the ash melting furnace is complicated, additional installation space is required, and work on site increases. There is nothing to do.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing an ash melting furnace to which a level measuring device of the present invention is applied. FIG. 2 is an explanatory diagram showing an overview of the level measurement method of the present invention. FIG. 3 is a graph showing the relationship between the electrode height and the nitrogen supply pressure.

The level measuring device 1 is applied to an ash melting furnace 50 such as a plasma electric melting furnace.
The ash melting furnace 50 includes a furnace main body 51, an electrode (main electrode) 53 that is provided in the furnace main body 51 so as to be movable up and down and has a hollow hole 52, an elevating means 54 for elevating and lowering the electrode 53, A gas supply means 55 for supplying the inert gas A into the furnace main body 51 through the hollow hole 52, a furnace bottom electrode 56 installed at the furnace bottom, and a target for supplying the melt B to the furnace main body 51. It comprises a melt supply means 57, an outlet 58 for discharging the molten slag S, a start electrode 59 used at the start, and the like.

  A material B to be melted such as incinerated ash is stored in a container and continuously charged into the furnace main body 51 by a material to be melted supply means 57 such as a screw conveyor. The furnace main body 51 is formed of a refractory material that can withstand a high temperature of 1800 ° C. or higher, the outer periphery thereof is covered with a heat insulating material, and a cooling jacket is provided outside thereof.

  A graphite main electrode 53 (minus electrode) that is inserted into the furnace main body 51 so as to be able to move up and down substantially vertically from the top of the furnace and maintain a certain distance from the melt B in the furnace, and installed at the furnace bottom. Furnace bottom electrode 56 (plus electrode) is provided, and the DC voltage (200 to 500 V) of the DC power supply (capacity: about 600 to 1000 kWH / T / melted material) applied between both electrodes 53 and 56 is provided. A current flows and a plasma arc is generated. As a result, the melt B is heated to 1300 ° C. to 1600 ° C., and becomes a molten slag S in sequence.

Since the melted material B before melting has low electrical conductivity, the start electrode 59 is inserted into the furnace main body 51 at the time of start-up, and this is used as a positive electrode. Wait for B to melt. When the material to be melted B is melted, its conductivity increases, so that the start electrode 59 is switched to the furnace bottom electrode 56.
The inside of the furnace body 51 is maintained in a reducing atmosphere to prevent oxidation of the molten slag S, the main electrode 53 and the like, and an inert gas A such as nitrogen from the gas supply means 55 is formed in a hollow cylindrical shape. Through the hollow hole 52 of the main electrode 53 thus formed, it is continuously supplied into the furnace main body 51 as a peep window purge.

  When the material to be melted B is melted, volatile components and carbon are gasified to become a gas containing carbon monoxide, while non-combustible components such as iron, metals, glass, sand and the like are in a molten state. The gas enters the combustion chamber via the outlet duct 60, where the unburned portion is completely burned by the combustion air sent by the combustion air fan, and then exhausted from the combustion chamber and cooled. It is led to the chimney through the filter.

Since the to-be-melted material B contains incinerated ash, silica, alumina, calcia, iron, and the like, when this is melted in the furnace, the molten slag mainly composed of silica, alumina, and calcia is upward. As it floats, the molten metal containing iron as a main component sinks downward, the molten metal layer M and the molten slag layer S are sequentially formed from the bottom of the furnace, and two separated layers are formed.
Then, the molten slag layer S continuously overflows from the outlet 58, falls into a slag water cooling tank filled with water, becomes a granulated slag, and is carried out by a carry-out conveyor.
The molten metal layer M gradually increases in thickness while accumulating in the furnace bottom. When the layer thickness from the furnace bottom exceeds a predetermined layer thickness, at least a part of the molten metal layer M is discharged to the outside of the furnace to perform so-called hot water removal. Is called.

The level measuring apparatus 1 is applied to such an ash melting furnace 50, and is provided in the furnace body 51 so as to be movable up and down, and has an electrode (main electrode) 53 provided with a hollow hole 52, and a lifting means for moving the electrode 53 up and down. 54, gas supply means 55 for supplying the inert gas A into the furnace body 51 through the hollow hole 52 of the electrode 53, and back pressure detection means 2 for detecting the back pressure of the inert gas A, The calculation means 3 for calculating the molten slag level SL and the molten metal level ML from the change in the increase rate of the back pressure due to the back pressure detection means 2 is provided.
The level measuring apparatus 1 also includes an infrared camera means 4 for detecting the lower end position of the electrode 53.

Although not shown, the gas supply means 55 includes an inert gas source such as nitrogen, a pressure reducing valve, a constant flow valve, and the like.
The back pressure detection means 2 is provided connected to the electrode 53 side of the gas supply means 55.

  The infrared camera means 4 is installed outside the viewing window 5 provided in the furnace body 51 on the outlet 58 side.

  The calculation means 3 is based on the signal from the elevating means 54, the signal from the back pressure detection means 2, and the signal from the infrared camera means 4, and the molten slag level SL, the molten metal level ML, the thickness ST of the molten slag layer S, and the molten metal. The thickness MT of the layer M is calculated.

Next, the operation will be described based on such a configuration.
As shown in FIGS. 2 and 3, it is known that when a gas is blown into a liquid, the back pressure of the gas changes according to the specific gravity and immersion depth of the liquid.
Applying this principle, when the electrode 53 is lowered by the elevating means 54 while the inert gas A such as nitrogen from the gas supply means 55 is ejected from the tip thereof through the hollow hole 52 of the electrode 53, the furnace The increase rate of the back pressure of the inert gas A changes in each boundary layer of the gas portion and the molten slag and the molten slag and the molten metal due to the difference in specific gravity between the inner gas, the molten slag S and the molten metal M. Therefore, when the back pressure of the inert gas A is measured by the back pressure detecting means 2 and calculated by the calculating means 3, the molten slag level SL and the molten metal level ML can be detected from these changing points.

  The thickness ST of the molten slag layer S can be calculated from the moving distance of the electrode 53 from the molten slag level SL to the molten metal level ML. The movement distance of the electrode 53 can be obtained by calculating a signal from the lifting / lowering means 54 using the calculation means 3.

The calculation of the thickness MT of the molten metal layer M requires a reference height. In the present invention, the height of the slag outlet is used. The calculation of the thickness MT of the molten metal layer M is performed as follows, for example.
(1) The electrode 53 is raised by the elevating means 54 to a height at which the lower end of the electrode 53 can be discriminated in the image of the infrared camera means 4.
(2) The height of the slag outlet is set in advance in the image of the infrared camera means 4. The distance C from the furnace bottom to the height of the slag outlet is known. A distance D from the height of the slag outlet to the lower end of the electrode 53 is measured by the infrared camera means 4. Therefore, the sum of the distance C from the furnace bottom to the height of the slag outlet and the distance D is the distance C + D from the furnace bottom to the lower end of the electrode 53.
(3) The electrode 53 is lowered by the elevating means 54, and the molten metal level ML is detected. Let E be the electrode movement distance from the lower end position of the electrode 53 at the position (1) to the molten metal level ML.
(4) The difference between the distance C + D calculated in (2) and the movement distance E of the electrode 53 in (3) is defined as the thickness MT of the molten metal layer M (C + DE in FIG. 1).

The schematic diagram which shows the ash melting furnace to which the level measuring apparatus of this invention is applied. Explanatory drawing which shows the outline | summary of the level measuring method of this invention. The graph which shows the relationship between electrode height and nitrogen supply pressure.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Level measuring device, 2 ... Back pressure detection means, 3 ... Calculation means, 4 ... Infrared camera means, 5 ... Viewing window, 50 ... Ash melting furnace, 51 ... Furnace main body, 52 ... Hollow hole, 53 ... Electrode (main Electrode), 54 ... elevating means, 55 ... gas supply means, 56 ... furnace bottom electrode, 57 ... melt supply means, 58 ... outlet, 59 ... start electrode, 60 ... outlet duct, A ... inert gas, B ... melted material, C ... distance from the furnace bottom to the height of the slag outlet, D ... distance from the lower end of the electrode to the height of the slag outlet, E ... distance from the lower end of the electrode to the molten metal level, S ... melting Slag (layer), M ... Molten metal (layer), SL ... Molten slag level, ML ... Molten metal level, ST ... Thickness of molten slag layer, MT ... Thickness of molten metal layer.

Claims (2)

  In an ash melting furnace that supplies inert gas into the furnace body from the hollow hole of the electrode that can be raised and lowered, the back pressure of the inert gas supplied into the furnace body is measured while the electrode is lowered. A method for measuring the level of an ash melting furnace, characterized by detecting a molten slag level and a molten metal level from a change in the increase rate of back pressure. An electrode provided in the furnace body so as to be movable up and down and having a hollow hole, a lifting means for raising and lowering the electrode, a gas supply means for supplying an inert gas into the furnace body through the hollow hole of the electrode, And a back pressure detecting means for detecting the back pressure of the inert gas, and a calculating means for calculating the molten slag level and the molten metal level from the change in the increase rate of the back pressure due to the back pressure detecting means. An ash melting furnace level measuring device characterized by

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