JP2010060229A - Electrode operating method for burned ash melting furnace - Google Patents

Abstract

The generation of CO gas can be kept low even when the electrode is stopped for a long time.
In an incineration ash melting furnace in which incineration ash A is melted by discharging electric current from a graphite electrode 3 capable of moving up and down while blowing combustion air and discharging from the graphite electrode 3, electric power is supplied to the graphite electrode 3 to cause discharge. The first retracted position Y and the second retracted position Z are set above the operation position X to be operated, and the graphite electrode 3 is raised to the first retracted position Y at the time of normal power failure for a relatively short time. At the time of unsteady power stop for a long time, the graphite electrode 3 is raised to the second retracted position Z above the first retracted position Y.
[Selection] Figure 1

Description

  The present invention relates to an electrode operation method for an incineration ash melting furnace, and more particularly to an electrode operation method capable of suppressing CO emission.

An incineration ash melting furnace is known that reduces the volume of waste incineration ash, sewage, human waste, sludge incineration ash, etc. to make them harmless, and an example thereof is disclosed in Patent Document 1. In the disclosed incineration ash melting furnace, a plurality of graphite electrodes are provided by vertically passing the furnace lid, and the incineration ash is heated and melted by arc discharge generated from these graphite electrodes. At this time, combustion air is blown into the furnace, combustible gas generated at the time of melting is burned, and discharged as exhaust gas.
JP-A-7-280448

  By the way, in the conventional incineration ash melting furnace, the graphite electrode that penetrates the furnace lid and protrudes into the furnace is oxidized and consumed by the atmosphere in the furnace in addition to the consumption accompanying the discharge. Since the furnace temperature is usually 1000 ° C. or higher, the gas generated by graphite oxidation of the electrode is usually CO 2. However, if electrode energization is stopped for a long time (stopping electricity) by inspection of the exhaust gas duct or partial replacement of the refractory, etc., the temperature generated in the furnace decreases and the gas generated by graphite oxidation does not oxidize to CO2, but remains in CO. As a result, there is a problem that the CO concentration in the exhaust gas becomes high.

  This invention solves such a subject, and it aims at providing the electrode operating method of the incineration ash melting furnace which can suppress generation | occurrence | production of CO low, even when the electrode is stopped for a long time. .

  In order to achieve the above object, in the present invention, incineration in which incineration ash (A) is melted by discharge from the graphite electrode (3) by energizing the graphite electrode (3) that can be moved up and down while blowing combustion air. In the ash melting furnace, the first retraction position (Y) and the second retraction position (Z) are set above the operation position (X) where the graphite electrode (3) is energized to generate a discharge, and the time is relatively short. The graphite electrode (3) is raised to the first retracted position (Y) at the time of normal power stop, and the graphite electrode (3) is moved above the first retracted position (Y) at the time of unsteady power stop for a relatively long time. To the second retracted position (Z).

  In the present invention, the graphite electrode is raised to the first retraction position where the lower end of the electrode does not adhere to the base metal M and does not require time to return to energization at the time of normal stopping for a relatively short time. At the time of non-stationary power interruption for a relatively long time, the graphite electrode is raised to the second retracted position above the first retracted position, and at this position, the exposed length of the graphite electrode into the furnace body becomes short, Oxidation consumption of the electrode carbon in a state where the ambient temperature is lowered is minimized, and the CO concentration in the exhaust gas is kept low.

  In addition, the code | symbol in the said parenthesis shows the correspondence with the specific means as described in embodiment mentioned later.

  As described above, according to the electrode operating method for the incineration ash melting furnace of the present invention, the generation of CO can be suppressed even when the electrode is stopped for a long time.

  FIG. 1 is a schematic sectional view showing an example of an incineration ash melting furnace. In FIG. 1, a container-like furnace body 1 opened upward is closed by a furnace lid 2. A plurality of air-cooled electrode tubes 21 (only one of which is shown in the figure) are vertically penetrated in the furnace lid 2, and the graphite electrodes 3 are inserted through these electrode tubes 21 so as to be movable up and down. Yes. The graphite electrode 3 is held by a known electrode lifting device 4 and is moved up and down. The electrode lifting device 4 is set so that the graphite electrode can be selectively positioned at three positions in the vertical direction. The three positions are an operation position X, a first retraction position Y, and a second retraction position Z, which will be described later, and are higher in this order. The graphite electrode is positioned at the three positions by detecting it with a limit switch or the like.

  During normal operation in which the incinerated ash is melted, the graphite electrode 3 is held at the lowest operating position X as shown in FIG. 1 and melted in the lower end of the graphite electrode 3 and the furnace body 1 by energization. An arc discharge D is generated between the base metal M and the base metal M. The operation position X is set so that the lower end of the graphite electrode 3 is positioned LX upward from the melting surface of the base metal M. In this state, the graphite electrode 3 has a length of LY and is in the furnace body 1. Is exposed. An example of LX at the operation position X is 20 to 30 mm, and LY is 1580 to 1570 mm.

  An incineration ash supply port 22 is opened in the furnace lid 2, and the incineration ash A supplied and supplied from here into the furnace body 1 is heated and melted by the arc heat of the electrode 3. A combustion air supply port 11 is opened in the side wall of the furnace body 1, and the combustion air B is supplied into the furnace body 1 from this, and the combustible gas generated at the time of melting is combusted by the combustion air B. The exhaust gas C generated at this time is discharged out of the furnace body 1 through a gas discharge port 23 opened in the furnace lid 2. In FIG. 1, the slag layer that covers the surface of the base metal and the tap holes provided in the furnace body are not shown.

  Table 1 shows an example of the furnace atmosphere temperature during normal operation and the gas concentrations of CO, CO2, and O2 in the exhaust gas C. The CO and CO2 concentrations in the table are O2 12% equivalent values. According to this, the atmospheric temperature in the furnace is maintained at 1000 to 1300 ° C., the CO concentration is 27 ppm, and 4% of CO in terms of 12% of O2 shown in the “Guidelines for Prevention of Dioxins Concerning Garbage Disposal” The time average regulation value of 30 ppm or less is satisfied.

  In order to add a new graphite electrode or the like, the electrode energization may be stopped for about 10 minutes (normal power stop). In this case, as shown in FIG. 2, the graphite electrode 3 is moved to the first retracted position. Raise to Y. The first retreat position Y is an upper position close to the melting surface of the base metal M so that the lower end of the electrode does not adhere and solidify on the base metal M, and it does not take time to return to energization. An example of LX in this case Is about 300 mm, and LY is about 1300 mm.

  Table 2 shows an example of a change over time in the furnace atmosphere temperature and the concentration of each gas in the exhaust gas C at the normal power stop. The concentrations of CO and CO2 are instantaneous values in terms of O2 12%. According to this, the furnace atmosphere temperature dropped to 850 ° C. and the CO concentration increased to 35 ppm 15 minutes after the power stop, but the average for 4 hours is 30 ppm or less. Therefore, the CO concentration does not become a problem if the power is stopped for about 10 minutes.

  However, when the electrode energization is stopped for about half a day (unsteady power stop) by cleaning the exhaust gas duct or replacing the refractory, as shown in Table 2, the graphite electrode is held at the first retracted position. In addition, the CO concentration in the exhaust gas C gradually increases with the passage of time and the atmospheric temperature, and when the static electricity is stopped for 30 minutes or more, the 4-hour average CO concentration greatly exceeds the guideline regulation value of 30 ppm. When the static electricity is stopped for 90 minutes or more, the evaporation amount of carbon in the graphite electrode decreases due to the decrease in the atmospheric temperature, and the CO concentration starts to decrease, but the decrease rate is small, and the average CO concentration for 4 hours exceeds 30 ppm. Will remain.

  Therefore, in the present embodiment, when performing unsteady power interruption for a long time, the graphite electrode 3 is raised to the second retracted position Z as shown in FIG. LX at the second retracted position Z is, for example, about 1000 mm, and LY is about 600 mm. Although it is preferable to reduce LY since the exposed area of the electrode into the furnace body 1 is reduced, the thermal influence on the mechanical part around the electrode tube 21 due to the lower end of the heated graphite electrode 3 rising and approaching It is necessary to consider the trade-off.

  At the second retreat position Z, the exposed length LY of the graphite electrode 3 into the furnace body 1 is shortened, so that the oxidative consumption of the electrode carbon in the state where the ambient temperature is lowered is minimized. As a result, as shown in Table 3, the CO concentration in the exhaust gas C is 30 ppm, 30 minutes, 60 minutes, 90 minutes after the power stop, and the 4-hour average value of O212% converted value is 30 ppm of the above-mentioned guideline regulation value. Maintain the following: In addition, the CO concentration in Table 3 is 30 minutes after stopping electricity, and the instantaneous value for 60 minutes exceeds 30 ppm, but the average value for 4 hours is 30 ppm or less.

It is a schematic sectional drawing of the incineration ash melting furnace at the time of normal operation in one Example of this invention. It is a schematic sectional drawing of the incineration ash melting furnace at the time of a normal power stop. It is a schematic sectional drawing of the incineration ash melting furnace at the time of unsteady electric stop.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Furnace body, 2 ... Furnace lid, 22 ... Incineration ash supply port, 23 ... Gas discharge port, 3 ... Graphite electrode, 4 ... Electrode raising / lowering device, X ... Operation position, Y ... 1st evacuation position, Z ... 2nd Retraction position.

Claims (1)

In an incineration ash melting furnace that energizes a graphite electrode that can be moved up and down while blowing combustion air and melts the incineration ash by discharge from the graphite electrode, above the operation position that energizes the graphite electrode to cause discharge A first retracted position and a second retracted position are set, and the graphite electrode is raised to the first retracted position during a normal power stop, and the graphite electrode is moved above the first retracted position during an unsteady power stop. A method for operating an electrode of an incineration ash melting furnace, wherein the electrode is moved to a second retreat position.

Images