JPS638365B2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a method for treating sludge.

Generally, when treating various types of sludge such as sewage sludge and human waste sludge, they are incinerated in a sludge incinerator, and the resulting incineration residue, ash, has a high moisture content to prevent it from dissipating.
After humidifying the water to a level of 20 to 30%, it is disposed of in a landfill.
However, this landfill disposal requires a vast amount of land, and there is a risk of secondary pollution such as the scattering of the ash after the landfill and the elution of polymeric substances in the ash, so the ash is further melted using arc heat in an arc furnace. It is conceivable to treat it to reduce its volume and stabilize it. In other words, if you improve the Yale arc furnace used for steelmaking, etc., create an arc between the molten metal and the electrode, and put the ash into the furnace, thermal decomposition will occur in a high-temperature reducing atmosphere. The organic matter in the ash is gasified, the inorganic matter is turned into molten slag, and some of the metals are gasified and the rest are distributed into the slag and molten metal. When the molten slag obtained by this method is cooled and solidified, its volume is reduced to less than half that of the original ash, no heavy metals are released, and it can be effectively used as aggregate for concrete. However, in general, a multi-bed incinerator 1 as shown in Fig. 1 is used as a sludge incinerator, and the sludge dewatered cake fed through the inlet 2 is dried and preheated in a preheating zone 3, and then heated in a combustion zone 4 by a burner 5. After combustion under auxiliary combustion, the ash becomes ash, which is cooled by cold air in the cooling zone 6 and discharged from the furnace through the ash outlet 7.The ash is further cooled to near room temperature by humidification and natural heat radiation to prevent dissipation and extinguish fire. It will be done. Therefore, if a treatment process is adopted in which the cooled ash is put into an arc furnace and melted, approximately
The ash, which was at a high temperature of 600 to 800 degrees Celsius, has to be cooled down and then reheated using arc heat.
Electricity costs are low and it is uneconomical. Furthermore, even if all the sensible heat of the high-temperature ash was used to preheat the combustion air in the incinerator, the electricity cost would be greater than the fuel cost required to supply the same amount of heat, so the fuel cost due to air preheating would be higher than the fuel cost required to supply the same amount of heat. This is uneconomical because the increase in electricity costs for reheating is greater than the savings.

This invention has been made in view of the above-mentioned points, and it is an object of the present invention to provide a sludge treatment method that requires less electric power for melting in an arc furnace and can economically melt sludge.

However, in this invention, sludge is incinerated in a sludge incinerator, and the resulting high-temperature incinerated ash is directly charged into a closed-type arc furnace without forced cooling.
The method is characterized in that the incinerated ash is melted by the arc heat of an arc generated between an electrode and a conductive material in the arc furnace.

The method of this invention will be explained in detail below based on the embodiment shown in FIG. In addition, the parts in the figure with the same reference numerals as in FIG. 1 indicate the same parts as in FIG. 1.

In other words, the sludge incinerator is a multi-bed type combustion furnace 8 that is equipped with only a pre-heating zone 3 and a combustion zone 4 and has no cooling zone, and the high-temperature ash that passes through the combustion zone 4 and is discharged from the ash outlet 9 is used as a sludge incinerator. is conveyed by a conveyor 10 without being forcedly cooled and directly placed into a closed arc furnace 11. It is preferable to surround the conveyor 10 with a duct 12 and further cover this duct with a heat insulating material 13. This allows the amount of natural heat dissipation of the ash to be kept low, and the ash can be transported to the arc furnace while maintaining a higher temperature. The ash put into the arc furnace 11 is thermally decomposed by the arc heat of the arc generated between the electrode 14 and the conductive material 15 such as molten metal or graphite at the bottom of the furnace, and the organic matter is gasified and discharged from the duct 16. , used as fuel in incinerators. Further, the inorganic substance becomes molten slag 17. At this time, the ash fed into the arc furnace 11 is heated to a temperature of 600 to 800°C.
Therefore, less electricity is required for ash melting. According to the inventors' experimental results, for example, sewage sludge incineration ash at room temperature containing 20 to 30% moisture due to humidification (sample A), sewage sludge incineration ash at room temperature without humidification (sample B), and 700℃ sewage Sludge incineration ash (sample C)
When put into an arc furnace, the amount of electricity required for the melting process is 0.672 kWh for sample A, 0.453 kWh for sample B, and 0.325 kWh for sample C (all per 1 kg of ash). It can be seen that a large reduction in melting power can be achieved.

In the above embodiment, if the arc furnace 11 can be installed below the ash outlet 9, the ash may be directly dropped from the ash outlet 9 into the arc furnace 11 through a duct or the like without using the conveyor 10.

As explained above, according to the present invention, sludge is incinerated in a sludge incinerator, and the resulting high-temperature incinerated ash is directly supplied to an arc furnace without cooling such as forced air cooling or water cooling, and is melted by arc heat. Since sludge is treated, sludge incineration, preheating, etc. can be done economically using auxiliary combustion fuel, which is cheaper than electricity.
The electric power required for melting in the arc furnace is small, and sludge can be melted and processed economically by effectively using fuel and electric power. Additionally, equipment for cooling and humidifying the ash after incineration is not required, simplifying the equipment and reducing equipment costs.

[Brief explanation of the drawing]

FIG. 1 is a schematic longitudinal cross-sectional view of a conventional sludge incinerator, and FIG. 2 is an equipment layout diagram showing an example of the apparatus used to carry out the method of the present invention. 3... Pre-heating zone, 4... Combustion zone, 8... Multi-bed incinerator, 9... Ash outlet, 10... Conveyor, 11
... Arc furnace, 14 ... Electrode, 15 ... Conductive material,
17... Molten slag.

Claims (1)

[Claims] 1 The sludge is incinerated in a sludge incinerator, and the resulting high-temperature incinerated ash is directly charged into a closed arc furnace without forced cooling, and generated between the electrode and the conductive material in the arc furnace. A sludge treatment method characterized by melting the incineration ash using the arc heat of an electric arc.