1. Field of the Invention
The present invention relates to a method for melting and treating waste such as sewage sludge, sludge of a water purification plant and incinerated ash of refuse.
Generally, waste water treatment sludge, for example, sewage sludge, is melted and treated after it has been incinerated so as to be collected as a solid slag. The waste like refuse including garbage is also treated in the same manner as the waste water treatment sludge or is incinerated in an incinerator and thereafter the resulting incinerated ash is melted and treated to be collected as a solid slag. Such slag collected from the waste is re-utilized as aggregate for road building, aggregate for building purposes and as a material for use in a waterway in a playground, a tennis court and even in a flower garden. The present invention can be generally applied to a method of melting and treating and the re-utilizing household waste and industrial waste.
2. Description of the Prior Art
Generally, it is necessary for the melting and treating waste such as sewage sludge, sludge of a water purification plant and incinerated ash of refuse, that such melting and treating is done at low cost.
Conventionally, the waste such as sewage sludge, sludge of a water purification plant and incinerated ash of refuse is melted and treated by a melting furnace having auxiliary burning means. In such a melting and treatment, oil has been generally used as an auxiliary fuel, because the amount of heat produced by burning of waste water treatment sludge and incinerated ash of refuse is insufficient for melting and treating such waste or it is not sufficient for obtaining a sufficient rate of treatment. Accordingly, in order to obtain a sufficient amount of heat for the melting treatment, and to obtain a sufficient rate of treatment, it is necessary to use a large amount of oil. However, oil is much too expensive and a limited resource. As a result, in a conventional melting and treating method using oil as a fuel the expenses are too high.
Particularly, sludge having a relatively high melting point, which is obtained from a water treatment in a water purification plant, needs a large amount of auxiliary fuel in a melting treatment process which requires an extremely high temperature inside a melting furnace. As a result, a problem arose because durability of furnace materials such as a fire-proof wall and the like which forms the melting furnace was lowered. An attempt to solve such problems has been made by mixing the waste with a melting-point depression agent so as to lower the melting-point of the waste. However, such melting-point lowering agent commercially available up to now is extremely expensive, so that the melting treatment cost per unit of the waste such as water treatment sludge has risen. In addition, in an even worse situation resulted because a larger amount of melting-point lowering agent than the amount of the waste to be treated had to be added and thus a plant or an apparatus for such a melting treatment is rather large.
Household wastes and industrial waste usually contain plastic material besides garbage. It is impossible to treat such plastic material or even if it is possible to treat it, it is extremely difficult to treat it. Therefore, it is preferred and desirable to economically carry out the treatment of such plastic material contained in the waste.