Furnaces – Refuse incinerator – With means for advancing or handling refuse or residue
Reexamination Certificate
2001-07-25
2002-10-15
Lazarus, Ira S. (Department: 3749)
Furnaces
Refuse incinerator
With means for advancing or handling refuse or residue
C110S235000, C110S342000, C110S346000, C110S1010CD, C110S219000, C110S203000
Reexamination Certificate
active
06463864
ABSTRACT:
FIELD OF ART
The present invention relates to gasification and melting furnace and method for wastes wherein organic matters contained in municipal solid wastes and/or industrial solid wastes, which may be together referred to simply as “wastes” hereinafter, are gasified, then a gas (also referred to as “energy gas” hereinafter) employable as fuel is recovered, low-boiling metals contained in the wastes are recovered as dust, and ash and valuable metals (also referred to simply as “metals”) contained in those wastes are recovered as molten slag and molten metals, respectively. Particularly, the invention is concerned with gasification and melting furnace and method permitting a stable operation over a long period.
As examples of wastes are included municipal refuses typical of which are garbages, plastic and iron scraps, shredder dusts of discarded automobiles and household appliances, bottom ash, and landfill wastes containing earth and sand.
BACKGROUND ART
In Japanese Patent Laid Open No. Hei 9-314100 there is disclosed a high-temperature reactor operating method for treating wastes.
The said high-temperature reactor operating method is characterized in that at least two oxygen lances are disposed below a wastes inlet in such a manner as to enhance the flow of molten waste and that at least two oxygen lances are disposed above the wastes inlet in such a manner as to obstruct the flow of rising gas components.
In the above publication, however, there is disclosed neither any concrete method nor any mode of embodiment about how to enhance the flow of molten waste and how to obstruct the flow of rising gas components.
The present inventors presume that introduced gases and gases resulting from decomposition of wastes form a rising flow to be discharged to the exterior of the system.
Thus, there is no such a downward flow as reinforces the flow of molten waste, but an upward flow is dominant. Likewise, there is no such flow as obstructs the flow of rising gas components, either. Therefore, it is difficult to artificially operate such a flow as obstructs the flow of rising gas components.
The present inventors think that the technique disclosed in the above publication is not clearly described and is based on principles contrary to the natural law and that therefore it is difficult to practice the said technique.
In Japanese Patent Laid Open No. Hei 10-148317 there are disclosed gasification and melting furnace and method wherein a series of steps comprising gasifying and melting wastes, dehydration and thermal decomposition, and reforming the resulting gas (indicating reforming up to CO, CO
2
, H
2
, and H
2
O) can be carried out in a single furnace without using the expensive coke and which can produce a clean energy gas not containing tar or dioxin. The gasification and melting furnace and method disclosed in the above publication is hereinafter referred to as the prior art.
The prior art relates to a gasification and melting technique for wastes using as a basic configuration a furnace which is provided at an upper portion thereof with both wastes inlet and gas outlet, also provided at a lower portion thereof with a molten slag/metal outlet, and further provided intermediate between the upper and lower portions with plural stages of tuyeres permitting a combustion sustaining gas and fuel to be independently blown off therethrough into the furnace. Further, as a development from the basic configuration the prior art is concerned with a gasification and melting technique for wastes which includes lances disposed in upper positions and capable of moving vertically toward the interior of the furnace and blowing off a combustion sustaining gas and fuel each independently, means for measuring the position of wastes introduced into the furnace, means for measuring the temperature of a middle portion, and means for measuring the temperature of an upper portion. This conventional technique is for separating wastes into an energy gas containing CO and H
2
as main components, as well as molten slag and metals.
However, having tuyeres or lances for blowing off a combustion sustaining gas and fuel each independently give rise to problems such that at the time of blowing off fuel from a tuyere or a lance there is formed a low temperature region within the furnace due to an endothermic reaction induced by a thermal decomposition of hydrocarbons contained in the fuel, or in the case of a solid fuel the temperature is also reduced by a carrier gas used for blowing off the fuel. Even in the case where a solid or liquid fuel is not blown off into the furnace, it is necessary that a purge gas be allowed to flow constantly for preventing a fuel feed pipe from being clogged. Consequently, a low temperature region is formed in part of a fire spot and melting of slag and metal components contained in a thermal decomposition residue becomes unstable at an area below that low temperature region, thus making it impossible to effect a stable operation.
For preventing the occurrence of such a low temperature region it has so far been necessary to blow off not only fuel but also a combustion sustaining gas necessary for the combustion of the fuel. As a result, the amount of the combustion sustaining gas used per unit volume of wastes treated increases and the process efficiency is deteriorated.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a method and apparatus capable of preventing the occurrence of a low temperature region in a gasification and melting furnace, concentrating a fire spot for the combustion of wastes and thereby stably recovering molten slag and various metals, as well as an energy gas, which are high in added value.
Having repeated tests in a gasification and melting furnace, the prevent inventors became aware of the following points (A) to (E).
(A) As to a lance disposed at the center of the furnace, it is not only unnecessary but also detrimental to provide equipment for blowing off a combustion sustaining gas and fuel each independently.
Regarding LPG and LNG used as gas fuels and petroleum used as a liquid fuel, they themselves contain much hydrocarbons and hydrogen, so due to an endothermic reaction caused by thermal decomposition a low temperature region is formed in part of a fire spot even if a combustion sustaining gas is fed simultaneously with the introduction of fuel. Melting of slag and metal components contained in a thermal decomposition residue present below the fire spot becomes unstable due to the drop in temperature of the fire spot, with consequent formation of an unmelted portion or a re-solidified portion. Thus, a melting region is not formed stably and the flowing-down of melt becomes intermittent, resulting in that the furnace operation becomes unstable. When blowing off a solid fuel, it is necessary to use a carrier gas which is not combustion-sustainable, and this carrier gas strikes concentratively against an upper-end surface of wastes introduced into the furnace and promotes the cooling action, so that the furnace operation becomes still more unstable.
(B) Also as to an upper tuyere, like the furnace center lance, it is not necessary to blow off fuel because it is intended to reform and burn the gas resulting from thermal decomposition of the wastes.
(C) By disposing the furnace center lance along a central axis (also referred to as “furnace axis” hereinafter) of the furnace it is made possible to melt the wastes concentratively at the central portion of the furnace and hence the furnace operation becomes extremely stable. Besides, by melting the wastes concentratively at a fire spot portion, a high temperature region is spaced apart from the furnace side wall and hence it is possible to prevent the furnace refractory from locally becoming high in temperature, so that the durability of the furnace refractory can be improved to a remarkable extent.
For melting the wastes concentratively at the central portion of the furnace it is important to control the position of an upper end surface of the wastes (also referred to as “i
Furukawa Noboru
Isaka Katsuya
Ishida Hiroaki
Matsubara Hitoshi
Matsukura Yoshinori
Lazarus Ira S.
Rinehart K. B.
Sumitomo Metal Industries Ltd.
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