Furnaces – Process – Treating fuel constituent or combustion product
Reexamination Certificate
1998-04-27
2001-02-13
Price, Carl D. (Department: 3743)
Furnaces
Process
Treating fuel constituent or combustion product
C110S345000, C110S203000, C110S215000, C110S220000, C110S229000, C110S250000
Reexamination Certificate
active
06186081
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for working up waste such as, e.g., residual waste from domestic garbage, industrial waste, bulky refuse or sewage sludge, in which the waste or the sewage sludge is subjected to pyrolysis under an oxygen-poor atmosphere and the solids are subjected to mechanical treating and screening. The invention also relates to an arrangement for carrying out said process.
2. Description of the Related Art
For working up waste it has already been suggested to subject waste comprised of domestic garbage, industrial waste similar to domestic garbage, bulky refuse and sewage sludge to pyrolysis in a first process step. After such a pyrolysis, which was carried out at temperatures of below 500° C. and, most frequently, at temperatures of approximately 450° C. under oxygen-deficient conditions, in known processes cooling to temperatures of below 150° C. was, for instance, realized by means of a cooling vibration conveyor, whereupon a coarse fraction and a fine fraction were formed in a screening means. In the course of that conversion or carbonization at low temperatures, it could be determined that the coarse fraction primarily contained ferritic metals, nonferrous metals and inert material such as, e.g., glass, ceramics, stones and porcelain, whereas the fine fraction contained almost all of the carbon from the waste charged. The fine fraction having grain sizes of above 1 mm in known processes was comminuted and subjected to high-temperature combustion along with the low temperature carbonization gas. Due to the elevated carbon concentration in the fine fraction, a fuel having a high calorific value was provided. Subsequent high-temperature combustion was used to produce energy and, in particular, to produce electric energy or long-distance energy. This high temperature combustion produced an ash melt or slag which could be granulated to a vitrified slag granulate material in a water bath.
Furthermore, it has already been suggested, following the pyrolysis of residual waste, to carry out an extensive chemical reduction in a first step, whereupon oxidation was conducted in several steps in order to be able to discharge valuable substances and, in particular, metal fractions separately.
SUMMARY OF THE INVENTION
The invention aims at further developing a process of the initially defined kind with a view to enabling the formation of slag fractions free of heavy metals and, in particular, free of chromium while enhancing energy utilization such that the slag fractions may be directly used as a cement grinding additive or pozzolanic starting material and the metallic portions can be recovered in a better way.
To solve these objects, the process according to the invention essentially resides in that a screened coarse fraction mechanically separated from metals is charged into a metal bath reactor, a screened fine fraction is charged via a nozzle into the metal bath by means of a carrier gas in order to carburize the metal bath and the pyrolysis gas is used at least partially as a combustion gas for smelting and heating the slag bath floating on the metal bath. By providing a metal bath reactor immediately downstream to the conversion or low temperature carbonization effected in a pyrolysis reactor, the fractions occurring separately after screening can be used in a manner so as to allow for the quantitative separation of heavy metals and nonferrous heavy metals from the mineral phases. By charging via a nozzle the screened fine fraction into the metal bath by aid of a carrier gas, the metal bath can be carburized in a suitable manner. Such a carburized metal bath subsequently is reacted with the molten slag fraction or the molten solids from pyrolysis, whereby metallic portions from that slag fraction are reduced into the metal bath and a slag product free of heavy metals and nonferrous heavy metals is obtained. Due to the high calorific value of the low temperature carbonization gas, or pyrolysis gas, the latter may be used for smelting and heating the slag bath floating on the metal bath, thereby achieving a high efficiency without additional energy introduction. Purer end products are thus obtained without additional energy supply. The process stands out for its high economy. At the same time, a high-quality pozzolan is produced for the cement industry. Due to the reduction of metallic portions taking place in the metal bath reactor, even problematic substances such as, for instance, galvanization sludges, sewage sludges and car shredder light fractions may be employed without contamination of the end product such that altogether pure end products are formed. Metallic portions can be discharged with the metal bath and subsequently worked up separately.
Advantageously, the process according to the invention is carried out in a manner that an inert gas and, in particular, nitrogen is used as a carrier gas for charging via nozzles the fine fraction into the metal bath.
Mechanical processing enables a considerable portion of the metallic fraction to be separated after pyrolysis and after cooling of the pyrolysis coke using, for instance, magnetic separators, wherein the high carbon portion of the fine fraction, which optionally has been additionally disintegrated by means of a roll type crusher, allows for direct injection into the iron bath reactor. In order to safely keep the desired reduction potential of the metal bath and to burn excess carbon in the bath, it is advantageously proceeded in a manner that oxygen or air is blown into the metal bath via cooled tuyeres and, in particular, such oxygen or air is enveloped by hydrocarbons. By adjusting the respective amounts of fine fraction and oxygen blown in, the reduction potential of the metal bath required for the quantitative reduction of metallic portions in the slag bath may be adjusted within desired limits.
Advantageously, an iron bath is charged as the metal bath. Particularly efficient combustion of the pyrolysis gas formed during pyrolysis is feasible if, corresponding to a preferred further development of the process according to the invention, the pyrolysis gases are burnt with hot air and/or oxygen by means of burners opening into the reactor space above the slag bath. In that case, conventional burners may be employed, to which hot air or oxygen is fed through a central channel and the pyrolysis gases are fed via an annular channel.
The hot offgas formed during the gasification of the carbon contained in the metal and during the combustion of the pyrolysis gas (which is used for melting the slags) also contains chemical energy. Advantageously, such metal bath reactor offgases are used for preheating the hot combustion gases for burning the pyrolysis gas, to which end the process is carried out in a manner that the hot combustion gases is heated by the metal bath reactor offgases.
The overall process, including waste pretreatment, runs exothermally, i.e., at an excess of energy such that quite a considerable amount of pyrolysis gases may, for instance, be converted into electric energy. Further energy utilization of the energy generated by the cooled metal bath reactor offgases (hereinafter referred to as energetic utilization) advantageously may be realized by burning a portion of the pyrolysis gases with the cooled metal bath reactor offgases leaving the recuperative heat exchanger, and with air. The combustion offgases after energy utilization are subjected to offgas purification, to which end these gases are burnt in a further combustion chamber under air supply. Following energy utilization, which naturally may also reside in producing long-distance energy, conventional smoke gas purification takes place, wherein the process advantageously is carried out such that dusts and, in particular, filter dusts are withdrawn from offgas purification and subjected to basic (alkaline) washing, whereupon the hydroxide sludges formed are charged onto the slag bath of the metal bath reactor. Closing of the recirculatory system in order to safely dispose o
Ciric Ljiljana V.
Pillsbury Madison & Sutro LLP
Price Carl D.
“HolderBank”Financiere Glarus AG
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