Furnaces – Process – Treating fuel constituent or combustion product
Reexamination Certificate
2003-03-27
2004-09-28
Rinehart, Kenneth (Department: 3749)
Furnaces
Process
Treating fuel constituent or combustion product
C110S346000
Reexamination Certificate
active
06796251
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for treating incineration residues from an incineration plant, in particular a waste incineration plant, in which the incineration material is incinerated on a furnace grate, and the incineration residues produced are brought to an elevated temperature by suitably controlling the incineration.
2. Description of the Related Art
In a process of this type, which is known from EP 0 667 490 B1, the incineration material from the furnace grate is heated to such an extent that the slag which is formed in the process is at a temperature which is just below the melting point of this slag before it reaches a melting stage arranged outside the furnace grate. In this process, therefore, the incineration is controlled in such a manner that at the end of the furnace grate the slag is at the highest possible temperature, in order to keep the energy required in the downstream melting stage as low as possible. However, this process does not involve any sintering or melting of the slag. In order nevertheless to obtain the desired slag quality, therefore, a downstream melting stage is required. This downstream melting stage not only requires a suitable device, but also, despite the procedure described above, an increased outlay on energy.
To achieve the desired quality of the slag, the inorganic and organic pollutants constituents which remain from the waste are of importance. Inorganic pollutant constituents which need to be mentioned are in particular heavy metals and salts, while the organic pollutants are attributable in particular to incomplete incineration. For assessment of the quality of the slag, it is also important how the pollutants which are present are washed out in elution tests. Moreover, mechanical properties are of importance in assessing the suitability for construction engineering purposes, e.g. in landfill sites, earthworks or road building.
On account of the high temperatures involved in treating the incineration residues in a melting stage, molten incineration residues are characterized by low levels of organic compounds. While typical slags from waste incineration plants still include unburnt material, usually measured as the loss on ignition, of from 1 to 5% by weight, the loss on ignition of fused incineration residues is less than 0.3% by weight. In addition, fused incineration residues are characterized by low levels of heavy metals and salts which can be leached out, since these are either evaporated or are incorporated in the vitreous matrix which forms when the molten material cools.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a process in which the incineration operation is influenced and controlled in such a way that a fully sintered slag of the desired quality is obtained without using downstream melting or vitrification units, and the drawbacks of dust being formed at the airtight closure of the incineration chamber are avoided with a low level of outlay on equipment, and a low water consumption becomes possible.
The term “fully sintered slag” is understood as meaning a material which consists of sintered and/or fused lumps which typically have a grain size of at least 2 mm to 8 mm. These lumps consist of garbage incineration residues which have been agglomerated by complete or surface fusion.
On account of gases being released during sintering or fusion, the sintered or fused lumps may quite possibly have a porous structure. Any porosity in the fully sintered slag is attributable to the temperature of the molten slag in the incineration bed not being high enough to effect a sufficiently low viscosity and therefore to expel gas bubbles, a technique which in the glass industry is known as refining. In this respect, the fully sintered slag differs from typical vitrified slags which are obtained in downstream high-temperature processes carried out in crucible furnaces lined with refractory material or other melting units.
Moreover, the fully sintered slag may also contain constituents of waste, such as glass or metals, which pass through the furnace grate virtually unaffected by the incineration operation, i.e. in the narrow sense are neither fused nor sintered in the incineration bed, but do have the desired properties in terms of fitting and pollutants which can be leached out.
In accordance with Hammerli (Müll und Abfall 31, Beiheft Entsorgung von Schlacken und sonstigen Rest-stoffen, [Disposal of slags and other residues supplement], page 142, 1994), the term “sintering” denotes a specific case of fusion and freezing. In the text which follows, therefore, the term sintering goes beyond the use of this term as “superficial fusion of particles to one another or together” which is often customary in scientific fields. The sintered lumps of the fully sintered slag may quite possibly also be completely or partially melted.
In the text which follows, the term residual slag denotes slag constituents which are not sintered and/or fused. Residual slag is characterized by a smaller grain size than that of the fully sintered slag as well as a higher loss on ignition and a higher level of pollutants which can be leached out.
It is known from DE 701 606 C to convey the incineration residues into a slag remover, which has an introduction shoot and a slag removal vessel with rising discharge spout and from there to remove the incineration residues by means of a discharge ram. In the process, the water for quenching the slag is fed to the slag removal vessel, only the same amount of fresh water being introduced into this slag removal vessel as is discharged with the slag on account of its moisture content. In this case, an equilibrium concentration is established with regard to numerous substances and compounds, e.g. salts, which are present in the residues, so that it is impossible to lower their concentration. This results in the slag having unsatisfactory properties with regard to its ability to form landfill and to be processed further to form construction materials. Another reason for this drawback is that there is no division or classification of the incineration residues into fractions with better properties and those with worse properties, and consequently the incineration residues produced as a whole inevitably have unsatisfactory properties.
It is known from DE 44 23 927 A1 to feed the incineration residues which come out of a furnace directly, without prior quenching in a water bath, to the primary cleaning stage. The dry slag which has undergone primary cleaning is separated into at least two fractions. All the particles which are smaller than 2 mm are allocated to a first fraction, and the remaining particles are allocated to a second fraction. As this process continues, the second fraction is in turn separated, in a screening stage, into at least two fractions, and all the particles which are smaller than 27 to 35 mm are allocated to a third fraction, while the remaining particles are allocated to a fourth fraction. In this way, fractions of incineration residues with satisfactory properties are obtained. Drawbacks of this process are the considerable amounts of dust produced and problems with achieving an airtight closure of the incineration chamber.
The object set above is achieved, starting from the process explained in the introduction, in two different ways depending on the composition of the incineration material.
According to the invention, the first way consists in the fact that the incineration is controlled in such a way that sintering and/or fusing of the incineration residues to form slag takes place as early as in the incineration bed of the main incineration zone, that all the incineration residues produced are quenched in a wet slag remover and are conveyed out of the latter, that the wet incineration residues which come out of the wet slag remover are firstly divided into two fractions by means of a mechanical separation operation, after which the main fraction, which substantially includes a coarse fraction and an oversize
Busch Michael
Gohlke Oliver
Horn Joachim
Martin Johannes
Cohen & Pontani, Lieberman & Pavane
Martin GmbH für Umwelt-und Energietechnik
Rinehart Kenneth
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