Furnaces – With control means responsive to a sensed condition – Feed control
Reexamination Certificate
2003-09-26
2004-11-23
Rinehart, Kenneth (Department: 3749)
Furnaces
With control means responsive to a sensed condition
Feed control
C110S250000, C110S235000, C110S242000, C110S238000, C110S342000, C110S1010CD, C110S1010CF
Reexamination Certificate
active
06820564
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an apparatus for the conversion of waste, including the processing, treatment or disposal of waste. In particular, the present invention is directed to a system and method for decongesting a furnace in a plasma torch based waste processing plant.
BACKGROUND
The processing of waste including municipal waste, medical waste, toxic and radioactive waste by means of plasma-torch based waste processing plants is well known. Referring to
FIG. 1
, a typical prior art plasma-based processing plant (
1
) comprises a processing chamber (
10
) typically in the form of a vertical shaft, in which typically solid, and also mixed (i.e., generally, solid plus liquid and/or semiliquid), waste (
20
) is introduced at the upper end thereof via a waste inlet means comprising an air lock arrangement (
30
). One or a plurality of plasma torches (
40
) at the lower end of the chamber (
10
) heats the column (
35
) of waste in the chamber (
10
), converting the waste into gases that are channeled off via outlet (
50
), and a liquid material (
38
) (typically molten metals and/or slag) which is periodically or continuously collected at the lower end of the chamber (
10
) via reservoir (
60
). Oxidising fluid, such as air, oxygen or steam (
70
) may be provided at the lower end of the chamber (
10
) to convert carbon, produced in the processing of organic waste, into useful gases such as CO and H
2
, for example. A similar arrangement for dealing with solid waste is described in U.S. Pat. No. 5,143,000, the contents of which are incorporated herein by reference thereto.
Two problems commonly encountered that prevent smooth operation of such processing plants or furnaces are:—
(One) Bridging.
(Two) Unprocessed solid deposition.
The bridging phenomenon relates to a blockage that occurs as a result of the passage of solid material through a channel such as the chamber (
10
), the problem being further exacerbated when some of the solids liquefy. Many organic materials that may be found in the waste column (
35
) undergo a number of transformations during processing in the chamber (
10
). These transformations include, as a function of increasing temperature, the formation of gas products, the formation of liquid and semi-liquid pitch or bitumen, the evaporation of the pitch and charcoal or coke formation at high temperatures. These transformations may be occurring simultaneously at different parts of the furnace due to the temperature profile in the chamber (
10
). Thus, while raw or unprocessed waste may be found at the upper end of the waste column (
35
), the organic materials are converted to charcoal at the bottom end of the waste column (
35
), and to bitumen in a central portion of the waste column (
35
).
During the bitumnisation process of the organic waste, several pieces of bituminised waste may coalesce to form a full or partial bridge blockage in the furnace, as illustrated at (A) in FIG.
1
.
Inorganic waste is normally dealt with at the lower, hotter parts of the chamber (
10
). Because of the non-homogenous composition of the waste and the temperature profile within the chamber (
10
), some inorganic waste may melt at higher portions of the chamber (
10
), and flow downwards, adhering to other waste and in some cases causing several pieces of waste to adhere to one another, resulting in a blockage. In fact, the molten waste may adhere to the walls of the chamber (
10
) and even crystalise there if the wall temperature is lower than the melting point of the waste, also leading to a bridge-type phenomenon within the chamber (
10
).
Another type of bridging phenomenon may occur as a direct result of the passage of solid waste through the furnace—a bridge-type formation, similar to a vaulted ceiling in form, can occur naturally within the refuse column, particular when the refuse is in granulated form, as illustrated at (B) in FIG.
1
. The bridge-type formation provides a stable load bearing structure for the column of refuse, redirecting the weight of the column from the centre thereof to the edges in contact with the walls of the chamber (
10
), thereby preventing the flow of refuse via gravity through the furnace. The presence of a bridging phenomenon within the chamber (
10
) results in a reduction or total stoppage of the feed rate of waste through chamber (
10
).
Japanese Patent Application No. 10019221A2 addresses a bridging phenomenon problem by providing a number of mechanical devices which are inserted into the column of refuse from the sides or from the top of the furnace. These devices provide an external mechanical force to the waste in a direction towards the inside of the furnace, accomplished by either rotating members or axially displaceable members. While possibly effective in some cases, the mechanical devices are subject to a great deal of wear and tear and to high thermal stresses, and need to be replaced or serviced fairly frequently. Further, when not needed, the devices actually represent a partial blockage with respect to the column. The devices are also able to directly apply force in relatively isolated points within the furnace. Furthermore, incorporation of such mechanical devices in a furnace made from refractory material is not straightforward. Japanese Patent Publication Nos. JP 10 110917 and JP 10 089645 each describe a vertical melting furnace which is externally bulged to form a combustion space, thereby enabling continuous waste disposal. While these two patents are directed towards the prevention of bridging, they are not particularly effective in this regard, nor do not provide any solution to removing a bridging phenomena or for reducing propagation thereof
French Patent No. 2,708,217 describes a plasma-torch based system in which the plasma arc is permanently submerged between the liquid products and the torch, within a reaction zone of the material being treated. Japanese Patent Application No. 05346218 describes a waste melting furnace in which a waste feed device, and air feed pipe and an auxiliary fuel feed device are provided to monitor and control melting conditions of the waste in order to minimise consumption of the auxiliary fuel. U.S. Pat. No. 4,831,944 describes another type of furnace wherein the plasma jets are inclined with respect to the corresponding radius of the column. U.S. Pat. No. 4,848,250 is directed to an apparatus and method for converting refuse to thermal energy, metal and slag devoid of particulate material. However, none of these references is directed to the problem of bridging, nor do they provide a solution therefore, less so in the manner of the present invention.
Waste material may comprise many different substances, some of which may have very high melting temperatures. Such substances may include, for example, refractory bricks, some types of rocks and stones, and also aluminium oxide (Al
2
O
3
). Furthermore, the waste may also contain products having a high aluminium content, and the aluminium may be oxidised to aluminium oxide by the hot oxidising means provided at the lower end of the chamber (
10
). The melting temperature for aluminium oxide is about 2050° C., and the melting point for other oxides that may also be found or formed within the waste column (
35
) include for example about 2825° C. for Magnesium oxide (MgO), and about 2630° C. for calcium oxide (CaO). However, the temperature at the lower end of the chamber (
10
), i.e., of the liquid material (
38
) is in the order of between about 1500° C. and about 1650° C. Thus, unprocessed solid deposition occurs when certain types of solid waste having a high melting temperature, or when some substances are transformed into oxides having a high melting temperature, rather than liquefy persist in a solid state during the normal operation of the furnace. The deposition of such solids at the lower end of the chamber (
10
) leads to blockage thereat, preventing run-off of liquid material (
38
) (typically molten metals and/or slag) to reservoir (
60
), as illustrated at (C) in FIG.
1
. The same problem may occur
Gnedenko Valeri G.
Pegaz David
Souris Alexandre L.
Browdy and Neimark , P.L.L.C.
E.E.R. Environmental Energy Resources Ltd.
Rinehart Kenneth
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