Furnaces – Fuel feeders – Feeder responsive to fuel bed height
Reexamination Certificate
2003-09-30
2004-10-26
Rinehart, Kenneth (Department: 3749)
Furnaces
Fuel feeders
Feeder responsive to fuel bed height
C110S1010CD, C110S185000, C110S186000, C110S250000, C110S259000, C110S238000, C110S242000
Reexamination Certificate
active
06807913
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 Hr, 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 are commonly encountered that prevent smooth operation of such processing plants or furnaces:—
(a) Unprocessed solid deposition.
(b) Bridging.
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 when the viscosity of molten material is increased significantly due to a change in its composition. Thus, while this problem does not directly affect the feed rate of the waste through chamber (
10
), the flow rate of the liquid material (
38
) may be drastically reduced or stopped, which indirectly results in some reduction in the flow rate of refuse through the chamber (
10
). In the art, such “unprocessed solids” need to be treated with fluxing agent, which enable the solids to dissolve therein, forming solutions with relatively lower crystallisation temperature and of lower viscosity than the unprocessed solids may have in the liquid state. The resulting solutions are subsequently melted and removed from the lower part of chamber (
10
) in the normal manner. For example, Calcium Oxide (CaO), and Aluminum Oxide (Al
2
O
3
) each have relatively high individual melting points. However, if mixed together with quartz (Silicon Oxide (SiO
2
) ) in appropriate proportions (e.g., SiO
2-62
%, CaO-23.25%, Al
2
O
3-14.75
%), the resulting mixture begins to melt at about 1165° C., and liquid droplets begin to form at about 1450° C., which is well within the temperature range existing at the lower end of the chamber (
10
). Similarly, while the existence of quartz (SiO2) or Aluminium Oxide (Al
2
O
3
) each increase viscosity and thus decrease the fluidity of liquid material (
38
), the addition of fluxing agents such as CaO, MgO, MnO, FeO serve to decrease viscosity of the liquid material (
38
) and thus to promote run-off thereof. In some cases, Aluminium Oxide can act as a fluxing agent, the addition of small quantities thereof to slag containing large amounts of CaO having the effect of lowering the viscosity of the mixture. Unprocessed solids may be dissolved in liquid slag if in contact therewith, since the liquid slag comprises many different compounds in a dissociated state, enabling many different crystal compositions to be formed at different temperatures. The dissolving process is accelerated if the viscosity and surface tension of the melt are low, and these parameters will depend on the composition of the solids as well as of the melt, and on the temperature of the melt. It is also known that raising the temperature of the slag also serves to reduce its viscosity.
In the prior art, if and when it is determined that solid deposition has occurred, fluxing agents are then provided at the top end of the chamber (
10
) (typically manually) at the waste inlet means of the apparatus, which is somewhat ineffective since the agents have to percolate through the whole column of refuse, or at least pass together with the refuse to the lower part of the chamber, which takes a lot of time. If there is also bridging within the chamber (
10
), the fluxing agents cannot be applied to the solids, and thus the furnace has to be shut down, the refuse removed from the chamber and the bridging destroyed manually, before the solids can be accessed. Of course, by then all of the slag at the lower end of the chamber (
10
) has also solidified.
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 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 and for the prevention of bridging. 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 are directed to the problem of unprocessed solids deposition, nor do they provide a solution therefore, less so in the manner of the present invention.
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 transforma
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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