Furnaces – Utilizing powdered fuel – Having rotary flow means
Reexamination Certificate
2000-11-02
2002-07-23
Bennett, Henry (Department: 3749)
Furnaces
Utilizing powdered fuel
Having rotary flow means
C110S260000, C110S263000, C110S204000, C110S234000
Reexamination Certificate
active
06422160
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an apparatus for the combustion of vanadium-containing fuels.
Vanadium-containing fuels are obtained as residues during pretroleum refining. These residues are generally burned in spiral flow or rotary heaters and vanadium and compounds thereof, together with other recyclable constituents of the residues are obtained in slag and ash form, which can advantageously undergo further treatment. Simultaneously the heat released during combustion can be recovered.
A spiral flow heater for the heat treatment of carbon-containing residues from petroleum refining is known from DE 41 14 171 C2. Carbon-containing materials with non-flammable constituents and pollutants are supplied in a predetermined particle size tangentially in a delivery air flow to a combustion chamber and burned at temperatures above the slag melting point. The combustion air is tangentially blown in such a way that a direct contact and sticking of slag to an inner lining of the combustion chamber are avoided. As a result of cooling, the slag is discharged in solid form.
It has been found that during the combustion of vanadium-containing carbon black dust in a spiral flow furnance spontaneously liquid slag is produced at the common burner chamber temperatures.
The spontaneous slag sticking is particularly disadvantageous in the vicinity of the supply nozzles for the pulverized fuel-air mixture and the air nozzles for the combustion air. Even after relatively short operating periods the nozzles suffer slag penetration leading to a restriction and disturbance to heater operation.
SUMMARY OF THE INVENTION
The object of the invention is to provide an apparatus and a method for the combustion of vanadium-containing fuels, particularly from petroleum refining, which permit a substantially troublefree and particularly efficient recovery of vanadium and hot gas production without any slag penetration of the feed nozzles.
According to the invention, this object is achieved by an apparatus having a combustion area, a start burner and feeds for a pulverized fuel-air mixture and combustion air, as well as with a flue gas outlet and slag discharge means, in which a top burner is located above the combustion area and is formed in a top cover as a top cover burner. In the cover of the top burner are located at least the start burner and the supply for the pulverized fuel-air mixture with at least one dust nozzle. The at least one dust nozzle is positioned in such a way that the pulverized fuel-air mixture is introduced into the combustion area on a secant to the cross-sectional surface thereof and under an angle between 35° and 65° to the longitudinal axis of the combustion area or alternatively coaxially to the start burner.
From the method standpoint, the object is achieved in that the vanadium-containing residues from petroleum refining or also other vanadium-containing fuels are fed to a top burner, which is located in a top cover of a combustion area. According to the invention, the pulverized fuel-air mixture is supplied following a secant to the cross-sectional surface of the combustion area and under an angle between 35° and 65° to the longitudinal axis thereof or, in an alternative construction, coaxially to a start burner located in the top cover of the combustion area and is burned with short burn-out times and an adjustable ignition front.
The method and apparatus according to the invention are based on the surprisingly high reactivity of the vanadium-containing residues and an extremely rapid ignition and short burn-out times of the vanadium-containing pulverized fuel. Tests have shown that the high reacitivity and high combusiton speed and the formation of a highly corrosive, liquid slag can be attributed to metallic constituents of the fuel, which oxidize. It is assumed that the metallic constituents have a catalytic action on the combustion and bring about the formation of the spontaneous, liquid slag. During combustion vanadium is converted into vanadium pentoxide, which has a melting point of 672° C. In mixtures with further metal oxides, e.g. nickel and iron oxides, there is a slag melting point between 700 and 850° C., which is extremely low compared with other slags. Therefore, the possible combustion temperatures are always above this melting point, so that basically, liquid slag is unavoidable. In order to ensure that no function-preventing sticking occurs in a combustion chamber and particularly in the vicinity of the feed nozzles for the pulverized fuelair mixture, for combustion air or other media, according to the invention a top cover or roof burner is provided and the feed nozzles are oriented in such a way that a return flow of liquid slag is prevented. With a defined flow guidance and nozzle shaping a substoichiometric combustion zone is obtained directly after the pulverized fuel has passed out of the dust nozzles, so that spontaneous slag formation in the vicinity of the dust nozzles is prevented. Moreover, the defined flow guidance makes it possible to endure an adequate, predeterminable spacing between the nozzles and the formation of liquid slags.
In a first apparatus embodiment the dust burner is constituted by a top burner in a top cover with a frustum-like cover wall. Eccentrically within the top cover are provided a predeterminable number of dust nozzles, which are constructed in lance-like manner. By means of said dust nozzles the pulverized fuel is blown in on secants under a predeterminable angle to the longitudinal axis of the refractory lined combustion chamber. Directly after passing out of the dust nozzles no secondary combustion air is supplied, so that there are near-stoichiometric to pronounced substoichiometric ratios in said first combustion zone, e.g. with &lgr;=0.2 to 1.0.
The arrangement of the dust nozzles or lances in the cover of the combustion chamber prevents a clogging of the nozzles with slag in this embodiment. It is advantageous that the dust exit velocity can be modified for changing the ignition front of the dust in a predeterminable spacing with respect to the nozzle. Appropriately the velocities of the pulverized fuel supplied are between 10 and 45 m/sec, preferably 20 m/sec.
Tests have shown that the reactivity of the vanadium-containing fuel is decisively dependent on the vanadium and oxygen content of the residues. With a lower vanadium and oxygen content it is advantageous to compensate the slower reaction speed by a better mixing of the pulverized fuel and the air. In respect of the apparatus, such a mixing can be implemented by spin means or swirling devices in the preferably annular combustion air duct of the top or roof burner.
For the supply secondary air to the combustion chamber there can be provided a stepped air supply by means of several, preferably two air nozzles. Specially shaped flaps in the air nozzles make it possible to change the exit velocity of the combustion air for different mass flows. Thus, the ash/slag ratio can be varied. In addition, the combustion air exit velocity effects the burn-out, so that the latter can also be controlled via the exit velocity of the combustion air.
In a second apparatus embodiment a top burner is placed in a roof or cover of a combustion area which, as in the first apparatus and method embodiment, is formed in a refractory lined combustion chamber. Thus, the top burner is located in a cover of the refractory lined combustion chamber and can also be referred to as a cover or head burner.
It is advantageous that the refractory lining of the preferably cylindrical combustion chamber can serve as an ignition aid and a double jacket for preheating the combustion air. Combuation is largely ended within a relatively small combustion chamber volume. A waste heat boiler, which follows the refractory lined combustion chamber, can have a smaller volume than when no lined combustion chamber is used. Obviously cost advantages result from this solution.
It is also appropriate for the top burner to have a start burner, which is preferably operated with gas or oil a
Baetz Andre Michael
Goerner Klaus
Schmaus Friedrich
Wulfert Holger
Bennett Henry
Binehart K. B.
Jacobson & Holman PLLC
Loesche GmbH
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