EP3124864A1

EP3124864A1 - Surface melting furnace and method for operating surface melting furnace

Info

Publication number: EP3124864A1
Application number: EP15770414.9A
Authority: EP
Inventors: Fumiaki KAMBAYASHI; Youji YOSHIOKA; Fumiki HOSHO; Masaharu Okada; Kenichiro SHINOHARA
Original assignee: Kubota Corp
Current assignee: Kubota Corp
Priority date: 2014-03-28
Filing date: 2015-03-27
Publication date: 2017-02-01
Anticipated expiration: 2035-03-27
Also published as: EP3124864B1; WO2015147239A1; EP3124864A4; JP2015190701A; JP6305805B2

Abstract

In order to suppress the volatilization of phosphorus and improve melt treatment efficiency, a surface melting furnace 1 includes a furnace chamber 4, a treatment-target supply mechanism 8, and a edge portion of air-supply mechanism 20. The furnace chamber 4 includes auxiliary burners and air supply mechanisms 11 on the approximately center of its furnace ceiling 2, and has a slag port 3 a on its furnace bottom 3. The treatment-target supply mechanism 8 is configured to supply a treatment target to the furnace chamber 4 from a treatment-target container 7 disposed around the furnace chamber 4. The edge portion of air-supply mechanism 20 is configured to supply air toward the surface of the treatment target just having been put into the furnace chamber 4 by the treatment-target supply mechanism 8 to suppress reduction reactions of phosphorus oxides contained in combustible waste.

Description

[TECHNICAL FIELD]

The present invention relates to a surface melting furnace that melt-treats a treatment target containing phosphorus and a combustible material and to a method for operating the surface melting furnace.

[BACKGROUND ART]

Surface melting furnaces are configured to include furnace chambers including combustion burners and air supply mechanisms on the approximately centers of furnace ceilings and having slag ports on furnace bottoms, and treatment-target supply mechanisms that supply treatment targets from treatment-target containers disposed around the furnace chambers to the furnace chambers.
Use of such surface melting furnaces for melt-treating treatment targets containing phosphorus and combustible materials has had a problem in that larger furnaces are necessitated to treat the same quantity of the treatment targets because throughput per unit area of furnace beds is low for the reason that air required for combustion and melting is supplied from air supply mechanisms disposed on the approximately centers of the furnace ceilings, which prevents the air from being sufficiently supplied to areas that necessitate the air for efficient combustion of combustible contents, for example.
Patent document 1 is intended to provide surface melting furnaces that can improve melt-treatment speeds of self-combusting dry-distillation residues containing uncombusted carbon. Patent document 1 proposes surface melting furnaces in which annular supply paths are formed between inner cylinders and outer cylinders to let treatment targets fall under their own weights in a filled state, the lower ends of the annular supply paths are configured to communicate with combustion chambers, and air-supply mechanisms for supplying combustion air to annular accumulated portions of the dry-distillation residues facing the combustion chambers are included.
When the waste is self-combusting materials such as the dry-distillation residues, the dry-distillation residues can be efficiently combustion-melt-treated by supplying combustion air to the dry-distillation residues heated by the combustion burners.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

[Patent document 1] Japanese Unexamined Patent Application Publication No. H10-122523

SUMMARY OF INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

The surface melting furnaces disclosed in Patent document 1 have been configured to use the combustion burners as main heat sources for melting combustible waste and to efficiently combust and melt the dry-distillation residues by supplying combustion air to the dry-distillation residues heated by the combustion burners.
For this reason, when the heat of combustion of the combustible waste is used as the heat sources for melting without using the combustion burners as the heat sources, supplying large quantities of combustion air from the air-supply mechanisms may cool the surfaces of the combustible waste and disrupt thermal decomposition and melt treatment. There has been another problem in that the combustible waste scatters in the furnaces and is discharged through the slag ports in an unmolten state.
Accordingly, it has been difficult to actively supply combustion air to the dry-distillation residues, and the problem that throughput per unit area of the furnace beds is low has not been solved.
There has been another problem in that air supplied by the air-supply mechanisms spirally downward along the surfaces of the treatment targets strengthens swirling flows in the furnaces, the swirling force acts on slag falling through the slag ports, and the slag adheres to and accumulates on wall surfaces of secondary chambers.
In addition, if the supply quantities of the air supplied from the air-supply mechanisms are regulated so that the air will flow along the sloping directions of the surfaces of the treatment targets or spirally flow down along the surfaces of the treatment targets in order to prevent the combustible waste from scattering, combustible gas generated by thermal decomposition of the combustible waste supplied to the furnace chambers flows up toward the furnace ceilings, and accordingly the combustion air supplied from the air-supply mechanisms is consumed in the combustion of the combustible gas. For this reason, there also has been a problem in that the combustion air is in short supply in areas adjacent to the surfaces of the combustible waste.
Particularly when treatment targets containing phosphorus and combustible materials are melt-treated as the treatment targets, oxygen gets scarce because sufficient air cannot be supplied to fixed carbon contents remaining on the surfaces of the treatment targets after thermal decomposition, and it has not been possible to effectively prevent phosphorus from volatilizing into exhaust gas.
The volatilized phosphorus has flown through flues together with the exhaust gas, has been cooled and condensed through processes of treatment in exhaust-gas treatment equipment, and has deposited as phosphoric acid dust, resulting in blocking of exhaust-gas flow paths of boilers, air preheaters, and other components.
In view of the problems described above, the present invention has an object to provide a surface melting furnace that can suppress the volatilization of phosphorus and improve melt treatment efficiency even when a treatment target containing phosphorus and a combustible material is melt-treated, and a method for operating the surface melting furnace.

MEANS FOR SOLVING THE PROBLEMS

To achieve the object above, a first characteristic configuration of a surface melting furnace according to the present invention is, as set forth in claim 1 in the document of claims, that a surface melting furnace configured to melt-treat a treatment target includes a furnace chamber, a treatment-target supply mechanism, and a edge portion of air-supply mechanism. The treatment target contains phosphorus and a combustible material. The furnace chamber has a slag port and includes a burner and an air supply mechanism. The treatment-target supply mechanism is configured to supply the treatment target to the furnace chamber from a treatment-target container communicating with the furnace chamber. The edge portion of air-supply mechanism is configured to supply air toward a portion of the surface of the treatment target in the furnace chamber. The portion is adjacent to a portion in which the treatment-target container communicates with the furnace chamber.
The burner and the air supplied from the air supply mechanism heat the treatment target in the furnace, and the surface melts and falls through the slag port. The combustible material in the treatment target supplied to the furnace chamber is thermally decomposed by the temperature in the furnace chamber and generates combustible gas. The combustible gas combusts while flowing up.
The air supplied from the edge portion of air-supply mechanism toward the surface of the treatment target causes a fixed carbon content remaining on a portion adjacent to the surface of the treatment target due to the thermal decomposition of the combustible material to combust. The remainder of oxygen suppresses reduction reactions of phosphorus compounds and phosphorus oxides and thus suppresses the volatilization of phosphorus. Accordingly, the air is efficiently supplied to the combustible gas and the fixed carbon content, and the melt-treatment efficiency is significantly increased. The furnace can be configured to be smaller to obtain the same throughput, and the melting throughput increases when the same size of furnaces are used.
A second characteristic configuration of the same is, as set forth in claim 2 in the same document, that the edge portion of air-supply mechanism may be configured to supply the air to the surface of a thermal-decomposition area, in addition to the first characteristic configuration described above. The thermal-decomposition area may be located on the upstream side beyond a melting area in which the surface of the treatment target melts in the furnace chamber.
Since the air supplied from the edge portion of air-supply mechanism is supplied to the surface of the thermal-decomposition area on the upstream side beyond the melting area, the volatilization of phosphorus contained in the treatment target is effectively suppressed.
A third characteristic configuration of the same is, as set forth in claim 3 in the same document, that the edge portion of air-supply mechanism may be configured to supply the air to cause the oxygen concentration on the surface of the thermal-decomposition area to be equal to or higher than 1 vol%, in addition to the second characteristic configuration described above.
If the air is supplied from the edge portion of air-supply mechanism so that the oxygen concentration on the surface of the thermal-decomposition area will be equal to or higher than 1 vol%, reduction reactions of phosphorus compounds and phosphorus oxides are effectively suppressed, and the volatilization of phosphorus is suppressed.
A fourth characteristic configuration of the same is, as set forth in claim 4 in the same document, that the edge portion of air-supply mechanism may include a uniformizing mechanism configured to uniformly supply the air to the surface of the treatment target, in addition to any one of the first to the third characteristic configurations described above.
Since the uniformizing mechanism evenly supplies the air to the surface of the treatment target, the volatilization of phosphorus is effectively suppressed over the whole area.
A fifth characteristic configuration of the same is, as set forth in claim 5 in the same document, that the uniformizing mechanism may include a swirler disposed on the edge portion of air-supply mechanism, in addition to the fourth characteristic configuration described above.
Since the swirler supplies the air in a diffusing manner, the air can be evenly supplied to the surface of the treatment target without configuring the installation intervals of air supply nozzles, for example, that constitute the edge portion of air-supply mechanism to be small.
A sixth characteristic configuration of the same is, as set forth in claim 6 in the same document, that the edge portion of air-supply mechanism may be configured to supply the air at a flow velocity lower than a scattering velocity of the treatment target, in addition to any one of the first to the fifth characteristic configurations described above.
The flow velocity of the air supplied toward the surface of the treatment target is adjusted so that the treatment target containing the combustible material will be melt-treated without scattering in the furnace. Accordingly, the volatilization of phosphorus is effectively suppressed without affecting the melt treatment.
A seventh characteristic configuration of the same is, as set forth in claim 7 in the same document, that the edge portion of air-supply mechanism may include a plurality of nozzles along a thermal-decomposition area, in addition to any one of the first to the sixth characteristic configurations described above. The thermal-decomposition area may be located on an upstream side beyond a melting area in which the surface of the treatment target melts in the furnace chamber.
Since the air is supplied from the nozzles disposed along the thermal-decomposition area, the air is evenly and uniformly supplied to the surface of the treatment target in the thermal-decomposition area, and the volatilization of phosphorus is effectively suppressed over a large area.
A eighth characteristic configuration of the same is, as set forth in claim 8 in the same document, that the edge portion of air-supply mechanism may include a tubular cavity and a plurality of nozzles, in addition to any one of the first to the seventh characteristic configurations described above. The tubular cavity may be formed in a refractory material layer constituting a furnace ceiling. The nozzles may extend from the cavity toward the furnace chamber.
When a plurality of nozzles are disposed on the furnace ceiling, the installation operation of accessory equipment such as an air-supply header pipe is required in addition to the operation to install the nozzles through a refractory wall of the furnace ceiling. In addition, the strength of the furnace ceiling may decrease.
However, if the tubular cavity is formed in the refractory material layer and the nozzles are disposed to extend from the cavity toward the furnace chamber, the tubular cavity functions as the air-supply header pipe. The need for installing a large accessory equipment such as the air-supply header pipe in the space above the furnace ceiling is thus eliminated. In addition, since the nozzles do not run through the furnace ceiling, the strength of the furnace can be sufficiently ensured.
A ninth characteristic configuration of the same is, as set forth in claim 9 in the same document, that a quantity of the air supplied from the edge portion of air-supply mechanism may be set to be within a range of 10% to 50% of a total quantity of air required for melt treatment, in addition to any one of the first to the eighth characteristic configurations described above.
The air supplied to the furnace chamber is supplied from the air supply mechanism in the furnace ceiling and the edge portion of air-supply mechanism. The thermal-decomposition gas generated by thermal decomposition on the surface of the treatment target flows up in the furnace chamber and combusts using the air supplied from the edge portion of air-supply mechanism and the air supply mechanism. The fixed carbon content on the surface of the treatment target combusts mainly using the air supplied from the edge portion of air-supply mechanism. The remainder of oxygen suppresses reduction reactions of phosphorus compounds and phosphorus oxides and thus suppresses the volatilization of phosphorus.
In this case, setting the quantity of the air supplied from the edge portion of air-supply mechanism to be within the range of 10% to 50% of the total quantity of the air required for melt treatment improves the consumption balance of air, increases the melt treatment efficiency, and effectively suppresses the volatilization of phosphorus.
A tenth characteristic configuration of the same is, as set forth in claim 10 in the same document, that an inner cylinder and an outer cylinder may be disposed concentrically, a gap between the inner cylinder and the outer cylinder may constitute the treatment-target container, the treatment-target supply mechanism may be configured to annularly supply the treatment target to the furnace chamber by relative rotation of the inner cylinder and the outer cylinder, and the edge portion of air-supply mechanism may be configured to supply the air toward the surface of the annular treatment target, in addition to any one of the first to the ninth characteristic configurations described above. The inner cylinder may be integrally formed around a furnace ceiling. The outer cylinder may be integrally formed around a furnace bottom.
Homogeneous melt treatment becomes possible if the edge portion of air-supply mechanism that supplies air toward the surface of the annular treatment target is disposed on the rotary surface melting furnace in which the treatment target is annularly supplied to the furnace chamber by relative rotation of the inner cylinder and the outer cylinder.
A characteristic configuration of a method for operating a surface melting furnace according to the present invention is, as set forth in claim 11 in the same document, that a method for operating a surface melting furnace includes putting a treatment target in a treatment-target container. The surface melting furnace includes a furnace chamber and a treatment-target supply mechanism. The furnace chamber has a slag port and includes a burner and an air supply mechanism. The treatment-target supply mechanism is configured to supply the treatment target to the furnace chamber from the treatment-target container around the furnace chamber. The treatment target contains phosphorus and a combustible material. Part of a total quantity of air required for melt treatment is supplied to the surface of the treatment target immediately after being supplied to the furnace chamber by the treatment-target supply mechanism to maintain the surface of the treatment target in an oxidizing atmosphere.
Part of the total quantity of the air required for melt treatment is supplied so that the oxidizing atmosphere will be maintained on the surface of the treatment target. Thus, the fixed carbon content remaining after the thermal decomposition combusts, and the remainder of oxygen suppresses reduction reactions of phosphorus compounds and phosphorus oxides and thus suppresses the volatilization of phosphorus.

EFFECTS OF INVENTION

As described above, the present invention has enabled provision of a surface melting furnace that can suppress the volatilization of phosphorus and improve melt treatment efficiency even when a treatment target containing phosphorus and a combustible material is melt-treated, and provision of a method for operating the surface melting furnace.

BRIEF DESCRIPTION OF DRAWINGS

[Fig. 1] Fig. 1 is an illustrative diagram of a rotary surface melting furnace according to the present invention.
[Fig. 2] Fig. 2A and Fig. 2B are illustrative diagrams of a main part of the rotary surface melting furnace.
[Fig. 3] Fig. 3A, Fig. 3B, and Fig. 3C are illustrative diagrams of a edge portion of air-supply mechanism.
[Fig. 4] Fig. 4 is an illustrative diagrams of a main part of the rotary surface melting furnace.
[Fig. 5] Fig. 5 is an illustrative diagram of a main part of the edge portion of air-supply mechanism.
[Fig. 6] Fig. 6A and Fig. 6B are illustrative diagrams of a main part of a surface melting furnace according to another embodiment.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

The following describes embodiments of a surface melting furnace and a method for operating the surface melting furnace according to the present invention.
Fig. 1 shows a rotary surface melting furnace 1 that is an embodiment of the surface melting furnace. The surface melting furnace 1 is a furnace for melt-treating a treatment target containing phosphorus and a combustible material. The surface melting furnace 1 includes a furnace chamber 4, a treatment-target container 7 disposed around the furnace chamber 4 and communicating with the furnace chamber 4, a treatment-target supply mechanism 8 that supplies the treatment target to the furnace chamber 4 communicating with the treatment-target container 7, and other components. On the approximately center of a furnace ceiling 2 of the furnace chamber 4, two auxiliary burners 10 provided with air supply mechanisms 11 are disposed. The furnace chamber 4 has a slag port 3 a on its furnace bottom 3.
An inner cylinder 5 integrally formed with the furnace ceiling 2 around the furnace ceiling 2 and an outer cylinder 6 integrally formed with the furnace bottom 3 around the furnace bottom 3 are disposed concentrically. The gap between the inner cylinder 5 and the outer cylinder 6 is configured to constitute the treatment-target container 7.
The lower part of the outer cylinder 6 has a portion for coupling a drive mechanism 13. The inner cylinder 5 and the outer cylinder 6 are configured to rotate relative to each other due to rotation of the outer cylinder 6 caused by the drive mechanism 13. A plurality of cutout blades 8 constituting the treatment-target supply mechanism are disposed on the lower part of the inner cylinder 5 along the circumferential direction.
The cutout blades 8 are constituted of plate-like sloping blades that guide the treatment target, which is moving in the tangential direction on the lower part of the inner cylinder 5 due to the rotation of the outer cylinder 6, to the furnace chamber 4. The cutout blades 8 due to the relative rotation of the inner cylinder 5 and the outer cylinder 6 annularly supplies the treatment target contained in the treatment-target container 7 to the furnace chamber 4, and the treatment target forms a bowl shape in the furnace chamber 4. When the treatment target has a high fluidity, relative rotation of the inner cylinder 5 and the outer cylinder 6 annularly supplies the treatment target to the furnace chamber 4 without the cutout blades 8.
In addition, the rotary surface melting furnace 1 includes a edge portion of air-supply mechanism 20 that supplies air toward the surface of the treatment target immediately after being supplied to the furnace chamber 4, in other words, a portion of the annular treatment target adjacent to a portion in which the treatment-target container 7 communicates with the furnace chamber 4, that is, to the surface of a thermal-decomposition area R1.
A water-sealing mechanism 14 water-seals a boundary between the outer cylinder 6 and an edge of a cover 5a extending from the upper part of the inner cylinder 5 toward the outer cylinder 6. A hopper 15 provided with a double damper mechanism 15a is disposed above the cover 5a. A screw conveyor mechanism 16 puts the treatment target into the treatment-target container 7. The furnace ceiling 2, the furnace bottom 3, the inner cylinder 5, and the outer cylinder 6 are constituted of refractory walls in which refractory bricks or other materials are stacked. A water-cooling jacket is disposed around the furnace ceiling 2 and a portion adjacent to the slag port of the furnace bottom 3 to cover the refractory walls in the furnace chamber 4 from the outside.
A water tank that catches molten slag produced by melting the treatment target is disposed below the slag port 3a. A flue is formed to laterally extend immediately below the slag port 3a. Exhaust-gas treatment equipment such as a secondary combustion device, heat recovery devices such as a waste-heat boiler and an air preheater, a cooling tower, a bag filter, a scrubber, and a white-smoke preventing device are disposed along the flue. Purified exhaust gas is emitted from a chimney.
The treatment targets containing phosphorus and combustible materials are mainly sewage sludge and include other waste such as animal and plant residues such as livestock excreta and food waste and pulverized municipal solid waste.
When starting up the rotary surface melting furnace 1, the auxiliary burners 10 are ignited to preheat the furnace chamber 4 to a temperature equal to or higher than 1,000°C. After that, the outer cylinder 6 is rotated via the drive mechanism 13 to supply the treatment target, and the auxiliary burners 10 are stopped after melting of the treatment target is started. After that, the treatment target continues to melt by spontaneous combustion. When the heat quantity from the spontaneous combustion does not meet the heat quantity required for the melting, use of the auxiliary burners 10 is continued.
The combustible material in treatment target put in the furnace chamber 4 is thermally decomposed by the furnace temperature in the thermal-decomposition area R1, which is an annular area within about 500 mm from the inner cylinder 5, which is a supply position to the furnace chamber, toward the slag port 3 a, which is the center of the furnace (see Fig. 2A). The thermal-decomposition gas generated combusts at a high temperature using the air supplied from the edge portion of air-supply mechanism 20 and the air supply mechanisms 11 in the furnace ceiling 2 (see Fig. 2B).
Fixed carbon and an inorganic material that are residues after thermal decomposition of the combustible material are heated to about 1,300°C by the radiant heat reflected by the furnace ceiling 2, for example. The fixed carbon component combusts in the solid state in the thermal-decomposition area R1 using the air supplied from the edge portion of air-supply mechanism 20 (see Fig. 2B). The inorganic material melts in a melting area R2, flows down toward the slag port 3 a while melting, and flows out of the slag port 3 a.
Combustion gas is induced toward the chimney by an induced draft fan on the downstream side of the flue, cooled and purified in the exhaust-gas treatment equipment described above, and emitted from the chimney. Air to be supplied from the air supply mechanisms 11 into the furnace is preheated to about 200°C by steam from the boiler, the air preheater, or another hot air generator.
The edge portion of air-supply mechanism 20 functions to supply air toward the surface of the treatment target just having been put into the furnace chamber 4 to suppress the volatilization of phosphorus contained in the treatment target. A quantity of the air supplied from the edge portion of air-supply mechanism 20 is preferably set to be within a range of 10% to 50% of the total quantity of air required for melt treatment.
The air supplied by the edge portion of air-supply mechanism 20 is supplied not in a direction swirling in the furnace but straightly toward the surface of the treatment target. Accordingly, a swirling flow is less likely to be generated in the furnace chamber 4, and the swirling force hardly acts on slag falling through the slag port. Possibilities of adhesion to the wall surface of a secondary chamber thus decrease.
The air supplied to the furnace chamber 4 is supplied from the air supply mechanisms 11 in the furnace ceiling 2 and the edge portion of air-supply mechanism 20. The thermal decomposition gas generated by the thermal decomposition of the combustible material on the surface of the treatment target flows up in the furnace chamber and combusts using the air supplied from the edge portion of air-supply mechanism 20 and the air supply mechanisms 11. The fixed carbon content on the surface of the treatment target combusts mainly using the air supplied from the edge portion of air-supply mechanism 20, and the fixed carbon content is also used to suppress the volatilization of phosphorus.
In other words, the air supplied from the edge portion of air-supply mechanism 20 toward the surface of the treatment target causes the fixed carbon content remaining on a portion adjacent to the surface of the treatment target after the thermal decomposition to combust. The remainder of oxygen suppresses reduction reactions of phosphorus compounds and phosphorus oxides and thus suppresses the volatilization of phosphorus.
Setting the quantity of the air supplied from the edge portion of air-supply mechanism 20 to be within the range of 10% to 50% of the total quantity of the air required for melt treatment improves the consumption balance of air, increases the melt treatment efficiency, and effectively suppresses the volatilization of phosphorus. The total quantity of the air required for melt treatment is about 1.0 to 1.2 times the value of the theoretical quantity of air required for combustion of the treatment target and the burners and is a value that is set as appropriate depending on properties of the treatment target. A quantity of air supplied from the edge portion of air-supply mechanism 20 of more than 50% of the total quantity of air acts to decrease the ambient temperature on the thermal-decomposition area R1 and decreases the treatment efficiency.
As described above, air is uniformly supplied to the thermal-decomposition area R1 and is efficiently supplied to the fixed carbon content by including the edge portion of air-supply mechanism 20 constituted of a plurality of nozzles disposed along the thermal-decomposition area R1 located on the upstream side beyond the melting area R2 in which the surface of the treatment target melts in the furnace chamber 4.
Accordingly, the volatilization of phosphorus is suppressed, the combustion speed in the thermal-decomposition area R1 increases, and the temperature increases due to generation of heat by combustion. This increase in the temperature further speeds up each of drying of the treatment target and thermal decomposition, combustion, and melting of the combustible material.
Accordingly, the melt-treatment efficiency is increased. The furnace can be configured to be smaller to obtain the same throughput, and the melting throughput increases when the same size of furnaces are used.
The edge portion of air-supply mechanism 20 is preferably configured to supply air so that the oxygen concentration on the surface of the thermal-decomposition area R1 will be equal to or higher than 1 vol%, and configured to supply air preferably at a flow velocity lower than a scattering velocity of the treatment target, more preferably at a flow velocity lower than a scattering velocity of the combustible material.
If the air supplied from the edge portion of air-supply mechanism 20 is supplied so that the oxygen concentration on the surface of the thermal-decomposition area R1 located on the upstream side beyond the melting area R2 will be equal to or higher than 1 vol%, reduction reactions of phosphorus compounds and phosphorus oxides are effectively suppressed, and accordingly the volatilization of phosphorus is suppressed.
In addition, the flow velocity of the air supplied toward the surface of the treatment target is adjusted so that the treatment target containing the combustible material will be melt-treated without scattering in the furnace. Accordingly, reduction reactions of phosphorus compounds and phosphorus oxides are effectively suppressed, and the volatilization of phosphorus is suppressed.
In other words, blocking of the exhaust-gas treatment equipment, the flue, and the like due to adhesion of volatilized phosphorus is prevented, or a time period until the blocking is extended, so that the melting equipment can be operated over a long period without cleaning or the like, and maintenance costs are reduced. In addition, decrease in phosphorus adhered to a heat exchanger enables stable heat recovery without decrease in the quantity of heat recovery, and reduces loads on a fan, which contributes to saving of energy.
The flow velocity of air at which the treatment target does not scatter in the furnace is not a numerical value fixed to a constant value but a value that varies widely depending on the average particle diameter, the average density, the percentage of moisture content, and the like of the treatment target and is set as appropriate in accordance with the treatment target. For example, when the treatment target is dry sludge having a percentage of moisture content of about 20 to 30% produced through drying treatment of sewage sludge, scattering is prevented if the flow velocity of air along the surface of the dry sludge is within a range of about 5 m/s to 6 m/s.
Specifically, the edge portion of air-supply mechanism 20 is configured to include a plurality of tubular nozzles 20a located on an outer peripheral-edge portion of the furnace ceiling 2 so as to be located on a circumference equally distant from the center of the furnace in a plan view, an annular air header pipe 21 that supplies air to the nozzles 20a, and an air supply pipe 22 that supplies to the air header pipe 21 air preheated to about 200°C by the air preheater or the like. Air to be supplied to the air supply mechanisms 11 is also supplied from the air supply pipe 22 via a flow control mechanism.
As shown in Fig. 3A, to supply air uniformly to the thermal-decomposition area R1 using the tubular nozzles 20a, for example, the tips of the cylindrical nozzles 20a may be located at a height of about 420 mm when air is supplied using the cylindrical nozzles 20a at a flow velocity of about 5 m/s on the surface of the treatment target because the air diffuses at a ratio of 0.6 in the radial direction to one unit of the distance in the shaft center direction of each of the cylindrical nozzles. In a surface melting furnace having a diameter of the furnace bottom 3 of 4 m, about 25 cylindrical nozzles 20a may be disposed.
As shown in Fig. 3B, when swirler nozzles 20b in which swirl vanes 20c are inserted into tubular nozzles are used, air becomes larger in diameter while swirling and is uniformly supplied to the surface of the treatment target. When the same quantity of air is pushed in, the number of the nozzles can be smaller than in the case the tubular nozzles 20a are used. The swirler nozzles 20b are an embodiment of a uniformizing mechanism that uniformly supplies air to the surface of the treatment target. As the uniformizing mechanism, a configuration in which a larger number of tubular nozzles are disposed can be employed.
In addition, as shown in Fig. 3C, use of flat nozzles 20d, which are another embodiment of the uniformizing mechanism, having slit-like nozzle tips can reduce the number of nozzles while more uniformly supplying air to the annular thermal-decomposition area R1.
Fig. 4 shows a state in which the nozzles 20a constituting the edge portion of air-supply mechanism 20 are disposed on the peripheral edge portion of the furnace ceiling 2. Each of the nozzles 20a is coupled to the air header pipe in the space above the nozzles.
Each of the nozzles 20a may be disposed in a vertical posture or in an posture facing a cutout portion in which the treatment target is cut out and supplied to the furnace chamber 4. The cutout portion is a portion in which the inner cylinder 5 intersects with the thermal-decomposition area R1, in other words, in which the furnace chamber 4 communicates with the treatment-target container 7.
In the embodiments described above, the example in which the annular air header pipe 21 is disposed in the space above the furnace ceiling 2 to supply air to each of the nozzles 20a has been described. However, each of the nozzles 20a is required to be disposed through the furnace ceiling 2 in this case, and the strength of the furnace ceiling 2 may decrease.
For this reason, as shown in Fig. 5, an annular cavity 2b may be formed in a refractory wall 2a constituting the furnace ceiling 2, and the cavity 2b may be configured to be the air header pipe 21. Openings 2c facing the furnace chamber may be then formed on the lower face of the cavity 2b at predetermined intervals, and paths 2d in the refractory wall to the openings 2c may be configured to function as the nozzles 20a.
Such a configuration enables air to be supplied to the cavity 2b through a through hole formed in one place on the upper side of the furnace ceiling 2, and the configuration can prevent the strength of the furnace ceiling 2 from decreasing.
In the embodiments described above, the case in which the surface melting furnace is the rotary surface melting furnace 1 has been described as an example. The surface melting furnace according to the present invention is, however, not limited to the rotary surface melting furnace 1 and can be applied to other types of surface melting furnaces, needless to say.
For example, the present invention can be applied to a surface melting furnace 1 having the slag port 3a at the center of the furnace bottom 3 and including a plurality of push-in mechanisms 30 for inputting the treatment target disposed around the furnace bottom 3, as shown in Fig. 6A. This surface melting furnace is a type of surface melting furnace in which both the outer cylinder 6 constituted integrally with the furnace bottom 3 and the inner cylinder 5 constituted integrally with the furnace ceiling 2 are secured, and the push-in mechanisms 30 supply the treatment target into the furnace.
As shown in Fig. 6B, the present invention can be applied to a surface melting furnace 1 having the slag port 3 a at the edge of the furnace bottom 3 and including a plurality of push-in mechanisms 30 for inputting the treatment target disposed on the opposite side. In any of these embodiments, the push-in mechanisms 30 are the treatment-target supply mechanism.
In other words, the present invention is only required to be a surface melting furnace including a edge portion of air-supply mechanism that supplies air for suppressing reduction of phosphorus compounds and phosphorus oxides contained in a treatment target and for gasifying a combustible material, toward the surface of the treatment target containing phosphorus and the combustible material just having been put into a furnace chamber by a treatment-target supply mechanism.
As described above, the method for operating a surface melting furnace according to the present invention is a method for operating the surface melting furnace including a furnace chamber having a slag port and including a burner and an air supply mechanism, and a treatment-target supply mechanism configured to supply a treatment target to the furnace chamber from a treatment-target container around the furnace chamber. The method includes putting the treatment target containing phosphorus and a combustible material in the treatment-target container, and supplying part of a total quantity of air required for melt treatment to the surface of the treatment target immediately after being supplied to the furnace chamber by the treatment-target supply mechanism to maintain the surface of the treatment target in an oxidizing atmosphere.
In the embodiments described above, the example in which gas containing oxygen is used as air has been described. However, the air is only required to contain oxygen. The atmospheric air may be used as it is, or air that has been subjected to a process of enriching oxygen or reducing nitrogen may be used.
The embodiments described above are only examples of the present invention. A specific configuration of each component can be modified and designed as appropriate as long as the operations and effects of the present invention can be obtained.

DESCRIPTION OF SYMBOLS

1:: Surface melting furnace
2:: Furnace ceiling
3:: Furnace bottom
3a:: Slag port
4:: Furnace chamber
5:: Inner cylinder
6:: Outer cylinder
8:: Treatment-target supply mechanism
20:: Edge portion of air-supply mechanism

Claims

A surface melting furnace configured to melt-treat a treatment target,
the treatment target comprising:
phosphorus; and

a combustible material,
the surface melting furnace comprising:
a furnace chamber having a slag port, the furnace chamber comprising:
a burner; and

an air supply mechanism;

a treatment-target supply mechanism configured to supply the treatment target to the furnace chamber from a treatment-target container communicating with the furnace chamber; and

a edge portion of air-supply mechanism configured to supply air toward a portion of a surface of the treatment target in the furnace chamber, the portion adjacent to a portion in which the treatment-target container communicates with the furnace chamber.
The surface melting furnace according to claim 1,
wherein the edge portion of air-supply mechanism is configured to supply the air to a surface of a thermal-decomposition area, the thermal-decomposition area being located on an upstream side beyond a melting area in which the surface of the treatment target melts in the furnace chamber.
The surface melting furnace according to claim 2,
wherein the edge portion of air-supply mechanism is configured to supply the air to cause an oxygen concentration on the surface of the thermal-decomposition area to be equal to or higher than 1 vol%.
The surface melting furnace according to any one of claims 1 to 3,
wherein the edge portion of air-supply mechanism comprises a uniformizing mechanism configured to uniformly supply the air to the surface of the treatment target.
The surface melting furnace according to claim 4,
wherein the uniformizing mechanism comprising a swirler disposed on the edge portion of air-supply mechanism.
The surface melting furnace according to any one of claims 1 to 5,
wherein the edge portion of air-supply mechanism is configured to supply the air at a flow velocity lower than a scattering velocity of the treatment target.
The surface melting furnace according to any one of claims 1 to 6,
wherein the edge portion of air-supply mechanism comprises a plurality of nozzles along a thermal-decomposition area, the thermal-decomposition area being located on an upstream side beyond a melting area in which the surface of the treatment target melts in the furnace chamber.
The surface melting furnace according to any one of claims 1 to 7,
wherein the edge portion of air-supply mechanism comprising:
a tubular cavity in a refractory material layer constituting a furnace ceiling; and

a plurality of nozzles extending from the cavity toward the furnace chamber.
The surface melting furnace according to any one of claims 1 to 8,
wherein a quantity of the air supplied from the edge portion of air-supply mechanism is set to be within a range of 10% to 50% of a total quantity of air required for melt treatment.
The surface melting furnace according to any one of claims 1 to 9,
wherein an inner cylinder integrally formed around a furnace ceiling and an outer cylinder integrally formed around a furnace bottom are disposed concentrically,
wherein a gap between the inner cylinder and the outer cylinder constitutes the treatment-target container,
wherein the treatment-target supply mechanism is configured to annularly supply the treatment target to the furnace chamber by relative rotation of the inner cylinder and the outer cylinder, and
wherein the edge portion of air-supply mechanism is configured to supply the air toward a surface of the annular treatment target.
A method for operating a surface melting furnace,
the surface melting furnace comprising:
a furnace chamber having a slag port, the furnace chamber comprising:
a burner; and

an air supply mechanism; and

a treatment-target supply mechanism configured to supply a treatment target to the furnace chamber from a treatment-target container around the furnace chamber,

the method comprising:
putting the treatment target in the treatment-target container, the treatment target comprising:
phosphorus; and

a combustible material; and

supplying part of a total quantity of air required for melt treatment to a surface of the treatment target immediately after being supplied to the furnace chamber by the treatment-target supply mechanism to maintain the surface of the treatment target in an oxidizing atmosphere.