In-Furnace Gas Injection Port

Abstract

Tertiary nozzle of port for gas injection into furnace includes a contracted flow producing channel provided obliquely toward central axis from the upstream side of gas flow so that the gas flow has a velocity component heading from the outer circumferential side of the port toward the central axis and a velocity component heading along the central axis toward the interior of the furnace, and including louver disposed for guiding so that the gas flows along the surface of throat wall of enlarged pipe configuration wherein the gas channel is enlarged at a furnace wall opening disposed at an outlet area of the contracted flow producing channel. Accordingly, there can be provided a gas injection port that not depending on conditions, such as the flow rate of gas injected from the port, without inviting any complication of apparatus structuring or cost increase, enables preventing of the growth in lump form of clinker caused by ash adhesion and fusion on the wall surface of throat enlarged pipe portion of the furnace.

Description

TECHNICAL FIELD

The present invention relates to a port for gas injection into a furnace such as a boiler, and in particular to a port for gas injection into a furnace such as a boiler advantageous in preventing ash adhesion to a furnace opening.

BACKGROUND ART

Various types of ports for injecting gas such as air and exhaust gas into a furnace are disposed on the wall of a furnace such as a boiler. They include, for example, a burner for injecting fuel and combustion air as a combustion apparatus and an after air port (AAP) (which is also referred to as an over firing air port (OFA)) for feeding two-stage combustion air. The gas injection port described in the present specification is not limited to an after air port but includes a port for feeding exhaust gas and a burner port for combusting fuel, as long as it is a port for injecting gas into a furnace. Further, a wall surface of an enlarged pipe configuration opened on a furnace on which the port is disposed is to be referred to as a throat wall or a throat enlarged pipe portion (a furnace wall surface portion at which the opening is gradually increased in diameter toward the outlet side of the furnace).

Of these ports, there is aport in which such an appropriate structure is adopted that gas injection flow from the outer circumferential side of the port toward the central axis direction is increased and allowed to pass through a throat wall in such a manner that the gas injection flow can arrive at the center of a furnace to facilitate gas mixture in the vicinity of the furnace wall, thereby providing a so-called contracted flow, which is a flow involving gas around the throat wall while the gas injection flow concentrates on the central axis of the port.

Patent Documents 1 and 2 given below have disclosed inventions of after air ports for feeding into a furnace two-stage combustion air which involves the contracted flow.

In a structure of a gas injection port appropriate in forming the contracted flow of the gas injection in the vicinity of a port opening, there is a possibility that clinker may grow in lump form by ash adhesion and fusion on the throat wall of a furnace and clinker in lump form may be detach or drop off from the wall surface, thereby inhibiting the function and performance of the port.

Further, as techniques for preventing the growth of clinker in lump form caused by ash adhesion and fusion on the throat wall opened on a furnace, there are inventions such as a pulverized coal burner (Patent Document 3), a burner throat wall (Patent Document 4) and an over firing air port (Patent Document 5) for preventing adhesion of clinker on the throat wall.

Still further, as low NOx combustion technology for keeping the concentration of nitrogen oxides (NOx) in conventional exhaust gas to a lower level, there has been employed a two-stage combustion method. The present inventor and others have been engaged in development of an after air port (AAP) for supplying insufficient combustion air for completely burning combustion gas which has been reduced and burnt by a burner.

AAPs have been so far developed, mainly aiming at providing such a structure that is able to prevent the escape of unburned gas from a burner combustion region inside a furnace. FIG. 13 shows a structural diagram of a conventional rotating-type AAP.

In the AAP shown in FIG. 13, primary air 9 is supplied to a furnace 34 through a primary nozzle 1. A secondary nozzle 2 is mounted on the outer circumference of the primary nozzle 1, thereby supplying secondary air 10.

It is necessary to arrange properly the above-structured AAP on the furnace 34. However, there is a limit to the number of AAPs that can be arranged. Thus, for the purpose of enhancing a mixture of air with unburned gas in the vicinity of the AAPs and at the center of the furnace 34, the secondary nozzle 2 is structured so as to be provided with a rotator 7, a rotating secondary air flow obtained by the rotator 7 is used for mixing air with unburned gas inside the furnace 34 in the vicinity of the AAPs, and a strong air injection flow from the primary nozzle 1 to the center of the furnace 34 is used to mix air with unburned gas (Patent Document 6).

Further, the rotating secondary air flow obtained by using the rotator 7 is insufficient in spreading the rotating air flow and there is a case where unburned gas may not be well mixed with combustion air at a region along the inner wall 34a of the furnace 34. As a method for coping with the above problem, the present applicant has proposed an AAP equipped with a tertiary nozzle for tertiary air having a drift unit capable of supplying combustion air to the outer circumference of the secondary nozzle 2 having the rotator 7 in a direction along the inner wall 34a of the furnace 34 (Patent Document 7).

Patent Document 1: Japanese Published Unexamined Patent

Application (JP-A) No. 2006-132811

Patent Document 2: JP-A No. 2006-132798

Patent Document 3: Japanese Published Unexamined Utility Model Application No. 6-6909

Patent Document 4: Japanese Patent No. 3668989

Patent Document 5: JP-A No. Hei-10-122546

Patent Document 6: JP-A No. Sho-62-138607

Patent Document 7: JP-A No. Hei-9-112816

DISCLOSURE OF THE INVENTION

When a gas injection flow, such as air concentrated from the outer circumferential side of the above-described port toward the central axis direction, or a so-called contracted flow, is increased in effects, ambient gas is strongly involved by the contracted flow inside a furnace in the vicinity of an opening of the port, thereby combustion ash associated with gas is more often brought into contact with the wall surface of a throat enlarged pipe portion particularly in a coal-burning boiler. According to conventional techniques, where the contracted flow of the gas injection flow is increased in effects, ash adhesion or growth of clinker is not effectively prevented particularly on a furnace throat wall of a burner port.

According to the description of Patent Document 4, high-pressure injection air for aspiration is used for suppressing partial adhesion of ash to the wall surface of the throat portion with the lapse of time, by which a system may be complicated in structure or there may be an increase in cost and weight. Further, according to the invention described in Patent Document 3, when the gas flow heading from the outer circumferential side of the furnace throat wall of the burner port toward the central axis direction is increased to enhance the effects of the contracted flow, there may be a decrease in effectively preventing ash adhesion to the wall surface of the throat enlarged pipe portion.

Further, in the invention described in Patent Document 5, when the gas flow heading from the outer circumferential side of an airport toward the central axis of the port is increased to enhance the effects of the contracted flow, there may be a decrease in effectively preventing ash adhesion to the throat wall of a furnace.

A sufficient effect in preventing ash adhesion may not also be obtained in a case where the flow rate of gas such as air for preventing the adhesion of ash to the throat wall of the furnace must be reduced in order to keep a predetermined air ratio.

Still further, in a conventional AAP disclosed in Patent Document 6 and others, it is difficult to carry unburned gas around the AAP by using a rotating air flow, while a penetrating force is kept with a strong air injection flow.

In addition, in a simply-structured AAP disclosed in Patent Document 7 or others in place of the rotating-type AAP, it is possible to prevent the escape of unburned gas at a region along the inner wall 34a of the furnace 34 and ash adhesion to the furnace wall surface. However, there may be a slight shortage of air injection flow for combustion arriving at the center of the furnace 34, thus resulting in a possible failure in a quick mixture of unburned gas with air.

An object of the present invention is to provide a gas injection port which is able to prevent the growth of clinker in lump form caused by ash adhesion and fusion to the wall surface of a throat enlarged pipe portion of a furnace irrespective of conditions such as the flow rate of injection gas or without inviting a complicated structure of a system or cost increase, and where air is used as gas, combustion air in the vicinity of the furnace wall is stably mixed with unburned gas, and the combustion air is reliably brought to the center inside the furnace, thus making it possible to decrease the concentration of NOx in combustion gas.

The above object can be obtained by the following solutions.

The invention described in claim 1 is an in-furnace gas injection port which is disposed on a furnace wall of the furnace, comprising a contracted flow producing channel having a velocity component flowing toward the central axis of gas flow perpendicular to the furnace wall and a velocity component flowing along the central axis, and provided obliquely toward the central axis from the upstream side of gas flow, a throat enlarged pipe portion in which a gas channel formed on a furnace wall opening on the downstream side of the contracted flow producing channel is gradually enlarged in a direction of the gas flow, and a louver (guide plate) which is disposed on the contracted flow producing channel for guiding gas flowing through the contracted flow producing channel so as to flow along the wall surface of the throat enlarged pipe portion.

Gas guided by the louver as constituted in the invention of claim 1 effectively flows in the vicinity of the wall surface of the throat enlarged pipe portion, thereby eliminating a negative pressure in the vicinity of the wall surface of the enlarged pipe portion. Therefore, gas flowing along the wall surface on the outer circumference (a nozzle partition wall constituting the channel) of the contracted flow producing channel can be effectively guided to the wall surface side of the throat enlarged pipe portion, thereby it is less likely to cause ash adhesion to the throat enlarged pipe portion and the wall surface in the vicinity thereof due to the involvement of ash. Further, conventionally, an injection hole for injecting a coolant such as air is disposed separately at a gas injection port in place of a louver. As compared with the above case, the invention described in claim 1 is able to reduce the pressure loss resulting from gas injection flow by using the louver and simplified in structure, thus eliminating a necessity for providing a sealing air adjustor for preventing the ash adhesion and attaining a reduction in weight of a system and the saving of iron and steel products.

Further, the gas flow injected from the contracted flow producing channel of the invention described in claim 1 covers a gas flow arriving at the central portion inside the furnace and a gas flow accelerating a mixture of gas in the vicinity of the furnace wall, by which the gas injection port can be used as an AAP for a two-stage combustion burner to attain a highly reliable fuel combustion which is lower in NOx and CO combustion.

The invention described in claim 2 is the in-furnace gas injection port described in claim 1 in which the leading end of the louver on the upstream side of gas flow is located on a surface obtained by extending the outer circumferential wall surface of the contracted flow producing channel toward the central axis direction or on the upstream side of gas flow from the thus extended surface and an enlarged pipe portion gradually enlarged in a direction of gas flow so as to run along the wall surface of the throat enlarged pipe portion is provided at the downstream side portion of gas flow of the louver.

Incidentally, where a so-called contracted flow in which a gas injection flow flowing through the contracted flow producing channel of the present invention flows toward the central axis of a gas injection port is relatively increased, there is developed a negative pressure in the vicinity of the wall surface of the throat enlarged pipe portion disposed at a port opening of the furnace at which the port is disposed, thereby ash is more likely to adhere to the wall surface of the throat enlarged pipe portion. In this instance, a case where the contracted flow of gas is increased is, for example, a case where a gas channel on the upstream side of the gas flow at the port disposed on the furnace wall surface is made up of only the contracted flow producing channel, or a case where the flow ratio of the contracted flow producing channel is 30% or more if another channel is available, a case where a radius of the throat portion on the furnace wall (length Ds given in FIG. 10) is 1.1 times or lower than a radius (length Db given in FIG. 10) at the inner circumferential downstream end of the contracted flow producing channel (site b given in FIG. 10), or a case where an inclined angle is from 30° to 70° with respect to the central axis of the port on the contracted flow producing channel.

According to the invention described in claim 2, the leading end portion of the louver on the upstream side of gas flow is located on a surface obtained by extending the outer circumferential wall surface of the contracted flow producing channel to the central axis direction or on the upstream side of gas flow from the thus extended surface. Therefore, gas guided into the louver flows effectively in the vicinity of the wall surface of the throat enlarged pipe portion, thereby eliminating a negative pressure in the vicinity of the wall surface of the enlarged pipe portion. As a result, gas flowing along the outer circumferential wall surface of the contracted flow producing channel (a nozzle partition wall constituting the channel) is effectively guided to the wall surface side of the throat enlarged pipe portion, thereby it is less likely to cause ash adhesion to the wall surface in the vicinity of the throat enlarged pipe portion due to the involvement of ash.

As described so far, according to the invention described in claim 2, in addition to the effects obtained by the invention described in claim 1, gas is guided to the louver, thus making it possible to further prevent ash adhesion to the throat enlarged pipe portion.

The invention described in claim 3 is the in-furnace gas injection port described in claim 1 or claim 2 which is provided with a mechanism for changing the ratio of a velocity component of air flow flowing through the contracted flow producing channel along the central axis to a velocity component of air flow flowing toward the central axis.

According to the invention described in claim 3, the ratio of a velocity component flowing along the central axis direction to a velocity component flowing toward the central axis direction is changed, thus making it possible to adjust a direction of gas injection flow after each of the velocity components inside a furnace is merged. Where gas is air, an air-short unburned gas region localized inside the furnace is favorably mixed with combustion air, thereby reducing an unburned portion of fuel. Further, these two velocity components are adjusted for the rotating strength, thus making it possible to adjust a mixture state of gas after being merged.

The invention described in claim 4 is the in-furnace gas injection port described in claim 3 which is provided with a damper starting to open from the near surface side to the furnace so that gas flows along the outer circumferential wall surface of the contracted flow producing channel and capable of adjusting an aperture of the contracted flow producing channel.

According to the invention described in claim 4, in a case where the damper is moved from a state that the contracted flow producing channel is kept closed toward a direction at which the channel is opened to adjust an aperture of the channel, if the damper is started to open from the near surface side to the furnace of the contracted flow producing channel, air flows into a part closer to the throat enlarged pipe portion inside the contracted flow producing channel even in a state that the gas flow rate flowing through the contracted flow producing channel is reduced (a state that the damper is almost closed). As a result, gas is guided into a louver, thereby preventing ash adhesion to the throat enlarged pipe portion.

The invention described in claim 5 is the in-furnace gas injection port described in any one of claims 1 through 4 which is provided with a rotating member for rotating gas between the louver and the wall surface of the throat enlarged pipe portion. It is noted that in order to absorb a heat stretching difference, the louver may be divided into a plurality of louvers in a circumferential direction of the gas injection port and disposed.

According to the invention described in claim 5, gas flowing between the louver and the wall surface of the throat enlarged pipe portion is rotated by means of the rotating member and can be injected into the furnace. Therefore, some of the contracted flow can easily flow from the contracted flow producing channel into a space between the louver and the wall surface of the throat enlarged pipe portion, and a gas flow which seals the inner wall surface of the furnace flows effectively in the vicinity of the wall surface of the throat enlarged pipe portion, thereby eliminating a negative pressure in the vicinity of the wall surface of the throat enlarged pipe portion. As a result, it is possible to prevent ash adhesion in the vicinity of the furnace wall surface of the throat enlarged pipe portion due to the involvement of ash.

The invention described in claim 6 is the in-furnace gas injection port described in any one of claims 1 through 5, in which a length of the throat enlarged pipe portion in a gas flow direction formed at the downstream side end portion of the louver is ½ or lower than a length of the wall surface of the throat enlarged pipe portion in a gas flow direction.

According to the invention described in claim 6, where a length of the throat enlarged pipe portion in a gas flow direction formed at the downstream end of the louver is ½ or lower than a length of the wall surface of the throat enlarged pipe portion in a gas flow direction, ash is less likely to adhere to an exposed surface inside the enlarged pipe portion of the louver (a surface between the e portion and the f portion in FIG. 12).

The invention described in claim 7 is the in-furnace gas injection port described in any one of claims 1 through 6 in which the contracted flow producing channel is given as a tertiary nozzle and a primary nozzle is disposed inside from the tertiary nozzle and a secondary nozzle is disposed outside the primary nozzle, through which each gas flows along the central axis.

According to the invention described in claim 7, if the gas injection port is used as an AAP disposed on the furnace wall at the downstream portion of a two-stage combustion burner, no ash is adhered to the furnace wall, thus making it possible to attain a highly reliable fuel combustion which is lower in NOx and CO combustion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a boiler in which an after air port or a burner of the present invention is used.

FIG. 2 is a schematic sectional view of the after air port of Embodiment 1 in the present invention.

FIG. 3 is a perspective view in which the after air port of Embodiment 1 is partially omitted.

FIG. 4 is a drawing in which the air port is viewed from the inside of a furnace of Embodiment 1.

FIG. 5 is a flow velocity distribution diagram of air flow at an AAP outlet portion obtained by using an AAP model in FIG. 2.

FIG. 6 is a flow velocity distribution diagram of air flow at the AAP outlet portion obtained by using the AAP model in FIG. 2.

FIG. 7 is a flow velocity distribution diagram of air flow at the AAP outlet portion obtained by using the AAP model in FIG. 2.

FIG. 8 is a schematic sectional view showing an after air port of Embodiment 2 of the present invention.

FIG. 9 is a schematic sectional view showing an after air port in which a louver of a comparative example in comparison with Embodiment 2 of the present invention is disposed along the furnace throat enlarged pipe portion.

FIG. 10 is a schematic sectional view showing an after air port in which a louver of a comparative example in comparison with Embodiment 2 of the present invention is disposed on a tertiary nozzle.

FIG. 11 is a schematic sectional view of an after air port of Embodiment 3 of the present invention.

FIG. 12 is a schematic sectional view of a part of the after air port for explaining the dimensional relationship where the louver of Embodiment 3 of the present invention and the throat enlarged pipe portion are arranged inside the after air port.

FIG. 13 is a schematic sectional view of an after air port of Embodiment 4 of the present invention.

FIG. 14 is a longitudinal sectional view showing an AAP structure according to a conventional technique.

FIG. 15 is a longitudinal sectional view of an AAP structure according conventional technique.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an explanation will be made for the air port of the present invention and the usage thereof by referring to the drawings.

First, an explanation will be made for a two-stage combustion boiler in which the after air port of the present invention is used by referring to an entire structure of the boiler given in FIG. 1.

A plurality of burners 30 are arranged so as to face each other on a pair of facing furnace walls of the furnace 34 of a boiler, and after air ports 31 are disposed so as to face each other above a place at which the burners are placed. An air fuel mixture of less than a theoretical air ratio (for example, 0.8) is injected into a flame region inside the furnace 34 from the burners 30, thereby forming an incomplete combustion region (not illustrated) inside the furnace. The after air ports 31 are to supply air insufficient in effecting combustion to combustible gas at the incomplete combustion region, thereby facilitating the combustion.

In the present embodiment, fuel to be supplied to the burners 30 is supplied to the burners 30 from a pulverized coal supply line 33 as pulverized coal which is obtained by crushing coal inside a bunker 29 by means of a mill 35. Additionally, a total air quantity for coal combustion is controlled by an air supply system, and the air quantity is distributed to the burners 30 and the after air ports 31. More specifically, air supplied from a blower 36 is branched into an air supply line 37a on the burners 30 side and an air supply line 37b on the after air ports 31 side, which are respectively guided from window boxes 39a, 39b into the burners 30 and the after air ports 31.

Distribution of air flow rate to the line 37a and the line 37b is adjusted by the damper 40a on the burners 30 side and the damper 40b on the after air ports 31 side. The blower 36 is controlled for the output so that a total air flow rate gives a value having specified oxygen concentrations of exhaust gas.

Air of less than a theoretical air ratio is supplied from the air supply line 37a to the burners 30 and pulverized coal is also pneumatically delivered from the pulverized coal supply line 33 thereto. An air fuel mixture injected from the burners 30 into the furnace 34 is less than air quantity necessary for effecting complete combustion, thus resulting in incomplete combustion. At this time, it is possible to reduce NOx. Since fuel undergoes incomplete combustion, a flow of combustible gas is formed downstream of the burners 30.

Air entered through the air supply line 37b into the window box 39b of the after air ports 31 is distributed into a primary nozzle 1, a secondary nozzle 2 and a tertiary nozzle 3 of the air ports 31 to be described later, and supplied to the flow of combustible gas (incomplete combustion region) inside the furnace. The air is mixed with the flow of combustible gas to effect complete combustion, giving combustion gas, thereby heating water and vapor by heat exchangers 42 such as a superheater, evaporator, fuel economizer, and a reheater mounted inside the furnace 34 to produce steam, and thereafter flowing into an outlet of the furnace 34. Further, boiler water pipes (not illustrated) are arranged on the wall surface of a boiler furnace and heated by combustion of fuel inside the furnace 34 to produce steam.

EMBODIMENT 1

Next, an explanation will be made for aspects of the after airport (hereinafter referred to as “port” or “AAP”) 31 applied to the boiler furnace 34 by referring to the following embodiments.

FIG. 2 is a sectional view of the port 31 in the present embodiment (a sectional view taken along line A-A′ in FIG. 4). FIG. 3 is a perspective view in which the port 31 is partially omitted. FIG. 4 is a drawing of the port 31 which is viewed from the furnace 34 side.

The port 31 is arranged inside the window box 39b, and the air nozzle mechanism thereof is provided with a primary nozzle 1, a secondary nozzle 2 for injecting air of rotating flow along the outer circumference of the primary nozzle 1 as secondary air 10 and a tertiary nozzle 3 for injecting air of flow heading from the outside of the primary nozzle 1 to the central axis C of the port 31 as tertiary air 11.

The primary nozzle 1, the secondary nozzle 2 and the tertiary nozzle 3 are of a coaxial nozzle structure. The primary nozzle 1, the secondary nozzle 2 and the tertiary nozzle 3 are arranged respectively at the center, outside the primary nozzle 1 and outside the secondary nozzle 2. The primary nozzle 1 is formed in a straight tubular shape, having an air injection hole 1A (FIG. 3) at the front end and an air intake hole 1B at the rear end. A primary damper 5 adjusts an opening area of the air intake hole 1B, thereby adjusting the flow rate of primary air. The primary nozzle 1 injects air of straight advancing flow parallel to the central axis C of the port 31 as primary air 9. The opening area of the air intake hole 1B can be changed by allowing the primary damper 5 to slide on the outer circumference of the primary nozzle 1 by means of an adjusting lever 15 connected to the primary damper 5 to have a handle outside the window box 39b.

The secondary nozzle 2 is provided with an annular air intake hole 2B (FIG. 3) at the rear end, and a tubular secondary air channel is formed between the inner circumference of the secondary nozzle 2 and the outer circumference of the primary nozzle 1. Secondary air 10 flowing from the air intake hole 2B is given a rotating force by a secondary air resistor (a deflection plate) 7, injected from the secondary nozzle outlet (front end) 2A in association with a rotating flow along the outer circumference of the primary nozzle 1. An opening area of the air intake hole 2B on the secondary nozzle 2 can be changed by allowing the secondary damper 6 to slide toward the central axis C of the port 31 by means of an adjusting lever 16 connected to a cylindrical secondary damper 6 to have a handle outside the window box 39b, by which the flow rate of the secondary air is adjusted. A plurality of secondary air resistors 7 are attached to a secondary air intake hole 2B by operating a resistor drive 13 to activate a cooperating mechanism (not illustrated) so that the deflection angle thereof can be similarly changed via a supporting axis 7a and arranged at the secondary air intake hole 2B in a circumferential direction. The secondary air resistors 7 are changed in deflection angle, thus making it possible to change a rotating force imparted to the secondary air 10.

The tertiary nozzle 3 is provided with a conical front wall 301 and a conical rear wall 302 arranged so as to face the front wall 301, and a conical air channel of the tertiary nozzle 3 is formed between the front wall 301 and the rear wall 302. An air intake hole 3B of the tertiary nozzle 3 (FIG. 3) is formed in an annular shape, and the opening area can be changed by allowing a tertiary damper 8 to slide along the central axis C of the port 31 by means of an adjusting lever 17 which is connected to the cylindrical tertiary damper 8 and provided with a handle outside the window box 39b, by which the flow rate of tertiary air is adjusted. The front wall 301 is coupled to the rear wall 302 via a plurality of connection plates 4 arranged at the air intake hole 3B. The outlet 3A of the tertiary nozzle 3 is connected to the leading end of the secondary nozzle 2 and formed in such a manner that tertiary air 11 is merged with secondary air 10 and injected into the furnace 34 as air flow 12.

In this instance, the secondary air 10 which has flown into the secondary nozzle 2 flows into the furnace 34 in a direction parallel to the central axis C of the port 31. Further, the secondary air 10 is given a rotating force from the secondary air resistor 7 and injected into the furnace 34. On the other hand, the tertiary nozzle 3 is inwardly inclined to a direction of the central axis C of the port 31, and tertiary air 11 flowing into the tertiary nozzle 3 is preferably structured in forming a contracted flow concentrating on the port 31 in a direction of the central axis C. A flow ratio of the secondary air 10 to the tertiary air 11 is changed, thus making it possible to adjust a direction at which the air flow 12 is injected after the secondary air 10 is merged with the tertiary air 11.

For example, on the assumption that a flow rate of the tertiary air 11 is set to be 0, an inward velocity component of air flow 12 after the secondary air 10 is merged with the tertiary air 11 (a velocity component heading toward the center of the air flow 12) is given as 0. Further, on the assumption that a flow rate of the secondary air 10 is set to be 0, the air flow 12 is increased in inward velocity component occupied by the tertiary air 11 and then injected in a direction at which the tertiary nozzle 3 is inclined (an obliquely inward direction) The air flow 12 is adjusted for the injection direction, by which an air-short unburned gas region localized inside the furnace 34 is preferably mixed with combustion air to reduce an unburned portion of fuel. Further, a state of mixture can be adjusted by a rotating strength of the secondary air 10.

In order to adjust an air flow ratio of the primary air 9 to the secondary air 10 to the tertiary air 11 at the port 31, the primary damper 5, secondary damper 6 and tertiary damper 8 are used.

Fuels such as coal and heavy oil contain ash therein. Where these fuels are used, the tertiary air 11 is increased in flow rate and the air flow 12 is concentrated on the port 31 in a direction of the central axis C to give a so-called contracted flow, thus causing a greater turbulence around the contracted flow. Therefore, ambient combustion gas can be easily associated by the contracted flow, and ash fused in a high-temperature combustion gas 25 rising inside the furnace 34 may also be associated and adhered in the vicinity of a water pipe 23 at an outlet of the port 31 to form an ash adhesion layer 18. This state is shown graphically in a sectional view of the port 31 given in FIG. 14.

When the ash adhesion layer 18 grows to form clinker, it may hinder air fluidity or cause the breakage of the water pipe 23 due to falling off of the clinker. In these instances, it is necessary to reduce the potential for ash adhesion to an outlet portion of the port 31.

FIG. 5 to FIG. 7 show a mechanism of ash adhesion and preventive measures.

FIG. 5 to FIG. 7 show the flow velocity distribution (data based on observed results) at the outlet of the port 31. The longitudinal axis indicates a distance of an AAP from the central axis C in a range from −100 to 2300 mm, with C given as an original point, whereas the horizontal axis indicates a distance from the AAP inside the furnace 34 in a range from 0 to 5000 mm. In the flow rate distribution diagrams, brown indicates a range of 25 to 30 m/s; red, 20 to 25 m/s; pink, 15 to 20 m/s; yellow, 10 to 15 m/s; green, 5 to 10 m/s; blue, 0 to 5 m/s; mazarine, −5 to 0 m/s; and dark mazarine, −10 to −5 m/s. It is noted that minus symbols in mazarine and dark mazarine indicate reverse flow regions. Further, the AAP model used was of a life size (an AAP with dimensions applicable to a 1000 MW boiler), and the experiment was conducted at an air flow rate corresponding to that of an actual machine. However, since the air temperature was an ordinary temperature, the flow velocity was decreased in absolute value. The flow was measured by changing the flow rate of rotating air of the secondary air 10 and that of the primary air 9, with the contracted flow rate of the tertiary air 11 kept constant.

FIG. 5 is a flow velocity distribution diagram of the furnace 34 in a case where the rotation-free straight advancing primary air 9, the secondary air 10 and the tertiary air 11 flow in the respective quantities of 14%, 62% and 24% as a total. From this drawing, it is apparent that a reverse flow region is formed to a smaller extent at the center portion of the furnace 34.

FIG. 6 shows a case where the primary air 9, the secondary air 10 of a weak rotating flow and the tertiary air 11 are in the respective quantities of 0%, 70% and 30%. Further, FIG. 7 shows a case where the primary air 9, the secondary air 10 of a strong rotating flow and the tertiary air 11 are in the respective quantities of 0%, 63% and 37%. From FIG. 6 and FIG. 7, it is apparent that little difference is found in spread of the air injection flows inside the furnace 34 but a difference is found in flow velocity distribution at the center portion of the furnace 34. It is noted that the lower sides of FIG. 5 to FIG. 7 correspond to the central axis C of the AAP.

When attention is given to the spread of high-speed air injection flows in FIG. 5 to FIG. 7, the air injection flows do not run along a spread portion of the outlet on the furnace throat wall 26, which is less clear due to the fact that the measured site is spaced away from the leading end portion of the AAP, and all the air injection flows are influenced by the contracted flow. In other words, since the air injection flows are detached from the furnace throat wall 26 shown in FIG. 2, a reverse flow takes place although being at a small region, and there is the potential that particles of ash associated with the flows may adhere to the wall and grow thereafter.

In the conventional technique AAP given in FIG. 14, such a state is shown that the air flow 12 (secondary air 10 merged with the tertiary air 11) is detached from the furnace throat wall 26 to give a contracted flow. Therefore, the ash adhesion layer 18 given in FIG. 14 is formed on the furnace throat wall 26.

Therefore, in the present embodiment, as shown in FIG. 2, a louver 32 from the outlet of the tertiary nozzle 3 along the furnace throat wall 26 is mounted to provide a clearance between the louver 32 and the furnace throat wall 26 from the outlet of the tertiary nozzle 3 through which a partial flow 11′, or a part of the tertiary air 11, flows. According to the above structure, the flow 11′, or a part of the tertiary air 11, flows so as to seal the surface of the throat wall 26, thereby making it possible to suppress to the minimum extent combustion-derived ash in association with the contracted flow of the tertiary air 11 from adhering to the surface of the throat wall 26.

FIG. 2 shows a state in which the ash adhesion layer 18 is formed at an inclined region on the furnace throat wall 26. In the present embodiment, it is impossible to eliminate ash in this region. However, ash adhered to the region will not influence the performance of an AAP or the performance of a boiler, which may be negligible. The ash adhesion layer 18 shown in FIG. 14 detaches or drops off into the AAP when the boiler is halted, thus influencing the performance of the AAP. For this reason, the layer must be eliminated.

EMBODIMENT 2

FIG. 8 shows a sectional view of the port 31 of Embodiment 2. Additionally, FIG. 9 and FIG. 10 are schematic diagrams of the port 31, which is a comparative example for comparison with the port 31 of Embodiment 2 given in FIG. 8.

As the port shown in FIG. 8, the primary nozzle 1, the secondary nozzle 2 and the tertiary nozzle 3 are shown, through which the primary air, the secondary air and the tertiary air flow respectively in a concentric manner. At least such a structure is acceptable that a flow from the outer circumference of the tertiary nozzle 3 in the present embodiment toward the central axis C of the port is increased and allowed to flow through a port opening of the furnace 34 (throat wall 26), thereby the air injection flow is able to appropriately form a so-called contracted flow. In other words, the primary nozzle 1 and the secondary nozzle 2 are not essential in forming the so-called contracted flow.

Air flowing through the primary nozzle 1, which is a central air nozzle of the port 31, forms a straight advancing flow. A secondary air resistor 7 having the rotating function is provided at an inlet of the secondary nozzle 2, and a major portion including the end portion of the furnace 34 side on the secondary nozzle 2 (an outlet of the secondary nozzle) is a straight tube, with the central axis C of the port being at the center. Therefore, the radius Da at the end portion of the tube inlet of the secondary nozzle 2 given in FIG. 8 is equal to the radius Db at the end portion of the tube outlet thereof.

Further, the tertiary nozzle 3, which is different from the primary nozzle 1 and the secondary nozzle 2, forms an injection flow having an inclined angle of 30° to 70° with respect to the central axis C of the port and is constituted so as to obtain effects of contracted flow.

The effects of contracted flow are those generating a strong associated gas 20, which is an ambient gas inside the furnace 34, in the vicinity of the throat wall 26 at which a gas channel formed at an opening of the port on the furnace wall is enlarged.

The air flow rate of the primary nozzle 1 is adjusted by using a damper 5 disposed at an air intake hole 1B of the primary nozzle 1 to operate an adjusting lever 15 from outside the window box 39b, thus adjusting an aperture of the air intake hole 1B of the primary nozzle 1. Further, the air flow rate of the secondary nozzle 2 is adjusted by using a damper 6 disposed at an air intake hole 2B of the secondary nozzle 2 to operate an adjusting lever 16 from outside the window box 39b, thus adjusting an aperture of the air intake hole 2B of the secondary nozzle 2 and at the same time a resistor 7 disposed at the air intake hole 2B of the secondary nozzle 2 is rotated by a secondary air resistor drive 13, thereby adjusting an air rotating strength. Still further, the air flow rate of the tertiary nozzle 3 is adjusted by using a damper 8 disposed at an air intake hole 3B of the tertiary nozzle 3 to operate an adjusting lever 17 from outside the window box 39b, thus adjusting an aperture of the air intake hole 3B of the tertiary nozzle 3.

A throat portion 26 of the furnace wall on the outlet side of the tertiary nozzle 3 (the side heading to the inside of the furnace 34) is gradually enlarged in diameter to the downstream side of gas flow with respect to the central axis C of the port 31 as it moves downstream. Additionally, when the tertiary damper 8 is fully closed, a rotating flow from the throat wall 26 of the enlarged pipe configuration and the secondary nozzle 2 forms air flow spreading in a radial direction of the central axis C of the port.

Additionally, in order to prevent ash adhesion on the throat wall 26 of the enlarged pipe configuration on the outlet side of the tertiary nozzle 3, there is provided a ring-shaped louver 32 which guides a flow 11′ or a part of the tertiary air 11 into the throat wall 26 in an outer circumferential direction and the cross section of which is enlarged as it moves toward the furnace 34 side. The leading end of the louver 32 on the upstream side of gas flow (an inlet side of the air nozzle 3) is disposed so as to be located on an extended line E of the outer circumferential partition wall of the tertiary nozzle 3 or on the upstream side of gas flow (an inlet side of the air nozzle; a direction moving away from the inside of the furnace) from the extended line E.

Features of the present embodiment will be explained by comparison with FIG. 9 and FIG. 10.

The port 31 of the present embodiment shown in FIG. 8 is provided with a ring-shaped louver 32 which is enlarged in cross section toward the side closer to the inside of the furnace 34 of the throat wall 26 so as to be parallel to the furnace wall surface of the throat wall 26 of enlarged pipe configuration on the outlet side of the tertiary nozzle 3(the side toward the inside of the furnace 34).

On the other hand, FIG. 9 and FIG. 10 show sectional views of the port 31 which is substantially similar in constitution to that given in FIG. 8. A difference in constitution from the port 31 given in FIG. 8 is that in which in FIG. 9, the leading end of a louver 32″ on the upstream side of gas flow is provided so as to be located on the downstream side of gas flow from an extended line E of the outer circumferential partition wall of the tertiary nozzle 3 and in FIG. 10, all the louvers 32″ are disposed so as to be located inside the contracted flow at which a gas flow from the tertiary nozzle 3 heads to the central axis C of the port.

The leading end portion of the louver 32 on the upstream side of gas flow in the present embodiment shown in FIG. 8 is disposed in a projecting manner so as to block a part of the tertiary nozzle 3. Therefore, the leading end portion of the louver 32 on the upstream side creates obstacles to the contracted flow of the tertiary air 11 flowing through the tertiary nozzle 3, a dynamic pressure is generated by the tertiary air 11 on the outer circumference of the louver 32 (the side of the throat wall 26), and a flow 11′, or a part of the tertiary air 11, flows between the louver 32 and the throat wall 26 of enlarged pipe configuration. The flow 11′ flowing between the louver 32 and the throat wall 26, which serves as sealing air, is guided by the louver 32, by which an associated gas flow (a sealing air flow on the wall surface) 20 inside the furnace wall surface which flows in the vicinity of the throat wall 26 inside the furnace 34 flows effectively along the inner wall surface of the furnace 34 in the vicinity of the throat wall 26 of the port 31, thus making it possible to eliminate a negative pressure in the vicinity of the wall surface of the throat wall 26.

On the other hand, in the constitution given in FIG. 9 and FIG. 10, the associated gas flow 20 in the vicinity of the side wall surface of the furnace 34 is influenced by the flow 11′, or a part of the tertiary air 11, generated in the vicinity of the throat wall 26, which is a furnace opening, from an arrangement relationship between the louvers 32′, 32″ and the tertiary nozzle 3, thereby giving a circulating flow. Therefore, an ash adhesion layer 18 is formed on the throat wall 26 of the furnace 34.

As described so far, in the constitution of the present embodiment given in FIG. 8, it is less likely to cause ash adhesion to the wall surface constituting the throat wall 26 of enlarged pipe configuration at the outlet of the tertiary nozzle 3 due to the involvement of ash, which may take place in the constitution given in FIG. 9 and FIG. 10.

Additionally, a radius (Dg) of the leading end of the louver 32 on the downstream side of gas flow (the furnace side) is set to be less than one time, preferably less than 0.95 times a minimum radius (Ds) (hereinafter, sometimes referred to as “throat diameter,” refer to FIG. 12) of the throat wall 26 of enlarged pipe configuration of the tertiary nozzle 3.

The radius of the leading end of the louver 32 on the downstream side of gas flow (the furnace side) is set to be less than one time of the radius of the throat wall 26 of enlarged pipe configuration, thereby if the louver 32 is made in an integrated manner (constituted so as not to be divided), it is easy to dispose the louver 32 outside the furnace 34 or to draw it outside the furnace 34. Further, it is easier to dispose the louver 32 outside the furnace 34 or the like when the radius is set to be less than 0.95 times, with a manufacturing tolerance taken into account. It is noted that the louver 32 is not made in an integrated manner but may be constituted to be divided in a circumferential direction so that it can be easily taken outside the furnace 34

However, it is desirable that the length of a flat surface of the louver 32 on which the diameter is enlarged as it moves to the downstream side of gas flow (a length connecting e part given in FIG. 12 (a circumferential direction) with f part (a circumferential direction)) is set to be ½ or lower than the length of the wall surface of the throat wall 26 of enlarged pipe configuration in a gas flow direction (a length connecting h part given in FIG. 12 (a circumferential direction) with i part (a circumferential direction)) so that ash is less likely to adhere to the flat surface. This is not limited to the present embodiment but generally applicable to the present invention.

Additionally, if a spreading angle of the louver 32 in a gas flow direction is equal to or greater than a spreading angle of the throat wall 26 of enlarged pipe configuration of the port 31, it is possible to guide air in a quantity effective in preventing ash adhesion.

Still further, it is desirable that the damper 8 at the inlet area of the tertiary nozzle 3 is arranged on the side spaced away from the furnace 34 at the inlet area of the nozzle 3 and allowed to slide to a direction at which the damper 8 is brought closer to the furnace 34 when the damper 8 is used to close an air intake hole 3B of the tertiary nozzle 3. This is because even in a state that air flow rate on closure of the inlet area of the nozzle 3 is reduced (a state that the damper 8 is almost closed), air flows to a part closer to the throat wall 26 of enlarged pipe configuration at the port 31 inside the tertiary nozzle 3, thereby air is guided into the louver 32, thus making it possible to prevent ash adhesion to the throat wall 26 of enlarged pipe configuration.

It is noted that the damper 8 is illustrated as such that in which a cylindrical member slides substantially parallel to the central axis C of the port. However, a plurality of butterfly-type valves or flaps may be arranged so that the rotating axes are placed circumferentially at a position parallel to the central axis C of the port 31. This constitution is not limited to the present embodiment but also applicable to each of the following embodiments.

In the present embodiment given in FIG. 8, the port 31 is of a triple structure. The above effects can be obtained by the port 31 which is not provided with the primary nozzle 1 or the secondary nozzle 2 but constituted only by the tertiary nozzle 3 which is of a contracted flow structure. It is noted that the port 31 which is constituted only by the tertiary nozzle 3 may be used in other embodiments.

Where an air nozzle such as the secondary nozzle 2 is disposed inside the tertiary nozzle 3 given in FIG. 8, with respect to a line F formed by a virtual cylinder for gas straight advancement including the end portion (point b given in FIG. 12(a)) of the partition wall constituting the secondary nozzle 2 on the downstream side of gas flow (a line parallel to the central axis C of the port including point b given in FIG. 12(a)), it is desirable that the end portion of the louver 32 on the upstream side (point c given in FIG. 12(a)) is arranged in such a range that an angle θ formed by a line G connecting the end portion (point b given in FIG. 12(a))1 with the end portion of the louver 32 on the upstream side of the gas flow (point c given in FIG. 12(a)) is lower than 15 degrees (refer to FIG. 12(a)).

This is because where the damper 8 at the inlet area of the tertiary nozzle 3 is fully closed and air is allowed to flow from the secondary nozzle 2, air injected from the secondary nozzle 2 is injected while spreading inside the port 31 but the spreading angle of the injection flow is normally at about 15 degrees. For this reason, the end portion of the louver 32 on the upstream side is arranged inside a range held between the line F and the line G, thereby even where the secondary air is not subjected to rotation, gas flows through an outer circumferential channel of the louver 32, and the gas flow can be guided in an outer circumferential direction in the vicinity of the wall surface of the throat wall 26. In other words, as compared to a conventional case where an injection hole is separately disposed for injecting a coolant such as air, according to the constitution of the present embodiment, under any operating conditions of the port 31, it is possible to prevent ash adhesion to the throat wall 26 or the wall surface in the vicinity thereof. Further, it is possible to reduce a pressure loss on supplying gas from the port 31 to the furnace 34, simplify the structure of the port 31, eliminate a necessity for installing a seal air adjustor for suppressing ash adhesion, reduce the weight of accessories of the furnace 34 and save iron and steal products as a whole.

Additionally, the louver 32 is structured so as to be supported on the outer channel wall of the tertiary nozzle 3 constituting the contracted flow by means of fixing ribs 27 (refer to FIG. 11). Normally, in a boiler furnace 34, thermal expansion is different depending on individual parts of the furnace 34, by which a distance between the wall surface of the furnace 34 constituting the outer circumference portion of an outermost circumferential air nozzle (the tertiary nozzle 3 in the case of FIG. 8) and the central axis C of the port is changed according to operating loads. The louver 32 or the like is fixed from inside the port 31, thus making it possible to keep constant a clearance between the throat wall 26 of enlarged pipe configuration of the port 31 and the louver 32

EMBODIMENT 3

FIG. 11 is a schematic diagram of the port 31 showing the present embodiment 3. In the constitution given in FIG. 11, the same parts as those of the constitution given in FIG. 8 are given the same numerals or symbols, an explanation of which will be omitted here.

In the present embodiment, a parallel portion 26a which is constant in cross section of the channel and parallel to the central axis C is provided on the throat wall 26 of enlarged pipe configuration of the port 31. Further, a cylindrical portion 32a running along the parallel portion 26a is also provided on the louver 32. Additionally, the contracted flow from the tertiary nozzle 3 partially flows into a space between the louver 32 and the throat wall 26 of enlarged pipe configuration, a flow 11′, or a part of the tertiary air 11 which seals the surface of the throat wall 26 of the furnace 34, flows effectively in the vicinity of the wall surface of the throat wall 26, thus making it possible to eliminate a negative pressure in the vicinity of the wall surface of the throat wall 26. It is, therefore, less likely to cause ash adhesion in the vicinity of the throat wall 26 due to the involvement of ash.

FIG. 12(a) is an enlarged view showing an outlet area of the port 31 given in FIG. 11, in which the leading end portion of the louver 32 on the upstream side of gas flow (point c) is disposed so as to be located on an extended line E of the outer circumferential wall surface (front wall) 301 of the tertiary nozzle 3 constituting the contracted flow or on the upstream side of gas flow (a direction spaced away from the inside of the furnace) from the extended line E. Additionally, the radius Dg of the leading end on the furnace 34 of the louver 32 is set to be less than one time of the radius Ds of the throat wall 26 so that the louver 32 can be inserted from the window box 39b. More specifically, the radius Ds of the parallel portion 26a on the throat wall 26 of enlarged pipe configuration is set to be greater than the radius Dg of a maximum diameter portion of the louver 32 (radius Dg<radius Ds). In reality, with a manufacturing tolerance taken into account, the radius Ds of the parallel portion 26a on the throat wall 26 of enlarged pipe configuration is desirably set to be less than 0.95 times the radius Dg of the maximum diameter portion of the louver 32 (Ds<0.95 Dg).

The radius Dp of the parallel portion 32a of the louver 32 is set to be 20% or lower than the radius Ds of the parallel portion 26a of the throat wall 26 (1.0 Ds>Dp>0.8 Ds; however, the length Dp is a radius of the cylindrical portion 32a of the louver 32 (a part parallel to the central axis C of the port)), and if a spreading angle of the louver 32 is made equal to or greater than a spreading angle of the throat wall 26 of the port 31, it is possible to guide air in a quantity effective in preventing ash adhesion to the throat wall 26. However, when the continued effect of contracted flow by gas flowing through the tertiary nozzle 3 is taken into account, it is desirable that the radius Dp is made smaller by about 10% with respect to the radius Ds (1.0 Ds>Dp≧0.9 Ds). In other words, where an excessively great quantity of air is allocated in preventing ash adhesion to the throat wall 26 of the furnace 34, inhibited is an original aim of forming the contracted flow that an air injection flow for controlling combustion is allowed to arrive at the central portion of the furnace 34 and gases in the vicinity of the furnace wall are also mixed in a facilitating manner. It is not desirable that the air injection flow heading from the outer circumference side of the port 31 to the direction of the central axis C is increased and allowed to pass through the throat portion 26, thus resulting in a failure in keeping such a flow that involves gas inside the furnace 34 around the throat portion 26, while the air injection flow is concentrated on the central axis C of the port 31.

It is noted that FIG. 12(a) shows a case where the radius of the port, Da (point a; a radius of an introduction part of the secondary nozzle 2) and Db (point b; the edge portion of the partition wall constituting the secondary nozzle 2 on the down stream side of gas flow) are substantially equal to a radius of the throat wall 26, Ds (a radius of the parallel portion on the throat wall 26). However, similar effects can be obtained in a case where the radius of the throat wall 26, Ds, is greater or smaller than the radius of the secondary nozzle 2, Da and Db.

For example, as shown in FIG. 12(b), also in a case where the radius of the throat wall 26, Ds, is greater than the radius of the secondary nozzle 2, Da and Db, it is desirable that with respect to a line F (a line parallel to the central axis C of the port including point b given in FIG. 12(b)) formed by a virtual cylinder for air advancement including the end portion of a partition wall constituting the secondary nozzle 2 on the downstream side of gas flow (point b given in FIG. 12(b)), the end portion of the louver 32 on the upstream side is arranged in such a range that an absolute value of an angle θ formed by a line G connecting the end portion (point b given in FIG. 12(b)) with the end portion of the louver 32 on the upstream side (point c given in FIG. 12) is lower than 15 degrees.

However, it is desirable that the length of a flat surface of the louver 32 on which the diameter is enlarged as it moves to the downstream side of gas flow (a length connecting e part given in FIG. 12 (a circumferential direction) with f part (a circumferential direction)) is set to be ½ or lower than the length of the wall surface of the throat wall 26 in a gas flow direction (a length connecting h part given in FIG. 12 (a circumferential direction) with i part (a circumferential direction)) so that ash is less likely to adhere to the flat surface.

It is noted that in FIG. 12(b), the radius of the throat wall 26, Ds, is set to be greater than the radius of the louver 32, Dg, thereby the louver 32 can be easily drawn outside the furnace wall.

EMBODIMENT 4

FIG. 13 is a schematic diagram showing the port 31 of the present embodiment 4. In the constitution given in FIG. 13, the same parts as those of the constitution given in FIG. 2 are given the same numerals or symbols, an explanation of which will be omitted here.

In the present embodiment, as similar in constitution given in FIG. 11, a parallel portion 26a which is constant in the cross section area of the channel and parallel to the central axis C is disposed on the throat wall 26, and a cylindrical portion 32a is also disposed on the louver 32. A rotator 22 for inducing a circumferential flow velocity component of the throat wall 26 is disposed between the parallel portion 26a and the cylindrical portion 32a of the louver 32.

Thereby, the contracted flow from the tertiary nozzle 3 partially flows into a space between the louver 32 and the throat wall 26, the air flow 11′ for sealing the surface of the throat wall 26 of the furnace 34 effectively flows in the vicinity of the wall surface on the throat wall 26 of enlarged pipe configuration, thus making it possible to eliminate a negative pressure in the vicinity of the wall surface of throat wall 26. As a result, it is less likely to cause ash adhesion in the vicinity of the throat wall 26 due to the involvement of ash.

Further, there is a decreased projected area of the surface orthogonal to the central axis C of the port on the louver 32 when viewed from the furnace side, thus making it possible to decrease the irradiation heat amount received from flame. As a result, the louver 32 can be decreased in temperature, and heat loss such as thermal deformation and corrosion at high temperature sites is less likely to take place.

Still further, in a case where the ring-shaped louver 32 for guiding gas flow in a direction of the throat wall 26, which is enlarged in the cross sectional area, is disposed at the leading end of the rotator 22 on the downstream of gas flow, it is possible to prevent ash adhesion in the vicinity of a nozzle due to the involvement of ash.

INDUSTRIAL APPLICABILITY

The present invention is not limited to a furnace of a boiler but may be applicable to a furnace wall surface of a combustion apparatus to which ash generated from combustion of coal or others can easily adhere.

Claims

1. An in-furnace gas injection port which is disposed on a furnace wall of the furnace, comprising:

a contracted flow producing channel having a velocity component flowing toward the central axis of gas flow perpendicular to the furnace wall and a velocity component flowing along the central axis, and provided obliquely toward the central axis from the upstream side of gas flow;

a throat enlarged pipe portion in which a gas channel formed on a furnace wall opening on the downstream side of the contracted flow producing channel is gradually enlarged in a direction of the gas flow; and

a louver disposed on the contracted flow producing channel for guiding so that gas flowing through the contracted flow producing channel can flow along the wall surface of the throat enlarged pipe portion and whose leading end portion on the upstream side of gas flow is located on a surface obtained by extending the outer circumferential wall surface of the contracted flow producing channel toward the central axis or on the upstream side of gas flow from the thus extended surface and which has at the downstream part of gas flow an enlarged pipe portion gradually enlarged in a direction of gas flow so as to run along the wall surface of the throat enlarged pipe portion.

2. (canceled)

3. The in-furnace gas injection port as set forth in claim 1, comprising a mechanism for changing a ratio of the velocity component of air flow flowing through the contracted flow producing channel along the central axis and the velocity component of air flow flowing toward the central axis.

4. The in-furnace gas injection port as set forth in claim 3, comprising a damper starting to open from the near surface side to the furnace so that gas flows along the outer circumferential wall surface of the contracted flow producing channel and capable of adjusting an aperture of the contracted flow producing channel.

5. The in-furnace gas injection port as set forth in claim 1, comprising a rotating member for rotating gas between the louver and the wall surface of the throat enlarged pipe portion.

6. The in-furnace gas injection port as set forth in claim 1, wherein a length of the enlarged pipe portion in a gas flow direction formed at the downstream end portion of the louver is ½ or lower than a length of the wall surface of the throat enlarged pipe portion in a gas flow direction.

7. The in-furnace gas injection port as set forth in claim 1, wherein the contracted flow producing channel is given as a tertiary nozzle and a primary nozzle is disposed inside from the tertiary nozzle and a secondary nozzle is disposed outside the primary nozzle through which each gas flows along the central axis.

8. The in-furnace gas injection port as set forth in claim 3, comprising a rotating member for rotating gas between the louver and the wall surface of the throat enlarged pipe portion.

9. The in-furnace gas injection port as set forth in claim 4, comprising a rotating member for rotating gas between the louver and the wall surface of the throat enlarged pipe portion.

10. The in-furnace gas injection port as set forth in claim 3, wherein a length of the enlarged pipe portion in a gas flow direction formed at the downstream end portion of the louver is ½ or lower than a length of the wall surface of the throat enlarged pipe portion in a gas flow direction.

11. The in-furnace gas injection port as set forth in claim 4, wherein a length of the enlarged pipe portion in a gas flow direction formed at the downstream end portion of the louver is ½ or lower than a length of the wall surface of the throat enlarged pipe portion in a gas flow direction.

12. The in-furnace gas injection port as set forth in claim 5, wherein a length of the enlarged pipe portion in a gas flow direction formed at the downstream end portion of the louver is ½ or lower than a length of the wall surface of the throat enlarged pipe portion in a gas flow direction.

13. The in-furnace gas injection port as set forth in claim 8, wherein a length of the enlarged pipe portion in a gas flow direction formed at the downstream end portion of the louver is ½ or lower than a length of the wall surface of the throat enlarged pipe portion in a gas flow direction.

14. The in-furnace gas injection port as set forth in claim 9, wherein a length of the enlarged pipe portion in a gas flow direction formed at the downstream end portion of the louver is ½ or lower than a length of the wall surface of the throat enlarged pipe portion in a gas flow direction.

15. The in-furnace gas injection port as set forth in claim 3, wherein the contracted flow producing channel is given as a tertiary nozzle and a primary nozzle is disposed inside from the tertiary nozzle and a secondary nozzle is disposed outside the primary nozzle through which each gas flows along the central axis.

16. The in-furnace gas injection port as set forth in claim 4, wherein the contracted flow producing channel is given as a tertiary nozzle and a primary nozzle is disposed inside from the tertiary nozzle and a secondary nozzle is disposed outside the primary nozzle through which each gas flows along the central axis.

17. The in-furnace gas injection port as set forth in claim 5, wherein the contracted flow producing channel is given as a tertiary nozzle and a primary nozzle is disposed inside from the tertiary nozzle and a secondary nozzle is disposed outside the primary nozzle through which each gas flows along the central axis.

18. The in-furnace gas injection port as set forth in claim 8, wherein the contracted flow producing channel is given as a tertiary nozzle and a primary nozzle is disposed inside from the tertiary nozzle and a secondary nozzle is disposed outside the primary nozzle through which each gas flows along the central axis.

19. The in-furnace gas injection port as set forth in claim 9, wherein the contracted flow producing channel is given as a tertiary nozzle and a primary nozzle is disposed inside from the tertiary nozzle and a secondary nozzle is disposed outside the primary nozzle through which each gas flows along the central axis.

20. The in-furnace gas injection port as set forth in claim 6, wherein the contracted flow producing channel is given as a tertiary nozzle and a primary nozzle is disposed inside from the tertiary nozzle and a secondary nozzle is disposed outside the primary nozzle through which each gas flows along the central axis.

21. The in-furnace gas injection port as set forth in claim 10, wherein the contracted flow producing channel is given as a tertiary nozzle and a primary nozzle is disposed inside from the tertiary nozzle and a secondary nozzle is disposed outside the primary nozzle through which each gas flows along the central axis.

22. The in-furnace gas injection port as set forth in claim 11, wherein the contracted flow producing channel is given as a tertiary nozzle and a primary nozzle is disposed inside from the tertiary nozzle and a secondary nozzle is disposed outside the primary nozzle through which each gas flows along the central axis.

23. The in-furnace gas injection port as set forth in claim 12, wherein the contracted flow producing channel is given as a tertiary nozzle and a primary nozzle is disposed inside from the tertiary nozzle and a secondary nozzle is disposed outside the primary nozzle through which each gas flows along the central axis.

24. The in-furnace gas injection port as set forth in claim 13, wherein the contracted flow producing channel is given as a tertiary nozzle and a primary nozzle is disposed inside from the tertiary nozzle and a secondary nozzle is disposed outside the primary nozzle through which each gas flows along the central axis.

25. The in-furnace gas injection port as set forth in claim 14, wherein the contracted flow producing channel is given as a tertiary nozzle and a primary nozzle is disposed inside from the tertiary nozzle and a secondary nozzle is disposed outside the primary nozzle through which each gas flows along the central axis.