FI104758B - Combustion arrangement - Google Patents

Description

, 104758

This invention relates to a combustion apparatus according to the preamble of claim 1 and, for example, to a combustion apparatus for a pulverized coal boiler.

5 In a pulverized coal combustion boiler, the combustion apparatus injects a mixture of pulverized coal and air into the furnace through a feed tube. The mixture is injected and ignited to form a flame in the furnace. As disclosed in U.S. Patent 4,545,307, a radially outwardly flaming flame retaining ring is provided at the end of the alloy feed pipe. Along the flame-maintaining ring 10, the mixture swirls so that the powdered carbon is concentrated near the flame-maintaining ring. As a result, ignition takes place at the end of the feed tube of the alloy in the furnace to form a high-temperature, strong reduction flame, which makes it possible to prevent the formation of NOx.

15 The flame-retaining ring is covered with ash and kept in a reducing atmosphere and is still exposed to high temperatures due to the heat emitted from the furnace. These conditions can cause the flame-retaining ring to melt or, when not functioning properly, the growth of the slag in the flame-retaining ring, i.e., promote slagging under certain conditions. The melting of the flame-retaining ring or the growth of the slag results in a deterioration of the effect of the flame-retaining ring, an increase in NOx of nitric oxides, or problems with the device.

The combustion apparatus according to the invention is characterized by what is said in the characterizing part of independent claim 1. According to the invention. . Preferred embodiments of the combustion device are the subject of dependent claims 2 to 9.

Accordingly, it is an object of the present invention to provide a combustion device capable of performing low nitrogen oxide NOx combustion in a stabilized manner, regardless of the unit capacity or operating load of the combustion device.

Until now, in the present invention, radiation from a flame is cut off and one of the three factors (namely, high temperature, reduction and presence of ash) is eliminated.

According to the present invention there is provided a protrusion extending into the furnace on one side of the flame retaining means from the inside of the furnace I! 35 enough to prevent radiation from entering the flame retaining means and preventing excessive temperature rise to prevent melting of the flame retaining means and slagging in the flame retaining means.

Fig. 1 is a sectional view of the projection shown in Fig. 1, Fig. 4 is a fragmentary front view of the protrusion of Fig. 3, taken along lines II-II in Fig. 1; Fig. 5 is an enlarged fragmentary front view of the projection of Fig. 1, 10 Fig. 6 is a sectional view taken along the lines of Fig. 5, Fig. 7 is a partially fragmentary front view showing a variant of the projection, Fig. 8 Figure 9 is a fragmentary sectional view illustrating another embodiment of the protrusion, Figure 10 is a sectional view of another embodiment of the combustion apparatus, Figure 11 is a side view illustrating the conical portion of the ground carbon / air separator shown in Figure 10,

Figure 12 is a front view taken along lines XII-XII of Figure 11

13 is a side view illustrating a conical portion of a second ground carbon / air separator;

Figure 14 is a front view taken along lines XIV-XIV of Figure 13

25 is a side view illustrating the conical portion of another ground carbon / air separator,

Figure 16 is a front view taken along lines XVI-XVI of Figure 15

17 through 19 are sectional views illustrating other variations of the conical portion of the ground carbon / air separator, respectively, and Figure 20 is a sectional view of a different combustion device.

Referring to Figure 1, the burner has a bent blend feed tube 1. The burner serves to burn the pulverized carbon as a powder fuel in air containing oxygen 35. The other end of the alloy feed pipe 1 is through the opening 22 3 104758 formed in the furnace wall 2 through the opening 22 3 104758 of the furnace 2 and is connected at one end to a coal grinder (not shown). A mixture of ground carbon and primary air flows through the mixture feed tube 1. The mixture is ignited to form a flame in the furnace 2.

A flame-retaining ring 3 having the shape of an "L" letter 5 is arranged in the circumferential end portion of the alloy supply pipe 1. As shown in detail in Fig. 2, the annular flow channel 4 is arranged radially outwardly of the alloy supply pipe 1 so that it is concentric with it. The tertiary air is supplied to the furnace 2 through the flow channel 4.

A ring-shaped protrusion 6 is disposed between the mixture feed pipe 1 and the flow passage 4. The protrusion 6 extends into the furnace 2 on the other side of the flame-maintaining ring 3. The outer peripheral wall 61 of the projection 6 extends parallel to the alloy feed pipe 1 and its inner peripheral wall 62 expands radially outwardly from its end portion. Both peripheral walls 61 and 62 terminate in end plate 63.

Referring to Figures 1 and 3, the interior of the projection 6 is divided into two layers by a partition tube 64. 62 and through the duct portion defined by the alloy supply pipe 1 as indicated by arrows and then flowing into the furnace 2. As the inner peripheral wall 62 of the projection 20 6 expands radially outwardly from its end portion, the secondary air is decelerated to its speed. shower. This makes it possible to form a high temperature reduction flame in a stable manner. Thus, it is possible to prevent NOx production of nitric oxides.

· * '- 25 The flame-retaining ring 3 is under a reduction atmosphere and the powdered carbon concentrates in the vicinity of the flame-retaining ring due to the vortex. In addition, the flame-retaining ring 3 is usually exposed to high temperatures due to radiant heat from the furnace as shown in dashed lines in Figures 1 and 3. However, since the protrusion 6 extends to the other side 30 of the flame-retaining ring 3 to moderately cut off the radiation entering the flame-retaining ring 2, the flame-retaining ring 3 is prevented from being too "high". (e.g., above 50 MW), the flame retaining ring 3 can be prevented from melting or suffering from slag production.

«4 104758

On the other hand, the projection 6 has now been brought into a state where it is covered with ash and is placed in a reduction atmosphere and is still exposed to high temperatures due to the radiating heat from the furnace 2. Therefore, it is possible that the protrusion 6 suffers from slagging. To cope with this in the present kek-5 protuberance, the protrusion 6 is not located in the reduction atmosphere but in the oxidation atmosphere. By doing so, one of the occurrences of slagging can be eliminated, thereby enabling the occurrence of slagging to be prevented.

To form the oxidation atmosphere, the end plate 63 is provided with a plurality of radial slots 631 spaced at equal intervals as shown in Figures 4-6. Part of the secondary air is ejected from these slots 631 and guided by baffles 632 so that it flows circumferentially to the surface of the projection 6. Thus, the protrusion 6 can be kept under an oxidation atmosphere, which results in the prevention of slag production.

In this embodiment, it is noted that the secondary air cools the projection 6 while flowing the channel portion defined by the outer peripheral wall 61 and partition tube 64 of the projection 6, the channel portion defined by the inner peripheral wall 62 of the projection 6, and channel section. A flow of secondary air at about 300 ° C will cause the projection to be at or below 950 ° C, where hardly any slag is produced at 20 ° C. Thus, it becomes possible to aggravate the presence of slag in the projection 6 as well as to extend the lifetime of the projection. On the other hand, since the secondary air temperature increases by about 40 ° C due to the radiant heat from the furnace 2, the combustion efficiency can be improved.

In the variant shown in Figures 7 and 8, a plurality of circumferential slots 633 are arranged at equal intervals on the end plate 63 such that a portion of the secondary air is directed by the baffle 634 to radially outwardly to the surface of the projection 6. As a result, slag production can be inhibited as in the above embodiment. In another variation shown in Figure 9, the end plate 63 is partially cut and inclined.

In another embodiment shown in Fig. 10, to make the mixture concentrate around the mixture feed pipe 1, a larger carbon / air separating rod portion 7 is disposed coaxially inside the mixture feed pipe 1. The separating part 7 is attached to the mixture feed pipe 1 from its shaft arm 71. The separating part 7 also has a conical portion 72 which defines a taper portion of the pipe in cooperation with the machine part 11 provided in the mixture feed pipe 1. In the taper section of the tube, the speed of the mixture is reduced. Further, the separating portion 7 comprises a straight circular cylindrical portion 73 and a conical portion 74 extending from the straight circular cylindrical portion, thereby limiting the flow of the mixture downstream. The straight circular cylindrical portion 73 cooperates with the feed pipe 1 of the alloy 5 to define therebetween the duct portion I of the alloy, which remains constant in cross-section. The conical portion 74 cooperates with the alloy feed pipe 1 to define between them the alloy passage portion II, whose cross-sectional area gradually increases in the direction of the alloy flow.

The velocity of the mixture increases in the channel portion I. As the mixture flows through the flower portion II, the powdered carbon is separated from the mixture due to its inertia and then flows radially outward. As a result, the ground carbon is concentrated near the flame retaining ring. Therefore, even if the combustion plant load is reduced (for example, down to about 30% of the crusher load), it is possible to carry out a very efficient combustion with less nitrogen oxide and NOx produced. However, if the tapered portion 74 tapers unevenly, it is possible that the mixture may separate from the tapered portion. Once the separation occurs, the powdered carbon already concentrated once near the flame-retaining ring is brought back radially due to the inwardly separated flow, leading to the possibility that the concentration of powdered carbon near the flame-retaining ring will be reduced. In addition, it is impossible to determine the place where such a distinction is made. Therefore, in this embodiment, it is designed that the flow separation takes place precisely, that is, in the predetermined portions of the conical portion. Furthermore, these portions where the separation takes place are circumferential. In other words, the parts where separation is prevented from occurring, * 25 are equally circumferentially spaced. Thus, the concentration of carbon: the carbon concentration near the flame-retaining ring becomes uniformly circumferential and therefore it is possible to perform a stabilized combustion.

So far, in the present invention, the conical portion 74 consists of parts: 741, each of which tapers at an angle θι to the axial direction, and portions of 30,742, each of which tapers at an angle θ2 (> θι) of axial direction alternating with parts 742. 11 -14 are shown.

The tapering angle θι is in the range of 5 ° to 15 ° and the tapering angle θ2 is in the range of 25 ° to 65 °; within the precincts of. Separation occurs in parts 742 but does not occur in parts 741. Li-; further, the area taken up by parts 741 is made larger than that taken by parts 742. Thus, the effect of the separation of 35 doin can be minimized, thereby increasing the combustion so stabilized. The sections 741 and 742 may be joined evenly (as shown in Fig. 12) or steeply (as shown in Fig. 14). The tapered angle θ2 of the portion where separation occurs is not limited to 25 ° to 65 °. Even when the tapering angle θ2 is 90 °, i.e. even when part 742 is the gap shown in Figures 15 and 16, the same effect can be obtained.

Further, as shown in Figures 17-19, parts 741 and 742 may be arranged asymmetrically.

Incidentally, although the protrusion and the separating portion of the ground carbon / air are together in this embodiment, these may be provided separately.

Further, the present invention is applicable to the 10 powdered coal combustor shown in Fig. 20 provided with a starter oil burner 8 and an auxiliary gas burner 9. The oil burner 8 extends through the separating section 7 to the tip of the conical section 74. The gas burner 9 extends through the inner peripheral wall 62 to the furnace 2 to such an extent that it can be prevented from being exposed to radiation from within the furnace 2.

The present invention can be used, for example, in a pulverized coal boiler burner.

• · * · «• {!

Claims (9)

A combustion device comprising: a mixture feed tube (1) exposed to a fireplace (2) for feeding a mixture of powdered fuel and oxygen-containing gas into said fireplace (2), a first gas feed channel (4) located radially out of the inlet pipe of said mixture to supply oxygen-containing gas into said fireplace (2), a second gas inlet duct (5) located radially between said first gas inlet duct (4) and said inlet pipe of said mixture (1) for supplying oxygen-containing gas into said fireplace (2), and bursting means (6) located radially between said inlet duct (4) of said first gas and said mixture inlet pipe (1) and extending with an exposed end surface into in said fireplace (2) past an exposed end of said feed tube (1) of said mixture, characterized in that said projection means (6) defines a portion of said second gas supply channel (5) by being breathable for flow of oxygen-containing gas therein. Combustion device according to claim 1, characterized in that the free end surface of said exposed end surface (6) is flat. 3. Combustion device according to claim 1 or 2, characterized in that said projection means (6) has an inner peripheral wall (62) which is inclined radially sealed in the direction of said fireplace (2). IN Combustion device according to any one of claims 1-3, characterized in that it further comprises a pulverized fuel / oxygen-containing gas separating element (7) located within said feed tube (1) of said mixture, coaxially therewith, separating element (7) comprises a straight circular cylindrical section (73) which cooperates with said mixing inlet pipe (1) to define therebetween a feeding channel section (I) of said mixture having a constant uniform cross-sectional area, and a section (74) extending from said straight cylindrical section (73) and tapered toward the downstream side of the flow so as to cooperate with said mixing inlet pipe (1) to define therebetween an additional mixing inlet channel portion (1). II) having a cross-sectional area which gradually increases in the direction of the mixing flow. Combustion device according to claim 4, characterized in that said conical sections have a first section (742) in which the separation of the flow is caused to occur and a second section (743) in which the separation of the flow is not caused to take place. and the first and second sections (742,743) of the conical section (74) alternate peripherally. Combustion device according to any of claims 1 to 5, characterized in that said burst means (6) comprise an opening (631, 633) through which a portion of the oxygen-containing gas flowing inside the burst means (6) projects in the direction against said exposed end of said projection means (6). Combustion device according to any one of claims 1 to 6, characterized in that said blasting means (6) is placed radially between said first gas inlet channel (4) and said second gas inlet channel (5). Combustion device according to any one of claims 1 to 7, characterized in that said hollow part of said blasting means (6) forms part of said second gas supply channel (5). 20 Combustion device according to any one of claims 1 to 8, characterized in that it further comprises means for maintaining a position and which are arranged on an exposed end portion of the feed tube of said mixture. • · • ·! * «I" |