Pulverized coal burner

Abstract: In pulverized coal burning boiler for generating steam for power generation or factory, a larger capacity of the burner can be achieved without increasing number of the burners attached to the boiler and without increasing the capacity per each of the burners. A pulverized coal mixture to be supplied in tangential direction with respect to imaginary circle in horizontal plane of furnace is made rich on centeral side of the imaginary circle by arranging a rich/lean separating body within the pulverized coal mixture nozzle, or dividing front end of the pulverized coal mixture vertically into upper and lower portions so as to introduce ignition promoting air between the nozzle front end and injecting outlet port, or biasing the pulverized coal mixture nozzle with respect to the air nozzle, thereby making it possible to enlarge the capacity of the pulverized coal burner.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a pulverized coal burning boiler for generating a steam for a power plant, a factory and the like. Description of the Prior Art A conventional boiler of this kind will be described below with reference to Figs. 4 to 7. Reference numeral 01 denotes a boiler furnace main body, and a plurality of burner main bodies 02 are disposed in a vertical direction at each of four corners therein. The burner main body 02 is constituted by. a combustion air nozzle 03, an auxiliary air nozzle 04, a pulverized coal mixture nozzle 05, etc. and a pulverized coal mixture 10, a combustion air 11, a main burner air 12 and an additional air 13 are supplied thereto through a pulverized coal mixture feeding pipe 06, an air feeding duct 07, a main burner air duct 08 and an additional air duct 09. Reference numeral 14 denotes an additional air nozzle disposed at an upper position, reference numeral 15 denotes a furnace, and a pulverized coal flame 16 is formed in the furnace 15. Reference numeral 17 denotes an air adjusting damper assembled in each of the burner main bodies 02, reference numeral 18 denotes an imaginary circle imagined in the furnace 15 for explanation purpose, and reference numeral 19 denotes a fire vortex formed in the furnace 15. In the conventional pulverized coal burning boiler provided with the means mentioned above, a coal fed to a coal pulverizing apparatus (not shown) is finely pulverized, is mixed with a carrying air (a hot air) simultaneously fed so as to form the pulverized coal mixture 10, and is fed to the pulverized coal mixture nozzle 05 provided in the burner main body 02 through the pulverized coal mixture feeding pipe 06. The burner main bodies 02 are provided at four corners of the boiler furnace main body 01, and plural sets of burners, each burner comprising the combustion air nozzle 03, the pulverized coal mixture nozzle 05 provided in a center portion thereof and the auxiliary air nozzle 04 provided above and below the combustion air nozzle 03, are installed within each of the burner main bodies 02. (Here, there is a case that the burner main bodies 02 are provided not only at four corners of the boiler furnace main body 01, but also on a wall surface as shown in Fig. 6.) Each set of these nozzles, that is, the combustion air nozzle 03, the auxiliary air nozzle 04 and the pulverized coal mixture nozzle 05, is installed in such a manner as to blow the pulverized coal mixture 10 and the main burner air 12 in a tangential direction of an imaginary circle 18 which is set at a center portion on a horizontal cross section of the boiler furnace main body 01. A construction drawing of the conventional pulverized coal mixture nozzle 05 will be shown in Fig. 7. The additional air nozzles 14 are provided at four corners above the burner main bodies 02 in the boiler furnace main body 01. The additional air nozzle 14 is installed in such a manner as to blow the additional air 13 in a tangential direction of an imaginary circle 18 which has a same diameter as that of the imaginary circle 18 with respect to the respective nozzles 03, 04 and 05 of the burner main body 02 and is set at a center portion on a horizontal cross section of the boiler furnace main body 01. The pulverized coal mixture 10 supplied to the pulverized coal mixture nozzle 05 provided in the burner main body 02 is blown into the furnace 15 from the nozzle 05. On the other hand, the combustion air 11 is fed through the air feeding duct 07 by a feeding apparatus (not shown), and is branched 'into the main burner air 12 and the additional air 13 before entering the burner main body 02. The main burner air 12 is fed to the burner main body 02 through the main burner air duct 08, and is blown into the furnace 15 from the combustion air nozzle 03 and the auxiliary air nozzle 04. An amount of the main burner air 12 is generally set to be equal to or less than a stoichiometric mixture ratio of an amount of the pulverized coal blown as the pulverized coal mixture 10 so as to hold a portion of the furnace 15 below the additional air nozzle 14 in a reducing atmosphere, thereby reducing a nitrogen oxide (hereinafter referred to as to NOx for short) generated by burning the pulverized coal. The main burner air 12 and the branched additional air 13 are fed to the additional air nozzle 14, and blown into the furnace 15 so as to be used for completing a burning of a combustible portion left in the combustion gas due to the reduction combustion. The pulverized coal mixture 10 blown into the furnace 15 from the four' corners of the boiler furnace main body 01 is ignited by an ignition source (not shown), and forms the pulverized coal flame 16. The pulverized-coal flame 16 becomes a swirling flow so as to form the fire vortex 19, and ascend in the furnace 15 with swirling, thereby performing a swirling combustion. As mentioned above, the amount of the main burner air 12 blown from the burner main body 02 is equal to or less than the stoichiometric mixture ratio of the amount of the pulverized coal blown as the pulverized coal mixture 10 from the pulverized coal mixture nozzle 05, so that the portion of the furnace 15 below the additional air nozzle 14 portion becomes a reducing atmosphere. Accordingly, a combustion exhaust gas generated by burning the pulverized coal becomes to contain a combustible portion, however, NOx in the combustion exhaust gas generated by burning the pulverized coal is reduced so that an intermediate product such as NH3 and HCN is generated in place thereof. In the reduction of NOx in this reducing area, it is important to efficiently diffuse and mix the main burner air 12 and the pulverized coal mixture 10 so as to burn, and the more completely an oxygen supplied by the main burner air 12 is consumed, the higher a rate of NOx reduction becomes. The combustion exhaust gas containing the combustible portion is blown with the additional air 13 in the additional air nozzle 14 portion, and the combustion thereof is completed till an outlet of the furnace. In the conventional pulverized coal combustion mentioned above, in the case that a diameter of the imaginary circle 18 set in the center portion on the horizontal cross section of the boiler furnace main body 01 is excessively small, the pulverized coal flames 16 collide with each other, so that a formation of the fire vortex 19 becomes insufficient and the combustion is deteriorated. On the contrary, in the case that the diameter of the imaginary circle 18 is excessively large, the pulverized coal flames 16 collide with a side wall of the furnace 15 so that a phenomenon that a slagging occurs violently and a combustion is deteriorated is generated. Accordingly, a determination of the diameter of the imaginary circle 18 has so far been carefully performed by taking actual results into consideration. Nevertheless, a negative pressure is generated between the side wall of the furnace 15 and the pulverized coal flame 16 by the main burner air 12 blown at a high speed, so that the fire vortex 19 formed by the pulverized coal flames 16 becomes a hollow doughnut-shaped fire vortex 19 having a diameter significantly larger than the diameter of the imaginary circle 18 and flows in the furnace 15 due to a so-called Coanda effect in which the pulverized coal flame 16 is drawn near the side wall. Therefore, the slagging occurs violently. Since a blowing momentum of the pulverized coal mixture 10 blown from the pulverized coal mixture nozzle 05 becomes large when a capacity of'the burner becomes large, a degree of collision of the pulverized coal flame 16 with side wall of the furnace 15 is increased, and in addition thereto, it becomes difficult to secure a stable ignitability. As a result, the conventional pulverized coal burner has a disadvantage that it is hard to increase the capacity. In the case of intending to increase the capacity of the boiler, an combustion rate is necessarily increased, however, in order to deal with this, it is necessary (1) to increase a number of the burners attached to the boiler and (2) to increase the capacity of each of the burners. Among them, the increase of the number of the burners is performed by increasing a number of stages of the burners since the number of the burners on the horizontal cross section of the boiler furnace main body 01 is fixed, however, in this manner, a height of the boiler is increased, so that a cost for constructing the boiler is increased. Accordingly, in order to increase the capacity of the boiler, it is necessary to increase the capacity of each of the burners, however, when the combustion forming the fire vortex 19 is performed by the conventional burner, the blowing momentum of the pulverized coal mixture 10 blown from the pulverized coal mixture nozzle 05 is increased, together with an increase of the capacity of the burner, so that a degree of collision of the pulverized coal flame 16 with the side wall of the furnace 15 is increased. Therefore, there are problems that an amount of slagging is increased and it becomes difficult to secure the stability of ignition of the pulverized coal flame 16. From JP 58129105 A there is known a pulverized coal burning boiler comprising a furnace and pulverized coal burners for supplying a pulverized coal mixture in a tangential direction of an imaginary circle in a horizontal plane of the furnace. A rich/lean separating body in the form of a deflector block is mounted within a pulverized coal supply pipe to generate thick or thin concentration of pulverized coal. US 5 593 298 A describes a pollutant reducing modification of a tangential fired furnace in which air flow-restricting blades which restrict air flow from a main air-fuel compartment discharge portion or close a part of the area of the main air-fuel compartment discharge face to direct a larger proportion of the air required for complete combustion of the fuel from the main air-fuel compartment on a path outside of a fire ball in the furnace firing chamber. SUMMARY OF THE INVENTION An object of the present invention is to solve the problems in the conventional prior art mentioned above and provide a pulverized coal burning boiler which has an increased capacity of the pulverized coal burner. According to the invention there is provided a pulverized coal burning boiler as defined in claim 1. A preferred embodiment of the invention is defined in the dependent claim. The invention is mad for achieving the objects mentioned above, and provides a pulverized coal burning boiler with a pulverized coal burner for supplying a pulverized coal mixture in a tangential direction of an imaginary circle in a horizontal plane of a furnace so as to be burned, characterized in that a rich/lean separating body is arranged within a pulverized coal mixture nozzle so that the pulverized coal mixture becomes rich on a central side of the imaginary circle. Accordingly, the pulverized coal mixture blown from the pulverized coal mixture nozzle is blown such that an outer peripheral side of a fire vortex formed in the central portion of the furnace is made lean and an inner portion side thereof is made rich, and a supply amount'of a combustion air supplied from a combustion air nozzle, for example, provided on the outer periphery of the pulverized coal mixture nozzle is increased on the lean pulverized coal mixture side, thereby the pulverized coal flame is prevented from colliding with the wall surface of the furnace, so that a slagging is reduced and it becomes possible to make a capacity of the pulverized coal burner larger. Further, the invention provides that a mixture injecting port of a front end of the pulverized coal mixture nozzle is divided into upper and lower portions and a means for introducing an ignition promoting air is provided between the divided injecting ports. Accordingly, an ignition stability of the pulverized coal flame is improved by dividing the pulverized coal mixture blown from the pulverized coal mixture nozzle into the upper and lower directions so as to reduce to half an amount of the pulverized coal mixture blown from one of the directions thereof and by blowing a high temperature combustion air between the pulverized coal mixtures flown from two directions, thereby making it possible to increase a capacity of the pulverized coal burner. Still further, the invention provides that a pulverized coal mixture nozzle is made eccentric with respect to an air nozzle so that the pulverized coal mixture becomes rich on a central side of the imaginary circle. Accordingly, an axis of the pulverized coal mixture nozzle and an axis of the air nozzle are moved and shifted to be eccentric with each other so that a concentration of the pulverized coal of the'pulverized coal mixture blown to an outer peripheral side of a fire vortex (near the wall surface of the furnace) formed in the furnace from the pulverized coal mixture nozzle is reduced and a concentration of the pulverized coal blown to an inner portion side of the fire vortex becomes rich, thereby the pulverized coal flame is prevented from colliding with the furnace wall and an amount of an air near the inner wall surface of the furnace is increased to form an oxidation atmosphere. Therefore, the molten ash is prevented from attaching by increasing an ash melting point. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an explanatory view as seen from a cross section along a line I-I in Fig. 2, which shows a system of a boiler in accordance with a first embodiment of the invention; Fig. 2 is a cross sectional view along a line II-II in Fig. 1, which shows a horizontal cross section of the boiler in Fig. 1; Figs. 3(a), 3(b) and 3(c) show a summary of a pulverized coal mixture nozzle in the boiler shown in Figs. 1 and 2, in which Fig. 3(a) is a schematic view showing a cross section along a line a-a in Fig. 3(b); Fig. 3(b) is a schematic view showing a cross section along a line b-b in Fig. 3(a) and Fig. 3(c) is a schematic view showing a cross section along a line c-c in Fig. 3(a); Fig. 4 is a schematic view as seen from a cross section along a line VI-VI in Fig. 5, which shows a system of a conventional boiler; Fig. 5 is a cross sectional view along a line VII-VII of a boiler shown in Fig. 4; Figs. 6(a), 6(b), 6(c) and 6(d) are schematic views which respectively show different aspects of an arrangement of a burner in the conventional boiler; and Figs. 7(a) and 7(b) show a pulverized coal mixture nozzle in the conventional boiler, in which Fig. 7(a) is a cross sectional view and Fig. 7(b) is a cross sectional view along a line B-B of fig. 7(a). DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the invention will be described below with reference to Figs. 1 to 3. In this case, in correspondence to the conventional ones mentioned above, reference numerals obtained by adding 100 to the reference numerals in the conventional ones will be attached to the same parts so that a mutual relation can be easily understood, and an overlapping description will be omitted as much as possible. Accordingly, since reference numerals 101 to 119 correspond to the reference numerals 01 to 19 in the conventional structure, a description will be simplified as much as possible, and an ignition promoting air hole 120 provided in a pulverized coal mixture nozzle 105, an ignition promoting air chamber 121, an ignition promoting air chamber inlet port 122, a guiding plate 123, a rich/lean separating body 124, etc. will be described in detail. A coal fed to a coal pulverizing apparatus (not shown) is pulverized there, is mixed with a carrying air (a hot air) simultaneously fed so as to form a pulverized coal mixture 110, and is fed to a pulverized coal mixture nozzle 105 provided in a burner main body 102 through a pulverized coal mixture transporting pipe 106. The pulverized coal mixture nozzle 105 is constituted by a pulverized coal mixture pipe connected to the pulverized coal mixture transporting pipe 106, and a mixture injecting nozzle attached to a front end thereof. The rich/lean separating body 124 is provided within the pulverized coal mixture pipe near an inlet of the mixture injecting nozzle. An injecting port of the mixture injecting nozzle is branched into upper and lower directions with an optional angle, for example, an angle of 10 degrees to 30 degrees in one direction with respect to a horizontal axis, and the ignition promoting air chamber 121 is provided between the upper and lower injecting ports. The combustion air nozzle 103 is provided on an outer periphery of the mixture injecting nozzle, and blows the main burner air 112 into the furnace 114 from a blowing port constituted by-the mixture injecting nozzle and the combustion air nozzle 103. The pulverized coal mixture 110 fed to the pulverized coal mixture nozzle 105 flows in a biased manner at the pulverized coal mixture pipe outlet portion by the rich/lean separating body 124. As a result, the pulverized coal mixture 110 is structured such that a concentration of the pulverized coal becomes lean on the rich/lean separating body 124 attaching side at the mixture injecting nozzle outlet port due to a force of inertia and a concentration of the pulverized coal on the opposite side not attaching the same becomes rich. A blowing port of the main burner air 112 formed by the mixture injecting nozzle and the combustion air nozzle 103 is formed wider on the lean pulverized coal side of the pulverized coal mixture 110 and narrower on the rich pulverized coal side. In a swirling combustion performed by forming the fire vortex 119 in a center portion of the furnace 115, a portion, blown into a central side of the fire vortex 119, of the pulverized coal mixture 110 injected from the mixture injecting nozzle becomes to an upstream side of the swirling combustion flow, so that said portion is in a state of easily igniting having a large radiant heat from the adjacent pulverized coal flame 116. Accordingly, the pulverized coal mixture 110 is set such that the rich pulverized coal side is blown to the central side of the fire vortex 119. In the main burner air 112 blown from the main burner air 112 blowing port formed by the mixture injecting nozzle and the combustion air nozzle 103, since an area of the main burner air 112 blowing port is set such that a blowing amount to the central side of the fire vortex 119 becomes less and a blowing amount to the outer peripheral side (a wall surface side of the furnace) of the fire vortex 119 becomes more, the pulverized coal flame 116 is prevented from colliding with the wall surface of the furnace 115, thereby restricting a generation of slagging and unburned component. In addition to the structure mentioned above, in accordance with this embodiment, a new device is further added to the mixture injecting nozzle in order to improve an ignition stability of the pulverized coal flame 116. That is, as mentioned above, the mixture injecting nozzle is structured such that the injecting port thereof is branched to the upper and lower directions with an optional angle, the ignition promoting air chamber 121 is provided between the upper and lower injecting ports, and the-guiding plate 123 and the ignition promoting air chamber inlet hole 122 are provided in the inlet of said air chamber 121. The ignition promoting air chamber 121 is formed by disposing a plate on a side facing to the furnace 115, and the ignition promoting air hole 120 is bored on the plate so as to blow the main burner air 112, which has flown to the ignition promoting air chamber 121 through the ignition promoting air chamber inlet hole 122, between two pulverized coal mixtures 110 injected from the mixture injecting nozzle. The main burner air 112 blown from the ignition promoting air hole 120 prevents flows of the pulverized coal mixture 110 blown from two injection ports of the mixture injecting nozzle from joining together earlier, and since a temperature of the main burner air 112 is high to be about 300 °C in comparison to a temperature of the pulverized coal mixture 110 which is generally 100 °C or less (in many cases, about 80 °C), an effect that a generation of a volatile matter between the pulverized coal mixtures 110 is promoted can be obtained, so that an igniting stability of the pulverized coal flame 116 can be secured. As mentioned above, in'accordance with the invention, by use of the rich/lean separating body disposed within the pulverized coal mixture nozzle, the concentration of the pulverized coal of the pulverized coal mixture blown into the furnace is made rich in the portion blowing to the central side of the fire vortex and lean in the portion blowing to the outer peripheral side, thereby preventing the pulverized coal flame from colliding with the wall surface of the furnace, and the slagging can be reduced and the capacity of the pulverized coal burner can be enlarged. Further, in accordance with the invention , by use of the ignition promoting air hole of the ignition promoting air chamber provided between-the upper and lower injecting outlet ports-at the front end of the pulverized coal mixture nozzle, a part of the high temperature main burner air is blown to the portion between the pulverized coal mixture injecting flows injected from the upper and lower injecting outlet ports, thereby preventing the upper and lower pulverized coal mixture injecting flows from being joined together earlier, and further, since the generation of the volatile matter is promoted, the pulverized coal flame can be stably ignited and burned, and the capacity of the pulverized coal burner can be enlarged. Still further, in accordance with the invention as recited in Claim 2, the axis of the pulverized coal mixture nozzle and the axis of the air nozzle are shifted to be eccentric with each other so that the concentration of the pulverized coal in the pulverized coal mixture blown from the pulverized coal mixture nozzle to the portion on the outer peripheral side of the fire vortex formed in the furnace, that is, the portion close to the wall surface of the furnace is made lean and the concentration of the pulverized coal blown to the portion the inner side of the fire vortex is made rich, thereby the pulverized coal flame is prevented from colliding with the furnace wall and the air amount near the furnace wall is increased so as to form an oxidation atmosphere and increase the ash melting point, and the molten slag is prevented from attaching.

Claims: A pulverized coal burning boiler comprising a furnace (115) and a pulverized coal burner (102) for supplying a pulverized coal mixture (110) in a tangential direction of an imaginary circle (118) in a horizontal plane of the furnace (115) so as to be burned, wherein a rich/lean separating body (124) is arranged within a pulverized coal mixture nozzle (105) of said pulverized coal burner (102) so that said pulverized coal mixture (110) becomes rich on a central side of said imaginary circle (118), characterized in that a mixture injecting port of a front end of said pulverized coal mixture nozzle (105) is divided into upper and lower portions and a means (120-123) for introducing an ignition promoting air (112) is provided between the divided injecting ports. The pulverized coal burning boiler as recited in claim 1, characterized in that said pulverized coal mixture nozzle (105) is made eccentric with respect to an air nozzle (103) surrounding said pulverized coal mixture nozzle (105) so that a blowing port for the air (112) formed by said pulverized coal mixture nozzle (105) and said air nozzle (103) is wider on the lean pulverized coal side of the pulverized coal mixture (110) and narrower on the rich pulverized coal side.

Inventors: ICHINOSE TOSHIMITSU, OGURI MASAHARU, OKAMOTO AKIYASU, SUZUKI TAKESHI, ICHINOSE, TOSHIMITSU, OGURI, MASAHARU, OKAMOTO, AKIYASU, SUZUKI, TAKESHI, Ichinose, Toshimitsu Nagasaki R &amp; D Center of Mits, Oguri, Masaharu, Choryo Engineering Co., Ltd., Okamoto, Akiyasu, Nagasaki R &amp; D Center of Mits, Suzuki, Takeshi, Nagasaki R &amp; D Center of Mits
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1998
Main classification: F23C5
IPC codes: F23D1, F23C5