TECHNICAL FIELD

The present invention relates to a solid fuel burner which conveys and burns a solid fuel and a combustion device including the solid fuel burner, and particularly to a solid fuel burner and a combustion device which are suitable for fuel particles having a large particle size such as biomass particles.

BACKGROUND ART

As a method for improving ignitability of a solid fuel burner used in a boiler of a thermal power generation plant, etc., and increasing stability of a flame, there are methods of increasing a fuel concentration or increasing an oxygen concentration of a fuel carrier gas.

For example, Patent Document 1 (Japanese Patent Laid-Open Publication No. 2016-133224) discloses a solid fuel burner provided with a fuel condensation flow passage (12) for condensing and concentrating solid fuel particles around a flame holder (16) installed in an opening portion of a burner. Patent Document 1 describes a configuration in which the fuel condensation flow passage (12) has a flow passage cross-sectional area gradually enlarged in a radial direction toward a downstream side, and describes improving ignitability and combustibility due to a high concentration of a solid fuel or a reduction in a velocity thereof, by making a flow rate in a fuel condensation flow passage outlet (12b) be slower than an inlet (12a).

CITATION LIST

Patent Document

Patent Document 1: Japanese Unexamined Patent Application Publication No. 2016-133224 (paragraphs “0023”-“0026”, “0034”-“0035”, and FIG. 1)Patent Document 2: Japanese Patent No. 4919844 (paragraphs “0021”-“0023”)Patent Document 3: Japanese Unexamined Patent Application Publication No. 2010-242999 (paragraph “0033”)

SUMMARY OF INVENTION

Technical Problem

When using biomass fuel as the solid fuel used in the prior art described in the above Patent Document 1, currently, pellets made of wood-based raw materials are frequently used as a fuel for mixing and burning in a coal (pulverized coal)-fired boiler for thermal power generation in Japan. Herein, the pellets are not used as they are, but fuel particles obtained by pulverizing and classifying the pellets in an improved mill (crusher and classifier) based on a coal mill (pulverized coal machine) are conveyed to the solid fuel burner by means of the carrier gas, and a mixed fluid of fuel particles and carrier gas is supplied to the burner to be burned in the same manner as pulverized coal.

However, it is more difficult for the biomass fuel to be pulverized than the coal, and an excessive pulverization power of the mill is required (about 10 times the power of the coal is generally required to make the same particle size as the coal from wood chips having a particle size of 50 mm), as well as it may be difficult to atomize to the same level as the current pulverized coal. In addition, if the biomass fuel is pulverized, a possibility of rapid combustion is increased, and measures to prevent the same are required. Due to these reasons, the biomass fuel is discharged from the mill in a state of fairly coarser particles than the coal (see Japanese Patent Publication No. 4919844, and Japanese Patent Laid-Open Publication No. 2010-242999, etc.).

In the configuration described in Patent Document 1, the flow rate in the fuel condensation flow passage is reduced. However, if the flow rate is too reduced on an upstream side of the burner (fuel nozzle) in the biomass fuel having coarse particles, the fuel particles may be adhered to and deposited on structures, and the like inside the nozzle.

It is a technical object of the present invention to prevent that the solid fuel particles obtained by pulverizing biomass fuel are adhered to and deposited on an inside of a nozzle.

Solution to Problem

In order to solve the above technical object, there is provided a solid fuel burner according to a first aspect of the present invention, including: a fuel nozzle through which a mixed fluid of solid fuel and a carrier gas thereof flows, and is opened toward a furnace; a combustion gas nozzle which is disposed on an outer peripheral side of the fuel nozzle to spray a combustion gas; a venturi provided in the fuel nozzle, in which a flow passage of the mixed fluid in the fuel nozzle is narrowed toward a center in a flow passage cross section; a fuel concentrator which is provided on the center side of the fuel nozzle to impart a velocity component to the mixed fluid in a direction away from the center of the fuel nozzle; and a flow passage partition member configured to partition the flow passage of the fuel nozzle into an inner side and an outer side in the flow passage cross section, wherein the flow passage partition member has a shape in which a cross-sectional area of an outer flow passage is enlarged toward a downstream end rather than an upstream end, the venturi at least has a contraction part in which a cross-sectional area of the flow passage of the mixed fluid is decreased toward the downstream side, and an expansion part disposed on the downstream side of the contraction part, in which the cross-sectional area of the flow passage of the mixed fluid is increased toward the downstream side, and an upstream end of the fuel concentrator is provided between an upstream end and a downstream end of the expansion part of the venturi, the fuel nozzle has an internal surface formed in a straight pipe shape from the downstream end of the expansion part to an opening portion of the venturi on the furnace side, and an inner diameter of the opening portion of the fuel nozzle on the furnace side is larger than an inner diameter of the upstream end of the venturi in the downstream end of the expansion part of the venturi.

A second aspect of the present invention is the solid fuel burner according to the first aspect, wherein a distance between a downstream end portion of the flow passage partition member and an opening end portion of the solid fuel burner on the furnace side in a flow direction of the mixed fluid is set in a range of ½ to 2 times an inner diameter of the fuel nozzle.

A third aspect of the present invention is the solid fuel burner according to the first aspect, including the flow passage partition member which is supported by a support member from an inner wall side of the fuel nozzle.

A fourth aspect of the present invention is the solid fuel burner according to the third aspect, wherein the support member is disposed so that a plurality of plate-shaped members are disposed so as to be linear when viewed from an opening face side of the fuel nozzle.

A fifth aspect of the present invention is the solid fuel burner according to the third aspect, wherein the support member is formed to have a large width so that a flow passage width in a circumferential direction of the fuel nozzle is narrowed toward the downstream side, and after reaching a maximum width, is formed to have a small width so that the flow passage width is gradually enlarged toward the downstream side.

In order to solve the above technical object, there is provided a combustion device according to a sixth aspect of the present invention including a plurality of stages in a vertical direction of a side wall surface of the furnace, and a plurality of burners provided in each stage in the furnace width direction, the combustion device including: at least one solid fuel burner according to the first aspect of the present invention.

A seventh aspect of the present invention is the combustion device according to the sixth aspect, including one or more of the solid fuel burners according to the first aspect of the present invention at least in an uppermost stage.

An eighth aspect of the present invention is the solid fuel burner according to the first aspect, wherein the cross-sectional area of the flow passage of the mixed fluid is formed so as to be monotonously increased or be the same as each other from the upstream end of the expansion part to the opening portion of the venturi on the furnace side.

Advantageous Effects

According to the first and sixth aspects of the present invention, the flow passage partition member has a shape in which the cross-sectional area of the outer flow passage expands toward the downstream end rather than the upstream end, and the upstream end of the fuel concentrator is provided between the upstream end and the downstream end of the expansion part of the venturi, such that increasing or decreasing the flow rate of the mixed fluid so as to pulsate is reduced. In addition, an occurrence of a low flow rate region in which fuel particles may be adhered, deposited and remain therein is prevented, and the flow rate is smoothly reduced. Thereby, it is possible to prevent the solid fuel particles obtained by pulverizing the biomass fuel from being adhered to and deposited on the inside of the nozzle. In addition, according to the first and sixth aspects of the present invention, an inner diameter (D1) of the opening portion of the fuel nozzle on the furnace side is larger than an inner diameter (D2) of the upstream end of the venturi (D1>D2) in the downstream end (V4) of the diameter expansion part (33c) of the venturi (33), such that the flow rate of the mixed fluid in the opening portion of the fuel nozzle is decreased, as well as ignitability and flame holding properties are improved.

According to the second aspect of the present invention, in addition to the effect of the first aspect of the present invention, as compared to a case in which the distance between the downstream end portion of the flow passage partition member and the opening end portion of the solid fuel burner on the furnace side is less than ½ times of the inner diameter of the fuel nozzle, damage caused by radiation from the furnace is reduced. In addition, as compared to a case in which the distance between the downstream end portion of the flow passage partition member and the opening end portion of the solid fuel burner on the furnace side is larger than two times the inner diameter of the fuel nozzle, it is possible to prevent the solid fuel burner from being large sized and long sized.

According to the third aspect of the present invention, in addition to the effect of the first or second aspect of the present invention, as compared to a case in which the flow passage partition member is not supported by the support member from the inner wall side of the fuel nozzle (for example, a case of being supported by an oil gun), when inserting and removing the oil gun into or from the fuel nozzle in the axial direction, for example, for maintenance of the solid fuel burner, it is possible to easily perform operations of assembly and disassembly of the solid fuel burner, without hindrance of the flow passage partition member.

According to the fourth aspect of the present invention, in addition to the effect of the third aspect of the present invention, it is possible to prevent the support member from hindering the flow of the mixed fluid. In addition, when viewed from the opening face side of the fuel nozzle, compared to a case in which a plurality of plate-shaped members are not disposed so as to be linear, a generation of vortex flow is prevented, as well as adhesion of the fuel to the support member and damage of each member due to ignition of the adhered fuel are reduced.

According to the fifth aspect of the present invention, in addition to the effect of the third aspect of the present invention, it is possible to prevent the support member from hindering the flow of the mixed fluid. In addition, the fuel may be condensed in the circumferential direction at a site where the width is formed large. Further, as compared to a case in which there is no portion of downstream side where the width becomes small, the generation of vortex flow is prevented, as well as adhesion of the fuel to the support member and damage of each member due to ignition of the adhered fuel are reduced.

According to the seventh aspect of the present invention, in addition to the effect of the sixth aspect of the present invention, it is possible to prevent the biomass fuel from falling to the furnace bottom of the furnace in an unignited state.

According to the eighth aspect of the present invention, in addition to the effect of the first aspect of the present invention, as compared to a case in which the cross-sectional area of the flow passage of the mixed fluid is monotonously decreased from the upstream end of the expansion part to the opening portion of the venturi on the furnace side, ignitability and flame holding properties are improved, as well as adhesion and deposition of fuel particles having a large particle size such as biomass fuel in the fuel nozzle are inhibited, and combustibility is improved.

