JPH03213901A - Method and burner for burning fuel by step supply - Google Patents

Abstract

PURPOSE: To restrict the accumulation of a thick slag at a burner part, by a method wherein a primary fuel and air are supplied via a throat, and a secondary fuel is supplied from a duct in an inner duct as jet penetrating into a secondary combustion zone to reduce high temperature corrosion caused in a steel pipe on a wall. CONSTITUTION: A primary fuel 7 is supplied through a duct 15 concentric or almost concentric with those in ducts 13 and 14. The fuel 7 is supplied at such a speed that the jet thereof penetrates into an internal recirculation zone and is mixed with a combustion product from a primary combustion zone 6 especially at the downstream end thereof to accomplish combustion in a secondary combustion zone 8. As indicated by the broken line, the duct 15 can be opened into a burner at a proper position within a range defined by a throat 2 and an inner wall 18 of a combustion chamber. This allows application for pulverized coal, oil residue and other all possible types of object.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a means for reducing NO in combustion gas by stepwise fuel supply means.
This invention relates to a method of burning fuel with low x content.

In summary, the present invention provides a method for reducing NOx in a staged fueling combustion process by providing two internal combustion chambers in the combustion chamber through an internal recirculation zone of the primary combustion zone (6) to the secondary combustion zone (8). Next, inject fuel (15). The stoichiometric coefficient of the system up to and including the secondary combustion zone is preferably from 0.70 to 0.90. A burner adapted to such a method has also been disclosed, which has a secondary fuel (15) concentrically inside with an inner annular duct (13) for the primary fuel and an outer annular duct (14) for the primary air. It has a duct for

Staged fuel supply means that two concentric annular ducts open near the throat that spreads into the combustion chamber, and a first part of fuel (hereinafter referred to as primary fuel) is supplied through the inside of the duct, and a first part of the fuel (hereinafter referred to as primary fuel) is supplied through the inside of the duct, and the first part of the fuel (hereinafter referred to as primary fuel) is supplied to the outside. This is a known type of process which uses at least one burner of the type provided with a duct (hereinafter referred to as a quoll) through which a swirled combustion air is supplied. The primary fuel and combustion air can be combusted within the combustion chamber in the primary combustion zone, which creates an internal recirculation zone (■RZ
) is formed. A second portion of fuel (hereinafter referred to as secondary fuel) is fed into the combustion chamber near the primary combustion zone and
The secondary fuel is produced under substoichiometric conditions in the secondary combustion zone downstream from the primary combustion zone.
ric conditions) so that the NOx formed within the primary combustion zone is at least partially reduced. Finally, a third combustion air is provided near the secondary combustion zone so that the remaining fuel is transferred to the burnout zone downstream of the secondary combustion zone.
The combustion products formed in the subsequent combustion zone can be burned off.

The invention also relates to a burner using this method.

This type of burner is currently known as a "vortex stabilized burner". A feature of such burners is that, during operation, an internal recirculation zone is formed, in which the combustion products of the primary combustion zone are recycled.

Kay Reichert, K. D. Lennart and W. Schreiber, ``Using the Combustion Stage Method'' in Proceedings of the 8th IFRF Members' Meeting, May 28-30, 1986, Noordwijkerhout. Test data of a multi-stage mixing burner
established-mixing burner usi
ng fuel staging) J revealed how secondary fuel is supplied by multiple channels through the walls of the combustion chamber.

Reichert and Lennert are named as the inventors of GB-A-2146113, along with G. Balatner, which is a method of transporting primary fuel, primary air, secondary fuel, and tertiary air from the center through ducts. It discloses that they are introduced concentrically in order. Inside the innermost ring (i.e. 1
The central space (inside the fuel duct) communicates with a zone described as the reflux zone.

Earl Leibel and Day Nixon describe staged fuel burners for rNOx control in the above-mentioned proceedings.
NOxcontrol) J showed how secondary fuel is supplied to each burner and how the supply is incorporated into the burner design. However, the fuel supply takes place outside the combustion air supply, and the primary fuel is supplied into the throat with the aid of a distribution head arranged like a ring in the combustion chamber. Within the scope of this application, such an arrangement is considered to be equivalent to fuel supply by means of the inner ring.

In US-A-4265615, a can-shaped combustor is divided into primary and secondary zones by certain restrictions. In this burner configuration, the primary fuel is injected from an annular duct with annular air inlets both radially inside and outside the duct. The secondary fuel is injected from the central duct and 1
It is led through the secondary zone to the secondary zone where it is combusted by the tertiary air supplied into this zone. All fuel and air flowing through the burner is swirled and directed to keep the primary and secondary fuel separate within the primary zone.

A disadvantage of the known methods and constructions is that the mixing of the secondary fuel with the combustion products from the primary combustion zone is insufficient and therefore difficult to optimize.

The structure and method of the burner of the present invention provides that the secondary fuel is supplied through at least one duct concentric or nearly concentric with the two rings, through which the secondary fuel is injected into the combustion chamber. It differs from CB-A-2146113 (which is considered to be very close to the prior art because of its structural and operational similarities). The burner structure and method of the present invention has various advantages. There is no need for extra passages through the walls of the combustion chamber for secondary fuel supply. The secondary fuel supply method makes the design of the burner particularly simple and simple. Furthermore, the secondary fuel can be fed at a low velocity at a distance from the walls of the combustion chamber. This means reducing hot corrosion that occurs on the steel pipes of this wall. This also limits the build-up of thick slag on the walls of the combustion chamber, especially on the burner portion thereof, compared to the state of the art.

The secondary fuel is injected into the combustion chamber at a velocity such that the fuel passes through the internal recirculation zone as a jet to the downstream end of the internal recirculation zone and mixes with the combustion products of the primary combustion zone. Preferably, the secondary fuel is fed into the combustion chamber at a rate of at least 30 s/s. This further optimizes the method according to the invention. Secondary fuel accounts for 10 to 30% of the fuel.
The stoichiometric coefficient of the secondary combustion zone is preferably between 0.60 and 1.0, especially between 0.70 and 0.
．． Preferably, it is between 90 and 90.

In another aspect, the invention comprises a quoll extending into a combustion chamber and a pair of concentric annular ducts opening in the vicinity of the quoll, the inner ring being intended for fuel supply and the outer ring for providing combustion air. It is also embodied in a type of burner intended for feeding and in which there are means for swirling the combustion air.

As mentioned above, in current practice such burners are known as "vortex stabilized burners". According to the invention, the burner is provided with at least one duct concentric or nearly concentric with the two rings for supplying secondary fuel during operation. Furthermore, during operation, the method according to the invention is optimized by opening into the burner flush with the inner wall of the fuel chamber, in a position from near the throat of the quoll to the end of the quoll. is achieved.

Embodiments of the invention will be described with reference to the drawings.

1 and 2 show fuel staged combustion according to the prior art with a burner 2 in the wall 3 of the stove.

Primary fuel 4 and combustion air 5 are supplied to the primary combustion zone and burned. This combustion generates NOx.

At the same time, a secondary fuel 7 is supplied and, after mixing with the combustion products of the primary combustion zone, a reburning zone 8 of the secondary combustion zone is supplied.
combusted under conditions of lower stoichiometry. This at least partially reduces the NOx formed in the primary combustion zone.

In principle, this reduction occurs according to the equation:

2NO+ CH-→N2+ Co+OH The combustion products from the secondary combustion zone still contain combustible components. These are burnt out in the burnout zone by tertiary air 9.

The burner used in this known method (see FIG. 2) comprises a first portion of fuel (primary fuel) 4 and combustion air 5.
It is often a swirl-stabilized burner that opens into the throat 12 of the quoll 11, with two concentric annular ducts (rings) 13 and 14 feeding the quartz. Combustion air is provided by a vortex (not shown). In this type of burner, internal recirculation 16 occurs within the primary combustion zone 6.

An embodiment according to the invention is shown in FIG. In this diagram, 2
The next fuel 7 is supplied through a duct 15 concentric or nearly concentric with the ducts 13 and 14. This fuel is supplied at such a rate that the jet penetrates the internal recirculation zone and mixes with the combustion products from the primary combustion zone, especially at its downstream end, and combustion occurs in the secondary combustion zone 8. . As shown in dashed lines in FIG. 3, the duct 15 may open into the burner at any suitable location within the limits of the throat 12 and the inner wall 18 of the combustion chamber.

The invention can be used with all types of fuels such as pulverized coal, oil, residue and gas.

The outcome of this operation, in terms of NOx content in the exhaust gas, depends, among other things, on the type of fuel and the location of the supply of the tertiary combustion air. However, the effect of the stoichiometric coefficient and the amount of secondary fuel, other things being equal, is determined by the parameter, i.e. the stoichiometric coefficient in the secondary combustion zone (this includes the secondary combustion zone). (Should be understood as the stoichiometric coefficient of all fuel and air supplied up to the secondary combustion zone).

FIG. 4 shows the characteristics of the present invention based on this.

The stoichiometric coefficient in the secondary combustion zone is from 0.70 to 0.
．． Preferably, it is between 90 and 90. The amount of secondary fuel used is preferably as low as possible, but remains in the range of 10 to 30% for practical reasons.

The embodiments of the present invention will be explained as follows.

(1) supplying primary fuel (4) and air (5) into concentric annular ducts inside (13) and outside (14) respectively of the burner for indoor combustion in a primary combustion zone (6); Secondary fuel (15) is further added with air to complete combustion of the combustion products from the primary zone (6) in the secondary combustion zone (8) under substoichiometric conditions. , a staged fuel supply combustion method in the combustion chamber for reducing NOx content, in which the primary fuel (4) and air (5) are supplied via the widened throat (12) of the quoll (11). and an annular duct (4,
5), characterized in that the chamber is supplied by a duct (7) in the inner duct (4) of 5).

(2) A method according to embodiment (1), in which the secondary fuel is supplied to the combustion chamber at a speed of at least 30 m/s.

(3) A method according to embodiment (1) or (2), wherein the secondary fuel is between 10 and 30% of the total fuel.

(4) The stoichiometric coefficient in the secondary combustion zone is 0°6
and 1.0.

(5) The method according to embodiment (4), wherein the stoichiometric coefficient is between 0.7 and 0.9.

(6) using at least one burner with a quoll opening into the combustion chamber near the throat of the quoll into which two concentric annular ducts open, and supplying the primary fuel through the inside of said concentric annular duct; supplying primary air through the outside of the concentric annular duct, simultaneously swirling the air, and directing the primary fuel and primary air within the combustion chamber in a primary combustion zone defined with an internal recirculation zone. combustion products from the primary combustion zone under lower stoichiometric conditions in a secondary combustion zone downstream of the primary zone; a staged fuel comprising injecting into a combustion chamber from a duct radially inward of said inner concentric annular duct for combustion, and further burning out any residual fuel of the first and second fuels by further supplying air; Supply combustion method.

(7) Quartz ring 11 that spreads into the combustion chamber and opens (12)
) and a pair of concentric annular ducts (13, 14) opening near the throat of the quall (11), the inner duct (13) being intended for fuel supply and the outer duct (1
4) is for supplying air for primary combustion.

The burner is provided with means for swirling the combustion air, and the burner is provided with a means for swirling the combustion air; During operation of the burner (8) used in the method according to any of the embodiments (1) to 6), in which one duct (15) is provided, the innermost duct (15) is
5) a burner according to embodiment (7) opening into the burner at a position between the throat (12) of the flared duct (11) and the end of the flared duct flush with the inner wall (18) of the combustion chamber;

[Brief explanation of drawings]

FIG. 1 shows the staged combustion of fuel for a stove according to the prior art. FIG. 2 shows the staged combustion of fuel for a stove according to the prior art. FIG. show.

Claims (3)

[Claims] (1) supplying primary fuel (4) and air (5) into concentric annular ducts inside (13) and outside (14) respectively of the burner for indoor combustion in a primary combustion zone (6); Combustion of combustion products from the primary zone (6)
Staged fuel in the combustion chamber to reduce NO_x content, in which secondary fuel (15) is further added with air for completion in the same chamber under substoichiometric conditions in the secondary combustion zone (8) The feeding combustion method comprises feeding the primary fuel (4) and air (5) through the widened throat (12) of the quoll (11) and the secondary fuel as a jet to the primary combustion zone (6). An annular duct (4,
5), characterized in that the chamber is supplied by a duct (7) in the inner duct (4) of 5). (2) using at least one burner with a quoll opening into the combustion chamber near the throat of the quoll into which two concentric annular ducts open, and supplying the primary fuel through the inside of said concentric annular duct; supplying primary air through the outside of the concentric annular duct, simultaneously swirling the air, and directing the primary fuel and primary air within the combustion chamber in a primary combustion zone defined with an internal recirculation zone. combustion products from the primary combustion zone under lower stoichiometric conditions in a secondary combustion zone downstream of the primary zone; a staged fuel comprising injecting into a combustion chamber from a duct radially inward of said inner concentric annular duct for combustion, and further burning out any residual fuel of the first and second fuels by further supplying air; Supply combustion method. (3) Quorl (11) that spreads into the combustion chamber and opens (12)
) and a pair of concentric annular ducts (13, 14) opening near the throat of the quoll (11), the inner duct (13) being intended for fuel supply and the outer duct (1
4) is intended for the supply of primary combustion air and is provided with means for swirling the combustion air;
Claims 1. At least one duct (15) is provided inside the rings and concentrically or nearly concentrically therewith and intended for supplying secondary fuel during operation.
A burner used in the method according to 1) or (2).