GB2034456A - Burner - Google Patents

Abstract

The invention relates to a burner for the vaporisation of coal dust to supply a reactor. The burner comprises a plurality of coal dust/carrier gas supplies 2 with a circular cross-section which merge in the burner housing 3 into sections of circular rings of the same diameter arranged concentrically round a central pipe 1 conveying vaporisation medium, which sections are equal in area to the associated coal dust/carrier gas supply over the whole distance of a profile change in the cross-section of flow and which, together, form a substantially closed but not joined 360 DEG circular ring at the burner mouth, as a result of which a uniting of a plurality of streams of dust is effected and a symmetrical uniform distribution of dust is ensured in the combustion reaction chamber. <IMAGE>

Description

SPECIFICATION A burner for the vaporisation or combustion of fuels in the form of dust The invention relates to a burner for the vaporisation offuels in the form of dust under pressures up to 50 bar wherein a fuel, for example brown-coal dust and a vaporisation medium or a mixture of vaporisation media can be supplied to a reactor in order to produce gas by vaporisation under pressure.

In prior art arrangements providing separate supply of fuels in the form of dust and vaporisation media into vaporisation chambers, generally called burners, relay on fuel in the form of dust being supplied through a pipe disposed centrally in the burner.

One or more such pipes are generally mounted concentrically round this central pipe so that annular passages are formed between the pipes. These passages serve to supply a vaporisation media or mixtu res of vaporisation media into the reaction chamber. The vaporisation medium or media emerge from these passages at the reaction chamber side from annular cross-sections or from bores which, being generally disposed in a ring, close the passages and then react with the central jet of dust.

Fuel in the form of dust, for example brown coal dust can be relatively easily supplied in a pipe of circular cross-section situated centrally in the burner. Experience has shown that fluidized browncoal dust can be conveyed relatively easily with a relatively high density of the jet of dust in a geometrically smooth and straight pipe having constant cross-sectional area, observing specific requirements of the dust.

In prior known installations for example Specification BRD 2536249, U.S. Patent 2702744, DDR Patent 127904 the principle of central conveyance of vaporisation substance in the burner is used. An important drawback of arrangements employing central emergence ofthevaporisation substance into the reaction chamber with a supply of vaporisation medium, for example oxygen, provided concentrically therewith, is because recirculating gas flowing out of the reaction chamber can mix with vaporisation medium flowing through the concentric annular jet supplying same, unless the stream of vaporisation medium is shielded from recirculating gas, for example by an additional steam screen. As a result some of the oxygen supplied is used for the oxidation of combustible recirculating gases.In the pressure vaporisation of dust, however, it is an advantage to supply all the vaporisation oxygen for combustion reaction with the dust and to eliminate unwanted side reactions of this oxygen for reasons of economy in the utilization of oxygen.

A further drawback of supplying all the coal dust to be vaporised in the reaction chamber in a single pipe--which leads to a central pipe arrangement for reasons of symmetry with respect to the burner is that with an intermittent non-continuous supply of coal dust, the operational reliability of the installation is reduced. Whereas, in general, the supply of the gaseous vaporisation medium is assured by way of continuous stream, irregularities in the density of the fuel dust stream can occur relatively easily during flow of fluidized dusts. Should considerable fluctuations in the supply of coal dust occur at the burner exit, damage to the burner and reaction chamber is possible if the resulting excess supply of oxygen is not immediately reduced by regulating the supply.

The invention seeks to reduce specific oxygen requirements during vaporisation of brown coal dust under pressure, ensuring and increasing the functional and operational reliability of a burnervaporis- ing coal dust under pressure, and minimizing space requirements for such burners, particularly heavy duty ones, as far as possible. The number of burners required should be small in relation to the output of the installation.

An object of the invention is to achieve a functionally correct and reliable operation of such a burner by appropriate geometrical formation and arrangement of the constructional parts conveying coal dust and vaporisation medium. The reliability of fuel dust supply is increased. The compact, inert stream of dust must be loosened on entering the reaction chamber and mix well with the vaporisation medium, which mixing must be thorough, particularly, in all load bearing regions of the burner. The burner construction must offer the possibility of a flame control and in the event of the absence of a stream of dust, ensure such a symmetrical flame form that the combustion or reaction chamber is not destroyed by unequal temperature distribution and operation is not appreciably disturbed.

It was found that the flow of coal dust fluidized in a carrier gas takes place unhindered even with the highest charge density of dust (up to 900 kg dust3 carrier gas) with profile changes in the crosssectional area of flow, if the following conditions are adhered to: In each section AL of the total burner length L in which the profile of the cross-sectional area of flow of the dust alters, the cross-sectional area is equal to the area of the supply of coal dust and carrier gas entering the burner. (Figures 2, 3, 4, 5).

The inclination of a surface or part of a surface bounding the cross-sectional area of the flow of the dust to the axis of flow resulting from the change in profile must not exceed 8".

It was further found that the stream of dust conveyed in high dust densities is evened or equalised by widening the cross-section of the vertically downward fuel dust conveying pipe before reaching the burner to 20% of the conveyor pipe width. The length of pipe section to be widened and the magnitude of such widening in cross-section depends on the conveying conditions in the whole pipeline.

According to this invention there is provided a burner for the vaporisation of fuels in the form of dust, comprising a housing having a central pipe and an annular outer conduit for supplying vaporisation media, distributing conduits for supplying mixtures of fuel dust and carrier gas of density up to 900 kg dust3 carrier gas in a reactor at a pressure up to 50 bar, wherein a plurality of fuel dust/carrier gas con duits of circular cross-sectional area of flow in said housing into sections of circular or annular rings disposed concentrically round said central pipe and which, over the distance of profile alteration the cross-sectional flow area is equal to the crosssectional area of the associated coal dust/carrier gas supply conduit, the sections of circular rings together forming a substantially closed circular ring at the burner mouth, whereby a plurality of streams of dust are united to provide a symmetrical, uniform distribution of dust in the reaction chamber.

The burner in accordance with the invention requires that the stream of coal dust and carrier gas enters the reactor or combustion chamber vertically downwards from two or more circular rings or sections of circular rings which are disposed concentricallywith respectto both the burner axis and the central pipe supplying vaporisation medium. The vaporisation medium (for example oxygen, water vapour or a mixture of oxygen and steam) may emerge from both a central pipe and from an outer ring conduit and then enters the reactor. The vaporisation medium from one of these two supply chambers may flow at an angle of at least 45" to the axis of the dust stream and towards the dust stream; the second stream of vaporisation medium preferably emerges axially, parallel to the stream of dust.Axial emergence of vaporisation medium parallel to the stream of dust flowing from the central pipe is effected when an optical orthermoelectrical flame control is provided through the central pipe conveying vaporisation medium. (Figures 1, 2, 4, 5).

The mixture of coal dust and carrier gas is preferably supplied to the burner by means of two or more coal dust/carrier gas supply conduits and may be divided between the same number of circular rings or sections of circular rings. Entry of coal dust fuel into the annular circular pipes or rings may be effected at about 45" to the horizontal obliquely downwards through tangential socket inlets which are equal in area to the pipes supplying coal dust and carrier gas and ensures a steady entry into the annular space. Fuel dust entry into sections of circular rings (Figures 2, 3, 4) may be effected through vertical down pipes which merge, in the burner, into sections of circular rings of equal area.Inlet pipes and circular rings or sections of circular rings preferably have the same cross-sectional area of flow at all points in arrangements of burners according to the invention. In one preferred burner, at least two circular rings are provided concentrically (Figure 5) or at least three 240 sections of circular rings (Figures 3, 4) which provide a closed double ring in staggered or otherwise spaced location, so as to ensure a substantially symmetrical flame on failure of a stream of dust.

The supply of coal dust and vaporisation medium preferably end in the plane of the burner mouth.

By use of multiple and separate streams of dust, the risk of oxygen leakage into parts of a burner installation following the reactor in the event of disruption in the supply of dust is eliminated or at least considerably reduced.

The different number of dust streams also offers the possibility of a variable mode of operation and an increase in the regulating width.

By way of example only, reference will now be made to the accompanying drawings illustrating an embodiment and in which: Figure 1 is a schematic illustration of a burner, and Figures 2 to 6 show alternative embodiments in section and elevation of burner constructions in accordance with the invention.

As shown in Figure 1, a burner housing 3 has three coal dust/carrier gas supply lines or conduits 2. Supply lines 1 and 4 are provided for the vaporisation medium, the former by way of central pipe, the latter by outer ring or annular conduit. Each fuel/carrier gas line 2 has a widened section 6 of pipe and is monitored by quantitative analyser 9 which transmits information to a vaporisation medium regulator 5. This regulator 5 controls regulating values 7 in the vaporisation medium supply lines 1 and 4. A flame control device 8 is associated with the central pipe vaporisation medium supply line 1.

As shown in Figures 1 and 2 through three coaldust/carrier gas supply conduits 2 having the same dimensional profile, a mixture of coal dust and carrier gas at a speed of 2-10 mls reaches a slightly widened pipe section 6 and thereafter reaches the burner housing 3. In the burner housing 3, the cross-section of the conveyor pipe 2 changes from circular shape into a section of a circular ring with a constant area, wherein these areas are considered perpendicular to the flow axis. The sections of circular ring each have a segment angle of about 1200 so that a spatially closed 360" circular ring is provided with dust flowing through the three coal-dust/carrier gas supplies 2 and a symmetrical flame form is ensured.

The required amount of vaporisation medium for both central pipe 1 and outer ring conduit 4 is adjusted proportionally by means of the regulating valves 7, the vaporisation medium regulator 5 and the quantitative analyser 9.

The vaporisation medium, which reaches speeds of about 15to 150 mls loosens the jetiof dust and by flowing obliquely towards the stream of dust ensures completely thorough mixing.

The flame can be monitored and controlled by means of the flame control device 8 connected through the central pipe conveying vaporisation medium 1.

Referring to Figures 1 and 5 the mixture of coal dust and carrier gas enters the oblique tangential socket 10 of the burner housing 3 at a speed of 2-10 mls, through two coal-dust/carrier gas supplies 2 having the same flow characteristic. The tangential socket 10 represents a transition of equal area from the circular pipe into a rectangular slot which terminates in the annular space 2 of the burner. The annular space has the same cross-sectional area as the coal-dust/carrier gas supply 2 and the tangential socket 10. The tangential socket 10 is inclined at450 to the burner axis.

At the burner mouth the jet of coal dust and carrier gas is loosened by the vaporisation medium from the outer ring 4 and the central pipe 1 as a result of the different approach flow directions and high speeds between 15 and 150 m/s. In the course of this flow, coal dust and vaporisation medium are thoroughly mixed. The annular supply of dust ensures completely symmetrical burning, being retained even in the event of failure of a fuel dust supply and enables a burner to be ignited with a different number of streams of dust.

The regulation of vaporisation medium and flame control are effected as previously described with reference to Figure 1.

Figures 3 and 4 show alternative embodiments wherein the three fuel dust/carrier gas conduits 2 are profiled to terminate at the burner exit in an arrangement of overlapping, circular ring segments of segment angle 240 , and concentric with the central vaporisation medium supply pipe.

Claims (6)

1. A burner for the vaporisation of fuels in the form of dust, comprising a housing having a central pipe and an annular outer conduit for supplying vaporisation media, distributing conduits for supplying mixtures of fuel dust and carrier gas of density up to 900 kg dust3 carrier gas in a reactor at a pressure up to 50 bar, wherein a plurality of fuel dust/carrier gas conduits of circular cross-sectional area of flow merge in said housing into sections of circular or annular rings disposed concentrically round said central pipe and which, over the distance of profile alterations the cross-sectional flow area is equal to the cross-sectional area of the associated coal-dust/carrier gas supply conduit, the sections of circular rings together forming a substantially closed circular ring at the burner mouth, whereby a plurality of streams of dust are united to provide a symmetrical, uniform distribution of dust in the reaction chamber.

2. A burner in accordance with Claim 1, wherein a plurality of fuel dust/carrier gas supply conduits lead into a burner housing, each coal-dust/carrier gas supply being of circular cross-section and merging into a rectangular slot of equal area before reaching the burner housing and leading uniformly and tangentially into a separate annular chamber, axially displaced in relation to the burner, the cross-sections of pipes carrying vaporisation medium, the crosssection of the tangential socket along the flow path and the axial annular chambers being equal in area and each fuel dust/carrier gas supply being capable of independent operation.

3. A burner in accordance with Claim 1, wherein at least three fuel dust/carrier gas supply conduits merge in the burner housing from circular crosssection into sections of circular or annular rings which lie on different diameters, being 2/n times the length of the associated whole circular ring, wherein n is the number of conveyor pipegand are disposed in staggered or spaced relation to each other providing two substantially closed rings for supplying fuel dust.

4. A burner in accordance with Claim 1 or 2, wherein optical orthermoelectrical probes for flame control and flame temperature measurement are mounted on or in the central pipe conveying vaporisation medium.

5. A burner in accordance with any one of Claims 1,2 or 3, wherein the fuel dust/carrier gas supply conduit has a vertically downward widened section prior to reaching the burner housing for flow equalisation, said widened section amounting to a maximum of 20% greater width than the preceding pipe section.

6. A burner for the vaporisation of fuels in the form of dust substantially as herein described with reference to and as illustrated in any of the accompanying drawings.