The present invention relates to a reactor for reducing thecontents of nitrogen oxides and sulphur oxides in combustion gases,which reactor comprises a post-combustion chamber to be connectedtogether with or after a combustion chamber.

A major problem in the combustion of liquid and solid fuels is thecontent of sulphur oxides and nitrogen oxides present in the fluegas. Thus many attempts have been made to reduce this oxide content,both by flue gas cleaning and by catalytic treatment of the exhaustgases.

The invention is based on the insight that it is possible toreduce the content of nitrogen oxides and sulphur oxides to aconsiderable extent if it is ensured that suitable oxidation andtemperature conditions prevail in the passageway between thecombustion chamber and the chimney.

Swedish Patent 7804761-0 (SE-B-413,158) discloses and apparatusfor the combustion of a mixture of gaseous or particulate,combustible material and combustion air. This apparatus is used forcombusting various gaseous or particulate materials containing carbonor carbon compounds, in such a complete manner that the combustiongases emitted are practically free from soot, carbon monoxide andhydrocarbon residues. It is, however, not stated in the patentspecification that the apparatus can be used for reducing thecontents of nitrogen oxides and sulphur oxides in combustion gases.

U.S. Pat. No. 4,481,889 discloses a method for afterburning fluegases by conducting the impure gases through a burner in anafterburner in which the exhaust gases, by being positively mixedwith a combustion gas, are subjected to complete combustion. In thisprocess, combustible gases are thus supplied to bring aboutafterburning of the flue gases.

DE-A-3,014,590 discloses a pre-combustion chamber for an oil- orgas-fired, fan-supported burner. This pre-combustion chamber servesto shape the generated flame and to retard it before entering thecombustion chamber. This apparatus thus serves as an intermediarybetween the burner and the combustion chamber, whereas not as areactor for reducing the contents of nitrogen oxides and sulphuroxides in combustion gases.

A reactor is provided for reducing the contents of nitrogen oxidesand sulphur oxides in combustion gases. The reactor is in the form ofa post-combustion chamber to be connected after a combustion chamber.The reactor has a casing including a generally cylindrical main parttransforming at its top into a dome-shaped outlet part with an outletopening. Around the casing of the reactor, there is provided aheat-insulated wall whose inner side has substantially the same shapeas the casing and which is eccentrically disposed in relation to thecasing. The casing of the reactor accommodates a partition which isconical and has its apex directed towards the outlet opening. A gapis formed between the shell and the partition. At the inlet end ofthe shell, an inlet funnel is provided at a certain distance from theinlet end so as to form a gap. A heat exchanger is provided forpreheating secondary air supplied through a secondary air intake intothe gap between the casing and the wall at a certain distance fromthe opening. At the bottom, the gap is connected to a collecting boxand an outlet pipe.

The invention will now be described in more detail hereinbelowwith reference to the accompanying drawings illustrating twoembodiments of the device according to the invention.
In the drawings
FIG. 1 is a vertical section schematically showing anembodiment of the reactor according to the invention;
FIG. 2 is a section taken along the line II-II in FIG.1.
FIG. 3 is a vertical section schematically showing anincineration plant using another embodiment of a reactor according tothe invention; and
FIG. 4 shows yet another embodiment of a reactor according tothe invention.

The arrangement shown inFIG. 1 comprises a reactor for reducing the contents ofnitrogen oxides and sulphur oxides in combustion gases. The reactorhas a casing or wall 10 with a substantially vertical,generally cylindrical shell 11 and a dome-shaped outlet end12 associated therewith. The dome-shaped outlet end has acentral outlet opening 13. The opposite end of the shell11 forms an inlet end 14. Inside the casing 10,the is provided a conical partition 15 which has its apexdirected towards the outlet end 13 and which is mounted onsupport members 16 in a manner to define an annular gap17 between the partition 15 and the casing 10.Instead of an annular gap, the connection between the upper and thelower part of the casing 10 may be in the form of at least twoedge recesses distributed around the periphery of the partition,suitably as disclosed in SE-B-413,158 which is included by reference.At the bottom of the reactor, there is provided an inlet funnel18 which leads the exhaust gases from a combustion chamber(not shown) into the reactor, so that the exhaust gases will beintroduced at a suitably high velocity and directed towards theconical inner side of the partition 15. Around the casing10, there is provided a further casing or wall 20 whichhas substantially the same shape as the casing 10 but largerdimensions so as to define a gap 21 between the casings10 and 20. The casing 10 is eccentricallydisposed in the casing 20. The casing 20 may be made ofa heat-insulating material, but may also be surrounded by such amaterial. In the illustrated embodiment, an external heat-insulation22 is used for the casing 20. The gap 21 betweenthe two casings is connected at the bottom to an annular collectingbox 23 connected to an outlet pipe 24, e.g. a chimney.

In the gap 21 between the two casings, there may beprovided a heat exchanger (not shown in more detail) for preheatingsecondary air. In the embodiment according to FIG. 1,secondary air is however supplied through an annular space 40formed between the casing 20 and the external heat-insulation22. The preheated secondary air is fed through a secondary airintake 25 into the space between the two casings at somedistance from the outlet opening 13.

Between the lower edge of the inlet end 14 of the innercasing 10 and the inlet funnel 18, there is defined anannular gap 19 for the separation of ash particles which havebeen separated in the post-combustion chamber 10 or formedduring the combustion therein.

When using the arrangement according to FIGS. 1 and2, it is advantageous to have the exhaust gases from thecombustion chamber arrive in the inlet funnel 18 at a maximumvelocity of 2 m/s. By the conical shape of the inlet funnel, the gasvelocity is increased and the gases are directed towards the innerside of the conical partition, residual carbon monoxide will oxidiseinto carbon dioxide, and this oxidation will proceed in the spaceabove the partition. From the outlet opening 13, the fluegases enter into the gap between the casings 10 and 20where afterburning and treatment of sulphur oxides and nitrogenoxides is performed under the action of the preheated secondary airwhich is supplied through the secondary air intake 25 andpreferably heated to a temperature of about 700° C. By theeccentric arrangement, intense mixing is achieved as well ascompression alternating with expansion of the flue gases which aremoving helically downwards to the collecting box 23 beforepassing out to the outlet pipe or chimney 24 at a temperatureof about 900° C.

The principle of the inventive device is based on experiments withideal turbulence for final oxidation of all hydrocarbon materialswith a controlled low partial pressure in the gas phase to achieve asufficient contact time with hot catalytic surfaces. The hot contactsurfaces initially consist of the material in the partition15. Behind this concave partition, there is thus a slowerturbulence in a reducing atmosphere in order to obtain the necessaryproduction of carbon monoxide for the process, e.g. for reducing thesulphur content in the combustion gases. In stoichiometric combustionand according to the following formulae, sulphur deposits by morethan 90% as sulphur droplet which have been sublimated during thecooling. Since the post-combustion chamber is vertically mounted, thesublimated sulphur, together with other particles, will automaticallypass to the ash bed through the gap between the inlet funnel18 and the inlet end 14.

When the post-combustion chamber is used in large-scale plants,the formula 2CO + SO₂ S + 2CO₂ applies.

For plants with over-stoichiometric combustion, formulae CO +O₂ CO + CO₂ and SO₂ + CO +H₂O H₂S + CO and SO₂ + H₂S S +H₂O apply.

If the gases entering the post-combustion chamber have atemperature of 900° C. and a flow velocity of at most 2 m/s, itis possible to obtain substantially soot- and particle-free exhaustgases when a catalysing surface exists on the conical partition 15and on other contact surfaces affecting the combustion gases.

The different formulae relating to the combustion chamber appearfrom the following.

The device according to the invention as illustrated in FIG.3 has substantially the same design as that in FIG. 1.The device in FIG. 3 is shown together with an incinerationplant of the type disclosed in Swedeish Patent 7804761-0(SE-B-413,158). For a more detailed description of this arrangement,reference is thus made to said patent specification which is includedby reference. The device in FIG. 3 is generally designated30. After this incineration device, there is a furthercombustion chamber 31 in which noxious waste or solid fuels,for instance, can be combusted. From this combustion chamber offurnace 31, the combustion gases flow through a gap 32up to the inlet funnel 18 and into the post-combustion chamberaccording to the invention. The gap 32 is formed between theincineration device 30 and a heat-insulated furnace wall33. At the lower end of the space defined by the furnace wall33, there is an ash outlet 34. Since thepost-combustion chamber or reactor in FIG. 3 is essentiallydesigned as in FIG. 1, equivalent parts have been given thesame reference numerals. In the embodiment shown in FIG. 3,the partition 15 extends as far as the inner side of thecylindrical shell surface 11, and edge openings are providedwhich extend obliquely through the partition 15 adjacent theshell surface, such that the passage between the space below thepartition and the space above it imparts a helical motion to the fluegases when entering the upper chamber above the partition 15.

FIG. 4 shows a further embodiment of a reactor according tothe present invention. Corresponding parts have been given the samereference numerals. The essential difference between the embodimentsof FIG. 1 and FIG. 4 is the way of supplying secondaryair through a secondary air intake 45. In this embodiment, thesecondary air intake 45 consists of a gap between two conicalwalls 40, 41. This gap is fed with secondary air whichmay have been preheated in any suitable manner. The air is eitherblown through the gap 45 or sucked therethrough as a result ofthe ejector effect produced by the exhaust gases entering the reactorthrough the inlet funnel 18.

In the embodiment of FIG. 4, the conical partition15 has been designed in the manner shown in theabove-mentioned SE-B-413,158, which means that there are provided atleast two through passages 17 formed of edge openingsdistributed around the circumference of the partition and extendingobliquely therethrough so as to impart a turbulent effect to the fluegases when passing between the inlet chamber and the outlet chamber.

The reactor according to the invention may advantageously be usedalso in incineration plants operating with a fluidised fuel bed.

I claim:

1. A reactor for reducing nitrogen oxides and sulphuroxides present in a combustion gas outlet stream from a combustionchamber, comprising:

a casing comprising a vertically oriented, generally cylindricalshell having a longitudinal axis, a downwardly opening inlet endarranged to receive said combustion chamber combustion gas outletstream and a generally dome-shaped outlet end having radiallycentrally located thereon an outlet opening;

a partition wall disposed within said casing at a locationintermediate said inlet end said outlet opening and dividing saidcasing into an inlet chamber adjacent said inlet end, and an outletchamber adjacent said outlet end; said partition wall being generallytransversally extending within said casing, so as to have a centerdisposed generally radially centrally of said generally cydrincalshell, and an outer perimeter disposed near an internal peripheralsidewall surface of said generally cylindrical shell;

means defining at least one opening from said inlet chamber intosaid outlet chamber adjacent said sidewall surface of said generallycylindrical shell and remotely of said center of said partition wall;

means providing a heat-insulating wall externally spaced from andenclosing said casing, thereby defining a space annularly betweensaid wall means and said cylindrical shell and terminally betweensaid wall means and said outlet end;

means defining a secondary air supply conduit means having anoutlet into one of:

said space, at a location spaced from said outlet opening; and

said inlet chamber;

an outlet pipe; means communicating said space, adjacent saidinlet end of said casing, with said outlet pipe;

a frusto-conically tapering inlet funnel projecting through saidinlet end, into said inlet chamber of said casing, said inlet funnelhaving a larger diameter inlet end disposed axially before said inletend of said shell and an outlet end disposed within said inletchamber, under said partition wall, whereby said combustion gasoutlet stream, in flowing through said inlet funnel into said inletchamber will be progressively reduced in transverse cross-sectionalarea;

said inlet funnel, where axially passing said inlet end of saidshell, being located generally radially centrally of said casing andbeing smaller in diameter than said inlet end of said shell, therebydefining an open annular gap for egress of ash particles from withinsaid casing.

2. The reactor of claim 1. wherein:

said at least one opening from said inlet chamber into said outletchamber is constituted by a plurality of openings formed obliquelythrough a perimetrically outer portion of said partition wall in sucha sense as to impart a swirling motion about said longitudinal axisto gas flowing from said inlet chamber into said outlet chamberthrough said openings.

3. The reactor of claim 1. wherein:

at least one of said shell, said outlet end of said casing andsaid partition wall contains a material having an ability to catalyzeoxygen of carbon and carbon compounds.

4. The reactor of claim 1. further including:

means effective upstream of said secondary air outlet, forpreheating secondary air flowing through said secondary air supplyconduit means.

5. The reactor of claim 1. wherein:

said secondary air supply conduit means has an inlet openingdisposed adjacent said inlet end of said inlet funnel, said outlet ofsaid secondary air supply conduit being disposed adjacent said outletend of said inlet funnel; said secondary air supply conduit, betweensaid inlet end and outlet of said secondary air suppy conduitextending externally upon said inlet funnel.

FIG.3

FIG. 4 Double backlash conus with ejector function for inlet secondary air.