WO2015062619A1 - Inserts pour brûleurs et systèmes de chauffage à tube radiant - Google Patents

Inserts pour brûleurs et systèmes de chauffage à tube radiant Download PDF

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Publication number
WO2015062619A1
WO2015062619A1 PCT/EP2013/072487 EP2013072487W WO2015062619A1 WO 2015062619 A1 WO2015062619 A1 WO 2015062619A1 EP 2013072487 W EP2013072487 W EP 2013072487W WO 2015062619 A1 WO2015062619 A1 WO 2015062619A1
Authority
WO
WIPO (PCT)
Prior art keywords
heating system
passage
porous
tube
exhaust gas
Prior art date
Application number
PCT/EP2013/072487
Other languages
English (en)
Inventor
Sandro GIANELLA
Luca Romelli
Alberto Ortona
Dimosthenis Trimis
Volker Uhlig
Robert Eder
Tobias GRÄMER
Joachim G. WÜNNING
Enrico CRESCI
Original Assignee
Erbicol Sa
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Erbicol Sa filed Critical Erbicol Sa
Priority to PCT/EP2013/072487 priority Critical patent/WO2015062619A1/fr
Publication of WO2015062619A1 publication Critical patent/WO2015062619A1/fr

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C3/00—Combustion apparatus characterised by the shape of the combustion chamber
    • F23C3/002—Combustion apparatus characterised by the shape of the combustion chamber the chamber having an elongated tubular form, e.g. for a radiant tube
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
    • F23D14/12—Radiant burners
    • F23D14/126—Radiant burners cooperating with refractory wall surfaces
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
    • F23D14/12—Radiant burners
    • F23D14/151—Radiant burners with radiation intensifying means other than screens or perforated plates
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C2900/00—Special features of, or arrangements for combustion apparatus using fluid fuels or solid fuels suspended in air; Combustion processes therefor
    • F23C2900/03009—Elongated tube-shaped combustion chambers

Definitions

  • the invention relates to the field of radiant tubes, recuperative burners and more generally to heating systems including a tubular member which defines a combustion chamber and a passage for the exhaust gas.
  • Prior art Radiant tubes are known in the art. They are typically used as indirect heating systems for heat treatments to be carried out under a protective gas atmosphere. For example, radiant tubes are commonly used for providing heat to an annealing process.
  • a radiant tube In a radiant tube, combustion takes place within the tube and exhaust gas are discharge at a tube end.
  • radiant tubes according to the geometry of the tube, including for example straight tubes, U-tubes and W-tubes, as well as embodiments with exhaust gas recirculation such as the so-called P-tube, double-P tube and A-tube.
  • Another known embodiment of a radiant tube is the single-ended tube, featuring a coaxial structure with two tubular walls and exhaust gas discharge through the annular space between them.
  • a purpose of a radiant tube is to transfer as much heat as possible to the process. To do so, it is desired to maximize the transfer heat from combustion flame and from the exhaust gas to the surrounding walls of the radiant tube. It is known that heat transfer takes place primarily by radiation in the first portion of the tube in the presence of the combustion flame, while heat transfer in the remaining part of the tube is substantially governed by convection.
  • the first portion of the tube, around and near the combustion chamber, is usually termed "high emissivity portion” while the second portion of the tube, until the outlet section, is termed "low emissivity portion".
  • the first leg of the tube is typically under high emissivity regime, while the second leg (after the U-turn) is typically under low emissivity regime.
  • WO 2008/036515 and US 6484795 disclose examples of spiral-like inserts for radiant tubes according to the prior art. Said inserts, however, are not fully satisfactory. In particular, it has been noted that despite the swirling motion and the larger contact area with the gas, the convective heat transfer in the presence of said spiral-like inserts remains relatively low.
  • the present invention also relates to burners which do not require radiant tubes, e.g. because a protective atmosphere is not required.
  • recuperative burners typically comprise an elongated tube member with a coaxial structure, including a tubular recuperator and an exhaust gas guide tube coaxially arranged around the recuperator.
  • Exhaust gas is passed in the annular space between said tubes, in order to pre-heat the combustion air and/or dilute the fresh charge, improve the temperature uniformity and lower the emissions.
  • Designers of said burners seek for maximization of the heat transferred from the exhaust gas to the tube-like recuperator, without drawbacks such as complication, cost or excessive pressure drop which may affect the combustion.
  • WO 2012/160095 discloses a solution to this problem by a textile-coated heat exchanger.
  • the heat exchanger surface is coated on one or both sides, over a ceramic intermediate layer, with a ceramic structure which is produced using a textile material soaked in a ceramic slip.
  • the aim of the invention is to further improve the above prior art.
  • one of the goals of the invention is a better heat exchange between a hot combustion gas and a tubular body, possibly with a coaxial structure, like for example a radiant tube or a recuperative burner.
  • a goal of the invention is a better heat transfer between hot gas and an inlet stream of combustion air.
  • a fired heating system comprising a tubular member configured to define a combustion chamber and a passage for combustion exhaust gas current, characterized by comprising at least one porous insert which is located in the passage of said combustion exhaust gas current, and is adapted to recover heat from said current.
  • Said tubular member may be a radiant tube or a tubular body of a burner.
  • said radiant tube can be made according to various known geometries including but not limited to: non recirculating tubes such as straight tube, U-tube, W-tube, Trident® tube; recirculating tubes such as P-tube, double-P tube, A-tube.
  • Said passage for the combustion exhaust gas is typically downstream said combustion chamber, for example in a radiant U-tube, or is coaxially arranged around said combustion chamber, for example in a single-ended radiant tube or in a recuperative burner.
  • Said porous insert is preferably positioned in a low-emissivity region of the tubular member, particularly in the case of radiant tubes.
  • the high emissivity region is understood as the portion of the tubular member around the combustion flame and where heat is transferred primarily through radiation.
  • the low emissivity region is understood as the portion of the tubular member where heat transfer takes place primarily by convection.
  • Said porous insert has preferably a porosity (or vacuum degree) between 20% and 95% and more preferably between 50% and 90%.
  • the porous insert has a foam structure; according to other preferred embodiments it has a lattice structure.
  • Said porous insert is preferably a ceramic porous insert, for example made of ceramic foam or lattice.
  • a suitable ceramic porous material for said insert is disclosed, for example, in EP-A-1591429.
  • An open cell foam ceramic material and a method for producing the same are disclosed in EP-A-1382590.
  • a particularly preferred material for the ceramic porous insert is silicon carbide SiC.
  • Other preferred materials are materials with similar coefficient of thermal expansion to the tube material.
  • Other preferred materials are ceramic oxide materials, like cordierite.
  • the porous material may be a metal porous material, e.g. made of metal wires.
  • porous inserts More than one porous inserts can be provided. In the embodiments with multiple porous inserts, the inserts may be identical or different.
  • one or more porous inserts are positioned in the path of exhaust gas and also in the path of a stream of combustion air, possibly mixed with recirculated exhaust gas. This is particularly the case of recuperative burners where inlet combustion air and a stream of exhaust gas pass through coaxial annular passages.
  • the heat transfer from the exhaust gas to the combustion air is enhanced to the advantage of pre-heating of the combustion air.
  • one or more porous inserts may have a cross section smaller than the available gas passage area.
  • one or more porous inserts which partially cover the gas passage area can have the shape of a solid cut from a horizontal cylinder. Said solid cut may be a horizontal cylindrical segment, which is defined as a solid cut from a horizontal cylinder by a plane parallel to the axis of cylinder, or may be different, e.g. having a cross section like a sector of a circle.
  • the porous inserts are substantially half-moon shaped, thus covering around 50% of the gas passage area.
  • the porous inserts designed to partially cover the available passage area can be arranged in such a way that they alternately cover different portions of the gas passage area.
  • said at least one insert can be formed, by way of non- limitative examples, as a ring or sleeve inserted within an inner tube and an outer tube which are parts of the tubular member.
  • a tubular member with a coaxial structure is found for example in single-ended radiant tubes or in recuperative burners comprising a burner tube, an air guide tube and an exhaust gas guide tube which are coaxially arranged.
  • inserts covering only a portion of the available passage area may have an open-ring structure, being for example C- shaped.
  • An aspect of the invention is also the use of a porous insert to enhance the efficiency of an industrial heating system, according to the attached claims.
  • Another aspect of the invention is a porous insert made of a ceramic or metal material, having a porosity between 20% and 95% and preferably between 50% and 90%, having a foam or lattice structure, and having the form of a plug, ring, or portion thereof, for use as heat transfer enhancer in an exhaust gas passage or inlet air passage of a radiant tube or recuperative burner.
  • the porous insert of the invention absorbs a substantial amount of heat from the effluent combustion gas, thanks to the porous structure. Some of the heat is then released by conduction and radiation, and the convective heat transfer, the turbulence of the flow and the residence time of the hot gas are increased, all the above effects concurring in a considerable enhancement of the heat transfer or heat recovery.
  • the increased amount of heat transferred to a radiant tube, or to incoming combustion air in a recuperative burner results in a reduced fuel consumption for a given duty and/or more heat delivered to the process for a given size of a radiant tube or burner.
  • the ability of the porous inserts to provide enhanced heat transfer is greater than the prior-art solutions.
  • Another advantage is a more uniform temperature profile of the tubular member, compared to the prior art, reducing the thermal stress of radiant tubes or burners.
  • the inserts increase the efficiency of the heat recovery.
  • ring-shaped porous inserts realized according to the invention and positioned between a burner tube and an exhaust gas guide tube increase the heat recovered from the exhaust gas in a significant manner, thus increasing efficiency and reducing fuel consumption.
  • porous inserts of the invention are their low cost and easy mounting. Hence, most of the conventional burners can be modified in accordance with the invention.
  • the porous inserts induce a certain pressure drop of the exhaust gas. This drawback will be normally overcompensated by the increased amount of heat transferred.
  • the embodiments of the invention with porous inserts covering only a portion of the available gas passage area have the additional advantage of reducing this pressure drop.
  • the insert may be arranged in such a way that they provide an alternate path of the hot gas which is also beneficial to the heat transfer.
  • Fig. 1 shows an embodiment of the invention applied to a radiant tube.
  • Figs. 2, 3 show a variant of the invention.
  • Fig. 4 shows an embodiment of the invention applied to a single-ended radiant tube.
  • Fig. 5 shows an embodiment of the invention applied to a recuperative burner.
  • FIG. 1 a first example of a heating system making use of the invention is shown, comprising a radiant tube 10 connected to a burner 1 1 and installed in a furnace 12.
  • the burner 1 1 has inlets for fuel Fu and oxidant A (for example air) which produce a flame F within the tube 10.
  • the tube 10 comprises a first leg 13 which contains the flame F and then substantially defines a combustion chamber, and a second leg 14 which defines a path for the hot exhaust gas G until they reach an outlet section 15 of said tube 10.
  • the first leg 13 substantially corresponds to a high emissivity region of the tube 10, whilst the second leg 14 substantially corresponds to a low emissivity region of the same tube 10.
  • a porous insert 16 in the form of a cylindrical plug is fitted in the leg 14 of the radiant tube 10, preferably near the outlet section 15.
  • Said porous insert 16 absorbs heat from the gas G, which is released by conduction and radiation to the tubular wall around, and increases convective heat transfer and residence time of the hot gas G in the tube leg 14. As a consequence, the amount of heat transferred from the effluent gas G to the tube 10 and then to the furnace 12 is increased.
  • Said porous insert 16 is preferably a ceramic porous insert with a foam structure or with a lattice structure.
  • the U-tube of Fig. 1 is shown for illustrative purpose as the invention is equally applicable to the various other radiant tubes which are known in the art, including straight once-through tube, W-tube, P-tube, double-P tube, Trident®, etc.
  • a recirculation is also provided, which means that a portion of the effluent gas G is mixed with the fresh mixture burning in the high- emissivity region.
  • More than one porous insert can be provided, according to various embodiments of the invention.
  • the porous insert(s) may have a cross section smaller than the actual passage area available to the gas, in such a way that the cross section available for passage of the effluent gas is only partially obstructed by the porous insert or by each one of the porous inserts.
  • Fig. 2 shows an example of an embodiment with multiple porous inserts smaller than the gas passage.
  • Said Fig. 2 shows the tube leg 14 fitted with a plurality of porous inserts 16A which cover around 50% of the gas passage area.
  • the porous inserts 16A are shaped as a solid cut from a cylindrical plug and they have a half-moon cross section, as elucidated in the view of Fig. 3.
  • Said inserts 16A are advantageously alternated (Fig. 2) in such a way that the gas passage section covered by a porous insert 16A is left free by the adjoining porous insert(s). By doing so, the pressure drop is reduced and, at the same time, it is avoided to leave a straight path for the gas G which may cause undesired bypass of the porous inserts 16A.
  • Fig. 4 shows an embodiment of the invention applied to a single-ended radiant tube 20 comprising an inner tube 21 and an outer tube 22.
  • the inner tube 21 contains the flame F and defines the combustion chamber and then the high-emissivity region.
  • the hot gases leaving the end section 24 of the inner tube 21 flow in the annular space 23 between tubes 21 and 22.
  • porous inserts are provided in said annular space 23, preferably near the outlet section 25 thereof.
  • the porous inserts take the form of annular rings 16B fitted around the inner tube 21 .
  • Said ring inserts 16B have an inner diameter substantially equal to the outer diameter of the tube 21 , and an outer diameter substantially equal to the inner diameter of tube 22.
  • Porous inserts may also be shaped as open rings to cover only a portion of the annular gas passage area in the space 23. For example C-shaped inserts may be used to this purpose.
  • Fig. 5 shows the application of the invention to a tubular burner generally denoted by numeral 30.
  • the burner 30 is a per se known kind of recuperative burner where the incoming combustion air is preheated by the exhaust gas, or at least a portion thereof.
  • the burner 30 comprises a tubular member with a coaxial structure made of several tube parts, namely a burner tube 31 , an air guide tube 32 and an exhaust gas guide tube 33.
  • Fuel is admitted in the combustion chamber, at the end of the burner tube 31 , via a gas lance inside said burner tube 31 .
  • the combustion air possibly mixed with recirculated exhaust gas, is admitted via an annular channel 35 between the outside wall of said burner tube 31 and the air guide tube 32, and enters the combustion chamber through a number of suitable holes 38 in the tube 31 .
  • Hot combustion gas stream leaves the burner tube 31 at an open end 36 and flows in a space 37 between said burner tube 31 and the exhaust gas guide tube 33.
  • one or more ring- shaped porous inserts 16C are provided in the annular space 37 and/or in the annular channel 35, as shown in the figure.
  • ring-shaped porous inserts may be positioned e.g. around a ceramic body of a burner. Examples Example 1
  • a 40 kW recuperative burner has been tested with a bare tube and with SiC foam rings. Conditions were the following: length of tube 1 meter; 10 foam rings distributed all over said tube length and having a thickness of 1 cm; reference furnace temperature of 1000 °C; Oxygen (O 2 ) content in the exhaust gas 3%. An increase of the efficiency from 58% to nearly 70% has been observed.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Gas Burners (AREA)

Abstract

La présente invention concerne un système de chauffage qui comprend un élément tubulaire (10, 20, 30), comme un tube radiant, conçu pour délimiter une chambre de combustion et un parcours pour un courant (G) de gaz d'échappement de combustion, qui comprend au moins un insert poreux (16, 16A, 16B, 16C), situé dans le parcours du courant de gaz d'échappement de combustion et qui est apte à récupérer la chaleur dudit courant et à la transférer audit élément tubulaire ou qui est apte à transférer ladite chaleur à l'air de combustion entrant. Des applications de l'invention comprennent des tubes radiants et des brûleurs récupérateurs.
PCT/EP2013/072487 2013-10-28 2013-10-28 Inserts pour brûleurs et systèmes de chauffage à tube radiant WO2015062619A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/EP2013/072487 WO2015062619A1 (fr) 2013-10-28 2013-10-28 Inserts pour brûleurs et systèmes de chauffage à tube radiant

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/EP2013/072487 WO2015062619A1 (fr) 2013-10-28 2013-10-28 Inserts pour brûleurs et systèmes de chauffage à tube radiant

Publications (1)

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WO2015062619A1 true WO2015062619A1 (fr) 2015-05-07

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3133344A1 (fr) * 2015-08-20 2017-02-22 AICHELIN Holding GmbH Bruleur a recuperation comprenant un recuperateur ceramique et procede de fabrication
WO2017074202A1 (fr) * 2015-10-26 2017-05-04 Aic Społka Akcyjna Échangeur de chaleur à combustion
US11397026B2 (en) * 2019-10-29 2022-07-26 Robertshaw Controls Company Burner for gas-fired furnace

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4355973A (en) * 1981-02-17 1982-10-26 Caterpillar Tractor Co. Radiant heating apparatus
US6484795B1 (en) 1999-09-10 2002-11-26 Martin R. Kasprzyk Insert for a radiant tube
EP1382590A2 (fr) 2002-07-19 2004-01-21 Erbicol SA Mousse céramIque à alvéoles ouvertes
EP1591429A1 (fr) 2004-04-19 2005-11-02 Erbicol SA Mousse céramique à cellules ouvertes avec des cavitées rondes et procédé de fabrication
WO2008036515A2 (fr) 2006-09-18 2008-03-27 Storm Development Llc Système de transfert de chaleur rayonnante
CN201531881U (zh) * 2009-10-29 2010-07-21 北京科技大学 一种燃气辐射管
WO2012160095A1 (fr) 2011-05-25 2012-11-29 Technische Universität Bergakademie Freiberg Échangeur de chaleur constitué d'un matériau céramique, destiné en particulier à des brûleurs à récupération, et procédé de fabrication dudit échangeur de chaleur

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4355973A (en) * 1981-02-17 1982-10-26 Caterpillar Tractor Co. Radiant heating apparatus
US6484795B1 (en) 1999-09-10 2002-11-26 Martin R. Kasprzyk Insert for a radiant tube
EP1382590A2 (fr) 2002-07-19 2004-01-21 Erbicol SA Mousse céramIque à alvéoles ouvertes
EP1591429A1 (fr) 2004-04-19 2005-11-02 Erbicol SA Mousse céramique à cellules ouvertes avec des cavitées rondes et procédé de fabrication
WO2008036515A2 (fr) 2006-09-18 2008-03-27 Storm Development Llc Système de transfert de chaleur rayonnante
CN201531881U (zh) * 2009-10-29 2010-07-21 北京科技大学 一种燃气辐射管
WO2012160095A1 (fr) 2011-05-25 2012-11-29 Technische Universität Bergakademie Freiberg Échangeur de chaleur constitué d'un matériau céramique, destiné en particulier à des brûleurs à récupération, et procédé de fabrication dudit échangeur de chaleur

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3133344A1 (fr) * 2015-08-20 2017-02-22 AICHELIN Holding GmbH Bruleur a recuperation comprenant un recuperateur ceramique et procede de fabrication
WO2017074202A1 (fr) * 2015-10-26 2017-05-04 Aic Społka Akcyjna Échangeur de chaleur à combustion
US11397026B2 (en) * 2019-10-29 2022-07-26 Robertshaw Controls Company Burner for gas-fired furnace

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