EP2045522A1 - Hybrider Brennkessel - Google Patents

Hybrider Brennkessel Download PDF

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Publication number
EP2045522A1
EP2045522A1 EP07425621A EP07425621A EP2045522A1 EP 2045522 A1 EP2045522 A1 EP 2045522A1 EP 07425621 A EP07425621 A EP 07425621A EP 07425621 A EP07425621 A EP 07425621A EP 2045522 A1 EP2045522 A1 EP 2045522A1
Authority
EP
European Patent Office
Prior art keywords
fuel
catalytic
catalytic element
boiler
comburent
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP07425621A
Other languages
English (en)
French (fr)
Inventor
Claudio Accordini
Giuseppe Toniato
Stefan Cimino
Francesco Donsi'
Gennaro Russo
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Riello SpA
Original Assignee
Riello SpA
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 Riello SpA filed Critical Riello SpA
Priority to EP07425621A priority Critical patent/EP2045522A1/de
Publication of EP2045522A1 publication Critical patent/EP2045522A1/de
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • F23D14/14—Radiant burners using screens or perforated plates
    • F23D14/145—Radiant burners using screens or perforated plates combustion being stabilised at a screen or a perforated plate
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D2900/00—Special features of, or arrangements for burners using fluid fuels or solid fuels suspended in a carrier gas
    • F23D2900/00001—Special features of, or arrangements for burners using fluid fuels or solid fuels suspended in a carrier gas local catalytic coatings applied to burner surfaces

Definitions

  • the present invention relates to a hybrid combustion boiler comprising an atmospheric hybrid burner.
  • a boiler made according to the principles of the method, a further object of the present invention, presents improved heat efficiency features with respect to the boilers of the known art, being at the same time less polluting and more stabile, quieter and safer during use.
  • the treatment of gaseous or vaporized fuels occurs in two stages, wherein the first stage contemplates the partial catalytic oxidation of the fuel and the second stage the homogenous phase conversion of the partially oxidised and preheated charge, with intermediate removal of the partial oxidation heat and transfer to a heat exchanger.
  • An innovative element of this burner consists mainly in the hybrid operation with intermediate heat removal, which allows to improve the heat efficiency of the burner itself, reduce the level of emission of polluting substances, and makes operation during use more stable and safer.
  • the present invention relates to a hybrid combustion boiler characterized in that it comprises an atmospheric hybrid burner having a catalytic element crossed by a fuel-rich mixture; between the catalytic element and the heat exchanger there is a secondary air flow introduction pipe, so as to obtain a flame given by the ignition of the reformed gas produced when the fuel-rich mixture crosses the catalytic element, so that the transfer of heat towards the heat exchanger occurs mainly by radiation IR throughout the visible and in the near infrared spectrum.
  • numeral 100 indicates as a whole a hybrid combustion boiler comprising a hybrid catalytic burner 10 and a heat exchanger SC.
  • the hybrid catalytic burner 10 in turn, comprises a preferably cylindrical catalytic element 11 comprising, in turn, a large gas-solid contact surface porous metallic substrate, on the surface of which there is deposited an active catalytic phase for the partial oxidation of a fuel-rich and primary air mixture.
  • the combustion ratio between the fuel and the primary air is higher than the upper flammability limit, and thus in lack of oxidazing agent.
  • the catalytic element 11 comprises a wire net, e.g. of the type described and claimed in European Patent Application EP 1 544 542 by the same applicant.
  • the fuel/air mixture flows according to a direction and sense identified by an arrow F1 essentially aligned among a longitudinal axis of symmetry (X) of the catalytic element 11.
  • radial flows (arrow F2) of the gaseous mixture are formed within the catalytic element 11, the distal end 11a of which is preferably capped, such flows crossing the wire netting by which the catalytic element 11 itself is formed.
  • flows are formed in the catalytic element 11 according to an arrow F2 perpendicular to the axis (X). Therefore, the outlet section of the gasses partially converted (reformed) by crossing through the meshes of the catalytic element 11 is constituted by the side surface of the catalytic element 11 itself in shape of thin cylindrical dome, being the gas flow passage at least partially inhibited in the upper part.
  • the wire netting on which the catalyzer is deposited also works as a stage of heat removal and direct transfer by radiation to a user, e.g. a heat exchanger SC.
  • the mixture of gases partially converted by crossing of the catalyzer coated netting of the catalytic element 11 is characterized by a lower heat value in proportion to the removal of a share of reaction heat generated on the catalyzer which is transferred to the heat exchanger SC through an infrared radiation emission by the catalytic element 11 itself.
  • the aforesaid combustion method also applies to fuels such as pure or mixed hydrogen characterized by very high adiabatic flame temperatures and subject to the formation of large amounts of NO x if burned in traditional diffusion flame systems.
  • the preheating of the partially oxidised fuel flow, output by the catalytic element 11 according to the arrows F2, and its high reactivity, mainly related to its high H2 content make the homogenous phase secondary combustion particularly stable and promote the containment of unburned hydrocarbon emissions even at relatively low adiabatic flame temperatures.
  • the control of the relative weight between the catalytic combustion stage and the homogeneous combustion stage is efficiently obtained by adjusting the "feeding efficiency ratio” ( ⁇ ), defined as the ratio between fuel and primary air actually fed to the burner 10 divided by the same ratio in stoichiometric conditions.
  • the temperature on the catalytic element 11, where a partial oxidation occurs is controlled by adjusting the equivalence ratio ( ⁇ ) so that the oxygen in the fuel/primary air mixture is always the limiting reactant, thus accurately determining in this manner the amount of heat generated on the surface of the catalytic element 11 itself, as well as that transferred by radiation to the heat exchanger SC.
  • the boiler 100 which is the main object of the present invention, it is possible to preserve the durability and the performances of the partial oxidation catalyzer by accurately controlling its operating temperature so that it is constantly under the limit level of use determined by its specific chemical formula.
  • the "contact time" of the fuel/comburent mixture with the "active catalytic phase” present in the catalytic element 11 ("contact time” being defined as the ratio between the volumetric fuel gas and primary air flow rate, at standard temperature and pressure, and the void volume constituted by the pores of the catalytic element 11 itself) is comprised between 1 and 600 ms, and more advantageously between 3 and 100 ms.
  • the distribution between the heat transmitted by radiation and the heat transmitted by convection by means of the burned gases may be simply controlled by varying the feeding ratio ( ⁇ ), providing the constraint that the mixture is rich (( ⁇ )>1) and that the temperature of the catalytic element 11 is not excessive so to avoid compromising functionality, durability, integrity and mechanical stability.
  • the feeding ratio ( ⁇ ) to the burner 10 is maintained higher than 1 and preferably higher than the ( ⁇ Max) value, which defines the upper flammability limit in air at ambient temperature and pressure of the specifically employed fuel.
  • the fuel mixture becomes progressively richer as the feeding ratio ( ⁇ ) increases to values higher than 1, and specifically higher than ( ⁇ Max); as a consequence, the partial catalytic oxidation of the fuel proceeds in lesser extent due to the decrease of the concentration of the limiting reagent reactant, constituted by the oxygen present in the primary air. Consequently, a lower fuel conversion in the catalytic stage determines the reduction of the temperature of the catalyzer, the reduction of the amount of heat transferred by radiation and/or by conduction towards the heat exchanger SC and, consequently, the increase of the share of secondary combustion in homogenous phase as well as the corresponding adiabatic flame temperature.
  • the adiabatic flame temperature of the secondary combustion decreases and consequently the heat formation of nitrogen oxides is gradually limited. Only in the case of hydrocarbon fuels, the CO emissions start to increase if the adiabatic flame temperature of the secondary combustion is excessively low.
  • the start-up procedure may proceed by igniting a partially premixed flame FLM downstream of the catalytic element 11, which allows the preheating to temperatures higher than the temperature threshold of the partial oxidation reaction (typically between 200°and 400°C).
  • the consequent beginning of the solid-catalyzed reactions causes the generation of heat inside the pores of the catalytic element 11 which is gradually heated and starts to transfer heat by radiation towards the heat exchanger SC, while the combustion continues to be completed by the diffusive or partially premixed flame FLM downstream of the catalytic element 11 until final stationary operation conditions are reached.
  • the catalytic element 11 comprises a metallic substrate, which presents a solid macro-porous structure with a high degree of void (preferably higher than 50%) with pores interconnected by tortuous channels without preferential directions so as to form an open mesh structure normally named as "foam” or "netting".
  • This metallic substrate consists of a material which is not active in the concerned reactions and which has a high mechanical resistance to heat shocks and is preferably formed by a material resistant to temperatures of at least 1000°C, chemically and physically stabile, and free from oxidation, separation, volatility or phase transaction phenomena at said temperatures.
  • the monolithic metallic substrate consists of an alloy of high-temperature-resistant materials, preferably of a metallic alloy chosen between FeCrAlY, Nickel Cr, Nichrome, Hastelloy X, Inconel 600-625, and made in the shape of a netting.
  • the "active catalytic phase”, deposited on the above-described macroporous substrate, is selected among those known in the field for the reaction and the production process of synthesis gas by means of partial oxidation of hydrocarbons, and is capable of supporting the conversion reaction of the hydrocarbon fraction of the fuel to H 2 and CO partial oxidation products, rather than to total oxidation of H 2 O and CO 2 , thus ensuring a high H 2 and CO conversion and selectivity also in autothermic operating conditions without preheating the input gaseous current.
  • the active catalytic phase is capable of fully oxidizing these compounds to H 2 O and CO 2 respectively, again restricted to the amount of oxygen contained in the primary air fed to the catalytic element in lack with respect to the stoichiometric value.
  • the "active catalytic phase” is constituted by a dispersion of a metal chosen among the noble metals Pt, Pd, Rh, Ir, Re, Ru, Au, Ni, Ag and transition metals V, Cr, Mn, Fe, Co, or by a mixture thereof, preferably by a dispersion of Rh, Ni, Pt, Co, Fe, Cr, Mn.
  • the “catalytic active phase” is present in amount comprised between 0.01 and 10% of the total weight of the catalyzer.
  • the “active catalytic phase” may be represented by a mixed transition metal oxide with perovskite structure and general formula AxA"1-xByB"1-yO3 ⁇ , wherein:
  • the "active catalytic phase” is finely dispersed on a large specific surface area support applied as a thin film onto the foam or wire netting substrate and preferably constituted by a refractory oxide with a low thermal expansion coefficient, provided with a good chemical affinity with the material by which said metallic substrate is formed.
  • the large surface area support layer consists of MgO, MgAl2O4, ZrO2, ⁇ -Al2O3 stabilized or not with La203, Ce02 or other stabilizer present in a total amount comprised between 1% and 10% by weight with respect to the total of the large surface area support layer.
  • the fuel-rich mixture crosses the meshes, or the pores of the catalytic element 11 at ambient temperature without being oxidised at all.
  • the fuel/primary air mixture being output from the holes, or the pores, of the catalytic element 11 is mixed with a flow of secondary air (indicated in the figure by the arrows F3) and ignited.
  • a flame front FLM is thus developed over the external cylindrical surface 11b of the catalytic element 11.
  • the flame front FML heats the catalytic element 11, which, having reached its threshold temperature starts to promote the partial oxidation reaction of the rich mixture.
  • the heat generated by the partial oxidation will transform the catalytic element 11 into a radiating system throughout the visible and in the near infrared spectrum.
  • An excellent percentage of the energy produced by the burner 10 will reach, in direct and/or indirect manner, the heat exchanger SC in which a heat conveying fluid, e.g. water, is heated.

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Catalysts (AREA)
EP07425621A 2007-10-05 2007-10-05 Hybrider Brennkessel Withdrawn EP2045522A1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP07425621A EP2045522A1 (de) 2007-10-05 2007-10-05 Hybrider Brennkessel

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP07425621A EP2045522A1 (de) 2007-10-05 2007-10-05 Hybrider Brennkessel

Publications (1)

Publication Number Publication Date
EP2045522A1 true EP2045522A1 (de) 2009-04-08

Family

ID=39203233

Family Applications (1)

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EP07425621A Withdrawn EP2045522A1 (de) 2007-10-05 2007-10-05 Hybrider Brennkessel

Country Status (1)

Country Link
EP (1) EP2045522A1 (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2012220135A (ja) * 2011-04-12 2012-11-12 Corona Corp 燃焼装置

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6030909A (ja) * 1983-08-01 1985-02-16 Matsushita Electric Ind Co Ltd ガスバ−ナの排ガス浄化方法
US5848887A (en) * 1996-11-26 1998-12-15 Carrier Corporation Low emission combustion system
US6145501A (en) * 1999-11-08 2000-11-14 Carrier Corporation Low emission combustion system
EP1544542A1 (de) 2003-12-18 2005-06-22 Riello S.p.a. Abdeckung eines Brennerkopfes, und Gasbrenner mit einer solchen Abdeckung

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6030909A (ja) * 1983-08-01 1985-02-16 Matsushita Electric Ind Co Ltd ガスバ−ナの排ガス浄化方法
US5848887A (en) * 1996-11-26 1998-12-15 Carrier Corporation Low emission combustion system
US6145501A (en) * 1999-11-08 2000-11-14 Carrier Corporation Low emission combustion system
EP1544542A1 (de) 2003-12-18 2005-06-22 Riello S.p.a. Abdeckung eines Brennerkopfes, und Gasbrenner mit einer solchen Abdeckung

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2012220135A (ja) * 2011-04-12 2012-11-12 Corona Corp 燃焼装置

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