IMPROVED ATOMIZER FOR A LIQUID FUEL BURNER

Abstract: The improved atomizer comprises a first (8) and a second (11) mixer for a fuel delivered through a central inlet means (3) and for an atomizing fluid delivered through a peripheral inlet means (4), the first mixer (8) including a first mixing chamber (9) whereto the fuel arrives from the central inlet means (3) and the atomizing fluid arrives from peripheral ducts (10), the second mixer (11) including a second mixing chamber (12) for the fuel and the atomizing fluid that complete their mixing therein and a plurality of outlet means (14) for the delivery of the completely atomized fuel to a firebox, the relations among the length, diameter and cross-sectional area of certain parts which cooperate in the atomizer being defined to impart an effective atomization to the fuel and supply an advantageous pencil of atomized fuel into a fire-box.

Description: The present invention relates to an improved atomizer for a liquid fuel burner. Particularly, the invention relates to an improved atomizer suitable to a burner for high viscosity liquid fuels or to two-phase mixtures such, for instance, coal-­ fuel oil or coal-water, having high viscosity and, in either case, by the assistance of air or steam as an atomizing fluid. In the European Patent application N o 84 101430.1-2301 the applicant discloses an atomizer which comprises a first and a second mixer for a fuel delivered through a central inlet means and for an atomizing fluid delivered through a peripheral inlet means. The first mixer includes a first mixing chamber whereto the fuel arrives from the central inlet means and the atomizing fluid arrives from the peripheral ducts.The second mixer includes a second mixing chamber for the fuel and the atomizing fluid that complete their mixing therein and includes a plurality of outlet means for the delivery of the completely atomized fuel to a firebox. The cross sectional area and the length of said central inlet means greatly exceed the cross sectional area and the length of said first mixing chamber, respectively; the cross sectional area of said second mixing chamber is several times that of said first mixing chamber; the slope of said peripheral ducts and of said outlet means with respect to the longitudinal axis of the atomizer are within certain ranges of angular values. The present invention relates to an atomizer of the type described above wherein certain features of some single parts and certain relations between the dimensions of the parts associated in imparting an effective atomization to the fuel and supplying an advantageous pencil of atomized fuel have been defined much better after having carried out trials and model tests. The description of the invention is supplied herebelow immediately with reference to the attached sole figure which is a longitudinal cross sectional view of an atomizer shown as an example of the invention. In general, the improved atomizer still comprises known features as a central inlet means 3 for some liquid fuel, a peripheral inlet means 4 for some atomizing fluid, a first cylindrical mixing chamber 9 within which a plurality of peripheral ducts 10 lead the fluid that atomizes the liquid fuel coming from said central inlet means 3, a second mixing chamber 12 which receives the partly atomized liquid fuel from the first cylindrical mixing chamber 9 and has a plurality of outlet means 14 for delivering the completely atomized fuel to a firebox,the longitudinal axis of the atomizer being the longitudinal axis of simmetry common to the central inlet means and to the first and second mixing chamber. In particular the atomizer 1 is urged on the device 2 by a ring nut 7 screwed on a thread of the device 2. The atomizer 1 comprises a first mixer 8 which contains a first cylindrical mixing chamber 9 in communication with a central inlet means 3 for the liquid fuel and also contains a plurality of n₁ peripheral ducts 10 angularly spaced by 360°/n₁(2 only are shown) for delivering within the chamber 9 the atomizing fluid coming from a peripheral inlet means 4. The peripheral ducts 10 are so directed that their longitudinal axis II-II cross at point A on the longitudinal axis I-I, the point A dividing the length of the chamber 9 in two lengths. The atomizer 1 comprises also a second mixer 11 which contains a second mixing chamber 12 that shows a first cylindrical portion and a second conical portion. A plurality of outlet means 14 (two only are shown) are open in the conical wall, the axis III-III of the outlet means 14 being perpendicular to the inner and outer conical walls of the mixer 11 and crossing at a point C within the chamber 12. The end wall B opposite to the chamber 9 is perpendicular to the axis I-I. The diameter of the central inlet means 3 is D₀; the diameter of the chamber 9 is D₁; the diameter of the cylindrical portion of the chamber 12 is D₂; the diameter of the end wall B is D₃. The diameter of each peripheral duct 10 is d₁; the diameter of each outlet means 14 is d₂. The cross sectional area of each of the ducts 10 is s₁. The length of the chamber 9 is L₁, divided by the crossing point A in two lengths, L₃ and L₄; the overhall length of the second mixing chamber 12 is L₂ and the length of the cylindrical portion of the chamber 12 is L₅. The outlet means 14 have inner and outer sharp edges. The length of the peripheral ducts 10 is l₁; the length of the outlet means 14 is l₂. More particularly, the ratio between the diameter D₀ of said central inlet means 3 and the diameter D₁ of the first cylindrical mixing chamber 9 is D₀/D₁ > 2; the plurality of peripheral ducts which lead the atomizing fluid to the first cylindrical mixing chamber 9 comprises at least three ducts 10, the ducts 10 being equally angularly spaced and having equal length l₁, equal diameter d₁ and their longitudinal axis crossing at a same point A on said longitudinal axis I-I within the first cylindrical mixing chamber 9; the second mixing chamber 12 having the overhall length L₂ divided in a first portion of cylindrical cross section having length L₅ and diameter D₂ such that L₅/D₂> 0.6, a second portion of conical shape comprising a plurality of outlet means 14, the axis III-III of the outlet means 14 being perpendicular to the inner conical wall and crossing at a same point C on said longitudinal axis I-I within said first portion, the end inner wall B of that conical portion being a circular wall having a diameter D₃ such that D₃≧ D₁, said end wall being perpendicular to said longitudinal axis I-I. Said crossing point A divides the length L₁ of the first cylindrical mixing chamber 9 in two lengths, a first one L₃ adjacent to the central inlet means 3, a second one L₄ adjacent to the second mixing chamber 12, such that the relation between each of said two lengths and the diameter D₁ of the first cylindrical mixing chamber 9 is L₃≦ 2D₁ and L₄≧2D₁; the relation between the length l₁ and the diameter d₁ of each of said n₁ peripheral ducts 10 is 2d₁ <l₁<5d₁ and the relation between the overhall cross sectional area n₁s₁ of said peripheral ducts 10 and the cross sectional area S₁ of the first cylindrical mixing chamber 9 is 0.5 S₁<n₁s₁<S₁. The relation between said overhall length L₂ and the diameter D₂ of said first portion of the second mixing chamber 12 is 0.6 D₂<L₂<1.2 D₂ and the relation between said diameter D₂ of the second mixing chamber 12 and the diameter D₁ of the first cylindrical mixing chamber 9 is D₂≧3D₁. The quantity of said outlet means 14 in the second mixing chamber 12 is n₂>3, the length l₂ and the diameter d₂ of said outlet means 14 are such that d₂<l₂<3d₂, the cross sectional area s₂ of each of said outlet means 14 being such that n₂s₂< n₁s₁ + S₁. The paramount advantages of the invented atomizer are: the preliminary mixing between the liquid fuel and the atomizing fluid in the first mixing chamber is very effective; the extension of the length L₃ provides for a convenient turbolence in the liquid fuel and the extension of the length L₄ provides for a first satisfactory mixing; the relations among the dimensions of the second mixing chamber avoid the coalescence in the drops drawn by the atomizing fluid from the first chamber with the liquid fraction that has not been atomized in the first mixing chamber; the separation of the atomizing fluid from the not yet atomized liquid fuel beam is caused,which helps the subsequent spreading of said beam on the walls of the chamber in the form of a thin film that enters the outlet means where the atomizing fluid further atomizes that liquid fuel; the relations among the cross sectional areas of the peripheral ducts, first mixing chamber and outlet means impart to the atomizing fluid such a pressure in the second mixing chamber that the above film in the outlet means is broken at the maximum extent. As a whole, the final atomization of the liquid fuel is very high.

Claims: 1. An improved atomizer for liquid fuel burner comprising a first (8) and a second (11) mixer for a fuel delivered through a central inlet means (3) and for an atomizing fluid delivered through a peripheral inlet means (4), the first mixer (8) including a first mixing chamber (9) whereto the fuel arrives from the central inlet means (3) and the atomizing fluid arrives from peripheral ducts (10), the second mixer (11) including a second mixing chamber (12) for the fuel and the atomizing fluid that complete their mixing therein and a plurality of outlet means (14) for the delivery of the completely atomized fuel to a firebox, the cross sectional area and the length of said central inlet means (3) greatly exceeding the cross sectional area and the length of said first mixing chamber (9), respectively; the cross sectional area of said second mixing chamber (12) being several times that of said first mixing chamber (9), the slope of said peripheral ducts (10) and of said outlet means (14) with respect to the longitudinal axis(I-I) of the atomizer being within certain ranges of angular values, characterized in that the ratio between the diameter (D₀) of said central inlet means (3) and the diameter (D₁) of the first cylindrical mixing chamber (9) is D₀/D₁ > 2; the plurality of peripheral ducts which lead the atomizing fluid to the first cylindrical mixing chamber (9) comprises at least three ducts (10), the ducts (10) being equally angularly spaced and having equal length(l₁), equal diameter(d₁) and their longitudinal axis crossing at a same point(A)on said longitudinal axis (I-I) within the first cylindrical mixing chamber (9); the second mixing chamber (12) having the overall length(L₂) divided in a first portion of cylindrical cross section having length (L₅) and diameter (D₂) such that L₅/D₂> 0.6, a second portion of conical shape comprising a plurality of outlet means (14), the axis (III-III) of the outlet means (14) being perpendicular to the inner conical wall and crossing at a same point (C) on said longitudinal axis(I-I) within said first portion, the end inner wall (B) of that conical portion being a circular wall having a diameter (D₃) such that D₃≧D₁, said end wall being perpendicular to said longitudinal axis (I-I). 2. An improved atomizer for liquid fuel burner according to claim 1 characterized in that said crossing point(A) divides the length (L₁) of the first cylindrical mixing chamber (9) in two lengths, a first one (L₃) adjacent to the central inlet means (3), a second one (L₄) adjacent to the second mixing chamber (12), such that the relation between each of said two lengths and the diameter (D₁) of the first cylindrical mixing chamber (9) is L₃≦2D₁ and L₄ ≧ 2D₁; the relation between the length (l₁) and the diameter (d₁) of each of said n₁ peripheral ducts (10) is 2d₁<l₁<5d₁ and the relation between the overhall cross sectional area n₁s₁ of said peripheral ducts (10) and the cross sectional area(S₁) of the first cylindrical mixing chamber (9) is 0.5 S₁<n₁s₁<S₁. 3. An improved atomizer for liquid fuel burner according to claims 1 and 2 characterized in that the relation between said overhall length (L₂) and the diameter (D₂) of said first portion of the second mixing chamber (12) is 0.6 D₂<L₂<1.2 D₂ and the relation between said diameter (D₂) of the second mixing chamber (12) and the diameter (D₁) of the first cylindrical mixing chamber (9) is D₂≧3D₁). 4. An improved atomizer for liquid fuel burner according to claims 1,2,3 characterized in that the quantity of said outlet means (14) in the second mixing chamber (12) is n₂>3, the length (1₂) and the diameter (d₂) of said outlet means (14) are such that d₂<l₂<3d₂, the cross sectional area(s₂)of each of said outlet means (14) being such that n₂s₂<n₁s₁ + S₁, the outlet means (14) having inner and outer sharp edges.

Inventors: GRAZIADIO, MARIO, LIGASACCHI, SERGIO
Applicants: ENTE NAZIONALE PER L'ENERGIA ELETTRICA - (ENEL)
Application year: 1986
Main classification: F23D11
IPC codes: F23D11, F23D1, B05B7