Method and apparatus for combustion of gaseous or liquid fuel

Abstract

A method and apparatus for combustion of fuel in a combustion chamber with a hydraulic diameter D. Fuel and a primary oxidant are introduced via a burner lance into the combustion chamber, having a certain mean velocity u1 at entry, and a secondary oxidant with a mean velocity of u2 is introduced into the combustion chamber. The burner lance has a position p that has a distance Id1I defined as the smallest distance between p and a combustion chamber centerline.

Claims

1. A method for combustion of gaseous or liquid fuel in a combustion chamber with a hydraulic diameter D, whereby the fuel as well as the primary oxidant are introduced via a burner lance into the combustion chamber, whereby fuel and primary oxidant have a certain mean velocity u.sub.1 at the entry from the burner lance into the combustion chamber, whereby the mean velocity u.sub.1 is defined as $u_1=\frac{\underset{i=1}{\overset{n}{.Math.}}{v}_i^2.Math.{\rho }_i.Math.A_i}{{\stackrel{.}{m}}_{\mathrm{ges}}},$ whereby v.sub.i is the velocity of each separate fluid in the burner lance, ρ.sub.i is the density of each separate fluid in the burner lance, A.sub.i is the cross-section for the flow of each separate fluid in the burner lance at the entry of the burner lance into the combustion chamber and {dot over (m)}.sub.ges is the overall mass flow in the burner lance and whereby a secondary oxidant with a mean velocity of u.sub.2 is introduced via a downcomer into the combustion chamber, wherein the burner lance is arranged such that a distance |d.sub.1| defined as the smallest distance between a tip p of the burner lance and a combustion chamber centerline a is smaller than a distance |d.sub.c| from an intersection point of the combustion chamber centerline a and a shortest line connecting the tip p of the burner lance and the combustion chamber centerline a to the intersection point i of the downcomer centerline c and an intersection area S of combustion chamber and downcomer, whereby the value of |d.sub.1| is such that $.Math.d_1.Math.=\left[1-{\left(d.Math.\frac{u_1}{u_2}\right)}^{\frac{1}{4}}\right].Math.\frac{D}{2}$ and that d is in the range of 0.05 to 0.15, wherein the mean velocity u.sub.1 is from 70 m/s to 140 m/s and the mean velocity u.sub.2 is from 10 m/s to 35 m/s.

2. The method according to claim 1, wherein the d is in the range of 0.09 to 0.11.

3. The method according to claim 1, wherein the primary and/or the secondary oxidant is air.

4. The method according to claim 1, wherein the total air ratio λ with $\lambda =\frac{{\stackrel{.}{m}}_{\mathrm{air}}}{{\stackrel{.}{m}}_{\mathrm{stoich}}}$ is in the range of 1.2 and 12.0.

5. The method according to claim 1, wherein the primary air ratio λ.sub.prim with ${\lambda }_{\mathrm{prim}}=\frac{{\stackrel{.}{m}}_{\mathrm{air}\text{-}\mathrm{prim}}}{{\stackrel{.}{m}}_{\mathrm{stoich}}}$ is in the range of 0.05 and 2.0.

6. The method according to claim 1, wherein the burner lance has a fuel capacity in the range of 2 and 6 MW.

7. A burner assembly comprising a combustion chamber with a centerline a, a hydraulic diameter D, a burner lance to introduce fuel and primary into the combustion chamber, whereby the mean velocity u.sub.1 is defined as $u_1=\frac{\underset{i=1}{\overset{n}{.Math.}}{v}_i^2.Math.{\rho }_i.Math.A_i}{{\stackrel{.}{m}}_{\mathrm{ges}}},$ whereby v.sub.i is the velocity of each separate fluid in the burner lance, ρ.sub.i is the density of each separate fluid in the burner lance, A.sub.i is the cross-section for the flow of each separate fluid in the burner lance at the entry of the burner lance into the combustion chamber and {dot over (m)}.sub.ges is the overall mass flow in the burner lance, whereby the burner assembly adapted such that fuel and primary oxidant have a certain mean velocity u.sub.1 at the entry from the burner lance into the combustion chamber, measured from a tip p of the burner lance and a downcomer adapted to introduce a secondary oxidant with a mean velocity of u.sub.2 into the combustion chamber, wherein the burner lance is arranged such that a distance |d.sub.1| defined as the smallest distance between the tip p of the burner lance and a combustion chamber centerline (a) is smaller than a distance |d.sub.c| from an intersection point of the combustion centerline (a) and a shortest line connecting the tip p of the burner lance and the combustion chamber centerline (a) to an intersection point (i) of the downcomer centerline (c) and an intersection area (S) of the combustion chamber and downcomer, whereby the value |d.sub.1| is such that $.Math.d_1.Math.=\left[1-{\left(d.Math.\frac{u_1}{u_2}\right)}^{\frac{1}{4}}\right].Math.\frac{D}{2}$ and that d is in the range of 0.05 to 0.15, wherein the mean velocity u.sub.1 is from 70 m/s to 140 m/s and the mean velocity u.sub.2 is from 10 m/s to 35 m/s.

8. The burner assembly according to claim 7, wherein the burner lance is arranged at an angle α from greater than 0° to 12° to the combustion chamber centerline a.

9. The burner assembly according to claim 7, wherein the burner lance points towards the downcomer.

10. The burner assembly according claim 7, wherein the combustion chamber's diameter D lies between 0.5 and 1.8 m.

11. The method according to claim 1, wherein the entire tip p of the burner lance is offset from the combustion chamber centerline a and positioned between the combustion centerline a and the intersection area S.

Description

(1) In the drawings:

(2) FIG. 1 shows a design of a pellet induration furnace according to the state of the art focusing on flow conditions,

(3) FIG. 2 shows a design of a pellet induration furnace according to the state of the art focusing on the temperature profile in the furnace,

(4) FIG. 3 shows a first design of a pellet induration furnace according to the invention focusing on flow conditions,

(5) FIG. 4 shows a first design of a pellet induration furnace according to the invention focusing on the temperature profile in the furnace,

(6) FIG. 5 shows a second design of a pellet induration furnace according to the invention focusing on flow conditions,

(7) FIG. 6 shows a second design of a pellet induration furnace according to the invention focusing on the temperature profile in the furnace.

(8) FIG. 1 shows a typical design of a pellet induration furnace, especially of an iron ore pellet induration furnace, according to the state of the art. A burner assembly 1 according to the state of the art, e.g. US 2016/0201904 A1 is shown in a sectional view.

(9) The burner assembly 1 features a combustion chamber 2 being cylindrical-shaped with a sectional diameter D, and, therefore, being symmetrical around its centerline a. The combustion chamber 2 works as a flame-reaction space.

(10) On the left side of FIG. 1, the combustion chamber 2 opens into a furnace 3. On the opposite side, a burner lance 4 is positioned at position o. As FIG. 1 depicts the situation known from the state of the art, position o is located on the centerline a, resulting in the distance |d.sub.1| being equal to 0.

(11) Furnace 3 is designed such that two burner assemblies, on opposite positions are used, which is indicted by the symmetry plane b.

(12) Via the burner lance 4, liquid or gaseous fuel as well as a primary oxidant, preferably air, are injected into the combustion chamber 2. Typically, also a control unit or equipment (not shown) is provided for controlling the supplies of fuel and primary air into the combustion chamber.

(13) The majority of oxidant is typically injected via a downcomer 5 through which secondary oxidant, e.g. preheated air, is flowing downwards into the combustion chamber 2. The lower part of the downcomer features a center line c next to its intersection area S with the combustion chamber 2. The intersection of the center line c and the intersection area S is defined as position. As shown via arrows 11, the secondary oxidant is passing the burner lance 4 and the flame 7 before it is creating a recirculation zone 12.

(14) Inside the furnace 3, the flue gas coming from the combustion chamber 2 is flowing downwards (shown via arrows 13), e.g. Into the pellet bed 6.

(15) In FIG. 2, basically the same structure is used. However, instead of gas stream lines, FIG. 2 shows a simplified temperature profile in the furnace, e.g. above a pellet bed 6. Thereby, T.sub.1 indicates a hot zone while T.sub.2 Indicates a colder zone. Typically a difference of at least 40 K is found between these two zones.

(16) In comparison, FIG. 3 shows the same burner and furnace assembly according to the invention. As described, the burner lance 4 is positioned in the position p with its smallest distance |d.sub.1| to the centerline a of the combustion chamber 2, where d.sub.1 is defined as

(17) $d_1=\left[1-{\left(d.Math.\frac{u_1}{u_2}\right)}^{\frac{1}{4}}\right].Math.\frac{D}{2},$
whereby d is in the range of 0.05 to 0.15. In case d.sub.1 ends up with a positive sign, position p is always closer to the downcomer than in the case it ends up with a negative sign.

(18) As shown in FIG. 3, the flame 7 interacts with the recirculation zone 12, so highly turbulent flow conditions are found in furnace 3.

(19) As a result, a better mixing of the gas flow is achieved inside the furnace 3, which is why FIG. 4 shows a more homogenous temperature profile, symbolized by a nearly identical size of T.sub.1 (hot zone) and T.sub.2 (colder zone) with a difference in CFD simulations of maximum 10 K between T.sub.1 and T.sub.2.

(20) FIGS. 5 and 6 correspond to FIGS. 3 and 4, but shows an inclined burner lance. The inclination angle α is measured between the centerline a of the combustion chamber and the centerline of the burner lance 4.

REFERENCE NUMBERS

(21) 1 burner assembly 2 combustion chamber 3 furnace 4 burner lance 5 downcomer 6 pellet bed 7 flame 11 flow of the secondary oxidant 12 recirculation zone 13 flow of the gas in the furnace T.sub.1 Temperature in the hot zone T.sub.2 Temperature in the colder zone a centerline of the combustion chamber α inclination angle b symmetry plane of the furnace c centerline of the downcomer (next to the intersection area S) D sectional diameter of the combustion chamber d dimensionless factor |d.sub.1| smallest distance of position p to the combustion chamber centerline a i intersection of the downcomer centerline c and the intersection area S of combustion chamber and downcomer o position of the burner lance according to the state of the art p position of the burner lance according to the invention S intersection area of combustion chamber (2) and downcomer (5) u.sub.1 mean velocity in the burner lance at the entry to the combustion chamber u.sub.2 mean velocity of the secondary oxidant in the downcomer