BURNER AND ASSEMBLY OF COMPACT BURNERS

Abstract

A premix burner made up of an air inlet tube of length L and a single specific gas injection, the gas injection includes an upstream gas injector, a mixer, a downstream gas injection situated at a distance L3 from an upstream end of the air inlet tube and a stabilizing element, where the gas injection constitutes a one-piece mechanical assembly that ensures a self-stable elementary flame.

Claims

1. Premix burner made up of an air inlet tube of length L and a single specific gas injection, said gas injection comprising an upstream gas injector, a mixer, a downstream gas injection situated at a distance L3 from an upstream end of the air inlet tube and a diffuser, wherein the gas injection constitutes a one-piece mechanical assembly that ensures a self-stable elementary flame.

2. Burner according to claim 1, wherein the air inlet tube has a length L and a diameter D1 such that the length L is between three and six times the diameter D1.

3. Burner according to claim 1, wherein the upstream gas injector is situated at a distance L1 from an upstream end of the air inlet tube of between 0.5 times the diameter D1 and the length L.

4. Burner according to claim 1, wherein the upstream gas injector comprises at least two elements of axes x and x that are disposed radially with respect to the air inlet tube, each element having gas injection holes disposed along its axis.

5. Burner according to claim 1, wherein the upstream gas injector comprises at least two mixing elements of axes y and y that are inclined with respect to the radius of the tube and connect the air inlet tube and the gas injection duct, and wherein each mixing element has gas injection holes (410) disposed along its axis y or y.

6. Burner according to claim 2, wherein the diffuser is situated at a distance L4 from an upstream end of the air inlet tube of between L and LD1.

7. Burner according to claim 1, wherein the diffuser has a cross section smaller than or equal to 0.5 times the cross section of the air inlet tube.

8. Burner according to claim 1, wherein the diffuser comprises a stabilizing element of diameter D5 and a concentrator of diameter D8 and length L7, the stabilizing element is pierced by holes distributed in two concentric circles of diameters D6 and D7, D7<D8<D6, and the length L7 is between 0 and D5.

9. Burner according to claim 6, wherein the downstream gas injection is situated at a distance L3 from an upstream end of the air inlet tube of between L4(0.5D1) and L4.

10. Burner according to claim 1, wherein the air inlet tube is prolonged by walls for mechanically protecting the flame.

11. Burner according to claim 1, wherein the walls for mechanically protecting the flame have a diameter D2 of between the diameter D1 of the air inlet tube and 5D1.

12. Burner according to claim 10, wherein the walls for mechanically protecting the flame have an inclination angle 2 with respect to the axis of the burner of between 0 and 20.

13. Burner according to claim 1, wherein the air inlet tube has a diameter D1, and a peripheral gas injection is situated at a distance L6 from an upstream end of the air inlet tube such that: 0(LL6)2*D1

14. Burner according to claim 1, wherein the mixer is situated at a distance L2 from an upstream end of the air inlet tube such that: (LL3)(LL2)L.

15. Burner according to claim 1, wherein the mixer has a cross section smaller than or equal to 0.5 times the cross section of the air inlet tube.

16. Burner according to claim 1, wherein it comprises a second, secondary air tube of diameter D4 that is concentric with the air tube of diameter D1 such that D4>D1.

17. Burner according to claim 1, wherein an intermediate gas injection is situated at a distance L8 from the upstream end of the air inlet tube such that L8>0.

18. Set, comprising a number Nmax of burners according to claim 1.

19. Set according to claim 18, wherein the number Nmax of burners deliver a power of between Pmax and Pmin, wherein the set is able to function with a number Nmin of burners, and wherein its power is variable depending on the number N of burners in operation, such that its variation in power Vp=(NmaxPmax)/(NminPmin).

20. Set of burners according to claim 18, further comprising m peripheral gas injections, such that m>1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Further advantages still may become apparent to a person skilled in the art on reading the following examples, illustrated by the appended figures, which are given by way of example:

[0055] FIG. 1 shows a cross section of a burner according to the disclosure,

[0056] FIG. 1a is a frontal view of the burner in FIG. 1,

[0057] FIG. 2 is a cross section of a burner with walls for mechanically protecting the flame,

[0058] FIG. 3 is a cross section of a burner with peripheral gas injections,

[0059] FIG. 4 is a cross section of a burner with a concentric second air tube,

[0060] FIG. 5a is a cross section of the diffuser,

[0061] FIG. 5b is a frontal view of the diffuser in FIG. 5a,

[0062] FIG. 6 is a frontal view of the air inlet with gas injections according to a first embodiment,

[0063] FIG. 7 is a frontal view of the air inlet with gas injections according to a second embodiment,

[0064] FIGS. 8a and 8b show different arrangements of burners in a set of burners according to the disclosure,

[0065] FIG. 9 is a set of burners with gas injections,

[0066] FIGS. 10 and 11 show different examples of possible settings of burners used in the applications of the minerals industry,

[0067] FIGS. 12a, 12b and 12c are examples of diffusers.

DETAILED DESCRIPTION

[0068] In the rest of the description, the term upstream will be used for the part of the burner that is situated further forward with respect to the stream of gas or to the stream of air, and the term downstream will be used for the part situated further away in the direction of said stream.

[0069] The burner 1 illustrated in FIG. 1 comprises an air inlet tube 2 of length L and axis Z, and a one-piece specific gas injection system 3 that is made up of several elements: [0070] a gas inlet duct 31 situated in the air inlet tube 2, [0071] an upstream gas injection 4 situated in the air inlet tube 2 at a distance L1 from the upstream end 20 of said tube 2, [0072] a downstream gas injection 6 situated at a distance L3 from the upstream end 20 of the air inlet tube 2 and inside the latter, [0073] an air/gas mixing element 5 situated inside the air inlet tube 2 at a distance L2 from the upstream end of said tube 2, [0074] a stabilizing element such as an air/gas diffuser 7 situated at a distance L4 from the end of the air inlet tube 2.

[0075] The gas arrives along the arrow G and the air along the arrow A and the secondary air along the arrow A2. The gas arrives via the specific gas injection system 3, passing through the duct 31 so as to exit through the upstream gas injection 4 and the downstream gas injection 6. For its part, the air flows through the air inlet tube 2.

[0076] The upstream gas injection 4 is illustrated in detail in FIGS. 6 and 7.

[0077] In the example illustrated in FIG. 6, it comprises two elements 40 that are disposed radially. They each start from the gas inlet duct 31 and extend as far as the air inlet tube 2. These elements 40 are perforated with holes 400 disposed in the downstream part. The holes 400 are either aligned at the middle or at the sides, or are distributed in a staggered manner as in FIG. 6.

[0078] In the example in FIG. 7, the elements 41 are inclined with respect to the radius of the air inlet tube 2 and each start from the gas inlet duct 31 and extend as far as the air inlet tube 2. They can have an aerodynamic shape.

[0079] The diffuser 7 is illustrated in detail in FIGS. 5a and 5b. It is made up of a disc 71, of diameter D5, which is pierced with holes 72, and of a concentrator 73. The concentrator 73 has a cylindrical shape of diameter D8 and length L7. The holes 72 are disposed at different concentric diameters: D6 and D7. A series of holes 720 of diameter D6 is disposed on the exterior of the concentrator 73 and a series of holes 721 of diameter D7 is disposed in the interior of the concentrator 73. The downstream gas injection 6 is positioned inside the concentrator 73. In the example illustrated, there are only two series of holes 720, 721, but there could be more thereof.

[0080] FIG. 2 shows a system for mechanically protecting the flame 82, said system being situated inside the firebox 8 and being made up of a wall 9 of conical shape of length L5 and of minimum inside diameter D2 that is situated at the downstream end 21 of the air inlet tube 2. The cone makes an angle 2 with respect to the axis X of the tube 2. The gas injections are not shown in this FIG. 2.

[0081] Peripheral gas injections 10 are disposed at the direct outer periphery of the air inlet tube 2 in the example in FIG. 3. They are fed by the specific gas injection system 3 of the burner 1. It is better to provide preferably two injections that are symmetric with respect to the axis X so as to balance the flame 82.

[0082] According to the variant in FIG. 4, the air inlet tube 2 is surrounded by a second, secondary air inlet tube 22 that is concentric and the same length, intermediate gas injections 11 being disposed in an annular space 23 defined by the two tubes 2 and 22. These intermediate gas injections 11 enter the annular space 23 over a length L8. The length L8 has to be other than zero in order to avoid gas being sent somewhere other than the annular space. Stabilizing elements, such as diffusers 70, are positioned at the outlet of the annular space 23.

[0083] FIGS. 10 and 11 illustrate different settings of burners according to the disclosure that can be used in the minerals industry with the premix technology with air factors R. The gas injections are not shown in these two figures.

[0084] In FIG. 10, the premix is set with an air factor R of between 1 and 2. It is apparent that in this case the flame 82 is long and as a result secondary air is introduced directly into the flame 82, bringing about excess air combustion and a small quantity of NOx in the primary zone 80 and a large quantity in the secondary zone 81.

[0085] In FIG. 11, the premix is set with an air factor R of between 0.25 and 1. In this case, the flame 82 is short and, as a result, the introduction of secondary air is impeded after the flame 82, bringing about combustion with a shortage of air and a low quantity of NOx both in the primary zone 80 and the secondary zone 81, there thus being a reburning effect.

[0086] FIGS. 12a, 12b and 12c show different variants of diffusers 7.

[0087] The burners 1 are disposed in a firebox 8 in different arrangements so as to constitute a set 12 of burners 1 such as those illustrated in FIG. 8a, 8b or 9. The number and arrangement of the burners in the set depend on the type of application in question and on the power desired.

[0088] In FIG. 8a, the burners 1 are aligned vertically in two vertical lines of five burners and two additional burners are disposed on each side at the middle so as to concentrate the flame 82.

[0089] In FIG. 8b, the burners 1 are aligned horizontally in a single line.

[0090] In FIG. 9, the burners 1 are aligned vertically in several vertical lines and peripheral gas injections 10 are positioned at the periphery of the firebox 8. It is possible to dispose further peripheral injections at other locations of the firebox 8.

[0091] Depending on the power desired, the number and arrangement of the burners 1 could vary. Depending on the characteristics of the combustion chamber, a minimum number of burners is necessary.

[0092] Thus, if the burner 1 has a maximum power Pmax=1 MW and a minimum power Pmin=0.2 MW, its variation in power is

Vp=(1/0.2)=5.

[0093] A set 12 of nine elementary burners will have a maximum power of Pmax=91=9 MW.

[0094] If the minimum number of burners 1 in service that is necessary for the operation of the combustion chamber is two, the minimum power of the set of burners will be Pmin=20.2=0.4 MW

[0095] The variation in power of the set 12 of burners will be

Vp=9/0.4=22.5.

Examples for an Ultra-Low NOx 32 MW Burner

[0096] The measurements were taken with a diameter D1 of 324 mm.

[0097] The values measured are the following: [0098] D1diameter of the air inlet tube 2 [0099] Llength of the air inlet tube 2 [0100] L1distance of the gas injection 4 from the upstream end 20 of the air inlet tube 2 [0101] L4distance of the diffuser 7 from the upstream end 20 of the air inlet tube 2 [0102] D8diameter of the concentrator 73 [0103] L7distance of the concentrator 73 from the upstream end 20 of the air inlet tube 2 [0104] L3distance of the downstream gas injection 6 from the upstream end 20 of the air inlet tube 2 [0105] D2inside diameter of the wall 9 [0106] 2angle 2 of the cone of the wall 9 with respect to the axis X of the tube 2 [0107] L6distance of the peripheral gas injection 10 from the upstream end 20 of the air inlet tube 2 [0108] L2distance of the mixer 5 from the upstream end 20 of the air inlet tube 2 [0109] L8distance of the intermediate gas injection 11 from the upstream end 20 of the air inlet tube 2; if the intermediate gas injection 11 is disposed upstream of the end 20, this length is negative.

[0110] DeltaP is the difference in pressure between the burner 1 and the firebox 8.

TABLE-US-00001 Lower Upper Value Dimension limit limit measured Technical result L 972 1944 1591 NOx < 10 ppm and optimized burner cost 500 NOx > 25 ppm 2500 off-market burner cost L1 162 1591 324 NOx < 10 ppm and DeltaP < 250 mmCE 50 DeltaP > 250 mmCE Element 40 of 2 3 NOx < 10 ppm and axis x/x optimized burner cost 1 Nox > 25 ppm No of holes per 20 NOx < 10 ppm element 40 of 10 NOx > 25 ppm axis x/x L4 1267 1591 1591 NOx < 10 ppm and CO < 20 ppm 1000 NOx > 25 ppm and CO < 10 ppm Cross section of 39661 15837 DeltaP < 250 mmCE diffuser 7 (mm.sup.2) 45239 DeltaP > 250 mmCE D8 37 78 58 stability of flame with R > 2 = YES 30 stability of flame with R > 2 = NO L7 0 142 50 stability of flame with R > 2 = YES 200 non-optimized burner cost L3 1429 1591 1571 stability of flame with R > 2 = YES 1200 stability of flame with R > 2 = NO D2 324 1620 1296 CO < 100 mg/Nm3 at 3% 1944 O2 weakening of mechanical integrity 2 0 20 7 CO < 100 mg/Nm3 at 3% 30 O2 stability of flame = NO L6 0 648 324 NOx < 10 ppm 972 weakening of air tube mechanical integrity L2 0 1591 644 NOx < 10 ppm no mixer NOx > 10 ppm Cross section of 39661 31729 DeltaP < 250 mmCE mixer 5 (mm.sup.2) 55525 DeltaP > 250 mmCE L8 0 50 NOx < 10 ppm and DeltaP < 250 mmCE 20 DeltaP > 250 mmCE and risk of gas injection into air box (values in mm)