FLAMELESS OXIDATION DEVICE, APPARATUS AND METHOD

Abstract

A device for the flameless oxidation of fuel includes a flameless oxidation burner, a first conduit to convey a fluid fuel phase to a first outlet and a direct primary jet including the fluid fuel phase outwardly therefrom. A second conduit is provided to convey a jacketing gas to a second outlet. The second conduit is disposed surrounding the first conduit so as to direct a jacketing jet of the jacketing gas outwardly therefrom surrounding the primary jet.

Claims

1. A device for the flameless oxidation of fuel comprising: a first conduit to convey a fluid fuel phase to a first outlet and direct a primary jet comprising the fluid fuel phase outwardly therefrom; a second conduit to convey a jacketing gas to a second outlet; wherein the second conduit is disposed surroundingly about the first conduit so as direct a jacketing jet of the jacketing gas outwardly therefrom surroundingly about the primary jet.

2. A device in accordance with claim 1 comprising: a first inlet to receive a supply of fuel in a fluid phase, a first outlet and a first conduit disposed as a channel means to convey the fuel in a fluid phase from the first inlet to the first outlet; a second inlet to receive a supply of jacketing gas, a second outlet and a second conduit disposed as a channel means to convey the jacketing gas from the second inlet to the second outlet.

3. A device in accordance with claim 2 comprising: a fuel supply in fluid communication with said first inlet; a jacketing gas supply in fluid communication with said second inlet.

4. A device in accordance with claim 3 wherein the jacketing gas supply comprises a supply in fluid communication with said second inlet of one or more gases selected from: a comburant gas; an exhaust gas; an inert gas.

5. A device in accordance with claim 3 wherein the fuel supply comprises a supply in fluid communication with said first inlet of pulverous coal in a carrier gas.

6. A device in accordance with claim 1 comprising an annular second outlet surroundingly disposed concentrically around a circular first outlet.

7. A device in accordance with any preceding claim 1 further comprising a third conduit to convey a comburant gas to a third outlet.

8. A device in accordance with claim 7 comprising a third conduit disposed surroundingly about the first and second conduits so as direct a comburant jet of the comburant gas outwardly therefrom surroundingly about the primary and jacketing jets.

9. A device in accordance with claim 7 comprising a plurality of third conduits arrayed surroundingly about the first and second conduits having a corresponding plurality of third outlets configured to produce a corresponding plurality comburant jets projecting outwardly beyond each third outlet surroundingly about the jacketing jet.

10. A device in accordance with claim 9 comprising concentrically disposed: a central circular first outlet, a second annular outlet surroundingly disposed about the first outlet, and an array of at least two third outlets, disposed about the second outlet

11. An apparatus for the flameless oxidation of fuel comprising: a reaction chamber having an internal reaction volume defined by one or more chamber walls; at least one device in accordance with claim 1 extending through the wall and disposed to direct a primary jet comprising a fluid fuel phase into the reaction volume via its first outlet and to direct a jacketing jet comprising a jacketing gas into the reaction volume via its second outlet surroundingly around the primary jet.

12. An apparatus in accordance with claim 11 wherein the at least one device comprises an oxidation device to direct a fuel jet and a jacketing jet towards an oxidation zone in the reaction chamber, and wherein the apparatus further comprises a comburant gas supply conduit arranged to supply comburant to the oxidation zone and/or an exhaust gas supply conduit arranged to supply hot recycled exhaust gas to the oxidation zone.

13. An apparatus in accordance with claim 12 wherein the oxidation device comprises a plurality of comburant gas supply conduits disposed surroundingly around the first and second conduits of the oxidation device.

14. An apparatus in accordance with claim 13 comprising a combustion apparatus for the flameless oxidation of fuel to generate heat in a furnace chamber.

15. A method of flameless oxidation of fuel comprising the steps of: directing a fluid fuel phase towards a flameless oxidation zone in a reaction chamber; causing a jacketing gas jet to be directed towards the said oxidation zone in a manner disposed surroundingly about the primary jet; supporting flameless oxidation of the fuel jet in the oxidation zone at least by supplying to the oxidation zone one or both of comburant gas and hot exhaust gas.

16. A method in accordance with claim 15 wherein the steps of directing a fluid fuel phase towards a flameless oxidation zone and causing a jacketing gas jet to be directed towards the said oxidation zone are respectively performed by causing a fluid fuel phase to be conveyed via a first conduit to a first outlet letting into the reaction chamber, and causing a jacketing gas to be conveyed via a second conduit to a second outlet letting into the reaction chamber disposed surroundingly about the first outlet.

17. A method in accordance with claim 15 wherein the jacketing gas comprises one or more gases selected from: a comburant gas; an exhaust gas; an inert gas.

18. A method in accordance with claim 15 wherein the fluid fuel phase is pulverous coal in a carrier gas.

Description

[0078] An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0079] FIG. 1 is a sectional side view of a prior art flameless oxidation burner to which the principles according to the invention could be applied, and illustrates the problem arising in particular with pulverised coal firing;

[0080] FIG. 2 is sectional side view of a flameless oxidation burner in accordance with an embodiment of the first aspect of the invention;

[0081] FIG. 3 is a partial section of a flameless oxidation chamber in accordance with a second aspect of the invention incorporating such a flameless oxidation burner and with a simple schematic representation of a possible fuel and gas supply system.

[0082] The simple schematic system shown in FIG. 1 shows a typical flameless oxidation system that includes a central fuel jet supply conduit to supply a fuel jet 1, which may contain oxygen and for example carrier combustion air, and spaced further supply conduits to deliver additional jets 3 which supply additional combustion air or air plus recycled flue gas to the combustion zone. Also in familiar manner, hot recirculated exhaust gas 2 is introduced in advance of an intended flameless reaction zone. The combustion air or air plus recycled flue gas is typically preheated and the induced exhaust gas maintains temperature in a reaction zone in the reaction chamber above the desired ignition temperature of the fuel phase and may additionally provide some further oxygen to support oxidation of the fuel.

[0083] The condition illustrated in FIG. 1 is the condition that the invention seeks to suppress, in which ignition can occur at the borders of the fuel jet in advance of the intended flameless reaction zone which can then cause ignition of a main flame instead of a flameless oxidation in the intended flameless reaction zone. This problem is particularly encountered in the use of pulverised coal as fuel, when transported by carrier air, where the oxygen in the carrier air in combination with the high reactivity of volatiles and the high combustion chamber temperatures can lead to unwanted self-ignition, but the problem is not limited to such fuel, and nor is the solution offered by the invention so limited.

[0084] As illustrated in FIG. 1, the effect of early contact with the hot recirculated exhaust gas 2 in advance of a intended flameless reaction zone can be to cause undesirable initial ignition of flames 4 at the border of the fuel jet (and in the particular case at the border of the fuel/combustion air jet). These flames 4 may then ignite a main flame 5 producing unwanted flame combustion of the fuel instead of the desired flameless oxidation.

[0085] FIG. 2 illustrates a comparable situation where the primary fuel jet has been modified in accordance with the principles of the invention. Again a simple schematic is shown including a primary fuel jet 1 which may contain oxygen such as carrier air, and is for example pulverised coal entrained in a suitable carrier gas such as carrier combustion air, and optional additional conduits deliver secondary additional jets 3 to supply for example combustion air or air plus recycled flue gas. The combustion air or air plus recycled flue gas is typically preheated and the internally recirculated exhaust gas 2 again maintains temperature in a reaction zone in the reaction chamber above the desired ignition temperature of the fuel phase and may additionally provide some further oxygen to support oxidation of the fuel.

[0086] In this case, an additional annular conduit surrounds the central conduit which supplies the fuel/air jet 1, and this supplies a jacketing jet 6 containing air, exhaust or a mixture of both (optionally with additionally or substitutionally provided other oxidatively inert gas), shielding the fuel/air jet from high exhaust temperatures and from the oxygen in the secondary air jets and in the exhaust gas, and thus suppressing flame formation at the border of the fuel/air jet.

[0087] Suppression of such initial flame formation at the border of the fuel/air jet controls oxidation conditions more effectively, prevents ignition of a main flame as illustrated in FIG. 1, and instead supports flameless oxidation in the flameless oxidation region 7.

[0088] FIG. 3 is a partial section of a flameless oxidation chamber in accordance with a second aspect of the invention incorporating such a flameless oxidation burner and with a simple schematic representation of a possible fuel and gas supply system.

[0089] A chamber wall 12 (shown as partial section of one side only) defines a reaction volume generally designated 13. A single burner 11 in accordance with the embodiment of FIG. 2 is shown let into the wall. A single burner is shown for simplicity. In a practical system multiple burners will usually be provided. The burner is structured in general as shown in FIG. 2 to deliver a central jet comprising fuel which may be entrained in a suitable carrier gas such as carrier combustion air jacketed by the jacketing jet, and optional secondary additional jets 3 to supply for example additional combustion air or air plus recycled flue gas to a flameless reaction zone generally designated 14. A hot recirculated exhaust gas conduit 2 supplies exhaust gas from an exhaust outlet of the chamber (omitted for clarity) in advance of the intended flameless reaction zone in familiar manner to control conditions and encourage flameless oxidation.

[0090] The system is distinctly characterised by the provision of a jacketing jet about the fuel jet. The jacketing gas of the jacketing jet is selected to be relatively less oxidising than, and to isolate the primary jet to some extent from early contact with, these hot recirculated exhaust gases, and is for example selected from a comburant gas, cold recirculated FGR, inert gas, or a mixture thereof. A simple schematic of a fuel and gas supply arrangement to effect this is provided in FIG. 3.

[0091] A source of fuel 22 which is for example in the preferred pulverised coal embodiment of the invention a coal pulveriser or silo supplies fuel which is for example pulverised coal entrained in carrier air via a supply conduit 24 to the central conduit of the burner of FIG. 2 and thus supplies the primary fuel jet 1.

[0092] The schematic representation also provides for completeness a source of cold recycled flue gas 17 supplied by the recycle conduit 18 from a flue outlet (omitted for clarity), a secondary comburant supply 16 which supplies comburant gas for example combustion air, and a source of oxidatively inert gas 15.

[0093] A jacketing gas supply control system 32 is in fluid communication with the sources 15, 16 and 17 and includes at least a selective flow control system whereby a jacketing gas comprising air, exhaust or a mixture of both optionally with additionally or substitutionally provided other oxidatively inert gas, is supplied via the supply conduit 34 to the annular conduit of the burner of FIG. 2 and thus supplies the jacketing jet 6.

[0094] A secondary comburant gas supply control system 42 is in fluid communication with the sources 16 and 17 and includes at least a selective flow control system whereby a comburant gas comprising air, exhaust or a mixture of both is supplied via the supply conduit 44 to the optional additional conduits of the burner of FIG. 2 and thus supplies the additional jets 3. A heater 43 may preheat the comburant gas to further control conditions at the flameless reaction zone and encourage flameless oxidation.