AU2007261826B2

AU2007261826B2 - Afterburner for gas from gasification plant

Info

Publication number: AU2007261826B2
Application number: AU2007261826A
Authority: AU
Inventors: Rolf B. Rummelhoff
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-06-23
Filing date: 2007-06-25
Publication date: 2012-11-29
Anticipated expiration: 2027-06-25
Also published as: EP2035749A1; EA200970034A1; AU2007261826A1; WO2007148991A1; CA2655989A1; NZ574243A; NO325990B1; US20130034817A1; NO20062946L

Abstract

The present invention relates to an afterburner for gas from a gasification plant. The afterburner provides an optimal mixture of combustible gas and air, permitting an optimal reaction between the 02 in the air and the gas and creating a mixture ratio that enables the load on a burner to be regulated without altering the mixture ratio between air and gas. This offers the possibility of optimal combustion even during regulation of the burner, over the whole of the relevant regulating range. The result is extremely good combustion and reduced emissions of 02, CO and NOx.

Description

1 Afterburner for gas from gasification plant The present invention relates to an afterburner for gas from a gasification plant. The afterburner provides an optimal mixture of combustible gas and air, permitting an optimal reaction between the 02 in the air and the gas and creating a mixture ratio 5 that enables the load on a burner to be regulated without altering the mixture ratio between air and gas. This offers the possibility of optimal combustion even during regulation of the burner, over the whole of the relevant regulating range. The result is extremely good combustion and reduced emissions of 02, CO and NOx. Background Art 10 During combustion of gas it is important that air and gas should be mixed to form a homogeneous mass and that the combustible gas is permitted to react fully with the 02 content in the air. This creates an optimal mixture of combustible gas and 02 which is crucial for achieving clean, good and efficient combustion of the gas. This in turn provides a high level of utilisation of the combustible gas and a low level of 15 emission of noxious gases and soot. Furthermore, for a plant for combustion of gas, whether it stems from wood fuel or oil (atomized oil), it is important to be able to vary the load on the burner unit over an appropriate load range in order to obtain a flexible plant. Relevant examples are combustion of gas from wood for production of steam which in turn is employed in 20 a steam turbine for production of electricity or combustion for heating oil which is circulated in a plant for heating and/or drying of, for example, wood. When the load on, for example, the electric generator increases, the energy supply to the steam turbine has to be increased and consequently the heating of the steam has to increase. This is accomplished through the supply of air and thereby also fuel. The 25 air volume is traditionally regulated by regulating the air flow to the burner in step with the load. This causes the air velocity and turbulence in the mixing zone to be reduced correspondingly which in turn leads to a less efficient mixture of air and gas. Amongst the known solutions are several for mixing combustible gas and air and a 30 common solution is the supply of air in connection with a constriction or venturi where gas from smouldering wood pulp is mixed with air and combusted. The fact which is particularly important and which forms the basis for the present invention is that the air is brought together with the combustible gas at high velocity and thereby with high turbulence. It is also important for the velocity of the air to be 35 maintained. This is particularly important when the burner installation has to be regulated as indicated above and it is important for the velocity to be maintained over the entire regulating range. It will therefore be possible to regulate the volume of air in the same way as in the combustion process, but in the mixing phase the air 2 velocity and turbulence are constant over the entire regulating range. In this way the good mixture of air and combustible gas is maintained and the reaction between the combustible gas and the air's 02 remains optimal at all regulating stages within the regulating range. This in turn leads to good, clean combustion and good utilisation 5 of the calorific value in the combustible gas. This is also crucial for keeping down the costs per produced power unit. Summary of the Invention On this basis, according to the present invention an afterburner is provided for mixing combustible gas and air, which afterburner comprises a substantially circular 10 mixing chamber with open ends where the combustible gas is introduced into the mixing chamber at the first end. The afterburner is characterised in that air is added to the mixing chamber along the mixing chamber's circumference through one or more openings in the wall of the mixing chamber from an air supply chamber so that the combustible gas and the air are mixed in the mixing chamber and where the 15 mixture of the combustible gas and the air are discharged from the other opening in the mixing chamber and where the air is introduced into the mixing chamber from the air supply chamber substantially tangentially to the interior of the mixing chamber and has a velocity generated by a fan in connection with the air supply chamber. In this way a swirl of air and combustible gas is created where the air 20 spins in a rotating motion through the afterburner. According to the so-called spin rate, the angular velocity w multiplied by the radius of the mixing chamber will be constant. In a preferred embodiment of the invention the diameter DI of the mixing chamber's air inlet and the diameter D2 of the mixing chamber's outlet are different and the diameter D1 of the mixing chamber's air inlet is preferably larger than the 25 diameter D2 of the mixing chamber's outlet. Since the spin rate is constant, the angular velocity will increase when the diameter is reduced. Furthermore, the air supply chamber may surround the part of the mixing chamber where the air inlet openings in the mixing chamber's walls are provided. This enables the air to be easily passed from the fan for supplying air to the afterburner 30 according to the invention. In a further embodiment an overflow chamber may be connected to the air supply chamber, which overflow chamber is provided with an outlet and a damper in connection with the outlet. By adjusting the damper the volume of air passing from the air supply chamber to the overflow chamber will be regulated. The volume of 35 air which is not supplied to the mixing chamber will thereby be regulated since it bypasses the inlet. In a further embodiment the overflow chamber may surround the whole or parts of the mixing chamber and is connected to the air supply chamber. In order to regulate the air to the mixing chamber, the position of the damper can 3 therefore be varied with the result that the damper varies the air flow out of the overflow chamber. In an embodiment the connection between the air supply chamber and the overflow chamber is substantially at the openings between the air supply chamber and the 5 mixing chamber. In different embodiments a cone may be provided at the inlet to the mixing chamber, forcing the combustible gas out towards the air inlet openings in the mixing chamber and assisting in creating swirling in the mixing chamber. In a further embodiment thereof, in the mixing chamber at the inlet to the mixing 10 chamber, a cone may be provided whose pointed end points towards the inlet to the chamber. At this cone, moreover, oil may be supplied which is atomized or is already atomized. The ingoing air to the mixing chamber has a velocity direction which is substantially tangential and the combustible gas has a velocity vector which is 15 substantially axial. The tangential velocity vector is determined by the air supply fan's capacity and pressure (combustion air). The axial velocity vector is determined by the area in the burner where the air flows, which in turn is determined by the ratio between DI and D2 as indicated above. The resulting velocity vector has a direction with an axial and a tangential component. Through 20 regulation of supplied air the resulting velocity vector will be altered by reducing the axial velocity while the tangential velocity is increased. The air velocity will therefore be varying with little variation and will be approximately constant over the regulating range, giving a higher velocity where the velocity would normally be reduced with known solutions, thereby producing the highly favourable combustion 25 possibilities provided by the invention. The invention further provides an afterburner for mixing combustible gas and air, which afterburner comprises a substantially circular mixing chamber with open ends, an inlet and an outlet, where the combustible gas is introduced into the mixing chamber at the inlet, and where air is added to the mixing chamber along the mixing 30 chamber's circumference through one or more openings in the wall of the mixing chamber from an air supply chamber so that the combustible gas and the air are mixed in the mixing chamber, and where the mixture of the combustible gas and the air is discharged from the outlet in the mixing chamber, and where the air is introduced into the mixing chamber from the air supply chamber substantially 35 tangentially to the interior of the mixing chamber and has a velocity generated by a fan in connection with the air supply chamber, characterised in that an overflow chamber is connected to the air supply chamber, which overflow chamber is provided with an outlet and a damper in connection with the outlet.

4 Brief Description The invention is further explained with reference to the attached figures, in which: Figure 1 is a cross sectional view from the side of an embodiment of the invention with mixing chamber together with chambers for air inlet and overflow. 5 Figure 2 illustrates the air inlet chamber in section A-A from figure 1. Figure 3 illustrates the overflow chamber in section B-B from figure 1. Figure 4 is a graphic presentation of air and gas velocity together with resulting velocity with full load on the burner. Figure 5 is a graphic presentation of air and gas velocity together with resulting 10 velocity with regulated load on the burner. Figures 6 and 7 illustrate alternative embodiments of the inlet to the afterburner according to the present invention. Best Modes Figure 1 is a cross sectional view from the side of an afterburner according to the 15 present invention with a mixing chamber 1, an inlet 2 for combustible gas and an outlet 3 for combustible gas mixed with air. Also illustrated is an air supply chamber 6 surrounding the mixing chamber with connections 4 to the mixing chamber 1. The air supplied to the air supply chamber 6 comes from a fan which gives the air a velocity and a pressure. An overflow chamber 7 is further illustrated 20 where excess air can be discharged and this is controlled by a damper 9 (fig. 3) at the outlet of the overflow chamber 7. The combustible gas enters the mixing chamber through the opening 2 and air is supplied through the openings 4 from the air supply chamber 6. If the load on the burner is reduced, the supply of air is regulated by letting some air pass through the 25 openings 5 and on out into the overflow chamber. This is regulated by the damper 9 (fig. 3) in the overflow chamber. It is further illustrated in figure 1 that the inlet for combustible gas has a diameter Dl while the outlet of mixed gas and air has a diameter D2. D2 is smaller than DI and this difference gives increased velocity to the air axially through the mixing 30 chamber. Furthermore, in cross section A-A from figure 1, figure 2 is a view from below (from the inlet side) of an air supply chamber 6. It shows that this has an inlet where the air is supplied by a fan. Moreover it is apparent that the air rotates in the chamber 6 and is admitted to the mixing chamber through the openings 8 with the 5 result that the air's direction is substantially tangential in the chamber 1 where the air meets the combustible gas and is mixed. The air here has a high velocity and high turbulence and the mixture with the combustible gas is highly effective and the gas essentially reacts fully with the air. This has been proved by means of 5 experiments and the following measurements of 02, CO and NOx have been made showing that the combustion gives values that are bordering on theoretical without smoke being observed from the chimney. This applied, furthermore, over the whole load range. Furthermore, in figure 3 the overflow chamber 7 is illustrated where excess air can 10 escape instead of being mixed into the mixing chamber 1. It also shows that the chamber 7 has an outlet with a damper 9 which is adjusted in order to remove air from the mixing chamber 1. If the damper 9 is completely closed, all the air goes to the mixing chamber while if the damper 9 is fully open, a substantial part of the air goes outside the mixing chamber 1. 15 Figure 4 further illustrates in a diagram the ratio between axial and tangential air velocity and the resulting air velocity and direction through the mixing chamber. Figure 5 further illustrates a corresponding diagram where the axial velocity is reduced as a result of less air supply (a greater proportion to the overflow chamber 7). Since the velocity ratio is constant, the angle of the resultant flow (the vector) 20 will be constant and the velocity will also be constant. Furthermore, in figures 6 and 7 alternative embodiments are illustrated where a cone 10 is mounted at the inlet 2 for combustible gas, forcing the gas out towards the peripheral edge of the chamber 1 where the gas meets the air (at high velocity) and is mixed. Figure 7 further illustrates that the cone 11 may contain an outlet 12 25 for supplying oil which has been or is being atomized. Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. 30 Each document, reference, patent application or patent cited in this text is expressly incorporated herein in their entirely by reference, which means that it should be read and considered by the reader as part of this text. That the document, reference, patent application, or patent cited in this text is not repeated in this text is merely for reasons of conciseness. 35 Reference to cited material or information contained in the text should not be understood as a concession that the material or information was part of the common general knowledge or was known in Australia or any other country.

Claims

1. An afterburner for mixing combustible gas and air, which afterburner comprises a substantially circular mixing chamber with open ends, an inlet and an outlet, where the combustible gas is introduced into the mixing chamber at the inlet, 5 and where air is added to the mixing chamber along the mixing chamber's circumference through one or more openings in the wall of the mixing chamber from an air supply chamber so that the combustible gas and the air are mixed in the mixing chamber, and where the mixture of the combustible gas and the air is discharged from the outlet in the mixing chamber, and where the air is introduced 10 into the mixing chamber from the air supply chamber substantially tangentially to the interior of the mixing chamber and has a velocity generated by a fan in connection with the air supply chamber, c h a r a c t e r i s e d i n that an overflow chamber is connected to the air supply chamber, which overflow chamber is provided with an outlet and a damper in connection with the outlet. 15

2. An afterburner according to claim 1, c h a r a c t e r i s e d i n that the diameter DI at the mixing chamber's inlet and the diameter D2 at the mixing chamber's outlet are different.

3. An afterburner according to claim 2, c h a r a c t e r i s e d i n that the diameter D1 at the mixing chamber's inlet is 20 larger than the diameter D2 at the mixing chamber's outlet.

4. An afterburner according to one of the claims 1-3, c h a r a c t e r i s e d i n that the air supply chamber surrounds the part of the mixing chamber where the air inlet openings in the mixing chamber's walls are provided. 25

5. An afterburner according to one of the claims 1-4, c h a r a c t e r i s e d i n that the overflow chamber surrounds the whole or parts of the mixing chamber and is connected to the air supply chamber.

6. An afterburner according to one of the claims 1-5, c h a r a c t e r i s e d i n that the damper's position can be varied with the 30 result that the damper varies the airflow out of the overflow chamber.

7. An afterburner according to one of the claims 1-6, c h a r a c t e r i s e d i n that the connection between the air supply chamber and the overflow chamber is substantially at the openings between the air supply chamber and the mixing chamber. 35

8. An afterburner according to any of the one of the claims 1-7, c h a r a c t e r i s e d i n that in the mixing chamber at the inlet to the mixing 7 chamber, a cone is provided whose pointed end points towards the inlet of the mixing chamber, at which cone oil may be supplied.

9. An afterburner according to claim I substantially as herein described with reference to the Examples. 5

10. An afterburner for mixing combustible gas and air, the afterburner being substantially as hereinbefore described with reference to: figs. 1-5; figs. 3-5, and 6; or figs. 3-5, and 7.