HIGH CAPACITY BURNER

Abstract

The invention comprises a burner comprising a burner head and supply openings for a fuel and an oxygen containing gas, a central tubular passage for the oxygen containing gas and a radially outward positioned passage for the fuel. The passage for fuel is fluidly connected to one or more fuel discharge openings at the burner head wherein the fuel discharge openings are directed inwardly such that in use, the fuel is injected into the stream of oxygen containing gas. The central passage is provided with an obstruction located between the supply opening for oxygen containing gas and the fuel discharge openings. The invention is also directed to a process using said burner.

Description

This application claims the benefit of European Application No. 07100646.4 filed Jan. 17, 2007 and U.S. Provisional Application No. 60/887098 filed Jan. 29, 2007.

FIELD OF THE INVENTION

The present invention relates to a burner comprising a burner head and supply openings for a fuel and an oxygen containing gas, a central tubular passage for the oxygen containing gas and a radial outward positioned passage for the fuel. The invention is also directed to process to operate a burner and to a process to start-up a gasification process using the burner process.

BACKGROUND OF THE INVENTION

Burners as above can be used as a start-up burner to start a pressurized coal gasification process. Examples of such coal gasification processes are for example described in WO-A-2004/005438 or WO-A-2006/117355. In such a start-up method the temperature and pressure in the gasification reactor are increased by combustion of a liquid oil fuel with oxygen in such a burner. The burner is typically a single fuel burner as opposed to a dual fuel burner because of their more simple design. When the pressure and temperature reach a pre-selected level the actual gasification of the coal can be started.

EP-A-108427 describes a burner having a burner head and supply openings for a coal fuel and an oxygen containing head. The burner has a central passage for the oxygen containing gas and fuel discharge openings for the coal fuel at the burner head.

U.S. Pat. No. 5,351,477 is directed to a dual fuel burner having separate fuel discharge openings for a gaseous and a liquid fuel.

A suited start-up burner desirably has a high heat capacity to compensate for heat losses to the wall and to achieve a high reactor temperature. Because of reactor dimensions a suitable start-up burner desirably further has a short flame length.

A suitable start-up burner will further be capable of operating with a stable flame in a large pressure range, starting at ambient and ranging to a more elevated pressure at which the actual gasification reactions are started.

The aim of the present invention is to provide a burner, which meets these requirements.

SUMMARY OF THE INVENTION

The present invention comprises a burner comprising a burner head and supply openings for a fuel and an oxygen containing gas, a central tubular passage for the oxygen containing gas and a radially outward positioned passage for the fuel,

• • wherein the passage for the fuel is fluidly connected to one or more fuel discharge openings at the burner head and wherein the fuel discharge openings are directed inwardly such that in use, the fuel is injected into the stream of oxygen containing gas and
  • wherein the central passage is provided with an obstruction located in the flow path for oxygen and
  • wherein at least part of the fuel discharge openings are located such that, in use, fuel is discharged in a stagnant zone as present at the downstream end of the obstruction.

Applicants found that the above burner can have a small diameter in combination with a short flame length and a high heating capacity.

The invention is also directed to a process to operate a burner by injecting a fuel into a stream of an oxygen containing gas in a stagnant zone as present downstream from an obstruction as present in the stream of oxygen located at a burner head of the burner and to a process to start-up a pressurized gasification reactor, which reactor is comprised of a vessel, an outlet conduit for product gas, which conduit is provided with a valve, a start-up burner and a burner for performing the gasification reaction, by

• • (i) performing the afore referred to process and simultaneously increasing the pressure in the vessel by throttling the valve, and
  • (ii) starting the gasification burner once the pressure and the temperature in the vessel has reached a target pressure level by introducing a solid carbonaceous feed and an oxygen containing gas to the burner while performing the afore referred to process.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic cross-sectional view of a preferred burner according to the present invention.

FIG. 2 is a combined device comprising a burner according to the present invention.

FIG. 3 is a schematic cross-sectional view of another preferred burner according to the present invention.

FIG. 4 is a cross-sectional view AA′ of the burner of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

The burner according to the invention is preferably a co-annular burner having a central passage for the oxygen containing gas and an annular passage for the fuel. The obstruction in the central passage may be a part extending inwardly from the wall of the central passage. The size of this part should be sufficient to create a stagnant zone just downstream of said part. The fuel discharge opening is located at said stagnant zone. A suitable obstruction is a swirl imparting means. Suitably such swirl imparting means are vanes fixed in the central passage of the burner.

Preferably at least part of the fuel discharge openings are located such that in use fuel is discharged in a stagnant zone as present at the downstream end of the obstruction. Such stagnant zones are present just downstream of, for example, the end of the vanes of the swirl imparting means near the inner wall of the central passage. Preferably the distance between the discharge opening and the obstruction is between 0 and 2 mm, more preferably between 0 and 1 mm. The volume of the stagnant zone will depend on the dimensions of the obstruction, e.g. the thickness of the swirl imparting means. For example, a more bulky swirler will result in a larger stagnant zone, which will allow a larger distance between the swirling means and the discharge opening.

Applicants found that by introducing at least part of the fuel at such a stagnant zone a more stable flame is obtained which allows operation at much higher gas velocities.

Without wishing to be bound by the following theory it is believed that in such stagnant zones partial oxidation reactions take place between oxygen and the fuel. The resultant intermediate reaction products are discharged from the stagnant zone by the high velocity flow of the mixture of oxygen containing gas and fuel. It is believed that these intermediate reaction products continuously ignite the mixture of fuel vapour as released from the fuel droplets and oxygen resulting in a stable flame.

The above burner is especially suited as a start-up burner in a gasification process. Other uses may also be envisaged.

In a gasification reactor a start-up burner will suitably be used in combination with an ignition burner and a means to detect a flame. The ignition burner is used to ignite the flame of the start-up burner. The means to detect the flame of the start-up burner and of the ignition burner is preferably done with flame eyes. Although other means such as for example ionisation detection are also possible. In a gasification reactor these different devices are typically present at separate positions, each requiring a separate passage through the pressure wall of the gasification reactor and separate passage through the reactor internal walls. Reactor internal walls can be comprised of refractory or can be so-called membrane walls.

The burner according to the invention can advantageously have a small diameter as explained above. Applicants have now found that it is attractive to combine the ignition burner and the start up burner and the flame detector in one apparatus. This is advantageous because for such a device only one passage through the pressure wall of the gasification reactor and through the reactor internal wall is required. The invention is thus also directed to a combined start-up burner, ignition burner and flame detector, wherein the start-up burner is a burner as described above. Preferably the combined device is a tubular apparatus wherein the start-up burner, the ignition burner and the flame detector means are positioned co-axial with the tubular apparatus. The ignition burner and the flame detector are well known and will therefore not be discussed here in great detail.

Applicants have found that the flame has such an improved stability that the use of a separate ignition burner may even be omitted. Instead of a separate ignition burner a sparking device, suitably an electric sparker, is present downstream of the stagnant zone at the burner head. The invention is thus also directed to a combined tubular apparatus comprising a burner provided with a sparking device as described above and a flame detector.

The invention is also directed to a process to operate a burner by injecting a fuel into a swirling stream of an oxygen containing gas at a burner head of the burner. The superficial velocity of the oxygen containing gas at the burner head of the burner may range from 40 to 360 m/s and preferably from 40 to 250 m/s. The advantages of the invention, namely a stable flame at high heating capacity, are achieved even more at a gas velocity of above 100 m/s. The velocity may advantageously be the sonic velocity of the gas as measured at the conditions of the space into which the flame of the burner is discharged. The fuel may be any gaseous or liquid hydrocabonaceous fuel. Preferably the fuel is a liquid hydrocarbonaceous fuel, preferably kerosene and more preferably gas oil or alternative hydrocarbon products boiling in the same boiling ranges as kerosene or gas oil. Such fuels are preferred because they are easy to obtain and transport. This process is preferably performed in a burner as such or in a combined device as described in this specification and figures.

The invention is also directed to a process to start-up a pressurized gasification reactor, which reactor is comprised of a vessel, an outlet conduit for product gas, which conduit is provided with a valve, a start-up burner and a burner for performing the gasification reaction. The pressurized gasification reactors are well known and for example described in Chapters 5.3.3-5.3.8 of Gasification by Christofer Higman and Maarten van der Burgt, 2003, Elsevier Science, Burlington Mass., pages 118-128.

In the preferred start-up process a burner as described above is used to increase the temperature in the gasification reactor from typically ambient conditions. The pressure is simultaneously increased by throttling the valve from typically ambient conditions. Once the pressure and the temperature in the vessel has reached a target pressure level a solid carbonaceous feed, for example coal or biomass, and an oxygen containing gas is provided to the gasification burner. At the elevated temperature the solid carbonaceous feed will auto-ignite and the gasification process is started. The temperature at which the solid carbonaceous feed is supplied to the gasification burner is suitably above 1200° C. The pressure at which the solid carbonaceous feed is supplied to the gasification burner is suitably above 10 bars. Once the partial oxidation of the solid carbonaceous fuel has started the start-up burner is extinguished and preferably removed from the reactor. The pressure is subsequently increased to the desired operating pressure, which may range from 30 to 80 bars.

FIG. 1 shows a burner (1) comprising a burner head (9) and supply openings (3,4) for an oxygen containing gas and a fuel respectively. The burner (1) is further provided with a central tubular passage (2) for the oxygen containing gas and a radially outward positioned annular passage (5) for the fuel. The passage (5) for fuel is fluidly connected to fuel discharge openings (7) at the burner head (9). The openings (7) are located in the inner wall (12) of the central tubular passage (2). The openings may be separate openings or more preferably one continuous slit like opening (7) as shown. The opening (7) is directed inwardly, in the direction of the central axis (10) such that in use the fuel is injected into the stream (11) of oxygen containing gas. The central passage (2) is provided with swirl imparting means (6) located between the supply opening (3) for oxygen containing gas and the fuel discharge opening (7). The swirl imparting means (6) provides, in use, a swirling motion to the oxygen containing gas (11) at the burner head (9).

In FIG. 1 a stagnant zone (13) is indicated at part (8) of the opening (7) located at the inner wall (12) of the central passage (2) and at the downstream end of the swirl means (6). At part (8) of slit opening (7) at least a portion of the fuel is discharged into stagnant zone (13). Slit openings (7), which are located further away from the stagnant zone, introduce fuel directly into the swirling gas stream (11).

FIG. 2 shows a combined device (15). Combined device (15) is a tubular apparatus having positioned co-axially a start-up burner (16) according to the present invention, a ignition burner (18) and a visual flame detector (17). The flame detector (17) is equipped with flame eyes, whereby the flame is detected from the backside of the flame. The start-up burner (16) is provided with supply means for an oxygen containing gas (19) and a fuel (20). The ignition burner (18) is provided with supply means for an oxygen containing gas (21) and a fuel (22). In the figure a flame (23) is shown schematically. In reality the size of the flame (23) may be greater than shown. Also shown is part of the pressure wall (24) of a gasification reactor and a membrane wall (25) comprised of inter-connected tubular parts in which, in use, water evaporates to provide cooling of the wall (25).

FIG. 3 shows another preferred burner (26) according to the present invention comprising a burner head (27) and supply openings (28, 29) for an oxygen containing gas and a fuel respectively. The burner (26) is further provided with a central tubular passage (30) for the oxygen containing gas and a radially outward positioned annular passage (31) for the fuel. The passage (31) for fuel is fluidly connected to a fuel discharge opening (32) at the burner head (27). The slit like opening (32) is located in the inner wall (33) of the central tubular passage (30). The opening (32) is directed inwardly, in the direction of the central axis (34) such that in use the fuel is injected into the stream (35) of oxygen containing gas. The central passage (30) is provided with four stud type obstructions (36) extending inwardly from wall (33) into passage (31) and located between the supply opening (28) for oxygen containing gas and the fuel discharge opening (32). The fuel discharge opening partly open into a stagnant zone (37) as present just downstream of the obstructions (36). FIG. 3 also shows a flame (38).

FIG. 4 is a cross sectional view AA′ of FIG. 3.

Claims

1. A burner comprising a burner head and supply openings for a fuel and an oxygen containing gas, a central tubular passage for the oxygen containing gas and a radially outward positioned passage for the fuel, wherein the passage for the fuel is fluidly connected to one or more fuel discharge openings at the burner head and wherein the fuel discharge openings are directed inwardly such that in use, the fuel is injected into the stream of oxygen containing gas and wherein the central passage is provided with an obstruction located in the flow path for oxygen and wherein at least part of the fuel discharge openings are located such that, in use, fuel is discharged in a stagnant zone as present at the downstream end of the obstruction.

2. A burner according to claim 1, wherein the obstruction is a swirl imparting means located between the supply opening for oxygen containing gas and the fuel discharge openings, which swirl imparting means provide, in use, a swirling motion to the oxygen containing gas at the burner head.

3. A burner comprising a burner head and supply openings for a fuel and an oxygen containing gas, a central tubular passage for the oxygen containing gas and a radially outward positioned passage for the fuel, wherein the passage for fuel is fluidly connected to one or more fuel discharge openings at the burner head and wherein the fuel discharge openings are directed inwardly such that in use the fuel is injected into the stream of oxygen containing gas and wherein the central passage is provided with swirl imparting means located between the supply opening for oxygen containing gas and the fuel discharge openings, which swirl imparting means provide, in use, a swirling motion to the oxygen containing gas at the burner head, wherein at least part of the fuel discharge openings are located such that in use, fuel is discharged in a stagnant zone as present at the downstream end of the swirl means.

4. A combined tubular apparatus comprising a burner according to claim 1, an ignition burner and a flame detector.

5. A process to operate a burner by injecting a fuel into a stream of an oxygen containing gas in a stagnant zone as present downstream from an obstruction present in the stream of oxygen located at a burner head of the burner.

6. A process according to claim 5, wherein the velocity of the oxygen containing stream is between 100 and 350 m/s.

7. A process to start-up a pressurized gasification reactor, which reactor is comprised of a vessel, an outlet conduit for product gas, which conduit is provided with a valve, a start-up burner and a burner for performing the gasification reaction, by

(i) performing the process according to claim 5 making use of the start-up burner and simultaneously increasing the pressure in the vessel by throttling the valve, and

(ii) starting the gasification burner once the pressure and the temperature in the vessel has reached a target pressure level by introducing a solid carbonaceous feed and an oxygen containing gas to the burner while performing the process according to claim 5.

8. A process according to claim 7, wherein the target pressure level is above 10 bar and wherein the target temperature level is above 1200° C.

9. A process according to claim 7, wherein after step (ii) is performed the pressure is increased to the desired operating pressure in the range of from 30 to 80 bars.