GB2286662A

GB2286662A - Combustion chamber with self-ignition

Info

Publication number: GB2286662A
Application number: GB9502250A
Authority: GB
Inventors: Thomas Sattelmayer; Petersenior
Original assignee: ABB Research Ltd Switzerland
Current assignee: ABB Research Ltd Switzerland
Priority date: 1994-02-11
Filing date: 1995-02-06
Publication date: 1995-08-23
Anticipated expiration: 2015-02-06
Also published as: GB9502250D0; GB2286662B; DE4404389A1; JPH07225012A

Description

4.

1 TITLE OF THE INVENTION Combustion chamber with self-ignition

BACKGROUND OF THE INVENTION

2286662 Field of the invention

The present invention relates to a combustion chamber in accordance with the preamble of Claim 1.

Discussion of background

In burner apparatus with a premixing section and a free outlet in the direction of outf low toward the downstream combustion space, there is frequently the problem of how to produce a stable f lame f ront in the simplest manner. Various proposals have already been disclosed in this regard but these are per se unsatisfactory. One exception among those disclosed hitherto is Patent Application EP-Al-321 809. the proposals of which represent a jump in quality both as regards flame stabilization and with regard to pollutant emissions, especially NOx emissions, and efficiency. However. there are firing systems in which, for various reasons, the abovementioned invention cannot be employed and, as a result, it is necessary in those cases to continue to operate with a technology which is essentially obsolete, whether it is necessary to have recourse to diffusion burners or to add vortex generators to the premixing section in the region of the flame front. In the first case, high Nox emissions must always be expected and the amount of these emitted is way behind current legal requirements in the countries which provide the most important markets; in the second case, a flashback, especially along the inner wall, where, by the very nature of things, the flow velocity in low, is still possible despite protection of the premixing section by the said vortex elements. A typical firing system in which the said techniques to prevent a flashback will inevitably fail is a combustion chamber designed for self-ignition.

This is generally a largely cylindrical tube into which working gases at a relatively high temperature f low in the axial direction and mix there with an injected fuel which triggers a self- ignition, the thermal preparation of the hot gases taking place exclusively within this tube. With such a configuration, space considerations alone make it impossible to f it premixing burners or means which would help to prevent a f lashback and, f or this reason, it has hitherto been necessary to f orego this essentially attractive combustion technique for the compact installation of a combustion chamber of this kind between two turbines mounted on one shaft.

SUMMARY OF THE INVENTION is Accordingly, one object of the invention as def ined in the claims is to provide means in the case of a combustion chamber of the type stated at the outset which effect flame stabilization. A further object of the invention is to minimize pollutant emissions, especially NOx. CO and UBC (- unsaturated hydrocarbons) emissions.

The essential advantage of the invention is to be regarded as the fact that stabilization of the flam front is achieved by means of the shaping of the combustion zone downstream of the inlet zone.

The flame front forms at the start of the combustion zone. In this plane, said zone has a jump in cross section, the size of this jump simultaneously defining the flow cross section proper of the combustion zone. Within this jump in cross section, which extends in a manner radially of f set f rom the cross section of the inlet zone, marginal zones in which vortex separations, i.e. vortex rings, arise due to the reduced pressure caused there by the flow - these vortex separations leading in turn to annular stabilization of the flame front - are formed during operation. This configuration is particularly advantageous where the combustion chamber is designed for self-ignition. This is because a combustion chamber 4 - 3 of this kind preferably has essentially the form of an annular or ring-shaped combustion chamber, is of short axial length and is f lowed through by a working gas at high temperature moving at high speed. The said peripheral vortex separations stabilize the flam front, with the result that additional precautions against f lashback of the flame are no longer required. There is no longer any need f or the introduction of a perturbing body for flame stabilization within the combustion zone either. By virtue of its geometrical simplicity, the configuration of this combustion chamber makes it ideal for manufacture from a ceramic material and this of f ers great advantages with regard to the cooling of the thermally highly stressed walls, is since a combustion chamber of this kind can be operated with a minimized flow of cooling air. Finally, this stabilization of the f lame f ront without a body leads to an increase in the efficiency of the system# and the availability of a combustion chamber of this kind is furthermore significantly increased.

Advantageous and expedient further developments of the solution to the problem of the invention are defined in the further. dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Fig. 1 shows a self-igniting combustion chamber which comprises an inlet and a combustion zone.

shows a combustion chamber with a symmetrical, uniform expansion of the cross section of the combustion zone and Fig. 3 shows a combustion chamber with a symmetrical expansion of the cross section of the Fig. 2 combustion zone, this expansion narrowing in the direction of flow.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views and the direction of f low of the media is indicated by arrows, Fig. 1 shows 10 a combustion chamber which substantially comprises a cylindrical tube. A combustion chamber of this kind can of course essentially take the f orm of a continuous annular axial or quasi-axial cylinder. such a combustion chamber can also comprise a number of is axially, quasi-axially or helically arranged and individually self-contained combustion spaces. Such combustion chambers are excellently suited for operation as self igniting combustion chambers placed between, in the direction of flow, two turbines mounted 20 on one shaf t. If such a combustion chamber is operated f or self -ignition, the turbine acting on the upstream side (not shown) is designed only for partial expansion of the working gases 7, with the result that these gases flow into the inlet zone 1 of the combustion 25 chamber at a fairly high temperature. Given such a mode - of operation and an annular configuration of the combustion chamber, a plurality of f uel lances 4 are arranged in the circumferential direction of the annular cylinder f orming the combustion chamber. these 30 lances being connected to one another as regards fuel supply by a ring main (not shown) for example. This combustion chamber accordingly has no burners as such: the fuel 5 injected into the working gases 7 by means of the lance 4 triggers a self -ignition as long as the 35 working gases 7 have the specific temperature which is capable of triggering the f uel-dependent self -ignition. If the combustion chamber is operated with a gaseous fuel, the working gases 7 must be at a temperature of about 1000C to trigger self-ignition. As explained 9 - A - 5 above. the fuel 5 supplied flows through the fuel lance 4 into a fuel nozzle 6 which is located approximately on the axis of the inlet zone 1 and which is provided at the end with a row of injection openings 11. These are preferably arranged in a ring around the circumference of the fuel nozzle 6 and are aligned in such a way as regards the injection of the fuel that optimum mixing occurs. The drawing shows injection of the fuel 5 obliquely to the direction of f low of the working gases 7. Depending on the type of fuel and manner of operation, it is also possible to arrange for the injection of fuel 5 to be directed counter to the flow of the working gases 7. Directly upstream of the fuel nozzle 6, on the inside and in the circumferential direction of the inner wall of the inlet zone 1. there are a number of vortex-generating elements 3, these preferably being of tetrahedral design and being cooled, the cooling air required to cool the elements 3 subsequently being added to the working gases 7. These elements 3 cause a swirling motion which accelerates and optimizes the mixing process taking place downstream and also simultaneously induces a backflow zone or a zone of reduced axial velocity in the region of the flame front, which will be discussed later.

After another section, which is kept very short,, the inlet zone 1 makes a transition to a combustion zone 2. The transition between the two zones is formed by a radial jump 8 in cross section on one side, which has the effect of a crescent-shaped expansion of the combustion zone 2. It is in this plane too that the flame front is established. In order to avoid a flashback of the flame into the interior of the inlet zone 1. the flame front must be kept stable and this is achieved by means of the jump 8 in cross section already mentioned. During operation, there forms within this jump 8 in cross section a marginal f low zone in which the reduced pressure prevailing in this zone gives rise to vortex separations which then lead to a stabilization of the flame front 9 or backflow zone.

t, Finallyr the hot gases 10 prepared in the combustion zone 2 act on a turbine (not shown) acting on the downstream side.

Fig. 2 shows a further combustion chamber designed for self-ignition, the jump 12 in cross section of which is kept symmetrical in the plane of the flame front 9. The radial extent of the jump 12 in cross section simultaneously produces the cross section of flow of the combustion zone 2. Within the expansion zone formed by the jump 12 in cross section there arise the vortex rings 13 shown symbolically in the figure,, these being directed in the counterclockwise direction and bringing about the stabilization described above of the flame front 9 for the reasons already explained. Compared with the jump in cross section on one side shown in Fig. 1, this configuration brings about a narrower arc formation of the flame front 9, which spans the entire cross section of the inlet zone 1.

Fig. 3 dif f ers f rom Fig. 2 in that the jump 14 in cross section is in the form of an annular trapezium, i.e. the expansion is subject to a constriction in the axial direction on one side of the combustion zone 2, i.e. a contraction of the cross section of f low. This contraction is introduced as a function of the flow parameters present. This is the case when, for example,- a relatively long reduced pressure zone is required to stabilize the flame front 9 or when, for example, the cross section of f low of the combustion zone 2 has to be reduced following the flame stabilization effect in order to increase the flow velocity. In general terms, the vortex rings 13 effect a jacketing of the flame front 9 and of the backflow zone and thus stabilize the combustion which takes place there.

obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise and as f (4 specifically described herein.

4

Claims

8 CLAIMS: 1. A combustion chamber with self ignition which essentially

comprises an inlet zone and a combustion zone, the two zones being arranged in succession and having the same direction of flow, wherein there is at the transition between the inlet zone and the combustion zone a jump in cross section which induces the cross section of flow of the combustion zone.

2. The combustion chamber as claimed in claim 1, wherein the jump in cross section is radially symmetrical.

3. The combustion chamber as claimed in claim 1, wherein the jump in cross section is radially symmetrical and has a contraction in cross section in the direction of flow of the combustion zone.

4. The combustion chamber as claimed in claim 1, 2 or 3 wherein the inlet zone has at least one fuel lance, wherein there are vortex-generating elements upstream of this fuel lance.

5. The combustion chamber as claimed in claim 4, wherein the vortexgenerating elements have a tetrahedral shape, wherein the elements are positioned in the circumferential direction of the inlet zone through which flow occurs, and wherein the elements narrow the cross section of the inlet zone in the direction of flow.

6. The combustion chamber as claimed in any preceding claim, wherein the combustion chamber has an annular form.

r t_ v 9 7. A combustion chamber substantially as herein described with reference to the accompanying drawings.

8. A gas turbine incorporating a combustion chamber as claimed in any of claims 1 to 7.