US2900930A

US2900930A - Combustion system for an intensified burning of solid, liquid or gaseous fuels in an annular combustion space

Info

Publication number: US2900930A
Application number: US675838A
Authority: US
Inventors: Cermak Josef
Original assignee: Individual
Current assignee: Individual
Priority date: 1956-08-11
Filing date: 1957-08-02
Publication date: 1959-08-25
Anticipated expiration: 1976-08-25

Description

1959 .1. CERMAK COMBUSTION SYSTEM FOR AN INTENSIFIED BURNING OF SOLID, LIQUID OR GASEOUS FUELS IN AN ANNULAR COMBUSTION SPACE Filed Aug. 2, 1957 INVENTOR JOSEF CEIPMAK United States Patent- COMBUSTION SYSTEM FOR AN INTENSIFIED BURNING 07F SOLID, LIQUID R GASEOUS FUELS IN AN ANNULAR COMBUSTION SPACE Josef Cermak, Prague, Czechoslovakia Application August 2, 1957, Serial No. 67 5,838

Claims priority, application Czechoslovakia August 11, 1956 Claims. (31. 110-28) The present invention relates to a combustion apparatus for achieving intensified combustion of solid, liquid or gaseous fuel-s in an annular combustion space.

By the term intensified combustion a high intensity of combustion is understood, which-expressed in calories released in 1 m of the volume of the combustion space per hour-exceeds 1.10 kcal./m.. /hour.

Devices for achieving the intensified combustion of solid fuels have already been proposed, wherein the burning content of the furnace effects a whirling (turbulent) motion. Such devices operate as a rule as slagging devices, i.e. the mineral residue of the fuel flows out of the combustion space in the form of a liquid slag.

Typical of a great number of such known devices are combustion chambers of the 'socalled cyclone or whirling type. Their common feature is a cylindrical combustion space, either vertical or horizontal, supplied with fuel and combustion air, either at one point at the circumference and approximately in tangential direction or through the end Wall so as to cause the burning contents flowing through the combustion space to assume a helical movement.

The products of combustion leave the furnace either through an upper or lower central aperture or through an aperture in the wall of the cylindrical jacket. The ratio of the height or length of the cylindrical combustion space to its diameter varies within the range of about ,113, up to about 5:1.

In those cases Where the fuel and combustion air are supplied at the circumference of the cylindrical space in the combustion chamber, this is effected practically at one point of the circumference, more particularly through a relatively narrow slot at the circumference of the cylinder. This causes the disadvantageous irregular flow and burning out of the fuel in such combustion chambers.

When fuel is supplied at one point of the circumference, the concentration of the oxidising agent is different at all points along the circumference of the cylindrical chamber, and is highly dependent on the momentary volatile contents of the fuel, on the specific surface of same (i.e. on the surface corresponding to a unit weight of the fuel) and in particular on the thermic history of the fuel grains (i.e. temperature as a function of the time) during their passage through the combustion space.

It has also been found that, in the above described existing combustion chambers, the burning contents of the furnace flow through the combustion space irregularly. The explanation for this phenomenon lies in the fact that for a part of the time these burning contents flow through the combustion space in the regular way until suddenly a shortcut takes place, that is, the fuel and air proceed along the shortest way between the inlet to the combustion space and the outlet therefrom. This shortcutting causes the escape of unbnrnt combustible gases and increased escape of mineral combustion residue.

Owing to this fact a combustion chamber of the described known type cannot be fully thermally loaded ice Le. a specific thermal intensity of about 5.10 kcaL/mfi/ hour cannot be exceeded.

In some combustion devices of the cyclone type, the above drawback is obviated by a careful distribution and control of the amount of the secondary air supplied to the individual parts of the cyclone combustion space. Considering the varying quality of the fuel this solution is disadvantageous in operation with respect to the changing amount of the air required, and is therefore undesirable.

Careful measurements have also shown that, in the vicinity of the central aperture in the central part of the cylindrical space, the contents of the same rotate as a wheel so that the circumferential velocity is directly proportional to the distance from the center of rotation. On the other hand adjacent to the outer circumference of the cylindrical space the movement is such, that the circumferential velocity is dependent on the radius in accordance with the hyperbolic 'law (principle of Whirl conservation). The intense whirling which is indispensable for an intensification of the combustion process occurs merely between the two above mentioned spaces i.e. in a relatively small volume.

All these facts and experiences have recently led to the search for another aerodynamically more favourable shape of the combustion chamber. Thus, for example, for small power generating units, in particular for mobile units, a system for burning solid fuel in a helical con1- bustion space with a cooled metal wall has been developed. This system is free from from the above mentioned drawbacks and allows therefore the construction of small devices having a high combustion intensity and high efiiciency. In the further development of the cotmbustion technique, in particular for large stationary power generating units, the use of combustion chambers in annular form has been considered, the latter offering a further possibility for increasing the efiiciency of the space combustion.

The present invention utilises the last mentioned possibilities for an intensified burning of solid, liquid or gaseous fuels in a combustion space which is generally toroidal or annular shape, being either circular in any radial cross section (a so called tours) or having any other suitable radial cross section.

The main object of the present invention is to provide a combustion apparatus having a toroidal or annular combustion space arranged to ensure favourable conditions for mixing and burning fuel and the separation of mineral residue so as to practically eliminate, or substantially reduce, the above mentioned drawbacks of the known combustion chambers.

The combustion chamber according to the present invention is characterised by the following three basic features:

(a) A central supply of fuel by means of fuel nozzles, which are arranged at the inner circumference of the toroidal or annular combustion space and open into this space in suitably chosen directions.

(b) The provision of a distribution head having the fuel admitted tangentially therein and arranged above the center of the toroidal or annular combustion space, said distribution head being connected with the fuel nozzles by means of tubes or flow channels and these fuel nozzles being arranged so as to make a sharp angle With the direction of rotation of the fuel stream.

(c) Arranged around the outer circumference of the toroidal or annular combustion space is a distribution space for the combustion supporting medium with one or more inlets and with a plurality of outlets opening approximately in tangential direction into the combustion space.

The combustion system according to the present invention shows a number of other particular features which will be apparent from the ensuing description.

The accompanying drawing shows in a simplified diagrammatic representation a combustion apparatus which is an illustrative embodiment of'the invention.

Fig. 1 is a vertical section taken along the plane II of Fig. 2; and

Fig. 2 a horizontal section taken along the plane II-II of Fig. 1.

The illustrated combustion apparatus has a combustion space 7 in the shape of a torus for burning solid fuel mixed with air and which is defined by an annular shell having its axis arranged vertically with a C-shaped cross section opening radially inward toward the vertical axis.

The apparatus further comprises the following main parts:

A distribution head 2, a system of tubes 4 terminating in fuel nozzles 6 opening into the combustion space 7, and a combustion air distribution space 9.

Fuel carried by a minimum amount of primary air enters through a tangential inlet 1 into the distribution head 2 which is preferably centrally arranged above the combustion space. The rotating stream of fuel and primary air is distributed by a cone 3 to the inlet portions of the tubes 4, which feed the fuel nozzles 6. The tubes 4 are inclined with respect to the central axis in the direction of rotation of the stream so as to exert the least possible hydraulic resistance to the latter and so as to have the maximum possible static pressure before the fuel nozzles 6. The tubes 4 may be provided with transparent parts 5 (e.g. of glass) through which the flow of fuel in the individual tubes may be observed.

The fuel nozzles 6 are arranged at the inner circumference of the toroidal or annular combustion space 7, preferably directly above the outlet 14 for the hot combustion products, so that the entering fuel mixture is heated up by the hot combustion products to a high temperature, just before the entry of the fuel mixture into the combustion space.

The fuel preferably issues from the fuel nozzles 6 into the combustion space 7 in the direction indicated by the arrow 8 shown both in Fig. l (in a vertical plane) and in Fig. 2 (in a horizontal plane). It is apparent, that this is an upwards slanting direction and at the same time also approximately tangential to the direction of rotation of the contents of combustion space.

The secondary combustion air is introduced in the example shown through an inlet 11 into the distribution space 9 and from the latter through the outlets 10 which open approximately in tangential direction 13 into the combustion space 7.

The hot exhaust gases leave the combustion space in the direction of the arrows 12 towards the outlet, through which the slag is also discharged. Arranged in front of the outlet for the exhaust gases is an annular dam 15, which ensures that a certain amount of liquid slag always remains in the combustion space.

Due to favourable conditions of outlay and operating conditions a highly eflicient and uniform combustion process is obtained in all parts of the apparatus. Such a combustion process cannot be achieved in the known cylindrical combustion spaces.

Prior to its entry into the combustion space 7 fuel is heated up to a high temperature at which it begins to gasify. The fuel is fed to the combustion space so as to assist to the highest possible degree the rotational movement of the contents of the combustion space. At the same time each particle of the fuel is forced to follow a relatively long path and a shortcut, as in cylindrical combustion chambers, cannot here occur. A premature impact of the ignited fuel particles against the wall of the heating surface and the difficulties caused thereby are thus also eliminated.

Under the influence of the rotational movement of the contents of the combustion space, the largest particles fly along a curved path 8 up to the contact with the wall, as shown in Fig. 2; this results in an extension of their paths and of the time during which they remain in the combustion space.

An intense sorting of the fuel particles according to the size of particles takes place simultaneously. The smallest grains are held up first in the rotating stream, and are ignited and burn out immediately in the zone 1. Larger particles fly along a longer path and are later ignited and burnt, in the zone II. The largest particles pass through the entire space and strike against the outer wall along which they continue their movement in zone III. These largest particles are ignited last and also burn out last. However, since the largest particles remain in the combustion space much longer than the average time during which the gaseous content of the combustion space remains in the latter, such large particles have ample time to burn out completely.

As a result of this size distribution of the particles in introduced fuel stream and further due to the fact that the fresh fuel is. introduced along the entire inner circumference of the combustion space substantially in a uniform way (through a relatively high number of fuel nozzles 6) a perfect utilisation of the entire volume of the combustion space for an intense combustion is achieved. The combustion space of toroidal or annular form, which, in the example described above, is in the shape of a torus, may therefore be thermally loaded to a far higher degree than any other combustion space.

The quick rotary movement of the contents of the combustion space, which is far quicker than in a cyclone type furnace, is made possible by admitting the secondary combustion air, which forms the major proportion of combustion air, into the combustion space at its outer circumference and in a uniform. manner. The uniform admission of this air in substantially tangential direction ensures a high speed of rotation of the contents of the furnace which results in a centrifugal force as well as the separation of coarser fuel grains and their longer stay in the furnace. By this advantageous method of admission of fuel and combustion air it is possible not only to ensure the ignition and burning out of the fuel at the right time, but also to achieve a high specific thermal loading of the furnace and a high efficiencythereof, as a result of which the device is relatively small and of light weight.

A highly favourable influence on the combustion is exerted by the fact, that the larger and largest fuel grains fly in a quick sequence through the streams of the oxidising agent supplied at the outer circumference of the combustion space. This advantage is not achieved in other intensified rotational furnaces.

As shown by the arrow 8 in Fig. l the fuel leaving the nozzles 6 is partially projected upwards against the ceiling of the combustion space. This ensures. permanent supplying of the top portion of the combustion space wall with fresh slag and the maintenance of a deposit thereof in a sufficient thickness.

The dam 15 serves to maintain a layer of slag in front of the outlet 14, said slag retaining the mineral residue from the combustion, separated by centrifugal action.

The above described example does not, of course, exhaust the possibilities of various arrangements of the combustion system within the framework of the present invention. Thus, for example, either all or part of the highly preheated secondary air (combustion air) may be fed to the distribution head 2 so as to cause a partial degasification of the fuel prior to its entry into the combustion space. Further, obvious structural arrangements may be employed in the combustion apparatus according to the invention in order to adapt such apparatus for intensified combustion of liquid or gaseous fuels' I claim:

1. A combustion apparatus comprising an annular shell arranged with its axis extending substantially vertically and having a generally C-shaped cross section opening radially inward toward said axis and defining a combustion space, said shell having an opening at the center of the bottom thereof for the downward discharge there through of products of combustion from said combustion space, means for supplying a mixture of primary air and fuel to said combustion space including a series of inlet nozzles arranged approximately in a circle adjacent said vertical axis of the annular shell and opening into the latter in directions that slant upwardly and are approximately tangential to said circle in which the nozzles are arranged, and means for supplying secondary air to said combustion space including a. series of inlet orifices distributed along the outer periphery of said annular shell and opening into said combustion space.

2. A combustion apparatus as in claim 1, wherein said inlet orifices for supplying secondary air to said combustion space open into the latter in directions that are approximately tangential to said outer periphery of the annular shell in the same directions as said inlet nozzles for supplying the mixture of primary air and fuel into the combustion space, so that the mixture of primary air and fuel and the secondary air are introduced tangentially into said combustion space at the inner and outer peripheries of said shell in the direction of rotation of the contents of said combustion space.

3. A combustion apparatus as in claim 2; wherein said means for supplying the mixture of primary air and fuel to said combustion space further includes tubes extending to said inlet nozzles through the central portion of said annular shell so that the mixture of primary air and fuel flowing through said tubes to said inlet nozzles is heated by the burning contents of said combustion space.

4. A combustion apparatus as in claim 3 wherein said tubes have portions extending close to said central opening in the bottom' of said annular shell.

5. A combustion apparatus as in claim 4; wherein the bottom of said annular shell curves upwardly toward said central opening to define a dam around the latter for retaining a quantity of slag at the bottom of the combustion space.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain Feb. 9, 1955