GB2169697A - Cooker hoods - Google Patents

Abstract

An extractor for destroying kitchen fumes 3 comprises a hood 1 for location above a source 2 of rising fumes, an impeller 10 for extracting air and fumes from the hood and delivering them to a catalytic combustor 12, a heater 11 for heating the air and fumes before entry into the combustor and a flow divider 14 for dividing the hot flow of air from the combustor into a portion which is vented to atmosphere via a pipe 16 and a portion which is returned to the hood and caused to flow transversely of the rising fumes. The transverse flow of hot air entrains the fumes which are drawn into the chamber 6 through openings 8. The heated air returned to the hood heats the chamber 4 sufficiently to reduce deposition of grease on the hood. <IMAGE>

Description

SPECIFICATION Fume-destroying extractor for kitchen fumes This invention relates to a fume-destroying extractor for kitchen fumes rising from for example hot oil or fat and to a hood for use in the extractor, It also relates to a method for extracting and destroying kitchen fumes.

Fumes rising from hot oil or fat have an unpleasant smell and their discharge to atmosphere creates a nuisance. This nuisance impedes the siting of so-called "fast-food" establishments in confined spaces such as are met in the centres of large towns and cities.

An efficient method of destroying the fumes would therefore allow such establishments to avail themselves of a wider range of sites.

Fumes rising from hot oil or fat can be easily removed by entraining them in a flow of air which is then extracted using a hood combined with an impellor. However the concentration of fumes in the air flow is too low for the fumes to be destroyed economically by combustion.

It is an object of this invention to provide an extractor in which fumes are destroyed by combustion.

Accordingly this invention provides a fumedestroying extractor for kitchen fumes which comprises a) a hood having an outlet and being suitable for location above a source of rising fumes, b) an impeller suitable for causing a stream of air and fumes to flow from the outlet of the hood, c) a heater suitable for heating the stream of air to a temperature of at least 200"C (and preferably at least 300"C), d) a catalytic combustor through which the stream of air can pass after it has been heated by the heater and e) a flow divider suitable for dividing the stream of heated air from the catalytic combustor into a first stream for venting to atmosphere and a second stream for returning to the hood wherein the hood is provided with means for receiving the second stream and causing it to flow transversely (preferably horizontally) of the rising fumes whilst exposing the second stream to the fumes and means for guiding the second stream and the fumes to the outlet of the hood. It has been found that the use of a transverse flow of hot air permits efficient extraction of the fumes and their efficient combustion in the catalytic combustor.

This invention also provides a hood having an outlet and being suitable for location above a source of rising fumes wherein the hood is provided with means for receiving a stream of heated air and for causing the stream to flow transversely (preferably horizontally) of the rising fumes and means for guiding the stream and fumes to the outlet.

A preferred means for imparting the transverse flow to the stream of heated air comprises a combination of a peripheral chamber (which preferably defines the outer perimeter of the hood) having at least one inwardly facing opening and a central chamber having at least one outwardly facing opening spaced from and at least approximately opposed to the opening in the peripheral chamber whereby the stream of air after entering one of the chambers is caused to flow out of the opening in that chamber and flows transversely of and is exposed to the rising fumes and is then sucked into the opening in the other chamber by the action of the impeller. It has been found that extraction is more efficient if the heated stream is received by the peripheral chamber and if it is the central chamber which communicates with the outlet of the hood.

The impeller is preferably located between the outlet of the hood and the heater. The impeller may be for example any conventional extractor fan of the type used in kitchen fume extractors. The heater is preferably a gas burner but other heaters using external energy sources may be used instead.

The catalytic combustor preferably comprises a catalyst containing at least one of the metals platinum, rhodium, palladium or ruthenium deposited on activated alumina (preferably ,-alumina) which in turn is supported on a channelled support (often called a honeycomb support) made from metal or ceramics material. Typical catalyst systems comprising ceramic channelled supports are described in GB 1330841 and typical metallic channelled supports are described in GB 1492929.

The flow divider is preferably adjustable so that it is possible to divert from 20 to 40% by volume of the stream from the catalytic combustor into the first stream which is the stream which is vented to atmosphere. This means that from 60 to 80% of the stream from the combustor is returned to the hood.

The air which is vented to atmosphere is replaced by air drawn in from around the source of the fumes. This flow of air from around the source helps to guide the fumes into the hood.

It is preferred that the impeller should generate an air flow having a speed of from 20 to 80 m/min and that the transverse flow of the heated stream should be located 250 to 1000 mm above the source of the fumes, for example above the level of the heated oil or fat. It is also preferred that the temperature of the heated air stream entering the hood should be from 300 to 400"C and that the temperature of the air leaving the hood should be from 150 to 250"C. Accordingly it is preferred that the heater should heat the air stream to from 270 to 370"C.

This invention also provides a method for extracting and destroying kitchen fumes which comprises a) causing a stream of air and fumes to flow from an outlet in a hood located over a source of rising fumes, b) heating the stream to at least 200"C and passing it through a catalytic combustor, c) venting part of the stream from the catalytic combustor to atmosphere and returning part to the hood, d) causing the heated stream which has been returned to the hood to flow transversely (preferably horizontally) of the rising fumes and to become exposed to the rising fumes and e) guiding the heated stream and fumes to the outlet in the hood.

The invention is further illustrated by the following preferred embodiment which is described with reference to the drawings of which Figure 1 is a flow diagram showing the relative positioning of features of this invention and Figure 2 is a section through a hood according to this invention.

Figure 1 shows a hood 1 located above a broiler-pan 2 filled with food cooking in hot fat (not shown) from which fumes 3 rise.

As can be seen from figure 2, hood 1 comprises a peripheral chamber 4 which defines the external periphery 5 of hood 1 and a cen tral chamber 6 depending from an upper portion of hood 1. Chamber 4 is provided with a peripherally extending opening 7 which faces horizontally inwards of hood 1 and is spaced from and opposed to a peripheral opening 8 provided in central chamber 6 and which faces horizontally outwards of hood 1.

An outlet 9 is provided in hood 1 at the top of central chamber 6. Outlet 9 communicates via impeller fan 10 with gas heater 11 and a catalytic combustor 12 comprising catalyst supported on channels 13. Operation of fan 10 draws a stream of air and fumes from outlet 9 into heater 11 where the stream can be heated to 350"C before passing through channels 13 in catalytic combustor 12 where catalytic combustion of the heated fumes occurs. The heated stream emerging from channels 13 is divided into first and second streams by a flow divider 14 comprising an adjustable valve 15. The valve is adjusted so that the first stream comprises about 25% of the volume of gas emerging from channels 13 and is vented to atmosphere along pipe 16.

The second stream is returned to peripheral chamber 4 which it heats to a temperature of from 300 to 350"C. The second stream leaves peripheral chamber 4 through opening 7 and is drawn into opening 8 in central chamber 6 by the action of fan 10. Accord ingly openings 7 and 8 co-operate to produce a horizontal stream of heated air which contacts and flows transversely of the rising fumes 3. Fumes 3 are entrained in the stream and are guided by central chamber 6 into outlet 9 from where the action of fan 10 causes them to be delivered to the catalytic combustor 12 as described above. A quantity of air from the surroundings to pan 2 is also drawn into opening 8 and the flow of this air (indicated by arrows 17) helps to guide the fumes 3 towards opening 8 in central chamber 6.

It has also been found that the second stream heats peripheral chamber 4 sufficiently to reduce if not eliminate the deposition of grease on hood 1.

This invention is further illustrated by the following Example.

EXAMPLE An extractor system as described with reference to Figures 1 and 2 was used to extract and destroy fumes rising from a broiler cooking burgers in fat. The fat was contained in a rectangular broiler pan in the top of which was an opening approximately 0.78 m long by 0.64 m wide. The hood was located about 45 cm above the surface of the broiler and the base of the hood as defined by the bottom edge of its peripheral chamber was approximately 1 m square. The impeller fan was operated so as to extract air and fumes from the outlet to the hood at a speed of 45 m/min.

The burner was adjusted so as to heat the stream to 350"C and the flow divider was set to divert from 25 to 30% by volume of the stream into the pipe from which it was vented to atmosphere. Sufficient of the fumes were destroyed in the catalytic combustor to prevent the vented stream from smelling of fat.

The catalytic combuster comprised platinum metal deposited on a w-alumina coating supported by a ceramic channelled support. It was found that the heated stream of air which was returned to the hood had a temperature of about 350"C on entering the peripheral chamber of the hood and a temperature of about 200"C on leaving the hood.

Claims (10)

1. A fume-destroying extractor for kitchen fumes (3) which comprises a) a hood (1) having an outlet (9) and being suitable for location above a source (2) of rising fumes (3), b) an impeller (10) suitable for causing a stream of air and fumes (3) to flow from the outlet (9) of the hood, c) a heater (11) suitable for heating the stream of air to a temperature of at least 200"C, d) a catalytic combustor (12) through which the stream of air can pass after it has been heated by the heater (11) and e) a flow divider (14) suitable for dividing the stream of heated air from the catalytic combustor (13) into a first stream for venting to atmosphere and a second stream for returning to the hood (1) wherein the hood (1) is provided with means (4and 7) for receiving the second stream and causing it to flow transversely of the rising fumes (3) whilst exposing the second stream to the fumes (3) and means (6) for guiding the second stream and the fumes to the outlet (9) of the hood.

2. An extractor according to claim 1 wherein the means for causing the second stream to flow transversely of the rising fumes (3) comprises a combination of a peripheral chamber having at least one inwardly facing opening (7) and a central chamber (6) having at least one outwardly facing opening (8) spaced from and at least approximately opposed to the opening (7) in the peripheral chamber (4) whereby the second stream of air after entering one of the chambers (4 or 6) flows out of the opening in that chamber and flows transversely of and is exposed to the rising fumes (3) and is then sucked into the opening in the other chamber (6 or 4) by the action of the impeller (10).

3. An extractor according to claim 2 wherein the second stream of air enters the peripheral chamber (4) and flows from the opening (7) in the peripheral chamber (4) to the opening (8) in the central chamber (6).

4. An extractor according to claim 3 wherein the impeller (10) is located between the outlet (9) from the hood (1) and the heater (11).

5. An extractor according to any one of the preceding claims wherein the flow divider (14) is adjustable so that it is possible to divert from 20 to 40% by volume of the stream from the catalytic combustor into the first stream.

6. A hood (1) having an outlet (9) and being suitable for location above a source (2) of rising fumes wherein the hood 1 is provided with means (4 or 6) for receiving a stream of heated air and for causing the stream to flow transversely of the rising fumes and means for guiding the stream and fumes to the outlet (9).

7. A hood (1) according to claim 6 wherein the means for causing the stream to flow transversely of the rising fumes comprises a combination of a peripheral chamber (4) having at least one inwardly facing opening (7) and a central chamber (6) having at least one outwardly facing opening (8) spaced from and at least approximately opposed to the opening (7) in the peripheral chamber (4).

8. A method for extracting and destroying kitchen fumes which comprises a) causing a stream of air and fumes to flow from an outlet (9) in a hood (1) located over a source (2) of rising fumes (3), b) heating the stream to at least 200"C and passing it through a catalytic combustor (12), c) venting part of the stream from the catalytic combustor (12) to atmosphere and returning part to the hood (1), d) causing the heated stream which has been returned to the hood (1) to flow transversely of the rising fumes (3) and to become exposed to the rising fumes fumes (3) and e) guiding the heated stream and fumes to the outlet (9) in the hood (1).

9. A method according to claim 8 wherein the temperature of the heated stream on entering the hood is from 300 to 400"C.

10. A method according to claim 8 or claim 9 wherein from 20 to 40% by volume of the steam from the catalytic combustor (12) is vented to atmosphere.