GB2076527A

GB2076527A - Cooker hoods

Info

Publication number: GB2076527A
Application number: GB8108585A
Authority: GB
Original assignee: WANSON CONSTR MAT THERM
Current assignee: WANSON CONSTR MAT THERM
Priority date: 1980-03-19
Filing date: 1981-03-19
Publication date: 1981-12-02
Also published as: GB2076527B; FR2478484A1

Abstract

Apparatus for the treatment of water vapour charged with air and with pollutant vapours and/or aerosols, which comprises a hood assembly 4 to collect the vapour to be treated from a fryer tank 1, a coalescing and dephlegmating filter 8 through which the vapour is first passed, a deflector 9 by which the separated-out liquid dropping from the filter 8 is caught and deflected into a basin which collects the separated-out oil and fat mixed with water, a compartment 12 for the condensation of the filtered vapour fitted with water sprayers 13, and an outer vessel 25b for collecting non-condensable vapour from the condenser 12. The non- condensible vapour is drawn up between cover 25b and condenser vessel 14a by an extraction fan 19 and is delivered into an exhaust duct 5 containing a gas burner 23. A flow valve 27 controlled by a thermostatic probe 20 controls the pressure inside the hood 4. The hot condensate is passed by a pump 16 through a recuperator 26 heated by the flue gas prior to utilisation. <IMAGE>

Description

SPECIFICATION Apparatus for the treatment of water vapour charged with air and with pollutant vapours and/or aerosols The invention relates to apparatus for the treatment of water vapour charged with air and with additional vapour and/or aerosol of at least one liquid pollutant, the boiling point of which may be higher than that of water.

The release of such vapour into the atmosphere often constitutes a nuisance to the environment but above all respresents a significant waste of energy.

Numerous attempts have been made to solve this problem. With the aim of reducing the polluting effect of these effluents, some attempts have envisaged burning them, but this involves prohibitive energy costs since the water vapour must be brought to the combustion temperature of the pollutants.

Another possibility would be to condense these vapours which would also permit recovery of their latent energy. The performance of such a condenser would however be very low, owing to the presence within the water vapour of air and effluents having a higher vapour pressure than water. Moreover, the condensate produced would be a very polluting fluid and would have no practical use.

The present invention aims to provide an apparatus for treating such vapours which will combine recovery of energy with the elimination of the environmental pollution.

The invention broadly comprises an apparatus for treating such polluted water vapour which includes a collector assembly for the water vapour to be treated, a coalescing and dephlegmating filter, a filtrate collecting basin, a chamber for the condensation of the filtered vapour, fitted with water sprayers, and a recuperator for noncondensable vapour.

Thus in one form the invention comprises apparatus for the treatment of water vapour mixed with air and with the additional vapour and/or aerosol of one or more liquid pollutants, which comprises in combination: A collector for the vapour mixture to be treated, the collector comprising a first hood provided with an outlet duct; a coalescing and dephlegmating filter placed above the outlet duct of the hood to separate out from the gaseous mixture discharged from the hood droplets and vapours of oil, fat and the like; an assembly for the recovery of oils and fats, comprising a deflector placed beneath the filter to catch and deflect the material separated out by the filter in the form of oil or fat and water, and a first collecting basin arranged to receive the deflected liquid from the deflector, the collecting basin having a first discharge means;; an assembly for the recovery of water vapour from the filtered gaseous mixture leaving the filter, comprising a condenser vessel defining a condensation chamber provided with internal water sprayers, through whose interior the gaseous mixture leaving the filter is passed, and a second collecting basin arranged to collect the condensate and sprayed water from the chamber and provided with a second discharge means for water; and an assembly for the collection of the noncondensible gaseous mixture discharged from the condenser vessel, comprising a cover vessel surrounding and spaced from the exterior of the condenser vessel to define therebetween a space into which the non-condensible gaseous mixture passes, the cover vessel having in its upper part a discharge opening which communicates via an extractor fan with an exhaust flue.

The coalescing and dephlegmating filter may be placed in the upper part of a filter compartment situated above the orifice of the outlet duct of the hood, the filter compartment having in its lower part and along the lower edge of its side wall an annular channel constituting the first collecting basin and provided with the first discharge means, and surmounted by the deflector the width of which is less than that of the filter compartment, the edge of the deflector being situated above the said annular channel. The discharge means of the annular channel preferably communicates with a separator for separating water from oil or fat.

In one construction, the condensation chamber receiving the water vapour which has passed through the filter is an annular chamber which is internally defined by the wall of the filter compartment, and externally by a dome concentric with the filter compartment, the lower edge of the dome ending some distance above the bottom of the second collecting basin which limits the condensation chamber at its base and which is provided with the second discharge means.

The water spraying nozzles of the condensation chamber may be arranged in this chamber around the exterior of the filter compartment and are supplied by a duct having a valve which is controlled in dependence on the output signal of a thermostat probe immersed in the liquid in the second collecting basin.

A gas flow valve may be disposed between the cover vessel and the extractor fan, the valve being controlled in dependence on the output signal of a thermostat probe placed in a conduit of slightly greater diameter than that of the probe, the conduit being open at both ends, one of these ends opening into the atmosphere and the other opening into the interior of the hood.

Furthermore, the apparatus may be provided with a burner assembly intended to render nonpolluting the non-condensable vapour discharged into the exhaust flue, the burner assembly being positioned in the exhaust flue upstream of the flue outlet into the atmosphere, and if desired with a heat recuperator for the exhaust flue. The heat recuperator may take the form of a tubular heat exchanger through which passes the water collected in the second collecting basin situated at the base of the condensation chamber.

The fryers used for cooking processes in the food industry constitute an ideal sphere for application of the invention which will enable the advantages of the invention to be more fully described.

Naturally this example is not meant to be restrictive and should not in any way limit the scope of the patent.

Thus whilst the invention may be carried into practice in various ways, one specific embodiment thereof will now be described by way of example only and with reference to the accompanying drawing, which is a diagrammatic side view in vertical section of a fryer provided with a vapour treatment apparatus embodying the invention.

In the illustrated embodiment, the fryer comprises a tank 1 filled with vegetable oil 2 kept at a temperature of approximately 1 800C by means of a heat exchanger 3 (oil/steam or oil/thermal fluid).

Experience has shown that 40 to 80% of the energy consumption of these fryers is lost through the exhaust flue, in the form of water vapour.

A hood 4 placed above the tank 1 collects the water vapour released during cooking of the food and releases these vapours through a discharge outlet 4a. The foodstuffs are continuously fed into the bath through inlet and outlet openings (respectively shown at 6 and 7) which prevent the hood from being totally sealed.

In order to avoid the escape of vapour into the atmosphere, a slightly negative pressure is maintained inside the hood. A certain quantity of air penetrates into the hood and mixes with the water vapour released during cooking. This introduction of unwanted air must be kept to a minimum so as to avoid rapid oxidation of the oil.

The intense boiling of the bath during cooking causes oil droplets and vapour to be taken up by the water vapour. In addition, the air drawn into the hood also becomes saturated with oil, thus forming a polluting and non-condensable effluent.

The invention provides additional apparatus to be placed above the hood 4 and intended to treat the effluent so as to make it innocuous to the environment.

This apparatus also permits recovery of the energy contained in the vapour in the form of usable hot water.

The additional apparatus is constructed in the following manner: The opening 4a at the top of the hood 4 allows the vapour from the tank 1 to enter into a filter chamber 8a at the upper end of which is a filter 8.

The vapour will then pass through the filter 8 which will have a coalescing and dephlegmating effect permitting the passage of water vapour but intercepting the droplets and oil and fat vapour. A deflector 9 shaped as a cupola is placed in the chamber 8a below the coalescing filter 8 so as to catch the separted-out material and deflect it into a collecting basin 10. The separated liquid material composed of oils and fats and a small proportion of water will then flow off the edge of the deflector 9 to drop into the annular collecting basin 10 mounted on the lower edge of the wall of the filter chamber 8a below the edge of the cupola 9, and will be passed to a gravity separator 11 where fats are evacuated via 11 (ter) and water via 1 1(bis).

The water vapour having lost its oil content is then passed from the filter 8 to a condenser 12 operating as follows: Water is sprayed downwardly through finelydispersing nozzles 13 into an annular condensing compartment 14 down through which the flow of vapour from the filter 8 also passes. The sprayed water will have a temperature in the range between 0 and 750C. This spraying will cause the condensation of the water vapour, thus causing heating of the sprayed water.

The condensing compartment 14 is formed within a domed condenser vessel 14a containing the filter 8 and filter chamber 8a. The condenser chamber 14 is formed between the side wall of the vessel 14a and the concentric wall 8b of the filter chamber 8a.

An annular collecting basin 1 5 located at the bottom of the condenser chamber 14, under the lower edge 14b of the wall of the condenser vessel 1 4a, will collect the hot water for recuperation consisting of the mixture of sprayed water and condensates.

This water having a maximum temperature of 9000 will be pumped by means of a pump 16 either to a utilisation system or to a water/water or water/air heat exchanger if the water recovered cannot be used as it is. A thermostat 17 placed in the annular basin 15 will keep the temperature of the water at a constant level by actuating the regulator 18 of a flow control valve 18a in the inlet duct for water for spraying.

The non-condensable effluents which have passed under the lower edge 14b of the condenser vessel 14 will be collected by a clocheshaped outer vessel 25b and sucked into an extractor fan 1 9 located at the top of the apparatus. The outer vessel 25b closely surrounds the domed condensing vessel 14a defining between them an annular-section space through which the non-condensable effluents are drawn by the fan 19 through the outlet 14c. A drop eliminator 25 is placed in the annular space between vessel 14a and vessel 25b, upstream of the outlet 1 4c and of the extractor fan inlet.

In order to limit as far as possible the quantity of air, and thus of non-condensable substances, introduced into the apparatus, a flow control valve 27 is placed in the fan inlet. Its setting is controlled by an air introduction detector under the hood 4 operating in the following manner: A thermostat probe 20 is mounted in a small openended tube 21 passing through the wall of the hood 4. If the latter is under slight negative pressure, a small flow of cold external air will penetrate into the hood 4 through the tube 21. If, on the other hand, the hood 4 is under slight positive pressure, a slight flow of hot vapour will escape through the tube 21 and will immediately be detected by the thermostat 20.A carefully selected setting of the thermostat 20 will permit the regulator 22 to maintain the hood 4 under a small negative pressure, thus limiting the air intake to a minimum, without the risk of polluting vapour escaping from the hood 4.

The discharge outlet of the extractor fan 1 9 is connected to an exhaust duct 5 which itself discharges into the atmosphere.

The small quantity of non-condensable substances passing through the extractor fan 19 will be rendered non-polluting by a gas burner 23 in the exhaust duct 5, which will bring the gas flow in the latter to a temperature above 70000.

The firing rate of this burner 23 will be regulated by a thermostat 24 placed in the gas exhaust duct 5.

For large-scale installations, a heat recuperator 26 may be placed in the exhaust duct 5. This recuperator 26 is a tubular heat-exchanger through which the water evacuated by the pump 16 is circulated in heat-exchange relationship with the heated flue gas in order to increase the temperature of the circulated water.

Claims

1. Apparatus for the treatment of water vapour mixed with air and with additional vapour and/or aerosol of one or more liquid pollutants, which comprise in combination: a collector for the vapour mixture to be treated, the collector comprising a hood provided with an outlet duct; a coalescing and dephlegmating filter placed above the outlet duct of the hood to separate out from the gaseous mixture discharged from the hood droplets and vapours of oil, fat and the like; a::n assembly for the recovery of oils and fats, comprising a deflector placed beneath the filter to catch and deflect the material separated out by the filter in the form of oil or fat and water, and a collecting basin arranged to receive the deflected liquid from the deflector, the collecting basin having a discharge means; an assembly for the recovery of water vapour from the filtered gaseous mixture leaving the filter, comprising a condenser vessel defining a condensation chamber provided with internal water sprayers, through whose interior the gaseous mixture leaving the filter is passed, and a second collecting basin arranged to collect the condensate and sprayed water from the chamber and provided with a water discharge means;; and an assembly for the collection of the noncondensible gaseous mixture discharged from the condenser vessel, comprising an outer vessel surrounding and spaced from the exterior of the condenser vessel to define therebetween a space into which the non-condensible gaseous mixture passes, the outer vessel having in its upper part a discharge opening which communicates via an extractor fan with an exhaust flue.

2. Apparatus according to Claim 1, in which the coalescing and dephlegmating filter is placed in the upper part of a filter compartment situated above the orifice of the outlet duct of the hood, the filter compartment having along the lower edge of its side wall an annular channel constituting the first collecting basin and provided with the first discharge means, and surmounted by the deflector the width of which is less than that of the filter compartment, the edge of the deflector being situated above the said annular channel.

3. Apparatus according to Claim 2, in which the discharge means of the said annular channel communicates with a separator for separating water from oil or fat.

4. Apparatus according to any one of Claims 1 to 3, in which the condensation chamber receiving the water vapour which has passed through the filter is an annular chamber which is internally defined by the wall of the filter compartment, and externally by a dome concentric with the filter compartment, the lower edge of the dome ending some distance above the bottom of the second collecting basin which limits the condensation chamber at its base and which is provided with the second discharge means.

5. Apparatus according to Claim 4, in which the water spray nozzles of the condensation chamber are arranged in this chamber around the exterior of the filter compartment and are supplied by a duct having a valve which is controlled in dependence on the output signal of a thermostat probe immersed in the liquid in the second collecting basin.

6. Apparatus according to Claim 5, in which a gas flow valve is disposed between the cover vessel and the extractor fan, the valve being controlled in dependence on the output signal of a thermostat probe placed in a conduit of slightly greater diameter than that of the probe, the conduit being open at both ends, one of these ends opening into the atmosphere and the other opening into the interior of the hood.

7. Apparatus according to any one of Claims 1 to 6, which includes a burner assembly intended to render non-polluting the non-condensable vapour discharged into the exhaust flue, the burner assembly being positioned in the exhaust flue upstream of the flue outlet into the atmosphere.

8. Apparatus according to any one of Claims 1 to 7, in which the exhaust flue is provided with a heat recuperator.

9. Apparatus according to Claim 8, in which the heat recuperator comprises a tubular heat exchanger through which passes the water collected in the second collecting basin situated at the base of the condensation chamber.

10. Apparatus for the treatment of a polluted water vapour and air mixture, substantially as specifically described herein with reference to the accompanying drawing.