GB2318970A - Smoke producing oven - Google Patents

Abstract

A smoke producing installation, for example for producing smoke for food treatment, comprises a hearth (5) and a vertical pot (6) located above and spaced slightly from the hearth. A stoker (3) automatically maintains fuel, for example peat, to a predetermined level within the pot. Air is drawn upwardly through the pot by a fan (16) which blows the resultant smoke into a mixing box (20). In the mixing box additional air is added to the smoke if required. Smoke from the box (20) is delivered via an outlet (23) for use or via a vent (25) if found to be of an unacceptable quality. The system operates under program control to maintain optimum smoke output by varying the fan speed (16) and, if necessary, by operating a pusher (8) to remove part of the fire from the hearth (5).

Description

SMOKE PRODUCING OVEN This invention relates to a smoke producing oven, that is to say an oven the prime objective of which is to produce smoke. Smoke is required in a variety of industrial processes, particularly in the treatment of food products and in the treatment of raw materials used in the production of certain alcoholic beverages, for example malt whiskey. Smoke for this purpose is produced in a so called "smoke producing oven".

Traditional smoke producing ovens have consisted of little more than an enclosure having an open hearth on which a fire of suitable material, e.g. peat is built. The peat burns slowly and produces copious quantities of smoke which is directed via a flue to the area where the smoke is required. Such ovens require constant attention to ensure that the fire remains adequately covered with peat and that no flames break through the surface of the peat. The break through of flames is a potential fire hazard to the installation, reduces the amount of smoke produced, and is liable to alter the chemical constitution of the smoke tha is produced to the extent that it may not be acceptable for the purposes intended.

Attempts have been made to mechanise the operation o smoke producing ovens, for example by providing mechanical feed for the incoming peat and mechanical ash disposal.

However, there has been no successful automation of the operation of smoke producing ovens.

A further disadvantage of known smoke producing ovens is that a relatively large installation, burning a large quantity of peat is required to produce a given quantity of smoke The present invention provides, in its preferred embodiment, a smoke producing oven which can be operated largely automatically under program control and which produces, from a relatively small installation, a large volume of smoke from a relatively small amount of fuel.

According to one aspect of the present invention there is provided a smoke producing oven comprising a hearth; a tubular pot extending vertically from a point spaced slightly above the hearth; a smoke outlet from an upper part of the pot; means for maintaining the pot filled to a predetermined level with material to be burnt; means for removing burning material from the hearth beneath the pot; and means for inducing a draught to flow upwardly through the pot to promote combustion of material on the hearth and in the lower portion of the pot.

The oven of the preferred invention is well suited to automated stoking using an appropriate stoker mechanism, and to automated ash removal by means of a suitable ash removal system. Further, by the use of appropriate temperature and/or optical sensors the combustion process on the hearth and in the lower portion of the pot may be controlled to produce optimum quantities of smoke at an optimum temperature.

At its simplest, the oven may be controlled by sensing the temperature of smoke leaving the smoke outlet. If the smoke temperature rises too high the draught inducing means may be controlled to reduce the through flow of air and thereby reduce the intensity of the fire and with it the smoke temperature. If this expedient is found to be insufficient to reduce the smoke temperature the means for removing burning material from the hearth may be operated to remove part or all of the fire from the hearth and allow the entire contents of the pot to drop. Additional fuel will automatically be added to the top of the pot by the stoker. The reduced fire size, coupled with the cooling effect of the newly added fuel (which typically may be somewhat wet) will have the effect of reducing the temperature. If the resultant temperature reduction of the smoke is too large, the draught may be increased to promote the fire on the hearth and in the lower portion of the pot.

Preferably, the oven forms part of a smoke producing installation which comprises, in addition to the oven, a smoke mixing box, and a diverter valve which permits smoke exiting the mixing box to be vented if system sensors determine that the smoke is unsatisfactory for its intended purpose. By this means, the application of unacceptable smoke to the product being treated can be avoided. This is an important improvement since, in the prior art, a product treated with smoke of an unacceptable quality could be permanently damaged and, under certain circumstances, could not subsequently be used.

The invention will be better understood from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying drawing wherein the single Figure illustrates schematically a preferred embodiment of the invention.

Referring to the drawing, there is illustrated a smoke producing installation 1 comprising a smoke producing oven 2, a stoker mechanism 3 and a smoke mixing and control assembly 4.

The smoke producing oven 2 comprising a fixed hearth 5 and a vertical tubular pot 6 located above the hearth.

The bottom of the pot is spaced from the hearth by a relatively small amount, for example typically 50mm.

Typically, the pot may be between 200mm and 400mm in diameter depending on the nature of the fuel to be used and the service demands for smoke. As illustrated, the pot 6 is provided with a cooling water jacket 7. A pusher 8, which may be operated by a hydraulic ram, is provided for pushing the lower part of fire on the hearth sideways onto a discharge ramp 9 from whence the burning and spent material will fall into a trough 10 for removal by an auger 11.

The stoker 3 receives bulk fuel, typically peat, from a hopper 12 and feeds the material along a feed tube 13 to maintain the pot 6 filled to a predetermined level 14. The level 14 is maintained by a sensor 15 which controls operation of the stoker 3.

A fan 16 draws smoke through an outlet pipe 17 of the oven. Because the feed tube 13 is filled with fuel little or no air can be drawn along it and according the fan 16 draws air upwardly through the pot 6, the air entering the system via the lower end of the pot 6.

In use, a fire 18 is established on the hearth 5 and in the lower portion of the pot 6. This fire is stimulated by the flow of air drawn by the fan 16 and produces significant heat and smoke. The heat travelling upwardly through the fuel in the upper portion of the pot 6 liberates further smoke from the fuel.

Smoke from the fan 16 is blown along a duct 19 into a mixing box 20. If desired, air from a suitable fan is blown into the mixing box through a duct 21 to be mixed with the smoke from the oven. The resultant mixture flows out of the mixing box 20 via an exit 22, and if of an acceptable quality flows onwardly through a duct 23 for use. If, however, system sensors indicate that the smoke is not of acceptable quantity, or if no smoke is required for use at any particular moment, a flap valve 2t may be operated to close the outlet 23 and divert the flow to a vent passage 25. Preferably, movement of the flap 24 to close the passage 23 occurs automatically if the smoke produced fails to meet required criteria which may be sensed automatically as the smoke leaves the box 20 via the exit 22.

The typical fuel for use in the installation is peat.

Peat, being a natural product, has variable characteristics and, in particular, the grain size, density and moisture content may vary significantly. Accordingly, if the oven was operated without appropriate controls unsatisfactory operating conditions could arise. For example, if a very light fuel of low water content was supplied the fire in the pot 6 could be so intense that an unacceptably high temperature would be produced in the outlet 17.

Alternatively, if the fuel was of high density and wet and unacceptably low volume of smoke could be produced.

Accordingly, the system preferably includes a number of sensors for determining, particularly, temperature at various points in the installation and is operated under automatic program control in light of the output of the various sensors. In particular, it is highly preferably that the temperature of the smoke in the outlet 17 is sensed and that the rate of air flow induced by the fan 16 and/or the operation of the pusher 8 is controlled in light of the sensed temperature. Essentially, the plant will operate under optimum conditions when the maximum volume of air is drawn by the fan 16 consistent with the outlet temperature from the pot remaining below a predetermined maximum. If the temperature at the outlet rises above the predetermined maximum the fan 16 is preferably controlled to reduce the air flow and thereby reduce the rate of combustion within the pot 6. This may in itself produce a sufficient reduction in temperature, in which case the fan speed may be increased automatically. The system will stabilise at the maximum acceptable flow rate consistent with the required maximum temperature.

There may, however, be instances in which reducing the air flow rate is insufficient to produce the required temperature drop and under these circumstances preferably the pusher 8 is operated to push the lower portion of the fire from the hearth 5 onto the ramp 9. When the pusher 8 is retracted after pushing the lower part of the fire onto the ramp 9 the entire contents of the pot 6 will drop and fresh material will be added to the top of the pot by the stoker under the control of the level sensor 15. The effect of this operation will be to reduce the fire size and add fresh material to the top of the pot. This operation will reduce the smoke temperature. If, subsequently, the smoke temperature is found to be too low, the speed of the fan 16 may again be increased to produce a brighter fire and a larger volume of smoke.

Claims (6)

CLAIMS:

1. A smoke producing oven comprising: a hearth; a tubular pot extending vertically from a point spaced slightly above the hearth; a smoke outlet from an upper part of the pot; means for maintaining the pot filled to a predetermined level with material to be burnt; means for removing burning material from the hearth beneath the pot; and means for inducing a draught to flow upwardly through the pot to promote combustion of material on the hearth and in the lower portion of the pot.

2. The oven of claim 1 comprising: means for sensing the temperature of smoke leaving the smoke outlet; and means for reducing the intensity of the fire in response to the temperature exceeding a predetermined value.

3. The oven of claim 2 wherein the means for reducing the intensity of the fire comprises means for reducing the draught.

4. The oven of claim 2 or claim 3 wherein the means for reducing the intensity of the fire comprises means for operating the means for removing burning material from the hearth to remove part or all of the fire from the hearth and allow the entire contents of the pot to drop.

5. A smoke producing installation comprising: a smoke producing oven according to any preceding claim; a smoke mixing box; and a diverter valve which permits smoke exiting the mixing box to be vented if system sensors determine that the smoke is unsatisfactory for its intended purpose.

6. A smoke producing oven substantially as hereinbefore described with reference to the accompanying drawing.