GB2219380A - Oven for drying and singeing hog carcasses - Google Patents

Abstract

Suspended hog carcasses are passed continuously through drying units 3 and singeing units 4, 5 and are turned in the singeing units to produce an even singeing. The carcasses enter and leave through reducing doors 10 and are dried initially by gas passed from a singeing unit. In the singeing units the carcasses are singed by oil or gas burners and by heat reflected from the unit walls. Combustion gas from the singeing units 4, 5 is passed through drying units 3, then is passed to a heat recovery system which may preheat air drawn in for combustion. <IMAGE>

Description

OVEN FOR DRYING AND SINGEING HOG CARCASSES.

The invention relates to a singer oven for singeing i.e. scorching and bracing the skin of hog carcasses in the slaughtering process of a hog slaughtering plant in a continous, non-stop process, particularly in connection with the processing of large numbers of hog carcasses in the slaughtering process.

Plants for singeing hog carcasses separately or in small numbers at a time are disclosed in e.g. Danish patent specification No. 73721 and 94605, in US patent specification No. 1,667,946 and 4,653,148, and in French patent specification No. 2540344 and 2549699, all of which disclose a gradual, discontinuos conveyance of hog carcasses for processing in a singer oven. US patent specification No.

1,667,946 and US patent specification No. 4,653,148 disclose embodiments closest to a continuous processing, however the continuity according to US 1,667,946 being limited to the relatively small number of hog carcasses which may be processed at a time in the separate, horizontal tunnel singer oven which at each end is provided with a closure mechnisms in the form of two doble swing door arrangements, whereas predrying and singeing according to US patent specification No. 4,653,148 are performed in seperate units without use of any special heat saving closure mechanisms. Other problems which the above mentioned patent specifications have attempted to solve are the ensuring of a uniform singeing of the whole surface of the hog carcass, see e.g.DK 73721, FR 2540344 and FR 2549699, as well as a sufficiently tight sealing of the oven chamber proper in order to avoid any heat waste in connection with transporting a hog carcass in and out of the chamber. However, these prior art drying and singeing methods with oven closure systems have either proved to be too complicated or uneconomical, especially when used in connection with large slaughtering processes wherein at least 150 hogs are processed per hour in a tunnel oven, or have only been used for dehairing operation due to an insufficient flow of the oven air as well as an insufficient heat transfer to the whole hog and a relatively large heat waste from the oven.

It is therefore the object of the present invention to provide a combined drying and singeing oven which eliminates the before mentioned drawbacks and which excels in having simple mechanical solutions and by being easily adaptable to large scale production in a slaughtering process where not only a dehairing operation is needed but also scorching and thus bracing of the skin.

This object is obtained by means of a singeing oven comprising a chamber; a conveyor arrangement along the ceiling of the oven for conveying carcasses, hung by the hind legs, through the chamber while turning the individual carcasses about a vertical axis; stationary burners arranged in the chamber for circulating gas around the carcasses during their passage through the oven to provide an initial drying of the surface of the hog carcass followed by singeing and scorching of the outer skin layer of the carcass and simultaneously bracing of the skin, the combustion gases generated by the singeing operation being used directly for the drying in a special drying section in the oven prior to the singeing of the carcasses; and a heat recovery system to which the combustion gases are conveyed; wherein the chamber is a horizontally elongate tunnel and comprises a number of drying and singeing sections which are aligned in sequence; that the oven has a closure mechanism at each of its inlet and outlet ends which ensures a permanent, substantially air and water tight, and noise containing, closing of the chamber; that the inside of the chamber is provided with guide rails for the automatic turning of each carcass around its vertical axis during the conveyance through the chamber; and that the inner walls of the oven chamber are provided with a heat reflecting material contributing to a uniform and high heat transfer from the burners to each entire carcass.

Each closure mechanism is preferably constructed as a rotary part cylindrical gate between two stationary part cylindrical walls mounted in the respective opposite side walls of the oven, each -gate having a vertical opening allowing unrestricted admission and removal of a hog carcass, hanging by the hind legs, and each mechanism being provided with sealing members between its stationary and rotary parts.

The aligned drying and singeing units are at their proper ends closed by the inlet and outlet units, the number of drying and singeing units used determining the length of the oven chamber corresponding to the desired capacity for a continuous processing of at least 150 hog carcasses per hour.

The burners may be oil or gas burners which are stationarily mounted in the oven chamber in such a manner that they, together with the radiant heat from the heat reflecting wall lining, produce a uniform singeing of the total surface of the individual hog carcasses during the continuous transport through the oven chamber.

Thus, the particularly new features of the invention compared to the prior art technique are that it is possible in the same elongate tunnel oven with only one inlet and one outlet unit to predry and singe hog carcasses in a number of drying and singeing units corresponding to the desired capacity, that the energy utilization is maximized by using only one oven chamber with a heat recovery method known per se together with a special heat reflecting material on the oven wall, that the oven chamber has such'a length that processing the hog carcasses is performed in a continuous process during the automatic conveyance of the carcasses through the chamber, the carcasses being turned on their vertical axis by means of automatic members to obtain a uniform irradiation from the heat reflecting materials upon all sides of the carcass and that the special construction of the inlet and outlet elements which fulfills the requirement for a continuous admission and removal of hog carcasses in the oven chamber also ensures a permanent air and heat tight as well as a noise reducing sealing at the ends of the chamber.These measures render the oven chamber suitable particularly for slaugthering processes of very large capacities where a continuous processing during the entire process is of significant importance, the prior art oven chamber constructions having been unable to fulfil these requirements, including especially the environmental requirements, such as a more harmonious working process compared to said prior art systems, a more gentle processing of the product and a higher thermal economy and a lower noise emission from the plant, as well as the requirements for a higher profitability in the production by processing a great number of hog carcasses at the same time in the oven chamber thus obtaining a higher degree of slaughtering efficiency of the plant.

The invention will be further explained in the following with reference to the drawing which diagrammmatically illustrates an example of the embodiment of the invention and wherein Fig. 1 shows a singeing oven according to the invention with the oven ceiling removed and Fig. 2 shows a cross sectional view according to the line II-II in Fig. 1.

From a preceeding section in a slaughtering process (not shown), see e.g. I. Wismer Petersen "Kd som levnedsmiddel" ("Meat as Foodstuff") II, paragraph 15 (DRS Publishers, Copenhagen 1975) optionally from an accumulating section formed to that purpose - hog carcasses (17) are conveyed continously and in large numbers ready for predrying and singeing and hung on a rail (9) by the hind legs in the combined tunnel drying and singeing oven (2, 3, 4, 5) which is mounted on a supporting device (18). The rail (8) is provided with special members in the form of a guide rail (12) for automatic turning of the hog carcass on its vertical axis during the admission into and the conveyance through the oven.The individual hog carcass (17) is introduced into an inlet unit (1) which is provided with a vertical opening (10a) in a pivotable cylinder gate (10) having a permanent, approximately air tight and subsequently heat tight as well as noise reducing sealing between the fixed parts of the unit and the movable cylinder gate Once the hog carcass has entered the unit (1), the gate (10) is automatically turned in such a manner that the opening (10a) will face the oven chamber during the advancing move of the carcass. During the conveyance through the inlet unit (1) towards the transition unit (2) of the oven chamber the hog carcass is kept in the indicated position by the guide rail (12).In the transition unit the further transport through the oven chamber of the hog carcasses is undertaken by a prior art conveyor system (11) - a conveyor system of the rotary type (Fig. 1) - which together with the rail (9) located below the oven ceiling continously convey the carcasses through the drying section of the oven (shown as oven unit 3) wherein the carcasses are dried by means of the heat from the generated smoke gas of the singeing section (4, 5). A singeing section consisting of the singeing elements (4, 5) is on the inside provided with stationary burners (13, 14) just as the outer insulated oven walls are coated with a heat reflecting material (8) on the inside thereby obtaining a uniform and high heat transfer from the burners to the individual hog carcass.The oven -walls are constructed in such a manner that the inside oven walls approximately have the general shape of a hog carcass leaving a minimum clearance thereby making the burners mounted in the oven chamber follow the shape of the hog carcass. In the singeing unit (4) the hog carcasses (17) are conveyed in the same position as the conveyors (11) have received them in the transition unit (2). In this position both flanks of the individual carcass are singed.

During the transition from the singeing unit (4) to the singeing unit (5) another guide rail (12a) assures that the individual carcass is turned 90 so that the back and the ventral side of the carcass are singed in the unit (5).

Immediately before a hog carcass is admitted to an outlet unit (6) and where the conveyor (11) "releases" the carcass, the further automatic conveyance is again undertaken by the rail (9) in connection with the guide rail (12a), and the hog carcass is admitted to and removed from the outlet unit by means of said automatic pivotable cylinder gate in the same manner as during the passage through the inlet unit (1), the outlet unit also ensuring a permant, approximately air, heat and partly noise tight sealing of the oven chamber. From the outlet unit the singed hog carcass is conveyed to the next processing stage (not shown) (the scraping off of the carbonised crust) or to another accumulating section placed before said stage.

The burners (13, 14) of the oven chamber are suitably arranged in such a manner that they are not placed directly under a hog carcass thus avoiding liquid dripping down into a burner just as the arrangement ensures a suitably high smoke gas velocity in the entire singeing section (4, 5).

The oven is provided with a prior art ventilation system (not shown) to draw the smoke gasses generated in the singeing sections (4, 5) in through the drying sections (3) for predrying of the hog carcasses, the smoke gasses subsequently being drawn through an air duct mounted in the transition unit to a heat recovery system (not shown) which recovers the smoke gas heat and guides it back as i.e.

preheated combustion air to the combustion system of the oven (13, 14) or for use in connection with water heating or steam production.

The semi-circular embodiment of a singeing oven in the horizontal plane does not in any way limit the invention as the arrangement of the oven sections in units makes it possible to construct both a straight as well as angular arrangement depending upon the outer space conditions for the oven just as the rotating conveyor for hog carcasses through the units of the plant illustrated in the drawing may be replaced by known straight or angular conveyor systems, or the like.

Comparative estimates for a slaughtering process for 250 hogs/hour in a singeing oven operating according to the prior art, discontinous principle i.e. processing one hog carcass at a time with subsequent frequent opening and closing of the oven chamber, and a singeing oven according to the invention operating according to the continuous principle described in this specification and having a permanently closed oven chamber and processing a large number of hog carcasses at the same time, show the following results:: Prior art oven system Oven system according to the invention Slaughtering speed (hog/hour) 250 250 Oil consumption per hog (1/hog) 0,45 0,37 Oil consumption per hour (1/hour) 112 92 Input effect (kW) 1100 900 Effect for singeing and maintaining the oven temperature (kW) 450 300 Effect transferred to hogs (estimate) (kW) 200 200 Recovered effect (kW) 450 500 Chimney loss (kW) 200 100 As will be seen the oil consumption is reduced by 18% and the heat recovery is increased by about 10%.

The energy saving thus obtained in the singeing oven according to the invention and subsequently the reduction in heat consumption in relation to the prior art systems are particularly due to: - the permanently closed oven chamber, - the subsequent reduced heat loss caused by the exchange of oven air with ambient air due to draught is avoided, - the reduced admission of cold air to be mixed with the hot smoke gasses whereby the reduction of the gas temperature is limited correspondingly, thus increasing the use of the smoke gasses for heat recovery, and - the reduction of heat radiation from the oven to the ambient air.

Claims (4)

1. l. A singeing oven for predrying and singeing, scorching and bracing the skin of hog carcasses in a hog slaughtening plant, the oven comprising a chamber; a conveyor arrangement along the ceiling of the oven for conveying carcasses, hung by the hind legs, through the chamber while turning the individual carcasses about a vertical axis; stationary burners arranged in the chamber for circulating gas around the carcasses during their passage through the oven to provide an initial drying of the surface of the hog carcass followed by singeing and scorching of the outer skin layer of the carcass and simultaneously bracing of the skin, the combustion gases generated by the singeing operation being used directly for the drying in a special drying section in the oven prior to the singeing of the carcasses; and a heat recovery system to which the combustion gases are conveyed; wherein the chamber is a horizontally elongate tunnel and comprises a number of drying and singeing sections which are aligned in sequence; the oven has a closure mechanism at each of its inlet and outlet ends which ensures a permanent, substantially air and water tight, and noise containing, closing of the chamber; the inside of the chamber is provided with guide rails for the automatic turning of each carcass around its vertical axis during the conveyance through the chamber; and the inner walls of the oven chamber are provided with a heat reflecting material contributing to a uniform and high heat transfer from the burners to each entire carcass.
2. 2. An oven according to claim l, in which each closure mechanism is constructed as a rotary part cylindrical gate (10) between two stationary part cylindrical walls mounted in the respective opposite side walls of the oven, each gate (10) having a vertical opening (10a) allowing unrestricted admission and removal of a hog carcass (17), hanging by the hind legs, and each mechanism being provided with sealing members between its stationary and rotary parts.
3. 3. An oven according to claim 1 or claim 2, in which the length of the chamber, the number of of drying and singeing units and the speed of the conveyor arrangements enables the processing of at least 150 hog carcasses per hour.
4. 4. An oven, substantially as described with reference to the accompanying drawings.