FIELD OF THE INVENTION

This invention relates to a cane trash burner, a method of operating a cane trash burner, a method of harvesting and/or processing sugar cane for sugar, as well as operating a sugar processing plant.

BACKGROUND OF THE INVENTION

In a conventional method of processing sugar cane for sugar extraction, the sugar cane is usually burned in the field prior to harvesting so as to burn off the leaves and other vegetable matters, or in other words the "trash", leaving behind the stalks which are then conveyed to a sugar processing plant or mill where the stalks are shredded / crushed to extract the sugar juice.

Burning of the trash in the field comes with environmental problems as well as a loss of energy. Energy loss is problematic as further processes such as juice purification, evaporation and crystallisation required to produce raw sugar consume large quantities of energy. Moreover, in-field burning of cane poses a problem of deterioration of the cane which will impact on the quality of the sugar produced.

Though some conventional methodologies and systems remove trash from cane stalks, collect it, bale it and transport it for storage as combustible fuel, these methodologies and systems involve multiple handling steps which are undesirably energy and labour intensive.

It is the object of the present invention to address the abovementioned problems, at least to conserve energy used in processing sugar cane to produce sugar, and/or to process sugar cane in a different manner. SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a cane trash burner comprising: a combustion chamber; an entrance opening through which sugar cane stalks or billets with adhering leaves and other vegetable matter or trash are introduced into the combustion chamber; an exit opening through which stalks or billets exit the burner having had the trash burned off; a combustion arrangement operable to ignite cane stalks or billets introduced into the combustion chamber; and one or more guide plates obliquely disposed within the combustion chamber for guiding or directing incoming sugar cane stalks or billets from the entrance opening to the exit opening under gravity, for example, in a sliding fashion, wherein the guide plates are selected and/or configured and/or arranged to provide a predetermined residence time of the sugar cane stalks or billets within the combustion chamber such that, in use, the trash is burned off the stalks or billets without substantial damage being caused to the sugar in the sugar cane stalks. The crane trash burner may comprise a plurality of guide plates provided substantially obliquely, to a vertical direction of movement of the cane stalks in the combustion chamber, wherein the guide plates are provided in a staggered relation to each other in the combustion chamber so as to provide for sufficient or suitable clearance from one plate to the next to avoid build-up of the material being processed. Differently defined, the crane trash burner may comprise a plurality of guide plates obliquely disposed with respect to a longitudinal axis of the cane trash burner, wherein the plates are provided in a zig-zag fashion within the combustion chamber. The guide plates may extend from an interior surface of the combustion chamber or may be supported by suitable support member/s. A resiliently biased plate may be biased to a normally closed position adjacent the entrance opening so as to keep the opening to the cane trash burner closed when there is an interruption in the cane supply. In particular, the resiliently biased plate may be a spring- loaded plate biased to the normally closed position.

The cane trash burner may comprise a heat transfer means disposed in the combustion chamber, wherein the heat transfer means comprises a heat transfer circuit of tubes containing a fluid suitable to be heated by heat generated in the combustion chamber.

The cane trash burner may comprise an electricity generating unit coupled to the heat transfer means to as to generate electricity using the vapour from the heated fluid from the heat transfer means to drive a turbine which is connected to a turbo-alternator.

The electricity generated by the electricity generating unit may be used to further process the sugar cane stalks to produce sugar or raw sugar, or for external users.

The angle of the guide plates in relation to incoming and/or incident cane stalks and/or the shape and/or dimension of the guide plates may be selected to provide a predetermined residence time in the combustion chamber between the entrance opening and the exit opening. The guide plates may be perforated to facilitate collection of soil and ash in the bottom of the burner.

The combustion chamber may comprise a flue to direct hot gas from within the combustion chamber to a pre-heater.

The combustion arrangement may comprise a gas burner to ignite the trash comprising the sugar cane leaves on the sugar cane stalks. The gas burner may be adjacent the entrance opening so as to ignite the trash comprising cane leave of sugar cane stalks or billets entering the combustion chamber.

A base of the combustion chamber may comprise a rotary valve so as to empty ash receivable adjacent the base of the combustion chamber. The cane trash burner may receive the sugar cane stalks to be burned by way of plough directing the cane stalks to the entrance opening.

A rubber flap may be provided adjacent the exit opening.

The combustion chamber may comprise one or more louvers for controlling air-fuel ratio within the combustion chamber.

The entrance opening may be at a higher elevation than the exit opening. According to a second aspect of the invention, there is provided a method of operating a cane trash burner for burning trash on sugar cane stalks or billets, the method comprising: receiving cane stalks or billets with trash at an entrance opening of a combustion chamber of the cane trash burner; igniting the received cane stalks or billets received from the entrance opening so as to burn the trash; and disposing guide plates obliquely to a longitudinal axis of the combustion chamber or obliquely to a vertical direction of travel of the sugar cane stalks through the combustion chamber so as to direct or guide the sugar cane stalks or billets from the entrance opening of the combustion chamber to an exit opening thereof.

The method may comprise selecting the angle of the guide plates to control the residence time of the sugar cane stalks in the combustion chamber, wherein the sugar cane stalks are guided or directed from the entrance opening to the exit opening under gravity by the guide plates.

The method may comprise disposing the guide plates in a zig-zag or staggered relation to each other within the combustion chamber.

The method may comprise disposing a heat transfer means within the combustion chamber or in thermal communication therewith. The method may comprise transferring heat generated by the combustion of the trash in the cane trash burner to an electricity generating unit, by way of the heat transfer means, for generating electricity, in use.

According to a third aspect of the invention there is provided a method of processing sugar cane in a sugar processing plant, for sucrose extraction, which method includes: harvesting sugar cane with a substantial amount of leaves adhering to the stalks; directing or guiding the stalks with leaves adhered thereto to a sugar processing plant for processing the sugar cane to produce raw sugar; burning the leaves and other vegetable matter in a cane trash burner as an initial step in processing the stalks in the sugar cane processing plant, wherein the residence time of the sugar cane stalks within the cane trash burner is controlled by way of one or more guide plates disposed obliquely within the cane trash burner so as to direct the cane stalks from an entrance opening of the cane trash burner to an exit opening of the cane trash burner, under gravity.

The method may comprise transferring heat generated by the combustion of the trash in the cane trash burner to an electricity generating unit for generating electricity.

The angle of the plates may be provided at at an angle greater than the angle of sliding friction.

The sugar cane may be harvested as wholestick cane or by chopper harvester as cane billets. The method comprising using the electricity generated to process the sugar cane to produce raw sugar, or other uses such as domestic lighting or production of by-products.

The method may comprise disposing the guide plates in a zig-zag or staggered relation to each other within a combustion chamber of the cane trash burner.

According to a fourth aspect of the invention, there is provided a sugar processing plant comprising a cane trash burner of the type described above.

It will be appreciated that the invention as described herein is described with reference primarily to the processing of cane stalks. However, it will be understood that the description and invention extends equally to sugar cane billets.

BRIEF DESCRIPTION OF THE DRAWING

The Figure illustrates a schematic sectional view through a cane trash burner in accordance with an example embodiment of the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of an embodiment of the present disclosure. It will be evident, however, to one skilled in the art that the present disclosure may be practiced without these specific details. In the Figure, reference numeral 10 generally indicates a cane trash burner in accordance with an example embodiment of the invention. The cane trash burner 10 is typically of an industrial type located at or in relatively close proximity to a sugar cane processing plant (not shown). It will be noted that prior to processing in the cane trash burner sugar cane is harvested at a sugar cane field with a substantial amount of sugar cane leaves and/or other vegetable material (the "trash") adhering to the stalks. In order to maintain the organic health of the sugar cane fields, it is proposed that the cane tops are cut from the cane stalks and left lying in said fields. The harvested stalks are then conveyed to a sugar processing plant (not shown) for processing the sugar cane to produce raw sugar. The cane trash burner 10 is then used to burn the trash on the stalks prior to processing as will be described below.

As alluded to above, though reference is made to cane "stalks", it will be appreciate that the burner 10 is also operable to process cane that has been harvested by a chopper harvester, and the cane is the presented in the form of billets with adhering trash. To this end the trash may comprise leave of the sugar cane plants, as well as other organic, and in certain instances inorganic, unwanted material adhering or attached to the cane stalks and/or billets.

To this end, the cane trash burner 10 comprises a combustion chamber 12 having an interior in which combustion of trash as described herein takes place. The chamber 12 comprises an entrance opening 14 through which sugar cane stalks 16 are receivable. The sugar cane stalks 16 have adhering trash as mentioned above.

A resiliently biased plate 18 is provided adjacent the entrance opening 14. The plate 18 is normally biased to the closed position, for example, under action of a loaded spring thereby normally closing off the opening entrance 14. The plate 18 is configured with a pre- determined spring loading such that it may only be opened in a pivot fashion to allow access to the interior of the chamber 12 on receipt of a pre-determined force being exerted thereon, for example, by a predetermined mass of the sugar cane stalks 16 bearing thereon. This is to limit entry of air into the chamber 12 unnecessarily thereby preserving combustion within the chamber 12. The trash burner 10 further comprises a combustion arrangement 20 operable to ignite the trash on cane stalks or billets 16 introduced into the combustion chamber 12. The combustion arrangement 20 comprises suitable gas burner/s and is located at least adjacent the entrance opening 14 so as to ignite the cane stalks 16 entering the chamber 12. The cane trash burner further comprises guide plates 22 obliquely disposed within the chamber 12 with the respect to longitudinal axis A of the chamber 12, in a staggered or zig-zag fashion as illustrated. In this way it would be appreciated that the guide plates 22 are provided effectively obliquely to the vertical direction (indicated by arrow B) of travel of the cane stalks 16 so that the burning stalks 16 slide down the combustion chamber 12 from the entrance opening 14 toward an exit opening 24 of the combustion chamber 12 in a zig-zag fashion in the general vertical direction of arrow B under gravity. To this end, it will be noted that the entrance opening 14 is at a higher elevation that the exit opening.

The plates 22 are perforated plates or woven wire mesh screens on a supporting framework and may on one example embodiment be constructed of steel, for example, stainless steel. The plates 22 may be selected of a material and/or shape and/or dimension, and may be disposed at a predetermined angle Θ with respect to the interior wall of the chamber 12 or axis A such that they cause the cane stalks 16 to slide down from the entrance opening 14 to the exit opening 24 with a predetermined residence time in the chamber 12 such that the sucrose in the sugar cane stalks 16 do not suffer substantial thermal damage during combustion of the trash. The length or each the plates 22 may be approximately between 3 - 4 m, and the plates 22 are staggered In a zig-zag fashion. The selection of the height of the chamber 12, particularly the height between the openings 14 and 24 may also be selected to control the residence time of the cane 16 in the chamber 12. In one example embodiment, the height from the end of one perforated plate 22 or wire mesh screen to the top of the next plate or screen is approximately 3 m.

The perforations in the guide plates 22 or mesh screens allow for dirt and ash byproducts from the combustion of the sugar cane stalks 16 to fall also in the direction of arrow B to a bottom region 12.1 of the combustion chamber and allow for adequate air flow through the plates or screens for complete combustion of the trash. In this way unwanted ash and sand resulting from the combustion of the sugar cane stalks 16 do not get transported with the burnt cane exiting the exit opening 24 and damaging crushing machinery associated with the processing of sugar cane stalks 16 to produce cane raw sugar. Incidentally, ash and sand collecting at the bottom region 12.1 of the chamber 12 may be collected and may be used as fertiliser in the sugar cane field.

The cane trash burner 10 may comprise a heat transfer means disposed in the combustion chamber, the heat transfer means comprises a network or circuit of heat transfer tubes 26, containing a fluid, for example, water, which is suitable to be heated or in other words absorb the heat generated within the combustion chamber 12 by the combustion of the trash. I The cane trash burner 10 also comprises an electricity generating unit (not shown) coupled to the heat transfer tubes 26 so as to generate electricity using heated water from the heat transfer tubes 26. Differently described, the thermal energy generated by the burning of the sugar cane trash may be used to heat water in the tubes 26 which is then in turn used by the electricity generated unit to generate electricity. To this end it would be appreciated that the electricity generating unit may use steam produced by the heating of water in tubes 26 to generate electricity for example, by way of a suitable conventional steam turbine or engines.

At the bottom of the cane trash burner 10 or in other words at the bottom portion 12.1 of the combustion chamber 12, a rotary valve 28 is provided so as to control removal of soil/ash released during burning of the trash within the combustion chamber 12. In this regard, the cane trash burner 10 comprises louvers 30 also to control the air-fuel ratio within the combustion chamber. A flue 32 is adjacent at a top portion of the combustion chamber 12 provided to direct hot gases to a pre-heater, for example.

A displaceable flap 33, for example, a resilient rubber flap 33 is provided adjacent the exit opening 24 to substantially close the same. The flap 33 is normally biased to close the opening 24 such that the burnt sugar cane stalks 16 forces the flap 33 to open when sufficient sugar cane stalks 16 bears upon the same. In this way, the rubber flap 33 prevents excessive air entering into the chamber 12 and disrupting combustion when there is no cane stalks 16 to exit the chamber 12. Exiting cane stalks 16 are generally received on a burnt cane conveyor 34 which is then used to transport the cane stalks 16 for further processing in the sugar cane plant (not shown).

For completeness it would be known that a plough generally indicating by reference numeral 36 is typically used to load the cane stalks 16 from a cane supply conveyor into the cane trash burner 10. Moreover, it will be noted that an ash conveyor 38 is typically provided adjacent the bottom of combustion chamber 12 so as to collect ash and sand for transport for use in a fashion as described above.

In use, with reference to the Figure, it will be noted that sugar cane is harvested at the field in a manner as described above and transported to a sugar cane plant in accordance with an example embodiment in which a cane trash burner 10 in accordance with an example embodiment of the invention is provided. The harvested sugar cane with the trash adhering thereto is then moved by a plough from the cane conveyor to the entrance opening 14 of the chamber 12. Once a sufficient force is presented on the plate 18 at the opening 14, for example, a sufficient mass sugar cane stalks 16 is presented, the plate 18 is displaced from the normally closed position to an open position to as to allow the sugar cane stalks 16 to enter the combustion chamber 12. The plate 18 then closes under spring action once the stalks 16 are inside and there is no force displacing same.

As the sugar cane stalks 16 enter the combustion chamber 12, they are ignited by the gas burner 20 and slide vertically under gravity in direction of arrow B along the angled plates 22 in a zig-zag fashion through the combustion chamber 12. The time of travel of the sugar cane stalks 16 on the plates is typically predetermined by the configuration of the plates 22 to ensure specific residence time or range of residence time of the stalks 16 in the chamber 12 so that the sucrose within the sugar cane stalks 16 is not substantially burned. As the stalks 16 combust, ash and sand adhering to the sugar cane stalks 16 pass through the perforated plates 22 and fall through to the bottom portion of the combustion chamber 12.1 where they may be removed subsequently by way of conveyor 38 for use as fertilizer described herein.

Moreover, heat generated in the combustion chamber 12 causes the fluid in the tubes 26 to heat and vaporise and actuate the electricity generating unit thereby to generate electricity which may be used to either control the operations of the cane extraction plant and/or for further processing of the sugar cane stalks 16 and/or for re-use in another way (for example to supply an electricity grid). Hot gases are directed via the flue 32 to a pre-heater to, for example pre-heat the fluid (water) for energy capture in the heat transfer network of pipes. It would be appreciated that louvers 30, and valve 28 are optionally actuated to control the air flow and air-fuel ratios within the combustion chamber 12 to provide optimal burning of the trash adhering to the sugar cane stalks 16 as well as to ensure that the combustion chamber 12 does not fall out of operating parameters.

Once burnt, having travelled through the combustion chamber 12 to reach outlet opening 24, the burnt sugar cane stalks 16 displace the flap 33 so as to open the same thereby allowing the burned cane stalks to move to a burned cane conveyor 34 for transport for further processing, for example, to a cane stalk shredder, etc.

The invention as described herein burns trash in a controlled manner with quick entry and removal from the combustion chamber so that no substantial thermal damage to the sugar in the cane occurs. In this way the invention also conserves electricity usage by recycling energy lost by the removal and burning of the trash in the field. Moreover the present invention avoids drawbacks associated with conventional processing of the sugar cane at the field, especially by reducing air pollution as well as negative effects on organic health of the soil that are the results of in-field burning of cane. Moreover, tops of the sugar cane which are removed at the field may be left in said field to conserve soil health in said field for future crops. Moreover, the present invention may make it possible to provide an additional income stream from sugar cane by harvesting the energy of the trash, possibly for electricity generation, or facilitating other energy-intensive processes such as sugar refining or producing by-products.