WO2013072721A1

WO2013072721A1 - Portable kiln for ashing of agricultural wastes

Info

Publication number: WO2013072721A1
Application number: PCT/IB2011/055159
Authority: WO
Inventors: Martin WOODE
Original assignee: SCHWARZ Jayson; GC TECHNOLOGY
Current assignee: SCHWARZ Jayson; GC TECHNOLOGY
Priority date: 2011-11-17
Filing date: 2011-11-17
Publication date: 2013-05-23
Anticipated expiration: 2014-05-17

Abstract

The present invention provides a portable kiln with the ability to control temperature under farm conditions for the combustion of agricultural waste. The kiln includes a central cylindrical combustion chamber. The central cylindrical combustion chamber includes a system for the control of combustion air to the combustion chamber. The kiln includes a second concentric cylinder surrounding the central cylindrical combustion chamber. The second concentric cylinder includes a system for the flow of cooling water through the first annulus between the central cylindrical combustion chamber and the second concentric cylinder. The kiln includes a system for the feeding of the agricultural waste into the central combustion chamber. The kiln includes a temperature-sensing device to measure and display the temperature within the central combustion chamber during the combustion of the agricultural waste. The kiln includes a system for the recovery of ash from the kiln. In operation, the temperature of combustion is controlled to between 550 °C and 650 °C by a combination of increasing the supply of combustion air when the temperature in the central combustion chamber falls to near 550 °C and the introduction of cooling flowing water when the temperature in the central combustion chamber approaches 650 °C.

Description

TITLE

PORTABLE KILN FOR ASHING OF AGRICULTURAL WASTES TECHNICAL FIELD

This invention relates to a portable kiln for the burning of agricultural wastes to form ashes in the production of potash.

BACKGROUND ART

Potash was originally produced by leaching wood ashes and evaporating the solution in an iron pot, thus extracting potassium fertilizer.

Potash is important for agriculture because it improves water retention, yield, nutritional value, texture and disease resistance of food crops. It has wide application to fruits and vegetables, rice, wheat and other grains, sugar, corn, soybeans, palm oil and cotton, all of which benefit from the nutrient's quality-enhancing properties. Economic growth in Asia and Latin America has greatly contributed to the increased use of potash-based fertilizers.

Because potash is a fertilizer for the above-mentioned plants, agricultural plant wastes become a reservoir of potassium from which potash can be recovered by extraction from the residue (ashes) which is left from the burning of such agricultural plant wastes. In particular, the agricultural plant wastes which are burned to ashes and from which potash is extracted, preferably are cocoa pod husks, plantain (and banana) peels and cola nut husks. Thus, potash may be recovered by extraction from the residue (ashes) left from the burning of the above preferred agricultural plant wastes.

Among the technical publications dealing with burning of agricultural wastes to form ashes from which potash is extracted are the following:

"Chemical Studies of Some Plant Wastes From Ghana" E.K. Ankrah, Journal of the Science of Food and Agriculture, Vol. 28, issue 10, pages 1229 - 1232, 1984. "Extraction of Potash From Cocoa Pod Husks' B. K. Simpsion et al, Agricultural Wastes, Vol. 13, issue 1, pages 69 -73, 1985.

"Effect of Ripening on the Chemical Composition of Plantain Peels and Pulp ",L.Welford -Abbey, et al, Journal of the Science of Food and Agriculture, Vol. 45, issue 4, pages 233-336 1988.

"Extraction and Potential Application of Caustic Potash From Kola Husk, Ugwu Pod Husk and Plantain Peels", A. A. Taiwo et al, Scientific Research and Essay, Vol. 3 (10), pages 515 -517, October 2008.

In the past, kilns for the burning of agricultural wastes to form ashes in the production of potash have generally been designed to be stationary and centralized with any

temperature control being done electronically.

In areas of Africa and other so-called "third world" countries, where it is desired to burn agricultural plant wastes, e.g., cocoa pod husks, plantain (and banana) peels and cola nut husks, it is not economically feasible to transport many tons of cocoa pod husks, plantain (and banana) peels and cola nut husks, to centralized points for incineration in a stationary kiln to obtain a very small amount, e.g., about 7% of husk mass in the ash.

There are many patents directed to kilns for the incineration of plant matter. Among them are:

US Patent No 4,734 166, issued Mar 29, 1988, to Angello,II, for "Furnace for the Selective Incineration or Carbonization of Waste Materials", where incineration is controlled by the introduction of selected amounts of air and the provision of an afterburner to provide a "clean" atmosphere of the kiln effluent.

US Patent No 4, 092,098 , issued May 30 1978 , to Monsanto Company for "Method and Apparatus for Improved In Situ Combustion of Pyro lysis Gases in a Kiln", where temperature control in direct fired rotary kilns was said to be solved by controlling the velocity of burner gases and the distribution of air at the burner end of the kiln. US Patent No 4,037,543, issued July 26, 1977, to Angello, II, for "Pollution Free Combustion Apparatus and Furnace", where the furnace can be operated to provide ash from which potash may be produced by regulating the amount of excess air to produce the ash at a combustion temperature of about 550 ° F up to about 1 ,500 °F. US Patent No 3,842,762, issued Oct 22,1974 to Grumman Ecosystems Corporation for "Apparatus for Disposing of Solid Wastes", which includes an air distribution system for burning in a controlled atmosphere.

US Patent No 4,793,269, issued Dec 27, 1988 to Westinghouse Electric Corp for "Kiln for Waste Disposal". There are also many patents which deal with the cooling of kilns and other furnaces. Among them are the following:

US Patent No. 5,350,296, issued Sep 27, 1994 to ABB Flakt AB, for a "Method and Device for Cooling a Rotary kiln".

US Patent No 5,230, 617, issued Jul 27,1993, to Klein et al, for "Furnace Shell Cooling System".

US Patent No 4,973,245, issued Nov 27, 1990 to Outokumpu Oy for "Method for Cooling a Kiln Furnace".

US Patent No. 4,584,180, issued Apr 22, 1986 to Cool Water Coal Gasification Program for "Gas Injection Apparatus". US Patent No. 4,206, 312 issued Jun 3, 1980 to Sidepal SA for "Cooled Jacket for Electric Arc Furnaces".

US Patent No. 4,199,652, issued Apr 22, 1980, to Longenecker for "Air Cooled Electric Arc Furnace". US Patent No 4,418,893, issued Dec 6 1983, to Combustion Engineering Inc for "Water Cooled Refractory Lined Furnaces".

US Patent No.4,091,228, issued May 23, 1078 to United States Steel Corporation for "Water Cooled Shell for Electric Arc Furnaces". SUMMARY OF INVENTION

TECHNICAL PROBLEM

One technical problem to be solved was that the combustion of agricultural plant wastes resulted in the recovery of only about 7.0% of the ash for the extraction of potash from the ashes. This makes the collection of agricultural wastes to centralized places for combustion uneconomical.

Another technical problem to be solved was that the combustion of agricultural plant wastes was fraught with problems of safety and quality control.

Yet another technical problem to be solved was that the combustion of agricultural plant wastes at uncontrolled temperatures resulted in the production of impure potash and a lower yield of potash.

These technical problems were attempted to be solved as described in the above mentioned paper "Extraction of Potash From Cocoa Pod Husks", by B. K. Simpson et al, published in "Agricultural Wastes," Vol. 13 issue 1 pages 69 -73, 1985. That paper described a potash incinerator, the main features of which were: 1) a cell grate on which the dry cocoa pod husks were burnt with an ash pit below it; 2) a combustion chamber through which the combustion products were carried out by natural draught for complete combustion; and 3) a chimney stack. This incinerator was thus an undercurrent type of incinerator with openings at the sides to regulate the amount of air that enters for rapid or slow combustion. There were, however, no other temperature control means. Yet, the technical problems remain to be solved. SOLUTION TO PROBLEM

The applicant has discovered that, to optimize the yield and quality of potash from the ashes of such agricultural wastes, preferably the ashes of cocoa pod husks, plantain (and banana) peels and cola nut husks, the combustion should be carried out within a controlled narrow temperature range of about 550 °C to about 650 °C. The applicant has noted that below about 550 °C, the production of ashes is incomplete and thus is not economical. The applicant has also noted that above about 650 °C potash forms ferrites with ferric oxide in the ash. The ferrite is subject to easy hydrolysis in an alkaline environment to hexahydroxyl ferrate, which is responsible for the brown coloring of organic potash thereby depreciating its value. To obtain a purer form of the potash it is first converted to the bicarbonate which is easier to crystallize out of solution. The potassium bicarbonate (KHCO3) is reconverted to potash (K2CO3) by decomposition in an oven.

The equations for such reactions are: K₂CO₃ + Fe₂0₃ =2KFe + C0₂; t = or greater than 600 degrees C. KFe0₂ + 2 H₂0 + 2KOH = K₃[Fe (OH)₆]. K₂C0₃ + CO₂ + H₂0 = 2KHC0₃

Accordingly, by applying those findings, the technical problems were addressed in the present invention by the provision of a novel kiln which provided combustion within a controlled narrow temperature range of about 550 °C to about 650 °C so more than about 70 % of the potash could be extracted from the ashes, there were minimal problems with safety and quality control and controlled temperatures resulted in the production of substantially pure potash.

Thus, one broad aspect of the present invention resides in a kiln for the combustion of agricultural wastes, especially cocoa pod husks, plantain (and banana) peels and cola nut husks. The kiln includes a central combustion chamber. The central combustion chamber includes a system for the control of combustion air to the combustion chamber. The kiln includes a second cylindrical chamber surrounding the central combustion chamber. The second cylindrical chamber includes a system for the flow of cooling water through the first annulus between the central combustion chamber and the second cylindrical chamber. The kiln includes a system for the feeding of the plant waste into the central combustion chamber. The kiln includes a temperature-sensing device to measure and display the temperature within the central combustion chamber during the combustion of the waste plant material. The kiln includes a system for the recovery of ash from the ashes. In operation, the temperature of combustion is controlled to between about 550 °C and about 650 °C by a combination of increasing the supply of combustion air when the temperature in the central combustion chamber falls to close to about 550 °C, and the introduction of cooling flowing water when the temperature in the central combustion chamber approaches about 650 °C. ADVANTAGEOUS EFFECTS OF THE INVENTION

By these three aspects of the present invention, substantially pure potash may be provided which can be used for fertilizer as well as in food products and pharmaceuticals. The organic potash produced by the present invention is a premium product which is useful in the production of animal feed supplements, cement, fire extinguishers, photographic chemicals, textiles, in brewing beer, as a catalyst for synthetic rubber manufacturing and in all applications where potash is needed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings

Fig 1 is an isometric view of one embodiment of the kiln of this invention; Fig 2 is an exploded view of the embodiment of the kiln of this invention shown in Fig 1 ; Fig 3 is a longitudinal section of an assembly drawing for the assembly of the

embodiment of the kiln of this invention shown in Fig 1; and

Fig 4 is a section along line IV-IV of the longitudinal section of an assembly drawing for the assembly of the embodiment of the kiln of this invention shown in Fig 3. DESCRIPTION OF EMBODIMENTS

DESCRIPTION OF FIG 1, FIG 2, FIG 3 AND FIG 4

As seen in Fig 1, the kiln 10 includes an outer cylinder 12 within which are a middle concentric cylinder 14, and an inner concentric cylinder 16. The inner cylinder 16 comprises the combustion chamber and it has a perforated base with a first annulus 18 between concentric cylinder 14 and concentric cylinder 16 (the combustion chamber), and a second annulus 20 between cylindrical outer shell 12 and concentric cylinder 14. These are shown and will be explained with reference to Fig 2, Fig 3 and Fig 4. The first annulus 18 between the inner concentric cylinder 16 and the middle concentric cylinder 14 forms an annular jacket which is adapted to be filled with water which acts as a heat dissipater to keep the temperature of the inner cylinder wall substantially constant, generally at about 100 degrees C. The second annulus 20 between the outer cylinder 12 and the middle concentric cylinderl4 is lagged with a thermal insulator, e.g. a glass fiber batt.

The outer cylinder 12 includes a partial top cover 22 made of two concentric cylinders 24, 26, and is also lagged with a thermal insulator, e.g. a glass fiber batt. The partial top cover 22 is provided with an exhaust vent 28 to exhaust the combustion chamber 16 and an opening 30 for the purpose of introducing agricultural waste for combustion.

A spring 32 includes an upper end 34 that engages a lever mechanism 36. Lever mechanism 36 includes a control rod 38 which actuates a cone shutter 150 of a cone and cap system for the purpose of controlling the discharge of agricultural waste from the cup feeder 44 of the cone and cap system into the combustion chamber 16. The cone and cap system allows the agricultural waste to be fed into the combustion chamber 16 in batches. The lever mechanism 36 is connected by pull cord 46 to a cylindrical handle 48 and a cylindrical pedal 50. The lever mechanism 36 is mechanically operated through a manual operation either by pedal 50 at the base of the kiln, or by handle 48 at the side of the kiln. The lower end 52 of spring 32 presses against a transverse projection 54 of a pusher bar 56.

An encircling ring 58 supports tube 60 leading from funnel 62 to the interior of first annulus 18, and drain tap 64 from the interior of first annulus 18 for the flow of cooling water through the annular jacket provided by the first annulus 18 between the inner concentric cylinder 16 and the middle concentric cylinder 14. The kiln 10 is supported on vertical posts providing stand 66. Beneath stand 66 is an ash collector 68. Beneath the perforated plate of the combustion chamber 16 are three manually-operated sliding gates 70, 72 and 74 which are positioned around outer cylinder 12. These sliding gates 70, 72 and 74 can be pulled either to widen or to narrow the air inlet slot 76 providing the inflow of air into the combustion chamber 16 as a means of temperature control. The combustion chamber 16 of the kiln 10 terminates in a frusto- conical bottom 78. The frusto-conical bottom 78 of the combustion chamber 16 is equipped with a shutter 80 which collects the ashes and which can be pulled out manually to discharge the ashes into an ash collector 68.

The kiln 10 is provided with a thermocouple 84 which is affixed to the body of the kiln 10, with probes extending within the combustion chamber 16.

Fig 2 shows in more detail some of the elements already described in Fig 1, namely: outer cylinder shell 12; middle concentric cylinder 14; inner concentric cylinderl6 (which is the combustion chamber); a first annulus 18 between middle concentric cylinder 14 and inner concentric cylinder 16; a second annulus 20 between outer cylinder 12 and middle concentric cylinder 14; partial top cover 22; two concentric cylinders 24, 26; exhaust vent 28; opening 30; spring 32; lever mechanism 36; control rod 38; cup feeder 44; pull cord 46; cylindrical handle 48; cylindrical pedal 50; cone shutter 150 of cup and cap system, only the lower plate 40 thereof being shown; tube 60; funnel 62; stand 66; ash collector 68; sliding gates 70, 72 and 74; frusto-conical bottom 78 of combustion chamber 16; and control shutter 80.

Now turning to Fig 3, an inner cylinder 82 of the outer cover 86 is provided. A pivot is connected to lever mechanism 36 which controls the action of the pulling cord 46. Pulling cord 46 is pulled either by cylindrical handle 48 or by cylindrical pedal 50. Spring 32 maintains the pulling cord 46 taut. Projecting through the cover 22 is the exhaust vent 28. Cup feeder 44 is for the purpose of feeding the agricultural waste into the kiln 10.

The kiln 10 is provided with a pair of handles 100. The terminus of the combustion chamber 16 is a frusto-conical end 78. A shutter 80 selectively opens and closes the frusto-conical end 78 to discharge ashes onto the ash collector 68.

Now turning to Fig 4, middle concentric cylinder 14 is pierced by the tube 60 leading from the funnel 62 selectively to pour cooling water into the first annulus 18 between middle concentric cylinder 14 and inner concentric cylinder 16 (i.e., the combustion chamber) to discharge water through drain tap 64. A thermocouple 84 projects through the cylindrical walls of outer cylinder 12, of middle concentric cylinder 14 and of inner concentric cylinder 16 (i.e., the combustion chamber) to the interior of the inner concentric cylinder 16 (i.e., the combustion chamber) to provide a running tally of the combustion temperature. A grate 90 is disposed atop the sliding gates 70, 72 and 74.

GENERALIZED DESCRIPTION OF THE KILN In more general terms, the kiln consists of three concentric cylinders erected on a common base and sealed at the top. The inner cylinder (the combustion chamber) has a perforated base. The annulus between the inner concentric cylinder and the middle cylinder forms a jacket which is adapted to be filled with water which acts as a heat dissipater to keep the temperature of the inner cylinder wall substantially constant at about 100 degrees C. The annulus between the outer cylinder and the middle concentric cylinder is lagged with a thermal insulator, e.g. a glass fiber batt. The top cover of the kiln is also made of two concentric cylinders and is also lagged with a thermal insulator, e.g. a glass fiber batt. A bucket-shaped funnel is provided in the top cover of the kiln. The bucket-shaped funnel includes a cone and cap system fitted underneath it to allow the agricultural waste to be fed into the combustion chamber in batches. The cone and cap system is mechanically operated by a lever system which is manually operated either by a pedal at the base of the kiln, or by a handle at the side of the kiln.

Beneath the perforated plate of the combustion chamber are three manually-operated sliding gates which are positioned around the combustion chamber. These sliding gates can be pulled either to widen or to narrow the slot providing the inflow of air into the combustion chamber as a means of temperature control. Temperature readings are made possible by a thermocouple which is affixed to the body of the kiln, with probes extending, preferably, to the middle of the combustion chamber. The frusto-conical bottom of the combustion chamber is equipped with an additional shutter which collects the ashes and which can be pulled out manually to discharge the ashes into an ash collector. According to aspects of the present invention, temperature control within the above- recited specified narrow range is achieved through the described novel control system which is constituted by the combination of evaporation of water in the water jacket and the use of excess air ratio through the mechanical manipulation of the sliding gate, the excess air ratio being greater than 1.5. EXAMPLE 1

This is an example of the controlled combustion of cocoa pod husks to produce ashes from which potash may be recovered, although it is equally applicable to the controlled combustion of the other agricultural wastes, e.g., plantain (and banana) peels and cola nut husks as mentioned hereinabove. The cocoa pod husks are subjected to controlled combustion in the above-described portable kiln at an average temperature of about 600 °C (i.e., between about 550 °C and about 650 °C) to produce ashes from which potash may be recovered. Ash yield from the dried husks consisted of about an average of 7.2%. The resulting ash contained about 75% potash as potassium carbonate. The potash may be extracted from the so-produced ashes by any conventional means. It attains a purity of over 99%.

Unlike mined potash which is contaminated with heavy metals (e.g., arsenic) the only impurities in this organic potash are iron, calcium and magnesium constituting less than 1%. This makes the organic potash a premium product which is suitable for the pharmaceutical and food industries. This potash is also useful in the production of animal feed supplements, cement, fire extinguishers, photographic chemicals, textiles, in brewing beer, as a catalyst for synthetic rubber manufacturing and in all applications where potash is needed. INDUSTRIAL APPLICABILITY

Potash is important for agriculture because it improves water retention, yield, nutritional value, texture and disease resistance of food crops. It has wide application in the farming of fruits, vegetables, rice, wheat and other grains, sugar, corn, soybeans and cotton, all of which benefit from the nutrient's quality enhancing properties. Potash-based fertilizers have greatly contributed to economic growth in Africa, Asia and Latin America.

In summary, the benefit of achieving this ability to produce substantially -pure potash from the ashes of agricultural wastes, preferably the ashes of cocoa pod husks, plantain (and banana) peels and cola nut husks, is that it generates a finished potash product, which unlike mined potash, is substantially free from arsenic, and is therefore useable in the food and the pharmaceutical additives industries.

As fully described above, applicant has discovered that to optimize the yield and quality of potash from agricultural wastes these agricultural wastes should be combusted to ashes within a controlled narrow temperature range of about 550 °C to about 650 °C. CITATION LIST

PATENT LITERATURE

US Patent No 3,842,762, issued Oct 22, 1974 to Grumman Ecosystems Corporation for "Apparatus for Disposing of Solid Wastes".

US Patent No 4,037,543, issued July 26, 1977, to Angello, II, for "Pollution Free Combustion Apparatus and Furnace".

US Patent No 4,091,228, issued May 23, 1978 to United States Steel Corporation for "Water Cooled Shell for Electric Arc Furnaces". US Patent No 4,092,098 , issued May 30 1978, to Monsanto Company for "Method and Apparatus for Improved In Situ Combustion of Pyro lysis Gases in a Kiln".

US Patent No 4,199,652, issued Apr 22, 1980, to Longenecker for "Air Cooled Electric Arc Furnace".

US Patent No 4,206,312 issued Jun 3, 1980 to Sidepal SA for "Cooled Jacket for Electric Arc Furnaces".

US Patent No 4,418,893, issued Dec 6 1983, to Combustion Engineering Inc for "Water Cooled Refractory Lined Furnaces".

US Patent No. 4,584,180, issued Apr 22, 1986 to Cool Water Coal Gasification Program for "Gas Injection Apparatus". US Patent No 4,734 166, issued Mar 29, 1988, to Angello II, for "Furnace for the Selective Incineration or Carbonization of Waste Materials".

US Patent No 4,793,269, issued Dec 27, 1988 to Westinghouse Electric Corp for "Kiln for Waste Disposal". US Patent No 4,973,245, issued Nov 27, 1990 to Outokumpu Oy for "Method for Cooling a Kiln Furnace".

US Patent No 5,230, 617, issued Jul 27,1993, to Klein et al, for "Furnace Shell Cooling System". US Patent No 5,350,296, issued Sep 27, 1994 to ABB Flakt AB, for a "Method and Device for Cooling a Rotary Kiln".

NON PATENT LITERATURE

"Chemical Studies of Some Plant Wastes From Ghana" E.K. Ankrah, Journal of the Science of Food and Agriculture, Vol. 28, issue 10, pages 1229 - 1232, 1984. "Extraction of Potash From Cocoa Pod Husks" B. K. Simpsion et al, Agricultural Wastes, Vol. 13, issue 1, pages 69 -73, 1985.

"Effect of Ripening on the Chemical Composition of Plantain Peels and Pulp" L.Welford -Abbey, et al, Journal of the Science of Food and Agriculture, Vol. 45, issue 4, pages 233-336, 1988. "Extraction and Potential Application of Caustic Potash From Kola Husk, Ugwu Pod Husk and Plantain Peels", A. A. Taiwo et al, Scientific Research and Essay, Vol. 3 (10), pages 515 -517, October 2008.

"Chemical studies of some plant wastes from Ghana" E.K. Ankrah Journal of the Science of Food and Agriculture, Vol 28, issue 10, pages 1229 - 1232, 1984. "Extraction of potash from cocoa pod husks" B. K. Simpson et al Agricultural Wastes, Vol 13 issue 1 pages 69 -73, 1985

Claims

A portable kiln for the combustion of agricultural wastes, preferably cocoa pod husks, plantain (and banana) peels and cola nut husks comprising: a central cylindrical combustion chamber, the central cylindrical combustion chamber including a system for the control of combustion air to the combustion chamber; a second concentric cylinder surrounding the central cylindrical combustion chamber, the second concentric cylinder including a system for the flow of cooling water through a first annulus between the central combustion chamber and the second concentric cylinder; a system for the feeding of the agricultural waste into the central combustion chamber; a temperature sensing device to measure and display the temperature within the central combustion chamber during the combustion of the agricultural waste; a system for the recovery of ash from the kiln; and a system to enable controlling the temperature of combustion to between about 550°C and about 650°C by a combination of increasing the supply of combustion air when the temperature in the central combustion chamber falls to about 550°C, and the introduction of cooling flowing water through the first annulus between the central combustion chamber and the second concentric cylinder when the temperature in the central combustion chamber approaches about 650°C. The portable kiln as claimed in claim 1 , wherein the three concentric cylinders are erected on a common base and are sealed at the top, and preferably wherein the inner combustion chamber cylinder has a perforated base.

The portable kiln as claimed in claim 1 or claim 2, wherein an annulus between the inner concentric combustion chamber cylinder and the middle cylinder forms a jacket which is adapted to be filled with water which acts as a heat dissipater to keep the temperature of the inner cylinder wall substantially constant at about 100 °C.

The portable kiln as claimed in any one of claims 1 to 3, inclusive, wherein an annulus between the outer cylinder and the middle concentric cylinder is lagged with a thermal insulator, e.g. a glass fiber batt, and also, preferably, wherein a top cover of the kiln is also made of two concentric cylinders and is also lagged with a thermal insulator, e.g. a glass fiber batt.

The portable kiln as claimed in any one of claims 1 to 4, inclusive, wherein the system for the feeding of the agricultural waste into the central combustion chamber comprises a funnel, preferably bucket-shaped in the top cover of the kiln, the funnel preferably including a cone and cap system fitted underneath it to allow the agricultural waste to be fed into the combustion chamber in batches, the cone and cap system preferably being mechanically operated by a lever system which is manually operated either by a pedal at the base of the kiln, or by a handle attached to the sides of the kiln.

6) The portable kiln as claimed in any one of claims 1 to 5, inclusive, wherein the

temperature sensing device to measure and display the temperature within the central combustion chamber during the combustion of the agricultural waste preferably comprises a thermocouple which is affixed to the body of the kiln, with probes extending, preferably, to the middle of the combustion chamber.

The portable kiln as claimed in any one of claims 1 to 6, inclusive, wherein a system to enable controlling the temperature of combustion to between about 550 °C and about 650 °C by increasing the supply of combustion air when the temperature in the central combustion chamber falls to near 550 °C, preferably comprises three manually-operated sliding gates beneath the perforated plate of the combustion chamber and which are positioned around the combustion chamber, the sliding gates being structured to be able to be pulled either to widen or to narrow the slot providing the inflow of air into the combustion chamber as a means of temperature control, preferably where the excess air ratio is greater than 1.5.

The portable kiln as claimed in any one of claims 1 to 7, inclusive, wherein the system to enable controlling the temperature of combustion to between about 550 °C and about 650 °C preferably comprises the introduction of cooling flowing water through the first annulus between the central combustion chamber and the second concentric cylinder when the temperature in the central combustion chamber approaches 650 °C either manually by reading the temperature of the thermocouple or automatically by means of a signal generated by the thermocouple.

The portable kiln as claimed in any one of claims 1 to 8, inclusive, wherein a frusto- conical bottom of the combustion chamber is equipped with an additional shutter which collects the ashes and which can be pulled out manually to discharge the ashes into an ash collector.