Biomass carbonisation system

Abstract

There is disclosed a system for carbonisation of biomass, such as coconut shells. The system uses a rotary kiln and a feeder located at a first end of the rotary kiln for feeding biomass into the kiln

Description

The present invention relates to a biomass carbonisation system for producing activated carbon. Background Activated carbon / activated charcoal is a charcoal material that has been reheated and oxidized (“activated”) to increase porousness. Organic material, such as biomass, can be turned into activated charcoal / carbon. Coconut shells are often used to create activated carbon due to their sustainability and physical properties. The coconut shells first go through a charring process, also known as pyrolysis. This is heating of the shells in the absence of oxygen. Pyrolysis of coconut shells typically takes place in a rotary kiln or drum kiln where the shells are subject to temperatures between 300°C and 500°C. This stage takes about 12 hours. This stage typically takes around 12 hours in a drum kiln and 30 to 60 minutes in an industrialised rotary kiln. The air flow is cut off to the bottom layer of the drum to allow the shells to cool. This creates coconut charcoal, also known as coconut carbon. Oxygen absence in an industrialised rotary kiln is typically achieved by a suction fan or draft fan. The next step is to activate the coconut carbon / charcoal. A steam process is used for activation, this is where an inert gas is brought to a temperature of around 800°C to 1100°C in a rotary kiln, creating steam which dehydrates the charcoal. The traditional methods for generating activated charcoal from biomass require high temperature for extensive periods of time, which in turn requires a lot of fuel- making the process expensive. As not all parts of the coconut, or biomass, can be turned into activated charcoal, this creates waste. Waste can attract unwanted pests, such as mosquitos, affecting the health of the nearby population. 27 10 25 It is an aim of the invention to provide an apparatus and method that mitigates one or more of the above-mentioned problems. 5 Statements of invention According to a first aspect of the invention there is provided biomass carbonisation system comprising; a rotary kiln for carbonising biomass, a feeder located at a first end of the rotary kiln for feeding biomass into the kiln, at least one burner for heating the kiln, a discharge receiver located at a second end of the rotary kiln for receiving io discharged biomass from the rotary kiln, wherein the rotary kiln is polygonal in cross section, and the system further comprises a support fuel chamber located below the kiln for combusting waste biomass and heating the kiln, wherein the support fuel burner comprises a cuboid and is uniformly aligned with the bottom section of the polygonal kiln. 15 According to a second aspect of the invention there in provided a method for carbonising biomass comprising; putting biomass into a feeder, moving the biomass into a rotary kiln having a polygonal cross section using a feeder, heating the rotary kiln with at least one burner, charring the biomass in the rotary kiln, discharging the 20 charred biomass from the kiln into a discharge container, providing additional heat to the rotary kiln by burning waste biomass in a support fuel chamber heating. Optional features are defined in the dependent claims. 25 Detailed description Practicable embodiments of the invention are described in further detail below with reference to the accompanying drawings, of which: Figure 1 shows a schematic side view of the biomass carbonisation system 30 in accordance with an example of the invention. Figure 2 shows a schematic cutaway view of the biomass carbonisation system in accordance with an example of the invention. Figure 3 shows a schematic cross-sectional view of part of the biomass carbonisation system in accordance with an example of the invention. 27 10 25 The combustion system 102 comprises a rotary kiln 108, a biomass combustion chamber 109, at least one burner (not shown), and a carbon discharge system 110. The rotary kiln 108 is the primary combustion chamber. The rotary kiln 108 comprises a first end located at the waste feed system 101 and a second end located at the carbon discharge system 110. The hydraulic ram 107 pushes the biomass into a first end of the rotary kiln 108, the biomass then travels through the rotary kiln 108. The rotary kiln 108 comprises an elongate prism. The rotary kiln 108 comprises a polygonal cross section. Preferably the rotary kiln 108 has a hexagonal cross section. The kiln 108 comprises a minimum horizontally slope of 1 degree. The slope may be of the order of 1 degree horizontally. For example, the horizontal slope may be between 1 °, 2°, or 3°, and 5°, 8°, and 9°. Preferably the horizontal slope of the rotary kiln is 5°. The slope of the kiln 108 allows the easy of movement of the biomass from the waste feed system 101 to the carbon discharge system 110. The kiln 108 comprises a variable speed gear motor (not shown). The variable speed gear motor drives the rotation of the kiln via a girth gear. The kiln 108 is supported on trunnions located across the length of the kiln 108. The drive system design of the kiln shall allow for the variable speed control of the speed of the rotary kiln between 0.2rpm to 2rpm. The rotation speed of the kiln may be of the order of 1rpm. For example, the rotation speed may be between 0.1 rpm, 0.2rpm, or 0.3rpm, and 1 rpm, 2rpm, and 3rpm. The rotary kiln 108 is equipped with at least one burner (not shown). The burner is located externally and heats the kiln 108 from the outside. The burner may be located underneath the kiln 108. The burner may be located at the first end of the kiln 108. The rotary kiln 108 may comprise a plurality of burners along the length of the kiln 108. There may be provided first burner located at the first end of the kiln 108 and second burner located at the second end of the kiln 108. There may be provided a plurality of burners spaced equally along the entire length of the kiln 108. The burners may be dual fuel (liquid and gas) operation burners. The burners may be capable of combusting heavy oil. There is also provided a biomass combustion chamber 109 located beneath the rotary kiln 108. The biomass combustion chamber 109 is a support fuel chamber. The biomass combustion chamber 109 may be provided under the entire length of rotary kiln 108. Alternatively, the biomass combustion chamber 109 may extend under part of the length of the rotary kiln 108. The biomass combustion chamber 109 may be located under the middle of the kiln 108 between the first and second ends and may only heat the middle section of the kiln 108. The biomass combustion chamber 109 combusts biomass which is not intended for carbonisation. The biomass combustion chamber 109 combusts waste biomass as fuel. In this example, the biomass combustion chamber 109 combusts the husks of the coconuts. The biomass combustion chamber 109 is a support fuel chamber. The biomass combustion chamber 109 is fed by a separate waste feed system 111 to the rotary kiln 108. The first waste feed system 101 feeds the rotary kiln 108 and the second waste feed system 111 feeds the biomass combustion chamber 109. The second waste feed system 111 comprises a hopper, a receiving box and a conveyor. Waste biomass which cannot be used for carbonisation, such as coconut husks, can be loaded into the second waste feed system 111 to feed the biomass combustion chamber 109. The second waste feed system 111 comprises a conveyor located below the hopper. The biomass combustion chamber conveyor may comprise a screw conveyor. The receiving box surrounds the screw conveyor. The screw conveyor can be used to transport granular biomass waste, such as coconut husk, to the biomass chamber to be used as fuel. The screw conveyor may comprise stainless steel un order to withstand high temperatures and corrosion. The screw conveyor comprises an explosion proof motor which drives the screw conveyor. The biomass combustion chamber 109 deposits the remains of the biomass after combustion into an end box (not shown). The biomass combustion chamber 109 may be heated by flue gas from the rotary kiln 108. The biomass combustion chamber 109 heats the rotary kiln 108. The biomass combustion chamber 109 supports the burner or burners to heat the rotary kiln 108. The biomass combustion chamber 109 comprises a cuboid. The biomass combustion chamber being comprising cuboid creates the optimum arrangement for combustion of high flow rate gas streams. The biomass combustion chamber 109 may comprise an air blower. The air blower provides air supply to the biomass combustion chamber 109 when combusting biomass. The biomass combustion chamber 109 is designed to combust waste biomass as fuel to support the burners and reduce the natural gas and fossil fuel usage. This additional combustion within the biomass combustion chamber 109 provides thermal energy to the rotary kiln for the carbonisation of biomass. The biomass combustion chamber 109 is lined with a layer of castable high alumina refractory. The thickness of the layer may be of the order of 100mm. For example, the thickness may be between 50mm, 60mm, or 70mm, and 100mm, 150mm, and 200mm. Preferably the thickness of the high alumina refractory which lines the biomass combustion chamber is 120mm. The biomass combustion chamber 109 is of a size that it can be powered by flue gas. The flue gas provides the necessary energy for the combustion of the waste biomass. The burner or burners bring the kiln 108 to its operational temperature. The operational temperature is maintained by the biomass combustion chamber 109 and an additional burner or additional burners if required. The carbon discharge system 110 is located at the second end of the rotary kiln 108. The carbon discharge system 110 comprises a breaching box 112 and a trap door within the breaching box 112. The product resulting from the combustion in the kiln 108 passively drops in the breeching box 112. The breeching box comprises a refractory material lining. The trap door is located at the breeching box 112. The trap door is mass sensitive. The mass sensitive trap door holds the product of the rotary kiln 108 until it reaches a set mass when it then swings open and drops the product into a box for further cooling and storage. The mass at which the door swings open is calculated based on the output of the kiln 108 to allow the product to be held until it cools to a set temperature. The temperature at the second end of the kiln 108 is lower than at the first end of the kiln 108. The second end of the kiln 108 requires a lower temperature such that the biomass product can being cooling before it reaches the discharge system 110. Figure 2 shows a schematic cutaway view of the biomass carbonisation system in accordance with an example of the invention. The air pollution control system 103, comprises a hot cyclone (now shown), a wet scrubber system 113, a dewatering cyclone (not shown), at least one blower (now shown), a second combustion chamber 114 and a flue gas exhaust stack (now shown). Flue gasses from the rotary kiln 108 are directed into a pipe. The pipe comprises a line to the secondary combustion chamber 114 and a bypass line. The bypass line may be directed to the biomass combustion chamber 109 or other parts of the biomass combustion system that require thermal energy. The bypass line comprises an isolation valve. The isolation valve controls the flow of the flue gasses from the rotary kiln 108 through the bypass line to other parts of the biomass combustion system such as the biomass combustion chamber 109. The bypass line may comprise an induced draft fan. The induced draft providing suction to create a flow flue gas within the flue gas bypass line. When flue gasses are not directed to the bypass line, they enter the secondary combustion chamber 114. The secondary combustion chamber 114 combusts volatile gases. The secondary combustion chamber 114 combusts the gas with oxygen to turn any carbon monoxide into carbon dioxide. The secondary combustion chamber ensures gas concentrations in the flue gas is low enough to be emitted into the atmosphere. The secondary combustion chamber also removes moisture from the flue gas. The biomass combustion chamber may intermittently send flue gas through the secondary combustion chamber to remove moisture. The secondary combustion chamber may comprise an emergency stack. The emergency stack is used to discharge flue gas in case of a process failure, for example failure of the induced draft fan. The preferred dimensions of the secondary combustion chamber are: • Diameter: 1.35m • Length: 6.77m • Volume: 9.75m3 The flue gasses from the secondary combustion chamber are directed into the hot cyclone. The hot cyclone may be located at the second end of the rotary kiln 108. The hot cyclone may be installed immediately after the rotary kiln 108. The hot cyclone comprises stainless steel and a high alumina refractory concrete lining to withstand the high temperatures of the flue gas stream. The hot cyclone collects fly ash out of the flue gas stream from the rotary kiln. The hot cyclone operates on vortex separation. The air flow within the hot cyclone forced the fly ash particulates to settle at the bottom of the hot cyclone. Fly ash with a diameter of 30 microns or more are trapped at the bottom of the hot cyclone. The hot cyclone may comprise boiler plate steel. The de-dusted flue gas from the hot cyclone is then transferred into a series of wet scrubber arrangements for further cooling and cleaning of the flue gas stream prior to discharge to atmosphere. The wet scrubber system 113 may comprise a quench scrubber and a packed bed scrubber. Alternatively, the wet scrubber system may comprise a quench scrubber. The quench scrubber comprises a storage tank for storing water. Water is used by the quench scrubber to cool the flue gas to a temperature below 100°C. The quench scrubber may comprise a venturi throat. The venturi throat of the quench scrubber comprises a fixed diameter. The venturi throat maximises the collection of any remnant fly ash in the flue gas stream. The quenching action prevents the possible reformation of dioxins and furans downstream of the air pollution control system 103. The quench scrubber comprises a water recirculation system. A 100% redundancy is provided for the pumps delivering the quench solution to the quench scrubber. The liquid effluent from the quench scrubber will be routed to a system of of sedimentation and clarification chambers. The liquid from the sedimentation and clarification chambers is then passed through a bed of activated charcoal for further purification before being discarded. The packed bed scrubber comprises a plurality of pall rings, at least one pump and a storage tank. Scrubber solution is stored within the storage tank and pumped through the plurality of pall rings of the packed bed scrubber. The scrubber solution is pumped through the packed bed scrubber in a direction opposite to the flue gas. The counter-current motion of the flue gas and scrubber solution remove acid and toxic gases such as SOx, NOx, and HCI through a process of absorption and neutralisation. The scrubbing solution comprises a recirculation system. The scrubbing solution feed system is 100% redundant to reduce operational failure. The quench scrubber is connected to the dewatering cyclone. If a packed bed scrubber is included in the wet scrubber system, the flue gas is passed from the quench scrubber to the packed bed scrubber and then to the dewatering cyclone. If no packed bed scrubber is present, the flue gasses pass directly from the quench scrubber to the dewatering cyclone. The dewatering cyclone comprises a mist eliminator. The dewatering cyclone operates vortex separation to remove remnant moisture from the flue gas stream. The air pollution control system may comprise a plurality of dewatering cyclones. The flue gas exhaust stack comprises pipe stack and an induced fan. The pipe stack may comprise steel. The pipe stack may comprise 30m. The pipe stack may comprise a support skirt and base arrangement. The base arrangement may be bolted to a concrete foundation. The induced fan is located between the exhaust stack and the dewatering cyclone / cyclones. The induced fan forces flue gasses out of the biomass combustion system 100 and into the atmosphere. The at least one blower comprises a fan and an electric motor. The electric motor comprises an explosion proof high speed electric motor. The fan may be a centrifugal fan. The blower is of a size that it is capable of handling 200% of the flue gasses and leak-air generated in the carbonisation system. The blower has a maximum unlet gas flow rate of around 11,000acfm. The biomass carbonisation system may comprise a control panel 100. The control panel comprises a PLC system. The control panel allows remote operation of the biomass carbonisation system 100. The biomass carbonisation system 100 may further comprise a plurality of sensors. The sensors may comprise any one of a combination of temperature sensors, fluid level sensors, or flowrate sensors. The sensors are placed across the carbonisation system 100 to obtain operational data such that the apparatus of the system can be controlled to operate at maximum efficiency. The conveyors may be controlled by the control panel. The electric motors driving the screw conveyor and the belt conveyor 104 may be controlled by the control panel to restrict the volume of biomass entering the primary combustion chamber and the secondary combustion chamber. The hydraulic ram 107 may be controlled by the control system. The rotation of the rotary kiln 108 may be controlled by the control system. The variable speed gear motor may be controlled by the control system. There may be at least one temperature monitor provided along the length of the rotary kiln 108. There may be a plurality of temperature sensor provided alone the length of the rotary kiln 108. There may be temperature sensors located at the first end of kiln, the second end of the kiln and at the centre of the kiln. The burner or burners are controlled by the control system. The burner or burners may be ignited remotely by via the control system. The packed bed scrubber may be controlled by the control panel. Biooil created from the biomass combustion chamber 109 may be monitored at the end box of the biomass combustion chamber 109. The flue gas exhaust stack may comprise a continuous emission monitoring system. The continuous emission monitoring system allows for live emission monitoring of the biomass carbonisation system 100. Based on emission monitoring, operational conditions can be adjusted for maximum system efficiency. Figure 3 shows a schematic cross-sectional view of part of the biomass carbonisation system in accordance with an example of the invention. The biomass carbonisation system is mounted on a structural support system 300. The structural support system 300 may also support the scrubbing solution and water recirculation systems of the air pollution control system. The structural support comprises a skid 301. The skid 301 is approximately 12m by 5m. The skin may comprise a plurality of 300mm I-beams. The support structure is designed to support the entirety of the biomass carbonisation system. The rotary kiln 108 is located at one end of the skid 301. The rotary kiln 108 comprises an elongate prism encased in a cylindrical cover 302. The external cylindrical cover 301 allows for easy rotation of the kiln 108. The rotary kiln 108 has an internal hexagonal cross section. Alternatively, the rotary kiln 108 may comprise any polygonal shape. It is essential the internal walls of the kiln 108 comprise a plurality of substantially flat surfaces. The flat sections or surfaces of the internal walls of the kiln provide for improved heat transfer. The carbonisation method is created by indirect heating and therefore improved heat transfer increases efficiency of the carbonisation system. The rotary kiln 108 comprises a layer of castable high alumina refractory on the internal walls of the kiln 303. The thickness of the layer 303 may be of the order of 100mm. For example, the thickness may be between 50mm, 60mm, or 70mm, and 100mm, 150mm, and 200mm. Preferably the thickness of the high alumina refractory on the wall of the kiln is 120mm. The layer of castable high alumina refractory on the walls of the kiln to conserve heat during the process. The refractory prevents the loss of heat to the environment from the combustion operations within kiln. The biomass combustion chamber 109 may uniformly align with the bottom section of the polygonal kiln 108. The uniform alignment creates more efficient heat transfer process from the biomass combustion chamber 109 to the polygonal kiln 108. The biomass combustion chamber may comprise carbon steel. The kiln comprises a variable speed gear motor. The variable speed gear motor drives the rotation of the kiln via a girth gear. The kiln is supported on a plurality of trunnions 304 located across the length of the kiln. In this example there are two trunnions 304. Each trunnion comprises a pillow block bearing 305 and a steel roller 306. The trunnions may be spaced approximately 4 meters apart below the rotary kiln. The preferred dimensions of the polygonal rotary kiln are as follows: • Diameter: 1.52m • Refractory thickness: 224mm • Wall thickness: 19mm • ID: 1.26m • Length: 9m The minimum internal volume of the rotary kiln may be 7.36m3. The preferred internal volume of the rotary kiln is 11.87 m3. The kiln may comprise boiler plate steel. The kiln may comprise 19mm thick boiler plate steel. All motors used in the carbonisation system are explosion proof. The flue gas from the carbonisation process are heavy with usable fuels and hence easily combustible near a spark. Should there be an accidental leak in the kiln, this could lead to an electrical fire hazard. Method of carbonisation of biomass The biomass carbonisation can be used with any suitable biomass for carbonisation. This example uses coconuts. Firstly, the coconuts shells are emptied and the husks removed. The coconut shells are loaded onto the belt conveyor 104 of the first waste feeding system 101. The belt conveyor 104 and is controlled by the control panel. The belt conveyor 104 may transport 300 kg of biomass per hour. Biomass on the belt conveyor 104 is elevated to the hopper 105 and falls off the end of the conveyor 104 into the hopper 105. The hopper 105 directs the biomass into a receiving box 106. The hydraulic ram 107 then pushes the biomass into the rotary kiln 109. The hydraulic ram 107 is time controlled to load the biomass into the primary combustion chamber every 10 mins. The kiln is sized to carbonize a minimum of 300kg of biomass every hour at a temperature of 600°C. The kiln is designed for continuous operation. The kiln is angled at 5 degrees off horizontal. The 5 degree angle allows for the easy movement biomass from the loading end of the kiln (the first end) to the discharge end of the kiln (the second end). The kiln shall be sized to ensure a minimum residence time of 30 minutes. The kiln is driven by a variable speed gear motor via a girth gear and supported on trunnions across the length of the kiln. The drive system which rotates the kiln allows for the variable speed of rotation between 0.2rpm to 2.0 rpm. The rotary kiln or primary combustion chamber is equipped with at least one burner to create a combustion temperature of up to 1200°C. Preferably the rotary kiln operates at the following parameters: • Feed Rate: 300kg / hr • Heat Release Rate (Q): 6.5 x 106BTU / Hr • Acceptable Heat Release Rate (qh): <25,000Btu / h-ft3 • L / D Ratio (Minimum): 4 • Desired Heat Release Rate: 15,500BTU / h-ft3 Once the biomass has passed through the kiln it passively drops into a discharge receiver. The discharge receiver comprises a mass sensitive trap door which holds the discharges biomass until it reaches a set temperature which is low enough to store. The mass which forces the trap door to open is calculate based on how much mass is created within the time taken for the mass to cool to a low enough temperature for storage. Flue gas is created by the rotary kiln. Flue gasses from the rotary kiln 108 are directed into a pipe. The pipe comprises a line to the secondary combustion chamber 114 and a bypass line. The bypass line may be directed to the biomass combustion chamber 109 or other parts of the biomass combustion system that require thermal energy. The bypass line comprises an isolation valve. The isolation valve controls the flow of the flue gasses from the rotary kiln 108 through the bypass line to other parts of the biomass combustion system such as the biomass combustion chamber 109. The bypass line may comprise an induced draft fan. The induced draft providing suction to create a flow flue gas within the flue gas bypass line. The biomass combustion chamber is heated using the flue gas from the rotary kiln. The husks of the coconut, also referred to as waste biomass, are loaded into a hopper of a second waste feed system. The husks pass through the second hopper and onto a screw conveyor where they are loaded into the biomass combustion chamber. Air is introduced to the biomass combustion chamber by a blower when the husks are combusting. The husks combusting in the biomass combustion chamber provides thermal energy to the rotary kiln. This reduces the burners needed to heat the rotary kiln to its operational temperature. The flue gas from the biomass combustion chamber intermittently is sent through the second combustion chamber to remove moisture from the flue gas. The combusted husks passively drop into an end box located at the opposite end to the biomass combustion chamber to the second waste feed system. When flue gasses are not directed to the bypass line, they enter the secondary combustion chamber 114. The secondary combustion chamber 114 combusts volatile gases within the flue gas. The secondary combustion chamber ensures gas concentrations in the flue gas is low enough to be emitted into the atmosphere. The flue gas then enters a hot cyclone from the secondary combustion chamber 114. The hot cyclone removes fly ash with a diameter of 30 microns or more from the flue gas. The flue gas is then transferred into a wet scrubber system for further cooling and cleaning of the flue gas stream prior to discharge into the atmosphere. The wet scrubber system may comprise a quench scrubber and a packed ped scrubber. Alternatively, the wet scrubber system may comprise a quench scrubber. The first scrubber of the wet scrubber system the flue gas is passed through is a quench scrubber. The quench scrubber uses water to cool the flue gasses to below 100°C. The quench scrubber comprises a storage tank. The storage tank is for storing water for the quench scrubber. The water storage tank comprises an isolated system. The water emitted from the quench scrubber is routed to a set of sedimentation and clarification chambers and finally passed through a bed of activated charcoal for further purification. The water then may be reused by the quench scrubber. The scrubber solution tank comprises an isolated system. The flue gasses pass from the wet scrubber system into an induced draft fan, also referred to as a blower. The blower is capable of handling 200% of the flue gases and leak-air generated in the biomass carbonisation system. The system is rated for a maximum inlet gas flow rate of about 11,000acfm. The flue gasses move from the blower to the dewatering cyclones. The dewatering cyclones remove moisture from the flue gasses using a mist eliminator. The flue gasses pass from the dewatering cyclones into the flue gas exhaust stack. The flue gas exhaust stack maintains a maximum static pressure of -3.0mmH20. The flue gasses are emitted from the flue gas exhaust stack into the atmosphere. This is monitored using a continuous emission monitoring system. The continuous emission monitoring system ensures the air pollution control system is working efficiently. Various operational advantages to the carbonisation of the biomass for the production of high-grade carbon. This includes: • 40% improved fuel efficiency • Higher production capacity in polygonal kiln due improved contact area • Introduction of thermal energy from biomass combustion chamber • Improved disposal of waste biomass in biomass combustion chamber • Improved system energy performance • Improved product quality due to reduced ash content (higher surface contact in polygonal kiln) • Ease of construction of carbonisation chambers versus cylindrical rotary kilns • Improved combustion of biomass feed material due to improved contact area in polygonal rotary kiln Method of activation of carbonised biomass The biomass carbonisation system can also be used for the activation of carbon / charcoal as a stand-alone activity. Biomass, such as coconut shells, that have been carbonised as above, are cooled and stored for a batch activation process. Due to material losses during the carbonisation process, there is typically 30% to 40% of the initial mass remaining after carbonisation. Carbon produced from daily operations of the biomass combustion system is expected to be about 30% to 40% weight of the initial biomass. The carbonisation product is loaded into the kiln 109 using the waste feeding system 101 as described in the method of carbonisation of biomass. The hydraulic ram 107 is time controlled to load the carbonisation product into the primary combustion chamber every 10 mins. The kiln is sized to activate a minimum of 300kg of the carbonisation product every hour at a temperature of 900°C. Steam is introduced into the kiln for the activation of the carbonisation product. The steam is produced using a steam generator which is connected to the rotary kiln using carbon steel piping for introduction of the steam into the kiln. The carbonisation product becomes activated in the kiln. The product of the activation process is activated carbon / charcoal. Once the carbonisation product has passed through the kiln it passively drops into a discharge receiver. The mass sensitive trap door which holds the discharges the activated carbon / charcoal until it reaches a set temperature which is low enough to store. Flue gas is created by the rotary kiln and directed into the biomass combustion chamber. The biomass combustion chamber is heated using the flue gas from the rotary kiln. The steam generator may utilise thermal energy from the flue gas from the rotary kiln. The flue gas stream from the activation kiln is directed to the secondary combustion chamber for the combustion of volatile gases prior to environmental discharge. Following combustion in the secondary combustion chamber, the flue gas stream then goes to an exhaust stack using and induced draft fan where it is released to the atmosphere. The enhanced polygonal kiln is utilized in the activation process and the provides significant energy savings using the biomass burning box in comparison to a cylindrical rotary kiln. 27 10 25

Claims

1. A biomass carbonisation system comprising:a rotary kiln for carbonising biomass;5 a feeder located at a first end of the rotary kiln for feeding biomass into the kiln;at least one burner for heating the kiln;a discharge receiver located at a second end of the rotary kiln for receiving discharged biomass from the rotary kiln;wherein the rotary kiln is polygonal in cross section;io and the system further comprises a support fuel chamber located below the kiln for combusting waste biomass and heating the kiln;wherein the support fuel burner comprises a cuboid and is uniformly aligned with the bottom section of the polygonal kiln.15 2. The system of claim 1, wherein the kiln is hexagonal in cross section.

3. The system of claim 1 or 2, wherein the kiln is positioned at a 5 degree horizontal tilt.20 4. The system of any preceding claim, wherein the feeder comprises a hydraulic ram for pushing biomass into the kiln.

5. The system of any preceding claim, further comprising a variable speed gear motor for driving the rotary kiln.

256. The system of any preceding claim, wherein said at least one burner is located at the first end of the rotary kiln.30 7. The system of any preceding claim, wherein the feeder comprises a beltconveyor.27 10 258. The system of any preceding claim, comprising a second feeder for feeding the support fuel chamber, wherein the second feeder comprises a screw conveyor.

9. The system of any preceding claim, wherein the discharge receiver comprises a 5 mass sensitive trap door for holding discharged biomass from the kiln until it reaches a temperature low enough for storage.10.The system of any preceding claim, further comprising at least one temperature sensor provided along the length of the rotary kiln.io11 .The system of claim 10, wherein the at least one temperature sensor comprises a plurality of temperature sensor provided at the beginning, middle and end of the rotary kiln.15 12.The system according to any preceding claim, further comprising and airpollution control system.

13. A method for carbonising biomass comprising: putting biomass into a feeder;20 moving the biomass into a rotary kiln having a polygonal cross section using a feeder;heating the rotary kiln with at least one burner;charring the biomass in the rotary kiln;discharging the charred biomass from the kiln into a discharge container;25 providing additional heat to the rotary kiln by burning waste biomass in a cuboid support fuel chamber located below the rotary kiln and aligned with the bottom section of the kiln.

14. The method of claim 13, wherein the feeder provides the kiln with 300kg of 30 biomass per hour.15.The method of claims 13 to 14, wherein the kiln operates at a temperature of600°C.16.The method of claims 13 to 15, wherein the support fuel chamber is fuelled by flue gas from rotary kiln.5 17.The method of claims 13 to 16, wherein the temperature of the kiln is monitoredand the at least one burner is controlled remotely.27 10 25

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