GB2481212A

GB2481212A - A biogas production apparatus

Info

Publication number: GB2481212A
Application number: GB1009971.1A
Authority: GB
Inventors: Arvind Rajput
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-06-15
Filing date: 2010-06-15
Publication date: 2011-12-21
Anticipated expiration: 2030-06-15
Also published as: GB201009971D0; GB2481212B

Abstract

A Biogas digestion apparatus comprises a composter 2, preferably made of a high thermal conductivity material, which is built inside an anaerobic digester tank 1. The anaerobic digester tank 1 may contain feedstock (food waste paste) mixed with water which is inputted in to the tank at inlet 5 after passing through grinder 7. The composter 2 is typically submerged under the feedstock in the anaerobic digester tank and fed via inlet 18 with composting material such as garden waste. The composter maybe supplied with air via inlet 26 and the digested material maybe released via outlet 19. The heat generated by the hot composting process is transferred to the feedstock in the anaerobic digester tank via the composter's high thermal conductivity walls thus raising its temperature to assist anaerobic digestion which produces biogas. Advantageously, the biogas produced in the process is then fed to a storage tank from where it is further fed to a biogas consumption system.

Description

Apparatus for Biocias �roduction.

Field of the Invention:

This invention relates to Biogas production and Hot Composting apparatus or materials.

Note: For the purpose of this document the term low temperatures' refers to temperatures below 32 degree Celsius.

Background of the Invention:

The recycling of food waste currently proves to be a major environmental challenge and various initiatives are being undertaken to tackle this problem. Some current solutions like community projects have been successful to a limited extent and are not completely green as collection of food waste involves 002 emissions from vehicles collecting this waste. Also these solutions are not currently widespread and a considerable amount of food waste goes to landfill. The most efficient way to deal with food waste would be to tackle it at source i.e. if it could be recycled domestically. Some solutions have been developed, in particular, ARTI (Appropriate Rural Technologies Institute) in India has developed a compact domestic biogas digester which uses Anaerobic Digestion to recycle food waste and produce biogas for domestic use. This is the ideal way of dealing with food waste but unfortunately the solution only works well in temperatures above 32 deg C as the anaerobic digestion process relies on bacteria which thrive successfully in a certain temperature range (32 to 37 deg C). Therefore, in lower temperatures the Biogas Digester would need to be heated to the optimal temperature range by using electric or other heaters which generate C02 emissions directly or indirectly.

Hot Composting is a process which uses aerobic digestion for converting organic matter into compost thereby producing heat as a bi-product.

The invented apparatus uses the Hot Composting process and the Biogas production process to achieve an eco-friendly process for the production of Biogas in low temperatures.

Statement of the Invention:

The invented apparatus uses the hot composting process to aid the bio-digestion process for production of biogas and puts forward an innovatively designed apparatus for a Biogas digester plus composter which can be run in low temperatures (below 32 deg C) without the need of additional heating during its normal operation. The key feature of the invention is a Biogas Digester tank containing inside itself a composter made of high thermal conductivity material which facilitates an efficient transfer of heat generated from the hot composting material to the matter (water and food waste paste) in the Biogas Digester tank thereby raising its temperature and allowing anaerobic digestion and the production of biogas to occur in low temperatures (below 32 deg C) where the Biogas Digester would not have worked by itself due to low temperatures.

Advantages of the Invention: The invented apparatus has the following key advantages: * The food waste can be dealt with at source (domestically) and eliminates the emissions produced in transporting food waste.

* The food waste does not go to landfill, thereby benefiting the environment, where food recycling schemes are not in place.

* Domestic consumers are more likely to recycle food waste as it rewards them for their efforts by providing them with biogas fuel and compost for their own use.

* The invented apparatus uses completely natural processes during its normal operation and enables the use of domestic Biogas Digesters in low temperatures.

* The invented apparatus due to its unique design minimises the heat losses during the bio digestion processes (biogas production and compost production).

* The invented apparatus design can be used for large scale operations as well by combining large scale Biogas production and large scale composting operations.

Summary of the Invention:

A Biogas Digester plus Composter design is disclosed where a composter made of high thermal conductivity material is built inside a Biogas Digester tank containing feedstock (food waste paste) mixed with water. The composter is submerged under the matter in the tank and fed with composting material for hot composting. The heat generated by the hot composting process is transferred to the matter in the tank via the composter's high thermal conductivity walls thus raising its temperature to allow anaerobic digestion. The biogas produced in the process is then fed to a storage tank via a non-return valve and stored for use.

In the preferred embodiment the storage tank is made of two drums of different sizes, with the larger drum being filled with water and the small drum being inverted into the larger drum.

In one embodiment, the storage tank is a bellow type construction.

In one embodiment, the storage tank is made of a high tensile strength fabric which is spring loaded to maintain pressure in the tank.

Preferably, the composter is displaced to one side of the Digester tank (whilst still being surrounded by the matter in the tank) thereby reducing the required lengths of the inlet and outlet to allow easy access for adding I removing composting material.

In one embodiment, the composter is further displaced to one side of the Digester tank such that its wall is partially merged with the Biogas Digesters wall and doors are built into the shared sidewall to allow easy access inside the composter for its operation, servicing and maintenance.

This shared sidewall is made of low thermal conductivity material to avoid heat losses and can be covered by insulating material.

In the preferred embodiment, the composter has an inlet through the top of the side wall of the Digester tank for adding composting material and an outlet through the bottom of the sidewall of the Digester tank to enable removal of the composted material. The inlet and outlet of the composter protrude out from the sidewalls of the Digester tank and are covered by lids to prevent the loss of heat.

Preferably, the inlet and outlet are made of low thermal conductivity material in order to prevent heat losses to the external environment.

Preferably the composter's inlet lid is hinged type flap and has a bimetallic strip at its lip such that the strip pushes the lid open when temperature inside the composter reaches temperatures above 60 -65 deg c. This will prevent the aerobic bacteria being inactivated due to high temperatures.

In the preferred embodiment, the composter's outlet lid is a hinged flap which can be latched close to prevent the inadvertent flow of composting material from the outlet.

Preferably, the leachate drained from the composter outlet can be drawn to a collector placed under the Digester by means of a drain pipe.

Preferably, the composter has an airtight and watertight lid on top which can be opened for servicing and repairs.

In the preferred embodiment, the base of the composter is angled / sloping with the lower end towards the outlet to allow the composting material to slide out easily. The base of the composter has supports/struts running between the composter's base and the inner wall of the Digester tanks base.

In the preferred embodiment, the Digester tank used for anaerobic digestion is made of low thermal conductivity material and holds the water mixed with the feedstock and the composter.

The Digester tank has an inlet for adding the feedstock and outlets for the effluent and the biogas produced.

Preferably, Digester has an airtight lid on top which can be opened for servicing and maintenance if required.

In the preferred embodiment, the inlet of the Digester is in the form of a pipe taller than the digester and is connected to the digester at the bottom of the sidewall of the digester. A manual handle driven grinder is fitted to the mouth of the inlet pipe so that the food waste (feed) added can be mixed with water and ground into a paste before entering the digester. Supports to the inlet pipe are attached to the exterior wall of the digester to support the pipe when the grinder is In the preferred embodiment, the composter has an aerating pipe running inwards through its outlet and feeding a network of vertical aeration pipes.

In one embodiment, the composter has an aerating pipe running inwards through its outlet and feeding a single vertical aeration pipe.

In one embodiment, the digester containing the composter is placed on a hollow stand and has an aeration pipe that is run from the outside vertically through base of the digester and the base of the composter into the composting material to aerate it using external air and assist the hot composting process. In this embodiment, preferably, a fan is attached to the base of the digester below the inlet of the above mentioned aeration pipe. This fan can be run by linking it to the manual grinder by means of a geared or pulley mechanism so that it blows air into the compost when the handle of the manual grinder is rotated.

In the preferred embodiment, a fan/stirrer is placed inside the digester, at the point of inlet at the bottom of the digester and is linked by rods via a geared mechanism to the grinder. The grinder with the manual handle forms the rotating means for the fan in this embodiment. This fan/stirrer will assist in mixing and spreading the feed in the digester tank when the grinder is operated.

Due to the rods and the geared mechanism linking the fan to the grinder being built within the inlet pipe the need of puncturing an additional hole for the rod at the bottom of the digester and associated sealing of the hole is eliminated.

Preferably, plurality of fans can be attached along the length rods in the of the inlet pipe in order to aid mixing and to create suction and pressure to force the feed paste mixed with water inside the Digester tank thus distributing the feed across the digester.

Preferably, the fan at the bottom of the digester near the inlet can be linked to the grinder and run via a pulley type mechanism.

In one embodiment, the rod bearing the fan at the inlet of the digester is further elongated to run across the available internal width / diameter of the Digester and plurality of fans are attached to it along its length in order to mix the matter in the digester.

In one embodiment of the apparatus, the fan/stirrer mechanism and grinder is omitted.

In one embodiment of the apparatus, the grinder is not attached to the mouth of the inlet pipe and is maintained as a separate entity in the form of a container with a spout and the grinder attached on the top of the container such that the food waste can be mixed with water, ground to a paste and collected in the container ready to feed the Biogas Digester. In this embodiment, the grinder is attached to a stirrer inside the container to aid mixing. In this embodiment the fan / stirring mechanism in the Biogas Digester can still be retained and be driven by a rotating wheel with a handle attached to the mouth of the inlet pipe which in this case forms the rotating means for the fan.

In one embodiment, the grinder at the mouth of the inlet pipe is driven electrically.

In one embodiment, horizontal plates are fixed inside the Biogas digester and submerged inside the matter in the Biogas Digester in order to increase the surface area inside the digester.

Preferably, the inlet pipe of the digester is offset in position from the inlet and outlet of the composter so that it does not interfere while adding or drawing material from the composter.

Preferably, the digester tank and the gas storage tank are fixed with PRVs (Pressure relief valves) for safety.

Preferably, the apparatus can be connected to a wind powered turbine or solar panels wired to a heating element submerged in the matter within the apparatus in order to raise the temperature of the matter to the optimal range for Biogas production.

Preferably the heating element is connected to the power supply via a thermal cut out switch which cuts out the power supply to the heating element when the temperature of the matter in the digester reaches above optimum operating temperature.

Preferably, the non-return valve fitted between the digester and storage tank is made of low thermal conductivity material and is fitted as near as possible to the digester. This is in order to minimise the heat losses via the surface area of the outlet pipe and the storage tank.

Preferably, the gas outlet of the gas storage tank of Biogas Digester will be connected to a burner capable of burning the produced Biogas or another means of converting biogas energy into mechanical or heat energy.

Preferably, the apparatus itself can be placed in or surrounded by composting material if such material is available in large quantities.

Preferably, the invented apparatus can have an insulation jacket covering it to further minimise heat losses from the digester, especially during winter season.

Preferably, the biogas outlet of the storage tank will have a steel wood filter to filter out undesirable gases form the biogas.

In one embodiment, the effluent outlet of the digester is a sealed by a screw on lid to prevent leakage of gas in case of a fault. In this embodiment, the cap will need to be opened when feeding the Biogas Digester.

Preferably, the top of the Biogas Digester has hard points so that the gas storage tank can be placed on top of the digester in order to save space occupied on the ground.

Preferably, the biogas storage tank has a stop-cock at its gas outlet which can be used to stop the outflow of gas if required.

Preferably, humidity and temperature monitors can be fixed to the apparatus to measure the temperature of the matter in the digester and temperature and humidity of the matter in the composter.

Preferably, a pressure gauge can be fixed to the storage tank to measure the pressure of gas in the storage tank.

Preferably, the storage tank and the digester tank have indicators to show the level of water and matter, respectively, contained in them.

In one embodiment of the apparatus, the composter has an outlet at its top for hot gases to flow out. This outlet has a pipe made of high thermal conductivity material connected to it which runs though the matter in the Digester thereby transferring heat from the gases to the matter in the digester and cooling the gases. This pipe exits the digester at the bottom such that the outlet of the pipe is much lower than its inlet from the composter and the cooled gases gradually flow out of the apparatus.

Introduction to Drawings:

Figure 1: shows the section of the apparatus with the Digester tank containing the composter inside it, as in the preferred embodiment.

Figure 2: shows the section of the apparatus with the biogas storage tank, as in the preferred embodiment.

Detailed description of preferred embodiment:

An apparatus designed for production of biogas in low temperatures (below 32 deg C) is disclosed which uses the anaerobic digestion process for production of biogas assisted by the heat generated by the hot composting process to maintain the temperature of matter in the biogas digester at a temperature range in which biogas producing bacteria can thrive. The end products produced by the apparatus are compost, biogas, slurry and leachate.

The apparatus is made of three major components: (1) A Biogas digester -A tank, made of low thermal conductivity material, with an inlet for feedstock and outlets for biogas and slurry produced in the bio-digestion process.

(2) A composter made of heat conducting I high thermal conductivity material with inlets for composting material and airflow and outlets for composted material and leachate. This composter is built inside the Biogas Digester such that it is submerged under and surrounded by the matter contained in the biogas digester.

(3) A Storage tank for storing biogas produced from the anaerobic digestion process.

The construction of the above mentioned components is as follows: (1) Biogas Digester -The biogas digester 1 is a tank made of low thermal conductivity material. The digester has an airtight lid 4 on top which can be opened for servicing or repairs.

The digester has an inlet pipe 5 which is taller than the digester and runs externally and vertically alongside the outer wall of the digester and feeds into the digester at the bottom of the sidewall. The inlet pipe is held in place by attaching it to the sidewall of the digester by means of solid supports 6 which wrap around the girth of the pipe and are fixed to the sidewall of the digester.

The inlet pipe has a manual handle driven grinder 7, with a funnel shaped mouth and a lid, attached to its mouth such that when the food waste mixed with water is placed in the grinder and the handle of the grinder is turned the ground food waste paste flows into the inlet pipe and thus into the digester. The grinder is also attached to a fan 8, via a geared mechanism 9, to aid the flow and distribution of the food waste across the digester. This fan 8 is placed inside the digester near the inlet and is connected to the grinder by means of rods 33 with a geared mechanism 9 at the corner. These rods run from the bottom of the grinder into the inlet pipe and connect to the fan inside the digester. The grinder in this embodiment forms the rotating means for the fan at the bottom of the digester.

The digester has an outlet 10 on its side wall for the effluent to flow out. The opening to the outlet is covered I blocked from inside the tank by means of a flap door 11, with a rubber seal, in contact with a float 12 via a v shaped rod which controls the flap doors' opening and closing. The flap door is hinged above the outlet and is spring loaded at the bottom, by a spring 13 connected to the sidewall of the Digester, to aid the closing of the flap door. The rod connected to the float is in a v shape and is hinged at the bottom of the v shape (See Figure 1).

This float mechanism controls the outward flow of effluent from the digester tank and is built so that the effluent flows out of the digester tank only when matter is added to the tank thereby maintaining the original level of matter in the tank. The level of the matter in the tank is maintained such that the outlet itself is always submerged under the matter i.e. the level of the matter in the tank is slightly higher than the top edge of the outlet.

The digester also has an outlet 14 at the top for the biogas produced. This outlet is connected to a pipe 15, which feeds the storage tank, via a NRV 16 (non return valve).

The digester also has a drain plug 17 at the bottom so that it can be drained for maintenance if required.

The composter's inlet 18 (for composting material) and outlet 19 (for composted material and leachate) pass through the sidewall of the digester.

The digester is also fixed with heating element 20 with an electric plug, to heat the matter in the digester, which can be connected to standard electric power supply so that the matter can be heated to the optimal temperature in case the digester has been left unused or if it fails over.

The digester has supports 21 at its bottom, made of low thermal conductivity material, which keeps it clear of the ground level.

(2) Composter -The composter 2 is made of high thermal conductivity material and is placed inside the Digester tank 1. The composter is built so that it is always submerged under the matter inside the Digester tank i.e. below the maximum level of matter in the digester tank.

The composter has a sloping inlet pipe 18 built through the sidewall of the digester. The inlet is covered with a lid 22 which prevents the outflow of hot gases and can be opened while feeding the composter.

The base 23 of the composter is sloping such that the lower end is nearer to the sidewall of the digester from where outlet to the composter is built. This slope aids the easy removal of composted material from the composter. The sloping base of the composter is supported by struts 24 running between the inner wall of the digester and the outer wall of the base of the composter. The composter's outlet has a lid 25 which is closed by means of a latch and is opened to remove the composted material when ready. The bottom third of the lid is made of mesh so that the leachate can flow out of the composter and can be collected outside the composter.

An aeration pipe 26 runs from the outside, to the bottom of the interior of the composter, through the outlet of the composter. This pipe feeds a network of other pipes which run vertically through the composter and have mesh covered holes at various points to aerate the composting material. An adapter is provided along with the composter, this adapter has one end which attaches to the aeration pipe 26 and the other end which fits into a standard hand or foot pump. This adapter can be used to pump air inside the composter to aerate it and to clear of the perforations in the aerating pipes of any blockages.

(3) Gas Storage tank -The gas storage tank 3 is made of low thermal conductivity material and comprises of two drums 27 and 28 (one slightly smaller in diameter than the other) and a frame 29.

The larger drum 27 is filled with water and the smaller drum 28 is inverted and placed inside the larger drum. The smaller drum is raised in height when the gas fills up inside it. A frame 29, made of hollow pipes, to support the smaller drum and to prevent it from falling over is built around the storage tank. The smaller tank has an inlet 30 at the top for the biogas being produced in the digester and being fed into the storage tank via a NRV 16 (non return valve) feeding a flexible hose 15. The smaller tank also has an outlet 31 for Biogas at its top connected to a flexible hose 32 which feeds the Biogas consuming system. Weights can be placed on top of the smaller drum in order to increase the pressure of the biogas.

Working: The Biogas digester is fed with a mix of water and food waste which is then ground by the grinder at its inlet and passed into the digester tank. The matter in the digester is then acted upon by anaerobic bacteria and biogas is produced. Since the temperature of the digester needs to be maintained between 32 & 37°C (89.6-98.6°F) the digester may need heating to initially start it. The heating element in the digester can be connected to domestic electric supply to initiate this process and can then be disconnected. The additional heat required during the anaerobic digestion process can be supplied by the hot composting process taking place in the composter contained within the digester. The effluent produced from the digester can either be used for watering plants in the garden or be recycled in the digester.

The composter is fed with a mix of garden waste which is preferably controlled such that it has a C:N (carbon to nitrogen) ratio of 30:1 e.g. A mix of two parts of grass cutting mixed with one part fallen leaves will achieve this ratio. The hot composting process will generate heat which will be transferred to the matter in the digester by virtue of the composter walls being built of high thermal conductivity material. After the hot composting is over the composted material can be extracted via the outlet of the composter. Also during the hot composting process leachate will be produced which will flow out of the mesh in the composters outlet door. This leachate can be collected in a separate container placed at the bottom of the apparatus. Some leachate will also flow back through the aeration pipes and can be collected in the same container.

The gas produced in the digester is then transferred from the gas outlet at the top of the digester via NRV to a flexible hose which feeds the storage tank. The NRV prevents the backflow of gas into the digester and also acts as a thermal cut out between the digester and the storage tank thereby eliminating the heat losses which would have occurred via the surface area of the storage tank.

The storage tank rises in height as it fills up with the Biogas. The Biogas is then fed to a stove or another biogas consuming system via a flexible hose. The pressure of the biogas can be increased by adding weights on top of the storage tank.

Claims

CLAIMS: 1. A Biogas production apparatus comprising of a Composter inside a Biogas Digester.
2. The Biogas production apparatus according to claim 1, in which the composter is made of high thermal conductivity material.
3. The Biogas production apparatus according to claim 1, in which the Biogas Digester has a fan at the bottom of the digester near the inlet, where the said fan is connected to a rotating means by rods and a geared mechanism contained within the inlet pipe of the Biogas Digester.
4. The Biogas production apparatus according to claim 1, in which the outlet from the digester tank is such that the outlet is always submerged under the matter inside the biogas digester and is covered, from inside the tank by a hinged flap door, where the flap door is in contact with a hinged float mechanism such that the flap door is opened, allowing the matter to flow out, when additional matter is added to the Biogas Digester tank via the inlet pipe and the flap door closes, stopping the outward flow of matter, when the level of the matter falls to the original amount of matter in the Biogas Digester tank.