Title of Invention

"A NATURAL DRAFT GASIFIER FOR CONVERTING AGRICULTURAL RESIDUES INTO COMBUSTIBLE GAS"

Abstract

This invention relates to a natural draft gasifier (1) for converting agricultural residues (biomass) into combustible gas comprising a biomass holder or hopper (2) connected at its lower end to load a reactor (3) with biomass to generate producer gas through combustion, the reactor having a burner (4) at its top, the said residues being supported by a grate (5) at the lower end of the reactor and an air inlet port (7) for introduction of air to support said combustion.

Full Text

FIELD OF INVENTION This invention relates to a natural draft gasifier. BACKGROUND Gasification is a partial combustion process where with the controlled air input, biomass like agricultural residues is converted into a combustible gas known as Producer gas (P gas). P gas has two major applications. After cooling and filtration, it can be used together with a small amount of diesel to operate diesel engines. Petrol engines can be operated totally on P gas. Another use of P gas is to generate heat for thermal application by directly burning it. The equipment used for gasification is known as a gasifier. PRIOR ART Basically, the gasifiers can be classified into three types. Forced draft, induced draft, and natural draft, out of which first two are most common. Natural draft based gasifiers work on the principle of chimney effect and generate P gas without needing any artificial draft. It consists of a perforated plate at one end and the P gas pipe having burner at it's top at the other end of the reactor. Inside the gasifier, a grate is provided for the purpose of holding the biomass and filtering the ash which falls in the ash zone. Gasifier is loaded with the biomass from the biomass loading port which is to be kept closed during the gasifier operation. Biomass is set on fire from the perforated plate side. Gases moves horizontally through the biomass and reach to the burner. The combustion zone also keeps on moving horizontally till the exhaustion of the complete batch of biomass. The drawback of this gasifier is that it can be operated in batch mode only. The design configuration is such that recharging can not be done during operation which makes the existing design unsuitable for applications where thermal energy is required on continuous basis. OBJECTS OF THE INVENTION An object of this invention is to propose a novel construction of a natural draft gasifier. Another object of this invention is to propose a natural draft gasifier which obviates the disadvantages associated with those of the prior art. Yet another object of this invention is to propose a natural draft gasifier which is capable of being recharged without causing an interruption in the operation thereof. Still another object of this invention is to propose a natural draft gasifier which is operable over a wide range of woody biomass fuels as a feedstock. BRIEF DESCRIPTION OF THE INVENTION A natural draft gasifier for converting agricultural residues (biomass) into combustible gas comprising a biomass holder or hopper connected at its lower end to load a reactor with biomass to generate producer gas through combustion, the reactor having a burner at its top, the said residues being supported by a grate at the lower end of the reactor and an air inlet port for introduction of air to support said combustion. DESCRIPTION WITH REFERENCE TO ACCOMPANYING DRAWING Further objects and advantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawing and wherein Fig.l shows the natural draft gasifier of the present invention. The gasifier 1 comprises a biomass holder or hopper 2 connected at its lower converging end to the P gas generation section or reactor 3 which has a P gas burning unit or gas burner 4 at its top, ash removal unit or grate 5 at its lower end and an ash pit 6 with gasifier air input port 7 at the bottom. Biomass hopper 2 is of cylindrical shape and may be fabricated out of sheet metal. Hopper 2 has a lid 2a which can have water, sand or similar material kept in the annular ring provided at its top for sealing purpose. The lower converging section of hopper is connected to reactor 3. The reactor is a cylindrical shaped structure made of sheet metal and internally lined with heat resistant material such as a fire brick lining 8 to withstand high temperatures of upto 1000 degrees celsius. The dimensions of the reactor i.e. diameter and height are determined based on the rate of gasification needed to achieve the required P gas generation rate. A firing port 9 is provided on the lower side of the reactor through which with the help of a burning stick, biomass in side the reactor is initially ignited. Grate unit 5 provided at the lower end of reactor 3 can be of circular or rectangular shape and it is made of stainless steel or cast iron or any other metal or alloy. Ash scrapper 10 made of stainless steel or cast iron is provided with grate which can be operated either manually or mechanically. The dimensions of grate 5 are such as it's gross and open area are estimated on the basis of the thermal energy demand and the thermochemical properties of the biomass feedstocks. Ash pit 6 provided below the grate is made of sheet metal with internal lining of insulating material. It's volumetric capacity is decided on the basis of the biomass gasification rate, ash content of the biomass feedstock and system's operation schedule. Gasifier air input port 7 is provided at the bottom. Air gets aspirated in from port 7 and it enters into reactor 3 through grate 5. Gasifier air input port 7 is basically a cylindrical pipe. It's one end is connected to the ash pit. The other end is of rotating type and has perforations. This perforated end is suspended in water. Here water acts as a seal. More the perforations are open, more will be the air input rate. Gas generation rate is directly proportional to air input rate. Control mechanism for gasifitr air input port can be of manual, or mechanical type. Producer gas burner 4 is a cylindrical unit having it's shell body made of sheet metal. Burner 4 has a burner plate 4a plate of stainless steel or cast iron and size and number of P gas ports are decided on the basis of P gas generation rate. Burner 4 is lined from inside with heat resistant material such as fire bricks lining 4b and a wool insulation lining 4c from the outside which can withstand temperatures upto 1200 degrees Celsius. Air swirlers 11 are provided tangentially above the burner plate from where air enters tangentially and get mixed with the P gas coming out from the P gas ports. This P gas burner can be kept at the top of the reactor or near to it depending on the type of the application. • Initially, biomass is loaded in reactor 3 upto the level. A small amount of kerosene or similar fuel is sprinkled on it and using a burning stick the biomas is set on fire. Initially gasifier air input port is kept open. Within five to ten minutes, a glowing char bed is formed on grate S. Gasifier input air port 7 is then closed and gasifier is completely •filled with biomass. Biomass level in the hopper should not be allowed to go below the lower end of it's cylindrical portion. Gasifier air input port 7 is opened. A reactions series of thermochemical reactons take place in the reactor section of the gasifier which form different reaction zones like combustion zone Bl reduction zone B2 pyrolysis zone B3 and drying zone B4. Combustion zone Bl is formed above the grate which generates the heat energy through conversion of some amount of carbon and hydrogen present in the biomass in to carbon dioxide and water vapors respectively. In combustion zone Bl , the temperature varies bet-ween 800 to 1000 deg celsius. Carbon dioxide and water vapours along with other products of combustion zone move upward and get reacted with the hot charcoal bed in the reduction zone section 82, converting carbon dioxide and water vapours intc carbon monoxide and hydrogen respectively. This hot gas mixture then moves upward and form a pryolysis zone B3 where the biomass gets converted into charcoal and generate the combustible gases like methane & hydrogen. 8 Above the pyrolysis zone is the biomass drying zone in which the hot P gas at the temperature above 300 deg Celsius moves through the biomass bed, drying it in the process. The wet P gas reaches to the P gas burner. During the gasifier operation, the whole biomass bed in the gasifier keeps on moving in the down ward direction i.e. raw biomass from the hopper to the drying zone, dried biomass from drying zone to pyrolysis zone, charred biomass from pyrolysis zone to reduction zone, and un converted charcoal to the combustion zone. Ash scrapping unit is required to be operated after certain interval of time to unload the ash in the ash pit. P gas moves upward and goes to the burner. P gas burner as explained in the preceeding paragraph, is of air swirling type. P gas enters in the combustion chamber through gas ports and gets mixed with the swirling air entering from the tangentially placed air ports of the burner. Arrangement is also made to provide control on the burner air input rate. P gas generation rate is controlled by varying the Gasifier air input port opening. More the gasifier air input port area open, more will be the P gas generation rate. The main aim of this invention is to provide a natural draft gasifier which can be recharged without interrupting operation and capable of accepting the wide range of woody biomass fuels in terms of physical and chemical properties as the feedstocks for generation of P gas. CLAIM 1. A natural draft gasifier (1) for converting agricultural residues (biomass) into combustible gas comprising a biomass holder or hopper (2) connected at its lower end to load a reactor (3) with biomass to generate producer gas through combustion, the reactor having a burner (4) at its top, the said residues being supported by a grate (5) at the lower end of the reactor and an air inlet port (7) for introduction of air to support said combustion. 2. A natural draft gasifier as claimed in claim 1 wherein said burner has a burner plate (4a) and tangential burner airports (11) in said burner. 3. A natural draft gasifier as claimed in claim 2 wherein said tangential burner air ports are disposed above the burner plate from where air is mixed tangentially. 4. A natural draft gasifier as claimed in claim 1 wherein said burner plate separates the burner from the reactor. .11 ; ' i' •, ' ' '. ' 5. A natural draft gasifier as claimed in claims 1& 2 wherein said burner has an outer lining of wool insulation lining and an inner lining of firebricks (4b). 6. A natural draft gasifier as claimed in claim 1 comprising a firing port (9) disposed above said grate and extending through a well of said reactor. 7. A natural draft gasifier as claimed in claim 1 wherein an ash scrapper (10) is provided below said grate. 8. A natural draft gasifier substantially as herein described and illustrated.

Documents:

916-del-2000-abstract.pdf

916-del-2000-claims.pdf

916-del-2000-correspondence-others.pdf

916-del-2000-correspondence-po.pdf

916-del-2000-description (complete).pdf

916-del-2000-drawings.pdf

916-del-2000-form-1.pdf

916-del-2000-form-19.pdf

916-del-2000-form-2.pdf

916-del-2000-form-3.pdf

916-del-2000-gpa.pdf

916-del-2000-petition-138.pdf

916-del-2000-petition-others.pdf

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