CLIAMS:CLAIMS

We Claim:

1. A combined draft apparatus for gasification of fuel comprising of:
a central enclosure closed at the top having a gasification zone, a producer gas holding zone above the gasification zone and a gas collection zone below the gasification;
the said gasification zone of the enclosure comprises of inner and outer walls spaced apart defining an annular space between them, said annular space being closed at the top and bottom ends and having an inlet on the outer wall to receive air from an external blower or fan; the said inner wall has a plurality of spaced apertures arranged in one circumferential path extending up the wall providing air to the gasification zone;
a means to supply fuel to the enclosure till the upper limit of the gasification zone;
a grate fixed below the gasification zone to hold the fuel; one or more valve at the bottom of collection zone for the exit of the producer gas; and
at least one outlet for the collection of ash.

2. An apparatus as claimed in claim wherein the said enclosure may optionally have a producer gas exit in the producer gas holding zone.

3. An apparatus as claimed in any of the preceding claims, wherein the said the inner wall of the gasification zone of the central enclosure is sloping.

4. An apparatus as claimed in any of the preceding claims wherein the said fuel may be a bio-fuel.

5. An apparatus as claimed in claim any of the preceding claims, where in the said the number of apertures and the size of the aperture is pre-determined and corresponds to the amount of air to be fed in to the gasifier.

6. A method of producing producer gas by gasification of fuel comprising the steps of :

a. supplying fuel to a gasification zone in a central enclosure closed at the top having a gasification zone, a producer gas holding zone above the gasification zone and a gas collection zone below the gasification; the said gasification zone of the enclosure comprises of inner and outer walls spaced apart defining an annular space between them, said annular space being closed at the top and bottom ends and having an inlet on the outer wall to receive air from an external blower or fan; the said inner wall has a plurality of spaced apertures arranged in one circumferential path extending up the wall providing air to the gasification zone; a means to supply fuel to the enclosure till the upper limit of the gasification zone; a grate fixed below the gasification zone to hold the fuel; one or more valve at the bottom of collection zone for the exit of the producer gas; and at least one outlet for the collection of ash; and
b. pyrolysing said fuel in the gasification zone by supplying pre-determined amount of air through the apertures in the inner wall.

7. A method as claimed in claim 6 wherein the said enclosure may optionally have a producer gas exit in the producer gas holding zone.

8. A method as claimed in claims 6 or 7 wherein the said the inner wall of the gasification zone of the central enclosure is sloping.

9. A method as claimed in claims 6, 7 or 8 wherein the said fuel may be a bio-fuel.

10. A method as claimed in claims 6, 7, 8 or 9 wherein the said the number of apertures and the size of the aperture is pre-determined and corresponds to the amount of air to be fed in to the gasifier.
,TagSPECI:FIELD OF THE INVENTION
The present invention relates to apparatuses and methods for combustion of solid fuels; particularly to combustion apparatuses for gasification and combustion of multiple solid fuels and the methods thereof; more particularly to apparatuses and methods employing both co-current and counter current gasification processes for gasification and combustion of solid fuels.

BACK GROUND OF THE INVENTION
There is a dire need for the use and adaption of cleaner and environment-friendly power generation methods. Due to fast depletion of the fossil fuel, there is an acute need to make use efficient of renewable sources of energy. Energy in crop residues, Wood residues, and biomass crops all present attractive possibilities for reducing our dependence on fossil fuels.

Gasification of solid bio-fuels for production of producer gas and its consequent combustion is known. It is an established technology for power generation and has undergone number of improvements over the years to overcome many of the limitations of the conventional combustion systems with highest efficiency which converts solid fuels in to a clean gas that can be used 100% Gas Engine mode for power generation.

US2354963 teaches a combustion device comprising of a gasification chamber generating producer gas and having a grate for the supply of air with a mixing and ignition. chamber (or more such chambers) having an opening or more openings to the gasification chamber and serving to mix the gases with air and to ignite the mixture so that the final combustion is effected in a fire box or the like arranged after the mixing and ignition chamber. A partial vacuum is produced in the reactor space by the jet of air, which sucks along product gas from the reactor space to cause a so-called ejector action according to Bernoulli's principle. This device is not suitable for high temperature operations as at high temperatures in the feed column, pellets would disintegrate long before they reach the grate.

Gasifiers and their improvements are further described in US6112677; US6336449; WO9426849A1 and US2010/03236338. None of the devices described above significantly decreases the problems related to gasification of solid fuel, particularly with regard to feeding of secondary air into the product gas and/or the structural solutions of the reactor space, because a mixing of combustion air and product gas that is sufficient to ensure complete combustion and optimum efficiency cannot be achieved. They are cumbersome and require large set-up as well. Scaling down and scaling up of the device based on the requirement is impossible.

Gasifiers are usually classified as being counter-current, co-current, or side-draft (cross-current). With counter-current gasifiers, air is blown or drawn up through a grate supporting the feedstock, producing producer gas by gasification of the bio-fuels. This producer gas passes up through to the combustion zone for combustion. The unburned fuel exits at the top for further use.

Co-current gas reactor, on the other hand force the producer gas down through the combustion area by means of air pressure or air suction to an exit for use. Co-current gas reactors were developed in an effort to reduce tar content in gas used to power internal combustion engines. In conventional co-current systems, the air enters through peripheral jets directed toward the centre of the air-tight cylindrical fuel and combustion chamber just above a funnel-shaped or conical bottom to initiate gasification. As the feedstock is devolatized by combustion and heat, it shrinks into pieces of carbon or char which accumulate in a conical bottom and are supported on a grate below the throat. The chars form a red-hot bed which reduces CO2 to combustible CO and also cracks the tars into stable gases. This gas can be cleaned and cooled for use in an engine to generate power by mitigating emissions compared over conventional route.

WO2007/102032A2 discloses a two-stage combined co-current-counter current gasifier which is used for the thermochemical process that converts solid carbonaceous materials into combustible gases, has as first (pyrolysis) stage a counter current reactor, placed above the second (gasification) stage which is a co-current reactor and is characterized in that between the two stages a diaphragm is present, which cuts off the gaseous flow between the counter current reactor and the co-current reactor, while allowing the solid pieces falling from the counter current reactor to pass to the co-current reactor and allows to the pressure from air feed (6) to force the pyrolysis gases pass through pipe.

Therefore there is a need the art to overcome technical problems of the prior art. There is a further need in the art to develop an efficient, economical and environment friendly solution to the problems associated with the prior art.

OBJECTS OF THE INVENTION
It is an object of the invention to develop a bio mas gasifiers by incorporating the operational advantages of counter-current and co-current gasification.

It is yet another object of the invention to provide a novel co-current gasifier whose linear design allows for compact modular design in order to accommodate a wide variety of energy demands for the single size product unit that can be “stacked” with others for producing different energy output demands.

It is yet another object of the invention to produce heat and power at all levels of industries from flexible conditions.

It is another object of the invention to develop an apparatus that can handle optimum size, extreme moisture and high bulk density feedstock in proposition with low bulk density feed materials like leafy/powdery feedstock e.g. sugarcane trash and bagasse, cow dung and other agro waste materials in balled or briquetted forms.

SUMMARY OF THE INVENTION
To overcome the limitations of the prior art and meet the objects of the invention it is disclosed herein a combined draft apparatus for gasification of fuel comprising of: a central enclosure closed at the top having a gasification zone, a producer gas holding zone above the gasification zone and a gas collection zone below the gasification; the said gasification zone of the enclosure comprises of inner and outer walls spaced apart defining an annular space between them, said annular space being closed at the top and bottom ends and having an inlet on the outer wall to receive air from an external blower or fan; the said inner wall has a plurality of spaced apertures arranged in one circumferential path extending up the wall providing air to the gasification zone; a means to supply fuel to the enclosure till the upper limit of the gasification zone; a grate fixed below the gasification zone to hold the fuel; one or more valve at the bottom of collection zone for the exit of the producer gas; and at least one outlet for the collection of ash.

Also disclosed herein is a method of producing producer gas by gasification of fuel comprising the steps of: a) supplying fuel to a gasification zone in a central enclosure closed at the top having a gasification zone, a producer gas holding zone above the gasification zone and a gas collection zone below the gasification; the said gasification zone of the enclosure comprises of inner and outer walls spaced apart defining an annular space between them, said annular space being closed at the top and bottom ends and having an inlet on the outer wall to receive air from an external blower or fan; the said inner wall has a plurality of spaced apertures arranged in one circumferential path extending up the wall providing air to the gasification zone; a means to supply fuel to the enclosure till the upper limit of the gasification zone; a grate fixed below the gasification zone to hold the fuel; one or more valve at the bottom of collection zone for the exit of the producer gas; and at least one outlet for the collection of ash; and b) pyrolysing said fuel in the gasification zone by supplying pre-determined amount of air through the apertures in the inner wall.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG 1 is a perspective view of one of the embodiments of the invention
FIG 2A is a cross-sectional view of one of the embodiments of the invention
FIG 2B is a cross-sectional view of one of the embodiments of the invention
FIG 3 is a perspective view of one of the embodiments of the invention
FIG 3A is a cross-sectional view of one of the embodiments of the invention
FIG 3B is a cross-sectional view of one of the embodiments of the invention

DETAILED DESCRIPTION OF THE INVENTION
Referring to Fig 1, a combined draft gasifier(101) for the efficient conversion of biomass materials to generate heat energy comprises of a central enclosure(100) closed at the top having a gasification zone(1), a producer gas holding zone(2) above the gasification zone(1) and a gas collection zone(3) below the gasification zone(1) is shown. The gasification zone (1) of the enclosure (100) comprises of inner (4) and outer (5) walls spaced apart defining an annular space between them. The annular space is closed at the top and bottom ends and has an inlet (6) on the outer wall (5) to receive air from an external blower or fan (not shown). The inner wall(4) has a plurality of spaced apertures(7) arranged in one circumferential path extending up the wall providing air to the gasification zone(1). Fuel is supplied through a fuel inlet (9) by a conveyor to the enclosure (100) till the upper limit of the gasification zone (1). A grate (10) fixed below the gasification zone (1) holds the fuel. One or more valve98) at the bottom of collection zone provides the exit of the producer gas and its subsequent use. The enclosure may optionally have a producer gas exit (12) in the producer gas holding zone. An ash collector (11) below the enclosure collects the ash for subsequent disposal.

The enclosure (100) includes at least two generally triangularly shaped air ducts positioned longitudinally across an enclosed housing defining a combustion chamber. The air ducts have sloping sides which downwardly converge towards one another to define at least one open-bottom V-shaped channel, the sloping sides primarily supporting the biomass fuel which will be combusted to derive producer gas. The air ducts are hallow and are in fluid communication with a high pressure air source at one end, and with the gasification chamber through the air jet openings near there apexes. The high pressure exits out through the air jet openings placed along the top edges of the air ducts which provides primary aircraft for gasification of the biomass in the channels. The producer gas passes down between the channels and horizontally to an exit (12). The enclosure (100) may optionally have a second set of apertures (13) as shown Fig 2.

Gasifiers (101) disclosed here operates on counter-current assisted co-current gasification to generate tar free gas. The inventions were achieved from the incorporation of operational advantages of counter current and co-current gasification. The claimed gasification system consists of a stratified counter-current gasification assisted co-current gasification which operates simultaneously on both modes. The design of the gas reactor is particularly flexible to scale-up for any rated capacity. The length, width and height of the reactor can be scaled up to any proportions. The shell of the gas reactor designed is constructed using Mild Steel (MS) and Stainless Steel (SS) sheet with suitable thickness on civil foundations, structures, platform and likewise. The MS/SS plate is either rectangular type or rolled in bending machine to round have a single joint welding.

This approach in designing instigates production cost and time reduction. It augments the feedstock and pyrolyzed products to flow freely downwards in stratified reactor avoiding edge losses and prevents clinker formation on sharp edges. Thus, it is a square, rectangular, round shape in cross section with perfect dimensions based on combustion engineering calculations and the scaling-up of this design is highly acceptable and easy. The interior of the gas reactor shell inner surface is lined with multi-composition layers of fire crate grade, glass powder, wood ash, refractory brick powder and whytheat-A (90% alumina) dense castable to suitable thickness depending of models respectively. The exterior of the shell is lined glass wool (20), ceramic blanket supported by chicken mesh enclosed in an aluminium cladding

The feedstock for gasification is conveyed through hopper through suitable conveying device from ground level and the hopper gets closed with a top slide door by motorized or pneumatic or hydraulic mechanism based operation on the top after filling the chamber. The bottom slide door is opened after ensuring the closing of top slide door. These arrangements are made to ensure uniform charging of feedstock into the gas reactor which prevents feedstock load on the counter-current, co-current gasification zones (1) and moving grate assembly (10). The top slide door and the bottom slide door arrangement of the hopper ascertains leak proof environment inside the gas reactor which are operating under pressure mode. One more slide door can be provided between the top and bottom slide door assembly if needed for added safety.

The grates (10) may be moving grates with horizontal rod assembly operating on shaft arrangements are placed extremely below the co-current throat which discharges the ash uniformly preventing clinker formation and bed pressure drop and thus improving the gasification efficiency.

The enclosure or shell (100) of the high temperature Biomass gas reactor designed is constructed using Mild Steel (MS) and Stainless Steel (SS) sheet with suitable thickness. The MS/SS plate is rolled have a single joint welding. This approach in designing instigates production cost and time reduction. It augments the pyrolyzed products to flow freely downwards in stratified reactor avoiding edge losses and prevents clinker formation on sharp edges.

The invention deals with a multi-condition acceptable advanced biomass gas reactor which is a square, rectangular, outer round shaped which can be operated on all types of firewood, coal, coconut husk, coconut shell, coconut fronds, mango seed, cow dung and any powdery bio-fuel or agro-wastes in bailed briquetted or pellet form that generates tar free gas while removing ash and particulate in the proficient manner. This reactor operates on stratified counter-current assisted co-current gasification mode operating slightly above atmospheric pressure for flexible rating with combined draft gasification and single conical gas outlet. The gasification zone (1) temperature is maintained above 10000C and above to achieve tar-free gas.

Another object of the proposed invention was to allow the linear or rectangular shape to provide feedstock introduction into the gasification area without deterioration of the air injection flow path or the grates. A still further object of the invention was to combine the use of a pre-heater that is self-sustained to give greater gasification efficiency and to allow the use of a moist fuel.

In the power mode of operation, the producer gas passes through multi-cyclone ash separator followed by immersion type venturi scrubber for gas cleaning, vertical column damper with dry filter and finally passing through coarse and fine filters. The cleaned and cooled gases are passed through a buffer tanks and uniformly distributed to engine for power generation. All the above dimensions and values claimed can be scaled up or down in length, width, height, diameter and numbers and likewise with respect to capacity of gas reactor designed to be accepted and accommodated for meeting the clients demand.

This proposed high temperature tar-free gas reactor is fully insulated by a special surface lining methodology to achieve maximum thermal efficiency on hot gas condition as well as cold gas efficiency with tar-free gas. The pressure drop across the rotary grates with adjustable options based on size feed stock for gasification can be uniformly maintained during operation which will help to gasify small particles and pellets also.

ADVANTAGES
1. The invention combines the operational advantages of counter-current and co-current gasification.
2. It can be operated on all types of firewood, coal, refused derived fuel, rubber waste, leather waste, coconut husk, coconut shell, coconut fronds, mango seed, cow dung and any powdery bio-fuel or agro-wastes in balled, briquetted or pellet form converted to a free gas by removing ash and particulate in the proficient manner.
3. This system can handle optimum size, extreme moisture and high bulk density feedstock in proportion with low bulk density feed materials like leafy trash/powdery feedstock e.g. sugarcane trash and bagasse, and other agro-waste materials in bailed or briquetted forms.
4. This gas reactor can accommodate any kind of feedstock feed on optimum size (from 50mm of length X 50mm of diameter to 300mm of length X100mm of diameter)even with higher bulk density (from 350 to 1500 Kg/m3) that is highly comparable over woody feedstock (i.e., around 400kg/m3) and powdery feedstock (i.e., around 60kg/m3) and acceptable with large woods and large sticks with higher moisture (up to 50%) acceptability compared against earlier works.
5. The oxidizing agent (Air) inlet temperature for sustained gasification can be achieved at ambient temperature regimes and even at extreme temperatures below 280C also without any pre-heating process. The rating capacity with feedstock can be doubled while using wood chips or pellets. It works under pressure below 300 mm of water column. The gas reactor with moving gate mechanism with adjustable options based on size feedstock for gasification are designed operated at low speed to minimise char ash generation and thus achieved a very high gasification efficiency.