An agro biomass gasification system and a method for agro biomass gasification.

The invention relates to an agro biomass gasification system and a method for agro biomass gasification.

Agro biomass is a key biomass source for various end

applications including energy production. The agro biomass is generally the residue of agricultural production which is characterized by low density, high moisture and ash content, and is high in inorganic such as calcium, magnesium and potassium.

One way to gasify the agro biomass is to use a co-current gasification technology. A producer gas which is combustible in nature, generated from this way is low in terms of energy content and high in terms of contaminants. Furthermore use of the producer gas for power generation result in frequent operation issues such as channeling in the reactor, high pressure drop accompanied by sudden stoppage of generation of combustible gases and frequent maintenance due to contaminant level in the gas exceeding permissible or tolerable limits.

Another way to gasify the agro biomass is to use a

combination of updraft and downdraft gasification

technologies. This involves embedding the updraft and down draft operations into a single reactor with isolation vales. But it becomes complex to handle and doesn't suit high ash content fuels like agro biomass.

The object of the invention is to produce a producer gas having high calorific value by gasifying agro biomass easily and efficiently. According to an embodiment of the invention, an agro biomass gasification system includes a producer gas gasifier for receiving an agro gas produced from gasification of an agro biomass, and for gasifying a solid biomass along with the agro gas in presence of an oxidizer to produce a producer gas. This approach generates the producer gas of high

calorific value which can be used for power generation application .

According to another embodiment, the agro gas comprises contaminants and the producer gas gasifier is further adapted to remove contaminants by cracking the contaminants. This helps to remove contaminants which can hamper operation of power generation.

According to yet another embodiment, the producer gas

gasifier is adapted to crack the contaminants by using charcoal. The cracking of the contaminants by using charcoal is an easy and cost efficient way to remove the contaminants. According to an exemplary embodiment, the producer gas gasifier is adapted to produce the charcoal while gasifying the solid biomass and the agro gas, so that, the charcoal can be re-used for cracking the contaminants of the agro-gas. This provides a self-sustainable way to produce charcoal to be used as a part of the feed along with solid biomass inside the producer gas gasifier.

According to another embodiment, the gasification system includes a charcoal extraction device for extracting the charcoal from the producer gas gasifier. The extracted charcoal from the producer gas gasifier is re-used later inside the producer gas gasifier for removing contaminants from the synthesis gas. According to one embodiment, the gasification system includes an agro gas gasifier adapted to receive the agro biomass, and adapted to gasify the agro biomass in presence of the

oxidizer to produce the agro gas. This provides for a simple way to gasify the agro biomass to provide an agro gas

regularly and in a self-sustainable way.

According to another embodiment, the agro gas gasifier adapted to gasify the agro biomass by atleast partial

combustion or pyrolysis of the agro biomass. This provides charcoal as by-product which can be used as fuel for cooking, industrial application etc.

According to an exemplary embodiment, the gasification system includes a gas cleaning system adapted to clean the producer gas. This provides more refined producer gas which includes less amount of contaminants in respect to the one produced by the producer gas gasifier.

According to one embodiment, the gasification system includes a prime mover which adapted to receive the producer gas to produce energy and an exhaust heat, and a heat exchanger to transmit heat from the exhaust heat to the oxidizer. This helps to pre-heat the oxidizer which in place enhances the gasification process of the agro biomass.

FIGURE illustrates a block diagram of an assembly of an agro biomass gasification system for producing producer gas from the agro biomass.

The above-mentioned and other features of the invention will now be addressed with reference to the drawings of a

preferred embodiment of the present agro biomass gasification system. The illustrated embodiment of the gasification system is intended to illustrate, but not limit the invention. The drawings contain the following figures, in which like numbers refers to like parts, throughout the description and

drawings. FIGURE depicts an embodiment of the invention for gasifying agro biomass 4 to produce producer gas 7 having calorific values higher in respect to general gasification of the agro biomass 4. According to the embodiment, a system 1 includes an agro gas gasifier 9, a producer gas gasifier 2, a gas cleaning system 10, a prime mover 11 and a heat exchanger 12 coupled together to produce the producer gas 7 and energy using the producer gas 7. The agro gas gasifier 9 receives the agro biomass 4 and an oxidizer 6 inside the gasifier 9 through provisions for agro biomass and oxidizer inlet. The gasifier 9 gasifies the agro biomass 4 in presence of the oxidizer 6 to produce an agro gas 3. Alternatively, the agro gas gasifier 9 can gasify the agro biomass 4 in absence of the oxidizer 6 through pyrolysis process .

In an alternate embodiment, the agro gas gasifier 9 also produces charcoal 8 as by-product while producing the agro gas 3 during gasification of the agro biomass 4 due to partial combustion or/and pyrolysis of the agro biomass 4 by removing moisture and other volatile constituents from agro biomass 4. The partial combustion or/and pyrolysis is

achieved by controlling the flow of the oxidizer 6 through an oxidizer flow control mechanism 15. The oxidizer flow control mechanism 15 is a mechanical control valve like ball-check valve, control valve, gate valve, shut-off valve, etc which can be handled manually or automated for increasing and decreasing flow of the oxidizer 6. When the mechanical valve 15 is closed then flow of oxidizer 6 will be totally stopped resulting in pyrolysis and if the mechanical valve 15 is partially opened then the oxidizer 6 is controllably flown resulting in partial combustion. The agro gas 3 produced by the agro gas gasifier 9 is further received by the producer gas gasifier 2, wherein the producer gas gasifier 2 also receives a solid biomass 5. The solid biomass 5 and the agro gas 3 are gasified in presence of the oxidizer 6 to produce the producer gas 7.

The producer gas gasifier 2 also produces charcoal 8 while producing the producer gas 7 from gasification of the agro gas 3 and the solid biomass 5. The charcoal 8 produced in this case is re-used by the producer gas gasifier 2 to produce the producer gas by removing contaminants from the agro gas 3 by cracking the contaminants. Alternatively, the charcoal 8 used in the cracking of the contaminants of the agro gas 3 can also be additionally provided using an

external source. Yet alternatively, the charcoal 8 used in the cracking of the contaminants of the agro gas 3 need not come from the charcoal 8 produced by the producer gas

gasifier 2, rather the charcoal 8 can wholly be provided by the external source.

The charcoal 8 generated by the producer gas gasifier 2 is collected by a charcoal extraction device 14, wherefrom the charcoal 8 can be re-used inside the producer gas gasifier 2. Alternatively, the charcoal 8 produced inside the agro gas gasifier 9 can also be collected by the charcoal extraction device 14. Yet, alternatively, the charcoal 8 so collected inside the charcoal extraction device 14, can be further utilized for any other utility like for cooking purpose as a fuel, etc.

The gasifier 2, 9 are based on thermo-chemical reactor technology. Inside the thermo-chemical reactor 2, 9, the carbonaceous material 3, 4, 5, i.e., agro biomass 4, solid biomass 5 and the agro gas 3 are gasified in presence or absence of oxidizer 6 undergoing through various complex physical and chemical processes like drying, pyrolysis, combustion and reduction processes to produce the gases. The oxidizer 6 can be air, oxygen, steam or combination of air, oxygen or steam or any such element which can gasify biomass inside the gasifier 2, 9. Agro biomass 4 can be any residue of agricultural crops, agro processing or plantation. This could be both of low, medium and high ash content and varying moisture. A few examples of agro biomass but not limited to these are rice husk, rice straw, sugar cane trash, bagasse, coir pith, jute waste, sawdust etc.

Solid biomass 5 can be any solid stalk of plant matter, which includes sources such as forest, plantation, weeds and agricultural crops. A few examples of solid biomass but not limited to these are casuarina, eucalyptus, juliflora

prosopis, coconut shells, mulberry stalks, cotton stalks etc.

The agro gas 3 and the producer gas 7 are primarily composed of various gaseous species like Carbon monoxide (CO) ,

Hydrogen (¾) , Methane (CH ₄ ) , Carbon dioxide (CO ₂ ) and

Nitrogen (N ₂ ) . The agro gas 3 comprises high traces of contaminants like tar. The agro gas is poor in terms of H2 and CO but rich in terms of C02, CH4 and tar. Whereas the producer gas 7 is rich in terms of H2 and CO but poor in terms of C02, CH4 and tar.

The producer gas 7 also includes various impurities like dust particles, tar, water vapor or any such impurities. So, the producer gas 7 is cleaned using a gas cleaning system 10 to remove the impurities before taking the producer gas 7 to the prime mover 11 for producing energy.

In an alternate embodiment, the producer gas 7 flowing out of the gasifier 2 can be cleaned using the gas cleaning system 10 before being received by at least the gas engine 11.

The gas cleaning system 10 may include gas cleaning

techniques like cyclone, wet-scrubbing techniques such as water and oil scrubbers and bubblers, cloth filters,

electrostatic precipitators for removal of impurities from the producer gas 7. The producer gas 7 after being cleaned will move into a prime mover 11 to generate energy by using the producer gas 7. The prime mover 11 can be an engine or turbine or any other device capable of generating energy in either thermal, electrical or pressure form for doing some mechanical work. While generating energy, the prime mover 11 also generates exhaust heat 13 as by-product.

Initially, during the start of the gasification system 1, the gasifier 2, 9 can be cold i.e. at ambient temperature or in warm condition. Thus, the gasification system 1 will take certain time to further warm up. So, to reduce the warm up time, additional heat need to be supplied to the gasification system 1 for heating up of gasifier walls during the start-up process, the system 1 uses the exhaust heat 13 generated by the prime mover 11 as a by-product while generating energy. The exhaust heat 13 flows through the heat exchanger 12 to transfer heat from the exhaust heat 13 to the oxidizer 6, wherein the oxidizer 6 after receiving heat flows to the gasifier 2, 9 for providing additional heat to the gasifier 2, 9. As a result, the start-up time to start the

gasification system 1 will be reduced. In one embodiment, the oxidizer 6 after receiving heat moves into an oxidation or combustion zone of the gasifier 2, 9 directly for reducing the start-up time.