Claims:We Claim:

1. A system for producing energy in the form of biogas, and/or electricity and fertilizer from agro residue, the system comprising:
a feed preparation unit having a size reduction means for reducing size of the agro residue;
a blending unit capable of receiving the agro residue from the feed preparation unit, wherein the blending unit blends predefined quantities of the agro residue, culture, slurry, and water
a bioreactor capable of receiving the blended mixture from the blending unit, the bioreactor having a plurality of openings adapted on the lower portion thereof, wherein biomethanation process takes place inside the bioreactor;
a feeding unit for uniform distribution of high solids, fibrous, agro residue as biomass substrate inside the bioreactor;
a extraction unit capable of extracting the digestate from the bioreactor after biogas production, the extraction unit having a jet distributor fixed to the plurality of openings at the bottom of the bioreactor, wherein liquid jets are passed into the bioreactor at controlled interval of time through the plurality of openings;
a fertilizer unit capable storing the fertilizer received from a solid liquid separator configured within the extraction unit, wherein the solid liquid separator squeezes the digestate and, the solid and the liquid parts of the digestate are separated as fertilizer;
a biogas storage unit capable of storing the biogas from the bioreactor; and
a biogas scrubbing unit for scrubbing the biogas to remove hydrogen sulphide, carbon dioxide, moisture and other trace gases.

2. The system as claimed in claim 1, wherein size reduction means includes a hammer mill and the like.

3. The system as claimed in claim 1, wherein the feeding unit includes a pump for feeding the agro residue from the blending unit to bioreactor.

4. The system as claimed in claim 1, wherein shape of the bioreactor is made as section of an inverted ‘V’.

5. A method for producing energy in the form of biogas, and/or electricity and fertilizer from agro residue, the method comprising:
reducing size of the agro residue;
blending the predefined quantities of the agro residue, culture, slurry, and water;
adding the blended mixture to the bioreactor for biomethanation;
distributing high solids, fibrous, agro residue uniformly as biomass substrate inside the bioreactor by means of feeding unit;
extracting digestate from the bioreactor after biogas production by using extraction unit, wherein liquid jets are passed into the bioreactor from the plurality of openings configured at lower portion thereof at controlled interval;
sorting fertilizer received from a solid liquid separator configured within the extraction unit, wherein the solid liquid separator squeezes the digestate and solid and the liquid parts of the digestate are separated as fertilizer;
storing the biogas received from the bioreactor; and
scrubbing the biogas to remove hydrogen sulphide, carbon dioxide, moisture and other trace gases.

6. The method as claimed in claim 1, wherein size of the agro residue is reduced by using a hammer mill and the like.

7. The method as claimed in claim 1, wherein the agro residue is fed to the bioreactor by using a pump.
, Description:Field of invention

The present invention relates to an integrated system and method for producing energy in the form of biogas, and/or electricity and fertilizer from a single biomass source, and more specifically, the present invention relates to the system and method for producing energy from high solids, fibrous material substrate, specifically from agricultural residue.

Background of the invention

There are three main reasons for producing energy and heat from agro residues:
1) Market demand for electricity and/or heat;
2) Potential for substantial energy production;
3) Avoiding open field burning of the agro residues.

The current technologies available to produce electricity and heat from agro residues include direct combustion, biomethanation, pyrolysis and gasification. The process of combustion, pyrolysis and gasification of the agro residue creates problems in the equipment since at high temperature the inorganic components in the agro residues react with one another and sometimes with the material of construction of the equipment used.

In biomethanation of the agro residue i.e. in anaerobic fermentation process, the major challenge is to have raw material and microbes available everywhere inside the bioreactor to efficiently convert the agro residue into biogas. There are various biochemical and chemical pre-treatment techniques available for processing of the agro residue to produce electricity and heat. However, these technologies are too expensive to use in combination with biogas production. Further, open field burning of the agro residue causes huge loss of precious nutrients in the biomass and at the same time it pollutes the environment. Moreover, the heat generated by burning the agro residue kills useful microbes in the soil, leading to poor soil health and loss of fertility. In fact, open field burning of biomass also increases the water requirement of the next crop cycle, as the moisture from the soil evaporates with the increase in temperature during burning.

Accordingly, there exists a need to provide a system and method for producing energy, heat and organic fertilizer from the agro residue which overcomes abovementioned drawbacks.

Objects of the invention

An object of the present invention is to generate fertilizer and biogas based energy by using agro residues/ products as biomass substrate.

Another object of the present invention is to abate pollution created by open field burning of agro residue.

Yet another object of the present invention is to recover saline land by utilization of the agro residues as manure/organic fertilizer.

Still another object of the present invention is to create livelihood for those with land rendered useless due to over use of chemical fertilizers and/or increase in ground water levels and salts.

One more object of the present invention is to provide an integrated system wherein the energy consumption of the system itself is less than 20 percent of the energy in biogas produced.

Another object of the present invention is to use part of the biogas produced to generate energy required to operate the system, such that it becomes independent of grid utility.

Further object of the present invention is utilization of the biogas produced by converting it to various forms as like: electricity, compressed biogas (as substitute for Natural Gas and LPG).

Summary of the invention

Accordingly, the present invention provides a system for producing energy in the form of biogas, and/or electricity and fertilizer from agro residue, in one aspect. The system comprises a feed preparation unit having a size reduction means for reducing size of the agro residue. The system further comprises a blending unit capable of receiving the agro residue from the feed preparation unit. The blending unit blends predefined quantities of the agro residue, culture, slurry, and water therein. The system furthermore includes a bioreactor capable of receiving the blended mixture from the blending unit. The bioreactor includes a plurality of openings adapted on the lower portion thereof. The biomethanation process takes place inside the bioreactor. The system also includes a feeding unit for uniform distribution of high solids, fibrous, agro residue as biomass substrate inside the bioreactor and a extraction unit capable of extracting the digestate from the bioreactor after biogas production. The extraction unit includes a jet distributor fixed to the plurality of openings at the bottom of the bioreactor, wherein liquid jets are passed into the bioreactor at controlled interval of time through the plurality of openings;

The system includes a fertilizer unit for processing the manure received from a solid liquid separator configured within the extraction unit. The solid liquid separator squeezes the digestate and, the solid and the liquid parts of the digestate are separated as fertilizer. The system also includes a biogas storage unit for storing the biogas from the bioreactor and a biogas scrubbing unit for scrubbing the biogas to remove hydrogen sulphide, carbon dioxide, moisture and other trace gases.

In another aspect, the present invention provides a method for producing energy in the form of biogas, and/or electricity and fertilizer from agro residue. The method comprises reducing size of the agro residue. Further, the method includes blending the predefined quantities of the agro residue, culture, slurry, and water. Furthermore, the method includes adding the blended mixture to the bioreactor for biomethanation. Thereafter, the method includes distributing high solids, fibrous, agro residue uniformly as biomass substrate inside the bioreactor by means of feeding unit. Also, the method includes extracting digestate from the bioreactor after biogas production by using extraction unit, wherein liquid jets are passed into the bioreactor from the plurality of openings configured at lower portion thereof at controlled interval. The method further includes sorting fertilizer received from a solid liquid separator configured within the extraction unit, wherein the solid liquid separator squeezes the digestate and solid and the liquid parts of the digestate are separated as fertilizer. The method also includes storing the biogas received from the bioreactor and scrubbing the biogas to remove hydrogen sulphide, carbon dioxide, moisture and other trace gases.

Brief description of the drawings

Figure 1 shows a schematic drawing of a system for producing energy in the form of biogas, and/or electricity and fertilizer from agro residue, in accordance with the present invention.

Detailed description of the invention

The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiments.

The present invention provides a system and method for biogas production, electricity production, utilization of the generated heat to stabilize the digestion process, organic fertilizer and utilizing the fertilizer produced to increase the land fertility and also for culturing aquatic life, thereby reducing salinity of the soil.

The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures. These reference numbers are shown in bracket in the following description.

Referring now to figure 1, there is shown a system (100) for producing energy in the form of biogas, and/or electricity and fertilizer from agro residue. The system (100) comprises a feed preparation unit (10), a blending unit (20), a bioreactor (30), a feeding unit (40), an extraction unit (50), a fertilizer unit (60), a biogas storage unit (70) and scrubbing unit (80).

The feed preparation unit (10) includes a size reduction means (12) for reducing size of the agro residue. In an embodiment, the size reduction means (12) is a hammer mill or any other size reduction equipment known in the art or combination thereof. The feed preparation unit (10) extracts the pulverised feed either physically and/ or pneumatically, separates the biomass from air by carrying it by means equipment such as settling chamber, cyclone bag filter and the like. The feed preparation unit (10) sends the pulverised agro residue to the blending unit (20).

Specifically, the blending unit (20) receives the pulverised agro residue from the feed preparation unit (10) by means of a conveyor (14). The blending unit (20) blends predefined quantities of the agro residue, culture, slurry, and water and sends the same to the bioreactor (30). The culture required for biomethanation may be obtained from any existing biomethanation plant.

The bioreactor (30) receives the blended mixture from the blending unit (20). The bioreactor (30) includes a plurality of openings (30a) adapted on the lower portion thereof. In an embodiment, the plurality of openings are capable being closed as and when required. The biomethanation process takes place inside the bioreactor. In preferred embodiment, the shape of the bioreactor (30) is made as a conical inverted ‘V’.

The feeding unit (40) uniformly distributes high solids, fibrous, agro residue as biomass substrate inside the bioreactor (30). In an embodiment, the feeding unit (40) includes a progressive cavity pump and/or any other suitable pump known in the art along with piping required for taking the blended mixture from the blending unit (20) to the bioreactor (30). The pump is capable of handling high solid non-viscous, fibrous mix and maintains high solids thereby reducing water requirement for the biomethanation process. Moreover, since the feed mix in the bioreactor (30) includes high solids and there is hardly any free liquid available, it avoids floatation of the biomass and scum formation within the bioreactor (30). This is very critical for smooth operation and functioning of the bioreactor (30).
Specifically, the feeding unit (40) ensures uniform distribution of high solids, fibrous, agro residue/product as biomass substrate inside the bioreactor (30), thereby overcoming the problem of pilling up of the biomass substrate inside the bioreactor (30). As the biomass is getting distributed at the time of feeding, there is formation of very small heaps, if any. Also, as the level inside the bioreactor is being maintained by extracting material at same rate, from the bottom of the vessel.

The conical inverted V shape of the bioreactor (30) is an essential design parameter for the extraction unit (50). The shape of the bioreactor (30) prevents fibrous feed bridging inside the bioreactor (30) and thereby ensuring uninterrupted system operation for continuous biogas generation.

The fibrous biomass in the bioreactor (30) has a tendency to mesh and bridge, which makes its movement difficult inside the bioreactor (30). As the feed is well blended, there is no need for any stirring inside the bioreactor (30). Also it would not be possible to stir such fibrous high solid biomass. The biomethanation process requires a desired residence time inside the bioreactor. Hence, the feed must go in and come out of the bioreactor in First-in-First-out (FIFO) basis. The biomass is thus fed from top of the bioreactor (30) and extracted from the bottom.

Once the biogas is produced in the bioreactor (30), the extraction unit (50) extracts the digestate from the bioreactor (30). Further, extraction is also done with specially designed jet distributor arrangement within the bioreactor (30). The bottom layers of the biomass in the bioreactor (30) are removed in the extraction. The extraction unit (50) includes a jet distributor (52) fixed to the plurality of openings at the bottom of the bioreactor (30). The liquid jets are passed into the bioreactor (30) at controlled interval of time through the plurality of openings. Specifically, the numbers of jets are designed according to size of bioreactor and the biomass substrate used for biogas generation.

The digestate from the bioreactor (30) is extracted through an actuated extraction valve (32) and is squeezed by means of a solid liquid separator (34). The solid and the liquid parts of the digestate are separated. The solid and the liquid parts of the digestate are used as manure and stored in the fertilizer unit (60). The value of the manure/fertilizer is enhanced by addition of minerals and herbal extract. The biogas produced from the bioreactor (30) is stored in the a biogas storage unit (70) and can be utilized for running engine of the electricity generator, as cooking gas, it can be cleaned and compressed for replacing other fuels such as CNG, LPG, PNG, and the like. Specifically, the biogas scrubbing unit (80) is used for scrubbing the biogas to remove hydrogen sulphide, carbon dioxide, moisture and other trace gases. In an embodiment, scrubbing technology and designs are selected based on the requirements at the user point. Specifically, water scrubbing, chemical scrubbing, pressure swing adsorption, temperature swing adsorption, cryogenic separation of components, and the like are used.

The biogas obtained from the system is used for power generator (90). For electricity generation as end use of the biogas, often, carbon dioxide is not removed from the biogas and only hydrogen sulphide is brought down to levels acceptable to the engine, turbine, and boiler which operates the prime mover of the power generator (90). In case the gas is to be used as replacement of CNG, LPG or PNG, the scrubbing is done accordingly and the cleaned biogas is further pressurized depending on the requirements.

The organic fertilizer produced is used for cultivation and also aids in saline land recovery. Part of the energy generated by the system can be used for operating the entire plant.

The extracted slurry after the digestate from the bioreactor (30) has nutrient value for plants. It can be further enhanced by adding certain micronutrients and minerals and converting it to organic fertilizer. The slurry is passed through the solid-liquid separator (34), wherein part of the solids are recycled as culture for the fresh feed and the balance solids are sent to fertilizer unit (60) for incorporating additives, blending, drying, weighing, bagging and the like. The fertilizer / manure can be bagged, or despatched loose. It may or may not be pelletized.

The liquid portion of the slurry is recycled to the feed preparation system for blending it with the incoming fresh substrate and some portion of the recycled manure. Depending on the process design, the manure culture can be separated and sent back before or after the solid-liquid separator.

The system (100) optionally includes waste heat recovery system (90B), and biogas cleaning i.e. scrubbing and compression system (90A) depending on the end use requirement.

The engine exhaust generally comes out at temperatures over 400 degree and could be as high as 600 degree Celsius. The recovered heat could be in the form of hot water or steam. The magnitude of energy recovered could be comparable to the power rating of the engine itself; e.g. a 500 kW engine can very well provide heat at 500 kW.
If biogas is cleaned and compressed, it can replace CNG, LPG or other fuels. The pressures for cleaned biogas storage could be around 200 bar and even over 250 bar at times.

Advantages of the invention

1. The system (100) and method harness energy from the biomass by converting it into fertilizer and biogas.

2. The system (100) and method of the present invention is based on a single or multiple biomass sources to create value added produce which is used for cultivation, and the organic carbon and the microbes in the manure helps in making even a piece of saline land fertile.

3. The system (100) and method helps in avoiding killing of useful microbes in the soil by open field burning of biomass, leading to poor soil health and loss of fertility.

4. The system (100) and method requires no chemicals. Hence, the output manure can be used as base for organic fertilizer.

5. Energy in the in the system (100) by way of biogas is produced through the anaerobic process; it can be further converted to desired forms like electricity or compressed bio-methane.

6. Waste heat recovery system, which is part of the present invention, helps in making the method further efficient and using the recovered heat to maintain the bioreactor temperature within desired limits.

7. The system (100) and method requires less than 20% of the energy that is generated from the biogas it produces, making the solution viable.

8. The system (100) and method offers possibility of creating further value addition steps by using the manure for mushroom plantation before converting to fertilizer.

9. The water rejected from the system (100) can be used to grow special biomass which can become animal feed or raw material for health foods or nutrition supplements. The water could be further used for aquaculture.

10. There is practically no waste stream coming out of the biogas fertilizer energy plant based on agro residue / produce. Every output is a product. In fact, even the carbon dioxide from the plant can be put to productive use before it is released to the atmosphere.

11. There is no net carbon dioxide addition to the atmosphere through the system (100).

12. The system (100) can be managed to become a “zero effluent” solution.

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.