Claims:We claim:

1. A two-stage anaerobic biogas digester with enhanced anaerobic digestion arrangement, wherein the digester comprises:

• a first digester connected to a feedstock grinder-cum-feeder disposed at a higher level for supplying biomaterials thereto by gravitational flow for conducting anaerobic digestion of the biomaterials therein;

• a second digester connected downstream the first digester for supplying partially digested biomaterials slurry thereto by gravitational flow for conducting further anaerobic digestion of the biomaterials therein;

• a slurry pit disposed downstream the second digester for collecting the digested biomaterial slurry to be used as compost and fertilizer;

wherein the first and second digesters comprise a respective lower anaerobic digester and a domed tank floating above the slurry and in the water jacket and disposed in the lower anaerobic digester for collecting the biogas produced by anaerobic digestion of the biomaterials supplied to the two-stage biogas digester.

2. Two-stage anaerobic biogas digester as claimed in claim 1, wherein the respective water jacket has a U-shaped section filled with water and having the inverted straight wall of the floating domed tank continuously submerged therein for preventing any leakage of the biogas generated therein.

3. Two-stage anaerobic biogas digester as claimed in claim 1, wherein a plurality of vertical agitators or stirrers depend from the roof of the floating domed tank and extending in a sealing manner through the bottom thereof into the lower anaerobic digester for thorough mixing of the biomaterial slurry supplied and being digested therein.

4. Two-stage anaerobic biogas digester as claimed in claim 2, wherein each vertical agitator or stirrer is driven by an electric motor mechanically coupled thereto.
5. Two-stage anaerobic biogas digester as claimed in claim 1, wherein a plurality of horizontal agitators or stirrers mounted from the side of the lower anaerobic digester.

6. Two-stage anaerobic biogas digester as claimed in claim 4, wherein each horizontal agitator or stirrer is driven by a pump for hydraulic stirring to facilitate the recirculation of the biomaterial slurry being digested therein and for breaking the scum produced therein.

7. Two-stage anaerobic biogas digester as claimed in any one of the claims 1 to 6, wherein the upper level of the biomaterial slurry in the second bio-digester is at the lower level of the pipe connecting the two digesters.

8. Two-stage anaerobic biogas digester as claimed in any one of the claims 1 to 7, wherein the upper level of the slurry pit disposed downstream the second bio-digester is at a lower level than the pipe connecting the same with the slurry pit.

9. Two-stage anaerobic biogas digester as claimed in any one of the claims 1 to 8, wherein the bio-digestion anaerobic digestion efficiency is substantially enhanced by splitting the anaerobic digestion processes into hydrolysis, acidogenenesis, acetogenesis and methanogenesis divided between first and second bio-digesters.

10. Two-stage anaerobic biogas digester as claimed in claim 9, wherein the overall digestion efficiency of the biogas generation therein is in a range of 80-90%.

Dated: this 29th day of June 2017. SANJAY KESHARWANI
APPLICANT’S PATENT AGENT , Description:FIELD OF INVENTION

The present invention relates to anaerobic biogas digesters. In particular, the present invention relates to water-sealed anaerobic biogas digesters. More particularly, the present invention relates to two-stage gravitational flow, water-sealed anaerobic biogas digesters with mechanical agitators mounted on the floating dome and laterally mounted hydraulic agitators for improved anaerobic digestion efficiency.

BACKGROUND OF THE INVENTION

The biogas digesters have been receiving increased consideration because of their capability to transfer waste into useful energy. The farm wastes, industrial biological process wastes or any other biologically degradable material can be converted into useful energy and nutrient-rich fertilizers. Biogas digesters works on the principle of anaerobic digestion, in which the biological materials are acted upon by microorganisms.

Unlike the composting process, the digestion process for producing the biogas is carried out under anaerobic conditions, i.e. with zero oxygen availability. The biogas so produced contains about 55–70% of methane, which forms the primary component of the natural gas and the rest of the biogas composition basically consists of carbon dioxide and some traces of hydrogen sulphide, nitrogen etc.

Renewable energy has become need of the hour with rapidly depleting natural resources. On the other hand, safe waste disposal is a challenge that the world is facing now. Biogas is one such solution which can effectively address both the abovementioned challenges and offers to establish a green and clean economy.

Biogas installations are not new, but the effectiveness of the existing biogas plants has not been so good that it can harness the energy efficiently and economically. The lack of understanding the issues and challenges facing the biogas generation has been the key issue in expansion of this promising field.

Standard KVIC model of biogas plant has been used widely in India, because this model proves to be efficient enough for Indian conditions, with many advantages and disadvantages thereof. The efficiency levels have been lower to even for the newly developed CSTR type digesters.

Therefore, it is the need of the hour to address this critical issue by expediting the issues linked with the KVIC model bio-digesters to remove the disadvantages associated with it and to make it useful even for higher loads and increased feed rates and to achieve a higher efficiency.

The major advantage is that the cost impact of improving the KVIC model of bio-digester is very low due to a simplified configuration of the two-stage bio-digester made according to the present invention.

DISADVANTAGES WITH THE PRIOR ART

The main disadvantage of the conventional bio-digester (Figure 1) discussed above is that the standard model of KVIC digester is a single stage without provision of any stirrer or water jacket to prevent biogas leakage. Although, the flow is a gravitational flow even in a standard KVIC model, however is has only one digester and the achievable efficiency levels are of the order of about 70%.

Therefore, there is an existing need for improving the efficiency of the conventional single-stage KVIC type of bio-digesters to make it more cost-effective and that too without any complex and expensive fitments thereon.

OBJECTS OF THE INVENTION

Some of the objects of the present invention - satisfied by at least one embodiment of the present invention - are as follows:

An object of the present invention is to provide a two-stage bio-digester for improving the anaerobic digestion process therein.
Another object of the present invention is to provide a two-stage bio-digester which is based on gravitational flow for improving the anaerobic digestion process therein.

Still another object of the present invention is to provide a two-stage bio-digester which prevents biogas leakage by providing a water-sealing therein.

Yet another object of the present invention is to provide a two-stage bio-digester equipped with twin-agitation for excellent digestion of biomaterials fed therein.

A still further object of the present invention is to provide a two-stage bio-digester, gravitational flow, anaerobic digester with mechanical agitators or stirrers for a homogenous mixing of the biomaterials for an efficient digestion thereof.

A yet further object of the present invention is to provide a two-stage bio-digester, gravitational flow, anaerobic digester with hydraulic agitators or stirrers for an improved mixing and scum breakage for an efficient digestion thereof.

These and other objects and advantages of the present invention will become more apparent from the following description, when read with the accompanying figures of drawing, which are however not intended to limit the scope of the present invention in any way.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a two-stage anaerobic biogas digester with enhanced anaerobic digestion arrangement, wherein the digester comprises:

• a first digester connected to a feedstock grinder-cum-feeder disposed at a higher level for supplying biomaterials thereto by gravitational flow for conducting anaerobic digestion of the biomaterials therein;

• a second digester connected downstream the first digester for supplying partially digested biomaterials slurry thereto by gravitational flow for conducting further anaerobic digestion of the biomaterials therein;

• a slurry pit disposed downstream the second digester for collecting the digested biomaterial slurry to be used as compost and fertilizer;

wherein the first and second digesters comprise a respective lower anaerobic digester and a domed tank floating above the slurry in the water jacket and disposed in the lower anaerobic digester for collecting the biogas produced by anaerobic digestion of the biomaterials supplied to the two-stage biogas digester.

Typically, the respective water jacket has a U-shaped section filled with water and having the inverted straight wall of the floating domed tank continuously submerged therein for preventing any leakage of the biogas generated therein.

Typically, a plurality of vertical agitators or stirrers depend from the roof of the floating domed tank and extending in a sealing manner through the bottom thereof into the lower anaerobic digester for thorough mixing of the biomaterial slurry supplied and being digested therein.

Typically, each vertical agitator or stirrer is driven by an electric motor mechanically coupled thereto.

Typically, a plurality of horizontal agitators or stirrers mounted from the side of the lower anaerobic digester.

Typically, each horizontal agitator or stirrer is driven by a pump for hydraulic stirring to facilitate the recirculation of the biomaterial slurry being digested therein and for breaking the scum produced therein.

Typically, the upper level of the biomaterial slurry in the second bio-digester is at the lower level of the pipe connecting the two digesters.

Typically, the upper level of the slurry pit disposed downstream the second bio-digester is at a lower level than the pipe connecting the same with the slurry pit.
Typically, the bio-digestion anaerobic digestion efficiency is substantially enhanced by splitting the anaerobic digestion processes into hydrolysis, acidogenenesis, acetogenesis and methanogenesis divided between first and second bio-digesters.

Typically, the overall digestion efficiency of the biogas generation therein is in a range of 80-90%.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will be briefly described with reference to the accompanying drawings, wherein:

Figure 1 shows a conventional biogas digester, i.e. a standard KVIC model (http://www.eplantscience.com/index/images/Biotechnology/chapter20/154_large.jpg).

Figure 2 shows a schematic arrangement of the biogas digester configured in accordance with the present invention.

Figure 3 shows an enlarged view of the digester 1 of biogas digester of Fig. 2.

Figure 4 shows the bio-digester units 220, 230 of the two-stage biogas digester 200 of Fig. 2 disposed at different levels for enabling a gravitational flow therebetween.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

In the following, the biogas digester configured in accordance with the present invention will be described in more details with reference to the accompanying drawings without limiting scope and ambit of the present invention in any way.

Figure 1 shows a conventional biogas digester 100, which is of a standard KVIC model. It includes a compost tank 110, a hollow domed gas tank 120 floating inside the digester 110 and a manure tank 130. The digester 100 is provided with an inlet 102 disposed above ground to supply biomaterial 104 such as animal dung, via an inlet pipe 106 connected to one side of the lower portion 112 of the compost tank 110 and the other side thereof is connected to an outlet pipe 116 for sending the digested semi-solid waste residue 112 collected in the lower portion of the compost tank 110 to the manure storage tank 130. This semi-solid residue 112 is useful to be used as manure to be delivered through an outlet 132 to be added to soil as bio-fertilizers 134. The anaerobic digester 110 is preferably disposed underground in the soil 108 and the hollow domed gas tank 120 floating inside the digester 110 is partially disposed above ground 10. The biogas 122 produced in the bio-digester 100 accumulates above the scum 114 which is floating above the semi-solid residue 112. This biogas 122 is taken out via an outlet pipe 124 fitted on the top most point of the hollow domed gas tank 120, e.g. for cooking 126 and lighting 128 purposes. This conventional biogas digester 100 has an efficiency of about 70%, which needs to be improved further to make it more cost-effective.

Figure 2 shows a schematic arrangement of the two-stage biogas digester 200 configured in accordance with the present invention, whereby the efficiency of the biogas digester can be substantially increased, i.e. raised above 85%. It includes a feedstock grinder 210, a first bio-digester 220, a second bio-digester 230 and a slurry pit 250, each of the units 210, 220, 230 and 250 are successively disposed at a lower level with respect to its preceding unit. The bio-digester units 220, 230 include a lower anaerobic digester 226, 236 and a respective domed biogas tank 228, 238 floating above the anaerobic digester 226, 236 configured with a respective water jacket 225, 235 having U-shaped section on the top walls thereof, for sealing any biogas leakage from the biogas digester 200. The domed tanks 228 and 238 float in the respective water jackets 225, 235 of the anaerobic digesters 226, 236 by sliding on a corresponding guide pipe 223 and 233. Each unit 220, 230 is also equipped with a plurality of vertically disposed mechanically operated agitators or stirrers 222, 232 and extending through the bottom thereof into the lower anaerobic digesters for continuous mixing of the biomaterial to be converted into a slurry of digested biomaterial or manure 225, 235 and biogas 227, 237 is generated therein by anaerobic bio-digestion process occurring inside the respective bio-digester unit 220, 230. The hydraulically operated agitators or stirrers 224, 234 are provided for mixing the biomaterial and breaking the scum for enhanced bio-digestion. The vertically mounted agitators or stirrers 222 are operated by a respective motor 221, while the hydraulically mounted agitators or stirrers 224 are operated by a respective hydraulic pump 229. The biogas generated in the bio-digesters 220, 230 is taken out through a respective opening in the dome roofs via biogas outlet pipes with the joint outlet 245 connectable directly to the biogas application or the storage tank thereof.

Figure 3 shows an enlarged view of the digester 1 of the biogas digester of Fig. 2, in which bio-digester unit 220 is equipped with a plurality of vertically disposed and mechanically operated agitators or stirrers 222 for continuous mixing of the biomaterial to be separated into bio-digested slurry or manure 225 and biogas 227 produced therein by bio-digestion process occurring inside the bio-digester unit 220. Whereas, the hydraulically operated agitators or stirrers 224 are provided for mixing the biomaterial and breaking the scum for enhanced bio-digestion. The vertically mounted agitators or stirrers 222 are operated by an electrical motor 221, while the laterally mounted agitators or stirrers 224 are operated by a respective hydraulic pump 229. In addition, a water-jacket 225 is disposed between the anaerobic digester 226 and the domed hollow gas tank 228 for sealing any biogas leakage from the biogas digester unit 220. A similar arrangement is provided for the second bio-digester unit 230 of the biogas digester 200 configured in accordance with the present invention. Since the dome digester 228 is floating above the bio-digested slurry 225, the dome 228 remains clean and free of odour to make its surroundings hygienic.

Figure 4 shows the bio-digester units 220, 230 of the two-stage biogas digester 200 of Fig. 2, which are disposed at different levels for enabling a gravitational flow therebetween. Accordingly, the maximum height of the biological material fed into the first bio-digester unit 220 is higher by a height H1 with respect to the maximum height of the biological material fed into the second bio-digester unit 230, which is also the maximum height of the outlet pipe of the first bio-digester unit 220. Similarly, the maximum height of the biological material fed into the second bio-digester unit 230 is higher by a height H2 with respect to the maximum height of the outlet pipe of the second bio-digester unit 230, which is at a higher level than the slurry pit 250.

WORKING OF THE INVENTION

The two-stage, gravitational flow bio-digester with floating dome digesters disposed at different levels are deployed with agitators or stirrers vertically mounted on the floating domed biogas tanks thereof helps in mixing the biomaterial slurry supplied inside the digester for uniform bacteria distribution across the entire digester chamber. Further, the deployment of the agitators or stirrers horizontally mounted on the lower anaerobic digester helps in breaking the scum when the impeller is in the top position, i.e. when the floating dome digester is full. These hydraulic agitators also help in improving the efficiency by recirculating the slurry inside the digester to create additional agitation thereof.
The major advantage of the two-stage digester developed from the single-stage bio-digester of KVIC model substantially improves the efficiency by splitting the processes in anaerobic digestion hydrolysis, acidogenenesis, acetogenesis and methanogenesis divided between first and second stage.

This leads to an improved methanogenesis in the second digester which in turn is a significant factor for improving the overall efficiency of this bio-digester. The flow in the bio-digester tanks from the feeding point to the slurry tank is by a gravitational flow, and thus requires no pumps or forced flow methods to be employed therein.

This also leads to very low scavenging losses because of the simple method used for inducing the slurry flow within the improved bio-digester. The continuous flow from inlet to the slurry tank also continuous moves the slurry inside the digestion for optimum results in this anaerobic bio-digestion process.

Furthermore, the dome digester floats in a water jacket as compared to the floating dome in slurry in the conventional KVIC model. This water jacket seals the gap existing between the dome digester and the anaerobic digester to avoid any biogas leakage therefrom.
Another advantage of this improved bio-digester is that the dome digester is not floating in slurry and therefore, the dome surface remains clean and free from odour. This also improves the overall aesthetic value by keeping the surroundings clean and odour-free by enhancing the hygiene.

The efficiency of this two-stage, gravitational flow, anaerobic bio-gas digester is over 85%, which is substantially higher than the efficiency of about 70% of the conventional KVIC bio-digester.

TECHNICAL ADVANTAGES AND ECONOMIC SIGNIFICANCE

The two-stage, gravitational flow, anaerobic bio-gas digester configured in accordance with the present invention has the following technical and economic advantages:

• Higher efficiency.

• Better Aesthetics and enhances overall hygiene around the plant site.

• Cleaner and odour free surroundings.

• Low scavenging losses.

• No biogas leakage due to water-jacket, thus a fireproof and safe plant.

The exemplary embodiments described in this specification are intended merely to provide an understanding of various manners in which this embodiment may be used and to further enable the skilled person in the relevant art to practice this invention. The description provided herein is purely by way of example and illustration.

Although, the embodiments presented in this disclosure have been described in terms of its preferred embodiments, the skilled person in the art would readily recognize that these embodiments can be applied with modifications possible within the spirit and scope of the present invention as described in this specification by making innumerable changes, variations, modifications, alterations and/or integrations in terms of materials and method used to configure, manufacture and assemble various constituents, components, subassemblies and assemblies, in terms of their size, shapes, orientations and interrelationships without departing from the scope and spirit of the present invention.

While considerable emphasis has been placed on the specific features of the preferred embodiment described here, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiments without departing from the principles of the invention.

These and other changes in the preferred embodiment of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

Many of the fastening, connection, processes and other means and components utilized in this invention are widely known and used in the field of the invention described, and their exact nature or type is not necessary for an understanding and use of the invention by a person skilled in the art and they will not therefore be discussed in significant detail.

The numerical values given of various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher or lower than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the disclosure unless there is a statement in the specification to the contrary.

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, shall be understood to implies including a described element, integer or method step, or group of elements, integers or method steps, however, does not imply excluding any other element, integer or step, or group of elements, integers or method steps.

The use of the expression “a”, “at least” or “at least one” shall imply using one or more elements or ingredients or quantities, as used in the embodiment of the disclosure in order to achieve one or more of the intended objects or results of the present invention.

Also, any reference herein to the terms ‘left’ or ‘right, ‘up’ or ‘down, or ‘top’ or ‘bottom’ are used as a matter of mere convenience, and are determined by standing at the rear of the machine facing in its normal direction of travel.

Furthermore, the various components shown or described herein for any specific application of this invention can be widely known or used in the art by persons skilled in the art and each will likewise not therefore be discussed in significant detail. When referring to the figures, like parts are numbered the same in all of the figures.