|Title of Invention
AN ANAEROBIC DIGESTER ASSEMBLY
|This invention relates to an anaerobic digester assembly comprising an inclinedly disposed digester chamber having an inlet means to introduce DOC in slurry form prepared with water to said digester chamber, vertically; a gas outlet at the other end thereof and a discharge outlet located at the base of said digester chamber connecting to digestate collection system for discharging spent feed, said digestate collection system provided with automatic level control means. Fig.l
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
& The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
(See section 10 and rule 13)
TITLE OF THE INVENTION An Anaerobic Digester Assembly
Tata Consulting Engineers Limited, having its registered office at Matulya Centre-A, 249 Senapati Bapat Marg, Lower Parel (W), Mumbai - 400 013, Maharashtra, India, and its Corporate office at 4th floor, 247 Park, Tower "A" & "B", LBS Marg, Vikhroli West, Mumbai 400 083, Maharashtra, India
Gupta Purshottam Das and Vijapure Mohaimin Ara both Indian nationals of Tata Consulting Engineers Limited
PREAMBLE TO THE DESCRIPTION
The following complete specification particularly describes the nature of the invention and the manner in which it is to be performed.
FIELD OF THE INVENTION
This invention relates to an inclined cylindrical anaerobic digester in which slurry enters from one end, moves slowly in plug flow manner to the other end. It is a non-chambered digester where the forward moving organic material decomposes and generates biogas mainly comprises of methane and carbon dioxide.
BACKGROUND OF THE INVENTION
With ever increasing energy demand and limited fossil fuels resources worldwide attention is focused on utilization of non-conventional form of energy. This has lead to the augment of biodiesel industry wherein the feedstock mainly comprises of cash crops. These cash crops also include inedible varieties of vegetable oils extracted from tree borne oil seeds like Jatropha, Karanj etc. Disposal of the de-oiled cake (DOC) generated from these tree borne seeds that remains after the extraction of oil, is of concern. These DOC are unfit for any other use particularly for animal feed as it contains certain harmful components such as Phorbol ester and Curcin. The total solid content of DOC found to be as high as 93% out of which about 86% is the volatile solid. High percentage of volatile solid provides good opportunity of biogas generation while it gets decomposed. And therefore, these de-oiled cakes are suitable for fermentation in an aerobic digester and to generate useful biogas; a source of energy.
This invention pertains to a simple and effective digester design which ferments feedstock of high solid content, particularly de-oiled cake in a plug flow manner. The name "plug flow" is used for designs that are unstirred and tubular. In this the feed passes in a sequential manner from inlet to outlet. The innovative digester configuration leads to retention and growth of desired microorganisms and thus making fermentation process sustainable on continuous basis.
There are various designs of digesters used for the fermentation process and unlike the prior art digesters of this type which have employed either horizontal digester or horizontal digesters with compartments, this invention employs an inclined plug flow digester for smooth movement of slurry in a controlled manner. Few of the advantages of this type of simple digester include adjustability of digester volume depending on the available quantity of feed material. Also such digesters can be operated by semiskilled workers in rural areas due to its simpler operation.
The inclined positioning of the digester chamber enables free flow of the slurry there through. Separate chambers and mix up chambers are avoided. Non-obstructive flow prevents sedimentations.
OBJECTS OF THE INVENTION
An object of this present invention is to present a digester design established from
bench scale experimental work,
A further object of this present invention is to provide a simple feeding and
discharging system for the anaerobic digester.
At another object of this present invention is to provide a continuous fermentation
process without any form of agitation or mixing of slurry inside digester.
An object of this invention is to avoid pre-treatment of feed material prior to feeding
to main digester in a pre-digester.
A further object of this invention is directed to the digester which generates high
volume of gas using a low volume digester.
A further object of this invention is to provide a novel anaerobic digester which avoids
scum formation during its operation.
Further object of this invention is to facilitate self regulation of pH value and thus to
avoid any external means for its control during the fermentation process.
Yet another object of this invention is to fabricate a digester with minimum number of
ports to mitigate gas leakage.
Further object of this invention is to provide means of heating to maintain the digester temperature within the required range.
STATEMENT OF INVENTION:
An anaerobic digester assembly comprising an inclinedly disposed digester chamber having an inlet means to introduce DOC in slurry form prepared with optimum water to said digester chamber, vertically; a gas outlet at the other end thereof and a discharge outlet located at the base of said digester chamber connecting to digestate collection system for discharging spent feed, said digestate collection system provided with automatic level control means.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows an anaerobic digester assembly according to the invention Figure 2 shows the digester chamber according to the invention Figure 3 shows the discharge handling feature of the invention Figure 4 shows a portion of the digester in accordance with the invention
DETAILED DESCRIPTION OF THE INVENTION
The invention provides a method for a continuous digester system that utilizes anaerobic microbes to convert organic material particularly de-oiled cake generated from biodiesel industry, into useful biogas. It also provides collection of digested material that is rich in nitrogen, phosphorous and potassium (NPK); suitable for use as fertilizer/ manure.
This invention will now be described with reference to the schematic drawings shown in FIGS. 1 to FIG. 4.
FIG. 1 shows an anaerobic digester assembly 10 interconnected with different parts namely a feed supply means 12, a digester chamber 14, a gas collection means 16, and a digestate collection means 18. The slurry is prepared by mixing grinded DOC with water in the feed tank 20 in a predetermined ratio. The pump 22 conveys the prepared slurry into the digester inlet 24. The slurry is so fed that it falls into the digester vertically. This helps in prevention of accumulation of feed at the inlet as well promotes its movement in the digester. During operation the slurry passes into the digester tank, remains therein for a predetermined amount of time and is then removed via the outlet.
The digester system 14 produces biogas, which is a predominant mixture of methane and carbon dioxide, that flows through a conduit 34 and gets collected into a gas collection tank 32 which can be further processed as per end user needs. The slurry transverses the digester length and gets removed into discharge tank 40.
Referring now to FIG. 2. the digester chamber 14 according to the invention can be seen in detail. The digester is a cylindrical, closed air tight horizontal anaerobic tank wherein the slurry is introduced through inlet 24. The inlet is so positioned as to let the slurry fall vertically in the digester. The inlet is coordinated with the minimum slurry level which would be maintained in the digester and would avoid the exposure of the inlet pipe into the gas space. The height of feed inlet point from digester bottom is maintained in the range of 0.2D-0.3D where D is the digester diameter. Water to DOC ratio in feed preparation is an important factor to achieve optimum biogas generation. The water/DOC ratio on weight basis is maintained in the range of 4 to 6 . The digester has a gas disengaging space 28 ranging between 15-25% of the digester volume. This gas space, determined experimentally, maintains the slurry at levels such that slurry does not over fill the digester thereby leaving no gas space as well as too low thereby causing gas to escape. 48 is the experimentally determined normal slurry level maintained in the digester.
The design of the digester is also such that at optimum hydraulic retention time it provides highest gas production for a particular feed rate. The gas production potential of the de-oiled cake has been established between 280-300 Nm3/ton. Also the biogas obtained has a composition in the range of 65-70% methane and 35-30% carbon dioxide. The 5-6 ratio of digester length to diameter (L/D) is an important design factor of the present invention wherein it helps in fixing another important design parameter hydraulic retention time for different feed rates at minimum along with good gas production rate. The biogas production rate as high as 2.3 Nm /day/m of digester volume could be achieved with optimum DOC feed rate of 8.0 kg/day/m3 of digester volume.
The feed handling feature is also illustrated here. The slurry contains material which becomes denser than water during entry as well during digestion and hence tends to settle down 26 and accumulate in the digester. The problem is overcome by maintaining the digester at an inclination 30 with the horizontal. The inclination facilitates non obstructive movement of the slurry. The inclination maintained is neither too high nor too low as high inclination will cause fresh feed to short circuit towards the outlet while too low will hamper the plug flow movement of the slurry. The inclination determined experimentally in the present invention prevents short circuiting of the feed thereby flowing out before its desired retention period which in turn dispenses the need for chambers/compartments to retain the bacterial mass since feed's settling characteristic would create dead spaces within the chambers and hence reduce effective volume of the digester.
The digester basically converts complex organic substance into biogas with the help of consortia of microbes. Within a digester there is a bacterial environment which is characterized by different phases namely hydrolysis phase, acidogenic phase, acetogenic phase and methanogenic phase. Usually in plug flow digesters hydrolytic microbes are present near the inlet of the digester which break down complex organic material into simpler forms and the methanogenic bacteria are present near the outlet
which use products of other phases present in between to produce methane. The inclination is such that although it aids the slurry movement however it does not cause mixing up of the different zones since it is undesirable to mix a certain microbial group with another as it can it interfere with the efficient operation of the digester.
The digester design doesn't require external pH control. The ph varies in the range of 5 to 8 between inlet and outlet ends of the digester. Thus the fermentation is self sustaining on a continuous basis without any external pH control mechanism. Once the slurry reaches the opposite end of the digester it is discharged through the outlet 38.
Referring to FIG. 3, the discharge handling feature of the invention is illustrated. The outlet of the digester 38 connects to digestate collection system 18. The outlet positioning is such that only the digested matter flows out. In this invention it is fixed at the inclined base of the digester. This position helps in outflow of the digestate under the action of gravity. It is so designed as to serve a dual purpose. The tank 40 is a hopper styled container which receives the discharge from the digester. It is further connected to an inverted U shaped pipe. One method of working of this system is that the hopper shape allows the discharge to separate out its constituents into respective solid and liquid fraction leaving the solids at the bottom and liquid to rise into the connected pipe 44 from where the excess liquid is drained out through the drain line 46. The solid fraction of the digested slurry is removed from the outlet 42 to be used further as manure. This arrangement helps avoiding the use of a separate unit operation for handling the digestate. Another important use of this design is to maintain a constant slurry level in the digester. The digestate tank volume is so designed as to contain the displaced quantity of slurry in lieu of the similar quantity fed on daily basis. This displaced slurry discharges into the tank 40, fills up and rises into the connected pipe 44. The height of the drain siphon pipe 44 is fixed as per the required slurry level inside the digester. Once the liquid in the pipe reaches the
desired slurry level, the discharge of the digestate stops automatically since the required head to maintain slurry level is provided by the liquid in the pipe 44,
Another embodiment of the invention is the heating mechanism used for maintaining the metallic digester at the required temperature. Referring to FIG.4 a portion of the digester is enclosed in a chamber of brick and mortar 50. This chamber is heated up by incinerating locally available low grade combustible materials inside the hollow space 52. An opening is provided both at the front 53 A and the back end 53 B of the chamber which serves the purpose for putting the material used for heating inside the chamber, for venting of the generated gases as well as for the removal of the incinerated material .
The above embodiments of the invention shown and described in some details are for a predetermined set of operating parameters and conditions and the ranges so mentioned are experimentally established. Therefore the invention is limited within the scope of the appended claims. Obvious modifications and alterations known to person skilled in the art are within the scope of the ambit of the appended claims.
1. An anaerobic digester assembly comprising an inclinedly disposed digester chamber having an inlet means to introduce DOC in slurry form prepared with water to said digester chamber, vertically: a gas outlet at the other end thereof and a discharge outlet located at the base of said digester chamber connecting to digestate collection system for discharging spent feed, said digestate collection system provided with automatic level control means.
2. The digester assembly as claimed in claim 1, wherein said digester chamber is inclined from the horizontal plane.
3. The digester assembly as claimed in claims 1 and 2. wherein said feed inlet is located at 0.2 D to 0.3 D above the bottom of said digester, D being the diameter of said digester.
4. The digester assembly as claimed in claims 1 to 3, wherein said digester chamber has a length to diameter ratio ranging from 5 to 6 and a gas disengaging space ranging from 15% to 25% of its volume.
5. The digester assembly as claimed in claims 1 to 4, wherein said automatic level control means comprises drain siphon pipe fixed as per the required slurry level inside said digester chamber
6. The digester assembly as claimed in claims 1 to 5, wherein the digester chamber is metallic and is enclosed in a chamber for providing external heating.
7. The digester assembly as claimed in claims 1 to 6, wherein the gas outlet is connected to conduits and gas collection tanks for storing the gas produced.
8. The digester assembly as claimed in claims 1 to 7, wherein the feed is slurry of de-oiled cake (DOC) prepared with water 4 to 6 times of DOC weight and the gas produced is biogas.
9. A method for producing biogas by anaerobic fermentation of biomass such as de-oiled cake in an anaerobic digester assembly as claimed in any one of the preceding claims, comprising the steps of feeding a slurry of the biomass to the digester chamber vertically, allowing it to ferment in an conventional manner recovering the biogas produced through the gas outlet and the spent mass from the outlet at the base.
10. An anaerobic digester assembly substantially as herein described with reference to the figures shown in the accompanying drawings.
|Indian Patent Application Number
|PG Journal Number
|Date of Filing
|Name of Patentee
|TATA CONSULTING ENGINEERS LIMITED
|MATULYA CENTRE-A, 249 SENAPATI BAPAT MARG,LOWER PAREL (W),MUMBAI 400 013.MAHARASHTRA, INDIA.AND ITS CORPORATE OFFICE AT 4TH FLOOR, 247 PARK,TOWER "A" &"B", LBS MARG,VIKHROLI WEST, MUMBAI 400 083,MAHARASHTRA, INDIA
|PCT International Classification Number
|PCT International Application Number
|PCT International Filing date