Description:4. DESCRIPTION
FIELD OF THE INVENTION
Present invention relates to a continuous stirred tank reactor (CSTR) based biogas plant. The biogas plant as per present invention is provided with; an arrangement for feed slurry preparation that remove oil and wax present in waste; an inbuilt mechanisms for mixing of digested feed slurry with fresh feed slurry; means for controlling temperature, pH and agitation of the feed slurry in the reactor; a device for feed slurry level monitoring; removal of moisture and hydrogen sulphide gas from the biogas; a unique biogas two stage pressure safety and control arrangement and a foam trapping system.
The said biogas plant is easy to operate. It is provided with an automatic control means for parameters such as pressure, temperature and pH in the reactor. It is provided with a means for biogas purification and an antifoaming arrangement. The said biogas plant is suitable for numerous raw materials. The said biogas plant produces biogas efficiently in all weather and has an application in the field of waste to energy, waste management, anaerobic digestion of waste and biogas production.
BACKGROUND OF THE INVENTION
In a biogas plant anaerobic digestion of the feedstock which is in the form of slurry is occurred in an oxygen-free environment generating biogas and a nutrient-rich byproduct called digestate that can be used as a fertilizer. Biogas plants are provided with major systems namely a system for preparing feed stock, a digester or reactor in which biogas is produced by anaerobic digestion of the feed stock, a biogas purification system and a biogas storage system that collects and store biogas produced in the digester or reactor for further use. Depending on the quantity of feed waste to be digested and volume of biogas production, a biogas plant might have more than one digester and gas holders.
Biogas is a mixture of methane, carbon dioxide and other trace gases that can be converted to heat, electricity or light. Small-scale biogas reactors are typically designed to produce biogas at the household or community level in rural areas. Installation of small scale biogas plants for fulfilling requirement of gas for cooking and heating of homes, hostels, restaurants, community kitchens etc. is gaining more attention in the developed nations. These small scale biogas plants are using kitchen waste, municipal waste, waste water, garden waste, animal manure generated at home, hostels, restaurants, community kitchens etc. as a as feedstock.
Various factors affecting biogas production includes type, form and content of feedstock; temperature in anaerobic digester; pH of the feedstock slurry and change in pH at different stages of the anaerobic digestion; Biochemical Oxygen Demand (BOD); Chemical Oxygen Demand (COD); Carbon Nitrogen ration of organic matter of feedstock; total and volatile solids and their particle size in the feedstock slurry; moisture content of the substrate; Organic loading rate; hydraulic retention time; presence of other nutrients in feedstock slurry.
DESCRIPTION OF THE RELATED ART
Indian patent no. 170593 discloses an improved plant and process for generating source of energy from biomass to produce biogas using kitchen waste as substrate comprising an anaerobic digester having hopper at the top, an outlet for biogas leading to gas holder tank, an outlet for sludge, a predigester compartment wherein major portion of the predigestor remaining dipped into liquid content of anaerobic digester, a shaft with two propellers one at top and design to mix and push the content downward while another at the bottom and designed to mix and push the content upward for keeping the content in the mix condition for optimum biogas generation.
Patent publication no. WO 2010/100309 A1 discloses a method and device for the recycling and exploitation of biodegradable domestic waste produced in the dwellings of a community, by means of prefabricated biogas-production plants, in order to produce electricity and fertilizer and to heat water wherein the waste is ground in a grinder provided in the kitchen sinks and is conveyed, by means of a network separate from the sewage network, to a biogas-production plant formed by digesters, where biogas is produced by means of anaerobic digestion. The said invention includes safety and control mechanisms, a biogas consumer, a biogas reservoir and a place where the inert material resulting from biodigestion can be deposited. This material can be used as fertilizer. Optionally, the waste can originate from gardens. The biogas is consumed in the consumer and used to produce electrical power, mechanical power or to heat water. The electrical power generated may be fed into the grid.
The utility patent no. CN 213266481 U discloses a biogas resource utilization system of a kitchen waste treatment plant. The said system comprises a waste heat utilization system and a drying system. The said waste heat utilization system comprises a waste heat boiler, a lithium bromide unit, a cylinder sleeve water heat dissipation water tank, a lithium bromide unit hot water adjusting valve, a plate heat exchanger, a waste heat boiler water supply adjusting valve, a plant heating and ventilation system, an anaerobic tank heat preservation system, an anaerobic tank heat preservation system hot water adjusting valve and an oil-water separation system.
Patent no. CN 113854317 A discloses a kitchen biogas slurry concentrated solution and brassinolide mixed plant growth regulator. The plant growth regulator is formed by mixing 100-1500 parts by mass of kitchen biogas slurry concentrated solution and 0.001-0.02 part by mass of brassinolide, and the kitchen biogas slurry concentrated solution is obtained by concentrating kitchen biogas slurry by 100-1500 times. The kitchen biogas slurry and the brassinolide are compounded, so that the drug effect of the plant growth regulator is remarkably improved.
Patent publication no. DE 102008038040 A1 discloses a biogas plant comprises a converting device having a multi-chamber device for controlled small-scale conversion of biomass that is in the range of below 20 tons of biomass per year into biogas, a sucking device to avoid an unintentional leakage of gas from an interior of the biogas plant by using a negative pressure, and a quantity monitor to monitor a minimum quantity of biomass. The said multi-chamber device has a processing chamber for small-scale processing of the biomass, a liquefaction chamber for small-scale execution of hydrolysis, and/or a gas production chamber. The multi-chamber device has a processing chamber for small-scale processing of the biomass, a liquefaction chamber for small-scale execution of hydrolysis, a gas production chamber for small-scale production of gas, and/or a homogenizing device to small-scale process of the supplied biomass to a homogeneous mass. The homogenizing device has a cutting tool for homogeneously cutting the filled biomass. The biogas plant is formed as continuously operating biogas plant with a pressure vessel loaded with biogas by using a pump and a unit for simultaneously cooling the pressure vessel, and is formed as an anaerobic small reactor, which converts the biomass into biogas enclosed by air. An independent claim is included for a power supply system.
Patent application no. DE3408454 discloses a small biogas plant with integrated gas and agitator bellows, consisting of a flexible, rectangular container in which a bellows made of flexible material is incorporated, the same not directly with the volume, of the container is connected but its volumes indirectly is connected via a gas line of the volumes of the container and the gas formed by the tube from the container in the bellows can get, the same expands due to it and thus a stirring and constant mixing of the digested liquid of the container and the one resting on this bellows digestion liquid keeps the gas resting in this bellows under pressure at all times.
OBJECT OF THE INVENTION
Principal object the present invention is to provide a continuous stirred tank reactor (CSTR) based biogas plant.
Another object of the present invention is to provide the continuous stirred tank reactor (CSTR) based biogas plant that efficiently removes oil and wax content within feedstock coming from kitchen waste during the segregation stage in feed preparation resulting into increased biogas production and minimization of operational issues in the continuous stirred tank reactor (CSTR).
Another object of the present invention is to provide the continuous stirred tank reactor (CSTR) based biogas plant having a closed loop process that re introduces digested slurry from the continuous stirred tank reactor (CSTR) while fresh slurry preparation resulting into enhanced biogas production by retaining the active bacteria culture, reduction of water requirement, shortening of the retention time due to enhanced microbial activity, and minimize costs through an enhanced and efficient microbial culture.
Another object of the present invention is to provide the continuous stirred tank reactor (CSTR) based biogas plant with feed slurry level indicator system facilitating real time monitoring of the continuous stirred tank reactor (CSTR) content volume, enabling precise control over fresh feedstock loading and effluent discharge resulting into optimization of digester operation, streamlines feedstock loading management, enhancement of process stability and mitigates the risk of overloading or underfeeding, ultimately contributing to improved biogas yield and system longevity.
Another object of the present invention is to provide the continuous stirred tank reactor (CSTR) based biogas plant having a defoamer setup which filters foam within the continuous stirred tank reactor (CSTR), preventing pipeline blockages, pressure fluctuations, and equipment damage.
Another object of the present invention is to provide the continuous stirred tank reactor (CSTR) based biogas plant with a specially designed agitator with a unique biogas sealing system that is working at gentle speed 30 to 60 rpm, ensuring even distribution bacterial colonies, increase the efficiency up to the mark and works seamlessly within the system without any leakage issue around the moving parts.
Another object of the present invention is to provide the continuous stirred tank reactor (CSTR) based biogas plant with an intelligent closed loop pH control system that control pH of the continuous stirred tank reactor (CSTR) in a range of 6.8 – 7.2.
Another object of the present invention is to provide the continuous stirred tank reactor (CSTR) based biogas plant with an integrated heating system that controls the temperature of the continuous stirred tank reactor (CSTR) content in a range of 35 – 55 C.
Another object of the present invention is to provide the continuous stirred tank reactor (CSTR) based biogas plant with a biogas pressure regulating and purification module for maintaining pressure of the biogas in the continuous stirred tank reactor (CSTR) within the specified limit and removal of moisture and hydrogen sulphide from the biogas.
Another object of the present invention is to provide the continuous stirred tank reactor (CSTR) based biogas plant with a smart biogas meter to acquire, store and retrieve real-time data on biogas production, as well as the pressure within the digester.
Another object of the present invention is to provide the continuous stirred tank reactor (CSTR) based biogas plant with biogas storage module equipped with a distinctive piping that which efficiently sucks stored biogas during vacuum conditions generated during biogas discharge.
SUMMARY OF THE INVENTION
A continuous stirred tank reactor (CSTR) based multi-feed biogas plant is consisting of a waste washing and crushing module for washing, crushing and preparing homogeneous feed slurry of food waste, a feed slurry collection and pumping module in fluid communication with the waste washing and crushing module for receiving and pumping of the feed slurry, a continuous stirred tank reactor (CSTR) module in fluid communication with the feed slurry collection and pumping module for receiving the feed slurry pumped by the feed slurry collection and pumping module for it anaerobic digestion, a biogas pressure regulating and purification module in fluid communication with the continuous stirred tank reactor (CSTR) module for regulating pressure of biogas in the continuous stirred tank reactor (CSTR) module and purification of the biogas by removing moisture and hydrogen sulphide (H2S) and, a biogas storage module in fluid communication with the biogas pressure regulating and purification module via a smart biogas meter for collection and storage of purified biogas.
The continuous stirred tank reactor (CSTR) module is provided with a horizontal cylindrical cell is provided with a drainage line, a fertilizer line, a man hole, support mountings,, heaters, an agitator system with sealing connection, a level indicator, a pH control system, biogas outlets in fluid communication with the cylindrical cell via antifoaming systems, a pressure gauge and a safety valve.
The continuous stirred tank reactor (CSTR) based multi-feed biogas plant as per present invention attains objectives as stated by overcoming the limitations of the prior art.
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the invention as per the present patent application are described with reference to the following drawings in which like elements are labeled similarly. The present invention will be more clearly understood from the detailed description and the accompanying drawings, wherein:
FIG. 1 is a block diagram showing various modules of a continuous stirred tank reactor (CSTR) based multi-feed biogas plant.
FIG. 2 is a schematic diagram showing a waste washing and crushing module.
FIG. 3 is an enlarge view of detail A as per FIG. 2.
FIG. 4 is a schematic layout showing overall construction of a continuous stirred tank reactor (CSTR) based multi-feed biogas plant.
FIG. 5 is a schematic diagram showing a feed slurry collection and pumping module.
FIG. 6 is a schematic diagram showing front view of a continuous stirred tank reactor (CSTR) module.
FIG. 7 is a schematic diagram of a continuous stirred tank reactor (CSTR) module in side views
FIG. 8 is a schematic diagram showing a continuous stirred tank reactor (CSTR) module in a top view.
FIG. 9 is a schematic diagram showing an agitator system with sealing connection.
FIG. 10 is a schematic diagram showing a level indicator mounted on top portion of the cylindrical cell of the continuous stirred tank reactor (CSTR).
FIG. 11 is a schematic diagram showing biogas outlets (20, 23) in fluid communication with the cylindrical cell via antifoaming systems for discharging of biogas from the cylindrical cell.
FIG. 12 is a schematic diagram showing a pH control system (29) for maintaining pH of the feed slurry inside the cylindrical cell of the continuous stirred tank reactor (CSTR).
FIG. 13 is a schematic diagram showing a biogas pressure regulating and purification module in a front view.
FIG. 14 is a schematic diagram showing a biogas pressure regulating and purification module in a top view.
FIG. 15 is a schematic diagram showing a detail construction of a condensation unit of a biogas pressure regulating and purification module.
FIG. 16 is a schematic diagram showing a biogas storage module.
List of designations/ reference numbers in figure
1. a segregation table
2. a crusher unit inlet
3. a crusher unit
4. a belt and pulley mechanism with protection cover
5. a motor
6. a sieve mesh with drainage connection
7. a table frame with housing
8. a washing system
9. a water spray nozzle
10. a feed slurry inlet
11. a feed slurry collection tank
12. a feed slurry pump
13. a feed slurry supply line
14. a cylindrical cell
15. support mountings
16. a feeding pipe
18. a level indicator
18A. an indicator tube
18B. a floater
18C. a metal road
18D. a floating ball
19. a pressure gauge
20. a biogas outlet
20A. an antifoaming system
21. an agitator system with sealing connection
21A. a motor
21B. a shaft coupling
21C. a larger diameter pipe
21D. an agitator shaft,
22. a safety valve
23. a biogas outlet
23A. an antifoaming system
24. a man hole
25. an agitator blade
26. heaters
27. a drainage line
28. a fertilizer line
29. a pH control system
29A. a pH sensor connection
29B. a support pipe
29C. a pH sensor
29D. a lime dosing pump
31. a vertical cylindrical enclosure
31A. a gas inlet connection
31B. a flanged gas outlet connection
31C. a condensation unit
31D. plurality of leg support
31E. a water drain pipe
31F. a water column
31G. an absorption bed
31H. a height of the water column (31F)
32. a biogas storage balloon
32A. a biogas inlet connection
32B. a biogas outlet connection
41. a biogas slurry overflow line
42. an outlet of the feeding pipe
43. a circular plate
44. holes in the circulate plate (43)
45. pipes welded to the circulate plate (43)
46. a water line for washing of food waste
47. a water line for preparing feed slurry
101. a waste washing and crushing module
102. a feed slurry collection and pumping module
103. a continuous stirred tank reactor (CSTR) module
104. a biogas pressure regulating and purification module
105. a biogas storage module
DETAILED DESCRIPTION OF THE INVENTION
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. The description of illustrative embodiments according to principles of the present invention is intended to be read in connection with the accompanying drawings, which are to be considered as a part of the entire written description. In the description of embodiments of the invention disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms and directives thereof are for convenience of description only and do not require that the apparatus be constructed or operated in a particular manner unless explicitly indicated as such. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Moreover, the features and benefits of the invention are illustrated by reference to the exemplified embodiments. Accordingly, the invention expressly should not be limited to such exemplary embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features; the scope of the invention being defined by the claims appended hereto.
FIG. 1 shows a block diagram of a continuous stirred tank reactor (CSTR) based multi-feed biogas plant. FIG. 4 shows schematic overall layout of the continuous stirred tank reactor (CSTR) based multi-feed biogas plant along with interaction between various modules.
As shown in FIG. 1 and FIG. 4, continuous stirred tank reactor (CSTR) based multi-feed biogas plant is consisting of a waste washing and crushing module (101), a feed slurry collection and pumping module (102) in fluid communication with the waste washing and crushing module (101), a continuous stirred tank reactor (CSTR) module (103) in fluid communication with the feed slurry collection and pumping module (102), a biogas pressure regulating and purification module (104) in fluid communication with the continuous stirred tank reactor (CSTR) module (103) and a biogas storage module (105) in fluid communication with the biogas pressure regulating and purification module (104) via a smart biogas meter (30).
As shown in FIG. 1, in the waste washing and crushing module (101), biodegradable waste is manually segregated and washed thoroughly to remove oil and wax content, then washed waste is crushed to reduce particle size to improve the efficiency. During the crushing, feed slurry overflown from the continuous stirred tank reactor (CSTR) module (103) is added. Then, feed slurry from the waste washing and crushing module (101) is transferred and collected to the feed slurry collection and pumping module (102) where homogeneous slurry is prepared and culture and other additives are added if required for improving digestion of the feedstock. This feed slurry is then pumped to the continuous stirred tank reactor (CSTR) module (103) where biogas is generated by digestion of the feed slurry. Digested slurry which is rich in nutrient is discharged from the continuous stirred tank reactor (CSTR) module (103) for maintaining feed slurry level while adding fresh feed slurry. This digested slurry can be used as a fertilizer. Biogas produced and collected in the empty space of the continuous stirred tank reactor (CSTR) module (103) above feed slurry level is transported into the biogas pressure regulating and purification module (104) where moisture and other harmful impurities are removed from the biogas. The biogas pressure regulating and purification module (104) also maintains operating pressure inside the the continuous stirred tank reactor (CSTR) module (103). Purified biogas discharged from the biogas pressure regulating and purification module (104) is then stored in a biogas storage module (105).
In anaerobic digester feedstock can be very slow to breakdown because they contain chemicals that inhibit the growth and activity of the microorganisms, they create physical problems like floating, foaming or clumping, and block impellors and pipes in biogas plants, or their molecular structure is poorly accessible to microorganisms and their enzymes (for instance because of their highly crystalline structure or low surface area). The waste washing and crushing module (101) is used for washing, crushing and preparing homogeneous feed slurry of food waste. FIG. 2-3 shows detail construction of the waste washing and crushing module (101). The waste washing and crushing module (101) is consisting of a segregation table (1) for segregation of food waste, a washing system (8) attached to the segregation table (1) for washing the segregated food waste, a crusher unit (3) attached to the segregation table (1) and positioned beside the washing system (8) for crushing the segregated and washed food waste and water lines for supplying water for washing and the feed slurry preparation. As shown in FIG. 3, food waste to be washed is placed in a sieve mesh with drainage connection (6) of the washing system (8) wherein the food waste is washed using water from a water spray nozzle (9). Washed food waste retains in the sieve mesh and water containing oil and wax drained through the drainage connection. Washed food waste is feed to the crusher unit (3) from a crusher unit inlet (2). The crusher unit (3) is provided with a motor (5) which operates a crusher blade using a belt and pulley mechanism with protection cover (4) for crushing the food waste. A table frame with housing (7) mounts all the parts of the waste washing and crushing module (101).
As shown in FIG. 4, two water lines (46, 47), one for washing of food waste (46) at the washing system (8) and another for preparing feed slurry at the crusher unit (3) are provided. As shown in FIG. 4, a biogas slurry overflow line (41) is installed from the continuous stirred tank reactor (CSTR) module (103) to the crusher unit (3). Another end of the biogas overflow line (41) is dipped inside the feed slurry of the continuous stirred tank reactor (CSTR) for maintaining anaerobic condition. In situation of accumulation of feed slurry above specified maximum level in a cylindrical tank (14) of the continuous stirred tank reactor (CSTR) module (103), excess feed slurry from the continuous stirred tank reactor (CSTR) module (103) will flow to the crusher unit (3) where it will mixed with the fresh slurry. This prevents wastage of the feed slurry, provides microorganism culture and reduces water requirement for feed slurry preparation. In present invention, 75% of digested feed slurry from the continuous stirred tank reactor (CSTR) module (103) is supplied back to the crusher unit (3).
As shown in FIG. 5, feed slurry from the crusher unit (3) of the waste washing and crushing module (101) is transferred to a feed slurry collection tank (11) of the feed slurry collection and pumping module (102) by gravity via a feed slurry inlet (10). The feed slurry from the feed slurry collection tank (11) is transferred to the continuous stirred tank reactor (CSTR) module (103) via a feed slurry supply line (13) and a feeding pipe (16) with its outlet (42) positioned near bottom portion of a cylindrical cell (14) of the continuous stirred tank reactor (CSTR) module (103) so that the outlet (42) always remains dipped below the feed slurry level in the cylindrical cell (14). This helps in maintaining anaerobic condition in the cylindrical cell (14) of the continuous stirred tank reactor (CSTR) module (103).
FIG. 6-8 shows the continuous stirred tank reactor (CSTR) module (103). It is provided with a horizontal cylindrical cell (14). In another embodiment of the present invention, the continuous stirred tank reactor (CSTR) module (103) is provided with a vertical cylindrical cell (14). As shown in FIG. 6-8, the continuous stirred tank reactor (CSTR) module (103) is provided with the cylindrical cell (14) having a drainage line (27) at the bottom portion of an end face of the cylindrical cell (14) for draining the digested sludge and a fertilizer line (28) with its one end dipped into the biogas slurry (for maintaining anaerobic condition) at a top portion of the end face of the cylindrical cell (14) for draining of fertilizer. A man hole (24) is provided at the top portion of a cylindrical face of the cylindrical cell (14) for maintenance purpose. Support mountings (15) are provided for supporting the cylindrical cell (14) on the ground surface. Heaters (26) are provided on an outer cylindrical bottom surface of the cylindrical cell (14) for maintaining the temperature of the feed slurry in the cylindrical cell (14) by heating. An agitator system with sealing connection (21) is mounted on the top portion of the cylindrical surface of the cylindrical cell (14) for agitating the feed slurry. A level indicator (18) mounted on top portion of the cylindrical surface of the cylindrical cell (14) for the feed slurry level measurement. A pH control system (29) for maintaining pH of the feed slurry inside the cylindrical cell (14) is mounted on the outer surface of the cylindrical cell (14). Biogas outlets (20, 23) in fluid communication with the cylindrical cell (14) via antifoaming systems (20A, 23A) are provided at the top cylindrical surface of the cylindrical cell (14) for discharging of biogas from the cylindrical cell (14) along with a pressure gauge (19) for measuring pressure inside the cylindrical cell (14) and a safety valve (22) for maintaining safe pressure in the cylindrical cell (14).

Anaerobic digesters require adequate agitation of feed slurry to maintain optimal conditions. The purpose of agitation is to distribute the nutrients in the anaerobic digester uniformly, to form a suspension of liquid and solid parts, to avoid sedimentation of particles, to ensure uniform heat distribution, to prevent foam formation and to enable gas lift from the fermentation substrate at high dry matter (DM) contents. FIG. 9 shows a schematic diagram the agitator system with sealing connection (21). As shown in FIG. 9 a motor (21A) is mounted on and rigidly fixed to the top cylindrical surface of the cylindrical cell (14). A shaft of the motor (21A) is coupled to an agitator shaft (21D) using a shaft coupling (21B). An agitator blade is (25) mounted on the agitator shaft (21D) and is located inside the cylindrical cell (14). The agitator blade (25) is rotated at 30-60 rpm for continuously agitating feed slurry inside the cylindrical cell (14). A larger diameter pipe (21C) is assembled surrounding an agitator shaft (21D) with its one end dipped into the feed slurry and other end welded to an inner surface of the cylindrical cell (14). This sealing arrangement prevents leakage of biogas from the shaft coupling (21B) entry hole in the cylindrical cell (14).
Maintaining optimum quantity of the feed slurry in the continuous stirred tank reactor (CSTR) is important for maximizing biogas production. Due to the physical nature of the slurry, use of the conventional level indicators used for measuring level of different liquid will not serve the purpose. Hence, a special type of level indicators is design. FIG. 10 shows the level indicator (18) mounted on top cylindrical surface of the cylindrical cell of the continuous stirred tank reactor (CSTR). An indicator tube (18A) is mounted on and fastens to an outer side of the top cylindrical surface of the cylindrical cell (14). A slider (18B) is assembled to slide inside the indicator tube (18A). One end of a metal rod (18C) is attached to the floater (18B) and another end of the metal rod (18C) is extended out of the indicator tube (18A). A floating ball (18D) is attached to this another end of the metal rod (18C) extended out of the indicator tube (18C). The level indicator (18) is assembled with the cylindrical cell (14) such that the floating ball (18D) remains in direct contact with the surface of the feed slurry inside the cylindrical cell (14). With the change in the level of the feed slurry inside the cylindrical cell (14), vertical position of the floating ball (18D) changes. This change in position of the floating ball is transferred to the slider (18B) via the metal rod (18C) affecting position of the slider (18B) inside the indicator tube (18A). The indicator tube is provided with calibration markings showing level of the feed slurry inside the cylindrical cell (14) based on the position of slider (18B).
FIG. 11 shows biogas outlets (20, 23) in fluid communication with the cylindrical cell (14) via antifoaming systems (20A, 23A) for discharging of biogas from the cylindrical cell (14). The antifoaming systems (20A, 23A) are kept in fluid communication with the cylindrical cell (14) using piping connections (20B, 23B). The antifoaming systems (20A, 23A) are of larger diameter compared to diameter of the piping connections (20B, 23B) and filled with packing material for breaking down foams mechanically. Biogas discharged from the cylindrical cell (14) using the biogas outlets (20, 23) is passed through the antifoaming systems (20A, 23A) in which foam discharged with the biogas from the cylindrical tank (14) is arrested in the packing material. This eliminates problems like biogas pipeline blockage, pressure fluctuation, pressure gauge and safety valve damage etc. The experience of the operators of biogas plants shows that problems with foam formation are often caused by using inadequate substrates, and also occur during the start-up process or when the addition of grain is increased suddenly. Heavy foam formation may also indicate suboptimal operating conditions or an unsuitable operation policy. Whatever the reason may be foam-related problems in biogas reactors range from crust formation on the reactor wall, failure of pushers, dirt and blockage of gas and condensate pipes and recirculation pump due to the retention of foam solids, to over-foaming and a complete standstill of the plant. Hence, it is necessary to remove foam from the biogas discharged from the continuous stirred tank reactor (CSTR).
Generally, the pH was above 6 and below 7, which is suitable for most methanogenic bacteria to function. A neutral pH is favorable for biogas production, since most of the methanogens grow best at the pH range of 6.7 – 7.5. Feed slurry pH changes with the reaction time also. Hence, it is important to control pH of the feed slurry in the continuous stirred tank reactor (CSTR). FIG. 12 shows pH control system (29) for maintaining pH of the feed slurry inside the cylindrical cell (14) of the continuous stirred tank reactor (CSTR). A support pipe (29B) is dipped inside the feed slurry and welded with the cylindrical cell (14) with its one end open to atmosphere. A lime dosing pump (29D) in fluid communication with the cylindrical cell (14) for supplying lime to the feed slurry is installed. A pH sensor (29C) is attached to another end of the support pipe (29B). The pH sensor (29C) output is communicated to a control panel. Based on the output of pH sensor (29C), the control panel predicts pH of the feed slurry in the cylindrical cell (14) on real time basis which is then compared with the set standard pH value range. If pH value of the feed slurry in the cylindrical cell (14) is found outside the set standard pH value range, then the control panel operates the lime dosing pump (29D) to supply lime to the feed slurry to maintain pH value of the feed slurry within the set standard pH value range.
Water vapour drastically reduces the net calorific value (NCV) of biogas. Therefore, prior to using biogas as energy, it is advisable to reduce its moisture content as much as possible by any means available. Such moisture reduction is also necessary to prevent the accumulation of condensates in the gas line and thus prevent the formation of corrosive acids, as well as the clogging of pipes. The water vapour content of the biogas is directly related to both the operating temperature of the biogas production system and the ambient temperature in general. Raw biogas containing H2S (even in trace amounts) must also be treated before its end-use application, as H2S is toxic and corrosive. FIG. 13-14 shows the biogas pressure regulating and purification module (104). Biogas discharged from the biogas outlets (20, 23) is supplied to a vertical cylindrical enclosure (31) from a biogas inlet connection (31A). The biogas inlet connection (31A) is welded on an outer periphery of the vertical cylindrical enclosure (31). A flanged biogas outlet connection (31B) is welded to a top end of the vertical cylindrical enclosure (31). Plurality of leg support (31D) supporting the vertical cylindrical enclosure (31) on a bottom portion are provided. A condensation unit (31C) is mounted inside the vertical cylindrical enclosure (31) in between the biogas inlet connection (31A) and the flanged biogas outlet connection (31B). Biogas entering to the vertical cylindrical enclosure (31) through the biogas inlet connection (31A) is passed through the condensation unit (31C) having extended biogas flow path wherein moisture present in biogas is condensed before it discharged from the flanged biogas outlet connection (31B). Condense moisture of biogas is separated from biogas stream by gravity and is accumulated at a bottom end of the vertical cylindrical enclosure (31) in the form of water from where it drained through a drain pipe (31E) along with a valve welded to the bottom end of the vertical cylindrical enclosure (31) by overflow of the water column (31F).
An absorption bed (31G) is mounted inside the vertical cylindrical enclosure (31) in between the condensation unit (31C) and the flanged gas outlet connection (31B) for removal of hydrogen sulphide (H2S) from the biogas passing through it before it discharge from the flanged gas outlet connection (31B). The absorption bed (31G) is made up of an absorbent material that selectively capture and binds hydrogen sulphide (H2S) molecules from biogas stream passing though it preventing its release into atmosphere.
FIG. 15 shows a detail construction of the condensation unit (31C). The condensation unit (31C) is made up of a circular plate (43) with multiple holes (44). Pipes (45) that are open at both ends are joined to this circular plate (43) at one end after passing it through the holes (44) provided on the circular plate (43). The condensation unit (31C) is positioned inside the vertical cylindrical enclosure (31) such that the biogas entering into the vertical cylindrical enclosure (31) through the biogas connection inlet (31A) pass through the condensation unit (31C) before it is discharged from the flanged biogas outlet connection (31B). The condensation unit (31C) provides extended surface area and additional flow resistance to condense water vapour from biogas flowing through it.
As shown in FIG. 13-14, the water drain pipe (31E) is dipped into a water column (31F) of a height (31H) creating pressure head. When pressure of biogas inside the cylindrical cell (14) is greater than the pressure due to the water column (31F), biogas is discharge to atmosphere from the water drain pipe (31E) via the water column (31F) in form of biogas bubbles. This arrangement acts as a buffer pressure regulating arrangement in situation when the safety valve (22) fails. Pressure inside the continuous stirred tank reactor (CSTR) is controlled by maintaining height of the water column (31F).
Purified biogas discharged from the flanged gas outlet connection (31B) is passed through a smart meter (30). This smart meter (30) measures and stored biogas pressure inside the cylindrical cell (14), biogas flow rate and total biogas production on real time basis. These stored data can be retrieved for future use.
FIG. 16 shows the biogas storage module (105). The biogas storage module (5) is consisting of a biogas storage balloon (32) provided with a biogas inlet connection (32A) in fluid communication with the smart biogas meter (30) and a biogas outlet connection (32B). This module is used for storing biogas wherein biogas is stored in the biogas storage balloon (32). The biogas inlet connection (32A) is designed such that it automatically operates and sucks biogas from the continuous stirred tank reactor (CSTR) module (103) via the biogas pressure regulating and purification module (104) because of a vacuum condition generated inside the biogas storage balloon (32) due to biogas discharge from the biogas outlet connection (32B).

BEST METHOD OF PERFORMING THE INVENTI ON
The continuous stirred tank reactor (CSTR) based multi-feed biogas plant as per present invention is implemented with following specifications.
Sr. No. Description Specification Capacity
1. CSTR Prefabricated Digester with horizontal mixer and C channel reinforcement rings of volume 5 m3; Material thickness: 7 mm main tank (4 mm mild steel (MS) plate + 3 mm fiber reinforced plastic (FRP) lining; 8 mm side walls (5 mm MS plate + 3 mm FRP linings) 100 kg
2. Agitator system Impeller agitator assembly with mechanical gas Seal; material: stainless steel grade SS304; motor - 1 Hp 1 Hp
3. the biogas pressure regulating system Automatic Safety release valve with variable Pressure limits; Material: stainless steel 316; minimum pressure: 0.5 bar Continuous
4. Heater Belt type heater attached with the cylindrical cell for maintaining uniform temperature; Type: advance micro type ceramic belt type Heater capacity : 2 kw x 6 units; temperature up to 70 0C maintained using sensors 2 kW
5. Gas Purifciation and Moisture trap Continuous purification setup and Moisture trap to remove moisture, H2S , Ammonia and other gases; Material: MS with epoxy and antirust; purification setup: Chemical Scrubber , Activated Carbon Scrubber , Moisture trap Continuous
6. Gas Booster Blower type gas booster; Material: MS with internal Chromium plating; Motor: 1.5 Hp; pressure Head: 300 m 1.5 HP
7. Gas Storage Balloon PVC Coated gas storage balloon with moisture removal and safety release mechanisms; Material: 3 Layer PVC coated polyester fabric 10 m3
8. Pipeline UPVC Pipline upto 28 bar pressure handling Biogas pipeline
9. Pretreatment Tank a pretreatment Tank; Material: PVC with epoxy coating 100 l capacity
10. Output slurry Tank Material: PVC with epoxy coating 100 l capacity
11. Intake slurry pump For intake of shredder waste into digester 100 Kg/h
12. Control Panel Control all connected Machine (Make - Biofics); Switchgear: Chintz/L&T/Schneider; wire: Plycab/ RR Kabel
13. Smart Biogas Merter Biogas meter capable of measuring gas pressure. daliy production of biogas quantify and cost savings achieved by biogas in comparison to LPG
14. Waste Cruher Chopper with grinder,Segregation table attached with Crusher; Material: MS with epoxy and stailess steel SS -304 Blades and noncontact surfaces MS powder coated Motor - 2 HP for particle chopping size of 10 mm
15. Bacteria Culture Two different enzymes are used for faster biogas production and increasing methane content
16. Foundation Total area required 15 x 30 square feet, RCC and PCC Foundation work (450 square foot) , Claims:We claim:
1. A continuous stirred tank reactor (CSTR) based multi-feed biogas plant consisting of:
a waste washing and crushing module (101) for washing, crushing and preparing homogeneous feed slurry of food waste;
a feed slurry collection and pumping module (102) in fluid communication with the waste washing and crushing module (101) for receiving and pumping of the feed slurry;
a continuous stirred tank reactor (CSTR) module (103) in fluid communication with the feed slurry collection and pumping module (102) for receiving the feed slurry pumped by the feed slurry collection and pumping module (102) for it anaerobic digestion;
a biogas pressure regulating and purification module (104) in fluid communication with the continuous stirred tank reactor (CSTR) module (103) for regulating pressure of biogas in the continuous stirred tank reactor (CSTR) module (103) and purification of the biogas by removing moisture and hydrogen sulphide (H2S) and;
a biogas storage module (105) in fluid communication with the biogas pressure regulating and purification module (104) via a smart biogas meter (30) for collection and storage of purified biogas;
characterized in that
the waste washing and crushing module (101) is consisting of a segregation table (1) for segregation of food waste, a washing system (8) attached to the segregation table (1) for washing the segregated food waste, a crusher unit (3) attached to the segregation table (1) and positioned beside the washing system (8) for crushing the segregated and washed food waste and water lines for supplying water for washing and the feed slurry preparation,
a biogas slurry overflow line (41) from the continuous stirred tank reactor (CSTR) module (103) to the crusher unit (3) is given for the feed slurry preparation,
the feed slurry collection and pumping module (102) pump the feed slurry received from the waste washing and crushing module (101) to the continuous stirred tank reactor (CSTR) module (103) using a feeding pipe (16) with its outlet (42) positioned near bottom portion of a cylindrical cell (14) of the continuous stirred tank reactor (CSTR) module (103) so that the outlet (42) always remains dipped below the feed slurry level in the cylindrical cell (14),
the continuous stirred tank reactor (CSTR) module (103) is provided with the cylindrical cell (14) having a drainage line (27) at the bottom portion for draining the digested sludge, a fertilizer line (28) at the bottom portion for draining of fertilizer, a man hole (24) at the top portion for maintenance purpose, support mountings (15) for supporting the cylindrical cell (14), heaters (26) on outer bottom surface of the cylindrical cell (14) for maintaining the temperature of the feed slurry in the cylindrical cell (14) by heating, an agitator system with sealing connection (21) mounted on it for agitating the feed slurry, a level indicator (18) mounted on its top portion for the feed slurry level measurement, a pH control system (29) for maintaining pH of the feed slurry inside the cylindrical cell (14), biogas outlets (20, 23) in fluid communication with the cylindrical cell (14) via antifoaming systems (20A, 23A) for discharging of biogas from the cylindrical cell (14), a pressure gauge (19) for measuring pressure inside the cylindrical cell (14) and a safety valve (22),
the agitator system with sealing connection (21) is consisting of a motor (21A) mounted on and rigidly fixed to the cylindrical cell (14) and configured to rotate an agitator blade (25) located inside the cylindrical cell (14) for continuously agitating feed slurry and a larger diameter pipe (21C) surrounding an agitator shaft (21D) with its one end dipped into the feed slurry and other end welded to an inner surface of the cylindrical cell (14) preventing leakage of biogas from the motor (21A) shaft entry hole in the cylindrical cell (14),
the level indicator (18) is consisting of an indicator tube (18A) mounted on and fasten to an outer surface of the cylindrical cell (14), a slider (18B) assembled to slide inside the indicator tube (18A) with a movement of a floating ball (18D) kept in direct contact with the feed slurry inside the cylindrical cell (14) and attached to the slider (18B) using a metal road (18C),
the antifoaming systems (20A, 23A) are kept in fluid communication with the cylindrical cell (14) using piping connections (20B, 23B) wherein the antifoaming systems (20A, 23A) are of larger diameter compared to diameter of the piping connections (20B, 23B) and filled with packing material for breaking down foams mechanically,
the pH control system (29) is consisting of a support pipe (29B) dipped inside the feed slurry and welded with the cylindrical cell (14) with its one end open to atmosphere, a lime dosing pump (29D) in fluid communication with the cylindrical cell (14) for supplying lime to the feed slurry, a pH sensor (29C) attached to another end of the support pipe (29B) and configured to operate the lime dosing pump (29D) via a control panel for supplying required quantity of lime to the feed slurry for pH control,
the biogas pressure regulating and purification module (104) is consisting of a vertical cylindrical enclosure (31), a biogas inlet connection (31A) welded on an outer periphery of the vertical cylindrical enclosure (31), a flanged biogas outlet connection (31B) welded to a top end of the vertical cylindrical enclosure (31), plurality of leg support (31D) supporting the vertical cylindrical enclosure (31) on a bottom portion, a condensation unit (31C) mounted inside the vertical cylindrical enclosure (31) in between the biogas inlet connection (31A) and the flanged biogas outlet connection (31B) for removing moisture from the biogas entering into the vertical cylindrical enclosure (31) from the biogas inlet connection (31A) and discharged through the flanged biogas outlet connection (31B), a water drain pipe (31E) along with a valve welded to a bottom end of the vertical cylindrical enclosure (31) for draining of condense moisture and discharging biogas for pressure regulation and an absorption bed (31G) mounted inside the vertical cylindrical enclosure (31) in between the condensation unit (31C) and the flanged biogas outlet connection (31B) for removal of hydrogen sulphide (H2S) from the biogas before discharging it from the flanged biogas outlet connection (31B),
the condensation unit (31C) is made up of a circular plate (43) with multiple holes (44) and pipes (45) open at both ends and joined to this circular plate (43) at one end after passing it through the holes (44) provided on the circular plate (43) wherein the condensation unit (31C) is positioned inside the vertical cylindrical enclosure (31) such that the biogas entering into the vertical cylindrical enclosure (31) through the biogas connection inlet (31A) pass through the condensation unit (31C) before it is discharged from the flanged biogas outlet connection (31B),
the water drain pipe (31E) is dipped into a water column (31F) of a height (31H) creating pressure head wherein biogas is discharge to atmosphere from the water drain pipe (31E) and then through the water column (31F) in form of biogas bubbles on attaining biogas pressure level inside the vertical cylindrical enclosure (31) greater than the pressure head of the water column (31F),
condensed moisture of the biogas is separated from the biogas stream by gravity and drained from the water drain pipe (31E) by overflow of the water column (31F) and,
the biogas storage module (5) is consisting of a biogas storage balloon (32) provided with a biogas inlet connection (32A) in fluid communication with the smart biogas meter (30) and a biogas outlet connection (32B).
2. The continuous stirred tank reactor (CSTR) based multi-feed biogas plant as claimed in claim 1, wherein 75% of digested feed slurry from the continuous stirred tank reactor (CSTR) module (103) is supplied back to the crusher unit (3) for fresh feed slurry preparation.
3. The continuous stirred tank reactor (CSTR) based multi-feed biogas plant as claimed in claim 1, wherein the agitator blade (25) is rotated at 30-60 rpm.
4. The continuous stirred tank reactor (CSTR) based multi-feed biogas plant as claimed in claim 1, wherein pressure inside the continuous stirred tank reactor (CSTR) is controlled by maintaining height of the water column (31F).
5. The continuous stirred tank reactor (CSTR) based multi-feed biogas plant as claimed in claim 1, wherein the absorption bed (31G) is madeup of an absorbent material that selectively capture and binds hydrogen sulphide (H2S) molecules from biogas stream passing though it preventing its release into atmosphere.
6. The continuous stirred tank reactor (CSTR) based multi-feed biogas plant as claimed in claim 1, wherein the biogas inlet connection (32A) is configured to automatically operates and sucks biogas from the continuous stirred tank reactor (CSTR) module (103) via the biogas pressure regulating and purification module (104) because of a vacuum condition generated inside the biogas storage balloon (32) due to biogas discharge from the biogas outlet connection (32B).