Description:Field of the invention

[0001] The present invention relates to a system and method for generating biogas. More specifically, the present invention relates to a system and method for generating biogas from Napier grass, food waste and agricultural waste.

Background of the invention

[0002] The increasing global population and rapid urbanization have led to significant challenges in managing food waste and agricultural waste effectively and sustainably. Traditional waste disposal methods, such as landfilling and incineration, pose substantial environmental hazards, including greenhouse gas emissions, soil and water contamination, and the depletion of landfill space. Consequently, there is a growing demand for innovative waste management solutions that not only mitigate environmental impacts but also contribute to energy generation and resource recovery.

[0003] Anaerobic digestion has emerged as a promising technology for the conversion of Napier grass, food waste and agricultural waste into valuable biogas, primarily composed of methane and carbon dioxide. Biogas serves as a renewable energy source that can be utilized for electricity generation, heating, or as a transportation fuel, thereby reducing reliance on fossil fuels and lowering carbon emissions. Additionally, the byproduct of anaerobic digestion, known as digestate, can be processed and used as a nutrient-rich fertilizer, promoting sustainable agricultural practices.

[0004] Despite its potential, existing biogas generation systems often face several limitations that hinder their widespread adoption and efficiency. One major challenge is feedstock processing inefficiency. Inadequate preprocessing of Napier grass, food waste and agricultural waste, such as insufficient shredding or size reduction, can lead to suboptimal digestion performance and reduced biogas yields. Effective feedstock preparation is essential to enhance the surface area available for microbial activity, thereby improving the overall efficiency of the digestion process. Furthermore, many biogas plants are designed with a fixed capacity in mind, making it challenging to scale up or down based on varying waste inputs or energy demands. This lack of scalability and modularity limits the applicability of biogas systems in diverse settings and hinders their ability to adapt to changing requirements.

[0005] Another critical issue lies in the operation and control of the digester. Maintaining optimal conditions within the digester, including temperature, pH, viscosity, and mixing, is crucial for effective anaerobic digestion. Fluctuations in these parameters can disrupt microbial activity, prolong retention times, and decrease overall system efficiency. Precise control mechanisms are necessary to ensure a stable and conducive environment for the microorganisms responsible for breaking down organic matter. Additionally, achieving uniform heat distribution in all seasons is challenging for available biogas plants, affecting optimal microbial activity. Seasonal temperature fluctuations can lead to inconsistent biogas production, impacting the plant's reliability and output.

[0006] Operational stability is further compromised by the quality of feedstock. Available shredders often produce inconsistent particle sizes, leading to uneven digestion, fluctuations in feedstock quality and quantity, and reduced biogas production efficiency. Variability in feedstock characteristics can destabilize the digestion process, making it difficult to maintain consistent biogas yields. Moreover, shredders and stirring mechanisms can become jammed or blocked by different types of waste, causing downtime and maintenance issues. Such mechanical failures disrupt the continuous operation of biogas plants, leading to decreased productivity and increased maintenance costs. The energy consumption of these components is another concern, as shredders and stirring mechanisms can be energy-intensive, increasing the overall operational costs of the biogas plant and reducing the net energy gain from biogas production.

[0007] Monitoring and automation present additional challenges. Many current systems lack advanced monitoring and control mechanisms, making it difficult to regulate digestion conditions in real-time. This deficiency can result in inconsistent biogas production and increased operational costs due to the need for manual interventions. Enhanced automation and real-time monitoring are essential to optimize the digestion process and ensure continuous, efficient biogas generation. Furthermore, the digestate produced from the biogas plant emits strong odors due to the anaerobic digestion process, which generates odorous compounds such as hydrogen sulphide. The lack of real-time monitoring of odor emissions makes it difficult to manage odor issues proactively, while inadequate ventilation can lead to the accumulation of odors in and around the biogas plant, causing environmental and social concerns.

[0008] Efficient digestate management is also a significant concern. The removal and handling of digestate are essential to prevent system overloads and ensure continuous operation. Existing methods often rely on manual processes, which are labour-intensive and prone to errors. Additionally, digestate can have an imbalanced nutrient profile, making it less effective or even harmful as a fertilizer if not managed correctly. Developing automated and reliable digestate management solutions is necessary to maintain system stability and maximize resource recovery. Moreover, many biogas plants do not fully utilize the byproducts of digestion, limiting the potential for nutrient recovery and environmental benefits.

[0009] Biogas purification and storage further complicate the biogas generation process. The presence of contaminants such as carbon dioxide, moisture, and hydrogen sulphide in biogas necessitates effective purification processes to make the biogas suitable for various applications. Available biogas plants often produce biogas with lower methane content and higher levels of impurities, reducing its energy value and necessitating more extensive purification processes that increase operational complexity and costs. Additionally, safe and efficient storage solutions are required to handle the compressed biogas, ensuring its availability for electricity generation, heating, or as a transportation fuel.

[0010] Maintenance and scalability pose ongoing challenges for existing systems. Frequent maintenance requirements and limited scalability can impede the long-term viability and adaptability of biogas generation systems to varying waste volumes and operational demands. Developing systems that are easy to maintain and can be scaled to accommodate different levels of waste input is crucial for the widespread implementation and success of anaerobic digestion technologies. Furthermore, slow digestion rates in older biogas plants result in longer processing times and lower biogas yields, hampering the overall efficiency of the biogas production process and limiting its economic feasibility. Additionally, waste produced from every household is not adequately managed by existing biogas plant designs, leading to domestic waste management issues and reducing the potential of biogas systems to contribute significantly to comprehensive waste management strategies.

[0011] Addressing these challenges necessitates the development of an integrated biogas generation system that incorporates advanced feedstock processing, precise control and monitoring mechanisms, efficient digestate management, and robust biogas purification and storage solutions. Furthermore, ensuring ease of maintenance and scalability is crucial for the practical implementation and expansion of such systems in diverse settings, ranging from small-scale agricultural operations to large municipal waste management facilities.

[0012] Therefore, there is a need for a system and method for generating biogas using Napier grass, food waste and agricultural waste which overcomes one or more drawbacks of the above-mentioned prior art.

Objects of the invention

[0013] The object of the present invention is to provide a system and method for generating biogas from Napier grass, food waste and agricultural waste.

[0014] Another object of the present invention is to provide a system and method for generating biogas from Napier grass, food waste and agricultural waste that allow for easy addition or removal of units to adjust capacity as needed, ensuring maximum efficiency output.

[0015] Another one object of the present invention is to a system and method for generating biogas from Napier grass, food waste and agricultural waste that integrate control systems that adjust stirring intensity and frequency based on real-time monitoring of microbial activity and substrate conditions.

[0016] Further object of the present invention is to provide a system and method for generating biogas from Napier grass, food waste and agricultural waste with simplified components that require minimal maintenance, ensuring long-term reliability and reduced operational costs.

[0017] One more object of the present invention is to provide a system and method for generating biogas from Napier grass, food waste and agricultural waste with simple installation mechanisms that reduce production time and labour costs, ensuring efficiency during Biogas Machine manufacturing.

[0018] Yet another more object of the present invention is to provide a system and method for generating biogas from Napier grass, food waste and agricultural waste that incorporate scrubbers and biogas filters that can neutralize and absorb odorous gases, as well as filter the biogas to remove impurities, odor, and moisture content.

[0019] Still one more object of the present invention is to provide a system and method for generating biogas from Napier grass, food waste and agricultural waste with reliability and consistent output despite seasonal temperature changes, enhancing the stability and efficiency of the anaerobic digestion process.

Summary of the invention

[0020] According to the present invention a system and method for generating biogas from Napier grass, food waste and agricultural waste is provided. The system includes a feed processing unit with a hopper, a shredder, a digestion unit, a stirring mechanism, a monitoring and control unit, a digestate management unit, a solenoid valve, a digestate collection system, a digestate bag holder, a biogas collection and storage unit, a biogas filtration unit, a compressor unit, a gas storage tank, a CBG filling valve, a structural and maintenance unit and a union tank separator.

[0021] The feed processing unit includes a hopper configured to receive Napier grass, food waste and agricultural waste. The shredder is operably connected to the hopper for reducing the size of the Napier grass, food waste and agricultural waste. The digestion unit includes a digester tank having an interior chamber for anaerobic digestion of the Napier grass, food waste and agricultural waste. The stirring mechanism is arranged within the interior chamber of the digestor tank for mixing digester contents. The motor is operably coupled to the stirring mechanism. The monitoring and control unit includes at least one of a temperature sensor, a pH sensor, a viscosity sensor, a level sensor, or a rotor sensor operably connected to the digester tank for monitoring and regulating the digestion conditions. The digestate management unit includes a digestate outlet pipe connected to the digester tank for removing the processed digestate. The solenoid valve is disposed along the digestate outlet pipe for controlling the digestate flow. The digestate collection system includes a digestate bag positioned beneath the digestate outlet pipe. The digestate bag holder is provided for supporting the digestate bag and a weight sensor is arranged to measure the weight of the digestate bag. The biogas collection and storage unit include a gas outlet pipe extending from the digester tank for extracting the biogas. The biogas filtration unit configured to remove at least one of carbon dioxide, moisture, or hydrogen sulphide. The compressor unit is connected to the biogas filtration unit for compressing the purified biogas. The gas storage tank is configured to store the compressed biogas. A CBG filling valve is provided for transferring the compressed biogas to an external system. The structural and maintenance unit includes a tank connector pipe arranged between the digester tank and downstream components for material transfer. The union tank separator is positioned between the digester tank and the tank connector pipe for facilitating the detachment during maintenance.

[0022] In an aspect of the invention, the hopper includes a limit switch sensor arranged to detect the waste level and activate or deactivate the shredder based on a predefined threshold.

[0023] In an aspect of the invention, the shredder includes a blocking sensor configured to detect blockages and halt shredder operation upon detection of a blockage.

[0024] In an aspect of the invention, the shredder includes a waste inlet pipe extending from the shredder for transferring processed waste.

[0025] In an aspect of the invention, the system includes a thermal insulation layer enclosing the digester tank.

[0026] In an aspect of the invention, the stirring mechanism includes a central shaft with radially extending blades configured to mix the digester contents.

[0027] In an aspect of the invention, the viscosity sensor is operably connected to the stirring mechanism motor and transmits signals to adjust the rotational speed of the stirring mechanism based on the detected viscosity of the digester contents.

[0028] In an aspect of the invention, the digester tank is configured to maintain a retention time of less than 25 days for anaerobic digestion.

[0029] In an aspect of the invention, the digester tank includes a buffering agent inlet configured to introduce a chemical buffer to regulate the pH level.

[0030] In an aspect of the invention, the biogas filtration unit comprises a carbon filter, an iron wool filter, and a moisture filter configured to remove contaminants from the biogas before compression.

[0031] In an aspect of the invention, the weight sensor is operably connected to an alarm system configured to generate an alert when the digestate bag reaches a predefined weight threshold.

[0032] In an aspect of the invention, the generator is operably connected to the gas storage tank and configured to convert compressed biogas into electrical energy.

[0033] In an aspect of the invention, a method for generating biogas from Napier grass, food waste and agricultural waste is provided. Initially the waste level in the hopper is detected using a limit switch sensor. The Napier grass, food waste and agricultural waste is then shredded using a shredder to produce shredded waste. The blockage is then sensed and detected using a blocking sensor. The shredded waste is then transferred into a digester tank through a waste inlet pipe. The shredded waste is maintained in the digester tank under anaerobic conditions. The digestion conditions are then monitored and regulated using at least one of a temperature sensor, a pH sensor, a viscosity sensor, a level sensor, or a rotor sensor. The contents of the digester tank are mixed using a stirring mechanism driven by a motor. The digestate from the digester tank is removed through a digestate outlet pipe. The controlling digestate flow is then controlled using a solenoid valve. Finally, the digestate in the digestate bag is collected and positioned beneath the digestate outlet pipe.

[0034] In an aspect of the invention, the weight of the digestate bag is measured using a weight sensor, and an alert is generated when the weight exceeds a predefined threshold.

[0035] In an aspect of the invention, a tank connector pipe and a union tank separator facilitate the transfer of digestate and allow for maintenance operations.

[0036] In an aspect of the invention, the digester tank is maintained at a temperature of approximately 37°C to optimize microbial digestion.

[0037] In an aspect of the invention, the digester tank maintains a retention time of less than 25 days for anaerobic digestion.

[0038] In an aspect of the invention, the pH level within the digester tank is regulated between 6.8 and 7.0 by adding a buffering agent.

[0039] In an aspect of the invention, biogas is extracted from the digester tank through a gas outlet pipe and transported for filtration.

[0040] In an aspect of the invention, the extracted biogas is filtered to remove at least one of carbon dioxide, moisture, or hydrogen sulphide using a biogas filtration unit.

[0041] In an aspect of the invention, the filtered biogas is compressed using a compressor and stored in a gas storage tank.

[0042] In an aspect of the invention, compressed biogas is transferred to an external biogas distribution system through a CBG filling valve.

Brief Description of drawings

[0043] The advantages and features of the present invention will be understood better with reference to the following detailed description and claims taken in conjunction with the accompanying drawings, wherein like elements are identified with like symbols, and in which:

[0044] Figure 1 and Figure 2 illustrates the schematic representation of a system for generating biogas from Napier grass, food waste and agricultural waste;

[0045] Figure 3 illustrates a method for a system for generating biogas from Napier grass, food waste and agricultural waste; and

[0046] Figure 4 illustrates a sustainable biogas production cycle, that utilizes Napier grass, food waste, and agricultural waste as primary feedstocks thereby establishing a circular economy.

Detailed description of the invention

[0047] An embodiment of this invention, illustrating its features, will now be described in detail. The words "comprising," "having," "containing," and "including," and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items.

[0048] The present invention relates to a system and method for generating biogas. More specifically, the present invention relates to a system for generating biogas from Napier grass, food waste and agricultural waste. The system is structured to efficiently process Napier grass, food waste and agricultural waste, convert it into biogas through anaerobic digestion, purify and compress the biogas for storage, and effectively manage the resulting digestate. The system includes multiple interconnected units, each designed to perform a specific function in the biogas production process

[0049] The terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items.

[0050] The disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms.

[0051] Referring now to Figure 1, a system (100) for generating biogas from Napier grass, food waste and agricultural waste is provided. The system (100) includes a feed processing unit with a hopper (1), a shredder (4), a digestion unit (50), a stirring mechanism (14), a monitoring and control unit (60, 70), a digestate management unit (80), a solenoid valve (20), a digestate collection system, a digestate bag holder (22), a biogas collection and storage unit (90), a biogas filtration unit (28), a compressor unit (29), a gas storage tank (30), a CBG filling valve (31), a structural and maintenance unit (95), and a union tank separator (10).

[0052] The feed processing unit (33) includes a hopper (1) configured to receive Napier grass, food waste and agricultural waste. Specifically, the feed processing unit (33) is responsible for receiving and preparing Napier grass, food waste and agricultural waste before it enters the digestion unit (50). The hopper (1) serves as the primary intake point for organic materials such as food waste, agricultural residues, and other biodegradable substances. The hopper (1) provides a controlled and measured supply of waste to the system (100). The hopper (1) includes a limit switch sensor (2) arranged to detect the waste level and activate or deactivate the shredder (4) based on a predefined threshold.

[0053] The shredder (4) is operably connected to the hopper (1) for reducing the size of the Napier grass, food waste and agricultural waste. Specifically, the shredder (4) reduces the size of the Napier grass, food waste and agricultural waste, thereby increasing the surface area of the Napier grass, food waste and agricultural waste and making it more suitable for microbial digestion. The shredder (4) ensures that the waste is broken down into smaller, more uniform particles, improving the efficiency of the digestion process. The shredded waste is then transferred into the digestion unit (50) through a waste inlet pipe (6), which facilitates the smooth and continuous transfer of processed waste material. Further, the shredder (4) includes a blocking sensor (5) configured to detect blockages and halt the operation of the shredder (4) upon detection of a blockage. The shredder (4) further includes a waste inlet pipe (6) extending from the shredder (4) for transferring the processed waste.

[0054] The digestion unit (50) includes a digester tank (7) having an interior chamber for anaerobic digestion of the Napier grass, food waste and agricultural waste. The interior chamber of the digester tank (7) provides an oxygen-free environment, allowing microbial activity to break down the organic material and produce biogas. The digestion process results in the formation of biogas as well as digestate, which is used as an organic fertilizer. Inside the digester tank (7), a stirring mechanism (14) is arranged to provide uniform mixing of the digester contents.

[0055] More specifically, the stirring mechanism (14) is arranged within the interior chamber of the digester tank (7) for mixing digester contents. The motor (13) is operably coupled to the stirring mechanism (14). The stirring mechanism (14) prevents the formation of sediment layers and ensures that all organic matter is evenly exposed to microbial action. The motor (13) operably coupled to the stirring mechanism (14) drives the mixing process. The motor (13) facilitates continuous blending of the digester contents, thereby maintaining optimal conditions for anaerobic digestion. Additionally, the digester tank (7) is enclosed by a thermal insulation layer (11) to regulate and maintain an optimal temperature. The insulation layer (11) helps retain heat within the digester tank (7).

[0056] The monitoring unit (60) includes at least one of a temperature sensor (16), a pH sensor (17), a viscosity sensor (15), a level sensor (18), or a rotor sensor (14) operably connected to the digester tank (7) for monitoring and regulating the digestion conditions. The temperature sensor (16) ensures that the internal temperature of the digester tank (7) remains within the optimal range for microbial activity. If any fluctuations are detected, corrective actions can be taken by the control unit (70) to maintain the necessary temperature conditions.

[0057] The pH sensor (17) monitors the acidity or alkalinity of the digester contents. Since microbial digestion requires a stable pH level typically between 6.8 and 7.0, the system (100) includes a buffering agent inlet (12) for introducing chemical buffers such as sodium bicarbonate (NaHCO₃) to maintain the pH within the desired range.

[0058] The viscosity sensor (15) is operably connected to the stirring mechanism (14) and transmits signals to adjust the rotational speed of the stirring mechanism (14) based on the detected viscosity of the digester contents. The level sensor (18) detects the volume of digestate and biogas inside the digester tank (7), preventing overflows and ensuring optimal system operation. The rotor sensor (14) monitors the operation of the stirring mechanism (14), ensuring that the motor (13) functions properly and maintains a consistent mixing action.

[0059] After digestion, the processed organic matter is converted into digestate, which is a nutrient-rich byproduct that can be used as an organic fertilizer. The digestate management unit (80) facilitates the removal, collection, and handling of this byproduct. The digestate management unit (80) includes a digestate outlet pipe (19) connected to the digester tank (7) for removing the processed digestate. The digester tank (7) is configured to maintain a retention time of less than 25 days for anaerobic digestion.

[0060] The solenoid valve (20) is disposed along the digestate outlet pipe (19) for controlling digestate flow. Specifically, the flow of digestate is controlled by the solenoid valve (20), which can be either manually or electronically actuated to regulate the discharge rate, providing a controlled removal process and preventing any overflow from occurring.

[0061] Further, the digestate management unit (80) includes a digestate bag (21) positioned beneath the digestate outlet pipe (19). The digestate bag holder (22) is provided for supporting the digestate bag (21), and a weight sensor (23) is arranged to measure the weight of the digestate bag (21). Specifically, the weight sensor (23) is operably connected to an alarm system (24) configured to generate an alert when the digestate bag (21) reaches a predefined weight threshold. When the digestate bag (21) reaches the predefined weight threshold, the system (100) generates an alert, signalling that the digestate bag (21) needs to be replaced or emptied.

[0062] The biogas collection and storage unit (90) are responsible for capturing, purifying, compressing, and storing the biogas produced during digestion. A gas outlet pipe (25) extends from the digester tank (7) to extract the generated biogas. The biogas contains impurities such as carbon dioxide (CO₂), moisture, and hydrogen sulphide (H₂S), which must be removed before storage. The biogas filtration unit (28) comprises a carbon filter, an iron wool filter, and a moisture filter configured to remove contaminants from the biogas before compression.

[0063] Once filtered, the purified biogas is compressed using a compressor unit (29) to reduce its volume, making storage more efficient. The compressed biogas is then stored in a gas storage tank (30), which holds the gas until it is ready for use. The compressor unit (29) is connected to the biogas filtration unit (28) to ensure a steady flow of purified biogas into the gas storage tank (30).

[0064] The gas storage tank (30) is configured to store the compressed biogas, ensuring that the gas remains available for utilization. Further, a CBG filling valve (31) is provided for transferring the compressed biogas to an external system, allowing it to be used for various applications, such as fuelling vehicles or supplying gas to households and industries.

[0065] Furthermore, the system (100) includes a structural and maintenance unit (95), including a tank connector pipe (8) that links the digester tank (7) to downstream components. The tank connector pipe (8) allows smooth material transfer within the system (100).

[0066] Additionally, a union tank separator (10) is positioned between the digester tank (7) and the tank connector pipe (8). The union tank separator (10) facilitates easy detachment of the digester tank (7) during maintenance, allowing the system (100) to be cleaned and serviced without disrupting the entire process.

[0067] Additionally, the system (100) includes a generator (32) that is operably connected to the gas storage tank (30). The generator (32) converts stored biogas into electrical energy, providing an additional energy source that can be used to power various operations.

[0068] Referring now to Figure 3, a method (200) for generating biogas from Napier grass, food waste and agricultural waste is provided. The method (200) is described in conjunction with the system (100).

[0069] The method (200) starts at Step 210.

[0070] At Step 220, the Napier grass, food waste and agricultural waste is received in a hopper (1). The hopper (1) serves as the primary intake point for biodegradable waste, including food waste, agricultural residues, and other organic materials. The hopper (1) accommodates different waste consistencies, ensuring a controlled flow of material into the system (100). The hopper (1) prevents overloading so that the subsequent shredding process functions efficiently without disruptions.

[0071] At Step 230, the waste level in the hopper (1) is detected using a limit switch sensor (2). The limit switch sensor (2) continuously monitors the amount of waste inside the hopper (1) and determines whether additional waste can be loaded or if processing should commence. When the waste reaches a predefined threshold, the limit switch sensor (2) activates the shredder (4), providing a seamless transition from storage to processing. If the waste level is too low, the system (100) remains on standby until a sufficient amount of waste is available.

[0072] At Step 240, the Napier grass, food waste and agricultural waste is shredded using a shredder (4) to produce shredded waste. The shredding process reduces the size of the Napier grass, food waste and agricultural waste, thereby increasing its surface area and making it more accessible for microbial digestion. The shredder (4) consists of rotating blades or cutting mechanisms designed to uniformly break down the waste into smaller fragments.

[0073] At Step 250, the system (100) detects and stops the shredder (4) upon sensing a blockage using a blocking sensor (5). Specifically, if the shredder (4) encounters hard or fibrous materials that may obstruct the operation, the blocking sensor (5) automatically halts the shredder (4) to prevent mechanical damage. Upon detecting a blockage, an alarm system (24) generates an alert, notifying operators of the issue.

[0074] At Step 260, the shredded waste is transferred into a digester tank (7) through a waste inlet pipe (6). The waste inlet pipe (6) serves as a conduit between the shredder (4) and the digester tank (7), providing a smooth and continuous transfer of processed waste. The waste inlet pipe (6) prevents clogging and maintains an even distribution of shredded material within the digester tank (7).

[0075] At Step 270, the shredded waste is maintained in the digester tank (7) under anaerobic conditions. In the present invention, the digester tank (7) is a sealed, oxygen-free chamber that fosters microbial activity responsible for breaking down the organic material. The anaerobic digestion process leads to the production of biogas and digestate. The digester tank (7) is equipped with a thermal insulation layer (11) to regulate temperature and support microbial activity. Additionally, a retention time of less than 25 days is maintained to ensure complete digestion of the waste while maximizing biogas production.

[0076] At Step 280, digestion conditions are continuously monitored and regulated using at least one of a temperature sensor (16), a pH sensor (17), a viscosity sensor (15), a level sensor (18), or a rotor sensor (14). The temperature sensor (16) ensures that the internal environment remains at an optimal temperature around 37°C for mesophilic digestion, to maximize microbial efficiency. The pH sensor (17) monitors the acidity or alkalinity of the digester contents. If the pH deviates from the optimal range of 6.8 to 7.0, a buffering agent inlet (12) introduces chemical buffers such as sodium bicarbonate (NaHCO₃) to restore balance. The viscosity sensor (15) measures the consistency of the digestate, maintaining a proper fluidity level for microbial action. The level sensor (18) tracks the accumulation of digestate and biogas inside the digester tank (7), preventing overflows and ensuring stable operation. The rotor sensor (14) monitors the performance of the stirring mechanism (14), ensuring continuous and effective mixing of the digester contents.

[0077] At Step 290, the contents of the digester tank (7) are mixed using a stirring mechanism (14) driven by a motor (13). The stirring mechanism (14) includes a central shaft with radially extending blades that rotate to maintain homogeneous conditions within the digester tank (7). The motor (13) operates at controlled intervals to optimize energy consumption while maintaining effective agitation. The rotational speed of the stirring mechanism (14) is adjusted based on viscosity sensor (15) readings, allowing real-time optimization of digestion conditions.

[0078] At Step 300, digestate is removed from the digester tank (7) through a digestate outlet pipe (19). The digestate is the byproduct of anaerobic digestion, consisting of nutrient-rich material that is used as organic fertilizer. The digestate outlet pipe (19) ensures controlled discharge, allowing for efficient collection and processing. The flow of digestate is managed to prevent over-accumulation inside the digester tank (7). The tank connector pipe (8) and a union tank separator (10) facilitate the transfer of digestate, allowing for easy maintenance operations.

[0079] At Step 310, the digestate flow is controlled using a solenoid valve (20). The solenoid valve (20) is an electronically controlled valve that regulates the discharge rate of digestate. The solenoid valve (20) prevents sudden surges in flow, ensuring that the digestate is released in a controlled and manageable manner. In an embodiment, the solenoid valve (20) is programmed to operate based on pre-set conditions or adjusted manually, depending on the specific requirements of the system (100).

[0080] At Step 320, the digestate is collected in a digestate bag (21) positioned beneath the digestate outlet pipe (19). The digestate bag (21) serves as a temporary storage unit for processed digestate, preventing spills and enabling easy transportation. The collected digestate can be used directly as organic fertilizer in agricultural applications. The digestate bag (21) handles varying moisture levels, ensuring that both solid and semi-liquid digestate can be effectively stored and transported. A weight sensor (23) is used to measure the weight of the digestate bag (21), and when the weight exceeds a predefined threshold, an alert system (24) notifies operators to replace or empty the bag, preventing overflow and ensuring continuous operation.

[0081] The biogas generated is extracted from the digester tank (7) through a gas outlet pipe (25) and is transported for filtration. The extracted biogas contains methane (CH₄) along with impurities such as carbon dioxide (CO₂), moisture, and hydrogen sulphide (H₂S), which must be removed before usage. The biogas filtration unit (28) is designed to remove at least one of carbon dioxide (CO₂), moisture, or hydrogen sulphide (H₂S) from the extracted biogas. The biogas filtration unit (28) comprises a carbon filter, an iron wool filter, and a moisture filter to ensure the purification of biogas before further processing.

[0082] After filtration, the purified biogas is compressed using a compressor unit (29) and stored in a gas storage tank (30). The compression process reduces the gas volume, making storage more efficient and ensuring that the biogas remains available for use over extended periods. Finally, the compressed biogas is transferred to an external biogas distribution system through a CBG filling valve (31).

[0083] The method (200) ends at step 330.

[0084] By way of a non-limiting example, a working embodiment of the biogas generation system (100) is described in detail. The system (100) processes a composition consisting of cow dung (20%), food waste (10%), Napier grass (50%), and water (20%) by weight. The organic material undergoes mechanical shredding using a shredder (4), reducing the particle size to 5-10 mm, followed by thorough mixing to achieve a homogeneous slurry, ensuring efficient microbial digestion. The prepared organic material is then loaded into a digester tank (7) which is a Continuous Stirred Tank Reactor (CSTR) with a capacity of 1000 litres, maintained at 37°C under atmospheric pressure for mesophilic anaerobic digestion. To regulate digestion conditions, sodium bicarbonate (NaHCO₃) is added at 0.1% by weight as a buffering agent, ensuring the pH remains between 6.8 and 7.0.

[0085] Additionally, a nutrient solution containing trace elements such as iron (Fe), cobalt (Co), and nickel (Ni) is introduced to support microbial metabolism and enhance biogas yield. The digester tank (7) operates with a Hydraulic Retention Time (HRT) of 25 days and an Organic Loading Rate (OLR) of 12 kg of volatile solids per cubic meter per day, ensuring optimal conversion of organic matter into biogas.

[0086] During digestion, the stirring mechanism (14), comprising a motor (13) central shaft with radially extending blades, continuously mixes the digester contents to prevent sedimentation and ensure uniform microbial distribution. The resulting biogas, composed of methane (CH₄) (60%), carbon dioxide (CO₂) (35%), and other gases including hydrogen sulphide (H₂S) and ammonia (NH₃) (5%), is extracted through a gas outlet pipe (25) and passed through a biogas filtration unit (28) containing a carbon filter (28a), an iron wool filter (28b), and a moisture filter (28c) to remove impurities.

[0087] The filtered biogas is then compressed using a compressor unit (29) and stored in a gas storage tank (30), with a CBG (Compressed Biogas) filling valve (31) enabling transfer for external applications, such as electricity generation or vehicle fuelling. Simultaneously, the digestate is discharged through a digestate outlet pipe (19), regulated by a solenoid valve (20), and collected in a digestate bag (21) supported by a digestate bag holder (22). The weight sensor (23) monitors the digestate accumulation, triggering an alert via an alarm system (24) when the digestate reaches a predefined threshold, ensuring timely collection and preventing overflow. The collected digestate is rich in essential nutrients and is utilized as an organic fertilizer.

[0088] In an aspect of the invention, a sustainable biogas production cycle as shown in Figure 4, that utilizes Napier grass, food waste, and agricultural waste as primary feedstocks thereby establishing a circular economy is provided. The sustainable biogas production cycle begins with sourcing Napier grass, where farmers grow and harvest this fast-growing, high-biomass fodder crop and supply it to the biogas plant through borrowing arrangements. Upon arrival, the grass is transported by trucks or tractors and undergoes chopping and pre-treatment to reduce size for efficient microbial digestion. The pre-treated Napier grass, along with food waste and agricultural residues, is then fed into an anaerobic digester which is a sealed tank where in the absence of oxygen, microbial activity breaks down the organic material in stages such as hydrolysis, acidogenesis, acetogenesis, and methanogenesis. This process generates raw biogas, comprising primarily methane along with carbon dioxide and traces of hydrogen sulphide, as well as a nutrient-rich slurry. The raw biogas is subsequently purified by extracting methane and removing contaminants such as CO₂, H₂S, and moisture, resulting in biogas that is approximately 95% methane. The high-purity biogas is then utilized in various ways: it is compressed into high-pressure cylinders as compressed biogas (CBG) for use as a transport fuel, piped into households as cooking gas, and directed into gas engines to generate electricity for household use and even to charge electric vehicles. Meanwhile, the remaining digestate is processed into organic fertilizer, which is used for irrigation and soil enrichment. The organic slurry is supplied back to farmers, improving soil fertility, improving crop yields, and reducing dependence on chemical fertilizers. Ultimately, the process creates a circular economy where waste is converted into valuable energy and agricultural inputs, ensuring sustainability, reducing environmental impact, and promoting energy security.

[0089] Thus, the present system has the advantage of providing a system for generating biogas from Napier grass, food waste and agricultural waste. The system allows for the easy addition or removal of units to adjust capacity as needed, ensuring maximum efficiency output and scalability to meet varying waste inputs and energy demands. The integration of control systems enables automatic adjustment of stirring intensity and frequency based on real-time monitoring of microbial activity and substrate conditions, optimizing biogas production and maintaining process stability. Additionally, the system features simplified components that require minimal maintenance, ensuring long-term reliability and reducing operational costs. Simple installation mechanisms further reduce production time and labour costs, enhancing overall efficiency during deployment. The incorporation of scrubbers and biogas filters effectively neutralizes and absorbs odorous gases while removing impurities, odor, and moisture content from the biogas, resulting in high-purity gas suitable for various applications. Furthermore, the system maintains reliability and consistent output despite seasonal temperature changes, thereby enhancing the stability and efficiency of the anaerobic digestion process.

[0090] 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, and 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 omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present invention.
, Claims:We Claim:

1. A system (100) for generating biogas from Napier grass, food waste and agricultural waste, the system (100) comprising:
a feed processing unit (33) with a hopper (1) configured to receive Napier grass, food waste and agricultural waste;
a shredder (4) operably connected to the hopper (1) for reducing the size of the Napier grass, food waste and agricultural waste;
a digestion unit (50) including a digester tank (7) having an interior chamber configured for anaerobic digestion of Napier grass, food waste and agricultural waste;
a stirring mechanism (14) arranged within the interior chamber of the digester tank (7), the stirring mechanism (14) including a motor (13) coupled to a central shaft with radially extending blades for mixing the digester contents;
a monitoring unit (60) including at least one of a temperature sensor (16), a pH sensor (17), a viscosity sensor (15), a level sensor (18), or a rotor sensor (18) operably connected to the digester tank (7) for monitoring and regulating the digestion conditions;
a control unit (70) to adjust operational parameters based on inputs from at least one of the temperature sensors (16), pH sensor (17), viscosity sensor (15), level sensor (18), or the rotor sensor (14);
a digestate management unit (80) including a digestate outlet pipe (19) connected to the digester tank (7) for removing processed digestate;
a solenoid valve (20) disposed along the digestate outlet pipe (19) for controlling digestate flow;
a digestate bag (21) positioned beneath the digestate outlet pipe (19);
a digestate bag holder (22) for supporting the digestate bag and a weight sensor (23) arranged to measure the weight of the digestate bag (21);
a biogas collection and storage unit (90) including a gas outlet pipe (25) extending from the digester tank (7) for extracting biogas;
a biogas filtration unit (28) configured to remove at least one of carbon dioxide, moisture, or hydrogen sulphide;
a compressor unit (29) connected to the biogas filtration unit (28) for compressing purified biogas;
a gas storage tank (30) configured to store the compressed biogas;
a CBG (compressed biogas) filling valve (31) for transferring the compressed biogas;
a structural and maintenance unit (95) including a tank connector pipe (8) for material transfer; and
a union tank separator (10) positioned between the digester tank (7) and the tank connector pipe (8) for facilitating detachment and reattachment of the digester tank during maintenance.
2. The system (100) as claimed in claim 1, wherein the hopper (1) includes a limit switch sensor (2) to detect the waste level and activate or deactivate the shredder (4) based on a predefined threshold.
3. The system (100) as claimed in claim 1, wherein the shredder (4) includes a blocking sensor (5) configured to detect blockages and halt the operation of the shredder (4) upon detection of a blockage.
4. The system (100) as claimed in claim 1, wherein the shredder (4) includes a waste inlet pipe (6) extending from the shredder (4) for transferring processed waste.
5. The system (100) as claimed in claim 1, wherein the viscosity sensor (15) is operably connected to the stirring mechanism (14) and transmits signals to adjust the rotational speed of the stirring mechanism (14) based on the detected viscosity of the digester contents.
6. The system (100) as claimed in claim 1, wherein the digester tank (7) is configured to maintain a retention time of less than 25 days for anaerobic digestion.
7. The system (100) as claimed in claim 1, wherein the digester tank (7) includes a buffering agent inlet configured to introduce a chemical buffer to regulate the pH level.
8. The system (100) as claimed in claim 1, wherein the biogas filtration unit (28) includes a carbon filter, an iron wool filter, and a moisture filter configured to remove contaminants from the biogas before compression.
9. The system (100) as claimed in claim 1, wherein the weight sensor (23) is operably connected to an alarm system (24) in the control unit (70) configured to generate an alert when the digestate bag (21) reaches a predefined weight threshold.
10. The system (100) as claimed in claim 1, wherein a generator (32) is operably connected to the gas storage tank (30) and configured to convert compressed biogas into electrical energy.
11. A method (200) for generating biogas from Napier grass, food waste and agricultural waste, the method (200) comprising the steps of:
receiving Napier grass, food waste and agricultural waste in a hopper (1);
detecting the waste level in the hopper (1) using a limit switch sensor (2);
shredding the Napier grass, food waste and agricultural waste using a shredder (4) to produce shredded waste;
detecting and stopping the shredder (4) upon sensing a blockage using a blocking sensor (5);
transferring the shredded waste into a digester tank (7) through a waste inlet pipe (6);
maintaining the shredded waste in the digester tank (7) under anaerobic conditions;
monitoring and regulating digestion conditions using at least one temperature sensor (16), a pH sensor (17), a viscosity sensor (15), a level sensor (18), or a rotor sensor (18);
mixing the contents of the digester tank (7) using a stirring mechanism (14) driven by a motor (13);
removing digestate from the digester tank (7) through a digestate outlet pipe (19);
controlling digestate flow using a solenoid valve (20); and
collecting the digestate in a digestate bag (21) positioned beneath the digestate outlet pipe (19).
12. The method (200) as claimed in claim 11, wherein the weight of the digestate bag (21) is measured using a weight sensor (23), and an alert is generated when the weight exceeds a predefined threshold.
13. The method (200) as claimed in claim 11, wherein a tank connector pipe (8) and a union tank separator (10) facilitate the transfer of digestate and allow for maintenance operations.
14. The method (200) as claimed in claim 11, wherein the digester tank (7) is maintained at a temperature of approximately 37°C to optimize microbial digestion.
15. The method (200) as claimed in claim 11, wherein the digester tank (7) maintains a retention time of less than 25 days for anaerobic digestion.
16. The method (200) as claimed in claim 11, wherein the pH level within the digester tank (7) is regulated between 6.8 and 7.0 by adding a buffering agent.
17. The method (200) as claimed in claim 11, wherein biogas is extracted from the digester tank (7) through a bio gas outlet pipe (25) and transported for filtration.
18. The method (200) as claimed in claim 11, wherein the extracted biogas is filtered to remove at least one of carbon dioxide, moisture, or hydrogen sulphide using a biogas filtration unit (28).
19. The method (200) as claimed in claim 11, wherein the filtered biogas is compressed using a compressor unit (29) and stored in a gas storage tank (30).
20. The method (200) as claimed in claim 11, wherein compressed biogas is transferred to an external biogas distribution system through a CBG (compressed biogas) filling valve (31).