HAZOP Study for Compressed Biogas (CBG) Plant at Adarsh Gaushala, Gwalior: Enhancing Safety and Efficiency
HAZOP Study for Compressed Biogas (CBG) Plant at Adarsh Gaushala, Gwalior: Enhancing Safety and Efficiency
Summary
The HAZOP study successfully identified hazards and operability issues related to feed handling, digester operations, and biogas purification. Actionable recommendations were made to enhance safety, reliability, and efficiency, ensuring compliance with industry standards.
Overview of the CBG Plant
The Compressed Biogas (CBG) plant at Adarsh Gaushala, Laltipara, Gwalior, processes 100 tons per day (TPD) of cattle dung and 20 TPD of source-segregated Organic Fraction of Municipal Solid Waste (OFMSW) to produce biogas. Besides biogas, the plant produces valuable by-products like manure, Fiber Organic Manure (FOM), and Liquid Fiber Organic Manure (LFOM).
Scope of the HAZOP Study
The Hazard and Operability (HAZOP) study focused on assessing the safety and efficiency of the CBG plant. The study analyzed critical systems, including feed preparation, digester operations, biogas purification, and utility systems such as water and power, to identify potential risks and suggest improvements.
Key systems analyzed included:
- Feed preparation and slurry transfer
- Digester and recirculation systems
- Gas purification and storage
- Slurry separation
- Utility systems: water, power, and chemical dosing
Objectives
The HAZOP study aimed to:
- Identify deviations from the design and performance criteria that could lead to unsafe conditions or inefficiencies.
- Assess design integrity concerning mechanical and process safety, focusing on pressure management, flow control, and temperature regulation.
- Evaluate operability risks like equipment failures, operational errors, and process upsets.
- Review existing safety measures and recommend improvements.
- Ensure compliance with safety, environmental, and operational standards.
Process Description of the CBG Plant
The plant converts cattle dung and source-segregated organic waste (OFMSW) into biogas through the following key stages:
- Feed Preparation: Cattle dung is screened, mixed with water, and transferred to digesters as slurry.
- Digester Operations: The slurry undergoes anaerobic digestion in three digesters, maintained under specific conditions. Slurry and gas recirculation ensure uniform digestion.
- Biogas Purification: Biogas is purified by removing H₂S and CO₂, stored in a biogas balloon, and then compressed for vehicle dispensing.
- Solid-Liquid Separation (SLS): The digested slurry is separated into solid (wet cake) and liquid fractions. The wet cake is dried, and leachate is either recycled or further processed.
- Dispensing: Compressed biogas is dispensed to vehicles at a CBG station.
Methodology
The HAZOP study used PHA Pro software to ensure thorough analysis. Key steps included:
- Node Selection: Identified critical equipment and process sections from P&IDs.
- Defining Parameters: Established process parameters, design intents, and operational criteria.
- Deviation Identification: Applied guidewords (e.g., No, More, Less) to identify potential deviations.
- Cause and Consequence Analysis: Analyzed deviations for causes and consequences.
- Safeguard Evaluation: Reviewed existing safeguards and recommended improvements
- Recommendations: Suggested additional safeguards and procedural improvements where needed.
Nodes Studied
Nine critical nodes were evaluated, covering major equipment and processes:
- Feed preparation and slurry to digesters
- Digester recirculation and slurry transfer
- Digested slurry transfer to the drying yard
- Recycle water system
- Biogas purification, compression, and bottling
- Raw and hot water system
- Inoculum dosing
- Caustic dosing for H₂S scrubbing
- Cooling water system
Challenges Identified
- System Interfaces: Evaluating the interfaces between subsystems, particularly between the OFMSW feed system and gas purification.
- Waste Composition Variability: Variations in cattle dung and municipal waste composition impacted process efficiency and methane production, requiring careful management.
- Digester Overpressure: Insufficient gas venting systems posed pressure management risks.
- Purification System Issues: The CO₂ scrubber’s performance affected biogas purity.
- SLS Filter Clogging: Filter blockages in the Solid-Liquid Separator due to changing slurry composition.
- Safeguard Adequacy: Assessing whether existing safeguards were sufficient, particularly for methane handling and compression.
- Operational Training: Ensuring personnel were adequately trained, especially for emergency response and handling pressurized biogas.
Recommendations for Improvement
The HAZOP study made several key recommendations to enhance plant safety and efficiency:
- Develop and implement Standard Operating Procedures (SOPs) for all critical operations.
- Provide regular training for plant personnel to improve safety awareness and emergency preparedness.
- Establish preventive maintenance schedules for equipment like pumps, strainers, and filters.
- Regularly inspect and clean filters to prevent clogs in the SLS and purification systems.
- Review and upgrade existing safeguards, particularly in areas like CO₂ scrubbing and overpressure protection.
Conclusion
The HAZOP study at Adarsh Gaushala, Gwalior, identified critical risks and proposed effective mitigation strategies. By implementing the recommended actions, the plant can improve process safety and operational efficiency. Continuous monitoring and periodic reviews are essential for addressing new risks and maintaining safety compliance.