Introduction
Fertilizer production facilities, especially those involving Ammonium Nitrate (AN), operate with inherently high process risks due to the use of reactive chemicals such as ammonia and nitric acid. To ensure a safe and efficient design, prevent operational failures, and comply with international safety standards, a detailed Hazard and Operability (HAZOP) Study and Safety Integrity Level (SIL) Classification Study were conducted. These studies are critical in identifying process hazards, improving system reliability, and defining Safety Instrumented Functions (SIFs) in line with IEC 61508 and IEC 61511 functional safety standards.
Methodology
HAZOP Study involved dividing process units into logical nodes based on P&IDs. Guidewords like No, More, Less, Reverse, and Other Than were used to identify parameter deviations. Each deviation was analyzed for causes, consequences, safeguards, and recommendations. A risk matrix was applied to rank the severity and likelihood of each scenario.
SIL Study identified Safety Instrumented Functions (SIFs) from HAZOP findings and Cause & Effect diagrams. SIL levels were determined using Layer of Protection Analysis (LOPA). Independent Protection Layers (IPLs) and event frequencies were evaluated to assign SIL ratings.
Outcome
- HAZOP identified several critical safety and operability issues, leading to actionable recommendations such as the implementation of alarms, interlocks, and procedural improvements.
- SIL analysis validated the reliability of over 50 SIFs across the facility, most of which were rated SIL 1 or SIL a to address key risk scenarios.
- The combined studies enhanced risk awareness, improved safety architecture, and ensured alignment with international standards.
HAZOP & SIL Study – Ammonium Nitrate Melt Plant project
The study was carried out for the Ammonium Nitrate Melt Plant at Rashtriya Chemicals & Fertilizers Ltd. (RCF), Trombay, Maharashtra. The objective was to expand fertilizer production capacity while ensuring high levels of safety and operational reliability.
Scope and System Details
The HAZOP and SIL Study covered the following systems and sub-sections:
1. Ammonia and Nitric Acid Feed Systems
- Reactor operation
- Ammonia-nitric acid ratio control
- pH correction loops and safety interlocks
2. Ammonium Nitrate Solution Systems
- Separator , AN Solution Tank
- Transfer lines to battery limits
3. Scrubbing and Steam Purification Systems
- Venturi Scrubber , Cyclonic Column
- Scrubbing Pumps, Purifier Exchanger
4. Process Steam and Condensate Handling
- Shell and tube heat exchangers for purification
- Multi-effect condensate cleaning and recycling
5. Multi-Effect Evaporation (MEE) Section
- Three-effect falling film evaporators
- Vapor-liquid separators and surface condensers
6. Critical Safety Instrumented Functions (SIFs)
- High-high pressure and temperature trips
- Low-level alarms in scrubbers and condensate tanks
- Emergency shutdown interlocks for MOVs and control valves
7. Utility Systems
- Low-pressure steam distribution
- Cooling water and nitrogen purging systems
- Seal water systems for MEE section
Conclusion
The HAZOP and SIL assessments for the Ammonium Nitrate Melt Plant at RCF successfully established a comprehensive safety framework for the facility. The structured identification of hazards, detailed risk evaluation, and classification of critical SIFs resulted in significant improvements in process safety, operational control, and regulatory compliance. The study outcomes not only reduced potential risks but also supported the safe scale-up of fertilizer production, contributing to long-term plant reliability and environmental stewardship.