CASE STUDY

HAZOP studyfor CNG mother Station at Duliajan and Hazarigaon of AGCL

Introduction to AGCL’s CNG Mother Stations

Assam Gas Company Ltd., a Govt. of Assam Undertaking was incorporated on March 31, 1962 in Shillong as a limited company wholly owned by the Government of Assam to carry out all kinds of business related to natural gas in India. The Company can transport over 5.5 MMSCMD of natural gas.

Assam Gas Company Limited has awarded iFluids Engineering to carry out a Hazard and Operability (HAZOP) study for the CNG mother station at Duliajan & Hazarigaon, Assam. This document identifies the methodology and results proposed by iFluids Engineering as well as accepted by Assam Gas Company Limited for the completion of the HAZOP study.

Assam Gas Company Limited has a CNG mother station at Hazarigon & Duliajan. The HAZOP study was conducted using the documents available at the CNG mother station.

  • Hazarigaon station has the following facilities,
    • METERING SKID (1 no, Capacity- 1200SCMH)
    • RECIPROCATING GAS COMPRESSOR (1 no, Compressor Capacity – 1200 SCMH)
  • Duliajan station has the following facilities
    • METERING SKID (1 no, Capacity- 2400SCMH)
    • RECIPROCATING GAS COMPRESSOR (2 nos, Compressor Capacity – 1200 SCMH)
  • The CNG station is classified into the following categories:
    • Online stations
    • Mother Stations
    • Daughter Booster Stations
    • Daughter Stations.

The CNG Station receives CNG through a pipeline of 19 – 22 kg/cm2g or mobile cascade from nearby mother stations above 250 Kg/cm2g. After getting compressed via compressor, the gas would be sent to Dispensing Units (DU) and Cascade in Online and Mother stations. The compressed gas at 250 kg/cm2g would be sent to Dispensing Units (DU) to Daughter Booster stations. Also, the gas would be sent to Dispensing Units (DU) without compression in Daughter stations which is mentioned in the below figures.

Diagram illustrating the distribution of compressed natural gas (CNG) through a steel pipeline system. It shows the flow from a mother station, online station, daughter station, and daughter booster station. Key components include CNG compressors, storage cascades, mobile cascades, boosters, dispensers, and CNG vehicles. Pressure levels are indicated at various stages, with the mother and online stations compressing gas to 250 kg/cm² before distribution. Mobile cascades transport CNG to daughter stations, where boosters regulate pressure for vehicle refueling
Steel pipeline – Natural Gas Carrier

FIGURE 1 – PROCESS FLOW DIAGRAM FOR CNG STATIONS

Daughter Booster Stations are equipped with Booster Compressors and station cascade including Priority Panel. This arrangement helps to unload more than 75% of the incoming LCV Cascade volume for dispensing.

CNG is dispensed to vehicles based on the principle of pressure equilibrium. Once the pressure of a mobile cascade drops below 200 bar at the daughter station, vehicles get less amount of gas, which is below 200 bar. With each fill thereafter, the amount of gas dispensed to vehicles starts decreasing and the filling time starts increasing, thereby leaving the customer dissatisfied.

Daughter booster stations address this issue. These are similar to daughter stations. However, to cater to customers concerning the amount of gas dispensed as well as filling time, a booster compressor (hydraulic type with variable suction pressure) is installed in between the mobile storage and the CNG dispenser. The booster compressor increases the pressure above 200 bar as the pressure of the mobile cascade falls below 200 bar. Thus, the maximum amount of gas stored in the mobile cascade is dispensed to the daughter booster station.

The scope of work is to carry out a HAZOP study for the CNG mother station at Hazarigon & Duliajan and this study covers different components and equipments associated with the facility description.

The main objective of the HAZOP study is the early identification of hazards that are associated with process and operation and to reduce the probability and consequences of an incident that would have a detrimental impact on Humans, Facilities, Properties, and the Environment.

Objectives of HAZOP

The Objectives of HAZOP are as follows:

Infographic displaying the key objectives of HAZOP (Hazard and Operability) analysis. The four main objectives are: (1) Hazard Identification, (2) Cause Analysis, (3) Risk Assessment & Mitigation, and (4) Operational Efficiency Improvement. Each objective is represented in a distinct colored rectangular box with an arrow symbol on the left side, indicating progression
Objectives of HAZOP
  • To identify hazards associated with Processes and Operations.
  • To identify credible causes such as manual/equipment/instrument failures that are likely to cause hazards.
  • To qualitatively assess the risk (L/M/H/S) and provide recommendations to prevent/overcome hazards if required which shall be assessed using the qualitative judgment of likelihood and consequence ranking of an incident.
  • In addition to these issues, HAZOP occasionally identifies items that could improve unit operation and the efficiency of the process.

Methodology Employed in the HAZOP Analysis

iFluids Engineering follows a systematic approach to conducting HAZOP studies:

Methodology Employed In The Hazop Analysis Infographic illustrating the methodology employed in HAZOP (Hazard and Operability) analysis. The five key steps shown are: (1) Process Flow Diagram (PFD) Review, (2) Node Selection, (3) Deviation Analysis, (4) Risk Assessment, and (5) Mitigation Strategies. The design uses a circular flow with color-coded steps and a central label highlighting the methodology
Methodology Employed in the HAZOP Analysis
  1. Process Flow Diagram (PFD) Review: Understanding the layout and design of the CNG stations.
  2. Node Selection: Breaking down the system into manageable study sections.
  3. Deviation Analysis: Identifying potential risks related to pressure, temperature, and flow variations.
  4. Risk Assessment: Evaluating the likelihood and severity of identified deviations.
  5. Mitigation Strategies: Proposing control measures, alarms, and operational improvements.

As a first step, each facility (Hazarigon & Duliajan) has been separated into 4 nodes based on the Operation. And HAZOP study has been done for each node separately. The credible causes and consequences were identified for each parameter deviation. Then the available safeguards have been identified to mitigate the cause and consequences for each deviation.

The recommendations provided in the event of existing safeguards were found to be not sufficient. In both facilities, insufficient safeguards in the Compressor system for Pressure deviation & temperature deviation were found. Hence, it is recommended to implement a Position indicator for SSV & Running indication for Cooling fans respectively. As a general recommendation, it has been advised to maintain the Instrument calibration schedule, and records and to implement SOP for Hydro testing of cascade cylinders in Cascade storage.

Key Findings and Recommendations

  • Leak Detection Improvements: Installation of advanced gas detectors at critical points.
  • Emergency Shut-Down Systems: Enhancements in automated response systems for gas leaks.
  • Operator Training: Regular safety drills and competency development programs.
  • Ventilation Enhancements: Improved airflow systems to prevent gas accumulation.

Conclusion

The HAZOP study plays a vital role in optimizing the safety and operational efficiency of AGCL’s CNG mother stations. iFluids Engineering’s detailed risk analysis and recommendations ensure adherence to industry best practices, making the facilities safer and more reliable.

Ensure the safety and efficiency of your CNG facilities with expert HAZOP analysis. Contact iFluids Engineering today for a consultation and customized risk assessment solutions. By incorporating these SEO improvements, the webpage will achieve better visibility in search engine results, effectively reaching professionals seeking expertise in HAZOP studies for CNG facilities.