Assam Gas Company Ltd. (AGCL), 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 has the capacity to transport over 5.5 MMSCMD of natural gas.
AGCL has awarded iFluids Engineering to carry out a Quantitative risk assessment (QRA) study for CNG mother station at Hazarigaon, Assam. This document identifies the methodology and results proposed by iFluids Engineering as well as accepted by Assam Gas Company Limited for completion of QRA study.
AGCL has a CNG mother stationat Hazarigon & Duliajan. QRA study has been conducted with the documents available for Duliajan CNG mother station, the summary and the results of the study are applicable to CNG mother station located in the Hazarigaon region.
The CNG stations are classified into the following categories:
- Online stations
- Mother Stations
- Daughter Booster Stations
- Daughter Stations
The CNG Station is a Station that 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. Later the gas would be sent to DU after compression to 250 kg/cm2g in Daughter Booster stations. Also, the gas would be sent to DU without compression in Daughter stations. Compressor with a Capacity of 1200 SCMH and metering skid with a capacity of 10 – 1200 SCMH is available in these stations.
Daughter Booster 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 bars at daughter stations, vehicles get less amount of gas, which is below 200 bars. 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 the issue. These are similar to daughter stations. However, to cater customers with respect to amount of gas dispensed and filling time, a booster compressor (the 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 once 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 assessment will be based on hazards that may occur during the operation of the project according to the information available. The scope of work is limited to the different components associated with the proposed facility. The following facilities are covered under the QRA study for the Project.
- Mobile cascade (2 Nos.)
- Booster Compressor and Stationary Cascade (2 Nos.)
- Dispenser (1 No.)
The main objective of this study is to evaluate the potential risk levels for personnel due to the accidental release of hazardous materials from loss of containment scenarios from the facilities and to demonstrate that individual risks are within the broadly acceptable regions. The Objectives of QRA are as follows:
- Identification of Hazards and Major Loss of Containment (LOC) events
- Calculation of physical effects of failure case scenarios which include Estimation of Jet Fire, Pool Fire heat radiation distances, Flammable gas dispersion distances, and overpressure explosion distances
- Failure Frequency evaluation
- Societal risk quantification and Potential Loss of Life estimation
- Perform Risk assessment to confirm that risks can be reduced consistent with ALARP principle according to the UK HSE risk acceptance criteria
- Recommend Risk-reducing measures to ensure that all risks are in ALARP or Acceptable region.
The adequacy of Escape, Muster, Evacuation, and Rescue systems will be assessed according to information available. The scope of work is limited to the different components associated with the proposed facility. The following facilities are covered under the EMERA study for the Project.
- CNG Filling station- Duliajan
- CNG Filling station- Hazarigaon
The objective of Escape, Muster, Evacuation, and Rescue Analysis (EMERA) is to systematically address the effects of accidental events on adequacy and availability of Escape, Muster, Evacuation, and Rescue (EMER) systems and to perform their intended functions. The study shall cover the following:
- Escape routes analysis – Each area in the facility is to be assessed in terms of provision of escape provisions following OGP guidelines.
- Evacuation time analysis – The objective of evacuation time analysis is to assess if the assembly area and evacuation facilities can endure fire events for the period required for the personnel in the plant to evacuate;
- Evacuation provision analysis – To check for adequate provision of the evacuation facility, such that all personnel could safely evacuate the facility when required; and
- Rescue provision analysis – To assess the provision of rescue facilities for suitability and adequacy.
- Provide suitable recommendations for impaired escape routes.