QRA Study For S4 Facilities of Sembcorp North-West Power Company Limited, Bangladesh Terminal

Dual Fuel Combined Cycle Power Plant is the type of power plant. The plant is situated on the Bank of Jamuna River. Natural gas is supplied by PGCL at 10 bar to Natural Gas Conditioning Station of SNWPCL where it is filtered and fed into the Gas Booster Compressor (GBC). The GBC increases the gas pressure to around 40 bar. After passing through the GBC the gas is again filtered at the Final Filtering Station and enters the GT combustion chamber.

Atmospheric air is drawn in through the GT air intake system where it is filtered and compressed. After that, the combustion chamber is fed with it. Inside the combustion chamber the compressed air and gas mixture is ignited. After ignition the mixture expands by gaining thermal energy which it dissipates as it passes through the turbine blades forcing the turbine shaft to rotate.

This rotary motion of the turbine is converted to electrical energy in the GT generator. The exhaust flue gas of the gas turbine is utilized to create superheated steam in the Heat Recovery Steam Generator (HRSG). The High Pressure (HP) steam, Intermediate Pressure (IP) steam and Low Pressure (LP) steam from the HRSG is fed into the Steam Turbine (ST) where they dissipate their energy and rotates the turbine shaft. This rotary motion of the shaft is converted to electrical energy by the ST generator. Finally, the power which is generated by the GTG & STG is transmitted to the grid by 230 KV switch yard.

HSD is used as back up fuel. NWPGCL has constructed an HSD unloading and pumping station at the railway station and an HSD supply pipeline has been constructed up to the Saidabad Power Generation Complex by NWPGCL. Three days of HSD supply will be stored in two tanks with capacity equivalent to 15 days operation at 80% output on HSD, while the plant is running on Gas.

The following equipment play the parts for SNWPCL for generation of 414 MW:

  • Heat Recovery Steam Generator
  • Steam Turbine, Gas Turbine
  • Steam & Gas Turbine Generator
  • Power Transformer
  • Cooling water system
  • Main stack & Bypass stack
  • 6 Nos. Black start generators
  • 2 HSD tanks & unloading pumps
  • Hydrogen generator
  • Gas receiving and metering station
  • Transformer area
  • Gas booster station
  • Warehouse & Accommodation

The exhaust gas has been taken away from the stack of the 324 MW GT and passed through Heat Recovery Steam Generator (HRSG) in which groundwater is fed after treatment (demineralization & desalination) to produce the steam and then the steam is passed through steam turbine coupled with 50 Hz generator to produce 142.5 MW. The output voltage is stepped up to 230kV by power transformer connected to the 230 kV grid sub-station of PGCB to evacuate power to the national grid. The flue gas is discharged to the atmosphere through a bypass stack of adequate height.

Electricity is generated in the power plant at 11 KV. The voltage is stepped up to 230 KV through a step-up Transformer. This high voltage (230 KV) supply is connected to the existing 230KV Sub-station, through 230 kV overhead transmission line. There is one line for evacuation. Transmission voltage is 230KV and length of the line is about 900 meters. Generation voltages are 18kV and 15.75KV. Transmission voltage is 230KV and it is AC transmission.

The scope of Work is to carry out Quantitative Risk Assessment (QRA) study for S4 Facilities and Major hazard associated with the S1, S2, S3 facility which has an impact on S4 of Sembcorp North-West Power Company Limited, Bangladesh.

The major goal of this study is to assess the potential risk levels for workers resulting from the unintentional discharge of hazardous materials from the facilities under loss of containment scenarios and to show that individual risks fall within the generally acceptable ranges.

The following are the QRA goals:

  • To assess the risks to personnel, assets, and production posed by the facilities and determine their significance. This will help to decide how best the risks can be reduced.
  • To determine the acceptability of the calculated risk at the facilities and identification of the key risk contributors. By source and location, risk factors must be recognized.
  • Comparing risks of the design options being considered. This makes it easier to find design possibilities with low risk and choose the solution that makes the most sense from a risk and other technological and commercial standpoint.
  • For risk prioritization and resource allocation for implementation of safety measures.
  • Assess the risk of having container office at the eastern side of Gas Turbine Hall
  • Assess the Individual risk associated with the facility.
  • Assess the Societal risk associated with the facility.
  • To critically evaluate the existing safeguards and determine their adequacy in relation to the identified risk.
  • To provide clear and unambiguous recommendations for risk reduction where necessary to ensure that the facilities risks are controlled within acceptable limits.
  • Applying the principle of ALARP to demonstrate that the risk levels are in the tolerable region and the practicality of incorporating any additional risk reduction measures or potential design.

As part of the QRA study, hazard scenarios were identified for the project facility and consequence analysis was carried out using DNV PHAST software version 8.7. The risk analysis was carried out using DNV SAFETI software version 8.7 to obtain risk results in the form of LSIR contours and F-N curve. These risk results were assessed based on the Risk Acceptance Criteria and the Individual Risk Per Annum for the people at the risk ranking locations found to lie in the ACCEPTABLE region for locations and the societal risk falls broadly in the ACCEPTABLE region.