END USER FEATURE / EMISSIONS
Conventional GCP shutdown practice
Under conventional operational protocols, when a GCP is taken offline for planned or unplanned maintenance, the turbine drivers are not fully de-fueled. Instead, they are maintained in a“ hot standby” condition by sustaining a minimum fuel gas flow- typically in the range of 100 to 150 MSCF per GCP- through the main fuel gas supply valve. This practice is adopted primarily to:
• Minimise the time required for restart and return to service.
• Preserve thermal gradients in the turbine casing, reducing thermal fatigue risk.
• Maintain control system readiness and valve actuator responsiveness.
While these motivations are valid, the energy penalty associated with sustained minimum fuel flow over extended shutdown durations is substantial. Shutdown events at GCP facilities may range from a few hours( for minor interventions) to several days or weeks( for major maintenance campaigns). During this period, fuel gas is combusted without performing any useful compression work, resulting in direct GHG emissions and direct economic cost.
Regulatory and corporate context
Saudi Aramco has committed to achieving net-zero Scope 1 and Scope 2 greenhouse gas emissions by 2050, with interim reduction targets established under its Decarbonization and Emissions Elimination Program( DEEP). Flaring reduction and fuel gas conservation are among the highest-priority actions under this framework. Concurrently, the Kingdom of Saudi Arabia’ s Vision 2030 roadmap emphasises diversification, sustainability, and the responsible stewardship of natural resources. On an international level, the Zero Routine Flaring initiative by the World Bank and the UNEP Climate and Clean Air Coalition have drawn heightened scrutiny to hydrocarbon venting and combustion in upstream operations. Fuel gas consumed non-productively during standby periods, while distinct from flaring in regulatory classification, contributes identically to atmospheric CO2 loading.
Full fuel gas valve closure during shutdown
The central innovation of this initiative is conceptually straightforward but operationally significant: during GCP’ s shutdown events, the main fuel gas supply valve is fully closed rather than throttled to minimum flow. The pilot valve- a smaller, independently controlled valve providing ignition-ready fuel gas for turbine restart- is retained in its normal position, ensuring that turbine restart capability is preserved without sustaining combustion. This approach draws on principles analogous to“ fast plant shutdown” strategies used in advanced gas turbine optimisation, where the objective is to eliminate all non-essential combustion during non-operational periods. The distinction between main fuel gas valve and pilot valve functions is critical to the technical viability of the approach( Table 1)
Control system & valve logic modifications
Implementation of the optimised shutdown strategy required modifications to the Distributed Control System( DCS) and Safety Instrumented System( SIS) logic governing the GCP. Key engineering activities included:
• Review and revision of the Cause and Effect( C & E) matrix to include full closure of the main fuel gas valve as part of the planned shutdown sequence.
• Verification that the pilot valve control loop remained independent and unaffected by the main valve closure signal during standby.
• Verification of interlock logic to prevent the train’ s main valve from reopening until turbine pre-start checks are confirmed.
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