Many gas turbine operators in the oil and gas industry choose to operate equipment in a configuration known as “N+1”; this describes the scenario in which the number of gas turbine engines that are simultaneously running at any given time is one greater than would be required to deliver the load requirement for the installation. The reason for choosing to operate in this way is that should one engine trip, a sufficient power capacity remains amongst the running engines to deliver the entire load requirement for the installation, avoiding a disruption to production. Avoiding a disruption to production can also help to avoid unnecessary emissions, because in some instances, the inability to provide the full required power for an installation may result in increased flaring, or worse still, may require a compressor to go offline resulting in the release of unburnt methane in to the atmosphere.

Unfortunately, operating “N+1” leads to a lower average power setting for each of the running gas turbine engines. This reduces the thermal efficiency of the gas turbines and has a significant effect on fuel consumption and CO2 emissions; the increase of which can be greater than 25%. However, the deployment of a battery for emergency backup power could provide a method of avoiding “N+1” operation. If a battery can be installed that provides the missing power of a single gas turbine for a 30 minute period following a trip, this provides plenty of time for the operator to bring a spare engine online without disrupting production.

The thermal efficiency of simple cycle gas turbine engines peaks at around 40%. If a waste heat recovery system is deployed to generate power from the exhaust heat, the overall plant efficiency can increase to over 60%. In the best case this could reduce fuel consumption and CO2 emissions by a third, which provides enormous potential using existing and proven technology. Waste heat recovery engines can be effectively applied to both industrial and aero-derivative gas turbine engines, with different waste heat technologies being available, each having their individual advantages and suitability for a given application.

Investing in technology such as this now will also prove advantageous if the energy transition forces us towards alternative fuels, because future fuels could be more expensive and more limited in supply than todays fuels, in which case minimising their consumption will be attractive.

Carbon-neutral and zero-carbon fuels represent the final step for gas turbine operators who have completed hardware efficiency updates, optimized their operating profiles, and see economic advantages in moving beyond carbon capture.

Ammonia

Ammonia may offer a path to carbon-free operation for sites with ready access to the fuel and to liquid fuel storage. Ammonia has roughly half the energy density, as well as higher NO_x emissions, than diesel but storage and emissions treatment strategies exist in the market today.

Methanol

Methanol offers a 10% reduction in CO₂ and a 70% reduction in NO_x emissions versus diesel. Both “gray” carbon-emitting and “green” carbon-neutral variants are produced today, with “gray” methanol widely traded throughout the world. Operators converting to methanol operation can switch from the carbon-emitting “gray” variant to the carbon-neutral “green” variant simply by changing their fuel vendor.

Hydrogen

Hydrogen offers both zero-carbon and low-NO_x operation. When blended with methane, high concentrations of hydrogen are required to achieve significant reductions in emissions. For example, to reduce a natural gas-burning site’s CO₂ footprint by 10% would require a hydrogen concentration of 25% by volume. Access to hydrogen can come from some combination of onsite generation of green hydrogen, splitting ammonia, or receipt of a hydrogen blend into the existing gas transmission lines.

Each operator should consider their specific site’s operating requirements and layout in assessing alternative fuel solutions. Methanol conversions from diesel should generally be economically feasible for backup power stations today while gas transmission lines and peak power plants may consider carbon capture technologies as a stopgap solution until hydrogen economies of scale are reached later this decade.

Siemens Energy AGT offers a variety of solutions and site studies to guide customers on their net-zero journeys.

Turbomachinery upgrades

The overall thermal efficiency that can be achieved from a gas turbine package (and therefore also the heat rate and CO₂ emissions properties) is affected by both the efficiency characteristic of each of the individual components, and the conditions at which they are operating. Consequently, the thermal efficiency of an existing package could be optimised by carefully understanding the current hardware configuration and how it is operating, and assessing various upgrade options to identify improvement opportunities.

Power turbines: Power turbines operate within a speed window that is influenced by the driven equipment, and this speed window is typically sufficiently narrow that the power turbine characteristics do not change significantly. Therefore the greatest opportunity for power turbines upgrades to improve emissions and heat rate properties of the package is an improvement in the baseline efficiency of the power turbine. Within the AGT product line, upgraded blades, vanes and tip seals are available for some power turbine variants which give up to 3% increase in PT efficiency, fuel flow and CO₂ emissions. The upgrades also increase temperature, power and life capability which can provide more flexibility in the operation, potentially opening up other options for decarbonisation potential.

Gas generators: The efficiency of gas generators is influenced both by the turbomachinery itself and how it is operated. Within the AGT fleet there is a wide variation in the gas turbine operating conditions. Upgrade options for both compressors and turbines are available for a variety of AGT products that can either improve the efficiency at the current operating conditions or can change the power capacity of the engine(s) in such a way that they can be operated in a condition which is closer to the optimum. In some cases the reduction in fuel consumption and CO₂ emissions can be significant. There are numerous hardware configuration options that could be considered, and individual performance assessments can be conducted by Siemens Energy to identify potential benefits and which hardware configurations may be considered.

A general overview of current DLE capability and the new DLE development that is being looked at for A35, A20 and A05. Dry Low Emissions combustors produce minimal NOx­ emissions without the use of water injection. Hydrogen-capable DLE combustors gas turbines connected to gas pipelines to continue operations when hydrogen is injected into those gas lines, and without the need for onsite water.

AGT gas turbines have intrinsic capability to operate on hydrogen with existing DLE combustors, and AGT continues to push the limits of hydrogen blending to provide up to 100% H2 DLE capability by 2030.