Pipeline natural gas

Pipeline gas is the standard fuel for most new turbines. Even so, gas composition varies between networks and over time. Buyers should provide the turbine supplier with a full gas analysis and the expected range of variation, including heating value, inert content and heavier hydrocarbons.

Turbines with dry low-emission combustors can be sensitive to rapid changes in gas quality. The supplier should confirm acceptable limits and any monitoring needed.

LNG and regasified gas

Gas from LNG terminals can differ from local pipeline gas, often with higher heating value. Projects relying on LNG should confirm the composition range from the terminal and check it against the turbine fuel specification.

Where a site may switch between pipeline gas and LNG, the combustion system must handle both without retuning each time.

Liquid fuel backup

Many turbines can burn diesel or light distillate as a backup fuel. Dual-fuel capability allows the plant to keep running if gas supply is interrupted. It requires liquid fuel nozzles, a fuel forwarding system, storage tanks and often water injection for emissions control.

Buyers should confirm how long the turbine can run on liquid fuel, how emissions limits are met and how often liquid fuel systems must be exercised to stay reliable.

Fuel switching under load

Some turbines can transfer from gas to liquid fuel and back while carrying load. This is valuable for critical loads such as data centers or industrial processes. Transfer performance varies between models and combustion systems.

Ask the supplier for tested transfer capability, including the load range in which transfer is allowed and any temporary output reduction.

LPG and propane

Liquefied petroleum gas, propane and butane can fuel turbines in places without natural gas networks. They require vaporisation equipment and careful control of fuel temperature and composition. Not all combustion systems accept these fuels.

Confirm suitability and emissions performance with the supplier before planning a project around LPG.

Associated and process gases

Oilfield associated gas, refinery off-gases and other process gases can be valuable fuels, reducing flaring and fuel costs. They often contain heavy hydrocarbons, hydrogen sulphide or variable heating value, which require treatment and special combustion hardware.

Gas conditioning skids that remove liquids and contaminants are usually needed. Industrial turbines with conventional combustors often tolerate these gases better than low-emission versions.

Hydrogen blending

Interest in hydrogen blending is growing, and many suppliers offer turbines capable of burning a share of hydrogen mixed with natural gas. Our article on hydrogen-capable turbines covers the questions in detail.

For most projects today, hydrogen capability is a future option rather than an operating requirement. Buyers should understand what upgrades would be needed later.

Combustion systems and emissions

The combustion system decides which fuels a turbine can burn and at what emissions level. Dry low-emission systems achieve low nitrogen oxides on gas but may have narrower fuel limits. Conventional diffusion combustors accept a wider range of fuels but usually need water or steam injection, or after-treatment, to meet strict limits.

Our guides to turbine combustion and NOx control explain the trade-offs.

Fuel treatment and storage

Every fuel needs some treatment. Gas may need filtering, heating and pressure regulation. Liquid fuel needs filtration, water removal and storage that prevents contamination. Process gases may need extensive conditioning.

Include treatment and storage in the project budget and layout from the start, rather than treating them as add-ons.

Fuel quality limits and warranties

Turbine warranties and service agreements usually depend on fuel meeting the supplier’s specification. Fuel outside the limits can void warranties or increase maintenance costs. Buyers should understand the limits and how compliance will be monitored.

Regular fuel sampling and online analysers help prove compliance and detect problems early.

Running hours on backup fuel

Dual-fuel turbines that rarely run on liquid fuel can suffer from coked nozzles, stale fuel and seized valves when the backup is finally needed. A routine of periodic transfers to liquid fuel, with the forwarding system, nozzles and controls exercised under load, keeps the backup ready. Stored distillate should be sampled and polished on a schedule, and tank capacity should match the longest gas interruption the site is designed to ride through.

Permits sometimes cap running hours on liquid fuel. Check those limits early, because they decide how much testing is allowed and how long the plant may legally run on backup during a gas outage.

Fuel cost and future flexibility

Fuel prices and availability change over a plant’s life. A turbine ordered with wider fuel capability, or with a clear upgrade path, can adapt to new supply options without a major rebuild. Weigh the extra capital cost against the value of that option, using realistic scenarios for gas supply, liquid fuel prices and emissions rules over the expected life of the plant.

Specifying flexibility in the RFQ

State the fuels required, their composition ranges, the need for dual-fuel or switching capability, emissions limits for each fuel and the expected running hours on each. Ask suppliers to confirm capability with reference installations and test data.

Clear fuel requirements in the request for quotation avoid costly changes after order and help compare bids on equal terms.

Why a turbine needs a starter

The compressor in a gas turbine absorbs a large share of the power the turbine produces. At low speed, combustion cannot produce enough power to drive the compressor and accelerate the shaft. The starter turns the rotor up to a speed where combustion can begin, then helps accelerate it until the turbine is self-sustaining.

Once that point is reached, the starter disengages or switches off, and the turbine accelerates to operating speed under its own power.

The start sequence

A typical start begins with the rotor on turning gear or at rest. The starter accelerates the shaft to purge speed, and air is blown through the turbine and exhaust to clear any fuel or gas that may have collected. After the purge, speed is adjusted for ignition, fuel is admitted and igniters light the combustors.

Flame detectors confirm ignition. The starter and combustion then accelerate the unit to self-sustaining speed, after which the starter drops out and the unit reaches full speed, ready for synchronising.

Electric motor starters

Many industrial gas turbines, especially smaller and older frames, use an electric motor, often coupled through a torque converter or clutch, to crank the shaft. The motor needs a substantial electrical supply during the start, which must be available from the grid, auxiliary transformer or a black start generator.

Electric starters are relatively simple and robust, but their supply must be designed for the motor’s starting current.

Static frequency converters

Large heavy-duty turbines commonly use a static frequency converter, sometimes called a load commutated inverter. It feeds variable frequency power into the main generator, which then runs as a motor to turn the shaft. This avoids a separate starting motor but needs a power supply sized for the start and adds power electronics that must be maintained.

Some plants share one converter between several units, which saves cost but means only one unit can start at a time.

Hydraulic and pneumatic starters

Aeroderivative and smaller turbines often use hydraulic starters, driven by an electric or diesel-powered hydraulic pump, or pneumatic starters driven by compressed air. Pipeline compressor turbines may use gas expansion starters that use pipeline gas pressure, with vented gas managed according to the site’s safety and environmental rules.

Hydraulic and pneumatic systems are compact and can support fast starts. Our article on what an aeroderivative gas turbine is explains why those units suit rapid starting.

Diesel engine cranking

Some older heavy-duty units were started by a diesel engine coupled through a torque converter. This arrangement can start a turbine without an external electrical supply, which made it attractive for black start duty. It requires maintenance of the diesel engine and its fuel supply alongside the turbine.

When refurbishing older units, owners sometimes replace diesel starters with electric or hydraulic systems to reduce maintenance.

Power for the start

Every starting system needs energy from somewhere: the grid, an auxiliary transformer, a black start diesel, batteries or compressed gas. Auxiliaries such as lube oil pumps, ventilation and controls also need power during the start. The total demand must be available whenever a start is required.

If a plant must start without the grid, the black start supply must be sized for the starter plus all auxiliaries. Our guide to black start scope for new turbines covers that design.

Common start failures

Failed starts often come from the starting system and its supports rather than the turbine core: a starter that cannot reach purge speed, a clutch that fails to engage or disengage, low supply voltage, hydraulic leaks, igniter faults or flame detector problems. Fuel supply issues and control faults also cause starts to abort.

Our article on common gas turbine trip causes covers faults after the unit is running.

Start reliability and testing

For units that must start on demand, such as peaking or backup plants, start reliability is a key measure. Track each start attempt, its outcome and the cause of any failure. Test starts at regular intervals, and include the starting system in the maintenance programme with inspection of clutches, couplings, motors, converters and hydraulic or air systems.

Recording start time from command to synchronising helps spot slow degradation before it becomes a failed start.

Choosing a starting system

For new turbines, the starting system is usually defined by the manufacturer for each model, sometimes with options. Owners should check the system’s supply needs, start time, how many consecutive starts it allows and whether it can support black start. These points matter especially for data center and peaking plants that must start quickly and reliably.

Ask for the starting system’s maintenance requirements and spare parts list as part of the purchase.

Why turbines trip

The protection system monitors speed, temperatures, pressures, vibration, flame and many other signals. When a value crosses a trip limit, the system shuts off fuel and brings the unit down safely. Some faults cause an alarm first, giving operators time to act; others trip immediately because the risk of damage is too high.

Trips can come from genuine equipment problems, from faulty instruments that report false values or from external events such as grid faults. Separating these causes is the first step in reducing trips.

Combustion problems and flame-out

If the flame becomes unstable or goes out, flame detectors signal a loss of flame and the unit trips to prevent unburnt fuel from accumulating. Causes include fuel supply disturbances, incorrect combustion tuning, worn fuel nozzles and, in low emissions combustors, operation close to lean limits.

Regular combustion tuning and inspections keep the flame stable. Our article on gas turbine combustion explains how combustors work and why tuning matters.

Vibration

High vibration on bearings or the casing indicates imbalance, misalignment, rubbing, bearing wear or loose components. Vibration trips protect the rotor from serious damage. Sudden changes in vibration deserve immediate investigation, while slow trends can be planned into maintenance.

Faulty vibration probes or wiring can also cause false trips. Checking the instrument chain before assuming a mechanical problem saves time and avoids unnecessary inspections.

Exhaust temperature spread

Thermocouples around the exhaust measure temperature at many points. A large difference between them, called spread, may indicate a failed combustor, blocked fuel nozzle or damaged hot section part. High spread can trigger an alarm or a trip.

Failed thermocouples produce false spread readings, so maintaining the thermocouple set is part of avoiding unnecessary trips. Trends in spread over time are a valuable early warning of hot section problems.

Lube oil and bearings

Low lube oil pressure, high bearing temperature or high oil temperature trip the unit to protect the bearings. Causes include pump failure, blocked filters, cooler problems, oil contamination and low oil level.

Routine oil analysis, filter changes and checks on pumps and coolers prevent most of these trips. Backup pumps should be tested regularly so they start when needed.

Fuel gas pressure and quality

Turbines need fuel gas within a defined pressure range and with stable composition. Pressure drops caused by pipeline events, compressor trips or regulator faults can cause flame-out or trip the unit on low pressure. Liquids or contaminants in the gas damage nozzles and destabilise combustion.

Good fuel gas conditioning, filtration and pressure control, plus coordination with the gas supplier, reduce fuel-related trips. Units with backup liquid fuel can transfer if gas supply fails, provided the transfer system is maintained and tested.

Overspeed and governor problems

Overspeed protection trips the unit if the shaft speed rises too high, for example after a sudden loss of load. Governor and fuel valve problems can cause speed to swing or rise. Overspeed trips must never be bypassed and should be tested as the manufacturer requires.

Load rejection events on island systems are a common cause. Correct governor tuning and load shedding schemes help the unit ride through them.

Instrumentation and controls

Many trips come from instruments and controls rather than the turbine itself: failed sensors, loose wiring, power supply faults or software problems. Ageing control systems with obsolete parts are particularly prone to this kind of trip.

Redundant sensors with voting logic reduce false trips. Our article on controls upgrades and obsolescence discusses when replacing a control system is worthwhile.

Generator and grid events

Generator protection trips the unit for faults such as loss of excitation, reverse power or internal electrical faults. Grid disturbances such as voltage dips and frequency excursions can also trip turbines if protection settings are too tight.

Coordinated protection settings and grid code studies help units stay on line during disturbances while still protecting equipment.

Trips on new units during early operation

New turbines often show a cluster of trips in their first months. Many come from commissioning issues such as loose terminations, sensor calibration, control logic settings or fuel system debris rather than design faults. A structured early-operation review, with the supplier involved, closes these issues quickly. Keep the commissioning team engaged until trip rates settle, and record each fix so the lesson carries to the next unit.

Investigating trips and reducing them

Every trip should be investigated: record the first-out alarm, gather trend data, identify the root cause and take corrective action. A trip log that records causes over time shows patterns and helps target improvements.

Regular inspections at the intervals recommended by the manufacturer catch many problems before they cause trips. Our article on gas turbine inspection intervals explains how those inspections are scheduled.

Hydrogen behaves differently from natural gas

Hydrogen burns faster and hotter than natural gas and has a much lower energy content per unit volume. That affects combustion stability, flame temperature, emissions and the volume of fuel the system must deliver. It also makes hydrogen more prone to leaking and to causing certain metals to become brittle.

For these reasons, adding hydrogen is not simply a matter of changing the fuel contract. The combustor, fuel system, controls and safety systems may all be affected.

Blend percentage: by volume or by energy

Hydrogen capability is usually stated as a percentage blend. Check whether the figure is by volume or by energy. Because hydrogen has low energy per volume, a blend that sounds high by volume delivers a much smaller share of the energy.

Ask what blend the turbine can burn as supplied, what blend requires modifications, and whether the higher figure has been demonstrated on that model or is a development target.

Combustor technology

Low-emission combustors designed for natural gas can tolerate a certain hydrogen share before flame stability and flashback become concerns. Higher shares may need a different combustor design. Our page on gas turbine combustion explains the basics.

Ask whether a combustor change would be needed for higher blends, how long it would take and whether the turbine’s other parts are already suitable.

Emissions and NOx

Hotter hydrogen flames tend to raise nitrogen oxide formation. Combustors and emissions controls must be designed to keep within permit limits at the blends intended. Emissions may also need to be measured and reported differently when hydrogen is in the fuel.

Confirm with each bidder the emissions guarantees at each blend level. The NOx control guide covers the control options.

Fuel system and materials

Hydrogen requires attention to piping materials, seals, valves and instruments. Metering and fuel control must handle varying blend ratios. Where hydrogen is blended on site, a mixing skid and gas analysis are needed.

Check whether the turbine package’s fuel system is rated for hydrogen at the stated blend, and what parts would need replacing for higher blends.

Safety

Hydrogen leaks are hard to see and ignite easily. Enclosure ventilation, gas detection, fire detection and hazardous area classification must reflect hydrogen. These requirements can affect the turbine enclosure and the surrounding plant layout.

Plan for this at the design stage. Retrofitting hazardous area equipment later is more disruptive than allowing for it from the start.

Controls and operation

Turbine controls must manage fuel changes, blend ratios and the transition between fuels. Ask whether the controls can handle varying hydrogen content in real time and whether the turbine can switch back to natural gas automatically if hydrogen supply is interrupted.

Operators need training on the new hazards and procedures. Include this in the plan for any hydrogen operation.

Supply reality

A hydrogen-capable turbine is only useful if hydrogen is available at the site in sufficient quantity, purity and pressure. For most sites today, supply is uncertain and the turbine will run on natural gas for years. That is not a reason to ignore capability, but it is a reason to weigh its value realistically.

Consider capability as an option for the future. The value lies in avoiding a costly redesign if hydrogen becomes available, not in immediate use.

Hydrogen and the rest of the plant

Hydrogen capability is not only about the turbine. Fuel supply pipework, metering stations, compressors, gas detection, ventilation and hazardous area classification across the plant may all need to change for higher blends. A turbine rated for a high blend in a plant whose fuel system and safety design are not suitable cannot use that capability.

Ask the EPC contractor to show how the plant layout, materials and safety systems would change at each blend level, and which changes can be built in at little extra cost during initial construction.

Emissions permits may also need revision. Some permits are written around natural gas, and burning a hydrogen blend could require new monitoring or a permit variation.

Questions for every bidder

Ask: what blend by volume and by energy is possible as supplied; what has been demonstrated on this model; what modifications are needed for higher blends; what emissions are guaranteed at each blend; which fuel system parts are rated for hydrogen; what safety changes are required; and what the upgrade path costs in time and scope.

Write the answers into the technical specification. Our page on turbine purchase specifications explains how to structure the request so answers can be compared.

Signs that controls are becoming a risk

Common signs include difficulty finding spare cards and power supplies, failing displays, loss of vendor support, limited documentation, and a growing number of unexplained trips. Software on old workstations that run unsupported operating systems adds cyber risk.

Another sign is the effort needed to make a small change. If simple alarm or logic changes require rare skills or take weeks, the system is a constraint on operations.

Upgrade options

The scope can range from replacing individual modules to replacing the entire turbine control system, including the logic, the operator interface, the protection and the input and output hardware. A partial upgrade, such as new operator stations only, is cheaper but leaves the core hardware at risk.

A full replacement gives a new platform with current support, and it allows better diagnostics and integration with plant control. Choose by risk and by what the plant can accept in outage time.

Scope decisions: what to replace

Decide whether to replace the field wiring, junction boxes and sensors at the same time. Old wiring may have degraded insulation and old sensors drift. Replacing them adds cost but reduces the risk of chasing faults after the new controller is running.

Also decide whether to retain the turbine’s existing speed, temperature and vibration sensors, and whether to upgrade fuel valves and actuators. The best results come when the controller, the sensors and the actuators form a coherent set.

Protection functions and safety

Overspeed, flame detection, over-temperature and vibration protection are safety functions. Any change to them needs careful design and testing, and often involves independent protection hardware. Never migrate protection logic by transcription alone; review each function against the turbine manufacturer’s requirements.

Ask for a documented design review and a written test plan for every protective function.

Software migration and documentation

Recover the existing logic, set points, tuning and alarm lists before the old system is removed. Where documentation is missing, reverse engineer it from the running system and the drawings. Mistakes in this step produce operating differences that are found only under rare conditions.

Keep a clear record of changes and approvals, and store backups of both old and new configurations.

Cybersecurity

Modern controllers are networked, and that creates new risks. Plan network segmentation, access control, patching, logging and backup for the new system. Decide how remote access will be provided, if at all, and who is responsible for maintaining security over time.

Include security requirements in the specification, not as an afterthought.

Outage planning and testing

Most of the work can be prepared offline: factory acceptance testing with simulators, cabinet build and loop checks. The outage is for removal, installation, wiring, loop testing, functional tests and first firing.

Plan enough time. Tests that are compressed at the end of an outage tend to be skipped, and problems then appear on first start. Use the outage to combine controls work with inspections described in gas turbine inspection intervals.

Commissioning and tuning

After first fire, tuning of start sequences, fuel schedules, temperature control and load response takes time. Allow for several starts and load runs, and keep the control engineers on site until the machine has run reliably.

Train operators on the new interface before handover. Provide quick reference guides and keep the old drawings for comparison.

Pitfalls on controls projects

The most common pitfalls are incomplete recovery of the old logic, underestimated field wiring condition, tight outage schedules that squeeze testing, unclear responsibility between the controls supplier and the turbine supplier and operators who see the new screens for the first time at start-up.

A clear scope document, a single project manager and a realistic outage plan help with all of them.

Documents to require at handover

Ask for the final logic and configuration files, as-built drawings, loop sheets, test reports and sign-off records, set point lists, backup copies stored in two places, the cybersecurity design and the training records.

These documents make the next change simpler and protect the owner from being tied to one supplier for support.

Questions to ask a controls supplier

Ask for references on the same turbine model, the planned support period for the platform, the way software updates are delivered, the training offered and the spares strategy. Ask who will be on site during first fire and for how long.

Also ask what happens if the supplier is acquired or stops supporting the platform. A good answer includes source code or configuration escrow and a clear support commitment.

Business case and links to lifecycle cost

The cost of an upgrade should be compared with the cost of unplanned outages, the cost of scarce spares and the value of longer life for the turbine. Our article on gas turbine lifecycle cost shows how to include controls in a lifecycle view.

Where a turbine is remanufactured, as with a reman GE Frame 6B, the controls scope is usually defined as part of the package, so ask what is included.

The three main inspection levels

A combustion inspection covers the fuel nozzles, liners, transition pieces and related parts that wear fastest. A hot gas path inspection goes further, opening the turbine section to inspect and replace nozzles and buckets or blades exposed to the highest temperatures. A major inspection opens the whole machine, including the compressor, and is the longest and most expensive outage.

Aeroderivative turbines follow a similar logic but often swap the whole gas generator for a refurbished one, which shortens the site outage.

Hours, starts and trips

Manufacturers set intervals in fired hours, in starts, or in a combination of both, with factors for trips and fast starts. A turbine running baseload accumulates hours; a peaking unit accumulates starts. Each trip from full load counts as several normal starts because of the thermal stress.

That is why the same model can need inspections at very different calendar intervals depending on how it is run.

How duty and fuel change the picture

Running on liquid fuel, peak firing, water or steam injection and poor inlet filtration can all shorten intervals. Dirty air erodes the compressor; contaminated fuel attacks hot section parts. Good filtration, fuel quality control and avoiding unnecessary trips extend the life of components.

Our page on inlet air filtration explains how cleaner air protects the compressor.

Planning outages and spares

Inspections need parts on site before the outage starts: combustion hardware, hot gas path sets, seals and consumables. Many owners keep a rotable set of hot section parts that is refurbished between outages. Outage planning also covers cranes, specialist tools, inspectors and accommodation for the crew.

Plants with several units stagger their inspections so that firm capacity is maintained.

Using inspection intervals to compare turbines

When comparing turbines for a project, look at the interval structure as well as the price. A turbine with longer intervals, or one that allows module exchange instead of long site outages, can deliver more energy over its life. The cost of parts at each inspection, and whether they can be refurbished rather than replaced, also shapes long-term value.

A simple model that combines the expected operating profile with the inspection pattern shows how many outages each option will need over the project life, how long they will last and what they will cost.

Records and remaining life

Accurate records of hours, starts, trips and parts history are essential, both for maintenance planning and for resale value. When a used or remanufactured turbine is offered, these records show how much life remains before the next inspection. USP&E’s remanufactured GE Frame 6B units, for example, are refurbished to zero hours.

Our gas turbine operations and maintenance page explains how we run turbines between inspections.

Where NOx comes from

Most NOx in a gas turbine is thermal NOx, formed when nitrogen and oxygen in the air combine at very high flame temperatures. The hotter the flame and the longer gas stays at that temperature, the more NOx forms. Control methods either lower the peak flame temperature or remove NOx from the exhaust afterwards.

Method 1: dry low NOx combustion

Dry low NOx combustors, known as DLN or DLE depending on the maker, mix fuel and air thoroughly before burning, so the flame burns lean and cooler. They are now standard on many new heavy-duty and aeroderivative turbines burning natural gas. Their limits: they are designed for natural gas within a specified composition range, they need careful tuning across the load range, and low emissions are usually only guaranteed above a minimum load. Fuel quality matters; see the fuel gas section of our new gas turbine buying guide.

Method 2: water or steam injection

Injecting demineralised water or steam into the combustor cools the flame and cuts NOx on conventional diffusion combustors. It is common on dual-fuel units when running on liquid fuel. The trade-offs are a supply of high-purity water, a water treatment plant, and slightly higher fuel use and maintenance. On sites where water is scarce, this can be a deciding factor.

Method 3: selective catalytic reduction

Selective catalytic reduction (SCR) removes NOx from the exhaust by injecting ammonia or urea solution upstream of a catalyst, which converts NOx to nitrogen and water. It can reach very low outlet levels and is often required in strict air quality areas, usually combined with DLN or water injection. The catalyst must sit in a specific exhaust temperature window, which on simple cycle units often means a tempering air system, and it adds reagent storage, handling and catalyst replacement to the operating plan.

Comparing the options

Monitoring and permits

Many permits require continuous emissions monitoring of NOx and often carbon monoxide, with records kept for the regulator. Low NOx tuning can raise carbon monoxide at part load, so permits and operating ranges must be agreed together. In the USA, limits depend on the location, the size of the plant and federal and state rules, so the permit strategy should be settled before the turbine is ordered.

Questions to ask before ordering

What NOx and CO levels does the maker guarantee, at what loads and ambient conditions? What fuel composition range applies? Is water or a catalyst system needed to meet the permit? What are the tuning and inspection intervals for the combustor? These answers belong in the specification. Our page on commissioning gates covers how emissions are proven during start-up, and power station design shows where emissions equipment sits in the layout.

For US hyperscale campuses, the same questions apply to the New USP&E FX-45 45MW Modular Gas Turbine for the Hyperscale Data Center sector in the USA.

The lifecycle cost stack

Fuel: model it on your real profile

Published heat rates are usually at base load under standard conditions. Your plant may run at part load, at altitude, in hot weather or with frequent starts. Ask each bidder for heat rate at the load points you expect, corrected for your site, then multiply by your expected hours at each point and your fuel price forecast. Small differences in heat rate become large sums over a turbine’s life.

Maintenance: hours, starts and the plan

Gas turbine maintenance intervals are counted in operating hours, starts, or a combination, depending on the maker. A peaking plant with many starts and a baseload plant with few will reach inspections at very different times on the same model. Compare the maintenance plan against your duty, the cost and duration of each inspection, and whether parts can be repaired or must be replaced. A long-term service agreement can fix much of this cost; our main site explains what an LTSA covers.

Availability: the hidden cost

Every day a turbine is down for an outage, the plant either loses revenue or buys power from somewhere else. Compare outage durations for each inspection type, the supplier’s parts holdings and repair turnaround, and how quickly support can reach your site. For remote plants, a unit with slightly lower efficiency and much faster support may win.

Fit with your plant and your future

Check frequency (50 or 60 Hz), fuel flexibility (gas only, dual fuel, ability to burn hydrogen blends where relevant), emissions performance against your permit, footprint, and whether the unit suits simple cycle now and combined cycle later. A unit that blocks a later upgrade costs value even if it is efficient today.

A scoring sheet for tenders

1. Lifecycle fuel cost at your load profile (highest weight in most baseload cases).
2. Capital and installation through an EPC proposal.
3. Planned maintenance cost and outage days over the evaluation period.
4. Support: parts, service network, response time to your site.
5. Technical fit: frequency, fuel flexibility, emissions, footprint, upgrade path.
6. Delivery time and its value to your project.
7. Residual value at the end of the evaluation period.

Weight the criteria for your project before bids arrive, and bring them to a single net present value where you can. Our new gas turbines buying guide covers the procurement steps, and our new versus used comparison covers the condition question.

Data to request from every bidder

• Performance at your site conditions: output and heat rate at base load and at your expected part-load points.
• Degradation assumptions between washes and between major inspections.
• Maintenance plan: intervals in hours and starts, scope and typical duration of each inspection.
• Parts and repair: which hot section parts are repairable, typical repair cycles, lead times.
• Availability record for the model in similar duty, with references.
• Emissions guarantees across the load range.
• Delivery schedule, factory testing and site support during commissioning.

Put the data into the same model for every option, using the same fuel price, hours and discount rate. Differences that look small on a data sheet often decide the comparison once they are multiplied across years of running.

New, used or modular

Lifecycle thinking applies to all three. A new unit has the longest life ahead and the newest technology. A used or remanufactured unit can deliver power sooner at lower capital cost, with life that depends on its history and refurbishment. Modular units let capacity grow in steps, keeping early capital lower. Our own modular option is the New USP&E FX-45 45MW Modular Gas Turbine for the Hyperscale Data Center sector in the USA, aimed at campuses that add capacity in stages.

From Wing to Power Station

Several of the best-known aeroderivatives trace straight back to aircraft. GE’s LM2500 grew out of the engine family that powered wide-body airliners and military transports, and the LM6000 came from a later member of the same family. Rolls-Royce turned airliner engines into the industrial RB211 and Trent ground units, now sold under Siemens Energy names, while the FT8 traces back to a Pratt and Whitney airliner engine.

In each case the aviation engineering, materials and manufacturing scale carry across. Millions of flight hours have refined the hot section, the bearings and the controls long before a unit ever reaches a power plant.

How an Aeroderivative Gas Turbine Works

The heart of the machine is the gas generator, the part inherited from the aircraft. It has three main stages, and the description below follows the common two-shaft arrangement.

1. Compressor: rows of rotating and stationary blades squeeze incoming air to high pressure.
2. Combustor: fuel is injected into the compressed air and burned continuously, raising its temperature sharply.
3. High-pressure turbine: the hot gas expands through turbine blades that drive the compressor on the same shaft.
4. Power turbine: the gas leaving the gas generator still carries a great deal of energy, so it passes through a separate free power turbine that turns the generator.

On a jet aircraft, that leftover energy would leave as thrust or drive a large fan. On the ground, the power turbine captures it as shaft power instead. Some designs use a single shaft or a different spool layout, but the principle is the same: a flight-proven core feeding a turbine built for generation. Our page on the gas turbine compressor section goes deeper into the first stage.

What Changes When a Jet Engine Goes to Ground

Turning a flight engine into a power plant involves more than bolting on a generator. The main changes are:

• The fan or propulsion stages are removed or replaced, and a power turbine is added.
• The combustor and fuel system are redesigned for pipeline natural gas, liquid fuel or both.
• Emissions control is added, either water or steam injection, or dry low emissions combustors.
• The unit is packaged with an acoustic enclosure, inlet air filtration, exhaust ducting, lube oil and control systems.
• The generator, gearbox where needed and switchgear are matched to the site’s frequency and voltage.

Strengths and Limits

These traits explain where aeroderivatives tend to appear: peaking plants, mobile fast power, offshore platforms, pipeline compressor stations, naval ships and, more recently, on-site power for data centers. For a head-to-head view against heavy industrial machines on a data center campus, read our aeroderivative versus frame comparison.

Maintenance: Swap, Do Not Wait

One of the defining features of aeroderivative ownership is how major maintenance is done. Because the gas generator is relatively small and light, it can be removed from the package and replaced with a spare or lease engine, often within days. The removed engine then goes to a specialist shop for overhaul while the plant keeps running.

Between overhauls, operators rely on borescope inspections, oil analysis, vibration monitoring and careful inlet filter management. Dust, salt and humidity are the enemies of compressor blades, so filtration design matters as much as the turbine itself on desert, coastal and tropical sites.

Aeroderivative Families in Service

Several engine families dominate the market. GE Vernova’s LM2500 and LM6000 are derived from aircraft engines in the CF6 family and are widely used in power generation, oil and gas and marine service; the LM2500 is also the core of the trailer-mounted TM2500. Siemens Energy offers aeroderivative units that trace back to Rolls-Royce aircraft engines, and Mitsubishi Power Aero offers the FT8 family, which descends from a Pratt & Whitney aircraft engine.

Each family has its own output range, fuel flexibility, emissions technology and service network. When comparing them, look beyond nameplate output to performance at your site temperature and altitude, the availability of lease engines for exchange, and the depth of local technical support. Package suppliers also differ in how they arrange enclosures, controls, fuel systems and balance of plant around the same core engine.

Where Aeroderivatives Earn Their Place

• Peaking plants that start and stop many times a day to follow demand or balance renewables.
• Data center campuses and industrial sites that need fast-starting on-site power in compact footprints.
• Remote and island grids, where units can be shipped in quickly and maintained by engine exchange.
• Oil and gas facilities, where the same engines drive compressors and generators.

Buying an Aeroderivative Gas Turbine

Owners can choose new units, surplus units with low hours, or overhauled engines in refreshed packages. The right answer depends on how soon power is needed, the expected running hours and the fuel available. Our overview of the GE gas turbine lineup describes models the team supplies and services independently of the manufacturer.

USP&E supplies new and used gas turbines and builds and operates the plants around them, with 150+ power projects in 45+ countries over 24+ years and ISO 9001 and ISO 45001 systems. To see how turbines are being applied in two of the fastest-growing markets, read about turbine power for data centers and mines.

Why New Turbines Take Time

A new gas turbine is a complex machine with long-lead parts: forgings, castings, hot section components and the generator itself. Packaging, controls, testing and shipping come on top. When many buyers order at once, each of those steps queues behind the others.

Owners also lose time before the order. Specifications that are not ready, approvals that stall and contracts negotiated late all push the build position back. A clear purchase specification shortens that phase, and our guide to writing a turbine purchase specification and RFQ covers what it should contain.

The Four Routes to Turbine Power

None of these is right for every site. Many campuses use more than one: a surplus or refurbished unit for early power, then new units for the long term.

Combining Routes Into a Power Plan

A phased plan matches each route to a stage of the campus. Early halls are energised from whatever can be delivered and installed first. New units ordered at the same time arrive for later phases. When the permanent plant is complete, the early units can stay as spare capacity or move to another site.

• Secure early power first, then lock the long-lead order, rather than waiting for one perfect answer.
• Design the switchgear and foundations so early and permanent units share the same connection points where possible.
• Check that early units fit the air permit and noise limits, not just the delivery date.
• Keep the commissioning team the same across phases so lessons carry forward.

Checking Surplus and Refurbished Units

Faster routes still need care. A never-installed unit that sat in storage for years may need preservation checks and seal replacements. A used unit needs a records review, a borescope inspection and a clear statement of remaining life. Our comparison of new and used gas turbines lists the checks.

Factory and site testing apply to every route. Even a new unit should be witnessed at the factory where possible; see our page on factory acceptance for new turbines.

How USP&E Helps

USP&E holds and sources new, surplus and refurbished turbines and builds the plant around them, with 25,000 MW contracted since 2002 and 150+ power projects in 45+ countries. For US hyperscale campuses, the company offers the New USP&E FX-45 45MW Modular Gas Turbine for the Hyperscale Data Center sector in the USA.

Browse turbines that are in stock now to see what could reach a site soonest. USP&E’s quality and safety systems are certified to ISO 9001 and ISO 45001, and the team can provide O&M once the plant is running.