Gas turbine fuel control has become more important than ever. Whether due to emissions mandates, maintaining efficiency, plant profitability or increasing the lifespan of a facility, operators and owners are looking for ways to achieve a tighter rein on fuel usage. Here are the top five reasons why now is a good time to upgrade your fuel system.

There are a great many gas turbines around that have been in operation for ten, twenty, thirty or more years. Machines that have been in heavy use are likely to have worn fuel valves, unreliable shutoffs, or systems that aren’t responsive enough to operator instructions. But even peaking turbines that have seen infrequent usage can suffer badly due to faulty fuel control systems or components. 

The Gas Fuel Shutoff and Control System from Continental Controls includes fuel metering, redundant pneumatic shutoff valves, pilot valves, flow measurement, NOx feedback, fuel heating value measurement, and gas leakage elimination via a coaxial valve.

As these units age further, components wear. This can lead to problems in starting up the machine as well as unscheduled outages and maintenance personnel continually having to babysit the fuel controls. 

Additionally, there are many turbines out there with fuel control systems that are either poorly supported or have been made obsolete by the OEM. There comes a point when it becomes too much of a burden to continually scramble to find components or keep aging controls running.

In this day and age, speed is everything. Operators demand turbomachinery that is going to start up rapidly on demand, and shutdown instantly should problems arise. The fuel control system must match these expectations. This means valves that provide the precise fuel mix and fuel shutoffs that do the job in a timely manner. 

Yet fuel controls don’t always measure up. In some cases, aging facilities have installed manual ball valves to keep their fuel control systems running. There is no place for such technology in a modern gas turbine plant. Even standard fuel control systems may not be good enough for current conditions. Response times of half a second to a second (and as much as two seconds for a slow motor) are commonplace. Such systems operate at risk. 

Pneumatically actuated valves are required with response times of 200 milliseconds or less. Only then, can the operator have peace of mind that shutoffs will occur rapidly enough to avoid damage. Furthermore, pneumatic systems are available that only need 1 amp at 24 volts DC. 

Fuel metering valves must also be able to function at the right pace. All-electric fuel control valves offer real-time flow control to dispense the right amount of fuel at the right time, as requested by the turbomachinery control system. This has everything to do with achieving performance objectives, while avoiding the possibility of falling out of emissions compliance.

Not so long ago, plants operated with large teams of skilled operations and maintenance personnel. But the demand to do a lot more with far fewer personnel has drastically shifted the skills picture in facilities. Couple that with an aging workforce with a steady parade of retirements and there is no place for finicky or unreliable turbine systems. 

Fuel controls, therefore, must not be the weak link. Instead of being composed of multiple components cobbled together over the years that require constant attention, they must be unified into one comprehensive, automated fuel metering, shutoff, and control system. Ideally, such pre-assembled systems would include electric actuation at low power to eliminate the need for additional high-powered electrical lines to be fed into them to operate motor-driven valves. It is even possible to operate the fuel control valves at the same pressure as the incoming gas. 

Such systems ease the burden on less-experienced plant personnel by offering them an engineered solution that is tested, integrated, and can be dropped in place. Veteran staff may be able to purchase the various components and competently tie everything together – if they have the time. But the generation entering the workforce demands fit-and-forget, leak-free systems. They want to spend their time on the big picture – overall performance, plant economics and emissions compliance – not in the routine of adjusting valves, checking for leaks, and troubleshooting fuel control issues.

Standards are continually evolving. Safety standards have altered markedly over the last twenty years. These days SIL 2 or 3 safety levels are the norm for new valves. Fast shutoff of fuel to the gas turbine is another aspect of safety. The flow of gas must cease immediately as dictated by plant control systems or whenever there is a loss of pilot pressure.

 Older systems lack the safety capabilities of the latest fuel controls. The latest systems offer redundant pneumatic shutoff valves, and a block-and-bleed architecture to prevent leaks. In addition, they offer pilot valves: A spring-loaded piston is activated by system pressure to open the valve; when pressure is released, the valve closes at once. This safety feature is an important fail-safe mechanism. Those relying on all-electric systems, however, can experience shutdown delays in the event of a power cut. 

There are plenty of other standards that apply. Those wishing to operate in Europe must meet ATEX requirements, which are steadily refined. In North America, valves, components, and systems are subject to ASME certification. Similarly, emissions regulations become ever more stringent. Gas turbine operators must maintain NOx and other emissions below regulated limits. More recently, gaseous methane compliance has been added to the compliance burden. 

This Gas Fuel Shutoff and Control System manifold by Continental Controls with integrated controller and sensors for temperature, pressure, and other parameters has been operating successfully on a gas turbine in Southern California.

Older fuel controls are found lacking when it comes to some of these standards. They struggle to remain in compliance and lack the flexibility to deal with shifts from high BTU to low BTU fuel, or vice versa. However, systems are available with complete fuel control assemblies fully certified and tested to meet local requirements.

Inefficient fuel systems exert a significant impact on plant performance and profitability. The ability to rapidly start, stop and adjust the various elements of fuel control translates directly into improved economics and an ability to meet market demands. Older systems lack the necessary degree of responsiveness. 

Component or system unreliability opens the door to unexpected shutdowns. This can mean the difference between a profitable and unprofitable facility. Those investing in modern, end-to-end fuel controls gain more certainty of performance. With that comes lowered risk and more predictable economic outcomes.

The Gas Fuel Shutoff and Control System from Continental Controls is a complete fuel train inclusive of fuel metering, redundant pneumatic shutoff valves that meet safety and other industry standards, pilot valves, flow measurement, NOx feedback, fuel heating value measurement, and gas leakage elimination via a coaxial valve. This integrated system includes a controller with sensors for temperature, pressure, and other parameters. All components are preassembled, welded, tested, certified, and delivered on one manifold. 

The design allows for precision flow, pressure, or position control measurement even with changing backpressure or other effects from the application that may cause other measurement techniques to be less accurate. Fuel flow measurement, for example, is available to the user for control, display, and logging purposes at ±2% reading accuracy or 0.5% of full scale, whichever is greatest. Fuel flow control is conducted by an electronic computer assembly. This computer receives the 4 to 20 mA fuel demand signal and compares it to the fuel flow signal from the built-in flowmeter. It then adjusts the throttling orifice to change the fuel flow as necessary to make the measured fuel flow equal to the fuel demand. Control is based on mass flow calculation, not just pressure or position. 

It provides fire-safe and fast natural gas shutoff, is SIL 2 to 3 certified, and can close in less than 200 milliseconds. The system is pressure tested with valves that close bubble tight with loss of pilot pressure. This integrated solution is suitable for operators and repackagers looking to repair or replace an existing fuel system on gas turbines up to 50 MW.

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Five reasons why you should upgrade your fuel system. 

Turbine fuel control

Noise levels in plants necessitates the use of headsets and audio systems for tours, training, and worker communication.

Peter Drucker once said, “The most important thing in communication is hearing what isn’t said.” With all due respect to the founder of modern management theory, if Drucker had spent more time on the floor of an energy plant he may well have declared that the most important thing in commu­nication is hearing what is said.

Energy plants are noisy places. The level of noise can vary by the plant’s source of power and one’s location relative to operating equipment. A sound level of 80 decibels (dB) is considered unpleasant, 85 is the threshold for loud, and 110 is categorized as extremely loud. The thresholds for pain and potential perma­nent hearing loss are 140 and 150 deci­bels, respectively.

The mean noise levels are somewhat similar for coal plants and gas plants, with both averaging between 80 and 85 dB. However, prolonged exposure to noise in a gas-powered plant tends to be greater, with a time-weighted average (TWA) of 78 dB versus 69 for coal.

Wind power is relatively quiet, despite the complaints made by some who are opposed to construction of turbines near their homes. 55 dB are produced imme­diately adjacent to the turbine itself. 300 meters away (the minimum distance to nearby homes) the sound only averages 43 dB. At 500 meters the noise level falls to 38 dB.

However, noise levels from individual pieces of equipment in any of these plant types can run as high as 155 dB when they run combustion turbines or diesel engines. That can lead to hearing-related safety issues and workers compensation claims. The Bureau of Reclamation, which oversees management of water resources including dams and hydroelec­tric plants, reports that one fourth to one fifth of its workers compensation costs related to hearing loss. Noise exposure over time, even at lower decibels, can have a cumulative effect. This can result in other health issues, including cardiovascular problems.

Despite noise abatement measures to protect people from hearing loss, the noise generated by the operation of equipment can make it hard to hear someone else speak. The human voice is typically measured at only 60 dB. This makes it susceptible to audio blurring even in a relatively quiet plant. A background noise level of 85 dB means that people have to raise their voices to be heard by someone standing three feet away.

85 dB may seem innocuous, but noise at that level can create more problems than those resulting from 150 dB. Why? At the higher level, it is obvious to all parties that communication is impossible. There is no chance of misinterpreting a message that can’t be heard at all. However, when people talk over back­ground noise in the 85 dB range, a single word or phrase may be misunderstood without either party being aware of it. That can lead to poor decisions, ineffi­cient performance, weakened collabora­tion, and accidents.

By equipping anyone who works in a noisy energy plant with a communica­tion system consisting of a headset or earphone with a microphone, the speak­er’s voice can be transmitted directly to a receiver that allows it to be heard through another set of earphones. Such systems, originally designed for tours of noisy factories, are hands-free when used with a head-worn microphone. With this system in place, there are no issues in hearing instruct ions, warnings, or sharing of information. The only remaining barrier to communication will be hearing what isn’t said.

The energy industry has a problem with high decibel work environments.

Noise levels at energy plants

WHAT TRENDS HAVE YOU OBSERVED OVER THE PAST YEAR?

Especially with personnel working remotely, we’ve seen an increase in companies connecting and tracking equipment with sensors and other Internet of Things (IoT) hardware and software to enhance their preventative maintenance capabilities. The coupling industry is catching up with the rest of the world in terms of the data revolution. But even there, demand has exploded in terms of end user interest about how couplings are designed and selected, how they are manufactured, how they operate, how they are maintained, and how they are serviced.

Just like you and I track our orders from Amazon and get regular updates during the process, customers are looking for the same easily accessible live data for couplings. The procurement team needs quick access to product information to make purchases. Project managers are looking at Gantt charts to understand more about the process and status while couplings are being designed and manufactured. Installation and maintenance teams need access to manuals and service experts. The Regal Kop-Flex team is building a complete digital customer experience (DCX) to support these goals.

WHAT ADJUSTMENTS IS REGAL MAKING IN RESPONSE?

We have embraced smart manufacturing via Perceptiv monitoring and diagnostics. Our team utilizes remote monitoring for some customer critical equipment, providing real-time alerts and monthly performance reports. Integrating all a facility’s mechanical components is possible, and we are evaluating the cost benefits and overall ROI of doing so. For some, having their critical equipment monitored is enough, while others want to integrate our components into their existing smart ecosystem.

For example, we have been gathering data from couplings that allows plant operators to make better maintenance decisions by monitoring performance trends with the Kop-Flex Powerlign torque monitoring system. It allows users to minimize emissions and fuel costs by tracking performance trends in connected equipment. This system can be purchased new with couplings or retrofitted to existing Kop-Flex or other brand couplings.

Our Perceptiv intelligence group uses an array of torque monitoring solutions for online monitoring, predictive maintenance and failure analysis. This includes the use of augmented reality tools. Additionally, there is definitely a trend to have spares for all critical equipment. It minimizes downtime if you have a spare coupling to hand instead of having one shipped. Some customers send the main coupling back to our Kop-Flex team for recertification.

A Regal technician installing Perceptiv remote monitoring technology.

WHAT NEW PRODUCTS OR SERVICES ARE YOU OFFERING?

Regal continues to expand Perceptiv on-site and remote monitoring and diagnostics to help our customers install and monitor equipment 24/7 or as needed. These tools save money by diagnosing potential problems before they happen. Examples include torque monitoring, vibration observation, and motor current signal analysis.

The Regal Tag-It Program powered by Perceptiv intelligence is an asset management platform to view details on mechanical and electrical assets in operation and reduce redundant or obsolete inventory. The program creates a path for continuous facility improvement by enabling faster maintenance and simplifying the MRO procurement process. In addition, users can easily add Perceptiv wireless monitoring to keep an eye on critical equipment. This 24/7 monitoring technology will help customers to increase equipment reliability and maximize production. The combination of hardware, software and “humanware” provides a new way for users to interact with Regal products and their equipment. All of this helps customers to harness the power of IoT in their facilities.

We expanded our coupling recertification program to repair, rebuild, and recertify couplings removed from service to API 671 standards. This allows our customers to have a lower-cost recertification coupling available for future planned outages or emergencies. Customers can recertify their disc, diaphragm, and gear couplings for up to 50% savings from the cost a new item. Ship the used/worn coupling to one of Regal’s worldwide repair facilities, where they will be disassembled and undergo a non-invasive cleaning. Evaluation determines the material integrity and flexible elements, then we remove and replace any hardware, if necessary. They are then reassembled and rebalanced in accordance with API 671 or original OEM specifications. After a final inspection, they are returned to the customer within 4 weeks.

We also offer a Max-C resilient coupling that provides damping for applications with shock loading or cyclic torques. The Max-C can be mated to disc or diaphragm couplings to tune the drive train. They are frequently used on synchronous and variable frequency drive motors.

Dan Phillips, Technical Director, Monitoring and Diagnostics, Regal, discusses couplings, the Internet of Things, remote monitoring, diagnostics, and smarter maintenance practices.

Q&A: Making maintenance smarter via remote monitoring and digital tools

ISFD technology, shown here as part of a Flexure Pivot tilt pad journal bearing, provides precise stiffness and damping to increase the dynamic stability of the rotor/bearing system. Courtesy of Waukesha Bearings.

Waukesha Bearings provides custom-engineered hydrodynamic fluid film bearings, active magnetic bearings systems, and damper and seal technologies for turbomachinery across the oil & gas, power generation, marine, and industrial markets. Engineers apply design codes and predictive tools to tailor thrust, journal, or combination bearings to achieve optimum performance across the machine operating range.

The Waukesha Bearings Maxalign tilting pad journal bearing, for example, features a specialized ball and socket pivot, along with Directed Lubrication and trailing edge cooling to increase reliability and reduce power loss for rotating equipment with shaft diameters greater than 300 mm. Engineers optimize the bearing size and pad materials and tailor insulation, hydrostatic jacking, and instrumentation according to requirements.

“Each application is unique so we design each bearing to meet performance requirements, whether they are tilt pad or fixed profile, babbitt, bronze, polymer or ceramic, and small, medium, or large,” said Andrea Masala, Product Manager, Waukesha Bearings.

Waukesha Bearings fluid film bearing solutions support the market move toward decarbonization. For supercritical CO2, hydrogen, and other high[1]power density applications, the integral squeeze film damper and pocket damper seals help ensure stable rotordynamic systems.

Fluid film journal bearings with ISFD technology are ideal for applications requiring optimized stiffness and damping. Initially used as a problem solver for turbomachinery experiencing high vibrations due to rotor unbalance or instability, ISFD technology is used on high-speed and high-power density applications, such as integrally geared and inline compressors.

As compressors and turbines are designed for higher pressures and speeds to achieve the full potential of hydrogen and sCO2, the integration of ISFD technology enables rotor/bearing systems with journal peripheral speeds above 130m/s.

“The controlled stiffness and damping of ISFD technology, and the precise placement of critical speeds and rotor modes that this allows, will help address potential destabilizing forces in the system and minimize unbalance response,” said Masala.

Stability can be enhanced further with the application of pocket damper seals. Based on bulk-flow analysis, they can cope with a range of speeds and gas conditions to counter seal-induced instabilities. Waukesha Bearings is also working on new pocket damper seals to further increase damping characteristics and lower leakage.

Waukesha Magnetic Bearings has been involved in magnetic bearing technology development for more than 30 years. Challenging applications in high pressures and aggressive gas have driven the market towards a mechanical solution with controller architecture. High controller functionality is available for both low-power controllers (for applications below 1 MW) and high-power controllers (for applications above 25 MW).

Modularity is another element of Waukesha Magnetic Bearings systems. The Zephyr controller, for instance, allows enough flexibility to integrate software and hardware features within the same enclosure. Automated commissioning is also available. This is a repeatable process that provides commissioning and maintenance autonomy for OEMs and end users, with available training, remote support and field service from active magnetic bearing (AMB) specialists.

The skid-mounted magnetic bearing controller introduced by Waukesha Magnetic Bearings in 2019, reduces installation time and avoids the need for long field cables from the controller to the machine. Skid mounted AMB controllers can provide modularity for different size units, oil free operation, and the convenience of remote maintenance that fluid film bearings cannot. Skid mounted AMB’s primary application is in turboexpanders for gas processing plants, but have also been applied in various industries and services.

The ARES AMB Turboexpander-Compressor from L.A. Turbine features the industry’s first on-skid magnetic bearing controller. Courtesy of L.A. Turbine.

Brush seals are commonly used in gas and steam turbines to minimize leakage and improve performance. They are also applied to increase the efficiency of compressors operating on fluid film or magnetic bearing systems.

The Waukesha Bearings’ brush seal is closely packed with alloy bristles that deflect with rotor movement and experience minimal wear. This brings about a smaller leakage gap between the sealing surface and rotor. The bristle strips can be replaced without throwing away the seal assembly.

On AMB-equipped compressors, brush seals protect and augment labyrinth seals. The gap between the levitated rotor and labyrinth seal must correspond to the distance from the rotor to the auxiliary bearings. Otherwise during coast down, the rotor would contact and roll the labyrinth seal teeth. Augmenting labyrinth seals with brush seals reduces sealing clearances and leakage during operation. Upon rotor delevitation, the bristles deflect in response to rotor weight, protecting the seal. The bristles return to their original state once the rotor is levitated.

Modular brush seal assembly on an AMB-equipped compressor. Courtesy of Waukesha Bearings.

Custom-engineered solutions rely upon rotordynamic analysis. In AMB-equipped turbomachinery, the bearings, rotor, and process are deeply integrated in shaping machine dynamics. Waukesha Bearings’ engineers collaborate with OEM engineers throughout design and development to understand application needs and support rotor design optimization. Direct measurement of forces and displacement with magnetic bearings, and correlation with operating conditions, allows the characterization of mechanical and process interaction. Control algorithms address destabilizing seal effects and process upset conditions.

“In traditional power generation and oil & gas applications, we see OEMs and end users push equipment to produce more power from the same footprint, operate more efficiently and be more operationally flexible,” said Masala. “From a fluid film bearing perspective, that translates into requirements for power loss reduction, higher load capacity, highly tuned bearing dynamic characteristics, and the ability to handle higher temperatures, frequent starts and stops, and off-design conditions. These demands are being met with a combination of design elements, such as trailing edge cooling, ISFD technology and damper seals, and advanced bearing materials, such as polymer and aluminum tin.”

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Fluid film bearings, active magnetic bearings systems, and damper and seal technologies for turbomachinery. 

Vendor spotlight: Waukesha Bearings

The WTUI show covered all aspects of the maintenance and repair of aeroderivative gas turbines. Courtesy of MTU Maintenance. 

The Western Turbine Users, Inc. (WTUI) show occurred virtually this year spread over three weeks. Due to print magazine deadlines, we could only summarize the first half of the event in the previous issue. Here are the highlights from the latter sessions: 

Jason Miller, Director of Reliability for GridSME, provided an overview of the combustion turbine from the perspective of the California Independent System Operator (CAISO). He said gas generation has been rising in share over last ten years in the region. 

“There is still a place for gas, especially in the peaking market,” said Miller. 

He drew attention to the August 2020 period when the state suffered rolling blackouts (the same happened this year). Unanticipated high demand was satisfied by natural gas facilities despite heat-related forced outages. In Miller’s view, gas saved things from getting worse. 

“There was no fault found with the gas fleet related to any the blackouts,” he said. 

Miller also explained the need for natural gas generation to provide reactive power and grid stability. “Renewables are not synchronous machines, so you need reactive energy injected for frequency response and to stabilize the grid,” he said. He’s worried that bodies like CAISO and LA DWP are retiring a lot of rotating generators, particularly steam generators. That amounts to 3 GW of retirements in the next 4 years (1 GW this year). Over the same period, a large amount of battery storage is due to be added. Miller believes this represented an opportunity for gas turbines to work in tandem with battery plants to serve peaking and other markets

The last two days of WTUI featured vendors pro-viding insight and tips on aeroderivative gas turbine operations & maintenance. Rikki Blair, Director of Operations, EthosEnergy, talked about extending the life of assets. His company does reverse engineering using blue light scanning and 3D modeling as well as 3D prototyping using production 3D printing. A prototype is done in plastic. Once con-firmed it is then printed in metal. This can be aluminum, nickel, steel, cobalt, or titanium. 

Blair laid out an LM2500 case study. It suffered compressor degradation despite a lot of offline water washing. GTE provided a high-pressure online water wash without detergent that raised availability by 2%, performance by 1 to 4%, reduced fuel consumption, and lowered emissions. It also used less water that offline water washes and cut down the wash cycle from 110 minutes to 30 minutes.

Maintenance work being done on an LM2500. Courtesy of MTU Maintenance. 

Another example discussed was an LM6000 controls retrofit for a Texas peaker. Four units at two different sites experienced reliability issues, slow start ups, and were not meeting output demands. An upgrade to poorly configured control raised output by up to 2%. It also solved grid synchronization problems to satisfy 10 min startup to full load condition. This was accomplished using the icon control system. The project also corrected UPS, power distribution, and wiring issues. Blair said EthosEnergy had done over 100 controls upgrades on LM engines. 

Mcleod Stephens Jr., General Manager at Braden Filtration, followed with a briefing on the history of filter cartridge design, media, styles, and evolving technologies. He laid out the various factors to consider in selecting the right filter for the right turbine and environmental conditions. 

Maintaining and upgrading LM series turbines to reliably meet the demands of today’s grid, with the topic chosen by David Cicconi, Turbine Business Development Manager at Emerson. The focus of that session was on upgrade options avail-able to users of legacy Woodward and GE control systems. Using a case study of a recent project, he detailed a variety of upgrade solutions and enhancements available for these units, as well as some lessons learned to ensure success in managing such an upgrade.

For example, he mentioned Ovation control optimizations that could be done to improve the reliability and on-time dispatch of automatic pre-start. Another feature, automatic NOx water adjustment instantaneously compensates for variation in ambient conditions. Emerson offers a retrofit for some Woodward and GE systems. This drop-in replacement matches the footprint, is easy to install, and fully factory tested. 

Monitoring the health of bearings was the topic presented by Simon Wilson, Sales Director, Energy & Industrial, GasTops. He explained that bearing damage events and unreliable detection technologies are causes of unplanned shutdowns in aeroderivative gas turbines. Damage typically occurs gradually over time and may be predicted in advance using detection technology. GasTops offers Oil Debris Monitoring (ODM) and MetalSCAN online condition monitoring as well as oil, filter, and chip analysis.

Field Results from ice blasting were outlined by Bobbi Monacelli, President, US Cleanblast. He tied this into high-pressure compressor (HPC) efficiency improvements and overall life extension. He touched upon performance tests on ice blasting by GE, which revealed improvements in com-pressor efficiency, increased mass flow, and a MW power gain. 

The process is used to eliminate dirt and hydrocarbons in the compressor, which lead to lower power. Monacelli said that if water washing is becoming less and less effective and a borescope inspection shows that the machine is dirty, ice blasting is a possible option. 

A plant in Georgia, for example, gained 3 MW by using the technique on an LM6000. The HPC and casing was cleaned by ice in only 12 to 18 hours. This resulted in no damage to the substrate. As well as being much faster than cleaning by hand, the compressor is much cleaner when ice is used.

 The following session featured Bob Tollett, Director of Marketing, at Liburdi Turbine Services. He covered how to maximize component repair yields to reduce engine overhaul costs. His company is involved in a great many hot section combustion repairs, as well as first and second stage blade and nozzle repairs. He recommended blade alloy rejuvenation to return blades to an as-new state. He also touched upon vacuum-heat treatment to restore the micro-structure and improve the creep strength of components. 

Many users deal with grid stability and frequency response issues. Mike Toll, Account Manager at Woodward, took up this subject during the last day of the virtual WTUI event. 

“Grid fluctuations are caused by imbalance of electrical supply and demand,” said Toll. “Without compensation, the frequency varies with generation and load changes.” 

If, for example, consumption is greater than production – perhaps in the early evening if there is no wind would – frequency drops. If consumption is less than production – perhaps the middle of the day when the sun shines and the wind blows – the energy produced has nowhere to go and frequency rises.

There is still a place for gas, especially in the peaking market," said Jason Miller, Director of Reliability for GridSME. 

Toll detailed various control system approaches to dealing with frequency and instability challenges. Droop, for example, is a control method that automatically varies gas turbine out-put in response to changes in frequency. When grid frequency decreases, unit load increases, and vice versa. He also touched upon local MW set-point control, automatic generation control (AGC), remote MW setpoint, and primary frequency controls that can be implemented. 

WTUI tries to cover as much ground as possible related to LM series O&M. The last few hours of the show featured a great many topics. Patrick Jansen, Chief Services Officer, VBR Turbine Partners, promoted Decide, a system that tracks the component behavior and degradation over time. It combines historical and ongoing engine health condition monitoring data to provide predictive maintenance. Jeff Bause, CEO of Noxco, presented on emissions compliance. Pierre Ansmann, Global Marketing Director, Arnold Group, educated the audience on thermal insulation for LM2500/6000 exhaust collectors as a way to reduce package temperature. Florian Winkler, Marketing Manager, EMW filtertechnik, covered the benefits of (H)EPA GT air intake filters. His presentation helped users to make better filtration choices. Finally, Jon Neal, Head of Global Field Service at Brush Group, tackled how to avoid forced outages through site-specific preventive maintenance of generators based on operating condition and environment. 

The 2022 WTUI show will take place from March 27-30 in Long Beach, CA. For more information, visit WTUI.com

Show highlights the many aspects of LM Series operations and maintenance. 

Western Turbine Users part II

The B&B-AGEMA MMX combustor design is being used in a Kawasaki turbine. 

BY JENS DICKHOFF, ATSUSHI HORIKAWA, AND HARALD FUNKE

A transformation of the energy market is ongoing. Renewable energy rose from 5,451 terawatt hours (TWh) in 2000 to 9,824 TWh in 2019. But there is a need for large-scale energy storage to satisfy power demands when solar and wind are offline.

Hydrogen is regarded by some as the green energy carrier of the future. But it faces technical and regulatory challenges. Gas turbines operating on some or 100% hydrogen will play a key role in the transition. They are a proven technology, provide electricity and process heat, and can be sized from kilowatts up to several hundred megawatts.

However, hydrogen combustion is not entirely straightforward, because of its extreme flammability range and flame speed that can lead to flashbacks. It also requires the right combustion technique to keep NOx production low. Wet NOx combustion is the current method used, where water or steam is injected into the combustion chamber to reduce the combustion temperature. The water/steam must be free from impurities. While reducing NOx emissions effectively, this approach is still not environmentally sound or efficient.

Dry low Emission (DLE) technology is likely to be the answer. But the combustion process means that engineers must think outside the typical lean combustion-low NOx box to develop new techniques.

To date, good progress has been made in achieving 30% volume H2 with only minor adjustments to the combustion chamber. But the pathway to 100% H2 is far from easy. 30% volume equates to 5% mass or 11% of energy when mixed with methane. Even 60% volume means around 15% mass. These fractions are acceptable for today when large amounts of H2 are anyway unavailable. But they are not sufficient for decentralized reconversion plants.

Another factor to consider is that at typical fuel-air ratios (e.g. Lambda 2.3) the turbulent flame speed starts to rapidly increase at around 35% to 40% volume H2 and reaches its maximum at around 70%. At that point, the danger of flashbacks for premixed combustors is extremely high. When the flame travels upstream and anchors in an undesired region such as a small step, it can quickly destroy parts of the burner structure.

Increasing the air cross flow velocity is also problematic. The pressure drop of the combustor section would increase, reducing overall machine efficiency. Additionally, burner geometries are not always perfectly smooth and typically feature small steps where flow can recirculate and autoignition can take place. This can trigger flash backs and represents a random phenomenon. Therefore, it is difficult to detect in tests since all burners are slightly different and manufacturing process quality control plays an important role here, which also has an impact on component price. Finally, the flow velocity on the wall is zero by definition. In contrast to methane, hydrogen is more prone to boundary layer flashbacks due to the higher flammability range and flame speed.

The MMX combustor design used in the Kawasaki turbine. Combustor development and engine demonstration projects were conducted via outsourced projects and grants from NEDO.

The real challenge, therefore, is how to burn greater than 90% volume of hydrogen at low emissions, without a water/steam admixture, and to fulfil safety, emission, pressure drop, and lifetime requirements inside the gas turbine. The only technology on the market bringing these points together is called Micromix (MMX) combustion.

In research and development since the late 1980s by Aachen University of Applied Sciences (AcUAS, FH Aachen), it has been the subject of many collaborative project s. These have primarily involved B&B-AGEMA and Kawasaki Heavy Industries (KHI). The basic ideas behind the concept are:

NOx suppression by residence time reduction. 

Jet-in-cross-flow mixing for flashback safety.

To suppress NOx formation, one can either lower the flame temperature or reduce the residence time of fuel/air inside the high temperature zone of the flame. NOx molecules can only form under certain fuel/air conditions and high temperatures. The best course is for N and O molecules to reach colder zones behind the flame before they undergo a chemical bond.

Pure hydrogen cannot burn. A diffusion flame is consequently flash-back safe whilst pre-mixed flames will always carry risk. By the jet-in-crossflow mixing process, rapid premixing lowers the average flame temperature. If the flame travels towards the H2 injector, the mixture becomes too rich to burn and is forced to travel back to its intended position without damage to burner components.

Early designs proved out the general concept and highlighted issues to overcome. By incorporating computational fluid dynamics (CFD) through the help of AcUAS and Kawasaki, this combustor technology was introduced into the Kawasaki M1A-17 gas turbine (2 MW).

Reactive flow simulations were performed in Siemens Simcenter STAR-CCM+ to study aerodynamic flow parameters and the combustion structures (flame shapes). The aim was to find the optimal design and length of the flame to ensure low NOx combustion and reduce the number of injectors. Simulations included reactive chemistry to predict the flame shape, size, and temperature signature. Siemens Digital Industry Services provided model tuning.

As a result of this research, AcUAS and B&B-AGEMA developed the fourth and fifth generation MMX combustor. It includes a new flame shape with very low NOx properties, based on CFD simulation, which was never considered before. The team developed a prototype burner.

MMX Combustor for an aircraft Auxiliary Power Unit (APU) application.

An air-cooled borescope was developed to visualize the MMX flames inside the can combustor under full pressure. This optical monitoring device is equipped with an infrared or white light endoscope which can be inserted into the combustor.

The head is located downstream of the flames and exposed to the highest temperatures (>1300°C). This assisted in verifying combustor performance.

The overall target was to have less than 35 PPM NOx at 100% hydrogen from 50% to 100% load, with low NOx values at part-load operation as well. Additional requirements were stable ignition, no flashback, and an acceptable pressure drop. With an intensive program of CFD simulation, design optimization and benchmark validation on low- and high-pressure test rigs, an MMX burner design successfully met these targets.

The recent focus has been on implementing this technology into industrial turbines. In 2020, the Japanese New Energy and Industrial Technology Development Organization (NEDO) and KHI announced a successful demonstration of the first DLE 100%-hydrogen-fuelled gas turbine under commercial operating conditions in the port of Kobe, Japan.

New DLE combustor addresses NOx emissions and flashback. 

Hydrogen combustion

Steam turbine blade being Low Plasticity Burnishing (LPB) processed in a milling machine.

Steam turbines provide an efficient means of producing electricity. Improving the corrosion fatigue performance and damage tolerance of steam turbine blades can offer overhaul and maintenance cost savings, improved reliability, and reduced outages.

The application of surface residual compressive stress to components can enhance fatigue strength and reduces the effects of applied tensile stresses. Shot peening has been used for decades to reduce overall operating tensile stresses in steam turbine components. However, corrosion pits, erosion, fret[1]ting, and other damage can penetrate shot peening’s shallow layer of residual compression, providing a starting point for stress corrosion cracking and fatigue failures. Instead of settling for shallow compression, the introduction of a deep layer of compressive residual stress can extend service life.

To test the benefits of deep compression, high cycle fatigue tests were done on Type 410 stainless steel, a common alloy widely used in steam turbine applications, to compare the corrosion fatigue benefits of Low Plasticity Burnishing (LPB) to shot peening.

LPB is also a mechanical surface treatment, but it imparts a controlled layer of compression that is deeper than most surface damage. LPB was developed in the 1990s to keep cold work low when introducing compressive residual stress. 20 years of studying residual stresses led to the conclusion that residual compression introduced using high levels of cold working could be wiped out from in-service thermal and mechanical loads.

The first step in the investigation was to obtain sample specimens of 410SS machine-finished by low stress grinding (LSG) to serve as a baseline. Compressive stress was introduced either by LPB or shot peening. The LPB process is performed on conventional CNC machine tools and robots. Shot peening was done using a conventional air blast peening system.

Next to be tested was the fatigue strength of samples subjected to either mechanical damage or simulated corrosion and stress corrosion cracking. Mechanical damage simulates what can happen to the surface of the turbine blade from common fatigue damage mechanisms like foreign object damage, fretting, corrosion pitting, or erosion.

Mechanical damage was simulated through an electrical discharge machining (EDM) notch with a depth of 0.01 in. (0.25mm). For a portion of the LPB-treated samples, a deeper notch depth of 0.02 in. (0.51mm) also was investigated.

High cycle fatigue tests show that shot peening the 410 SS samples provided a modest improvement over the baseline condition with mechanical damage. Residual stress distributions revealed that the 0.01 in. (0.25 mm) notch completely penetrated the compressive layer introduced by shot peening minimizing any fatigue life benefit from shallow compression.

However, the deep compression provided by LPB doubled the fatigue strength and improved fatigue life near the endurance limit by a factor of over 100 compared to the shot peen condition. Even with damage twice as deep, the LPB-processed samples outperformed those that had been shot-peened.

When subjected to corrosion damage and salt exposure, simulated by testing samples in an active corrosion medium of a 3.5% weight NaCl solution after first exposing them to stress corrosion cracking (SCC) in the same medium, the LPB-processed samples again demonstrated double the fatigue strength.

Surface roughness measurements indicated roughness values of 19.5 μin for the baseline sample, 157.1 μin for the shot peened sample, and 4.5 μin for the LPB-processed sample. The roughness value for the shot peened sample is nominally 35X higher than that of the LPB-processed sample. Shot peening dimples produce a rough surface that can adversely impact fluid flow at the blade surface.

Some steam turbine manufacturers are now implementing LPB on their blades upfront to reduce overhaul and maintenance issues. Others use LPB as a faster and more economical repair technique. Depending on the steam turbine, manufacturers can apply LPB with the turbine blades installed on the rotor. LPB as a surface treatment does not add material or change the blade’s balance like traditional welding repair methods.

A repair solution for steam turbine compressor failures. 

Deep compression

The journey towards net-zero is underway. Many nations have made some sort of commitment to eliminating CO2 emissions by the midpoint of the century. How that ought to be achieved, however, is a different story entirely.

 suggests a new tactic for reducing global CO2 emissions – targeting the hyper-polluting power plant. The study, aptly named 

Reducing CO2 emissions by targeting the world’s hyper-polluting power

 found that 17% to 49% of global electricity-based CO2 emissions could be eliminated using this approach.

The study draws its emissions data from an updated version of 2009’s Carbon Monitoring for Action file (CARMA), which tracks CO2 emissions from the world’s power plants. The newest version, created in 2018, “consists of 29,078 fossil-fuel powered plants from 221 countries,” according to the study. CARMA draws from 3 key data sets: plant-level emissions reports, global-plant and company-level data, and country-specific power production data.

In countries like the US, Japan, South Korea, Germany, and Australia, 5% of polluters are responsible for 75% - 89.6% of emissions. This trend scales globally, with the top 5% of the world’s polluters contributing to 73% of all electricity-based CO2 emissions. China’s top 5% is responsible for much less CO2 output – around 24.5% - due to the country’s distribution of emissions evenly amongst different sized plants.

The study goes on to suggest that targeting this top 5% with reforms could significantly reduce global emissions levels. It suggests four key changes along with an estimate of the reduction in CO2. These include lowering intensities to match a national - then international - average, switching to natural gas, and implementing carbon capture technology (with the assumption that 85% of carbon is captured).

The results show that the implementation of all 4 policies could be highly effective in reducing electricity-based CO2 emissions. South Korea, for example, could reduce its electricity-based CO2 emissions by a whopping 76%. Similarly, the US could reduce its carbon output by 63.7%. China, the outlier in this list, would only reduce its CO2 output by 20.7%.

According to the study, implementation of these policies could reduce global electricity-based CO2 emissions by up to 48.9%. Merely switching the world’s plants to natural gas would result in a reduction of 29.5%.

The paper concludes by offering its main takeaway: “Findings suggest that instead of relying on sweeping environmental initiatives, substantial environmental progress can be made through selectively targeting nation’s hyper-polluters – the worst of the worst – that are responsible for the lion’s share of their carbon pollution.”

One key limitation, as the study points out, is the difficulty in enforcing such policy changes at a global scale. Furthermore, some countries benefit much less from such an approach. China may benefit more from targeting 10% of its polluters instead of 5%. This is due to its distribution of emissions across plants.

There is also the issue of data accuracy. The study points out that some plants either do not report their CO2 emissions or they keep them confidential. Thus, the study provides estimates of emissions in the absence of accurate data. The study believes that while some small plants may have been left off the list, the estimates for the largest power plants are reliably accurate. 

A new study suggests that 5% of the world's power plants are responsible for 73% of all electricity-based CO2 emissions. 

Reducing emissions by targeting hyper-polluting power plants

Turbomachinery Blog features postings from experts in all areas of turbomachinery, such as: gas turbines, machine diagnostics, materials, repairs, and aftermarket parts, and encourages users to participate, with reader engagement and interaction as its primary purpose.

NevadaNano, announced that Crowcon Detection Instruments Ltd. uses the Molecular Property Spectrometer (MPS) sensors in their new Gasman flammable gas detection products. A single MPS sensor accurately reports 0-100% LEL across 19 flammable gases, including hydrogen, with a single factory calibration and no field maintenance over their lifetime.

The Gasman with MPS is ATEX Zone 0 approved, allowing operators to enter areas where an explosive gas atmosphere is present. In addition, the Gasman with MPS is hydrogen ready. A single MPS sensor accurately detects hydrogen and common hydrocarbons without recalibration in a fail-safe, poison-resistant solution.

Articles

The Gasman with MPS is ATEX Zone 0 approved.

NevadaNano sensors used in Gasman flammable gas detection products

SKF has completed the acquisition of Rubico Consulting AB, an industrial consultancy firm with 10 employees based in Luleå, Sweden.

Rubico Consulting AB specializes in visualization and analysis of signal data. This expertise will be integrated into SKF’s offer around the rotating shaft, as well as powering new technology areas such as bearings with fiber-optic sensors.

Victoria Van Camp, President, SKF Technology, says: “Rubico’s expertise in signal processing enhances our existing technology base, spanning from traditional IoT hardware to the latest in edge computing. The patented edge algorithm developed by Rubico simplifies and automates analysis of machine data and is an enabler for wireless, energy efficient systems.”

The company specializes in visualization and analysis of signal data.

SKF acquires industrial consultancy firm

CTCI announced that it has won a contract to carry out engineering, procurement, and construction (EPC) work for the Sun Ba Combined Cycle Power Plant Phase 2 Project in southern Taiwan with consortium partner, Siemens Energy. The plant will include a new 1,100 MW generating unit to provide power primarily to Southern Taiwan Science Park once it comes online in 2024.

Located in Shan Shang District, Tainan, Sun Ba Power Plant is owned by Sun Ba Power Corp., a private utility company. As part of power plant expansion, CTCI is responsible for the civil works and balance-of-plant. Generated power will be sold to state utility company Taipower.

Siemens Energy's scope of supply includes the plant’s power island, consisting of two SGT6-9000HL gas turbines, one SST-5000 steam turbine, three SGen6-2000P generators, two heat recovery steam generators, and the SPPA-T3000 control system. Siemens will also provide long-term service over 25 years.

CTCI Wins Sun Ba Power Plant phase 2 contract in partnership with Siemens Energy

GE announced that the modernization of Elpedison S.A.’s Thessaloniki Power Plant in Greece was completed safely and successfully. GE upgraded Elpedison’s power generation assets, consisting of a GE 9F.03 gas turbine and a Franco Tosi-supplied steam turbine. GE also installed digital solutions to help increase the plant’s output by over 20MW (equal to powering 17,000 Greek households) and reduce its start-up costs by 10 percent.

GE showcased its total plant solutions by installing its DLN 2.6+ combustor system, its OpFlex software solution and its Advanced Gas Path (AGP) technology on its 9F gas turbine. In addition, GE provided a new HP/IP rotor for the plant’s Franco Tosi steam turbine. These upgrades were made to reduce the impact of degradation on the rotor components. The project also included the implementation of GE Digital’s Operations Performance Management (OPM) software solution.

The project was completed during a gas turbine major overhaul by FieldCore, the field services execution team owned by GE.

GE announces the successful completion of Elpedison’s Thessaloniki power plant modernization in Greece

Klaus Brun is the Director of R&D at Elliott Group. He is also the past Chairs of the Board of Directors of the ASME International Gas Turbine Institute and the IGTI Oil & Gas applications committee. Rainer Kurz is the Manager for Systems Analysis at Solar Turbines Incorporated in San Diego, CA. He is an ASME Fellow since 2003 and the chair of the IGTI Oil and Gas Applications Committee.


As engineers, we usually operate under the mantra “if it ain’t broke, don’t fix it.” If an old piece of plant equipment operates effectively, we maintain it with tender loving care. Otherwise we don’t touch it. This approach has served us well in the turbomachinery industry, with many legacy machines worldwide functioning well after more than 50 years of service. Some “dinosaur” refinery compressors actually exceed 80 years and still work properly.

But there are reasons — economic, performance, and environmental — that drive us to replace these machines with newer models. They may break too often or cost too much to maintain. Spare parts may no longer be available. A degraded machine’s efficiency may be too low, or it may not otherwise meet design flow, pressure, or power requirements of a growing plant. It may be incapable of handling process changes like higher pressures or pressure ratios and the resulting rotordynamic challenges. Finally, environmental concerns and regulatory requirements may force the retirement of old equipment when it cannot meet acceptable emissions or other standards.

Industrial machinery like compressors, turbines, and expanders has come a long way over the last 100 years. Efficiency has improved, emissions have been reduced, and reliability/availability generally has increased. But there are cases where the newest equipment is not always better than what has been operating for a long time, particularly if operating conditions have remained the same.

Admittedly, older machines were sometimes engineered and manufactured “heavier” than modern machines. Older design tools were not as accurate as today’s advanced FEA and CFD methods. More conservative design margins were required. Increasing the energy density of the machine reduces capital cost per power installed. This has led to cost savings, smaller footprints, less weight, often better aerodynamics with better range and efficiencies, and more head per compressor casing — but not necessarily a more rugged machine.

Modern aerodynamic blades have been refined and optimized and typically are very efficient. They have complex 3D shapes and some-times operate on tighter margins of aerodynamic stability. We have learned a lot over the last 50 years about rotordynamics, blade dynamics, and bearing/seal design. Our design tools have gone through many generations of improvements and validation using test data. Although modern rotor and blade designs may not always look as rugged as previous generations, if properly designed, they are as reliable and have similar life expectancies.

Does it make more sense to uprate/overhaul/refurbish/repair an old machine or replace it with a newer model?

But there are exceptions: By cramming more head into a compression stage, sometimes newer machines may have lower efficiencies. Since they run faster with higher tip speeds, compressible effects can lead to larger aero losses.

The question thus becomes: Does it make more sense to uprate/overhaul/refurbish/repair an old machine or replace it with a newer model? The answer depends on many factors, including maintenance cost, service parts availability, performance and the machine’s ability to meet current safety, environmental or operational requirements. Another factor is whether the OEM still supports the machine and has the capability to bring the old machine to required new standards.

This discussion is too long to cover in a single article. But the following examples provide some insights into a few technical advances that did not necessarily result in more reliable machines:

Example 1: Most very old reciprocating compressors installed on U.S. pipelines are low-speed (up to 350 rpm) integral machines. These large, heavy machines manufactured prior to the 1960s have proven reliable and efficient. Nonetheless, for the past 25 years, pipeline operators have mostly installed high-speed, (up to 2000 rpm) separable compressors. They’re not nearly as reliable as old integral machines, and their efficiency is substantially lower because of higher flow, pulsation, and valve losses. But operators prefer the much lower initial cost (on a per-horsepower basis) over efficiency and availability and have been slowly replacing their integral machines with high-speed, separable reciprocating compressors.

Example 2: Dry gas seals were introduced about 40 years ago. After some infancy issues, they have proven reliable and effective in avoiding the introduction of oil into the process stream. Dry gas seals have completely replaced wet seals in the market, and for the last 15 years, few wet seals have been utilized in new compressors. However, in some dirty compression applications with significant particulate matter in the gas stream or other solid contamination, dry gas seals are sometimes less reliable than older wet seals, which are better at handling particulate matter. Yet it is nearly impossible to purchase compressors with wet seals anymore since very few OEMs offer them as an option

 Example 3: To meet ever stricter NOx air emissions requirements, gas turbine OEMs have developed dry low NOx (lean premixed) combustion systems. In parallel, to increase output power and efficiencies, firing temperatures have drastically increased over the last 30 years, requiring advanced super alloys and complex but very sensitive cooling schemes. Conventional low-temperature diffusion flame combustors used between 30 and 60 years ago are generally more forgiving. But they simply do not meet modern emissions standards and today’s expectations for total plant efficiencies.

Many turbomachines still operate well after 30 and sometimes 50 years of service. If a machine is well maintained, restaged, refurbished, over-hauled, and repaired as necessary, it can operate well beyond its original 25-year API target design life. There are even cases where older machines are more efficient and reliable than newer machines.

When considering the replacement of older machines with newer models, take care to evaluate the impact that doing so may have on all aspects of operation, performance, and emissions of a plant. Legacy equipment that has been in operation for decades may not necessarily be inferior to modern equipment when all factors are considered. It is often possible to update, upgrade, and overhaul equipment for much less money than it costs to buy new. When considering replacing an old machine versus refurbishing or overhauling it, take into account not just efficiency but also reliability, operability, range and maintenance costs.

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The phrase "if it ain't broke, don't fix it" has served us well in the turbomachinery industry. 

Myth: New turbomachinery is always better than older machines 

Atlas Copco has acquired the assets of NATEV GmbH. The company was founded in 2010 and specializes in position solutions for assembly tools used in industrial production. NATEV develops systems for real-time positioning and imaging solutions in close cooperation with key customers in the automotive industry. Products include hardware and software used to monitor and error proof defined production steps linked to the tightening processes. The business will be integrated into the MVI Tools and Assembly Systems Division in the Industrial Technique Business Area.

Some of NATEV GmbH's products include hardware and software used to monitor production steps linked to the tightening process. 

Atlas Copco acquires positioning technology company 

FS-Curtis – part of the Fusheng Industrial family of companies – recently launched its ECO-Turbo centrifugal air compressor. The Oil-Free, Class 0 compressor uses an FS-Elliott engineered airend and is suitable for use in industries and applications where 100% oil-free compressed air is required with higher demand, ranging from 185 kW to 250 kW drive power at a final compression pressure of up to 125 psi. The design has been optimized with a wear-free compression principle which results in lower maintenance and fewer downtimes. The ECO-Turbo’s design fully encapsulates the compressor’s air, lubrication, cooling, and control systems. In addition, the compressor’s small footprint saves space and allows for easy installation.

FS-Curtis debuted its ECO-Turbo centrifugal compressor. 

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