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The theme of this year’s show demonstrated the continued importance of turbomachinery in everyday life.
The 52nd Turbomachinery & 39th International Pump Users Symposia (TPS 2023) in Houston, TX, held at the George R. Brown Convention Center Sept. 25 – 28, 2023, was host to more than 322 turbomachinery and pump exhibitors and around 5,000 attendees.
Michael Webber, Ph.D., a professor at the University of Texas at Austin and John J. McKetta Centennial Energy Chair in Engineering, kicked off the conference by stressing the importance of turbomachinery in the modern world, particularly in the energy-generation sector, during the keynote address.
TPS’s technical sessions continue to take a different approach by offering attendees several technical categories, including lectures (standard presentation of new technologies), tutorials (educational), case studies (shorter but problem-solving), and short courses.
New at this year’s show was “an increase in support companies, particularly on leading-edge technologies such as advanced materials, advanced diagnostics for monitoring, and advanced manufacturing,” said Dr. Eric Petersen, Director of the Turbomachinery Laboratory at Texas A&M University.
“And in addition to increasing attendance and new technologies, we want to stress the involvement of younger engineers—early-career engineers—to ensure continuity in both the ability of engineers to design and operate turbomachines and to continue to propagate that knowledge,” Petersen said. “We’re also interested in broadening our scope of short courses with additional/newer topics.”
Petersen iterated that this year’s theme, the continued importance of turbomachines in everyday life, was reflected by the show’s attendance—a combination of long-time attendees and new engineers.
Compressing and Pumping Hydrogen
A day-one tutorial on Applications and Technology for Hydrogen Compression and Pumping offered an overview of the various hydrogens and the methods used to produce each gas, as well as compression, cost, and leakage challenges.
Marybeth McBain, Manager at Elliott Group, said the various iterations of hydrogen fuel bring up issues regarding cost, wear-and-tear on current pipeline assets, and embrittlement—each requiring a careful approach to hydrogen.
Hydrogen Production and Cost
McBain said that even with tax credits, hydrogen is expensive to produce at scale. However, she cited the initial price hikes of LNG in which plant operators were worried LNG was too expensive: “The industry stepped up and started looking at ways to make power plants more modular to offset construction costs and to standardize equipment to lower manufacturing costs.” After which the cost of LNG came down. She encouraged attendees to consider this when it comes to the cost of hydrogen, “and how technology can catch up and give us that cost-competitiveness.”
Beyond cost are secondary concerns regarding what percentage of hydrogen would actually make a meaningful difference in carbon emissions, as using 30% hydrogen doesn’t reduce your use of natural gas by 30%; in fact, McBain said it would only reduce natural gas by 15%. She also pointed out the impact hydrogen has on carbon-steel blends (U.S. pipelines are made of several different blends) and compressor requirements—each of which must be considered when transitioning the energy economy to a hydrogen-based model.
Karl Wygant, Senior Manager at Elliott Group, tackled the challenges presented by the compression of a light gas such as hydrogen, including sealing, embrittlement of materials and coating, and temperature constraints. Although titanium is used with most gases for compression at high speeds, hydrogen’s corrosive properties present challenges for the metal, making it unsuitable for hydrogen applications.
Wygant said, “What does work well is some of the aluminum series; [aluminum] shows good resistance to hydrogen embrittlement,” although it does encounter issues at high temperatures as tip speed increases. However, newer impeller designs or advanced material integration may reduce gas corrosion or the lack of materials suited for increased tip speed. Wygant said integrally geared compressors may be a solution at a higher tip speed and introducing inter/pre-coolers could manage an increase in temperature. Aluminum could be integrated with several coolers to regulate temperature, addressing a primary challenge when compressing hydrogen for industrial-scale operations.
Enver Karakas, Director at Elliott Group, said hydrogen requires a much lower liquefaction temperature than ammonia, raising the cost of this process in comparison to the liquefaction of other gases. Handling liquid hydrogen presents a host of challenges, as the gas is highly flammable and corrosive, and the minuscule molecular size causes hydrogen to leak from the system into the atmosphere. Karakas said a submerged motor design and material consistency could minimize stresses on the components within the system.
Karakas also recommended the use of cryogenic expanders to increase liquid production by 3-5%. Liquid expanders for hydrogen liquefaction achieve higher efficiency through improved cooling and energy recovery systems, counteracting the properties of hydrogen and ammonia that would typically make this process dangerous or ineffective.
Troubleshooting Aero-Performance Issues
On Wednesday morning, speakers offered guidance on how to resolve aero-performance-related issues both in the field and on an OEM production test stand.
Jim Sorokes, an aerodynamic independent consultant at Fox Innovation & Technology, kicked off the discussion by asking, “Could we have avoided the problem in the first place? Did we do our due diligence in evaluating the technology that was used in the machine when it was being built?” He further stressed that there must be open communication between the OEM and end user to define suitable levels of design verification.
“It’s best to identify any issues before the machine leaves the test stand,” he said.
The first step, according to Sorokes, is to gain an understanding of the scope of the problem: Is it a mechanical issue, an aero-performance issue, or both? Is it only happening at low- or high-flow? Have I seen this issue before or is it new? Ultimately, you want to determine whether the issue is specific to this type of compressor or this application. The OEM can help get this process started.
Next, determine who will be involved in this process—the OEM? Who from the client’s company? Is a third party involved? Who is in charge? Who’s leading the effort within each organization that’s involved?
Foundational in this process, however, is communication. “Communication is vital,” Sorokes said. “It must be open, honest, and thorough, and there must be a willingness to share data. Team members must avoid back-channel communication."
Trends in Performance Testing
Yuri Biba, Principal Aerodynamic Engineer at Siemens Energy, laid out trends in performance testing, including excess internal leakage, inlet and discharge losses, compressor fouling corrosion, and the impact of various manufacturing assembly mistakes.
“Excess internal leakage can be caused by damage to the seals, which causes incorrect clearness, which causes more leakage—this could occur over time or suddenly,” Biba said. An example he used was leakage in an eye labyrinth seal, which led to lower efficiency and reduced capacity.
Further, Biba said inlet losses could be caused by a blockage, improper upstream piping, etc. Excess inlet losses cause a larger pressure drop than is expected between the inlet flange and the eye of the first impeller. This decreases the flange-to-flange performance and shifts the performance curve toward lower flows.
Another issue seen in the field is fouling/corrosion caused by deposits on the flow path, foreign material ingested into the machine, or chemical reactions during the compression process. As a result, performance decreases over time. Additionally, excess mechanical vibrations can also result from significant fouling and/or corrosion.
Biba said there are times when a compressor is assembled incorrectly; for example, stationary components can be installed in the wrong orientation. A mistake in compressor assembly may result in large pressure drops or unsteady flow. These sorts of mistakes are relatively easy to investigate, however, if one has access to the view the machine internals.
Computational Fluid Dynamics
Kurt Aikens, Aerodynamic Engineer at Fox Innovation & Technology, detailed a common analysis tool used in root-cause analyses and for evaluating performance issues: computational fluid dynamics (CFD).
“CFD is more time-intensive [than the new tools that Biba discussed], but in exchange for that we get significantly more detail about what may be going on,” Aikens said. “CFD resolves the full 3D characteristics of the flow field by approximating the solution to conservation of mass, momentum, and energy.”
It is based on fundamental fluid dynamics, but it’s up to the user to choose what 3D geometry is relevant to the problem at hand. “Simple CFD setups are reliable for calculations near the design point where losses are at a minimum,” Aikens said. “They can also be accurate for predicting the overload capacity for impellers operating at higher tip Mach numbers.” Among other things, CFD is also reliable for predicting the relative performance impact of subtle changes in geometry.
CFD predictions, however, are influenced by many factors, including mesh resolution, surface boundary conditions, the choice of steady versus unsteady, turbulence models, and interface conditions. Complex issues may require including more geometric detail, such as multiple stages, 360-degree analyses of some or all components, or switching to unsteady state analysis.
One challenge for steady-stage simulations is accurately predicting stall/surge. The biggest problem with CFD, however, is computational cost. With lower costs, fewer assumptions would need to be made, improving simulation fidelity. Even in its current state, Aikens said that CFD is wildly popular for improving the understanding of and evaluating solutions to aero-performance issues.
The Rise in Demand for LNG
The day-two tutorial, Turbomachinery in LNG Production Plants, offered attendees a review of major turbomachinery in LNG plants, focusing on how compressors, pumps, and gas turbines fit into the various LNG plant cycles.
Klaus Brun, Director at Elliott Group, said LNG “is typically liquefied at temperatures ranging from -260°F to -280°F, which varies depending on the type of gas chosen for liquefaction.” Originally derived from small-scale refrigeration compressors, modern LNG liquefaction converts a feed gas into a finished fuel product for power generation, heavy-duty transport, alternative fuels, etc.
Brun introduced an extensive list of compressors used in LNG applications, as well as the purpose of a compressor in an LNG train.
“Compressors pressurize and refrigerate the gas to prepare it for storage and transportation as a finished product, but the sheer variety of available compressors allows for unique focuses in LNG production,” he said. Examples of compressor models commonly used in modern LNG production include:
This machinery, in addition to the rest of the LNG train, processes natural gas so that it is safe for large-scale industrial applications.
Brian Pettinato, Manager at Elliott Group, stressed that determining the size of a compressor in an LNG train is vital for optimal efficiency. “The sizing is determined by the flow and available technology: The larger the amount of flow you have to get through, the more you tend to scale up the compressor.”
Pettinato said the various degrees of testing that a compressor arrangement undergoes are to identify excessive vibration and assess the performance efficiency of the equipment. Operators may use mechanical running tests, performance tests, or full-load full-pressure inert gas string tests—a costly option—to determine inconsistencies and improve the compressor operation guided by speed, inlet vanes, and suction throttling.
Cryogenic Pumps and Expanders
Enver Karakas, Manager at Elliott Group, introduced the role of cryogenic pumps and expanders within an LNG application, but stressed, “To use a pump, you have to liquefy the gas. So while pumps may be more efficient in terms of transporting fuel, there are a lot of processes that need to first take place to be able to use the pump.”
Pumps for LNG processes transfer and pressurize the fluid while it’s in liquid form, while cryogenic liquid expanders disperse the fluid through a Joule-Thomson (JT) valve. Karakas emphasized the importance of proper cooling in an LNG train to avoid issues such as high flammability and to improve the overall quality of the gas, citing a submerged motor-driven pump design as favorable for this process “… so that the OEM doesn’t need to worry about certification for hazardous areas. Putting the motor in fluids means I don’t have to worry about classifications for hazardous areas. Another benefit is the cooling by the LNG fluid,” he said.
Turbine and Motor Components
Rainer Kurz, Manager of Gas Compressor Engineering at Solar Turbines, offered a simple overview of gas turbines, electric motors, and steam turbines. He said the two primary methods of combustion in a gas turbine are conventional combustion and low NOx combustion. The available driver power and speed have to be matched to the LNG compressors. For the best efficiency and economy, the gas turbines should run at maximum power.
According to Derrick Bauer, Manager at Elliott Group, the types of materials chosen to construct LNG components must be properly heat treated and field tested to ensure operational safety, as a poorly tempered metal could cause a catastrophic failure when subjected to high pressures, corrosive gas, or extreme temperatures. Metals with high nickel content, low carbon content, cleanliness, proper heat treatment, and small grain size are optimal for inclusion in LNG equipment.
Bauer advised the audience to avoid metals with two specific qualities: high carbon content and low alloy content. Carbon steels and low alloy steels are susceptible to the “ductile-to-brittle” transition, in which a material exposed to LNG processes over time begins to weaken, crack, erode, and eventually fail. Testing of the material’s toughness is required prior to its integration into components, so OEMs often conduct Charpy v-notch impact testing to ensure the material can endure massive amounts of stress. The test applies an immediate downward force to the material in an effort to shatter it, then data is collected to determine the resistance of the material in an LNG application. Conducting material testing is perhaps the foremost step in preventing catastrophic failure at LNG plants.