Impact of Thermodynamic Property Accuracy on Compressor Performance

Figure 1: Multi-Section Compressor on Factory Test Stand

Knowledge of centrifugal compressor thermodynamic performance is critical to initial acceptance and, once installed, periodic or continuous health monitoring to ensure that the operation is consistent with the original design expectations. The accurate determination of this performance is dependent upon a number of factors. These include uncertainties associated with measured parameters of pressures and temperatures, composition of gas mixtures, and the calculated thermodynamic properties that are derived from these parameter measurements. 

Industry standards, ASME PTC 10 and the ISO equivalent, ISO 5389, define some fundamental compressor performance measures that are universally accepted to describe their thermodynamic behavior. The polytropic work (or poly-tropic head) represents the useful work that is applied to the gas to raise its pressure from suction to discharge conditions. It is expressed by the following equation based upon the work of Schultz and the definition of a polytropic process for an ideal gas:

This equation shows that the polytropic work (Wp) is only dependent upon the compressor suction and discharge values of pressure (P), temperature (T), specific volume (v), and the gas molecular weight (MW). The average polytropic exponent, n, included in these relations is also derived from these parameters. These properties are all available from some equations of state for the gas. However, the polytropic work (useful work) does not represent the total amount of work required by the compression process. 

An additional amount of work known as the lost work is consumed to raise the gas from suction to discharge pressure. Lost work manifests itself as an increase in the thermodynamic property of entropy of the gas or gas mixture and an additional increase in temperature above what would be expected for only the useful work also known as an isentropic process. The combined useful and lost work result in an increase in the total energy of the gas, also referred to as the increase in the thermodynamic property of enthalpy. Thus, the ratio of the polytropic work to the total enthalpy increase of the gas defines the polytropic efficiency of the compression process.

All thermodynamic properties needed to calculate compressor performance can be derived from three progressively complex thermodynamic models. The simplest, a perfect gas, requires only the pressure, temperature and gas molecular weight to obtain the specific volume, or its reciprocal the gas density, and the polytropic work. The enthalpy and entropy are calculated using constant values of the specific heat for a given gas or gas mixture and the temperature differential from suction to discharge of the compressor.

As the gas behavior becomes more complex, the perfect gas model needs to be modified with the addition of the specific heats becoming a func-tion of the temperature. This results in a more involved functional relationship with temperature needed to calculate the enthalpies and entropies required. An added parameter, the gas compressibility factor Z, is also introduced but its value is held at unity with the specific volume derived being equal to that of the perfect gas relation.

The most complex thermodynamic model is the real gas model. There is a compressibility factor, Z, which is a function of both the pressure and temperature with a more complex calculation of the specific volume than the simpler models. Additionally, the specific heat parameters are also functions of both pressure and temperature, resulting in more difficult relations needed to calculate the resulting enthalpies and entropies.

Figure 2: Pressure-Enthalpy Diagram for Methane

A more visual comparison of the enthalpy behavior of a gas is available through the examination of a pressure versus enthalpy diagram for a substance. Figure 2 is such a diagram for pure methane. The red isotherms which display near vertical linear characteristics at low pressures and higher temperature values reflect ideal gas behavior. These isotherms demonstrate increasing curvature at higher pressures which indicates progressive real gas performance with influences of both temperature and pressure present. A perfect gas would display consistent deviations in enthalpy for equal deviations in temperature and this is approximately noted at the lowest pressure levels and moderate temperatures where the changes in specific heat with temperature are minimal.

Although perfect and ideal gas relations may be limited in their application to given pressure and temperature conditions, it is assumed that real gas relations are valid across a broad range of con-ditions including ideal gas conditions. The corresponding values of specific volume (compressibility factor), enthalpy and entropy are more generally applicable when compared to the sim-pler perfect and ideal gas thermodynamic models.

A substantial number of equations of state (EOS) have been developed over the past century to describe the thermodynamic behavior of substances, including several particularly focused on the vapor phase. The ideal gas EOS is generally applicable to simple molecules at low pressures due to the limited interactions between the particles that are relatively sparsely distributed in relation to one another within an arbitrary volume. As pressures increase and the gas molecules become more populated within a fixed volume and complex in both geometry and electro-magnetic polarity, the resulting attractive and repul-sive forces impact the ability of the ideal gas EOS to accurately describe the thermodynamic behavior. Under these more challenging conditions, more complicated relations are needed to ade-quately predict the gas properties. Although generally expressed as a single compressibility factor, Z, applied to the ideal gas EOS, the equations behind the determination of the compressibility factor and other, associated properties can be quite complicated. 

Six selected real gas equations of state will be included in the following comparisons due to their typical application with gas compression. They can be separated into the four major categories provided below along with some historical perspective:

The van der Waals EOS was one of the first proposed beyond the ideal gas EOS. Subsequent improvements to the van der Waals equation included the Redlich-Kwong (R-K), Soave, and the Peng-Robinson (P-R) EOSs, including a number of others. These became known as cubic equations of state due to the fact that they expressed the pressure in terms of a cubic relationship to the specific volume. Alternatively, the compressibility factor could also be expressed as a third-degree polynomial which could be solved explicitly. The R-K EOS included only two com-ponent specific parameters that were derived from the critical pressure and temperature of that component. The Soave and P-R EOSs included a third parameter that was named the Pitzer acentric factor which was experimentally determined and further accounted for molecular polarity and non-sphericity.

Observations demonstrated that the cubic equations of state provided estimations of the compressibility factor that were offset from experimental values across a wide range of pressure and temperature conditions. Peneloux initially proposed a volume-translation method for the Soave equation of state that addressed this shift. Several other volume translation methods have been pro-posed for cubic equations of state. The method proposed by Jhaveri and Youngren has been included here as applied to the P-R EOS and is designated as the VTPR EOS for comparison.

A more complex equation of state was proposed by Beattie-Bridgeman that included higher order specific volume terms and was considered to be more accurate than the cubic equations of state at the time. Benedict, Webb and Rubin proposed an expansion of this relation and Starling added additional terms which resulted in the BWRS EOS with a total of eleven empirically derived constants for each gas component, three more than its predecessor. Although significantly more complicated than the cubic equations of state, these thermodynamic models claim increased accuracy.

More recent variations of this class of equations of state offer additional accuracy but include more than thirty empirically derived constants for indi-vidual gas components. The actual Virial Equation of State is a similar power series expansion with constants that are a function of temperature.

3. Corresponding States Principle Equations of StateThe Corresponding States Principle (CSP) is based upon the fact that different gases demon-strate similar thermodynamic characteristics when the pressure and temperature are normalized with their respective critical values. A number of alternate versions of various equations of state have also been developed using the normalized (reduced) pressure and temperature as variables. 

Probably the most accurate of these was devel-oped by Lee and Kesler and later modified by Plöcker, known as the Lee-Kesler-Plöcker (LKP) EOS. It is based upon the BWRS EOS using “simple” fluid and “reference” fluids combined with the Pitzer acentric factor for the selected gas or gas mixture.

While not being included in this comparison, there are some notable generalized CSP equations of state that can be utilized with reasonable expected accuracies. A generalized equation of state is one that does not require a detailed gas mixture composition but rather simply a presumed hydrocarbon mixture molecular weight and mole fraction compositions of the sour/acid gas components of nitrogen, carbon dioxide and hydrogen sulfide. The hydrocarbon mixture molecular weight is used to calculate values of pseudo-reduced values of pressure and temperature. Two of the more accurate generalized CSP equations of state are those developed by Dranchuk-Purvis-Robinson and Dranchuk-Abou-Kassem. These are typically used in oil and gas production applications where detailed gas mixture compositions are not known or variations are expected.

A recent and stated highly accurate new form of an equation of state is the one developed by the Groupe Européen de Recherches Gazières (GERG). It is based upon the Helmholtz free energy which is a function of the internal energy and entropy of a substance and one of the fundamental thermodynamic energy functions. Similar to the virial family of equations of state, it is dependent upon a large number of empirically obtained constants for each of the included gas components. 

Figure 3: Equation of State Comparison for Typical Natural Gas.

Figure 4: Equation of State Comparison for Carbon Dioxide.

The accuracy of any equation of state for a given single component gas or gas mixture can be validated by comparing its predicted compressibility factor (or specific volume) over a range of pressures and temperatures against laboratory measured values. There is a substantial amount of this laboratory generated PvT data available in the public technical literature. Usually, it is in the form of specific measured data points along isotherms across a range of pressures. This existing data may be utilized to verify the accuracy of a given equation of state proposed to evaluate a compressor application with the same or comparable single component gas or gas mixture. However, unique gas compositions may benefit from the generation of more specific experimental PvT data for the intended range of operating con-ditions. A number of laboratories exist that are capable of generating this data.

One example of an accuracy evaluation is provided in Figure 3 for a typical natural gas mixture. It is approximately 90% methane, 3% ethane, 1.5% propane, 1.7% carbon dioxide, and 1.7% nitrogen by volume. The experimental data was collected along a 170oF (76.7C) isotherm and a pressure range from atmospheric to 6000 psia (413.7 Bara). The experimental data points are provided as black triangles. Curves for the six different equations of state evaluated are included and designated in the legend.

The cubic equations of state display the largest deviations from the measured data. It should be noted that the volume-translated Peng-Robinson, VTPR EOS, shows improved agreement. The remaining equations of state demonstrate very good agreement with the experimental data. One final observation that should be highlighted is the good agreement with all equations of state. The exception is the R-K EOS at pressures below approximately 500 psia (34.5 Bara) along this isotherm. This is due to the behavior of this mixture at the lower pressures approaching those of an ideal gas at this relatively moderate temperature.

A second example is presented in Figure 4 for pure carbon dioxide across an increased pressure range up to a maximum of over 18,000 psia (1241 Bara). Good agreement is once again demonstrated for most of the equations of state evaluated with the largest deviations evident for the simpler, cubic equations of state.

These two figures are fairly representative for a large number of gas mixtures. But it is prudent to have a discussion between the equipment manufacturer and end user concerning the most appropriate equation of state to utilize for a specific application. As noted previously, if there is not ade-quate shared experience for unique gas mixtures, it may require the development of a program to empirically determine PvT data for the mixture and evaluation against a number of different equations of state to determine the most accurate.

The volumetric behavior of the gas is demonstrated through a comparison of PvT data and an equation of state. However, it is not obvious how this translates to other thermodynamic properties such as the internal energy, enthalpy and entropy. The perfect and ideal gas models described above state that these properties are related to the specific heats with the ideal gas model having the specific heats also being a function of the temperature. Experimental determination of specific heats is achieved through the use of a calorimeter, where an amount of energy is added to a thermally isolated gas sample and the increase in temperature is measured. A perfect gas would result in constant values of the measured specific heats over successive tests at different initial temperatures. But an ideal gas would reflect a temperature dependent value.

The real gas thermodynamic model is based upon the assumption that the specific heats are functions of both temperature and pressure. Although calorimeters exist that can measure specific heats at elevated pressures, most of this data has been derived from equipment that is designed to operate at relatively low pressures. Analyses of these real gas thermodynamic functions show that they can be expressed as the sum of the ideal gas value and an isothermal term that is a function of the pressure. This additive pressure dependent term is often referred to as the departure, or residual, function. Further mathematical evaluation can express these departure functions in terms of the compressibility factor which relates the value of the departure function to the value and accuracy of the compressibility factor. A few investigations into the accuracy of the departure functions as related to the predicted accuracy of the compress-ibility factor have confirmed this relationship. It is therefore plausible to assume that equation of state accuracy in the prediction of the compress-ibility factor can be extended to these additional thermodynamic parameters.

EQUATION OF STATE IMPACTS ON COMPRESSOR PERFORMANCE

It follows that equation of state differences in prediction of compressibility factor and the associated thermodynamic parameters may also influence the calculation of compressor thermodynamic performance parameters. These differences can readily be illustrated by comparing calculated polytropic work and efficiency for the various example equations of state based upon a common set of suction and discharge pressures and temperatures. Representative performance curves are first selected from actual applications with comparable gas compositions and suction conditions. 

One of the evaluated equations of state is designated as the baseline and discharge pressures and temperatures are calculated for defined suction conditions at a number of points along the baseline performance curves. These sets of suction and discharge pres-sures and temperatures are then utilized to calculate polytropic work and efficiency for each of the equations of state. They are also used to plot performance curves, essentially in the same fashion as would occur in the case of acquired test data.

Baseline data included in the following comparisons was determined using the GERG EOS due to its demonstrated minimal deviation from published PvT data. Two examples are presented with both based upon the typical natural gas com-position defined previously. The first example addresses the comparative performance of a low-pressure case with a common suction pressure of 100 psia (6.89 Bara) and temperature of 100oF (37.8C). Discharge pres-sures range from approximately 208 psia (14.34 Bara) at higher inlet volumetric flows to 273 psia (18.82 Bara) at low flows near surge. Seven spe-cific operating points were evaluated and are presented in Figures 5 and 6. Polytropic work is plotted in Figure 5 versus an arbitrary range of inlet volumetric flow rates. Good agreement is displayed between the various equations of state.

Figure 5: Polytropic Work for Low Pressure Natural Gas.

Figure 6: Polytropic Efficiency For Low Pressure Natural Gas.

Although there appears to be more deviation in the polytropic efficiency than the polytropic work, a closer look at the scaling in Figure 6 also confirms good agreement between the different equations of state. These results could lead one to believe that there are insignificant differences based upon the choice of an equation of state. However, it should be recognized that there was little deviation in predicted compressibility factor in this range of pressures in Figure 3. Gas properties within this range of pressures and temperatures are near ideal with compressibility factor values near unity and with minimal differences between suction and discharge conditions between the equations of state. 

As the pressure range of the compression application increases, differences in predicted compressibility factors become more evident. Using a similar procedure to predict discharge pressure and temperatures from defined suction conditions and a selected baseline polytropic work and efficiency curves, a comparison of calculated polytropic work and efficiency character-istics can be developed for the chosen set of equations of state. 

Figure 7: Polytropic Work For High Pressure Natural Gas.

Figure 7 provides these curves using a common suction conditions of 2000 psia (137.9 Bara) and 100oF (37.8C) with discharge pressures ranging from 4349 psia (299.8 Bara) to 5553 psia (382.9 Bara) as determined with the GERG EOS.

Good agreement is evident among the more complex, virial type equations of state in comparison to obvious deviations with the cubic based equations of state. Significant deviations are noted for the R-K EOS across the entire inlet volumetric flow range, whereas the amount of deviation is decreased for the P-R EOS and minimized further for the VTPR EOS. This behavior lends credibility to the proposition that equation of state compressibility factor accuracy also translates to reduced uncertainty in the prediction of compressor performance.

An equivalent evaluation of the polytropic efficiency is presented in Figure 8 for the higher-pressure case. Once again, greater deviation from the baseline is evident for the cubic equations of state. However, it is noted that the VTPR EOS displays greater deviation than the P-R EOS. This apparent shift in efficiency is due to the differences in the prediction of the enthalpy of the gas mixture at suction and discharge conditions, specifically the departure enthalpy term which is also a function of the compressibility factor. 

Recall that the efficiency is the ratio of the polytropic work to the enthalpy rise from suction to discharge conditions.

Figure 8: Polytropic Efficiency For High Pressure Natural Gas.

These examples demonstrate that the choice of equation of state used to estimate the thermodynamic properties can impact the calculation of recognized compressor performance parameters, particularly as gas conditions progressively depart from ideal gas behavior. A robust equation of state should adequately predict both ideal and real gas conditions. While these examples address a representative gas composition and set  of operating conditions, the results may not apply to all potential applications. An evaluation of the most accurate equation of state for a specific application should be com-pleted to ensure the most accurate estimates of compressor performance parameters are obtained. It should be noted that the gas power required for the different equations of state at a common inlet volumetric flow rate shows less deviation across the wide range of conditions. This is due to a cancelation of compressibility factors between the polytropic head and flow rate relations, but does relate to a difference in mass flow rate for a common value of volumetric flow rate. 

The information provided in this article leads to the following recommendations with respect to the application of a given equation of state in the evalu-ation of compressor thermodynamic performance.

1. Equipment supplier and user, or user’s representative, should discuss and agree upon the most appropriate equation of state for a specific application. This should be determined prior to equipment purchase commitment and utilized for both compressor and compression facility design activities.

2. If adequate information is not available to support the use of a specific equation of state, a program should be initiated to collect PvT data for the spe-cific gas/gas mixture across the anticipated pressure and temperature range of the application. This should be followed by an analysis of various equations of state to establish the most accurate.

3. Consistent use of a common equation of state should be utilized for initial compressor design and performance prediction, any planned ASME PTC 10 Type 1 (full pressure, similar gas composition) factory testing, field testing, and longer term operational compressor per-formance monitoring.

4. Given that factory ASME PTC 10 Type 2 testing is normally performed with inert gases at near ideal gas conditions, use of a common equation of state may not be necessary due to minimal deviations in thermodynamic properties. 

◦Mark R. Sandberg, P.E. is the owner of Sandberg Turbomachinery Consulting. For more information, read the paper“A More Comprehensive Evaluation of Equation of State Influences on Compressor Performance Determination,” at https://oaktrust.library.tamu.edu/bitstream/handle/1969.1/166804. 

Compressor performance and thermodynamics

Control systems for gas turbines, steam tur-bines and compressors have become more complex. They now incorporate emis-sions-based algorithms (such as DLE and DLN), model-specific diagnostic routines, safety certified protection logic, and cybersecure firewall programs in recent years. This increased complexity is part of the reason why more turbomachinery owners are asking control manufacturers to provide long-term support services for their installed control systems. This is becoming an emerging trend in the market. Plant owners are requiring turbomachinery control manufacturers to provide long-term support for installed contol systems.

The outsourcing of the management of turbomachinery controls is becoming more common. 

High employee turnover coupled with increased control system complexity is forcing turbomachinery owners to question how best to support their plants and turbomachinery long term. Some refinery and petrochemical owners, for example, demand that control manufacturers sign long-term service contracts before allowing the control system to be installed.

A long-term service contract with the turbomachinery control manufacture is seen as a way for plant owners to reduce yearly personnel training expenses, ensure they have access to control system specialists and the latest versions of hardware, software, and cyber-security protection. It eliminates the need to train plant personnel on control systems. Long-term service contracts for turbomachinery controls typically include requirements for many dif-ferent levels of support, including emergency phone support, email support, remote computer support, local technician services, revision control support, and plant personnel training services.

Depending on the plant’s network security requirements and applicable regulations, remote support can be as simple as plant personnel sharing their computer screen via Teams or Zoom. Alternatively, it can be as sophisticated as a secure remote link where a remote support team can log into a system, monitor, troubleshoot, and perform software patch updates as required. In such an environment, plants need cybersecurity expertise and protection. With these types of OEM-provided services, the plant is assured that service engineers are routinely trained on the lat-est system algorithms, network configurations, and cybersecurity patches. They also have access to factory experts to resolve system problems. 

Most turbomachinery owners also require the control manufacturer to provide some level of local support to ensure quick response in the case of system failure or emergency event as well as provide periodic training to plant operators and engineers. 

Woodward offers long-term support services for installed control systems. 

Where turbomachinery availability is key for critical processes and plants, 24/7 access and response time by a local service engineer is a usual require-ment. Depending on the plant the local service engineer(s) may be required to spend a certain number of days in the plant and to be on-call. As control manufacturers are continually making improvements to their products, many plants are now including hardware, software, and cyber security revision control within long-term service contracts. This inclusion ensures that the control manufacture is routinely updating the control system with the latest version of control components, software programs, and security logic.

Responding to this emerging trend, Woodward provides long-term support services to turbomachinery owners globally, assisting them to keep plants operational and control systems up to date. Woodward offers a range of remote and site-based services, for all of its turbomachinery product lines. It is open to customizing service contracts for each plant’s support requirements. 

■Rich Kamphaus is Global Sales Director for Steam Turbine and Compressor Markets at Woodward, a provider of control systems for the turbomachinery, aerospace, industrial, military, power generation, and transporta-tion markets. For more information, visit woodward.com 

Direct turbomachinery controls 

Design and engineering software lies back of every aspect of turbomachinery and facility layout. These tools are used to figure out how to increase efficiency, heighten performance, lower costs, decrease emissions, and find the best way to arrange and integrate equipment and systems. 

There are a great many trends and influences impacting this slice of the market. And the vendor community has risen to the challenge. Let’s hear from the experts: 

Concepts NREC offers a suite of software tools starting from preliminary design through full 3D computational fluid dynamics (CFD), finite element analysis (FEA) and 5-axis machining of turbomachinery. Together, the software is called the Agile Engineering Design System. New for 2022 is CyCAL, which allows the design of turbomachinery within a larger system and includes thermodynamic cycle analysis. CyCAL will be a new platform to bring together all tools in a single user environment.

“Engineers need to look at many aspects of a design in addition to the aero/hydrodynamic performance of the primary flow path,” said Peter Weitzman, President, Software Division of Concepts NREC. “A successful designer needs to simultaneously consider off-design performance, secondary (leakage, bleed, injection) flow, rotordy-namics, and product life.” 

In addition, it is not enough to look at the turbo components in isolation. Every piece of turbomachinery sits inside some larger system to accomplish a specific thermodynamic cycle. If the cycle/system layout is decided first and imposed on the turbomachinery designer, then optimal system performance may not be achieved. The turbomachinery needs to be designed concur-rently with the cycle/system to achieve competitive product performance.

Design trends are receiving a lot of impetus lately from the launch industry. The most critical part of a rocket engine is the turbopump, and designers of engines needs to design the engine cycle and turbopumps as a single system. Customers in the rocket industry want better software to accommodate engine cycle and turbopump design, and these improvements are becoming available to anyone designing turbomachinery.

“Our latest software releases have really been about moving beyond design point performance of the primary flow path,” said Weitzman. “We have added capabilities to design and analyze secondary flow in leakage paths for all classes of turbomachinery. CyCAL provides optimized cycle/system design and analysis capability.” 

The SoftInWay AxSTREAM platform is a fully integrated design, analysis, and optimization soft-ware solution for turbomachinery propulsion and power generation systems. The software includes advanced meanline/streamline, CFD, and FEA solvers, as well as thermodynamic cycle and hydraulic network modeling, rotor dynamics analysis and AI capabilities. Additionally, users can do true clean-sheet design through its generative design solver which can automatically create a design space and narrow down the design intent without introducing too much designer bias into the equation. This can help engineers make decisions about how many stages a machine should have, what the optimal configuration is, and other key thermodynamic and geometric decisions before having to go through meanline analysis or later stages in the design process. 

Valentine Moroz. Chief Operating Officer, SoftInWay has observed some definite trends on the simulation side. “We’re seeing a push towards integrated end-to-end solutions both by means of internal development and through partnerships/acquisitions between small software venders and large companies,” he said. “We’re also seeing the industry trend towards use of digital twins, AI, and high-performance computing (HPC).” 

Within the turbomachinery industry, Moroz added, there are three main development strategies: 

1. Complete clean-sheet design for novel applications (especially in areas such as hydrogen, fuel cells, electric vehicles, etc.) where there is no in-house expertise.

2. Trimming and scaling to adjust existing designs to fit into a new design application (the focus here being a reduction in development time, cost, and risk). 

3. Throwing as much computing power as possible at older designs to try and maximize optimization.It is important to fully understand the objec-tives of a design project before beginning.

“When a project kicks off without a clear understanding of the engineering intent across all teams, it often will lead to conflicting ideas about the project requirements across management, the technical team, and the financial team,” said Moroz. “It is important to establish the engi-neering intent early on to understand what tools you actually need to make your project a success.” 

The TURBOdesign Suite by ADT is an integrated platform for the development of turbomachinery systems, starting from meanline design and covering 3D blade design using inverse design technology with automatic optimization capabili-ties. Inverse design is a unique design method to:

• Satisfy the turbomachinery requirements from the first iterations (e.g., compressors pressure ratio, head in pumps or pressure rise in fans);

• To rapidly develop high efficiency blades, using blade loading as an aerodynamic design input parameters which correlates with performances;

• Accurate surrogate models with small design matrix, requiring up to two orders of magni-tude less computational costs compared to conventional direct optimization methods;

• Develop general design know-how by under-standing the blade loading requirements for product series and similar applications;

• A three-dimensional design approach ideally suited for additive manufacturing.

Over the past few years ADT has enhanced its software to facilitate design exploration and opti-mization at various stages of the design workflow and across all turbomachinery applications. This includes development of integrated design explo-ration, optimization and ML/AI loops starting from a handful of basic requirements such an engine log line for example, and development of automated design, analysis and optimization workflows for 3D blade design/volutes linked with 3D CFD/FEA and multiphysics. In addition, direct interfaces and couplings with major CAE systems are available for integration within existing design environments and facilitating data transfer across programs. Finally, interactive, machine learning-driven user guidance during the design process provides feedback based on live user input parameters.

Maturing turbomachinery components and systems efficiency levels combined with tougher competition and stricter regulatory requirements are driving the search for designs that offer higher efficiency, particularly across multiple areas of the operating conditions that coincide with the lifecycle operations of the system. Smaller and more compact turbomachinery packages, too, are required to reduce weight and material costs in electrification and high-volume productions. 

“Some of the main market drivers are an overall lack of skilled turbomachinery design engineers in the industry compared to a growing demand,” said Professor Mehrdad Zangeneh, Managing Director of Advanced Design Technology. “In addition, development of new products required for decar-bonization which asks for novel system cycles and product configurations.”

Southwest Research Institute (SwRI) manages the Numerical Propulsion System Simulation (NPSS) Consortium. The NPSS software is an engineering simulation and design environment that enables engineers to develop customizable system models. Applications primarily include aerospace systems, engine models for aircraft propulsion applications, thermal management systems, liquid rocket propulsion systems, and energy generation systems. It comes with a library of standard models and components. SwRI manages the licensing and sales of the NPSS software. Additionally, its engineers provide engineering services for developing custom NPSS models, or designing engineering systems for a wide portfolio of propulsion and energy related systems.

Charles Krouse, NPSS Consortium Manager at Southwest Research Institute (SwRI) said that customers, these days, are increasingly interested in (1) electric/hybrid-electric propulsion systems, (2) high-speed propulsions applications, and (3) interfaces between modeling tools. The trend towards electric and hybrid-electric propulsion systems, for example, is being driven primarily by environmental concerns. Although aircraft propulsion only accounts for a small percentage of total carbon emissions (2-3%), emissions reduction targets are approaching quickly, especially for the slow-changing aircraft industry. Furthermore, as the general population sees significant progress in industries such as renewable energy and electric cars, they are beginning to point fingers at the aircraft industry for not adopting environmentally friendly technologies. 

The market for high-speed propulsion applications is being driven by factors such as the hyper-sonic arms race, supersonic business jet startups, and the billionaire space race. With the threat of hypersonic weapons from potential adversaries, the U.S. government is investing in hypersonic weapons. Supersonic jet companies, on the other hand, are being funded by private investors. There seems to be a convergence of technologies that has promised to make supersonic flight affordable, and startups such as Boom Supersonic, Hermeus, Spike Aerospace, and others are racing to beat the incumbents such as Lockheed Martin. 

Krouse added that the trend towards robust interfaces is being driven by the growing number of specialized engineering tools, increasing computational capabilities, and requirements for a heavier focus on model-based design practices. 

“As computational capabilities increase, engineers are able link multiple subsystem models together and simulate more complex models of whole aircraft systems,” said Krouse. “However, linking subsystems models together  between tools requires signif icant computer science expertise to understand the underlying computer architectures.”

NPSS software was traditionally modelled turbomachinery systems. Since turbomachinery applications are now commonly coupled with electric/ hybrid-electric systems, the organization has added the capability to model electric systems in NPSS software, including components such as motors, generators, inverters, and resistors. This capability will be available in its next release. 

SwRI has also developed a supersonic propul-sion model as part of an internal research and development effort. The purpose of this project was to develop improved capabilities for modeling critical components, such as the combustor, inlet, and isolator in high-speed air-breathing propul-sion applications. Additionally, the organization developed a system to demonstrate the transition from subsonic flight to supersonic flight, using a turbine-based combined cycle (TBCC). 

Advances have been made, too, in the area of interfaces. Recently, SwRI developed APIs for NPSS to interface with python and java computer languages, which are in addition to the existing interfaces to standard languages such as C/C++ and Fortran. This allows NPSS users to complete their development work in their preferred programming language and communicate with the NPSS simulation environment. 

In addition, SwRI has been working to resolve some of the challenges connected with additive manufacturing (AM). The AM process can some-times create anomalies such as voids that may lead to fatigue crack formation, growth, and fracture. Customary integrity analysis methods for conven-tional materials have significant limitations for AM applications.

However, a zone-based probabilistic damage tolerance (PDT) methodology is a promising framework for the assessment and certification of AM parts. This approach calculates the probability of fracture due to the formation and growth of fatigue cracks at material or manufacturing anomalies. The component is subdivided into different zones each having different properties, such as material properties, non-destructive inspection (NDI) probability of detection (POD), and anomaly distributions. The Darwin software developed by SwRI provides practical implemen-tation of zone-based PDT methods.

Originally developed to address rogue material anomalies in titanium rotors for aircraft engines, Darwin has expanded to address a range of integ-rity threats. It is used, for example, to ensure the structural integrity of conventional safety-critical components in turbomachinery. NASA and the FAA are actively funding research at SwRI to evaluate the wider use of Darwin for AM applications and to enhance its capabilities towards this goal. 

When asked what trends he had observed, Jeff Erno, Expert Solution Architect, Dassault Systèmes named three: A need for integration between geometry (CAD) and analysis (CAE); home-grown design and analysis solutions (due to lack of commercial off the shelf or COTS software), that were needed in the 1980s and 1990s to be competitive, are needing an upgrade and possibly a rewrite from legacy FORTAN and C programming methods; and demand for collabo-ration and storage for analytical results.

“Innovation is driving legacy home-grown tools to adapt, which is difficult to do with legacy programming methods,” said Erno. “Older more manual methods aren’t cutting it.”

The company has adjusted to these trends via geometry and analysis methods ported into a single, unified platform, promoting fast rerunning of analysis to evaluate performance as the design changes. Such changes are incorporated into Dassalt’s SolidWorks, Catia and Simulia lines. Such tools offer geometry and analysis integrated associatively allowing replay when the design changes. In addition, platform-based collaboration allows designers to work with other designers and with analysts to evaluate performance. 

Rahul Garg, Vice President, Industrial Machinery, Siemens Digital Industries Software, has observed a movement towards improved renewable energy adoption to ensure turbomachinery grows progressively more energy efficient. This includes adopting new fuel types; adjusting their operations for cleaner output; and using inte-grated cloud software to source, manage and store their turbomachinery solutions. 

“Companies are leveraging technology to solve complex issues that arise across the machine lifecycle to continu-ously improve their processes,” said Garg. "For instance, some companies utilize simulation software that leverages a digital twin. This digital twin can help them foresee thermal and dynamic deformations and address the problem before it arises in late-stage development.” 

A major impetus for these trends is digitalization. The benefits include augmented cross-domain collaboration; project data reuse for faster order fulfillment; enhanced machine development via the use of a digital twin; improved lifecycle service maintenance through digital twin and low-code tools; and task automation enabling greater time to devote to functional projects. 

To that end, Siemens developed its cloud-based Xcelerator portfolio to help clients respond to turbomachinery trends and tackle market demands. The company is actively enhancing this cloud approach to simplify adoption through pre-configured industry processes, capturing experience inside templates. Xcelerator offers various design, analysis and engineering solu-tions. Xcelerator products can integrate with other engineering tools.

Design and Engineering Software

The latest buzzword in the turbomachinery industry is the digital twin. It’s being praised as the holy grail for everything from failure prevention and maintenance reduction to life extension, improved operation, and parts fore-casting. While the digital-twin concept offers defi-nite value for machinery operation, some of these claims stretch the truth. It’s worthwhile to discuss what a digital twin really is, what it can do, and where its limitations lie. 

A digital twin is a computer virtual represen-tation and simulation of a real physical object or process. Although the idea has been around for a long time, the basic concept and definition were introduced in 2002 by Michael Grieves, then at the University of Michigan, as a model for Product Lifecycle Management. NASA then coined the term in 2010 in a Roadmap Report. The digital twin consists of three parts: the physical object, the digital or virtual product, and the connections between the two. The concept has branched out into different types, such as the digital-twin aggregate (DTA), where multiple digital twins operate in parallel to simulate a complex system.

Implementing a simple digital twin or a more complex DTA requires data about the real-time status of the real-life object, as well as the ability to operate, maintain, or repair the real system remotely via a parallel digital twin representation. Think of Apollo 13, where the ground-based engineers were able to determine how to rescue the mission remotely by simulating all operations and failure scenarios to identify a viable solution. Thus, “the ultimate vision for a digital twin is to be able to create, test and build [our] equipment in a virtual environment” (John Vickers, NASA, 2010). 

In its purest form, the digital twin is a product and technology development tool. That means it is also an alternative to big data approaches, where correlation is assumed to be a proxy for causation. The digital twin is essentially a computer simulation program that uses real-life data to create simulations that can predict how a physical asset will perform. Artificial intelligence, self-learning, and software data analytics can also be utilized to enhance and refine the output. 

But, to quote Lewis Carroll’s Humpty Dumpty in Through the Looking-Glass, “When I use a word, it means just what I choose it to mean.” So, what does “digital twin” mean in current turbomachinery discussions about condition monitoring, predictive interventions, condition-based repair and process optimization? 

The distinction between a simulation model and a digital twin is not really clear. The basic components of a digital twin are a model and some real-life operational data. That’s nothing new. For decades, we have used performance models — in the form of performance curves or compressor maps, for example — to determine the health of equipment by simply comparing the expected behavior (from the curves) to measured performance data. The difference between a model and a digital twin (i.e., “a digital twin without a physical twin is a model”) does not help because the performance curves actually reflect the behavior of a real machine.

The added feature of a true digital twin versus a simple model is that a digital twin can adapt to changes of the physical object over time. For example, if a machine shows wear or has perfor-mance degradation, a true digital twin can adjust whereas a simple model simulation cannot. The digital twin thus provides added value in that it provides a more accurate representation of the current state of the machine. This can be of significant value when scheduling maintenance and repairs or predicting remaining life since the digital twin’s updated parameters directly relate to known physical failure mechanisms. 

One of the key insights of digital-twin operation is that the simulation model used in the background does not have to be complicated. The use of performance curves noted above can be part of a digital twin. But updating the model to the current state of the machine using measured data is not trivial. Measured data is always subject to condition, measurement, and statistical uncertainties. The digital-twin correction using actual data (from operations, field, and factory testing) must be treated as a statistical process — the more data, the better the model improve-ment. The sourcing of test data from multiple (more or less) identical machines helps signifi-cantly when correcting the model. This means that a manufacturer with a large number of machines in operation (gas turbines, steam turbines, compressors etc.) has an advantage when building a digital twin. 

The minimum requirements for the model used in a digital twin are simply that it is sufficiently physics-based, accurate, and quick to run. The concept of a digital twin, leaving all the hype aside, is based on existing and mature technologies. Overuse of the term may lead to underutilization when potential adopters become cynical of the buzzwords and shiny presentations. Using the concept requires trust in the model, the data, and the algorithms used to update the model. Supervision by human experts is still required for checking the plausi-bility of the model outcomes and digital-twin recommendations. 

■Klaus Brun is the Director of R&D at Elliott Group. He is also the past Chair of the Board of Directors of the ASME International Gas Turbine Institute and the IGTI Oil & Gas applications committee.

Rainer Kurz is the Manager of Gas Compressor Engineering at Solar Turbines Incorporated in San Diego, CA. He is an ASME Fellow since 2003 and the past chair of the IGTI Oil and Gas Applications Committee.

Any views or opinions presented in this article are solely those of the authors and do not necessarily represent those of Solar Turbines Incorporated, Elliott Group, or any of their affiliates

The Digital Twin Knows it All  

Many manufacturers, vendors, engineering firms, and operators have real-ized the importance of lessons learned during different stages of design, devel-opment, and machinery introduction. Too often, those lesson-learned documents have been lists with an overwhelming number of items. Unfortunately, many of the same mistakes are repeated by engineers, vendors, contractors, and operators in subsequent projects. Let’s review a few ways to improve modern turbomachinery. 

The bulk of the design review is done by design experts and engineers. However, there are two groups of people that should be included in each segment of the design review process: the commissioning/start-up team, and the people who will operators operate and maintain the machinery. In many cases a common shortfall is that companies do not select the operations team at the time of machinery selection. It is wise for operating companies to assign operation leads and superin-tendents as soon as possible and have their inputs on all key matters. A similar principle is applicable for the commissioning team. The exchange of data and information between engineering and commissioning is vital. There should be lines of communication estab-lished to help key people communicate each other and transfer vital data, feedback, and experience. 

• High-level requirements by client representatives: It is useful if client representatives establish and explain their high-level requirements and expectations to engineering firms and vendors/manufacturers. Of course, some of the expectations might not be achievable and others might not be reasonable considering technical, budget, or time-schedule constraints. However, it is important to discuss these matters as early as possible. It will be found that while some expectations might not be achievable in the way initially thought, alternatives might be formulated which can achieve those expectations at a reasonable cost and without greatly extending delivery times. It is best to not be in a rush to oppose such expec-tations. It is advisable to spend some time and resources to find a way to achieve them in a more suitable way. 

• Operator feedback: If there was a problem in operation, the best way (and usually the only way) to inform the engineering team (and subsequently vendors/manufacturers) and rectify the problem is via operator feedback. 

• Communication with the commissioning team: The communication between the engineering team (vendors/manufacturers) and commissioning leads is vital. The commis-sioning team need data and documents to plan and prepare for their tasks. Feedback from the commissioning team is also important to consider provisions for smoother and commissioning and start-up practices. Combined with modern monitoring systems, automation provides an opportunity for improved reliability and availability. However, there is such a thing as over-automation. 

Automation is a major trend in plants and facilities. Automated operation is cost effective, efficient, advantageous, productive, and more easy to manage. Combined with modern monitoring systems, automation provides an opportunity for improved reliability and availability. However, there is such a thing as over-automation. 

The basic principle is to leave ordinary, repetitive tasks to control systems and provide operators with tools to do their own tasks better. In an over-automated plant, automation hinders operators from operating efficiently. In some cases, operators cannot intervene and override the automated system when there was a problem. 

A general guideline is to buy new turbomachinery rather than second hand. In many cases, it can cost more to rehabilitate and revamp second-hand turbomachinery that to purchase new equipment. There may also be cracks, corrosion, and erosion that has not been detected. Manufacturer warrantee should be mentioned as a key benefit of new equipment. 

Whatever equipment is used, shop inspection is crucial yet is often overlooked. It should not be left only to third-party inspectors. Such inspectors are beneficial and are nearly always needed. In fact, third-party inspection is often a mandatory requirement. However, inspectors from the oper-ating company, engineer consultants, the main EPC contractor, and others are often needed to inspect machinery at various stages. 

■ Amin Almasi is a Chartered Professional Engineer in Australia and U.K. (M.Sc. and B.Sc. in mechanical engineering). He is a senior consultant specializing in rotating equipment, condition monitoring and reliability

SELECTION, PURCHASE,AND OPERATION OF TURBOMACHINERY

Speed sensors for turbomachinery provide the input for overspeed protection systems. A faulty sensor leads to an unreliable input signal, which has a negative influence on the accuracy and reliability of the system. 

There are several considerations that must be made to select the right sensor, which can be categorized in environmental and machine-related considerations. Machine considerations include: expected minimum and maximum speed; the target to be measured and its specifications; any limitations on the weight and size at the mounting location; and the necessary cable length. On the environmental side, factors to consider include: the expected ambient temperature; if the measurement takes place in explosion hazardous areas (ATEX) or in a corrosive environment; and if strong electromag-netic fields are present. 

A sinusoidal output signal from a variable reluctance sensor.

For industrial speed measurements there are three main types of measurement sensor:

• Variable reluctance (VR) sensors – also known as: passive sensors, electromagnetic sensors or magnetic pickup sensors (MPU).

• Eddy current sensors – also known as: proxim-ity sensors or displacement sensors.

• Hall-effect sensors – also known as: active sensors.

A VR sensor uses a magnetic field to measure changes in the distance between the sensor tip and the target object. The sensor contains a coil that is wrapped around a magnet which causes a change in the magnetic field (flux) and the coil as the teeth of a gear pass the sensor. The moving gear creates a varying flux that induces a voltage in the coil; the frequency of which is related to the rotational speed. The signal is a sinusoidal wave of which the amplitude is dependent on the target size, speed and distance.

VR sensors do well in high-temperature applica-tions. Some can function in temperatures of more than 300°C. Moreover, VR sensors are easy to use and reliable. As this type of sensor has a two-wire connection, it often fits within legacy infrastructures.

However, the amplitude of the signal depends on a factor of the size, speed, and distance of the target. If the speed is too low, the gear tooth too small, or the distance to the target material too much, the signal will be flattened and not usable. On the other hand, if the speed is high, the gear tooth large or the distance is small, the signal will show high pulses. The application and positioning of VR sensors requires special attention and expertise to function properly. As these types of sensors do not function well with low speed, they are unsuitable for low or zero-speed detection.

An eddy current sensor on a slotted speed wheel gives a square wave output signal.

An eddy current sensor uses an electromagnetic field to measure changes in the distance to an object. As a pole wheel moves past the sensor, it measures a variation in distance; close (tooth) and far (notch). The rotational speed can be deter-mined based on the time between these events.

One advantage of eddy current sensors is that the measuring principle shows both the pulses and the position with respect to the teeth. This provides insight into the set distance to the teeth of the target object. They are available with a dynamic current output, which allows for long cabling (up to 1000m). Sensors with a dynamic current output are less affected by cable imped-ance as compared to Hall-effect sensors, eddy cur-rent sensors based on voltage signals, and VR sensors.

But it should be understood that at high speed, saturation may occur, causing the signal shape to flatten. When the gear teeth move past the sensor at high speed, an eddy current sensor barely detects a difference in distances. The higher the frequency, the less effective an eddy current sensor will be for speed measurements.

Hall-effect sensor generates a square wave output signal.

A Hall-effect sensor measures changes in magnet’s magnetic field, caused by the ferromagnetic target material. The sensors have built-in signal condi-tioners, which generate a clear square wave signal. In contrast to VR sensors, Hall-effect sensors are sensitive to the size of the magnetic flux rather than the speed at which it changes. Hall-effect speed sensors have a broad measurement range and can be used to measure both low-speed or sta-tionary parts and high-speed parts.

A Hall-effect sensor directly provides a digital output which is easy to transmit and process. Further, they usually feature internal signal pro-cessing. The signal is digitalized and amplified, making it less susceptible to electromagnetic inter-ferences (EMI). However, Hall-effect sensors are limited to applications that operate in tempera-tures ranging from -40 °C to +150 °C due to built-in electronics. Moreover, Hall-effect sensors require a 3-wire connection. Also, the trigger level is defined in the Hall-effect sensor and cannot be changed.

TYPICAL SENSOR APPLICATIONS AND REPLACEMENT OPTIONS

Any application requires different sensors and sensor features. However, three types of turboma-chinery can be distinguished, with each having a default sensor type provided by the OEM. The recommended sensor replacements after end-of-life are may differ for specific applications.

• Large land-based turbines (power industry) are typically provided with eddy current or Hall-effect sensors by the OEM. Based on the frequency range and signal stability, a Hall-effect sensor is recommended when the default sen-sor has reached end-of-life.

• Industrial turbines (process industry, oil & gas industry) are typically provided with eddy cur-rent or Hall-effect sensors by the OEM. Based on the frequency range and signal stability, a Hall-effect sensor is recommended when the default sensor has reached end-of-life. 

• Aeroderivative turbines are typically provided with magnetic pick-up sensors (VR) by the OEM due to their normal operation in harsh environments. When it suits the application, Hall-effect sensors are recommended after the default sensor has reach end-of-life.

AuthorL Daniël Visser works for Istec, a provider of machine protection and monitoring solutions that suit an increasingly demanding environ-ment and takes care of sensors and systems during operational life. An in-depth overview of each sen-sor can be found in the book Speed. It covers topics such as speed measurements, overspeed protection, sensor types, functional safety & SIL, and API 670. It can be requested for free at www.istec.com/book-speed

SENSORS FOR SPEED MEASUREMENTS

New gas turbine orders worldwide (units in red, MW in blue), courtesy of Dora Partners.

The 32nd Annual Meeting Western Turbine Users Inc. (WTUI) conference kicked off this week with its traditional overview of gas turbine trends. Delivered by Mark Axford of Axford Turbine Consultants and Tony Brough of Dora Partners, the big news was a thriving aeroderivative market – and tepid large frame turbine sales.

New gas turbine orders down overall 12% (measured in MW) in 2021 but up on 8.5% in the number of units. But looking deeper at the numbers, aeroderivative unit orders in 2021 were up 11% for the year. When viewed outside of the volatile Russian market, aeroderivative unit orders were up 110%. Further, North American aeroderivative unit and ME orders were both up more than 300% in 2021. The LM6000 accounted for more than 50% of the MW orders and the LM2500+ for about 50% of the unit orders.

Worldwide, the LM2500+ dominates the market. It has a five-year share of 33% of all aeroderivative orders, 25% higher than the LM6000 in second place. The LM2500 and LM2500+ each have fleets in excess of 1200, with the Lm2500+ now leading. The LM6000 lies behind at around 1150.

“The LM2500+ continues to be the strongest GT and has been so for a long time,” said Brough.

The GE/Baker Hughes combo accounts for 80-90% of non-Russian aeroderivative unit orders. And, of course, the LM2500+ and LM6000 are the main contributors. This fits with an overall trend of lower sales in power generation and higher sales in oil & gas. In North America, the number of mechanical drive units sold in the past seven years is double what it was in the previous seven years.

Whatever the forecast, renewables are always expected to be up sharply. Yet, Brough believes gas turbines have a strong role to play over the long term. He noted all the attention on hydrogen but said this market will experience slow but steady progress. Meanwhile almost 400 hydrogen electrolyzer projects are already operational or under construction and nearly 500 more are at the feasibility or concept stage. About 50 plan to convert hydrogen into ammonia as a storage mechanism.

“It is unwise to dismiss hydrogen, but a lot of challenges have yet to be overcome in its utilization,” said Brough.

North American market share in MWs for aeroderivatives. Courtesy of Dora Partners.

Mark Axford continued the presentation by showing the long downtrend in the gas turbine sector. 2021 was down 12% in overall gas turbine MW orders (including large-frame machines) and up slightly in unit orders.

“What was an annual GT market of 60 GW a few years ago is now a 30 GW market,’ said Axford.

But he echoed Broughs sentiments about the aeroderivative sector.Texas was a major contributor to the 2021 sure in aero orders, partly in response to the early 2021 power grid failures in that state.

He went into more detail about aero orders. Siemens Energy managed 19 sales in 2021 (up from zero in 2020) of its A35, A45, and A65 machines (formerly Rolls-Royce) yet it has ended their production.Mitsubishi’s stewardship of the FT9 MobilePac (formerly PWPS) pushed sales from 0 to 6 for the year.

There were 22 LM2500+ G4s ordered in 2020 and 47 in 2021. From 0 orders of the LM2500 Xpress in 2020, GE managed 17 last year. The TM2500 trailer increased from six to nine orders, and the LM6000 from 4 to 26 in 2021. GE LM9000 had a dire year, dropping to 0 from 20 in 2020. And the LMS100 continues fail to register any sales for the second year running.

GE U.S. aero orders in 2021 included 6 LM2500Xpress’ to Colorado Springs Utilities, 10 LM6000s to TVA, 2 TM2500 G4s to Entergy of Louisiana, 4 TM2500 G4’s to two power plants in northern California, 4 LM6000s to the Salt River Project in Arizona, and two LM6000s to WattBridge (ProEnergy in Texas).

“The LM2500Xpress is less expensive than a trailer-mounted TM2500 and can be relocated,” said Axford. “RWE in Germany also ordered 11 LM2500Xpress units.”

Meanwhile, ProEnergy has carved out a niche for itself. It refurbishes LM6000 gensets, making them more affordable, especially for those running less than 1000 hours. Its subsidiary WattBridge Energy owns and operates peaking plants within the Texas ERCOT system. This includes 38 LM6000s already and more are planned.

How about 2022? Axford forecasts MW orders to be down 10% in the U.S. and it to be an overall down year worldwide, particular for large-frame machines.

“But it should be a good year for small aero, especially if restrictions on oil and gas are lifted,” said Axford.

Finally, he expressed skepticism about the realities of hydrogen generation replacing natural gas for power generation.

“There are dozens of on-going test projects with hydrogen fuel but in my judgment, hydrogen will not become a mainstream fuel for gas turbines,” said Axford. “Perhaps a niche market will evolve for blending 5-10% hydrogen into the gas supply of regional markets.”

Strong Aeroderivative Market, Weak Large Frame 

A PTA machinery train by MAN Energy Solutions including an integrally geared compressor, steam turbine, expander and motor/generator.

MAN Energy Solutions (MAN ES), a daughter company of Volkswagen, employs around 14,000 people at over 120 sites globally. As a major player in advanced engineering for more than 250 years, it has built a portfolio of technology solutions for the marine, energy and industrial sectors.


Gas and Steam Turbines
MAN ES offers modular, heavy-duty single- and twin-shaft gas turbines in a power range between 6 MW and 12 MW. It is currently upgrading this portfolio to operate on up to 100 % hydrogen. In addition, it offers expansion turbines, which are becoming important in energy recovery in many industrial processes.
On the steam turbine side, MAN ES can deliver back-pressure or condensing-type models in a power output range from about 1 MW up to about 50 MW. For mechanical drive the range goes from about 1 MW to about 80 MW. Such machines have been part of the company’s bread and butter business for a great many years. It boasts 1,350 customer references.


A centrifugal compressor train for offshore gas production by MAN ES.

Compressors
Compressors and turnkey compressor train solutions manufactured by MAN Energy Solutions sit at the heart of many processes in various industry sectors such as industrial gases, oil and gas, chemical and petrochemical, LNG, CO2, urea, purified terephthalic acid or nitric acid. The portfolio includes centrifugal, axial, integrally geared, isothermal and process gas screw compressors as well as vacuum blowers for the paper industry.
“I see great potential for the future of conventional machines, which can be further enhanced for hydrogen and ammonia applications,” said Mathias Scherer André, Senior Vice President, Head of Sales & Project Management Industries at MAN Energy Solutions. “Our customers in the tissue, paper and cardboard production increasingly purchase our TURBAIR vacuum blowers because of the reduced water and electricity consumption compared to conventional water ring pumps.”
In addition to a wide range of conventional centrifugal compressors with a vertical or horizontal parting line, the company offers oil-free hermetically sealed centrifugal compressors with integrated high-speed motor drives. These come under the product lines HOFIM and MOPICO. They present broad application possibilities and benefits. Whether as subsea, unmanned topside, or even as a heat pump unit, the machine concept can be configured for different demands and equipped with application-specific features.
The HOFIM motor-compressor was initially developed as a solution for gas storage. But customers now apply the technology in various other segments. Most recently, it has been deployed as the core element of MAN’s new cross-sector ETES (Electro-Thermal Energy Storage) Heat Pump unit. This is based on the operating principle of a heat pump, but on an industrial scale.

Two ETES Heat Pump systems are being installed this year in a new district heating plant in the Danish port city of Esbjerg. With an overall heating capacity of 50 MW, the plant will supply around 100,000 local inhabitants with approximately 235,000 MWh of heat annually. Renewable power from nearby wind farms and seawater will be used as a heat source for the generation of heating energy. The new plant will guarantee an emission-free alternative to the city’s current coal-fired power plant.
“This represents a new chapter in the success story of our HOFIM compressor – an important one that marks the path towards a decarbonized future,” said Scherer André. “Energy in all its shapes and sizes plays a fundamental role in the future of our planet. That is why MAN ES is contributing to the climate goals established in the Paris Agreement.”


Accordingly, the company is:
Advocating a Maritime Energy Transition and offering a range of alternative propulsion technologies to reduce fuel consumption and emissions.
Developing new technologies for the generation and storage of energy to deal with fluctuating renewable energies and lower the carbon footprint of power plants.
Implementing digital transformation to make industrial processes more efficient and reliable.


Carbon Capture, Utilization, and Storage
MAN ES actively supports its customers in the reduction, balancing, and avoiding of CO2 emissions by offering CO2 compression technology solutions with the integrally geared product line. In the Carbon Capture, Utilization, and Storage (CCUS) field, MAN ES has more than 30 running references around the world.
Aker Carbon Capture has entered into a cooperation partnership with MAN ES to offer energy efficient CCUS compression solutions. Jointly developed ‘Carbon Capture Heat Recovery’ technology (CCWHR) is applicable to large facilities, such as the Heidelberg Cement Norcem cement plant in Brevik, Norway, where the world’s first carbon capture facility for large-scale cement production will soon be realized. From the summer of 2024, 400,000 tons of CO2 will be captured annually from the factory – corresponding to 50 % of its overall emissions. Carbon will be compressed and liquefied with technologies from Aker Carbon Capture and MAN ES, and transported by ship to an underground storage location.


Hydrogen Turbomachinery
MAN ES already has decades of hydrogen compression experience, especially for refinery applications. In the mid- to long-term, the company sees a huge demand for turbocompressors to transport and store large quantities of green hydrogen. With the acquisition of H-Tec Systems, its technology portfolio now spans from green hydrogen production with electrolysers, across transport, and storage, to downstream processes and end consumers of carbon-free fuels in the marine and energy sector.
“We are open for pilot projects in this field to demonstrate the technical and economic viability of large-scale state-of-the-art hydrogen technologies,” said Scherer André.

MAN employee using the augmented reality-assisted MAN EyeTech tool


Turbomachinery Services
MAN PrimeServ operates a vast network of service centers all over the world. Its focus is shifting away from simple parts and on-site maintenance towards extensive digital monitoring of compression equipment. It provides a suite of digital services to get more out of the equipment at lower cost, such as dynamic simulation, simulation-based control software, FAT (Final Acceptance Test), remote virtual commissioning, operator training simulator, virtual sensors, performance monitoring, and PrimeServ assist for remote monitoring with its connection to the MAN CEON Cloud, MAN’s digital service platform.
“The journey through unmanned operation to fully autonomous operation is well on the way,” said Scherer André.
Regional PrimeServ service centers offer long-term service agreements, inspections and spare parts deliveries, revamps, and complex rebuilds. Customers can utilize these services to have turbomachines operating unmanned or they can leave the monitoring of machine health status to MAN ES by opting for the PrimeServ Assist application. In addition, MAN EyeTech enables immediate support for troubleshooting activities or overhauls. This augmented reality-assisted application allows mobile collaboration to be set up via data glasses, or other video-capable terminals like smartphones or laptops.
“Digital tools proved to be of paramount importance after the pandemic’s arrival: since 2020, we have successfully executed fully remote commissioning of compressor trains,” said Scherer André.

MAN ES emphasizes digital tools and decarbonization

This week’s PowerGen 2022 conference in Dallas, Texas featured some fighting talk from former Texas Governor and U.S. Secretary of Energy Rick Perry. He questioned the feasibility of achieving the net-zero targets set for 2050 and defended the use of fossil fuels and nuclear power.

He campaigned for a balanced approach, saying we need all sources of generation to power the nation. He made it clear that regardless of the plans for wind, solar, batteries, and hydrogen, we are going to need fossil fuels for a long time into the future. He also called for more attention to be paid to areas such as carbon capture, utilization, and storage (CCUS) and small modular reactors (SMRs) for nuclear power.

"Does anybody think that we're going to be able to address all of the needs of the United States by 2035, with just renewables?” said Perry. “ And if the world went to net zero by 2050, it would be one of the most apocalyptic loss of life in the world's history.”

You can read our full report on the PowerGen 2022 conference in the July/August issue of Turbomachinery International

Articles

Fossil Fuel Fighting Talk 

Schneider Electric held a press conference at PowerGen to release its vision for the grid of the future along with some supporting products. This is aimed at the energy transition and helping to meet the set target of removing 10 Gigatons a year of CO2 for the next 10 years.

Schneider offers a serious of EcoStruxure for Power and Grid products and services.. These are primarily aimed at the utility industry and include services for distributed energy resources (DER), grid optimization, as well as new platform-as-a service offerings wherein the utility leaves all data center building, operations, and maintenance to Schneider. In this way, the utility gained access to the latest software and updates without having to upgrade its systems or purchase more. Everything is rolled into the subscription. The idea is to allow the utility and focus on its core competencies as opposed to becoming mired down in IT.

Schneider is offering these cloud services in partnership with Microsoft Azure. The term Energy-as-a-Service is being used for these services. But as one spokesperson pointed out, utilities have been in that business for more than a hundred years. The latest stage is greater digitalization.

In this model, Schneider will incur all capital costs and will own the equipment. Several utilities have already signed on to services such as:

SureSeT MV switchgear with the EvoPacT circuit breaker. 

Grid to Prosumer approach to the lifecycle of DER management with simple to complex workflows.

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