Revamping a Turbomachine Train

The demands of the plant construction and energy sector after a shorter response time for questions upon newly defined operating points of a turbomachine train are one of the biggest challenges in the service business. This becomes particularly obvious if the future points can only be realized by redesigning the flow-relevant components. Often, it is necessary to have more time to check the dynamic behavior of the train, than in the development of the appropriate revamp measures for the core machine itself.

In addition to the different utilization rates of the affected departments, the causes of the delays often lie in the lack of interface quality between the design/ calculation and train integration team. On top of that, a certain amount of time will be required by manufacturers of the critical components such as gearboxes or drives to perform a lateral check. This lateral check is not only mandatory, in case of a component modification such as changing the transmission ratio or upgrading the drive, but it is also necessary if the coupling between the train components must be changed to ensure torsional stability.

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          Figure 1 – Flow Chart 

The flow chart to the right shows the general process flow from revamping a turbomachine train. On the line to the left of the figure, the revamp’s main processes are shown. The process flow starts with the revamp of the core machine and ends with the fulfillment of the feasibility criterion in the torsional analysis. A calculation tool is usually available for each process step. It results from in-house development, university’s research or from a commercial manufacturer. Overall, in a process flow as per above, several tools which come from different manufacturers are used.

Normally, each tool outputs its result in a text file whose content conforms to the ASCII standard and is unstructured. The fact that the output file is unstructured, makes it clear, an update or a completion of the tool means an enormous effort for the company which is responsible for the train integration. It must examine the individual interfaces and adapt them as necessary. Furthermore, it must also carry out the immensely important work of the benchmarking of the overall result.

Implementing a text file with a hierarchical data structure as output is one of the simplest solution approaches to fix the interface problem. However, because most of the tools historically have been written in the obsolete programming language, writing the results in a hierarchical data structure is very difficult to achieve. Another approach is the application of an integrated development environment for turbomachinery. Because all tools come from a single manufacturer, the interface quality is now guaranteed. To apply the core competencies of the machine manufacturer, the environment should be able to integrate the specific characteristics of flow-relevant components such as loss and leakage models into the calculation.

Check out  SoftInWay’s integrated platform AxSTREAM for flow path design and redesign

Axial Compressor Challenges in Hyperloop Designs

Back when the California high-speed rail project was announced, Elon Musk (CEO of SpaceX and Tesla Inc. and perhaps the most admired tech leader of present day) was not only disappointed with this project, but also introduced an alternative to this system called the Hyperloop in 2012.  Since the abstract of this project was introduced, many engineers around the world have started to evaluate the feasibility of this “5th Mode of Transportation”.

Hyperloop Alpha Conceptual Design Sketch
Hyperloop Alpha Conceptual Design Sketch

The general idea for the Hyperloop consists of a passenger pod operating within a low-pressure environment suspended by air bearings.  At the realistic speeds estimated by NASA of 620 mph, the pod will be operating in the transonic region.  While Japan’s mag-lev bullet train has succeeded at achieving speeds of up to 374 mph, the scale and complexity of a ground transportation system rising above 600 mph bring to surface an unusual number of engineering challenges. As well, brand new designs such as the one proposed by Musk have a certain amount of risk involved due to this technology inherently having no previous run history on a large scale.

Of the many concerns with his original design, perhaps the largest resides on how to design and operate the axial compressor in front of these pods. The supposed function of the compressor is two-fold. The first function would be to overcome the Kantrowitz limit. Musk uses an analogy between the pod and tube and a syringe:

“Whenever you have a capsule or pod (I am using the words interchangeably) moving at high speed through a tube containing air, there is a minimum tube to pod area ratio below which you will choke the flow. What this means is that if the walls of the tube and the capsule are too close together, the capsule will behave like a syringe and eventually be forced to push the entire column of air in the system. Not good.”

Aero Booster
Figure 2 – Safran Aero Boosters Low-Pressure Compressor – Assembly View

An onboard compressor in front of the pod will allow the collected column of air traveling in front of the pod to flow through the system without compromising the increasing velocities of the pod. A second function of the compressor would be to supply air to the air bearings that support the weight of the capsule throughout the passage.

Traditionally, axial compressors are coupled with a complimentary turbine at the exhaust that provides mechanical power to the compressor. In the hyperloop, the proposed compressor arrangement will be driven by electric motors instead of turbines. This is a relatively new design that has only been tested on a handful of electric powered jet aircrafts for research purposes. Furthermore, Musk proposed a compression ratio of about 20:1, which would require several compression stages for an axial compressor arrangement and an intercooler system. The temperature increases resulting from this high order compression require a complex cooling method or a traditional steam pressure vessel for the proper dumping of hot air. A final challenge on the compressor end would be the fact that it will be operating at a very low pressure. Only a handful of companies like Safran Aero Boosters have the necessary experience with low-pressure compression.

In general, while this new proposed mode of transportation is very exciting and innovative from an engineering standpoint, the following challenges specific to the on-board compressor will require serious collaborations amongst the leaders in the compressor design industry:

  • Electric Motor Driven Compressor
  • High Compression Ratio – 20:1
  • Complex intercooler system
  • Low-Pressure Compression Environment

If you would like to learn more about SoftInWay’s integrated platform for axial compressors, please visit our axial compressor page

Liquid Rocket Propulsion with SoftInWay

Preliminary Design of Fuel Turbine

Operation of most liquid-propellant rocket engines, first introduced by Robert Goddard in 1926- is simple. Initially, a fuel and an oxidizer are pumped into a combustion chamber, where they burn to create hot gases of high pressure and high speed. Next, the gases are further accelerated through a nozzle before leaving the engine. Nowadays, liquid propellant propulsion systems still form the back-bone of the majority of space rockets allowing humanity to expand its presence into space. However, one of the big problems in a liquid-propellant rocket engine is cooling the combustion chamber and nozzle, so the cryogenic liquids are first circulated around the super-heated parts to bring the temperature down.

Rotordynamics analysis
Rotordynamics Analysis

Because of the high pressure in the combustion chamber needed to accelerate the hot gas mixture, a feed system is essential to pressurise and to transport the propellant from the propellant tank(s) to the thrust chamber. In today’s rocket engines, propellant pressurization is accomplished by either (turbo)-pumps or by a high pressure gas that is released into the propellant tank(s), thereby forcing the propellants out of the tank(s). In space engineering, especially for high total impulse, short duration launcher missions, the choice is almost exclusively for pump-fed systems.

To design such systems, a highly sophisticated and complete tool is required. SoftInWay has developed AxSTREAM, the most integrated engineering platform in the market, for turbomachinery design, analysis and optimization. The long experience in the field along with the use of AxSTREAM allow SoftInWay to support its customers in the space industry. Below, you can catch a glimpse at AxSTREAM’s capabilities through a demonstration project of the RL10-A3-3 fed system. The RL10-A3-3 rocket engine is a regeneratively cooled, turbopump fed engine with a single chamber and a rated thrust of 15,000 lb at an altitude of 200,000 ft., and a nominal specific impulse of 444 sec. Propellants are liquid oxygen and liquid hydrogen injected at a nominal oxidizer-to-fuel ratio of 5:1 [1]. The design focused creating new rotating parts of the RL10-A3-3 feed system as presented in Figures 1 and 2, including full scope of rotordynamics analysis.

New Rotating Parts for RL10-A3-3 Feed System

Contact us for an AxSTREAM demonstration and attend one of our training courses to get a trial with AxSTREAM and become SoftInWay’s next success story.

References

[1]https://pslhistory.grc.nasa.gov/PSL_Assets/History/C%20Rockets/Design%20Report%20for%20RL-10-A-3-3.pdf

The Future of Nuclear Power Plants

With the blast of the French nuclear power plant a few weeks ago, safety of nuclear power plant designs has fallen under more scrutiny. Although according to sources the blast took place in the turbine hall and no nuclear leak was found, this event has brought more attention to improved design and operation standards.

Following the incident earlier this month Toshiba, a Japanese multinational company, announced the resignation of its chairman following a $6.3 billion loss in their nuclear sector –also withdrawing from the nuclear business. The two back to back events have highlighted the main two problems of nuclear power: high cost and environmental/safety concerns. Said to be a green technology, nuclear power raises concerns with potential nuclear meltdown and risk of safety from toxic waste, accompanying the fact that building a new plant cost around $5,000.00 per kilowatt of capacity with around 6 years of lead time. Each dollar invested on a nuclear power plant has about 2-10 less carbon savings and is 20-40 times slower compared to other alternatives. Yes, evidently nuclear power is found to be very reliable, enabling consistent baseload energy production at any time of day and night. Though, it has been questioned whether this reliability is worth the high cost of nuclear production, in fact all nuclear plants are still operating with 100% subsidized.

Transatomic power, a company started by two MIT PhD candidates, came up with a new approach to safer and cheaper nuclear reactors. Utilizing molten salt reactors, which has not really been used commercially and so far is only existed in paper, the technology is promised to cut initial cost and increase safety. Today’s conventional nuclear reactor is cooled by water, due to the high operating temperature, failure to do so will open the risk of radiation leak as well as hydrogen explosion. The high boiling point of salt helps solve some of the problems associated with the technology. The new design also incorporates ways of producing faster neutrons, enabling the reactor to burn most waste materials, thus keep waste to minimum. The ability of this smaller unit to be made in a factory (and not onsite) as well as cost reduction on the safety side makes this attractive economically as well. That being said, this generation 4 nuclear reactor is still in design and development will take years and high capital cost.

References:

https://www.nytimes.com/2017/02/14/business/toshiba-chairman-nuclear-loss.html?_r=0

http://fortune.com/2017/02/16/toshiba-nuclear-power-plants/

Turbomachinery Rotor Dynamics – Latest Modelling & Simulation CAE for Design and Analysis, using SoftInWay’s Integrated Tool

The Rotor-Dynamic System of a typical turbomachine consists of rotors, bearings and support structures. The aim of the designer undertaking analysis is to understand the dynamics of the rotating component and its implication. Today the industry practices and specifications rely heavily on the accuracy of rotor-dynamic simulated predictions to progressively reduce empirical iterations and save valuable time (as repeated direct measurements are always not feasible). Be it a centrifugal pump or compressor, steam or gas turbine, motor or generator, the lateral rotor-dynamic behavior is the most critical aspect in determining the reliability and operability. Such analytical predictions are often tackled using computer models and accuracy in representing the physical system is of paramount importance.  Prior to analysis it is necessary to create a detailed model, and hence element such as cylindrical, conical , inner bore fillet/chamfer, groove/jut, disk / blade root and shroud, copy/mirror option, bearing element and position definition are built. Stations (rather than nodes) having six DOF (degrees of freedom) are used to model rotor-dynamic systems. Typically for lateral critical analysis each station has four DOF, two each translational and rotational (angular). Decoupled analysis followed by coupled lateral, torsional and axial vibration makes prediction realistic and comprehensive. The mathematical model has four essential components, i.e. rotating shafts with distributed mass and elasticity, disks, bearing and inevitable synchronous imbalance excitation. Components such as impellers, wheels, collars, balance rings, couplings – short axial length and large diameter either keyed or integral on shaft are best modelled as lumped mass. Bearings, dampers, seals, supports, and fluid-induced forces can be simulated with their respective characteristics. Bearing forces are linearized using dynamic stiffness and damping coefficients and together with foundation complete the bearing model. The governing equation of motion for MDOF system require  determination of roots (Eigenvalue) and Eigen Vectors. Lateral analyses – such as static deflection and bearing loads, critical speed analysis, critical speed map, unbalance response analysis, whirl speed and stability analysis, torsional modal and time transient analyses are then performed.Aashish blog 1 image

Indeed rotor-dynamic modelling with practical experience and engineering judgement improves accuracy.  Its ability to model complexities such as flexible supports, foundation, rotor seal interaction, and instabilities while making the CAE model comprehensive, user friendly, and fully integrated with other well proven and mature suites for flow path and  blade design makes SofInWay’s software platform unique.

Integrated Approach within AxSTREAM® Platform

Suited to meet the diverse needs of designers, analysts and users of turbomachinery, SoftInWay’s webinar in collaboration with Test Devices Inc scheduled on Mar 2, 2017, 10 AM EST helps you to understand HOW rather than why. It will  cover rotor and bearing types, principles of an integrated approach to rotor-dynamics system design and simulation, purpose and procedures for rotor-dynamic and structural analysis. The software demonstration will include modelling features, import/export options, lateral and torsional capabilities, bearing analyses and modelling capabilities, and case studies. It will also briefly highlight fundamentals such as characteristic influence of shaft rotational on natural frequencies in comparison to classical natural frequencies and modes in structures, gyroscopic effects, rigid vs flexible rotors, free and forced vibration as applicable to turbomachine rotors, impact of bearing characteristics and concept of cross coupling, modes, Campbell diagram, stead and transient response, instabilities, condition monitoring, testing, evaluation and acceptance criteria (log dec and margins) and much more. Testing methods covered by Tech Devices Inc. highlight testing procedures and methods for design validation and building confidence that the design exceeds expectations.

 

The Challenges for Turbomachinery Startups

Globalization, increase in defense expenditure by different countries, economic development and growth of air traffic has all resulted in the need for various turbomachinery components. The turbomachinery industry as a whole has seen extensive growth over the last few years and is poised to grow further in the next few decades. The development of Turbomachinery components namely turbines, compressors, pumps, turbopumps, turbochargers are a niche field with the technology limited to just a handful of major players. The recent interest in Un-manned aerial vehicles for military and defense applications, the environmental concerns and rising fuel cost has paved the way for development of small gas turbines and turbomachinery for waste heat recovery systems. Since the market is large and capital cost is not very high due to the equipment size, there is greater interest among technologist and entrepreneurs to step into the business of turbomachinery.photographer-and-plater_1160-733

However, turbomachinery design is still a niche field and require technical expertise, which is again limited. Naturally to get into the league of turbomachinery developers and to compete with established players many startups look at the short cuts which usually is copying of designs from existing players, scaling competitors’ products etc. Though this can help them in getting a product into the market sooner with lower cost on design, this is quite dangerous to the industry as copying designs, scaling etc. results in poor products with performance not being competitive which will lead to the premature killing of the product as a whole. For any startups in turbomachinery, they need to have state of the art product, which can compete with existing players who are well established in the industry.

Developing a new product requires not only huge investments but also time to develop prototype, test, collect feedback etc. This is a major challenge which every turbomachinery startups face, however existing players are blessed with the extensive test and operational data available with them, which is generated over the years. To overcome this challenge the best alternative for turbomachinery startup is to connect with a design house like SoftInWay Inc. who can collaborate and support in developing the product from concept to manufacturing. SoftInWay Inc. in the last decade has helped many companies to develop state of the art turbomachinery through the engineering consultancy, training and technology transfer.

If you would like to know how SoftInWay Inc. can partner with you to realize your dreams, please contact info@softinway.com / India@softinway.com / Switzerland@softinway.com / Ukraine@softinway.com

Double Flash System Application in Geothermal Power

Geothermal power market has been showing sustainable growth globally, with many installations in developing countries. As people turn to renewable sources while demand for energy is experiencing rapid growth, geothermal is found to be a reliable energy source and current development is calculated to increase global capacity by over 25%. Geothermal power plants can usually be divided into several types of cycles, including binary, flash, double flash and more. Flash power plants are found to be the most common forms of geothermal power plant and specifically, we are going to talk about the double flash cycle.

A flash system produces high pressure dry steam to move the turbine, generating electricity after going through a flash separator. A double flash system uses two flashes separating systems in order to generate more steam from the geothermal liquid and increase cycle output. The cycle starts with high temperature fluid extracted from a geothermal source to a high pressure separator (HPS) for flashing. The HPS produces a saturated steam that enters the high pressure turbine and the remaining brine is directed into a secondary low pressure separator (LPS). Reducing the flashing pressure increases the mixture quality in the LPS, which results in higher steam production. Low pressure saturated steam is mixed with the steam flow exhausted from the high pressure turbine and the resulting steam flow is directed to the low pressure turbine and produces more electricity. Steam that is exhausted from the low pressure turbine will then be compressed and injected back to the ground. In a flash system, separator pressure has a significant effect on the amount of power generated from the system – and the flashing pressures also influence double flash cycle significantly. In order to optimize one design, the value of parameters versus cost of operations should be taken into account.

A double flash system is able to achieve better energy utilization than a single flash cycle, which means that the application has a higher efficiency. At the same geofluid conditions, double flash systems are able to give you a higher capacity. That being said, since this is a more complex system the application of such technology would not be economically feasible for some applications.

References:

http://www.doiserbia.nb.rs/img/doi/0354-9836/2016%20OnLine-First/0354-98361600074L.pdf

https://www.geothermal-energy.org/pdf/IGAstandard/SGW/2013/Pambudi.pdf

https://www.geothermal-energy.org/pdf/IGAstandard/WGC/2010/2612.pdf

The Feasibility of Bringing Back Coal

Power generation and energy sectors happen to be very politically volatile. With our new leader in the USA taking control, we are expecting a shift in technology trends. The topic of bringing more coal fired power plants back to the equation has been brought up quite often, coming after Trump’s skeptical statement regarding global warming and climate-change. To follow that statement, Donald Trump pledged to lift restriction on US agencies funding new coal plants in other parts of the world. In addition, Australia’s minister also has been arguing regarding adding new coal power plants into the mix. As world’s largest coal exporter, it should economically make sense for Australia to forego with the plan.

There are three major categories that typically determine whether a technology would be suitable to be implemented: cost to public, reliability of supply and environmental impact. The old coal power generator is found to be less reliable as well as less environmentally friendly. Consequently, a new technology must be used to provide “cleaner” energy from coal. Southern Company has become one of the first private sectors using new technology to produce energy from coal.  The technology is said to be generating electricity while at the same time capturing carbon dioxide from coal. Maybe if this technology is implemented, we will come back to coal.Power Plant

That being said, what is clean coal technology? Coal is currently known to be the biggest enemy to environment, however clean coal seeks to reduce emission. Before burning the coal, some technology purifies the coal to remove unwanted minerals. Then control the burning to minimize the harsh emission, installing wet scrubbers or desulfurization systems, electrostatic precipitators and Low NOx burners among many other processes.

There are two main problems with clean coal: unproven and expensive. Operating cost for Southern company quadrupled to about $1 billion from the original estimate according to a report. Not only that, the initial cost of investment of this power plant is also two times over budget. Not to say that the same case would be applied to other clean coal power plant, but at the time being, installation of this technology is expensive. Until this could be studied further, seems like cost would be hovering well above standard normal. Another downside is that coal plants are inflexible. While they do give a very constant supply of power, they can’t easily increase or decrease supply –and when they do, it’s economically unreliable. This doesn’t eliminate the chances of coal making a comeback in the future, however, for the time being coming back to coal seems unreasonable since the renewables seems to be making a very positive growth towards the future.

References: 

https://www.theguardian.com/commentisfree/2017/jan/24/no-new-coal-is-not-feasible-on-price-reliability-or-emissions

http://www.bloombergquint.com/technology/2017/01/27/after-2-6-billion-writedown-clean-coal-giant-set-for-opening

Surge Conditions of Centrifugal and Axial Compressors

Centrifugal and axial compressors must operate within certain parameters dictated by both the constraints of the given application as well as a number of mechanical factors.  In general, integrated control systems allow compressors to navigate dynamically within their stable operating range.   Typical operating ranges for compressors are represented on a plot of volumetric flow rate versus compression ratio.  Compressors have a wide number of applications, from household vacuum cleaners to large 500 MW gas turbine units.  Compression ratios found in refrigeration applications are typically around 10:1, while in air conditioners they are usually between 3:1 and 4:1.  Of course, multiple compressors can be arranged in series to increase the ratio dramatically to upwards of 40:1 in gas turbine engines.  While compressors in different applications range dramatically in their pressure ratios, similar incidents require engineers to carefully evaluate what is the proper operating range for the particular compressor design.

Dan Post 10
Figure 1- Typical Performance Map Limits – Compressor Ratio (Rc) vs. Volumetric Flow Rate (Qs)

For intensive applications of centrifugal and axial compressors, the phenomenon of surge resides as one of the limiting boundary conditions for the operation of the turbomachine. Essentially, surge is regarded as the phenomena when the energy contained in the gas being compressed exceeds the energy imparted by the rotating blades of the compressor. As a result of the energetic gas overcoming the backpressure, a rapid flow reversal will occur as the gas expands back through the compressor. Once this gas expands back through to the suction of the compressor, the operation of the compressor returns back to normal. However, if preventative measures are not taken by the appropriate controls system or any implemented mechanical interruptions, the compressor will return to a state of surge. This cyclic event is referred to as surge cycling and can result in serious damage to the rotor seals, rotor bearings, driver mechanisms, and overall cycle operation.

Because of surge and other phenomena such as stall, engineers must embed proper control systems that effectively handle different off-design conditions seen in particular compressor arrangements. Depending on the application, certain compressors will rarely operate away from their design point, and such control systems are not necessary. However, in advanced applications such as large gas turbine unit compressors, controls systems allow the compressor to navigate within a range between the choke, stall, minimum speed, and maximum speed limits. The chart seen in Figure 1 describes the operating range of a compressor using a Rc—Qs map. In many cases, an antisurge valve (ASV) working in conjunction with an antisurge PI controller will action open or closed based on varying transient conditions seen on the compressor. For design purposes, it is vital to understand compressor limits in order to properly develop or outsource a compressor based on the performance metrics needed for the application.

A Primer on Compressor Design

As technology has evolved, so has the refrigeration industry. What were once holes in the ground filled with ice and snow have transformed into the modern high-efficiency compression machinery we have become so familiar with today. However, as common as these devices have become, the design process remains a challenge. This is where a combination of scientific knowledge, experience and creative initiative comes into play. While there are, of course, several variations in terms of the application of each design step, the guidelines presented here could be applied not only to refrigeration compressors, but also to compressors used in many other processes and industries.

There are a number of steps to consider throughout the compressor design process, and each step has to relate back to the original design concept. Experience has shown that having a starting concept and an end goal in mind is imperative. Namely, before you can begin the process, you need to know where you are starting and where you want to end up. With this in mind, before we can even get started with preliminary design, blade profiling and analysis of computational fluid dynamics (CFD), it is important to take out a piece of paper and start brainstorming. Consideration of the different refrigeration technologies (cycles), is always a great place to start, so we can ensure we will design the best compressor for the application. The cycle will directly impact the rest of the compressor design decisions, so this is not a step that can be bypassed. This article’s discussion begins with cyclic compression.

Cycle design and optimization 

Cyclic refrigeration units are used for reducing and maintaining the temperature of a body below the general temperature of its surroundings. In a refrigerator, heat is pumped from a low-temperature heat source to high-temperature surroundings. According to the second law of thermodynamics, this process can only be performed with some aid of external work. The vapor-compression refrigeration cycle (which is a type of cyclic refrigeration) is used in most household refrigerators, as well as in many large industrial systems. The advantages of choosing this route are that the technology is mature, the costs are relatively low and the process has the capacity to be driven directly with electrical or mechanical energy.

For initial consideration of the compressor, we must perform calculations to determine the operating conditions and system function, the type of working fluids and the system size and requirements, as well as the economic analysis of the whole cycle. By completing these steps prior to beginning the preliminary design, we are establishing boundary conditions, performance requirements and geometric constraints for the compressor before committing to a design that may or may not be realistic.

FIGURE 1. While there are numerous compressor types frequently used in the process industries, centrifugal compressors are among the most ubiquitous
FIGURE 1. While there are numerous compressor types frequently used in the process industries, centrifugal compressors are among the most ubiquitous

Next, we must determine the type of compressor we want to use for the refrigeration cycle. For the purposes of this article, we will focus on the centrifugal configuration (Figure 1). However, many other options exist, including reciprocating, scroll, helical and rotary compressors.

To elaborate on the output from cycle calculations, we also need to know several specific data points for the proposed compressor, including the required pressure ratio, discharge pressure, volumetric flowrate of the refrigerant, application requirements and the assumed required economics. At this stage, the procedure feels much more like science than art.

Next, the designers need to decide whether they want to design a compressor using an existing similar design (requiring them to scale up or down and optimize the design) or to start from scratch with something completely new. For the purposes of this article, let’s focus on a new design. Now that these decisions have been made, let’s revisit that piece of paper from the brainstorming session and launch into the design process to make the project a reality.

*  This is an excerpt from an article written by Valentine Moroz, SoftInWay’s COO, which appeared in Chemical Engineering Magazine. To read the rest of the article, please follow the link