APPLICATION OF DIGITAL TWIN CONCEPT FOR SUPERCRITICAL CO2 OFF-DESIGN PERFORMANCE AND OPERATION ANALYSES

This is an excerpt from a technical paper, presented at the ASME Turbo Expo 2020 online conference and written by Leonid Moroz, Maksym Burlaka, Tishun Zhang, and Olga Altukhova. Follow the link at the end of the post to read the full study! 

Introduction

The attempts to simulate transient and steady-state sCO2 cycles off-design performance were performed by numerous authors [1], [2], [3], [4], and [5]. Some of them studied the dynamic behavior of regulators, some studied different control strategies or off-design behavior in different scenarios, which definitely has certain utility in the development of the reliable technology of sCO2 cycle simulation. Nevertheless, they used rather simplified models of components, especially turbomachinery and heat exchangers, which are of crucial importance to correctly simulate cycle performance.

The authors of this paper attempted to apply the digital twin concept to a simulation of off-design and part-load modes of the sCO2 bottoming cycle considering real machine characteristics and performance, which nobody tried to apply in this area.

On IGTC Japan 2015, SoftInWay Inc. has published a paper “Evaluation of Gas Turbine Exhaust Heat Recovery Utilizing Composite Supercritical CO2 Cycle”. The paper considered combinations of different bottoming sCO2 cycles for a specific middle power gas turbine. It mainly studied the advantages of different types of sCO2 cycles to increase the power production utilizing GTU waste heat.

The present paper is a further study based on that so the Cycle 2 [6] from that previous paper was selected as the sCO2 bottoming PGU layout in the present paper for subsequent analysis. The cycle is a combination of recompression cycle and simple cycle which offers 16.13 MW as output. GE LM6000-PH DLE gas turbine, was used as the heat source for bottoming PGU. According to GE official brochure [7], the GE LM6000 offers 40 MW to over 50 MW with up to 42% efficiency and 99% fleet reliability in a flexible, compact package design for utility, industrial and oil and gas applications. GE LM6000-PH DLE provides 53.26 MW output with exhaust temperature at 471 ℃ and exhaust flow at 138.8 kg/s. (This information came from GE products specification from 2015. It appears that GE continuously modifying the parameters of its turbines along with the naming of different modifications. Therefore, today’s parameters and configuration names might be slightly different comparing to 2015) Exhaust gas pressure was assumed to be 0.15 MPa. These parameters were taken to analyze the bottoming PGU and are presented below in TABLE 1.

SELECTED SET OF GE LM6000-PH DLE PARAMETERS
TABLE 1: SELECTED SET OF GE LM6000-PH DLE PARAMETERS

The digital twin (DT) concept is the developing technology that allows simulation of object behavior during its life cycle or in specified time due to changing ambient conditions, for example. The DT is applicable for performance tuning, digital machine building, healthcare, smart cities, etc [8] that allows decreasing the time and costs of development and optimize the object on the developing stage. GE has raised DT concepts for power plants to continually improves its ability to model and track the state of the plants [9].

In the context of this paper, DT is a simulation system comprised of physicist-based models organized in a special algorithmic structure that allows simulating the behavior of sCO2 PGU under alternating ambient conditions and grid demands.

The DT in this study was created utilizing AxSTREAM® Platform, which includes multiple software tools. The following software tools were utilized in this study: AxCYCLE™ was used to perform cycle thermodynamic calculation; solution generator in AxSTREAM® helped with finding possible machine geometry with given boundary conditions when performing preliminary design for compressors and turbines at design point; parameters and performance of turbomachinery including mass flow rate, pressure, power, efficiencies, etc. were calculated by Meanline/Streamline solver in AxSTREAM® for design and off-design conditions; AxSTREAM NET™ is a 1D system modeling solver and it was introduced here to simulate performance of heat exchangers (HEX) and pressure drop in the pipes involved in the cycle; AxSTREAM ION™ was used to integrate all modules and tools together in one simulation system. Read More

Hydrogen Energy: History, Applications, and Future Developments

A Brief History Of The Discovery Of Hydrogen 

The release of combustible gas during the interaction of metals and acids was observed as early as the 16th century. That is, during the formation of chemistry as a science. The famous English scientist Henry Cavendish had studied the substance since 1766, and gave it the name “combustible air”. When burned, this gas produced water. Unfortunately, the scientist’s adherence to the theory of phlogiston (the theory that suggested the existence of a fire-type element in materials) prevented him from coming to the correct conclusions.

Henry Cavendish (1731 – 1810)
Henry Cavendish (1731 – 1810) Source: https://www.butterflyfields.com/henry-cavendish-contributions-in-science/

In 1783 the French chemist and naturalist A. Lavoisier, together with the engineer J. Meunier, and with the help of special gas meters carried out the synthesis of water, and then its analysis by means of decomposition of water vapor with hot iron. Thus, scientists were able to come to the correct conclusions, and dismantle the phlogiston theory. They found that “combustible air” is not only a part of water but can also be obtained from it. In 1787, Lavoisier put forward the assumption that the gas under study is a simple substance and, accordingly, belongs to the number of primary chemical elements. He named it hydrogene (from the Greek words hydor – water + gennao – I give birth), that is, “giving birth to water”.

Antoine-Laurent
Antoine-Laurent
de Lavoisier (1743 – 1794). Source: https://educalingo.com/en/dic-en/lavoisier

A Little About The Properties Of Hydrogen 

In a free state and under normal conditions, hydrogen is a gas, and is colorless, odorless and tasteless. Hydrogen has almost 14.5 times mass less than air. It usually exists in combination with other elements, such as oxygen in water, carbon in methane, and organic compounds. Because hydrogen is chemically extremely active, it is rarely present as an unbound element. Read More

The Top 5 Coolest Turbomachinery Inventions (According to Us!)

As the leading authority on turbomachinery design, redesign, analysis, and optimization, we work with a wide range of machines from small water pumps and blowers to massive steam turbines, jet engines, and liquid rocket engines. While all of these machines have a certain “cool factor” to them since, after all, we’ve proven they make the world go round; some machines take coolness to the next level. Today, we’re taking a look at 5 of the coolest specific turbomachinery inventions, according to us.

Number 5 – The Arabelle Turbines

Starting with number 5, we have a pair of steam turbines, each known as “Arabelle”. You may be asking yourself “So what, steam turbines are everywhere.” You would be right, but these two have a bit of a size advantage. In fact, they’re the largest steam turbines in the world.

Designed and built by General Electric in France, these turbines are, according to GE, “longer than an Airbus 380 and taller than the average man. A pair of them, each capable of producing 1770 megawatts, is now set to cross the English Channel to provide energy for generations” (1).

They’ll be installed in a new nuclear power plant known as Hinkley Point C in Somerset. Their 1.7 gigawatt output will be enough to power 6 million homes, which is 7% of the UK’s power consumption. (1) The output and sheer size of the turbines aren’t the only large number either, the project costs nearly 24 billion US dollars.

A CAD model of the Arabelle steam turbines, image courtesy of General Electric.
A CAD model of the Arabelle steam turbines, image courtesy of General Electric.

The sheer size and performance figures have earned GE a place on our list of top 5 cool turbomachines!

Number 4 – The Garrett 3571VA Variable Geometry Turbocharger

This is one only gearheads and diesel-fans may recognize, but even then, it’s an obscure one. This Garrett turbocharger was a game changer for diesel engines used in light and medium duty trucks, specifically the Navistar International VT365, also known as the Ford 6.0 Liter Powerstroke engine. Read More

Gas Turbine Cooling System Design Procedures

Introduction

State-of-the-art gas turbine engines usually work under extremely high temperatures. This is directly related to efficiency of the gas turbines – in order to receive the maximum thermodynamics value, it is necessary to increase the gas temperature after the combustion chamber. Engine temperature can be higher than blades’ metal temp up to 500-600 K. Blades, nozzles, and the GT details are manufactured with special heat-resistant steels and in some cases, they require a special coating. That allows them to resist turning into liquid metal under these working temperatures like the T-1000 did in the “Terminator 2: Judgment Day” movie even under high temperatures :).

Picture 1 – T-1000 from Terminator 2
Picture 1 – T-1000 from Terminator 2. Source

However, metal has the property of “creep” – this is the tendency of hard metal to move slowly or permanently deform under stress. This occurs as a result of prolonged exposure to high stresses above the yield point, especially when exposed to high temperatures. Obviously, the solution to this problem is a cooling system for heat-stressed parts, which has allowed the gas temperature to increase by 600 K compared with uncooled machines. Since the gas turbines usually work with air, the simplest way to cool the system is by using this. Typically, the air exhausts to different parts of the compressors and is supplied to the cooling paths and blades which influence the thermodynamics efficiency of the gas turbine engine. Thus, it is crucial to ensure enough cooling to remove the heat on the one hand and on the other hand – to receive the lowest amount of air which requires cooling. Read More

Performance Testing of Axial Compressors

Performance testing is a key part of the design and development process of advanced axial compressors.  These are widely used in the modern world and can be found in nearly every industry, and include the core compressor for aeropropulsion turbofan engines, as well as aeroderivative gas turbine engines for power generation.  An example of this are the turbine engines shown in Figure 1 and 2, which feature an industrial gas turbine and a high bypass ratio turbofan engine with a multistage high-pressure core compressor. The development time of these machines can involve numerous expensive design-build-test iterations before they can become an efficient and competitive product. This places a great importance on the accuracy of the data taken during the performance tests during the development of the compressor since the test data taken is often used to anchor the loss models within the design tools. Modern axial compressors typically have high aerodynamic loadings per stage for improved system efficiency and requires precise aerodynamic matching of the stages to achieve the required pressure ratio with high efficiency. Variable geometry inlet guide vanes and stators in the first few stages are typically required to provide acceptable operability while maintaining high efficiency and adequate stall margin.

Industrial gas turbine for power generation.
Figure 1. Industrial gas turbine for power generation. Source
Figure 2. Turbofan engine for aeropropulsion.
Figure 2. Turbofan engine for aeropropulsion. Source

Performance Testing of Axial Compressors

Axial compressors all undergo a thorough design and development phase in which performance testing is vital to their ultimate success as a product. Performance testing during the development phase of these high-power density machines can ensure that the design meets the specified requirements or can identify a component within the turbomachine which falls short of its expected performance, and may require further development, and possible redesign. Performance testing can also ensure that the unit can meet all the conditions specified and not merely the guaranteed condition. Aerodynamic performance testing multistage axial compressors during the early part of development is often done in phases. The development test program is planned and executed with a design of experiments approach and includes varying the air flow and shaft rotational speed as well as the variable geometry schedule in order to fully characterize the compressor. In the first phase, the front block of the compressor is built and tested at corrected (referenced) air flow rate, inlet pressure, temperature and shaft rotational speed. Instrumentation includes utilizing traditional rakes and surveys at the exit, to obtain spanwise distributions of pressure, temperature, and flow angles. Testing in phases is typically done for two reasons. Read More

Vertical Pumps: What Are They, Where Are They Used and How To Design Them?

Introduction

Vertical pump designs are similar to conventional pumps, with some unique differences in their applications.  Pumps use centrifugal force to convert mechanical energy into kinetic energy and increase the pressure of the liquid. Vertical pumps move liquids in the vertical direction upwards through a pipe. All pumps pressurize liquids, which are mostly incompressible. Unlike compressible gases, it is impossible to compress liquids, therefore the volumetric flow rate can not be reduced. Therefore liquids are transported by pumping and the inlet volume flow rate is equal to the exit volume flow rate.

Vertical centrifugal pumps are simply designed machines, and have similarities to their horizontal counterparts. A casing called a volute contains an impeller mounted perpendicularly on an upright (vertical) rotating shaft. The electric drive motor uses its mechanical energy to turn the pump impeller with blades, and imparts kinetic energy to the liquid as it begins to rotate. These pumps can be single stage or multistage with several in-line stages mounted in series.

The centrifugal force through the impeller rotor causes the liquid and any particulates within the liquid to move radially outward, away from the impeller center of rotation at high tangential velocity. The swirling flow at the exit of the impeller is then channeled into a diffusion system which can be a volute or collector, which diffuses the high velocity flow and converts the velocity into high pressure. In vertical pumps, the high exit pressure enables the liquid to be pumped to high vertical locations. Thus the pump exit pressure force is utilized to lift the liquid to high levels, and usually at high residual pressure even at the pipe discharge.

Applications of Vertical Pumps

An “in line” vertical pump is illustrated in Figure 1 (Reference 1), where the flow enters horizontally and exits horizontally and can be mounted such that the center line of the inlet and discharge pipes are in line with each other.  This is a centrifugal pump with a tangential scroll at the inlet that redirects the flow by 90 degrees and distributes it circumferentially and in the axial direction into the impeller eye. The discharge is a simple volute that collects the tangential flow from the impeller exit, and redirects it into the radial direction.

in line Pump - Figure 1
An “in line” Vertical Pump. Source

Figure 2 shows a vertical pump that has a vertical intake that directs the flow straight into the eye of the pump rotor. At the impeller exit, the tangential flow is collected by a volute and diffused in an exit cone. An elbow after the exit cone redirects the flow into the vertical direction to lift the liquid to the desired altitude. (Reference 2). Read More

Charles Parsons and His Contribution to Engineering

Welcome to this special edition of the SoftInWay blog! While we at SoftInWay are known for helpful articles about designing various machines, retrofitting, and rotordynamics, we believe it is also important to examine the lives of some of the men and women behind these great machines.

The compound steam turbine is one of the greatest inventions, not just in turbomachinery but around the world. Once it was introduced to the marine industry, the steam turbine exploded in popularity as a means of allowing ships to travel faster and farther than ever before. It would go on to become a critical part in the naval arms race that preceded the First World War. The steam turbine not only revolutionized marine and naval propulsion, it became one of the best ways to generate electricity. After its inception, the steam turbine became one of the best ways to reliably generate power on a large scale, and make electricity the regular utility that it is today. But who invented the modern steam turbine?

Sir Charles Parsons
Image courtesy of Wikimedia

Sir Charles Algernon Parsons, (1854 – 1931), is the inventor of the modern steam turbine. The work he undertook in his life had a massive impact on the world, continuing the legacy of James Watt by bringing steam technology into the modern era. Born on June 13th 1854 into an Anglo-Irish family, Sir Charles Parsons was born into a well-respected family with roots in County Offaly, Ireland. In fact the town now known as Birr was then known as Parsonstown, from the early 1600’s through to 1899. Parsons was the sixth son of the 3rd Earl of Rosse, and had a family lineage that had made great strides in the areas of military, political, and physical science. The family’s castle in Birr, which is still owned by the Parsons family and is the permanent residence of the 7th Earl of Rosse, was a rendezvous for men of science during the childhood of Sir Charles. Suffice it to say, there was no better place for a future-engineer to grow up. He alongside his brothers would receive private tutorship from Sir Robert Ball and Dr Johnstone Stoney, famous Irish astronomer and physicist, respectively. Read More

Basics of Steam Turbine Design

Steam turbines account for more than half of the world’s electricity production in power plants around the world and will continue to be the dominant force in electricity power generation for the foreseeable future. The enhancement of steam turbine efficiency is increasingly important as the urgency to reduce CO2 emissions into the atmosphere is a problem at the forefront of power production. Increasing efficiency in steam turbines, and other components of power plants, will help meet the growing demands for electricity worldwide while reducing harmful greenhouse emissions.

Figure 1 Steam Turbine with Long Last-Stage Blades
Figure 1. Steam Turbine with Long Last-Stage Blades. Source

Steam turbines are used in coal-fired, nuclear, geothermal, natural gas-fired, and solar thermal power plants. Also steam turbines are increasingly needed to stabilize fluctuating power demands from solar and wind power stations as renewable energy sources grow worldwide. The current emphasis on steam turbine development is for increasing efficiency, mainly by increasing steam turbine capacity, as well as increasing operational availability, which translates to rapid start up and shut down procedures.  Read More

Choosing the Right Turbomachinery Component

Traditionally the engineering process starts with Front End Engineering Design (FEED) which is essentially the conceptual design to realize the feasibility of the project and to get an estimate of the investments required. This step is also a precursor to defining the scope for Engineering Procurement and Construction Activities (EPC). Choosing the right EPC consultant is crucial as this shapes the final selection of the equipment in the plant including turbomachinery.

Large thermal power machine

Choosing the right component for the right application is not an easy task. Too many times, one ends up choosing a component that is not the best choice by far. This is quite true when we look at component selections in the process industries compared to those in a power plant where the operating conditions are more or less constant. This improper selection of components is due to multiple reasons such as: insufficient research and studies; limitation of time, resources, budget etc. Read More

Unsteady Flow Simulation in Hydraulic Systems

[:en]An unsteady flow is one where the parameters change with respect to time. In general, any liquid flow is unsteady. But if a hydraulic system is working at constant boundary conditions, then the parameters of the fluid flow change slowly; thus this flow is considered steady. At the same time, if the parameters of the fluid flow oscillate over time relative to some constant value, then it called quasi-steady flow 1.

In practice, most fluid flows are steady or quasi-steady. Examples of the three flows are presented in Figure 1. Steady flow is presented by a simple pipe. The quasi-steady flow is represented by a sharpened edge channel. The unsteady flow is presented by an outflow from a reservoir.

Figure 1 - Different Types of Fluid Flow
Figure 1 – Different Types of Fluid Flow
Different Cases of Unsteady Flow

During operations, hydraulic systems act for long intervals at steady conditions which are called operating modes. Change between two different operating modes occurs over a short time interval (called a transient mode). If any hydraulic system works more than 95% of the time at these operating modes though, why is the unsteady flow is so important? Because the loads depend on time intervals. If the load is less, then the maximum system pressure is higher. Read More