An Integrated Design System for Gas Turbines

In my earlier blog titled “Optimizing the Cooling Holes in Gas Turbine Blades, I wrote about how optimizing the cooling flow through turbine blades is important considering both performance and reliability. The design process differs between different designers and depends on a number of factors including expertise, availability of design tools, statistical or empirical data, corporate procedure and so on. That being said, the ultimate goal is to provide a design which is considered optimal. Though the designer is often satisfied on completion of a design and when the machine is put into operation, there is always the feeling  that we could have done better if there were more resources and time. Integrating the entire design process with multidisciplinary optimization provides a great opportunity to arrive at the optimal design rapidly with less manual intervention and effort.

axstream
Figure 1: Integrated AxSTREAM® Platform

Figure 1 shows the integrated approach to design a cooled gas turbine using multidisciplinary tools in an optimization environment. The flow path design starts from the conceptual stage to arrive at the optimal flow path geometry, accounting for a preliminary estimate of the cooling flow. Detailed design requires accurate estimation of the cooling flow considering the actual geometries and the material temperatures. Using ID head and flow simulation tools such as AxSTREAM® NET, the cooling flow can be modelled to produce the optimal geometric dimension in an iterative process to further fine tune the flow path performance. To meet the performance and reliability objectives, multidisciplinary optimization can be achieved via the integrated modules. The process when further integrated with a CAD package can help in generating the optimized geometry that can be taken for prototype development.

To learn more about how the AxSTREAM® platform can help you obtain an optimized gas turbine design quickly and accurately, please contact sales@softinway.com; info@softinway.com.

Fatigue in Turbomachinery

This post is based on DeLuca’s publication about fatigue phenomena in gas turbines [1]. One of the most significant characteristics of a gas turbine is its durability. Especially for the aerospace industry where engines must meet not only propulsion but also safety requirements, the failure of gas turbine blades is a major concern. The “cyclic” loading of the components associated with generator excursions is one of the principal sources of degradation in turbomachinery. In addition, fatigue can be caused during the manufacturing of the components. There are three commonly recognized forms of fatigue: high cycle fatigue (HCF), low cycle fatigue (LCF) and thermal mechanical fatigue (TMF).The principal distinction between HCF and LCF is the region of the stress strain curve (Figure 1) where the repetitive application of the load (and resultant deformation or strain) is taking place.

gas-turbine-alloy
Figure 1 – The stress vs. strain curve for a typical gas turbine alloy

HCF is metal fatigue that results from cracking or fracturing generally characterized by the failure of small cracks at stress levels substantially lower than stresses associated with steady loading. HCF occurs as a result from a combination of steady stress, vibratory stress and material imperfections [2].  It is initiated by the formation of a small, often microscopic, crack. HCF is characterized by low amplitude high frequency elastic strains. An example of this would be an aerofoil subjected to repeated bending. One source of this bending occurs as a compressor or turbine blade passes behind a stator vane. When the blade emerges into the gas path it is bent by high velocity gas pressure. Changes in rotor speed change the frequency of blade loading. The excitation will, at some point, match the blade’s resonant frequency which will cause the amplitude of vibration to increase significantly.

In contrast, LCF is characterized by high amplitude low frequency plastic strains. A good example of LCF damage is of the damage which is caused by local plastic strains at the attachment surfaces between a turbine blade and the turbine disk. Most turbine blades have a variety of features like holes, interior passages, curves and notches. These features raise the local stress level to the point where plastic strains occur. Turbine blades and vanes usually have a configuration at the base referred to as a dovetail or fir tree.
In the case of thermal mechanical fatigue (present in turbine blades, vanes and other hot section components) large temperature changes result in significant thermal expansion and contraction and therefore significant strain excursions. These strains are reinforced or countered by mechanical strains associated with centrifugal loads as the engine speed changes. The combination of these events causes material degradation due to TMF.

As you can see, it is important to take into account stresses on gas turbine blades in order to determine the viability of the component. AxCFD and AxSTRESS are both vital tools that can help you quantify the stresses on your blades and make the correct decision for the choice of materials and operation conditions of the machine.

Reference:

[1] D.P.DeLuca, “Understanding fatigue”, United Technologies Pratt & Whitney;
[2] Sanford Fleeter, Chenn Zhou, Elias N. Houstin, John R. Rice, “Fatigue life prediction of turbomachine blading”, Purdue University.

Component Matching of Industrial Gas Turbines

An important first step in understanding the gas turbine design process is the knowledge of how individual components act given their particular boundary conditions. However, in order to effectively leverage these individual design processes, a basic knowledge of how these components interact with each other is essential to the overall performance of a gas turbine unit. The power and efficiency outputs of a gas turbine are the result of a complex interaction between different turbomachines and a combustion system. Therefore, performance metrics for a gas turbine are not only based on the respective performances of each turbine, compressor, and combustion system, but also on their interactions. The concept of component matching becomes crucial in understanding how to deal with these systems simultaneously.

two-shaft-gas-turbine
Figure 2 – Simplified Two-Shaft Gas Turbine Arrangement Modeled in AxCYCLE

In general, gas turbines for industrial applications consist of a compressor, a power turbine, and a gas generator turbine designed into one of two arrangements. The first arrangement invokes the use of the gas generator turbine to drive the air compressor, and a power turbine to load the generator on a separate shaft. This two-shaft arrangement allows the speed of the gas generator turbine to only depend on the load applied to the engine. On a single-shaft arrangement, the system obviously cannot exist at varied speeds and the power turbine coupled with the gas generator turbine would be responsible for driving both the generator and the compressor. A simplified diagram of each arrangement is displayed in Figures 1 and 2.

gas-turbine-arrangement-in-axcycle
Figure 1- Single-Shaft Gas Turbine Arrangement in AxCYCLE (Power Turbine and Gas Generator Turbine Considered One Turbine)

The efficiency of gas turbine engines can be improved substantially by increasing the firing temperature of the turbine, however, it is important to remember that the surface of the components exposed to the hot gas must remain below a safe working temperature consistent with the mechanical strength and corrosion resistance of the employed materials. Along with this firing temperature limit, obvious upper bounds exist on the speed of the gas generator due to mechanical failures and reduced lifetimes at high RPMs. These two limits help construct a particular range at which the engine can perform. There is a certain “match” temperature that controls whether the engine will be operating at its maximum gas generator speed (speed toping) or its maximum firing temperature (temperature topping). At ambient temperatures above the match temperature, the engine will operate at its max firing temperature and below its max generator speed. In a similar vein, the engine will operate at its max generator speed and below its max firing temperature at ambient conditions below the match temperature. The match temperature is the ambient temperature at which the engine reaches both limits, and it represents the highest efficiency of that engine.

axmap
Figure 3 – Off-Design Analysis for an Axial Turbine using AxSTREAM’s AxMAP Module

This match temperature is not a trivial or fixed value. Several auxiliary factors cause changes in the gas engine’s match temperature, which must be appropriately accounted for in the gas turbine design. The following factors alter the match point of any gas engine

  • – Changes in the fuel properties
  • – Reduction in compressor or turbine efficiency due to fouling, increased leakage, tip clearance, and material roughness variations
  • – Accessory loads imparted by pumps and other secondary systems
  • – Inlet and Exhaust losses

These auxiliary factors along with the routine changes described by varying ambient temperature, ambient pressure, humidity, load, and power turbine speed all contribute to the complexity involved in properly designing a gas turbine.  Correctly analyzing off-design conditions becomes an art of variable manipulation and generally requires the use of cohesive design and analysis platforms for proper evaluation.  SoftInWay’s integrated software platform allows for streamlined manipulation of your gas turbine design together with immediate off-design analysis based on any prescribed changes.  If you would like to learn about how our AxSTREAM platform assists with off-design analysis in gas turbines and other turbomachinery, please visit our software page.

 

References:

http://turbolab.tamu.edu/proc/turboproc/T29/t29pg247.pdf

Concentrated Solar Power

As time goes by, the demand for energy rises while finite resources gradually diminish. The concept of going ‘green’ or using infinite resources has become more and more common in the marketplace. With this in mind, the abundance and reliability of solar energy makes for an attractive alternative. This is because solar power is different. This statement, of course, begs the question of HOW solar power differs.

Common traditional power plants still utilizes finite fuel. Steam power plants, for example, use the fuel as an energy source to boil water which, in turn, allows the the steam to turn the turbine and drive the generator to produce electricity. Concentrated solar power systems, however, use heat energy from the sun as a heat source – which is renewable. This system works by using utilizing mirrors or mirror-like materials to concentrate energy from the sun and then takes that energy to produce steam. The system can also store the energy that is absorbed during the day, to be used at night when the sun is not present. There are a few different types of concentrated solar power systems which one can choose from.

solar
Source
  1. Parabolic Trough: This type of solar power uses a curved mirror to focus the sun’s energy to a receiver tube with high temperature heat transfer fluid which absorbs the sun’s energy and passes it through  a heat exchanger to heat water which produces steam.
  2. Compact Linear Fresnel Reflector: The working principle of this solar power type is rather similar to parabolic trough, though instead of using a curved mirror, this application utilizes flat mirrors which are more economical. These mirrors act as reflectors to focus the solar energy into the tubes to generate high-pressure steam.
  3. Power Tower: The power tower uses heliostats to track the sun movement and focus the solar energy to a receiver in the middle which is installed into an elevated tower. This application has been found to have better efficiencies compared to other types of solar power and can run on a higher temperature. The use of molten salt as a transfer fluid for the power tower applications is relatively common and helps improve efficiency.
  4. Dish-Engine: This type of solar power utilizes mirrors that are designed to be distributed over a dish surface to concentrate solar power to a receiver in the middle. The application runs on a very high temperature and uses transfer fluid with a very high boiling point to power a high requirement engine.

 

Newer applications tend to lead to the installation and use of power tower design, since this design allows technology storage implementation which can be seen as a reliable option for the future of concentrated solar power application, not to mention the economic benefit it has compared to other technology storage implementation.

References:
http://www.seia.org/policy/solar-technology/concentrating-solar-power
https://cleantechnica.com/2016/10/31/how-csp-works/

Heat Recovery Steam Generator Design

Heat recovery steam generators (HRSGs) are used in power generation to recover heat from hot flue gases (500-600 °C), usually originating from a gas turbine or diesel engine. The HRSG consists of the same heat transfer surfaces as other boilers, except for the furnace. Since no fuel is combusted in a HRSG, the HRSG have convention based evaporator surfaces, where water evaporates into steam. A HRSG can have a horizontal or vertical layout, depending on the available space. When designing a HRSG, the following issues should be considered:

hrsg-boiler
Figure 1: Schematic of a HRSG boiler
  • The pinch-point of the evaporator and the approach temperature of the economizer
  • The pressure drop of the flue gas side of the boiler
  • Optimization of the heating surfaces

The pinch-point (the smallest temperature difference between the two streams in a system of heat exchangers) is found in the evaporator, and is usually 6-10 °C, which can be seen in Figure 2. To maximize the steam power of the boiler, the pinch-point must be chosen as small as possible. The approach temperature is the temperature difference of the input temperature in the evaporator and the output of the economizer. This is often 0-5 °C. The pressure

hrsg-boiler-2
Figure 2: Example of a heat load graph for HRSG boiler

drop (usually 25-40 mbar) of the flue gas side also has an effect on the efficiency of power plant. The heat transfer of the HRSG is primarily convective. The flow velocity of the flue gas has an influence on the heat transfer coefficient. The evaporator of heat recovery boiler can be of natural or forced circulation type. The heat exchanger type of the evaporator can be any of parallel-flow, counter-flow or cross-flow. In parallel-flow arrangement the hot and cold fluids move in the same direction and in counter-flow heat exchanger fluids move in opposite direction.

 

The Significance of Quantifying Uncertainties in Turbomachinery CFD

The increased use of CFD for turbomachinery design is an outcome of the increasing accuracy thanks to high computational resources. Although the benefits of such computations are strong, the approximations and errors derived from CFD could significantly affect the prediction of crucial parameters such as flow temperature and heat transfer. This article will present the challenges related to uncertainties in turbomachinery CFD, based on “Uncertainty Quantification in Computational Fluid Dynamics and Aircraft Engines” [1]

The exact definition of boundary conditions presents one of the biggest challenges in CFD and turbomachinery given the high accuracy needed to determine the distributions of the non-uniform conditions to which turbomachinery components are subjected [2].

An additional limitation related to CFD is known as geometric uncertainty. It should be noted that, in a geometric model, a lot of details are neglected for simplicity and speed or because they are unknown, which leads to differences between the real model and the simulated one. However, even if all the details are included along with secondary air systems, they could be affected by manufacturing of the components. A study [3] quantified the change of the stage efficiency due to manufacturing errors in the rotor end-wall and to different interaction between the purge flow and the main flow.

Moreover, grid dependence analysis is a fundamental task of every numerical simulation and must be considered as such. In fact, grid spacing effects can be responsible for the poor prediction of both flow structures (i.e. von Karman Vortex Street, shock intensity and position, secondary flows…) and integral parameters such as stagnation losses. For those reasons, the effects of computational grid on the obtained results must be accounted for, when performing high-fidelity computational fluid dynamics.

Another uncertainty arises due to the improper selection between steady and unsteady simulations. For instance, when it comes to losses prediction, Pullan [4] demonstrated that a steady simulation generates 10 % less losses compared with the unsteady one. Another classical error caused by a steady simulation is the analysis of the redistribution for a hot spot in the rotor row [5].

cfd-post-processing

Along with the use of accurate boundary conditions to analyze turbomachinery flows, the simulation of component interaction is equally important. For example, an accurate methodology for the exchange of turbulence information across the interfaces is essential, especially concerning the evaluation of the turbulent length scale.

Finally, attention must be paid to the simulation of cooling devices since design is affected by geometrical uncertainty, numerical accuracy, fluid/solid interaction and boundary conditions variability [6]. It could be argued that the numerical simulation of a cooled, transonic high-pressure vane is one of the most challenging topics in CFD. Geometric uncertainty is so high that a 10 % variation of cooling hole diameter would generate an increase of 40 K in the local metal temperature of the vane [7].

Most of the described problems are related to the stochastic uncertainty, which is a function of the knowledge problem physics and the complexity of the algorithm. Then, numerical accuracy can rise with an improved knowledge of the physics and with the computational resources, while uncertainty quantification should be a strong support in the analysis and design of turbomachinery.

References:

[1] F. Montomoli et al., Uncertainty Quantification in Computational Fluid Dynamics and Aircraft Engines, SpringerBriefs in Applied Sciences and Technology, DOI 10.1007/978-3-319-14681-2_2
[2] Salvadori, S., Montomoli, F., Martelli, F., Chana, K. S., Qureshi, I., & Povey, T. (2012). Analysis on the effect of a nonuniform inlet profile on heat transfer and fluid flow in turbine stages. Journal of Turbomachinery, 134(1), 011012-1-14. doi:10.1115/1.4003233.
[3] Adami, P., Martelli, F., & Cecchi, S. (2007). Analysis of the shroud leakage flow and mainflow interactions in high-pressure turbines using an unsteady computational fluid dynamics approach. Proceedings of the IMechE Part A: Journal of Power and Energy, 21. doi:10.1243/09576509JPE466.
[4] Pullan, G. (2006). Secondary flows and loss caused by blade row interaction in a turbine stage. ASME Journal of Turbomachinery, 128(3), 484–491.
[5] Butler, T. L., Sharma, O. P., Joslyn, H. D., & Dring, R. P. (1989). Redistribution of an inlet temperature distortion in an axial flow turbine stage. AIAA Journal of Propulsion and Power, 5, 64–71.
[6] Montomoli, F., Massini, M., & Salvadori, S. (2011). Geometrical uncertainty in turbomachinery: Tip gap and fillet radius. Elsevier Computers and Fluids, 46(1), 362–368. doi:10.1016/j.compfluid.2010.11.031.
[7] Bunker, R. S. (2009). The effects of manufacturing tolerances on gas turbine cooling. ASME Journal of Turbomachinery, 131, 041018-1-11. doi:10.1115/1.3072494.

The Economic Optimization of Renewable Energy

clean-blog-postGlobal warming is a very popular topic at the present time. With the upwards trend of clean technology and the realization that strict climate policy should be implemented, demand of renewable energy has sky-rocketed while conservative plant popularity continues to fall. Additionally, the number of coal power plants have significantly dropped since its peak era, as they are now known as the largest pollutant contribution, producing nitrogen, sulfur oxide and carbon dioxides.

Renewable energy comes from many sources: hydropower, wind power, geothermal energy, bioenergy and many more. The ability to replenish and have no limit on usage and application makes renewable energy implementation attractive. To make this even better, it also produces low emission. Theoretically, with the usage of renewable energy, human-kind should be able to meet their energy needs with minimal environmental damage. With growth rates ranging from 10% to 60% annually, renewable energy is getting cheaper through the technological improvements as well as market competition. In the end, the main goal is to maximize profit while minimizing our carbon footprint.  Since the technology is relatively new, capital costs are still considerably higher compared to more traditional (–and naturally harmful) implementations. This begs the question of exactly how we maximize the economic potential of a renewable energy power generation plant.

Living up to the full potential of any power generation plant starts with the design process. Solar power plants are one environmentally friendly option.  During the design process, designers should take into consideration the type and quality of the solar panels as it is important to see the economic-efficiency tradeoff before jumping into an investment. Looking into the power conversion is also one of the most important steps one should take into consideration since it would be worthless to produce more energy than what is able to be transferred and put to use and low energy generation would mean less gross income.

Geothermal power plants are another option. Many studies have shown that boundary conditions on each component play a big role in determining the plant’s capacity and efficiency. High efficiency is definitely desired to optimize the potential of a power plant and minimized the energy loss. That being said, it is important to take into account the economic sacrifice. Regardless of how good the technology is, if it doesn’t make any profit, it would not make sense for one to invest in such technology. Low capital cost but high operating expenses would hurt the economic feasibility in the long run, whereas high capital cost and low operating expense could still be risky since that would mean a higher lump sum of investment upfront which may or may not breakeven or be profitable depending on the fluctuation of energy market.

Modern technology allows investors and the engineering team to make this prediction based on models developed by the experts. SoftInWay just recently launched our economic module, so check out AxCYCLE to optimize your power plant!

Reference:
[1] http://scholarscompass.vcu.edu/cgi/viewcontent.cgi?article=4483&context=etd
[2] http://www.sciencedirect.com/science/article/pii/S0038092X12002022

Creating Vacuum – Turbo Molecular Pumps

In Physics, a “Vacuum” is defined as the absence of matter in a control volume. Generally, total vacuum is an ideal extreme condition. Therefore, in reality we experience partial vacuum where ambient pressure is different from zero but much lower than the ambient value.

Depending on the pressure we can have different degrees of vacuum, ranging from low vacuum (at 1×105 to 3×103 Pa) to extremely high vacuum (at pressures <10-10 Pa). For the purpose of comparison, space vacuum might present pressures down to ~10-14 Pa in the interstellar regions.

Vacuum is needed in research and several industrial sectors for a wide range of different applications and purposes. The main way to create vacuum is by first using primary vacuum pumps -machines that relying on the general principles of viscous fluid dynamics.

With the decrease of pressure, the distance the gas/fluid molecules will travel before they collide with each other (also called mean free path or MFP) increases. When MFP increases, it reaches a level where gas molecules are no longer interacting with each other, and the laws of continuum fluid mechanics are no longer valid.

At 1 bar, the MFP of the molecules is ~70 nm whereas in a high vacuum the MFP might increase from 10cm up to 1Km. In these conditions, we use the so-called “secondary vacuum pumps”. Though the principle of pumping a gas or fluid at very low pressure ranges is different from conventional pumps, some of them resemble the operation and design of turbopumps and are called turbo molecular pumps.

vacuum-pump
Figure 1: Schematic of a turbomolecular vacuum pump – from Wikimedia Commons

Turbo molecular pumps, introduced in 1958, are drag axial pumps (or momentum transfer pumps) used in high vacuum to pump fluid from pressures below 102 Pa. Similarly to conventional compressors, they consist of multiple stages made of a rotor and stator component. They operate transferring impulses from the rapidly moving blades to the gas molecules and pushing them towards the outlet while increasing the pressure to the one at the inlet of the backing pump.

When the molecules of the vacuum chamber enter the first stage, they are hit by the rotor blade surfaces (thin metal plates with almost no “aerofoil” features) which propels them in the stator section hitting the stator plates and moving them through the following stages. The plates’ orientation increases through the stages to adapt to the pressure variation, with some designs showing an increase of near 90 degree angles. These pumps work in parallel with primary pumps downstream (or backing pumps), which are used to bring the fluid to ambient pressure before discharging it.

holweck
Figure 2: Schematic of a Holweck stage– from Pfeiffer Vacuum

Turbomolecular pumps can work if the molecules hit by  the rotor blades reach the stator fins without colliding with other molecules. This can be achieved by reducing the gap of rotor and stator plates to be smaller than the MFP, however for manufacturing limitations, this gap is in the order 1mm. For this reason, a turbo molecular pump can work effectively when the MFP at the exhaust is of the same order of magnitude, hence exhaust pressures lower than 10Pa. Very low clearances also influence the design of the last stages of the pump. In fact, some designs may present a last stage showing a helical type channel, which is called a Holweck stage design.

To create the directed motion of the gas molecules, the rotor blade tips should move at a very high speed, so the operating rotational speeds for these machines vary from 30000 to 90000 rpm. This may create high stresses and heat due to friction in the bearing system and so consequently some exotic solutions, such as magnetic levitation bearings,  can be used with increased costs of the single unit.

A further drawback is that bigger molecules are pumped more efficiently, whereas smaller ones (such as hydrogen or helium) are more difficult to pump and remove to create a higher level vacuum. This aspect can however be alleviated by the integration of Holwech stages which increases the effectiveness of dragging smaller molecules.

 

What is an Integrated Coal Gasification Combined Cycle (IGCC) and What are the Advantages?

integrated-coal-gasification-combined-cycle-igcc
Source: http://www.slideshare.net/AbhijitPrasad4/integrated-gasification-combined-cycle-plant

Though fossil fueled power plants aren’t as commonly used anymore, coal fired power generation is still a major source of global electricity, making up about 25% of the market in total. Compared to other options in fossil fuel power generation, coal is found to be the most economical choice as well as a reliable option. Making demands that are heavily reliant on other fuels, such as oil-fired for example, slowly levers to coal power generation. The global reserve of coal can be found in abundance when compared to other energy sources (such as oil for example) as there is about 3 times more of it. Also, IGCC comes with an economic benefit as the price of coal has remained relatively constant, which results in a higher degree of confidence when relying on coal as an energy source in the future.

How Does an IGCC Work?

The system uses a high pressure gasifier to turn coal and other carbon based fuels such as high-sulfur coal, heavy petroleum residues and biomass into pressurized clean coal synthesis gas (also known as syngas). The solid coal is gas-fired to produce syngas by gasifying coal in a closed pressurized reactor with a shortage of oxygen to ensure that coal is broken down by the heat and pressure. Before going out of the system, the syngas runs through a pre-combustion separation process to remove impurities,  starting with water-gas-shift reaction to increase concentration of hydrogen and efficiency during combustion process, to a physical separation process (through variable methods). After that, a fairly pure syngas is used as a fuel in a combustion turbine that produces electricity. Waste heat contained in a gas turbine’s exhaust is used to produce steam from feed water that further turns a steam turbine to generate additional electricity.

What are the Advantages of IGCC?

IGCC is currently found to be the cleanest of coal technology with lower emission (especially for carbon dioxide by 10%) and is about 30-40 percent more efficient. Using syngas in gas turbines results in a higher output that is less dependent on temperature when compared with natural gas. Additionally, looking into the economic benefit of this technology, IGCC produces couple by-products, from chemicals to materials for industrial use that could be sold for side economic benefits.

References:

http://www.global-greenhouse-warming.com/integrated-gasification-combined-cycle-IGCC.html

https://en.wikipedia.org/wiki/Integrated_gasification_combined_cycle

 

 

Utilization of Supercritical CO2 Bottoming Cycles

In the ever-expanding market for waste-heat recovery methods, different approaches have been established in order to combat the latest environmental restrictions while achieving more attractive power plant efficiencies.  As gas turbine cycles continue to expand within the energy market, one particular technology has seen a significant upsurge due to a number of its beneficial contributions.  Supercritical CO2 (S-CO2) bottoming cycles have allowed low power units to utilize waste heat recovery economically.  For many years, the standard for increasing the efficiency level of a GTU (Gas Turbine Unit) was to set up a steam turbine Rankine cycle to recycle the gas turbine exhaust heat.  However, the scalability constraints of the steam system restrict its application to only units above 120MW.

sco2_cycle
Supercritical Co2 Cycle

HRSGs (Heat Recovery Steam Generators) are water-to-steam boilers which capture the waste heat exhaust of GTUs and convert this heat into energy in the form of high-pressure, high-temperature steam.  These systems can exist in a single or modular fashion depending on the scope of the project.  Modular HRSGs consist of any number of low pressure, intermediate pressure, and high pressure sections.  Each section allows for the extraction of gas turbine exhaust heat using separate steam drum and evaporator sections.  Even in a single pressure HRSG combined cycle, the immense amount of auxiliary equipment, the high installation costs, and the frequent maintenance necessary for such a system prevent them from providing viable heat recovery for low power GTUs.

With the introduction of a different fluid, gas turbines of small and medium size are able to utilize waste heat recovery.  Unlike steam, a supercritical CO2 system is designed to lie in the simply in the gaseous phase.  This single-phase fluid design removes the boiling process necessary for a steam system and therefore results in higher fluid temperatures and cycle efficiencies.  As well, the high energy density reduces the system component’s size and cost, and offers higher system efficiencies, reduced footprints, and significantly easier installation methods.  While all these advantages do exist within a supercritical CO2 system, working with a relatively new fluid presents different challenges that have not had the time and exposure with engineering experts as steam and gas systems have.  In particular, developing a turbine that will most efficiently run under this new fluid presents perhaps the tallest demand within the supercritical cycle. The task becomes to embrace these challenges for the benefit of higher efficiencies, lower O&M costs, and reduced greenhouse emissions.

For a more in-depth look at SoftInWay’s involvement in the S-CO2 sector, please follow this link or contact us for more information

 

References:

  1. http://www.echogen.com/documents/why-sco2-can-displace-steam.pdf
  2. http://www.softinway.com/wp-content/uploads/2015/12/IGTC2015-EvaluationOfGasTurbineExhaustHeatRecoveryUtilizingSCO2Cycle.pdf