Gas Turbine Lubrication Systems

Gas turbines have had a presence in many industries for more than a century. They are a unique technology for either producing an energy or propelling a vehicle and the efficiency of modern gas turbines is being improved continuously. One of them, a cooling system, has been described in earlier blogs. Another is the lubrication system of a gas turbine which we will cover in this blog. This  system, similar to that of a piston engine or a steam turbine, provides lubrication to decrease mechanical losses and prevent of wear on friction surfaces. Another function is the removal of heat released during friction by high rotational part and transmitted from the hot part of a turbine.  The basic units which need lubrication are the bearings supporting a shaft of a gas turbine 2.

Modern Dual Journal
Figure 1. The construction of modern dual journal4
Elements for lubrication

In a common case, gas turbine installation contains three main journal bearings used to support the gas turbine rotor 3. Additionally, thrust bearings are also maintained at the rotor-to-stator axial position 4. Click here for additional information about optimization of journal bearings. The bearing has important elements in its construction to prevent leakages from a lubrication system. The work, design and analysis of labyrinth seals is describe here.

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Optimization of the Closed Supercritical CO2 Brayton Cycle with the Detailed Simulation of Heat Exchangers

Recently scientists and engineers have turned their attention again to carbon dioxide as a working fluid to increase the efficiency of the Brayton cycle. But why has this become such a focus all of a sudden?

The first reason is the economical benefit. The higher the efficiency of the cycle is, the less fuel must be burned to obtain the same power generation. Additionally, the smaller the amount of fuel burned, the fewer emission. Therefore, the increase in efficiency also positively affects the environmental situation. Also, by lowering the temperature of the discharged gases, it is possible to install additional equipment to clean exhaust gases further reducing pollution.

So how does all of this come together? Figure 1 demonstrates a Supercritical CO2 power cycle with heating by flue gases modeled in AxCYCLE™. This installation is designed to utilize waste heat after some kind of technological process. The thermal potential of the exhaust gases is quite high (temperature 800° C). Therefore, at the exit from the technological installation, a Supercritical CO2 cycle was added to generate electrical energy. It should be noted: if the thermal potential of waste gases is much lower, HRSG can be used. More information on HRSG here: http://blog.softinway.com/en/introduction-to-heat-recovery-steam-generated-hrsg-technology/

Any cycle of a power turbine installation should consist of at least 4 elements : 2 elements for changing the pressure of the working fluid (turbine and compressor) and 2 elements for changing the temperature of the body (heater and cooler). The cycle demonstrated in Figure 1 has an additional regenerator, which makes it possible to use a part of the heat of the stream after the turbine (which should be removed in the cooler) to heat the stream after the compressor. Thus, part of the heat is returned to the cycle. This increases the efficiency of the cycle, but it requires the introduction of an additional heat exchanger.

The heat exchangers used in the sCO2 cycle are of three basic types: heaters, recuperators, and coolers. Typical closed Brayton cycles using sCO2 as the working fluid require a high degree of heat recuperation.

Supercritical CO2 Power Cycle with Heating by Flue Gases
Figure 1 – Supercritical CO2 Power Cycle with Heating by Flue Gases

Having examined this scheme and examined the process in detail, we can draw the following conclusions about the advantages of this cycle which is demonstrated in Figure 2: Read More

Improving Efficiency, One Rocket at a Time (An Excerpt from Exceptional People Magazine)

The following is an excerpt from  Exceptional People Magazine, conducted by Monica Davis and focused on profiling SoftInWay’s CEO, Dr. Leonid Moroz.   The article appeared in the September/October 2019 issue. A link to the full interview can be found here

Turbomachinery design is critical in industries like aerospace, oil and gas, defense, and clean technology. Dr. Leonid Moroz’s company, SoftInWay Inc., also helps some of the world’s largest manufacturers of turbines, turbochargers, pumps, and fans. But Moroz is happy to explain that his company’s innovations also impact the car you drive, the vacuum cleaner you use, the air conditioning in which you work, and the electricity needed to power your mobile phone.

Leonid Moroz
Dr. Leonid Moroz, CEO of SoftInWay

A lover of music and athletics as a child, Moroz knew early on that engineering held promise as a lifelong career. So he started his career as a Group Leader at TurboAtom. TurboAtom, while a state-owned entity, is one of the world’s top thermal, nuclear, and hydropower plant turbine construction companies. It’s a company that operates at the level of companies like General Electric and Siemens.

Moroz designed both gas and steam turbines during his eight years at TurboAtom. While he was there, he also earned his Ph.D. in Turbomachinery from the Kharkiv Polytechnic Institute in Ukraine.

When he founded global aerospace engineering leader SoftInWay, Inc. in 1999, he intended to assist turbomachinery manufacturers needing his expertise. What evolved from that intent has revolutionized engineering design and allowed improved efficiencies for multiple system types: Its flagship software, AxSTREAM.

AxSTREAM helps engineers develop efficient turbomachinery flow path design, redesign, analysis, and optimization. Under Moroz’ direction, AxSTREAM itself has also evolved into a design platform supporting rapid development of a new generation of liquid rocket engines.

Still a relatively small company, SoftInWay supports over 400 companies worldwide and works closely with universities, research laboratories, and government organizations. The company takes its educational responsibilities seriously, continually offering webinars, training sessions, educational blogs, and online workshops on topics like When To Upgrade Your Pump, The Pros and Cons of Wind Energy, and Radial Outflow Turbine Design.

Moroz loves to talk about his work, his company, its innovations, and his team. He’s proud to have had the same group of engineers for 30 years, so SoftInWay feels more like a family than a workplace. As the company has become a leading global R&D engineering company, it has expanded to encompass locations in Boston, Massachusetts; Zug, Switzerland; Ukraine; and India.

Yes, Moroz’ specialty is indeed a bit technical for people who aren’t in turbomachinery engineering design. But Moroz and his team clearly enjoy what they’re doing because it benefits society and makes life easier and more comfortable in myriad ways.

Next time you switch on that ShopVac or Hoover, be sure to thank Dr. Leonid Moroz.

Monica: We often take for granted how engineering plays a huge role in our daily lives. How much of the world depends on the kind of technology and engineering capabilities you produce?

Dr. Moroz: Quite substantially. For example, society produces a lot of waste and heat. If you have options, it utilizes waste and heat to produce power, or it is thrown away. We’ve helped companies to utilize this energy and to produce power to heat or cool our houses, to prepare food, and to help our businesses survive.

Image from a SoftInWay Classroom Course

Another example again would be launchers design. Launchers are important for turbomachinery. A significant part of space development depends on turbomachinery inside those launchers.

It’s important to understand two directions where people can utilize turbomachinery with power consumption and power generation. Power generation is when you produce power, so we need to be more efficient, but the second part, when we get this power, we need to cool our houses, we need to cool our cars, and so on, and again, it’s turbomachinery.

You can be sure that you utilize turbomachinery to develop an air conditioning system that is efficient and is quite substantially in large buildings.

Power consumption for air conditioning is like 30 or 40 percent of the overall power consumption. Can you imagine if you were to decrease this by 10 to 20 percent? It would be a considerable saving…Read the full interview here

 

Considerations when Designing Turbomachinery with sCO2 as a Working Fluid

Supercritical CO2 (sCO2) power cycles offer higher efficiency for power generation than conventional steam Rankine cycles and gas Brayton cycles over a wide range of applications, including waste heat recovery, concentrated solar power, nuclear, and fossil energy. sCO2 cycles operate at high pressures throughout the cycle, resulting in a working fluid with a higher density, which will lead to smaller equipment sizes, smaller carbon footprint, and therefore lower cost. However, the combinations of pressure, temperature, and density in sCO2 power cycles are outside the experience of many designers. Challenges in designing sCO2 cycles include turbomachinery aerodynamic and structural design, bearings, seals, thermal management and rotordynamics. According to the report from Sandia National Lab, compressors operating near critical point and turbines have received only TRL (technical readiness level) 4 and 5 out of 9. This blog discusses the impact on turbomachinery design.

Radial or Axial

The selection of radial or axial for turbomachinery is typically performed based on the operating conditions (adiabatic head H and inlet volumetric flow Q). Non-dimensional turbomachinery parameters of specific speed Ns and specific diameter Ds can be selected from NsDs charts to estimate size, speed, and type of turbomachinery. Turbomachinery types for a sCO2 recompression cycle with scales ranging from 100 kW to over 300 MW have been studied and concluded that systems below 10 MW will likely feature only radial turbines and compressors with a single-stage or low stage counts. Such recompression cycle can be simulated in AxCYCLE™ tool which is shown in Figure 1. As size increases, the most efficient configuration for the turbine and recompressor transitions from radial to axial at approximately 30 MW and 100 MW, respectively. Suitable types of turbomachinery and its components for different power range can be reviewed in Figure 2. A radial configuration for the main compressor was expected at all scales due to its lower volume flow and wider range to facilitate variation in gas properties due to operation near the critical point.

Recompression Cycle simulated in AxCYCLE
Figure 1 – Recompression Cycle Simulated in AxCYCLE

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Introduction to Heat Recovery Steam Generated (HRSG) Technology

The acronym HRSG (Heat Recovery Steam Generated) is in different sources describing the operation of cogeneration and heating plants, but what does it mean? Heat Recovery Steam Generated (HRSG) technology is a recycling steam generator which uses the heat of exhaust from a gas turbine to generate steam for a steam turbine generating electricity.

The simplest scheme of a Combined Cycle Gas Turbine (CCGT) is presented in Figure 1.

The simplest scheme of CCGT
Figure 1: The simplest scheme of CCGT.

In Figure 1, the exhaust flue gases temperature on the outlet of the turbine is equal to 551.709 ℃. This is a too high a temperature to release the gasses into the environment. The excess heat is able to be disposed of while receiving additional electric power which is approximately equivalent to 30% of the capacity of a gas turbine.

To reach the maximum economical and eco-friendly criteria possible for the installation, many pieces of equipment are used including: a waste heat boiler (HRSG); turbines with a selection for a deaerator (Turbine With Extraction, Deaerator); feed and condensate pumps (PUMP2, PUMP); a condenser (Condenser); and a generator (Generator 2). Exhaust gases entering into the HRSG transfer heat to water which is supplied by the condensate pump from the steam turbine condenser to the deaerator and further by the feed pump to the HRSG. Here boiling of water and overheating of the steam occurs. Moving further, the steam enters the turbine where it performs useful work.

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Oil Systems for Turbine Lubrication

The oil system is an integral element of the turbine unit, which largely determines its reliability and trouble-free operation. The main purpose of the turbine lubricating oil system is to provide fluid friction in the bearings of turbines, generators, feed pumps, and gearboxes.

An oil system should provide:

– continuous supply of the required amount of oil in all modes of operation of the turbine unit, which guarantees:

  • – prevention of wear on friction surfaces;
  • – reduction of friction power losses;
  • – removal of heat released during friction and transmitted from the hot parts of the turbine

– maintaining the required temperature of the oil in the system; and

– cleaning the oil from contamination.

At the same time, the necessary qualities of the lubricating oil system are reliability, safety of operation, ease of maintenance.

The pressure and the temperature of the oil should be constantly monitored during operation of the turbine unit. Specifically, the lube oil temperature after the bearings requires special attention. Overheating of the bearing leads to wear of the working parts and changes in the properties of the lubricant itself. The quality of the lube oil is controlled by physicochemical characteristics such as density and viscosity. The system leaks must be stopped quickly and oil replenished on time. These factors will significantly extend the service life of the steam turbine.

Nowadays, computer simulation is a very powerful and useful tool. It helps you predict the processes occurring in the bearing chambers, and determine the flow of the working fluid when the operating modes change, all without installing expensive experimental equipment.

We suggest using the 1D-Analysis AxSTREAM NET™ tool to simulate the lubrication system. This software product allows you to quite simply, clearly and quickly build the desired model. It provides a flexible method to represent fluid path as a set of 1D elements, which easily can be connected to each other to form a thermal-fluid network. The program calculates fluid flow parameters for inlet and outlet of each element. There are many different components that allow you to simulate stationary and non-stationary modes. Also there is a convenient library of fluids. It is also possible for a user to add fluids of their choice.

The example of modeling in AxSTREAM NET™ is the system of oil supply for the K-500-240 turbine. This turbine is quite massive with bearing loads of up to 450 kN. The schematic diagram of the oil supply K-500-240-2 is shown in Figure 1.

Figure 1 Principle Scheme of K-500-240 Steam Turbine
Figure 1. Principle Scheme of K-500-240 Steam Turbine.

 

(1 – main tank; 2 & 3 – pumps; 4 – oil cooler; 5 – damp tank; 6 – journal bearings; 7 – thrust bearing).

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An Overview of Axial Fans

Axial fans have become indispensable in everyday applications starting from ceiling fans to industrial applications and aerospace fans.  The fan has become a part of every application where ventilation and cooling is required, like in a condenser, radiator, electronics etc., and they are available in the wide range of sizes from few millimeters to several meters. Fans generate pressure to move air/gases against the resistance caused by ducts, dampers, or other components in a fan system. Axial-flow fans are better suited for low-resistance, high-flow applications and can have widely varied operating characteristics depending on blade width and shape, number of blades, and tip speed.

Fan Types

The major types of axial flow fans are: propeller, tube axial, and vane axial.

  • – Propellers usually run at low speeds and handle large volumes of gas at low pressure. Often used as exhaust fans these have an efficiency of around 50% or less.
  • – Tube-axial fans turn faster than propeller fans, enabling operation under high-pressures 2500 – 4000 Pa with an efficiency of up to 65%.
  • – Vane-axial fans have guide vanes that improve the efficiency and operate at pressures up to 5000 Pa. Efficiency is up to 85%.
Types of Fans
Figure 1 Different Types of Axial Fans
Aerodynamic Design of an Axial Fan

The aerodynamic design of an axial fan depends on its applications. For example, axial fans for industrial cooling applications operate at low speeds and require simple profile shapes. When it comes to aircraft applications however, the fan must operate at very high speeds, and the aerodynamic design requirements become significantly different from more traditional fan designs. Read More

Complex Modeling of a Waste Heat Boiler

Introduction

Waste heat boilers are a sophisticated piece of equipment important for recovering heat and in turn protecting the environment. Waste heat boilers are needed during the operation of facilities in the energy sector such as gas turbine plants and diesel engines, as well as in metallurgy and other industries where excessive heat of high temperature up to 1,000 degrees form during the technological processes. Waste heat boilers are used to recover excess heat energy, as well as to increase the overall efficiency of the cycle. Another feature of waste-heat boilers used at these installations is to protect the environment – by disposing of harmful emissions.

This article discusses the accurate modeling of these sophisticated waste heat boilers. We will consider the simulation of a Heat Recovery Steam Generator (HRSG), which is used in a combined steam-gas cycle for utilizing the outgoing heat from a gas turbine plant and generating superheated steam, using the programs thermal-fluid network approach and complexes of optimization.

The HRSG has four main heat exchangers: cast-iron economizer, boiling type steel economizer, evaporator with separator, and superheater.

On the one side of the HRSG, feed water is supplied from the cycle, and on another side, hot gas is supplied from the gas turbine in the process of operation.  The water is preheated and goes to the steel economizer where the boiling process begins in the tubes. After the process in the economizers, the water goes to the shell side of the evaporator, where its active boiling occurs. In the separator, the steam-water mixture is divided into saturated steam and overflow. Saturated steam is sent to the superheater, where superheated steam is formed and goes to the steam turbine cylinder. Overflow water returns to the steam formation. An induced-draft fan is used for gas circulation and removal in the HRSG. The HRSG model also has a spray attemperator for steam cooling. The operation principle of desuperheater is the following: feed water is taken from the economizer and goes to the superheater section, passes to superheated steam flow through nozzles, finely divided water droplets mix, heat up and evaporate and as a result, the steam is cooled.

HRSG Flows Direction
Picture 1 – HRSG Flows Direction
Different Approaches

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To Retrofit or Not to Retrofit – 7 Questions to Help you Decide

One of the challenges of maintaining infrastructure is deciding how best to keep the operational costs in check while delivering the highest amount of service. This is especially true for aging equipment. One option is to replace the equipment with a newer version entirely, continue to maintain the existing machine, or a third option, retrofit the current machine with updated features.

Retrofitting is a term used in the manufacturing industry to describe how new or updated parts are fitted to old or outdated assemblies to improve function, efficiency or additional features unavailable in the earlier versions.

steam turbine in repair process, machinery, pipes, tubes, at power plant
steam turbine in repair process, machinery, pipes, tubes, at a power plant

Retrofitting, like any investment of capital requires careful thought.  SoftInWay’s Manage ring Director, Abdul Nassar has put together a simple list of questions to ask yourself before committing to a retrofit project.  Answering these seven questions before you start can save you considerable time and effort. Read More

A Basic Guide to Reverse Engineering

Reverse Engineering, or back engineering, is a term used for the process of examining an object to see how it works in order to duplicate or enhance the object when you don’t have the original drawings/models or manufacturing information about an object.

There are two major reasons reverse engineering is used:

  1.  create replacement parts to maintain the function of older machines;
  2.  improve the function of existing machines while meeting all existing constraints.

 

Figure 1 Uses of Reverse Engineering
Figure 1: Uses of Reverse Engineering

Reverse engineering is extremely important in turbomachinery for replacement parts in turbines or compressors which have been operating for many years. Documentation, reports and drawings for a significant amount of these machines is not available due to a variety of reasons, therefore keeping these important machines running is a challenge. One of the options to deal with this issue is to buy the modern analogue of the machine, which is not always feasible due to economic constraints or that there is no replacement available.  Reverse engineering of the worn out parts might be the best option in the majority of cases.

In any case, the process to recovery original geometry of the object is the first and major step for all reverse engineering projects, whether you want just replacing/replicate parts or proceed with an upgrade to the machine.

Basic Steps to Any Reverse Engineering Project

Any reverse engineering process consist of the following phases:

  1. Data collection: The object needs to be taken apart and studied.  Starting in ancient times, items were disassembles and careful hand measurements were taken to replicate items.  Today, we employ advanced laser scanning tool and 3D modeling techniques to record the required information in addition to any existing documentation, drawings or reports which exists.
  2. Data processing: Once you have the data, it needs to be converted to useful information.  Computers are essential for this stage as it can involve the processing of billions of coordinates of data converting this information into 2D drawings or 3D models by utilizing CAD systems.
  3. Data modeling: This step was not available in beginning of reverse engineering. People just tried to replicate and manufacture a similar object based on the available data. Nowadays, engineers can utilize digital modelling, which represents all details of the geometrical and operational conditions of the object through a range of operation regimes. Typically, performance analysis and structural evaluation are done at this stage, by utilizing thermo/aerodynamic analytical tool, including 3D CFD and FEA approaches.
  4. Improvement/redesign of the object: If required, this is the step where innovations can be created to improve the effectiveness of the object based on the collected data about the object’s geometry and operation.
  5. Manufacturing: After the part is been modeled and meets the design requirements, the object can be manufactured to replace a worn out part, or to provide increased functionality.
Reverse Engineering in Today’s World

It very common to find the situations where reverse engineering is necessary for parts replacement, particularly with turbomachinery – steam or gas turbines, compressors and pumps. Many of these machines have been in operation for many years and experienced damaging effects of use over that time – like water droplets and solid particles erosion, corrosion, foreign objects, and unexpected operating conditions. Besides these expected needed repairs, some other reasons for reverse engineering might arise from a components part failure, as well as part alterations needed due to previous overhauls and re-rates.

All the conditions mentioned above require not only recovering the original geometry but also an understanding of the unit’s history, material properties and current operating conditions.

This article focuses on reverse engineering objects which have experienced significant change in their geometry due to the challenges of long term operation and their shape could not be directly recovered by traditional methods – like direct measurement or laser scanning.  Pictures below are examples of such objects – steam turbines blading with significant damage of the airfoils with different causes such as mechanical, water/solid particle erosion, and deposit.

Figure 2 Water droplet erosion on steam turbines long blades
Figure 2: Water droplet erosion on steam turbines long blades
Figure 3 Steam turbine blading with mechanical damage
Figure 3: Steam turbine blading with mechanical damage
Figure 4 Steam turbine control stage nozzles solid particle erosion
Figure 4 Steam turbine control stage nozzles solid particle erosion
Figure 5 Deposits on Rotating Blades
Figure 5: Deposits on Rotating Blades

In the situations shown above, recovering the original geometry may be impossible if an engineer only has the undamaged portion of original part to work with. Which means that relying on undamaged portion of an original part it may be impossible to recover the needed portion due to significant level of damage.

Looking at the eroded turbine blading in Figure 1, recovering these airfoils with sufficient accuracy based on only a scan of the original part, would be very difficult, if not impossible, considering that 1/3 to ½ of the needed profile is wiped out by erosion.

In order to recover the full airfoil shape for turbines / compressors / or pumps blading, the information about flow conditions – angles, velocities, pressure, temperature – is required to recreate the airfoils profiles and a complete 3D blade.

In many cases with significant blading damage, the information obtained from aero/thermodynamic analysis is the only source of the information available for a designer and the only possible way to recover turbomachinery blading. In fact, in such a situation, the new variant of the airfoils is developed based on aero/thermodynamic information and by considering the remaining portion of the part, which would be the most accurate representation of the original variant. A structural evaluation should also be performed for any recovered part to ensure blading structural reliability in addition to the aero/thermodynamic study.

All of these engineering steps require employment of dedicated engineering design and analysis tools, which can perform:

  • – Accurate modelling of the turbo machinery flow path,
  • – 1D/2D aero/thermodynamic analysis and in some cases 3D CFD,
  • – Profiling and 3D staking of the blading,
  • – Structural evaluation, including 3D FEA tools.

SoftInWay’s team offers a comprehensive set of turbomachinery design and analysis tools within the integrated AxSTREAM® platform, which covers many steps, required for reverse engineering activities.

In Figure 6 below, a process diagram shows how AxSTREAM® products are used for reverse engineering.

Process Diagram
Figure 6: Process diagram of AxSTREAM® products use in reverse engineering

After data collection, most of the geometry recovering steps are processed by AxSTREAM® modules:

  • AxSLICE™ to process original geometry data, available from the scanned cloud of points.
  • AxSTREAM® solver to perform 1D/2D aero/thermodynamic
  • AxSTREAM® profiler to recover profile shape and 3D airfoil stacking.
  • AxSTRESS™ for structural evaluation and 3D design.
  • AxCFD™ for detailed aerodynamic analysis and performance evaluation.

Geometry recovered in this way is now ready to be used to develop detailed 3D CAD models and 2D drawings for further technological and/or manufacturing processing.

As an example of such capabilities, Figure 7 demonstrates the reverse engineering process for the 1000 mm last stage of 200 MW steam turbine with significantly damaged blades due to water erosion.

It is possible to recognize and extract the profile angles with a specialized tool – AxSLICE™, obtain slices on the desired number of sections and insert the extracted geometric data to an AxSTREAM® project.

200 MW steam turbine water eroded 1000mm last stage blade reverse engineering process using AxSTREAM and upgraded variant of the blade
Figure 7: 200 MW steam turbine water eroded 1000mm last stage blade reverse engineering process using AxSTREAM® and upgraded variant of the blade.

The AxSTREAM® platform can provide seamless reverse engineering process for all components of complex turbomachinery.

Meet an Expert! 

Boris Frolov Dr. Boris Frolov is the Director of Engineering at SoftInWay, Inc. and manages all of the turbomachinery consulting activities. He has over 35 years of experience in steam/gas turbines design, analysis and testing.

Earning his PhD in turbine stages optimization with controlled reaction, he is an expert in steam turbines aerodynamics and long buckets aeromechanics. Dr. Frolov has over 50 publications and 7 registered patents and he shares this vast knowledge as a lecturer in steam turbines, gas dynamics and thermodynamics for students studying power engineering sciences. Prior to joining SoftInWay, he was the engineering manager at GE Steam Turbines.