MAPNA TURBINE ENGINEERING & MANUFACTURING CO. (TUGA… Review-No... · designed by TUGA. It takes an in-depth look at the design stage of this steam turbine, to be used in an incineration

MAPNA TURBINE ENGINEERING & MANUFACTURING CO. (TUGA)

echnical eviewNo.9 - March 2018Willpower to Empower Generations

Cover PageMST-35WTE Steam Turbine Rotor

MAPNA Turbine • March 2018 1

Dear Colleagues, Partners and Professionals,

Continuous improvement through research and broadening our technical expertise in addition to developing new technologies let us offer proven solutions that meet expectations and support the ever-increasing demands of the industry in a sustainable way. A brief account of a few recent achievements and technological breakthroughs is presented to you, our valued readers, in this edition of MAPNA Turbine Technical Review.

The first article introduces MST-35WTE; the first waste-to-energy steam turbine designed by TUGA. It takes an in-depth look at the design stage of this steam turbine, to be used in an incineration plant to turn municipal waste into power.

The second essay is a tremendous success story of the design and implementation of an effective wet compression system proven to bring about a substantial performance boost for the broad fleet of MGT-70 heavy-duty gas turbines. The technology employed is aimed at negating the adverse impacts of high ambient temperature on the machine performance by water injection into the compressor section.

In line with the emerging technologies, MAPNA Group, as a key player in the field of turbo-machinery, aims at taking full advantage of Additive Manufacturing. To do so, several sample components have been produced by AM, including Axial Swirler of an MGT-70 burner. Manufacturing and qualification activities are elaborated on in the third essay.

The fourth article outlines systematic design stages of an axial compressor. The use of the developed axial compressor test

rig has enabled MAPNA Turbine to further validate and optimize in-house designs and approaches, via implementation of performance tests and practical measurements. The test rig will surely serve as a ground to further promote innovation, research and development in the field of axial compressor technology.

Last but definitely not least, the fifth article provides a detailed scrutiny of a comprehensive set of experimental measurements carried out on the prototype of MGT-70(3) gas turbine. The tests conducted were meant to extensively quantify the machine internal parameters, and assess overall performance over a wide range of operational and ambient conditions.

Please join us in relishing detailed account of the a.m. titles, in this issue of the Technical Review.

Respectfully,

Mohammad Owliya, PhD

Deputy General Director

MAPNA Turbine Company (TUGA)

March 2018

Editorial

MAPNA Turbine • March 20182

Table of Contents

MST-35WTE, In Action to Turn Garbage into Power!

Design and Implementation of Wet Compression System for MGT-70 Fleet

Additive Manufacturing Technology to Play a Key Role in the Evolution of the MGT-70 Gas Turbine Series

Towards Excellence in Designing Axial Compressors

Scrutiny of Measurements Performed on MGT-70(3) Gas Turbine Prototype

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01We have a moral obligation to take care of our environment and to preserve the planet for future generations the way we have inherited it from our ancestors.

Each day, a huge amount of municipal waste is produced and dumped in the countryside, destroying the environment. The height of waste piles has exceeded 100 meters in some suburban areas of the country. Since the waste is pressed

under tons of weight, the leachate oozes out and penetrates into the underground water resources which could lead to the outbreak of serious infectious diseases among communities.

Moreover, the accumulation of waste would give rise to a heaven for vermin: insects, rodents, etc., to live around and grow, which could in turn put the public health at risk.

MST-35WTE, In Action to Turn Garbage into Power!Introduction

Incineration plants could be a right solution to this problem, where large quantities of waste are simply burnt in special boilers to produce steam used for electrical power generation via a steam turbine generator.

To reduce pollution emissions from the flue gas stream inside the boiler, it is passed through a sequence of fine

filtration and treatment processes before being discharged into the atmosphere. Furthermore, total emissions of hazardous air pollutants from municipal waste incineration plants are comparable to that of an automobile which makes it a viable option to build and locate such facilities in the hearts of cities.

Fig. 1: A Pile of waste dumped in the countryside


Initial DesignHaving clarified with the client the main steam parameters together with specifications of the extractions and the condenser pressure, the following Heat

Balance Diagram (HBD) was produced with which, the design of the machine could be kicked off.

With the HBD on hand, the first step was to determine the LP-end, i.e., the exhaust annulus area and so the last stage blades. It is to be mentioned that for a machine of such size, using a reduction transmission is considered a big disadvantage since a 90 MW machine is generally designed in a way to rule out the need for any load gearbox.This implies that the steam turbine running speed must be equal to that of the generator, i.e., 3000 rpm.

For this purpose, a blade at 3000 rpm was developed. It is a quite high back

pressure blade which suits best both dry cooling systems as well as high ambient temperature conditions.

The entire steam path including several blade sections each comprising a number of blade stages from the preceding steam admission to the first steam extraction was then designed. The blade sections were categorized as HP1, HP2, IP and LP sections. For each section, calculations had to be done in order to determine the diameters of the first and last blade stages.

Fig. 2: MST-35WTE Steam Turbine Heat Balance Diagram

Design MilestonesIn early 2015, negotiations started with companies that specialize in treatment and energy recovery of waste by designing and building waste-to-energy conversion plants.

MAPNA Turbine was called on to provide the steam turbine, associated control system and generator for total amount of 90

MW electrical power the end user of which is the municipality of Tehran, the capital of Iran. There are two options available, the first being 3X30 MW units and the second, a single 90 MW unit. The latter was opted for now and hence MAPNA Turbine started to proceed accordingly.


Fig. 3: Last stage blade (courtesy of Franco Tosi Meccanica, Italy)

Waste-to-Energy steam turbines normally operate at fixed inlet pressure which necessitates the application of either one or two special blade stages at the beginning of the steam path just after the inlet valves called Rateau stage or Curtis stages, depending upon the design constraints. This avoids dramatic drop of efficiency since the fixed inlet pressure has to drop to what is required upstream of the first stage at different partial load cases. By using a Rateau stage, part of the efficiency drop is made up for by some extra power.

In order to keep the efficiency of the Rateau stage as high as possible at each load case, the inlet steam chest has to be split into 4, 6 or 8 isolated arcs depending upon design requirements. Each arc is fed from its relevant valve, so that steam may flow through 2 out of 4 arcs at 50% of the nominal load.

The steam path layout was then to be selected and unlike gas turbines there are plenty of ways to do so. It can be a single or double flow steam turbine and/or single cylinder, double or even a multi-casing machine, with their own pros and cons and specific applications.

Single flow steam path suits best extraction turbines in which there are a number of steam bleed-offs throughout the steam path. Furthermore, dealing with partial arc admission is easier in comparison with double flow steam path layout. On the other hand, the total thrust forces applied on the blades and thus the rotor are a lot less in a double flow steam turbine as the forces applied on the HP section approximately balance out those at the IP/LP sections as schematically shown in Fig. 4. Therefore, the net thrust force is low enough to be easily borne by the thrust bearings.


Fig. 4: Schematic representation of thrust forces in single and double steam path layouts

Fig. 5: Optimization of the HP sections

Comprehensive evaluation of the options available finally resulted in the selection of a single flow steam path with steam entering the machine through multiple inlet valves each connected to an isolated arc.

The inlet steam initially passes through a Rateau stage and then enters the first high pressure section (HP1). There is an extraction between the first and second high pressure sections (HP1 & HP2). Part

of the flow is also extracted in the second extraction after the HP2 section and the rest flows on to the IP section in the same direction as in the HP section. The third and the last extraction is also made between the intermediate pressure (IP) and low pressure (LP) sections.

The number of blade stages for each section was then calculated with the results being 9 stages for HP1, 7 for HP2, and 3 for IP and LP sections each.

Detailed DesignSteam Path OptimizationHaving finished the design of steam path layout, the next step was optimization of the steam path in order to get the highest possible power through an analysis called row-by-row calculations. This was mainly achieved using Microsoft Excel and MATLAB® user-defined codes and functions.

The airfoil shape was copied for all the drum stages; however the scale and stagger angle of each row was to be calculated and optimized. Another flexible parameter was the blades’ height. These three parameters were subject to optimization, so that the best possible efficiency was produced for the HP sections.


Fig. 6: A sketch of the MST-35WTE rotor used for dynamic calculations

Fig. 7: A snapshot of a sample GUI developed for impulse blade design

The same was also carried out for IP section. In the meantime, the LP section was adopted from another steam turbine with all its features and then customized to fit the IP section and the exhaust hood.

Preliminary Rotor DynamicsIn order to make sure that the dynamic behavior of the turbine would be acceptable, a sketch of the rotor was drawn and modeled, so that natural frequencies and mode shapes of the rotor were determined. Thus far, there has

been no information from the generator side. Once the generator is designed and its reduction model is created, the rotor dynamic calculations must be repeated.

The results of this analysis showed wide margins between natural frequencies and the running speed of the rotor and its harmonies also being large enough to ensure safe operation of the machine. A sketch of the rotor representing mass and stiffness diameters used for evaluation of the rotor dynamics are shown in Fig. 6.

MATLAB®GUI ProgramsGraphical User Interfaces (GUIs) have been developed in MATLAB® GUI development environment in order to facilitate usage of the previously mentioned Microsoft Excel user-defined codes in a considerably

more user-friendly manner. A snapshot of a sample GUI developed for implementation of mechanical calculations of the impulse Rateau stage is shown in Fig. 7. Such programs have also been developed for performing the calculations related to bolts, thrust forces and drum stages as well.


Mechanical CalculationsAll main components of the machine such as outer casing, rotor, blade carriers, etc., were subject to mechanical calculations under thermal conditions in order to make

sure of the mechanical durability of these parts and components. Sample results are provided in Figs. 8 and 9 for outer casing and blade carrier of the HP1 section, respectively.

Nodal temperature results which show that due to outer surface insulation, the stress is uniform all over the wall.

There is no inner casing used in this machine.

Coupled thermal displacement analysis. The highest stress occurs at the steam admission volute and bolts.

Mechanical analysis for the casing flange and bolts. M110 and M90 stud bolts have been used.

All blade sections are accommodated in carriers supported by the outer casing.

Stress levels at bolt holes and supports can be seen in the picture shown below.

The analyses show good mechanical strength.

Fig. 8: Sample simulation results of the mechanical analysis performed on the outer casing

Fig. 9: Sample simulation results of the mechanical analysis performed on the blade carrier of the HP1 section

MST-35WTE OutlineA preliminary cross-sectional sketch of the MST-35WTE along with a part list of major components identified is presented in Fig. 10.


Fig. 10: MST-35WTE cross-sectional view

Fig. 11: 3D model of the MST-35WTE steam turbine rotor

A more complete and detailed outline of the MST-35WTE steam turbine would be available once specific information of the auxiliary systems’ suppliers are provided and integrated into the model.

Three-dimensional models of the MST-35WTE steam turbine rotor in addition to a complete model of the machine are represented in Figs. 11 and 12, respectively.

MST-35WTE Design FeaturesA few design features of the MST-35WTE are listed below:

• Partial arc admission, 4 arcs in the upper half

• Reaction blading resulting in higher efficiency values

• Robust last stage rotary blades

• Free standing last stage rotary blades for easier assembly and disassembly

• Three extractions for process consumptions

• Optimized, single flow steam path with Rateau stage at the steam entrance to generate more power

• Compact design to minimize the turbine foot print

• Axial exhaust compatible with ACC cooling systems

• Utilizing blade carriers in lieu of inner casing

• Multiple inlet valves

• Steam entrance on top of the outer casing


Item Description Value Unit1 Main steam pressure 58 bar2 Main steam temperature 397 °C3 Main steam flow rate 114 kg/s4 Extraction #1 pressure 17.7 bar5 Extraction #1 temperature 253 °C6 Extraction #2 pressure 5.2 bar7 Extraction #2 temperature 153 °C8 Extraction #3 pressure 1.13 bar9 Extraction #3 temperature 103 °C

10 Condenser pressure (abs.) 0.09 bar11 Exhaust quality 85 %12 Power 90,000 kW13 Isentropic efficiency 86 %14 Dimensions 6.1 x 4.5 x 4.2 m15 Weight 135000 kg

MST-35WTE SpecificationsDetailed specifications of the MST-35WTE steam turbine are presented in table below:

Table 1 - MST35WTE steam turbine specifications

Fig. 12: Complete 3D model of the MST-35WTE steam turbine


02Design and Implementation of Wet Compression System for MGT-70 FleetAbstractGas turbine performance in a constant-volume flow process is impacted by the environmental conditions: The higher the temperature, the lower the performance of the machine. The rather intense variation of the weather all over Iran and the great number of hot days, and the impact on power output of the power plants in line with consumption peaks, have necessitated planning toward grid management and

peak shaving. One effective way to boost machine performance is deploying Wet Compression process to reduce the temperature of the input air, through injecting water into the vertical air intake duct. MAPNA Turbine undertook design and supply of the system and it was implemented in PAREHSAR Combined Cycle Power Plant.

IntroductionIncreasing demand for electricity along with the high performance of gas turbines in dealing with grid load variations and feasibility of heat regeneration using the exhaust gas has resulted in increasing use of the machines throughout the country. MAPNA Turbine, as the manufacturer of MGT-70 machines, has played a great role in developing combined cycle power stations to serve this purpose. Standard design conditions are 15°C and 60% humidity whereas the power stations have been built in locations with far different environmental conditions and most of them experience a lot of hot days in a typical year. The direct impact of high

temperature on the machine performance in hot areas of the country justified a study of compressor inlet air cooling methods whose results are given in the present work.

The most common and the most feasible methods to apply the cooling are based on evaporative process technologies in which, the injected water to the compressor inlet absorbs the heat and evaporates to accomplish the cooling process. In recent years, interest has grown to conduct Wet Compression and inject water into the compressor; as such, it is even used to increase propulsion in aircrafts during soaring.


In this paper, along with introducing and comparing different evaporative cooling methods, their effects on the MGT-70 machines are studied for a few subject cities, based on the available 5-year

meteorological data, for the first time. Then, the implementation of the Wet Compression System in PAREHSAR power station is elaborated on.

Evaporative SystemsWet Compression is a cooling method in which, spraying nozzles are located around the compressor inlet right after the silencer. Water is sprayed into the inlet air in ultra-small (less than 25 microns) particles [1]. It is noteworthy that in this method is the feasibility of water overspray into the compressor to achieve a continuous cooling. This has brought about an advantage for this method compared with other evaporative cooling processes.

Wet Compression process improves the machine performance through three processes: Cooling as a result of evaporation in the vertical duct of the air intake system, compressor air cooling and expansion of the water vapour in the turbine section. Wet Compression process may be applied in two forms: Hot Wet Compression (Swirl Flash) or Cold Wet Compression.

At the first glance, Wet Compression can come across similar to Fogging System, but there are a few fundamental differences between the two:

• Water is injected into the air at the very beginning of the air intake duct in the Fogging System, whereas in Wet Compression, it is sprayed in the compressor inlet and even right into the compressor.

• Fogging can cool the inlet air down to a certain extent based on the saturation limit and efficiency of the evaporative system. In Wet Compression, however, a more effective cooling can be implemented, as water particles are sprayed into the compressor and with the rise of temperature inside the compressor even more capacity to inject water is created.

• Fogging, improves the efficiency through cooling the air intake duct only, whereas in Wet Compression, on top of cooling down the inlet air, the air inside the compressor is cooled down and the intercooling results in less required energy by the compressor to compress the air.

• Last but not the least, as opposed to

Fogging that rather heavily depends on the relative humidity of the inlet air and hence not reliable in humid environments, Wet Compression can be used in all climates, including humid environment, and demonstrates a more effective performance.

There are also differences between Wet Compression and Wet Medium Cooling:

• Redesign and manufacturing of Air Intake inlet to accommodate porous planes associated with the Wet Medium Cooling will involve a long downtime for the machine, whereas the only change to get the Wet Compression System implemented is installation of Water spraying lances downstream of the vertical air intake duct.

• The porous medium required in wet cooling is installed before the air intake filters at the duct inlet, whereas the spraying nozzles of the Wet Compression are installed either at the compressor inlet or right after the silencer.

• As is the case with Fogging, wet cooling can cool the air down to a certain extent whereas there is no such limitation in Wet Compression.

Comparison between Different Evaporative Cooling Systems


MethodsThermoflow® software package has proven to be an inclusive and strong tool to design and simulate power generation units all over the world. Using its GT PRO which is one of the major modules of the package, the initial draft design is identified and performance evaluation is then carried out. Then, using GT MASTER module of the package, off-design simulation i.e. taking into account different environmental and input air conditions, is accomplished. This includes:

• Verifying the results produced in GT PRO module of Thermoflow® taking into account the environmental conditions and real data for MGT-70

• Studying the meteorological data from the authorised meteorology organization in any 3-hour interval of a complete day for a 5-year period, based on which to identify ‘Hot Season of the Year’ (at least one event of 30+°C experienced)

Power Plant/ City Start of Hot Season End of Hot Season Number of

Hot daysAltitude

(m)RASHT July 8 August 24 48 36.7

MAHSHAHR April 1 November 4 217 6.2

Table 1 - ‘Hot Season of the Year’ and height data for each subject city

Table 2 - Pressure losses taken into account

• Identifying the subject hot day of the year based on the average humidity and 3-hour interval temperatures along the 24 hours of each day, and specifying the reduction in temperature caused by the cooling system (evaporation efficiency of 85% for Wet Medium and 90% for Fogging [2] as per the following equation):

• Specifying the overspray water based on 0.5% for Cold Wet Compression System and Swirl Flash (Top Hat) Compression System. The pressure losses per section/system are given in table 2 below:

Inlet Air Cooling System DP [mbar]Air Intake 10Fogging 0.2Media 1

Wet Compression 0.2Swirl Flash 0.2

• Specifying the design temperature for the cooling system (The temperature than which, the air temperature is lower in 90% of the Hot Season)

• Calculating the dimensionless power output (P*) in the hot day of the year in GT MASTER module


ResultsMaking use of the principles discussed in the previous section, evaporative cooling methods for hot days of RASHT and MAHSHAHR power plants were implemented and analysed in Thermoflow®. Diagrams 1 and 2 depict the results. As you can see, Wet Compression leads to the highest power output increase all along the 24 hours of the hot day. Furthermore, Fogging and Wet Medium are shown to have rather similar effect on

the power output increase for both cities and deploying Wet Compression and Swirl Flash Compression produces better results. This is on account of inter-stage water evaporation in the compressor and an increase of the mass flow in the Gas Turbine operating fluid. The additional mass flow increases the enthalpy of the air entering the chamber which in turn increases the power output of the turbine section.

The effect of the evaporative cooling methods on the machine efficiency in RASHT is shown in Diagram 3 below. As you can see, Wet Compression results in a

higher efficiency compared with Swirl Flash Compression, Fogging and Wet Medium cooling methods.

Diagram 1 - Power Output resulting from deploying different evaporative cooling methods for RASHT Power Plant

Diagram 2 - Power Output resulting from deploying different evaporative cooling methods for MAHSHAHR Power Plant


Table 3 - Average consumed water per evaporative cooling method per city (kg/s)

Table 4 - Environmental conditions at PAREHSAR Power Plant

Diagram 3 - Efficiency resulting from deploying different evaporative cooling methods for RASHT Power Plant

The following table shows the water consumption in different evaporative cooling methods. Given the required amount of water to cool down the inlet air and the operating air inside the

compressor, Wet Compression and Swirl Flash Compression consume more water compared with Wet Media and Fogging methods.

Evaporative Cooling Method Rasht (kg/s) Mahshahr (kg/s)Wet Media 0.56 2.05

Fogging 0.58 2.17Swirl Flash 3.14 5.38

Wet Compression 3.01 4.81

The First ImplementationBased on the studies done on environmental conditions of PAREHSAR power station and the specific requirements, Wet Compression cooling system was chosen

and designed for unit one of the power plant. Below are the environmental conditions for PAREHSAR Power Plant:

Dry Bulb Temperature Barometric Pressure Relative Humidity21 °C 1019.8 mbar 80%

The required water by the Wet Compression System is injected through the nozzles installed on the vertical duct into the input air to the compressor. There are 24 lances on the vertical duct and over 1000 nozzles of swirl jet type are laid out on these

lances. The lance arrangement layout is denser above the inlet cone where the mainstream of the inlet air flows, and as we get further away from the centre of the inlet cone, the number of the lances decreases.


FOR WELDING PROCEDURE SPECIFICATIONSEE DOCUMENT E1601-460000923-80-0

SIDED BUTT WELD-MANUAL TIGALL WELDINGS FOR PIPING ARE SINGLE

10 11 12

A

B

C

D

12

Project Title

Assembly No.

Designed byCreated byChecked byApproved by

MaterialWeight(kg)

Tolerance

Reference Document No.

Release Date

RevFormatScaleUnit Sheet

Document Type

Document No.

Responsible Dept.

ENG.R&D1/1mm 0

08.08.2017

AghaeiAbdolahiFardAnsari

PR-AD-01-WCS01-A-309

Wet Compression-Nozzle Rod Array ArrangementWet Compression (Parehsar)

Reference Document

Fig. 1: Lance Layout in the Vertical Duct Section

Fig. 2: Locating the right positions for lances in the Air Intake Vertical Duct

Fig. 3: Installation of the lances in the Air Intake Vertical Duct


Ambient temperature and relative humidity affect directly the required water by the Wet Compression System. The higher the relative humidity, the lower the consumed water to reach the saturation conditions. On the other hand, there are other limitations on deploying the Wet Compression System dictated directly by the machine itself. All these have been used in to correct the control logic of the system.

Ranges for ambient temperature and relative humidity as per the valid meteorological data are given in table 5. The resulted increase in the power output and the demineralised water required in different conditions are calculated using the Thermoflow® package, as presented in tables 5 and 6 below. The data provided is at 0.85% overspray; sea level elevation; pure Methane gas fuel (LHV=45795 kJ/kg) and inlet and outlet pressure loss of 10 mbar conditions.

T ambient 30%RH 70%RH 100%RH20 °C 18.163 16.383 12.91940 °C 28.697 18.159 12.394

T ambient 30%RH 70%RH 100%RH

20 °C 4.689 (Mechanical Limit, at 0.51% Over spray) 5.198 4.369

40 °C 7.335 5.163 3.984

The required water in Wet Compression depends on the ambient conditions. That is why there are six pumps in the relevant pump skid of which the required number will be used based on the demanded amount of demineralised water. Regarding the nozzle layout in the

vertical duct, to prevent nozzle clogging and eliminate detrimental impact on the coatings of compressor blades and vanes, specifications of the demineralised water are of utmost importance. The required specifications are gathered in table 7.

Table 5 - Expected power increase [MW] @ 0.85% overspray and different site conditions

Table 6 - Required water flow rate [kg/s] @ 0.85% overspray and different site conditions

Table 7 - Required quality of the Demineralised Water

Conductivity <1.0 µS/cmSodium & Potassium <0.05 mg/l

Calcium <1 mg/lChlorine & Fluorine <0.05 mg/l

SiO2 <0.02 mg/lPH 5.0-7.5

The general layout of the Wet Compression System equipment installed in PAREHSAR power plant and the interior view of the

system container are shown in Figs. 4 and 5 respectively.


Fig. 4: General layout of the Wet Compression System equipment in Parehsar power plant

Fig. 5: Interior view of the Wet Compression System Container

Fig. 6: A screenshot of the trends for gas and steam turbines, during the operation of the Wet Compression System

To analyze the potential impacts of the Wet Compression System, the coatings of compressor blading and air intake will be monitored during the unit inspections. Coating system of the vertical duct is adequately resistant and no modification of that is required, whereas for the internal faces of the compressor cone and bearing pedestal, the thickness of the applied coating will need to increase. All required activities in this area are due for completion during the machine inspections.

Upon conclusion of installations and commissioning, the first Wet Compression System designed and developed by MAPNA Turbine was tested in Parehsar power plant on the 21th of November 2017. Given the ambient temperature and relative humidity in the cold season, only 3 pumps of the Wet Compression System were deployed and an increase of about 15 MW was achieved for gas turbine (from 141 MW to 156.7 MW) as shown in Fig. 6.


ConclusionsA Thermoflow® simulation of various methods of evaporative cooling, applied on the MGT-70 inlet air, showed that Wet Compression resulted in the most increase in the power output of the machine in all studied points (ambient conditions). On one hand, deployment of this technology through equipping the existing gas turbine

machines with the Wet Compression System can optimize the operation of power stations and make up for ambient-imposed losses, and on the other hand, given the independence of the Wet Compression System, operation in all ambient conditions is made possible.

References[1] ‘The TopHat turbine cycle’, Modern Power Systems, 04.20.2001 (Online). Available at: http://www.modernpowersystems.com/features/featurethe-tophat-turbine-cycle/

[2] M.Chaker,C.B.Meher-Homji T.Mee II, A. Nicolson, ‘Inlet Fogging of Gas Turbine Engines-Detailed Climatic Analysis of Gas turbine Evaporative Cooling Potential’, Proceedings of ASME Turbo Expo 2001.


03Additive Manufacturing Technology to Play a Key Role in the Evolution of the MGT-70 Gas Turbine SeriesAbstractMAPNA Turbine, as a key player in the field of turbo-machinery, aim at taking advantage of Additive Manufacturing technology (AM) in the production of their machines as well as a tool in producing prototypes. As one of the first steps to reach this goal, it was decided to choose a specimen to be produced by additive manufacturing technology. After going through the entire path of part selection, design for AM, manufacturing, inspection and qualification; a prototype of the part is

produced. In this article, the manufacturing process and the relevant destructive qualification tests carried out by MAPNA Turbine Blade (PARTO) are generally reviewed. The manufactured specimen successfully passed all the qualification tests and the best condition of production route was identified. Therefore the component was approved and now it has been assembled in an MGT-70 gas turbine to undergo the operational tests as the first additively manufactured prototype.

IntroductionDue to some unique features such as flexible design techniques, wide range of material properties, high rate of production, high buy to fly ratio, etc., additive manufacturing (AM) processes have become more attractive in the few past years. These processes give the designers the power to conceive more complex parts, the manufacturers the power to fabricate parts with higher production rate at a relatively low cost, and finally the organization the competitive advantage to compete more powerfully

in the market. Therefore, it stands to reason that most pioneers in various industries like biotechnology, energy and aerospace have a tendency to implement the technology [1].

Despite the aforementioned facts, the technology development is still on the rise and it is anything but simple to apply in production lines, especially in the field of metal-work. Some of the most critical challenges are listed below [2]:

• The right shape of part in comparison


with the model

• Part qualification

• Uniform properties of the raw materials

• Part size and material limitations

• Uniform properties in serial productions

• Anisotropy of the part properties

• Economical concerns of the process

Furthermore, one case study of implementation of the additive manufacturing process instead of the common investment casting in a real

turbine component was investigated. The project was conducted by a joint technical team consisting of MAPNA Turbine and MAPNA Turbine Blade (PARTO) representatives. It is acknowledged that the components were manufactured and the metallurgical tests were carried out by MAPNA Turbine Blade (PARTO).

After successfully passing all the designed qualification tests to ensure the quality of the part, the first additively manufactured prototype was assembled on an MGT-70 gas turbine for testing in service conditions.

Materials & MethodsPart SelectionAccording to the following parameters, axial swirler of MGT-70 was selected to be produced using additive manufacturing process:

• Maximum part size is less than 20 cm; therefore it can be produced by the candidate SLM machine.

• The base material is Hastelloy X whose relative powder grade is available

• The production method of the swirler is investment casting and the properties of the AM parts are more comparable to castings than forgings.

• The swirler can be assembled/ disassembled individually on the

turbine without disassembling other parts.

• The part can be inspected visually and metallurgically during the minor inspections of the turbine.

• The risk of the failure is not too high in comparison with other options for the specimen.

Additive Manufacturing & Related ProcessesThe original axial swirler is made of Hastelloy X super alloy. It is one of the solid solution nickel based super alloys. The relative grade of the AM powder is very similar to the original one and manufactured by many powder suppliers. The chemical analysis of the material is shown in Table 1.

Element C Si Mn Cr Mo Ti Al W Co Ni Fe Cu B S P

Value 0.01 < 1.00 < 1.00 22.00 9.00 < 0.15 < 0.5 0.20-1.00 1.50 Base 19.00 < 0.5 < 0.01 < 0.03 < 0.04

Table 1 - Chemical Analysis of the Hastelloy X Material [3]

The component was manufactured by Selective Laser Melting (SLM) method using EOS M290 machine. In addition, for the qualification tests the relative near net shape test pieces were manufactured with parameters similar to the main component.

After production, a heat treatment cycle was performed. It should be noted that the part undergoes heat treatment with the right platform and supports to prevent distortion. At last, all the supports

were removed by machining, grinding and polishing to produce the final net shape component. The AM axial swirler is illustrated in Fig. 1.

Moreover, to improve mechanical properties at high temperatures and compare the properties to the former condition, an additional special post-processing was carried out on some heat treated samples.


Qualification TestsMicrostructure evaluations were carried out on the samples to control the porosities (number, type, orientation and distribution) and microstructure (second phases, dendritic structure and uniformity). To do so, some samples were cross cut parallel to the build direction to evaluate the microstructure using optical and electron scanning microscopes.

Based on the service conditions of the swirler, the following mechanical properties have been evaluated:

• Tensile properties at room temperature

• Tensile properties at 816 °C

• Stress Rupture at 816 °C and 103 MPa load

Fig. 1: Additively manufactured Swirler of the MGT-70 burner

Fig. 2: Microstructure evaluation of cross sections parallel to the build direction by optical microscope

(a) as-built (b) after heat treatment (c) after heat treatment + special post process

(a) (b) (c)

Results & DiscussionMetallurgical ResultsThe microstructure of the AM samples in different conditions by OM and SEM is shown in Figs. 2 and 3, respectively. The laser path pattern are obvious in Fig. 2-a. The width of each line is about 70 µm that represents the diameter of the melt pool. But the microstructure shows an extreme inhomogeneity and segregation due to high cooling rate of the melt pool.

It is reasonable that heat treatment process increases the homogeneity of the microstructures based on the inter-diffusion

of the atoms induced by heating. Fig. 2-b shows clear grain boundaries of Hastelloy X. But there are some discontinuities in grains or at gain boundaries. High rate of cooling during the AM process causes incomplete fusion of powders or improper solidification of the melt pool. These porosities reduce the properties of the material and shall be omitted especially in long time services [4]. The Fig. 2-c shows related microstructure after post-process. It is clear that post-process dramatically decreases the amount of defects and maintains the uniform grain boundaries.


Fig. 3: Microstructure evaluation of cross sections parallel to the build direction by optical microscope

(a) as-built (b) after heat treatment (c) after heat treatment + special post process

Fig. 4: Normalized mechanical properties of test bars produced in different conditions (a) tensile properties at room temperature (b) UTS at 816°C

(c) Stress rupture at 816°C and 103 MPa

(a)

(a)

(b)

(b)

(c)

(c)

Fig. 3-a, illustrates the morphology of the as-built AM sample on a larger scale by SEM. The lack-of-fusion zones are distributed in the microstructures. Also, some micro segregation and cast-like areas are obvious in the middle of the figure.

As mentioned previously, after the heat treatment, grain boundaries are exposed which is illustrated in Figs. 3-b and 3-c.

Geometry features and trans-granular nature of the discontinuities, reveal that this originates from lack of local heat treatment in those specific zones rather than a metallurgical culprit. Therefore, the risk of ending up with such defects can be mitigated through a parameter modification or post-processing. The microstructure of samples with post-processing corroborates this.

Cast-like areas

Mechanical PropertiesFig. 4 illustrates mechanical test results at room temperature, high temperature, and long-term high temperature. All diagrams comprise the three conditions of casting; additively manufactured + heat treatment and additively manufactured + heat treatment + post process. It should be noted that all values are normalized.

Yield stress and UTS of tensile tests at

room temperature are shown in Fig. 4-a. The AM samples have tensile strengths of about twice as high as that of the casting samples. This is attributed to the extra fine AM micro structures. But the post process has little effect on the tensile properties at RT. It shows that the defects are too small to have any effect on the strength, but can still lower the elongation upon failure; consistent with the report of Lewandowski et al. [4].


The results of the tensile properties at high temperature are similar to those at room temperature. But the values associated with the AM samples at high temperature are closer to those associated with casting samples compared with the test results at room temperature. This is also related to the fine structure of AM which is less effective at high temperature.

The influence of the defect is more severe in longer term properties and life at high temperature due to lower toughness and

creep strength. Fig. 4-c illustrates that the life of the post processed sample is about twice as long as that of the castings and the Additive Manufactured ones without post-processing. Therefore, the post-processing is essential especially for components in high temperature service conditions.

Again, it should be noted that all the AM samples (with/without post-processing) have better properties than the minimum casting requirements.

ConclusionsAfter the qualification tests of the samples, it is established that the swirler can be fabricated through additive manufacturing process. All the required mechanical properties at room temperature show an excellent enhancement with properties considerably better than those of the cast specimens. In addition, the high temperature properties meet the minimum component required specifications. The post processed sample showed a better enhancement in high temperature mechanical properties in comparison to the sample without post processing. But both of them have better properties than those of the standard castings.

As a result, the AM swirler has successfully passed the tests and fulfilled the expectations. Therefore, it was assembled in a real MGT-70 gas turbine as a prototype for some operational tests.

To establish the AM process as the reliable manufacturing process of the swirler, it is necessary to investigate the geometrical and metallurgical properties of the material after a specific period of service lifetime, but it can be said that the first additively manufactured component has been deployed in a MAPNA Turbine product.

References[1] “Wohlers Report 2017: 3D Printing and Additive Manufacturing State of the Industry Annual Worldwide Progress Report”, Wohlers Associates, Inc., 2017.

[2] W.Gao, Y.Zhang, D.Ramanujan, K.Ramani, Y.Chen, C.B.Williams, CC.L.Wang, Y.C.Shin, S.Zhang, P.D.Zavattieri, “The status, challenges, and future of additive manufacturing in engineering”, Computer-Aided Design, 69, 2015, PP. 65–89.

[3] TUGA Doc. No. MTS39902, “Specification for Additively Manufactured Turbine Parts Made of Hastelloy X”.

[4] J. J. Lewandowski, M. Seifi, “Metal Additive Manufacturing: A Review of Mechanical Properties”, the Annual Review of Materials Research, 2016, PP.14.1-14.36.


04Towards Excellence in Designing Axial CompressorsIntroductionThe present work provides an account of the systematic approach in design of a 5-stage axial compressor. To complement the design verification process, MAPNA Turbine’s axial compressor test bench was also made use of. The design of the test bench was a part of MAPNA Turbine’s comprehensive axial compressor laboratory development program to serve three main purposes:

1- Verify and optimize the design carried out through using software packages and analytical tools

2- Performance test of manufactured compressors

3- Evaluation of design modifications (e.g. wet compression, variable vane optimization, fouling effects, etc.) on the

existing fleet

The designed machine is a 5-stage axial compressor with variable inlet guide vanes. The pressure ratio of the compressor is 3.2 with isentropic efficiency of 88% and mass flow rate of 18 kg⁄s at 15000 rpm. The present article outlines the design procedure of the mentioned axial compressor which has been accomplished by taking into account both mechanical and aerodynamic aspects through a careful trial and error procedure. In-house Development and completion of the relevant design software is considered as one of the greatest achievements of this project. However, accredited commercial software packages have also been employed for flow analysis and mechanical simulations.

Aerodynamic DesignThe required inputs for aerodynamic design include mass flow rate, isentropic efficiency, pressure ratio and surge margin of the compressor. The output comprises 3D geometry of compressor blades which provides the nearest performance to the defined input data. In aerodynamic design, several approaches are applied in

a complex computational process. These approaches include:

Mean-line DesignIn this procedure, a close estimation of the compressor size, load distribution in various steps and the overall performance of the compressor is established.


Through-flow DesignIn this approach, radial equilibrium equations along with equations of velocity triangle distribution are applied in order to extract velocity triangles in various sections of compressor blades. Sections of blades are designed based on several conventional profiles such as DCA, NACA 65 and NACA 63 by using the extracted velocity triangle and empirical relations.

Generation of the 3D GeometryAt this step, 2D blade profiles are designed and put on guide curve in order to obtain 3D geometry at each stage. Subsequently, designed blades are assembled together in order to achieve the 3D geometry of the axial compressor. This approach is able to generate geometries with sweep, which are used in novel compressors. A flowchart of the design procedure carried out is presented in Fig. 1.

Fig. 1: Axial compressor design flowchart

OptimizationSeveral parameters are required to design an axial compressor. Some of these parameters are defined based on experience; however, most of them require performance computations to be carried out considering aerodynamic and mechanical constraints to deal with. Load distribution on blades, mechanical stresses applied on blade roots, Mach number and the angle of flow are some of the most important constraints. Due to multiplicity of the parameters involved and the design constraints, an optimization process is carried out to end up with appropriate design parameters, taking into account all the mechanical and aerodynamic constraints in order to design a compressor

with a performance as close as possible to the design inputs.

A meshed 3D geometry and the relevant sample simulation results representing flow streamlines within the designed compressor path are shown in Figs. 2 & 3, respectively.

In order to make sure that the implemented design is adequate, performance curves as well as detailed flow patterns within all stages of the compressor are further investigated. Pressure-Efficiency curve obtained from the numerical simulations is compared with the initial aerodynamic design code, as shown in Fig. 4. The proximity of the curves is due to the corrections made to the developed design tools on the effects of: span-wise mixing, end-wall boundary layer, etc.


Fig. 2: Meshed 3D geometry of the designed compressor

Fig. 3: Representation of flow streamlines within the compressor

Fig. 4: Efficiency vs. pressure ratio of the designed compressor

Mach number contours on the mid-span of the blades of different stages are also shown in Fig. 5.


Fig. 5: Mach number contours over different stages of the compressor

Fig. 6: 3D Representation of a typical rotary blade

Mechanical DesignMechanical design of the compressor test case was carried out using CAD and analytical means. Each component meets its specific requirements. Having the flow path established, the design procedure begins with flow components i.e. rotary and stationary blades and continues to other parts of the rotor and casing. Designed core properties are then used to specify compatible sub-structure and mountings. Other components including gearbox mounting and air delivery facility are also taken into account. A description of design-by-analysis approach adopted for the design of each and every component is further outlined below:

RotorPreliminary design of the axial compressor blades is initiated after the pre-aerodynamic airfoil is sized and the speed range, number of blades and stages as well as other parameters are determined. Mechanical properties of the presented airfoil geometry define initial disk design and its cross sectional shapes. Simulation activities are then performed to optimize the aeromechanical behavior (i.e. flutter and forced response) of the blades. A 3D representation of a typical rotary blade is shown in Fig. 6.

In order to avoid probable flutter within the operating range of the machine, geometrical features of the blades such as sweep and dihedral angles were modified iteratively using the in-house software called FluVib. According to the results, no flutter will occur over the operating range of the machine, consistent with the empirical results provided by the literature.

Among all designs available, the dovetail attachment scheme was chosen for installation of the blades onto the disks. The design characteristics were also optimized so as to increase the contact area between the blades and disks as much as practicable. A cross-sectional view of the proposed dovetail attachment design is shown in Fig. 7.


Fig. 7: Cross-section view of a typical dovetail attachment design of a rotary blade

Fig. 8: A typical compressor rotary disk

Fig. 9: Compressor Rotor assembly

Compressor blade disks are designed so that strength conditions as well as isolated blades vibrations and maximum torque transition capability are all ensured to be equal to the specified values or within

acceptable ranges. An outline of a typical rotary disk is illustrated in Fig. 8. Disks are assembled together using tie rod stacking scheme. The assembled compressor rotor is also shown in Fig. 9.

Rotor DynamicsA comprehensive rotor dynamic analysis was carried out in order to better understand the loads generated during operation of the designed compressor and also to make sure that the operating speed is far enough apart from the critical speed of the rotor. A simplified model was

proposed based on distribution of the mass and stiffness in the rotor.

Each blade disk is considered as a lumped mass in the geometrical model developed for numerical studies with distribution of masses over the length of the rotor. Heavy items outside the rotor span, i.e., the distance between the bearings on either


side of the rotor, such as half-coupling are also included in the model. The whole rotor is considered to stand on bearings connected to the ground via radial springs, i.e., those related to struts, base frame, etc. In addition to stiffness, the bearings introduce damping characteristics to the model as well. The effects of casings stiffness were also considered in the model using either lumped mass or beam element for parts with considerable bending attribute.

The aim of the design was to make sure that the rigid rotor assumption was realistic. This implies that high-velocity balance of the rotor could be avoided and an increased life time could also be achieved. A rigid rotor is presumed to operate below the first flexible vibrational mode of the rotor and to investigate the matter; the critical speed of the rotor is calculated given the damping and stiffness characteristics of the bearings. The results demonstrated satisfactory performance of the rotor as the first critical speed of the rotor is well above the operating range of the rotor.

Bearings The selection of the bearings was limited only to the rolling contact bearings to provide adequate stiffness required by the design of rotor dynamics and the results of analyses performed. Therefore, precision cylindrical rollers were selected due to their high angular velocity and stiffness. Lubricant feed and assembly precision also had to be taken into account since these might have great impact on overall prices.

As the angular velocity of the rotor reaches the operating point, heat generation inside bearings increases dramatically to levels which make employing ceramic coated contact surfaces as well as forced lubrication schemes inevitable.

To facilitate mounting and also to control bearing stiffness, the bearings are selected to have a central conical hole which allows for controlling the applied preload and bearing stiffness by adjusting the outer diameter increment of the bearing. A hydro-dynamical thrust pad bearing is also employed to withstand thrust forces of the rotor.

CasingsThe overall design procedure of the casings was implemented through four

design stages. The first stage, taking care of different configurations based on assembly procedures, bearing locations and stator blades insertion scheme led to a general assembly consisting of three compartments, i.e., inlet, middle and outlet casings. The inlet casing will be used to accommodate the IGVs and the rotor bearings will also be placed within the inlet and outlet casings.

The middle casing is split vertically along the rotor and accommodates stationary blades or vanes. The outlet casing is also attached to the exhaust casing.

The second design stage was dealing with internal pressure bearing strength using the guidelines of API-617 international standard. The blade-loss and thermal loading effects were also addressed using the guidelines provided in ASME SEC VIII as well as available analytical formulas. Prior specifying the thickness for each casing, materials were selected taking manufacturing processes required as well as highest stresses encountered simultaneously into account.

In the third design stage, the connection between the root of vanes and the middle casing were analyzed. Assembly procedures and manufacturing processes in addition to the stresses encountered were again main factors to take into account. The stiffness of the struts which has a direct effect on the rotor dynamics was also analyzed during the last design stage.

In addition to compressor casings, the compressor inlet also comprises a plenum which acts as a sub-sonic diffuser and is designed according to the guidelines of the ASME SEC VIII. The plenum is attached to the compressor inlet using a rubber material with a relatively low stiffness.

Inlet Guide Vanes (IGVs)The designed compressor is equipped with a row of 37 vanes known as Inlet Guide Vanes (IGVs) installed at the inlet of the compressor just before the rotary blades of the first stage of the compressor.

The relative angle of the airflow entering the compressor is controlled by adjusting the IGVs angular position and hence avoiding the flow separation and compressor stall during operation of the machine.


Different IGV mechanisms including linkage and geared types which are among the most common mechanisms for turbo-machinery applications were analyzed and compared based on performance, efficiency, accuracy, reliability, cost and required manufacturing processes.

The quantitative and qualitative analyses carried out by weighting the design parameters led to selection of the geared type mechanism as the most appropriate

option for the designed compressor.

As shown in Fig. 10, the geared mechanism comprises two main parts; rack and pinions. The pinions are installed on each IGV providing rotational motion and the rack is mounted on the inlet casing to engage with the pinions. An electrical actuator with linear motion capability is also employed as an actuation device for the system to provide the required motion of the rack.

Fig. 10: IGV Mechanism

The sizing of different parts of the IGV mechanism including diameters of the rack and pinions were also finalized via detailed kinematic simulation of the mechanism carried out to achieve the required angular position of the vanes. The loads were also calculated for each part by carrying out in-depth static and dynamic analyses to make sure of the adequate strength of each part.

Sub-structure & MountingsThe axial compressor test case is connected to a ground-mounted electrical motor and subsequent gearbox and output shaft, on a T-Slotted substrate all together consisting MAPNA Turbine axial compressor test bench.

The sub-structure shown in Fig. 11, accommodates gearbox, coupling guard, exhaust volute, axial compressor and supports of the IGV mechanism’s jack. It consists of a base frame with lifting lugs on which there are two skids equipped with lifting lugs, accommodating gearbox and

axial compressor each. Such an assembly was developed to address vibrational and alignment concerns.

The gearbox skid provides a platform for torque meter and coupling guard, meanwhile the compressor skid accommodates spring-plate mounted compressor core as well as adjustable supports of the exhaust volute and IGV jack mounting.

To make sure of the safe and smooth operation of the axial compressor, the structural safety of all parts and components were taken into account in addition to other criteria including accessibility, manufacturability, alignment requirements and transportation.

The main acting loads on the structure include abnormal operation of the machine, erection and transportation; unsteady vibration and subsequent loading.


Fig. 11: Sub-structure assembly of the axial compressor test case (Compressor mounting points shown in red)

A series of in-depth finite element analyses was carried out in order to assess vibrational characteristics of the axial compressor.

Such analyses were also conducted to optimize stress bearing capacity as well as material consumption.

ProspectsWith a number of gas turbine upgrade, design and redesign programs in sight, developing new software packages and test bench facilities in the field of turbo-machinery are deemed to be extremely crucial for MAPNA Turbine. The development of the axial compressor test bench has been part of the comprehensive plan of experimental infrastructures development pursued by MAPNA Turbine.

A careful scrutiny of the design process of a transonic axial compressor test case

was provided in the present article. The design process carried out led to the development of several in-house design tools and approaches that could be further validated and optimized via implementation of performance tests and experimental measurements. This will serve as a proven, scientific ground to promote innovation, research and development in the field of axial compressor engineering and design.


05Scrutiny of Measurements Performed on MGT-70(3) Gas Turbine Prototype

IntroductionMGT-70(3) gas turbine is the latest upgraded version of the MGT-70 gas turbine family introduced by MAPNA Turbine recently. The main improvements implemented on this newly upgraded machine include:

3D Airfoil Design of the First Four Stages of the Compressor Optimization of the IGV blades as well as the blades and vanes of the first four stages of the compressor leading to increase in the compressor air mass flow rate, enhanced compression ratio and thereby isentropic efficiency of the compressor.

New Journal-Thrust Bearing DesignRe-design of journal-thrust bearing component at the compressor side, increasing mechanical strength of the machine.

3D Airfoil Design of Turbine Blades and VanesRe-design of turbine blades and vanes at all four stages as well as using advanced materials and improved coatings leading to higher power output and efficiency of the gas turbine.

Obviously, experimental tests were needed to assess the overall performance of the newly upgraded MGT-70(3) gas turbine to make sure whether the improvements in the design parameters were achieved and also to introduce careful adjustments to design models, if necessary.

So, due to the nature and multiplicity of changes introduced, substantial in some cases, it was necessary to not rely just upon the ordinary performance tests occasionally carried out, focusing generally on the overall inputs and outputs. Instead, it was decided to perform extensive measurements on the parameters inside the MGT-70(3) gas turbine prototype. So, an extensive testing project was also defined and finely pursued along with the design project itself.

Such experimental data have the power to verify the claimed design improvements or refute them altogether. In the case of the MGT-70(3) gas turbine, due to the fact that it was practically the first MAPNA Turbine’s experience in the design of gas turbine compressors, the experimental verification was even more important.


The test project was decided to be implemented along with an upgrading project for installation and mounting of the test equipment to be carried out in parallel to the rest of required upgrading operations.

Unit 6 of PARAND Combined Cycle Power Plant was chosen for this purpose and in parallel to the beginning of machining operations of the components, the required modifications as well as machining provisions needed to accommodate test equipment on related components were covered. The installation of test equipment and instruments was later carried on during the assembly of the parts and components of the machine.

It is to be noted that, the PARAND Combined Cycle Power Plant located 40 km south of Tehran, the capital of Iran, comprises 6 units of different versions of the MGT-70 gas turbine series.

Selection of the PARAND Combined Cycle Power Plant for implementation of the experimental tests is deemed to be the best possible choice from different perspectives. First and foremost, it is a power

plant owned by MAPNA Group and rather close to the MAPNA Turbine Company. Moreover, there are different versions of the MGT-70 gas turbine series concurrently in operation at this power plant which makes it possible to draw comparisons between operational performances of different gas turbines in the same ambient conditions. Prior to the implementation of the latest upgrades and concurrent test project, there were five V94.2 Ver.3 gas turbines with nominal power output of 157 MW as well as an MGT-70(1) gas turbine with nominal power output of 166 MW in operation at the Power Plant. Unit 6 of PARAND Combined Cycle Power Plant equipped with an MGT-70 gas turbine was selected as the platform to implement the latest upgrade and associated test project for the first time. The current essay mainly deals with the test project as the MGT-70(3) machine design improvements and enhancements have been extensively discussed elsewhere, in the preceding editions of the Technical Review.

The specifications of the MGT-70(3) gas turbine are listed in Table 1.

Parameter (Unit) ValuePower Output* (MW) 185 MWEfficiency (%) 36.4%Compressor Inlet Air Mass Flow Rate (kg/s) 545Compressor Ratio (-) 12Turbine Inlet Temperature (°C) 1090

* ISO Rated Power

Generally, the experimental tests carried out on the MGT-70(3) gas turbine prototype fall into the following three categories:

• Fluid Dynamic Tests for Aerodynamic Measurements in Turbine and Compressor Sections

• Components Temperature and Combustion Chamber Emission Levels Measurement Tests

• Gas Turbine’s Mechanical Design Verification Tests

Table 1 - MGT-70(3) gas turbine specifications


Fluid Dynamic Tests for Aerodynamic Measurements in Turbine and CompressorTwo test categories were defined and carried out for this purpose. The first category was devoted to the gas turbine performance tests generally carried out following the installation and commissioning of each new gas turbine unit or upgrade and overhaul projects. The only difference in implementing the performance tests of the first MGT-70(3) gas turbine prototype was the duration of the tests scheduled to take place within a 7-month period. This led to production of a significant amount of performance data for the MGT-70(3) gas turbine over a wide range of operational and ambient conditions.

The second category of tests aimed at evaluating the design conditions of gas turbine and compressor. These tests were far more comprehensive than the general performance tests such that all flow characteristics were measured at different stages of the designed compressor and gas turbine. Measurements of wall pressure and temperature at different stages of the gas turbine and compressor were also implemented in this category of tests. However, in the first four stages of the newly designed compressor, such measurements were carried out even in between compressor stages.

Furthermore, measurements of main flow characteristics along the span of the blades, covering pressure, temperature, velocity components, flow direction and Mach number were carried out using 5-hole probes, typically shown in Fig. 1.

The most important feature of such measurements was the capability of moving along the length or span of the blade using traverse system at both compressor and turbine compartments with an extra capability of probe rotation at turbine compartment. This makes it possible to move along the radial direction in tiny steps so that flow characteristics measurements are carried out in this direction. This category of tests also made it possible to conduct flow characteristics measurements at the exit of the compressor diffuser using specially designed rakes made up of 5-hole probes.

Unlike the first category of tests which enabled the analyzer to get merely the general parameters of a main component inside the machine, the second category of tests allowed detailed flow patterns to be specified in passing through different stages.

Overall, thirty traverse systems equipped with 5-hole probes were installed at the compressor compartment in addition to the four installed in the gas turbine. Three rakes made up of 5-hole probes were also used at the compressor diffuser outlet. There were also four to six pressure taps along with relevant thermocouples installed on the wall at different locations.

The data acquisition sensors were sufficient to produce experimental data that was used as the best criteria for evaluation of the overall performance of the compressor, turbine and the whole machine subsequently. The data simply makes it possible to compare test results with expected design outputs for different operational conditions.

So, the accuracy of design outputs as well as the numerical simulations and analyses performed was thoroughly investigated, contributing to a better understanding of the cases that numerical calculations might lead to overestimates, underestimates or even a wrong estimation of a physical phenomenon due to different working conditions, simplifications made or modeling approaches adopted. It allows us to face, analyze and fix each problem with a wider perspective.

The aerodynamic measurements planned to be implemented in the gas turbine, included hub and shroud wall pressure and temperature measurements as well as hot gas flow parameters comprising overall pressure, temperature, velocity, Mach number and flow angle at two different sections of the fourth stage of the gas turbine. A schematic representation of measurement points of the MGT-70(3) gas turbine prototype along with typical 5-hole moving probes is shown in Fig.1.


Fig. 1: Schematic representation of the MGT-70(3) gas turbine aerodynamicparameters measurement points and sections

Fig. 2: Static pressure distribution measured over the hub & shroud of the MGT-70(3) gas turbine

A comparison carried out between the acquired data and the results of the numerical simulations, not only verified the aerodynamic design process of the MGT-70(3) gas turbine but also demonstrated the acceptable precision of the numerical codes.

Fig. 2 shows static pressure distribution

measured over the MGT-70(3) gas turbine hubs and shrouds along with the results of the computational fluid dynamics (CFD) studies. As can be seen, there is only a slight difference between the calculated and measured static pressure values implying the rather high precision of the numerical codes and methods applied.

Fig. 3 represents normalized velocity distribution of the hot gas at the inlet of the fourth stage of the MGT-70(3) gas turbine. The differences between numerical and measured values at mid-span sections are apparently smaller than those near to the walls. This is primarily related to the more complex flow patterns near the walls due

to the presence of vortex-affected flows. Furthermore, it is to be noted that, the silo-type design of the MGT-70 gas turbine series would result in asymmetric flow parameters at traverse measuring points, although the flow is assumed to be symmetric in order to reduce the computational costs of the CFD simulations.


Fig. 3: Normalized velocity distribution of the hot gas at the inlet of the fourth stage of the MGT-70(3) gas turbine

Combustion Chamber Pollution Emissions & Components Temperature MeasurementsAims and Scope of the MGT-70(3) Gas Turbine Combustion Chamber TestsGiven the magnitude of the changes introduced at this compartment, the field tests carried out on the combustion chambers of the upgraded MGT-70(3) gas turbine included measurement of emission levels as well as temperature and its distribution over the surfaces of the components. So, the main goals associated with the combustion chamber measurement tests were as follows:

• Validation of the CFD analyses performed

• Development of an experimental - computational framework to accurately predict the temperature of the combustion chamber components

• Obtaining the temperature of the combustion chamber components in order to perform lifetime and thermo-mechanical analyses

• Measurement and evaluation of the MGT-70(3) gas turbine emission levels

Thermocouples Installation Points The selection of the components and parts of the combustion chamber for

temperature measurements which serves as the first step to design combustion chamber compartment tests depends on the vulnerability of each part or component to the inflicted thermal loading, in the first place. Identification of the critical parts and components was carried out based on the periodic inspection reports available as well as numerical analyses performed.

Based on these criteria and due to some practical test considerations, temperature measurement of the mixing chamber and inner casing parts was put on the agenda.

So, 40 type K thermocouples were employed to measure the temperature of the mixing chamber and inner casing components each, comprising an overall of 80 K-type thermocouples used for this purpose. The thermocouples were installed on the left hand side of the inner casing and the left-side mixing chamber as shown in Fig. 4. The washing holes on either side of the outer shell provided a pathway for the wires of the thermocouples installed on the mixing chamber. Several holes were also created on the center casing to provide room to conduct the wires of the thermocouples installed on the inner casing.


Surface Temperature Measurement Calibration TestsPrior to installation of thermocouples and measurement of temperatures on the mixing chamber and inner casing components, several experiments were designed and carried out in order to come up with the most appropriate mounting

procedure of thermocouples on metal surfaces and also to run a measurement accuracy check. Fig. 5 represents photographs of the fabricated test setup. During these tests, surface temperature measurement errors of thermocouples at different mounting arrangements were calculated and subsequently the most precise method was determined.

Fig. 4: Schematic representation of thermocouples installation points on mixing chamber (left) and inner casing (right) components

Fig. 5: Surface temperature measurement calibration tests setup

Thermocouples Installation Procedure The installation process of thermocouples on combustion chamber components began following the implementation of measurement calibration tests. Photographs of the MGT-70(3) gas turbine mixing chamber and inner casing following the installation of thermocouples and related equipment and connections - such as sealing glands and extension wires - are presented in Fig. 6. Installation of thermocouples on the outer surfaces of the components was achieved via spot welding method using strips of the same material as the base metal.

Emissions & Temperature Measurement Results The data acquisition process of the installed thermocouples lasted 6 months at different ambient and operational conditions including gas and liquid diffusion as well as premixed modes of operation, different Turbine Inlet Temperatures (TITs) and loads.

Sample normalized measured temperatures corresponding to a specific operating conditions of the MGT-70(3) gas turbine as listed in table 2, are presented in Fig. 7.


Fig. 6: Temperature measurement test equipment installed on combustion chamber components; thermocouples installed on the inner casing (top left); sealing glands and thermocouple

connections (top right); thermocouples installed on the mixing chamber (bottom left); extension wires attached to thermocouple connections (bottom right)

Parameter [Unit] ValueAmbient Pressure [pa] 88885Ambient Temperature [°C] 39.6Relative Humidity [%] 12.25Power [MW] 126TIT [°C] 1070

Table 2 - Operating conditions of the MGT-70(3) gas turbine corresponding tothe temperature measurements provided

Initial comparison between the test results and computational analyses is indicative of the acceptable precision of the MGT-

70(3) gas turbine combustion chamber reactive flow simulations.

Fig. 7: Normalized measured temperature at each thermocouple installation point located on the mixing chamber (left) and inner casing (right) components


Fig. 8: Vibrational data collecting, processing and displaying cycle (courtesy of FOGALE nanotech)

It is to be noted that, based on the emissions measurements carried out in the upgraded MGT-70(3) gas turbine, no meaningful differences were observed in NOx emission

levels between TITs of 1060°C and 1090°C, and the emission levels remained almost unchanged.

MGT-70(3) Gas Turbine Mechanical Design Validation TestsDuring the MGT-70(3) gas turbine upgrading project, several parts of the MGT-70 gas turbine underwent major modifications namely geometrical modifications and loading of the rotary blades of the first four stages of the compressor as well as those of all four stages of the turbine compartment. Structural dynamics including forced vibrations (due to aerodynamic oscillatory loadings) and aero-elastic instability phenomenon (due to fluid solid interactions) are among the main design and evaluation criteria of the blades.

At design stage, some criteria were taken into account to make sure of the safe operation of the blades with the new conditions based on the design knowledge and prior experiences in this regard and the design was carried out within the safe operating bounds.

It is to be noted that, the vibration amplitude of the rotating blades is difficult to be determined using numerical tools and shall be checked and ensured necessarily using experimental methods.

Blade Tip Clearance (BTC) & Blade Tip Timing (BTT) Tests • Sensors & Data Acquisition System

It was decided to take advantage of the knowledge and technology of a company specialized in the field of rotating blades vibration measurement to carry out the tests in this regard. Following some correspondence with several corporations, the FOGALE nanotech Group; Turbomachinery division expressed their interest to cooperate with MAPNA Turbine in this project and sent an initial proposal following the receipt of the request for proposal and preliminary contacts. In the proposal, the general concept of a vibration measurement method called BTT was described and a number of sensors of the same type were introduced for the compressor and turbine compartments separately. Data transfer cables, data acquisition method and the operating software were also briefly introduced. An illustrative cycle of vibrational data collecting, processing and displaying is presented in Fig. 8.

The principles of capacitive resistance measurement for carrying out calculations related to BTT and BTC are so that the capacitive resistance between the blade and sensor tip is measured, but other error factors are removed or filtered out. This takes place in a way that the capacitive resistance between the guard wall and

wire as well as that induced by the leakage from the guard wall are filtered out, and so is the capacitive resistance between the guard wall and earth. A schematic representation of capacitive resistance generally encountered in a typical sensor measurement is presented in Fig. 9.


Fig. 9: Capacitive resistance in typical sensor measurements (courtesy of FOGALE nanotech)

Fig. 10: Typical blade tip deflection

The signals received by the Data Acquisition system (DAQ), if measured via maximum capacitive resistance amplitude indicate minimum clearance of the blade tip and as the capacitive resistance becomes

smaller and smaller, it means that the clearance between the blade tip and sensor (BTC) has increased. Variation of typical blade tip deflection over time is plotted vs. revolution in Fig. 10.

If the theoretical blade peak location is compared with the actual peak location, the blade vibrations (BTT) would be measured; FOGALE nanotech claim that they employ a method for curve fitting which is even more continuous and reproducible than other common methods. One can identify dominant frequencies of

a blade by carrying out Fourier analysis on blade movement information over time. This is accomplished using Capablade Supervisor® software and the results are presented as a spectrogram diagram. A typical spectrogram diagram is presented in Fig. 11.

Fig. 11: Typical spectogram diagram


Fig. 12: Installation points of the sensors on leading edges of the blades of the compressor first stage

Fig. 13: Installation points of the sensors on trailing edges of the blades of the compressor first stage

The spectrogram diagram represents frequency-domain vibrational response of the system which was used later to develop a Campbell diagram representing natural frequencies of the system at different rotational speeds.

• Installation of Sensors

Nine sensors were installed on the blades of the first and second stages of the compressor each (on two planes of the leading and trailing edges), comprising an overall number of eighteen CP200 sensors installed at the compressor compartment. Installation points of the sensors on the

blades of the compressor first stage are pinpointed in drawings presented in Figs. 12 and 13.

Installation of the CP200 sensors was carried out using bar supports with shim washers at the end to provide the required pressure to fix and keep the sensors in place, as shown in Fig. 14.

During installation, the clearance between the casing and sensor tip is measured at several points and required adjustments are carried out to make sure that the clearances are within the permissible tolerance, as shown in Fig. 15.


Fig. 14: A photograph of CP200 sensor support prior to installation in place (top right); CP200 sensor support installed on the casing (top left); CP200 sensor support outline drawing (bottom)

Fig. 15: Measurement of the clearance between the sensor tip and casing

An overall number of eighteen CP1000 sensors were also installed at the gas turbine compartment; six sensors for each of the second, third and fourth stages. Each sensor was installed on the shroud segment

adjacent to the tip of the corresponding blade. The installation planes of the sensors as well as installation points at each stage are shown schematically in Figs. 16 and 17, respectively.


The turbine-side CP1000 sensors were installed using specific flanges shown in Fig. 18.

Fig. 16: Installation planes of CP1000 sensors in the MGT-70(3) gas turbine

Fig. 18: Photographs of CP1000 sensors installed in place using special flanges (top panels); CP1000 sensor flange support outline drawing (bottom panel)

Fig. 17: Installation points of CP1000 sensors at second, third and fourth stages of the MGT-70(3) gas turbine


Fig. 19: Blade tip clearance values (Minimum, Average, Maximum) measured at the first stage of the MGT-70(3) compressor

Fig. 20: Blade tip clearance values (Minimum, Average, Maximum) measured at the second stage of the MGT-70(3) gas turbine

• Measurement Results Sample BTC measurements for the first stage of the compressor and the second stage of the gas turbine are represented in Figs. 19 and 20 respectively.

Figs. 21 and 22 show comparisons of the results of the Finite Element Method (FEM) analysis with the experimental BTT measurements and as can be observed,

there is a good agreement between the numerical calculations and experimental measurements.


Fig. 21: Comparison of FEM analysis results with the experimental BTT measurements at the first stage of the MGT-70(3) compressor

Fig. 22: Comparison of FEM analysis results with the experimental BTT measurements at the second stage of the MGT-70(3) gas turbine

Strain GaugingStrain gauging is employed to obtain dynamic stresses of the blades of the third and fourth stages of the MGT-70(3) gas turbine. In order to do so, the strain gauges must withstand high temperatures of almost up to 800 °C. Besides, due to installation on rotary equipment, the usage

of a data transfer system seems inevitable.

Two opposite blades at each stage were chosen and three strain gauges were installed on each blade. Installation points of the strain gauges at the third and fourth stages of the MGT-70(3) gas turbine are shown schematically in Fig. 23.

Rotating Speed (rpm)

Operating Range

FEM BTTN

atur

al F

requ

ency

(Hz)

Nat

ural

Fre

quen

cy (H

z)

Rotating Speed (rpm)


Fig. 23: Installation points of the strain gauges at the third and fourth stages of the MGT-70(3) gas turbine rotor

Fig. 24: Telemetry data transfer system (datatel) installed at the end of the tie-rod of the MGT-70(3) gas turbine

The relevant wirings were implemented from the blades to the disks and then through the tie-rod to the end where the data could be transferred to the data

acquisition system using telemetry data transfer capsules (datatel), as shown in Fig. 24.

Stationary Telemetry Module

Rotary Telemetry Module

Data Transfer Capsules

3rd Stage

4th Stage


Fig. 26: Campbell diagram constructed from strain gauge measurements data at the fourth stage of the MGT-70(3) gas turbine

Comparison of the results of the experimental strain gauge measurements with those obtained from numerical calculations shows that there is a good

agreement between the results. Such a trend is also observed for all other parameters, confirming the accuracy of the design procedures carried out.

Fig. 25: Campbell diagram constructed from strain gauge measurements data at the third stage of the MGT-70(3) gas turbine

Sample strain gauge measurements for the third and fourth stages of the MGT-70(3)

gas turbine are presented as Campbell diagrams in Figs. 25 and 26, respectively.

Factory: Mapna blvd., Fardis, Karaj, I.R.Iran.Post code: 31676-43594 Tel: +98 (26) 36630010 Fax: +98 (26) 36612734

Head Office: 231 Mirdamad Ave. Tehran, I.R.Iran.P.O.Box: 15875-5643Tel: +98 (21) 22908581Fax: +98 (21) 22908654

[email protected]

© MAPNA Group 2018The technical and other data contained in this Technical Review is provided for information only and may not apply in all cases.GR196-0

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MAPNA TURBINE ENGINEERING & MANUFACTURING CO. (TUGA… Review-No... · designed by TUGA. It takes an in-depth look at the design stage of this steam turbine, to be used in an incineration