Intermediate Pressure Turbine Research Articles

Aeroderivative Mechanical Drive Gas Turbines: The Design of Intermediate Pressure Turbines

Gas turbines engine designers are leaning toward aircraft engine architectures due to their footprint, weight, and performance advantages. Such engines need some modifications to both the combustion system, to comply with emission limits, and turbine rotational speed. Aeroderivative engines maintain the same legacy aircraft engine architecture and replace the fan and booster with a higher speed compressor booster driven by a single-stage intermediate turbine. A multistage free power turbine (FPT) sits on a separate shaft to drive compressors for liquefied natural gas (LNG) applications or generators. The intermediate-power turbine (IPT) design is important for the engine performance as it drives the booster compressor and sets the inlet boundary conditions to the downstream power turbine. This paper describes the experience of Baker Hughes, a GE company (BHGE) in the design of the intermediate turbine that sits in between a GE legacy aircraft engine core exhaust and the downstream power turbine. This paper focuses on the flow path of the turbine center frame (TCF)/intermediate turbine and the associated design, as well as on the 3D steady and unsteady computational fluid dynamics (CFD)-assisted design of the IPT stage to control secondary flows in presence of through flow curvature induced by the upstream TCF.

Parameters calculation of thermal power plant dynamic model using steam cycle data

Standard models are created to carry out power system dynamic studies. One of the major problems in this regard is the parameter identification of these models. These parameters are not constant and may change due to extensive use and the large number of repairs, modifications and overhaul of the units, and, consequently, they cannot provide a reliable basis for further use. Thus, actual parameters need to be determined. This paper determines the actual parameters of a real 150 MW tandem compound, single reheat steam turbine located in the Egyptian network since 1986 using the available unit steam cycle data. The time constants of Steam Chest, reheater and cross over are calculated. The power fractions of high pressure (HP), intermediate pressure (IP) and low pressure (LP) turbine stages are also estimated. The calculated parameters are compatible with IEEEG1 general steam turbine model. Finally, parameters validation is investigated by comparing the actual and simulated turbine power response. Also governor and turbine speed responses are provided. The simulation is carried out by DIgSILENT power factory software.

Microstructural characterization and mechanical properties of sand cast and investment cast alloy 625 for HP/IP casing applications for advanced fossil fired power plants

Alloy 625 is a candidate material for high temperature sections of High Pressure (HP)/ Intermediate Pressure (IP) turbine casings for Advanced Ultra Super Critical (AUSC) power plants. This material is expected to operate at steam temperature of 710°C approx. and pressure of 300 ata approx. After carrying out a detailed literature survey, it was observed that microstructural information and mechanical properties data on Alloy 625 cast material is limited. Hence, this study was undertaken for obtaining of mechanical properties and microstructures at room temperature through two manufacturing techniques namely, conventional sand casting and investment casting. Mechanical properties data includes tensile testing and impact testing. The data obtained from this study is essential for design of casings. The details of the study and results obtained are discussed and presented in this work.

Characterisation of turbine behaviour for an engine overspeed prediction model

This paper focuses on the characterisation of turbine overspeed behaviour to be integrated into an engine overspeed model capable of predicting the terminal speed of the high pressure turbine (HPT) in the event of a high pressure shaft failure. The engine considered in this study features a single stage HPT with a shrouded contra-rotating rotor with respect to the single stage intermediate pressure turbine (IPT). The HPT performance is characterised in terms of torque and mass flow function for a range of expansion ratios at various non-dimensional rotational speeds (NH), up to 200% of the design value. Additionally, for each HPT expansion ratio and NH, the change in capacity of the downstream IPT, for different IPT non-dimensional rotational speeds (NI), also needs to be characterised due to the extremely positive incidence angle of the flow from the upstream rotor. An automated toolkit is developed to generate these characteristic maps for both the HPT and IPT.An unlocated high pressure shaft failure will result in rearward movement of the rotor sub-assembly. This causes changes in the rotor tip and rim seal regions, and in the rim seal leakage flow properties. Therefore, in the present work, a high fidelity characterisation of turbine behaviour with the inclusion of tip and rim seals is carried out at three different displacement locations, 0 mm, 10 mm and 15 mm, to improve terminal speed estimation. Furthermore, there is a possibility of damage to the tip seal fins of the HPT rotor due to unbalance in the spool that may result in contact between the rotor aerofoil tip and the casing. Consequently, another set of characteristics are generated with damaged tip fins at each displacement location.It is observed from the characteristics that the torque of the HPT rotor decreases with increasing NH. The HPT mass flow function initially decreases and then increases with an increase in NH. The IPT mass flow function initially remains similar and then decreases with increase in NH above values of 150%. The HPT rotor torque and IPT mass flow function decrease with rearward movement of the HPT rotor sub-assembly for all values of NH. With worn tip seal fins all parameters mentioned previously are lower than in the nominal undamaged case. The high fidelity characterisation of turbines that follows the sequence of events after a shaft failure, as described in this work, can provide accurate predictions of terminal speed and thus act as a tool for testing design modifications that can result in better management and control of the over-speed event.

Advanced exergoenvironmental evaluation for a coal-fired power plant of near-zero air pollutant emission

Advanced exergy and exergoenvironmental analyses based on life cycle assessment (LCA) are conducted to an SCPP with and without dust, SO2 and NOX mitigation controls. The analyses show that environmental impacts of components are mainly caused by exergy destruction while combustion chamber (COM) still has great potential to reduce pollutant environmental impact reduced by 99.5% by near-zero air pollutant emission standards. Avoidable environmental impact within each component is endogenous other than most regenerative feedwater heaters. COM has the largest environmental impact of exergy destruction but lower avoidable part compared with superheat transfer (SH) including boiling process. Reheat transfer (RH) shows similar avoidable environmental impact but less exergy destruction in contrast with COM. Turbines play well in exergy efficiency and over 50% of environmental impact within intermediate-pressure turbine (IP) can be avoided. Air preheater (APH) displays a higher avoidable environmental impact than condenser (CND) albeit lower exergy destruction. Pumps and fans have small environmental impacts with over 45% can be avoided. Most environmental impact related to pollutant formation is avoidable and endogenous except for wet flue gas desulfurization (WFGD) which imposes a negative environmental impact on other components. The specific environmental impact of electricity generation is higher than European.

Thermo-economic analysis on the impact of improving inter-stage packing seals in a 500 MW class supercritical steam turbine power plant

The use of brush seals in turbomachinery has increased steadily in recent years because they reduce leakage and improve operating stability. This study evaluates the performance enhancement of a 500MW-class steam turbine plant that results from replacing conventional seals with brush add-up seals for the inter-stage packing seal locations. Leakage flow rates of all seal locations in high- and intermediate-pressure turbines were estimated, and the brush add-up seal was found to reduce leakage by 50–68%. The entire power plant was simulated using a stage-by-stage turbine model and stage efficiency correction. With the advanced seals in all inter-stage locations of the high- and intermediate-pressure turbines, 0.44% and 0.33% increases in power output and efficiency were predicted. A larger performance benefit was observed with the installation in the high-pressure turbine. An economic analysis shows that the seal replacement is quite cost-effective. The predicted net present value was quite large compared to the initial cost, and the estimated payback period was less than a year. The replacement in all the high-pressure turbine stages and in the front stages of the intermediate-pressure turbine stages has the highest business value.

Test uncertainty reduction via a modified method for estimating steam turbine HP-IP packing leakage

PurposeThis study aims to introduce a new modified method for estimating steam turbine high pressure (HP)-intermediate pressure (IP) leakage flow based on the experimental data extracted from a 250 MW re-heat steam turbine.Design/methodology/approachEffects of measurement uncertainties on the test results are investigated and key parameters are specified via a new modified method to diminish the test uncertainties. The recommended method is based on a constant IP turbine pressure ratio at the same loads. Considering this assumption, it was found that the turbine pressure ratio can be achieved in the second and the third tests with a much longer duration.FindingsThe results showed that the cross-over temperature is a major parameter in the leakage flow estimation tests, whereas hot reheat and cross-over pressures are the next priorities. It was also observed that as the cross-over temperature varies by 1°C, the estimated leakage flow error significantly differs by up to 72.6 per cent.Originality/valueIt is concluded that the present modified HP-IP leakage flow estimation method seems to be more accurate in comparison with previously proposed methods in literature.

Influence of a circular strainer on unsteady flow behavior in steam turbine control valves

The influence of a circular strainer on unsteady flow behavior in steam turbine control valves, which are commonly placed between an intermediate-pressure turbine and a boiler in thermal power plants, was numerically studied. A porous-medium model, which established the dependencies of the pressure drop through the strainer on the magnitude and direction of the fluid flow’s velocity, was validated by experimental measurements in a water flow test rig. As the benchmark configuration, a valve without a strainer was used for comparison. The turbulent steam flow in the complex serpentine channel was simulated with the implementation of the proposed porous model for the strainer. The numerical results demonstrated that placing the strainer in the main valve resulted in dramatic changes of the flow patterns in the main valve’s chamber and its diffuser, and even in the downstream throttle valve. The complex steam flow in the main valve was efficiently managed by the circular strainer, significantly reducing the cross-sectional force on the main valve’s spindle; this is attributed to attenuated oscillation of the annular flow around the main valve’s seat. As for the downstream throttle valve, the pressure drop and the fluctuating lateral force on the spindle were intensified, which was shown to be closely related to the continuous impingement of the flow onto the throttle valve’s cavity wall. In comparison with the configuration without a strainer, the placement of the strainer in the main valve gave rise to a pair of intensified secondary vortices in the diffuser section behind the throttle valve.

An optimized power conversion system concept of the integral, inherently-safe light water reactor

The integral, inherently safe light water reactor (I2S-LWR) has been developed to significantly enhance passive safety capabilities while maintaining cost competitiveness relative to the current light water reactor (LWR) fleet. The compact heat exchangers of the I2S-LWR preclude boiling of the secondary fluid, which decreases the probability of heat exchanger failure, but this requires the addition of a flash drum, which negatively affects the overall plant thermodynamic efficiency. A state of the art Rankine cycle is proposed for the I2S-LWR to increase the thermodynamic efficiency by utilizing a flash drum with optimized operational parameters. In presenting this option for power conversion in the I2S-LWR power plant, the key metric used in rating the performance is the overall net thermodynamic efficiency of the cycle. In evaluating the flash-Rankine cycle, three basic industrial concepts are evaluated, one without an intermediate pressure turbine, one with an intermediate turbine and one reheat stream, and one with an intermediate turbine and two reheat streams. For each configuration, a single-path multi-variable optimization is undertaken to maximize the thermal efficiency. The third configuration with an intermediate turbine and 2 reheat streams is the most effective concept, with an optimized efficiency of 35.7%.

Dissimilar welding of the creep resistant steels CB2 and P92 with flux cored wires

The new boron-alloyed 9Cr-1.5Mo-1Co cast steel designated as CB2 is used for intermediate pressure turbine inner casings with steam temperature up to 620 °C. To connect the casing with a pipe made of P92 steel, dissimilar welding is necessary. As flux cored arc welding (FCAW) is a highly productive welding process, the applicability of flux cored wires is evaluated. Therefore, three test welds in vertical-up position were produced with different welding procedures: the first with P92 tungsten inert gas (TIG) welding for root and second pass and P92 FCAW for intermediate and final passes; the second with P92 TIG welding for root and second pass and CB2 FCAW for intermediate and final passes; and the third with CB2 flux cored wire for all layers as no CB2 TIG rod is available yet. Cross-weld tensile tests and impact tests on weld metal and heat-affected zones were carried out after post weld heat treatment (PWHT) of 2 × 730 °C for 12 h. The differences in mechanical and technological properties are discussed, as well as the hardness profiles in the cross sections. Thermokinetic calculations with the software package MatCalc estimate the long-term microstructural evolution of precipitates depending on the chemical composition of the weld metal.

Thermodynamic Model of the Influence of N2 Leakage on Heat Rate in Power Plant

The steam leakage in HP&IP (high pressure and intermediate pressure) turbine through midspan packing (N2 packing) is called N2 leakage for short. When this leakage changes, its effects on the turbine’s power, superheating heat, reheating heat, and heat rate are analyzed by using the small deviation theory, with the main steam flow kept constant. It was proved that as N2 leakage changed, the HP turbine power and reheating heat changed significantly while that of IP&LP (intermediate pressure and low pressure) turbines changed little. Besides, the calculations pertaining to a supercritical 660 MW steam turbine in variable conditions are carried out. The results indicated that when N2 leakage increased, the change of those parameters was nearly linear, which agreed with the theoretical analysis. The results also demonstrated that the leakage affected the heat rate mainly by changing the HP turbine power and reheating heat. However, as the LP turbine power accounted for a large proportion of the total power of turbines, the impact of its change on the heat rate also should be taken into account.

A novel lignite pre-drying system with low-grade heat integration for modern lignite power plants

The lignite pre-drying process plays an important role in modern lignite power plants and the fluidized bed dryer with internal heat utilization is a promising drying method which has both high efficiency and cost-effectiveness. After conducting an in-depth analysis of a typical lignite pre-drying power plant, this work proposed a novel lignite pre-drying system with low-grade heat integration. Through system integration, the low-temperature evaporation of the lignite was recovered to heat the combustion air, while the residual heat from the flue gases was used to heat the feed or condensed water, thereby saving a portion of heat from the steam bleeds of the high and intermediate pressure turbines. The results for a 1,000 MW lignite-fired power plant showed that, the proposed pre-drying system could yield an increase in net plant efficiency of approximately 3.6 % points and a reduction in the cost of electricity of $1.83/(MW h). The thermodynamic and economic performances were each superior to those of the existing pre-drying system, convincingly demonstrating that the research of this paper may provide a promising integrated lignite pre-drying method for the next-generation of lignite-fired power plants.

A modelling approach to assessing the feasibility of the integration of power stations with steam electrolysers

Hydrogen, combined with fuel cell technology, is an option for reducing our reliance on hydrocarbon-based fuels. Solid oxide electrolyser cells (SOECs) have been studied as a possible technology to produce hydrogen from steam. As the current global energy mix is heavily reliant on hydrocarbon-based fuels, utilising existing technologies such as coal fired power plants, combined with SOECs in an integrated system, may enable a path towards reducing carbon dioxide emissions as well as creating a way of introducing ‘cleaner’ fuel.In this work, a steady state model of a SOEC was developed and used to assess the feasibility of using hot steam from a power plant as feed to a SOEC. The main objective was to study the ways of improving the SOEC efficiency. The most favourable feed for the SOEC was to extract steam prior to the intermediate pressure turbine, which showed SOEC efficiency improvement of 25% compared with conventional SOEC operation of heating water at 25°C.The thermoneutral point of 4644Am−2 was shown to be a guide for assessing design and operation options with heat integration possibilities after this point. For scenarios of 7% steam extraction and a purely H2 production plant, 250MW (7500kgh−1) and 290MW (8700kgh−1) H2 can be produced with SOECs sized at 43,300 and 50,100m2, respectively.

Energy and exergy analysis of a super critical thermal power plant at various load conditions under constant and pure sliding pressure operation

The objective of this paper is to perform an energetic and exergetic analysis on a 660 MWe coal fired supercritical thermal power plant at 100%, 80% and 60% of normal continuous rating (NCR) conditions under constant pressure as well as pure sliding pressure operation and to highlight the benefits of the latter over the former. The energetic input, energetic output, exergetic input, exergetic output, energetic and exergetic efficiencies of various components of the supercritical thermal power plant are estimated at 660 MWe, 528 MWe and 396 MWe load under both constant pressure as well as pure sliding pressure operation. Also the energy losses and exergy destruction in various components of a power plant i.e. Boiler, high pressure turbine (HPT), intermediate pressure turbine (IPT), low pressure turbine (LPT), condenser, gland steam coolers, condensate extraction pumps, low pressure heaters (LPH), drip pumps (DP), deaerator (D), boiler feed pump (BFP) and high pressure heaters (HPH) have been calculated. The results have shown that the boiler has the maximum rate of exergy destruction than any other component in the power plant. After the boiler, turbine has the maximum rate of exergy destruction than any other component of the power plant. The study reveals that there is a significant reduction in the rate of exergy destruction at part load conditions for the turbine in case of sliding pressure operation in comparison to constant pressure operation. The rate of exergy destruction in the turbine at 100%, 80% and 60% of NCR conditions is 49.16 MW/43.22 MW/43.92 MW for constant pressure operation and 47.66 MW/37.88 MW/28.94 MW respectively. The BFP power input reduces by 9.39%, 21.52% and 42.5% respectively at 100%, 80% and 60% of NCR conditions if the unit runs in sliding pressure mode compared to constant pressure mode.

Solar–thermal hybridization of advanced zero emissions power cycle

Four different integration schemes for the Advanced Zero Emissions Power (AZEP) cycle with a parabolic trough are proposed and analyzed: vaporization of high-pressure stream, preheating of high-pressure stream, heating of intermediate-pressure turbine inlet stream, and heating of low-pressure turbine inlet stream. The power outputs from these integration schemes are compared with each other and with the sum of the power outputs from corresponding stand-alone AZEP cycle and solar–thermal cycle. Vaporization of high-pressure stream has the highest power output among the proposed integration schemes. Both the vaporization and heating of intermediate-pressure turbine inlet stream integration schemes have higher power output than the sum of the power outputs from corresponding stand-alone AZEP cycle and solar–thermal cycle. A comparison of the proposed vaporization scheme with existing hybrid technologies without carbon capture and storage (CCS) shows that it has a higher annual incremental solar efficiency than most hybrid technologies. Moreover, it has a higher solar share compared to hybrid technologies with higher incremental efficiency. Hence, AZEP cycles are a promising option to be considered for solar–thermal hybridization.

Design and Analysis of High-pressure Casing of a Steam Turbine

Contact pressure and pretension in bolts-analysis has been made easier in recent years due to the availability of high computational capabilities and flexibility in the computational methods using finite element analysis. In the present work, one such analysis is carried out blending the hand calculations and steady-state finite element analysis to evaluate the contact pressure in a high pressure steam turbine casing. The work involves design considerations, design checks, validation and sensitivity analysis to achieve the design criteria to fulfill the structural requirements for mechanical integrity. During the last several years the primary changes to the design of steam turbines have focused on improving their efficiency, reliability and reducing operating costs. Siemens Power Generation, for example, has improved the overall efficiency and availability of its steam turbines by decreasing the steam flow energy losses in each of the steam turbines components. The steam turbine unit largely influences the efficiency and reliability of power stations. Any improvement in the design of steam turbine enables more efficient use of fuel and results in reduced cost. The high pressure steam at 565°C and 156bar pressure passes through the high pressure turbine. The exhaust steam from this section is returned to the boiler for reheating before being used. On leaving the boiler reheater, steam enters the intermediate pressure turbine at 565°C and 40.2bar pressure. From the intermediate pressure turbine, the steam continues its expansion in the three Low pressure turbines. The steam entering the turbine is at 306°C and 6.32bar. To get the most work out of the steam, the exhaust pressure is kept very low. The casing thus witnesses, energy of the steam turned into work in HP and IP stages. So, the design of the casing is a very important aspect.

A Novel Lignite Pre-drying System Incorporating a Supplementary Steam Cycle Integrated with a Lignite Fired Supercritical Power Plant

A novel lignite pre-drying system incorporating a supplementary steam cycle integrated with a lignite fired supercritical power plant was proposed and thermodynamically evaluated using the EBSILON Professional software. Differing from the conventional pre-drying systems, the steam bleed for the dryer in the proposed system is drawn from the intermediate pressure turbine and put through a separated turbine called T-turbine. With the T-turbine installed, the superheating requirement of the bleed for the dryer and for some regenerative heaters is significantly reduced, thus leading to a further increase in the lignite fired power plant efficiency. The simulation results show that the net power plant efficiency improved by 2.6% and the cost of electricity reduced by up to 1.26 $/MWh can be achieved, compared with the reference case. The exergy destruction can also be significantly reduced in the proposed lignite pre-drying system. The concept of the novel integrated system may provide a promising method for lignite pre-drying in the future generation lignite power plants.

Thermodynamic Analysis of a Steam Power Plant with Double Reheat and Feed Water Heaters

A steam cycle with double reheat and turbine extraction is presented. Six heaters are used, three of them at high pressure and the other three at low pressure with deaerator. The first and second law analysis for the cycle and optimization of the thermal and exergy efficiencies are investigated. An exergy analysis is performed to guide the thermodynamic improvement for this cycle. The exergy and irreversibility analyses of each component of the cycle are determined. Effects of turbine inlet pressure, boiler exit steam temperature, and condenser pressure on the first and second laws' efficiencies are investigated. Also the best turbine extraction pressure on the first law efficiency is obtained. The results show that the biggest exergy loss occurs in the boiler followed by the turbine. The results also show that the overall thermal efficiency and the second law efficiency decrease as the condenser pressure increases for any fixed outlet boiler temperature, however, they increase as the boiler temperature increases for any condenser pressure. Furthermore, the best values of extraction pressure from high, intermediate, and low pressure turbine which give the maximum first law efficiencies are obtained based on the required heat load corresponding to each exit boiler temperature.

Improving Intermediate Pressure Turbine Performance by Using a Nonorthogonal Stator

Intermediate pressure (IP) turbines in high bypass ratio civil aeroengines are characterized by a significant increase in radius and a low aspect ratio stator. Conventional aerodynamic designs for the IP turbine stator have had leading and trailing edges orthogonal to the hub and casing end walls. The IP turbine rotor, however, is stacked radially due to stress limits. These choices inevitably lead to a substantial gap between the IP stator and rotor at the outer diameter in a duct that is generally diffusing the flow due to the increasing radius. In this low Mach number study, the IP stator is redesigned, incorporating compound sweep so that the leading and trailing edges are no longer orthogonal to the end walls. Computational investigations showed that the nonorthogonal stator reduces the flow diffusion between the stator and rotor, which yields two benefits: The stator trailing edge velocity was reduced, as was the boundary layer growth on the casing end wall within the gap. Experimental measurements confirm that the turbine with the nonorthogonal stator has an increased efficiency by 0.49%, while also increasing the work output by 4.6%, at the design point.

Exergy Analysis of Thermodynamic System of Power Plant Based on Structural Theory

An energy model was developed based on the fuel-product concept. The matrix equation for exergy balance of regenerative system was established, and the mathematical model for exergy analysis of thermal system was structured. Exergy losses, exergy loss rate, exergy loss coefficient and exergy efficiency of the main components of a domestic N600-24.2/566/566 power plant were calculated based on this model. The results showed that the exergy efficiency of high pressure heaters are higher than that of low pressure heaters; the exergy efficiency of grade group of the intermediate pressure turbine are higher than the grade group of high pressure turbine and low pressure turbine. The exergy efficiency of the last grade group of low pressure turbine is the lowest. The exergy efficiency of the governing stage and the last grade group of low pressure turbine are 82.999% and 85.911%; the coefficient of exergy loss is maximum in the boiler (39.204%); the exergy effciency of superheater and reheater are 51.52% and 51.7%. Therefore, superheater and reheater have the largest energy conservation potential. Governing stage and low pressure turbine have more energy conservation potential.