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Differential Expansion Sensitivity Studies during Steam Turbine Startup
KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi. (Concentrated Solar Power)ORCID-id: 0000-0002-8888-4474
KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
2015 (Engelska)Ingår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, nr 6, artikel-id GTP-15-1419Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

In order to improve the startup flexibility of steam turbines, it becomes relevant to analyze their dynamic thermal behavior. In this work, the relative expansion between rotor and casing was studied during cold-start conditions. This is an important property to monitor during startup given that clearances between rotating and stationary components must be controlled in order to avoid rubbing. The investigation was performed using a turbine thermal simplified model from previous work by the authors. The first step during the investigation was to extend and refine the modeling tool in order to include thermomechanical properties. Then, the range of applicability of the model was validated by a twofold comparison with a higher order finite element (FE) numerical model and measured data of a cold start from an installed turbine. Finally, sensitivity studies were conducted with the aim of identifying the modeling assumptions that have the largest influence in capturing the correct thermal behavior of the turbine. It was found that the assumptions for the bearing oil and intercasing cavity temperatures have a large influence ranging between ±25% from the measured values. In addition, the sensitivity studies also involved increasing the initial temperature of the casing in order to reduce the peak of differential expansion. Improvements of up to 30% were accounted to this measure. The studies performed serve as a base toward further understanding the differential expansion during start and establishing future clearance control strategies during turbine transient operation.

Ort, förlag, år, upplaga, sidor
American Society of Mechanical Engineers (ASME) , 2015. Vol. 138, nr 6, artikel-id GTP-15-1419
Nyckelord [en]
Thermal expansion, Steam Turbines
Nationell ämneskategori
Maskinteknik
Forskningsämne
Energiteknik
Identifikatorer
URN: urn:nbn:se:kth:diva-156419DOI: 10.1115/1.4031643ISI: 000374713500011Scopus ID: 2-s2.0-84947466310OAI: oai:DiVA.org:kth-156419DiVA, id: diva2:766677
Forskningsfinansiär
Energimyndigheten
Anmärkning

QC 20160122

Tillgänglig från: 2014-11-28 Skapad: 2014-11-28 Senast uppdaterad: 2017-08-14Bibliografiskt granskad
Ingår i avhandling
1. Steam Turbine Thermal Modeling for Improved Transient Operation
Öppna denna publikation i ny flik eller fönster >>Steam Turbine Thermal Modeling for Improved Transient Operation
2014 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The growing shares of renewable energy sources in the market and solar thermal power applications have set higher requirements on steam turbine operation.These requirements are related to flexibility during transients. A key aspect sought of such flexibility is the capability for fast starts. Due to the varying temperature gradients during start-up, the speed at which the turbine can start is constrained by thermal stresses and differential expansion. These phenomena either consume component lifetime or may result in machine failure if not carefully controlled. In order to accomplish faster starts while ensuring that lifing requirements are preserved, it is important to analyze the thermal behavior of the machine. For this, a transient thermal model was developed with a focus on adaptability to different turbine sizes and geometries. The model allows for simple and fast prediction of thermo-mechanical properties within the turbine metal, more importantly, of the temperature distribution and the associated thermal expansion. The next step of this work was to validate the assumptions and simplifications of the model. This was done through the study and comparison of two turbines against measured operational data from their respective power plants. Furthermore,validation studies also included comparisons concerning the geometric detail level of the model. Overall, comparison results showed a large degree of agreement with respect to the measured data and between the geometric detail levels. The validated model was then implemented in studies related to reducing start-up times and peak differential expansion. For this, the potential effects of turbine temperature maintaining modifications were investigated and quantified.The modifications studied included: increasing gland steam pressure, increasing back pressure and increasing barring speed. Results yielded significant improvements starting from 9.5% in the start-up times and 7% in the differential expansion.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2014. s. 63
Serie
TRITA-KRV, ISSN 1100-7990 ; 14:06
Nyckelord
steam turbines, transients, start-up, finite element model, heat transfer
Nationell ämneskategori
Maskinteknik
Forskningsämne
Energiteknik
Identifikatorer
urn:nbn:se:kth:diva-156196 (URN)978-91-7595-367-0 (ISBN)
Presentation
2014-12-05, Sal Learning Theater (M235), Brinellvägen 68, KTH, Stockholm, 11:00 (Engelska)
Opponent
Handledare
Anmärkning

QC 20141128

Tillgänglig från: 2014-11-28 Skapad: 2014-11-24 Senast uppdaterad: 2014-11-28Bibliografiskt granskad
2. Improving Concentrating Solar Power Plant Performance through Steam Turbine Flexibility
Öppna denna publikation i ny flik eller fönster >>Improving Concentrating Solar Power Plant Performance through Steam Turbine Flexibility
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The amount of incoming solar energy to earth is greater than any other source. Among existing technologies to harness solar energy there is concentrating solar power (CSP). One advantage of CSP is that is dispatchable, meaning that it can provide power even when the sun is not shining. However, CSP is undergoing challenges which hinder its development such as operating variabilities caused by the fluctuations of the sun or the fact that these systems are not yet cost competitive with respect to other technologies.  

One way of improving the performance of CSP plants (CSPPs) is by increasing their operational flexibility, specifically their capability for fast starts. In this way it is possible for the CSPP to harness the solar energy as soon as possible, thus producing more energy and increasing its profitability. Over 90% of CSPPs use a steam turbine to generate electricity. Steam turbines are not currently designed with the flexibility required by the CSP application. Steam turbine start-up is limited by thermal stress and differential expansion. If not carefully controlled, these phenomena either consume lifetime or even result in machine failure.

The aim of this work was to understand the improvement potential of steam turbine start-up and quantify this in terms of CSPP performance indicators. For this, a thermo-mechanical steam turbine model was developed and validated. The model was then used to analyze potential improvements and thermal constraints to steam turbine start-up operation. Furthermore, a CSP plant techno-economic model was developed including steam turbine details. This modeling approach including two levels of detail allowed for the particularities of the component to be included within the dynamics of the plant and thus be able to connect the perspectives of the equipment manufacturer with those of the plant operator. Reductions of up to 11.4% in the cost of electricity were found in the studies carried out.

Ort, förlag, år, upplaga, sidor
KTH Royal Institute of Technology, 2017. s. 75
Serie
TRITA-KRV ; 17/04
Nyckelord
Concentrating Solar Power, Steam Turbines, Transients, Start-up
Nationell ämneskategori
Energiteknik
Forskningsämne
Energiteknik
Identifikatorer
urn:nbn:se:kth:diva-211780 (URN)978-91-7729-388-0 (ISBN)
Disputation
2017-09-08, M3, Brinellvägen 64, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Forskningsfinansiär
Energimyndigheten
Anmärkning

QC 20170814

Tillgänglig från: 2017-08-14 Skapad: 2017-08-11 Senast uppdaterad: 2017-08-15Bibliografiskt granskad

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Förlagets fulltextScopusDifferential Expansion Sensitivity Studies During Steam Turbine Startup

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