Start up optimization of Combined Cycle Power Plants: Controller development and real plant test results

In the fast start-up for combined cycle power plants (CCPP), the thermal stresses of the steam turbine rotor are generally controlled by the steam temperatures or flow rates by using gas turbines (GTs), steam turbines, and desuperheaters to avoid exceeding the thermal stress limits. However, this thermal stress sensitivity to steam temperatures and flow rates depends on the start-up sequence due to the relatively large time constants of the heat transfer response in the plant components. In this paper, a coordinated control method of gas turbines and steam turbine is proposed for thermal stress control, which takes into account the large time constants of the heat transfer response. The start-up processes are simulated in order to assess the effect of the coordinated control method. The simulation results of the plant start-ups after several different cool-down times show that the thermal stresses are stably controlled without exceeding the limits. In addition, the steam turbine start-up times are reduced by 22–28% compared with those of the cases where only steam turbine control is applied.

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Optimizing Lifetime Consumption and Increasing Flexibility Using Enhanced Lifetime Assessment Methods With Automated Stress Calculation From Long-Term Operation Data

Volume 5B: Oil and Gas Applications; Steam Turbines ◽

10.1115/gt2013-95068 ◽

2013 ◽

Cited By ~ 8

Author(s):

Jan Vogt ◽

Thomas Schaaf ◽

Klaus Helbig

Keyword(s):

Power Plants ◽

Low Cycle Fatigue ◽

Combined Cycle ◽

Transient Temperature ◽

Steam Turbines ◽

Transfer Coefficients ◽

Term Operation ◽

Flexible Mode ◽

Start Up ◽

Safety Margins

In the past most of the steam turbines were designed as base load machines. Due to new market requirements based on the effect of renewable energies, power plant operators are forced to operate with more frequent start-up events and load changes, resulting in a fundamental higher low cycle fatigue (LCF) lifetime consumption. Traditional methods of lifetime assessment often use representative start-ups, for the calculation of LCF damage, which can provide very conservative results with reasonable safety margins. For a high number of starts these safety margins may result in an overestimation of the LCF damage. At Alstom, an enhanced method for lifetime assessment has been developed, that evaluates the actual lifetime consumption from real operation data in an automated manner and provides much more realistic results. The operation data is used to calculate the transient temperature distribution and heat transfer coefficients along the rotor for each start-stop cycle. The corresponding stress distribution in the rotor is evaluated by means of a Finite-Element-method analysis. Finally the number of remaining cycles is extracted for the most critical locations using material data. In combination with the creep damage the lifetime consumption is evaluated. The entire process is highly automated, but also facilitates easy monitoring through the lifetime engineer by graphic presentation of calculation results. Using this enhanced method of lifetime assessment, the computed lifetime consumption is closer to the actual value, supporting the planning of overhauls and component replacements and minimizing the risk of failure or forced outages. The utilization of remaining lifetime can be optimized in favour of a more flexible mode of operation (e.g. low load operation and fast start-up) or extension of operational lifetime for conventional and combined cycle power plants.

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Rotor-Blade Interaction During Blade Resonance Drive-Through

10.1115/gt2021-59160 ◽

2021 ◽

Author(s):

Roland Grein ◽

Ulrich Ehehalt ◽

Christian Siewert ◽

Norbert Kill

Keyword(s):

Power Plants ◽

Renewable Energy Sources ◽

Cyclic Fatigue ◽

Combined Cycle ◽

Plant Design ◽

Steam Turbines ◽

Rotating Speed ◽

Start Up ◽

Blade Vibrations ◽

Fast Start

Abstract In the future energy landscape, combined cycle power plants will increasingly take the role of providing balancing power for fluctuating renewable energy sources due to their high availability and fast start-up times. This implies more frequent cycling, a larger number of speed cycles and thus new challenges for plant design and operation. One of these challenges is a potential increase of cyclic fatigue incurred by last-stage blades during start-up and coast-down. Blade vibrations might be induced by synchronous shaft vibrations when the blade resonance is excited by lateral shaft vibrations. In this paper, we report measurement results of shaft and blade vibrations observed at some Siemens Energy steam turbines. Apart from the expected increase of blade vibrations when the double rotating speed crosses the blade resonance, a distinctive dip of shaft vibrations at the low-pressure turbine bearings is observed. We argue that this phenomenon is likely related to the aforementioned interaction between blade and shaft vibrations and present a theoretical framework to describe this interaction and the observed effect.

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Optimizing the start-up operations of combined cycle power plants using soft computing methods

Logic Journal of IGPL ◽

10.1093/jigpal/jzr013 ◽

2011 ◽

Vol 20 (4) ◽

pp. 648-656 ◽

Cited By ~ 3

Author(s):

I. Bertini ◽

M. De Felice ◽

A. Pannicelli ◽

S. Pizzuti

Keyword(s):

Soft Computing ◽

Power Plants ◽

Computing Methods ◽

Combined Cycle ◽

Start Up ◽

Soft Computing Methods

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The Effect and Remedy of Nozzle Loads on Boiler Feed Pumps

ASME 2004 Power Conference ◽

10.1115/power2004-52157 ◽

2004 ◽

Author(s):

Alan P. Flory ◽

William C. Livoti

Keyword(s):

Power Plants ◽

Base Plate ◽

Combined Cycle ◽

Real Cost ◽

Start Up ◽

Commercial Operation ◽

Current Design ◽

Ring Section ◽

Section Type ◽

Motor Vibration

Many frequently encountered start-up and operational problems in current design combined cycle power plants can be traced to pipe strain and nozzle loads placed upon pumps. This is most dramatic when the boiler feed pump is affected. Many of the symptoms are significant and can include misalignment, dynamic (changing) alignment, pump or motor vibration, bearing problems, mechanical seal failures and seizure of equipment on start-up and shutdown. While these are all nuisance items that can plague plant shake-down and commissioning, some can generate huge costs and plant unscheduled outages. More profoundly, these symptoms are often all present, making accurate diagnosis of the true cause very difficult. The real cost of these problems can be seen in plants missing commercial operation dates. Some of the piping issues that can cause these symptoms will be discussed, items including hydraulic aspects of the piping design, straight runs, horizontal runs, venting, location of minimum flow valve, and pipe hanger location. Also, the use of pre-fabricated pipe and spool pieces will be discussed. A short discussion will also be presented on how these piping issues impact various designs of pumps, such as barrel pumps, horizontal split case and ring section type pumps. This will also include some comments on pump mounting issues such as base-plate installation, the use of pin & key blocks and pedestal design. All of the discussions will be summarized and then presented with several recommendations for piping repair, operational changes, and material reinforcement. Optional pump features will be presented, indicating what items can be used to improve operation and reliability when abnormal nozzle loads are expected, including comments on internal clearances, wear part metallurgy and bearing upgrades. These recommendations will be compared against several field experiences for confirmation, with some focus on nozzle load data vs. design, and operation prior to and after strain removal. This combination of field results and engineering analysis of this topic should prove quite useful to the engineer attempting to diagnose any symptoms found in the field. Often times several symptoms may be present, making diagnosis difficult and it is only the methodical steps of symptom elimination that will get the new power plant on the way to commercial operation.

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Thermal Modeling of HRSG Transient Behavior in Combined Cycle Power Plants

Volume 4: Cycle Innovations; Electric Power; Industrial and Cogeneration; Manufacturing Materials and Metallurgy ◽

10.1115/gt2006-90718 ◽

2006 ◽

Author(s):

Sepehr Sanaye ◽

Moein Rezazadeh ◽

Jalaleddin Oladi ◽

Gholam Hossein Sadeghpoor ◽

Farid Bashiri ◽

...

Keyword(s):

Steady State ◽

Power Plants ◽

Cold Start ◽

Combined Cycle ◽

Operating Conditions ◽

Master Program ◽

Load Change ◽

Start Up ◽

Program Software ◽

Transient And Steady State

Combined Cycle Power Plants (CCPP) are attractive electricity generation systems due to high cycle efficiency and quick response of the system to load change. Heat recovery steam generator (HRSG) is an important part of a CCPP and it is important to predict the HRSG operating conditions in transient and steady state modes. It should be emphasized that the biggest pressure and thermal stresses are imposed on HRSG superheater and evaporator tubes banks during transient periods (cold start up and load change). Due to these effects a software program was developed for analyzing the HRSG transient and steady state operating conditions. The HRSG software included arbitrary number of pressure levels (usually up to three) and any number of elements (superheater, evaporator, economizer, desuperheater and duct burner). In this paper theories and equations (mass/energy balance and heat transfer coefficients) applied for HRSG thermal analysis are described. Also HRSG program software outputs were compared with real data collected from HRSG cold start-up at Tehran CCPP with specified geometry and arrangement of elements. The closeness of two groups of data in this transient and steady state modes was acceptable. The numerical outputs in steady state condition also were found very close to GT MASTER program software outputs.

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F307 DYNAMIC SIMULATION AND OPTIMIZATION OF START-UP PROCESSES IN COMBINED CYCLE POWER PLANTS

The Proceedings of the International Conference on Power Engineering (ICOPE) ◽

10.1299/jsmeicope.2003.3._3-411_ ◽

2003 ◽

Vol 2003.3 (0) ◽

pp. _3-411_-_3-416_

Author(s):

Masakazu SHIRAKAWA ◽

Masashi NAKAMOTO ◽

Shunji HOSAKA

Keyword(s):

Dynamic Simulation ◽

Power Plants ◽

Combined Cycle ◽

Simulation And Optimization ◽

Start Up

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Impact of Operating Regime on Economic Performamnce of Combined Cycle Power Plants

Volume 5: Turbo Expo 2005 ◽

10.1115/gt2005-68803 ◽

2005 ◽

Author(s):

Mircea Fetescu

Keyword(s):

Economic Performance ◽

Capital Investment ◽

Power Plants ◽

Operating Regime ◽

Combined Cycle ◽

Economic Feasibility ◽

Start Up ◽

Wide Range ◽

The Impact ◽

Base Load

It is accepted that CCPP has the highest fuel conversion efficiency among fossil fuel fired generation technologies. The extensive installed base of CCPP worldwide is justified by additional advantages: low capital investment, short construction time, low environmental impact and high operating flexibility. The operating flexibility, with fast loading and deloading and short start-up and shutdown durations, allows CCPPs to fulfill a wide range of operating duties, such cycling, intermediate load to base load, grid frequency or voltage control and part load operation; mostly on a competitively generated cost basis. The traditional approach to CCPP development is to design an optimised plant, taking into consideration the technical and economic boundary conditions of a specific project. This includes assumptions for operating regime: base load, intermediate load or cycling with daily start-up and shutdown. In a deregulated environment, plants are dispatched on merit. The assumptions related to operating regime and used for optimising the configuration of a particular CCPP, often deviate significantly during commercial operation. The objective of this work is to evaluate the impact of the operating regime on CCPP economic performance. During the economic feasibility evaluation of a power project it is frequently considered that the main factors affecting the electricity generation cost, are capital cost and fuel cost. As far as the operating regime is concerned, a number for yearly operating hours is then assumed and eventually sensitivity is considered. The content of this work is an investigation on how the capital, fuel and O&M costs, components of the generation costs, are affected by the utilisation factor, by operating modes and loads, frequency and duration of start-up and shudown [s&s] of the plant. The conclusion of the paper is that both, operating regime and operating procedure have an important impact on economic performance of combined cycle plants. Annual operating hours and the number of s&s influence the factors which contribute to the profitability and competitiveness of the plant, such as EOH, availability, performance degradation, O&M costs and directly the average plant output and efficiency. Finally the economic performance of combined cycle plants can be significantly improved by re-visiting the conceptual design and the operating concept.

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