Optimization of boiler start-up using a nonlinear boiler model and hard constraints

Krüger, Klaus; Franke, Rüdiger; Rode, Manfred

doi:10.1016/j.energy.2004.03.022

Cited by 72 publications

(39 citation statements)

References 14 publications

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“…where more frequent and shorter start-ups and shut-downs are necessary in order to realize the short-term power requests from the electrical load dispatcher [4]. Fast start-up and shutdown of the power units are desired to reduce fuel oil consumption during start-up and to decrease emissions of pollutants into the atmosphere.…”

Section: Optimierte Erwärmung Zylindrischer Druckbehältermentioning

confidence: 99%

“…For practical reasons the optimum temperature in the ramp form is preferred. It is possible to increase the fluid temperature stepwise at the beginning of the heating process and then increase the fluid temperature 1 3 where more frequent and shorter start-ups and shut-downs are necessary in order to realize the short-term power requests from the electrical load dispatcher [4]. Fast start-up and shutdown of the power units are desired to reduce fuel oil consumption during start-up and to decrease emissions of pollutants into the atmosphere.…”

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confidence: 99%

“…Estimation of the maximum thermal stress enables the optimization of the bypass mode [6]. In both papers drum is considered as a thick-walled cylinder in which the temperature distribution is a function of radius and time [4][5].Allowable heating rates of thick-walled boiler pressure components are calculated in engineering practice using European Standard [7] which is based on the quasi-steady state temperature distribution inside the pressure element. Quasi steady state temperature distribution is formed in the thick-walled element after heating it at a constant rate for a long time [8].…”

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Optimum heating of cylindrical pressure vessels

Dzierwa

Taler

2015

Forsch Ingenieurwes

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A method for determining time-optimum fluid temperature changes during heating of the thick walled cylinder was presented. Optimum fluid temperature changes were determined both for the cylindrical pressure vessels without holes. Heating of the hollow cylinder will be carried out in such a way that the circumferential thermal stress at the inner surface is equal to the allowable stress value. Optimum fluid temperature changes were assumed in the form of simple time functions containing unknown parameters. The unknown parameters were determined from the condition that the circumferential thermal stress at the inner surface of the hollow cylinder without holes is equal to the allowable stress at given time points. An over-determined system of nonlinear algebraic equations was solved for unknown parameters using the least squares method. At first, the thermal stress was calculated using the discrete form of the Duhamel integral. The Finite Element Method (FEM) was used to determine the circumferential thermal stress in the second method. For practical reasons the optimum temperature in the ramp form is preferred. It is possible to increase the fluid temperature stepwise at the beginning of the heating process and then increase the fluid temperature 1 3 where more frequent and shorter start-ups and shut-downs are necessary in order to realize the short-term power requests from the electrical load dispatcher [4]. Fast start-up and shutdown of the power units are desired to reduce fuel oil consumption during start-up and to decrease emissions of pollutants into the atmosphere.The major limiting factor relevant to fast power plant start-ups is maximum allowable thermal stress for thickwalled components such as headers of superheaters and reheaters, boiler drums and steam turbine rotors. Any exceeding of the stress limit reduces lifetime of these components. The new control system proposed by Krüger et al. [4] aims at improving of the start-up procedures of boilers and explicitly takes the thermal stress values of critical components into account.Taking into account the increasing share of wind farms in the production of electricity, combined-cycle gas and steam power plants must be quickly activated to supply the missing electrical energy into the power system when the wind velocity drops. The heat recovery steam generator (HRSG) is a critical element limiting fast start-up of the gas and steam power units. During the start-up period, HRSG components, especially the drum, are subject to high thermal stresses, which are caused by the non-uniform temperature distribution over the component wall thickness.To avoid excessive thermal stresses in the boiler drum, the flue gas exiting a gas turbine flows directly to the chimney bypassing the HRSG [6]. It makes possible to deliver electricity to the grid at the expense of low efficiency of the gas and steam unit. The gas bypass is open during the initial stage of the start-up. Estimation of the maximum thermal stress enables the optimization of the bypass mode [6]. ...

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Section: Optimierte Erwärmung Zylindrischer Druckbehältermentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Optimum heating of cylindrical pressure vessels

Dzierwa

Taler

2015

Forsch Ingenieurwes

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“…The major limiting factor relevant to fast steam boiler start-ups are the maximum allowable thermal stresses in thick-walled components such as headers of superheaters and reheaters, boiler drum and T and Y shaped junctions in steam pipelines [1][2]. Optimization of heating and cooling of thick boiler components is the subject of many studies [3][4][5], since too rapid heating or cooling element causes high thermal stresses.…”

Section: Introductionmentioning

confidence: 99%

Optimum heating of boiler drums

Dzierwa¹

2014

ZN PRz Mechanika

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In a paper, a method for determining time-optimum medium temperature changes is presented. The heating of the pressure elements will be conducted so that the circumferential stress caused by pressure and fluid temperature variations at the edge of the opening at the point of stress concentration, does not exceed the allowable value. In contrast to present standards, the stress distribution at two points at the edge of the hole is taken into consideration. Optimum fluid temperature changes are approximated by simple time functions. The temperature of medium at the beginning of the heating process was varied steeply and then the temperature was increased with a constant rate.

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“…These problems occur in many different fields and contexts, including optimal control, parameter and state estimation, and design optimization. Examples of applications are minimization of material and energy consumption during setpoint transitions in power plants [39] and chemical processes [52], estimating occupancy and ambient air flow in buildings [61], and optimal experimental design for estimation of kinetic parameters in fed-batch processes [10].…”

Section: Introductionmentioning

confidence: 99%

Symbolic elimination in dynamic optimization based on block-triangular ordering

Magnusson

Åkesson

2017

Optimization Methods and Software

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We consider dynamic optimization problems for systems described by differential-algebraic equations (DAEs). Such problems are usually solved by discretizing the full DAE. We propose techniques to symbolically eliminate many of the algebraic variables in a preprocessing step before discretization. These techniques are inspired by the causalization and tearing techniques often used when solving DAE initial value problems. Since sparsity is crucial for some dynamic optimization methods, we also propose a novel approach to preserving sparsity during this procedure.The proposed methods have been implemented in the open-source JModelica.org platform. We evaluate the performance of the methods on a suite of optimal control problems solved using direct collocation. We consider both computational time and probability of solving the problem in a timely manner. We demonstrate that the proposed methods often are an order of magnitude faster than the standard way of discretizing the full DAE, and also significantly increase probability of successful convergence.

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Optimization of boiler start-up using a nonlinear boiler model and hard constraints

Cited by 72 publications

References 14 publications

Optimum heating of cylindrical pressure vessels

Optimum heating of cylindrical pressure vessels

Optimum heating of boiler drums

Symbolic elimination in dynamic optimization based on block-triangular ordering

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