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1

The assessment of selected properties of welded joints in high-strength steels

Tuz Lechosław

Biuletyn Instytutu Spawalnictwa w Gliwicach

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2020

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Vol. 64, No. 4

73--79

EN

The use of technologically advanced structural materials entails the necessity of adjusting typical welding processes to special requirements resulting from the limited weldability of certain material groups. Difficulties obtaining high-quality joints may be the consequence of deteriorated mechanical properties and structural changes in materials (beyond requirements of related standards). One of the aforementioned materials is steel characterised by a guaranteed yield point of 1300 MPa, where high strength is obtained through the addition of slight amounts of carbide-forming elements and the application of complex heat treatment processes. A heat input during welding may worsen the aforesaid properties not only in the weld but also in the adjacent material. The tests discussed in the article revealed that the crucial area was that heated below a temperature of 600°C, where the hardness of the material decreased from approximately 520 HV to 330 HV.

PL

Wykorzystanie nowoczesnych materiałów konstrukcyjnych niesie za sobą konieczność dostosowania typowych procesów spawalniczych do specjalnych wymagań wynikających z ograniczonej ich spawalności. Trudności w uzyskaniu złączy spawanych o wysokiej jakości mogą być konsekwencją zmniejszonych właściwości mechanicznych lub zmian w strukturze materiału, co wykracza poza wymagania norm przedmiotowych. Przykładem takiej stali jest stal o gwarantowanej granicy plastyczności 1300 MPa, gdzie wysoką wytrzymałość uzyskuje się przez dodatek niewielkich ilości pierwiastków węglikotwórczych i złożonych procesów obróbki cieplnej. Powoduje to, że wprowadzenie ciepła podczas spawania może pogarszać te właściwości nie tylko w samej spoinie, ale i w materiale przyległym. Wykonane badania wykazały, że krytycznym miejscem jest obszar nagrzewany poniżej 600°C, gdzie następuje zmniejszenie twardości materiału z ok. 520 HV do 330 HV.

2

Thermodynamic analysis and profitability study of a power unit with an added CO2 capture plant

Kowalczyk Ł., Niegodajew P., Drobniak S., Elsner W.

Journal of Power Technologies

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2016

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Vol. 96, nr 4

276--284

EN

Concerns over greenhouse gas emissions are driving a requirement for newly built coal power units to satisfy the so-called “capture ready” conditions. This paper presents the a thermo-economic analysis supplemented by a cost evaluation of a power unit for ultra-supercritical parameters expanded by an amine-based CO2 capture plant. The analysis was performed with the use of an integrated package containing the IPSEpro, MATLAB and Revenue Requirement Method implemented in MOExcel. The 0D model of a post combustion capture installation was developed based on complex CFD calculations of the absorber and stripper. A number of CFD simulations were conducted to create a large database, which was then utilized to develop suitable correlations describing the process Thermodynamic and economic calculations were performed in respect of a power plant coupled with a CO2 separation unit for a varying ratio of amine solvent to the exhaust gas stream (L/G). A local minimum for reboiler heat duty was found for L/G≈3.5 revealing the optimal post combustion capture configuration. It was observed that complementing the power unit with a post-combustion capture (PCC) installation causes a slight increase in the investment costs due to the drop in efficiency, but more important is the rise in total cost due to the investment associated with the CO2 capture plant. It was found that about 14 years is required to compensate the investment cost of the PCC installation.

3

Evaluation of IPSEpro extended by MATLAB applied to steam turbine cycle analysis

Elsner W., Kowalczyk Ł., Marek M.

Journal of Power Technologies

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2015

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Vol. 95, nr 3

192--200

EN

This paper investigates thermodynamic optimization of a supercritical coal fired power plant. The main goal of the study was to assess IPSEpro software combined with MATLAB environment, aimed at multiobjective optimization of the thermal cycle in a relatively short timeframe. To verify the methodology, calculations were carried out using the IPSEpro (standalone) approach and IPSEpro-MATLAB with fmincon function. The decision functions were: thermal efficiency, gross power efficiency and total power load. It was shown that the results obtained with the IPSEpro standalone approach are similar to those obtained with the IPSEpro- MATLAB package. This means that the IPSEpro-MATLAB approach can be successfully used in future calculations. The evident benefit of the newly developed methodology is a significant reduction in computational time compared to the referenced method. It was shown that the computational time depends on both the methodology and the chosen objective function. The results show that the detected optimal point also depends on the shape of the objective function distribution. Optimization of the thermodynamic parameters of the sample ultra-supercritical power plant enables an increase in output power from 900 MW to 909.44 MW.

4

Comparative analysis of optimisation methods applied to thermal cycle of a coal fired power plant

Kowalczyk Ł., Elsner W.

Archives of Thermodynamics

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2013

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Vol. 34, no. 4

175--186

EN

The paper presents a thermodynamic optimization of 900 MW power unit for ultra-supercritical parameters, modified according to AD700 concept. The aim of the study was to verify two optimisation methods, i.e., the finding the minimum of a constrained nonlinear multivariable function (fmincon) and the Nelder-Mead method with their own constrain functions. The analysis was carried out using IPSEpro software combined with MAT-LAB, where gross power generation efficiency was chosen as the objective function. In comparison with the Nelder-Mead method it was shown that using fmincon function gives reasonable results and a significant reduction of computational time. Unfortunately, with the increased number of decision parameters, the benefit measured by the increase in efficiency is becoming smaller. An important drawback of fmincon method is also a lack of repeatability by using different starting points. The obtained results led to the conclusion, that the Nelder-Mead method is a better tool for optimisation of thermal cycles with a high degree of complexity like the coal-fired power unit.