Examination of HA230 turbine transition duct

Abstract

The present paper reports the results of an examination of a service run transition duct from one of Siemens' industrial gas turbines and the correlation between the findings for this, and those from the studies undertaken on laboratory exposed Haynes alloy 230 material. The studies have shown that there are changes in the microstructure and hardness of the material that can be related to temperature and time of exposure, and the information gained can lead to estimations of the average component operating temperature. Metallographic studies revealed a high level of heterogeneity of the grains in this transition duct.     

Evaluation,degradation and life assessment of coatings for land based combustion turbines

Abstract

Use of metallic and thermal barrier coatings to protect hot section blades and vanes of combustion turbines for power generation has been common practice for the past three and one decades respectively. Because these coatings must be optimised with respect to both different forms of corrosion and modes of operation (base load versus peak load), their performance may be machine specific. Industrial end users generally do not have detailed knowledge of the failure mechanisms of the coatings and the basis for selecting coatings to suit specific requirements, topics the present review seeks to address. The evolution of protective coatings, coating failure mechanisms and a methodology for selecting machine specific coatings are described. The methodology, which can be used to rank and optimise coating systems and to predict the remaining life of coatings, forms the basis of a computer code known as COATLIFE. The ingredients of this methodology, i.e. degradation modelling and thermomechanical fatigue life prediction, are reviewed.     

Surface modification of polypropylene film using N2O-containing flames

Contact-angle measurements and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize polypropylene (PP) films that were exposed to laminar premixed air: natural gas flames containing small quantities of nitrous oxide. During combustion, the nitrous oxide generates gas-phase nitrogen oxides that lead to the affixation of nitrogen-containing functional groups to the PP surfaces. Treatment of PP in nitrous oxide-containing flames also leads to an increase in surface oxidation and markedly improves wettability when compared with standard flame treatments. The chemical form of the nitrogen affixed to the PP surface is strongly dependent on the flame equivalence ratio. Fuel-lean flames tend to affix highly oxidized forms of nitrogen such as nitrate and nitro groups, while fuel-rich flames tend to affix less-oxidized nitrogen groups such as nitroso, oxime, amide, and amine. A computational model, SPIN, was used to elucidate the chemistry of the flame as it impinges upon the cooled PP surface. The SPIN modeling indicates that the principal reactive gas-phase species at or near the PP surface are O₂, OH, H, NO, NO₂, HNO, and N₂O. A number of possible reactions between these species and the PP can account for the formation of the various nitrogen functional groups observed.     

Oxidation behaviour of Ni–Cr based alloy containing Si during high temperature application in an oil burner

Abstract

In certain modern oil burners, the combustion reaction is started in a flame tube. In the combustion atmosphere, the tube material is exposed to high temperatures and temperature changes. Nickel–chromium alloys are used to meet the requirement of high oxidation resistance. The paper presents the results on the oxidation behaviour of the silicon containing alloy 603 exposed to a low NO_x burner at temperatures of 950 and 1000°C up to 2000 h. Beneath a chromia scale silica precipitates formed at the beginning of exposure, which grew laterally establishing a nearly continuous interlayer. The interlayer disintegrated during the continued exposure. A thinner chromia scale was observed for alloy 603 compared with the scales observed for aluminium containing nickel–chromium alloys. This was attributed to a pronounced scale spallation. After 1000 h at 1000°C catastrophic oxidation of alloy 603 occurred involving Mo oxide and internal chromium oxide.     

Oxyfuel concept development

Abstract

The reduction of greenhouse gas emissions and replacement of fossil fuels by renewable energy sources are important national and international targets. Oxyfuel (oxygen combustion technology) is one of the most promising technologies enabling carbon capture and storage from flue gases. The aim of oxyfuel concept development is to study different oxygen production technologies, combustion processes, CO₂ capture methods and integrate those to optimised concept. The goal is to create technical readiness for demonstration of oxygen combustion by using state of the art knowledge, experiments, modelling and simulation. Demonstration plan for oxygen combustion for an existing power plant(s) in Finland will be prepared. Main results will be an evaluation of oxygen combustion business potential for implementation in existing and new power plants, and improvement of competitiveness of Finnish companies in energy sector by developing CO₂ free power production technologies.

Before oxygen combustion can be demonstrated in full scale, small scale testing and model development must be done. Material exposure conditions in oxygen combustion will differ from any present day environment. Current high temperature steel grades have not been developed or tested for such aggressive conditions. VTT (Technical Research Centre of Finland) has in Jyväskylä unique small scale combustors applicable for oxygen combustion research.     

EFFECTS OF INJECTION STRATEGY ON D.I. DIESEL ENGINE COMBUSTION

Experiments are conducted to develop an understanding of how split injections can affect the combustion and emission characteristics of a D.I. diesel engine with a common-rail injection system. The ratio of the amount of fuel injected between two injection pulses and the injection interval is varied keeping the injected fuel quantity constant. Results show that under the 70D90-10 injection pattern, the engine achieves the lower NOx-smoke emissions and BSFC compared with the single injection pattern. The heat release rate and the temperature show that the split injections increase the initial premixed burn and retards the diffusion burn. With the balance of these two effects, the maximum in-cylinder temperature decreases while the 50% heat release point is held at almost the same crank angle. Therefore, both NOx emission and BSFC are improved while keeping the smoke emission at the same level.     

Combustion synthesis and characterisation of lanthanum hexa-aluminate

Abstract

Lanthanum hexa-aluminate (LHA) is considered a promising material for thermal barrier coatings for gas turbine applications as well as oxidation resistant coatings for fibres in oxide based ceramic composites. Combustion synthesis has attractive advantages such as simple experimental setup, low cost, short reaction time, energy savings due to exothermic reaction, better control of stoichiometry and fine powder size. The present study involves combustion synthesis of LHA using lanthanum and aluminium nitrates as oxidising precursors, and urea as fuel. The precursor salts were dissolved in a minimum amount of deionised water and the solution was heated in a mantle heater to temperatures of around 300–350°C, at which combustion takes place with rapid evolution of gas. The LHA powder was also prepared by a precipitation route for comparative study. The as synthesised powders were calcined at up to 1450°C and subjected to X-ray diffraction for phase evolution studies. Product powders were then characterised. The influence of the lanthanum/aluminium molar ratio in the starting composition and the effect of temperature on the formation sequences of lanthanum monoaluminate (LMA) and LHA and on the conversion of LMA to LHA are discussed.     

Modified metal injection moulding process of 316L stainless steel powders using thermosetting binder

Abstract

A modified metal injection moulding (MIM) process of 316L stainless steels powders using an acrylic thermosetting resin has been developed. Gas and water atomised 316L powders were used. In order to optimise the mixing and moulding steps, different volume fractions of the two components were investigated. Mixing of metal powder and binder was carried out at room temperature and immediately moulding was performed by pouring the slurry in the moulds. It was then heated at 90°C to permit the polymerisation and cross linking of the resin. Different heating cycles, rates, and atmospheres were studied by means of thermogravimetrical analysis. The data obtained were used to establish the best debinding cycle. The debound samples were sintered at different temperatures and high densities (98% of theoretical) were obtained. Materials in as moulded (green part), debound (brown part), and sintered conditions were examined by means of SEM.     

Fire and Pesticides, A Review and Analysis of Recent Work

There are a number of circumstances that involve the burning of toxic materials, including pesticides, herbicides, insecticides, and poisonous plant or plant products. Toxicity issues of smoke from the Anacardiaceae family and the Oleander are discussed and contrasted with that from pesticides, herbicides, insecticides, and other organic materials. Work in two major European programs is reviewed. Survival fractions in smoke of 1 to 10% can be expected for some toxic compounds in fires. Survival fractions are dependent not only upon the specific toxic compound but on the fire scenario and other fuels present. Of importance, flaming combustion mat not ensure destruction of such compounds in real fire incidents.