Developing the Flow Path For the K-1250-6.9/25 Turbine Unit Using the Optimal Design Methods

The paper considers the main principles that are used to develop the flow paths (FP) of the high-pressure cylinders (HPC), intermediate-pressure cylinders (IPC), and low-pressure cylinders (LPC) for the K-1250-6.9/25 turbine unit. It describes approaches to the numerical experiment when designing flow paths, the advantage of which is lower labor, time and financial costs and higher informativeness compared to the physical experiment on flow paths. When designing the flow paths of high- and intermediate-pressure cylinders (HIPC), the numerical experiment is performed using the three-dimensional viscous-flow method. For this purpose, a three-dimensional model of the blade system in the flow path is built, which consists of a large number of finite volumes (elements) in the shape of hexagons, in each of which the integration of the equations of gas dynamics is performed. When developing LPC, the method of parameterization and analytical profiling of the blade crown sections is used, where the profiles are described by the curves of the fourth and fifth orders with the condition of providing the minimum value of the maximum curvature and monotonicity of variation of the three-dimensional blade geometry along height. This method allows obtaining the optimal profiles of the cross sections of the blades, which correspond to the current flow lines to the fullest extent, and minimizing the profile energy losses when the flow flows around the blades.

Cld-St-And-Bearing Assemblages in the Central Southalpine Basement: Markers of an Evolving Thermal Regime during Variscan Convergence

Multiscale structural analysis was carried out to explore the sequence of superposed pre-Alpine chloritoid–staurolite–andalusite metamorphic assemblages in the polydeformed Variscan basement of the upper Val Camonica, in the central Southalpine domain. The dominant fabric in the upper Val Camonica basement is the late-Variscan S2 foliation, marked by greenschist facies minerals and truncated by the base of Permian siliciclastic sequences. The intersection with the sedimentary strata defines a Permianage limit on the pre-Alpine tectonometamorphic evolution and exhumation of the Variscan basement. The detailed structural survey revealed that the older S1 foliation was locally preserved in low-strained domains. S1 is a composite fabric resulting from combining S1a and S1b: in the metapelites, S1a was supported by chloritoid, garnet, and biotite and developed before S1b, which was marked by staurolite, garnet, and biotite. S1a and S1b developed at intermediate pressure amphibolite facies conditions during the Variscan convergence, S1a at T = 520–550 °C and P ≃ 0.8 GPa, S1b at T = 550–650 °C and P = 0.4–0.7 GPa. The special feature of the upper Val Camonica metapelites is andalusite, which formed between the late D1b and early D2 tectonic events. Andalusite developed at T = 520–580 °C and P = 0.2–0.4 GPa in pre-Permian times, after the peak of the Variscan collision and before the exhumation of the Variscan basement and the subsequent deposition of the Permian covers. It follows that the upper Val Camonica andalusite has a different age and tectonic significance as compared to that of other pre-Alpine andalusite occurrences in the Alps, where andalusite mostly developed during exhumation of high-temperature basement rocks in Permian–Triassic times.

Performance Optimizations of the Transcritical CO2 Two-Stage Compression Refrigeration System and Influences of the Auxiliary Gas Cooler

To optimize the performance of the transcritical CO2 two-stage compression refrigeration system, the energy analysis and the exergy analysis are conducted. It is found that higher COP, lower compression power, and less exergy destruction can be achieved when the auxiliary gas cooler is applied. Moreover, the discharge temperature of the compound compressor (HPS) can be reduced by decreasing the temperature at the outlet of the auxiliary gas cooler (Tagc,out). When the Tagc,out is reduced from 30 to 12 ℃, the discharge temperature of the compound compressor (HPS) can be decreased by 13.83 ℃. Furthermore, the COP and the exergy efficiency can be raised by enhancing the intermediate pressure. Based on these results, the optimizations of system design and system operation are put forward. The application of the auxiliary gas cooler can improve the performance of the transcritical CO2 two-stage compression refrigeration system. Operators can decrease the discharge temperature of the compound compressor (HPS) by reducing the Tagc,out, and increase the COP and the exergy efficiency by enhancing the intermediate pressure.

Towards a High-Pressure Microchannel Reactor for Fuel Characterization

Within the area of combustion, externally heated microtubes have been introduced to study the combustion characteristics of fuels and fuel blends. Microreactors have advantages over other conventional fuel testing methods because of their potential to test small volumes (< 20 μl) at high throughput. In this work, a high-pressure microreactor is designed and implemented to test fuels up to a pressure of 20 bar where automated testing reduces test time substantially. The novelty of this device is its capability to operate at pressure exceeding the current state of the art of 12 bar. The combustion behavior of fuels is tested in an externally heated quartz tube, with a diameter less than the conventional quenching diameter of the fuel. The ultimate objective of the experiment is to investigate the impact of fuel on flame characteristics. The ability to reach engine relevant pressure conditions and its inherent small volume requirements make this device a potential candidate for measurements of laboratory transportation fuels and fuel blends. For initial validation, tests from an earlier intermediate pressure experiment with ethane/air and nitrogen mixtures are repeated. Chemiluminescence images are taken to evaluate the combustion characteristics in terms of the three classical flame regimes: weak flames, Flames with Repetitive Extinction, and Ignition (FREI) and normal flames. Previous results at intermediate pressure showed that as the pressure increases, the weak flame and FREI regimes shift towards lower velocities. Also, as dilution level increase (i.e. reducing oxygen concentration), the transition from the weak flame to FREI becomes less abrupt and is completely lost for marginal oxygen concentration. The objective of this study is to document flame dynamics at higher pressures.

Managing Risks Associated With Turbine First Steam Admission Following Inadequate Boiler Cleaning

Unit 6 of the recently completed six-unit Medupi coal-fired power station was the first unit to go into commercial operation. Synchronisation of the generator to the transmission grid had occurred five months before commercial operation. Prior to the admission of first steam to the turbines, the boiler underwent a three stage cleaning process, which was performed by the boiler contractor, to ensure that debris left over in the boiler from construction was removed and to avoid damage to the turbine when steam was admitted. Steam blowing of the boiler was the penultimate stage of boiler cleaning and contractually the steam would have been deemed clean when the steam cleanliness acceptance criteria were met. The steam cleanliness acceptance criteria, which were set by the turbine contractor, relate to the number and size of indentations caused by particles striking a given area of each target plate situated in the temporary piping downstream of the inlet valves of the high pressure and intermediate pressure turbines. For each target plate, values were prescribed for these variables and for the flow conditions that should prevail in the pipe upstream. The boiler contractor had to meet these requirements. Unfortunately, there was a mismatch between the steam cleanliness requirements set by the turbine contractor and those included in the boiler contract. The less stringent steam cleanliness requirements set for the boiler contractor in the boiler contract meant that the boiler would not be adequately cleaned, from the point of view of the turbine contractor. The boiler contractor designed a temporary pipework system for the steam blow-through process that permitted steam to bypass the turbines and exhaust to the atmosphere through a silencer. During steam blowing, the prescribed pipe flow conditions for accepting the steam were not being met, even after a large number of blows had been conducted. Mathematical modelling of the process revealed that the required pipe flow conditions could not be attained at the intermediate pressure turbine inlet and as such, the steam blow-through pipework was inadequately sized. The solution was to redesign the temporary pipework, and manufacture and install a new system of pipework, all of which would have taken a couple of months. Business needs required an alternative solution, and so a decision had to be taken on the way forward. Engineering judgement, based on operating and maintenance experience with the current fleet, suggested that the steam was sufficiently clean to be admitted to the turbine, with little risk. Of the two feasible options available to the project team, admission of steam after a defined number of blows was accepted. Care had to be exercised to manage the risk that the potential turbine contractor non-compliance to any of the performance guarantee conditions could be blamed on poor steam quality. An analysis of the risks associated with this option was conducted and controls were adopted to mitigate the risks. Eventually, steam was admitted to the turbines. Subsequent inspections and tests conducted on the turbines indicated minimal damage and no loss of performance. This paper describes the Medupi Unit 6 steam blow-through problem and the analytical process that revealed the inadequacy of the blow-through pipework. It describes also the process of analysing the risks associated with admission of first steam to the turboset, the decision processes that were followed to admit the steam, and the process of managing the identified risks through the controls that were put in place.