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Università: Politecnico di Milano
Corso di laurea: Energy Engineering
Materia: Energy Conversion A
Docente: Valenti
Anno accademico: 2020-2021
Classificazione: Altro materiale
Formato originale: PDF
Testo: Testo ricercabile

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Materiale universitario di Energy Conversion A per il corso di Energy Engineering presso Politecnico di Milano. Il documento tratta: ENERGY CONVERSION A PROJECT WORKS – 2020/21 GROUP MEMBERS • Ellakany Youssef Moustafa • Longoni Roberto • Gad Khaled Sayed Abdelhafiz Elsayed • Berthelon Jean Paul SUMMARY Group members…

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ENERGY CONVERSION A PROJECT WORKS – 2020/21 GROUP MEMBERS • Ellakany Youssef Moustafa • Longoni Roberto • Gad Khaled Sayed Abdelhafiz Elsayed • Berthelon Jean Paul SUMMARY Group members ......................................................................................................................................................................... 1 ECONOMICS OF POWER PLANTS ................................................................................................................................................ 3 Introduction ...................................................................................................................................................................................................................3 Total specific annual cost ...........................................................................................................................................................................................4 Fixed costs .................................................................................................................................................................................................................4 Variable costs ...........................................................................................................................................................................................................6 Incentives, externalities and carbon tax.................................................................................................................................................................9 Incentives…

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CARBON TAX (BREAKEVEN POINT) Governments can rise or lower the carbon tax to promote better technologies from the environment point of view or green energy technologies. We used excel solver to compute two carbon taxes so that NGSC plants would be economically preferable to coal-based plants: Break even point Carbon tax 30 €/t given by the text LCOE New carbon tax with solver NGSC 0,110538 PCSC 0,090301 65 €/t USC 0,085685 84,6 €/t CONCLUSIONS 1. The slope of the line connecting the origin to the rightmost point of each curve represent the specific cost of electricity for each plant. As such, we can conclude that without considering any incentive or externality we can use a variety of plants to cover the energy demand. Hydro is perfect to cover peaks (low availability), while coal or natural gas-based plants are cheaper for the basic power generation. 2. Incentives make clean technologies slope negative, so that their curve intersect common technologies: their levelled cost of electricity is lower and they become economically worth to build. 16

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This represents an exergy loss from the plant rather than exergy destruction within its components. To examine how evaporation pressure affects the distribution of losses, the results are grouped into nine categories: • Condensate extraction and feedwater pump losses. • Irreversibilities during steam turbine expansion. • Auxiliary consumption and electromechanical conversion losses. • Condenser heat-rejection losses. • Residual exergy discharged through the stack. • Heat-transfer irreversibilities within the HRSG arising from finite temperature differences. • Thermal losses through the HRSG insulation. • Exhaust-gas pressure-drop losses through the HRSG. • Water-side pressure-drop losses in the economizers. Each contribution is assigned to one category only to avoid double counting. The plotted values are 100 Δ𝜂𝜂II,𝑗𝑗 , expressed in percentage points. The chart shows that increasing evaporation pressure reduces the contribution associated with heat transfer within the HRSG, while increasing stack losses and turbine expansion irreversibilities. Condenser losses decrease moderately, whereas the remaining contributions are comparatively small. These competing trends explain why increasing evaporation pressure does not necessarily improve the overall second-law performance. The second-law analysis identifies four dominant contributions: heat-transfer irreversibilities within the HRSG, stack losses, condenser losses, and turbine expansion irreversibilities. Increasing evaporation pressure reduces the HRSG 35

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COMPRESSION Normalized compression losses increase with the overall compression ratio in all four configurations. Their magnitude depends on both the exergy destroyed in the compressors and the fuel-exergy input used for normalization. The intercooled cycle exhibits the lowest normalized compression losses over the common comparison range. Its higher fuel requirement increases the normalization denominator, reducing the relative contribution of compression irreversibility. This should not be interpreted as an improvement in the prescribed compressor polytropic efficiency, which remains unchanged. The simple cycle shows a steeper increase because compression irreversibility rises while the fuel input decreases with β. In the recuperative configurations, the progressive reduction in heat recovery increases the fuel required to maintain TIT under the investigated conditions. The resulting increase in fuel-exergy input moderates the growth of normalized compression losses, producing flatter curves. Their comparatively high values at low β also reflect the small fuel input achieved through recuperation. EXPANSION LOSSES 50

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The aspect ratio also follows an almost linear trend. This can be explained by considering the scaling of geometrically similar machines: the mean diameter is inversely related to rotational speed, since smaller machines generally rotate faster. At the same time, the blade height remains almost constant because the volume flow rate does not significantly change. As a consequence, increasing the rotational speed reduces the diameter and modifies the blade aspect ratio accordingly. In the loss analysis, the outlet kinetic energy loss is not included, since this contribution is not a real loss for the first stage of a multi-stage machine: part of the kinetic energy can still be recovered by the following stage. The reported losses therefore include profile losses, secondary losses, and annulus losses. Profile losses are mainly associated with blade surface roughness, boundary layer growth, possible flow separation, and turbulence generated by the blade geometry. These losses reach their minimum close to the optimal rotational speed, where the blade velocity and flow angles are better matched. Secondary losses include additional three-dimensional flow effects, such as vortical structures, leakage phenomena, and interactions between boundary layers. Their trend is linked to the aspect ratio: as the geometry changes with rotational speed, the relative importance of end-wall and clearance effects also changes. Annulus losses are related to the unguided flow region between two consecutive blade rows. These losses increase significantly at high rotational speed, where the flow field becomes more demanding and twisted blades may become necessary to preserve acceptable incidence and flow guidance along the blade span. 66

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