Development of turbomachines for renewable energy systems and energy-saving applications

Abstract Turbomachines play a significant role in some key sectors as aircraft and marine propulsion, power production, heat ventilation and air conditioning and chemical processing. The success of dynamic machines is connected to the wide variety of demands that they can cover, together with their compactness, reliability and availability. In this respect, such machines are the favourite candidate to support an efficient exploitation of some renewable energy sources and the development of energy-saving systems. Innovative plants require machines which can work with new fluids (e.g. Organic Rankine Cycle systems) or in new operating conditions (e.g. high-flexibility or new pressure ratios) and it poses new challenging aspects in the preliminary machinery design. Moreover, another challenging aspect is how innovative techniques (e.g. high-integrated design systems, 3D printing) can be integrated in the design process and how much they can affect the machine development and final performance. Two case studies are presented to focus the attention on such aspects, discussing preliminary design and prototyping of "unconventional" turbomachines

development of a solar cavity receiver with a short term storage system

Abstract The technological progress carried out in the development of high-temperature materials has led to the design of new concentrated solar power plants, like Dish-Micro Gas Turbines (Dish-MGTs). This study proposes a novel cavity receiver for small-scale Dish-MGT plants with a phase-change material storage system integrated inside the receiver container. Such a storage system provides a proper thermal inertia to the component, to level the effects of short-term solar radiation fluctuations which can reduce plant performance and, in the worst cases, damage seriously the MGT. In the paper, results related to CFD steady-state and transient (charge and discharge storage phases) analyses are presented and discussed

Analysis of diabatic compressed air energy storage systems with artificial reservoir using the levelized cost of storage method

A detailed analysis has been carried out to assess the thermodynamic and economic performance of Diabatic Compressed Air Energy Storage (D-CAES) systems equipped with above-ground artificial storage. D-CAES plant arrangements based on both Steam Turbine (ST) and Gas Turbine (GT) technologies are taken into consideration. The influence of key design quantities (ie, storage pressure, turbine inlet pressure, turbine inlet temperature) on efficiency, capital and operating costs is analysed in detail and widely discussed. Finally, D-CAES design solutions are compared with Battery Energy Storage (BES) systems on the basis of the Levelized Cost of Storage (LCOS) method. Results show that the adoption of D-CAES can lead to better economic performance with respect to mature and emerging BES technologies. D-CAES ST based solutions can achieve a LCOS of 28 €cent/kWh, really close to that evaluated for the better performing BES system. Interesting LCOS values of 20 €cent/kWh have been attained by adopting D-CAES plant solutions based on GT technology

Techno-economic analysis of a sCO2 power plant for waste heat recovery in steel industry

Abstract Industrial facilities release a large amount of heat as a by-product of their processes. To improve environmental performance and increase process profitability, a portion of the waste heat can be recovered and employed for power generation by recovery systems. Supercritical carbon dioxide (sCO2) plants are emerging as potential alternatives to the well-established technologies for waste heat recovery (WHR) power generation in heavy industry. This paper offers a preliminary techno-economic analysis of a waste heat-to-power system based on a sCO2 closed-loop for a heavy-industrial process. By conducting a parametric investigation on the WHR sCO2 system's key design parameters, a number of preferable configurations from a thermodynamic perspective were initially identified; they were subsequently analyzed from the economic point of view in terms of net present value (NPV) and pay-back period (PBP). The privileged WHR system configuration achieved an overall efficiency of 30.4% and a power output of 21.6 kWe, providing an NPV of almost US k$ 376 with a PBP of approximately 4.5 years

Design of power-blocks for medium-scale supercritical carbon dioxide plants

For power production, the emerging technologies of supercritical carbon dioxide (S-CO2) cycles show potential advantages if compared to conventional plants. The current bottleneck in exploiting such cycles is the development of novel components such as turbomachines and heat-exchangers. This paper focuses on the layout arrangement and machinery design of a novel power block for a 10 to 15 MW supercritical carbon dioxide plant. The applied design procedure involves 0D and 1D models implemented using an in-house Fortran code, and 3D computational fluid dynamics (CFD) analyses using ANSYS-CFX. Novel configurations of the power block were designed, starting with the same primary thermal source. At nominal conditions, expected overall output powers from 13.2 to 16.2 MW were found. Finally, some qualitative considerations were included in the discussion to compare the analysed arrangements

WIND TURBINE ISTALLATION FOR HIGH ELEVATIONS

The strong drive to exploit wind energy has recently led to new types of location for wind turbine installations being considered, including mountain regions and, to be more specific, areas at elevations coming between 800 and 2,500 m asl. Authoritative sources, such as the European Wind Energy Association (EWEA), have estimated that 20-25% of the approximately 60,000 MW expected to be installed in Europe between now and 2010 will be situated in cold-climate areas, and a part of them will be on hills and mountains. The installation of wind farms in the mountains consequently demands an in-depth analysis, in the design of such plant, into both the methods for assessing the resource and the more or less direct transfer of procedures and technologies developed for conventional sites. For the time being, the IEC standards (originally developed to provide a reference picture relating to conventional sites) fail to provide recommendations on this type of site, where the structure of the flow field is substantially more complex in terms of its effect on the stresses involved.The present work outlines the main features of mountain wind farm sites and discusses the effects of some of said features on the structural assessment of the turbines destined for such installations in the light of the IEC standard requirements.The work illustrate that the installation of wind turbines in mountain sites must consider different site-related features from those used to develop the requirements of the IEC standards.The examples given here indicate that, based on the standards, these features influence both energy generation and the turbine's working life. Only an adequate understanding of these features can lead to a cost-effective sizing of the turbines.This type of approach can lead to a site-specific design concept, and only certain components are structurally adequate for the stress characteristics of a given site. These procedures will then have to be transferred to the standards, overcoming the conflict between the minimum standard requirements specifying the fundamental elements to consider in the project and the set of parameters describing the external conditions that demand a turbine of equivalent sturdiness in comparable applications

Charge and discharge analyses of a PCM storage system integrated in a high-temperature solar receiver

Solar Dish Micro Gas Turbine (MGT) systems have the potential to become interesting small-scale power plants in off-grid or mini-grid contexts for electricity or poly-generation production. The main challenging component of such systems is the solar receiver which should operate at high temperatures with concentrated solar radiations, which strongly vary with time. This paper deals with the design and the analysis of a novel solar receiver integrated with a short-term storage system based on Phase Change Materials to prevent sudden variations in the maximum temperature of the MGT working fluid. Particularly, the charge and discharge behavior of the storage system was analyzed by means of Computational Fluid Dynamic methods to evaluate the potentiality of the concept and the component capabilities. Achieved results were highly satisfactory: the novel solar receiver has a good thermal inertia and can prevent relevant fluctuations in the working fluid temperature for 20-30 min

Internal Power Recovery in Cryogenic Cooling Plants Part I: Expander Development

The amount of the electrical power required by refrigeration systems is relevant worldwide. It is evaluated in the order of 15% of the total electricity production taking refrigeration and air-conditioning into consideration. For this reason, in the last years several energy saving techniques have been proposed to reduce the power demand of such plants. The paper deals with the development of an innovative internal recovery system for cryogenic cooling plants. Such a system consists in a Compressor-Expander Group (CEG) designed on the basis of the automotive turbocharging technology. In particular, the paper is focused on the design of the expander, the critical component of the CEG system. Due to the low volumetric flow entering the expander and the high expansion ratio, a commercial turbocharger expander wheel was strongly modified. It was equipped with a transonic nozzle, designed to have a radially inflow full admission. To verify the performance of such a machine and suggest improvements, two different set of nozzles have been designed and modelled by means of the commercial Ansys-CFX software. In the paper, steady-state 3D CFD simulations of the second-generation prototype are presented and compared with the initial ones