Techno-economic analysis of expander-based configurations for natural gas liquefaction

The use of liquefied natural gas (LNG) as a marine fuel is rapidly growing because of the possible economic advantages over conventional fuels and stricter environmental regulations. Production of LNG is energy intensive because of the required temperature level of around -160\ub0C. Three main types of refrigeration cycles have been developed. The present work focuses on the comparison of six expander-based configurations, which in spite of the higher power consumption, are more compact, flexible and easier to operate. They are optimised from a thermodynamic perspective: the exergetic efficiency is found to range between 17 % and 33 % for a specific power consumption down to 1340 kJ/kg. Multi-objective optimisations are performed to simultaneously minimise the net power consumption and the heat transfer conductance as an indicator of the required heat transfer area. The latter ranges between 50 kW/K and 300 kW/K. A trade-off between power consumption and heat transfer area is found, which justifies a further economic analysis. A simplified economic analysis is set based on a discounted cash flow model. The unitary profit ranges between 0.5 and 0.9 DKK/kg of produced LNG. The most profitable expander-based configuration is the dual-refrigerant cycle with nitrogen in the bottoming refrigeration cycle. Finally, the influence of the cost correlations on the economic outcome is assessed: the compressors represent the major costs, which leads to the coincidence of the thermodynamic and economic optima

Optimum design and performance of a solar dish microturbine using tailored component characteristics

Versión revisada. Embargo 24 mesesThe aim of the paper is to find the optimum design and performance of solar microturbines powered by parabolic dish collectors using an innovative methodology which integrates the design and off-design models of the total system. In contrast to the common practice of assigning an estimated efficiency to the engine turbomachinery (generalized performance maps), the procedure hereinafter produces the specific geometry and the characteristic maps of compressor and turbine, according to their inlet/outlet thermodynamic states and working cycle boundary conditions. With this global approach, a sensitivity analysis is performed to search for the pressure ratio that maximizes the solar-to-electric efficiency at design point for a constant air mass flow rate and turbine inlet temperature. Maximum values in the range 18.0–21.7% are obtained for a pressure ratio of 3.2 when the turbine inlet temperature changes between 800 °C (base-case system) and 900 °C. The methodology allows also to simulate the performance of the system when different design DNIs are considered with the aim to maximize the annual yield of the system. Simulations performed for Beijing, Seville and San Diego showed that quite different DNIs (610–815 W/m2) are to be chosen to get the maximum annual (average) efficiency: 11–16% for the base-case system and 14–19% for a more advanced design.Comisión Europea Grant Agreement No. 30895

Experimental performance evaluation of a multi-diaphragm pump of a micro-ORC system

Abstract The performance of micro-scale ORC systems strongly depends on the performance of their key components. While the heat exchangers and expander have been extensively investigated, the pump has only received limited attention. The main purpose of this work is the experimental characterization of a multi-diaphragm positive displacement pump, integrated in an experimental ORC system with a rated power output of 4kWel. The study focuses on the experimental evaluation of the pump performance and on cavitation phenomena. A detailed presentation of the experimental procedure and results is supplied. A great effort has been spent in calculating the global and volumetric pump efficiencies for a wide range of operational conditions, which reach maximum values around 45-48% and 95%, respectively. With regards to cavitation issues, the effect of the available Net Positive Suction Head at the pump inlet has been deeply investigated both at partial and full load to obtain guidelines for stable operation. Finally, an extensive dataset of steady-state operating points has been used to calibrate an improved version of a semi-empirical model previously developed for positive displacement ORC pumps. Special attention has been given to the ability of the model to accurately predict the behaviour and performance of the pump at different, properly chosen, steady-state conditions. Relative errors in between 0.5%, for the outlet temperature, and 10%, for the electric power consumption, are achieved

Synthesis and parameter optimization of a combined sugar and ethanol production process integrated with a CHP system

The combined sugar and ethanol production process from sugar cane is a paradigmatic application for energy integration strategies because of the high number of hot and cold streams involved, the external hot utility requirement at two temperature levels for juice evaporation and crystallization, and the electricity demand for juice extraction by milling. These conditions make it convenient to combine the sugar-cane process with a CHP system fuelled by bagasse, the main by-product from juice extraction. The strategies, tools and expertise on energy integration developed separately by the research teams authoring this paper are applied here jointly to optimize the synthesis and the design parameters of the process and of the total site starting from the basic idea of dissociating the heat exchanger network design problem from the total site synthesis problem. At first the minimization of the external heat requirement for the process alone is pursued and results show that a one third reduction can be achieved by optimal heat integration. Then the use of the by-product bagasse for on-site power generation is considered and two bagasse-fuelled CHP systems are optimized along with some parts of the sugar and ethanol production process in order to obtain maximum total site net power. Results show a variety of interesting scenarios of combined sugar, ethanol and electricity production plants with considerably high electricity output

Fault location in a marine low speed two stroke diesel engine using the characteristic curves method

When a malfunction occurs in a marine main engine system, the impact of the anomaly will propagate through the system, affecting the performance of all relevant components in the system. The phenomenon of fault propagation in the system caused by induced factors can interfere with fault localization, making the latter a difficult task to solve. This paper aims at showing how the "characteristic curves method" is able to properly locate malfunctions also when more malfunctions appear simultaneously. To this end, starting from the working principle of each component of a real marine diesel engine system, comprehensive and reasonable thermal performance parameters are chosen to describe their characteristic curves and include them in a one-dimensional thermodynamic model. In particular, the model of a low-speed two stroke MAN 6S50 MC-C8.1 diesel engine is built using the AVL Boost software and obtaining errors lower than 5% between simulated values and test bench data. The behavior of the engine is simulated considering eight multi-fault concomitant phenomena. On this basis, the fault diagnosis method proposed in this paper is verified. The results show that this diagnosis method can effectively isolate the fault propagation phenomenon in the system and quantify the additional irreversibility caused by the Induced factors. The fault diagnosis index proposed in this paper can quickly locate the abnormal components

Fuel and Product definitions in cost accounting evaluations: is it a solved problem?

Exergoeconomic cost evaluations are based on the principle that costs are apportioned among mass and energy streams in proportion to the exergy that is carried by the Fuel and Product streams of the energy system components. The Specific Exergy Costing (SPECO) method was developed to find a general and unambiguous \u201cprocess based\u201d criterion to define the Fuel and Product of each component based on the record of all additions and removals of exergy to and from the mass and energy streams of the real energy system. This criterion in conjunction with the so called Fuel and Product Rules allows one to directly extract the exact number of auxiliary equations that are needed to evaluate costs. Several examples have been already shown in the last years to demonstrate the reduction of ambiguities in the Fuel and Product definitions and in turn in cost calculations deriving by the use of the SPECO approach. Other more specific examples of application to components having a \u201cdouble purpose\u201d are considered in this paper to compare the SPECO approach with other approaches, and to demonstrate the more reliable costs obtained by the former also in these cases

A Criterion to Define Cross-Flow Fans Design Parameters

The paper presents an original criterion to parameterize systematically a cross-flow fan configuration according to the most significant variables defining the geometry and then affecting performance and efficiency. This choice of parameters has proved to be effective in a systematic series of experimental tests aimed at investigating directions for design improvement

A new thermoeconomic method for the location of causes of malfunctions in energy systems

Diagnosis procedures primarily aim at locating the control volumes where anomalies occurred. This is not a simple task since the effects of anomalies generally propagate through the whole system and affect the behavior of several components. Some components may therefore present a reduced efficiency, although they are not sources of operation anomalies, due to nonflat efficiency curves. These induced effects are a big obstacle in the use of thermoeconomic techniques for the search of the origin of the anomalies. On the other hand, the real cause of the alteration of component behavior is the modification of its characteristic curve, due to degradation or failures. According to this concept, a new approach, based on an indicator measuring the alteration of the characteristic curve of the component affected by the operation anomaly, is proposed and applied to a test case power plant