Techno-Economic Optimization Of A Stand-Alone Hybrid Microgrid For The Rural Electrification In Sub Saharan Africa

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.This paper is focused on the design of a stand-alone micro-grid for rural electrification. The aim of this work is to define the best mix of energy sources and the optimal size of the energy storage for a small isolated village on the Ghana seaside. We obtain the optimal solution by simulating one year of operation for several different combinations of prime movers and battery sizes and comparing the economic performance in terms of levelized cost of electricity. We adopt a rolling-horizon strategy to simulate the micro-grid operation, which optimizes generators and loads schedule over a 12 hours time horizon. We solve a Mixed Integer Linear Programming problem for each time step, exploiting weather forecast for predicting the energy available from sun and wind and taking into account a realistic operation of each component like energy losses and costs during start-up of dispatchable generators and ageing cost for the battery. The optimal configuration found includes a 30 kWel wind turbine, a 60 kWel photovoltaic array, a 30 kWel biomass fired ORC and a 50 kWel diesel. The limited use of the diesel engine in the optimal solution demonstrates that energy access in a sustainable and economic way is possible even in rural contexts. Finally, two sensitivity analyses are presented varying the cost of the biomass and the error of wind speed forecast.cf201

Selection Maps for ORC and CO2Systems for Low-Medium Temperature Heat Sources

Low-medium temperature heat sources in the range 5 - 50 MWthare made available by many industrial fields but they may also be of interest for biomass and solar energy applications. ORC has been proposed in the last 20 years as a reliable solution for the exploitation of these energy sources since the alternative represented by steam cycles leads to an inefficient conversion of such small available thermal powers. However, the use of organic fluids involves a number of safety and environmental issues, either related to fluid flammability (for hydrocarbons) or to their high-Global Warming Potential (for halogenated fluids), and of limitations to the achievable cycle maximum temperature, due to fluids thermal decomposition. To overcome these limitations, CO2-based transcritical and supercritical cycles have been proposed, in recent years, as a viable option for waste heat recovery applications. The present work aims to present a fair comparison between CO2and ORC power plants for waste heat recovery applications

Modeling of ultra super critical power plants integrated with the chilled ammonia process

Abstract As carbon dioxide anthropogenic generation and climate change appear to be correlated, carbon capture becomes necessary, in particular if applied to coal-fired power plants. The Chilled Ammonia Process (CAP) is a promising technology to be proved for the purpose. This work investigates the integration of Ultra Super Critical (USC) power plants with CAP, conducting a parametric investigation on the design parameters to find the optimum and analyzing then on the details of the power block. The commercial code Aspen Plus and the in-house research code GS are employed. With respect to a reference plant, carbon capture reduces the net electrical power by 19% and the net electrical efficiency by 8.5 percent points. The performance index SPECCA is also utilized. The optimum SPECCA is 3.18 MJ/kg CO 2 , which is to be compared to 4.2 MJ/kg CO 2 for conventional amine

Energy and exergy analyses for the carbon capture with the Chilled Ammonia Process (CAP)

Abstract Post-combustion carbon capture in existing power plants is a strategic technology that can reduce emissions from power generation. The proven approach is scrubbing with amines. However, its drawbacks are energy requirement, 3 to 5 MJ per kg of captured CO 2 , as well as solution corrosion and solvent degradation. An alternative approach is scrubbing with chilled aqueous ammonia. This technology aims at mitigating energy usage and solving corrosion and degradation issues. Here an approximate model of the CO 2 - H 2 O- NH 3 system is coupled with a proposed process to evaluate mass, energy and entropy flows. For 1 kg of captured CO 2 , the simulation yields a steam extraction of 0.59 kg, equivalent to a heat duty exceeding slightly 1.5 MJ and a generation loss approaching closely 0.1 kWh, an auxiliary consumption of 0.1 kWh and a delta of almost 0.18 kWh with respect to the ideal case. Assuming a cost of electricity of 7c/kWh, the sole operation of the capture system totals 14C/ton_ CO 2

Reduced order modeling of the Shell-Prenflo entrained flow gasifier

Pre-combustion capture applied to an integrated gasification combined cycle is a promising solution for greenhouse gas emission’s mitigation. For optimal design and operation of this cycle, detailed simulation of entrained flow gasifiers and their integration in the flowsheet analysis is required. This paper describes the development of a reduced order model (ROM) for the Shell–Prenflo gasifier family, used for chemicals and power production because of its high efficiency and compatibility with a wide range of coal quality. Different from CFD analysis, ROM is computationally very efficient, taking around 1 min in a typical desktop or laptop computer, hence enabling the integration of the gasifier model and the overall power plant flowsheet simulation. Because of the gasifier complexity, which includes several gas recirculation loops and a membrane wall, particular attention is paid to: (i) the two-phase heat exchange process in the gasifier wall; and, (ii) the syngas quench process. Computed temperature, composition, velocity and reaction rate profiles inside the gasifier show good agreement with available data. The calculated cold gas efficiency is 82.5%, close to the given value of 82.8%. Results and several sensitivity analyses describe the implementation of the model to explore the potential for operating gasifiers beyond the design point.MIT-Italy ProgramProgetto Roberto Rocc

Field Performance Evaluation of ORC Geothermal Power Plants Using Radial Outflow Turbines

This paper, after a brief description of the radial outflow turbine and of its main features, discloses the field performances evaluation of two operating geothermal ORC (Organic Rankine Cycle) plants installed by Exergy Spa in Turkey. The work describes the test procedure, the measurements and calculation methods used to obtain the turbine efficiency as well as overall power cycle performance from the set of available experimental data

Power Block Off-design Control Strategies for Indirect Solar ORC Cycles

AbstractThe performance of a 5MWel indirect ORC cycle coupled to linear solar collectors with different technologies is assessed, aiming at evaluating the effect of different control strategies on annual electricity output. Two different solutions are considered for solar collectors: a state-of-the-art parabolic trough collector with Therminol VP1 as heat transfer fluid (HTF), reaching 390°C as maximum temperature within the solar field, and a cheaper Linear Fresnel Reflector (LFR) with Therminol 55, limited to an operating temperature of 310°C. A simplified procedure is firstly proposed in order to identify the organic fluid that guarantees the highest performance under design conditions. Toluene is the selected working fluid in a saturated regenerative Rankine cycle configuration. After fluid selection, a more detailed analysis involving turbine sizing and piping estimate is carried on in order to set optimal on-design parameters such as the evaporating pressure of the working fluid. Finally, yearly electricity production is calculated taking into account off-design performance of all plant components as a function of the effective solar radiation. Two different off-design control strategies are considered for the turbine, namely sliding pressure and constant pressure at the turbine inlet. The levelized cost of electricity (LCOE) is computed for both cases. For high temperature collectors the LCOE results respectively about 180 €/MWh with partial admission and 175 €/MWh with sliding pressure off-design control strategy. LFR technology leads to similar LCOE when its specific cost is about half than the parabolic trough collector

Alternative Layouts for the Carbon Capture with the Chilled Ammonia Process

Many alternatives are being investigated for the carbon capture, but none appears to have been proved as the choice for full-scale applications. This work considers the Chilled Ammonia Process for coal-fired Ultra Super Critical power plants. Three layouts are simulated with Aspen Plus and the Extended UNIQUAC thermodynamic model. Compared to a traditional layout, stripping of the wash water of the absorber or, better, splitting the rich solution between the middle and the top of the column limits greatly the ammonia slip. Moreover, splitting the regeneration over two levels reduces substantially the electric loss due to stream extraction from the turbine. The simulations show that the net electric efficiency drops from 45.5% to 33.5-34.5%, the SPECCA index is 3.8-4.3 MJth/kg_CO2 and the heat duties are 2.7-2.9 MJth/kg_CO2. The performances may improve greatly upon optimization of the parameters