Robust multi-objective optimization of gasifier and solid oxide fuel cell plant for electricity production using wood

Biomass is an attractive renewable and stored energy that can be converted to transportation fuels, chemicals and electricity using bio-chemical and thermo-chemical conversion routes. Notably, biofuels have relatively lower greenhouse gas emissions compared to the fossil fuels. A biomass gasifier can convert lignocellulosic biomass such as wood into syngas, which can be used in Solid Oxide Fuel Cell (SOFC) to produce heat and electricity. SOFC has very good thermodynamic conversion efficiency for converting methane or hydrogen into electricity, and integration of SOFC with gasifier gives heat integration opportunities that allow one to design systems with electricity production efficiencies as high as 70%. Generally, process design and operational optimization problems have conflicting performance objectives, and Multi-Objective Optimization (MOO) methods are applied to quantify the trade-offs among the objectives and to obtain the optimal values of design and operating parameters. This study optimizes biomass gasifier and SOFC plant for annual profit and annualized capital cost, simultaneously. A Pareto front has been obtained by solving Moo problem, and then net flow method is used to identify some optimal solutions from the Pareto front for the implementation into next phase. The constructed composite curves, which notify maximum amount of possible heat recovery, and first law efficiency also indicate better performance of the integrated plant. Uncertainty of market and operating parameters has been added to the optimization problem, and robust MOO of the integrated plant has been performed, which retains less sensitive Pareto solutions during the optimization. Finally, Pareto solutions obtained via normal and robust MOO approaches are considered for uncertainty analysis, and Pareto solutions obtained via robust MOO found to be less sensitive. (C) 2017 Elsevier Ltd. All rights reserved.

Thermo-Economic Optimisation of Solar Tower Thermal Power Plants

James Spelling

Amidst a backdrop of rapidly increasing world-wide electricity demand, solar thermal power generation shows great potential for supplying the electricity needs of numerous countries in the Sun-belt regions of the world. In these regions, the absence of significant biomass, hydrological or geothermal reserves makes solar thermal power the most promising solution for meeting that most fundamental of demands: energy. Amidst the different options available for harnessing the Sun’s power, solar thermal technologies have been shown capable of producing electricity at the most economically viable rates [32]. However, all currently existing solar thermal power plants have been based around the use of Rankine, or steam turbine, cycles which are limited in the efficiencies they can achieve. In order to make better use of the Sun’s energy, higher efficiency cycles should be used. With their high concentration ratios, solar thermal power tower systems are amongst the best options for making use of the Sun’s potential. As the energy delivery temperature of central receiver systems is higher, they harness the solar radiation at a higher exergy level [4]. This higher temperature also opens the road to the use of more advanced thermodynamic cycles. Hybrid fossil-fuel – solar systems are also imaginable [13], as the energy delivery temperature is compatible with standard gas turbine cycles. Hybrid systems can help mitigate the requirements of thermal energy storage, as well as reducing the perceived risk when investing in new solar technology, which stimulates research and development, as well as providing employment. Recent developments in the field of high temperature volumetric receivers [10] along with rock- based packed-bed storage systems have opened up an interesting possibility. High temperature receivers allow the use of higher-efficiency combined-cycle setups, whereas packed-bed units offer the possibility of cheap storage. Larger storage volumes allow pure-solar systems to extend their power production into the night, making hybrid options less attractive. This is compounded by the common practice of guaranteeing a preferred tariff for electricity sales from pure-solar sources With this in mind, a complete dynamic model of a power plant based on the pure-solar concept has been elaborated. The performance of the setup is evaluated over a range of days, using solar insolation profiles obtained from satellite data. In order to examine different design options and their impact on the performance of the power plant, a multi-objective, thermo-economic optimisation of both the power plant superstructure and operating conditions was performed using the new, dynamic models. By means of an evolutionary algorithm [17], a family of Pareto-optimal points were obtained, representing the trade-off between increased power plant efficiency, and lower levelised energy costs. Through use of optimisation, it was shown that exergetic efficiencies in the region of 21-27% can be achieved, for relatively low power outputs of between 3 and 11 MWe. These configurations correspond with levelised electricity costs in the region of 14-21 UScts/kWhe. In most regions, the use of solar power is encouraged by the guarantee of a preferential tariff for electricity sales from renewable sources. Sale of electricity at a price of around 24 UScts/kWhe [32] should therefore be imaginable, ensuring the economic viability of solar thermal power tower systems. It can be concluded that, when properly designed, solar thermal power plants based on combined cycles are both economically and thermodynamically promising. By raising the efficiency of the plant, the size of the solar collector field is diminished, increasing the otherwise low energy densities of solar power systems. By reducing the levelised electricity costs, solar thermal power plants become more economically viable, accelerating their construction and thus, hopefully, reducing our dependence on fossil-fuels.

2009

Methodology for the identification of promising integrated biorefineries

Ayse Dilan Celebi

Steady increase in global energy consumption, greenhouse gas emissions, and depletion of fossil energy resources, together with increased attention towards sustainable development has prompted researchers to discover economical and environmentally competitive non-petroleum alternatives and biomass is considered to be one of the most promising renewable sources of energy and carbon of this matter to address the aforementioned issues within a biorefinery platform. A biorefinery is an integrated processing facility that converts biomass into transportation fuels, value-added chemicals, heat, and electricity via biochemical and thermochemical conversion routes. Integrated biorefineries are capable of mimicking petroleum refineries via application of advanced process synthesis methods including modeling, simulation, integration and optimization techniques. This thesis presents a comprehensive synthesis methodology for the integration of bioprocessing technologies in biorefineries by addressing techno-economic and environmental sustainability analysis. The proposed systematic design approach combines advanced process modeling approaches, process integration techniques, and multi-objective optimization algorithms to assess the performance of the overall system with respect to economic, environmental, and energetic indicators. The design strategy is applied based on different case studies. Results indicate that multi-product processes can yield significant cost and environmental benefits. Additionally, the integration of biochemical and catalytic processes with thermochemical conversion pathways results in increased carbon efficiency and economic and environmental competitiveness. Synergies between biorefineries and energy system are assessed by integrating industrial plants with a cogeneration system producing biofuels and process heat. In doing so, system efficiency is increased by coupling the proposed cogeneration system with carbon capture and sequestration (CCS) and power-to-gas technologies to store the renewable intermittent electricity in the form of biofuels. The results exhibit that through system expansion, integrated biorefinery systems allow us to imitate fossil refineries with a large spectrum of bio-based products. This further increases the resource efficiency while offering a promising solution to mitigate CO2 emissions and hence reaching the longer-term decarbonization target set by the Paris Agreement.

EPFL2019

The role of process integration techniques in the thermo-economic optimization of energy conversion systems

François Maréchal, Laurence Tock

Within the goal of reducing greenhouse gas emissions and supplying sustainable energy, complex integrated energy conversion systems have to be designed by taking into account thermodynamic, economic and environmental considerations simultaneously. The process performance highly depends on the quality of the process integration and on the energy conversion, in particular, on how the heat requirements are balanced and how the combined heat and power generation is integrated. In chemical processes, the heat requirements after heat recovery are typically satisfied by the energy conversion system, while for fuel and electricity producing processes, the requirements are balanced by waste and process streams available on-site. The optimal internal heat recovery and utility integration can be computed by applying heat cascade models that are solved by using mathematical programming techniques. The mass and energy balances of the process unit operations are therefore satisfied by the optimal energy conversion system integration without having to explicitly model the heat exchanger network. The presented thermo-economic optimization approach combines flowsheeting and process integration techniques with economic evaluation and life-cycle assessment in a multi-objective optimization framework. The advantage of including the process integration model in the design process is that the influence of the process design and operation is reflected on the thermo-environomic performance of an energy balanced system in which the heat supplied from energy resources is integrated. The methodology has been successfully applied to study CO2 capture concepts in power plants using natural gas, coal or biomass resources, to analyse thermo-chemical H2 production processes and to evaluate different biofuel processes producing Fischer-Tropsch fuel, methanol, dimethylether and H2 by biomass gasification. The potential performance improvement through process integration is revealed for each case. In particular, it is highlighted how the optimization of the combined cycle valorizing the excess heat and of heat pumping options improve the process efficiency by simultaneously maximizing the combined production of fuel, captured CO2, heat and power. This shows that this computer-aided process design strategy combining flowsheeting, energy integration, cost assessment and multi-objective optimization is a powerful tool to systematically generate different process options, assess trade-offs and reveal process improvements through process integration.

2013