1,720,966 research outputs found
A bilevel decomposition method for the simultaneous heat integration and synthesis of steam/organic Rankine cycles
No full textThis work tackles the simultaneous synthesis and design of heat exchanger networks (HEN) integrated with complex utility systems, such as Heat Recovery Steam Cycles or Organic Rankine Cycles. Thanks to the combination of two superstructures (Rankine cycles and HEN), all the key heat integration options between process and utility system can be considered, and the trade-off between efficiency and costs is optimized. The superstructure for complex utility systems involves streams with variable flow rate. The resulting MINLP problem is very challenging due to its large number of binary variables and nonconvex terms. We present a novel bilevel decomposition algorithm, combining the outer-approximation linearization technique with McCormick relaxation, valid redundant constraints, piecewise linearization of cost functions and “nested” integer cuts. The algorithm successfully tackled real-world problems with up to 35 streams showing considerable improvements in solution quality and computational time over commercial MINLP solvers and meta-heuristic algorithms
A novel sequential synthesis algorithm for the integrated optimization of Rankine cycles and heat exchanger networks
No full textThe research theme of this work is the optimization of the heat integration and heat recovery in energy systems and chemical processes, specifically, the optimal synthesis and design of Rankine cycles (e.g., heat recovery cycles, heat pump cycles, etc.) integrated with the heat exchanger network. The challenging synthesis problem is formulated as a Mixed Integer NonLinear Program and tackled with a novel sequential algorithm based on the idea of optimizing the independent mass flow rates of the Rankine cycle superstructure with a derivative-free algorithm. At the lower level, for fixed Rankine cycle and utility mass flow rates, the synthesis of the heat exchanger network is performed with an efficient sequential algorithm. The proposed algorithm is compared against three state-of the-art approaches on six real-world case studies including Organic Rankine cycles, heat pumps/CHP cycles and heat recovery steam cycles with multiple pressure levels. Results indicate that the proposed algorithm finds optimal or near-optimal design solutions for all case studies proving its applicability as an effective design tool
Heat integration and heat recovery steam cycle optimization for a low-carbon lignite/biomass-to-jet fuel demonstration project
No full textThis paper reports the heat integration study for a demonstration plant to co-process lignite and woody biomass into jet fuel with CO2 capture and storage. Since all the main process reactions are exothermic and convert approximately 65% of the feedstock chemical energy into heat, designing an efficient heat recovery steam cycle and heat exchanger network is essential for the overall thermo-economic performance. Different integration options for the plant's heat recovery steam cycle are analyzed and compared, considering costs and the key technical limitations. The design of the heat recovery steam cycle and heat exchanger network is optimized with an energy targeting methodology, a sequential synthesis method and a recently proposed simultaneous methodology. Given the high specific costs of the units caused by the novelty and small size and of the demonstration plant, the techno-economic optimization returns solutions with considerably lower efficiency (up to −5% percentage points) and power output (up to −18%) compared to the energy targeting methodology. The difference in optimal HRSC designs and performance are minor (less than −2% power output) for full-scale plants based on mature technologies
Design Optimization and Dynamic Simulation of Steam Cycle Power Plants: A Review
Full text linkAfter more than one century from its first use for electric power production, steam cycles are still the object of continuous research and development efforts worldwide. Indeed, owing to its favorable thermodynamic properties, steam cycles are not only used in coal-fired power plants but in a large variety of applications such as combined cycles, concentrated solar power plants and polygeneration plants. On the other hand, to cope with the efficiency and flexibility requirements set by today’s energy markets, the design and the operation of steam cycles must be carefully optimized. A key rule is played by the simulation and optimization codes developed in the last 30 years. This paper provides an introduction to the main types of simulation and optimization problems (design, off-design operation and dynamic), an overview of the mathematical background (possible solution approaches, numerical methods and available software), and a review of the main scientific contributions
Multiperiod optimization of heat exchanger networks with integrated thermodynamic cycles and thermal storages
No full textThis work proposes a multiperiod synthesis methodology to optimize simultaneously the utility systems, Rankine cycles and Heat Exchanger Networks considering different expected operating modes and off-design operating conditions. Heat exchangers are modeled with different approaches depending on the type of off-design control measure. The problem is formulated as a nonconvex MINLP. Being too challenging for general purpose MINLP solvers, a bilevel decomposition algorithm is specifically developed. One case study consists in designing a flexible Organic Rankine Cycle able to deal with different operating modes, and the returned solution shows a considerable improvement in economics compared to a single-period design. The other two case studies are an Integrated Gasification Combined Cycle able to operate in two different modes, and a flexible Integrated Solar Combined Cycle power plant. Despite the large number of hot/cold streams and technical design/operational constraints, the proposed method can find very good solutions featuring cost-effective designs
Simultaneous Multiperiod Optimization of Rankine Cycles and Heat Exchanger Networks
No full textThis work addresses the multiperiod synthesis and optimization of integrated Heat Exchanger Networks (HEN) and Rankine cycles for plants with demanding operational flexibility requirements. A general and systematic synthesis methodology has been developed to optimize simultaneously the utility systems, Rankine cycles and HENs considering different expected operating modes, seeking for the solution with the minimum Total Annual Costs (TAC). Heat exchangers have been modelled with different approaches depending on the type of control measure (with/without by-pass) in off-design operation. The problem is formulated as a challenging nonconvex MINLP and solved with a bilevel decomposition method, specifically developed to address this class of problems. We present the results of the proposed methodology applied to an extremely challenging problem, with 35 streams and 2 operating modes (periods), consisting in the design of an Integrated Gasification Combined Cycle (IGCC)
Simultaneous Synthesis and Optimization of Refrigeration Cycles and Heat Exchangers Networks
No full textThis work proposes a simultaneous approach for the synthesis and design optimization of refrigeration cycles integrated with heat exchanger networks. The methodology includes a novel refrigeration cycle superstructure capable of reproducing a wide range of cycle architectures, and an effective solution algorithm (based on the decomposition of the problem on two levels) to tackle the challenging Mixed-Integer Nonlinear Program. In addition to optimizing the cycle and heat exchanger network structure, the methodology can optimize cycle pressures and temperatures (including superheating and subcooling degree of the working fluid). The application to a literature case study indicates that the proposed approach yields solutions that are considerably better in terms of economic than those published in the literature
Techno-economic prospects for producing Fischer-Tropsch jet fuel and electricity from lignite and woody biomass with CO2 capture for EOR
Full text linkThis study explores the prospective techno-economic performance of facilities that produce low- and net-negative-carbon liquid transportation fuels and electricity with CO2 capture for enhanced oil recovery. The lignite and biomass-to-jet fuel process is based on KBR's TRIG gasifier, Rectisol (for sulfur removal and CO2 capture), fixed-bed low temperature Fischer-Tropsch synthesis of liquid fuels, and Brayton/Rankine combined cycles to convert synthesis/refining off-gases and waste heat to electricity. This work leverages a recent, highly-detailed assessment of a prospective first-of-a-kind (FOAK) demonstration facility to develop highly detailed Aspen Plus process simulations for nine prospective Nth-of-a-kind (NOAK) plant equipment configurations. Component-level capital costs from the FOAK study are scaled and adjusted to reflective prospective learning-by-doing to estimate capital costs for the NOAK designs. NOAK plant economic performance is found to be largely insensitive to variations in plant configurations and electricity output fraction, but biomass input fraction significantly affects profitability. Facilities that consume only carbon–neutral biomass, with no lignite co-feed, have significantly net-negative carbon emissions and the most favorable prospective economics when carbon emissions are priced. For these facilities, the crude oil price required for plant economic viability falls rapidly from 120/tonne CO2eq. In general, plants that co-fire lignite with biomass are less profitable (than 100% biomass plants) due to their higher net greenhouse gas emissions
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