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Finding an optimal retrofit for existing plants is a very challenging problem, since it often requires rigorous process models for describing the currently operating process and consequently the corresponding optimization problems typically become very complex. One of the possible ways to optimize such a complex problem is to limit the process alternatives considered, which bears the risk to overlook the optimal solution. Herein, a superstructure-based methodology is proposed for optimal retrofit of a CO 2 capture pilot plant using rigorous rate-based model for the reactive distillation. The methodology is applied to the Boryeong pilot plant in South Korea. Process alternatives implemented in the superstructure are selected based on thermodynamic analysis of the pilot plant and operational experience. As a result, the problem size of the superstructure can be substantially reduced and optimization can be performed using commercially available process simulators and optimization solvers. The optimum process configuration and operating conditions are obtained stochastically using a genetic algorithm. Results indicate that the optimum retrofit process includes three stages solvent recirculation, lean vapor recompression, and mechanical vapor recompression. Thermal energy and total energy consumption in the optimal retrofit process are reduced about 59% and 27%, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A split concept for boilers and heat recovery steam generators (HRSG), where flue gas recycling is required for controlling the maximal temperature, is proposed for reducing the heat exchange area and/or the recycling power requirements. The concept is demonstrated in the context of an HRSG of a pressurized oxy-coal combustion process, where the hot flue gas entering the HRSG is diluted by recycled flue gas to comply with the temperature constraint. The split concept proposes splitting the hot flue gas prior to dilution, and introducing the splitted fraction, with or without a secondary recycling stream, at an intermediate point in the HRSG. As a result, the split allows for lower recycling power requirements (lower diluent flowrate) and a smaller heat exchange area because the average temperature difference between the hot and cold streams in the heat exchanger is increased. Multi-objective optimization, for area and power requirements, is performed and the Pareto front is constructed. Results include a reduction by 37% without a change in the compensation power requirements, or a decrease in the power requirements by 18% (corresponding to 0.15 percentage points in cycle efficiency increase) while simultaneously reducing the area by 12%. [Copyright &y& Elsevier]

Abstract: The performance of a regenerative solid TES (thermal energy storage) system with enhancement heat transfer structures is analyzed. Thermal energy is transferred from a hot heat transfer fluid to the storage unit core elements during charge, and from the core elements to the cold heat transfer fluid during discharge. Herein, concrete as the solid storage material, nitrate solar salt as the heat transfer fluid, and aluminum plates as the heat transfer structures are considered. The discharge process from uniform initial temperature is studied with different configurations (pure concrete and concrete enhanced by transfer structures), operation strategies (laminar versus turbulent flow regimes), and dimensions. The results show a significant decrease in the cost of the TES system when heat transfer structures are added, as well as higher discharge efficiency and lower discharge time period. The amount of solar salt needed for this configuration is also decreased by the use of the heat transfer structures and is five time less than that of a two-tank system. [Copyright &y& Elsevier]

Abstract: Recently, various alternatives to batteries, such as microfabricated fuel cell systems, have been proposed for portable power generation. In large-scale power production plants emphasis is placed on energy conversion efficiency. On the other hand, the intrinsic design objective for portable power generation devices is the energy density, i.e., the electrical energy generated from a given mass or volume of device and fuel cartridge. It is plausible to stipulate that an increase in the energy conversion efficiency of a system leads to an increase in energy density, but we demonstrate through theoretical analysis and case studies that the two metrics are not equivalent. In some cases, such as systems with a combination of fuels, maximizing efficiency leads to drastically different design, operation and performance than maximizing energy density. Another interesting observation is that, due to interaction between components, maximal component efficiency does not always imply maximal system efficiency. [Copyright &y& Elsevier]

Abstract: In this article, a new model and a biomimetic pattern for heliostat field layout optimization are introduced. The model, described and validated herein, includes a detailed calculation of the annual average optical efficiency accounting for cosine losses, shading and blocking, aberration and atmospheric attenuation. The model is based on a discretization of the heliostats and can be viewed as ray tracing with a carefully selected distribution of rays. The prototype implementation is sufficiently fast to allow for field optimization. Parameters are introduced for the radially staggered layout and are optimized with the objective of maximizing the annual insolation weighted heliostat field efficiency. In addition, inspired by the spirals of the phyllotaxis disc pattern, a new biomimetic placement heuristic is described and evaluated, which generates layouts of both higher insolation-weighted efficiency and higher ground coverage than radially staggered designs. Specifically, this new heuristic is shown to improve the existing PS10 field by 0.36% points in efficiency while simultaneously reducing the land area by 15.8%. Moreover, the new pattern achieves a better trade-off between land area usage and efficiency, i.e., it can reduce the area requirement significantly for any desired efficiency. Finally, the improvement in area becomes more pronounced with an increased number of heliostats, when maximal efficiency is the objective. While minimizing the levelized cost of energy (LCOE) is typically a more practical objective, results of the case study presented show that it is possible to both reduce the land area (i.e. footprint) of the plant and number of heliostats for fixed energy collected. By reducing the capital cost of the plant at no additional costs, the effect is a reduction in LCOE. [Copyright &y& Elsevier]

Using organic Rankine cycles (ORC) for waste heat recovery in vehicles promises significant reductions in fuel consumption. Controlling the organic Rankine cycle, however, is difficult due to the highly transient exhaust gas conditions. To tackle this issue, nonlinear model predictive control (NMPC) has been proposed and approximate NMPC solutions have been investigated to reduce computational demand. Herein, we compare (i) an idealized economic NMPC (eNMPC) scheme as a benchmark to (ii) a NMPC enforcing minimal superheat and (iii) a PI controller with dynamic feed-forward term (PI-ff) in a control case study with highly transient disturbances. We show that, for an ORC system with supersonic turbine, the economic control problem can be reduced to a single-input single-output superheat tracking problem combined with a decoupled steady-state real-time optimization (RTO) of turbine operation, assuming an idealized condenser. Our results indicate that the NMPC enforcing minimal superheat provides good control performance with negligible losses in average power compared to the full solution of the economic NMPC problem and that even PI-ff only results in marginal losses in average power compared to the model-based controllers. • Control of organic Rankine cycles for automotive waste heat recovery is investigated. • An eNMPC, a tracking NMPC and a PI controller with feedforward term are implemented. • The optimal control problem is reduced to a SISO tracking problem with decoupled RTO. • Operation under PI controller results only in marginally smaller power production. [ABSTRACT FROM AUTHOR]

Recovering waste heat from the exhaust gas of diesel trucks using an organic Rankine cycle (ORC) is considered a promising option to reduce emissions and fuel consumption. As the system operates under highly transient boundary conditions, the development of a predictive model accounting for its dynamic behavior is of high relevance. In this contribution, such a model is presented. Evaporator and condenser are modeled using a dynamic moving boundary model, while pump and turbine are represented with pseudo-steady state models, as dynamics are assumed to be negligible here. A fundamental thermodynamic equation of state based on the free Helmholtz energy is implemented for the working fluid ethanol. As unknown parameters, e.g., in heat transfer, occur, a parameter estimation is conducted with the use of measurement data. The model is then validated using different experimental data. It is able to capture the system dynamics well both qualitatively and quantitatively, e.g., the mean relative temperature deviations are all smaller than 4%. [ABSTRACT FROM AUTHOR]

Abstract: Four different integration schemes for the Advanced Zero Emissions Power (AZEP) cycle with a parabolic trough are proposed and analyzed: vaporization of high-pressure stream, preheating of high-pressure stream, heating of intermediate-pressure turbine inlet stream, and heating of low-pressure turbine inlet stream. The power outputs from these integration schemes are compared with each other and with the sum of the power outputs from corresponding stand-alone AZEP cycle and solar–thermal cycle. Vaporization of high-pressure stream has the highest power output among the proposed integration schemes. Both the vaporization and heating of intermediate-pressure turbine inlet stream integration schemes have higher power output than the sum of the power outputs from corresponding stand-alone AZEP cycle and solar–thermal cycle. A comparison of the proposed vaporization scheme with existing hybrid technologies without carbon capture and storage (CCS) shows that it has a higher annual incremental solar efficiency than most hybrid technologies. Moreover, it has a higher solar share compared to hybrid technologies with higher incremental efficiency. Hence, AZEP cycles are a promising option to be considered for solar–thermal hybridization. [Copyright &y& Elsevier]

[Display omitted] • Model-based fuel design for conventional, flex fuel, ultra-high efficiency SI engines. • Production cost and GWI of optimized, selectively produced fuels. • Promising 100% biofuel with low GWI/low cost for ultra-high efficiency engine. • Fuels for ultra-high efficiency and flex fuel engines show better cost/GWI trade-off. • Results motivate replacing today's conventional SI engines with advanced ones. Road transportation needs to abandon fossil fuels. One promising alternative are renewable fuels for internal combustion engines. We consider three competing types of spark-ignition engines, i.e., conventional spark-ignition engines (CSIEs), flexible fuel vehicle engines (FFVEs), and ultra-high efficiency engines (UHEEs), which all have different fuel requirements. To determine which engine-fuel combination is optimal regarding fuel production cost and global warming impact (GWI), we apply our integrated fuel and process design method [König, et al. 2020. Comput. Chem. Eng.]. Specifically, we consider 47 pre-screened fuel species, their selective production routes from renewable resources, and a surrogate for optional blending of fossil gasoline. The designed FFVE (UHEE) fuels reduce GWI by up to 87% (84%) compared to fossil gasoline. In contrast, optimal CSIE fuels only achieve up to 60% GWI reduction and only at higher cost. The superior production performance of selectively-produced UHEE and FFVE fuels motivates replacement of today's CSIE technology. [ABSTRACT FROM AUTHOR]

Waste heat recovery for trucks via organic Rankine cycle is a promising technology to reduce fuel consumption and emissions. As the vehicles are operated in street traffic, the heat source is subject to strong fluctuations. Consequently, such disturbances have to be considered to enable safe and efficient operation. Herein, we find optimal operating policies for several representative scenarios by means of dynamic optimization and discuss the implications on control strategy design. First, we optimize operation of a typical driving cycle with data from a test rig. Results indicate that operating the cycle at minimal superheat is an appropriate operating policy. Second, we consider a scenario where the permissible expander power is temporarily limited, which is realistic in street traffic. In this case, an operating policy with flexible superheat can reduce the losses associated with operation at minimal superheat by up to 53% in the considered scenario. As the duration of power limitation increases, other constraints might become active which results in part of the exhaust gas being bypassed, hence reduced savings. • Optimal operation of automotive waste heat recovery with ORC by dynamic optimization. • A validated model of the ORC process is used for optimization. • Operation at minimal superheat is recommended when only safety constraints apply. • If expansion power output is temporarily limited, increased superheat is recommended. • Implications on control structure are discussed. [ABSTRACT FROM AUTHOR]