A mixed integer quadratic programming formulation for the economic dispatch of generators with prohibited operating zones

In this paper, an optimisation-based approach is proposed using a mixed integer quadratic programming model for the economic dispatch of electrical power generators with prohibited zones of operation. The main advantage of the proposed approach is its capability to solve case studies from the literature to global optimality quickly and without any targeting of solution procedures. (c) 2006 Elsevier B.V. All rights reserved

A multi-objective optimisation model for a general polymer electrolyte membrane fuel cell system

This paper presents an optimisation model for a general polymer electrolyte membrane (PEM) fuel cell system Suitable for efficiency and size trade-offs investigation. Simulation of the model for a base case shows that for a given output power, a more efficient system is bigger and vice versa. Using the weighting method to perform a multi-objective optimisation, the Pareto sets were generated for different stack output powers. A Pareto set, presented as a plot of the optimal efficiency and area of the membrane electrode assembly (MEA), gives a quantitative description of the compromise between efficiency and size. Overall, our results indicate that, to make the most of the size-efficiency trade-off behaviour, the system must be operated at an efficiency of at least 40% but not more than 47%. Furthermore, the MEA area should be at least 3 cm(2) W-1 for the efficiency to be practically useful. Subject to the constraints imposed on the model, which are based on technical practicalities, a PEM fuel cell system such as the one presented in this work cannot operate at an efficiency above 54%. The results of this work, specifically the multi-objective model, will form a useful and practical basis for subsequent techno-economic studies for specific applications. (C) 2009 Elsevier B.V. All rights reserved

Process Analysis -- The importance of mass and energy balances

Process engineering includes the generation, study and analysis of process designs. All processes must obey some fundamental laws of conservation. We can group these into conservation of matter and conservation of energy. Mass and energy balances are fundamental operations in the analysis of any process. This chapter describes some of their basic principles

Nature-Inspired Optimisation Approaches and the New Plant Propagation Algorithm

Nature-inspired algorithms are proving to be very successful on complex optimisation problems. A new algorithm, inspired by the way plants, and in particular the strawberry plant, propagate is presented. The algorithm is explained, tested on standard test functions, and compared with the well known Nelder-Mead algorithm. The new approach is then applied to a complex process design problem that arises in Chlorobenzene purification, a problem that exhibits strong nonlinear behaviour and has a small feasible region

A framework for the analysis of the security of supply of utilising carbon dioxide as a chemical feedstock

Recent developments in catalysts have enhanced the potential for the utilisation of carbon dioxide as a chemical feedstock. Using the appropriate energy efficient catalyst enables a range of chemical pathways leading to desirable products. In doing so, CO2 provides an economically and environmentally beneficial source of C1 feedstock, while improving the issues relating to security of supply that are associated with fossil-based feedstocks. However, the dependence on catalysts brings other supply chains into consideration, supply chains that may also have security of supply issues. The choice of chemical pathways for specific products will therefore entail an assessment not only of economic factors but also the security of supply issues for the catalysts. This is a multi-criteria decision making problem. In this paper, we present a modified 4A framework based on the framework suggested by the Asian Pacific Energy Research centre for macro-economic applications. The 4A methodology is named after the criteria used to compare alternatives: availability, acceptability, applicability and affordability. We have adapted this framework for the consideration of alternative chemical reaction processes using a micro-economic outlook. Data from a number of sources were collected and used to quantify each of the 4A criteria. A graphical representation of the assessments is used to support the decision maker in comparing alternatives. The framework not only allows for the comparison of processes but also highlights current limitations in the CCU processes. The framework presented can be used by a variety of stakeholders, including regulators, investors, and process industries, with the aim of identifying promising routes within a broader multi-criteria decision making process

Desalination of shale gas produced water: a rigorous design approach for zero-liquid discharge evaporation systems

Shale gas has recently emerged as a promising energy source to face the increasing global demand. This paper introduces a new rigorous optimization model for the simultaneous synthesis of single and multiple-effect evaporation (SEE/MEE) systems, considering mechanical vapor recompression (MVR) and energy recovery. The proposed model has been especially developed for the desalination of high-salinity produced water from shale gas hydraulic fracturing (“fracking”). Its main objective is to enhance the system energy efficiency through the reduction of brine discharges. Therefore, the outflow brine salinity should be near to salt saturation conditions to achieve zero liquid discharge (ZLD). The multiple-effect superstructure is comprised by several effects of horizontal-tube falling film evaporation. Due to the inclusion of the electric-driven mechanical compressor, no other external energy source is needed in the SEE/MEE system. A more accurate process design is attained through the calculation of the overall heat transfer coefficients in function of the individual coefficients for the falling boiling film and vapor condensation. Additionally, the SEE/MEE-MVR model allows the estimation of the major geometrical characteristics of the evaporation system. The non-linear programming (NLP)-based model is optimized using the CONOPT solver under GAMS by the minimization of the process total annualized cost. Thermal analysis is carried out to evaluate the effects of the feed salinity and geometrical parameters on system heat transfer performance. The results highlight the ability of the developed model to rigorously design SEE/MEE-MVR systems by improving their cost-effectively and reaching ZLD conditions

Mathematical modelling of intensified extraction for spent nuclear fuel reprocessing

Small scale extractors seem to be a promising intensified alternative to the conventional solvent extraction technologies, because of the well described hydrodynamics, enhanced mass transfer, and good phase separation at the end. One of the most interesting applications of intensified extractions is the reprocessing of spent nuclear fuel. Operating in small channels can reduce the volumes of involved hazardous materials and the residence times, thus minimising the degradation of the solvent and its regeneration cost. Finally, nuclear criticality safety may be easily achieved. In this paper, the application of small channels on spent nuclear fuel reprocessing has been investigated. A mathematical model of a multi-component liquid-liquid extraction has been developed. The multi-component system consists of U, Pu, HNO 3 , HNO 2 , Zr, Ru, Tc, Np(IV), Np(V) and Np(VI), the organic solvent is a mixture of 30% (v/v) Tri-Butyl Phosphate (TBP) and a paraffinic diluent. A segmented flow pattern, with the aqueous phase dispersed in a continuous organic phase, has been assumed. Calculations for the estimation of mass transfer, redox reactions, pressure drop, nuclear criticality and TBP hydrolysis have been included in the model. To increase the flow rates, the number of small channels was increased (scale out) and a comb-like manifold was considered to ensure good flow distribution in each channel. The problem is formulated as a mixed integer nonlinear programming problem and is implemented in the General Algebraic Modeling System (GAMS). The results show that this alternative technology for liquid-liquid extraction offers advantages, especially in terms of solvent degradation and low holdup volume

The Plant Propagation Algorithm: Modifications and Implementation

The Plant Propagation Algorithm, epitomised by the Strawberry Algorithm, has been previously successfully tested on low dimensional continuous optimisation problems. It is a neighborhood search algorithm. In this paper, we introduce a robust and efficient version of the algorithm and explain how it can be implemented to compete with one of the best available alternatives, namely the Artificial Bee Colony algorithm and we present an improved and more effective variant on standard continuous optimisation test problem instances in high dimensions. Computational and comparative results are included

Optimal integrated energy systems design incorporating variable renewable energy sources

The effect of variability in renewable input sources on the optimal design and reliability of an integrated energy system designed for off-grid mining operation is investigated via a two-stage approach. Firstly, possible energy system designs are generated by solving a deterministic non-linear programming (NLP) optimization problem to minimize the capital cost for a number of input scenarios. Two measures of reliability, the loss of power supply probability (LPSP) and energy index of reliability (EIR), are then evaluated for each design based on the minimization of the external energy required to satisfy load demands under a variety of input conditions. Two case studies of mining operations located in regions with different degrees of variability are presented. The results show that the degree of variability has an impact on the design configuration, cost and performance, and highlights the limitations associated with deterministic decision making for high variability systems

Process intensification applied to spent nuclear fuel reprocessing: An alternative flowsheet using small channels

Commercial plants for spent nuclear fuel reprocessing rely on the Plutonium Uranium Extraction (PUREX) process, based on traditional liquid–liquid extraction technologies. In this paper, an alternative flowsheet for spent nuclear fuel reprocessing is proposed, based on small-scale extractors to overcome some of the issues related to the conventional technologies, such as solvent degradation, size and nuclear criticality control. The main goal of the process is to preclude the risk of nuclear proliferation, hence a mixed uranium/plutonium oxide is produced instead of pure plutonium. A superstructure optimisation based framework has been used to identify a process with several benefits over the conventional process. Novel flow configurations and organic solvent composition have been investigated. A large number of components and chemical reactions are included in the framework. The resulting model is a mixed integer nonlinear optimisation problem, implemented in the General Algebraic Modeling System (GAMS). The most promising flowsheet identified is more cost effective than the conventional one. Furthermore, advantages in terms of safety and separation efficiency have been achieved. It was found that increasing the inner diameter of the small channels up to 2.5 mm, as well as increasing the tributyl phosphate fraction in the organic solvent, are advantageous