Lost in optimisation of water distribution systems? A literature review of system operation

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Optimisation of the operation of water distribution systems has been an active research field for almost half a century. It has focused mainly on optimal pump operation to minimise pumping costs and optimal water quality management to ensure that standards at customer nodes are met. This paper provides a systematic review by bringing together over two hundred publications from the past three decades, which are relevant to operational optimisation of water distribution systems, particularly optimal pump operation, valve control and system operation for water quality purposes of both urban drinking and regional multiquality water distribution systems. Uniquely, it also contains substantial and thorough information for over one hundred publications in a tabular form, which lists optimisation models inclusive of objectives, constraints, decision variables, solution methodologies used and other details. Research challenges in terms of simulation models, optimisation model formulation, selection of optimisation method and postprocessing needs have also been identified

Advanced decision support through real-time optimization in the process industry

En la industria de procesos se puede obtener un aumento de la eficiencia de las plantas de producción, bien mediante la sustitución de procesos o equipos antiguos por otros más modernos y eficientes, o bien operando de forma más eficiente las instalaciones actuales en lugar de realizar grandes inversiones con tiempos de amortización inciertos. Si nos centramos en esta segunda línea de acción, hoy en día la toma de decisiones es conceptualmente más compleja que en el pasado, debido al rápido crecimiento que ha tenido la tecnología últimamente y a que los sistemas de comunicación han generado un gran número de alternativas entre las que se ha de elegir. Además, una decisión incorrecta o subóptima, con la complejidad estructural de los problemas actuales, a menudo resulta en un aumento de los costes a lo largo de la cadena de producción. A pesar de ello, el uso de sistemas de apoyo a la toma de decisiones (DSS) sigue siendo atípico en las industrias de procesos debido a los esfuerzos que se requieren en términos de desarrollo y mantenimiento de modelos matemáticos y al desafío de formulaciones matemáticas complejas, los exigentes requisitos computacionales y/o la difícil integración con la infraestructura de control o planificación existente. Esta tesis contribuye en la reducción de estas barreras desarrollando formulaciones eficientes para la optimización en tiempo real (RTO) en una planta industrial. En particular, esta tesis busca mejorar la operación de tres secciones interconectadas de una fábrica de producción de fibra de viscosa: una red de evaporación, una de sistema de enfriamiento y una red de recuperación de calor.Departamento de Ingeniería de Sistemas y AutomáticaDoctorado en Ingeniería Industria

Hydropower sheduling in basins with heavy ecological and human restrictions

The problem of water resources management aims to calculate the optimal energy bids of a set of hydro plants and to estimate costs for consumptive and nonconsumptive volumes of water, when meeting European and local regulations, consumption requirements and basin rights of use, respecting environmental flows, possible congestions in the electric transmission system and other important concerns. The goal of this thesis is to advance in the development of an effective tool for the management of hydro basins with different economic, social, policy, normative, restrictions and resources characteristics. In first case, an optimisation problem for calculating the best offers of a set of hydro power plants is proposed, considering ecological flows and social consumptions. In the simulations, the costs related to the social consumptions and ecological requirements are compared in a relatively small real Spanish basin, for short-term (24-hour) planning. In second case, an improved representation of the market and the optimization of the hydro plants are integrated in a nested algorithm, to calculate local prices and optimal energy bids in a congested electrical system. The algorithm is applied to a real basin in Italy. In a third case, uncertainties in the resources, improved representations of the hydro plants and environmental constraints are integrated in a large basin, in southern Spain. Stochastic scenarios are used to evaluate the significance of uncertainties in a 72-hours horizon. The study provides a new tool for the coordinated management of large basins, complying with ecological restrictions and governmental regulation on water resource allocation and considering the technical characteristics of hydropower plants and the hydropower production profits.El problema de gestión de recursos hídricos busca determinar las ofertas óptimas de energía para un conjunto de centrales hidroeléctricas y también una estimativa de los costos del agua para los volúmenes consutivos y no consuntivos, cumpliendo normativas europeas y locales, las necesidades de consumo y los derechos de uso de las cuencas, las posibles congestiones en el sistema de transmisión eléctrica y otras cuestiones relevantes. El objetivo de esta tesis es avanzar en el desarrollo de una herramienta eficaz para la gestión de cuencas con diferentes características económicas, sociales, políticas, normativas, restrictivas y de recursos. En el primer caso estudiado, se propone un problema de optimización para el cálculo de las ofertas óptimas de un conjunto de centrales hidroeléctricas, en una cuenca española relativamente pequeña, considerando los flujos ecológicos y los consumos sociales. En las simulaciones de planificación a corto plazo (24 horas), se comparan los costes relacionados con los consumos sociales y los requisitos ecológicos. En el segundo caso de estudio, se integran en un algoritmo iterativo una representación mejorada del mercado y la optimización de las centrales hidroeléctricas, a fin de calcular precios locales y ofertas óptimas de energía en un sistema eléctrico congestionado. El algoritmo es aplicado a una cuenca real en el Norte de Italia. En el tercer caso de estudio, las incertidumbres asociadas a los recursos y una representación mejorada de las centrales hidroeléctricas, junto con las limitaciones ambientales, se integran en un modelo que representa una cuenca real de tamaño significativo en el sur de España. Se utilizan escenarios estocásticos para evaluar la influencia de las incertidumbres en un horizonte de 72 horas. El estudio proporciona así una nueva herramienta para la gestión coordinada de grandes cuencas, cumpliendo con las restricciones ecológicas y la regulación gubernamental sobre asignación de recursos hídricos, teniendo en cuenta las características técnicas de las centrales hidroeléctricas y los beneficios de producción de la energía hidroeléctrica.Programa Oficial de Doctorado en Ingeniería Eléctrica, Electrónica y AutomáticaPresidente: Luis Fernández Beites.- Secretario: María Ángeles Moreno López de Saa.- Vocal: Juan Ignacio Pérez Día

Newly proposed strategies to increase the energy efficiency of water systems

One of the main challenges in the water industry consists of the reduction of environmental impacts, as well as the containment of energy use. In this research work, new solutions to achieve a sustainable management of water networks have been developed and organized in three lines of research. The main line of research is based on the optimal location of hydraulic devices within a water distribution network in order to maximize the energy production and water savings, as well as to minimize the investment cost. Firstly, the installation of only Pumps As Turbines (PATs) has been analyzed within a literature synthetic network and a new Mixed Integer Non-Linear Programming (MINLP) model has been developed to perform the optimization. Such an optimization model has been defined by a thorough mathematical formulation in order to deal with the extremely hard technical and computational complexities affecting the optimization procedure. In this research, only deterministic solvers have been employed to search the optima, and a comparison of their performance has been also carried out. Most of the computations have been performed by a global optimization solver, which potentially finds the global optimum in both convex and non-convex problems, but is also used to find good quality local optima in very complex problems, where the achievement of the exact solution may require infinite computational time. Compared to other studies in literature on the same network, the proposed study accounts for crucial hydraulic aspects, such as the phenomenon of flow reversion during the day affecting the installation and the operation of the devices, as well as the need for installing machines generating a power above a minimum fixed value. A comparison with such previous literature works has been carried out in order to highlight the effectiveness of the newly proposed optimization procedure. Moreover, to develop a more realistic and comprehensive mathematical model, the simultaneous installation of PATs and Pressure Reducing Valves (PRVs) has been also modeled by the introduction of new variables and mathematical constraints. Indeed, in presence of large water savings but small energy recovery, a PRV might be a more viable solution than a PAT. Compared to other studies in literature optimizing the only location of PATs within the same synthetic network, the simultaneous installation of valves and turbines, as well as the formulation of new hydraulic constraints, has significantly increased the value of the optimization model. In addition, the optimization has been extended to a real water distribution network serving the Blackstairs region (IE), with the aim of testing the robustness of the model and of the optimization procedure in more complex and larger problems. Indeed, the computational complexity affecting the optimization procedure increases according to the size of the network and the mathematical formulation proposed for the synthetic network might be not suitable for such a more complex case study. Compared to the synthetic network where the pressure reduction up to defined minimum requirements has not compromised the hydraulic operation of the system, in the analyzed real water network the exploitation of the available excess pressure to save both water and energy raises the need for employing also pumping systems to supply the most remote nodes of the network. The installation of pumping systems within the network has been therefore included within the optimization procedure and the outcome has been a new model for a Global Optimization of Hydraulic Devices Location (GOHyDeL), suitable for any water distribution network. Such a new model has been the result of progressive findings and hard attempts to deal with the enormous complexities arising during the computation. In all the performed optimization, the maximized water and energy savings and the minimized installation costs have been assessed according to a cost model used by previous authors in literature, in order to make a more straightforward comparison with such literature works. However, more recent cost models available in literature have been also employed to achieve more reasonable and realistic values of the results. According to the comparison between results obtained by using different cost models, despite the employment of more recent models leading to significantly larger investment costs and, thus, smaller values of NPV, the solutions are quite similar in terms of location of installed devices, and the achieved savings are comparable as well. However, among all the devices, the PRVs have resulted to be more affected by the choice of the cost model, due to the strong dependency of the valve costs on the pipe diameter. On the whole, beyond the large feasibility of the model within the optimal location field, a remarkable value of the proposed research also results from the new formulation of mathematical constraints and variables, which requires less computational effort and could find application also in more general optimization problems. The second line of research defines and compares two alternative strategies to supply a real water distribution network. The first solution consists of an elevated reservoir, which is located upstream of a water distribution network and is supplied from the water source by a pumping system. In this scheme, the excess pressure is not dissipated by a traditional valve, but rather a pump as turbine is installed to contain the pressure, thus water leakage, and also recover energy. The second hydraulic scheme instead consists of a pump supplying the downstream network directly from the source. In this scheme there is not an excess pressure to convert in energy, since the elevated reservoir is bypassed and the flow is pumped to the network with lower head. Such new schemes represent two different strategies to increase the energy efficiency of a supply system, as alternatives to the use of elevated reservoir with dissipation of the excess pressure by means of pressure reducing valves. The two schemes have been properly designed in order to find the devices, in terms of diameter and rotational speed, minimizing the energy requirements, thus maximizing the energy efficiency of the whole system. Given the water network supplying a small village in Ballacolla area (IE), the direct supply of the network has resulted a more efficient strategy than the indirect supply scheme with energy recovery. Moreover, the two schemes have been compared by varying the operating conditions, thus considering different combinations of distance and elevation of the source from the water distribution network. The energy audit of the two schemes has been assessed by new energy efficiency indices and also by literature indices. The comparison has showed that the convenience of a scheme over the other significantly depends on the operating conditions. However, with equal values of pumping head in both the schemes, the indirect scheme with energy recovery is up to 5 % more convenient than the direct pumping scheme, which is instead more efficient if the pumping head could be reduced up to 6 %. In the third line of research a new strategy to save energy in the urban water management is presented. The proposed solution consists of a mixed PAT-pump turbocharger, that is a PAT-equipped turbopump exploiting an excess pressure within the fresh water network to produce energy, which is entirely used to carry a wastewater stream towards a treatment plant. In this system, the excess pressure is converted by the PAT in a mechanical torque, which in turn supplies the pump mounted on the same shaft. Such a plant arises whenever wastewater pumping station and excess pressure point could be co-located, thus in low ground areas where high clean-water pressures occur and sewage networks are equipped with pumping systems due to the need to treat the wastewater. In this application, the water distribution network serving Ballacolla area (IE) has been assumed as case study, since it is suitable for the installation of this kind of plant. A preliminary geometric selection of the devices has been performed by a new selection method based on the maximum daily averaged values of fresh and wastewater discharge. Then, the behavior of the plant has been simulated for several wastewater hydrographs by a new mathematical model. The benefits of the plants have been assessed and compared with a conventional wastewater pumping system working in ON/OFF mode. According to the comparison, the higher Net Present Value (NPV) of the MPP plant proves the advantage of this scheme over the conventional system, at least until the useful life of the plant is reached

Lost in optimisation of water distribution systems? A literature review of system design

This is the final version of the article. Available from MDPI via the DOI in this record.Optimisation of water distribution system design is a well-established research field, which has been extremely productive since the end of the 1980s. Its primary focus is to minimise the cost of a proposed pipe network infrastructure. This paper reviews in a systematic manner articles published over the past three decades, which are relevant to the design of new water distribution systems, and the strengthening, expansion and rehabilitation of existing water distribution systems, inclusive of design timing, parameter uncertainty, water quality, and operational considerations. It identifies trends and limits in the field, and provides future research directions. Exclusively, this review paper also contains comprehensive information from over one hundred and twenty publications in a tabular form, including optimisation model formulations, solution methodologies used, and other important details

A framework for the near-real-time optimization of integrated oil & gas midstream processing networks

The oil and gas industry plays a key role in the world’s economy. Vast quantities of crude oil, their by-products and derivatives are produced, processed and distributed every day. Indeed, producing and processing significant volumes of crude oil requires connecting to wells in different fields that are usually spread across large geographical areas. This crude oil is then processed by Gas Oil Separation Plants (GOSPs). These facilities are often grouped into clusters that are within approximate distance from each other and then connected laterally via swing lines which allow shifting part or all of the production from one GOSP to another. Transfer lines also exist to allow processing intermediate products in neighbouring GOSPs, thereby increasing complexity and possible interactions. In return, this provides an opportunity to leverage mathematical optimization to improve network planning and load allocation. Similarly, in major oil producing countries, vast gas processing networks exist to process associated and non-associated gases. These gas plants are often located near major feed sources. Similar to GOSPs, they are also often connected through swing lines, which allow shifting feedstock from some plants to others. GOSPs and gas plants are often grouped as oil and gas midstream plants. These plants are operated on varied time horizons and plant boundaries. While plant operators are concerned with the day-to-day operation of their facility, network operators must ensure that the entire network is operated optimally and that product supply is balanced with demand. They are therefore in charge of allocating load to individual plants, while knowing each plants constraints and processing capabilities. Network planners are also in charge of producing production plans at varied time-scales, which vary from yearly to monthly and near-real time. This work aims to establish a novel framework for optimizing Oil and Gas Midstream plants for near-real time network operation. This topic has not been specifically addressed in the existing literature. It examines problems which involve operating networks of GOSPs and gas plants towards an optimal solution. It examines various modelling approaches which are suited for this specific application. It then focuses at this stage of the research on the GOSP optimization problem where it addresses optimizing the operation of a complex network of GOSPs. The goal is to operate this network such that oil production targets are met at minimum energy consumption, and therefore minimizing OpEx and Greenhouse Gas Emissions. Similarly, it is often required to operate the network such that production is maximized. This thesis proposes a novel methodology to formulate and solve this problem. It describes the level of fidelity used to represent physical process units. A Mixed Integer Non-Linear Programming (MINLP) problem is then formulated and solved to optimize load allocation, swing line flowrates and equipment utilization. The model demonstrates advanced capabilities to systematically prescribe optimal operating points. This was then applied to an existing integrated network of GOSPs and tested at varying crude oil demand levels. The results demonstrate the ability to minimize energy consumption by up to 51% in the 50% throughput case while meeting oil production targets without added capital investment.Open Acces