Modelling electro-osmotic flow in porous media: a review

PurposeThis paper aims to provide a comprehensive literature review on modelling electro-osmotic flow in porous media.Design/methodology/approachModelling electro-osmosis in fluid systems without solid particles has been firstly introduced. Then, after a brief description of the existing approaches for porous media modelling, EOF in porous media has been considered by analysing the main contributions to the development of this topic.FindingsThe analysis of literature has highlighted the absence of an universal model to analyse electro-osmosis in porous media, whereas many different methods and assumptions are used.Originality/valueFor the first time, the existing approaches for modelling electro-osmotic flow in porous have been collected and analysed in order to provide detailed indications for future works concerning this topic

Heat and fluid flow in electro-osmotically driven systems

A numerical investigation of heat and fluid flow in electro-osmotically driven systems is presented, by considering plain channels and channels packed with charged solid particles. The results show that the introduction of charged solid particles a_ects the internal potential distribution, fluid flow and temperature distribution in the channel. Under the analysed conditions, the effect on heat transfer is confined to the centre of the channel. This topic needs to be further investigated since it is of interest in practical applications

Assessing the Eco-Sustainability of Sewage Sludge Management

Sludge management has become one the most challenging issues for wastewater treatment plants, especially due to strict regulations for its reuse or disposal. Indeed, on one hand, the practices commonly used for sewage sludge management are no longer readily acceptable, on the other hand, new policies need to present affordable standards. At the same time, unlocking the potential of sewage sludge is recognized as a way to improve circular economy and sustainability of wastewater sector, as promoted by the European Green Deal. For these reasons, both the industrial and academic communities are investigating new solutions to improve the sustainability of sludge treatment. In this context, assessing the environmental and economic sustainability of sludge management is fundamental to compare different strategies. The pertinent available literature on sludge management proposes indicators that take into account: - specific aspects, such as production, reuse or treatment/disposal costs; - different categories of environmental impact through the methodology of life cycle assessment. This work aims at defining a comprehensive and intuitive assessment method that allows taking into account both the economic and the environmental impact of sludge management. A benchmarking of the most common practices for sludge management as well as of virtuous case studies proposed in the literature is carried out in order to identify different classes of environmental and economic sustainability that could be used to assess different scenarios. The proposed assessment method is finally demonstrated by applying it to a case study

A Biomass-Based Polygeneration System for Historical Building: An Energy Analysis

Combined cooling, heating, and power systems (CCHP) are considered one of the most efficient energy systems since they have a less detrimental environmental impact, and therefore sustainable energy savings, and eventually less CO2 emissions. An even higher advantage is possible when a renewable energy fuel source (e.g., Biomass) is used. The proposed study presents the energy modeling of a 100 kWe capacity, biomass-based CCHP system retrofitted to a historical building, located in Perugia, Italy. Two well-known simulation software’s, ASPEN Plus and TRNSYS, are purposely integrated. In the first phase of the study, a wood biomass combustion-based externally fired gas turbine is modeled in Aspen Plus. In the later phase, a historical building “Sant’ Apollinare” model, and the remaining CCHP system are developed in TRNSYS. The transient system is modeled such that it fulfills the peak heating and cooling demand of the retrofitted building. The main components of the system are: a heat exchanger, storage tanks, a single-stage LiBr-H2O absorption chiller, and balance of plant components. A heat exchanger recovers heat from the gas cycle, which is then utilized for heating and cooling of the end-user building, biomass drying, and domestic hot water (DHW) supply. A storage tank supplies direct heat to the end-user in winters and drives the absorption chiller in summer. The results of the model provide data on the performance parameters of different components of the CCHP system such as temperature, power consumption, and energy profiles that allow evaluating the overall energy performance of the CCHP system

Geothermal energy for drying of wastewater sludge and electricity production

Waste treatment and disposal and electric energy production are crucial challenges in geographically disadvantaged areas, such as small islands, due to limited connection with mainland. Scarce land availability, environmental restrictions and tourism activity, that often characterize small islands, make difficult to adopt ordinary technical solutions, increasing these issues. Then, the most common strategy for waste disposal is shipping to the mainland, whereas electricity generation is based on the importation of fossil fuels for local production. Both these options make small islands strongly dependent on the mainland, and cause significant energetic, environmental and economic costs. For these reasons, the use of renewable energy sources for waste treatment and energy production is particularly attracting in small islands. In this work, geothermal energy at medium enthalpy is considered to produce heat for thermal drying of wastewater sludge and to power an Organic Rankine Cycle system for electric energy production. The analysis is carried out for the case study of a small Italian island. The geo-fluid, through an air-water heat exchanger, heats fresh air to produce the desiccant current for sludge drying, which is carried out by using a belt convective dryer, operating in the range of 90.0-180°C. The dryer is designed to achieve a final solids content of dry sludge higher than 90.0%. A fraction of the desiccant current exiting the dryer is recirculated in order to reduce thermal energy demand of the dryer and, at the same time, the flow rate of exhausts to be treated. Before reinjection, the geo-fluid powers a small-scale ORC system, designed to self-supply the proposed layout, providing electricity for the dryer and the geo-fluid pumps, and to produce electricity for the wastewater treatment facilities. An energy analysis of the proposed system is carried out through the software Aspen PLUS, and an economic and environmental model is developed to assess its profitability. This model estimates the economic and environmental benefits coming from sludge drying, which significantly decreases the amount of sludge to be transported and disposed, and from the use of a renewable energy source with respect to conventional fossil fuels, for sludge treatment and electric energy production

Using flow obstructions in electro-osmotic systems for fluid flow enhancement

A numerical investigation of Electro-Osmotic Flow (EOF) in plain channels and channels with obstructions is presented. The aim of the work is to analyse fluid flow enhancement in EO systems due to flow obstructions. The results show that the introduction of flow obstructions allows to increase the range of channel width in which EOF is effective, and to produce higher fluid flow rates than those corresponding to plain channels. The results also show that beyond a channel width of 100μm, EOF driven systems are possible only if flow obstructions are employed

Combined heat and power production based on sewage sludge gasification: An energy-efficient solution for wastewater treatment plants

The main operating costs of wastewater treatment plants are related to the energy consumption and the disposal of by-products. Energy recovery from sewage sludge may be a solution to face both these challenges, improving the sustainability of wastewater treatment plants and making them an example of a circular economy. In this work, the energy and economic analysis of an integrated combined heat and power system based on sewage sludge gasification is proposed. The whole process is simulated by using the commercial software Aspen Plus®. A restricted equilibrium model is used to simulate the gasification of sewage sludge in an atmospheric fluidized bed reactor using air as a gasification agent. Syngas produced from gasification is used as a fuel in an internal combustion engine for combined heat and power production. Different solutions are compared: the internal combustion engine is supposed to be fuelled with syngas or with syngas and methane. In line with the pertinent literature on integrated biomass gasification–internal combustion engine systems, the engine is modeled by combining a compressor, a combustor and a turbine to simulate the four thermodynamic steps of an internal combustion engine. Electric and thermal energy produced by the system is used to supply a fraction of the demand for wastewater and sludge treatment. The energy analysis is carried out for a real wastewater treatment plant that serves 1.2 million of population equivalent, located in Southern Italy. The obtained results are used to carry out an energy and economic analysis, which aims at assessing the feasibility and environmental benefits of the proposed system over conventional technologies

Solar-based systems

This chapter describes solar-based polygeneration systems. After a brief overview of the most used solar technologies, different solar-based polygeneration systems presented in the literature are illustrated. The operation and the methodology used for the analysis of such systems are described. Then, for each example, the plant location, the solar technology used, the produced outputs, and the achieved efficiency are illustrated. This chapter also presents an example of a solar-based polygeneration system, with a detailed description of the system layout and the operation strategy. A dynamic simulation model of such a system is developed to carry out its energy and economic analysis. Finally, daily, weekly, and yearly results carried out with the dynamic simulation are presented