Solar Desalination

This study evaluated the feasibility of utilizing low-grade heat sources such as solar energy and waste heat from industrial processes for desalination. The premise of the approach is that saline waters can be desalinated by evaporation and condensation of fresh water at near-ambient temperatures at low pressures. Low pressures can be achieved naturally in the head space of water columns of height equal to the local barometric head. By connecting the head space of such a saline water column to that of a distilled water column, and by maintaining the temperature of the former about 15-20 degrees C above that of the latter, fresh water can be evaporated from the saline column and condensed in the distilled water column. In this study, it is proposed to use thermal energy storage (TES) system to heat the head space of the saline water column. The TES can be maintained at the desired temperature using solar energy and/or waste heat from thermal power plants, refrigeration plants or air conditioning units. This paper presents an integrated process model developed to evaluate the feasibility of combining solar energy with an absorption refrigeration system (ARS) to provide the energy to the TES. Results of this study show that the heat rejected by an existing ARS of cooling capacity of 3.25 kW (~1 ton of refrigeration) is adequate to produce desalinated water at a rate of 5 kg/hr, with an additional energy input of 150 kJ/kg of desalinated water. The total solar panel area required for this application was 25 m2 . Performance curves and guidelines for preliminary design of such an integrated system are presented

Synergism of microwaves and ultrasound for advanced biorefineries

Conventional energy sources are limited and non-renewable and their consumption contributes to greenhouse gas emissions. The world is in need of advanced biorefineries to meet ever growing energy demands associated with population growth and economic development. An advanced biorefinery should use renewable and sustainable (both in quality and quantity) feedstock that gives rise to higher energy gains with minimum non-renewable energy and resource consumption. Development of advanced biorefineries is currently encircled by two major issues. The first issue is to ensure adequate biofuel feedstock supplies while the second issue is to develop resource-efficient technologies for the feedstock conversion to maximize energy and economic and environmental benefits. While microalgae, microbial derived oils, and agricultural biomass and other energy crops show great potential for meeting current energy demands in a sustainable manner, process intensification and associated synergism can improve the resource utilization efficiency. Synergism of process intensification tools is important to increase energy efficiency, reduce chemical utilization and associated environmental impacts, and finally process economics

Exergy Evaluation of Desalination Processes

Desalination of sea or brackish water sources to provide clean water supplies has now become a feasible option around the world. Escalating global populations have caused the surge of desalination applications. Desalination processes are energy intensive which results in a significant energy portfolio and associated environmental pollution for many communities. Both electrical and heat energy required for desalination processes have been reduced significantly over the recent years. However, the energy demands are still high and are expected to grow sharply with increasing population. Desalination technologies utilize various forms of energy to produce freshwater. While the process efficiency can be reported by the first law of thermodynamic analysis, this is not a true measure of the process performance as it does not account for all losses of energy. Accordingly, the second law of thermodynamics has been more useful to evaluate the performance of desalination systems. The second law of thermodynamics (exergy analysis) accounts for the available forms of energy in the process streams and energy sources with a reference environment and identifies the major losses of exergy destruction. This aids in developing efficient desalination processes by eliminating the hidden losses. This paper elaborates on exergy analysis of desalination processes to evaluate the thermodynamic efficiency of major components and process streams and identifies suitable operating conditions to minimize exergy destruction. Well-established MSF, MED, MED-TVC, RO, solar distillation, and membrane distillation technologies were discussed with case studies to illustrate the exergy performances

Energy aspects of microalgal biodiesel production

Algal biodiesel production will play a significant role in sustaining future transportation fuel supplies. A large number of researchers around the world are investigating into making this process sustainable by increasing the energy gains and by optimizing resource-utilization efficiencies. Although, research is being pursued aggressively in all aspects of algal biodiesel production from microalgal cell cultivation, cell harvesting, and extraction and transesterification steps to the final product separation and purification, there is a large disparity in the data presented in recent reports making it difficult to assess the real potential of microalgae as a future energy source. This article discusses some of the key issues in energy consumption in the process of algal biodiesel production and identifies the areas for improvement to make this process energy-positive and sustainable

2015 ASEE Southeast Section Conference Algal Research -A Case for Teaching Environmental Engineering

Abstract Active research provides excellent opportunities for teaching engineering design principles. In this paper, algal research is used as basis to teach environmental engineering concepts and train the emerging civil and environmental engineers is presented. Research focused on algal cultivation, harvesting, processing for biofuel production and beneficial applications to resolve energy-environmental issues has provided opportunities for a number of undergraduate and graduate civil and environmental engineering students at Mississippi State University. Coagulation, flocculation, sedimentation and filtration concepts and design principles were taught through practical demonstrations for the junior and senior civil engineering students in the environmental engineering laboratory. The source water was collected from the algae contaminated ponds at the Mississippi State University campus. The student learning was greatly enhanced by the practical and hands-on research experiences provided to them, and it was evidenced by the number of research excellence awards received at local, regional and national conferences and national level design competitions. This paper discusses the integration of research activities into environmental engineering courses (junior, senior and graduate level courses) and the enrichment of student learning experiences and their success. Keywords Environmental engineering, research based instruction, higher order of learning, cognitive skills, project-based learnin

Assessment of Sustainability Indicators for Biodiesel Production

Biodiesel production may provide a sustainable route to reduce environmental pollution caused by fossil fuel consumption. In order to minimize environmental impacts of biodiesel production, the chemical process should be optimized to minimize waste generation and energy consumption. Therefore, it is important to design biodiesel chemical reactions and processes using green chemistry and green engineering principles to develop sustainable chemical processes. This study provides the results of the synergistic effect of microwave and ultrasound irradiations to produce biodiesel using ethanol or methanol as the alcohol donor. The biodiesel yields are presented along with their respective green metrics, such as atom economy, environmental factor (E-factor), atom economy (utilization) or atomic efficiency, mass intensity, reaction mass efficiency, atom utilization, and stoichiometric factor. These green metrics are crucial to determine the sustainability and environmental impact of biodiesel production. Evaluation of these green metrics indicates that methanol is a better alternative for biodiesel production provided it is derived from renewable sources. Sustainability indicator concepts used for biodiesel production in this study can be applied to various biofuels and other chemical reaction designs, synthesis and process development

Nuclear cogeneration for cleaner desalination and power generation – A feasibility study

Population growth, economic development, groundwater impairment due to salt water intrusion and local vulnerabilities caused by rising sea levels prompt immediate necessity for customized adaptation strategies for the cities of Homestead and Miami in Florida. This paper presents a feasibility study of nuclear energy driven cogeneration plant for water and power production in Homestead, FL. Miami-Dade and Homestead, Florida is home to the Turkey Point Nuclear Generating Facility. The focus of this study is to investigate the economic feasibility of a seawater desalination facility on the site of an existing nuclear generating plant. While the cost of seawater desalination is often too great to overcome, it is hypothesized that sharing the infrastructure and processes with a power generating facility will lower the cost of producing freshwater. The analysis was completed with the aid of the desalination modeling software, DEEP. First, we estimate the population growth and water demands for Homestead, FL and then identify a suitable water desalination plant configuration based on freshwater and power production costs. We then compare cogeneration (water and power) schemes based on different energy sources and desalination technologies. The energy sources considered are nuclear energy, oil and natural gas for steam turbine and combined cycle power plants. In addition, we evaluate the water and power production costs for hybrid desalination configurations. Finally, the freshwater costs through nuclear desalination were assessed with other options and conventional ground water system costs. Environmental emissions saved through nuclear desalination and the need for considering this option despite the high costs are discussed in detail. The study concluded that reverse osmosis desalination plant powered by nuclear energy produced water at the lowest cost which is still three times the cost of current water rates in Homestead, Florida

Renewable and sustainable approaches for desalination

Freshwater and energy are essential commodities for well being of mankind. Due to increasing population growth on the one hand, and rapid industrialization on the other, today's world is facing unprecedented challenge of meeting the current needs for these two commodities as well as ensuring the needs of future generations. One approach to this global crisis of water and energy supply is to utilize renewable energy sources to produce freshwater from impaired water sources by desalination. Sustainable practices and innovative desalination technologies for water reuse and energy recovery (staging, waste heat utilization, hybridization) have the potential to reduce the stress on the existing water and energy sources with a minimal impact to the environment. This paper discusses existing and emerging desalination technologies and possible combinations of renewable energy sources to drive them and associated desalination costs. It is suggested that a holistic approach of coupling renewable energy sources with technologies for recovery, reuse, and recycle of both energy and water can be a sustainable and environment friendly approach to meet the world's energy and water needs. High capital costs for renewable energy sources for small-scale applications suggest that a hybrid energy source comprising both grid-powered energy and renewable energy will reduce the desalination costs considering present economics of energy.Desalination Renewable energy Energy cost Water reuse Reverse osmosis Cogeneration Green house gases Environment