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Exhaust steam utilization in waste-to-energy strategies: From district heating to desalination
... Today, centralized heat supply plays a very important role in providing heat energy to consumers in many countries of Europe, Asia, and America, because it is the most widespread form of combined production of heat and electricity [1][2][3][4]. ...
The object of the research is central heating points (CTP) in Ukraine. The problem that is being solved in the work is the need to modernize and automate existing CTPs. The importance of the problem is the presence of a large number of CTPs in Ukraine, which require urgent modernization of morally outdated equipment and automation of management of their work modes, which must be carried out in stages without removing them from operational status. The need for modernization and further automation of the existing CTPs in Ukraine is substantiated, which is that this will allow increasing the efficiency of the CTPs through the use of modern technical equipment, software and trained specialists in the automated management of the process of heat supply to consumers. And it will also allow to reduce the cost of heat supply tariffs due to the reduction of non-production costs and to reduce the number of service personnel who manage work modes in manual mode. During the martial law, the timely resolution of problems with high-quality heat supply of the population acquires special importance. The result of the conducted research is a theoretical analysis of the quality work of CTPs in the EU countries, realization of their capabilities and prospects for further use in order to transfer their experience to Ukraine. A theoretical analysis of the number and modern technical equipment of CTPs in Ukraine at the present time was also conducted. As a result of the research conducted on the existing CTPs in Ukraine, a survey of their technical condition was carried out, specific directions for the phased modernization and automation of their equipment were developed and proposed, and additional measures were taken regarding the thermal modernization of main pipelines and modern thermal insulation of buildings and structures. The possibility of practical implementation – step-by-step modernization and automation of the CTP, increasing the technical and technological capabilities of the equipment and reducing the tariffs for heat and water supply for consumers.
Energy efficiency is considered an important indicator after the efficiency term is one framework of economic planning. The review results show that the gained energy is completely different in industries due to the production line, raw material, used fuel, system automation, application of thermodynamic rules, and energy recovery applications. The thermal parameters of the machining system are the main indicators to determine the system's efficiency. Dynamic behavior, effectiveness, and thermal capacity limitation are some parameters used for the optimization of machining energy efficiency. The temperature, pressure, flow rate, and other operating conditions as a function of time are the physical quantities to determine the dynamic behavior. The machining tools are intensive energy-consuming types of equipment and mostly consume electricity in manufacturing industries.
The general approach for cost-effective planning is to set a complete energy-efficient system. Mass, energy, and exergy analyses are the general bases for the efficiency consideration of heat generation. But the easiest and most expeditious energy recovery is observed in effective machining like micromechanical systems and hybrid systems, up to 20% of overall losses can be recovered. If the general usage of steam to produce electricity is considered, controlling the existing configuration will improve energy efficiency by applying quantitative optimization of the electricity usage. This quantity can be increased by an extra 20%. To optimize the entire cogeneration or trigeneration machining system, a holistic approach is needed that improves the system's energy efficiency by up to 65%. The energy efficiency is increased in the range from 3 to 35% by innovative EMS. Air leaks are causing the highest energy losses in CA systems. More than 90% energy efficiency can be achieved with an appropriate CAES system mostly in isothermal and high-pressure conditions for machining purposes. Moreover, the recovered energy will mitigate GHGs. And it is strict that, any developing plan of countries which contains an energy efficiency strategy, is necessary to sustain a habitable earth.
Ion-exchange membranes (IEMs) are utilized in numerous established, emergent, and emerging applications for water, energy, and the environment. This article reviews the five different types of IEM selectivity, namely charge, valence, specific ion, ion/solvent, and ion/uncharged solute selectivities. Technological pathways to advance the selectivities through the sorption and migration mechanisms of transport in IEM are critically analyzed. Because of the underlying principles governing transport, efforts to enhance selectivity by tuning the membrane structural and chemical properties are almost always accompanied by a concomitant decline in permeability of the desired ion. Suppressing the undesired crossover of solvent and neutral species is crucial to realize the practical implementation of several technologies, including bioelectrochemical systems, hypersaline electrodialysis desalination, fuel cells, and redox flow batteries, but the ion/solvent and ion/uncharged solute selectivities are relatively understudied, compared to the ion/ion selectivities. Deepening fundamental understanding of the transport phenomena, specifically the factors underpinning structure-property-performance relationships, will be vital to guide the informed development of more selective IEMs. Innovations in material and membrane design offer opportunities to utilize ion discrimination mechanisms that are radically different from conventional IEMs and potentially depart from the putative permeability-selectivity tradeoff. Advancements in IEM selectivity can contribute to meeting the aqueous separation needs of water, energy, and environmental challenges.
This research proposes a hybrid system consisting of a parabolic trough solar field coupled with a waste incineration facility to produce power and desalinated water in Jordan. To predict the performance of the proposed system, EBSILON Professional (13.02) was used to simulate the entire system and for a more realistic simulation process, a prime sample of 100 tons of municipal waste from Jordan was obtained, processed, and homogenised, after which 4 kg was brought to Germany for laboratory analysis. The laboratory results were inserted into EBSILON. Solar radiation data were adapted from meteonorms and input to EBSILON. Heat transfer between the receiver wall and the heat transfer fluid was analysed to calculate the time required to increase the temperature of the Heat Transfer Fluid from the influent temperature to the desired effluent temperature. The results show that this system can produce 34 MWe of power and 13,824 m³/d of distilled water. On the 1st January, the temperature of the heat transfer fluid in the solar field was increased by 6 °C for 20 min in an open cycle. After 5h, it reached 390 °C in a closed cycle, assuming a fixed direct normal irradiance. Economically, five scenarios were analysed to assess the impact of the cost of heat harvested to produce this amount of water on the annual cost of handling each ton of garbage which was approximately 57 US$ in the first year of operation and 19.5 US$ in the 15th year of plant operation (for the scenario in which the tariff of power sales was considered to evaluate the cost of heat for water desalination).
Background
The Middle East and North African (MENA) countries are rapidly growing in population with very limited access to freshwater resources. To overcome this challenge, seawater desalination is proposed as an effective solution, as most MENA countries have easy access to saline water. However, desalination processes require massive demand for energy, which is mostly met by fossil fuel-driven power plants. The rapid technological advancements in renewable energy technologies, along with their gradually decreasing cost place renewable energy-driven power plants and processes as a promising alternative to conventional fuel-powered plants.
Aim of Review
In the current work, renewable energy-powered desalination in the MENA region is investigated. Various desalination technologies and renewable energy resources, particularly those available in MENA are discussed. A detailed discussion of suitable energy storage technologies for incorporation into renewable energy desalination systems is also included.
Key Scientific Concepts of Review
The progress made in implementing renewable energy into power desalination plants in MENA countries is summarized and analyzed by describing the overall trend and giving recommendations for the potential amalgamation of available renewable energies (REs) and available desalination technologies. Finally, a case study in the MENA region, the Al-khafji solar seawater reverse osmosis (SWRO) desalination plant in the Kingdom of Saudi Arabia KSA, is used to demonstrate the implementation of REs to drive desalination processes.
There is interest for desalination technologies powered by solar energy as arid areas are typically bestowed with good solar potential. In response to a US DOE call for solar desalination analysis tools, we developed an open-source solar energy desalination analysis tool, sedat, for techno-economical evaluation of desalination technologies and selection of regions with the highest potential for using solar energy to power desalination plants. It is expected that this software will simplify the planning, design, and valuation of solar desalination systems in the U.S. and worldwide. Sedat uses Dash for integrating various layers of large volumes of GIS data with Python-based models of solar energy generation and desalination technologies. It derives time-series of energy generation and water production, with details of plant performance and suggestions for improving the solar-desalination coupling. This paper summarizes the various phases of the tool’s development, presents example results showing the potential, under multiple objectives, of solar desalination in parts of the U.S. southwest, and discusses method details that would be useful for future model development.
Nowadays, desalination continues to expand globally, which is one of the most effective solutions to solve the problem of the global drinking water shortage. However, desalination is not a fail-safe process and has many environmental and human health consequences. This paper investigated the desalination procedure of seawater with different technologies, namely, multi-stage flash distillation (MSF), multi-effect distillation (MED), and reverse osmosis (RO), and with various energy sources (fossil energy, solar energy, wind energy, nuclear energy). The aim was to examine the different desalination technologies’ effectiveness with energy sources using three assessment methods, which were examined separately. The life cycle assessment (LCA), PESTLE, and multi-criteria decision analysis (MCDA) methods were used to evaluate each procedure. LCA was based on the following impact analysis and evaluation methods: ReCiPe 2016, IMPACT 2002+, and IPCC 2013 GWP 100a; PESTLE risk analysis evaluated the long-lasting impact on processes and technologies with political, economic, social, technological, legal, and environmental factors. Additionally, MCDA was based on the Technique for Order Preference by Similarity to the Ideal Solution (TOPSIS) method to evaluate desalination technologies. This study considered the operational phase of a plant, which includes the necessary energy and chemical needs, which is called “gate-to-gate” analysis. Saudi Arabia data were used for the analysis, with the base unit of 1 m3 of the water product. As the result of this study, RO combined with renewable energy provided outstanding benefits in terms of human health, ecosystem quality, and resources, as well as the climate change and emissions of GHGs categories.
District heating and cooling systems represent a valuable infrastructure that can facilitate the integration of various energy sources into urban energy systems. One of those sources is municipal waste. By applying the waste-to-energy concept, landfilled waste amounts can be significantly reduced, and heat, cold and electricity can be produced via combined heat and power plants. This research investigates the possibility of integration of combined heat and power waste incineration plant into the existing gas-based district heating system in the central European city. To secure 365 days of heat demand, the influence of the introduction of a warm district cooling system is simulated, where heat is distributed via the existing heat distribution network to distributed chillers, building sites locations. The results show 33% higher energy-from-waste potential in summer compared to winter, which is an opposite trend to heating demand and compatible with yearly distribution of energy needs for covering cooling demand. Despite the identified compatibility on a seasonal scale, to cover up to 100% of district cooling energy consumption with energy-from-waste, heat storage is needed, due to differences in short-term heat production and demand. This synergy has positive effects on the energy production efficiency and operation of the waste to energy plant and district heating system which results in the highest reduction in fuel consumption as well as in decrease in greenhouse gas emissions. Results of this research can be used for a better understanding of interactions between analysed technologies/systems in the wide range of cities with a continental climate.
This paper reports the first known comprehensive survey of combustion operating conditions across the wide range of municipal waste-to-energy facilities in the U.S. The survey was conducted in a step-wise fashion. Once the population of 188 units operating at over 70 facilities was defined, this population was stratified by distinguishing characteristics of combustion technology. Stratum-level estimates for operating conditions were determined from data collected in the survey. These stratum-level values were weighted by corresponding design capacity share and combined to infer national-level operating parameter estimates representative of the overall population. Survey results show that typical municipal waste-to-energy combustion operating conditions in the U.S. are (1) furnace temperature above 1160 °C, (2) gas residence time above 2.4 s, (3) exit gas concentrations of nearly 10% for oxygen (dry basis), and (4) over 16% for moisture. These operating parameter values can serve as benchmarks for laboratory-scale studies representative of municipal waste-to-energy combustion as typically practiced in the U.S.
Municipal solid waste (MSW) is increasingly considered a source of energy and materials rather than an environmental and socioeconomic problem. Incineration using the grate-firing technique is one of the best available technologies for thermal treatment of non-recyclable MSW with energy recovery. The transition to a circular economy brings a new challenge to the Waste to Energy (WtE) industry. Due to advanced waste management schemes, the calorific value of the input waste is likely to decrease. Nevertheless, WtE plant designers and operators have aimed to increase the energy and material recovery efficiency of their installations, while maintaining or even decreasing operation and maintenance costs. For these reasons, there is a need for better understanding of the chemical and physical phenomena involved in the MSW incineration process. Accurate numerical modelling of MSW packed bed combustion can substantially contribute to this objective.
The literature on similar fields such as coal and biomass combustion has delineated many crucial aspects of modelling solid fuel combustion in grate-firing applications. However, the know-how obtained in these fields cannot be one on one transferred to MSW incineration because MSW is much more inhomogeneous in composition and thermophysical properties. This paper first presents an overview of MSW's chemical and thermophysical properties. Then, the heterogeneous nature of MSW and its complex thermal degradation behaviour are used as a basis to discuss the suitability of the available numerical methodologies. Finally, current challenges in the modelling of waste beds are identified, with relevance to improving the performance of industrial WtE plants.
We achieve a significant improvement in thermodynamic-based flux analysis (TFA) by introducing multivariate treatment of thermodynamic variables and leveraging component contribution, the state-of-the-art implementation of the group contribution methodology. Overall, the method greatly reduces the uncertainty of thermodynamic variables.
Results
We present multiTFA, a Python implementation of our framework. We evaluated our application using the core Escherichia coli model and achieved a median reduction of 6.8 kJ/mol in reaction Gibbs free energy ranges, while three out of 12 reactions in glycolysis changed from reversible to irreversible.
Availability and implementation
Our framework along with documentation is available on https://github.com/biosustain/multitfa.
Supplementary information
Supplementary data are available at Bioinformatics online.
Thermal desalination is yet a reliable technology in the treatment of brackish water and seawater; however, its demanding high energy requirements have lagged it compared to other non-thermal technologies such as reverse osmosis. This review provides an outline of the development and trends of the three most commercially used thermal or phase change technologies worldwide: Multi Effect Distillation (MED), Multi Stage Flash (MSF), and Vapor Compression Distillation (VCD). First, state of water stress suffered by regions with little fresh water availability and existing desalination technologies that could become an alternative solution are shown. The most recent studies published for each commercial thermal technology are presented, focusing on optimizing the desalination process, improving efficiencies, and reducing energy demands. Then, an overview of the use of renewable energy and its potential for integration into both commercial and non-commercial desalination systems is shown. Finally, research trends and their orientation towards hy-bridization of technologies and use of renewable energies as a relevant alternative to the current problems of brackish water desalination are discussed. This reflective and updated review will help researchers to have a detailed state of the art of the subject and to have a starting point for their research, since current advances and trends on thermal desalination are shown.
District heating (DH) is an important technology in future smart energy systems as it allows for an efficient implementation of various renewable energy sources. As DH develops towards lower temperatures and renewable electricity production increases, new types of heat sources become relevant. Thus, the aim of this article is to assess the potential for utilizing four unconventional excess heat (UEH) sources in DH systems, namely: Data centers, wastewater treatment, metros and service sector buildings. The main method used to assess the UEH potentials is an energy system analysis focusing on the availability and economic feasibility of utilizing the UEH sources in national contexts. The analysis consists of 2015 and 2050 scenarios for Germany, Spain and France. The results show a potential for utilizing the UEH potentials in all three countries, both in 2015 and 2050 systems. The potentials are highest in the 2050 scenarios, primarily due to larger DH shares. Furthermore, the potentials are limited by competition with other heat supply sources, conjunction with heat demands and feasible heat pump operation. In conclusion, the four UEH sources could impact the local DH systems, but in a national energy system context they are expected to play a minor role.
Evaluation of different alternatives for enhancement in a waste combustion process enables adequate decisions to be made for improving its efficiency. Exergy analysis has been shown be an effective tool in assessing the overall efficiency of a system. However, the conventional exergy method does not provide information of the improvements possible in a real process. The purpose of this paper is to evaluate state-of-the art techniques applied in a municipal solid-waste fired heat and power plant. The base case plant is evaluated first; the results are then used to decide upon which technical modifications should be introduced and they are thereafter evaluated. A modified exergy-based method is used to discover the improvement potential of both the individual components and the overall base case plant. The results indicate that 64% of exergy destruction in the overall process can theoretically be improved. The various modifications selected involve changing the bed material, using a gasifier followed by a gas boiler and incorporating a more durable material into the boiler walls. In addition, changing the heating medium of the incoming air (from steam to flue gas) along with a reduction in the stack temperature and the integration of flue gas condensation were considered for utilizing the exergy in the flue gases. The modification involving gasifier, gas boiler and flue gas condensation proved to be the best option, with the highest exergy efficiency increment of 21%. Keywords: Theoretical process, Exergy efficiency, Flue gas condensation, Municipal solid-waste fired plant, Improvement potential, Gasification-combustion process
Saint Barthélemy (St. Barth) is a Caribbean island located in the Leeward Islands of the Lesser Antilles. The island’s small size, lack of natural resources, socioeconomic features, and geographic isolation make it an interesting case study for matters of sustainability, specifically freshwater production and waste management. Interviews were conducted with residents of the island to determine the factors that motivate or discourage sustainable behavior with regards to these environmental issues. A sense of civic duty, the simplicity of environmental regulations, rapid communication and implementation, socioeconomic stability and affluence, and economic incentives each served to promote environmental stewardship and sustainable decision-making, while government priorities and persistent habits tended to hinder such behavior. The results of this study could be applied to other island communities with similar characteristics to determine how we, as a global society, can move towards a more sustainable future.
pyTFA and matTFA are the first published implementations of the original TFA paper. Specifically, they include explicit formulation of Gibbs energies and metabolite concentrations, which enables straightforward integration of metabolite concentration measurements.
Motivation
High-throughput analytic technologies provide a wealth of omics data that can be used to perform thorough analyses for a multitude of studies in the areas of Systems Biology and Biotechnology. Nevertheless, most studies are still limited to constraint-based Flux Balance Analyses (FBA), neglecting an important physicochemical constraint: thermodynamics. Thermodynamics-based Flux Analysis (TFA) in metabolic models enables the integration of quantitative metabolomics data to study their effects on the net-flux directionality of reactions in the network. In addition, it allows us to estimate how far each reaction operates from thermodynamic equilibrium, which provides critical information for guiding metabolic engineering decisions.
Results
We present a Python package (pyTFA) and a Matlab toolbox (matTFA) that implement TFA. We show an example of application on both a reduced and a genome-scale model of E. coli., and demonstrate TFA and data integration through TFA reduce the feasible flux space with respect to FBA.
Availability and implementation
Documented implementation of TFA framework both in Python (pyTFA) and Matlab (matTFA) are available on www.github.com/EPFL-LCSB/.
Supplementary information
Supplementary data are available at Bioinformatics online.
Projected water temperatures at six sites in the Gulf of Mexico and Caribbean Sea were used to forecast potential effects of climate change on the growth, abundance and distribution of Gambierdiscus and Fukuyoa species, dinoflagellates associated with ciguatera fish poisoning (CFP). Data from six sites in the Greater Caribbean were used to create statistically downscaled projections of water temperature using an ensemble of eleven global climate models and simulation RCP6.0 from the WCRP Coupled Model Intercomparison Project Phase 5 (CMIP5). Growth rates of five dinoflagellate species were estimated through the end of the 21st century using experimentally derived temperature vs. growth relationships for multiple strains of each species. The projected growth rates suggest the distribution and abundance of CFP-associated dinoflagellate species will shift substantially through 2099. Rising water temperatures are projected to increase the abundance and diversity of Gambierdiscus and Fukuyoa species in the Gulf of Mexico and along the U.S. southeast Atlantic coast. In the Caribbean Sea, where the highest average temperatures correlate with the highest rates of CFP, it is projected that Gambierdiscus caribaeus, Gambierdiscus belizeanus and Fukuyoa ruetzleri will become increasingly dominant. Conversely, the lower temperature-adapted species Gambierdiscus carolinianus and Gambierdiscus ribotype 2 are likely to become less prevalent in the Caribbean Sea and are expected to expand their ranges in the northern Gulf of Mexico and farther into the western Atlantic. The risks associated with CFP are also expected to change regionally, with higher incidence rates in the Gulf of Mexico and U.S. southeast Atlantic coast, with stable or slightly lower risks in the Caribbean Sea.
Discussion about utilization of waste for energy production (waste-to-energy, WTE) has moved on to next development phase. Waste fired power plants are discussed and researched. Present results of simulation prove that increase of net electrical efficiency above 20 % for units processing 100 kt/y is problematic and tightly bound with increased investments. Lower cogeneration production leads to ineffective utilization of energy, which is documented in present paper with help of primary energy savings criterion. Once sole electricity production is compelled by limited local heat demand, application of non-conventional arrangements is highly beneficial to secure effective energy utilization. In the paper a system where municipal solid waste incinerator is integrated with combined gas-steam cycle is evaluated in the same manner.
As a renewable and environmentally friendly energy source, biomass (i.e., any organic non-fossil fuel) and its utilization are gaining an increasingly important role worldwide. Grate-firing is one of the main competing technologies in biomass combustion for heat and power production, because it can fire a wide range of fuels of varying moisture content, and requires less fuel preparation and handling. The basic objective of this paper is to review the state-of-the-art knowledge on grate-fired boilers burning biomass: the key elements in the firing system and the development, the important combustion mechanism, the recent breakthrough in the technology, the most pressing issues, the current research and development activities, and the critical future problems to be resolved. The grate assembly (the most characteristic element in grate-fired boilers), the key combustion mechanism in the fuel bed on the grate, and the advanced secondary air supply (a real breakthrough in this technology) are highlighted for grate-firing systems. Amongst all the issues or problems associated with grate-fired boilers burning biomass, primary pollutant formation and control, deposition formation and corrosion, modelling and computational fluid dynamics (CFD) simulations are discussed in detail. The literature survey and discussions are primarily pertaining to grate-fired boilers burning biomass, though these issues are more or less general. Other technologies (e.g., fluidized bed combustion or suspension combustion) are also mentioned or discussed, to some extent, mainly for comparison and to better illustrate the special characteristics of grate-firing of biomass. Based on these, some critical problems, which may not be sufficiently resolved by the existing efforts and have to be addressed by future research and development, are outlined.
Prominent among problems of developing nations are access to affordable and reliable energy as well as clean and livable environment. The abovementioned points coincide with the sustainable development goals 7 (SDG 7) and 11 (SDG 11) of the United Nations (UN), respectively. Adopting waste-to-energy system could leverage on the possibility of reducing the adverse environmental impact occasioned by waste generation and ensuring production of renewable and sustainable energy while achieving circular economy. A review of most commonly used technologies for solid waste management worldwide, such as incineration, pyrolysis, gasification, anaerobic digestion, and landfilling with gas recovery in order to achieve waste-to-energy nexus is presented. A brief discussion on the economic, environmental and social impact as well as the implementation levels, some challenges and possible solutions to the implementation of the mentioned technologies for both developed and developing countries are included. This paper also addresses waste-to-energy (WtE) as a contributor to achieving sustainable development. It is evident from this paper that the waste stream of developing countries contained 50-56% food and garden wastes making anaerobic digestion technology more appropriate for treatment. Incineration is widely adopted in developed countries with more than 1,700 incineration plants operational worldwide. This paper offers to add to the pool of literature while helping researchers and decision-makers to make an informed decision on the feasibility of WtE as a pathway for sustainable waste management and renewable energy generation.
New developments in pressure- and thermally driven membrane desalination technologies offer the potential to cost-effectively treat high-salinity waters, especially when powered by low-cost solar electricity and thermal energy. This paper presents a comparative techno-economic assessment of the state-of-the-art most promising pressure- and thermally driven membrane technologies for high recovery desalination, namely, osmotically-assisted reverse osmosis (OARO) and batch-operated vacuum-air-gap membrane distillation (batch V-AGMD), to produce potable water while concentrating brine within the range of 140–290 g/L TDS for minimum-liquid-discharge (MLD) and zero-liquid-discharge (ZLD) applications. It is shown that both OARO and batch V-AGMD can treat feedwater and brines with TDS in the range of 30–125 g/L with corresponding fresh water recovery rates of 85–25%. When low cost solar electricity and thermal energy are used, the resulting levelized cost of water (LCOW) from OARO is in the range of 0.70–6.28 $/m³, and that from batch-V-AGMD is in the range of 1.74–2.77 $/m³. OARO is more cost-effective than batch V-AGMD when feedwater salinity is below 70 g/L and recovery below 75%, whereas batch V-AGMD is more cost-effective at higher recovery rates and salinity levels. The sensitivity of this comparison on energy prices and module costs is discussed.
The abundant resource of low-temperature heat sources (≈80–120 °C), e.g., low-concentration solar collectors or shallow geothermal wells, hold huge potential to be a renewable energy supply. A proposed method for harnessing such low-grade heat is to use the heat to distill a solution and then utilize the produced concentration difference to generate work, by means of salinity gradient power (SGP) technologies. In this application, the energy efficiency of the distillation process (ratio between produced mixing free energy and consumed heat) becomes a fundamental performance parameter. This study systematically analyzes the energy efficiency of direct contact membrane distillation (DCMD). This technique is often billed as an emergent membrane innovation that can use low-temperature thermal sources and additionally has the advantages of compactness and relatively simple implementation. However, we show that DCMD always has lower efficiencies than traditional vacuum distillation to achieve the same separation. In particular, the efficiency is smaller at high concentrations, which is desired for the distillation–SGP approach of energy conversion. The main source of entropy production in membrane distillation is the unavoidable thermal conduction across the membrane. Alternatively, vacuum membrane distillation could be a better candidate to regenerate the salinity gradient in low-grade heat utilization with distillation–SGP.
With the increasing urbanization, global generation of Municipal Solid Waste (MSW) is expected to increase to 3.4 billion tons by 2050. Annually, 1.9 billion tons of MSW is generated with each person contributing 218 kg of MSW to this projected grand total. In Kampala, the annual MSW collection exceeds 350,000 tons which is disposed at the city’s landfill which has exceeded its capacity. This has side effects including environmental contamination, methane gas generation promoting global warming, and labour issues. No research has been conducted towards assessing the potential of energy recovery from the city’s MSW by incineration. In this paper, the techno-economic assessment of energy recovery from MSW in Kampala city using incineration was done. Waste data was collected through sampling upon delivery at the landfill. Chemical composition of the waste was determined by proximate analysis and calculation of the elemental composition followed by determination of the calorific value. A MSW incineration plant was designed based on a mass burn incineration. The design parameters were determined using thermodynamic equations and Peng Robison’s equations of state. Simulation was done using Aspen Plus and Hysys, for a plant combusting 220,000 tons per annum of MSW at a feed rate of 27 tons of MSW per hour. The economic analysis was done assuming that the project was a Public Private Partnership debt financed by 75 % with an interest rate of LIBOR plus 5 % margin over a term of 15 years. Results showed that the composition of the waste was largely organic with an 80% composition. The Lower Heating Value was 6.12 MJ/kg with a moisture content of 25%. The elemental composition was 43.47% Carbon, 5.52% Hydrogen, and 41% Oxygen with absence of Nitrogen and Sulfur. The ash content was reported at 6.65 %. From the simulations, the plant is capable of exporting 774 kWh of electricity per ton of MSW to the national grid, capable of powering 1,062 medium income households in Uganda. A capital investment of USD157 million with the sale of electricity and a gate fee as the sources of revenue for a project running for 25 years was considered. The resulting Net Present Value was USD 30 million with a project Internal Rate of Return of 12.6 % and a payback period of 6 years. Thus, the present study demonstrates the possibilities to increase the adoption and use of renewable and clean energy, prioritise energy efficiency, and biodiversity for a green and sustainable Kampala city. Moreover, the results provide immediate technical information for policy makers and potential investors in the development of waste to energy projects in Uganda.
Solar electricity enables the advancement and deployment of technologies that are strongly influenced by clean energy availability and cost. The economics of both desalination and hydrogen production from water electrolysis are dominated by the cost of energy, and the availability of inexpensive solar energy creates markets and offers incentives to the desalination and electrolyzer industries to further advance their technologies. This study focuses on the production of high-purity water and hydrogen from seawater. Current electrolyzers require deionized water so they need to be coupled with desalination units. We show that such coupling is cost-effective in hydrogen generation, and it also offers benefits to thermal desalination, which can utilize waste heat from electrolysis. Furthermore, such coupling can be optimized when electrolyzers operate at high current density, using low-cost solar and/or wind electricity, as such operation increases both hydrogen production and heat generation. Results of techno-economic modeling of polymer electrolyte membrane (PEM) electrolyzers, define thresholds of electricity pricing, current density, and operating temperature that make clean electrolytic hydrogen cost-competitive with hydrogen from steam methane reforming (SMR). By using 2020 hourly electricity pricing in California and Texas, we estimate that hydrogen can be produced from seawater in coupled desalination-electrolyzer systems at prices near $2/kg H2, reaching cost parity with hydrogen produced from SMR.
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While mechanical vapor compression is typically applied for the concentration of brine, new approaches that are less costly and less energy intensive are needed to facilitate minimal and zero liquid discharge. Several variations of reverse osmosis for high-salinity desalination and increasing recovery rates beyond the pressure limitation of conventional RO have been proposed in the literature. The promise of these enhanced RO approaches entails a reduction in energy consumption when compared with thermal desalination methods. In this paper, low-salt rejection reverse osmosis (LSRRO), cascading osmotically mediated reverse osmosis (COMRO), and osmotically assisted reverse osmosis (OARO) were comparatively assessed via module-scale, cost optimization models to gain an accurate perspective of the performance differences between each of these configurations. We quantified the optimal levelized cost of water (LCOW) of each technology for the case of desalinating feedwater at 70 g/L at 75% recovery, which would result in a brine concentration near 250 g/L, a level that allows further treatment with crystallizers. For baseline scenarios, LCOW results for LSRRO, COMRO, and OARO were 6.63, 7.90, and 5.14 $/m³ of product water, respectively, while the corresponding specific energy consumption (SEC) values were 28.9, 12.8, and 10.3 kWh/m³. A sensitivity analysis is also presented.
In this paper, municipal solid waste (MSW) based electricity production and district heating (DH) potential of Turkey are considered. Three MSW based waste-to-energy (WtE) scenarios is developed: (i) Scenario-I, a DH system integrated into a gas turbine power plant (GTPP), (ii) Scenario-II, a DH system integrated into an organic Rankine cycle (ORC), and (iii) Scenario-III, which is based solely on a DH system. As a result of the thermodynamic and thermoeconomic analyzes of these developed scenarios using an existing MSW-based cogeneration facility's actual operating data, the system with the most extended payback period (about 5 years) is found as the GTPP-DH system developed in Scenario-I, which also has the highest investment cost. On the other hand, the system with the shortest payback period (about 2 years) is found as the DH system developed in Scenario-III, which also has the lowest investment cost. Overall exergy efficiencies of the GTTP-DH, ORC-DH, and DH systems are found to be 41.86%, 16.15%, and 31.87%, respectively. When the developed WtE scenarios adapted to the pilot provinces selected from each geographical region of Turkey, it is found that the GTPP system developed in Scenario-I can increase the power generation capacity of MSW plants for each province by about 20%.
Waste-to-energy (WTE) facilities combust both biogenic and nonbiogenic materials comprising municipal solid waste (MSW) in addition to managing waste, leading to a lack of clarity on the life cycle climate change impact (LCCCI) as an electricity generator. In order to investigate the LCCCI of this resource, a cradle-to-gate life cycle assessment (LCA) of a WTE facility in Jamesville, NY, was performed utilizing system expansion to account for avoided landfilling emissions, additional metals recycling, and the loss of potential electricity generation from landfill gas. The LCCCI of electricity from this WTE facility ranges from 0.664 to 0.951 kg CO2eq/kWh before system expansion, which reduced the impact to -0.280 to 0.593 kg CO2eq/kWh when accounting for avoided waste management emissions. Combustion is the leading contributor of GHG emissions from cradle-to-gate, and sensitivity analysis indicates that the nonbiogenic fraction of the waste most significantly influences the LCCCI before including cobenefits. The fraction of methane from landfills that is not captured is the most influential variable under system expansion. Before system expansion, the LCCCI of this system is comparable to that of electricity from fossil fuels. With system expansion, the LCCCI ranges from below that of renewable energy to comparable to natural gas based electricity. These results disagree with claims in the reviewed literature that WTE can avoid GHG emissions overall, although avoided emissions reduce the magnitude of its impact.
An advanced waste-to-energy system integrated with a coal-fired power plant has been proposed to improve the energy utilization of municipal solid waste. In the new design, the energy gained from the waste-to-energy boiler is employed to heat the feedwater and partial cold reheat steam of the coal power plant, and the feedwater of the waste-to-energy boiler is provided by the heat regeneration system of the coal power plant. Consequently, the energy obtained from the waste incineration products is injected into the steam cycle of the coal power plant, and the waste-to-electricity efficiency can be significantly boosted. Based on a 500 t/day waste-to-energy plant and a 630 MW coal power plant, the proposed hybrid scheme was evaluated compared with the conventional separate one. The results show that the waste-to-electricity efficiency is promoted by 9.16% points with an additional net power output of 3.71 MW, attributed to the suggested integration. Furthermore, the energy-saving mechanism of the novel concept was revealed by energy and exergy analyses. Finally, the new design was economically examined, which indicates that the dynamic payback period of the proposed waste-to-energy plant is only 3.55 years, which is 5.87 years shorter than that of the conventional one.
This paper focuses on waste management and waste to energy (WTE) for district heating in S. Korea. The chemical formula for the materials disposed of in volume base waste fee (VBWF) bags that are processed in WTE plants was calculated as: C 6 H 9.9 O 2.3 , with a heat of formation of 27.6 MJ/kg. The average heating value for the 35 WTE plants was 9.7 MJ/kg, and the average amount of energy recovered was calculated at 1.5 MWh/ton waste processed. 22 of the 35 WTE plants comply with the limits of the R1 formula for energy recovery plants (R1 > 0.61), as introduced by the EU. It was estimated that 8% of the district heating demand is provided by WTE in S. Korea. WTE plants can contribute to about 0.6% to the total electricity demand of S. Korea and aid the efforts of the nation to phase out the dependence on fossil fuels. The average dioxin emissions of all WTE plants were 0.005 ng TEQ/Nm 3 (limit:0.1 ng TEQ/Nm 3), and most of the other pollutants examined indicated a tenfold to hundred-fold lower emissions than the national and the EU standards. S. Korea indicated an improved performance in sustainable waste management, with combined recycling/ composting and WTE rates of about 80%, as compared to the average of the EU-28 with 65%, and the US with 36.5%, even if the EU and the US had higher GDP/capita (PPP) than S. Korea.
Sea-water desalination has emerged as the key alternative to overcome demand-supply gap of potable water, worldwide. This paper aims to carry out a technology review of sea-water desalination, technologies in an integrated framework of economic, environmental and ecological analyses. The economic analysis here refers to a project/technology development effort analysis in the context of national economy. The cost per unit output from this perspective is the economic cost. In an environmental analysis, the higher specific energy consumption in a process vis-àvis the best technology option in the project area is measured in terms of certified emission reduction. In ecosystem analysis, the accent is to find out whether the technology disrupts the existing eco-system. Such a disturbance entails a huge ecological cost. The cost quantified per unit output is arrived at as the reduction in GDP in the project affected area due to the direct and indirect effects of adverse ecological effects; these effects are deduced using specifically developed I-O tables 'with and without' technology options, for the project area. The choice of technology is the one with the minimum composite cost per unit output. The composite cost in the context is the sum of economic cost, the environmental cost and the ecological cost per unit output. The framework is applied in the technology review of low-temperature thermal desalination process and its impact on project areas of Lakshadweep islands and Thoothukodi district vis-à-vis the alternative RO process of sea-water desalination technology.
The solid waste management is, in different contexts, a very critical issue. The use of landfills can no longer be considered a satisfactory environmental solution, therefore new methods have to be chosen and waste-to-energy (WTE) plants would provide an answer. Today's WTE plants are a far cry from their polluting predecessors. Using modern combustion and pollution control technology, WTE plants are able to retrieve considerable amounts of energy from waste combustion while minimizing emissions. As we know, is possible to recover thermal energy by combusting municipal solid waste (MSW) for electricity generation and district heating. However, with everincreasing population and rapid growth of industrialization, there is a great demand for fresh water. So, many communities in arid regions could use thermal energy inherent in MSW to desalinate seawater. This paper makes an initial assessment of this concept and concludes that useful quantities of fresh water can be so produced by linking the two processes with significant saving in fuel consumption, determining relevant economic benefits.
Municipal solid waste incinerators are designed to enhance the electrical efficiency obtained by the plant as much as possible. For this reason strong integration between the flue gas cleaning system and the heat recovery system is required. To provide higher electrical efficiencies acid gas neutralization process has the major importance in flue gas cleaning system. At least four technologies are usually applied for acid gas removal: dry neutralization with Ca(OH)2 or with NaHCO3, semi-dry neutralization with milk of lime and wet scrubbing. Nowadays, wet scrubbers are rarely used as a result of the large amount of liquid effluents produced; wet scrubbing technology is often applied as a final treatment after a dry neutralization. Operating conditions of the plant were simulated by using Aspen Plus in order to investigate the influences of four different technologies on the electrical efficiency of the plant. The results of the simulations did not show a great influence of the gas cleaning system on the net electrical efficiency, as the difference between the most advantageous technology (neutralization with NaHCO3) and the worst one, is about 1%.
In Brescia, Italy, heat is delivered to 70% of 200.000 city inhabitants by means of a district heating system, mainly supplied by a waste to energy plant, utilizing the non recyclable fraction of municipal and industrial solid waste (800,000 tons/year, otherwise landfilled), thus saving annually over 150,000 tons of oil equivalent and over 400,000 tons of CO2 emissions.This study shows how the performance of the waste-to-energy cogeneration plant can be improved by optimising the condensation system, with particular focus on the combination of wet and dry cooling systems.The analysis has been carried out using two subsequent steps: in the first one a schematic model of the steam cycle was accomplished in order to acquire a knowledge base about the variables that would be most influential on the performance. In the second step the electric power output for different operating conditions was predicted and optimized in a homemade program. In more details, a thermodynamic analysis of the steam cycle, according to the design operating condition, was performed by means of a commercial code (Thermoflex©) dedicated to power plant modelling. Then the off-design behaviour was investigated by varying not only the ambient conditions but also several parameters connected to the heat rejection rate, like the heat required from district heating and the auxiliaries load. Each of these parameters has been addressed and considered in determining the overall performance of the thermal cycle. After that, a complete prediction of the cycle behaviour was performed by simultaneously varying different operating conditions. Finally, a Matlab© computer code was developed in order to optimize the net electric power as a function of the way in which the condensation is operated. The result is an optimum set of variables allowing the wet and dry cooling system to be regulated in such a way that the maximum power is achieved. The best strategy consists in using the maximum amount of heat rejection in the wet cooling system to reduce the operational cost of the dry one.
Municipal solid waste (MSW) is produced in a substantial amount with minimal fluctuations throughout the year. The analysis of carbon neutrality of MSW on a life cycle basis shows that MSW is about 67% carbon-neutral, suggesting that only 33% of the CO2 emissions from incinerating MSW are of fossil origin. The waste constitutes a “renewable biofuel” energy resource and energy from waste (EfW) can result in a net reduction in CO2 emissions. In this paper, we explore an approach to extracting energy from MSW efficiently – EfW/gas turbine hybrid combined cycles. This approach innovates by delivering better performance with respect to energy efficiency and CO2 mitigation. In the combined cycles, the topping cycle consists of a gas turbine, while the bottoming cycle is a steam cycle where the low quality fuel – waste is utilized. This paper assesses the viability of the hybrid combined cycles and analyses their thermodynamic advantages with the help of computer simulations. It was shown that the combined cycles could offer significantly higher energy conversion efficiency and a practical solution to handling MSW. Also, the potential for a net reduction in CO2 emissions resulting from the hybrid combined cycles was evaluated.
Recently, large numbers of high capacity TVC/MEB (multi-effect thermal vapor compression combined withconventinalmulti effect boiling) desalting units have been built or ordered in the UAE and elsewhere. An in-depth comparison between the predominantly used MSF and the TVC/MEB is conducted in this paper to show the reasons of this trend to used the newly used TVC/MEB units. The TVC/MEB units operate at lower top brine temperature TBT to limit the risk of scale formation and corrosion. This decreases the difference between TBT and last effect (stage) temperature Tn, and this tends toincrease the heat transfer surface area of the TVC/MEB compared to the MSF system. However, the high heat transfer rates in film boiling in TVC/MEB evaporators keep the heat transfer area the same in both systems. Moreover, the TVC/MEB system has more merits copared to the MSF such as: it has better response to the variation of steam supply, less footprint area, less pumping energy, and the ability to operate at different modes than the design.
The criteria as well as the methods and measurements of wind tunnel simulation on wind effects on air-cooled condensers in a power plant were discussed. The parameter of re-circulation was suggested to describe the wind effects on the efficiency of the condenser. The result of practical project models shows that great wind effects of both wind speed and the angle of the incident flow on the efficiency of the condenser. It is recommended that in the initial stage of a new or an extension power plant, which is equipped with an air-cooled system, the wind tunnel simulation is necessary and helpful. Combined with the local wind climate data, a more reasonable, economic and safety schematic design of a power plant could be achieved.
This two-part paper assesses four strategies for energy recovery from municipal solid waste (MSW) by dedicated waste-to-energy (WTE) plants generating electricity through a steam cycle. The feedstock is the residue after materials recovery (MR), assumed to be 35% by weight of the collected MSW. In strategy 1, the MR residue is fed directly to a grate combustor. In strategy 2, the MR residue is first subjected to light mechanical treatment. In strategies 3 and 4, the MR residue is converted into RDF, which is combusted in a fluidized bed combustor. To examine the relevance of scale, we considered a small waste management system (WMS) serving 200,000 people and a large WMS serving 1,200,000 people. A variation of strategy 1 shows the potential of cogeneration with district heating. The assessment is carried out by a Life Cycle Analysis where the electricity generated by the WTE plant displaces electricity generated by fossil fuel-fired steam plants. Part A focuses on mass and energy balances, while Part B focuses on emissions and costs. Results show that treating the MR residue ahead of the WTE plant reduces energy recovery. The largest energy savings are achieved by combusting the MR residue "as is" in large scale plants; with cogeneration, primary energy savings can reach 2.5% of total societal energy use.
Incineration: process and technology
- Hulgaard