Energy Recovery Strategy Research Articles

Energy performance of air-conditioning systems using an indirect evaporative cooling combined with a cooling/reheating treatment

The energetic performance of an integrated energy-recovery system for air-conditioning applications consisting of an indirect evaporative cooling equipment combined with a cooling/reheating unit is analyzed numerically using an in-house-developed computer code. Simulations are performed for a wide variety of operating conditions and main features of the heat exchangers. The minor energy consumption consequent to the energy transfer from outdoor air to saturated indoor air to be exhausted and, subsequently, to supply air to be reheated is compared with that deriving from the adoption of traditional energy recovery strategies, and calculated by introducing a cooling effectiveness parameter. An empirical dimensionless correlation that expresses the cooling effectiveness parameter as a function of the several independent variables considered is also proposed.

Evaluation of EVs energy consumption influencing factors, driving conditions, auxiliaries use, driver's aggressiveness

This paper presents a simulation study dealing with the influence of different factors on the energy consumption of an electric vehicle (EV). Due to the limited quantity of energy embedded in the battery, EVs are very sensitive to parameters which can influence their energy consumption and then can induce huge variations in their actual range. Among all these factors, driving conditions, auxiliaries' impact, driver's aggressiveness and braking energy recovery strategy are to be considered as the main factors influencing the EV energy consumption. The objective of this paper is thus to simulate and quantify the influence of each factor independently. For this, a virtual EV simulator has been created and validated through EVs experiments on a climatic 4WD chassis dyno in the frame of a project sponsored by the French ADEME and with the help of PSA, Renault and Tazzari car manufacturers. This simulator, validated thanks to a limited number of experimental results, has been then used on a very large range of operating conditions and hypotheses to extrapolate experimental results and help the analyses of influencing factors.

PAT Design Strategy for Energy Recovery in Water Distribution Networks by Electrical Regulation

In the management of water distribution networks, large energy savings can be yielded by exploiting the head drop due to the network pressure control strategy, i.e., for leak reductions. Hydropower in small streams is already exploited, but technical solutions combining efficiency and economic convenience are still required. In water distribution networks, an additional design problem comes out from the necessity of ensuring a required head drop under variable operating conditions, i.e., head and discharge variations. Both a hydraulic regulation (HR)—via a series-parallel hydraulic circuit- and an electrical regulation (ER)—via inverter- are feasible solutions. A design procedure for the selection of a production device in a series-parallel hydraulic circuit has been recently proposed. The procedure, named VOS (Variable Operating Strategy), is based on the overall plant efficiency criteria and is applied to a water distribution network where a PAT (pump as a turbine) is used in order to produce energy. In the present paper the VOS design procedure has been extended to the electrical regulation and a comparison between HR and ER efficiency and flexibility within a water distribution network is shown: HR was found more flexible than ER and more efficient. Finally a preliminary economic study has been carried out in order to show the viability of both systems, and a shorter payback period of the electromechanical equipment was found for HR mode.

Integrated Process Modeling of Energy Consumption, Energy Recovery and Nutrient Management Strategies for Wastewater Treatment Plant Retrofits

Integrated Process Modeling of Energy Consumption, Energy Recovery and Nutrient Management Strategies for Wastewater Treatment Plant Retrofits

Off-design analysis of ORC and CO2 power production cycles for low-temperature surplus heat recovery

In process industry large amounts of energy are rejected to the ambient. Recovery of this surplus energy is a wide topic. Among the strategies for energy recovery, production of electricity is very interesting, due to the versatility of this form of energy. For the relatively low temperature heat, which is most commonly encountered for industrial surplus heat, the Organic Rankine Cycle is a well established technology. The transcritical Rankine Cycle recently received special attention due to its performances for energy recovery from low temperature sources. CO2 is a natural candidate as working fluid for this technology. It combines high performance, low cost, low toxicity, is non-flammable and has no environmental impact. This paper focuses on the off-design operation of Rankine cycles and compares the behaviour of transcritical CO2 cycles and an ORC cycle with R-123 as working fluid. The main observation is that the ORC is very sensitive to reduction in available heat, and will with only small changes get droplets in the inlet of the expander. This shows that it is reasonable to operate the ORC with some degrees superheat, to have a buffer. Superheating the outlet 5 to 10 K has only a small effect on the cycle performance. However the gained robustness is also relatively small. With small increments in the available heat source, the CO2 cycle also seem to have a marginally better response without control of the process, which indicates that it is more robust and less in need of detailed control.

Research on Control System of Hybrid Regenerative Braking and Low Speed Energy Recovery

The energy utilization is crucial for electric or hybrid vehicles to solve the problem of braking energy recovery, especially of low speed energy recovery. In this paper, the energy transform model of electric vehicle in braking state is analyzed, and the half bridge control main circuit was selected. The energy recovery strategies and methods on the breaking process of low speed were researched. The concrete realization of parameters decision and system control was given. The results show that the energy recovery strategy and electric vehicle model can improve the energy transform efficiency in low speed state.

Material and energy recovery in integrated waste management systems. An evaluation based on life cycle assessment

This paper reports the environmental results, integrated with those arising from mass and energy balances, of a research project on the comparative analysis of strategies for material and energy recovery from waste, funded by the Italian Ministry of Education, University and Research. The project, involving the cooperation of five University research groups, was devoted to the optimisation of material and energy recovery activities within integrated municipal solid waste (MSW) management systems. Four scenarios of separate collection (overall value of 35%, 50% without the collection of food waste, 50% including the collection of food waste, 65%) were defined for the implementation of energetic, environmental and economic balances. Two sizes of integrated MSW management system (IWMS) were considered: a metropolitan area, with a gross MSW production of 750,000 t/year and an average province, with a gross MSW production of 150,000 t/year. The environmental analysis was conducted using Life Cycle Assessment methodology (LCA), for both material and energy recovery activities. In order to avoid allocation we have used the technique of the expansion of the system boundaries. This means taking into consideration the impact on the environment related to the waste management activities in comparison with the avoided impacts related to the saving of raw materials and primary energy. Under the hypotheses of the study, both for the large and for the small IWMS, the energetic and environmental benefits are higher than the energetic and environmental impacts for all the scenarios analysed in terms of all the indicators considered: the scenario with 50% separate collection in a drop-off scheme excluding food waste shows the most promising perspectives, mainly arising from the highest collection (and recycling) of all the packaging materials, which is the activity giving the biggest energetic and environmental benefits. Main conclusions of the study in the general field of the assessment of the environmental performance of any integrated waste management scheme address the importance of properly defining, beyond the design value assumed for the separate collection as a whole, also the yields of each material recovered; particular significance is finally related to the amount of residues deriving from material recovery activities, resulting on average in the order of 20% of the collected materials.

LCA of local strategies for energy recovery from waste in England, applied to a large municipal flow

An intense waste management (WM) planning activity is currently undergoing in England to build the infrastructure necessary to treat residual wastes, increase recycling levels and the recovery of energy from waste. From the analyses of local WM strategic and planning documents we have identified the emerging of three different energy recovery strategies: established combustion of residual waste; pre-treatment of residual waste and energy recovery from Solid Recovered Fuel in a dedicated plant, usually assumed to be a gasifier; pre-treatment of residual waste and reliance on the market to accept the ‘fuel from waste’ so produced. Each energy recovery strategy will result in a different solution in terms of the technology selected; moreover, on the basis of the favoured solution, the total number, scale and location of thermal treatment plants built in England will dramatically change. To support the evaluation and comparison of these three WM strategy in terms of global environmental impacts, energy recovery possibilities and performance with respect to changing ‘fuel from waste’ market conditions, the LCA comparison of eight alternative WM scenarios for a real case study dealing with a large flow of municipal wastes was performed with the modelling tool WRATE. The large flow of waste modelled allowed to formulate and assess realistic alternative WM scenarios and to design infrastructural systems which are likely to correspond to those submitted for approval to the local authorities. The results show that all alternative scenarios contribute to saving abiotic resources and reducing global warming potential. Particularly relevant to the current English debate, the performance of a scenario was shown to depend not from the thermal treatment technology but from a combination of parameters, among which most relevant are the efficiency of energy recovery processes (both electricity and heat) and the calorific value of residual waste and pre-treated material. The contribution and relative importance of recycling and treatment/recovery processes change with the impact category. The lack of reprocessing plants in the area of the case study has shown the relevance of transport distances for recyclate material in reducing the efficiency of a WM system. Highly relevant to the current English WM infrastructural debate, these results for the first time highlight the risk of a significant reduction in the energy that could be recovered by local WM strategies relying only on the market to dispose of the ‘fuel from waste’ in a non dedicated plant in the case that the SRF had to be sent to landfill for lack of treatment capacity.

Energy balance of dark anaerobic fermentation as a tool for sustainability analysis

A process aimed at producing energy needs to produce more energy than the energy necessary to run the process itself in order to be energetically sustainable. In this paper, an energy balance of a batch anaerobic bioreactor has been defined and calculated, both for different operative conditions and for different reactor scales, in order to analyze the sustainability of hydrogen production through dark anaerobic fermentation. Energy production in the form of hydrogen and methane, energy to warm up the fermentation broth, energy loss during fermentation and energy for mixing and pumping have been considered in the energy balance. Experimental data and literature data for mesophilic microorganism consortia have been used to calculate the energy balance. The energy production of a mesophilic microorganism consortium in a batch reactor has been studied in the 16–50 °C temperature range. The hydrogen batch dark fermentation resulted to only have a positive net production of energy over a minimal reactor dimension in summer conditions with an energy recovery strategy. The best working temperature resulted to be 20 °C with 20% of available energy. Hydrogen batch dark fermentation may be coupled with other processes to obtain a positive net energy by recovering energy from the end products of hydrogen dark fermentation. As an example, methane fermentation has been considered to energetically valorize the end products of hydrogen fermentation. The combined process resulted in a positive net energy over the whole range of tested reactor dimension with 45–90% of available energy.

Energy Recovery from Wastewater Treatment Plants in the United States: A Case Study of the Energy-Water Nexus

This manuscript uses data from the U.S. Environmental Protection Agency to analyze the potential for energy recovery from wastewater treatment plants via anaerobic digestion with biogas utilization and biosolids incineration with electricity generation. These energy recovery strategies could help offset the electricity consumption of the wastewater sector and represent possible areas for sustainable energy policy implementation. We estimate that anaerobic digestion could save 628 to 4,940 million kWh annually in the United States. In Texas, anaerobic digestion could save 40.2 to 460 million kWh annually and biosolids incineration could save 51.9 to 1,030 million kWh annually.

Energy use and recovery strategies within wastewater treatment and sludge handling at pulp and paper mills

This paper presents an inclusive approach with focus on energy use and recovery in wastewater management, including wastewater treatment (WWT) and sludge handling. Process data from three Swedish mills and a mathematical model were used to evaluate seven sludge handling strategies. The results indicate that excess energy use in WWT processes counters the potential energy recovery in the sludge handling systems. Energy use in WWT processes is recommended to aim for sufficient effluent treatment, not for sludge reduction. Increased secondary sludge production is favourable from an energy point of view provided it is used as a substrate for heat, biogas or electricity production.

Energy recovery from municipal waste: A case study for a middle-sized Italian district

This paper reports the main outcome of research to compare and assess the merits of alternative strategies for energy recovery from municipal solid waste downstream of material recovery for an Italian province. Strategies analysed are based on well-established combustion technologies available at the commercial scale in the Italian market in comparison with an innovative but not yet proven option of refuse derived fuel gasification and subsequent co-combustion of syngas in a combined cycle power plant. The comparison is made using mass and energy balances, environmental assessment and economic analysis. From an energetic point of view, the best strategy is the one based on the refuse derived fuel gasification, which, on the contrary, does not show interesting environmental results. In this perspective, the best results are from strategies based on a dedicated plant, particularly when unsorted residual waste collected downstream of material recovery is used. Finally, from an economic point of view, the strategy with gasification allows the highest revenues from the sale of energy.

DEVELOPMENT OF POWERTRAIN CONTROLLER FOR MILD HYBRID ELECTRIC VEHICLE

Based on the detailed analysis of power demand of driver, engine operating area optimization and brake energy recovery strategy, an energy management strategy of hybrid electric vehicle(HEV), together with the hardware and software system of powertrain controller, is developed to analyze specific mild HEV. Through the hardware-in-the-loop test and real vehicle calibration test, the functions of powertrain controller are validated. The test results show that by using this power-train controller, HEV can achieve better control performance, with not only 16.9% fuel consumption reduced but also lower emissions than Euro III.

Energy performance of independent air dehumidification systems with energy recovery measures

Independent air dehumidification provides an attractive alternative to traditional coupled air dehumidification with reduced energy use, better humidity control and indoor air quality. According to this concept, latent load is treated by an independent system and the sensible load is treated by chilled-ceiling panels. In this work, four independent air dehumidification systems with energy recovery strategies are proposed. They are as follows: system 1, mechanical dehumidification with heat pump; system 2, mechanical dehumidification with sensible heat exchanger; system 3, mechanical dehumidification with membrane-based total heat exchanger; and system 4: a heat pump incorporating an active desiccant wheel and evaporative cooler. They are compared with a mechanical dehumidification system with no heat recovery. Hour-by-hour energy analysis is performed on the systems proposed. The results show that the system of mechanical dehumidification with membrane total heat recovery (system 3) consumes the least primary energy. However, since, the systems employ energy recovery measures, the energy savings for the four systems are in the same order, around 4.40×10 6 kJ per person.

Alternative strategies for energy recovery from municipal solid waste: Part B: Emission and cost estimates

This two-part paper assesses four strategies for energy recovery from Municipal Solid Waste (MSW) by dedicated Waste-To-Energy (WTE) plants. In strategy 1, the residue of Material Recovery (MR) is fed directly to a grate combustor, while in strategy 2 the grate combustor comes downstream of light mechanical treatment. In strategies 3 and 4, the MR residue is converted into Refuse Derived Fuel (RDF), in a fluidized cumbuster bed. The results of Part A, devoted to mass and energy balances, clearly show that pre-treating the MR residue in order to increase the heating value of the feedstock fed to the WTE plant has marginal effects on the energy efficiency of the WTE plant. When considering the efficiency of the whole strategy of waste management, the energy balances show that the more thorough the pre-treatment, the smaller the amount of energy recovered per unit of MR residue. Starting from the heat/mass balances illustrated in Part A, Part B examines the environmental impacts and economics of the various strategies by means of a Life Cycle Assessment (LCA). Results show that treating the MR residues ahead of the WTE plant does not provide environmental or economic benefits. RDF production worsens almost all impact indicators because it reduces net electricity production and thus the displacement of power plant emissions; it also increases costs, because the benefits of improving the quality of the material fed to the WTE plant do not compensate the cost of such improvement.

Alternative strategies for energy recovery from municipal solid waste: Part A: Mass and energy balances

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.

Minimizing RO energy consumption under variable conditions of operation

Specific energy consumption (SEC) for reverse osmosis (RO) desalination systems has usually been estimated using simplistic analyses that consider an average duty point of operation for a certain plant. Amore sophisticated and comprehensive approach that accounts for the effects of variable parameters of operation on SEC was recently described, introducing the concept of the “hydraulic envelope”. Variable parameters include flow rates at variable recoveries, feed temperature and salinity with their resulting pressure requirements, pressure losses caused by membrane fouling, and pressure losses caused by system controls such as feed throttle valves. This paper will explore in greater detail various energy recovery strategies under variable parameters of operation. Particular attention will be paid to a recently developed, innovative energy recovery configuration that uses a motor-driven booster pump coupled to a Pelton turbine, the so-called ‘PROP’, instead of a single-component high-pressure feed pump. This new energy recovery concept can not only be applied to single-stage RO plants, but also as a highly effective interstage booster for dual-stage Brine Conversion Systems (BCS). The concept has been submitted for patenting. Results of the analysis suggest that the key issue for minimizing SEC is to control the plant over the entire width of the operational range without creating throttling losses. This can only be achieved by using hydraulic equipment that allows for feed pressure adjustment at minimum energy dissipation and eliminates the need for throttling valves. It is shown that the newly developed ‘PROP’ concept provides minimum SEC over the entire range of the hydraulic envelope of a plant, while at the same time allowing for maximum hydraulic dynamic control efficiency of the RO unit. In addition, the ‘PROP’ offers a significant savings potential in terms of capital costs compared to conventional energy recovery strategies.