Electrical Energy Recovery Research Articles

Evaluation of methane generation rate and energy recovery potential of municipal solid waste using anaerobic digestion and landfilling: A case study of Dhanbad, India.

In this study, two most common biological waste to energy conversion techniques have been analysed and compared on the basis of methane generation and energy recovery potential. The biogas generation potential has been estimated using anaerobic co-digestion experiment. The main substrate used for this study was food waste, while cow dung and anaerobic digester sludge were used as co-digestion substrates. Food waste was used because of its maximum composition (36% of total wastes) in the study area (Dhanbad city, India) with high biogas generation potential. Cow dung acted as a natural buffer, while anaerobic digester sludge was a source of active inoculum. Based on the maximum biogas yield of 402 mL g-1 VS and annual food waste generation rate in the study area, the energy recovery potential using anaerobic digestion was estimated to be 6.59 × 106 kWh year-1. Presently, the wastes in the mixed form are being dumped on a large abandoned land with an approximate area of 93 ha in the outskirts of Dhanbad city in an uncontrolled manner. The annual landfill gas generation from the existing landfill has been estimated using Landfill Gas Emissions Model (LandGEM) based on the waste characteristics, anticipated landfill life and other region-specific parameters of the present study area. The maximum electrical energy recovery potential of 44.62 × 105 kWh from landfill gas has been estimated for the year 2041. Although, the results are based on the waste generation and characteristics of Dhanbad city, the comparison methodology can be applied to other cities.

MnO2@MXene/Carbon Cloth as an Anode for Microbial Fuel Cells

AbstractHydrophobicity of carbon‐based anodes hinders bacterial adhesion and biofilm formation. Herein, MnO2@MXene coated carbon cloth (CC) was designed as an anode for microbial fuel cells (MFCs). The anode integrated the hydrophilicity and conductivity of MXene with the biocompatibility of MnO2. This unique structure promoted bacterial colonisation and biofilm formation on the anode surface. MnO2@MXene enhanced electricity generation performance and wastewater degradation efficiency owing to the synergistic effect of MXene and MnO2. The MFC achieved a short startup time and an effective extracellular electron transfer process. The MnO2@MXene/CC anode ensured a higher power density and efficient decolourisation in MFCs. The MFC device achieved a high maximum power density of 746.3 mW/m2 and a Congo red decolourisation efficiency of 87.6 % at 48 h. This work offers a potential strategy for the effective degradation of wastewater and recovery of electrical energy.

Investigation of a low-pressure flash evaporation desalination system powered by ocean thermal energy

To alleviate the consequences of the freshwater crisis and fully utilize marine resources in tropical coastal areas, this study presents a low-pressure flash evaporation desalination system driven by ocean thermal energy (OTE). Through gravity and atmospheric pressure, a natural vacuum can be formed in the evaporator, which achieves flash evaporation for warm surface seawater. Then, the vapour is condensed into freshwater via an inner coil condenser with flowing cold deep seawater. Using a water pump to fill the evaporator intermittently, the non-condensable gas accumulated in the desalination process can be thoroughly discharged. Based on the process of mass and heat transfer inside the system, a thermodynamic model was developed. Several performance evaluation indices, including water productivity, specific electrical energy consumption (SEEC) and recovery ratio (RR), were experimentally investigated under different parameters. The results indicate that productivity and SEEC are higher with increasing seawater flow rate and decreasing deep seawater temperature. Under a warm seawater temperature of 30 °C and a deep cold seawater temperature of 8 °C, the system obtained a maximum water productivity of 5.3 kg/h, and the corresponding SEEC and RR were 0.126 kWh/kg and 1.5%, respectively. Finally, compared with solar-driven desalination systems, the proposed OTE desalination system requires less energy consumption, which shows an attractive application prospect.

Degradation and utilization of EPS from excessive activated sludge by interaction of electrogenesis and light stimulation

Sticky and gel-like extracellular polymeric substances (EPS) could provide the protective shielding and prevent the microbial cellrupture and lysis as well as increase the difficulty of excessive activated sludge (EAS) biodegradation. Microbial fuel cells (MFCs) are able to accelerate the degradation of EPS and gain electric energy recovery from wastewater simultaneously. In order to discover the role of light stimulation on MFC performance, four reactors were operated in dark (SD), in LED light (SL), in electrogenesis (ED) and in combination of electrogenesis and light (EL), respectively. EPS characteristic, electrochemical performance and anodic microbial community structures were investigated and compared. The results showed that single light stimulation distinctly improved the total EPS especially polysaccharides content in soluble EPS, and Pseudomonas (31.85% relative abundance) as well as Acinetobacter (10.2% relative abundance) became the dominant genera. Single electrogenesis mainly promoted degradation of negatively charged proteins, which was further proved by the enrichment of typical proteolytic and amino acids fermented bacterial genera like Proteiniphilum and Cloacibacillus. Furthermore, the electrochemical activated Petrimonas and syntrophic Syntrophomonas occupied the dominant position indicating the existence of interspecific electron transfer. Moreover, the predominance of Acinetobacter (44.2% relative abundance) and Escherichia/shigella (7.09% relative abundance) in EL reactor implied the synergetic improvement of electrogenesis and light stimulation. In the interaction effect, light stimulation optimized the electricity generation and proteins degradation of MFC.

Bioelectrochemical assisted landfill technology for the stabilization and valorization of food waste anaerobic digestate

Anaerobic digestion provides an important approach for food waste treatment and valorization, yet a considerable amount of digestate is produced. The appropriate management and utilization of food waste anaerobic digestate is highly desirable for solving both environmental and economic concerns currently. This work innovatively develops a natural potential difference assisted landfill technology (shown as BESAL) for food waste digestate treatment and energy recovery. The results demonstrate the electrochemical assistant accelerates the stabilization of digestate, provides extra 14.89% of organic matter removal and 20.92 mW/m2 of electrical energy recovery over conventional treatment. BESAL promotes the removal of soluble matters in digestate extraction, prevents 13.07 mg/g ammonium-N and 32.87% of total VFAs from accumulation. BESAL also performs gene level stabilization by inhibiting/eliminating microbial and pathogenic gene to ensure the biosafety in its product. Integrated landfill with bioelectrochemical assistance provides a promising option for organic waste stabilization and valorization.

Direct recovery of electrical energy from municipal wastewater by microbial fuel cells with Low voltage booster rectifier (LVBR)

Direct recovery of electrical energy from municipal wastewater by microbial fuel cells with Low voltage booster rectifier (LVBR)

Energy Analysis of Concentrated Photovoltaic/Thermal Panels with Nanofluids

In this study, a prototype system was established for location heating application and electricity generation through utilizing two concentrated photovoltaic thermal panels (CPV/T) possessing flat surface receivers connected in series with each other. The purpose of the system is to supply the heating needs of a room in winter season and to meet the electricity requirement of the equipment used in this system. In the analysis of the installed system, different refrigerants (10% mono propylene glycol + 90% water and 0.5% Al2O3-water nanofluid) were tested at three different flow rates (0.4 m3/h, 0.5 m3/h, 0.6 m3/h). Throughout the experiments, the fan-coil air outlet temperature used to heat the room was adjusted to 35 °C with an inverter and a process control device. The results attained from the experiments carried out using different fluids throughout different months and days (April-May) have demonstrated that the thermal and electrical efficiencies of the system are found to be in good agreement with each other when evaluated in terms of the fluids utilized. The highest electrical energy recovery was found as 268 W at 0.6 m3/h flow rate for propylene glycol-water mixture and 194 W at 0.5 m3/h flow rate for nanomixture. The total thermal energy efficiency for the system using different fluids was found to be around 22%. The total thermal energy gain of the system was also calculated as 2312 W at 0.6 m3/h for the propylene glycol mixture and 2041 W at 0.5 m3/h for the nanomixture.

Investigations on Biogas Recovery from Anaerobic Digestion of Raw Sludge and Its Mixture with Agri-Food Wastes: Application to the Largest Industrial Estate in Oman

This work is intended to evaluate the technical, environmental, and economic feasibility of converting the sludge produced at an industrial estate’s wastewater treatment plant (WWTP) in Oman into energy through anaerobic digestion (AD). In this study, three different scenarios were analyzed. They concerned the digestion of the total amount of the produced sludge alone (240 m3 day−1) (scenario 1), and its co-digestion with wet agri-food wastes (AFW) at rates of two tonnes day−1 (scenario 2) and ten tonnes day−1 (scenario 3). Based on the analyses of sludge samples, an intensive literature review regarding sludge and AFW Physico-chemical and energetic characteristics and the use of the cost–benefit analysis (CBA) approach, it was found that, for the overall duration of the project (20 years), the AD of the sludge alone (scenario 1) permitted the production of 43.9 GWh of electricity, the reduction of greenhouse gas (GHG) emissions (more than 37,000 tonnes equivalent CO2 (TCO2)) and exhibited positive net present value (NPV: $393,483) and an internal return rate (IRR) of 19.4%. Co-digesting sludge with AFW significantly increased all of these key performance indicators. For instance, scenario 3 results in the recovery of electrical energy of 82.2 GWh and avoids the emission of 70,602 tCO2. Moreover, a higher NPV and IRR of $851,876 and 21.8%, respectively, and a payback period (PBP) of only seven years were calculated. The sensitivity analysis revealed that a decrease in total expenses by 15% results in a significant increase of the NPV and the IRR to $1,418,704 and 33.9%, respectively, for scenario 3. Considering a pessimistic assumption (an increase of the total expenses by 15%), all studied scenarios remain attractive. For instance, for scenario 3, the NPV, IRR, and PBP were evaluated to $285,047, 13.5%, and 9 years, respectively. Therefore, the co-digestion of sludge with agri-food wastes for energy recovery purposes could be considered a promising, eco-friendly, and economically viable approach in the Omani industrial estates.

A Comparative Study of Energy Consumption and Recovery of Autonomous Fuel-Cell Hydrogen–Electric Vehicles Using Different Powertrains Based on Regenerative Braking and Electronic Stability Control System

Today, with the increasing transition to electric vehicles (EVs), the design of highly energy-efficient vehicle architectures has taken precedence for many car manufacturers. To this end, the energy consumption and recovery rates of different powertrain vehicle architectures need to be investigated comprehensively. In this study, six different powertrain architectures—four independent in-wheel motors with regenerative electronic stability control (RESC) and without an RESC, one-stage gear (1G) transmission, two-stage gear (2G) transmission, continuously variable transmission (CVT) and downsized electric motor with CVT—were mathematically modeled and analyzed under real road conditions using nonlinear models of an autonomous hydrogen fuel-cell electric vehicle (HFCEV). The aims of this paper were twofold: first, to compare the energy consumption performance of powertrain architectures by analyzing the effects of the regenerative electronic stability control (RESC) system, and secondly, to investigate the usability of a downsized electrical motor for an HFCEV. For this purpose, all the numerical simulations were conducted for the well-known FTP75 and NEDC urban drive cycles. The obtained results demonstrate that the minimum energy consumption can be achieved by a 2G-based powertrain using the same motor; however, when an RESC system is used, the energy recovery/consumption rate can be increased. Moreover, the results of the article show that it is possible to use a downsized electric motor due to the CVT, and this powertrain significantly reduces the energy consumption of the HFCEV as compared to all the other systems. The results of this paper present highly significant implications for automotive manufacturers for designing and developing a cleaner electrical vehicle energy consumption and recovery system.

Energy recovery for hybrid hydraulic excavators: flywheel-based solutions

Hybridization is an effective method to reduce fuel consumption and emissions of toxic pollutants generated by hydraulic excavators (HEs). This paper first reviews various hybrid HEs architectures with electrical, hydraulic, or flywheel-based energy recovery systems (ERSs). Flywheel-based ERS is not widely used in HEs but has achieved widespread concern in the automotive field. In light of this, the differences between HEs and automobiles are discussed to highlight the potential of flywheel-based ERSs in HEs. Then, the paper compares corresponding energy storage devices in these ERSs from many aspects. The comparison shows that flywheels display many advantages over other energy storage devices. Meanwhile, the drawbacks of flywheels are discussed in detail, indicating that the drawbacks can be offset by other advantages. The results show that the flywheel-based ERS is competitive with the electrical and hydraulic competitors for HEs. Finally, the challenges to the flywheel technology and future work are presented.

Time-Optimal Low-Level Control and Gearshift Strategies for the Formula 1 Hybrid Electric Powertrain

Today, Formula 1 race cars are equipped with complex hybrid electric powertrains that display significant cross-couplings between the internal combustion engine and the electrical energy recovery system. Given that a large number of these phenomena are strongly engine-speed dependent, not only the energy management but also the gearshift strategy significantly influence the achievable lap time for a given fuel and battery budget. Therefore, in this paper we propose a detailed low-level mathematical model of the Formula 1 powertrain suited for numerical optimization, and solve the time-optimal control problem in a computationally efficient way. First, we describe the powertrain dynamics by means of first principle modeling approaches and neural network techniques, with a strong focus on the low-level actuation of the internal combustion engine and its coupling with the energy recovery system. Next, we relax the integer decision variable related to the gearbox by applying outer convexification and solve the resulting optimization problem. Our results show that the energy consumption budgets not only influence the fuel mass flow and electric boosting operation, but also the gearshift strategy and the low-level engine operation, e.g., the intake manifold pressure evolution, the air-to-fuel ratio or the turbine waste-gate position.

Considerations to Approach Membrane Biofouling in Microbial Fuel Cells

Among bioelectrochemical systems, those referred to as microbial fuel cells (MFCs) are widely implemented for wastewater management and simultaneous recovery of electrical energy. MFCs are fundamentally assisted by bacterial populations, mostly mixed cultures to be more exact that, after oxidizing the substrate, are capable of facilitating the passage of electrons to an electron acceptor, usually the anode. However, certain undesired bacterial strains often colonize not only the electrode but the membrane separator over time and cause severe biofouling. The membrane is an architectural element of many MFCs and determines the efficiency of the system. In this paper, this issue is overviewed briefly and some considerations concerning how to approach the problem are presented.

Time-optimal gearshift and energy management strategies for a hybrid electric race car

Modern Formula 1 race cars are hybrid electric vehicles equipped with an internal combustion engine and an electric energy recovery system. In order to achieve the fastest possible lap time, the components’ operation must be carefully optimized, and the energy management must account for the impact of the gearshift strategy on the overall performance. This paper presents an algorithm to calculate the time-optimal energy management and gearshift strategies for the Formula 1 race car. First, we leverage a convex modeling approach to formulate a mathematical description of the powertrain including the gearbox, preserving convexity for a given engine speed trajectory. Second, we devise a computationally efficient algorithm to compute the energy management and gearshift strategies for minimum lap time, under consideration of given fuel and battery consumption targets. In particular, we combine convex optimization, dynamic programming and Pontryagin’s minimum principle in an iterative scheme to solve the arising mixed-integer optimization problem. We showcase our algorithm with a case study for the Bahrain racetrack, underlining the interactions between energy management and gear selection. Finally, we use our approach as a benchmark to evaluate the sub-optimality of a heuristic gearshift rule. Our results show that using an optimized engine speed threshold for upshifts can yield close-to-optimal results. However, already deviations smaller than 4% from the best possible threshold can increase lap time by more than 100ms, highlighting the importance of jointly optimizing energy management and gearshift strategies.

Bio-Electrochemical Enhancement of Hydrogen and Methane Production in a Combined Anaerobic Digester (AD) and Microbial Electrolysis Cell (MEC) from Dairy Manure

Anaerobic digestion (AD) is a biological-based technology that generates methane-enriched biogas. A microbial electrolysis cell (MEC) uses electricity to initiate bacterial oxidization of organic matter to produce hydrogen. This study determined the effect of energy production and waste treatment when using dairy manure in a combined AD and MEC (AD-MEC) system compared to AD without MEC (AD-only). In the AD-MEC system, a single chamber MEC (150 mL) was placed inside a 10 L digester on day 20 of the digestion process and run for 272 h (11 days) to determine residual treatment and energy capacity with an MEC included. Cumulative H2 and CH4 production in the AD-MEC (2.43 L H2 and 23.6 L CH4) was higher than AD-only (0.00 L H2 and 10.9 L CH4). Hydrogen concentration during the first 24 h of MEC introduction constituted 20% of the produced biogas, after which time the H2 decreased as the CH4 concentration increased from 50% to 63%. The efficiency of electrical energy recovery (ηE) in the MEC was 73% (ηE min.) to 324% (ηE max.), with an average increase of 170% in total energy compared to AD-only. Chemical oxygen demand (COD) removal was higher in the AD-MEC (7.09 kJ/g COD removed) system compared to AD-only (6.19 kJ/g COD removed). This study showed that adding an MEC during the digestion process could increase overall energy production and organic removal from dairy manure.

Integrated biorefinery routes of biohydrogen: Possible utilization of acidogenic fermentative effluent

Biohydrogen production and integration possibilities are vital towards hydrogen economy and sustainability of the environment. Acidogenic fermentation is acquiring great interest and it is one of the prime pathways to produce biohydrogen and short chain carboxylic acids. In addition to hydrogen recovery, simultaneously nearly 60 percent of the organics may get converted to ethanol, 1,3propanediol and organic acids. Besides, these organics (fermentative effluents) can be used indirectly as a raw material for the generation of value- added products such as biolipid, polyhydroxyalkanoates, excess hydrogen, methane and electrical energy recovery. In this regard, this review has been assessed as a valuable biorefinery for biofuel and value- added products recovery. The biorefinery can be used to minimize entire cost of the approach by obtaining extra profits.

Comparative assessment of single-stage and two-stage anaerobic digestion for biogas production from high moisture municipal solid waste.

BackgroundAnaerobic digestion (AD) is a suitable process for treating high moisture MSW with biogas and biofertilizer production. However, the low stability of AD performance and low methane production results from high moisture MSW due to the fast acidify of carbohydrate fermentation. The effects of organic loading and incineration fly ash addition as a pH adjustment on methane production from high moisture MSW in the single-stage AD and two-stage AD processes were investigated.ResultsSuitable initial organic loading of the single-stage AD process was 17 gVS L−1 at incineration fly ash (IFA) addition of 0.5% with methane yield of 287 mL CH4 g−1 VS. Suitable initial organic loading of the two-stage AD process was 43 gVS L−1 at IFA addition of 1% with hydrogen and methane yield of 47.4 ml H2 g−1 VS and 363 mL CH4 g−1 VS, respectively. The highest hydrogen and methane production of 8.7 m3 H2 ton−1 of high moisture MSW and 66.6 m3 CH4 ton−1 of high moisture MSW was achieved at organic loading of 43 gVS L−1 at IFA addition of 1% by two-stage AD process. Biogas production by the two-stage AD process enabled 18.5% higher energy recovery than single-stage AD. The 1% addition of IFA into high moisture MSW was useful for controlling pH of the two-stage AD process with enhanced biogas production between 87–92% when compared to without IFA addition. Electricity production and energy recovery from MSW using the coupled incineration with biogas production by two-stage AD process were 9,874 MJ ton−1 MSW and 89%, respectively.ConclusionsThe two-stage AD process with IFA addition for pH adjustment could improve biogas production from high moisture MSW, as well as reduce lag phase and enhance biodegradability efficiency. The coupled incineration process with biogas production using the two-stage AD process was suitable for the management of MSW with low area requirement, low greenhouse gas emissions, and high energy recovery.

Optimal low-level control strategies for a high-performance hybrid electric power unit

In this paper we present models and optimization algorithms to compute the optimal low-level control strategies for hybrid electric powertrains. Specifically, we study the minimum-fuel operation of a turbocharged internal combustion engine coupled to an electrical energy recovery system, consisting of a battery and two motors connected to the turbocharger and to the wheels, respectively. First, we combine physics-based modeling approaches with neural networks to identify a piecewise affine model of the power unit accounting for the internal dynamics of the engine, and formulate the minimum-fuel control problem for a given driving cycle. Second, we parse the control problem to a mixed-integer linear program that can be solved with off-the-shelf optimization algorithms that guarantee global optimality of the solution. Finally, we validate our model against a high fidelity nonlinear simulator and showcase the presented framework with a case-study for racing applications. Our results show that cylinder deactivation and turbocharger electrification can decrease fuel consumption up to 4% and 8%, respectively.

Regenerative braking as a way to recover lost energy in hybrid vehicles

Very rapid development of the automotive industry forces designers to implement new solutions. One of them is the construction of braking systems, which can enable the recovery of part of the energy lost during the braking process in hybrid vehicles. The article presents the basic types of hybrid drives currently used in motor vehicles. The principle of operation of the mechanical and electrical energy recovery system had been discussed, and the vehicles in which such solutions had been applied were indicated.

Energy recovery in oil refineries by means of a Hydraulic Power Recovery Turbine (HPRT) handling viscous liquids

Chemical plants like oil refineries involve energy intensive processes. Several energy efficiency interventions are being performed in oil refineries to meet the latest emission targets, but few of them are related to the energy recovery from process liquids. In this paper, an energy recovery study of an Italian oil refinery is presented: specifically, a Hydraulic Power Recovery Turbine (HPRT), coupled with the shaft of the feed pump used in the same process, is used to replace a Pressure Reducing Valve (PRV). The machine is installed in the H2S removal process and it exploits the Selexol® solvent. A new model that predicts the Best Efficiency Point (BEP) of the HPRT in turbine mode when handling liquids different from water is discussed and validated through operational BEP data. The HPRT supplies 349.3 kW to the feed pump, leading to a yearly electric energy recovery of 2966 MWh and a maximum PayBack Period (PBP) close to 9 years considering the installation, the Carbon Dioxide Equivalent (CDE) allowances and both operational and maintenance costs. The obtained PBP is quite high, but the installation costs would be fairly lower if the HPRT is already considered in the design phase of the chemical process.

An electro-mechanical braking energy recovery system based on coil springs for energy saving applications in electric vehicles

Regenerative braking system is a promising energy recovery mechanism to achieve energy saving in EVs (electric vehicles). This paper focuses on a novel mechanical and electrical dual-pathway braking energy recovery system (BERS) based on coil springs for energy saving applications in EVs. With the aims of maximizing energy recovery efficiency, mechanical and electrical recovery strategies are respectively employed under two different brake situations of inching braking and emergency braking. This system mainly consists of three parts, including the mechanical module, electrical module and control module. The mechanical module utilizes coil springs to store the kinetic energy in the form of elastic potential energy which can be utilized to provide a part of the starting torque for EVs. The electrical module enables recovery of the braking energy into the vehicle battery. The control module controls the mechanical module and the electrical module to work coordinately to select an appropriate energy recovery pathway under different braking modes. A full-size prototype, manufactured and based on this design, is introduced. Simulations and experiments of the proposed regenerative braking system are conducted to verify the system. Auxiliary starting torque of 12.7 N m, maximum voltage of 3.5 V and total energy recovery efficiencies of 0.53 can be obtained, verifying that the proposed braking energy recovery system is effective and beneficial for vehicle energy savings.