Energy Recovery Performance Research Articles

Geographic distribution of net-zero energy wastewater treatment in China

In China, significant differences in climatic conditions, economic development levels, treatment processes used, and population density inevitably lead to regional patterns in the energy recovery and consumption of wastewater treatment plants (WWTPs). However, research is still lacking on characteristics of WWTPs in different regions and how potential patterns affect the energy self-sufficiency of WWTPs in China. In this study, the geographic distribution of the energy self-sufficiency of municipal wastewater treatment in China is investigated based on a net-zero energy (NZE) model. The results indicated that only 19% of the investigated WWTPs could generate enough energy to offset their energy consumption under their existing operating conditions. The maximum self-sufficiency rate was 186.43% among all of the investigated WWTPs in eastern China. Therefore, their current wastewater treatment operation strategies are not conducive to energy recovery. However, 30% of the investigated WWTPs could realize 100% energy self-sufficiency by adjusting their metabolic substrate allocation. There is a higher probability of achieving the NZE status in eastern and northeastern China due to more effective operations, higher chemical oxygen demand (COD) removals, and higher economic levels. A higher energy consumption and worse energy recovery performance lead to a low probability of achieving NZE in western China. However, in western China, there is a great potential for improving the energy self-sufficiency of the WWTPs by regulating their metabolic material allocations. These findings provide a nationwide perspective on energy-saving and emission reduction measures for WWTPs and facilitate the attainment of energy neutralization in the WWTPs in China.

Numerical Investigation into the Gas Production from Hydrate Deposit under Various Thermal Stimulation Modes in a Multi-Well System in Qilian Mountain.

The primary objective of this study was to investigate the energy recovery performance of the permafrost hydrate deposit in the Qilian Mountain at site DK-2 using depressurization combined with thermal injection by the approach of numerical simulation. A novel multi-well system with five horizontal wells was applied for large-scale hydrate mining. The external heat is provided by means of water injection, wellbore heating, or the combinations of them through the central horizontal well, while the fluids are extracted outside from the other four production wells under constant depressurization conditions. The injected water can carry the heat into the hydrate deposit with a faster rate by thermal convection regime, while it also raises the local pressure obviously, which results in a strong prohibition effect on hydrate decomposition in the region close to the central well. The water production rate is always controllable when using the multi-well system. No gas seepage is observed in the reservoir due to the resistance of the undissociated hydrate. Compared with hot water injection, the electric heating combined with normal temperature water flooding basically shows the same promotion effect on gas recovery. Although the hydrate regeneration is more severe in the case of pure electric heating, the external heat can be more efficiently assimilated by gas hydrate, and the efficiency of gas production is best compared with the cases involving water injection. Thus, pure wellbore heating without water injection would be more suitable for hydrate development in deposits characterized by low-permeability conditions.

Study on Energy Recovery Performance of Linear Active Heave Compensation System

In order to verify the feasibility of the energy recovery of the linear active heave compensation device under the descent compensation condition, the author established a schematic diagram of the hydraulic system based on the heave compensation principle, performed a simulation analysis of the hydraulic system model in a cycle, analysed energy loss of the system under specific sea conditions. Therefore, it is concluded that the gravity potential energy of the load under the descent compensation condition has great potential for recovery. Based on the results of the demonstration, the article proposes an electro-hydraulic energy recovery system of the linear active heave compensation device based on a hydraulic motor-generator. The system model is simulated and analysed in a single cycle under standard operating conditions. The results show that: When the system parameters match reasonably, the heave compensation device has a higher compensation accuracy. The energy recovery rate of the system under the down compensation condition reaches 21.6%, and the effect of energy saving is great. At the same time, simulation analysis shows that under the premise of ensuring the compensation accuracy, changes in the quantitative motor displacement and the viscous friction coefficient of the generator will affect the energy recovery efficiency to varying degrees.

Energy harvesting and vibration reduction by sandwiching piezoelectric elements into elastic damping components with parallel-grooved structures

In this study a method for simultaneous energy harvesting via friction-induced vibration and vibration reduction is proposed and implemented by sandwiching a piezoelectric patch between two layers of elastic damping components. A test bench that provides good repeatability and generates friction-induced vibration is developed. The experimental results show that the elastic damping components significantly suppress friction-induced vibration. The fluctuating voltage signals indicated the feasibility of the proposed approach for energy harvesting via friction-induced vibration. Several parallel grooves are fabricated on the surface of the elastic damping components to investigate the influence of damping components with different structures on the vibration reduction and energy recovery performance. The results show that the grooved damping components provide a greater reduction in the vibration level of the system than the smooth damping components, but the voltage signals are also weaker. Numerical analysis are performed in ABAQUS 6.14. The unstable mode shape shows that the elastic damping components and piezoelectric patch produce relatively large deformation, demonstrating the feasibility of the proposed energy harvesting approach. The results obtained from the implicit dynamic analysis are identical to the experimental results. Therefore, the implicit dynamic analysis is used to provide some reasonable explanations for the experimental phenomena.

Cold energy recovery performance study for liquefied natural gas (LNG) regasification process

The Earth's cleanest burning fossil fuel - natural gas (NG), is primarily methane (CH4) with smaller quantities of other hydrocarbons. As the grid is decarbonizing, the role of NG on the road to a decarbonized future is indisputable. NG is often compressed and converted into liquified natural gas (LNG) that occupies 600 times less space than its gaseous form, optimizing its storability and delivery efficiency. This logistical flexibility helps improve the security of NG supplies worldwide and is making LNG one of the fastest-growing energy markets. At the LNG terminals, LNG is converted back into its gaseous state by regasification, then, distributed across the network, from remote production areas to distant markets where NG supplies are needed. Regasification of LNG releases a significant amount of cold energy. This paper examines the effect of Open Rack Vaporizer (ORV) efficiency and the potential of recoverable cold energy in the LNG regasification process. All data were collected from the industry-leading LNG regasification terminal in Malaysia - The Pengerang LNG (Two) SDN. Bhd. (PLNG2). The results of this study showed that the monthly potential of recoverable cold energy is around 43 MW and the efficiency of ORV is ranged from 60 % to 95 %. In addition, it has been found that the flow rate of LNG and the flow rate of seawater are two significant parameters that affect the potential recoverable cold energy.

An Optimal Torque Distribution Strategy for Four-Motorized-Wheel Electric Vehicle Considering Energy Conversation

In this paper, an optimal torque distribution strategy (OTDS) for four-motorized-wheel electric vehicle (4MWEV) is proposed aiming at improving the tractive efficiency and braking energy recovery performance. Based on the motor efficiency map, the objective functions of tractive efficiency and braking energy recycling are established first. Under driving conditions, genetic algorithm (GA) is proposed to obtain the optimal torque distribution ratio of front and rear axles considering the constraints of motor characteristics and desired torque. During braking conditions, an exhaustive search method (ESM) is proposed to improve the energy recovery performance considering the constraints of motor characteristics, battery, braking theory and ECE Regulations. For the realization of efficient and accurate computation, a control scheme of off-line optimization and on-line allocation based on the optimal torque distribution ratio map is presented, which stores the optimal ratios in all available motor operating regions into two-dimensional lookup tables. Finally, co-simulation experiments based on MATLAB/Simulink and Carsim are conducted to verify the effectiveness of the proposed OTDS under NEDC and UDDS driving cycles. Comparing to the typical torque distribution strategy (TTDS), the simulation results demonstrate that the proposed OTDS can enhance the energy-saving performance by 7.01% under NEDC and 6.69% under UDDS.

Development and performance evaluation of a comprehensive automotive energy recovery system with a refined energy management strategy

The development of automotive energy recovery technologies which mainly include the recovery of braking, vibration and exhaust energy have been highly promoted due to pressing energy issues. Nonetheless, the comprehensive study of energy recovery technologies applied simultaneously to a vehicle rarely receives attention. The recovered energy introduces further complications for the power sources system, which drives the refinement of the existing energy management strategy. This paper presents a novel comprehensive automotive energy recovery system. Energy conversion mechanism and energy saving potential are thoroughly explored based on the developed comprehensive energy recovery models. Bench tests are conducted to demonstrate the energy recovery performance and the effectiveness of the proposed scheme. Based on the analysis of energy flow, a novel assistant power balance strategy is developed to ensure the fair use and storage of the recovered energy and increase the energy conversion efficiency. Comparative analyses in typical cycles with various road disturbance are carried out to validate the effect of developed energy management method. The results indicate that profit of proposed strategy increases with the amount of the recovered energy and fuel economy can be well improved.

Integrating a supercapacitor with capacitive deionization for direct energy recovery from the desalination of brackish water

The importance of energy recovered from desalination techniques has been of considerable interest because of increasing water scarcity and energy crises. Capacitive deionization (CDI), a promising desalination technology using pairs of carbon electrodes under an electric field, has an attractive advantage in that energy stored during the charging step for salt removal can be further recovered during the discharging step. In this research, an energy recovery system based on a four-switch buck-boost converter with variable frequency was successfully constructed to transfer electric energy from a CDI module to a supercapacitor. The effects of the influent NaCl concentration and the distance between two oppositely placed electrodes were investigated on both the desalination behavior and energy recovery performance. The experimental procedure involved a charging step for ion removal, stop-flow operation for energy recovery, and discharging step for electrode regeneration. For the desalination of a 10 mM NaCl solution, a deionization capacity of 10.1 mg g−1 and a total energy input of 0.09 kWh m−3 were obtained. Overall, as demonstrated, a higher energy recovery ratio was achieved with a higher influent NaCl concentration and a shorter distance between the two electrodes. Significantly, up to 49.6% of the energy stored in the CDI module while reducing the salinity of a 50 mM NaCl solution could be directly recovered, indicating that the energy recovery system based on a four-switch buck-boost converter shows superior performance. The utilization of CDI integrated with a supercapacitor in this work holds great potential in both low-energy-requirement desalination and high-efficiency energy storage.

A Study of Exhaust Waste Heat Recovery in Internal Combustion Engines

This research presents an investigation of an energy recovery solution from exhaust gases in internal combustion based on the heat exchange to distil fresh water from the sea water. Consequently, an optimization of the flow field design of the heat exchanger was performed using the commercial computational fluid dynamics (CFD) software. The result of this research showed that the energy recovery performance of the exchanger strictly depends on the engine load, which can reach a value of approximately 33% at the full load condition of the research engine. These results might forecast a future application of the optimized exchanger’s flow-field design in automotive waste heat recovery in order to improve the internal combustion engine efficiency.

Spatial targeting evaluation of energy and environmental performance of waste-to-energy processing

Waste-to-energy supply chains are important potential contributors to minimising the environmental impacts of municipal solid waste by reducing the amounts of waste sent to landfill, as well as the fossil fuel consumption and environmental footprints. Accounting for the spatial and transport properties of the waste-to-energy supply chains is crucial for understanding the problem and improving the supply chain designs. The most significant challenge is the distributed nature of the waste generation and the household energy demands. The current work proposes concepts and a procedure for targeting the size of the municipal solid waste collection zone as the first step in the waste-to-energy supply chains synthesis. The formulated concepts and the provided case study reveal trends of reducing the net greenhouse gas savings and energy recovery by increasing the collection zone size. Population density has a positive correlation with the greenhouse gas saving and energy recovery performance. For smaller zone size the energy recovery from waste approaches and in some cases may surpass the energy spent on waste transportation. The energy recovery and greenhouse gas savings remain significant even for collection zones as large as 200 km2. The obtained trends are discussed and key directions for future work are proposed.

Thermal performance of a multi-loop pump-driven heat pipe as an energy recovery ventilator for buildings

Building energy consumption could benefit from air-to-air energy recovery ventilators. A triple-loop pump-driven heat pipe system was developed for energy recovery from exhaust air in buildings. The thermal performances of the single-loop and triple-loop systems were studied and compared experimentally under winter and summer conditions. The improvement of loop number and the uniformity of temperature difference distribution was discussed. Results indicated that heat transfer capacity and coefficient of performance increased with indoor and outdoor temperature difference, and the variation of temperature effectiveness depended on working conditions. The energy recovery performance of the triple-loop system was better than the single-loop system. The heat transfer capacity, temperature effectiveness, and coefficient of performance of the triple-loop system increased by 3.0%, 0.6%, and 56.7% in summer conditions with an indoor and outdoor temperature difference of 7.5 °C, and by 22.4%, 22.6%, and 53.5% in winter conditions with an indoor and outdoor temperature difference of 31.9 °C. The uniformity of temperature difference distribution could be improved clearly with increasing loop number in winter conditions but not obviously in summer conditions. The variation coefficient of temperature difference decreased from 17.2% to 10.2% in winter conditions, and from 4.5% to 3.9% in summer conditions.

Performance evaluation of regenerative braking systems

This research evaluates the energy gain from a regenerative braking system (RBS) in a commercial electric vehicle (EV), the OEM Mitsubishi i-MiEV. Measurements were conducted in a controlled environment on a commercial chassis dynamometer using international drive cycle standards. The energy recovery of the vehicle was modelled and the output of the model was compared with results from the chassis dynamometer driving. The experiments were original as they coupled changes in energy recovered and driving range due to the RBS settings with investigations into the time of use of the friction brake. Performance tests used two different drive cycle speed profiles and various RBS settings to compare energy recovery performance for a broad range of driving styles. The results show that due to reduced energy consumption, the RBS increased the driving range by 11–22% depending on RBS settings and the drive cycle settings on the dynamometer. The results further showed that driving an EV with a RBS uses the friction brakes more efficiently, which will reduce brake pad wear. This has the potential to improve air quality due to reduced brake pad dust and reduces the maintenance costs of the vehicle. The findings were significant since they showed that friction time of use, a parameter neglected in RBS testing, plays an important part in the efficient operation of an EV. The overall results from the vehicle energy recovery modelling showed good agreement with the data from drive cycle testing and the model has potential to be further developed to gain greater insight into vehicle RBS braking behaviour for EVs in general.

A Combined Heat- and Power-Driven Membrane Capacitive Deionization System

Here, we experimentally investigate an alternative membrane capacitive deionization (MCDI) system cycle, which aims to reduce the required electrical energy demand for water treatment. The proposed heat and power combined MCDI system utilizes waste heat to control the electrostatic potential of the charged electrodes during the charging (desalination) and discharging (energy recovery) processes. The experimental findings suggest that with an increase in the temperature of the brine from 20 to 50 °C, the electrical energy consumed can be reduced by nearly 10%. We also show that the dependence of electrostatic potential on concentration may limit energy recovery performance (power), when moving toward higher water recoveries. Alternative desalination cycles can be further explored through evaluating non-isothermal and non-adiabatic system operation.

An Evaluation on Energy Recovery Performance of the Ventilation System in Multi-Residential Building by Field Measurement

An Evaluation on Energy Recovery Performance of the Ventilation System in Multi-Residential Building by Field Measurement

Simultaneous molecular and process design for waste heat recovery

Processing streams featuring low temperatures are common in industrial systems. Because of low temperatures it turns out to be a challenge to use these type of streams for energy recovery. This is especially true if water is used as the main fluid for energy recovery since large amounts of energy are required for water vaporization. To cope with this energy problem different types of organic fluids used in Rankine-like thermodynamic cycles have been proposed. However, high cost and sustainability issues (i.e. large toxicity) related to organic fluids call for the design of a new type of working fluids suitable for low-temperature energy recovery. This generation of new working fluids should feature target properties such as high vapor pressure and low flammability and toxicity values. Moreover, the performance of these new working fluids also depends on the operating conditions of the thermodynamic cycle where such working fluids will be used. In this work we address the simultaneous product and process design problem of working fluids for energy recovery from low-temperature energy sources in Rankine-like cycles to obtain improved optimal solutions. We compare the energy recovery performance of both the new family of working fluids and processing conditions against similar energy performance obtained using organic fluids previously used for the same aim. By using a system of coupled cycles, work production was increased. Moreover, the new working fluids feature improved safety margins. The results indicate the benefits of the simultaneous product and process design approach and permit us to identify a family of working fluids with better sustainability characteristics.

Innovative use of membrane contactor as condenser for heat recovery in carbon capture.

The gas-liquid membrane contactor generally used as a nonselective gas absorption enhancement device is innovatively proposed as a condenser for heat recovery in liquid-absorbent-based carbon capture. The membrane condenser is used as a heat exchanger to recover the latent heat of the exiting vapor from the desorber, and it can help achieve significant energy savings when proper membranes with high heat-transfer coefficients are used. Theoretical thermodynamic analysis of mass and heat transfer in the membrane condensation system shows that heat recovery increases dramatically as inlet gas temperature rises and outlet gas temperature falls. The optimal split mass flow rate is determined by the inlet gas temperature and the overall heat-transfer coefficient in the condensation system. The required membrane area is also strongly dependent on the overall heat-transfer coefficient, particularly at higher inlet gas temperatures. Mass transfer across the membrane has an insignificant effect on heat transfer and heat recovery, suggesting that membrane wetting may not be an issue when a membrane condenser is used for heat recovery. Our analysis provides important insights into the energy recovery performance of the membrane condensation system as well as selection of operational parameters, such as split mass flow rate and membrane area, thickness, and thermal conductivity.

Prediction of Waste Heat Energy Recovery Performance in a Naturally Aspirated Engine Using Artificial Neural Network

The waste heat from exhaust gases represents a significant amount of thermal energy, which has conventionally been used for combined heating and power applications. This paper explores the performance of a naturally aspirated spark ignition engine equipped with waste heat recovery mechanism (WHRM). The experimental and simulation test results suggest that the concept is thermodynamically feasible and could significantly enhance the system performance depending on the load applied to the engine. The simulation method is created using an artificial neural network (ANN) which predicts the power produced from the WHRM.

Mechanical Hybrid KERS Based on Toroidal Traction Drives: An Example of Smart Tribological Design to Improve Terrestrial Vehicle Performance

We analyse in terms of efficiency and traction capabilities a recently patented traction drive, referred to as the double roller full-toroidal variator (DFTV). We compare its performance with the single roller full-toroidal variator (SFTV) and the single roller half-toroidal variator (SHTV). Modeling of these variators involves challenging tribological issues; the traction and efficiency performances depend on tribological phenomena occurring at the interface between rollers and disks, where the lubricant undergoes very severe elastohydrodynamic lubrication regimes. Interestingly, the DFTV shows an improvement of the mechanical efficiency over a wide range of transmission ratios and in particular at the unit speed ratio as in such conditions in which the DFTV allows for zero-spin, thus strongly enhancing its traction capabilities. The very high mechanical efficiency and traction performances of the DFTV are exploited to investigate the performance of a flywheel-based Kinetic Energy Recovery System (KERS), where the efficiency of the variator plays an important role in determining the overall energy recovery performance. The energy boost capabilities and the round-trip efficiency are calculated for the three different variators considered in this study. The results suggest that the energy recovery potential of the mechanical KERS can be improved with a proper choice of the variator.

Analysis of energy recovery potential using innovative technologies of waste gasification

In this paper, two alternative thermo-chemical processes for waste treatment were analysed: high temperature gasification and gasification associated to plasma process. The two processes were analysed from the thermodynamic point of view, trying to reconstruct two simplified models, using appropriate simulation tools and some support data from existing/planned plants, able to predict the energy recovery performances by process application. In order to carry out a comparative analysis, the same waste stream input was considered as input to the two models and the generated results were compared. The performances were compared with those that can be obtained from conventional combustion with energy recovery process by means of steam turbine cycle. Results are reported in terms of energy recovery performance indicators as overall energy efficiency, specific energy production per unit of mass of entering waste, primary energy source savings, specific carbon dioxide production.

Effects of fouling on performance of retrofitted heat exchanger networks: A thermo-hydraulic based analysis

The energy recovery performance of crude pre-heat trains (PHTs) in oil refineries is typically impaired by deposition over time of fouling on the thermal surfaces. Such time varying effects are normally not considered in the design or retrofit of heat exchangers networks. In this paper, the importance of taking into account such effects is demonstrated, by means of a case study. An existing industrial PHT network is simulated using a dynamic, distributed mathematical model for shell-and-tube heat exchangers undergoing crude oil fouling. To systematically assess the impact of fouling at the network level, several key performance indicators are proposed and used to analyse three retrofit options aimed at maximising overall heat recovery. Simulation results show that network designs that maximise energy recovery at steady state are not the best when fouling occurs. It is concluded that a proper retrofit design must include consideration of time varying fouling effects.