Article
Thermodynamics
Le Minh Quan, Helmut Yabar, I. D. A. A. Warmadewanthi, Ali Yuzir
Summary: This study proposes an improved model using Aspen Plus to predict the performance of sewage sludge updraft gasification more accurately. By increasing the number of tar compositions in the model, the accuracy of syngas composition prediction was enhanced.
ENERGY CONVERSION AND MANAGEMENT
(2022)
Article
Energy & Fuels
Pawel Ziolkowski, Pawel Madejski, Milad Amiri, Tomasz Ku, Kamil Stasiak, Navaneethan Subramanian, Halina Pawlak-Kruczek, Janusz Badur, Lukasz Niedzwiecki, Dariusz Mikielewicz
Summary: The article discusses the thermodynamic analysis of a negative CO2 emission power plant using zero-dimensional mathematical models, showing the potential for achieving negative emissions through a novel gas cycle using gasified sewage sludge. Results from different thermodynamic codes offer consistent trends even in the absence of experimental data. The study highlights the importance of precise modeling for carbon capture and storage systems and demonstrates the positive environmental impact of the proposed solution.
Article
Energy & Fuels
Mingtao Hu, Wenyi Deng, Yaxin Su, Lihua Wang, Guang Chen
Summary: The study found that a steam-CO2 mixed atmosphere is beneficial for increasing the yield and quality of syngas during the gasification of sewage sludge. H2 is mainly produced between 400 to 700 degrees Celsius, with a maximum concentration of 76.2 vol% under a steam/CO2 ratio of 36. Steam promotes the formation of oxygen-containing compounds, while fixed carbon is consumed through the Boudouard reaction and steam reforming reaction.
Article
Engineering, Environmental
Dorette Muller-Stover, Rhys Thompson, Changyong Lu, Tobias Pape Thomsen, Nadia Glaesner, Sander Bruun
Summary: Thermal conversion of phosphorus-rich waste materials offers advantages such as bioenergy generation and concentration of plant nutrients. The study found that particle size management and post-process oxidation can affect the plant availability of phosphorus in the final products. Different thermal processes modify the chemical and physical structure of the feedstock in varying ways, impacting phosphorus speciation and plant availability in the residual ashes or carbonization products.
Article
Energy & Fuels
Zhidong Chen, Yichen Hou, Mingyu Liu, Guoqiang Zhang, Kai Zhang, Dongke Zhang, Lijun Yang, Yanqiang Kong, Xiaoze Du
Summary: A system integrating sewage sludge drying, incineration, and power generation was proposed and analyzed in terms of thermodynamics and economics. Among the three alternative schemes considered, Scheme 2 showed the best performance with the lowest electricity cost and a relatively short payback period.
Article
Chemistry, Physical
Muhammad Abdullah Khan, Salman Raza Naqvi, Syed Ali Ammar Taqvi, Muhammad Shahbaz, Imtiaz Ali, Muhammad Taqi Mehran, Asif Hussain Khoja, Dagmar Juchelkova
Summary: In this study, air gasification of sewage sludge was conducted in a lab-scale bubbling fluidized bed gasifier. The gasification process was modeled using artificial neural networks to predict the hydrogen production from product gas composition at various temperatures and equivalence ratios.
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
(2022)
Article
Green & Sustainable Science & Technology
Usama Mohamed, Ying-jie Zhao, Qun Yi, Li-juan Shi, Guo-qing Wei, William Nimmo
Summary: The study examined the life cycle energy use, CO2 emissions, and cost input of biomass gasification and biomass/coal gasification power generation plants, comparing them with coal combustion technologies. Gasification power plants demonstrated lower energy input and CO2 emissions but higher costs, while coal power plants showed lower energy and cost input but higher CO2 emissions.
Article
Thermodynamics
Michael J. Greencorn, S. David Jackson, Justin S. J. Hargreaves, Souvik Datta, Manosh C. Paul
Summary: Partially recycling CO2-rich exhaust gases can realize the direct utilization of carbon dioxide in a bioenergy system. Analysis shows the potential for system improvements under limited recycling ratios. Gasification system efficiency and specific emissions can be enhanced through exhaust gas recycling (EGR). The coupling between gasification equilibrium temperature and exhaust gas temperature is an important factor in the EGR-enhanced gasification system.
ENERGY CONVERSION AND MANAGEMENT
(2022)
Article
Engineering, Environmental
Xiaoxu Fu, Wei Ping Chan, Vernette Chin, Yinn Zhao Boon, Wenqian Chen, Ya Zhao, Stephan Heberlein, Yan Gu, James Oh, Grzegorz Lisak
Summary: A high-temperature slagging gasifier was used to co-treat sludge-based waste materials with municipal solid waste (MSW), resulting in successful co-gasification and recovery of reusable slag and recyclable metals. The stable operation of the gasifier was achieved through proper control of temperature profiles, melting of inorganic residues, smooth discharge of molten slag, and effective flue gas emissions control. The waste-derived slag was found to be environmentally safe and showed potential as sustainable construction materials, as indicated by toxicity tests and life cycle assessment.
CHEMICAL ENGINEERING JOURNAL
(2023)
Article
Engineering, Environmental
Shuai Guo, DanDan Xu, Xingcan Li, Chenchen Zhao
Summary: This study optimized the preparation and gasification performance of sewage sludge hydrochar through the use of response surface methodology. The optimal conditions for hydrochar yield, higher heating value, and gasification activity index were determined by varying the carbonization temperature, residence time, and acetic acid concentration. The results provide valuable insights for guiding sewage sludge hydrothermal carbonization and further optimization of thermochemical conversion.
JOURNAL OF ENVIRONMENTAL CHEMICAL ENGINEERING
(2022)
Article
Chemistry, Physical
You-Hsin Chen, Thi Ngoc Lan Thao Ngo, Kung-Yuh Chiang
Summary: This research investigates enhanced hydrogen production in sewage sludge and industrial wastewater sludge co-gasification. The experimental results demonstrate that the high catalytic Fe/Mn content in industrial wastewater sludge increases hydrogen production, with the produced gas heating value and cold gas efficiency falling within acceptable ranges.
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
(2021)
Article
Thermodynamics
Changyifan Ren, Dianqi Hu, Yunan Chen, Liejin Guo
Summary: An auto-thermal supercritical water co-gasification system was developed for H2 and heat production from sewage sludge and coal. Thermodynamic analysis and life cycle environmental impact assessment were performed, showing the sensitivity of H2 yield to the proportion of preheated water and dry coal to dry sewage sludge. Adding 21% dry coal was necessary when the system was energy self-sufficient to treat sewage sludge directly.
ENERGY CONVERSION AND MANAGEMENT
(2023)
Article
Thermodynamics
Fan Zhang, Shuzhong Wang, Yanhui Li, Wenjing Chen, Lili Qian
Summary: A novel supercritical water system was proposed to treat sewage sludge harmlessly in this work, utilizing supercritical water gasification and oxidation. The study found that increasing treatment temperature, reducing moisture content, and oxidation coefficient could significantly improve the energy efficiency of the system.
ENERGY CONVERSION AND MANAGEMENT
(2021)
Article
Environmental Sciences
Abid Farooq, Chang Hyun Ko, Y. -K. Park
Summary: This study investigated the potential of steam gasification of sewage sludge using different temperatures and bimetallic catalysts. The higher temperature (800 degrees C) resulted in higher gas yield and syngas selectivity. The incorporation of nickel in the Al-MCM48 support improved gasification reactions compared to HZSM-5. The addition of promoters such as cobalt and iron allowed for the formation of Ni-Fe and Ni-Co alloys, leading to higher gas yield and overall H2 and CO selectivity.
ENVIRONMENTAL RESEARCH
(2023)
Article
Energy & Fuels
Ning Guo, Michal T. Lewandowski, Corinna Netzer
Summary: Thermal treatment of sewage sludge using gasification and combustion can produce sterilized bio-char and recover energy. Employing the MILD combustion regime can benefit the heat balance and reduce emissions. The composition of the fuel samples has a significant impact on SOx and NOx emissions, while high moisture content in the feedstock enhances pollutant formation.
Article
Energy & Fuels
Przemyslaw Seruga, Malgorzata Krzywonos, Emilia den Boer, Lukasz Niedzwiecki, Agnieszka Urbanowska, Halina Pawlak-Kruczek
Summary: The continuous growth of the world population and the recent energy crisis have led to increasing volumes of municipal waste and the need for more local and renewable energy sources. This paper presents a study on the dry anaerobic digestion of municipal biowaste in an industrial-scale plant. The results show that it is possible to achieve an average biogas production rate of 120 Nm(3)/ton of fresh waste, leading to a positive energy balance and reduced CO2 emissions. Additionally, the conversion of biowaste allows for the production of high-quality fertilizers and has benefits for soil protection and the environment as a whole.
Article
Thermodynamics
Lukasz Witanowski, Piotr Klonowicz, Piotr Lampart, Piotr Klimaszewski, Tomasz Suchocki, Lukasz Jedrzejewski, Dawid Zaniewski, Pawel Ziolkowski
Summary: The paper presents a CFD-based Nelder-Mead optimization method for a 10 kW single-stage axial turbine in an ORC system. The objective function is defined as the total-to-static isentropic efficiency. Multi-point linear regression is used to determine the significance of the objective function arguments and select the variables that contribute most to improving the objective function value. This approach helps reduce the number of optimized parameters and computational time.
Article
Thermodynamics
Pawel Ziolkowski, Kamil Stasiak, Milad Amiri, Dariusz Mikielewicz
Summary: The primary objective of the study is to develop a negative carbon dioxide gas power plant using sewage sludge for electricity production while benefiting the environment. A mathematical model is proposed to estimate thermodynamic parameters related to the gasification process and changes in temperature, pressure, etc. The integration of gas-steam turbine model with gasification reactor model is a key innovation, allowing the analysis of the gasification products' impact on turbine output.
Article
Thermodynamics
Lukasz Witanowski, Piotr Klonowicz, Piotr Lampart, Pawel Ziolkowaki
Summary: This paper focuses on the multi-objective efficiency optimization of a one-stage axial ORC turbine using an Implicit Filtering algorithm. The efficiency is improved in both modes of operation by changing the rotor profiles and the shape of endwall contours of the rotor domain.
Article
Thermodynamics
Hao Luo, Xinyan Liu, Lukasz Niedzwiecki, Xiaoqin Wu, Weigang Lin, Bona Lu, Wei Wang, Hao Wu
Summary: This study analysed the effects of model dimensionality, particle shrinkage, and boundary layer reactions on particle-scale modelling of biomass char conversion under pulverized fuel combustion conditions using six models. The 1D_SPM_BH model with consideration of intra-particle heat and mass transfer, particle shrinkage, and boundary layer reactions was found to be the most appropriate model for biomass char conversion. The 0D_Cons model provided a good approximation for small particle size at specific temperatures, while the 0D_SPM model overestimated the char conversion rate. Considering intra-particle heat and mass transfer improved the model prediction of char conversion time and reaction contributions, and boundary layer reactions had a significant effect on char conversion prediction for large particles and high temperatures.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2023)
Article
Engineering, Environmental
Hao Luo, Xiaobao Wang, Xiaoqin Wu, Lukasz Niedzwiecki, Halina Pawlak-Kruczek, Xinyan Liu, Qingang Xiong
Summary: The multi-fluid model is commonly used to study heat transfer between gas and solid in bubbling fluidized beds, but it is difficult to implement a one-dimensional model considering intra-particle temperature inhomogeneity. To solve this issue, a corrected coefficient is introduced to quantitively feature the effects of intra-particle temperature inhomogeneity on external heat transfer, forming a corrected zero-dimensional model. The results show that the corrected model predicts the temperature profiles more accurately and has comparable computational efficiency compared to the original model.
CHEMICAL ENGINEERING JOURNAL
(2023)
Article
Chemistry, Physical
Tomasz Ochrymiuk, Marcin Froissart, Pawel Madejski, Janusz Badur
Summary: This paper presents and discusses the various concepts involved in the mathematical modeling of fluid-solid interactions in the catalytic combustion processes occurring within a porous burner. It addresses the relevant physical and chemical phenomena, compares mathematical models, proposes a hybrid two/three-field model, estimates the interphase transfer coefficients, discusses proper constitutive equations and closure relations, and generalizes the Terzaghi concept of stresses. Selected examples of model application are presented and described. Finally, a numerical verification example is used to demonstrate the application of the proposed model.
Article
Chemistry, Multidisciplinary
Lukasz Niedzwiecki, Krzysztof Moscicki, Anton Bijl, Pawel Owczarek, Amit Arora, Mateusz Wnukowski, Christian Aragon-Briceno, Halina Vishwajeet, Halina Pawlak-Kruczek, Eddy Bramer, Gerrit Brem, Artur Pozarlik
Summary: This study investigates the influence of hydrothermal carbonization (HTC) on the kinetics of fast pyrolysis of agricultural biomass (miscanthus), as well as the effects of in situ use of a CaO catalyst. The results show that HTC can improve the quality of pyrolysis oil by reducing the oxygen content in biomass. Moreover, the addition of CaO catalyst during HTC process further enhances the pyrolysis reaction.
APPLIED SCIENCES-BASEL
(2023)
Article
Energy & Fuels
Halina Pawlak-Kruczek, Agnieszka Urbanowska, Lukasz Niedzwiecki, Michal Czerep, Marcin Baranowski, Christian Aragon-Briceno, Malgorzata Kabsch-Korbutowicz, Amit Arora, Przemyslaw Seruga, Mateusz Wnukowski, Jakub Mularski, Eddy Bramer, Gerrit Brem, Artur Pozarlik
Summary: Hydrothermal carbonization (HTC) is a thermochemical process that converts low-quality biomass and organic waste into hydrochar. Improved mechanical dewatering of HTC-treated biomass is demonstrated, along with the recovery of physical enthalpy and condensable hydrocarbons through flashing-off of steam. A membrane system is considered for purifying the effluent and recovering chemical energy from the retentate, with the biomethane potential of condensates calculated for further energy recovery.
Article
Thermodynamics
Halina Pawlak-Kruczek, Jakub Mularski, Michal Ostrycharczyk, Michal Czerep, Marcin Baranowski, Tadeusz Maczka, Krzysztof Sadowski, Patryk Hulisz
Summary: This study investigates the combustion of pulverized coal with unburned char recovered from the ash of an industrial boiler. Two plasma burners are installed to improve the combustion efficiency and reduce the amount of unburned fuel. CFD modeling and laboratory tests are used to analyze the combustion behavior, and the results show that the use of plasma burners improves the mixing and temperature distribution, resulting in higher temperatures at the combustion chamber outlet.
Article
Thermodynamics
Pawel Madejski, Krzysztof Banasiak, Pawel Ziolkowski, Dariusz Mikielewicz, Jaroslaw Mikielewicz, Tomasz Kus, Michal Karch, Piotr Michalak, Milad Amiri, Pawel Dabrowski, Kamil Stasiak, Navaneethan Subramanian, Tomasz Ochrymiuk
Summary: The paper presents the computational analysis results of the Spray-Ejector Condenser (SEC) development, which plays a crucial role in the negative CO2 gas power plant (nCO(2)PP) cycle. The proposed design of the ejector-condenser ensures efficient vapor condensation and CO2 compression, making it suitable for gas power cycle application.
Article
Green & Sustainable Science & Technology
Muhammad Yousaf Arshad, Salaha Saeed, Ahsan Raza, Anum Suhail Ahmad, Agnieszka Urbanowska, Mateusz Jackowski, Lukasz Niedzwiecki
Summary: This research demonstrates the potential of black soldier fly larvae (BSFL) as an effective method for kitchen waste treatment, achieving significant waste reduction and superior compost quality compared to traditional methods. Life cycle assessment confirms the sustainability advantages of BSFL, and machine learning achieves high accuracy in predicting optimal conditions.
Review
Green & Sustainable Science & Technology
Muhammad Yousaf Arshad, Muhammad Azam Saeed, Muhammad Wasim Tahir, Ahsan Raza, Anam Suhail Ahmad, Fasiha Tahir, Bartlomiej Borkowski, Tadeusz Maczka, Lukasz Niedzwiecki
Summary: This comprehensive review paper provides a multifaceted examination of the applications of non-thermal plasma in addressing the challenge of tar removal within biomass-oriented technologies. It highlights the importance of empirical investigations and theoretical modeling in advancing plasma-based technologies for sustainable energy.
Article
Ecology
Adil Mehmood, Muhammad Wasim Tahir, Muhammad Azam Saeed, Muhammad Yousaf Arshad, Huma Hussain, Jakub Mularski, Lukasz Niedzwiecki
Summary: The depletion of fossil-based fuels and environmental deterioration require the aggressive development of renewable energy technologies. Biomass gasification is a promising approach, and CFD modeling shows potential in advancing gasification systems. Mixing CO2 with gasification agents is explored as a potential CCU strategy. The research investigates the effect of gasifying agent composition, air-to-steam ratio, oxygen, and CO2 mixing on the quality of syngas. The results suggest that a 50%-50% air-steam mixture produces the best quality syngas, while oxygen has a negligible impact, and a mixture of air-steam-CO2 = 23%-50%-15% is optimal for high-quality syngas.
Article
Thermodynamics
Dariusz Mikielewicz, Milad Amiri, Michal Klugmann, Jaroslaw Mikielewicz
Summary: An analytical model for direct steam condensation in the presence of inert gas in a spray ejector condenser (SEC) has been developed. The model takes into account the continuity, momentum, and energy equations for the steam-carbon dioxide mixture, as well as the mechanisms of direct contact condensation due to heat transfer and concentration. The model predicts the temperature drop between the inlet and outlet of the mixing section, showing the effect of different flow rates and the presence of CO2 on the efficiency of the condensation process in SEC.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2023)
Article
Thermodynamics
Yong Cheng, Fukai Song, Lei Fu, Saishuai Dai, Zhiming Yuan, Atilla Incecik
Summary: This paper investigates the accessibility of wave energy absorption by a dual-pontoon floating breakwater integrated with hybrid-type wave energy converters (WECs) and proposes a hydraulic-pneumatic complementary energy extraction method. The performance of the system is validated through experiments and comparative analysis.
Article
Thermodynamics
Jing Gao, Chao Wang, Zhanwu Wang, Jin Lin, Runkai Zhang, Xin Wu, Guangyin Xu, Zhenfeng Wang
Summary: This study aims to establish a new integrated method for biomass cogeneration project site selection, with a focus on the application of the model in Henan Province. By integrating Geographic Information System and Multiple Criterion Decision Making methods, the study conducts site selection in two stages, providing a theoretical reference for the construction of biomass cogeneration projects.
Article
Thermodynamics
Mert Temiz, Ibrahim Dincer
Summary: The current study presents a hybrid small modular nuclear reactor and solar-based system for sustainable communities, integrating floating and bifacial photovoltaic arrays with a small modular reactor. The system efficiently generates power, hydrogen, ammonia, freshwater, and heat for residential, agricultural, and aquaculture facilities. Thermodynamic analysis shows high energy and exergy efficiencies, as well as large-scale ammonia production meeting the needs of metropolitan areas. The hybridization of nuclear and solar technologies offers advantages of reliability, environmental friendliness, and cost efficiency compared to renewable-alone and fossil-based systems.
Editorial Material
Thermodynamics
Wojciech Stanek, Wojciech Adamczyk
Article
Thermodynamics
Desheng Xu, Yanfeng Li, Tianmei Du, Hua Zhong, Youbo Huang, Lei Li, Xiangling Duanmu
Summary: This study investigates the optimization of hybrid mechanical-natural ventilation for smoke control in complex metro stations. The results show that atrium fires are more significantly impacted by outdoor temperature variations compared to concourse/platform fires. The gathered high-temperature smoke inside the atrium can reach up to 900 K under a 5 MW train fire energy release. The findings provide crucial engineering insights into integrating weather data and adaptable ventilation protocols for smoke prevention/mitigation.
Article
Thermodynamics
Da Guo, Heping Xie, Mingzhong Gao, Jianan Li, Zhiqiang He, Ling Chen, Cong Li, Le Zhao, Dingming Wang, Yiwei Zhang, Xin Fang, Guikang Liu, Zhongya Zhou, Lin Dai
Summary: This study proposes a new in-situ pressure-preserved coring tool and elaborates its pressure-preserving mechanism. The experimental and field test results demonstrate that this tool has a high pressure-preservation capability and can maintain a stable pressure in deep wells. This study provides a theoretical framework and design standards for the development of similar technologies.
Article
Thermodynamics
Aolin Lai, Qunwei Wang
Summary: This study assesses the impact of China's de-capacity policy on renewable energy development efficiency (REDE) using the Global-MSBM model and the difference-in-differences method. The findings indicate that the policy significantly enhances REDE, promoting technological advancements and marketization. Moreover, regions with stricter environmental regulations experience a higher impact.
Article
Thermodynamics
Mostafa Ghasemi, Hegazy Rezk
Summary: This study utilizes fuzzy modeling and optimization to enhance the performance of microbial fuel cells (MFCs). By simulating and analyzing experimental data sets, the ideal parameter values for increasing power density, COD elimination, and coulombic efficiency were determined. The results demonstrate that the fuzzy model and optimization methods can significantly improve the performance of MFCs.
Article
Thermodynamics
Zhang Ruan, Lianzhong Huang, Kai Wang, Ranqi Ma, Zhongyi Wang, Rui Zhang, Haoyang Zhao, Cong Wang
Summary: This paper proposes a grey box model for fuel consumption prediction of wing-diesel hybrid vessels based on feature construction. By using both parallel and series grey box modeling methods and six machine learning algorithms, twelve combinations of prediction models are established. A feature construction method based on the aerodynamic performance of the wing and the energy relationship of the hybrid system is introduced. The best combination is obtained by considering the root mean square error, and it shows improved accuracy compared to the white box model. The proposed grey box model can accurately predict the daily fuel consumption of wing-diesel hybrid vessels, contributing to operational optimization and the greenization and decarbonization of the shipping industry.
Article
Thermodynamics
Huayi Chang, Nico Heerink, Junbiao Zhang, Ke He
Summary: This study examines the interaction between off-farm employment decisions between couples and household clean energy consumption in rural China, and finds that two-paycheck households are more likely to consume clean energy. The off-farm employment of women is a key factor driving household clean energy consumption to a higher level, with wage-employed wives having a stronger influence on these decisions than self-employed ones.
Article
Thermodynamics
Hanguan Wen, Xiufeng Liu, Ming Yang, Bo Lei, Xu Cheng, Zhe Chen
Summary: Demand-side management is crucial to smart energy systems. This paper proposes a data-driven approach to understand the relationship between energy consumption patterns and household characteristics for better DSM services. The proposed method uses a clustering algorithm to generate optimal customer groups for DSM and a deep learning model for training. The model can predict the possibility of DSM membership for a given household. The results demonstrate the usefulness of weekly energy consumption data and household socio-demographic information for distinguishing consumer groups and the potential for targeted DSM strategies.
Article
Thermodynamics
Xinglan Hou, Xiuping Zhong, Shuaishuai Nie, Yafei Wang, Guigang Tu, Yingrui Ma, Kunyan Liu, Chen Chen
Summary: This study explores the feasibility of utilizing a multi-level horizontal branch well heat recovery system in the Qiabuqia geothermal field. The research systematically investigates the effects of various engineering parameters on production temperature, establishes mathematical models to describe their relationships, and evaluates the economic viability of the system. The findings demonstrate the significant economic feasibility of the multi-level branch well system.
Article
Thermodynamics
Longxin Zhang, Songtao Wang, Site Hu
Summary: This investigation reveals the influence of tip leakage flow on the modern transonic rotor and finds that the increase of tip clearance size leads to a decline in rotor performance. However, an optimal tip clearance size can extend the rotor's stall margin.
Article
Thermodynamics
Kristian Gjoka, Behzad Rismanchi, Robert H. Crawford
Summary: This paper proposes a framework for assessing the performance of 5GDHC systems and demonstrates it through a case study in a university campus in Melbourne, Australia. The results show that 5GDHC systems are a cost-effective and environmentally viable solution in mild climates, and their successful implementation in Australia can create new market opportunities and potential adoption in other countries with similar climatic conditions.
Article
Thermodynamics
Jianwei Li, Guotai Wang, Panpan Yang, Yongshuang Wen, Leian Zhang, Rujun Song, Chengwei Hou
Summary: This study proposes an orientation-adaptive electromagnetic energy harvester by introducing a rotatable bluff body, which allows for self-regulation to cater for changing wind flow direction. Experimental results show that the output power of the energy harvester can be greatly enhanced with increased rotatory inertia of the rotating bluff body, providing a promising solution for harnessing wind-induced vibration energy.