Cogeneration Research Articles

Real-time optimization for integrated R2 charging and refueling stations in a multi-carrier energy system considering hydrogen chain management

This study presents a real-time optimization-based strategy for sustainable energy management using an energy hub that integrates combined heat and power (CHP) units, heat pumps, and fuel-cell technology to meet community electricity, heating, and cooling demands. It incorporates renewable-based R2 stations that leverage photovoltaic and wind power, integrated with hydrogen production and storage, to supply stationary energy consumers and the transportation sector. The system provides hydrogen for fuel cell electric vehicles (FCEVs) and electricity for electric vehicles (EVs). Integrating the R2 station with the primary energy hub optimizes the use of locally generated power, reducing dependence on external sources. Hydrogen fuel is produced on-site and off-site, focusing on solving the capacitated routing problem for efficient delivery. The system's architecture is modeled using a mixed-integer linear programming (MILP) approach. According to the results, no energy is drawn from the grid to meet the end-user's electricity demand.

Potential for carbon dioxide removal of carbon capture and storage on biomass‐fired combined heat and power production

AbstractCarbon Dioxide Removals (CDR) and Carbon Capture and Storage (CCS) have received a lot of attention as a tool to mitigate climate change and reach climate neutrality. Bioenergy with Carbon Capture and Storage (BECCS) is seen as one of the more promising CDRs, and from 2026, the Danish utility Ørsted is establishing the first BECCS plants in Denmark. We present a case study of BECCS by installing CCS at a biomass‐fired CHP plant and the aim is to quantify the CDR potential and carbon dynamics of the BECCS system. Moreover, the study aims to quantify the emissions related to capturing and store CO2. The GHG emissions from CCS including heat, electricity, transport and storage are approximately 100 kgCO2/t stored CO2and the carbon payback time of the BECCS system is 3–4 years relative to leaving the wood in the forest or at processing industries. The main driver of the payback time is the additional use of biomass to operate CCS which shifts the timing of CO2emissions more towards the present. The additional biomass use also increases supply chain emissions, and on top of that, only 90% of the direct CO2emissions from the CHP plant are captured. The study illustrates the importance of temporal scope in assessing the CDR potential of BECCS. With continuous use of biomass, GHG emissions are 207 kgCO2/t stored CO2in year 1 and −742 kgCO2/t stored CO2in year 99. This study reveals inconsistencies in the assessment of the CDR potential of BECCS in the literature. There is a considerable need for further research within this field to assess how BECCS can contribute to mitigating climate change and on the appropriate scale of BECCS deployment.

Effect of furnace temperature and oxygen concentration on combustion and CO/NO emission characteristics of sewage sludge

Addressing the growing energy crisis, the development and utilization of solid waste have become a critical research areas. Sewage sludge, rich in organic matter, can serve as an alternative fuel to coal. This study employs a thermogravimetric analyzer to investigate the combustion characteristics of sewage sludge at heating rates of 10, 20, and 40 °C/min. Additionally, a horizontal tube furnace is utilized to analyze the CO and NO emission characteristics during sewage sludge combustion at varying oxygen concentrations and temperatures. Results indicate that at a constant gas velocity, the primary factor influencing combustion characteristics and CO/NO emissions is the composition difference. Higher furnace temperatures lead to lower CO generation and increased combustion efficiency. The conversion of coke-N to NO rises with increasing temperature. Moreover, higher furnace temperatures decrease the conversion of fuel-N to NO. Increasing oxygen concentration reduces the ignition concentration limit of sewage sludge. The lowest NOx emissions were recorded at an oxygen concentration of 21 vol%. This study provides essential data for reducing coal consumption and enhancing the safe and efficient treatment of sewage sludge.

Intelligent modeling of combined heat and power unit under full operating conditions via improved crossformer and precise sparrow search algorithm

The flexible operation capability of combined heat and power (CHP) unit under full operating conditions must be promoted to suppress the power grid fluctuation in large-scale integration of renewable energy. However, obtaining CHP unit model under large-scale variable loads and deep peak shaving is extremely challenging. To this end, an intelligent modeling method incorporating improved crossformer and precise sparrow search algorithm is designed to provide reference for flexible controller design. Firstly, to address the strong time dependence of CHP unit boiler-turbine coupling process, a bidirectional gated recurrent unit is employed as the position encoding to extract the hidden temporal feature. Secondly, a novel encoder structure with multi-receptive field convolution module is designed to enhance the local feature extraction capability of the network, which is conducive to the analysis of multivariable coupling characteristics of CHP unit. On this basis, a precise sparrow search algorithm with stronger search ability is formed by combining Tent chaotic mapping, osprey optimization algorithm, Cauchy mutation and quantum behavior, which provides support for the dynamic characteristics analysis of CHP unit. The time dependence, local feature information and optimal parameter settings are fully considered in the comprehensive modeling scheme, which results in an accurate identification model for CHP unit under full operating conditions. Finally, the effectiveness of the proposed method is verified based on the actual operating data of a 350 MW CHP unit. The accuracy of established model is greater than 99.4 %, which can well reflect the nonlinear characteristics of the unit. Therefore, the built model can be used for controller design and simulation analysis.

Assessing the emissions reduction potential and economic feasibility of small-scale (

Small-scale combined heat and power (CHP) for residential applications has been demonstrated in different regions throughout the world. CHP can enable resilience in energy supply and serve as a transitional technology as the grid progresses to higher fractions of low carbon electricity production. However, there are very limited feasibility assessments in the context of US climate zones, policies, and economic factors. To address this gap, we assess how the economic feasibility and emissions impact of a small-scale, natural gas CHP system compares considering the local electrical grid in seven climate zones and six subgrid regions across the United States. This is accomplished using an in-house Python program alongside EnergyPlus that is used to size the CHP and/or thermal storage systems according to representative electrical and thermal demand profiles for multifamily residential buildings, optimizes CHP and thermal storage energy dispatch throughout the year to meet demands, assesses the system’s economic feasibility, and calculates the carbon emission reduction or increase relative to the local electrical grid. For the baseline cases considered, carbon emissions can be reduced by up to 12% for regions with high required thermal load and/or electricity derived from high carbon emitting sources. In many scenarios, carbon emissions increased. Furthermore, the economic feasibility of the systems, even considering recent incentives, remains a significant barrier. The resulting Python program is open-source and designed for use by both researchers and building owners to conduct their own small-scale CHP feasibility assessments.

Techno-economic analysis and optimization of a binary geothermal combined district heat and power plant for Puga Valley, India

This article investigates the energy, exergy, and economic performance of a Puga Valley-specific binary geothermal combined district heat and power plant, taking into account geotechnical data and related cost functions. The power plant uses an organic Rankine cycle (ORC) with R123 as the working fluid, utilizing waste heat for district heating to enhance efficiency. Variations in operating and design parameters such as geothermal fluid flow rate, temperature, and ORC temperature of the evaporator and condenser are found to have significant effects on the overall performance of the system and cost rate. A multi-objective grey wolf optimization technique based on artificial neural networks has been used to determine the ideal values of the above-mentioned parameters. The optimization study revealed a Pareto optimal curve with overall exergy efficiency and total cost rate as objective functions from which the optimal point was identified using the technique for order preference by similarity to the ideal solution (TOPSIS) method. While operating the proposed CHP plant at TOPSIS optimal point, the plant delivers a net electrical output of 1.08 MW alongside 4.19 MW of thermal energy, resulting in a total cost rate of 33.84 USD/h, with energy and exergy efficiencies peaking at 32.26 % and 36.8 %, respectively. The exergy analysis at the optimal point also revealed a notable reduction of 550 kW in the total exergy destruction rate compared with the base-case scenario. Furthermore, the design requirements of a 5 MW net power output CHP plant for effective recovery of the Puga Valley geothermal resource are discussed.

Convex relaxation of two-stage network-constrained stochastic programming for CHP microgrid optimal scheduling

Different from most studies only incorporating economic aspect into operation scheduling, this paper develops a novel network-constrained framework that can address both economic and secure issues for combined heating and power (CHP) microgrids integrated with wind power considering uncertainties. According to quadratically constrained programs, a two-stage network-constrained stochastic programming (TSNCSP) model is formulated to improve economic benefits and meanwhile capture active/reactive power and off-nominal bus voltage constraints in the full decision variable domain. In the first stage, namely day-ahead, the schedule of transacted electricity with the upstream power grid and the generation cost of heat is determined according to the forecast information. In the second stage, namely real-time, a recourse function of adjustable resources is defined to reduce the expected cost incurred by the perturbation of random wind power outputs. Moreover, the original non-convex problem is innovatively transformed into a semidefinite programming through incorporation of demand response program (DRP), duality, complementary slackness, and relaxation techniques to improve the solving efficiency. Finally, a proposition is presented and proved that provides a sufficient condition for the exactness of the proposed convex relaxation. Numerical simulations on the 33-bus test system verify the effectiveness of the proposed framework in multi-period scenario-based scheduling problems.

Optimizing multi-energy systems with enhanced robust planning for cost-effective and reliable operation

This paper introduces a comprehensive and resilient multi-energy system (MES) designed for independent planning and real-time implementation. A robust daily coordinated planning model is proposed, incorporating adjustable optimization with fundamental operational and uncertainty constraints. The model integrates various energy sources and systems, including photovoltaics, wind turbines, combined heat and power (CHP) units, energy storage system (ESS), electric vehicle (EV), electric boilers, and power-to-gas (P2G) facilities, to manage electricity, natural gas, and heat demands. The objective is to minimize MES operational costs while meeting electricity and heat requirements, considering renewable energy uncertainties. It includes the development of a two-stage flexible robust optimization model that accounts for energy equilibrium, capacity constraints, and demand response mechanisms. The model incorporates price-based demand response with both switchable and interruptible loads, enhancing system controllability and flexibility. Additionally, a scenario generation and reduction technique based on the Kantorovich distance is employed to effectively manage forecast errors and uncertainties. A novel modified Slime Mold Algorithm (SMA) is utilized to solve the optimization problem, demonstrating superior convergence and computational efficiency compared to traditional meta-heuristics. The slime mold algorithm is further enhanced with chaos theory, using a sine map to introduce dynamic exploration capabilities. The findings indicate that the proposed multi-energy system model effectively balances electricity, natural gas, and heat loads while accommodating renewable energy fluctuations. The enhanced slime mold algorithm provides optimal solutions swiftly, ensuring reliable and cost-effective multi-energy system operation.

Sustainable management of family life and finance in the context of digital capabilities - data flow dynamics

In recent years, biorefining Municipal Solid Waste (MSW) has gained attention as a promising solution to the challenges of waste management and resource shortages, while also advancing sustainability goals. This research focuses on the European Union, analyzing the material flow and sustainability of biorefining systems and evaluating their impact on society, the economy, and the natural environment. The final products of the integrated material recovery processes, including recycling (18.3 %), heavy metals (3.6 %), fiber (1.4 %), hydrogen sulfate (7.4 %), recoverable water (14.8 %), fertilizer (8.4 %), and electric power (0.126 MWH/t MSW), are derived from the combined operations of material recovery facilities, pulverization, chemical conversion, wastewater treatment plants (WWTP), and combined heat and power (CHP) systems. The CHP system recovers energy from sources such as refuse-derived fuel (RDF), other disposable waste, charcoal, and natural gas produced by material recovery facilities, chemical conversion, and anaerobic digestion (AD) systems. Levulinic acid (LA), priced at 52 Euro/t, generates a profit of 220 Euro/t, excluding any subsidies. Potential reductions in carbon dioxide emissions are estimated at 2.5 and 1.4 kg CO2 equivalents per kilogram of levulinic acid (LA) and fertilizer, respectively, and 0.18 kg CO2 equivalents per megajoule of electrical power. This study underscores the importance of sustainable management practices in the context of digital capabilities, emphasizing the data flow dynamics essential for optimizing family life and finance in achieving sustainability.

Compound catalyst of ReMoSx@HSSZ-39 and SAPO-34 zeolites for high performance conversion of CO2 to C2-4 hydrocarbons

We report here a high-performance catalyst ReMoSx@HSSZ-39 compounded with SAPO-34 for conversion of CO2 to C2-4 hydrocarbons, in which the ReMoSx clusters are responsible for highly efficient hydrogenation of CO2 to methanol as the intermediate and then the surrounding zeolitic acid sites for further conversion of methanol to hydrocarbons. The investigation finds that uniform ReMoSx clusters can be reliably fabricated in zeolitic cages by co-introduction of rhenium and molybdenum species into the HSSZ-39 zeolite and followed by sulfidation, which constitutes an intimate bifunction catalyst through better cooperation of ReMoSx clusters and the zeolitic acid sites. Compared with MoSx@HSSZ-39, the introduction of rhenium significantly suppresses CO generation. By mixing some SAPO-34 zeolite, with increased density of protonic acid, more than 86 % C2-4 hydrocarbons in organic products and only 21 % CO at 32.5 % of CO2 conversion are obtained and the composite catalyst shows excellent stability with more than 95 % C2-4 hydrocarbons in organic products, less than 30 % CO and above 26.6 % of CO2 conversion after 1000 h on stream.

Degradation pathways and product formation mechanisms of asphaltene in supercritical water

Asphaltene is the compound with the most complex structure and the most difficult degradation in oily sludge, which is the key to limit the efficiency of supercritical water oxidation treatment of oily sludge. In this paper, the supercritical water oxidation process of asphaltene was investigated in terms of free radical reaction, degradation pathway, and product generation mechanism using ReaxFF molecular dynamics simulation method. The results showed that increasing temperature, increasing O2, and increasing H2O have different effects on HO2·generation. Benzene rings undergo fusion and condensation through hydrogenation abstraction and oxygen addition reactions, subsequently breaking down into long-chain alkanes. Increasing O2 can effectively promote the ring-opening of nitrogen-containing heterocycles. -COOH is the most important intermediate fragment for CO and CO2 generation, and there is a reaction competition with -CHO3 and -CO3. When the number of oxygen molecules increases from 300 to 700, the reaction frequency of -CHO3 and -CO3 to generate CO and CO2 increases by 17.14 % and 12.77 %·H2O determines the production of H2 by controlling the number of H·radicals present. As the amount of H2O increases from 500 to 1500, the product ratio of H2 increases from 12.73 % to 21.31 %. Environmental implicationAsphaltene is the most structurally complex organic matter in oily sludge, and its presence makes it difficult for oily sludge to be completely degraded by conventional treatment methods such as pyrolysis and incineration. Polycyclic aromatic hydrocarbons (PAHs) represented by asphaltene increase the carcinogenicity and mutagenicity of oily sludge, and even irreversibly pollute soil and groundwater. Supercritical water oxidation, as an efficient organic waste treatment technology, can realize harmlessness in a green and efficient way. So the study on the mechanism of supercritical water oxidation of asphaltene is of great significance for environmental protection.

Coordinated economic and low‐carbon operation strategy for a multi‐energy greenhouse incorporating carbon capture and emissions trading

AbstractGreenhouses need to supply CO2 to crops while simultaneously emitting CO2. To effectively harness the dual functionality of greenhouses as a carbon source and carbon consumer, this work incorporates carbon capture and emissions trading into a multi‐energy greenhouse (MEG), which is equipped with various power and heat sources such as photovoltaic (PV) panels and a combined heat and power (CHP) unit and proposes that the captured CO2 should be used to feed crops on‐site. A low‐carbon economic operation method is proposed for the coordinated environment‐energy‐carbon management of the MEG, and it considers various factors, including the power purchase/carbon supply costs, carbon emissions trading income, temperature/humidity/light intensity and CO2 concentration requirements for crops, and operational constraints of various energy/environmental regulation equipment. The proposed method is validated using a tomato MEG. The results highlight the significant economic and environmental benefits of introducing carbon capture, emissions trading, and utilisation into MEGs.

Key Factors for Electrochemical Carbon Dioxide Reduction at Ni-N-C Catalysts

Electrochemical carbon dioxide reduction reaction (CO2RR) has the potential to adequately contribute to addressing the energy and environmental challenges faced by the humanity today. The surplus of CO2 produced by burning fossil fuels can be transformed into valuable products by CO2RR. An effective use of this approach on a large scale requires active, selective, and stable CO2 reduction electrocatalysts. Additionally, insightful understanding of interfacial behavior such as water wetting and carbonate formation at the electrode is required to enhance the performance and durability of CO2RR electrocatalysts.1 Atomically dispersed Ni-N-C materials have attracted attention due to their superior selectivity for CO generation.2 Their activity and selectivity of CO2RR are influenced by the metal center and local atomic defects in M-N-C catalysts.3 In addition to catalyst structures, electrode composition and structure have also substantial impact on the activity and selectivity of CO2RR. Particularly, ionomer compositions and the electrode fabrication process can alter the hydrophobicity of the electrode and the local pH on the catalyst, resulting in considerable changes in CO2RR activity and selectivity.In this presentation, we will report on the performance of various electrodes fabricated with the Ni-N-C catalyst, using different types of ionomers and measured in a flow cell and zero-gap electrolyzer at > 100 mA/cm2 current densities for CO2RR. We will also introduce an approach that aims at reducing carbonate formation at the CO2RR electrolyzer cathode by the modifications to the electrolyte composition, the CO2 inlet humidity, and the electrochemical cell temperature. Acknowledgement Research presented in this work was supported by the Laboratory Directed Research and Development program of Los Alamos National Laboratory under project number 20230065DR. References (1) Sa, Y. J.; Lee, C. W.; Lee, S. Y.; Na, J.; Lee, U.; Hwang, Y. J. Catalyst–electrolyte interface chemistry for electrochemical CO2 reduction. Chemical Society Reviews 2020, 49 (18), 6632-6665.(2) Wu, J.; Sharifi, T.; Gao, Y.; Zhang, T.; Ajayan, P. M. Emerging Carbon-Based Heterogeneous Catalysts for Electrochemical Reduction of Carbon Dioxide into Value-Added Chemicals. Advanced Materials 2019, 31 (13), 1804257.(3) Liang, S.; Huang, L.; Gao, Y.; Wang, Q.; Liu, B. Electrochemical Reduction of CO2 to CO over Transition Metal/N-Doped Carbon Catalysts: The Active Sites and Reaction Mechanism. Advanced Science 2021, 8 (24), 2102886.

Modulating the Electronic Structure of Metal Halide Perovskites for Efficient Selective CO2 Photoreduction to CO

Metal halide perovskites (MHPs) have recently held great promise for solar-to-fuel conversion via artificial photosynthesis technology. However, the conversion efficiency of most MHP photocatalysts is still far below that necessary for their practical implementation. Modulating the electronic structure is a promising strategy to solve this issue. Here, taking Cs2AgBiBr6 as a prototype, we investigate the interplay between the local electronic structure of Cs2AgBiBr6 and its photocatalytic performance via introducing heteroatoms. Theoretical calculations reveal that Au heteroatom-mediated orbital rehybridization induces high electron densities and tailors the d-band center of Cs2AgBiBr6, endowing more upshifted d-band center and enhanced adsorption strength of intermediates, thereby resulting in decreased energy barriers for selective CO2 photoreduction to CO product. Experimentally, we report the Cu-incorporated Cs2AgBiBr6 catalyst for selective photoreduction of CO2 to CO in a solid-gas system without sacrificial agents, yielding an on average CO generation rate of 47.3 μmol g−1 with approximately 100% selectively, outperforming the pure Cs2AgBiBr6 and comparable to the reported MHP-based photocatalysts. This work showcases modulating the electronic structure of MHP photocatalysts offering a powerful route for effective solar fuel generation.

Copper nanoclusters derived from copper phthalocyanine as real active sites for CO2 electroreduction: Exploring size dependency on selectivity ‐ A mini review

AbstractThe electrochemical reduction reaction of CO2 (CO2RR) holds promise for converting CO2 into valuable fuels and chemicals, particularly when powered by renewable electricity, thereby aiding in reducing atmospheric CO2 levels and addressing climate change. Copper phthalocyanine and its derivatives (Cu‐Pcs) have attracted significant attention as versatile electrocatalytic materials with high selectivity toward various hydrocarbon products. However, the real active sites of Cu‐Pcs for different products vary, and there is a lack of comprehensive summary. To address this gap, we analyze and summarize previous research, yielding the following insights: Cu‐Pcs undergo reconstruction and demetallization during CO2RR, with Cu(II) converting to Cu(0), forming transient copper nanoclusters (Cu NCs). The selectivity for CO2RR products closely correlates with the size of those derived Cu NCs. Specifically, reversible Cu NCs with ultrasmall sizes (≤2 nm), which revert to Cu‐Pcs after electrolysis, exhibit high selectivity toward CH4. As Cu NCs increase in size, there is a higher CO coverage, promoting CO generation. When Cu NCs exceed a critical threshold size (approximately 15 nm), C‐C coupling can occur, facilitating the formation of multicarbon (C2+) products. Furthermore, the structure of macrocycles, types of functional groups, and properties of carbon substrates influence the size and electron density of Cu NCs, thereby impacting the selectivity of CO2RR products.

Distributed multienergy and low-carbon heating technology for rural areas in northern China

In the context of China's “double carbon” policy and “rural revitalization” strategy, clean and low-carbon heating in rural areas of the northern China has become a key problem that needs to be urgently addressed. Practice has proved that “coal-to-gas” and “coal-to-electricity” projects have various limitations, such as high operating cost, high carbon emission, and high cost of distribution network upgrade, making them unsuitable for nationwide promotion. To address this issue, this research proposes a distributed multienergy and low-carbon heating (DMLH) system, which integrates the photovoltaic power generation, combined heat and power (CHP) system, heat storage, and newly developed multisource efficient heat pump (MEHP). The MEHP operates by simultaneously absorbing heat from air and waste heat sources of the CHP generation, providing a stable and efficient heat output. The multienergy complementary operating strategy of the DMLH system has been presented, considering variations of heating demand and environmental temperature. Comprehensive case studies were performed under typical and extremely cold winter scenarios to examine the effectiveness of the DMLH system. Simulation results revealed that 66.7 % of the operating cost can be reduced by the proposed system in typical scenario and the heat supply stability of MEHP has been considerably enhanced compared to a single-stage heat pump system. Furthermore, the DMLH system has low-level requirement of distribution network capability, which is conducive to promotion in the rural areas of northern China.

RETRACTED: Life cycle analysis of biowaste-to- biogas/biomethane processes: Cost and environmental assessment of four different biowaste scenarios organic fraction of municipal solid waste and secondary sewage sludge

Biowaste-to-biogas processes have been introduced to design a valuable and green renewable plant to achieve a sustainable society and environment. The biomethane production process through biogas upgrading instead of designing a combined heat and power (CHP) system can be more attractive. This study presents a life cycle analysis (LCA) from both cost and environmental standpoints for four biowaste-to-biogas/biomethane process scenarios. Biogas production is achieved through anaerobic co-digestion of the organic fraction of municipal solid waste (OF-MSW) and secondary sewage sludge (S-SS), incorporating a pre-treatment process based on the dark co-fermentation process (DCFP). Each scenario offers distinct methods for utilizing the hydrogen-rich gas and biogas, with varying degrees of energy recovery and efficiency. Two sensitivity studies were conducted under various utilizations of the recovered biomethane and the anticipated electricity mix. Scenario SC-1 (CHP-from-biogas) was found to be the most co-friendly favorable in eight out of eleven impact categories (under the CML/IA technique). Further, biogas upgrading-integrated options exhibited lower impacts. Replacing biomethane instead of petrol in scenarios with upgraded biogas was identified as the most effective approach against climate change. Financial analysis indicated that all layouts are economically viable, each demonstrating a positive NPV over a 20-year period (up to $11.57 million).

Technological and economical analysis of the heat recovery system from flue gas in a thermal waste treatment plant

A heat recovery system from flue gas increases the overall efficiency of a district heating or CHP plant, as the system recovers the waste energy contained in the flue gas at the chimney outlet. This makes it possible to increase thermal energy production with the same fuel consumption. A method for calculating the thermodynamic parameters of municipal waste incineration plants was developed as part of the work carried out. The mathematical models prepared made it possible to analyse the impact of the heat recovery system from flue gas on technical and economic parameters and the environment, including, among other things, an estimate of the annual amount of heat recovered, the amount of additional electricity consumed, the amount of condensate treated, the estimated capital expenditure, operating profits and operating costs. The results of the analyses were the basis for designing and constructing a heat recovery system from flue gas equipped with a condensation heat exchanger for the municipal waste incineration plant in Cracow. The calculation results were compared with the measurement results obtained during the test run of the constructed installation.

Energy saving scheduling of power and two steam loads for a CHP system consisting of multiple CHP units integrated with steam ejectors

Combined heat and power (CHP) can effectively enhance the energy efficiency of thermal power plants. However, the heat-dominated operation mode restricts the CHP unit's operation flexibility which is essential for the power grid for peak shaving. The double-extraction CHP unit, which cogenerates power and two-pressure steam for industrial or municipal heating users, is typical, complex, and widely applied. The integration of steam ejectors is an effective way to enhance the operational flexibility of the double-extraction CHP unit, which makes the scheduling of power and two steam loads very complicated. Therefore, the scheduling model of a CHP system consisting of multiple CHP units integrated with steam ejectors is developed in this study to achieve energy saving. A reference CHP system with four 1000 MW CHP units with steam ejectors is analyzed, and the operational flexibility and energy consumption characteristics of the units are analyzed. Then, the scheduling of power and two steam loads within a typical day is conducted. The results show that the coal consumption is reduced by 0.65–3.10 t h−1 compared with the original heating mode.

Thermo-economic optimization on a combined heat and power system with supercritical Rankine cycle for power-to-heat batteries

The global energy structure is transforming to low-carbon, and it is urgent to construct a sustainable energy system mainly based on renewables. The power-to-heat batteries (P2HBs) show great potential for large-scale energy storage by converting low-cost renewable power to heat. This paper aims to study the thermodynamic and economic advantages of the P2HB integrated with a supercritical steam Rankine cycle (RC) to achieve combined heat and power (CHP) generation. Firstly, a system model of P2HB-CHP consuming grid valley power is developed. The system includes three sub-systems: P2HB, steam generator, and CHP. Thermodynamic and economic analysis models are developed, and the average exergy efficiency (ηav) and net present value (NPV) are formulated as performance evaluation targets, respectively. The genetic algorithm is used to perform multi-parameter optimization of the system. The thermodynamic optimization results show that the maximum ηav of supercritical P2HB-CHP is 0.47 %, 1.16 %, and 1.44 % higher than that of subcritical P2HB-CHP when the high working temperature of the molten salt reaches 505 °C, 570 °C, and 640 °C, respectively. The largest proportion of anergy is generated by electric heaters, over 72 %. The next largest proportion is heat exchangers, which is related to the heat transfer temperature differences. The results of the economic analysis show that the maximum NPV of supercritical P2HB-CHP is lower by 158 M$, lower by 74 M$, and higher by 55 M$ than that of subcritical P2HB-CHP when the high working temperature of the molten salt is reached 505 °C, 570 °C, and 640 °C, respectively. The high efficiency of supercritical RC reduces the costs of electric heaters and molten salts, but sets high demands on the heat exchangers. Although high-temperature molten salt results in high energy efficiency, the increased cost of molten salt reduces the profitability of the system.