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The pulp and paper industry is a power-intensive technology so great attention to reducing its own energy consumption and declining the waste of available energy should be devoted. In the current investigation, the energy-exergy approach of a pulp and paper company integrated with a chemical recovery of black liquor (BL) and soda is studied actually for one year. The chemical BL recovery system that has the primary benefits to avoid environmental pollution by burning organic waste and recycling the soda is also comprehensively investigated. Natural gas (NG) and BL are utilized in power boiler (PB) and recovery boiler (RB), respectively. Moreover, in the present implementation, the chemical reactions of NG and BL are presented. The obtained results show that the percentages of energy losses in the condenser, RB, evaporators, and PB are 49.16, 19.28, 14.22, and 3.96%, respectively. The average values of exergy destruction percentages in RB and PB around the year are 41.63 and 33.5%, respectively. The maximum system overall exergy efficiency is 32.09% at an environment temperature of 290 K, whereas the energy efficiency of the system is 53.7%.

Under the challenge of global energy transition, coal-fired cogeneration systems are undergoing a technical revolution towards enhanced efficiency, heating capacity, and flexibility. In this paper, four schemes using a steam ejector integrated into a cogeneration system are designed. Considering operational safety, integrated locations are selected at the front and back of high- and medium-pressure turbines. Subsequently, the thermodynamic and operational characteristics under both design and off-design conditions are analyzed based on a model built in EBSILON Professional. Finally, a sensitivity analysis of the heating process is conducted. The results show that the integration of steam ejectors can increase the waste heat recovery ratio of exhaust steam by 18.42–45.61% under design conditions. The largest waste heat recovery ratio is obtained in System 4, resulting in the power generation efficiency ( η g ) and gross energy utilization efficiency ( η p ) of 81.95% and 65.53%, respectively. Meanwhile, the steam ejector can expand the power-load regulation range of the cogeneration system, and System 4 has the lowest lower power limit among all the systems. The η p values of Systems 1–4 reach extreme values at different mixed steam pressures of the ejector. Increasing the pinch point temperature difference reduces the power load η g and η p of Systems 1–4. The results provide technical solutions for improving the heating capacity and efficient and flexible operation of cogeneration systems. [ABSTRACT FROM AUTHOR]

In this paper, an integrated system based on low-concentrated photovoltaic/thermal (LCPV/T) technology and efficient vacuum membrane distillation (VMD) seawater desalination utilizing the energy of solar is established. Through a theoretical analysis and a series of experiments, this paper explores the temperature change of a single VMD process, and the variation trend of single-day membrane flux with solar irradiation and temperature parameters. In addition, the changes in solar irradiation, temperatures of the integrated system, membrane flux, and thermoelectric properties in different seasons are also analyzed. A mathematical model was established to calculate the relationship between membrane flux and temperature difference. The experimental results show that the membrane flux of VMD is 2.73 L/(m2·h); the simulated seawater can achieve a desalination rate of 99.9%. After economic analysis, the operating incomes of the system under sunny weather conditions in different seasons were all positive. [ABSTRACT FROM AUTHOR]

In order to improve the comprehensive utilization rate of energy in power plants, the author puts forward the research of artificial intelligence control system for heat and power plant waste heat recovery. In the heating system of waste heat recovery, intelligent time-sharing and zoning control is set according to user needs, which enables the heating system to adjust the temperature of heating water outlet in real time according to the dynamic change of outdoor climate, in the heating system of waste heat recovery, intelligent time-sharing and zoning control is set according to user needs, which enables the heating system to adjust the temperature of heating water outlet in real time according to the dynamic change of outdoor climate. The results show that the energy saving rate of time-sharing heating increases with the increase of outdoor temperature, when the outdoor temperature is 8 1, the energy saving rate is 0.35, in addition, the energy saving rate of the heating system is not only related to the outdoor temperature, but also to the length of the intermittent period, it is obvious that the longer the intermittent period is, the higher the energy saving rate is. In conclusion, the application of time division temperature control technology in the heating system greatly improves the energy saving effect of buildings, saves energy, and has extremely high economic, environmental and social benefits, which is worth advocating and promoting. [ABSTRACT FROM AUTHOR]

This paper presents the design of undervoltage relay settings for an industrial plant with cogeneration units to prevent critical loads from tripping due to voltage sags. The critical loads that are sensitive to voltage sags in the plant have been identified from actual system fault contingencies. The power quality of these loads is enhanced by quickly islanding the subsystem with cogeneration units before tie line tripping with an external Taipower system. According to the transient stability analysis of the rest of the industrial power system near a Taipower network, the critical loads that are nonsensitive to voltage sags are disconnected from external system faults in time to restore the system stability with the execution of proper load shedding. To ensure the normal operation of critical and voltage-sensitive loads by considering the voltage tolerance curves, the proper relay settings for tie line tripping of the internal subsystem has been determined. This way, the critical loads and cogeneration units in the industrial power systems can be survived from system faults to mitigate the production loss of industrial customers. [ABSTRACT FROM AUTHOR]

In this paper, an integrated system based on low-concentrated photovoltaic/thermal (LCPV/T) technology and efficient vacuum membrane distillation (VMD) seawater desalination utilizing the energy of solar is established. Through a theoretical analysis and a series of experiments, this paper explores the temperature change of a single VMD process, and the variation trend of single-day membrane flux with solar irradiation and temperature parameters. In addition, the changes in solar irradiation, temperatures of the integrated system, membrane flux, and thermoelectric properties in different seasons are also analyzed. A mathematical model was established to calculate the relationship between membrane flux and temperature difference. The experimental results show that the membrane flux of VMD is 2.73 L/(m2·h); the simulated seawater can achieve a desalination rate of 99.9%. After economic analysis, the operating incomes of the system under sunny weather conditions in different seasons were all positive.

The paper presents results of a parametric analysis of a hightemperature nuclear-reactor cogeneration system. The aim was to investigate the power efficiency of the system generating heat for a high-temperature technological process and electricity in a Brayton cycle and additionally in organic Rankine cycles using R236ea and R1234ze as working fluids. The results of the analyses indicate that it is possible to combine a 100 MW high-temperature gas-cooled nuclear reactor with a technological process with the demand for heat ranging from 5 to 25 MW, where the required temperature of the process heat carrier is at the level of 650°C. Calculations were performed for various pressures of R236ea at the turbine inlet. The cogeneration system maximum power efficiency in the analysed cases ranges from ~35.5% to ~45.7% and the maximum share of the organic Rankine cycle systems in electric power totals from ~26.9% to ~30.8%. If such a system is used to produce electricity instead of conventional plants, carbon dioxide emissions can be reduced by about 216.03-147.42 kt/year depending on the demand for process heat, including the reduction achieved in the organic Rankine cycle systems by about 58.01-45.39 kt/year (in Poland). [ABSTRACT FROM AUTHOR]

This paper presents a computer technology called hybrid particle swarm optimization (HPSO) algorithm, to solve the economic dispatch (ED) problem of cogeneration systems. First outlined the status of the power system development and technical discussion, followed by test cases from the literature are used to evaluate the accuracy and validity of the algorithm. The HPSO algorithm combines genetic algorithm-specific mutation factor (MF) characteristics and the disturbance mechanism (DM), then used the exponential function to control the MF. A generating capacity adjustment mechanism (GCAM) is designed help the algorithm effectively identify the global optimum, effectively enhance the performance of the algorithm, the advantages of reducing computation time and the search range is reached. [ABSTRACT FROM AUTHOR]

Under the challenge of global energy transition, coal-fired cogeneration systems are undergoing a technical revolution towards enhanced efficiency, heating capacity, and flexibility. In this paper, four schemes using a steam ejector integrated into a cogeneration system are designed. Considering operational safety, integrated locations are selected at the front and back of high- and medium-pressure turbines. Subsequently, the thermodynamic and operational characteristics under both design and off-design conditions are analyzed based on a model built in EBSILON Professional. Finally, a sensitivity analysis of the heating process is conducted. The results show that the integration of steam ejectors can increase the waste heat recovery ratio of exhaust steam by 18.42–45.61% under design conditions. The largest waste heat recovery ratio is obtained in System 4, resulting in the power generation efficiency (ηg) and gross energy utilization efficiency (ηp) of 81.95% and 65.53%, respectively. Meanwhile, the steam ejector can expand the power-load regulation range of the cogeneration system, and System 4 has the lowest lower power limit among all the systems. The ηp values of Systems 1–4 reach extreme values at different mixed steam pressures of the ejector. Increasing the pinch point temperature difference reduces the power load ηg and ηp of Systems 1–4. The results provide technical solutions for improving the heating capacity and efficient and flexible operation of cogeneration systems.

Abstract The solar thermoelectric generation（STEG）cogeneration system can provide heating and electric power simultaneously. Precedent studies on the STEG system were focused on getting higher electrical efficiency of the system and creating a new record. Optimization of thermal performance and evaluation of thermal efficiency are usually completed by calculation or numerical simulation. In this paper, a novel design of STEG cogeneration system was proposed. The system can work in three modes according to seasonal demand of hot water and electric power. A series of experiments were carried out in different working modes under variable conditions to evaluate the performance of the system. The results show that the system can generate 0.2 kW·h of electrical energy and about 100L of hot water at 41 °C in 1 day when solar irradiation is 1000 W/m2. The collector efficiency and electrical efficiency are calculated to be 42.2% and 2.1%, respectively. [ABSTRACT FROM AUTHOR]

This paper presents the protective relay settings of tie line tripping and design of load-shedding scheme for an integrated steelmaking industrial power system to ensure system stability after a severe fault contingency on an external utility power network. The transient stability analysis of the industrial power system with the equivalent external Taipower system has been executed for an actual fault contingency in 2005. The mathematical models of 13 cogeneration units in the plant and several large generators of a nearby Taipower thermal plant are included in the computer simulation to solve the system transient response for the fault contingency to verify the accuracy of the models used. To prevent tripping of critical loads due to an external fault contingency, the undervoltage and under/overfrequency relays with proper settings are applied for the tripping of external and internal tie lines. To restore system stability of the industrial power system for the islanding operation after tie line tripping, load shedding is designed to disconnect a proper amount of noncritical loads by considering the governor response and protective constraints of cogeneration units. According to the transient stability analysis of the industrial power system with the proposed protective relay settings and load-shedding scheme, it is found that the voltage sag and oscillation problem caused by fault contingency in the external Taipower system can be mitigated if the tie line tripping is executed in time to prevent the shutdown of critical loads and tripping of cogeneration units. [ABSTRACT FROM AUTHOR]

Abstract: The Cooling, Heating, and Power (CHP) systems have been widely recognized as a key alternative for thermal and electric energy generation because of the outstanding energy efficiency, reduced environmental emissions, and relative independence from centralized power grids. Nevertheless, the total energy cost of CHP systems can be highly dependent on the operation of individual components. This paper presents an energy dispatch algorithm that minimizes the cost of energy (e.g., cost of electricity from the grid and cost of natural gas into the engine and boiler) based on energy efficiency constrains for each component. A deterministic network flow model of a typical CHP system is developed as part of the algorithm. The advantage of using a network flow model is that the electric and thermal energy flows through the CHP equipment can be readily visualized allowing for easier interpretation of the results. This algorithm has been used in simulations of a case study on the operation of an existing micro-CHP system. The results from the simulation are presented in the paper to demonstrate the economical advantages resulting from optimal operation. [Copyright &y& Elsevier]

This paper investigates the effect of boiler steam system on transient response of turbine generators for an incinerator plant. By performing the test of cogeneration units, the mathematical models of turbine generator, governor, and boiler have been identified, which are used in the computer simulation to solve the steam pressure and system frequency of the cogeneration system for islanding operation after tie line tripping. Due to the variation of trash heat value, the power output of the cogeneration unit is stochastically varied with the steam generation for normal operation, which will cause the dynamic change of tie line power flows. For the severe fault contingency of external power systems, the cogeneration system will be isolated by tie line tripping, and the system frequency response is then determined by including the boiler effect to represent the dynamic steam generation. Because of more sluggish response of the boiler system caused by unstable trash heat value, the transient response of the incinerator governor system is inferior to that of conventional industrial cogeneration systems. To maintain the system stability for successful islanding operation of the incinerator plant, the amount of load shedding after tie line tripping has to be properly determined based on the transient stability analysis by considering the response of boiler system. [ABSTRACT FROM AUTHOR]

In regards to the cogeneration system in Northern China, mainly supported by combined heat and power (CHP) plants, it usually offers limited operation flexibility due to the joint production of electric and thermal power. For that large-scale wind farms included in the cogeneration system, a large amount of wind energy may have to be wasted. To solve this issue, the utilization of the electric energy storages and the thermal energy auxiliaries are recommended, including pumped hydro storage (PHS), compressed air energy storage (CAES), hydrogen-based energy storage (HES), heat storage (HS), electric boilers (EB), and heat pumps (HP). This paper proposes a general evaluation method to compare the performance of these six different approaches for promoting wind power integration. In consideration of saving coal consumption, reducing CO2 emissions, and increasing investment cost, the comprehensive benefit is defined as the evaluation index. Specifically, a wind-thermal conflicting expression (WTCE) is put forward to simplify the formulation of the comprehensive benefit. Further, according to the cogeneration system of the West Inner Mongolia (WIM) power grid, a test system is modelled to perform the comparison of the six different approaches. The results show that introducing the electric energy storages and the thermal energy auxiliaries can both contribute to facilitating wind power integration, and the HP can provide the best comprehensive benefit. [ABSTRACT FROM AUTHOR]

This paper investigates the optimum size of Micro Gas Turbine Cogeneration Systems (MGT-CGSs) in a sewage treatment plant in relation to its economic performance. A sewage treatment plant in a cold region was adopted as a model, and three units of MGT-CGS with power output capacity of 30, 65 and 200 kW were simulated to utilize biogas produced in-house in the plant. The energy balance of the system was first studied, and economic performance using Net Present Value method was carried out. It was found that a configuration with optimum combination of 3 types of MGTs (MGT-Combined) stated above had the highest power generation efficiency. However, MGT-Combinedneededmore units of MGT resulting in higher capital investment. Although all configurations of MGT-CGSs studied can generate Net Present Value (NPV) in the range of US$2,640,000-3,100,00, MGT-200had the highest NPV. MGT-200 had15% higher NPV compared to the lowest one,MGT-30. MGT-200 can generate the highest NPV because it had thelowest capital investment cost, while having high power cost savings. [ABSTRACT FROM AUTHOR]

In the subtropical urban area with a high density of buildings, district cooling system is regarded as an efficient alternative to supply cooling to a group of buildings with high efficiency and low cost. Appropriate design can render the district cooling system to achieve good performance. This paper attempts to study the performance of the district cooling system integrated with different energy technologies in a new development area. Performance of district cooling system with thermal storage system is calculated to level the energy consumption and reduce monthly bill. Results are compared with that of hydro pumped storage system and recommendations are given about the design and control the thermal storage system under current local tariff. The performance of district cooling system integrated with the combined cooling, heating and power system is also investigated to make full use of the primary energy. Performance of the system designed based on two ways are studied. Results show that the cogeneration system is beneficial for both the investors and users. Suggestions are given to help improve the performance of the district cooling system in the new development area by coupling with different energy technologies. [ABSTRACT FROM AUTHOR]

Nowadays, several technologies for desalination processes are available and widely employed. However, they consume a considerable amount of energy and involve high capital and operating costs. Therefore, the techno-economic analysis of a system coupling different energy sources with the desalination processes is of value. The possibility of coupling a small gas turbine combined heat and power system (GT CHP) with hybrid desalination plants (HDPs) has been assessed in this study. The proposed gas turbine power generation system, based on a single-stage centrifugal compressor and an uncooled centripetal turbine, provides design simplicity and reasonable installation costs for the power generating plant. The hybrid desalination technique, based on the use of two different desalination technologies, i.e., Reverse Osmosis (RO) and a thermal desalination process, has been chosen to better exploit the electrical and thermal energy produced by the mini CHP plant. The proposed solution is numerically investigated from both thermodynamic and economic points of view, and the results of the thermodynamic analysis of the cycle are used as input for the evaluation of the amount of freshwater produced and of costs. The economic assessment of standalone desalination systems is also shown for the comparison with the hybrid solutions here proposed. Results show that the total cost of the water produced by MED + RO was less than the total cost of the water obtained by MSF + RO, and that the energy cost of MED + RO hybrid desalination system was about 15% less than that for stand-alone RO desalination technology. Thus, the MED + RO hybrid desalination system can be considered a promising solution for the coupling with the proposed mini GT CHP plant, which, due to the small size and cost, as well as the easy installation, can be easily applied in off-grid or remote areas. [ABSTRACT FROM AUTHOR]

This paper presents a developed general computer program, which is a flexible computational tool for biomass energy surveying of an interested wide geographical area (w.g.a.) and its properly selected interior zones for the purpose of identifying possible cogeneration or combined heat and power (CHP) unit installations in proper site locations, which in turn are fully assessed in techno-economic terms. In addition the program, based on the available in the w.g.a. forms of solid biomass and the geographic distribution of the pertinent feedstock, makes a hierarchical order of these taking into account their quantities and energy characteristics, which ultimately leads to definite combinations and thus to desired mixed solid biomass fuel for steady annual contribution (or with seasonal preference in order to reduce the storage costs) of the participating solid biomass residues to be used for the fuel supply of the associated CHP unit. Last the program is conducive to performing reliable sensitivity analysis work as function of key system parameters or quantities. As a case study a w.g.a., belonging to the north-east part of Eastern Macedonia-Thrace Region of Greece, is thoroughly analyzed taking into account the specific techno-economical constraints applicable (due to national energy and development laws, etc.) to this area and the pertinent practical results are presented. [Copyright &y& Elsevier]

The integration of absorption chillers in micro-cogeneration systems based on micro-gas turbines can be useful as an appropriate strategy to increase the total system energy efficiency. Since it is an area intensive in technology, it is necessary to develop and use models of simulation, which can predict the behavior of the whole system and of each component individually, at different operating conditions. This work is part of a research project in high efficiency cogeneration systems, whose purpose at this stage is to model a micro-cogeneration system, which is composed of a micro gas turbine, Capstone C30, a compact cross flow finned tube heat exchanger and an absorption chiller. The entire model is composed of specifically interconnected models, developed and validated for each component. The simulation of the microturbine used a thermodynamic analytic model, which contains a procedure used to obtain the micro turbine characteristic performance curves, which is closed with the thermodynamic Brayton cycle model. In the cogeneration system discussed in this paper, the compact heat exchanger was used to heat thermal oil, which drives an absorption chiller. It was designed, characterized and installed in a cogeneration system installed at the Centre d'Innovació Tecnològica en Revalorització Energètica i Refrigeració, Universtat Rovira i Virgili. Its design led to the heat exchanger model, which was coupled with the micro turbine model. Presented in this work is a comparison between the data from the model and the experiments, demonstrating good agreement between both results.

Surging in energy demand makes it necessary to improve performance of plant equipment and optimize operation of thermal power plants. Inasmuch as thermal power plants depend on fossil fuels, their optimization can be challenging due to the environmental issues which must be considered. Nowadays, the vast majority of power plants are designed based on energetic performance obtained from first law of thermodynamic. In some cases, energy balance of a system is not appropriate tool to diagnose malfunctions of the system. Exergy analysis is a powerful method for determining the losses existing in a system. Since exergy analysis can evaluate quality of the energy, it enables designers to make intricate thermodynamic systems operates more efficiently. These days, power plant optimization based on economic criteria is a critical problem because of their complex structure. In this study, a comprehensive analysis including energy, exergy, economic (3‐E) analyses, and their applications related to various thermal power plants are reviewed and scrutinized. Several thermal power plants in combined cycles are reviewed comprehensively in the present study. Results of the studies based on energy, exergy, and economic analyses are represented for each type of thermal power plants. Integrating thermal power plants with other cycles will enhance the energetic efficiency. Systems integrating will increase investment cost for the power plants. Exergy analysis provide useful information for enhancement of plants' efficiency. [ABSTRACT FROM AUTHOR]

We propose a solar thermal cogeneration system using a cylindrical thermoelectric module for efficient solar energy convergence. Numerical simulations are presented to evaluate the system efficiency compared with a conventional pillar-type thermoelectric cogeneration system. We consider the effects of thermal radiation, contact resistances, and heat flux in the connecting wire, which significantly affect the system efficiency. Compared with the pillar-type device, the cylindrical device can achieve a higher heat flux and lower thermal radiation loss from the sides. In particular, the thermal radiation loss from the sides becomes negligible in a scaled-up cylindrical device. When the areas of the light-absorbing layer are the same in both devices, the power efficiencies, which are defined as power extracted from the module over input heat to the module, are comparable, but the system efficiency, which is defined as extracted heat from the module over input heat to the module, of the cylindrical device is higher than that of the pillar-type device. In the case of the unileg cylindrical device, where the hot side is connected to the cold side by the Cu wire, the system efficiency increased but the power efficiency decreased owing to the heat flux through the Cu wire. On the other hand, the p-n couple cylindrical device can overcome the trade-off and achieve system efficiency as high as 91.6%, including 8.1% power efficiency. [ABSTRACT FROM AUTHOR]

In regards to the cogeneration system in Northern China, mainly supported by combined heat and power (CHP) plants, it usually offers limited operation flexibility due to the joint production of electric and thermal power. For that large-scale wind farms included in the cogeneration system, a large amount of wind energy may have to be wasted. To solve this issue, the utilization of the electric energy storages and the thermal energy auxiliaries are recommended, including pumped hydro storage (PHS), compressed air energy storage (CAES), hydrogen-based energy storage (HES), heat storage (HS), electric boilers (EB), and heat pumps (HP). This paper proposes a general evaluation method to compare the performance of these six different approaches for promoting wind power integration. In consideration of saving coal consumption, reducing CO2 emissions, and increasing investment cost, the comprehensive benefit is defined as the evaluation index. Specifically, a wind-thermal conflicting expression (WTCE) is put forward to simplify the formulation of the comprehensive benefit. Further, according to the cogeneration system of the West Inner Mongolia (WIM) power grid, a test system is modelled to perform the comparison of the six different approaches. The results show that introducing the electric energy storages and the thermal energy auxiliaries can both contribute to facilitating wind power integration, and the HP can provide the best comprehensive benefit.

A residential cogeneration system (CGS) is highlighted because of its efficient energy usage on both the supplier and consumer sides. It generates electricity and heat simultaneously; however, there is insufficient information on the efficiency according to the condition of usage. In this study, we analysed the performance data measured by the home energy management system (HEMS) and the lifestyle data of residents in a condominium of 356 flats where fuel cell CGS was installed in each flat. The electricity generated by CGS contributed to an approximately 12% reduction in primary energy consumption and CO2 emission, and the rate of generation by the CGS in the electric power demand (i.e., contribution rate) was approximately 38%. The electricity generation was mainly affected by the use of electricity up to 4 MWh/household/year. Gas or water use also impacted electric power generation, with water use as the primary factor affecting the contribution rate. Electric power generation changes monthly, mainly based on the water temperature. From these results, we confirmed that a CGS has substantial potential to reduce energy consumption and CO2 emission in condominiums. Thus, it is recommended for installation of fuel cell CGS in existing and new buildings to contribute to the energy-saving target of the Japanese Government in the residential sector. [ABSTRACT FROM AUTHOR]

The search for new fuels to supersede fossil fuels has been intensified these recent decades. Among these fuels, hydrogen has attracted much interest due to its advantages, mainly cleanliness and availability. It can be produced from various raw materials (e.g., water, biomass) using many resources, mainly water electrolysis and natural gas reforming. However, water electrolysis combined with renewable energy sources is the cleanest way to produce hydrogen while reducing greenhouse gases. Besides, hydrogen can be used by fuel cells for producing both electrical and thermal energy. The aim of this work was towards efficient integration of this system into energy efficient buildings. The system is comprised of a photovoltaic system, hydrogen electrolyzer, and proton exchange membrane fuel cell operating as a cogeneration system to provide the building with both electricity and thermal energy. The system's modeling, simulations, and experimentations were first conducted over a short-run period to assess the system's performance. Reported results show the models' accuracy in analyzing the system's performance. We then used the developed models for long-run testing of the hybrid system. Accordingly, the system's electrical efficiency was almost 32%. Its overall efficiency reached 64.5% when taking into account both produced electricity and thermal energy. [ABSTRACT FROM AUTHOR]