Waste Heat Recovery Process Research Articles

Comparative thermoeconomic analysis of integrated hybrid multigeneration systems with hydrogen production for waste heat recovery in cement plants

The cement industry is a widely used and energy-consuming sector, making it one of the largest CO2 emitters, primarily to meet its energy demands. Therefore, this research aims to evaluate the waste heat recovery process from a cement factory to fulfill a portion of its energy requirements. In this study, four scenarios have been evaluated, including power production scenarios, hydrogen production scenarios, methanation production process evaluation scenarios, blending hydrogen with natural gas, oxy-fuel combustion scenarios, and scenarios for producing the required freshwater for the factory and the water electrolysis process. The results show that the steam Rankine cycle with the reheating process and the organic Rankine cycle with methanol working fluid with a production capacity of 24.35 MW, and a payback period of 2.4 years with levelized cost of energy being 0.005809 $/kWh, is the most favorable scenario for the power generation cycle. Also, the process of alkaline electrolysis with a hydrogen production rate of 0.1648 kg/s, and a payback period of 5.816 years, and also with the levelized cost of hydrogen being 1.001 $/kg, happened to be the most suitable hydrogen production scenario compared to other electrolysis scenarios such as PEM and SOEC. Moreover, the process of water desalination by reverse osmosis with the energy consumption of 2.7 MW of power is capable of supplying all the required water of the factory and the water electrolysis process, and it was determined as the most suitable scenario for supplying the required water.

An efficient molten steel slag gas quenching process: Integrating carbon solidification and waste heat recovery

The iron and steel-making industries have garnered significant attention in research related to low-carbon transitions and the reuse of steel slag. This industry is known for its high carbon emissions and the substantial amount of steel slag it generates. To address these challenges, a waste heat recovery process route has been developed for molten steel slag, which integrates CO2 capture and fixation as well as efficient utilization of steel slag. This process involves the use of lime kiln flue gas from the steel plant as the gas quenching agent, thereby mitigating carbon emissions and facilitating carbonation conversion of steel slag while simultaneously recovering waste heat. The established carbonation model of steel slag reveals that the insufficient diffusion of CO2 gas molecules within the product layer is the underlying mechanism hindering the carbonation performance of steel slag. This finding forms the basis for enhancing the carbonation performance of steel slag. The results of Aspen Plus simulation indicate that 1 t of steel slag (with a carbonation conversion rate of 15.169 %) can fix 55.19 kg of CO2, process 6.08 kmol of flue gas (with a carbon capture rate of 92.733 %), and recover 2.04 GJ of heat, 0.43 GJ of exergy, and 0.68 MWh of operating cost. These findings contribute to the development of sustainable and efficient solutions for steel slag management, with potential applications in the steel production industry and other relevant fields.

Experimental study and process evaluation of coproduction graphene, acetylene and hydrogen from methane pyrolysis by thermal plasma

This paper developed a process for the coproduction of graphene, acetylene and hydrogen from methane pyrolysis by thermal plasma. Bench-scale tests under three specific energy input (SEI) were carried out to investigate the morphology of carbon nanomaterials and the product selectivity. The process was evaluated by exergy and exergoeconomic analyses. Results indicated that a higher SEI improved the selectivity of graphene nanoflakes (GNFs) and reduced their defects. The product selectivity of GNFs played a critical role in the decrease of total fuel exergy per unit of GNFs as the SEI increased. The plasma reactor exhibited the highest exergy loss ratio in the entire process due to heat dissipation. The quenching device exhibited the second-highest exergy loss ratio in the process, stemming from irreversible entropy increase causing exergy loss. Improving the design of the plasma reactor to enhance thermal efficiency and implementing a feasible waste heat recovery system were identified as effective strategies to enhance exergy efficiency. Excluding consideration of co-products, GNFs with high SEI had the lowest cost of 199.41 CNY/kg, when co-products were considered, the lowest cost decreases by 30%, and the low SEI had the lowest GNFs cost at 140.71 CNY/kg. This indicated that there was enough investment potential to tailor the properties of GNFs produced by such processes for application scenarios. The unit exergy cost of GNFs decreased from 0.89 CNY/MJ to 0.80 CNY/MJ as the SEI of the plasma reactor increased. Subsequently, it rose to 1.16 CNY/MJ. Prioritizing the increase in investment costs for the plasma reactor to reduce exergy loss costs should be considered first, and optimizing the waste heat recovery process was also a key direction to minimize exergy loss costs.

Experimental investigation of axial finned tube evaporator thermal distillation system using for diesel engine waste heat recovery process

The study aims to improve the waste thermal energy retrieval from flue gas of an internal combustion engine (ICE). The recovered waste heat energy was used for distillation by using a thermal distillation system. The performance of the thermal distillation unit was investigated by varying the evaporator (boiler) type and engine load (25, 50, 75 %). Four different types of boilers were used including one smooth copper tube and other three were two, three and four axial finned copper tube evaporators. The impact of boiler type and engine load on the net retrieved energy and exergy, net energy and exergy efficiency, and distillate yield rate of thermal distillation unit was also examined. The results showed that the net extracted heat energy and exergy for axial finned tube evaporator was approximately 26.823 – 45.513 % and 7.614 – 25.203 W higher than that of smooth tubes evaporator at 25 and 75 % engine load, respectively. The distillation yield was found to be ~ 2.35 liter/ hour in the case of four axial finned tube boiler at 75 % engine load.

Optimizing industrial Energy: An Eco-Efficient system for integrated Power, Oxygen, and methanol production using coke plant waste heat and electrolysis

This research presents a novel, eco-efficient hybrid system designed for the simultaneous production of power, oxygen, and methanol. It utilizes energy from coke plants and incorporates state-of-the-art waste heat recovery processes (WHRPs). The system effectively merges electricity and methanol production with WHRPs, improving both environmental sustainability and economic feasibility in industrial energy transformation. It consists of a fuel reforming and combustion unit, a waste heat recovery unit, a unit for hydrogen gas production through water electrolysis, and a methanol synthesis module. This configuration enables the production of 12.72 MW of electricity, 0.51 kg/s of oxygen, and 0.53 kg/s of methanol, achieving an energy productivity of 46.8 % and an exergy efficiency of 85.13 %. The economic analysis indicates competitive costs of $0.099 per kWh for electricity and $0.56 per kg for methanol. The system surpasses current technologies in thermodynamic efficiency, operational and product costs, and reduced CO2 emissions, demonstrating its potential as a sustainable and economically sound solution for industrial energy challenges. It supports global sustainability initiatives and fits within the circular economy concept.

Maximizing energy efficiency in wastewater treatment plants: A data-driven approach for waste heat recovery and an economic analysis using Organic Rankine Cycle and thermal energy storage

Maximizing energy efficiency through waste heat recovery (WHR) processes is crucial for sustainable and eco-friendly operations across multiple industries, notably in wastewater treatment plants (WWTPs). This work proposes a comprehensive approach for assessing the WHR feasibility in WWTPs, structured in two main objectives. Firstly, an Artificial Neural Network (ANN) model is developed to accurately predict WHR based on operational data, including biogas temperature, biogas pressure, daily production in kWh, and WHR values in kWhth. The second objective focuses on economically evaluating the WHR feasibility based on the estimated WHR values obtained by the ANN model, and then realistically assessing the economic feasibility of integrating the Organic Rankine Cycle (ORC) and Seasonal Thermal Energy Storage (STES) systems. With an application to the As-Samra WWTP located in Jordan, the developed ANN model demonstrates promising results in the validation phase, with a root mean square error (RMSE) of 2206 kWh/day, a mean absolute error (MAE) of 1674 kWh/day, and an R-squared (R2) value of 68%. On the other hand, the economic analysis reveals that an optimal ORC system of 412.14 kWe capacity yields a Net Present Value (NPV) of 2.09 million US dollars, a Levelized Cost of Energy (LCOE) of 0.0749 USD/kWh, a Payback Period (PBP) of 4.8 years, and annual revenues of 428 kUSD. This work also investigates the techno-economic feasibility of integrating ORC-STES. Results indicate that the LCOE and PBP are highly affected by the ORC's capital cost, and integrating STES increases the LCOE to 0.0824 USD/kWh, rendering its integration with ORC infeasible. This study aims to advance the understanding and application of WHR in WWTPs, paving the way for more efficient and sustainable practices in the field.

A fuel gas waste heat recovery-based multigeneration plant integrated with a LNG cold energy process, a water desalination unit, and a CO2 separation process

Development of the multigeneration plants based on the simultaneous production of water and energy can solve many of the current problems of these two major fields. In addition, the integration of fossil power plants with waste heat recovery processes in order to prevent the release of pollutants in the environment can simultaneously cover the environmental and thermodynamic improvements. Besides, the addition of a carbon dioxide (CO2) capturing cycles with such plants is a key issue towards a sustainable environment. Accordingly, a novel waste heat recovery-based multigeneration plant integrated with a carbon dioxide separation/liquefaction cycle is proposed and investigated under multi-variable assessments (energy/exergy, financial, and environmental). The offered multigeneration system is able to generate various beneficial outputs (electricity, liquefied CO2 (L-CO2), natural gas (NG), and freshwater). In the offered system, the liquified natural gas (LNG) cold energy is used to carry out condensation processes, which is a relatively new idea. Based on the results, the outputs rates of net power, NG, L-CO2, and water were determined to be approximately 42.72 MW and 18.01E+03, 612 and 3.56E+03 kmol/h, respectively. Moreover, the multigeneration plant was efficient about 32.08% and 87.72%, respectively, in terms of energy and exergy. Economic estimates indicated that the unit product costs of electricity and liquefied carbon dioxide production, respectively, were around 0.0466 USD per kWh and 0.0728 USD per kg-CO2. Finally, the total released CO2 was about 0.034 kg per kWh. According to a comprehensive comparison, the offered multigeneration plant can provide superior environmental, thermodynamic, and economic performances compared to similar plants. Moreover, there was no need to purchase electricity from the grid.

A low-carbon polygeneration system based on a waste heat recovery system, a LNG cold energy process, and a CO2 liquefaction and separation unit

Abstract Expanding energy conversion plants that simultaneously produce water and energy can address multiple issues in these two major fields. Additionally, utilizing waste heat energy from fossil fuel-driven plants rather than releasing it into the atmosphere can provide both thermodynamic and environmental benefits. A new polygeneration plant that integrates a waste heat recovery process and a CO2 liquefaction and separation process is developed and analyzed through a multi-criteria assessment (thermodynamic, economic, and environmental). The plant is capable of producing several advantageous products, including power, natural gas, desalinated water, and liquefied CO2. The polygeneration plant employs cold energy of liquefied natural gas (LNG) for condensation processes, a novel approach. Results indicate a net power rate of ~41.96 MW, with 166.8, 4912.8, and 972.6 mol/s for liquefied CO2, natural gas, and desalinated water, sequentially. The plant exhibits energy efficiency and exergy efficiency of ~31.6% and ~86.5%, respectively. The cost feasibility shows that electricity production carries a unit cost of 0.0474 US$/kWh, while liquefied CO2 production cost was about 0.0742 US$/kgCO2. The plant is estimated to emit roughly 0.0343 kg/kWh of carbon dioxide. The energy and exergy efficiencies decrease by ~9% and 2%, respectively, as the seawater feed rate increases from 13 to 23 kg/s. A comprehensive comparison indicates that the studied polygeneration plant yields superior economic, thermodynamic, and environmental performance compared to similar facilities. Furthermore, the proposed plant is capable of meeting its own power demands and does not require electricity from the grid.

Effect of orientation and nanoparticle addition of a encapsulated phase change material on heat transfer in a packed bed thermal energy storage system – A numerical analysis

Thermal energy storage technology research is growing globally due to the increased awareness of the clean energy demand and limitations of fossil fuel commodities. The packed bed latent heat thermal energy storage (PBLHTES) system is one among it promising a greater number of applications like solar water heating, industrial waste heat recovery process, thermal power generations, thermal comfort of buildings etc., Due to the high latent heat capacities, available in wide temperature ranges and minimal volume change, solid-to-liquid phase change materials (PCMs) are more attractive than any other latent heat materials to use in the PBLHTES system. Although, the low conductivity of PCM restricts the heat transfer while the charging and discharging periods. Therefore, it is necessary to incorporate thermal enhancement techniques in a PBLHTES system to improve the melting rate of the PCM. In this work, it is attempted to carry the 2-D numerical analysis of PBLHTES system provided with encapsulated PCM staggered in the flow direction of heat transfer fluid. The numerical results are validated with the experimental work. The effect of the inclination of PCM capsules with the flow direction (0°, 2.5°, 5°, 7.5°, and 10°), the addition of Multi-walled carbon nanotubes (MWCNT) nanoparticles (0 %, 1 %, 2 %, 3 %, 4 %, and 5 %) on energy absorbed by the PCM are studied. Also, the contours of temperature distribution and liquid fraction of the PCM with time are presented. The results revealed that the temperature distribution of HTF rises when PCM spheres orientated to the HTF shifted from 0 to 2.5° later it reduces. Though HTF temperature rises, the PCM temperature, liquid Fraction and energy absorbed decline when the capsules inclined to the flow direction. This is mainly due to the reason that the HTF moves outwards from the flow direction and towards the edges of the container, which makes the HTF carry a more amount of heat without sharing with the PCM capsules. Therefore, these arrangements will be helpful to switch over the ideal high-temperature HTF at the outlet without charging the TES system and vice versa. An improvement of 13.16 % melting rate is observed from 0 to 3 % of a nanoparticle addition and only 4 % enhancement is noted from 3 to 5 % MWCNT deposition. The effect of nanoparticles on energy absorbed by the PCM is nearly constant after 3 % of Multi-walled carbon nanotubes (MWCNT) addition. Therefore, this is the optimum MWCNT volume concentration to be added. The maximum energy absorbed with 3 % MWCNT for 60 min of time is 98.7 kJ and 97 kJ which are 3.5 % and 3.65 % more than the pure PCM for the standard case (0°) and 2.5° angle of attack of EPCMs with the flow direction.

Effect of Furnace Structure on Burden Distribution and Gas Flow in Sinter Vertical Cooling Furnace

Sinter sensible heat recovery via a vertical cooling furnace is a new type of waste heat recovery process proposed based on coke dry quenching. However, the segregation of the burden in a vertical cooling furnace is serious, resulting in a large amount of cooling gas escaping from the short-circuit channel of the vertical cooling furnace, which seriously affects the uniform gas–solid heat transfer in the furnace. To improve the burden distribution and gas flow in such a furnace, this paper proposes a Venturi-type vertical cooling furnace. Based on the single silo of a vertical cooling furnace in Meishan Steel, a slot model was established, and the improvement effect of the Venturi furnace structure on the burden distribution and gas flow was studied using the DEM–CFD coupling method. The results show that compared with the existing furnace type, the inclined wall of the Venturi furnace changed the direction of the high Dnv (average diameter) channel from vertical to inclined-vertical and reduced the Dnv from >0.033 m to 0.028~0.03 m in the vertical part of the variable-diameter section, thus reducing the influence area of the high Dnv channel. The minimum and average values of the voidage in the contraction part of the variable-diameter section increased from 0.28 and 0.315 to 0.31 and 0.33, respectively, which caused the voidage distribution to change from U-shaped to W-shaped along the longitudinal direction while simultaneously reducing the longitudinal fluctuation range of the voidage from 0.28~0.39 to 0.298~0.37. The gas flow direction changed from vertical-upward to vertical-inclined-upward, which increased the gas–solid contact. The gas velocity increased significantly. In the vertical section, the average gas velocity was 2.34 m/s, which was 30.73% higher than the velocity of 1.79 m/s of the existing furnace type. In the variable-diameter section, the average gas velocity was 3.52 m/s, which was 72.55% higher than the velocity of 2.04 m/s of the existing furnace type. The high-speed gas channel basically only existed in the sidewall area and the center area of the vertical section, and the length was reduced from 3.11 m to 2.52 m, which reduced the influence area. In the variable-diameter section, the high-speed gas channel disappeared, and the uniformity of the gas velocity distribution was greatly improved. The gas pressure drop increased from 4140 Pa to 6410 Pa, with an increase of 54.83%. Therefore, when designing the Venturi furnace type, it was necessary to take into consideration the improvement in the gas velocity distribution and the increase in the pressure drop. The research results of this paper can provide guidance for the structure optimization of the sinter vertical cooling furnace.

Nanofluids as a Waste Heat Recovery Medium: A Critical Review and Guidelines for Future Research and Use

The thermal energy storage and conversion process possesses high energy losses in the form of waste heat. The losses associated with energy conversion achieve almost 90% of the worldwide energy supply, and approximately half of these losses are waste heat. Hence, waste heat recovery approaches intend to recuperate that large amount of wasted heat from chimneys, vehicles, and solar energy systems, among others. The novel class of thermal fluids designated by nanofluids has a high potential to be employed in waste heat recovery. It has already been demonstrated that nanofluids enhance energy recovery efficiency by more than 20%. Also, the use of nanofluids can improve the energy capacity of steelworks systems by around three times. In general, nanofluids can improve efficiency and reduce exergy destruction and carbon emissions in devices like heat exchangers. The current work summarizes the application of nanofluids in waste heat recovery and discusses the involved feasibility factors. Also, the critical survey of more than one hundred scientific papers enabled the overview of the environmental aspects of the nanofluid’s waste heat recovery. Finally, it discusses the main limitations and prospects of the use of nanofluids in waste heat recovery processes.

Numerical simulation of waste heat recovery process from the hot stripped gas in carbon capture process by using ceramic membrane

CO2 chemical absorption process suffers from the high CO2 regeneration heat requirement, so a rich solvent-split mechanism was put forward to recover the waste heat from the hot stripped gas for reducing the regeneration heat consumption. Ceramic membrane-based transport membrane condenser (TMC) can provide a higher heat transfer efficiency, therefore better meet the requirements for waste heat recovery from the hot stripped gas. The ceramic membrane structure is a key factor affecting the heat recovery performance, which has been neglected by previous studies. For investigating the effect of membrane structure, in this study, a condensation and mass transfer model was firstly constructed using the computational fluid dynamics approach to describe the process of waste heat recovery from the hot stripped gas. The errors between the simulated outlet temperature of stripped gas or CO2-rich solvent and the experimental ones are about 1.74 %, indicating the satisfactory accuracy of the model. Based on the model, the effects of ceramic membrane structure and physical parameters on the waste heat recovery performance were comprehensively investigated. The results showed that reducing the wall thickness or inner diameter of ceramic membrane contributes to improving the waste heat recovery efficiency of TMC. Notably, there may be an optimal membrane area beyond which the improvement of waste heat recovery is difficult. Additionally, when the thermal conductivity of ceramic membrane exceeds a critical value (∼10 W/(m K) in this study), the improvement of waste heat recovery performance may be difficult only by increasing the thermal conductivity. This study provides an important guidance for the selection of ceramic membranes for waste heat recovery process from the stripped gas in the future.

A new biomass-natural gas dual fuel hybrid cooling and power process integrated with waste heat recovery process: Exergoenvironmental and exergoeconomic assessments

The integration of gas turbine cycle (GTC)-based energy processes with a biomass gasification process employing a post-combustion approach, in addition to improving the reliability and performance of the energy cycle, can reduce the current crisis in the energy sector and balance the environmental impacts of the hybrid energy cycle. The present paper develops a multi-criteria evaluation and optimization of a novel hybrid cooling and power process (HCPP) based on GTC and post-combustion-based biomass gasification process integrated with downstream cycles. Two fuels (i.e., natural gas and biomass) are utilized simultaneously to produce energy in the proposed process. In addition, the downstream cycles are based on two organic Rankine cycles (ORCs) and a refrigeration unit to recover waste heat. The performance of the developed HCPP has been evaluated and discussed from the thermodynamic-conceptual, exergoenvironmental and exergoeconomic points of view. Additionally, a tri-objective optimization is applied to identify optimal inputs and outputs variables. The overall results indicated that the proposed HCPP can produce 13 MW of electric power and 7.6 MW of cooling load. The thermal and exergy efficiencies of the system were 70.1% and 42.85%, respectively. Moreover, the values of levelized cost of energy (LCOE) and product unit environmental impact (PUEI) were calculated as 0.0748 USD/kWh and 0.0184 Pts/kWh, respectively. However, under tri-objective optimization, the values of LCOE and PUEI can be reduced by approximately 9.4% and 16.8%. The effect of different parameters was also discussed and evaluated through a parametric analysis. Furthermore, the conceptual assessment and design of the solar field was developed for a hypothetical scenario and configuration (based on geographical conditions of a certain region).

Simulation and multi-aspect analysis of a novel waste heat recovery process for a power plant producing electricity, heating, desalinated water, liquefied carbon dioxide, and natural gas

This paper presents a novel multigeneration framework based on fossil fuels, which offers several advantages such as high thermodynamic efficiency, low electricity and liquid carbon dioxide (CO2) production costs, and significantly reduced pollutant emissions. The simulation was carried out using the Aspen HYSYS software. The thermodynamic analysis revealed that the process achieves a total exergy efficiency of 86 % and an energy efficiency of 31.36 %. The integrated system yields various products, including 597.6 kmol/h of liquid CO2, 3484 kmol/h of desalinated water, 17,600 kmol/h of natural gas for the trunk line, and 41742.1 kW of power. The analyses further demonstrated that the total exergy destruction in the process amounts to 118071 kW, with contributions from the HPGU, NHPGU, MNPGU, and CSLU units of 30.1 %, 22.23 %, 30.36 %, and 17.29 %, respectively. Regarding environmental impact, the analysis revealed that the indirect emissions from the process are negligible. When the CO2 recovery rate exceeds 99 %, the direct emission amounts to 153.72 kg/h, and the pollution intensity of the proposed scheme is 3.68 gCO2/kWhel, which is lower than that of other technologies. Additionally, the economic analysis indicated that the production costs of CO2 and electricity in the proposed process are 0.075 $/kgCO2 and 0.048 $/kWh, respectively.

An intelligent design and environmental consideration of a green-building system utilizing biomass and solar having a bidirectional interaction with the grid to achieve a sustainable future

As a result of climate change and environmental pollutants becoming more prevalent in the environment, this paper introduces an innovative approach to energy systems that uses smart building technologies and renewable energy sources to mitigate climate change and promote sustainability. The central concept of this method is to hybridize solar and biomass resources in order to meet the heating, cooling, and electricity needs of a residential neighborhood over the year. The system is driven by an intelligent design of photovoltaic thermal panels combined with an efficient heater. This idea reduces the solar system cost and increases the independency from the local heating and cooling networks when the sun is unavailable. Besides, the waste heat recovery process is introduced to utilize the additional heat to charge the chiller and space heating demand and avoid releasing excess heat into the environment as much as possible. Multiple controllers are employed to launch a bidirectional connection with the electricity grid to sell or buy energy to or from the grid based on production, demand, and usage. The system’s affordability, effectiveness, and environmental sustainability are assessed comprehensively via TRNSYS software and MATLAB-developed code. According to the results, the proposed smart system achieves a very low emission rate of 14 kg.CO2/MWh with an affordable energy cost of 76.3 $/MWh. The results further reveal that while the system chiefly depends on biomass in cold hours to meet the heating demand, most of the building’s cooling need is provided by the photovoltaic thermal panels in summer, signifying the importance of renewable energy resources combination. It is noteworthy that due to the combination of green energy sources, the amount of carbon dioxide emission is significantly reduced by 35%. In addition, the net electricity is positive 2300 h of the year, meeting the demand, charging the chiller and tank, and seeling the additional to the grid, offsetting a significant portion of the annual energy costs. The results eventually showed that while the minimum energy cost of 79 $/MWh was obtained in April, the performance efficiency and emission rate reached the maximum and minimum values of 41.5% and 10.5 kg.CO2/MWh in December.

Waste heat recovery and cascade utilization of CO2 chemical absorption system based on organic amine method in heating season

In this paper, we proposed a waste heat recovery route of CO2 chemical absorption systems, which can realize waste heat recovery and cascade utilization in heating season. Simulation methods were used to study carbon capture systems and absorption heat pump, experimental methods were used to study the contact heat transfer characteristics of packed tower, and three organic amine solutions were involved: MEA (2-Aminoethanol), MEA& MDEA (N-Methyldiethanolamine) and AMP (2-Amino-2-methyl-1-propanol). The outlet gas temperature of carbon capture system is 47.7 °C∼58.8 °C, the temperature of lean solution is 73.3 °C∼95.0 °C, the absorption heat pump can increase the return water from 40 °C to 85 °C∼97 °C, the heat transfer end difference between flue gas and water in packed tower can be less than 1.0 °C. The system can achieve energy conservation and CO2 emission reduction effect, over 80% of the solution waste heat were recovered, the two-stage gas waste heat recovery process can improve boiler efficiency by over 19%.

Feasibility Study on A Novel Waste Heat Recovery Process of Industrial Waste Salt Based on High Temperature Melting Dry Method

Industrial waste salt is mainly produced by industrial production processes of pesticides, drug synthesis, printing and dyeing, as well as solid-liquid separations, concentration and crystallization of solution, and sewage treatment, etc. At the present stage, the annual output of waste salt in China has exceeded 2.0×107 tons and the high-temperature melting method is considered to be a promising treatment method, but there are problems such as molten salt adhesion and agglomeration, unused high-temperature sensible heat, and waste of water resources. A novel process for waste heat recovery by high temperature melting dry method is proposed in this paper, using a combination of centrifugal granulation and waste heat recovery to dispose high-temperature molten salt and effectively recover heat. Through thermal equilibrium analysis and calculation, the waste heat recovering efficiency of the waste heat recovery using the novel process can reach up to 98%. Taking the annual treatment of 100,000 tons of waste salt as an example, the benefits of effective heat recovery converted to standard coal could be approximately 5 billion. While efficiently utilizing waste heat resources, the novel process brings considerable economic benefits to enterprises, has good industrial application prospects, and helps to advance the process of national hazardous waste solid waste treatment.

Thermo-environmental multi-aspect study and optimization of cascade waste heat recovery for a high-temperature fuel cell using an efficient trigeneration process

This study suggests a novel cascade waste heat recovery process for a solid oxide fuel cell power plant. The present process utilizes a trigeneration model producing electricity, cooling, and hydrogen using the energetic stream exiting the upper power plant. This model consists of a two-stage steam Rankine cycle, an ejector refrigeration cycle, a thermoelectric generator, and a low-temperature electrolyzer. After precise thermal and electrochemical simulations, a multi-aspect sensitivity analysis is regarded from the thermo-environmental point of view. Afterward, a multi-objective optimization procedure is applied through the non-dominated sorting genetic algorithm-II. The main difference between the present model and those evaluated in the literature review is its combined cooling and power cycle, which significantly increases the overall performance. According to the sensitivity analysis, the fuel cell operating temperature is the most crucial parameter affecting the studied variables. From the optimization, the optimum objective functions, i.e., exergy efficiency and carbon dioxide emission, are found to be 58.02 % and 252.5 kg/MWh, respectively. In addition, the optimum net generated power, cooling output, and hydrogen production rate are computed to be 508.8 kW, 161.9 kW, and 0.6 kg/h, respectively. Besides, the optimum energy efficiency and exergoenvironmental impact index are equal to 68.2 % and 0.7, respectively.

Advanced Exergy Analysis of an Absorption Chiller/Kalina Cycle Integrated System for Low-Grade Waste Heat Recovery

Exergy analysis and advanced exergy analysis of an absorption chiller/Kalina cycle integrated system are conducted in this research. The exergy destruction of each component and overall exergy efficiency of the cascade process have been obtained. Advanced exergy analysis investigates the interactions among different components and the actual improvement potential. Results show that among all the equipment, the largest exergy destruction is in the generators and absorber. System exergy efficiency is obtained as 35.52%. Advanced analysis results show that the endogenous exergy destruction is dominant in each component. Interconnections among different components are not significant but very complicated. It is suggested that the improvement priority should be given to the turbine. Performance improvement of this low-grade waste heat recovery process is still necessary because around 1/4 of the total exergy destruction can be avoided. Exergy and advanced exergy analysis in this work locates the position of exergy destruction, quantifies the process irreversibility, presents the component interactions and finds out the system improvement potential. This research provides detailed and useful information about this absorption chiller/Kalina cycle integrated system.

Wannier-Mott excitons in alkali metal-based nitridorhenate: A DFT study

To better understand the electronic, structural, optical, and transport properties of the alkali metal-based nitridorhenate (Li 5 ReN 4 ), first-principles calculations were performed using the full potential linearized augmented plane wave (FP-LAPW) method within the generalised gradient approximation (GGA) framework. The ground-state properties were computed for an orthorhombic structure (Pmmn-59). Both the band structure and the total density of states were carried out. Based on the band structure, the Li 5 ReN 4 compound is a direct band semiconductor with a bandgap value of 2.68 eV. In addition, the optical properties were calculated, indicating that lithium nitridorhenate is a highly absorbent material. The effective masses of the electrons and holes were calculated. Also, we investigate the connection between exciton binding energy and band structure. Moreover, the exciton for Li 5 ReN 4 is a weak exciton of the Mott-Wannier type. Furthermore, the transport properties were investigated using the semi-classical Boltzmann theory as implemented in the BoltzTraP code. Owing to its semiconducting nature, the material has a high Seebeck coefficient (S) of 287 μV/K at 300 K. At 300 K and 400 K, the predicted thermoelectric figure of merit was 0.790 and 0.802. Each of these results shows that our compound is a strong choice for applications in photovoltaic, optoelectronic, and thermoelectrical devices. Additionally, based on the observation of thermoelectric figure of merit, the Li 5 ReN 4 compound is also suitable for waste heat regeneration or waste heat recovery process. The calculated charge density distribution of Li 5 ReN 4 along (011).