Utilization Of Low-grade Waste Heat Research Articles

Energy, exergy, economic and environmental (4E) analysis of a novel power/refrigeration cascade system to recover low-grade waste heat at 90–150 °C

Facing the increasingly serious global problem of energy shortage and CO 2 emissions, the recovery and utilization of low-grade waste heat have become one of the important ways to alleviate this problem. For the low-grade waste heat (90–150 °C) that is difficult to recover, a novel power/refrigeration cascade system is proposed in this work to realize the conversion from waste heat to electricity. Based on verifying the accuracy of the model and simulation, the system is analyzed from four aspects: energy, exergy, economy and environment. The analysis results show that when the turbine inlet pressure is 14 MPa and the refrigeration temperature is 2 °C, the thermal efficiency of the system is 0.068 and the exergy efficiency is 0.33. The focus of thermodynamic performance improvement is on CO 2 generator, LiBr absorber and LiBr generator. The annualized total cost of the system is 3.04 × 10 6 $, and the focus of system economic performance should be on the turbine and CO 2 pump. The life cycle assessment results show that the damage of the system to the environment mainly focuses on climate change and photochemical ozone formation, and the impact on the environment in the operation stage accounts for 99%. This work provides the possibility for the further application of a low-grade waste heat utilization system, and also provides a certain reference for the comprehensive analysis of similar processes. • A power/refrigeration cascade system for recovering low-grade waste heat of 90–150 °C. • Energy, exergy, economy and environment (4 E) modeling and analysis of the system. • Life cycle assessment results show that the system is beneficial to the environment.

Magnetically tightened form-stable phase change materials with modular assembly and geometric conformality features

Phase change materials have attracted significant attention due to their promising applications in many fields like solar energy and chip cooling. However, they suffer leakage during the phase transition process and have relatively low thermal conductivity. Here, through introducing hard magnetic particles, we synthesize a kind of magnetically tightened form-stable phase change materials. They achieve multifunctions such as leakage-proof, dynamic assembly, and morphological reconfiguration, presenting superior high thermal (increasing of 1400–1600%) and electrical (>104 S/m) conductivity, and prominent compressive strength, respectively. Furthermore, free-standing temperature control and high-performance thermal and electric conversion systems based on these materials are developed. This work suggests an efficient way toward exploiting a smart phase change material for thermal management of electronics and low-grade waste heat utilization.

Parametric analysis and system optimization of a novel steam production system by synthetic cascade utilization of industrial waste heat

A great deal of waste heat is released in many industrial procedures, resulting in not only serious energy waste but also heat pollution. To alleviate this phenomenon, in-depth analyses of a steam generation system, whose novelty lies in synthesis of mechanical vapor recompression and thermal power conversion processes for dealing with low-grade waste heat utilization, are performed. Determination of organic Rankine cycle (ORC) working fluid and thermal power conversion cycle are conducted in detail. Then, parameter analyses and optimization are investigated. The simulation results show that the ORC–based system performs well in efficiency improvement and cost reduction with 69.41% higher exergy efficiency and 9.66% lower cost per ton of steam than the transcritical carbon dioxide-based system. In addition, there is an optimum flow rate of ORC working fluid for thermodynamic performance. A lower steam compression ratio and a higher heat source temperature are beneficial to improve techno-economic performance. At last, according to optimized results, the steam production yield and exergy efficiency of the ORC–based system are 2.50% and 44.31% under the 100 °C heat source condition, as well as the cost per ton of recycled steam is 7.67 $/ton. The optimizations of the system, working fluid, and parameters provide valuable information for improving system performance.

High-efficiency thermoelectrochemical conversion system based on H+-ion concentration cell stack

In fossil energy utilization processes, only about one-third of fuels is used effectively upon conversion, while the rest becomes waste heat. Therefore, making full use of waste heat is an effective way to save energy. Nowadays, the moderate-high temperature heat utilization systems continue to mature and develop. However, existing heat-to-electricity energy conversion technologies are not very efficient for utilization of low-grade waste heat. Herein, based on our previous finding in H+-ion concentration power generator, we design a cell stack structure in series to optimize and improve its thermal-to-electric performance with temperatures ranging from 50 °C to 170 °C. This experiment reveals that the thermal-to-electric conversion efficiency of 3-cell stack can reach up to 17.86%, which is more than twice as likely to a single-cell (8.39%). The electrochemical kinetic analysis and temperature distribution thermoanalysis results convince us that this tandem device is beneficial to the development for low-level heat recovery.

Enlarged temperature lift of hybrid compression-absorption heat transformer via deep thermal coupling

The energy level mismatch between heat sources and industry users has posed a huge barrier for the wide application of local waste heat recovery, which cannot be efficiently addressed by traditional options due to the limited temperature lift. To fill this gap, a hybrid heat transformer is proposed to achieve large temperature lift via deep thermal coupling between compression and absorption sub-cycles. Firstly, simulation shows that 42.1 kW heat output (at 100 °C) is provided with the costs of 20.0 kW electricity and 67.4 kW waste heat (at 45 °C), resulting in a COP of 2.15 and a large temperature lift of 55 °C. Secondly, an experimental prototype was established for performance validation, which stably upgraded the waste heat from 47–51 °C to 99–102 °C with an overall COP of 1.81. Further investigation shows that the proposed system is quite flexible with waste heat source temperatures of 30–60 °C and output temperatures of 90–115 °C. Such an effective heat transformer with large temperature lift could be promoted for the efficient utilization of low-grade waste heat, and contribute to the industrial decarbonization.

Recovery and Utilization of Low-Grade Waste Heat in the Oil-Refining Industry Using Heat Engines and Heat Pumps: An International Technoeconomic Comparison

We assess the technoeconomic feasibility of onsite electricity and steam generation from recovered low-grade thermal energy in oil refineries using organic Rankine cycle (ORC) engines and mechanical vapour compression (MVC) heat pumps in various countries. The efficiencies of 34 ORC and 20 MVC current commercial systems are regressed against modified theoretical models. The resulting theoretical relations predict the thermal efficiency of commercial ORC engines within 4–5% and the coefficient of performance (COP) of commercial MVC heat pumps within 10–15%, on average. Using these models, the economic viability of ORC engines and MVC heat pumps is then assessed for 19 refinery streams as a function of heat source and sink temperatures, and the available stream thermal energy, for gas and electricity prices in selected countries. Results show that: (i) conversion to electrical power with ORC engines is, in general, economically feasible for heat-source temperatures >70 °C, however with high sensitivity to energy prices; and (ii) steam generation in MVC heat pumps, even more sensitive to energy prices, is in some cases not economical under any conditions—it is only viable with high gas/low electricity prices, for large heat sources (>2 MW) and higher temperatures (>140 °C). In countries and conditions with positive economics, payback periods down to two years are found for both technologies.

Thermodynamic and parametric analysis of a coupled LiBr/H2O absorption chiller/Kalina cycle for cascade utilization of low-grade waste heat

Low-grade waste heat refers to the thermal energy that is widely available in various industrial processes and different energy utilization processes. In present work, a LiBr/H2O absorption chiller and a Kalina cycle have been integrated in cascade to achieve full utilization of low-grade waste heat. A parametric analysis has been conducted to investigate the effect of key operational parameters in terms of turbine-inlet pressure, turbine-outlet pressure, ammonia concentration, segment temperature and refrigeration temperature. The coupled system is then compared with the Kalina cycle without absorption chiller, in terms of the turbine-outlet pressure and the net power output. Moreover, the comparisons between two systems are illustrated in the temperature-entropy diagram. Results show that the optimal turbine-inlet pressures in all studied cases are obtained as 3200–3300 kPa for given conditions. System net power output decreases obviously with higher turbine-outlet pressure while increases with the increasing ammonia concentration. At refrigeration temperature of 2 ℃, the coupled system produces the maximum electricity output because the system can reach to a lower turbine-outlet pressure. The optimal thermal efficiency is 0.1678. After being integrated with an absorption chiller, the net power output of the Kalina cycle is improved by nearly 45%. This paper provides a performance-enhanced power generation system for cascade utilization of low-grade waste heat.

The increasing of the energy efficiency of nuclear power plants with fast neutron reactors by utilizing waste heat using heat pumps

Today, an important task for the economy is to increase the efficiency of using primary fuel. At present, for nuclear power plants with VVER reactors, thermal efficiency is about 33%, with fast neutron reactors - more than 40%. This means that most of the heat produced is released into the atmosphere. In this paper, we consider methods to solve the problem of increasing energy efficiency by the example of NPPs with fast neutron reactors due to the utilization of low-grade waste heat. The results of practical implementation of utilization of low-potential thermal energy of thermal and nuclear power plants using heat pumps were generalized. The analysis of the utilization efficiency of waste heat from various NPP systems was performed.

Thermoeconomic analysis of optimization potential for CO 2 vapor compression cycle: From transcritical to supercritical operation for waste heat recovery from the steam condenser

Recent research has been focused on the utilization of low-grade waste heat, and the industrial high-temperature heat pump can be an alternative technology because of its simplicity and outstanding performance. However, the use of carbon dioxide in vapor compression heat pumps with high-temperature heat source is still to be optimized because of low critical temperature. In the present study, a system for waste heat recovery from the steam condenser using CO2 vapor compression cycle is modeled from the energetic, exergetic, and economic perspectives, and optimized system performances are obtained by dual-objective Jaya algorithm. Potential optimized operating strategies for transcritical cycle are discussed by the parametric study and T-s diagrams. The transcritical and supercritical cycles are further compared with each other considering different steam temperatures. The optimization strategies of transcritical cycle are based on the main purpose to improve the evaporation potential and achieve transcritical cycles with the critical point inside the closed region surrounded by the process curves, so lower superheating degree and minimum temperature difference of gas cooler, higher evaporating temperature, and more return water cooling should be employed in order to promote the cycle performances. In comparison with transcritical cycles performances, the supercritical operation shows superior performances, which are less sensitive to the variations of return water temperature.

INCREASE IN CHELYABINSK HEATING SYSTEM EFFICIENCY BY UTILIZATION OF LOW-GRADE WASTE HEAT

We consider the possibility of improving the heat supply system in Chelyabinsk through the introduction of heat pump technology for the disposal of low-grade waste heat. The paper analyzes the problems of the heat supply system in Russia. The majority of consumers in large cities of the central Russia are supplied with heat energy through the centralized heat supply system. This approach is largely outdated and inapplicable to the modern energy system. We propose the method for increasing the efficiency of centralized heating using heat pumps. This paper makes the evaluation of the effectiveness of the use of this method, namely performs a calculation study, the final result of which is estimation of efficiency of low-grade waste heat utilization in the Chelyabinsk heat supply system. For this purpose, we have previously analyzed the sources of information on the ways of utilization of waste thermal energy, the principles of the heat pumps operation, and the classification of urban sources of waste heat. The first stage of this study is the development of a calculation technique that makes it possible to estimate at varying initial parameters of the heat supply system objects. The developed technique allows estimating the efficiency of using heat pumps for each category of municipal sources of waste heat energy: energy (CHP, boilers, heating networks) and non-energy (residential, public and production facilities) ones. The second stage is the application of this technique to Chelyabinsk. As a starting point for this stage, we take the data which characterize the climatic features, energy parameters of the sources of centralized heating supply, as well as data on the population, economy and industrial facilities in Chelyabinsk. The result of the study is the numerical value of the efficiency of waste heat utilization in Chelyabinsk.

Effect of temperature gradients in (reverse) electrodialysis in the Ohmic regime

Electrodialysis (ED) and reverse electrodialysis (RED) are processes for the production of desalinated water (ED) and power (RED). Temperature of the feed streams can strongly influence the performance of both processes. In this research, commercial membranes are used for the investigation of temperature and temperature gradients on ED and RED processes. We find that the energy required for ED processes can be reduced by 9% if the temperature of one of the feed streams is increased by 20°C, while maintaining the charge-selectivity of the membranes. The direction of the temperature gradient did not have a significant influence on the efficiency and selectivity of ED in the Ohmic regime. In RED, we find an increase in obtained gross power density over 25% for the process when one feed stream is heated to 40°C instead of 20°C. This work experimentally demonstrates that utilization of low-grade waste heat from industrial processes can yield significant reduction of energy costs in ED processes, or result in higher power densities for RED systems where the increase in temperature of a single feed stream already yields significant efficiency improvements.

On low-grade waste heat utilization from a supercritical steam power plant using an ORC-bottoming cycle coupled with two sources of heat

This paper analyzes a waste heat recovery system based on a binary vapor cycle composed of an organic Rankine cycle (ORC) bottoming a supercritical steam cycle. The organic Rankine cycle is supplied by two heat sources. The first one is waste heat from a steam boiler, which condenses flue gases to 200MWt at 90°C and preheats the fluid with a low boiling point. The second one is a steam condenser, which also acts as a low-boiling-point fluid vapor generator. Steam condensation temperatures was tested in the range 55–115°C. Usage of a low-boiling-point fluid instead of steam in range of the low temperature (below 100°C) has several advantages. One advantage is the possibility for the effective utilization of a large amount of low-grade waste heat from a supercritical steam cycle. For the most efficient configuration, 22.92MW of additional electrical energy is generated. The thermal efficiency of the waste heat recovery system is 11.46%, which is 71.75% of the Carnot efficiency. Usage of an organic Rankine cycle for bottoming the supercritical steam cycle also provides cubature reduction of the power plant. For the most efficient case, a steam volume flow at the new steam turbine outlet is reduced by 88% compared to a reference stream turbine. The volume flow at the ORC turbine outflow is reduced by 54%. Numerical analyses of the thermodynamic cycles, before and after modifications, are carried out using computational flow mechanics, mainly, with in-house code.

Durability of thermochemical heat storage demonstrated through long-term repetitive CaCl2/H2O reversible reactions

Thermochemical heat storage is a promising technology for improving thermal energy efficiency. In this study, CaCl2 and H2O were selected as the reactant and working medium, respectively, assuming the utilization of low-grade waste heat. To investigate the durability of the CaCl2/H2O reaction, 1000 repetitive operations were conducted at the same 110 °C charging and discharging temperatures. During the long-term repetitions, a decrease in the average volumetric power density was observed. The peak value in repetitions 901–1000 was 11% lower than the peak value in the initial 50 repetitions. This trend was mainly caused by a decrease in the heat transfer rate; it was observed after the repetitive experiments that reactant particles had moved out of the heat exchanger. Although a decreasing trend in the power density was observed, a peak value of Q = 320 kW/m3 and a conversion ratio of approximately 0.7 were observed in repetitions 901–1000. In addition, approximately 90% of the stored heat was released in all 1000 repetitions. Thus, using long-term repetitions (1000), this study confirmed the durability of the CaCl2/H2O reaction for thermochemical heat storage.

Thermoeconomic analysis of configuration methods for modular Organic Rankine Cycle units in low-temperature applications

Organic Rankine Cycle (ORC) is a promising technology for the utilization of low-grade waste heat. However, due to tailor-made power plants for different heat source temperatures, specific investment costs are still too high to be profitable. This study compares two different methods to configure a modular ORC in the temperature range of 373–463K. The first method assumes a simple adaption of the mass flow rate within the ORC (mass flow method). In the second method, simultaneous adaption of mass flow rate and working pressure (combined method) take place. The common purpose of both methods is the optimization of the net power output for heat source temperatures lower and higher than the reference plant. Analyses are carried out for common fluorinated refrigerants (R227ea and R236ea) as well as for iso-alkanes (isobutane and isopentane). It is shown that within a wide range of temperatures the deviation in net power output between the simpler mass flow method and the more sophisticated combined method is below 10%. However, the deviation strongly depends on the location of the pinch point and on the choice of the working fluid. In general, it is shown that the mass flow method in combination with a working fluid, for which the pinch point is located at the beginning of the preheating, is thermodynamically favorable for plant manufacturers. Economic analyses subsequently compare both methods with respect to payback period and cash flow. Additional investment costs for the combined method are allowed to be up to 10% in order to reach higher profitability than units with mass flow method.

Thermochemical Heat Storage Performance in the Gas/Liquid-Solid Reactions of SrCl<sub>2</sub> with NH<sub>3</sub>

Thermochemical heat storage is a promising technology for improving energy efficiency through the utilization of low-grade waste heat. The formation of a SrCl2 ammine complex was selected as the reaction system for the purpose of this study. Discharge characteristics were evaluated in a packed bed reactor for both the gas-solid reaction and the liquid-solid reaction. The average power of the gas-solid reaction was influenced by the pressure of the supplied ammonia gas, with greater powers being recorded at higher ammonia pressure. For the liquid-solid reaction, the obtained average power was comparable to that obtained for the gas-solid reaction at 0.2 MPa. Moreover, the lower heat transfer resistance in the reactor was observed, which was likely caused by the presence of liquid ammonia in the system. Finally, the short-term durability of the liquid-solid reaction system was demonstrated over 10 stable charge/discharge cycles.

Research on Improved CCHP System Based on Comprehensive Performance Evaluation Criterion

In view of energy consumption characteristics of a typical industrial park, to further improve the low-grade waste heat utilization of CCHP system, an improved CCHP triple-generation system (ITRI) equipped with thermal storage device (TSD) and electric chiller (EC) is proposed. A comprehensive performance evaluation criterion (CPEC) is established, the capacity of triple-generation system is configured by using nonlinear programming method. A hybrid operating mode optimization strategy is proposed based on the different CPEC values of different operating mode. The results demonstrate that: after adopting ITRI, compared with traditional triple-generation system (TTRI), although annual cost increased by 0.63%, the primary energy consumption rate and lower carbon dioxide emissions decreased by 5.45% and 3.72% respectively, CPEC value increased by 19.7%. This paper has a theoretical guidance for design of triple-generation system in new industrial park and has a certain reference value for operating mode optimization of triple-generation system in the industrial parks which has been built.

A Comparative Study of Integrated Coal Gasification Combined- Cycle Power Plants (ICGCC) with Kalina Cycle

Low grade waste heat utilization and new combustion technology are challenging tasks for researchers to achieve these objectives. This paper is concerned with the integration of coal gasification system with a combined gas turbine, steam turbine power plant cycles and with ammonia-water cycle, which is known as Kalina cycle. Al-maghara coal in North Sinai is used as the solid fuel in gasification process.Three cycles configurationsare compared as follows: Scheme (A) with dual pressure Heat recovery boiler with the condenser of steam cycle as the evaporator for Kalina cycle,scheme (B) with heat recovery boiler for both of steam and Kalina cycleand scheme (C), similar to scheme (A), but with a superheating in Kalina cycleto identify the most promising one for implementation. Key parameters of Kalina cycle were the main elements of comparison. Results revealed that scheme (A) has the best performance with regard to the output power, thermal efficiency and specific fuel consumption. Substantially, the integration of Kalina cycle with coal gasification combined cycle counterbalances the reduction of the overall efficiency due to the gasification thermal efficiency. Therefore, integration of Kalina cycle in the ICGCC is justified.Furthermore, part load calculations were made for scheme (A) and identified that the integration of Kalina cycle to ICGCC imposed restrictions to Kalina cycle constrains, so that it is more economical to keep such configuration of combined plants at nearly full load conditions.

Low-grade Waste Heat Utilization In Activated Carbon Production

Low-grade Waste Heat Utilization In Activated Carbon Production

Membrane-based humidity pump: performance and limitations

Moisture is usually transported from a fluid of high humidity to a fluid of relatively low humidity through a membrane. Membrane-based humidity pump works in another way: moisture is transported from a dryer air stream to a humid air stream under the driving force of thermal gradients in membrane. With humidity pump, a continuous air dehumidification can be realized by the utilization of low-grade waste heat. In this article, through finite difference simulations of the coupled heat and mass transfer in the unit, the performance and limitations of a membrane-based humidity pump are analyzed. The effects of various thermodynamic and dynamic parameters of membrane on the performance of humidity pump are discussed. It is found that even though the operational parameters can be optimized to enhance the thermo-osmosis rate of water vapor, the key role is played by a factor named humidity pump. Furthermore, when the humidity pump factor is bigger than 0.02 mK −1/7.5 kJ 1/3, the permeability is bigger than 1.0×10 −5 kg m −2 s −1, and the humidity pump can be used in commercial applications.