Energy-utilization Diagram Research Articles

A novel Ca-Ni looping with carbonation heat thermochemical regeneration method for post-combustion CO2 capture: System integration, energy-saving mechanism, and performance sensitivity analysis

Thermal coupling between the calcium looping (CaL) process and chemical looping combustion (CaL-CLC) offers advantages to avoid electricity consumption of air separation, and the CaL-CLC has presented superior performance realizing CO2 capture. However, in these CaL-CLC and CaL configurations for post-combustion CO2 capture, the carbonation heat is recovered for steam generation with a significant temperature difference, leading to considerable irreversible loss. To prevent the temperature mismatch during carbonation heat recovery, this paper proposes the concept of Ca-Ni looping with the carbonation heat thermochemical regeneration method. Additionally, a novel system integrating with a combined cycle is introduced to effectively decarbonize flue gas. Results show that the proposed system has superior performance compared with the reference system based on the Ca-Cu looping method. The specific energy consumption for CO2 avoided (SPECCA) decreased from 2.13 MJ/kg CO2 in the reference system to 1.43 MJ/kg CO2. Exergy analysis indicates that a total 6.3 % exergy destruction reduction is realized by replacing the Cu-based chemical looping combustion with the Ni-based oxidation reaction for calcination heat supply. Furthermore, the energy utilization diagram (EUD) reveals the mechanism of exergy destruction reduction caused by the thermal coupling between reaction processes. Besides, the impact of key operating parameters on the proposed system performance is investigated. Overall, the proposed Ca-Ni looping with carbonation heat regeneration method enhances the utilization of mid-temperature carbonation heat by converting it into high-grade thermal energy suitable for combined cycles, thereby offering a promising alternative for low-energy-consumption CO2 capture.

A novel dual-stage intercooled and recuperative gas turbine system integrated with transcritical organic Rankine cycle: System modeling, energy and exergy analyses

Gas-fired power generation, characterized by high efficiency, low carbon emissions, and flexibility, contributes significantly to the global energy transition. In the present work, a novel dual-stage intercooled and recuperative gas turbine system integrated with transcritical organic Rankine cycle (dICR-GT-tORC) was proposed. System modeling was carried out based on Thermoflex software for different configurations to evaluate the energetic and exergetic performances. It was found that the dICR-GT-tORC exhibited improved thermodynamic performance compared to the gas turbine simple cycle and dICR-GT system, with the system net energy efficiency/exergy efficiency/specific work increasing from 43.88%/41.80%/567 kJ·kgair−1 and 57.21%/54.49%/684 kJ·kgair−1 to 62.48%/59.52%/745 kJ·kgair−1, respectively. An energy utilization diagram analysis revealed that the energy cascade utilization was achieved by coupling a bottoming tORC to fully utilize the waste heat from intercoolers and the exhaust gas. Furthermore, the dICR-GT-tORC demonstrated enhanced environmental performance, reducing the CO2 emission rate by a maximum value of 29.8%. Additionally, the impacts of key parameters, including the organic working fluid selection, the minimum temperature difference at the pinch point of recuperators and the terminal exhaust gas temperature on the system performance were investigated. It was indicated that the proposed system could be applicable in various practical scenarios from thermodynamic and environmental perspectives.

Proposal and thermodynamic investigation of pressurized calcium looping integrated with chemical looping combustion for tail-end CO2 capture in a retrofitted natural gas combined cycle power plant

The integration of tail-end calcium looping into an existing natural gas combined cycle (NGCC) power plant has minimal impact on CO2 capture retrofits. However, a high volume of flue gas needs to be preheated before entering the carbonator, and the relatively high energy consumption of oxygen production exacerbates the energy penalty of the NGCC system with tail-end CO2 capture. This paper proposes the method of pressurized calcium looping integrated with chemical looping combustion (PCaL-CLC). It employs the PCaL-CLC method to reduce the energy penalty and energy consumption of the NGCC system with tail-end CO2 capture. Results show that the proposed system using the PCaL-CLC method achieves a 3.0% reduction in energy penalty, decreasing from 9.1% in the reference system employing the calcium looping method to 6.1% in the proposed system. Besides, the specific energy consumption for CO2 avoided (SPECCA) declines from 4.43 MJLHV/kg CO2 to 2.76 MJLHV/kg CO2. Exergy analysis and energy utilization diagrams reveal the underlying reason for improving system performance. Furthermore, by optimizing the operating parameters of the gas turbine and equipping it with advanced heat recovery steam generation, an energy penalty of 2.9% and a SPECCA of 1.21 MJLHV/kg CO2 are achieved without CO2 compression, which is superior to those of amine scrubbing and hot-end calcium looping CO2 capture technologies. The proposed PCaL-CLC method offers an alternative approach to reducing the energy consumption of tail-end CO2 capture in existing natural gas combined cycle power plants.

Efficient coal-based power generation via optimized supercritical water gasification with chemical recuperation

Supercritical water gasification (SCWG) is promising as a clean coal technology and is an emerging topic of interest in sustainable energy. Here, we introduce a clean and efficient power generation system that optimizes SCWG of coal through chemical recuperation. Central to our approach is the innovative utilization of both exhaust and a portion of the syngas as dual heat sources for gasification, simultaneously producing the requisite supercritical water. This chemical recuperation strategy effectively enhances the transformation of coal chemical energy into syngas. The introduced system achieves power generation and exergy efficiencies of 56.64 and 55.30%, respectively, outperforming those of a baseline system by 8.43 and 8.23%, respectively. This gain is primarily attributed to the irreversible losses in the gasification, air separation, and heat-exchange processes of the introduced system, which were reduced by 8.75, 2.47, and 4.17%, respectively, compared with the corresponding values of the baseline system. In order to elucidate and validate the reduced irreversible losses in the introduced system compared with those in the baseline system, we incorporated the energy utilization diagram methodology into our analysis. In summary, the introduced system represents a pivotal advancement in clean and efficient coal-based power generation and underscores the need for continuous innovation in this sector.

Temperature-entropy and energy utilization diagrams for energy, exergy, and energy level analysis in solar water splitting reactions

Solar hydrogen production by water splitting reaction is an important route to realize the storage of solar energy. The involvement of light and chemical energy can reduce the high reaction temperature of direct thermochemical water splitting reactions, but the pivotal issues such as energy, exergy, and energy level relationships behind the temperature reduction remain under-researched. A graphic analysis of water splitting reactions using the temperature-entropy and energy utilization diagrams is proposed to research the energy, exergy, and energy level relationships. The energy composition and conversion mechanisms with the light and chemical energy are presented in the diagrams by comparing with direct thermochemical water splitting reactions. Three cases, including the photocatalytic, photo-thermochemical, and methane steam reforming reactions, are studied to explain the effect of light, the synergistic effect of heat and light, and the effect of chemical energy in reducing the temperature of water splitting reactions. The energy levels of light and methane are higher than those of hydrogen, thus lowering the energy level of heat and reducing reaction temperatures. The discovery of the energy level required for hydrogen production will provide guidance for reducing its temperature.

Proposal and evaluation of a hydrogen and electricity cogeneration system based on thermochemical complementary utilization of coal and solar energy

In this study, an efficient and clean hydrogen and electricity cogeneration system based on thermochemical complementary utilization of coal and solar energy is proposed, and the feature is that steam-to-methane ratio in the high-temperature syngas generated by supercritical water coal gasification is more than 3:1. Thus, without injecting new steam into syngas and only further increasing the temperature will provide very suitable reaction conditions for hydrogen production by steam methane self-reforming in syngas, which has lower energy consumption relative to a conventional reforming process. Through thermochemical complementary utilization, the solid fuel coal and solar energy are first converted into methane-rich syngas by supercritical water coal gasification, then methane-rich syngas and solar energy are converted into hydrogen-rich syngas by steam methane self-reforming, realizing the cascade utilization of chemical energy. Hydrogen is separated from the hydrogen-rich syngas by pressure swing adsorption, and the purge gas is introduced into the gas turbine to generate electricity. The results show that the total energy and exergy efficiencies of the integrated system are 49.37% and 49.84%, respectively, which increased by 4.91 and 4.97 percentage points relative to the reference system. In the integrated system, the hydrogen output is 452.40 MW (13582 kg/h, 28 bar), the electricity output is 209.47 MW, and the chemical energy of the syngas is 978.49 MW, which is approximately 49.14% higher than that of 656.09 MW in the reference system. Energy utilization diagram revealed that the key to the improved performance in the integrated system lies in the reduction of exergy destruction during the fuel conversion and heat exchange, which decreased by 3.76 and 6.68 percentage points relative to the reference system, respectively. This work provides a competitive option for large-scale hydrogen and electricity cogeneration systems.

Proposal and assessment of a solar-coal thermochemical hybrid power generation system

The thermochemical complementarity is an efficient path to improve the utilization efficiency of coal and address the intermittence of solar energy. In this paper, a solar-coal thermochemical hybrid power generation system based on supercritical water gasification is proposed, and the feature is that the low gasification temperature of 650 °C makes it feasible to use concentrated solar energy to provide reaction heat for the gasification process. The energy and exergy analysis methods are used to evaluate the thermodynamic performance of the system with a net power output of 500 MW. The results show that the net power generation efficiency and exergy efficiency of the proposed system can reach 53.06 % and 52.24 %, respectively, which are approximately 6.94 and 6.83 percentage points higher than those of the reference system. The significant role of thermochemical method is that the chemical energy of syngas produced by the proposed system is 851.57 MW, which is increased by approximately 29.70 %. Through the energy utilization diagram analysis, it is found that the key to performance improvement is that the exergy destruction of the fuel conversion process and heat exchange process are decreased by 10.36 % and 54.68 %, respectively. Finally, the proposed system has better performance and lower exergy destruction. The solar thermal energy of low energy level is converted into syngas chemical energy of high energy level, and the upgrading of solar energy is achieved. In addition, the proposed system is simpler, and eliminates the air separation unit and syngas purification unit. This work provides a promising method for the complementary utilization of solar energy and coal.

Thermodynamic performance study of a new diesel-fueled CLHG/SOFC/STIG cogeneration system with CO2 recovery

A new type of diesel-fueled cogeneration system is proposed in this study. The system mainly includes solid oxide fuel cell, chemical looping hydrogen generation and steam injection gas turbine cycle. The system can effectively avoid the carbon deposition of solid oxide fuel cell, recovering CO2 without separation energy consumption. Additionally, it adopts the way of centralized supply of steam and air, thus reducing the complexity and loss of the system. On this basis, the system is comprehensively evaluated by sensitivity analysis, exergy analysis, energy utilization diagram analysis and exergoeconomic analysis. It is found that the total power efficiency, exergy efficiency and fuel energy saving ratio of the new system can reach 64%, 60% and 60% respectively. Meanwhile, the power production cost of the new system is 51.25 $/GJ, and the optimization suggestion of the system is given according to the result of exergoconomic analysis. The proposed system provides a theoretical basis and new idea for the design and construction of diesel-fueled energy supply system.

A novel hydrogen production system based on the three-step coal gasification technology thermally coupled with the chemical looping combustion process

Coal gasification technology is a significant process for the coal-based hydrogen production system and is considered as a key technology in the transition to “Hydrogen Economy”. To decrease the exergy destruction and enhance the cold gas efficiency of the coal gasification process, a novel three-step gasification technology thermally coupled with the chemical looping combustion process is proposed. And the hydrogen production system with CO2 recovery is integrated based on the three-step gasification technology. Results indicated that the cold gas efficiency of the three-step coal gasification technology is 86.9%, which is 10.1% points enhanced compared with GE gasification technology. Besides, the novel system has an energy efficiency of 62.3%, which is 3.1% higher than that of the reference system. Exergy analysis presented that the employment of the three-step gasification technology contributed to the reduction of system exergy destruction by 4.2%. Furthermore, the energy utilization diagram (EUD) suggested that matching between endothermic reactions and exothermic reactions plays important role in the enhancement of cold gas efficiency.

Analysis and evaluation of the energy saving potential of the CO2 chemical absorption process

Carbon Capture and Storage (CCS) plays an important role in dealing with global warming, while the high energy consumption of CO2 separation is the critical gap interfering with the development and deployment of CCS. The aim of this work is to identify the energy saving potentials of different CO2 separation technical measures from the level of thermodynamic principles. The energy saving mechanism of these two technical measures is investigated through analysis of energy consumption and exergy destruction distributions and further disclosed by the Energy Utilization Diagram (EUD) method. The results indicate that the relative importance of absorbent innovation and process upgrading will change for emission sources with different CO2 concentrations. Absorbent innovation is more sensible for emission sources with higher CO2 concentrations, while the role of process upgrading will be enhanced for low-concentration sources. Moreover, absorbent innovation can affect the reboiler duty from the perspective of both energy quantity and energy quality, while process upgrading mainly affects the energy amount of the reboiler duty. Through comparison of diverse absorbents, the results indicate that the field is still in the key stage of absorbent innovation for current chemical absorption technology. Upon transition to lower reboiler (<2.5) duty and lower IAP (<1.5), process upgrading can be expected to be a more effective and faster way to save energy than absorbent innovation.

Exergy analysis and optimization of MED–TVC system with different effect group divisions

Multi-effect distillation-thermal vapor compression (MED–TVC) systems have attracted increasing attention due to their relatively low steam consumption. In this work, comprehensive thermal and exergy analyses of MED and MED–TVC systems were implemented. Besides, a detailed energy utilization diagram (EUD) analysis was conducted to reveal the mechanism of the internal exergy loss. According to the EUD analysis, TVC could solve energy level mismatch and improve energy utilization. However, the system's exergy loss was greatly increased. With the introduction of TVC, the performance ratio (Pr) increased from 10.88 to 14.11, and the energy consumption (Q) decreased from 224.09 kJ/kg-Mp to 181.30 kJ/kg-Mp. In addition, a countercurrent grouping feed was adopted in the system. The influence of the suction position combined with different effect group division methods for the 13-effect MED–TVC system was also investigated. Five different effect group division methods were analyzed in terms of system efficiency, performance ratio, exergy destruction, and energy consumption. The results indicated that a more uniform distribution of effects among the effect groups was beneficial for improving the performance of the MED–TVC system. Furthermore, both the Pr and system exergy efficiency (y) improved with an increase in the suction effect number.

Energy and exergy analyses of S–CO2 coal-fired power plant with reheating processes

S–CO2 (Supercritical-CO2) coal-fired power plant is a promising technology for efficient and clean utilization of coal for power generation. The conversion and transfer of the energy and exergy in the power plants with double-reheat and single-reheat processes are studied. With the main gas parameters of 32 MPa/893.15 K, the power generation efficiencies of the S–CO2 coal-fired power plant with double-reheat and single-reheat processes are 49.06% and 48.72%, respectively. The corresponding exergy efficiencies are 48.02% and 47.69%, respectively. The origins of exergy destructions in different units are studied using the Energy Utilization Diagram (EUD) method. The exergy distributions of the power plants are presented. For the power plant with double-reheat process, the work output, the exergy exhaust into the atmosphere, the exergy destruction in combustion process, the exergy destruction in heat transfer processes, the exergy destruction caused by pressure loss, and the exergy destructions in turbo systems account for 48.02%, 9.66%, 20.45%, 17.56%, 1.08%, and 3.23% of the total exergy input of the power plant, respectively.

Sustainable hydrogen production from oil palm derived wastes through autothermal operation of supercritical water gasification system

Abstract Hydrogen generation from empty fruit bunch and palm oil mill effluent through supercritical water gasification was studied on system level. The effect of alternative H2 separation process (Palladium Membrane or Pressure Swing Adsorption), H2S adsorption (zinc oxide or activated carbon) and inclusion of steam methane reformer on net H2 yield and system efficiency were examined under auto-thermal operation. Waste heat recovery by generating low pressure steam utilizable in palm oil mill were conducted to minimize exergy loss. At the lowest biomass concentration considered in this study (15 wt% empty fruit bunch), inclusion of steam methane reformer reduced the net H2 yield as product gas was mainly used as fuel. However, at high biomass concentration (25 wt% empty fruit bunch and palm oil mill effluent), the net H2 yield increased by up to 98%. Energy efficiency of 70% (without reformer) and 58.3% (with reformer) was achieved using high biomass concentration under optimal operating condition for H2 production. Exergy analysis revealed that 62.5–70.8% of total exergy loss was attributed to furnace and gasifier. Energy utilization diagram further revealed about 72–87% of the unit exergy loss was attributed to feed preheating. Waste heat recovery through steam generation raised the system efficiency by 5–18%.

Performance Analysis and Evaluation of a Supercritical CO2 Rankine Cycle Coupled with an Absorption Refrigeration Cycle

The utilization of sensible waste heat such as flue gas and industrial surplus heat is essential for energy saving. Supercritical CO2 power generation cycle is a promising way to be used in this field. In this paper, a new supercritical CO2 Rankine cycle coupled with an absorption refrigeration cycle is proposed, which consists of a reheating supercritical CO2 cycle, a mixed-effect LiBr-H2O absorption refrigeration cycle and solar subsystem including evacuated-tube collector and a hot water storage tank. The system has four variants according to the presence or absence of solar subsystem and net cooling energy output. The thermodynamic model of the proposed system was established and its performance was evaluated. The proposed system is able to realize cascade utilization of flue gas waste heat and efficient conversion of solar energy. It has much higher thermodynamic efficiency than the reference system (i.e., the conventional supercritical CO2 Brayton cycle). Taking combined power and cooling system driven by flue gas waste heat and solar energy as an example, its thermal efficiency and exergy efficiency are 20.37% and 54.18% respectively, compared with the 14.74% and 35.96% of the reference system. Energy Utilization Diagrams (EUD) are implemented to investigate the irreversible losses and variation of the exergy destruction in the energy conversion process. Parametric analysis in two key parameters is conducted to provide guidance for the system optimal design.

Study on weak link of energy utilization in oil transfer station system: Insights from energy level analysis method

In this paper, an energy level analysis model of oil transfer station system is established, which is divided into oil transfer station subsystem and pipeline network subsystem. From the perspective of the level of energy, the system is evaluated and optimized by virtue of using energy level analysis method and combining with the ”three box” analysis model. Moreover, the energy level evaluation indexes of import and export, energy level difference and energy level balance coefficient, are calculated in terms of the calculation results. Then the energy utilization diagrams (EUD) are drawn, it can be seen that more than 95% of the supply energy in the oil transfer station subsystem is provided by gas. The energy level difference of the heating furnace is the largest, which can be seen intuitively that the heating furnace is the weak link of energy utilization in the whole system. Based on the influencing factors, the corresponding energy saving and consumption reduction measures are preliminarily proposed.

Exergy cascade release pathways and exergy efficiency analysis for typical indirect coal combustion processes

Indirect coal combustion can solve some problems such as low efficiency and air pollution during traditional coal combustion, this research investigates energy release characteristics of indirect combustion and aims to achieve maximum energy utilisation. Firstly, Energy Utilization Diagrams Methodology was used to explore exergy cascade release pathways and exergy losses for typical indirect combustion such as supercritical water gasification re-combustion, steam reforming re-combustion, and chemical-looping combustion, which are compared with direct combustion. It is pointed out that indirect combustion has changed release pathways of chemical exergy, and decreased energy level difference between chemical exergy in fuel and thermal energy in combustion, then exergy losses is reduced and exergy in fuel is released step by step. Secondly, to prove that indirect combustion can indeed reduce exergy losses and improve exergy efficiency in the combustion process, supercritical water gasification re-combustion with least exergy losses was selected and exergy analysis model was established by energy quality coefficient. Results show that thermal efficiency and exergy efficiency of supercritical water gasification re-combustion reaches as high as 94.8% and 79.5%, respectively, 2.23% and 19.61% higher than those of traditional coal-fired boilers. As a result, energy matching and conversion are more reasonable in indirect coal combustion processes.

Optimal Design Method for Absorption Heat Pump Cycles Based on Energy-Utilization Diagram

Optimization for energy systems is considered at three levels: synthesis (configuration), design (component characteristics), and operation. This paper aims to evaluate the system performance and margins for improvement of two absorption heat pump systems, including an absorber heat exchanger (AHX) and a solution heat exchanger (SHX), and perform their design/operation optimization efficiently based on an energy-utilization diagram (EUD) for performance improvement. Before optimization, exergy efficiency is higher in the SHX cycle, while the margin for improvement is larger in the AHX cycle. The optimization attempts to reduce exergy destruction in the components where dominant exergy destruction caused by heat transfer occurs. In the absorber, the operating points are adjusted to make the temperature slopes at the hot and cold sides coincide. The design parameters in other components are adjusted to improve the heat transfer performances. The distribution of exergy destruction of each component leads to improve exergy efficiency. After these improvements, exergy efficiency is higher in the AHX cycle. It is concluded that we could efficiently realize the design/operation optimization of thermodynamic systems using an EUD, because the diagram presents both exergy destruction and margin for improvement at the components comprehensively, as well as the operating properties of working fluids.

Novel Coal-Steam Gasification With a Thermochemical Regenerative Process for Power Generation

In this paper, a novel high-efficiency coal gasification technology is proposed in which a regenerative unit is applied to recover syngas sensible heat to generate steam; then, the high-temperature steam is used to gasify coke from a pyrolyzer. Through such a thermochemical regenerative unit, the sensible heat with a lower energy level is upgraded into syngas chemical energy with a higher energy level; therefore, high cold gas efficiency (CGE) is expected from the proposed system. aspenplus software is selected to simulate the novel coal gasification system, and the key parameters are validated by experimentation. Then energy, exergy, and energy-utilization diagram (EUD) analyses are applied to disclose the plant performance enhancement mechanism. It is revealed that 83.2% of syngas sensible heat can be recovered into steam agent with the CGE upgraded to 90%. In addition, with the enhancement of CGE, the efficiency of an integrated gasification combined cycle (IGCC) based on the novel gasification system can be as high as 51.82%, showing a significant improvement compared to 45.2% in the general electric company (GE) gasification-based plant. In the meantime, the irreversible destruction of the gasification procedure is reduced to 25.7% through thermochemical reactions. The increase in the accepted energy level (Aea) and the decreases in the released energy level (Aed) and heat absorption (ΔH) contribute to the reduction in exergy destruction in the gasification process. Additionally, since the oxygen agent is no longer used in the IGCC, 34.5 MW exergy destruction in the air separation unit (ASU) is avoided.

Thermodynamic Study and Exergetic Analysis of the Integrated SOFC-GT-Kalina Power Cycle

In this paper the SOFC-GT-Kalina (solid oxide fuel cell, gas turbine, and Kalina cycle) integrated system is proposed. The system uses Kalina cycle as the bottoming cycle to recovery the waste heat from the gas turbine to generate power. Kalina cycle uses ammonia-water mixture as the work fluid which has sliding-temperature boiling characteristics. By comparing with the SOFC-GT-ST (solid oxide fuel cell, gas turbine, and steam turbine cycle) system as the reference system, the systems are simulated by Aspen Plus through analyzing the overall system performance. Electrical and exergy efficiency of the proposed system are 74.41% and 71.93%, and electrical and exergy efficiency of the reference system are 71.45% and 69.07%, proving the superiority of Kalina cycle for waste heat recovery. In addition, the exergy losses of each component are studied, and the detail performance analysis of the proposed system is presented, consisting of thermal analysis, exergy analysis and EUD (Energy-utilization diagram) analysis, which intuitively disclosed the causes of exergy loss. Additionally, it was revealed that there exists an optimal current density at 350 mA/cm2 for power and power density.

Exergy Destruction Mechanism of Coal Gasification by Combining the Kinetic Method and the Energy Utilization Diagram

Gasification is the core unit of coal-based production systems and is also the site where one of the largest exergy destruction occurs. This paper reveals the exergy destruction mechanism of carbon gasification through a combined analysis of the kinetic method and the energy utilization diagram (EUD). Instead of a lumped exergy destruction using the traditional “black-box” and other models, the role of each reaction in carbon gasification is revealed. The results show that the exergy destruction caused by chemical reactions accounts for 86.3% of the entire carbon gasification process. Furthermore, approximately 90.3% of exergy destruction of chemical reactions is caused by the exothermal carbon partial oxidation reaction (reaction 1), 6.0% is caused by the carbon dioxide gasification reaction (reaction 2), 2.4% is caused by the steam gasification reaction (reaction 3), and 1.3% is caused by other reactions under the base condition. With increasing O2 content α and decreasing steam content β, the proportion of exergy destruction from reaction 1 decreases due to the higher gasification temperature (a higher energy level of energy acceptor in EUD), while the proportions of other reactions increase. This shows that the chemical efficiency is optimal when the extent of reactions 1 and 3 is equal and the shift reaction extent approaches zero at the same time.