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In CO 2 capture retrofit unit of existing coal-fired power plants, energy level mismatch between extraction steam from turbines and CO 2 regeneration process always results in large exergy destruction and low thermal efficiency. Thus, a new CO 2 capture system driven by double absorption heat transformer is proposed. Through the absorption heat transformer, low-temperature steam is upgraded into a higher energy level to match the temperature of CO 2 regeneration. Also, flue gas heat is partly recovered to preheat the circulating water from CO 2 capture process to further decrease system energy penalty. Aspen Plus 11.0 is used to simulate the system and parameters of key processes are validated by experimental values. It is shown that with 90% CO 2 capture, the thermal efficiency of the power plant with proposed CO 2 capture system is enhanced by 1.25 percentage points compared with traditional method. And the efficiency enhancement of the proposed system has a trend of increase first and then decrease with CO 2 capture rate growth. For a 350 MW coal-fired power plant, the optimum CO 2 capture rate is 53.65% and the corresponding efficiency enhancement is 2.06 percentage points. Exergy analysis shows that the exergy destruction in CO 2 separation and steam condensation process can decrease by 49.5% in the proposed system, and thereby the exergy efficiency is 1.85 percentage points higher than the conventional method. Furthermore, the cost of CO 2 avoided and cost of electricity of the proposed system will be reduced by 10.7 $/t-CO 2 and 1.9 $/MW h, respectively.

A new solar-hybrid fuel-fired distributed energy system incorporating thermochemical reaction driven by mid- and low-temperature solar heat and exhaust heat is proposed, for increased solar energy utilization and exhaust heat recovery efficiency. Solar energy is upgraded to syngas (H2 and CO) chemical energy via the solar thermochemical process of the methanol decomposition reaction, and the syngas drives the internal combustion engine to output power. Some of the exhaust heat is stored and drives the methanol decomposition reaction to supplement the syngas via the chemical recuperation process, enhancing the exergy efficiency of the exhaust heat recovery. The overall energy efficiency and net efficiency of solar energy to electricity conversion are improved by integrating solar thermochemistry and chemical recuperation, and excellent off-design thermodynamic performance under varying user loads and solar irradiation levels is achieved. The overall energy efficiency, exergy efficiency, and net solar-energy-to-electricity efficiency reach 80.55%, 42.18% and 24.66%, respectively. These research findings indicate that the proposed system embodies an efficient and stable approach towards utilization of solar energy and clean fuel in distributed energy systems.

Cooling dehumidification driven by power is widely used in industrial processes to obtain dry air, but the main drawback is its large power consumption. In these processes, large amounts of low-temperature waste heat are released to the environment directly, so there is a great energy-saving potential to recover low-temperature waste heat and generate dry air. A new two-stage liquid desiccant dehumidification system with the cascade utilization of low-temperature heat is proposed. The waste heat is used in a cascade manner. The higher-temperature heat is used to generate a strong desiccant solution, which will be used in the first-stage dehumidifier. The lower-temperature heat is used to drive a single-effect absorption refrigerator and provide cooling energy to the second-stage dehumidifier. Simulation results showed that the proposed system can reduce electricity consumption by 92.29% compared with the conventional cooling dehumidification system driven by power. The ratio of electricity savings to absorbed heat can reach 7.35%. The advantage of the cascade utilization of the low-temperature heat was further illuminated by studying the driving force in the dehumidifiers, and a preliminary economic and environmental analysis was performed. The increased initial investment can be recovered in only 3.39 years. Approximately 11,028 tons of standard coal are saved per year, and a reduction of 27,488 tons CO2 can also be realized per year. Finally, a parametric sensitivity analysis was conducted to optimize the system performance. This study may provide a new method to perform dehumidification by efficiently using a low-temperature heat source.

This study proposes an efficient, flexible and low-carbon combined heating and power (CHP) system with solar energy and methanol as energy inputs. The system features a modular design combining concentrated photovoltaics, methanol thermochemistry and internal combustion engines that enable efficient power generation, effective energy storage and flexible, demand-driven supply of heat and power. Cascaded utilization of solar energy results in a high net solar-to-electric efficiency of 38.9%, while tunable output flexibility of energy allocation between heat and power leads to both coal saving ratio and CO2 emission saving ratio in a wide range between 16.9% and 100%. Effective solar energy storage via methanol-derived syngas enables off-sun operations under normal energy demand conditions up to a few days, and attains round-the-clock heat supply with 41% carbon consumption and CO2 emission savings. The proposed system showcases a practical and efficient means of solar energy utilization complemented by fossil fuels, and provides a potential solution towards imminent energy and environmental challenges worldwide.

The hot and humid air containing marine aerosols on tropical islands or coastal areas always leads to serious equipment corrosion and affects the living comfort of residents. Conventionally, an air-conditioning system can only provide cool dry air, and the marine aerosol removal process consumes expendable materials. To simplify the procedure and reduce the energy consumption, a novel hybrid air-conditioning system combined with marine aerosol removal is proposed in this paper. The novel system achieves multiple functions based on the characteristics of liquid-desiccant dehumidification and phase transitions of the ternary solution system, and it can be driven by a low-temperature heat source. Simulation and thermodynamic analysis of the combined system are presented, and the results show that the humidity ratio of the supply air can reach 6.83 g/kg (dry air), with a temperature of 21.14 °C. Compared with the conventional cooling dehumidification system utilizing vapor compression refrigeration driven by power, the power saving ratio (PSR) and the equivalent power generation efficiency (ηeq) of the proposed system can reach 93.11% and 9.8%, respectively. Further, exergy analyses are carried out, and the results show the air handling process of the novel system has a considerable energy saving potential. Besides, a crystallization experiment is conducted to verify the feasibility of the key NaCl separation process. Finally, economic analyses are carried out, which indicate that the novel system achieves competitive economic performance. This study provides a new hybrid air-conditioning technology for simultaneous cooling, dehumidification and marine aerosol removal by using low-temperature heat.

This work aims at optimizing life cycle performance of a hybrid combined cooling heating and power (CCHP) system incorporating with solar energy and natural gas. A basic natural gas CCHP system containing power generation unit, heat recovery system, hybrid cooling system and storage tank, is integrated with solar photovoltaic (PV) and/or heat collector. LCA optimization methodology is proposed to optimize the configuration and variable load operation of the solar-assisted CCHP system to minimize the life cycle environmental impact. CCHP schemes in following electrical load (FEL) and following thermal load (FTL) strategies are optimized by different objectives respectively. Analysis and comparison are performed on life cycle environmental impacts caused by global warming potential, acidification potential and respiratory effect potential. The influences of main independent decision variables are discussed to discover the generic configuration rules for hybrid CCHP system. The results indicate that FTL strategy is superior to FEL strategy at taking the environmental compensation of surplus products from the hybrid CCHP system into consideration.

Using concentrated solar thermal energy to drive endothermic thermochemical reactions offers promising prospects for the efficient utilization of solar energy by upgrading solar energy to high-quality chemical energy. A 100 kWe power generation pilot plant with mid-and-low temperature solar thermochemistry is designed, modeled, constructed, and tested in this work. The mid-and-low temperature solar thermochemistry and power generation are investigated experimentally, and successfully integrated operation is achieved for the first time. In the pilot plant, solar energy is upgraded into the chemical energy of solar fuel (H2 and CO) through the solar thermochemical process of the methanol decomposition reaction. The solar fuel is then fed to an internal combustion engine to generate power, achieving efficient and stable conversion of solar energy to electricity. The solar generation pilot plant is constructed, including four solar thermochemistry units (with a solar field area of 198 m2), power generation unit (100 kWe), syngas storage unit (with a volume of 19.2 m3), preheating unit, and measurement instrumentation. The thermodynamic performance of the pilot plant is tested under varying solar irradiation levels and power loads. The catalyst bed temperature distribution, methanol decomposition rate, and solar-to-chemical energy efficiency are experimentally investigated. The solar thermochemistry generates with catalyst bed temperatures of 70–290 °C, and a methanol conversion rate exceeding 80% is achieved. The solar-to-chemical energy efficiency is in the range of 37.12–45.51% for solar fluxes of 404–761 W/m2. The system achieves an electrical efficiency of 24.73%, and it can provide a fuel saving of 16.71% compared with direct methanol combustion systems.

Full chain energy performance is applied to a hybrid combined cooling, heating and power (CCHP) system running with methanol and solar energy. Results show that the overall energy efficiencies of six different cases range from 40% to 50% in summer condition, and 38% to 47% in winter condition. Combined with the traditional methanol production process, the CCHP systems are not energy efficient compared to the traditional energy supply systems from a full chain viewpoint no matter whether the solar energy is utilized. While combined with a polygeneration (PG) or polygeneration with CO2 capture (PG + CC) process, the CCHP system could achieve obvious improvements in overall energy efficiency due to the benefits from cogeneration and solar energy utilization, and thus could yield a high fossil energy saving ratio in comparison with the traditional energy supply system. The findings presented in this paper indicate that the complementation utilization of solar energy and fossil fuels through thermochemistry reactions is energy efficient and could be one of the potential options to utilize solar energy.