Search

Solar thermochemical processes inherently included the conversion of solar thermal energy into chemical energy. In this paper, a new mechanism of upgrading the energy level of solar thermal energy at around 200[degrees]C was revealed based on the second law thermodynamics and was then experimentally proven. An expression was derived to describe the upgrading of the energy level from low-grade solar thermal energy to high-grade chemical energy. The resulting equation explicitly reveals the interrelations of energy levels between middle-temperature solar thermal energy and methanol fuel, and identifies the interactions of mean solar flux and the reactivity of methanol decomposition. The proposed mechanism was experimentally verified by using the fabricated 5 kW prototype of the receiver/reactor. The agreement between the theoretical and the experimental results proves the validity of the mechanism for upgrading the energy level of low-grade solar thermal energy by integrating clean synthetic fuel. Moreover, the application of this new middle-temperature solar/methanol hybrid thermochemical process into a combined cycle is expected to have a net solar-to-electric efficiency of about 27.8%, which is competitive with other solar-hybrid thermal power plants using high-temperature solar thermal energy. The results obtained here indicate the possibility of utilizing solar thermal energy at around 200[degrees]C for electricity generation with high efficiency by upgrading the energy level of solar thermal energy, and provide an enhancement to solar thermal power plants with the development of this low-grade solar thermochemical technology in the near future. [DOI: 10.1115/1.2840609]

This paper proposes a novel multifunctional energy system (MES), in which hydrogen and electricity are cogenerated and about 90% of C[O.sub.2] is removed. By integrating the methane/steam reforming reaction and combustion of coal, the natural gas and coal are utilized synthetically, and coal is burned to provide high-temperature thermal energy to the methane/steam reforming reaction. Afterwards, the resulting syngas enters a pressure swing adsorption (PSA) unit to separate about 70% of hydrogen, thereby significantly increasing the concentration of carbon dioxide from nearly 20% to 43% in the PSA tail gas. As a result, the overall efficiency of the new system becomes 63.2%. Compared to a conventional natural gas-based hydrogen plant and a coal-firing steam power plant without C[O.sub.2] removal (the overall efficiency of the two systems is 63.0%), the energy penalty for C[O.sub.2] removal in the new system is almost totally avoided. Based on the graphical exergy analysis, we propose that the integration of synthetic utilization of fossil fuel (natural gas and coal) and the C[O.sub.2] removal process plays a significant role in zero energy penalty for C[O.sub.2] removal and its liquefaction in the MES. The result obtained here provides a new approach for C[O.sub.2] removal with zero or low thermal efficiency reduction (energy penalty) within an energy system. [DOI: 10.1115/1.2799532]

This paper manufactured an original middle-temperature solar receiver/reactor prototype, positioned along the focal line of one-axis parabolic trough concentrator, representing the development of a new kind of solar thermochemical technology. A 5 kW prototype solar reactor at around 200-300[degrees]C, which is combined with a linear receiver, was originally manufactured. A basic principle of the design of the middle-temperature solar reactor is identified and described. A representative experiment of solar-driven methanol decomposition was carried out. Experimental tests were conducted from 200[degrees]C to 300[degrees]C under mean solar flux of 300--800 W/[m.sup.2] and at a given methanol feeding rate of 2.1 L/h. The conversion of methanol decomposition yielded up to 50-95%, and the efficiency of solar thermal energy conversion to chemical energy reached 30-60%. The experimental results obtained here prove that the novel solar receiver/reactor prototype introduced in this paper can provide a promising approach to effectively utilize middletemperature solar thermal energy by means of solar thermochemical processes. [DOI: 10.1115/1.2769698]

A new kind of multifunctional energy system (MES) with multifossil fuels and multiproducts is proposed in this paper. This new system consumes coal and natural gas as fuel simultaneously, and cogenerates methanol and power Coal and natural gas are utilized synthetically based on the method of dual-fuel reforming, which integrates the methane/steam reforming and the combustion of coal. During the dual-fuel reforming process, combustion of coal provides high-temperature thermal energy to methane/steam reforming reaction to product syngas. Then, the chemical energy of syngas is used efficiently since the new system integrates the chemical process and power plant. In this manner, the energy including both chemical energy of fuels and thermal energy can be used more effectively from the viewpoint of the whole system. As a result, the total energy efficiency of this new system was about 60-66%. Compared with the conventional systems, the new system provides an energy savings of about 8-15%. The results obtained here indicate that this new system may provide a new way to utilize coal and natural gas more efficiently and economically. [DOI: 10.1115/1.2432895]

A procedure for analyzing the performance of non-isothermal solar reactors for methanol decomposition was developed, based on a model of thermal loss from direct steam generation collector and a comprehensive kinetic model of methanol decomposition employing BASF K3-110 catalyst. It was found that catalytic bed temperature tends towards a certain value, which depends on the chemical reaction type, radiation intensity and collector structure mainly. For a beam incidence angle of 0[degrees], system efficiency increases from 56% at a radiation intensity of 400 W [m.sup.-2] to almost 58% at a radiation intensity of 1000 W [m.sup.2]. For a radiation intensity of 400 W [m.sub.2] beam incidence angle of 20[degrees], absorber length of l0 m, feed temperature of 373 K and ratio of reaction section of 0.9, the mole flow rate of feed in the range of 0.21 0.23 mol [s.sup.-1] results in a maximum quantity of reacted methanol of 0.146 mol [s.sup.-1], while a mole flow rate of feed of 0.15 tool [s.sup.-1] leads to a maximum system efficiency of 54.2%. The research indicates that the pre-heating section should be as short as possible for effective use of solar energy. Keywords: Methanol decomposition; Trough collector; Solar energy; Non-isothermal reactor

In this paper we propose a novel C[O.sub.2]-recovering hybrid solar-fossil combined cycle with the integration of methane-fueled chemical-looping combustion, and investigate the system with the aid of the Energy-Utilization Diagram (EUD). Chemical-looping combustion (CLC) consists of two successive reactions: first, methane fuel is oxidized by metal oxide(NiO)as an oxygen carrier (reduction of metal oxide); and second, the reduced metal (Ni) is successively oxidized by combustion air (the oxidation of metal). The oxidation of methane with NiO requires a relative low-grade thermal energy at 300[degrees]C-500[degrees]C. Then concentrated solar thermal energy at approximately 450[degrees]C-550[degrees]C can be utilized to provide the process heat for this reaction. By coupling solar thermal energy with methane-fueled chemical-looping combustion, the energy level of solar thermal energy at around 450[degrees]C-550[degrees]C can be upgraded to the chemical energy of solid fuel Ni for better utilization of solar energy to generate electricity. The synergistic integration of solar thermal energy and chemical-looping combustion could make the exergy efficiency and the net solar-to-electric efficiency of the solar hybrid system more than 60% and 30%, respectively, at a turbine inlet temperature (TIT) of 1200[degrees]C. At the same time, this new system has an extremely important advantage of directly suppressing the environmental impact due to lack of energy penalty for C[O.sub.2] recovery. Approximately 9-15 percentage points higher efficiency can be achieved compared to the conventional natural gas-fired combined cycle with C[O.sub.2] separation. The results obtained here are promising and indicate that this novel solar hybrid combined cycle offers the new possibility of C[O.sub.2] mitigation using both green energy and fossil fuels. These results also provide a new approach for highly efficient use of solar thermal energy to generate electricity. [DOI: 10.1115/1.2212443]

In this paper, we have proposed a new solar thermal power cycle which integrates methanol decomposition and middle-temperature solar thermal energy, and investigated its features based on the principle of the cascade utilization of chemical exergy. Also, the methanol decomposition with a catalyst was experimentally studied at temperatures of 150-300[degrees]C and under atmospheric pressure. The chemical energy released by methanol fuel in this cycle consisted of two successive processes: solar energy drives the thermal decomposition of methanol in a solar receiver-reactor, and the syn-gas of resulting products is combusted with air, namely, indirect combustion alter methanol decomposition. As a result, the net solar-to-electric efficiency of the proposed cycle could be 35% at the collector temperature of 220[degrees]C and the turbine inlet temperature of 1300[degrees]C, and the exergy loss in the indirect combustion of methanol was about 7% points lower than that in the direct combustion of methanol. The promising results obtained in this study indicated that this new solar thermal power cycle could make significant improvements both in the efficient use of the chemical energy of clean synthetic fuel and in the middle-temperature solar thermal energy in a power system. Keywords: Middle-temperature solar energy; Methanol decomposition: Thermal power cycle

Co3O4 nanomaterials are grown in situ on nickel foam by a facile two-step method, and their electrochemical properties for supercapacitors and electrochemical H2 production are systematically investigated. As an electrode material for supercapacitors, the Co3O4/NF nanomaterials have a specific capacitance of 4705 mF/cm2 at a current density of 2.5 mA/cm2 in 6 M KOH solution with good cycling stability. The asymmetric supercapacitor assembled with Co3O4/NF (positive) and activated carbon (negative) exhibits high energy storage capacity (2023 mF/cm2 at 5 mA/cm2), good rate performance and cycling stability. In addition, the Co3O4/NF nanocomposites exhibit excellent catalytic performance in electrolytic aquatic hydrogen. In 1 M KOH electrolyte, a potential of only 225 mV is required to provide a current density of 30 mA/cm2. Furthermore, increasing the temperature enhances the catalytic performance of the material, which provides the possibility of using industrial production waste heat to catalyze hydrogen production. Therefore, this study not only shows the great potential of Co3O4/NF nanocomposites as a supercapacitor cathode material, but also indicates its great opportunity for hydrogen production. [ABSTRACT FROM AUTHOR]

Co3O4 nanorods were successfully synthesized by a facile two-step method and showed outstanding electrochemical performances in KOH and urea electrolyte. The Co3O4 nanorods showed high purity phase and covered the surface of carbon cloth. As the electrode materials for hydrogen generation, it only required the hydrogen evolution reaction (HER) overpotential of 0.46 V to deliver the current density of 40 mA/cm2 for HER and urea oxidation reaction potential (UOR vs RHE) of 1.62 V at 10 mA/cm2. Remarkably, the assembled electrolyzer with Co3O4/CC and Pt foil as two electrodes demonstrated low potentials and a stable long cycle life. Therefore, the study displays a promising direction to explore the practical and effective ways for hydrogen production by overall urea electrolysis. [ABSTRACT FROM AUTHOR]

An effective strategy to design platinum group metal (PGM) free redox catalysts for "low temperature" CO2 splitting followed with methane partial oxidation was proposed and validated. Composites of mixed ionic-electronic conductive (MIEC) oxides were found to be highly effective at relatively low temperatures (600–750 °C). Specifically, perovskite structured LaNi0.35Fe0.65O3 and rock salt structured Ce0.85Gd0.1Cu0.05O2−δ, as two compatible yet structurally distinct MIEC oxides, were integrated into composite redox catalyst particles. Resulting from the synergistic effect of the two MIEC phases, 90% CO2 to CO conversion was demonstrated at 750 °C. Up to 90% methane conversion with 96% CO selectivity was also achieved in the methane POx step. The redox catalysts were characterized in detail to illustrate the underlying mechanisms for the synergistic effects. Electrical conductivity relaxation (ECR) measurements indicated significantly lowered activation energy for lattice oxygen (O2−) migration (0.43 eV). The enhanced oxygen migration in turn led to reversible exsolution of active transition metal nanoparticles (Ni–Fe alloy) from the mixed oxide, serving as active sites for methane activation while further enhancing lattice oxygen exchange, as confirmed by in situ X-ray diffraction and transmission electron microscopy. As a result, the composite redox catalysts demonstrate superior redox activity, coke resistance, and long term redox stability, making them potentially suitable for CO2 utilization and methane partial oxidation under a hybrid redox process scheme. [ABSTRACT FROM AUTHOR]

Gynostemma pentaphyllum has gained increasing interest in recent years for its widespread use as a medicinal plant, dietary supplement, herbal tea, and vegetable in China. This herb possesses many beneficial functions, such as anti-tumor, anti-inflammatory, cholesterol lowering, strengthening of the immune system, and blood pressure regulating activities. However, due to an absence of information, the major material components of Gynostemma pentaphyllum remain unknown. A method for the comprehensive profiling of components in Gynostemma pentaphyllum is reported using high performance liquid chromatography – electrospray ionization – quadrupole time-of-flight tandem mass spectrometry (HPLC-ESI-QTOF-MS/MS) in this study. As a result, a total of 36 compounds including flavonoid glycosides and gypenosides were characterized or tentatively identified. Four gypenosides were tentatively identified as potentially new compounds in Gynostemma pentaphyllum. These results provided a reference for comprehensive characterization of ingredients in Gynostemma pentaphyllum and are significant for the utilization of Gynostemma pentaphyllum. [ABSTRACT FROM AUTHOR]