Countercurrent reactor design and flowsheet for iodine-sulfur thermochemical water splitting process

A conceptual design is presented for the I/S process for the production of hydrogen using a high-temperature nuclear heat source to split water. The process includes a countercurrent reactor being developed by CEA within the framework of an international collaboration (I-NERI project) with DOE at General Atomics (San Diego, CA). A ProsimPlus? model of the flowsheet indicates 600 kJ high-temperature heat and 69 kJ electric power are consumed per mole of H₂ product (with an assumed pressure of 120 bars). The net thermal efficiency would be 38% (HHV basis) if electric power is available at a conversion efficiency of 45%.     

Biodiesel production by esterification of palm fatty acid distillate

Production of fatty acid methyl ester (FAME) from palm fatty acid distillate (PFAD) having high free fatty acids (FFA) was investigated in this work. Batch esterifications of PFAD were carried out to study the influence of: including reaction temperatures of 70–100 °C, molar ratios of methanol to PFAD of 0.4:1–12:1, quantity of catalysts of 0–5.502% (wt of sulfuric acid/wt of PFAD) and reaction times of 15–240 min. The optimum condition for the continuous esterification process (CSTR) was molar ratio of methanol to PFAD at 8:1 with 1.834 wt% of H₂SO₄ at 70 °C under its own pressure with a retention time of 60 min. The amount of FFA was reduced from 93 wt% to less than 2 wt% at the end of the esterification process. The FAME was purified by neutralization with 3 M sodium hydroxide in water solution at a reaction temperature of 80 °C for 15 min followed by transesterification process with 0.396 M sodium hydroxide in methanol solution at a reaction temperature of 65 °C for 15 min. The final FAME product met with the Thai biodiesel quality standard, and ASTM D6751-02.     

Packed-bed thermal storage for concentrated solar power – Pilot-scale demonstration and industrial-scale design

A thermal energy storage system, consisting of a packed bed of rocks as storing material and air as high-temperature heat transfer fluid, is analyzed for concentrated solar power (CSP) applications. A 6.5 MWh_th pilot-scale thermal storage unit immersed in the ground and of truncated conical shape is fabricated and experimentally demonstrated to generate thermoclines. A dynamic numerical heat transfer model is formulated for separate fluid and solid phases and variable thermo-physical properties in the range of 20–650 °C, and validated with experimental results. The validated model is further applied to design and simulate an array of two industrial-scale thermal storage units, each of 7.2 GWh_th capacity, for a 26 MW_el round-the-clock concentrated solar power plant during multiple 8 h-charging/16 h-discharging cycles, yielding 95% overall thermal efficiency.     

Analysis of the hybrid copper oxide–copper sulfate cycle for the thermochemical splitting of water for hydrogen production

The hybrid copper oxide–copper sulfate water-splitting thermochemical cycle involves two principal steps: (1) hydrogen production from the electrolysis of water, SO₂(g) and CuO(s) at room temperature and (2) the thermal decomposition of the CuSO₄ product to form oxygen and SO₂, which is recycled to the first step. A four-reaction version of the cycle (known in the literature as Cycle H-5) was used as the basis of the present work. For several of the four reactions, a rotating batch reactor sequence is proposed in order to overcome equilibrium limitations.Pinch technology was used to optimize heat integration. Sensitivity analyses revealed it to be economically more attractive to use a 10 °C approach to minimize heat loss (rather than 20 °C). Using standard Aspen Plus features and the Peng–Robinson equation of state for separations involving oxygen and sulfur oxides, a proposed flowsheet for the cycle was generated to yield “Level 3” results.A cost analysis of the designed plant (producing 100 million kmol/yr hydrogen) indicates a total major equipment cost of approximately $45 million. This translates to a turnkey plant price (excluding the cost of the high-temperature heat source or electrolyzer internals) of approximately $360 million. Based on a $2.50/kg selling price for hydrogen, gross annual revenue could be on the order of $500 million, resulting in a reasonable payback period when all capital and operating costs are considered.Previous efficiency estimates using Level 1 and Level 2 methods gave the process efficiency in the neighborhood of 47–48%. The Level 3 efficiency computation was 24–25% depending on the approach temperature used for recuperation. If the low quality heat rejected by the process can be recovered and used elsewhere, the Level 3 analysis could be as high as 51–53%.     

A solar-powered traveling-wave thermoacoustic electricity generator

Traveling-wave thermoacoustic electricity generator is a new external-combustion type device capable of converting heat such as solar energy into electric power. In this paper, a 1 kW solar-powered traveling-wave thermoacoustic electricity generation system is designed and fabricated. The system consists of a traveling-wave thermoacoustic electricity generator, a solar dish collector and a heat receiver. In the preliminary tests, using electric cartridge heaters to simulate the solar energy, a maximum electric power of 481 W and a maximum thermal-to-electric efficiency of 15.0% were achieved with 3.5 MPa pressurized helium and 74 Hz working frequency. Then, after integrating the traveling-wave thermoacoustic electricity generator with the solar dish collector and the heat receiver, the solar-powered experiments were performed. In the experiments, a maximum electric power of about 200 W was obtained. However, due to the solar dish collector problems, the heating temperature of the receiver was much lower than expected. Optimizations of the collector and the heat receiver are under way.     

Liquid sodium versus Hitec as a heat transfer fluid in solar thermal central receiver systems

Selection of an appropriate HTF is important for minimising the cost of the solar receiver, thermal storage and heat exchangers, and for achieving high receiver and cycle efficiencies. Current molten salt HTFs have high melting points (142–240 °C) and degrade above 600 °C. Sodium’s low melting point (97.7 °C) and high boiling point (873 °C) allow for a much larger range of operational temperatures. Most importantly, the high temperatures of sodium allow the use of advanced cycles (e.g. combined Brayton/Rankine cycles). In this study, a comparison between the thermophysical properties of two heat transfer fluids (HTFs), Hitec (a ternary molten salt 53% KNO₃ + 40% NaNO₂ + 7% NaNO₃) and liquid sodium (Na), has been carried out to determine their suitability for use in high-temperature concentrated solar thermal central-receiver systems for power generation. To do this, a simple receiver model was developed to determine the influences of the fluids’ characteristics on receiver design and efficiency. While liquid sodium shows potential for solar thermal power systems due to its wide range of operation temperatures, it also has two other important differences – a high heat transfer coefficient (～an order of magnitude greater than Hitec) and a low heat capacity (30–50% lower than Hitec salt). These issues are studied in depth in this model. Overall, we found that liquid sodium is potentially a very attractive alternative to molten salts in next generation solar thermal power generation if its limitations can be overcome.     

Methanol decomposition fuel processor for portable power applications

A new fuel processor approach for portable fuel cell power sources significantly improves upon microreformers by overcoming the difficulties with heat deficiencies and contaminants in the product hydrogen. Instead of reforming, the processor uses methanol decomposition to enable the byproduct, carbon monoxide (CO), to be used as the heat source. A hydrogen permselective membrane segregates the CO for combustion in an integrated burner, maximizes the decomposition conversion, and provides pure hydrogen for a fuel cell. Discharging the CO-rich retentate through an ejector to draw combustion air into the burner greatly simplifies the system. High and stable hydrogen yields are attained with optimized catalysts and fuel compositions. The resultant simple, efficient, and self-heating processor produces 85% of the hydrogen content of the fuel. A 20 W autonomous power source based on this novel fuel processor demonstrates a fuel energy density >1.5 Wh g^?1_(electrical), nearly twice as high as microreformer power sources.     

Fuel effects on start-up energy and efficiency for automotive PEM fuel cell systems

This paper investigates the effects of various fuels on hydrogen production for automotive PEM fuel cell systems. Gasoline, methanol, ethanol, dimethyl ether and methane are compared for their effects on fuel processor size, start-up energy and overall efficiencies for 50 kW_e fuel processors. The start-up energy is the energy required to raise the temperature of the fuel processor from ambient temperature (20 °C) to that of the steady-state operating temperatures. The fuel processor modeled consisted of an equilibrium-ATR (autothermal), high-temperature water gas shift (HTS), low-temperature water gas shift (LTS) and preferential oxidation (PrOx) reactors. The individual reactor volumes with methane, dimethyl ether, methanol and ethanol were scaled relative to a gasoline-fueled fuel processor meeting the 2010 DOE technical targets. The modeled fuel processor volumes were, 25.9 L for methane, 30.8 L for dimethyl ether, 42.5 L for gasoline, 43.7 L for ethanol and 45.8 L for methane. The calculated fuel processor start-up energies for the modeled fuels were, 2712 kJ for methanol, 3423 kJ for dimethyl ether, 6632 kJ for ethanol, 7068 kJ for gasoline and 7592 kJ for methane. The modeled overall efficiencies, correcting for the fuel processor start-up energy using a drive cycle of 33 miles driven per day, were, 38.5% for dimethyl ether, 38.3% for methanol, 37% for gasoline, 34.5% for ethanol and 33.2% for methane assuming a steady-state efficiency of 44% for each fuel.     

Biodiesel production by esterification of oleic acid with short-chain alcohols under ultrasonic irradiation condition

Production of fatty acid ethyl ester (FAEE) from oleic acid (FFA) with short-chain alcohols (ethanol, propanol, and butanol) under ultrasonic irradiation was investigated in this work. Batch esterification of oleic acid was carried out to study the effect of: test temperatures of 10–60 °C, molar ratios of alcohol to oleic acid of 1:1–10:1, quantity of catalysts of 0.5–10% (wt of sulfuric acid/wt of oleic acid) and irradiation times of 10 h. The optimum condition for the esterification process was molar ratio of alcohol to oleic acid at 3:1 with 5 wt% of H₂SO₄ at 60 °C with an irradiation time of 2 h.     

A novel polygeneration system integrating the acetylene production process and fuel cell

This paper presents a novel polygeneration system that integrates the acetylene process and the use of fuel cells. The system produces acetylene and power by a process of the partial oxidation/combustion (POC) of natural gas process, a water–gas shift reactor, a fuel cell and a waste heat boiler auxiliary system to recover the exhaust heat and gas from the fuel cell. Based on 584.3 kg/h of natural gas feedstock, a POC reactor temperature of 1773 K, an absorber pressure of 1.013 MPa and a degasser pressure of 0.103 MPa, the simulation results show that the new system achieved acetylene production of 1.9 MW, net electricity production of 1.7 MW, power generation efficiency of 26.8% and exergy efficiency of 43.4%, which was 20.2% higher than the traditional acetylene production process. The new system's exergy analysis and the flow rate of the products were investigated, and the results revealed that the energy conversion and systematic integration mechanism demonstrated the improvement of natural gas energy conversion efficiency.     

Boiling two-phase flow and efficiency of co- and counter-current microchannel heat exchangers with gas heating

To learn how to utilize the exhaust heat from a high-temperature gas product of a methanol reformer, the present study experimentally investigates the boiling two-phase flow in co- and counter-current microchannel heat exchangers (MCHE) with gas heating. Boiling two-phase flow patterns, two-phase flow instability, and efficiency are explored. The working fluid on the hot and cold sides are helium and liquid methanol, respectively. The silicon-based MCHE, which has dimensions of 20 mm × 20 mm, is designed with 18 parallel microchannels on both sides and is prepared using microfabrication processes. Four types of two-phase flow patterns – bubbly-elongated slug flow, annular flow, annular flow with liquid film breakup, and dryout are identified in both types of MCHE that are studied. A flow pattern map is then constructed on the plane of the methanol mass flux versus heat flux for both types of MCHE. In the counter-current MCHE, the efficiency increases significantly with an increase in the mass flux in both the single- and two-phase flow regions, while the effect of mass flux is insignificant in the co-current MCHE. In the two-phase flow region, the efficiency of both types of MCHEs gradually increases with an increase in the hot-side thermal power until the CHF is approached. The highest efficiency obtained in the present study is about 0.85 and 0.90 for the co- and counter-current MCHEs, respectively.     

Performance of low-temperature differential Stirling engines

In this paper, two single-acting, twin power piston and four power pistons, gamma-configuration, low-temperature differential Stirling engine are designed and constructed. The engine performance is tested with air at atmospheric pressure by using a gas burner as a heat source. The engine is tested with various heat inputs. Variations of engine torque, shaft power and brake thermal efficiency at various heat inputs with engine speed and engine performance are presented. The Beale number obtained from testing of the engines is also investigated. The results indicate that, for twin power piston engine, at a maximum actual heat input of 2355 J/s with a heater temperature of 589 K, the engine produces a maximum torque of 1.222 N m at 67.7 rpm, a maximum shaft power of 11.8 W at 133 rpm, and a maximum brake thermal efficiency of 0.494% at 133 rpm, approximately. For the four power pistons engine, the results indicate that at the maximum actual heat input of 4041 J/s with the heater temperature of 771 K, the engine produces a maximum torque of 10.55 N m at 28.5 rpm, a maximum shaft power of 32.7 W at 42.1 rpm, and a maximum brake thermal efficiency of 0.809% at 42.1 rpm, approximately.     

New dry and wet Zn-polyaniline bipolar batteries and prediction of voltage and capacity by ANN

Chemically synthesized polyaniline doped with perchlorate ion was used as the electroactive material of the cathode in the construction of bipolar rechargeable batteries based on carbon doped polyethylene (CDPE) as a conductive substrate of the bipolar electrodes. A significant improvement in the originally poor adherence between the polymer foil and electroactive material layer of the anode was achieved by chemical pretreatment (etching) and single-sided metallization of the polymer foil with copper. A thin layer of optalloy was electroplated onto the surface of the copper-coated polymer foil to increase the battery overvoltage. A mixture of 1 wt% electrochemically synthesized optalloy, 92 wt% electrochemically synthesized zinc powder, 2 wt% MgO, 4 wt% ZnO and 1 wt% sodium carboxymethyl cellulose (CMC) was used as the anode mixture. Then, the electroactive mixture of the anode was coated onto the metallized surface of the CDPE. Graphite powder was used to coat the other side of the CDPE at 90 °C at 1 t cm⁻² pressure This side was coated with a cathode mixture containing 80 wt% polyaniline powder, 18 wt% graphite powder and 2 wt% acetylene black. The battery electrolyte contained 1 M Zn(ClO₄)₂ and 0.5 M NH₄ClO₄ and 1.0 × 10⁻⁴ M Triton X-100 at pH 3.2. Both 3.2 V dry and wet bipolar batteries were constructed using a bipolar electrode and tested successfully during 200 charge–discharge cycles. The battery possessed a high capacitance of 130 mAh g⁻¹ and close to 100% columbic efficiency. The loss of capacity during charge–discharge cycles for the wet bipolar battery was less than that for the dry bipolar battery. Self-discharge of the dry and wet batteries during a storage time of 30 days was about 0.64% and 0.45% per day, respectively. An artificial neural network (ANN) was used to model the voltage and battery available capacity (BAC) only for the dry bipolar battery at different currents and different times of discharge.     

High-temperature sulfuric acid decomposition over complex metal oxide catalysts

Activity and stability of FeTiO₃, MnTiO₃, NiFe₂O₄, CuFe₂O₄, NiCr₂O₄, 2CuO·Cr₂O₃, CuO and Fe₂O₃ for the atmospheric decomposition of concentrated sulfuric acid in sulfur-based thermochemical water splitting cycles are presented. Catalyst activity was determined at temperatures from 725 to 900 °C. Catalytic stability was examined at 850 °C for up to 1 week of continuous operation. The results were compared to a 1.0 wt% Pt/TiO₂ catalyst. Surface area by nitrogen physisorption, X-ray diffraction analyses, and temperature programmed desorption and oxidation were used to characterize fresh and spent catalyst samples.Over the temperature range, the catalyst activity of the complex oxides followed the general trend: 2CuO·Cr₂O₃ > CuFe₂O₄ > NiCr₂O₄ ≈ NiFe₂O₄ > MnTiO₃ ≈ FeTiO₃. At temperatures less than 800 °C, the 1.0 wt% Pt/TiO₂ catalyst had higher activity than the complex oxides, but at temperatures above 850 °C, the 2CuO·Cr₂O₃ and CuFe₂O₄ samples had the highest activity.Surface area was found to decrease for all of the metal oxides after exposure to reaction conditions. In addition, the two complex metal oxides that contained chromium were not stable in the reaction environment; both leached chromium into the acid stream and decomposed into their individual oxides. The FeTiO₃ sample also produced a discoloration of the reactor due to minor leaching and converted to Fe₂TiO₅. Fe₂O₃, MnTiO₃ and NiFe₂O₄ were relatively stable in the reaction environment. In addition, CuFe₂O₄ catalyst appeared relatively promising due to its high activity and lack of any leaching issues; however it deactivated in week-long stability experiments.Complex metal oxides may provide an attractive alternative to platinum-based catalyst for the decomposition of sulfuric acid; however, the materials examined in this study all displayed shortcomings including material sintering, phase changes, low activity at moderated temperatures due to sulfate formation, and decomposition to their individual oxides. More effort is needed in this area to discover metal oxide materials that are less expensive, more active and more stable than platinum catalysts.     

Energy and exergy analyses of OMW solar drying process

The energy and exergy analyses of the drying process of olive mill wastewater (OMW) using an indirect type natural convection solar dryer are presented. Olive mill wastewater gets sufficiently dried at temperatures between 34 °C and 52 °C. During the experimental process, air relative humidity did not exceed 58%, and solar radiation ranged from 227 W/m² to 825 W/m². Drying air mass flow was maintained within the interval 0.036–0.042 kg/s. Under these experimental conditions, 2 days were needed to reduce the moisture content to approximately one-third of the original value, in particular from 3.153 g_water/g_{dry matter} down to 1.000 g_water/g_{dry matter}.Using the first law of thermodynamics, energy analysis was carried out to estimate the amounts of energy gained from solar air heater and the ratio of energy utilization of the drying chamber. Also, applying the second law, exergy analysis was developed to determine the type and magnitude of exergy losses during the solar drying process. It was found that exergy losses took place mainly during the second day, when the available energy was less used. The exergy losses varied from 0 kJ/kg to 0.125 kJ/kg for the first day, and between 0 kJ/kg and 0.168 kJ/kg for the second. The exergetic efficiencies of the drying chamber decreased as inlet temperature was increased, provided that exergy losses became more significant. In particular, they ranged from 53.24% to 100% during the first day, and from 34.40% to 100% during the second.     

Optical efficiency of a PV–thermal hybrid CPC module for high latitudes

The advantage of PV–thermal hybrid systems is their high total efficiency. By using concentrating hybrid systems, the cost per energy produced is reduced due to simultaneous heat and electricity production and a reduced PV cell area. In this article, the optical efficiency of a water-cooled PV–thermal hybrid system with low concentrating aluminium compound parabolic concentrators is discussed. The system was built in 1999 in Älvkarleby, Sweden (60.5° N, 17.4° E) with a geometric concentration ratio of C=4 and 0.5 kW_p electric power. The yearly output is 250 kWh of electricity per square metre solar cell area and 800 kWh of heat at low temperatures per square metre solar cell area. By using numerical data from optical measurements of the components (glazing, reflectors, and PV cells) the optical efficiency, η_opt, of the PV–CPC system has been determined to be 0.71, which is in agreement with the optical efficiency as determined from thermal and electrical measurements. Calculations show that optimised antireflection-treated glazing and reflectors could further increase the electric power yield.     

Hydrogen and dry ice production through phase equilibrium separation and methane reforming

A clean hydrogen (99.9999%) and dry ice production process is proposed, which is based on phase equilibrium (PE) separation and methane reforming. Heat and power integration studies are carried out for the proposed process, by formulating and solving the minimum hot/cold/electric utility cost problem for the associated heat exchange network. The optimum operating cost of the proposed process is shown to be lower than the corresponding cost of the conventional PSA (pressure swing adsorption) based process, if the produced dry ice is sold for as low as 2 cents kg-dry-ice⁻¹ or if an equivalent CO₂ sequestration credit is conceded.     

Hydrogen storage in an activated carbon bed: Effect of energy release on storage capacity of the tank

Thermal effects during dynamic charging of a two-liter, adsorbent, packed bed, hydrogen storage tank were studied through numerical modeling. For packed-bed materials having adsorption capacities smaller than 2 wt%, the conversion to heat of the mechanical work required to feed the tank produces more than 60% of the temperature increase that occurs during the charging process. However, for materials having adsorption capacities greater than 3 wt%, 60% of the heating is due to the adsorption process. The temperature increase for a material that would fulfill the DOE recommendation of 6 wt% storage capacity is 130 K. This reduces the storage capacity by 20% relative to what would be obtained from an isothermal charging process. Simulations showed that the limitation in the storage capacity can be reduced to less than 10%, if a packed bed having an effective conductivity of a few W m^?1 K^?1 can be used.     

Renewable hydrogen generation by steam reforming of glycerol over zirconia promoted ceria supported catalyst

The study focuses on hydrogen production from steam reforming of glycerol over nickel based catalyst promoted by zirconia and supported over ceria. Catalyst was prepared by the wet-impregnation method and characterized by BET surface area analysis, X-ray diffraction technique and scanning electron microscopy (SEM) analysis. The performance of the catalyst was evaluated in terms of hydrogen yield, selectivity and glycerol conversion at 700 °C in a tubular fixed bed reactor. The effect of glycerol concentration in feed, space time (W/F_AO), temperature and time on stream (TOS) was analyzed for the catalyst Ni–ZrO₂/CeO₂ which showed the complete conversion of glycerol and high H₂ yield that corresponds to 3.95 mol of H₂ out of 7 mol. Thermodynamic analysis was also carried out using Aspen HYSYS for system having glycerol concentration 10 wt% and 20 wt% and experimental results were compared with thermodynamics. Kinetic study was carried out for the steam reforming of glycerol over Ni–ZrO₂/CeO₂ catalyst using the power law model. The values of activation energy and order of reaction were found to be 43.4 kJ/mol and 0.3 respectively.     

Solid/vapour sorption heat transformer: Design and performance

A high temperature high lift solid sorption based heat transformer has been successfully designed and tested. The sorption reactor concept is based on a tube-fin heat exchanger where the heat exchanging fluids can flow through the hollow fins. The plates were brazed together with porous metal foam that was impregnated with either of the sorbents, LiCl and MgCl₂. The adsorbate is ammonia. The batch system was tested as to the power delivered at high temperatures, 150–200 °C. Peak power at 200 °C was about 0.8 kW, the average power about 0.4 kW. The thermal efficiency, COP, was calculated from the experimental results to be 0.11. This is only 40% of the expected theoretical value and can largely be attributed to the thermal mass of the reactor.