Hydrogen production by biomass gasification in supercritical water using concentrated solar energy: System development and proof of concept

A novel system of hydrogen production by biomass gasification in supercritical water using concentrated solar energy has been constructed, installed and tested at the State Key Laboratory of Multiphase Flow in Power Engineering (SKLMF). The “proof of concept” tests for solar-thermal gasification of biomass in supercritical water (SCW) were successfully carried out. Biomass model compounds (glucose) and real biomass (corn meal, wheat stalk) were gasified continuously with the novel system to produce hydrogen-rich gas. The effect of direct normal solar irradiation (DNI) and catalyst on gasification of biomass was also investigated. The results showed that the maximal gasification efficiency (the mass of product gas/the mass of feedstock) in excess of 110% were reached, hydrogen fraction in the gas product also approached to 50%. The experimental results confirmed the feasibility of the system and the advantage of the process, which supports future work to address the technical issues and develop the technology of solar-thermal hydrogen production by gasification of biomass in supercritical water.     

Study of cracking of methane for hydrogen production using concentrated solar energy

In this study, the cracking phenomenon of methane taking place in a cylindrical cavity of 16 cm in diameter and 40 cm in length under the heat of concentrated solar radiation without any catalyst is analysed. Three cases have been chosen; in all cases the primary phase contains methane and hydrogen gases. In the first case, we consider two phases; the secondary phase is a homogeneous carbon black powder with 50 nm of diameter; in the second case we have three phases where the two secondary phases are a particles powder with two diameters 20 and 80 nm and finally, a third case of five phases with a powder of four different diameters 20, 40, 60 and 80 nm. The low Reynolds K-ε turbulence model was applied. A calculation code "ANSYS FLUENT" is used to simulate the cracking phenomena where an Eulerian – Eulerian model is applied. The choice of several diameters greatly increases the calculation time but it approaches more of the physical reality of the radiation by these particles during the cracking. Results have shown that increasing the number of diameters gives higher cracking rates; the case of the powder of 4 different diameters gives the highest cracking rate. A parametric study as a function of the inlet velocity, carbon particle diameters and the intensity of solar radiation is realized. For the cracking heat, provided by the choice of the two concentrators of 5 and 16 MW/m² used in this simulation, the CH₄ inlet velocity is a decisive parameter for the cracking rate. Any increase in the inlet velocity requires more heat and this leads to a decrease in the cracking rate. For a velocity not exceeding 0.177 m/s (i.e. 0.3 L/min), both solar concentrations give the same amount of hydrogen produced. These quantities of hydrogen obtained reach maximum values for an inlet flow rate of CH₄ between 0.58 L/min (i.e. 0.34 m/s) and 0.62 L/min (i.e. 0.3655 m/s) for both reactors. The results are interpreted and compared with experimental work.     

Hydrogen production by water electrolysis and off-grid solar PV

This work concerns a methodology for PV-H₂ hybrid system design that consider the weather data and the electrical variables of the subsystems to perform energy balances and to assess the systems in terms of the capacity and operation of the components, and the resulting costs.Two configurations (with and without batteries) and two locations (Madrid and Fisciano) were studied to find the best trade-off between the efficiency and sizes of the subsystems. Directly connected systems operate at intersection points between the PV output and electrolyzer (EL) input curves for different solar irradiance levels, while the battery assisted systems reduce the sizes of EL at the expense of higher energy loss and additional cost of batteries (B). It was found how is not convenient to operate the EL at fixed rate, resulting in high PV and B sizes, as well as power unbalances in winter and summer. Solutions are to run the EL at a minimal load at night and change the intensity of daytime operations to achieve null cumulative energy each season.The H₂ supplied by these systems has the merit of being sustainable (renewable) and autonomous (avoiding power constraints in off-grid locations), and the costs are around 6–7 €/kg_H2.     

Hydrogen production via biomass gasification,and modeling by supervised machine learning algorithms

Prediction of clean hydrogen production via biomass gasification by supervised machine learning algorithms was studied. Lab-scale gasification studies were performed in a steel fixed bed updraft gasifier having a cyclone separator. Pure oxygen, and dried air with varying flow rates (0.05–0.3 L/min) were applied to produce syngas (H₂, CH₄, CO). Gas compositions were monitored via on-line gas analyzer. Various regression models were created by using different Machine Learning (ML) algorithms which are Linear Regression (LR), K Nearest Neighbors (KNN) Regression, Support Vector Machine Regression (SVMR) and Decision Tree Regression (DTR) algorithms to predict the value of H₂ concentration based on the other parameters that are time, temperature, CO, CO₂, CH₄, O₂ and heating value. The highest hydrogen value in syngas was found around 35% vol. after gasification experiments with higher heating value (HHV) of approximately 3400 kcal/m³0.05 L/min and 0.015 L/min were the optimum flow rates for dried air and pure oxygen, respectively. In modeling section, it was observed that H₂ concentrations were being reflected effectively by the concentrations estimated through the proposed model structures, and by having r² values of 0.99 which were ascertained between actual and model results.     

Hydrogen gas production from food wastes by electrohydrolysis using a statical design approach

Hydrogen gas production was investigated by electrohydrolysis of food waste due to its high organic content. Different voltages generated by DC power supply were applied to food waste in order to produce hydrogen gas. Effects of the DC voltage, reaction time and initial solid content on cumulative hydrogen gas production, hydrogen gas content in the gas phase and total organic carbon (TOC) removal were investigated by using a Box-Behnken statistical experiment design approach. The most suitable voltage/reaction time/solid content values resulting in the highest hydrogen gas content (99%), the highest cumulative hydrogen gas formation (7000 mL) and total organic carbon removal (33%) were determined as 5 V/75 h/20%. The results indicated that food wastes constitute a good source for H₂ gas production by electrohydrolysis. Hydrogen gas produced by electrohydrolysis of food waste can be directly used in fuel cells due to its high putrity.     

Photocatalytic hydrogen production under direct solar light in a CPC based solar reactor: Reactor design and preliminary results

In despite of so many types of solar reactors designed for solar detoxification purposes, few attempts have been made for photocatalytic hydrogen production, which in our option, is one of the most promising approaches for solar to chemical energy conversion. Addressing both the similarity and dissimilarity for these two processes and by fully considering the special requirements for the latter reaction, a Compound Parabolic Concentrator (CPC) based photocatalytic hydrogen production solar reactor has been designed for the first time. The design and optimization of this CPC based solar reactor has been discussed in detail. Preliminary results demonstrated that efficient photocatalytic hydrogen production under direct solar light can be accomplished by coupling tubular reactors with CPC concentrators. It is anticipated that this first demonstration of concentrator-based solar photocatalytic hydrogen production would draw attention for further studies in this promising direction.     

Design,modeling and testing of a standalone single axis active solar tracker using MATLAB/Simulink

This paper presents the design, modeling and testing of an active single axis solar tracker. The compactness of the proposed solar tracker enables it to be mounted onto the wall. The solar irradiance is detected by two light-dependent resistor (LDR) sensors that are located on the surface of the photovoltaic (PV) panel. The smart tracker system operates at different modes to provide flexibility to accommodate different weather conditions and preference for different users. The PV panel rotates automatically based on the sun irradiance during the day while at night; the system is in ‘sleep’ mode in order to reduce the energy consumption. A computer model of the standalone solar tracker system is first modeled using MATLAB?/Simulink?. The efficiency over the fixed solar panel, the power generated and the types of PV systems to achieve the required level of efficiency can be determined before actual implementation. The experimental testing shows some agreement with the simulation results.     

Assessment of uncertainty in solar collector modeling and testing

The basic scope of solar collector testing is the determination of the collector efficiency by conducting measurements under specific conditions defined by international standards. The experimental results of testing lead to determination of the parameters of a more or less complex model, usually a 2- or 3-parameter single node steady-state model, which describes the collector behavior. In the present study, a systematic analysis of the contribution of all the uncertainty components on the basis of the ISO 9806-1 test procedure is carried out in order to determine the final uncertainty in the characteristic equation parameters and the instantaneous efficiency of the collector. A step-by-step methodology, based on specific statistical tools, for evaluation of the suitability of the collector models already in use, is proposed. This methodology not only allows an evaluation of the reliability of the testing procedure itself, but also a quantification of the goodness-of-fit. Furthermore, if the uncertainty in the characteristic equation parameters is known, the uncertainty in the collector instantaneous efficiency to be predicted can be assessed. This is essential for the reliability of the results of design tools, for which collector efficiency is a key parameter.     

Hydrogen production via steam reforming of coke oven gas enhanced by steel slag-derived CaO

Steel slag, a waste from steelmaking plant, has been proven to be good candidate resources for low-cost calcium-based CO₂ sorbent derivation. In this work, a cheap and sintering-resistance CaO-based sorbent (CaO (SS)) was prepared from low cost waste steel slag and was applied to enhance catalytic steam reforming of coke oven gas for production of high-purity hydrogen. This steel slag-derived CaO possessed a high and stable CO₂ capture capacity of about 0.48 g CO₂/g sorbent after 35 adsorption/desorption cycles, which was mainly ascribed to the mesoporous structure and the presence of MgO and Fe₂O₃. Product gas containing 95.8 vol% H₂ and 1.4 vol% CO, with a CH₄ conversion of 91.3% was achieved at 600 °C by steam reforming of COG enhanced by CaO (SS). Although high temperature was beneficial for methane conversion, CH₄ conversion was remarkably increased at lower operation temperatures with the promotion effects from CaO (SS), and CO selectivity has been also greatly decreased. Reducing WHSV could increase methane conversion and reduce CO selectivity due to longer reactants residence time. Reducing C/A could increase methane conversion and hydrogen recovery factor, and also decrease CO selectivity. When being mixed with catalyst during SE-SRCOG, CaO (SS) with a uniform size distribution favored methane conversion due to the high utilization efficiency of catalyst. Promising stability of CaO (SS) in cyclic reforming/calcination tests was evidenced with a hydrogen recovery factor >2.1 and CH₄ conversion of 82.5% at 600 °C after 10 cycles using CaO (SS) as sorbent.     

Heat and mass transfer analysis of a suspension of reacting particles subjected to concentrated solar radiation – Application to the steam-gasification of carbonaceous materials

A chemical reactor for the steam-gasification of carbonaceous materials (e.g. coal, coke, biomass) using high-temperature solar process heat is modeled by means of a two-phase formulation that couples radiative, convective, and conductive heat transfer to the chemical kinetics for polydisperse suspensions of reacting particles. The governing mass and energy conservation equations are solved by applying advanced Monte–Carlo and finite-volume techniques with smoothing and underrelaxation. Validation is accomplished by comparing the numerically calculated temperatures, product compositions, and chemical conversions with the experimentally measured values obtained from testing a 5 kW solar reactor prototype in a high-flux solar furnace. A unique feature of the reactor concept is that the gas-particle flow is directly exposed to concentrated solar radiation, providing efficient radiative heat transfer to the reaction site for driving the high-temperature highly endothermic process.     

Hydrogen production by hybrid process combined with assistance of solar and electric energies

To increase the efficiency for hydrogen production by solar decomposition of water in the photoelectrochemical local cell, it was advantageous to decompose an acidic aqueous electrolyte containing Fe³⁺ ions. In the photo-cell having an n-type semiconductor anode illuminated with solar light, the electrolyte decomposed to oxygen and Fe²⁺ ions with a quantum efficiency of ca 38% for light below 400 nm. The electrolyte containing the Fe²⁺ ions produced was electrolysed in the cell having a packed bed carbon anode and a platinum cathode deposited on a cation exchange membrane, producing hydrogen and Fe³⁺ ions with less than 1.0 V at 50 mA cm^?2 and was then fed back to the photo-cell.     

Screening of water-splitting thermochemical cycles potentially attractive for hydrogen production by concentrated solar energy

Hydrogen, a promising and clean energy carrier, could potentially replace the use of fossil fuels in the transportation sector. Currently, no environmentally attractive, large-scale, low-cost and high-efficiency hydrogen production process is available for commercialization. Solar-driven water-splitting thermochemical cycles may constitute one of the ultimate options for CO₂-free production of hydrogen. The method is environmentally friendly since it uses only water and solar energy. First, the potentially attractive thermochemical cycles must be identified based on a set of criteria. To reach this goal, a database that contains 280 referenced cycles was established. Then, the selection and evaluation of the promising cycles was performed in the temperature range of 900–2000 °C, suitable to the use of concentrated solar energy. About 30 cycles selected for further investigations are presented in this paper. The principles and basis for a thermodynamic evaluation of the cycles are also given.     

燃煤改烧石油焦CFB锅炉改造与运行特性研究

介绍某项目循环流化床锅炉完成的燃煤改烧石油焦改造设计和运行特性.运行结果表明,锅炉通过实施纯烧石油焦针对性改造后,纯烧石油焦情况下,锅炉运行状态非常稳定,运行参数满足设计要求,NOx原始排放达到超低排放要求.     

Hydrogen production and storage analysis of a system by using TRNSYS

In this study, hydrogen production and storage were investigated. The Transient System Simulation Program (TRNSYS) and Generic Optimization Program (GenOpt) packages were combined for the design and optimization of a system that produces hydrogen from water and stores the hydrogen it produced in the compressed gas tank. The system design is based on the electricity grid. Electrical energy produced in photovoltaic (PV) panels was used to electrolyze water. The systems for Izmir, Istanbul and Ankara provinces which are in different climate zones of Turkey were optimized and the annual system performances based on the optimum angles were analyzed. For the mentioned provinces, the PV tilt angles which minimize electricity drawn from the grid at the electrolyzer are also investigated. The electrical energy produced in the photovoltaic panels, the hydrogen and oxygen amounts produced, the efficiency of the electrolyzer, the gas and pressure levels in the hydrogen tank were compared. According to the results of the analysis, the annual total power produced in photovoltaic panels is 42803.66 kW in İzmir, 42573.74 kW in Istanbul and 44613.95 kW in Ankara. Hydrogen levels produced in the system are calculated as 10488.39 m³ year⁻¹ in Izmir, 9824.70 m³ year⁻¹ in Istanbul, and 10368.65 m³ year⁻¹ in Ankara.     

Hydrogen production and CO2 fixation by flue-gas treatment using methane tri-reforming or coke/coal gasification combined with lime carbonation

The production of hydrogen and the fixation of CO₂ can be achieved by treatment of flue gases derived from fossil fuel fired power plants via catalytic methane tri-reforming or by coal gasification in the presence of CaO. A two-step process is designed to be carried out in two reactors: a) a catalytic gasifier or steam-reformer, operating exothermally at 900–1000 K, with inputs of the flue gas, a carbonaceous source, steam and air, as well as CaO from the calciner, and outputs of H₂, and of “spent” CaCO₃ to the calciner; b) a calciner, operating endothermally at 1100–1300 K, with inputs of spent CaCO₃ from the gasifier, make-up fresh CaCO₃, and outputs of CO₂, as well as of CaO, partly recycled to the gasifier and partly processed in a cement plant. Thermochemical equilibrium calculations along with mass/energy balances indicate that for flue-gas treatment by tri-reforming, CO₂ emission avoidance of up to ∼59% and fossil fuel savings of up to ∼75% may be attained when concentrated solar energy is supplied as high-temperature process heat for the calcination step, all relative to conventional H₂ production by coal gasification. If instead fossil fuel would be used to drive the calcination step, the CO₂ emission avoidance and the fuel savings would be only 20% and 67%, respectively. Estimated annual H₂ production from a coal-fired 500 MWe burner by the proposed flue-gas treatment using either CH₄-tri-reforming or coal gasification would amount to 0.7 × 10⁶ or 0.6 × 10⁶ metric tons H₂, respectively. Estimated fossil fuel consumption for H₂ production by tri-reforming or coke gasification would be 149 or 143 GJ fuel/ton H₂.     

Stepwise production of CO-rich syngas and hydrogen via solar methane reforming by using a Ni(II)–ferrite redox system

The methane reforming process combined with metal–oxide reduction was examined on iron-based oxides of Ni(II)–, Zn(II)–, and Co(II)–ferrites, for the purpose of converting solar high-temperature heat to chemical fuels of CO-rich syngas and reduced metal oxide as storage and transport of solar energy. It was found that the Ni(II)-doping effectively improves the reactivity of magnetite as an oxidant for methane reforming. A two-step cyclic steam reforming of methane, which produces CO-rich syngas and hydrogen uncontaminated with carbon oxides alternately in the separate steps, was successfully demonstrated by using a ZrO₂-supported Ni(II)–ferrite (Ni_0.39Fe_2.61O₄/ZrO₂) as a working material in the temperature range of 1073–1173 K. The produced CO-rich syngas had the H₂/CO ratio that was more suitable for methanol production than that produced by a conventional single-step steam reforming. This syngas production using the Ni_0.39Fe_2.61O₄/ZrO₂ as an oxidant was also demonstrated under direct irradiation by a solar-simulated, high-flux visible light in laboratory-scale fixed bed system. The directly-irradiated Ni_0.39Fe_2.61O₄/ZrO₂ particles acted simultaneously as good radiant absorbers and reactive chemical reactants to yield more than 90% of methane conversion to a 2:1 molar mixture of CO and H₂ under flux irradiation of 500 kW m⁻² in the residence time less than 1 s.     

An experimental implementation and testing of a concentrated hybrid photovoltaic/thermal system with monocrystalline solar cells using linear Fresnel reflected mirrors

Integration of solar concentrators with photovoltaic (PV) systems reduces the required number of PV panels, which often account for the major costs of PV systems. The linear Fresnel reflector mirror is considered more effective because of its simplicity and effortless fabrication. An experimental test rig of a concentrated PV/thermal system that employs a linear configuration and horizontal absorber was built for evaluating its electrical and thermal performances. The considered concentrator consists of various widths of flat glass mirrors, which positioned with different angles, and with sun light focusing on the PV cells that fixed over an active cooling system. The experimental investigation of the proposed concentrated PV/thermal system shows that higher electrical and thermal efficiencies can be achieved at comparatively high temperature levels than that typically utilized in a nonconcentrated PV/thermal system. The characteristics of PV cells also indicate that the electrical efficiency values in case of no concentration and with concentration ratio of 6.0 are 9.6%, and 11%, respectively. The measured values for the inlet and outlet cooling water temperatures of the receiver showed that the maximum outlet temperature reached was 75°C with a flow rate of 0.025 L/min, and the product thermal efficiency was 62.3%. These obtained results illustrate an adequate and good thermal and electrical performance under the meteorological weather conditions of the province of Al‐Karak in Jordan.