Solar Reforming Research Articles

A review of solar methane reforming systems

Because of the increasing demand for energy and the associated rise in greenhouse gas emissions, there is much interest in the use of renewable sources such as solar energy in electricity and fuels generation. One problem with solar energy, however, is that it is difficult to economically convert the radiation into usable energy at the desired locations and times, both daily and seasonally. One method to overcome this space-time intermittency is through the production of chemical fuels. In particular, solar reforming is a promising method for producing chemical fuels by reforming and/or water/carbon dioxide splitting. In this paper, a review of solar reforming systems is presented, as well as a comparison between these systems and a discussion on areas for potential innovation including chemical looping and membrane reactors. Moreover, a brief overview of catalysis in the context of reforming is presented.

Efficiency potential of indirectly heated solar reforming with open volumetric solar receiver

In solar reforming, the heating value of natural gas is increased by utilization of concentrated solar radiation. Hence, it is a process for storing solar energy in a stable and transportable form that also permits further conversion into liquid fuels like methanol. The feasibility of solar reforming is proved. However, its overall process efficiency potential has not been studied systematically. In this work, an indirectly heated solar reforming process with air as heat transfer fluid is designed and modelled to produce syngas suitable for subsequent methanol synthesis. For provision of solar high temperature heat, an open volumetric receiver is implemented into the process model and the overall performance is investigated. Results show the paramount significance of the air return ratio of the receiver and its ability to achieve high efficiencies at temperatures above 850 °C. For realistic air return ratios, design point process efficiencies of 19% can be achieved, for an increased air return ratio, values up to 23% are feasible. The determined corresponding annual efficiencies are 12% and 14% respectively. Considering its relative technical simplicity this makes indirectly heated solar reforming a promising technology to overcome the current limitations of solar energy in the medium term.

Integrated Solar Thermochemical Reaction System for Steam Methane Reforming

Solar-aided upgrade of the energy content of fossil fuels, such as natural gas, can provide a near-term transition path towards a future solar-fuel economy and reduce carbon dioxide emission from fossil fuel consumption. Both steam and dry reforming a methane-containing fuel stream have been studied with concentrated solar power as the energy input to drive the highly endothermic reactions but the concept has not been demonstrated at a commercial scale. Under a current project with the U.S. Department of Energy, PNNL is developing an integrated solar thermochemical reaction system that combines solar concentrators with micro- and meso-channel reactors and heat exchangers to accomplish more than 20% solar augment of methane higher heating value. The objective of our three-year project is to develop and prepare for commercialization such solar reforming system with a high enough efficiency to serve as the frontend of a conventional natural gas (or biogas) combined cycle power plant, producing power with a levelized cost of electricity less than 6¢/kWh, without subsidies, by the year 2020. In this paper, we present results from the first year of our project that demonstrated a solar-to-chemical energy conversion efficiency as high as 69% with a prototype reaction system.

Ultra-low loading Ru/γ-Al2O3: A highly active and stable catalyst for low temperature solar thermal reforming of methane

Converting solar radiation into chemical energy is an attractive method to increase the energy content of methane by driving endothermic upgrading processes, such as methane steam reforming. Although such solar thermochemical conversions would increase natural gas product yields and reduce greenhouse gas emissions, current costs of solar facilities are prohibitively high. Parabolic troughs, which are a mature and relatively inexpensive form of solar concentrator, are limited to temperatures of ca. 400–600°C. In this regime, commercial methane steam reforming Ni-based catalysts have low activity and rapidly deactivate due to oxidation and coking. Catalysts based on platinum group metals are much more active and stable but their high cost limits their use. Here, we investigate Ru-based catalysts with ultra-low metal loadings for low-temperature methane steam reforming. We show that a Ru/γ-Al2O3 (0.15wt% loading) catalyst outperforms the commercial (12wt% Ni) catalyst by two orders of magnitude in terms of methane conversion normalized by metal loading. Systematic evaluation of catalytic performance over a range of Ru loadings and operating conditions shows a pronounced optimum in catalytic activity versus metal loading. Characterization studies reveal a strong correlation between the catalytic activity and the Ru nanoparticle size distribution. The catalyst features excellent stability at industrially relevant conditions and low steam-to-carbon ratios, making it an attractive option for low-temperature solar reforming of methane.

Redox reforming based, integrated solar-natural gas plants: Reforming and thermodynamic cycle efficiency

As demand for energy continues to rise, the concern over the increase in emissions grows, prompting much interest in using renewable energy resources such as solar energy. However, there are numerous issues with using solar energy including intermittency and the need for storage. A potential solution is the concept of hybrid solar-fossil fuel power generation. Previous work has shown that utilizing solar reforming in conventional power cycles has higher performance compared to other integration methods. Most previous studies have focused on steam or dry reforming and on specific component analysis rather than a systems level analysis. In this article, a system analysis of a hybrid cycle utilizing redox reforming is presented. Important cycle design and operation parameters such as the oxidation temperature and reformer operating pressure are identified and their effect on both the reformer and cycle performance is discussed. Simulation results show that increasing oxidation temperature can improve reformer and cycle efficiency. Also shown is that increasing the amount of reforming water leads to a higher reformer efficiency, but can be detrimental to cycle efficiency depending on how the reforming water is utilized.

Solar Powered Steam-methane Reformer Economics

With funding from the U.S. Department of Energy (DOE) and SolarThermoChemical LLC, PNNL is developing a solar-powered steam-methane reformer (SMR). The reformer sits at the focal point of a parabolic dish concentrator, with the concentrated solar energy providing the endothermic heat of reaction. The result is a syngas comprising mostly H2 and CO with a heating value approximately 27% higher than the entering natural gas.On-sun testing completed in 2013 achieved a solar-to-chemical energy conversion efficiency as high as 69%, based on the ratio of incremental chemical energy created to direct normal insolation striking the parabolic dish concentrator. Advanced designs are expected to improve upon this performance. Details regarding the design and performance of the solar reformer are presented elsewhere.This paper describes the projected economics of the parabolic dish SMR system. The key metrics are the levelized cost of electricity for a modified, combined-cycle power plant that operates with natural gas or syngas from the dish SMR, and the levelized cost of chemical energy based on the incremental chemical energy produced in the SMR. The latter can be compared to the levelized cost of natural gas over the life of the solar-powered system. Initial capital and annual maintenance cost estimates for each system component are also presented.

Optimization of a hybrid solar-fossil fuel plant: Solar steam reforming of methane in a combined cycle

In this article, an analysis of solar reforming as the solar integration method for a hybrid solar-fossil fuel cycle is presented. The solar reformer is integrated with a solar tower and steam reforming of methane is studied. The tower reformer system is integrated with a standard combined cycle, and the design and operation of the hybrid cycle are optimized for highest annual work output for a fixed fuel input and solar collector area. A heuristic two step procedure is used for the optimization: first, both the design and operation of the plant is optimized for every hour and then in the second step, the design is fixed at the average value determined by the first step and the operation of the plant is again optimized for every hour. The optimization results indicate that the tower reforming integration method is a promising integration option in that this type of hybrid cycle yields high incremental solar efficiencies compared to alternatives. Moreover, the analyzed hybrid cycle has a higher efficiency for a fixed CO2 emissions compared to a linear combination of solar only and fossil fuel only cycles of comparable complexity.

4-5-1 ソーラー改質用Ni/MgO-Al_2O_3触媒デバイスの開発(4-5 太陽熱発電・水素製造3,Session 4 新エネルギー)

4-5-1 ソーラー改質用Ni/MgO-Al_2O_3触媒デバイスの開発(4-5 太陽熱発電・水素製造3,Session 4 新エネルギー)

Catalytic reforming of methane with CO2 over metal foam based monolithic catalysts

Solar reforming of natural gas has been considered as the promising conversion route of solar fuels with the concentrated solar heat. The present work focuses on investigating the catalytic reforming reaction over metal foam based monolithic catalysts. The 2 wt.%Ru/Al2O3/AISI 316 foam and 5 wt.%Ni/Al2O3/AISI 316 foam were prepared via the process of coating and impregnation. The catalytic properties of 5 wt.%Ni/Al2O3/AISI 316 foam and 2 wt.%Ru/Al2O3/AISI 316 foam for the methane reforming with carbon dioxide were tested in a continuous-flow fixed-bed reaction system. The results showed that the 2 wt.%Ru/Al2O3/AISI 316 foam exhibited higher catalytic activity and long-term stability for CO2 reforming of methane. The 316 stainless steel metal foam matrix had the very low catalytic performance for methane reforming with CO2 and the Al2O3 coating played a key role on the reactivity of the resulting catalysts.

A Novel Multifunctional Energy System for CO2 Removal by Solar Reforming of Natural Gas

In this paper, a novel multifunctional energy system (MES) fueled by natural gas and solar radiation is proposed. In this MES, hydrogen and electricity are cogenerated and approximately 92% of CO2 derived from natural gas is removed. The solar concentrated process provides high-temperature thermal energy to the methane/steam reforming reaction. The resulting syngas enters a pressure swing adsorption unit to separate approximately 80% of hydrogen. This process significantly increases the concentration of carbon dioxide in syngas from nearly 19% to 49%, which decreases energy consumption in CO2 removal. As a result, the overall power efficiency of the new system becomes about 39.2%. Compared to a conventional natural gas-based hydrogen plant with CO2 removal and a concentrated solar power tower plant, the overall power efficiency of the new system is increased by 7.9 percentage points. Based on the graphical exergy analysis, the integration of synthetic utilization of natural gas and solar radiation, combination of the hydrogen production plant and power plant, and integration of the energy utilization processes and CO2 separation were found to play significant roles to improve thermodynamic performance. The result obtained here provides a new approach for highly efficient use of solar radiation by hybrid natural gas.

4-2-4 石英窓型ソーラー改質器のためのNi系触媒デバイスの開発(4-2 太陽熱発電・水素製造2,Session 4 新エネルギー,研究発表)

4-2-4 石英窓型ソーラー改質器のためのNi系触媒デバイスの開発(4-2 太陽熱発電・水素製造2,Session 4 新エネルギー,研究発表)

Ni/MgO–Al 2O 3 and Ni–Mg–O catalyzed SiC foam absorbers for high temperature solar reforming of methane

Ni catalyst supported on MgO–Al 2O 3 (Ni/MgO–Al 2O 3) prepared from hydrotalcite, and Ni–Mg–O catalyst are studied in regard to their activity in the CO 2 reforming of methane at high temperatures in order to develop a catalytically activated foam receiver–absorber for use in solar reforming. First, the activity of their powder catalysts is examined. Ni/MgO–Al 2O 3 powder catalyst exhibits a remarkable degree of high activity and thermal stability as compared with Ni–Mg–O powder catalyst. Secondly, a new type of catalytically activated ceramic foam absorber – Ni/MgO–Al 2O 3/SiC – and Ni–Mg–O catalyzed SiC foam absorber are prepared and their activity is evaluated using a laboratory-scale receiver–reactor with a transparent quartz window and a sun-simulator. The present Ni-based catalytic absorbers are more cost effective than conventional Rh/ γ-Al 2O 3 catalyzed alumina and SiC foam absorbers and the alternative Ru/ γ-Al 2O 3 catalyzed SiC foam absorbers. Ni/MgO–Al 2O 3 catalyzed SiC foam absorber, in particular, exhibits superior reforming performance that provides results comparable to that of Rh/ γ-Al 2O 3 catalyzed alumina foam absorber under a high flux condition or at high temperatures above 1000 °C. Ni/MgO–Al 2O 3 catalyzed SiC foam absorber will be desirable for use in solar receiver–reactor systems to convert concentrated high solar fluxes to chemical fuels via endothermic natural-gas reforming at high temperatures.

Molten-Salt Tubular Absorber/Reformer (MoSTAR) Project: The Thermal Storage Media of Na2CO3–MgO Composite Materials

The molten-salt tubular absorber/reformer (MoSTAR) project aims to develop a novel type of “double-walled” tubular absorber/reformer with molten-salt thermal storage at high temperature for use in solar natural-gas reforming and solar air receiver, and to demonstrate its performances on the sun with a 5 kWt dish-type solar concentrator. The new concept of double-walled reactor tubes is proposed for use in a solar reformer by Niigata University, Japan, and involves packing a molten/ceramic composite material in the annular region between the internal catalyst tube and the exterior solar absorber wall. This solar tubular absorber concept may be also applied to solar air receiver for solar thermal power generation. The MoSTAR project includes the development of molten-salt thermal storage media, the new design and the fabrication of absorber/reformer with the double-walled absorber tubes, and finally the solar demonstration on the 5 kWt dish concentrator of Inha University in Korea. In this paper, thermal storage media of the series of Na2CO3–MgO composite materials were tested in a double-walled reformer tube with a thermal storage capacity of about 0.3 kWh. The chemical reaction performances for dry reforming of methane during cooling or heat-discharge mode of the reactor tube were investigated using an electric furnace. The experimental results obtained under feed gas mixture of CH4/CO2=1:3 at a residence time of 0.3 s and at 1 atm showed that the single reactor tube with 90 wt % Na2CO3/10 wt % MgO composite material successfully maintained a high methane conversion above 90% with about 0.9 kW reforming scale based on high heating value during 45 min of the heat-discharge mode. The chemical reaction performances of the reactor tube were investigated also for the solar-simulating operation mode. The application of the new reactor tubes to solar tubular reformers is expected to help realize stable operation of the solar reforming process under fluctuating insolation during a cloud passage.

Hydrogen production characteristics of a bioethanol solar reforming system with solar insolation fluctuations

Abstract The development of a bioethanol steam reforming system (FBSR) is considered as a means of distributing energy using PEM fuel cells. Small-scale solar collectors (collection areas on the order of several m 2 ) are installed in a house as a method for applying the FBSR. However, the temperature distribution of a reforming catalyst fluctuates under conditions of unstable solar insolation. Therefore, heat transfer analysis applied in reforming the catalyst layer of the reactor and the temperature distribution and transient response characteristics of the gas composition of the process were investigated. As a case study, meteorological data for representative days in March and August in Sapporo, Japan were recorded, and the hydrogen production speed, power generation output and amount of electricity purchased were analyzed. The results showed that although fluctuations in solar insolation affected the efficiency of the FBSR, the average efficiency of each representative day exceeded 40%. By installing two solar collectors, each with a collection area of 1 m 2 , 21–25% of the average power demand of an individual house can be supplied.

Development of a Fast Operation Algorithm of a Small-Scale Fuel Cell System With Solar Reforming

The small-scale bioethanol steam reforming system (FBSR), using sunlight applied to a heat source, is a very clean method, which can supply fuel to a fuel cell. However, it is difficult to analyze the operation planning of this system with high precision. If such an analytical algorithm is developed, the optimum operation of this system will be realized by the command of the control device. However, the difficulty of weather forecasts, such as solar radiation and outside-air-temperature, to date has made it difficult to achieve rapid and highly precise results and to analyze the system operation. In this paper, an algorithm, which analyzes the operation planning of the FBSR on arbitrary days, is developed using the neural network. The weather pattern for the past 1 year is input into this algorithm, and the operation planning of the FBSR, based on the same weather pattern, is given as a training signal. In this paper, the operation results of the system obtained via genetic algorithm (GA) were used as the training signal for the neural network. Operation planning (the amount of hydrogen production and the amount of exhaust heat storage) of the system on arbitrary days could be obtained rapidly by ensuring that input data (the weather and energy-demand patterns) are channeled into the learned neural network following this study. Moreover, in order to investigate the accuracy of the operational analysis via the proposed algorithm, it is compared with the analysis result of operation planning using the GA.

Study on a Bioethanol Solar Reforming System with the Solar Insolation Fluctuation in Consideration of Heat Chemical Reaction

Study on a Bioethanol Solar Reforming System with the Solar Insolation Fluctuation in Consideration of Heat Chemical Reaction

High-temperature carbonate/MgO composite materials as thermal storage media for double-walled solar reformer tubes

The composite materials of molten alkali-carbonate/MgO-ceramics are examined as thermal storage media in a tubular reformer using a double-walled reactor tube of a laboratory scale. The concept of a double-walled reformer tube is proposed as a solar tubular reformer and involves packing a molten salt/ceramic composite material in the annular region between the internal catalyst tube and the exterior solar absorber wall. The composite materials of Na 2CO 3, K 2CO 3, and Li 2CO 3 with magnesia are tested as thermal storage media. The reforming performances of the composite materials are tested in the cooling mode of the double-walled reactor tube. The experimental result obtained under feed gas mixture of CH 4/CO 2 = 1:3 at 1 atm shows that the use of 80 wt%Na 2CO 3/20 wt%MgO composite material successfully delayed the cooling time of the catalyst bed by 5–19 min in comparison to the case without a composite material. In addition, the Li 2CO 3/MgO and Na 2CO 3/MgO composite materials relatively revealed good performances: they prolonged the cooling time by over 10 min in the gas hourly space velocity (GHSV) range of 5000–12,500 h −1. The application of the reactor tubes to solar tubular reformers is expected to realize stable operation of the solar reforming process under fluctuating insolation during cloud passage.

Development of Distributed Energy System due to Bio-ethanol PEM Fuel Cell with Solar Reforming : Part 2-High-speed analysis of the operation plan using a neural network

Development of Distributed Energy System due to Bio-ethanol PEM Fuel Cell with Solar Reforming : Part 2-High-speed analysis of the operation plan using a neural network

Dynamics of a solar thermochemical reactor for steam-reforming of methane

A nonlinear dynamic model is developed for a steam/methane-reforming reactor that uses concentrated solar radiation as the source of high-temperature process heat. The model incorporates a set of lumped-parameter reservoirs for mass and energy. For each reservoir, the unsteady mass and energy conservation equations are formulated, which couple conduction, convection, and radiation heat transfer with the temperature dependent chemical conversion. Radiative exchange, the dominant heat transfer mode at above 800 K, is solved by a band-approximation Monte Carlo technique. The dynamic model is applied to predict the transient behavior of a 400 kW prototype solar reformer in operational modes of purging, thermal testing, startup, chemical reaction, shutdown, and cyclical operation. Time constants vary between 2 s for species transport and 1 × 10 5 s for thermal energy transport through ceramic insulation. Validation is accomplished by comparing modeled and experimentally measured outlet gas temperatures obtained from reactor tests in a solar tower facility.

Simulation of a Volumetric Solar Reformer

The Directly-Irradiated Annular Pressurized Receiver (DIAPR) volumetric solar absorber was adapted to operate as a methane reformer by coating the absorber pins with catalyst. A computational model is applied to assess and improve the system design. The simulation entails the solution of reactive flow and heat transfer. A detailed parametric study is presented and analyzed here. An experimental system based on the present results was built and testing is currently underway.