太阳能甲烷重整制氢研究进展

A review on solar methane reforming for hydrogen production

氢能是零碳、高密度的能量载体,目前主要来自天然气、煤炭等化石能源。随着“双碳”战略的深入推进和能源低碳转型的加速,可持续氢能的重要性日益凸显,但现有主要制氢技术与能源重大需求之间的错位也日益突出。单一太阳能制氢受到成本、技术成熟度、基础设施等多方面因素制约,短期内尚无法大规模替代化石能源制氢。基于甲烷重整反应的强吸热特性,太阳能驱动的甲烷重整可吸收最高相当于甲烷高位热值23%的太阳热能,并以化学能的形式实现太阳能储存和利用,达到同时提升氢能中太阳能占比与降低制氢碳排放的有益效果。因此,太阳能驱动天然气重整制氢技术有望在近中期发挥重要作用。传统甲烷重整与太阳能聚光集热技术的简单结合,仍需800~1000℃的反应温度与1000以上的高聚光比,不仅导致高辐射热损失和对流热损失,而且难以解决传统重整制氢系统复杂、碳排放高等关键技术挑战。在Le Chatelier原理基础上,通过产物吸收强化降低重整反应温度,有望突破与太阳能聚光技术结合的瓶颈。进一步,通过突破甲烷转化源头制氢与脱碳的协同,有望解决传统重整制氢的高温、高能耗、高碳排放挑战。从热力学和动力学双视角综述了太阳能甲烷重整制氢与脱碳的研究进展,并从聚光集热技术、重整反应器和制氢系统三方面分析阐述了当前太阳能甲烷重整制氢技术的发展趋势。具体分析了反应温度高、聚光不可逆损失大、能耗高等问题的原因,并从反应流程设计角度重点关注可同时降低温度、提高产物选择性、促进碳氢组分协同转化的新原理、新方法。其中,通过吸附剂、膜分离等方式分离单一产物可将反应温度降至500~600℃;通过交替分离2种或以上目标产物,可将反应温度进一步降低至400℃或以下,在槽式聚光、等温、常压条件下实现甲烷向H_(2)与CO_(2)的近100%转化与近100%产物选择性,同时实现反应温度、制氢脱碳能耗的大幅下降以及制氢装置的大幅简化和高度集成。在大力发展可再生能源、促进能源低碳转型的新形势下,甲烷重整作为一种传统制氢技术,通过热力学思路、流程设计与制氢方法的创新,有望实现与太阳能光热技术的深入结合,并为近中期可持续氢能技术的突破开辟更加广阔的未来。

Hydrogen energy is a zero-carbon,high-density energy carrier,predominantly derived from fossil fuels such as natural gas or coal.As the global push toward achieving"carbon peak and neutrality"goals intensifies and the transition to low-carbon energy accelerates,the importance of sustainable hydrogen energy is becoming increasingly evident.However,the mismatch between current hydrogen production technologies and the growing energy demand is becoming more pronounced.Single solar-driven hydrogen production technologies remain limited by factors such as high production costs,technological immaturity,and inadequate infrastructure,preventing them from replacing fossil fuel-based methods on a large scale in the near term.The highly endothermic nature of the methane reforming reaction enables solar-driven methane reforming to absorb solar thermal energy up to 23%of the higher heating value of methane,by which solar energy can also be stored and converted to chemical energy,increasing the proportion of solar energy in hydrogen energy while simultaneously reducing carbon emissions in hydrogen production.Therefore,solar-driven natural gas reforming technology for hydrogen production is expected to play a pivotal role in the near-to mid-term.However,the simple integration of traditional SMR with concentrating solar technology still requires reaction temperatures of 800 to 1000℃and high concentration ratios exceeding 1000.These requirements result in large radiative and convective heat losses,and fail to address critical technical challenges,such as the complexity and high carbon emissions of traditional SMR system.Lowering the reaction temperature of methane reforming through product separation by Le Chatelier's principle has the potential to overcoming the bottleneck in integrating with solar concentrating technologies.Furthermore,the synergistic hydrogen production and decarbonization at the origin of methane conversion could effectively address the challenges of high temperature,high energy consumption and high carbon emissions associated with traditional methane reforming.The advancements in solar methane reforming technology for hydrogen production and decarbonization from both thermodynamic and kinetic perspectives were reviewed.The trends of development of conventional solar methane reforming from concentrating solar technologies,reforming reactors and hydrogen production systems were analyzed.The fundamental reasons underlying critical challenges of conventional solar methane reforming technologies were also analyzed,such as high reaction temperatures,high irreversible losses in solar concentration and high energy consumption.Furthermore,new principles and methods from the perspective of reaction process design was focused on that can simultaneously reduce reaction temperature,improve product selectivity,and promote the synergistic conversion of hydrogen and carbon constituents.Methane reforming with single-product separation of CO_(2) or hydrogen using sorbent or membrane can reduce reaction temperatures to 500-600℃.A further reduction to 400℃or below can be achieved by sequentially separating two or more target products,reaching near-complete methane conversion and H_(2)&CO_(2) product selectivity under isothermal and atmospheric pressure conditions with solar trough concentrators,significantly reducing reaction temperature and energy consumption for hydrogen production and decarbonization while greatly simplifying and consolidating the hydrogen production system with a high level of integration.Under the new circumstances of vigorously developing renewable energy and promoting low-carbon energy transition,innovations in thermodynamic approaches,process design,and hydrogen production methods offer the potential for traditional methane reforming to achieving deep integration with solar thermal technologies.Such integration is expected to open up broader prospects for breakthroughs in sustainable hydrogen technologies in the near-to mid-term.