A comprehensive review on mainly hydrogen production based on waste heat recovery for single and multigeneration energy systems

Hydrogen (H2), which is considered an energy-carrier zero-emission fuel, is a viable long-term tackle to the growing energy demand, increasing greenhouse gas emissions, and resource depletion associated with the use of fossil fuels. One of the various ways to produce H2 is waste heat recovery, which is a major issue in the energy sector because over half of the energy produced globally is wasted as heat. Compiling the most recent and relevant research on waste heat recovery for single and multigeneration, primarily H2, such as power generation, freshwater production, cooling and heating loads, etc., is the goal of this review study. The methodology includes three stages. Firstly, relevant research papers are selected by searching, filtering and screening, according to the research trends and growth areas. Secondly, the research state and gaps are determined by statistically analyzing the retrieved data. Thirdly, the types, concepts and control strategies for various waste heat recovery systems for H2 generation and other products are investigated critically from a technical, environmental and economic point of view. The gathered data is organized, depending on the number of products out of the system. According to the critical revision, the two main concepts of waste heat recovery are either employing an external waste heat source as the recovery system's main energy input or recovering the system's residual heat to increase performance. Recent waste heat recovery systems primarily rely on renewable resources such as biomass or water splitting, and these systems are the motivation behind the production of H2 as a value chain. Since they can recover low-temperature waste heat, thermoelectric generator (TEG) and organic Rankine cycle (RC) are the most widely used and effective recovery units in the recovery systems process. Gas turbine cycles (GTC), such as the Brayton cycle (BC), are suitable for medium- and high-temperature waste heat. The solid oxide electrolyzer cell (SOEC) (energy efficiency between 70 and 90 %) and proton exchange membrane electrolyzer (PEME) (energy efficiency between 60 and 80 %) are the most reliable and efficient units for H2 production when compared to other water electrolysis techniques. Furthermore, the most efficient cycles for creating H2 utilizing thermochemical electrolysis processes are the copper-chlorine (Cu-Cl) and vanadium-chlorine cycles (V-Cl) because of their high performance. The cost of creating H2 from SOEC can vary from 0.84 to 6.16 $/kg, while for PEME, the cost ranges between 0.78 and 16.53 $/kg H2. The system design, durability, lack of appropriate materials, thermal and physical connections between various components, and other concerns are some of the challenges it encounters in terms of scalability. Furthermore, it is noted that there are new technologies that have not yet been investigated, and that experimental and computational fluid dynamics (CFD) research is deficient when compared to analytical studies. This may be because creating a waste heat recovery system takes a lot of time and money.