Assessing the waste heat recovery potential of liquid organic hydrogen carrier chains

Proper thermal management can improve the efficiency of hydrogen storage chains based on liquid organic hydrogen carriers (LOHC). The energy and exergy efficiencies of 24 LOHC chains, which are differentiated by two hydrogen sources (SEL: hydrogen from electrolyzer and SINDU: industrial by-product), three hydrogen consumers (CPEMFC: proton exchange membrane fuel cell, CSOFC: solid oxide fuel cell, and CINDU: industrial consumer), and four LOHC pairs are calculated based on thermodynamic modeling. Possible strategies for the heat integration between the heat sources (including hydrogenation heat, heat generated by hydrogen consumer, and the high-temperature LOHC fluids) and the heat sinks (including LOHC preheating, hydrogen preheating, dehydrogenation, and external heating purposes) are designed for these chains. In the four selected LOHC pairs, dibenzyltoluene (DBT) is found to be the most favorable LOHC pair for the implementation of WHR strategies, mainly because of low heat demand for preheating (8.9% of the stored hydrogen energy) and a high dehydrogenation rate. The WHR strategies significantly improve the energy efficiency of LOHC chains by up to 21.7% points for the chains with CINDU and 40.8% points for chains with CSOFC or CPEMFC, which makes LOHC chains more efficient than traditional compressed or liquid hydrogen chains in several scenarios, i.e., the DBT chain with CPEMFC have the highest energy efficiency (70.4% for SEL/69.5% for SINDU), while the DBT chain with SINDU and CSOFC has the highest exergy efficiency (60.6%). For the remaining combinations of the remaining hydrogen sources and consumers, the compressed hydrogen chains are the most efficient.