Feasibility Study on Dehydrogenation of LOHC Using Excess Exhaust Heat From a Hydrogen Fueled Micro Gas Turbine

Abstract

In recent years, renewable energy technologies have received increasing attention. However, the constant availability of renewable energies is not predictable, so that technologies for excess energy storage become increasingly important. One possibility for the technical implementation of such a storage technology is to bind hydrogen, produced using this excess energy, to liquid organic compounds, so-called Liquid Organic Hydrogen Carriers (LOHC), where hydrogen is bound to a H2-lean LOHC molecule in an exothermal hydrogenation reaction. The dehydrogenation process releases the stored hydrogen in an endothermal reaction. This technology offers advantages such as storage and transport safety, along with the high energy density. LOHC systems can assist in the realization of future distributed energy supply networks, as well. Micro gas turbines (MGT) play an important role in distributed energy supply, so that the coupling of a hydrogen fueled MGT with a reactor for the dehydrogenation process is a desirable achievement. In such a combined system, the excess exhaust enthalpy can be used to maintain the endothermal dehydrogenation reaction without affecting the overall efficiency of the gas turbine. This paper investigates the feasibility of a direct coupling between a hydrogen fueled recuperated micro gas turbine and the dehydrogenation process using the excess exhaust heat. For this purpose, a numerical simulation based on energy balances and thermodynamic equilibrium is implemented to model the process. Primary criteria for the evaluation of the process feasibility are the MGTs exhaust gas temperature, the exhaust gas mass flow rate, and the LOHC mass flow rate through the dehydrogenation unit. These three parameters specify the mass flow rate of LOHC, which can be dehydrogenated and thus, the mass flow rate of released hydrogen. Using the implemented numerical model, the suitability of two different LOHCs, N-Ethylcarbazole and an industrial heat transfer oil is investigated at two different pressure levels with respect to thermodynamic feasibility and process efficiency. The results show that the usable excess enthalpy in the exhaust gas of the investigated Turbec T100 MGT is sufficient to release enough hydrogen for re-use as fuel in the micro turbine process for three of the four investigated cases.