*Article* **Thermodynamic and Technical Issues of Hydrogen and Methane-Hydrogen Mixtures Pipeline Transmission**

**Szymon Kuczy ´nski, Mariusz Łaciak, Andrzej Olijnyk, Adam Szurlej and Tomasz Włodek \***

AGH University of Science and Technology, Drilling, Oil and Gas Faculty, Krakow PL30059, Poland; skuczyns@agh.edu.pl (S.K.); laciak@agh.edu.pl (M.Ł.); aoliinyk@agh.edu.pl (A.O.); szua@agh.edu.pl (A.S.) **\*** Correspondence: twlodek@agh.edu.pl; Tel.: +48-12-617-3668

Received: 27 December 2018; Accepted: 4 February 2019; Published: 12 February 2019

**Abstract:** The use of hydrogen as a non-emission energy carrier is important for the innovative development of the power-generation industry. Transmission pipelines are the most efficient and economic method of transporting large quantities of hydrogen in a number of variants. A comprehensive hydraulic analysis of hydrogen transmission at a mass flow rate of 0.3 to 3.0 kg/s (volume flow rates from 12,000 Nm3/h to 120,000 Nm3/h) was performed. The methodology was based on flow simulation in a pipeline for assumed boundary conditions as well as modeling of fluid thermodynamic parameters for pure hydrogen and its mixtures with methane. The assumed outlet pressure was 24 bar (g). The pipeline diameter and required inlet pressure were calculated for these parameters. The change in temperature was analyzed as a function of the pipeline length for a given real heat transfer model; the assumed temperatures were 5 and 25 ◦C. The impact of hydrogen on natural gas transmission is another important issue. The performed analysis revealed that the maximum participation of hydrogen in natural gas should not exceed 15%–20%, or it has a negative impact on natural gas quality. In the case of a mixture of 85% methane and 15% hydrogen, the required outlet pressure is 10% lower than for pure methane. The obtained results present various possibilities of pipeline transmission of hydrogen at large distances. Moreover, the changes in basic thermodynamic parameters have been presented as a function of pipeline length for the adopted assumptions.

**Keywords:** hydrogen; hydrogen pipelines; hydrogen transmission; pipeline transmission; pressure drop; energy storage
