Quantitative evaluation of leakage flow rate in the sealing part using graphite gland packing to mount a hydrogen separation membrane tube for HI decomposition membrane reaction

The thermal efficiency of hydrogen production in the thermochemical iodine-sulfur (or sulfur-iodine) can be effectively enhanced using a membrane reactor for the HI decomposition reaction (about 500 °C) for hydrogen production. The attachment of ceramic tubes, made of brittle materials, for hydrogen separation membranes to a tube plate via sealing parts is a critical aspect of this process. A quantitative procedure was specified to make an expanded graphite grand packing exhibit sealing performance. The applicability of the method was tested during 50 thermal cycles ranging between 25°C-450 °C and gas pressure of 0.3–0.9 MPa. The leakage flow rate using a dummy membrane tube and helium gas (a tracer gas) was approximately 2 × 10⁻⁵ Pa m³ s⁻¹. This value is comparable to the detection limit of the standard bubble leak test, indicating the effectiveness of this sealing procedure. Furthermore, the leakage flow rate was proportional to the differential pressure applied to the sealing part, suggesting a molecular flow type. This allows for estimating the leakage flow rate by introducing the conductance of flow paths, formulated based on the molecular kinetic theory of gases. An estimation method of the leakage flow rate at any packing size and any pressure difference is proposed, which can help design future practical membrane reactors.