Patent ID: 12209706

DETAILED DESCRIPTION

Referring toFIGS.1and2, a composite storage tank system100of the invention comprises an organic matrix composite tank for storing gaseous hydrogen at high pressure (e.g. 300 bar or greater), the tanks comprising an organic matrix composite shell or wall102enclosing and defining a gas storage volume116. The tank has a cylindrical central section106defining a central longitudinal axis101of the tank and domed or hemispherical end portions108A,108B. A metal fitting110passes through end portion108B and allows the tank to be charged with gaseous hydrogen and discharged. A lithium aluminium deuteride element (LiAlD2)112is incorporated into the composite wall102of the tank, specifically within resin comprised in the wall102. Electrical contacts113contact respective positions on the element112and extend to the exterior of the tank, allowing the electrical resistance of the element112to be measured or monitored. The system100comprises a resistance meter198, each connecting leads of which is in electrical contact with a respective electrical contact113. The tank further comprises a polymer liner118(not shown inFIG.1), for example of polyethylene or polypropylene, and is therefore a so-called ‘Type IV’ tank, although the invention is equally applicable to a ‘Type V’ tank. The element112is at a specific axial position z and azimuthal position □ with respect to the axis101. A portion of hydrogen leaking through the polymer liner118and composite wall102in the vicinity of the sample112is adsorbed by the element112causing its electrical resistance to change. The more hydrogen is adsorbed by the element112, the greater its electrical resistance. The resistance indicated by the resistance meter198therefore provides an indication of the total amount of hydrogen which has leaked from tank in the vicinity of the element112when taken together with the original resistance of the element112. Since the amount of hydrogen which has leaked through the composite wall102in the vicinity of the sample112depends inter alia on the extent of micro-cracking and/or delamination of the composite wall102, the electrical resistance of the element112also provides an indication of the physical condition of the composite wall102in the vicinity of the element112. Since a portion of hydrogen leaking through the composite wall102is adsorbed by the element112, the element112serves to reduce leakage to the exterior of the tank in addition to allowing an amount of hydrogen leaking past the element112and the physical condition of the composite wall102in the vicinity of the element112to be determined.

FIG.3illustrates one possible example form for the change in electrical resistance of the element112overtime. In a first time period1, the tank does not leak in the vicinity of the element112and the electrical resistance of the element112is therefore constant over the period1. At the end of time period1, the liner118and composite wall102begin to leak at a first rate over a time period2and the electrical resistance of the element112increases with time as it adsorbs hydrogen at a rate corresponding to the first rate. At the end of the time period2, increased physical degradation of the composite wall102in the vicinity of the element112(e.g. microcracking and/or delamination) caused by charging and discharging of the tank causes the rate of hydrogen leakage to increase to a second rate greater than the first rate over a time period3and consequently the rate of change of the electrical resistance of the element112increases more quickly than is the case in time period2. The electrical resistance corresponding to a point X, at the end of time period3, corresponds to the total amount of gaseous hydrogen that has leaked from the tank100from t=0 up to the end of period3and also to the physical condition of the composite wall102at the time corresponding to point X in the vicinity of the element112.

If no physical degradation of the composite wall102occurs, then the increase in electrical resistance of the sample112results entirely from background leakage due to the very small size of the hydrogen molecule, and if desired the electrical resistance of the element may be restored or reset to its value at t=0 by heating the element112to evolve gaseous hydrogen which has been adsorbed during the time periods1,2and3.

In another embodiment, multiple hydride/metal elements may be included at different axial and azimuthal positions in the composite wall of a composite storage tank in order to allow estimation of historical hydrogen leakage and wall condition at multiple positions in the composite wall of the composite storage tank.

In a further embodiment of the invention, a hydride, or a metal capable forming a hydride in the presence of gaseous hydrogen, is integrated in the composite wall of an organic composite gaseous hydrogen storage tank by including the hydride or metal within a carbon fibre winding during manufacture of the tank. The angle of the winding during manufacture of the tank is aligned with carbon fibres of the winding to prevent stresses that could arise due to different thermal expansion coefficients of the hydride or metal and the carbon fibre. By incorporating a hydride or metal within a carbon fibre winding during tank manufacture, leakage of hydrogen at all or almost all positions in the composite wall of the finished tank may be detected, and an estimate of the overall physical condition of the composite wall at all or almost all positions within the wall may be made.

A still further embodiment of the invention comprises a composite storage tank similar to that ofFIGS.1and2, except that the electrical contacts113are omitted and the dielectric constant of a hydride or metal element comprised in the composite wall of the tank is measured in order to determine the amount of hydrogen which has been adsorbed by the element. For example, a capacitive structure including the hydride/metal element could be formed and the capacitance of the structure measured in order to determine the dielectric constant of the hydride/metal element.