Patent Publication Number: US-2022228713-A1

Title: Hydrogen storage tank with leak management functionality

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is based upon and claims the benefit of priority from British Patent Application No. GB 2100662.2, filed on Jan. 19, 2021, the entire contents of which are herein incorporated by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to storage of gaseous hydrogen, particularly for use in transport applications, including aeronautical applications. 
     Description of Related Art 
     The use of gaseous hydrogen as a fuel is of increasing interest in transport applications, including aeronautical applications, due an absence of CO 2  generation at the point of use. However, storage of gaseous hydrogen in a storage tank presents several technical challenges, one of which is the management of hydrogen which leaks from the tank. Leakage of gaseous hydrogen from hydrogen storage tanks is common, due to the very small size of the hydrogen molecule (120 pm). Loss of hydrogen by leakage wastes fuel, presents an explosion risk, particularly where a tank is located in a enclosed area, and may also lead to degradation of metallic parts by embrittlement. 
     SUMMARY 
     According to an example, a hydrogen storage tank has a composite laminate wall, a hydrogen-porous layer in contact with the outer surface of the composite laminate wall and a hydrogen-non-porous layer in contact with the outer surface of the hydrogen-porous layer, the hydrogen-non-porous layer having an output port for venting hydrogen which passes through the composite laminate wall and the hydrogen-porous layer from the interior of the tank. The hydrogen storage tank allows gaseous hydrogen which leaks from the tank to be collected, thus avoiding potential explosion and/or embrittlement of metal parts. Collected hydrogen may be used, for example in a fuel cell or gas turbine engine, rather than simply being wasted. The hydrogen-non-porous layer is non-porous to hydrogen which leaks through the composite laminate wall of the tank. 
     The hydrogen-porous layer may comprise open-cell foam or may consist of an open-cell foam layer. Alternatively, the hydrogen-porous layer may be a layer of fibrous material. 
     The hydrogen-non-porous layer may be layer of rubber-based or polymeric material or alternatively a closed-cell foam layer. 
     Preferably the hydrogen-non-porous layer is separable from the hydrogen-porous layer and replaceable. 
     The hydrogen-non-porous layer is preferably permanently mechanically deformable so that a history of impacts experienced by the tank may be recorded over time; such a history gives an indication of the likely current structural condition of the tank. 
     The tank may be generally cylindrical and may comprise a plurality of impact-protecting ribs on the exterior of the tank, the ribs extending azimuthally and/or longitudinally with respect to the central longitudinal axis of the tank. The ribs may be integral with the hydrogen-non-porous layer, or applied to it. The ribs provide the tank with impact protection. 
     According to another example, apparatus comprises a hydrogen storage tank as described above and a measuring system for measuring the flow rate of hydrogen passing through the output port of the hydrogen storage tank. The flow rate and/or its rate of change may be used to infer the structural condition of the tank. 
     According to a further example, apparatus comprises a hydrogen storage tank as described above, a hydrogen-fueled fuel cell or a hydrogen-fueled gas turbine engine and a conveying system arranged to convey hydrogen from the output port of the tank to the fuel cell or gas turbine engine. The apparatus provides for hydrogen which leaks from the hydrogen storage tank to be used in the fuel cell or gas turbine engine rather than simply wasted. A measuring system may be provided for measuring the flow rate of hydrogen within the conveying system. The apparatus may comprise a compressor arranged to increase the pressure of hydrogen within the conveying system prior to its delivery to the fuel cell or gas turbine engine. 
     According to a further example, an aircraft comprises apparatus as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Examples are described below with reference to the accompanying drawings in which: 
         FIG. 1  is a side view of a first example tank; 
         FIG. 2  is longitudinal cross-section through a portion of the wall of the  FIG. 1  tank in a plane which includes the central longitudinal axis of the tank; and 
         FIG. 3  is a longitudinal cross-section through a portion of the wall of a second example tank in a plane which includes the central longitudinal axis of the tank. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , a first example hydrogen storage tank  100  has a generally cylindrical body with hemispherical domed ends, one domed end having main fuel port  106  allowing an internal storage volume  120  of the tank  100  to be filled with gaseous hydrogen and discharged. The tank  100  has a central longitudinal axis  102 . The wall  115  of the tank  100  comprises a polymer liner  112 , a composite laminate wall  114 , a hydrogen-porous layer  110  in contact with the outer surface of the composite laminate wall  114  and a hydrogen-non-porous layer  104  in contact with the outer surface of the hydrogen-porous layer  110 . The hydrogen-non-porous layer  104  allows hydrogen which leaks from the internal storage volume  120  through the liner  112 , composite laminate wall  114  and hydrogen-porous layer  110  to be captured and removed via an output port  108  in the hydrogen-non-porous layer  104 . A conduit  109  couples to the output port  108  to the exterior of the tank  100 . 
     The conduit  109  may be connected by a conveying system to a second hydrogen storage tank for collection of hydrogen which has leaked from storage volume  120  of the tank  100 . Alternatively, the conveying system may transfer hydrogen which has leaked from the tank  100  to a PEM fuel cell or a hydrogen-burning gas turbine engine. The conveying system may include a flow meter for measuring the rate at which hydrogen leaks from the tank  100 . Where the conveying means is arranged to transport hydrogen from the conduit  109  to a fuel-cell or gas turbine engine, a compressor may be used increase the pressure of the hydrogen prior to its input to the fuel-cell or gas turbine engine. Measurements over time of the flow rate of hydrogen leaking from the internal storage volume  120  of the tank  100  through the output port  108  may be used to detect degradation of the composite laminate wall  114 , for example by micro-cracking or de-lamination. A high rate of leakage compared to the rate of leakage when the tank  100  is first brought into service, or a sudden increase in the rate of leakage, may indicate imminent failure of the tank  100 , allowing for its timely replacement. 
     The hydrogen storage tank  100  is a so-called ‘Type IV’ tank due to the presence of the polymer liner  112 , however in a variant tank the liner  112  may be omitted so that the variant tank is a so-called ‘Type V’ tank. 
     The hydrogen-porous layer  110  may be an open-cell foam layer or may comprise open-cell foam. Preferably the layer  104  is permanently mechanically deformable, allowing impacts experienced by the tank  100  to be recorded. The mechanical integrity of the tank  100  may be inferred at least in part from a history of impacts experienced by the tank  100 . Alternatively, the hydrogen-porous layer  110  may be a layer of fibrous material. 
     The hydrogen-non-porous layer  104  may be a flexible rubber-based or polymeric layer, since the layer  104  is only required to contain leaked hydrogen at approximately atmospheric pressure rather than at the pressure within the internal storage volume  120  of the tank  100 . The hydrogen-non-porous layer  104  may alternatively be a layer of closed-cell foam material. 
     The hydrogen-non-porous layer  104  may be separable from the hydrogen-porous layer  110  and replaceable since it is the outer layer of the tank  100 . The layer  104  can be tested to ensure its gas-tightness by applying a small positive pressure to the port  108  and monitoring its decay over time. 
       FIG. 3  shows a longitudinal cross-section through a portion of the wall  215  of a second generally cylindrical example hydrogen storage tank, the cross-section including the central longitudinal axis  202  of the tank. The wall  215  of the second example tank has a structure similar to that of the wall  115  of the tank  100  of  FIGS. 1 and 2 ; parts in  FIG. 3  which correspond to parts in  FIG. 2  are labelled with reference numerals differing by 100 from those labelling the corresponding parts in  FIG. 2 . The hydrogen-non-porous layer  214  has a plurality of ribs  216  each of which extends azimuthally with respect to the central longitudinal axis  202  of the tank. The ribs  216  provide impact protection for parts of the wall  215  disposed radially inwardly of the layer  214 . In a variant of the second example tank, a series of longitudinal ribs, each extending parallel to the central longitudinal axis  202  of the tank, are formed integrally with the layer  214  and distributed in azimuth around periphery of tank. 
     In other variants of the second example tank, azimuthal and/or longitudinal ribs may be applied to the outer surface of the hydrogen-non-porous layer rather than being formed integrally with it.