Patent Application
20070214830
The present invention relates to the storage and manipulation of gases, and more particularly to the storage and control of excess hydrogen gas produced by boil-off and mass transfer losses from stationary storage and filling systems.
Hydrogen storage technology is a necessary prerequisite for the development of many advances in the area of alternative fuel sources. Hydrogen is the cleanest and most abundant of these energy sources. In particular, mobile applications, such as hydrogen-propelled vehicles, place a demand on the infrastructure to provide safe, efficient, and inexpensive delivery of hydrogen to the end user.
A number of current storage technologies are available. Compressed gaseous hydrogen (CGH2) involves storage of hydrogen gas under high pressures of for example between 35 and 70 MPa. Liquid hydrogen (LH2) involves storage of liquefied hydrogen gas. These technologies involve several technical challenges, notably low storage densities, in the case of both methods, and hydrogen boil-off in the case of LH2.
An alternative storage mechanism is provided by the physisorption of hydrogen molecules on high-surface materials like activated carbons, zeoliths, metal-organic frameworks (MOFs) or polymers of intrinsic microporosity (PIMs). Since the interaction of the hydrogen and the substrate material is quite weak, it is necessary to apply operating pressures from 10 to 50 bar and operating temperatures of about 25K to 150K.
During the operation of the filling facility, particularly the refilling of LH2 into a primary tank apparatus, some hydrogen can be lost to the environment. This occurs primarily because the associated pipes and machinery have to be cooled down toward 20K, but also for fundamental thermodynamic reasons. The losses from boil-off, tanking, and other mass transfer activities have to be minimized for commercial, safety, and environmental reasons.
A customer might be required to pay for the lost hydrogen during re-filling. Alternatively, the operator of the station may be required to absorb these losses. Therefore, it is very attractive from a commercial standpoint to minimize these losses as much as possible.
For safety reasons, hydrogen should not be released into the environment of a pump. Under certain conditions, this can create a fire or an explosive hazard. Hydrogen could react exothermically with oxygen to form water and to release large amounts of energy, as for example in a fire or in an explosion. From a safety standpoint limiting the amounts of hydrogen gas released will drastically reduce the oxygen reaction hazards.
Hydrogen release may also have environmental effects. Hydrogen gas that is lost during refilling or as boil-off could reach the upper atmosphere. Here it could react via a complex chemical reaction with ozone to form water, thereby decomposing critical atmospheric ozone. This consequence would also be limited by preventing release of hydrogen.
Another consideration in the construction of a stationary fueling application is the stability of the flow rate. Some of the stationary applications, such as a stationary internal combustion engine (ICE) or a stationary fuel cell, require a stable flow of hydrogen gas to operate effectively. Excess hydrogen gas generated through mass transfer and spot heating could disrupt the orderly flow of hydrogen gas to these applications.
Some attempts have been made to remedy these effects. Re-liquefaction would help mitigate some of these factors but would be very expensive and require additional equipment. Compression would also be expensive and require additional equipment. Catalytic burning of the lost hydrogen has also been proposed, but this is wasteful since the resulting water cannot, itself, be used for energy generation.
Therefore, what remains needed in the art is a means of controlling the excess hydrogen gas produced through its use as a fuel in stationary applications.
The present invention is a hydrogen tank system designed to collect, store and transfer excess hydrogen gas that has been generated in the normal course of the operation of a hydrogen fueled stationary application. Within the framework of this invention, a cryoadsorption hydrogen storage apparatus is added to the conventional setup of a stationary hydrogen fueled application, such as a hydrogen filling station. The hydrogen tank system would serve as a hydrogen collection system, an intermediate hydrogen storage system, and a hydrogen transfer system to cope with the amount of excess hydrogen gas generated during the normal activities of hydrogen delivery, such as a hydrogen filling station for filling of LH2 vehicles, during boil-off mode of the main LH2 storage tank, etc. Further, the cryoadsorption hydrogen storage apparatus may serve as a reserve tank, which may be utilized in mobile as well as stationary applications.
Other stationary applications of hydrogen fueling impose more stringent requirements in the management of excess released hydrogen gas. More involved stationary applications, such as those that include stationary internal combustion engines or stationary fuel cells, require a relatively stable flow of hydrogen gas. The intermediate storage system according to the present invention will smooth the flow rate of outgoing hydrogen and therefore will address this problem.
The hydrogen tank system according to the present invention is designed in such a way as to minimize mass transfer losses of hydrogen from the system into the environment and to minimize heat transfer from the environment into the system.
The hydrogen tank system consists of a primary tank apparatus and the above referenced cryoadsorption hydrogen storage apparatus, as well as tubing, detectors, valves, and regulators required to manage the collection, storage and transfer of the excess hydrogen gas.
The primary tank apparatus consists of at least one liquid hydrogen (LH2) storage tank, conventional in the art, as well as the required tubes, hoses, valves and regulators necessary to connect the primary tank apparatus to the cryoadsorption hydrogen storage apparatus. The LH2 can be dispensed directly from the primary tank apparatus to an external tank, such as for example the fuel tank of a mobile hydrogen fueled device. In the operation of the hydrogen tank system, excess hydrogen gas will inevitably be produced; however, this excess hydrogen gas is collected by the cryoadsorption hydrogen storage apparatus.
The cryoadsorption hydrogen storage apparatus can consist of a single cryoadsorption unit, or a group thereof configured in series, in parallel, or in a more general topological structure. The cryoadsorption units are connected by means of pipes or tubes and controlled via valves. Particular elements of the piping aid in the modulation of temperature in the cryoadsorption units.
The hydrogen tank system additionally provides means to transfer hydrogen gas from the cryoadsorption hydrogen storage apparatus to external functional modules. These functional modules can be stationary hydrogen-fueled applications, such as for example stationary internal combustion engines, stationary fuel cells, other devices, such as re-liquifiers, compressors or other cryoadsorption units, or even mobile fuel tanks. Each of these functional modules is connected by means of pipes and tubes to the primary storage tank, the cryoadsorption hydrogen storage apparatus, or both.
Accordingly, it is an object of the present invention to provide a means to collect, store and transfer excess hydrogen gas which evolves in the normal operation of stationary devices fueled by a hydrogen tank system.
This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment.
Referring now to the Drawing,
With reference to
With reference to
The first supply valve 126a to the cooling jacket 118 and the second supply valve 126b to the cryoadsorption unit 112 are both open and the third supply valve 126c to the functional modules 106 is closed. The cooling jacket 118 is vented by means of an outlet pipe 128 connected to the functional modules 106. The cryoadsorption unit 112 is connected to the functional modules 106 by means of a outlet pipe 130 regulated by a functional module control valve 132, which is closed. Further in this configuration of the hydrogen tank system 100′, hydrogen gas released from the storage tank apparatus 102 is routed to the cryoadsorption unit 112 and to the cooling jacket 118. Direct flow to the functional modules 106 is prevented.
With reference to
Hydrogen gas is released from the cryoadsorption units by applying heat via, for example, an electrical heater of a heat exchanger with the external environment, by reducing the operating pressure, or a combination of both. The materials used, the structural design, and techniques of operation of the cryoadsorption units of the cryoadsorption hydrogen storage apparatus are exemplified in U.S. patent application Ser. No. 11/348,107, filed on Feb. 6, 2006, which disclosure is hereby herein incorporated by reference.
In order to increase the hydrogen collection capacity of the hydrogen tank system according to the present invention, additional cryoadsorption units may be added. With reference to
Certain types of the functional modules 106 require a carefully regulated flow of hydrogen gas. With reference to
With reference to
To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.
