This invention relates to an apparatus and a method for filling a vessel, such as a fuel tank, with a compressed gas, such as hydrogen, safely over a minimum period of time without overheating the vessel.
Gaseous hydrogen is expected to supplant liquid hydrocarbon fuels, such as gasoline and diesel, as the fuel of choice for automobiles, trucks and buses due to its obvious environmental advantage. Hydrogen burns cleanly and does not produce greenhouse gases such as CO and CO2 as a combustion by-product.
The practical considerations associated with the large scale storage and dispensing of gaseous hydrogen fuel for motor vehicles presents different problems from those associated with the handling of liquid fuels due to the gaseous nature of the hydrogen. One problem, as yet not satisfactorily addressed, is that of filling fuel tanks of various capacities, different pressures, and different ullage with gaseous hydrogen safely, over a time period comparable with the time required to fill a fuel tank of comparable energy capacity with a liquid fuel.
Safety demands that a tank not be filled too fast to avoid overheating. Additionally, any charging of a tank with compressed gas will cause the gas within the tank to heat up, increasing its pressure, the volume being fixed. The increase in gas temperature and pressure within a tank can prevent the tank from being filled to capacity when the tank is filled to a maximum working pressure. After filling, the heat dissipates to the ambient, cooling the gas and reducing its pressure within the tank. Once cool, the tank can accept more gas (up to its maximum working pressure) requiring that the tank be “topped off” by charging it with additional gas so that it is filled to capacity. Depending upon the rate of fill, the tank may need to be topped off several times before it is completely filled. These steps of filling and cooling are impractical and require too much time compared with filling of a tank with liquid.