Patent Application
20210404603
The instant nonprovisional patent application claims priority to the following provisional application which is incorporated by reference in its entirety herein for all purposes: U.S. Provisional Patent Application No. 63,220,454, filed on Jul. 9, 2021.
Recently, there is a growing focus on shifting from polluting fossil fuels to sustainable mobility solutions using hydrogen gas. Accordingly, it is desirable to be able to store compressed gas within a tank or other pressure vessel in an efficient manner, at the highest capacity, lowest possible weight, and a reduced cost.
Another emerging trend is the increasing availability of natural gas as a fuel source. Such natural gas may be stored on-board in gaseous form as compressed natural gas (CNG), with economic merits of CNG being dependent upon density of the stored CNG. Again, it is desirable to store compressed gas within a tank or other pressure vessel in a efficient manner, at the highest capacity, lowest possible weight, and a reduced cost.
On-board storage of gaseous hydrogen fuel involves pressures ranging from 20 MPa to 85 MPa and natural gas fuel involves pressures ranging from 20 MPa to 25 MPa. Tanks or pressure vessels comprising a polymer or metallic shell that is overwrapped by continuous filament reinforcements have been used for hydrogen and natural gas on-board fuel storage since the 90's. Such fiber-reinforced tanks or pressure vessels are typically 90% lighter than all-steel tanks but continue to be significantly expensive.
Sirosh et al (U.S. Pat. Nos. 5,253,778, 5,494,188, 5,938,209, 9,618,157) have disclosed methods to fabricate fiber-reinforced tanks or pressure vessels with an inner shell or liner and fiber-reinforced composite outer layers that are placed on the liner in its entirety but do not teach the use of localized end-domes to optimize the structure to reduce its weight and cost.
Wood et al (U.S. Pat. No. 8,858,857) have disclosed a method to fabricate fiber-reinforced tanks or pressure vessels at a high rate using dry fiber preform or braid that is placed on a liner in its entirety and further injected with resin but do not teach the use of localized end-domes to optimize the structure to reduce its weight and cost.
Weisberg (U.S. Pat. No. 8,545,657) has disclosed a method to rapidly build fiber-reinforced structures by placing resinated filament layers on a mandrel, however doe snot teach optimization of tanks or pressure vessels.
Wexler et al (U.S. Pat. No. 11,000,988) have disclosed a method to fabricate long braided tubes with resinated filaments and bend them into conformable-shaped pressure containment units, but do not teach the use of localized reinforcements to reduce weight and cost.
The embodiment disclosed herein relates to an optimized tank or pressure vessel, and a process for producing an optimized tank or pressure vessel.
Certain embodiments are directed to tanks or pressure vessels that have an inner corrosion resistant and permeation resistant shell made of aluminum alloy or thermoplastic polymer, and an outer concentric shell that includes high strength fiber-reinforcement utilizing a combination of traditional filament winding, high-speed tubular braiding and/or fiber placement. Embodiments employ pre-formed endcaps that are incorporated in the end-domes of the tanks or pressure vessels. In certain embodiments the pre-formed endcaps are configured with fiber reinforcements in a predominantly hoop direction with respect of the axis of the tank or pressure vessel. In other embodiments the pre-formed endcaps are configured with fiber reinforcements in a predominantly longitudinal direction with respect to the axis of the tank or pressure vessel.
The following detailed description is of the best presently contemplated modes of carrying out the invention. This description is not to be taken in a limiting sense but is made merely for the purpose of illustrating general principles of embodiments of the invention. The scope of the invention is best defined by the appended claims.
Compressed gas tanks or pressure vessels are commonly cylindrical in shape with a straight cylindrical portion that is capped by two end-domes with or without polar openings to accommodate entry and egress of gas. Lightweight tanks or vessels are manufactured by overwrapping an inner shell as the corrosion-resistant and permeation-resistant liner with high strength fiber-reinforcement, either by filament winding, braiding or fiber placement methods. These processes are sometimes co-mingled.
Filament-winding process involves impregnating continuous fiber-reinforcement in a resin and winding over the rotating liner core, while moving parallel to the core, to achieve a ply structure consisting of cross and circumferential windings. Dry winding, without resin or little resin is also feasible.
Braiding process involves placing dry filaments on the liner core and achieving crossing and intertwining of the filaments by revolving and oscillating bobbins. In some cases, the dry filament preform is infused with a resin using a process such as resin transfer molding. Both methods have their advantages and disadvantages in orienting reinforcing fibers most efficiently to carry the pressure loads to achieve weight and cost minimization.
Fiber placement involves patches of fiber-resin fabric on a rotating liner core, to achieve a ply structure consisting or fibers oriented in pre-determined directions, for optimal structural performance.
The end-domes of fiber-reinforced tanks or pressure vessels experience high stresses around the polar openings and hence more susceptible to failure than the cylindrical part. A concentrated amount of reinforcing fibers oriented in the circumferential (“hoop”) direction around the openings is helpful to manage the high stresses around the polar openings.
The end-domes of fiber-reinforced tanks or pressure vessels experience high stresses at the “knee” area, or the transition between the cylindrical area and the domes. Fibers generally oriented in the longitudinal direction by the knee region helps to reduce the bending stresses in this region.
The straight cylindrical part of fiber-reinforced tanks or pressure vessels requires considerable circumferential reinforcement since the stresses in the circumferential direction is always double that of the stresses in the longitudinal direction. An optimum design needs to accommodate these different, and seemingly conflicting requirements—a high burst pressure and a large internal volume at the lowest possible weight and cost. This makes the design and manufacture of optimum pressure vessels a considerably complex optimization problem.
Filament winding works well to build the end domes since the thickness of the plies increases inversely proportional to the radius, thereby achieving a thick layer around the polar openings. Additionally, filament winding allows building near-longitudinal angles at the knee region, to support the bending stresses in that transitional region. However, to use filament winding to fulfill these localized reinforcing necessities, the continuous filaments need to traverse the entire cylindrical region, from fore end-dome to the aft end-dome. This constraint leads to excessive material usage, resulting in significant disadvantages in terms of weight and cost. Filament winding is also relatively slow, due to the common requirement to impregnate the fiber with wet resin. However, filament winding allows placement of near-circumferential “hoop” filaments, which are essential to carry the high stresses in the cylindrical portion of the vessel.
Braiding is one of the most versatile and cost-efficient processes for production of fiber preforms for building fiber-reinforced composite shells. Braiding is cost-efficient due to its layup speed and reduced material waste, which is even more important when expensive carbon fibers are used. Building a pressure vessel using braiding, however, is challenging since braiders are specialized for the manufacturing of fiber layers with fiber directions between 20° and 70° with respect to the longitudinal axis. Pressure vessels generally requires 90° layers around the dome polar openings and across the straight cylindrical section. Unlike in filament winding where there is a geometric relationship between the fiber angle and the radius of the core, the fiber angle in braiding depends on the relative speed of the bobbins and the take up. A smaller angle is the result of a faster take-up speed. To build thickness around the polar openings, the fiber tow may have to be narrowed, which leads to overlaps, distortion of fiber alignment and subsequent reduction in material properties.
Netting analysis shown in
Where
⊖=sin−1(r/R) Equation 3
These thicknesses given in Equations 1 and 2 represent the pure fiber thicknesses and without the resin. To obtain the composite laminate thickness with the resin included, we simply use the rule of mixtures:
t
lΘ
=t
fΘ
/v
f
A Equation 4
t
l90
=t
f90
/v
f Equation 5
As seen in these equations, the classical design of fiber-reinforced tanks or pressure vessels involve helical (nearly longitudinal or close to 0 degrees) and hoop (nearly circumferential or close to 90 degrees) fiber angles with respect to the longitudinal axis of the pressure vessel. Such angles can be readily achieved in filament winding, but difficult or impossible in braiding. The graph in
The pre-formed endcaps disclosed in the present invention compensate for the inability of braiders to achieve close to 90-degree build up around the polar openings and longitudinal reinforcement at the dome knee regions.
A filament winding step may be beneficially added to the braiding process to laydown hoop layers on the straight cylindrical portion of the pressure vessel.
While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention.
