Many believe the future in automobiles lies with a hydrogen based fuel system. Air Products is committed to pushing this technology forward and making it available to consumers as soon as possible. The method for storing and delivering hydrogen to a fuel cell vehicle is still a topic of mush debate. This project centers around the use of a hydrogen liquid carrier. This fuel will be kept at or near atmospheric conditions with respect to temperature and pressure; however, the carrier fluid can not be exposed to air. The carrier liquid is charged with hydrogen, which can be stripped from the fresh fluid by a reactor in a car. The only products of this is spent carrier fluid and water after the fuel cell has used the hydrogen. The goal of this project is to model this system and show its feasibility. The analog system will use water as the carrier system and CO2 as the hydrogen gas. The fresh liquid carrier will be modeled as DI water with sodium bicarbonate dissolved within. For this analog system, there are two equally important fluid loops, the refueling loop and the car loop.
During the refueling loop, fresh liquid carrier fluid must be pumped into the car, while at the same time spent liquid carrier must be pumped from the car to the station. In order to conserve space on the car, a dual volume tank must be used to hold both the fresh and spent liquid carrier. After refueling has occurred, the fresh liquid carrier will be used by the car loop. This loop will produce spent liquid carrier fluid and CO2 gas. The spent liquid carrier fluid will be returned to the dual volume storage tank until refueling has occurred.
There is one key unit in both loops, and therefore the main focus of this project. The dual volume storage tank must be shown to be a viable means to receive, store, and deliver both types of liquid carrier fluid. The dual bladder passive plate design is proven to meet all design criteria. This dual volume tank was built from scratch, with the idea of retrofitting an old car gas tank. In order to demonstrate how the dual volume tank will work, and complete refueling and car loop was built around it. Before the prototype was built Matlab coding was written for both the refueling and car loops.
The prototype is an all around success. Using only commonly available parts, a complete station and refueling loop was completed. The dual volume storage tank can hold up to 5 gallons of fresh fluid and refill at a rate of 1 gallon per minute. The car loop can operate at ease with a flow rate of 0.05 gallons per minute. Another success for the prototype was its ability to operate under anaerobic conditions. A hermetic system was not possible, but all substances, including O2, are accounted for. While using an inert fluid flush the connection between station and car was cleared of air before the fresh and spent liquid carrier fluids traveled through the refueling lines.
1) Design and prototype a hermetic dual volume hydrogen liquid carrier storage and delivery system for fuel cell vehicles
2) Demonstrate the hermetic operation of the prototype unit using an analogous gas-liquid system (e.g. CO2-water) in a closed loop system
3) Demonstrate an integrated approach to produce an overall system that will exhibit the concept of fresh and spent liquid carrier delivery, storage, and circulation
4) Demonstrate that the system can remove the CO2 from the water in a reactor to emulate removal of the fuel gas, H2, from its liquid carrier
In order to choose the best design for the dual volume storage tank, a design matrix was implemented. The design matrix enabled the team to choose three finalist ideas. After careful consideration amongst the team and with the sponsor a final design was selected, the dual bladder with passive plate design. Once a design for the dual volume storage tank was achieved, two engineering principles were used to guide the overall project design, the energy equation and conservation of mass. There are two distinct loops in which a working fluid must travel. In each loop there exists pieces of equipment, pipes, and valves that must be accounted for. The energy equation was applied to both loops in order to determine pump sizing. It was determined that the refueling loop would need a 5.5507 maximum feet of head in order to fill the fresh bag in the dual volume storage tank and generate the pressure needed to evacuate the spent bag at the same time. Due to scaling the fresh bag from 20 gallons to 5 gallons, a flow rate of 1 gallon per minute is needed. The head for the two pumps in the car loop are very different. Due to the effects of gravity, a very small pump is needed to get the fresh fluid into the CSTR. But the second pump in the car loop requires a head of 4.75 feet. The flow rate for fresh fluid into the reactor was not effected by scaling the prototype, and stayed at 0.05 gallons per minute. Conservation of mass is crucial to the design of the continuously stirred reactor (CSTR). It is in this vessel that the DI water with dissolved sodium bicarbonate will interact with a 1 molar solution of hydrochloric acid. In order to better facilitate the reaction and evolve CO2 at a faster rate, heat and stirring is added. A hot plate is used to raise the temperature of the reaction and a metal stir bar inside the CSTR facilitates a swirling motion.
Solid Edge Representation of Dual Volume Storage Tank
The entire prototype contains over 100 parts. All parts were bought based upon ease of availability at local stores or online. The Hydrogen Liquid Carrier Team would like to especially thank Richner's Auto Parts for donating an old 12 gallon truck gas tank, Penn State Food Service for donating several soda bags to be used as the fuel bladders, and all of the Penn State Professor's for their advice. A working prototype was built with less than $800. However, due to the build time and complexity of the design, manufacturing on a large scale would have to be altered. If large scale manufacturing occurred, parts could be created to fit within the overall design, instead of using available parts to complete the design.
This design project shows that a liquid carrier system is a viable option for the storage and delivery of hydrogen to a fuel cell vehicle. An inert fluid flush system can be used to clear refueling lines of air before the carrier fluid enters the line. However, there will be some inert fluid trapped in the line and captured in the fresh bag of the dual volume storage tank when fresh fluid is pumped through the lines. The inert fluid must be cheap, readily available, and have no negative effects upon the carrier fluid. Creating a dual volume storage tank is possible. There will always be some volume loss between the outside shell and the fresh bag, but this loss can be minimized if both are designed together and for each other. Flow rates needed for both refueling and hydrogen delivery within the car are easily obtainable. Even using off the shelf components, the prototype demonstrated how anaerobic connections and seals are reliable in a system using carrier fluid.
Hydrogen Liquid Carrier Team: Travis Burke, Brandon Harmer, Patrick Jones, Joshua Middaugh, & Joshua Nichols